Density, Electrical Conductivity and Viscosity of Hg(0.8)Cd(0.2)Te Melt

NASA Technical Reports Server (NTRS)

Li, C.; Scripa, R. N.; Ban, H.; Su, C.-H.; Lehoczky, S. L.

2004-01-01

The density, viscosity, and electrical conductivity of Hg(0.8)Cd(0.2)Te melt were measured as a function of temperature. A pycnometric method was used to measure the melt density in the temperature range of 1072 to 1122 K. The viscosity and electrical conductivity were determined using a transient torque method from 1068 to 1132 K. The density result from this study is within 0.3% of the published data. However, the current viscosity result is approximately 30% lower than the existing data. The electrical conductivity of Hg(0.8)Cd(0.2)Te melt as a function of temperature, which is not available in the literature, is also determined. The analysis of the temperature dependent electrical conductivity and the relationship between the kinematic viscosity and density indicated that the structure of the melt appeared to be homogeneous when the temperature was above 1090 K. A structural transition occurred in the Hg(0.8)Cd(0.2)Te melt as the temperature was decreased to below 1090 K

Density, Electrical Conductivity and Viscosity of Hg(sub 0.8)Cd(sub 0.2)Te Melt

NASA Technical Reports Server (NTRS)

Li, C.; Scripa, R. N.; Ban, H.; Lin, B.; Su, C.-H.; Lehoczky, S. L.

2004-01-01

The density, viscosity, and electrical conductivity of Hg(sub 0.8)Cd(sub 0.2)Te melt were measures as a function of temperature. A pycnometric method was used to measure the melt density in the temperature range of 1072 to 1122 K. The viscosity and electrical conductivity were determined using a transient torque method from 1068 to 1132 K. The density result from this study is within 0.3% of the published data. However, the current viscosity result is approximately 30% lower than the existing data. The electrical conductivity of Hg(sub 0.8)Cd(sub 0.2)Te melt as a function of temperature, which is not available in the literature, is also determined. The analysis of the temperature dependent electrical conductivity and the relationship between the kinematic viscosity and density indicated that the structure of the melt appeared to be homogeneous when the temperature was above 1090 K. A structural transition occurred in the Hg(sub 0.8)Cd(sub 0.2)Te melt as the temperature was decreased to below 1090 K.

Monte Carlo Study of Melting of a Model Bulk Ice.

NASA Astrophysics Data System (ADS)

Han, Kyu-Kwang

The methods of NVT (constant number, volume and temperature) and NPT (constant number, pressure and temperature) Monte Carlo computer simulations are used to examine the melting of a periodic hexagonal ice (ice Ih) sample with a unit cell of 192 (rigid) water molecules interacting via the revised central force potentials of Stillinger and Rahman (RSL2). In NVT Monte Carlo simulation of P-T plot for a constant density (0.904g/cm^3) is used to locate onset of the liquid-solid coexistence region (where the slope of the pressure changes sign) and estimate the (constant density) melting point. The slope reversal is a natural consequence of the constant density condition for substances which expand upon freezing and it is pointed out that this analysis is extremely useful for substances such as water. In this study, a sign reversal of the pressure slope is observed near 280 K, indicating that the RSL2 potentials reproduce the freezing expansion expected for water and support a bulk ice Ih system which melts <280 K. The internal energy, specific heat, and two dimensional structure factors for the constant density H_2O system are also examined at a range of temperatures between 100 and 370 K and support the P-T analysis for location of the melting point. This P-T analysis might likewise be useful for determining a (constant density) freezing point, or, with multiple simulations at appropriate densities, the triple point. For NPT Monte Carlo simulations preliminary results are presented. In this study the density, enthalpy, specific heat, and structure factor dependences on temperature are monitored during a sequential heating of the system from 100 to 370 K at a constant pressure (1 atm.). A jump in density upon melting is observed and indicates that the RSL2 potentials reproduce the melting contraction of ice. From the dependences of monitored physical properties on temperature an upper bound on the melting temperature is estimated. In this study we made the first analysis and calculation of the P-T curve for ice Ih melting at constant volume and the first NPT study of ice and of ice melting. In the NVT simulation we found for rho = 0.904g/cm^3 T_ {rm m} ~eq 280 K which is much closer to physical T_ {rm m} than any other published NVT simulation of ice. Finally it is shown that RSL2 potentials do a credible job of describing the thermodynamic properties of ice Ih near its melting point.

Greater-than-bulk melting temperatures explained: Gallium melts Gangnam style

NASA Astrophysics Data System (ADS)

Gaston, Nicola; Steenbergen, Krista

2014-03-01

The experimental discovery of superheating in gallium clusters contradicted the clear and well-demonstrated paradigm that the melting temperature of a particle should decrease with its size. However the extremely sensitive dependence of melting temperature on size also goes to the heart of cluster science, and the interplay between the effects of electronic and geometric structure. We have performed extensive first-principles molecular dynamics calculations, incorporating parallel tempering for an efficient exploration of configurational phase space. This is necessary, due to the complicated energy landscape of gallium. In the nanoparticles, melting is preceded by a transitions between phases. A structural feature, referred to here as the Gangnam motif, is found to increase with the latent heat and appears throughout the observed phase changes of this curious metal. We will present our detailed analysis of the solid-state isomers, performed using extensive statistical sampling of the trajectory data for the assignment of cluster structures to known phases of gallium. Finally, we explain the greater-than-bulk melting through analysis of the factors that stabilise the liquid structures.

The Melting Point of Palladium Using Miniature Fixed Points of Different Ceramic Materials: Part II—Analysis of Melting Curves and Long-Term Investigation

NASA Astrophysics Data System (ADS)

Edler, F.; Huang, K.

2016-12-01

Fifteen miniature fixed-point cells made of three different ceramic crucible materials (Al2O3, ZrO2, and Al2O3(86 %)+ZrO2(14 %)) were filled with pure palladium and used to calibrate type B thermocouples (Pt30 %Rh/Pt6 %Rh). A critical point by using miniature fixed points with small amounts of fixed-point material is the analysis of the melting curves, which are characterized by significant slopes during the melting process compared to flat melting plateaus obtainable using conventional fixed-point cells. The method of the extrapolated starting point temperature using straight line approximation of the melting plateau was applied to analyze the melting curves. This method allowed an unambiguous determination of an electromotive force (emf) assignable as melting temperature. The strict consideration of two constraints resulted in a unique, repeatable and objective method to determine the emf at the melting temperature within an uncertainty of about 0.1 μ V. The lifetime and long-term stability of the miniature fixed points was investigated by performing more than 100 melt/freeze cycles for each crucible of the different ceramic materials. No failure of the crucibles occurred indicating an excellent mechanical stability of the investigated miniature cells. The consequent limitation of heating rates to values below {± }3.5 K min^{-1} above 1100° C and the carefully and completely filled crucibles (the liquid palladium occupies the whole volume of the crucible) are the reasons for successfully preventing the crucibles from breaking. The thermal stability of the melting temperature of palladium was excellent when using the crucibles made of Al2O3(86 %)+ZrO2(14 %) and ZrO2. Emf drifts over the total duration of the long-term investigation were below a temperature equivalent of about 0.1 K-0.2 K.

Theoretical analysis of heat flow in horizontal ribbon growth from a melt. [silicon metal

NASA Technical Reports Server (NTRS)

Zoutendyk, J. A.

1978-01-01

A theoretical heat flow analysis for horizontalribbon growth is presented. Equations are derived relating pull speed, ribbon thickness, thermal gradient in the melt, and melt temperature for limiting cases of heat removal by radiation only and isothermal heat removal from the solid surface over the melt. Geometrical cross sections of the growth zone are shown to be triangular and nearly parabolic for the two respective cases. Theoretical pull speed for silicon ribbon 0.01 cm thick, where the loss of latent heat of fusion is by radiation to ambient temperature (300 K) only, is shown to be 1 cm/sec for horizontal growth extending 2 cm over the melt and with no heat conduction either to or from the melt. Further enhancement of ribbon growth rate by placing cooling blocks adjacent to the top surface is shown to be theoretically possible.

Melting in Superheated Silicon Films Under Pulsed-Laser Irradiation

NASA Astrophysics Data System (ADS)

Wang, Jin Jimmy

This thesis examines melting in superheated silicon films in contact with SiO2 under pulsed laser irradiation. An excimer-laser pulse was employed to induce heating of the film by irradiating the film through the transparent fused-quartz substrate such that most of the beam energy was deposited near the bottom Si-SiO2 interface. Melting dynamics were probed via in situ transient reflectance measurements. The temperature profile was estimated computationally by incorporating temperature- and phase-dependent physical parameters and the time-dependent intensity profile of the incident excimer-laser beam obtained from the experiments. The results indicate that a significant degree of superheating occurred in the subsurface region of the film. Surface-initiated melting was observed in spite of the internal heating scheme, which resulted in the film being substantially hotter at and near the bottom Si-SiO2 interface. By considering that the surface melts at the equilibrium melting point, the solid-phase-only heat-flow analysis estimates that the bottom Si-SiO2 interface can be superheated by at least 220 K during excimer-laser irradiation. It was found that at higher laser fluences (i.e., at higher temperatures), melting can be triggered internally. At heating rates of 1010 K/s, melting was observed to initiate at or near the (100)-oriented Si-SiO2 interface at temperatures estimated to be over 300 K above the equilibrium melting point. Based on theoretical considerations, it was deduced that melting in the superheated solid initiated via a nucleation and growth process. Nucleation rates were estimated from the experimental data using Johnson-Mehl-Avrami-Kolmogorov (JMAK) analysis. Interpretation of the results using classical nucleation theory suggests that nucleation of the liquid phase occurred via the heterogeneous mechanism along the Si-SiO2 interface.

Experimental research of phase transitions in a melt of high-purity aluminum

NASA Astrophysics Data System (ADS)

Vorontsov, V. B.; Pershin, V. K.

2017-12-01

This scientific work is devoted to the studying of the genetic connection structures of solid and liquid phases. In this paper Fourier analysis of acoustic emission (AE) signals accompanying heating of high purity aluminum from the melting point up to 860 °C was performed. The experimental data allowed to follow the dynamics of disorder zones in the melt with increasing melt temperature up to their complete destruction. The presented results of spectral analysis of the signals were analyzed from the standpoint of the theory of cluster melting metals.

Visualization analysis of tiger-striped flow mark generation phenomena in injection molding

NASA Astrophysics Data System (ADS)

Owada, Shigeru; Yokoi, Hidetoshi

2016-03-01

The generation mechanism of tiger-striped flow marks of polypropylene (PP)/rubber/talc blends in injection molding was investigated by dynamic visualization analysis in a glass-inserted mold. The analysis revealed that the behavior of the melt flow front correlates with the flow mark generation. The cloudy part in the tiger-striped flow marks corresponded to the low transcription rate area of the melt diverging near the cavity wall, while the glossy part corresponded to the high transcription rate area of the melt converging toward the cavity wall side. The melt temperature at the high transcription rate area was slightly lower than that at the low transcription rate area. These phenomena resulted due to the difference in the temperature of the melt front that was caused by the asymmetric fountain flow. These results suggest the followings; At the moment when the melt is broken near the one side of cavity wall due to piling the extensional strains up to a certain level, the melt spurts out near the broken side. It results in generating asymmetric fountain flow temporarily to relax the extensional front surface, which moves toward the opposite side to form the high transcription area.

Nb-Based Nb-Al-Fe Alloys: Solidification Behavior and High-Temperature Phase Equilibria

NASA Astrophysics Data System (ADS)

Stein, Frank; Philips, Noah

2018-03-01

High-melting Nb-based alloys hold significant promise for the development of novel high-temperature materials for structural applications. In order to understand the effect of alloying elements Al and Fe, the Nb-rich part of the ternary Nb-Al-Fe system was investigated. A series of Nb-rich ternary alloys were synthesized from high-purity Nb, Al, and Fe metals by arc melting. Solidification paths were identified and the liquidus surface of the Nb corner of the ternary system was established by analysis of the as-melted microstructures and thermal analysis. Complementary analysis of heat-treated samples yielded isothermal sections at 1723 K and 1873 K (1450 °C and 1600 °C).

Greenland Ice Sheet Surface Temperature, Melt, and Mass Loss: 2000-2006

NASA Technical Reports Server (NTRS)

Hall, Dorothy K.; Williams, Richard S., Jr.; Luthcke, Scott B.; DiGirolamo, Nocolo

2007-01-01

Extensive melt on the Greenland Ice Sheet has been documented by a variety of ground and satellite measurements in recent years. If the well-documented warming continues in the Arctic, melting of the Greenland Ice Sheet will likely accelerate, contributing to sea-level rise. Modeling studies indicate that an annual or summer temperature rise of 1 C on the ice sheet will increase melt by 20-50% therefore, surface temperature is one of the most important ice-sheet parameters to study for analysis of changes in the mass balance of the ice-sheet. The Greenland Ice Sheet contains enough water to produce a rise in eustatic sea level of up to 7.0 m if the ice were to melt completely. However, even small changes (centimeters) in sea level would cause important economic and societal consequences in the world's major coastal cities thus it is extremely important to monitor changes in the ice-sheet surface temperature and to ultimately quantify these changes in terms of amount of sea-level rise. We have compiled a high-resolution, daily time series of surface temperature of the Greenland Ice Sheet, using the I-km resolution, clear-sky land-surface temperature (LST) standard product from the Moderate-Resolution Imaging Spectroradiometer (MODIS), from 2000 - 2006. We also use Gravity Recovery and Climate Experiment (GRACE) data, averaged over 10-day periods, to measure change in mass of the ice sheet as it melt and snow accumulates. Surface temperature can be used to determine frequency of surface melt, timing of the start and the end of the melt season, and duration of melt. In conjunction with GRACE data, it can also be used to analyze timing of ice-sheet mass loss and gain.

[MSW incineration fly ash melting by DSC-DTA].

PubMed

Li, Rundong; Chi, Yong; Li, Shuiqing; Wang, Lei; Yan, Jianhua; Cen, Kefa

2002-07-01

Melting characteristics of two kinds of municipal solid waste incineration(MSWI) fly ash were studied in this paper by high temperature differential scanning calorimetry and differential temperature analysis. MSWI fly ash was considered as hazardous waste because it contains heavy metals and dioxins. The experiments were performed in either N2 or O2 atmosphere in temperature range of 20 degrees C-1450 degrees C at various heating rates. Two different MSW incineration fly ashes used in the experiments were collected from our country and France respectively. The process of fly ash melting exhibits two reactions occurring at temperature ranges of about 480 degrees C-670 degrees C and 1136 degrees C-1231 degrees C, respectively. The latent heat of polymorphic transformation and fusion were approximately 20 kJ/kg and 700 kJ/kg, while the total heat required for melting process was about 1800 kJ/kg. The paper also studied effect of CaO to melting. A heat flux thermodynamic model for fly ash melting was put forward and it agrees well with experimental data.

Analysis of Summer 2002 Melt Extent on the Greenland Ice Sheet using MODIS and SSM/I Data

NASA Technical Reports Server (NTRS)

Hall, Dorothy K.; Williams, Richard S., Jr.; Steffen, Konrad; Chien, Y. L.; Foster, James L.; Robinson, David A.; Riggs, George A.

2004-01-01

Previous work has shown that the summer of 2002 had the greatest area of snow melt extent on the Greenland ice sheet ever recorded using passive-microwave data. In this paper, we compare the 0 degree isotherm derived from the Moderate-Resolution Imaging Spectroradiometer (MODIS) instrument, with Special Sensor Microwave/Imager (SSM/I)-derived melt, at the time of the maximum melt extent in 2002. To validate the MODIS-derived land-surface temperatures (LSTs), we compared the MODIS LSTs with air temperatures from nine stations (using 11 different data points) and found that they agreed to within 2.3 plus or minus 2.09 C, with station temperatures consistently lower than the MODIS LSTs. According to the MODIS LST, the maximum surface melt extended to approximately 2300 m in southern Greenland; while the SSM/I measurements showed that the maximum melt extended to nearly 2700 m in southeastern Greenland. The MODIS and SSM/I data are complementary in providing detailed information about the progression of surface and near-surface melt on the Greenland ice sheet.

Analysis of Summer 2002 Melt Extent on the Greenland Ice Sheet using MODIS and SSM/I Data

NASA Technical Reports Server (NTRS)

Hall, Dorothy K.; Williams, Richard S.; Steffen, Konrad; Chien, Janet Y. L.

2004-01-01

Previous work has shown that the summer of 2002 had the greatest area of snow melt extent on the Greenland ice sheet ever recorded using passive-microwave data. In this paper, we compare the 0 deg. isotherm derived from the Moderate-Resolution Imaging Spectroradiometer (MODIS) instrument, with Special Sensor Microwave/Imager (SSM/I)-derived melt, at the time of the maximum melt extent in 2002. To validate the MODIS derived land-surface temperatures (LSTs), we compared the MODIS LSTs with air temperatures from nine stations (using 11 different data points) and found that they agreed to within 2.3 +/- 2.09 C, with station temperatures consistently lower than the MODIS LSTs. According to the MODIS LST, the maximum surface melt extended to approx. 2300 m in southern Greenland; while the SSM/I measurements showed that the maximum melt extended to nearly 2700 m in southeastern Greenland. The MODIS and SSM/I data are complementary in providing detailed information about the progression of surface and near- surface melt on the Greenland ice sheet.

Analysis of summer 2002 melt extent on the Greenland ice sheet using MODIS and SSM/I data

USGS Publications Warehouse

Hall, D.K.; Williams, R.S.; Steffen, K.; Chien, Janet Y.L.

2004-01-01

Previous work has shown that the summer of 2002 had the greatest area of snow melt extent on the Greenland ice sheet ever recorded using passive-microwave data. In this paper, we compare the 0?? isotherm derived from the Moderate-Resolution Imaging Spectroradiometer (MODIS) instrument, with Special Sensor Microwave/Imager (SSM/I)-derived melt, at the time of the maximum melt extent in 2002. To validate the MODIS-derived land-surface temperatures (LSTs), we compared the MODIS LSTs with air temperatures from nine stations (using 11 different data points) and found that they agreed to within 2.3??2.09??C, with station temperatures consistently lower than the MODIS LSTs. According to the MODIS LST, the maximum surface melt extended to ???2300 m in southern Greenland; while the SSM/I measurements showed that the maximum melt extended to nearly 2700 m in southeastern Greenland. The MODIS and SSM/I data are complementary in providing detailed information about the progression of surface and near-surface melt on the Greenland ice sheet.

Analysis of summer 2002 melt extent on the Greenland ice sheet using MODIS and SSM/I data

USGS Publications Warehouse

Hall, D. K.; Williams, R.S.; Steffen, K.; Chien, Janet Y.L.

2004-01-01

Previous work has shown that the summer of 2002 had the greatest area of snow melt extent on the Greenland ice sheet ever recorded using passive-microwave data. In this paper, we compare the 0deg isotherm derived from the Moderate-Resolution Imaging Spectroradiometer (MODIS) instrument, with Special Sensor Microwave/Imager (SSM/I)-derived melt, at the time of the maximum melt extent in 2002. To validate the MODIS-derived land-surface temperatures (LSTs), we compared the MODIS LSTs with air temperatures from nine stations (using 11 different data points) and found that they agreed to within 2.3 plusmn 2.09 degC, with station temperatures consistently lower than the MODIS LSTs. According to the MODIS LST, the maximum surface melt extended to ~2300 m in southern Greenland; while the SSM/I measurements showed that the maximum melt extended to nearly 2700 m in southeastern Greenland. The MODIS and SSM/I data are complementary in providing detailed information about the progression of surface and near-surface melt on the Greenland ice sheet.

Characterization of crystal forms of β-estradiol thermal analysis, Raman microscopy, X-ray analysis and solid-state NMR

NASA Astrophysics Data System (ADS)

Variankaval, N. E.; Jacob, K. I.; Dinh, S. M.

2000-08-01

The structure and select crystalline properties of a common drug (estradiol) used in a transdermal drug delivery system are investigated. Four different crystal forms of estradiol (EA, EC, ED and EM) were prepared in the laboratory and characterized by thermal analysis, optical microscopy, Raman microspectroscopy, and solid-state NMR. Variable temperature X-ray studies were carried out on form A (EA) to determine whether the crystal structure changed as a function of temperature. These four forms exhibited different thermal behavior. EA and EC had similar melting points. This study clearly shows that water cannot be released from the crystal lattice of EA unless melting is achieved, and exposing EA to temperatures below the melting point only results in a partial release of hydrogen bonded water. EC was prepared by melting EA and subsequently cooling it to room temperature. Form EC was anhydrous, as it did not exhibit water loss, as opposed to EA, which had about 3.5% water in its crystal structure. ED was very difficult to prepare and manifested itself only as a mixture with EC. Its melting point was about 10°C lower than that of EC. It is thought to be an unstable form due to its simultaneous occurrence with EC and the inability to isolate it. EM is a solvate of methanol, not a polymorph. Its melting point was similar to EA and EC. From thermogravimetry/differential thermal analysis and differential scanning calorimetry data, it was apparent that estradiol formed a hemisolvate with methanol. All four forms had different morphologies. Raman microscopy was carried out on the different crystal forms. The spectra of EC and ED were almost identical. Thermal analysis revealed that this is due to the highly unstable nature of ED and its tendency to either convert spontaneously to EC or occur in mixtures with it.

Dynamics of DNA breathing: weak noise analysis, finite time singularity, and mapping onto the quantum Coulomb problem.

PubMed

Fogedby, Hans C; Metzler, Ralf

2007-12-01

We study the dynamics of denaturation bubbles in double-stranded DNA on the basis of the Poland-Scheraga model. We show that long time distributions for the survival of DNA bubbles and the size autocorrelation function can be derived from an asymptotic weak noise approach. In particular, below the melting temperature the bubble closure corresponds to a noisy finite time singularity. We demonstrate that the associated Fokker-Planck equation is equivalent to a quantum Coulomb problem. Below the melting temperature, the bubble lifetime is associated with the continuum of scattering states of the repulsive Coulomb potential; at the melting temperature, the Coulomb potential vanishes and the underlying first exit dynamics exhibits a long time power law tail; above the melting temperature, corresponding to an attractive Coulomb potential, the long time dynamics is controlled by the lowest bound state. Correlations and finite size effects are discussed.

Analysis of impact melt and vapor production in CTH for planetary applications

DOE PAGES

Quintana, S. N.; Crawford, D. A.; Schultz, P. H.

2015-05-19

This study explores impact melt and vapor generation for a variety of impact speeds and materials using the shock physics code CTH. The study first compares the results of two common methods of impact melt and vapor generation to demonstrate that both the peak pressure method and final temperature method are appropriate for high-speed impact models (speeds greater than 10 km/s). However, for low-speed impact models (speeds less than 10 km/s), only the final temperature method is consistent with laboratory analyses to yield melting and vaporization. Finally, a constitutive model for material strength is important for low-speed impacts because strengthmore » can cause an increase in melting and vaporization.« less

Analysis of impact melt and vapor production in CTH for planetary applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Quintana, S. N.; Crawford, D. A.; Schultz, P. H.

This study explores impact melt and vapor generation for a variety of impact speeds and materials using the shock physics code CTH. The study first compares the results of two common methods of impact melt and vapor generation to demonstrate that both the peak pressure method and final temperature method are appropriate for high-speed impact models (speeds greater than 10 km/s). However, for low-speed impact models (speeds less than 10 km/s), only the final temperature method is consistent with laboratory analyses to yield melting and vaporization. Finally, a constitutive model for material strength is important for low-speed impacts because strengthmore » can cause an increase in melting and vaporization.« less

Study of ultrasonic melt treatment on the quality of horizontal continuously cast Al-1%Si alloy.

PubMed

Li, Xin-Tao; Li, Ting-Ju; Li, Xi-Meng; Jin, Jun-Ze

2006-02-01

The fluctuation of the melt temperature in a tundish was measured during casting and experiments were conducted to investigate the effects of ultrasonic melt treatment on the surface quality and solidification structures of Al-1%Si ingots. The results show that the uniformity of melt temperature was enhanced with the application of ultrasonic melt treatment. When the ultrasonic power is 1,000W, the surface quality was evidently improved and grains of cast ingots were refined. Moreover, EPMA analysis was adopted to study the relationship between the ultrasonic power and boundary segregation of Si element. The result shows that boundary segregation is suppressed with the increase of ultrasonic power and the phenomenon was theoretically interpreted.

Phase relations in the system NaCl-KCl-H2O. Part I: Differential thermal analysis of the NaCl-KCl liquidas at 1 atmosphere and 500, 1000, 1500, and 2000 bars

USGS Publications Warehouse

Chou, I.-Ming

1982-01-01

A simple differential thermal analysis (DTA) technique has been developed to study phase relations of various chemical systems at elevated pressures and temperatures. The DTA system has been calibrated against known melting temperatures in the system NaCl-KCl. Isobaric sections of the liquidus in the system NaCl-KCl have been determined at pressures of 1 atmosphere and 500, 1000, 1500, and 2000 bars. Using the least-squares method, the following equation was used to fit the experimental data: T(??C)= ??? i=0 6aiXiKCl where T is the liquidus temperature, XKCl is mole fraction of KCl, and ai (listed below) are the derived empirical constants. {A table is presented}. The liquidus temperatures estimated from these equations are within ??3??C of experimental values. The measured liquidus temperatures at 1 atmosphere agree with the best available data to within 5??C. The melting temperatures for pure end members at higher pressures agree with the values calculated from the Simon equation (Clark, 1959) to within 3??C. No previous melting data are available for the intermediate compositions at elevated pressures. Using the data in both heating and cooling scans, the minimum melting temperature at 1 atmosphere in the system was located at 658?? ?? 3??C where the sample has an equimolar composition. ?? 1982.

Estimating the time of melt onset and freeze onset over Arctic sea-ice area using active and passive microwave data

USGS Publications Warehouse

Belchansky, Gennady I.; Douglas, David C.; Mordvintsev, Ilia N.; Platonov, Nikita G.

2004-01-01

Accurate calculation of the time of melt onset, freeze onset, and melt duration over Arctic sea-ice area is crucial for climate and global change studies because it affects accuracy of surface energy balance estimates. This comparative study evaluates several methods used to estimate sea-ice melt and freeze onset dates: (1) the melt onset database derived from SSM/I passive microwave brightness temperatures (Tbs) using Drobot and Anderson's [J. Geophys. Res. 106 (2001) 24033] Advanced Horizontal Range Algorithm (AHRA) and distributed by the National Snow and Ice Data Center (NSIDC); (2) the International Arctic Buoy Program/Polar Exchange at the Sea (IABP/POLES) surface air temperatures (SATs); (3) an elaborated version of the AHRA that uses IABP/POLES to avoid anomalous results (Passive Microwave and Surface Temperature Analysis [PMSTA]); (4) another elaborated version of the AHRA that uses Tb variance to avoid anomalous results (Mean Differences and Standard Deviation Analysis [MDSDA]); (5) Smith's [J. Geophys. Res. 103 (1998) 27753] vertically polarized Tb algorithm for estimating melt onset in multiyear (MY) ice (SSM/I 19V–37V); and (6) analyses of concurrent backscattering cross section (σ°) and brightness temperature (Tb) from OKEAN-01 satellite series. Melt onset and freeze onset maps were created and compared to understand how the estimates vary between different satellite instruments and methods over different Arctic sea-ice regions. Comparisons were made to evaluate relative sensitivities among the methods to slight adjustments of the Tbcalibration coefficients and algorithm threshold values. Compared to the PMSTA method, the AHRA method tended to estimate significantly earlier melt dates, likely caused by the AHRA's susceptibility to prematurely identify melt onset conditions. In contrast, the IABP/POLES surface air temperature data tended to estimate later melt and earlier freeze in all but perennial ice. The MDSDA method was least sensitive to small adjustments of the SMMR–SSM/I inter-satellite calibration coefficients. Differences among methods varied by latitude. Freeze onset dates among methods were most disparate in southern latitudes, and tended to converge northward. Surface air temperatures (IABP/POLES) indicated freeze onset well before the MDSDA method, especially in southern peripheral seas, while PMSTA freeze estimates were generally intermediate. Surface air temperature data estimated latest melt onset dates in southern latitudes, but earliest melt onset in northern latitudes. The PMSTA estimated earliest melt onset dates in southern regions, and converged with the MDSDA northward. Because sea-ice melt and freeze are dynamical transitional processes, differences among these methods are associated with differing sensitivities to changing stages of environmental and physical development. These studies contribute to the growing body of documentation about the levels of disparity obtained when Arctic seasonal transition parameters are estimated using various types of microwave data and algorithms.

Challenges in Melt Furnace Tests

NASA Astrophysics Data System (ADS)

Belt, Cynthia

2014-09-01

Measurement is a critical part of running a cast house. Key performance indicators such as energy intensity, production (or melt rate), downtime (or OEE), and melt loss must all be understood and monitored on a weekly or monthly basis. Continuous process variables such as bath temperature, flue temperature, and furnace pressure should be used to control the furnace systems along with storing the values in databases for later analysis. While using measurement to track furnace performance over time is important, there is also a time and place for short-term tests.

Nucleated Poly(L-lactic acid) with N, N‧-oxalyl bis(benzoic acid) dihydrazide

NASA Astrophysics Data System (ADS)

Tian, Liang-Liang; Cai, Yan-Hua

2018-04-01

One of the major challenges in the field of Poly(L-lactic acid) (PLLA) is the enhancement of crystallization. In the present work, the evaluation of the influence of N, N‧-oxalyl bis(benzoic acid) dihydrazide (TBOD), as a novel organic nucleating agent, on the non-isothermal crystallization, melting behavior, and thermal stability of PLLA was performed using differential scanning calorimeter and thermogravimetric analysis. Non-isothermal crystallization measurement revealed that TBOD had an excellent accelerating effect for the crystallization of PLLA in cooling, and upon the addition of 3 wt% TBOD, PLLA exhibited the highest onset crystallization temperature and the crystallization peak temperature, as well as the largest non-isothermal crystallization enthalpy. In particular, when the TBOD concentration was 1 wt% ∼ 3 wt%, the onset crystallization temperatures were higher than the theoretical ceiling temperature of crystallization, thoroughly demonstrating the powerful crystallization promoting ability of TBOD. Additionally, the non-isothermal crystallization behavior of PLLA/TBOD depended on the TBOD concentration, cooling rate as well as the final melting temperature. The melting behavior of PLLA/TBOD after non-isothermal crystallization further confirmed the effect of TBOD on the crystallization process and crystal structure of PLLA, and the appearance of the double melting peaks during melting stages was attribute to the melting-recrystallization. For melting behavior after isothermal crystallization, the crystallization temperature and crystallization time significantly affected the melting behavior of PLLA/TBOD. The addition of TBOD could not change the thermal decomposition profile of the PLLA, but the thermal stability did not regularly decrease with increasing of TBOD concentration, indicating that there might exist intermolecular interaction between PLLA and TBOD.

Toward a coherent model for the melting behavior of the deep Earth's mantle

NASA Astrophysics Data System (ADS)

Andrault, D.; Bolfan-Casanova, N.; Bouhifd, M. A.; Boujibar, A.; Garbarino, G.; Manthilake, G.; Mezouar, M.; Monteux, J.; Parisiades, P.; Pesce, G.

2017-04-01

Knowledge of melting properties is critical to predict the nature and the fate of melts produced in the deep mantle. Early in the Earth's history, melting properties controlled the magma ocean crystallization, which potentially induced chemical segregation in distinct reservoirs. Today, partial melting most probably occurs in the lowermost mantle as well as at mid upper-mantle depths, which control important aspects of mantle dynamics, including some types of volcanism. Unfortunately, despite major experimental and theoretical efforts, major controversies remain about several aspects of mantle melting. For example, the liquidus of the mantle was reported (for peridotitic or chondritic-type composition) with a temperature difference of ∼1000 K at high mantle depths. Also, the Fe partitioning coefficient (DFeBg/melt) between bridgmanite (Bg, the major lower mantle mineral) and a melt was reported between ∼0.1 and ∼0.5, for a mantle depth of ∼2000 km. Until now, these uncertainties had prevented the construction of a coherent picture of the melting behavior of the deep mantle. In this article, we perform a critical review of previous works and develop a coherent, semi-quantitative, model. We first address the melting curve of Bg with the help of original experimental measurements, which yields a constraint on the volume change upon melting (ΔVm). Secondly, we apply a basic thermodynamical approach to discuss the melting behavior of mineralogical assemblages made of fractions of Bg, CaSiO3-perovskite and (Mg,Fe)O-ferropericlase. Our analysis yields quantitative constraints on the SiO2-content in the pseudo-eutectic melt and the degree of partial melting (F) as a function of pressure, temperature and mantle composition; For examples, we find that F could be more than 40% at the solidus temperature, except if the presence of volatile elements induces incipient melting. We then discuss the melt buoyancy in a partial molten lower mantle as a function of pressure, F and DFeBg/melt. In the lower mantle, density inversions (i.e. sinking melts) appear to be restricted to low F values and highest mantle pressures. The coherent melting model has direct geophysical implications: (i) in the early Earth, the magma ocean crystallization could not occur for a core temperature higher than ∼5400 K at the core-mantle boundary (CMB). This temperature corresponds to the melting of pure Bg at 135 GPa. For a mantle composition more realistic than pure Bg, the right CMB temperature for magma ocean crystallization could have been as low as ∼4400 K. (ii) There are converging arguments for the formation of a relatively homogeneous mantle after magma ocean crystallization. In particular, we predict the bulk crystallization of a relatively large mantle fraction, when the temperature becomes lower than the pseudo-eutectic temperature. Some chemical segregation could still be possible as a result of some Bg segregation in the lowermost mantle during the first stage of the magma ocean crystallization, and due to a much later descent of very low F, Fe-enriched, melts toward the CMB. (iii) The descent of such melts could still take place today. There formation should to be related to incipient mantle melting due to the presence of volatile elements. Even though, these melts can only be denser than the mantle (at high mantle depths) if the controversial value of DFeBg/melt is indeed as low as suggested by some experimental studies. This type of melts could contribute to produce ultra-low seismic velocity anomalies in the lowermost mantle.

In situ spectroscopy and spectroelectrochemistry of uranium in high-temperature alkali chloride molten salts.

PubMed

Polovov, Ilya B; Volkovich, Vladimir A; Charnock, John M; Kralj, Brett; Lewin, Robert G; Kinoshita, Hajime; May, Iain; Sharrad, Clint A

2008-09-01

Soluble uranium chloride species, in the oxidation states of III+, IV+, V+, and VI+, have been chemically generated in high-temperature alkali chloride melts. These reactions were monitored by in situ electronic absorption spectroscopy. In situ X-ray absorption spectroscopy of uranium(VI) in a molten LiCl-KCl eutectic was used to determine the immediate coordination environment about the uranium. The dominant species in the melt was [UO 2Cl 4] (2-). Further analysis of the extended X-ray absorption fine structure data and Raman spectroscopy of the melts quenched back to room temperature indicated the possibility of ordering beyond the first coordination sphere of [UO 2Cl 4] (2-). The electrolytic generation of uranium(III) in a molten LiCl-KCl eutectic was also investigated. Anodic dissolution of uranium metal was found to be more efficient at producing uranium(III) in high-temperature melts than the cathodic reduction of uranium(IV). These high-temperature electrolytic processes were studied by in situ electronic absorption spectroelectrochemistry, and we have also developed in situ X-ray absorption spectroelectrochemistry techniques to probe both the uranium oxidation state and the uranium coordination environment in these melts.

Processing of ash and slag waste of heating plants by arc plasma to produce construction materials and nanomodifiers

NASA Astrophysics Data System (ADS)

Buyantuev, S. L.; Urkhanova, L. A.; Kondratenko, A. S.; Shishulkin, S. Yu; Lkhasaranov, S. A.; Khmelev, A. B.

2017-01-01

The resultsare presented of plasma processing slag and ash waste from coal combustion in heating plants. Melting mechanism of ashand slagraw material is considered by an electromagnetic technological reactor. The analysis was conducted of temperature and phase transformations of raw material when it is heated up to the melting point, and also determination of specific energy consumption by using a generalized model of the thermodynamic analysis of TERRA. The study of materials melting temperature conditions and plum of melt was carried with high-temperature thermal imaging method, followed by mapping and 3D-modeling of the temperature fields. The investigations to establish the principal possibilities of using slag waste of local coal as raw material for the production of mineral (ash and slag) fibers found that by chemical composition there are oxides in the following ranges: 45-65% SiO2; 10-25% Al2O3; 10-45% CaO; 5-10% MgO; other minerals (less than 5%). Thus, these technological wastes are principally suitable for melts to produce mineral wool by the plasma method. An analysis of the results shows the melting point of ash and slag waste - 1800-2000 °C. In this case the specific energy consumption of these processes keeps within the limits of 1.1-1.3 kW*h/kg. For comparison it should be noted that the unit cost of electricity in the known high-melting industrial installations 5-6 kW*h/kg. Upon melting ash and slag waste, which contains up to 2-5% of unburned carbon, carbon nanomaterials were discovered.in the form of ultrafine soot accumulating as a plaque on the water-cooled surfaces in the gas cleaning chamber. The process of formation of soot consists in sublimation-desublimation of part of carbon which is in ash and slag, and graphite electrode. Thus, upon melting of ash and slag in the electromagnetic reactor it is possible to obtain melt, and in the subsequent mineral high quality fiber, which satisfies the requirements of normative documents, and simultaneously to receive a condensed product in the form of carbon sublimated nanoparticles, which can be found further use in construction materials, in particular in high-strength concrete and other materials.

Poly(ether ester) Ionomers as Water-Soluble Polymers for Material Extrusion Additive Manufacturing Processes.

PubMed

Pekkanen, Allison M; Zawaski, Callie; Stevenson, André T; Dickerman, Ross; Whittington, Abby R; Williams, Christopher B; Long, Timothy E

2017-04-12

Water-soluble polymers as sacrificial supports for additive manufacturing (AM) facilitate complex features in printed objects. Few water-soluble polymers beyond poly(vinyl alcohol) enable material extrusion AM. In this work, charged poly(ether ester)s with tailored rheological and mechanical properties serve as novel materials for extrusion-based AM at low temperatures. Melt transesterification of poly(ethylene glycol) (PEG, 8k) and dimethyl 5-sulfoisophthalate afforded poly(ether ester)s of sufficient molecular weight to impart mechanical integrity. Quantitative ion exchange provided a library of poly(ether ester)s with varying counterions, including both monovalent and divalent cations. Dynamic mechanical and tensile analysis revealed an insignificant difference in mechanical properties for these polymers below the melting temperature, suggesting an insignificant change in final part properties. Rheological analysis, however, revealed the advantageous effect of divalent countercations (Ca 2+ , Mg 2+ , and Zn 2+ ) in the melt state and exhibited an increase in viscosity of two orders of magnitude. Furthermore, time-temperature superposition identified an elevation in modulus, melt viscosity, and flow activation energy, suggesting intramolecular interactions between polymer chains and a higher apparent molecular weight. In particular, extrusion of poly(PEG 8k -co-CaSIP) revealed vast opportunities for extrusion AM of well-defined parts. The unique melt rheological properties highlighted these poly(ether ester) ionomers as ideal candidates for low-temperature material extrusion additive manufacturing of water-soluble parts.

Synchrotron X-ray spectroscopic investigations of an Nb-bearing silicate melt in contact with an aqueous fluid

NASA Astrophysics Data System (ADS)

Mayanovic, R. A.; Anderson, A. J.; Bassett, W. A.; Chou, I.

2006-05-01

Understanding the structural properties of trace elements in hydrous silicate melts in contact with a hydrothermal fluid is fundamentally important for a better assessment of the role of such elements in silicate melts being subjected to hydrothermal processes. We describe the use of synchrotron x-ray microprobe techniques and the modified hydrothermal diamond-anvil cell for in-situ spectroscopic analysis of individual phases of a silicate-melt/fluid system. Synchrotron X-ray fluorescence (XRF) and Nb K-edge X-ray absorption fine structure (XAFS) measurements were made on sectors ID20 and ID13 at the Advanced Photon Source, at the Argonne National Laboratory, on a Nb-bearing granitic glass in H2O and separately in a 1 M Na2CO3 aqueous solution at temperatures ranging from 25 to 880 °C and at up to 700 MPa of pressure. Individual phases of the Nb-glass/fluid system (at low temperatures) or the hydrous-silicate-melt/fluid system (at elevated temperatures) were probed using an X-ray beam focused to a diameter of 5 μm at the location of the sample. XRF analysis shows that the Nb partitions selectively from the hydrous silicate melt into the aqueous fluid at high temperatures in the Nb-glass/Na2CO3/H2O system but not so in the Nb-glass/H2O system. Analysis of XAFS spectra measured from the hydrous silicate melt phase of the Nb-glass/H2O sample in the 450 to 700 °C range shows that the first shell contains six oxygen atoms at a distance of ~1.98 Å. Our results suggest that reorganization of the silicate structure surrounding Nb occurs in the melt when compared to that of the starting glass. The X-ray absorption near edge structure (XANES) spectra show a pre-edge peak feature located at ~18995 eV that exhibits sharpening and becomes more intensified in the 450 to 700 °C range. Fitting of the Nb K-edge XANES spectra measured from the melt is accomplished using FEFF8.28 and an atomic model NbSi4O6-4(Na, K). The model is based on the structure of fresnoite (Ba2TiSi2O8), in which an NbO6 octahedron unit is substituted for the TiO5 unit, four Na and four K atoms are placed alternately on nearby Ba atom sites, and four Si atoms are arranged in a single plane intersecting the NbO6 unit. The results from fitting indicate that the local structure of Nb in the silicate melt is altered from its local structure in the quenched glass before heating and in the glass after heating in the diamond anvil cell. The importance of in situ analysis of melts and hydrothermal fluids at various temperatures and pressures is discussed in the context of our study.

Competitive amplification of differentially melting amplicons (CADMA) enables sensitive and direct detection of all mutation types by high-resolution melting analysis.

PubMed

Kristensen, Lasse S; Andersen, Gitte B; Hager, Henrik; Hansen, Lise Lotte

2012-01-01

Sensitive and specific mutation detection is of particular importance in cancer diagnostics, prognostics, and individualized patient treatment. However, the majority of molecular methodologies that have been developed with the aim of increasing the sensitivity of mutation testing have drawbacks in terms of specificity, convenience, or costs. Here, we have established a new method, Competitive Amplification of Differentially Melting Amplicons (CADMA), which allows very sensitive and specific detection of all mutation types. The principle of the method is to amplify wild-type and mutated sequences simultaneously using a three-primer system. A mutation-specific primer is designed to introduce melting temperature decreasing mutations in the resulting mutated amplicon, while a second overlapping primer is designed to amplify both wild-type and mutated sequences. When combined with a third common primer very sensitive mutation detection becomes possible, when using high-resolution melting (HRM) as detection platform. The introduction of melting temperature decreasing mutations in the mutated amplicon also allows for further mutation enrichment by fast coamplification at lower denaturation temperature PCR (COLD-PCR). For proof-of-concept, we have designed CADMA assays for clinically relevant BRAF, EGFR, KRAS, and PIK3CA mutations, which are sensitive to, between 0.025% and 0.25%, mutated alleles in a wild-type background. In conclusion, CADMA enables highly sensitive and specific mutation detection by HRM analysis. © 2011 Wiley Periodicals, Inc.

Low temperature fused deposition modeling (FDM) 3D printing of thermolabile drugs.

PubMed

Kollamaram, Gayathri; Croker, Denise M; Walker, Gavin M; Goyanes, Alvaro; Basit, Abdul W; Gaisford, Simon

2018-07-10

Fused deposition modelling (FDM) is the most commonly investigated 3D printing technology for the manufacture of personalized medicines, however, the high temperatures used in the process limit its wider application. The objective of this study was to print low-melting and thermolabile drugs by reducing the FDM printing temperature. Two immediate release polymers, Kollidon VA64 and Kollidon 12PF were investigated as potential candidates for low-temperature FDM printing. Ramipril was used as the model low melting temperature drug (109 °C); to the authors' knowledge this is the lowest melting point drug investigated to date by FDM printing. Filaments loaded with 3% drug were obtained by hot melt extrusion at 70 °C and ramipril printlets with a dose equivalent of 8.8 mg were printed at 90 °C. HPLC analysis confirmed that the drug was stable with no signs of degradation and dissolution studies revealed that drug release from the printlets reached 100% within 20-30 min. Variable temperature Raman and solid state nuclear magnetic resonance (SSNMR) spectroscopy techniques were used to evaluate drug stability over the processing temperature range. These data indicated that ramipril did not undergo degradation below its melting point (which is above the processing temperature range: 70-90 °C) but it was transformed into the impurity diketopiperazine upon exposure to temperatures higher than its melting point. The use of the excipients Kollidon VA64 and Kollidon 12PF in FDM was further validated by printing with the drug 4-aminosalicylic acid (4-ASA), which in previous work was reported to undergo degradation in FDM printing, but here it was found to be stable. This work demonstrates that the selection and use of new excipients can overcome one of the major disadvantages in FDM printing, drug degradation due to thermal heating, making this technology suitable for drugs with lower melting temperatures. Copyright © 2018 Elsevier B.V. All rights reserved.

Mechanism Research on Melting Loss of Coppery Tuyere Small Sleeve in Blast Furnace

NASA Astrophysics Data System (ADS)

Chai, Yi-Fan; Zhang, Jian-Liang; Ning, Xiao-Jun; Wei, Guang-Yun; Chen, Yu-Ting

2016-01-01

The tuyere small sleeve in blast furnace works under poor conditions. The abnormal damage of it will severely affect the performance of the blast furnace, thus it should be replaced during the damping down period. So it is of great significance that we study and reduce the burnout of tuyere small sleeve. Melting loss is one case of its burnout. This paper studied the reasons of tuyere small sleeve's melting loss, through computational simulation and microscopic analysis of the melting section. The research shows that the temperature of coppery tuyere small sleeve is well distributed when there is no limescale in the lumen, and the temperature increases with the thickness of limescale. In addition, the interruption of circulating water does great harm to the tuyere small sleeve. The melting loss of tuyere small sleeve is caused by iron-slag erosion, with the occurrence of the melt metallurgical bonding and diffusion metallurgical combination.

Methods for Melting Temperature Calculation

NASA Astrophysics Data System (ADS)

Hong, Qi-Jun

Melting temperature calculation has important applications in the theoretical study of phase diagrams and computational materials screenings. In this thesis, we present two new methods, i.e., the improved Widom's particle insertion method and the small-cell coexistence method, which we developed in order to capture melting temperatures both accurately and quickly. We propose a scheme that drastically improves the efficiency of Widom's particle insertion method by efficiently sampling cavities while calculating the integrals providing the chemical potentials of a physical system. This idea enables us to calculate chemical potentials of liquids directly from first-principles without the help of any reference system, which is necessary in the commonly used thermodynamic integration method. As an example, we apply our scheme, combined with the density functional formalism, to the calculation of the chemical potential of liquid copper. The calculated chemical potential is further used to locate the melting temperature. The calculated results closely agree with experiments. We propose the small-cell coexistence method based on the statistical analysis of small-size coexistence MD simulations. It eliminates the risk of a metastable superheated solid in the fast-heating method, while also significantly reducing the computer cost relative to the traditional large-scale coexistence method. Using empirical potentials, we validate the method and systematically study the finite-size effect on the calculated melting points. The method converges to the exact result in the limit of a large system size. An accuracy within 100 K in melting temperature is usually achieved when the simulation contains more than 100 atoms. DFT examples of Tantalum, high-pressure Sodium, and ionic material NaCl are shown to demonstrate the accuracy and flexibility of the method in its practical applications. The method serves as a promising approach for large-scale automated material screening in which the melting temperature is a design criterion. We present in detail two examples of refractory materials. First, we demonstrate how key material properties that provide guidance in the design of refractory materials can be accurately determined via ab initio thermodynamic calculations in conjunction with experimental techniques based on synchrotron X-ray diffraction and thermal analysis under laser-heated aerodynamic levitation. The properties considered include melting point, heat of fusion, heat capacity, thermal expansion coefficients, thermal stability, and sublattice disordering, as illustrated in a motivating example of lanthanum zirconate (La2Zr2O7). The close agreement with experiment in the known but structurally complex compound La2Zr 2O7 provides good indication that the computation methods described can be used within a computational screening framework to identify novel refractory materials. Second, we report an extensive investigation into the melting temperatures of the Hf-C and Hf-Ta-C systems using ab initio calculations. With melting points above 4000 K, hafnium carbide (HfC) and tantalum carbide (TaC) are among the most refractory binary compounds known to date. Their mixture, with a general formula TaxHf 1-xCy, is known to have a melting point of 4215 K at the composition Ta4HfC 5, which has long been considered as the highest melting temperature for any solid. Very few measurements of melting point in tantalum and hafnium carbides have been documented, because of the obvious experimental difficulties at extreme temperatures. The investigation lets us identify three major chemical factors that contribute to the high melting temperatures. Based on these three factors, we propose and explore a new class of materials, which, according to our ab initio calculations, may possess even higher melting temperatures than Ta-Hf-C. This example also demonstrates the feasibility of materials screening and discovery via ab initio calculations for the optimization of "higher-level" properties whose determination requires extensive sampling of atomic configuration space.

Analysis of HIV using a high resolution melting (HRM) diversity assay: automation of HRM data analysis enhances the utility of the assay for analysis of HIV incidence.

PubMed

Cousins, Matthew M; Swan, David; Magaret, Craig A; Hoover, Donald R; Eshleman, Susan H

2012-01-01

HIV diversity may be a useful biomarker for discriminating between recent and non-recent HIV infection. The high resolution melting (HRM) diversity assay was developed to quantify HIV diversity in viral populations without sequencing. In this assay, HIV diversity is expressed as a single numeric HRM score that represents the width of a melting peak. HRM scores are highly associated with diversity measures obtained with next generation sequencing. In this report, a software package, the HRM Diversity Assay Analysis Tool (DivMelt), was developed to automate calculation of HRM scores from melting curve data. DivMelt uses computational algorithms to calculate HRM scores by identifying the start (T1) and end (T2) melting temperatures for a DNA sample and subtracting them (T2 - T1 =  HRM score). DivMelt contains many user-supplied analysis parameters to allow analyses to be tailored to different contexts. DivMelt analysis options were optimized to discriminate between recent and non-recent HIV infection and to maximize HRM score reproducibility. HRM scores calculated using DivMelt were compared to HRM scores obtained using a manual method that is based on visual inspection of DNA melting curves. HRM scores generated with DivMelt agreed with manually generated HRM scores obtained from the same DNA melting data. Optimal parameters for discriminating between recent and non-recent HIV infection were identified. DivMelt provided greater discrimination between recent and non-recent HIV infection than the manual method. DivMelt provides a rapid, accurate method of determining HRM scores from melting curve data, facilitating use of the HRM diversity assay for large-scale studies.

Analysis of HIV Using a High Resolution Melting (HRM) Diversity Assay: Automation of HRM Data Analysis Enhances the Utility of the Assay for Analysis of HIV Incidence

PubMed Central

Cousins, Matthew M.; Swan, David; Magaret, Craig A.; Hoover, Donald R.; Eshleman, Susan H.

2012-01-01

Background HIV diversity may be a useful biomarker for discriminating between recent and non-recent HIV infection. The high resolution melting (HRM) diversity assay was developed to quantify HIV diversity in viral populations without sequencing. In this assay, HIV diversity is expressed as a single numeric HRM score that represents the width of a melting peak. HRM scores are highly associated with diversity measures obtained with next generation sequencing. In this report, a software package, the HRM Diversity Assay Analysis Tool (DivMelt), was developed to automate calculation of HRM scores from melting curve data. Methods DivMelt uses computational algorithms to calculate HRM scores by identifying the start (T1) and end (T2) melting temperatures for a DNA sample and subtracting them (T2–T1 = HRM score). DivMelt contains many user-supplied analysis parameters to allow analyses to be tailored to different contexts. DivMelt analysis options were optimized to discriminate between recent and non-recent HIV infection and to maximize HRM score reproducibility. HRM scores calculated using DivMelt were compared to HRM scores obtained using a manual method that is based on visual inspection of DNA melting curves. Results HRM scores generated with DivMelt agreed with manually generated HRM scores obtained from the same DNA melting data. Optimal parameters for discriminating between recent and non-recent HIV infection were identified. DivMelt provided greater discrimination between recent and non-recent HIV infection than the manual method. Conclusion DivMelt provides a rapid, accurate method of determining HRM scores from melting curve data, facilitating use of the HRM diversity assay for large-scale studies. PMID:23240016

Effective Identification on Adulteration of Polyethylene With Post-consumer Ones

NASA Astrophysics Data System (ADS)

Zhao, S.; Qin, W. B.; Guo, J. F.; Liu, J.; Wang, Y. L.; Zhang, W.; Zhao, X. Y.; Wang, L.

2018-05-01

This paper mainly describes the effective identification of the adulteration of polyethylene with post-consumer ones. Degradation would be happened when multiple processings occurred. The melt flow index (MFI) analysis, thermal gravimetric analysis (TGA), differential scanning calorimeter (DSC) were used to characterize the processability and thermal stabilities of virgin polyethylene and recycled polyethylene which adulterated post-consumer PE. The results indicated that MFI of PE increased with the increasing doping content. Adulterating reclaimed PE had effects on the thermal stability of PE, which led to lower thermal decomposition temperature. Melting peak of recycled LLDPE varied from merely single to double, which differently compared differently with virgin LLDPE. Besides, with the doping content of post-consumer LDPE, the melting temperature had a decreasing tendency.

Rate limits in silicon sheet growth - The connections between vertical and horizontal methods

NASA Technical Reports Server (NTRS)

Thomas, Paul D.; Brown, Robert A.

1987-01-01

Meniscus-defined techniques for the growth of thin silicon sheets fall into two categories: vertical and horizontal growth. The interactions of the temperature field and the crystal shape are analyzed for both methods using two-dimensional finite-element models which include heat transfer and capillarity. Heat transfer in vertical growth systems is dominated by conduction in the melt and the crystal, with almost flat melt/crystal interfaces that are perpendicular to the direction of growth. The high axial temperature gradients characteristic of vertical growth lead to high thermal stresses. The maximum growth rate is also limited by capillarity which can restrict the conduction of heat from the melt into the crystal. In horizontal growth the melt/crystal interface stretches across the surface of the melt pool many times the crystal thickness, and low growth rates are achievable with careful temperature control. With a moderate axial temperature gradient in the sheet a substantial portion of the latent heat conducts along the sheet and the surface of the melt pool becomes supercooled, leading to dendritic growth. The thermal supercooling is surpressed by lowering the axial gradient in the crystal; this configuration is the most desirable for the growth of high quality crystals. An expression derived from scaling analysis relating the growth rate and the crucible temperature is shown to be reliable for horizontal growth.

In-situ determination of the oxidation state of iron in Fe-bearing silicate melts

NASA Astrophysics Data System (ADS)

Courtial, P.; Wilke, M.; Potuzak, M.; Dingwell, D. B.

2005-12-01

Terrestrial lavas commonly contain up to 10 wt% of iron. Furthermore, rocks returned from the Moon indicate lunar lava containing up to 25 wt% of iron and planetary scientists estimated that the martian mantle has about 18 wt% of iron. An experimental challenge in dealing with Fe-bearing silicate melts is that the oxidation state, controlling the proportions of ferric and ferrous iron, is a function of composition, oxygen fugacity and temperature and may vary significantly. Further complications concerning iron originate from its potential to be either four-, six- or even five-fold coordinated in both valence states. Therefore, the oxidation state of iron was determined in air for various Fe-bearing silicate melts. Investigated samples were Na-disilicate (NS), one atmosphere anorthite-diopside eutectic (AD) and haplogranitic (HPG8) melts containing up to 20, 20 and 10 wt% of iron, respectively. XANES spectra at the Fe K-edge were collected for all the melts at beamline A1, HASYLAB, Hamburg, using a Si(111) 4-crystal monochromator. Spectra were collected for temperatures up to 1573 K using a Pt-Rh loop as heating device. The Fe oxidation state was determined from the centroid position of the pre-edge feature using the calibration of Wilke et al. (2004). XANES results suggest that oxidation state of iron does not change within error for NS melts with addition of Fe, while AD and HPG8 melts become more oxidised with increasing iron content. Furthermore, NS melts are well more oxidised than AD and HPG8 melts that exhibit relatively similar oxidation states for identical iron contents. The oxidation state of iron for NS melts appears to be slightly temperature-dependent within the temperature range investigated (1073-1573 K). However, this trend is stronger for AD and HPG8 melts. Assuming that glass reflects a picture of the homogeneous equilibria of the melt, the present in-situ Fe-oxidation states determined for these melts were compared to those obtained on quenched glasses from different temperatures, when possible, using wet-chemical analysis (i.e., K-dichromate potentiometry). Both datasets agree reasonably well (within 10 %). References: Wilke et al. (2004) Chemical Geology, 213, 71-87.

The melting and solidification of nanowires

NASA Astrophysics Data System (ADS)

Florio, B. J.; Myers, T. G.

2016-06-01

A mathematical model is developed to describe the melting of nanowires. The first section of the paper deals with a standard theoretical situation, where the wire melts due to a fixed boundary temperature. This analysis allows us to compare with existing results for the phase change of nanospheres. The equivalent solidification problem is also examined. This shows that solidification is a faster process than melting; this is because the energy transfer occurs primarily through the solid rather than the liquid which is a poorer conductor of heat. This effect competes with the energy required to create new solid surface which acts to slow down the process, but overall conduction dominates. In the second section, we consider a more physically realistic boundary condition, where the phase change occurs due to a heat flux from surrounding material. This removes the singularity in initial melt velocity predicted in previous models of nanoparticle melting. It is shown that even with the highest possible flux the melting time is significantly slower than with a fixed boundary temperature condition.

Determination of the liquidus temperature of tin using the heat pulse-based melting and comparison with traditional methods

NASA Astrophysics Data System (ADS)

Joung, Wukchul; Park, Jihye; Pearce, Jonathan V.

2018-06-01

In this work, the liquidus temperature of tin was determined by melting the sample using the pressure-controlled loop heat pipe. Square wave-type pressure steps generated periodic 0.7 °C temperature steps in the isothermal region in the vicinity of the tin sample, and the tin was melted with controllable heat pulses from the generated temperature changes. The melting temperatures at specific melted fractions were measured, and they were extrapolated to the melted fraction of unity to determine the liquidus temperature of tin. To investigate the influence of the impurity distribution on the melting behavior, a molten tin sample was solidified by an outward slow freezing or by quenching to segregate the impurities inside the sample with concentrations increasing outwards or to spread the impurities uniformly, respectively. The measured melting temperatures followed the local solidus temperature variations well in the case of the segregated sample and stayed near the solidus temperature in the quenched sample due to the microscopic melting behavior. The extrapolated melting temperatures of the segregated and quenched samples were 0.95 mK and 0.49 mK higher than the outside-nucleated freezing temperature of tin (with uncertainties of 0.15 mK and 0.16 mK, at approximately 95% level of confidence), respectively. The extrapolated melting temperature of the segregated sample was supposed to be a closer approximation to the liquidus temperature of tin, whereas the quenched sample yielded the possibility of a misleading extrapolation to the solidus temperature. Therefore, the determination of the liquidus temperature could result in different extrapolated melting temperatures depending on the way the impurities were distributed within the sample, which has implications for the contemporary methodology for realizing temperature fixed points of the International Temperature Scale of 1990 (ITS-90).

Climate change and forest fires synergistically drive widespread melt events of the Greenland Ice Sheet.

PubMed

Keegan, Kaitlin M; Albert, Mary R; McConnell, Joseph R; Baker, Ian

2014-06-03

In July 2012, over 97% of the Greenland Ice Sheet experienced surface melt, the first widespread melt during the era of satellite remote sensing. Analysis of six Greenland shallow firn cores from the dry snow region confirms that the most recent prior widespread melt occurred in 1889. A firn core from the center of the ice sheet demonstrated that exceptionally warm temperatures combined with black carbon sediments from Northern Hemisphere forest fires reduced albedo below a critical threshold in the dry snow region, and caused the melting events in both 1889 and 2012. We use these data to project the frequency of widespread melt into the year 2100. Since Arctic temperatures and the frequency of forest fires are both expected to rise with climate change, our results suggest that widespread melt events on the Greenland Ice Sheet may begin to occur almost annually by the end of century. These events are likely to alter the surface mass balance of the ice sheet, leaving the surface susceptible to further melting.

Measurement of Nanomolar Dissociation Constants by Titration Calorimetry and Thermal Shift Assay – Radicicol Binding to Hsp90 and Ethoxzolamide Binding to CAII

PubMed Central

Zubrienė, Asta; Matulienė, Jurgita; Baranauskienė, Lina; Jachno, Jelena; Torresan, Jolanta; Michailovienė, Vilma; Cimmperman, Piotras; Matulis, Daumantas

2009-01-01

The analysis of tight protein-ligand binding reactions by isothermal titration calorimetry (ITC) and thermal shift assay (TSA) is presented. The binding of radicicol to the N-terminal domain of human heat shock protein 90 (Hsp90αN) and the binding of ethoxzolamide to human carbonic anhydrase (hCAII) were too strong to be measured accurately by direct ITC titration and therefore were measured by displacement ITC and by observing the temperature-denaturation transitions of ligand-free and ligand-bound protein. Stabilization of both proteins by their ligands was profound, increasing the melting temperature by more than 10 ºC, depending on ligand concentration. Analysis of the melting temperature dependence on the protein and ligand concentrations yielded dissociation constants equal to 1 nM and 2 nM for Hsp90αN-radicicol and hCAII-ethoxzolamide, respectively. The ligand-free and ligand-bound protein fractions melt separately, and two melting transitions are observed. This phenomenon is especially pronounced when the ligand concentration is equal to about half the protein concentration. The analysis compares ITC and TSA data, accounts for two transitions and yields the ligand binding constant and the parameters of protein stability, including the Gibbs free energy and the enthalpy of unfolding. PMID:19582223

Laser induced heating of coated carbon steel sheets: Consideration of melting and Marangoni flow

NASA Astrophysics Data System (ADS)

Shuja, S. Z.; Yilbas, B. S.

2013-04-01

Laser induced melting of coated carbon steel workpiece is simulated. The coating materials include tungsten carbide, alumina, and boron are incorporated in the simulations. The coating thickness is kept constant at 7.5 μm in the analysis. The enthalpy porosity method is used to account for the phase change in the irradiated region. The study is extended to include the influence of laser intensity transverse mode pattern (β) on the resulting melting characteristics. It is found that peak temperature predicted at the surface is higher for alumina and boron coatings than that of tungsten carbide coating. The influence of the laser intensity transverse mode pattern on the melting characteristics is considerable. Surface temperature predicted agrees with the thermocouple data.

Experimental study and numerical simulation of the salinity effect on water-freezing point and ice-melting rate

NASA Astrophysics Data System (ADS)

Qin, N.; Wu, Y.; Wang, H. W.; Wang, Y. Y.

2017-12-01

In this paper, based on the background of snowmelt de-icing tools, we studied the effect of salt on freezing point and melting rate of ice through laboratory test and FLUENT numerical simulation analysis. It was confirmed that the freezing point is inversely proportional to the salt solid content, and with the salt solid content increasing, the freezing process of salt water gradually accepts the curing rule of non-crystal solids. At the same temperature, an increase in the salt solid content, the ice melting rate increase by the empirical formula linking the melting time with temperature and salt content. The theoretical aspects of solid/fluid transformation are discussed in detail.

REVIEWS OF TOPICAL PROBLEMS: Universal viscosity growth in metallic melts at megabar pressures: the vitreous state of the Earth's inner core

NASA Astrophysics Data System (ADS)

Brazhkin, Vadim V.; Lyapin, A. G.

2000-05-01

Experimental data on and theoretical models for the viscosity of various types of liquids and melts under pressure are reviewed. Experimentally, the least studied melts are those of metals, whose viscosity is considered to be virtually constant along the melting curve. The authors' new approach to the viscosity of melts involves the measurement of the grain size in solidified samples. Measurements on liquid metals at pressures up to 10 GPa using this method show, contrary to the empirical approach, that the melt viscosity grows considerably along the melting curves. Based on the experimental data and on the critical analysis of current theories, a hypothesis of a universal viscosity behavior is introduced for liquids under pressure. Extrapolating the liquid iron results to the pressures and temperatures at the Earth's core reveals that the Earth's outer core is a very viscous melt with viscosity values ranging from 102 Pa s to 1011 Pa s depending on the depth. The Earth's inner core is presumably an ultraviscous (>1011 Pa s) glass-like liquid — in disagreement with the current idea of a crystalline inner core. The notion of the highly viscous interior of celestial bodies sheds light on many mysteries of planetary geophysics and astronomy. From the analysis of the pressure variation of the melting and glass-transition temperatures, an entirely new concept of a stable metallic vitreous state arises, calling for further experimental and theoretical study.

Thermophoretic melting curves quantify the conformation and stability of RNA and DNA

PubMed Central

Wienken, Christoph J.; Baaske, Philipp; Duhr, Stefan; Braun, Dieter

2011-01-01

Measuring parameters such as stability and conformation of biomolecules, especially of nucleic acids, is important in the field of biology, medical diagnostics and biotechnology. We present a thermophoretic method to analyse the conformation and thermal stability of nucleic acids. It relies on the directed movement of molecules in a temperature gradient that depends on surface characteristics of the molecule, such as size, charge and hydrophobicity. By measuring thermophoresis of nucleic acids over temperature, we find clear melting transitions and resolve intermediate conformational states. These intermediate states are indicated by an additional peak in the thermophoretic signal preceding most melting transitions. We analysed single nucleotide polymorphisms, DNA modifications, conformational states of DNA hairpins and microRNA duplexes. The method is validated successfully against calculated melting temperatures and UV absorbance measurements. Interestingly, the methylation of DNA is detected by the thermophoretic amplitude even if it does not affect the melting temperature. In the described setup, thermophoresis is measured all-optical in a simple setup using a reproducible capillary format with only 250 nl probe consumption. The thermophoretic analysis of nucleic acids shows the technique’s versatility for the investigation of nucleic acids relevant in cellular processes like RNA interference or gene silencing. PMID:21297115

The solubility of carbon monoxide in silicate melts at high pressures and its effect on silicate phase relations. [in terrestrial and other planetary interiors

NASA Technical Reports Server (NTRS)

Eggler, D. H.; Mysen, B. O.; Hoering, T. C.; Holloway, J. R.

1979-01-01

Autoradiographic analysis and gas chromatography were used to measure the solubility in silicate melts of CO-CO2 vapors (30 to 40% CO by thermodynamic calculation) in equilibrium with graphite at temperatures up to 1700 deg C and pressures to 30 kbar. At near-liquidus temperatures CO-CO2 vapors were found to be slightly more soluble than CO2 alone. As a result of the apparently negative temperature dependence of CO solubility, the solubility of CO-CO2 at superliquidus temperatures is less than that of CO2. Melting points of two silicates were depressed more by CO than by CO2. Phase boundary orientations suggest that CO/CO + CO2 is greater in the liquid than in the vapor. The effect of the presence of CO on periodotite phase relations was investigated, and it was found that melts containing both CO and CO2 are nearly as polymerized as those containing only CO2. These results suggest that crystallization processes in planetary interiors can be expected to be about the same, whether the melts contain CO2 alone or CO2 and CO.

Internal stress-induced melting below melting temperature at high-rate laser heating

NASA Astrophysics Data System (ADS)

Hwang, Yong Seok; Levitas, Valery I.

2014-06-01

In this Letter, continuum thermodynamic and phase field approaches (PFAs) predicted internal stress-induced reduction in melting temperature for laser-irradiated heating of a nanolayer. Internal stresses appear due to thermal strain under constrained conditions and completely relax during melting, producing an additional thermodynamic driving force for melting. Thermodynamic melting temperature for Al reduces from 933.67 K for a stress-free condition down to 898.1 K for uniaxial strain and to 920.8 K for plane strain. Our PFA simulations demonstrated barrierless surface-induced melt nucleation below these temperatures and propagation of two solid-melt interfaces toward each other at the temperatures very close to the corresponding predicted thermodynamic equilibrium temperatures for the heating rate Q ≤1.51×1010K/s. At higher heating rates, kinetic superheating competes with a reduction in melting temperature and melting under uniaxial strain occurs at 902.1 K for Q = 1.51 × 1011 K/s and 936.9 K for Q = 1.46 × 1012 K/s.

Model of melting (crystallization) process of the condensed disperse phase in the smoky plasmas

NASA Astrophysics Data System (ADS)

Dragan, G. S.; Kolesnikov, K. V.; Kutarov, V. V.

2018-01-01

The paper presents an analysis of the causes of a formation of spatial ordered grain structures in a smoky plasma. We are modeling the process of melting (crystallization) of a condensed phase in this environment taking into account the screened electrostatic interaction and the diffusion-drift force. We discuss an influence of the charge on the melting temperatures.

Flash melting of tantalum in a diamond cell to 85 GPa

DOE Office of Scientific and Technical Information (OSTI.GOV)

Karandikar, Amol; Boehler, Reinhard

2016-02-09

Here, we demonstrate a new level of precision in measuring melting temperatures at high pressure using laser flash-heating followed by Scanning Electron Microscopy and Focused Ion Beam Milling. Furthermore, the new measurements on tantalum put unprecedented constraints on its highly debated melting slope, calling for a reevaluation of theoretical, shock compression and diamond cell approaches to determine melting at high pressure. X-ray analysis of the recovered samples confirmed the absence of chemical reactions, which likely played a significant role in previous experiments.

Tin in granitic melts: The role of melting temperature and protolith composition

NASA Astrophysics Data System (ADS)

Wolf, Mathias; Romer, Rolf L.; Franz, Leander; López-Moro, Francisco Javier

2018-06-01

Granite bound tin mineralization typically is seen as the result of extreme magmatic fractionation and late exsolution of magmatic fluids. Mineralization, however, also could be obtained at considerably less fractionation if initial melts already had enhanced Sn contents. We present chemical data and results from phase diagram modeling that illustrate the dominant roles of protolith composition, melting conditions, and melt extraction/evolution for the distribution of Sn between melt and restite and, thus, the Sn content of melts. We compare the element partitioning between leucosome and restite of low-temperature and high-temperature migmatites. During low-temperature melting, trace elements partition preferentially into the restite with the possible exception of Sr, Cd, Bi, and Pb, that may be enriched in the melt. In high-temperature melts, Ga, Y, Cd, Sn, REE, Pb, Bi, and U partition preferentially into the melt whereas Sc, V, Cr, Co, Ni, Mo, and Ba stay in the restite. This contrasting behavior is attributed to the stability of trace element sequestering minerals during melt generation. In particular muscovite, biotite, titanite, and rutile act as host phases for Sn and, therefore prevent Sn enrichment in the melt as long as they are stable phases in the restite. As protolith composition controls both the mineral assemblage and modal contents of the various minerals, protolith composition eventually also controls the fertility of a rock during anatexis, restite mineralogy, and partitioning behavior of trace metals. If a particular trace element is sequestered in a phase that is stable during partial melting, the resulting melt is depleted in this element whereas the restite becomes enriched. Melt generation at high temperature may release Sn when Sn-hosts become unstable. If melt has not been lost before the breakdown of Sn-hosts, Sn contents in the melt will increase but never will be high. In contrast, if melt has been lost before the decomposition of Sn-hosts, the small volume of the high-temperature melt will not be diluted by low-temperature, low-Sn melts and, therefore, could have high Sn-contents. The combination of multiple melt extractions and Sn-mobilization at high temperature results in strong Sn enrichment in late, high-temperature melts. Metal enrichment during partial melting becomes particularly efficient, if the sedimentary protolith had experienced intense chemical alteration as the loss of Na and Ca together with a relative enrichment of K favors muscovite-rich metamorphic mineral assemblages that produce large amounts of melt during muscovite dehydration melting.

Effect of Injection Molding Melt Temperatures on PLGA Craniofacial Plate Properties during In Vitro Degradation.

PubMed

de Melo, Liliane Pimenta; Salmoria, Gean Vitor; Fancello, Eduardo Alberto; Roesler, Carlos Rodrigo de Mello

2017-01-01

The purpose of this article is to present mechanical and physicochemical properties during in vitro degradation of PLGA material as craniofacial plates based on different values of injection molded temperatures. Injection molded plates were submitted to in vitro degradation in a thermostat bath at 37 ± 1°C by 16 weeks. The material was removed after 15, 30, 60, and 120 days; then bending stiffness, crystallinity, molecular weights, and viscoelasticity were studied. A significant decrease of molecular weight and mechanical properties over time and a difference in FT-IR after 60 days showed faster degradation of the material in the geometry studied. DSC analysis confirmed that the crystallization occurred, especially in higher melt temperature condition. DMA analysis suggests a greater contribution of the viscous component of higher temperature than lower temperature in thermomechanical behavior. The results suggest that physical-mechanical properties of PLGA plates among degradation differ per injection molding temperatures.

Molecular dynamics simulation of UO2 nanocrystals melting under isolated and periodic boundary conditions

NASA Astrophysics Data System (ADS)

Boyarchenkov, A. S.; Potashnikov, S. I.; Nekrasov, K. A.; Kupryazhkin, A. Ya.

2012-08-01

Melting of uranium dioxide (UO2) nanocrystals has been studied by molecular dynamics (MD) simulation. Ten recent and widely used sets of pair potentials were assessed in the rigid ion approximation. Both isolated (in vacuum) and periodic boundary conditions (PBC) were explored. Using barostat under PBC the pressure dependences of melting point were obtained. These curves intersected zero near -20 GPa, saturated near 25 GPa and increased nonlinearly in between. Using simulation of surface under isolated boundary conditions (IBC) recommended melting temperature and density jump were successfully reproduced. However, the heat of fusion is still underestimated. These melting characteristics were calculated for nanocrystals of cubic shape in the range of 768-49 152 particles (volume range of 10-1000 nm3). The obtained reciprocal size dependences decreased nonlinearly. Linear and parabolic extrapolations to macroscopic values are considered. The parabolic one is found to be better suited for analysis of the data on temperature and heat of melting.

Phase field study of surface-induced melting and solidification from a nanovoid: Effect of dimensionless width of void surface and void size

NASA Astrophysics Data System (ADS)

Basak, Anup; Levitas, Valery I.

2018-05-01

The size effect and the effects of a finite-width surface on barrierless transformations between the solid (S), surface melt (SM), and melt (M) from a spherical nanovoid are studied using a phase field approach. Melting (SM → M and S → M) from the nanovoid occurs at temperatures which are significantly greater than the solid-melt equilibrium temperature θe but well below the critical temperature for solid instability. The relationships between the SM and M temperatures and the ratio of the void surface width and width of the solid-melt interface, Δ ¯ , are found for the nanovoids of different sizes. Below a critical ratio Δ¯ * , the melting occurs via SM and the melting temperature slightly reduces with an increase in Δ ¯ . Both S → SM and SM → M transformations have a jump-like character (excluding the case with the sharp void surface), causing small temperature hysteresis. However, the solid melts without SM for Δ ¯>Δ¯ * , and the melting temperature significantly increases with increasing Δ ¯ . The results for a nanovoid are compared with the melting/solidification of a nanoparticle, for which the melting temperatures, in contrast, are much lower than θe. A linear dependency of the melting temperatures with the inverse of the void radius is shown. The present study shows an unexplored way to control the melting from nanovoids by controlling the void size and the width and energy of the surface.

Quasi-equilibrium melting of quartzite upon extreme friction

NASA Astrophysics Data System (ADS)

Lee, Sung Keun; Han, Raehee; Kim, Eun Jeong; Jeong, Gi Young; Khim, Hoon; Hirose, Takehiro

2017-06-01

The friction on fault planes that controls how rocks slide during earthquakes decreases significantly as a result of complex fault-lubrication processes involving frictional melting. Fault friction has been characterized in terms of the preferential melting of minerals with low melting points--so-called disequilibrium melting. Quartz, which has a high melting temperature of about 1,726 °C and is a major component of crustal rocks, is not expected to melt often during seismic slip. Here we use high-velocity friction experiments on quartzite to show that quartz can melt at temperatures of 1,350 to 1,500 °C. This implies that quartz within a fault plane undergoing rapid friction sliding could melt at substantially lower temperatures than expected. We suggest that depression of the melting temperature is caused by the preferential melting of ultra-fine particles and metastable melting of β-quartz at about 1,400 °C during extreme frictional slip. The results for quartzite are applicable to complex rocks because of the observed prevalence of dynamic grain fragmentation, the preferential melting of smaller grains and the kinetic preference of β-quartz formation during frictional sliding. We postulate that frictional melting of quartz on a fault plane at temperatures substantially below the melting temperature could facilitate slip-weakening and lead to large earthquakes.

On the Composition and Temperature of the Terrestrial Planetary Core

NASA Astrophysics Data System (ADS)

Fei, Yingwei

2013-06-01

The existence of liquid cores of terrestrial planets such as the Earth, Mar, and Mercury has been supported by various observation. The liquid state of the core provides a unique opportunity for us to estimate the temperature of the core if we know the melting temperature of the core materials at core pressure. Dynamic compression by shock wave, laser-heating in diamond-anvil cell, and resistance-heating in the multi-anvil device can melt core materials over a wide pressure range. There have been significant advances in both dynamic and static experimental techniques and characterization tool. In this tal, I will review some of the recent advances and results relevant to the composition and thermal state of the terrestrial core. I will also present new development to analyze the quenched samples recovered from laser-heating diamond-anvil cell experiments using combination of focused ion beam milling, high-resolution SEM imaging, and quantitative chemical analysi. With precision milling of the laser-heating spo, the melting point and element partitioning between solid and liquid can be precisely determined. It is also possible to re-construct 3D image of the laser-heating spot at multi-megabar pressures to better constrain melting point and understanding melting process. The new techniques allow us to extend precise measurements of melting relations to core pressures, providing better constraint on the temperature of the cor. The research is supported by NASA and NSF grants.

Boring and Sealing Rock with Directed Energy Millimeter-Waves

NASA Astrophysics Data System (ADS)

Woskov, P.; Einstein, H. H.; Oglesby, K.

2015-12-01

Millimeter-wave directed energy is being investigated to penetrate into deep crystalline basement rock formations to lower well costs and to melt rocks, metals, and other additives to seal wells for applications that include nuclear waste storage and geothermal energy. Laboratory tests have established that intense millimeter-wave (MMW) beams > 1 kW/cm2 can melt and/ or vaporize hard crystalline rocks. In principle this will make it possible to create open boreholes and a method to seal them with a glass/ceramic liner and plug formed from the original rock or with other materials. A 10 kW, 28 GHz commercial (CPI) gyrotron system with a launched beam diameter of about 32 mm was used to heat basalt, granite, limestone, and sandstone specimens to temperatures over 2500 °C to create melts and holes. A calibrated 137 GHz radiometer view, collinear with the heating beam, monitored real time peak rock temperature. A water load surrounding the rock test specimen primarily monitored unabsorbed power at 28 GHz. Power balance analysis of the laboratory observations shows that the temperature rise is limited by radiative heat loss, which would be expected to be trapped in a borehole. The analysis also indicates that the emissivity (absorption efficiency) in the radiated infrared range is lower than the emissivity at 28 GHz, giving the MMW frequency range an important advantage for rock melting. Strength tests on one granite type indicated that heating the rock initially weakens it, but with exposure to higher temperatures the resolidified black glassy product regains strength. Basalt was the easiest to melt and penetrate, if a melt leak path was provided, because of its low viscosity. Full beam holes up to about 50 mm diameter (diffraction increased beam size) were achieved through 30 mm thick basalt and granite specimens. Laboratory experiments to form a seal in an existing hole have also been carried out by melting rock and a simulated steel casing.

Pore Formation and Mobility Investigation (PPMI): Description and Initial Analysis of Experiments Conducted aboard the International Space Station

NASA Technical Reports Server (NTRS)

Grugel, R. N.; Anilkumar, A. V.; Lee, C. P.

2003-01-01

Flow visualization experiments during the controlled directional melt back and re-solidification of succinonitrile (SCN) and SCN-water mixtures were conducted using the Pore Formation and Mobility Investigation (PFMI) apparatus in the glovebox facility (GBX) aboard the International Space Station. The study samples were initially 'cast' on earth under 450 millibar of nitrogen into 1 cm ID glass sample tubes approximately 30 cm in length, containing 6 in situ thermocouples. During the Space experiments, the processing parameters and flow visualization settings are remotely monitored and manipulated from the ground Telescience Center (TSC). The ground solidified sample is first subjected to a unidirectional melt back, generally at 10 microns per second, with a constant temperature gradient ahead of the melting interface. Bubbles of different sizes are seen to initiate at the melt interface and, upon release from the melting solid, translate at different speeds in the temperature field ahead of them before coming to rest. Over a period of time these bubbles dissolve into the melt. The gas-laden liquid is then directionally solidified in a controlled manner, generally starting at a rate of 1 micron /sec. Observation and preliminary analysis of bubble formation and mobility in pure SCN samples during melt back and the subsequent structure resulting during gas generation upon re-solidification are presented and discussed.

Pore Formation and Mobility Investigation (PFMI): Description and Initial Analysis of Experiments Conducted aboard the International Space Station

NASA Technical Reports Server (NTRS)

Grugel, R. N.; Anilkumar, A. V.; Lee, C. P.

2002-01-01

Flow visualization experiments during the controlled directional melt back and re-solidification of succinonitrile (SCN) and SCN-water mixtures were conducted using the Pore Formation and Mobility Investigation (PFMI) apparatus in the glovebox facility (GBX) aboard the International Space Station. The study samples were initially "cast" on earth under 450 millibar of nitrogen into 1 cm ID glass sample tubes approximately 30 cm in length, containing 6 in situ thermocouples. During the Space experiments, the processing parameters and flow visualization settings are remotely monitored and manipulated from the ground Telescience Center (TSC). The ground solidified sample is first subjected to a unidirectional melt back, generally at 10 microns per second, with a constant temperature gradient ahead of the melting interface. Bubbles of different sizes are seen to initiate at the melt interface and, upon release from the melting solid, translate at different speeds in the temperature field ahead of them before coming to rest. Over a period of time these bubbles dissolve into the melt. The gas-laden liquid is then directionally solidified in a controlled manner, generally starting at a rate of 1 micron /sec. Observation and preliminary analysis of bubble formation and mobility in pure SCN samples during melt back and the subsequent structure resulting during gas generation upon re-solidification are presented and discussed.

Preparation, melting behavior and thermal stability of poly(lactic acid)/poly(propylene carbonate) blends processed by vane extruder

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zou, Wei, E-mail: zw55624@163.com; Chen, Rongyuan; Zhang, Haichen

Poly (lactic acid) (PLA)/Poly (propylene carbonate) (PPC) blends were prepared by vane extruder which is a type of novel polymer processing extruder based on elongation force field. Scanning electron microscope (SEM), differential scanning calorimetry (DSC) and thermogravimetric (TG) were used respectively to analyze the compatibility, the melting behavior and thermal stability properties of PLA/PPC blends affected by the different content of PPC. The results showed that with the increase of the PPC content, the glass transition temperature of PLA was reduced, and the glass transition temperature of PPC was increased, which indicated that PLA and PPC had partial compatibility. Themore » cold crystallization temperature of PLA increased with the increase of the PPC content, which showed that PPC hindered the cold crystallization process of PLA. The addition of PPC had little impact on the melting process of PLA, and the melting temperature of PLA was almost kept the same value. Thermogravimetric analysis showed that the thermal stability of PPC was worse than that of PLA, the addition of PPC reduced the thermal stability of PLA.« less

Phase Diagram of HgTe -ZnTe Pseudobinary and Density, Heat Capacity, and Enthalphy of Mixing of Hg(sub 1-x)Zn(sub x)Te Pseudobinary Melts

NASA Technical Reports Server (NTRS)

Su, Ching-Hua; Sha, Yi-Gao; Mazuruk, K.; Lehoczky, S. L.

1996-01-01

In this article, the solidus temperatures of the Hg(sub 1-x) Zn(sub x)Te pseudobinary phase diagram for several compositions in the low x region were measured by differential thermal analysis and the HgTe-ZnTe pseudobinary phase diagram was constructed. The densities of two HgZnTe melts, x = 0.10 and 0.16, were determined by an in situ pycnometric technique in a transparent furnace over, respectively, 110 and 50 C ranges of temperature. The thermodynamic properties of the melts, such as the heat capacity and enthalpy of mixing, were calculated for temperatures between the liquidus and 1500 C by assuming an associated solution model for the liquid phase.

Laser pulse heating of steel mixing with WC particles in a irradiated region

NASA Astrophysics Data System (ADS)

Shuja, S. Z.; Yilbas, B. S.; Ali, H.; Karatas, C.

2016-12-01

Laser pulse heating of steel mixing with tungsten carbide (WC) particles is carried out. Temperature field in the irradiated region is simulated in line with the experimental conditions. In the analysis, a laser pulse parameter is introduced, which defines the laser pulse intensity distribution at the irradiated surface. The influence of the laser parameter on the melt pool size and the maximum temperature increase in the irradiated region is examined. Surface temperature predictions are compared with the experimental data. In addition, the distribution of WC particles and their re-locations in the treated layer, due to combination of the natural convection and Marangoni currents, are predicted. The findings are compared to the experimental data. It is found that surface temperature predictions agree well with the experimental data. The dislocated WC particles form a streamlining in the near region of the melt pool wall, which agree with the experimental findings. The Gaussian distribution of the laser pulse intensity results in the maximum peak temperature and the maximum flow velocity inside the melt pool. In this case, the melt pool depth becomes the largest as compared to those corresponding to other laser pulse intensity distributions at the irradiated surface.

Molecular-dynamics study of propane-hydrate dissociation: Fluctuation-dissipation and non-equilibrium analysis.

PubMed

Ghaani, Mohammad Reza; English, Niall J

2018-03-21

Equilibrium and non-equilibrium molecular-dynamics (MD) simulations have been performed to investigate thermal-driven break-up of planar propane-hydrate interfaces in contact with liquid water over the 260-320 K range. Two types of hydrate-surface water-lattice molecular termination were adopted, at the hydrate edge with water, for comparison: a 001-direct surface cleavage and one with completed cages. Statistically significant differences in melting temperatures and initial break-up rates were observed between both interface types. Dissociation rates were observed to be strongly dependent on temperature, with higher rates at larger over-temperatures vis-à-vis melting. A simple coupled mass and heat transfer model, developed previously, was applied to fit the observed dissociation profiles, and this helps us to identify clearly two distinct hydrate-decomposition régimes; following a highly temperature-dependent break-up phase, a second well-defined stage is essentially independent of temperature, in which the remaining nanoscale, de facto two-dimensional system's lattice framework is intrinsically unstable. Further equilibrium MD-analysis of the two-phase systems at their melting point, with consideration of the relaxation times gleaned from the auto-correlation functions of fluctuations in a number of enclathrated guest molecules, led to statistically significant differences between the two surface-termination cases; a consistent correlation emerged in both cases between the underlying, non-equilibrium, thermal-driven dissociation rates sampled directly from melting with that from an equilibrium-MD fluctuation-dissipation approach.

Molecular-dynamics study of propane-hydrate dissociation: Fluctuation-dissipation and non-equilibrium analysis

NASA Astrophysics Data System (ADS)

Ghaani, Mohammad Reza; English, Niall J.

2018-03-01

Equilibrium and non-equilibrium molecular-dynamics (MD) simulations have been performed to investigate thermal-driven break-up of planar propane-hydrate interfaces in contact with liquid water over the 260-320 K range. Two types of hydrate-surface water-lattice molecular termination were adopted, at the hydrate edge with water, for comparison: a 001-direct surface cleavage and one with completed cages. Statistically significant differences in melting temperatures and initial break-up rates were observed between both interface types. Dissociation rates were observed to be strongly dependent on temperature, with higher rates at larger over-temperatures vis-à-vis melting. A simple coupled mass and heat transfer model, developed previously, was applied to fit the observed dissociation profiles, and this helps us to identify clearly two distinct hydrate-decomposition régimes; following a highly temperature-dependent break-up phase, a second well-defined stage is essentially independent of temperature, in which the remaining nanoscale, de facto two-dimensional system's lattice framework is intrinsically unstable. Further equilibrium MD-analysis of the two-phase systems at their melting point, with consideration of the relaxation times gleaned from the auto-correlation functions of fluctuations in a number of enclathrated guest molecules, led to statistically significant differences between the two surface-termination cases; a consistent correlation emerged in both cases between the underlying, non-equilibrium, thermal-driven dissociation rates sampled directly from melting with that from an equilibrium-MD fluctuation-dissipation approach.

On the melting temperature measurements of metals under shock compression by pyrometry

NASA Astrophysics Data System (ADS)

Dai, Chengda; Hu, Jianbo; Tan, Hua

2009-06-01

The high-pressure melting temperatures are of interest in validating equation of state and modeling constitutive equation. The determination of melting temperatures for metals at megabars by pyrometry experiments is principally associated with the one-dimensional models for heat flow through dissimilar media: Grover-Urtiew model (J. App. Phys. 1974, 45: 146-152) and Tan-Ahrens model (High Press. Res. 1990, 2: 159-182). In the present work, we analyzed the insufficiency of Grover-Urtiew model in determining melting temperatures from observed interface temperatures. Based on the Tan-Ahrens model, we extracted the upper and lower bound on melting temperature at interface pressure, and proposed that the median of the both bounds was a good approximation to the melting temperatures at interface pressure. Pyrometry experiments were performed on tantalum, and the high-pressure melting temperatures were evaluated by application of the proposed approximation. The obtained results were compared with available theoretical calculations.

Melt Flow before Crystal Seeding in Cz Si Growth with Transversal MF

NASA Astrophysics Data System (ADS)

Iizuka, Masaya; Mukaiyama, Yuji; Demina, S. E.; Kalaev, V. V.

2017-06-01

Industrial Cz growth of Si crystal of 300 mm and higher diameter usually requires DC magnetic fields (MFs) to suppress turbulence in the melt. We present 3D unsteady analysis of melt turbulent convection in an industrial Cz system coupled with the effect of the transversal MF for different argon gas flow rates for the stage before crystal seeding. We have performed detailed 2D axisymmetric modeling of global heat transfer in the whole Cz furnace. Radiative heat fluxes obtained in 2D modeling have been used in detailed 3D steady and unsteady modeling of crystallization zone. LES method is applied as a predictive approach for modeling of turbulent flow of silicon melt. We have obtained flow structure and temperature distribution in the melt, which were different from previously reported data. We have observed a well-fixed dark spike which includes low temperature melt area on the melt free surface in MF cases. These results indicates that MF and argon flow rate conditions are important to achieve stable positioning of the dark spike on the melt free surface for optimized crystal seeding without uncontrollable meltdown and single crystal structure loss.

Update on the Greenland Ice Sheet Melt Extent: 1979-1999

NASA Technical Reports Server (NTRS)

Abdalati, Waleed; Steffen, Konrad

2000-01-01

Analysis of melt extent on the Greenland ice sheet is updated to span the time period 1979-1999 is examined along with its spatial and temporal variability using passive microwave satellite data. In order to acquire the full record, the issue of continuity between previous passive microwave sensors (SMMR, SSM/I F-8, and SSM/I F-11), and the most recent SSM/I F-13 sensor is addressed. The F-13 Cross-polarized gradient ratio (XPGR) melt-classification threshold is determined to be -0.0154. Results show that for the 21-year record, an increasing melt trend of nearly 1 %/yr is observed, and this trend is driven by conditions on in the western portion of the ice sheet, rather than the east, where melt appears to have decreased slightly. Moreover, the eruption of Mt. Pinatubo in 1991 is likely to have had some impact the melt, but not as much as previously suspected. The 1992 melt anomaly is 1.7 standard deviations from the mean. Finally, the relationship between coastal temperatures and melt extent suggest an increase in surface runoff contribution to sea level of 0.31 mm/yr for a 1 C temperature rise.

Investigation of Thermal and Viscoelastic Properties of Polymers Relevant to Hot Melt Extrusion, IV: Affinisol™ HPMC HME Polymers.

PubMed

Gupta, Simerdeep Singh; Solanki, Nayan; Serajuddin, Abu T M

2016-02-01

Most cellulosic polymers cannot be used as carriers for preparing solid dispersion of drugs by hot melt extrusion (HME) due to their high melt viscosity and thermal degradation at high processing temperatures. Three HME-grade hydroxypropyl methylcelluloses, namely Affinisol™ HPMC HME 15 cP, Affinisol™ HPMC HME 100 cP, and Affinisol™ HPMC HME 4 M, have recently been introduced by The Dow Chemical Co. to enable the preparation of solid dispersion at lower and more acceptable processing temperatures. In the present investigation, physicochemical properties of the new polymers relevant to HME were determined and compared with that of Kollidon(®) VA 64. Powder X-ray diffraction (PXRD), modulated differential scanning calorimetry (mDSC), thermogravimetric analysis (TGA), moisture sorption, rheology, and torque analysis by melt extrusion were applied. PXRD and mDSC showed that the Affinisol™ polymers were amorphous in nature. According to TGA, the onset of degradation for all polymers was >220°C. The Affinisol™ polymers exhibited less hygroscopicity than Kollidon(®) VA 64 and another HPMC polymer, Methocel™ K100LV. The complex viscosity profiles of the Affinisol™ polymers as a function of temperature were similar. The viscosity of the Affinisol™ polymers was highly sensitive to the shear rate applied, and unlike Kollidon(®) VA 64, the viscosity decreased drastically when the angular frequency was increased. Because of the very high shear rate encountered during melt extrusion, Affinisol™ polymers showed capability of being extruded at larger windows of processing temperatures as compared to that of Kollidon(®) VA 64.

Glacier Melt Detection in Complex Terrain Using New AMSR-E Calibrated Enhanced Daily EASE-Grid 2.0 Brightness Temperature (CETB) Earth System Data Record

NASA Astrophysics Data System (ADS)

Ramage, J. M.; Brodzik, M. J.; Hardman, M.

2016-12-01

Passive microwave (PM) 18 GHz and 36 GHz horizontally- and vertically-polarized brightness temperatures (Tb) channels from the Advanced Microwave Scanning Radiometer for EOS (AMSR-E) have been important sources of information about snow melt status in glacial environments, particularly at high latitudes. PM data are sensitive to the changes in near-surface liquid water that accompany melt onset, melt intensification, and refreezing. Overpasses are frequent enough that in most areas multiple (2-8) observations per day are possible, yielding the potential for determining the dynamic state of the snow pack during transition seasons. AMSR-E Tb data have been used effectively to determine melt onset and melt intensification using daily Tb and diurnal amplitude variation (DAV) thresholds. Due to mixed pixels in historically coarse spatial resolution Tb data, melt analysis has been impractical in ice-marginal zones where pixels may be only fractionally snow/ice covered, and in areas where the glacier is near large bodies of water: even small regions of open water in a pixel severely impact the microwave signal. We use the new enhanced-resolution Calibrated Passive Microwave Daily EASE-Grid 2.0 Brightness Temperature (CETB) Earth System Data Record product's twice daily obserations to test and update existing snow melt algorithms by determining appropriate melt thresholds for both Tb and DAV for the CETB 18 and 36 GHz channels. We use the enhanced resolution data to evaluate melt characteristics along glacier margins and melt transition zones during the melt seasons in locations spanning a wide range of melt scenarios, including the Patagonian Andes, the Alaskan Coast Range, and the Russian High Arctic icecaps. We quantify how improvement of spatial resolution from the original 12.5 - 25 km-scale pixels to the enhanced resolution of 3.125 - 6.25 km improves the ability to evaluate melt timing across boundaries and transition zones in diverse glacial environments.

Bubble Formation and Transport during Microgravity Materials Processing: Model Experiments on the Space Station

NASA Technical Reports Server (NTRS)

Grugel, R. N.; Anilkumar, A. V.; Lee, C. P.

2003-01-01

Flow Visualization experiments on the controlled melting and solidification of succinonitrile were conducted in the glovebox facility of the International Space Station (ISS). The experimental samples were prepared on ground by filling glass tubes, 1 cm ID and approximately 30 cm in length, with pure succinonitrile (SCN) under 450 millibar of nitrogen. Porosity in the samples arose from natural shrinkage, and in some cases by direct insertion of nitrogen bubbles, during solidification of the liquid SCN. The samples were processed in the Pore Formation and Mobility Investigation (PFMI) apparatus that is placed in the glovebox facility (GBX) aboard the ISS. Experimental processing parameters of temperature gradient and translation speed, as well as camera settings, were remotely monitored and manipulated from the ground Telescience Center (TSC) at the Marshall Space Flight Center. During the experiments, the sample is first subjected to a unidirectional melt back, generally at 10 microns per second, with a constant temperature gradient ahead of the melting interface. The temperatures in the sample are monitored by six in situ thermocouples. Real time visualization of the controlled directional melt back shows bubbles of different sizes initiating at the melt interface and, upon dislodging from the melting solid, migrating at different speeds into the temperature field ahead of them, before coming to rest. The thermocapillary flow field set up in the melt, ahead of the interface, is dramatic in the context of the large bubbles, and plays a major role in dislodging the bubble. A preliminary analysis of the observed bubble formation and mobility during melt back and its implication to future microgravity experiments is presented and discussed.

Bubble Formation and Transport during Microgravity Materials Processing: Model Experiments on the International Space Station

NASA Technical Reports Server (NTRS)

Grugel, R. N.; Anilkumar, A. V.; Lee, C. P.

2003-01-01

Flow Visualization experiments on the controlled melting and solidification of succinonitrile were conducted in the glovebox facility of the International Space Station (ISS). The experimental samples were prepared on ground by filling glass tubes, 1 cm ID and approximately 30 cm in length, with pure succinonitrile (SCN) under 450 millibar of nitrogen. Porosity in the samples arose from natural shrinkage, and in some cases by direct insertion of nitrogen bubbles, during solidification of the liquid SCN. The samples were processed in the Pore Formation and Mobility Investigation (PFMI) apparatus that is placed in the glovebox facility (GBX) aboard the ISS. Experimental processing parameters of temperature gradient and translation speed, as well as camera settings, were remotely monitored and manipulated from the ground Telescience Center (TSC) at the Marshall Space Flight Center. During the experiments, the sample is first subjected to a unidirectional melt back, generally at 10 microns per second, with a constant temperature gradient ahead of the melting interface. The temperatures in the sample are monitored by six in situ thermocouples. Real time visualization of the controlled directional melt back shows bubbles of different sizes initiating at the melt interface and, upon dislodging from the melting solid, migrating at different speeds into the temperature field ahead of them, before coming to rest. The thermocapillary flow field set up in the melt, ahead of the interface, is dramatic in the context of the large bubbles, and plays a major role in dislodging the bubble. A preliminary analysis of the observed bubble formation and mobility during melt back and its implication to future microgravity experiments is presented and discussed.

High resolution melting (HRM) analysis of DNA--its role and potential in food analysis.

PubMed

Druml, Barbara; Cichna-Markl, Margit

2014-09-01

DNA based methods play an increasing role in food safety control and food adulteration detection. Recent papers show that high resolution melting (HRM) analysis is an interesting approach. It involves amplification of the target of interest in the presence of a saturation dye by the polymerase chain reaction (PCR) and subsequent melting of the amplicons by gradually increasing the temperature. Since the melting profile depends on the GC content, length, sequence and strand complementarity of the product, HRM analysis is highly suitable for the detection of single-base variants and small insertions or deletions. The review gives an introduction into HRM analysis, covers important aspects in the development of an HRM analysis method and describes how HRM data are analysed and interpreted. Then we discuss the potential of HRM analysis based methods in food analysis, i.e. for the identification of closely related species and cultivars and the identification of pathogenic microorganisms. Copyright © 2014 Elsevier Ltd. All rights reserved.

Thermal behavior of gamma-irradiated low-density polyethylene/paraffin wax blend

NASA Astrophysics Data System (ADS)

Abdou, Saleh M.; Elnahas, H. H.; El-Zahed, H.; Abdeldaym, A.

2016-05-01

The thermal properties of low-density polyethylene (LDPE)/paraffin wax blends were studied using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and melt flow index (MFI). Blends of LDPE/wax in ratios of 100/0, 98/2, 96/4, 94/6, 92/8, 90/10 and 85/15 (w/w) were prepared by melt-mixing at the temperature of 150°C. It was found that increasing the wax content more than 15% leads to phase separation. DSC results showed that for all blends both the melting temperature (Tm) and the melting enthalpy (ΔHm) decrease linearly with an increase in wax content. TGA analysis showed that the thermal stability of all blends decreases linearly with increasing wax content. No clear correlation was observed between the melting point and thermal stability. Horowitz and Metzger method was used to determine the thermal activation energy (Ea). MFI increased exponentially by increasing the wax content. The effect of gamma irradiation on the thermal behavior of the blends was also investigated at different gamma irradiation doses. Significant correlations were found between the thermal parameters (Tm, ΔHm, T5%, Ea and MFI) and the amount of wax content and gamma irradiation.

Internal stress-induced melting below melting temperature at high-rate laser heating

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hwang, Yong Seok, E-mail: yshwang@iastate.edu; Levitas, Valery I., E-mail: vlevitas@iastate.edu

In this Letter, continuum thermodynamic and phase field approaches (PFAs) predicted internal stress-induced reduction in melting temperature for laser-irradiated heating of a nanolayer. Internal stresses appear due to thermal strain under constrained conditions and completely relax during melting, producing an additional thermodynamic driving force for melting. Thermodynamic melting temperature for Al reduces from 933.67 K for a stress-free condition down to 898.1 K for uniaxial strain and to 920.8 K for plane strain. Our PFA simulations demonstrated barrierless surface-induced melt nucleation below these temperatures and propagation of two solid-melt interfaces toward each other at the temperatures very close to the corresponding predicted thermodynamicmore » equilibrium temperatures for the heating rate Q≤1.51×10{sup 10}K/s. At higher heating rates, kinetic superheating competes with a reduction in melting temperature and melting under uniaxial strain occurs at 902.1 K for Q = 1.51 × 10{sup 11 }K/s and 936.9 K for Q = 1.46 × 10{sup 12 }K/s.« less

Primary melt and fluid inclusions in regenerated crystals and phenocrysts of olivine from kimberlites of the Udachnaya-East Pipe, Yakutia: The problem of the kimberlite melt

NASA Astrophysics Data System (ADS)

Tomilenko, A. A.; Kuzmin, D. V.; Bul'bak, T. A.; Sobolev, N. V.

2017-08-01

The primary melt and fluid inclusions in regenerated zonal crystals of olivine and homogeneous phenocrysts of olivine from kimberlites of the Udachnaya-East pipe, were first studied by means of microthermometry, optic and scanning electron microscopy, electron and ion microprobe analysis (SIMS), inductively coupled plasma mass-spectrometry (ICP MSC), and Raman spectroscopy. It was established that olivine crystals were regenerated from silicate-carbonate melts at a temperature of 1100°C.

Enthalpies of melting of LnSF compounds (Ln = La, Ce, Pr, Nd, Sm)

NASA Astrophysics Data System (ADS)

Andreev, P. O.; Mikhalkina, O. G.; Andreev, O. V.; Elyshev, A. V.

2015-05-01

The melting temperatures and enthalpies of such congruently melting compounds as LaSF ( T m = 1713 ± 7 K, Δ H = 45.7 ± 4.6 kJ/mol), CeSF ( T m = 1683 ± 7 K, Δ H = 40.7 ± 4.1 kJ/mol), PrSF ( T m = 1661 ± 7 K, Δ H = 39.7 ± 4.0 kJ/mol), NdSF ( T m = 1654 ± 7 K, Δ H = 40.2 ± 4.0 kJ/mol), and SmSF ( T m = 1587 ± 7 K, Δ H = 36.1 ± 3.6 kJ/mol) are determined via synchronous thermal analysis. The tetrad effect is evident in the change of the melting temperatures and enthalpies of LnSF compounds (Ln = La, Ce, Pr, Nd, Sm) depending on r(Ln3+).

Studies on the reactive melt infiltration of silicon and silicon-molybdenum alloys in porous carbon

NASA Technical Reports Server (NTRS)

Singh, M.; Behrendt, D. R.

1992-01-01

Investigations on the reactive melt infiltration of silicon and silicon-1.7 and 3.2 at percent molybdenum alloys into porous carbon preforms have been carried out by process modeling, differential thermal analysis (DTA) and melt infiltration experiments. These results indicate that the initial pore volume fraction of the porous carbon preform is a critical parameter in determining the final composition of the raction-formed silicon carbide and other residual phases. The pore size of the carbon preform is very detrimental to the exotherm temperatures due to liquid silicon-carbon reactions encountered during the reactive melt infiltration process. A possible mechanism for the liquid silicon-porous (glassy) carbon reaction has been proposed. The composition and microstructure of the reaction-formed silicon carbide has been discussed in terms of carbon preform microstructures, infiltration materials, and temperatures.

Significance of DNA bond strength in programmable nanoparticle thermodynamics and dynamics.

PubMed

Yu, Qiuyan; Hu, Jinglei; Hu, Yi; Wang, Rong

2018-04-04

Assembly of nanoparticles (NPs) coated with complementary DNA strands leads to novel crystals with nanosized basic units rather than classic atoms, ions or molecules. The assembly process is mediated by hybridization of DNA via specific base pairing interaction, and is kinetically linked to the disassociation of DNA duplexes. DNA-level physiochemical quantities, both thermodynamic and kinetic, are key to understanding this process and essential for the design of DNA-NP crystals. The melting transition properties are helpful to judge the thermostability and sensitivity of relative DNA probes or other applications. Three different cases are investigated by changing the linker length and the spacer length on which the melting properties depend using the molecular dynamics method. Melting temperature is determined by sigmoidal melting curves based on hybridization percentage versus temperature and the Lindemann melting rule simultaneously. We provide a computational strategy based on a coarse-grained model to estimate the hybridization enthalpy, entropy and free energy from percentages of hybridizations which are readily accessible in experiments. Importantly, the lifetime of DNA bond dehybridization based on temperature and the activation energy depending on DNA bond strength are also calculated. The simulation results are in good agreement with the theoretical analysis and the present experimental data. Our study provides a good strategy to predict the melting temperature which is important for the DNA-directed nanoparticle system, and bridges the dynamics and thermodynamics of DNA-directed nanoparticle systems by estimating the equilibrium constant from the hybridization of DNA bonds quantitatively.

Numerical analysis of melt-solid interface shapes and growth rates of gallium antimonide in a single-zone vertical Bridgman furnace

NASA Astrophysics Data System (ADS)

Dutta, P. S.; Bhat, H. L.; Kumar, Vikram

1995-09-01

Numerical analysis has been carried out to determine the deviation of the growth rate from the ampoule lowering rate and the shape of the isotherms during the growth of gallium antimonide using the vertical Bridgman technique in a single-zone furnace. Electrical analogues have been used to model the thermal behaviour of the growth system. The standard circuit analysis technique has been used to calculate the temperature distribution in the growing crystal under various growth conditions. The effects of furnace temperature gradient near the melt-solid interface, the ampoule lowering rate, the ampoule geometry, the thermal conductivity of the melt, the mode of heat extraction from the tip of the ampoule and the extent of lateral heat loss from the side walls of the ampoule on the shape of isotherms in the crystal have been evaluated. The theoretical results presented here agree well with our previously obtained experimental results.

Multiphysics Modeling for Dimensional Analysis of a Self-Heated Molten Regolith Electrolysis Reactor for Oxygen and Metals Production on the Moon and Mars

NASA Technical Reports Server (NTRS)

Dominguez, Jesus A.; Sibille, Laurent

2010-01-01

The technology of direct electrolysis of molten lunar regolith to produce oxygen and molten metal alloys has progressed greatly in the last few years. The development of long-lasting inert anodes and cathode designs as well as techniques for the removal of molten products from the reactor has been demonstrated. The containment of chemically aggressive oxide and metal melts is very difficult at the operating temperatures ca 1600 C. Containing the molten oxides in a regolith shell can solve this technical issue and can be achieved by designing a self-heating reactor in which the electrolytic currents generate enough Joule heat to create a molten bath. In a first phase, a thermal analysis model was built to study the formation of a melt of lunar basaltic regolith irradiated by a focused solar beam This mode of heating was selected because it relies on radiative heat transfer, which is the dominant mode of transfer of energy in melts at 1600 C. Knowing and setting the Gaussian-type heat flux from the concentrated solar beam and the phase and temperature dependent thermal properties, the model predicts the dimensions and temperature profile of the melt. A validation of the model is presented in this paper through the experimental formation of a spherical cap melt realized by others. The Orbitec/PSI experimental setup uses an 3.6-cm diameter concentrated solar beam to create a hemispheric melt in a bed of lunar regolith simulant contained in a large pot. Upon cooling, the dimensions of the vitrified melt are measured to validate the thermal model. In a second phase, the model is augmented by multiphysics components to compute the passage of electrical currents between electrodes inserted in the molten regolith. The current through the melt generates Joule heating due to the high resistivity of the medium and this energy is transferred into the melt by conduction, convection and primarily by radiation. The model faces challenges in two major areas, the change of phase as temperature increases, and the dominance of radiative heat flux as heat transfer mechanism within the melt the change of phase concerns the regolith itself which is present in states ranging from a fine grain regolith with low thermal conductivity and low density to a vitrified melt with much higher thermal conductivity, and higher density. As the regolith is heated, it starts to soften around 1300 C the melt iS very viscous and evolving gas bubbles out in thick, lava-like fashion. By 1600 C the regolith is completely melted and the viscosity is low The second challenge resides in the proper modeling of the radiative heat flux requiring the addition of the computing-demanding radiative-heat-transfer function to the general heat transfer equation. The model Includes temperature-dependent properties (density, thermal conductivity, heat capacity, and viscosity, and absorption coefficients) and solves the radiative heat flux equation assuming gray (fine grains) and semi-transparent (melt) media and using an absorption coefficient spectral found in the literature for terrestrial minerals similar in composition to those of lunar regolith simulant

Thermodynamics of Oligonucleotide Duplex Melting

ERIC Educational Resources Information Center

Schreiber-Gosche, Sherrie; Edwards, Robert A.

2009-01-01

Melting temperatures of oligonucleotides are useful for a number of molecular biology applications, such as the polymerase chain reaction (PCR). Although melting temperatures are often calculated with simplistic empirical equations, application of thermodynamics provides more accurate melting temperatures and an opportunity for students to apply…

Chemical State Mapping of Degraded B4C Control Rod Investigated with Soft X-ray Emission Spectrometer in Electron Probe Micro-analysis.

PubMed

Kasada, R; Ha, Y; Higuchi, T; Sakamoto, K

2016-05-10

B4C is widely used as control rods in light water reactors, such as the Fukushima Daiichi nuclear power plant, because it shows excellent neutron absorption and has a high melting point. However, B4C can melt at lower temperatures owing to eutectic interactions with stainless steel and can even evaporate by reacting with high-temperature steam under severe accident conditions. To reduce the risk of recriticality, a precise understanding of the location and chemical state of B in the melt core is necessary. Here we show that a novel soft X-ray emission spectrometer in electron probe microanalysis can help to obtain a chemical state map of B in a modeled control rod after a high-temperature steam oxidation test.

Neutralization of Hydroxide Ion in Melt-Grown NaCl Crystals

NASA Technical Reports Server (NTRS)

Otterson, Dumas A.

1961-01-01

Many recent studies of solid-state phenomena, particularly in the area of crystal imperfections, have involved the use of melt-grown NaCl single crystals. Quite often trace impurities in these materials have had a prominent effect on these phenomena. Trace amounts of hydroxide ion have been found in melt-grown NaCl crystals. This paper describes a nondestructive method of neutralizing the hydroxide ion in such crystals. Crystals of similar hydroxide content are maintained at an elevated temperature below the melting point of NaCl in a flowing atmosphere containing. dry hydrogen chloride. Heat treatment is continued until an analysis of the test specimens shows no excess hydroxide ion. A colorimetric method previously described4 is used for this analysis.

Non-graphite crucible for high temperature applications

DOEpatents

Holcombe, Cressie E.; Pfeiler, William A.

1996-01-01

A multi-piece crucible for high temperature applications comprises a tubular side wall member having a lip on the inside surface and a bottom member or members forming a container for containing a melt of a material during a high temperature melt-casting operations. The multi-piece design prevents cracking of the crucible or leakage of the melt from the crucible during the melt-casting operation. The lip of the tubular member supports the bottom member. The contacting surfaces where the lip of the tubular side wall member contacts the bottom member of the multi-piece crucible contains a ceramic sealing material. The ceramic sealing material forms a seal sufficient to prevent the melt of the material from leaking out of the multi-piece crucible during the melt-casting process. The multi-piece crucible is made of a material which is chemically inert to the melt and has structural integrity at the melting point temperature of the melt, or of a material coated with such a material. The multi-piece crucible is contained in a thermal can assembly of a high temperature induction furnace during a high temperature melt-casting operation. One embodiment of the multi-piece crucible comprises a tubular member having a vertical slot filled with a ceramic sealing material to provide expansion of the tubular member without cracking during the high temperature melt-casting operation.

Non-graphite crucible for high temperature applications

DOEpatents

Holcombe, C.E.; Pfeiler, W.A.

1996-01-09

A multi-piece crucible for high temperature applications comprises a tubular side wall member having a lip on the inside surface and a bottom member or members forming a container for containing a melt of a material during a high temperature melt-casting operations. The multi-piece design prevents cracking of the crucible or leakage of the melt from the crucible during the melt-casting operation. The lip of the tubular member supports the bottom member. The contacting surfaces where the lip of the tubular side wall member contacts the bottom member of the multi-piece crucible contains a ceramic sealing material. The ceramic sealing material forms a seal sufficient to prevent the melt of the material from leaking out of the multi-piece crucible during the melt-casting process. The multi-piece crucible is made of a material which is chemically inert to the melt and has structural integrity at the melting point temperature of the melt, or of a material coated with such a material. The multi-piece crucible is contained in a thermal can assembly of a high temperature induction furnace during a high temperature melt-casting operation. One embodiment of the multi-piece crucible comprises a tubular member having a vertical slot filled with a ceramic sealing material to provide expansion of the tubular member without cracking during the high temperature melt-casting operation. 9 figs.

Coupled phase field, heat conduction, and elastodynamic simulations of kinetic superheating and nanoscale melting of aluminum nanolayer irradiated by picosecond laser.

PubMed

Hwang, Yong Seok; Levitas, Valery I

2015-12-21

An advanced continuum model for nanoscale melting and kinetic superheating of an aluminum nanolayer irradiated by a picosecond laser is formulated. Barrierless nucleation of surface premelting and melting occurs, followed by a propagation of two solid-melt interfaces toward each other and their collision. For a slow heating rate of Q = 0.015 K ps(-1) melting occurs at the equilibrium melting temperature under uniaxial strain conditions T = 898.1 K (i.e., below equilibrium melting temperature Teq = 933.67 K) and corresponding biaxial stresses, which relax during melting. For a high heating rate of Q = 0.99-84 K ps(-1), melting occurs significantly above Teq. Surprisingly, an increase in heating rate leads to temperature reduction at the 3 nm wide moving interfaces due to fast absorption of the heat of fusion. A significant, rapid temperature drop (100-500 K, even below melting temperature) at the very end of melting is revealed, which is caused by the collision of two finite-width interfaces and accelerated melting in about the 5 nm zone. For Q = 25-84 K ps(-1), standing elastic stress waves are observed in a solid with nodal points at the moving solid-melt interfaces, which, however, do not have a profound effect on melting time or temperatures. When surface melting is suppressed, barrierless bulk melting occurs in the entire sample, and elastodynamic effects are more important. Good correspondence with published, experimentally-determined melting time is found for a broad range of heating rates. Similar approaches can be applied to study various phase transformations in different materials and nanostructures under high heating rates.

Direct Observation of Pore Formation and Bubble Mobility during Controlled Melting and Resolidification in Microgravity

NASA Technical Reports Server (NTRS)

Grugel, Richard N.; Anilkumar, A. V.; Lee, C. P.

2004-01-01

Detailed studies on the controlled melting and subsequent re-solidification of succinonitrile were conducted in the microgravity environment aboard the International Space Station (ISS) using the PFMI apparatus (Pore Formation and Mobility Investigation) located in the ISS glovebox facility (GBX). Samples were initially prepared on ground by filling glass tubes, 1 cm ID and approximately 30 cm in length, with pure succinonitrile (SCN) under 450 millibar of nitrogen. During Space processing, experimental parameters like temperature gradient and translation speed, for melting and solidification, were remotely monitored and controlled from the ground Telescience Center (TSC) at the Marshall Space Flight Center. Real time visualization during controlled melting revealed bubbles of different sizes initiating at the solid/liquid interface, and traveling up the temperature gradient ahead of them. Subsequent controlled re-solidification of the SCN revealed the details of porosity formation and evolution. A preliminary analysis of the melt back and re- solidification and its implications to future microgravity materials processing is presented and discussed.

Thermal diffusivity of rhyolitic glasses and melts: effects of temperature, crystals and dissolved water

NASA Astrophysics Data System (ADS)

Romine, William L.; Whittington, Alan G.; Nabelek, Peter I.; Hofmeister, Anne M.

2012-12-01

Thermal diffusivity ( D) was measured using laser-flash analysis on pristine and remelted obsidian samples from Mono Craters, California. These high-silica rhyolites contain between 0.013 and 1.10 wt% H2O and 0 to 2 vol% crystallites. At room temperature, D glass varies from 0.63 to 0.68 mm2 s-1, with more crystalline samples having higher D. As T increases, D glass decreases, approaching a constant value of ˜0.55 mm2 s-1 near 700 K. The glass data are fit with a simple model as an exponential function of temperature and a linear function of crystallinity. Dissolved water contents up to 1.1 wt% have no statistically significant effect on the thermal diffusivity of the glass. Upon crossing the glass transition, D decreases rapidly near ˜1,000 K for the hydrous melts and ˜1,200 K for anhydrous melts. Rhyolitic melts have a D melt of ˜0.51 mm2 s-1. Thermal conductivity ( k = D· ρ· C P) of rhyolitic glass and melt increases slightly with T because heat capacity ( C P) increases with T more strongly than density ( ρ) and D decrease. The thermal conductivity of rhyolitic melts is ˜1.5 W m-1 K-1, and should vary little over the likely range of magmatic temperatures and water contents. These values of D and k are similar to those of major crustal rock types and granitic protoliths at magmatic temperatures, suggesting that changes in thermal properties accompanying partial melting of the crust should be relatively minor. Numerical models of shallow rhyolite intrusions indicate that the key difference in thermal history between bodies that quench to obsidian, and those that crystallize, results from the release of latent heat of crystallization. Latent heat release enables bodies that crystallize to remain at high temperatures for much longer times and cool more slowly than glassy bodies. The time to solidification is similar in both cases, however, because solidification requires cooling through the glass transition in the first case, and cooling only to the solidus in the second.

Texturing by cooling a metallic melt in a magnetic field.

PubMed

Tournier, Robert F; Beaugnon, Eric

2009-02-01

Processing in a magnetic field leads to the texturing of materials along an easy-magnetization axis when a minimum anisotropy energy exists at the processing temperature; the magnetic field can be applied to a particle assembly embedded into a liquid, or to a solid at a high diffusion temperature close to the melting temperature or between the liquidus and the solidus temperatures in a region of partial melting. It has been shown in many experiments that texturing is easy to achieve in congruent and noncongruent compounds by applying the field above the melting temperature T m or above the liquidus temperature of alloys. Texturing from a melt is successful when the overheating temperature is just a few degrees above T m and fails when the processing time above T m is too long or when the overheating temperature is too high; these observations indicate the presence of unmelted crystals above T m with a size depending on these two variables that act as growth nuclei. A recent model that predicts the existence of unmelted crystals above the melting temperature is used to calculate their radius in a bismuth melt.

Effect of Injection Molding Melt Temperatures on PLGA Craniofacial Plate Properties during In Vitro Degradation

PubMed Central

Fancello, Eduardo Alberto

2017-01-01

The purpose of this article is to present mechanical and physicochemical properties during in vitro degradation of PLGA material as craniofacial plates based on different values of injection molded temperatures. Injection molded plates were submitted to in vitro degradation in a thermostat bath at 37 ± 1°C by 16 weeks. The material was removed after 15, 30, 60, and 120 days; then bending stiffness, crystallinity, molecular weights, and viscoelasticity were studied. A significant decrease of molecular weight and mechanical properties over time and a difference in FT-IR after 60 days showed faster degradation of the material in the geometry studied. DSC analysis confirmed that the crystallization occurred, especially in higher melt temperature condition. DMA analysis suggests a greater contribution of the viscous component of higher temperature than lower temperature in thermomechanical behavior. The results suggest that physical-mechanical properties of PLGA plates among degradation differ per injection molding temperatures. PMID:29056968

Bacterial Communities of Surface Mixed Layer in the Pacific Sector of the Western Arctic Ocean during Sea-Ice Melting

PubMed Central

Ha, Ho Kyung; Kim, Hyun Cheol; Kim, Ok-Sun; Lee, Bang Yong; Cho, Jang-Cheon; Hur, Hor-Gil; Lee, Yoo Kyung

2014-01-01

From July to August 2010, the IBRV ARAON journeyed to the Pacific sector of the Arctic Ocean to monitor bacterial variation in Arctic summer surface-waters, and temperature, salinity, fluorescence, and nutrient concentrations were determined during the ice-melting season. Among the measured physicochemical parameters, we observed a strong negative correlation between temperature and salinity, and consequently hypothesized that the melting ice decreased water salinity. The bacterial community compositions of 15 samples, includicng seawater, sea-ice, and melting pond water, were determined using a pyrosequencing approach and were categorized into three habitats: (1) surface seawater, (2) ice core, and (3) melting pond. Analysis of these samples indicated the presence of local bacterial communities; a deduction that was further corroborated by the discovery of seawater- and ice-specific bacterial phylotypes. In all samples, the Alphaproteobacteria, Flavobacteria, and Gammaproteobacteria taxa composed the majority of the bacterial communities. Among these, Alphaproteobacteria was the most abundant and present in all samples, and its variation differed among the habitats studied. Linear regression analysis suggested that changes in salinity could affect the relative proportion of Alphaproteobacteria in the surface water. In addition, the species-sorting model was applied to evaluate the population dynamics and environmental heterogeneity in the bacterial communities of surface mixed layer in the Arctic Ocean during sea-ice melting. PMID:24497990

Bacterial communities of surface mixed layer in the Pacific sector of the western Arctic Ocean during sea-ice melting.

PubMed

Han, Dukki; Kang, Ilnam; Ha, Ho Kyung; Kim, Hyun Cheol; Kim, Ok-Sun; Lee, Bang Yong; Cho, Jang-Cheon; Hur, Hor-Gil; Lee, Yoo Kyung

2014-01-01

From July to August 2010, the IBRV ARAON journeyed to the Pacific sector of the Arctic Ocean to monitor bacterial variation in Arctic summer surface-waters, and temperature, salinity, fluorescence, and nutrient concentrations were determined during the ice-melting season. Among the measured physicochemical parameters, we observed a strong negative correlation between temperature and salinity, and consequently hypothesized that the melting ice decreased water salinity. The bacterial community compositions of 15 samples, includicng seawater, sea-ice, and melting pond water, were determined using a pyrosequencing approach and were categorized into three habitats: (1) surface seawater, (2) ice core, and (3) melting pond. Analysis of these samples indicated the presence of local bacterial communities; a deduction that was further corroborated by the discovery of seawater- and ice-specific bacterial phylotypes. In all samples, the Alphaproteobacteria, Flavobacteria, and Gammaproteobacteria taxa composed the majority of the bacterial communities. Among these, Alphaproteobacteria was the most abundant and present in all samples, and its variation differed among the habitats studied. Linear regression analysis suggested that changes in salinity could affect the relative proportion of Alphaproteobacteria in the surface water. In addition, the species-sorting model was applied to evaluate the population dynamics and environmental heterogeneity in the bacterial communities of surface mixed layer in the Arctic Ocean during sea-ice melting.

Characterization of ash melting behaviour at high temperatures under conditions simulating combustible solid waste gasification.

PubMed

Niu, Miaomiao; Dong, Qing; Huang, Yaji; Jin, Baosheng; Wang, Hongyan; Gu, Haiming

2018-05-01

To achieve high-temperature gasification-melting of combustible solid waste, ash melting behaviour under conditions simulating high-temperature gasification were studied. Raw ash (RA) and gasified ash (GA) were prepared respectively by waste ashing and fluidized bed gasification. Results of microstructure and composition of the two-ash indicated that GA showed a more porous structure and higher content of alkali and alkali earth metals among metallic elements. Higher temperature promoted GA melting and could reach a complete flowing state at about 1250°C. The order of melting rate of GA under different atmospheres was reducing condition > inert condition > oxidizing condition, which might be related to different existing forms of iron during melting and different flux content with atmosphere. Compared to RA, GA showed lower melting activity at the same condition due to the existence of an unconverted carbon and hollow structure. The melting temperature for sufficient melting and separation of GA should be at least 1250°C in this work.

New multicomponent solder alloys of low melting pointfor low-cost commercial electronic assembly

NASA Astrophysics Data System (ADS)

Al-Ganainy, G. S.; Sakr, M. S.

2003-09-01

The requirements of the telecommunications, automobile, electronics and aircraft industries for non-toxic solders with melting points close to that of near-eutectic Pb-Sn alloys has led to the development of new Sn-Zn-In solder alloys. Differential thermal analysis (DTA) shows melting points of 198, 195, 190 and 185 +/- 2 °C for the alloys Sn-9Zn, Sn-9Zn-2In, Sn-9Zn-4In and Sn-9Zn-6In, respectively. An equation that fits the data relating the melting point to the In content in the solders is derived. The X-ray diffraction patterns are analyzed to determine the phases that exist in each solder. The stress-strain curves are studied in the temperature range from 90 to 130 °C for all the solders except for those that contain 4 wt% of In, where the temperature range continues to 150 °C. The work-hardening parameters, y (the yield stress), f (the fracture stress), and the parabolic work-hardening coefficient X, increase with increasing indium content in the solders at all working temperatures. They decrease with increasing working temperature for each solder, and show two relaxation stages only for the Sn-9Zn-4In solder around a temperature of 120 °C. (

Greenland ice sheet melt from MODIS and associated atmospheric variability.

PubMed

Häkkinen, Sirpa; Hall, Dorothy K; Shuman, Christopher A; Worthen, Denise L; DiGirolamo, Nicolo E

2014-03-16

Daily June-July melt fraction variations over the Greenland ice sheet (GIS) derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) (2000-2013) are associated with atmospheric blocking forming an omega-shape ridge over the GIS at 500 hPa height. Blocking activity with a range of time scales, from synoptic waves breaking poleward (<5 days) to full-fledged blocks (≥5 days), brings warm subtropical air masses over the GIS controlling daily surface temperatures and melt. The temperature anomaly of these subtropical air mass intrusions is also important for melting. Based on the years with the greatest melt (2002 and 2012) during the MODIS era, the area-average temperature anomaly of 2 standard deviations above the 14 year June-July mean results in a melt fraction of 40% or more. Though the summer of 2007 had the most blocking days, atmospheric temperature anomalies were too small to instigate extreme melting. Short-term atmospheric blocking over Greenland contributes to melt episodesAssociated temperature anomalies are equally important for the meltDuration and strength of blocking events contribute to surface melt intensity.

Automated realization of the gallium melting and triple points

NASA Astrophysics Data System (ADS)

Yan, X.; Duan, Y.; Zhang, J. T.; Wang, W.

2013-09-01

In order to improve the automation and convenience of the process involved in realizing the gallium fixed points, an automated apparatus, based on thermoelectric and heat pipe technologies, was designed and developed. This paper describes the apparatus design and procedures for freezing gallium mantles and realizing gallium melting and triple points. Also, investigations on the melting behavior of a gallium melting point cell and of gallium triple point cells were carried out while controlling the temperature outside the gallium point cells at 30 °C, 30.5 °C, 31 °C, and 31.5 °C. The obtained melting plateau curves show dentate temperature oscillations on the melting plateaus for the gallium point cells when thermal couplings occurred between the outer and inner liquid-solid interfaces. The maximum amplitude of the temperature fluctuations was about 1.5 mK. Therefore, the temperature oscillations can be used to indicate the ending of the equilibrium phase transitions. The duration and amplitude of such temperature oscillations depend on the temperature difference between the setting temperature and the gallium point temperature; the smaller the temperature difference, the longer the duration of both the melting plateaus and the temperature fluctuations.

A coupled melt-freeze temperature index approach in a one-layer model to predict bulk volumetric liquid water content dynamics in snow

NASA Astrophysics Data System (ADS)

Avanzi, Francesco; Yamaguchi, Satoru; Hirashima, Hiroyuki; De Michele, Carlo

2016-04-01

Liquid water in snow rules runoff dynamics and wet snow avalanches release. Moreover, it affects snow viscosity and snow albedo. As a result, measuring and modeling liquid water dynamics in snow have important implications for many scientific applications. However, measurements are usually challenging, while modeling is difficult due to an overlap of mechanical, thermal and hydraulic processes. Here, we evaluate the use of a simple one-layer one-dimensional model to predict hourly time-series of bulk volumetric liquid water content in seasonal snow. The model considers both a simple temperature-index approach (melt only) and a coupled melt-freeze temperature-index approach that is able to reconstruct melt-freeze dynamics. Performance of this approach is evaluated at three sites in Japan. These sites (Nagaoka, Shinjo and Sapporo) present multi-year time-series of snow and meteorological data, vertical profiles of snow physical properties and snow melt lysimeters data. These data-sets are an interesting opportunity to test this application in different climatic conditions, as sites span a wide latitudinal range and are subjected to different snow conditions during the season. When melt-freeze dynamics are included in the model, results show that median absolute differences between observations and predictions of bulk volumetric liquid water content are consistently lower than 1 vol%. Moreover, the model is able to predict an observed dry condition of the snowpack in 80% of observed cases at a non-calibration site, where parameters from calibration sites are transferred. Overall, the analysis show that a coupled melt-freeze temperature-index approach may be a valid solution to predict average wetness conditions of a snow cover at local scale.

Rationalizing the role of structural motif and underlying electronic structure in the finite temperature behavior of atomic clusters

NASA Astrophysics Data System (ADS)

Susan, Anju; Joshi, Kavita

2014-04-01

Melting in finite size systems is an interesting but complex phenomenon. Many factors affect melting and owing to their interdependencies it is a challenging task to rationalize their roles in the phase transition. In this work, we demonstrate how structural motif of the ground state influences melting transition in small clusters. Here, we report a case with clusters of aluminum and gallium having same number of atoms, valence electrons, and similar structural motif of the ground state but drastically different melting temperatures. We have employed Born-Oppenheimer molecular dynamics to simulate the solid-like to liquid-like transition in these clusters. Our simulations have reproduced the experimental trends fairly well. Further, the detailed analysis of isomers has brought out the role of the ground state structure and underlying electronic structure in the finite temperature behavior of these clusters. For both clusters, isomers accessible before cluster melts have striking similarities and does have strong influence of the structural motif of the ground state. Further, the shape of the heat capacity curve is similar in both the cases but the transition is more spread over for Al36 which is consistent with the observed isomerization pattern. Our simulations also suggest a way to characterize transition region on the basis of accessibility of the ground state at a specific temperature.

Dielectric spectroscopy for the determination of the glass transition temperature of pharmaceutical solid dispersions.

PubMed

O'Donnell, Kevin P; Woodward, W H Hunter

2015-06-01

The purpose of this study was to evaluate analytical techniques for the measurement of the glass transition temperature of HPMC and formulated solid dispersions thereof. Unmodified samples of various grades of HPMC and solid dispersions of HPMC and itraconazole produced by hot melt extrusion were analyzed by thermomechanical analysis, differential scanning calorimetry, thermally stimulated depolarization current and dielectric spectroscopy. It was found that dielectric spectroscopy offers the best accuracy and reproducibility for analysis of the base HPMC powders regardless of the substitution type or viscosity grade and that the obtained results were not frequency dependent. The results of dielectric measurements of solid dispersions prepared by hot melt extrusion were compared with predicted values of the Gordon-Taylor equation. It was found that time-temperature superposition effects and small molecule frequency dependence makes broadly applying determination of the glass transition temperature in drug dispersions by dielectric spectroscopy prohibitively difficult.

Reactive melt infiltration of silicon-molybdenum alloys into microporous carbon preforms

NASA Technical Reports Server (NTRS)

Singh, M.; Behrendt, D. R.

1995-01-01

Investigations on the reactive melt infiltration of silicon-1.7 and 3.2 at.% molybdenum alloys into microporous carbon preforms have been carried out by modeling, differential thermal analysis (DTA), and melt infiltration experiments. These results indicate that the pore volume fraction of the carbon preform is a very important parameter in determining the final composition of the reaction-formed silicon carbide and the secondary phases. Various undesirable melt infiltration results, e.g. choking-off, specimen cracking, silicon veins, and lake formation, and their correlation with inadequate preform properties are presented. The liquid silicon-carbon reaction exotherm temperatures are influenced by the pore and carbon particle size of the preform and the compositions of infiltrants. Room temperature flexural strength and fracture toughness of materials made by the silicon-3.2 at.% molybdenum alloy infiltration of medium pore size preforms are also discussed.

Optimization of KOH etching parameters for quantitative defect recognition in n- and p-type doped SiC

NASA Astrophysics Data System (ADS)

Sakwe, S. A.; Müller, R.; Wellmann, P. J.

2006-04-01

We have developed a KOH-based defect etching procedure for silicon carbide (SiC), which comprises in situ temperature measurement and control of melt composition. As benefit for the first time reproducible etching conditions were established (calibration plot, etching rate versus temperature and time); the etching procedure is time independent, i.e. no altering in KOH melt composition takes place, and absolute melt temperature values can be set. The paper describes this advanced KOH etching furnace, including the development of a new temperature sensor resistant to molten KOH. We present updated, absolute KOH etching parameters of n-type SiC and new absolute KOH etching parameters for low and highly p-type doped SiC, which are used for quantitative defect analysis. As best defect etching recipes we found T=530 °C/5 min (activation energy: 16.4 kcal/mol) and T=500 °C/5 min (activation energy: 13.5 kcal/mol) for n-type and p-type SiC, respectively.

Vapor-Saturated Melting of Fertile Peridotite Revisited: A new Experimental Approach and Re-evaluation of the Hydrous Peridotite Solidus

NASA Astrophysics Data System (ADS)

Grove, T. L.

2001-12-01

The vapor-saturated melting relations of peridotite have been determined for a fertile mantle composition of Hart and Zindler (1986, Chem Geol 57: 247) over the pressure range of 1.2 to 2.4 GPa. For example, at 1.2 GPa melt is present at a temperature of 980° C and at 2.4 GPa melt is present at 920° C. These temperatures should be viewed as maximum values for the vapor-saturated solidus (although see below) because the initial melting temperature of multi-phase, multicomponent systems can often be difficult to detect. At 2.4 GPa the melt composition is highly silica-undersaturated and very aluminous ( ~ 21 wt. % Al2O3). Wet mantle melts are thought to be high in silica, but this is not the case for these hydrous melts. At 1.2 GPa, melt fractions are too small to allow reliable analysis. The experiments have been carried out in a piston cylinder apparatus using Au capsules. The starting material is an oxide mixture containing 14.5 wt. % H2O added as brucite. Free water present in the experiment after quenching indicates subsolidus conditions. The absence of fluid in experiments above the vapor-saturated solidus shows that all of the free H2O is dissolved in the melt. The high H2O content of the starting material moves the bulk composition close to the vapor-saturated melt composition, therefore increasing the amount of melt produced close to the solidus and making detection of low melt fraction possible. Studies of the hydrous peridotite solidus carried out between 1970 and 1975 by Mysen and Boettcher, Kushiro and others, Green and Millhollen and others at 2.0 GPa ranged from < 800 to ~ 1000° C, a variation of over 200 degrees. In a subduction zone environment a fluid-rich component released from the slab ascends into hotter overlying mantle and melting initiates at the vapor-saturated solidus. Melting would begin at a depth of ~ 75 km in the mantle wedge, for a realistic thermal structure. Melting would continue as these initial H2O-rich buoyant melts ascend into hotter, shallower mantle and re-equilibrate with their surroundings. The initiation of melting deep in the mantle wedge has implications for both chemical and mechanical processes in the subduction zone environment.

Thermoplastic polyimide NEW-TPI (trademark)

NASA Technical Reports Server (NTRS)

Hou, Tan-Hung; Reddy, Rakasi M.

1990-01-01

Thermal and rheological properties of a commercial thermoplastic polyimide, NEW-TPI (trademark), were characterized. The as-received material possesses initially a transient crystallite form with a bimodal distribution in peak melting temperatures. After the melting of the initial crystallite structure, the sample can be recrystallized by various thermal treatments. A bimodal or single modal melting peak distribution is formed for annealing temperatures below or above 360 C, respectively. The recrystallized crystallinities are all transient in nature. The polymers are unable to be recrystallized after being subjected to elevated temperature annealing above 450 C. The recrystallization mechanism was postulated, and a simple kinetics model was found to describe the behavior rather satisfactory under the conditions of prolonged thermal annealing. Rheological measurements made in the linear viscoelastic range support the evidence observed in the thermal analysis. Furthermore, the measurements sustain the manufacturer's recommended processing window of 400 to 420 C for this material.

Balance of oxygen throughout the conversion of a high-level waste melter feed to glass

DOE PAGES

Lee, SeungMin; Hrma, Pavel; Kloužek, Jaroslav; ...

2017-07-03

Gases evolve from nuclear waste melter feed during conversion to glass in response to heating. This article is focused on oxygen mass balance based on the stoichiometry of feed melting reactions and evolved-gas analysis data. Whereas O 2-producing and -consuming batch-melting reactions are complete in the reacting and primary-foam layers of the cold cap, O 2 from redox reactions continues to evolve as long as melt temperature increases, and thus generates secondary foam. Also, we discuss the relationship between the oxygen mass balance and the temperature-dependent iron redox ratio and the O 2 partial pressure, as they evolve during themore » feed-to-glass conversion.« less

Balance of oxygen throughout the conversion of a high-level waste melter feed to glass

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, SeungMin; Hrma, Pavel; Kloužek, Jaroslav

Gases evolve from nuclear waste melter feed during conversion to glass in response to heating. This article is focused on oxygen mass balance based on the stoichiometry of feed melting reactions and evolved-gas analysis data. Whereas O 2-producing and -consuming batch-melting reactions are complete in the reacting and primary-foam layers of the cold cap, O 2 from redox reactions continues to evolve as long as melt temperature increases, and thus generates secondary foam. Also, we discuss the relationship between the oxygen mass balance and the temperature-dependent iron redox ratio and the O 2 partial pressure, as they evolve during themore » feed-to-glass conversion.« less

On melt solutions for the growth of CaTiO3 crystals

NASA Astrophysics Data System (ADS)

Klimm, Detlef; Schmidt, Max; Wolff, Nora; Guguschev, Christo; Ganschow, Steffen

2018-03-01

When calcium titanate crystals are grown from stoichiometric melts, they crystallize in the cubic perovskite structure. Upon cooling to room temperature they undergo subsequent phase transitions to tetragonal and orthorhombic modifications. These phase transitions are disruptive and result in severely damaged crystals. This paper presents differential thermal analysis data for several prospective solvents, with the aim to identify a system offering the possibility to perform crystal growth of undistorted CaTiO3 crystals by crystallizing them significantly below the melting point directly in the low temperature modification. From mixtures CaF2:TiO2:CaTiO3 = 3:1:1 (molar ratio) the growth of undistorted, at least millimeter-sized CaTiO3 crystals is possible.

A Two-Dimensional Liquid Structure Explains the Elevated Melting Temperatures of Gallium Nanoclusters.

PubMed

Steenbergen, Krista G; Gaston, Nicola

2016-01-13

Melting in finite-sized materials differs in two ways from the solid-liquid phase transition in bulk systems. First, there is an inherent scaling of the melting temperature below that of the bulk, known as melting point depression. Second, at small sizes changes in melting temperature become nonmonotonic and show a size-dependence that is sensitive to the structure of the particle. Melting temperatures that exceed those of the bulk material have been shown to occur for a very limited range of nanoclusters, including gallium, but have still never been ascribed a convincing physical explanation. Here, we analyze the structure of the liquid phase in gallium clusters based on molecular dynamics simulations that reproduce the greater-than-bulk melting behavior observed in experiments. We observe persistent nonspherical shape distortion indicating a stabilization of the surface, which invalidates the paradigm of melting point depression. This shape distortion suggests that the surface acts as a constraint on the liquid state that lowers its entropy relative to that of the bulk liquid and thus raises the melting temperature.

In-situ temperature field measurements and direct observation of crystal/melt at vertical Bridgman growth of lead chloride under stationary and dynamic arrangement

NASA Astrophysics Data System (ADS)

Král, Robert; Nitsch, Karel

2015-10-01

Influence of growth conditions, i.e. temperature gradient in the furnace and the pulling rate, on the position and the shape of the crystal/melt interface during vertical Bridgman growth was studied. The position and the shape of the crystal/melt interface are a key factor for describing the final quality of growing crystal. Following two methods for characterization of its position and shape were used: (i) direct observation and (ii) direct temperature field measurement during simulated vertical Bridgman growth. As a model compound a lead chloride is used. Three different ampoule positions in two different temperature gradients in the furnace and two experimental arrangements - stationary (0 mm/h pulling rate) and dynamic (3 mm/h pulling rate) were analyzed. Obtained temperature data were projected as 2D planar cut under radial symmetry and denoted as isolevels. Their further conversion by linear approximation into isotherms allowed detail analysis of heat conditions in the system during simulated growth by comparison of isotherms 500 °C (m.p. of lead chloride) at different growth conditions.

A slow atomic diffusion process in high-entropy glass-forming metallic melts

NASA Astrophysics Data System (ADS)

Chen, Changjiu; Wong, Kaikin; Krishnan, Rithin P.; Embs, Jan P.; Chathoth, Suresh M.

2018-04-01

Quasi-elastic neutron scattering has been used to study atomic relaxation processes in high-entropy glass-forming metallic melts with different glass-forming ability (GFA). The momentum transfer dependence of mean relaxation time shows a highly collective atomic transport process in the alloy melts with the highest and lowest GFA. However, a jump diffusion process is the long-range atomic transport process in the intermediate GFA alloy melt. Nevertheless, atomic mobility close to the melting temperature of these alloy melts is quite similar, and the temperature dependence of the diffusion coefficient exhibits a non-Arrhenius behavior. The atomic mobility in these high-entropy melts is much slower than that of the best glass-forming melts at their respective melting temperatures.

A geochemical study of the winonaites: Evidence for limited partial melting and constraints on the precursor composition

NASA Astrophysics Data System (ADS)

Hunt, Alison C.; Benedix, Gretchen K.; Hammond, Samantha J.; Bland, Philip A.; Rehkämper, Mark; Kreissig, Katharina; Strekopytov, Stanislav

2017-02-01

The winonaites are primitive achondrites which are associated with the IAB iron meteorites. Textural evidence implies heating to at least the Fe, Ni-FeS cotectic, but previous geochemical studies are ambiguous about the extent of silicate melting in these samples. Oxygen isotope evidence indicates that the precursor material may be related to the carbonaceous chondrites. Here we analysed a suite of winonaites for modal mineralogy and bulk major- and trace-element chemistry in order to assess the extent of thermal processing as well as constrain the precursor composition of the winonaite-IAB parent asteroid. Modal mineralogy and geochemical data are presented for eight winonaites. Textural analysis reveals that, for our sub-set of samples, all except the most primitive winonaite (Northwest Africa 1463) reached the Fe, Ni-FeS cotectic. However, only one (Tierra Blanca) shows geochemical evidence for silicate melting processes. Tierra Blanca is interpreted as a residue of small-degree silicate melting. Our sample of Winona shows geochemical evidence for extensive terrestrial weathering. All other winonaites studied here (Fortuna, Queen Alexander Range 94535, Hammadah al Hamra 193, Pontlyfni and NWA 1463) have chondritic major-element ratios and flat CI-normalised bulk rare-earth element patterns, suggesting that most of the winonaites did not reach the silicate melting temperature. The majority of winonaites were therefore heated to a narrow temperature range of between ∼1220 (the Fe, Ni-FeS cotectic temperature) and ∼1370 K (the basaltic partial melting temperature). Silicate inclusions in the IAB irons demonstrate partial melting did occur in some parts of the parent body (Ruzicka and Hutson, 2010), thereby implying heterogeneous heat distribution within this asteroid. Together, this indicates that melting was the result of internal heating by short-lived radionuclides. The brecciated nature of the winonaites suggests that the parent body was later disrupted by a catastrophic impact, which allowed the preservation of the largely unmelted winonaites. Despite major-element similarities to both ordinary and enstatite chondrites, trace-element analysis suggests the winonaite parent body had a carbonaceous chondrite-like precursor composition. The parent body of the winonaites was volatile-depleted relative to CI, but enriched compared to the other carbonaceous classes. The closest match are the CM chondrites; however, the specific precursor is not sampled in current meteorite collections.

Are ``Hot Spots'' Hot? - An Overview

NASA Astrophysics Data System (ADS)

Foulger, G. R.

2010-12-01

The term “hot spot” is taken variously to imply a) the presence of excessive volcanism, or b) that the melt formed in an unusually hot source. Case b) is intrinsic to the plume hypothesis. Temperature anomalies of 200-300 degrees Celsius are expected, though there is widespread downward-revision of this where observations do not support it. It is not self-evident that “hot spots” are hot in the sense of case b), despite the fact that this is widely assumed. Furthermore, a hot source is not strongly supported by observations, and is at odds with many data. The temperature of the mantle has been studied using many different methods. Global oceanic heat flow values were recently assessed, but reveal no evidence for elevated temperatures around proposed plume localities. Mapping surface heat flow is only sensitive to anomalies at the level of 100 degrees Celsius, however. Seismological methods include correlating velocity with crustal thickness at LIPs, measuring transition zone thickness, and mapping velocity, e.g., using tomography. The first of these does not find evidence for elevated temperatures. The latter two are both sensitive to the presence of partial melt and variations in rock composition, in addition to temperature, which is the weakest potential effect. They thus cannot be used as thermometers. In particular, it cannot be assumed that red = hot and blue = cold in tomographic cross sections. Petrological and geochemical approaches include the “global systematics”. This has now been shown to not work for estimating temperature and its application should be discontinued. Mineralogical phase relationships are applied by comparing data from laboratory melting experiments to observations. Olivine control-line analysis has been extensively used in attempts to measure the differences in melt-formation temperature between mid-ocean ridges and melting anomalies. Difficulties arise in choosing the correct olivine geothermometer and because picrite glass is lacking from any melting anomaly except Hawaii. The results must be compared with a measure of the temperature of “normal mantle”. This is usually taken to be the temperature of melt formation beneath mid-ocean ridges, but the correct choice is controversial. Furthermore, this cannot be assumed to represent the potential temperature of the mantle in general. The surface conduction layer may extend much deeper than the depth of extraction of MORB, so melt extracted from greater depths, e.g., from beneath the base of the lithosphere in old parts of the ocean basins, may form at higher temperatures. It is easier to assume that the mantle beneath “hot spots” is hot than it is to show unequivocally that it is true. This endeavor is perhaps the most direct way of testing the plume hypothesis, but it is also one of the most challenging.

The thermo-elastic instability model of melting of alkali halides in the Debye approximation

NASA Astrophysics Data System (ADS)

Owens, Frank J.

2018-05-01

The Debye model of lattice vibrations of alkali halides is used to show that there is a temperature below the melting temperature where the vibrational pressure exceeds the electrostatic pressure. The onset temperature of this thermo-elastic instability scales as the melting temperature of NaCl, KCl, and KBr, suggesting its role in the melting of the alkali halides in agreement with a previous more rigorous model.

Numerical analysis of phase change materials for thermal control of power battery of high power dissipations

NASA Astrophysics Data System (ADS)

Xia, X.; Zhang, H. Y.; Deng, Y. C.

2016-08-01

Solid-fluid phase change materials have been of increasing interest in various applications due to their high latent heat with minimum volume change. In this work, numerical analysis of phase change materials is carried out for the purpose of thermal control of the cylindrical power battery cells for applications in electric vehicles. Uniform heat density is applied at the battery cell, which is surrounded by phase change material (PCM) of paraffin wax type and contained in a metal housing. A two-dimensional geometry model is considered due to the model symmetry. The effects of power densities, heat transfer coefficients and onset melting temperatures are examined for the battery temperature evolution. Temperature plateaus can be observed from the present numerical analysis for the pure PCM cases, with the temperature level depending on the power densities, heat transfer coefficients, and melting temperatures. In addition, the copper foam of high thermal conductivity is inserted into the copper foam to enhance the heat transfer. In the modeling, the local thermal non-equilibrium between the metal foam and the PCM is taken into account and the temperatures for the metal foam and PCM are obtained respectively.

Temperature Dependence of Density, Viscosity and Electrical Conductivity for Hg-Based II-VI Semiconductor Melts

NASA Technical Reports Server (NTRS)

Li, C.; Ban, H.; Lin, B.; Scripa, R. N.; Su, C.-H.; Lehoczky, S. L.

2004-01-01

The relaxation phenomenon of semiconductor melts, or the change of melt structure with time, impacts the crystal growth process and the eventual quality of the crystal. The thermophysical properties of the melt are good indicators of such changes in melt structure. Also, thermophysical properties are essential to the accurate predication of the crystal growth process by computational modeling. Currently, the temperature dependent thermophysical property data for the Hg-based II-VI semiconductor melts are scarce. This paper reports the results on the temperature dependence of melt density, viscosity and electrical conductivity of Hg-based II-VI compounds. The melt density was measured using a pycnometric method, and the viscosity and electrical conductivity were measured by a transient torque method. Results were compared with available published data and showed good agreement. The implication of the structural changes at different temperature ranges was also studied and discussed.

Mass transfer in the Earth's interior: fluid-melt interaction in aluminosilicate-C-O-H-N systems at high pressure and temperature under oxidizing conditions

NASA Astrophysics Data System (ADS)

Mysen, Bjorn

2018-12-01

Understanding what governs the speciation in the C-O-H-N system aids our knowledge of how volatiles affect mass transfer processes in the Earth's interior. Experiments with aluminosilicate melt + C-O-H-N volatiles were, therefore, carried out with Raman and infrared spectroscopy to 800 °C and near 700 MPa in situ in hydrothermal diamond anvil cells. The measurements were conducted in situ with the samples at the desired temperatures and pressures in order to avoid possible structural and compositional changes resulting from quenching to ambient conditions prior to analysis. Experiments were conducted without any reducing agent and with volatiles added as H2O, CO2, and N2 because both carbon and nitrogen can occur in different oxidation states. Volatiles dissolved in melt comprise H2O, CO3 2-, HCO3 -, and molecular N2, whereas in the coexisting fluid, the species are H2O, CO2, CO3 2-, and N2. The HCO3 -/CO3 2- equilibrium in melts shift toward CO3 2- groups with increasing temperature with ΔH = 114 ± 22 kJ/mol. In fluids, the CO2 abundance is essentially invariant with temperature and pressure. For fluid/melt partitioning, those of H2O and N2 are greater than 1 with temperature-dependence that yields ΔH values of - 6.5 ± 1.5 and - 19.6 ± 3.7 kJ/mol, respectively. Carbonate groups, CO3 2- are favored by melt over fluid. Where redox conditions in the Earth's interior exceed that near the QFM oxygen buffer (between NNO and MW buffers), N2 is the stable nitrogen species and as such acts as a diluent of both fluids and melts. For fluids, this lower silicate solubility, in turn, enhances alkalinity. This means that in such environments, the transport of components such as high field strength cations, will be enhanced. Effects of dissolved N2 on melt structure are considerably less than on fluid structure.[Figure not available: see fulltext.

Ab initio molecular dynamics study of high-pressure melting of beryllium oxide

PubMed Central

Li, Dafang; Zhang, Ping; Yan, Jun

2014-01-01

We investigate, through first-principles molecular dynamics simulations, the high-pressure melting of BeO in the range 0 ≤ p ≤ 100 GPa. The wurtzite (WZ), zinc blend (ZB), and rocksalt (RS) phases of BeO are considered. It is shown that below 40 GPa, the melting temperature for the WZ phase is higher than that for the ZB and RS phases. When the pressure is beyond 66 GPa, the melting temperature for the RS phase is the highest one, in consistent with the previously reported phase diagram calculated within the quasiharmonic approximation. We find that in the medium pressure range between 40 to 66 GPa, the ZB melting data are very close to those of RS, which results from the fact that the ZB structure first transforms to RS phase before melting. The ZB-RS-liquid phase transitions have been observed directly during the molecular dynamics runs and confirmed using the pair correlation functions analysis. In addition, we propose the melting curve of BeO in the form Tm = 2696.05 (1 + P/24.67)0.42, the zero-pressure value of 2696.05 K falling into the experimental data range of 2693 ~ 2853 K. PMID:24759594

Investigation of transient melting of tungsten by ELMs in ASDEX Upgrade

NASA Astrophysics Data System (ADS)

Krieger, K.; Sieglin, B.; Balden, M.; Coenen, J. W.; Göths, B.; Laggner, F.; de Marne, P.; Matthews, G. F.; Nille, D.; Rohde, V.; Dejarnac, R.; Faitsch, M.; Giannone, L.; Herrmann, A.; Horacek, J.; Komm, M.; Pitts, R. A.; Ratynskaia, S.; Thoren, E.; Tolias, P.; ASDEX-Upgrade Team; EUROfusion MST1 Team

2017-12-01

Repetitive melting of tungsten by power transients originating from edge localized modes (ELMs) has been studied in the tokamak experiment ASDEX Upgrade. Tungsten samples were exposed to H-mode discharges at the outer divertor target plate using the Divertor Manipulator II system. The exposed sample was designed with an elevated sloped surface inclined against the incident magnetic field to increase the projected parallel power flux to a level were transient melting by ELMs would occur. Sample exposure was controlled by moving the outer strike point to the sample location. As extension to previous melt studies in the new experiment both the current flow from the sample to vessel potential and the local surface temperature were measured with sufficient time resolution to resolve individual ELMs. The experiment provided for the first time a direct link of current flow and surface temperature during transient ELM events. This allows to further constrain the MEMOS melt motion code predictions and to improve the validation of its underlying model assumptions. Post exposure ex situ analysis of the retrieved samples confirms the decreased melt motion observed at shallower magnetic field line to surface angles compared to that at leading edges exposed to the parallel power flux.

Size-Dependent Melting Behavior of Colloidal In, Sn, and Bi Nanocrystals

PubMed Central

Liu, Minglu; Wang, Robert Y.

2015-01-01

Colloidal nanocrystals are a technologically important class of nanostructures whose phase change properties have been largely unexplored. Here we report on the melting behavior of In, Sn, and Bi nanocrystals dispersed in a polymer matrix. This polymer matrix prevents the nanocrystals from coalescing with one another and enables previously unaccessed observations on the melting behavior of colloidal nanocrystals. We measure the melting temperature, melting enthalpy, and melting entropy of colloidal nanocrystals with diameters of approximately 10 to 20 nm. All of these properties decrease as nanocrystal size decreases, although the depression rate for melting temperature is comparatively slower than that of melting enthalpy and melting entropy. We also observe an elevated melting temperature during the initial melt-freeze cycle that we attribute to surface stabilization from the organic ligands on the nanocrystal surface. Broad endothermic melting valleys and very large supercoolings in our calorimetry data suggest that colloidal nanocrystals exhibit a significant amount of surface pre-melting and low heterogeneous nucleation probabilities during freezing. PMID:26573146

Using Flory-Huggins phase diagrams as a pre-formulation tool for the production of amorphous solid dispersions: a comparison between hot-melt extrusion and spray drying.

PubMed

Tian, Yiwei; Caron, Vincent; Jones, David S; Healy, Anne-Marie; Andrews, Gavin P

2014-02-01

Amorphous drug forms provide a useful method of enhancing the dissolution performance of poorly water-soluble drugs; however, they are inherently unstable. In this article, we have used Flory-Huggins theory to predict drug solubility and miscibility in polymer candidates, and used this information to compare spray drying and melt extrusion as processes to manufacture solid dispersions. Solid dispersions were prepared using two different techniques (hot-melt extrusion and spray drying), and characterised using a combination of thermal (thermogravimetric analysis and differential scanning calorimetry), spectroscopic (Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction methods. Spray drying permitted generation of amorphous solid dispersions across a wider drug concentration than melt extrusion. Melt extrusion provided sufficient energy for more intimate mixing to be achieved between drug and polymer, which may improve physical stability. It was also confirmed that stronger drug-polymer interactions might be generated through melt extrusion. Remixing and dissolution of recrystallised felodipine into the polymeric matrices did occur during the modulated differential scanning calorimetry analysis, but the complementary information provided from FTIR confirms that all freshly prepared spray-dried samples were amorphous with the existence of amorphous drug domains within high drug-loaded samples. Using temperature-composition phase diagrams to probe the relevance of temperature and drug composition in specific polymer candidates facilitates polymer screening for the purpose of formulating solid dispersions. © 2013 Royal Pharmaceutical Society.

Non-graphite crucible for high temperature applications

DOEpatents

Holcombe, C.E.; Pfeiler, W.A.

1994-08-02

A multi-piece crucible for high temperature applications comprises a tubular side wall member having a lip on the inside surface and a bottom member or members forming a container for containing a melt of a material during a high temperature melt-casting operations. The multi-piece design prevents cracking of the crucible or leakage of the melt from the crucible during the melt-casting operation. The lip of the tubular member supports the bottom member. The contacting surfaces where the lip of the tubular side wall member contacts the bottom member of the multi-piece crucible contains a ceramic sealing material. The ceramic sealing material forms a seal sufficient to prevent the melt of the material from leaking out of the multi-piece crucible during the melt-casting process. The multi-piece crucible is made of a material which is chemically inert to the melt and has structural integrity at the melting point temperature of the melt, or of a material coated with such a material. 6 figs.

Non-graphite crucible for high temperature applications

DOEpatents

Holcombe, Cressie E.; Pfeiler, William A.

1994-01-01

A multi-piece crucible for high temperature applications comprises a tubular side wall member having a lip on the inside surface and a bottom member or members forming a container for containing a melt of a material during a high temperature melt-casting operations. The multi-piece design prevents cracking of the crucible or leakage of the melt from the crucible during the melt-casting operation. The lip of the tubular member supports the bottom member. The contacting surfaces where the lip of the tubular side wall member contacts the bottom member of the multi-piece crucible contains a ceramic sealing material. The ceramic sealing material forms a seal sufficient to prevent the melt of the material from leaking out of the multi-piece crucible during the melt-casting process. The multi-piece crucible is made of a material which is chemically inert to the melt and has structural integrity at the melting point temperature of the melt, or of a material coated with such a material.

Genome-Wide Association Study in Arabidopsis thaliana of Natural Variation in Seed Oil Melting Point: A Widespread Adaptive Trait in Plants.

PubMed

Branham, Sandra E; Wright, Sara J; Reba, Aaron; Morrison, Ginnie D; Linder, C Randal

2016-05-01

Seed oil melting point is an adaptive, quantitative trait determined by the relative proportions of the fatty acids that compose the oil. Micro- and macro-evolutionary evidence suggests selection has changed the melting point of seed oils to covary with germination temperatures because of a trade-off between total energy stores and the rate of energy acquisition during germination under competition. The seed oil compositions of 391 natural accessions of Arabidopsis thaliana, grown under common-garden conditions, were used to assess whether seed oil melting point within a species varied with germination temperature. In support of the adaptive explanation, long-term monthly spring and fall field temperatures of the accession collection sites significantly predicted their seed oil melting points. In addition, a genome-wide association study (GWAS) was performed to determine which genes were most likely responsible for the natural variation in seed oil melting point. The GWAS found a single highly significant association within the coding region of FAD2, which encodes a fatty acid desaturase central to the oil biosynthesis pathway. In a separate analysis of 15 a priori oil synthesis candidate genes, 2 (FAD2 and FATB) were located near significant SNPs associated with seed oil melting point. These results comport with others' molecular work showing that lines with alterations in these genes affect seed oil melting point as expected. Our results suggest natural selection has acted on a small number of loci to alter a quantitative trait in response to local environmental conditions. © The American Genetic Association. 2016. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Triple point fcc-hcp-liquid in the Fe phase diagram determined by in-situ XANES diagnostic and post-mortem XRD and FIB-SEM analysis.

NASA Astrophysics Data System (ADS)

Morard, G.; Boccato, S.; Rosa, A. D.; Anzellini, S.; Miozzi Ferrini, F.; Laura, H.; Garbarino, G.; Harmand, M.; Guyot, F. J.; Boulard, E.; Kantor, I.; Irifune, T.; Torchio, R.

2017-12-01

Iron is the main constituent of planetary cores. Studying its phase diagram under high pressure is necessary to constrain properties of planetary interiors, and to model key parameters such as the generation of magnetic field. Though, strong controversy on the melting curve of pure Fe still remains. Recently, Aquilanti et al, (PNAS, 2015) reported a Fe melting curved based on XANES measurements which is in open disagreement with previous X-ray diffraction results (Anzellini et al, Science, 2013). Discrepancies in the melting temperature exceed several hundred degrees close to Mbar pressures, which may be related to differences in temperature measurement techniques, melting diagnostics, or to chemical reactions of the sample with the surrounding medium. We therefore performed new in situ high P/T XANES experiments on pure Fe (up to 115 GPa and 4000 K) at the ESRF beamline ID24, combining the energy dispersive absorption set up with laser heated diamond anvil cells. X-ray diffraction maps were collected from all recovered samples in order to identify and characterize laser-heated spots. The XANES melting criterion was further cross checked by analyzing the recovered sample textures using FIB cutting techniques and SEM imaging. We found systematically that low melting temperatures are related to the presence of Fe3C, implying that in those cases chemical reactions occurred during heating resulting in carbon contamination from the diamonds. These low melting points fall onto the melting line reported by Aquilanti et al, (2015). Uncontaminated points are in agreement with the melting curve of Anzellini et al, (2013) within their uncertainties. Moreover, this data set allowed us to refine the location of the triple point in the Fe phase diagram at 105 (±10) GPa and 3600 (±200) K, which may imply a small kink in the melting curve around this point. This refined Fe phase diagram could be then used to compute thermodynamic models for planetary cores.

Basal melt beneath whillans ice stream and ice streams A and C

NASA Technical Reports Server (NTRS)

Joughin, I.; Teluezyk, S.; Engelhardt, H.

2002-01-01

We have used a recently derived map of the velocity of Whillans Ice Stream and Ice Streams A and C to help estimate basal melt. Temperature was modeled with a simple vertical advection-diffusion equation, 'tuned' to match temperature profiles. We find that most of the melt occurs beneath the tributaries where larger basal shear stresses and thicker ice favors greater melt (e.g., 10-20 mm/yr). The occurrence of basal freezing is predicted beneath much of the ice plains of Ice Stream C and Whillans Ice Stream. Modelled melt rates for when Ice Stream C was active suggest there was just enough melt water generated in its tributaries to balance basal freezing on its ice plain. Net basal melt for Whillans Ice Stream is positive due to smaller basal temperature gradients. Modelled temperatures on Whillans Ice Stream, however, were constrained by a single temperature profile at UpB. Basal temperature gradients for Whillans B1 and Ice Stream A may have conditions more similar to those beneath Ice Streams C and D, in which case, there may not be sufficient melt to sustain motion. This would be consistent with the steady deceleration of Whillans stream over the last few decades.

Influence of Melt Superheating Treatment on Solidification Characteristics and Rupture Life of a Third-Generation Ni-Based Single-Crystal Superalloy

NASA Astrophysics Data System (ADS)

Su, Haijun; Wang, Haifeng; Zhang, Jun; Guo, Min; Liu, Lin; Fu, Hengzhi

2018-05-01

The influence of melt superheating treatment on the melt properties, solidification characteristics, and rupture life of a third-generation Ni-based single-crystal superalloy was investigated to reveal the critical temperature range of melt structure evolution and its effect on rupture life. The results showed that the viscosity of superalloy decreased but the surface tension increased with increasing superheating temperature. Two characteristic temperature points where the melt viscosity and undercooling degree suddenly change were determined to be 1600 °C and 1700 °C, respectively. Similarly, the stability of the solidification interface firstly improved and then weakened with increasing superheating temperature. The dendrite arms were well refined and the segregation was reduced at 1700 °C. In addition, the rupture life obtained at 1100 °C and 137 MPa increased by approximately 30 pct, approaching the rupture life of the corresponding superalloy containing 2 pct Ru, with increasing superheating temperature from 1500 °C to 1700 °C. When the melt was further heated to 1800 °C, the rupture life decreased. The evolutions of solidification characteristics and rupture life with increasing melt superheating temperature were attributed to changes in the melt structure.

A 400-year ice core melt layer record of summertime warming in the Alaska Range

NASA Astrophysics Data System (ADS)

Winski, D.; Osterberg, E. C.; Kreutz, K. J.; Wake, C. P.; Ferris, D. G.; Campbell, S. W.; Baum, M.; Raudzens Bailey, A.; Birkel, S. D.; Introne, D.; Handley, M.

2017-12-01

Warming in high-elevation regions has socially relevant impacts on glacier mass balance, water resources, and sensitive alpine ecosystems, yet very few high-elevation temperature records exist from the middle or high latitudes. While many terrestrial paleoclimate records provide critical temperature records from low elevations over recent centuries, melt layers preserved in alpine glaciers present an opportunity to develop calibrated, annually-resolved temperature records from high elevations. We present a 400-year temperature record based on the melt-layer stratigraphy in two ice cores collected from Mt. Hunter in the Central Alaska Range. The ice core record shows a 60-fold increase in melt frequency and water equivalent melt thickness between the pre-industrial period (before 1850) and present day. We calibrate the melt record to summer temperatures based on local and regional weather station analyses, and find that the increase in melt production represents a summer warming of at least 2° C, exceeding rates of temperature increase at most low elevation sites in Alaska. The Mt. Hunter melt layer record is significantly (p<0.05) correlated with surface temperatures in the central tropical Pacific through a Rossby-wave like pattern that induces high temperatures over Alaska. Our results show that rapid alpine warming has taken place in the Alaska Range for at least a century, and that conditions in the tropical oceans contribute to this warming.

Investigating methods to estimate melting event parameters over Arctic sea- ice using SSM/I, OKEAN, and RADARSAT Data

NASA Astrophysics Data System (ADS)

Belchansky, G.; Eremeev, V.; Mordvintsev, I.; Platonov, N.; Douglas, D.

The melting events (early melt, melt onset, melt ponding, freeze-up onset) over Arctic sea-ice area are critical for climate and global change studies. They are combined with accuracy of surface energy balances estimates (due to contrasts in the short wave albedo of snow and ice, open water or melt ponds) and drives a number of important processes (onset of snow melt, thawing of boreal forest, etc). M icrowave measurements identify seasonal transition zones due to large differences in emissivity during melt onset, melt ponding and freeze-up periods. This report presents near coincident observation of backscatter cross section (0 ) and brightness temperature (Tb) from Russian OKEAN 01 satellite series, backscatter cross section (0) from RADARSAT-1, brightness temperatures (Tbs) from SSM/I sensors, and near-surface temperature derived from the International Arctic Buoy Program data (IABP) (Belchansky and Douglas, 2000, 2002). To determine the melt duration (time of freeze-up onset minus time of melt onset) passive and active microwave methods were developed. These methods used differences between SSM /I 19.3GHz,H and SSM/I 37.0 GHz, H channels (SSM/I Tb), OKEAN 0 (9.52GHz, VV) and Tb (37.47 GHz, H) channels, RADARSAT-1 0 (5.3GHz, HH), and a threshold technique. An evolution of the SSM/I Tb, OKEAN-01 0 and Tb, RADARSAT ScanSAR 0, MEAN ( 0), SD(0) and SD(0 ) / MEAN(0 ) as function of time was investigated along FY and MY dominant type ice areas during January 1996 through December 1998. The SSM/I, OKEAN and RADARSAT melt onset and freeze up onset algorithms were constructed. The SSM/I algorithm was based- on analysis of the SSM/I Tb. The OKEAN and RADARSAT ScanSAR algorithms were based, respectively, on analysis of OKEAN 0 and Tb of MY and FY sea ice at each MY and FY ice region (200 km by 200 km) determined in OKEAN imagery prior to melting period and changes in RADARSAT SD(0 ) / MEAN(0) of sea-ice during different stages of melting processes at each ice site (75 km by 75 km) determined prior to spring period in ScanSAR imagery. The averaged 12-h near surface temperatures derived from the IABP wer e used to analyze changes in the SSM/I Tb, OKEAN 0 and OKEAN Tb, RADARSAT SD(0) / MEAN(0), and to estimate respective thresholds associated with the melt onset and freeze-up onset. To highlight the sources of differences among various sensors results were compared to understand how the average the melt onset, melt duration and freeze-up onset estimates varied between different instruments and algorithms. A discrepancy in estimates resulted due to the nature of active and passive microwave measurements, frequency and polarization, number of channels, temperature and emissivity effects, and algorithm types. Higher spatial resolution of OKEAN-01 and RADARSAT-1 SAR was an important characteristic for obtaining better estimates of melting parameters. The SSM/ data provide a spatial resolution with global coverageI suitable for circulation models. Therefore OKEAN-01 and RADARSAT measurements can complement SSM/I data. These studies contribute to the growing body of documentation about the levels of disparity obtained when Arctic seasonal transition parameters are calculated using various types of satellite sensors and algorithms. ACKNOWLEDGEMENTS This work was carried out with the support from the International Arctic Research Center and Cooperative Institute for Arctic Research (IARC/CIFAR), University of Alaska Fairbanks. We would like to acknowledge the Alaska SAR Facility (Fairbanks), the National Snow and Ice Data Center (University of Colorado), and the Global Hydrology Resource Center, respectively, for providing RADARSAT images, the DMSP SSM/I Daily Polar Gridded Tb and Sea Ice Concentrations, the single-pass SSM/I brightness temperature data. REFERENCES Belchansky, G. I. and Douglas, D. C. (2000). Classification methods for monitoring Arctic sea-ice using OKEAN passive / active two-channel microwave data. J. Remote Sensing of Environment, Elsevier Science, New York. 73 (3): 307 -322. Belchansky, G. I. and Douglas, D. C. (2002). Seasonal comparisons of sea ice concentration estimates derived from SSM /I, OKEAN, and RADARSAT data. J. Remote Sensing of Environment, Elsevier Science, New York, 81 (1): 67-81.

Sulfate Fining Chemistry in Oxidized and Reduced Soda-Lime-Silica Glasses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matyas, Josef; Hrma, Pavel R.

2005-05-13

Various reducing agents were used and their additions were varied to (1) increase glass quality through eliminating defects from silica scum, (2) decrease SOx emissions through changing the kind and quantity of reducing agents, and (3) improve production efficiency through increased flexibility of glass redox control during continuous processing. The work included measuring silica sand dissolution and sulfate decomposition in melts from glass batches. Glass batches were heated at a temperature-increase rate deemed similar to that experienced in the melting furnace. The sulfate decomposition kinetics was investigated with thermogravimetric analysis-differential thermal analysis and evolved gas analysis. Sulfur concentrations in glassesmore » quenched at different temperatures were determined using X-ray fluorescence spectroscopy. The distribution of residual sand (that which was not dissolved during the initial batch reactions) in the glass was obtained as a function of temperature with optical microscopy in thin-sections of melts. The fraction of undissolved sand was measured with X-ray diffraction. The results of the present study helped Visteon Inc. reduce the energy consumption and establish the batch containing 0.118 mass% of graphite as the best candidate for Visteon glass production. The improved glass batch has a lower potential for silica scum formation and for brown fault occurrence in the final glass product. It was established that bubbles trapped in the melt even at 1450 C have a high probability to be refined when reaching the hot zone in the glass furnace. Furthermore, silica sand does not accumulate at the glass surface and dissolves faster in the batch with graphite than in the batch with carbocite.« less

In situ study at high pressure and temperature of the environment of water in hydrous Na and Ca aluminosilicate melts and coexisting aqueous fluids

NASA Astrophysics Data System (ADS)

Le Losq, Charles; Dalou, Célia; Mysen, Bjorn O.

2017-07-01

The bonding and speciation of water dissolved in Na silicate and Na and Ca aluminosilicate melts were inferred from in situ Raman spectroscopy of the samples, in hydrothermal diamond anvil cells, while at crustal temperature and pressure conditions. Raman data were also acquired on Na silicate and Na and Ca aluminosilicate glasses, quenched from hydrous melts equilibrated at high temperature and pressure in a piston cylinder apparatus. In the hydrous melts, temperature strongly influences O-H stretching ν(O-H) signals, reflecting its control on the bonding of protons between different molecular complexes. Pressure and melt composition effects are much smaller and difficult to discriminate with the present data. However, the chemical composition of the melt + fluid system influences the differences between the ν(O-H) signals from the melts and the fluids and, hence, between their hydrogen partition functions. Quenching modifies the O-H stretching signals: strong hydrogen bonds form in the glasses below the glass transition temperature Tg, and this phenomenon depends on glass composition. Therefore, glasses do not necessarily record the O-H stretching signal shape in melts near Tg. The melt hydrogen partition function thus cannot be assessed with certainty using O-H stretching vibration data from glasses. From the present results, the ratio of the hydrogen partition functions of hydrous silicate melts and aqueous fluids mostly depends on temperature and the bulk melt + fluid system chemical composition. This implies that the fractionation of hydrogen isotopes between magmas and aqueous fluids in water-saturated magmatic systems with differences in temperature and bulk chemical composition will be different.

Arrhenius analysis of anisotropic surface self-diffusion on the prismatic facet of ice.

PubMed

Gladich, Ivan; Pfalzgraff, William; Maršálek, Ondřej; Jungwirth, Pavel; Roeselová, Martina; Neshyba, Steven

2011-11-28

We present an Arrhenius analysis of self-diffusion on the prismatic surface of ice calculated from molecular dynamics simulations. The six-site water model of Nada and van der Eerden was used in combination with a structure-based criterion for determining the number of liquid-like molecules in the quasi-liquid layer. Simulated temperatures range from 230 K-287 K, the latter being just below the melting temperature of the model, 289 K. Calculated surface diffusion coefficients agree with available experimental data to within quoted precision. Our results indicate a positive Arrhenius curvature, implying a change in the mechanism of self-diffusion from low to high temperature, with a concomitant increase in energy of activation from 29.1 kJ mol(-1) at low temperature to 53.8 kJ mol(-1) close to the melting point. In addition, we find that the surface self-diffusion is anisotropic at lower temperatures, transitioning to isotropic in the temperature range of 240-250 K. We also present a framework for self-diffusion in the quasi-liquid layer on ice that aims to explain these observations.

Effect of surface tension anisotropy on cellular morphologies

NASA Technical Reports Server (NTRS)

Mcfadden, G. B.; Coriell, S. R.; Sekerka, R. F.

1988-01-01

A three-dimensional weakly nonlinear analysis for conditions near the onset of instability at the crystal-melt interface was carried out to second order, taking into account the effects of latent heat generation and surface-tension anisotropy of the crystal-melt interface; particular consideration was given to the growth of a cubic crystal in the 001-, 011-, and 111-line directions. Numerical calculations by McFadden et al. (1987), performed for an aluminum-chromium alloy with the assumption of a linear temperature field and an isotropic surface tension, showed that only hexagonal nodes (and not hexagonal cells) occurred near the onset of instability. The results of the present analysis indicate that the nonlinear temperature field (which occurs when thermal conductivities of the crystal and the melt are different and/or the latent heat effects are not negligible) can modify this result and, for certain alloys and processing conditions, can cause the occurrence of hexagonal cells near the onset of instability.

Preparation and Properties of a Novel Microcrystalline Cellulose-Filled Composites Based on Polyamide 6/High-Density Polyethylene

PubMed Central

Xu, Shihua; Yi, Shunmin; He, Jun; Wang, Haigang; Fang, Yiqun; Wang, Qingwen

2017-01-01

In the present study, lithium chloride (LiCl) was utilized as a modifier to reduce the melting point of polyamide 6 (PA6), and then 15 wt % microcrystalline cellulose (MCC) was compounded with low melting point PA6/high-density polyethylene (HDPE) by hot pressing. Crystallization analysis revealed that as little as 3 wt % LiCl transformed the crystallographic forms of PA6 from semi-crystalline to an amorphous state (melting point: 220 °C to none), which sharply reduced the processing temperature of the composites. LiCl improved the mechanical properties of the composites, as evidenced by the fact that the impact strength of the composites was increased by 90%. HDPE increased the impact strength of PA6/MCC composites. In addition, morphological analysis revealed that incorporation of LiCl and maleic anhydride grafted high-density polyethylene (MAPE) improved the interfacial adhesion. LiCl increased the glass transition temperature of the composites (the maximum is 72.6 °C). PMID:28773169

Numerical analysis of fluid flow and heat transfer during melting inside a cylindrical container for thermal energy storage system

NASA Astrophysics Data System (ADS)

Bellan, Selvan; Cheok, Cho Hyun; Gokon, Nobuyuki; Matsubara, Koji; Kodama, Tatsuya

2017-06-01

This paper presents a numerical analysis of unconstrained melting of high temperature(>1000K) phase change material (PCM) inside a cylindrical container. Sodium chloride and Silicon carbide have been used as phase change material and shell of the capsule respectively. The control volume discretization approach has been used to solve the conservation equations of mass, momentum and energy. The enthalpy-porosity method has been used to track the solid-liquid interface of the PCM during melting process. Transient numerical simulations have been performed in order to study the influence of radius of the capsule and the Stefan number on the heat transfer rate. The simulation results show that the counter-clockwise Buoyancy driven convection over the top part of the solid PCM enhances the melting rate quite faster than the bottom part.

Modeling of a Turbofan Engine with Ice Crystal Ingestion in the NASA Propulsion System Laboratory

NASA Technical Reports Server (NTRS)

Veres, Joseph P.; Jorgenson, Philip C. E.; Jones, Scott M.; Nili, Samaun

2017-01-01

The main focus of this study is to apply a computational tool for the flow analysis of the turbine engine that has been tested with ice crystal ingestion in the Propulsion Systems Laboratory (PSL) at NASA Glenn Research Center. The PSL has been used to test a highly instrumented Honeywell ALF502R-5A (LF11) turbofan engine at simulated altitude operating conditions. Test data analysis with an engine cycle code and a compressor flow code was conducted to determine the values of key icing parameters, that can indicate the risk of ice accretion, which can lead to engine rollback (un-commanded loss of engine thrust). The full engine aerothermodynamic performance was modeled with the Honeywell Customer Deck specifically created for the ALF502R-5A engine. The mean-line compressor flow analysis code, which includes a code that models the state of the ice crystal, was used to model the air flow through the fan-core and low pressure compressor. The results of the compressor flow analyses included calculations of the ice-water flow rate to air flow rate ratio (IWAR), the local static wet bulb temperature, and the particle melt ratio throughout the flow field. It was found that the assumed particle size had a large effect on the particle melt ratio, and on the local wet bulb temperature. In this study the particle size was varied parametrically to produce a non-zero calculated melt ratio in the exit guide vane (EGV) region of the low pressure compressor (LPC) for the data points that experienced a growth of blockage there, and a subsequent engine called rollback (CRB). At data points where the engine experienced a CRB having the lowest wet bulb temperature of 492 degrees Rankine at the EGV trailing edge, the smallest particle size that produced a non-zero melt ratio (between 3 percent - 4 percent) was on the order of 1 micron. This value of melt ratio was utilized as the target for all other subsequent data points analyzed, while the particle size was varied from 1 micron - 9.5 microns to achieve the target melt ratio. For data points that did not experience a CRB which had static wet bulb temperatures in the EGV region below 492 degrees Rankine, a non-zero melt ratio could not be achieved even with a 1 micron ice particle size. The highest value of static wet bulb temperature for data points that experienced engine CRB was 498 degrees Rankine with a particle size of 9.5 microns. Based on this study of the LF11 engine test data, the range of static wet bulb temperature at the EGV exit for engine CRB was in the narrow range of 492 degrees Rankine - 498 degrees Rankine , while the minimum value of IWAR was 0.002. The rate of blockage growth due to ice accretion and boundary layer growth was estimated by scaling from a known blockage growth rate that was determined in a previous study. These results obtained from the LF11 engine analysis formed the basis of a unique “icing wedge.”

Making mushy magma chambers in the lower continental crust: Cold storage and compositional bimodality

NASA Astrophysics Data System (ADS)

Jackson, Matthew; Blundy, Jon; Sparks, Steve

2017-04-01

Increasing geological and geophysical evidence suggests that crustal magma reservoirs are normally low melt fraction 'mushes' rather than high melt fraction 'magma chambers'. Yet high melt fractions must form within these mush reservoirs to explain the observed flow and eruption of low crystallinity magmas. In many models, crystallinity is linked directly to temperature, with higher temperature corresponding to lower crystallinity (higher melt fraction). However, increasing temperature yields less evolved (silicic) melt composition for a given starting material. If mobile, low crystallinity magmas require high temperature, it is difficult to explain how they can have evolved composition. Here we use numerical modelling to show that reactive melt flow in a porous and permeable mush reservoir formed by the intrusion of numerous basaltic sills into the lower continental crust produces magma in high melt fraction (> 0.5) layers akin to conventional magma chambers. These magma-chamber-like layers contain evolved (silicic) melt compositions and form at low (close to solidus) temperatures near the top of the mush reservoir. Evolved magma is therefore kept in 'cold storage' at low temperature, but also at low crystallinity so the magma is mobile and can leave the mush reservoir. Buoyancy-driven reactive flow and accumulation of melt in the mush reservoir controls the temperature and composition of magma that can leave the reservoir. The modelling also shows that processes in lower crustal mush reservoirs produce mobile magmas that contain melt of either silicic or mafic composition. Intermediate melt compositions are present but are not within mobile magmas. Silicic melt compositions are found at high melt fraction within the magma-chamber like layers near the top of the mush reservoir. Mafic melt compositions are found at high melt fraction within the cooling sills. Melt elsewhere in the reservoir has intermediate composition, but remains trapped in the reservoir because the local melt fraction is too low to form a mobile magma. The model results are consistent with geochemical data suggesting that lower crustal magma reservoirs supply silicic and mafic melts to arc volcanoes, but intermediate magmas are formed by mixing in shallower reservoirs. We suggest here that lower crustal magma chambers primarily form in response to changes in bulk composition caused by melt migration and chemical reaction in a mush reservoir. This process is different to the conventional and widely applied models of magma chamber formation. Similar processes are likely to operate in shallow mush reservoirs, but will likely be further complicated by the presence of volatile phases, and mixing of different melt compositions sourced from deeper mush reservoirs.

The Analysis and Modeling of Phase Stability and Multiphase Designs in High Temperature Refractory Metal-Silicon-Boron Alloys

DTIC Science & Technology

2009-01-27

high temperature mechanical properties , it was confirmed that the three phase eutectic structure exhibited exceptionally high strength and creep...microstructurc constituent, offer an attractive property balance of high melting temperature, oxidation resistance and useful high temperature mechanical ...design of new multiphase high-temperature alloys with balanced environmental and mechanical properties . 15. SUBJECT TERMS Phase Stability, Alloying

The gallium melting-point standard: a determination of the liquid-solid equilibrium temperature of pure gallium on the International Practical Temperature Scale of 1968.

PubMed

Thornton, D D

1977-01-01

The sharpness and reproducibility of the gallium melting point were studied and the melting temperature of gallium in terms of IPTS-68 was determined. Small melting-point cells designed for use with thermistors are described. Nine gallium cells including three levels of purity were used in 68 separate determinations fo the melting point. The melting point of 99.99999% pure gallium in terms of IPTS-68 is found to be 29.771(4) +/- 0.001(4) degree C; the melting range is less than 0.0005 degree C and is reproducible to +/- 0.0004 degree C.

Pb-free Sn-Ag-Cu ternary eutectic solder

DOEpatents

Anderson, Iver E.; Yost, Frederick G.; Smith, John F.; Miller, Chad M.; Terpstra, Robert L.

1996-06-18

A Pb-free solder includes a ternary eutectic composition consisting essentially of about 93.6 weight % Sn-about 4.7 weight % Ag-about 1.7 weight % Cu having a eutectic melting temperature of about 217.degree. C. and variants of the ternary composition wherein the relative concentrations of Sn, Ag, and Cu deviate from the ternary eutectic composition to provide a controlled melting temperature range (liquid-solid "mushy" zone) relative to the eutectic melting temperature (e.g. up to 15.degree. C. above the eutectic melting temperature).

Pb-free Sn-Ag-Cu ternary eutectic solder

DOEpatents

Anderson, I.E.; Yost, F.G.; Smith, J.F.; Miller, C.M.; Terpstra, R.L.

1996-06-18

A Pb-free solder includes a ternary eutectic composition consisting essentially of about 93.6 weight % Sn-about 4.7 weight % Ag-about 1.7 weight % Cu having a eutectic melting temperature of about 217 C and variants of the ternary composition wherein the relative concentrations of Sn, Ag, and Cu deviate from the ternary eutectic composition to provide a controlled melting temperature range (liquid-solid ``mushy`` zone) relative to the eutectic melting temperature (e.g. up to 15 C above the eutectic melting temperature). 5 figs.

Effect of plasma spray processing variations on particle melting and splat spreading of hydroxylapatite and alumina

NASA Astrophysics Data System (ADS)

Yankee, S. J.; Pletka, B. J.

1993-09-01

Splats of hydroxylapatite (HA) and alumina were obtained via plasma spraying using systematically varied combinations of plasma velocity and temperature, which were achieved by altering the primary plasma gas flow rate and plasma gas composition. Particle size was also varied in the case of alumina. Splat spreading was quantified via computer- aided image analysis as a function of processing variations. A comparison of the predicted splat dimensions from a model developed by Madejski with experimental observations of HA and alumina splats was performed. The model tended to underestimate the HA splat sizes, suggesting that evaporation of smaller particles occurred under the chosen experimental conditions, and to overestimate the observed alumina splat dimensions. Based on this latter result and on the surface appearance of the substrates, incomplete melting appeared to take place in all but the smaller alumina particles. Analysis of the spreading data as a function of the processing variations indicated that the particle size as well as the plasma temperature and velocity influenced the extent of particle melting. Based on these data and other considerations, a physical model was developed that described the degree of particle melting in terms of material and processing parameters. The physical model correctly predicted the relative splat spreading behavior of HA and alumina, assuming that spreading was directly linked to the extent of particle melting.

The gallium melting-point standard: its role in our temperature measurement system.

PubMed

Mangum, B W

1977-01-01

The latest internationally-adopted temperature scale, the International Practical Temperature Scale of 1968 (amended edition of 1975), is discussed in some detail and a brief description is given of its evolution. The melting point of high-purity gallium (stated to be at least 99.99999% pure) as a secondary temperature reference point is evaluated. I believe that this melting-point temperature of gallium should be adopted by the various medical professional societies and voluntary standards groups as the reaction temperature for enzyme reference methods in clinical enzymology. Gallium melting-point cells are available at the National Bureau of Standards as Standard Reference Material No. 1968.

Hot cracking susceptibility of fillers 52 and 82 in alloy 690 welding

NASA Astrophysics Data System (ADS)

Wu, Weite; Tsai, C. H.

1999-02-01

The hot cracking susceptibility of fillers 52 and 82 in a alloy 690 weldment is analyzed by the Varestraint test. Weld characteristics, microstructure, hardness distribution, and thermal analysis of the two filler metals are also examined. The weld metal of both fillers develops an extremely dense oxide layer. A stainless steel brush cannot remove the oxide layer, and a grinder may be needed between weld passes to assure a sound weld. Differential temperature analysis (DTA) shows that filler 82 has a lower melting point and a wider melting/solidification temperature differential (Δ T). These characteristics correlate with greater hot cracking susceptibility of filler 82 than 52 in Varestraint tests. The hot cracks are intergranular and are caused by elements segregating in grain boundies.

Partial melting kinetics of plagioclase-diopside pairs

NASA Astrophysics Data System (ADS)

Tsuchiyama, Akira

1985-09-01

Partial melting experiments on plagioclase (An60) and diopside have been carried out using pairs of large crystals to investigate textures and kinetics of melting. The experiments were done at one atmosphere pressure as a function of temperature (1,190 1,307° C) and time (1.5 192 h). Melting took place mainly at the plagioclase-diopside contact planes. Reaction zones composed of fine mixtures of calcic plagioclase and melt were developed from the surface of the plagioclase crystal inward. There exists a critical temperature, below which only a few % melting can occur over the duration of the experiments. This sluggish melting is caused by slow NaSi-CaAl diffusion in plagioclase, because the plagioclase crystal must change its composition to produce albite-rich cotectic melts. Diffusion in the solid also affects the chemical composition of the melts. During initial melting, potassium is preferentially extracted from plagioclase because K-Na diffusion in plagioclase is faster than that of NaSi-CaAl. This also causes a shift in the cotectic compositions. Above the “critical temperature”, on the other hand, melting is promoted by a metastable reaction in which the plagioclase composition does not change, and which produces melts with compositional gradients along the original An60-diopside tie line. The critical temperature is determined by the intersection of the cotectic and the An60-diopside tie line. Interdiffusion coefficients of plagioclase-diopside components in the melt are estimated from melting rates above the critical temperature by using a simplified steady-state diffusion model (e.g., 10-8 cm2/sec at 1,300° C). Many examples of reaction zones due to partial melting have been described as spongy or fingerprint-like textures in xenoliths. Metastable melting above the critical temperature is considered to take place in natural melting where there is a high degree of melting. However, we cannot exclude the possibility of disequilibrium created by sluggish melting controlled by diffusion in the minerals. If melting occurs close to the solidus, this process can be important even for partial melting in the upper mantle.

Greenland Ice Sheet Melt from MODIS and Associated Atmospheric Variability

NASA Technical Reports Server (NTRS)

Hakkinen, Sirpa; Hall, Dorothy K.; Shuman, Christopher A.; Worthen, Denise L.; DiGirolamo, Nicolo E.

2014-01-01

Daily June-July melt fraction variations over the Greenland Ice Sheet (GIS) derived from the MODerate-resolution Imaging Spectroradiometer (MODIS) (2000-2013) are associated with atmospheric blocking forming an omega-shape ridge over the GIS at 500hPa height (from NCEPNCAR). Blocking activity with a range of time scales, from synoptic waves breaking poleward ( 5 days) to full-fledged blocks (5 days), brings warm subtropical air masses over the GIS controlling daily surface temperatures and melt. The temperature anomaly of these subtropical air mass intrusions is also important for melting. Based on the largest MODIS melt years (2002 and 2012), the area-average temperature anomaly of 2 standard deviations above the 14-year June-July mean, results in a melt fraction of 40 or more. Summer 2007 had the most blocking days, however atmospheric temperature anomalies were too small to instigate extreme melting.

Stability and melting of Fe3C at high pressure and temperature: Implication for the carbon in the Earth's core

NASA Astrophysics Data System (ADS)

Takahashi, S.; Ohtani, E.; Sakai, T.; Hirao, N.; Ohishi, Y.

2012-12-01

The Earth's core is regarded as an Fe-Ni alloy but its density is lower than that of pure Fe at the core conditions. Therefore, the Earth's core is supposed to contain light elements and carbon is one of the candidates of the light elements to explain the density deficit of the Earth's core. Nakajima et al. (2009) reported the melting temperature of Fe3C up to around 30 GPa based on textual observations, the chemical analysis of the quenched run products and in situ X-ray diffraction experiments using a Kawai-type multi anvil apparatus. Lord et al. (2009) reported melting temperatures of Fe3C up to 70 GPa, which was determined by the temperature plateau during increasing laser power using a laser-heated diamond anvil cell. They also suggested Fe+Fe7C3 is a stable subsolidus phase. There are obvious discrepancies between the melting curve and the stable subsolidus phase reported by Nakajima et al. (2009) and those reported by Lord et al. (2009). In this study, the melting temperatures of Fe3C and a subsolidus phase relation were determined based on in situ X-ray diffraction experiments. This study aims to reveal the stability field of Fe3C and the melting temperature of Fe3C and to discuss the behaviors of carbon in the Earth's core. We have performed experiments using a laser-heated diamond anvil cell combined with in situ X-ray diffraction experiment at BL10XU beamline, SPring-8 synchrotron facility. An NaCl powder and a rhenium or tungsten foil were used for the insulator and gasket, respectively. Melting of the sample was determined by disappearance of the X-ray diffraction peaks. We determined the melting relation of Fe3C up to 145 GPa by in situ X-ray diffraction experiments. Present results are close to Nakajima et al. (2009) up to 30 GPa but become close to that reported by Lord et al. (2009) at higher pressure conditions. The solidus temperature extrapolated to the ICB pressure, 330 GPa, is 5400 K. We also confirmed that Fe3C is stable as a subsolidus phase at least up to 237 GPa and 4100 K. This strongly suggests that Fe3C is a potential candidate of the Earth's inner core although we need further studies at the inner core conditions.

Some physical aspects of fluid-fluxed melting

NASA Astrophysics Data System (ADS)

Patiño Douce, A.

2012-04-01

Fluid-fluxed melting is thought to play a crucial role in the origin of many terrestrial magmas. We can visualize the fundamental physics of the process as follows. An infinitesimal amount of fluid infiltrates dry rock at the temperature of its dry solidus. In order to restore equilibrium the temperature must drop, so that enthalpy is released and immediately reabsorbed as enthalpy of melting. The amount of melt produced must be such that the energy balance and thermodynamic equilibrium conditions are simultaneously satisfied. We wish to understand how an initially dry rock melts in response to progressive fluid infiltration, under both batch and fractional melting constraints. The simplest physical model for this process is a binary system in which one of the components makes up a pure solid phase and the other component a pure fluid phase, and in which a binary melt phase exists over certain temperature range. Melting point depression is calculated under the assumption of ideal mixing. The equations of energy balance and thermodynamic equilibrium are solved simultaneously for temperature and melt fraction, using an iterative procedure that allows addition of fluid in infinitesimal increments. Batch melting and fractional melting are simulated by allowing successive melt increments to remain in the system (batch) or not (fractional). Despite their simplified nature, these calculations reveal some important aspects of fluid-fluxed melting. The model confirms that, if the solubility of the fluid in the melt is sufficiently high, fluid fluxed melting is an efficient mechanism of magma generation. One might expect that the temperature of the infiltrating fluid would have a significant effect on melt productivity, but the results of the calculations show this not to be the case, because a relatively small mass of low molecular weight fluid has a strong effect on the melting point of minerals with much higher molecular weights. The calculations reveal the somewhat surprising result that fluid infiltration produces more melt during fractional melting than during batch melting. This behavior, which is opposite to that of decompression melting of a dry solid, arises because the melting point depression effect of the added fluid is greater during fractional melting than during batch melting, which results in a greater release of enthalpy and, therefore, greater melt production for fractional melting than for batch melting, for the same total amount of fluid added. The difference may be considerable. As an example, suppose that 0.1 mols of H2O infiltrate 1 mol or silicate rock. Depending on the rock composition this may corresponds to ˜ 1 wt% H2O. For a given choice of model parameters (initial temperature, heat capacity and entropy of fusion), about 28% of the rock melts during fractional melting, versus some 23 % during batch melting. Fluid fluxing is a robust process of melt generation, without which magmatism at Earth's convergent plate margins would be impossible.

Poly(vinyl methyl ether) hydrogels at temperatures below the freezing point of water-molecular interactions and states of water.

PubMed

Pastorczak, Marcin; Dominguez-Espinosa, Gustavo; Okrasa, Lidia; Pyda, Marek; Kozanecki, Marcin; Kadlubowski, Slawomir; Rosiak, Janusz M; Ulanski, Jacek

2014-01-01

Water interacting with a polymer reveals a number of properties very different to bulk water. These interactions lead to the redistribution of hydrogen bonds in water. It results in modification of thermodynamic properties of water and the molecular dynamics of water. That kind of water is particularly well observable at temperatures below the freezing point of water, when the bulk water crystallizes. In this work, we determine the amount of water bound to the polymer and of the so-called pre-melting water in poly(vinyl methyl ether) hydrogels with the use of Raman spectroscopy, dielectric spectroscopy, and calorimetry. This analysis allows us to compare various physical properties of the bulk and the pre-melting water. We also postulate the molecular mechanism responsible for the pre-melting of part of water in poly(vinyl methyl ether) hydrogels. We suggest that above -60 °C, the first segmental motions of the polymer chain are activated, which trigger the process of the pre-melting.

Liquid structure and temperature invariance of sound velocity in supercooled Bi melt

DOE Office of Scientific and Technical Information (OSTI.GOV)

Emuna, M.; Mayo, M.; Makov, G.

2014-03-07

Structural rearrangement of liquid Bi in the vicinity of the melting point has been proposed due to the unique temperature invariant sound velocity observed above the melting temperature, the low symmetry of Bi in the solid phase and the necessity of overheating to achieve supercooling. The existence of this structural rearrangement is examined by measurements on supercooled Bi. The sound velocity of liquid Bi was measured into the supercooled region to high accuracy and it was found to be invariant over a temperature range of ∼60°, from 35° above the melting point to ∼25° into the supercooled region. The structuralmore » origin of this phenomenon was explored by neutron diffraction structural measurements in the supercooled temperature range. These measurements indicate a continuous modification of the short range order in the melt. The structure of the liquid is analyzed within a quasi-crystalline model and is found to evolve continuously, similar to other known liquid pnictide systems. The results are discussed in the context of two competing hypotheses proposed to explain properties of liquid Bi near the melting: (i) liquid bismuth undergoes a structural rearrangement slightly above melting and (ii) liquid Bi exhibits a broad maximum in the sound velocity located incidentally at the melting temperature.« less

Melting line of polymeric nitrogen

NASA Astrophysics Data System (ADS)

Yakub, L. N.

2013-05-01

We made an attempt to predict location of the melting line of polymeric nitrogen using two equations for Helmholtz free energy: proposed earlier for cubic gauche-structure and developed recently for liquid polymerized nitrogen. The P-T relation, orthobaric densities and latent heat of melting were determined using a standard double tangent construction. The estimated melting temperature decreases with increasing pressure, alike the temperature of molecular-nonmolecular transition in solid. We discuss the possibility of a triple point (solid-molecular fluid-polymeric fluid) at ˜80 GPa and observed maximum of melting temperature of nitrogen.

The melting mechanism in binary Pd0.25Ni0.75 nanoparticles: molecular dynamics simulations

NASA Astrophysics Data System (ADS)

Domekeli, U.; Sengul, S.; Celtek, M.; Canan, C.

2018-02-01

The melting mechanism for Pd0.25Ni0.75 alloy nanoparticles (NPs) was investigated using molecular dynamics (MD) simulations with quantum Sutton-Chen many-body potentials. NPs of six different sizes ranging from 682 to 22,242 atoms were studied to observe the effect of size on the melting point. The melting temperatures of the NPs were estimated by following the changes in both the thermodynamic and structural quantities such as the total energy, heat capacity and Lindemann index. We also used a thermodynamics model to better estimate the melting point and to check the accuracy of MD simulations. We observed that the melting points of the NPs decreased as their sizes decreased. Although the MD simulations for the bulk system yielded higher melting temperatures because of the lack of a seed for the liquid phase, the melting temperatures determined for both the bulk material and the NPs are in good agreement with those predicted from the thermodynamics model. The melting mechanism proceeds in two steps: firstly, a liquid-like shell is formed in the outer regions of the NP with increasing temperature. The thickness of the liquid-like shell increases with increasing temperature until the shell reaches a critical thickness. Then, the entire Pd-Ni NP including core-related solid-like regions melts at once.

In Situ Optical Observation of High-Temperature Geological Processes With the Moissanite Cell

NASA Astrophysics Data System (ADS)

Walte, N.; Keppler, H.

2005-12-01

A major drawback of existing techniques in experimental earth and material sciences is the inability to observe ongoing high-temperature processes in situ during an experiment. Examples for important time-dependent processes include the textural development of rocks and oxide systems during melting and crystallization, solid-state and melt-present recrystallization and Ostwald ripening, and bubble nucleation and growth during degassing of glasses and melts. The investigation of these processes by post-mortem analysis of a quenched microstructure is time consuming and often unsatisfactory. Here, we introduce the moissanite cell that allows optical in situ observation of long-term experiments at high temperatures. Moissanite is a transparent gem-quality type of SiC that is characterized by its hardness and superior chemical and thermal resistance. Two moissanite windows with a thickness and diameter of several millimeters are placed into sockets of fired pyrophyllite and fixed onto two opposite metal plates. The sockets are wrapped with heating wire and each window is connected to a thermocouple for temperature control. The sample is placed directly between the moissanite windows and the cell is assembled similarly to a large diamond anvil cell. In situ observation of the sample is done with a microscope through observation windows and movies are recorded with an attached digital camera. Our experiments with the new cell show that temperatures above 1200°C can be maintained and observed in a sample for several days without damaging the cell nor the windows. Time-lapse movies of melting and crystallizing natural and synthetic rocks and of degassing glasses and melts will be presented to show the potential of the new technique for experimental earth and material science.

Local melting in Al-Mg-Zn-alloys

NASA Astrophysics Data System (ADS)

Droenen, Per-Erik; Ryum, Nils

1994-03-01

The internal melting of several Al-Mg-Zn-alloys has been studied by rapid upquenching in a salt bath of specimens slowly cooled at a rate of 2 °C/h down to 375 °C. The melting reaction was studied metallographically in the light- and electron-scanning microscope, and local concentrations were measured in the microprobe. Local melting of both the equilibrium phases T and η was observed to occur. There were, however, essential differences between the melting kinetics for the two phases. While the T-phase particles melted spontaneously at temperatures at or above the invariant temperature, 489 °C, and after some period of time at lower temperatures, the η-phase particles either melted spontaneously at or above the invariant temperature, T - 475 °C, or dissolved into the matrix at temperatures below 475 °C. This difference in behavior can be accounted for if the α(Al)-η section is not a quasi-binary section. The industrial implications of the internal melting in these alloys are discussed and compared to the same reaction in the Al-Mg-Si alloys. A model is developed in the Appendix to quantify the different behaviors of these two classes of alloys.

Experimental constraints on melting temperatures in the MgO-SiO2 system at lower mantle pressures

NASA Astrophysics Data System (ADS)

Baron, Marzena A.; Lord, Oliver T.; Myhill, Robert; Thomson, Andrew R.; Wang, Weiwei; Trønnes, Reidar G.; Walter, Michael J.

2017-08-01

Eutectic melting curves in the system MgO-SiO2 have been experimentally determined at lower mantle pressures using laser-heated diamond anvil cell (LH-DAC) techniques. We investigated eutectic melting of bridgmanite plus periclase in the MgO-MgSiO3 binary, and melting of bridgmanite plus stishovite in the MgSiO3-SiO2 binary, as analogues for natural peridotite and basalt, respectively. The melting curve of model basalt occurs at lower temperatures, has a shallower dT / dP slope and slightly less curvature than the model peridotitic melting curve. Overall, melting temperatures detected in this study are in good agreement with previous experiments and ab initio simulations at ∼25 GPa (Liebske and Frost, 2012; de Koker et al., 2013). However, at higher pressures the measured eutectic melting curves are systematically lower in temperature than curves extrapolated on the basis of thermodynamic modelling of low-pressure experimental data, and those calculated from atomistic simulations. We find that our data are inconsistent with previously computed melting temperatures and melt thermodynamic properties of the SiO2 endmember, and indicate a maximum in short-range ordering in MgO-SiO2 melts close to Mg2SiO4 composition. The curvature of the model peridotite eutectic relative to an MgSiO3 melt adiabat indicates that crystallization in a global magma ocean would begin at ∼100 GPa rather than at the bottom of the mantle, allowing for an early basal melt layer. The model peridotite melting curve lies ∼ 500 K above the mantle geotherm at the core-mantle boundary, indicating that it will not be molten unless the addition of other components reduces the solidus sufficiently. The model basalt melting curve intersects the geotherm at the base of the mantle, and partial melting of subducted oceanic crust is expected.

Method For Synthesizing Extremely High-Temperature Melting Materials

DOEpatents

Saboungi, Marie-Louise; Glorieux, Benoit

2005-11-22

The invention relates to a method of synthesizing high-temperature melting materials. More specifically the invention relates to a containerless method of synthesizing very high temperature melting materials such as borides, carbides and transition-metal, lanthanide and actinide oxides, using an Aerodynamic Levitator and a laser. The object of the invention is to provide a method for synthesizing extremely high-temperature melting materials that are otherwise difficult to produce, without the use of containers, allowing the manipulation of the phase (amorphous/crystalline/metastable) and permitting changes of the environment such as different gaseous compositions.

Method for synthesizing extremely high-temperature melting materials

DOEpatents

Saboungi, Marie-Louise; Glorieux, Benoit

2007-11-06

The invention relates to a method of synthesizing high-temperature melting materials. More specifically the invention relates to a containerless method of synthesizing very high temperature melting materials such as carbides and transition-metal, lanthanide and actinide oxides, using an aerodynamic levitator and a laser. The object of the invention is to provide a method for synthesizing extremely high-temperature melting materials that are otherwise difficult to produce, without the use of containers, allowing the manipulation of the phase (amorphous/crystalline/metastable) and permitting changes of the environment such as different gaseous compositions.

Method for Synthesizing Extremeley High Temperature Melting Materials

DOEpatents

Saboungi, Marie-Louise and Glorieux, Benoit

2005-11-22

The invention relates to a method of synthesizing high-temperature melting materials. More specifically the invention relates to a containerless method of synthesizing very high temperature melting materials such as borides, carbides and transition-metal, lanthanide and actinide oxides, using an Aerodynamic Levitator and a laser. The object of the invention is to provide a method for synthesizing extremely high-temperature melting materials that are otherwise difficult to produce, without the use of containers, allowing the manipulation of the phase (amorphous/crystalline/metastable) and permitting changes of the environment such as different gaseous compositions.

Polymer alloys with balanced heat storage capacity and engineering attributes and applications thereof

DOEpatents

Soroushian, Parviz

2002-01-01

A thermoplastic polymer of relatively low melt temperature is blended with at least one of thermosets, elastomers, and thermoplastics of relatively high melt temperature in order to produce a polymer blend which absorbs relatively high quantities of latent heat without melting or major loss of physical and mechanical characteristics as temperature is raised above the melting temperature of the low-melt-temperature thermoplastic. The polymer blend can be modified by the addition of at least one of fillers, fibers, fire retardants, compatibilisers, colorants, and processing aids. The polymer blend may be used in applications where advantage can be taken of the absorption of excess heat by a component which remains solid and retains major fractions of its physical and mechanical characteristics while absorbing relatively high quantities of latent heat.

An assessment of the CORCON-MOD3 code. Part 1: Thermal-hydraulic calculations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Strizhov, V.; Kanukova, V.; Vinogradova, T.

1996-09-01

This report deals with the subject of CORCON-Mod3 code validation (thermal-hydraulic modeling capability only) based on MCCI (molten core concrete interaction) experiments conducted under different programs in the past decade. Thermal-hydraulic calculations (i.e., concrete ablation, melt temperature, melt energy, concrete temperature, and condensible and non-condensible gas generation) were performed with the code, and compared with the data from 15 experiments, conducted at different scales using both simulant (metallic and oxidic) and prototypic melt materials, using different concrete types, and with and without an overlying water pool. Sensitivity studies were performed in a few cases involving, for example, heat transfer frommore » melt to concrete, condensed phase chemistry, etc. Further, special analysis was performed using the ACE L8 experimental data to illustrate the differences between the experimental and the reactor conditions, and to demonstrate that with proper corrections made to the code, the calculated results were in better agreement with the experimental data. Generally, in the case of dry cavity and metallic melts, CORCON-Mod3 thermal-hydraulic calculations were in good agreement with the test data. For oxidic melts in a dry cavity, uncertainties in heat transfer models played an important role for two melt configurations--a stratified geometry with segregated metal and oxide layers, and a heterogeneous mixture. Some discrepancies in the gas release data were noted in a few cases.« less

Assessing glacier melt contribution to streamflow at Universidad Glacier, central Andes of Chile

NASA Astrophysics Data System (ADS)

Bravo, Claudio; Loriaux, Thomas; Rivera, Andrés; Brock, Ben W.

2017-07-01

Glacier melt is an important source of water for high Andean rivers in central Chile, especially in dry years, when it can be an important contributor to flows during late summer and autumn. However, few studies have quantified glacier melt contribution to streamflow in this region. To address this shortcoming, we present an analysis of meteorological conditions and ablation for Universidad Glacier, one of the largest valley glaciers in the central Andes of Chile at the head of the Tinguiririca River, for the 2009-2010 ablation season. We used meteorological measurements from two automatic weather stations installed on the glacier to drive a distributed temperature-index and runoff routing model. The temperature-index model was calibrated at the lower weather station site and showed good agreement with melt estimates from an ablation stake and sonic ranger, and with a physically based energy balance model. Total modelled glacier melt is compared with river flow measurements at three sites located between 0.5 and 50 km downstream. Universidad Glacier shows extremely high melt rates over the ablation season which may exceed 10 m water equivalent in the lower ablation area, representing between 10 and 13 % of the mean monthly streamflow at the outlet of the Tinguiririca River Basin between December 2009 and March 2010. This contribution rises to a monthly maximum of almost 20 % in March 2010, demonstrating the importance of glacier runoff to streamflow, particularly in dry years such as 2009-2010. The temperature-index approach benefits from the availability of on-glacier meteorological data, enabling the calculation of the local hourly variable lapse rate, and is suited to high melt regimes, but would not be easily applicable to glaciers further north in Chile where sublimation is more significant.

Results from a lab study of melting sea ice

NASA Astrophysics Data System (ADS)

Wiese, M.; Griewank, P.; Notz, D.

2012-04-01

Sea-ice melting is a complex process which is not fully understood yet. In order to study sea-ice melt in detail we perform lab experiments in an approximately 2x0.7x1.2 m large tank in a cold room. We grow sea ice with different salinities at least 10 cm thick. Then we let the ice melt at different air temperatures and oceanic heat fluxes. During the melt period, we measure the evolution of ice thickness, internal temperature, salinity and surface temperature. We will present results from roughly five months of experiments. Topics will include the influence of bulk salinity on melt rates and the surface temperature. The effects of flushing on the salinity evolution and detailed thermal profiles will also be included. To investigate these processes we focus on the energy budget and the salinity evolution. These topics are linked since the thermodynamic properties of sea ice (heat capacity, heat conductivity and latent heat of fusion) are very sensitive to salinity variations. For example the heat capacity of sea ice increases greatly as the temperature approaches the melting point. This increase results in non-linear temperature profiles and enhances heat conduction into the ice. The salinity evolution during the growth phase has been investigated and measured in multiple studies over the last decades. In contrast there are no detailed lab measurements of melting ice available to quantify the effects of flushing melt water and ponding. This is partially due to the fact that the heterogeneity of melting sea ice makes it much more difficult to measure representative values.

Determination of melt pool dimensions using DOE-FEM and RSM with process window during SLM of Ti6Al4V powder

NASA Astrophysics Data System (ADS)

Zhuang, Jyun-Rong; Lee, Yee-Ting; Hsieh, Wen-Hsin; Yang, An-Shik

2018-07-01

Selective laser melting (SLM) shows a positive prospect as an additive manufacturing (AM) technique for fabrication of 3D parts with complicated structures. A transient thermal model was developed by the finite element method (FEM) to simulate the thermal behavior for predicting the time evolution of temperature field and melt pool dimensions of Ti6Al4V powder during SLM. The FEM predictions were then compared with published experimental measurements and calculation results for model validation. This study applied the design of experiment (DOE) scheme together with the response surface method (RSM) to conduct the regression analysis based on four processing parameters (exactly, the laser power, scanning speed, preheating temperature and hatch space) for predicting the dimensions of the melt pool in SLM. The preliminary RSM results were used to quantify the effects of those parameters on the melt pool size. The process window was further implemented via two criteria of the width and depth of the molten pool to screen impractical conditions of four parameters for including the practical ranges of processing parameters. The FEM simulations confirmed the good accuracy of the critical RSM models in the predictions of melt pool dimensions for three typical SLM working scenarios.

Melting-solidification transition of Zn nanoparticles embedded in SiO2: Observation by synchrotron x-ray and ultraviolet-visible-near-infrared light

NASA Astrophysics Data System (ADS)

Amekura, H.; Tanaka, M.; Katsuya, Y.; Yoshikawa, H.; Ohnuma, M.; Matsushita, Y.; Kobayashi, K.; Kishimoto, N.

2010-11-01

Melting-solidification transition of Zn nanoparticles (NPs) with the mean diameter of 11.5 nm, embedded in silica glass, was investigated by glancing incident x-ray diffraction (GIXRD) at high temperatures using synchrotron radiation (SR). With increasing temperature, 101Zn diffraction peak gradually decreases up to ˜360 °C and then steeply decreases. This is due to the melting of Zn NPs, which completes around 420 °C. With decreasing temperature, the solidification of the NPs begins around ˜310 °C. The temperature hysteresis with a width of ˜110 °C was observed. With temperature, the diffraction angle shows a shift without hysteresis, which is ascribed to thermal expansion of Zn NP lattice. Thermal expansion coefficient of Zn NPs was determined as 24.4×10-6 K-1 along the ⟨101⟩ direction. Optical absorption spectroscopy shows a broad ultraviolet (UV) peak which was observed at even higher temperatures than the melting temperature but shifts to the low-energy side with the melting. The energy shift in the UV peak also shows the temperature hysteresis which resembles with the melting-solidification hysteresis recorded by SR-GIXRD. The melting-solidification transition is also detectable by the optical absorption spectroscopy in the UV-visible-near-infrared region.

Extended T-index models for glacier surface melting: a case study from Chorabari Glacier, Central Himalaya, India

NASA Astrophysics Data System (ADS)

Karakoti, Indira; Kesarwani, Kapil; Mehta, Manish; Dobhal, D. P.

2016-10-01

Two enhanced temperature-index (T-index) models are proposed by incorporating meteorological parameters viz. relative humidity, wind speed and net radiation. The models are an attempt to explore different climatic variables other than temperature affecting glacier surface melting. Weather data were recorded at Chorabari Glacier using an automatic weather station during the summers of 2010 (July 10 to September 10) and 2012 (June 10 to October 25). The modelled surface melt is validated against the measured point surface melting at the snout. Performance of the developed models is evaluated by comparing with basic temperature-index model and is quantified through different efficiency criteria. The results suggest that proposed models yield considerable improvement in surface melt simulation . Consequently, the study reveals that glacier surface melt depends not only on temperature but also on weather parameters viz. relative humidity, wind speed and net radiation play a significant role in glacier surface melting. This approach provides a major improvement on basic temperature-index method and offers an alternative to energy balance model.

Fiber structure formation in melt spinning of bio-based aliphatic co-polyesters

NASA Astrophysics Data System (ADS)

Qin, Qing; Takarada, Wataru; Kikutani, Takeshi

2015-05-01

High-speed melt spinning of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH) with the 3-hydroxyhexanoate composition of 5.4 mol% was carried out. Melting temperature of this polymer is 141.5°C. It has been reported that PHBH fibers of good appearance can be prepared through the melt spinning process only when extrusion temperature is lower than the melting temperature of pure PHB (176 °C). The high-speed melt spinning experiment in this study revealed that the crystallization of PHBH proceeded at high take-up velocities even when the extrusion temperature was higher than the melting temperature of PHB. This result is considered to be due to the enhancement of crystallization through the application of high tensile stress to the molten polymer in the spinning line. As-spun fibers showed sufficiently high mechanical properties. On the other hand, crystalline orientation of α-form crystal increased with an increase in the take-up velocity and the existence of a small amount of β-form crystals was detected at high take-up velocities. This is another indication for the occurrence of crystallization under high tensile stress.

Comparison of water gel desserts from fish skin and pork gelatins using instrumental measurements.

PubMed

Zhou, Peng; Regenstein, Joe M

2007-05-01

The objective of this study was to compare water gel desserts from various gelatins using instrumental measurements. The puncture test and texture profile analysis (TPA) with compression were determined at 25% and 75% deformation; the melting properties were determined rheologically by monitoring the change of storage modulus (G') with increasing temperature. The measurements with 25% deformation were always nondestructive, while measurements with 75% deformation were mostly destructive. Desserts made from Alaska pollock gelatin (AG) or gelatin mixtures containing AG were more resistant to the destruction caused by the large deformation than tilapia gelatin and pork gelatins. In addition, the gel dessert made from AG melted at a lower temperature than those from tilapia skin gelatin and pork gelatins, while desserts made from gelatin mixtures reflected the melting properties of the separate gelatins.

Temperature Dependence of Electrical Resistance of Woven Melt-Infiltrated SiCf/SiC Ceramic Matrix Composites

NASA Technical Reports Server (NTRS)

Appleby, Matthew P.; Morscher, Gregory N.; Zhu, Dongming

2016-01-01

Recent studies have successfully shown the use of electrical resistance (ER)measurements to monitor room temperature damage accumulation in SiC fiber reinforced SiC matrix composites (SiCf/SiC) Ceramic Matrix Composites (CMCs). In order to determine the feasibility of resistance monitoring at elevated temperatures, the present work investigates the temperature dependent electrical response of various MI (Melt Infiltrated)-CVI (Chemical Vapor Infiltrated) SiC/SiC composites containing Hi-Nicalon Type S, Tyranno ZMI and SA reinforcing fibers. Test were conducted using a commercially available isothermal testing apparatus as well as a novel, laser-based heating approach developed to more accurately simulate thermomechanical testing of CMCs. Secondly, a post-test inspection technique is demonstrated to show the effect of high-temperature exposure on electrical properties. Analysis was performed to determine the respective contribution of the fiber and matrix to the overall composite conductivity at elevated temperatures. It was concluded that because the silicon-rich matrix material dominates the electrical response at high temperature, ER monitoring would continue to be a feasible method for monitoring stress dependent matrix cracking of melt-infiltrated SiC/SiC composites under high temperature mechanical testing conditions. Finally, the effect of thermal gradients generated during localized heating of tensile coupons on overall electrical response of the composite is determined.

Atmospheric Drivers of Greenland Surface Melt Revealed by Self-Organizing Maps

NASA Technical Reports Server (NTRS)

Mioduszewski, J. R.; Rennermalm, A. K.; Hammann, A.; Tedesco, M.; Noble, E. U.; Stroeve, J. C.; Mote, T. L.

2016-01-01

Recent acceleration in surface melt on the Greenland ice sheet (GrIS) has occurred concurrently with a rapidly warming Arctic and has been connected to persistent, anomalous atmospheric circulation patterns over Greenland. To identify synoptic setups favoring enhanced GrIS surface melt and their decadal changes, we develop a summer Arctic synoptic climatology by employing self-organizing maps. These are applied to daily 500 hPa geopotential height fields obtained from the Modern Era Retrospective Analysis for Research and Applications reanalysis, 1979-2014. Particular circulation regimes are related to meteorological conditions and GrIS surface melt estimated with outputs from the Modèle Atmosphérique Régional. Our results demonstrate that the largest positive melt anomalies occur in concert with positive height anomalies near Greenland associated with wind, temperature, and humidity patterns indicative of strong meridional transport of heat and moisture. We find an increased frequency in a 500 hPa ridge over Greenland coinciding with a 63% increase in GrIS melt between the 1979-1988 and 2005-2014 periods, with 75.0% of surface melt changes attributed to thermodynamics, 17% to dynamics, and 8.0% to a combination. We also confirm that the 2007-2012 time period has the largest dynamic forcing relative of any period but also demonstrate that increased surface energy fluxes, temperature, and moisture separate from dynamic changes contributed more to melt even during this period. This implies that GrIS surface melt is likely to continue to increase in response to an ever warmer future Arctic, regardless of future atmospheric circulation patterns.

Thermodynamic Stability Analysis of Tolbutamide Polymorphs and Solubility in Organic Solvents.

PubMed

Svärd, Michael; Valavi, Masood; Khamar, Dikshitkumar; Kuhs, Manuel; Rasmuson, Åke C

2016-06-01

Melting temperatures and enthalpies of fusion have been determined by differential scanning calorimetry (DSC) for 2 polymorphs of the drug tolbutamide: FI(H) and FV. Heat capacities have been determined by temperature-modulated DSC for 4 polymorphs: FI(L), FI(H), FII, FV, and for the supercooled melt. The enthalpy of fusion of FII at its melting point has been estimated from the enthalpy of transition of FII into FI(H) through a thermodynamic cycle. Calorimetric data have been used to derive a quantitative polymorphic stability relationship between these 4 polymorphs, showing that FII is the stable polymorph below approximately 333 K, above which temperature FI(H) is the stable form up to its melting point. The relative stability of FV is well below the other polymorphs. The previously reported kinetic reversibility of the transformation between FI(L) and FI(H) has been verified using in situ Raman spectroscopy. The solid-liquid solubility of FII has been gravimetrically determined in 5 pure organic solvents (methanol, 1-propanol, ethyl acetate, acetonitrile, and toluene) over the temperature range 278 to 323 K. The ideal solubility has been estimated from calorimetric data, and solution activity coefficients at saturation in the 5 solvents determined. All solutions show positive deviation from Raoult's law, and all van't Hoff plots of solubility data are nonlinear. The solubility in toluene is well below that observed in the other investigated solvents. Solubility data have been correlated and extrapolated to the melting point using a semiempirical regression model. Copyright © 2016 American Pharmacists Association®. Published by Elsevier Inc. All rights reserved.

The Temperature of the Icelandic Mantle Plume from Aluminium-in-Olivine Thermometry

NASA Astrophysics Data System (ADS)

Matthews, S.; Shorttle, O.; Maclennan, J.

2015-12-01

Temperature is a key control on the physical properties of the mantle, in particular the extent of melting during upwelling. It is not, however, a unique control on many of the parameters used to estimate mantle temperature. For example igneous crustal thickness which has often been used as a first-order proxy for mantle temperature, is also affected by mantle lithology and plume flux. Alternatives to geophysical indicators of mantle temperature are petrological thermometers. However, these record crystallisation temperatures, therefore a series of assumptions about the coupled melt- solid mantle thermal history must be made when calculating back to mantle potential temperature. In this study we investigate how these assumptions may affect mantle temperature estimates and how crystallisation temperatures may offer insights into the melting and melt transport processes, focussing on a new set of crystallisation temperature estimates we have made on primitive Icelandic basalts.We used the aluminium-in-olivine thermometer of Coogan et al. (2014) to estimate crystallisation temperatures of olivine phenocrysts in a suite of samples from the Northern Volcanic Zone (NVZ) of Iceland. The data suggest that within a single volcanic system crystallisation temperature depends strongly on the olivine forsterite content, thus the history of melt evolution, and how the eruption samples this, must be considered when extrapolating to mantle temperature. To assess the influence of the assumptions required to obtain mantle temperature we constructed a simple thermal model incorporating varying proportions of lherzolite, pyroxenite and harzburgite undergoing decompression melting. A trade off between increasing mantle temperature and decreasing pyroxenite (or increasing harzburgite) in the source is observed. Using this dataset and our model, calculations reveal a potential temperature of 1470±130 °C for Iceland, and a temperature excess of 150±40 °C relative to ambient mantle. These estimates are consistent with temperatures estimated using crustal thickness and melt chemistry.

The melt-recrystallization behavior of highly oriented α-iPP fibers embedded in a HIPS matrix.

PubMed

Ye, Liwei; Li, Huihui; Qiu, Zhaobin; Yan, Shouke

2015-03-21

The melt-recrystallization behavior of α-iPP fibers embedded in an amorphous HIPS matrix has been studied by means of optical microscopy. The amorphous HIPS serving as a supporter of iPP fibers does not become involved in the nucleation and crystallization process of the molten highly oriented iPP fibers. It also does not provide any birefringence under the optical microscope with crossed polarizers. This enables the study of orientation-induced β-iPP crystallization through a control of the melting status of the fibers. Through melting the fibers at different temperatures above 175 °C and subsequent recrystallization, some β-iPP crystals were always produced. The content of the β-iPP crystal depends strongly on the melting temperature and melting time of the iPP fibers. It was confirmed that melting the iPP fibers at relatively lower temperature, e.g. 176 °C, less amount of β-iPP crystals were observed. The content of β-iPP crystal enhances first with increasing melting temperature and then decreases with further increase of the fiber melting temperature. The β-iPP crystallization is found to be most favorable upon melting the fibers at 178 °C for 2 min. This demonstrates the requirement of a certain chain or chain segment orientation for generating β-iPP crystallization on the one hand, while higher orientation of the iPP chains or chain segments encourages the growth of iPP crystals in the α-form on the other hand. This has been further confirmed by varying the melting time of the fiber at different temperatures, since relaxation of the iPP molecular chains at a fixed temperature is time dependent. Moreover, the complete transformation of α-iPP fibers in some local places into β-iPP crystals implies that the αβ-transition may not be required for the orientation-induced β-iPP crystallization.

Identification of squid species by melting temperature shifts on fluorescence melting curve analysis (FMCA) using single dual-labeled probe

NASA Astrophysics Data System (ADS)

Koh, Eunjung; Song, Ha Jeong; Kwon, Na Young; Kim, Gi Won; Lee, Kwang Ho; Jo, Soyeon; Park, Sujin; Park, Jihyun; Park, Eun Kyeong; Hwang, Seung Yong

2017-06-01

Real time PCR is a standard method for identification of species. One of limitations of the qPCR is that there would be false-positive result due to mismatched hybridization between target sequence and probe depending on the annealing temperature in the PCR condition. As an alternative, fluorescence melting curve analysis (FMCA) could be applied for species identification. FMCA is based on a dual-labeled probe. Even with subtle difference of target sequence, there are visible melting temperature (Tm) shift. One of FMCA applications is distinguishing organisms distributed and consumed globally as popular food ingredients. Their prices are set by species or country of origin. However, counterfeiting or distributing them without any verification procedure are becoming social problems and threatening food safety. Besides distinguishing them in naked eye is very difficult and almost impossible in any processed form. Therefore, it is necessary to identify species in molecular level. In this research three species of squids which have 1-2 base pair differences each are selected as samples since they have the same issue. We designed a probe which perfectly matches with one species and the others mismatches 2 and 1 base pair respectively and labeled with fluorophore and quencher. In an experiment with a single probe, we successfully distinguished them by Tm shift depending on the difference of base pair. By combining FMCA and qPCR chip, smaller-scale assay with higher sensitivity and resolution could be possible, andc furthermore, enabling results analysis with smart phone would realize point-of-care testing (POCT).

A petrologic, thermodynamic and experimental study of brachinites: Partial melt residues of an R chondrite-like precursor

NASA Astrophysics Data System (ADS)

Gardner-Vandy, Kathryn G.; Lauretta, Dante S.; McCoy, Timothy J.

2013-12-01

The primitive achondrites provide a window into the initial melting of asteroids in the early solar system. The brachinites are olivine-dominated meteorites with a recrystallized texture that we and others interpret as evidence of partial melting and melt removal on the brachinite parent body. We present a petrologic, thermodynamic and experimental study of the brachinites to evaluate the conditions under which they formed and test our hypothesis that the precursor material to the brachinites was FeO-rich compared to the precursors of other primitive achondrites. Petrologic analysis of six brachinites (Brachina, Allan Hills (ALH) 84025, Hughes 026, Elephant Moraine (EET) 99402, Northwest Africa (NWA) 3151, and NWA 4969) and one brachinite-like achondrite (NWA 5400) shows that they are meteorites with recrystallized texture that are enriched in olivine (⩾80 vol.%) and depleted in other minerals with respect to a chondritic mineralogy. Silicates in the brachinites are FeO-rich (Fa32-36). Brachinite-like achondrite Northwest Africa 5400 is similar in mineralogy and texture to the brachinites but with a slightly lower FeO-content (Fa30). Thermodynamic calculations yield equilibration temperatures above the Fe,Ni-FeS cotectic temperature (∼950 °C) for all meteorites studied here and temperatures above the silicate eutectic (∼1050 °C) for all but two. Brachina formed at an fO2 of ∼IW, and the other brachinites and NWA 5400 formed at ∼IW - 1. All the meteorites show great evidence of formation by partial melting having approximately chondritic to depleted chondritic mineralogies, equilibrated mineral compositions, and recrystallized textures, and having reached temperatures above that required for melt generation. In an attempt to simulate the formation of the brachinite meteorites, we performed one-atmosphere, gas-mixing partial melting experiments of R4 chondrite LaPaz Ice Field 03639. Experiments at 1250 °C and an oxygen fugacity of IW - 1 produce residual phases that are within the mineralogy and mineral compositions of the brachinites. These experiments provide further evidence for the formation of brachinites as a result of partial melting of a chondritic precursor similar in mineralogy and mineral compositions to the R chondrites.

Influence of Crucible Materials on High-temperature Properties of Vacuum-melted Nickel-chromium-cobalt Alloy

NASA Technical Reports Server (NTRS)

Decker, R F; Rowe, John P; Freeman, J W

1957-01-01

A study of the effect of induction-vacuum-melting procedure on the high-temperature properties of a titanium-and-aluminum-hardened nickel-base alloy revealed that a major variable was the type of ceramic used as a crucible. Reactions between the melt and magnesia or zirconia crucibles apparently increased high-temperature properties by introducing small amounts of boron or zirconium into the melts. Heats melted in alumina crucibles had relatively low rupture life and ductility at 1,600 F and cracked during hot-working as a result of deriving no boron or zirconium from the crucible.

Stabilizing Crystal Oscillators With Melting Metals

NASA Technical Reports Server (NTRS)

Stephens, J. B.; Miller, C. G.

1984-01-01

Heat of fusion provides extended period of constant temperature and frequency. Crystal surrounded by metal in spherical container. As outside temperature rises to melting point of metal, metal starts to liquefy; but temperature stays at melting point until no solid metal remains. Potential terrestrial applications include low-power environmental telemetering transmitters and instrumentation transmitters for industrial processes.

Research into the rationality and the application scopes of different melting models of nanoparticles

NASA Astrophysics Data System (ADS)

Fu, Qingshan; Xue, Yongqiang; Cui, Zixiang; Duan, Huijuan

2017-07-01

A rational melting model is indispensable to address the fundamental issue regarding the melting of nanoparticles. To ascertain the rationality and the application scopes of the three classical thermodynamic models, namely Pawlow, Rie, and Reiss melting models, corresponding accurate equations for size-dependent melting temperature of nanoparticles were derived. Comparison of the melting temperatures of Au, Al, and Sn nanoparticles calculated by the accurate equations with available experimental results demonstrates that both Reiss and Rie melting models are rational and capable of accurately describing the melting behaviors of nanoparticles at different melting stages. The former (surface pre-melting) is applicable to the stage from initial melting to critical thickness of liquid shell, while the latter (solid particles surrounded by a great deal of liquid) from the critical thickness to complete melting. The melting temperatures calculated by the accurate equation based on Reiss melting model are in good agreement with experimental results within the whole size range of calculation compared with those by other theoretical models. In addition, the critical thickness of liquid shell is found to decrease with particle size decreasing and presents a linear variation with particle size. The accurate thermodynamic equations based on Reiss and Rie melting models enable us to quantitatively and conveniently predict and explain the melting behaviors of nanoparticles at all size range in the whole melting process. [Figure not available: see fulltext.

Solid-liquid and liquid-solid transitions in metal nanoparticles.

PubMed

Hou, M

2017-02-22

The melting and solidification temperatures of nanosystems may differ by several hundred Kelvin. To understand the origin of this difference, transitions in small metallic nanoparticles on the atomic scale were analyzed using molecular dynamics (MD). Palladium was used as a case study, which was then extended to a range of other elemental metals. It was argued that in realistic environments, such as gases at low pressure (of the order of 1 mbar), heat transfers allow the microcanonical thermal equilibrium evolution of the nanoparticles between successive collisions with gas atoms. This is shown to have no significant influence on the mechanism of melting, whereas in an isolated nanoparticle, solidification triggers a huge and rapid increase in temperature. A simple relationship between the melting and solidification temperatures was found, indicating that the magnitude of the latent heat of melting governs undercooling. Whereas melting occurs via heterogeneous nucleation, solidification displays characteristics of spinodal decomposition. Consistently, the melting temperature scales with the surface-to-volume ratio, whereas the solidification temperature displays no significant dependence on the particle size.

High resolution melt curve analysis based on methylation status for human semen identification.

PubMed

Fachet, Caitlyn; Quarino, Lawrence; Karnas, K Joy

2017-03-01

A high resolution melt curve assay to differentiate semen from blood, saliva, urine, and vaginal fluid based on methylation status at the Dapper Isoform 1 (DACT1) gene was developed. Stains made from blood, saliva, urine, semen, and vaginal fluid were obtained from volunteers and DNA was isolated using either organic extraction (saliva, urine, and vaginal fluid) or Chelex ® 100 extraction (blood and semen). Extracts were then subjected to bisulfite modification in order to convert unmethylated cytosines to uracil, consequently creating sequences whose amplicons have melt curves that vary depending on their initial methylation status. When primers designed to amplify the promoter region of the DACT1 gene were used, DNA from semen samples was distinguishable from other fluids by a having a statistically significant lower melting temperature. The assay was found to be sperm-significant since semen from a vasectomized man produced a melting temperature similar to the non-semen body fluids. Blood and semen stains stored up to 5 months and tested at various intervals showed little variation in melt temperature indicating the methylation status was stable during the course of the study. The assay is a more viable method for forensic science practice than most molecular-based methods for body fluid stain identification since it is time efficient and utilizes instrumentation common to forensic biology laboratories. In addition, the assay is advantageous over traditional presumptive chemical methods for body fluid identification since results are confirmatory and the assay offers the possibility of multiplexing which may test for multiple body fluids simultaneously.

Development of advanced Czochralski growth process to produce low cost 150 kg silicon ingots from a single crucible for technology readiness

NASA Technical Reports Server (NTRS)

1980-01-01

The design and development of an advanced Czochralski crystal grower are described. Several exhaust gas analysis system equipment specifications studied are discussed. Process control requirements were defined and design work began on the melt temperature, melt level, and continuous diameter control. Sensor development included assembly and testing of a bench prototype of a diameter scanner system.

Experimental Investigation of Concrete Runway Snow Melting Utilizing Heat Pipe Technology

PubMed Central

Su, Xin; Ye, Qing; Fu, Jianfeng

2018-01-01

A full scale snow melting system with heat pipe technology is built in this work, which avoids the negative effects on concrete structure and environment caused by traditional deicing chemicals. The snow melting, ice-freezing performance and temperature distribution characteristics of heat pipe concrete runway were discussed by the outdoor experiments. The results show that the temperature of the concrete pavement is greatly improved with the heat pipe system. The environment temperature and embedded depth of heat pipe play a dominant role among the decision variables of the snow melting system. Heat pipe snow melting pavement melts the snow completely and avoids freezing at any time when the environment temperature is below freezing point, which is secure enough for planes take-off and landing. Besides, the exportation and recovery of geothermal energy indicate that this system can run for a long time. This paper will be useful for the design and application of the heat pipe used in the runway snow melting. PMID:29551957

Experimental Investigation of Concrete Runway Snow Melting Utilizing Heat Pipe Technology.

PubMed

Chen, Fengchen; Su, Xin; Ye, Qing; Fu, Jianfeng

2018-01-01

A full scale snow melting system with heat pipe technology is built in this work, which avoids the negative effects on concrete structure and environment caused by traditional deicing chemicals. The snow melting, ice-freezing performance and temperature distribution characteristics of heat pipe concrete runway were discussed by the outdoor experiments. The results show that the temperature of the concrete pavement is greatly improved with the heat pipe system. The environment temperature and embedded depth of heat pipe play a dominant role among the decision variables of the snow melting system. Heat pipe snow melting pavement melts the snow completely and avoids freezing at any time when the environment temperature is below freezing point, which is secure enough for planes take-off and landing. Besides, the exportation and recovery of geothermal energy indicate that this system can run for a long time. This paper will be useful for the design and application of the heat pipe used in the runway snow melting.

Hot cracking susceptibility of fillers 52 and 82 in alloy 690 welding

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, W.; Tsai, C.H.

1999-02-01

The hot cracking susceptibility of fillers 52 and 82 in a alloy 690 weldment is analyzed by the Varestraint test. Weld characteristics, microstructure, hardness distribution, and thermal analysis of the two filler metals are also examined. The weld metal of both fillers develops an extremely dense oxide layer. A stainless steel brush cannot remove the oxide layer, and a grinder may be needed between weld passes to assure a sound weld. Differential temperature analysis (DTA) shows that filler 82 has a lower melting point and a wider melting/solidification temperature differential ({Delta} T). These characteristics correlate with greater hot cracking susceptibilitymore » of filler 82 than 52 in Varestraint tests. The hot cracks are intergranular and are caused by elements segregating in grain boundaries.« less

Effect of Hydrogen and Carbon on the Melting Temperature of the Core

NASA Astrophysics Data System (ADS)

Nakajima, Y.; Sakamaki, K.; Takahashi, E.; Fukai, Y.; Suzuki, T.; Funakoshi, K.

2007-12-01

The temperature of the Earth's outer core has been discussed based on the melting temperature of Fe- O-S alloys (e.g., Boehler, 1996). Although hydrogen and carbon are the possible candidates of the core component, their effects on the melting temperature of iron at high-pressures are unclear. Using a Kawai-type multi-anvil apparatus at SPring-8 synchrotron, we carried out a series of melting experiments on FeH and Fe3C up to 20 and 28 GPa, respectively. In the experiments on FeH, Fe sponge mixed with MgO was packed into a NaCl container with a hydrogen source, LiAlH4 (e.g., Fukai et al., 1989). During heating under high-pressures, hydrogenation of iron was observed by volume change. The phase boundary between ɛ'-phase (low-temperature phase) and γ-phase (high-temperature phase) of iron-hydride was determined using both cooling and heating experiments. Hydrogen concentrations in the γ-FeHx and ɛ'-FeHx were calculated based on the excess volume data from that of pure iron. It is found that γ-FeHx and ɛ'-FeHx synthesized in our experiments at pressures between 10 and 20 GPa are nearly stoichiometric FeH. Melting temperature of the γ-FeH was determined by the abrupt change in the X-ray diffraction patterns (crystalline to amorphous). The melting temperatures were determined to be 1473, 1473, 1493, 1573 and 1593 K at 10, 11.5, 15, 18 and 20 GPa, respectively. In the experiments using Fe3C, the synthesized Fe3C powder was encapsulated in a MgO container. In the diffraction sequences during heating, the peaks of Fe3C disappeared, and the new peaks identified as those of Fe7C3 were observed with halo caused by liquid. Finally, the Fe7C3 peaks disappeared, and only the halo pattern was observed. Based on these observations, the incongruent melting of Fe3C to Fe7C3 and liquid is estimated to occur at 1823 and 1923 K at 19.7 and 27.0 GPa, respectively. The liquidus temperatures of the Fe3C composition are found to be at 2098 and 2198 K at 19.5 and 26.8 GPa, respectively. The melting temperatures of Fe3C determined by our experiments are >700 K lower than that of the previous estimation based on thermodynamic calculation (Wood, 1993). Our experimental results show a possibility that the hydrogen and carbon lower the melting temperature of iron (outer core) dramatically. The melting temperatures of γ-FeH and Fe3C at 20 GPa are already 500 K lower than that of pure iron estimated by Anderson and Isaak (2000). Extrapolating our experimental melting curves for FeH and Fe3C to core pressures using Lindemann's melting law, we obtained the melting temperatures to be ~2600 and ~2900 K at the core-mantle boundary (CMB), respectively. In the presence of both hydrogen and carbon, melting temperature of the Earth's outer core could be >1500 K lower than that of the previous estimates, implying that the temperature gap at CMB could be much smaller than the current estimates.

Structure and mechanical properties of parts obtained by selective laser melting of metal powder based on intermetallic compounds Ni3Al

NASA Astrophysics Data System (ADS)

Smelov, V. G.; Sotov, A. V.; Agapovichev, A. V.; Nosova, E. A.

2018-03-01

The structure and mechanical properties of samples are obtained from metal powder based on intermetallic compound by selective laser melting. The chemical analysis of the raw material and static tensile test of specimens were made. Change in the samples’ structure and mechanical properties after homogenization during four and twenty-four hours were investigated. A small-sized combustion chamber of a gas turbine engine was performed by the selective laser melting method. The print combustion chamber was subjected to the gas-dynamic test in a certain temperature and time range.

[A DNA study of rat liver oligonucleosomes enriched by transcriptionally active genes during induction due to the administration of an amino acid mixture].

PubMed

Vardevanian, P O; Davtian, A M; Tiratsuian, S G; Vardevanian, A O

1990-01-01

A highly active fraction of rat liver oligonucleosome DNA has been isolated and studied by means of thermal denaturation after induction by amino acid mixture or hydrocortisone. A considerable redistribution of DNA content has been shown in sucrose gradient fractions during these forms of induction. The changes are revealed in melting temperature, differential melting profile of DNA, isolated from actively transcribed chromatine fractions. Analysis of melting profiles shows changes of GC content of oligonucleosome DNA, suggesting that there are differences in activation during two studied forms of induction.

EFFECTS OF LASER RADIATION ON MATTER. LASER PLASMA: Laser—ultrasonic formation of melts of high-speed tool steels

NASA Astrophysics Data System (ADS)

Gureev, D. M.

1994-09-01

A study was made of the influence of ultrasonic vibrations on the processes of heat and mass transfer, and of structure formation during ultrafast crystallisation of laser melts of T1 high-speed tool steel. Acoustic flows which appeared in laser melts effectively smoothed out the temperature inhomogeneities and flattened the relief of the molten surface even when the laser radiation acted for just ~1 ms. The transformation of the mechanical energy of ultrasonic vibrations into heat increased the depth of the laser melt baths and suppressed crack formation. The observed changes in the structural and phase composition appeared as a change in the microhardness of the solidified laser melts. The geometry of coupling of ultrasound into a laser melt influenced the changes in the microhardness, suggesting a need for a more detailed analysis of the structure formation processes in the course of ultrafast crystallisation of laser melts in an ultrasonic field.

Solidification and Re-melting Phenomena During Slurry Preparation Using the RheoMetal™ Process

NASA Astrophysics Data System (ADS)

Payandeh, M.; Sabzevar, Mohsen Haddad; Jarfors, A. E. W.; Wessén, M.

2017-12-01

The melting sequence of the enthalpy exchange material (EEM) and formation of a slurry in the RheoMetal™ process was investigated. The EEM was extracted and quenched, together with a portion of the slurry at different processing times before complete melting. The EEM initially increased in size/diameter due to melt freezing onto its surface, forming a freeze- on layer. The initial growth of this layer was followed by a period of a constant diameter of the EEM with subsequent melting and decrease of diameter. Microstructural characterization of the size and morphology of different phases in the EEM and in the freeze-on layer was made. Dendritic equiaxed grains and eutectic regions containing Si particles and Cu-bearing particles and Fe-rich particles were observed in the as-cast EEM. The freeze-on layer consisted of dendritic aluminum tilted by about 30 deg in the upstream direction, caused by the rotation of the EEM. Energy dispersion spectroscopy analysis showed that the freeze-on layer had a composition corresponding to an alloy with higher melting point than the EEM and thus shielding the EEM from the surrounding melt. Microstructural changes in the EEM showed that temperature rapidly increased to 768 K (495 °C), indicated by incipient melting of the lowest temperature melting eutectic in triple junction grain boundary regions with Al2Cu and Al5Mg8Si6Cu2 phases present. As the EEM temperature increased further the binary Al-Si eutectic started to melt to form a region of a fully developed coherent mushy state. Experimental results and a thermal model indicated that as the dendrites spheroidized near to the interface at the EEM/freeze-on layer reached a mushy state with 25 pct solid fraction, coherency was lost and disintegration of the freeze-on layer took place. Subsequently, in the absence of the shielding effect from the freeze-on Layer, the EEM continued to disintegrate with a coherency limit of a solid fraction estimated to be 50 pct.

Analysis of loss-of-coolant accident for a fast-spectrum lithium-cooled nuclear reactor for space-power applications

NASA Technical Reports Server (NTRS)

Turney, G. E.; Petrik, E. J.; Kieffer, A. W.

1972-01-01

A two-dimensional, transient, heat-transfer analysis was made to determine the temperature response in the core of a conceptual space-power nuclear reactor following a total loss of reactor coolant. With loss of coolant from the reactor, the controlling mode of heat transfer is thermal radiation. In one of the schemes considered for removing decay heat from the core, it was assumed that the 4 pi shield which surrounds the core acts as a constant-temperature sink (temperature, 700 K) for absorption of thermal radiation from the core. Results based on this scheme of heat removal show that melting of fuel in the core is possible only when the emissivity of the heat-radiating surfaces in the core is less than about 0.40. In another scheme for removing the afterheat, the core centerline fuel pin was replaced by a redundant, constant temperature, coolant channel. Based on an emissivity of 0.20 for all material surfaces in the core, the calculated maximum fuel temperature for this scheme of heat removal was 2840 K, or about 90 K less than the melting temperature of the UN fuel.

The liquid wood heat flow and material properties as a function of temperature

NASA Astrophysics Data System (ADS)

Mazurchevici, Simona; Quadrini, Fabrizio; Nedelcu, Dumitru

2018-03-01

There are three types of ‘liquid wood’, Arbofill, Arboblend and Arboform and will replace plastics materials in the near future taking into account the biodegradability and higher properties versus common used plastics materials. In order to get more information about the materials properties of ‘liquid wood’ the granules and samples obtained by injection molding were studied using Differential Scanning Calorimetry (DSC) and Dynamic Mechanical Analysis (DMA) for Arboform L,V3 Nature-‘liquid wood’ (A-LW) and Arboform L, V3 Nature reinforced with Aramid Fibers (A-LWAF).In case of A-LW granule studied, the DSC analysis presents that at 97 °C appears an endoderm peak which represents the crystallization of the material, at 175 °C the exoderm peak which means the melting point of the material. After the tested granule cooling period of time this one was tested again and the endoderm peak disappears, which means that crystallization of material disappeared. The melting point of the second test decreases slightly at 174.6 °C. Also, the new test shows that at 61.7 °C the glass transition temperature appears and the melting point slightly decreases. In case of A-LW samples the DSC analyses shows that the melting point increased by 2.77 °C compared to the melting point of Arboform granule. The material behavior is more or less the same without the crystallization area.

Energy-efficient modification of reduction-melting for lead recovery from cathode ray tube funnel glass

DOE Office of Scientific and Technical Information (OSTI.GOV)

Okada, Takashi, E-mail: t-okada@u-fukui.ac.jp; Yonezawa, Susumu

2013-08-15

Highlights: • We recovered Pb from cathode ray tube funnel glass using reduction melting process. • We modified the melting process to achieve Pb recovery with low energy consumption. • Pb in the funnel glass is efficiently recovered at 1000 °C by adding Na{sub 2}CO{sub 3}. • Pb remaining in the glass after reduction melting is extracted with 1 M HCl. • 98% of Pb in the funnel glass was recovered by reduction melting and HCl leaching. - Abstract: Lead can be recovered from funnel glass of waste cathode ray tubes via reduction melting. While low-temperature melting is necessary formore » reduced energy consumption, previously proposed methods required high melting temperatures (1400 °C) for the reduction melting. In this study, the reduction melting of the funnel glass was performed at 900–1000 °C using a lab-scale reactor with varying concentrations of Na{sub 2}CO{sub 3} at different melting temperatures and melting times. The optimum Na{sub 2}CO{sub 3} dosage and melting temperature for efficient lead recovery was 0.5 g per 1 g of the funnel glass and 1000 °C respectively. By the reduction melting with the mentioned conditions, 92% of the lead in the funnel glass was recovered in 60 min. However, further lead recovery was difficult because the rate of the lead recovery decreased as with the recovery of increasing quantity of the lead from the glass. Thus, the lead remaining in the glass after the reduction melting was extracted with 1 M HCl, and the lead recovery improved to 98%.« less

Degree of polymerization of glucan chains shapes the structure fluctuations and melting thermodynamics of a cellulose microfibril.

PubMed

Chang, Rakwoo; Gross, Adam S; Chu, Jhih-Wei

2012-07-19

A Staggered LATtice (SLAT) model is developed for modeling cellulose microfibrils. The simple representation of molecular packing and interactions employed in SLAT allows simulations of structure fluctuations and phase transition of cellulose microfibrils at sufficiently long and large scales for comparison with experiments. Glucan chains in the microfibril are modeled as connected monomers, each corresponding to a cellobiose subunit, and the surrounding space around the cellulose is composed of solvent cells. Interaction parameters of monomer-monomer interactions were parametrized based on the results of atomistic molecular dynamics simulations. The monomer-solvent interaction was optimized to give a melting temperature of ∼695 K for the 36-glucan chain model cellulose microfibril, which is consistent with the estimation based on experimental data. Monte Carlo simulations of the SLAT model also capture experimentally measured X-ray diffraction patterns of cellulose as a function of temperature, including the region of melting transition, as well as predict the highly flexible regions in the microfibril. Beyond the diameter of ∼3 nm, we found that melting temperature of the cellulose microfibril is not significantly shifted by changing the thickness. On the other hand, a slight decrease in the degree of polymerization of glucan chains is shown to enhance structure fluctuations through the ends of glucan chains, i.e., the defect sites, and thereby significantly reduce the melting temperature. Analysis of the sizes, densities, and lifetimes of defect structures in the microfibril indicates a significant extent of fluctuations on the surfaces even at room temperature and that defect statistics are strong but distinct functions of temperature and solvent quality. The SLAT model is the first of its kind for simulating cellulosic materials, and this work shows that it can be used to incorporate information obtained from atomistic simulations and experimental data to enable the aforementioned findings through computation.

A 400-Year Ice Core Melt Layer Record of Summertime Warming in the Alaska Range

NASA Astrophysics Data System (ADS)

Winski, Dominic; Osterberg, Erich; Kreutz, Karl; Wake, Cameron; Ferris, David; Campbell, Seth; Baum, Mark; Bailey, Adriana; Birkel, Sean; Introne, Douglas; Handley, Mike

2018-04-01

Warming in high-elevation regions has societally important impacts on glacier mass balance, water resources, and sensitive alpine ecosystems, yet very few high-elevation temperature records exist from the middle or high latitudes. While a variety of paleoproxy records provide critical temperature records from low elevations over recent centuries, melt layers preserved in alpine glaciers present an opportunity to develop calibrated, annually resolved temperature records from high elevations. Here we present a 400-year temperature proxy record based on the melt layer stratigraphy of two ice cores collected from Mt. Hunter in Denali National Park in the central Alaska Range. The ice core record shows a sixtyfold increase in water equivalent total annual melt between the preindustrial period (before 1850 Common Era) and present day. We calibrate the melt record to summer temperatures based on weather station data from the ice core drill site and find that the increase in melt production represents a summer warming rate of at least 1.92 ± 0.31°C per century during the last 100 years, exceeding rates of temperature increase at most low-elevation sites in Alaska. The Mt. Hunter melt layer record is significantly (p < 0.05) correlated with surface temperatures in the central tropical Pacific through a Rossby wave-like pattern that enhances high temperatures over Alaska. Our results show that rapid alpine warming has taken place in the Alaska Range for at least a century and that conditions in the tropical oceans contribute to this warming.

Structural Fluctuations and Thermophysical Properties of Molten II-VI Compounds

NASA Technical Reports Server (NTRS)

Su, Ching-Hua; Zhu, S.; Li, C.; Scripa, R.; Lehoczky, S. L.; Kim, Y. M.; Baird, J. K.; Lin, B.; Ban, H.; Benmore, Chris;

A noise thermometry investigation of the melting point of gallium at the NIM

NASA Astrophysics Data System (ADS)

Zhang, J. T.; Xue, S.

2006-06-01

This paper describes a study of the melting point of gallium with the new NIM Johnson noise thermometer (JNT). The new thermometer adopts the structure of switching correlator and commutator with the reference resistor maintained at the triple point of water. The electronic system of the new thermometer is basically the same as the current JNT, but the preamplifiers have been improved slightly. This study demonstrates that examining the characteristics of the noise signals in the frequency domain is of critical importance in constructing an improved new thermometer, where a power spectral analysis is found to be critical in establishing appropriate grounding for the new thermometer. The new JNT is tested on measurements of the thermodynamic temperature of the melting point of gallium, which give the thermodynamic temperature of 302.9160 K, with an overall integration time of 190 h and a combined standard uncertainty of 9.4 mK. The uncertainty analysis indicates that a standard combined uncertainty of 3 mK could be achieved with the new thermometer over an integration period of 1750 h.

Kinetic parameters and structural variations in Cu-Al-Mn and Cu-Al-Mn-Mg shape memory alloys

NASA Astrophysics Data System (ADS)

Canbay, Canan Aksu

2017-02-01

In this work polycrystalline Cu-Al-Mn and Cu-Al-Mn-Mg SMAs were fabricated by arc melting. The thermal analysis was made to determine the characteristic transformation temperatures of the samples and kinetic parameters. Also the effect of Mg on transformation temperatures and kinetic parameters detected. The structural analysis was made to designate the diffraction planes of martensite phase at room temperature and this was supported by optical measurement observations.

Characterization of Rhenium Oxides Using ESCA

NASA Technical Reports Server (NTRS)

Panda, Binayak; Jones, Clyde S. (Technical Monitor)

2001-01-01

Rhenium as an engineering material has the following properties: (1) high melting point (one of the refractory metals); (2) high strength at elevated temperatures; (3) excellent toughness at room temperature; (4) low vapor pressure at melting point; (5) low coefficient of thermal expansion; (6) high impact and wear resistance; (7) compatibility with elements such as carbon and platinum; (8) conservation of properties in the presence of hydrogen, water vapor, and nitrogen oxides; and (9) poor oxidation resistance. This viewgraph presentation gives an overview of rhenium oxide characterization, including details on its history, experimental procedure using ESCA, and the analysis of the oxides (spectra and effects of ion sputtering).

Analysis of curing of a sustained release coating formulation by application of NIR spectroscopy to monitor changes associated with glyceryl monostearate.

PubMed

Howland, Harris; Fahmy, Raafat; Hoag, Stephen W

2015-01-01

For controlled release, latex or pseudolatex coatings to function as designed, it must be cured at temperatures at or slightly above the polymer's glass transition temperature. The focus of this study is to develop an understanding of the curing process and to develop near infrared spectroscopy as a tool for monitoring curing. Differential scanning calorimetry studies were used to determine how the thermal properties of glyceryl monostearate (GMS) and its polymorphic forms relate to the extent of Eudragit® polymer coat curing at different curing temperatures. The different GMS melting endotherms were used to monitor the extent of curing and as references for model development. The calculated melting peak areas for the GMS were plotted versus time and found to be dependent on time and temperature used for curing. Principal component analysis and parallel factor analysis were used to investigate the effect of curing on the films and showed that spectral changes could be could be directly related to the changes associated with the GMS during curing. Partial least square models developed could predict the extent of curing and the final state of GMS post curing.

Thermophysical properties of liquid Ni around the melting temperature from molecular dynamics simulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rozas, R. E.; Department of Physics, University of Bío-Bío, Av. Collao 1202, P.O. Box 5C, Concepción; Demiraǧ, A. D.

Thermophysical properties of liquid nickel (Ni) around the melting temperature are investigated by means of classical molecular dynamics (MD) simulation, using three different embedded atom method potentials to model the interactions between the Ni atoms. Melting temperature, enthalpy, static structure factor, self-diffusion coefficient, shear viscosity, and thermal diffusivity are compared to recent experimental results. Using ab initio MD simulation, we also determine the static structure factor and the mean-squared displacement at the experimental melting point. For most of the properties, excellent agreement is found between experiment and simulation, provided the comparison relative to the corresponding melting temperature. We discuss themore » validity of the Hansen-Verlet criterion for the static structure factor as well as the Stokes-Einstein relation between self-diffusion coefficient and shear viscosity. The thermal diffusivity is extracted from the autocorrelation function of a wavenumber-dependent temperature fluctuation variable.« less

Ab-initio calculations on melting of thorium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mukherjee, D., E-mail: debojyoti@barc.gov.in; Sahoo, B. D.; Joshi, K. D.

2016-05-23

Ab-initio molecular dynamics study has been performed on face centered cubic structured thorium to determine its melting temperature at room pressure. The ion-electron interaction potential energy calculated as a function of temperature for three volumes (a{sub 0}){sup 3} and (1.02a{sub 0}){sup 3} and (1.04a{sub 0}){sup 3} increases gradually with temperature and undergoes a sharp jump at ~2200 K, ~2100 K and ~1800 K, respectively. Here, a{sub 0} = 5.043 Å is the equilibrium lattice parameter at 0 K obtained from ab-initio calculations. These jumps in interaction energy are treated as due to the onset of melting and corresponding temperatures asmore » melting point. The melting point of 2100 K is close to the experimental value of 2023 K. Further, the same has been verified by plotting the atomic arrangement evolved at various temperatures and corresponding pair correlation functions.« less

Fabrication of a Mo based high temperature TZM alloy by non-consumable arc melting technique

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chakraborty, S.P.; Krishnamurthy, N., E-mail: spc@barc.gov.in

High temperature structural materials are in great demand for power, chemical and nuclear industries which can perform beyond 1000 °C as super alloys usually fail. In this regard, Mo based TZM alloy is capable of retaining strength up to 1500 °C with excellent corrosion compatibility against molten alkali metals. Hence, currently this alloy is considered an important candidate material for high temperature compact nuclear and fusion reactors. Due to reactive nature of Mo and having high melting point, manufacturing this alloy by conventional process is unsuitable. Powder metallurgy technique has limited success due to restriction in quantity and purity. Thismore » paper deals with fabrication of TZM alloy by nonconsumable tungsten arc melting technique. Initially a ternary master alloy of Mo-Ti-Zr was prepared which subsequently by dilution method, was converted into TZM alloy gradually by external addition of Mo and C in various proportions. A number of melting trials were conducted to optimize the process parameters like current, voltage and time to achieve desired alloy composition. The alloy was characterized with respect to composition, elemental distribution profile, microstructure, hardness profile and phase analysis. Well consolidated alloy button was obtained having desired composition, negligible material loss and having microstructure as comparable to standard TZM alloy. (author)« less

Performance of a cylindrical phase-change thermal energy storage unit

NASA Astrophysics Data System (ADS)

Jacobson, D. L.; Ponnappan, R.

1983-05-01

The high-temperature performance of a eutectic salt Phase Change Material (PCM) in a cylindrical Thermal Energy Storage Container (TESC) sample is evaluated by means of an experimental apparatus with a water-circulated calorimeter. The phase change characteristics of the salt during melting and solidification were observed by monitoring the external axial temperature profile of the container, and the analysis of the phase change heat transfer in the cylindrical geometry was based on the modified heat balance integral method of Tien (1980), which provides the solidification rate and time. Melting point (983 K), freezing point (944 K), latent heat of fusion (782.26 J/gm) and thermal diffusivity (0.00799 sq cm/sec) results are in agreement with those found in the literature. The experimental and analytical results of the nondimensionalized heat transfer resistance as a function of the solidified or melted weight fraction are compared.

Melting heat transport of nanofluidic problem over a Riga plate with erratic thickness: Use of Keller Box scheme

NASA Astrophysics Data System (ADS)

Iqbal, Z.; Azhar, Ehtsham; Mehmood, Zaffar; Maraj, E. N.

Present article is a study of stagnation point flow over Riga plate with erratic thickness. Riga plate is an electromagnetic surface in which electrodes are assembled alternatively. This arrangement generates electromagnetic hydrodynamic behavior in the fluid flow. This is an attempt to investigate influence of melting heat, thermal radiation and viscous dissipation effects on Riga plate. A traversal electric and magnetic fields are produced by Riga plate. It causes Lorentz force parallel to wall which contributes in directing flow pattern. Physical problem is modeled and reduced nonlinear system is solved numerically. Comparative analysis is carried out between solutions obtained by Keller Box Method and shooting technique with Runge-Kutta Fehlberg method of order 5. It is noted that melting heat transfer reduces temperature distribution whereas radiation parameter upsurge it. Velocity is accelerated by modified Hartman number and Eckert number contributes in raising temperature.

Investigation of the Parameters of Sealed Triple-Point Cells for Cryogenic Gases

NASA Astrophysics Data System (ADS)

Fellmuth, B.; Wolber, L.

2011-01-01

An overview of the parameters of a large number of sealed triple-point cells for the cryogenic gases hydrogen, oxygen, neon, and argon is given that have been determined within the framework of an international star intercomparison to optimize the measurement of melting curves as well as to establish complete and reliable uncertainty budgets for the realization of temperature fixed points. Special emphasis is given to the question, whether the parameters are primarily influenced by the cell design or the properties of the fixed-point samples. For explaining surprisingly large periods of the thermal recovery after the heat pulses of the intermittent heating through the melting range, a simple model is developed based on a newly defined heat-capacity equivalent, which considers the heat of fusion and a melting-temperature inhomogeneity. The analysis of the recovery using a graded set of exponential functions containing different time constants is also explained in detail.

Water freezing and ice melting

DOE PAGES

Malolepsza, Edyta; Keyes, Tom

2015-10-12

The generalized replica exchange method (gREM) is designed to sample states with coexisting phases and thereby to describe strong first order phase transitions. The isobaric MD version of the gREM is presented and applied to freezing of liquid water, and melting of hexagonal and cubic ice. It is confirmed that coexisting states are well sampled. The statistical temperature as a function of enthalpy, T S(H), is obtained. Hysteresis between freezing and melting is observed and discussed. The entropic analysis of phase transitions is applied and equilibrium transition temperatures, latent heats, and surface tensions are obtained for hexagonal ice↔liquid and cubicmore » ice↔liquid, with excellent agreement with published values. A new method is given to assign water molecules among various symmetry types. As a result, pathways for water freezing, ultimately leading to hexagonal ice, are found to contain intermediate layered structures built from hexagonal and cubic ice.« less

Experimental testing of olivine-melt equilibrium models at high temperatures

NASA Astrophysics Data System (ADS)

Krasheninnikov, S. P.; Sobolev, A. V.; Batanova, V. G.; Kargaltsev, A. A.; Borisov, A. A.

2017-08-01

Data are presented on the equilibrium compositions of olivine and melts in the products of 101 experiments performed at 1300-1600°C, atmospheric pressure, and controlled oxygen fugacity by means of new equipment at the Vernadsky Institute. It was shown that the available models of the olivine-melt equilibrium describe with insufficient adequacy the natural systems at temperatures over 1400°C. The most adequate is the model by Ford et al. (1983). However, this model overestimates systematically the equilibrium temperature with underestimating by 20-40°C at 1450-1600°C. These data point to the need for developing a new, improved quantitative model of the olivine-melt equilibrium for high-temperature magnesian melts, as well as to the possibility of these studies on the basis of the equipment presented.

The anomalously high melting temperature of bilayer ice.

PubMed

Kastelowitz, Noah; Johnston, Jessica C; Molinero, Valeria

2010-03-28

Confinement of water usually depresses its melting temperature. Here we use molecular dynamics simulations to determine the liquid-crystal equilibrium temperature for water confined between parallel hydrophobic or mildly hydrophilic plates as a function of the distance between the surfaces. We find that bilayer ice, an ice polymorph in which the local environment of each water molecule strongly departs from the most stable tetrahedral structure, has the highest melting temperature (T(m)) of the series of l-layer ices. The melting temperature of bilayer ice is not only unusually high compared to the other confined ices, but also above the melting point of bulk hexagonal ice. Recent force microscopy experiments of water confined between graphite and a tungsten tip reveal the formation of ice at room temperature [K. B. Jinesh and J. W. M. Frenken, Phys. Rev. Lett. 101, 036101 (2008)]. Our results suggest that bilayer ice, for which we compute a T(m) as high as 310 K in hydrophobic confinement, is the crystal formed in those experiments.

Welding pool measurement using thermal array sensor

NASA Astrophysics Data System (ADS)

Cho, Chia-Hung; Hsieh, Yi-Chen; Chen, Hsin-Yi

2015-08-01

Selective laser melting (SLM) is an additive manufacturing (AM) technology that uses a high-power laser beam to melt metal powder in chamber of inert gas. The process starts by slicing the 3D CAD data as a digital information source into layers to create a 2D image of each layer. Melting pool was formed by using laser irradiation on metal powders which then solidified to consolidated structure. In a selective laser melting process, the variation of melt pool affects the yield of a printed three-dimensional product. For three dimensional parts, the border conditions of the conductive heat transport have a very large influence on the melt pool dimensions. Therefore, melting pool is an important behavior that affects the final quality of the 3D object. To meet the temperature and geometry of the melting pool for monitoring in additive manufacturing technology. In this paper, we proposed the temperature sensing system which is composed of infrared photodiode, high speed camera, band-pass filter, dichroic beam splitter and focus lens. Since the infrared photodiode and high speed camera look at the process through the 2D galvanometer scanner and f-theta lens, the temperature sensing system can be used to observe the melting pool at any time, regardless of the movement of the laser spot. In order to obtain a wide temperature detecting range, 500 °C to 2500 °C, the radiation from the melting pool to be measured is filtered into a plurality of radiation portions, and since the intensity ratio distribution of the radiation portions is calculated by using black-body radiation. The experimental result shows that the system is suitable for melting pool to measure temperature.

Eutectic melting temperature of the lowermost Earth's mantle

NASA Astrophysics Data System (ADS)

Andrault, D.; Lo Nigro, G.; Bolfan-Casanova, N.; Bouhifd, M.; Garbarino, G.; Mezouar, M.

2009-12-01

Partial melting of the Earth's deep mantle probably occurred at different stages of its formation as a consequence of meteoritic impacts and seismology suggests that it even continues today at the core-mantle boundary. Melts are important because they dominate the chemical evolution of the different Earth's reservoirs and more generally the dynamics of the whole planet. Unfortunately, the most critical parameter, that is the temperature profile inside the deep Earth, remains poorly constrained accross the planet history. Experimental investigations of the melting properties of materials representative of the deep Earth at relevant P-T conditions can provide anchor points to refine past and present temperature profiles and consequently determine the degree of melting at the different geological periods. Previous works report melting relations in the uppermost lower mantle region, using the multi-anvil press [1,2]. On the other hand, the pyrolite solidus was determined up to 65 GPa using optical observations in the laser-heated diamond anvil cell (LH-DAC) [3]. Finally, the melting temperature of (Mg,Fe)2SiO4 olivine is documented at core-mantle boundary (CMB) conditions by shock wave experiments [4]. Solely based on these reports, experimental data remain too sparse to draw a definite melting curve for the lower mantle in the relevant 25-135 GPa pressure range. We reinvestigated melting properties of lower mantle materials by means of in-situ angle dispersive X-ray diffraction measurements in the LH-DAC at the ESRF [5]. Experiments were performed in an extended P-T range for two starting materials: forsterite and a glass with chondrite composition. In both cases, the aim was to determine the onset of melting, and thus the eutectic melting temperatures as a function of pressure. Melting was evidenced from drastic changes of diffraction peak shape on the image plate, major changes in diffraction intensities in the integrated pattern, disappearance of diffraction rings, and changes in the relation between sample-temperature and laser-power. In this work, we show that temperatures higher than 4000 K are necessary for melting mean mantle at the 135 GPa pressure found at the core mantle boundary (CMB). Such temperature is much higher than that from estimated actual geotherms. Therefore, melting at the CMB can only occur if (i) pyrolitic mantle resides for a very long time in contact with the outer core, (ii) the mantle composition is severely affected by additional elements depressing the solidus such as water or (iii) the temperature gradient in the D" region is amazingly steep. Other implications for the temperature state and the lower mantle properties will be presented. References (1) Ito et al., Phys. Earth Planet. Int., 143-144, 397-406, 2004 (2) Ohtani et al., Phys. Earth Planet. Int., 100, 97-114, 1997 (3) Zerr et al., Science, 281, 243-246, 1998 (4) Holland and Ahrens, Science, 275, 1623-1625, 1997 (5) Schultz et al., High Press. Res., 25, 1, 71-83, 2005.

Modified Laser Flash Method for Thermal Properties Measurements and the Influence of Heat Convection

NASA Technical Reports Server (NTRS)

Lin, Bochuan; Zhu, Shen; Ban, Heng; Li, Chao; Scripa, Rosalia N.; Su, Ching-Hua; Lehoczky, Sandor L.

2003-01-01

The study examined the effect of natural convection in applying the modified laser flash method to measure thermal properties of semiconductor melts. Common laser flash method uses a laser pulse to heat one side of a thin circular sample and measures the temperature response of the other side. Thermal diffusivity can be calculations based on a heat conduction analysis. For semiconductor melt, the sample is contained in a specially designed quartz cell with optical windows on both sides. When laser heats the vertical melt surface, the resulting natural convection can introduce errors in calculation based on heat conduction model alone. The effect of natural convection was studied by CFD simulations with experimental verification by temperature measurement. The CFD results indicated that natural convection would decrease the time needed for the rear side to reach its peak temperature, and also decrease the peak temperature slightly in our experimental configuration. Using the experimental data, the calculation using only heat conduction model resulted in a thermal diffusivity value is about 7.7% lower than that from the model with natural convection. Specific heat capacity was about the same, and the difference is within 1.6%, regardless of heat transfer models.

The melting curve of iron to 250 gigapascals - A constraint on the temperature at earth's center

NASA Technical Reports Server (NTRS)

Williams, Quentin; Jeanloz, Raymond; Bass, Jay; Svendsen, Bob; Ahrens, Thomas J.

1987-01-01

The melting curve of iron, the primary constituent of earth's core, has been measured to pressures of 250 gigapascals with a combination of static and dynamic techniques. The melting temperature of iron at the pressure of the core-mantle boundary (136 GPa) is 4800 + or - 200 K, whereas at the inner core-outer core boundary (330 GPa), it is 7600 + or - 500 K. A melting temperature for iron-rich alloy of 6600 K at the inner core-outer core boundary and a maximum temperature of 6900 K at earth's center are inferred. This latter value is the first experimental upper bound on the temperature at earth's center, and these results imply that the temperature of the lower mantle is significantly less than that of the outer core.

Properties of sugar-based low-melting mixtures

NASA Astrophysics Data System (ADS)

Fischer, Veronika; Kunz, Werner

2014-05-01

Physico-chemical properties of ternary sugar-based low-melting mixtures were determined. Choline chloride, urea and glucose or sorbitol, serving as sugars, were blended in various compositions. The refractive index, density, viscosity, decomposition temperatures and glass transition temperatures were measured. Further, the influence of temperature and water content was investigated. The results show that the mixtures are liquid below room temperature and the viscosity and density are dependent on the temperature and composition. Moreover, the viscosity decreases with increasing water content. These mixtures are biodegradable, low toxic, non-volatile, non-reactive with water and can be accomplished with low-cost materials. In consideration of these advantages and a melting point below room temperature, these low-melting mixtures can be a good alternative to ionic liquids as well as environmentally unfriendly and toxic solvents.

Hugoniot temperatures and melting of tantalum under shock compression determined by optical pyrometry

NASA Astrophysics Data System (ADS)

Dai, Chengda; Hu, Jianbo; Tan, Hua

2009-08-01

LiF single crystal was used as transparent window (anvil) to tamp the shock-induced free surface expansion of Ta specimen, and the Ta/LiF interface temperature was measured under shock compression using optical pyrometry technique. The shock temperatures and/or melting temperatures of Ta up to ˜400 GPa were extracted from the observed interface temperatures based on the Tan-Ahrens' model for one-dimensional heat conduction across metal/window ideal interface in which initial melting and subsequent solidification were considered under shock loading. The obtained data within the experimental uncertainties are consistent with the results from high-pressure sound velocity measurements. The temperature of the partial melting on Ta Hugoniot is estimated to be ˜9700 K at 300 GPa, supported by available results from theoretical calculations.

Melting of Fe-Si-O alloys: the Fate of Coexisting Si and O in the Core

NASA Astrophysics Data System (ADS)

Arveson, S. M.; Lee, K. K. M.

2017-12-01

The light element budget of Earth's core plays an integral role in sustaining outer core convection, which powers the geodynamo. Many experiments have been performed on binary iron compounds, but the results do not robustly agree with seismological observations and geochemical constraints. Earth's core is almost certainly made up of multiple light elements, so the future of core composition studies lies in ternary (or higher order) systems in order to examine interactions between light elements. We perform melting experiments on Fe-Si-O alloys in a laser-heated diamond-anvil cell to 80 GPa and 4000 K. Using 2D multi- wavelength imaging radiometry together with textural and chemical analysis of quenched samples, we measure the high-pressure melting curves and determine partitioning of light elements between the melt and the coexisting solid. Quenched samples are analyzed both in map view and in cross section using scanning electron microscopy (SEM) and electron microprobe analysis (EPMA) to examine the 3D melt structure and composition. Partitioning of light elements between molten and solid alloys dictates (1) the density contrast at the ICB, which drives compositional convection in the outer core and (2) the temperature of the CMB, an integral parameter for understanding the deep Earth. Our experiments suggest silicon and oxygen do not simply coexist in the melt and instead show complex solubility based on temperature. Additionally, we do not find evidence of crystallization of SiO2 at low oxygen content as was recently reported.11 Hirose, K., et al., Crystallization of silicon dioxide and compositional evolution of the Earth's core. Nature, 2017. 543(7643): p. 99-102.

Shock-induced superheating and melting curves of geophysically important minerals

NASA Astrophysics Data System (ADS)

Luo, Sheng-Nian; Ahrens, Thomas J.

2004-06-01

Shock-state temperature and sound-speed measurements on crystalline materials, demonstrate superheating-melting behavior distinct from equilibrium melting. Shocked solid can be superheated to the maximum temperature, Tc'. At slightly higher pressure, Pc, shock melting occurs, and induces a lower shock temperature, Tc. The Hugoniot state, ( Pc, Tc), is inferred to lie along the equilibrium melting curve. The amount of superheating achieved on Hugoniot is, ΘH+= Tc'/ Tc-1. Shock-induced superheating for a number of silicates, alkali halides and metals agrees closely with the predictions of a systematic framework describing superheating at various heating rates [Appl. Phys. Lett. 82 (12) (2003) 1836]. High-pressure melting curves are constructed by integration from ( Pc, Tc) based on the Lindemann law. We calculate the volume and entropy changes upon melting at ( Pc, Tc) assuming the R ln 2 rule ( R is the gas constant) for the disordering entropy of melting [J. Chem. Phys. 19 (1951) 93; Sov. Phys. Usp. 117 (1975) 625; Poirier, J.P., 1991. Introduction to the Physics of the Earth's Interior. Cambridge University Press, Cambridge, 102 pp.]. ( Pc, Tc) and the Lindemann melting curves are in excellent accord with diamond-anvil cell (DAC) results for NaCl, KBr and stishovite. But significant discrepancies exist for transition metals. If we extrapolate the DAC melting data [Phys. Rev. B 63 (2001) 132104] for transition metals (Fe, V, Mo, W and Ta) to 200-400 GPa where shock melting occurs, shock temperature measurement and calculation would indicate ΘH+˜0.7-2.0. These large values of superheating are not consistent with the superheating systematics. The discrepancies could be reconciled by possible solid-solid phase transitions at high pressures. In particular, this work suggests that Fe undergoes a possible solid-solid phase transition at ˜200 GPa and melts at ˜270 GPa upon shock wave loading, and the melting temperature is ˜6300 K at 330 GPa.

Generation of Primary Kilauea Magmas: Constraints on Pressure, Temperature and Composition of Melts

NASA Astrophysics Data System (ADS)

Gudfinnsson, G. H.; Presnall, D. C.

2004-12-01

Picrite glasses from the submarine extension of Kilauea, Puna Ridge, which contain up to 15.0 wt% MgO, are the most magnesian glass samples reported from Hawaii. Their compositions form a distinct olivine fractionation trend. A comparison of this trend with phase relations of garnet lherzolite in the CaO-MgO-Al2O3-SiO2 (CMAS) and CaO-MgO-Al2O3-SiO2-Na2O-FeO (CMASNF) system indicates that melts parental to the Hawaiian picrites are produced by melting of a garnet lherzolite source at a pressure of 5 ± 1 GPa. The primary melt composition for Kilauea proposed by Clague et al. (1995), which has 18.4 wt% MgO, is close to the expected 5 GPa melt composition. By using the pressure-independent CMASNF geothermometer (Gudfinnsson and Presnall, 2001), we obtain a temperature of formation of 1450° C for the most magnesian Puna Ridge glass after correction for the presence of 0.4 wt% H2O and 0.7 wt% CO2. This assumes that the glass is not much modified after separation from the lherzolite source. However, comparison with phase relations in the CMAS system strongly suggests that the most magnesian Puna Ridge glasses are the product of some olivine fractionation, and therefore give temperature considerably lower than that of the source. When applied to the proposed Kilauea primary melt composition of Clague et al. (1995), the CMASNF geothermometer gives a melting temperature of 1596° C or about 1565° C after correction for the presence of volatiles. This compares well with the anhydrous solidus temperature of 1600 ± 15° C at 5 GPa for the fertile KR4003 lherzolite (Lesher et al., 2003), which has the complete garnet lherzolite phase assemblage present at the solidus at this pressure. This consistency supports use of phase relations from the CMAS system and the CMASNF geothermometer to the Puna Ridge picrite compositions. With the pressure and temperature of melting known, one can calculate the potential temperature of the Hawaiian mantle, provided certain conditions are met. The calculation assumes that the temperature at the point of melt segregation is close to the temperature of the solid adiabat. If extensive melting has occurred prior to the segregation, this will be incorrect. Secondly, it is assumed that the melting is occurring at the non-conducting part of the geotherm. Provided this is the case and the Kilauea primary melt composition truly represents a near-primary melt composition, we derive a potential temperature for the mantle beneath Kilauea of about 1500° C. The very high temperature and pressure conditions for magma generation at Hawaii appear to be unmatched by any other currently active volcanism on the Earth. Thus, of all the candidates for plume status, Hawaii appears to be the most robust.

A study on the impact of hydroxypropyl methylcellulose on the viscosity of PEG melt suspensions using surface plots and principal component analysis.

PubMed

Oh, Ching Mien; Heng, Paul Wan Sia; Chan, Lai Wah

2015-04-01

An understanding of the rheological behaviour of polymer melt suspensions is crucial in pharmaceutical manufacturing, especially when processed by spray congealing or melt extruding. However, a detailed comparison of the viscosities at each and every temperature and concentration between the various grades of adjuvants in the formulation will be tedious and time-consuming. Therefore, the statistical method, principal component analysis (PCA), was explored in this study. The composite formulations comprising polyethylene glycol (PEG) 3350 and hydroxypropyl methylcellulose (HPMC) of ten different grades (K100 LV, K4M, K15M, K100M, E15 LV, E50 LV, E4M, F50 LV, F4M and Methocel VLV) at various concentrations were prepared and their viscosities at different temperatures determined. Surface plots showed that concentration of HPMC had a greater effect on the viscosity compared to temperature. Particle size and size distribution of HPMC played an important role in the viscosity of melt suspensions. Smaller particles led to a greater viscosity than larger particles. PCA was used to evaluate formulations of different viscosities. The complex viscosity profiles of the various formulations containing HPMC were successfully classified into three clusters of low, moderate and high viscosity. Formulations within each group showed similar viscosities despite differences in grade or concentration of HPMC. Formulations in the low viscosity cluster were found to be sprayable. PCA was able to differentiate the complex viscosity profiles of different formulations containing HPMC in an efficient and time-saving manner and provided an excellent visualisation of the data.

FAST TRACK COMMUNICATION: Directional annealing-induced texture in melt-spun (Sm12Co88)99Nb1 alloy

NASA Astrophysics Data System (ADS)

Jayaraman, T. V.; Rogge, P.; Shield, J. E.

2010-07-01

Developing texture in nanocrystalline permanent magnet alloys is of significant importance. Directional annealing is shown to produce texture in the permanent magnet alloy (Sm12Co88)99Nb1. Melt spinning produced isotropic grain structures of the hard magnetic metastable SmCo7 phase, with grain sizes of ~300 nm. Conventional annealing of melt-spun (Sm12Co88)99Nb1 alloy produced Sm2Co17 phase with random crystallographic orientation. Directional annealing of melt-spun (Sm12Co88)99Nb1 alloy, with appropriate combinations of annealing temperature and translational velocity, produced Sm2Co17 phase with (0 0 0 6) in-plane texture, as determined by x-ray diffraction analysis and magnetic measurements. The magnetization results show out-of-plane remanence higher than the in-plane remanence resulting in the degree of 'magnetic' texture in the order of 25-40%. Coercivity values above 2 kOe were maintained. The texture development via directional annealing while minimizing exposure to elevated temperatures provides a new route to anisotropic high-energy permanent magnets.

Assessment for Melting Temperature Measurement of Nucleic Acid by HRM.

PubMed

Wang, Jing; Pan, Xiaoming; Liang, Xingguo

2016-01-01

High resolution melting (HRM), with a high sensitivity to distinguish the nucleic acid species with small variations, has been widely applied in the mutation scanning, methylation analysis, and genotyping. For the aim of extending HRM for the evaluation of thermal stability of nucleic acid secondary structures on sequence dependence, we investigated effects of the dye of EvaGreen, metal ions, and impurities (such as dNTPs) on melting temperature ( T m ) measurement by HRM. The accuracy of HRM was assessed as compared with UV melting method, and little difference between the two methods was found when the DNA T m was higher than 40°C. Both insufficiency and excessiveness of EvaGreen were found to give rise to a little bit higher T m , showing that the proportion of dye should be considered for precise T m measurement of nucleic acids. Finally, HRM method was also successfully used to measure T m s of DNA triplex, hairpin, and RNA duplex. In conclusion, HRM can be applied in the evaluation of thermal stability of nucleic acid (DNA or RNA) or secondary structural elements (even when dNTPs are present).

Modification of Pawlow's thermodynamical model for the melting of small single-component particles

NASA Astrophysics Data System (ADS)

Barybin, Anatoly; Shapovalov, Victor

2011-02-01

A new approach to the melting of small particles is proposed to modify the known Pawlow's model by taking into account the transfer of material from solid spherical particles to liquid ones through a gas phase. Thermodynamical analysis gives rise to a differential equation for the melting point Tm involving such size-dependent and temperature-dependent parameters of a material as the surface tensions σs(l ), molar heat of fusion ΔHm and molar volumes vs(l ). Solution of this equation has shown that all the limiting cases for size-independent situations coincide with results known in the literature and our analysis of size-dependent situations gives results close to the experimental data previously obtained by other authors for some metallic particles.

Molecular dynamics for near melting temperatures simulations of metals using modified embedded-atom method

NASA Astrophysics Data System (ADS)

Etesami, S. Alireza; Asadi, Ebrahim

2018-01-01

Availability of a reliable interatomic potential is one of the major challenges in utilizing molecular dynamics (MD) for simulations of metals at near the melting temperatures and melting point (MP). Here, we propose a novel approach to address this challenge in the concept of modified-embedded-atom (MEAM) interatomic potential; also, we apply the approach on iron, nickel, copper, and aluminum as case studies. We propose adding experimentally available high temperature elastic constants and MP of the element to the list of typical low temperature properties used for the development of MD interatomic potential parameters. We show that the proposed approach results in a reasonable agreement between the MD calculations of melting properties such as latent heat, expansion in melting, liquid structure factor, and solid-liquid interface stiffness and their experimental/computational counterparts. Then, we present the physical properties of mentioned elements near melting temperatures using the new MEAM parameters. We observe that the behavior of elastic constants, heat capacity and thermal linear expansion coefficient at room temperature compared to MP follows an empirical linear relation (α±β × MP) for transition metals. Furthermore, a linear relation between the tetragonal shear modulus and the enthalpy change from room temperature to MP is observed for face-centered cubic materials.

Molecular dynamics simulation of melting of 2D glassy monatomic system

NASA Astrophysics Data System (ADS)

Nhu Tranh, Duong Thi; Van Hoang, Vo; Thu Hanh, Tran Thi

2018-01-01

The melting of two-dimensional (2D) glassy monatomic systems is studied using the molecular dynamics simulation with Lennard-Jones-Gauss interaction potential. The temperature dependence of various structural and dynamical properties of the systems during heating is analyzed and discussed via the radial distribution functions, the coordination number distributions, the ring statistics, the mobility of atoms and their clustering. Atomic mechanism of melting is also analyzed via tendency to increase mobility and breaking clusters of atoms upon heating. We found that melting of a 2D glass does not follow any theory of the melting of 2D crystals proposed in the past. The melting exhibits a homogeneous nature, i.e. liquid-like atoms occur homogeneously throughout the system and melting proceeds further leading to the formation of an entire liquid phase. In addition, we found a defined transition temperature region in which structural and dynamical properties of systems strongly change with increasing temperature.

Shear melting and high temperature embrittlement: theory and application to machining titanium.

PubMed

Healy, Con; Koch, Sascha; Siemers, Carsten; Mukherji, Debashis; Ackland, Graeme J

2015-04-24

We describe a dynamical phase transition occurring within a shear band at high temperature and under extremely high shear rates. With increasing temperature, dislocation deformation and grain boundary sliding are supplanted by amorphization in a highly localized nanoscale band, which allows for massive strain and fracture. The mechanism is similar to shear melting and leads to liquid metal embrittlement at high temperature. From simulation, we find that the necessary conditions are lack of dislocation slip systems, low thermal conduction, and temperature near the melting point. The first two are exhibited by bcc titanium alloys, and we show that the final one can be achieved experimentally by adding low-melting-point elements: specifically, we use insoluble rare earth metals (REMs). Under high shear, the REM becomes mixed with the titanium, lowering the melting point within the shear band and triggering the shear-melting transition. This in turn generates heat which remains localized in the shear band due to poor heat conduction. The material fractures along the shear band. We show how to utilize this transition in the creation of new titanium-based alloys with improved machinability.

Satellite-derived, melt-season surface temperature of the Greenland Ice Sheet (2000-2005) and its relationship to mass balance

USGS Publications Warehouse

Hall, D.K.; Williams, R.S.; Casey, K.A.; DiGirolamo, N.E.; Wan, Z.

2006-01-01

Mean, clear-sky surface temperature of the Greenland Ice Sheet was measured for each melt season from 2000 to 2005 using Moderate-Resolution Imaging Spectroradiometer (MODIS)–derived land-surface temperature (LST) data-product maps. During the period of most-active melt, the mean, clear-sky surface temperature of the ice sheet was highest in 2002 (−8.29 ± 5.29°C) and 2005 (−8.29 ± 5.43°C), compared to a 6-year mean of −9.04 ± 5.59°C, in agreement with recent work by other investigators showing unusually extensive melt in 2002 and 2005. Surface-temperature variability shows a correspondence with the dry-snow facies of the ice sheet; a reduction in area of the dry-snow facies would indicate a more-negative mass balance. Surface-temperature variability generally increased during the study period and is most pronounced in the 2005 melt season; this is consistent with surface instability caused by air-temperature fluctuations.

History dependent crystallization of Zr41Ti14Cu12Ni10Be23 melts

NASA Astrophysics Data System (ADS)

Schroers, Jan; Johnson, William L.

2000-07-01

The crystallization of Zr41Ti14Cu12Ni10Be23 (Vit 1) melts during constant heating is investigated. (Vit 1) melts are cooled with different rates into the amorphous state and the crystallization temperature upon subsequent heating is studied. In addition, Vit 1 melts are cooled using a constant rate to different temperatures and subsequently heated from this temperature with a constant rate. We investigate the influence of the temperature to which the melt was cooled on the crystallization temperature measured upon heating. In both cases the onset temperature of crystallization shows strong history dependence. This can be explained by an accumulating process during cooling and heating. An attempt is made to consider this process in a simple model by steady state nucleation and subsequent growth of the nuclei which results in different crystallization kinetics during cooling or heating. Calculations show qualitative agreement with the experimental results. However, calculated and experimental results differ quantitatively. This difference can be explained by a decomposition process leading to a nonsteady nucleation rate which continuously increases with decreasing temperature.

Reinforced fluropolymer nanocomposites with high-temperature superconducting Bi2Sr2CaCu2Oy

NASA Astrophysics Data System (ADS)

Jayasree, T. K.

2014-10-01

Bismuth Strontium Calcium Copper Oxide (Bi2Sr2CaCu2Oy)/Polyvinylidene fluoride (PVDF) nanocomposite was prepared and their thermal properties were analyzed. The composite consists of the polyvinylidene fluoride (PVDF) as an insulating polymer matrix, and homogenously distributed Bismuth strontium calcium copperoxide (2212) nanoparticles. SEM data shows flaky grains of the superconductor coated and linked by polymer. Differential scanning calorimetry (DSC) results indicated that the melting point was not affected significantly by the addition of BSCCO. However, the addition of superconducting ceramic resulted in an extra melting peak at a lower temperature (145°C). Thermogravimetric analysis of the samples shows that the onset decomposition temperature of the PVDF matrix was decreased by the addition of SC filler.

Use and Limitations of a Climate-Quality Data Record to Study Temperature Trends on the Greenland Ice Sheet

NASA Astrophysics Data System (ADS)

Hall, D. K.; Comiso, J. C.; Shuman, C. A.; Koenig, L.; DiGirolamo, N. E.

2011-12-01

Enhanced melting of the Greenland Ice Sheet has been documented in recent literature along with surface-temperature increases measured using infrared satellite data since 1981. Using a recently-developed climate-quality data record, 11- and 12-year trends in the clear-sky ice-surface temperature (IST) of the Greenland Ice Sheet have been studied using the Moderate-Resolution Imaging Spectroradiometer (MODIS) IST product. Daily and monthly MODIS ISTs of the Greenland Ice Sheet beginning on 1 March 2000 and continuing through 31 December 2010 are now available at 6.25-km spatial resolution on a polar stereographic grid as described in Hall et al. (submitted). This record will be elevated in status to a climate-data record (CDR) when more years of data become available either from the MODIS on the Terra or Aqua satellites, or from the Visible Infrared Imager Radiometer Suite (VIIRS) to be launched in October 2011. Maps showing the maximum extent of melt for the entire ice sheet and for the six major drainage basins have been developed from the MODIS IST dataset. Twelve-year trends in the extent of melt and duration of the melt season on the ice sheet vary in different drainage basins with some basins melting progressively earlier over the course of the study period. Some (but not all) of the basins also show a progressively-longer duration of melt. Twelve-year trends in IST are compared with in-situ data, and climate data from the Modern Era Retrospective-Analysis for Research and Applications (MERRA) Reanalysis. Hall, D.K., J.C. Comiso, N.E. DiGirolamo, C.A. Shuman, J. Key and L.S. Koenig, submitted for journal publication: A Satellite-Derived Climate-Quality Data Record of the Clear-Sky Surface Temperature of the Greenland Ice Sheet.

Plastification of polymers in twin-screw-extruders: New visualization technic using high-speed imaging

DOE Office of Scientific and Technical Information (OSTI.GOV)

Knieper, A., E-mail: Alexander.Knieper@lbf.fraunhofer.de, E-mail: Christian.Beinert@lbf.fraunhofer.de; Beinert, C., E-mail: Alexander.Knieper@lbf.fraunhofer.de, E-mail: Christian.Beinert@lbf.fraunhofer.de

The initial melting of the first granules through plastic energy dissipation (PED) at the beginning of the melting zone, in the co-rotating twin-screw extruder is visualized in this work. The visualization was created through the use of a high speed camera in the cross section of the melting zone. The parameters screw speed, granule-temperature, temperature-profile, type of polymer and back pressure were examined. It was shown that the screw speed and the temperature-profile have significant influence on the rate of initial melting.

PRIMELT3 MEGA.XLSM software for primary magma calculation: Peridotite primary magma MgO contents from the liquidus to the solidus

NASA Astrophysics Data System (ADS)

Herzberg, C.; Asimow, P. D.

2015-02-01

An upgrade of the PRIMELT algorithm for calculating primary magma composition is given together with its implementation in PRIMELT3 MEGA.xlsm software. It supersedes PRIMELT2.xls in correcting minor mistakes in melt fraction and computed Ni content of olivine, it identifies residuum mineralogy, and it provides a thorough analysis of uncertainties in mantle potential temperature and olivine liquidus temperature. The uncertainty analysis was made tractable by the computation of olivine liquidus temperatures as functions of pressure and partial melt MgO content between the liquidus and solidus. We present a computed anhydrous peridotite solidus in T-P space using relations amongst MgO, T and P along the solidus; it compares well with experiments on the solidus. Results of the application of PRIMELT3 to a wide range of basalts shows that the mantle sources of ocean islands and large igneous provinces were hotter than oceanic spreading centers, consistent with earlier studies and expectations of the mantle plume model.

The Role of Lug Preheating, Melt Pool Temperature, and Lug Entrance Delay on the Cast-on-Strap Joining Process

NASA Astrophysics Data System (ADS)

Pahlavan, Sohrab; Nikpour, Saman; Mirjalili, Mostafa; Alagheband, Ali; Azimi, Mohammadyousef; Taji, Iman

2017-07-01

This work deals with effective parameters in the cast-on-strap (COS) process during which grid lugs of a lead-acid battery are joined together by a strap. The effects of lug preheating, melt pool temperature, and lug entrance delay on the quality of joints and casting defects were investigated. Lug preheating was found to propitiously reduce joint internal voids because of flux elimination. Its adverse effect on lowering lug wettability, however, made it unfavorable under the experimental conditions. The melt pool temperature also showed a two-sided effect depending on the process conditions. Raising the temperature increases the strap melt fluidity, which improves the joint contact area; however, it has a negative effect on lug wettability by flux evaporation. Besides, higher temperatures cause more lug back-melting and, hence, lower relative contact lengths. Therefore, an intermediate temperature of 683 K (410 °C) was found to make the most proper condition. Moreover, the case at which the lugs enter the mold coincident with its filling by the melt rendered the best joint quality. In this condition, the melt flows through the interlug spaces, which helps the voids to escape, resulting in the better joint interface. As the conclusion, the lug entrance time has the most effective role on joint quality, considering that lug preheating does not show any improving effect.

THE MELTING MECHANISM OF DNA TETHERED TO A SURFACE

PubMed Central

QAMHIEH, KHAWLA; WONG, KA-YIU; LYNCH, GILLIAN C.; PETTITT, B. MONTGOMERY

2009-01-01

The details of melting of DNA immobilized on a chip or nanoparticle determines the sensitivity and operating characteristics of many analytical and synthetic biotechnological devices. Yet, little is known about the differences in how the DNA melting occurs between a homogeneous solution and that on a chip. We used molecular dynamics simulations to explore possible pathways for DNA melting on a chip. Simulation conditions were chosen to ensure that melting occurred in a submicrosecond timescale. The temperature was set to 400 K and the NaCl concentration was set to 0.1 M. We found less symmetry than in the solution case where for oligomeric double-stranded nucleic acids both ends melted with roughly equal probability. On a prepared silica surface we found melting is dominated by fraying from the end away from the surface. Strand separation was hindered by nonspecific surface adsorption at this temperature. At elevated temperatures the melted DNA was attracted to even uncharged organically coated surfaces demonstrating surface fouling. While hybridization is not the simple reverse of melting, this simulation has implications for the kinetics of hybridization. PMID:19802357

Fluorescence x-ray absorption fine structure studies of Fe-Ni-S and Fe-Ni-Si melts to 1600 K

NASA Astrophysics Data System (ADS)

Manghnani, M. H.; Hong, X.; Balogh, J.; Amulele, G.; Sekar, M.; Newville, M.

2008-04-01

We report NiK -edge fluorescence x-ray absorption fine structure spectra (XAFS) for Fe0.75Ni0.05S0.20 and Fe0.75Ni0.05Si0.20 ternary alloys from room temperature up to 1600 K. A high-temperature furnace designed for these studies incorporates two x-ray transparent windows and enables both a vertical orientation of the molten sample and a wide opening angle, so that XAFS can be measured in the fluorescence mode with a detector at 90° with respect to the incident x-ray beam. An analysis of the Ni XAFS data for these two alloys indicates different local structural environments for Ni in Fe0.75Ni0.05S0.20 and Fe0.75Ni0.05Si0.20 melts, with more Ni-Si coordination than Ni-S coordination persisting from room temperature through melting. These results suggest that light elements such as S and Si may impact the structural and chemical properties of Fe-Ni alloys with a composition similar to the earth’s core.

Improving the Desulfurization Degree of High-Grade Nickel Matte via a Two-Step Oxidation Roasting Process

NASA Astrophysics Data System (ADS)

Xi, Zhao; Wang, Zhixing; Li, Xinhai; Guo, Huajun; Yan, Guochun; Wang, Jiexi

2018-05-01

Generally, sulfur elimination from nickel matte was incomplete in the one-step oxidation roasting process. In this work, X-ray diffraction, scanning electron microscopy/energy-dispersive X-ray spectroscopy, and chemical analysis of the roasted products were carried out to explain this phenomenon. The results indicated that the melting of heazlewoodite was the main limiting factor. Thereafter, the oxidation mechanism of high-grade nickel matte from room temperature to 1000 °C was studied. It was found that the transformation from heazlewoodite (Ni3S2) to nickel sulfide (NiS) took place from 400 °C to 520 °C. Considering that the melting temperature of NiS was much higher than that of Ni3S2, a low-temperature roasting step was suggested to suppress the melting of heazlewoodite. Under the optimum conditions (520 °C for 120 minutes followed by 800 °C for 80 minutes), the degree of desulfurization reached 99.52 pct. These results indicated that the two-step oxidation roasting method could be a promising process for producing low-sulfur calcine from high-grade nickel matte.

Solid state characterization of E2101, a novel antispastic drug.

PubMed

Kushida, Ikuo; Ashizawa, Kazuhide

2002-10-01

E2101, a novel antispastic drug, was found to exist in at least two polymorphs that were confirmed by X-ray powder diffraction (XRD). These two species are designated forms I and II. The physicochemical and thermodynamic properties of these polymorphs were characterized by variable temperature XRD, thermal analysis, hygroscopicity measurements, and dissolution studies. The transition temperature was also estimated from the solubilities determined at various temperatures. The E2101 polymorphs were anhydrous and adsorbed little moisture under high humidity conditions. The melting onsets and heats of fusion for form I were 148.1 +/- 0.2 degrees C and 38.2 +/- 1.0 kJ/mol, respectively, and for form II were 139.8 +/- 0.4 degrees C and 35.2 +/- 0.5 kJ/mol, respectively. The intrinsic dissolution rate of form II in JP 2 medium was 1.5-fold faster than that of form I, corresponding to the rank order of the aqueous solubility and the enthalpy of fusion. Accordingly, form I was thought to be thermodynamically more stable than form II and thus suitable for further development. According to the thermal analysis and variable temperature XRD results, the recrystallization of form I occurred at approximately 145 degrees C after form II melted, however, no crystal transition behavior was observed below the lower melting point. The DSC thermograms at various heating rates and van't Hoff plots from the solubility studies indicated that the polymorphic pair would be monotropic. Copyright 2002 Wiley-Liss Inc. and the American Pharmaceutical Association

Surface-tension-driven flow in a glass melt

NASA Technical Reports Server (NTRS)

Mcneil, Thomas J.; Cole, Robert; Shankar Subramanian, R.

1985-01-01

Motion driven by surface tension gradients was observed in a vertical capillary liquid bridge geometry in a sodium borate melt. The surface tension gradients were introduced by maintaining a temperature gradient on the free melt surface. The flow velocities at the free surface of the melt, which were measured using a tracer technique, were found to be proportional to the applied temperature difference and inversely proportional to the melt viscosity. The experimentally observed velocities were in reasonable accord with predictions from a theoretical model of the system.

The distribution of chromium among orthopyroxene, spinel and silicate liquid at atmospheric pressure

NASA Technical Reports Server (NTRS)

Barnes, S. J.

1986-01-01

The Cr distributions for a synthetic silicate melt equilibrated with bronzitic orthopyroxene and chromite spinel between 1334 and 1151 C over a range of oxygen fugacities between the nickel-nickel oxide and iron-wuestite buffers are studied. The occurrence, chemical composition, and structure of the orthopyroxene-silicate melt and the spinel-silicate melt are described. It is observed that the Cr content between bronzite and the melt increases with falling temperature along a given oxygen buffer and decreases with falling oxygen fugacity at a given temperature; however, the Cr content of the melt in equilibrium with spinel decreases with falling temperature and increases with lower oxygen fugacity.

Understanding Vesuvius magmatic processes: Evidence from primitive silicate-melt inclusions in medieval scoria clinopyroxenes (Terzigno formation)

USGS Publications Warehouse

Lima, A.; Belkin, H.E.; Torok, K.

1999-01-01

Microthermometric investigations of silicate-melt inclusions and electron microprobe analyses were conducted on experimentally homogenized silicate-melt inclusions and on the host clinopyroxenes from 4 scoria samples of different layers from the Mt. Somma-Vesuvius medieval eruption (Formazione di Terzigno, 893 A.D.). The temperature of homogenization, considered the minimum trapping temperature, ranges from 1190 to 1260??5 ??C for all clinopyroxene-hosted silicate melt inclusions. The major and minor-element compositional trends shown by Terzigno scoria and matrix glass chemical analysis are largely compatible with fractional crystallization of clinopyroxene and Fe-Ti oxides. Sulfur contents of the homogenized silicate-melt inclusions in clinopyroxene phenocrysts compared with that in the host scoria show that S has been significantly degassed in the erupted products; whereas, Cl has about the same abundance in the inclusions and in host scoria. Fluorine is low (infrequently up to 800 ppm) in the silicate-melt inclusions compared to 2400 ppm in the bulk scoria. Electron microprobe analyses of silicate-melt inclusions show that they have primitive magma compositions (Mg# = 75-91). The composition of the host clinopyroxene phenocrysts varies from typical plinian-related (Mg#???85) to non-plinian related (Mg#???85). The mixed source of the host clinopyroxenes and primitive nature of the silicate-melt inclusions implies that these phenocrysts, in part, may be residual and/or have a polygenetic origin. The similar variation trends of major and minor-elements between homogenized silicate-melt inclusions from the Terzigno scoria, and silicate-melt inclusions in olivine and diopside phenocrysts from plinian eruptions (Marianelli et al., 1995) suggest that the trapped inclusions represent melts similar to those that supplied the plinian and sub-plinian magma chambers. These geochemical characteristics suggest that the Vesuvius magmatic system retained a vestige of the most recent plinian event.

Solidus and liquidus profiles of chondritic mantle: Implication for melting of the Earth across its history

NASA Astrophysics Data System (ADS)

Andrault, Denis; Bolfan-Casanova, Nathalie; Nigro, Giacomo Lo; Bouhifd, Mohamed A.; Garbarino, Gaston; Mezouar, Mohamed

2011-04-01

We investigated the melting properties of a synthetic chondritic primitive mantle up to core-mantle boundary (CMB) pressures, using laser-heated diamond anvil cell. Melting criteria are essentially based on the use of X-rays provided by synchrotron radiation. We report a solidus melting curve lower than previously determined using optical methods. The liquidus curve is found between 300 and 600 K higher than the solidus over the entire lower mantle. At CMB pressures (135 GPa), the chondritic mantle solidus and liquidus reach 4150 (± 150) K and 4725 (± 150) K, respectively. We discuss that the lower mantle is unlikely to melt in the D″-layer, except if the highest estimate of the temperature profile at the base of the mantle, which is associated with a very hot core, is confirmed. Therefore, recent suggestions of partial melting in the lowermost mantle based on seismic observations of ultra-low velocity zones indicate either (1) a outer core exceeding 4150 K at the CMB or (2) the presence of chemical heterogeneities with high concentration of fusible elements. Our observations of a high liquidus temperature as well as a large gap between solidus and liquidus temperatures have important implications for the properties of the magma ocean during accretion. Not only complete melting of the lower mantle would require excessively high temperatures, but also, below liquidus temperatures partial melting should take place over a much larger depth interval than previously thought. In addition, magma adiabats suggest very high surface temperatures in case of a magma ocean that would extend to more than 40 GPa, as suggested by siderophile metal-silicate partitioning data. Such high surface temperature regime, where thermal blanketing is inefficient, points out to a transient character of the magma ocean, with a very fast cooling rate.

Numerical Simulations of the Thermodynamic Process of Granite Formation on the Geological model of In-situ Melting

NASA Astrophysics Data System (ADS)

Chen, Z.; Wang, Y. J.; Chen, G. N.; Liu, J.; Liu, Y. J.

2017-12-01

The In-situ Melting model of granite reveals that granitic magma generated by anatexis is layer-like and magma convection results in thickening of the layer. On the basis and by integrating the research findings on rheological transitions of rocks in crustal melting, we simulated the thermodynamic process of granite formation by using Underworld1.7. The size of the numerical model is 100km×25km with free-slip boundary. The solidus temperature is postulated being 600° and the fusing-off temperatures is 705° that corresponds to the solid-liquid transition (SLT) of the partial melting system with the melt fraction percentage around 40%. The viscosities of rock and magma are separately calculated according to this melt percentage. The model runs on Tian-He2 supercomputer and the result indicates: 1) when temperature exceeds the solidus of rock, anatexis appears in the area below the 600° isotherm; 2) when temperature surpasses the fusing-off temperature of rock, a magma layer occurs in the area below 705° isotherm; 3) the initiation of magma convection accompanied with stoping is at the temperature around 739.6°, and the upper surface of magma layer, i.e. the MI (magma interface)/SLT (solid-liquid transition) moves upwards with time; 4) the velocity of the upward motion of MI/SLT depends on the bottom temperature and the thickness of magma layer depends on the duration of convection. Summing up, this modeling result demonstrates that the In-situ Melting model of granite meets the basic principle of physics and reveals details on the thermodynamic circumstances interacting with the development of melting and granite formation.Acknowledgement: This research is financially supported by NSFC (No 41372223, No 41230206 and No 41574087).

An observational and thermodynamic investigation of carbonate partial melting

NASA Astrophysics Data System (ADS)

Floess, David; Baumgartner, Lukas P.; Vonlanthen, Pierre

2015-01-01

Melting experiments available in the literature show that carbonates and pelites melt at similar conditions in the crust. While partial melting of pelitic rocks is common and well-documented, reports of partial melting in carbonates are rare and ambiguous, mainly because of intensive recrystallization and the resulting lack of criteria for unequivocal identification of melting. Here we present microstructural, textural, and geochemical evidence for partial melting of calcareous dolomite marbles in the contact aureole of the Tertiary Adamello Batholith. Petrographic observations and X-ray micro-computed tomography (X-ray μCT) show that calcite crystallized either in cm- to dm-scale melt pockets, or as an interstitial phase forming an interconnected network between dolomite grains. Calcite-dolomite thermometry yields a temperature of at least 670 °C, which is well above the minimum melting temperature of ∼600 °C reported for the CaO-MgO-CO2-H2O system. Rare-earth element (REE) partition coefficients (KDcc/do) range between 9-35 for adjacent calcite-dolomite pairs. These KD values are 3-10 times higher than equilibrium values between dolomite and calcite reported in the literature. They suggest partitioning of incompatible elements into a melt phase. The δ18O and δ13C isotopic values of calcite and dolomite support this interpretation. Crystallographic orientations measured by electron backscattered diffraction (EBSD) show a clustering of c-axes for dolomite and interstitial calcite normal to the foliation plane, a typical feature for compressional deformation, whereas calcite crystallized in pockets shows a strong clustering of c-axes parallel to the pocket walls, suggesting that it crystallized after deformation had stopped. All this together suggests the formation of partial melts in these carbonates. A Schreinemaker analysis of the experimental data for a CO2-H2O fluid-saturated system indeed predicts formation of calcite-rich melt between 650-880 °C, in agreement with our observations of partial melting. The presence of partial melts in crustal carbonates has important physical and chemical implications, including a drastic drop in rock viscosity and significant change in the dynamics and distribution of fluids within both the contact aureole and the intrusive body.

Mechanical stiffening and thermal softening of rare earth chalcogenides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shriya, S.; Varshney, Dinesh; Singh, Namita, E-mail: namita.singh.2050@gmail.com

2014-04-24

The pressure and temperature dependent elastic properties such as melting temperature nature in REX; (RE = La, Pr, Eu; X = O, S, Se, Te) chalcogenides is computed with emphasis on charge transfer interactions and covalent contribution in the effective interionic interaction potential. The pressure dependent elastic constants and melting temperature confirms that REX chalcogens lattice get stiffened as a consequence of bond compression and bond strengthening, however thermal softening arose due to bond expansion and bond weakening is evidenced from temperature dependence of melting temperature (T{sub M})

Development of a double-stage DDIA apparatus and its application to in-situ melting experiments at high pressures

NASA Astrophysics Data System (ADS)

Jing, Z.; Wang, Y.; Tange, Y.; Hilairet, N.; Yu, T.; Sakamaki, T.

2010-12-01

Melting experiments at high pressures are critical to our studies on the chemical evolution and dynamics of Earth and other terrestrial planets. A large volume press can generate a homogeneous and stable high-temperature environment, which is the key to melting experiments. However, previous in-situ melting experiments using a large volume press were often restricted to relatively low pressures. In order to expand the P-T conditions, a double-stage 6-8 configuration (6 first-stage anvils and 8 second stage-anvils) has been developed in a DDIA apparatus (DDIA-30), recently installed at the GSECARS Beamline 13-ID-D at the Advanced Photon Source. 27 mm DIA-type first-stage anvils and 14 mm second-stage anvils with the truncation edge length (TEL) of 1.5 mm are employed. A cell assembly that is suitable for synchrotron X-ray studies developed by Tange et al. (2008) has been adopted for melting experiments. High pressure and temperature conditions are generated up to 27 GPa and 2473 K by using tungsten carbide anvils, and up to 35 GPa and 1773 K by using sintered diamond anvils. Both LaCrO3 and TiB2 heater materials have been successfully applied for high-temperature generation. Although TiB2 shows a decrease of resistance at temperatures higher than 2000 K at 20 GPa, we are able to achieve 2473 K with temperature fluctuations in the range of ±30 K. Using tungsten carbide anvils and TiB2 heaters, we have determined the melting curve of gold up to 20 GPa. We constrain the melting temperature based on the disappearance of the gold peaks in energy dispersive X-ray diffraction patterns and the change of sample shape in the radiographic images. The combination of these two observations can reduce the uncertainties in melting temperatures to within 100 K. The measured melting temperatures of gold at 8, 13, and 20 GPa are consistent with the low-pressure results (up to 6 GPa) such as Mirwald and Kennedy (1979). Melting experiments with sintered diamond anvils are currently under development. This will enable us to conduct melting experiments up to 50 GPa on Fe alloys and silicates.

Molecular dynamics simulation of Coulomb explosion, melting and shock wave creation in silicon after an ionization pulse

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Zhongyu; Shao, Lin, E-mail: lshao@tamu.edu; Chen, Di

Strong electronic stopping power of swift ions in a semiconducting or insulating substrate can lead to localized electron stripping. The subsequent repulsive interactions among charged target atoms can cause Coulomb explosion. Using molecular dynamics simulation, we simulate Coulomb explosion in silicon by introducing an ionization pulse lasting for different periods, and at different substrate temperatures. We find that the longer the pulse period, the larger the melting radius. The observation can be explained by a critical energy density model assuming that melting required thermal energy density is a constant value and the total thermal energy gained from Coulomb explosion ismore » linearly proportional to the ionization period. Our studies also show that melting radius is larger at higher substrate temperatures. The temperature effect is explained due to a longer structural relaxation above the melting temperature at original ionization boundary due to lower heat dissipation rates. Furthermore, simulations show the formation of shock waves, created due to the compression from the melting core.« less

Modeling the melting of multicomponent systems: the case of MgSiO3 perovskite under lower mantle conditions

PubMed Central

Di Paola, Cono; P. Brodholt, John

2016-01-01

Knowledge of the melting properties of materials, especially at extreme pressure conditions, represents a long-standing scientific challenge. For instance, there is currently considerable uncertainty over the melting temperatures of the high-pressure mantle mineral, bridgmanite (MgSiO3-perovskite), with current estimates of the melting T at the base of the mantle ranging from 4800 K to 8000 K. The difficulty with experimentally measuring high pressure melting temperatures has motivated the use of ab initio methods, however, melting is a complex multi-scale phenomenon and the timescale for melting can be prohibitively long. Here we show that a combination of empirical and ab-initio molecular dynamics calculations can be used to successfully predict the melting point of multicomponent systems, such as MgSiO3 perovskite. We predict the correct low-pressure melting T, and at high-pressure we show that the melting temperature is only 5000 K at 120 GPa, a value lower than nearly all previous estimates. In addition, we believe that this strategy is of general applicability and therefore suitable for any system under physical conditions where simpler models fail. PMID:27444854

Production of Synthetic Nuclear Melt Glass

PubMed Central

Molgaard, Joshua J.; Auxier, John D.; Giminaro, Andrew V.; Oldham, Colton J.; Gill, Jonathan; Hall, Howard L.

2016-01-01

Realistic surrogate nuclear debris is needed within the nuclear forensics community to test and validate post-detonation analysis techniques. Here we outline a novel process for producing bulk surface debris using a high temperature furnace. The material developed in this study is physically and chemically similar to trinitite (the melt glass produced by the first nuclear test). This synthetic nuclear melt glass is assumed to be similar to the vitrified material produced near the epicenter (ground zero) of any surface nuclear detonation in a desert environment. The process outlined here can be applied to produce other types of nuclear melt glass including that likely to be formed in an urban environment. This can be accomplished by simply modifying the precursor matrix to which this production process is applied. The melt glass produced in this study has been analyzed and compared to trinitite, revealing a comparable crystalline morphology, physical structure, void fraction, and chemical composition. PMID:26779720

Solid-solid phase transformation via internal stress-induced virtual melting, significantly below the melting temperature. Application to HMX energetic crystal.

PubMed

Levitas, Valery I; Henson, Bryan F; Smilowitz, Laura B; Asay, Blaine W

2006-05-25

We theoretically predict a new phenomenon, namely, that a solid-solid phase transformation (PT) with a large transformation strain can occur via internal stress-induced virtual melting along the interface at temperatures significantly (more than 100 K) below the melting temperature. We show that the energy of elastic stresses, induced by transformation strain, increases the driving force for melting and reduces the melting temperature. Immediately after melting, stresses relax and the unstable melt solidifies. Fast solidification in a thin layer leads to nanoscale cracking which does not affect the thermodynamics or kinetics of the solid-solid transformation. Thus, virtual melting represents a new mechanism of solid-solid PT, stress relaxation, and loss of coherence at a moving solid-solid interface. It also removes the athermal interface friction and deletes the thermomechanical memory of preceding cycles of the direct-reverse transformation. It is also found that nonhydrostatic compressive internal stresses promote melting in contrast to hydrostatic pressure. Sixteen theoretical predictions are in qualitative and quantitative agreement with experiments conducted on the PTs in the energetic crystal HMX. In particular, (a) the energy of internal stresses is sufficient to reduce the melting temperature from 551 to 430 K for the delta phase during the beta --> delta PT and from 520 to 400 K for the beta phase during the delta --> beta PT; (b) predicted activation energies for direct and reverse PTs coincide with corresponding melting energies of the beta and delta phases and with the experimental values; (c) the temperature dependence of the rate constant is determined by the heat of fusion, for both direct and reverse PTs; results b and c are obtained both for overall kinetics and for interface propagation; (d) considerable nanocracking, homogeneously distributed in the transformed material, accompanies the PT, as predicted by theory; (e) the nanocracking does not change the PT thermodynamics or kinetics appreciably for the first and the second PT beta <--> delta cycles, as predicted by theory; (f) beta <--> delta PTs start at a very small driving force (in contrast to all known solid-solid transformations with large transformation strain), that is, elastic energy and athermal interface friction must be negligible; (g) beta --> alpha and alpha --> beta PTs, which are thermodynamically possible in the temperature range 382.4 < theta < 430 K and below 382.4 K, respectively, do not occur.

Femtosecond laser melting of silver nanoparticles: comparison of model simulations and experimental results

NASA Astrophysics Data System (ADS)

Cheng, Chung-Wei; Chang, Chin-Lun; Chen, Jinn-Kuen; Wang, Ben

2018-05-01

Ultrafast laser-induced melting of silver nanoparticles (NPs) using a femtosecond laser pulse is investigated both theoretically and experimentally. The sintered Ag structure fabricated from printed Ag NP ink using femtosecond laser (1064 nm, 300 fs) irradiation is experimentally studied. A two-temperature model with dynamic optical properties and particle size effects on the melting temperature of Ag NPs is considered. The rapid phase change model is incorporated to simulate the Ag NPs' ultrafast laser-induced melting process, and a multi-shot melting threshold fluence predicted from the simulated single-shot melting threshold is developed.

Precise new shock temperatures in forsterite and in silicate liquids: phase transitions and heat capacity at high pressure

NASA Astrophysics Data System (ADS)

Asimow, P. D.; Fat'yanov, O. V.; Su, C.; Ma, X. J.

2017-12-01

Shock temperature measurements in transparent samples provide key constraints on the phase transitions and thermodynamic properties of materials at high pressure and temperature. Such measurements are necessary, for example, to allow equation of state measurements taken along the Hugoniot to be translated to P-V-T space. We have recently completed a detailed study of the accuracy and reproducibility of calibration of our 6-channel fast pyrometer. We have also introduced improved analysis procedures of the time-dependent multi-wavelength radiance signal that avoid the need for a greybody assumption and therefore have better precision than earlier results. This has motivated (a) renewed study of the shock temperature of forsterite in the superheating, partial melting, and complete melting regimes, (b) pre-heated diopside-anorthite glass shock temperature experiments for comparison to pre-heated silicate liquid equation of state results, and (c) new soda-lime glass shock temperature experiments. Single-crystal synthetic forsterite samples were shocked along (100) to pressures between 120 and 210 GPa on the Caltech two-stage light gas gun. Uncertainties on most results are 50 K. Results above the onset of partial melting at 130 GPa are consistent with Lyzenga and Ahrens (1980) data and show a low P-T slope consistent with a partial melting interval. Complete melting may occur, given sufficient time, at about 210 GPa. The experiment at 120-130 GPa is anomalous, showing two-wave structure and time- and wavelength-dependent scattering suggesting a subsolidus phase transition behind the shock front. The amount of super-heating, if any, is far smaller than claimed by Holland and Ahrens (1997). Steady radiation profiles, high emissivity, and consistency from channel to channel provide high precision (±40 K) in diopside-anorthite liquid shocked from just above the glass transition to high pressure. Temperatures are colder than expected for a model with constant heat capacity, providing direct evidence that multicomponent silicate liquids show a major increase in heat capacity in the P-T range appropriate to terrestrial magma oceans (<150 GPa, <5000 K).

Zirconium, hafnium, and rare earth element partition coefficients for ilmenite and other minerals in high-Ti lunar mare basalts - An experimental study

NASA Technical Reports Server (NTRS)

Mckay, G.; Wagstaff, J.; Yang, S.-R.

1986-01-01

Partition coefficients were determined for Gd, Lu, Hf and Zr among ilmenite, armalcolite, and synthetic high-Ti mare basaltic melts at temperatures from 1122 deg to 1150 deg, and at oxygen fugacities of IW x 10 exp 0.5, by in situ analysis with an electron microprobe, using samples doped to present concentration levels. Coefficients for Zr were also measured for samples containing 600-1600 ppm Zr using this microprobe. In addition, coefficients were determined for Hf and Zr between chromian ulvospinel and melt, for Hf between pigeonite and melt, and for Lu between olivine and melt by microprobe analysis of samples doped to present levels. Values measured using the microprobe were in agreement with the values measured by analyzing mineral separates from the same run products by isotope dilution. Coefficient values for ilmenite are less than 0.01 for the LREE, are around 0.1 for the HREE, and are several times greater than this for Zr and Hf.

Mathematical modeling of radiative-conductive heat transfer in semitransparent medium with phase change

NASA Astrophysics Data System (ADS)

Savvinova, Nadezhda A.; Sleptsov, Semen D.; Rubtsov, Nikolai A.

2017-11-01

A mathematical phase change model is a formulation of the Stefan problem. Various formulations of the Stefan problem modeling of radiative-conductive heat transfer during melting or solidification of a semitransparent material are presented. Analysis of numerical results show that the radiative heat transfer has a significant effect on temperature distributions during melting (solidification) of the semitransparent material. In this paper conditions for application of various statements of the Stefan problem are analyzed.

Melting of size-selected gallium clusters with 60-183 atoms.

PubMed

Pyfer, Katheryne L; Kafader, Jared O; Yalamanchali, Anirudh; Jarrold, Martin F

2014-07-10

Heat capacities have been measured as a function of temperature for size-selected gallium cluster cations with between 60 and 183 atoms. Almost all clusters studied show a single peak in the heat capacity that is attributed to a melting transition. The peaks can be fit by a two-state model incorporating only fully solid-like and fully liquid-like species, and hence no partially melted intermediates. The exceptions are Ga90(+), which does not show a peak, and Ga80(+) and Ga81(+), which show two peaks. For the clusters with two peaks, the lower temperature peak is attributed to a structural transition. The melting temperatures for clusters with less than 50 atoms have previously been shown to be hundreds of degrees above the bulk melting point. For clusters with more than 60 atoms the melting temperatures decrease, approaching the bulk value (303 K) at around 95 atoms, and then show several small upward excursions with increasing cluster size. A plot of the latent heat against the entropy change for melting reveals two groups of clusters: the latent heats and entropy changes for clusters with less than 94 atoms are distinct from those for clusters with more than 93 atoms. This observation suggests that a significant change in the nature of the bonding or the structure of the clusters occurs at 93-94 atoms. Even though the melting temperatures are close to the bulk value for the larger clusters studied here, the latent heats and entropies of melting are still far from the bulk values.

Changing surface-atmosphere energy exchange and refreezing capacity of the lower accumulation area, West Greenland

NASA Astrophysics Data System (ADS)

Charalampidis, C.; van As, D.; Box, J. E.; van den Broeke, M. R.; Colgan, W. T.; Doyle, S. H.; Hubbard, A. L.; MacFerrin, M.; Machguth, H.; Smeets, C. J. P. P.

2015-11-01

We present 5 years (2009-2013) of automatic weather station measurements from the lower accumulation area (1840 m a.s.l. - above sea level) of the Greenland ice sheet in the Kangerlussuaq region. Here, the summers of 2010 and 2012 were both exceptionally warm, but only 2012 resulted in a strongly negative surface mass budget (SMB) and surface meltwater run-off. The observed run-off was due to a large ice fraction in the upper 10 m of firn that prevented meltwater from percolating to available pore volume below. Analysis reveals an anomalously low 2012 summer-averaged albedo of 0.71 (typically ~ 0.78), as meltwater was present at the ice sheet surface. Consequently, during the 2012 melt season, the ice sheet surface absorbed 28 % (213 MJ m-2) more solar radiation than the average of all other years. A surface energy balance model is used to evaluate the seasonal and interannual variability of all surface energy fluxes. The model reproduces the observed melt rates as well as the SMB for each season. A sensitivity analysis reveals that 71 % of the additional solar radiation in 2012 was used for melt, corresponding to 36 % (0.64 m) of the 2012 surface lowering. The remaining 64 % (1.14 m) of surface lowering resulted from high atmospheric temperatures, up to a +2.6 °C daily average, indicating that 2012 would have been a negative SMB year at this site even without the melt-albedo feedback. Longer time series of SMB, regional temperature, and remotely sensed albedo (MODIS) show that 2012 was the first strongly negative SMB year, with the lowest albedo, at this elevation on record. The warm conditions of recent years have resulted in enhanced melt and reduction of the refreezing capacity in the lower accumulation area. If high temperatures continue, the current lower accumulation area will turn into a region with superimposed ice in coming years.

Long-Term Stability of WC-C Peritectic Fixed Point

NASA Astrophysics Data System (ADS)

Khlevnoy, B. B.; Grigoryeva, I. A.

2015-03-01

The tungsten carbide-carbon peritectic (WC-C) melting transition is an attractive high-temperature fixed point with a temperature of . Earlier investigations showed high repeatability, small melting range, low sensitivity to impurities, and robustness of WC-C that makes it a prospective candidate for the highest fixed point of the temperature scale. This paper presents further study of the fixed point, namely the investigation of the long-term stability of the WC-C melting temperature. For this purpose, a new WC-C cell of the blackbody type was built using tungsten powder of 99.999 % purity. The stability of the cell was investigated during the cell aging for 50 h at the cell working temperature that tooks 140 melting/freezing cycles. The method of investigation was based on the comparison of the WC-C tested cell with a reference Re-C fixed-point cell that reduces an influence of the probable instability of a radiation thermometer. It was shown that after the aging period, the deviation of the WC-C cell melting temperature was with an uncertainty of.

Effect of modification of isotactic polypropylene by additives of polyamide 6/66 on structural characteristics of composites

NASA Astrophysics Data System (ADS)

Vorontsov, N. V.; Popov, A. A.; Margolin, A. L.

2017-12-01

Changes in the supramolecular structure of polymer composites based on isotactic polypropylene (PP) and polyamide 6/66 (PA) are studied depending on the PP : PA ratio. Temperatures and enthalpies of melting and crystallization of both PP and PA and their composites are determined depending on the composition of the mixtures. It was shown that the initial melting point of a composite does not change with increasing PA content in the blends. The crystallization temperature of the mixtures is shown to increase with the addition of PA and becomes much higher than the crystallization temperatures of both PP and PA. The observed effect can be due to a strong interaction between the PP and PA molecules, thus decreasing the molecular mobility and increasing the crystallization temperature. The crystallization and melting of PP-PA mixtures are found to proceed at the close temperatures, although the crystallization and melting temperatures of pure PP and pure PA differ widely. The melting and crystallization enthalpies decrease with increasing PA concentration in the mixtures, which indicates a decrease in the degree of crystallinity of the composite.

Characterization of Mullite-Zirconia Composite Processed by Non-Transferred and Transferred Arc Plasma

NASA Astrophysics Data System (ADS)

Yugeswaran, S.; Selvarajan, V.; Lusvarghi, L.; I. Y. Tok, A.; D. Siva Rama, Krishna

2009-04-01

The arc plasma melting technique is a simple method to synthesize high temperature reaction composites. In this study, mullite-zirconia composite was synthesized by transferred and non-transferred arc plasma melting, and the results were compared. A mixture of alumina and zircon powders with a mole ratio of 3: 2 were ball milled for four hours and melted for two minutes in the transferred and non-transferred mode of plasma arcs. Argon and air were used as plasma forming gases. The phase and microstructural formation of melted samples were investigated by X-ray diffraction (XRD) and scanning electron microscope (SEM). The microstructure of the composites was found to be affected by the mode of melting. In transferred arc melting, zirconia flowers with uniform lines along with mullite whiskers were obtained. In the case of non-transferred arc plasma melting, mullite whiskers along with star shape zirconia were formed. Differential thermal analysis (DTA) of the synthesized mullite-zirconia composites provided a deeper understanding of the mechanisms of mullite formation during the two different processes.

Formation and characterization of mullite fibers produced by inviscid melt-spinning

NASA Astrophysics Data System (ADS)

Xiao, Zhijun

IMS is a technique used to form fibers from low viscosity melts by means of stream stabilization in a reactant gas, in this case propane. Mullite (3Alsb2Osb3*2SiOsb2) was selected as the material to be fiberized. A stable mullite melt was obtained at 2000sp°C. Some short fibers and shot were formed in the fiber forming experiments. Crucible material selection is a prerequisite for proper application of the IMS technique. The effect of two crucible materials-graphite and boron nitride were studied. A carbothermal reaction occurred between the mullite melt and the graphite crucible. Boron nitride was selected as the crucible material because a relatively stable melt could be obtained. Operating environment is another factor that affects IMS mullite fiber formation. The effects of vacuum, nitrogen and argon on mullite melting behavior were studied. Argon gas was selected as the operating environment. A 2sp3 factorial design was developed to study the effect of such variables as temperature, holding time at the temperature, and heating rate on mullite melting behavior. The effects of the variables and interactions were calculated. Temperature has the biggest positive effect, holding time is the second, heating rate just has a very small negative effect. A detailed investigation of the mullite decomposition mechanism and kinetics was conducted in this work. A solid reaction mechanism was proposed. The kinetic results and IR analysis support the proposed mechanism. The carbon source inside the furnace led to the decomposition of mullite. A feasible experimental technique was developed to prevent the decomposition of mullite. The experiments with this design completely controlled the mullite decomposition. The short fibers, shot and some side products formed in the fiber forming experiments were characterized using XRD, XRF and SEM-EDS. The composition of the short fiber and shot was in the range of mullite composition. XRD showed that the diffraction pattern of shot is that of mullite.

Cyclic phase change in a cylindrical thermal energy storage capsule

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hasan, M.; Mujumdar, A.S.; Weber, M.E.

1983-12-01

This paper is concerned with a practical melting/freezing problem in conjunction with the more realistic case of a cyclic phase change thermal energy storage device. In this model the phase change medium is encapsulated in long cylindrical tubes, the surface temperature of which is allowed to vary sinusoidally with time about the discrete freezing temperature. Initial temperature of the medium is assumed to be constant at a temperature above or below the freezing/melting temperature. Natural convection in the melt is assumed to be negligible and the variations in the depth of freezing and/or melting in each half cycle is ignored.more » Depending on the half-cycle parameters the problem is simplified to either freezing or melting. The governing one-dimensional heat diffusion equations for both phases are solved by the Finite Integral Transform techniques. The kernels for the transformation are the time-dependent eigen functions separately defined for each phases. This extended transform method can accomodate any time-dependent surface temperature variation. The application of the transform generated a series of coupled, nonlinear first order differential equations, which are solved by Runge Kutta-Verner fifth and sixth order method. Dimensionless solutions of temperature variations in both phases, fusion front position and the fraction solidified (or melted) are displayed graphically to aid in practical calculations. For the special case of a constant surface temperature, comparisons are made between the present results and the existing integral and purely numerical results. The results are found to compare favourably. Results for fractional solidification (or melting and interface position are also compared with the simple Conduction Shape Factor method, after allowing for the time-dependent boundary conditions. Once again the results agree reasonably well.« less

Transport Properties of LiTFSI-Acetamide Room Temperature Molten Salt Electrolytes Applied in an Li-Ion Battery

NASA Astrophysics Data System (ADS)

Yang, Chao-Chen; Hsu, Hsin-Yi; Hsu, Chen-Ruei

2007-11-01

In the present work some transport properties of the binary room temperature molten salt (RTMS) lithium bis(trifluoromethane sulfone)imide (LiTFSI)-acetamide [LiN(SO2CF3)2-CH3CONH2], applied in an Li-ion battery, have been investigated. The phase diagram was determined by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The result reveals that the binary RTMS has an eutectic point at 201 K and the 30 mol% LiTFSI composition. The electric conductivity was measured using a direct current computerized method. The result shows that the conductivities of the melts increase with increasing temperature and acetamide content. The densities of all melts decrease with increasing temperature and acetamide content. The equivalent conductivities were fitted by the Arrhenius equation, where the activation energies were 18.15, 18.52, 20.35, 25.08 kJ/mol for 10, 20, 30, 40 mol% LiTFSI, respectively. Besides the relationships between conductivity, density composition and temperature, of the ion interaction is discussed.

Melting of Iron to 290 Gigapascals

NASA Astrophysics Data System (ADS)

Sinmyo, R.; Hirose, K.; Ohishi, Y.

2017-12-01

The Earth's core is composed mainly of iron. Since liquid core coexists with solid core at the inner core boundary (ICB), the melting point of iron at 330 gigapascals offers a key constraint on core temperatures. However, previous results using a laser-heated diamond-anvil cell (DAC) have been largely inconsistent with each other, likely because of an intrinsic large temperature gradient and its temporal fluctuation. Here we employed an internal-resistance-heated DAC and determined the melting temperature of pure iron up to 290 gigapascals, the highest ever in static compression experiments. A small extrapolation indicates a melting point of 5500 ± 80 kelvin at the ICB, about 500-1000 degrees lower than earlier shock-compression data. It suggests a relatively low temperature for the core-mantle boundary, which avoids global melting of the lowermost mantle in the last more than 1.5 billion years.

Air temperature thresholds to evaluate snow melting at the surface of Alpine glaciers by T-index models: the case study of Forni Glacier (Italy)

NASA Astrophysics Data System (ADS)

Senese, A.; Maugeri, M.; Vuillermoz, E.; Smiraglia, C.; Diolaiuti, G.

2014-03-01

The glacier melt conditions (i.e.: null surface temperature and positive energy budget) can be assessed by analyzing meteorological and energy data acquired by a supraglacial Automatic Weather Station (AWS). In the case this latter is not present the assessment of actual melting conditions and the evaluation of the melt amount is difficult and simple methods based on T-index (or degree days) models are generally applied. These models require the choice of a correct temperature threshold. In fact, melt does not necessarily occur at daily air temperatures higher than 273.15 K. In this paper, to detect the most indicative threshold witnessing melt conditions in the April-June period, we have analyzed air temperature data recorded from 2006 to 2012 by a supraglacial AWS set up at 2631 m a.s.l. on the ablation tongue of the Forni Glacier (Italian Alps), and by a weather station located outside the studied glacier (at Bormio, a village at 1225 m a.s.l.). Moreover we have evaluated the glacier energy budget and the Snow Water Equivalent (SWE) values during this time-frame. Then the snow ablation amount was estimated both from the surface energy balance (from supraglacial AWS data) and from T-index method (from Bormio data, applying the mean tropospheric lapse rate and varying the air temperature threshold) and the results were compared. We found that the mean tropospheric lapse rate permits a good and reliable reconstruction of glacier air temperatures and the major uncertainty in the computation of snow melt is driven by the choice of an appropriate temperature threshold. From our study using a 5.0 K lower threshold value (with respect to the largely applied 273.15 K) permits the most reliable reconstruction of glacier melt.

Temperature of Earth's core constrained from melting of Fe and Fe0.9Ni0.1 at high pressures

NASA Astrophysics Data System (ADS)

Zhang, Dongzhou; Jackson, Jennifer M.; Zhao, Jiyong; Sturhahn, Wolfgang; Alp, E. Ercan; Hu, Michael Y.; Toellner, Thomas S.; Murphy, Caitlin A.; Prakapenka, Vitali B.

2016-08-01

The melting points of fcc- and hcp-structured Fe0.9Ni0.1 and Fe are measured up to 125 GPa using laser heated diamond anvil cells, synchrotron Mössbauer spectroscopy, and a recently developed fast temperature readout spectrometer. The onset of melting is detected by a characteristic drop in the time-integrated synchrotron Mössbauer signal which is sensitive to atomic motion. The thermal pressure experienced by the samples is constrained by X-ray diffraction measurements under high pressures and temperatures. The obtained best-fit melting curves of fcc-structured Fe and Fe0.9Ni0.1 fall within the wide region bounded by previous studies. We are able to derive the γ-ɛ-l triple point of Fe and the quasi triple point of Fe0.9Ni0.1 to be 110 ± 5GPa, 3345 ± 120K and 116 ± 5GPa, 3260 ± 120K, respectively. The measured melting temperatures of Fe at similar pressure are slightly higher than those of Fe0.9Ni0.1 while their one sigma uncertainties overlap. Using previously measured phonon density of states of hcp-Fe, we calculate melting curves of hcp-structured Fe and Fe0.9Ni0.1 using our (quasi) triple points as anchors. The extrapolated Fe0.9Ni0.1 melting curve provides an estimate for the upper bound of Earth's inner core-outer core boundary temperature of 5500 ± 200K. The temperature within the liquid outer core is then approximated with an adiabatic model, which constrains the upper bound of the temperature at the core side of the core-mantle boundary to be 4000 ± 200K. We discuss a potential melting point depression caused by light elements and the implications of the presented core-mantle boundary temperature bounds on phase relations in the lowermost part of the mantle.

Temperature of Earth's core constrained from melting of Fe and Fe 0.9Ni 0.1 at high pressures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Dongzhou; Jackson, Jennifer M.; Zhao, Jiyong

The melting points of fcc- and hcp-structured Fe 0.9Ni 0.1 and Fe are measured up to 125 GPa using laser heated diamond anvil cells, synchrotron Mossbauer spectroscopy, and a recently developed fast temperature readout spectrometer. The onset of melting is detected by a characteristic drop in the time integrated synchrotron Mfissbauer signal which is sensitive to atomic motion. The thermal pressure experienced by the samples is constrained by X-ray diffraction measurements under high pressures and temperatures. The obtained best-fit melting curves of fcc-structured Fe and Fe 0.9Ni 0.1 fall within the wide region bounded by previous studies. We are ablemore » to derive the gamma-is an element of-1 triple point of Fe and the quasi triple point of Fe0.9Ni0.1 to be 110 ± 5 GPa, 3345 ± 120 K and 116 ± 5 GPa, 3260 ± 120 K, respectively. The measured melting temperatures of Fe at similar pressure are slightly higher than those of Fe 0.9Ni 0.1 while their one sigma uncertainties overlap. Using previously measured phonon density of states of hcp-Fe, we calculate melting curves of hcp-structured Fe and Fe 0.9Ni 0.1 using our (quasi) triple points as anchors. The extrapolated Fe 0.9Ni 0.1 melting curve provides an estimate for the upper bound of Earth's inner core-outer core boundary temperature of 5500 ± 200 K. The temperature within the liquid outer core is then approximated with an adiabatic model, which constrains the upper bound of the temperature at the core side of the core -mantle boundary to be 4000 ± 200 K. We discuss a potential melting point depression caused by light elements and the implications of the presented core -mantle boundary temperature bounds on phase relations in the lowermost part of the mantle.« less

The dry-heat loss effect of melt-spun phase change material fibres.

PubMed

Tjønnås, Maria Suong; Færevik, Hilde; Sandsund, Mariann; Reinertsen, Randi E

2015-01-01

Phase change materials (PCM) have the ability to store latent heat when they change phases, a property that gives clothing that incorporates PCM its cooling effect. This study investigated the effect of dry-heat loss (cooling) of a novel melt-spun PCM fibre on the basis of the area covered, mass, the latent heat of fusion and melting temperature, compared to a known PCM clothing product. PCM fibres with melting temperatures of 28.4 and 32.0°C and PCM packs with melting temperatures of 28.0 and 32.0°C were studied. The results showed that the PCM fibres had a larger initial peak cooling effect than that of the PCM packs. The duration of the cooling effect of PCM fibres was primarily dependent on the PCM mass and the latent heat of fusion capacity, and secondly on the covered area and melting temperature of the PCM. This study investigates the cooling effect of PCM fibres on a thermal manikin. The PCM fibres had a high but short-lasting cooling effect. This study contributes to the knowledge of how the body's temperature regulation may be affected by the cooling properties of clothing that incorporates PCM.

History dependent crystallization of Zr{sub 41}Ti{sub 14}Cu{sub 12}Ni{sub 10}Be{sub 23} melts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schroers, Jan; Johnson, William L.

The crystallization of Zr{sub 41}Ti{sub 14}Cu{sub 12}Ni{sub 10}Be{sub 23} (Vit 1) melts during constant heating is investigated. (Vit 1) melts are cooled with different rates into the amorphous state and the crystallization temperature upon subsequent heating is studied. In addition, Vit 1 melts are cooled using a constant rate to different temperatures and subsequently heated from this temperature with a constant rate. We investigate the influence of the temperature to which the melt was cooled on the crystallization temperature measured upon heating. In both cases the onset temperature of crystallization shows strong history dependence. This can be explained by anmore » accumulating process during cooling and heating. An attempt is made to consider this process in a simple model by steady state nucleation and subsequent growth of the nuclei which results in different crystallization kinetics during cooling or heating. Calculations show qualitative agreement with the experimental results. However, calculated and experimental results differ quantitatively. This difference can be explained by a decomposition process leading to a nonsteady nucleation rate which continuously increases with decreasing temperature. (c) 2000 American Institute of Physics.« less

LaRC TPI 1500 series polymers

NASA Technical Reports Server (NTRS)

Hou, Tan-Hung; Bai, Jia-Mo

1990-01-01

The crystallization behavior and the melt flow properties of two batches of 1500 series LaRC-TPI polymers from Mitsui Toatsu Chemicals (MTC) were investigated. The characterization methods include Differential Scanning Calorimetry, the x ray diffractography and the melt rheology. The as-received materials possess initial crystalline melting peak temperatures of 295 and 305 C, respectively. These materials are less readily recrystallizable at elevated temperatures when compared to other semicrystalline thermoplastics. For the samples annealed at temperatures below 330 C, a semicrystalline polymer can be obtained. On the other hand, a purely amorphous structure is realized in the samples annealed at temperatures above 330 C. Isothermal crystallization kinetics were studied by means of the simple Avrami equation. The viscoelastic properties at elevated temperatures below and above glass transition temperature of the polymers were measured. Information with regard to the molecule sizes and distributions in these polymers were also extracted from melt rheology.

Cubic zirconia in >2370 °C impact melt records Earth's hottest crust

NASA Astrophysics Data System (ADS)

Timms, Nicholas E.; Erickson, Timmons M.; Zanetti, Michael R.; Pearce, Mark A.; Cayron, Cyril; Cavosie, Aaron J.; Reddy, Steven M.; Wittmann, Axel; Carpenter, Paul K.

2017-11-01

Bolide impacts influence primordial evolution of planetary bodies because they can cause instantaneous melting and vaporization of both crust and impactors. Temperatures reached by impact-generated silicate melts are unknown because meteorite impacts are ephemeral, and established mineral and rock thermometers have limited temperature ranges. Consequently, impact melt temperatures in global bombardment models of the early Earth and Moon are poorly constrained, and may not accurately predict the survival, stabilization, geochemical evolution and cooling of early crustal materials. Here we show geological evidence for the transformation of zircon to cubic zirconia plus silica in impact melt from the 28 km diameter Mistastin Lake crater, Canada, which requires super-heating in excess of 2370 °C. This new temperature determination is the highest recorded from any crustal rock. Our phase heritage approach extends the thermometry range for impact melts by several hundred degrees, more closely bridging the gap between nature and theory. Profusion of >2370 °C superheated impact melt during high intensity bombardment of Hadean Earth likely facilitated consumption of early-formed crustal rocks and minerals, widespread volatilization of various species, including hydrates, and formation of dry, rigid, refractory crust.

Fused Bead Analysis of Diogenite Meteorites

NASA Technical Reports Server (NTRS)

Mittlefehldt, D.W.; Beck, B.W.; McSween, H.Y.; Lee, C.T. A.

2009-01-01

Bulk rock chemistry is an essential dataset in meteoritics and planetary science [1]. A common method used to obtain the bulk chemistry of meteorites is ICP-MS. While the accuracy, precision and low detection limits of this process are advantageous [2], the sample size used for analysis (approx.70 mg) can be a problem in a field where small and finite samples are the norm. Fused bead analysis is another bulk rock analytical technique that has been used in meteoritics [3]. This technique involves forming a glass bead from 10 mg of sample and measuring its chemistry using a defocused beam on a microprobe. Though the ICP-MS has lower detection limits than the microprobe, the fused bead method destroys a much smaller sample of the meteorite. Fused bead analysis was initially designed for samples with near-eutectic compositions and low viscosities. Melts generated of this type homogenize at relatively low temperatures and produce primary melts near the sample s bulk composition [3]. The application of fused bead analysis to samples with noneutectic melt compositions has not been validated. The purpose of this study is to test if fused bead analysis can accurately determine the bulk rock chemistry of non-eutectic melt composition meteorites. To determine this, we conduct two examinations of the fused bead. First, we compare ICP-MS and fused bead results of the same samples using statistical analysis. Secondly, we inspect the beads for the presence of crystals and chemical heterogeneity. The presence of either of these would indicate incomplete melting and quenching of the bead.

Continous Monitoring of Melt Composition

NASA Technical Reports Server (NTRS)

Frazer, R. E.; Andrews, T. W.

1984-01-01

Compositions of glasses and alloys analyzed and corrected in real time. Spectral analysis and temperature measurement performed simultaneously on molten material in container, such as open-hearth furnace, crucible or tank of continuous furnace. Speed of analysis makes it possible to quickly measure concentration of volatile elements depleted by prolonged heating.

Comment on 'Water-fluxed melting of the continental crust: A review' by R.F. Weinberg and P. Hasalová

NASA Astrophysics Data System (ADS)

Clemens, J. D.; Stevens, G.

2015-10-01

In this invited 'review' article, the authors come to the conclusion that fluid-present partial melting reactions are of widespread occurrence and critical importance in the processes of high-grade metamorphism and crustal differentiation. In their abstract, the authors correctly restate the conclusions of Clemens and Droop (1998) that it is not necessarily the case that melts formed by fluid-present reactions (even by H2O-saturated melting) cannot leave their sources. This realisation is not actually relevant to the question of formation and ascent of granitic magmas by crustal partial melting. Although they refer to Clemens and Watkins (2001), the authors seem ignore the main point of the argument presented therein, namely that the distribution of temperature and H2O contents in felsic igneous systems is only compatible with derivation of the magmas by fluid-absent partial melting reactions at high-temperature, granulite-facies conditions. Neither fluid-saturated nor fluid-deficient partial melting could have resulted in the observed covariation in temperature and melt H2O content.

Multicomponent homogeneous alloys and method for making same

DOEpatents

Dutta, Partha S.; Miller, Thomas R.

2003-09-02

The present application discloses a method for preparing a homogeneous ternary or quaternary alloy from a quaternary melt. The method includes providing a family of phase diagrams for the quaternary melt which shows (i) composition/temperature data, (ii) tie lines connecting equilibrium liquid and solid compositions, and (iii) isotherms representing boundaries of a miscibility gap. Based on the family of phase diagrams, a quaternary melt composition and an alloy growth temperature is selected. A quaternary melt having the selected quaternary melt composition is provided and a ternary or quaternary alloy is grown from the quaternary melt at the selected alloy growth temperature. A method for making homogeneous ternary or quaternary alloy from a ternary or quaternary melt is also disclosed, as are homogeneous quaternary single-crystal alloys which are substantially free from crystal defects and which have the formula A.sub.x B.sub.1-x C.sub.y D.sub.1-y, x and y being the same or different and in the range of 0.001 to 0.999.

Numerical study of melt flow under the influence of heater-generating magnetic field during directional solidification of silicon ingots

NASA Astrophysics Data System (ADS)

Li, Zaoyang; Qi, Xiaofang; Liu, Lijun; Zhou, Genshu

2018-02-01

The alternating current (AC) in the resistance heater for generating heating power can induce a magnetic field in the silicon melt during directional solidification (DS) of silicon ingots. We numerically study the influence of such a heater-generating magnetic field on the silicon melt flow and temperature distribution in an industrial DS process. 3D simulations are carried out to calculate the Lorentz force distribution as well as the melt flow and heat transfer in the entire DS furnace. The pattern and intensity of silicon melt flow as well as the temperature distribution are compared for cases with and without Lorentz force. The results show that the Lorentz force induced by the heater-generating magnetic field is mainly distributed near the top and side surfaces of the silicon melt. The melt flow and temperature distribution, especially those in the upper part of the silicon region, can be influenced significantly by the magnetic field.

Surface texturing of superconductors by controlled oxygen pressure

DOEpatents

Chen, N.; Goretta, K.C.; Dorris, S.E.

1999-01-05

A method of manufacture of a textured layer of a high temperature superconductor on a substrate is disclosed. The method involves providing an untextured high temperature superconductor material having a characteristic ambient pressure peritectic melting point, heating the superconductor to a temperature below the peritectic temperature, establishing a reduced pO{sub 2} atmosphere below ambient pressure causing reduction of the peritectic melting point to a reduced temperature which causes melting from an exposed surface of the superconductor and raising pressure of the reduced pO{sub 2} atmosphere to cause solidification of the molten superconductor in a textured surface layer. 8 figs.

Surface texturing of superconductors by controlled oxygen pressure

DOEpatents

Chen, Nan; Goretta, Kenneth C.; Dorris, Stephen E.

1999-01-01

A method of manufacture of a textured layer of a high temperature superconductor on a substrate. The method involves providing an untextured high temperature superconductor material having a characteristic ambient pressure peritectic melting point, heating the superconductor to a temperature below the peritectic temperature, establishing a reduced pO.sub.2 atmosphere below ambient pressure causing reduction of the peritectic melting point to a reduced temperature which causes melting from an exposed surface of the superconductor and raising pressure of the reduced pO.sub.2 atmosphere to cause solidification of the molten superconductor in a textured surface layer.

Hybrid analysis (barcode-high resolution melting) for authentication of Thai herbal products, Andrographis paniculata (Burm.f.) Wall.ex Nees.

PubMed

Osathanunkul, Maslin; Suwannapoom, Chatmongkon; Khamyong, Nuttaluck; Pintakum, Danupol; Lamphun, Santisuk Na; Triwitayakorn, Kanokporn; Osathanunkul, Kitisak; Madesis, Panagiotis

2016-01-01

Andrographis paniculata Nees is a medicinal plant with multiple pharmacological properties. It has been used over many centuries as a household remedy. A. paniculata products sold on the markets are in processed forms so it is difficult to authenticate. Therefore buying the herbal products poses a high-risk of acquiring counterfeited, substituted and/or adulterated products. Due to these issues, a reliable method to authenticate products is needed. High resolution melting analysis coupled with DNA barcoding (Bar-HRM) was applied to detect adulteration in commercial herbal products. The rbcL barcode was selected to use in primers design for HRM analysis to produce standard melting profile of A. paniculata species. DNA of the tested commercial products was isolated and their melting profiles were then generated and compared with the standard A. paniculata. The melting profiles of the rbcL amplicons of the three closely related herbal species (A. paniculata, Acanthus ebracteatus and Rhinacanthus nasutus) are clearly separated so that they can be distinguished by the developed method. The method was then used to authenticate commercial herbal products. HRM curves of all 10 samples tested are similar to A. paniculata which indicated that all tested products were contained the correct species as labeled. The method described in this study has been proved to be useful in aiding identification and/or authenticating A. paniculata. This Bar-HRM analysis has allowed us easily to determine the A. paniculata species in herbal products on the markets even they are in processed forms. We propose the use of DNA barcoding combined with High Resolution Melting analysis for authenticating of Andrographis paniculata products.The developed method can be used regardless of the type of the DNA template (fresh or dried tissue, leaf, and stem).rbcL region was chosen for the analysis and work well with our samplesWe can easily determine the A. paniculata species in herbal products tested. Abbreviations used: bp: Base pair, Tm: Melting temperature.

The Optimisation of Processing Condition for Injected Mould Polypropylene-Nanoclay-Gigantochloa Scortechinii based on Melt Flow Index

NASA Astrophysics Data System (ADS)

Othman, M. H.; Rosli, M. S.; Hasan, S.; Amin, A. M.; Hashim, M. Y.; Marwah, O. M. F.; Amin, S. Y. M.

2018-03-01

The fundamental knowledge of flow behaviour is essential in producing various plastic parts injection moulding process. Moreover, the adaptation of advanced polymer-nanocomposites such as polypropylene-nanoclay with natural fibres, for instance Gigantochloa Scortechinii may boost up the mechanical properties of the parts. Therefore, this project was proposed with the objective to optimise the processing condition of injected mould polypropylene-nanoclay-Gigantochloa Scortechini fibres based on the flow behaviour, which was melt flow index. At first, Gigantochloa Scortechinii fibres have to be preheated at temperature 120°C and then mixed with polypropylene, maleic anhydride modified polypropylene oligomers (PPgMA) and nanoclay by using Brabender Plastograph machine. Next, forms of pellets were produced from the samples by using Granulator machine for use in the injection moulding process. The design of experiments that was used in the injection moulding process was Taguchi Method Orthogonal Array -L934. Melt Flow Index (MF) was selected as the response. Based on the results, the value of MFI increased when the fiber content increase from 0% to 3%, which was 17.78 g/10min to 22.07 g/10min and decreased from 3% to 6%, which was 22.07 g/10min to 20.05 g/10min and 3%, which gives the highest value of MFI. Based on the signal to ratio analysis, the most influential parameter that affects the value of MFI was the melt temperature. The optimum parameter for 3% were 170°C melt temperature, 35% packing pressure, 30% screw speed and 3 second filling time.

Use and Limitations of a Climate-Quality Data Record to Study Temperature Trends on the Greenland Ice Sheet

NASA Technical Reports Server (NTRS)

Hall, Dorothy K.; Comiso, Josefino C.; Shuman, Christopher A.; Koenig, Lora S.; DiGirolamo, Nicolo E.

2011-01-01

Enhanced melting of the Greenland Ice Sheet has been documented in recent literature along with surface-temperature increases measured using infrared satellite data since 1981. Using a recently-developed climate-quality data record, 11- and 12-year trends in the clear-sky ice-surface temperature (IST) of the Greenland Ice Sheet have been studied using the Moderate-Resolution Imaging Spectroradiometer (MODIS) IST product. Daily and monthly MODIS ISTs of the Greenland Ice Sheet beginning on 1 March 2000 and continuing through 31 December 2010 are now available at 6.25-km spatial resolution on a polar stereographic grid as described in Hall et al. (submitted). This record will be elevated in status to a climate-data record (CDR) when more years of data become available either from the MODIS on the Terra or Aqua satellites, or from the Visible Infrared Imager Radiometer Suite (VIIRS) to be launched in October 2011. Maps showing the maximum extent of melt for the entire ice sheet and for the six major drainage basins have been developed from the MODIS IST dataset. Twelve-year trends of the duration of the melt season on the ice sheet vary in different drainage basins with some basins melting progressively earlier over the course of the study period. Some (but not all) of the basins also show a progressively-longer duration of melt. IST 12-year trends are compared with in-situ data, and climate data from the Modern Era Retrospective-Analysis for Research and Applications (MERRA) Reanalysis.

Response of Arctic Snow and Sea Ice Extents to Melt Season Atmospheric Forcing Across the Land-Ocean Boundary

NASA Astrophysics Data System (ADS)

Bliss, A. C.; Anderson, M. R.

2011-12-01

Little research has gone into studying the concurrent variations in the annual loss of continental snow cover and sea ice extent across the land-ocean boundary, however, the analysis of these data averaged spatially over three study regions located in North America and Eastern and Western Russia, reveals a distinct difference in the response of anomalous snow and sea ice conditions to the atmospheric forcing. This study compares the monthly continental snow cover and sea ice extent loss in the Arctic, during the melt season months (May-August) for the period 1979-2007, with regional atmospheric conditions known to influence summer melt including: mean sea level pressures, 925 hPa air temperatures, and mean 2 m U and V wind vectors from NCEP/DOE Reanalysis 2. The monthly hemispheric snow cover extent data used are from the Rutgers University Global Snow Lab and sea ice extents for this study are derived from the monthly passive microwave satellite Bootstrap algorithm sea ice concentrations available from the National Snow and Ice Data Center. Three case study years (1985, 1996, and 2007) are used to compare the direct response of monthly anomalous sea ice and snow cover areal extents to monthly mean atmospheric forcing averaged spatially over the extent of each study region. This comparison is then expanded for all summer months over the 29 year study period where the monthly persistence of sea ice and snow cover extent anomalies and changes in the sea ice and snow conditions under differing atmospheric conditions are explored further. The monthly anomalous atmospheric conditions are classified into four categories including: warmer temperatures with higher pressures, warmer temperatures with lower pressures, cooler temperatures with higher pressures, and cooler temperatures with lower pressures. Analysis of the atmospheric conditions surrounding anomalous loss of snow and ice cover over the independent study regions indicates that conditions of warmer temperatures advected via southerly winds are effective at forcing melt, while conditions of anomalously cool temperatures with persistent, strong northeasterly winds in the later melt season months are also effective at removing anomalous extents of sea ice cover, likely through ice divergence. Normalized sea ice extent anomalies, regardless of the snow cover, tend to persist in the same positive or negative directions (or remain near normal) from month to month over the summer season in 73.6% of cases from June to July, in 69% of cases from July to August, and in 54% of cases for the entire season (June-August) for the 29 year study period. However, when shifts in the sea ice extent anomaly directions from the conditions present in the early melt season occur, it is generally associated with a shift in the atmospheric conditions forcing the change in sea ice extent loss for the region.

Experimental Constraints on the Partitioning Behavior of F, Cl, and OH Between Apatite and Basaltic Melt

NASA Technical Reports Server (NTRS)

McCubbin, Francis M.; Barnes, Jessica J.; Vander Kaaden, Kathleen E.; Boyce, Jeremy W.; Ustunisik, Gokce; Whitson, Eric S.

2017-01-01

The mineral apatite is present in a wide range of planetary materials. The presence of volatiles (F, Cl, and OH) within its crystal structure (X-site) have motivated numerous studies to investigate the partitioning behavior of F, Cl, and OH between apatite and silicate melt with the end goal of using apatite to constrain the volatile contents of planetary magmas and mantle sources. A number of recent experimental studies have investigated the apatite-melt partitioning behavior of F, Cl, and OH in magmatic systems. Apatite-melt partitioning of volatiles are best described as exchange equilibria similar to Fe-Mg partitioning between olivine and silicate melt. However, the partitioning behavior is likely to change as a function of temperature, pressure, oxygen fugacity, apatite composition, and melt composition. In the present study, we have conducted experiments to assess the partitioning behavior of F, Cl, and OH between apatite and silicate melt over a pressure range of 0-6 gigapascals, a temperature range of 950-1500 degrees Centigrade, and a wide range of apatite ternary compositions. All of the experiments were conducted between iron-wustite oxidation potentials IW minus 1 and IW plus 2 in a basaltic melt composition. The experimental run products were analyzed by a combination of electron probe microanalysis and secondary ion mass spectrometry (NanoSIMS). Temperature, apatite crystal chemistry, and pressure all play important roles in the partitioning behavior of F, Cl, and OH between apatite and silicate melt. In portions of apatite ternary space that undergo ideal mixing of F, Cl, and OH, exchange coefficients remain constant at constant temperature and pressure. However, exchange coefficients vary at constant temperature (T) and pressure (P) in portions of apatite compositional space where F, Cl, and OH do not mix ideally in apatite. The variation in exchange coefficients exhibited by apatite that does not undergo ideal mixing far exceeds the variations induced by changes in temperature (T) or pressure (P) . In regions where apatite undergoes ideal mixing of F, Cl, and OH, temperature has a stronger effect than pressure on the partitioning behavior, but both are important. Furthermore, fluorine becomes less compatible in apatite with increasing pressure and temperature. We are still in the process of analyzing our experimental run products, but we plan to quantify the effects of P and T on apatite-melt partitioning of F, Cl, and OH.

Thermal Diffusivity for III-VI Semiconductor Melts at Different Temperatures

NASA Technical Reports Server (NTRS)

Ban, H.; Li, C.; Lin, B.; Emoto, K.; Scripa, R. N.; Su, C.-H.; Lehoczky, S. L.

2004-01-01

The change of the thermal properties of semiconductor melts reflects the structural changes inside the melts, and a fundamental understanding of this structural transformation is essential for high quality semiconductor crystal growth process. This paper focused on the technical development and the measurement of thermal properties of III-VI semiconductor melts at high temperatures. Our previous work has improved the laser flash method for the specialized quartz sample cell. In this paper, we reported the results of our recent progress in further improvements of the measurement system by minimizing the free convection of the melt, adding a front IR detector, and placing the sample cell in a vacuum environment. The results for tellurium and selenium based compounds, some of which have never been reported in the literature, were obtained at different temperatures as a function of time. The data were compared with other measured thermophysical properties to shed light on the structural transformations of the melt.

Melting temperatures of H2O up to 72 GPa measured in a diamond anvil cell using CO2 laser heating technique.

PubMed

Kimura, T; Kuwayama, Y; Yagi, T

2014-02-21

The melting curve of H2O from 49 to 72 GPa was determined by using a laser-heated diamond anvil cell. Double-sided CO2 laser heating technique was employed in order to heat the sample directly. Discontinuous changes of the heating efficiency attributed to the H2O melting were observed between 49 and 72 GPa. The obtained melting temperatures at 49 and 72 GPa are 1200 and 1410 K, respectively. We found that the slope of the melting curve significantly decreases with increasing pressure, only 5 K/GPa at 72 GPa while 44 K/GPa at 49 GPa. Our results suggest that the melting curve does not intersect with the isentropes of Uranus and Neptune, and hence, H2O should remain in the liquid state even at the pressure and temperature conditions found deep within Uranus and Neptune.

Temperature Compensated Piezoelectric Materials

DTIC Science & Technology

1976-06-01

and indicated no major phase changes between room temperature and the melting point of LijSiO-,. Various shielding — 1 .2- arrangements and...experiments. The DTA experiments showed a small endothermic peak at about 1030° and then the melting point at 1200oC. High temperature x-ray diffraction... melting point was lowered about 150° es* so that a boule could be grown without extraneous heat shields, but the boulep were still cracked. A thin

A theoretical approach to study the melting temperature of metallic nanowires

DOE Office of Scientific and Technical Information (OSTI.GOV)

Arora, Neha; Joshi, Deepika P.

2016-05-23

The physical properties of any material change with the change of its size from bulk range to nano range. A theoretical study to account for the size and shape effect on melting temperature of metallic nanowires has been done. We have studied zinc (Zn), indium (In), lead (Pb) and tin (Sn) nanowires with three different cross sectional shapes like regular triangular, square and regular hexagonal. Variation of melting temperature with the size and shape is graphically represented with the available experimental data. It was found that melting temperature of the nanowires decreases with decrement in the size of nanowire, duemore » to surface effect and at very small size the most probable shape also varies with material.« less

Cooling vests with phase change materials: the effects of melting temperature on heat strain alleviation in an extremely hot environment.

PubMed

Gao, Chuansi; Kuklane, Kalev; Holmér, Ingvar

2011-06-01

A previous study by the authors using a heated thermal manikin showed that the cooling rates of phase change material (PCM) are dependent on temperature gradient, mass, and covering area. The objective of this study was to investigate if the cooling effects of the temperature gradient observed on a thermal manikin could be validated on human subjects in extreme heat. The subjects wore cooling vests with PCMs at two melting temperatures (24 and 28°C) and fire-fighting clothing and equipment, thus forming three test groups (vest24, vest28 and control group without the vest). They walked on a treadmill at a speed of 5 km/h in a climatic chamber (air temperature = 55°C, relative humidity = 30%, vapour pressure = 4,725 Pa, and air velocity = 0.4 m/s). The results showed that the PCM vest with a lower melting temperature (24°C) has a stronger cooling effect on the torso and mean skin temperatures than that with a higher melting temperature (28°C). Both PCM vests mitigate peak core temperature increase during the resting recovery period. The two PCM vests tested, however, had no significant effect on the alleviation of core temperature increase during exercise in the heat. To study the possibility of effective cooling of core temperature, cooling garments with PCMs at even lower melting temperatures (e.g. 15°C) and a larger covering area should be investigated.

Liquidus Diagram of the Ba-Y-Cu-O System in the Vicinity of the Ba2YCu3O6+x Phase Field

PubMed Central

Wong-Ng, Winnie; Cook, Lawrence P.

1998-01-01

This paper describes the melting equilibria in the vicinity of the high Tc phase Ba2YCu3O6+x, including evidence for two Ba-Y-Cu-O immiscible liquids. Melting equilibria have been investigated in purified air using a combination of differential thermal analysis (DTA), thermogravimetric analysis (TGA), powder x-ray diffraction (XRD), MgO wick entrapment of liquid for analysis, scanning electron microscopy (SEM) coupled with energy dispersive x-ray analysis (EDS), and hydrogen reduction for determination of copper oxidation state. For relatively barium-rich compositions, it was necessary to prepare the starting materials under controlled atmosphere conditions using BaO. A liquidus diagram was derived from quantitative data for the melts involved in various melting reactions. In general the 1/2(Y2O3) contents of the melts participating in these equilibria were low (mole fraction <4 %). The primary phase field of Ba2YCu3O6+x occurs at a mole fraction of <2.0 % 1/2Y2O3 and lies very close along the BaO-CuOx edge, extending from a mole fraction of ≈43 % CuO to a mole fraction of ≈76 % CuO. It is divided by a liquid miscibility gap and extends on either side about this gap. The topological sequence of melting reactions associated with the liquidus is presented as a function of temperature. Implications for the growth of Ba2YCu3O6+x crystals are discussed. PMID:28009382

Sintering mechanism of the CaF2 on hydroxyapatite by a 10.6-l microm CO2 laser.

PubMed

Wu, Cheng-Chei; Roan, Rong-Tai; Chen, Jeng-Huey

2002-01-01

Laser has been reported as a heat source for melting and re-crystallization. Occurring at about 1100 degrees C, the melting of surface dental enamel along with re-crystallization might have an assistant role in the therapy of hypersensitive tooth, apical sealing of endodontic surgery in dentistry, preventive dentistry for pit and fissure sealing, and fluoridation. For laser to be accepted in clinical applications, it is desired that, studies must show the incorporation of CaF(2) into hydroxyapatite could reduce the sintering temperature for the sake of safety. In this study, the Sharplan 20XJ CO(2) laser with 10.6- microm wavelength was set under the following parameters: power, 5 W; repetitive mode, 0.1 second; beam, focused. Fluorite was added to hydroxyapatite as a synthetic compound to lower the sintering temperature. Human dental enamel without caries was used for in vitro sintering test. Scanning electron microscopy (SEM), X-ray diffractometer (XRD), Fourier transforming infrared spectroscopy (FTIR), and differential thermal analysis/thermogravimetric analysis (DAT/TGA) were used for the investigation of sintering mechanism of CaF(2). Fusion between hexagonal shape crystals and cubic shape crystals (CaF(2)) were observed under SEM study. Hexagonal shape crystals indicated the formation of fluorapatite under XRD analysis. Under FTIR study, we examined reductions of water (3445 cm(-1)) and hydroxyl bands (3567 and 627 cm(-1)) in irradiated compounds. From the DTA pattern of synthetic compound, it showed the endothermic reaction reaching its peak point around 1180 +/- 20 degrees C. It was attributed to the phase transformation and/or initial melting. In this study, we proposed the interrelationship of the eutectics between initiator (CaF(2)) and the reaction product (calcium hydroxide) that reduced the sintering temperature. It appeared that the co-eutectics interacted to reduce the sintering temperature of hydroxyapatite below 800 degrees C and that the key eutectic was calcium hydroxide. The clinical feasibility of the melting and re-crystallization of hydroxyapatite under 10.6-microm CO(2) laser would be therefore enhanced. Copyright 2002 Wiley-Liss, Inc.

When Does the Warmest Water Reach Greenland?

NASA Astrophysics Data System (ADS)

Grist, J. P.; Josey, S. A.; Boehme, L.; Meredith, M. P.; Laidre, K. L.; Heide-Jørgensen, M. P.; Kovacs, K. M.; Lydersen, C.; Davidson, F. J. M.; Stenson, G. B.; Hammill, M. O.; Marsh, R.; Coward, A.

2016-02-01

The warmest water reaching the east and west coast of Greenland is found between 200 and 600 m, in the warm Atlantic Water Layer (WL). Temperature changes within the WL have been highlighted as a possible cause of accelerated melting of tidewater glaciers and therefore are an important consideration for understanding global sea level rise. However, a limited number of winter observations of the WL have prohibited determining its seasonal variability. To address this, temperature data from Argo profiling floats, a range of sources within the World Ocean Database, and unprecedented coverage from marine-mammal borne sensors have been analyzed for the period 2002-2011. A significant seasonal range in temperature ( 1-2°C) is found in the warm layer, in contrast to most of the surrounding ocean. The magnitude of the seasonal cycle is thus comparable with the 1990s warming that was associated with an increased melt rate in a marine terminating glacier of West Greenland. The phase of the seasonal cycle exhibits considerable spatial variability; with high-resolution ocean model trajectory analysis suggesting it is determined by the time taken for waters to be advected from the subduction site in the Irminger Basin. For western Greenland, the annual temperature maximum occurs near or after the turn of the calendar year. This is significant because a recent study suggested that it is in the non-summer months when fjord-shelf exchanges allow the WL to most strongly influence glacier melt rate. However this is also the time of the year when the WL is least well observed. It is therefore clear that year-round subsurface temperature measurements are still required for a complete description of the WL seasonality, and in particular to ensure that the ice-melting potential of the WL is not underestimated.

Rapid detection and differentiation of avian infectious bronchitis virus: an application of Mass genotype by melting temperature analysis in RT-qPCR using SYBR Green I

PubMed Central

OKINO, Cintia Hiromi; MONTASSIER, Maria de Fátima Silva; de OLIVEIRA, Andressa Peres; MONTASSIER, Helio José

2018-01-01

A method based on Melting Temperature analysis of Hypervariable regions (HVR) of S1 gene within a RT-qPCR was developed to detect different genotypes of avian infectious bronchitis virus (IBV) and identify the Mass genotype. The method was able to rapidly identify the Mass genotype among IBV field isolates, vaccine attenuated strains and reference M41 strain in allantoic liquid and also directly in tissues. The RT-qPCR developed detected the virus in both tracheal and pulmonary samples from M41-infected or H120-infected birds, in a larger post-infection period compared to detection by standard method of virus isolation. RT-qPCR method tested provided a sensitivity and rapid approach for screening on IBV detection and Mass genotyping from IBV isolates. PMID:29491226

Thermal properties of polyethylene reinforced with recycled–poly (ethylene terephthalate) flakes.

NASA Astrophysics Data System (ADS)

Ruqiyah Nik Hassan, Nik; Mazni Ismail, Noor; Ghazali, Suriati; Nuruzzaman, Dewan Muhammad

2018-04-01

In this study, recycled plastic bottles (RPET) were used as a filler in high density polyethylene (HDPE) thermoplastic. The plastic sheet of RPET/HDPE was prepared by using hot and cold press machine. The effects of RPET addition and hot press process to the thermal properties of the composite RPET/HDPE were investigated using differential scanning calorimetry (DSC) and thermogravimetric (TGA). Results from DSC analysis show that the melting point of HDPE slightly shifted to a higher temperature for about 2°C to 4°C with the addition of RPET as a filler. The starting degradation temperature of RPET/HDPE composite examined from TGA analysis also seen to be slightly increased. It was observed that the incorporation of recycled PET flakes into HDPE is achievable using hot press process with slight improvement seen in both melting point and thermal stability of the composite compared to the neat HDPE.

Molecular dynamics study of CO2 hydrate dissociation: Fluctuation-dissipation and non-equilibrium analysis.

PubMed

English, Niall J; Clarke, Elaine T

2013-09-07

Equilibrium and non-equilibrium molecular dynamics (MD) simulations have been performed to investigate thermal-driven break-up of planar CO2 hydrate interfaces in liquid water at 300-320 K. Different guest compositions, at 85%, 95%, and 100% of maximum theoretical occupation, led to statistically-significant differences in the observed initial dissociation rates. The melting temperatures of each interface were estimated, and dissociation rates were observed to be strongly dependent on temperature, with higher dissociation rates at larger over-temperatures vis-à-vis melting. A simple coupled mass and heat transfer model developed previously was applied to fit the observed dissociation profiles, and this helps to identify clearly two distinct régimes of break-up; a second well-defined region is essentially independent of composition and temperature, in which the remaining nanoscale, de facto two-dimensional system's lattice framework is intrinsically unstable. From equilibrium MD of the two-phase systems at their melting point, the relaxation times of the auto-correlation functions of fluctuations in number of enclathrated guest molecules were used as a basis for comparison of the variation in the underlying, non-equilibrium, thermal-driven dissociation rates via Onsager's hypothesis, and statistically significant differences were found, confirming the value of a fluctuation-dissipation approach in this case.

Micro- and nano-CT textural analysis of an experimental volcanic fulgurite.

NASA Astrophysics Data System (ADS)

Cimarelli, Corrado; Yilmaz, Tim; Colombier, Mathieu; Villanova, Julie; Höfer, Lucas; Hess, Kai-Uwe; Ruthensteiner, Bernhard; Dingwell, Donald

2017-04-01

Fulgurites are natural glasses formed by cloud to ground lightning discharges causing rapid heating into rocks or unconsolidated sediments. Volcanic lightning can determine the re-melting and even ablation of newly formed or just deposited volcanic tephra during explosive eruptions. In this case the pristine material is already constituted by glass that can be further modified by the discharge. Although volcanic lightning discharges are generally less energetic than those produced by thunderclouds, the high temperatures reached by the lightning channel are well in excess of the low melting temperature of glass material. Here we have experimentally reproduced a fulgurite by single impulse voltage discharges (134 kV, 331 A, 10.5 J) on a target glass material. We have chosen borosilicate glass fibers (180 microns nominal length) as starting material to better account for the structural and chemical modification of the single particles after discharge-melting. The structure of the small fulgurite is best resolved through X-ray micro- and nano-computed tomography. Micro-CT analysis was carried out on a phoenix nanotom m with a voxelsize of 1 µm3. Additionally a 3D reconstruction with a voxel size of 150 nm3 has been analyzed at the new nano-analysis beamline ID16B at the ESRF. 3D analysis was carried out using Avizo 9.2 software, which allows non-destructive analysis of the fragile structure of the sample. The sample shows the channel-like structure typical for natural fulgurites with an inner void channel and internal wall constituted by the melted fibers. About 33% of the total solid volume of the fulgurite is melted to form the inner wall. The inner wall is characterized by nano- to micro-metric vesicles determined by volatile exsolution (mainly H2O) during the instantaneous heating and trapped in the low viscosity melt by the subsequent rapid quenching. Progressively outward the fulgurite shows the intricate delicate structure of the pristine glass fibers. Our results demonstrate that structural and chemical alteration of low viscosity glass material is possible by small impulse discharges with relatively low currents, thus reproducing a plausible scenario for electrical discharges during volcanic eruptions. Our experiment opens the opportunity for systematic constrained experimental investigation of the modification induced by volcanic lightning on tephra.

Application of temporal moments and other signal processing algorithms to analysis of ultrasonic signals through melting wax

DOE PAGES

Lau, Sarah J.; Moore, David G.; Stair, Sarah L.; ...

2016-01-01

Ultrasonic analysis is being explored as a way to capture events during melting of highly dispersive wax. Typical events include temperature changes in the material, phase transition of the material, surface flows and reformations, and void filling as the material melts. Melt tests are performed with wax to evaluate the usefulness of different signal processing algorithms in capturing event data. Several algorithm paths are being pursued. The first looks at changes in the velocity of the signal through the material. This is only appropriate when the changes from one ultrasonic signal to the next can be represented by a linearmore » relationship, which is not always the case. The second tracks changes in the frequency content of the signal. The third algorithm tracks changes in the temporal moments of a signal over a full test. This method does not require that the changes in the signal be represented by a linear relationship, but attaching changes in the temporal moments to physical events can be difficult. This study describes the algorithm paths applied to experimental data from ultrasonic signals as wax melts and explores different ways to display the results.« less

Analysis of the shrinkage at the thick plate part using response surface methodology

NASA Astrophysics Data System (ADS)

Hatta, N. M.; Azlan, M. Z.; Shayfull, Z.; Roselina, S.; Nasir, S. M.

2017-09-01

Injection moulding is well known for its manufacturing process especially in producing plastic products. To measure the final product quality, there are lots of precautions to be taken into such as parameters setting at the initial stage of the process. Sometimes, if these parameters were set up wrongly, defects may be occurred and one of the well-known defects in the injection moulding process is a shrinkage. To overcome this problem, a maximisation at the precaution stage by making an optimal adjustment on the parameter setting need to be done and this paper focuses on analysing the shrinkage by optimising the parameter at thick plate part with the help of Response Surface Methodology (RSM) and ANOVA analysis. From the previous study, the outstanding parameter gained from the optimisation method in minimising the shrinkage at the moulded part was packing pressure. Therefore, with the reference from the previous literature, packing pressure was selected as the parameter setting for this study with other three parameters which are melt temperature, cooling time and mould temperature. The analysis of the process was obtained from the simulation by Autodesk Moldflow Insight (AMI) software and the material used for moulded part was Acrylonitrile Butadiene Styrene (ABS). The analysis and result were obtained and it found that the shrinkage can be minimised and the significant parameters were found as packing pressure, mould temperature and melt temperature.

High-Melting Lipid Mixtures and the Origin of Detergent-Resistant Membranes Studied with Temperature-Solubilization Diagrams

PubMed Central

Sot, Jesús; Manni, Marco M.; Viguera, Ana R.; Castañeda, Verónica; Cano, Ainara; Alonso, Cristina; Gil, David; Valle, Mikel; Alonso, Alicia; Goñi, Félix M.

2014-01-01

The origin of resistance to detergent solubilization in certain membranes, or membrane components, is not clearly understood. We have studied the solubilization by Triton X-100 of binary mixtures composed of egg sphingomyelin (SM) and either ceramide, diacylglycerol, or cholesterol. Solubilization has been assayed in the 4–50°C range, and the results are summarized in a novel, to our knowledge, form of plots, that we have called temperature-solubilization diagrams. Despite using a large detergent excess (lipid/detergent 1:20 mol ratio) and extended solubilization times (24–48 h) certain mixtures were not amenable to Triton X-100 solubilization at one or more temperatures. DSC of all the lipid mixtures, and of all the lipid + detergent mixtures revealed that detergent resistance was associated with the presence of gel domains at the assay temperature. Once the system melted down, solubilization could occur. In general adding high-melting lipids limited the solubilization, whereas the addition of low-melting lipids promoted it. Lipidomic analysis of Madin-Darby canine kidney cell membranes and of the corresponding detergent-resistant fraction indicated a large enrichment of the nonsolubilized components in saturated diacylglycerol and ceramide. SM-cholesterol mixtures were special in that detergent solubilization was accompanied, for certain temperatures and compositions, by an independent phenomenon of reassembly of the partially solubilized lipid bilayers. The temperature at which lysis and reassembly prevailed was ∼25°C, thus for some SM-cholesterol mixtures solubilization occurred both above and below 25°C, but not at that temperature. These observations can be at the origin of the detergent resistance effects observed with cell membranes, and they also mean that cholesterol-containing detergent-resistant membrane remnants cannot correspond to structures existing in the native membrane before detergent addition. PMID:25517149

X-ray sensing materials stability: influence of ambient storage temperature on essential thermal properties of undoped vitreous selenium

NASA Astrophysics Data System (ADS)

Tonchev, D.; Mani, H.; Belev, G.; Kostova, I.; Kasap, S.

2014-12-01

Amorphous selenium (a-Se) is currently used in x-ray image detectors as an x-ray photoconductor. Normally a-Se films used in device applications are fabricated by the evaporation of vitreous bulk material loaded into boats in a typical vacuum deposition system. The resistance against crystallization is an important factor in both film and bulk forms of a-Se. Previous work has indicted that the resistance to crystallization is surprisingly more pronounced around 35 °C [1]. In this work we have therefore examined the essential thermal properties of vitreous selenium (99.999%) samples that have been stored at different temperatures. The thermal characterization experiments involved a series of DSC (Differential Scanning Calorimetry) measurements in which have monitored the glass transition and melting endotherms, and the crystallization exotherm in heating-cooling-heating scans. In DSC experiments, a sample would be heated to a temperature above the melting temperature, equilibrated, then cooled at a fixed rate down to 20 °C, then equilibrated and finally scanned again under a heating schedule. The samples were isothermally stored at temperatures corresponding to 18, 35 and 55 °C. The thermal analysis results show that there are distinct differences in the thermal properties. We have examined the stability in terms of the difference in the crystallization onset temperature (Tc) and the onset of glass transition temperature (Tg). We also examined the Hruby coefficient (Kgl) of these samples, that is Kgl = (Tc - Tg)/(Tm - Tc) where Tc is the crystallization onset temperature and Tm is the melting onset temperature. We have found Kgl to depend on the storage temperature. Surprisingly, we observed that the Hruby coefficient is actually larger at 35 °C compared to the values at 18 and 55 °C.

Effect of calcium and phosphorus, residual lactose, and salt-to-moisture ratio on the melting characteristics and hardness of cheddar cheese during ripening.

PubMed

Chevanan, N; Muthukumarappan, K

2007-05-01

Meltability, melt profile parameters, and hardness of cheddar cheese prepared with varying levels of calcium (Ca) and phosphorus (P) content, residual lactose content, and salt-to-moisture ratio were studied at 0, 1, 2, 4, 6, and 8 mo of ripening. Meltability, melt profile parameters, and hardness of cheddar cheeses measured at 0, 1, 2, 4, 6, and 8 mo of ripening showed significant interaction between the levels of Ca and P, residual lactose, salt-to-moisture ratio, and ripening time for most of the properties studied. cheddar cheese prepared with high Ca and P (0.67% Ca and 0.53% P) resulted in up to 6.2%, 4.5%, 9.6%, 5.0%, and 22.8% increase in softening time, softening temperature, melting time, melting temperature, and hardness, respectively, and 23.5%, 9.6%, and 3.2% decrease in meltability, flow rate, and extent of flow, respectively, compared to the cheddar cheese prepared with low Ca and P (0.53% Ca and 0.39% P). cheddar cheese prepared with high lactose (1.4%) content resulted in up to 7.7%, 7.0%, 4.9%, 4.2%, and 24.6% increase in softening time, softening temperature, melting time, melting temperature, and hardness, respectively, and 14.7%, 12.7%, and 2.8% decrease in meltability, flow rate, and extent of flow respectively compared to the cheddar cheese prepared with low lactose (0.78%) content. cheddar cheese prepared with high salt-to-moisture ratio (6.4%) resulted in up to 21.8%, 11.3%, 12.9%, 4.1%, and 29.4% increase in softening time, softening temperature, melting time, melting temperature, and hardness, respectively, and 13.2%, 28.6%, and 2.6% decrease in meltability, flow rate, and extent of flow, respectively, compared to the cheddar cheese prepared with low salt-to-moisture ratio (4.8%) during ripening.

Melting Penetration Simulation of Fe-U System at High Temperature Using MPS_LER

NASA Astrophysics Data System (ADS)

Mustari, A. P. A.; Yamaji, A.; Irwanto, Dwi

2016-08-01

Melting penetration information of Fe-U system is necessary for simulating the molten core behavior during severe accident in nuclear power plants. For Fe-U system, the information is mainly obtained from experiment, i.e. TREAT experiment. However, there is no reported data on SS304 at temperature above 1350°C. The MPS_LER has been developed and validated to simulate melting penetration on Fe-U system. The MPS_LER modelled the eutectic phenomenon by solving the diffusion process and by applying the binary phase diagram criteria. This study simulates the melting penetration of the system at higher temperature using MPS_LER. Simulations were conducted on SS304 at 1400, 1450 and 1500°C. The simulation results show rapid increase of melting penetration rate.

Simulated glass-forming polymer melts: dynamic scattering functions, chain length effects, and mode-coupling theory analysis.

PubMed

Frey, S; Weysser, F; Meyer, H; Farago, J; Fuchs, M; Baschnagel, J

2015-02-01

We present molecular-dynamics simulations for a fully flexible model of polymer melts with different chain length N ranging from short oligomers (N = 4) to values near the entanglement length (N = 64). For these systems we explore the structural relaxation of the supercooled melt near the critical temperature T c of mode-coupling theory (MCT). Coherent and incoherent scattering functions are analyzed in terms of the idealized MCT. For temperatures T > T c we provide evidence for the space-time factorization property of the β relaxation and for the time-temperature superposition principle (TTSP) of the α relaxation, and we also discuss deviations from these predictions for T ≈ T c. For T larger than the smallest temperature where the TTSP holds we perform a quantitative analysis of the dynamics with the asymptotic MCT predictions for the late β regime. Within MCT a key quantity, in addition to T c, is the exponent parameter λ. For the fully flexible polymer models studied we find that λ is independent of N and has a value (λ = 0.735 ) typical of simple glass-forming liquids. On the other hand, the critical temperature increases with chain length toward an asymptotic value T c (∞) . This increase can be described by T c (∞) - T c(N) ∼ 1/N and may be interpreted in terms of the N dependence of the monomer density ρ, if we assume that the MCT glass transition is ruled by a soft-sphere-like constant coupling parameter Γ c = ρ c T c (-1/4), where ρ c is the monomer density at T c. In addition, we also estimate T c from a Hansen-Verlet-like criterion and MCT calculations based on structural input from the simulation. For our polymer model both the Hansen-Verlet criterion and the MCT calculations suggest T c to decrease with increasing chain length, in contrast to the direct analysis of the simulation data.

Macrosegregation During Re-melting and Holding of Directionally Solidified Al-7 wt.% Si Alloy in Microgravity

NASA Astrophysics Data System (ADS)

Lauer, M.; Ghods, M.; Angart, S. G.; Grugel, R. N.; Tewari, S. N.; Poirier, D. R.

2017-08-01

As-cast aluminum-7 wt.% ailicon alloy sample rods were re-melted and directionally solidified on Earth which resulted in uniform dendritically aligned arrays. These arrays were then partially back-melted through an imposed, and constant, temperature gradient in the microgravity environment aboard the International Space Station. The mushy zones that developed in the seed crystals were held for different periods prior to initiating directional solidification. Upon return, examination of the initial mushy-zone regions exhibited significant macrosegregation in terms of a solute-depleted zone that increased as a function of the holding time. The silicon (solute) content in these regions was measured on prepared longitudinal sections by electron microprobe analysis as well as by determining the fraction eutectic on several transverse sections. The silicon content was found to increase up the temperature gradient resulting in significant silicon concentration immediately ahead of the mushy-zone tips. The measured macrosegregation agrees well with calculations from a mathematical model developed to simulate the re-melting and holding process. The results, due to processing in a microgravity environment where buoyancy and thermosolutal convection are minimized, serve as benchmark solidification data.

Assessment for Melting Temperature Measurement of Nucleic Acid by HRM

PubMed Central

2016-01-01

High resolution melting (HRM), with a high sensitivity to distinguish the nucleic acid species with small variations, has been widely applied in the mutation scanning, methylation analysis, and genotyping. For the aim of extending HRM for the evaluation of thermal stability of nucleic acid secondary structures on sequence dependence, we investigated effects of the dye of EvaGreen, metal ions, and impurities (such as dNTPs) on melting temperature (T m) measurement by HRM. The accuracy of HRM was assessed as compared with UV melting method, and little difference between the two methods was found when the DNA T m was higher than 40°C. Both insufficiency and excessiveness of EvaGreen were found to give rise to a little bit higher T m, showing that the proportion of dye should be considered for precise T m measurement of nucleic acids. Finally, HRM method was also successfully used to measure T ms of DNA triplex, hairpin, and RNA duplex. In conclusion, HRM can be applied in the evaluation of thermal stability of nucleic acid (DNA or RNA) or secondary structural elements (even when dNTPs are present). PMID:27833775

Caldron For High-Temperature Alloys

NASA Technical Reports Server (NTRS)

Geringer, Henry J.

1989-01-01

Induction-heated caldron melts high-temperature alloys. Prevents sort of contamination of melts occurring during arc melting in ceramic crucibles. Liquefies 200 grams of solid metal components of alloy like niobium aluminum and makes alloy homogeneous in less than 3 minutes. Plugged sleeve constitutes main body of caldron. Coolant flows through sleeve to prevent it from melting. Mandrel-wound induction coils adjusted to tune source of power. Also serves as mold for casting alloys into such shapes as bars.

Molecular mechanism of melting of a helical polymer crystal: Role of conformational order, packing and mobility of polymers

NASA Astrophysics Data System (ADS)

Cheerla, Ramesh; Krishnan, Marimuthu

2018-03-01

The molecular mechanism of melting of a superheated helical polymer crystal has been investigated using isothermal-isobaric molecular dynamics simulation that allows anisotropic deformation of the crystal lattice. A detailed microscopic analysis of the onset and progression of melting and accompanying changes in the polymer conformational order, translational, and orientation order of the solid along the melting pathway is presented. Upon gradual heating from room temperature to beyond the melting point at ambient pressure, the crystal exhibits signatures of premelting well below the solid-to-liquid melting transition at the melting point. The melting transition is manifested by abrupt changes in the crystal volume, lattice energy, polymer conformation, and dynamical properties. In the premelting stage, the crystal lattice structure and backbone orientation of the polymer chains are retained but with the onset of weakening of long-range helical order and interchain packing of polymers perpendicular to the fibre axis of the crystal. The premelting also marks the onset of conformational defects and anisotropic solid-state diffusion of polymers along the fibre axis. The present study underscores the importance of the interplay between intermolecular packing, interactions, and conformational dynamics at the atomic level in determining the macroscopic melting behavior of polymer crystals.

Measuring the Surface Temperature of the Cryosphere using Remote Sensing

NASA Technical Reports Server (NTRS)

Hall, Dorothy K.

2012-01-01

A general description of the remote sensing of cryosphere surface temperatures from satellites will be provided. This will give historical information on surface-temperature measurements from space. There will also be a detailed description of measuring the surface temperature of the Greenland Ice Sheet using Moderate-Resolution Imaging Spectroradiometer (MODIS) data which will be the focus of the presentation. Enhanced melting of the Greenland Ice Sheet has been documented in recent literature along with surface-temperature increases measured using infrared satellite data since 1981. Using a recently-developed climate data record, trends in the clear-sky ice-surface temperature (IST) of the Greenland Ice Sheet have been studied using the MODIS IST product. Daily and monthly MODIS ISTs of the Greenland Ice Sheet beginning on 1 March 2000 and continuing through 31 December 2010 are now freely available to download at 6.25-km spatial resolution on a polar stereographic grid. Maps showing the maximum extent of melt for the entire ice sheet and for the six major drainage basins have been developed from the MODIS IST dataset. Twelve-year trends of the duration of the melt season on the ice sheet vary in different drainage basins with some basins melting progressively earlier over the course of the study period. Some (but not all) of the basins also show a progressively-longer duration of melt. The consistency of this IST record, with temperature and melt records from other sources will be discussed.

Structure and Thermal Expansion of YSZ and La 2Zr 2O 7 Above 1500°C from Neutron Diffraction on Levitated Samples

DOE PAGES

Ushakov, Sergey V.; Navrotsky, Alexandra; Weber, Richard J. K.; ...

2015-07-28

High-temperature time-of-flight neutron diffraction experiments were performed in this paper on cubic yttria-stabilized zirconia (YSZ, 10 mol% YO 1.5) and lanthanum zirconate (LZ) prepared by laser melting. Three spheroids of each composition were aerodynamically levitated and rotated in argon flow and heated with a CO 2 laser. Unit cell, positional and atomic displacement parameters were obtained by Rietveld analysis. Below ~1650°C the mean thermal expansion coefficient (TEC) for YSZ is higher than for LZ (13 ± 1 vs. 10.3 ± 0.6) × 10 -6/K. From ~1650°C to the onset of melting of LZ at ~2250°C, TEC for YSZ and LZmore » are similar and within (7 ± 2) × 10 -6/K. LZ retains the pyrochlore structure up to the melting temperature with Zr coordination becoming closer to perfectly octahedral. Congruently melting LZ is La deficient. The occurrence of thermal disordering of oxygen sublattice (Bredig transition) in defect fluorite structure was deduced from the rise in YSZ TEC to ~25 × 10 -6/K at 2350°C–2550°C with oxygen displacement parameters (U iso) reaching 0.1 Å 2, similar to behavior observed in UO 2. Acquisition of powder-like high-temperature neutron diffraction data from solid-levitated samples is feasible and possible improvements are outlined. Finally, this methodology should be applicable to a wide range of materials for high-temperature applications.« less

High temperature investigation of the solid/liquid transition in the PuO2-UO2-ZrO2 system

NASA Astrophysics Data System (ADS)

Quaini, A.; Guéneau, C.; Gossé, S.; Sundman, B.; Manara, D.; Smith, A. L.; Bottomley, D.; Lajarge, P.; Ernstberger, M.; Hodaj, F.

2015-12-01

The solid/liquid transitions in the quaternary U-Pu-Zr-O system are of great interest for the analysis of core meltdown accidents in Pressurised Water Reactors (PWR) fuelled with uranium-dioxide and MOX. During a severe accident the Zr-based cladding can become completely oxidised due to the interaction with the oxide fuel and the water coolant. In this framework, the present analysis is focused on the pseudo-ternary system UO2-PuO2-ZrO2. The melting/solidification behaviour of five pseudo-ternary and one pseudo-binary ((PuO2)0.50(ZrO2)0.50) compositions have been investigated experimentally by a laser heating method under pre-set atmospheres. The effects of an oxidising or reducing atmosphere on the observed melting/freezing temperatures, as well as the amount of UO2 in the sample, have been clearly identified for the different compositions. The oxygen-to-metal ratio is a key parameter affecting the melting/freezing temperature because of incongruent vaporisation effects. In parallel, a detailed thermodynamic model for the UO2-PuO2-ZrO2 system has been developed using the CALPHAD method, and thermodynamic calculations have been performed to interpret the present laser heating results, as well as the high temperature behaviour of the cubic (Pu,U,Zr)O2±x-c mixed oxide phase. A good agreement was obtained between the calculated and experimental data points. This work enables an improved understanding of the major factors relevant to severe accident in nuclear reactors.

Reactive Melt Infiltration of Silicon-Niobium Alloys in Microporous Carbons

NASA Technical Reports Server (NTRS)

Singh, M.; Behrendt, D. R.

1994-01-01

Studies of the reactive melt infiltration of silicon-niobium alloys in microporous carbon preforms prepared by the pyrolysis of a polymer precursor have been carried out using modeling, Differential Thermal Analysis (DTA), and melt infiltration. Mercury porosimetry results indicate a very narrow pore size distribution with virtually all the porosity within the carbon preforms open to infiltrants. The morphology and amount of the residual phases (niobium disilicide and silicon) in the infiltrated material can be tailored according to requirements by careful control of the properties (pore size and pore volume) of the porous carbon preforms and alloy composition. The average room temperature four-point flexural strength of a reaction-formed silicon carbide material (made by the infiltration of medium pore size carbon preform with Si - 5 at. % Nb alloy) is 290 +/- 40 MPa (42 +/- 6 ksi) and the fracture toughness is 3.7 +/- 0.3 MPa square root of m. The flexural strength decreases at high temperatures due to relaxation of residual thermal stresses and the presence of free silicon in the material.

A Binary Eutectic Mixture of TNAZ and R-Salt Explosives

NASA Astrophysics Data System (ADS)

Sandstrom, Mary; Manner, Virginia; Pemberton, Steven; Lloyd, Joseph; Tappan, Bryce

2011-06-01

TNAZ is a high performing explosive that is melt castable. However, the casting process can be problematic since TNAZ has a high vapor pressure exacerbated by a fairly high melting temperature. In order to mitigate the ill effects of its high vapor pressure, including a lower melting explosive was explored by making a series of mixtures of TNAZ and R-Salt. Initially, a eutectic temperature and composition was theoretically determined. Then a phase diagram was constructed from a series and mixtures by differential scanning calorimetery (DSC). The vapor pressure of the eutectic composition was determined by thermogravimetric analysis (TGA). Cylinder testing of the eutectic composition was carried out in copper tubes, 5'' long with 1/2 ``inner diameter and 1/16'' thick walls. The detonation velocity was measured using wire switches along the cylinder length and the expanding wall velocity was measured using PDV gauges. A rough evaluation of JWL equation-of-state parameters has been carried out. A more detailed evaluation is in progress.

Thermodynamic limitations on the resolution obtainable with metal replicas.

PubMed

Woodward, J T; Zasadzinski, J A

1996-12-01

The major factor limiting resolution of metal-shadowed surfaces for electron and scanning tunnelling microscopy is the granularity of the metal film. This granularity had been believed to result from a recrystallization of the evaporated film, and hence could be limited by use of higher melting point materials for replication, or inhibited by adding carbon or other impurities to the film. However, evaporated and sputtered films of amorphous metal alloys that do not crystallize also show a granularity that decreases with increasing alloy melting point. A simple thermodynamic analysis shows that the granularity results from a dewetting of the typically low surface energy sample by the high surface energy metal film, similar to the beading up of drops of spilled mercury. The metal granularity and the resulting resolution of the metal-coated surface is proportional to the mobility of the metal on the surface after evaporation, which is related to the difference in temperature between the melting point of the metal and the sample surface temperature.

Comparison between the liquidus temperature and triple-point temperature of tin realized by heat pulse-based melting

NASA Astrophysics Data System (ADS)

Joung, Wukchul; Pearce, Jonathan V.; Park, Jihye

2018-06-01

In this work, the consistency of the heat pulse-based melting technique, which was used to determine the liquidus temperature of tin, was examined by comparing the liquidus temperatures of tin at 101 325 Pa and at the vapour pressure of tin (i.e. the triple-point temperature), both of which were realized by heat pulse-based melting. Periodic square wave-type temperature steps with an amplitude of 0.7 °C were generated in the isothermal region of the pressure-controlled loop heat pipe, and the tin sample, having a segregated impurity distribution established by the prior outward slow freezing, was melted by application of the temperature step-based heat pulses. The triple-point temperature was found to be lower than the liquidus temperature of tin at 101 325 Pa by 3.23 mK with an expanded measurement uncertainty of 0.24 mK (i.e. a coverage factor of k  =  2), while the ideal temperature difference calculated from the ITS-90 given pressure coefficient (i.e. 3.3  ×  10‑8 K Pa‑1) is about 3.34 mK. The difference between the measured temperature difference and ideal temperature difference was attributed to the incomplete removal of the gases in the tin triple-point cell. Overall, these results further corroborated the notion that the heat pulse-based melting technique was shown to yield results consistent with the prescription of the ITS-90, and to be a reliable method in terms of the realization of the fixed-point temperatures.

3-D Modeling of Directional Solidification of a Non-Dilute Alloy with Temperature and Concentration Fields Coupling via Materials Properties Dependence and via Double Diffusive Convection

NASA Technical Reports Server (NTRS)

Bune, Andris V.; Gillies, Donald C.; Lehoczky, Sandor L.

1998-01-01

Numerical simulation of the HgCdTe growth by the vertical Bridgman method was performed using FIDAP finite element code. Double-diffusive melt convection is analyzed, as the primary factor at controls inhomogeneity of the solidified material. Temperature and concentration fields in the model are also coupled via material properties, such as thermal and solutal expansion coefficients with the dependence on both temperature and concentration, and melting temperature evaluation from pseudobinary CdTe-HgTe phase diagram. Experimental measurements were used to obtain temperature boundary conditions. Parametric study of the melt convection dependence on the gravity conditions was undertaken. It was found, that the maximum convection velocity in the melt can be reduced under certain conditions. Optimal conditions to obtain a near flat solidified interface are discussed. The predicted interface shape is in agreement with one obtained experimentally by quenching. The results of 3-D calculations are compared with previous 2- D findings. A video film featuring 3-D melt convection will be presented.

Density of jadeite melts under high pressure and high temperature conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

SAKAMAKI, Tatsuya

2017-01-01

The density of the jadeite (NaAlSi2O6) melt has been measured up to 6.5 GPa and 2273 K using the X–ray absorption technique at beamline 13–BM–D of the Advanced Photon Source. A fit of the pressure–density–temperature data to the high temperature Birch–Murnaghan equation of state yielded the following thermoelastic parameters: density, ρ0 = 2.36 g/cm3, isothermal bulk modulus, KT0 = 21.5 ± 0.8 GPa, its pressure derivative, K0' = 8.9 ± 1.2, and the temperature derivative (∂KT/∂T)P = -0.0021 ± 0.0011 GPa/K at a reference temperature T0 = 1473 K. The densification of jadeite melt at low pressures is primarily dominatedmore » by topological changes in the structure, including a decrease in T–O–T angle and breaking and reforming of the T–O bond (T = Si4+, Al3+). Compressibilities of jadeite, albite, diopside, phonolite and peridotite melts display a systematic trend: the K0–K0' plot of these silicate melts exhibits an inverse linear relation.« less

Melting Point Depression and Fast Diffusion in Nanostructured Brazing Fillers Confined Between Barrier Nanolayers

NASA Astrophysics Data System (ADS)

Kaptay, G.; Janczak-Rusch, J.; Jeurgens, L. P. H.

2016-08-01

Successful brazing using Cu-based nanostructured brazing fillers at temperatures much below the bulk melting temperature of Cu was recently demonstrated (Lehmert et al. in, Mater Trans 56:1015-1018, 2015). The Cu-based nano-fillers are composed of alternating nanolayers of Cu and a permeable, non-wetted AlN barrier. In this study, a thermodynamic model is derived to estimate the melting point depression (MPD) in such Cu/AlN nano-multilayers (NMLs) as function of the Cu nanolayer thickness. Depending on the melting route, the model predicts a MPD range of 238-609 K for Cu10nm/AlN10nm NMLs, which suggests a heterogeneous pre-melting temperature range of 750-1147 K (476-874 °C), which is consistent with experimental observations. As suggested by basic kinetic considerations, the observed Cu outflow to the NML surface at the temperatures of 723-1023 K (450-750 °C) can also be partially rationalized by fast solid-state diffusion of Cu along internal interfaces, especially for the higher temperatures.

Semicrystalline polyamide engineering thermoplastics based on the renewable monomer, 1,9-nonane diamine: Thermal properties and water absorption

DOE PAGES

Kugel, Alex; He, Jie; Samanta, Satyabrata; ...

2012-08-27

Here, a series of poly(1,9-nonamethylene adipamide-co-1,9-nonamethylene terephthalamide) copolymers were produced using melt polymerization and the thermal properties, crystal structure, and moisture uptake characterized. The results confirmed that the copolymers exhibit isomorphism. As expected, glass transition temperature and the apparent melting temperature increased with increasing terephthalmide content. Using the difference in the apparent melting temperature to the crystallization temperature as a measure of relative crystallization rate, it was observed that crystallization rate decreased as the terephthalamide content of the copolymer was increased from 0 to 50 mole percent but then sharply increased when increased beyond 50 mole percent. This behavior maymore » be the result of extensive inter- and intramolecular interactions in the melt associated with terephthalmide units in the polymer chain that nucleate crystallization upon cooling below the equilibrium melting temperature. Comparing the thermal properties of copolymers possessing an excess of terephthalmide units to the commodity polyamide Nylon 6,6, it is believed that these copolymers may have utility as partially renewable engineering thermoplastics.« less

The crystallization of tough thermoplastic resins in the presence of carbon fibers

NASA Technical Reports Server (NTRS)

Theil, Michael H.

1988-01-01

The presence of carbon fibers increased the crystallization rates of both PEEK and PPS thermoplastic polymers. The effect was most pronounced at higher crystallization temperatures. Isothermal crystallization rates were analyzed by applying classical phenomenological nucleation theory. Unusually high values of the so-called Avrami exponent were found for neat PEEK. Isothermal crystallization of PEEK and PPS polymers produced crystalline samples having a wide variety of melting temperatures. The melting as observed by differential scanning calorimetry occurred as dual endotherms which were called primary (higher temperature) and secondary melting peaks. Each primary peak accounted for most of the crystallinity present. The secondary peaks represented the melting of crystallites formed later than those attributable to the primary endotherms. The presence of carbon fibers increased the thermal stability of both PEEK and PPS crystallites as manifested by higher temperatures for the primary melting peaks. This may be attributable to increased crystallite size, greater crystallite perfection, and/or favorable modification of the crystallite interface. Over the range studied, crystallization temperature strongly influenced the positions of the secondary peaks but not the primary peaks.

Antifreeze protein-induced superheating of ice inside Antarctic notothenioid fishes inhibits melting during summer warming

PubMed Central

Cziko, Paul A.; DeVries, Arthur L.; Evans, Clive W.; Cheng, Chi-Hing Christina

2014-01-01

Antifreeze proteins (AFPs) of polar marine teleost fishes are widely recognized as an evolutionary innovation of vast adaptive value in that, by adsorbing to and inhibiting the growth of internalized environmental ice crystals, they prevent death by inoculative freezing. Paradoxically, systemic accumulation of AFP-stabilized ice could also be lethal. Whether or how fishes eliminate internal ice is unknown. To investigate if ice inside high-latitude Antarctic notothenioid fishes could melt seasonally, we measured its melting point and obtained a decadal temperature record from a shallow benthic fish habitat in McMurdo Sound, Antarctica. We found that AFP-stabilized ice resists melting at temperatures above the expected equilibrium freezing/melting point (eqFMP), both in vitro and in vivo. Superheated ice was directly observed in notothenioid serum samples and in solutions of purified AFPs, and ice was found to persist inside live fishes at temperatures more than 1 °C above their eqFMP for at least 24 h, and at a lower temperature for at least several days. Field experiments confirmed that superheated ice occurs naturally inside wild fishes. Over the long-term record (1999–2012), seawater temperature surpassed the fish eqFMP in most summers, but never exceeded the highest temperature at which ice persisted inside experimental fishes. Thus, because of the effects of AFP-induced melting inhibition, summer warming may not reliably eliminate internal ice. Our results expose a potentially antagonistic pleiotropic effect of AFPs: beneficial freezing avoidance is accompanied by melting inhibition that may contribute to lifelong accumulation of detrimental internal ice crystals. PMID:25246548

Antifreeze protein-induced superheating of ice inside Antarctic notothenioid fishes inhibits melting during summer warming.

PubMed

Cziko, Paul A; DeVries, Arthur L; Evans, Clive W; Cheng, Chi-Hing Christina

2014-10-07

Antifreeze proteins (AFPs) of polar marine teleost fishes are widely recognized as an evolutionary innovation of vast adaptive value in that, by adsorbing to and inhibiting the growth of internalized environmental ice crystals, they prevent death by inoculative freezing. Paradoxically, systemic accumulation of AFP-stabilized ice could also be lethal. Whether or how fishes eliminate internal ice is unknown. To investigate if ice inside high-latitude Antarctic notothenioid fishes could melt seasonally, we measured its melting point and obtained a decadal temperature record from a shallow benthic fish habitat in McMurdo Sound, Antarctica. We found that AFP-stabilized ice resists melting at temperatures above the expected equilibrium freezing/melting point (eqFMP), both in vitro and in vivo. Superheated ice was directly observed in notothenioid serum samples and in solutions of purified AFPs, and ice was found to persist inside live fishes at temperatures more than 1 °C above their eqFMP for at least 24 h, and at a lower temperature for at least several days. Field experiments confirmed that superheated ice occurs naturally inside wild fishes. Over the long-term record (1999-2012), seawater temperature surpassed the fish eqFMP in most summers, but never exceeded the highest temperature at which ice persisted inside experimental fishes. Thus, because of the effects of AFP-induced melting inhibition, summer warming may not reliably eliminate internal ice. Our results expose a potentially antagonistic pleiotropic effect of AFPs: beneficial freezing avoidance is accompanied by melting inhibition that may contribute to lifelong accumulation of detrimental internal ice crystals.

Melt structure and self-nucleation of ethylene copolymers

NASA Astrophysics Data System (ADS)

Alamo, Rufina G.

A strong memory effect of crystallization has been observed in melts of random ethylene copolymers well above the equilibrium melting temperature. These studies have been carried out by DSC, x-ray, TEM and optical microscopy on a large number of model, narrow, and broad copolymers with different comonomer types and contents. Melt memory is correlated with self-seeds that increase the crystallization rate of ethylene copolymers. The seeds are associated with molten ethylene sequences from the initial crystals that remain in close proximity and lower the nucleation barrier. Diffusion of all sequences to a randomized melt state is a slow process, restricted by topological chain constraints (loops, knots, and other entanglements) that build in the intercrystalline region during crystallization. Self-seeds dissolve above a critical melt temperature that demarcates homogeneity of the copolymer melt. There is a critical threshold level of crystallinity to observe the effect of melt memory on crystallization rate, thus supporting the correlation between melt memory and the change in melt structure during copolymer crystallization. Unlike binary blends, commercial ethylene-1-alkene copolymers with a range in inter-chain comonomer composition between 1 and about 15 mol % display an inversion of the crystallization rate in a range of melt temperatures where narrow copolymers show a continuous acceleration of the rate. With decreasing the initial melt temperature, broadly distributed copolymers show enhanced crystallization followed by a decrease of crystallization rate. The inversion demarcates the onset of liquid-liquid phase separation (LLPS) and a reduction of self-nuclei due to the strong thermodynamic drive for molecular segregation inside the binodal. The strong effect of melt memory on crystallization rate can be used to identify liquid-liquid phase separation in broadly distributed copolymers, and offers strategies to control the state of copolymer melts in ways of technological relevance for melt processing of LLDPE and other random olefin copolymers. References: B. O. Reid, et al., Macromolecules 46, 6485-6497, 2013 H. Gao, et al., Macromolecules 46, 6498-6506, 2013 A. Mamun et al., Macromolecules 47, 7958-7970, 2014 X. Chen et al., Macromol. Chem. Phys. 216, 1220 -1226, 2015 M. Ren et al., Macromol. Symp. 356, 131-141, 2015 Work supported by the NSF (DMR1105129).

Studies of thermal dissolution of RDX in TNT melt

NASA Astrophysics Data System (ADS)

Suvorova, N. A.; Hamilton, V. T.; Oschwald, D. M.; Balakirev, F. F.; Smilowitz, L. B.; Henson, B. F.

2017-01-01

The thermal response of energetic materials is studied due to its importance in issues of material safety and surety. Secondary high explosives which melt before they thermally decompose present challenging systems to model due to the addition of material flow. Composition B is a particularly challenging system due to its multiphase nature with a low melt component (TNT) and a high melt component (RDX). The dissolution of RDX crystals in molten TNT at the temperature below RDX melting point has been investigated using hot stage microscopy. In this paper, we present data on the dissolution rate of RDX crystals in molten TNT as a function of temperature above the TNT melt.

Kinetic limit of heterogeneous melting in metals.

PubMed

Ivanov, Dmitriy S; Zhigilei, Leonid V

2007-05-11

The velocity and nanoscale shape of the melting front are investigated in a model that combines the molecular dynamics method with a continuum description of the electron heat conduction and electron-phonon coupling. The velocity of the melting front is strongly affected by the local drop of the lattice temperature, defined by the kinetic balance between the transfer of thermal energy to the latent heat of melting, the electron heat conduction from the overheated solid, and the electron-phonon coupling. The maximum velocity of the melting front is found to be below 3% of the room temperature speed of sound in the crystal, suggesting a limited contribution of heterogeneous melting under conditions of fast heating.

Greenland in Warm (1.5 °C) and Warmer (RCP 8.5) Worlds: The Influence of the Paris Agreement on Ice Sheet Surface Melting

NASA Astrophysics Data System (ADS)

Reusch, D. B.

2017-12-01

Melting on the surface of the Greenland ice sheet has been changing dramatically as global air temperatures have increased in recent decades, including melt extent often exceeding the 1981-2010 median through much of the melt season and the onset of intermittent melt moving to earlier in the year. To evaluate potential future change, we investigate surface melting characteristics under both "low" (limited to 1.5 °C) and "high" (RCP 8.5) warming scenarios including analysis of differences in scenario outcomes. Climatologies of melt-relevant variables are developed from two publicly available ensembles of CESM1-CAM5-BGC GCM runs: the 30-member Large Ensemble (CESM LE; Kay et al. 2015) for historical calibration and the RCP 8.5 scenario and the 11-member Low Warming ensemble (CESM LW; Sanderson et al. 2017) for the 1.5 °C scenario. For higher spatial resolution (15 km) and improved polar-centric model physics, we also apply the regional forecast model Polar WRF to decadal subsets (1996-2005; 2071-80) using GCM data archived at sub-daily resolution for boundary conditions. Models were skill-tested against ERA-Interim Reanalysis (ERAI) and AWS observations. For example, CESM LE tends to overpredict both maximum (above-freezing) and minimum daily average surface temperatures compared to observations from the GC-Net Swiss Camp AWS. Ensembles of members differing only by initial conditions allow us to also estimate intramodel uncertainty. Historical (1981-2000) CESM LE spatially averaged July temperatures are 2 +/- 0.2 °C cooler than ERAI while local anomalies in individual members reach up to +/- 2 °C. As expected, Greenland does not escape future (2081-2100) warming (and expectations of more widespread surface melting) even in the LW scenario, but positive changes versus ERAI are mostly coastal (2-3 °C) with the interior showing only minor change (+/- 1 °C). In contrast, under RCP 8.5, the entire ice sheet has warmed by 2-6 °C, or a median increase of 5 °C versus LW. Adjusting for the CESM cold bias versus ERAI pushes these values even closer to more frequent melting conditions. We combine these measures of model skill and intramodel variability to develop improved estimates of uncertainty for our estimates of future surface melting based on calibrations of models to passive microwave observations of melting.

Solid state thin film battery having a high temperature lithium alloy anode

DOEpatents

Hobson, David O.

1998-01-01

An improved rechargeable thin-film lithium battery involves the provision of a higher melting temperature lithium anode. Lithium is alloyed with a suitable solute element to elevate the melting point of the anode to withstand moderately elevated temperatures.

Emplacement conditions of komatiite magmas from the 3.49 Ga Komati Formation, Barberton Greenstone Belt, South Africa1

NASA Astrophysics Data System (ADS)

Parman, S. W.; Dann, J. C.; Grove, T. L.; de Wit, M. J.

1997-08-01

This paper provides new constraints on the crystallization conditions of the 3.49 Ga Barberton komatiites. The compositional evidence from igneous pyroxene in the olivine spinifex komatiite units indicates that the magma contained significant quantities of dissolved H2O. Estimates are made from comparisons of the compositions of pyroxene preserved in Barberton komatiites with pyroxene produced in laboratory experiments at 0.1 MPa (1 bar) under anhydrous conditions and at 100 and 200 MPa (1 and 2 kbar) under H2O-saturated conditions on an analog Barberton composition. Pyroxene thermobarometry on high-Ca clinopyroxene compositions from ten samples requires a range of minimum magmatic water contents of 6 wt.% or greater at the time of pyroxene crystallization and minimum emplacement pressures of 190 MPa (6 km depth). Since high-Ca pyroxene appears after 30% crystallization of olivine and spinel, the liquidus H2O contents could be 4 to 6 wt.% H2O. The liquidus temperature of the Barberton komatiite composition studied is between 1370 and 1400°C at 200 MPa under H2O-saturated conditions. When compared to the temperature-depth regime of modern melt generation environments, the komatiite mantle source temperatures are 200°C higher than the hydrous mantle melting temperatures inferred in modern subduction zone environments and 100°C higher than mean mantle melting temperatures estimated at mid-ocean ridges. When compared to previous estimates of komatiite liquidus temperatures, melting under hydrous conditions occurs at temperatures that are ˜ 250°C lower than previous estimates for anhydrous komatiite. Mantle melting by near-fractional, adiabatic decompression takes place in a melting column that spans ˜ 38 km depth range under hydrous conditions. This depth interval for melting is only slightly greater than that observed in modern mid-ocean ridge environments. In contrast, anhydrous fractional melting models of komatiite occur over a larger depth range (˜ 130 km) and place the base of the melting column into the transition zone.

Containerless Manufacture of Glass Optical Fibers

NASA Technical Reports Server (NTRS)

Naumann, R. J.; Ethridge, E. C.

1985-01-01

Contamination and crystallization reduced in proposed process. Solid optical fiber drawn from an acoustically levitated lump of molten glass. New material added in solid form, melted and then moved into main body of molten glass. Single axis acoustic levitation furnances levitate glass melts at temperature up to about 700 degrees C. Processing in unit limited to low-melting temperature glasses.

46 CFR 153.908 - Cargo viscosity and melting point information; measuring cargo temperature during discharge...

Code of Federal Regulations, 2014 CFR

2014-10-01

... 46 Shipping 5 2014-10-01 2014-10-01 false Cargo viscosity and melting point information; measuring... Cargo viscosity and melting point information; measuring cargo temperature during discharge: Categories... lading, a written statement of the following: (1) For Category A or B NLS, the cargo's viscosity at 20 °C...

46 CFR 153.908 - Cargo viscosity and melting point information; measuring cargo temperature during discharge...

Code of Federal Regulations, 2013 CFR

2013-10-01

... 46 Shipping 5 2013-10-01 2013-10-01 false Cargo viscosity and melting point information; measuring... Cargo viscosity and melting point information; measuring cargo temperature during discharge: Categories... lading, a written statement of the following: (1) For Category A or B NLS, the cargo's viscosity at 20 °C...

46 CFR 153.908 - Cargo viscosity and melting point information; measuring cargo temperature during discharge...

Code of Federal Regulations, 2012 CFR

2012-10-01

... 46 Shipping 5 2012-10-01 2012-10-01 false Cargo viscosity and melting point information; measuring... Cargo viscosity and melting point information; measuring cargo temperature during discharge: Categories... lading, a written statement of the following: (1) For Category A or B NLS, the cargo's viscosity at 20 °C...

Greenland ice sheet surface temperature, melt and mass loss: 2000-06

USGS Publications Warehouse

Hall, D.K.; Williams, R.S.; Luthcke, S.B.; DiGirolamo, N.E.

2008-01-01

A daily time series of 'clear-sky' surface temperature has been compiled of the Greenland ice sheet (GIS) using 1 km resolution moderate-resolution imaging spectroradiometer (MODIS) land-surface temperature (LST) maps from 2000 to 2006. We also used mass-concentration data from the Gravity Recovery and Climate Experiment (GRACE) to study mass change in relationship to surface melt from 2003 to 2006. The mean LST of the GIS increased during the study period by ???0.27??Ca-1. The increase was especially notable in the northern half of the ice sheet during the winter months. Melt-season length and timing were also studied in each of the six major drainage basins. Rapid (<15 days) and sustained mass loss below 2000 m elevation was triggered in 2004 and 2005 as recorded by GRACE when surface melt begins. Initiation of large-scale surface melt was followed rapidly by mass loss. This indicates that surface meltwater is flowing rapidly to the base of the ice sheet, causing acceleration of outlet glaciers, thus highlighting the metastability of parts of the GIS and the vulnerability of the ice sheet to air-temperature increases. If air temperatures continue to rise over Greenland, increased surface melt will play a large role in ice-sheet mass loss.

Controlled Electrochemical Deformation of Liquid-Phase Gallium.

PubMed

Chrimes, Adam F; Berean, Kyle J; Mitchell, Arnan; Rosengarten, Gary; Kalantar-zadeh, Kourosh

2016-02-17

Pure gallium is a soft metal with a low temperature melting point of 29.8 °C. This low melting temperature can potentially be employed for creating optical components with changeable configurations on demand by manipulating gallium in its liquid state. Gallium is a smooth and highly reflective metal that can be readily maneuvered using electric fields. These features allow gallium to be used as a reconfigurable optical reflector. This work demonstrates the use of gallium for creating reconfigurable optical reflectors manipulated through the use of electric fields when gallium is in a liquid state. The use of gallium allows the formed structures to be frozen and preserved as long as the temperature of the metal remains below its melting temperature. The lens can be readily reshaped by raising the temperature above the melting point and reapplying an electric field to produce a different curvature of the gallium reflector.

Method of casting articles of a bulk-solidifying amorphous alloy

DOEpatents

Lin, X.; Johnson, W.L.; Peker, A.

1998-08-25

A casting charge of a bulk-solidifying amorphous alloy is cast into a mold from a temperature greater than its crystallized melting temperature, and permitted to solidify to form an article. The oxygen content of the casting charge is limited to an operable level, as excessively high oxygen contents produce premature crystallization during the casting operation. During melting, the casting charge is preferably heated to a temperature above a threshold temperature to eliminate heterogeneous crystallization nucleation sites within the casting charge. The casting charge may be cast from above the threshold temperature, or it may be cooled to the casting temperature of more than the crystallized melting point but not more than the threshold temperature, optionally held at this temperature for a period of time, and thereafter cast. 8 figs.

Method of casting articles of a bulk-solidifying amorphous alloy

DOEpatents

Lin, Xianghong; Johnson, William L.; Peker, Atakan

1998-01-01

A casting charge of a bulk-solidifying amorphous alloy is cast into a mold from a temperature greater than its crystallized melting temperature, and permitted to solidify to form an article. The oxygen content of the casting charge is limited to an operable level, as excessively high oxygen contents produce premature crystallization during the casting operation. During melting, the casting charge is preferably heated to a temperature above a threshold temperature to eliminate heterogeneous crystallization nucleation sites within the casting charge. The casting charge may be cast from above the threshold temperature, or it may be cooled to the casting temperature of more than the crystallized melting point but not more than the threshold temperature, optionally held at this temperature for a period of time, and thereafter cast.

Assessing the effects of different prebiotic dietary oligosaccharides in sheep milk ice cream.

PubMed

Balthazar, C F; Silva, H L A; Vieira, A H; Neto, R P C; Cappato, L P; Coimbra, P T; Moraes, J; Andrade, M M; Calado, V M A; Granato, D; Freitas, M Q; Tavares, M I B; Raices, R S L; Silva, M C; Cruz, A G

2017-01-01

The objective of this study was to assess the effects of different prebiotic dietary oligosaccharides (inulin, fructo-oligosaccharide, galacto-oligossacaride, short-chain fructo-oligosaccharide, resistant starch, corn dietary oligosaccharide and polydextrose) in non-fat sheep milk ice cream processing through physical parameters, water mobility and thermal analysis. Overall, the fat replacement by dietary prebiotic oligosaccharides significantly decreased the melting time, melting temperature and the fraction and relaxation time for fat and bound water (T 22 ) while increased the white intensity and glass transition temperature. The replacement of sheep milk fat by prebiotics in sheep milk ice cream constitutes an interesting option to enhance nutritional aspects and develop a functional food. Copyright © 2016 Elsevier Ltd. All rights reserved.

Thermodynamic Properties of M2EO4, M2Mo x O3 x + 1 and Double Chromates (M = Li, Na, K, Rb, Cs; E = Cr, Mo, W)

NASA Astrophysics Data System (ADS)

Suponitskiy, Yu. L.; Zolotova, E. S.; Dyunin, A. G.; Liashenko, S. E.

2018-03-01

The phase transition temperatures of chromates and molybdates of certain alkali metals, and the melting temperature and enthalpy of polymorphic transformations for tungstates, are determined by means of thermal analysis. Enthalpies of dissolution of rubidium and cesium chromates in water and enthalpies of dissolution of alkali metal tungstates in a melt at 923 K are measured via calorimetry. Standard enthalpies of formation of sought chromates are calculated. The linear correlations between the enthalpies of formation of sulfates, selenates, chromates, tungstates, and molybdates are established, and a linear correlation within - (Δ G o ox)-1-(Δ MV)ox)-1 coordinates is found for isopolymolybdates.

Novel polyimide compositions based on 4,4': Isophthaloyldiphthalic anaydride (IDPA)

NASA Technical Reports Server (NTRS)

Pratt, J. Richard (Inventor); Saintclair, Terry L. (Inventor)

1989-01-01

A series of twelve high temperature, high performance polyimide compositions based on 4,4'-isophthaloyl diphthalic anhydride (IDPA) was prepared and characterized. Tough, film-forming, organic solvent-insoluble polyimides were obtained. Three materials were semicrystalline. Several gave excellent long-term thermooxidative stability by isothermal thermogravimetric analysis (ITGA) at 300 C and 350 C in air when compared to Kapton H film (duPont). One extensively studied material displayed different levels of semicrystallinity over a wide range of final cure time/temperatures. The polyimide from IDPA and 1,3-bis (4-aminophenoxy 4'-benzoyl) benzene exhibited multiple crystallization and melting behavior, implying the existence of two kinetic and two thermodynamic crystallization and melting transitions by differential scanning calorimetry (DSC).

Passive microwave derived snowmelt timing: significance, spatial and temporal variability, and potential applications

NASA Astrophysics Data System (ADS)

Semmens, Kathryn Alese

Snow accumulation and melt are dynamic features of the cryosphere indicative of a changing climate. Spring melt and refreeze timing are of particular importance due to the influence on subsequent hydrological and ecological processes, including peak runoff and green-up. To investigate the spatial and temporal variability of melt timing across a sub-arctic region (the Yukon River Basin (YRB), Alaska/Canada) dominated by snow and lacking substantial ground instrumentation, passive microwave remote sensing was utilized to provide daily brightness temperatures (Tb) regardless of clouds and darkness. Algorithms to derive the timing of melt onset and the end of melt-refreeze, a critical transition period where the snowpack melts during the day and refreezes at night, were based on thresholds for Tb and diurnal amplitude variations (day and night difference). Tb data from the Special Sensor Microwave Imager (1988 to 2011) was used for analyzing YRB terrestrial snowmelt timing and for characterizing melt regime patterns for icefields in Alaska and Patagonia. Tb data from the Advanced Microwave Scanning Radiometer for EOS (2003 to 2010) was used for determining the occurrence of early melt events (before melt onset) associated with fog or rain on snow, for investigating the correlation between melt timing and forest fires, and for driving a flux-based snowmelt runoff model. From the SSM/I analysis: the melt-refreeze period lengthened for the majority of the YRB with later end of melt-refreeze and earlier melt onset; and positive Tb anomalies were found in recent years from glacier melt dynamics. From the AMSR-E analysis: early melt events throughout the YRB were most often associated with warm air intrusions and reflect a consistent spatial distribution; years and areas of earlier melt onset and refreeze had more forest fire occurrences suggesting melt timing's effects extend to later seasons; and satellite derived melt timing served as an effective input for model simulation of discharge in remote, ungauged snow-dominated basins. The melt detection methodology and results present a new perspective on the changing cryosphere, provide an understanding of melt's influence on other earth system processes, and develop a baseline from which to assess and evaluate future change. The temporal and spatial variability conveyed through the regional context of this research may be useful to communities in climate change adaptation planning.

Major and trace element modeling of mid-ocean ridge mantle melting from the garnet to the plagioclase stability fields: Generating local and global compositional variability

NASA Astrophysics Data System (ADS)

Brown, S. M.; Behn, M. D.; Grove, T. L.

2017-12-01

We present results of a combined petrologic - geochemical (major and trace element) - geodynamical forward model for mantle melting and subsequent melt modification. The model advances Behn & Grove (2015), and is calibrated using experimental petrology. Our model allows for melting in the plagioclase, spinel, and garnet fields with a flexible retained melt fraction (from pure batch to pure fractional), tracks residual mantle composition, and includes melting with water, variable melt productivity, and mantle mode calculations. This approach is valuable for understanding oceanic crustal accretion, which involves mantle melting and melt modification by migration and aggregation. These igneous processes result in mid-ocean ridge basalts that vary in composition at the local (segment) and global scale. The important variables are geophysical and geochemical and include mantle composition, potential temperature, mantle flow, and spreading rate. Accordingly, our model allows us to systematically quantify the importance of each of these external variables. In addition to discriminating melt generation effects, we are able to discriminate the effects of different melt modification processes (inefficient pooling, melt-rock reaction, and fractional crystallization) in generating both local, segment-scale and global-scale compositional variability. We quantify the influence of a specific igneous process on the generation of oceanic crust as a function of variations in the external variables. We also find that it is unlikely that garnet lherzolite melting produces a signature in either major or trace element compositions formed from aggregated melts, because when melting does occur in the garnet field at high mantle temperature, it contributes a relatively small, uniform fraction (< 10%) of the pooled melt compositions at all spreading rates. Additionally, while increasing water content and/or temperature promote garnet melting, they also increase melt extent, pushing the pooled composition to lower Sm/Yb and higher Lu/Hf.

The surface morphology of crystals melting under solutions of different densities

NASA Technical Reports Server (NTRS)

Fang, Dacheng; Hellawell, A.

1988-01-01

Examples of solids melting beneath liquids are described for cases where the bulk liquid volume is stabilized against convection by a positive vertical temperature gradient, either with, or without local density inversion at the melting interface. The examples include ice melting beneath brine or methanol solutions and tin or lead melting under molten Sn-20 wt pct Pb or Pb-20 wt pct Sn, respectively. Without density inversion the melting is slow, purely diffusion controlled and the interfaces are smooth; with convection assisted melting the rate increases by some two orders of magnitude and the interfaces develop a rough profile - in the case of ice both irregular and quasi-steady state features are observed. The observations are discussed in terms of prevailing temperature and concentration gradients.

Abrupt Greenland Ice Sheet runoff and sea water temperature changes since 1821, recorded by coralline algae

NASA Astrophysics Data System (ADS)

Kamenos, N.; Hoey, T.; Bedford, J.; Claverie, T.; Fallick, A. E.; Lamb, C. M.; Nienow, P. W.; O'Neill, S.; Shepherd, I.; Thormar, J.

2012-12-01

The Greenland Ice Sheet (GrIS) contains the largest store of fresh water in the northern hemisphere, equivalent to ~7.4m of eustatic sea level rise, but its impacts on current, past and future sea level, ocean circulation and European climate are poorly understood. Previous estimates of GrIS melt, from 26 years of satellite observations and temperature driven melt-models over 48 years, show a trend of increasing melt. There are however no runoff data of comparable duration with which to validate temperature-based runoff models, or relationships between the spatial extent of melt and runoff. Further, longer runoff records that extend GrIS melt records to centennial timescales will enable recently observed trends to be put into a better historical context. We measured Mg/Ca, δ18O and structural cell size in annual growth bands of red coralline algae to reconstruct: (1) near surface sea water temperature; and, (2) melt/runoff from the GrIS. (1) Temperature: we reconstructed the longest (1821-2009) sub-annual resolution record of water temperature in Disko Bugt (western Greenland) showing an abrupt change in temperature oscillation patterns during the 1920s which may be attributable to the interaction between atmospheric temperature and mass loss from Jakobshavn Isbrae glacier. (2) GrIS runoff: using samples from distal parts of Søndre Strømfjord we produced the first reconstruction of decadal (1939-2002) GrIS runoff. We observed significant negative relationships between historic runoff, relative salinity and marine summer temperature. Our reconstruction shows a trend of increasing reconstructed runoff since the mid 1980s. In situ summer marine temperatures followed a similar trend. We suggest that since 1939 atmospheric temperatures have been important in forcing runoff. Subject to locating in situ coralline algae samples, these methods can be applied across hundreds to thousands of years. These results show that our technique has significant potential to enhance understanding of runoff from large ice sheets as it will enable melt reconstruction over centennial-millennial time scales.; Red coralline algal thalli (Lithothamnion glaciale) similar to those used in Greenland reconstructions. Each thallus is 5cm in diameter.

Ice Particle Analysis of the Honeywell AL502 Engine Booster

NASA Technical Reports Server (NTRS)

Bidwell, Colin S.; Rigby, David L.

2015-01-01

A flow and ice particle trajectory analysis was performed for the booster of the Honeywell ALF502 engine. The analysis focused on two closely related conditions one of which produced an icing event and another which did not during testing of the ALF502 engine in the Propulsion Systems Lab (PSL) at NASA Glenn Research Center. The flow analysis was generated using the NASA Glenn GlennHT flow solver and the particle analysis was generated using the NASA Glenn LEWICE3D v3.63 ice accretion software. The inflow conditions for the two conditions were similar with the main differences being that the condition that produced the icing event was 6.8 K colder than the non-icing event case and the inflow ice water content (IWC) for the non-icing event case was 50% less than for the icing event case. The particle analysis, which considered sublimation, evaporation and phase change, was generated for a 5 micron ice particle with a sticky impact model and for a 24 micron median volume diameter (MVD), 7 bin ice particle distribution with a supercooled large droplet (SLD) splash model used to simulate ice particle breakup. The particle analysis did not consider the effect of the runback and re-impingement of water resulting from the heated spinner and anti-icing system. The results from the analysis showed that the amount of impingement for the components were similar for the same particle size and impact model for the icing and non-icing event conditions. This was attributed to the similar aerodynamic conditions in the booster for the two cases. The particle temperature and melt fraction were higher at the same location and particle size for the non-icing event than for the icing event case due to the higher incoming inflow temperature for the non-event case. The 5 micron ice particle case produced higher impact temperatures and higher melt fractions on the components downstream of the fan than the 24 micron MVD case because the average particle size generated by the particle breakup was larger than 5 microns which yielded less warming and melting. The analysis also showed that the melt fraction and wet bulb temperature icing criterion developed during tests in the Research Altitude Test Facility (RATFac) at the National Research Council (NRC) of Canada were useful in predicting icing events in the ALF502 engine. The development of an ice particle impact model which includes the effects of particle breakup, phase change, and surface state is necessary to further improve the prediction of ice particle transport with phase change through turbomachinery.

Density Determination of Metallic Melts from Diffuse X-Ray Scattering

NASA Astrophysics Data System (ADS)

Brauser, N.; Davis, A.; Greenberg, E.; Prakapenka, V. B.; Campbell, A.

2017-12-01

Liquids comprise several important structural components of the deep Earth, for example, the present outer core and a hypothesized magma ocean early in Earth history. However, the physical properties of the constituent materials of these structures at high pressures and temperatures are less well constrained than their crystalline counterparts. Determination of the physical properties of these liquids can inform geophysical models of the composition and structure of the Earth, but methods for studying the physical properties of liquids at high pressure and temperatures are underdeveloped. One proposed method for direct determination of density of a melt requires analysis of the diffuse scattered X-ray signal of the liquid. Among the challenges to applying this technique to high-pressure melts within a laser heated diamond anvil cell are the low signal-to-noise ratio and overlapping diffraction peaks from the crystalline components of the sample assembly interfering with the diffuse scattering from the liquid. Recent advances in instrumentation at synchrotron X-ray sources have made this method more accessible for determination of density of melted material. In this work we present the technique and report the densities of three high-pressure melts of the FCC metals iron, nickel, and gold derived from diffuse scattered X-ray spectra collected from in situ laser-heated diamond anvil cell synchrotron experiments. The results are compared to densities derived from shock wave experiments.

Changing Surface-Atmosphere Energy Exchange and Refreezing Capacity of the Lower Accumulation Area, West Greenland

NASA Astrophysics Data System (ADS)

Charalampidis, C.; van As, D.; Machguth, H.; Smeets, P.; van den Broeke, M. R.; Box, J. E.

2014-12-01

We present five years (2009-2013) of automatic weather station (AWS) data from the lower accumulation area (1840 m above sea level) of the Kangerlussuaq region, western Greenland ice sheet. The summers of 2010 and 2012 were both exceptionally warm, but only 2012 resulted in negative surface mass budget (SMB) and surface runoff. The observed runoff was due to a large ice fraction in the upper 10 m of firn that prevented melt water from percolating to available pore space below. Analysis of the in situ data reveals a relatively low 2012 summer albedo of ~0.7 as melt water was present at the surface. Consequently, during the 2012 melt season the surface absorbed 30% (213 MJ m-2) more solar radiation than in 2010. We drive a surface energy balance model with the AWS data to evaluate the seasonal and interannual variability of all surface energy fluxes. The model is able to reproduce the observed melt rates as well as the SMB for each season. While the drive for melt is solar radiation, year-to-year differences are controlled by terrestrial radiation, apart from 2012 when solar radiation dominated melt. Sensitivity tests reveal that 72% of the excess solar energy in 2012 was used for melt, corresponding to 40% (0.67 m) of the 2012 surface ablation. The remaining ablation (0.99 m) was primarily due to the relatively high atmospheric temperatures up to +2.6 °C daily average, indicating that 2012 would have been a negative SMB year in the lower accumulation area even without the melt-albedo feedback. Longer time series of SMB, regional temperature and remotely sensed albedo (MODIS) suggest that 2012 was the first negative SMB year with the lowest albedo at this elevation on record. The warming conditions of the last years resulted in enhanced melt and reduction of the refreezing capacity of the lower accumulation area. If the warming continues the lower accumulation area will be transformed into superimposed ice.

Meteorological Drivers of West Antarctic Ice Sheet and Ice Shelf Surface Melt

NASA Astrophysics Data System (ADS)

Scott, R. C.; Nicolas, J. P.; Bromwich, D. H.; Norris, J. R.; Lubin, D.

2017-12-01

We identify synoptic patterns and surface energy balance components driving warming and surface melting on the West Antarctic Ice Sheet (WAIS) and ice shelves using reanalysis and satellite remote sensing data from 1973-present. We have developed a synoptic climatology of atmospheric circulation patterns during the summer melt season using k-means cluster and composite analysis of daily 700-mb geopotential height and near-surface air temperature and wind fields from the ECMWF ERA-Interim reanalysis. Surface melt occurrence is detected in satellite passive microwave brightness temperature observations (K-band, horizontal polarization) beginning with the NASA Nimbus-5 Electrically Scanning Microwave Radiometer (ESMR) and continuing with its more familiar descendants SMMR, SSM/I and SSMIS. To diagnose synoptic precursors and physical processes driving surface melt we combine the circulation climatology and multi-decadal records of cloud cover with surface radiative fluxes from the Extended AVHRR Polar Pathfinder (APP-x) project. We identify three distinct modes of regional summer West Antarctic warming since 1979 involving anomalous ridging over West Antarctica (WA) and the Amundsen Sea (AS). During the 1970s, ESMR data reveal four extensive melt events on the Ross Sea sector of the WAIS also linked to AS blocking. We therefore define an Amundsen Sea Blocking Index (ASBI). The ASBI and synoptic circulation pattern occurrence frequencies are correlated with the tropical Pacific (ENSO) and high latitude Southern Annular Mode (SAM) indices and the West Antarctic melt index. Surface melt in WA is favored by enhanced downwelling infrared and turbulent sensible heat fluxes associated with intrusions of warm, moist marine air. Consistent with recent findings from the Atmospheric Radiation Measurement (ARM) West Antarctic Radiation Experiment (AWARE), marine advection to the Ross sector is favored by El Niño conditions in the tropical Pacific and a negative SAM. We also find that El Niño-related blocking favors warming and melting on the marine-based ice streams draining from Wilkes Basin, East Antarctica.

First experimental observations on melting and chemical modification of volcanic ash during lightning interaction.

PubMed

Mueller, S P; Helo, C; Keller, F; Taddeucci, J; Castro, J M

2018-01-23

Electrification in volcanic ash plumes often leads to syn-eruptive lightning discharges. High temperatures in and around lightning plasma channels have the potential to chemically alter, re-melt, and possibly volatilize ash fragments in the eruption cloud. In this study, we experimentally simulate temperature conditions of volcanic lightning in the laboratory, and systematically investigate the effects of rapid melting on the morphology and chemical composition of ash. Samples of different size and composition are ejected towards an artificially generated electrical arc. Post-experiment ash morphologies include fully melted spheres, partially melted particles, agglomerates, and vesiculated particles. High-speed imaging reveals various processes occurring during the short lightning-ash interactions, such as particle melting and rounding, foaming, and explosive particle fragmentation. Chemical analyses of the flash-melted particles reveal considerable bulk loss of Cl, S, P and Na through thermal vaporization. Element distribution patterns suggest convection as a key process of element transport from the interior of the melt droplet to rim where volatiles are lost. Modeling the degree of sodium loss delivers maximum melt temperatures between 3290 and 3490 K. Our results imply that natural lighting strikes may be an important agent of syn-eruptive morphological and chemical processing of volcanic ash.

Reversibility between glass and melting transitions of poly(oxyethylene)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Qui, Wulin; Pyda, Marek; Nowak-Pyda, Elisabieta

2005-01-01

The heat capacities, C{sub p}, of poly(oxyethylene), POE, with molar masses from 1500 to 900,000 Da, were analyzed by differential scanning calorimetry (DSC), quasi-isothermal, temperature-modulated DSC (TMDSC), and wide-angle X-ray diffraction (WAXD). There is no change in crystal structure before melting, but the lattice parameters increase rapidly in the melting region. Perfected extended-chain and once- or twice-folded crystals of the oligomers with a molar mass above 1100 Da melt practically fully irreversibly and permit direct measurement of the thermodynamic C{sub p}. The folded-chain crystals of high molar mass show some locally reversible melting. The reversing, apparent C{sub p} depends onmore » molar mass and amplitude and frequency of modulation. After separation from the latent heat effects, the reversible, thermodynamic C{sub p} depends on the melting temperature for low molar masses and increases beyond the vibrational C{sub p} due to conformational motion. Molar masses of 8000-20,000 have almost the same C{sub p}. These observations permit a quantitative discussion of the thermodynamic C{sub p} and the locally reversible melting of the globally metastable POE in the melting range. The increase in C{sub p} between 250 K and the melting temperature is interpreted as a glass transition within the crystal.« less

Melting and solidification characteristics of a mixture of two types of latent heat storage material in a vessel

NASA Astrophysics Data System (ADS)

Yu, JikSu; Horibe, Akihiko; Haruki, Naoto; Machida, Akito; Kato, Masashi

2016-11-01

In this study, we investigated the fundamental melting and solidification characteristics of mannitol, erythritol, and their mixture (70 % by mass mannitol: 30 % by mass erythritol) as potential phase-change materials (PCMs) for latent heat thermal energy storage systems, specifically those pertaining to industrial waste heat, having temperatures in the range of 100-250 °C. The melting point of erythritol and mannitol, the melting peak temperature of their mixture, and latent heat were measured using differential scanning calorimetry. The thermal performance of the mannitol mixture was determined during melting and solidification processes, using a heat storage vessel with a pipe heat exchanger. Our results indicated phase-change (fusion) temperatures of 160 °C for mannitol and 113 and 150 °C for the mannitol mixture. Nondimensional correlation equations of the average heat transfer during the solidification process, as well as the temperature and velocity efficiencies of flowing silicon oil in the pipe and the phase-change material (PCM), were derived using several nondimensional parameters.

Sn–Ag–Cu nanosolders: Melting behavior and phase diagram prediction in the Sn-rich corner of the ternary system

PubMed Central

Roshanghias, Ali; Vrestal, Jan; Yakymovych, Andriy; Richter, Klaus W.; Ipser, Herbert

2015-01-01

Melting temperatures of Sn–Ag–Cu (SAC) alloys in the Sn-rich corner are of interest for lead-free soldering. At the same time, nanoparticle solders with depressed melting temperatures close to the Sn–Pb eutectic temperature have received increasing attention. Recently, the phase stability of nanoparticles has been the subject of plenty of theoretical and empirical investigations. In the present study, SAC nanoparticles of various sizes have been synthesized via chemical reduction and the size dependent melting point depression of these particles has been specified experimentally. The liquidus projection in the Sn-rich corner of the ternary SAC system has also been calculated as a function of particle size, based on the CALPHAD-approach. The calculated melting temperatures were compared with those obtained experimentally and with values reported in the literature, which revealed good agreement. The model also predicts that with decreasing particle size, the eutectic composition shifts towards the Sn-rich corner. PMID:26082567

Alloy Development, Processing and Characterization of Devitrified Titanium Base Microcrystalline Alloys.

DTIC Science & Technology

1984-12-01

quench rates (10V 10V [/sec). Since the heat transport and temperature profile of Ti melt in the cold copper crucible are not well known, melting...experiments in a cold copper crucible by arc heating were conducted using Ti-6.3Si alloy. The temperature measurement at both the surface and the bottom of the...melt spinning compart- ment B, and ribbon processing chamber C. The pre-melted alloy ingot is . - " charged directly into a cold copper crucible while

The importance of accurate interaction potentials in the melting of argon nanoclusters

NASA Astrophysics Data System (ADS)

Pahl, E.; Calvo, F.; Schwerdtfeger, P.

The melting temperatures of argon clusters ArN (N = 13, 55, 147, 309, 561, and 923) and of bulk argon have been obtained from exchange Monte Carlo simulations and are compared using different two-body interaction potentials, namely the standard Lennard-Jones (LJ), Aziz and extended Lennard-Jones (ELJ) potentials. The latter potential has many advantages: while maintaining the computational efficiency of the commonly used LJ potential, it is as accurate as the Aziz potential but the computer time scales more favorably with increasing cluster size. By applying the ELJ form and extrapolating the cluster data to the infinite system, we are able to extract the melting point of argon already in good agreement with experimental measurements. By considering the additional Axilrod-Teller three-body contribution as well, we calculate a melting temperature of T meltELJ = 84.7 K compared to the experimental value of T meltexp = 83.85 K, whereas the LJ potential underestimates the melting point by more than 7 K. Thus melting temperatures within 1 K accuracy are now feasible.

Superheating of ice crystals in antifreeze protein solutions

PubMed Central

Celik, Yeliz; Graham, Laurie A.; Mok, Yee-Foong; Bar, Maya; Davies, Peter L.; Braslavsky, Ido

2010-01-01

It has been argued that for antifreeze proteins (AFPs) to stop ice crystal growth, they must irreversibly bind to the ice surface. Surface-adsorbed AFPs should also prevent ice from melting, but to date this has been demonstrated only in a qualitative manner. Here we present the first quantitative measurements of superheating of ice in AFP solutions. Superheated ice crystals were stable for hours above their equilibrium melting point, and the maximum superheating obtained was 0.44 °C. When melting commenced in this superheated regime, rapid melting of the crystals from a point on the surface was observed. This increase in melting temperature was more appreciable for hyperactive AFPs compared to the AFPs with moderate antifreeze activity. For each of the AFP solutions that exhibited superheating, the enhancement of the melting temperature was far smaller than the depression of the freezing temperature. The present findings clearly show that AFPs adsorb to ice surfaces as part of their mechanism of action, and this absorption leads to protection of ice against melting as well as freezing. PMID:20215465

Molecular dynamics simulations of spinels: LiMn2O4 and Li4Mn5O12 at high temperatures

NASA Astrophysics Data System (ADS)

Ledwaba, R. S.; Matshaba, M. G.; Ngoepe, P. E.

2015-04-01

Energy storage technologies are critical in addressing the global challenge of clean sustainable energy. Spinel lithium manganates have attracted attention due to their electrochemical properties and also as promising cathode materials for lithium-ion batteries. The current study focused on the effects of high temperatures on the materials, in order to understand the sustainability in cases where the battery heats up to high temperature and analysis of lithium diffusion aids in terms of intercalation host compatibility. It is also essential to understand the high temperature behaviour and lithium ion host capability of these materials in order to perform the armorphization and recrystalization of spinel nano-architectures. Molecular dynamics simulations carried out to predict high temperature behaviour of the spinel systems. The NVE ensemble was employed, in the range 300 - 3000K. The melting temperature, lithium-ion diffusion and structural behaviour were monitored in both supercell systems. LiMn2O4 indicated a diffusion rate that increased rapidly above 1500K, just before melting (˜1700K) and reached its maximum diffusion at 2.756 × 10-7 cm2s-1 before it decreased. Li4Mn5O12 indicated an exponential increase above 700K reaching 8.303 × 10-7 cm2s-1 at 2000K and allowing lithium intercalation even above its melting point of around 1300K. This indicated better structural stability of Li4Mn5O12 and capability to host lithium ions at very high temperatures (up to 3000 K) compared to LiMn2O4.

The genotyping of infectious bronchitis virus in Taiwan by a multiplex amplification refractory mutation system reverse transcription polymerase chain reaction.

PubMed

Huang, Shr-Wei; Ho, Chia-Fang; Chan, Kun-Wei; Cheng, Min-Chung; Shien, Jui-Hung; Liu, Hung-Jen; Wang, Chi-Young

2014-11-01

Infectious bronchitis virus (IBV; Avian coronavirus) causes acute respiratory and reproductive and urogenital diseases in chickens. Following sequence alignment of IBV strains, a combination of selective primer sets was designed to individually amplify the IBV wild-type and vaccine strains using a multiplex amplification refractory mutation system reverse transcription polymerase chain reaction (ARMS RT-PCR) approach. This system was shown to discriminate the IBV wild-type and vaccine strains. Moreover, an ARMS real-time RT-PCR (ARMS qRT-PCR) was combined with a high-resolution analysis (HRMA) to establish a melt curve analysis program. The specificity of the ARMS RT-PCR and the ARMS qRT-PCR was verified using unrelated avian viruses. Different melting temperatures and distinct normalized and shifted melting curve patterns for the IBV Mass, IBV H120, IBV TW-I, and IBV TW-II strains were detected. The new assays were used on samples of lung and trachea as well as virus from allantoic fluid and cell culture. In addition to being able to detect the presence of IBV vaccine and wild-type strains by ARMS RT-PCR, the IBV Mass, IBV H120, IBV TW-I, and IBV TW-II strains were distinguished using ARMS qRT-PCR by their melting temperatures and by HRMA. These approaches have acceptable sensitivities and specificities and therefore should be able to serve as options when carrying out differential diagnosis of IBV in Taiwan and China. © 2014 The Author(s).

Advanced Cooling for High Power Electric Actuators

DTIC Science & Technology

1993-01-01

heat and heat transfer rates. At point B, the fluid temperature reaches the melting temperature of the PCM and it starts to melt , storing energy in the...working fluid through the duty cycle represented by the square wave in the upper half of the figure. Starting at point A, the actuator goes to peak load...form of latent heat. As the solid material melts , the coolant temperature continues to rise, but at a much lower rate, as the heat conducts through the

Structural, compositional, and sensorial properties of United States commercial ice cream products.

PubMed

Warren, Maya M; Hartel, Richard W

2014-10-01

Commercial vanilla ice cream products from the United States (full fat, low fat, and nonfat) were analyzed for their structural, behavioral (i.e., melt rate and drip-through), compositional, and sensorial attributes. Mean size distributions of ice crystals and air cells, drip-through rates, percent partially coalesced fat, percent overrun and total fat, and density were determined. A trained panel carried out sensory analyses in order to determine correlations between ice cream microstructure attributes and sensory properties using a Spectrum(TM) descriptive analysis. Analyses included melt rate, breakdown, size of ice particulates (iciness), denseness, greasiness, and overall creaminess. To determine relationships and interactions, principle component analysis and multivariate pairwise correlation were performed within and between the instrumental and sensorial data. Greasiness and creaminess negatively correlated with drip-through rate and creaminess correlated with percent total fat and percent fat destabilization. Percent fat did not determine the melt rate on a sensorial level. However, drip-through rate at ambient temperatures was predicted by total fat content of the samples. Based on sensory analysis, high-fat products were noted to be creamier than low and nonfat products. Iciness did not correlate with mean ice crystal size and drip-through rate did not predict sensory melt rate. Furthermore, on a sensorial level, greasiness positively correlated with total percent fat destabilization and mean air cell size positively correlated with denseness. These results indicate that commercial ice cream products vary widely in composition, structure, behavior, and sensory properties. There is a wide range of commercial ice creams in the United States market, ranging from full fat to nonfat. In this research we showed that these ice creams vary greatly in their microstructures, behaviors (the melt/drip-though, collapse, and/or stand up properties of ice cream products at ambient temperatures), and sensory properties. © 2014 Institute of Food Technologists®

Solid state thin film battery having a high temperature lithium alloy anode

DOEpatents

Hobson, D.O.

1998-01-06

An improved rechargeable thin-film lithium battery involves the provision of a higher melting temperature lithium anode. Lithium is alloyed with a suitable solute element to elevate the melting point of the anode to withstand moderately elevated temperatures. 2 figs.

Design, fabrication, and evaluation of a partially melted ice particle cloud facility

NASA Astrophysics Data System (ADS)

Soltis, Jared T.

High altitude ice crystal clouds created by highly convective storm cells are dangerous to jet transport aircraft because the crystals are ingested into the compressor section, partially melt, accrete, and cause roll back or flame out. Current facilities to test engine particle icing are not ideal for fundamental mixed-phase ice accretion experiments or do not generate frozen droplet clouds under representative conditions. The goal of this research was to develop a novel facility capable of testing fundamental partially melted ice particle icing physics and to collect ice accretion data related to mixed-phase ice accretion. The Penn State Icing Tunnel (PSIT) has been designed and fabricated to conduct partially melted ice particle cloud accretion. The PSIT generated a cloud with air assisted atomizing nozzles. The water droplets cool from the 60psi pressure drop as the water exited the nozzle and fully glaciate while flowing in the -11.0°C tunnel air flow. The glaciated cloud flowed through a duct in the center of the tunnel where hot air was introduced. The temperature of the duct was regulated from 3.3°C to 24°C which melted particle the frozen particle from 0% to 90%. The partially melted particle cloud impinged on a temperature controlled flat plate. Ice accretion data was taken for a range of duct temperature from 3.3°C to 24°C and plate temperature from -4.5°C to 7.0°C. The particle median volumetric diameter was 23mum, the total water content was 4.5 g/m 3, the specific humidity was 1.12g/kg, and the wet bulb temperature ranged from 1.0°C to 7.0°C depending on the duct temperature. The boundaries between ice particle bounce off, ice accretion, and water run off were determined. When the particle were totally frozen and the plate surface was below freezing, the ice particle bounced off as expected. Ice accretion was seen for all percent melts tested, but the plate temperature boundary between water runoff and ice accretion increased from 0°C at 8% melt to 3°C at 90%. There were two types of ice accretion with a transition zone in between. The first type of ice was opaque in color and had a rough surface. This ice occurred roughly from 6.0°C to 12.0°C duct temperatures (8% to 50% melt). The qualitative characteristics of the ice were produced from the low water content in the cloud. The water that was available froze instantly and trapped ice particle. Duct temperatures greater than 17.5°C (80% melt) produced ice that was clear and smooth. The water in the surface did not freeze instantly due to the high water content creating a water film that froze. A mixed-phase cloud dynamics model from NASA Glenn was used to estimate the percent melt of the cloud exiting the duct. There was no way to validate the model by directly measuring the percent melt of the cloud, so single particle melt experiments were conducted and compared to the model. A 0.05g/L solution of rhodamine b was sprayed into a levitator and droplets formed at the nodes of the wave. A 532nm green laser was used to illuminate the dye, and the water emitted orange 593nm light given the luminescent properties of the ink. The emitted light intensity was recorded, and a linear relationship between the light intensity of ice to the light intensity of water was used to determine the percent melt of a droplet. The droplets were frozen with a cold flow of nitrogen gas via a liquid nitrogen heat exchanger. The droplets melted under natural convection when the cold nitrogen was shut off. Fifteen cases were compared with droplet diameters ranging from 324mum to 1112mum, air temperatures from 16°C to 31°C, and relative humidities from 41% to 100%. The average discrepancy between predictions and results for the cases that melted slower than ten seconds was 13% while the cases that melted faster than 10 second had 64% discrepancy between the model and experiment. To explain the discrepancy between the experiment and model, sensitivity studies of the model were conducted. It was seen that the melt time from the model was most sensitive to ambient temperature (1s/°C). It was also seen that the thermistors used in the experiment were accurate to 0.7°C. Transient effects of the rhodamine b caused an overshoot in light intensity, making it difficult to accurately determine the melting stop time. These factors led to the difference in melt time between the model and experiments. A 2.7s difference between model and experiments was deemed to be a successful correlation between predictions and experimental results given the model sensitivity to temperature, the difficulty in measuring temperatures at the position of the droplet, and the transient characteristics of rhodamine b.

Analytical solutions for combined close-contact and natural convection melting in horizontal cylindrical heat storage capsule

DOE Office of Scientific and Technical Information (OSTI.GOV)

Saitoh, T.S.; Hoshi, A.

1998-07-01

Melting and solidification of a phase change material (PCM) in a capsule is of practical importance in latent heat thermal energy storage (LHTES) systems which are considered to be very promising to reduce a peak demand of electricity in the summer season and carbon dioxide (CO{sub 2}) emissions. Two melting modes are involved in melting of capsules. One is close-contact melting between the solid bulk and the capsule wall, and another is natural convection melting in the liquid region. Close-contact melting processes for a single enclosure have been solved using several numerical methods (e.g., Saitoh and Kato (1994)). In additionmore » close-contact melting heat transfer characteristics including melt flow in the liquid film under inner wall temperature distribution were analyzed and simple approximate equations were already presented by Saitoh and Hoshi (1997). The effects of Stefan number and variable temperature profile etc. were clarified in detail. And the melting velocity of the solid bulk under various conditions was also studied theoretically. In addition the effects of variable inner wall temperature on molten mass fraction were investigated. The present paper reports analytical solutions for combined close-contact and natural convection melting in horizontal cylindrical capsule. Moreover, natural convection melting in the liquid region were analyzed in this report. The upper interface shape of the solid bulk is approximated by a circular arc throughout the melting process. For the sake of verification, close-contact melting heat-transfer characteristics including natural convection in the liquid region were studied experimentally. Apparent shift of upper solid-liquid interface is good agreement with the experiment. The present simple approximate solutions will be useful to facilitate designing of the practical capsule bed LHTES systems.« less

Partial melting of TTG gneisses: crustal contamination and the production of granitic melts

NASA Astrophysics Data System (ADS)

Meade, F. C.; Masotta, M.; Troll, V. R.; Freda, C.; Johnson, T. E.; Dahren, B.

2011-12-01

Understanding partial melting of ancient TTG gneiss terranes is crucial when considering crustal contamination in volcanic systems, as these rocks are unlikely to melt completely at magmatic temperatures (1000-1200 °C) and crustal pressures (<500 MPa). Variations in the bulk composition of the gneiss, magma temperature, pressure (depth) and the composition and abundance of any fluids present will produce a variety of melt compositions, from partial melts enriched in incompatible elements to more complete melts, nearing the bulk chemistry of the parent gneiss. We have used piston cylinder experiments to simulate partial melting in a suite of 12 gneisses from NW Scotland (Lewisian) and Eastern Greenland (Ammassalik, Liverpool Land) under magma chamber temperature and pressure conditions (P=200 MPa, T=975 °C). These gneisses form the basement to much of the North Atlantic Igneous Province, where crustal contamination of magmas was commonplace but the composition of the crustal partial melts are poorly constrained [1]. The experiments produced partial melts in all samples (e.g. Fig 1). Electron microprobe analyses of glasses indicate they are compositionally heterogeneous and are significantly different from the whole rock chemistry of the parent gneisses. The melts have variably evolved compositions but are typically trachy-dacitic to rhyolitic (granitic). This integrated petrological, experimental and in-situ geochemical approach allows quantification of the processes of partial melting of TTG gneiss in a volcanic context, providing accurate major/trace element and isotopic (Sr, Pb) end-members for modeling crustal contamination. The experimental melts and restites will be compared geochemically with a suite of natural TTG gneisses, providing constraints on the extent to which the gneisses have produced and subsequently lost melt. [1] Geldmacher et al. (2002) Scottish Journal of Geology, v.38, p.55-61.

Experimental Investigation of the Viscosity of Iron-rich Silicate Melts under Pressure

NASA Astrophysics Data System (ADS)

Edwards, P. M.; Lesher, C. E.; Pommier, A.; O'Dwyer Brown, L.

2017-12-01

The transport properties of silicate melts govern diffusive flow of momentum, heat, and mass in the interior of terrestrial planets. In particular, constraining melt viscosity is critical for dynamic modeling of igneous processes and is thus key to our understanding of magma convection and mixing, melt migration in the mantle, and crystal-liquid fractionation. Among the different constituents of silicate melts, iron is of significant importance as it highly influences some of their properties, such as surface tension, compressibility, and density. We present an experimental study of the viscosity of natural and synthetic iron-rich silicate melts under pressure. In situ falling-sphere measurements of viscosity have been conducted on hedenbergite (CaFeSi2O6) and iron-rich peridotite melts from 1 to 7 GPa and at temperatures between 1750 and 2100 K, using the multi-anvil apparatus at the GSECARS beamline at the Advanced Photon Source, Argonne National Lab. We used double reservoir capsules, with the bottom reservoir containing the sample, while a more refractory material is placed in the upper reservoir (e.g., diopside, enstatite, forsterite). This configuration allows the fall of two rhenium spheres across the sample at different temperatures. Melt viscosity is calculated using Stokes' law and the terminal velocity of the spheres. We observe that melt viscosity slightly decreases with increasing temperature and increasing pressure: for instance, the viscosity of the hedenbergite melt decreases from 1.26 Pa•s to 0.43 Pa•s over the 1 - 3.5 GPa pressure range and between 1820 and 1930 K. Our experimental data are used to develop a viscosity model of iron-rich silicate melts under pressure. Results will be compared with previous viscosity works on iron-free and iron-bearing silicate liquids in order to discuss the effect of iron on melt viscosity and structure at pressure and temperature conditions relevant to terrestrial mantles.

Simulation results of influence of constricted arc column on anode deformation and melting pool swirl in vacuum arcs with AMF contacts

NASA Astrophysics Data System (ADS)

Wang, Lijun; Zhang, Xiao; Huang, Xiaolong; Jia, Shenli

2017-11-01

In the process of vacuum arc breaking, the energy injected into the anode will cause anode melting, evaporation, and deformation, resulting in the formation of the anode melting pool. The anode activities have great influence on the arc behavior. When the arc current is large enough, even the influence of axial magnetic field is considered, the arc column still is in contraction state, which means the arc burns only on a part of the electrode. In this paper, the model of anode melting pool deformation and rotation is used, and the model includes anode melting and solidification module, magneto-hydro-dynamic module of the anode melting pool, the volume of fraction method, and the current continuity equation. In this paper, the diffuse arc area is selected as 100%, 75%, and 50%, respectively. The anode temperature and deformation, the anode melting layer thickness, and the rotational velocity of the anode melting pool are obtained. The results show that when the current is at 17.5 kA (rms) and the diffuse arc area is 100%, the anode's maximum temperature is 1477 K and the crater depth is 0.83 mm. But when the diffuse arc areas are 75% and 50%, the anode's maximum temperatures reach 1500 K and 1761 K, and the crater depths reach 1.2 mm and 3 mm, respectively. Arc contraction will lead to more serious anode deformation. A similar result is obtained when the simulation current is 12.5 kA. Under the similar situation, the simulation results in the crater depth, the residual melt layer thickness, the rotational speed of the melting pool, and the maximum temperature of the anode at current zero are in good agreement with the experimental results.

Warpage analysis on thin shell part using glowworm swarm optimisation (GSO)

NASA Astrophysics Data System (ADS)

Zulhasif, Z.; Shayfull, Z.; Nasir, S. M.; Fathullah, M.; Hazwan, M. H. M.

2017-09-01

The Autodesk Moldflow Insight (AMI) software was used in this study to focuses on the analysis in plastic injection moulding process associate the input parameter and output parameter. The material used in this study is Acrylonitrile Butadiene Styrene (ABS) as the moulded material to produced the plastic part. The MATLAB sortware is a method was used to find the best setting parameter. The variables was selected in this study were melt temperature, packing pressure, coolant temperature and cooling time.

Three-Phase Melting Curves in the Binary System of Carbon Dioxide and Water

NASA Astrophysics Data System (ADS)

Abramson, E. H.

2017-10-01

Invariant, three-phase melting curves, of ice VI in equilibrium with solid CO2, of ice VII in equilibrium with solid CO2, and of solid CO2 in simultaneous equilibrium with a majority aqueous and a majority CO2 fluid, were explored in the binary system of carbon dioxide and water. Diamond-anvil cells were used to develop pressures of 5 GPa. Water exhibits a large melting temperature depression (73°C less than its pure melting temperature of 253°C at 5 GPa) indicative of large concentrations of CO2 in the aqueous solution. The melting point of water-saturated CO2 does not show a measureable departure from that of the pure system at temperatures lower than ∼200°C and only 10°C at 5 GPa (from 327°C).

Melting and Its Influence on the Long-term Evolution of the Lower Mantle Heterogeneities (LLSVP and ULVZ)

NASA Astrophysics Data System (ADS)

Fomin, I.; Tackley, P. J.

2017-12-01

Recent investigations have shown mantle solidus close to the range of proposed core-mantle boundary (CMB) temperatures (e.g. [Andrault et al., 2011, 2014], [de Koker et al., 2013]). Certain fraction of distinct rocks may reduce the effective melting temperature to values below the CMB temperature. It is especially true for iron enriched materials such as MORB [Nomura et al., 2011], BIF [Kato et al., 2016], iron-rich periclase [Boukare et al., 2015] and other rock species used to explain observed seismic anomalies. Computer simulations allow to study evolution and stability for chemically distinct piles proposed from geophysical data. Previous researches (e.g. [Mulyukova et al., 2015]) found those piles stirring in several hundreds of Ma. Our investigation adds influence of melting and following chemical differentiation on preservation of such structures.We present StagYY code [Tackley et al., 2008] with extended set of routines to model melting, melt redistribution and melt-dependent rheology in addition to solid-state mantle convection to reveal fate of chemically distinct piles in long-term (millions of years) perspective. A new point of our approach is usage of chemically independent oxides to describe rock composition and physical properties. Thin layers homogenize in few tens of millions of years despite whether melting happens or not. Thick structures (like periclase piles proposed for ULVZ [Wicks et al., 2010] or MORB-bearing domes for LLSVP [Ohta et al., 2008]) undergo partial melting if CMB temperature is above 3700K. Melt migration results in extraction of fusible components and therefore segregation of iron-enriched material. However, we weren't able to obtain any stabilized layer of iron-rich partially molten material at the CMB, because ongoing interaction and reequilibration of melt and solid results in buoyant liquids spreading to the adjacent mantle. Rheological influence of melt on bulk rock properties reduces time pile can exist.Our modeling puts severe constraints on the presence and fate of chemical heterogeneities in the lowermost mantle. Melting enhances stirring of such heterogeneities and generally no silicate melt can be stabilized at CMB for long time. Only low CMB temperatures (generally lower than 3700 K) allow anomalies to exist for geological periods of time (hundreds of Ma).

Shifts in coastal Antarctic marine microbial communities during and after melt water-related surface stratification.

PubMed

Piquet, Anouk M-T; Bolhuis, Henk; Meredith, Michael P; Buma, Anita G J

2011-06-01

Antarctic coastal waters undergo major physical alterations during summer. Increased temperatures induce sea-ice melting and glacial melt water input, leading to strong stratification of the upper water column. We investigated the composition of micro-eukaryotic and bacterial communities in Ryder Bay, Antarctic Peninsula, during and after summertime melt water stratification, applying community fingerprinting (denaturing gradient gel electrophoresis) and sequencing analysis of partial 18S and 16S rRNA genes. Community fingerprinting of the eukaryotic community revealed two major patterns, coinciding with a period of melt water stratification, followed by a period characterized by regular wind-induced breakdown of surface stratification. During the first stratified period, we observed depth-related differences in eukaryotic fingerprints while differences in bacterial fingerprints were weak. Wind-induced breakdown of the melt water layer caused a shift in the eukaryotic community from an Actinocyclus sp.- to a Thalassiosira sp.-dominated community. In addition, a distinct transition in the bacterial community was found, but with a few days' delay, suggesting a response to the changes in the eukaryotic community rather than to the mixing event itself. Sequence analysis revealed a shift from an Alpha- and Gammaproteobacteria to a Cytophaga-Flavobacterium-Bacteroides-dominated community under mixed conditions. Our results show that melt water stratification and the transition to nonstabilized Antarctic surface waters may have an impact not only on micro-eukaryotic but also bacterial community composition. © 2011 Federation of European Microbiological Societies. Published by Blackwell Publishing Ltd. All rights reserved.

Spectroscopic and thermal properties of Sm3+ doped iron lead bismuthate glasses

NASA Astrophysics Data System (ADS)

Narwal, P.; Yadav, A.; Dahiya, M. S.; Vishal, Rohit, Agarwal, A.; Khasa, S.

2018-05-01

The results of the structural, physical, thermal and electrical properties of the glass compositions xFe2O3•(100-x)(3Bi2O3•PbO)• Sm2O3(1 mol%) where x=0, 1, 5, 10, 12, 15 mol% prepared via melt quench technique were studied. The synthesized compositions were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and differential thermal analysis (DTA). The IR study reveals that present system is build up with lead in tetrahedral coordination and bismuth in trigonal as well as octahedral coordination. Density and molar volume have been calculated using Archimedes principle, and the variation in their values has been correlated with structural changes in the glass matrix based on the IR study. The variation in the characteristic temperatures (glass transition temperature Tg, crystallization temperature Tp and melting temperature Tm) with different heating rate and change in the composition of iron oxide were analyzed and reported in the present study.

Development and characterization of a microheater array device for real-time DNA mutation detection

NASA Astrophysics Data System (ADS)

Williams, Layne; Okandan, Murat; Chagovetz, Alex; Blair, Steve

2008-04-01

DNA analysis, specifically single nucleotide polymorphism (SNP) detection, is becoming increasingly important in rapid diagnostics and disease detection. Temperature is often controlled to help speed reaction rates and perform melting of hybridized oligonucleotides. The difference in melting temperatures, Tm, between wild-type and SNP sequences, respectively, to a given probe oligonucleotide, is indicative of the specificity of the reaction. We have characterized Tm's in solution and on a solid substrate of three sequences from known mutations associated with Cystic Fibrosis. Taking advantage of Tm differences, a microheater array device was designed to enable individual temperature control of up to 18 specific hybridization events. The device was fabricated at Sandia National Laboratories using surface micromachining techniques. The microheaters have been characterized using an IR camera at Sandia and show individual temperature control with minimal thermal cross talk. Development of the device as a real-time DNA detection platform, including surface chemistry and associated microfluidics, is described.

Development and characterization of a microheater array device for real-time DNA mutation detection

NASA Astrophysics Data System (ADS)

Williams, Layne; Okandan, Murat; Chagovetz, Alex; Blair, Steve

2008-02-01

DNA analysis, specifically single nucleotide polymorphism (SNP) detection, is becoming increasingly important in rapid diagnostics and disease detection. Temperature is often controlled to help speed reaction rates and perform melting of hybridized oligonucleotides. The difference in melting temperatures, Tm, between wild-type and SNP sequences, respectively, to a given probe oligonucleotide, is indicative of the specificity of the reaction. We have characterized Tm's in solution and on a solid substrate of three sequences from known mutations associated with Cystic Fibrosis. Taking advantage of Tm differences, a microheater array device was designed to enable individual temperature control of up to 18 specific hybridization events. The device was fabricated at Sandia National Laboratories using surface micromachining techniques. The microheaters have been characterized using an IR camera at Sandia and show individual temperature control with minimal thermal cross talk. Development of the device as a real-time DNA detection platform, including surface chemistry and associated microfluidics, is described.

Scrap melting model for steel converter founded on interfacial solid/liquid phenomena

NASA Astrophysics Data System (ADS)

Kruskopf, Ari; Holappa, Lauri

2017-12-01

The primary goal in steel converter operation is the removal of carbon from the hot metal. This is achieved by blowing oxygen into the melt. The oxidation of carbon produces a lot of heat. To avoid too high temperatures in the melt cold scrap (recycled steel) is charged into the converter. The melting rate is affected by heat and carbon mass transfer. A process model for steel converter is in development. This model is divided into several modules, which are fluid dynamics, heat- and mass-transfer, scrap melting and chemical reactions. This article focuses on the development of the scrap melting module. A numerical model for calculating temperature and carbon concentration in the melt is presented. The melt model is connected with the solid scrap model via solid/liquid interface. The interface model can take into account solidification of iron melt, melting of solidified layer, a situation without such phase changes, and scrap melting. The aim is to predict the melting rate of the scrap including the properties of the hot metal. The model is tested by calculating the melting rates for different scrap thicknesses. All of the stages in the interface model were taking place in the test calculations.

Interaction between Edge-Driven Convection and Mantle Plumes

NASA Astrophysics Data System (ADS)

Manjón-Cabeza Córdoba, A.; Ballmer, M.

2017-12-01

Intraplate volcanism can occur in a variety of geodynamic settings. Its characteristics can inform about the underlying mantle dynamics. A non-negligible number of intraplate oceanic volcanoes are located close to continental shelves (e.g. Bermuda, Canary Islands, Cape Verde…). In these regions, any putative plumes would interact with Edge-Driven Convection (EDC), a mode of Small-Scale Convection that is triggered along steps of lithospheric thickness. We have systematically explored 2-D geodynamic models of EDC, varying e.g. the viscosity of the mantle, geometry of the edge, potential temperature, etc. In addition, we study the influence of a mantle plume with variable excess temperature and buoyancy flux at a given distance to the edge. The mantle-convection code is coupled with a new melting parameterization that considers the depletion effect on productivity. We apply this parameterization not only to predict the extent of melting for a given lithology, but also the major-element composition of extracted melts for comparison with geochemical data. Results show that the first EDC upwellings are always localized in the oceanic domain at a distance from the continental margin that depends on mantle viscosity. The initial geometry of the edge does not have a significant influence on the "steady-state" shape of EDC. Depending on the distance of the plume from the edge and plume vigor, the plume is either deflected or enhanced by EDC. The mix of materials that melts in the mantle, as well as the amount of melting, is controlled by the interaction of the plume with EDC (e.g., with melting restricted to fertile heterogeneities in the end-member EDC case). Because several model parameters affect this interaction and related melting, a joint analysis of major-element and trace-element composition of hotspot lavas is required to constrain mantle processes.

Experiment and ANSYS simulation analysis for metal aluminum solid and fluid conversion

NASA Astrophysics Data System (ADS)

Wang, Y.-Y.; Guo, P.; Wu, Y.; Zhang, Z.-L.; Jiang, S.-M.

2017-11-01

In this paper, study on metal aluminum solid and fluid conversion was carried out by using crucible resistance furnace, and observing the phenomenon of metal aluminum solid and fluid conversion. In the experiment, the same shape aluminum block was kept under the same heating rate and heated by the resistance furnace. The experimental results show that the melting point of metal aluminum is between 650°C and 660°C, and after the melting point, the metal aluminum began to melt when it maintained for a long period of time, however, when the temperature is higher than the melting point, the aluminum will melt very quickly. In addition, in ANSYS simulation, the solid aluminum melted completely at 670°C in 5430 seconds, much longer than the actual experiment, it due to the heating rate was faster, not in an ideal experimental environment and there is heat exchange with the outside world and convection, at the same time, the aluminum block may contain impurities, so the actual melting time could be shorter than the simulation. In this paper, it was explored for the liquid and solid conversion in depth, and had a certain actual value.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jo, J.C.; Shin, W.K.; Choi, C.Y.

Transient heat transfer problems with phase changes (Stefan problems) occur in many engineering situations, including potential core melting and solidification during pressurized-water-reactor severe accidents, ablation of thermal shields, melting and solidification of alloys, and many others. This article addresses the numerical analysis of nonlinear transient heat transfer with melting or solidification. An effective and simple procedure is presented for the simulation of the motion of the boundary and the transient temperature field during the phase change process. To accomplish this purpose, an iterative implicit solution algorithm has been developed by employing the dual-reciprocity boundary-element method. The dual-reciprocity boundary-element approach providedmore » in this article is much simpler than the usual boundary-element method in applying a reciprocity principle and an available technique for dealing with the domain integral of the boundary element formulation simultaneously. In this article, attention is focused on two-dimensional melting (ablation)/solidification problems for simplicity. The accuracy and effectiveness of the present analysis method have been illustrated through comparisons of the calculation results of some examples of one-phase ablation/solidification problems with their known semianalytical or numerical solutions where available.« less

Melting of isolated tin nanoparticles

PubMed

Bachels; Guntherodt; Schafer

2000-08-07

The melting of isolated neutral tin cluster distributions with mean sizes of about 500 atoms has been investigated in a molecular beam experiment by calorimetrically measuring the clusters' formation energies as a function of their internal temperature. For this purpose the possibility to adjust the temperature of the clusters' internal degrees of freedom by means of the temperature of the cluster source's nozzle was exploited. The melting point of the investigated tin clusters was found to be lowered by 125 K and the latent heat of fusion per atom is reduced by 35% compared to bulk tin. The melting behavior of the isolated tin clusters is discussed with respect to the occurrence of surface premelting.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cebe, Peggy; Partlow, Benjamin P.; Kaplan, David L.

Using fast scanning calorimetry (FSC), we investigated the glass transition and crystal melting of samples of B. mori silk fibroin containing Silk I and/or Silk II crystals. Due to the very short residence times at high temperatures during such measurements, thermal decomposition of silk protein can be significantly suppressed. FSC was performed at 2000 K/s using the Mettler Flash DSC1 on fibroin films with masses around 130–270 ng. Films were prepared with different crystalline fractions (ranging from 0.26 to 0.50) and with different crystal structures (Silk I, Silk II, or mixed) by varying the processing conditions. These included water annealingmore » at different temperatures, exposure to 50% MeOH in water, or autoclaving. The resulting crystal structure was examined using wide angle X-ray scattering. Degree of crystallinity was evaluated from Fourier transform infrared (FTIR) spectroscopy and from analysis of the heat capacity increment at the glass transition temperature. Silk fibroin films prepared by water annealing at 25 °C were the least crystalline and had Silk I structure. FTIR and FSC studies showed that films prepared by autoclaving or 50% MeOH exposure were the most crystalline and had Silk II structure. Intermediate crystalline fraction and mixed Silk I/Silk II structures were found in films prepared by water annealing at 37 °C. FSC results indicate that Silk II crystals exhibit endotherms of narrower width and have higher mean melting temperature Tm(II) = 351 ± 2.6 °C, compared to Silk I crystals which melt at Tm(I) = 292 ± 3.8 °C. Films containing mixed Silk I/Silk II structure showed two clearly separated endothermic peaks. Evidence suggests that the two types of crystals melt separately and do not thermally interconvert on the extremely short time scale (0.065 s between onset and end of melting) of the FSC experiment.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Praher, B., E-mail: bernhard.praher@jku.at, E-mail: klaus.straka@jku.at, E-mail: jesenka.usanovic@jku.at, E-mail: georg.steinbichler@jku.at; Straka, K., E-mail: bernhard.praher@jku.at, E-mail: klaus.straka@jku.at, E-mail: jesenka.usanovic@jku.at, E-mail: georg.steinbichler@jku.at; Usanovic, J., E-mail: bernhard.praher@jku.at, E-mail: klaus.straka@jku.at, E-mail: jesenka.usanovic@jku.at, E-mail: georg.steinbichler@jku.at

We developed novel non-invasive ultrasound based systems for the measurement of temperature distributions in the screw-ante chamber, the detection of unmelted granules and for the monitoring of the plasticizing process along the screw channel. The temperature of the polymer melt stored in the screw ante-chamber after the plasticization should be homogeneous. However, in reality the polymer melt in the screw ante-chamber is not homogeneous. Due to the fact the sound velocity in a polymer melt is temperature depending, we developed a tomography system using the measured transit times of ultrasonic pulses along different sound paths for calculating the temperature distributionmore » in radial direction of a polymer melt in the screw ante-chamber of an injection moulding machine. For the detection of unmelted granules in the polymer melt we implemented an ultrasound transmission measurement. By analyzing the attenuation of the received pulses it is possible to detect unwanted inclusions. For the monitoring of the plasticizing process in the channels of the screw an ultrasonic pulse is transmitted into the barrel. By analyzing the reflected pulses it is possible to estimate solid bed and melt regions in the screw channel. The proposed systems were tested for accuracy and validity by simulations and test measurements.« less

Neutron-absorber release device

DOEpatents

VAN Erp, Jan B.; Kimont, Edward L.

1976-01-01

A resettable device is provided for supporting an object, sensing when an environment reaches a critical temperature and releasing the object when the critical temperature is reached. It includes a flexible container having a material inside with a melting point at the critical temperature. The object's weight is supported by the solid material which gives rigidity to the container until the critical temperature is reached at which point the material in the container melts. The flexible container with the now fluid material inside has insufficient strength to support the object which is thereby released. Biasing means forces the container back to its original shape so that when the temperature falls below the melting temperature the material again solidifies, and the object may again be supported by the device.

Experimental determination of the thermal conductivity of liquid UO2 near the melting point

NASA Astrophysics Data System (ADS)

Sheindlin, M.; Staicu, D.; Ronchi, C.; Game-Arnaud, L.; Remy, B.; Degiovanni, A.

2007-05-01

The article gives an account of measurements of the thermal conductivity of liquid UO2. The sample was heated up to above the melting point by a laser pulse of a controlled shape, and the produced thermogram of temperature history was measured by a fast and accurate pyrometer with a time resolution of 10 μs. The experiment shows that the rate of temperature increase during the ascending part of the pulse changes moderately across the melting point. Due to the high power input, this effect cannot be explained in terms of the sole intake of latent heat of fusion. By solving the related heat transfer equation with a 2D-axisymmetric numerical model, it is demonstrated that this feature depends principally on heat conduction in the sample, and proves that the thermal conductivities of solid and liquid are not very different. A theoretical sensitivity study assessing the influence of the liquid thermal conductivity on the pulse temperature evolution showed that the conductivity of the liquid can be deduced from the fitting of the thermograms with a numerical precision of the order of 1%. The analysis reveals that the thermal conductivity is weakly correlated with the effective heat losses during the pulse and to the melting enthalpy, so that the uncertainty in its evaluation by fitting the experimental thermograms with model predictions is satisfactory. The value of the thermal conductivity of liquid UO2 near the melting point resulted to be 2.6±0.35 W m-1 K-1, where the magnitude of the uncertainty is much lower than the scatter of the previously published, discordant measurements.

Miniature Fixed Points as Temperature Standards for In Situ Calibration of Temperature Sensors

NASA Astrophysics Data System (ADS)

Hao, X. P.; Sun, J. P.; Xu, C. Y.; Wen, P.; Song, J.; Xu, M.; Gong, L. Y.; Ding, L.; Liu, Z. L.

2017-06-01

Miniature Ga and Ga-In alloy fixed points as temperature standards are developed at National Institute of Metrology, China for the in situ calibration of temperature sensors. A quasi-adiabatic vacuum measurement system is constructed to study the phase-change plateaus of the fixed points. The system comprises a high-stability bath, a quasi-adiabatic vacuum chamber and a temperature control and measurement system. The melting plateau of the Ga fixed point is longer than 2 h at 0.008 W. The standard deviation of the melting temperature of the Ga and Ga-In alloy fixed points is better than 2 mK. The results suggest that the melting temperature of the Ga or Ga-In alloy fixed points is linearly related with the heating power.

Evaluation of the most suitable threshold value for modelling snow glacier melt through T- index approach: the case study of Forni Glacier (Italian Alps)

NASA Astrophysics Data System (ADS)

Senese, Antonella; Maugeri, Maurizio; Vuillermoz, Elisa; Smiraglia, Claudio; Diolaiuti, Guglielmina

2014-05-01

Glacier melt occurs whenever the surface temperature is null (273.15 K) and the net energy budget is positive. These conditions can be assessed by analyzing meteorological and energy data acquired by a supraglacial Automatic Weather Station (AWS). In the case this latter is not present at the glacier surface the assessment of actual melting conditions and the evaluation of melt amount is difficult and degree-day (also named T-index) models are applied. These approaches require the choice of a correct temperature threshold. In fact, melt does not necessarily occur at daily air temperatures higher than 273.15 K, since it is determined by the energy budget which in turn is only indirectly affected by air temperature. This is the case of the late spring period when ablation processes start at the glacier surface thus progressively reducing snow thickness. In this study, to detect the most indicative air temperature threshold witnessing melt conditions in the April-June period, we analyzed air temperature data recorded from 2006 to 2012 by a supraglacial AWS (at 2631 m a.s.l.) on the ablation tongue of the Forni Glacier (Italy), and by a weather station located nearby the studied glacier (at Bormio, 1225 m a.s.l.). Moreover we evaluated the glacier energy budget (which gives the actual melt, Senese et al., 2012) and the snow water equivalent values during this time-frame. Then the ablation amount was estimated both from the surface energy balance (MEB from supraglacial AWS data) and from degree-day method (MT-INDEX, in this latter case applying the mean tropospheric lapse rate to temperature data acquired at Bormio changing the air temperature threshold) and the results were compared. We found that the mean tropospheric lapse rate permits a good and reliable reconstruction of daily glacier air temperature conditions and the major uncertainty in the computation of snow melt from degree-day models is driven by the choice of an appropriate air temperature threshold. Then, to assess the most suitable threshold, we firstly analyzed hourly MEB values to detect if ablation occurs and how long this phenomenon takes (number of hours per day). The largest part of the melting (97.7%) resulted occurring on days featuring at least 6 melting hours thus suggesting to consider their minimum average daily temperature value as a suitable threshold (268.1 K). Then we ran a simple T-index model applying different threshold values. The threshold which better reproduces snow melting results the value 268.1 K. Summarizing using a 5.0 K lower threshold value (with respect to the largely applied 273.15 K) permits the best reconstruction of glacier melt and it results in agreement with findings by van den Broeke et al. (2010) in Greenland ice sheet. Then probably the choice of a 268 K value as threshold for computing degree days amount could be generalized and applied not only on Greenland glaciers but also on Mid latitude and Alpine ones. This work was carried out under the umbrella of the SHARE Stelvio Project funded by the Lombardy Region and managed by FLA and EvK2-CNR Committee.

Microgravity Studies of Liquid-Liquid Phase Transitions in Alumina-Yttria Melts

NASA Technical Reports Server (NTRS)

Guynes, Buddy (Technical Monitor); Weber, Richard; Nordine, Paul

2004-01-01

The scientific objective of this research is to increase the fundamental knowledge base for liquid- phase processing of technologically important oxide materials. The experimental objective is to define conditions and hardware requirements for microgravity flight experiments to test and expand the experimental hypotheses that: 1. Liquid phase transitions can occur in undercooled melts by a diffusionless process. 2. Onset of the liquid phase transition is accompanied by a large change in the temperature dependence of melt viscosity. Experiments on undercooled YAG (Y3A15012)- and rare earth oxide aluminate composition liquids demonstrated a large departure from an Arrhenian temperature dependence of viscosity. Liquid YAG is nearly inviscid at its 2240 K melting point. Glass fibers were pulled from melts undercooled by ca. 600 K indicating that the viscosity is on the order of 100 Pans (1000 Poise) at 1600 K. This value of viscosity is 500 times greater than that obtained by extrapolation of data for temperatures above the melting point of YAG. These results show that the liquids are extremely fragile and that the onset of the highly non-Arrhenian viscosity-temperature relationship occurs at a temperature considerably below the equilibrium melting point of the solid phases. Further results on undercooled alumina-yttria melts containing 23-42 mole % yttrium oxide indicate that a congruent liquid-liquid phase transition occurs in the undercooled liquids. The rates of transition are inconsistent with a diffusion-limited process. This research is directed to investigation of the scientifically interesting phenomena of polyamorphism and fragility in undercooled rare earth oxide aluminum oxide liquids. The results bear on the technologically important problem of producing high value rare earth-based optical materials.

Heterogeneous to homogeneous melting transition visualized with ultrafast electron diffraction

DOE Office of Scientific and Technical Information (OSTI.GOV)

None

The ultrafast laser excitation of matters leads to non-equilibrium states with complex solid-liquid phase transition dynamics. We used electron diffraction at mega-electronvolt energies to visualize the ultrafast melting of gold on the atomic scale length. For energy densities approaching the irreversible melting regime, we first observed heterogeneous melting on time scales of 100 ps to 1000 ps, transitioning to homogeneous melting that occurs catastrophically within 10-20 ps at higher energy densities. We showed evidence for the heterogeneous coexistence of solid and liquid. We determined the ion and electron temperature evolution and found superheated conditions. Our results constrain the electron-ion couplingmore » rate, determine the Debye temperature and reveal the melting sensitivity to nucleation seeds.« less

Eutectic melting in the MgO-SiO2 system and its implication to Earth's lower mantle evolution

NASA Astrophysics Data System (ADS)

Baron, M. A.; Lord, O. T.; Myhill, R.; Thomson, A.; Wang, W.; Tronnes, R. G.; Walter, M. J.

2017-12-01

Eutectic melting curves in the system MgO-SiO2 have been experimentally studied at lower mantle pressures using laser-heated diamond anvil cell (LH-DAC) techniques. We investigated eutectic melting of bridgmanite plus periclase in the MgO-MgSiO3 binary and bridgmanite plus stishovite in the MgSiO3-SiO2 sub-system as the simplest models of natural peridotite and basalt. The eutectic melting have been detected on the basis of the thermal perturbations (i.e. melting plateau) during the experiment but also post-experimental textural and chemical analyses of the recovered samples. We also performed a suite of sub-solidus experiments in order to compare and bracket the eutectic melting experiments. The melting curve of model basalt occurs at lower temperatures, has a shallower dT/dP slope and slightly less curvature than the model peridotitic melting curve. Overall, melting temperatures detected in this study are in good agreement with previous experiments and ab initio simulations at 25 GPa (Liebske and Frost, 2012; de Koker et al., 2013). However, at higher pressures the measured eutectic melting curves are systematically lower in temperature than curves extrapolated on the basis of thermodynamic modelling of low-pressure experimental data, and those calculated from atomistic simulations. In turn, when comparing with previously published solidus curves obtained for natural basalt and peridotite (e.g. Fiquet et al., 2010; Andrault et al. 2011; Nomura et al. 2014; Hirose et al. 1999; Andrault et al. 2014 and Pradhan et al. 2015) the melting curves from this study are higher. However, the difference in temperature is less significant than previously though. Based on the comparison of the curvature of the model peridotite eutectic relative to an MgSiO3 melt adiabat we infer that crystallization in a global magma ocean would begin at 100 GPa rather than at the bottom of the mantle, allowing for an early basal melt layer. The model peridotite melting curve lies 500 K above the mantle geotherm at the core-mantle boundary, indicating that it will not be molten. The model basalt melting curve intersects the geotherm at the base of the mantle, and partial melting of subducted oceanic crust is therefore expected.

Hot and solid gallium clusters: too small to melt.

PubMed

Breaux, Gary A; Benirschke, Robert C; Sugai, Toshiki; Kinnear, Brian S; Jarrold, Martin F

2003-11-21

A novel multicollision induced dissociation scheme is employed to determine the energy content for mass-selected gallium cluster ions as a function of their temperature. Measurements were performed for Ga(+)(n) (n=17 39, and 40) over a 90-720 K temperature range. For Ga+39 and Ga+40 a broad maximum in the heat capacity-a signature of a melting transition for a small cluster-occurs at around 550 K. Thus small gallium clusters melt at substantially above the 302.9 K melting point of bulk gallium, in conflict with expectations that they will remain liquid to below 150 K. No melting transition is observed for Ga+17.

The Growth and Characterization of the Bismuth Strontium-Calcium 2212 Superconductor

NASA Astrophysics Data System (ADS)

Moulton, Linda Vidale

A miniaturized float zone technique, sometimes referred to as the Laser-heated Pedestal Growth (LHPG) method, was used to produce high quality crystals of the incongruently melting rm Bi_2Sr_2CaCu _2O_{8+delta} (2212) superconductor. The main focus of this research was to (1) produce superconducting samples having different compositions, (2) identify the melt compositions and growth temperatures which produced these samples, and (3) determine the variation of their superconducting transition temperature (T _{rm C}) with composition and processing conditions. The rm Bi_2(Sr,Ca) _3Cu_2O_{8+delta} crystallization experiments were supplemented by a series of similar experiments on the incongruently melting compound rm Ca_3Al_2O_6. The phase equilibria in the CaO-rm Al_2O _3 system has been thoroughly studied, and by analyzing the float-zone growth of this simpler and better-characterized material, it was verified that phase equilibria information and solidification behavior could be extracted from and explained by these solidification experiments. Two different types of nonplanar, crystal/melt interface morphologies were observed in the rm Ca_3Al_2O_6 experiments. Each reflected the influence of the phase equilibria in the CaO-rm Al_2O_3 system and component segregation in the melt. The molten zone compositions were found to approach those predicted by the CaO-rm Al_2O_3 phase diagram as the growth rate decreased, in accordance with the Burton-Prim Slichter relationship. Excellent agreement was obtained between actual phases found to coexist at the rm Ca_3Al_2O_6 /melt interface and the predictions of classical crystal growth theory. Based on the results of the rm Ca _3Al_2O_6 crystallization study, the crystal/melt equilibria in the far more complex rm Bi_2O_3-SrO-CaO-CuO system was evaluated by determining the phases formed during the superconductor growth experiments. The melt compositions were found to be rm Bi_2O_3 -rich and SrO-poor relative to the compositions of the 2212 crystals grown from them. The CaO and CuO segregation coefficients, on the other hand, were observed to be near unity. As one would expect for an incongruently -melting compound, segregation at the solidification front generally decreased with increasing crystallization temperature, but all the segregation coefficients were not observed to simultaneously approach unity. The superconducting transition temperatures (T _{rm C}'s) of six as-crystallized samples having homogeneous crystal compositions were also measured. Sample T_{rm C} was observed to increase with increasing growth temperature and, therefore, change with crystal composition. The results of this study suggested that it is desirable to grow crystals at the highest possible crystallization temperature since they will: (1) have the highest as-grown T_{rm C} 's, and (2) solidify with the least component segregation at the growth interface. In addition, the analysis presented here suggests that such growth is not recommended at higher growth rates, since crystals with mid-range solidus compositions (and consequently, moderate growth temperatures) should crystallize most reliably as single-phase samples at higher growth rates.

Experimental correlation of melt structures, nucleation rates, and thermal histories of silicate melts

NASA Technical Reports Server (NTRS)

Boynton, W. V.; DRAKE; HILDEBRAND; JONES; LEWIS; TREIMAN; WARK

1987-01-01

The theory and measurement of the structure of liquids is an important aspect of modern metallurgy and igneous petrology. Liquid structure exerts strong controls on both the types of crystals that may precipitate from melts and on the chemical composition of those crystals. An interesting aspect of melt structure studies is the problem of melt memories; that is, a melt can retain a memory of previous thermal history. This memory can influence both nucleation behavior and crystal composition. This melt memory may be characterized quantitatively with techniques such as Raman, infrared and NMR spectroscopy to provide information on short-range structure. Melt structure studies at high temperature will take advantage of the microgravity conditions of the Space Station to perform containerless experiments. Melt structure determinations at high temperature (experiments that are greatly facilitated by containerless technology) will provide invaluable information for materials science, glass technology, and geochemistry. In conjunction with studies of nucleation behavior and nucleation rates, information relevant to nucleation in magma chambers in terrestrial planets will be acquired.

The judgment of the All-melted-moment during using electron beam melting equipment to purify silicon

NASA Astrophysics Data System (ADS)

Han, Xiaojie; Meng, Jianxiong; Wang, Shuaiye; Jiang, Tonghao; Wang, Feng; Tan, Yi; Jiang, Dachuan

2017-06-01

Experiment has proved that the rate of impurity removal depends on the pressure and the temperature of the vacuum chamber during using electron beam to smelt silicon, and the amount of removed-impurity depends on time when other conditions are the same. In the actual production process, smelting time is a decisive factor of impurity removal amount while pressure and temperature of the vacuum chamber is certain due to a certain melting power. To avoiding the influence of human control and improving the quality of production, thinking of using cooling water temperature to estimate the state of material during metal smelting is considered. We try to use the change of cooling water temperature to judge that when silicon is all melted and to evaluate the effectiveness of this method.

Comparative analysis of changes in gene expression due to RNA melting activities of translation initiation factor IF1 and a cold shock protein of the CspA family.

PubMed

Phadtare, Sangita; Severinov, Konstantin

2009-11-01

In Escherichia coli, temperature downshift elicits cold shock response, which is characterized by induction of cold shock proteins. CspA, the major cold shock protein of E. coli, helps cells to acclimatize to low temperature by melting the secondary structures in nucleic acids and acting as a transcription antiterminator. CspA and its homologues contain the cold shock domain and belong to the oligomer binding protein family, which also includes S1 domain proteins such as IF1. Structural similarity between IF1 and CspA homologues suggested a functional overlap between these proteins. Indeed IF1 can melt secondary structures in RNA and acts as transcription antiterminator in vivo and in vitro. Here, we show that in spite of having these critical activities, IF1 does not complement cold-sensitivity of a csp quadruple deletion strain. DNA microarray analysis shows that overproduction of IF1 and Csp leads to changes in expression of different sets of genes. Importantly, several genes which were previously shown to require Csp proteins for their expression at low temperature did not respond to IF1. Moreover, in vitro, we show that a transcription terminator responsive to Csp does not respond to IF1. Our results suggest that Csp proteins and IF1 have different sets of target genes as they may be suppressing the function of different types of transcription termination elements in specific genes.

Investigation of the H7 ordinary chondrite, Watson 012: Implications for recognition and classification of Type 7 meteorites

NASA Astrophysics Data System (ADS)

Tait, Alastair W.; Tomkins, Andrew G.; Godel, Bélinda M.; Wilson, Siobhan A.; Hasalova, Pavlina

2014-06-01

Despite the fact that the number of officially classified meteorites is now over 45,000, we lack a clearly defined sequence of samples from a single parent body that records the entire range in metamorphic temperatures from pristine primitive meteorites up to the temperatures required for extensive silicate partial melting. Here, we conduct a detailed analysis of Watson 012, an H7 ordinary chondrite, to generate some clarity on the textural and chemical changes associated with equilibrium-based silicate partial melting in chondritic meteorites. To do this we compare the textures in the meteorite with those preserved in metamorphic contact aureoles on Earth. The most distinctive texture generated by the partial melting that affected Watson 012 is an extensively interconnected plagioclase network, which is clearly observable with a petrographic microscope. Enlarged metal-troilite grains are encapsulated at widenings in this plagioclase network, and this is clearly visible in reflected light. Together with these features, we define a series of other characteristics that can be used to more clearly classify chondritic meteorites as being of petrologic Type 7. To provide comprehensive evidence of silicate partial melting and strengthen the case for using simple petrographic observations to classify similar meteorites, we use high-resolution X-ray computed tomography to demonstrate that the plagioclase network has a high degree of interconnectedness and crystallised as large (cm-scale) skeletal crystals within an olivine-orthopyroxene-clinopyroxene framework, essentially pseudomorphing a melt network. Back-scattered electron imaging and element mapping are used to show that some of the clino- and orthopyroxene in Watson 012 also crystallised from silicate melt, and the order of crystallisation was orthopyroxene → clinopyroxene → plagioclase. X-ray diffraction data, supported by bulk geochemistry, are used to show that plagioclase and ortho- and clinopyroxene were added to the Watson 012 sample by through-flowing basaltic melt. Along with the absence of glass and granophyre, this interconnected network of coarse-grained skeletal plagioclase indicates that the sample cooled slowly at depth within the parent body. The evidence of melt flux indicates that Watson 012 formed in the presence of a gravitational gradient, and thus at significant distance from the centre of the H chondrite parent body (the gravitational gradient at the centre would be zero). Our interpretation is that incipient silicate partial melting in Watson 012 occurred when a region of radiogenically heated H6 material located at considerable depth (possibly at ∼15-20 km from surface) was heated by an additional ca. 200-300 °C in association with a large shock event. Due to insulation at depth within an already hot parent body, the post-shock temperature equilibrated and remained above the solidus long enough for widespread equilibrium-based silicate partial melting, and for melt to migrate. Although the observed melting may have been facilitated by additional heating from an impact event, this is not an example of instantaneous shock melting, which produces thermal disequilibrium at short length scales and distinctly different textures. A small number of H, L and LL chondrites have been previously classified as being of petrologic Type 7; with our new criteria to support that classification, these represent our best opportunity to explore the transition from high temperature sub-solidus metamorphism through the onset of silicate partial melting in three different parent bodies.

Partitioning of Mo, P and other siderophile elements (Cu, Ga, Sn, Ni, Co, Cr, Mn, V, and W) between metal and silicate melt as a function of temperature and silicate melt composition

NASA Astrophysics Data System (ADS)

Righter, K.; Pando, K. M.; Danielson, L.; Lee, Cin-Ty

2010-03-01

Metal-silicate partition coefficients can provide information about the earliest differentiation histories of terrestrial planets and asteroids. Systematic studies of the effects of key parameters such as temperature and melt composition are lacking for many elements. In particular, data for Mo is scarce, but given its refractory nature, is of great value in interpreting metal-silicate equilibrium. Two series of experiments have been carried out to study Mo and P partitioning between Fe metallic liquid and basaltic to peridotitic silicate melt, at 1 GPa and temperatures between 1500 and 1900 °C. Because the silicate melt utilized was natural basalt, there are also measurable quantities of 9 other siderophile elements (Ni, Co, W, Sn, Cu, Mn, V, Cr, Ga and Zn). The Ni and Co data can be used to assess consistency with previous studies. In addition, the new data also allow a first systematic look at the temperature dependence of Cu, Ga, Sn, Cr, Mn V and W for basaltic to peridotitic melts. Many elements exhibit an increase in siderophile behavior at higher temperature, contrary to popular belief, but consistent with predictions from thermodynamics. Using these new data we examine DMomet/sil and DPmet/sil in detail and show that increasing temperature causes a decrease in the former and an increase in the latter, whereas both increase with MgO content of the silicate melt. The depletions of Mo and P in the mantle of the Earth can be explained by metal-silicate equilibrium at magma ocean conditions — both elements are satisfied at PT conditions of an intermediate depth magma ocean for the Earth 22.5 GPa and 2400 °C.

Development of Economical Improved Thick Film Solar Cell Contact

NASA Technical Reports Server (NTRS)

Ross, B.

1979-01-01

Materials were surveyed to provide candidates for an all metal electrode paste system. These consisted of a major constituent metal powder, a low melting metal powder suitable for a liquid phase sintering medium, and a powder material suitable as an etchant for silicon dioxide at sintering temperatures. By means of thermal gravimetric analysis a suitable binder was identified for low temperature fired inks.

Temperature and pressure dependences of kimberlite melts viscosity (experimental-theoretical study)

NASA Astrophysics Data System (ADS)

Persikov, Eduard; Bykhtiyarov, Pavel; Cokol, Alexsander

2016-04-01

Experimental data on temperature and pressure dependences of viscosity of model kimberlite melts (silicate 82 + carbonate 18, wt. %, 100NBO/T = 313) have been obtained for the first time at 100 MPa of CO2 pressure and at the lithostatic pressures up to 7.5 GPa in the temperature range 1350 oC - 1950 oC using radiation high gas pressure apparatus and press free split-sphere multi - anvil apparatus (BARS). Experimental data obtained on temperature and pressure dependences of viscosity of model kimberlite melts at moderate and high pressures is compared with predicted data on these dependences of viscosity of basaltic melts (100NBO/T = 58) in the same T, P - range. Dependences of the viscosity of model kimberlite and basaltic melts on temperature are consistent to the exponential Arrenian equation in the T, P - range of experimental study. The correct values of activation energies of viscous flow of kimberlite melts have been obtained for the first time. The activation energies of viscous flow of model kimberlite melts exponentially increase with increasing pressure and are equal: E = 130 ± 1.3 kJ/mole at moderate pressure (P = 100 MPa) and E = 160 ± 1.6 kJ/mole at high pressure (P = 5.5 GPa). It has been established too that the viscosity of model kimberlite melts exponentially increases on about half order of magnitude with increasing pressures from 100 MPa to 7.5 GPa at the isothermal condition (1800 oC). It has been established that viscosity of model kimberlite melts at the moderate pressure (100 MPa) is lover on about one order of magnitude to compare with the viscosity of basaltic melts, but at high pressure range (5.5 - 7.5 GPa), on the contrary, is higher on about half order of magnitude at the same values of the temperatures. Here we use both a new experimental data on viscosity of kimberlite melts and our structural chemical model for calculation and prediction the viscosity of magmatic melts [1] to determine the fundamental features of viscosity of kimberlite and basaltic magmas at the T, P - parameters of the Earth's crust and upper mantle. The Russian Foundation for Basic Research (project 15-05-01318) and the Russian Science Foundation (project 14-27-00054) are acknowledged for the financial support. [1] Persikov, E.S. & Bukhtiyarov, P.G. (2009) Russian Geology & Geophysics, 50, No 12, 1079-1090.

Constraints on the Locations of Volcanic Arcs (August Love Medal Lecture)

NASA Astrophysics Data System (ADS)

England, Philip

2010-05-01

Partial melting of the mantle in subduction zones is a leading mechanism of chemical differentiation of the Earth. Whereas the broad outlines of Earth's other major system of partial melting - the oceanic ridges - seem clear, the greater dynamic and thermodynamic complexities of subduction zones obscure fundamental aspects of the system, in particular the conditions under which melting initiates and the pathways by which the melt travels towards the Earth's surface. The vast majority of studies of these problems rest on interrogation of petrological and/or geochemical data on rocks erupted at the volcanic arcs, but this approach has resulted in the co-existence of mutually incompatible explanations for the locations of the volcanic arcs. An alternative to the complexity of petrological and geochemical argument is to focus on the geometrical simplicity of volcanic arcs. The observations (i) that the fronts to volcanic arcs fit small circles to within about 10 km and (ii) that the depth to the slab beneath the arc fronts correlates negatively with the descent speed of the slab provide a strong clue to the melting processes occurring at depth. Localized release of fluids by reactions taking place near the top of the slab are incapable of explaining this correlation. However, scaling analysis based on the physics of heat transfer in the wedge shows that such a correlation is predicted if the location of the arcs is controlled by a temperature-critical process taking place in the mantle wedge above the slab. Numerical experiments using realistic physical properties for the mantle in subduction zones support the scaling analysis and, when combined with the observed positions of the arcs, strongly imply that the arcs are localized above the places where the mantle wedge reaches a critical temperature of ~1250o-1300oC. Therefore, despite the importance of hydrous fluids for the overall magmatic budget in subduction zones, it is melting in the region above the anhydrous solidus that determines the location of the arcs. Heat carried by magma rising from this region is sufficient to modify the thermal structure of the wedge and determine the pathway through which both wet and dry melts reach the surface.

The temperature of the Icelandic mantle from olivine-spinel aluminum exchange thermometry

NASA Astrophysics Data System (ADS)

Matthews, S.; Shorttle, O.; Maclennan, J.

2016-11-01

New crystallization temperatures for four eruptions from the Northern Volcanic Zone of Iceland are determined using olivine-spinel aluminum exchange thermometry. Differences in the olivine crystallization temperatures between these eruptions are consistent with variable extents of cooling during fractional crystallization. However, the crystallization temperatures for Iceland are systematically offset to higher temperatures than equivalent olivine-spinel aluminum exchange crystallization temperatures published for MORB, an effect that cannot be explained by fractional crystallization. The highest observed crystallization temperature in Iceland is 1399 ± 20°C. In order to convert crystallization temperatures to mantle potential temperature, we developed a model of multilithology mantle melting that tracks the thermal evolution of the mantle during isentropic decompression melting. With this model, we explore the controls on the temperature at which primary melts begin to crystallize, as a function of source composition and the depth from which the magmas are derived. Large differences (200°C) in crystallization temperature can be generated by variations in mantle lithology, a magma's inferred depth of origin, and its thermal history. Combining this model with independent constraints on the magma volume flux and the effect of lithological heterogeneity on melt production, restricted regions of potential temperature-lithology space can be identified as consistent with the observed crystallization temperatures. Mantle potential temperature is constrained to be 1480-30+37 °C for Iceland and 1318-32+44 °C for MORB.

HAZARDS OF THERMAL EXPANSION FOR RADIOLOGICAL CONTAINER ENGULFED IN FIRE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Donna Post Guillen

2013-05-01

Fire accidents pose a serious threat to nuclear facilities. It is imperative that transport casks or shielded containers designed to transport/contain radiological materials have the ability to withstand a hypothetical fire. A numerical simulation was performed for a shielded container constructed of stainless steel and lead engulfed in a hypothetical fire as outlined by 10 CFR §71.73. The purpose of this analysis was to determine the thermal response of the container during and after the fire. The thermal model shows that after 30 minutes of fire, the stainless steel will maintain its integrity and not melt. However, the lead shieldingmore » will melt since its temperature exceeds the melting point. Due to the method of construction of the container under consideration, ample void space must be provided to allow for thermal expansion of the lead upon heating and melting, so as to not overstress the weldment.« less

Powder metallurgy inspired low-temperature fabrication of high-performance stereocomplexed polylactide products with good optical transparency

PubMed Central

Bai, Dongyu; Liu, Huili; Bai, Hongwei; Zhang, Qin; Fu, Qiang

2016-01-01

Stereocomplexation between enantiomeric poly(l-lactide) (PLLA) and poly(d-lactide) (PDLA) provides an avenue to greatly enhance performance of eco-friendly polylactide (PLA). Unfortunately, although the manufacturing of semicrystalline polymers generally involves melt processing, it is still hugely challenging to create high-performance stereocomplexed polylactide (sc-PLA) products from melt-processed high-molecular-weight PLLA/PDLA blends due to the weak crystallization memory effect of stereocomplex (sc) crystallites after complete melting as well as the substantial degradation of PLA chains at elevated melt-processing temperatures of ca. 240–260 °C. Inspired by the concept of powder metallurgy, here we report a new facile route to address these obstacles by sintering of sc-PLA powder at temperatures as low as 180–210 °C, which is distinctly different from traditional sintering of polymer powders performed at temperatures far exceeding their melting temperatures. The enantiomeric PLA chain segments from adjacent powder particles can interdiffuse across particle interfaces and co-crystallize into new sc crystallites capable of tightly welding the interfaces during the low-temperature sintering process, and thus highly transparent sc-PLA products with outstanding heat resistance, mechanical strength, and hydrolytic stability have been successfully fabricated for the first time. PMID:26837848

Powder metallurgy inspired low-temperature fabrication of high-performance stereocomplexed polylactide products with good optical transparency

NASA Astrophysics Data System (ADS)

Bai, Dongyu; Liu, Huili; Bai, Hongwei; Zhang, Qin; Fu, Qiang

2016-02-01

Stereocomplexation between enantiomeric poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA) provides an avenue to greatly enhance performance of eco-friendly polylactide (PLA). Unfortunately, although the manufacturing of semicrystalline polymers generally involves melt processing, it is still hugely challenging to create high-performance stereocomplexed polylactide (sc-PLA) products from melt-processed high-molecular-weight PLLA/PDLA blends due to the weak crystallization memory effect of stereocomplex (sc) crystallites after complete melting as well as the substantial degradation of PLA chains at elevated melt-processing temperatures of ca. 240-260 °C. Inspired by the concept of powder metallurgy, here we report a new facile route to address these obstacles by sintering of sc-PLA powder at temperatures as low as 180-210 °C, which is distinctly different from traditional sintering of polymer powders performed at temperatures far exceeding their melting temperatures. The enantiomeric PLA chain segments from adjacent powder particles can interdiffuse across particle interfaces and co-crystallize into new sc crystallites capable of tightly welding the interfaces during the low-temperature sintering process, and thus highly transparent sc-PLA products with outstanding heat resistance, mechanical strength, and hydrolytic stability have been successfully fabricated for the first time.

Powder metallurgy inspired low-temperature fabrication of high-performance stereocomplexed polylactide products with good optical transparency.

PubMed

Bai, Dongyu; Liu, Huili; Bai, Hongwei; Zhang, Qin; Fu, Qiang

2016-02-03

Stereocomplexation between enantiomeric poly(l-lactide) (PLLA) and poly(d-lactide) (PDLA) provides an avenue to greatly enhance performance of eco-friendly polylactide (PLA). Unfortunately, although the manufacturing of semicrystalline polymers generally involves melt processing, it is still hugely challenging to create high-performance stereocomplexed polylactide (sc-PLA) products from melt-processed high-molecular-weight PLLA/PDLA blends due to the weak crystallization memory effect of stereocomplex (sc) crystallites after complete melting as well as the substantial degradation of PLA chains at elevated melt-processing temperatures of ca. 240-260 °C. Inspired by the concept of powder metallurgy, here we report a new facile route to address these obstacles by sintering of sc-PLA powder at temperatures as low as 180-210 °C, which is distinctly different from traditional sintering of polymer powders performed at temperatures far exceeding their melting temperatures. The enantiomeric PLA chain segments from adjacent powder particles can interdiffuse across particle interfaces and co-crystallize into new sc crystallites capable of tightly welding the interfaces during the low-temperature sintering process, and thus highly transparent sc-PLA products with outstanding heat resistance, mechanical strength, and hydrolytic stability have been successfully fabricated for the first time.

Superheater Corrosion In Biomass Boilers: Today's Science and Technology

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sharp, William

2011-12-01

This report broadens a previous review of published literature on corrosion of recovery boiler superheater tube materials to consider the performance of candidate materials at temperatures near the deposit melting temperature in advanced boilers firing coal, wood-based fuels, and waste materials as well as in gas turbine environments. Discussions of corrosion mechanisms focus on the reactions in fly ash deposits and combustion gases that can give corrosive materials access to the surface of a superheater tube. Setting the steam temperature of a biomass boiler is a compromise between wasting fuel energy, risking pluggage that will shut the unit down, andmore » creating conditions that will cause rapid corrosion on the superheater tubes and replacement expenses. The most important corrosive species in biomass superheater corrosion are chlorine compounds and the most corrosion resistant alloys are typically FeCrNi alloys containing 20-28% Cr. Although most of these materials contain many other additional additions, there is no coherent theory of the alloying required to resist the combination of high temperature salt deposits and flue gases that are found in biomass boiler superheaters that may cause degradation of superheater tubes. After depletion of chromium by chromate formation or chromic acid volatilization exceeds a critical amount, the protective scale gives way to a thick layer of Fe{sub 2}O{sub 3} over an unprotective (FeCrNi){sub 3}O{sub 4} spinel. This oxide is not protective and can be penetrated by chlorine species that cause further acceleration of the corrosion rate by a mechanism called active oxidation. Active oxidation, cited as the cause of most biomass superheater corrosion under chloride ash deposits, does not occur in the absence of these alkali salts when the chloride is present as HCl gas. Although a deposit is more corrosive at temperatures where it is molten than at temperatures where it is frozen, increasing superheater tube temperatures through the measured first melting point of fly ash deposits does not necessarily produce a step increase in corrosion rate. Corrosion rate typically accelerates at temperatures below the first melting temperature and mixed deposits may have a broad melting temperature range. Although the environment at a superheater tube surface is initially that of the ash deposits, this chemistry typically changes as the deposits mature. The corrosion rate is controlled by the environment and temperature at the tube surface, which can only be measured indirectly. Some results are counter-intuitive. Two boiler manufacturers and a consortium have developed models to predict fouling and corrosion in biomass boilers in order to specify tube materials for particular operating conditions. It would be very useful to compare the predictions of these models regarding corrosion rates and recommended alloys in the boiler environments where field tests will be performed in the current program. Manufacturers of biomass boilers have concluded that it is more cost-effective to restrict steam temperatures, to co-fire biofuels with high sulfur fuels and/or to use fuel additives rather than try to increase fuel efficiency by operating with superheater tube temperatures above melting temperature of fly ash deposits. Similar strategies have been developed for coal fired and waste-fired boilers. Additives are primarily used to replace alkali metal chloride deposits with higher melting temperature and less corrosive alkali metal sulfate or alkali aluminum silicate deposits. Design modifications that have been shown to control superheater corrosion include adding a radiant pass (empty chamber) between the furnace and the superheater, installing cool tubes immediately upstream of the superheater to trap high chloride deposits, designing superheater banks for quick replacement, using an external superheater that burns a less corrosive biomass fuel, moving circulating fluidized bed (CFB) superheaters from the convective pass into the hot recirculated fluidizing medium and adding an insulating layer to superheater tubes to raise their surface temperature above the dew point temperature of alkali chlorides. These design changes offer advantages but introduce other challenges. For example, operating with superheater temperatures above the dew point of alkali chlorides could require the use of creep-resistant tube alloys and doesn't eliminate chloride corrosion. Improved test methods that can be applied within this project include automated dimensional metrology to make a statistical analysis of depth of penetration and corrosion product thickness, and simultaneous thermal analysis measurements to quantify the melting of complex ashes and avoid the unreliability of the standard ash fusion test. Other important developments in testing include the installation of individually-temperature-controlled superheater loops for corrosion testing in operating boilers and temperature gradient testing.« less

Structure and thermal expansion of Lu 2O 3 and Yb 2O 3 up to the melting points

DOE PAGES

Pavlik, Alfred; Ushakov, Sergey V.; Navrotsky, Alexandra; ...

2017-08-24

Knowledge of thermal expansion and high temperature phase transformations is essential for prediction and interpretation of materials behavior under the extreme conditions of high temperature and intense radiation encountered in nuclear reactors. We studied the structure and thermal expansion of Lu 2O 3 and Yb 2O 3 were studied in oxygen and argon atmospheres up to their melting temperatures using synchrotron X-ray diffraction on laser heated levitated samples. Both oxides retained the cubic bixbyite C-type structure in oxygen and argon to melting. In contrast to fluorite-type structures, the increase in the unit cell parameter of Yb 2O 3 and Lumore » 2O 33 with temperature is linear within experimental error from room temperature to the melting point, with mean thermal expansion coefficients (8.5 ± 0.6) · 10 -6 K -1 and (7.7 ± 0.6) · 10 -6 K -1, respectively. There is no indication of a superionic (Bredig) transition in the C-type structure or of a previously suggested Yb 2O 3 phase transformation to hexagonal phase prior to melting.« less

Synchrotron radiation study on the high-pressure and high-temperature phase relations of KAlSi3O8

NASA Astrophysics Data System (ADS)

Urakawa, S.; Kondo, T.; Igawa, N.; Shimomura, O.; Ohno, H.

1994-10-01

In situ X-ray diffraction study on KAlSi3O8 has been performed using the cubic type high pressure apparatus, MAX90, combined with synchrotron radiation. We determined the phase relations of sanidine, the wadeite-type K2Si4O9+kyanite (Al2SiO5)+coesite (SiO2) assemblage, and hollandite-type KAlSi3O8, including melting temperatures of potassic phases, up to 11 GPa. Our data on subsolidus phase boundaries are close to the recent data of Yagi and Akaogi (1991). Melting relations of sanidine are consistent with the low pressure data of Lindsley (1966). The breakdown of sanidine into three phases reduces melting temperature, and wadeite-type K2Si4O9 melts first around 1500° C in three phase coexisting region. Melting point of hollandite-type KAlSi3O8 is between 1700° C and 1800° C at 11 GPa. If these potassic phases host potassium in the earth's mantle, the true mantle solidus temperature will be much lower than the reported dry solidus temperature of peridotite.

Structure and thermal expansion of Lu 2O 3 and Yb 2O 3 up to the melting points

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pavlik, Alfred; Ushakov, Sergey V.; Navrotsky, Alexandra

Knowledge of thermal expansion and high temperature phase transformations is essential for prediction and interpretation of materials behavior under the extreme conditions of high temperature and intense radiation encountered in nuclear reactors. We studied the structure and thermal expansion of Lu 2O 3 and Yb 2O 3 were studied in oxygen and argon atmospheres up to their melting temperatures using synchrotron X-ray diffraction on laser heated levitated samples. Both oxides retained the cubic bixbyite C-type structure in oxygen and argon to melting. In contrast to fluorite-type structures, the increase in the unit cell parameter of Yb 2O 3 and Lumore » 2O 33 with temperature is linear within experimental error from room temperature to the melting point, with mean thermal expansion coefficients (8.5 ± 0.6) · 10 -6 K -1 and (7.7 ± 0.6) · 10 -6 K -1, respectively. There is no indication of a superionic (Bredig) transition in the C-type structure or of a previously suggested Yb 2O 3 phase transformation to hexagonal phase prior to melting.« less

Local melting in Al embedded with TiNi powder induced by microarea self-propagating high-temperature synthesis

NASA Astrophysics Data System (ADS)

Yamamoto, Tokujiro

2014-10-01

Microarea self-propagating high-temperature synthesis (microSHS) was ignited by the heat of mixing generated at the boundaries between an Al matrix and TiNi particles during plastic deformation at room temperature. The temperature of the boundaries was rapidly increased by microSHS; the temperature elevation resulted in local melting of the TiNi particle and the surrounding Al matrix, because the heat of mixing was localized in the vicinity of the TiNi particle although the amount of the heat of mixing was limited. Since the amount of the local melting region induced by microSHS is restricted, not only major elements (i.e. Al, Ti and Ni) but also impurities were involved in the solidification followed by local melting. As a result, ?FeNi nanoprecipitates, which have not been reported in SHS studies, were formed by inclusion of Fe, initially included as an impurity in raw materials. The formation mechanism of ?FeNi nanoprecipitates is discussed based on reference to the Al-Fe-Ni ternary alloy phase diagram. It is expected that local melting induced by microSHS is a key phenomonon for amorphization during severe plastic deformation of elemental sheets.

On a possible melting curve of C60 fullerite

NASA Astrophysics Data System (ADS)

Zubov, V. I.; Rodrigues, C. G.; Zubov, I. V.

2003-07-01

We study the thermodynamic properties of the high-temperature modification of fullerites on the basis of the Girifalco intermolecular potential. In the present work, using Lindemann's melting criterion, we estimate a possible melting curve Tm(P) of C60 fullerite. To take into account the lattice anharmonicity, which has a strong effect at T > 700 K, we use the correlative method of unsymmetrized self-consistent field. To check this approach, first we have applied it to solid Ar. In the range between its triple point Tt = 83.807 K and 260 K we obtained the mean square relative deviation from experimental data of about 0.7%. The melting curve for C60 fullerite has been calculated from the melting point at normal pressure estimated at 1500 K up to 15 kbar, which corresponds to Tm = 4000 K, i.e. to the temperature estimated by Kim and Tománek [Phys. Rev. Lett. 72, 2418 (1994)] as that of the decomposition of the C60 molecule itself. The temperature dependence of the melting pressure is approximated very well by the Simon equation (Pm(T)/bar - 1)/b = (T/T0)c with T0 = 1500 K, b = 6643.8, and c = 1.209. The temperature dependence of the molar volume along the melting curve is described by Vs(T) = Vs(T0) - 29.20 ln (T/T0.

Melting in super-earths.

PubMed

Stixrude, Lars

2014-04-28

We examine the possible extent of melting in rock-iron super-earths, focusing on those in the habitable zone. We consider the energetics of accretion and core formation, the timescale of cooling and its dependence on viscosity and partial melting, thermal regulation via the temperature dependence of viscosity, and the melting curves of rock and iron components at the ultra-high pressures characteristic of super-earths. We find that the efficiency of kinetic energy deposition during accretion increases with planetary mass; considering the likely role of giant impacts and core formation, we find that super-earths probably complete their accretionary phase in an entirely molten state. Considerations of thermal regulation lead us to propose model temperature profiles of super-earths that are controlled by silicate melting. We estimate melting curves of iron and rock components up to the extreme pressures characteristic of super-earth interiors based on existing experimental and ab initio results and scaling laws. We construct super-earth thermal models by solving the equations of mass conservation and hydrostatic equilibrium, together with equations of state of rock and iron components. We set the potential temperature at the core-mantle boundary and at the surface to the local silicate melting temperature. We find that ancient (∼4 Gyr) super-earths may be partially molten at the top and bottom of their mantles, and that mantle convection is sufficiently vigorous to sustain dynamo action over the whole range of super-earth masses.

Melting and Freezing of Metal Clusters

NASA Astrophysics Data System (ADS)

Aguado, Andrés; Jarrold, Martin F.

2011-05-01

Recent developments allow heat capacities to be measured for size-selected clusters isolated in the gas phase. For clusters with tens to hundreds of atoms, the heat capacities determined as a function of temperature usually have a single peak attributed to a melting transition. The melting temperatures and latent heats show large size-dependent fluctuations. In some cases, the melting temperatures change by hundreds of degrees with the addition of a single atom. Theory has played a critical role in understanding the origin of the size-dependent fluctuations, and in understanding the properties of the liquid-like and solid-like states. In some cases, the heat capacities have extra features (an additional peak or a dip) that reveal a more complex behavior than simple melting. In this article we provide a description of the methods used to measure the heat capacities and provide an overview of the experimental and theoretical results obtained for sodium and aluminum clusters.

On the role of quantum ion dynamics for the anomalous melting of lithium

NASA Astrophysics Data System (ADS)

Elatresh, Sabri; Bonev, Stanimir

2011-03-01

Lithium has attracted a lot of interest in relation to a number of counterintuitive electronic and structural changes that it exhibits under pressure. One of the most remarkable properties of dense lithium is its anomalous melting. This behavior was first predicted theoretically based on first-principles molecular dynamics (FPMD) simulations, which treated the ions classically. The lowest melting temperature was determined to be about 275~K at 65~GPa. Recent experiments measured a melting temperature about 100~K lower at the same pressure. In this talk, we will present FPMD calculations of solid and liquid lithium free energies up to 100 GPa that take into account ion quantum dynamics. We examine the significance of the quantum effects for the finite-temperature phase boundaries of lithium and, in particular, its melting curve. Work supported by NSERC, Acenet, and LLNL under Contract DE-AC52-07NA27344.

Dynamics of upper mantle rocks decompression melting above hot spots under continental plates

NASA Astrophysics Data System (ADS)

Perepechko, Yury; Sorokin, Konstantin; Sharapov, Victor

2014-05-01

Numeric 2D simulation of the decompression melting above the hot spots (HS) was accomplished under the following conditions: initial temperature within crust mantle section was postulated; thickness of the metasomatized lithospheric mantle is determined by the mantle rheology and position of upper asthenosphere boundary; upper and lower boundaries were postulated to be not permeable and the condition for adhesion and the distribution of temperature (1400-2050°C); lateral boundaries imitated infinity of layer. Sizes and distribution of lateral points, their symmetry, and maximum temperature varied between the thermodynamic condition for existences of perovskite - majorite transition and its excess above transition temperature. Problem was solved numerically a cell-vertex finite volume method for thermo hydrodynamic problems. For increasing convergence of iterative process the method of lower relaxation with different value of relaxation parameter for each equation was used. The method of through calculation was used for the increase in the computing rate for the two-layered upper mantle - lithosphere system. Calculated region was selected as 700 x (2100-4900) km. The time step for the study of the asthenosphere dynamics composed 0.15-0.65 Ma. The following factors controlling the sizes and melting degree of the convective upper mantle, are shown: a) the initial temperature distribution along the section of upper mantleb) sizes and the symmetry of HS, c) temperature excess within the HS above the temperature on the upper and lower mantle border TB=1500-2000oC with 5-15% deviation but not exceed 2350oC. It is found, that appearance of decompression melting with HS presence initiate primitive mantle melting at TB > of 1600oC. Initial upper mantle heating influence on asthenolens dimensions with a constant HS size is controlled mainly by decompression melting degree. Thus, with lateral sizes of HS = 400 km the decompression melting appears at TB > 1600oC and HS temperature (THS) > 1900oC asthenolens size ~700 km. When THS = of 2000oC the maximum melting degree of the primitive mantle is near 40%. An increase in the TB > 1900oC the maximum degree of melting could rich 100% with the same size of decompression melting zone (700 km). We examined decompression melting above the HS having LHS = 100 km - 780 km at a TB 1850- 2100oC with the thickness of lithosphere = 100 km.It is shown that asthenolens size (Lln) does not change substantially: Lln=700 km at LHS = of 100 km; Lln= 800 km at LHS = of 780 km. In presence of asymmetry of large HS the region of advection is developed above the HS maximum with the formation of asymmetrical cell. Influence of lithospheric plate thicknesses on appearance and evolution of asthenolens above the HS were investigated for the model stepped profile for the TB ≤ of 1750oS with Lhs = 100km and maximum of THS =2350oC. With an increase of TB the Lln difference beneath lithospheric steps is leveled with retention of a certain difference to melting degrees and time of the melting appearance a top of the HS. RFBR grant 12-05-00625.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Evans, III, Boyd Mccutchen; Kisner, Roger A.; Ludtka, Gail Mackiewicz

A method of making a single crystal comprises heating a material comprising magnetic anisotropy to a temperature T sufficient to form a melt of the material. A magnetic field of at least about 1 Tesla is applied to the melt at the temperature T, where a magnetic free energy difference .DELTA.G.sub.m between different crystallographic axes is greater than a thermal energy kT. While applying the magnetic field, the melt is cooled at a rate of about 30.degree. C./min or higher, and the melt solidifies to form a single crystal of the material.

Northeast Atlantic Igneous Province volcanic margin development

NASA Astrophysics Data System (ADS)

Mjelde, R.; Breivik, A. J.; Faleide, J. I.

2009-04-01

Early Eocene continental breakup in the NE Atlantic Volcanic Province (NAIP) was associated with voluminous extrusive and intrusive magmatism, and initial seafloor spreading produced anomalously thick oceanic crust. Recent publications based on crustal-scale wide-angle seismic data show that there is a positive correlation between igneous crustal thickness (H) and average P-wave velocity (Vp) on all investigated margins in the NAIP. Vp can be used as a proxy for crustal composition, which can be related to the mode of mantle melting. A positive H-Vp correlation indicates that excessive mantle melting the first few million years after breakup was driven by an initial increased temperature that cools off as seafloor spreading develops, consistent with a mantle plume model. Variations in mantle composition can explain excess magmatism, but will generate a negative H-Vp correlation. Active mantle convection may increase the flux of mantle rocks through the melting zone above the rate of passive corner flow, which can also produce excessive magmatism. This would produce little H-Vp correlation, and place the curve lower than the passive flow melting curve in the diagram. We have compiled earlier published results with our own analyses of published and unpublished data from different groups to look for systematic variations in the mantle melting mode along the NAIP margins. Earlier studies (Holbrook et al., 2002, White et al, 2008) on the southeast Greenland conjugate system, indicate that the thick igneous crust of the southern NAIP (SE Greenland ? Hatton Bank) was dominated by increased mantle temperature only, while magmatism closer to the southern side of and including the Greenland-Iceland-Færøy Ridge (GIFR) was created by combined temperature increase and active mantle convection. Recent publications (Breivik et al., 2008, White et al, 2008) north of the GIFR for the Norway Basin segment, indicate temperature dominated magmatism between the Jan Mayen Fracture Zone (JMFZ) system and the Færøy archipelago. Our unpublished data on the conjugate margin of the eastern Jan Mayen ridge confirm this. North of the JMFZ, early magmatism appears to be caused by the combined effect of elevated temperature and convection, while there is a rapid transition to predominantly temperature dominated melting ~2 M.y. after breakup. This is similar to the northern conjugate East Greenland profiles we examined (Voss and Jokat, 2007), while the southern of their two profiles indicates that convection is not turned off at that side. Conjugate differences in igneous crustal thickness further indicate asymmetric conjugate magmatic development. For comparison, we applied the same analysis to data from the Vøring Spur located off the Vøring Margin, and the igneous crust beneath the Jan Mayen Island. Both show little H-Vp correlation with generally lowVp, indicating that these igneous features were created through low-degree mantle melting created by some kind of mantle convection without an elevated temperature component.

System for Repairing Cracks in Structures

NASA Technical Reports Server (NTRS)

Smith, Stephen W. (Inventor); Newman, John A. (Inventor); Piascik, Robert S. (Inventor); Glaessgen, Edward H. (Inventor)

2014-01-01

A first material with a known maximum temperature of operation is coated with a second material on at least one surface of the first material. The coating has a melting temperature that is greater than the maximum temperature of operation of the first material. The coating is heated to its melting temperature until the coating flows into any cracks in the first material's surface.

Triplex-mediated analysis of cytosine methylation at CpA sites in DNA.

PubMed

Johannsen, Marie W; Gerrard, Simon R; Melvin, Tracy; Brown, Tom

2014-01-18

Modified triplex-forming oligonucleotides distinguish 5-methyl cytosine from unmethylated cytosine in DNA duplexes by differences in triplex melting temperatures. The discrimination is sequence-specific; dramatic differences in stabilisation are seen for CpA methylation, whereas CpG methylation is not detected. This direct detection of DNA methylation constitutes a new approach for epigenetic analysis.

Vitrification of waste with conitnuous filling and sequential melting

DOEpatents

Powell, James R.; Reich, Morris

2001-09-04

A method of filling a canister with vitrified waste starting with a waste, such as high-level radioactive waste, that is cooler than its melting point. Waste is added incrementally to a canister forming a column of waste capable of being separated into an upper zone and a lower zone. The minimum height of the column is defined such that the waste in the lower zone can be dried and melted while maintaining the waste in the upper zone below its melting point. The maximum height of the column is such that the upper zone remains porous enough to permit evolved gases from the lower zone to flow through the upper zone and out of the canister. Heat is applied to the waste in the lower zone to first dry then to raise and maintain its temperature to a target temperature above the melting point of the waste. Then the heat is applied to a new lower zone above the melted waste and the process of adding, drying and melting the waste continues upward in the canister until the entire canister is filled and the entire contents are melted and maintained at the target temperature for the desired period. Cooling of the melted waste takes place incrementally from the bottom of the canister to the top, or across the entire canister surface area, forming a vitrified product.

Improved mechanical properties of thermoelectric (Bi 0.2Sb 0.8) 2Te 3 by nanostructuring

DOE PAGES

Lavrentev, M. G.; Osvenskii, V. B.; Parkhomenko, Yu. N.; ...

2016-06-01

Temperature-dependent strength of Bi-Sb-Te under uniaxial compression is investigated. Bi-Sb-Te samples were produced by three methods: vertical zone-melting, hot extrusion, and spark plasma sintering (SPS). For zone-melted and extruded samples, the brittle-ductile transition occurs over a temperature range of 200-350 °C. In nanostructured samples produced via SPS, the transition is observed in a narrower temperature range of 170-200 °C. At room temperature, the strength of the nanostructured samples is higher than that of zone-melted and extruded samples, but above 300 °C, all samples decrease to roughly the same strength.

Improved mechanical properties of thermoelectric (Bi 0.2Sb 0.8) 2Te 3 by nanostructuring

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lavrentev, M. G.; Osvenskii, V. B.; Parkhomenko, Yu. N.

Temperature-dependent strength of Bi-Sb-Te under uniaxial compression is investigated. Bi-Sb-Te samples were produced by three methods: vertical zone-melting, hot extrusion, and spark plasma sintering (SPS). For zone-melted and extruded samples, the brittle-ductile transition occurs over a temperature range of 200-350 °C. In nanostructured samples produced via SPS, the transition is observed in a narrower temperature range of 170-200 °C. At room temperature, the strength of the nanostructured samples is higher than that of zone-melted and extruded samples, but above 300 °C, all samples decrease to roughly the same strength.

Temperature-profile detector

DOEpatents

Not Available

1981-01-29

Temperature profiles at elevated temperature conditions are monitored by use of an elongated device having two conductors spaced by the minimum distance required to normally maintain an open circuit between them. The melting point of one conductor is selected at the elevated temperature being detected, while the melting point of the other is higher. As the preselected temperature is reached, liquid metal will flow between the conductors creating short circuits which are detectable as to location.

Temperature profile detector

DOEpatents

Tokarz, Richard D.

1983-01-01

Temperature profiles at elevated temperature conditions are monitored by use of an elongated device having two conductors spaced by the minimum distance required to normally maintain an open circuit between them. The melting point of one conductor is selected at the elevated temperature being detected, while the melting point of the other is higher. As the preselected temperature is reached, liquid metal will flow between the conductors, creating short circuits which are detectable as to location.

Mutual interaction between high and low stereo-regularity components for crystallization and melting behaviors of polypropylene blend fibers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kawai, Kouya; Takarada, Wataru; Kikutani, Takeshi, E-mail: kikutani.t.aa@m.titech.ac.jp

Crystallization and melting behaviors of blend fibers of two types of polypropylene (PP), i.e. high stereo-regularity/high molecular weight PP (HPP) and low stereo-regularity/low molecular weight PP (LPP), was investigated. Blend fibers consisting of various HPP/LPP compositions were prepared through the melt spinning process. Differential scanning calorimetry (DSC), temperature modulated DSC (TMDSC) and wide-angle X-ray diffraction (WAXD) analysis were applied for clarifying the crystallization and melting behaviors of individual components. In the DSC measurement of blend fibers with high LPP composition, continuous endothermic heat was detected between the melting peaks of LPP at around 40 °C and that of HPP atmore » around 160 °C. Such endothermic heat was more distinct for the blend fibers with higher LPP composition indicating that the melting of LPP in the heating process was hindered because of the presence of HPP crystals. On the other hand, heat of crystallization was detected at around 90 °C in the case of blend fibers with LPP content of 30 to 70 wt%, indicating that the crystallization of HPP component was taking place during the heating of as-spun blend fibers in the DSC measurement. Through the TMDSC analysis, re-organization of the crystalline structure through the simultaneous melting and re-crystallization was detected in the cases of HPP and blend fibers, whereas re-crystallization was not detected during the melting of LPP fibers. In the WAXD analysis during the heating of fibers, amount of a-form crystal was almost constant up to the melting in the case of single component HPP fibers, whereas there was a distinct increase of the intensity of crystalline reflections from around 100 °C, right after the melting of LPP in the case of blend fibers. These results suggested that the crystallization of HPP in the spinning process as well as during the conditioning process after spinning was hindered by the presence of LPP.« less

Surface Hydrological Processes of Rock Glaciated Basins in the San Juan Mountains, Colorado

NASA Astrophysics Data System (ADS)

Mateo, E. I.

2017-12-01

Glaciers in the western United States have been examined in terms of their summer meltwater contributions to regional hydrological systems. In the San Juan Mountains of Colorado where glaciers do not and cannot exist due to a rising zero-degree isotherm, rock glaciers take the place of valley glaciers during the summer runoff period. Most of the rock glaciers in Colorado are located on a northerly slope aspect, however, there are multiple in the southwest region of the state that occur on different aspects. This study asked how slope aspect and rising air temperatures influenced the hydrological processes of streams below rock glaciers in the San Juan Mountains during the 2016 summer season. This project focused on three basins, Yankee Boy basin, Blue Lakes basin, and Mill Creek basin, which are adjacent to each other and share a common peak, Gilpin Peak. Findings of this one-season study showed that air temperature significantly influenced stream discharge below each rock glacier. Discharge and air temperature patterns indicate a possible air temperature threshold during late summer when rock glacier melt increased at a greater rate. The results also suggest that slope aspect of rock glacier basins influences stream discharge, but temperature and precipitation are likely larger components of the melt regimes. The continuation of data collection during the 2017 summer season has allowed for more detailed analysis of the relationship between air temperature and rock glacier melt. This continual expansion of the original dataset is crucial for understanding the hydrological processes of surface runoff below rock glaciers.

Aluminosilicate melts and glasses at 1 to 3 GPa: Temperature and pressure effects on recovered structural and density changes

USGS Publications Warehouse

Bista, S; Stebbins, Jonathan; Hankins, William B.; Sisson, Thomas W.

2015-01-01

In the pressure range in the Earth’s mantle where many basaltic magmas are generated (1 to 3 GPa) (Stolper et al. 1981), increases in the coordination numbers of the network-forming cations in aluminosilicate melts have generally been considered to be minor, although effects on silicon and particularly on aluminum coordination in non-bridging oxygen-rich glasses from the higher, 5 to 12 GPa range, are now well known. Most high-precision measurements of network cation coordination in such samples have been made by spectroscopy (notably 27Al and 29Si NMR) on glasses quenched from high-temperature, high-pressure melts synthesized in solid-media apparatuses and decompressed to room temperature and 1 bar pressure. There are several effects that could lead to the underestimation of the extent of actual structural (and density) changes in high-pressure/temperature melts from such data. For non-bridging oxygen-rich sodium and calcium aluminosilicate compositions in the 1 to 3 GPa range, we show here that glasses annealed near to their glass transition temperatures systematically record higher recovered increases in aluminum coordination and in density than samples quenched from high-temperature melts. In the piston-cylinder apparatus used, rates of cooling through the glass transition are measured as very similar for both higher and lower initial temperatures, indicating that fictive temperature effects are not the likely explanation of these differences. Instead, transient decreases in melt pressure during thermal quenching, which may be especially large for high initial run temperatures, of as much as 0.5 to 1 GPa, may be responsible. As a result, the equilibrium proportion of high-coordinated Al in this pressure range may be 50 to 90% greater than previously estimated, reaching mean coordination numbers (e.g., 4.5) that are probably high enough to significantly affect melt properties. New data on jadeite (NaAlSi2O6) glass confirm that aluminum coordination increase with pressure is inhibited in compositions low in non-bridging O atoms.

Crystallization from high temperature solutions of Si in copper

DOEpatents

Ciszek, Theodore F.

1994-01-01

A liquid phase epitaxy method for forming thin crystalline layers of device quality silicon having less than 5X10.sup.16 Cu atoms/cc impurity, comprising: preparing a saturated liquid solution melt of Si in Cu at about 16% to about 90% wt. Si at a temperature range of about 800.degree. C. to about 1400.degree. C. in an inert gas; immersing a substrate in the saturated solution melt; supersaturating the solution by lowering the temperature of the saturated solution melt and holding the substrate immersed in the solution melt for a period of time sufficient to cause growing Si to precipitate out of the solution to form a crystalline layer of Si on the substrate; and withdrawing the substrate from the solution.

Understanding Melt-Memory of Commercial Polyolefins

NASA Astrophysics Data System (ADS)

Alamo, Rufina

Self-nucleation (SN) or controlling self-generated seeds in a polymer melt is an avenue to increase the rate of solidification of semicrystalline polymers of commercial relevance. Self-nuclei are remains in the melt of the segmental self-assembly to form polymer crystallites providing a path to enhance primary crystal nucleation. SN has been extensively studied in homopolymers such as iPP. Recently, a strong memory effect of crystallization has been observed in melts of random ethylene copolymers well above the equilibrium melting temperature. The melt memory is associated with clusters or seeds that remain in the melt from the copolymer's sequence length partitioning. Cooling from progressively lower self-seeded melt temperatures, ethylene copolymers with a broad inter-chain comonomer composition (1 - 15 mol%) display first the expected accelerated crystallization, followed by a decrease in the rate in a range of melt temperatures where narrow copolymers show a continuous acceleration of the rate. This unusual inversion of the crystallization rate was postulated to arise from the onset of liquid-liquid phase separation (LLPS) between comonomer-rich and comonomer-poor components of the broad copolymer. The UCST type phase diagram of these commercial copolymers has been documented via SANS using a blend of components, some deuterated, to reproduce the broad distribution. Furthermore, the components that contribute to LLPS have been identified by the crystallization behavior of molar mass fractions. The influence of long chain branching on the topology of copolymer melts has been analyzed using model 3-arm stars hydrogenated polybutadienes. The effect of melt viscosity on strength of melt memory is also evident when SN data of random ethylene copolymers are compared with those of propylene-ethylene copolymers. The strong dependence of melt viscosity on melt memory, and a critical threshold crystallinity level to observe the effect of melt memory on crystallization rate, support the kinetic nature of the SN phenomenon. Support from NSF, DMR-1105129 and DMR-1607786 is gratefully acknowledged.

Melting Behavior of Volcanic Ash relevant to Aviation Ash Hazard

NASA Astrophysics Data System (ADS)

Song, W.; Hess, K.; Lavallee, Y.; Cimarelli, C.; Dingwell, D. B.

2013-12-01

Volcanic ash is one of the major hazards caused by volcanic eruptions. In particular, the threat to aviation from airborne volcanic ash has been widely recognized and documented. In the past 12 years, more than 60 modern jet airplanes, mostly jumbo jets, have been damaged by drifting clouds of volcanic ash that have contaminated air routes and airport facilities. Seven of these encounters are known to have caused in-flight loss of engine power to jumbo jets carrying a total of more than 2000 passengers. The primary cause of engine thrust loss is that the glass in volcanic ash particles is generated at temperatures far lower than the temperatures in the combustion chamber of a jet engine ( i.e. > 1600 oC) and when the molten volcanic ash particles leave this hottest section of the engine, the resolidified molten volcanic ash particles will be accumulated on the turbine nozzle guide vanes, which reduced the effective flow of air through the engine ultimately causing failure. Thus, it is essential to investigate the melting process and subsequent deposition behavior of volcanic ash under gas turbine conditions. Although few research studies that investigated the deposition behavior of volcanic ash at the high temperature are to be found in public domain, to the best our knowledge, no work addresses the formation of molten volcanic ash. In this work, volcanic ash produced by Santiaguito volcano in Guatemala in November 8, 2012 was selected for study because of their recent activity and potential hazard to aircraft safety. We used the method of accessing the behavior of deposit-forming impurities in high temperature boiler plants on the basis of observations of the change in shape and size of a cylindrical coal ash to study the sintering and fusion phenomena as well as determine the volcanic ash melting behavior by using characteristic temperatures by means of hot stage microscope (HSM), different thermal analysis (DTA) and Thermal Gravimetric Analysis (TGA) to investigate the sintering process of volcanic ash. In order to analyze the mineral transformation and microstructure evolution, the qualitative as well as quantitative crystalline phase analysis of volcanic ash samples directly taken from furnace by per 100 oC in the range of between 100 and 1400 oC as well as evaluation of microstructure of volcanic ash taken from from furnace by per 20 oC in the range of between 1000 and 1300 oC has been made by X-ray diffraction (XRD) and observed by scanning electron microscopy (SEM). Finally, we obtain the viscosity temperature curve for volcanic ash during melting process on the basis of the characteristic temperature obtained by HSM.

A study of the applicability of gallium arsenide and silicon carbide as aerospace sensor materials

NASA Technical Reports Server (NTRS)

Hurley, John S.

1990-01-01

Most of the piezoresistive sensors, to date, are made of silicon and germanium. Unfortunately, such materials are severly restricted in high temperature environments. By comparing the effects of temperature on the impurity concentrations and piezoresistive coefficients of silicon, gallium arsenide, and silicon carbide, it is being determined if gallium arsenide and silicon carbide are better suited materials for piezoresistive sensors in high temperature environments. The results show that the melting point for gallium arsenide prevents it from solely being used in high temperature situations, however, when used in the alloy Al(x)Ga(1-x)As, not only the advantage of the wider energy band gas is obtained, but also the higher desire melting temperature. Silicon carbide, with its wide energy band gap and higher melting temperature suggests promise as a high temperature piezoresistive sensor.

Hybrid analysis (barcode-high resolution melting) for authentication of Thai herbal products, Andrographis paniculata (Burm.f.) Wall.ex Nees

PubMed Central

Osathanunkul, Maslin; Suwannapoom, Chatmongkon; Khamyong, Nuttaluck; Pintakum, Danupol; Lamphun, Santisuk Na; Triwitayakorn, Kanokporn; Osathanunkul, Kitisak; Madesis, Panagiotis

2016-01-01

Background: Andrographis paniculata Nees is a medicinal plant with multiple pharmacological properties. It has been used over many centuries as a household remedy. A. paniculata products sold on the markets are in processed forms so it is difficult to authenticate. Therefore buying the herbal products poses a high-risk of acquiring counterfeited, substituted and/or adulterated products. Due to these issues, a reliable method to authenticate products is needed. Materials and Methods: High resolution melting analysis coupled with DNA barcoding (Bar-HRM) was applied to detect adulteration in commercial herbal products. The rbcL barcode was selected to use in primers design for HRM analysis to produce standard melting profile of A. paniculata species. DNA of the tested commercial products was isolated and their melting profiles were then generated and compared with the standard A. paniculata. Results: The melting profiles of the rbcL amplicons of the three closely related herbal species (A. paniculata, Acanthus ebracteatus and Rhinacanthus nasutus) are clearly separated so that they can be distinguished by the developed method. The method was then used to authenticate commercial herbal products. HRM curves of all 10 samples tested are similar to A. paniculata which indicated that all tested products were contained the correct species as labeled. Conclusion: The method described in this study has been proved to be useful in aiding identification and/or authenticating A. paniculata. This Bar-HRM analysis has allowed us easily to determine the A. paniculata species in herbal products on the markets even they are in processed forms. SUMMARY We propose the use of DNA barcoding combined with High Resolution Melting analysis for authenticating of Andrographis paniculata products.The developed method can be used regardless of the type of the DNA template (fresh or dried tissue, leaf, and stem).rbcL region was chosen for the analysis and work well with our samplesWe can easily determine the A. paniculata species in herbal products tested. Abbreviations used: bp: Base pair, Tm: Melting temperature PMID:27041863

Convective melting in a magma chamber: theory and numerical experiment.

NASA Astrophysics Data System (ADS)

Simakin, A.

2012-04-01

We present results of the numerical modeling of convective melting in a magma chamber in 2D. Model was pointed on the silicic system approximated with Qz-Fsp binary undersaturated with water. Viscosity was calculated as a function of the melt composition, temperature and crystal content and comprises for the pure melt 104.5-105.5 Pas. Lower boundary was taken thermally insulated in majority of the runs. Size of FEM (bilinear elements) grid for velocity is 25x25 cm and for the integration of the density term 8x8 cm. Melting of the chamber roof proceeds with the heat supply due to the chaotic thermo-compositional convection and conductive heat loose into melted substrate. We compare our numerical data with existing semi-analytical models. Theoretical studies of the assimilation rates in the magma chambers usually use theoretical semi-analytical model by Huppert and Sparks (1988) (e.g., Snyder, 2000). We find that this model has strong points: 1) Independence of the melting rate on the sill thickness (Ra>>Rac) 2) Independence of the convective heat transfer on the roof temperature 3) Determination of the exponential thermal boundary layer ahead of the melting front and weak points: 1) Ignoring the possibility of the crystallization without melting regime for narrow sills and dykes. 2)Neglecting of two-phase character of convection. 3)Ignoring of the strong viscosity variation near the melting front. Independence of convective flux from the sill size (at Ra>>Rac) allows reducing of computational domain to the geologically small size (10-15 m). Concept of exponential thermal boundary layer is also rather important. Length scale (L0) of this layer is related to the melting rate and thermal diffusivity coefficient kT as L0=kT/um and at the melting rate 10 m/yr becomes about 2 m. Such small scale implies that convective melting is very effective (small conductive heat loss) and part of the numerical domain filled with roof rocks can be taken small. In the H&S model conditions for the intruded magma to crystallize first and then switch to the roof melting or only crystallize were not defined. We did this in our numerical experiments in terms of the initial magma and roof rocks temperatures for particular sill size. Neglecting strong viscosity variation in the boundary layer at the melting front leads to the overestimation of the melting rate by H&S model on approximately 70% at Tm=940oC. At Tm =800oC effect of the crystals present in descending plumes compensates viscosity increase and numerical Um practically coincides with theoretical one (difference 8%). Some researchers (Huber et al., 2010) use empirical and scaling results obtained from stagnant-lid convection (Davaille and Jaupart, 1993). We find that the later model is not applicable to the melting problem since super-exponential dependence of the viscosity from temperature is valid providing full solidification below eutectic temperature Ts. "Melting temperature" at the stagnant-lid style of convection is defined by Arhenius rheological parameters and bulk melt temperature and can be less than Ts. Our numerical study was applied to the estimation of the possible time frame and efficiency of the remelting of the silicic pyroclastics by superheated rhyolites in the caldera environment (Simakin and Bindeman, 2012). Literature. 1)Davaille, A. and Jaupart, C. (1993) J. Fluid. Mech., 253: 141-166. 2) Huppert, H.E. and Sparks, R.S.J. (1988) J. Petrol., 29: 599-624. 3)Huber, C., Bachmann, O., Dufek, J. (2010) J. Volcanol. Geotherm. Res., 195: 97-105. 4)Jaupart, C. and Brandeis, G. (1986) Earth Planet. Sci. Lett. 80: 183-199. 5)Simakin, A.G. and Bindeman, I.N. (2012) Remelting in caldera and rift environments and the genesis of hot, "recycled" rhyolites. Earth Planet. Sci. Lett. (in review). 6) Snyder, D. (2000) Earth Planet. Sci. Lett. 175: 257-273.

Temperature dependent micro-rheology of a glass-forming polymer melt studied by molecular dynamics simulation.

PubMed

Kuhnhold, A; Paul, W

2014-09-28

We present a Molecular Dynamics simulation study of a micro-rheological probing of the glass transition in a polymer melt. Our model system consists of short bead-spring chains and the temperature ranges from well above the glass transition temperature to about 10% above it. The nano-particle clearly couples to the slowing down of the polymer segments and the calculated storage and loss moduli reveal the approach to the glass transition. At temperatures close to the mode coupling Tc of the polymer melt, the micro-rheological moduli measure the local viscoelastic response of the cage of monomers surrounding the nano-particle and no longer reveal the true melt moduli. The incoherent scattering function of the nano-particle exhibits a stretched exponential decay, typical for the α-process in glass forming systems. We find no indication of a strong superdiffusive regime as has been deduced from a recent experiment in the same temperature range but for smaller momentum transfers.

Experimental and theoretical evidence for bilayer-by-bilayer surface melting of crystalline ice

PubMed Central

Sánchez, M. Alejandra; Kling, Tanja; Ishiyama, Tatsuya; van Zadel, Marc-Jan; Mezger, Markus; Jochum, Mara N.; Cyran, Jenée D.; Smit, Wilbert J.; Bakker, Huib J.; Shultz, Mary Jane; Morita, Akihiro; Donadio, Davide; Nagata, Yuki; Bonn, Mischa; Backus, Ellen H. G.

2017-01-01

On the surface of water ice, a quasi-liquid layer (QLL) has been extensively reported at temperatures below its bulk melting point at 273 K. Approaching the bulk melting temperature from below, the thickness of the QLL is known to increase. To elucidate the precise temperature variation of the QLL, and its nature, we investigate the surface melting of hexagonal ice by combining noncontact, surface-specific vibrational sum frequency generation (SFG) spectroscopy and spectra calculated from molecular dynamics simulations. Using SFG, we probe the outermost water layers of distinct single crystalline ice faces at different temperatures. For the basal face, a stepwise, sudden weakening of the hydrogen-bonded structure of the outermost water layers occurs at 257 K. The spectral calculations from the molecular dynamics simulations reproduce the experimental findings; this allows us to interpret our experimental findings in terms of a stepwise change from one to two molten bilayers at the transition temperature. PMID:27956637

Variability of Surface Temperature and Melt on the Greenland Ice Sheet, 2000-2011

NASA Technical Reports Server (NTRS)

Hall, Dorothy K.; Comiso, Josefino, C.; Shuman, Christopher A.; Koenig, Lora S.; DiGirolamo, Nicolo E.

2012-01-01

Enhanced melting along with surface-temperature increases measured using infrared satellite data, have been documented for the Greenland Ice Sheet. Recently we developed a climate-quality data record of ice-surface temperature (IST) of the Greenland Ice Sheet using the Moderate-Resolution Imaging Spectroradiometer (MODIS) 1ST product -- http://modis-snow-ice.gsfc.nasa.gov. Using daily and mean monthly MODIS 1ST maps from the data record we show maximum extent of melt for the ice sheet and its six major drainage basins for a 12-year period extending from March of 2000 through December of 2011. The duration of the melt season on the ice sheet varies in different drainage basins with some basins melting progressively earlier over the study period. Some (but not all) of the basins also show a progressively-longer duration of melt. The short time of the study period (approximately 12 years) precludes an evaluation of statistically-significant trends. However the dataset provides valuable information on natural variability of IST, and on the ability of the MODIS instrument to capture changes in IST and melt conditions indifferent drainage basins of the ice sheet.

Mixing effects in a ternary Hf-Zr-Ni metallic melt

NASA Astrophysics Data System (ADS)

Nowak, B.; Holland-Moritz, D.; Yang, F.; Evenson, Z.; Meyer, A.

2018-03-01

We study the effect of the substitution of Zr by Hf on the dynamical behavior in the Zr36Ni64 melt. A reduced measured self-diffusion coefficient and a higher measured melt viscosity for an increased amount of Hf were observed. The ternary Hf10Zr25Ni65 melt, which exhibits a pronounced deviation from Arrhenius behavior over a studied temperature range of 550 K, can be accurately described by the scaling law of mode-coupling theory (MCT) with almost equal parameters for the self-diffusion and the viscosity. Although we only substitute alloy components with a nearly equal atomic size and the measured overall packing fraction remains almost unchanged, the dynamics in Hf10Zr25Ni65 are slower compared to Zr36Ni64 . This corresponds also to a higher critical temperature Tc and might be induced by different chemical interactions in the melts. The increased Tc results in a significantly smaller difference between liquidus and critical temperature Δ TLC=TL-Tc for the ternary melt in comparison with Zr36Ni64 , which may favor the glass formation in the Hf10Zr25Ni65 melt.

Pressure Induced Liquid-to-Liquid Transition in Zr-based Supercooled Melts and Pressure Quenched Glasses.

PubMed

Dmowski, W; Gierlotka, S; Wang, Z; Yokoyama, Y; Palosz, B; Egami, T

2017-07-26

Through high-energy x-ray diffraction and atomic pair density function analysis we find that Zr-based metallic alloy, heated to the supercooled liquid state under hydrostatic pressure and then quenched to room temperature, exhibits a distinct glassy structure. The PDF indicates that the Zr-Zr distances in this glass are significantly reduced compared to those quenched without pressure. Annealing at the glass transition temperature at ambient pressure reverses structural changes and the initial glassy state is recovered. This result suggests that pressure causes a liquid-to-liquid phase transition in this metallic alloy supercooled melt. Such a pressure induced transition is known for covalent liquids, but has not been observed for metallic liquids. The High Pressure Quenched glasses are stable in ambient conditions after decompression.

Investigation of medium and high temperature phase change materials

NASA Technical Reports Server (NTRS)

Heine, D.; Kraehling, H.

1979-01-01

A detailed description of the programs for acquisition and analysis of the test results is given. Basically it concerns three programs. The TEST program controls the recording of the test data. With the THELLI program it is possible to follow the temperature curve recorded for each individual thermoelement during the test. With the AUSW program the test data can be analyzed, to determine, for example, the melting point and the start of melting. The first results of the service life tests are discussed. From these it is attempted to draw inferences for the subsequent tests. An attempt is made to focus on the determination of the area-related mass loss, the reduction in thickness and the corrosion rate as well as optical and scanning electron microscope evaluation.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Volokitin, Oleg, E-mail: volokitin-oleg@mail.ru; Volokitin, Gennady, E-mail: vgg-tomsk@mail.ru; Skripnikova, Nelli, E-mail: nks2003@mai.ru

Among silica-based materials vitreous silica has a special place. The paper presents the melting process of a quartz particle under conditions of low-temperature plasma. A mathematical model is designed for stages of melting in the experimental plasma-chemical reactor. As calculation data show, quartz particles having the radius of 0.21≤ r{sub p} ≤0.64 mm completely melt at W = 0.65 l/s particle feed rate depending on the Nusselt number, while 0.14≤ r{sub p} ≤0.44 mm particles melt at W = 1.4 l/s. Calculation data showed that 2 mm and 0.4 mm quartz particles completely melted during and 0.1 s respectively. Thus,more » phase transformations occurred in silicon dioxide play the important part in its heating up to the melting temperature.« less

Molecular dynamics study of the melting of a supported 887-atom Pd decahedron.

PubMed

Schebarchov, D; Hendy, S C; Polak, W

2009-04-08

We employ classical molecular dynamics simulations to investigate the melting behaviour of a decahedral Pd(887) cluster on a single layer of graphite (graphene). The interaction between Pd atoms is modelled with an embedded-atom potential, while the adhesion of Pd atoms to the substrate is approximated with a Lennard-Jones potential. We find that the decahedral structure persists at temperatures close to the melting point, but that just below the melting transition, the cluster accommodates to the substrate by means of complete melting and then recrystallization into an fcc structure. These structural changes are in qualitative agreement with recently proposed models, and they verify the existence of an energy barrier preventing softly deposited clusters from 'wetting' the substrate at temperatures below the melting point.

The electrical conductivity during incipient melting in the oceanic low velocity zone

PubMed Central

Sifré, David; Gardés, Emmanuel; Massuyeau, Malcolm; Hashim, Leila; Hier-Majumder, Saswata; Gaillard, Fabrice

2014-01-01

A low viscosity layer in the upper mantle, the Asthenosphere, is a requirement for plate tectonics1. The seismic low velocities and the high electrical conductivities of the Asthenosphere are attributed either to sub-solidus water-related defects in olivine minerals2-4 or to a few volume percents of partial melt5-8 but these two interpretations have shortcomings: (1) The amount of H2O stored in olivine is not expected to be higher than 50 ppm due to partitioning with other mantle phases9, including pargasite amphibole at moderate temperatures10, and partial melting at high temperatures9; (2) elevated melt volume fractions are impeded by the too cold temperatures prevailing in the Asthenosphere and by the high melt mobility that can lead to gravitational segregation11,12. Here we determined the electrical conductivity of CO2-H2O-rich melts, typically produced at the onset of mantle melting. Electrical conductivity modestly increases with moderate amounts of H2O and CO2 but it dramatically increases as CO2 content exceeds 6 wt% in the melt. Incipient melts, long-expected to prevail in the asthenosphere10,13-15, can therefore trigger its high electrical conductivities. Considering depleted and enriched mantle abundances in H2O and CO2 and their effect on the petrology of incipient melting, we calculated conductivity profiles across the Asthenosphere for various plate ages. Several electrical discontinuities are predicted and match geophysical observations in a consistent petrological and geochemical framework. In moderately aged plates (>5Ma), incipient melts most likely trigger both the seismic low velocities and the high electrical conductivities in the upper part of the asthenosphere, whereas for young plates4, where seamount volcanism occurs6, higher degree of melting is expected. PMID:24784219

Electrical conductivity during incipient melting in the oceanic low-velocity zone.

PubMed

Sifré, David; Gardés, Emmanuel; Massuyeau, Malcolm; Hashim, Leila; Hier-Majumder, Saswata; Gaillard, Fabrice

2014-05-01

The low-viscosity layer in the upper mantle, the asthenosphere, is a requirement for plate tectonics. The seismic low velocities and the high electrical conductivities of the asthenosphere are attributed either to subsolidus, water-related defects in olivine minerals or to a few volume per cent of partial melt, but these two interpretations have two shortcomings. First, the amount of water stored in olivine is not expected to be higher than 50 parts per million owing to partitioning with other mantle phases (including pargasite amphibole at moderate temperatures) and partial melting at high temperatures. Second, elevated melt volume fractions are impeded by the temperatures prevailing in the asthenosphere, which are too low, and by the melt mobility, which is high and can lead to gravitational segregation. Here we determine the electrical conductivity of carbon-dioxide-rich and water-rich melts, typically produced at the onset of mantle melting. Electrical conductivity increases modestly with moderate amounts of water and carbon dioxide, but it increases drastically once the carbon dioxide content exceeds six weight per cent in the melt. Incipient melts, long-expected to prevail in the asthenosphere, can therefore produce high electrical conductivities there. Taking into account variable degrees of depletion of the mantle in water and carbon dioxide, and their effect on the petrology of incipient melting, we calculated conductivity profiles across the asthenosphere for various tectonic plate ages. Several electrical discontinuities are predicted and match geophysical observations in a consistent petrological and geochemical framework. In moderately aged plates (more than five million years old), incipient melts probably trigger both the seismic low velocities and the high electrical conductivities in the upper part of the asthenosphere, whereas in young plates, where seamount volcanism occurs, a higher degree of melting is expected.

Continuum model of tensile fracture of metal melts and its application to a problem of high-current electron irradiation of metals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mayer, Alexander E., E-mail: mayer@csu.ru, E-mail: mayer.al.evg@gmail.com; Mayer, Polina N.

2015-07-21

A continuum model of the metal melt fracture is formulated on the basis of the continuum mechanics and theory of metastable liquid. A character of temperature and strain rate dependences of the tensile strength that is predicted by the continuum model is verified, and parameters of the model are fitted with the use of the results of the molecular dynamics simulations for ultra-high strain rates (≥1–10/ns). A comparison with experimental data from literature is also presented for Al and Ni melts. Using the continuum model, the dynamic tensile strength of initially uniform melts of Al, Cu, Ni, Fe, Ti, andmore » Pb within a wide range of strain rates (from 1–10/ms to 100/ns) and temperatures (from melting temperature up to 70–80% of critical temperature) is calculated. The model is applied to numerical investigation of a problem of the high-current electron irradiation of Al, Cu, and Fe targets.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Das, Chandan K.; Singh, Jayant K., E-mail: jayantks@iitk.ac.in

The solid-liquid coexistence of a Lennard-Jones fluid confined in slit pores of variable pore size, H, is studied using molecular dynamics simulations. Three-stage pseudo-supercritical transformation path of Grochola [J. Chem. Phys. 120(5), 2122 (2004)] and multiple histogram reweighting are employed for the confined system, for various pore sizes ranging from 20 to 5 molecular diameters, to compute the solid-liquid coexistence. The Gibbs free energy difference is evaluated using thermodynamic integration method by connecting solid-liquid phases under confinement via one or more intermediate states without any first order phase transition among them. Thermodynamic melting temperature is found to oscillate with wallmore » separation, which is in agreement with the behavior seen for kinetic melting temperature evaluated in an earlier study. However, thermodynamic melting temperature for almost all wall separations is higher than the bulk case, which is contrary to the behavior seen for the kinetic melting temperature. The oscillation founds to decay at around H = 12, and beyond that pore size dependency of the shift in melting point is well represented by the Gibbs-Thompson equation.« less

Electrochemistry of Europium(III) Chloride in 3 LiCl – NaCl, 3 LiCl – 2 KCl, LiCl – RbCl, and 3 LiCl – 2 CsCl Eutectics at Various Temperatures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schroll, Cynthia A.; Chatterjee, Sayandev; Levitskaia, Tatiana G.

Here we report the effect of changing the eutectic melt composition on the electrochemical properties of europium(III) chloride under pyroprocessing conditions. The number of electrons transferred, redox potentials and diffusion coefficients were determined using various electrochemical and spectroelectrochemical techniques in four different eutectic mixtures (3 LiCl - NaCl, 3 LiCl - 2 KCl, 3 LiCl - RbCl, and 3 LiCl - 2 CsCl) while varying the temperature of the melt. It was determined that Eu3+ undergoes a one electron reduction to Eu2+ in each melt at all temperatures evaluated. Within all the melts a positive shift in the redox potentialmore » as well as an increase in the diffusion coefficient for Eu3+ was observed as the temperature increased. Also observed was a positive shift in the redox potential and increase in the diffusion coefficient for Eu3+ as the weighted average of the cationic radii for the melt decreased.« less

Understanding homogeneous nucleation in solidification of aluminum by molecular dynamics simulations

NASA Astrophysics Data System (ADS)

Mahata, Avik; Asle Zaeem, Mohsen; Baskes, Michael I.

2018-02-01

Homogeneous nucleation from aluminum (Al) melt was investigated by million-atom molecular dynamics simulations utilizing the second nearest neighbor modified embedded atom method potentials. The natural spontaneous homogenous nucleation from the Al melt was produced without any influence of pressure, free surface effects and impurities. Initially isothermal crystal nucleation from undercooled melt was studied at different constant temperatures, and later superheated Al melt was quenched with different cooling rates. The crystal structure of nuclei, critical nucleus size, critical temperature for homogenous nucleation, induction time, and nucleation rate were determined. The quenching simulations clearly revealed three temperature regimes: sub-critical nucleation, super-critical nucleation, and solid-state grain growth regimes. The main crystalline phase was identified as face-centered cubic, but a hexagonal close-packed (hcp) and an amorphous solid phase were also detected. The hcp phase was created due to the formation of stacking faults during solidification of Al melt. By slowing down the cooling rate, the volume fraction of hcp and amorphous phases decreased. After the box was completely solid, grain growth was simulated and the grain growth exponent was determined for different annealing temperatures.

Vertical melting of a stack of membranes

NASA Astrophysics Data System (ADS)

Borelli, M. E. S.; Kleinert, H.; Schakel, A. M. J.

2001-02-01

A stack of tensionless membranes with nonlinear curvature energy and vertical harmonic interaction is studied. At low temperatures, the system forms a lamellar phase. At a critical temperature, the stack disorders vertically in a melting-like transition.

The Evolution of the Celsius and Kelvin Temperature Scales and the State of the Art

NASA Astrophysics Data System (ADS)

Pellicer, Julio; Amparo Gilabert, M.; Lopez-Baeza, Ernesto

1999-07-01

A physical analysis is given of the evolution undergone by the Celsius and Kelvin temperature scales, from their definition to the present day. It is shown that in the temperature interval between the melting point of ice and the boiling point of water, the Celsius and Kelvin scales, both born centigrade by definition and actually become so afterwards by experimental determination as well, are not so any longer, either by definition or by experimental determination.

Congruent melting of gallium nitride at 6 GPa and its application to single-crystal growth.

PubMed

Utsumi, Wataru; Saitoh, Hiroyuki; Kaneko, Hiroshi; Watanuki, Tetsu; Aoki, Katsutoshi; Shimomura, Osamu

2003-11-01

The synthesis of large single crystals of GaN (gallium nitride) is a matter of great importance in optoelectronic devices for blue-light-emitting diodes and lasers. Although high-quality bulk single crystals of GaN suitable for substrates are desired, the standard method of cooling its stoichiometric melt has been unsuccessful for GaN because it decomposes into Ga and N(2) at high temperatures before its melting point. Here we report that applying high pressure completely prevents the decomposition and allows the stoichiometric melting of GaN. At pressures above 6.0 GPa, congruent melting of GaN occurred at about 2,220 degrees C, and decreasing the temperature allowed the GaN melt to crystallize to the original structure, which was confirmed by in situ X-ray diffraction. Single crystals of GaN were formed by cooling the melt slowly under high pressures and were recovered at ambient conditions.

Thermal processing of a poorly water-soluble drug substance exhibiting a high melting point: the utility of KinetiSol® Dispersing.

PubMed

Hughey, Justin R; Keen, Justin M; Brough, Chris; Saeger, Sophie; McGinity, James W

2011-10-31

Poorly water-soluble drug substances that exhibit high melting points are often difficult to successfully process by fusion-based techniques. The purpose of this study was to identify a suitable polymer system for meloxicam (MLX), a high melting point class II BCS compound, and investigate thermal processing techniques for the preparation of chemically stable single phase solid dispersions. Thermal and solution based screening techniques were utilized to screen hydrophilic polymers suitable for immediate release formulations. Results of the screening studies demonstrated that Soluplus(®)(SOL) provided the highest degree of miscibility and solubility enhancement. A hot-melt extrusion feasibility study demonstrated that high temperatures and extended residence times were required in order to render compositions amorphous, causing significant degradation of MLX. A design of experiments (DOE) was conducted on the KinetiSol(®) Dispersing (KSD) process to evaluate the effect of processing conditions on the chemical stability and amorphous character of MLX. The study demonstrated that ejection temperature significantly impacted MLX stability. All samples prepared by KSD were substantially amorphous. Dissolution analysis of the KSD processed solid dispersions showed increased dissolution rates and extent of supersaturation over the marketed generic MLX tablets. Copyright © 2011 Elsevier B.V. All rights reserved.

Pressure-Induced Melting of Confined Ice.

PubMed

Sotthewes, Kai; Bampoulis, Pantelis; Zandvliet, Harold J W; Lohse, Detlef; Poelsema, Bene

2017-12-26

The classic regelation experiment of Thomson in the 1850s deals with cutting an ice cube, followed by refreezing. The cutting was attributed to pressure-induced melting but has been challenged continuously, and only lately consensus emerged by understanding that compression shortens the O:H nonbond and lengthens the H-O bond simultaneously. This H-O elongation leads to energy loss and lowers the melting point. The hot debate survived well over 150 years, mainly due to a poorly defined heat exchange with the environment in the experiment. In our current experiment, we achieved thermal isolation from the environment and studied the fully reversible ice-liquid water transition for water confined between graphene and muscovite mica. We observe a transition from two-dimensional (2D) ice into a quasi-liquid phase by applying a pressure exerted by an atomic force microscopy tip. At room temperature, the critical pressure amounts to about 6 GPa. The transition is completely reversible: refreezing occurs when the applied pressure is lifted. The critical pressure to melt the 2D ice decreases with temperature, and we measured the phase coexistence line between 293 and 333 K. From a Clausius-Clapeyron analysis, we determine the latent heat of fusion of two-dimensional ice at 0.15 eV/molecule, being twice as large as that of bulk ice.

Performance analysis of phase-change material storage unit for both heating and cooling of buildings

NASA Astrophysics Data System (ADS)

Waqas, Adeel; Ali, Majid; Ud Din, Zia

2017-04-01

Utilisation of solar energy and the night ambient (cool) temperatures are the passive ways of heating and cooling of buildings. Intermittent and time-dependent nature of these sources makes thermal energy storage vital for efficient and continuous operation of these heating and cooling techniques. Latent heat thermal energy storage by phase-change materials (PCMs) is preferred over other storage techniques due to its high-energy storage density and isothermal storage process. The current study was aimed to evaluate the performance of the air-based PCM storage unit utilising solar energy and cool ambient night temperatures for comfort heating and cooling of a building in dry-cold and dry-hot climates. The performance of the studied PCM storage unit was maximised when the melting point of the PCM was ∼29°C in summer and 21°C during winter season. The appropriate melting point was ∼27.5°C for all-the-year-round performance. At lower melting points than 27.5°C, declination in the cooling capacity of the storage unit was more profound as compared to the improvement in the heating capacity. Also, it was concluded that the melting point of the PCM that provided maximum cooling during summer season could be used for winter heating also but not vice versa.

Temperatures and Melt Water Contents at the Onset of Phenocryst Growth in Quaternary Nepheline-Normative Basalts Erupted along the Tepic-Zacoalco Rift in Western Mexico

NASA Astrophysics Data System (ADS)

Mesa, J.; Lange, R. A.; Pu, X.

2017-12-01

Nepheline-normative, high-Mg basalts erupted from the western Mexican arc, along the Tepic-Zacoalco rift (TZR), have a trace-element signature consistent with an asthenosphere source, whereas calc-alkaline basalts erupted from the central Mexican arc in the Michoacan-Guanajuato volcanic field (MGVF) have a trace-element signature consistent with a mantle source strongly affected by subduction fluids. In this study, olivine-melt thermometry and plagioclase-liquid hygrometry are used to constrain the temperature and melt water content of the alkaline TZR basalts. The presence of diffusion-limited growth textures in olivine and plagioclase phenocrysts provide preliminary evidence of rapid growth during ascent. For each basalt sample, a histogram of all analyzed olivines in each sample allows the most Fo-rich composition to be identified, which matches the calculated composition at the liquidus via MELTS (Ghiorso & Sack, 1995; Asimow & Ghiorso, 1998) at fO2 values of QFM +2. Therefore a newly developed olivine-melt thermometer, based on DNiol/liq (Pu et al., 2017) was used to calculate temperature at the onset of olivine crystallization during ascent. Temperatures range from 1076-1247°C, whereas those calculated using an olivine-melt thermometer based on DMgol/liq range from 1141-1236 °C. Olivine-melt thermometers based on DMgol/liq are sensitive to melt H2O content, therefore ΔT = TMg - TNi (≤ 82 degrees) may be used as a qualitative indicator of melt H2O (≤ 2.6 wt% H2O; Pu et al., 2017). When temperatures from the Ni-thermometer are applied to the most calcic plagioclase in each sample (Waters & Lange, 2015), calculated melt H2O contents range from 1.3-1.9 (± 0.4) wt%. These values are significantly lower than those obtained from high-Mg calc-alkaline basalts from the MGVF using similar methods (1.9-5.0 wt%; Pu et al., 2017), consistent with a reduced involvement of slab-derived fluids in the origin of the alkaline TZR basalts from western Mexico.

Melting relations in the iron-sulfur system at ultra-high pressures - Implications for the thermal state of the earth

NASA Technical Reports Server (NTRS)

Williams, Quentin; Jeanloz, Raymond

1990-01-01

The melting temperatures of FeS-troilite and of a 10-wt-pct sulfur iron alloy have been measured to pressures of 120 and 90 GPa, respectively. The results document that FeS melts at a temperature of 4100 (+ or - 300) K at the pressure of the core-mantle boundary. Eutecticlike behavior persists in the iron-sulfur system to the highest pressures of measurements, in marked contrast to the solid-solutionlike behavior observed at high pressures in the iron-iron oxide system. Iron with 10-wt-pct sulfur melts at a similar temperature as FeS at core-mantle boundary conditions. If the sole alloying elements of iron within the core are sulfur and oxygen and the outer core is entirely liquid, the minimum temperature at the top of the outer core is 4900 (+ or - 400) K. Calculations of mantle geotherms dictate that there must be a temperature increase of between 1000 and 2000 K across thermal boundary layers within the mantle. If D-double-prime is compositionally stratified, it could accommodate the bulk of this temperature jump.

Decreasing electrical resistivity of silver along the melting boundary up to 5 GPa

NASA Astrophysics Data System (ADS)

Littleton, Joshua A. H.; Secco, Richard A.; Yong, Wenjun

2018-04-01

The electrical resistivity of Ag was experimentally measured at high pressures up to 5 GPa and at temperatures up to ∼300 K above melting. The resistivity decreased as a function of pressure and increased as a function of temperature as expected and is in very good agreement with 1 atm data. Observed melting temperatures at high pressures also agree well with previous experimental and theoretical studies. The main finding of this study is that resistivity of Ag decreases along the pressure- and temperature-dependent melting boundary, in conflict with prediction of resistivity invariance. This result is discussed in terms of the dominant contribution of the increasing energy separation between the Fermi level and 4d-band as a function of pressure. Calculated from the resistivity using the Wiedemann-Franz law, the electronic thermal conductivity increased as a function of pressure and decreased as a function of temperature as expected. The decrease in the high pressure thermal conductivity in the liquid phase as a function of temperature contrasts with the behavior of the 1 atm data.

Simulation of the temperature distribution in crystals grown by Czochralski method

NASA Technical Reports Server (NTRS)

Dudokovic, M. P.; Ramachandran, P. A.

1985-01-01

Production of perfect crystals, free of residual strain and dislocations and with prescribed dopant concentration, by the Czochralski method is possible only if the complex, interacting phenomena that affect crystal growth in a Cz-puller are fully understood and quantified. Natural and forced convection in the melt, thermocapillary effect and heat transfer in and around the crystal affect its growth rate, the shape of the crystal-melt interface and the temperature gradients in the crystal. The heat transfer problem in the crystal and between the crystal and all other surfaces present in the crystal pulling apparatus are discussed at length. A simulation and computer algorithm are used, based on the following assumptions: (1) only conduction occurs in the crystal (experimentally determined conductivity as a function of temperature is used), (2) melt temperature and the melt-crystal heat transfer coefficient are available (either as constant values or functions of radial position), (3) pseudo-steady state is achieved with respect to temperature gradients, (4) crystal radius is fixed, and (5) both direct and reflected radiation exchange occurs among all surfaces at various temperatures in the crystal puller enclosure.

Thermocapillary flow and melt/solid interfaces in floating-zone crystal growth under microgravity

NASA Technical Reports Server (NTRS)

Lan, C. W.; Kou, Sindo

1990-01-01

Computer simulation of steady-state axisymmetrical heat transfer and fluid flow was conducted to study thermocapillary flow and melt/solid interfaces in floating-zone crystal growth under microgravity. The effects of key variables on the extent of thermocapillary flow in the melt zone, the shapes of melt/solid interfaces and the length of the melt zone were discussed. These variables are: (1) the temperature coefficient of surface tension (or the Marangoni number), (2) the pulling speed (or the Peclet number), (3) the feed rod radius, (4) the ambient temperature distribution, (5) the heat transfer coefficient (or the Biot number), and (6) the thermal diffusivity of the material (or the Prandtl number).

The Vaguries of Pyroxene Nucleation and the Resulting Chondrule Textures

NASA Technical Reports Server (NTRS)

Lofgren, G. E.; Le, L.

2004-01-01

Pyroxene is a major phase in chondrules, but often follows olivine in the crystallization sequence and depending on the melting temperature and time may not nucleate readily upon cooling. Dynamic crystallization experiments based on total or near total melting were used to study PO (porphyritic olivine) and PP (Porphyritic pyroxene) compositions as defined by. The experiments showed that pyroxene nucleated only at subliquidus temperatures in the PP melts and rarely in the PO melts. Porphyritic chondrules with phenocrysts of both olivine and pyroxene (POP chondrules) were not easily produced in the experiments. POP chondrules are common and it is important for deciphering their formation that we understand pyroxene nucleation properties of chondrule melts.

Kinetics of the melting front movement in process of centrifugal induction surfacing of powder material with nanoscale modificaters

NASA Astrophysics Data System (ADS)

Sasnouski, I.; Kurylionak, A.

2018-03-01

For solving the problem of improving the powder coatings modified by nanostructure components obtained by induction surfacing method tribological characteristics it is necessary to study the kinetics of the powdered layer melting and define the minimum time of melting. For powdered layer predetermined temperature maintenance at sintering mode stage it is required to determine the temperature difference through blank thickness of the for one hundred-day of the define the warm-up swing on of the stocking up by solving the thermal conductivity stationary problem for quill (hollow) cylinder with internal heat source. Herewith, since in practice thickness of the cylinder wall is much less then its diameter and the temperature difference is comparatively small, the thermal conductivity dependence upon the temperature can be treated as negligible. As it was shown by our previous studies, in the induction heating process under powdered material centrifugal surfacing (i.e. before achieving the melting temperature) the temperature distribution in powdered layer thickness may be considered even. Hereinafter, considering the blank part induction heating process quasi-stationarity under Fo big values, it is possible to consider its internal surface heating as developing with constant velocity. As a result of development the melting front movement mathematical model in a powdered material with nanostructure modifiers the minimum surfacing time is defined. It allows to minimize negative impact of thermal influence on formation of applied coating structure, to raise productivity of the process, to lower power inputs and to ensure saving of nonferrous and high alloys by reducing the allowance for machining. The difference of developed mathematical model of melting front movement from previously known is that the surface temperature from which the heat transfer occures is a variable and varies with a time after the linear law.

Melting and glass transition for Ni clusters.

PubMed

Teng, Yuyong; Zeng, Xianghua; Zhang, Haiyan; Sun, Deyan

2007-03-08

The melting of NiN clusters (N = 29, 50-150) has been investigated by using molecular dynamics (MD) simulations with a quantum corrected Sutton-Chen (Q-SC) many-body potential. Surface melting for Ni147, direct melting for Ni79, and the glass transition for Ni29 have been found, and those melting points are equal to 540, 680, and 940 K, respectively. It shows that the melting temperatures are not only size-dependent but also a symmetrical structure effect; in the neighborhood of the clusters, the cluster with higher symmetry has a higher melting point. From the reciprocal slopes of the caloric curves, the specific heats are obtained as 4.1 kB per atom for the liquid and 3.1 kB per atom for the solid; these values are not influenced by the cluster size apart in the transition region. The calculated results also show that latent heat of fusion is the dominant effect on the melting temperatures (Tm), and the relationship between S and L is given.

Volume and Surface Properties of a Bismuth-Containing Separating Nickel Melt

NASA Astrophysics Data System (ADS)

Filippov, K. S.

2017-11-01

The influence of a bismuth impurity on the properties of solid and liquid alloys in the concentration range that obeys Henry's law is considered. The structural and physicochemical properties, specifically, the density and the surface tension, of real melts are studied on relatively pure metals. The changes in the properties of the melts are estimated from changes in the temperature dependences of the density and the surface tension upon heating and cooling and in the concentration dependences of these parameters at a constant temperature. These dependences exhibit a correlation between the volume and surface properties of the melts: the density and the surface tension increase or decrease simultaneously. The introduction of bismuth in the nickel melt is accompanied by the appearance of a relatively strong compression effect (i.e., a decrease in the melt volume). At a certain bismuth content in the melt, the compression effect weakens because of the appearance of an excess phase or its associates and melt separation.

Analysis of moving surface structures at a laser-induced boiling front

NASA Astrophysics Data System (ADS)

Matti, R. S.; Kaplan, A. F. H.

2014-10-01

Recently ultra-high speed imaging enabled to observe moving wave patterns on metal melts that experience laser-induced boiling. In laser materials processing a vertical laser-induced boiling front governs processes like keyhole laser welding, laser remote fusion cutting, laser drilling or laser ablation. The observed waves originate from temperature variations that are closely related to the melt topology. For improved understanding of the essential front mechanisms and of the front topology, for the first time a deeper systematic analysis of the wave patterns was carried out. Seven geometrical shapes of bright or dark domains were distinguished and categorized, in particular bright peaks of three kinds and dark valleys, often inclined. Two categories describe special flow patterns at the top and bottom of the front. Dynamic and statistical analysis has revealed that the shapes often combine or separate from one category to another when streaming down the front. The brightness of wave peaks typically fluctuates during 20-50 μs. This variety of thermal wave observations is interpreted with respect to the accompanying surface topology of the melt and in turn for governing local mechanisms like absorption, shadowing, boiling, ablation pressure and melt acceleration. The findings can be of importance for understanding the key process mechanisms and for optimizing laser materials processing.

A concept for non-invasive temperature measurement during injection moulding processes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hopmann, Christian; Spekowius, Marcel, E-mail: spekowius@ikv.rwth-aachen.de; Wipperfürth, Jens

2016-03-09

Current models of the injection moulding process insufficiently consider the thermal interactions between melt, solidified material and the mould. A detailed description requires a deep understanding of the underlying processes and a precise observation of the temperature. Because todays measurement concepts do not allow a non-invasive analysis it is necessary to find new measurement techniques for temperature measurements during the manufacturing process. In this work we present the idea of a set up for a tomographic ultrasound measurement of the temperature field inside a plastics melt. The goal is to identify a concept that can be installed on a specializedmore » mould for the injection moulding process. The challenges are discussed and the design of a prototype is shown. Special attention is given to the spatial arrangement of the sensors. Besides the design of a measurement set up a reconstruction strategy for the ultrasound signals is required. We present an approach in which an image processing algorithm can be used to calculate a temperature distribution from the ultrasound scans. We discuss a reconstruction strategy in which the ultrasound signals are converted into a spartial temperature distribution by using pvT curves that are obtained by dilatometer measurements.« less

Assessment of Greenland Outlet Glacier Albedo Variability

NASA Astrophysics Data System (ADS)

Stroeve, J.

2003-04-01

Recent studies have shown that the coastal regions of the Greenland ice sheet are thinning rapidly. Analysis of passive microwave satellite data since 1979 have revealed a corresponding positive trend in the areal extent of melt. This trend was emphasized in 2002, when the total area of surface melt on the Greenland ice sheet surpased the maximum melt extent from the past 24 years by more than 9%. Increases in coastal temperatures have certainly contributed to melting near the margins. However, the high rate of thinning in the coastal regions, up to several m/yr, cannot be explained by increases in temperatures alone. Some of the thinning is likely creep thinning resulting from discharge velocities that exceed balance velocities. In order to better understand the role of ablation in the recent thinning rates, the variability in the surface albedo at four outlet glaciers is analyzed from 1981 to 2000 using the AVHRR Polar Pathfinder data set. The four glaciers analyzed are the following: Storstrommen (77N, 23W), Kangerdlugssuaq (68N, 33W), Petermann (81N, 62W) and Jakobshavn (69N, 50W). Clear sky albedo changes over time from May through September for the period 1981-2000 are presented. These months are chosen in order to capture the full cycle of melt onset and refreeze. The albedo record at the glaciers shows large seasonal and interannual variability. Resuls indicate a steady decrease in surface albedo during the summer months from 1981 to 2000, particularly in the Jakobshavn drainage basin.

Effects of mold design of aspheric projector lens for head up display

NASA Astrophysics Data System (ADS)

Chen, Chao-Chang A.; Tang, Jyun-Cing; Teng, Lin-Ming

2010-08-01

This paper investigates the mold design and related effects on an aspheric projector lens for Head Up Display (HUD) with injection molding process. Injection flow analysis with a commercial software, Moldex3D has been used to simulate this projector lens for filling, packing, shrinkage, and flow-induced residual stress. This projector lens contains of variant thickness due to different aspheric design on both surfaces. Defects may be induced as the melt front from the gate into the cavity with jet-flow phenomenon, short shot, weld line, and even shrinkage. Thus, this paper performs a gate design to find the significant parameters including injection velocity, melt temperature, and mold temperature. After simulation by the Moldex3D, gate design for the final assembly of Head Up Display (HUD) has been obtained and then experimental tests have been proceeded for verification of short-shot, weight variation, and flow-induced stress. Moreover, warpage analysis of the Head Up Display (HUD) can be integrated with the optical design specification in future work.

Thermodynamic analysis of sol-gel transition of gelatin in terms of water activity in various solutions.

PubMed

Miyawaki, Osato; Omote, Chiaki; Matsuhira, Keiko

2015-12-01

Sol-gel transition of gelatin was analyzed as a multisite stoichiometric reaction of a gelatin molecule with water and solute molecules. The equilibrium sol-gel transition temperature, Tt , was estimated from the average of gelation and melting temperature measured by differential scanning calorimetry. From Tt and the melting enthalpy, ΔHsol , the equilibrium sol-to-gel ratio was estimated by the van't Hoff equation. The reciprocal form of the Wyman-Tanford equation, which describes the sol-to-gel ratio as a function of water activity, was successfully applied to obtain a good linear relationship. From this analysis, the role of water activity on the sol-gel transition of gelatin was clearly explained and the contributions of hydration and solute binding to gelatin molecules were separately discussed in sol-gel transition. The general solution for the free energy for gel-stabilization in various solutions was obtained as a simple function of solute concentration. © 2015 Wiley Periodicals, Inc.

Investigating the highest melting temperature materials: A laser melting study of the TaC-HfC system.

PubMed

Cedillos-Barraza, Omar; Manara, Dario; Boboridis, K; Watkins, Tyson; Grasso, Salvatore; Jayaseelan, Daniel D; Konings, Rudy J M; Reece, Michael J; Lee, William E

2016-12-01

TaC, HfC and their solid solutions are promising candidate materials for thermal protection structures in hypersonic vehicles because of their very high melting temperatures (>4000 K) among other properties. The melting temperatures of slightly hypostoichiometric TaC, HfC and three solid solution compositions (Ta 1-x Hf x C, with x = 0.8, 0.5 and 0.2) have long been identified as the highest known. In the current research, they were reassessed, for the first time in the last fifty years, using a laser heating technique. They were found to melt in the range of 4041-4232 K, with HfC having the highest and TaC the lowest. Spectral radiance of the hot samples was measured in situ, showing that the optical emissivity of these compounds plays a fundamental role in their heat balance. Independently, the results show that the melting point for HfC 0.98 , (4232 ± 84) K, is the highest recorded for any compound studied until now.

Investigating the highest melting temperature materials: A laser melting study of the TaC-HfC system

NASA Astrophysics Data System (ADS)

Cedillos-Barraza, Omar; Manara, Dario; Boboridis, K.; Watkins, Tyson; Grasso, Salvatore; Jayaseelan, Daniel D.; Konings, Rudy J. M.; Reece, Michael J.; Lee, William E.

2016-12-01

TaC, HfC and their solid solutions are promising candidate materials for thermal protection structures in hypersonic vehicles because of their very high melting temperatures (>4000 K) among other properties. The melting temperatures of slightly hypostoichiometric TaC, HfC and three solid solution compositions (Ta1-xHfxC, with x = 0.8, 0.5 and 0.2) have long been identified as the highest known. In the current research, they were reassessed, for the first time in the last fifty years, using a laser heating technique. They were found to melt in the range of 4041-4232 K, with HfC having the highest and TaC the lowest. Spectral radiance of the hot samples was measured in situ, showing that the optical emissivity of these compounds plays a fundamental role in their heat balance. Independently, the results show that the melting point for HfC0.98, (4232 ± 84) K, is the highest recorded for any compound studied until now.

Investigating the highest melting temperature materials: A laser melting study of the TaC-HfC system

PubMed Central

Cedillos-Barraza, Omar; Manara, Dario; Boboridis, K.; Watkins, Tyson; Grasso, Salvatore; Jayaseelan, Daniel D.; Konings, Rudy J. M.; Reece, Michael J.; Lee, William E.

2016-01-01

TaC, HfC and their solid solutions are promising candidate materials for thermal protection structures in hypersonic vehicles because of their very high melting temperatures (>4000 K) among other properties. The melting temperatures of slightly hypostoichiometric TaC, HfC and three solid solution compositions (Ta1−xHfxC, with x = 0.8, 0.5 and 0.2) have long been identified as the highest known. In the current research, they were reassessed, for the first time in the last fifty years, using a laser heating technique. They were found to melt in the range of 4041–4232 K, with HfC having the highest and TaC the lowest. Spectral radiance of the hot samples was measured in situ, showing that the optical emissivity of these compounds plays a fundamental role in their heat balance. Independently, the results show that the melting point for HfC0.98, (4232 ± 84) K, is the highest recorded for any compound studied until now. PMID:27905481

Magma Supply at the Arctic Gakkel Ridge: Constraints from Peridotites and Basalts

NASA Astrophysics Data System (ADS)

Sun, C.; Dick, H. J.; Hellebrand, E.; Snow, J. E.

2015-12-01

Crustal thickness in global ridge systems is widely believed to be nearly uniform (~7 km) at slow- and fast-spreading mid-ocean ridges, but appears significantly thinner (< ~4 km) at ultraslow-spreading ridges. At the slowest-spreading Arctic Gakkel Ridge, the crust becomes extremely thin (1.4 - 2.9 km; [1]). The thin crust at the Gakkel and other ultraslow-spreading ridges, has been attributed to lithosphere thickening, ancient mantle depletion, lower mantle temperature, ridge obliquity, and melt retention/focusing. To better understand the magma supply at ultraslow-spreading ridges, we examined melting dynamics by linking peridotites and basalts dredged along the Gakkel Ridge. We analyzed rare earth elements in clinopyroxene from 84 residual peridotites, and estimated melting parameters for individual samples through nonlinear least squares analyses. The degrees of melting show a large variation but mainly center at around 7% assuming a somewhat arbitrary but widely used depleted MORB mantle starting composition. Thermobarometry on published primitive basaltic glasses from [2] indicates that the mantle potential temperature at the Gakkel Ridge is ~50°C cooler than that at the East Pacific Rise. The ridge-scale low-degree melting and lower mantle potential temperature place the final depth of melting at ~30 km and a melt thickness of 1.0 or 2.9 km for a triangular or trapezoidal melting regime, respectively. The final melting depth is consistent with excess conductive cooling and lithosphere thickening suggested by geodynamic models, while the estimated melt thickness is comparable to the seismic crust (1.4 - 2.9 km; [1]). The general agreement among geochemical analyses, seismic measurements, and geodynamic models supports that lower mantle potential temperature and thick lithosphere determine the ridge-scale low-degree melting and thin crust at the Gakkel Ridge, while melt retention/focusing and excess ancient mantle depletion are perhaps locally important at short length scales (e.g., < 50 - 100 km). [1] Jokat and Schmidt-Aursch (2007) Geophys. J. Int. (2007) 168, 983-998. [2] Gale et al. (2012) J. Petrology, 55, 1051-1082.

Melting of KCl and pressure calibration from in situ ionic conductivity measurements in a multi-anvil apparatus

NASA Astrophysics Data System (ADS)

Li, J.; Dong, J.; Zhu, F.

2017-12-01

Melting plays an unparalleled role in planetary differentiation processes including the formation of metallic cores, basaltic crusts, and atmospheres. Knowledge of the melting behavior of Earth materials provides critical constraints for establishing the Earth's thermal structure, interpreting regional seismic anomalies, and understanding the nature of chemical heterogeneity. Measuring the melting points of compressed materials, however, have remained challenging mainly because melts are often mobile and reactive, and temperature and pressure gradients across millimeter or micron-sized samples introduce large uncertainties in melting detection. Here the melting curve of KCl was determined through in situ ionic conductivity measurements, using the multi-anvil apparatus at the University of Michigan. The method improves upon the symmetric configuration that was used recently for studying the melting behaviors of NaCl, Na2CO3, and CaCO3 (Li and Li 2015 American Mineralogist, Li et al. 2017 Earth and Planetary Science Letters). In the new configuration, the thermocouple and electrodes are placed together with the sample at the center of a cylindrical heater where the temperature is the highest along the axis, in order to minimize uncertainties in temperature measurements and increase the stability of the sample and electrodes. With 1% reproducibility in melting point determination at pressures up to 20 GPa, this method allows us to determine the sample pressure to oil load relationship at high temperatures during multiple heating and cooling cycles, on the basis of the well-known melting curves of ionic compounds. This approach enables more reliable pressure measurements than relying on a small number of fixed-point phase transitions. The new data on KCl bridge the gap between the piston-cylinder results up to 4 GPa (Pistorius 1965 J. of Physics and Chemistry of Solids) and several diamond-anvil cell data points above 20 GPa (Boehler et al. 1996 Physical Review). We will examine the effect of solid-state phase transition on the melting curves of halides and test the validity of various melting theories.

Picritic glasses from Hawaii

USGS Publications Warehouse

Clague, D.A.; Weber, W.S.; Dixon, J.E.

1991-01-01

ESTIMATES of the MgO content of primary Hawaiian tholeiitic melts range from 8wt% to as high as 25wt% (refs 1, 2). In general, these estimates are derived from analysis of the whole-rock composition of lavas, coupled with the compositions of the most magnesian olivine phenocrysts observed. But the best estimate of magma composition comes from volcanic glass, as it represents the liquid composition at the time of quenching; minimal changes occur during the quenching process. Here we report the discovery of tholeiitic basalt glasses, recovered offshore of Kilauea volcano, that contain up to 15.0 wt% MgO. To our knowledge, these are the most magnesian glasses, and have the highest eruption temperatures (??? 1,316 ??C), yet found. The existence of these picritic (high-MgO) liquids provides constraints on the temperature structure of the upper mantle, magma transport and the material and thermal budgets of the Hawaiian volcanoes. Furthermore, picritic melts are affected little by magma-reservoir processes, and it is therefore relatively straightforward to extrapolate back to the composition of the primary melt and its volatile contents.

In-situ detection of convection and rotation striations by growth interface electromotive force spectrum

NASA Astrophysics Data System (ADS)

Zhu, Yunzhong; Tang, Feng; Yang, Xin; Yang, Mingming; Ma, Decai; Zhang, Xiaoyue; Liu, Yang; Lin, Shaopeng; Wang, Biao

2018-04-01

Nanoscale growth striations, induced by the crystal rotation and melt convection, are in-situ detected by the growth interface electromotive force (GEMF) spectrum during Czochralski (CZ) crystal growth. Specifically, the intensity and period of rotation and convection striations could be precisely revealed under different rotation rates. This is because the GEMF spectrum is affected by the combination effort of temperature difference in crystal rotation path and the melt flow in growth interface. Furthermore, the spectrum analysis (Fourier transform) reveals remarkable characteristics of periodic flow oscillation. More interestingly, in different rotation rates, the corresponding convection period and intensity show particular regularity that could barely be observed in semitransparent and high-temperature melt. Therefore, the GEMF spectrum reflects the subtle changes of a growing crystal that is far beyond the detecting precision of sensors in current CZ equipment. On the basis of this paper and our previous work, the real-time feedback of multiscale striations is established. GEMF spectrum could be a promising approach to reveal striation formation mechanism and optimize crystal quality.

Manufacturing of Dysprosium-Iron Alloys by Electrolysis in Fluoride-Based Electrolytes: Oxide Solubility Determinations

NASA Astrophysics Data System (ADS)

Martinez, Ana Maria; Støre, Anne; Osen, Karen Sende

2018-04-01

Electrolytic production of light rare earth elements and alloys takes place in a fluoride-based electrolyte using rare earth oxides as raw material. The optimization of this method, mainly in terms of the energy efficiency and environmental impact control, is rather challenging. Anode effects, evolution of fluorine-containing compounds, and side cathode reactions could largely be minimized by a good control of the amount of rare earth oxide species dissolved in the fluoride-based electrolyte and their dissolution rate. The oxide content of the fluoride melts REF3-LiF (RE = Nd, Dy) at different compositions and temperatures were experimentally determined by carbothermal analysis of melt samples. The highest solubility values of oxide species, added as Dy2O3 and Dy2(CO3)3, were obtained to be of ca. 3 wt pct (expressed as Dy2O3) in the case of the equimolar DyF3-LiF melt at 1323 K (1050 °C). The oxide saturation values increased with the amount of REF3 present in the molten bath and the working temperature.

An Investigation into the Polymorphism and Crystallization of Levetiracetam and the Stability of its Solid Form.

PubMed

Xu, Kailin; Xiong, Xinnuo; Guo, Liuqi; Wang, Lili; Li, Shanshan; Tang, Peixiao; Yan, Jin; Wu, Di; Li, Hui

2015-12-01

Levetiracetam (LEV) crystals were prepared using different solvents at different temperatures. The LEV crystals were systematically characterized by X-ray powder diffraction (XRPD) and morphological analysis. The results indicated that many kinds of crystal habits exist in a solid form of LEV. To investigate the effects of LEV concentration, crystallization temperature, and crystallization type on crystallization and solid phase transformation of LEV, multiple methods were performed for LEV aqueous solution to determine if a new solid form exists in solid-state LEV. However, XRPD data demonstrate that the LEV solid forms possess same spatial arrangements that are similar to the original solid form. This result indicates that the LEV concentration, crystallization temperature, and crystallization type in aqueous solution have no influence on the crystallization and solid phase transformation of LEV. Moreover, crystallization by sublimation, melt cooling, and quench cooling, as well as mechanical effect, did not result in the formation of new LEV solid state. During melt cooling, the transformation of solid form LEV is a direct process from melting amorphous phase to the original LEV crystal phase, and the conversion rate is very quick. In addition, stability investigation manifested that LEV solid state is very stable under various conditions. © 2015 Wiley Periodicals, Inc. and the American Pharmacists Association.

AC Calorimetry and Thermophysical Properties of Bulk Glass-Forming Metallic Liquids

NASA Technical Reports Server (NTRS)

Johnson, William L.

2000-01-01

Thermo-physical properties of two bulk metallic glass forming alloys, Ti34Zr11Cu47Ni8 (VIT 101) and Zr57Nb5Ni12.6Al10CU15.4 (VIT 106), were investigated in the stable and undercooled melt. Our investigation focused on measurements of the specific heat in the stable and undercooled liquid using the method of AC modulation calorimetry. The VIT 106 exhibited a maximum undercooling of 140 K in free radiative cooling. Specific heat measurements could be performed in stable melt down to an undercooling of 80 K. Analysis of the specific heat data indicate an anomaly near the equilibrium liquidus temperature. This anomaly is also observed in y the temperature dependencies of the external relaxation time, the specific volume, and the surface tension; it is tentatively attributed to a phase separation in the liquid state. The VIT 101 specimen exhibited a small undercooling of about 50 K. Specific heat measurements were performed in the stable and undercooled melt. These various results will be combined with ground based work such as the measurement of T-T-T curves in the electrostatic levitator and low temperature viscosity and specific heat measurements for modeling the nucleation kinetics of these alloys.

Melting icebergs to produce fresh water and mechanical energy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Camirand, W.M.; Hautala, E.; Randall, J.M.

1981-10-20

Fresh water and mechanical energy are obtained from melting of icebergs. Warm surface seawater is contacted with a fluid, which is vaporized. The resulting vapor is used to generate mechanical energy and then is condensed by contacting it with cold melt water from the iceberg. The fluid is regenerated with a concomitant elevation in the temperature of the melt water. The warmer melt water is cycled to the body of the iceberg to facilitate its melting and produce additional cold melt water, which is apportioned as fresh water and water cycled to condense the aforesaid vapor. In an alternate embodimentmore » of the invention warm seawater is evaporated at reduced pressure. Mechanical energy is generated from the vapor, which is then condensed by direct and intimate contact with cold melt water from the iceberg. The resultant fresh water is a mixture of condensed vapor and melt water from the iceberg and has a temperature greater than the cold melt water. This fresh water mixture is contacted with the body of the iceberg to further melt it; part of the cold melt water is separated as fresh water and the remainder is cycled for use in condensing the vapor from the warm surface seawater.« less

Optical and thermodynamic properties of MgO from radiative shock temperature and sound speed measurements on samples preheated to 2300 K

NASA Astrophysics Data System (ADS)

Fatýanov, O. V.; Asimow, P. D.

2013-12-01

Thermodynamic properties of MgO, one of the major end-members of deep planetary interiors, play a significant role in the processes inside the Earth's lower mantle. Of particular importance in geophysics and geochemistry is the MgO melting behavior at high pressure. Despite considerable theoretical and experimental efforts over decades, it remains essentially unknown. The melting temperature predictions for MgO at 135 GPa, the Earth's core-mantle boundary pressure, range from 5 to 9 kK. In a continuous effort to resolve this inconsistency and to probe the P-T region previously unexplored, we developed a technique for radiative shock temperature measurements in single-crystal MgO preheated to 2300 K. Large ventilated Mo capsules were employed to hold ~20 mm long MgO crystals with controlled longitudinal thermal gradients. These hot targets were impacted by 0.8 mm thick Ta flyers launched at 6.5 to 7.5 km/s on the Caltech two-stage light-gas gun. Six spectral radiance histories from MgO shock front were recorded in every shot with 3 ns time resolution over 440-750 nm or 500-830 nm spectral range. The majority of our experiments showed smooth pressure dependence of MgO shock temperature and sound speed consistent with the solid phase at 197-243 GPa. Although most observed temperatures are ~700 K lower and sound speeds ~1 km/s higher than the model predictions, the pressure slopes for both parameters are in close agreement with those calculated for the solid phase. Unconfirmed data from a single experiment at 239 GPa and 8.3 kK showed correlated temperature and sound speed anomalies (both values lower than expected) that may be explained by partial melting. Our past and recent data on shock-compressed preheated MgO suggest its melting curve above 200 GPa is higher than the extrapolation of the experiments of Zerr & Boehler or the theoretical calculation by Strachan et. al. These results, features of shock experiments with 2300 K pre-heat temperatures, data analysis, and future plans will be discussed.

Rheology Guided Rational Selection of Processing Temperature To Prepare Copovidone-Nifedipine Amorphous Solid Dispersions via Hot Melt Extrusion (HME).

PubMed

Yang, Fengyuan; Su, Yongchao; Zhang, Jingtao; DiNunzio, James; Leone, Anthony; Huang, Chengbin; Brown, Chad D

2016-10-03

The production of amorphous solid dispersions via hot melt extrusion (HME) relies on elevated temperature and prolonged residence time, which can result in potential degradation and decomposition of thermally sensitive components. Herein, the rheological properties of a physical mixture of polymer and an active pharmaceutical ingredient (API) were utilized to guide the selection of appropriate HME processing temperature. In the currently studied copovidone-nifedipine system, a critical temperature, which is substantially lower (∼13 °C) than the melting point of crystalline API, was captured during a temperature ramp examination and regarded as the critical point at which the API could molecularly dissolve into the polymer. Based on the identification of this critical point, various solid dispersions were prepared by HME processing below, at, and above the critical temperature (both below and above the melting temperature (T m ) of crystalline API). In addition, the resultant extrudates along with two control solid dispersions prepared by physical mixing and cryogenic milling were assessed by X-ray diffraction, differential scanning calorimetry, hot stage microscopy, rheology, and solid-state NMR. Physicochemical properties of resultant solid dispersions indicated that the identified critical temperature is sufficient for the polymer-API system to reach a molecular-level mixing, manifested by the transparent and smooth appearance of extrudates, the absence of API crystalline diffraction and melting peaks, dramatically decreased rheological properties, and significantly improved polymer-API miscibility. Once the critical temperature has been achieved, further raising the processing temperature only results in limited improvement of API dispersion, reflected by slightly reduced storage modulus and complex viscosity and limited improvement in miscibility.

Pre-melting Behaviour in fcc Metals

NASA Astrophysics Data System (ADS)

Pamato, M. G.; Wood, I. G.; Dobson, D. P.; Hunt, S.; Vocadlo, L.

2016-12-01

Although the Earth's core is accepted to be made of an iron-nickel alloy with a few percent of light elements, its exact structure and composition are still unknown. Seismological and mineralogical models in the Earth's inner core do not agree, with mineralogical models derived from ab initiocalculations predicting shear-wave velocities up to 30% greater than seismically observed values. Recent computer simulations revealed that such difference may be explained by a dramatic, non-linear, softening of the elastic constants of Fe prior to melting. Up to date, computer calculations are the only result on pre-melting of direct applicability to the Earth's core and it is essential to systematically investigate such phenomena at inner core pressures and temperatures. Measuring the pressure dependence of pre-melting effects at such conditions and to the required precision is however extremely challenging. Also, pre-melting effects have been observed or suggested to occur in other materials, particularly noble metals, which exhibit large departures from linearity (modulus defects) at elevated temperatures. The aim of this study is to investigate to what extent pre-melting behaviour occurs in the physical properties of other metals at more experimentally tractable conditions. In particular, we report measurements of density and thermal expansion coefficients of both pure and alloyed gold (Au) up to their melting points. Au is an ideal test material since it crystallises in a simple monatomic face-centred structure and has a relatively low melting temperature. Precise measurements of unit cell lattice parameters were performed using a PANalytical X'Pert Pro powder diffractometer, equipped with an incident beam monochromator (giving very high resolution diffraction patterns) and with environmental stages covering the range from 40 K to 1373 K, with a readily achievable temperature resolution of 1K. We will discuss the circumstances under which pre-melting occurs, its mechanism(s), the effect of impurities and defects in the solid, and the consequences of pre-melting in the Earth's core.

Warpage analysis on thin shell part using response surface methodology (RSM)

NASA Astrophysics Data System (ADS)

Zulhasif, Z.; Shayfull, Z.; Nasir, S. M.; Fathullah, M.; Hazwan, M. H. M.

2017-09-01

The optimisation of moulding parameters appropriate to reduce warpage defects produce using Autodesk Moldflow Insight (AMI) 2012 software The product is injected by using Acrylonitrile-Butadiene-Styrene (ABS) materials. This analysis has processing parameter that varies in melting temperature, mould temperature, packing pressure and packing time. Design of Experiments (DOE) has been integrated to obtain a polynomial model using Response Surface Methodology (RSM). The Glowworm Swarm Optimisation (GSO) method is used to predict a best combination parameters to minimise warpage defect in order to produce high quality parts.

Crystalline nucleation in undercooled liquids: a Bayesian data-analysis approach for a nonhomogeneous Poisson process.

PubMed

Filipponi, A; Di Cicco, A; Principi, E

2012-12-01

A Bayesian data-analysis approach to data sets of maximum undercooling temperatures recorded in repeated melting-cooling cycles of high-purity samples is proposed. The crystallization phenomenon is described in terms of a nonhomogeneous Poisson process driven by a temperature-dependent sample nucleation rate J(T). The method was extensively tested by computer simulations and applied to real data for undercooled liquid Ge. It proved to be particularly useful in the case of scarce data sets where the usage of binned data would degrade the available experimental information.

Correlation analysis of the heat capacity and thermal expansion of solid mercury

NASA Astrophysics Data System (ADS)

Bodryakov, V. Yu.; Babintsev, Yu. N.

2015-06-01

A detailed analysis of the correlation between the volumetric thermal expansion coefficient o( T) and heat capacity C( T) of solid mercury has been performed. It has been shown that there is a clear correlation dependence o( C) not only in the low-temperature range, where it is linear and known as the Grüneisen law, but also up to the melting point of mercury. The dependence o( C) substantially deviates from the low-temperature linear behavior when the heat capacity reaches the classical Dulong-Petit limit of 3 R.

Influence of the Cavity Length on the Behavior of Hybrid Fixed-Point Cells Constructed at INRIM

NASA Astrophysics Data System (ADS)

Battuello, M.; Girard, F.; Florio, M.

2015-03-01

Hybrid cells with double carbon/carbon sheets are used at the Istituto Nazionale di Ricerca Metrologica (INRIM) for the realization of both pure metal fixed points and high-temperature metal-carbon eutectic points. Cells for the Cu and Co-C fixed points have been prepared to be used in the high-temperature fixed-point project of the Comité Consultatif de Thermométrie. The results of the evaluation processes were not completely satisfactory for the INRIM cells because of their low transition temperatures with respect to the best cells, and of a rather large melting range for the Co-C cell. A new design of the cells was devised, and considerable improvements were achieved with respect to the transition temperature, and the plateau shape and duration. As for the Cu point, the duration of the freezing plateaux increased by more than 50 % and the freezing temperature increased by 18 mK. As for the Co-C point, the melting temperature, expressed in terms of the point of inflection of the melting curve, increased by about 70 mK. The melting range of the plateaux, expressed as a difference was reduced from about 180 mK to about 130 mK, with melting times increased by about 50 %, as a consequence of an improvement of flatness and run-off of the plateaux.

Temperature-Induced Transitions in the Structure and Interfacial Rheology of Human Meibum

PubMed Central

Leiske, Danielle L.; Leiske, Christopher I.; Leiske, Daniel R.; Toney, Michael F.; Senchyna, Michelle; Ketelson, Howard A.; Meadows, David L.; Fuller, Gerald G.

2012-01-01

Meibomian lipids are the primary component of the lipid layer of the tear film. Composed primarily of a mixture of lipids, meibum exhibits a range of melt temperatures. Compositional changes that occur with disease may alter the temperature at which meibum melts. Here we explore how the mechanical properties and structure of meibum from healthy subjects depend on temperature. Interfacial films of meibum were highly viscoelastic at 17°C, but as the films were heated to 30°C the surface moduli decreased by more than two orders of magnitude. Brewster angle microscopy revealed the presence of micron-scale inhomogeneities in meibum films at higher temperatures. Crystalline structure was probed by small angle x-ray scattering of bulk meibum, which showed evidence of a majority crystalline structure in all samples with lamellar spacing of 49 Å that melted at 34°C. A minority structure was observed in some samples with d-spacing at 110 Å that persisted up to 40°C. The melting of crystalline phases accompanied by a reduction in interfacial viscosity and elasticity has implications in meibum behavior in the tear film. If the melt temperature of meibum was altered significantly from disease-induced compositional changes, the resultant change in viscosity could alter secretion of lipids from meibomian glands, or tear-film stabilization properties of the lipid layer. PMID:22339874

Annealing study of poly(etheretherketone)

NASA Technical Reports Server (NTRS)

Cebe, Peggy

1988-01-01

Annealing of PEEK has been studied for two materials cold-crystallized from the rubbery amorphous state. The first material is a low molecular weight PEEK; the second is commercially available neat resin. Differential scanning calorimetry was used to monitor the melting behavior of annealed samples. The effect of thermal history on melting behavior is very complex and depends upon annealing temperature, residence time at the annealing temperature, and subsequent scanning rate. Thermal stability of both materials is improved by annealing, and for an annealing temperature near the melting point, the polymer can be stabilized against reorganization during the scan. Variations of density, degree of crystallinity, and X-ray long period were studied as a function of annealing temperature for the commercial material.

Melting behavior of mixed U-Pu oxides under oxidizing conditions

NASA Astrophysics Data System (ADS)

Strach, Michal; Manara, Dario; Belin, Renaud C.; Rogez, Jacques

2016-05-01

In order to use mixed U-Pu oxide ceramics in present and future nuclear reactors, their physical and chemical properties need to be well determined. The behavior of stoichiometric (U,Pu)O2 compounds is relatively well understood, but the effects of oxygen stoichiometry on the fuel performance and stability are often still obscure. In the present work, a series of laser melting experiments were carried out to determine the impact of an oxidizing atmosphere, and in consequence the departure from a stoichiometric composition on the melting behavior of six mixed uranium plutonium oxides with Pu content ranging from 14 to 62 wt%. The starting materials were disks cut from sintered stoichiometric pellets. For each composition we have performed two laser melting experiments in pressurized air, each consisting of four shots of different duration and intensity. During the experiments we recorded the temperature at the surface of the sample with a pyrometer. Phase transitions were qualitatively identified with the help of a reflected blue laser. The observed phase transitions occur at a systematically lower temperature, the lower the Pu content of the studied sample. It is consistent with the fact that uranium dioxide is easily oxidized at elevated temperatures, forming chemical species rich in oxygen, which melt at a lower temperature and are more volatile. To our knowledge this campaign is a first attempt to quantitatively determine the effect of O/M on the melting temperature of MOX.

Gaussian decomposition of high-resolution melt curve derivatives for measuring genome-editing efficiency

PubMed Central

Zaboikin, Michail; Freter, Carl

2018-01-01

We describe a method for measuring genome editing efficiency from in silico analysis of high-resolution melt curve data. The melt curve data derived from amplicons of genome-edited or unmodified target sites were processed to remove the background fluorescent signal emanating from free fluorophore and then corrected for temperature-dependent quenching of fluorescence of double-stranded DNA-bound fluorophore. Corrected data were normalized and numerically differentiated to obtain the first derivatives of the melt curves. These were then mathematically modeled as a sum or superposition of minimal number of Gaussian components. Using Gaussian parameters determined by modeling of melt curve derivatives of unedited samples, we were able to model melt curve derivatives from genetically altered target sites where the mutant population could be accommodated using an additional Gaussian component. From this, the proportion contributed by the mutant component in the target region amplicon could be accurately determined. Mutant component computations compared well with the mutant frequency determination from next generation sequencing data. The results were also consistent with our earlier studies that used difference curve areas from high-resolution melt curves for determining the efficiency of genome-editing reagents. The advantage of the described method is that it does not require calibration curves to estimate proportion of mutants in amplicons of genome-edited target sites. PMID:29300734

Melting Behavior of Al/Pb/Sn/Al Multilayered Thin Films

NASA Astrophysics Data System (ADS)

Khan, Patan Yousaf; Devi, M. Manolata; Biswas, Krishanu

2015-09-01

Metals or alloy nanoparticles (NPs) have been reported to exhibit superheating on melting when coated with higher melting point material or embedded in a matrix. This is due to the suppression of the heterogeneous nucleation of the melt at the epitaxial interface. For 2D thin films, this necessary condition is not feasible because even if a thin film is sandwiched between higher melting temperature materials with coherent interfaces, the heterogeneous nucleation of melt is possible at various detects. However, it has earlier been reported that 2D thin films of the pure metal sandwiched by other materials can exhibit superheating by suppression of melt growth. In order to probe this effect in case of alloy thin films, the present investigation has been carried out on Pb/Sn multilayers sandwiched between Al layers. The present study shows that such sandwiched thin films prepared by accumulative roll bonding process cause the formation of biphasic NPs in the intermixed region of Pb and Sn. Al layers undergo severe plastic deformation, leading to the generation of dislocations and sub-grain boundaries. DSC (differential canning calorimeter) thermograms of the films indicate superheating of 3 K to 6 K (or 3 °C to 6 °C). Theoretical analysis using currently available literatures has been carried out to justify the finding in the present investigation.

Apparatus for growing a dendritic web

DOEpatents

Duncan, Charles S.; Piotrowski, Paul A.; Skutch, Maria E.; McHugh, James P.

1983-06-21

A melt system including a susceptor-crucible assembly having improved gradient control when melt replenishment is used during dendritic web growth. The improvement lies in the formation of a thermal barrier in the base of the receptor which is in the form of a vertical slot in the region of the susceptor underlying the crucible at the location of a compartmental separator dividing the crucible into a growth compartment and a melt replenishment compartment. The result achieved is a step change in temperature gradient in the melt thereby providing a more uniform temperature in the growth compartment from which the dendritic web is drawn.

Effect of Melt Temperature on Surface Films Formed on Molten AZ91D Alloy Protected by Graphite Powder

NASA Astrophysics Data System (ADS)

Li, Weihong; Zhou, Jixue; Ma, Baichang; Wang, Jinwei; Wu, Jianhua; Yang, Yuansheng

2017-12-01

Graphite powder was adopted to prevent AZ91D alloy from oxidizing during melting and casting. The microstructure of the resultant surface films, formed at 933 K, 973 K, 1013 K, and 1053 K (660 °C, 700 °C, 740 °C, and 780 °C) for 30 minutes, was investigated by scanning electron microscopy, energy dispersive spectrometer, and X-ray diffraction, and the phase composition of the surface films was analyzed by the standard Gibbs free energy change of the reactions between the graphite powder, the alloy melt, and the ambient atmosphere. The effect and mechanism of melt temperature on the resultant surface films were also discussed. The results indicated that the surface films, of which the surface morphology comprised folds and wrinkles, were composed of a protective layer and MgF2 particles. The protective layer was contributive to the prevention of the molten alloy from oxidizing, and consisted of magnesium, oxygen, fluorine, carbon, and a small amount of aluminium existing in the form of MgO, MgF2, C, and MgAl2O4. The layer thickness was 200 to 900 nm. The melt temperature may affect the surface films through the increased interaction between the graphite powder, the melt, and the ambient atmosphere. The oxygen content and thickness of the protective layer decreased and then increased, while the height of the folds increased with melt temperature.

Water and Melting in Back-arc Basins: New perspectives from the Eastern Lau Spreading Center

NASA Astrophysics Data System (ADS)

Langmuir, C. H.; Bezos, A.; Escrig, S.; Michael, P. J.

2007-12-01

Since the work of Stolper and Newman (EPSL, 1994) it has been well recognized that water and extent of melting correlate positively in back-arc basin basalts. Quantification of this effect has been used to determine the effect of water content in the source on extent of melting. The slope of the relationship δF/δH2Oo is linear, and varies from one back-arc basin to another. MELTS and other modeling (Hirschmann et al., J. Petrol., 1999; Gaetani and Grove, Contrib. Mineral. Pet. 1998; Geophys. Mon., 2003; Kelley et al., JGR, 2006) has led to the suggestion that the slope varies regularly with mantle temperature, and that water has a much larger effect on melting at higher compared to lower temperatures. This modeling has been done in the context of isothermal, isobaric addition of water. For back-arcs worldwide, a critical aspect of the data is that more hydrous basalts have very low Fe contents, even when corrected appropriately for hydrous fractionation. This leads to clear negative correlations between Fe and H2O corrected back to mantle values at Fo90. The 3 wt.% variations in Fe content are not compatible with isobaric models, and require very different melting conditions for hydrous basalts as compared to anhydrous back-arc basalts. Back-arc basin basalts also plot on the global correlations of axial depth and Na8.0, and this relationship has been used to estimate mantle temperatures in back-arc basins, which on this basis extend to very high values. New data on major elements, trace elements and water from the Eastern Lau Spreading Center (ELSC), along with a re-evaluation of global back-arc data and modeling of mantle melting in the context of a polybaric spreading center environment (Langmuir et al., Geophys. Mon., 2006) provide new perspectives on these issues. The ELSC1 segment has a lower δF/δH2Oo than both the Mariana and Manus Basins, which would suggest the lowest temperature. However, its extent of melting inferred from its "F" intercept (on a plot of F vs. water in the source) is similar to the Marianas, suggesting a similar temperature, and its Na contents are as low as Manus, suggesting a high temperature. These inconsistent results can be understood from quantitative models and a more realistic melting process beneath back-arc spreading centers. δF/δH2Oo does not change with mantle temperature. In the back-arc environment, there are two independent halves of the melting regime, the "dry side" and the "wet side." The dry side undergoes polybaric fractional melting like other ocean ridges. The wet side (somehow) produces low pressure equilibrium hydrous melts with high water and low Fe contents. Mixing between the two creates the back-arc arrays. Large variations of Fe and Ti that anti-correlate linearly with water reflect this two component mixing in the back-arc. Both Ti and Na are mobile in the back-arc mantle, and source depletion and enrichment is an essential factor for evaluation of mantle temperature variations. Despite the low Na contents in the Lau Basin does not appear to be particularly hot, and instead is derived from a depleted mantle with low Na contents at only modestly elevated potential temperatures of 1400 degrees.