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Sample records for direct reaction sintering

  1. Direct Observations of Silver Nanoink Sintering and Eutectic Remelt Reaction with Copper

    SciTech Connect

    Elmer, J. W.; Specht, Eliot D

    2010-01-01

    Ag nanoink sintering kinetics and subsequent melting is studied using in-situ synchrotron based x-ray diffraction. Direct observations of Ag nanoink sintering on Cu demonstrate its potential for materials joining since the Ag nanoink sinters at low temperatures but melts at high temperatures. Results show low expansion coefficient of sintered Ag, non-linear expansion as Ag densifies and interdiffuses with Cu above 500 C, remelting consistent with bulk Ag, and eutectic reaction with Cu demonstrating its usefulness as a high temperature bonding medium

  2. Sintering of reaction bonded silicon nitride

    NASA Technical Reports Server (NTRS)

    Mangels, J. A.

    1983-01-01

    A process to produce sintered reaction-bonded Si3N4 (SRBSN) articles has been developed. This process consists of the addition of an appropriate sintering aid to reaction-bonded Si3N4 followed by sintering between 1780 and 2000 C, using an over pressure of nitrogen. The principal advantage of this process is the low sintering shrinkages of 5 to 10 percent. The properties and microstructure of two SRBSN systems sintered with MgO and Y2O3 additives are described and were found to be comparable to corresponding hot-pressed Si3N4 systems. Examples of applications of both systems are illustrated, demonstrating near net shape fabrication capability of the process.

  3. Computer Modeling of Direct Metal Laser Sintering

    NASA Technical Reports Server (NTRS)

    Cross, Matthew

    2014-01-01

    A computational approach to modeling direct metal laser sintering (DMLS) additive manufacturing process is presented. The primary application of the model is for determining the temperature history of parts fabricated using DMLS to evaluate residual stresses found in finished pieces and to assess manufacturing process strategies to reduce part slumping. The model utilizes MSC SINDA as a heat transfer solver with imbedded FORTRAN computer code to direct laser motion, apply laser heating as a boundary condition, and simulate the addition of metal powder layers during part fabrication. Model results are compared to available data collected during in situ DMLS part manufacture.

  4. Direct metal laser sintering: a digitised metal casting technology.

    PubMed

    Venkatesh, K Vijay; Nandini, V Vidyashree

    2013-12-01

    Dental technology is undergoing advancements at a fast pace and technology is being imported from various other fields. One such imported technology is direct metal laser sintering technology for casting metal crowns. This article will discuss the process of laser sintering for making metal crowns and fixed partial dentures with a understanding of their pros and cons.

  5. Sintered-reaction Bonded Silicon Nitride Densified by a Gas Pressure Sintering Process Effects of Rare Earth Oxide Sintering Additives

    SciTech Connect

    Lee, S. H.; Ko, J. W.; Park, Y. J.; Kim, H. D.; Lin, Hua-Tay; Becher, Paul F

    2012-01-01

    Reaction-bonded silicon nitrides containing rare-earth oxide sintering additives were densified by gas pressure sintering. The sintering behavior, microstructure and mechanical properties of the resultant specimens were analyzed. For that purpose, Lu2O3-SiO2 (US), La2O3-MgO (AM) and Y2O3-Al2O3 (YA) additive systems were selected. Among the tested compositions, densification of silicon nitride occurred at the lowest temperature when using the La2O3-MgO system. Since the Lu2O3-SiO2 system has the highest melting temperature, full densification could not be achieved after sintering at 1950oC. However, the system had a reasonably high bending strength of 527 MPa at 1200oC in air and a high fracture toughness of 9.2 MPa m1/2. The Y2O3-Al2O3 system had the highest room temperature bending strength of 1.2 GPa

  6. Sinterable Powders from Laser Driven Reactions

    DTIC Science & Technology

    1982-03-01

    4 flow rate on the resulting Si powder particle size (reaction cell pressure of 0.6 atm). 39 21. The effect of SiR 4 flow rate on the ratio of Si...should be expected, therefore, that the relative emissivity of the SiR 4 flame will fall somewhere between following a /K dependence and following...electron diffraction. The diffraction patterns were identical to those for Si powder made from SiH 4 . The powders from SiR 4 and C2H4 runs showed

  7. Sinterable Powders from Laser Driven Reactions

    DTIC Science & Technology

    1979-07-01

    18) line was based on information from the liter- ature (Tindal, et. al., 1942) rather than direct correlation with spectro- graphic data. Amonia ...number of lines to be measured; (2) laser intensity was sufficiently low to preclude virtually any heating of the silane or amonia . Two methods were used...manometer. Electronic grade (Airco) silane was used from the tank after many freeze-pump-thaw cycles; anhydrous (Airco) NH3 was treated similarly. The

  8. Pressureless Reaction Sintering of AlON using Aluminum Orthophosphate as a Transient Liquid Phase

    SciTech Connect

    Michael Bakas; Henry Chu

    2009-01-01

    Use of aluminum oxynitride (AlON) in transparent armor systems has been difficult due to the expense and limitations of the processing methods currently necessary to achieve transparency. Development of a pressureless processing method based on direct reaction sintering of alumina and aluminum nitride powders would reduce costs and provide a more flexible and practical manufacturing method. It may be possible to develop such a processing method using liquid phase sintering; as long as the liquid phase does not remain in the final sample. AlPO4 forms a liquid phase with Al2O3 and AlN at the temperatures required to sinter AlON, and slowly decomposes into P2O5 and alumina. Therefore, it was investigated as a possible transient liquid phase for reaction-sintered AlON. Small compacts of alumina and aluminum nitride with up to of 15wt% AlPO4 additive were pressed and sintered. It was found that AlPO4 formed the requisite transient liquid phase, and it was possible to adjust the process to produce AlON samples with good transmission and densities of 3.66-3.67 g/cc. XRD confirmed the samples formed were AlON, with no trace of any remaining phosphate phases or excess alumina or aluminum nitride. Based on the results, it was concluded that AlPO4 could be utilized as a transient liquid phase to improve the density and transmission of AlON produced by pressureless reaction sintering.

  9. Reaction sintering of alumina{endash}aluminide alloys (3A)

    SciTech Connect

    Claussen, N.; Garcia, D.E.; Janssen, R.

    1996-11-01

    A novel pressureless reaction sintering process is presented for the fabrication of Al{sub 2}O{sub 3}{endash}aluminide alloys (3A). Compacts of intensively milled metal oxide{endash}aluminum mixtures are heat-treated in vacuum or inert atmosphere such that the exothermic reactions take place in a controlled manner essentially at temperatures below the melting point of Al. Dense, homogeneous microstructures were obtained with a variety of Al{sub 2}O{sub 3}-matrix systems with interpenetrating networks of aluminides of Ti, Fe, Nb, Mo, Zr, Ni, etc. By adding modifiers in the form of oxides or metals, volume and phase composition as well as properties can be tailored in a wide range. {copyright} {ital 1996 Materials Research Society.}

  10. Development of a reaction-sintered silicon carbide matrix composite

    NASA Astrophysics Data System (ADS)

    Sayano, A.; Sutoh, C.; Suyama, S.; Itoh, Y.; Nakagawa, S.

    SiC matrix composites reinforced with continuous SiC-based fibres using reaction sintering (RS) for matrix processing were produced and their mechanical and physical properties were studied. Mechanical behaviour of SiCf/SiC (RS) composites in tension and in flexure exhibits improved toughness and a non-catastrophic failure due to fibre crack bridging and pullout from the matrix, and the composites exhibit high thermal conductivity, high Young's modulus and reduced porosity. Moreover, SiCf/SiC (RS) composites showed improved thermal shock resistance in comparison to monolithic RS-SiC. SiC matrix processing by RS leads to reduced production times and lower costs when compared with other methods such as polymer impregnation and pyrolysis (PIP) or chemical vapour infiltration (CVI). Composite prototypes were also produced for feasibility demonstration, and it was verified that the method could be applied to produce large parts and complex shapes.

  11. Comparison of properties of sintered and sintered reaction-bonded silicon nitride fabricated by microwave and conventional heating

    SciTech Connect

    Tiegs, T.N.; Kiggans, J.O. Jr.; Lin, H.T.; Willkens, C.A.

    1994-10-01

    A comparison of microwave and conventional processing of silicon nitride-based ceramics was performed to identify any differences between the two, such as improved fabrication parameters or increased mechanical properties. Two areas of thermal processing were examined: (1) sintered silicon nitride (SSN) and (2) sintered reaction-bonded silicon nitride (SRBSN). The SSN powder compacts showed improved densification and enhanced grain growth. SRBSN materials were fabricated in the microwave with a one-step process using cost-effective raw materials. The SRBSN materials had properties appropriate for structural applications. Observed increases in fracture toughness for the microwave processed SRBSN materials were attributable to enhanced elongated grain growth.

  12. Comparison of properties of sintered and sintered reaction-bonded silicon nitride fabricated by microwave and conventional heating

    SciTech Connect

    Tiegs, T.N.; Kiggans, J.O. Jr.; Lin, H.T.

    1995-10-01

    A comparison of microwave and conventional processing of silicon nitride-based ceramics was performed to identify any differences between the two, such as improved fabrication parameters or increased mechanical properties. Two areas of thermal processing were examined: sintered silicon nitride (SSN) and sintered reaction-bonded silicon nitride (SRBSN). The SSN powder compacts showed improved densification and enhanced grain growth. SRBSN materials were fabricated in the microwave with a one-step process using cost-effective raw materials. The SRBSN materials had properties appropriate for structural applications. Observed increases in fracture toughness for the microwave processed SRBSN materials were attributable to enhanced elongated grain growth.

  13. Effect of attrition milling on the reaction sintering of silicon nitride

    NASA Technical Reports Server (NTRS)

    Herbell, T. P.; Glasgow, T. K.; Yeh, H. C.

    1978-01-01

    Silicon powder was ground in a steel attrition mill under nitrogen. Air-exposed powder was compacted, prefired in helium, and reaction-sintered in nitrogen-4 v/o hydrogen. For longer grinding times, oxygen content, surface area and compactability of the powder increased; and both alpha/beta ratio and degree of nitridation during sintering increased. Iron content remained constant.

  14. Effect of attrition milling on the reaction sintering of silicon nitride

    NASA Technical Reports Server (NTRS)

    Herbell, T. P.; Glasgow, T. K.; Yeh, H. C.

    1978-01-01

    Silicon powder was ground in a steel attrition mill under nitrogen. Air exposed powder was compacted, prefired in helium, and reaction sintered in nitrogen-4 v/o hydrogen. For longer grinding times, oxygen content, surface area and compactability of the powder increased; and both alpha/beta ratio and degreee of nitridation during sintering increased. Iron content remained constant.

  15. Sintering Behavior of Metal Powders Involving Microwave-Enhanced Chemical Reaction

    NASA Astrophysics Data System (ADS)

    Takayama, Sadatsugu; Saito, Yasushi; Sato, Motoyasu; Nagasaka, Takuya; Muroga, Takeo; Ninomiya, Yoshihiko

    2006-03-01

    Copper powder compacts were sintered by microwave radiation in air. In this procedure, the samples were sintered by microwave in air without using any special atmosphere, only by protecting them in a container filled with ceramic powder. The enhancement of the deoxidation reaction by the microwave was observed. The samples were analyzed by using scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) analysis. The samples were deoxidized on the surface and were well sintered to the edge from the inside throughout the entire cross section. The tensile strength of the copper samples sintered by the microwave in air was higher than that found in conventional sintering in N2 gas. No other differences were noticed between the samples sintered by the microwave under the air-rich conditions and in the conventional furnace in H2+N2 gas. The microwave-sintered copper samples were of good quality; for example, the tensile strength measured throughout the cross section was the same as that for the samples sintered in H2+N2 gas by the conventional method.

  16. Hot isostatic pressing of direct selective laser sintered metal components

    NASA Astrophysics Data System (ADS)

    Wohlert, Martin Steven

    2000-10-01

    A new manufacturing process combining the benefits of Selective Laser Sintering (SLS) and Hot Isostatic Pressing (HIP) has been developed to permit Rapid Prototyping of high performance metal components. The new process uses Direct Metal SLS to produce a gas impermeable HIP container from the same powdered material that will eventually compose the bulk of the part. The SLS generated capsule performs the functions of the sheet metal container in traditional HIP, but unlike a sheet metal container, the SLSed capsule becomes an integral part of the final component. Additionally, SLS can produce a capsule of far greater geometric complexity than can be achieved by sheet metal forming. Two high performance alloys, Ti-6Al-4V and Inconel 625, were selected for use in the development of the new process. HIP maps were constructed to predict the densification rate of the two materials during HIP processing. Comparison to experimentally determined densification behavior indicated that the maps provide a useful qualitative description of densification rates; however, the accuracy of quantitative predictions was greatly enhanced by tuning key material parameters based on a limited number of experimental HIP cycles. Microstructural characterization of SLS + HIP samples revealed two distinct regions within the components. The outer SLS processed capsule material exhibited a relatively coarse microstructure comparable to a cast, or multi-layer welded structure. No layer boundaries were discernible in the SLS material, with grains observed to grow epitaxially from previously deposited material. The microstructure of the HIP consolidated core material was similar to conventionally HIP processed powder materials, featuring a fine grain structure and preserved prior particle boundaries. The large variation in grain size between the capsule and core materials was reflected in hardness measurements conducted on the Alloy 625 material; however, the variation in hardness was less

  17. Sintering behavior of ultrafine silicon carbide powders obtained by vapor phase reaction

    NASA Technical Reports Server (NTRS)

    Okabe, Y.; Miyachi, K.; Hojo, J.; Kato, A.

    1984-01-01

    The sintering behavior of ultrafine SiC powder with average particle size of about 0.01-0.06 microns produced by a vapor phase reaction of the Me4Si-H2 system was studied at the temperature range of 1400-2050 deg. It was found that the homogeneous dispersion of C on SiC particles is important to remove the surface oxide layer effectively. B and C and inhibitive effect on SiC grain growth.

  18. Gelcasting of silicon preforms for the production of sintered reaction-bonded silicon nitride

    SciTech Connect

    Kiggans, J.O. Jr.; Nunn, S.D.; Tiegs, T.N.; Davisson, C.C.; Coffey, D.W.; Maria, J.P.

    1995-12-31

    Gelcasting of silicon metal for the production of sintered reaction-bonded silicon nitride (SRBSN) was investigated in order to identify associated advantages over conventional forming techniques, i.e., die and isostatic pressing. Compacts were formed from identical powder mixtures by both gelcasting and pressing, and were nitrided and sintered to produce SRBSN ceramics using both conventional and microwave heating. Characterization of the samples included measurement of green density, green and nitrided pore structure, weight gain during nitridation, final density, microstructure, toughness, and flexural strength. It was found that a more uniform pore structure existed in the green gelcast samples. It is believed that this pore configuration aided in nitridation, and manifested itself in a more uniform final microstructure. In addition, improved mechanical properties were achieved in the gelcast samples. This improvement can be attributed to green microstructure homogeneity. An additional finding of this study was that microwave hearing combined with gelcast forming resulted in SRBSN materials with improved mechanical properties.

  19. Effect of composition on the processing and properties of sintered reaction-bonded silicon nitride

    SciTech Connect

    Tiegs, T.N.; Kiggans, J.O.; Montgomery, F.C.; Lin, H.T.; Barker, D.L.; Snodgrass, J.D.; Sabolsky, E.M.; Coffey, D.W.

    1996-04-01

    The type of silicon powder and sintering additive were found to influence the processing and final mechanical properties of sintered reaction bonded silicon nitride. High purity silicon powders produced low {alpha}-Si{sub 3}N{sub 4} content during nitridation. The Si powder type had no apparent effect on densification. More complete nitridation and higher room temperature mechanical properties were observed for the Si powders with higher Fe contents. However, the higher Fe contents resulted in greater high temperature strength degradation and so there was better high temperature strength retention with the higher purity Si. High {alpha}-Si{sub 3}N{sub 4} contents were found after nitridation with {alpha}-Si{sub 3}N{sub 4} seeded materials and with MgO-Y{sub 2}O{sub 3} as the sintering additive. Densification was inhibited by refractory additives, such as Y{sub 2}O{sub 3}-SiO{sub 2}. The highest room temperature strength and fracture toughness values correlated to high nitrided {alpha}-Si{sub 3}N{sub 4} contents. The high temperature strength behavior was similar for all additive types.

  20. Effect of Sintering Temperature on Electrical Properties of Chip on Glass Module with Direct Printing Method

    NASA Astrophysics Data System (ADS)

    Lee, Young-Chul; Kim, Yongil; Jung, Seung-Boo

    2012-09-01

    In order to apply the direct printing method to the fabrication of chip on glass (COG) modules, we examined that the effect of the sintering temperature on the electrical properties of a COG module with direct printing method. Firstly, we fabricated an Ag conductive circuit on a glass substrate by the screen-printing method. To investigate its the effect on the electrical properties of the circuit, it was sintered at various temperatures, such as 150, 200, 250, and 300 °C for 30 min. Subsequently, we conducted Au electro-plating for the fabrication of a Si dummy chip. Finally, the flip-chip bonding process was conducted using anisotropic conductive film (ACF). The printed Ag circuits were well formed on the quartz substrate without any shorts or remarkable changes compared with the initial design. The electrical properties of the printed Ag circuits improved with increasing sintering temperature. The conductive particles in the ACF were well deformed in between the Au bumps and printed Ag pads after the bonding process. The four-point probe method was employed to measure the connection resistance of the joints constructed with the Au bumps on the Si chip and printed Ag circuit on the quartz substrate. The resistances of the interconnections drastically decreased with increasing sintering temperature, i.e., subsequently converged from 11.8 Ω to 7.36 mΩ.

  1. Effect of Oxidation on the Densification of Sinterable RBSN (Reaction-Bonded Silicon Nitride).

    DTIC Science & Technology

    1986-01-01

    pressure/temperature cycle. Some bars were preoxidized at 10000C prior to sintering to increase the oxygen content (SiO2 ) of the speci- - mens and...tering process. Those kinetics are influenced by the amount and stability of each component or compound formed and the reaction path. Additionally...yttrium-nitrogen apatite (Y5Si301 2N) with a small amount of free silicon also detected. The densities of the specimens were between 2.4 and 2.5 g/cc

  2. Fracture of yttria-doped, sintered reaction-bonded silicon nitride

    NASA Technical Reports Server (NTRS)

    Govila, R. K.; Mangels, J. A.; Baer, J. R.

    1985-01-01

    Flexural strength of an yttria-doped, slip-cast, sintered reaction-bonded silicon nitride was evaluated as a function of temperature (20 to 1400 C in air), applied stress, and time. Static oxidation at 700 to 1400 C was investigated in detail; in tests at 1000 C in air, the material showed anomalous weight gain. Flexural stress-rupture testing at 800 to 1200 C in air indicated that the material is susceptible to stress-enhanced oxidation and early failure. Fractographic evidence for time-dependent and -independent failures is presented.

  3. Improved reaction sintered silicon nitride. [protective coatings to improve oxidation resistance

    NASA Technical Reports Server (NTRS)

    Baumgartner, H. R.

    1978-01-01

    Processing treatments were applied to as-nitrided reaction sintered silicon nitride (RSSN) with the purposes of improving strength after processing to above 350 MN/m2 and improving strength after oxidation exposure. The experimental approaches are divided into three broad classifications: sintering of surface-applied powders; impregnation of solution followed by further thermal processing; and infiltration of molten silicon and subsequent carburization or nitridation of the silicon. The impregnation of RSSN with solutions of aluminum nitrate and zirconyl chloride, followed by heating at 1400-1500 C in a nitrogen atmosphere containing silicon monoxide, improved RSSN strength and oxidation resistance. The room temperature bend strength of RSSN was increased nearly fifty percent above the untreated strength with mean absolute strengths up to 420 MN/m2. Strengths of treated samples that were measured after a 12 hour oxidation exposure in air were up to 90 percent of the original as-nitrided strength, as compared to retained strengths in the range of 35 to 60 percent for untreated RSSN after the same oxidation exposure.

  4. Controlled metal-semiconductor sintering/alloying by one-directional reverse illumination

    DOEpatents

    Sopori, Bhushan L.

    1993-01-01

    Metal strips deposited on a top surface of a semiconductor substrate are sintered at one temperature simultaneously with alloying a metal layer on the bottom surface at a second, higher temperature. This simultaneous sintering of metal strips and alloying a metal layer on opposite surfaces of the substrate at different temperatures is accomplished by directing infrared radiation through the top surface to the interface of the bottom surface with the metal layer where the radiation is absorbed to create a primary hot zone with a temperature high enough to melt and alloy the metal layer with the bottom surface of the substrate. Secondary heat effects, including heat conducted through the substrate from the primary hot zone and heat created by infrared radiation reflected from the metal layer to the metal strips, as well as heat created from some primary absorption by the metal strips, combine to create secondary hot zones at the interfaces of the metal strips with the top surface of the substrate. These secondary hot zones are not as hot as the primary hot zone, but they are hot enough to sinter the metal strips to the substrate.

  5. Fabrication and evaluation of solid-oxide fuel cell anodes employing reaction-sintered yttria-stabilized zirconia

    NASA Astrophysics Data System (ADS)

    Storjohann, Daniel; Daggett, James; Sullivan, Neal P.; Zhu, Huayang; Kee, Robert J.; Menzer, Sophie; Beeaff, Dustin

    This paper reports on the fabrication and performance of solid-oxide fuel cell (SOFC) anodes utilizing yttria reaction-sintered zirconia (YRSZ). Through the reaction-sintering process, the technical-grade YSZ commonly used in the Ni-YSZ anode cermet is replaced with lower-cost ZrO 2 and Y 2O 3 materials. When sintered in the presence of nickel oxide, ZrO 2 and Y 2O 3 form cubic-phase YSZ at temperatures characteristic of SOFC processing (1400-1550 ° C). Reaction sintering enables the formation of YSZ during cell fabrication, reducing SOFC anode raw-materials cost and the number of SOFC-fabrication processes. This paper reports the results of a broad range of characterization and performance measurements to evaluate the YRSZ material, including (1) crystal structure, (2) morphology, (3) pore-size distribution, (4) electronic resistivity, (5) fracture strength, (6) gas transport and catalytic activity, and (7) electrochemical performance. Material properties and performance are found to be comparable to or better than equivalent materials fabricated by conventional processes.

  6. Controlling Directed Self-Assembly and Sintering of Gold Nanorods in Patterned Block Copolymer Thin Films

    NASA Astrophysics Data System (ADS)

    Lai, Fengyuan

    As the miniaturization of electronic devices continues, proper thermal management is crucial to ensure the optimum performance and reliability of such devices within their specification. Of primary interest are the so-called thermal interface materials to minimize the thermal resistance between the heat source and the heat sink. To this end, polymer nanocomposites composed of a polymer matrix and nanoscale fillers with high thermal conductivity have attracted tremendous attention. It has been demonstrated that the formation of a nanoparticle assembly inside the polymer matrix provides a continuous pathway for efficient heat transfer, and thus it is essential for achieving high thermal conductivity. In this work, we explored the ability to direct the self-assembly of gold nanorods (AuNRs) via patterned block copolymer (BCP) thin films. Selective sequestration of AuNRs with various aspect ratios in one block domain was achieved, with over 30% of the surface covered by an ordered AuNR assembly orienting parallel to the geometric confinement. The final nanostructure resulting from the directed self-assembly process is determined by the competition between thermodynamic consideration and kinetic factors. The coalescence and sintering of the AuNR assembly was accomplished by both furnace thermal annealing and rapid thermal annealing at low temperatures. The mechanism through which efficient sintering occurred is investigated with scanning electron microscopy. It is found that the sintering process initially takes place locally, resulting in small AuNR aggregates. Eventually the aggregates grow into a globally continuous, percolating network structure. In addition, the overall heat transfer coefficient was measured in an environmental scanning electron microscope by following droplet growth over time. The present study opens up new opportunities to accomplish controlled assembly of nanoparticles with high concentration for different nanorod-based applications as well as

  7. Enhancement of thermal shock resistance of reaction sintered mullite–zirconia composites in the presence of lanthanum oxide

    SciTech Connect

    Kumar, P.; Nath, M.; Ghosh, A.; Tripathi, H.S.

    2015-03-15

    Mullite–zirconia composites containing 20 wt.% zirconia were prepared by reaction sintering of zircon flour, sillimanite beach sand and calcined alumina. 0 to 8 mol% of La{sub 2}O{sub 3} with respect to zirconia was used as sintering aid. The effect of additive on the various physical, microstructures, mechanical and thermo-mechanical properties was studied. Quantitative phase analysis shows the change in tetragonal zirconia content with incorporation of lanthanum oxide. La{sub 2}O{sub 3} addition has significantly improved the thermal shock resistance of the samples. Samples without additive retained only 20% of initial flexural strength after 5 cycles, whereas samples containing 5 mol% La{sub 2}O{sub 3} retained almost 78% of its initial flexural strength even after 15 thermal shock cycles. - Highlights: • Mullite–zirconia composites were prepared by reaction sintering route utilizing zircon and sillimanite beach sand. • Lanthanum oxide was used as sintering aid. • The presence of lanthanum oxide decreased the densification temperature. • Lanthanum oxide significantly improved the thermal shock resistance of the composites.

  8. Direct Selective Laser Sintering/Melting of High Density Alumina Powder Layers at Elevated Temperatures

    NASA Astrophysics Data System (ADS)

    Deckers, J.; Meyers, S.; Kruth, J. P.; Vleugels, J.

    Direct selective laser sintering (SLS) or selective laser melting (SLM) are additive manufacturing techniques that can be used to produce three-dimensional ceramic parts directly, without the need for a sacrificial binder. In this paper, a low laser energy density is applied to SLS/SLM high density powder layers of sub-micrometer alumina at elevated temperatures (up to 800̊C). In order to achieve this, a furnace was designed and built into a commercial SLS machine. This furnace was able to produce a homogeneously heated cylindrical zone with a height of 60 mm and a diameter of 32 mm. After optimizing the layer deposition and laser scanning parameters, two ceramic parts with a density up to 85% and grain sizes as low as 5 μm were successfully produced.

  9. Direct selective laser sintering of high performance metals: Machine design, process development and process control

    NASA Astrophysics Data System (ADS)

    Das, Suman

    1998-11-01

    This dissertation describes the development of an advanced manufacturing technology known as Direct Selective Laser Sintering (Direct SLS). Direct SLS is a laser based rapid manufacturing technology that enables production of functional, fully dense, metal and cermet components via the direct, layerwise consolidation of constituent powders. Specifically, this dissertation focuses on a new, hybrid net shape manufacturing technique known as Selective Laser Sintering/Hot Isostatic Pressing (SLS/HIP). The objective of research presented in this dissertation was to establish the fundamental machine technology and processing science to enable direct SLS fabrication of metal components composed of high performance, high temperature metals and alloys. Several processing requirements differentiate direct SLS of metals from SLS of polymers or polymer coated powders. Perhaps the most important distinguishing characteristic is the regime of high temperatures involved in direct SLS of metals. Biasing the temperature of the feedstock powder via radiant preheat prior to and during SLS processing was shown to be beneficial. Preheating the powder significantly influenced the flow and wetting characteristics of the melt. During this work, it was conclusively established that powder cleanliness is of paramount importance for successful layerwise consolidation of metal powders by direct SLS. Sequential trials were conducted to establish optimal bake-out and degas cycles under high vacuum. These cycles agreed well with established practices in the powder metallurgy industry. A study of some of the important transport mechanisms in direct SLS of metals was undertaken to obtain a fundamental understanding of the underlying process physics. This study not only provides an explanation of phenomena observed during SLS processing of a variety of metallic materials but also helps in developing selection schemes for those materials that are most amenable to direct SLS processing. The

  10. Fabrication of water-cooled laser silicon mirror by direct laser sintering.

    PubMed

    He, Chongwen; Zhu, Haihong; Hu, Panpan

    2014-04-21

    Coppery heat sink with micro pores and Sub-millimeter channel has been fabricated by direct laser sintering on the back of the silicon mirror. To verify the heat dissipation capability of the fabricated heat sink, a Twyman-Green interferometer was employed to measure the thermal deformation of the silicon mirror radiated by a high power laser. It is shown that the thermal deformation of the mirror increases with the irradiating time and laser intensity. The heat balance can be achieved after several seconds of laser irradiation even when the net absorbed laser power density is up to 5.3 × 10(5) W/m(2). The time for reaching the heat balance also increases with the laser intensity. The maximum thermal deformation of the mirror is 0.65 µm if the net absorbed laser power density is 5.3 × 10(5) W/m(2).

  11. Nondestructive Evaluation of the J-2X Direct Metal Laser Sintered Gas Generator Discharge Duct

    NASA Technical Reports Server (NTRS)

    Esther, Elizabeth A.; Beshears, Ronald D.; Lash, Rhonda K.

    2012-01-01

    The J-2X program at NASA's Marshall Space Flight Center (MSFC) procured a direct metal laser sintered (DMLS) gas generator discharge duct from Pratt & Whitney Rocketdyne and Morris Technologies for a test program that would evaluate the material properties and durability of the duct in an engine-like environment. DMLS technology was pursued as a manufacturing alternative to traditional techniques, which used off nominal practices to manufacture the gas generator duct's 180 degree turn geometry. MSFC's Nondestructive Evaluation (NDE) Team performed radiographic, ultrasonic, computed tomographic, and fluorescent penetrant examinations of the duct. Results from the NDE examinations reveal some shallow porosity but no major defects in the as-manufactured material. NDE examinations were also performed after hot-fire testing the gas generator duct and yielded similar results pre and post-test and showed no flaw growth or development.

  12. Corrosion of Ti6Al4V pins produced by direct metal laser sintering

    NASA Astrophysics Data System (ADS)

    de Damborenea, J. J.; Arenas, M. A.; Larosa, Maria Aparecida; Jardini, André Luiz; de Carvalho Zavaglia, Cecília Amélia; Conde, A.

    2017-01-01

    Direct Metal Laser Sintering (DMLS) technique allows the manufacturing a wide variety of medical devices for any type of prosthetic surgery (HIP, dental, cranial, maxillofacial) as well as for internal fixation devices (K-Wires or Steinmann Pins). There are a large number of research studies on DMLS, including microstructural characterization, mechanical properties and those based on production quality assurance but the influence of porosity in the corrosion behavior of these materials not been sufficiently considered. In the present paper, surgical pins of Ti6Al4V have been produced by DMLS. After testing in a phosphate buffered saline solution, the surface of the titanium alloy appeared locally covered by a voluminous white oxide. This unexpected behavior was presumably due to the existence of internal defects in the pins as result of the manufacturing process. The importance of these defects-that might act as crevice nucleation sites- has been revealed by electrochemical techniques and confirmed by computed tomography.

  13. Reaction of Unalloyed and Cr-Mo Alloyed Steels with Nitrogen from the Sintering Atmosphere

    NASA Astrophysics Data System (ADS)

    Dlapka, Magdalena; Gierl-Mayer, Christian; Calderon, Raquel de Oro; Danninger, Herbert; Bengtsson, Sven; Dudrova, Eva

    2016-12-01

    Nitrogen is usually regarded as an inert sintering atmosphere for PM steels; however, this cannot be taken for granted in particular for steels alloyed with nitride forming elements. Among those elements, chromium has become more and more important as an alloying element in sintered low alloy structural steels in the last decade due to the moderate alloying cost and the excellent mechanical properties obtainable, in particular when sinter hardening is applied. The high affinity of Cr to oxygen and the possible ways to overcome related problems have been the subject of numerous studies, while the fact that chromium is also a fairly strong nitride forming element has largely been neglected at least for low alloy steel grades, although frequently used materials like steels from Cr and Cr-Mo prealloyed powders are commonly sintered in atmospheres consisting mainly of nitrogen. In the present study, nitrogen pickup during sintering at different temperatures and for varying times has been studied for Cr-Mo prealloyed steel grades as well as for unalloyed carbon steel. Also the effect of the cooling rate and its influence on the properties, of the microstructure and the composition have been investigated. It showed that the main nitrogen uptake occurs not during isothermal sintering but rather during cooling. It could be demonstrated that a critical temperature range exists within which the investigated CrM-based steel is particularly sensitive to nitrogen pickup.

  14. Modeling of microstructure evolution in direct metal laser sintering: A phase field approach

    NASA Astrophysics Data System (ADS)

    Nandy, Jyotirmoy; Sarangi, Hrushikesh; Sahoo, Seshadev

    2017-02-01

    Direct Metal Laser Sintering (DMLS) is a new technology in the field of additive manufacturing, which builds metal parts in a layer by layer fashion directly from the powder bed. The process occurs within a very short time period with rapid solidification rate. Slight variations in the process parameters may cause enormous change in the final build parts. The physical and mechanical properties of the final build parts are dependent on the solidification rate which directly affects the microstructure of the material. Thus, the evolving of microstructure plays a vital role in the process parameters optimization. Nowadays, the increase in computational power allows for direct simulations of microstructures during materials processing for specific manufacturing conditions. In this study, modeling of microstructure evolution of Al-Si-10Mg powder in DMLS process was carried out by using a phase field approach. A MATLAB code was developed to solve the set of phase field equations, where simulation parameters include temperature gradient, laser scan speed and laser power. The effects of temperature gradient on microstructure evolution were studied and found that with increase in temperature gradient, the dendritic tip grows at a faster rate.

  15. Reaction sintering of two-dimensional silicon carbide fiber-reinforced silicon carbide composite by sheet stacking method

    NASA Astrophysics Data System (ADS)

    Yoshida, Katsumi; Mukai, Hideki; Imai, Masamitsu; Hashimoto, Kazuaki; Toda, Yoshitomo; Hyuga, Hideki; Kondo, Naoki; Kita, Hideki; Yano, Toyohiko

    2007-08-01

    Two-dimensionally plain woven SiC fiber-reinforced SiC composite has been developed by reaction sintering using a sheet stacking method in order to further increase mechanical and thermal properties of the composite and to obtain flexibility of manufacturing process of 2D woven SiC/SiC composites which can be applied to the fabrication of larger parts. In addition, sinterability and mechanical properties of the composite were investigated. In this study, relative density of the composites was about 90-93% and a dense composite could be obtained by reaction sintering using the sheet stacking method. The bulk density and maximum bending strength of SiC/SiC composite with a C/SiC weight ratio of 0.6 were higher than that of the composite with C/SiC ratios of 0.5 or 0.7. The values were 2.9 g/cm 3 and 200 MPa, respectively. However, the composites obtained in this study fractured in almost brittle manner due to the lower fiber volume fraction.

  16. Densification of Reaction Bonded Silicon Nitride with the Addition of Fine Si Powder Effects on the Sinterability and Mechanical Properties

    SciTech Connect

    Lee, Sea-Hoon; Cho, Chun-Rae; Park, Young-Jo; Ko, Jae-Woong; Kim, Hai-Doo; Lin, Hua-Tay; Becher, Paul F

    2013-01-01

    The densification behavior and strength of sintered reaction bonded silicon nitrides (SRBSN) that contain Lu2O3-SiO2 additives were improved by the addition of fine Si powder. Dense specimens (relative density: 99.5%) were obtained by gas-pressure sintering (GPS) at 1850oC through the addition of fine Si. In contrast, the densification of conventional specimens did not complete at 1950oC. The fine Si decreased the onset temperature of shrinkage and increased the shrinkage rate because the additive helped the compaction of green bodies and induced the formation of fine Si3N4 particles after nitridation and sintering at and above 1600oC. The amount of residual SiO2 within the specimens was not strongly affected by adding fine Si powder because most of the SiO2 layer that had formed on the fine Si particles decomposed during nitridation. The maximum strength and fracture toughness of the specimens were 991 MPa and 8.0 MPa m1/2, respectively.

  17. The effect of preparation conditions on the structure and mechanical properties of reaction-sintered silicon nitride

    NASA Technical Reports Server (NTRS)

    Heinrich, J.

    1980-01-01

    The microstructure of reaction sintered silicon nitride (RSSN) was changed over a wide range by varying the grain density, grain size of the silicon starting powder, nitriding conditions, and by introducing artificial pores. The influence of single microstructural parameters on mechanical properties like room temperature strength, creep behavior, and resistance to thermal shock was investigated. The essential factors influencing these properties were found to be total porosity, pore size distribution, and the fractions of alpha and beta Si3N4. In view of high temperature engineering applications of RSSN, potentials for optimizing the material's properties by controlled processing are discussed.

  18. In-Situ X-Ray Diffraction Observations of Low Temperature Ag-Nanoink Sintering and High Temperature Eutectic Reaction with Copper

    SciTech Connect

    Elmer, J. W.; Specht, Eliot D

    2012-01-01

    Nanoinks, which contain nm sized metallic particles suspended in an organic dispersant fluid, are finding numerous microelectronic applications. Nanoinks sinter at much lower temperatures than bulk metals due to their high surface area to volume ratio and small radius of curvature, which reduces their melting points significantly below their bulk values. The unusually low melting and sintering temperatures have unique potential for materials joining since their melting points increase dramatically after initial sintering. In this paper Ag nanoink is studied using in-situ synchrotron based x-ray diffraction to follow the kinetics of the initial sintering step by analysis of diffraction patterns, and to directly observe the high remelt temperature of sintered nanoinks. Ag nanoink is further explored as a possible eutectic bonding medium with copper by tracking phase transformations to high temperatures where melting occurs at the Ag-Cu eutectic temperature, demonstrating nanoinks as a viable eutectic bonding medium.

  19. Direct Metal Laser Sintering Titanium Dental Implants: A Review of the Current Literature

    PubMed Central

    Mangano, F.; Chambrone, L.; van Noort, R.; Miller, C.; Hatton, P.; Mangano, C.

    2014-01-01

    Statement of Problem. Direct metal laser sintering (DMLS) is a technology that allows fabrication of complex-shaped objects from powder-based materials, according to a three-dimensional (3D) computer model. With DMLS, it is possible to fabricate titanium dental implants with an inherently porous surface, a key property required of implantation devices. Objective. The aim of this review was to evaluate the evidence for the reliability of DMLS titanium dental implants and their clinical and histologic/histomorphometric outcomes, as well as their mechanical properties. Materials and Methods. Electronic database searches were performed. Inclusion criteria were clinical and radiographic studies, histologic/histomorphometric studies in humans and animals, mechanical evaluations, and in vitro cell culture studies on DMLS titanium implants. Meta-analysis could be performed only for randomized controlled trials (RCTs); to evaluate the methodological quality of observational human studies, the Newcastle-Ottawa scale (NOS) was used. Results. Twenty-seven studies were included in this review. No RCTs were found, and meta-analysis could not be performed. The outcomes of observational human studies were assessed using the NOS: these studies showed medium methodological quality. Conclusions. Several studies have demonstrated the potential for the use of DMLS titanium implants. However, further studies that demonstrate the benefits of DMLS implants over conventional implants are needed. PMID:25525434

  20. Magnetic field effects on liquid-phase reactive sintering of MnBi

    NASA Astrophysics Data System (ADS)

    Mitsui, Yoshifuru; Abematsu, Ken-ichi; Umetsu, Rie Y.; Takahashi, Kohki; Koyama, Keiichi

    2016-02-01

    Magnetic fields effects on liquid-phase reaction sintering on MnBi were investigated. The liquid-phase reaction was so fast even in a zero field that the fraction of in-field sintered ferromagnetic MnBi phase was independent of the external magnetic field. However, the ferromagnetic MnBi crystals in the in-field sintered sample were oriented along the external magnetic field direction. The Lotgering factor of the in-field sintered sample was 0.99. This result indicated that almost completely anisotropic MnBi phase could be obtained by in-field liquid phase reactive sintering.

  1. Can the use of pulsed direct current induce oscillation in the applied pressure during spark plasma sintering?

    PubMed Central

    Salamon, David; Eriksson, Mirva; Nygren, Mats; Shen, Zhijian

    2012-01-01

    The spark plasma sintering (SPS) process is known for its rapid densification of metals and ceramics. The mechanism behind this rapid densification has been discussed during the last few decades and is yet uncertain. During our SPS experiments we noticed oscillations in the applied pressure, related to a change in electric current. In this study, we investigated the effect of pulsed electrical current on the applied mechanical pressure and related changes in temperature. We eliminated the effect of sample shrinkage in the SPS setup and used a transparent quartz die allowing direct observation of the sample. We found that the use of pulsed direct electric current in our apparatus induces pressure oscillations with the amplitude depending on the current density. While sintering Ti samples we observed temperature oscillations resulting from pressure oscillations, which we attribute to magnetic forces generated within the SPS apparatus. The described current–pressure–temperature relations might increase understanding of the SPS process. PMID:27877472

  2. Can the use of pulsed direct current induce oscillation in the applied pressure during spark plasma sintering?

    PubMed

    Salamon, David; Eriksson, Mirva; Nygren, Mats; Shen, Zhijian

    2012-02-01

    The spark plasma sintering (SPS) process is known for its rapid densification of metals and ceramics. The mechanism behind this rapid densification has been discussed during the last few decades and is yet uncertain. During our SPS experiments we noticed oscillations in the applied pressure, related to a change in electric current. In this study, we investigated the effect of pulsed electrical current on the applied mechanical pressure and related changes in temperature. We eliminated the effect of sample shrinkage in the SPS setup and used a transparent quartz die allowing direct observation of the sample. We found that the use of pulsed direct electric current in our apparatus induces pressure oscillations with the amplitude depending on the current density. While sintering Ti samples we observed temperature oscillations resulting from pressure oscillations, which we attribute to magnetic forces generated within the SPS apparatus. The described current-pressure-temperature relations might increase understanding of the SPS process.

  3. Comparison of residual stresses in Inconel 718 simple parts made by electron beam melting and direct laser metal sintering

    DOE PAGES

    Kolbus, Lindsay M.; Payzant, E. Andrew; Cornwell, Paris A.; ...

    2015-01-10

    Residual stress profiles were mapped using neutron diffraction in two simple prism builds of Inconel 718: one fabricated with electron beam melting and the other with direct laser sintering. Spatially indexed stress-free cubes were obtained by EDM sectioning equivalent prisms of similar shape. The (311) interplanar spacing examined for the EDM sectioned sample was compared to the interplanar spacings calculated to fulfill force and moment balance. We have shown that Applying force and moment balance is a necessary supplement to the measurements for the stress-free cubes with respect to accurate stress calculations in additively manufactured components. Furthermore, our work hasmore » shown that residual stresses in electron beam melting parts are much smaller than that of direct laser metal sintering parts.« less

  4. Comparison of residual stresses in Inconel 718 simple parts made by electron beam melting and direct laser metal sintering

    SciTech Connect

    Kolbus, Lindsay M.; Payzant, E. Andrew; Cornwell, Paris A.; Watkins, Thomas R.; Babu, Sudarsanam Suresh; Dehoff, Ryan R.; Duty, Chad E.; Lorenz, M.; Ovchinnikova, O. S.

    2015-01-10

    Residual stress profiles were mapped using neutron diffraction in two simple prism builds of Inconel 718: one fabricated with electron beam melting and the other with direct laser sintering. Spatially indexed stress-free cubes were obtained by EDM sectioning equivalent prisms of similar shape. The (311) interplanar spacing examined for the EDM sectioned sample was compared to the interplanar spacings calculated to fulfill force and moment balance. We have shown that Applying force and moment balance is a necessary supplement to the measurements for the stress-free cubes with respect to accurate stress calculations in additively manufactured components. Furthermore, our work has shown that residual stresses in electron beam melting parts are much smaller than that of direct laser metal sintering parts.

  5. Comparison of Residual Stresses in Inconel 718 Simple Parts Made by Electron Beam Melting and Direct Laser Metal Sintering

    NASA Astrophysics Data System (ADS)

    Sochalski-Kolbus, L. M.; Payzant, E. A.; Cornwell, P. A.; Watkins, T. R.; Babu, S. S.; Dehoff, R. R.; Lorenz, M.; Ovchinnikova, O.; Duty, C.

    2015-03-01

    Residual stress profiles were mapped using neutron diffraction in two simple prism builds of Inconel 718: one fabricated with electron beam melting (EBM) and the other with direct laser metal sintering. Spatially indexed stress-free cubes were obtained by electrical discharge machining (EDM) equivalent prisms of similar shape. The (311) interplanar spacings from the EDM sectioned sample were compared to the interplanar spacings calculated to fulfill stress and moment balance. We have shown that applying stress and moment balance is a necessary supplement to the measurements for the stress-free cubes with respect to accurate stress calculations in additively manufactured components. In addition, our work has shown that residual stresses in electron beam melted parts are much smaller than that of direct laser metal sintered parts most likely due to the powder preheating step in the EBM process.

  6. Direct Reactions studies at RIBF new facility

    NASA Astrophysics Data System (ADS)

    Motobayashi, Tohru

    2009-10-01

    The RIKEN RI Beam Factory (RIBF) is the firs realization of new-generation facilities with beams of unstable nuclei. It is based on heavy-ion primary beams accelerated to 345 MeV/nucleon for all elements up to uranium. When the goal intensity, 1 pμA, is reached, RIBF allows production of about thousand new isotopes with the yield higher than 1 particle par day. Since the RI beam energy after production by in-flight fission and/or projectile fragmentation is be around 200-300 MeV/nucleon, the direct reaction is one of the useful processes for spectroscopy of uncle very far from the stability. Several experiments were proposed and a few of them have been performed with intense (currently) ^48Ca primary beams. The ZeroDegree Spectrometer, which is already operational, can be used to identify the product of a direct reaction in inverse kinematics coupled with, for example, measurement of γ-rays from excited states in the product. Construction of SAMURAI, a large-acceptance spectrometer, has been started. Decays of unbound states or breakup products from various types of direct reaction will be measured in coincidence. Experimental and theoretical issues to be considered for the specific conditions in this new opportunity will be discussed together with brief overview of near-term research.

  7. Amyloplast Distribution Directs a Root Gravitropic Reaction

    NASA Astrophysics Data System (ADS)

    Kordyum, Elizabeth

    Immobile higher plants are oriented in the gravitational field due to gravitropim that is a physiological growth reaction and consists of three phases: reception of a gravitational signal by statocytes, its transduction to the elongation zone, and finally the organ bending. As it is known, roots are characterized with positive gravitropism, i. e. they grow in the direction of a gravitational vector, stems - with negative gravitropism, i. e. they grow in the direction opposite to a gravitational vector. According to the Nemec’s and Haberlandt’s starch-statolith hypothesis, amyloplasts in diameter of 1.5 - 3 μ in average, which appear to act as gravity sensors and fulfill a statolythic function in the specialized graviperceptive cells - statocytes, sediment in the direction of a gravitational vector in the distal part of a cell, while a nucleus is in the proximal one. There are reasonable data that confirm the amyloplasts-statoliths participation in gravity perception: 1) correlation between the statoliths localization and the site of gravity sensing, 2) significant redistribution (sedimentation) of amyloplasts in statocytes under gravistimulation in comparison with other cell organelles, 3) root decreased ability to react on gravity under starch removal from amyloplasts, 4) starchless Arabidopsis thaliana mutants are agravitropic, 5) amyloplasts-statoliths do not sediment in the absence of the gravitational vector and are in different parts or more concentrated in the center of statocytes. Plant tropisms have been intensively studied for many decades and continue to be investigated. Nevertheless, the mechanisms by which plants do so is still not clearly explained and many questions on gravisensing and graviresponse remain unanswered. Even accepted hypotheses are now being questioned and recent data are critically evaluated. Although the available data show the Ca2+ and cytoskeleton participation in graviperception and signal transduction, the clear evidence

  8. Sintering in Laser Sintering

    NASA Astrophysics Data System (ADS)

    Bourell, David L.

    2016-03-01

    Laser sintering is a popular additive manufacturing technology, particularly for service parts. Invented by C. Deckard in the mid-1980s, the approach of using a laser to densify a powder bed selectively has been extensively researched and has been applied to metals, ceramics, polymers and composites. In the traditional powder-metallurgical sense, sintering involves solid-state atomic transport resulting in neck formation and eventual densification in a powder mass. The use of the term "sintering" as a descriptive term for the powder-bed additive manufacturing process has been problematical to the technical community, because the predominant densification mechanism has been shown for most applications to be melting and reflow. The term has perpetuated as a name for the additive manufacturing process, at least for polymers. The technical term "sintering" is accurately associated with laser sintering insofar as powder pre-processing and part post-processing are concerned. It may also be used to describe formation of "part cake". This paper describes the circumstances surrounding the coining of the term, "laser sintering" and provides some examples of how sintering is used in pre- and post-processing.

  9. Fabrication of protective-coated SiC reinforced tungsten matrix composites with reduced reaction phases by spark plasma sintering

    NASA Astrophysics Data System (ADS)

    Umer, Malik Adeel; Lee, Dongju; Waseem, Owais Ahmed; Ryu, Ho Jin; Hong, Soon Hyung

    2016-05-01

    SiC reinforced tungsten matrix composites were fabricated via the spark plasma sintering process. In order to prevent an interfacial reaction between the SiC and tungsten during sintering, TiOx coated SiC particles were synthesized by a solution-based process. TiOx layer coated SiC particles were treated in high temperature nitriding conditions or annealed in a high temperature vacuum to form TiN or TiC coated SiC particles, respectively. The TiC layers coated on SiC particles successfully prevented tungsten from reacting with SiC; hence the proposed process resulted in successful fabrication of the SiC/W composites. The mechanical properties such as compressive strength and flexural strength of the composites were measured. Additionally, the effect of SiC on the high temperature oxidative ablation of tungsten was also investigated. The addition of SiC resulted in an improved oxidative ablation resistance of the tungsten-based composites.

  10. First direct 3D visualisation of microstructural evolutions during sintering through X-ray computed microtomography

    SciTech Connect

    Bernard, Dominique . E-mail: bernard@icmcb.u-bordeaux.fr; Gendron, Damien; Heintz, Jean-Marc; Bordere, Sylvie; Etourneau, Jean

    2005-01-03

    X-ray computed microtomography (XCMT) has been applied to ceramic samples of different materials to visualise, for the first time at this scale, real 3D microstructural evolutions during sintering. Using this technique, it has been possible to follow the whole sintering process of the same grains set. Two materials have been studied; a glass powder heat treated at 700 deg. C and a crystallised lithium borate (Li{sub 6}Gd(BO{sub 3}){sub 3}) powder heat treated at 720 deg. C. XCMT measurements have been done after different sintering times. For each material, a sub-volume was individualised and localised on the successive recordings and its 3D images numerically reconstructed. Description of the three-dimensional microstructures evolution is proposed. From the 3D experimental data, quantitative evolutions of parameters such as porosity and neck size are presented for the glass sample. Possibilities offered by this technique to study complex sintering processes, as for lithium borate, are illustrated.

  11. Sintering of the reaction products of combustion of alloys in nitrogen

    SciTech Connect

    Maksimov, Y.M.; Raskolenko, L.G.; Zepakova, O.K.; Ziatdinov, M.K.

    1986-05-01

    An investigation of the mechanism of compacting of Fe-V alloy with a sigma-phase structure, a low porosity composite material consisting of alpha-iron and a filler of delta-vanadium nitride, is made after the synthesis surge. Alloys containing 50 wt.% Fe were prepared by sintering in a vacuum furnace of powders of type VEL-1 vandium and special purity carbonyl iron. The mechanism of compacting was studied on specimens in hardened water. Metallographic investigations were made on MIM-7 and PMT-3 instruments and the phase analysis on a DRON-2 instrument. Rapid compacting in combustion of sigma-FeV in nitrogen is determined by combining of the solid-liquid drops formed in the combustion front and consisting of molten iron and vanadium nitrides.

  12. Silver conductive features on flexible substrates from a thermally accelerated chain reaction at low sintering temperatures.

    PubMed

    Chen, Shih-Pin; Kao, Zhen-Kai; Lin, Jeng-Lung; Liao, Ying-Chih

    2012-12-01

    In this study, a simple and effective silver ink formulation was developed to generate silver tracks with high electrical conductivity on flexible substrates at low sintering temperatures. Diethanolamine (DEA), a self-oxidizing compound at moderate temperatures, was mixed with a silver ammonia solution to form a clear and stable solution. After inkjet-printed or pen-written on plastic sheets, DEA in the silver ink decomposes at temperatures higher than 50 °C and generates formaldehyde, which reacts spontaneously with silver ammonia ions to form silver thin films. The electrical conductivity of the inkjet-printed silver films can be 26% of the bulk silver after heating at 75 °C for 20 min and show great adhesion on plastic sheets.

  13. Ultrasmooth reaction-sintered silicon carbide surface resulting from combination of thermal oxidation and ceria slurry polishing.

    PubMed

    Shen, Xinmin; Dai, Yifan; Deng, Hui; Guan, Chaoliang; Yamamura, Kazuya

    2013-06-17

    An ultrasmooth reaction-sintered silicon carbide surface with an rms roughness of 0.424 nm is obtained after thermal oxidation for 30 min followed by ceria slurry polishing for 30 min. By SEM-EDX analysis, we investigated the thermal oxidation behavior of RS-SiC, in which the main components are Si and SiC. As the oxidation rate is higher in the area with defects, there are no scratches or cracks on the surface after oxidation. However, a bumpy structure is formed after oxidation because the oxidation rates of Si and SiC differ. Through a theoretical analysis of thermal oxidation using the Deal-Grove model and the removal of the oxide layer by ceria slurry polishing in accordance with the Preston equation, a model for obtaining an ultrasmooth surface is proposed and the optimal processing conditions are presented.

  14. Development of Continuous, Direct Feedback Control Systems for Sintering of Metallic Components

    SciTech Connect

    Diran Apelian; Marc M. Baum

    2006-09-18

    N,N.-Ethylenebisstearimide (EBS) is one of the most commonlyused lubricants in the powder metallurgy (PM) industry in the sintering process. During sintering, the lubricated powder compacts are heat-treated to temperatures in excess of 1,200 °C thus fusing adjacent particles and yielding a part with improved mechanical strength. Delubrication commonly is achieved in the first zone of a sintering furnace by heating the part to temperatures in the 500-600 °C temperature range at a fixed rate and under controlled atmospheric conditions; this strategy minimizes defects, carbon contamination, and compact deformation. The de-lubricated part then enters the second zone (commonly in the 1200-1300 °C temperature range) for sintering. The third zone cools the sintered part at a desired rate to obtain the requisite micro-structural properties. Controlled delubrication is imperative towards achieving high quality parts for the following reasons: the elevated thermal gradient at the transition between the first and second zones can cause parts to expand rapidly and develop microscopic fissures (.blistering.); improper gas flows and belt speeds can lead to carbon deposition on the part and at the grain boundaries (sooting); delubrication products deposit throughout the furnace, even in the coolers, which are far removed from the preheating chamber, leading to significant maintenance costs; pollutants emitted in the exhaust stream of furnaces operating inefficiently are increasingly of environmental concern. In practice, lubricant removal is difficult to control, which often leads to reduced yields in PM manufacturing processes. Throughput is another important issue: process control ideally should lead to a delubrication cycle that yields defect-free parts in a minimum of furnace time, thereby increasing productivity and reducing the net energy consumption. Efficient process control requires rapid monitoring of suitable indicators, preferably gasphase products of delubrication

  15. Apparatus for direct measurement of ash fusion and sintering behavior at elevated temperatures and pressures

    NASA Astrophysics Data System (ADS)

    Khan, M. Rashid

    1989-10-01

    Ash fusion, sintering, and deposition may impose serious operational difficulties in conventional and advanced coal-combustion systems. Conventional ash fusion techniques (e.g., ASTM methods) determine the qualitative behavior of ash samples at atmospheric pressure. Presently, there is no known available technique that can measure the behavior of coal ash at elevated temperatures and pressures. In the literature, methods based on electrical resistance or shrinkage of coal ash have been reported at atmospheric pressure (elevated temperatures) conditions. A high-pressure microdilatometer (HPMD) has been developed to investigate ash fusion and sintering behavior at elevated pressures and temperatures by the simultaneous measurement of the temperature of initial contraction and electrical resistivity of samples. This novel technique facilitates the measurement of ash properties over a wide range of temperature, pressure, and gas atmosphere (oxidizing, reducing, or inert). The operating principle of the HPMD includes measuring the temperature at which there is a significant ``shift'' in the electrical resistivity (and/or sample volume) that represents ash sintering and fusion. Sintering occurs through the formation of solid-state, particle-to-particle ``necks'' or the appearance of a molten phase, which allows a path for electrical conductance. The ability to perform both resistivity and shrinkage measurements simultaneously or independently at elevated pressures makes the HPMD truly unique. The HPMD can also be used to investigate the swelling and softening behavior of pyrolyzing coal at elevated pressures and relatively rapid heating rates. The HPMD can provide insights into the sintering/fusion of coal ash or coal swelling at a range of conditions: (a) the influences of various gas atmospheres can be investigated, (b) the effects of pressure can be studied, (c) different temperature/heating rate schemes can be used (constant rates, isothermal holds below or above the

  16. Apparatus and method for direct measurement of coal ash sintering and fusion properties at elevated temperatures and pressures

    DOEpatents

    Khan, M. Rashid

    1990-01-01

    A high-pressure microdilatometer is provided for measuring the sintering and fusion properties of various coal ashes under the influence of elevated pressures and temperatures in various atmospheres. Electrical resistivity measurements across a sample of coal ash provide a measurement of the onset of the sintering and fusion of the ash particulates while the contraction of the sample during sintering is measured with a linear variable displacement transducer for detecting the initiation of sintering. These measurements of sintering in coal ash at different pressures provide a mechanism by which deleterious problems due to the sintering and fusion of ash in various combustion systems can be minimized or obviated.

  17. Structure and properties of porous TiNi(Co, Mo)-based alloy produced by the reaction sintering

    NASA Astrophysics Data System (ADS)

    Artyukhova, Nadezda; Yasenchuk, Yuriy; Chekalkin, Timofey; Gunther, Victor; Kim, Ji-Soon; Kang, Ji-Hoon

    2016-10-01

    Modern medical technologies have developed many new devices that can be implanted into humans to repair, assist or take the place of diseased or defective bones, arteries and even organs. The materials, especially porous ones, used for these devices have evolved steadily over the past twenty years with TiNi-based alloys replacing stainless steels and titanium. The aim of the paper is to presents results for examination of porous TiNi(Co,Mo)-based alloys intended further to be used in clinical practice. The structure and properties of porous TiNi-based alloys obtained by reaction sintering of Ti and Ni powders with additions of Co and Mo have been studied. It has been shown that alloying additions both Co and Mo inhibit the compaction of nickel powders in the initial stage of sintering. The maximum irreversible strain of porous samples under loading in the austenitic state is fixed with the Co addition, and the minimum one is fixed with the Mo addition. The Co addition leads to the fact that the martensite transformation in the TiNi phase becomes close to a one-step, and the Mo addition leads to the fact that the martensite transformation becomes more uniform. Both Co and Mo lead to an increase in the maximum accumulated strain as a result of the formation of temperature martensite. The additional increase in the maximum accumulated strain of the Ti50Ni49Co1 alloy is caused by decreased resistance of the porous Ni γ -based mass during the load.

  18. Establishing Antibacterial Multilayer Films on the Surface of Direct Metal Laser Sintered Titanium Primed with Phase-Transited Lysozyme

    PubMed Central

    Guan, Binbin; Wang, Haorong; Xu, Ruiqing; Zheng, Guoying; Yang, Jie; Liu, Zihao; Cao, Man; Wu, Mingyao; Song, Jinhua; Li, Neng; Li, Ting; Cai, Qing; Yang, Xiaoping; Li, Yanqiu; Zhang, Xu

    2016-01-01

    Direct metal laser sintering is a technology that allows the fabrication of titanium (Ti) implants with a functional gradation of porosity and surface roughness according to three-dimensional (3D) computer data. The surface roughness of direct metal laser sintered titanium (DMLS-Ti) implants may provide abundant binding sites for bacteria. Bacterial colonization and subsequent biofilm formation can cause unsatisfactory cell adhesion and implant-related infections. To prevent such infections, a novel phase-transited lysozyme (PTL) was utilized as an initial functional layer to simply and effectively prime DMLS-Ti surfaces for subsequent coating with antibacterial multilayers. The purpose of the present study was to establish a surface with dual biological functionality. The minocycline-loaded polyelectrolyte multilayers of hyaluronic acid (HA) and chitosan (CS) formed via a layer-by-layer (LbL) self-assembly technique on PTL-functionalized DMLS-Ti were designed to inhibit pathogenic microbial infections while allowing the DMLS-Ti itself and the modified coatings to retain acceptable biocompatibility. The experimental results indicate that the DMLS-Ti and the hydrogel treated surfaces can inhibit early bacterial adhesion while completely preserving osteoblast functions. This design is expected to gain considerable interest in the medical field and to have good potential for applications in multifunctional DMLS-Ti implants. PMID:27821857

  19. Establishing Antibacterial Multilayer Films on the Surface of Direct Metal Laser Sintered Titanium Primed with Phase-Transited Lysozyme

    NASA Astrophysics Data System (ADS)

    Guan, Binbin; Wang, Haorong; Xu, Ruiqing; Zheng, Guoying; Yang, Jie; Liu, Zihao; Cao, Man; Wu, Mingyao; Song, Jinhua; Li, Neng; Li, Ting; Cai, Qing; Yang, Xiaoping; Li, Yanqiu; Zhang, Xu

    2016-11-01

    Direct metal laser sintering is a technology that allows the fabrication of titanium (Ti) implants with a functional gradation of porosity and surface roughness according to three-dimensional (3D) computer data. The surface roughness of direct metal laser sintered titanium (DMLS-Ti) implants may provide abundant binding sites for bacteria. Bacterial colonization and subsequent biofilm formation can cause unsatisfactory cell adhesion and implant-related infections. To prevent such infections, a novel phase-transited lysozyme (PTL) was utilized as an initial functional layer to simply and effectively prime DMLS-Ti surfaces for subsequent coating with antibacterial multilayers. The purpose of the present study was to establish a surface with dual biological functionality. The minocycline-loaded polyelectrolyte multilayers of hyaluronic acid (HA) and chitosan (CS) formed via a layer-by-layer (LbL) self-assembly technique on PTL-functionalized DMLS-Ti were designed to inhibit pathogenic microbial infections while allowing the DMLS-Ti itself and the modified coatings to retain acceptable biocompatibility. The experimental results indicate that the DMLS-Ti and the hydrogel treated surfaces can inhibit early bacterial adhesion while completely preserving osteoblast functions. This design is expected to gain considerable interest in the medical field and to have good potential for applications in multifunctional DMLS-Ti implants.

  20. Preliminary study on atmospheric-pressure plasma-based chemical dry figuring and finishing of reaction-sintered silicon carbide

    NASA Astrophysics Data System (ADS)

    Shen, Xinmin; Deng, Hui; Zhang, Xiaonan; Peng, Kang; Yamamura, Kazuya

    2016-10-01

    Reaction-sintered silicon carbide (RS-SiC) is a research focus in the field of optical manufacturing. Atmospheric-pressure plasma-based chemical dry figuring and finishing, which consist of plasma chemical vaporization machining (PCVM) and plasma-assisted polishing (PAP), were applied to improve material removal rate (MRR) in rapid figuring and ameliorate surface quality in fine finishing. Through observing the processed RS-SiC sample in PCVM by scanning white-light interferometer (SWLI), the calculated peak-MRR and volume-MRR were 0.533 μm/min and 2.78×10-3 mm3/min, respectively. The comparisons of surface roughness and morphology of the RS-SiC samples before and after PCVM were obtained by the scanning electron microscope and atomic force microscope. It could be found that the processed RS-SiC surface was deteriorated with surface roughness rms 382.116 nm. The evaluations of surface quality of the processed RS-SiC sample in PAP corresponding to different collocations of autorotation speed and revolution speed were obtained by SWLI measurement. The optimal surface roughness rms of the processed RS-SiC sample in PAP was 2.186 nm. There were no subsurface damages, scratches, or residual stresses on the processed sample in PAP. The results indicate that parameters in PAP should be strictly selected, and the optimal parameters can simultaneously obtain high MRR and smooth surface.

  1. Investigation on the formation of projections and cracks in anodic oxidation of reaction-sintered silicon carbide

    NASA Astrophysics Data System (ADS)

    Peng, Kang; Shen, Xinmin; Yamamura, Kazuya; Zhang, Xiaonan; Wang, Dong

    2017-01-01

    Among the present oxidation-assisted polishing (OAP) technique, anodic oxidation is a promising method to process reaction-sintered silicon carbide (RS-SiC) with the assistance of abrasive polishing. Projections and cracks are inevitably formed in the anodic oxidation of RS-SiC for the volume expansion force. Evolvements of the oxide morphologies along with different oxidation voltage and different oxidation time are investigated by scanning electron microscope (SEM). It can be found that when the oxidation time stays the same, size of the projections and cracks on the oxidized RS-SiC sample is gradually enlarged. Meanwhile, when the oxidation voltage stays the same, size of the projections and cracks on the oxidized RS-SiC sample is also enlarged. Details of projections and cracks on the oxidized RS-SiC sample are obtained by the SEM with high magnification. Based on the theoretical derivation, it can be concluded that the formations of projections and cracks depend on the inner volume expansion force and the resultant force generated from other grains. Research on formation of projections and cracks in anodic oxidation of RS-SiC can promote the process level of RS-SiC products.

  2. Effects of Sm2O3 Content on the Microstructure and Mechanical Properties of Post-Sintered Reaction-Bonded β-SiAlON

    NASA Astrophysics Data System (ADS)

    Li, Yanjun; Liu, Donghua; Zeng, Cunfeng; Shi, Zhongqi; Jin, Zhihao

    2016-03-01

    β-SiAlON materials were fabricated by a reaction bonding combining post-sintering route using raw materials of Si, Al2O3, AlN, etc. Sm2O3 was used as sintering additive with the content of 0, 2, 4, and 6 wt.%, respectively. The reaction-bonded β-SiAlON (RB-β-SiAlON) were post sintered at 1750 °C for 6 h. XRD results showed that the phase composition of both RB-β-SiAlON and post-sintered RB-β-SiAlON (PSRB-β-SiAlON) was β-SiAlON. For RB-β-SiAlON, the apparent porosity was decreased with the increase of Sm2O3 content, while the bending strength (σf) and Vicker's hardness (HV10) was increased accordingly. After the post-sintering procedure, nearly full densified PSRB-β-SiAlON was obtained and the mechanical properties were significantly improved with the addition of Sm2O3 additive. The σf and HV10 of the PSRB-β-SiAlON (4 wt.% Sm2O3) achieved 520 MPa and 16.4 GPa, respectively, which were as 3.5 and 6.3 times high as those of the corresponding RB-β-SiAlON. The Young's modulus (E) and the fracture toughness (K IC) of the dense PSRB-β-SiAlON were increased with the increase of the Sm2O3 content.

  3. Development of energy-absorbing reaction-sintered Si3N4 surface layers on hot-pressed Si3N4

    NASA Technical Reports Server (NTRS)

    Brennan, J. J.

    1981-01-01

    Energy-absorbing Si3N4 surface layers on dense Si3N4 substrates were formed by in-place nitridation of fine-grained silicon powder. Ballistic impact tests performed on samples with 1-mm thick layers at room temperature and 1370 C showed up to an eightfold increase in the energy necessary to fracture the substrate. For maximum impact resistance, a small amount (about 20 vol %) of residual Si must be present in the reaction-sintered Si3N4 surface layer. Thermal cycling to 1370 C did not affect impact resistance, even though a considerable amount of SiO2 formed within the reaction-sintered Si3N4 layer during cycling. Erosion testing of samples in a Mach 0.8 burner rig at 1370 C resulted in minimal surface recession of the surface layer. Chemically vapor-deposited SiC-coated material similarly tested exhibited no surface recession.

  4. Experimental analysis on semi-finishing machining of Ti6Al4V additively manufactured by direct melting laser sintering

    NASA Astrophysics Data System (ADS)

    Imbrogno, Stano; Bordin, Alberto; Bruschi, Stefania; Umbrello, Domenico

    2016-10-01

    The Additive Manufacturing (AM) techniques are particularly appealing especially for titanium aerospace and biomedical components because they permit to achieve a strong reduction of the buy-to-fly ratio. However, finishing machining operations are often necessary to reduce the uneven surface roughness and geometrics because of local missing accuracy. This work shows the influence of the cutting parameters, cutting speed and feed rate, on the cutting forces as well as on the thermal field observed in the cutting zone, during a turning operation carried out on bars made of Ti6Al4V obtained by the AM process called Direct Metal Laser Sintering (DMLS). Moreover, the sub-surface microstructure alterations due to the process are also showed and commented.

  5. A newly-developed effective direct current assisted sintering technique for electrolyte film densification of anode-supported solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Liu, Yajie; Hao, Xiaoming; Wang, Zhenhua; Wang, Jiawei; Qiao, Jinshuo; Yan, Yiming; Sun, Kening

    2012-10-01

    In order to lower the sintering temperature and shorten firing time, a novel, effective and facile technique has been developed for sintering Yttria-stabilized zirconia (YSZ) electrolyte thin film. Herein this technique, which employs a weak direct current (DC), is used for the first time in the manufacture of the anode-supported solid oxide fuel cell (SOFC). A single cell is directly assembled using a pre-sintered anode/electrolyte and screen printed cathode and subsequently sintered under electric assistance from room temperature to 800 °C at a heating rate of 5 °C min-1. A fully dense YSZ electrolyte film can be observed by scanning electron microscopy (SEM) and the open circuit voltages (OCVs) are in accordance with theoretical values, confirming that the cell possesses a dense YSZ film. Using hydrogen fuel, the maximum power density of this cell was 0.8, 1.1 and 1.4 W cm-2 at 650, 700 and 750 °C, respectively. We believe this DC assisted sintering technique (DC-AST) may not only reduce the cost, but also maintain the anode nanostructure, thus offering a potentially useful manufacturing technique for SOFCs.

  6. Chemical Reactions Directed Peptide Self-Assembly

    PubMed Central

    Rasale, Dnyaneshwar B.; Das, Apurba K.

    2015-01-01

    Fabrication of self-assembled nanostructures is one of the important aspects in nanoscience and nanotechnology. The study of self-assembled soft materials remains an area of interest due to their potential applications in biomedicine. The versatile properties of soft materials can be tuned using a bottom up approach of small molecules. Peptide based self-assembly has significant impact in biology because of its unique features such as biocompatibility, straight peptide chain and the presence of different side chain functionality. These unique features explore peptides in various self-assembly process. In this review, we briefly introduce chemical reaction-mediated peptide self-assembly. Herein, we have emphasised enzymes, native chemical ligation and photochemical reactions in the exploration of peptide self-assembly. PMID:25984603

  7. Chemical reactions directed Peptide self-assembly.

    PubMed

    Rasale, Dnyaneshwar B; Das, Apurba K

    2015-05-13

    Fabrication of self-assembled nanostructures is one of the important aspects in nanoscience and nanotechnology. The study of self-assembled soft materials remains an area of interest due to their potential applications in biomedicine. The versatile properties of soft materials can be tuned using a bottom up approach of small molecules. Peptide based self-assembly has significant impact in biology because of its unique features such as biocompatibility, straight peptide chain and the presence of different side chain functionality. These unique features explore peptides in various self-assembly process. In this review, we briefly introduce chemical reaction-mediated peptide self-assembly. Herein, we have emphasised enzymes, native chemical ligation and photochemical reactions in the exploration of peptide self-assembly.

  8. Research on optimal process parameters in thermally oxidation-assisted polishing of reaction-sintered silicon carbide

    NASA Astrophysics Data System (ADS)

    Shen, Xinmin; Yamamura, Kazuya; Zhang, Xiaonan; Zhang, Xiangpo; Wang, Dong; Peng, Kang

    2016-10-01

    Reaction-sintered silicon carbide (RS-SiC) has been widely used in space telescope systems for its excellent physical and mechanical properties. Thermally oxidation-assisted polishing is a practical machining method to obtain RS-SiC parts with high precision, and the research focus is optimization of process parameters, because there are bumpy structures on the oxidized RS-SiC. By atomic force microscopy (AFM) detection, the distributions of oxides on the oxidized RS-SiC sample are quantitative analyzed when the thermal oxidation time is 5min, 30min, and 60min, and the calculated average differences of oxide heights between the initial Si grains and SiC grains are 10.7nm, 25.1nm, and 35.2nm, respectively. Meanwhile, the volume expansion coefficient in oxidation of Si/SiC to SiO2 is 2.257 and 2.194, respectively. Through theoretical derivation based on the Deal-Grove model, the numerical relationship between differences of oxide heights and thermal oxidation time is obtained. Combining with the material removal rate of oxide by ceria slurry in the abrasive polishing, the obtained surface quality can be precisely forecasted and controlled. The oxidized RS-SiC sample, when the oxidation time is 30min, is polished with different times to verify the theoretical analysis results. When the polishing times are 20min, 30min, and 40min, the obtained differences of oxide heights by the AFM detection are consistent with theoretical calculated results. Research on the optimal process parameters in thermally oxidation-assisted polishing of RS-SiC can improve the process level of RS-SiC sample and promote the application of SiC parts.

  9. Toward Direct Reaction-in-Flight Measurements

    NASA Astrophysics Data System (ADS)

    Wilhelmy, Jerry; Bredeweg, Todd; Fowler, Malcolm; Gooden, Matthew; Hayes, Anna; Rusev, Gencho; Caggiano, Joseph; Hatarik, Robert; Henry, Eugene; Tonchev, Anton; Yeaman, Charles; Bhike, Megha; Krishichayan, Krishi; Tornow, Werner

    2016-03-01

    At the National Ignition Facility (NIF) neutrons having energies greater than the equilibrium 14.1 MeV value can be produced via Reaction-in-Flight (RIF) interactions between plasma atoms and upscattered D or T ions. The yield and spectrum of these RIF produced neutrons carry information on the plasma properties as well as information on the stopping power of ions under plasma conditions. At NIF the yield of these RIF neutrons is predicted to be 4-7 orders of magnitude below the peak 14 MeV neutron yield. The current generation of neutron time of flight (nTOF) instrumentation has so far been incapable of detecting these low-yield neutrons primarily due to high photon backgrounds. To date, information on RIF neutrons has been obtained in integral activation experiments using reactions with high energy thresholds such as 169Tm(n,3n)167Tm and 209Bi(n,4n) 206Bi. Initial experiments to selectively suppress photon backgrounds have been performed at TUNL using pulsed monoenergetic neutron beams of 14.9, 18.5, 24.2, and 28.5 MeV impinging on a Bibenzyl scintillator. By placing 5 cm of Pb before the scintillator we were able to selectively suppress the photons from the flash occurring at the production target and enhance the n/_signal by ~6 times.

  10. Direct Reactions for Nuclear Structure and Nuclear Astrophysics

    SciTech Connect

    Jones, Katherine Louise

    2014-12-18

    Direct reactions are powerful probes for studying the atomic nucleus. Modern direct reaction studies are illuminating both the fundamental nature of the nucleus and its role in nucleosynthetic processes occurring in the cosmos. This report covers experiments using knockout reactions on neutron-deficient fragmentation beams, transfer reactions on fission fragment beams, and theoretical sensitivity studies relating to the astrophysical r-process. Results from experiments on 108,106Sn at the NSCL, and on 131Sn at HRIBF are presented as well as the results from the nucleosynthesis study.

  11. Maxillary overdentures supported by four splinted direct metal laser sintering implants: a 3-year prospective clinical study.

    PubMed

    Mangano, Francesco; Luongo, Fabrizia; Shibli, Jamil Awad; Anil, Sukumaran; Mangano, Carlo

    2014-01-01

    Purpose. Nowadays, the advancements in direct metal laser sintering (DMLS) technology allow the fabrication of titanium dental implants. The aim of this study was to evaluate implant survival, complications, and peri-implant marginal bone loss of DMLS implants used to support bar-retained maxillary overdentures. Materials and Methods. Over a 2-year period, 120 implants were placed in the maxilla of 30 patients (18 males, 12 females) to support bar-retained maxillary overdentures (ODs). Each OD was supported by 4 implants splinted by a rigid cobalt-chrome bar. At each annual follow-up session, clinical and radiographic parameters were assessed. The outcome measures were implant failure, biological and prosthetic complications, and peri-implant marginal bone loss (distance between the implant shoulder and the first visible bone-to-implant contact, DIB). Results. The 3-year implant survival rate was 97.4% (implant-based) and 92.9% (patient-based). Three implants failed. The incidence of biological complication was 3.5% (implant-based) and 7.1% (patient-based). The incidence of prosthetic complication was 17.8% (patient-based). No detrimental effects on marginal bone level were evidenced. Conclusions. The use of 4 DMLS titanium implants to support bar-retained maxillary ODs seems to represent a safe and successful procedure. Long-term clinical studies on a larger sample of patients are needed to confirm these results.

  12. Maxillary Overdentures Supported by Four Splinted Direct Metal Laser Sintering Implants: A 3-Year Prospective Clinical Study

    PubMed Central

    Mangano, Francesco; Shibli, Jamil Awad; Anil, Sukumaran

    2014-01-01

    Purpose. Nowadays, the advancements in direct metal laser sintering (DMLS) technology allow the fabrication of titanium dental implants. The aim of this study was to evaluate implant survival, complications, and peri-implant marginal bone loss of DMLS implants used to support bar-retained maxillary overdentures. Materials and Methods. Over a 2-year period, 120 implants were placed in the maxilla of 30 patients (18 males, 12 females) to support bar-retained maxillary overdentures (ODs). Each OD was supported by 4 implants splinted by a rigid cobalt-chrome bar. At each annual follow-up session, clinical and radiographic parameters were assessed. The outcome measures were implant failure, biological and prosthetic complications, and peri-implant marginal bone loss (distance between the implant shoulder and the first visible bone-to-implant contact, DIB). Results. The 3-year implant survival rate was 97.4% (implant-based) and 92.9% (patient-based). Three implants failed. The incidence of biological complication was 3.5% (implant-based) and 7.1% (patient-based). The incidence of prosthetic complication was 17.8% (patient-based). No detrimental effects on marginal bone level were evidenced. Conclusions. The use of 4 DMLS titanium implants to support bar-retained maxillary ODs seems to represent a safe and successful procedure. Long-term clinical studies on a larger sample of patients are needed to confirm these results. PMID:25580124

  13. Summary of Liquid Oxygen/Hydrogen, Direct Metal Laser Sintering Injector Testing and Evaluation Effort at Marshall Space Flight Center

    NASA Technical Reports Server (NTRS)

    Barnett, Gregory; Bullard, David B.

    2015-01-01

    The last several years have witnessed a significant advancement in the area of additive manufacturing technology. One area that has seen substantial expansion in application has been laser sintering (or melting) in a powder bed. This technology is often termed 3D printing or various acronyms that may be industry, process, or company specific. Components manufactured via 3D printing have the potential to significantly reduce development and fabrication time and cost. The usefulness of 3D printed components is influenced by several factors such as material properties and surface roughness. This paper details three injectors that were designed, fabricated, and tested in order to evaluate the utility of 3D printed components for rocket engine applications. The three injectors were tested in a hot-fire environment with chamber pressures of approximately 1400 psia. One injector was a 28 element design printed by Directed Manufacturing. The other two injectors were identical 40 element designs printed by Directed Manufacturing and Solid Concepts. All the injectors were swirl-coaxial designs and were subscale versions of a full-scale injector currently in fabrication. The test and evaluation programs for the 28 element and 40 element injectors provided a substantial amount of data that confirms the feasibility of 3D printed parts for future applications. The operating conditions of previously tested, conventionally manufactured injectors were reproduced in the 28 and 40 element programs in order to contrast the performance of each. Overall, the 3D printed injectors demonstrated comparable performance to the conventionally manufactured units. The design features of the aforementioned injectors can readily be implemented in future applications with a high degree of confidence.

  14. Directional sensitivity of "first trial" reactions in human balance control.

    PubMed

    Oude Nijhuis, Lars B; Allum, John H J; Borm, George F; Honegger, Flurin; Overeem, Sebastiaan; Bloem, Bastiaan R

    2009-06-01

    Support-surface movements are commonly used to examine balance control. Subjects typically receive a series of identical or randomly interspersed multidirectional balance perturbations and the atypical "first trial reaction" (evoked by the first perturbation) is often excluded from further analysis. However, this procedure may obscure vital information about neurophysiological mechanisms associated with the first perturbation and, by analogy, fully unexpected falls. We studied first trial reactions, aiming to clarify their directional impact on postural control and to characterize the underlying neurophysiological substrate. We instructed 36 subjects to maintain balance following support-surface rotations in six different directions. Perturbations in each direction were delivered in blocks, consisting of 10 serial stimuli. Full body kinematics, surface reactive forces, and electromyographic (EMG) responses were recorded. Regardless of direction, for the very first rotation, displacement of the center of mass was 15% larger compared with the ensuing nine identical rotations (P < 0.0001). This first trial reaction immediately reemerged whenever a new perturbation direction was introduced. First trial reactions (and near-falls) were greatest for backward-directed rotations and smallest for laterally directed rotations. This directional dependence coincided with early changes in vertical head accelerations. First trial reactions in EMG responses involved larger amplitudes in general and earlier muscle response onsets in upper body muscles. These findings show that first trial reactions are associated with significantly increased postural instability, mainly due to increased response amplitudes. Although rapid habituation occurs following presentation of identical stimuli, subjects immediately become unstable again when the perturbation direction suddenly changes. Excessive responses due to a failure to combine proprioceptive and vestibular cues effectively may explain

  15. Fundamental studies of retrograde reactions in direct liquefaction

    SciTech Connect

    Serio, M.A.; Solomon, P.R.; Bassilakis, R.; Kroo, E.

    1989-01-01

    Most of the proposed processing schemes for improving liquefaction yields involve favoring bond-breaking and radical stabilization reactions over the retrograde reactions. The retrograde reactions are often encountered before liquefaction temperatures are reached. The objective of this program is to elucidate and model the retrograde reaction chemistry in direct coal liquefaction through the application of experimental techniques and theoretical models which have been successfully employed at Advanced Fuel Research (AFR) and SRI International (a subcontractor) to understand and predict coal reaction behavior. The study of retrograde reactions is being done using an integrated approach using extensive characterization of the liquefaction chemistry of three kinds of systems: (1) model polymers; (2) coal; and (3) modified coals.

  16. Direct studies of (α,p) reactions with HELIOS

    NASA Astrophysics Data System (ADS)

    Lai, Jianping; Blackmon, J. C.; Deibel, C. M.; Dimarco, D.; Gardiner, H.; Lauer, A.; Santiago-Gonzalez, D.; Williams, C.; Digiovine, B.; Greene, J.; Rohrer, J.; Helios Group At Argonne National Lab Collaboration

    2014-09-01

    In a variety of astrophysical processes, (α,p) type reactions have significant effects on final energy output and elemental abundances. However, only a handful of reactions have been measured due to technical limitations. Innovative new equipment and techniques, therefore, are necessary to extend measurement limits of these reactions rates. The HELIcal Orbit Spectrometer(HELIOS), serves as an important tool in studying reactions using radioactive ion beams at the Argonne Tandem Linac Accelerator System facility. With a specially designed gas target, we are able to study (α,p) reaction directly. HELIOS can separate protons from reactions with different energy states and the heavy recoils can be detected in coincidence by a high efficiency gas ionization detector. This combination has been successful in our pilot experiments. A series of (α,p) experiments using this setup in HELIOS are planned. We will start with 20Ne(α,p), which is crucial in Type Ia supernovae. A direct measurement of 30S(α,p), a key reaction in X ray burst, is also included in the near future plans and the beam development of 30S is in progress. Preliminary results will be presented. In a variety of astrophysical processes, (α,p) type reactions have significant effects on final energy output and elemental abundances. However, only a handful of reactions have been measured due to technical limitations. Innovative new equipment and techniques, therefore, are necessary to extend measurement limits of these reactions rates. The HELIcal Orbit Spectrometer(HELIOS), serves as an important tool in studying reactions using radioactive ion beams at the Argonne Tandem Linac Accelerator System facility. With a specially designed gas target, we are able to study (α,p) reaction directly. HELIOS can separate protons from reactions with different energy states and the heavy recoils can be detected in coincidence by a high efficiency gas ionization detector. This combination has been successful in our pilot

  17. Recent Direct Reaction Experimental Studies with Radioactive Tin Beams

    SciTech Connect

    Jones, K. L.; Ahn, S.; Allmond, J. M.; Ayres, A.; Bardayan, D. W.; Baugher, T.; Bazin, D.; Berryman, J. S.; Bey, A.; Bingham, C.; Cartegni, L.; Cerizza, G.; Chae, K. Y.; Cizewski, J. A.; Gade, A.; Galindo-Uribarri, A.; Garcia-Ruiz, R. F.; Grzywacz, R.; Howard, M. E.; Kozub, R. L.; Liang, J. F.; Manning, B.; Matoš, M.; McDaniel, S.; Miller, D.; Nesaraja, C. D.; O'Malley, P. D.; Padgett, S.; Padilla-Rodal, E.; Pain, S. D.; Pittman, S. T.; Radford, D. C.; Ratkiewicz, A.; Schmitt, K. T.; Shore, A.; Smith, M. S.; Stracener, D. W.; Stroberg, S. R.; Tostevin, J.; Varner, R. L.; Weisshaar, D.; Wimmer, K.; Winkler, R.

    2015-01-01

    Direct reaction techniques are powerful tools to study the single-particle nature of nuclei. Performing direct reactions on short-lived nuclei requires radioactive ion beams produced either via fragmentation or the Isotope Separation OnLine (ISOL) method. Some of the most interesting regions to study with direct reactions are close to the magic numbers where changes in shell structure can be tracked. These changes can impact the final abundances of explosive nucleosynthesis. The structure of the chain of tin isotopes is strongly influenced by the Z = 50 proton shell closure, as well as the neutron shell closures lying in the neutron-rich, N = 82, and neutron-deficient, N = 50, regions. Here, we present two examples of direct reactions on exotic tin isotopes. The first uses a one-neutron transfer reaction and a low-energy reaccelerated ISOL beam to study states in Sn-131 from across the N = 82 shell closure. The second example utilizes a one-neutron knockout reaction on fragmentation beams of neutron-deficient Sn-106,108Sn. In conclusion, In both cases, measurements of γ rays in coincidence with charged particles proved to be invaluable.

  18. Recent Direct Reaction Experimental Studies with Radioactive Tin Beams

    DOE PAGES

    Jones, K. L.; Ahn, S.; Allmond, J. M.; ...

    2015-01-01

    Direct reaction techniques are powerful tools to study the single-particle nature of nuclei. Performing direct reactions on short-lived nuclei requires radioactive ion beams produced either via fragmentation or the Isotope Separation OnLine (ISOL) method. Some of the most interesting regions to study with direct reactions are close to the magic numbers where changes in shell structure can be tracked. These changes can impact the final abundances of explosive nucleosynthesis. The structure of the chain of tin isotopes is strongly influenced by the Z = 50 proton shell closure, as well as the neutron shell closures lying in the neutron-rich, Nmore » = 82, and neutron-deficient, N = 50, regions. Here, we present two examples of direct reactions on exotic tin isotopes. The first uses a one-neutron transfer reaction and a low-energy reaccelerated ISOL beam to study states in Sn-131 from across the N = 82 shell closure. The second example utilizes a one-neutron knockout reaction on fragmentation beams of neutron-deficient Sn-106,108Sn. In conclusion, In both cases, measurements of γ rays in coincidence with charged particles proved to be invaluable.« less

  19. Microwave sintering process model.

    PubMed

    Peng, Hu; Tinga, W R; Sundararaj, U; Eadie, R L

    2003-01-01

    In order to simulate and optimize the microwave sintering of a silicon nitride and tungsten carbide/cobalt toolbits process, a microwave sintering process model has been built. A cylindrical sintering furnace was used containing a heat insulating layer, a susceptor layer, and an alumina tube containing the green toolbit parts between parallel, electrically conductive, graphite plates. Dielectric and absorption properties of the silicon nitride green parts, the tungsten carbide/cobalt green parts, and an oxidizable susceptor material were measured using perturbation and waveguide transmission methods. Microwave absorption data were measured over a temperature range from 20 degrees C to 800 degrees C. These data were then used in the microwave process model which assumed plane wave propagation along the radial direction and included the microwave reflection at each interface between the materials and the microwave absorption in the bulk materials. Heat transfer between the components inside the cylindrical sintering furnace was also included in the model. The simulated heating process data for both silicon nitride and tungsten carbide/cobalt samples closely follow the experimental data. By varying the physical parameters of the sintering furnace model, such as the thickness of the susceptor layer, the thickness of the allumina tube wall, the sample load volume and the graphite plate mass, the model data predicts their effects which are helpful in optimizing those parameters in the industrial sintering process.

  20. Organoaluminum-mediated direct cross-coupling reactions.

    PubMed

    Minami, Hiroki; Saito, Tatsuo; Wang, Chao; Uchiyama, Masanobu

    2015-04-07

    We present a direct cross-coupling reaction between arylaluminum compounds (ArAlMe2 ⋅LiCl) and organic halides RX (R=aryl, alkenyl, alkynyl; X=I, Br, and Cl) without any external catalyst. The reaction takes place smoothly, simply upon heating, thereby enabling the efficient and chemo-/stereoselective formation of biaryl, alkene, and alkyne coupling products with broad functional group compatibility.

  1. SINTERING METHOD

    DOEpatents

    Googin, J.M.

    1963-11-01

    Methods of making articles by powder metallurgy techniques are presented. An article is made by packing a metal powder into a desired shape, raising the temperature of the powder compact to a sintering temperature in the presence of a reducing gas, and alternately increasing and decreasing the pressure of the gas while the temperatume is being raised. The product has a greater density than can be achieved by sintering for the same length of time at a constant gas pressure. (AEC)

  2. Direct measurements of radiative capture reactions with DRAGON

    NASA Astrophysics Data System (ADS)

    Christian, Gregory

    2015-10-01

    Direct measurements of radiative proton and alpha capture reactions are crucial for understanding nucleosynthesis in a variety of astrophysical environments, including classical novae, supernovae, X-Ray bursts, and quiescent stellar burning. Often the most important reactions have very low cross sections or involve unstable targets, making laboratory measurements extremely challenging. The detector of recoils and gammas of nuclear reactions (DRAGON) at TRIUMF is a recoil mass separator designed to measure radiative capture reactions in inverse kinematics, with beam suppression factors as high as 1016. When combined with the intense radioactive beams available at the ISAC-I facility, DRAGON's capabilities are unique and world-leading. In this talk, I will give a brief technical overview of DRAGON before presenting results from recent experiments. Some highlights include the first-ever direct measurement of 38K(p , γ) 39Ca, a crucial reaction for determining the endpoint of nova nucleosynthesis, and measurements of 76Se(α , γ) 80Kr. The latter measurements determine the rate of the reverse reaction, 80Kr(γ , α) 76Se, an important waiting point in the synthesis of the p-nuclei. I will also discuss future (and ongoing) developments at DRAGON, including the commissioning of a new chamber for high-precision elastic scattering measurements and plans to determine the 330 keV resonance strength in 18F(p , γ) 19Ne via measurements of 15O(α , γ) 19Ne and 15O + α elastic scattering.

  3. Direct reactions for nuclear structure required for fundamental symmetry tests

    NASA Astrophysics Data System (ADS)

    Garrett, P. E.; Rand, E. T.; Diaz Varela, A.; Ball, G. C.; Bildstein, V.; Faestermann, T.; Hadinia, B.; Hertenberger, R.; Jamieson, D. S.; Jigmeddorj, B.; Leach, K. G.; Svensson, C. E.; Wirth, H.-F.

    2016-09-01

    A program of nuclear structure studies to support fundamental symmetry tests has been initiated. Motivated by the search for an electric dipole moment in 199Hg, the structure in the vicinity has been explored via direct reaction studies. To date, these have included the 198,200Hg(d, d') inelastic scattering reactions, with the aim to obtain information on the E2 and E3 strength distributions, and the 198Hg(d, p) and 200Hg(d, t) reactions to obtain information on the single-particle states in 199Hg. The studies using the 200Hg targets have been fully analyzed using the FRESCO reaction code yielding the E2 and E3 strength distribution to 4 MeV in excitation energy, and the (d, t) single- particle strength to over 3 MeV in excitation energy.

  4. Direct measurements of astrophysically important α-induced reactions

    NASA Astrophysics Data System (ADS)

    Avila, Melina

    2016-03-01

    Understanding stellar evolution is one of the primary objectives of nuclear astrophysics. Reaction rates involving α-particles are often key nuclear physics inputs in stellar models. For instance, there are numerous (α , p) reactions fundamental for the understanding of X-ray bursts and the production of 44Ti in core-collapse supernovae. Furthermore, some (α , n) reactions are considered as one of the main neutron sources in the s-process. However, direct measurements of these reactions at relevant astrophysical energies are experimentally challenging because of their small cross section and intensity limitation of radioactive beams. The active target system MUSIC offers a unique opportunity to study (α , p) and (α , n) reactions because its segmented anode allows the investigation of a large energy range in the excitation function with a single measurement. Recent results on the direct measurement of (α , n) and (α , p) measurements in the MUSIC detector will be discussed. This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics, under Contract Number DE-AC02-06CH11357. This research used resources of ANL's ATLAS facility, which is a DOE Office of Science User.

  5. Degradation of artificial sweeteners via direct and indirect photochemical reactions.

    PubMed

    Perkola, Noora; Vaalgamaa, Sanna; Jernberg, Joonas; Vähätalo, Anssi V

    2016-07-01

    We studied the direct and indirect photochemical reactivity of artificial sweeteners acesulfame, saccharin, cyclamic acid and sucralose in environm entally relevant dilute aqueous solutions. Aqueous solutions of sweeteners were irradiated with simulated solar radiation (>290 nm; 96 and 168 h) or ultraviolet radiation (UVR; up to 24 h) for assessing photochemical reactions in surface waters or in water treatment, respectively. The sweeteners were dissolved in deionised water for examination of direct photochemical reactions. Direct photochemical reactions degraded all sweeteners under UVR but only acesulfame under simulated solar radiation. Acesulfame was degraded over three orders of magnitude faster than the other sweeteners. For examining indirect photochemical reactions, the sweeteners were dissolved in surface waters with indigenous dissolved organic matter or irradiated with aqueous solutions of nitrate (1 mg N/L) and ferric iron (2.8 mg Fe/L) introduced as sensitizers. Iron enhanced the photodegradation rates but nitrate and dissolved organic matter did not. UVR transformed acesulfame into at least three products: iso-acesulfame, hydroxylated acesulfame and hydroxypropanyl sulfate. Photolytic half-life was one year for acesulfame and more than several years for the other sweeteners in surface waters under solar radiation. Our study shows that the photochemical reactivity of commonly used artificial sweeteners is variable: acesulfame may be sensitive to photodegradation in surface waters, while saccharin, cyclamic acid and sucralose degrade very slowly even under the energetic UVR commonly used in water treatment.

  6. Fabrication of Al matrix composite reinforced with submicrometer-sized Al2O3 particles formed by combustion reaction between HEMM Al and V2O5 composite particles during sintering

    NASA Astrophysics Data System (ADS)

    Woo, Kee Do; Kim, Jae Hwang; Kwon, Eui Pyo; Moon, Min Seok; Lee, Hyun Bom; Sato, Tatsuo; Liu, Zhiguang

    2010-04-01

    To fabricate an Al-V matrix composite reinforced with submicron-sized Al2O3 and AlxVy (Al3V, Al10V) phases, high energy mechanical milling (HEMM) and sintering were employed. By increasing the milling time, the size of mechanically milled powder was significantly reduced. In this study, the average powder size of 59 μm for Al, and 178 μm for V2O5 decreased with the formation of a new product, Al-Al2O3-AlxVy, with a size range from 1.3 μm to 2.6 μm formed by the in-situ combustion reaction during sintering of HEM milled Al and V2O5 composite powders. The in-situ reaction between Al and V2O5 during the HEMM and sintering transformed the Al2O3 and AlxVy (Al3V, Al10V) phases. Most of the reduced V reacted with excess the Al to form AlxVy (Al3V, Al10V) with very little V dissolved into Al matrix. By increasing the milling time and weight percentage of V2O5, the hardness of the Al-Al2O3-AlxVy composite sintered at 1173 K increased. The composite fabricated with the HEMM Al-20wt.%V2O5 composite powder and sintering at 1173 K for 2 h had the highest hardness.

  7. Directed long-range molecular migration energized by surface reaction

    NASA Astrophysics Data System (ADS)

    Harikumar, K. R.; Polanyi, John C.; Zabet-Khosousi, Amir; Czekala, Piotr; Lin, Haiping; Hofer, Werner A.

    2011-05-01

    The recoil of adsorbates away (desorption) and towards (reaction) surfaces is well known. Here, we describe the long-range recoil of adsorbates in the plane of a surface, and accordingly the novel phenomenon of reactions occurring at a substantial distance from the originating event. Three thermal and three electron-induced surface reactions are shown by scanning tunnelling microscopy to propel their physisorbed ethylenic products across the rough surface of Si(100) over a distance of up to 200 Å before an attachment reaction. The recoil energy in the ethylenic products comes from thermal exoergicity or from electronic excitation of chemisorbed alkenes. We propose that the mechanism of migration is a rolling motion, because the recoiling molecule overcomes raised surface obstacles. Electronic excitation of propene causes directional recoil and often end-to-end inversion, suggesting cartwheeling. Ab initio calculations of the halogenation and electron-induced reactions support a model in which asymmetric forces between the molecule and the surface induce rotation and therefore migration.

  8. SinterHab

    NASA Astrophysics Data System (ADS)

    Rousek, Tomáš; Eriksson, Katarina; Doule, Ondřej

    2012-05-01

    This project describes a design study for a core module on a Lunar South Pole outpost, constructed by 3D printing technology with the use of in-situ resources and equipped with a bio-regenerative life support system. The module would be a hybrid of deployable (CLASS II) and in-situ built (CLASS III) structures. It would combine deployable membrane structures and pre-integrated rigid elements with a sintered regolith shell for enhanced radiation and micrometeorite shielding. The closed loop ecological system would support a sustainable presence on the Moon with particular focus on research activities. The core module accommodates from four to eight people, and provides laboratories as a test bed for development of new lunar technologies directly in the environment where they will be used. SinterHab also includes an experimental garden for development of new bio-regenerative life support system elements. The project explores these various concepts from an architectural point-of-view particularly, as they constitute the building, construction and interior elements. The construction method for SinterHab is based on 3D printing by sintering of the lunar regolith. Sinterator robotics 3D printing technology proposed by NASA JPL enables construction of future generations of large lunar settlements with little imported material and the use of solar energy. The regolith is processed, placed and sintered by the Sinterator robotics system which combines the NASA ATHLETE and the Chariot remotely controlled rovers. Microwave sintering creates a rigid structure in the form of walls, vaults and other architectural elements. The interior is coated with a layer of inflatable membranes inspired by the TransHab project. The life-support system is mainly bio-regenerative and several parts of the system are intrinsically multifunctional and serve more than one purpose. The plants for food production are also an efficient part of atmosphere revitalization and water treatment. Moreover

  9. Template directed reactions of 2-aminoadenylic acid derivatives

    NASA Technical Reports Server (NTRS)

    Webb, T. R.; Orgel, L. E.

    1982-01-01

    The template-directed oligomerization of activated derivatives of 2-aminoadenylic acid (paA) on polyuridylic acid (poly(U)) in aqueous buffers was studied. The reaction differs from that of adenylic acid (pA) under identical conditions, in that only di- and tri-nucleotides are observed as substantial products rather than a longer sequence of oligomers. The reaction of paA also differs from that of pA in that it does not require Mg (2+), and is less susceptible to increased temperature. The relevance of these observations to the chemical evolution of polynucleotide replication is discussed. Improved syntheses of paA and its diphosphate are reported.

  10. Direct reaction experimental studies with beams of radioactive tin ions

    SciTech Connect

    Jones, K. L. Ayres, A.; Bey, A.; Burcher, S.; Cartegni, L.; Cerizza, G.; Ahn, S.; Allmond, J. M.; Beene, J. R.; Galindo-Uribarri, A.; Liang, J. F.; Nesaraja, C. D.; Pain, S. D.; Radford, D. C.; Schmitt, K. T.; Smith, M. S.; Stracener, D. W.; Varner, R. L.; Bardayan, D. W.; Baugher, T.; and others

    2015-10-15

    The tin chain of isotopes provides a unique region in which to investigate the evolution of single-particle structure, spreading from N = 50 at {sup 100}Sn, through 10 stable isotopes and the N = 82 shell closure at {sup 132}Sn out into the r-process path. Direct reactions performed on radioactive ion beams are sensitive spectroscopic tools for studying exotic nuclei. Here we present one experiment knocking out neutrons from tin isotopes that are already neutron deficient and two reactions that add a neutron to neutron-rich {sup 130}Sn. Both techniques rely on selective particle identification and the measurement of γ rays in coincidence with charged ions. We present the goals of the two experiments and the particle identification for the channels of interest. The final results will be presented in future publications.

  11. Direct Reaction Experimental Studies with Beams of Radioactive Tin Ions

    SciTech Connect

    Jones, K. L.; Ahn, S.H.; Allmond, James M; Ayres, A.; Bardayan, Daniel W; Baugher, T.; Bazin, D.; Beene, James R; Berryman, J. S.; Bey, A.; Bingham, C. R.; Cartegni, L.; Chae, K. Y.; Gade, A.; Galindo-Uribarri, Alfredo {nmn}; Garcia-Ruiz, R.F.; Grzywacz, Robert Kazimierz; Howard, Meredith E; Kozub, R. L.; Liang, J Felix; Manning, Brett M; Matos, M.; McDaniel, S.; Miller, D.; Nesaraja, Caroline D; O'Malley, Patrick; Padgett, S; Padilla-Rodal, Elizabeth; Pain, Steven D; Pittman, S. T.; Radford, David C; Ratkiewicz, Andrew J; Schmitt, Kyle; Smith, Michael Scott; Stracener, Daniel W; Stroberg, S.; Tostevin, Jeffrey A; Varner Jr, Robert L; Weisshaar, D.; Wimmer, K.

    2015-01-01

    The tin chain of isotopes provides a unique region in which to investigate the evolution of single-particle structure, spreading from N = 50 at Sn-100, through 10 stable isotopes and the N = 82 shell closure at Sn-132 out into the r-process path. Direct reactions performed on radioactive ion beams are sensitive spectroscopic tools for studying exotic nuclei. Here we present one experiment knocking out neutrons from tin isotopes that are already neutron deficient and two reactions that add a neutron to neutron-rich Sn-130. Both techniques rely on selective particle identification and the measurement of gamma rays in coincidence with charged ions. We present the goals of the two experiments and the particle identification for the channels of interest. The final results will be presented in future publications.

  12. Direct Catalytic Asymmetric Mannich-Type Reaction of Alkylamides.

    PubMed

    Arteaga, Fernando Arteaga; Liu, Zijian; Brewitz, Lennart; Chen, Jianyang; Sun, Bo; Kumagai, Naoya; Shibasaki, Masakatsu

    2016-05-20

    Direct enolate formation coupled with subsequent enantioselective C-C bond formation remains a topic of intense interest in asymmetric catalysis. This methodology is achieved even with low acidic amides without an electron-withdrawing group at the α-position in the context of a Mannich-type reaction. Acetate-, propionate-, and butyrate-type 7-azaindoline amides served as enolate precursors to afford the desired Mannich adducts with high stereoselectivity, and ligand-enabled diastereo-divergency provided access to both anti/syn diastereomers. The facile transformation of the amide moiety ensures the synthetic utility of the Mannich adducts.

  13. MgAl2O4(001) based magnetic tunnel junctions made by direct sputtering of a sintered spinel target

    NASA Astrophysics Data System (ADS)

    Belmoubarik, Mohamed; Sukegawa, Hiroaki; Ohkubo, Tadakatsu; Mitani, Seiji; Hono, Kazuhiro

    2016-03-01

    We developed a fabrication process of an epitaxial MgAl2O4 barrier for magnetic tunnel junctions (MTJs) using a direct sputtering method from an MgAl2O4 spinel sintered target. Annealing the sputter-deposited MgAl2O4 layer sandwiched between Fe electrodes led to the formation of a (001)-oriented cation-disorder spinel with atomically sharp interfaces and lattice-matching with the Fe electrodes. A large tunnel magnetoresistance ratio up to 245% at 297 K (436% at 3 K) was achieved in the Fe/MgAl2O4/Fe(001) MTJ as well as an excellent bias voltage dependence. These results indicate that the direct sputtering is an alternative method for the realization of high performance MTJs with a spinel-based tunnel barrier.

  14. Effect of process parameters on hardness, temperature profile and solidification of different layers processed by direct metal laser sintering (DMLS)

    NASA Astrophysics Data System (ADS)

    Ahmed, Sazzad Hossain; Mian, Ahsan; Srinivasan, Raghavan

    2016-07-01

    In DMLS process objects are fabricated layer by layer from powdered material by melting induced by a controlled laser beam. Metallic powder melts and solidifies to form a single layer. Solidification map during layer formation is an important route to characterize micro-structure and grain morphology of sintered layer. Generally, solidification leads to columnar, equiaxed or mixture of these two types grain morphology depending on solidification rate and thermal gradient. Eutectic or dendritic structure can be formed in fully equiaxed zone. This dendritic growth has a large effect on material properties. Smaller dendrites generally increase ductility of the layer. Thus, materials can be designed by creating desired grain morphology in certain regions using DMLS process. To accomplish this, hardness, temperature distribution, thermal gradient and solidification cooling rate in processed layers will be studied under change of process variables by using finite element analysis, with specific application to Ti-6Al-4V.

  15. Direct Measurement of Mercury Reactions In Coal Power Plant Plumes

    SciTech Connect

    Leonard Levin

    2005-12-31

    Recent field and pilot-scale results indicate that divalent mercury emitted from power plants may rapidly transform to elemental mercury within the power plant plumes. Simulations of mercury chemistry in plumes based on measured rates to date have improved regional model fits to Mercury Deposition Network wet deposition data for particular years, while not degrading model verification fits for remaining years of the ensemble. The years with improved fit are those with simulated deposition in grid cells in the State of Pennsylvania that have matching MDN station data significantly less than the model values. This project seeks to establish a full-scale data basis for whether or not significant reduction or oxidation reactions occur to mercury emitted from coal-fired power plants, and what numerical redox rate should apply for extension to other sources and for modeling of power plant mercury plumes locally, regionally, and nationally. Although in-stack mercury (Hg) speciation measurements are essential to the development of control technologies and to provide data for input into atmospheric fate and transport models, the determination of speciation in a cooling coal combustion plume is more relevant for use in estimating Hg fate and effects through the atmosphere. It is mercury transformations that may occur in the plume that determine the eventual rate and patterns of mercury deposited to the earth's surface. A necessary first step in developing a supportable approach to modeling any such transformations is to directly measure the forms and concentrations of mercury from the stack exit downwind to full dispersion in the atmosphere. As a result, a study was sponsored by EPRI and jointly funded by EPRI, the U.S Department of Energy (DOE), and the Wisconsin Department of Administration. The study was designed to further our understanding of plume chemistry. The study was carried out at the We Energies Pleasant Prairie Power Plant, Pleasant Prairie, Wisconsin, just

  16. Correlations probed in direct two-nucleon removal reactions

    SciTech Connect

    Simpson, E. C.; Tostevin, J. A.

    2010-10-15

    Final-state-exclusive momentum distributions of fast, forward-traveling residual nuclei, following two-nucleon removal from fast secondary radioactive beams of projectile nuclei, can and have now been measured. Assuming that the most important reaction mechanism is the sudden direct removal of a pair of nucleons from a set of relatively simple, active shell-model orbital configurations, such distributions were predicted to depend strongly on the total angular momentum I carried by the two nucleons--the final-state spin for spin 0{sup +} projectiles. The sensitivity of these now-accessible observables to specific details of the (correlated) two-nucleon wave functions is of importance. We clarify that it is the total orbital angular momentum L of the two nucleons that is the primary factor in determining the shapes and widths of the calculated momentum distributions. It follows that, with accurate measurements, this dependence upon the L makeup of the two-nucleon wave functions could be used to assess the accuracy of (shell- or many-body-) model predictions of these two-nucleon configurations. By using several tailored examples, with specific combinations of active two-nucleon orbitals, we demonstrate that more-subtle structure aspects may be observed, allowing such reactions to probe and/or confirm the details of theoretical model wave functions.

  17. Effect of Process Parameter on Barium Titanate Stannate (BTS) Materials Sintered at Low Sintering

    NASA Astrophysics Data System (ADS)

    Shukla, Alok; Bajpai, P. K.

    2011-11-01

    Ba(Ti1-xSnx)O3 solid solutions with (x = 0.15, 0.20, 0.30 and 0.40) are synthesized using conventional solid state reaction method. Formation of solid solutions in the range 0 ≤ x ≤0.40 is confirmed using X-ray diffraction technique. Single phase solid solutions with homogeneous grain distribution are observed at relatively low sintering by controlling process parameters viz. sintering time. Composition at optimized temperature (1150 °C) sintered by varying the sintering time, stabilize in cubic perovskite phase. The % experimental density increase with increasing the time of sintering instead of increasing sintering temperature. The lattice parameter increases by increasing the tin composition in the material. This demonstrates that process parameter optimization can lead to single phase at relatively lower sintering-a major advantage for the materials used as capacitor element in MLCC.

  18. On the Mechanism of Oxazoline-Directed Metalations: Evidence for Nitrogen-Directed Reactions.

    PubMed

    Sammakia, Tarek; Latham, Hallie A.

    1996-03-08

    We recently described a method for the synthesis of ferrocene complexes possessing planar chirality which relies on the asymmetric deprotonation of chiral ferrocenyloxazolines. The unexpected stereochemical outcome of these reactions led us to examine whether the metalation is directed by the oxygen or the nitrogen of the oxazoline. In this paper, we describe the synthesis of a constrained ferrocenyloxazoline (compound 13) in which oxygen- and nitrogen-directed metalations provide different stereochemical outcomes. Our results show that nitrogen is responsible for the directive effects of the oxazoline when alkyllithium reagents are used to deprotonate the ferrocene. The implications of this result on the origin of asymmetric induction in the metalation of the unconstrained ferrocenyloxazolines 19 and 20 are discussed.

  19. Optical and biological properties of transparent nanocrystalline hydroxyapatite obtained through spark plasma sintering.

    PubMed

    Li, Zhong; Thompson, Brianna C; Dong, Zhili; Khor, Khiam Aik

    2016-12-01

    Transparent bioceramics have attracted a large amount of research interest as they facilitate direct observation of biointerfacial reactions. Thus far, attempts to achieve transparent hydroxyapatite have been focused on augmenting the sintering pressure and/or extending the sintering duration. This study aims at fabricating transparent HA using a direct and fast spark plasma sintering process with appropriate starting powder and moderate sintering pressure. Three types of raw powder, namely micro-spheres, nano-rods and nano-spheres, were sintered to investigate the optical and biological properties of the compacted pellets. It was found that in terms of transparency, the micro-sphere pellet sintered at 1000°C stood out with an in-line transmittance as high as 84% achieved at 1300nm for a 2mm thick sample. In addition, pellets fabricated from micro-spheres demonstrated the highest cell viability in in vitro biological tests with L929 cells. Living cells cultured on a transparent micro-sphere pellet could be directly and clearly observed by light microscopy. It is thus concluded that the micro-sphere powder is the most desirable raw material to manufacture transparent hydroxyapatite because it could enable dense pellets with notably high transparency and outstanding in vitro biocompatibility to be readily obtained.

  20. Enabling direct nanoscale observations of biological reactions with dynamic TEM

    PubMed Central

    Evans, James E.; Browning, Nigel D.

    2013-01-01

    Biological processes occur on a wide range of spatial and temporal scales: from femtoseconds to hours and from angstroms to meters. Many new biological insights can be expected from a better understanding of the processes that occur on these very fast and very small scales. In this regard, new instruments that use fast X-ray or electron pulses are expected to reveal novel mechanistic details for macromolecular protein dynamics. To ensure that any observed conformational change is physiologically relevant and not constrained by 3D crystal packing, it would be preferable for experiments to utilize small protein samples such as single particles or 2D crystals that mimic the target protein's native environment. These samples are not typically amenable to X-ray analysis, but transmission electron microscopy has imaged such sample geometries for over 40 years using both direct imaging and diffraction modes. While conventional transmission electron microscopes (TEM) have visualized biological samples with atomic resolution in an arrested or frozen state, the recent development of the dynamic TEM (DTEM) extends electron microscopy into a dynamic regime using pump-probe imaging. A new second-generation DTEM, which is currently being constructed, has the potential to observe live biological processes with unprecedented spatiotemporal resolution by using pulsed electron packets to probe the sample on micro- and nanosecond timescales. This article reviews the experimental parameters necessary for coupling DTEM with in situ liquid microscopy to enable direct imaging of protein conformational dynamics in a fully hydrated environment and visualize reactions propagating in real time. PMID:23315566

  1. Nickel-Catalyzed Reactions Directed toward the Formation of Heterocycles.

    PubMed

    Kurahashi, Takuya; Matsubara, Seijiro

    2015-06-16

    Heterocycles have garnered significant attention because they are important functional building blocks in various useful molecules, such as pharmaceuticals, agricultural chemicals, pesticides, and materials. Several studies have been conducted regarding the preparation of heterocyclic skeletons with an emphasis on selectivity and efficiency. Three strategies are typically employed to construct cyclic molecules, namely, cyclization, cycloaddition, and ring-size alterations. Although each method has certain advantages, cycloaddition may be superior from the viewpoint of divergence. Specifically, cycloadditions enable the construction of rings from several pieces. However, the construction of heterocycles via cycloadditions is more challenging than the construction of carbocycles. For heterocycle construction, simple pericyclic reactions rarely work smoothly because of the large HOMO-LUMO gap unless well-designed combinations, such as electron-rich dienes and aldehydes, are utilized. Thus, a different approach should be employed to prepare heterocycles via cycloadditions. To this end, the use of metallacycles containing heteroatoms is expected to serve as a promising solution. In this study, we focused on the preparation of heteroatom-containing nickelacycles. Because nickel possesses a relatively high redox potential and an affinity for heteroatoms, several methods were developed to synthesize heteronickelacycles from various starting materials. The prepared nickelacycles were demonstrated to be reasonable intermediates in cycloaddition reactions, which were used to prepare various heterocycles. In this Account, we introduce the following four methods to prepare heterocycles via heteronickelacycles. (1) Direct oxidative insertion of Ni(0) to α,β-unsaturated enone derivatives: treatment of 3-ethoxycarbonyl-4-phenyl-3-buten-2-one with Ni(0) afforded an oxa-nickelacycle, which reacted with alkynes to give pyrans. (2) Substitution of a part of a cyclic compound with

  2. Sintering Characteristics of Indian Chrome Ore Fines

    NASA Astrophysics Data System (ADS)

    Nandy, Bikash; Chaudhury, Manoj Kumar; Paul, Jagannath; Bhattacharjee, D.

    2009-10-01

    Chrome ore concentrate consists of high-temperature melting oxides such as Cr2O3, MgO, and Al2O3. The presence of these refractory constituents makes the ore a very high melting mineral. Hence, it is difficult to produce sinter from chrome ore by a pyrometallurgical route. Currently, chrome ore is ground to below 75 μm, pelletized, heat hardened through carbothermic reaction at 1300 °C to 1400 °C, and then charged into a submerged electric arc furnace (EAF), along with lumpy ore for ferrochrome/charge-chrome production. Electricity is a major cost element in this extraction process. This work explores the sinterability of chrome ore. The objective of this study was to: (1) determine whether chrome ore is sinterable and, if so, (2) ascertain ways of achieving satisfactory properties at a low temperature of sintering. Sintering of the raw material feed could be a way to reduce electricity consumption, because during sintering a partial reduction of minerals is expected along with agglomeration. Studies carried out by the authors show that it is possible to agglomerate chrome ore fines through sintering. The chrome ore sinter thus produced was found to be inferior in strength, comparable to that of an iron ore sinter, but strength requirements may not be the same for both. Because the heat generation during chrome ore sintering is high owing to some exothermic reactions, compared with iron ore, and because chrome ore contains a high amount of fines, shallow-bed-depth sinter cake production was attempted in the laboratory-scale pot-sintering machine. The sintered product was found to be a good conductor of electricity because of the presence of phases such as magnetite and maghemite. This characteristic of the chrome ore sinter will subsequently have a favorable impact in terms of power consumption during the production of ferrochrome in a submerged EAF. The sinter made was melted in the arc furnace and it was found that the specific melting energy is comparable to

  3. Fundamental studies of retrograde reactions in direct liquefaction

    SciTech Connect

    Serio, M.A.; Solomon, P.R.; Kroo, E.; Charpenay, S.; Bassilakis, R.

    1991-12-17

    The overall objective of the program was to improve the understanding of retrograde reactions and their dependencies on coal rank and structure, and/or coal modifications and reaction conditions. Because retrograde reactions are competitive with bond breaking reactions, an understanding of both is required to shift the competition in favor of the latter. Related objectives were to clarify the conflicting observations reported in literature on such major topics as the role of oxygen groups in retrograde reactions and to provide a bridge from very fundamental studies on pure compounds to phenomenological studies on actual coal. This information was integrated into the FG-DVC model, which was improved and extended to the liquefaction context.

  4. Tribological Behavior of Aluminum Alloy AlSi10Mg-TiB2 Composites Produced by Direct Metal Laser Sintering (DMLS)

    NASA Astrophysics Data System (ADS)

    Lorusso, Massimo; Aversa, Alberta; Manfredi, Diego; Calignano, Flaviana; Ambrosio, Elisa Paola; Ugues, Daniele; Pavese, Matteo

    2016-08-01

    Direct metal laser sintering (DMLS) is an additive manufacturing technique for the production of parts with complex geometry and it is especially appropriate for structural applications in aircraft and automotive industries. Aluminum-based metal matrix composites (MMCs) are promising materials for these applications because they are lightweight, ductile, and have a good strength-to-weight ratio This paper presents an investigation of microstructure, hardness, and tribological properties of AlSi10Mg alloy and AlSi10Mg alloy/TiB2 composites prepared by DMLS. MMCs were realized with two different compositions: 10% wt. of microsize TiB2, 1% wt. of nanosize TiB2. Wear tests were performed using a pin-on-disk apparatus on the prepared samples. Performances of AlSi10Mg samples manufactured by DMLS were also compared with the results obtained on AlSi10Mg alloy samples made by casting. It was found that the composites displayed a lower coefficient of friction (COF), but in the case of microsize TiB2 reinforcement the wear rate was higher than with nanosize reinforcements and aluminum alloy without reinforcement. AlSi10Mg obtained by DMLS showed a higher COF than AlSi10Mg obtained by casting, but the wear rate was higher in the latter case.

  5. Chemical Reaction Engineering: Current Status and Future Directions.

    ERIC Educational Resources Information Center

    Dudukovic, M. P.

    1987-01-01

    Describes Chemical Reaction Engineering (CRE) as the discipline that quantifies the interplay of transport phenomena and kinetics in relating reactor performance to operating conditions and input variables. Addresses the current status of CRE in both academic and industrial settings and outlines future trends. (TW)

  6. Direct Measurement of {sup 21}Na+{alpha} Stellar Reaction

    SciTech Connect

    Binh, D. N.; Kubono, S.; Yamaguchi, H.; Hayakawa, S.; Hashimoto, T.; Kahl, D.; Teranishi, T.; Iwasa, N.; Kume, N.; Kato, S.; Khiem, L. H.; Tho, N. T.; Wakabayashi, Y.

    2010-08-12

    The measurement of the resonant alpha scattering and the {sup 21}Na({alpha}, p) reaction were performed for the first time in inverse kinematics with the thick target method using a {sup 21}Na radioisotope (RI) beam. This paper reports the current result of alpha scattering measurement and its astrophysics implication.

  7. Probing the Tetrahymena group I ribozyme reaction in both directions.

    PubMed

    Karbstein, Katrin; Carroll, Kate S; Herschlag, Daniel

    2002-09-17

    The Tetrahymena L-21 ScaI ribozyme derived from the self-splicing group I intron catalyzes a reversible reaction analogous to the first step of self-splicing: CCCUCUA (S) + [UC]G right harpoon over left harpoon CCCUCU (P) + [UC]GA. To relate our understanding of the ribozyme to the self-splicing reaction and to further the mechanistic dissection of the ribozyme reaction, we have established a quantitative kinetic and thermodynamic framework for the forward and reverse reaction of the L-21 ScaI ribozyme under identical conditions. Examination of the framework shows that binding of products is cooperative with binding enhanced 5-fold, as was observed previously for binding of the substrates. Further, binding of UCGA is 12-fold weaker than binding of the unphosphorylated UCG, analogous to the 20-fold weaker binding of phosphorylated S relative to P; the molecular interactions underlying the stronger binding of UCG were traced to the 3'-hydroxyl group of UCG. The symmetrical effects on binding of substrates and products result in the equilibrium between ribozyme-bound species, K(int), that is essentially unperturbed from the solution equilibrium, K(ext) (K(int) = [E.P.UCGA]/[E.S.UCG] = 4.6 and K(ext) = [P][UCGA]/[S][UCG] = 1.9). Last, we show that the pK(a) values of the nucleophiles in the forward and reverse reactions are >/=10. This observation suggests that metal ion activation of the nucleophile and stabilization of the leaving group can only account for a portion of the rate enhancement of this ribozyme. These and prior results suggest that the Tetrahymena group I ribozyme, analogous to protein enzymes, uses multiple catalytic strategies to achieve its large rate enhancement.

  8. Direct reaction measurements with a (132)Sn radioactive ion beam

    SciTech Connect

    Jones, K. L.; Chae, K. Y.; Kapler, R.; Ma, Zhanwen; Moazen, Brian; Cizewski, J. A.; Hatarik, Robert; Pain, S. D.; Swan, T. P.; Nunes, F. M.; Adekola, Aderemi S; Bardayan, Daniel W; Blackmon, Jeff C; Chae, Kyung Yuk; Liang, J Felix; Nesaraja, Caroline D; Pain, Steven D; Shapira, Dan; Smith, Michael Scott; Chipps, Kelly A; Erikson, Luke; Livesay, R. J.; Harlin, Christopher W; Patterson, N. P.; Thomas, J. S.; Kozub, R. L.; Shriner, Jr., John F

    2011-01-01

    The (d,p) neutron transfer and (d,d) elastic scattering reactions were measured in inverse kinematics using a radioactive ion beam of {sup 132}Sn at 630 MeV. The elastic scattering data were taken in a region where Rutherford scattering dominated the reaction, and nuclear effects account for less than 8% of the elastic scattering cross section. The magnitude of the nuclear effects, in the angular range studied, was found to be independent of the optical potential used, allowing the transfer data to be normalized in a reliable manner. The neutron-transfer reaction populated a previously unmeasured state at 1363 keV, which is most likely the single-particle 3p{sub 1/2} state expected above the N=82 shell closure. The data were analyzed using finite-range adiabatic-wave calculations and the results compared with the previous analysis using the distorted-wave Born approximation. Angular distributions for the ground and first-excited states are consistent with the previous tentative spin and parity assignments. Spectroscopic factors extracted from the differential cross sections are similar to those found for the one-neutron states beyond the benchmark doubly magic nucleus {sup 208}Pb.

  9. Direct reaction measurements with a 132Sn radioactive ion beam

    SciTech Connect

    Jones, Katherine L.; Nunes, Filomena M.; Adekola, Aderemi S.; Bardayan, Dan W.; Blackmon, Jeff; Chae, K. Y.; Chipps, Kelly A.; Cizewski, Jolie A.; Erikson, Luke E.; Harlin, C.; Hatarik, R.; Kapler, R.; Kozub, Raymond L.; Liang, J. F.; Livesay, Ronald J.; Ma, Zhongguo J.; Moazen, B. H.; Nesaraja, Caroline D.; Pain, Steven D.; Patterson, N. P.; Shapira, Dan; Shriner, Jr., John F.; Smith, Michael S.; Swan, Thomas P.; Thomas, Jeff S.

    2011-09-01

    The (d,p) neutron transfer and (d,d) elastic scattering reactions were measured in inverse kinematics using a radioactive ion beam of 132Sn at 630 MeV. The elastic scattering data were taken in a region where Rutherford scattering dominated the reaction, and nuclear effects account for less than 8% of the elastic scattering cross section. The magnitude of the nuclear effects, in the angular range studied, was found to be independent of the optical potential used, allowing the transfer data to be normalized in a reliable manner. The neutron-transfer reaction populated a previously unmeasured state at 1363 keV, which is most likely the single-particle 3p1/2 state expected above the N = 82 shell closure. The data were analyzed using finite-range adiabatic-wave calculations and the results compared with the previous analysis using the distorted-wave Born approximation. Angular distributions for the ground and first-excited states are consistent with the previous tentative spin and parity assignments. Spectroscopic factors extracted from the differential cross sections are similar to those found for the one-neutron states beyond the benchmark doubly magic nucleus 208Pb.

  10. Immediate, non-submerged, root-analogue direct laser metal sintering (DLMS) implants: a 1-year prospective study on 15 patients.

    PubMed

    Mangano, Francesco Guido; De Franco, Michele; Caprioglio, Alberto; Macchi, Aldo; Piattelli, Adriano; Mangano, Carlo

    2014-07-01

    This study evaluated the 1-year survival and success rate of root-analogue direct laser metal sintering (DLMS) implants, placed into the extraction sockets of 15 patients. DLMS is a technology which allows solids with complex geometry to be fabricated by annealing metal powder microparticles in a focused laser beam, according to a computer-generated three-dimensional (3D) model; the fabrication process involves the laser-induced fusion of titanium microparticles, in order to build, layer-by-layer, the desired object. Cone-beam computed tomography (CBCT) acquisition and 3D image conversion, combined with the DLMS process, allow the fabrication of custom-made, root-analogue implants (RAIs). CBCT images of 15 non-restorable premolars (eight maxilla; seven mandible) were acquired and transformed into 3D models: from these, custom-made, root-analogue DLMS implants with integral abutment were fabricated. Immediately after tooth extraction, the RAIs were placed in the sockets and restored with a single crown. One year after implant placement, clinical and radiographic parameters were assessed: success criteria included absence of pain, suppuration, and exudation; absence of implant mobility and absence of continuous peri-implant radiolucency; distance between the implant shoulder and the first visible bone-to-implant contact <1.5 mm from initial surgery; and absence of prosthetic complications. At the 1-year follow-up, no implants were lost, for a survival rate of 100 %. All implants were stable, with no signs of infection. The good conditions of the peri-implant tissues were confirmed by the radiographic examination, with a mean DIB of 0.7 mm (±0.2). The possibility of fabricating custom-made, RAI DLMS implants opens new interesting horizons for immediate placement of dental implants.

  11. DIRECT MEASUREMENT OF MERCURY REACTIONS IN COAL POWER PLANT PLUMES

    SciTech Connect

    Leonard Levin

    2006-06-01

    This project was awarded under U.S. Department of Energy (DOE) National Energy Technology Laboratory (NETL) Program Solicitation DE-PS26-02NT41422 and specifically addresses Program Area of Interest: No.5--Environmental and Water Resources. The project team includes the Electric Power Research Institute (EPRI) as the contractor and the University of North Dakota Energy & Environmental Research Center (EERC) and Frontier Geosciences as subcontractors. Wisconsin Energies and its Pleasant Prairie Power Plant acted as host for the field-testing portion of the research. The project is aimed at clarifying the role, rates, and end results of chemical transformations that may occur to mercury that has been emitted from elevated stacks of coal-fired electric power plants. Mercury emitted from power plants emerges in either its elemental, divalent, or particulate-bound form. Deposition of the divalent form is more likely to occur closer to the source than that of the other two forms, due to its solubility in water. Thus, if chemical transformations occur in the stack emissions plume, measurements in the stack may mischaracterize the fate of the material. Initial field and pilot plant measurements have shown significant and rapid chemical reduction of divalent to elemental mercury may occur in these plumes. Mercury models currently assume that the chemical form of mercury occurring in stacks is the same as that which enters the free atmosphere, with no alteration occurring in the emissions plume. Recent data indicate otherwise, but need to be evaluated at full operating scale under field conditions. Prestbo and others have demonstrated the likelihood of significant mercury chemical reactions occurring in power plant plumes (Prestbo et al., 1999; MDNR-PPRP, 2000; EERC, 2001). This experiment will thus increase our understanding of mercury atmospheric chemistry, allowing informed decisions regarding source attribution. The experiment was carried out during the period August 22

  12. DIRECT MEASUREMENT OF MERCURY REACTIONS IN COAL POWER PLANT PLUMES

    SciTech Connect

    Leonard Levin

    2004-01-01

    This project was awarded under U.S. Department of Energy (DOE) National Energy Technology Laboratory (NETL) Program Solicitation DE-PS26-02NT41422 and specifically addresses Program Area of Interest: No.5--Environmental and Water Resources. The project team includes the Electric Power Research Institute (EPRI) as the contractor and the University of North Dakota Energy & Environmental Research Center (EERC) and Frontier Geosciences as subcontractors. Wisconsin Energies and its Pleasant Prairie Power Plant acted as host for the field-testing portion of the research. The project is aimed at clarifying the role, rates, and end results of chemical transformations that may occur to mercury that has been emitted from elevated stacks of coal-fired electric power plants. Mercury emitted from power plants emerges in either its elemental, divalent, or particulate-bound form. Deposition of the divalent form is more likely to occur closer to the source than that of the other two forms, due to its solubility in water. Thus, if chemical transformations occur in the stack emissions plume, measurements in the stack may mischaracterize the fate of the material. Initial field and pilot plant measurements have shown significant and rapid chemical reduction of divalent to elemental mercury may occur in these plumes. Mercury models currently assume that the chemical form of mercury occurring in stacks is the same as that which enters the free atmosphere, with no alteration occurring in the emissions plume. Recent data indicate otherwise, but need to be evaluated at full operating scale under field conditions. Prestbo and others have demonstrated the likelihood of significant mercury chemical reactions occurring in power plant plumes (Prestbo et al., 1999; MDNR-PPRP, 2000; EERC, 2001). This experiment will thus increase our understanding of mercury atmospheric chemistry, allowing informed decisions regarding source attribution. The experiment was carried out during the period August 22

  13. Behavior of New Zealand Ironsand During Iron Ore Sintering

    NASA Astrophysics Data System (ADS)

    Wang, Zhe; Pinson, David; Chew, Sheng; Rogers, Harold; Monaghan, Brian J.; Pownceby, Mark I.; Webster, Nathan A. S.; Zhang, Guangqing

    2016-02-01

    A New Zealand ironsand sample was characterized by scanning electron microscopy (SEM), X-ray fluorescence spectroscopy, qualitative and quantitative X-ray diffraction, and electron probe microanalysis. The titanomagnetite-rich ironsand was added into an industrial sinter blend in the proportion of 5 wt pct, and the mixture was uniaxially pressed into cylindrical tablets and sintered in a tube furnace under flowing gas with various oxygen potentials and temperatures to develop knowledge and understanding of the behavior of titanium during sintering. An industrial sinter with the addition of 3 wt pct ironsand was also examined. Both the laboratory and industrial sinters were characterized by optical and SEM. Various morphologies of relict ironsand particles were present in the industrial sinter due to the heterogeneity of sintering conditions, which could be well simulated by the bench-scale sintering experiments. The assimilation of ironsand during sintering in a reducing atmosphere started with the diffusion of calcium into the lattice of the ironsand matrix, and a reaction zone was formed near the boundary within individual ironsand particles where a perovskite phase was generated. With increasing sintering temperature, in a reducing atmosphere, ironsand particles underwent further assimilation and most of the titanium moved from the ironsand particles into a glass phase. In comparison, more titanium remained in the original ironsand particles when sintered in air. Ironsand particles are more resistant to assimilation in an oxidizing atmosphere.

  14. Experimental Guidance of ISB Corrections via Direct Nuclear Reactions

    NASA Astrophysics Data System (ADS)

    Leach, K. G.; Garrett, P. E.; Ball, G. C.; Bangay, J. C.; Bianco, L.; Demand, G. A.; Faestermann, T.; Finlay, P.; Green, K. L.; Hertenberger, R.; Kriicken, R.; Phillips, A. A.; Rand, E. T.; Sumithrarachchi, C. S.; Svensson, C. E.; Towner, I. S.; Triambak, S.; Wirth, H.-F.; Wong, J.

    2011-09-01

    The most recent isospin-symmetry-breaking corrections, δc, of Towner and Hardy for superallowed Fermi β-decay transitions, have included the opening of specific core orbitals. This change has resulted in significant deviations in some of the δc factors from their previous calculations, and an improved agreement of the individual corrected Script Ft values with the overall world average of the 13 most precise cases. While this is consistent with the conserved-vector-current (CVC) hypothesis of the Standard Model, these new calculations must be thoroughly tested, and guidance must be given for the improvement of calculations for the upper-pf shell nuclei. Using the (d,t) reaction mechanism to probe the single neutron wavefunction overlap, information regarding the relevant shell-model configurations needed in the calculation can be determined. An experiment was therefore performed with a 22 MeV polarized deuterium beam from the MP tandem Van de Graaff accelerator in Munich, Germany. Using the Q3D magnetic spectrograph, and a cathode-strip focal-plane detector, outgoing tritons were analyzed at 9 angles between 10° and 60°, up to an excitation energy of 4.8 MeV. This proceeding reports the motivational and experimental details for the 64Zn(d,t)63Zn transfer work presented.

  15. Methods of flash sintering

    DOEpatents

    Raj, Rishi; Cologna, Marco; Francis, John S.

    2016-05-10

    This disclosure provides methods of flash sintering and compositions created by these methods. Methods for sintering multilayered bodies are provided in which a sintered body is produced in less than one minute. In one aspect, each layer is of a different composition, and may be constituted wholly from a ceramic or from a combination of ceramic and metallic particles. When the body includes a layer of an anode composition, a layer of an electrolyte composition and a layer of a cathode composition, the sintered body can be used to produce a solid oxide fuel cell.

  16. Evaluation of sintering effects on SiC-incorporated UO2 kernels under Ar and Ar-4%H2 environments

    NASA Astrophysics Data System (ADS)

    Silva, Chinthaka M.; Lindemer, Terrence B.; Hunt, Rodney D.; Collins, Jack L.; Terrani, Kurt A.; Snead, Lance L.

    2013-11-01

    Silicon carbide (SiC) is suggested as an oxygen getter in UO2 kernels used for tristructural isotropic (TRISO) particle fuels and to prevent kernel migration during irradiation. Scanning electron microscopy and X-ray diffractometry analyses performed on sintered kernels verified that an internal gelation process can be used to incorporate SiC in UO2 fuel kernels. Even though the presence of UC in either argon (Ar) or Ar-4%H2 sintered samples suggested a lowering of the SiC up to 3.5-1.4 mol%, respectively, the presence of other silicon-related chemical phases indicates the preservation of silicon in the kernels during sintering process. UC formation was presumed to occur by two reactions. The first was by the reaction of SiC with its protective SiO2 oxide layer on SiC grains to produce volatile SiO and free carbon that subsequently reacted with UO2 to form UC. The second process was direct UO2 reaction with SiC grains to form SiO, CO, and UC. A slightly higher density and UC content were observed in the sample sintered in Ar-4%H2, but both atmospheres produced kernels with ˜95% of theoretical density. It is suggested that incorporating CO in the sintering gas could prevent UC formation and preserve the initial SiC content.

  17. Enantioselective desymmetrization of prochiral cyclohexanone derivatives via the organocatalytic direct Aldol reaction.

    PubMed

    Jiang, Jun; He, Long; Luo, Shi-Wei; Cun, Lin-Feng; Gong, Liu-Zhu

    2007-02-21

    Asymmetric desymmetrization of 4-substituted cyclohexanones using proline amide-catalyzed direct aldol reaction afforded beta-hydroxyketones with three stereogenic centers in high enantioselectivities of up to >99% ee.

  18. Sintered wire cesium dispenser photocathode

    DOEpatents

    Montgomery, Eric J; Ives, R. Lawrence; Falce, Louis R

    2014-03-04

    A photoelectric cathode has a work function lowering material such as cesium placed into an enclosure which couples a thermal energy from a heater to the work function lowering material. The enclosure directs the work function lowering material in vapor form through a low diffusion layer, through a free space layer, and through a uniform porosity layer, one side of which also forms a photoelectric cathode surface. The low diffusion layer may be formed from sintered powdered metal, such as tungsten, and the uniform porosity layer may be formed from wires which are sintered together to form pores between the wires which are continuous from the a back surface to a front surface which is also the photoelectric surface.

  19. Fundamental studies of retrograde reactions in direct liquefaction. Topical report, September 30, 1988--September 30, 1989

    SciTech Connect

    Serio, M.A.; Solomon, P.R.; Bassilakis, R.; Kroo, E.

    1989-12-31

    Most of the proposed processing schemes for improving liquefaction yields involve favoring bond-breaking and radical stabilization reactions over the retrograde reactions. The retrograde reactions are often encountered before liquefaction temperatures are reached. The objective of this program is to elucidate and model the retrograde reaction chemistry in direct coal liquefaction through the application of experimental techniques and theoretical models which have been successfully employed at Advanced Fuel Research (AFR) and SRI International (a subcontractor) to understand and predict coal reaction behavior. The study of retrograde reactions is being done using an integrated approach using extensive characterization of the liquefaction chemistry of three kinds of systems: (1) model polymers; (2) coal; and (3) modified coals.

  20. Reaction cross sections for two direct simulation Monte Carlo models: Accuracy and sensitivity analysis

    NASA Astrophysics Data System (ADS)

    Wysong, Ingrid; Gimelshein, Sergey; Gimelshein, Natalia; McKeon, William; Esposito, Fabrizio

    2012-04-01

    The quantum kinetic chemical reaction model proposed by Bird for the direct simulation Monte Carlo method is based on collision kinetics with no assumed Arrhenius-related parameters. It demonstrates an excellent agreement with the best estimates for thermal reaction rates coefficients and with two-temperature nonequilibrium rate coefficients for high-temperature air reactions. This paper investigates this model further, concentrating on the non-thermal reaction cross sections as a function of collision energy, and compares its predictions with those of the earlier total collision energy model, also by Bird, as well as with available quasi-classical trajectory cross section predictions (this paper also publishes for the first time a table of these computed reaction cross sections). A rarefied hypersonic flow over a cylinder is used to examine the sensitivity of the number of exchange reactions to the differences in the two models under a strongly nonequilibrium velocity distribution.

  1. Microstructural and continuum evolution modeling of sintering.

    SciTech Connect

    Braginsky, Michael V.; Olevsky, Eugene A.; Johnson, D. Lynn; Tikare, Veena; Garino, Terry J.; Arguello, Jose Guadalupe, Jr.

    2003-12-01

    deformation during. The continuum portion is based on a finite element formulation that allows 3D components to be modeled using SNL's nonlinear large-deformation finite element code, JAS3D. This tool provides a capability to model sintering of complex three-dimensional components. The model was verified by comparing to simulations results published in the literature. The model was validated using experimental results from various laboratory experiments performed by Garino. In addition, the mesoscale simulations were used to study anisotropic shrinkage in aligned, elongated powder compacts. Anisotropic shrinkage occurred in all compacts with aligned, elongated particles. However, the direction of higher shrinkage was in some cases along the direction of elongation and in other cases in the perpendicular direction depending on the details of the powder compact. In compacts of simple-packed, mono-sized, elongated particles, shrinkage was higher in the direction of elongation. In compacts of close-packed, mono-sized, elongated particles and of elongated particles with a size and shape distribution, the shrinkage was lower in the direction of elongation. We also explored the concept of a sintering stress tensor rather than the traditional sintering stress scalar concept for the case of anisotropic shrinkage. A thermodynamic treatment of this is presented. A method to calculate the sintering stress tensor is also presented. A user-friendly code that can simulate microstructural evolution during sintering in 2D and in 3D was developed. This code can run on most UNIX platforms and has a motif-based GUI. The microstructural evolution is shown as the code is running and many of the microstructural features, such as grain size, pore size, the average grain boundary length (in 2D) and area (in 3D), etc. are measured and recorded as a function of time. The overall density as the function of time is also recorded.

  2. Sintering titanium powders

    SciTech Connect

    Gerdemann, Stephen J.; Alman, David E.

    2005-09-01

    Recently, there has been renewed interest in low-cost titanium. Near-net-shape powder metallurgy offers the potential of manufacturing titanium articles without costly and difficult forming and machining operations; hence, processing methods such as conventional press-and-sinter, powder forging and powder injection molding are of interest. The sintering behavior of a variety of commercial and experimental titanium powders was studied. Commercial powders were acquired that were produced different routes: (i) sponge fines from the primary titanium processing; (ii) via the hydride-dehydride process; and (iii) gas atomization. The influence of vacuum sintering time (0.5 to 32 hrs) and temperature (1200, 1275 or 1350°C) on the microstructure (porosity present) of cold pressed powders was studied. The results are discussed in terms of the difference in powder characteristics, with the aim of identify the characteristics required for full density via press-and-sinter processing. Near-net-shape tensile bars were consolidated via cold pressed and sintered. After sintering, a sub-set of the tensile bars was hot-isostatic pressed (HIPed). The microstructure and properties of the bars were compared in the sintered and HIPed conditions.

  3. Microwave sintering of ceramics

    SciTech Connect

    Snyder, W.B.

    1989-01-01

    Successful adaptation of microwave heating to the densification of ceramic materials require a marriage of microwave and materials technologies. Using an interdisciplinary team of microwave and materials engineers, we have successfully demonstrated the ability to density ceramic materials over a wide range of temperatures. Microstructural evolution during microwave sintering has been found to be significantly different from that observed in conventional sintering. Our results and those of others indicate that microwave sintering has the potential to fabricate components to near net shape with mechanical properties equivalent to hot pressed or hot isostatically pressed material. 6 refs., 11 figs.

  4. SINTERED REFRACTORY MASS

    DOEpatents

    Williams, A.E.

    1955-09-01

    A method is given for joining sintered masses of refractory compounds. It consists in maintaining the masses in contact with each other by application of a moderate pressure, while they are at sintering temperature. The sintered masses are subjected to am applied pressure of about 1/2 to 1 ton per square inch of the surface in contact for about 10 minutes, and the temperature employed may be fropn about 1400 deg C to 2000 deg C. Refractory oxides to which the invention may be applied are beryllia, alumina, thoria, and magnesia.

  5. Sintered superhard materials.

    PubMed

    Wentorf, R H; Devries, R C; Bundy, F P

    1980-05-23

    Diamond or cubic boron nitride particles can be sintered into strong masses at high temperatures and very high pressures at which these crystalline forms are stable. Most of the desirable physical properties of the sintered masses, such as hardness and thermal conductivity, approach those of large single crystals; their resistance to wear and catastrophic splitting is superior. The sintered masses are produced on a commercial scale and are increasingly used as cutting tools on hard or abrasive materials, as wire-drawing dies, in rock drills, and in special high-pressure apparatus.

  6. Sintered superhard materials

    SciTech Connect

    Wentorf, R.H.; DeVries, R.C.; Bundy, F.P.

    1980-01-01

    Diamond of cubic boron nitride particles can be sintered into strong masses at high temperatures and very high pressures at which these crystalline forms are stable. Most of the desirable physical properties of the sintered masses, such as hardness and thermal conductivity, approach those of large single crystals; their resistance to wear and catastrophic splitting is superior. The sintered masses are produced on a commercial scale and are increasingly used as cutting tools on hard or abrasive materials, as wire-drawing dies, in rock drills, and in special high-pressure apparatus.

  7. Ferritin reactions: direct identification of the site for the diferric peroxide reaction intermediate.

    PubMed

    Liu, Xiaofeng; Theil, Elizabeth C

    2004-06-08

    Ferritins managing iron-oxygen biochemistry in animals, plants, and microorganisms belong to the diiron carboxylate protein family and concentrate iron as ferric oxide approximately 10(14) times above the ferric K(s). Ferritin iron (up to 4,500 atoms), used for iron cofactors and heme, or to trap DNA-damaging oxidants in microorganisms, is concentrated in the protein nanocage cavity (5-8 nm) formed during assembly of polypeptide subunits, 24 in maxiferritins and 12 in miniferritins/DNA protection during starvation proteins. Direct identification of ferritin ferroxidase (F(ox)) sites, complicated by multiple types of iron-ferritin interactions, is now achieved with chimeric proteins where putative F(ox) site residues were introduced singly and cumulatively into an inactive host, an L maxiferritin. A dimagnesium ferritin cocrystal model guided site design and the diferric peroxo F(ox) intermediates (A at 650 nm) monitored activity. Diferric peroxo formation in chimeric and WT proteins had similar K(app) values and Hill coefficients. Catalytic activity required cooperative ferrous substrate binding to two sites A (E, EXXH) and B (E, QXXD). The weaker B sites in ferritin contrast with stronger B sites (E, EXXH) in diiron carboxylate oxygenases, explaining diferric oxo/hydroxo product release in ferritin vs. diiron cofactor retention in oxygenases. Codons for Q/H and D/E differ by single nucleotides, suggesting simple DNA mutations relate site B diiron substrate sites and diiron cofactor sites in proteins. The smaller k(cat) values in chimeras indicate the absence of second-shell residues important for ferritin substrate-product channeling that, when identified, will outline the entire iron path from ferritin pores through the F(ox) site to the mineral cavity.

  8. Microwave sintering of ceramic materials

    NASA Astrophysics Data System (ADS)

    Karayannis, V. G.

    2016-11-01

    In the present study, the potential of microwave irradiation as an innovative energy- efficient alternative to conventional heating technologies in ceramic manufacturing is reviewed, addressing the advantages/disadvantages, while also commenting on future applications of possible commercial interest. Ceramic materials have been extensively studied and used due to several advantages they exhibit. Sintering ceramics using microwave radiation, a novel technology widely employed in various fields, can be an efficient, economic and environmentally-friendlier approach, to improve the consolidation efficiency and reduce the processing cycle-time, in order to attain substantial energy and cost savings. Microwave sintering provides efficient internal heating, as energy is supplied directly and penetrates the material. Since energy transfer occurs at a molecular level, heat is generated throughout the material, thus avoiding significant temperature gradients between the surface and the interior, which are frequently encountered at high heating rates upon conventional sintering. Thus, rapid, volumetric and uniform heating of various raw materials and secondary resources for ceramic production is possible, with limited grain coarsening, leading to accelerated densification, and uniform and fine-grained microstructures, with enhanced mechanical performance. This is particularly important for manufacturing large-size ceramic products of quality, and also for specialty ceramic materials such as bioceramics and electroceramics. Critical parameters for the process optimization, including the electromagnetic field distribution, microwave-material interaction, heat transfer mechanisms and material transformations, should be taken into consideration.

  9. Analysis of weblike network structures of directed graphs for chemical reactions in methane plasmas

    SciTech Connect

    Sakai, Osamu Nobuto, Kyosuke; Miyagi, Shigeyuki; Tachibana, Kunihide

    2015-10-15

    Chemical reactions of molecular gases like methane are so complicated that a chart of decomposed and/or synthesized species originating from molecules in plasma resembles a weblike network in which we write down species and reactions among them. Here we consider properties of the network structures of chemical reactions in methane plasmas. In the network, atoms/molecules/radical species are assumed to form nodes and chemical reactions correspond to directed edges in the terminology of graph theory. Investigation of the centrality index reveals importance of CH{sub 3} in the global chemical reaction, and difference of an index for each radical species between cases with and without electrons clarifies that the electrons are at an influential position to tighten the network structure.

  10. The Trojan Horse method for nuclear astrophysics: Recent results for direct reactions

    SciTech Connect

    Tumino, A.; Gulino, M.; Spitaleri, C.; Cherubini, S.; Romano, S.; Cognata, M. La; Pizzone, R. G.; Rapisarda, G. G.; Lamia, L.

    2014-05-09

    The Trojan Horse method is a powerful indirect technique to determine the astrophysical factor for binary rearrangement processes A+x→b+B at astrophysical energies by measuring the cross section for the Trojan Horse (TH) reaction A+a→B+b+s in quasi free kinematics. The Trojan Horse Method has been successfully applied to many reactions of astrophysical interest, both direct and resonant. In this paper, we will focus on direct sub-processes. The theory of the THM for direct binary reactions will be shortly presented based on a few-body approach that takes into account the off-energy-shell effects and initial and final state interactions. Examples of recent results will be presented to demonstrate how THM works experimentally.

  11. Catalytic asymmetric direct-type 1,4-addition reactions of simple amides.

    PubMed

    Suzuki, Hirotsugu; Sato, Io; Yamashita, Yasuhiro; Kobayashi, Shū

    2015-04-08

    The development of catalytic asymmetric direct-type reactions of less acidic carbonyl compounds such as amides and esters has been a challenging theme in organic chemistry for decades. Here we describe the asymmetric direct 1,4-addition reactions of simple amides with α,β-unsaturated carbonyl compounds using a catalytic amount of a novel chiral catalyst consisting of a potassium base and a macrocyclic chiral crown ether. The desired 1,5-dicarbonyl compounds were obtained in high yields with excellent diastereo- and enantioselectivities. This is the first example of a highly enantioselective catalytic direct-type reaction of simple amides. In addition, the structure of the chiral potassium catalyst has been investigated by X-ray crystallographic, dynamic (1)H NMR, and MALDI-TOF MS analyses.

  12. Sintered wire annode

    DOEpatents

    Falce, Louis R.; Ives, R. Lawrence

    2007-12-25

    A plurality of high atomic number wires are sintered together to form a porous rod that is parted into porous disks which will be used as x-ray targets. A thermally conductive material is introduced into the pores of the rod, and when a stream of electrons impinges on the sintered wire target and generates x-rays, the heat generated by the impinging x-rays is removed by the thermally conductive material interspersed in the pores of the wires.

  13. Fabrication of 200 mm Diameter Sintering Body of Skutterudite Thermoelectric Material by Spark Plasma Sintering

    NASA Astrophysics Data System (ADS)

    Tomida, T.; Sumiyoshi, A.; Nie, G.; Ochi, T.; Suzuki, S.; Kikuchi, M.; Mukaiyama, K.; Guo, J. Q.

    2016-11-01

    Filled skutterudite is a promising material for thermoelectric power generation because its ZT value is relatively high. However, mass production of high-performance thermoelectric materials remains a challenge. This study focused on the sintering process of thermoelectric materials. Large-diameter n-type (Yb or La, Ca, Al, Ga, In)0.8(Co, Fe)4Sb12 skutterudite sintering bodies with a small thickness were successfully produced by the spark plasma sintering (SPS) method. When direct current flows through the thermoelectric sintering body during the SPS pulse, the Peltier effect causes a temperature difference within the sintering body. To eliminate the Peltier effect, an electrical insulating material was inserted between the punch (electrode) and the sintering body. In this way, an n-type La-filled skutterudite sample with a diameter of 200 mm, thickness of 21 mm, and weight of 5 kg was successfully produced. The thermoelectric properties and microstructures of the sample were almost the same throughout the whole sintering body, and the dimensionless figure of merit reached 1.0 at 773 K.

  14. Noncovalent Substrate-Directed Enantioselective Heck Reactions: Synthesis of S- and P-Stereogenic Heterocycles.

    PubMed

    de Azambuja, Francisco; Carmona, Rafaela C; Chorro, Tomaz H D; Heerdt, Gabriel; Correia, Carlos Roque D

    2016-08-01

    S- and P-Stereogenic heterocycles were synthesized by a remarkably simple enantioselective Heck desymmetrization reaction based on the unprecedented noncovalent directing effect of S=O and P=O functionalities. Selected prochiral symmetric substrates were efficiently arylated using the recently disclosed chiral PyraBOx ligand under mild and open-flask reaction conditions. Several five-membered aryl- sulfones, sulfoxides, and phosphine oxides were synthesized in good to excellent yields, in good to high diastereoselectivity, and enantiomeric ratios up to 98:2. Theoretical calculations also support the noncovalent directing effect of the S=O and P=O functionalities during the arylation process.

  15. Investigation of photochemical reaction products of glucose formed during direct UV detection in CE.

    PubMed

    Schmid, Thomas; Himmelsbach, Markus; Buchberger, Wolfgang W

    2016-04-01

    In CE, saccharides are accessible to direct UV detection due to a photochemical reaction in the detection window of the separation capillary resulting in the formation of UV absorbing substances. Employing a CE method that allows long in-capillary irradiation with subsequent UV and MS detection, the present study could identify several reaction products of glucose. Among these were UV absorbing substances so far unknown to be formed during direct UV detection with the chemical formulas C4 H6 O2 , C5 H6 O4 , C5 H8 O3, and C6 H8 O5 . Investigations of the impact of the irradiation time revealed differences between these reaction products suggesting differing reaction mechanisms especially for the smallest products. More detailed information could be obtained by experiments with isotope-labeled substrates performed to determine the parts of glucose that are converted to the particular reaction products. In addition, structural formulas for the reaction products were suggested based on HPLC-MS/MS measurements of off-line irradiated glucose solutions which revealed the existence of functional groups such as carboxylic acid or aldehyde groups.

  16. Acylsilanes in Iridium-Catalyzed Directed Amidation Reactions and Formation of Heterocycles via Siloxycarbenes.

    PubMed

    Becker, Peter; Pirwerdjan, Ramona; Bolm, Carsten

    2015-12-14

    Exposing ortho-amido aroylsilanes to visible light or heat leads to cyclization reactions that provide N-heterocyclic compounds via siloxycarbenes as key intermediates. The previously unreported starting materials have been prepared by directed amidations of aromatic acylsilanes in the presence of an iridium catalyst followed by N-alkylation.

  17. Some acyclic analogues of nucleotides and their template-directed reactions

    NASA Technical Reports Server (NTRS)

    Tohidi, Mahrokh; Orgel, Leslie E.

    1989-01-01

    Bismonophosphoimidazolides of acyclic analogues of guanosine IV and adenosine V were synthesized. They undergo oligomerization in the presence of complementary polynucleotide templates. Details of their synthesis and their subsequent template- and nontemplate-directed reactions are described, and their possible relevance to the origin of life is discussed.

  18. Online mutability of step direction during rapid stepping reactions evoked by postural perturbation.

    PubMed

    Tripp, Bryan P; McIlroy, William E; Maki, Brian E

    2004-03-01

    Stepping reactions are often triggered rapidly in response to loss of balance. It has been unclear whether spatial step parameters are defined at time of step-initiation or whether they can be modulated online, during step execution, in response to sensory feedback about the evolving state of instability. This study explored the capacity to actively alter step direction subsequent to step initiation in six healthy young-adult subjects. To elicit forward-step reactions, subjects were released suddenly from a tethered forward lean. A second perturbation (medio-lateral support-surface translation) was applied at lags of 0-200 ms. Active reaction to the second perturbation was determined primarily through analysis of swing-leg hip-abductor activation. In addition, to gauge the biomechanical consequence of the changes in muscle activation, we compared the measured medio-lateral swing-foot displacement to that predicted by a simple passive mechanical model. Perturbations at 0-100 ms lag evoked active medio-lateral swing-foot deviation, allowing balance to be recovered with a single step. However, when the second perturbation occurred near foot-off (200-ms lag), there was no evidence of active alteration of step direction and subjects typically required additional steps to recover balance. The results suggest that step direction can be reparameterized during early stages of stepping reactions, but that step direction was not actively modulated in response to perturbation arising near start of swing phase.

  19. Expanding the enzyme universe: accessing non-natural reactions by mechanism-guided directed evolution.

    PubMed

    Renata, Hans; Wang, Z Jane; Arnold, Frances H

    2015-03-09

    High selectivity and exquisite control over the outcome of reactions entice chemists to use biocatalysts in organic synthesis. However, many useful reactions are not accessible because they are not in nature's known repertoire. In this Review, we outline an evolutionary approach to engineering enzymes to catalyze reactions not found in nature. We begin with examples of how nature has discovered new catalytic functions and how such evolutionary progression has been recapitulated in the laboratory starting from extant enzymes. We then examine non-native enzyme activities that have been exploited for chemical synthesis, with an emphasis on reactions that do not have natural counterparts. Non-natural activities can be improved by directed evolution, thus mimicking the process used by nature to create new catalysts. Finally, we describe the discovery of non-native catalytic functions that may provide future opportunities for the expansion of the enzyme universe.

  20. Electrical Property of Conventionally Sintered ZnO

    NASA Astrophysics Data System (ADS)

    Tak, S. K.; Shekhwat, M. S.; Mangal, R.

    ZnO powder was synthesized by solid state reaction method. The synthesized powder was granulated and pressed using uni-axial press for preparing the pallets. The prepared pellets were sintered in conventional furnace at different temperatures (900-1300° C). The phase study was done by powder X-ray diffraction and it was found that the there is no other phase present in the synthesized material but the peak intensity is increasing with temperature. The crystallite size of the synthesized ZnO powder was found to be increase with temperature. The effect of sintering on grain growth is investigated by scanning electron microscopy (SEM). SEM revels that the average grain size is increases with increase in sintering temperature. AC impedance of these samples was decreased markedly with increased sintering temperature. In present work the effect of sintering temperatures and hold time on micro structural and electrical properties of ZnO ceramics is carried out.

  1. Reduction reaction analysis of nanoparticle copper oxide for copper direct bonding using formic acid

    NASA Astrophysics Data System (ADS)

    Fujino, Masahisa; Akaike, Masatake; Matsuoka, Naoya; Suga, Tadatomo

    2017-04-01

    Copper direct bonding is required for electronics devices, especially power devices, and copper direct bonding using formic acid is expected to lower the bonding temperature. In this research, we analyzed the reduction reaction of copper oxide using formic acid with a Pt catalyst by electron spin resonance analysis and thermal gravimetry analysis. It was found that formic acid was decomposed and radicals were generated under 200 °C. The amount of radicals generated was increased by adding the Pt catalyst. Because of these radicals, both copper(I) oxide and copper(II) oxide start to be decomposed below 200 °C, and the reduction of copper oxide is accelerated by reactants such as H2 and CO from the decomposition of formic acid above 200 °C. The Pt catalyst also accelerates the reaction of copper oxide reduction. Herewith, it is considered that the copper surface can be controlled more precisely by using formic acid to induce direct bonding.

  2. Field assisted sintering of ceramic materials

    NASA Astrophysics Data System (ADS)

    Stanciu, Lia Antoaneta

    2003-06-01

    The objective of this dissertation is to provide an understanding of the processing mechanisms of ceramic materials under an electrical field. Different parameters of the process, such as the electrical field, the heating rate, the holding time, and the precursor powder characteristics are studied in connection with their individual effect on the microstructural evolution and properties. The work reviews the fundamentals of sintering in the presence and in the absence of an electrical field, electrical conductivity in ceramics, precursor powder preparation methods for ceramic processing, as well as the relationship between the thermal properties and the neck formation in the first sintering stage. The ceramic materials that are chosen for the sintering studies are: Al2O3, TiO2, Al2TiO5 and MoSi2. Two type of precursors are used for the studies on Al 2TiO5: an amorphous sol-gel nanosize, and a crystalline coprecipitated micron size powder. Comparative studies on the effect of the heating rates in FAST on the conductive MoSi2 versus non-conductive Al2 O3 are also presented. The initial sintering stages of alpha-Al 2O3, which displays the maximum sintering activity under electrical field, are studied by a thermo-optical measurement method (TOM). The TOM method measures in-situ the thermal diffusivity of the powder. All the materials are characterized after sintering by XRD, FTIR, SEM, TEM, density and thermal diffusivity by TOM. The results show that the electrical field application enhances the kinetics of non-conductive oxide ceramics (Al2TiO5) formation by reaction sintering of the individual oxides. It also increases the rate of the neck formation during first sintering stage, and reduces porosity, thus improving the final density of non-conductive Al2O3. The sol-gel precursor powders with nanosize particles and a higher degree of homogeneity result in improved densification of the final consolidated part as compared to micron size or mechanically mixed precursors

  3. Evaluation of sintering effects on SiC incorporated UO2 kernels under Ar and Ar-4%H2 environments

    SciTech Connect

    Silva, Chinthaka M; Lindemer, Terrence; Hunt, Rodney Dale; Collins, Jack Lee; Terrani, Kurt A; Snead, Lance Lewis

    2013-01-01

    Silicon carbide (SiC) is suggested as an oxygen getter in UO2 kernels used for TRISO particle fuels to lower oxygen potential and prevent kernel migration during irradiation. Scanning electron microscopy and X-ray diffractometry analyses performed on sintered kernels verified that internal gelation process can be used to incorporate SiC in urania fuel kernels. Sintering in either Ar or Ar-4%H2 at 1500 C lowered the SiC content in the UO2 kernels to some extent. Formation of UC was observed as the major chemical phase in the process, while other minor phases such as U3Si2C2, USi2, U3Si2, and UC2 were also identified. UC formation was presumed to be occurred by two reactions. The first was the SiC reaction with its protective SiO2 oxide layer on SiC grains to produce volatile SiO and free carbon that subsequently reacted with UO2 to form UC. The second process was direct UO2 reaction with SiC grains to form SiO, CO, and UC, especially in Ar-4%H2. A slightly higher density and UC content was observed in the sample sintered in Ar-4%H2, but the use of both atmospheres produced kernels with ~95% of theoretical density. It is suggested that incorporating CO in the sintering gas would prevent UC formation and preserve the initial SiC content.

  4. Sintering of calcium phosphate bioceramics.

    PubMed

    Champion, E

    2013-04-01

    Calcium phosphate ceramics have become of prime importance for biological applications in the field of bone tissue engineering. This paper reviews the sintering behaviour of these bioceramics. Conventional pressureless sintering of hydroxyapatite, Ca10(PO4)6(OH)2, a reference compound, has been extensively studied. Its physico-chemistry is detailed. It can be seen as a competition between two thermally activated phenomena that proceed by solid-state diffusion of matter: densification and grain growth. Usually, the objective is to promote the first and prevent the second. Literature data are analysed from sintering maps (i.e. grain growth vs. densification). Sintering trajectories of hydroxyapatite produced by conventional pressureless sintering and non-conventional techniques, including two-step sintering, liquid phase sintering, hot pressing, hot isostatic pressing, ultrahigh pressure, microwave and spark plasma sintering, are presented. Whatever the sintering technique may be, grain growth occurs mainly during the last step of sintering, when the relative bulk density reaches 95% of the maximum value. Though often considered very advantageous, most assisted sintering techniques do not appear very superior to conventional pressureless sintering. Sintering of tricalcium phosphate or biphasic calcium phosphates is also discussed. The chemical composition of calcium phosphate influences the behaviour. Similarly, ionic substitutions in hydroxyapatite or in tricalcium phosphate create lattice defects that modify the sintering rate. Depending on their nature, they can either accelerate or slow down the sintering rate. The thermal stability of compounds at the sintering temperature must also be taken into account. Controlled atmospheres may be required to prevent thermal decomposition, and flash sintering techniques, which allow consolidation at low temperature, can be helpful.

  5. Bond selectivity in electron-induced reaction due to directed recoil on an anisotropic substrate

    NASA Astrophysics Data System (ADS)

    Anggara, Kelvin; Huang, Kai; Leung, Lydie; Chatterjee, Avisek; Cheng, Fang; Polanyi, John C.

    2016-12-01

    Bond-selective reaction is central to heterogeneous catalysis. In heterogeneous catalysis, selectivity is found to depend on the chemical nature and morphology of the substrate. Here, however, we show a high degree of bond selectivity dependent only on adsorbate bond alignment. The system studied is the electron-induced reaction of meta-diiodobenzene physisorbed on Cu(110). Of the adsorbate's C-I bonds, C-I aligned `Along' the copper row dissociates in 99.3% of the cases giving surface reaction, whereas C-I bond aligned `Across' the rows dissociates in only 0.7% of the cases. A two-electronic-state molecular dynamics model attributes reaction to an initial transition to a repulsive state of an Along C-I, followed by directed recoil of C towards a Cu atom of the same row, forming C-Cu. A similar impulse on an Across C-I gives directed C that, moving across rows, does not encounter a Cu atom and hence exhibits markedly less reaction.

  6. Direct measurement of the 22Ne(p,γ)23Na reaction cross section at LUNA

    NASA Astrophysics Data System (ADS)

    Ferraro, Federico; LUNA Collaboration

    2016-06-01

    The 22Ne(p, γ)23Na reaction takes part in the NeNa cycle of hydrogen burning, influencing the production of the elements between 20Ne and 27Al in red giant stars, asymptotic giant stars and classical novae. The 22Ne(p,γ)27Na reaction rate is very uncertain because of a large number of tentative resonances in the Gamow window, where only upper limits were quoted in literature. A direct measurement of the 22Ne(p, γ)23Na reaction cross section has been carried out at LUNA using a windowless differential-pumping gas target with two high- purity germanium (HPGe) detectors. A new measurement with a 4π bismuth germanate (BGO) summing detector is ongoing. During the HPGe phase of the experiment the strengths of the resonances at 156.2 keV, 189.5 keV and 259.7 keV have been directly measured for the first time and their contribution to the reaction rate has been calculated. The decay scheme of the newly discovered resonances has been established as well and some improved upper limits on the unobserved resonances have been put. The BGO detector with its 70% γ-detection efficiency allows to measure the cross section at lower energy. In order to further investigate the resonances at 71 keV and 105 keV and the direct-capture component, the data taking is ongoing.

  7. Direct detection of pyridine formation by the reaction of CH (CD) with pyrrole: a ring expansion reaction

    SciTech Connect

    Soorkia, Satchin; Taatjes, Craig A.; Osborn, David L.; Selby, Talitha M.; Trevitt, Adam J.; Wilson, Kevin R.; Leone, Stephen R.

    2010-03-16

    The reaction of the ground state methylidyne radical CH (X2Pi) with pyrrole (C4H5N) has been studied in a slow flow tube reactor using Multiplexed Photoionization Mass Spectrometry coupled to quasi-continuous tunable VUV synchrotron radiation at room temperature (295 K) and 90 oC (363 K), at 4 Torr (533 Pa). Laser photolysis of bromoform (CHBr3) at 248 nm (KrF excimer laser) is used to produce CH radicals that are free to react with pyrrole molecules in the gaseous mixture. A signal at m/z = 79 (C5H5N) is identified as the product of the reaction and resolved from 79Br atoms, and the result is consistent with CH addition to pyrrole followed by Helimination. The Photoionization Efficiency curve unambiguously identifies m/z = 79 as pyridine. With deuterated methylidyne radicals (CD), the product mass peak is shifted by +1 mass unit, consistent with the formation of C5H4DN and identified as deuterated pyridine (dpyridine). Within detection limits, there is no evidence that the addition intermediate complex undergoes hydrogen scrambling. The results are consistent with a reaction mechanism that proceeds via the direct CH (CD) cycloaddition or insertion into the five-member pyrrole ring, giving rise to ring expansion, followed by H atom elimination from the nitrogen atom in the intermediate to form the resonance stabilized pyridine (d-pyridine) molecule. Implications to interstellar chemistry and planetary atmospheres, in particular Titan, as well as in gas-phase combustion processes, are discussed.

  8. Sintering of Synroc D

    SciTech Connect

    Robinson, G.

    1982-06-01

    Sintering has been investigated as a method for the mineralization and densification of high-level nuclear defense waste powder. Studies have been conducted on Synroc D composite powder LS04. Optimal densification has been found to be highly dependent on the characteristics of the starting material. Powder subjected to milling, which was believed to reduce the level of agglomeration and possibly particle size, was found to densify better than powder not subjected to this milling. Densities of greater than 95% of theoretical could be achieved for samples sintered at 1150 to 1200/sup 0/C. Mineralogy was found to be as expected for Synroc D for samples sintered in a CO/sub 2//CO atmosphere where the Fe/sup +2//Fe/sup +3/ ratio was maintained at 1.0 to 5.75. In a more oxidizing, pure CO/sub 2/ atmosphere a new phase, not previously identified in Synroc D, was found.

  9. Direct observation of ferromagnetism in grain boundary phase of Nd-Fe-B sintered magnet using soft x-ray magnetic circular dichroism

    SciTech Connect

    Nakamura, T.; Yasui, A.; Kotani, Y.; Iwai, H.; Akiya, T.; Ohkubo, T.; Hono, K.; Hirosawa, S.; Gohda, Y.

    2014-11-17

    We have investigated the magnetism of the grain boundary (GB) phase in a Nd{sub 14.0}Fe{sub 79.7}Cu{sub 0.1}B{sub 6.2} sintered magnet using soft x-ray magnetic circular dichroism (XMCD) at the Fe L{sub 2,3}-edges. Soft XMCD spectra were measured from the fractured surface that was confirmed to be covered with a thin GB phase by Auger electron spectroscopy. The magnetic moment of Fe in the GB phase was estimated to be m{sub GB}=1.4 μ{sub B} at 30 °C using the sum rule analysis for XMCD spectra, which is 60% of that of Fe in the Nd{sub 2}Fe{sub 14}B compound. The temperature dependence of m{sub GB} evaluated with reference to Fe in the Nd{sub 2}Fe{sub 14}B phase indicated that the Curie temperature of the GB phase is more than 50 °C lower compared to that of Nd{sub 2}Fe{sub 14}B.

  10. Network structural analysis using directed graph for chemical reaction analysis in weakly-ionized plasmas

    NASA Astrophysics Data System (ADS)

    Nobuto, Kyosuke; Mizui, Yasutaka; Miyagi, Shigeyuki; Sakai, Osamu; Murakami, Tomoyuki

    2016-09-01

    We visualize complicated chemical reaction systems in weakly-ionized plasmas by analysing network structure for chemical processes, and calculate some indexes by assuming interspecies relationships to be a network to clarify them. With the current social evolution, the mean size of general data which we can use in computers grows huge, and significance of the data analysis increases. The methods of the network analysis which we focus on in this study do not depend on a specific analysis target, but the field where it has been already applied is still limited. In this study, we analyse chemical reaction systems in plasmas for configuring the network structure. We visualize them by expressing a reaction system in a specific plasma by a directed graph and examine the indexes and the relations with the characteristic of the species in the reaction system. For example, in the methane plasma network, the centrality index reveals importance of CH3 in an influential position of species in the reaction. In addition, silane and atmospheric pressure plasmas can be also visualized in reaction networks, suggesting other characteristics in the centrality indexes.

  11. Atmospheric chemistry. Direct kinetic measurement of the reaction of the simplest Criegee intermediate with water vapor.

    PubMed

    Chao, Wen; Hsieh, Jun-Ting; Chang, Chun-Hung; Lin, Jim Jr-Min

    2015-02-13

    Carbonyl oxides, or Criegee intermediates, are important transient species formed in the reactions of unsaturated hydrocarbons with ozone. Although direct detection of Criegee intermediates has recently been realized, the main atmospheric sink of Criegee intermediates remains unclear. We report ultraviolet absorption spectroscopic measurements of the lifetime of the simplest Criegee intermediate, CH2OO, at various relative humidity levels up to 85% at 298 kelvin. An extremely fast decay rate of CH2OO was observed at high humidity. The observed quadratic dependence of the decay rate on water concentration implied a predominant reaction with water dimer. On the basis of the water dimer equilibrium constant, the effective rate coefficient of the CH2OO + (H2O)2 reaction was determined to be 6.5 (±0.8) × 10(-12) cubic centimeters per second. This work would help modelers to better constrain the atmospheric concentrations of CH2OO.

  12. DIRECT COMPARISON OF KINETIC AND LOCAL EQUILIBRIUM FORMULATIONS FOR SOLUTE TRANSPORT AFFECTED BY SURFACE REACTIONS.

    USGS Publications Warehouse

    Bahr, Jean M.; Rubin, Jacob

    1987-01-01

    Modeling transport of reacting solutes in porous media often requires a choice between models based on the local equilibrium assumption (LEA) and models involving reaction kinetics. Direct comparison of the mathematical formulations for these two types of transport models can aid in this choice. For cases of transport affected by surface reaction, such a comparison is made possible by a new derivation procedure. This procedure yields a kinetics-based formulation that is the sum of the LEA formulation and one or more kinetically influenced terms. The dimensionless form of the new kinetics-based formulation facilitates identification of critical parameter groupings which control the approach to transport behavior consistent with LEA model predictions. Results of numerical experiments demonstrate that criteria for LEA applicability can be expressed conveniently in terms of these parameter groupings. The derivation procedure is demonstrated for examples of surface reactions including first-order reversible sorption, Langmuir-type kinetics and binary, homovalent ion exchange.

  13. Synthetic Studies on Tricyclic Diterpenoids: Direct Allylic Amination Reaction of Isopimaric Acid Derivatives†

    PubMed Central

    Timoshenko, Mariya A.; Kharitonov, Yurii V.; Shakirov, Makhmut M.; Bagryanskaya, Irina Yu.

    2015-01-01

    Abstract A selective synthesis of 7‐ or 14‐nitrogen containing tricyclic diterpenoids was completed according to a strategy in which the key step was the catalyzed direct allylic amination of methyl 14α‐hydroxy‐15,16‐dihydroisopimarate with a wide variety of nitrogenated nucleophiles. It was revealed that the selectivity of the reaction depends on the nature of nucleophile. The catalyzed reaction of the mentioned diterpenoid allylic alcohol with 3‐nitroaniline, 3‐(trifluoromethyl)aniline, and 4‐(trifluoromethyl)aniline yield the subsequent 7α‐, 7β‐ and 14αnitrogen‐containing diterpenoids. The reaction with 2‐nitroaniline, 4‐nitro‐2‐chloroaniline, 4‐methoxy‐2‐nitroaniline, phenylsulfamide, or tert‐butyl carbamate proceeds with the formation of 7α‐nitrogen‐substituted diterpenoids as the main products. PMID:27308214

  14. Partial reactions and chemical rescue of site-directed mutants of Rubisco as mechanistic probes

    SciTech Connect

    Harpel, M.R.; Larimer, F.W.; Lee, E.H.; Mural, R.J.; Smith, H.B.; Soper, T.S.; Hartman, F.C.

    1991-01-01

    Given the current state of knowledge of the reaction pathways catalyzed by D-ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and the elucidation of the three-dimensional structure of several different forms of the enzyme, sit-directed mutagenesis offers the potential to decipher catalytic roles of active-site residues and to unravel the functional significance of various structural elements. Especially intriguing are intersubunit, electrostatic interactions at the active site between Glu48 and Lys168 of the nonactivated (noncarbamylated) enzyme and between Glu48 and Lys329 of the activated (carbamylated) enzyme. In this paper, we describe two approaches to address the roles of electrostatic interactions at the active site and the roles of the participant residues: (1) characterization of pertinent site-directed mutants, including their abilities to catalyze partial reactions and (2) subtle alteration of the active-site microenvironment by manipulation of these proteins with exogenous reagents.

  15. Partial reactions and chemical rescue of site-directed mutants of Rubisco as mechanistic probes

    SciTech Connect

    Harpel, M.R.; Larimer, F.W.; Lee, E.H.; Mural, R.J.; Smith, H.B.; Soper, T.S.; Hartman, F.C.

    1991-12-31

    Given the current state of knowledge of the reaction pathways catalyzed by D-ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and the elucidation of the three-dimensional structure of several different forms of the enzyme, sit-directed mutagenesis offers the potential to decipher catalytic roles of active-site residues and to unravel the functional significance of various structural elements. Especially intriguing are intersubunit, electrostatic interactions at the active site between Glu48 and Lys168 of the nonactivated (noncarbamylated) enzyme and between Glu48 and Lys329 of the activated (carbamylated) enzyme. In this paper, we describe two approaches to address the roles of electrostatic interactions at the active site and the roles of the participant residues: (1) characterization of pertinent site-directed mutants, including their abilities to catalyze partial reactions and (2) subtle alteration of the active-site microenvironment by manipulation of these proteins with exogenous reagents.

  16. The direct oxidative diene cyclization and related reactions in natural product synthesis

    PubMed Central

    2016-01-01

    Summary The direct oxidative cyclization of 1,5-dienes is a valuable synthetic method for the (dia)stereoselective preparation of substituted tetrahydrofurans. Closely related reactions start from 5,6-dihydroxy or 5-hydroxyalkenes to generate similar products in a mechanistically analogous manner. After a brief overview on the history of this group of transformations and a survey on mechanistic and stereochemical aspects, this review article provides a summary on applications in natural product synthesis. Moreover, current limitations and future directions in this area of chemistry are discussed. PMID:27829917

  17. The direct reaction field hamiltonian: Analysis of the dispersion term and application to the water dimer

    NASA Astrophysics Data System (ADS)

    Thole, B. T.; Van Duijnen, P. Th.

    1982-10-01

    The induction and dispersion terms obtained from quantum-mechanical calculations with a direct reaction field hamiltonian are compared to second order perturbation theory expressions. The dispersion term is shown to give an upper bound which is a generalization of Alexander's upper bound. The model is illustrated by a calculation on the interactions in the water dimer. The long range Coulomb, induction and dispersion interactions are reasonably reproduced.

  18. Direct dynamics study on hydrogen abstraction reaction of CF 3CHOHCF 3 with OH radical

    NASA Astrophysics Data System (ADS)

    Wang, Ying; Liu, Jing-Yao; Li, Ze-Sheng

    2007-05-01

    Dual-level direct dynamics method is employed to investigate the H-abstraction reaction CF 3CHOHCF 3 with OH radical. Two hydrogen-abstraction reaction channels are possible: one from the methylene (-CH-) position and the other from the hydroxyl (-OH) position. The minimum energy path is calculated at the B3LYP/6-311G(d,p) level, and the energetic information is further refined by a new powerful and inexpensive BMC-CCSD method. To testify the accuracy of the structures and the energies, the recently developed hybrid density functional theory BB1K and higher level MC-QCISD are applied to this system. Hydrogen-bonded complexes are presented at both reactants and products sides of these two channels, which indicating that the reaction may proceed via an indirect mechanism. The rate constants for each reaction channel are evaluated by canonical variational transition state theory (CVT) with a small-curvature tunneling correction (SCT) over a wide range of temperatures from 200 to 2000 K. The calculated CVT/SCT rate constants are in good agreement with the available experimental values in the temperature region 250-430 K. The present results indicate that the two channels are competitive. At lower temperature, the reaction occurs mainly via the hydroxyl-H-abstraction channel, while the methylene-H-abstraction channel is preferred when the temperature is higher than 273 K.

  19. Reactive sintering and reactive hot

    NASA Astrophysics Data System (ADS)

    Murray, J. C.; German, R. M.

    1992-09-01

    NbAl3 has been synthesized from elemental powders by reactive sintering (RS) and reactive hot isostatic pressing (RHIP). Both processes involve a self-propagating exothermic reaction between the constituent powders to form an intermetallic compound. The RHIP approach uses simultaneous external pressurization to make a higher density product. This study focused on developing a method to use reactive synthesis to form high-density NbAl3 compacts. High RS and RHIP densities were possible with the appropriate raw materials and processing parameters. These include powder purity, particle sizes, degassing, heating rate, furnace temperature, and compaction pressures. Near full density was attained with RHIP, and up to 95 pct density was attained with RS.

  20. Ab initio study of the H + HONO reaction: Direct abstraction versus indirect exchange processes

    SciTech Connect

    Hsu, C.C.; Lin, M.C.; Mebel, A.M.; Melius, C.F.

    1997-01-02

    The mechanism of the H + HONO reaction (for which no experimental data are available) has been elucidated by ab initio molecular orbital calculations using modified G2 and BAC-MP4 methods. These results indicate that the reaction occurs predominantly by two indirect metathetical processes. One produces OH + HNO and H{sub 2}O + NO from the decomposition of vibrationally excited hydroxyl nitroxide, HN(O)OH, formed by H atom addition to the N atom of HONO. The other produces H{sub 2}O + NO from the decomposition of vibrationally excited dihydroxylamino radical, N(OH){sub 2}, formed by H atom addition to the terminal O atom. These indirect displacement processes are much more efficient than the commonly assumed, direct H-abstraction reaction producing H{sub 2} + NO{sub 2}. A transition-state theory calculation for the direct abstraction reaction and RRKM calculations for the two indirect displacement processes give rise to the following rate constants, in units of cm{sup 3} molecule{sup -1} s{sup -1} for the 300-3500 K temperature range under atmospheric conditions: k{sub H(2)} = 3.33 x 10{sup -16}T{sup 1.55} exp(-3328.5/T), k{sub OH} = 9.36 x 10{sup -14}T{sup 0.86} exp(-2500.8/T), k{sub H(2)O} = 1.35 x 10{sup -17}T{sup 1.89} exp-(-1935.7/T), where the rate constant for H{sub 2}O production represents the sum from both indirect displacement reactions. 32 refs., 3 figs., 7 tabs.

  1. Extrusion of spark plasma sintered aluminum-carbon nanotube composites at various sintering temperatures.

    PubMed

    Kwon, Hansang; Kawasaki, Akira

    2009-11-01

    The combined processes of spark plasma sintering and hot extrusion were used to fabricate a multi-walled carbon nanotube (MWCNT) reinforced aluminum (Al) matrix composite. The structural defects of carbon nanotubes (CNT) at various sintering temperatures were investigated by Raman spectroscopy. A small amount of Al liquid phase was generated and it reacted with disordered CNTs, even during the solid-state spark plasma sintering process. The influence of Al carbides generated by the reaction between Al and disordered CNTs is discussed from a microstructural viewpoint and in relation to tensile strength. We conclude that structurally controlled CNTs could potentially be attractive for metal matrix applications, and could significantly improve the mechanical properties of AI-CNT composites.

  2. Direct-Reaction Studies by Particle-Gamma Coincidence Spectroscopy Using HPGe-CsI and HPGe-Si Arrays

    SciTech Connect

    Allmond, James M

    2013-01-01

    Particle- and particle- - coincidence spectroscopy has several advantages in the study of direct reactions(particularly in inverse kinematics) since it can generally allow determination of: decay paths; high-precision level energies; multipolarities of transitions; and cross sections. Techniques for studying direct reactions by particle- coincidence spectroscopy are presented for two cases: (1) heavy-ion reactions with HPGe-CsI, and (2) light-ion reactions with HPGe-Si. Future direct-reaction studies with radioactive ion beams (RIBs) will mostly involve low beam intensities and inverse kinematics (i.e., Abeam>Atarget), which eliminates the traditional use of magnetic spectrometers. Particle- coincidence spectroscopy currently provides the most viable method to study direct reactions with nuclei of any level density. In the present study, the capabilities and limitations of the technique are explored.

  3. Direct-reaction studies by particle-{gamma} coincidence spectroscopy using Csi-Hpge and Si-Hpge arrays

    SciTech Connect

    Allmond, J. M.

    2013-04-19

    Particle-{gamma} and particle-{gamma}-{gamma} coincidence spectroscopy has several advantages in the study of direct reactions (particularly in inverse kinematics) since it can generally allow determination of: decay paths; high-precision level energies; multipolarities of transitions; and cross sections. Techniques for studying direct reactions by particle-{gamma} coincidence spectroscopy are presented for two cases: (1) heavy-ion reactions with CsI-HPGe, and (2) light-ion reactions with Si-HPGe. Future direct-reaction studies with radioactive ion beams (RIBs) will mostly involve low beam intensities and inverse kinematics (i.e., A{sub beam}>A{sub target}), which eliminates the traditional use of magnetic spectrometers. Particle-{gamma} coincidence spectroscopy currently provides the most viable method to study direct reactions with nuclei of any level density. In the present study, the capabilities and limitations of the technique are explored.

  4. Microwave versus conventional sintering of silicon carbide tiles

    SciTech Connect

    Kass, M.D.; Caughman, J.B.O.; Forrester, S.C.; Akerman, A.

    1997-05-07

    Silicon carbide is being evaluated as an armor material because of its lightweight, high-hardness, and excellent armor efficiency. However, one of the problems associated with silicon carbide is the high cost associated with achieving fully dense tiles. Full density requires either hot pressing and sintering or reaction bonding. Past efforts have shown that hot pressed tiles have a higher armor efficiency than those produced by reaction bonded sintering. An earlier stuy showed that the acoustic properties of fully-dense silicon carbide tiles were enhanced through the use of post-sintered microwave heat treatments. One of the least expensive forming techniques is to isostatically press-and-sinter. In this study, the authors have used microwave energy to densify silicon carbide green bodies. Microwave sintering has been demonstrated to be a very quick way to sinter ceramics such as alumina to exceptionally high densities. Previous work has shown that microwave post treatment of fully-dense reaction bonded silicon carbide tiles significantly improves the acoustic properties of the tiles. These properties include Poisson`s ratio, Young`s modulus, shear modulus, and bulk modulus.

  5. Microwave sintering versus conventional sintering of NiCuZn ferrites. Part I: Densification evolution

    NASA Astrophysics Data System (ADS)

    Zhu, Jianhua; Ouyang, Chenxin; Xiao, Shumin; Gao, Yongyi

    2016-06-01

    This work reports the recent study on the microwave sintering (MS) versus conventional sintering (CS) of NiCuZn ferrites, with particular interests in the densification evolution. NiCuZn ferrite powders were synthesized through the solid state reaction route. Densification behaviors of ferrite samples under the two types of thermal sources were monitored in real-time. Meanwhile, the influences of additives (1 wt% BSZ glass or 1 wt% Bi2O3) on the densifications were also investigated. Both constant heating rate (CHR) and master sintering curve (MSC) models were used to evaluate the sintering activation energy (Q). Results demonstrated that the microwave-enhanced diffusion mainly occurs at the intermediate sintering stage. The Q-value estimated by MSC method agreed well with that from CHR method. With the influence of microwave electromagnetic field, the activation energy of NiCuZn ferrites was decreased by roughly 100-150 kJ/mol. In addition, doping a small amount of additives could improve densification degree and reduce the minimal energy to activate diffusion mechanisms.

  6. Direct measurement of Criegee intermediate (CH2OO) reactions with acetone, acetaldehyde, and hexafluoroacetone.

    PubMed

    Taatjes, Craig A; Welz, Oliver; Eskola, Arkke J; Savee, John D; Osborn, David L; Lee, Edmond P F; Dyke, John M; Mok, Daniel W K; Shallcross, Dudley E; Percival, Carl J

    2012-08-14

    Criegee biradicals, i.e., carbonyl oxides, are critical intermediates in ozonolysis and have been implicated in autoignition chemistry and other hydrocarbon oxidation systems, but until recently the direct measurement of their gas-phase kinetics has not been feasible. Indirect determinations of Criegee intermediate kinetics often rely on the introduction of a scavenger molecule into an ozonolysis system and analysis of the effects of the scavenger on yields of products associated with Criegee intermediate reactions. Carbonyl species, in particular hexafluoroacetone (CF(3)COCF(3)), have often been used as scavengers. In this work, the reactions of the simplest Criegee intermediate, CH(2)OO (formaldehyde oxide), with three carbonyl species have been measured by laser photolysis/tunable synchrotron photoionization mass spectrometry. Diiodomethane photolysis produces CH(2)I radicals, which react with O(2) to yield CH(2)OO + I. The formaldehyde oxide is reacted with a large excess of a carbonyl reactant and both the disappearance of CH(2)OO and the formation of reaction products are monitored. The rate coefficient for CH(2)OO + hexafluoroacetone is k(1) = (3.0 ± 0.3) × 10(-11) cm(3) molecule(-1) s(-1), supporting the use of hexafluoroacetone as a Criegee-intermediate scavenger. The reactions with acetaldehyde, k(2) = (9.5 ± 0.7) × 10(-13) cm(3) molecule(-1) s(-1), and with acetone, k(3) = (2.3 ± 0.3) × 10(-13) cm(3) molecule(-1) s(-1), are substantially slower. Secondary ozonides and products of ozonide isomerization are observed from the reactions of CH(2)OO with acetone and hexafluoroacetone. Their photoionization spectra are interpreted with the aid of quantum-chemical and Franck-Condon-factor calculations. No secondary ozonide was observable in the reaction of CH(2)OO with acetaldehyde, but acetic acid was identified as a product under the conditions used (4 Torr and 293 K).

  7. Synchronization of Coupled Reaction-Diffusion Neural Networks With Directed Topology via an Adaptive Approach.

    PubMed

    Zhang, Hao; Sheng, Yin; Zeng, Zhigang

    2017-03-15

    This paper investigates the synchronization issue of coupled reaction-diffusion neural networks with directed topology via an adaptive approach. Due to the complexity of the network structure and the presence of space variables, it is difficult to design proper adaptive strategies on coupling weights to accomplish the synchronous goal. Under the assumptions of two kinds of special network structures, that is, directed spanning path and directed spanning tree, some novel edge-based adaptive laws, which utilized the local information of node dynamics fully are designed on the coupling weights for reaching synchronization. By constructing appropriate energy function, and utilizing some analytical techniques, several sufficient conditions are given. Finally, some simulation examples are given to verify the effectiveness of the obtained theoretical results.

  8. Direct numerical simulation of shear localization and decomposition reactions in shock-loaded HMX crystal

    DOE PAGES

    Austin, Ryan A.; Barton, Nathan R.; Reaugh, John E.; ...

    2015-05-14

    A numerical model is developed to study the shock wave ignition of HMX crystal. The model accounts for the coupling between crystal thermal/mechanical responses and chemical reactions that are driven by the temperature field. This allows for the direct numerical simulation of decomposition reactions in the hot spots formed by shock/impact loading. The model is used to simulate intragranular pore collapse under shock wave loading. In a reference case: (i) shear-enabled micro-jetting is responsible for a modest extent of reaction in the pore collapse region, and (ii) shear banding is found to be an important mode of localization. The shearmore » bands, which are filled with molten HMX, grow out of the pore collapse region and serve as potential ignition sites. The model predictions of shear banding and reactivity are found to be quite sensitive to the respective flow strengths of the solid and liquid phases. In this regard, it is shown that reasonable assumptions of liquid-HMX viscosity can lead to chemical reactions within the shear bands on a nanosecond time scale.« less

  9. Direct numerical simulation of shear localization and decomposition reactions in shock-loaded HMX crystal

    SciTech Connect

    Austin, Ryan A.; Barton, Nathan R.; Reaugh, John E.; Fried, Laurence E.

    2015-05-14

    A numerical model is developed to study the shock wave ignition of HMX crystal. The model accounts for the coupling between crystal thermal/mechanical responses and chemical reactions that are driven by the temperature field. This allows for the direct numerical simulation of decomposition reactions in the hot spots formed by shock/impact loading. The model is used to simulate intragranular pore collapse under shock wave loading. In a reference case: (i) shear-enabled micro-jetting is responsible for a modest extent of reaction in the pore collapse region, and (ii) shear banding is found to be an important mode of localization. The shear bands, which are filled with molten HMX, grow out of the pore collapse region and serve as potential ignition sites. The model predictions of shear banding and reactivity are found to be quite sensitive to the respective flow strengths of the solid and liquid phases. In this regard, it is shown that reasonable assumptions of liquid-HMX viscosity can lead to chemical reactions within the shear bands on a nanosecond time scale.

  10. Anisotropic constitutive model and FE simulation of the sintering process of slip cast traditional porcelain

    SciTech Connect

    Sarbandi, B.; Besson, J.; Boussuge, M.; Ryckelynck, D.

    2010-06-15

    Slip cast ceramic components undergo both sintering shrinkage and creep deformation caused by gravity during the firing cycle. In addition sintering may be anisotropic due to the development of preferential directions during slip casting. Both phenomena induce complex deformations of parts which make the design of casting molds difficult. To help solving this problem, anisotropic constitutive equations are proposed to represent the behavior of the ceramic compacts during sintering. The model parameters are identified using tests allowing to characterize both sintering and creep. The model was implemented in a finite element software and used to simulate the deformation of a traditional ceramic object during sintering.

  11. Anisotropic constitutive model and FE simulation of the sintering process of slip cast traditional porcelain

    NASA Astrophysics Data System (ADS)

    Sarbandi, B.; Besson, J.; Boussuge, M.; Ryckelynck, D.

    2010-06-01

    Slip cast ceramic components undergo both sintering shrinkage and creep deformation caused by gravity during the firing cycle. In addition sintering may be anisotropic due to the development of preferential directions during slip casting. Both phenomena induce complex deformations of parts which make the design of casting molds difficult. To help solving this problem, anisotropic constitutive equations are proposed to represent the behavior of the ceramic compacts during sintering. The model parameters are identified using tests allowing to characterize both sintering and creep. The model was implemented in a finite element software and used to simulate the deformation of a traditional ceramic object during sintering.

  12. Chemical Reactions and Mechanical Properties of the Directly Bonded Ge-Si Interface

    NASA Astrophysics Data System (ADS)

    Byun, Ki Yeol; Ferain, Isabelle; Yu, Ran; Colinge, Cindy

    2011-12-01

    In this study, chemical reactions and mechanical properties of directly bonded Ge-Si interfaces are investigated. The Ge-Si bonded interface has been systematically characterized as a function of the thermal budget (200 °C and 300 °C), which demonstrated that the formation of a thin GeO2 cap layer by radical pre-treatment can reduce the generation rate of voids at the bonded interface significantly. Patterning of one of the wafers prior to bonding can help to achieve high bonding quality thanks to enhanced out-diffusion of reaction by-products and stress reduction at the bonded interface. Both numerical modeling and structural analysis show that the presence of diffusion path (channels) at the bonded interfaces result in a maximum bond strength and minimum stress at the bonded interface.

  13. Direct Observation of Sulfur Radicals as Reaction Media in Lithium Sulfur Batteries

    SciTech Connect

    Wang, Qiang; Zheng, Jianming; Walter, Eric; Pan, Huilin; Lv, Dongping; Zuo, Pengjian; Chen, Honghao; Deng, Z. D.; Liaw, Bor Y.; Yu, Xiqian; Yang, Xiao-Qing; Zhang, Ji-Guang; Liu, Jun; Xiao, Jie

    2015-01-09

    Lithium sulfur (Li-S) battery has been regaining tremendous interest in recent years because of its attractive attributes such as high gravimetric energy, low cost and environmental benignity. However, it is still not conclusively known how polysulfide ring/chain participates in the whole cycling and whether the discharge and charge processes follow the same pathway. Herein, we demonstrate the direct observation of sulfur radicals by using in situ electron paramagnetic resonance (EPR) technique. Based on the concentration changes of sulfur radicals at different potentials and the electrochemical characteristics of the cell, it is revealed that the chemical and electrochemical reactions in Li-S cell are driving each other to proceed through sulfur radicals, leading to two completely different reaction pathways during discharge and charge. The proposed radical mechanism may provide new perspectives to investigate the interactions between sulfur species and the electrolyte, inspiring novel strategies to develop Li-S battery technology.

  14. Direct Observation of Sulfur Radicals as Reaction Media in Lithium Sulfur Batteries

    DOE PAGES

    Wang, Qiang; Zheng, Jianming; Walter, Eric; ...

    2015-01-09

    Lithium sulfur (Li-S) battery has been regaining tremendous interest in recent years because of its attractive attributes such as high gravimetric energy, low cost and environmental benignity. However, it is still not conclusively known how polysulfide ring/chain participates in the whole cycling and whether the discharge and charge processes follow the same pathway. Herein, we demonstrate the direct observation of sulfur radicals by using in situ electron paramagnetic resonance (EPR) technique. Based on the concentration changes of sulfur radicals at different potentials and the electrochemical characteristics of the cell, it is revealed that the chemical and electrochemical reactions in Li-Smore » cell are driving each other to proceed through sulfur radicals, leading to two completely different reaction pathways during discharge and charge. The proposed radical mechanism may provide new perspectives to investigate the interactions between sulfur species and the electrolyte, inspiring novel strategies to develop Li-S battery technology.« less

  15. Direct Observation of Sulfur Radicals as Reaction Media in lithium Sulfur Batteries

    SciTech Connect

    Wang, Qiang; Zheng, Jianming; Walter, Eric D.; Pan, Huilin; Lu, Dongping; Zuo, Pengjian; Chen, Honghao; Deng, Zhiqun; Liaw, Bor Yann; Yu, Xiqian; Yang, Xiaoning; Zhang, Jiguang; Liu, Jun; Xiao, Jie

    2014-12-09

    Lithium sulfur (Li-S) battery has been regaining tremendous interest in recent years because of its attractive attributes such as high gravimetric energy, low cost and environmental benignity. However, it is still not conclusively known how polysulfide ring/chain participates in the whole cycling and whether the discharge and charge process follow the same pathway. Herein, we demonstrate the direct observation of sulfur radicals by using in situ electron paramagnetic resonance (EPR) technique. Based on the concentration changes of sulfur radicals at different potentials, it is revealed that the chemical and electrochemical reactions in Li-S cell are driven each other to proceed through sulfur radicals, leading to two completely different reaction pathways during discharge and charge. The proposed radical mechanism may provide new insights to investigate the interactions between sulfur species and the electrolyte, inspiring novel strategies to develop Li-S battery technology.

  16. Magnetic properties of LiZnCu ferrite synthesized by the microwave sintering method

    NASA Astrophysics Data System (ADS)

    Khot, Sujata S.; Shinde, Neelam S.; Basavaiah, Nathani; Watawe, Shrikant C.; Vaidya, Milind M.

    2015-01-01

    Lithium ferrites have attracted considerable attention because they have been used as replacements for garnets due to their low cost. A series of polycrystalline ferrite samples were prepared with the composition of LiXZn(0.6-2X)Cu0.4Fe2O4(X=0.05, 0.1, 0.15, 0.2, 0.25, 0.3) at chemical reaction temperature 150 °C by sintering with microwave assisted combustion method. The characterization shows the formation of single phase cubic structure when carried out by using the X-rays technique and I-R technique. Magnetization parameters such as saturation magnetization, coercivity, magnetic moment were calculated by using the Hysteresis graph. The Curie temperature obtained using the susceptibility data are found to be in the range 350-700 °C. Anhysteric remanent magnetization is used for estimating the grain size and domain structure of the composition. An attempt has been made to synthesis the nano-particles at lower reaction temperature by using non-conventional microwave sintering method. The advantage of this method is its lower sintering temperature and time compared to the conventional ceramic technique and direct formation of nano-ferrites without ball-milling.

  17. Sintered composite filter

    DOEpatents

    Bergman, W.

    1986-05-02

    A particulate filter medium formed of a sintered composite of 0.5 micron diameter quartz fibers and 2 micron diameter stainless steel fibers is described. Preferred composition is about 40 vol.% quartz and about 60 vol.% stainless steel fibers. The media is sintered at about 1100/sup 0/C to bond the stainless steel fibers into a cage network which holds the quartz fibers. High filter efficiency and low flow resistance are provided by the smaller quartz fibers. High strength is provided by the stainless steel fibers. The resulting media has a high efficiency and low pressure drop similar to the standard HEPA media, with tensile strength at least four times greater, and a maximum operating temperature of about 550/sup 0/C. The invention also includes methods to form the composite media and a HEPA filter utilizing the composite media. The filter media can be used to filter particles in both liquids and gases.

  18. Sintered wire cathode

    DOEpatents

    Falce, Louis R.; Ives, R. Lawrence

    2009-06-09

    A porous cathode structure is fabricated from a plurality of wires which are placed in proximity to each other in elevated temperature and pressure for a sintering time. The sintering process produces the porous cathode structure which may be divided into a plurality of individual porous cathodes, one of which may be placed into a dispenser cathode support which includes a cavity for containing a work function reduction material such as BaO, CaO, and Al.sub.2O.sub.3. The work function reduction material migrates through the pores of the porous cathode from a work replenishment surface adjacent to the cavity of the dispenser cathode support to an emitting cathode surface, thereby providing a dispenser cathode which has a uniform work function and therefore a uniform electron emission.

  19. SINTERING METAL OXIDES

    DOEpatents

    Roake, W.E.

    1960-09-13

    A process is given for producing uranium dioxide material of great density by preparing a compacted mixture of uranium dioxide and from 1 to 3 wt.% of calcium hydride, heating the mixture to at least 675 deg C for decomposition of the hydride and then for sintering, preferably in a vacuum, at from 1550 to 2000 deg C. Calcium metal is formed, some uranium is reduced by the calcium to the metal and a product of high density is obtained.

  20. Liquid Phase Sintering

    NASA Technical Reports Server (NTRS)

    2004-01-01

    Industry spends billions of dollars each year on machine tools to manufacture products out of metal. This includes tools for cutting every kind of metal part from engine blocks to Shuttle main engine components. Cutting tool tips often break because of weak spots or defects in their composition. Based on a new concept called defect trapping, space offers a novel environment to study defect formation in molten metal materials as they solidify. After the return of these materials from space, researchers can evaluate the source of the defect and seek ways to eliminate them in products prepared on Earth. A widely used process for cutting tip manufacturing is liquid phase sintering. Compared to Earth-sintered samples which slump due to buoyancy induced by gravity, space samples are uniformly shaped and defects remain where they are formed. By studying metals sintered in space the US tool industry can potentially enhance its worldwide competitiveness. The Consortium for Materials Development in Space along with Wyle Labs, Teledyne Advanced Materials, and McDornell Douglas have conducted experiments in space.

  1. Direct Assembly of Prenylated Heteroarenes through a Cascade Minisci Reaction/Dehydration Sequence

    PubMed Central

    Tan, Dong‐Hang; Zeng, Yao‐Fu; Liu, Yao; Lv, Wen‐Xin; Li, Qingjiang

    2016-01-01

    Abstract The prenyl group is an important component in bioactive compounds. Herein, we report the assembly of prenylated heteroarenes through a cascade Minisci reaction and acid‐promoted dehydration sequence. The use of potassium (3‐hydroxy‐3‐methylbut‐1‐yl)trifluoroborate as a new coupling reagent allows the direct introduction of prenyl and 3‐hydroxy‐3‐methylbutyl groups to a wide variety of electron‐deficient heteroarenes. Synthetic application is also demonstrated. PMID:28032022

  2. Direct nuclear-pumped lasers using the He-3/n,p/H-3 reaction

    NASA Technical Reports Server (NTRS)

    Deyoung, R. J.; Jalufka, N. W.; Hohl, F.

    1978-01-01

    A description is presented of experimental results concerning a specific class of direct nuclear-pumped lasers classified as 'volumetric nuclear lasers'. In the considered laser system a fissioning gas, He-3, is mixed with the lasing gas to form a homogeneous mixture, resulting in uniform volume excitation. In typical volumetric nuclear lasers a fast-burst reactor is used as a source of neutrons which penetrate a polyethylene moderator. Here the fast neutrons are thermalized. After thermalization, neutrons scatter into the laser cell. Nuclear reactions produce a proton of 0.56 MeV and a tritium ion of 0.19. These ions produce secondary electrons which pump the laser medium creating a population inversion. The results reported demonstrate direct nuclear pumping of He-3-Ar, Xe, Kr, and Cl with the considered system.

  3. A Preliminary Attempt at Sintering an Ultrafine Alumina Powder Using Microwaves

    DTIC Science & Technology

    1994-09-01

    residue and if not completely 12 burned-off may cause undesirable localized chemical reactions or crack formations in the sintered product. 2. Sintering...carefully controlled to reduce stress cracks resulting from severe thermal gradients between the hot interior and the relatively cooler surface...is expected to minimize residual thermal stresses and crack formation during sintering thus allowing for fabrications of larger samples with more

  4. Directed surfaces structures and interfaces for enhanced electrocatalyst activity, selectivity, and stability for energy conversion reactions

    SciTech Connect

    Jaramillo, Thomas F.

    2016-04-20

    In this project, we have employed a systematic approach to develop active, selective, and stable catalyst materials for important electrochemical reactions involving energy conversion. In particular, we have focused our attention on developing active catalyst materials for the hydrogen evolution reaction (HER), oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). HER: We have synthesized and investigated several highly active and acid stable non-precious metal HER catalysts, including: [Mo3S13]2- nanoclusters (Nature Chemistry, 2014) and molybdenum phosphosulfide (MoP|S) (Angewandte Chemie, 2014). We have also aimed to engineer these catalyst formulations in a membrane electrode assembly (MEA) for fundamental studies of water electrolysis at high current densities, approximately 1 A/cm2 (ChemSusChem, 2015). We furthermore investigated transition metal phosphide (TMP) catalysts for HER by a combined experimental–theoretical approach (Energy & Environmental Science, 2015). By synthesizing different TMPs and comparing experimentally determined HER activities with the hydrogen adsorption free energies, ΔGH, calculated by density functional theory, we showed that the TMPs follow a volcano relationship for the HER. Using our combined experimental–theoretical model, we predicted that the mixed metal TMP, Fe0.5Co0.5P, should have a near-optimal ΔGH. We synthesized several mixtures of Co and Fe phosphides alloys and confirmed that Fe0.5Co0.5P exhibits the highest HER activity of the investigated TMPs (Energy & Environmental Science, 2015). The understanding gained as to how to improve catalytic activity for the HER, particularly for non-precious metal materials, is important to DOE targets for sustainable H2 production. OER: We have developed a SrIrO3/IrOx catalyst for acidic conditions (submitted, 2016). The Sr

  5. Probable new type of reaction mechanism: Double. cap alpha. direct transfer process

    SciTech Connect

    Xu Shu-wei; Wu Guo-hua; Miao Rong-zhi; Han Fei

    1983-10-01

    It is assumed that /sup 8/Be consists of two ..cap alpha.. particles which are close to each other in configuration space. A spectroscopic density of /sup 8/Be cluster in the residue nuclei is then obtained, which is proportional to the square of the preformation probability of ..cap alpha.. particle at nuclear surface. Using the improved method of parametrization of EFR-DWBA overlap integral,/sup 1//sup en-dash//sup 2/ we calculate the double differential energy spectra and angular distributions of ..cap alpha.. particles for the reactions /sup 209/Bi (/sup 12/C, ..cap alpha..) /sup 217/Fr and extract the preformation probability of ..cap alpha.. particle at the surface of /sup 217/Fr nuclei from fitting the experimental data. The agreement within the range of calculation error between the preformation probabilities extracted from transfer reactions and ..cap alpha.. decay suggests that the reaction /sup 209/Bi(/sup 12/C, ..cap alpha..) /sup 217/Fr may be explained as a double ..cap alpha.. direct transfer process.

  6. Direct kinetic measurements of reactions between the simplest Criegee intermediate CH2OO and alkenes.

    PubMed

    Buras, Zachary J; Elsamra, Rehab M I; Jalan, Amrit; Middaugh, Joshua E; Green, William H

    2014-03-20

    The simplest Criegee Intermediate (CH2OO), a well-known biradical formed in alkene ozonolysis, is known to add across double bonds. Here we report direct experimental rate measurements of the simplest Criegee Intermediate reacting with C2–C4 alkenes obtained using the laser flash photolysis technique probing the recently measured B(1)A′ ← X(1)A′ transition in CH2OO. The measured activation energy (298–494 K) for CH2OO + alkenes is Ea ≈ 3500 ± 1000 J mol(–1) for all alkyl substituted alkenes and Ea = 7000 ± 900 J mol(–1) for ethene. The measured Arrhenius pre-exponential factors (A) vary between (2 ± 1) × 10(–15) and (11 ± 3) × 10(–15) cm(3) molecule(–1) s(–1). Quantum chemical calculations of the corresponding rate coefficients reproduce qualitative reactivity trends but overestimate the absolute rate coefficients. Despite the small Ea's, the CH2OO + alkene rate coefficients are almost 2 orders of magnitude smaller than those of similar reactions between CH2OO and carbonyl compounds. Using the rate constants measured here, we estimate that, under typical atmospheric conditions, reaction with alkenes does not represent a significant sink of CH2OO. In environments rich in C═C double bonds, however, such as ozone-exposed rubber or emission plumes, these reactions can play a significant role.

  7. Electrified emotions: Modulatory effects of transcranial direct stimulation on negative emotional reactions to social exclusion.

    PubMed

    Riva, Paolo; Romero Lauro, Leonor J; Vergallito, Alessandra; DeWall, C Nathan; Bushman, Brad J

    2015-01-01

    Social exclusion, ostracism, and rejection can be emotionally painful because they thwart the need to belong. Building on studies suggesting that the right ventrolateral prefrontal cortex (rVLPFC) is associated with regulation of negative emotions, the present experiment tests the hypothesis that decreasing the cortical excitability of the rVLPFC may increase negative emotional reactions to social exclusion. Specifically, we applied cathodal transcranial direct current stimulation (tDCS) over the rVLPFC and predicted an increment of negative emotional reactions to social exclusion. In Study 1, participants were either socially excluded or included, while cathodal tDCS or sham stimulation was applied over the rVLPFC. Cathodal stimulation of rVLPFC boosted the typical negative emotional reaction caused by social exclusion. No effects emerged from participants in the inclusion condition. To test the specificity of tDCS effects over rVLPFC, in Study 2, participants were socially excluded and received cathodal tDCS or sham stimulation over a control region (i.e., the right posterior parietal cortex). No effects of tDCS stimulation were found. Our results showed that the rVLPFC is specifically involved in emotion regulation and suggest that cathodal stimulation can increase negative emotional responses to social exclusion.

  8. Direct visualization of a cycloaddition reaction on frozen asymmetric Si dimers at room temperature

    NASA Astrophysics Data System (ADS)

    Baik, Jaeyoon; Ihm, Kyuwook; Ha, Taekyun; An, Ki-Seok; Ahn, Joung Real; Park, Chong-Yun

    2016-07-01

    We firstly report an experimental visualization of a cycloaddition reaction on RT frozen asymmetric Si dimers. The frozen Si dimers with a local c(4 × 2) order were prepared by pinning flip-flopping Si dimers by using molecules. This RT pristine c(4 × 2) structure was used to determine what Si atom of an asymmetric Si dimer bonds to a molecule at the initial stage of the RT cycloaddition reaction, which has been a long-standing puzzling issue. This made it possible to compare directly experimental cycloaddition reactions with theoretical ones. As a prototype for the experiment, a 1,3-butadiene molecule adsorbed between Si dimer rows was used. The 1,3-butadiene molecule was found to prefer a symmetric Si pair on the frozen Si dimers, i.e., two electrophilic lower atoms of asymmetric Si dimers. This result is consistent with the theoretical prediction that a 1,3-diene molecule prefers a symmetric Si pair on the Si(001)c(4 × 2) surface. This experimental approach can also be applied to other studies for the adsorption of a molecule on a Si(001) surface at room temperature.

  9. Zone sintering of ceramic fuels

    DOEpatents

    Matthews, R. Bruce; Chidester, Kenneth M.; Moore, H. Gene

    1994-01-01

    Cold pressed UC.sub.2 fuel compacts are sintered at temperatures greater than about 1850.degree. C. while in contact with a sintering facilitator material, e.g., tantalum, niobium, tungsten or a metal carbide such as uranium carbide, thereby allowing for a reduction in the overall porosity and leaving the desired product, i.e., a highly dense, large-grained uranium dicarbide. The process of using the sintering facilitator materials can be applied in the preparation of other carbide materials.

  10. Sinterable Powders from Laser Driven Reactions

    DTIC Science & Technology

    1980-07-01

    151.5 Ether 19 Isopentyl Ether 2.82 a 22.9 a 173.2 Aliphatic Acids 20 Propionic Acid 3.30 e 26.7 a 141.0 1.10 a 21 Butyric Acid 2.97 a 26.5 a 163.5 1.54...A 0 17 2-Pent anone A 00 18 2-Heptanone A O Ether 19 Isopentyl Ether B* Aliphatic Acids 20 Propionic Acid B 0 21 Butyric Acid B* Aldehydes 22...Not Measured 60 with a very low dielectric constants such as n-hexane, cyclohexane, n-octane, benzene, toluene, xylene, isopentyl ether, propionic

  11. Stereodynamics of the F + HD(v = 0, j = 1) reaction: direct vs. resonant mechanisms.

    PubMed

    Aldegunde, Jesús; Jambrina, Pablo G; de Miranda, Marcelo P; Sáez Rábanos, Vicente; Aoiz, F Javier

    2011-05-14

    The stereodynamics and mechanism of the F + HD(v = 0, j = 1) → HF (DF) + D (H) reactions have been thoroughly analysed at collision energies in the 0-160 meV range. Specifically, this study is focused on (i) the comparison between the stereodynamics of the collisions leading to HF and DF formation, and (ii) the stereodynamical fingerprints of the resonance that occurs at low collision energies in the HF channel and whose manifestation in the total cross section is greatly diminished for initial j > 0. While previous studies were limited to the analysis of integral cross sections (ICS), differential cross sections (DCS) and reaction probabilities, in the present work we have included the analysis of vectorial quantities such as the direction of the initial rotational angular momentum and internuclear axis, and their effect on reactivity. In particular, polarisation parameters (PP) and polarisation dependent differential cross sections (PDDCS), quantities that describe how the intrinsic HD rotational angular momentum and molecular axis polarisations contribute to reaction, are calculated and examined. The evolution of the PPs with the collision energy differs markedly between the two reaction channels. For the DF channel, the PP values are small and change very little in the energy range in which DF formation is appreciable. In contrast, rapid fluctuations in the magnitude and sign of the PPs are observed in the HF channel at low collision energies in and around the resonance. As the collision energy increases, direct (non-resonant) scattering prevails, and the various quantities are reasonably well accounted for by the QCT calculations, as in the case of the DF channel. The intrinsic directional information has been used to access the extent of control that can be achieved through polarisation of the HD molecule prior to collision. It was found that the same extrinsic preparation leads to very different outcomes on the HF channel DCS when the collision energy is

  12. Report on the sintering and properties of MgO and MgO-5% TiC

    SciTech Connect

    Bengisu, M.; Inal, O.T.

    1992-07-01

    Sintering of technical grade MgO yields higher fractional densities compared to pure MgO. TiC reacts with MgO under sintering of MgO-TiC composites in air, yielding Mg{sub 2}TiO{sub 4} and CO or CO{sub 2}. This can be suppressed in vacuum by plasma sintering. Plasma sintering of MgO at 1300 C and short times does not produce satisfactory results. 5 vol% TiC increases the sinterability of MgO during conventional air sintering; larger additions (50 vol%) decrease sinterability due to macropores formed by gaseous reaction product. Microwave sintering of MgO is possible. Mechanical properties of MgO are improved by additions of small amounts of TiC to starting powders.

  13. Biomimetic versus Sintered Calcium Phosphates: The in vitro Behavior of Osteoblasts and Mesenchymal Stem Cells.

    PubMed

    Sadowska, Joanna Maria; Guillem-Marti, Jordi; Montufar, Edgar B; Espanol, Montserrat; Ginebra, Maria-Pau

    2017-01-20

    The fabrication of calcium phosphates using biomimetic routes, namely, precipitation processes at body temperature, results in distinct features compared to conventional sintered calcium phosphate ceramics, such as a high specific surface area and micro or nanometric crystal size. The aim of this paper is to analyze the effects of these parameters on cell response, focusing on two bone cell types: rat mesenchymal stem cells (rMSCs) and human osteoblastic cells (SaOS-2). Biomimetic calcium deficient hydroxyapatite (CDHA) was obtained by a low temperature setting reaction, and α-tricalcium phosphate (α-TCP) and β- tricalcium phosphate (β-TCP) were subsequently obtained by sintering CDHA either at 1400 °C or 1100 °C. Sintered stoichiometric hydroxyapatite (HA) was also prepared using ceramic routes. The materials were characterized in terms of specific surface area, skeletal density, porosity and pore size distribution. SaOS-2 cells and rMSCs were seeded either directly on the surfaces of the materials or on glass coverslips subsequently placed on top of the materials to expose the cells to the CaP-induced ionic changes in the culture medium while avoiding any topography-related effects. CDHA produced higher ionic fluctuations in both cell culture media than sintered ceramics, with a strong decrease of calcium and a release of phosphate. Indirect contact cell cultures revealed that both cell types were sensitive to these ionic modifications, resulting in a decrease in proliferation rate, more marked for CDHA, this effect being more pronounced for rMSCs. In direct contact cultures, good cell adhesion was found on all materials, but whereas cells were able to proliferate on the sintered calcium phosphates, cell number was significantly reduced with time on biomimetic CDHA, which was associated to a higher percentage of apoptotic cells. Direct contact of the cells with biomimetic CDHA resulted also in higher ALP activity for both cell types as compared to sintered

  14. Production of sintered porous metal fluoride pellets

    DOEpatents

    Anderson, L.W.; Stephenson, M.J.

    1973-12-25

    Porous pellets characterized by a moderately reactive crust and a softer core of higher reactivity are produced by forming agglomerates containing a metal fluoride powder and a selected amount ofwater. The metal fluoride is selected to be sinterable and essentially non-reactive with gaseous fluorinating agents. The agglomerates are contacted with a gaseous fluorinating agent under controlled conditions whereby the heat generated by localized reaction of the agent and water is limited to values effccting bonding by localized sintering. Porous pellets composed of cryolite (Na/sub 3/AlF/sub 6/) can be used to selectively remove trace quantities of niobium pentafluoride from a feed gas consisting predominantly of uranium hexafluoride. (Official Gazette)

  15. Thermoluminescence properties of sintered ZnO

    NASA Astrophysics Data System (ADS)

    Borbón-Nuñez, H. A.; Cruz-Vázquez, C.; Bernal, R.; Kitis, G.; Furetta, C.; Castaño, V. M.

    2014-11-01

    New pellet-shaped ZnO phosphors were synthesized using a controlled chemical reaction. Some samples were sintered at 1123, 1173 or 1223 K during 24 h in air, and then exposed to beta particle irradiation in the dose range from 25 to 800 Gy to investigate their thermoluminescence (TL) properties. By considering their sensitivity, reproducibility, and fading features, samples sintered at 1173 K exhibit the best dosimetric characteristics. From computerized glow curve deconvolution that was carried out using a general order equation, the kinetics parameters were computed, and it was found that the glow curves are composed by six individual TL peaks with kinetics order ranging from 1.2 to 1.8.

  16. Activated sintering of zirconium dioxide

    NASA Astrophysics Data System (ADS)

    Panin, V. E.; Slosman, A. I.; Matrenin, S. V.

    1996-02-01

    A new phenomenon has been observed — the activated sintering of a zirconium ceramic in the hydrogen-nitrogen plasma of a glow discharge. It is shown that the activation energy is considerably lower than the activation energy for sintering in a vacuum furnace. This makes it possible to reduce sintering temperature, refine the grains, and improve the mechanical properties of the ceramic. It is proposed that the mechanism by which sintering is activated is connected with the activating effect of hydrogen during a structural transformation involving the formation of oxynitride phases.

  17. A Macroscopic Reaction: Direct Covalent Bond Formation between Materials Using a Suzuki-Miyaura Cross-Coupling Reaction

    PubMed Central

    Sekine, Tomoko; Kakuta, Takahiro; Nakamura, Takashi; Kobayashi, Yuichiro; Takashima, Yoshinori; Harada, Akira

    2014-01-01

    Cross-coupling reactions are important to form C–C covalent bonds using metal catalysts. Although many different cross-coupling reactions have been developed and applied to synthesize complex molecules or polymers (macromolecules), if cross-coupling reactions are realized in the macroscopic real world, the scope of materials should be dramatically broadened. Here, Suzuki-Miyaura coupling reactions are realized between macroscopic objects. When acrylamide gel modified with an iodophenyl group (I-gel) reacts with a gel possessing a phenylboronic group (PB-gel) using a palladium catalyst, the gels bond to form a single object. This concept can also be adapted for bonding between soft and hard materials. I-gel or PB-gel selectively bonds to the glass substrates whose surfaces are modified with an electrophile or nucleophile, respectively. PMID:25231557

  18. Spark plasma sintering of titanium aluminide intermetallics and its composites

    NASA Astrophysics Data System (ADS)

    Aldoshan, Abdelhakim Ahmed

    Titanium aluminide intermetallics are a distinct class of engineering materials having unique properties over conventional titanium alloys. gamma-TiAl compound possesses competitive physical and mechanical properties at elevated temperature applications compared to Ni-based superalloys. gamma-TiAl composite materials exhibit high melting point, low density, high strength and excellent corrosion resistance. Spark plasma sintering (SPS) is one of the powder metallurgy techniques where powder mixture undergoes simultaneous application of uniaxial pressure and pulsed direct current. Unlike other sintering techniques such as hot iso-static pressing and hot pressing, SPS compacts the materials in shorter time (< 10 min) with a lower temperature and leads to highly dense products. Reactive synthesis of titanium aluminide intermetallics is carried out using SPS. Reactive sintering takes place between liquid aluminum and solid titanium. In this work, reactive sintering through SPS was used to fabricate fully densified gamma-TiAl and titanium aluminide composites starting from elemental powders at different sintering temperatures. It was observed that sintering temperature played significant role in the densification of titanium aluminide composites. gamma-TiAl was the predominate phase at different temperatures. The effect of increasing sintering temperature on microhardness, microstructure, yield strength and wear behavior of titanium aluminide was studied. Addition of graphene nanoplatelets to titanium aluminide matrix resulted in change in microhardness. In Ti-Al-graphene composites, a noticeable decrease in coefficient of friction was observed due to the influence of self-lubrication caused by graphene.

  19. Flash sintering of ceramic materials

    NASA Astrophysics Data System (ADS)

    Dancer, C. E. J.

    2016-10-01

    During flash sintering, ceramic materials can sinter to high density in a matter of seconds while subjected to electric field and elevated temperature. This process, which occurs at lower furnace temperatures and in shorter times than both conventional ceramic sintering and field-assisted methods such as spark plasma sintering, has the potential to radically reduce the power consumption required for the densification of ceramic materials. This paper reviews the experimental work on flash sintering methods carried out to date, and compares the properties of the materials obtained to those produced by conventional sintering. The flash sintering process is described for oxides of zirconium, yttrium, aluminium, tin, zinc, and titanium; silicon and boron carbide, zirconium diboride, materials for solid oxide fuel applications, ferroelectric materials, and composite materials. While experimental observations have been made on a wide range of materials, understanding of the underlying mechanisms responsible for the onset and latter stages of flash sintering is still elusive. Elements of the proposed theories to explain the observed behaviour include extensive Joule heating throughout the material causing thermal runaway, arrested by the current limitation in the power supply, and the formation of defect avalanches which rapidly and dramatically increase the sample conductivity. Undoubtedly, the flash sintering process is affected by the electric field strength, furnace temperature and current density limit, but also by microstructural features such as the presence of second phase particles or dopants and the particle size in the starting material. While further experimental work and modelling is still required to attain a full understanding capable of predicting the success of the flash sintering process in different materials, the technique non-etheless holds great potential for exceptional control of the ceramic sintering process.

  20. Enantioselective direct Mannich reactions of cyclic β-ketoesters catalyzed by chiral phosphine via a novel dual-reagent catalysis.

    PubMed

    Lou, Yan-Peng; Zheng, Chang-Wu; Pan, Ren-Ming; Jin, Qiao-Wen; Zhao, Gang; Li, Zhong

    2015-02-06

    A combination of an amino acid derived chiral phosphine catalyst and methyl acrylate efficiently catalyzed the direct Mannich reaction of cyclic β-ketoesters and N-Boc-aldimines. The dual-reagent catalysis was presumed to function through the formation of a zwitterion, which catalyzed the reaction with excellent stereocontrol via a hydrogen-bonding assisted chiral ion-pair pathway.

  1. Direct access to ketones from aldehydes via rhodium-catalyzed cross-coupling reaction with potassium trifluoro(organo)borates.

    PubMed

    Pucheault, Mathieu; Darses, Sylvain; Genet, Jean-Pierre

    2004-12-01

    A direct cross-coupling reaction of aromatic aldehydes with potassium trifluoro(organo)borates afforded ketones in high yields and under mild conditions in the presence of a rhodium catalyst and acetone. This new reaction, involving a formal aldehyde C-H bond activation, is believed to proceed via a Heck-type mechanism followed by hydride transfer to acetone.

  2. Characterization of spark plasma sintered Ag nanopowders.

    PubMed

    Fu, Y Q; Shearwood, C; Xu, B; Yu, L G; Khor, K A

    2010-03-19

    The low temperature sintering behaviour of nanocrystalline Ag powder (with an average size of 70 nm) was characterized. Using spark plasma sintering (SPS), the Ag nanopowders can be successfully sintered at low pressure for only 5 min without external heating, and the sintering density increases and porosity decreases significantly with increase in the sintering temperature. Nanoindentation has been used to characterize the SPS sintered Ag samples. The mechanisms of the low sintering temperature behaviour of the nano-Ag powder and the nanoscale mechanical performance have been discussed. Compression tests were also used to characterize the mechanical properties of the sintered Ag sample with a maximum strain up to 15%.

  3. Microwave sintering of multiple articles

    DOEpatents

    Blake, Rodger D.; Katz, Joel D.

    1993-01-01

    Apparatus and method for producing articles of alumina and of alumina and silicon carbide in which the articles are sintered at high temperatures using microwave radiation. The articles are placed in a sintering container which is placed in a microwave cavity for heating. The rates at which heating and cooling take place is controlled.

  4. Detection of Mycoplasma Contamination Directly from Culture Supernatant Using Polymerase Chain Reaction.

    PubMed

    Pisal, R V; Hrebíková, H; Chvátalová, J; Kunke, D; Filip, S; Mokrý, J

    2016-01-01

    Ensuring mycoplasma-free cell culture is of prime importance as they severely affect cellular characteristics leading to experimental artefacts and spurious results. Various methods persist for mycoplasma detection; out of the whole array of methods polymerase chain reaction (PCR) is the most favoured one because it is highly sensitive, specific and quick. The PCR-based detection procedure involves three steps: cell culture supernatant collection, DNA isolation, and PCR. We have modified this procedure so that cell culture supernatant can directly be used for PCR without the need for DNA extraction. This modification makes the procedure quicker and more sensitive because loss of mycoplasma DNA is prevented and this loss becomes more significant when the level of mycoplasma contamination is very low.

  5. Action Video Games Improve Direction Discrimination of Parafoveal Translational Global Motion but Not Reaction Times.

    PubMed

    Pavan, Andrea; Boyce, Matthew; Ghin, Filippo

    2016-10-01

    Playing action video games enhances visual motion perception. However, there is psychophysical evidence that action video games do not improve motion sensitivity for translational global moving patterns presented in fovea. This study investigates global motion perception in action video game players and compares their performance to that of non-action video game players and non-video game players. Stimuli were random dot kinematograms presented in the parafovea. Observers discriminated the motion direction of a target random dot kinematogram presented in one of the four visual quadrants. Action video game players showed lower motion coherence thresholds than the other groups. However, when the task was performed at threshold, we did not find differences between groups in terms of distributions of reaction times. These results suggest that action video games improve visual motion sensitivity in the near periphery of the visual field, rather than speed response.

  6. Effect of milling and leaching on the structure of sintered silicon

    NASA Technical Reports Server (NTRS)

    Yeh, H. C.; Glasgow, T. K.; Herbell, T. P.

    1980-01-01

    The effects of attrition milling and acid leaching on the sintering behavior and the resultant structures of two commercial silicon powders were investigated. Sintering was performed in He for 16 hours at 1200, 1250, and 1300 C. Compacts of as-received Si did not densify during sintering. Milling reduced the average particle size to below 0.5 microns and enhanced densification (1.75 g/cc). Leaching milled Si further enhanced densification (1.90 g/cc max.) and decreased structural coarsening. After sintering, the structure of the milled and leached powder compacts appears favorable for the production of reaction bonded silicon nitride.

  7. Efficient and directed peptide bond formation in the gas phase via ion/ion reactions.

    PubMed

    McGee, William M; McLuckey, Scott A

    2014-01-28

    Amide linkages are among the most important chemical bonds in living systems, constituting the connections between amino acids in peptides and proteins. We demonstrate the controlled formation of amide bonds between amino acids or peptides in the gas phase using ion/ion reactions in a mass spectrometer. Individual amino acids or peptides can be prepared as reagents by (i) incorporating gas phase-labile protecting groups to silence otherwise reactive functional groups, such as the N terminus; (ii) converting the carboxyl groups to the active ester of N-hydroxysuccinimide; and (iii) incorporating a charge site. Protonation renders basic sites (nucleophiles) unreactive toward the N-hydroxysuccinimide ester reagents, resulting in sites with the greatest gas phase basicities being, in large part, unreactive. The N-terminal amines of most naturally occurring amino acids have lower gas phase basicities than the side chains of the basic amino acids (i.e., those of histidine, lysine, or arginine). Therefore, reagents may be directed to the N terminus of an existing "anchor" peptide to form an amide bond by protonating the anchor peptide's basic residues, while leaving the N-terminal amine unprotonated and therefore reactive. Reaction efficiencies of greater than 30% have been observed. We propose this method as a step toward the controlled synthesis of peptides in the gas phase.

  8. Direct and sensitive detection of a pathogenic protozoan, Toxoplasma gondii, by polymerase chain reaction.

    PubMed Central

    Burg, J L; Grover, C M; Pouletty, P; Boothroyd, J C

    1989-01-01

    We applied the polymerase chain reaction to detection of the pathogenic protozoan Toxoplasma gondii based on our identification of a 35-fold-repetitive gene (the B1 gene) as a target. Using this procedure, we were able to amplify and detect the DNA of a single organism directly from a crude cell lysate. This level of sensitivity also allowed us to detect the B1 gene from purified DNA samples containing as few as 10 parasites in the presence of 100,000 human leukocytes. This is representative of the maximal cellular infiltration (10(5)/ml) in 1 ml of cerebrospinal fluid obtained from patients with toxoplasmic encephalitis. The B1 gene is present and conserved in all six T. gondii strains tested to date, including two isolates from patients with acquired immunodeficiency syndrome. No signal was detected by using this assay and DNAs from a variety of other organisms, including several which might be found in the central nervous system of an immunocompromised host. This combination of sensitivity and specificity should make detection of the B1 gene based on polymerase chain reaction amplification a very useful method for diagnosis of toxoplasmosis both in immunocompromised hosts and in congenitally infected fetuses. Images PMID:2768467

  9. Direct Determination of the Simplest Criegee Intermediate (CH2OO) Self Reaction Rate.

    PubMed

    Buras, Zachary J; Elsamra, Rehab M I; Green, William H

    2014-07-03

    The rate of self-reaction of the simplest Criegee intermediate, CH2OO, is of importance in many current laboratory experiments where CH2OO concentrations are high, such as flash photolysis and alkene ozonolysis. Using laser flash photolysis while simultaneously probing both CH2OO and I atom by direct absorption, we can accurately determine absolute CH2OO concentrations as well as the UV absorption cross section of CH2OO at our probe wavelength (λ = 375 nm), which is in agreement with a recently published value. Knowing absolute concentrations we can accurately measure kself = 6.0 ± 2.1 × 10(-11)cm(3) molecule(-1) s(-1) at 297 K. We are also able to put an upper bound on the rate coefficient for CH2OO + I of 1.0 × 10(-11) cm(3) molecule(-1) s(-1). Both of these rate coefficients are at least a factor of 5 smaller than other recent measurements of the same reactions.

  10. Monitoring transcranial direct current stimulation induced changes in cortical excitability during the serial reaction time task.

    PubMed

    Ambrus, Géza Gergely; Chaieb, Leila; Stilling, Roman; Rothkegel, Holger; Antal, Andrea; Paulus, Walter

    2016-03-11

    The measurement of the motor evoked potential (MEP) amplitudes using single pulse transcranial magnetic stimulation (TMS) is a common method to observe changes in motor cortical excitability. The level of cortical excitability has been shown to change during motor learning. Conversely, motor learning can be improved by using anodal transcranial direct current stimulation (tDCS). In the present study, we aimed to monitor cortical excitability changes during an implicit motor learning paradigm, a version of the serial reaction time task (SRTT). Responses from the first dorsal interosseous (FDI) and forearm flexor (FLEX) muscles were recorded before, during and after the performance of the SRTT. Online measurements were combined with anodal, cathodal or sham tDCS for the duration of the SRTT. Negative correlations between the amplitude of online FDI MEPs and SRTT reaction times (RTs) were observed across the learning blocks in the cathodal condition (higher average MEP amplitudes associated with lower RTs) but no significant differences in the anodal and sham conditions. tDCS did not have an impact on SRTT performance, as would be predicted based on previous studies. The offline before-after SRTT MEP amplitudes showed an increase after anodal and a tendency to decrease after cathodal stimulation, but these changes were not significant. The combination of different interventions during tDCS might result in reduced efficacy of the stimulation that in future studies need further attention.

  11. Direct Numerical Simulation of biomass pyrolysis and combustion with gas phase reactions

    NASA Astrophysics Data System (ADS)

    Awasthi, A.; Kuerten, J. G. M.; Geurts, B. J.

    2016-09-01

    We present Direct Numerical Simulation of biomass pyrolysis and combustion in a turbulent channel flow. The model includes simplified models for biomass pyrolysis and char combustion along with a model for particle tracking. The gas phase is modelled as a mixture of reacting gas species. The gas-particle interactions for mass, momentum, and energy exchange are included by two-way coupling terms. The effect of two-way coupling on the conversion time of biomass particles is found noticeable for particle volume fractions > 10-5. We also observe that at constant volume fraction the effect of two-way coupling increases as the particle size is reduced, due to the higher total heat exchange area in case of smaller particles. The inclusion of gas phase homogeneous reactions in the DNS model decreases the biomass pyrolysis time due to higher gas temperatures. In contrast, including gas phase reactions increases the combustion time of biomass due to the lower concentration of oxygen at the particle surface.

  12. Anode reaction mechanism and crossover in direct dimethyl ether fuel cell

    NASA Astrophysics Data System (ADS)

    Mizutani, Itsuko; Liu, Yan; Mitsushima, Shigenori; Ota, Ken-ichiro; Kamiya, Nobuyuki

    The anode reaction mechanism and the crossover of a direct dimethyl ether fuel cell (DDMEFC) have been investigated. This was done by considering the anode products of the half-cell and DDMEFC experiments. It was found that the CO 2 current efficiency of the DDMEFC was almost 1 at 30-80 °C and that this value was higher than that of a DMFC. The main by-products of the DDMEFC were methyl formate and methanol whose amounts are negligibly small compared to CO 2. With respect to crossover, the influence of DME on the oxygen reduction reaction (ORR) was examined with a half-cell, and the amount of crossover of DME was measured while operating an actually constructed DDMEFC. From these experiments, it was found that DME does not influence the ORR as much as methanol under similar conditions. Furthermore, the amount of crossover of DME decreased with an increase in temperature and current density and it was one-half that of methanol on open circuit and at 80 °C. The CO 2 current efficiency of the DDMEFC is higher than that of a DMFC, and the influence of crossover in the DDMEFC is less than that in the DMFC. Since the temperature dependence of the reactivity of DME is larger than that of methanol, the higher output is expected for the DDMEFC at the elevated temperature. Therefore, the DDMEFC has a promising potential as a portable power source in the future.

  13. A research on sintering characteristics and mechanisms of dried sewage sludge.

    PubMed

    Wang, Xingrun; Jin, Yiying; Wang, Zhingyu; Mahar, Rasool Bux; Nie, Yongfeng

    2008-12-30

    This study investigates the sintering behavior of dried sewage sludge and the related sintering mechanisms, considering sintering temperature and sintering time. Experimental results indicate that the characteristics are primarily influenced by sintering temperature. When the sintering temperature is increased from 1020 to 1050 degrees C, the specimens' compressive strength and bulk density increase significantly, while water absorption decreases obviously, indicating an improvement of densification due to sintering. However, the compressive strength cannot meet the requirement for traditional ceramic products due to the release of organic matters and the formation of big pores in the products. Phosphorus in sewage sludge initially takes reactions with the formation of calcium magnesium phosphate and aluminum phosphate during sintering, which are helpful for enhancing the compressive strength. So, some materials with high contents of Al could be used to enhance the compressive strength of products. Heavy metals are fixed primarily inside the sintered specimens, with the As, Pb, Cd, Cr, Ni, Cu, Zn concentrations in the leachate found to be in the range of China regulatory requirements. These results reveal the feasibility of recycling dried sewage sludge by sintering as a construction material.

  14. Manufacture of sintered silicon nitrides

    NASA Technical Reports Server (NTRS)

    Iwai, T.

    1985-01-01

    Sintered silicon nitrides are manufactured by sintering Si3N powder containing 2 to 15% in wt of a powder mixture composed of nitride powder of lanthanide or Y 100 parts and AIN powder less than 100 parts at 1500 to 1900 deg. temperature under a pressure of less than 200 Kg/sq. cm. The sintered Si3N has high mechanical strength in high temperature. Thus, Si3N4 93.0, Y 5.0 and AlN 2.0% in weight were wet mixed in acetone in N atom, molded and sintered at 1750 deg. and 1000 Kg/sq. cm. to give a sintered body having high hardness.

  15. Processing of bulk Al7075 alloy by spark plasma sintering

    NASA Astrophysics Data System (ADS)

    Málek, P.; Molnárová, O.; Cinert, J.; Lukáč, F.; Chráska, T.

    2017-02-01

    The main advantages of powder metallurgy processing route are the possibility to produce near-net-shape compacts and to minimize the finish machining and material loss. The main problem in particle consolidation process is to suppress porosity, to remove oxide layers, and to retain the microstructure of powder materials. Spark plasma sintering (SPS) combines concurrent uniaxial pressure and direct heating by a pulsed DC current. Sintering occurs at relatively low temperatures for a short time and does not influence significantly the microstructure in the interiors of original powder particles. The efficiency of SPS in producing compacts with low porosity might be dependent on the distribution of particle size in original powder material. The gas atomized Al7075 powder was sieved to several charges and then sintered by SPS. Microstructure of sintered compacts was studied by light and scanning electron microscopy. The phase composition was investigated using X-ray diffraction. The mechanical behaviour was tested by bending tests.

  16. Novel bulk carbon nanotube materials for implant by spark plasma sintering.

    PubMed

    Wang, Wei; Omori, Mamoru; Watari, Fumio; Yokoyama, Atsuro

    2005-12-01

    Novel, bulk multiwall carbon nanotubes (MWCNTs) sintered with polycarbosilane (PCS) as a binder agent were fabricated by spark plasma sintering (SPS), and their microstructure and properties were investigated. Sintering was done with 20-60 MPa pressure at 1200 degrees C. SEM and TEM observations showed that the nanosized tube microstructure was preserved even after sintering, and tubes adhered to each other with the nanosized nodules of SiC pyrolyzed form PCS as revealed by X-ray diffraction. Bulk density and Vickers hardness were found to increase, whereas the specific surface area decreased, as PCS content and sintering pressure increased. Through animal experiments, the inflammatory reaction of CNTs/PCS material was found to be slightly increased with increasing PCS content. In conclusion, sintered CNTs had physical and mechanical properties close to bone, and their good biocompatibility based on tissue response served to pave their way as a suitable implant material in the future.

  17. Direct kinetic measurements of Criegee intermediate (CH₂OO) formed by reaction of CH₂I with O₂.

    PubMed

    Welz, Oliver; Savee, John D; Osborn, David L; Vasu, Subith S; Percival, Carl J; Shallcross, Dudley E; Taatjes, Craig A

    2012-01-13

    Ozonolysis is a major tropospheric removal mechanism for unsaturated hydrocarbons and proceeds via "Criegee intermediates"--carbonyl oxides--that play a key role in tropospheric oxidation models. However, until recently no gas-phase Criegee intermediate had been observed, and indirect determinations of their reaction kinetics gave derived rate coefficients spanning orders of magnitude. Here, we report direct photoionization mass spectrometric detection of formaldehyde oxide (CH(2)OO) as a product of the reaction of CH(2)I with O(2). This reaction enabled direct laboratory determinations of CH(2)OO kinetics. Upper limits were extracted for reaction rate coefficients with NO and H(2)O. The CH(2)OO reactions with SO(2) and NO(2) proved unexpectedly rapid and imply a substantially greater role of carbonyl oxides in models of tropospheric sulfate and nitrate chemistry than previously assumed.

  18. [Comparison of direct microscopy, culture and polymerase chain reaction methods for the diagnosis of cutaneous leishmaniasis].

    PubMed

    Ertabaklar, Hatice; Özlem Çalışkan, Serçin; Boduç, Erengül; Ertuğ, Sema

    2015-01-01

    Cutaneous leishmaniasis (CL) is an endemic disease especially in Southeastern Anatolia of Turkey and recently shows a trend for spread to other regions of the country including the Aegean region. The diagnosis of CL is based on combined evaluation of epidemiological data with the clinical symptoms and laboratory findings. Direct microscopic examination and culture methods are mainly used in the routine diagnosis of CL, while molecular methods are mainly used for research. The aim of this study was to detect the presence of Leishmania spp. in samples obtained from CL-suspected patients by using direct microscopy, culture and polymerase chain reaction (PCR) methods and to compare the results. A total of 55 patients who were admitted to Parasitology Laboratory of Adnan Menderes University Hospital, Aydin (located at Aegean region in Turkey), between 2012-2014 were included in the study. Smear preparations from the skin lesions of cases were fixed and stained with Giemsa, and the presence of amastigote forms were evaluated by direct microscopy. NNN medium was used for the cultivation of samples. Total genomic DNA of Leishmania from the samples were extracted with a commercial kit (NucleoSpin Tissue(®) Kit, Macherey-Nagel, Germany) and PCR was performed by using 13A and 13B primers to amplify the 116 base pair fragment of Leishmania spp. specific kinetoplast DNA. Amastigotes were observed in 29 (53%) of the 55 samples by direct microscopy, promastigotes were detected among 34 (62%) samples in culture, and parasite-specific amplicons were revealed in 30 (55%) samples by PCR. All assays were positive in 24 patients while in 18 patients all of the tests yielded negative results. Thirty-seven (67%) out of 55 cases were diagnosed as CL when reactivity in at least one of these three methods were considered as positive. Accordingly the positivity rates of the methods were 78.4% (29/37) for direct microscopy, 92% (34/37) for culture and 81.1% (30/37) for PCR in CL

  19. Cleaning surfaces of sintered beryllium oxide

    NASA Astrophysics Data System (ADS)

    Musket, R. G.

    A practical procedure for preparing atomically clean, debris-free surfaces on sintered beryllium oxide specimens has been developed. Chemical, ion-sputter, and UV/ozone cleaning technique were examined in efforts to improve the surface cleanliness. Characterization of the surfaces were performed using Auger electron spectroscopy (AES) to determine the level of cleanliness and scanning electron microscopy (SEM) to examine the surface microtopography. In addition, Rutherford backscattering (RBS) provided information on both bulk and surface contamination. The essence of the practical procedure consists of ultrasonic cleaning in dilute nitric acid followed by a UV/ozone exposure. Such treatments reduced the surface impurity levels for elements with Z > 4 to less than 1 at%. The described procedure should be directly applicable to other sintered oxide materials.

  20. Direct coupling between stress, strain and adsorption reactions - A study on coal-CO2 systems

    NASA Astrophysics Data System (ADS)

    Hol, S.; Peach, C. J.; Spiers, C. J.

    2012-12-01

    Though it is well-known that adsorption reactions frequently assist deformation of porous rocks, very little understanding exists on the direct coupling with stress state and strain. One of the materials in which adsorption plays a large role is coal, as is observed in the particular case of Enhanced Coalbed Methane Production (ECBM), which involves the geological storage of CO2 and the recovery of CH4. In this case, adsorption and the associated swelling cause significant injectivity problems, which is experienced in almost all pilot field projects to date. This suggests that indeed a strong fundamental coupling exists between CO2 sorption, changes in the mechanical state of the coal matrix and changes in the transport properties of the system, and illustrates the need to understand coupled stress-strain-sorption behaviour. In this contribution, we describe several important observations made on coal-CO2 systems that can learn us about many other natural, stressed adsorbate-adsorbent systems. In our experiments, first of all, the adsorption of CO2 in the coal matrix gave rise to swelling. Although this is well-known, we found that the total volumetric strain occurring under unconfined conditions can be realistically modelled (up to at least 100 MPa) as the sum of an adsorption-related expansion term and an elastic compression term. Second, effective in situ stresses will directly reduce the sorption capacity, and associated swelling of the coal matrix significantly. Our general thermodynamic model for the effect of a 3D stress state on adsorbed CO2 concentration supports this observation, and also shows that "self-stressing", as a result of CO2 adsorption occurring under conditions of restricted or zero strain (i.e. fully constrained conditions), will more than double the expected in situ stresses. A constitutive equation was developed to describe the full coupling between stress state, total strain (i.e. combined strain of adsorption processes and poroelasticity

  1. Sintered silicon nitrode recuperator fabrication

    NASA Technical Reports Server (NTRS)

    Gatti, A.; Chiu, W. S.; Mccreight, L. R.

    1980-01-01

    The preliminary design and a demonstration of the feasibility of fabricating submodules of an automotive Stirling engine recuperator for waste heat recovery at 370 C are described. Sinterable silicon nitride (Sialon) tubing and plates were fabricated by extrusion and hydrostatic pressing, respectively, suitable for demonstrating a potential method of constructing ceramic recuperator-type heat exchangers. These components were fired in nitrogen atmosphere to 1800 C without significant scale formation so that they can be used in the as-fired condition. A refractory glass composition (Al2O3 x 4.5 CaO.MgO x 11SiO2) was used to join and seal component parts by a brazing technique which formed strong recuperator submodules capable of withstanding repeated thermal cycling to 1370 C. The corrosion resistance of these materials to Na2SO4 + NaCl carbon mixtures was also assessed in atmospheres of air, hydrogen and CO2-N2-H2O mixtures at both 870 C and 1370 C for times to 1000 hours. No significant reaction was observed under any of these test conditions.

  2. Direct observation of spin-like reaction fronts in planar energetic multilayer foils.

    SciTech Connect

    Adams, David Price; Hodges, V. Carter; Jones, Eric D., Jr.; McDonald, Joel Patrick

    2008-10-01

    Propagating reactions in initially planar cobalt/aluminum exothermic multilayer foils have been investigated using high-speed digital photography. Real-time observations of reactions indicate that unsteady (spinlike) reaction propagation leads to the formation of highly periodic surface morphologies with length scales ranging from 1 {micro}m to 1 mm. The characteristics of propagating spinlike reactions and corresponding reacted foil morphologies depend on the bilayer thickness of multilayer foils.

  3. Sintering techniques for microstructure control in ceramics

    NASA Astrophysics Data System (ADS)

    Rosenberger, Andrew T.

    Sintering techniques can be manipulated to enhance densification in difficult to sinter materials and to produce property enhancing microstructures. However, the interplay between materials, sintering techniques, and end properties is not fully understood in many material systems, and some fundamental aspects of sintering such as the nature of the effects of electric fields remains unknown. The processing property relationships were examined in two classes of materials; zirconium diboride ultra high temperature ceramic composites, and all solid lithium-ion battery phosphate materials. Investigation of zirconium diboride ceramics focused on the effects of zirconium carbide as a secondary or tertiary phase in ZrB2 and ZrB2 -- SiC. Addition of zirconium carbide was observed to increase flexural strength of composites up to 590MPa at 50wt% ZrC, significantly higher than the flexural strength of 380MPa observed in similarly prepared ZrB2 -- SiC. This difference was attributed to the absence of CTE mismatch induced residual stresses in the ZrB2 -- ZrC composites. A high temperature reaction between ZrB2 and TiC producing Zr1-xTixB2 -- ZrC composites was discovered and found to enhance densification while reducing the average grain size to as small as 1.4mum, lower than the starting powder size of 1.8mum. While a high flexural strength of 670MPa was observed, a strength dependence on the ZrC grain size indicative of CTE mismatch residual stresses was also seen. Finally, the oxidation and ablation resistance of ZrB2 -- ZrC -- SiC composites as a function of ZrC fraction and ZrC:SiC ratio was investigated. Above 5vol% ZrC, the oxidation and ablation resistance of the composites was significantly reduced due to ZrC oxidation, regardless of SiC content. While ZrC can significantly enhance the mechanical properties of the composite, the volume fraction must be kept low to avoid an undesirable reduction in the oxidation resistance. The influence of applied electrical fields

  4. Magnetic field effects on reactive sintering of MnBi

    NASA Astrophysics Data System (ADS)

    Abematsu, Ken-ichi; Mitsui, Yoshifuru; Taira, Atsushi; Miyazaki, Daiki; Takaki, Akio; Umetsu, Rie Y.; Takahashi, Kohki; Koyama, Keiichi

    2016-08-01

    Annealing temperature of reactive sintering of MnBi was optimized. The highest fraction of MnBi phase was obtained to be 93wt.% at annealing temperature of 280°C. Magnetic field effects on solid- and liquid-state sintering of MnBi were described. The reacted fraction of MnBi was enhanced by the application of magnetic field of 15 T for solid- state sintering. In contract, reacted fraction was not influenced by magnetic field for liquid-state sintering. Both of in- field solid- and liquid-state sintered samples realized the highly crystal orientation of MnBi phase along the applied magnetic field direction. The Lotgering factor of the MnBi phase was obtained to be 1.0 for both in-field sintered samples, which was an "almost complete" uniaxial orientation. Due to the crystal orientation, anisotropic magnetic properties exhibited. The anisotropy field of the bulk sample was evaluated to be 4 T at room temperature, which also suggested the uniaxial orientation of the sample.

  5. MORATE: a program for direct dynamics calculations of chemical reaction rates by semiempirical molecular orbital theory

    NASA Astrophysics Data System (ADS)

    Truong, Thanh N.; Lu, Da-hong; Lynch, Gillian C.; Liu, Yi-Ping; Melissas, Vasilios S.; Stewart, James J. P.; Steckler, Rozeanne; Garrett, Bruce C.; Isaacson, Alan D.; Gonzalez-Lafont, Angels; Rai, Sachchida N.; Hancock, Gene C.; Joseph, Tomi; Truhlar, Donald G.

    1993-04-01

    We present a computer program, MORATE (Molecular Orbital RATE calculations), for direct dynamics calculations of unimolecular and bimolecular rate constants of gas-phase chemical reactions involving atoms, diatoms, or polyatomic species. The potential energies, gradients, and higher derivatives of the potential are calculated whenever needed by semiempirical molecular orbital theory without the intermediary of a global or semiglobal fit. The dynamical methods used are conventional or variational transition state theory and multidimensional semiclassical approximations for tunneling and nonclassical reflection. The computer program is conveniently interfaced package consisting of the POLYRATE program, version 4.5.1, for dynamical rate calculations, and the MOPAC program, version 5.03, for semiempirical electronic structure computations. All semiempirical methods available in MOPAC, in particular MINDO/3, MNDO, AM1, and PM3, can be called on to calculate the potential and gradient. Higher derivatives of the potential are obtained by numerical derivatives of the gradient. Variational transition states are found by a one-dimensional search of generalized-transition-state dividing surfaces perpendicular to the minimum-energy path, and tunneling probabilities are evaluated by numerical quadrature.

  6. Catalytic Direct-type 1,4-Addition Reactions of Alkylazaarenes.

    PubMed

    Suzuki, Hirotsugu; Igarashi, Ryo; Yamashita, Yasuhiro; Kobayashi, Shū

    2017-04-10

    1,4-addition reactions of alkylazaarenes catalyzed by strong Brønsted bases have been developed for the first time. The desired reactions with α,β-unsaturated amides proceeded under mild reaction conditions to give the 1,4-adducts in high yields. Both ortho- and para-substituted azaarenes afforded the desired adducts in high yields. Regioselective reactions of di- or trimethylpyridine were found to be possible depending on the acidity of the α-hydrogen atoms. Furthermore, a candidate of allosteric protein kinase modulators was synthesized in two steps. An asymmetric variant of this reaction was also found to be feasible.

  7. Ceramic powder for sintering materials

    NASA Technical Reports Server (NTRS)

    Akiya, H.; Saito, A.

    1984-01-01

    Surface activity of ceramic powders such as MgO and Al2O3, for use in sintering with sp. emphasis on their particle size, shape, particle size distribution, packing, and coexisting additives and impurities are reviewed.

  8. Electrical sintering of nanoparticle structures.

    PubMed

    Allen, Mark L; Aronniemi, Mikko; Mattila, Tomi; Alastalo, Ari; Ojanperä, Kimmo; Suhonen, Mika; Seppä, Heikki

    2008-04-30

    A method for sintering nanoparticles by applying voltage is presented. This electrical sintering method is demonstrated using silver nanoparticle structures ink-jet-printed onto temperature-sensitive photopaper. The conductivity of the printed nanoparticle layer increases by more than five orders of magnitude during the sintering process, with the final conductivity reaching 3.7 × 10(7) S m(-1) at best. Due to a strong positive feedback induced by the voltage boundary condition, the process is very rapid-the major transition occurs within 2 µs. The best obtained conductivity is two orders of magnitude better than for the equivalent structures oven-sintered at the maximum tolerable temperature of the substrate. Additional key advantages of the method include the feasibility for patterning, systematic control of the final conductivity and in situ process monitoring. The method offers a generic tool for electrical functionalization of nanoparticle structures.

  9. Direct dynamics simulations of the product channels and atomistic mechanisms for the OH(-) + CH3I reaction. Comparison with experiment.

    PubMed

    Xie, Jing; Sun, Rui; Siebert, Matthew R; Otto, Rico; Wester, Roland; Hase, William L

    2013-08-15

    Electronic structure and direct dynamics calculations were used to study the potential energy surface and atomic-level dynamics for the OH(-) + CH3I reactions. The results are compared with crossed molecular beam, ion imaging experiments. The DFT/B97-1/ECP/d level of theory gives reaction energetics in good agreement with experiment and higher level calculations, and it was used for the direct dynamics simulations that were performed for reactant collision energies of 2.0, 1.0, 0.5, and 0.05 eV. Five different pathways are observed in the simulations, forming CH3OH + I(-), CH2I(-) + H2O, CH2 + I(-) + H2O, IOH(-) + CH3, and [CH3--I--OH](-). The SN2 first pathway and the proton-transfer second pathway dominate the reaction dynamics. Though the reaction energetics favor the SN2 pathway, the proton-transfer pathway is more important except for the lowest collision energy. The relative ion yield determined from the simulations is in overall good agreement with experiment. Both the SN2 and proton-transfer pathways occur via direct rebound, direct stripping, and indirect mechanisms. Except for the highest collision energy, 70-90% of the indirect reaction for the SN2 pathway occurs via formation of the hydrogen-bonded OH(-)---HCH2I prereaction complex. For the proton-transfer pathway the indirect reaction is more complex with the roundabout mechanism and formation of the OH(-)---HCH2I and CH2I(-)---HOH complexes contributing to the reaction. The majority of the SN2 reaction is direct at 2.0, 1.0, and 0.5 eV, dominated by stripping. At 0.05 eV the two direct mechanisms and the indirect mechanisms have nearly equal contributions. The majority of the proton-transfer pathway is direct stripping at 2.0, 1.0, and 0.5 eV, but the majority of the reaction is indirect at 0.05 eV. The product relative translational energy distributions are in good agreement with experiment for both the SN2 and proton-transfer pathways. For both, direct reaction preferentially transfers the product

  10. One step sintering of homogenized bauxite raw material and kinetic study

    NASA Astrophysics Data System (ADS)

    Gao, Chang-he; Jiang, Peng; Li, Yong; Sun, Jia-lin; Zhang, Jun-jie; Yang, Huan-ying

    2016-10-01

    A one-step sintering process of bauxite raw material from direct mining was completed, and the kinetics of this process was analyzed thoroughly. The results show that the sintering kinetics of bauxite raw material exhibits the liquid-phase sintering behavior. A small portion of impurities existed in the raw material act as a liquid phase. After X-ray diffraction analyses, scanning electron microscopy observations, and kinetics calculations, sintering temperature and heating duration were determined as the two major factors contributing to the sintering process and densification of bauxite ore. An elevated heating temperature and longer duration favor the densification process. The major obstacle for the densification of bauxite material is attributed to the formation of the enclosed blowhole during liquid-phase sintering.

  11. A New Direct Single-Molecule Observation Method for DNA Synthesis Reaction Using Fluorescent Replication Protein A

    PubMed Central

    Takahashi, Shunsuke; Kawasaki, Shohei; Miyata, Hidefumi; Kurita, Hirofumi; Mizuno, Takeshi; Matsuura, Shun-ichi; Mizuno, Akira; Oshige, Masahiko; Katsura, Shinji

    2014-01-01

    Using a single-stranded region tracing system, single-molecule DNA synthesis reactions were directly observed in microflow channels. The direct single-molecule observations of DNA synthesis were labeled with a fusion protein consisting of the ssDNA-binding domain of a 70-kDa subunit of replication protein A and enhanced yellow fluorescent protein (RPA-YFP). Our method was suitable for measurement of DNA synthesis reaction rates with control of the ssλDNA form as stretched ssλDNA (+flow) and random coiled ssλDNA (−flow) via buffer flow. Sequentially captured photographs demonstrated that the synthesized region of an ssλDNA molecule monotonously increased with the reaction time. The DNA synthesis reaction rate of random coiled ssλDNA (−flow) was nearly the same as that measured in a previous ensemble molecule experiment (52 vs. 50 bases/s). This suggested that the random coiled form of DNA (−flow) reflected the DNA form in the bulk experiment in the case of DNA synthesis reactions. In addition, the DNA synthesis reaction rate of stretched ssλDNA (+flow) was approximately 75% higher than that of random coiled ssλDNA (−flow) (91 vs. 52 bases/s). The DNA synthesis reaction rate of the Klenow fragment (3′-5′exo–) was promoted by DNA stretching with buffer flow. PMID:24625741

  12. Electrical Sintering of Silver Nanoparticle Ink Studied by In-Situ TEM Probing

    PubMed Central

    Hummelgård, Magnus; Zhang, Renyun; Nilsson, Hans-Erik; Olin, Håkan

    2011-01-01

    Metallic nanoparticle inks are used for printed electronics, but to reach acceptable conductivity the structures need to be sintered, usually using a furnace. Recently, sintering by direct resistive heating has been demonstrated. For a microscopic understanding of this Joule heating sintering method, we studied the entire process in real time inside a transmission electron microscope equipped with a movable electrical probe. We found an onset of Joule heating induced sintering and coalescence of nanoparticles at power levels of 0.1–10 mW/m3. In addition, a carbonization of the organic shells that stabilize the nanoparticles were found, with a conductivity of 4 105 Sm−1. PMID:21390314

  13. PLANETESIMAL FORMATION INDUCED BY SINTERING

    SciTech Connect

    Sirono, Sin-iti

    2011-06-01

    Sintering of H{sub 2}O ice proceeds in an icy dust aggregate as the temperature increases due to the infall to the central star. By numerical simulations, I show that fragmentation of the aggregate by sintering occurs at a particular region of a protoplanetary nebula. The fragments accumulate at the region because their infalling velocity is low. The dust surface density exceeds the critical surface density required for gravitational instability to form planetesimals.

  14. The sintering of nitrogen ceramics

    SciTech Connect

    Hampshire, S.

    1986-01-01

    The mechanism of densification with oxide additives and the role of the ..cap alpha..-BETA phase transformation is investigated in a detailed kinetic study. Selected compositions in the Si-Al-O-N system are detailed, with and without additives. Although the work is mainly concerned with the identification of the mechanisms of sintering, some property measurements on a sintered BETA-sialon are reported and the feasibility of preparing pure ..cap alpha..-sialon phases is explored.

  15. Method of sintering ceramic materials

    DOEpatents

    Holcombe, Cressie E.; Dykes, Norman L.

    1992-01-01

    A method for sintering ceramic materials is described. A ceramic article is coated with layers of protective coatings such as boron nitride, graphite foil, and niobium. The coated ceramic article is embedded in a container containing refractory metal oxide granules and placed within a microwave oven. The ceramic article is heated by microwave energy to a temperature sufficient to sinter the ceramic article to form a densified ceramic article having a density equal to or greater than 90% of theoretical density.

  16. Method of sintering ceramic materials

    DOEpatents

    Holcombe, C.E.; Dykes, N.L.

    1992-11-17

    A method for sintering ceramic materials is described. A ceramic article is coated with layers of protective coatings such as boron nitride, graphite foil, and niobium. The coated ceramic article is embedded in a container containing refractory metal oxide granules and placed within a microwave oven. The ceramic article is heated by microwave energy to a temperature sufficient to sinter the ceramic article to form a densified ceramic article having a density equal to or greater than 90% of theoretical density. 2 figs.

  17. The effects of sintering temperature on dielectric constant of Barium Titanate (BaTiO3)

    NASA Astrophysics Data System (ADS)

    Sandi, DianisaKhoirum; Supriyanto, Agus; Anif; Jamaluddin; Iriani, Yofentina

    2016-02-01

    Barium Titanate (BT) has been synthesized using solid-state reaction method. Raw materials are Barium Carbonate (BaCO3) and Titanium Dioxide (TiO2). These materials are mixed for 6 h and sintered at a temperature of 1000oC, 1100oC, and 1200oC for 2 h. The sintering temperature was varied to investigate its effects on microstructure and dielectric constant of BT. The XRD patterns showed that BT becomes homogenous, with the large lattice parameter as the increase of sintering temperature. The crystal structure of BT is tetragonal. The crystalline size and crystallinity of BT at a sintering temperature of 1000oC are 37 nm and 97%. Those values for BT at a sintering temperature of 1100oC are 38 nm and 96%. At a sintering temperature of 1200oC, the values are 41 nm and 97%. The dielectric constant of BT at a sintering temperature of 1000oC, 1100oC, and 1200oC are 148, 163, and 185, respectively. It can be concluded that sintering temperature affects microstructure and dielectric constant of BT. High sintering temperature produces a high dielectric constant of BT. It indicates that crystalline size increases.

  18. Estimation of Sintering Kinetics of Oxidized Magnetite Pellet Using Optical Dilatometer

    NASA Astrophysics Data System (ADS)

    Sandeep Kumar, T. K.; Viswanathan, Neelakantan Nurni; Ahmed, Hesham M.; Andersson, Charlotte; Björkman, Bo

    2015-04-01

    The quality of magnetite pellet is primarily determined by the physico-chemical changes the pellet undergoes as it makes excursion through the gaseous and thermal environment in the induration furnace. Among these physico-chemical processes, the oxidation of magnetite phase and the sintering of oxidized magnetite (hematite) and magnetite (non-oxidized) phases are vital. Rates of these processes not only depend on the thermal and gaseous environment the pellet gets exposed in the induration reactor but also interdependent on each other. Therefore, a systematic study should involve understanding these processes in isolation to the extent possible and quantify them seeking the physics. With this motivation, the present paper focusses on investigating the sintering kinetics of oxidized magnetite pellet. For the current investigation, sintering experiments were carried out on pellets containing more than 95 pct magnetite concentrate from LKAB's mine, dried and oxidized to completion at sufficiently low temperature to avoid sintering. The sintering behavior of this oxidized pellet is quantified through shrinkage captured by Optical Dilatometer. The extent of sintering characterized by sintering ratio found to follow a power law with time i.e., Kt n . The rate constant K for sintering was determined for different temperatures from isothermal experiments. The rate constant, K, varies with temperature as and the activation energy ( Q) and reaction rate constant ( K') are estimated. Further, the sintering kinetic equation was also extended to a non-isothermal environment and validated using laboratory experiments.

  19. Comparison of TiO2 photocatalysis, electrochemically assisted Fenton reaction and direct electrochemistry for simulation of phase I metabolism reactions of drugs.

    PubMed

    Ruokolainen, Miina; Gul, Turan; Permentier, Hjalmar; Sikanen, Tiina; Kostiainen, Risto; Kotiaho, Tapio

    2016-02-15

    The feasibility of titanium dioxide (TiO2) photocatalysis, electrochemically assisted Fenton reaction (EC-Fenton) and direct electrochemical oxidation (EC) for simulation of phase I metabolism of drugs was studied by comparing the reaction products of buspirone, promazine, testosterone and 7-ethoxycoumarin with phase I metabolites of the same compounds produced in vitro by human liver microsomes (HLM). Reaction products were analysed by UHPLC-MS. TiO2 photocatalysis simulated the in vitro phase I metabolism in HLM more comprehensively than did EC-Fenton or EC. Even though TiO2 photocatalysis, EC-Fenton and EC do not allow comprehensive prediction of phase I metabolism, all three methods produce several important metabolites without the need for demanding purification steps to remove the biological matrix. Importantly, TiO2 photocatalysis produces aliphatic and aromatic hydroxylation products where direct EC fails. Furthermore, TiO2 photocatalysis is an extremely rapid, simple and inexpensive way to generate oxidation products in a clean matrix and the reaction can be simply initiated and quenched by switching the UV lamp on/off.

  20. Optimization of the sintering atmosphere for high-density hydroxyapatite-carbon nanotube composites.

    PubMed

    White, Ashley A; Kinloch, Ian A; Windle, Alan H; Best, Serena M

    2010-10-06

    Hydroxyapatite-carbon nanotube (HA-CNT) composites have the potential for improved mechanical properties over HA for use in bone graft applications. Finding an appropriate sintering atmosphere for this composite presents a dilemma, as HA requires water in the sintering atmosphere to remain phase pure and well hydroxylated, yet CNTs oxidize at the high temperatures required for sintering. The purpose of this study was to optimize the atmosphere for sintering these composites. While the reaction between carbon and water to form carbon monoxide and hydrogen at high temperatures (known as the 'water-gas reaction') would seem to present a problem for sintering these composites, Le Chatelier's principle suggests this reaction can be suppressed by increasing the concentration of carbon monoxide and hydrogen relative to the concentration of carbon and water, so as to retain the CNTs and keep the HA's structure intact. Eight sintering atmospheres were investigated, including standard atmospheres (such as air and wet Ar), as well as atmospheres based on the water-gas reaction. It was found that sintering in an atmosphere of carbon monoxide and hydrogen, with a small amount of water added, resulted in an optimal combination of phase purity, hydroxylation, CNT retention and density.

  1. Direct polymerase chain reaction for detection of toxigenic Corynebacterium diphtheriae strains from the Republic of Georgia after prolonged storage.

    PubMed

    Kobaidze, K; Popovic, T; Nakao, H; Quick, L

    2000-02-01

    A total of 226 paired nose and throat swab specimens from 113 clinical diphtheria cases from the republic of Georgia were analyzed by direct polymerase chain reaction targeting both A and B subunits of the diphtheria toxin gene, tox. Even after prolonged transport and extensive storage (7-14 months) of the clinical specimens in silica gel packages, direct polymerase chain reaction detected the diphtheria tox gene in 54% of the specimens. Specimens obtained by throat swab were three times more likely than those obtained by nose swab to be positive for Corynebacterium diphtheriae.

  2. Adverse Reactions Due to Directly Observed Treatment Strategy Therapy in Chinese Tuberculosis Patients: A Prospective Study

    PubMed Central

    Lv, Xiaozhen; Tang, Shaowen; Xia, Yinyin; Wang, Xiaomeng; Yuan, Yanli; Hu, Daiyu; Liu, Feiying; Wu, Shanshan; Zhang, Yuan; Yang, Zhirong; Tu, Dehua; Chen, Yixin; Deng, Peiyuan; Ma, Yu; Chen, Ru; Zhan, Siyan

    2013-01-01

    Background More than 1 million tuberculosis (TB) patients are receiving directly observed treatment strategy (DOTS) therapy in China every year. As to the profile of adverse drug reactions (ADRs) due to DOTS therapy, no consensus has been reached. There is no report regarding ADRs due to DOTS therapy with a large Chinese TB population. This study aimed to determine the incidence and prognosis of ADRs due to DOTS therapy, and to evaluate their impact on anti-TB treatment in China. Methods A prospective population-based cohort study was performed during 2007–2008. Sputum smear positive pulmonary TB patients who received DOTS therapy were included and followed up for six to nine months in 52 counties of four regions in China. The suspected ADRs were recorded and reviewed by Chinese State Food and Drug Administration. Results A total of 4304 TB patients were included in this study. 649 patients (15.08%) showed at least one ADR and 766 cases in total were detected. The incidence (count) of ADR based on affected organ was: liver dysfunction 6.34% (273), gastrointestinal disorders 3.74% (161), arthralgia 2.51% (108), allergic reactions 2.35% (101), neurological system disorders 2.04% (88), renal impairment 0.07% (3) and others 0.05% (2). Most cases of ADRs (95%) had a good clinical outcome, while two with hepatotoxicity and one with renal impairment died. Compared with patients without ADRs, patients with ADRs were more likely to have positive smear test results at the end of the intensive phase (adjusted OR, 2.00; 95%CI, 1.44–2.78) and unsuccessful anti-TB outcomes (adjusted OR, 2.58; 95%CI, 1.43–4.68). Conclusions The incidence of ADRs due to DOTS therapy was 15.08%. Those ADRs had a substantial impact on TB control in China. This highlighted the importance of developing strategies to ameliorate ADRs both to improve the quality of patient care and to control TB safely. PMID:23750225

  3. Dual-level direct dynamics studies for the reactions of OH radical with bromine-substituted ethanes.

    PubMed

    Wang, Li; Liu, Jing-yao; Gao, Hong; Wan, Su-qin; Li, Ze-sheng

    2009-03-01

    The dynamic properties of the multichannel hydrogen abstraction reactions of CH(3)CH(2)Br + OH --> products and CH(3)CHBr(2) + OH --> products are studied by dual-level direct dynamics method. For each reaction, three reaction channels, one for alpha-hydrogen abstraction and two for beta-hydrogen abstractions, have been identified. The minimum energy paths (MEPs) of both the reactions are calculated at the Becke's half-and-half (BH&H)-Lee-Yang-Parr (LYP)/6-311G(d, p) level and the energy profiles along the MEPs are further refined with interpolated single-point energies (ISPE) method at the G2M(RCC5)//BH&H-LYP level. There are complexes with energies less than those of the reactants or products located at the entrance or exit channels, which indicates that the reactions may proceed via an indirect mechanism. By canonical variational transition-state theory (CVT) the rate constants are calculated incorporating the small-curvature tunneling (SCT) correction in the temperature range of 220-2000 K. The agreement of the rate constants with available experimental values for two reactions is good in the measured temperature range. The calculated results show that alpha-hydrogen abstraction channel is the major reaction pathway in the lower temperature for two reactions, while the contribution of beta-hydrogen abstraction will increase with the increase in temperature.

  4. New Direction in Hydrogeochemical Transport Modeling: Incorporating Multiple Kinetic and Equilibrium Reaction Pathways

    SciTech Connect

    Steefel, C.I.

    2000-02-02

    At least two distinct kinds of hydrogeochemical models have evolved historically for use in analyzing contaminant transport, but each has important limitations. One kind, focusing on organic contaminants, treats biodegradation reactions as parts of relatively simple kinetic reaction networks with no or limited coupling to aqueous and surface complexation and mineral dissolution/precipitation reactions. A second kind, evolving out of the speciation and reaction path codes, is capable of handling a comprehensive suite of multicomponent complexation (aqueous and surface) and mineral precipitation and dissolution reactions, but has not been able to treat reaction networks characterized by partial redox disequilibrium and multiple kinetic pathways. More recently, various investigators have begun to consider biodegradation reactions in the context of comprehensive equilibrium and kinetic reaction networks (e.g. Hunter et al. 1998, Mayer 1999). Here we explore two examples of multiple equilibrium and kinetic reaction pathways using the reactive transport code GIMRT98 (Steefel, in prep.): (1) a computational example involving the generation of acid mine drainage due to oxidation of pyrite, and (2) a computational/field example where the rates of chlorinated VOC degradation are linked to the rates of major redox processes occurring in organic-rich wetland sediments overlying a contaminated aerobic aquifer.

  5. Characteristic variation of spark plasma-sintered Ta compacts

    NASA Astrophysics Data System (ADS)

    Cho, Gue-Serb; Lim, Jung-Kyu; Choe, Kyeong-Hwan; Shin, Seung-Yong

    2010-05-01

    In the present study, we applied the SPS process to obtain a tantalum (Ta) compact for a sputtering target. Sintered Ta compacts were characterized with respect to microstructure, relative density, Vickers hardness and phase composition of the inside and the surface. By radio frequency (RF) thermal plasma treatment, a spherical ultra-fine Ta powder was obtained; however, the oxygen content increased due to severe passivation during powder handling. Higher sintering temperature and the RF plasma treatment increased the densification of the sintered compact and also the Vickers hardness. From XRD analysis, only Ta was identified in the cross section of compacts, and TaC formed by the reaction between Ta and the graphite mould was found in the surface of the compacts. The evacuation of the chamber and the reduction by the graphite mould promote the purification of the compact.

  6. Fundamental studies of retrograde reactions in direct liquefaction. Final report, September 20, 1988--November 20, 1990

    SciTech Connect

    Serio, M.A.; Solomon, P.R.; Kroo, E.; Charpenay, S.; Bassilakis, R.

    1991-12-17

    The overall objective of the program was to improve the understanding of retrograde reactions and their dependencies on coal rank and structure, and/or coal modifications and reaction conditions. Because retrograde reactions are competitive with bond breaking reactions, an understanding of both is required to shift the competition in favor of the latter. Related objectives were to clarify the conflicting observations reported in literature on such major topics as the role of oxygen groups in retrograde reactions and to provide a bridge from very fundamental studies on pure compounds to phenomenological studies on actual coal. This information was integrated into the FG-DVC model, which was improved and extended to the liquefaction context.

  7. Insight into organic reactions from the direct random phase approximation and its corrections

    SciTech Connect

    Ruzsinszky, Adrienn; Zhang, Igor Ying; Scheffler, Matthias

    2015-10-14

    The performance of the random phase approximation (RPA) and beyond-RPA approximations for the treatment of electron correlation is benchmarked on three different molecular test sets. The test sets are chosen to represent three typical sources of error which can contribute to the failure of most density functional approximations in chemical reactions. The first test set (atomization and n-homodesmotic reactions) offers a gradually increasing balance of error from the chemical environment. The second test set (Diels-Alder reaction cycloaddition = DARC) reflects more the effect of weak dispersion interactions in chemical reactions. Finally, the third test set (self-interaction error 11 = SIE11) represents reactions which are exposed to noticeable self-interaction errors. This work seeks to answer whether any one of the many-body approximations considered here successfully addresses all these challenges.

  8. Insight into organic reactions from the direct random phase approximation and its corrections

    NASA Astrophysics Data System (ADS)

    Ruzsinszky, Adrienn; Zhang, Igor Ying; Scheffler, Matthias

    2015-10-01

    The performance of the random phase approximation (RPA) and beyond-RPA approximations for the treatment of electron correlation is benchmarked on three different molecular test sets. The test sets are chosen to represent three typical sources of error which can contribute to the failure of most density functional approximations in chemical reactions. The first test set (atomization and n-homodesmotic reactions) offers a gradually increasing balance of error from the chemical environment. The second test set (Diels-Alder reaction cycloaddition = DARC) reflects more the effect of weak dispersion interactions in chemical reactions. Finally, the third test set (self-interaction error 11 = SIE11) represents reactions which are exposed to noticeable self-interaction errors. This work seeks to answer whether any one of the many-body approximations considered here successfully addresses all these challenges.

  9. Production of reactive sintered nickel aluminide

    SciTech Connect

    Cooper, R.M.

    1993-01-01

    Effort over the past 3 months was directed at increasing manufacturing capacity (ball milling) and improving product quality. Orders for the powder have increased, mainly for plasma spray powders. NiAl is an excellent coat between a metal and a ceramic, and its use instead of cobalt should extending operating range for carbide tools. The feather phase in the sintered Ni[sub 3]Al was identified to be a Ni-rich phase nucleated on the grain boundaries with 10 wt % Al composition. The ductile to brittle temperature of powder extruded NiAl was found to be between 500 and 600 C, and shows a 50% elongation at 600 C.

  10. Direct conversion from Jerusalem artichoke to hydroxymethylfurfural (HMF) using the Fenton reaction.

    PubMed

    Seo, Yeong Hwan; Han, Jong-In

    2014-05-15

    A simple method for hydroxymethylfurfural (HMF) production from non-crop biomass of the Jerusalem artichoke was developed using the Fenton reaction, in a mixture of 2-butanol and water. Four parameters (temperature, reaction time, Fe(2+) concentration, and H2O2 concentration) were identified as experimental factors, and HMF yield was selected as the response parameter. The experimental factors were optimised by employing Response Surface Methodology (RSM). The maximum HMF yield, of 46%, was obtained with a reaction time of 90 min, Fe(2+) concentration of 1.3 mM, and 0.47 M of H2O2 at 180 °C.

  11. Influence of sintering temperature on structure, microstructure and piezoelectric properties of doped BZT-BCT ceramics

    NASA Astrophysics Data System (ADS)

    Dang, Anh Tuan; Vo, Thanh Tung; Truong, Van Chuong; Le, Van Hong

    2017-01-01

    This work reports the influence of sintering temperature on structure, microstructure and piezoelectric properties of 0.48 Ba(Zr0.2Ti0.8)O3-0.52 (Ba0.7Ca0.3)TiO3(BZT-BCT) doped with ZnO nanoparticle ceramics manufactured by a conventional solid state reaction method. By increasing sintering temperature, the piezoelectric behaviors were improved and rose up to the best parameters at a sintering temperature of 1450∘C (d33 = 576 pC/N and kp = 0.55). The corresponding properties of undoped BZT-BCT ceramics were investigated as a comparison. The received results show that the sintering behavior and piezo-parameters of doped BZT-BCT samples are better than the undoped BZT-BCT samples at each sintering temperature.

  12. Preparation of functionalized cyclic enol phosphates by halogen-magnesium exchange and directed deprotonation reactions.

    PubMed

    Piller, Fabian M; Bresser, Tomke; Fischer, Markus K R; Knochel, Paul

    2010-07-02

    Cyclic enol phosphates were magnesiated by a halogen/magnesium exchange reaction or deprotonation using TMP-derived magnesium amide bases. The resulting magnesium reagents react readily with a wide range of electrophiles like allyl bromides and acid chlorides or can be used in Pd-catalyzed cross-coupling reactions. Several optically pure enol phosphates were prepared starting from readily available d-(+)-camphor derivatives.

  13. The Influence of Spark Plasma Sintering Temperature on the Microstructure and Thermoelectric Properties of Al,Ga Dual-Doped ZnO

    NASA Astrophysics Data System (ADS)

    Han, Li; Hung, Le Thanh; van Nong, Ngo; Pryds, Nini; Linderoth, Søren

    2013-07-01

    ZnO dual-doped with Al and Ga was prepared by spark plasma sintering using different sintering temperatures. The microstructural evolution and thermoelectric properties of the samples were investigated in detail. The samples obtained with sintering temperature above 1223 K had higher relative densities and higher electronic conductivity than the sample sintered at 1073 K. These results were supported by the solid-state reaction completion rate, which suggested that sintering temperature above 1223 K would be preferable for complete solid-state reaction of the samples. The sintering mechanism of ZnO particles and microstructure evolution at different sintering temperatures were investigated by simulation of the self-Joule-heating effect of the individual particles.

  14. Direct experimental probing and theoretical analysis of the reaction between the simplest Criegee intermediate CH2OO and isoprene.

    PubMed

    Decker, Z C J; Au, K; Vereecken, L; Sheps, L

    2017-03-13

    Recent advances in the spectroscopy of Criegee intermediates (CI) have enabled direct kinetic studies of these highly reactive chemical species. The impact of CI chemistry is currently being incorporated into atmospheric models, including their reactions with trace organic and inorganic compounds. Isoprene, C5H8, is a doubly-unsaturated hydrocarbon that accounts for the largest share of all biogenic emissions around the globe and is also a building block of larger volatile organic compounds. We report direct measurements of the reaction of the simplest CI (CH2OO) with isoprene, using time-resolved cavity-enhanced UV absorption spectroscopy. We find the reaction to be pressure-independent between 15-100 Torr, with a rate coefficient that varies from (1.5 ± 0.1) × 10(-15) cm(3) molecule(-1) s(-1) at room temperature to (23 ± 2) × 10(-15) cm(3) molecule(-1) s(-1) at 540 K. Quantum chemical and transition-state theory calculations of 16 unique channels for CH2OO + isoprene somewhat underpredict the observed T-dependence of the total reaction rate coefficient, but are overall in good agreement with the experimental measurements. This reaction is broadly similar to those with smaller alkenes, proceeding by 1,3-dipolar cycloaddition to one of the two conjugated double bonds of isoprene.

  15. Direct experimental probing and theoretical analysis of the reaction between the simplest Criegee intermediate CH 2 OO and isoprene

    DOE PAGES

    Decker, Z. C. J.; Au, K.; Vereecken, L.; ...

    2017-01-01

    Recent advances in the spectroscopy of Criegee intermediates (CI) have enabled direct kinetic studies of these highly reactive chemical species. The impact of CI chemistry is currently being incorporated into atmospheric models, including their reactions with trace organic and inorganic compounds. Isoprene, C5H8, is a doubly-unsaturated hydrocarbon that accounts for the largest share of all biogenic emissions around the globe and is also a building block of larger volatile organic compounds. We report direct measurements of the reaction of the simplest CI (CH2OO) with isoprene, using time-resolved cavity-enhanced UV absorption spectroscopy. We find the reaction to be pressure-independent between 15–100more » Torr, with a rate coefficient that varies from (1.5 ± 0.1) × 10–15 cm3 molecule–1 s–1 at room temperature to (23 ± 2) × 10–15 cm3 molecule–1 s–1 at 540 K. Quantum chemical and transition-state theory calculations of 16 unique channels for CH2OO + isoprene somewhat underpredict the observed T-dependence of the total reaction rate coefficient, but are overall in good agreement with the experimental measurements. Finally, this reaction is broadly similar to those with smaller alkenes, proceeding by 1,3-dipolar cycloaddition to one of the two conjugated double bonds of isoprene.« less

  16. Direct experimental probing and theoretical analysis of the reaction between the simplest Criegee intermediate CH2OO and isoprene

    DOE PAGES

    Decker, Z. C. J.; Au, K.; Vereecken, L.; ...

    2017-03-07

    Recent advances in the spectroscopy of Criegee intermediates (CI) have enabled direct kinetic studies of these highly reactive chemical species. The impact of CI chemistry is currently being incorporated into atmospheric models, including their reactions with trace organic and inorganic compounds. Isoprene, C5H8, is a doubly-unsaturated hydrocarbon that accounts for the largest share of all biogenic emissions around the globe and is also a building block of larger volatile organic compounds. We report direct measurements of the reaction of the simplest CI (CH2OO) with isoprene, using time-resolved cavity-enhanced UV absorption spectroscopy. We find the reaction to be pressure-independent between 15–100more » Torr, with a rate coefficient that varies from (1.5 ± 0.1) × 10–15 cm3 molecule–1 s–1 at room temperature to (23 ± 2) × 10–15 cm3 molecule–1 s–1 at 540 K. Quantum chemical and transition-state theory calculations of 16 unique channels for CH2OO + isoprene somewhat underpredict the observed T-dependence of the total reaction rate coefficient, but are overall in good agreement with the experimental measurements. Finally, this reaction is broadly similar to those with smaller alkenes, proceeding by 1,3-dipolar cycloaddition to one of the two conjugated double bonds of isoprene.« less

  17. Direct Reactions at Relativistic Energies: A New Insight into the Single-Particle Structure of Exotic Nuclei

    NASA Astrophysics Data System (ADS)

    Cortina-Gil, Dolores

    Direct reactions proceed in a single step, allowing to disentangle structural properties of nuclei from the reaction mechanism. The availability of radioactive beams gives rise to a renewed activity in this field enlarging the opportunities to explore the single-particle properties of exotic nuclei. Different kinds of direct reactions have been employed in different energy regimes. At high energies, the removal of one(two)-nucleon(s) (referred to as nucleon knockout in this text) from a fast exotic projectile has been extensively investigated, exploring the nuclear structure of the peripheral tail of wave functions and providing a direct insight into the single-particle properties. More than 25 years of experimental and theoretical work will be reviewed in this lecture. This exploration has recently been rejuvenated with the possibility of quasi-free scattering applied to rare isotopes. This method will be a substantial part of the program of future experimental facilities, with the results of pilot experiments now coming to light. Quasi-free scattering will complement the information gained with nucleon knockout studies, exploring deeper regions in the wave function and allowing the determination of spectral functions for both weakly and deeply bound nucleons. This lecture provides a general overview of the experimental achievements reached so far using both complementary techniques. A brief introduction to the reaction mechanisms and a simplified interpretation of the observables obtained will be presented.

  18. Dynamic Reaction Mechanisms of ClO(-) with CH3Cl: Comparison Between Direct Dynamics Trajectory Simulations and Experiment.

    PubMed

    Yu, Feng

    2016-03-24

    We have investigated the dynamic reaction mechanisms of *ClO¯ with CH3Cl (the asterisk is utilized to label a different Cl atom). Ab initio molecular dynamics simulations at the MP2/6-31+G(d,p) level of theory have been employed to compute the dynamic trajectories. On the basis of our simulations, the dynamic reaction pathways for the bimolecular nucleophilic substitution (SN2) reaction channel and SN2-induced elimination reaction channel are clearly illustrated. For the SN2 reaction channel, some trajectories directly dissociate to the final products of CH3O*Cl and Cl¯, whereas the others involve the dynamic Cl¯···CH3O*Cl intermediate complex. As to the SN2-induced elimination reaction channel, the trajectories lead to the final products of CH2O, HCl, and *Cl¯ through the dynamic Cl¯···CH3O*Cl intermediate complex. More significantly, the product branching ratios of Cl¯ and *Cl¯ predicted by our simulations are basically consistent with previous experimental results (Villano et al. J. Am. Chem. Soc. 2009, 131, 8227-8233).

  19. Low temperature sintering of Ag nanoparticles for flexible electronics packaging

    NASA Astrophysics Data System (ADS)

    Hu, A.; Guo, J. Y.; Alarifi, H.; Patane, G.; Zhou, Y.; Compagnini, G.; Xu, C. X.

    2010-10-01

    We achieve robust bonding of Cu wires to Cu pads on polyimide with silver nanopaste cured at 373 K. The paste is prepared by simply condensing Ag nanoparticle (NP) solution via centrifuging. The bonding is formed by solid state sintering of Ag NPs through neck growth and direct metallic bonding between clean Ag-Cu interfaces. Both experiment and Monte Carlo simulation confirm that the melting point of joint clusters increases during sintering. This creates improved bonds for use at an elevated operating temperature using Ag NPs.

  20. Sintered Lining for Heat-Pipe Evaporator

    NASA Technical Reports Server (NTRS)

    Ernst, D. M.; Eastman, G. Y.

    1985-01-01

    Hotspots eliminated by lining inner wall. Distribution of heat transfer liquid in heat-pipe evaporator improved by lining inner wall with layer of sintered metal. Sintered layer takes place of layer of screen wick formerly sintered or bonded to wall. Since sintered layer always full of liquid, no hotspot of type that previously arose where former screen wick did not fit properly against wall.

  1. Direct Measurements of Unimolecular and Bimolecular Reaction Kinetics of the Criegee Intermediate (CH3)2COO.

    PubMed

    Chhantyal-Pun, Rabi; Welz, Oliver; Savee, John D; Eskola, Arkke J; Lee, Edmond P F; Blacker, Lucy; Hill, Henry R; Ashcroft, Matilda; Khan, M Anwar H; Lloyd-Jones, Guy C; Evans, Louise; Rotavera, Brandon; Huang, Haifeng; Osborn, David L; Mok, Daniel K W; Dyke, John M; Shallcross, Dudley E; Percival, Carl J; Orr-Ewing, Andrew J; Taatjes, Craig A

    2017-01-12

    The Criegee intermediate acetone oxide, (CH3)2COO, is formed by laser photolysis of 2,2-diiodopropane in the presence of O2 and characterized by synchrotron photoionization mass spectrometry and by cavity ring-down ultraviolet absorption spectroscopy. The rate coefficient of the reaction of the Criegee intermediate with SO2 was measured using photoionization mass spectrometry and pseudo-first-order methods to be (7.3 ± 0.5) × 10(-11) cm(3) s(-1) at 298 K and 4 Torr and (1.5 ± 0.5) × 10(-10) cm(3) s(-1) at 298 K and 10 Torr (He buffer). These values are similar to directly measured rate coefficients of anti-CH3CHOO with SO2, and in good agreement with recent UV absorption measurements. The measurement of this reaction at 293 K and slightly higher pressures (between 10 and 100 Torr) in N2 from cavity ring-down decay of the ultraviolet absorption of (CH3)2COO yielded even larger rate coefficients, in the range (1.84 ± 0.12) × 10(-10) to (2.29 ± 0.08) × 10(-10) cm(3) s(-1). Photoionization mass spectrometry measurements with deuterated acetone oxide at 4 Torr show an inverse deuterium kinetic isotope effect, kH/kD = (0.53 ± 0.06), for reactions with SO2, which may be consistent with recent suggestions that the formation of an association complex affects the rate coefficient. The reaction of (CD3)2COO with NO2 has a rate coefficient at 298 K and 4 Torr of (2.1 ± 0.5) × 10(-12) cm(3) s(-1) (measured with photoionization mass spectrometry), again similar to rate for the reaction of anti-CH3CHOO with NO2. Cavity ring-down measurements of the acetone oxide removal without added reagents display a combination of first- and second-order decay kinetics, which can be deconvolved to derive values for both the self-reaction of (CH3)2COO and its unimolecular thermal decay. The inferred unimolecular decay rate coefficient at 293 K, (305 ± 70) s(-1), is similar to determinations from ozonolysis. The present measurements confirm the large rate coefficient for reaction of

  2. Characterization of polycrystalline cBN compacts sintered without any additives

    NASA Astrophysics Data System (ADS)

    Tan, N.; Liu, C. J.; Li, Y. J.; Dou, Y. W.; Wang, H. K.; Ma, H.; Kou, Z. L.; He, D. W.

    2011-01-01

    Sintered cubic boron nitride (cBN) is widely used in various industrial applications because of its extreme wear and corrosion resistance, thermal and electrical properties. Conventional cBN sintered compacts contain binder materials and the binder materials remarkably affect their mechanical and thermal properties. In this work, polycrystalline cBN (PcBN) compacts were sintered on WC-16 wt.%Co substrates without any sintering agent at static high pressure of 5.0 GPa and temperatures of 1550-1750°C1750circC-> for 3-20 min. Chemical reactions between cBN and substances infiltrated from the substrates occurred during the high pressure and high temperature (HPHT) sintering process. Reaction products and their contents strongly depended on the sintering temperatures and heat treatment times according to the X-ray diffraction (XRD) observations. Scanning electron microscopy (SEM) analysis showed that some samples sintered under some specific conditions had plenty of cBN-to-cBN bonding among cBN grains and homogeneous microstructures. We also found that the formation of the cBN-to-cBN bonding in the samples had given rise to an improvement in cutting performance.

  3. Dislocation generation during early stage sintering.

    NASA Technical Reports Server (NTRS)

    Sheehan, J. E.; Lenel, F. V.; Ansell, G. S.

    1973-01-01

    Discussion of the effects of capillarity-induced stresses on dislocations during early stage sintering. A special version of Hirth's (1963) theoretical calculation procedures modified to describe dislocation nucleation on planes meeting the sintering body's neck surface obliquely is shown to predict plastic flow at stress levels know to exist between micron size metal particles in the early stages of sintering.

  4. Zeolite-directed cascade reactions: cycliacyarylation versus decarboxyarylation of alpha,beta-unsaturated carboxylic acids.

    PubMed

    Chassaing, Stefan; Kumarraja, Mayilvasagam; Pale, Patrick; Sommer, Jean

    2007-09-27

    The interaction of alpha,beta-unsaturated carboxylic acids with benzene derivatives was investigated in H-zeolites and led to two distinct but competing processes, cycliacyarylation and decarboxyarylation. Interestingly, H-USY selectively induced the cycliacyarylation cascade reaction, whereas H-ZSM5 selectively promoted the decarboxyarylation cascade.

  5. Chitosan aerogel: a recyclable, heterogeneous organocatalyst for the asymmetric direct aldol reaction in water.

    PubMed

    Ricci, Alfredo; Bernardi, Luca; Gioia, Claudio; Vierucci, Simone; Robitzer, Mike; Quignard, Françoise

    2010-09-14

    Aerogel microspheres of chitosan, an abundant biopolymer obtained from marine crustaceans, have been successfully applied to catalyze the asymmetric aldol reaction in water, providing the products in high yields and with good stereoselectivity (up to 93% ee) and recyclability (up to 4 runs). Yields were favourably affected by additives such as DNP and stearic acid.

  6. Photophysical Study of a Series of Cyanines Part III. The Direct Photooxidation Reaction

    NASA Astrophysics Data System (ADS)

    Lepaja, Shukri; Strub, Henry; Lougnot, Daniel-Joseph

    1983-01-01

    The main degradative pathway of tricarbocyanine dyes in aerated solutions is demonstrated to be a photooxidation; using sensitization techniques and specific quenchers, this reaction is established to proceed via singlet oxygen for a part, and the site at which this species attacks the polymethinic skeleton is unambiguously determined. The major photoproduct is identified as being 1,3,3-trimethyl-2-indolinone.

  7. REUSABLE REACTION VESSEL

    DOEpatents

    Soine, T.S.

    1963-02-26

    This patent shows a reusable reaction vessel for such high temperature reactions as the reduction of actinide metal chlorides by calcium metal. The vessel consists of an outer metal shell, an inner container of refractory material such as sintered magnesia, and between these, a bed of loose refractory material impregnated with thermally conductive inorganic salts. (AEC)

  8. Effect of milling and leaching on the structure of sintered silicon

    NASA Technical Reports Server (NTRS)

    Yeh, H. C.; Glascow, T. K.; Herbell, T. P.

    1980-01-01

    Sintering was performed in He for 16 hours at 1200, 1250, and 1300 C. Compacts of as-received Si did not densify during sintering. Milling reduced the average particle size to below 0.5 micrometer and enhanced densification (1.75 g/cc). Leaching milled Si further enhanced densification (1.90 g/cc max.) and decreased structural coarsening. After sintering, the structure of the milled and leached powder compacts appears favorable for the production of reaction bonded silicon nitride.

  9. The First Example of Nickel-Catalyzed Silyl-Heck Reactions: Direct Activation of Silyl Triflates Without Iodide Additives

    PubMed Central

    McAtee, Jesse R.; Martin, Sara E. S.; Cinderella, Andrew P.; Reid, William B.; Johnson, Keywan A.

    2014-01-01

    For the first time, nickel-catalyzed silyl-Heck reactions are reported. Using simple phosphine-supported nickel catalysts, direct activation of silyl triflates has been achieved. These results contrast earlier palladium-catalyzed systems, which require iodide additives to activate silyl-triflates. These nickel-based catalysts exhibit good functional group tolerance in the preparation of vinyl silanes, and unlike earlier systems, allows for the incorporation of trialkylsilanes larger than Me3Si. PMID:24914247

  10. SINTERING OF NASCENT CALCIUM OXIDE

    EPA Science Inventory

    The paper discusses the measurement of the sintering rate of CaO in a nitrogen atmosphere at temperatures of 700-1100 C. CaO prepared from ultrapure CaCO3 was compared with an impure CaO derived from limestone. Both materials yielded an initial surface area of 104 sq m/g. The rat...

  11. Sintering additives for zirconia ceramics

    SciTech Connect

    Wu, S.

    1986-01-01

    This book is an overview of sintering science and its application to zirconia materials including CaO, MgO, and Y/sub 2/O/sub 3/-CeO/sub 2/ doped materials. This book is a reference for first-time exposure to zirconia materials technology, particularly densification.

  12. Sintering of polydisperse viscous droplets

    NASA Astrophysics Data System (ADS)

    Wadsworth, Fabian B.; Vasseur, Jérémie; Llewellin, Edward W.; Dingwell, Donald B.

    2017-03-01

    Sintering—or coalescence—of compacts of viscous droplets is driven by the interfacial tension between the droplets and the interstitial gas phase. The process, which occurs in a range of industrial and natural settings, such as the manufacture of ceramics and the welding of volcanic ash, causes the compact to densify, to become stronger, and to become less permeable. We investigate the role of droplet polydispersivity in sintering dynamics by conducting experiments in which populations of glass spheres with different size distributions are heated to temperatures above the glass transition interval. We quantify the progress of sintering by tracking changes in porosity with time. The sintering dynamics is modeled by treating the system as a random distribution of interstitial gas bubbles shrinking under the action of interfacial tension only. We identify the scaling between the polydispersivity of the initial droplets and the dynamics of bulk densification. The framework that we develop allows the sintering dynamics of arbitrary polydisperse populations of droplets to be predicted if the initial droplet (or particle) size distribution is known.

  13. Microwave sintering of boron carbide

    DOEpatents

    Blake, R.D.; Katz, J.D.; Petrovic, J.J.; Sheinberg, H.

    1988-06-10

    A method for forming boron carbide into a particular shape and densifying the green boron carbide shape. Boron carbide in powder form is pressed into a green shape and then sintered, using a microwave oven, to obtain a dense boron carbide body. Densities of greater than 95% of theoretical density have been obtained. 1 tab.

  14. Direct observation of redox reactions in Candida parapsilosis ATCC 7330 by Confocal microscopic studies

    PubMed Central

    Venkataraman, Sowmyalakshmi; Narayan, Shoba; Chadha, Anju

    2016-01-01

    Confocal microscopic studies with the resting cells of yeast, Candida parapsilosis ATCC 7330, a reportedly versatile biocatalyst for redox enzyme mediated preparation of optically pure secondary alcohols in high optical purities [enantiomeric excess (ee) up to >99%] and yields, revealed that the yeast cells had large vacuoles under the experimental conditions studied where the redox reaction takes place. A novel fluorescence method was developed using 1-(6-methoxynaphthalen-2-yl)ethanol to track the site of biotransformation within the cells. This alcohol, itself non-fluorescent, gets oxidized to produce a fluorescent ketone, 1-(6-methoxynaphthalen-2-yl)ethanone. Kinetic studies showed that the reaction occurs spontaneously and the products get released out of the cells in less time [5 mins]. The biotransformation was validated using HPLC. PMID:27739423

  15. Acid-Base Pairs in Lewis Acidic Zeolites Promote Direct Aldol Reactions by Soft Enolization.

    PubMed

    Lewis, Jennifer D; Van de Vyver, Stijn; Román-Leshkov, Yuriy

    2015-08-17

    Hf-, Sn-, and Zr-Beta zeolites catalyze the cross-aldol condensation of aromatic aldehydes with acetone under mild reaction conditions with near quantitative yields. NMR studies with isotopically labeled molecules confirm that acid-base pairs in the Si-O-M framework ensemble promote soft enolization through α-proton abstraction. The Lewis acidic zeolites maintain activity in the presence of water and, unlike traditional base catalysts, in acidic solutions.

  16. Direct site-selective arylation of enamides via a decarboxylative cross-coupling reaction.

    PubMed

    Gigant, Nicolas; Chausset-Boissarie, Laëtitia; Gillaizeau, Isabelle

    2013-02-15

    An efficient Pd-catalyzed decarboxylative cross-coupling reaction of simple enamides was achieved. Depending on the choice of the nitrogen-protecting group, a site-selective synthesis of mono- or diarylated framework(s) was performed under mild conditions. This unprecedented reactivity could be applied to the synthesis of a range of 2- or 2,4-diarylated nitrogen-containing bioactive derivatives.

  17. Reaction Ensemble Molecular Dynamics: Direct Simulation of the Dynamic Equilibrium Properties of Chemically Reacting Mixtures

    DTIC Science & Technology

    2006-09-01

    Therefore, dynamic quantities of reaction mixtures such as the velocity autocorrelation functions and the diffusion coefficients can be accurately...using the virial expression [25]. A standard NVT molecular dynamics method was em- ployed with the equations of motion solved using the Verlet leapfrog...configurational energy, pressure, and species concen- trations) are compared to quantities calculated by the RxMC approach. Second , the dynamic quantities

  18. Asymmetric synthesis of dihydropyranones from ynones by sequential copper(I)-catalyzed direct aldol and silver(I)-catalyzed oxy-Michael reactions.

    PubMed

    Shi, Shi-Liang; Kanai, Motomu; Shibasaki, Masakatsu

    2012-04-16

    Ynones as diene surrogates: the asymmetric synthesis of enantiomerically enriched substituted dihydropyranones is described. The products are obtained in two steps by a copper(I)-catalyzed direct aldol reaction of ynones followed by a silver-catalyzed oxy-Michael reaction. This easy method is compatible with both aromatic and aliphatic substrates, and provides excellent chemoselectivity under mild reaction conditions.

  19. Flash (Ultra-Rapid) Spark-Plasma Sintering of Silicon Carbide

    PubMed Central

    Olevsky, Eugene A.; Rolfing, Stephen M.; Maximenko, Andrey L.

    2016-01-01

    A new ultra-rapid process of flash spark plasma sintering is developed. The idea of flash spark plasma sintering (or flash hot pressing - FHP) stems from the conducted theoretical analysis of the role of thermal runaway phenomena for material processing by flash sintering. The major purpose of the present study is to theoretically analyze the thermal runaway nature of flash sintering and to experimentally address the challenge of uncontrollable thermal conditions by the stabilization of the flash sintering process through the application of the external pressure. The effectiveness of the developed FHP technique is demonstrated by the few seconds–long consolidation of SiC powder in an industrial spark plasma sintering device. Specially designed sacrificial dies heat the pre-compacted SiC powder specimens to a critical temperature before applying any voltage to the powder volume and allowing the electrode-punches of the SPS device setup to contact the specimens and pass electric current through them under elevated temperatures. The experimental results demonstrate that flash sintering phenomena can be realized using conventional SPS devices. The usage of hybrid heating SPS devices is pointed out as the mainstream direction for the future studies and utilization of the new flash hot pressing (ultra-rapid spark plasma sintering) technique. PMID:27624641

  20. Flash (Ultra-Rapid) Spark-Plasma Sintering of Silicon Carbide.

    PubMed

    Olevsky, Eugene A; Rolfing, Stephen M; Maximenko, Andrey L

    2016-09-14

    A new ultra-rapid process of flash spark plasma sintering is developed. The idea of flash spark plasma sintering (or flash hot pressing - FHP) stems from the conducted theoretical analysis of the role of thermal runaway phenomena for material processing by flash sintering. The major purpose of the present study is to theoretically analyze the thermal runaway nature of flash sintering and to experimentally address the challenge of uncontrollable thermal conditions by the stabilization of the flash sintering process through the application of the external pressure. The effectiveness of the developed FHP technique is demonstrated by the few seconds-long consolidation of SiC powder in an industrial spark plasma sintering device. Specially designed sacrificial dies heat the pre-compacted SiC powder specimens to a critical temperature before applying any voltage to the powder volume and allowing the electrode-punches of the SPS device setup to contact the specimens and pass electric current through them under elevated temperatures. The experimental results demonstrate that flash sintering phenomena can be realized using conventional SPS devices. The usage of hybrid heating SPS devices is pointed out as the mainstream direction for the future studies and utilization of the new flash hot pressing (ultra-rapid spark plasma sintering) technique.

  1. Pressure-assisted low-temperature sintering for paper-based writing electronics.

    PubMed

    Xu, L Y; Yang, G Y; Jing, H Y; Wei, J; Han, Y D

    2013-09-06

    With the aim of preparing paper-based writing electronics, a kind of conductive pen was made with nano-silver ink as the conductive component and a rollerball pen as the writing implement. This was used to direct-write conductive patterns on Epson photo paper. In order to decrease the sintering temperature, pressure was introduced to enhance the driving forces for sintering. Compared with hot sintering without pressure, hot-pressure can effectively improve the conductivity of silver coatings, reduce the sintering time and thus improve productivity. Importantly, pressure can achieve a more uniform and denser microstructure, which increases the connection strength of the silver coating. At the optimum hot-pressure condition (sintering temperature 120 ° C/sintering pressure 25 MPa/sintering time 15 min), a typical measured resistivity value was 1.43 × 10⁻⁷ Ω m, nine greater than that of bulk silver. This heat treatment process is compatible with paper and does not cause any damage to the paper substrates. Even after several thousand bending cycles, the resistivity values of writing tracks by hot-pressure sintering stay almost the same (from 1.43 × 10⁻⁷ to 1.57 × 10⁻⁷ Ω m). The stability and flexibility of the writing circuits are good, which demonstrates the promising future of writing electronics.

  2. Hot-spring sinter deposits in the Alvord-Pueblo Valley, Harney County, Oregon

    SciTech Connect

    Cummings, M.L.; St. John, A.M. . Dept. of Geology)

    1993-04-01

    Silica sinter deposits occur at Borax Lake, Alvord Hot Springs, and Mickey Springs in the Alvord-Pueblo Valley. Although the sinter deposits occur in areas of active hot springs, sinter is not being deposited. Hot springs are localized along faults that have been active since the Pleistocene. The sinter deposits formed after the drying of glacial Lake Alvord, but before and during extensive wind deflation of glacial-lacustrine sediments. At Mickey Springs, sinter rests directly on unaltered, unconsolidated lithic-rich sand. At Borax Lake, sinter overlies unaltered diatomite, but some armoring, presumably by silica, of the 30 m vent has developed. Field relations suggest rapid dumping of silica from solution without alteration of the country rock at the vent. Discharge of thermal fluids and cold groundwater along the same structure may have produced colloidal silica carried in a solution stripped of dissolved silica. Sinter is composed of opal-a, traces of detrital feldspar and quartz, and evaporation-related boracite. The concentration of Sb is similar among the three sinter deposits (20 to 70 ppm); however, As, Cs, and Br are highest at Borax Lake (5 to 560 ppm; 26 to 118 ppm; 5 to 1,040 ppm) while Hg is highest at Mickey Springs (1.0 to 5.2 ppm).

  3. Mechanistic evaluation of the effect of sintering on Compritol 888 ATO matrices.

    PubMed

    Rao, Monica; Ranpise, Anuradha; Borate, Sameer; Thanki, Kaushik

    2009-01-01

    The present research studied the effect of sintering technique in the development of a controlled release formulation for ketorolac tromethamine. The method consisted of mixing drug and wax powder (Compritol 888 ATO) along with lactose as diluent and talc as lubricant followed by direct compression at room temperature. The compressed fluffy matrices were kept at 80 degrees C for 1, 2, and 3 h for sintering. The sintered tablets were characterized by their physical parameters and in vitro dissolution profile. The sintering time markedly affected the drug release properties of Compritol 888 ATO matrices. It is notable that the release rate of ketorolac tromethamine from matrices was inversely related to the time of sintering. This may be due to the increase in the extent and firmness of sintering which further compacts the mass so that drug release is affected. Contact angle measurement and scanning electron microscopy analysis indicated that heat treatment caused the wax to melt and redistribute. This redistributed wax formed a network-like structure in which the drug along with lactose is entrapped. This particular formed matrix is responsible for retarding the drug release. Fourier transform infrared spectroscopy results did not show any drug-wax interaction due to sintering. Differential scanning calorimetric and powder X-ray diffraction studies ruled out the occurrence of solid solution and polymorphic changes of the drug. Drug release from the wax tablets with or without sintering was best described by the Higuchi equation.

  4. Flash (Ultra-Rapid) Spark-Plasma Sintering of Silicon Carbide

    NASA Astrophysics Data System (ADS)

    Olevsky, Eugene A.; Rolfing, Stephen M.; Maximenko, Andrey L.

    2016-09-01

    A new ultra-rapid process of flash spark plasma sintering is developed. The idea of flash spark plasma sintering (or flash hot pressing - FHP) stems from the conducted theoretical analysis of the role of thermal runaway phenomena for material processing by flash sintering. The major purpose of the present study is to theoretically analyze the thermal runaway nature of flash sintering and to experimentally address the challenge of uncontrollable thermal conditions by the stabilization of the flash sintering process through the application of the external pressure. The effectiveness of the developed FHP technique is demonstrated by the few seconds–long consolidation of SiC powder in an industrial spark plasma sintering device. Specially designed sacrificial dies heat the pre-compacted SiC powder specimens to a critical temperature before applying any voltage to the powder volume and allowing the electrode-punches of the SPS device setup to contact the specimens and pass electric current through them under elevated temperatures. The experimental results demonstrate that flash sintering phenomena can be realized using conventional SPS devices. The usage of hybrid heating SPS devices is pointed out as the mainstream direction for the future studies and utilization of the new flash hot pressing (ultra-rapid spark plasma sintering) technique.

  5. Pressure-assisted low-temperature sintering for paper-based writing electronics

    NASA Astrophysics Data System (ADS)

    Y Xu, L.; Y Yang, G.; Y Jing, H.; Wei, J.; Han, Y. D.

    2013-09-01

    With the aim of preparing paper-based writing electronics, a kind of conductive pen was made with nano-silver ink as the conductive component and a rollerball pen as the writing implement. This was used to direct-write conductive patterns on Epson photo paper. In order to decrease the sintering temperature, pressure was introduced to enhance the driving forces for sintering. Compared with hot sintering without pressure, hot-pressure can effectively improve the conductivity of silver coatings, reduce the sintering time and thus improve productivity. Importantly, pressure can achieve a more uniform and denser microstructure, which increases the connection strength of the silver coating. At the optimum hot-pressure condition (sintering temperature 120 ° C/sintering pressure 25 MPa/sintering time 15 min), a typical measured resistivity value was 1.43 × 10-7 Ω m, nine greater than that of bulk silver. This heat treatment process is compatible with paper and does not cause any damage to the paper substrates. Even after several thousand bending cycles, the resistivity values of writing tracks by hot-pressure sintering stay almost the same (from 1.43 × 10-7 to 1.57 × 10-7 Ω m). The stability and flexibility of the writing circuits are good, which demonstrates the promising future of writing electronics.

  6. Direct reforming of biogas on Ni-based SOFC anodes: Modelling of heterogeneous reactions and validation with experiments

    NASA Astrophysics Data System (ADS)

    Santarelli, Massimo; Quesito, Francesco; Novaresio, Valerio; Guerra, Cosimo; Lanzini, Andrea; Beretta, Davide

    2013-11-01

    This work focuses on the heterogeneous reactions taking place in a tubular anode-supported solid oxide fuel cell (SOFC) when the designated fuel is biogas from anaerobic digestion directly feeding the fuel cell. Operational maps of the fuel cell running on direct reforming of biogas were first obtained. Hence a mathematical model incorporating the kinetics of reforming reactions on Ni catalyst was used to predict the gas composition profile along the fuel channel. The model was validated against experimental data based on polarization curves. Also, the anode off-gas composition was collected and analyzed through a gas chromatograph. Finally, the model has been used to predict and analyze the gas composition change along the anode channel to evaluate effectiveness of the direct steam reforming when varying cell temperature, inlet fuel composition and the type of reforming process. The simulations results confirmed that thermodynamic-equilibrium conditions are not fully achieved inside the anode channel. It also outlines that a direct biogas utilization in an anode-supported SOFC is able to provide good performance and to ensure a good conversion of the methane even though when the cell temperature is far from the nominal value.

  7. Gravitational Role in Liquid Phase Sintering

    NASA Technical Reports Server (NTRS)

    Upadhyaya, Anish; Iacocca, Ronald G.; German, Randall M.

    1998-01-01

    To comprehensively understand the gravitational effects on the evolution of both the microstructure and the macrostructure during liquid phase sintering, W-Ni-Fe alloys with W content varying from 35 to 98 wt.% were sintered in microgravity. Compositions that slump during ground-based sintering also distort when sintered under microgravity. In ground-based sintering, low solid content alloys distort with a typical elephant-foot profile, while in microgravity, the compacts tend to spheroidize. This study shows that microstructural segregation occurs in both ground-based as well as microgravity sintering. In ground-based experiments, because of the density difference between the solid and the liquid phase, the solid content increases from top to the bottom of the sample. In microgravity, the solid content increases from periphery to the center of the samples. This study also shows that the pores during microgravity sintering act as a stable phase and attain anomalous shapes.

  8. Cold press sintering of simulated lunar basalt

    NASA Technical Reports Server (NTRS)

    Altemir, D. A.

    1993-01-01

    In order to predict the conditions for which the lunar regolith may be adequately sintered, experiments were conducted in which samples of simulated lunar basalt (MLS-1) were pressed at high pressures and then heated in an electric furnace. This sintering process may be referred to as cold press sintering since the material is pressed at room temperature. Although test articles were produced which possessed compressive strengths comparable to that of terrestrial concrete, the cold press sintering process requires very high press pressures and sintering temperatures in order to achieve that strength. Additionally, the prospect of poor internal heat transfer adversely affecting the quality of sintered lunar material is a major concern. Therefore, it is concluded that cold press sintering will most likely be undesirable for the production of lunar construction materials.

  9. Direct conversion of cellulose and hemicellulose to fermentable sugars by a microbially-driven Fenton reaction.

    PubMed

    Sekar, Ramanan; Shin, Hyun Dong; DiChristina, Thomas J

    2016-10-01

    The aim of this work was to develop a microbially-driven Fenton reaction that fragments cellulose and hemicellulose, degrades cellodextrins and xylodextrins, and produces short-chain oligosaccharides and monomeric sugars in a single bioreactor. The lignocellulose degradation system operates at neutral pH and does not require addition of conventional lignocellulose-degrading enzymes, thus avoiding problems associated with enzyme accessibility and specificity. The ability to produce useful bioproducts was demonstrated by production of the bioplastic polyhydroxybutyrate with the xylan degradation products as starting substrate.

  10. Statistical Hauser-Feshbach theory with width-fluctuation correction including direct reaction channels for neutron-induced reactions at low energies

    NASA Astrophysics Data System (ADS)

    Kawano, T.; Capote, R.; Hilaire, S.; Chau Huu-Tai, P.

    2016-07-01

    A model to calculate particle-induced reaction cross sections with statistical Hauser-Feshbach theory including direct reactions is given. The energy average of the scattering matrix from the coupled-channels optical model is diagonalized by the transformation proposed by Engelbrecht and Weidenmüller [C. A. Engelbrecht and H. A. Weidenmüller, Phys. Rev. C 8, 859 (1973), 10.1103/PhysRevC.8.859]. The ensemble average of S -matrix elements in the diagonalized channel space is approximated by a model of Moldauer [P. A. Moldauer, Phys. Rev. C 12, 744 (1975), 10.1103/PhysRevC.12.744] using the newly parametrized channel degree-of-freedom νa to better describe the Gaussian orthogonal ensemble (GOE) reference calculations. The Moldauer approximation is confirmed by a Monte Carlo study using a randomly generated S matrix, as well as the GOE threefold integration formula. The method proposed is applied to the 238U(n ,n' ) cross-section calculation in the fast-energy range, showing an enhancement in the inelastic scattering cross sections.

  11. Improvement of the Sintered Surface and Bulk of the Product Via Differentiating Laser Sintering (Melting) Modes

    NASA Astrophysics Data System (ADS)

    Saprykina, N. A.; Saprykin, A. A.; Arkhipova, D. A.; Borovikov, I. F.

    2016-08-01

    Selective laser sintering (melting) enables using metal powdered materials to manufacture products of any geometrical complexity, requiring no preliminary costs to prepare processing equipment. However, quality of the sintered surface is often inadequate as against the product manufactured traditionally. Manufacturing a high quality product requires solution of such vital task as prediction of the sintered surface roughness. The authors address to the effect of laser sintering modes on roughness of the surface, sintered of copper powdered material PMS-l (IIMC-1). The dependence of roughness of the surface layer sintered of copper powder material PMS-l upon sintering process conditions is expressed mathematically. The authors suggest differentiating sintering modes to improve the sintered surface and the bulk of the product and dividing them into rough, semi-finishing, and finishing ones.

  12. Spike synchronization and firing rate in a population of motor cortical neurons in relation to movement direction and reaction time.

    PubMed

    Grammont, F; Riehle, A

    2003-05-01

    We studied the dynamics of precise spike synchronization and rate modulation in a population of neurons recorded in monkey motor cortex during performance of a delayed multidirectional pointing task and determined their relation to behavior. We showed that at the population level neurons coherently synchronized their activity at various moments during the trial in relation to relevant task events. The comparison of the time course of the modulation of synchronous activity with that of the firing rate of the same neurons revealed a considerable difference. Indeed, when synchronous activity was highest, at the end of the preparatory period, firing rate was low, and, conversely, when the firing rate was highest, at movement onset, synchronous activity was almost absent. There was a clear tendency for synchrony to precede firing rate, suggesting that the coherent activation of cell assemblies may trigger the increase in firing rate in large groups of neurons, although it appeared that there was no simple parallel shifting in time of these two activity measures. Interestingly, there was a systematic relationship between the amount of significant synchronous activity within the population of neurons and movement direction at the end of the preparatory period. Furthermore, about 400 ms later, at movement onset, the mean firing rate of the same population was also significantly tuned to movement direction, having roughly the same preferred direction as synchronous activity. Finally, reaction time measurements revealed a directional preference of the monkey with, once again, the same preferred direction as synchronous activity and firing rate. These results lead us to speculate that synchronous activity and firing rate are cooperative neuronal processes and that the directional matching of our three measures--firing rate, synchronicity, and reaction times--might be an effect of behaviorally induced network cooperativity acquired during learning.

  13. Direct assembly of multiply oxygenated carbon chains by decarbonylative radical-radical coupling reactions

    NASA Astrophysics Data System (ADS)

    Masuda, Kengo; Nagatomo, Masanori; Inoue, Masayuki

    2016-10-01

    Pentoses and hexoses contain more than three oxygen-bearing stereocentres and are ideal starting materials for the synthesis of multiply oxygenated natural products such as sagittamide D, maitotoxin and hikizimycin. Here we demonstrate new radical-radical homocoupling reactions of sugar derivatives with minimal perturbation of their chiral centres. The radical exchange procedure using Et3B/O2 converted sugar-derived α-alkoxyacyl tellurides into α-alkoxy radicals via decarbonylation and rapidly dimerized the monomeric radicals. The robustness of this process was demonstrated by a single-step preparation of 12 stereochemically diverse dimers with 6-10 secondary hydroxy groups, including the C5-C10 stereohexad of sagittamide D and the enantiomer of the C51-C60 stereodecad of maitotoxin. Furthermore, the optimally convergent radical-radical cross-coupling reaction achieved a one-step assembly of the protected C1-C11 oxygenated carbon chain of the anthelmintic hikizimycin. These exceptionally efficient homo- and heterocoupling methods together provide a powerful strategy for the expedited total synthesis of contiguously hydroxylated natural products.

  14. A Si/SiGe quantum well based biosensor for direct analysis of exothermic biochemical reaction

    NASA Astrophysics Data System (ADS)

    Zhang, Lei; Dong, Tao

    2013-04-01

    A rapid and reliable detection system is needed in the area of label-free calorimetric measurement for monitoring biochemical reactions. In this paper, a thermal biosensor employing a Si/SiGe quantum well is proposed where the infrared radiation energy is carefully considered to increase the sensor's sensitivity. It applies a suspended functional film with a trench across the multilayers. A polydimethylsiloxane cover for the microfluidic channel is bonded with the sensor for the injection and removal of a small volume of solution (down to 500 nL). The resistance change of Si/SiGe quantum well material is read out through the wire bonding connection to the conductive pads of the sensor. A linear detection range from 0.5 to 150 mM and a relative standard deviation less than 1% are demonstrated in the enzymatic reaction test with urea solution. Characterizations on the quantum well film verifies a high temperature coefficient of resistance value and fine crystal lattice, which promises a notable sensitivity. The application of the wafer level transfer bonding process makes the sensor fabrication convenient and cost-effective.

  15. Dual-level direct dynamics studies for the hydrogen abstraction reaction of 1,1-difluoroethane with O( 3P)

    NASA Astrophysics Data System (ADS)

    Liu, Jing-yao; Li, Ze-sheng; Dai, Zhen-wen; Zhang, Gang; Sun, Chia-chung

    2004-01-01

    We present dual-level direct dynamics calculations for the CH 3CHF 2 + O( 3P) hydrogen abstraction reaction in a wide temperature range, based on canonical variational transition-state theory including small curvature tunneling corrections. For this reaction, three distinct transition states, one for α-abstraction and two for β-abstraction, have been located. The potential energy surface information is obtained at the MP2(full)/6-311G(d,p) level of theory, and higher-level single-point calculations for the stationary points are preformed at several levels, namely QCISD(T)/6-311+G(3df,3pd), G2, and G3 using the MP2 geometries, as well as at the G3//MP4SDQ/6-311G(d,p) level. The energy profiles are further refined with the interpolated single-point energies method at the G3//MP2(full)/6-311G(d,p) level. The total rate constants match the experimental data reasonable well in the measured temperature range 1110-1340 K. It is shown that at low temperature α-abstraction may be the major reaction channel, while β-abstraction will have more contribution to the whole reaction rate as the temperature increases.

  16. Dual-level direct dynamics studies for the reactions of dimethyl ether with hydrogen atom and methyl radical.

    PubMed

    Wu, Jia-Yan; Liu, Jing-Yao; Li, Ze-Sheng; Huang, Xu-Ri; Sun, Chia-Chung

    2003-04-15

    The dual-level direct dynamics approach is employed to study the dynamics of the CH(3)OCH(3) + H (R1) and CH(3)OCH(3) + CH(3) (R2) reactions. Low-level calculations of the potential energy surface are carried out at the MP2/6-311+G(d,p) level of theory. High-level energetic information is obtained at the QCISD(T) level of theory with the 6-311+G(3df,3pd) basis set. The dynamics calculations are performed using variational transition state theory (VTST) with the interpolated single-point energies (ISPE) method, and small-curvature tunneling (SCT) is included. It is shown that the reaction of CH(3)OCH(3) with H (R1) may proceed much easier and with a lower barrier height than the reaction with CH(3) radical (R2). The calculated rate constants and activation energies are in good agreement with the experimental values. The calculated rate constants are fitted to k(R1) = 1.16 x 10(-19) T(3) exp(-1922/T) and k(R2) = 1.66 x 10(-28) T(5) exp(-3086/T) cm(3) mol(-1) s(-1) over a temperature range 207-2100 K. Furthermore, a small variational effect and large tunneling effect in the lower temperature range are found for the two reactions.

  17. Exact model reduction with delays: closed-form distributions and extensions to fully bi-directional monomolecular reactions.

    PubMed

    Leier, Andre; Barrio, Manuel; Marquez-Lago, Tatiana T

    2014-06-06

    In order to systematically understand the qualitative and quantitative behaviour of chemical reaction networks, scientists must derive and analyse associated mathematical models. However, biochemical systems are often very large, with reactions occurring at multiple time scales, as evidenced by signalling pathways and gene expression kinetics. Owing to the associated computational costs, it is then many times impractical, if not impossible, to solve or simulate these systems with an appropriate level of detail. By consequence, there is a growing interest in developing techniques for the simplification or reduction of complex biochemical systems. Here, we extend our recently presented methodology on exact reduction of linear chains of reactions with delay distributions in two ways. First, we report that it is now possible to deal with fully bi-directional monomolecular systems, including degradations, synthesis and generalized bypass reactions. Second, we provide all derivations of associated delays in analytical, closed form. Both advances have a major impact on further reducing computational costs, while still retaining full accuracy. Thus, we expect our new methodology to respond to current simulation needs in pharmaceutical, chemical and biological research.

  18. Directed assembly of defined oligomeric photosynthetic reaction centres through adaptation with programmable extra-membrane coiled-coil interfaces.

    PubMed

    Swainsbury, David J K; Harniman, Robert L; Di Bartolo, Natalie D; Liu, Juntai; Harper, William F M; Corrie, Alexander S; Jones, Michael R

    2016-12-01

    A challenge associated with the utilisation of bioenergetic proteins in new, synthetic energy transducing systems is achieving efficient and predictable self-assembly of individual components, both natural and man-made, into a functioning macromolecular system. Despite progress with water-soluble proteins, the challenge of programming self-assembly of integral membrane proteins into non-native macromolecular architectures remains largely unexplored. In this work it is shown that the assembly of dimers, trimers or tetramers of the naturally monomeric purple bacterial reaction centre can be directed by augmentation with an α-helical peptide that self-associates into extra-membrane coiled-coil bundle. Despite this induced oligomerisation the assembled reaction centres displayed normal spectroscopic properties, implying preserved structural and functional integrity. Mixing of two reaction centres modified with mutually complementary α-helical peptides enabled the assembly of heterodimers in vitro, pointing to a generic strategy for assembling hetero-oligomeric complexes from diverse modified or synthetic components. Addition of two coiled-coil peptides per reaction centre monomer was also tolerated despite the challenge presented to the pigment-protein assembly machinery of introducing multiple self-associating sequences. These findings point to a generalised approach where oligomers or longer range assemblies of multiple light harvesting and/or redox proteins can be constructed in a manner that can be genetically-encoded, enabling the construction of new, designed bioenergetic systems in vivo or in vitro.

  19. Sinter-vein correlations at Buckskin Mountain, National district, Humboldt County, Nevada

    USGS Publications Warehouse

    Vikre, P.G.

    2007-01-01

    in veins and sinter. Acid-sulfate fluid of the second fluid regime was derived from oxidation of H2S and other volatiles exsolved from sinter-vein fluid. Acid-sulfate fluid produced (1) a subhorizontal zone of partially leached basinal deposits and rhyolite from the paleosurface to a depth of ???60 m, and (2) laterally pervasive zones, ???100 to 200 m thick, of quartz + alunite ?? hematite and quartz + kaolinite + pyrite in volcaniclastic deposits immediately beneath partially leached rocks, but this fluid did not decompose selenide-sulfide-precious metal phases in sinter. Paragenetically late vein and wall-rock assemblages, including marcasite + pyrite, calcite, and kaolinite-replaced K minerals, record deeper transition of sinter-vein fluid into acid-sulfate fluid in vein conduits. This transition occurred as regional subsidence, manifested by the Goosey Lake depression immediately east of Buckskin Mountain, lowered the pieziometric surface at Buckskin Mountain, terminated sinter deposition, and caused boiling and/or degassing of sinter-vein fluid. The timing of subsidence is recorded by a decrease in alunite ages, from ca. 15.8 to 15.6 Ma, with depth below sinter. Lateral replacement of sinter and partially leached epiclastic deposits and rhyolite by opal-A marks the termination of the two hydrothermal regimes that lasted ???0.5 m.y. and followed rhyolitic volcanism of similar duration. Veins and sinter display textures that attest to plastic deformation, spalling, and gravitational settling, and indicate fluid-flow direction, velocity, and density stratification which, with conduit topology, may have influenced precious metal tenor in the veins. Components of sinter and veins were transported as colloids, formed in supersaturated sinter-vein fluid, that aggregated or coagulated as incompetent gelatinous layers in shallow pools and in underlying, near-vertical conduits in rhyolite and initially crystallized as opal and chalcedony. The low thermal conductivity of

  20. Estimation of kinetic parameters for enzyme-inhibition reaction models using direct time-dependent equations for reactant concentrations.

    PubMed

    Goličnik, Marko

    2012-03-01

    To facilitate the determination of a reaction type and its kinetics constants for reversible inhibitors of Michaelis-Menten-type enzymes using progress-curve analysis, I present here an explicit equation for direct curve fitting to full time-course data of inhibited enzyme-catalyzed reactions. This algebraic expression involves certain elementary functions where their values are readily available using any standard nonlinear regression program. Hence this allows easy analysis of experimentally observed kinetics without any data conversion prior to fitting. Its implementation gives correct parameter estimates that are in very good agreement with results obtained using both the numerically integrated Michaelis-Menten rate equation or its exact closed-form solution which is expressed in terms of the Lambert W function.

  1. Investigation of chemical and electrochemical reactions mechanisms in a direct carbon fuel cell using olive wood charcoal as sustainable fuel

    NASA Astrophysics Data System (ADS)

    Elleuch, Amal; Halouani, Kamel; Li, Yongdan

    2015-05-01

    Direct carbon fuel cell (DCFC) is a high temperature fuel cell using solid carbon as fuel. The use of environmentally friendly carbon material constitutes a promising option for the DCFC future. In this context, this paper focuses on the use of biomass-derived charcoal renewable fuel. A practical investigation of Tunisian olive wood charcoal (OW-C) in planar DCFCs is conducted and good power density (105 mW cm-2) and higher current density (550 mA cm-2) are obtained at 700 °C. Analytical and predictive techniques are performed to explore the relationships between fuel properties and DCFC chemical and electrochemical mechanisms. High carbon content, carbon-oxygen groups and disordered structure, are the key parameters allowing the achieved good performance. Relatively complex chain reactions are predicted to explain the gas evolution within the anode. CO, H2 and CH4 participation in the anodic reaction is proved.

  2. Improvement of an acid phosphatase/DHAP-dependent aldolase cascade reaction by using directed evolution.

    PubMed

    van Herk, Teunie; Hartog, Aloysius F; Babich, Lara; Schoemaker, Hans E; Wever, Ron

    2009-09-04

    To enhance the phosphorylating activity of the bacterial nonspecific acid phosphatase from Salmonella enterica ser. typhimurium LT2 towards dihydroxyacetone (DHA), a mutant library was generated from the native enzyme. Three different variants that showed enhanced activity were identified after one round of epPCR. The single mutant V78L was the most active and showed an increase in the maximal DHAP concentration to 25 % higher than that of the wild-type enzyme at pH 6.0. This variant is 17 times more active than the wild-type acid phosphatase from Salmonella enterica ser. typhimurium LT2 in the acid phosphatase/aldolase cascade reaction at pH 6.0 and is also six times more active than the phosphatase from Shigella flexneri that we previously used.

  3. [Decoloration and degradation of direct pink 12B by microwave-promoted heterogeneous Fenton-like reaction].

    PubMed

    Zheng, Huai-Li; Xie, Li-Guo; Hu, Peng; Jiao, Shi-Jun; Hu, Xue-Bin; Liu, Lan; Wu, You-Quan

    2010-06-01

    Microwave-promoted heterogeneous Fenton-like reaction, the combination of Fenton-like reagent with microwave, is an efficient method for waste water treatment. In the present paper, the degradation of direct pink 12B (a kind of organic dye) was studied using this method was studied. Through numerous experiments, the influences of various parameters including the initial pH value, dosage of Fe-Ni-Mn/AlO3, dosage of H2O2 and microwave were investigated intensively. The characteristic curve of direct pink12B, the concentration-absorbency curve of direct pink12B, the orthogonal optimization tests and comparative tests were given. In this paper, the mechanisms of this reaction were also been probed. It is concluded from the experiments that the microwave can accelerate the process of degradation effectively. Under optimal conditions, the overall color removal was more than 99.0% within 10 min. In the study, all the characterization was carried out using UV-Vis spectral-analysis.

  4. A novel mechanism for direct real-time polymerase chain reaction that does not require DNA isolation from prokaryotic cells.

    PubMed

    Soejima, Takashi; Xiao, Jin-Zhong; Abe, Fumiaki

    2016-06-23

    Typically, polymerase chain reaction (PCR) is performed after DNA isolation. Real-time PCR (qPCR), also known as direct qPCR in mammalian cells with weak membranes, is a common technique using crude samples subjected to preliminary boiling to elute DNA. However, applying this methodology to prokaryotic cells, which have solid cell walls, in contrast to mammalian cells which immediately burst in water, can result in poor detection. We successfully achieved PCR elongation with the addition of 1.3 cfu of Cronobacter muytjensii to a newly developed direct qPCR master mix without performing any crude DNA extraction (detection limit of 1.6 × 10(0) cfu/ml for the test sample compared with a detection limit of 1.6 × 10(3) cfu/ml primarily for crude (boiling) or classical DNA isolation). We revealed that the chromosomal DNA retained in prokaryotic cells can function as a PCR template, similarly to the mechanism in in situ PCR. Elucidating this reaction mechanism may contribute to the development of an innovative master mix for direct qPCR to detect genes in a single bacterium with solid cell walls and might lead to numerous novel findings in prokaryotic genomics research.

  5. Feasibility of Traveling Wave Direct Energy Conversion of Fission Reaction Fragments

    NASA Technical Reports Server (NTRS)

    Tarditi, A. G.; George, J. A.; Miley, G. H.; Scott, J. H.

    2013-01-01

    Fission fragment direct energy conversion has been considered in the past for the purpose of increasing nuclear power plant efficiency and for advanced space propulsion. Since the fragments carry electric charge (typically in the order of 20 e) and have 100 MeV-range kinetic energy, techniques utilizing very high-voltage DC electrodes have been considered. This study is focused on a different approach: the kinetic energy of the charged fission fragments is converted into alternating current by means of a traveling wave coupling scheme (Traveling Wave Direct Energy Converter, TWDEC), thereby not requiring the utilization of high voltage technology. A preliminary feasibility analysis of the concept is introduced based on a conceptual level study and on a particle simulation model of the beam dynamics.

  6. Sintered composite medium and filter

    DOEpatents

    Bergman, Werner

    1987-01-01

    A particulate filter medium is formed of a sintered composite of 0.5 micron diameter quartz fibers and 2 micron diameter stainless steel fibers. A preferred composition is about 40 vol. % quartz and about 60 vol. % stainless steel fibers. The media is sintered at about 1100.degree. C. to bond the stainless steel fibers into a cage network which holds the quartz fibers. High filter efficiency and low flow resistance are provided by the smaller quartz fibers. High strength is provided by the stainless steel fibers. The resulting media has a high efficiency and low pressure drop similar to the standard HEPA media, with tensile strength at least four times greater, and a maximum operating temperature of about 550.degree. C. The invention also includes methods to form the composite media and a HEPA filter utilizing the composite media. The filter media can be used to filter particles in both liquids and gases.

  7. Nonenzymatic template-directed reactions on altritol oligomers, preorganized analogues of oligonucleotides

    NASA Technical Reports Server (NTRS)

    Kozlov, I. A.; Zielinski, M.; Allart, B.; Kerremans, L.; Van Aerschot, A.; Busson, R.; Herdewijn, P.; Orgel, L. E.; Bada, J. L. (Principal Investigator)

    2000-01-01

    Altritol nucleic acids (ANAs) are RNA analogues with a phosphorylated D-altritol backbone. The nucleobase is attached at the 2-(S)-position of the carbohydrate moiety. We report that ANA oligomers are superior to the corresponding DNA, RNA, and HNA (hexitol nucleic acid) in supporting efficient nonenzymatic template-directed synthesis of complementary RNAs from nucleoside-5'-phosphoro-2-methyl imidazolides. Activated ANA and HNA monomers do not oligomerize efficiently on DNA, RNA, HNA, or ANA templates.

  8. Microwave sintering studies on low loss (Zn, Mg)TiO3 dielectric resonator materials.

    PubMed

    Sirugudu, Roopas Kiran; Vemuri, Rama Krishna Murthy; Murty, B S

    2013-01-01

    Low dielectric loss Zn07Mg0.3TiO3 and MgTiO3 microwave dielectric resonators were prepared by the conventional solid state reaction method. The microwave interaction with these materials has been studied using both single-mode and multimode microwave furnaces operating at a frequency of 2.45 GHz. Microwave sintering could be achieved using a multimode microwave furnace only, whereas, interaction with a single-mode furnace showed plasma generation. Phase formation was observed by X-ray diffraction. Microwave dielectric characteristics such as dielectric constant (epsilon'), quality factor (Q x f) and temperature coefficient of resonant frequency (tauf) of microwave sintered samples were measured using a vector network analyzer and compared with conventional sintered ones. Microstructure of all the conventional and microwave sintered samples was observed using high resolution scanning electron microscope. Although epsilon' and tauf of the conventional and microwave sintered samples are found to be comparable, the quality factor (the vital characteristic of dielectric resonators) of microwave sintered samples are observed to be much lower than those obtained by conventional sintering. The difference in these values is discussed with respect to the grain size.

  9. Non-Sintered Nickel Electrode

    DOEpatents

    Bernard, Patrick; Dennig, Corinne; Cocciantelli, Jean-Michel; Alcorta, Jose; Coco, Isabelle

    2002-01-01

    A non-sintered nickel electrode contains a conductive support and a paste comprising an electrochemically active material containing nickel hydroxide and a binder which is a mixture of an elastomer and a crystalline polymer. The proportion of the elastomer is in the range 25% to 60% by weight of the binder and the proportion of the crystalline polymer is in the range 40% to 75% by weight of the binder.

  10. A Common Selection Rule for Organic Reactions in Terms of Signs of Direct and Indirect Interorbital Interactions

    NASA Astrophysics Data System (ADS)

    Gineityte, Viktorija

    2009-02-01

    The semilocalized approach to chemical reactivity suggested recently is overviewed with respect to both theory and applications. The principal attention is paid to formulation of a common selection rule for organic reactions and to demonstration of its validity to various heterolytic (i. e. nucleophilic and electrophilic) and pericyclic processes. The total energy of the whole reacting system (E) is represented in this approach in the form of power series with respect to all interfragmental interactions (fragments coincide with individual chemical bonds, phenyl rings, etc.). For any reaction, a certain decisive k-th-order energy correction E(k) may be revealed, the sign of which depends on the actual way of the process. The allowed and forbidden reactions are then defined as those described by negative (stabilizing) and positive (destabilizing) corrections E(k), respectively. The condition which ensures the negative sign of E(k) resolves itself into a universal requirement of coinciding signs of the principal direct and indirect interactions of basis orbitals localized on separate fragments (e. g. bond orbitals). This result forms the basis for the above-mentioned selection rule. Allowed (forbidden) ways of heterolytic reactions are exemplified by the back (frontal) attack of a nucleophile upon a substituted alkane in the SN2 process, the meta (ortho, para) attacks of electrophile upon the pyridine molecule, the addition of electrophile to the Cβ (Cα ) atom of a donor-containing derivative of ethene (D-CαH=Cβ H2), the trans (cis)-β -elimination processes of substituted alkanes, etc. Application of the same rule to pericyclic reactions is demonstrated to yield predictions coinciding with those of other approaches including the famous Woodward-Hoffmann rule.

  11. Ultra-fast and energy-efficient sintering of ceramics by electric current concentration

    PubMed Central

    Zapata-Solvas, E.; Gómez-García, D.; Domínguez-Rodríguez, A.; Todd, R. I.

    2015-01-01

    Electric current activated/assisted sintering (ECAS) techniques, such as electrical discharge sintering (EDS) or resistive sintering (RS), have been intensively investigated for longer than 50 years. In this work, a novel system including an electrically insulated graphite die for Spark Plasma Sintering (SPS) is described, which allows the sintering of any refractory ceramic material in less than 1 minute starting from room temperature with heating rates higher than 2000°C/min and an energy consumption up to 100 times lower than with SPS. The system alternates or combines direct resistive sintering (DRS) and indirect resistive sintering (IRS). Electrical insulation of the die has been achieved through the insertion of a film made of alumina fibers between the graphite die and the graphite punches, which are protected from the alumina fiber film by a graphite foil. This system localized the electric current directly through the sample (conductive materials) as in DRS and EDS, or through the thin graphite foil (non-conductive materials) as in IRS, and is the first system capable of being used under EDS or RS conditions independently combining current concentration/localization phenomena. PMID:25686537

  12. Low Temperature Sintering of PZT

    NASA Astrophysics Data System (ADS)

    Medesi, A.; Greiner, T.; Benkler, M.; Megnin, C.; Hanemann, T.

    2014-11-01

    This paper describes the fabrication and characterization of lead zirconate titanate (PZT) films fired in a liquid-phase sintering process at 900 °C in air. In detail the manufacturing of piezoelectric multilayers with internal pure silver (Tm = 961 °C) electrodes are reported. The feasibility of ten sintering aids in two different volume fractions was investigated for a commercial hard PZT powder (PIC 181, PI Ceramics) with respect to density, microstructure, mechanical behaviour, and piezoelectric properties. Li2O, Li2CO3, PbO, MnO2, V2O5, CuO, Bi2O3, the eutectic mixtures Cu2O·PbO and PbO·WO3 and the ternary system Li2CO3·Bi2O3·CuO (LBCu) have been tested as liquid phase sintering aids. The combination of PZT with LBCu showed the best results. With 5 vol.% LBCu an average relative density of 97% and a characteristic breaking strength of 77 MPa was achieved. Composition of PZT with 2 vol.% LBCu exhibits the highest averaged piezoelectrical charge constant (d33) of 181 pC/N.

  13. Nuclear Ordered Phases of Solid 3He in Silver Sinters

    NASA Astrophysics Data System (ADS)

    Schuberth, Erwin A.; Kath, Matthias; Bago, Simone

    2006-09-01

    To determine the exact spin structure of the nuclear magnetic ordered phases of solid 3He, the U2D2 low field and the high field phases above 0.4 T, a European Research and Training Network for neutron scattering from the ordered solid was established which consisted of a collaboration with the Hahn Meitner Institute, Berlin, and other European and US groups. For this experiment it is crucial to grow a single crystal within the sinter needed for cooling the solid to temperatures of the order of 500 μK and to keep it cold long enough to measure a magnetic neutron diffraction. The sinter is also necessary to absorb the major part (> 90%) of the heat generated by the neutron capture and decay reaction of the 3He nucleus. In this work we studied the growth of crystals in Ag sinters of different pore sizes and with different growth speeds to find an optimal way to obtain single crystalline samples, or at least samples with only a few grains. We used SQUID magnetometry and NMR to measure the magnetization in the ordered phases. They were indicated by the known drop of the intensity, both in the NMR signal and in the dc magnetization, for the U2D2 phase, and by an increase of about 30% for the high field phase. The best results for cooling were obtained with sinters made from 700 Å "Japanese powder" with a packing fraction of 50% which were annealed at 130 °C after sintering and then had a calculated particle size of about 4200 Å. In the dc magnetization we found a paramagnetic surface contribution from a few monolayers of 3He down to 500 μK in addition to the bulk magnetization.

  14. Amine-catalyzed direct aldol reactions of hydroxy- and dihydroxyacetone: biomimetic synthesis of carbohydrates.

    PubMed

    Popik, Oskar; Pasternak-Suder, Monika; Leśniak, Katarzyna; Jawiczuk, Magdalena; Górecki, Marcin; Frelek, Jadwiga; Mlynarski, Jacek

    2014-06-20

    This article presents comprehensive studies on the application of primary, secondary, and tertiary amines as efficient organocatalysts for the de novo synthesis of ketoses and deoxyketoses. Mimicking the actions of aldolase enzymes, the synthesis of selected carbohydrates was accomplished in aqueous media by using proline- and serine-based organocatalysts. The presented methodology also provides direct access to unnatural L-carbohydrates from the (S)-glyceraldehyde precursor. Determination of the absolute configuration of all obtained sugars was feasible using a methodology consisting of concerted ECD and VCD spectroscopy.

  15. Direct measurements of unimolecular and bimolecular reaction kinetics of the Criegee intermediate (CH3)2COO

    DOE PAGES

    Chhantyal-Pun, Rabi; Welz, Oliver; Savee, John D.; ...

    2016-10-18

    Here, the Criegee intermediate acetone oxide, (CH3)2COO, is formed by laser photolysis of 2,2-diiodopropane in the presence of O2 and characterized by synchrotron photoionization mass spectrometry and by cavity ring-down ultraviolet absorption spectroscopy. The rate coefficient of the reaction of the Criegee intermediate with SO2 was measured using photoionization mass spectrometry and pseudo-first-order methods to be (7.3 ± 0.5) × 10–11 cm3 s–1 at 298 K and 4 Torr and (1.5 ± 0.5) × 10–10 cm3 s–1 at 298 K and 10 Torr (He buffer). These values are similar to directly measured rate coefficients of anti-CH3CHOO with SO2, and inmore » good agreement with recent UV absorption measurements. The measurement of this reaction at 293 K and slightly higher pressures (between 10 and 100 Torr) in N2 from cavity ring-down decay of the ultraviolet absorption of (CH3)2COO yielded even larger rate coefficients, in the range (1.84 ± 0.12) × 10–10 to (2.29 ± 0.08) × 10–10 cm3 s–1. Photoionization mass spectrometry measurements with deuterated acetone oxide at 4 Torr show an inverse deuterium kinetic isotope effect, kH/kD = (0.53 ± 0.06), for reactions with SO2, which may be consistent with recent suggestions that the formation of an association complex affects the rate coefficient. The reaction of (CD3)2COO with NO2 has a rate coefficient at 298 K and 4 Torr of (2.1 ± 0.5) × 10–12 cm3 s–1 (measured with photoionization mass spectrometry), again similar to rate for the reaction of anti-CH3CHOO with NO2. Cavity ring-down measurements of the acetone oxide removal without added reagents display a combination of first- and second-order decay kinetics, which can be deconvolved to derive values for both the self-reaction of (CH3)2COO and its unimolecular thermal decay. The inferred unimolecular decay rate coefficient at 293 K, (305 ± 70) s–1, is similar to determinations from ozonolysis. The present measurements confirm the large rate coefficient for

  16. Direct measurements of OH and other product yields from the HO2 + CH3C(O)O2 reaction

    NASA Astrophysics Data System (ADS)

    Winiberg, Frank A. F.; Dillon, Terry J.; Orr, Stephanie C.; Groß, Christoph B. M.; Bejan, Iustinian; Brumby, Charlotte A.; Evans, Matthew J.; Smith, Shona C.; Heard, Dwayne E.; Seakins, Paul W.

    2016-03-01

    The reaction CH3C(O)O2 + HO2 → CH3C(O)OOH + O2 (Reaction R5a), CH3C(O)OH + O3 (Reaction R5b), CH3 + CO2 + OH + O2 (Reaction R5c) was studied in a series of experiments conducted at 1000 mbar and (293 ± 2) K in the HIRAC simulation chamber. For the first time, products, (CH3C(O)OOH, CH3C(O)OH, O3 and OH) from all three branching pathways of the reaction have been detected directly and simultaneously. Measurements of radical precursors (CH3OH, CH3CHO), HO2 and some secondary products HCHO and HCOOH further constrained the system. Fitting a comprehensive model to the experimental data, obtained over a range of conditions, determined the branching ratios α(R5a) = 0.37 ± 0.10, α(R5b) = 0.12 ± 0.04 and α(R5c) = 0.51 ± 0.12 (errors at 2σ level). Improved measurement/model agreement was achieved using k(R5) = (2.4 ± 0.4) × 10-11 cm3 molecule-1 s-1, which is within the large uncertainty of the current IUPAC and JPL recommended rate coefficients for the title reaction. The rate coefficient and branching ratios are in good agreement with a recent study performed by Groß et al. (2014b); taken together, these two studies show that the rate of OH regeneration through Reaction (R5) is more rapid than previously thought. GEOS-Chem has been used to assess the implications of the revised rate coefficients and branching ratios; the modelling shows an enhancement of up to 5 % in OH concentrations in tropical rainforest areas and increases of up to 10 % at altitudes of 6-8 km above the equator, compared to calculations based on the IUPAC recommended rate coefficient and yield. The enhanced rate of acetylperoxy consumption significantly reduces PAN in remote regions (up to 30 %) with commensurate reductions in background NOx.

  17. Direct measurements of OH and other product yields from the HO2 + CH3C(O)O2 reaction

    NASA Astrophysics Data System (ADS)

    Winiberg, F. A. F.; Dillon, T. J.; Orr, S. C.; Groß, C. B. M.; Bejan, I.; Brumby, C. A.; Evans, M. J.; Smith, S. C.; Heard, D. E.; Seakins, P. W.

    2015-10-01

    The reaction CH3C(O)O2 + HO2 → CH3C(O)OOH + O2 (Reaction R5a), CH3C(O)OH + O3 (Reaction R5b), CH3 + CO2 + OH + O2 (Reaction R5c) was studied in a series of experiments conducted at 1000 mbar and (293 ± 2) K in the HIRAC simulation chamber. For the first time, products, (CH3C(O)OOH, CH3C(O)OH, O3 and OH) from all three branching pathways of the reaction have been detected directly and simultaneously. Measurements of radical precursors (CH3OH, CH3CHO), HO2 and some secondary products HCHO and HCOOH further constrained the system. Fitting a comprehensive model to the experimental data, obtained over a range of conditions, determined the branching ratios α(R5a) = 0.37 ± 0.10, α(R5b) = 0.12 ± 0.04 and α(R5c) = 0.51 ± 0.12 (errors at 2σ level). Improved measurement/model agreement was achieved using k(R5) = (2.4 ± 0.4) × 10-11 cm3 molecule-1 s-1, which is within the large uncertainty of the current IUPAC and JPL recommended rate coefficients for the title reaction. The rate coefficient and branching ratios are in good agreement with a recent study performed by Groß et al. (2014b); taken together, these two studies show that the rate of OH regeneration through Reaction (R5) is more rapid than previously thought. GEOS-Chem has been used to assess the implications of the revised rate coefficients and branching ratios; the modelling shows an enhancement of up to 5 % in OH concentrations in tropical rainforest areas and increases of up to 10 % at altitudes of 6-8 km above the equator, compared to calculations based on the IUPAC recommended rate coefficient and yield. The enhanced rate of acetylperoxy consumption significantly reduces PAN in remote regions (up to 30 %) with commensurate reductions in background NOx.

  18. Directionality of electron-transfer reactions in photosystem I of prokaryotes: universality of the bidirectional electron-transfer model.

    PubMed

    Santabarbara, Stefano; Kuprov, Ilya; Poluektov, Oleg; Casal, Antonio; Russell, Charlotte A; Purton, Saul; Evans, Michael C W

    2010-11-25

    The electron-transfer (ET) reactions in photosystem I (PS I) of prokaryotes have been investigated in wild-type cells of the cyanobacterium Synechocystis sp. PCC 6803, and in two site-directed mutants in which the methionine residue of the reaction center subunits PsaA and PsaB, which acts as the axial ligand to the primary electron chlorophyll acceptor A(0), was substituted with histidine. Analysis by pulsed electron paramagnetic resonance spectroscopy at 100 K indicates the presence of two forms of the secondary spin-correlated radical pairs, which are assigned to [P(700)(+)A(1A)(-)] and [P(700)(+)A(1B)(-)], where A(1A) and A(1B) are the phylloquinone molecules bound to the PsaA and the PsaB reaction center subunits, respectively. Each of the secondary radical pair forms is selectively observed in either the PsaA-M688H or the PsaB-M668H mutant, whereas both radical pairs are observed in the wild type following reduction of the iron-sulfur cluster F(X), the intermediate electron acceptor between A(1) and the terminal acceptors F(A) and F(B). Analysis of the time and spectral dependence of the light-induced electron spin echo allows the resolution of structural differences between the [P(700)(+)A(1A)(-)] and [P(700)(+)A(1B)(-)] radical pairs. The interspin distance is 25.43 ± 0.01 Å for [P(700)(+)A(1A)(-)] and 24.25 ± 0.01 Å for [P(700)(+)A(1B)(-)]. Moreover, the relative orientation of the interspin vector is rotated by ~60° with respect to the g-tensor of the P(700)(+) radical. These estimates are in agreement with the crystallographic structural model, indicating that the cofactors bound to both reaction center subunits of prokaryotic PS I are actively involved in electron transport. This work supports the model that bidirectionality is a general property of type I reaction centers from both prokaryotes and eukaryotes, and contrasts with the situation for photosystem II and other type II reaction centers, in which ET is strongly asymmetric. A revised model

  19. Direct detection of Bacillus anthracis DNA in animals by polymerase chain reaction.

    PubMed Central

    Makino, S I; Iinuma-Okada, Y; Maruyama, T; Ezaki, T; Sasakawa, C; Yoshikawa, M

    1993-01-01

    Bacillus anthracis is a soil pathogen capable of causing anthrax. To establish a method for specifically detecting B. anthracis for practical applications, such as for the inspection of slaughterhouses, the cap region, which is essential for encapsulation in B. anthracis, was used in a DNA hybridization study by polymerase chain reaction (PCR). Oligonucleotide primers were designed to amplify a 288-bp DNA fragment within the capA gene by PCR. The amplified DNA sequence specifically hybridized to the DNA of B. anthracis but not to that of other bacterial strains tested. Since this PCR-based method efficiently and specifically detected the capA sequence of bacteria in blood and spleen samples of mice within 8 h after the administration of live B. anthracis, this PCR system could be used for practical applications. By using lysis methods in preparing the samples for PCR, it was possible to amplify the 288-bp DNA segment from samples containing very few bacteria, as few as only 1 sporeforming unit, indicating that the PCR detection method developed in this study will permit the monitoring of B. anthracis contamination in the environment. Images PMID:8458949

  20. Multiple Reaction Monitoring for Direct Quantitation of Intact Proteins Using a Triple Quadrupole Mass Spectrometer

    NASA Astrophysics Data System (ADS)

    Wang, Evelyn H.; Combe, Peter C.; Schug, Kevin A.

    2016-05-01

    Methods that can efficiently and effectively quantify proteins are needed to support increasing demand in many bioanalytical fields. Triple quadrupole mass spectrometry (QQQ-MS) is sensitive and specific, and it is routinely used to quantify small molecules. However, low resolution fragmentation-dependent MS detection can pose inherent difficulties for intact proteins. In this research, we investigated variables that affect protein and fragment ion signals to enable protein quantitation using QQQ-MS. Collision induced dissociation gas pressure and collision energy were found to be the most crucial variables for optimization. Multiple reaction monitoring (MRM) transitions for seven standard proteins, including lysozyme, ubiquitin, cytochrome c from both equine and bovine, lactalbumin, myoglobin, and prostate-specific antigen (PSA) were determined. Assuming the eventual goal of applying such methodology is to analyze protein in biological fluids, a liquid chromatography method was developed. Calibration curves of six standard proteins (excluding PSA) were obtained to show the feasibility of intact protein quantification using QQQ-MS. Linearity (2-3 orders), limits of detection (0.5-50 μg/mL), accuracy (<5% error), and precision (1%-12% CV) were determined for each model protein. Sensitivities for different proteins varied considerably. Biological fluids, including human urine, equine plasma, and bovine plasma were used to demonstrate the specificity of the approach. The purpose of this model study was to identify, study, and demonstrate the advantages and challenges for QQQ-MS-based intact protein quantitation, a largely underutilized approach to date.

  1. Electrocatalytic oxygen reduction reaction on perovskite oxides: series versus direct pathway.

    PubMed

    Poux, Tiphaine; Bonnefont, Antoine; Kéranguéven, Gwénaëlle; Tsirlina, Galina A; Savinova, Elena R

    2014-07-21

    The mechanism of the oxygen reduction reaction (ORR) on LaCoO(3) and La(0.8)Sr(0.2)MnO(3) perovskite oxides is studied in 1 M NaOH by using the rotating ring disc electrode (RRDE) method. By combining experimental studies with kinetic modeling, it was demonstrated that on perovskite, as well as on perovskite/carbon electrodes, the ORR follows a series pathway through the intermediate formation of hydrogen peroxide. The escape of this intermediate from the electrode strongly depends on: 1) The loading of perovskite; high loadings lead to an overall 4 e(-) oxygen reduction due to efficient hydrogen peroxide re-adsorption on the active sites and its further reduction. 2) The addition of carbon to the catalytic layer, which affects both the utilization of the perovskite surface and the production of hydrogen peroxide. 3) The type of oxide; La(0.8)Sr(0.2)MnO(3) displays higher (compared to LaCoO(3)) activity in the reduction of oxygen to hydrogen peroxide and in the reduction/oxidation of the latter.

  2. Direct determination of enzyme kinetic parameters from single reactions using a new progress curve analysis tool.

    PubMed

    Bäuerle, Felix; Zotter, Agnes; Schreiber, Gideon

    2016-10-15

    With computer-based data-fitting methods becoming a standard tool in biochemistry, progress curve analysis of enzyme kinetics is a feasible, yet seldom used tool. Here we present a versatile Matlab-based tool (PCAT) to analyze catalysis progress curves with three complementary model approaches. The first two models are based on the known closed-form solution for this problem: the first describes the required Lambert W function with an analytical approximation and the second provides a numerical solution of the Lambert W function. The third model is a direct simulation of the enzyme kinetics. Depending on the chosen model, the tools excel in speed, accuracy or initial value requirements. Using simulated and experimental data, we show the strengths and pitfalls of the different fitting models. Direct simulation proves to have the highest level of accuracy, but it also requires reasonable initial values to converge. Finally, we propose a standard procedure to obtain optimized enzyme kinetic parameters from single progress curves.

  3. Direct synthesis of thermochromic VO{sub 2} through hydrothermal reaction

    SciTech Connect

    Alie, David; Gedvilas, Lynn; Wang, Zhiwei; Tenent, Robert; Engtrakul, Chaiwat; Yan, Yanfa; Shaheen, Sean E.; Dillon, Anne C.; Ban, Chunmei

    2014-04-01

    Thermochromic VO{sub 2} was directly synthesized using hydrothermal techniques. The effects of formation conditions on the structure and morphology of the final product were studied through X-ray diffraction (XRD), and scanning electron microscopy (SEM). Unique hollow sphere morphology was observed for the synthesized VO{sub 2} powders. Ex-situ XRD studies after heat treatment confirmed the thermal stability of the VO{sub 2} structure. Thermochromic properties, as a consequence of the reversible structural transformation between monoclinic VO{sub 2} and tetragonal phases, were observed by Fourier transform infrared spectroscopy (FTIR). - Graphical abstract: Thermochromic VO{sub 2} crystals with hollow spherical and asterisk shape were directly synthesized using hydrothermal techniques. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) studies confirmed the thermal stability and the reversible thermochromic properties of the VO{sub 2} structure. - Highlights: • One-step synthesis of thermochromic VO{sub 2} monoclinic phase, and VO{sub 2} (A and B phases) using hydrothermal technique. VO{sub 2} (A), VO{sub 2} (B). • Identification of the relationship between synthesis conditions and the morphology/structure of the final products. • Formation of VO{sub 2} monoclinic phase with an interesting hollow sphere shape. • Demonstration of superior thermal stability of the VO{sub 2} monoclinic phase. • Characterizing the thermochromic properties of VO{sub 2} monoclinic phase.

  4. Rapid sintering of silicon nitride foams decorated with one-dimensional nanostructures by intense thermal radiation

    NASA Astrophysics Data System (ADS)

    Li, Duan; Guzi de Moraes, Elisângela; Guo, Peng; Zou, Ji; Zhang, Junzhan; Colombo, Paolo; Shen, Zhijian

    2014-08-01

    Silicon nitride foams were prepared by direct foaming and subsequent rapid sintering at 1600 °C. The intense thermal radiation generated under the pressureless spark plasma sintering condition facilitated necking of Si3N4 grains. The prepared foams possessed a porosity of ˜80 vol% and a compressive strength of ˜10 MPa, which required only ˜30 min for the entire sintering processes. Rapid growth of one-dimensional SiC nanowires from the cell walls was also observed. Thermodynamic calculations indicated that the vapor-liquid-solid model is applicable to the formation of SiC nanowires under vacuum.

  5. Rapid sintering of silicon nitride foams decorated with one-dimensional nanostructures by intense thermal radiation.

    PubMed

    Li, Duan; Guzi de Moraes, Elisângela; Guo, Peng; Zou, Ji; Zhang, Junzhan; Colombo, Paolo; Shen, Zhijian

    2014-08-01

    Silicon nitride foams were prepared by direct foaming and subsequent rapid sintering at 1600 °C. The intense thermal radiation generated under the pressureless spark plasma sintering condition facilitated necking of Si3N4 grains. The prepared foams possessed a porosity of ∼80 vol% and a compressive strength of ∼10 MPa, which required only ∼30 min for the entire sintering processes. Rapid growth of one-dimensional SiC nanowires from the cell walls was also observed. Thermodynamic calculations indicated that the vapor-liquid-solid model is applicable to the formation of SiC nanowires under vacuum.

  6. The influence of sintering on the dispersion of carbon nanotubes in ceramic matrix composites

    NASA Astrophysics Data System (ADS)

    Tapasztó, Orsolya; Lemmel, Hartmut; Markó, Márton; Balázsi, Katalin; Balázsi, Csaba; Tapasztó, Levente

    2014-10-01

    Optimizing the dispersion of carbon nanostructures in ceramic matrix composites is a fundamental technological challenge. So far most efforts have been focused on improving the dispersion of nanostructures during the powder phase processing, due to the limited information and control on their possible redistribution during the sintering. Here, we address this issue by comparing multi-walled carbon nanotubes reinforced Si3N4 composites prepared from the same starting powder dispersion but sintered using two different techniques. We employ ultra-small angle neutron scattering measurements to gain reliable information on the dispersion of nanostructures allowing a direct comparison of their redistribution during the sintering.

  7. Microstructure and properties of platelet-reinforced ceramics formed by the directed reaction of zirconium with boron carbide

    SciTech Connect

    Claar, T.D.; Johnson, W.B.; Andersson, C.A.; Schiroky, G.H.

    1989-08-01

    A new family of platelet-reinforced ceramics has been developed using the DIMOX (directed-metal oxidation) process. These materials consist of a metal carbide matrix reinforced with metal diboride platelets and a residual metal phase. Microstructure/property relationships are presented for the ZrB2/ZrC(x)/Zr system, which is formed by the directed reaction of molten zirconium with boron carbide. The metal content can be varied to tailor the mechanical, physical, and thermal properties. These platelet-reinforced ceramics exhibit an attractive combination of high strength (800-1030 MPa), high fracture toughness (11-23 MPa sq rt m), and high thermal conductivity (50-70 W/m K). The effects of the platelet and metal phases on the toughness and fracture behavior are shown. Engineering properties are presented and discussed relative to potential applications. 9 refs.

  8. Ortho-Functionalized Aryltetrazines by Direct Palladium-Catalyzed C-H Halogenation: Application to Fast Electrophilic Fluorination Reactions.

    PubMed

    Testa, Christelle; Gigot, Élodie; Genc, Semra; Decréau, Richard; Roger, Julien; Hierso, Jean-Cyrille

    2016-04-25

    A general catalyzed direct C-H functionalization of s-tetrazines is reported. Under mild reaction conditions, N-directed ortho-C-H activation of tetrazines allows the introduction of various functional groups, thus forming carbon-heteroatom bonds: C-X (X=I, Br, Cl) and C-O. Based on this methodology, we developed electrophilic mono- and poly-ortho-fluorination of tetrazines. Microwave irradiation was optimized to afford fluorinated s-aryltetrazines, with satisfactory selectivity, within only ten minutes. This work provides an efficient and practical entry for further accessing highly substituted tetrazine derivatives (iodo, bromo, chloro, fluoro, and acetate precursors). It gives access to ortho-functionalized aryltetrazines which are difficult to obtain by classical Pinner-like syntheses.

  9. Gyrotron-Based Microwave Sintering of Ceramics

    NASA Astrophysics Data System (ADS)

    Fliflet, A. W.; Bruce, R. W.; Fischer Lewis, R. P., III; Bender, B. A.; Chow, G.-M.; Rayne, R. J.; Kurihara, L. K.; Schoen, P. E.

    1997-11-01

    The development of powerful gyrotrons has opened up the millimeter-wave regime (>= 28 GHz) for processing ceramic materials. A number of studies of microwave sintering of ceramics have indicated that sintering proceeds much faster in microwave furnaces than in conventional furnaces, however, specific conclusions have been limited by the wide range of materials investigated and measurement difficulties. To assess the potential of high frequency microwave sintering, and to investigate the possibility of a specific microwave mechanism, the Naval Research Laboratory has recently undertaken a systematic study focused on the sintering of fine and ultra-fine grained alumina and titania compacts. This paper presents 35 GHz microwave sintering data obtained using a gyrotron-powered furnace and compares our data with results from other microwave and conventional sintering studies.

  10. Dye-sensitized solar cells based on nanocrystalline titania electrodes made at various sintering temperatures.

    PubMed

    Stathatos, Elias; Lianos, Panagiotis

    2007-02-01

    Dye-sensitized solar cells were made by using nanocrystalline titania deposited on Fluorine-doped SnO2 (FTO) electrodes. Nanocrystalline titania deposition was made by the sol-gel method using reverse micelles of bis(2-ethylhexyl) sulfosuccinate sodium salt (AOT) in cyclohexane as reaction medium. This surfactant could be easily removed from the deposited nanocomposite organic-inorganic film by simple rinsing with distilled water, without affecting titania adherence on FTO electrode. These nanocrystalline titania electrodes were used to make solar cells either without sintering or after sintering at various temperatures. Sintering extensively affected short circuit current but had small effect on device open-circuit voltage. Thus satisfactory photovoltaic response could be obtained even with devices made of non-sintered (room-temperature) titania.

  11. Enhancing the methanol tolerance of platinum nanoparticles for the cathode reaction of direct methanol fuel cells through a geometric design

    PubMed Central

    Feng, Yan; Ye, Feng; Liu, Hui; Yang, Jun

    2015-01-01

    Mastery over the structure of nanoparticles might be an effective way to enhance their performance for a given application. Herein we demonstrate the design of cage-bell nanostructures to enhance the methanol tolerance of platinum (Pt) nanoparticles while remaining their catalytic activity for oxygen reduction reaction. This strategy starts with the synthesis of core-shell-shell nanoparticles with Pt and silver (Ag) residing respectively in the core and inner shell regions, which are then agitated with saturated sodium chloride (NaCl) solution to eliminate the Ag component from the inner shell region, leading to the formation of bimetallic nanoparticles with a cage-bell structure, defined as a movable Pt core enclosed by a metal shell with nano-channels, which exhibit superior methanol-tolerant property in catalyzing oxygen reduction reaction due to the different diffusion behaviour of methanol and oxygen in the porous metal shell of cage-bell structured nanoparticles. In particular, the use of remarkably inexpensive chemical agent (NaCl) to promote the formation of cage-bell structured particles containing a wide spectrum of metal shells highlights its engineering merit to produce highly selective electrocatalysts on a large scale for the cathode reaction of direct methanol fuel cells. PMID:26578100

  12. Intramolecular SN2 reaction caused by photoionization of benzene chloride-NH3 complex: direct ab initio molecular dynamics study.

    PubMed

    Tachikawa, Hiroto

    2006-01-12

    Ionization processes of chlorobenzene-ammonia 1:1 complex (PhCl-NH3) have been investigated by means of full dimensional direct ab initio molecular dynamics (MD) method, static ab initio calculations, and density functional theory (DFT) calculations. The static ab initio and DFT calculations of neutral PhCl-NH3 complex showed that one of the hydrogen atoms of NH3 orients toward a carbon atom in the para-position of PhCl. The dynamics calculation for ionization of PhCl-NH3 indicated that two reaction channels are competitive with each other as product channels: one is an intramolecular SN2 reaction expressed by a reaction scheme [PhCl-NH3]+-->SN2 intermediate complex-->PhNH3++Cl, and the other is ortho-NH3 addition complex (ortho complex) in which NH3 attacks the ortho-carbon of PhCl+ and the trajectory leads to a bound complex expressed by (PhCl-NH3)+. The mechanism of the ionization of PhCl-NH3 is discussed on the basis of the theoretical results.

  13. Enhancing the methanol tolerance of platinum nanoparticles for the cathode reaction of direct methanol fuel cells through a geometric design

    NASA Astrophysics Data System (ADS)

    Feng, Yan; Ye, Feng; Liu, Hui; Yang, Jun

    2015-11-01

    Mastery over the structure of nanoparticles might be an effective way to enhance their performance for a given application. Herein we demonstrate the design of cage-bell nanostructures to enhance the methanol tolerance of platinum (Pt) nanoparticles while remaining their catalytic activity for oxygen reduction reaction. This strategy starts with the synthesis of core-shell-shell nanoparticles with Pt and silver (Ag) residing respectively in the core and inner shell regions, which are then agitated with saturated sodium chloride (NaCl) solution to eliminate the Ag component from the inner shell region, leading to the formation of bimetallic nanoparticles with a cage-bell structure, defined as a movable Pt core enclosed by a metal shell with nano-channels, which exhibit superior methanol-tolerant property in catalyzing oxygen reduction reaction due to the different diffusion behaviour of methanol and oxygen in the porous metal shell of cage-bell structured nanoparticles. In particular, the use of remarkably inexpensive chemical agent (NaCl) to promote the formation of cage-bell structured particles containing a wide spectrum of metal shells highlights its engineering merit to produce highly selective electrocatalysts on a large scale for the cathode reaction of direct methanol fuel cells.

  14. Direct detection of infectious bursal disease virus from clinical samples by in situ reverse transcriptase-linked polymerase chain reaction.

    PubMed

    Cardoso, Tereza C; Rosa, Ana C G; Astolphi, Rafael D; Vincente, Rafael M; Novais, Juliana B; Hirata, Karina Y; Luvizotto, Maria Cecilia R

    2008-08-01

    The presence of the very virulent (vv) Brazilian strain of infectious bursal disease virus (IBDV) was determined in the bursa of Fabricius, thymus and liver of 2-week-old broilers from a flock with a higher than expected mortality. For this purpose, a direct in situ reverse transcriptase (RT)-linked polymerase chain reaction (PCR) method was developed using specific primers for vvIBDV. Unlabelled forward and reverse biotinylated oligonucleotides were used for RT-PCR in a one-step method and the respective products were revealed by a direct enzymatic reaction. The results were compared with those obtained by standard RT-PCR using general primers for IBDV and virus isolation. The virus isolation, RT-PCR and in situ RT-PCR revealed positive results on the bursa of Fabricius in 86%, 80% and 100%, respectively. The in situ RT-PCR detected vvIBDV in all tested thymus and liver samples, whereas the standard RT-PCR detected virus in 80% and 90% of the samples, respectively. After three consecutive passages on chicken embryonated eggs, IBDV was isolated from 64% of the thymus samples and 30% of the liver samples. In the present study, no classical or antigenic variants of IBDV were detected. The developed in situ RT-PCR assay was able to detect the very virulent strain of IBDV with a higher sensitivity than the conventional RT-PCR and virus isolation.

  15. Virus-based Photo-Responsive Nanowires Formed By Linking Site-Directed Mutagenesis and Chemical Reaction

    NASA Astrophysics Data System (ADS)

    Murugesan, Murali; Abbineni, Gopal; Nimmo, Susan L.; Cao, Binrui; Mao, Chuanbin

    2013-05-01

    Owing to the genetic flexibility and error-free bulk production, bio-nanostructures such as filamentous phage showed great potential in materials synthesis, however, their photo-responsive behaviour is neither explored nor unveiled. Here we show M13 phage genetically engineered with tyrosine residues precisely fused to the major coat protein is converted into a photo-responsive organic nanowire by a site-specific chemical reaction with an aromatic amine to form an azo dye structure on the surface. The resulting azo-M13-phage nanowire exhibits reversible photo-responsive properties due to the photo-switchable cis-trans isomerisation of the azo unit formed on the phage. This result shows that site-specific display of a peptide on bio-nanostructures through site-directed genetic mutagenesis can be translated into site-directed chemical reaction for developing advanced materials. The photo-responsive properties of the azo-M13-phage nanowires may open the door for the development of light controllable smart devices for use in non-linear optics, holography data storage, molecular antenna, and actuators.

  16. The sintering behavior of ultrafine alumina particles

    SciTech Connect

    Bonevich, J.E.; Marks, L.D. )

    1992-06-01

    Ultrafine particles (UFPs) of aluminum oxide were prepared by an arc discharge, sintered in a custom-built ultrahigh vacuum (UHV) furnace system, and characterized in a high resolution electron microscope (HREM) operating under UHV conditions. The UFPs produced range in size from 20 to 50 nm and have highly faceted surfaces. The atomic structure of the UFPs corresponds to the cubic ({gamma}) and orthorhombic ({delta}) variants of the spinel structure. Sintering in these UFPs demonstrates three major issues. Surface faceting plays a major role in determining the final sintering geometry with sintering occurring predominantly on the closed-packed {l brace}111{r brace} facets. Surface diffusion is the predominant mechanism for sintering, as evidenced by the fact that many sintered particles have their initial adhesion structure locked-in' during sintering with no reorientation occurring. Furthermore, the necks formed during sintering have well-defined, atomically-sharp contact angles which suggests that the neck growth process is controlled by the faceted structures and may be modeled by a mechanism similar to crystal growth due to ledges, grain boundaries, and twins. The driving force for sintering can be considered as a chemical potential difference between facet surfaces and the neck region.

  17. On the sintering of silicon carbide

    NASA Technical Reports Server (NTRS)

    Gugel, E.

    1986-01-01

    This document deals with the sintering of silicon carbide using pressureless sintering. This technique makes it possible to sinter a primarily covalent material to usable densities up to over 98% thD without having to use a high amount of sinter additives as is the case with other non-oxide ceramic materials. The process takes place rapidly, and it is also possible to produce relatively thick-walled structural parts without major problems. This sheds more light on the true characteristics of silicon carbide in one structural part, since there is no second or nearly no second phase. Heat pressing has improved stability.

  18. Low temperature plasma sintering of silver nanoparticles

    NASA Astrophysics Data System (ADS)

    Ma, Siyuan; Bromberg, Vadim; Liu, Liang; Egitto, Frank D.; Chiarot, Paul R.; Singler, Timothy J.

    2014-02-01

    The fabrication of flexible electronics using the deposition of solution-processed nanomaterials generally requires low-temperature post-processing to optimize functionality. We studied sintering of silver nanoparticle (AgNP) films on glass substrates by applying argon (Ar) plasma to achieve improved electrical conductivity. This process meets the low temperature processing requirements for standard low-cost polymeric flexible substrates. The relationship between plasma parameters (such as power and sintering time) versus sintering results (such as electrical sheet resistance, sintered structure depth, materials composition variation, and film nanostructure) is reported for 23 and 77 nm diameter AgNPs. In addition, plasma processing typically induces a small surface thermal effect. We monitored the surface temperatures of the AgNP films in-situ during plasma sintering. By sintering control groups at these monitored surface temperatures using a vacuum oven, we confirmed that the resistivity due to plasma sintering is less than that produced by thermal sintering. Our data show that, the measured lowest resistivities for plasma sintered AgNP films are about only 5 and 12 times greater than the bulk Ag resistivity for 23 and 77 nm, respectively.

  19. Time Required to Initiate a Defensive Reaction to Direct and Feint Attacks in Fencing.

    PubMed

    Gutiérrez-Davila, Marcos; Rojas, F Javier; Gutiérrez-Cruz, Carmen; García, Carlos; Navarro, Enrique

    2016-12-01

    The two-fold purpose of this study was to analyze the time required by a fencer to initiate a defensive action in response to a direct attack, which involves identifying when the defending fencer detects the just-noticeable difference, and, secondly, to assess the effect that an attacker's rapid armed hand movement (feint attack) has on the time required to initiate a defensive move. Twenty-four elite fencers and a fencing master were included in the study. Four adapted force plates were installed on a scaffold used as a fencing piste. A 3D video analysis system recorded the location of 2 markers installed on the fencing master's shoulder and sword. The results confirm that the defending fencer has a mean movement time of 0.353 ± 0.028 s to perform the defensive action, which provides an advantage over the attacking fencer. The velocity of movement in the peripheral visual field has no influence on the time required by elite fencers to initiate a defensive action. This confirms the crucial role that response inhibition processes play when nonrelevant actions are perceived. Kinematic analysis of markers suggests that the eye movements of elite fencers are not the only source of information used while observing an attack.

  20. Comparison of the direct antiglobulin rosetting reaction (DARR) and direct immunofluorescence (DIF) for demonstration of sIg-bearing lymphocytes in pigs, sheep and cattle.

    PubMed Central

    Binns, R M; Licence, S T; Symons, D B; Gurner, B W; Coombs, R R; Walters, D E

    1979-01-01

    Tests with untreated and trypsin-treated red cells (rbc) from a variety of species showed that anti-Ig-coupled pig RBC are good indicator cells for the study of ruminant blood sIg + lymphocytes by the DARR test; coupled donkey and rabbit RBC are suitable for investigating pig lymphocytes. The different species showed the following percentages of sIg + lymphocytes (M +/- SE) by direct immunofluorescence (DIF) and the direct antiglobulin rosetting reaction (DARR) respectively:pigs 9.2 +/- 0.7% and 16.3 +/- 1.2%; sheep 20.2 +/- 1.2% and 33.1 +/- 1.6%; Cattle 13.5 +/- 1.4% and 28.9 +/- 3.5%. The mean ratio of sIg + lymphocytes shown by the two tests (DARR/DIF) for each species was 1.80 +/- 0.08 for pigs, 1.73 +/- 0.7 for sheep and 2.15 +/- 0.18 for cattle. Preincubation of pig and sheep lymphocytes at 37 degrees for 1 h did not alter the proportion of sIg + lymphocytes detected by either test. Thus the DARR test reveals a further population of sIg + lymphocytes in addition to that detected by immunofluorescence, whose number is proportional to the B population as measured by DIF and whose sIg is intimately associated with the membrane. PMID:374254

  1. Permeability, drying, and sintering of pressure filtered ceramic nanopowders

    NASA Astrophysics Data System (ADS)

    Sweeney, Sean M.

    2002-01-01

    point of drying (when fracture is most likely during drying). Agreement between maximum safe drying stresses and measured sample strengths is found to be good (to within better than a factor of 2) for boehmite samples, but not very good (off by a factor of ˜7) for nanocrystalline 3Y-TZP samples. Sub-critical crack growth is indicated as the source of this deviation in nanocrystalline 3Y-TZP samples. Literature studies of the sintering of chloride-derived 3Y-TZP nanopowders have documented numerous sintering problems including inability to reach full density, desintering, cracking, and the formation of a dense shell with less dense interior. To explain the poor sintering behavior of samples of one nanocrystalline 3Y-TZP powder, the origin of such a dense shell microstructure is determined. Three possible reasons for a dense shell microstructure are examined and rejected: exothermic reactions with the sintering atmosphere, pre-existing density gradients in the green compact, and thermal gradients occurring during sintering. A combination of gas flow/diffusion, thermodynamic, and sintering calculations are used to show that the evolution of a structure-coarsening gas (hydrogen chloride) during sintering causes the formation of a dense shell microstructure, and explains the poor densification behavior of this system. Two solutions to the problem are compared: (1) a thermal treatment composed of an extended hold at 1000°C to allow HCl gas removal before the onset of closed porosity (at about 90-93% of theoretical density), and (2) a chemical treatment performed by washing pre-sintered (500°C/30 min) samples at room temperature using a concentrated ammonium hydroxide solution to remove chlorides. The thermal treatment is found to be superior for removing residual chlorine and allowing full density to be achieved during sintering.

  2. Enhanced Sintering Kinetics in Aluminum Alloy Powder Consolidated Using DC Electric Fields

    NASA Astrophysics Data System (ADS)

    McWilliams, Brandon; Yu, Jian; Kellogg, Frank; Kilczewski, Steven

    2017-02-01

    Direct current (DC) electric currents were applied during sintering of aluminum alloy (AA5083) green powder compacts and it was found that the kinetics of sintering were greatly enhanced compared to samples processed without a field. In situ sintering kinetics during pressure-less sintering employing electric field strengths and amperages ranging from 0 to 56 V/cm and 0 to 3 A were quantified using digital image correlation. It was found that the application of a DC field during sintering results in a discontinuous change in volume at a critical temperature along with a transition in electrical properties of the compact from insulating to conductive. This effect is similar to the phenomena observed in the flash sintering process currently being actively researched for ceramic powder processing. The temperature at which the flash event occurs was found to be field strength dependent and doubling the field strength was found to decrease the flash temperature by 25 pct. Joule heating of the specimen was measured using thermal imaging and it was found to not contribute enough additional thermal energy to account for the substantially increased sintering rates observed in specimens processed using electric fields.

  3. Numerical study of the process parameters in spark plasma sintering (sps)

    NASA Astrophysics Data System (ADS)

    Chowdhury, Redwan Jahid

    Spark plasma sintering (SPS) is one of the most widely used sintering techniques that utilizes pulsed direct current together with uniaxial pressure to consolidate a wide variety of materials. The unique mechanisms of SPS enable it to sinter powder compacts at a lower temperature and in a shorter time than the conventional hot pressing, hot isostatic pressing and vacuum sintering process. One of the limitations of SPS is the presence of temperature gradients inside the sample, which could result in non-uniform physical and microstructural properties. Detailed study of the temperature and current distributions inside the sintered sample is necessary to minimize the temperature gradients and achieve desired properties. In the present study, a coupled thermal-electric model was developed using finite element codes in ABAQUS software to investigate the temperature and current distributions inside the conductive and non-conductive samples. An integrated experimental-numerical methodology was implemented to determine the system contact resistances accurately. The developed sintering model was validated by a series of experiments, which showed good agreements with simulation results. The temperature distribution inside the sample depends on some process parameters such as sample and tool geometry, punch and die position, applied current and thermal insulation around the die. The role of these parameters on sample temperature distribution was systematically analyzed. The findings of this research could prove very useful for the reliable production of large size sintered samples with controlled and tailored properties.

  4. EMF measurements across the front of combustion wave during layer by layer surface laser sintering of exothermal powder compositions

    NASA Astrophysics Data System (ADS)

    Shishkovskiy, I.; Sherbakov, V.; Morozov, Yu.

    2007-06-01

    Rapid prototyping (RP) and manufacturing (M) is a novel layer-by-layer fabrication technique which has become increasingly popular due to its inherent flexibility for the manufacture of simple and complex 3D parts. Early we had been shown opportunity of selective laser sintering (SLS) of different type powder systems (intermetallics, ceramics, ferrites, high-temperature superconductors), traditional use for self-propagated high-temperature synthesis (SHS). The non-thermal heating affect of an external electromagnetic field during SHS is related to the specific system under study due to differences in movement of defects and ions at the 'plasma-like' molten combustion wave front. We have developed and refined the testing scheme for electro-thermal phenomena studies which can directly influence on the SHS combustion wave front. This work studies electromotive force (EMF) measurements across the front of combustion wave during layer by layer surface laser sintering of exothermal powder compositions (Ni-Ti, Ni-Al). Analysis using an analog-digital-analog computer converter allowed some control of the laser movement and hence some control of the exothermal reaction - in so doing it provided near optimum conditions for forming layered 3D articles. Comparative results of structural-phase transformation during laser control SHS in reaction-capable compositions are presented.

  5. Making High-Temperature Superconductors By Melt Sintering

    NASA Technical Reports Server (NTRS)

    Golben, John P.

    1992-01-01

    Melt-sintering technique applied to YBa2Cu3O7-x system and to Bi/Ca/Sr/Cu-oxide system to produce highly oriented bulk high-temperature-superconductor materials extending to macroscopically usable dimensions. Processing requires relatively inexpensive and simple equipment. Because critical current two orders of magnitude greater in crystal ab plane than in crystal c direction, high degree of orientation greatly enhances critical current in these bulk materials, making them more suitable for many proposed applications.

  6. SELF SINTERING OF RADIOACTIVE WASTES

    DOEpatents

    McVay, T.N.; Johnson, J.R.; Struxness, E.G.; Morgan, K.Z.

    1959-12-29

    A method is described for disposal of radioactive liquid waste materials. The wastes are mixed with clays and fluxes to form a ceramic slip and disposed in a thermally insulated container in a layer. The temperature of the layer rises due to conversion of the energy of radioactivity to heat boillng off the liquid to fomn a dry mass. The dry mass is then covered with thermal insulation, and the mass is self-sintered into a leach-resistant ceramic cake by further conversion of the energy of radioactivity to heat.

  7. Simulation and Experimental Study on the Efficiency of Traveling Wave Direct Energy Conversion for Application to Aneutronic Fusion Reactions

    NASA Astrophysics Data System (ADS)

    Tarditi, Alfonso; Chap, Andrew; Miley, George; Scott, John

    2013-10-01

    A study based on both Particle-in-cell (PIC) simulation and experiments is being developed to study the physics of the Traveling Wave Direct Energy Converter (TWDEC,) with the perspective of application to aneutronic fusion reaction products and space propulsion. The PIC model is investigating in detail the key TWDEC physics process by simulating the time-dependent transfer of energy from the ion beam to an electric load connected to ring-type electrodes in cylindrical symmetry. An experimental effort is in progress on a TWDEC test article at NASA, Johnson Space Center with the purpose of studying the conditions for improving the efficiency of the direct energy conversion process. Using a scaled-down ion energy source, the experiment is primarily focused on the effect of the (bunched) beam density on the efficiency and on the optimization of the electrode design. The simulation model is guiding the development of the experimental configuration and will provide details of the beam dynamics for direct comparison with experimental diagnostics. Work supported by NASA, Johnson Space Center.

  8. Molecular typing for blood group antigens within 40 min by direct polymerase chain reaction from plasma or serum.

    PubMed

    Wagner, Franz F; Flegel, Willy A; Bittner, Rita; Döscher, Andrea

    2017-03-01

    Determining blood group antigens by serological methods may be unreliable in certain situations, such as in patients after chronic or massive transfusion. Red cell genotyping offers a complementary approach, but current methods may take much longer than conventional serological typing, limiting their utility in urgent situations. To narrow this gap, we devised a rapid method using direct polymerase chain reaction (PCR) amplification while avoiding the DNA extraction step. DNA was amplified by PCR directly from plasma or serum of blood donors followed by a melting curve analysis in a capillary rapid-cycle PCR assay. We evaluated the single nucleotide polymorphisms underlying the clinically relevant Fy(a) , Fy(b) , Jk(a) and Jk(b) antigens, with our analysis being completed within 40 min of receiving a plasma or serum sample. The positive predictive value was 100% and the negative predictive value at least 84%. Direct PCR with melting point analysis allowed faster red cell genotyping to predict blood group antigens than any previous molecular method. Our assay may be used as a screening tool with subsequent confirmatory testing, within the limitations of the false-negative rate. With fast turnaround times, the rapid-cycle PCR assay may eventually be developed and applied to red cell genotyping in the hospital setting.

  9. MORATE 6.5: A new version of a computer program for direct dynamics calculations of chemical reaction rate constants

    NASA Astrophysics Data System (ADS)

    Hu, Wei-Ping; Lynch, Gillian C.; Liu, Yi-Ping; Rossi, Ivan; Stewart, James J. P.; Steckler, Rozeanne; Garrett, Bruce C.; Isaacson, Alan D.; Lu, Da-hong; Melissas, Vasilios S.; Truhlar, Donald G.

    1995-08-01

    MORATE (Molecular Orbital RATE calculations) is a computer program for direct dynamics calculations of unimolecular and bimolecular rate constants of gas-phase chemical reactions involving atoms, diatoms, or polyatomic species. The dynamical methods used are conventional or variational transition state theory and multidimensional semiclassical approximations for tunneling and nonclassical reflection. Variational transition states are found by a one-dimensional search of generalized-transition-state dividing surfaces perpendicular to the minimum-energy path, and tunneling probabilities are evaluated by multidimensional semiclassical algorithms, including the small-curvature and large-curvature tunneling approximations and the microcanonical optimized multidimensional tunneling approximation. The computer program is a conventiently interfaced package consisting of the POLYRATE program, version 6.5, for dynamical rate constant calculations, and the MOPAC program, version 5.05mn, for semiempirical electronic structure computations. In single-level mode, the potential energies, gradients, and higher derivatives of the potential are computed whenever needed by electronic structure calculations employing semiempirical molecular orbital theory without the intermediary of a global or semiglobal fit. All semiempirical methods available in MOPAC, in particular MINDO/3, MNDO, AM1, and PM3, can be called on to calculate the potential, gradient, or Hessian, as required at various steps of the dynamics calculations, and, in addition, the code has flexible options for electronic structure calculations with neglect of diatomic differential overlap and specific reaction parameters (NDDO-SRP). In dual-level mode, MINDO/3, MNDO, AM1, PM3, or NDDO-SRP is used as a lower level to calculate the reaction path, and interpolated corrections to energies and frequencies are added; these corrections are based on higher-level data read from an external file.

  10. An investigation of the effect of pore scale flow on average geochemical reaction rates using direct numerical simulation

    SciTech Connect

    Molins, Sergi; Trebotich, David; Steefel, Carl I.; Shen, Chaopeng

    2012-03-30

    The scale-dependence of geochemical reaction rates hinders their use in continuum scale models intended for the interpretation and prediction of chemical fate and transport in subsurface environments such as those considered for geologic sequestration of CO2. Processes that take place at the pore scale, especially those involving mass transport limitations to reactive surfaces, may contribute to the discrepancy commonly observed between laboratory-determined and continuum-scale or field rates. In this study we investigate the dependence of mineral dissolution rates on the pore structure of the porous media by means of pore scale modeling of flow and multicomponent reactive transport. The pore scale model is composed of high-performance simulation tools and algorithms for incompressible flow and conservative transport combined with a general-purpose multicomponent geochemical reaction code. The model performs direct numerical simulation of reactive transport based on an operator-splitting approach to coupling transport and reactions. The approach is validated with a Poiseuille flow single-pore experiment and verified with an equivalent 1-D continuum-scale model of a capillary tube packed with calcite spheres. Using the case of calcite dissolution as an example, the high-resolution model is used to demonstrate that nonuniformity in the flow field at the pore scale has the effect of decreasing the overall reactivity of the system, even when systems with identical reactive surface area are considered. In conclusion, the effect becomes more pronounced as the heterogeneity of the reactive grain packing increases, particularly where the flow slows sufficiently such that the solution approaches equilibrium locally and the average rate becomes transport-limited.

  11. Towards reducing DBP formation potential of drinking water by favouring direct ozone over hydroxyl radical reactions during ozonation.

    PubMed

    De Vera, Glen Andrew; Stalter, Daniel; Gernjak, Wolfgang; Weinberg, Howard S; Keller, Jurg; Farré, Maria José

    2015-12-15

    When ozonation is employed in advanced water treatment plants to produce drinking water, dissolved organic matter reacts with ozone (O3) and/or hydroxyl radicals (OH) affecting disinfection byproduct (DBP) formation with subsequently used chlorine-based disinfectants. This study presents the effects of varying exposures of O3 and •OH on DBP concentrations and their associated toxicity generated after subsequent chlorination. DBP formation potential tests and in vitro bioassays were conducted after batch ozonation experiments of coagulated surface water with and without addition of tertiary butanol (t-BuOH, 10 mM) and hydrogen peroxide (H2O2, 1 mg/mg O3), and at different pH (6-8) and transferred ozone doses (0-1 mg/mg TOC). Although ozonation led to a 24-37% decrease in formation of total trihalomethanes, haloacetic acids, haloacetonitriles, and trihaloacetamides, an increase in formation of total trihalonitromethanes, chloral hydrate, and haloketones was observed. This effect however was less pronounced for samples ozonated at conditions favoring molecular ozone (e.g., pH 6 and in the presence of t-BuOH) over •OH reactions (e.g., pH 8 and in the presence of H2O2). Compared to ozonation only, addition of H2O2 consistently enhanced formation of all DBP groups (20-61%) except trihalonitromethanes. This proves that •OH-transformed organic matter is more susceptible to halogen incorporation. Analogously, adsorbable organic halogen (AOX) concentrations increased under conditions that favor •OH reactions. The ratio of unknown to known AOX, however, was greater at conditions that promote direct O3 reactions. Although significant correlation was found between AOX and genotoxicity with the p53 bioassay, toxicity tests using 4 in vitro bioassays showed relatively low absolute differences between various ozonation conditions.

  12. An investigation of the effect of pore scale flow on average geochemical reaction rates using direct numerical simulation

    SciTech Connect

    Molins, Sergi; Trebotich, David; Steefel, Carl; Shen, Chaopeng

    2012-03-30

    The scale-dependence of geochemical reaction rates hinders their use in continuum scale models intended for the interpretation and prediction of chemical fate and transport in subsurface environments such as those considered for geologic sequestration of CO{sub 2}. Processes that take place at the pore scale, especially those involving mass transport limitations to reactive surfaces, may contribute to the discrepancy commonly observed between laboratory-determined and continuum-scale or field rates. Here, the dependence of mineral dissolution rates on the pore structure of the porous media is investigated by means of pore scale modeling of flow and multicomponent reactive transport. The pore scale model is composed of high-performance simulation tools and algorithms for incompressible flow and conservative transport combined with a general-purpose multicomponent geochemical reaction code. The model performs direct numerical simulation of reactive transport based on an operator-splitting approach to coupling transport and reactions. The approach is validated with a Poiseuille flow single-pore experiment and verified with an equivalent 1-D continuum-scale model of a capillary tube packed with calcite spheres. Using the case of calcite dissolution as an example, the high-resolution model is used to demonstrate that nonuniformity in the flow field at the pore scale has the effect of decreasing the overall reactivity of the system, even when systems with identical reactive surface area are considered. The effect becomes more pronounced as the heterogeneity of the reactive grain packing increases, particularly where the flow slows sufficiently such that the solution approaches equilibrium locally and the average rate becomes transport-limited.

  13. Direct measurement of {sup 4}He({sup 12}C, {sup 16}O){gamma} reaction near stellar energy

    SciTech Connect

    Fujita, K.; Sagara, K.; Teranishi, T.; Goto, T.; Iwabuchi, R.; Matsuda, S.; Oba, N.; Taniguchi, M.; Yamaguchi, H.

    2010-08-12

    A cross section measurement with a direct {sup 16}O detection method for the reaction energy from E{sub cm} = 2.4 down to 0.7 MeV is planned at Kyushu University Tandem Laboratory (KUTL). To perform the experiment successfully and to get the quantitative information of the cross section within the 10% error, we have newly developed several instruments in 2009, such as a blow-in type windowless gas target and movable slit system placed in the recoil mass separator. By using the windowless blow-in gas target, a pressure of 24 Torr was achieved. The effective thickness along the beam axis was measured by p+{sup 4}He scattering. Thanks to the movable slits installed in a recoil mass separator and the trajectory analysis, we found effective reduction of background conditions from the {sup 12}C beam.

  14. Continuum quasiparticle random-phase approximation for astrophysical direct neutron capture reactions on neutron-rich nuclei

    NASA Astrophysics Data System (ADS)

    Matsuo, Masayuki

    2015-03-01

    I formulate a many-body theory to calculate the cross section of direct radiative neutron capture reaction by means of the Hartree-Fock-Bogoliubov mean-field model and the continuum quasiparticle random-phase approximation (QRPA). A focus is put on very-neutron-rich nuclei and low-energy neutron kinetic energy in the range from 1 keV to several MeV, which is relevant to the rapid neutron capture process of nucleosynthesis. I begin with the photoabsorption cross section and the E 1 strength function. Next, in order to apply the reciprocity theorem, I decompose the cross section into partial cross sections corresponding to different channels of one- and two-neutron emission decays of photo-excited states. A numerical example is shown for the photo-absorption of 142Sn and the neutron capture of 141Sn .

  15. Mutational analysis of a monoterpene synthase reaction: altered catalysis through directed mutagenesis of (-)-pinene synthase from Abies grandis.

    PubMed

    Hyatt, David C; Croteau, Rodney

    2005-07-15

    Two monoterpene synthases, (-)-pinene synthase and (-)-camphene synthase, from grand fir (Abies grandis) produce different product mixtures despite having highly homologous amino acid sequences and, presumably, very similar three-dimensional structures. The major product of (-)-camphene synthase, (-)-camphene, and the major products of (-)-pinene synthase, (-)-alpha-pinene, and (-)-beta-pinene, arise through distinct mechanistic variations of the electrophilic reaction cascade that is common to terpenoid synthases. Structural modeling followed by directed mutagenesis in (-)-pinene synthase was used to replace selected amino acid residues with the corresponding residues from (-)-camphene synthase in an effort to identify the amino acids responsible for the catalytic differences. This approach produced an enzyme in which more than half of the product was channeled through an alternative pathway. It was also shown that several (-)-pinene synthase to (-)-camphene synthase amino acid substitutions were necessary before catalysis was significantly altered. The data support a model in which the collective action of many key amino acids, located both in and distant from the active site pocket, regulate the course of the electrophilic reaction cascade.

  16. Method of sintering materials with microwave radiation

    DOEpatents

    Kimrey, Jr., Harold D.; Holcombe, Jr., Cressie E.; Dykes, Norman L.

    1994-01-01

    A method of sintering ceramic materials following: A compacted article comprising inorganic particles coated with carbon is provided, the carbon providing improved microwave coupling. The compacted article is then heated by microwave radiation to a temperature and for a period of time sufficient to sinter the compacted article.

  17. Sintered bauxite unlocks gas well

    SciTech Connect

    Not Available

    1980-09-01

    A 4-fold increase in production has followed the fracturing treatment of an Upshur County gas well and propping the fracture in the Cotton Valley Lime Formation with the most sintered bauxite ever used in E. Texas. The stimulation treatment for Texas Oil and Gas Corp.'s Parrish No. 1 well consisted of 465,000 lb of bauxite pumped into the low-permeability limestone at a depth of more than 2 miles. Sintered bauxite is stronger and several times more expensive than sand and is used to withstand closure pressures that would crush other proppants. The closure pressure increases as the producing pressure declines. Two and one-half months after the treatment, the well stabilized at a flow of 2.5 mmcfd, with flowing tubing pressure 710 psi; 28 bbl of condensate/day and 13 bbl of water/day. Before the fracturing, the flow was 560 mcfd, with flowing tubing pressure of 1495 psi; 3 bbl of condensate/day and 2 bbl of water/day.

  18. Rate control sintering of the uranium dioxide

    NASA Astrophysics Data System (ADS)

    Kuzmin, R. S.; Baranov, V. G.; Burlakova, M. A.; Mikhalchik, V. V.; Tenishev, A. V.

    2016-04-01

    The application of rate controlled sintering (RCS) technique for fabricating oxide fuel pellets in industrial conditions is investigated. Green pellets of UO2 (with no additives) which underwent industrial-type compacting were sintered in reducing Ar - 8% H2 medium using dynamic and isothermal RCS modes with exposure at 1600 °C during 8 hours. Decreasing shrinkage rate resulted in growth of sintered density for the dynamic RCS mode. Opposite to the results of earlier works [1,2], decreasing heating rate did not result in reducing sintering rate. Isothermal mode allowed sintering rate to be maintained between 0.1- 0.15%/min. Temperature-time modes obtained using RCS are close to the operation mode of through-type furnace used for mass production.

  19. Manufacture of high-density ceramic sinters

    NASA Technical Reports Server (NTRS)

    Hibata, Y.

    1986-01-01

    High density ceramic sinters are manufactured by coating premolded or presintered porous ceramics with a sealing material of high SiO2 porous glass or nitride glass and then sintering by hot isostatic pressing. The ceramics have excellent abrasion and corrosion resistances. Thus LC-10 (Si3N2 powder) and Y2O3-Al2O3 type sintering were mixed and molded to give a premolded porous ceramic (porosity 37%, relative bulk density 63%). The ceramic was dipped in a slurry containing high SiO2 porous glass and an alcohol solution of cellulose acetate and dried. The coated ceramic was treated in a nitrogen atmosphere and then sintered by hot isostatic pressing to give a dense ceramic sinter.

  20. Pressureless sintered beta-prime-Si3N4 solid solution - Fabrication, microstructure, and strength

    NASA Technical Reports Server (NTRS)

    Dutta, S.

    1977-01-01

    Pressureless sintering of beta-prime-Si3N4 solid solution was studied as a function of temperature using Si3N4, A1N, and Al2O3 as basic constituents. Y2O3-SiO2 additions were used to promote liquid-phase sintering. The sintered specimens were characterized with respect to density, microstructure, strength, oxidation, and thermal shock resistance. Density greater than 98 percent of theoretical was achieved by pressureless sintering at 1750 C. The microstructure consisted essentially of fine-grained beta-prime-Si3N4 solid solution as the major phase. Modulus of rupture strengths up to 483 M Pa were achieved at moderate temperature (1000 C), but decreased to 228 M Pa at 1380 C. This substantial strength loss was attributed to a 'glassy' grain boundary phase formed during cooling from the sintering temperature. The best oxidation resistance was exhibited by a composition containing 3 mol % Y2O3-SiO2 additives. Water quench thermal shock resistance was equivalent to that of reaction sintered silicon nitride but lower than hot-pressed silicon nitride.

  1. Pressureless sintered beta prime-Si3N4 solid solution: Fabrication, microstructure, and strength

    NASA Technical Reports Server (NTRS)

    Dutta, S.

    1977-01-01

    Si3N4, AlN, and Al2O3 were used as basic constituents in a study of the pressureless sintering of beta prime-Si3N4 solid solution as a function of temperature. Y2O3-SiO2 additions were used to promote liquid-phase sintering. The sintered specimens were characterized with respect to density, microstructure, strength, oxidation, and thermal shock resistance. Density greater than 98 percent of theoretical was achieved by pressureless sintering at 1750 C. The microstructure consisted essentially of fine-grained beta prime-Si3N4 solid solution as the major phase. Modulus of rupture strengths up to 483 MPa were achieved at moderate temperature (1000 C), but decreased to 228 MPa at 1380 C. This substantial strength loss was attributed to a glassy grain boundary phase formed during cooling from the sintering temperature. The best oxidation resistance was exhibited by a composition containing 3 mol % Y2O3-SiO2 additives. Water quench thermal shock resistance was equivalent to that of reaction sintered silicon nitride but lower than hot-pressed silicon nitride.

  2. Mechanism of Selective Desulphurization in Iron Ore Sintering Process by Adding Urea

    NASA Astrophysics Data System (ADS)

    Long, Hongming; Wu, Xuejian; Chun, Tiejun; Li, Jiaxin; Wang, Ping; Meng, Qingmin; Di, Zhanxia; Zhang, Xiangyang

    2017-02-01

    Iron ore sintering is an important part during the ironmaking process, and a large amount of SO2 is also generated. Our previous research shows that it is an effective way to reduce SO2 content of flue gas by adding urea to a special sintering material zone position. In this paper, the mechanism of selective desulphurization by adding urea during the iron ore sintering was carried out. The results show that 88.14 % desulphurization rate was obtained with the addition of 0.05 % urea particles at 100 mm height from the feed bottom. During the sintering process, when drying zone reached the added position of urea, large amounts of NH3 were generated by urea decomposition, and then reacted with SO2 to produce (NH4)2SO4 in the wetting zone. With the accumulated desulphurization reactions during the sintering, the low SO2 emission in the flue gas was achieved. Moreover, the addition of urea in the bottom zone avoided the ammonia present in the sintering ore and promoted the urea utilization efficiency.

  3. Effect of glow discharge sintering in the properties of a composite material fabricated by powder metallurgy

    NASA Astrophysics Data System (ADS)

    Cardenas, A.; Pineda, Y.; Sarmiento Santos, A.; Vera, E.

    2016-02-01

    Composite samples of 316 stainless steel and SiC were produced by powder metallurgy. Starting materials were mixed in different proportions and compacted to 700MPa. Sintering stage was performed by abnormal glow discharge plasma with direct current in an inert atmosphere of argon. The process was conducted at a temperature of 1200°C±5°C with a heating rate of 100°C/min. This work shows, the effectiveness of plasma sintering process to generate the first contacts between particles and to reduce vacancies. This fact is confirmed by comparing green and sintered density of the material. The results of porosity show a decrease after plasma sintering. Wear tests showed the wear mechanisms, noting that at higher SiC contents, the wear resistance decreases due to poor matrix-reinforcement interaction and by the porosity presence which causes matrix-reinforcement sliding.

  4. Pressureless sintered Sialons with low amounts of sintering aid

    NASA Technical Reports Server (NTRS)

    Arias, A.

    1978-01-01

    Two Beta prime - Sialons of composition Si2.6Al0.393y0.007O0.4N3.6 and Si2.6Al0.384Y0.014O0.4N3.6 were pressureless sintered from mixtures of Y2O3 and separately milled Beta -Si3N4, AlN, and SiO2. These Sialons had densities of over 98% of theoretical, four-point bend strengths of 460 and 155 MPa at room temperature and 1400 C, respectively, and 1400 C oxidation rates lower than those reported for hot pressed Si3N4 and for a stronger Sialon with 2.5 weight percentage Y2O3.

  5. A Comparative Analysis of Polymerase Chain Reaction and Direct Fluorescent Antibody Test for Diagnosis of Genital Herpes

    PubMed Central

    Patwardhan, Vrushali; Bhalla, Preena; Rawat, Deepti; Garg, Vijay Kumar; Sardana, Kabir; Sethi, Sumit

    2017-01-01

    Objective: To compare laboratory tests that can simultaneously detect and type herpes simplex virus (HSV) directly from the genital ulcer specimens in clinically suspected cases of genital herpes. Materials and Methods: A study was conducted over 10 months and 44 adult male and female patients clinically suspected with genital herpes were recruited. Genital ulcer swab specimens were subjected to glycoprotein-G gene-based conventional polymerase chain reaction (PCR) and commercially available direct fluorescent antibody (DFA) test and the results were compared. Results: PCR for HSV was positive in 82% (36/44) cases. DFA was positive in 68.2% (30/44) cases. There was 100% agreement between HSV types detected by DFA and PCR. The strength of agreement between the results was better in primary genital herpes than recurrent cases. Conclusion: PCR was found to be better in the detection of HSV in recurrent genital herpes patients. It is a better modality, especially when genital herpes clinically presents with ulcerative or crusted lesions, and is also a cheaper alternative as compared to DFA. PMID:28042218

  6. The Absence of Plasma in"Spark Plasma Sintering"

    SciTech Connect

    Hulbert, Dustin M.; Anders, Andre; Dudina, Dina V.; Andersson, Joakim; Jiang, Dongtao; Unuvar, Cosan; Anselmi-Tamburini, Umberto; Lavernia, Enrique J.; Mukherjee, Amiya K.

    2008-04-10

    Spark plasma sintering (SPS) is a remarkable method for synthesizing and consolidating a large variety of both novel and traditional materials. The process typically uses moderate uni-axial pressures (<100 MPa) in conjunction with a pulsing on-off DC current during operation. There are a number of mechanisms proposed to account for the enhanced sintering abilities of the SPS process. Of these mechanisms, the one most commonly put forth and the one that draws the most controversy involves the presence of momentary plasma generated between particles. This study employees three separate experimental methods in an attempt to determine the presence or absence of plasma during SPS. The methods employed include: in-situ atomic emission spectroscopy, direct visual observation and ultra-fast in-situ voltage measurements. It was found using these experimental techniques that no plasma is present during the SPS process. This result was confirmed using several different powders across a wide spectrum of SPS conditions.

  7. Direct sGC Activation Bypasses NO Scavenging Reactions of Intravascular Free Oxy-Hemoglobin and Limits Vasoconstriction

    PubMed Central

    Tabima, D. Marcela; Specht, Patricia A.C.; Tejero, Jesús; Champion, Hunter C.; Kim-Shapiro, Daniel B.; Baust, Jeff; Mik, Egbert G.; Hildesheim, Mariana; Stasch, Johannes-Peter; Becker, Eva-Maria; Truebel, Hubert

    2013-01-01

    Abstract Aims: Hemoglobin-based oxygen carriers (HBOC) provide a potential alternative to red blood cell (RBC) transfusion. Their clinical application has been limited by adverse effects, in large part thought to be mediated by the intravascular scavenging of the vasodilator nitric oxide (NO) by cell-free plasma oxy-hemoglobin. Free hemoglobin may also cause endothelial dysfunction and platelet activation in hemolytic diseases and after transfusion of aged stored RBCs. The new soluble guanylate cyclase (sGC) stimulator Bay 41-8543 and sGC activator Bay 60-2770 directly modulate sGC, independent of NO bioavailability, providing a potential therapeutic mechanism to bypass hemoglobin-mediated NO inactivation. Results: Infusions of human hemoglobin solutions and the HBOC Oxyglobin into rats produced a severe hypertensive response, even at low plasma heme concentrations approaching 10 μM. These reactions were only observed for ferrous oxy-hemoglobin and not analogs that do not rapidly scavenge NO. Infusions of L-NG-Nitroarginine methyl ester (L-NAME), a competitive NO synthase inhibitor, after hemoglobin infusion did not produce additive vasoconstriction, suggesting that vasoconstriction is related to scavenging of vascular NO. Open-chest hemodynamic studies confirmed that hypertension occurred secondary to direct effects on increasing vascular resistance, with limited negative cardiac inotropic effects. Intravascular hemoglobin reduced the vasodilatory potency of sodium nitroprusside (SNP) and sildenafil, but had no effect on vasodilatation by direct NO-independent activation of sGC by BAY 41-8543 and BAY 60-2770. Innovation and Conclusion: These data suggest that both sGC stimulators and sGC activators could be used to restore cyclic guanosine monophosphate-dependent vasodilation in conditions where cell-free plasma hemoglobin is sufficient to inhibit endogenous NO signaling. Antioxid. Redox Signal. 19, 2232–2243. PMID:23697678

  8. High pressure assisted WC/Co hardmetal sintering-effect of sintering temperature

    NASA Astrophysics Data System (ADS)

    Karimi, M. M.; Gomes, U. U.; Oliveira, M. P.; Guimarães, R. D. S.; Filgueira, M.

    2017-02-01

    WC/Co is widely used as cutting tools, because has a unique combination of high strength, hardness, toughness, and moderate stiffness, especially with fine grained WC and finely distributed cobalt. WC/Co powder mixture sinters by different methods such as vacuum sintering, microwave sintering and SPS. High pressure high temperature (HPHT) sintering is a proposed method that can results in better distribution of cobalt and avoid undesirable phases by using high pressure, high temperature and very low sintering time. In this study, a powder mixture of WC-10 wt% Co was sintered by HPHT at 1500 to 1900°C under a pressure of 7.7 GPa for 3 minutes. Microstructural/structural analyses were performed by SEM/EDS. Hardness and compression test were also done to obtain the effect of sintering parameters. It was found that HPHT sintering method improve properties of WC/Co hard metal. It was realized that increasing sintering temperature results in increasing density but hardness and compression strength increase by increasing sintering temperature up to 1800 °C and then decrease.

  9. Direct measurement of the 4He (12C, 16O) γ reaction cross section near stellar energies

    NASA Astrophysics Data System (ADS)

    Sagara, Kenshi

    2014-09-01

    The 12C+4He-->16O + γ reaction is one of the key reactions in stellar He-burning, but its total cross section at stellar energy (Ecm = 0.3 MeV) has not been measured yet, in spite of many experiments made in the world for about a half century. At Kyushu University Tandem accelerator Laboratory (KUTL), we have been making direct measurement of the 4He (12C, 16O) γ total cross section below Ecm = 2.4 MeV for about 20 years. We have measured the total cross section at Ecm = 2.4, 1.5 and 1.2 MeV. Now we are preparing to measure the cross section at 1.0 MeV. The direct measurement was made from Ecm = 5 MeV down to 1.9 MeV at Ruhr University, Bochum. We use a pulsed 12C beam and a windowless 4He target, and detect all the 16O recoils in a charge state. A usually continuum 12C beam from our tandem accelerator is pulsed by a pre-buncher, a main buncher, and a beam chopper. Our tandem accelerator was designed to be used at the acceleration voltage of 6-10 MV. For the 4He (12C, 16O) γ experiment we need to use it at 1.3-1.8 MV where beam transmission is very low, then we have invented an acceleration-deceleration method for the tandem accelerator. We have developed a blow-in windowless He target based on an original idea. To separate 16O recoils from the 12C beam, we developed a recoil-mass separator. To reject 12C backgrounds, we developed a long-time chopper, and an ionization chamber. Now, we are preparing to measure time-of-flight of 16O recoils and 12C backgrounds. Many original instruments and the experimental results will be presented. Finally we discuss what are necessary for future direct measurement of the 4He (12C, 16O) γ total cross section below 1.0 MeV, down to 0.7 MeV. A dynamitron accelerator and hard-working researchers may be inevitable. The 12C+4He-->16O + γ reaction is one of the key reactions in stellar He-burning, but its total cross section at stellar energy (Ecm = 0.3 MeV) has not been measured yet, in spite of many experiments made in the world

  10. Thermoelectric transport properties of polycrystalline titanium diselenide co-intercalated with nickel and titanium using spark plasma sintering

    SciTech Connect

    Holgate, T.C.; Zhu, S.; Zhou, M.; Bangarigadu-Sanasy, S.; Kleinke, H.; He, J.; Tritt, T.M.

    2013-01-15

    Polycrystalline samples of nickel intercalated (0-5%) TiSe{sub 2} were attempted via solid-state reaction in evacuated quartz tubes followed by densification using a spark plasma sintering process. X-ray diffraction data indicated that mixed NiSe{sub 2} and TiSe{sub 2} phases were present after initial synthesis by solid-state reaction, but a pure TiSe{sub 2} phase was present after the spark plasma sintering. While EPMA data reveals the stoichiometry to be near 1:1.8 (Ti:Se) for all samples, comparisons of the measured bulk densities to the theoretical densities suggest that the off stoichiometry is a result of the co-intercalation of both Ni and Ti rather than Se vacancies. Due to the presence of excess Ti (0.085-0.130 per formula) in the van der Waals gap of all the samples, the sensitive electron-hole balance is offset by the additional Ti-3d electrons, leading to an increase in the thermopower (n-type) over pristine, stoichiometric TiSe{sub 2}. The effects of the co-intercalation of both Ni and Ti in TiSe{sub 2} on the structural, thermal, and electrical properties are discussed herein. - Graphical abstract: Co-intercalation of nickel and excess titanium into the van der Waals gap of TiSe{sub 2} via solid state synthesis followed by spark plasma sintering results in a systematic shift in the ratio of hole and electron carrier concentration, which is close to unity for pristine TiSe{sub 2}. This directly affects the electrical transport properties, and as the structural disorder induced by intercalation suppresses the lattice thermal conductivity, co-intercalation is an effective route to enhance the thermoelectric properties of transition metal diselenides. Highlights: Black-Right-Pointing-Pointer Single phase bulk Ni and Ti co-intercalated TiSe{sub 2} samples prepared by spark plasma sintering. Black-Right-Pointing-Pointer Density and X-ray diffraction suggest that the Ni and excess Ti are ordered in the Van der Waals gap. Black-Right-Pointing-Pointer Co

  11. No direct by maternal effects interaction detected for pre-weaning growth in Romane sheep using a reaction norm model

    PubMed Central

    2013-01-01

    Background The pre-weaning growth of lambs, an important component of meat production, depends on maternal and direct effects. These effects cannot be observed directly and models used to study pre-weaning growth assume that they are additive. However, it is reasonable to suggest that the influence of direct effects on growth may differ depending on the value of maternal effects i.e. an interaction may exist between the two components. Methods To test this hypothesis, an experiment was carried out in Romane sheep in order to obtain observations of maternal phenotypic effects (milk yield and milk quality) and pre-weaning growth of the lambs. The experiment consisted of mating ewes that had markedly different maternal genetic effects with rams that contributed very different genetic effects in four replicates of a 3 × 2 factorial plan. Milk yield was measured using the lamb suckling weight differential technique and milk composition (fat and protein contents) was determined by infrared spectroscopy at 15, 21 and 35 days after lambing. Lambs were weighed at birth and then at 15, 21 and 35 days. An interaction between genotype (of the lamb) and environment (milk yield and quality) for average daily gain was tested using a restricted likelihood ratio test, comparing a linear reaction norm model (interaction model) to a classical additive model (no interaction model). Results A total of 1284 weights of 442 lambs born from 166 different ewes were analysed. On average, the ewes produced 2.3 ± 0.8 L milk per day. The average protein and fat contents were 50 ± 4 g/L and 60 ± 18 g/L, respectively. The mean 0–35 day average daily gain was 207 ± 46 g/d. Results of the restricted likelihood ratio tests did not highlight any significant interactions between the genotype of the lambs and milk production of the ewe. Conclusions Our results support the hypothesis of additivity of maternal and direct effects on growth that is currently applied in genetic

  12. Liquid phase sintering of silicon carbide

    DOEpatents

    Cutler, R.A.; Virkar, A.V.; Hurford, A.C.

    1989-05-09

    Liquid phase sintering is used to densify silicon carbide based ceramics using a compound comprising a rare earth oxide and aluminum oxide to form liquids at temperatures in excess of 1,600 C. The resulting sintered ceramic body has a density greater than 95% of its theoretical density and hardness in excess of 23 GPa. Boron and carbon are not needed to promote densification and silicon carbide powder with an average particle size of greater than one micron can be densified via the liquid phase process. The sintered ceramic bodies made by the present invention are fine grained and have secondary phases resulting from the liquid phase. 4 figs.

  13. Liquid phase sintering of silicon carbide

    DOEpatents

    Cutler, Raymond A.; Virkar, Anil V.; Hurford, Andrew C.

    1989-01-01

    Liquid phase sintering is used to densify silicon carbide based ceramics using a compound comprising a rare earth oxide and aluminum oxide to form liquids at temperatures in excess of 1600.degree. C. The resulting sintered ceramic body has a density greater than 95% of its theoretical density and hardness in excess of 23 GPa. Boron and carbon are not needed to promote densification and silicon carbide powder with an average particle size of greater than one micron can be densified via the liquid phase process. The sintered ceramic bodies made by the present invention are fine grained and have secondary phases resulting from the liquid phase.

  14. Thermal barrier coating resistant to sintering

    DOEpatents

    Subramanian, Ramesh; Sabol, Stephen M.

    2001-01-01

    A device (10) having a ceramic thermal barrier coating layer (16) characterized by a microstructure having gaps (18) with a sintering inhibiting material (22) disposed on the columns (20) within the gaps (18). The sintering resistant material (22) is stable over the range of operating temperatures of the device (10) and is not soluble with the underlying ceramic layer (16). For a YSZ ceramic layer (16) the sintering resistant layer (22) may preferably be aluminum oxide or yttrium aluminum oxide, deposited as a continuous layer or as nodules.

  15. Impact of sintering temperature on the structural, electrical, and optical properties of doped ZnO nanoparticle-based discs

    NASA Astrophysics Data System (ADS)

    Sendi, Rabab Khalid; Mahmud, Shahrom

    2012-11-01

    In the current study, 20 nm zinc oxide (ZnO) nanoparticles were used to make high-density ZnO discs doped with Bi2O3 and Mn2O3 via the conventional ceramic processing method. Different sintering temperatures were found to have significant impacts on the ZnO discs, especially on enhancing grain growth even at a low sintering temperature of only 980 °C. The strong solid-state reaction during sintering may be attributed to the high surface area of the 20 nm ZnO nanoparticles that promoted a strong surface reaction even at low sintering temperatures. Moreover, the sintering process also improved the grain crystallinity, as shown in the lowering of the intrinsic compressive stress based on the X-ray diffraction lattice constant and full-wave half-maximum data. The sintering temperatures also significantly influenced the electrical properties of the doped ZnO discs with a marked drop in the breakdown voltage from 330 V (sample at 980 °C) to 80 V (sample at 1380 °C). The resistivity also experienced a dramatic drop from 304.4 kΩ cm (sample at 980 °C) to 98.86 kΩ cm (sample at 1380 °C). The observed shift in the energy band-gap from a higher to a lower value may be attributed to the conversion of compressive stress to tensile stress with increasing sintering temperature. The Raman spectra indicate that the sintering temperatures and dopants in the discs had significant effects on the E2(high) phonon mode and ZnO crystal structures. Therefore, the sintering process can be used as a new technique for controlling the breakdown voltage of doped ZnO discs made from ZnO nanoparticles with improved structural and optical properties.

  16. A comparative study of conventionally sintered and microwave sintered nickel zinc ferrite

    SciTech Connect

    Rani, Rekha; Juneja, J. K.; Raina, K. K.; Kotnala, R. K.; Prakash, Chandra

    2014-04-24

    For the present work, nickel zinc ferrite having compositional formula Ni{sub 0.8}Zn{sub 0.2}Fe{sub 2}O{sub 4} was synthesized by conventional solid state method and sintered in conventional and microwave furnaces. Pellets were sintered with very short soaking time of 10 min at 1150 °C in microwave furnace whereas 4 hrs of soaking time was selected for conventional sintering at 1200 °C. Phase formation was confirmed by X-ray diffraction analysis technique. Scanning electron micrographs were taken for microstructural study. Dielectric properties were studied as a function of temperature. To study magnetic behavior, M-H hysteresis loops were recorded for both samples. It is observed that microwave sintered sample could obtain comparable properties to the conventionally sintered one in lesser soaking time at lower sintering temperature.

  17. Minimum energy of silver and copper nanoparticles for laser sintering (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Lee, Changmin; Hahn, Jae W.

    2016-09-01

    The electronics fabrication without using conventional deposition and photolithography has attracted an intense interest in the modern technology. The direct metal pattering based on the laser local sintering of nano ink is one of the alternative manufacturing methods. In this sintering process, some researchers have shown the mechanism of the heating particle. In this paper, we discuss the theoretical analysis of sintering process about silver and copper nanoparticles. For analyzing the sintering process, we use Shi's model to calculating the melting temperature and surface melting temperature with variation of the particle size. The absorption cross section with respect to wavelength of laser and particle size is calculated by Mie theory. From the results, we suggest the minimum energy per unit area of laser with respect to particle size and wavelength of the laser for the sintering process. These results suggest that the longer the wavelength of the laser, the higher minimum energy for sintering process in copper case. In the silver case, the wavelength of the laser has to be close to 350 nm which is near to the surface plasmon resonance frequency of the silver for minimum energy per unit area.

  18. Sintering of sponge and hydride-dehydride titanium powders

    SciTech Connect

    Alman, David E.; Gerdemann, Stephen J.

    2004-04-01

    The sintering behavior of compacts produced from sponge and hydride-dehydride (HDH) Ti powders was examined. Compacts were vacuum sintered at 1200 or 1300 deg C for 30, 60, 120, 240, 480 or 960 minutes. The porosity decreased with sintering time and/or temperature in compacts produced from the HDH powders. Compacts produced from these powders could be sintered to essentially full density. However, the sintering condition did not influence the amount of porosity present in compacts produced from the sponge powders. These samples could only be sintered to a density of 97% theoretical. The sintering behavior was attributed to the chemical impurities in the powders.

  19. Direct Photolysis of Fluoroquinolone Antibiotics at 253.7 nm: Specific Reaction Kinetics and Formation of Equally Potent Fluoroquinolone Antibiotics.

    PubMed

    Snowberger, Sebastian; Adejumo, Hollie; He, Ke; Mangalgiri, Kiranmayi P; Hopanna, Mamatha; Soares, Ana Dulce; Blaney, Lee

    2016-09-06

    Three fluoroquinolone-to-fluoroquinolone antibiotic transformations were monitored during UV-C irradiation processes. In particular, the following reactions were observed: enrofloxacin-to-ciprofloxacin, difloxacin-to-sarafloxacin, and pefloxacin-to-norfloxacin. The apparent molar absorptivity and fluence-based pseudo-first-order rate constants for transformation of the six fluoroquinolones by direct photolysis at 253.7 nm were determined for the pH 2-12 range. These parameters were deconvoluted to calculate specific molar absorptivity and fluence-based rate constants for cationic, zwitterionic, and anionic fluoroquinolone species. For a typical disinfection fluence of 40 mJ/cm(2), the apparent transformation efficiencies were inflated by 2-8% when fluoroquinolone products were not considered; moreover, the overall transformation efficiencies at 400 mJ/cm(2) varied by up to 40% depending on pH. The three product antibiotics, namely ciprofloxacin, sarafloxacin, and norfloxacin, were found to be equally or more potent than the parent fluoroquinolones using an Escherichia coli-based assay. UV treatment of a solution containing difloxacin was found to increase antimicrobial activity due to formation of sarafloxacin. These results highlight the importance of considering antibiotic-to-antibiotic transformations in UV-based processes.

  20. Investigation on natural diets of larval marine animals using peptide nucleic acid-directed polymerase chain reaction clamping.

    PubMed

    Chow, Seinen; Suzuki, Sayaka; Matsunaga, Tadashi; Lavery, Shane; Jeffs, Andrew; Takeyama, Haruko

    2011-04-01

    The stomach contents of the larvae of marine animals are usually very small in quantity and amorphous, especially in invertebrates, making morphological methods of identification very difficult. Nucleotide sequence analysis using polymerase chain reaction (PCR) is a likely approach, but the large quantity of larval (host) DNA present may mask subtle signals from the prey genome. We have adopted peptide nucleic acid (PNA)-directed PCR clamping to selectively inhibit amplification of host DNA for this purpose. The Japanese spiny lobster (Panulirus japonicus) and eel (Anguilla japonica) were used as model host and prey organisms, respectively. A lobster-specific PNA oligomer (20 bases) was designed to anneal to the sequence at the junction of the 18 S rDNA gene and the internal transcribed spacer 1 (ITS1) of the lobster. PCR using eukaryote universal primers for amplifying the ITS1 region used in conjunction with the lobster-specific PNA on a mixed DNA template of lobster and eel demonstrated successful inhibition of lobster ITS1 amplification while allowing efficient amplification of eel ITS1. This method was then applied to wild-caught lobster larvae of P. japonicus and P. longipes bispinosus collected around Ryukyu Archipelago, Japan. ITS1 sequences of a wide variety of animals (Ctenophora, Cnidaria, Crustacea, Teleostei, Mollusca, and Chaetognatha) were detected.

  1. Palladium(II)-Catalyzed C-H Bond Activation/C-C and C-O Bond Formation Reaction Cascade: Direct Synthesis of Coumestans.

    PubMed

    Neog, Kashmiri; Borah, Ashwini; Gogoi, Pranjal

    2016-12-02

    A palladium catalyzed cascade reaction of 4-hydroxycoumarins and in situ generated arynes has been developed for the direct synthesis of coumestans. This cascade strategy proceeds via C-H bond activation/C-O and C-C bond formations in a single reaction vessel. This methodology affords moderate to good yields of coumestans and is tolerant of a variety of functional groups including halide. The methodology was applied to the synthesis of natural product flemichapparin C.

  2. Intramolecular cyclization of a diruthenium complex: insight into the mechanism of heteroatom-directed intramolecular C-H/olefin coupling reactions.

    PubMed

    Gong, Dawei; Hu, Bowen; Shi, Jing; Chen, Dafa

    2015-07-28

    Complex 2, synthesized by the reaction of {(C5H4N)(μ2-η(5):η(1)-C9H5)}Ru3(CO)9 (1) with 1,5-hexadiene, could further transform to another diruthenium complex 3via intramolecular carbometalation. The results are relevant to the mechanism of transition-metal catalyzed heteroatom-directed intramolecular C-H/olefin coupling reactions.

  3. Direct dynamics trajectory study of the reaction of formaldehyde cation with D2: vibrational and zero-point energy effects on quasiclassical trajectories.

    PubMed

    Liu, Jianbo; Song, Kihyung; Hase, William L; Anderson, Scott L

    2005-12-22

    Quasiclassical, direct dynamics trajectories have been used to study the reaction of formaldehyde cation with molecular hydrogen, simulating the conditions in an experimental study of H2CO+ vibrational effects on this reaction. Effects of five different H2CO+ modes were probed, and we also examined different approaches to treating zero-point energy in quasiclassical trajectories. The calculated absolute cross-sections are in excellent agreement with experiments, and the results provide insight into the reaction mechanism, product scattering behavior, and energy disposal, and how they vary with impact parameter and reactant state. The reaction is sharply orientation-dependent, even at high collision energies, and both trajectories and experiment find that H2CO+ vibration inhibits reaction. On the other hand, the trajectories do not reproduce the anomalously strong effect of nu2(+) (the CO stretch). The origin of the discrepancy and approaches for minimizing such problems in quasiclassical trajectories are discussed.

  4. Rapid sintering of anisotropic, nanograined Nd-Fe-B by flash-spark plasma sintering

    NASA Astrophysics Data System (ADS)

    Castle, Elinor; Sheridan, Richard; Grasso, Salvatore; Walton, Allan; Reece, Mike

    2016-11-01

    A Spark Plasma Sintering (SPS) furnace was used to Flash-Sinter (FS) Nd-Fe-Dy-Co-B-Ga melt spun permanent magnetic material. During the 10 s "Flash" process (heating rate 2660 K min-1), sample sintering (to theoretical density) and deformation (54% height reduction) occurred. This produced texturing and significant magnetic anisotropy, comparable to conventional die-upset magnets; yet with much greater coercivities (>1600 kA m-1) due to the nanoscale characteristics of the plate-like sintered grains. These preliminary results suggest that Flash-SPS could provide a new processing route for the mass production of highly anisotropic, nanocrystalline magnetic materials with high coercivity.

  5. Effect of the reaction conditions on the performance of Au-Pd/TiO(2) catalyst for the direct synthesis of hydrogen peroxide.

    PubMed

    Piccinini, Marco; Ntainjua, Edwin; Edwards, Jennifer K; Carley, Albert F; Moulijn, Jacob A; Hutchings, Graham J

    2010-03-14

    The direct synthesis of hydrogen peroxide from H(2) and O(2) has been studied using a high activity AuPd/TiO(2) catalyst. In particular, the effect of variation in the reaction conditions on the productivity of hydrogen peroxide formation is investigated in detail. The effect of H(2)/O(2) molar ratio, temperature, total pressure and solvent composition has been studied and optimised conditions identified. In addition, the effect of carrying out the synthesis reaction in the presence of hydrogen peroxide is investigated and the competing reactions of hydrogen peroxide formation, decomposition and hydrogenation are discussed and optimal operating conditions are identified.

  6. Pressureless sintering of whisker-toughened ceramic composites

    DOEpatents

    Tiegs, Terry N.

    1993-01-01

    A pressureless sintering method is disclosed for use in the production of whisker-toughened ceramic composites wherein the sintered density of composites containing up to about 20 vol. % SiC whiskers is improved by reducing the average aspect ratio of the whiskers to from about 10 to about 20. Sintering aids further improve the density, permitting the production of composites containing 20 vol. % SiC with sintered densities of 94% or better of theoretical density by a pressureless sintering method.

  7. Pressureless sintering of whisker-toughened ceramic composites

    DOEpatents

    Tiegs, T.N.

    1993-05-04

    A pressureless sintering method is disclosed for use in the production of whisker-toughened ceramic composites wherein the sintered density of composites containing up to about 20 vol. % SiC whiskers is improved by reducing the average aspect ratio of the whiskers to from about 10 to about 20. Sintering aids further improve the density, permitting the production of composites containing 20 vol. % SiC with sintered densities of 94% or better of theoretical density by a pressureless sintering method.

  8. Pressureless sintering of whiskered-toughened ceramic composites

    DOEpatents

    Tiegs, Terry N.

    1994-01-01

    A pressureless sintering method is disclosed for use in the production of whisker-toughened ceramic composites wherein the sintered density of composites containing up to about 20 vol. % SiC whiskers is improved by reducing the average aspect ratio of the whiskers to from about 10 to about 20. Sintering aids further improve the density, permitting the production of composites containing 20 vol. % SiC with sintered densities of 94% or better of theoretical density by a pressureless sintering method.

  9. Sintered electrode for solid oxide fuel cells

    DOEpatents

    Ruka, Roswell J.; Warner, Kathryn A.

    1999-01-01

    A solid oxide fuel cell fuel electrode is produced by a sintering process. An underlayer is applied to the electrolyte of a solid oxide fuel cell in the form of a slurry, which is then dried. An overlayer is applied to the underlayer and then dried. The dried underlayer and overlayer are then sintered to form a fuel electrode. Both the underlayer and the overlayer comprise a combination of electrode metal such as nickel, and stabilized zirconia such as yttria-stabilized zirconia, with the overlayer comprising a greater percentage of electrode metal. The use of more stabilized zirconia in the underlayer provides good adhesion to the electrolyte of the fuel cell, while the use of more electrode metal in the overlayer provides good electrical conductivity. The sintered fuel electrode is less expensive to produce compared with conventional electrodes made by electrochemical vapor deposition processes. The sintered electrodes exhibit favorable performance characteristics, including good porosity, adhesion, electrical conductivity and freedom from degradation.

  10. Thermal barrier coating resistant to sintering

    DOEpatents

    Subramanian, Ramesh; Seth, Brig B.

    2005-08-23

    A device (10) is made, having a ceramic thermal barrier coating layer (16) characterized by a microstructure having gaps (18) with a sintering inhibiting material (22) disposed on the columns (20) within the gaps (18). The sintering resistant material (22) is stable over the range of operating temperatures of the device (10), is not soluble with the underlying ceramic layer (16) and is applied by a process that is not an electron beam physical vapor deposition process. The sintering inhibiting material (22) has a morphology adapted to improve the functionality of the sintering inhibiting material (22), characterized as continuous, nodule, rivulet, grain, crack, flake and combinations thereof and being disposed within at least some of the vertical and horizontal gaps.

  11. Silver Ink Formulations for Sinter-free Printing of Conductive Films

    NASA Astrophysics Data System (ADS)

    Black, Kate; Singh, Jetinder; Mehta, Danielle; Sung, Sarah; Sutcliffe, Christopher. J.; Chalker, Paul. R.

    2016-02-01

    Inkjet printing offers an attractive method for the deposition of metal interconnects in electronic systems and enables a low-cost, environmentally friendly route to manufacture. However, virtually all current metal inkjet processes require post-deposition sintering treatments to achieve the optimum electrical conductivity, because the growth mechanism involves coalescence of discrete nanoparticles. A manufacturing process that reduces the number of steps by directly printing silver, removing the need to sinter the printed metal, would be highly advantageous. Here we describe a, sinter-free process that results in the direct printing of crystalline silver. This process exploits the chemistries developed for Atomic Layer Deposition (ALD), to form the basis of a new ink formulation, which we term; Reactive Organometallic inks (ROM). These ROM ink formulations are capable of depositing low temperature, high conductivity metal films, without the need for subsequent sintering treatments. To reduce the temperature for direct formation of metallic Ag, we have added an alcohol as a catalytic reducing agent to dissociate the organometallic component. Silver films printed from our novel ROM ink, on a glass substrate at 120 °C, are electrically conductive with a typical resistivity as low as 39.2% that of bulk silver, without the need for sintering.

  12. Silver Ink Formulations for Sinter-free Printing of Conductive Films

    PubMed Central

    Black, Kate; Singh, Jetinder; Mehta, Danielle; Sung, Sarah; Sutcliffe, Christopher. J.; Chalker, Paul. R.

    2016-01-01

    Inkjet printing offers an attractive method for the deposition of metal interconnects in electronic systems and enables a low-cost, environmentally friendly route to manufacture. However, virtually all current metal inkjet processes require post-deposition sintering treatments to achieve the optimum electrical conductivity, because the growth mechanism involves coalescence of discrete nanoparticles. A manufacturing process that reduces the number of steps by directly printing silver, removing the need to sinter the printed metal, would be highly advantageous. Here we describe a, sinter-free process that results in the direct printing of crystalline silver. This process exploits the chemistries developed for Atomic Layer Deposition (ALD), to form the basis of a new ink formulation, which we term; Reactive Organometallic inks (ROM). These ROM ink formulations are capable of depositing low temperature, high conductivity metal films, without the need for subsequent sintering treatments. To reduce the temperature for direct formation of metallic Ag, we have added an alcohol as a catalytic reducing agent to dissociate the organometallic component. Silver films printed from our novel ROM ink, on a glass substrate at 120 °C, are electrically conductive with a typical resistivity as low as 39.2% that of bulk silver, without the need for sintering. PMID:26857286

  13. A study on flash sintering and related phenomena in titania and its composite with alumina

    NASA Astrophysics Data System (ADS)

    Shikhar

    In 2010, Cologna et. al. [1] reported that with a help of small electric field 120 Vcm-1, the sintering temperature of 3 mol % yittria stabilized zirconia could be brought down to 850°C from 1450°C. On top of reducing the temperature requirements, the green sample could be sintered from starting density of 50% to near full density in mere 5 seconds, a sintering rate three orders of magnitude higher than conventional methods. This discovery led to the emergence of a new field of enhanced sintering with electric field, named "Flash Sintering". The objective of this thesis is to understand the phenomenological behavior of flash-sintering and related phenomena on titania and its composites with alumina at elevated temperature. The possible mechanisms to explain flash sintering are discussed: Joule heating and the avalanche of defect generation [2], both induced by the rapid rise in conductivity just before the onset of the flash. Apparently, both mechanisms play a role. The thesis covers the response of pure titania and composites of titania-alumina under flash and compared with conventional sintering. We start with the sintering behavior of pure titania and observe lowering of sintering temperature requirements with higher applied electric field. The conductivity of titania during flash is also measured, and compared with the nominal conductivity of titania at equivalent temperatures. The conductivity during flash is determined to be have a different activation energy. For the composites of titania-alumina, effect of flash on the constrained sintering was studied. It is a known fact that sintering of one component of composite slows down when the other component of a different densification rate is added to it, called constrained sintering. In our case, large inclusions of alumina particles were added to nano-grained titania green compact that hindered its densification. Flash sintering was found to be overcoming this problem and near full densification was achieved

  14. Thermal barrier coating resistant to sintering

    DOEpatents

    Subramanian, Ramesh; Seth, Brij B.

    2004-06-29

    A device (10) is made, having a ceramic thermal barrier coating layer (16) characterized by a microstructure having gaps (18) with a sintering inhibiting material (22) disposed on the columns (20) within the gaps (18). The sintering resistant material (22) is stable over the range of operating temperatures of the device (10), is not soluble with the underlying ceramic layer (16) and is applied by a process that is not an electron beam physical vapor deposition process.

  15. Reactive sintering of TiAl–Ti5Si3 in situ composites

    SciTech Connect

    Alman, David E.

    2005-06-01

    TiAl with between 0 and 20 vol%Ti5Si3 was produced by reactive sintering (700 °C for 15 min in vacuum) of cold pressed compacts of elemental Ti, Al and Si powder. The results show that adding Si to Ti and Al reduces the swelling associated with reactive sintering of TiAl, as composites containing more than 5 vol%Ti5Si3 densified during reactive sintering. However, composites containing more than 10 vol%Ti5Si3 did not retain their shape and the TiAl+20 vol%Ti5Si3 composite completely melted during the sintering process. A thermodynamic analysis indicated that the simultaneous formation of TiAl and Ti5Si3 increases the adiabatic flame temperature during the reaction between the powders. In fact, the analysis predicted that the maximum temperature of the reaction associated with the formation TiAl+20 vol%Ti5Si3 should exceed the melting point of TiAl, and this was observed experimentally. Differential thermal analysis (DTA) revealed that an Al–Si eutectic reaction occurred in mixtures of Ti, Al and Si powders prior to the formation of the TiAl and Ti5Si3 phases. There was no such pre-reaction formation of a eutectic liquid in Ti and Al powder mixtures. The formation of the pre-reaction liquid and the increase in adiabatic flame temperature resulted in the melting that occurred and the enhanced densification (minimization of swelling) during reactive sintering of the in situ composites.

  16. Effect of sintering temperature and oxygen atmosphere on electrocaloric effect of BaTiO3 ceramics

    NASA Astrophysics Data System (ADS)

    Ren, Xue-Chong; Nie, Wei-Li; Bai, Yang; Qiao, Li-Jie

    2015-09-01

    This paper demonstrates the effect of sintering parameters on the electrocaloric effect (ECE) in BaTiO3 ferroelectric ceramics, especially the sintering temperature and atmosphere. The samples were prepared by solid-state reaction method. With the rise of sintering temperature from 1200 °C to 1350 °C, the grain size increases remarkably and the densification is improved. The 1350 °C sintered sample has better ferroelectricity and higher latent heat for ferroelectric-paraelectric phase transition than those of the 1200 °C sintered sample. Correspondingly, it exhibits much better ECE. If the sample is sintered in pure oxygen, instead of in air, all ferroelectricity, dielectric strength and ECE are further enhanced. The sample sintered at 1350 °C in oxygen exhibits an excellent ECE performance with ΔTmax = 1.37 K and ΔSmax = 1.75 J/kg K. Contribution to the Topical Issue "Materials for Dielectric Applications", edited by Maciej Jaroszewski and Sabu Thomas.

  17. B-branch electron transfer in reaction centers of Rhodobacter sphaeroides assessed with site-directed mutagenesis.

    PubMed

    de Boer, Arjo L; Neerken, Sieglinde; de Wijn, Rik; Permentier, Hjalmar P; Gast, Peter; Vijgenboom, Erik; Hoff, Arnold J

    2002-01-01

    Mutants of Rhodobacter (Rba.) sphaeroides are described which were designed to study electron transfer along the so-called B-branch of reaction center (RC) cofactors. Combining the mutation L(M214)H, which results in the incorporation of a bacteriochlorophyll, beta, for H(A) [Kirmaier et al. (1991) Science 251: 922-927] with two mutations, G(M203)D and Y(M210)W, near B(A), we have created a double and a triple mutant with long lifetimes of the excited state P(*) of the primary donor P, viz. 80 and 160 ps at room temperature, respectively. The yield of P(+)Q(A) (-) formation in these mutants is reduced to 50 and 30%, respectively, of that in wildtype RCs. For both mutants, the quantum yield of P(+)H(B) (-) formation was less than 10%, in contrast to the 15% B-branch electron transfer demonstrated in RCs of a similar mutant of Rba. capsulatus with a P(*) lifetime of 15 ps [Heller et al. (1995) Science 269: 940-945]. We conclude that the lifetime of P(*) is not a governing factor in switching to B-branch electron transfer. The direct photoreduction of the secondary quinone, Q(B), was studied with a triple mutant combining the G(M203)D, L(M214)H and A(M260)W mutations. In this triple mutant Q(A) does not bind to the reaction center [Ridge et al. (1999) Photosynth Res 59: 9-26]. It is shown that B-branch electron transfer leading to P(+)Q(B) (-) formation occurs to a minor extent at both room temperature and at cryogenic temperatures (about 3% following a saturating laser flash at 20 K). In contrast, in wildtype RCs P(+)Q(B) (-) formation involves the A-branch and does not occur at all at cryogenic temperatures. Attempts to accumulate the P(+)Q(B) (-) state under continuous illumination were not successful. Charge recombination of P(+)Q(B) (-) formed by B-branch electron transfer in the new mutant is much faster (seconds) than has been previously reported for charge recombination of P(+)Q(B) (-) trapped in wildtype RCs (10(5) s) [Kleinfeld et al. (1984b) Biochemistry 23

  18. Effect of Addition of Mill Scale on Sintering of Iron Ores

    NASA Astrophysics Data System (ADS)

    Wang, Zhe; Pinson, David; Chew, Sheng; Monaghan, Brian J.; Pownceby, Mark I.; Webster, Nathan A. S.; Rogers, Harold; Zhang, Guangqing

    2016-10-01

    Iron-rich (65 to 70 pct total Fe) mill scale generated during processing by steel mills can be recycled by using it as a ferrous raw material in the sintering process. The effect of mill scale addition on the phase formation of sintered specimens from an industrial sinter blend containing 0 to 15 wt pct mill scale was examined, and the mineral phases formed during sintering under various conditions ( T = 1523 K to 1598 K [1250 °C to 1325 °C] and gas compositions of pO2 = 0.5, 5 and 21 kPa) were quantitatively measured. For samples sintered in air (pO2 = 21 kPa), there was negligible effect of mill scale addition on the phases formed. The oxidation of the mill scale was complete, and phases such as Silico-Ferrite of Calcium and Aluminum (SFCA), SFCA-I, and hematite dominated. Under lower oxygen partial pressures (pO2 = 0.5 or 5 kPa), and throughout the temperature range examined, the mill scale was converted to magnetite, with the extent of reaction controlled by the hematite-magnetite conversion kinetics. When sintered in the gas mixture with pO2 = 5 kPa, an increase in the mill scale content from 0 to 15 wt pct resulted in a decrease of hematite and total SFCA phases and a corresponding increase in the amount of magnetite which formed. The oxidation of wustite in mill scale to magnetite decreased the local partial pressure of O2 and increased sintering temperature, which promoted the decomposition of hematite.

  19. A multi-component domino reaction for the direct access to polyfunctionalized indoles via intermolecular allylic esterification and indolation†

    PubMed Central

    Jiang, Bo; Yi, Mian-Shuai; Shi, Feng; Pindi, Suresh; McDowell, Patrick

    2013-01-01

    A novel multi-component reaction for the synthesis of polyfunctionalized indoles and bis-indoles has been established. The reaction pathways were controlled by varying enamines with different substitution patterns to give polyfunctionalized indoles and bis-indoles selectively. The reaction proceeds at a fast speed within 15–30 min with water as the major byproduct, which makes work-up convenient. PMID:22038299

  20. Spark Plasma Sintering of Ultracapacitors

    SciTech Connect

    Hill, Curtis W.; Boatner, Lynn A.; Tucker, Dennis; Kolopus, James A.; Cheng, Zhongyang

    2016-01-01

    A solid-state ultracapacitor module to replace standard electrochemical batteries would achieve major performance gains and mass/volume reduction. This report summarizes a project to evaluate an alternative sintering process to produce a solid-state ultracapacitor to overcome the limitations of both the electrochemical batteries presently in use on spacecraft and of currently available electrochemical ultracapacitors. It will provide a robust energy storage device with higher reliability, wider working temperature range, longer lifetime, and less weight and volume than electrochemical batteries. As modern electronics decrease in size, more efficient and robust remote power is needed. Current state-of-the-art rechargeable batteries cannot be rapidly charged, contain harmful chemicals, and suffer from early wear-out mechanisms. Solid-state ultracapacitors are recyclable energy storage devices that offer the promise of higher power and a greater number of charge/discharge cycles than current rechargeable batteries. In addition, the theoretical energy density when compared to current electrochemical batteries indicates that a significant weight savings is possible. This is a project to develop a very high density solid-state ultracapacitor with giant permittivity and acceptable dielectric loss to overcome the energy-density barrier such that it will be a suitable replacement for batteries.

  1. Effector-independent reduction in choice reaction time following bi-hemispheric transcranial direct current stimulation over motor cortex

    PubMed Central

    Drummond, Neil M.; Hayduk-Costa, Gabrielle; Leguerrier, Alexandra

    2017-01-01

    Increased reaction times (RT) during choice-RT tasks stem from a requirement for additional processing as well as reduced motor-specific preparatory activation. Transcranial direct current stimulation (tDCS) can modulate primary motor cortex excitability, increasing (anodal stimulation) or decreasing (cathodal stimulation) excitability in underlying cortical tissue. The present study investigated whether lateralized differences in choice-RT would result from the concurrent modulation of left and right motor cortices using bi-hemispheric tDCS. Participants completed a choice-RT task requiring either a left or right wrist extension. In forced-choice trials an illuminated target indicated the required response, whereas in free-choice trials participants freely selected either response upon illumination of a central fixation. Following a pre-test trial block, offline bi-hemispheric tDCS (1 mA) was applied over the left and right motor cortices for 10 minutes, which was followed by a post-tDCS block of RT trials. Twelve participants completed three experimental sessions, two with real tDCS (anode right, anode left), as well as a sham tDCS session. Post-tDCS results showed faster RTs for both right and left responses irrespective of tDCS polarity during forced-choice trials, while sham tDCS had no effect. In contrast, no stimulation-related RT or response selection differences were observed in free-choice trials. The present study shows evidence of an effector-independent speeding of response initiation in a forced-choice RT task following bi-hemispheric tDCS and yields novel information regarding the functional effect of bi-hemispheric tDCS. PMID:28263998

  2. Effect of sintering on electrical properties of yttrium doped Li-based NASICON compounds

    NASA Astrophysics Data System (ADS)

    Kothari, Dharmesh H.; Kanchan, D. K.; Dave, Gargi

    2015-08-01

    Electrical properties of Lithium based Li1.3Al0.3-xYxTi1.7(PO4)3 (LAYTP) system was prepared using solid state reaction route. The samples were subjected to differing duration of sintering. X-ray diffraction was used to investigate the microstructure while density measurement was performed to determine the effect of sintering on the density of the prepared samples. Electrical properties of the material were studied using impedance spectroscopy, in frequency range 20 MHz to 1 Hz and in temperature range 303 K to 423 K. It was found that sample with least amount of yttrium and which was sintered for least duration had superior conductivity over other samples. It was also found that grain boundary conductivity improved marginally for sample with higher proportion of yttrium heat treated for longer duration.

  3. Effect of sintering on electrical properties of yttrium doped Li-based NASICON compounds

    SciTech Connect

    Kothari, Dharmesh H.; Kanchan, D. K. Dave, Gargi

    2015-08-28

    Electrical properties of Lithium based Li{sub 1.3}Al{sub 0.3-x}Y{sub x}Ti{sub 1.7}(PO{sub 4}){sub 3} (LAYTP) system was prepared using solid state reaction route. The samples were subjected to differing duration of sintering. X-ray diffraction was used to investigate the microstructure while density measurement was performed to determine the effect of sintering on the density of the prepared samples. Electrical properties of the material were studied using impedance spectroscopy, in frequency range 20 MHz to 1 Hz and in temperature range 303 K to 423 K. It was found that sample with least amount of yttrium and which was sintered for least duration had superior conductivity over other samples. It was also found that grain boundary conductivity improved marginally for sample with higher proportion of yttrium heat treated for longer duration.

  4. Direct total cross section measurement of the 16O(α,γ)20Ne reaction at Ec.m.=2.26 MeV

    NASA Astrophysics Data System (ADS)

    Hager, U.; Brown, J. R.; Buchmann, L.; Carmona-Gallardo, M.; Erikson, L.; Fallis, J.; Greife, U.; Hutcheon, D.; Ottewell, D.; Ruiz, C.; Sjue, S.; Vockenhuber, C.

    2011-08-01

    In stellar helium burning, 16O represents the endpoint of the helium-burning sequence due to the low rate of 16O(α,γ)20Ne. We present a new direct measurement of the total capture reaction rate of 16O(α,γ)20Ne at Ec.m.=2.26MeV employing the DRAGON recoil separator. For the first time, the total S factor and its contributing direct capture transitions could be determined in one experiment.

  5. MgB2 superconductors with abnormally improved Jc sintered after autoxidation of milled original powders

    NASA Astrophysics Data System (ADS)

    Ma, Zongqing; Liu, Yongchang; Huo, Jie; Gao, Zhiming

    2009-12-01

    An autoxidation treatment of short-time milled original powders was introduced for the synthesis of MgB2 superconductors and the critical current density Jc of the sintered MgB2 bulks was measured. It is unusually found that the undoped MgB2 bulks sintered with those autoxided milled original powder exhibit abnormally excellent Jc (above 1×104 A cm-2 even at 3.5 T, 20 K). Combined with the investigation of sintering process, it was found that the autoxidation treatment of the milled powders affects the subsequent sintering process dramatically and finally leads to the formation of MgB2 nanocrystalline with lots of dislocation and self-generated MgO nanoinclusions embedded in them. This unique microstructure brought up a significant improvement of Jc at high fields. Besides, the formation mechanism of this unique microstructure during the sintering process was also discussed in detail. It suggested that the MgO preformed by the reaction between Mg and B2O3 in the interface between Mg particles and B particles might serve as nuclei for the heterogeneous nucleation of the MgB2 phase and finally be included in the MgB2 grains as they grew up. The present method provides possible windows for the development of practical MgB2 superconductors without adopting expensive nanodopants.

  6. Microwave sintering of nanopowder ZnNb2O6: Densification, microstructure and microwave dielectric properties

    NASA Astrophysics Data System (ADS)

    Bafrooei, H. Barzegar; Nassaj, E. Taheri; Hu, C. F.; Huang, Q.; Ebadzadeh, T.

    2014-12-01

    High density ZnNb2O6 ceramics were successfully fabricated by microwave sintering of ZnO-Nb2O5 and ZnNb2O6 nanopowders. Phase formation, microstructure and microwave electrical properties of the microwave sintered (MS) and microwave reaction sintered (MRS) specimens were examined using X-ray diffraction, field emission scanning electron microscopy and microwave dielectric properties measurement. Specimens were sintered in a temperature range from 950 to 1075 °C for 30 min at an interval of 25 °C using a microwave furnace operated at 2.45 GHz frequency, 3 kW power. XRD pattern revealed the formation of pure columbite phase of ZnNb2O6. The SEM micrographs show grain growth and reduction in porosity of specimens with the increase in sintering temperature. Good combination of microwave dielectric properties (εr~23.6, Qf~64,300 GHz and τf~-66 ppm/°C and εr~24, Qf~75,800 GHz and τf~-64 ppm/°C) was obtained for MS- and MRS-prepared samples at 1000 °C and 1050 °C for 30 min, respectively.

  7. The influence of Si on the microstructure and sintering behavior of ultrafine WC

    NASA Astrophysics Data System (ADS)

    Nanda Kumar, A. K.; Watabe, Masaaki; Kurokawa, Kazuya

    2012-11-01

    The microstructure of sintered nanoscale tungsten carbide powders with 1 wt % Si addition was found to be populated by an abnormally large number of elongated grains. Interrupted sintering experiments were conducted to clarify the origins of the excessive abnormal grain growth seen in the microstructure. It was observed that rapid coarsening occurred at high temperatures owing to the formation of a liquid phase. However, the grain shape evolution during this coarsening period was found to be a consequence of excessive stacking faults and micro twins on the basal planes probably generated by reaction of WC with Si. Analyses of the microstructures and the isothermal and non isothermal coarsening behaviors suggested that the platelet morphology evolved by defect-assisted nucleation and growth on faceted grains. Based on experimental evidence from samples interrupted at low temperatures and crystal growth theories, we discuss the possible mechanisms that eventually led to the rampant platelet-type morphology. Further, the influence of such rapid grain growth on the shrinkage rate during sintering is also discussed. In comparison with the cyclic coarsening-densification process of sintering in pure nanoscale WC, the addition of Si leads to only two distinct sintering stages: either densification dominated or coarsening dominated. Concurrent densification and coarsening cannot be sustained particularly in the presence of a liquid phase that significantly enhances coarsening.

  8. Phase development and sintering behaviour of biphasic HA-TCP calcium phosphate materials prepared from hydroxyapatite and bioactive glass.

    PubMed

    Behnamghader, A; Bagheri, N; Raissi, B; Moztarzadeh, F

    2008-01-01

    The composites of hydroxyapatite (HA) with 2.5 and 5 wt% of a double oxide (50 mol% CaO and 50 mol% P(2)O(5)) glass were prepared using the conventional powder mixing and sintering method. The addition of the glass significantly enhanced the decomposition process of HA into alpha tricalcium phosphate (alpha-TCP) for bodies sintered at 1,300 and 1,350 degrees C and beta-TCP phases for the ones sintered at 1,200, 1,250 and 1,300 degrees C. Microstructural characteristics, phase development and thermal behaviour were studied by SEM, XRD and STA. The effects of TCP phase content and phase transformation from beta-TCP to alpha-TCP on the sintering are discussed. The characterizations revealed considerable content of TCP in the form of large semi-islands due to important reactions between the fine HA and the glass mixed powders.

  9. Influence of Li-B-Si Additions on the Sintering and Microwave Dielectric Properties of Ba-Nd-Ti Ceramics

    NASA Astrophysics Data System (ADS)

    Li, Enzhu; Duan, Shuxin; Sun, Shumeng; Li, Hao; Mi, Yuean; Zhou, Xiaohua; Zhang, Shuren

    2013-12-01

    Li2O-B2O3-SiO2 (LBS) synthesized via a solid-state reaction process was chosen as a novel sintering aid for tungsten-bronze-type Ba4Nd9.3Ti18O54 (BNT) ceramic. The effects of LBS additions on the sintering behaviors, microstructures, and microwave dielectric properties of the BNT ceramic have been investigated, indicating that LBS addition obviously lowered the sintering temperature of the BNT ceramic without damaging its microwave dielectric properties. BNT ceramic doped with 3 wt.% and 4 wt.% LBS addition could be well sintered at 975°C and 950°C for 3 h and had excellent properties: ɛ r = 65.99, Q × f = 4943 GHz ( f = 4.4 GHz), τ f = 19 ppm/°C, and ɛ r = 64.56, Q × f = 4929 GHz ( f = 4.3 GHz), τ f = 11 ppm/°C, respectively.

  10. Reaction Mechanism for Direct Proton Transfer from Carbonic Acid to a Strong Base in Aqueous Solution II: Solvent Coordinate-Dependent Reaction Path.

    PubMed

    Daschakraborty, Snehasis; Kiefer, Philip M; Miller, Yifat; Motro, Yair; Pines, Dina; Pines, Ehud; Hynes, James T

    2016-03-10

    The protonation of methylamine base CH3NH2 by carbonic acid H2CO3 within a hydrogen (H)-bonded complex in aqueous solution was studied via Car-Parrinello dynamics in the preceding paper (Daschakraborty, S.; Kiefer, P. M.; Miller, Y.; Motro, Y.; Pines, D.; Pines, E.; Hynes, J. T. J. Phys. Chem. B 2016, DOI: 10.1021/acs.jpcb.5b12742). Here some important further details of the reaction path are presented, with specific emphasis on the water solvent's role. The overall reaction is barrierless and very rapid, on an ∼100 fs time scale, with the proton transfer (PT) event itself being very sudden (<10 fs). This transfer is preceded by the acid-base H-bond's compression, while the water solvent changes little until the actual PT occurrence; this results from the very strong driving force for the reaction, as indicated by the very favorable acid-protonated base ΔpKa difference. Further solvent rearrangement follows immediately the sudden PT's production of an incipient contact ion pair, stabilizing it by establishment of equilibrium solvation. The solvent water's short time scale ∼120 fs response to the incipient ion pair formation is primarily associated with librational modes and H-bond compression of water molecules around the carboxylate anion and the protonated base. This is consistent with this stabilization involving significant increase in H-bonding of hydration shell waters to the negatively charged carboxylate group oxygens' (especially the former H2CO3 donor oxygen) and the nitrogen of the positively charged protonated base's NH3(+).

  11. Characterization and Sintering of Armstrong Process Titanium Powder

    NASA Astrophysics Data System (ADS)

    Xu, Xiaoyan; Nash, Philip; Mangabhai, Damien

    2017-01-01

    Titanium and titanium alloys have a high strength to weight ratio and good corrosion resistance but also need longer time and have a higher cost on machining. Powder metallurgy offers a viable approach to produce near net-shape complex components with little or no machining. The Armstrong titanium powders are produced by direct reduction of TiCl4 vapor with liquid sodium, a process which has a relatively low cost. This paper presents a systematic research on powder characterization, mechanical properties, and sintering behavior and of Armstrong process powder metallurgy, and also discusses the sodium issue, and the advantages and disadvantages of Armstrong process powders.

  12. Vacuum-sintered body of a novel apatite for artificial bone

    NASA Astrophysics Data System (ADS)

    Tamura, Kenichi; Fujita, Tatsushi; Morisaki, Yuriko

    2013-12-01

    We produced regenerative artificial bone material and bone parts using vacuum-sintered bodies of a novel apatite called "Titanium medical apatite (TMA®)" for biomedical applications. TMA was formed by chemically connecting a Ti oxide molecule with the reactive [Ca10(PO4)6] group of Hydroxyapatite (HAp). The TMA powders were kneaded with distilled water, and solid cylinders of compacted TMA were made by compression molding at 10 MPa using a stainless-steel vessel. The TMA compacts were dried and then sintered in vacuum (about 10-3 Pa) or in air using a resistance heating furnace in the temperature range 1073-1773 K. TMA compacts were sintered at temperatures greater than 1073 K, thus resulting in recrystallization. The TMA compact bodies sintered in the range 1273-1773 K were converted into mixtures composed of three crystalline materials: α-TCP (tricalcium phosphate), β-TCP, and Perovskite-CaTiO3. The Perovskite crystals were stable and hard. In vacuum-sintering, the Perovskite crystals were transformed into fibers (approximately 1 µm in diameter × 8 µm in length), and the fiber distribution was uniform in various directions. We refer to the TMA vacuum-sintered bodies as a "reinforced composite material with Perovskite crystal fibers." However, in atmospheric sintering, the Perovskite crystals were of various sizes and were irregularly distributed as a result of the effect of oxygen. After sintering temperature at 1573 K, the following results were obtained: the obtained TMA vacuum-sintered bodies (1) were white, (2) had a density of approximately 2300 kg/m3 (corresponding to that of a compact bone or a tooth), and had a thermal conductivity of approximately 31.3 W/(m·K) (corresponding to those of metal or ceramic implants). Further, it was possible to cut the TMA bodies into various forms with a cutting machine. An implant made of TMA and inserted into a rabbit jaw bone was covered by new bone tissues after just one month because of the high

  13. Histological Comparison in Rats between Carbonate Apatite Fabricated from Gypsum and Sintered Hydroxyapatite on Bone Remodeling.

    PubMed

    Ayukawa, Yasunori; Suzuki, Yumiko; Tsuru, Kanji; Koyano, Kiyoshi; Ishikawa, Kunio

    2015-01-01

    Carbonate apatite (CO3Ap), the form of apatite found in bone, has recently attracted attention. The purpose of the present study was to histologically evaluate the tissue/cellular response toward the low-crystalline CO3Ap fabricated using a dissolution-precipitation reaction with set gypsum as a precursor. When set gypsum was immersed in a 100°C 1 mol/L Na3PO4 aqueous solution for 24 h, the set gypsum transformed into CO3Ap. Both CO3Ap and sintered hydroxyapatite (s-HAp), which was used as a control, were implanted into surgically created tibial bone defects of rats for histological evaluation. Two and 4 weeks after the implantation, histological sections were created and observed using light microscopy. The CO3Ap granules revealed both direct apposition of the bone matrix by osteoblasts and osteoclastic resorption. In contrast, the s-HAp granules maintained their contour even after 4 weeks following implantation which implied that there was a lack of replacement into the bone. The s-HAp granules were sometimes encapsulated with fibrous tissue, and macrophage polykaryon was occasionally observed directly apposed to the implanted granules. From the viewpoint of bone remodeling, the CO3Ap granules mimicked the bone matrix, suggesting that CO3Ap may be an appropriate bone substitute.

  14. Gravitational Effects on Distortion in Sintering

    NASA Technical Reports Server (NTRS)

    German, Randall M.

    2003-01-01

    During sintering a powder compact gains strength through low-temperature interparticle bonding, usually induced by solid-state surface diffusion, followed by further strength contributions from high-temperature densification. In cases where a liquid phase forms, sintering densification is accelerated and shape retention is sustained while open pores remain and contribute capillary forces. Unfortunately, sintering densification requires the compact become thermally softened to a point where creep strain rates reach levels near 10(exp -2)/s when the liquid forms. On the other hand, thermal softening of the powder compact substantially reduces the strength at high temperatures. Therefore, the in situ strength evolution during sintering is a primary focus to separate compact densification (as required for high performance) with minimized distortion (as required for net-shaping). With respect to gravitation effects on distortion during sintering there are two points of substantial weakness - prior to significant interparticle bonding and during final pore closure. This research is focused on understanding the competition among interparticle neck growth, densification, thermal softening, grain boundary wetting, capillary effects associated with liquid wetting and residual porosity, and gravity. Most surprising is the apparent role of gravity, where the deviatoric stress acting on the powder structure induces skeletal formation that reduces distortion. In contrast with theory, microgravity samples exhibit more distortion yet fail to fully densify. Results are presented on the experimental concepts supporting an emerging model of sintering strength evolution that enables understanding of both distortion and densification. The experiments have relied on tungsten heavy alloys, various combinations of dihedral angle, pore size, initial porosity, liquid:solid ratio, and heating rates. On Earth, the dominant factor with respect to distortion is the starting body heterogeneity

  15. Highly Conductive Cu-Cu Joint Formation by Low-Temperature Sintering of Formic Acid-Treated Cu Nanoparticles.

    PubMed

    Liu, Jingdong; Chen, Hongtao; Ji, Hongjun; Li, Mingyu

    2016-12-07

    Highly conductive Cu-Cu interconnections of SiC die with Ti/Ni/Cu metallization and direct bonded copper substrate for high-power semiconductor devices are achieved by the low-temperature sintering of Cu nanoparticles with a formic acid treatment. The Cu-Cu joints formed via a long-range sintering process exhibited good electrical conductivity and high strength. When sintered at 260 °C, the Cu nanoparticle layer exhibited a low resistivity of 5.65 μΩ·cm and the joints displayed a high shear strength of 43.4 MPa. When sintered at 320 °C, the resistivity decreased to 3.16 μΩ·cm and the shear strength increased to 51.7 MPa. The microstructure analysis demonstrated that the formation of Cu-Cu joints was realized by metallurgical bonding at the contact interface between the Cu pad and the sintered Cu nanoparticle layer, and the densely sintered layer was composed of polycrystals with a size of hundreds of nanometers. In addition, high-density twins were found in the interior of the sintered layer, which contributed to the improvement of the performance of the Cu-Cu joints. This bonding technology is suitable for high-power devices operating under high temperatures.

  16. Direct evidence for a substantive reaction between the Criegee intermediate, CH2OO, and the water vapour dimer.

    PubMed

    Lewis, Tom R; Blitz, Mark A; Heard, Dwayne E; Seakins, Paul W

    2015-02-21

    The C1 Criegee intermediate, CH2OO, reaction with water vapour has been studied. The removal rate constant shows a quadratic dependence on [H2O], implying reaction with the water dimer, (H2O)2. The rate constant, kCH2OO+(H2O)2 = (4.0 ± 1.2) × 10(-12) cm(3) molecule(-1) s(-1), is such that this is the major atmospheric sink for CH2OO.

  17. Simultaneous light-directed synthesis of mirror-image microarrays in a photochemical reaction cell with flare suppression.

    PubMed

    Sack, Matej; Kretschy, Nicole; Rohm, Barbara; Somoza, Veronika; Somoza, Mark M

    2013-09-17

    The use of photolabile protecting groups is a versatile and well-established means of synthesizing high complexity microarrays of biopolymers, such as nucleic acids and peptides, for high-throughput analysis. The synthesis takes place in a photochemical reaction cell which positions the microarray substrate at the focus of the optical system delivering the light and which can be connected to a fluidics system which delivers appropriate reagents to the surface in synchrony with the light exposure. Here we describe a novel photochemical reaction cell which allows for the simultaneous synthesis of microarrays on two substrates. The reaction cell positions both substrates within the limited depth-of-focus of the optical system while maintaining the necessary reagent flow conditions. The resulting microarrays are mirror images of each other but otherwise essentially identical. The new reaction cell doubles the throughput of microarray synthesis without increasing the consumption of reagents. In addition, a secondary flow chamber behind the reaction cell can be filled with an absorbent and index-matching fluid to eliminate reflections from light exiting the reaction cell assembly, greatly reducing unintended light exposure that reduces the sequence fidelity of the microarray probes.

  18. Effects of the sintering atmosphere on the superconductivity of SmFeAsO1 - xFx compounds

    NASA Astrophysics Data System (ADS)

    Ding, Y.; Sun, Y.; Wang, X. D.; Zhuang, J. C.; Cui, L. J.; Shi, Z. X.

    2011-09-01

    A series of SmFeAsO1 - xFx samples were prepared in quartz tubes filled with air of different pressures. The effects of the sintering atmosphere on the superconductivity were systematically investigated. The SmFeAsO1 - xFx system maintains a transition temperature (Tc) near 50 K until the concentration of oxygen in the quartz tubes increases to a certain threshold, after which Tc decreases dramatically. Fluorine losses, whether due to vaporisation, reactions with starting materials or reactions with oxygen, proved to be detrimental to the superconductivity of this material. The deleterious effects of the oxygen in the sintering atmosphere were also discussed in detail.

  19. Direct RNA detection without nucleic acid purification and PCR: Combining sandwich hybridization with signal amplification based on branched hybridization chain reaction.

    PubMed

    Xu, Yao; Zheng, Zhi

    2016-05-15

    We have developed a convenient, robust and low-cost RNA detection system suitable for high-throughput applications. This system uses a highly specific sandwich hybridization to capture target RNA directly onto solid support, followed by on-site signal amplification via 2-dimensional, branched hybridizing chain polymerization through toehold-mediated strand displacement reaction. The assay uses SYBR Green to detect targets at concentrations as low as 1 pM, without involving nucleic acid purification or any enzymatic reaction, using ordinary oligonucleotides without modification or labeling. The system was demonstrated in the detection of malaria RNA in blood and GAPDH gene expression in cell lysate.

  20. Spark Plasma Sintering of Titanium Spherical Particles

    NASA Astrophysics Data System (ADS)

    Abedi, Mohammad; Moskovskikh, Dmitry O.; Rogachev, Alexander S.; Mukasyan, Alexander S.

    2016-10-01

    The densification kinetics for sintering of titanium spherical particles under two different experimental schemes, i.e., current-assisted and current-insulated were investigated. It was shown that measurable densification rate differences between the two schemes are recognized only for the preheating stage. For current-assisted experiments, consolidation starts at lower temperatures than for current-insulated samples. Also at high heating rates, the change of sample porosity all through the preheating stage is higher for current-assisted conditions, while at relatively low heating rates ( i.e., less than 100 K/min) they are comparable. All through the isothermal sintering stage, at a temperature of 1073 K (800 °C), the shrinkage rates are comparable for both experimental schemes within the measurement accuracy. The explanation of the observed effects within the framework of conventional sintering theory is also provided.

  1. Nanostructured gold architectures formed through high pressure-driven sintering of spherical nanoparticle arrays.

    PubMed

    Wu, Huimeng; Bai, Feng; Sun, Zaicheng; Haddad, Raid E; Boye, Daniel M; Wang, Zhongwu; Huang, Jian Yu; Fan, Hongyou

    2010-09-22

    We have demonstrated pressure-directed assembly for preparation of a new class of chemically and mechanically stable gold nanostructures through high pressure-driven sintering of nanoparticle assemblies at room temperature. We show that under a hydrostatic pressure field, the unit cell dimension of a 3D ordered nanoparticle array can be reversibly manipulated allowing fine-tuning of the interparticle separation distance. In addition, 3D nanostructured gold architecture can be formed through high pressure-induced nanoparticle sintering. This work opens a new pathway for engineering and fabrication of different metal nanostructured architectures.

  2. Mechanical properties of hydroxyapatite-zirconia compacts sintered by two different sintering methods.

    PubMed

    Curran, Declan J; Fleming, Thomas J; Towler, Mark R; Hampshire, Stuart

    2010-04-01

    Microwave sintering is traditionally employed to reduce the sintering temperature required to densify powder compacts. The effect of microwave heating on hydroxyapatite (HA)-zirconia (ZrO2) green bodies has been investigated in order to understand how microwave energy may affect the physical and mechanical properties of the resultant densified composites. Laboratory synthesised nano-sized HA and a commercial nano-sized ZrO2 powder have been ball milled to create mixtures containing 0-5 wt% ZrO2 loadings. Compacts were microwave sintered at either 700, 1000 or 1200 degrees C with a 1 h hold time. Comparative firings were also performed in a resistive element furnace using the same heating profile in order to assess the differences between conventional and microwave heating on the physical, mechanical and microstructural properties of the composites. Samples sintered at 700 degrees C show little sign of densification with open porosities of approximately 50%. Composites conventionally sintered at 1000 degrees C were between 65 and 75% dense, whereas the samples microwave sintered at this temperature were between 55 and 65% dense. Samples sintered at 1200 degreesbC showed the greatest degree of densification (>80%) with a corresponding reduction in open porosities. TCP generation occurred as a consequence of sintering at 1200 degrees C, even with 0 wt% ZrO2, and increased degradation of the HA phase to form significant amounts of TCP occurred with increasing additions of ZrO2, along with increasing open porosity. Nanosized ZrO2 prevents the densification of the HA matrix by effectively pinning grain boundaries and this effect is more pronounced in the MS materials. Similar strengths are achieved between the microwave and conventionally sintered samples. Greater amount of open porosity and pore interconnectivity are seen in the MS samples, which are considered to be useful for biomedical applications as they can promote osteo-integration.

  3. Synthesis of BaTiO[subscript 3]-20wt%CoFe[subscript 2]O[subscript 4] Nanocomposites via Spark Plasma Sintering

    SciTech Connect

    Ghosh, Dipankar; Han, Hyuksu; Nino, Juan C.; Subhash, Ghatu; Jones, Jacob L.

    2012-10-23

    Barium titanate-20wt% cobalt ferrite (BaTiO{sub 3}-20wt%CoFe{sub 2}O{sub 4}) nanocomposites were sintered from nanocrystalline BaTiO{sub 3} and CoFe{sub 2}O{sub 4} powders using spark plasma sintering (SPS) and pressureless sintering (PS) techniques. Using SPS, dense polycrystalline composites were obtained at a sintering temperature as low as 860 C and a time of 5 min whereas PS required a higher sintering temperature (1150 C) and time (120 min) to obtain similarly dense composites. Microstructural analysis of the composites showed that both the techniques retained nanocrystalline grain sizes after sintering. High resolution X-ray diffraction measurements revealed that the BaTiO{sub 3}-20wt%CoFe{sub 2}O{sub 4} composites sintered by the SPS technique did not exhibit formation of any new phase(s) due to reaction between the BaTiO{sub 3} and CoFe{sub 2}O{sub 4} phases during sintering. However, the PS technique resulted in the formation of additional phases (other than the BaTiO{sub 3} and CoFe{sub 2}O{sub 4} phases) in the composites. While the composites synthesized by SPS were of superior phase-purity, evidence of Fe diffusion from the spinel to the perovskite phase was found from X-ray diffraction and permittivity measurements.

  4. New sintering process adjusts magnetic value of ferrite cores

    NASA Technical Reports Server (NTRS)

    Vinal, A. W.

    1964-01-01

    A two-phase sintering technique based on time and temperature permits reversible control of the coercive threshold of sintered ferrite cores. Threshold coercivity may be controlled over a substantial range of values by selective control of the cooling rate.

  5. Plasma sintering of beta″-alumina

    NASA Astrophysics Data System (ADS)

    Henrichsen, Matthew

    Sintering and phase conversion of beta″-alumina were investigated with static and ultra-rapid passthrough plasma firing. Ultra-rapid passthrough induction firing was used to differentiate the effects of rapid heating rates from plasma effects. Static plasma sintering at low pressures resulted in excessive sodium loss which prohibited the use of dilatometry. Sintering was characterized using the diameter profiles of partially fired tubes. Phase conversion was examined with x-ray diffraction of powdered sections of partially fired tubes. Ultra-rapid passthrough firing speeds ranged from 8 to ˜240 mm/min. Instantaneous shrinkage rates as large as 8%/sec were measured. Phase conversion and sintering were both rapid, and were complete in seconds. Tubes with densities above 97%, beta″-phase content above 98%, and ionic resistivity as low as 13.8 Ocm were produced. Two modes of cracking were identified for tubes in ultra-rapid firing. Both were related to the thickness of the tube wall and sinterability of the powder being fired. A finite element model of sintering and heat transfer was developed to aid in determining the causes of cracking. Cracks formed because of mechanical stress rather than thermal shock. Low levels of cobalt in the precursor materials greatly reduced specimen heating in the plasma. The surface of beta″-alumina, like that of alpha-alumina, is catalytic for recombination of ions and radical components from the plasma. Induction furnace firing produced heating rates lower than those in plasma heating. Fired tubes were oversintered and had duplex microstructures. Some specimens fired in the induction furnace were contaminated by carbon from the graphite susceptor. Two peaks were observed in shrinkage rate profiles of some tubes. A model of dimensional change from simultaneous sintering and phase conversion was constructed. The model produced shrinkage rate profiles similar to those observed in both plasma and induction firing. The multiple peaks

  6. Properties of oxide-hydroxide sintered ceramics

    NASA Astrophysics Data System (ADS)

    Levkov, R. V.; Kulkov, S. N.

    2017-02-01

    In this paper the study of porous ceramics obtained from aluminum hydroxide with gibbsite modification is presented. It was shown that aluminum hydroxide may be used for pore formation and pore volume in the sintered ceramics can be controlled by varying the aluminum hydroxide concentration and sintering temperature. It was shown that compressive strength of alumina ceramics increases by 40 times with decreasing the pore volume from 65 to 15%. Based on these results one can conclude that the obtained structure is very close to inorganic bone matrix and can be used as promising material for bone implants production.

  7. Process for microwave sintering boron carbide

    DOEpatents

    Holcombe, C.E.; Morrow, M.S.

    1993-10-12

    A method of microwave sintering boron carbide comprises leaching boron carbide powder with an aqueous solution of nitric acid to form a leached boron carbide powder. The leached boron carbide powder is coated with a glassy carbon precursor to form a coated boron carbide powder. The coated boron carbide powder is consolidated in an enclosure of boron nitride particles coated with a layer of glassy carbon within a container for microwave heating to form an enclosed coated boron carbide powder. The enclosed coated boron carbide powder is sintered within the container for microwave heating with microwave energy.

  8. Process for microwave sintering boron carbide

    DOEpatents

    Holcombe, Cressie E.; Morrow, Marvin S.

    1993-01-01

    A method of microwave sintering boron carbide comprises leaching boron carbide powder with an aqueous solution of nitric acid to form a leached boron carbide powder. The leached boron carbide powder is coated with a glassy carbon precursor to form a coated boron carbide powder. The coated boron carbide powder is consolidated in an enclosure of boron nitride particles coated with a layer of glassy carbon within a container for microwave heating to form an enclosed coated boron carbide powder. The enclosed coated boron carbide powder is sintered within the container for microwave heating with microwave energy.

  9. Fusibility and sintering characteristics of ash

    SciTech Connect

    Ots, A. A.

    2012-03-15

    The temperature characteristics of ash fusibility are studied for a wide range of bituminous and brown coals, lignites, and shales with ratios R{sub B/A} of their alkaline and acid components between 0.03 and 4. Acritical value of R{sub B/A} is found at which the fusion temperatures are minimal. The sintering properties of the ashes are determined by measuring the force required to fracture a cylindrical sample. It is found that the strength of the samples increases sharply at certain temperatures. The alkali metal content of the ashes has a strong effect on their sintering characteristics.

  10. Direct ab initio dynamics studies on the hydrogen-abstraction reactions of OH radicals with HOX (X = F, Cl, and Br).

    PubMed

    Wang, Li; Liu, Jing-Yao; Li, Ze-Sheng; Sun, Chia-Chung

    2004-03-01

    The hydrogen abstract reactions of OH radicals with HOF (R1), HOCl (R2), and HOBr (R3) have been studied systematically by a dual-level direct-dynamics method. The geometries and frequencies of all the stationary points are optimized at the MP2/6-311+G(2d, 2p) level of theory. A hydrogen-bonded complex is located at the product channel for the OH + HOBr reaction. To improve the energetics information along the minimum energy path (MEP), single-point energy calculations are carried out at the CCSD(T)/6-311++G(3df, 3pd) level of theory. Interpolated single-point energy (ISPE) method is employed to correct the energy profiles for the three reactions. It is found that neither the barrier heights (DeltaE) nor the H-O bond dissociation energies [D(H-O)] exhibit any clear-cut linear correlations with the halogen electronegative. The decrease of DeltaE and D(H-O) for the three reactions are in order of HOF > HOBr > HOCl. Rate constants for each reaction are calculated by canonical variational transition-state theory (CVT) with a small-curvature tunneling correction (SCT) within 200-2000 K. The agreement of the rate constants with available experimental values for reactions R2 and R3 at 298 K is good. Our results show that the variational effect is small while the tunneling correction has an important contribution in the calculation of rate constants in the low-temperature range. Due to the lack of the kinetic data of these reactions, the present theoretical results are expected to be useful and reasonable to estimate the dynamical properties of these reactions over a wide temperature range where no experimental value is available.

  11. Catalytic Asymmetric Reactions of 4‐Substituted Indoles with Nitroethene: A Direct Entry to Ergot Alkaloid Structures

    PubMed Central

    Romanini, Simone; Galletti, Emilio; Caruana, Lorenzo; Mazzanti, Andrea; Himo, Fahmi

    2015-01-01

    Abstract A domino Friedel–Crafts/nitro‐Michael reaction between 4‐substituted indoles and nitroethene is presented. The reaction is catalyzed by BINOL‐derived phosphoric acid catalysts, and delivers the corresponding 3,4‐ring‐fused indoles with very good results in terms of yields and diastereo‐ and enantioselectivities. The tricyclic benzo[cd]indole products bear a nitro group at the right position to serve as precursors of ergot alkaloids, as demonstrated by the formal synthesis of 6,7‐secoagroclavine from one of the adducts. DFT calculations suggest that the outcome of the reaction stems from the preferential evolution of a key nitronic acid intermediate through a nucleophilic addition pathway, rather than to the expected “quenching” through protonation. PMID:26486074

  12. Specificity of maltase to maltose in three different directions of reaction: hydrolytic, vanillyl alcohol glucoside and vanillyl alcohol isomaltoside synthesis.

    PubMed

    Dimitrijević, Aleksandra; Veličković, Dušan; Milosavić, Nenad; Bezbradica, Dejan

    2012-01-01

    Vanillyl alcohol glucoside is very attractive molecule due to its very powerful physiological activity. In this article, a detailed kinetic study of transglucosylation of vanillyl alcohol was performed. It was demonstrated that this reaction is very efficient (selectivity factor is 149) and occurred by a ping-pong mechanism with inhibition by glucose acceptor. At low concentration of vanillyl alcohol one additional transglucosylation product was detected. Its structure was determined to be α-isomaltoside of vanillyl alcohol, indicating that vanillyl alcohol glucoside is a product of the first transglucosylation reaction and a substrate for second, so the whole reaction mechanism was proposed. It was demonstrated that the rate of isomaltoside synthesis is two orders of magnitude smaller than glucoside synthesis, and that maltase has interestingly high K(m) value to maltose when vanillyl alcohol glucoside is second transglucosylation substrate.

  13. Spark Plasma Sintering Apparatus Used for the Formation of Strontium Titanate Bicrystals.

    PubMed

    Hughes, Lauren A; van Benthem, Klaus

    2017-02-09

    A spark plasma sintering apparatus was used as a novel method for diffusion bonding of two single crystals of strontium titanate to form bicrystals with one twist grain boundary. This apparatus utilizes high uniaxial pressure and a pulsed direct current for rapid consolidation of material. Diffusion bonding of strontium titanate bicrystals without fracture, in a spark plasma sintering apparatus, is possible at high pressures due to the unusual temperature dependent plasticity behavior of strontium titanate. We demonstrate a method for the successful formation of bicrystals at accelerated time scales and lower temperatures in a spark plasma sintering apparatus compared to bicrystals formed by conventional diffusion bonding parameters. Bond quality was verified by scanning electron microscopy. A clean and atomically abrupt interface containing no secondary phases was observed using transmission electron microscopy techniques. Local changes in bonding across the boundary was characterized by simultaneous scanning transmission electron microscopy and spatially resolved electron energy-loss spectroscopy.

  14. Multi-Scale Modeling of Liquid Phase Sintering Affected by Gravity: Preliminary Analysis

    NASA Technical Reports Server (NTRS)

    Olevsky, Eugene; German, Randall M.

    2012-01-01

    A multi-scale simulation concept taking into account impact of gravity on liquid phase sintering is described. The gravity influence can be included at both the micro- and macro-scales. At the micro-scale, the diffusion mass-transport is directionally modified in the framework of kinetic Monte-Carlo simulations to include the impact of gravity. The micro-scale simulations can provide the values of the constitutive parameters for macroscopic sintering simulations. At the macro-scale, we are attempting to embed a continuum model of sintering into a finite-element framework that includes the gravity forces and substrate friction. If successful, the finite elements analysis will enable predictions relevant to space-based processing, including size and shape and property predictions. Model experiments are underway to support the models via extraction of viscosity moduli versus composition, particle size, heating rate, temperature and time.

  15. The effect of electric field intensification at interparticle contacts in microwave sintering

    PubMed Central

    Qiao, Xiuchen; Xie, Xiaoying

    2016-01-01

    The nature of microwave sintering cannot be explained in the past and has been generally called microwave effect. Here we show that the E-field intensification is the reason of microwave fast sintering of solid state inorganic compounds. The intensification degree varied with dielectric constant of compound, distance between two particles, angle between the direction of E-field and the normal to the surface at the adjacent point of two spheres. Ultra-high temperature caused by E-field intensification leads to fusing of solid materials at contact zone and enhances the mass transportation. The key to develop a microwave energy-saved sintering method is to control the distance between particles and uniformity of particles instead of the particle size. PMID:27586521

  16. The ultraviolet photochemistry of diacetylene - Direct detection of primary products of the metastable C4H2* + C4H2 reaction

    NASA Technical Reports Server (NTRS)

    Bandy, Ralph E.; Lakshminarayan, Chitra; Frost, Rex K.; Zwier, Timothy S.

    1993-01-01

    The products of diacetylene's ultraviolet photochemistry over the 245-220 nm region were directly determined in experiments where C4H2 was excited within a small reaction tube attached to a pulsed nozzle. The products formed in the collisions of C4H2* with C4H2 were subsequently ionized by vacuum UV radiation (at 118 nm) in the ion source of a time-of-flight mass spectrometer. It was found that the reaction of C4H2* with C4H2 produces C6H2 (+C2H2), C8H2 (+2H,H2), and C8H3 (+H), confirming the results of Glicker and Okabe (1987). Under certain conditions, secondary products were observed. Mechanisms for the observed reactions are proposed.

  17. Sinterability studies on K 0.5Na 0.5NbO 3 using laser as energy source

    NASA Astrophysics Data System (ADS)

    Tian, Xiaoyong; Dittmar, Anne; Melcher, Jörg; Heinrich, Jürgen G.

    2010-08-01

    The sinterability of K 0.5Na 0.5NbO 3 (KNN) ceramics by a laser beam has been investigated in the present research. A 100 W CO 2 laser with a beam diameter of 0.6 mm has been used to sinter the KNN specimens prepared on a uniaxial pressing machine. The relations between laser power and thickness of densified layer, crystallographic structures and phase compositions have been studied. A comparison has been made between laser and furnace sintered KNN samples according to the SEM, XRD and XRF results. The possibility of KNN used for the layer-wise laser direct sintering 3D components has been confirmed in this paper.

  18. Visible-Light-Catalyzed Direct Benzylic C(sp(3))-H Amination Reaction by Cross-Dehydrogenative Coupling.

    PubMed

    Pandey, Ganesh; Laha, Ramkrishna

    2015-12-01

    A conceptually new and synthetically valuable cross-dehydrogenative benzylic C(sp(3))-H amination reaction is reported by visible-light photoredox catalysis. This protocol employs DCA (9,10-dicyanoanthracene) as a visible-light-absorbing photoredox catalyst and an amide as the nitrogen source without the need of either a transition metal or an external oxidant.

  19. Microwave sintering of single plate-shaped articles

    DOEpatents

    Katz, J.D.; Blake, R.D.

    1995-07-11

    Apparatus and method are disclosed for high temperature sintering of plate-shaped articles of alumina, magnesia, silica, yttria, zirconia, and mixtures thereof using microwave radiation. An article is placed within a sintering structure located within a sintering container which is placed in a microwave cavity for heating. The rates at which heating and cooling take place is controlled. 2 figs.

  20. Microwave sintering of single plate-shaped articles

    DOEpatents

    Katz, Joel D.; Blake, Rodger D.

    1995-01-01

    Apparatus and method for high temperature sintering of plate-shaped articles of alumina, magnesia, silica, yttria, zirconia, and mixtures thereof using microwave radiation. An article is placed within a sintering structure located within a sintering container which is placed in a microwave cavity for heating. The rates at which heating and cooling take place is controlled.

  1. Microwave sintering of Yb:YAG transparent laser ceramics

    NASA Astrophysics Data System (ADS)

    Esposito, Laura; Piancastelli, Andreana; Bykov, Yury; Egorov, Sergei; Eremeev, Anatolii

    2013-02-01

    Reactive sintering of YAG based ceramics is generally performed under high vacuum in graphite-free furnaces in order to guarantee the elimination of pores and absence of any contamination. An alternative densification technique is the field assisted process such as spark plasma sintering and microwave sintering. Both of these methods are characterized by very fast heating rates, low sintering temperatures and short sintering times. The microwave sintering process is different from electric resistance heating since heat is generated in the bulk of the powder compact through electromagnetic radiation absorption and creates within its body uniform temperature distribution. Microwave sintering of laser ceramics is advantageously distinguished by the absence of any elements having high temperature such as electric heaters or dies which materials can contaminate the sintered parts. In addition, the inverse temperature distribution that exists within the body under volumetric microwave heating is favorable for elimination of porosity. Microwave sintering of Yb:YAG samples were tested and the obtained results are presented. The samples were sintered on a gyrotron-based system operating at a frequency of 24 GHz with microwave power up to 6 kW. Reactive sintering of YAG doped with 1.0, 5.0, and 9.8 at.% Yb2O3 was performed in different temperature-time regimes. The microstructure and the optical transmittance of the obtained samples were compared to those of samples obtained by conventional high vacuum sintering.

  2. Sintering of alumina in microwave-induced oxygen plasma

    SciTech Connect

    Su, H.; Johnson, D.L.

    1996-12-01

    Small cylindrical tubes were sintered in a microwave-induced oxygen plasma, initiated and sustained inside a tunable, single-mode cavity. Temperature and shrinkage measurements of the specimens were achieved using an optical-fiber thermometer black-body sensor and a dilatometer, respectively. Sintering experiments at constant heating rate were accomplished to obtain the activation energy for sintering of alumina in the plasma and in a conventional rapid-heating furnace. Diffusion of aluminum interstitials along grain boundaries was believed to be the dominant sintering mechanism, with an estimated activation energy of 488 {+-} 20 kJ/mol for conventional sintering and an average activation energy of 468 {+-} 20 kJ/mol for plasma sintering. A comparison of specimens sintered in the plasma to those sintered in a conventional furnace under the same temperature-time excursions and oxygen pressures showed an athermal effect due to the plasma. To further explore this athermal effect, sintering experiments in plasmas of different oxygen pressure were conducted. The athermal effect was ascribed to an increase of aluminum interstitial concentration during plasma sintering. Sintering data were interpreted using the combined-stage sintering model.

  3. A highly enantioselective and regioselective organocatalytic direct Mannich reaction of methyl alkyl ketones with cyclic imines benzo[e][1,2,3]oxathiazine 2,2-dioxides.

    PubMed

    Wang, You-Qing; Cui, Xiao-Yu; Ren, Yuan-Yuan; Zhang, Yongna

    2014-12-07

    A highly enantioselective direct Mannich reaction of methyl alkyl ketones with cyclic imines benzo[e][1,2,3]oxathiazine 2,2-dioxides, catalyzed by the combination of cinchona alkaloid derived primary amine and TFA, is disclosed. For unsymmetrical methyl alkyl ketones, it is favoured that specific regioselective addition to the imine substrates occurs at the less-substituted methyl group by steric control.

  4. Separation of contributions of isovector E2 and E1 giant resonances in direct and inverse reactions with real and virtual photons

    NASA Astrophysics Data System (ADS)

    Dzhilavyan, L. Z.; Lapik, A. M.; Nedorezov, V. G.; Tulupov, B. A.

    2017-01-01

    A brief overview of the methods for separating the contributions of isovector electric quadrupole ( E2) and dominant dipole ( E1) giant resonances in atomic nuclei, which are excited in direct and inverse reactions with photons (real and virtual), is given. The basic parameters of isovector giant resonance E2, which were declared to date by applying some of these methods to the results with 208Pb, are also presented.

  5. [FeIII(SR)4]1- Complexes can be Synthesized by the Direct Reaction of Thiolates with FeCl3

    Technology Transfer Automated Retrieval System (TEKTRAN)

    It is shown that the previously characterized [FeIII(SR)4]1- (R=Et, i-Pr, Ph) complexes can be synthesized by the direct reaction of 4 equivalents of LiSR with FeCl3 in DMF solution. [FeIII(SR)4]1- complexes are synthetic analogs for the [FeIII(S-Cystein)4] center in rubredoxin proteins....

  6. Sintering of BaCe(0.85)Y(0.15)O3-(Beta) With/Without SrTiO Dopant

    NASA Technical Reports Server (NTRS)

    Dynys, Fred; Sayir, Ali; Heimann, Paula J.

    2004-01-01

    The sintering behavior of BaCe(0.85)Y(0.15)O3-(Beta) doped with SrTiO is described. Complete reaction and crystallization of perovskite phase by solid state was achieved by calcining at 1200 degrees C for 24 hours.Smaples were sintered at 1450 degrees C, 1550 degrees C, and 1650 degrees C. SrTiOsub3 enhanced sintering, while optimal dopant level was different for powders synthesized by solid state and co-precipitation. Both powders exhibit similar grain growth behavior.

  7. Sintering behavior of Lanthana-bearing nanostructured ferritic steel consolidated via spark plasma sintering

    DOE PAGES

    Pasebani, Somayeh; Charit, Indrajit; Butt, Darryl P.; ...

    2015-08-03

    Elemental powder mixture of Fe–14Cr–1Ti–0.3Mo–0.5La2O3 (wt%) composition is mechanically alloyed for different milling durations (5, 10 and 20 h) and subsequently consolidated via spark plasma sintering under vacuum at 950 °C for 7 min. The effects of milling time on the densification behavior and density/microhardness are studied. The sintering activation energy is found to be close to that of grain boundary diffusion. The bimodal grain structure created in the milled and sintered material is found to be a result of milling and not of sintering alone. The oxide particle diameter varies between 2 and 70 nm. As a result, facetedmore » precipitates smaller than 10 nm in diameter are found to be mostly La–Ti–Cr-enriched complex oxides that restrict further recrystallization and related phenomena.« less

  8. Sintering behavior of Lanthana-bearing nanostructured ferritic steel consolidated via spark plasma sintering

    SciTech Connect

    Pasebani, Somayeh; Charit, Indrajit; Butt, Darryl P.; Cole, James I.; Wu, Yaqiao; Burns, Jatuporn

    2015-08-03

    Elemental powder mixture of Fe–14Cr–1Ti–0.3Mo–0.5La2O3 (wt%) composition is mechanically alloyed for different milling durations (5, 10 and 20 h) and subsequently consolidated via spark plasma sintering under vacuum at 950 °C for 7 min. The effects of milling time on the densification behavior and density/microhardness are studied. The sintering activation energy is found to be close to that of grain boundary diffusion. The bimodal grain structure created in the milled and sintered material is found to be a result of milling and not of sintering alone. The oxide particle diameter varies between 2 and 70 nm. As a result, faceted precipitates smaller than 10 nm in diameter are found to be mostly La–Ti–Cr-enriched complex oxides that restrict further recrystallization and related phenomena.

  9. Fabrication and Thermoelectric Power Factor of CoSb3 Prepared using Modified Polyol Process and Evacuated- and-Encapsulated Sintering

    NASA Astrophysics Data System (ADS)

    Gharleghi, Ahmad; Chang, Hon-Zi; Chen, Yin-Chiao; Yang, Yao-Wei; Liu, Chia-Jyi

    2013-07-01

    Various reaction temperatures have been investigated to stabilize the CoSb3 phase obtained by a modified polyol process using a refluxing condenser. The resulting powders were cold-pressed and sintered in an evacuated-and- encapsulated ampoule for transport measurements. Single-phase CoSb3 could be produced for the reaction carried out at 448 K for a short duration of 15 min followed by evacuated-and-encapsulated sintering at 848 K for 5 h. In comparison with the sample sintered at 798 K, the sample sintered at 848 K exhibits lower resistivity and thermopower. Due to the sign crossover of the thermopower, the latter sample shows lower power factor for temperatures above 475 K.

  10. α and 3He production in the 7Be+28Si reaction at near-barrier energies: Direct versus compound-nucleus mechanisms

    NASA Astrophysics Data System (ADS)

    Sgouros, O.; Pakou, A.; Pierroutsakou, D.; Mazzocco, M.; Acosta, L.; Aslanoglou, X.; Betsou, Ch.; Boiano, A.; Boiano, C.; Carbone, D.; Cavallaro, M.; Grebosz, J.; Keeley, N.; La Commara, M.; Manea, C.; Marquinez-Duran, G.; Martel, I.; Nicolis, N. G.; Parascandolo, C.; Rusek, K.; Sánchez-Benítez, A. M.; Signorini, C.; Soramel, F.; Soukeras, V.; Stefanini, C.; Stiliaris, E.; Strano, E.; Strojek, I.; Torresi, D.

    2016-10-01

    The production of α and 3He particles, the cluster constituents of 7Be, in the 7Be+28Si reaction was studied at three near-barrier energies, namely 13, 20, and 22 MeV. Angular distribution measurements were performed at each energy, and the data were analyzed in both statistical model and Distorted-Wave Born Approximation (DWBA) frameworks in order to disentangle the degree of competition between direct and compound channels. The energy evolution of the ratio of direct to total reaction cross section was mapped in comparison with similar data for 6Li and 7Li projectiles on a 28Si target. The results indicate larger transfer contributions for collisions involving the mirror nuclei 7Be and 7Li than in the 6Li case. Fusion cross sections were deduced, taking into account the α -particle cross sections due to compound-nucleus formation and particle multiplicities deduced from our statistical model framework. It was found that fusion is compatible with systematics and single-barrier penetration cross sections to within an uncertainty band of 10% to 20%. Indications of fusion hindrance for 7Li and 7Be compared to 6Li, starting from the barrier and below it, are given. This hindrance is attributed to the existence of large transfer channels. Furthermore, the experimental results, analyzed in the DWBA framework, suggest 3He and 4He transfer as the dominant direct reaction mechanism.

  11. Concentration and temperature dependency of regio- and stereoselectivity in a photochemical [2 + 2] cycloaddition reaction (the Paternò-Büchi reaction): origin of the hydroxy-group directivity.

    PubMed

    Yabuno, Youhei; Hiraga, Yoshikazu; Takagi, Ryukichi; Abe, Manabu

    2011-03-02

    A set of photochemical oxetane formation reactions, i.e., the Paternò-Büchi (PB) reactions, of tetrahydrobenzofuranol derivatives 1a-d with benzophenone (BP) was investigated to examine poorly understood hydroxy-group directivity on regio- and stereoselectivity. The selectivities of the PB reactions for allylic alcohols 1a,d were found to be largely dependent upon the concentration of the allylic alcohols and the reaction temperature. The temperature-dependent change of the regioselectivity at high concentrations of allylic alcohols was similar to that of the hydroxy-protected methyl ether 1b and tetrahydrobenzofuran (1c). The effect of concentration on regioselectivity can be explained by the hydrogen-bonded aggregates, which mimic the selectivities observed during the PB reaction of 1b,c. The hydroxy-directed cis-selectivity of the higher-substituted oxetane 3a,d formed at low concentration of 1a,d was found to be larger than that at the higher concentration of 1a,d. The cis-selectivity of 3a,d was found to be higher than that of the lower-substituted oxetane 2a,d. The regioselectivity of the cis-configured oxetanes was higher than that of the trans-configured oxetanes. These experimental results strongly suggest that hydroxy-group directivity, induced by hydrogen-bonding stabilization, plays a role in controlling the regio- and stereoselectivity of the PB reactions. The steric effect was also responsible for the diastereoselectivity, as shown by the fact that the cis selectivity in 3d was higher than that in 3a. Computational studies at the (U)MP2 and (U)DFT level of theory revealed that hydrogen-bonding stabilization becomes important only in the excited complex (exciplex) between the triplet excited state of carbonyls and alkenes, in which the charge transfer occurs from the alkene to the excited carbonyl to make the carbonyl oxygen nucleophilic. No significant stabilization energy was found in the intermediary triplet state of biradicals. The combined

  12. Sintered diamond compacts using metallic cobalt binders

    NASA Technical Reports Server (NTRS)

    Libby, W. F.; Katzman, H.

    1972-01-01

    Method is developed for sintering diamond powder which uses metallic cobalt as binder. Present samples show maximum microhardness of over 3000 kg/sq mm on Knoop scale. Material may be used as hard surface coating or may compete with cubic boron nitride as abrasive grain.

  13. Sintered electrode for solid oxide fuel cells

    DOEpatents

    Ruka, R.J.; Warner, K.A.

    1999-06-01

    A solid oxide fuel cell fuel electrode is produced by a sintering process. An underlayer is applied to the electrolyte of a solid oxide fuel cell in the form of a slurry, which is then dried. An overlayer is applied to the underlayer and then dried. The dried underlayer and overlayer are then sintered to form a fuel electrode. Both the underlayer and the overlayer comprise a combination of electrode metal such as nickel, and stabilized zirconia such as yttria-stabilized zirconia, with the overlayer comprising a greater percentage of electrode metal. The use of more stabilized zirconia in the underlayer provides good adhesion to the electrolyte of the fuel cell, while the use of more electrode metal in the overlayer provides good electrical conductivity. The sintered fuel electrode is less expensive to produce compared with conventional electrodes made by electrochemical vapor deposition processes. The sintered electrodes exhibit favorable performance characteristics, including good porosity, adhesion, electrical conductivity and freedom from degradation. 4 figs.

  14. Barkhausen noise from sintered permanent magnets

    SciTech Connect

    Cuntze, G.; Brendel, H.; Hubert, A.

    1996-09-01

    The authors introduce the well known Barkhausen technique as a tool for investigation of reversal processes in hard magnetic nucleation-type material. First results of the experiments show the occurrence of correlated grain switching not to be neglectible in the samples of sintered Nd-Fe-B as the volume fraction of multiple Barkhausen jumps reaches 50% near coercivity.

  15. METHOD FOR PREPARATION OF SINTERABLE BERYLLIUM OXIDE

    DOEpatents

    Sturm, B.J.

    1963-08-13

    High-purity beryllium oxide for nuclear reactor applications can be prepared by precipitation of beryllium oxalate monohydrate from aqueous solution at a temperature above 50 deg C and subsequent calcination of the precipitate. Improved purification with respect to metallic impurities is obtained, and the product beryllium oxide sinters reproducibly to a high density. (AEC)

  16. Multistep sintering to synthesize fast lithium garnets

    NASA Astrophysics Data System (ADS)

    Xu, Biyi; Duan, Huanan; Xia, Wenhao; Guo, Yiping; Kang, Hongmei; Li, Hua; Liu, Hezhou

    2016-01-01

    A multistep sintering schedule is developed to synthesize Li7La3Zr2O12 (LLZO) doped with 0.2 mol% Al3+. The effect of sintering steps on phase, relative density and ionic conductivity of Al-doped LLZO has been evaluated using powder X-Ray diffraction (XRD), scanning electron microscopy (SEM), 27Al magic spinning nuclear magnetic resonance (NMR) spectroscopy and electrochemical impedance spectroscopy (EIS). The results show that by holding the sample at 900 °C for 6 h, the mixture of tetragonal and cubic garnet phases are obtained; by continuously holding at 1100 °C for 6 h, the tetragonal phase completely transforms into cubic phase; by holding at 1200 °C, the relative density increases without decomposition of the cubic phase. The Al-LLZO pellets after multistep sintering exhibit cubic phase, relative density of 94.25% and ionic conductivity of 4.5 × 10-4 S cm-1 at room temperature. Based on the observation, a sintering model is proposed and discussed.

  17. Identification of Sintered Irons with Ultrasonic Nonlinearity

    NASA Astrophysics Data System (ADS)

    Ohara, Y.; Kawashima, K.; Murase, M.; Hirose, N.

    2003-03-01

    Two kinds of sinters made of reduced and atomized iron powders were identified by nonlinear ultrasonic measurement to detect higher harmonics generated at micro gaps comparable to the incident wave amplitude using PZT contact transducers of 5 MHz and 10 MHz. Furthermore, the advantage of the nonlinear ultrasonic measurement was demonstrated by the attenuation coefficient measurement for same samples.

  18. Contact material for pressure-sintering ferrites

    NASA Technical Reports Server (NTRS)

    Wentworth, C.

    1970-01-01

    Pressure-sintering, in which the unfired laminated ferrite plane is placed between two flat punches and pressed during firing, reduces lateral firing shrinkage to less than one percent. A decrease in thickness of the laminate produces the required volume shrinkage. Phlogopite is the most suitable contact material investigated.

  19. Yttrium oxide transparent ceramics by low-temperature microwave sintering

    SciTech Connect

    Luo, Junming; Zhong, Zhenchen; Xu, Jilin

    2012-12-15

    Graphical abstract: The figure shows the SEM photos of the surfaces of the Y{sub 2}O{sub 3} transparent ceramic samples obtained by microwave sintering and vacuum sintering. It is clearly demonstrated that the grain distribution of the vacuum sintering sample is not uniform with the smallest and the largest particle size at about 2 μm and 15 μm respectively, while the grain distribution of microwave sintering sample is uniform with the average diameter at about 2–4 μm (the smallest reported so far) and with no abnormal growth-up or coarsening phenomenon. We have further found out that the smaller the grain size, the higher the mechanical and optical properties. Display Omitted Highlights: ► The microwave sintering temperature of the sample is lower compared with vacuum. ► The microwave sintering time of the sample is shorter compared with vacuum. ► The mechanical properties of the microwave sintering sample is improved greatly. ► The Y{sub 2}O{sub 3} grain of microwave sintering sample is the smallest reported so far. -- Abstract: Yttrium oxide (Y{sub 2}O{sub 3}) transparent ceramics samples have been successfully fabricated by microwave sintering processing at relatively low temperatures. In comparison with the vacuum sintering processing, Y{sub 2}O{sub 3} transparent ceramics can be obtained by microwave sintering at lower sintering temperature and shorter sintering time, and they possess higher transmittances and mechanical properties. The technologies of low-temperature microwave sintering and the relationships of the microstructures and properties of the specified samples have been investigated in detail. We have found out that the low-temperature microwave sintering technique has its obvious advantages over the conventional methods in manufacturing yttrium oxide transparent ceramics.

  20. Direct and compound-nucleus reaction mechanisms in the 7Be+58Ni system at near-barrier energies

    NASA Astrophysics Data System (ADS)

    Mazzocco, M.; Torresi, D.; Pierroutsakou, D.; Keeley, N.; Acosta, L.; Boiano, A.; Boiano, C.; Glodariu, T.; Guglielmetti, A.; La Commara, M.; Lay, J. A.; Martel, I.; Mazzocchi, C.; Molini, P.; Parascandolo, C.; Pakou, A.; Parkar, V. V.; Romoli, M.; Rusek, K.; Sánchez-Benítez, A. M.; Sandoli, M.; Sgouros, O.; Signorini, C.; Silvestri, R.; Soramel, F.; Soukeras, V.; Stiliaris, E.; Strano, E.; Stroe, L.; Zerva, K.

    2015-08-01

    The energy and angular distributions of 3He and 4He ions produced in the 7Be +58Ni reaction at a bombarding energy of 22 MeV have been measured for the first time. The yield of the heavier helium isotope was four to five times more abundant than that of its lighter counterpart, ruling out the possibility that in this energy range the 7Be reaction dynamics is dominated by the exclusive breakup process 7Be→3He +4He (Sα=1.586 MeV). Extensive kinematic and theoretical calculations suggest that the 3He ions mostly originate from the 4He-stripping process and the 4He production is mainly triggered by the fusion-evaporation channel. The role played by the breakup, 3He-stripping, 1 n -stripping, and 1 n -pickup processes is also discussed.

  1. Wavelength control of diastereodifferentiating Paterno-Buchi reaction of chiral cyanobenzoates with diphenylethene through direct versus charge-transfer excitation.

    PubMed

    Matsumura, Kazuyuki; Mori, Tadashi; Inoue, Yoshihisa

    2009-12-02

    In the diastereodifferentiating Paterno-Buchi reaction, the excited CT complex was distinctly different in structure and reactivity from the conventional exciplex, and the inherent diastereofacial selectivity and its temperature dependence were opposite to each other in these two excitation modes. Thus, the combined use of wavelength and temperature not only reveals the mechanistic details but also provides a new convenient, powerful tool for critically controlling the stereochemical outcomes of asymmetric photoreactions.

  2. Directional errors of movements and their correction in a discrete tracking task. [pilot reaction time and sensorimotor performance

    NASA Technical Reports Server (NTRS)

    Jaeger, R. J.; Agarwal, G. C.; Gottlieb, G. L.

    1978-01-01

    Subjects can correct their own errors of movement more quickly than they can react to external stimuli by using three general categories of feedback: (1) knowledge of results, primarily visually mediated; (2) proprioceptive or kinaesthetic such as from muscle spindles and joint receptors, and (3) corollary discharge or efference copy within the central nervous system. The effects of these feedbacks on simple reaction time, choice reaction time, and error correction time were studied in four normal human subjects. The movement used was plantarflexion and dorsiflexion of the ankle joint. The feedback loops were modified, by changing the sign of the visual display to alter the subject's perception of results, and by applying vibration at 100 Hz simultaneously to both the agonist and antagonist muscles of the ankle joint. The central processing was interfered with when the subjects were given moderate doses of alcohol (blood alcohol concentration levels of up to 0.07%). Vibration and alcohol increase both the simple and choice reaction times but not the error correction time.

  3. Sintering of Lunar and Simulant Glass

    NASA Technical Reports Server (NTRS)

    Cooper, Bonnie L.

    2007-01-01

    Most oxygen-extraction techniques are temperature-dependent, with higher temperatures resulting in higher oxygen yield. An example is hydrogen reduction, in which the optimum process temperature is 1050 C. However, glass-rich lunar soil begins to show the effects of sintering at temperatures of 900 C or lower. Sintering welds particles together due to viscous relaxation of the glass in the sample. One approach to avoid problems related to sintering, such as difficulty in removing waste material from the reactor, is to keep the soil in motion. One of several methods being studied to accomplish this is fluidized-bed processing techniques, in which the grains are kept in motion by the action of flowing reductant gas. The spent material can be removed from the chamber while still fluidized, or the fluidizing motion can continue until the material has cooled below approx. 500 C. Until end-to-end prototypes are built that can remove the heated soil, the most practical option is to keep the bed fluidized while cooling the waste material. As ISRU technology advances, another option will become valuable, which is to intentionally sinter the material to a great enough extent that it becomes a brick. The free iron in lunar soil is magnetic, and ferromagnetic bricks can be manipulated by robotic systems using electromagnetic end effectors. Finally, if an electromagnetic field is applied to the soil while the brick is being formed, the brick itself will become a magnet. This property can be used to create self-aligning bricks or other building materials that do not require fasteners. Although sintering creates a challenge for early lunar surface systems, knowledge gained during prototype development will be valuable for the advanced lunar outpost.

  4. Sintering of Lunar and Simulant Glass

    NASA Astrophysics Data System (ADS)

    Cooper, Bonnie L.

    2008-01-01

    Most oxygen-extraction techniques are temperature-dependent, with specific temperatures resulting in optimized oxygen yield. An example is hydrogen reduction, in which the optimum process temperature is 1050 °C. However, glass-rich lunar soil begins to show the effects of sintering at temperatures of 900 °C or lower. Sintering welds particles together due to viscous relaxation of the glass in the sample. One approach to avoid problems related to sintering, such as difficulty in removing waste material from the reactor, is to keep the soil in motion. One of several methods being studied to accomplish this is fluidized-bed processing techniques, in which the grains are kept in motion by the action of flowing reductant gas. The spent material can be removed from the chamber while still fluidized, or the fluidizing motion can continue until the material has cooled below ~500 °C. Until end-to-end prototypes are built that can remove the heated soil, the most practical option is to keep the bed fluidized while cooling the waste material. As ISRU technology advances, another option will become valuable, which is to intentionally sinter the material to a great enough extent that it becomes a brick. The free iron in lunar soil is magnetic, and ferromagnetic bricks can be manipulated by robotic systems using electromagnetic end effectors. Finally, if an electromagnetic field is applied to the soil while the brick is being formed, the brick itself will become a magnet. This property can be used to create self-aligning bricks or other building materials that do not require fasteners. Although sintering creates a challenge for early lunar surface systems, knowledge gained during prototype development will be valuable for the advanced lunar outpost.

  5. Laser sintering of conductive carbon paste on plastic substrate

    NASA Astrophysics Data System (ADS)

    Kelkar, Rohan; Kinzel, Edward C.; Xu, Xianfan

    2009-07-01

    We investigate fabrication of functional conductive carbon paste onto a plastic substrate using a laser. The method allows simultaneous sintering, patterning, and functionalization of the carbon paste. Experiments are carried out to optimize the laser-processing parameters. It is shown that sheet resistance values obtained by laser sintering are close to the one specified by the manufacturer using the conventional sintering method. Additionally, a heat transfer analysis using numerical methods is conducted to understand the relationship between the temperature during sintering and the sheet resistance values of sintered carbon wires. The process developed has the potential of producing carbon-based electronic components on low-cost plastic substrates.

  6. Laser sintering of conductive carbon paste on plastic substrate

    NASA Astrophysics Data System (ADS)

    Kinzel, Edward C.; Kelkar, Rohan; Xu, Xianfan

    2010-02-01

    This work investigates fabrication of functional conductive carbon paste onto a plastic substrate using a laser. The method allows simultaneous sintering, patterning, and functionalization of the carbon paste. Experiments are carried out to optimize the laser processing parameters. It is shown that sheet resistance values obtained by laser sintering are close to the one specified by the manufacturer using conventional sintering method. Additionally, a heat transfer analysis using numerical methods is conducted to understand the relationship between the temperature during sintering and the sheet resistance values of sintered carbon wires. The process developed in this work has the potential of producing carbon-based electronic components on low cost plastic substrates.

  7. Comparative sinterability of combustion synthesized and commercial titanium carbides

    SciTech Connect

    Manley, B.W.

    1984-11-01

    The influence of various parameters on the sinterability of combustion synthesized titanium carbide was investigaged. Titanium carbide powders, prepared by the combustion synthesis process, were sintered in the temperature range 1150 to 1600/sup 0/C. Incomplete combustion and high oxygen contents were found to be the cause of reduced shrinkage during sintering of the combustion syntheized powders when compared to the shrinkage of commercial TiC. Free carbon was shown to inhibit shrinkage. The activation energy for sintering was found to depend on stoichiometry (C/Ti). With decreasing C/Ti, the rate of sintering increased. 29 references, 16 figures, 13 tables.

  8. Pressureless sintering of whiskered-toughened ceramic composites

    DOEpatents

    Tiegs, T.N.

    1994-12-27

    A pressureless sintering method is disclosed for use in the production of whisker-toughened ceramic composites wherein the sintered density of composites containing up to about 20 vol. % SiC whiskers is improved by reducing the average aspect ratio of the whiskers to from about 10 to about 20. Sintering aids further improve the density, permitting the production of composites containing 20 vol. % SiC with sintered densities of 94% or better of theoretical density by a pressureless sintering method. 6 figures.

  9. Direct experimental probing and theoretical analysis of the reaction between the simplest Criegee intermediate CH 2 OO and isoprene

    SciTech Connect

    Decker, Z. C. J.; Au, K.; Vereecken, L.; Sheps, L.

    2017-01-01

    Recent advances in the spectroscopy of Criegee intermediates (CI) have enabled direct kinetic studies of these highly reactive chemical species. The impact of CI chemistry is currently being incorporated into atmospheric models, including their reactions with trace organic and inorganic compounds. Isoprene, C5H8, is a doubly-unsaturated hydrocarbon that accounts for the largest share of all biogenic emissions around the globe and is also a building block of larger volatile organic compounds. We report direct measurements of the reaction of the simplest CI (CH2OO) with isoprene, using time-resolved cavity-enhanced UV absorption spectroscopy. We find the reaction to be pressure-independent between 15–100 Torr, with a rate coefficient that varies from (1.5 ± 0.1) × 10–15 cm3 molecule–1 s–1 at room temperature to (23 ± 2) × 10–15 cm3 molecule–1 s–1 at 540 K. Quantum chemical and transition-state theory calculations of 16 unique channels for CH2OO + isoprene somewhat underpredict the observed T-dependence of the total reaction rate coefficient, but are overall in good agreement with the experimental measurements. Finally, this reaction is broadly similar to those with smaller alkenes, proceeding by 1,3-dipolar cycloaddition to one of the two conjugated double bonds of isoprene.

  10. Combining direct residence time measurements and biogeochemistry to calculate in-situ reaction rates in the hyporheic zone

    NASA Astrophysics Data System (ADS)

    Pittroff, Marco; Gilfedder, Benjamin

    2015-04-01

    The hyporheic zone is an active interface between groundwater, riparian and surface water systems. Exchange and reaction of water, nutrients, and organic matter occur due to variations in surface and groundwater flow regimes, bed topography and active biogeochemistry fuelled by bioavailable carbon. There has been an increasing focus on coupling the residence time of surface water in the hyporheic zone with biogeochemical reactions. However, there are very few tracers that can be used to measure residence times in-situ, especially in complex groundwater-surface water settings. In this work we have used the natural radioisotope Radon (222Rn) as an in-situ tracer for river water residence time in a riffle-pool sequence (Rote Main River), and combined this information with biogeochemical parameters (DOC and C quality, O3, NO3, CO2). We can clearly observe a dependence of reaction progress on the water residence times, with oxygen and nitrate reduction following inverse logarithmic trends as a function of time. By comparing with initial concentrations (the river end member) with riverbed levels we have estimated first-order in-situ reduction rates for nitrate and oxygen. Nitrate reduction rates are at the higher end of published values, which is likely due to the continual supply of bioavailable carbon from the river system. This work helps to better understand the function and efficiency of the hyporheic zone as a natural filter for redox sensitive species such as nitrate at the groundwater - steam interface. It also provides a useful method for estimating residence times in complex, higher order river systems.

  11. Microstructural prototyping of ceramics by kinetic engineering: applications of spark plasma sintering.

    PubMed

    Shen, Zhijian; Nygren, Mats

    2005-01-01

    The significance of kinetics on the development of microstructures in connection with sintering of ceramics is well recognized. In practice, however, it still remains a challenge to prepare designed microstructures via engineering the sintering kinetics because of an insufficient understanding of the different operative mechanisms that are in many cases overlapping. In this article the kinetic issues involved in sintering are described and discussed with respect to their potential for prototyping microstructures that yield desired properties. By exploiting and mastering the differences present in the kinetics of grain sliding, densification, chemical reactions, and grain growth, respectively, we have established processing principles for producing bulk ceramics with microstructures consisting of nano-sized grains, aligned grains, and/or non-equilibrium-phase constitutions, and for achieving radically improved superplasticity in brittle ceramics. Although the studies quoted in this article were mainly carried out by spark plasma sintering, more general implications of them are expected, including efficient particle sliding, deformation-induced dynamic ripening, superplastic deformation-induced dynamic ripening, and non-equilibrium integration.

  12. Effect of sintering on the microstructural and mechanical properties of meleagris gallopova hydroxyapatite.

    PubMed

    Pazarlioglu, S Serdar; Gokce, Hasan; Ozyegin, Sevgi; Salman, Serdar

    2014-01-01

    In this study, we obtained hydroxyapatite powders from the femur bones of meleagris gallopova at three steps and sintered at five different temperatures. The reactions, which occur during sintering of obtained powders, have been characterized by X-ray diffraction (XRD) patterns, scanning electron microscope (SEM), differential thermal analysis (DTA), thermo-gravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR) techniques. The mechanical properties of meleagris gallopova hydroxyapatite powders were determined by the measurements of density, hardness, porosity, activation energy for grain growth, variation of average grain sizes, fracture toughness and compression strength. The Fourier transform infrared spectra and the thermogravimetric analysis/differential thermal analysis thermograms of meleagris gallopova hydroxyapatite powders indicated that the presence of organic compounds were completely removed from the matrice. The X-ray diffraction patterns showed that decomposition of meleagris gallopova hydroxyapatite into tricalcium phosphate and calcium oxide was observed for the sintered samples at 1300°C. At the same temperature, formation of microcracks were also detected by scanning electron microscopy image. Mechanical tests showed that maximum hardness, fracture toughness and compression strength values were measured for the sintered samples at 1200°C.

  13. Modeling and simulation of titanium dioxide nanoparticle synthesis with finite-rate sintering in planar jets

    NASA Astrophysics Data System (ADS)

    Garrick, Sean C.; Wang, Guanghai

    2011-03-01

    Numerical simulations of titanium dioxide nanoparticle synthesis in planar, non-premixed diffusion flames are performed. Titania is produced by the oxidation of titanium tetrachloride using a methane-air flame. The flow field is obtained using the two-dimensional Navier-Stokes equations. The methane-air flame and oxidation of titanium tetrachloride are modeled via one-step reactions. Evolution of the particle field is obtained via a nodal method which accounts for nucleation, condensation, coagulation, and coalescence with finite-rate sintering. The modeling of finite-rate sintering is accomplished via the use of uniform primary-particle size distribution. Simulations are performed at two different jet-to-co-flow velocity ratios as well as with finite-rate and instantaneous sintering models. In doing so we elucidate the effect of fluid mixing and finite-rate sintering on the particle field. Results show that highly agglomerated particles are found on the periphery of the eddies, where the collisions leading to nanoparticle coagulation occur faster than nanoparticle coalescence.

  14. Diagnosis of. alpha. sub 1 -antitrypsin deficiency by enzymatic amplification of human genomic DNA and direct sequencing of polymerase chain reaction products

    SciTech Connect

    Newton, C.R.; Graham, A.; Powell, S.; Gammack, A.; Riley, J.; Markham, A.F. ); Kalsheker, N. )

    1988-09-12

    The authors have compared sequencing of cloned polymerase chain reaction (PCR) products and the direct sequencing of PCR products in the examination of individuals from six families affected with {alpha}{sub 1}-antitrypsin (AAT) deficiency. In families where paternity was in question they confirmed consanguinity by DNA fingerprinting using a panel of locus-specific minisatellite probes. They demonstrate that direct sequencing of PCR amplification products is the method of choice for the absolutely specific diagnosis of AAT deficiency and can distinguish normals, heterozygotes and homozygotes in a single, rapid and facile assay. Furthermore, they demonstrate the reproducibility of the PCR and a rapid DNA isolation procedure. They have also shown that two loci can be simultaneously amplified and that the PCR product from each locus can be independently examined by direct DNA sequencing.

  15. The role of nanopowder particle surfaces and grain boundary defects in the sintering of ZnO ceramics

    NASA Astrophysics Data System (ADS)

    Muktepavela, F.; Zabels, R.; Sursajeva, V.; Grigorjeva, L.; Kundzins, K.

    2012-08-01

    This work focuses on the characteristics of sintered ZnO ceramics and explores the role of source powder morphology in the process of sintering. The source ZnO powders had grained (d = 100 nm) and tetrapod-like (d=50-100 nm, l=3-10 μm) morphologies, they were compacted and sintered at 1200° C. The results have shown that ceramics sintered from the grained powder exhibit relatively high (8%) porosity at grain boundaries and as cavities within grains, which facilitates brittleness. Photoluminescence spectra for these ceramics besides a narrow exitonic band contain a broad "green" luminescence band attributed to defect states. The second ceramics sintered from the tetrapod-like powder has lower porosity (<2 %) Photoluminescence spectrum at 12 K revealed a narrow exitonic band with satellite peaks (1LO_Ex states) and almost negligible "green" band which is an indication of high quality of this ceramics. Experiments on bicrystals have shown that in the stage of grain growth the motion of grain boundaries is directly correlated to triple-junction mobility. The obtained results have been discussed from the point of contact phenomenon and evolution processes of the grain boundary microstructure at different sintering stages.

  16. Spark Plasma Sintering of Cryomilled Nanocrystalline Al Alloy - Part II: Influence of Processing Conditions on Densification and Properties

    NASA Astrophysics Data System (ADS)

    Liu, Dongming; Xiong, Yuhong; Topping, Troy D.; Zhou, Yizhang; Haines, Chris; Paras, Joseph; Martin, Darold; Kapoor, Deepak; Schoenung, Julie M.; Lavernia, Enrique J.

    2012-01-01

    In this study, nanostructured Al 5083 powders, which were prepared via cryomilling, were consolidated using spark plasma sintering (SPS). The influence of processing conditions, e.g., the loading mode, starting microstructure ( i.e., atomized vs cryomilled powders), sintering pressure, sintering temperature, and powder particle size on the consolidation response and associated mechanical properties were studied. Additionally, the mechanisms that govern densification during SPS were discussed also. The results reported herein suggest that the morphology and microstructure of the cryomilled powder resulted in an enhanced densification rate compared with that of atomized powder. The pressure-loading mode had a significant effect on the mechanical properties of the samples consolidated by SPS. The consolidated compact revealed differences in mechanical response when tested along the SPS loading axis and radial directions. Higher sintering pressures improved both the strength and ductility of the samples. The influence of grain size on diffusion was considered on the basis of available diffusion equations, and the results show that densification was attributed primarily to a plastic flow mechanism during the loading pressure period. Once the final pressure was applied, power law creep became the dominant densification mechanism. Higher sintering temperature improved the ductility of the consolidated compact at the expense of strength, whereas samples sintered at lower temperature exhibited brittle behavior. Finally, densification rate was found to be inversely proportional to the particle size.

  17. Synthesis of PtRu nanoparticles from the hydrosilylation reaction and application as catalyst for direct methanol fuel cell.

    PubMed

    Huang, Junchao; Liu, Zhaolin; He, Chaobin; Gan, Leong Ming

    2005-09-08

    Nanosized Pt, PtRu, and Ru particles were prepared by a novel process, the hydrosilylation reaction. The hydrosilylation reaction is an effective method of preparation not only for Pt particles but also for other metal colloids, such as Ru. Vulcan XC-72 was selected as catalyst support for Pt, PtRu, and Ru colloids, and TEM investigations showed nanoscale particles and narrow size distribution for both supported and unsupported metals. All Pt and Pt-rich catalysts showed the X-ray diffraction pattern of a face-centered cubic (fcc) crystal structure, whereas the Ru and Ru-rich alloys were more typical of a hexagonal close-packed (hcp) structure. As evidenced by XPS, most Pt and Ru atoms in the nanoparticles were zerovalent, except a trace of oxidation-state metals. The electrooxidation of liquid methanol on these catalysts was investigated at room temperature by cyclic voltammetry and chronoamperometry. The results concluded that some alloy catalysts showed higher catalytic activities and better CO tolerance than the Pt-only catalyst; Pt56Ru44/C have displayed the best electrocatalytic performance among all carbon-supported catalysts.

  18. Direct ab initio molecular dynamics study on a microsolvated SN2 reaction of OH-(H2O) with CH3Cl.

    PubMed

    Tachikawa, Hiroto

    2006-10-07

    Reaction dynamics for a microsolvated SN2 reaction OH-(H2O)+CH3Cl have been investigated by means of the direct ab initio molecular dynamics method. The relative center-of-mass collision energies were chosen as 10, 15, and 25 kcal/mol. Three reaction channels were found as products. These are (1) a channel leading to complete dissociation (the products are CH3OH+Cl- +H2O: denoted by channel I), (2) a solvation channel (the products are Cl-(H2O)+CH3OH: channel II), and (3) a complex formation channel (the products are CH3OH...H2O+Cl-: channel III). The branching ratios for the three channels were drastically changed as a function of center-of-mass collision energy. The ratio of complete dissociation channel (channel I) increased with increasing collision energy, whereas that of channel III decreased. The solvation channel (channel II) was minor at all collision energies. The selectivity of the reaction channels and the mechanism are discussed on the basis of the theoretical results.

  19. Ab initio direct classical trajectory investigation on the SN2 reaction of F- with NH2F: nonstatistical central barrier recrossing dynamics.

    PubMed

    Yu, Feng

    2012-02-05

    The bimolecular nucleophilic substitution (S(N)2) reaction of F(a)(-) with NH(2)F(b) has been investigated with the ab initio direct classical trajectory method. According to our trajectory calculations, a dynamic behavior of nonstatistical central barrier recrossing is revealed. Among the 64 trajectories calculated in this work, 45 trajectories follow the dynamic reaction pathways as assumed by statistical theory and other 19 trajectories with central barrier recrossings are nonstatistical. For the nonstatistical trajectories, the central barrier recrossings may originate from the inefficient kinetic energy transfer from the intramolecular modes of the NH(2)F(a) moiety in the dynamic F(b)(-)…H-NH-F(a) complex to the intermolecular modes of the dynamic F(b)(-)…H-NH-F(a) complex on the exit-channel potential energy surface. With respect to the dynamic behavior of the nonstatistical central barrier recrossing, the statistical theories such as the Rice-Ramsperger-Kassel-Marcus and transition state theories without further corrections cannot be used to model the reaction kinetics for this S(N)2 reaction.

  20. Direct ab initio molecular dynamics study on a microsolvated SN2 reaction of OH-(H2O) with CH3Cl

    NASA Astrophysics Data System (ADS)

    Tachikawa, Hiroto

    2006-10-01

    Reaction dynamics for a microsolvated SN2 reaction OH-(H2O)+CH3Cl have been investigated by means of the direct ab initio molecular dynamics method. The relative center-of-mass collision energies were chosen as 10, 15, and 25kcal/mol. Three reaction channels were found as products. These are (1) a channel leading to complete dissociation (the products are CH3OH+Cl-+H2O: denoted by channel I), (2) a solvation channel (the products are Cl-(H2O)+CH3OH: channel II), and (3) a complex formation channel (the products are CH3OH ⋯H2O+Cl-: channel III). The branching ratios for the three channels were drastically changed as a function of center-of-mass collision energy. The ratio of complete dissociation channel (channel I) increased with increasing collision energy, whereas that of channel III decreased. The solvation channel (channel II) was minor at all collision energies. The selectivity of the reaction channels and the mechanism are discussed on the basis of the theoretical results.

  1. Theoretical investigation of the hydrogen abstraction reaction of the OH radical with CH2FCH2F (HFC-152): a dual-level direct dynamics study.

    PubMed

    Taghikhani, Mahdi; Parsafar, G A

    2007-08-23

    The hydrogen abstraction reaction of the OH radical with CH(2)FCH(2)F (HFC-152) is studied theoretically over the 150-3000 K temperature range. In this study, the two most recently developed hybrid density functional theories, namely, BB1K and MPWB1K, are applied, and their efficiency in reaction dynamics calculation is discussed. The BB1K/6-31+G(d,p) method gives the best result for the potential energy surface (PES) calculations, including barrier heights, reaction path information (the first and second derivatives of PES), geometry of transition state structures, and even weak hydrogen bond orientations. The rate constants were obtained by the dual-level direct dynamics with the interpolated single-point energy method (VTST-ISPE) using the BB1K/MG3S//BB1K/6-31+G(d,p) quantum model. The canonical variational transition state theory (CVT) with the small-curvature tunneling correction methods are used to calculate the rate constants in comparison to the experimental data. The total rate constant and its temperature dependency in the form of a fitted three-parameter Arrhenius expression is k(T) = 5.4 x 10(-13)(T/298)3.13 exp{-322/T} cm3 molecule(-1) s(-1). A significant variational effect, which is not common generally for hydrogen-transfer reactions, is reported and analyzed.

  2. Density functional theory direct dynamics study on the hydrogen abstraction reaction of CF 3CHFCF 3+OH→CF 3CFCF 3+H 2O

    NASA Astrophysics Data System (ADS)

    Liu, Jing-yao; Li, Ze-sheng; Dai, Zhen-wen; Huang, Xu-ri; Sun, Chia-chung

    2002-08-01

    The hydrogen abstraction reaction CF 3CHFCF 3+OH has been studied by a dual-level direct dynamics method. The variational transition state calculations are performed with small curvature tunneling (SCT), and the interpolated single-point energies (ISPE) approach is employed to correct the classical energy profile. The rate constants are evaluated at the B3LYP/6-311++G(3df, 2p)//B3LYP/6-311G(d, p) level over the temperature range of 270-2000 K. The calculated results show reasonable agreement with the available experimental data in the 270-463 K range. It is found that the variational effect is significant for this reaction, and the tunneling effect is smaller.

  3. The first enantioselective organocatalytic Mukaiyama-Michael reaction: a direct method for the synthesis of enantioenriched gamma-butenolide architecture.

    PubMed

    Brown, Sean P; Goodwin, Nicole C; MacMillan, David W C

    2003-02-05

    The first enantioselective organocatalytic Mukaiyama-Michael reaction using alpha,beta-unsaturated aldehydes has been accomplished. The use of iminium catalysis has provided a new strategy for the enantioselective addition of 2-silyloxy furans to unsaturated aldehydes to generate a variety of butenolide systems, an important chiral synthon found among many natural isolates. The (2S,5S)-5-benzyl-2-tert-butyl-imidazolidinone amine catalyst has been found to mediate the conjugate addition of a wide variety of substituted and unsubstituted silyloxy furans to unsaturated aldehydes. A diverse range of aldehyde substrates can be accommodated in this new organocatalytic transformation. Application of this new asymmetric technology to the enantioselective total synthesis of spiculisporic acid and the corresponding 5-epi-spiculisporic acid analogue is also discussed.

  4. Chirality imprinting and direct asymmetric reaction screening using a stereodynamic Brønsted/Lewis acid receptor

    NASA Astrophysics Data System (ADS)

    Bentley, Keith W.; Proano, Daysi; Wolf, Christian

    2016-08-01

    Molecular recognition, activation and dynamic self-assembly with Brønsted and Lewis acids play a central role across the chemical sciences including catalysis, crystal engineering, supramolecular architectures and drug design. Despite this general advance, the utilization of the corresponding binding motifs for fast and robust quantitative chemosensing of chiral compounds in a complicate matrix has remained challenging. Here we show that a stereodynamic probe carrying complementary boronic acid and urea units achieves this goal with hydroxy carboxylic acids. Synergistic dual-site binding and instantaneous chirality imprinting result in characteristic ultraviolet and CD readouts that allow instantaneous determination of the absolute configuration, enantiomeric excess and concentration of the target compound even in complex mixtures. The robustness and practicality of this strategy for high-throughput screening purposes is demonstrated. Comprehensive sensing of only 0.5 mg of a crude reaction mixture of an asymmetric reduction eliminates cumbersome work-up protocols and minimizes analysis time, labour and waste production.

  5. Regulating emotions uniquely modifies reaction time, rate of force production, and accuracy of a goal-directed motor action.

    PubMed

    Beatty, Garrett F; Fawver, Bradley; Hancock, Gabriella M; Janelle, Christopher M

    2014-02-01

    We investigated how emotion regulation (ER) strategies influence the execution of a memory guided, ballistic pinch grip. Participants (N=33) employed ER strategies (expressive suppression, emotional expression, and attentional deployment) while viewing emotional stimuli (IAPS images). Upon stimulus offset, participants produced a targeted pinch force aimed at 10% of their maximum voluntary contraction. Performance measures included reaction time (RT), rate of force production, and performance accuracy. As hypothesized, attentional deployment resulted in the slowest RT, largest rate of force production, and poorest performance accuracy. In contrast, expressive suppression reduced the rate of force production and increased performance accuracy relative to emotional expression and attentional deployment. Findings provide evidence that emotion regulation strategies uniquely influence human movement. Future work should further delineate the interacting role that emotion regulation strategies have in modulating both affective experience and motor performance.

  6. Molecular simulation of AG nanoparticle nucleation from solution: redox-reactions direct the evolution of shape and structure.

    PubMed

    Milek, Theodor; Zahn, Dirk

    2014-08-13

    The association of Ag(+) ions and the early stage of Ag nanoparticle nucleation are investigated from molecular dynamics simulations. Combining special techniques for tackling crystal nucleation from solution with efficient approaches to model redox-reactions, we unravel the structural evolution of forming silver nanoparticles as a function of the redox-potential in the solution. Within a range of only 1 eV, the redox-potential is demonstrated to have a drastic effect on both the inner structure and the overall shape of the forming particles. On the basis of our simulations we identify surface charge and its distribution as an atomic scale mechanism that accounts for creating/avoiding 5-fold coordination polyhedra and thus the degree of (multiple)-twinning in silver nanoparticles.

  7. Solvent and temperature effects on diastereodifferentiating Paternó-Büchi reaction of chiral alkyl cyanobenzoates with diphenylethene upon direct versus charge-transfer excitation.

    PubMed

    Matsumura, Kazuyuki; Mori, Tadashi; Inoue, Yoshihisa

    2010-08-20

    In the Paternó-Büchi reaction of chiral p-cyanobenzoates (1) with 1,1-diphenylethene (2), we revealed that the excited charge-transfer (CT) complex formed upon selective excitation at the CT band is distinctly different in structure and reactivity from the conventional exciplex generated through the direct excitation of acceptor 1 which subsequently associates with donor 2. Thus, the favored diastereoface upon photocycloaddition, as well as the temperature- and solvent-dependent behavior of the product's diastereoselectivity, were highly contrasting, often opposite, to each other upon direct versus CT excitation. From the activation parameters obtained by the Eyring analyses of the diastereoselectivity, we are able to infer that the conventional exciplex is relatively flexible and susceptible to the environmental variants, whereas the CT complex is better pi-pi stacked and more rigid in the ground state and also in the excited state, leading to the significantly smaller differential activation enthalpies and entropies. More interestingly, the signs of the differential activation parameters determined for direct and CT excitation are consistently opposite to each other and the isokinetic temperatures calculated therefrom differ significantly, unambiguously revealing the distinctly different nature in structure and reactivity of these two excited-state complex species. Thus, the combined use of irradiation wavelength, temperature, and solvent provides us with a convenient, powerful tool not only for elucidating the mechanistic details of photoreaction but also for critically controlling the stereochemical outcomes of photochirogenic reaction.

  8. Multi-fragment site-directed mutagenic overlap extension polymerase chain reaction as a competitive alternative to the enzymatic assembly method.

    PubMed

    Wäneskog, Marcus; Bjerling, Pernilla

    2014-01-01

    Methods for introducing multiple site-directed mutations are important experimental tools in molecular biology. Research areas that use these methods include the investigation of various protein modifications in cellular processes, modifying proteins for efficient recombinant expression, and the stabilization of mRNAs to allow for increased protein expression. Introducing multiple site-directed mutations is also an important tool in the field of synthetic biology. There are two main methods used in the assembling of fragments generated by mutagenic primers: enzymatic assembly and overlap extension polymerase chain reaction (OE-PCR). In this article, we present an improved OE-PCR method that can be used for the generation of large DNA fragments (up to 7.4 kb) where at least 13 changes can be introduced using a genomic template. The improved method is faster (due to fewer reaction steps) and more accurate (due to fewer PCR cycles), meaning that it can effectively compete with the enzymatic assembly method. Data presented here show that the site-directed mutations can be introduced anywhere between 50 and 1800 bp from each other. The method is highly reliable and predicted to be applicable to most DNA engineering when the introduction of multiple changes in a DNA sequence is required.

  9. Degradation mechanism of Direct Pink 12B treated by iron-carbon micro-electrolysis and Fenton reaction.

    PubMed

    Wang, Xiquan; Gong, Xiaokang; Zhang, Qiuxia; Du, Haijuan

    2013-12-01

    The Direct Pink 12B dye was treated by iron-carbon micro-electrolysis (ICME) and Fenton oxidation. The degradation pathway of Direct Pink 12B dye was inferred by ultraviolet visible (UV-Vis), infrared absorption spectrum (IR) and high performance liquid chromatography-mass spectrometry (HPLC-MS). The major reason of decolorization was that the conjugate structure was disrupted in the iron-carbon micro-electrolysis (ICME) process. However, the dye was not degraded completely because benzene rings and naphthalene rings were not broken. In the Fenton oxidation process, the azo bond groups surrounded by higher electron cloud density were first attacked by hydroxyl radicals to decolorize the dye molecule. Finally benzene rings and naphthalene rings were mineralized to H2O and CO2 under the oxidation of hydroxyl radicals.

  10. Role of lithium borosilicate glass in the decomposition of MgTiO{sub 3}-based dielectric ceramic during sintering

    SciTech Connect

    Shin, Hee-Kyun; Shin, Hyunho . E-mail: hshin@kangnung.ac.kr; Jung, Hyun Suk; Cho, Seo-Yong; Kim, Jeong-Ryeol; Hong, Kug Sun

    2006-06-15

    The decomposition behaviour of 0.9MgTiO{sub 3}-0.1CaTiO{sub 3} dielectric ceramic during a liquid phase sintering by lithium borosilicate (LBS) glass was studied. The decompositions of MgTiO{sub 3} into MgTi{sub 2}O{sub 5} and Mg{sub 2}TiO{sub 4} were apparent during the sintering although the reactions are thermodynamically unfavourable in glass-free compositions. The role of the LBS glass in favouring the decomposition reaction was investigated in terms of the thermodynamic activity of the reaction product in the glass. The decomposition reactions were not necessarily harmful because of the high dielectric performance of the decomposition products, MgTi{sub 2}O{sub 5} (17.4 permittivity; 47,000 GHz quality factor) and Mg{sub 2}TiO{sub 4} (14.4 and 55,000 GHz, respectively)

  11. Vacuum Compatibility of Laser-Sintered Metals

    NASA Astrophysics Data System (ADS)

    Rivera, W. F.; Romero-Talamas, C. A.; Bates, E. M.; Birmingham, W. J.; Quinley, M.; Woodruff, S.; Stuber, J. E.; Sieck, P. E.; Melnik, P. A.

    2016-10-01

    We present the design and results of a mass spectrometry system used to assess vacuum compatibility of selective laser-sintered parts. The parts are disks with a thickness of 0.20 cm and a diameter of 8.25 cm, and are made of aluminum, stainless steel, inconel, and titanium. From preliminary results, titanium had the lowest partial pressure for hydrogen. Outgassing from laser-sintered parts is compared against parts with similar surface area that are manufactured with traditional methods. Outgassing is also measured while the part is heated, emulating the conditions at the edge of high temperature plasma confinement chambers. Each part is placed on a heated container that can vary in temperature inside the mass spectrometer's vacuum chamber. The partial pressures of elements up to 200 atomic mass units are analyzed to obtain outgassing data from each sample. This work supported under DOE SBIR Grant DE SC0011858.

  12. Development of fluidized bed cement sintering technology

    SciTech Connect

    Mukai, Katsuji

    1994-12-31

    In the new system presented in this paper, the cement clinker is sintered, not in a rotary kiln, but in two different furnaces: a spouted bed kiln and a fluidized bed kiln. The heat generated in the process of cooling the cement clinker is recovered by a fluidized bed cooler and a packed bed cooler, which are more efficient than the conventional coolers. Compared with the rotary kiln system, the new technology significantly reduces NO{sub x} emissions, appreciably cuts energy consumption, and reduces CO{sub 2} emissions as well. Thus, the new system is an efficient cement sintering system that is friendly to the global environment. In this paper, we describe this new technology as one of the applied technologies at an industrial level that is being developed in the Clean Coal Technology Project, and we present the results from test operations at our pilot plant.

  13. Enhanced dielectric constant and relaxor behavior realized by dual stage sintering of Sr0.5Ba0.5Nb2O6

    NASA Astrophysics Data System (ADS)

    Rathore, Satyapal S.; Vitta, Satish

    2014-04-01

    The relaxor ferroelectric compound, Sr0.5Ba0.5Nb2O6 (SBN50) was synthesized by solid state reaction followed by sintering under two different conditions: single and dual stage sintering. The impact of sintering process on structural and dielectric properties has been studied in detail using X-ray diffraction, scanning electron microscopy and broadband dielectric spectroscopy. The crystal structure determined by performing Rietveld refinement of X-ray diffractogram was found to be identical in both cases. SBN50 crystallizes in the ferroelectric tetragonal tungsten bronze, P4bm structure. It was observed that uniform grain growth can be controlled by dual stage sintering and relatively narrow distribution of grains can be achieved with an average grain size of ˜15 μm. The dielectric studies show that SBN50 exhibits a relaxor ferroelectric behavior with the transformation taking place at ˜ 380 K due to formation of polar nano regions. Although both single and dual stage sintered SBN50 exhibits relaxor behaviour, the maximum dielectric constant of dual stage sintered SBN50 is found to be 1550 compare to 1440 for single stage sintering.

  14. Direct measurements of the total rate constant of the reaction NCN + H and implications for the product branching ratio and the enthalpy of formation of NCN.

    PubMed

    Fassheber, Nancy; Dammeier, Johannes; Friedrichs, Gernot

    2014-06-21

    The overall rate constant of the reaction (2), NCN + H, which plays a key role in prompt-NO formation in flames, has been directly measured at temperatures 962 K < T < 2425 K behind shock waves. NCN radicals and H atoms were generated by the thermal decomposition of NCN3 and C2H5I, respectively. NCN concentration-time profiles were measured by sensitive narrow-line-width laser absorption at a wavelength of λ = 329.1302 nm. The obtained rate constants are best represented by the combination of two Arrhenius expressions, k2/(cm(3) mol(-1) s(-1)) = 3.49 × 10(14) exp(-33.3 kJ mol(-1)/RT) + 1.07 × 10(13) exp(+10.0 kJ mol(-1)/RT), with a small uncertainty of ±20% at T = 1600 K and ±30% at the upper and lower experimental temperature limits.The two Arrhenius terms basically can be attributed to the contributions of reaction channel (2a) yielding CH + N2 and channel (2b) yielding HCN + N as the products. A more refined analysis taking into account experimental and theoretical literature data provided a consistent rate constant set for k2a, its reverse reaction k1a (CH + N2 → NCN + H), k2b as well as a value for the controversial enthalpy of formation of NCN, ΔfH = 450 kJ mol(-1). The analysis verifies the expected strong temperature dependence of the branching fraction ϕ = k2b/k2 with reaction channel (2b) dominating at the experimental high-temperature limit. In contrast, reaction (2a) dominates at the low-temperature limit with a possible minor contribution of the HNCN forming recombination channel (2d) at T < 1150 K.

  15. Sintering and ripening resistant noble metal nanostructures

    DOEpatents

    van Swol, Frank B; Song, Yujiang; Shelnutt, John A; Miller, James E; Challa, Sivakumar R

    2013-09-24

    Durable porous metal nanostructures comprising thin metal nanosheets that are metastable under some conditions that commonly produce rapid reduction in surface area due to sintering and/or Ostwald ripening. The invention further comprises the method for making such durable porous metal nanostructures. Durable, high-surface area nanostructures result from the formation of persistent durable holes or pores in metal nanosheets formed from dendritic nanosheets.

  16. Rapid Sintering of Nano-Diamond Compacts

    SciTech Connect

    Osipov, A.; Nauyoks, S; Zerda, T; Zaporozhets, O

    2009-01-01

    Diamond compacts were sintered from nano-size diamond crystals at high pressure, 8 GPa, and temperature above 1500 degrees C for very short times ranging from 5 to 11 s. Structure and mechanical properties of the compacts have been characterized. Although we have not completely avoided graphitization of diamonds, the amount of graphite produced was low, less than 2%, and despite relatively high porosity, the compacts were characterized by high hardness, bulk and Young moduli.

  17. Sintering of viscous droplets under surface tension

    PubMed Central

    Vasseur, Jérémie; Llewellin, Edward W.; Schauroth, Jenny; Dobson, Katherine J.; Scheu, Bettina; Dingwell, Donald B.

    2016-01-01

    We conduct experiments to investigate the sintering of high-viscosity liquid droplets. Free-standing cylinders of spherical glass beads are heated above their glass transition temperature, causing them to densify under surface tension. We determine the evolving volume of the bead pack at high spatial and temporal resolution. We use these data to test a range of existing models. We extend the models to account for the time-dependent droplet viscosity that results from non-isothermal conditions, and to account for non-zero final porosity. We also present a method to account for the initial distribution of radii of the pores interstitial to the liquid spheres, which allows the models to be used with no fitting parameters. We find a good agreement between the models and the data for times less than the capillary relaxation timescale. For longer times, we find an increasing discrepancy between the data and the model as the Darcy outgassing time-scale approaches the sintering timescale. We conclude that the decreasing permeability of the sintering system inhibits late-stage densification. Finally, we determine the residual, trapped gas volume fraction at equilibrium using X-ray computed tomography and compare this with theoretical values for the critical gas volume fraction in systems of overlapping spheres. PMID:27274687

  18. Sintering of viscous droplets under surface tension

    NASA Astrophysics Data System (ADS)

    Wadsworth, Fabian B.; Vasseur, Jérémie; Llewellin, Edward W.; Schauroth, Jenny; Dobson, Katherine J.; Scheu, Bettina; Dingwell, Donald B.

    2016-04-01

    We conduct experiments to investigate the sintering of high-viscosity liquid droplets. Free-standing cylinders of spherical glass beads are heated above their glass transition temperature, causing them to densify under surface tension. We determine the evolving volume of the bead pack at high spatial and temporal resolution. We use these data to test a range of existing models. We extend the models to account for the time-dependent droplet viscosity that results from non-isothermal conditions, and to account for non-zero final porosity. We also present a method to account for the initial distribution of radii of the pores interstitial to the liquid spheres, which allows the models to be used with no fitting parameters. We find a good agreement between the models and the data for times less than the capillary relaxation timescale. For longer times, we find an increasing discrepancy between the data and the model as the Darcy outgassing time-scale approaches the sintering timescale. We conclude that the decreasing permeability of the sintering system inhibits late-stage densification. Finally, we determine the residual, trapped gas volume fraction at equilibrium using X-ray computed tomography and compare this with theoretical values for the critical gas volume fraction in systems of overlapping spheres.

  19. Liquid phase sintered compacts in space

    NASA Technical Reports Server (NTRS)

    Mookherji, T. K.; Mcanelly, W. B.

    1974-01-01

    A model that will explain the effect of gravity on liquid phase sintering was developed. Wetting characteristics and density segregation which are the two important phenomena in liquid phase sintering are considered in the model development. Experiments were conducted on some selected material combinations to study the gravity effects on liquid phase sintering, and to verify the validity of the model. It is concluded that: (1) The surface tension forces acting on solid particles in a one-g environment are not appreciably different from those anticipated in a 0.00001g/g sub 0 (or lower) environment. (2) The capillary forces are dependent on the contact angle, the quantity of the liquid phase, and the distance between solid particles. (3) The pores (i.e., bubbles) do not appear to be driven to the surface by gravity-produced buoyancy forces. (4) The length of time to produce the same degree of settling in a low-gravity environment will be increased significantly. (5) A low gravity environment would appear to offer a unique means of satisfactorily infiltrating a larger and/or complex shaped compact.

  20. Ceramic components manufacturing by selective laser sintering

    NASA Astrophysics Data System (ADS)

    Bertrand, Ph.; Bayle, F.; Combe, C.; Goeuriot, P.; Smurov, I.

    2007-12-01

    In the present paper, technology of selective laser sintering/melting is applied to manufacture net shaped objects from pure yttria-zirconia powders. Experiments are carried out on Phenix Systems PM100 machine with 50 W fibre laser. Powder is spread by a roller over the surface of 100 mm diameter alumina cylinder. Design of experiments is applied to identify influent process parameters (powder characteristics, powder layering and laser manufacturing strategy) to obtain high-quality ceramic components (density and micro-structure). The influence of the yttria-zirconia particle size and morphology onto powder layering process is analysed. The influence of the powder layer thickness on laser sintering/melting is studied for different laser beam velocity V ( V = 1250-2000 mm/s), defocalisation (-6 to 12 mm), distance between two neighbour melted lines (so-called "vectors") (20-40 μm), vector length and temperature in the furnace. The powder bed density before laser sintering/melting also has significant influence on the manufactured samples density. Different manufacturing strategies are applied and compared: (a) different laser beam scanning paths to fill the sliced surfaces of the manufactured object, (b) variation of vector length (c) different strategies of powder layering, (d) temperature in the furnace and (e) post heat treatment in conventional furnace. Performance and limitations of different strategies are analysed applying the following criteria: geometrical accuracy of the manufactured samples, porosity. The process stability is proved by fabrication of 1 cm 3 volume cube.