Sample records for crystal size effect
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NASA Astrophysics Data System (ADS)
Zhang, Boyu; Wang, Jun; Yaer, Xinba; Huo, Zhenzhen; Wu, Yin; Li, Yan; Miao, Lei; Liu, Chengyan; Zou, Tao; Ma, Wen
2015-07-01
Effect of crystal size distribution on thermoelectric performance of Lanthanum-doped strontium titanate (La-SrTiO3) ceramics are investigated in this study. Thermoelectric performance measurement, coupled with microstructure studies, shows that the electrical conductivity strongly depends on the crystal size, potential barrier on the grain boundary and porosity. Meantime, because the average potential barriers height are increased along with the reduction of crystal size, the Seebeck coefficients are increased by energy filtering effect at the large number of grain boundaries. As a result, by controlling of crystal size distribution, ZT value of La-SrTiO3 is improved.
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Bridgman growth of large-aperture yttrium calcium oxyborate crystal
DOE Office of Scientific and Technical Information (OSTI.GOV)
Wu, Anhua, E-mail: wuanhua@mail.sic.ac.cn; Jiang, Linwen; Qian, Guoxing
2012-09-15
Highlights: ► YCOB is a novel non-linear optical crystal possessing good thermal, mechanical and nonlinear optical properties. ► Large size crystal growth is key technology question for YCOB crystal. ► YCOB crystals 3 in. in diameter were grown with modified vertical Bridgman method. ► It is a more effective growth method to obtain large size and high quality YCOB crystal. -- Abstract: Large-aperture yttrium calcium oxyborate YCa{sub 4}O(BO{sub 3}){sub 3} (YCOB) crystals with 3 in. in diameter were grown with modified vertical Bridgman method, and the large crystal plate (63 mm × 68 mm × 20 mm) was harvested formore » high-average power frequency conversion system. The crack, facet growth and spiral growth can be effectively controlled in the as-grown crystal, and Bridgman method displays more effective in obtain large size and high quality YCOB crystal plate than Czochralski technique.« less
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Influences of powder granularity on crystallizing characteristics in mica-contained glass ceramic
NASA Astrophysics Data System (ADS)
Xu, L. N.; Kong, D. Y.; Tian, Q. B.; Lv, Z. J.
2017-09-01
A machinable mica-contained glass ceramic in the SiO2-Al2O3-MgO-F glassy system was prepared by ball milling and hot pressed sintering. Three kinds of powder sizes of base glass were chosen and the effects of the glass powder sizes on the crystallization were explored by x-ray diffraction and scanning electron microscopy techniques. The results indicate that mica crystal as a major phase and KFeSi2O6 and mullite as minor phases are crystallized. Applying pressure at 670°C has little influences on the types of crystal precipitated and the preferential growth of crystal. The powder sizes, however, have obvious effects on the morphology of precipitated mica crystals. In the glass sample with a powder size of d50=16.4 µm, the plate-shaped mica phase is precipitated. As the powder size decrease to 9.9 µm and 3.3 µm, however, the particle-shaped mica is formed instead of the plate-shaped crystals.
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Kile, D.E.; Eberl, D.D.
2003-01-01
Crystal growth experiments were conducted using potassium alum and calcite crystals in aqueous solution under both non-stirred and stirred conditions to elucidate the mechanism for size-dependent (proportionate) and size-independent (constant) crystal growth. Growth by these two laws can be distinguished from each other because the relative size difference among crystals is maintained during proportionate growth, leading to a constant crystal size variance (??2) for a crystal size distribution (CSD) as the mean size increases. The absolute size difference among crystals is maintained during constant growth, resulting in a decrease in size variance. Results of these experiments show that for centimeter-sized alum crystals, proportionate growth occurs in stirred systems, whereas constant growth occurs in non-stirred systems. Accordingly, the mechanism for proportionate growth is hypothesized to be related to the supply of reactants to the crystal surface by advection, whereas constant growth is related to supply by diffusion. Paradoxically, micrometer-sized calcite crystals showed proportionate growth both in stirred and in non-stirred systems. Such growth presumably results from the effects of convection and Brownian motion, which promote an advective environment and hence proportionate growth for minute crystals in non-stirred systems, thereby indicating the importance of solution velocity relative to crystal size. Calcite crystals grown in gels, where fluid motion was minimized, showed evidence for constant, diffusion-controlled growth. Additional investigations of CSDs of naturally occurring crystals indicate that proportionate growth is by far the most common growth law, thereby suggesting that advection, rather than diffusion, is the dominant process for supplying reactants to crystal surfaces.
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New developments on size-dependent growth applied to the crystallization of sucrose
NASA Astrophysics Data System (ADS)
Martins, P. M.; Rocha, F.
2007-12-01
The effect of crystal size on the growth rate of sucrose (C 12H 22O 11) at 40 °C is investigated from a theoretical and an experimental point of view. Based on new perspectives resulting from the recently introduced spiral nucleation model [P.M. Martins, F. Rocha, Surf. Sci. 601 (2007) 3400], crystal growth rates are expressed in terms of mass deposition per time and crystal volume units. This alternative definition is demonstrated to be size-independent over the considered supersaturation range. The conventional overall growth rate expressed per surface area units is found to be linearly dependent on crystal size. The advantages of the "volumetric" growth rate concept are discussed. Sucrose dissolution rates were measured under reciprocal conditions of the growth experiments in order to investigate the two-way effect of crystal size on mass transfer rates and on the integration kinetics. Both effects are adequately described by combining a well-established diffusion-integration model and the spiral nucleation mechanism.
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Effect of hydrazine based deproteination protocol on bone mineral crystal structure.
Karampas, I A; Orkoula, M G; Kontoyannis, C G
2012-05-01
In several bone deproteination protocols the chemical agent used for protein cleavage is hydrazine. The effect of hydrazine deproteination method on the crystal size and crystallinity of the bone mineral was studied. Bovine bones were subjected to this protocol and the crystal size and crystallinity of the remaining bone mineral were determined by X-ray Diffraction (XRD), by measuring the width at the half of the maximum intensity of the (002) reflection. It was found that hydrazine deproteination induces noteworthy increase of crystal size and crystallinity. The effect was enhanced by increasing hydrazine temperature from 25 to 55°C. Furthermore, infrared spectroscopy revealed that hydrazine facilitates the removal of carbonate and acid phosphate ions from bone mineral. It is proposed that the mechanism of modification of crystal size and crystallinity lies on the removal of these ions thus, resulting in crystal re-organization.
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NASA Technical Reports Server (NTRS)
Judge, Russell A.; Snell, Edward H.
1999-01-01
Part of the challenge of macromolecular crystal growth for structure determination is obtaining an appropriate number of crystals with a crystal volume suitable for X-ray analysis. In this respect an understanding of the effect of solution conditions on macromolecule nucleation rates is advantageous. This study investigated the effects of solution conditions on the nucleation rate and final crystal size of two crystal systems; tetragonal lysozyme and glucose isomerase. Batch crystallization plates were prepared at given solution concentration and incubated at set temperatures over one week. The number of crystals per well with their size and axial ratios were recorded and correlated with solution conditions. Duplicate experiments indicate the reproducibility of the technique. Results for each system showing the effect of supersaturation, incubation temperature and solution pH on nucleation rates will be presented and discussed. In the case of lysozyme, having optimized solution conditions to produce an appropriate number of crystals of a suitable size, a batch of crystals were prepared under exactly the same conditions. Fifty of these crystals were analyzed by x-ray techniques. The results indicate that even under the same crystallization conditions, a marked variation in crystal properties exists.
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NASA Astrophysics Data System (ADS)
Morikawa, Satoshi; Satake, Yuji; Takashiri, Masayuki
2018-06-01
The effects of crystal orientation and grain size on the thermoelectric properties of Bi2Te3 thin films were investigated by conducting experimental and theoretical analyses. To vary the crystal orientation and grain size, we performed oblique deposition, followed by thermal annealing treatment. The crystal orientation decreased as the oblique angle was increased, while the grain size was not changed significantly. The thermoelectric properties were measured at room temperature. A theoretical analysis was performed using a first principles method based on density functional theory. Then the semi-classical Boltzmann transport equation was used in the relaxation time approximation, with the effect of grain size included. Furthermore, the effect of crystal orientation was included in the calculation based on a simple semi-experimental model. A maximum power factor of 11.6 µW/(cm·K2) was obtained at an oblique angle of 40°. The calculated thermoelectric properties were in very good agreement with the experimentally measured values.
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NASA Astrophysics Data System (ADS)
Bondarenko, Yu. A.; Echin, A. B.; Surova, V. A.; Kolodyazhnyi, M. Yu.
2017-05-01
The effect of the conditions of directed crystallization (the temperature gradient and the crystallization rate) on the dendrite spacing, on the size of the particles of the hardening γ'-phase in the arms and arm spaces of the dendrites, on the volume fraction and size of the pores, on the size of the particles of the eutectic γ/γ'-phase, and on the features of dendritic segregation in a single-crystal castable refractory alloy is studied.
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NASA Technical Reports Server (NTRS)
Xie, Yu; Minnis, Patrick; Hu, Yong X.; Kattawar, George W.; Yang, Ping
2008-01-01
Spherical or spheroidal air bubbles are generally trapped in the formation of rapidly growing ice crystals. In this study the single-scattering properties of inhomogeneous ice crystals containing air bubbles are investigated. Specifically, a computational model based on an improved geometric-optics method (IGOM) has been developed to simulate the scattering of light by randomly oriented hexagonal ice crystals containing spherical or spheroidal air bubbles. A combination of the ray-tracing technique and the Monte Carlo method is used. The effect of the air bubbles within ice crystals is to smooth the phase functions, diminish the 22deg and 46deg halo peaks, and substantially reduce the backscatter relative to bubble-free particles. These features vary with the number, sizes, locations and shapes of the air bubbles within ice crystals. Moreover, the asymmetry factors of inhomogeneous ice crystals decrease as the volume of air bubbles increases. Cloud reflectance lookup tables were generated at wavelengths 0.65 m and 2.13 m with different air-bubble conditions to examine the impact of the bubbles on retrieving ice cloud optical thickness and effective particle size. The reflectances simulated for inhomogeneous ice crystals are slightly larger than those computed for homogenous ice crystals at a wavelength of 0.65 microns. Thus, the retrieved cloud optical thicknesses are reduced by employing inhomogeneous ice cloud models. At a wavelength of 2.13 microns, including air bubbles in ice cloud models may also increase the reflectance. This effect implies that the retrieved effective particle sizes for inhomogeneous ice crystals are larger than those retrieved for homogeneous ice crystals, particularly, in the case of large air bubbles.
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The Effect of Solution Conditions on the Nucleation Kinetics of Tetragonal Lysozyme Crystals
NASA Technical Reports Server (NTRS)
Judge, Russell A.; Baird, James K.; Pusey, Marc L.
1998-01-01
An understanding of protein crystal nucleation rates and the effect of solution conditions upon them, is fundamental to the preparation of protein crystals of the desired size and shape for X-ray diffraction analysis. The ability to predict the effect of supersaturation, temperature, pH and precipitant concentration on the number and size of crystals formed is of great benefit in the pursuit of protein structure analysis. In this study we experimentally examine the effect of supersaturation, temperature, pH and sodium chloride concentration on the nucleation rate of tetragonal chicken egg white lysozyme crystals. In order to do this batch crystallization plates were prepared at given solution concentrations and incubated at three different temperatures over the period of one week. The number of crystals per well with their size and dimensions were recorded and correlated against solution conditions. Duplicate experiments indicate the reproducibility of the technique. Although it is well known that crystal numbers increase with increasing supersaturation, large changes in crystal number were also correlated against solution conditions of temperature, pH and salt concentration over the same supersaturation ranges. Analysis of these results enhance our understanding of the effect of solution conditions such as the dramatic effect that small changes in charge and ionic strength can have on the number of tetragonal lysozyme crystals that form and grow in solution.
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NASA Astrophysics Data System (ADS)
Lenka, Maheswata; Sarkar, Debasis
2018-03-01
This work investigates the effect of internal seeding and an initial cooling/heating cycle on the final crystal size distribution (CSD) during a combined cooling/antisolvent crystallization of L-asparagine monohydrate from it's aqueous solution using isopropyl-alcohol as antisolvent. Internal seeds were generated by one-pot addition of various amounts of antisolvent to the crystallizer. It was then followed by a cooling/heating cycle to dissolve the fines produced and thus obtain a suitable initial seed. A combined cooling/antisolvent crystallization was then followed by employing a linear cooling profile with simultaneous addition of antisolvent with a constant mass flow rate to promote the growth of the internally generated seeds. The amount of initial antisolvent influences the characteristics of the internal seeds generated and the effect of initial amount of antisolvent on the final CSD is investigated. It was found that the introduction of a single cooling/heating cycle significantly improves the reproducibility of final CSD as well as the mean size. Overall, the study indicates that the application of internal seeding with a single cooling/heating cycle for fines dissolution is an effective technique to tailor crystal size distribution.
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Iyer, Sneha R; Gogate, Parag R
2017-01-01
The current work investigates the application of low intensity ultrasonic irradiation for improving the cooling crystallization of Mefenamic Acid for the first time. The crystal shape and size has been analyzed with the help of optical microscope and image analysis software respectively. The effect of ultrasonic irradiation on crystal size, particle size distribution (PSD) and yield has been investigated, also establishing the comparison with conventional approach. It has been observed that application of ultrasound not only enhances the yield but also reduces the induction time for crystallization as compared to conventional cooling crystallization technique. In the presence of ultrasound, the maximum yield was obtained at optimum conditions of power dissipation of 30W and ultrasonic irradiation time of 10min. The yield was further improved by application of ultrasound in cycles where the formed crystals are allowed to grow in the absence of ultrasonic irradiation. It was also observed that the desired crystal morphology was obtained for the ultrasound assisted crystallization. The conventionally obtained needle shaped crystals transformed into plate shaped crystals for the ultrasound assisted crystallization. The particle size distribution was analyzed using statistical means on the basis of skewness and kurtosis values. It was observed that the skewness and excess kurtosis value for ultrasound assisted crystallization was significantly lower as compared to the conventional approach. XRD analysis also revealed better crystal properties for the processed mefenamic acid using ultrasound assisted approach. The overall process intensification benefits of mefenamic acid crystallization using the ultrasound assisted approach were reduced particle size, increase in the yield and uniform PSD coupled with desired morphology. Copyright © 2016 Elsevier B.V. All rights reserved.
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Nanoscale effects of silica particle supports on the formation and properties of TiO2 nanocatalysts
NASA Astrophysics Data System (ADS)
Li, Aize; Jin, Yuhui; Muggli, Darrin; Pierce, David T.; Aranwela, Hemantha; Marasinghe, Gaya K.; Knutson, Theodore; Brockman, Greg; Zhao, Julia Xiaojun
2013-06-01
Small TiO2 crystals in the anatase phase are in high demand as photocatalysts. Stable TiO2 crystals in the anatase phase were obtained using a silica nanoparticle as a support. The focus of this study was to investigate the nanoscale effect of the silica support on the formation and properties of small anatase crystals. The experiments were carried out using powder X-ray diffraction, differential thermal analysis, transmission electron microscopy, and energy dispersion spectroscopy. The results showed that the size of the silica support played a crucial role in crystallization of TiO2 and regulation of TiO2 properties, including phase transition, crystal size, thermodynamic property and catalytic activity. A nanoscale curvature model of the spherical silica support was proposed to explain these size effects. Finally, the developed TiO2 catalysts were applied to the oxidation of methanol using a high-throughput photochemical reactor. The size effect of the silica supports on the TiO2 catalytic efficiency was demonstrated using this system.
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The effect of crystal size on tunneling phenomena in luminescent nanodosimetric materials
NASA Astrophysics Data System (ADS)
Pagonis, Vasilis; Bernier, Shannon; Vieira, Francisco Marques dos Santos; Steele, Shane
2017-12-01
The study of luminescence signals from nanodosimetric materials is an active research area, due to the many possible practical applications of such materials. In several of these materials it has been shown that quantum tunneling is a dominant mechanism for recombination processes associated with luminescence phenomena. This paper examines the effect of crystal size on quantum tunneling phenomena in nanocrystals, based on the assumption of a random distribution of electrons and positive ions. The behavior of such random distributions is determined by three characteristic lengths: the radius of the crystal R, the tunneling length a, and the initial average distance 〈d〉 between electrons and positive ions (which is directly related to the density of charges in the material). Two different cases are examined, depending on the relative concentrations of electrons and ions. In the first case the concentration of electrons is assumed to be much smaller than the concentration of positive ions. Examination of a previously derived analytical equation demonstrates two different types of crystal size effects. When the tunneling length a is much smaller than both R and 〈d〉, the analytical equations show that smaller crystals exhibit a faster tunneling recombination rate. However, when the tunneling length a is of the same order of magnitude as both R and 〈d〉, the opposite effect is observed, with smaller crystals exhibiting a slower tunneling recombination rate. As the crystal size increases, the rate of tunneling in both cases reaches the limit expected for bulk materials. In the second case we examine the situation where the concentrations of electrons and positive ions are equal at all times. In this situation there is no analytical equation available to describe the process, and the crystal size effects are simulated by using Monte Carlo (MC) techniques. The two opposite behaviors as a function of the crystal size are also observed in these MC simulations. The effect of sample temperature is also studied by extending the MC simulations to include thermal characteristics of the defects. The relevance of the simulated results for luminescence dosimetry is discussed.
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On geological interpretations of crystal size distributions: Constant vs. proportionate growth
Eberl, D.D.; Kile, D.E.; Drits, V.A.
2002-01-01
Geological interpretations of crystal size distributions (CSDs) depend on understanding the crystal growth laws that generated the distributions. Most descriptions of crystal growth, including a population-balance modeling equation that is widely used in petrology, assume that crystal growth rates at any particular time are identical for all crystals, and, therefore, independent of crystal size. This type of growth under constant conditions can be modeled by adding a constant length to the diameter of each crystal for each time step. This growth equation is unlikely to be correct for most mineral systems because it neither generates nor maintains the shapes of lognormal CSDs, which are among the most common types of CSDs observed in rocks. In an alternative approach, size-dependent (proportionate) growth is modeled approximately by multiplying the size of each crystal by a factor, an operation that maintains CSD shape and variance, and which is in accord with calcite growth experiments. The latter growth law can be obtained during supply controlled growth using a modified version of the Law of Proportionate Effect (LPE), an equation that simulates the reaction path followed by a CSD shape as mean size increases.
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Influence of computational domain size on the pattern formation of the phase field crystals
NASA Astrophysics Data System (ADS)
Starodumov, Ilya; Galenko, Peter; Alexandrov, Dmitri; Kropotin, Nikolai
2017-04-01
Modeling of crystallization process by the phase field crystal method (PFC) represents one of the important directions of modern computational materials science. This method makes it possible to research the formation of stable or metastable crystal structures. In this paper, we study the effect of computational domain size on the crystal pattern formation obtained as a result of computer simulation by the PFC method. In the current report, we show that if the size of a computational domain is changed, the result of modeling may be a structure in metastable phase instead of pure stable state. The authors present a possible theoretical justification for the observed effect and provide explanations on the possible modification of the PFC method to account for this phenomenon.
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Size effects on negative thermal expansion in cubic ScF{sub 3}
DOE Office of Scientific and Technical Information (OSTI.GOV)
Yang, C.; Guo, X. G.; Zhang, K.
2016-07-11
Scandium trifluoride (ScF{sub 3}), adopting a cubic ReO{sub 3}-type structure at ambient pressure, undergoes a pronounced negative thermal expansion (NTE) over a wide range of temperatures (10 K–1100 K). Here, we report the size effects on the NTE properties of ScF{sub 3}. The magnitude of NTE is reduced with diminishing the crystal size. As revealed by the specific heat measurement, the low-energy phonon vibrations which account for the NTE behavior are stiffened as the crystal size decreases. With decreasing the crystal size, the peaks in high-energy X-ray pair distribution function (PDF) become broad, which cannot be illuminated by local symmetry breaking. Instead,more » the broadened PDF peaks are strongly indicative of enhanced atomic displacements which are suggested to be responsible for the stiffening of NTE-related lattice vibrations. The present study suggests that the NTE properties of ReO{sub 3}-type and other open-framework materials can be effectively adjusted by controlling the crystal size.« less
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Coupled crystal orientation-size effects on the strength of nano crystals
Yuan, Rui; Beyerlein, Irene J.; Zhou, Caizhi
2016-01-01
We study the combined effects of grain size and texture on the strength of nanocrystalline copper (Cu) and nickel (Ni) using a crystal-plasticity based mechanics model. Within the model, slip occurs in discrete slip events exclusively by individual dislocations emitted statistically from the grain boundaries. We show that a Hall-Petch relationship emerges in both initially texture and non-textured materials and our values are in agreement with experimental measurements from numerous studies. We find that the Hall-Petch slope increases with texture strength, indicating that preferred orientations intensify the enhancements in strength that accompany grain size reductions. These findings reveal that texture is too influential to be neglected when analyzing and engineering grain size effects for increasing nanomaterial strength. PMID:27185364
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NASA Astrophysics Data System (ADS)
Lee, Sooyun; Lee, Choul-Ho; Kim, Woo-Sik
2017-07-01
The influence of the fluid dynamic motions of a periodic Taylor vortex and random turbulent eddy on the anti-solvent crystallization of L-threonine was investigated. The Taylor vortex flow and random turbulent eddy flow were generated by the inner cylinder rotation in a Couette-Taylor (CT) crystallizer and the impeller agitation in a mixed-suspension mixed product removal (MSMPR) crystallizer, respectively. Furthermore, the circumferentially sinusoidal fluctuation of a Taylor vortex was induced in an elliptical Couette-Taylor (ECT) crystallizer . The periodic Taylor vortex flows in the CT and ECT crystallizers resulted in a smaller crystal size and higher crystal recovery ratio of L-threonine than the random turbulent flow in the MSMPR crystallizer due to induction of a higher supersaturation, resulting in a higher nucleation in the CT and ECT crystallizers than in the MSMPR crystallizer. Thus, the crystal size was reduced and the crystal recovery ratio enhanced when increasing the rotation/agitation speed and feed flow rate in the CT, ECT, and MSMPR crystallizers. When increasing the temperature, the crystal size and crystal recovery ratio were both increased due an enhanced mass transfer for crystal growth. The crystal morphology changes according to the fluid dynamic motion with various crystallization conditions were well correlated in terms of the supersaturation.
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Albasan, Hasan; Lulich, Jody P; Osborne, Carl A; Lekcharoensuk, Chalermpol; Ulrich, Lisa K; Carpenter, Kathleen A
2003-01-15
To determine effects of storage temperature and time on pH and specific gravity of and number and size of crystals in urine samples from dogs and cats. Randomized complete block design. 31 dogs and 8 cats. Aliquots of each urine sample were analyzed within 60 minutes of collection or after storage at room or refrigeration temperatures (20 vs 6 degrees C [68 vs 43 degrees F]) for 6 or 24 hours. Crystals formed in samples from 11 of 39 (28%) animals. Calcium oxalate (CaOx) crystals formed in vitro in samples from 1 cat and 8 dogs. Magnesium ammonium phosphate (MAP) crystals formed in vitro in samples from 2 dogs. Compared with aliquots stored at room temperature, refrigeration increased the number and size of crystals that formed in vitro; however, the increase in number and size of MAP crystals in stored urine samples was not significant. Increased storage time and decreased storage temperature were associated with a significant increase in number of CaOx crystals formed. Greater numbers of crystals formed in urine aliquots stored for 24 hours than in aliquots stored for 6 hours. Storage time and temperature did not have a significant effect on pH or specific gravity. Urine samples should be analyzed within 60 minutes of collection to minimize temperature- and time-dependent effects on in vitro crystal formation. Presence of crystals observed in stored samples should be validated by reevaluation of fresh urine.
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Crystallization of calcium oxalate in minimally diluted urine
NASA Astrophysics Data System (ADS)
Bretherton, T.; Rodgers, A.
1998-09-01
Crystallization of calcium oxalate was studied in minimally diluted (92%) urine using a mixed suspension mixed product crystallizer in series with a Malvern particle sizer. The crystallization was initiated by constant flow of aqueous sodium oxalate and urine into the reaction vessel via two independent feed lines. Because the Malvern cell was in series with the reaction vessel, noninvasive measurement of particle sizes could be effected. In addition, aliquots of the mixed suspension were withdrawn and transferred to a Coulter counter for crystal counting and sizing. Steady-state particle size distributions were used to determine nucleation and growth kinetics while scanning electron microscopy was used to examine deposited crystals. Two sets of experiments were performed. In the first, the effect of the concentration of the exogenous sodium oxalate was investigated while in the second, the effect of temperature was studied. Calcium oxalate nucleation and growth rates were found to be dependent on supersaturation levels inside the crystallizer. However, while growth rate increased with increasing temperature, nucleation rates decreased. The favored phases were the trihydrate at 18°C, the dihydrate at 38° and the monohydrate at 58°C. The results of both experiments are in agreement with those obtained in other studies that have been conducted in synthetic and in maximally diluted urine and which have employed invasive crystal counting and sizing techniques. As such, the present study lends confidence to the models of urinary calcium oxalate crystallization processes which currently prevail in the literature.
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Dislocation, crystallite size distribution and lattice strain of magnesium oxide nanoparticles
NASA Astrophysics Data System (ADS)
Sutapa, I. W.; Wahid Wahab, Abdul; Taba, P.; Nafie, N. L.
2018-03-01
The oxide of magnesium nanoparticles synthesized using sol-gel method and analysis of the structural properties was conducted. The functional groups of nanoparticles has been analysed by Fourier Transform Infrared Spectroscopy (FT-IR). Dislocations, average size of crystal, strain, stress, the energy density of crystal, crystallite size distribution and morphologies of the crystals were determined based on X-ray diffraction profile analysis. The morphological of the crystal was analysed based on the image resulted from SEM analysis. The crystallite size distribution was calculated with the contention that the particle size has a normal logarithmic form. The most orientations of crystal were determined based on the textural crystal from diffraction data of X-ray diffraction profile analysis. FT-IR results showed the stretching vibration mode of the Mg-O-Mg in the range of 400.11-525 cm-1 as a broad band. The average size crystal of nanoparticles resulted is 9.21 mm with dislocation value of crystal is 0.012 nm-2. The strains, stress, the energy density of crystal are 1.5 x 10-4 37.31 MPa; 0.72 MPa respectively. The highest texture coefficient value of the crystal is 0.98. This result is supported by morphological analysis using SEM which shows most of the regular cubic-shaped crystals. The synthesis method is suitable for simple and cost-effective synthesis model of MgO nanoparticles.
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The Effect of Temperature and Solution pH on the Nucleation of Tetragonal Lysozyme Crystals
NASA Technical Reports Server (NTRS)
Judge, Russell A.; Jacobs, Randolph S.; Frazier, Tyralynn; Snell, Edward H.; Pusey, Marc L.
1999-01-01
Part of the challenge of macromolecular crystal growth for structure determination is obtaining crystals with a volume suitable for x-ray analysis. In this respect an understanding of the effect of solution conditions on macromolecule nucleation rates is advantageous. This study investigated the effects of supersaturation, temperature, and pH on the nucleation rate of tetragonal lysozyme crystals. Batch crystallization plates were prepared at given solution concentrations and incubated at set temperatures over 1 week. The number of crystals per well with their size and axial ratios were recorded and correlated with solution conditions. Crystal numbers were found to increase with increasing supersaturation and temperature. The most significant variable, however, was pH; crystal numbers changed by two orders of magnitude over the pH range 4.0-5.2. Crystal size also varied with solution conditions, with the largest crystals obtained at pH 5.2. Having optimized the crystallization conditions, we prepared a batch of crystals under the same initial conditions, and 50 of these crystals were analyzed by x-ray diffraction techniques. The results indicate that even under the same crystallization conditions, a marked variation in crystal properties exists.
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The deformation mechanisms and size effects of single-crystal magnesium
NASA Astrophysics Data System (ADS)
Byer, Cynthia M.
In this work, we seek to understand the deformation mechanisms and size effects of single-crystal magnesium at the micrometer scale through both microcompression experiments and finite element simulations. Microcompression experiments are conducted to investigate the impact of initial dislocation density and orientation on size effects. Micropillars are fabricated using a focused ion beam and tested in a Nanoindenter using a diamond fiat tip as a compression platen. Two different initial dislocation densities are examined for [0001] oriented micropillars. Our results demonstrate that decreasing the initial dislocation density results in an increased size effect in terms of increased strength and stochasticity. Microcompression along the [23¯14] axis results in much lower strengths than for [0001] oriented samples. Post-mortem analysis reveals basal slip in both [0001] and [23¯14] micropillars. The application of a stochastic probability model shows good agreement between theoretical predictions and experimental results for size effects with our values of initial dislocation density and micropillar dimensions. Size effects are then incorporated into a single-crystal plasticity model (modified from Zhang and Joshi [1]) implemented in ABAQUS/STANDARD as a user-material subroutine. The model successfully captures the phenomena typically associated with size effects of increasing stochasticity and strength with decreasing specimen size and also accounts for the changing trends resulting from variations in initial dislocation density that we observe in the experiments. Finally, finite element simulations are performed with the original (traditional, without size effects) crystal plasticity model [1] to investigate the relative activities of the deformation modes of single-crystal magnesium for varying degrees of misalignment in microcompression. The simulations reveal basal activity in all micropillars, even for perfectly aligned compression along the [0001] axis. Pyramidal < c + a > activity dominates until the misalignment increases to 2°, when basal slip takes over as the dominant mode. The stress-strain curves for the case of 0° misalignment agrees well with experimental curves, indicating that good alignment was achieved during the experiments. Through this investigation, we gain a better understanding of how to control the size effects, as well as the deformation mechanisms operating at the small scale in magnesium.
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Saw, M H; Hishamuddin, E; Chong, C L; Yeoh, C B; Lim, W H
2017-01-01
The effect of 0.1-0.7% (w/w) of polyglycerol esters (PGEmix-8) on palm oil crystallization was studied using focused beam reflectance measurement (FBRM) to analyze the in-line changes of crystal size distribution during the crystallization. FBRM results show that 0.1-0.5% (w/w) of PGEmix-8 did not significantly affect nucleation but slightly retarded crystal growth. The use of 0.7% (w/w) additive showed greater heterogeneous nucleation compared to those with lower dosages of additive. Crystal growth was also greatly reduced when using 0.7% (w/w) dosage. The morphological study indicated that the palm oil crystals were smaller and more even in size than when more additive was added. Isothermal crystallization studies using differential scanning calorimetry (DSC) showed increased inhibitory effects on palm oil crystal growth with increasing concentration of PGEmix-8. These results imply that PGEmix-8 is a nucleation enhancing and crystal growth retarding additive in palm oil crystallization at 0.7% (w/w) dosage. Copyright © 2016 The Author(s). Published by Elsevier Ltd.. All rights reserved.
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Pan, Bo; Shibutani, Yoji, E-mail: sibutani@mech.eng.osaka-u.ac.jp; Zhang, Xu
2015-07-07
Recent research has explained that the steeply increasing yield strength in metals depends on decreasing sample size. In this work, we derive a statistical physical model of the yield strength of finite single-crystal micro-pillars that depends on single-ended dislocation pile-up inside the micro-pillars. We show that this size effect can be explained almost completely by considering the stochastic lengths of the dislocation source and the dislocation pile-up length in the single-crystal micro-pillars. The Hall–Petch-type relation holds even in a microscale single-crystal, which is characterized by its dislocation source lengths. Our quantitative conclusions suggest that the number of dislocation sources andmore » pile-ups are significant factors for the size effect. They also indicate that starvation of dislocation sources is another reason for the size effect. Moreover, we investigated the explicit relationship between the stacking fault energy and the dislocation “pile-up” effect inside the sample: materials with low stacking fault energy exhibit an obvious dislocation pile-up effect. Our proposed physical model predicts a sample strength that agrees well with experimental data, and our model can give a more precise prediction than the current single arm source model, especially for materials with low stacking fault energy.« less
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Study on the temperature field of large-sized sapphire single crystal furnace
NASA Astrophysics Data System (ADS)
Zhai, J. P.; Jiang, J. W.; Liu, K. G.; Peng, X. B.; Jian, D. L.; Li, I. L.
2018-01-01
In this paper, the temperature field of large-sized (120kg, 200kg and 300kg grade) sapphire single crystal furnace was simulated. By keeping the crucible diameter ratio and the insulation system unchanged, the power consumption, axial and radial temperature gradient, solid-liquid surface shape, stress distribution and melt flow were studied. The simulation results showed that with the increase of the single crystal furnace size, the power consumption increased, the temperature field insulation effect became worse, the growth stress value increased and the stress concentration phenomenon occurred. To solve these problems, the middle and bottom insulation system should be enhanced during designing the large-sized sapphire single crystal furnace. The appropriate radial and axial temperature gradient was favorable to reduce the crystal stress and prevent the occurrence of cracking. Expanding the interface between the seed and crystal was propitious to avoid the stress accumulation phenomenon.
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Influence of mixing and ultrasound frequency on antisolvent crystallisation of sodium chloride.
Lee, Judy; Ashokkumar, Muthupandian; Kentish, Sandra E
2014-01-01
Ultrasound is known to promote nucleation of crystals and produce a narrower size distribution in a controlled and reproducible manner for the crystallisation process. Although there are various theories that suggest cavitation bubbles are responsible for sonocrystallisation, most studies use power ultrasonic horns that generate both intense shear and cavitation and this can mask the role that cavitation bubbles play. High frequency ultrasound from a plate transducer can be used to examine the effect of cavitation bubbles without the intense shear effect. This study reports the crystal size and morphology with various mixing speeds and ultrasound frequencies. The results show high frequency ultrasound produced sodium chloride crystals of similar size distribution as an ultrasonic horn. In addition, ultrasound generated sodium chloride crystals having a more symmetrical cubic structure compared to crystals produced by a high shear mixer. Copyright © 2013 Elsevier B.V. All rights reserved.
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Ni, Xuewen; Ke, Fan; Xiao, Man; Wu, Kao; Kuang, Ying; Corke, Harold; Jiang, Fatang
2016-11-01
Konjac glucomannan (KGM)-based aerogels were prepared using a combination of sol-gel and freeze-drying methods. Preparation conditions were chosen to control ice crystal growth and aerogel structure formation. The ice crystals formed during pre-freezing were observed by low temperature polarizing microscopy, and images of aerogel pores were obtained by scanning electron microscopy. The size of ice crystals were calculated and size distribution maps were drawn, and similarly for aerogel pores. Results showed that ice crystal growth and aerogel pore sizes may be controlled by varying pre-freezing temperatures, KGM concentration and glyceryl monostearate concentration. The impact of pre-freezing temperatures on ice crystal growth was explained as combining ice crystal growth rate with nucleation rate, while the impacts of KGM and glyceryl monostearate concentration on ice crystal growth were interpreted based on their influences on sol network structure. Copyright © 2016 Elsevier B.V. All rights reserved.
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NASA Astrophysics Data System (ADS)
Koshiro, Yoko; Watanabe, Manabu; Takai, Rikuo; Hagiwara, Tomoaki; Suzuki, Toru
Size and shape of ice crystals in frozen food materials are very important because they affect not only quality of foods but also the viability of industrial processing such as freeze-drying of concentration. In this study, 30%wt sucrose solution is used as test samples. For examining the effect of stabilizerspectine and xantan gum is added to the sucrose solution. They are frozen on the cold stage of microscope to be observed their growing ice crystals under the circumstance of -10°C. Their size and shape are measured and quantitatively evaluated by applying fractal analysis. lce crystal of complicated shape has large fractal dimension, and vice versa. It successflly categorized the ice crystals into two groups; one is a group of large size and complicated shape, and the other is a group of small size and plain shape. The critical crystal size between the two groups is found to become larger with increasing holding time. It suggests a phenomenological model for metamorphoses process of ice crystals. Further, it is indicated that xantan gum is able to suppress the smoothing of ice crystals.
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The Effect of Temperature and Solution pH on Tetragonal Lysozyme Nucleation Kinetics
NASA Technical Reports Server (NTRS)
Judge, Russell A.; Jacobs, Randolph S.; Frazier, Tyralynn; Snell, Edward H.; Pusey, Marc L.
1998-01-01
Part of the challenge of macromolecular crystal growth for structure determination is obtaining an appropriate number of crystals with a crystal volume suitable for x-ray analysis. In this respect an understanding of the effect of solution conditions on macromolecule nucleation rates is advantageous. This study investigated the effects of supersaturation, temperature and pH on the nucleation rate of tetragonal lysozyme crystals. Batch crystallization plates were prepared at given solution concentrations and incubated at set temperatures over one week. The number of crystals per well with their size and axial ratios were recorded and correlated with solution conditions, Duplicate experiments indicate the reproducibility of the technique, Crystal numbers were found to increase with increasing supersaturation and temperature. The most significant variable however, was pH, where crystal numbers changed by two orders of magnitude over the pH range 4.0 to 5.2. Crystal size varied also with solution conditions, with the largest crystals being obtained at pH 5.2. Having optimized the crystallization conditions, a batch of crystals were prepared under exactly the same conditions and fifty of these crystals were analyzed by x-ray techniques. The results indicate that even under the same crystallization conditions, a marked variation in crystal properties exists.
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NASA Astrophysics Data System (ADS)
Ma, Zhenye; Li, Cheng; Wu, Rujun; Chen, Rizhi; Gu, Zhenggui
2009-10-01
In this paper, a novel ceramic membrane anti-solvent crystallization (CMASC) method was proposed for the safe and rapid preparation ammonium perchlorate (AP) crystals, in which the acetone and ethyl acetate were chosen as solvent and anti-solvent, respectively. Comparing with the conventional liquid anti-solvent crystallization (LASC), CMASC which successfully introduces ceramic membrane with regular pore structure to the LASC as feeding medium, is favorable to control the rate of feeding rate and, therefore, to obtain size and morphology controllable AP. Several kinds of micro-sized AP particles with different morphology were obtained including polyhedral-like, quadrate-like to rod-like. The effect of processing parameters on the crystal size and shape of AP crystals such as volume ratio of anti-solvent to solvent, feeding pressure and crystallization temperature were investigated. It is found that higher volume ratio of anti-solvent to solvent, higher feeding pressure and higher temperature result in smaller particle size. Scaning electron microscopy (SEM) and X-ray diffraction (XRD) were used to characterize the resulting AP crystals. The nucleation and growth kinetic of the resulting AP crystals were also discussed.
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Descamps, Marc; Willart, Jean-François
2018-05-05
In the present paper we review different aspects of the crystallization of amorphous compounds in relation to specificities of the nucleation and growth rates. Its main purpose is: i) to underline the interest of a scaling analysis of recrystallization kinetics to identify similarities or disparities of experimental kinetic regimes. ii) to highlight the intrinsic link between the nucleation rate and growth rate with a temperature dependent characteristic transformation time τ(T), and a characteristic size ξ(T). The consequences on the influence of the sample size on kinetics of crystallization is considered. The significance of size effect and confinement for amorphous stabilization in the pharmaceutical sciences is discussed. Copyright © 2018. Published by Elsevier B.V.
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NASA Astrophysics Data System (ADS)
Klein, Johannes; Mueller, Sebastian P.; Helo, Christoph; Schweitzer, Silja; Gurioli, Lucia; Castro, Jonathan M.
2018-05-01
This study examines the combined effect of crystal-size distributions (CSD) and crystal shape on the rheology of vesicle free magmatic suspensions and provides the first practical application of an empirical model to estimate the relative effect of crystal content and CSD's on the viscosity of magma directly from textural image analysis of natural rock samples in the form of a user-friendly texture-rheology spreadsheet calculator. We extend and apply established relationships between the maximum packing fraction ϕm of a crystal bearing suspension and both its rheological properties and the polydispersity γ of a CSD. By using analogue rotational rheometric experiments with glass fibres and glass flakes in silicone oil acting as magma equivalent, this study also provides new insights in the relationship between ϕm and the aspect ratio rp of suspended particles.
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Kimura, Keisaku; Sato, Seiichi
2014-05-01
A conventional laser microscope can be used to derive the index of refractivity by the ratio of geometrical height of the transparent platelet to the apparent height of the normal incident light for very small crystals in the wide size range. We demonstrate that the simple method is effective for the samples from 100 μm to 16 μm in size using alkali halide crystals as a model system. The method is also applied for the surface fractured micro-crystals and an inclined crystal with microscopic size regime. Furthermore, we present two-dimensional refractive index mapping as well as two-dimensional height profile for the mixture of three alkali halides, KCl, KI, and NaCl, all are μm in size.
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2017-01-01
Gout is a disease with elusive treatment options. Reduction of the size of l-alanine crystals as a model crystal for gouty tophi with the use of a monomode solid-state microwave was examined as a possible therapeutic aid. The effect of microwave heating on l-alanine crystals in the presence of gold nanoparticles (Au NPs) in solution and synovial fluid (SF) in a plastic pouch through a synthetic skin patch was investigated. In this regard, three experimental paradigms were employed: Paradigm 1 includes the effect of variable microwave power (5–10 W) and variable heating time (5–60 s) and Au NPs in water (20 nm size, volume of 10 μL) in a plastic pouch (1 × 2 cm2 in size). Paradigm 2 includes the effect of a variable volume of 20 nm Au NPs in a variable volume of SF up to 100 μL in a plastic pouch at a constant microwave power (10 W) for 30 s. Paradigm 3 includes the effect of constant microwave power (10 W) and microwave heating time (30 s), constant volume of Au NPs (100 μL), and variable size of Au NPs (20–200 nm) placed in a plastic pouch through a synthetic skin patch. In these experiments, an average of 60–100% reduction in the size of an l-alanine crystal (initial size = 450 μm) without damage to the synthetic skin or increasing the temperature of the samples beyond the physiological range was reported. PMID:28983527
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Snow Crystal Orientation Effects on the Scattering of Passive Microwave Radiation
NASA Technical Reports Server (NTRS)
Foster, J. L.; Barton, J. S.; Chang, A. T. C.; Hall, D. K.
1999-01-01
For this study, consideration is given to the role crystal orientation plays in scattering and absorbing microwave radiation. A discrete dipole scattering model is used to measure the passive microwave radiation, at two polarizations (horizontal and vertical), scattered by snow crystals oriented in random and non random positions, having various sizes (ranging between 1 micrometers to 10,000 micrometers in radius), and shapes (including spheroids, cylinders, hexagons). The model results demonstrate that for the crystal sizes typically found in a snowpack, crystal orientation is insignificant compared to crystal size in terms of scattering microwave energy in the 8,100 gm (37 GHz) region of the spectrum. Therefore, the assumption used in radiative transfer approaches, where snow crystals are modeled as randomly oriented spheres, is adequate to account for the transfer of microwave energy emanating from the ground and passing through a snowpack.
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Analysis of Crystallization Kinetics
NASA Technical Reports Server (NTRS)
Kelton, Kenneth F.
1997-01-01
A realistic computer model for polymorphic crystallization (i.e., initial and final phases with identical compositions), which includes time-dependent nucleation and cluster-size-dependent growth rates, is developed and tested by fits to experimental data. Model calculations are used to assess the validity of two of the more common approaches for the analysis of crystallization data. The effects of particle size on transformation kinetics, important for the crystallization of many systems of limited dimension including thin films, fine powders, and nanoparticles, are examined.
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NASA Astrophysics Data System (ADS)
Mudalip, S. K. Abdul; Adam, F.; Parveen, J.; Abu Bakar, M. R.; Amran, N.; Sulaiman, S. Z.; Che Man, R.; Arshad, Z. I. Mohd; Shaarani, S. Md.
2017-06-01
This study investigate the effect of cooling rates on mefenamic acid crystallisation in ethyl acetate. The cooling rate was varied from 0.2 to 5 °C/min. The in-line conductivity system and turbidity system were employed to detect the onset of the crystallization process. The crystals produced were analysed using optical microscopy and Fourier transform infrared spectroscopy (FTIR). It was found that the crystals produced at different cooling rates were needle-like and exhibit polymorphic form type I. However, the aspect ratio and crystal size distributions were varied with the increased of cooling rate. A high crystals aspect ratio and narrower CSD (100-900 μm) was obtained at cooling rate of 0.5 °C/min. Thus, can be suggested as the most suitable cooling rate for crystallization of mefenamic acid in ethyl acetate.
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NASA Astrophysics Data System (ADS)
Carlson, William D.
1989-09-01
The spatial disposition, compositional zoning profiles, and size distributions of garnet crystals in 11 specimens of pelitic schist from the Picuris Range of New Mexico (USA) demonstrate that the kinetics of intergranular diffusion controlled the nucleation and growth mechanisms of porphyroblasts in these rocks. An ordered disposition of garnet centers and a significant correlation between crystal radius and near-neighbor distances manifest suppressed nucleation of new crystals in diffusionally depleted zones surrounding pre-existing crystals. Compositional zoning profiles require diffusionally controlled growth, the rate of which increases exponentially as temperature increases with time; an acceleration factor for growth rate can be estimated from a comparison of compositional profiles for crystals of different sizes in each specimen. Crystal size distributions are interpreted as the result of nucleation rates that accelerate exponentially with increasing temperature early in the crystallization process, but decline in the later stages because of suppression effects in the vicinity of earlier-formed nuclei. Simulations of porphyroblast crystallization, based upon thermally accelerated diffusionally influenced nucleation kinetics and diffusionally controlled growth kinetics, quantitatively replicate textural relations in the rocks. The simulations employ only two variable parameters, which are evaluated by fitting of crystal size distributions. Both have physical significance. The first is an acceleration factor for nucleation, with a magnitude reflecting the prograde increase during the nucleation interval of the chemical affinity for the reaction in undepleted regions of the rock. The second is a measure of the relative sizes of the porphyroblast and the diffusionally depleted zone surrounding it. Crystal size distributions for the Picuris Range garnets correspond very closely to those in the literature from a variety of other localities for garnet and other minerals. The same kinetic model accounts quantitatively for crystal size distributions of porphyroblastic garnet, phlogopite, sphene, and pyroxene in rocks from both regional and contact metamorphic occurrences. These commonalities indicate that intergranular diffusion may be the dominant kinetic factor in the crystallization of porphyroblasts in a wide variety of metamorphic environments.
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Q-space analysis of light scattering by ice crystals
NASA Astrophysics Data System (ADS)
Heinson, Yuli W.; Maughan, Justin B.; Ding, Jiachen; Chakrabarti, Amitabha; Yang, Ping; Sorensen, Christopher M.
2016-12-01
Q-space analysis is applied to extensive simulations of the single-scattering properties of ice crystals with various habits/shapes over a range of sizes. The analysis uncovers features common to all the shapes: a forward scattering regime with intensity quantitatively related to the Rayleigh scattering by the particle and the internal coupling parameter, followed by a Guinier regime dependent upon the particle size, a complex power law regime with incipient two dimensional diffraction effects, and, in some cases, an enhanced backscattering regime. The effects of significant absorption on the scattering profile are also studied. The overall features found for the ice crystals are similar to features in scattering from same sized spheres.
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Key to enhance thermoelectric performance by controlling crystal size of strontium titanate
NASA Astrophysics Data System (ADS)
Wang, Jun; Ye, Xinxin; Yaer, Xinba; Wu, Yin; Zhang, Boyu; Miao, Lei
2015-09-01
One-step molten salt synthesis process was introduced to fabricate nano to micrometer sized SrTiO3 powders in which effects of synthesis temperature, oxide-to-flux ratios and raw materials on the generation of SrTiO3 powders were examined. 100 nm or above sized pure SrTiO3 particles were obtained at relatively lower temperature of 900∘C. Micro-sized rhombohedral crystals with a maximum size of approximately 12 μm were obtained from SrCO3 or Sr(NO3)2 strontium source with 1:1 O/S ratio. Controlled crystal size and morphology of Nb-doped SrTiO3 particles are prepared by using this method to confirm the performance of thermoelectric properties. The Seebeck coefficient obtained is significantly high when compared with the reported data, and the high ratio of nano particles in the sample has a positive effect on the increase of Seebeck coefficient too, which is likely due to the energy filtering effect at large numbers of grain boundaries resulting from largely distributed structure.
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Borissova, A; Goltz, G E; Kavanagh, J P; Wilkins, T A
2010-07-01
Crystallization of calcium oxalate monohydrate in a section of a single kidney nephron (distal convoluted tubule) is simulated using a model adapted from industrial crystallization. The nephron fluid dynamics is represented as a crystallizer/separator series with changing volume to allow for water removal along the tubule. The model integrates crystallization kinetics and crystal size distribution and allows the prediction of the calcium oxalate concentration profile and the nucleation and growth rates. The critical supersaturation ratio for the nucleation of calcium oxalate crystals has been estimated as 2 and the mean crystal size as 1 mum. The crystal growth order, determined as 2.2, indicates a surface integration mechanism of crystal growth and crystal growth dispersion. The model allows the exploration of the effect of varying the input calcium oxalate concentration and the rate of water extraction, simulating real life stressors for stone formation such as dietary loading and dehydration.
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Light scattering by hexagonal ice crystals with distributed inclusions
NASA Astrophysics Data System (ADS)
Panetta, R. Lee; Zhang, Jia-Ning; Bi, Lei; Yang, Ping; Tang, Guanlin
2016-07-01
Inclusions of air bubbles or soot particles have significant effects on the single-scattering properties of ice crystals, effects that in turn have significant impacts on the radiation budget of an atmosphere containing the crystals. This study investigates some of the single-scattering effects in the case of hexagonal ice crystals, including effects on the backscattering depolarization ratio, a quantity of practical importance in the interpretation of lidar observations. One distinguishing feature of the study is an investigation of scattering properties at a visible wavelength for a crystal with size parameter (x) above 100, a size regime where one expects some agreement between exact methods and geometrical optics methods. This expectation is generally borne out in a test comparison of how the sensitivity of scattering properties to the distribution of a given volume fraction of included air is represented using (i) an approximate Monte Carlo Ray Tracing (MCRT) method and (ii) a numerically exact pseudo-spectral time-domain (PSTD) method. Another distinguishing feature of the study is a close examination, using the numerically exact Invariant-Imbedding T-Matrix (II-TM) method, of how some optical properties of importance to satellite remote sensing vary as the volume fraction of inclusions and size of crystal are varied. Although such an investigation of properties in the x>100 regime faces serious computational burdens that force a large number of idealizations and simplifications in the study, the results nevertheless provide an intriguing glimpse of what is evidently a quite complex sensitivity of optical scattering properties to inclusions of air or soot as volume fraction and size parameter are varied.
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Self-cavity lasing in optically pumped single crystals of p-sexiphenyl
NASA Astrophysics Data System (ADS)
Yanagi, Hisao; Tamura, Kenji; Sasaki, Fumio
2016-08-01
Organic single-crystal self-cavities are prepared by solution growth of p-sexiphenyl (p-6P). Based on Fabry-Pérot feedback inside a quasi-lozenge-shaped platelet crystal, edge-emitting laser is obtained under optical pumping. The multimode lasing band appears at the 0-1 or 0-2 vibronic progressions depending on the excitation conditions which affect the self-absorption effect. Cavity-size dependence of amplified spontaneous emission (ASE) is investigated with laser-etched single crystals of p-6P. As the cavity length of square-shaped crystal is reduced from 100 to 10 μm, ASE threshold fluence is decreased probably due to size-dependent light confinement in the crystal cavity.
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Su, Chia-Chi; Reano, Resmond L; Dalida, Maria Lourdes P; Lu, Ming-Chun
2014-06-01
The effects of process conditions, including upward velocity inside the column, the amount of added seed and seed size, the pH value of the precipitant or the phosphate stream and the Ba/P molar ratio in a fluidized-bed reactor (FBR) were studied with a view to producing BaHPO₄ crystals of significant size and maximize the removal of barium. XRD were used to identify the products that were collected from the FBR. Experimental results show that an upward velocity of 48 cmmin(-1) produced the largest BaHPO₄ crystals with a size of around 0.84-1.0mm. The addition of seed crystals has no effect on barium removal. The use of a seed of a size in the ranges unseeded<0.149-0.29 mm<0.149 mm<0.29-0.42 mm produced increasing amounts of increasingly large crystals. The largest BaHPO₄ crystals were obtained at pH 8.4-8.8 with a Ba/P molar ratio of 1.0. In the homogeneous and heterogeneous processes, around 98% of barium was removed at pH 8.4-8.6 and [Ba]/[P]=1.0. The XRD results show that a significant amount of barium phosphate (Ba₃(PO₄)₂) was obtained at pH 11. The compounds BaHPO₄ and BaO were present at a pH of below 10. Copyright © 2014 Elsevier Ltd. All rights reserved.
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Phenytoin crystal growth rates in the presence of phosphate and chloride ions
NASA Astrophysics Data System (ADS)
Zipp, G. L.; Rodríguez-Hornedo, N.
1992-09-01
Phenytoin crystal growth kinetics have been measured as a function of supersaturation in pH 2.2 phosphoric acid and pH 2.2 hydrochloric acid solutions. Two different methods were used for the kinetic analysis. The first involved a zone-sensing device which provided an analysis of the distribution of crystals in a batch crystallizer. Crystal growth rates were calculated from the increase in the size of the distribution with time. In the second method, growth rates were evaluated from the change in size with time of individual crystals observed under an inverted microscope. The results from each method compare favorably. The use of both techniques provides an excellent opportunity to exploit the strengths of each: an average growth rate from a population of crystals from batch crystallization and insight into the effect of growth on the morphology of the crystals from the individual crystal measurements.
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Effect of binder liquid type on spherical crystallization.
Maghsoodi, Maryam; Hajipour, Ali
2014-11-01
Spherical crystallization is a process of formation of agglomerates of crystals held together by binder liquid. This research focused on understanding the effect of type of solvents used as binder liquid on the agglomeration of crystals. Carbamazepine and ethanol/water were used respectively as a model drug and crystallization system. Eight solvents as binder liquid including chloroform, dichloromethane, isopropyl acetate, ethyl acetate, n-hexane, dimethyl aniline, benzene and toluene were examined to better understand the relationship between the physical properties of the binder liquid and its ability to bring about the formation of the agglomerates. Moreover, the agglomerates obtained from effective solvents as binder liquid were evaluated in term of size, apparent particle density and compressive strength. In this study the clear trend was observed experimentally in the agglomerate formation as a function of physical properties of the binder liquid such as miscibility with crystallization system. Furthermore, the properties of obtained agglomerates such as size, apparent particle density and compressive strength were directly related to physical properties of effective binder liquids. RESULTS of this study offer a useful starting point for a conceptual framework to guide the selection of solvent systems for spherical crystallization.
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2017-01-01
Crystal size and shape can be manipulated to enhance the qualities of the final product. In this work the steady-state shape and size of succinic acid crystals, with and without a polymeric additive (Pluronic P123) at 350 mL, scale is reported. The effect of the amplitude of cycles as well as the heating/cooling rates is described, and convergent cycling (direct nucleation control) is compared to static cycling. The results show that the shape of succinic acid crystals changes from plate- to diamond-like after multiple cycling steps, and that the time required for this morphology change to occur is strongly related to the type of cycling. Addition of the polymer is shown to affect both the final shape of the crystals and the time needed to reach size and shape steady-state conditions. It is shown how this phenomenon can be used to improve the design of the crystallization step in order to achieve more efficient downstream operations and, in general, to help optimize the whole manufacturing process. PMID:28867966
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Large scale crystallization of protein pharmaceuticals in microgravity via temperature change
NASA Technical Reports Server (NTRS)
Long, Marianna M.
1992-01-01
The major objective of this research effort is the temperature driven growth of protein crystals in large batches in the microgravity environment of space. Pharmaceutical houses are developing protein products for patient care, for example, human insulin, human growth hormone, interferons, and tissue plasminogen activator or TPA, the clot buster for heart attack victims. Except for insulin, these are very high value products; they are extremely potent in small quantities and have a great value per gram of material. It is feasible that microgravity crystallization can be a cost recoverable, economically sound final processing step in their manufacture. Large scale protein crystal growth in microgravity has significant advantages from the basic science and the applied science standpoints. Crystal growth can proceed unhindered due to lack of surface effects. Dynamic control is possible and relatively easy. The method has the potential to yield large quantities of pure crystalline product. Crystallization is a time honored procedure for purifying organic materials and microgravity crystallization could be the final step to remove trace impurities from high value protein pharmaceuticals. In addition, microgravity grown crystals could be the final formulation for those medicines that need to be administered in a timed release fashion. Long lasting insulin, insulin lente, is such a product. Also crystalline protein pharmaceuticals are more stable for long-term storage. Temperature, as the initiation step, has certain advantages. Again, dynamic control of the crystallization process is possible and easy. A temperature step is non-invasive and is the most subtle way to control protein solubility and therefore crystallization. Seeding is not necessary. Changes in protein and precipitant concentrations and pH are not necessary. Finally, this method represents a new way to crystallize proteins in space that takes advantage of the unique microgravity environment. The results from two flights showed that the hardware performed perfectly, many crystals were produced, and they were much larger than their ground grown controls. Morphometric analysis was done on over 4,000 crystals to establish crystal size, size distribution, and relative size. Space grown crystals were remarkably larger than their earth grown counterparts and crystal size was a function of PCF volume. That size distribution for the space grown crystals was a function of PCF volume may indicate that ultimate size was a function of temperature gradient. Since the insulin protein concentration was very low, 0.4 mg/ml, the size distribution could also be following the total amount of protein in each of the PCF's. X-ray analysis showed that the bigger space grown insulin crystals diffracted to higher resolution than their ground grown controls. When the data were normalized for size, they still indicated that the space crystals were better than the ground crystals.
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NASA Astrophysics Data System (ADS)
Wang, Chunyang; Du, Kui; Song, Kepeng; Ye, Xinglong; Qi, Lu; He, Suyun; Tang, Daiming; Lu, Ning; Jin, Haijun; Li, Feng; Ye, Hengqiang
2018-05-01
Low-angle grain boundaries generally exist in the form of dislocation arrays, while high-angle grain boundaries (misorientation angle >15 ° ) exist in the form of structural units in bulk metals. Here, through in situ atomic resolution aberration corrected electron microscopy observations, we report size-dependent grain-boundary structures improving both stabilities of electrical conductivity and mechanical properties in sub-10-nm-sized gold crystals. With the diameter of a nanocrystal decreasing below 10 nm, the high-angle grain boundary in the crystal exists as an array of dislocations. This size effect may be of importance to a new generation of interconnects applications.
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NASA Astrophysics Data System (ADS)
Martínez-Cruz, Nancy; Carrillo-Romo, Felipe; Jaramillo-Vigueras, David
2004-10-01
This paper analyzes the effect of polystyrensulfonic acid sodium salt (NaPSS), obtained by kinetic precipitation from solutions of polymers of molecular weight 245 000 and 38 000 g mol-1 in sodium bicarbonate (NaHCO3) itself precipitated from synthetic brine. Crystal size, shape and the additive adsorbed are reported. X shaped and hexagonal prisms crystals with different aspect ratios were obtained. The results show that with increasing polymer concentration the crystal size decreases, from 0.27 to 0.48 mm. Additionally, the higher molecular weight polymer shows both higher adsorption capacity and higher crystal habit modification. Crystal shape patterns were similar for both polymers; however, the higher molecular weight material induced changes at lower concentration. It was observed that the precipitation rate reached a minimum with increasing additive concentration.
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Time-evolution of grain size distributions in random nucleation and growth crystallization processes
NASA Astrophysics Data System (ADS)
Teran, Anthony V.; Bill, Andreas; Bergmann, Ralf B.
2010-02-01
We study the time dependence of the grain size distribution N(r,t) during crystallization of a d -dimensional solid. A partial differential equation, including a source term for nuclei and a growth law for grains, is solved analytically for any dimension d . We discuss solutions obtained for processes described by the Kolmogorov-Avrami-Mehl-Johnson model for random nucleation and growth (RNG). Nucleation and growth are set on the same footing, which leads to a time-dependent decay of both effective rates. We analyze in detail how model parameters, the dimensionality of the crystallization process, and time influence the shape of the distribution. The calculations show that the dynamics of the effective nucleation and effective growth rates play an essential role in determining the final form of the distribution obtained at full crystallization. We demonstrate that for one class of nucleation and growth rates, the distribution evolves in time into the logarithmic-normal (lognormal) form discussed earlier by Bergmann and Bill [J. Cryst. Growth 310, 3135 (2008)]. We also obtain an analytical expression for the finite maximal grain size at all times. The theory allows for the description of a variety of RNG crystallization processes in thin films and bulk materials. Expressions useful for experimental data analysis are presented for the grain size distribution and the moments in terms of fundamental and measurable parameters of the model.
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NASA Astrophysics Data System (ADS)
Lubenets, S. V.; Rusakova, A. V.; Fomenko, L. S.; Moskalenko, V. A.
2018-01-01
The anisotropy of microhardness of pure α-Ti single crystals, indentation size effect in single-crystal, course grained (CG) pure and nanocrystalline (NC) VT1-0 titanium, as well as the temperature dependences of the microhardness of single-crystal and CG Ti in the temperature range 77-300 K were studied. The minimum value of hardness was obtained when indenting into the basal plane (0001). The indentation size effect (ISE) was clearly observed in the indentation of soft high-purity single-crystal iodide titanium while it was the least pronounced in a sample of nanocrystalline VT1-0 titanium. It has been demonstrated that the ISE can be described within the model of geometrically necessary dislocations (GND), which follows from the theory of strain gradient plasticity. The true hardness and others parameters of the GND model were determined for all materials. The temperature dependence of the microhardness is in agreement with the idea of the governing role of Peierls relief in the dislocation thermally-activated plastic deformation of pure titanium as has been earlier established and justified in macroscopic tensile investigations at low temperatures. The activation energy and activation volume of dislocation motion in the strained region under the indenter were estimated.
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Paquay, Stefan; Both, Gert-Jan; van der Schoot, Paul
2017-07-01
When colloidal particles form a crystal phase on a spherical template, their packing is governed by the effective interaction between them and the elastic strain of bending the growing crystal. For example, if growth commences under appropriate conditions, and the isotropic crystal that forms reaches a critical size, growth continues via the incorporation of defects to alleviate elastic strain. Recently, it was experimentally found that, if defect formation is somehow not possible, the crystal instead continues growing in ribbons that protrude from the original crystal. Here we report on computer simulations in which we observe both the formation of ribbons at short interaction ranges and packings that incorporate defects if the interaction is longer-ranged. The ribbons only form above some critical crystal size, below which the nucleus is disk-shaped. We find that the scaling of the critical crystal size differs slightly from the one proposed in the literature, and we argue that this is because the actual morphology transition is caused by the competition between line tension and elastic stress, rather than the competition between chemical potential and elastic stress.
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NASA Astrophysics Data System (ADS)
Paquay, Stefan; Both, Gert-Jan; van der Schoot, Paul
2017-07-01
When colloidal particles form a crystal phase on a spherical template, their packing is governed by the effective interaction between them and the elastic strain of bending the growing crystal. For example, if growth commences under appropriate conditions, and the isotropic crystal that forms reaches a critical size, growth continues via the incorporation of defects to alleviate elastic strain. Recently, it was experimentally found that, if defect formation is somehow not possible, the crystal instead continues growing in ribbons that protrude from the original crystal. Here we report on computer simulations in which we observe both the formation of ribbons at short interaction ranges and packings that incorporate defects if the interaction is longer-ranged. The ribbons only form above some critical crystal size, below which the nucleus is disk-shaped. We find that the scaling of the critical crystal size differs slightly from the one proposed in the literature, and we argue that this is because the actual morphology transition is caused by the competition between line tension and elastic stress, rather than the competition between chemical potential and elastic stress.
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NASA Astrophysics Data System (ADS)
de Azevedo Jacqueline, Resende; Fabienne, Espitalier; Jean-Jacques, Letourneau; Inês, Ré Maria
2017-08-01
LASSBio-294 (3,4-methylenedioxybenzoyl-2-thienylhydrazon) is a poorly soluble drug which has been proposed to have major advantages over other cardiotonic drugs. Poorly water soluble drugs present limited bioavailability due to their low solubility and dissolution rate. An antisolvent crystallization processing can improve the dissolution rate by decreasing the crystals particle size. However, LASSBio-294 is also poorly soluble in organic solvents and this operation is limited. In order to open new perspectives to improve dissolution rate, this work has investigated LASSBio-294 in terms of its antisolvent crystallization in 1-ethyl-3-methylimidazolium methyl phosphonate [emim][CH3O(H)PO2] as solvent and water as antisolvent. Two modes of mixing are tested in stirred vessel with different pre-mixers (Roughton or T-mixers) in order to investigate the mixing effect on the crystal properties (crystalline structure, particle size distribution, residual solvent and in vitro dissolution rate). Smaller drug particles with unchanged crystalline structure were obtained. Despite the decrease of the elementary particles size, the recrystallized particles did not achieve a better dissolution profile. However, this study was able to highlight a certain number of findings such as the impact of the hydrodynamic conditions on the crystals formation and the presence of a gel phase limiting the dissolution rate.
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Large-volume protein crystal growth for neutron macromolecular crystallography.
Ng, Joseph D; Baird, James K; Coates, Leighton; Garcia-Ruiz, Juan M; Hodge, Teresa A; Huang, Sijay
2015-04-01
Neutron macromolecular crystallography (NMC) is the prevailing method for the accurate determination of the positions of H atoms in macromolecules. As neutron sources are becoming more available to general users, finding means to optimize the growth of protein crystals to sizes suitable for NMC is extremely important. Historically, much has been learned about growing crystals for X-ray diffraction. However, owing to new-generation synchrotron X-ray facilities and sensitive detectors, protein crystal sizes as small as in the nano-range have become adequate for structure determination, lessening the necessity to grow large crystals. Here, some of the approaches, techniques and considerations for the growth of crystals to significant dimensions that are now relevant to NMC are revisited. These include experimental strategies utilizing solubility diagrams, ripening effects, classical crystallization techniques, microgravity and theoretical considerations.
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NASA Astrophysics Data System (ADS)
Foster, J. L.; Chang, A. T. C.; Hall, D. K.; Wergin, W. P.; Erbe, E. F.; Barton, J.
1998-11-01
On Earth, the temperature regime is such that water is generally fairly close to its freezing point, and thus relatively small differences in climate affect how much snow and ice are present and whether or not the snow covering will be seasonal or last from one year to the next. On Mars, as on Earth, the presence of ice also plays a role in large-scale climate processes and it is important in controlling the abundance of atmospheric carbon dioxide (CO2) and water vapor. Passive microwave radiometry has been used to derive snow extent and snow depth on Earth, where scattering by snow (H2O) crystals is the dominant effect on the microwave radiation emanating from the ground and emerging from the snowpack. Microwave remote sensing may also prove to be useful for assessing the coverage and thickness of the frozen H2O and CO2 on Mars, but more exact information is needed on how both H2O crystals and frozen CO2 crystals scatter and absorb passive microwave radiation. In this study, CO2 crystals have been produced in a laboratory cold chamber with temperature conditions similar to those found on the polar caps of Mars, and detailed three-dimensional images of their size and shape have been made with a low-temperature scanning electron microscope. Unlike the much larger H2O snow crystals found on Earth, which typically range in size between 0.1 mm and 1.0 mm (radius), CO2 crystals are differently shaped and considerably smaller. Bipyramid crystals (base to base four-sided pyramids) are commonly observed, some as small as 1.0 μm. A discrete dipole model was employed to calculate the passive microwave radiation scattered and absorbed by crystals of various sizes and shapes. Modeling results indicate that the shape of the crystal, whether for frozen CO2 or H2O, is of little consequence in affecting extinction efficiency. However, owing to their smaller size, frozen CO2 crystals are more emissive than the H2O crystals in the 37 GHz region of the microwave spectrum. For the larger sizes of the modeled crystals, scattering dominates over absorption since the particles approach the size of the wavelength. The scattering values are 2 orders of magnitude larger than absorption for the 900 μm size snow particles. For CO2 crystals of 3.0 μm in size, absorption is 7 orders of magnitude greater than scattering.
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Pareja-Rivera, Carina; Cuéllar-Cruz, Mayra; Esturau-Escofet, Nuria
Here, in this contribution we use nonconventional methods that help to increase the success rate of a protein crystal growth, and consequently of structural projects using X-ray diffraction techniques. In order to achieve this purpose, this contribution presents new approaches involving more sophisticated techniques of protein crystallization, not just for growing protein crystals of different sizes by using electric fields, but also for controlling crystal size and orientation. Also, this latter was possible through the use of magnetic fields that allow to obtain protein crystals suitable for both high-resolution X-ray and neutron diffraction crystallography where big crystals are required. Thismore » contribution discusses some pros, cons and realities of the role of electromagnetic fields in protein crystallization research, and their effect on protein crystal contacts. Additionally, we discuss the importance of room and low temperatures during data collection. Finally, we also discuss the effect of applying a rather strong magnetic field of 16.5 T, for shorts and long periods of time, on protein crystal growth, and on the 3D structure of two model proteins.« less
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Pareja-Rivera, Carina; Cuéllar-Cruz, Mayra; Esturau-Escofet, Nuria; ...
2016-12-05
Here, in this contribution we use nonconventional methods that help to increase the success rate of a protein crystal growth, and consequently of structural projects using X-ray diffraction techniques. In order to achieve this purpose, this contribution presents new approaches involving more sophisticated techniques of protein crystallization, not just for growing protein crystals of different sizes by using electric fields, but also for controlling crystal size and orientation. Also, this latter was possible through the use of magnetic fields that allow to obtain protein crystals suitable for both high-resolution X-ray and neutron diffraction crystallography where big crystals are required. Thismore » contribution discusses some pros, cons and realities of the role of electromagnetic fields in protein crystallization research, and their effect on protein crystal contacts. Additionally, we discuss the importance of room and low temperatures during data collection. Finally, we also discuss the effect of applying a rather strong magnetic field of 16.5 T, for shorts and long periods of time, on protein crystal growth, and on the 3D structure of two model proteins.« less
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NASA Astrophysics Data System (ADS)
Tsai, Chun-Chien; Lee, Yao-Jen; Chiang, Ko-Yu; Wang, Jyh-Liang; Lee, I.-Che; Chen, Hsu-Hsin; Wei, Kai-Fang; Chang, Ting-Kuo; Chen, Bo-Ting; Cheng, Huang-Chung
2007-11-01
In this paper, location-controlled silicon crystal grains are fabricated by the excimer laser crystallization method which employs amorphous silicon spacer structure and prepatterned thin films. The amorphous silicon spacer in nanometer-sized width formed using spacer technology is served as seed crystal to artificially control superlateral growth phenomenon during excimer laser irradiation. An array of 1.8-μm-sized disklike silicon grains is formed, and the n-channel thin-film transistors whose channels located inside the artificially-controlled crystal grains exhibit higher performance of field-effect-mobility reaching 308cm2/Vs as compared with the conventional ones. This position-manipulated silicon grains are essential to high-performance and good uniformity devices.
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NASA Astrophysics Data System (ADS)
Price, C. J.
1993-03-01
The distribution of gross imperfections amongst populations of copper sulphate pentahydrate crystals grown under different conditions of purity and temperature are examined. The frequency of imperfection increases with decreasing crystal size. The nature of the imperfections vary with growth temperature and impurities present.
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NASA Astrophysics Data System (ADS)
Wu, Yu-Chun; Tai, Yu-Chuen
2013-06-01
The effects of solvents on the anatase crystallite size prepared by sol-gel microwave-assisted solvothermal method were investigated in this study. Eight different alcohol solvents classified into two groups, i.e. primary and secondary/ternary alcohols, were used as reaction media and the effects of solvent properties, such as dielectric constant, boiling point, and internal pressure during the solvothermal process, on the crystallite size and shape were analyzed. According to the experimental results, selecting the solvent type allowed not only the alteration of the crystallite size but also the crystallite shape without the need of any additives. The boiling point of solvent was determined as the major factor influencing the crystallite size. Among the solvents with similar boiling points, the solvent with a higher carbon number produced the smaller crystallite size because of steric hindrance effect. In addition, the carboxyl groups dissociated from the alcohol solvent can play a role as a structural capping agent to retard the anatase crystal growth along the [001] direction and led to a rectangular crystallite shape with preferred development in {001} facets. On the other hand, the alcoholysis reaction was found easily occurred between the primary alcohol and isopropoxide that effectively limited the hydrolysis and condensation processes but also suppressed the structural capping effect. Therefore, the anatase crystals prepared in the primary alcohols became exceptionally small and showed spherical shape. Finally, the anatase crystals prepared using isopropanol demonstrated the highest photocatalytic activity due to its evident preferred crystallization in the {001} facets.
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Thompson, Nishone; Boone-Kukoyi, Zainab; Shortt, Raquel; Lansiquot, Carisse; Kioko, Bridgit; Bonyi, Enock; Toker, Salih; Ozturk, Birol; Aslan, Kadir
2017-01-01
Gout is caused by the overproduction of uric acid and the inefficient metabolism of dietary purines in humans. Current treatments of gout, which include anti-inflammatory drugs, cyclooxygenase-2 inhibitors, and systemic glucocorticoids, have harmful side-effects. Our research laboratory has recently introduced an innovative approach for the decrystallization of biological and chemical crystals using the Metal-Assisted and Microwave-Accelerated Evaporative Decrystallization (MAMAD) technique. In the MAMAD technique, microwave energy is used to heat and activate gold nanoparticles that behave as “nano-bullets” to rapidly disrupt the crystal structure of biological crystals placed on planar surfaces. In this study, crystals of various sizes and compositions were studied as models for tophaceous gout at different stages (i.e., uric acid as small crystals (~10–100 μm) and L-alanine as medium (~300 μm) and large crystals (~4400 μm). Our results showed that the use of the MAMAD technique resulted in the reduction of the size and number of uric acid and L-alanine crystals up to >40% when exposed to intermittent microwave heating (up to 20 W power at 8 GHz) in the presence of 20 nm gold nanoparticles up to 120 s. This study demonstrates that the MAMAD technique can be potentially used as an alternative therapeutic method for the treatment of gout by effective decrystallization of large crystals, similar in size to those that often occur in gout. PMID:27763557
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Pb1-xMnxTe Crystals as a New Thermoelectric Material
NASA Astrophysics Data System (ADS)
Osinniy, V.; Jędrzejczak, A.; Domuchowski, W.; Dybko, K.; Witkowska, B.; Story, T.
2006-11-01
We studied experimentally thermoelectric properties of p-type bulk crystals of Pb1-xMnxTe and Pb1-x-yAgyMnxTe (0≤ x≤ 0.083 and y≤0.017) at room and liquid nitrogen temperatures. Model calculations of the thermoelectric figure of merit parameter (Z) involved the analysis of carrier concentration, carrier mobility, density of states as well as electronic and lattice contributions to the thermal conductivity of PbMnTe. In the analysis we took into account the main effect of Mn concentration on the band structure parameters of PbMnTe, i.e. the increase of the energy gap. The analysis of electrical, thermoelectric, and thermal properties of Pb1-xMnxTe crystals showed that, at room temperature, the maximum values of the parameter Z occur in crystals with Mn content 0.05≤ x≤0.07 and are comparable with a maximal value of Z observed in PbTe. At T=400 K the increase in the parameter Z by 10% is expected in Pb1-xMnxTe crystal (as compared to PbTe) for a very high concentration of holes of about p=5×1019 cm-3. The experimental data correctly reproduce the theoretical Z(p) dependence.
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Chutipongtanate, Somchai; Chaiyarit, Sakdithep; Thongboonkerd, Visith
2012-08-15
Dissolution therapy of calcium oxalate monohydrate (COM) kidney stone disease has not yet been implemented due to a lack of well characterized COM dissolution agents. The present study therefore aimed to identify potential COM crystal dissolution compounds. COM crystals were treated with deionized water (negative control), 5 mM EDTA (positive control), 5 mM sodium citrate, or 5mM sodium phosphate. COM crystal dissolution activities of these compounds were evaluated by phase-contrast and video-assisted microscopic examinations, semi-quantitative analysis of crystal size, number and total mass, and spectrophotometric oxalate-dissolution assay. In addition, effects of these compounds on detachment of COM crystals, which adhered tightly onto renal tubular cell surface, were also investigated. The results showed that citrate, not phosphate, had a significant dissolution effect on COM crystals as demonstrated by significant reduction of crystal size (approximately 37% decrease), crystal number (approximately 53% decrease) and total crystal mass (approximately 72% decrease) compared to blank and negative controls. Spectrophotometric oxalate-dissolution assay successfully confirmed the COM crystal dissolution property of citrate. Moreover, citrate could detach up to 85% of the adherent COM crystals from renal tubular cell surface. These data indicate that citrate is better than phosphate for dissolution and detachment of COM crystals. Copyright © 2012 Elsevier B.V. All rights reserved.
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Ultrasonically controlled particle size distribution of explosives: a safe method.
Patil, Mohan Narayan; Gore, G M; Pandit, Aniruddha B
2008-03-01
Size reduction of the high energy materials (HEM's) by conventional methods (mechanical means) is not safe as they are very sensitive to friction and impact. Modified crystallization techniques can be used for the same purpose. The solute is dissolved in the solvent and crystallized via cooling or is precipitated out using an antisolvent. The various crystallization parameters such as temperature, antisolvent addition rate and agitation are adjusted to get the required final crystal size and morphology. The solvent-antisolvent ratio, time of crystallization and yield of the product are the key factors for controlling antisolvent based precipitation process. The advantages of cavitationally induced nucleation can be coupled with the conventional crystallization process. This study includes the effect of the ultrasonically generated acoustic cavitation phenomenon on the solvent antisolvent based precipitation process. CL20, a high-energy explosive compound, is a polyazapolycyclic caged polynitramine. CL-20 has greater energy output than existing (in-use) energetic ingredients while having an acceptable level of insensitivity to shock and other external stimuli. The size control and size distribution manipulation of the high energy material (CL20) has been successfully carried out safely and quickly along with an increase in the final mass yield, compared to the conventional antisolvent based precipitation process.
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NASA Astrophysics Data System (ADS)
Prostomolotov, A. I.; Verezub, N. A.; Voloshin, A. E.
2014-09-01
A thermo-gravitational convection and impurity transfer in the melt were investigated using a simplified numerical model for Bridgman GaSb(Te) crystal growth in microgravity conditions. Simplifications were as follows: flat melt/crystal interface, fixed melt sizes and only lateral ampoule heating. Calculations were carried out by Ansys®Fluent® code employing a two-dimensional Navier-Stokes-Boussinesq and heat and mass transfer equations in a coordinate system moving with the melt/crystal interface. The parametric dependence of the effective segregation coefficient Keff at the melt/crystal interface was studied for various ampoule sizes and for microgravity conditions. For the uprising one-vortex flow, the resulting dependences were presented as Keff vs. Vmax-the maximum velocity value. These dependences were compared with the formulas by Burton-Prim-Slichter's, Ostrogorsky-Muller's, as well as with the semi-analytical solutions.
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Crystallization in a model glass: Influence of the boundary conditions
NASA Astrophysics Data System (ADS)
Jund, P.; Jullien, R.
1998-06-01
Using molecular dynamics calculations and the Voronoï tessellation, we study the evolution of the local structure of a soft-sphere glass vs. temperature starting from the liquid phase at different quenching rates. This study is done for different sizes and for two different boundary conditions, namely the usual cubic periodic boundary conditions and the isotropic hyperspherical boundary conditions for which the particles evolve on the surface of a hypersphere in four dimensions. Our results show that for small system sizes, crystallization can indeed be induced by the cubic boundary conditions. On the other hand, we show that finite-size effects are more pronounced on the hypersphere and that crystallization is artificially inhibited even for large system sizes.
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Large-volume protein crystal growth for neutron macromolecular crystallography
Ng, Joseph D.; Baird, James K.; Coates, Leighton; ...
2015-03-30
Neutron macromolecular crystallography (NMC) is the prevailing method for the accurate determination of the positions of H atoms in macromolecules. As neutron sources are becoming more available to general users, finding means to optimize the growth of protein crystals to sizes suitable for NMC is extremely important. Historically, much has been learned about growing crystals for X-ray diffraction. However, owing to new-generation synchrotron X-ray facilities and sensitive detectors, protein crystal sizes as small as in the nano-range have become adequate for structure determination, lessening the necessity to grow large crystals. Here, some of the approaches, techniques and considerations for themore » growth of crystals to significant dimensions that are now relevant to NMC are revisited. We report that these include experimental strategies utilizing solubility diagrams, ripening effects, classical crystallization techniques, microgravity and theoretical considerations.« less
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Large-volume protein crystal growth for neutron macromolecular crystallography
Ng, Joseph D.; Baird, James K.; Coates, Leighton; Garcia-Ruiz, Juan M.; Hodge, Teresa A.; Huang, Sijay
2015-01-01
Neutron macromolecular crystallography (NMC) is the prevailing method for the accurate determination of the positions of H atoms in macromolecules. As neutron sources are becoming more available to general users, finding means to optimize the growth of protein crystals to sizes suitable for NMC is extremely important. Historically, much has been learned about growing crystals for X-ray diffraction. However, owing to new-generation synchrotron X-ray facilities and sensitive detectors, protein crystal sizes as small as in the nano-range have become adequate for structure determination, lessening the necessity to grow large crystals. Here, some of the approaches, techniques and considerations for the growth of crystals to significant dimensions that are now relevant to NMC are revisited. These include experimental strategies utilizing solubility diagrams, ripening effects, classical crystallization techniques, microgravity and theoretical considerations. PMID:25849493
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Large-volume protein crystal growth for neutron macromolecular crystallography
DOE Office of Scientific and Technical Information (OSTI.GOV)
Ng, Joseph D.; Baird, James K.; Coates, Leighton
Neutron macromolecular crystallography (NMC) is the prevailing method for the accurate determination of the positions of H atoms in macromolecules. As neutron sources are becoming more available to general users, finding means to optimize the growth of protein crystals to sizes suitable for NMC is extremely important. Historically, much has been learned about growing crystals for X-ray diffraction. However, owing to new-generation synchrotron X-ray facilities and sensitive detectors, protein crystal sizes as small as in the nano-range have become adequate for structure determination, lessening the necessity to grow large crystals. Here, some of the approaches, techniques and considerations for themore » growth of crystals to significant dimensions that are now relevant to NMC are revisited. We report that these include experimental strategies utilizing solubility diagrams, ripening effects, classical crystallization techniques, microgravity and theoretical considerations.« less
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Morikawa, Satoshi; Inamoto, Takuya; Takashiri, Masayuki
2018-02-16
The effect of crystal grain size on the thermoelectric properties of nanocrystalline antimony telluride (Sb 2 Te 3 ) thin films was investigated by experiments and first-principles studies using a developed relaxation time approximation. The Sb 2 Te 3 thin films were deposited on glass substrates using radio-frequency magnetron sputtering. To change the crystal grain size of the Sb 2 Te 3 thin films, thermal annealing was performed at different temperatures. The crystal grain size, lattice parameter, and crystal orientation of the thin films were estimated using XRD patterns. The carrier concentration and in-plane thermoelectric properties of the thin films were measured at room temperature. A theoretical analysis was performed using a first-principles study based on density functional theory. The electronic band structures of Sb 2 Te 3 were calculated using different lattice parameters, and the thermoelectric properties were predicted based on the semi-classical Boltzmann transport equation in the relaxation time approximation. In particular, we introduced the effect of carrier scattering at the grain boundaries into the relaxation time approximation by estimating the group velocities from the electronic band structures. Finally, the experimentally measured thermoelectric properties were compared with those obtained by calculation. As a result, the calculated thermoelectric properties were found to be in good agreement with the experimental results. Therefore, we can conclude that introducing the effect of carrier scattering at the grain boundaries into the relaxation time approximation contributes to enhance the accuracy of a first-principles calculation relating to nanocrystalline materials.
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NASA Astrophysics Data System (ADS)
Morikawa, Satoshi; Inamoto, Takuya; Takashiri, Masayuki
2018-02-01
The effect of crystal grain size on the thermoelectric properties of nanocrystalline antimony telluride (Sb2Te3) thin films was investigated by experiments and first-principles studies using a developed relaxation time approximation. The Sb2Te3 thin films were deposited on glass substrates using radio-frequency magnetron sputtering. To change the crystal grain size of the Sb2Te3 thin films, thermal annealing was performed at different temperatures. The crystal grain size, lattice parameter, and crystal orientation of the thin films were estimated using XRD patterns. The carrier concentration and in-plane thermoelectric properties of the thin films were measured at room temperature. A theoretical analysis was performed using a first-principles study based on density functional theory. The electronic band structures of Sb2Te3 were calculated using different lattice parameters, and the thermoelectric properties were predicted based on the semi-classical Boltzmann transport equation in the relaxation time approximation. In particular, we introduced the effect of carrier scattering at the grain boundaries into the relaxation time approximation by estimating the group velocities from the electronic band structures. Finally, the experimentally measured thermoelectric properties were compared with those obtained by calculation. As a result, the calculated thermoelectric properties were found to be in good agreement with the experimental results. Therefore, we can conclude that introducing the effect of carrier scattering at the grain boundaries into the relaxation time approximation contributes to enhance the accuracy of a first-principles calculation relating to nanocrystalline materials.
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NASA Astrophysics Data System (ADS)
Rezaei, M.; Kermanpur, A.; Sadeghi, F.
2018-03-01
Fabrication of single crystal (SC) Ni-based gas turbine blades with a minimum crystal misorientation has always been a challenge in gas turbine industry, due to its significant influence on high temperature mechanical properties. This paper reports an experimental investigation and numerical simulation of the SC solidification process of a Ni-based superalloy to study effects of withdrawal rate and starter block size on crystal orientation. The results show that the crystal misorientation of the sample with 40 mm starter block height is decreased with increasing withdrawal rate up to about 9 mm/min, beyond which the amount of misorientation is increased. It was found that the withdrawal rate, height of the starter block and temperature gradient are completely inter-dependent and indeed achieving a SC specimen with a minimum misorientation needs careful optimization of these process parameters. The height of starter block was found to have higher impact on crystal orientation compared to the withdrawal rate. A suitable withdrawal rate regime along with a sufficient starter block height was proposed to produce SC parts with the lowest misorientation.
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NASA Technical Reports Server (NTRS)
Han, Qingyuan; Rossow, William B.; Chou, Joyce; Welch, Ronald M.
1997-01-01
Cloud microphysical parameterizations have attracted a great deal of attention in recent years due to their effect on cloud radiative properties and cloud-related hydrological processes in large-scale models. The parameterization of cirrus particle size has been demonstrated as an indispensable component in the climate feedback analysis. Therefore, global-scale, long-term observations of cirrus particle sizes are required both as a basis of and as a validation of parameterizations for climate models. While there is a global scale, long-term survey of water cloud droplet sizes (Han et al. 1994), there is no comparable study for cirrus ice crystals. In this paper a near-global survey of cirrus ice crystal sizes is conducted using ISCCP satellite data analysis. The retrieval scheme uses phase functions based upon hexagonal crystals calculated by a ray tracing technique. The results show that global mean values of D(e) are about 60 micro-m. This study also investigates the possible reasons for the significant difference between satellite retrieved effective radii (approx. 60 micro-m) and aircraft measured particle sizes (approx. 200 micro-m) during the FIRE I IFO experiment. They are (1) vertical inhomogeneity of cirrus particle sizes; (2) lower limit of the instrument used in aircraft measurements; (3) different definitions of effective particle sizes; and (4) possible inappropriate phase functions used in satellite retrieval.
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Klijn, Marieke E; Hubbuch, Jürgen
2018-04-27
Protein phase diagrams are a tool to investigate cause and consequence of solution conditions on protein phase behavior. The effects are scored according to aggregation morphologies such as crystals or amorphous precipitates. Solution conditions affect morphological features, such as crystal size, as well as kinetic features, such as crystal growth time. Common used data visualization techniques include individual line graphs or symbols-based phase diagrams. These techniques have limitations in terms of handling large datasets, comprehensiveness or completeness. To eliminate these limitations, morphological and kinetic features obtained from crystallization images generated with high throughput microbatch experiments have been visualized with radar charts in combination with the empirical phase diagram (EPD) method. Morphological features (crystal size, shape, and number, as well as precipitate size) and kinetic features (crystal and precipitate onset and growth time) are extracted for 768 solutions with varying chicken egg white lysozyme concentration, salt type, ionic strength and pH. Image-based aggregation morphology and kinetic features were compiled into a single and easily interpretable figure, thereby showing that the EPD method can support high throughput crystallization experiments in its data amount as well as its data complexity. Copyright © 2018. Published by Elsevier Inc.
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Shear induced orientation of edible fat and chocolate crystals
NASA Astrophysics Data System (ADS)
Mazzanti, Gianfranco; Welch, Sarah E.; Marangoni, Alejandro G.; Sirota, Eric B.; Idziak, Stefan H. J.
2003-03-01
Shear-induced orientation of fat crystallites was observed during crystallization of cocoa butter, milk fat, stripped milk fat and palm oil. This universal effect was observed in systems crystallized under high shear. The minor polar components naturally present in milk fat were found to decrease the shear-induced orientation effect in this system. The competition between Brownian and shear forces, described by the Peclet number, determines the crystallite orientation. The critical radius size, from the Gibbs-Thomson equation, provides a tool to understand the effect of shear at the onset stages of crystallization.
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Modeling solute clustering in the diffusion layer around a growing crystal.
Shiau, Lie-Ding; Lu, Yung-Fang
2009-03-07
The mechanism of crystal growth from solution is often thought to consist of a mass transfer diffusion step followed by a surface reaction step. Solute molecules might form clusters in the diffusion step before incorporating into the crystal lattice. A model is proposed in this work to simulate the evolution of the cluster size distribution due to the simultaneous aggregation and breakage of solute molecules in the diffusion layer around a growing crystal in the stirred solution. The crystallization of KAl(SO(4))(2)12H(2)O from aqueous solution is studied to illustrate the effect of supersaturation and diffusion layer thickness on the number-average degree of clustering and the size distribution of solute clusters in the diffusion layer.
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Lin, Xiuchun; Li, Jingyi; Ma, Si; Liu, Gesheng; Yang, Kun; Tong, Meiping; Lin, Daohui
2014-01-01
Controversial and inconsistent results on the eco-toxicity of TiO2 nanoparticles (NPs) are commonly found in recorded studies and more experimental works are therefore warranted to elucidate the nanotoxicity and its underlying precise mechanisms. Toxicities of five types of TiO2 NPs with different particle sizes (10∼50 nm) and crystal phases were investigated using Escherichia coli as a test organism. The effect of water chemistry on the nanotoxicity was also examined. The antibacterial effects of TiO2 NPs as revealed by dose-effect experiments decreased with increasing particle size and rutile content of the TiO2 NPs. More bacteria could survive at higher solution pH (5.0–10.0) and ionic strength (50–200 mg L−1 NaCl) as affected by the anatase TiO2 NPs. The TiO2 NPs with anatase crystal structure and smaller particle size produced higher content of intracellular reactive oxygen species and malondialdehyde, in line with their greater antibacterial effect. Transmission electron microscopic observations showed the concentration buildup of the anatase TiO2 NPs especially those with smaller particle sizes on the cell surfaces, leading to membrane damage and internalization. These research results will shed new light on the understanding of ecological effects of TiO2 NPs. PMID:25310452
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Nadra, Imad; Boccaccini, Aldo R; Philippidis, Pandelis; Whelan, Linda C; McCarthy, Geraldine M; Haskard, Dorian O; Landis, R Clive
2008-01-01
Macrophages may promote a vicious cycle of inflammation and calcification in the vessel wall by ingesting neointimal calcific deposits (predominantly hydroxyapatite) and secreting tumor necrosis factor (TNF)alpha, itself a vascular calcifying agent. Here we have investigated whether particle size affects the proinflammatory potential of hydroxyapatite crystals in vitro and whether the nuclear factor (NF)-kappaB pathway plays a role in the macrophage TNFalpha response. The particle size and nano-topography of nine different crystal preparations was analyzed by X-ray diffraction, Raman spectroscopy, scanning electron microscopy and gas sorbtion analysis. Macrophage TNFalpha secretion was inversely related to hydroxyapatite particle size (P=0.011, Spearman rank correlation test) and surface pore size (P=0.014). A necessary role for the NF-kappaB pathway was demonstrated by time-dependent I kappaB alpha degradation and sensitivity to inhibitors of I kappaB alpha degradation. To test whether smaller particles were intrinsically more bioactive, their mitogenic activity on fibroblast proliferation was examined. This showed close correlation between TNFalpha secretion and crystal-induced fibroblast proliferation (P=0.007). In conclusion, the ability of hydroxyapatite crystals to stimulate macrophage TNFalpha secretion depends on NF-kappaB activation and is inversely related to particle and pore size, with crystals of 1-2 microm diameter and pore size of 10-50 A the most bioactive. Microscopic calcific deposits in early stages of atherosclerosis may therefore pose a greater inflammatory risk to the plaque than macroscopically or radiologically visible deposits in more advanced lesions.
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Effect of temperature on the formation of creep substructure in sodium chloride single crystals
NASA Technical Reports Server (NTRS)
Raj, Sai V.; Pharr, George M.
1992-01-01
The effect of temperature on the substructure morphology and the cell and subgrain size was investigated experimentally in NaCl single crystals under creep in the temperature range 573-873 K. It is found that the effect of temperature on the cell and subgrain sizes is weak in comparison with the effect of stress. However, there was a qualitative change in the substructure morphology with temperature, with the cells and subgrains better defined at higher temperatures. The volume fraction of the cell boundaries decreased with increasing temperature, thereby indicating a refinement of the microstructure at higher temperatures.
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Effect of medicinal plants on the crystallization of cholesterol
NASA Astrophysics Data System (ADS)
Saraswathi, N. T.; Gnanam, F. D.
1997-08-01
One of the least desirable calcifications in the human body is the mineral deposition in atherosclerosis plaques. These plaques principally consist of lipids such as cholesterol, cholesteryl esters, phospholipids and triglycerides. Chemical analysis of advanced plaques have shown the presence of considerable amounts of free cholesterol identified as cholesterol monohydrate crystals. Cholesterol has been crystallized in vitro. The extracts of some of the Indian medicinal plants detailed below were used as additives to study their effect on the crystallization behaviour of cholesterol. It has been found that many of the herbs have inhibitory effect on the crystallization such as nucleation, crystal size and habit modification. The inhibitory effect of the plants are graded as Commiphora mughul > Aegle marmeleos > Cynoden dactylon > Musa paradisiaca > Polygala javana > Alphinia officinarum > Solanum trilobatum > Enicostemma lyssopifolium.
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NASA Astrophysics Data System (ADS)
Miyamoto, Ryoma; Utano, Tatsumi; Yasuhara, Shunya; Ishihara, Shota; Ohshima, Masahiro
2015-05-01
In this study, the core-back foam injection molding was used for preparing microcelluar polypropylene (PP) foam with either a 1,3:2,4 bis-O-(4-methylbenzylidene)-D-sorbitol gelling agent (Gel-all MD) or a fibros network polymer additive (Metablen 3000). Both agent and addiive could effectively control the celluar morphology in foams but somehow different ways. In course of cooling the polymer with Gel-all MD in the mold caity, the agent enhanced the crystal nucleation and resulted in the large number of small crystals. The crystals acted as effective bubble nucleation agent in foaming process. Thus, the agent reduced the cell size and increased the cell density, drastically. Furthermore, the small crystals provided an inhomogenuity to the expanding cell wall and produced the high open cell content with nano-scale fibril structure. Gell-all as well as Metablene 3000 formed a gel-like fibrous network in melt. The network increased the elongational viscosity and tended to prevent the cell wall from breaking up. The foaming temperature window was widened by the presence of the network. Especially, the temperature window where the macro-fibrous structure was formed was expanded to the higher temperature. The effects of crystal nucleating agent and PTFE on crystals' size and number, viscoelsticity, rheological propreties of PP and cellular morphology were compared and thorougly investigated.
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Color from hierarchy: Diverse optical properties of micron-sized spherical colloidal assemblies.
Vogel, Nicolas; Utech, Stefanie; England, Grant T; Shirman, Tanya; Phillips, Katherine R; Koay, Natalie; Burgess, Ian B; Kolle, Mathias; Weitz, David A; Aizenberg, Joanna
2015-09-01
Materials in nature are characterized by structural order over multiple length scales have evolved for maximum performance and multifunctionality, and are often produced by self-assembly processes. A striking example of this design principle is structural coloration, where interference, diffraction, and absorption effects result in vivid colors. Mimicking this emergence of complex effects from simple building blocks is a key challenge for man-made materials. Here, we show that a simple confined self-assembly process leads to a complex hierarchical geometry that displays a variety of optical effects. Colloidal crystallization in an emulsion droplet creates micron-sized superstructures, termed photonic balls. The curvature imposed by the emulsion droplet leads to frustrated crystallization. We observe spherical colloidal crystals with ordered, crystalline layers and a disordered core. This geometry produces multiple optical effects. The ordered layers give rise to structural color from Bragg diffraction with limited angular dependence and unusual transmission due to the curved nature of the individual crystals. The disordered core contributes nonresonant scattering that induces a macroscopically whitish appearance, which we mitigate by incorporating absorbing gold nanoparticles that suppress scattering and macroscopically purify the color. With increasing size of the constituent colloidal particles, grating diffraction effects dominate, which result from order along the crystal's curved surface and induce a vivid polychromatic appearance. The control of multiple optical effects induced by the hierarchical morphology in photonic balls paves the way to use them as building blocks for complex optical assemblies--potentially as more efficient mimics of structural color as it occurs in nature.
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Size-dependent cellular uptake mechanism and cytotoxicity toward calcium oxalate on Vero cells
NASA Astrophysics Data System (ADS)
Sun, Xin-Yuan; Gan, Qiong-Zhi; Ouyang, Jian-Ming
2017-02-01
Urinary crystals with various sizes are present in healthy individuals and patients with kidney stone; however, the cellular uptake mechanism of calcium oxalate of various sizes has not been elucidated. This study aims to compare the internalization of nano-/micron-sized (50 nm, 100 nm, and 1 μm) calcium oxalate monohydrate (COM) and dihydrate (COD) crystals in African green monkey renal epithelial (Vero) cells. The internalization and adhesion of COM and COD crystals to Vero cells were enhanced with decreasing crystal size. Cell death rate was positively related to the amount of adhered and internalized crystals and exhibited higher correlation with internalization than that with adhesion. Vero cells mainly internalized nano-sized COM and COD crystals through clathrin-mediated pathways as well as micron-sized crystals through macropinocytosis. The internalized COM and COD crystals were distributed in the lysosomes and destroyed lysosomal integrity to some extent. The results of this study indicated that the size of crystal affected cellular uptake mechanism, and may provide an enlightenment for finding potential inhibitors of crystal uptake, thereby decreasing cell injury and the occurrence of kidney stones.
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Effect of Mg2+ on acidic calcium phosphate phases grown by electrodeposition
NASA Astrophysics Data System (ADS)
Correia, Matheus Bento; Júnior, José Pedro Gualberto; Macedo, Michelle Cardinale S. S.; Resende, Cristiane Xavier; dos Santos, Euler Araujo
2017-10-01
In this work, the effect of Mg2+ ions on the electrodeposition of dicalcium phosphate dihydrate (DCPD), octacalcium phosphate (OCP) and calcium-deficient hydroxyapatite (CDHA) crystals on a commercially pure titanium (cp-Ti) substrate was evaluated. We demonstrated that Mg2+ ions could change the morphology of the coatings by inhibiting the growth rate of the OCP and CDHA crystals and diminishing the crystallite size of DCPD. The inhibition effect on OCP and CDHA was most likely due to a surface adsorption mechanism since no evidence of a doping process was observed using Rietveld refinement and electron diffraction analyses. Conversely, the presence of Mg2+ ions generated a favorable condition for the nucleation of a new Mg2+-rich DCPD crystal population, presenting smaller crystallite sizes.
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Chen, K.; Meng, W. J.; Mei, F.
2011-02-01
A single crystal Al specimen was molded at room temperature with long, rectangular, strip diamond punches. Quantitative molding response curves were obtained at a series of punch widths, ranging from 5 {micro}m to 550 nm. A significant size effect was observed, manifesting itself in terms of significantly increasing characteristic molding pressure as the punch width decreases to 1.5 {micro}m and below. A detailed comparison of the present strip punch molding results was made with Berkovich pyramidal indentation on the same single crystal Al specimen. The comparison reveals distinctly different dependence of the characteristic pressure on corresponding characteristic length. The presentmore » results show the feasibility of micro-/nano-scale compression molding as a micro-/nano-fabrication technique, and offer an experimental test case for size-dependent plasticity theories.« less
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NASA Astrophysics Data System (ADS)
Tahrin, Rabiatul Addawiyah Azwa; Azma, Nur Syafiqa; Kassim, Syara; Harun, Noor Aniza
2017-09-01
3-dimensional (3D) photonic crystals have been extended use in wide research and application from material to sensor. Nanoparticles of poly (methyl methacrylate) (PMMA) latex beads have been successfully prepared by green-chemistry approach where no surfactant, linking agent and solvent were involved. Regardless of the effect of initiator in polymerization reaction, this study presents the effect of temperature, monomer concentration, stirring speed and reaction period in order to tune the particle size. Its morphology of uniformity sized-tuned was confirming by using particle size analyzer (PSA) and scanning electron microscopy (SEM). The fabrication of 3D photonic crystals film by using self-assembly method to pattern the desired PMMA layers which is the most feasible, low cost method are also presented. The detailed properties of PMMA nanoparticles from this experimental study will be discussed and its potential used in photonic application will be explained.
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Farley, Christopher; Burks, Geoffry; Siegert, Thomas; Juers, Douglas H
2014-08-01
In macromolecular cryocrystallography unit-cell parameters can have low reproducibility, limiting the effectiveness of combining data sets from multiple crystals and inhibiting the development of defined repeatable cooling protocols. Here, potential sources of unit-cell variation are investigated and crystal dehydration during loop-mounting is found to be an important factor. The amount of water lost by the unit cell depends on the crystal size, the loop size, the ambient relative humidity and the transfer distance to the cooling medium. To limit water loss during crystal mounting, a threefold strategy has been implemented. Firstly, crystal manipulations are performed in a humid environment similar to the humidity of the crystal-growth or soaking solution. Secondly, the looped crystal is transferred to a vial containing a small amount of the crystal soaking solution. Upon loop transfer, the vial is sealed, which allows transport of the crystal at its equilibrated humidity. Thirdly, the crystal loop is directly mounted from the vial into the cold gas stream. This strategy minimizes the exposure of the crystal to relatively low humidity ambient air, improves the reproducibility of low-temperature unit-cell parameters and offers some new approaches to crystal handling and cryoprotection.
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Farley, Christopher; Burks, Geoffry; Siegert, Thomas; Juers, Douglas H.
2014-01-01
In macromolecular cryocrystallography unit-cell parameters can have low reproducibility, limiting the effectiveness of combining data sets from multiple crystals and inhibiting the development of defined repeatable cooling protocols. Here, potential sources of unit-cell variation are investigated and crystal dehydration during loop-mounting is found to be an important factor. The amount of water lost by the unit cell depends on the crystal size, the loop size, the ambient relative humidity and the transfer distance to the cooling medium. To limit water loss during crystal mounting, a threefold strategy has been implemented. Firstly, crystal manipulations are performed in a humid environment similar to the humidity of the crystal-growth or soaking solution. Secondly, the looped crystal is transferred to a vial containing a small amount of the crystal soaking solution. Upon loop transfer, the vial is sealed, which allows transport of the crystal at its equilibrated humidity. Thirdly, the crystal loop is directly mounted from the vial into the cold gas stream. This strategy minimizes the exposure of the crystal to relatively low humidity ambient air, improves the reproducibility of low-temperature unit-cell parameters and offers some new approaches to crystal handling and cryoprotection. PMID:25084331
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Wu, Congcong; Sun, Zhaomei; Liu, Li-Shang
2017-07-10
The surface crystallization of CaCO 3 on gold was monitored by a quartz crystal microbalance (QCM). Quantitative control of the grown crystals was realized by adjusting the ratio of two functional groups, -N(CH 3 ) 3 and -COOH, on SAMs. Crystals with uniform size, morphology and polymorphism were obtained. The amount of crystals formed was found to increase with an increase in the -COOH group. The proposed quantitative control of crystallization can be an effective mass amplification strategy for QCM to enhance its assay sensitivity.
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NASA Astrophysics Data System (ADS)
Deleer, B. G. M.
1981-11-01
Based on population balance, CSD behavior as a function of geometrical and operating variables was studied, using a crystallizer. A potash alum-water system, involving a separation technique which uses surface active agents and an apolar, organic liquid to separate potash alum crystals from mother liquid under the influence of gravity was used to check experimental findings against literature data. Results show action of annular settling spaces is strongly influenced by fluid velocities perpendicular to those directed upwards. The well-mixed volume decreases with increasing crystallizer size until a minimum effective volume is reached. As supersaturation is constant throughout the crystallizer volume under stationary operating conditions, the annular settling space behaves like a growth chamber for crystals in its volume. Swirl in the lower part of the annular volume introduces significant back mixing. Crystals within this space either grow and return to the well-mixed part, or withdraw from the annular volume permanently.
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Kim, Byeonggon; Kim, Hyun Gyu; Shim, Gyu-Yeop; Park, Ji-Sub; Joo, Kyung-Il; Lee, Dong-Jin; Lee, Joun-Ho; Baek, Ji-Ho; Kim, Byeong Koo; Choi, Yoonseuk; Kim, Hak-Rin
2018-01-10
We proposed and analyzed an optically isotropic nano-droplet liquid crystal (LC) doped with high k nanoparticles (NPs), exhibiting enhanced Kerr effects, which could be operated with reduced driving voltages. For enhancing the contrast ratio together with the light efficiencies, the LC droplet sizes were adjusted to be shorter than the wavelength of visible light to reduce depolarization effects by optical scattering of the LC droplets. Based on the optical analysis of the depolarization effects, the influence of the relationship between the LC droplet size and the NP doping ratio on the Kerr effect change was investigated.
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Hosokawa, Akihiro; Kato, Yoshiteru
2011-08-01
The purpose of this article is to study factors affecting color strength of printing on film-coated tablets by ultraviolet (UV) laser irradiation: particle size, crystal structure, or concentration of titanium dioxide (TiO2) in film, and irradiated UV laser power. Hydroxypropylmethylcellulose films containing 4.0% of TiO2, of which BET particle sizes were ranging from 126.1 to 219.8 nm, were irradiated 3.14W of UV laser at a wavelength 355 nm to study effects of TiO2 particle size and crystal structure on the printing. The films containing TiO2 concentration ranging from 1.0 to 7.7% were irradiated 3.14 or 5.39W of the UV laser to study effect of TiO2 concentration on the printing. The film containing 4.0% of TiO2, was irradiated the UV laser up to 6.42W to study effect of the UV laser power on the printing. The color strength of the printed films was estimated by a spectrophotometer as total color difference (dE). Particle size, crystal structure, and concentration of TiO2 in the films did not affect the printing. In the relationship between the irradiated UV laser power and dE, there found an inflection point (1.6W). When the UV laser power was below 1.6W, the films were not printed. When it was beyond the point, total color difference increased linearly in proportion with the irradiated laser power. The color strength of the printing on film was not changed by TiO2 particle size, crystal structure, and concentration, but could be controlled by regulating the irradiated UV laser power beyond the inflection point.
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Eberl, D.D.; Drits, V.A.; Środoń, Jan; Nüesch, R.
1996-01-01
Particle size may strongly influence the physical and chemical properties of a substance (e.g. its rheology, surface area, cation exchange capacity, solubility, etc.), and its measurement in rocks may yield geological information about ancient environments (sediment provenance, degree of metamorphism, degree of weathering, current directions, distance to shore, etc.). Therefore mineralogists, geologists, chemists, soil scientists, and others who deal with clay-size material would like to have a convenient method for measuring particle size distributions. Nano-size crystals generally are too fine to be measured by light microscopy. Laser scattering methods give only average particle sizes; therefore particle size can not be measured in a particular crystallographic direction. Also, the particles measured by laser techniques may be composed of several different minerals, and may be agglomerations of individual crystals. Measurement by electron and atomic force microscopy is tedious, expensive, and time consuming. It is difficult to measure more than a few hundred particles per sample by these methods. This many measurements, often taking several days of intensive effort, may yield an accurate mean size for a sample, but may be too few to determine an accurate distribution of sizes. Measurement of size distributions by X-ray diffraction (XRD) solves these shortcomings. An X-ray scan of a sample occurs automatically, taking a few minutes to a few hours. The resulting XRD peaks average diffraction effects from billions of individual nano-size crystals. The size that is measured by XRD may be related to the size of the individual crystals of the mineral in the sample, rather than to the size of particles formed from the agglomeration of these crystals. Therefore one can determine the size of a particular mineral in a mixture of minerals, and the sizes in a particular crystallographic direction of that mineral.
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The study of VOPc thin film transistors on modified substrates
NASA Astrophysics Data System (ADS)
Song, De; Xu, Qi; Cheng, Hongcang; Li, Bao-zeng; Shang, Yubin
2018-02-01
The vanadyl phthalocyanine (VOPc) organic thin film transistors (OTFTs) were fabricated on the various organosilane self-assembled monolayer (SAM) modified substrates. And the effect of the surface properties on the performance of these transistors was studied. The atomic force morphologies and X-ray diffraction (XRD) spectrums of vanadyl phthalocyanine films on different SAM-modified surfaces were studied. They reveal that the terminal functional groups of organosilane affect the growth of VOPc film and device performance. The VOPc film on octadecyltrichlorosilane (OTS) modified substrate has larger crystal size and effective crystal thickness than those on phenyltrichlorosilane (PTS), 1H,1H,2H,2H-Perfluorodec-yltrichlorosilane (FDTS) as well as non-modified substrate, which contributes the mobility of corresponding device several and several dozen times relative to other ones. The effective crystal thickness and crystal grain size of VOPc film on PTS is between that on OTS treated and that on non-modified substrate due to the stronger attractive force between VOPc and SiO2. The VOPc films' performance and effective crystal thickness on FDTS treated are worse than that on PTS due to the existents of attractive force between -CF3 and VOPc.
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NASA Technical Reports Server (NTRS)
Li, C.
1975-01-01
Computer programs are developed and used in the study of the combined effects of evaporation and solidification in space processing. The temperature and solute concentration profiles during directional solidification of binary alloys with surface evaporation were mathematically formulated. Computer results are included along with an econotechnical model of crystal growth. This model allows: prediction of crystal size, quality, and cost; systematic selection of the best growth equipment or alloy system; optimization of growth or material parameters; and a maximization of zero-gravity effects. Segregation in GaAs crystals was examined along with vibration effects on GaAs crystal growth. It was found that a unique segregation pattern and strong convention currents exist in GaAs crystal growth. Some beneficial effects from vibration during GaAs growth were discovered. The implications of the results in space processing are indicated.
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Zhang, Zhenzhen; Guo, Jiawen; Sun, Yali; Tian, Beimin; Zheng, Xiaojuan; Zhou, Ming; He, Lin; Zhang, Shaofeng
2018-05-01
The purpose of this study is to improve wear resistance and mechanical properties of lithium disilicate glass-ceramics by refining their crystal sizes. After lithium disilicate glass-ceramics (LD) were melted to form precursory glass blocks, bar (N = 40, n = 10) and plate (N = 32, n = 8) specimens were prepared. According to the differential scanning calorimetry (DSC) of precursory glass, specimens G1-G4 were designed to form lithium disilicate glass-ceramics with different crystal sizes using a two-step thermal treatment. In the meantime, heat-pressed lithium disilicate glass-ceramics (GC-P) and original ingots (GC-O) were used as control groups. Glass-ceramics were characterized using X-ray diffraction (XRD) and were tested using flexural strength test, nanoindentation test and toughness measurements. The plate specimens were dynamically loaded in a chewing simulator with 350 N up to 2.4 × 10 6 loading cycles. The wear analysis of glass-ceramics was performed using a 3D profilometer after every 300,000 wear cycles. Wear morphologies and microstructures were analyzed by scanning electron microscopy (SEM). One-way analysis of variance (ANOVA) was used to analyze the data. Multiple pairwise comparisons of means were performed by Tukey's post-hoc test. Materials with different crystal sizes (p < 0.05) exhibited different properties. Specifically, G3 with medium-sized crystals presented the highest flexural strength, hardness, elastic modulus and fracture toughness. G1 and G2 with small-sized crystals showed lower flexural strength, whereas G4, GC-P, and GC-O with large-sized crystals exhibited lower hardness and elastic modulus. The wear behaviors of all six groups showed running-in wear stage and steady wear stage. G3 showed the best wear resistance while GC-P and GC-O exhibited the highest wear volume loss. After crystal refining, lithium disilicate glass-ceramic with medium-sized crystals showed the highest wear resistance and mechanical properties. Copyright © 2018 Elsevier Ltd. All rights reserved.
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NASA Astrophysics Data System (ADS)
Zahari, Zakirah Mohd; Zubaidah Adnan, Siti; Kanthasamy, Ramesh; Saleh, Suriyati; Samad, Noor Asma Fazli Abdul
2018-03-01
The specification of the crystal product is usually given in terms of crystal size distribution (CSD). To this end, optimal cooling strategy is necessary to achieve the CSD. The direct design control involving analytical CSD estimator is one of the approaches that can be used to generate the set-point. However, the effects of temperature on the crystal growth rate are neglected in the estimator. Thus, the temperature dependence on the crystal growth rate needs to be considered in order to provide an accurate set-point. The objective of this work is to extend the analytical CSD estimator where Arrhenius expression is employed to cover the effects of temperature on the growth rate. The application of this work is demonstrated through a potassium sulphate crystallisation process. Based on specified target CSD, the extended estimator is capable of generating the required set-point where a proposed controller successfully maintained the operation at the set-point to achieve the target CSD. Comparison with other cooling strategies shows a reduction up to 18.2% of the total number of undesirable crystals generated from secondary nucleation using linear cooling strategy is achieved.
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NASA Technical Reports Server (NTRS)
Gatsonis, Nikos A.; Alexandrou, Andreas; Shi, Hui; Ongewe, Bernard; Sacco, Albert, Jr.
1999-01-01
Crystals grown from liquid solutions have important industrial applications. Zeolites, for instance, a class of crystalline aluminosilicate materials, form the backbone of the chemical process industry worldwide, as they are used as adsorbents and catalysts. Many of the phenomena associated with crystal growth processes are not well understood due to complex microscopic and macroscopic interactions. Microgravity could help elucidate these phenomena and allow the control of defect locations, concentration, as well as size of crystals. Microgravity in an orbiting spacecraft could help isolate the possible effects of natural convection (which affects defect formation) and minimize sedimentation. In addition, crystals will stay essentially suspended in the nutrient pool under a diffusion-limited growth condition. This is expected to promote larger crystals by allowing a longer residence time in a high-concentration nutrient field. Among other factors, the crystal size distribution depends on the nucleation rate and crystallization. These two are also related to the "gel" polymerization/depolymerization rate. Macroscopic bulk mass and flow transport and especially gravity, force the crystals down to the bottom of the reactor, thus forming a sedimentation layer. In this layer, the growth rate of the crystals slows down as crystals compete for a limited amount of nutrients. The macroscopic transport phenomena under certain conditions can, however, enhance the nutrient supply and therefore, accelerate crystal growth. Several zeolite experiments have been performed in space with mixed results. The results from our laboratory have indicated an enhancement in size of 30 to 70 percent compared to the best ground based controls, and a reduction of lattice defects in many of the space grown crystals. Such experiments are difficult to interpret, and cannot be easily used to derive empirical or other laws since many physical parameters are simultaneously involved in the process. At the same time, however, there is increased urgency to develop such an understanding in order to more accurately quantify the process. In order to better understand the results obtained from our prior space experiments, and design future experiments, a detailed fluid dynamic model simulating the crystal growth mechanism is required. This will not only add to the fundamental knowledge on the crystallization of zeolites, but also be useful in predicting the limits of size and growth of these important industrial materials. Our objective is to develop macro/microscopic theoretical and computational models to study the effect of transport phenomena in the growth of crystals grown in solutions. Our effort has concentrated so far in the development of separate macroscopic and microscopic models. The major highlights of our accomplishments are described.
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Global statistics of microphysical properties of cloud-top ice crystals
NASA Astrophysics Data System (ADS)
van Diedenhoven, B.; Fridlind, A. M.; Cairns, B.; Ackerman, A. S.; Riedi, J.
2017-12-01
Ice crystals in clouds are highly complex. Their sizes, macroscale shape (i.e., habit), mesoscale shape (i.e., aspect ratio of components) and microscale shape (i.e., surface roughness) determine optical properties and affect physical properties such as fall speeds, growth rates and aggregation efficiency. Our current understanding on the formation and evolution of ice crystals under various conditions can be considered poor. Commonly, ice crystal size and shape are related to ambient temperature and humidity, but global observational statistics on the variation of ice crystal size and particularly shape have not been available. Here we show results of a project aiming to infer ice crystal size, shape and scattering properties from a combination of MODIS measurements and POLDER-PARASOL multi-angle polarimetry. The shape retrieval procedure infers the mean aspect ratios of components of ice crystals and the mean microscale surface roughness levels, which are quantifiable parameters that mostly affect the scattering properties, in contrast to "habit". We present global statistics on the variation of ice effective radius, component aspect ratio, microscale surface roughness and scattering asymmetry parameter as a function of cloud top temperature, latitude, location, cloud type, season, etc. Generally, with increasing height, sizes decrease, roughness increases, asymmetry parameters decrease and aspect ratios increase towards unity. Some systematic differences are observed for clouds warmer and colder than the homogeneous freezing level. Uncertainties in the retrievals will be discussed. These statistics can be used as observational targets for modeling efforts and to better constrain other satellite remote sensing applications and their uncertainties.
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Global Statistics of Microphysical Properties of Cloud-Top Ice Crystals
NASA Technical Reports Server (NTRS)
Van Diedenhoven, Bastiaan; Fridlind, Ann; Cairns, Brian; Ackerman, Andrew; Riedl, Jerome
2017-01-01
Ice crystals in clouds are highly complex. Their sizes, macroscale shape (i.e., habit), mesoscale shape (i.e., aspect ratio of components) and microscale shape (i.e., surface roughness) determine optical properties and affect physical properties such as fall speeds, growth rates and aggregation efficiency. Our current understanding on the formation and evolution of ice crystals under various conditions can be considered poor. Commonly, ice crystal size and shape are related to ambient temperature and humidity, but global observational statistics on the variation of ice crystal size and particularly shape have not been available. Here we show results of a project aiming to infer ice crystal size, shape and scattering properties from a combination of MODIS measurements and POLDER-PARASOL multi-angle polarimetry. The shape retrieval procedure infers the mean aspect ratios of components of ice crystals and the mean microscale surface roughness levels, which are quantifiable parameters that mostly affect the scattering properties, in contrast to a habit. We present global statistics on the variation of ice effective radius, component aspect ratio, microscale surface roughness and scattering asymmetry parameter as a function of cloud top temperature, latitude, location, cloud type, season, etc. Generally, with increasing height, sizes decrease, roughness increases, asymmetry parameters decrease and aspect ratios increase towards unity. Some systematic differences are observed for clouds warmer and colder than the homogeneous freezing level. Uncertainties in the retrievals will be discussed. These statistics can be used as observational targets for modeling efforts and to better constrain other satellite remote sensing applications and their uncertainties.
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In situ encapsulation of liquids by means of crystallization
NASA Astrophysics Data System (ADS)
Hartwig, Anne; Ulrich, Joachim
2017-07-01
The in situ encapsulation process is due to its few process steps an innovative and cost effective alternative to common encapsulation techniques. It combines the well-known processes of pastillation and crystallization. This concept is proven with case studies of three xylitol capsules which vary in composition and size. It could be shown that the knowledge concerning the solubility of the components is essential to determine the suitable production conditions. The application of seed crystals and the temperatures during the process have major effects on the capsules quality. A fast crystallization of the capsules results in an instable shell. However, with increasing layer thickness of the shell, the crushing force that needs to be applied to break the capsules is increasing as well. But the stability which is related to the capsules size is decreasing with increasing diameter, even though layer thickness and crushing force are increasing, too.
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Bustamante, Eugenia L; Fernández, José L; Zamaro, Juan M
2014-06-15
The effect of the solvent on the synthesis process and on the nanocrystal characteristics of the zeolitic imidazolate framework-8 (ZIF-8) was investigated. A synthesis protocol at room temperature employing a series of aliphatic alcohols, water, dimethylformamide and acetone was employed. The results show that the solvent modifies the evolution of the reaction, altering the crystallization rates and nanocrystal sizes. Its hydrogen bond donation ability is the main factor that governs this effect. More precisely, the solvent modulates the formation of ZIF-8 nanocrystals with sizes in the range between 15 and 42 nm. When synthesized in alcohol and acetone, these nanocrystals form globular aggregates with sizes between 130 and 420 nm. In contrast, under the same synthesis conditions, when using water or dimethylformamide the ZIF phase is not developed. In alcohols other than methanol, the crystals develop pill-shaped morphologies with poorly defined facets. Moreover, a markedly fast growing kinetics is verified in these alcohols, leading to an ultra-fast crystallization of ZIF-8 in about 60s. These findings provide new information about the role of the solvent in the synthesis process of nanoZIF-8, which can be useful for controlling the crystallization rates and nanocrystal sizes of this material. Copyright © 2014 Elsevier Inc. All rights reserved.
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Reduction of glycine particle size by impinging jet crystallization.
Tari, Tímea; Fekete, Zoltán; Szabó-Révész, Piroska; Aigner, Zoltán
2015-01-15
The parameters of crystallization processes determine the habit and particle size distribution of the products. A narrow particle size distribution and a small average particle size are crucial for the bioavailability of poorly water-soluble pharmacons. Thus, particle size reduction is often required during crystallization processes. Impinging jet crystallization is a method that results in a product with a reduced particle size due to the homogeneous and high degree of supersaturation at the impingement point. In this work, the applicability of the impinging jet technique as a new approach in crystallization was investigated for the antisolvent crystallization of glycine. A factorial design was applied to choose the relevant crystallization factors. The results were analysed by means of a statistical program. The particle size distribution of the crystallized products was investigated with a laser diffraction particle size analyser. The roundness and morphology were determined with the use of a light microscopic image analysis system and a scanning electron microscope. Polymorphism was characterized by differential scanning calorimetry and powder X-ray diffraction. Headspace gas chromatography was utilized to determine the residual solvent content. Impinging jet crystallization proved to reduce the particle size of glycine. The particle size distribution was appropriate, and the average particle size was an order of magnitude smaller (d(0.5)=8-35 μm) than that achieved with conventional crystallization (d(0.5)=82-680 μm). The polymorphic forms of the products were influenced by the solvent ratio. The quantity of residual solvent in the crystallized products was in compliance with the requirements of the International Conference on Harmonization. Copyright © 2014 Elsevier B.V. All rights reserved.
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NASA Astrophysics Data System (ADS)
Lindsey, Adam C.; Zhuravleva, Mariya; Wu, Yuntao; Stand, Luis; Loyd, Matthew; Gokhale, Sasmit; Koschan, Merry; Melcher, Charles L.
2016-09-01
KCaI3:Eu crystals have been identified as very promising for use in spectroscopic detector applications related to nuclear nonproliferation and domestic security efforts. Initial studies have shown for small crystals a few mm3 in size with 3% europium dopant concentration, a high light yield of >70,000 ph/MeV and energy resolution of ≈3% at 662 keV is attainable which is comparable with the highest performance scintillators discovered. In this work, single crystals of KCaI3 with a range of Eu2+ doping between 0 and 5 at% substituting for Ca2+ were grown at 22 mm diameter and their performance for gamma-ray spectroscopy studied. Comparisons among crystals approximately Ø22 mm×22 mm (8.4 cm3 or ≈0.5 in3) provide a more accurate understanding of how scintillation performance changes with Eu doping and increased crystal size. KCaI3 in the undoped form is shown to be a highly efficient intrinsic scintillator with a defect-related emission at 404 nm which coexists with the Eu2+ 5d-4f emission in low dopant concentrations and is completely re-absorbed in more heavily doped crystals. For larger crystals, effects from self-absorption due to Eu activation become more evident by a near doubling of decay time for 0.5 in3 crystals as the activator is increased from 0.5 to 5.0 at% Eu. Comparisons of pulse-height spectra obtained for Ø22 mm×22 mm cylinders with varying Eu concentration suggests best performance is achieved using lower Eu additions closer to 0.5-1.0 at%. Using a modified crystal packaging featuring an offset reflector geometry, 0.5 in3 crystals of KCaI3:Eu can attain under 4% energy resolution at 662 keV.
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Compaction of Chromite Cumulates applying a Centrifuging Piston-Cylinder
NASA Astrophysics Data System (ADS)
Manoochehri, S.; Schmidt, M. W.
2012-12-01
Stratiform accumulations of chromite cumulates, such as the UG2 chromitite layer in the Bushveld Complex, is a common feature in most of the large layered mafic intrusions. The time scales and mechanics of gravitationally driven crystal settling and compaction and the feasibility of these processes for the formation of such cumulate layers is investigated through a series of high temperature (1280-1300 °C) centrifuge-assisted experiments at 100-2000 g, 0.4-0.6 GPa. A mixture of natural chromite, with defined grain sizes (means of 5 μm, 13 μm, and 52 μm), and a melt with a composition thought to represent the parental magma of the Bushveld Complex, was first chemically and texturally equilibrated at static conditions and then centrifuged. Centrifugation leads to a single cumulate layer formed at the gravitational bottom of the capsule. This layer was analysed for porosity, mean grain size, size distribution and also travelling distance of chromite crystals. The experimentally observed mechanical settling velocity of chromite grains in a suspension with ~ 24 vol% crystals is calculated to be about half (~ 0.53) of the Stokes settling velocity, consistent with a sedimentation exponent n of 2.35±0.3. The settling leads to a porosity of about 52 % in the chromite layer. Formation times of chromite orthocumulates with initial crystal content in the melt of 1 % and grain sizes of 2 mm are thus around 0.6 m/day. To achieve more compacted chromite piles, centrifugation times and acceleration were increased. Within each experiment the crystal content of the cumulate layer increases downward almost linearly at least in the lower 2/3 of the cumulate pile. Although porosity in the lowermost segment of the chromite layer decreases with increasing effective stress integrated over time, the absolute decrease is smaller than for experiments with olivine (from a previous study). Formation times of a ½ meter single chromite layer with 70 vol% chromite, is calculated to be around 20 years whereas this value is around 0.4 years for olivine cumulates. When considering a natural outcrop of a layered intrusion with multiple layers of about 50 meters height, adcumulate formation time decreases to a few months. With increasing the effective stress integrated over time, applied during centrifugation, crystal size distribution histograms move slightly toward larger grain sizes, but looking at mean grain sizes, a narrow range of changes can be observed. Classic crystal size distribution profiles corrected for real 3D sizes (CSDCorrectin program) of the chromite grains in different experiments illustrate a collection of parallel log-linear trends at larger grain sizes with a very slight overturn at small grain sizes. This is in close agreement with the idealized CSD plots of adcumulus growth.
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Macromolecule Crystal Quality Improvement in Microgravity: The Role of Impurities
NASA Technical Reports Server (NTRS)
Judge, Russell A.; Snell, Edward H.; Pusey, Marc L.; Sportiello, Michael G.; Todd, Paul; Bellamy, Henry; Borgstahl, Gloria E.; Pokros, Matt; Cassanto, John M.
2000-01-01
While macromolecule impurities may affect crystal size and morphology the over-riding question is; "How do macromolecule impurities effect crystal X-ray quality and diffraction resolution?" In the case of chicken egg white lysozyme, crystals can be grown in the presence of a number of impurities without affecting diffraction resolution. One impurity however, the lysozyme dimer, does negatively impact the X-ray crystal properties. Crystal quality improvement as a result of better partitioning of this impurity during crystallization in microgravity has been reported'. In our recent experimental work dimer partitioning was found to be not significantly different between the two environments. Mosaicity analysis of pure crystals showed a reduced mosaicity and increased signal to noise for the microgravity grown crystals. Dimer incorporation however, did greatly reduce the resolution limit in both ground and microgravity grown crystals. These results indicate that impurity effects in microgravity are complex and may rely on the conditions or techniques employed.
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NASA Astrophysics Data System (ADS)
Scotti, A.; Gasser, U.; Herman, E. S.; Han, Jun; Menzel, A.; Lyon, L. A.; Fernandez-Nieves, A.
2017-09-01
We investigate the phase behavior of suspensions of poly(N -isopropylacrylamide) (pNIPAM) microgels with either bimodal or polydisperse size distribution. We observe a shift of the fluid-crystal transition to higher concentrations depending on the polydispersity or the fraction of large particles in suspension. Crystallization is observed up to polydispersities as high as 18.5%, and up to a number fraction of large particles of 29% in bidisperse suspensions. The crystal structure is random hexagonal close-packed as in monodisperse pNIPAM microgel suspensions. We explain our experimental results by considering the effect of bound counterions. Above a critical particle concentration, these cause deswelling of the largest microgels, which are the softest, changing the size distribution of the suspension and enabling crystal formation in conditions where incompressible particles would not crystallize.
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NASA Astrophysics Data System (ADS)
Zhao, Yanlin; Yao, Jun; Wang, Mi
2016-07-01
On-line monitoring of crystal size in the crystallization process is crucial to many pharmaceutical and fine-chemical industrial applications. In this paper, a novel method is proposed for the on-line monitoring of the cooling crystallization process of L-glutamic acid (LGA) using electrical impedance spectroscopy (EIS). The EIS method can be used to monitor the growth of crystal particles relying on the presence of an electrical double layer on the charged particle surface and the polarization of double layer under the excitation of alternating electrical field. The electrical impedance spectra and crystal size were measured on-line simultaneously by an impedance analyzer and focused beam reflectance measurement (FBRM), respectively. The impedance spectra were analyzed using the equivalent circuit model and the equivalent circuit elements in the model can be obtained by fitting the experimental data. Two equivalent circuit elements, including capacitance (C 2) and resistance (R 2) from the dielectric polarization of the LGA solution and crystal particle/solution interface, are in relation with the crystal size. The mathematical relationship between the crystal size and the equivalent circuit elements can be obtained by a non-linear fitting method. The function can be used to predict the change of crystal size during the crystallization process.
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Dependence of Raman Spectral Intensity on Crystal Size in Organic Nano Energetics.
Patel, Rajen B; Stepanov, Victor; Qiu, Hongwei
2016-08-01
Raman spectra for various nitramine energetic compounds were investigated as a function of crystal size at the nanoscale regime. In the case of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20), there was a linear relationship between intensity of Raman spectra and crystal size. Notably, the Raman modes between 120 cm(-1) and 220 cm(-1) were especially affected, and at the smallest crystal size, were completely eliminated. The Raman spectral intensity of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), like that of CL-20's, depended linearly on crystal size. The Raman spectral intensity of 1,3,5-trinitroperhydro-1,3,5-triazine (RDX), however, was not observably changed by crystal size. A non-nitramine explosive compound, 2,4,6-triamino-1,3,5- trinitrobenzene (TATB), was also investigated. Its spectral intensity was also found to correlate linearly with crystal size, although substantially less so than that of HMX and CL-20. To explain the observed trends, it is hypothesized that disordered molecular arrangement, originating from the crystal surface, may be responsible. In particular, it appears that the thickness of the disordered surface layer is dependent on molecular characteristics, including size and conformational flexibility. Furthermore, as the mean crystal size decreases, the volume fraction of disordered molecules within a specimen increases, consequently, weakening the Raman intensity. These results could have practical benefit for allowing the facile monitoring of crystal size during manufacturing. Finally, these findings could lead to deep insights into the general structure of the surface of crystals. © The Author(s) 2016.
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Hammond, Robert B; Pencheva, Klimentina; Roberts, Kevin J; Auffret, Tony
2007-08-01
The poor solubility of potential drug molecules is a significant problem in the design of pharmaceutical formulations. It is well known, however, that the solubility of crystalline materials is enhanced when the particle size is reduced to submicron levels and this factor can be expected to enhance drug product bioavailability. Direct estimation of solubility enhancement, as calculated via the Gibbs-Thompson relationship, demands reasonably accurate values for the particle/solution interfacial tension and, in particular, its anisotropy with respect to the crystal product's habit and morphology. In this article, an improved, more molecule-centered, approach is presented towards the calculation of solubility enhancement factors in which molecular modeling techniques are applied, and the effects associated with both crystal habit modification and solvent choice are examined. A case study for facetted, acetyl salicylic acid (aspirin) crystals in equilibrium with saturated aqueous ethanol solution reveals that their solubility will be enhanced in the range (7-58%) for a crystal size of 0.02 microm, with significantly higher enhancement for crystal morphologies in which the hydrophobic crystal faces are more predominant than the hydrophilic faces and for solvents in which the solubility is smaller. (c) 2007 Wiley-Liss, Inc. and the American Pharmacists Association.
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Hsu, Wei-Hsiang; Hsiang, Hsing-I, E-mail: hsingi@mail.ncku.edu.tw; Chia, Chih-Ta
2013-12-15
CuIn{sub 0.7}Ga{sub 0.3}Se{sub 2}(CIGS) nano-crystals were successfully synthesized via a heating-up process. The non-coordinating solvent (1-octadecene) and selenium/cations ratio effects on the crystalline phase and crystallite size of CIGS nano-crystallites were investigated. It was observed that the CIGS nano-crystallite morphology changed from sheet into spherical shape as the amount of 1-octadecene addition was increased. CIGS nano-crystals were obtained in 9–20 nm sizes as the selenium/cations ratio increased. These results suggest that the monomer reactivity in the solution can be adjusted by changing the solvent type and selenium/cations ratio, hence affecting the crystallite size and distribution. - Graphical abstract: CuIn{sub 0.7}Ga{submore » 0.3}Se{sub 2}(CIGS) nano-crystals were successfully synthesized via a heating-up process in this study. The super-saturation in the solution can be adjusted by changing the OLA/ODE ratio and selenium/cation ratio.« less
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Analysis of submicron-sized niflumic acid crystals prepared by electrospray crystallization.
Ambrus, Rita; Radacsi, Norbert; Szunyogh, Tímea; van der Heijden, Antoine E D M; Ter Horst, Joop H; Szabó-Révész, Piroska
2013-03-25
Interest in submicron-sized drug particles has emerged from both laboratory and industrial perspectives in the last decade. Production of crystals in the nano size scale offers a novel way to particles for drug formulation solving formulation problems of drugs with low solubility in class II of the Biopharmaceutical Classification System. In this work niflumic acid nanoparticles with a size range of 200-800nm were produced by the novel crystallization method, electrospray crystallization. Their properties were compared to those from evaporative and anti-solvent crystallizations, using the same organic solvent, acetone. There is a remarkable difference in the product crystal size depending on the applied methods. The size and morphology were analyzed by scanning electron microscopy and laser diffraction. The structure of the samples was investigated using differential scanning calorimetry, Fourier-transformed infrared spectroscopy and X-ray powder diffraction. The particles produced using electrospray crystallization process were probably changing from amorphous to crystalline state after the procedure. Copyright © 2012 Elsevier B.V. All rights reserved.
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Sparsity-based image monitoring of crystal size distribution during crystallization
NASA Astrophysics Data System (ADS)
Liu, Tao; Huo, Yan; Ma, Cai Y.; Wang, Xue Z.
2017-07-01
To facilitate monitoring crystal size distribution (CSD) during a crystallization process by using an in-situ imaging system, a sparsity-based image analysis method is proposed for real-time implementation. To cope with image degradation arising from in-situ measurement subject to particle motion, solution turbulence, and uneven illumination background in the crystallizer, sparse representation of a real-time captured crystal image is developed based on using an in-situ image dictionary established in advance, such that the noise components in the captured image can be efficiently removed. Subsequently, the edges of a crystal shape in a captured image are determined in terms of the salience information defined from the denoised crystal images. These edges are used to derive a blur kernel for reconstruction of a denoised image. A non-blind deconvolution algorithm is given for the real-time reconstruction. Consequently, image segmentation can be easily performed for evaluation of CSD. The crystal image dictionary and blur kernels are timely updated in terms of the imaging conditions to improve the restoration efficiency. An experimental study on the cooling crystallization of α-type L-glutamic acid (LGA) is shown to demonstrate the effectiveness and merit of the proposed method.
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NASA Astrophysics Data System (ADS)
Choi, Byung Sang
Compared to overwhelming technical data available in other advanced technologies, knowledge about particle technology, especially in particle synthesis from a solution, is still poor due to the lack of available equipment to study crystallization phenomena in a crystallizer. Recent technical advances in particle size measurement such as Coulter counter and laser light scattering have made in/ex situ study of some of particle synthesis, i.e., growth, attrition, and aggregation, possible with simple systems. Even with these advancements in measurement technology, to grasp fully the crystallization phenomena requires further theoretical and technical advances in understanding such particle synthesis mechanisms. Therefore, it is the motive of this work to establish the general processing parameters and to produce rigorous experimental data with reliable performance and characterization that rigorously account for the crystallization phenomena of nucleation, growth, aggregation, and breakage including their variations with time and space in a controlled continuous mixed-suspension mixed-product removal (CMSMPR) crystallizer. This dissertation reports the results and achievements in the following areas: (1) experimental programs to support the development and validation of the phenomenological models and generation of laboratory data for the purpose of testing, refining, and validating the crystallization process, (2) development of laboratory well-mixed crystallizer system and experimental protocols to generate crystal size distribution (CSD) data, (3) the effects of feed solution concentration, crystallization temperature, feed flow rate, and mixing speed, as well as different types of mixers resulting in the evolution of CSDs with time from a concentrated brine solution, (4) with statistically designed experiments the effects of processing variables on the resultant particle structure and CSD at steady state were quantified and related to each of those operating conditions by studying the detailed crystallization processes, such as nucleation, growth, and breakage, as well as agglomeration. The purification of CaCl2 solution involving the crystallization of NaCl from the solution mixture of CaCl2, KCl, and NaCl as shipped from Dow Chemical, Ludington, in a CMSMPR crystallizer was studied as our model system because of its nucleation and crystal growth tendencies with less agglomeration. This project also generated a significant body of experimental data that are available at URL that is http://www.che.utah.edu/˜ring/CrystallizationWeb.
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NASA Astrophysics Data System (ADS)
Yilmaz, Hulusi
A comprehensive density functional theory study of atomic and the electronic properties of wurtzite gallium nitride (GaN) nanostructures with different sizes and shapes is presented and the effect of external electric field on these properties is examined. We show that the atomic and electronic properties of [101¯0] facet single-crystal GaN nanotubes (quasi-1D), nanowires (1D) and nanolayers (2D) are mainly determined by the surface to volume ratio. The shape dependent quantum confinement and strain effects on the atomic and electronic properties of these GaN nanostructures are found to be negligible. Based on this similarity between the atomic and electronic properties of the small size GaN nanostructures, we calculated the atomic and electronic properties of the practical size (28.1 A wall thickness) single-crystal GaN nanotubes through computational much economical GaN nanoslabs (nanolayers). Our results show that, regardless of diameter, hydrogen saturated single-crystal GaN tubes with the wall thickness of 28.1 A are energetically stable and they have a noticeably larger band gap with respect to the band gap of bulk GaN. The band gap of unsaturated single-crystal GaN tubes, on the other hand, is always smaller than the band gap of the wurtzite bulk GaN. In a separate study, we show that a transverse electric field induces a homojunction across the diameter of initially semiconducting GaN single-crystal nanotubes and nanowires. The homojunction arises due to the decreased energy of the electronic states in the higher potential region with respect to the energy of those states in the lower potential region under the transverse electric field. Calculations on single-crystal GaN nanotubes and nanowires of different diameter and wall thickness show that the threshold electric field required for the semiconductor-homojunction induction increases with increasing wall thickness and decreases significantly with increasing diameter.
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Applications of ultrasound to chiral crystallization, resolution and deracemization.
Xiouras, Christos; Fytopoulos, Antonios; Jordens, Jeroen; Boudouvis, Andreas G; Van Gerven, Tom; Stefanidis, Georgios D
2018-05-01
Industrial synthesis of enantiopure compounds is nowadays heavily based on the separation of racemates through crystallization processes. Although the application of ultrasound in solution crystallization processes (sonocrystallization) has become a promising emerging technology, offering several benefits (e.g. reduction of the induction time and narrowing of the metastable zone width, control over the product size, shape and polymorphic modification), little attention has been paid so far to the effects of ultrasound on chiral crystallization processes. Several recent studies have reported on the application of acoustic energy to crystallization processes that separate enantiomers, ranging from classical (diastereomeric) resolution and preferential crystallization to new and emerging processes such as attrition-enhanced deracemization (Viedma ripening). A variety of interesting effects have been observed, which include among others, enhanced crystallization yield with higher enantiomeric purity crystals, spontaneous mirror symmetry breaking crystallization, formation of metastable conglomerate crystals and enhanced deracemization rates. The objective of this review is to provide an overview of the effects of ultrasound on chiral crystallization and outline several aspects of interest in this emerging field. Copyright © 2018 Elsevier B.V. All rights reserved.
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NASA Technical Reports Server (NTRS)
Vekilov, Peter G.
2003-01-01
Insight into the crystallization processes of biological macromolecules into crystals or aggregates can provide valuable guidelines in many fundamental and applied fields. Such insight will prompt new means to regulate protein phase transitions in-vivo, e.g., polymerization of hemoglobin S in the red cells, crystallization of crystallins in the eye lens, etc. Understanding of protein crystal nucleation will help achieve narrow crystallite size distributions, needed for sustained release of pharmaceutical protein preparations such as insulin or interferon. Traditionally, protein crystallization studies have been related to the pursuit of crystal perfection needed to improve the structure details provided by x-ray, electron or neutron diffraction methods. Crystallization trials for the purposes of structural biology carried out in space have posed an intriguing question related to the inconsistency of the effects of the microgravity growth on the quality of the crystals.
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NASA Astrophysics Data System (ADS)
Wada, Y.; Kobayashi, T.; Matsumoto, M.; Onoe, K.
2017-10-01
To develop the technique for the control of the crystal composition and properties such as size distribution and morphology utilizing the contact reaction field around the minute droplets in atmospheric pressure plasma, fine spherical particles of hydroxyapatite ((Ca10(PO4)6(OH)2); HAp) were synthesized by a new plasma crystallization method. In this work, to elucidate the effects of the production region and crystal properties of hydroxyapatite for the liquid source composition, Ca2+ concentration and the Ca/P molar ratio in minute droplets were varied. The following results were obtained: (1) fine spherical HAp particles can be produced by the introduction of minute droplets with the initial Ca2+ concentration ((CCa)0) of 0.50 mol/l and the Ca/P molar ratio of 1.67. (2) When the (CCa)0 is set in the range higher than 1.00 mol/l at the constant Ca/P molar ratio of 1.67, fine spherical particles of β-TCP and HAp mixture are crystallized. (3) For the Ca/P molar ratio below 1.67, α-TCP and HAp co-precipitated. (4) The composition of the produced particles depends on both the reactant concentration and Ca/P molar ratio in the HAp source solution. (5) The dependence of the reactant concentration on the average size of the produced HAp particles is large compared with droplet size.
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NASA Astrophysics Data System (ADS)
Kutluay, Sinan; Şahin, Ömer; Ceyhan, A. Abdullah; İzgi, M. Sait
2017-06-01
In crystallization studies, newly developed technologies, such as Focused Beam Reflectance Measurement (FBRM) and Particle Vision and Measurement (PVM) are applied for determining on-line monitoring of a representation of the Chord Length Distribution (CLD) and observe the photographs of crystals respectively; moreover recently they are widely used. Properly installed, the FBRM ensures on-line determination of the CLD, which is statistically associated to the Crystal Size Distribution (CSD). In industrial crystallization, CSD and mean crystal size as well as external habit and internal structure are important characteristics for further use of the crystals. In this paper, the effect of residence time, stirring speed, feeding rate, supersaturation level and the polyelectrolytes such as anionic polyacrylamide (APAM) and non-ionic polyacrylamide (NPAM) on the CLD as well as the shape of boric acid crystals were investigated by using the FBRM G600 and the PVM V819 probes respectively in an MSMPR (Mixed Suspension Mixed Product Removal) crystallizer. The CSD and kinetic data were determined experimentally using continuous MSMPR crystallizer running at steady state. The population density of nuclei, the nucleation rate and the growth rate were determined from the experimental population balance distribution when the steady state was reached.
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Connection between the growth rate distribution and the size dependent crystal growth
NASA Astrophysics Data System (ADS)
Mitrović, M. M.; Žekić, A. A.; IIić, Z. Z.
2002-07-01
The results of investigations of the connection between the growth rate dispersions and the size dependent crystal growth of potassium dihydrogen phosphate (KDP), Rochelle salt (RS) and sodium chlorate (SC) are presented. A possible way out of the existing confusion in the size dependent crystal growth investigations is suggested. It is shown that the size independent growth exists if the crystals belonging to one growth rate distribution maximum are considered separately. The investigations suggest possible reason for the observed distribution maxima widths, and the high data scattering on the growth rate versus the crystal size dependence.
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Effects of organic matter on crystallization of struvite in biologically treated swine wastewater.
Capdevielle, Aurélie; Sýkorová, Eva; Béline, Fabrice; Daumer, Marie-Line
2016-01-01
A sustainable way to recover phosphorus (P) in swine wastewater involves a preliminary step of P dissolution followed by the separation of particulate organic matter (OM). The next two steps are firstly the precipitation of struvite crystals done by adding a crystallization reagent (magnesia) and secondly the filtration of the crystals. To develop the process successfully at an industrial scale, the control of the mechanisms of precipitation is the key point in order to obtain high value-added products, that is, big struvite crystals easy to harvest and handle. Experiments with process parameters optimized previously in a synthetic swine wastewater were performed on real swine wastewater to assess the role of the OM on struvite crystallization. After 24 h, with a pH increase to 6.8 only, 90% of the initial P was precipitated and 60% was precipitated as struvite. 80% of the solid recovered was in the fraction > 100 µm. The other forms recovered were brushite, amorphous calcium phosphate, NaCl, KCl and OM. The influence of OM on struvite precipitation in acidified swine wastewater was negative on the reaction kinetics but positive on the size of the struvite crystals. The presence of colloidal particles increased the size of the struvite crystals but slowed down the kinetics due to the viscosity induced by the repulsive force of the colloids. The maximum size of single struvite crystals (200 µm) was observed with the presence of particulate OM.
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NASA Astrophysics Data System (ADS)
Fischetti, Massimo V.; Vandenberghe, William G.
2016-04-01
We show that the electron mobility in ideal, free-standing two-dimensional "buckled" crystals with broken horizontal mirror (σh) symmetry and Dirac-like dispersion (such as silicene and germanene) is dramatically affected by scattering with the acoustic flexural modes (ZA phonons). This is caused both by the broken σh symmetry and by the diverging number of long-wavelength ZA phonons, consistent with the Mermin-Wagner theorem. Non-σh-symmetric, "gapped" 2D crystals (such as semiconducting transition-metal dichalcogenides with a tetragonal crystal structure) are affected less severely by the broken σh symmetry, but equally seriously by the large population of the acoustic flexural modes. We speculate that reasonable long-wavelength cutoffs needed to stabilize the structure (finite sample size, grain size, wrinkles, defects) or the anharmonic coupling between flexural and in-plane acoustic modes (shown to be effective in mirror-symmetric crystals, like free-standing graphene) may not be sufficient to raise the electron mobility to satisfactory values. Additional effects (such as clamping and phonon stiffening by the substrate and/or gate insulator) may be required.
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NASA Technical Reports Server (NTRS)
Barlow, Douglas A.; Baird, James K.; Su, Ching-Hua
2003-01-01
More than 75 years ago, von Weimarn summarized his observations of the dependence of the average crystal size on the initial relative concentration supersaturation prevailing in a solution from which crystals were growing. Since then, his empirically derived rules have become part of the lore of crystal growth. The first of these rules asserts that the average crystal size measured at the end of a crystallization increases as the initial value of the relative supersaturation decreases. The second rule states that for a given crystallization time, the average crystal size passes through a maximum as a function of the initial relative supersaturation. Using a theory of nucleation and growth due to Buyevich and Mansurov, we calculate the average crystal size as a function of the initial relative supersaturation. We confirm the von Weimarn rules for the case where the nucleation rate is proportional to the third power or higher of the relative supersaturation.
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Non-Isothermal Calorimetric Studies of the Crystallization of Lithium Disilicate Glass
NASA Technical Reports Server (NTRS)
Ray, C. S.; Day, D. E.; Huang, W.; Narayan, K. Lakshmi; Cull, T. S.; Kelton, K. F.
1996-01-01
The influence of preannealing treatments on the polymorphic crystallization of lithium disilicate glasses is examined. As expected, glasses heated at different rates through the temperature range where there is significant nucleation develop widely different numbers of nuclei. This can dramatically influence the stability and transformation characteristics of the annealed glass. Non-isothermal differential scanning calorimetry (DSC) and differential thermal analysis (DTA) measurements are demonstrated to be useful to probe the nucleation behavior. The first systematic investigations of particle size effects on the non-isothermal transformation behavior are presented and discussed. Based on DTA and microscopy experiments, we show that small particles of lithium disilicate glasses crystallize primarily by surface crystallization. The relative importance of surface versus volume crystallization is examined by varying particle size, by introducing nucleating agents and by exposing glasses to atmospheres of different water content. These data are analyzed quantitatively using a numerical model developed in a second paper following in this volume.
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Effects of Vacancy Cluster Defects on Electrical and Thermodynamic Properties of Silicon Crystals
Huang, Pei-Hsing; Lu, Chi-Ming
2014-01-01
A first-principle plane-wave pseudopotential method based on the density function theory (DFT) was employed to investigate the effects of vacancy cluster (VC) defects on the band structure and thermoelectric properties of silicon (Si) crystals. Simulation results showed that various VC defects changed the energy band and localized electron density distribution of Si crystals and caused the band gap to decrease with increasing VC size. The results can be ascribed to the formation of a defect level produced by the dangling bonds, floating bonds, or high-strain atoms surrounding the VC defects. The appearance of imaginary frequencies in the phonon spectrum of defective Si crystals indicates that the defect-region structure is dynamically unstable and demonstrates phase changes. The phonon dispersion relation and phonon density of state were also investigated using density functional perturbation theory. The obtained Debye temperature (θ D) for a perfect Si crystal had a minimum value of 448 K at T = 42 K and a maximum value of 671 K at the high-temperature limit, which is consistent with the experimental results reported by Flubacher. Moreover, the Debye temperature decreased with increases in the VC size. VC defects had minimal effects on the heat capacity (C v) value when temperatures were below 150 K. As the temperature was higher than 150 K, the heat capacity gradually increased with increasing temperature until it achieved a constant value of 11.8 cal/cell·K. The heat capacity significantly decreased as the VC size increased. For a 2 × 2 × 2 superlattice Si crystal containing a hexagonal ring VC (HRVC10), the heat capacity decreased by approximately 17%. PMID:24526923
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The size effects upon shock plastic compression of nanocrystals
NASA Astrophysics Data System (ADS)
Malygin, G. A.; Klyavin, O. V.
2017-10-01
For the first time a theoretical analysis of scale effects upon the shock plastic compression of nanocrystals is implemented in the context of a dislocation kinetic approach based on the equations and relationships of dislocation kinetics. The yield point of crystals τy is established as a quantitative function of their cross-section size D and the rate of shock deformation as τy ɛ2/3 D. This dependence is valid in the case of elastic stress relaxation on account of emission of dislocations from single-pole Frank-Read sources near the crystal surface.
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NASA Astrophysics Data System (ADS)
Bazlov, A. I.; Tsarkov, A. A.; Ketov, S. V.; Suryanarayana, C.; Louzguine-Luzgin, D. V.
2018-02-01
Effect of multiple alloying elements on the glass-forming ability, thermal stability, and crystallization behavior of Zr-based glass-forming alloys were studied in the present work. We investigated the effect of complete or partial substitution of Ti and Ni with similar early and late transition metals, respectively, on the glass-forming ability and crystallization behavior of the Zr50Ti10Cu20Ni10Al10 alloy. Poor correlation was observed between different parameters indicating the glass-forming ability and the critical size of the obtained glassy samples. Importance of the width of the crystallization interval is emphasized. The kinetics of primary crystallization, i.e., the rate of nucleation and rate of growth of the nuclei of primary crystals is very different from that of the eutectic alloys. Thus, it is difficult to estimate the glass-forming ability only on the basis of the empirical parameters not taking into account the crystallization behavior and the crystallization interval.
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Temperature lowering program for homogeneous doping in flux growth
NASA Astrophysics Data System (ADS)
Qiwei, Wang; Shouquan, Jia
1989-10-01
Based on the mass conservation law and the Burton-Prim-Slichter equation, the temperature program for homogeneous doping in flux growth by slow cooling was derived. The effect of various factors, such as initial supersaturation, solution volume, growth kinetic coefficient and degree of mixing in the solution on growth rate, crystal size and temperature program is discussed in detail. Theoretical analysis shows that there is a critical crystal size above which homogeneous doping is impossible.
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Computer Modeling of Non-Isothermal Crystallization
NASA Technical Reports Server (NTRS)
Kelton, K. F.; Narayan, K. Lakshmi; Levine, L. E.; Cull, T. C.; Ray, C. S.
1996-01-01
A realistic computer model for simulating isothermal and non-isothermal phase transformations proceeding by homogeneous and heterogeneous nucleation and interface-limited growth is presented. A new treatment for particle size effects on the crystallization kinetics is developed and is incorporated into the numerical model. Time-dependent nucleation rates, size-dependent growth rates, and surface crystallization are also included. Model predictions are compared with experimental measurements of DSC/DTA peak parameters for the crystallization of lithium disilicate glass as a function of particle size, Pt doping levels, and water content. The quantitative agreement that is demonstrated indicates that the numerical model can be used to extract key kinetic data from easily obtained calorimetric data. The model can also be used to probe nucleation and growth behavior in regimes that are otherwise inaccessible. Based on a fit to data, an earlier prediction that the time-dependent nucleation rate in a DSC/DTA scan can rise above the steady-state value at a temperature higher than the peak in the steady-state rate is demonstrated.
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Thakur, Anil S.; Robin, Gautier; Guncar, Gregor; Saunders, Neil F. W.; Newman, Janet; Martin, Jennifer L.; Kobe, Bostjan
2007-01-01
Background Crystallization is a major bottleneck in the process of macromolecular structure determination by X-ray crystallography. Successful crystallization requires the formation of nuclei and their subsequent growth to crystals of suitable size. Crystal growth generally occurs spontaneously in a supersaturated solution as a result of homogenous nucleation. However, in a typical sparse matrix screening experiment, precipitant and protein concentration are not sampled extensively, and supersaturation conditions suitable for nucleation are often missed. Methodology/Principal Findings We tested the effect of nine potential heterogenous nucleating agents on crystallization of ten test proteins in a sparse matrix screen. Several nucleating agents induced crystal formation under conditions where no crystallization occurred in the absence of the nucleating agent. Four nucleating agents: dried seaweed; horse hair; cellulose and hydroxyapatite, had a considerable overall positive effect on crystallization success. This effect was further enhanced when these nucleating agents were used in combination with each other. Conclusions/Significance Our results suggest that the addition of heterogeneous nucleating agents increases the chances of crystal formation when using sparse matrix screens. PMID:17971854
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Kim, Byeongsoo; Gil, Hyung Bae; Min, Sang-Gi; Lee, Si-Kyung; Choi, Mi-Jung
2014-01-01
This study investigates the effects of the gelatin concentration (10-40%, w/v), freezing temperatures (from -20℃ to -50℃) and freezing methods on the structural and physical properties of gelatin matrices. To freeze gelatin, the pressure-shift freezing (PSF) is being applied at 0.1 (under atmospheric control), 50 and 100 MPa, respectively. The freezing point of gelatin solutions decrease with increasing gelatin concentrations, from -0.2℃ (10% gelatin) to -6.7℃ (40% gelatin), while the extent of supercooling did not show any specific trends. The rheological properties of the gelatin indicate that both the storage (G') and loss (G") moduli were steady in the strain amplitude range of 0.1-10%. To characterize gelatin matrices formed by the various freezing methods, the ice crystal sizes which were being determined by the scanning electron microscopy (SEM) are affected by the gelatin concentrations. The ice crystal sizes are affected by gelatin concentrations and freezing temperature, while the size distributions of ice crystals depend on the freezing methods. Smaller ice crystals are being formed with PSF rather than under the atmospheric control where the freezing temperature is above -40℃. Thus, the results of this study indicate that the PSF processing at a very low freezing temperature (-50℃) offers a potential advantage over commercial atmospheric freezing points for the formation of small ice crystals. PMID:26760743
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NASA Technical Reports Server (NTRS)
Gibson, U. J.; Horrell, E. E.; Kou, Y.; Pusey, Marc
2000-01-01
We have measured the nucleation and aspect ratio of CEWL crystals grown by vapor diffusion in acetate, butyrate, carbonate, succinate, and phosphate buffers in a range of pH spanning the pK(sub a) of these buffers. The nucleation numbers drop off significantly in the vicinity of pK(sub a) for each of the buffers except the phosphate system, in which we used only the pH range around the second titration point(pK2). There is a concomitant increase in the sizes of the crystals. Some typical nucleation number results are shown. These data support and extend other observations. In addition, we have examined changes in aspect ratio which accompany the suppression of nucleation within each buffer system. The length of the face in the [001] direction was measured, and compared to the width of the (110) face in the [110] type directions. We find that while the aspect ratio of the crystals is affected by pH, it is dominated by a correlation with the size of the crystals. Small crystals are longer in the [0011 direction than crystals that are larger (higher pH within a buffer system). This relationship is found to hold independent of the choice of buffer. These results are consistent with those of Judge et al, who used a batch process which resulted in uniform sizing of crystals at each pH. In these experiments, we specifically avoid agitating the protein/salt buffer mixture when combining the two. This permits the formation of a range of sizes at a given pH. The results for a .05 M acetate 5% NaCl buffer are also shown. We will discuss these results in light of a growth model.
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A simple apparatus for controlling nucleation and size in protein crystal growth
NASA Technical Reports Server (NTRS)
Gernert, Kim M.; Smith, Robert; Carter, Daniel C.
1988-01-01
A simple device is described for controlling vapor equilibrium in macromolecular crystallization as applied to the protein crystal growth technique commonly referred to as the 'hanging drop' method. Crystal growth experiments with hen egg white lysozyme have demonstrated control of the nucleation rate. Nucleation rate and final crystal size have been found to be highly dependent upon the rate at which critical supersaturation is approached. Slower approaches show a marked decrease in the nucleation rate and an increase in crystal size.
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NASA Astrophysics Data System (ADS)
Arienti, Marco; Geier, Manfred; Yang, Xiaoyuan; Orcutt, John; Zenker, Jake; Brooks, Sarah D.
2018-05-01
We investigate the optical properties of ice crystals nucleated on atmospheric black carbon (BC). The parameters examined in this study are the shape of the ice crystal, the volume fraction of the BC inclusion, and its location inside the crystal. We report on new spectrometer measurements of forward scattering and backward polarization from ice crystals nucleated on BC particles and grown under laboratory-controlled conditions. Data from the Cloud and Aerosol Spectrometer with Polarization (CASPOL) are used for direct comparison with single-particle calculations of the scattering phase matrix. Geometrical optics and discrete dipole approximation techniques are jointly used to provide the best compromise of flexibility and accuracy over a broad range of size parameters. Together with the interpretation of the trends revealed by the CASPOL measurements, the numerical results confirm previous reports on absorption cross-section magnification in the visible light range. Even taking into account effects of crystal shape and inclusion position, the ratio between absorption cross-section of the compound particle and the absorption cross-section of the BC inclusion alone (the absorption magnification) has a lower bound of 1.5; this value increases to 1.7 if the inclusion is centered with respect to the crystal. The simple model of BC-ice particle presented here also offers new insights on the effect of the relative position of the BC inclusion with respect to the crystal's outer surfaces, the shape of the crystal, and its size.
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NASA Astrophysics Data System (ADS)
Sujiono, E. H.; Agus, J.; Samnur, S.; Triyana, K.
2018-05-01
The effects of molar ratios and sintering times on crystal structures and surface morphology on NdFeO3 oxide alloy have been studied. NdFeO3 oxide alloy formed by chemical preparation with solid reaction method using raw oxide Fe2O3 (99.9 %) and Nd2O3 (99.9 %) powders. In this article we reported the effects of molar ratios x = (–0.1, –0.2 and –0.3) and sintering times for 15 h and 20 h on crystal structures and surface morphology of Nd1+xFeO3 synthesized by solid-state reaction method. The results indicate that variation of molar ratio and sintering time has influenced the FWHM, crystalline size and grain size. The Nd1+xFeO3 have a major phase is NdFeO3, and other minor phases are Fe2O3, Nd2O3 and Nd(OH)3. The dominant intensity of hkl (121) with a value in FWHM, crystallite size, and grain size an indication the results will be applied as a gas sensor material as the focus of the further study.
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Deducing growth mechanisms for minerals from the shapes of crystal size distributions
Eberl, D.D.; Drits, V.A.; Srodon, J.
1998-01-01
Crystal size distributions (CSDs) of natural and synthetic samples are observed to have several distinct and different shapes. We have simulated these CSDs using three simple equations: the Law of Proportionate Effect (LPE), a mass balance equation, and equations for Ostwald ripening. The following crystal growth mechanisms are simulated using these equations and their modifications: (1) continuous nucleation and growth in an open system, during which crystals nucleate at either a constant, decaying, or accelerating nucleation rate, and then grow according to the LPE; (2) surface-controlled growth in an open system, during which crystals grow with an essentially unlimited supply of nutrients according to the LPE; (3) supply-controlled growth in an open system, during which crystals grow with a specified, limited supply of nutrients according to the LPE; (4) supply- or surface-controlled Ostwald ripening in a closed system, during which the relative rate of crystal dissolution and growth is controlled by differences in specific surface area and by diffusion rate; and (5) supply-controlled random ripening in a closed system, during which the rate of crystal dissolution and growth is random with respect to specific surface area. Each of these mechanisms affects the shapes of CSDs. For example, mechanism (1) above with a constant nucleation rate yields asymptotically-shaped CSDs for which the variance of the natural logarithms of the crystal sizes (??2) increases exponentially with the mean of the natural logarithms of the sizes (??). Mechanism (2) yields lognormally-shaped CSDs, for which ??2 increases linearly with ??, whereas mechanisms (3) and (5) do not change the shapes of CSDs, with ??2 remaining constant with increasing ??. During supply-controlled Ostwald ripening (4), initial lognormally-shaped CSDs become more symmetric, with ??2 decreasing with increasing ??. Thus, crystal growth mechanisms often can be deduced by noting trends in ?? versus ??2 of CSDs for a series of related samples.
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Probabilistic approach to lysozyme crystal nucleation kinetics.
Dimitrov, Ivaylo L; Hodzhaoglu, Feyzim V; Koleva, Dobryana P
2015-09-01
Nucleation of lysozyme crystals in quiescent solutions at a regime of progressive nucleation is investigated under an optical microscope at conditions of constant supersaturation. A method based on the stochastic nature of crystal nucleation and using discrete time sampling of small solution volumes for the presence or absence of detectable crystals is developed. It allows probabilities for crystal detection to be experimentally estimated. One hundred single samplings were used for each probability determination for 18 time intervals and six lysozyme concentrations. Fitting of a particular probability function to experimentally obtained data made possible the direct evaluation of stationary rates for lysozyme crystal nucleation, the time for growth of supernuclei to a detectable size and probability distribution of nucleation times. Obtained stationary nucleation rates were then used for the calculation of other nucleation parameters, such as the kinetic nucleation factor, nucleus size, work for nucleus formation and effective specific surface energy of the nucleus. The experimental method itself is simple and adaptable and can be used for crystal nucleation studies of arbitrary soluble substances with known solubility at particular solution conditions.
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Growth of high quality bulk size single crystals of inverted solubility lithium sulphate monohydrate
DOE Office of Scientific and Technical Information (OSTI.GOV)
Silambarasan, A.; Rajesh, P., E-mail: rajeshp@ssn.edu.in; Ramasamy, P.
2015-06-24
The paper summarizes the processes of growing large lithium sulfate monohydrate (LSMH) single crystals. We have established a procedure to grow high quality bulk size single crystals of inverted solubility LSMH by a newly developed unidirectional crystallization technique called the Sankeranarayenan - Ramasamy (SR) method. The convective flow of crystal growth processes from solution and the conditions of growing crystals of various aspects were discussed. Good quality LSMH single crystal is grown of the size 20 mmX80 mm without cracks, localized-defects and inclusions. The as-grown crystals are suitable for piezoelectric and nonlinear optical applications.
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The Effect of Additives on the Early Stages of Growth of Calcite Single Crystals
Freeman, Colin L.; Gong, Xiuqing; Levenstein, Mark A.; Wang, Yunwei; Kulak, Alexander; Anduix‐Canto, Clara; Lee, Phillip A.; Li, Shunbo; Chen, Li; Christenson, Hugo K.
2017-01-01
Abstract As crystallization processes are often rapid, it can be difficult to monitor their growth mechanisms. In this study, we made use of the fact that crystallization proceeds more slowly in small volumes than in bulk solution to investigate the effects of the soluble additives Mg2+ and poly(styrene sulfonate) (PSS) on the early stages of growth of calcite crystals. Using a “Crystal Hotel” microfluidic device to provide well‐defined, nanoliter volumes, we observed that calcite crystals form via an amorphous precursor phase. Surprisingly, the first calcite crystals formed are perfect rhombohedra, and the soluble additives have no influence on the morphology until the crystals reach sizes of 0.1–0.5 μm for Mg2+ and 1–2 μm for PSS. The crystals then continue to grow to develop morphologies characteristic of these additives. These results can be rationalized by considering additive binding to kink sites, which is consistent with crystal growth by a classical mechanism. PMID:28767197
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Color from hierarchy: Diverse optical properties of micron-sized spherical colloidal assemblies
Vogel, Nicolas; Utech, Stefanie; England, Grant T.; Shirman, Tanya; Phillips, Katherine R.; Koay, Natalie; Burgess, Ian B.; Kolle, Mathias; Weitz, David A.; Aizenberg, Joanna
2015-01-01
Materials in nature are characterized by structural order over multiple length scales have evolved for maximum performance and multifunctionality, and are often produced by self-assembly processes. A striking example of this design principle is structural coloration, where interference, diffraction, and absorption effects result in vivid colors. Mimicking this emergence of complex effects from simple building blocks is a key challenge for man-made materials. Here, we show that a simple confined self-assembly process leads to a complex hierarchical geometry that displays a variety of optical effects. Colloidal crystallization in an emulsion droplet creates micron-sized superstructures, termed photonic balls. The curvature imposed by the emulsion droplet leads to frustrated crystallization. We observe spherical colloidal crystals with ordered, crystalline layers and a disordered core. This geometry produces multiple optical effects. The ordered layers give rise to structural color from Bragg diffraction with limited angular dependence and unusual transmission due to the curved nature of the individual crystals. The disordered core contributes nonresonant scattering that induces a macroscopically whitish appearance, which we mitigate by incorporating absorbing gold nanoparticles that suppress scattering and macroscopically purify the color. With increasing size of the constituent colloidal particles, grating diffraction effects dominate, which result from order along the crystal’s curved surface and induce a vivid polychromatic appearance. The control of multiple optical effects induced by the hierarchical morphology in photonic balls paves the way to use them as building blocks for complex optical assemblies—potentially as more efficient mimics of structural color as it occurs in nature. PMID:26290583
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NASA Astrophysics Data System (ADS)
Bahtiar, A.; Rahmanita, S.; Inayatie, Y. D.
2017-05-01
Morphology of perovskite film is a key important for achieving high performance perovskite solar cells. Perovskite films are commonly prepared by two-step spin-coating method. However, pin-holes are frequently formed in perovskite films due to incomplete conversion of lead-iodide (PbI2) into perovskite CH3NH3PbI3. Pin-holes in perovskite film cause large hysteresis in current-voltage curve of solar cells due to large series resistance between perovskite layer-hole transport material. Moreover, crystal structure and grain size of perovskite crystal are also other important parameters for achieving high performance solar cells, which are significantly affected by preparation of perovskite film. We studied the effect of preparation of perovskite film using controlled spin-coating parameters on crystal structure and morphological properties of perovskite film. We used two-step spin-coating method for preparation of perovskite film with varied spinning speed, spinning time and temperature of spin-coating process to control growth of perovskite crystal aimed to produce high quality perovskite crystal with pin-hole free and large grain size. All experiment was performed in air with high humidity (larger than 80%). The best crystal structure, pin-hole free with large grain crystal size of perovskite film was obtained from film prepared at room temperature with spinning speed 1000 rpm for 20 seconds and annealed at 100°C for 300 seconds.
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McFarquhar, Greg
2011-07-25
Best estimate of cloud microphysical parameters derived using data collected by the cloud microphysical probes installed on the National Research Council (NRC) of Canada Convair-580 during ISDAC. These files contain phase, liquid and ice crystal size distributions (Nw(D) and Ni(D) respectively), liquid water content (LWC), ice water content (IWC), extinction of liquid drops (bw), extinction of ice crystals (bi), effective radius of water drops (rew) and of ice crystals (rei) and median mass diameter of liquid drops (Dmml) and of ice crystals (Dmmi) at 30 second resolution.
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Size-dependent and tunable crystallization of GeSbTe phase-change nanoparticles
NASA Astrophysics Data System (ADS)
Chen, Bin; Ten Brink, Gert H.; Palasantzas, George; Kooi, Bart J.
2016-12-01
Chalcogenide-based nanostructured phase-change materials (PCMs) are considered promising building blocks for non-volatile memory due to their high write and read speeds, high data-storage density, and low power consumption. Top-down fabrication of PCM nanoparticles (NPs), however, often results in damage and deterioration of their useful properties. Gas-phase condensation based on magnetron sputtering offers an attractive and straightforward solution to continuously down-scale the PCMs into sub-lithographic sizes. Here we unprecedentedly present the size dependence of crystallization for Ge2Sb2Te5 (GST) NPs, whose production is currently highly challenging for chemical synthesis or top-down fabrication. Both amorphous and crystalline NPs have been produced with excellent size and composition control with average diameters varying between 8 and 17 nm. The size-dependent crystallization of these NPs was carefully analyzed through in-situ heating in a transmission electron microscope, where the crystallization temperatures (Tc) decrease when the NPs become smaller. Moreover, methane incorporation has been observed as an effective method to enhance the amorphous phase stability of the NPs. This work therefore elucidates that GST NPs synthesized by gas-phase condensation with tailored properties are promising alternatives in designing phase-change memories constrained by optical lithography limitations.
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Munjal, Bhushan; Bansal, Arvind K
2015-01-01
The effect of tert-butyl alcohol (TBA) on isothermal crystallization kinetics of gemcitabine hydrochloride (GHCl) in frozen aqueous solutions was assessed by cold-stage microscopy. Addition of TBA (0%-5%, w/w) increased the value of Johnson-Mehl-Avrami rate constant (1.3-33.3 h⁻¹) and reduced the Avrami exponent (2.5-1.0). Thermodynamic parameters [enthalpy (ΔH(‡)), entropy (ΔS(‡)), and free energy (ΔG(‡)) of activation], calculated using Arrhenius and Eyring-Polanyi equations, established that TBA (2%, w/w) accelerated GHCl crystallization by reducing its ΔH(‡) (53.9 cf. 96.5 kJ/mol⁻¹) and ΔG(‡) (68.5 cf. 74.9 kJ/mol⁻¹). Further, to explore insights into the effect of TBA on nucleation and crystal growth of GHCl, crystallization kinetics data were deconvolved using Finke-Watzky model. This revealed that addition of TBA decreased ΔH(‡) of nucleation and increased ΔS(‡) of crystal growth, thereby reducing ΔG(‡) of nucleation and crystal growth by 11.7% and 4.2%, respectively. Finkey-Watzky model also predicted a reduction in the crystal size upon TBA addition, which was confirmed by comparing particle size of GHCl lyophilized in the presence and absence of TBA. In conclusion, TBA reduces ΔG(‡) of nucleation and crystal growth in a differential manner, thereby enhancing the crystallization kinetics of GHCl and affecting its morphological features. © 2014 Wiley Periodicals, Inc. and the American Pharmacists Association.
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NASA Astrophysics Data System (ADS)
Deshuang, Zheng; Ruirun, Chen; Tengfei, Ma; Hongsheng, Ding; Yanqing, Su; Jingjie, Guo; Hengzhi, Fu
2018-02-01
The coupling effects of melt treatment and ultrasonic treatment on the solidifying microstructure and mechanical performance of Ti44Al6Nb1Cr alloy are investigated. During melt treatment, a low superheat degree is beneficial for microstructure refinement, with the lamellar colony size decreasing from 512 to 243 μm, while a low cooling rate leads to the microstructure coarsening as the lamellar colony size enlarges from 458 to 615 μm. After coupling with ultrasonic treatment, under moderate superheat degree and cooling rate, the original coarse lamellar colony size is significantly refined to 56 and 38 μm, the compressive strength is improved by 60.71 and 47.89 pct, and the compressive strain is enlarged by 80.19 and 112.33 pct, respectively. It is found that the ultrasonic refining efficiency is dominated by the melt temperature, and there is an optimum temperature range near the crystallization temperature: a too-high temperature leads to the remelting of crystal nuclei, impairing the refining efficiency, whereas a too-low temperature results in high viscosity, hindering the ultrasonic effects. Under ultrasonic treatment, the melt supercooling is increased, leading to an extended constitutional supercooling region, which will enlarge the crystal nucleation; the solute enrichment is enhanced, forming a quasi-steady state with a higher solution concentration gradient, which improves the crystal growth velocity.
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Broadband sound blocking in phononic crystals with rotationally symmetric inclusions.
Lee, Joong Seok; Yoo, Sungmin; Ahn, Young Kwan; Kim, Yoon Young
2015-09-01
This paper investigates the feasibility of broadband sound blocking with rotationally symmetric extensible inclusions introduced in phononic crystals. By varying the size of four equally shaped inclusions gradually, the phononic crystal experiences remarkable changes in its band-stop properties, such as shifting/widening of multiple Bragg bandgaps and evolution to resonance gaps. Necessary extensions of the inclusions to block sound effectively can be determined for given incident frequencies by evaluating power transmission characteristics. By arraying finite dissimilar unit cells, the resulting phononic crystal exhibits broadband sound blocking from combinational effects of multiple Bragg scattering and local resonances even with small-numbered cells.
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Kile, D.E.; Eberl, D.D.
1999-01-01
The Crystal Peak area of the Pikes Peak batholith, near Lake George in central Colorado, is world-renowned for its crystals of amazonite (the blue-green variety of microcline) and smoky quartz. Such crystals, collected from individual miarolitic pegmatites, have a remakably small variation in crystal size within each pegmatite, and the shapes of plots of their crystal size distributions (CSDs) are invariably lognormal or close to lognormal in all cases. These observations are explained by a crystal growth mechanism that was governed initially by surface-controlled kinetics, during which crystals tended to grow larger in proportion to their size, thereby establishing lognormal CSDs. Surface-controlled growth was followed by longer periods of supply controlled growth, during which growth rate was predominantly size-independent, consequently preserving the lognormal shapes of the CSDs and the small size variation. The change from surface- to supply controlled growth kinetics may have resulted from an increasing demand for nutrients that exceeded diffusion limitations of the system. The proposed model for crystal growth in this locality appears to be common in the geologic record, and can be used with other information, such as isotopic data, to deduce physico-chemical conditions during crystal formation.
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NASA Technical Reports Server (NTRS)
Mitchell, David L.; Arnott, W. Patrick
1994-01-01
This study builds upon the microphysical modeling described in Part 1 by deriving formulations for the extinction and absorption coefficients in terms of the size distribution parameters predicted from the micro-physical model. The optical depth and single scatter albedo of a cirrus cloud can then be determined, which, along with the asymmetry parameter, are the input parameters needed by cloud radiation models. Through the use of anomalous diffraction theory, analytical expressions were developed describing the absorption and extinction coefficients and the single scatter albedo as functions of size distribution parameters, ice crystal shapes (or habits), wavelength, and refractive index. The extinction coefficient was formulated in terms of the projected area of the size distribution, while the absorption coefficient was formulated in terms of both the projected area and mass of the size distribution. These properties were formulated as explicit functions of ice crystal geometry and were not based on an 'effective radius.' Based on simulations of the second cirrus case study described in Part 1, absorption coefficients predicted in the near infrared for hexagonal columns and rosettes were up to 47% and 71% lower, respectively, than absorption coefficients predicted by using equivalent area spheres. This resulted in single scatter albedos in the near-infrared that were considerably greater than those predicted by the equivalent area sphere method. Reflectances in this region should therefore be underestimated using the equivalent area sphere approach. Cloud optical depth was found to depend on ice crystal habit. When the simulated cirrus cloud contained only bullet rosettes, the optical depth was 142% greater than when the cloud contained only hexagonal columns. This increase produced a doubling in cloud albedo. In the near-infrared (IR), the single scatter albedo also exhibited a significant dependence on ice crystal habit. More research is needed on the geometrical properties of ice crystals before the influence of ice crystal shape on cirrus radiative properties can be adequately understood. This study provides a way of coupling the radiative properties of absorption, extinction, and single scatter albedo to the microphysical properties of cirrus clouds. The dependence of extinction and absorption on ice crystal shape was not just due to geometrical differences between crystal types, but was also due to the effect these differences had on the evolution of ice particle size spectra. The ice particle growth model in Part 1 and the radiative properties treated here are based on analytical formulations, and thus represent a computationally efficient means of modeling the microphysical and radiative properties of cirrus clouds.
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Extraordinary wavelength reduction in terahertz graphene-cladded photonic crystal slabs
Williamson, Ian A. D.; Mousavi, S. Hossein; Wang, Zheng
2016-01-01
Photonic crystal slabs have been widely used in nanophotonics for light confinement, dispersion engineering, nonlinearity enhancement, and other unusual effects arising from their structural periodicity. Sub-micron device sizes and mode volumes are routine for silicon-based photonic crystal slabs, however spectrally they are limited to operate in the near infrared. Here, we show that two single-layer graphene sheets allow silicon photonic crystal slabs with submicron periodicity to operate in the terahertz regime, with an extreme 100× wavelength reduction from graphene’s large kinetic inductance. The atomically thin graphene further leads to excellent out-of-plane confinement, and consequently photonic-crystal-slab band structures that closely resemble those of ideal two-dimensional photonic crystals, with broad band gaps even when the slab thickness approaches zero. The overall photonic band structure not only scales with the graphene Fermi level, but more importantly scales to lower frequencies with reduced slab thickness. Just like ideal 2D photonic crystals, graphene-cladded photonic crystal slabs confine light along line defects, forming waveguides with the propagation lengths on the order of tens of lattice constants. The proposed structure opens up the possibility to dramatically reduce the size of terahertz photonic systems by orders of magnitude. PMID:27143314
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Wang, Weijie; Loke, Desmond; Shi, Luping; Zhao, Rong; Yang, Hongxin; Law, Leong-Tat; Ng, Lung-Tat; Lim, Kian-Guan; Yeo, Yee-Chia; Chong, Tow-Chong; Lacaita, Andrea L
2012-01-01
The quest for universal memory is driving the rapid development of memories with superior all-round capabilities in non-volatility, high speed, high endurance and low power. Phase-change materials are highly promising in this respect. However, their contradictory speed and stability properties present a key challenge towards this ambition. We reveal that as the device size decreases, the phase-change mechanism changes from the material inherent crystallization mechanism (either nucleation- or growth-dominated), to the hetero-crystallization mechanism, which resulted in a significant increase in PCRAM speeds. Reducing the grain size can further increase the speed of phase-change. Such grain size effect on speed becomes increasingly significant at smaller device sizes. Together with the nano-thermal and electrical effects, fast phase-change, good stability and high endurance can be achieved. These findings lead to a feasible solution to achieve a universal memory.
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Wang, Weijie; Loke, Desmond; Shi, Luping; Zhao, Rong; Yang, Hongxin; Law, Leong-Tat; Ng, Lung-Tat; Lim, Kian-Guan; Yeo, Yee-Chia; Chong, Tow-Chong; Lacaita, Andrea L.
2012-01-01
The quest for universal memory is driving the rapid development of memories with superior all-round capabilities in non-volatility, high speed, high endurance and low power. Phase-change materials are highly promising in this respect. However, their contradictory speed and stability properties present a key challenge towards this ambition. We reveal that as the device size decreases, the phase-change mechanism changes from the material inherent crystallization mechanism (either nucleation- or growth-dominated), to the hetero-crystallization mechanism, which resulted in a significant increase in PCRAM speeds. Reducing the grain size can further increase the speed of phase-change. Such grain size effect on speed becomes increasingly significant at smaller device sizes. Together with the nano-thermal and electrical effects, fast phase-change, good stability and high endurance can be achieved. These findings lead to a feasible solution to achieve a universal memory. PMID:22496956
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Grain size constraints on twin expansion in hexagonal close packed crystals
Kumar, Mariyappan Arul; Beyerlein, Irene Jane; Tome, Carlos N.
2016-10-20
Deformation twins are stress-induced transformed domains of lamellar shape that form when polycrystalline hexagonal close packed metals, like Mg, are strained. Several studies have reported that the propensity of deformation twinning reduces as grain size decreases. Here, we use a 3D crystal plasticity based micromechanics model to calculate the effect of grain size on the driving forces responsible for expanding twin lamellae. The calculations reveal that constraints from the neighboring grain where the grain boundary and twin lamella meet induce a stress reversal in the twin lamella. A pronounced grain size effect arises as reductions in grain size cause thesemore » stress-reversal fields from twin/grain boundary junctions to affect twin growth. We further show that the severity of this neighboring grain constraint depends on the crystallographic orientation and plastic response of the neighboring grain. We show that these stress-reversal fields from twin/grain boundary junctions will affect twin growth, below a critical parent grain size. Finally, these results reveal an unconventional yet influential role that grain size and grain neighbors can play on deformation twinning.« less
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Indentation size effects in single crystal copper as revealed by synchrotron x-ray microdiffraction
NASA Astrophysics Data System (ADS)
Feng, G.; Budiman, A. S.; Nix, W. D.; Tamura, N.; Patel, J. R.
2008-08-01
For a Cu single crystal, we find that indentation hardness increases with decreasing indentation depth, a phenomenon widely observed before and called the indentation size effect (ISE). To understand the underlying mechanism, we measure the lattice rotations in indentations of different sizes using white beam x-ray microdiffraction (μXRD); the indentation-induced lattice rotations are directly measured by the streaking of x-ray Laue spots associated with the indentations. The magnitude of the lattice rotations is found to be independent of indentation size, which is consistent with the basic tenets of the ISE model. Using the μXRD data together with an ISE model, we can estimate the effective radius of the indentation plastic zone, and the estimate is consistent with the value predicted by a finite element analysis. Using these results, an estimate of the average dislocation densities within the plastic zones has been made; the findings are consistent with the ISE arising from a dependence of the dislocation density on the depth of indentation.
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Macromolecular Crystal Quality
NASA Technical Reports Server (NTRS)
Snell, Edward H.; Borgstahl, Gloria E. O.; Bellamy, Henry D.; Curreri, Peter A. (Technical Monitor)
2001-01-01
There are many ways of judging a good crystal. Which we use depends on the qualities we seek. For gemstones size, clarity and impurity levels (color) are paramount. For the semiconductor industry purity is probably the most important quality. For the structural crystallographer the primary desideratum is the somewhat more subtle concept of internal order. In this chapter we discuss the effect of internal order (or the lack of it) on the crystal's diffraction properties.
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Effect of alkali ions (Na+, K+, Cs+) on reaction mechanism of CZTS nano-particles synthesis
NASA Astrophysics Data System (ADS)
Kumar, Suresh; Altosaar, Mare; Grossberg, Maarja; Mikli, Valdek
2018-04-01
The control of morphology, elemental composition and phase composition of Cu2ZnSnS4 (CZTS) nano-crystals depends on the control of complex formation and surface stabilization of nano-particles in solution-based synthesis in oleylamine. At temperatures ≥280 °C, the control of nano-crystal's morphology and homogenous growth is difficult because of fast poly-nuclear growth occurring at higher temperatures. In the present work the effect of oleylamine complex formation with different alkali ions (Na+, K+ and Cs+) on nano-crystals growth at synthesis temperature of 280 °C was studied. It was found that nano-powders synthesized in the presence of Na+ and K+ ions showed the formation of crystals of different sizes - small nano-particles (18 nm-30 nm), large aggregated crystals (few nm to 1 μm) and large single crystals (1 μm - 4 μm). The presence of Cs+ ions in the nano-powder synthesis in oleylamine-metal precursor-CsOH solution promoted growth of nano-crystals of homogenous size. It is proposed that the formed oleylamine-Cs complexes a) enhance the formation and stabilization of oleylamine-metal (Cu, Zn and Sn) complexes before the injection of sulphur precursor into the oleylamine-metal precursor solution and b) after addition of sulphur stabilize the fast nucleated nano-particles and promote diffusion limited growth.
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SEMICONDUCTOR TECHNOLOGY: An efficient dose-compensation method for proximity effect correction
NASA Astrophysics Data System (ADS)
Ying, Wang; Weihua, Han; Xiang, Yang; Renping, Zhang; Yang, Zhang; Fuhua, Yang
2010-08-01
A novel simple dose-compensation method is developed for proximity effect correction in electron-beam lithography. The sizes of exposed patterns depend on dose factors while other exposure parameters (including accelerate voltage, resist thickness, exposing step size, substrate material, and so on) remain constant. This method is based on two reasonable assumptions in the evaluation of the compensated dose factor: one is that the relation between dose factors and circle-diameters is linear in the range under consideration; the other is that the compensated dose factor is only affected by the nearest neighbors for simplicity. Four-layer-hexagon photonic crystal structures were fabricated as test patterns to demonstrate this method. Compared to the uncorrected structures, the homogeneity of the corrected hole-size in photonic crystal structures was clearly improved.
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NASA Astrophysics Data System (ADS)
Hao, Haiyan; Yao, Xi; Wang, Minqiang
2007-01-01
Homogeneous ZnSe nanocrystals doped SiO 2 glass was successfully prepared by sol-gel in situ crystallization method. The structure of the doped ZnSe nanocrystals was studied by X-ray diffraction (XRD). ZnSe nanocrystals in silica were about 4-10 nm analysed by transmission electron microscopy (TEM), which was consistent with the results of XRD estimated using Scherrer's formular. The quantum size effect in ZnSe nanocrystals was evidenced from the blue-shifts of the optical absorption edge, and the average size of ZnSe nanocrystals was estimated by the magnitude of blue shift according to the L.E. Brus' effective mass model. The size of ZnSe nanocrystals depending on annealing time and temperature was further discussed using XRF.
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Morphology of calcite crystals in clast coatings from four soils in the Mojave desert region
NASA Technical Reports Server (NTRS)
Chadwick, Oliver A.; Sowers, Janet M.; Amundson, Ronald G.
1989-01-01
Pedogenic calcite-crystal coatings on clasts were examined in four soils along an altitudinal gradient on Kyle Canyon alluvium in southern Nevada. Clast coatings were studied rather than matrix carbonate to avoid the effects of soil matrix on crystallization. Six crystal sizes and shapes were recognized and distinguished. Equant micrite was the dominant crystal form with similar abundance at all elevations. The distributions of five categories of spar and microspar appear to be influenced by altitudinally induced changes in effective moisture. In the drier, lower elevation soils, crystals were equant or parallel prismatic with irregular, interlocking boundaries while in the more moist, higher elevation soils they were randomly oriented, euhedral, prismatic, and fibrous. There was little support for the supposition that Mg(+2) substitution or increased (Mg + Ca)/HCO3 ratios in the precipitating solution produced crystal elongation.
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Ma, Meng; He, Zhoukun; Li, Yuhan; Chen, Feng; Wang, Ke; Zhang, Qing; Deng, Hua; Fu, Qiang
2012-12-01
Thin films of polystyrene (PS)/poly(ε-caprolactone) (PCL) blends were prepared by spin-coating and characterized by tapping mode force microscopy (AFM). Effects of the relative concentration of PS in polymer solution on the surface phase separation and dewetting feature size of the blend films were systematically studied. Due to the coupling of phase separation, dewetting, and crystallization of the blend films with the evaporation of solvent during spin-coating, different size of PS islands decorated with various PCL crystal structures including spherulite-like, flat-on individual lamellae, and flat-on dendritic crystal were obtained in the blend films by changing the film composition. The average distance of PS islands was shown to increase with the relative concentration of PS in casting solution. For a given ratio of PS/PCL, the feature size of PS appeared to increase linearly with the square of PS concentration while the PCL concentration only determined the crystal morphology of the blend films with no influence on the upper PS domain features. This is explained in terms of vertical phase separation and spinodal dewetting of the PS rich layer from the underlying PCL rich layer, leading to the upper PS dewetting process and the underlying PCL crystalline process to be mutually independent. Copyright © 2012 Elsevier Inc. All rights reserved.
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NASA Astrophysics Data System (ADS)
Hu, Lin; Wirth, Brian D.; Maroudas, Dimitrios
2017-08-01
We report results on the lattice thermal conductivities of tungsten single crystals containing nanoscale-sized pores or voids and helium (He) nanobubbles as a function of void/bubble size and gas pressure in the He bubbles based on molecular-dynamics simulations. For reference, we calculated lattice thermal conductivities of perfect tungsten single crystals along different crystallographic directions at room temperature and found them to be about 10% of the overall thermal conductivity of tungsten with a weak dependence on the heat flux direction. The presence of nanoscale voids in the crystal causes a significant reduction in its lattice thermal conductivity, which decreases with increasing void size. Filling the voids with He to form He nanobubbles and increasing the bubble pressure leads to further significant reduction of the tungsten lattice thermal conductivity, down to ˜20% of that of the perfect crystal. The anisotropy in heat conduction remains weak for tungsten single crystals containing nanoscale-sized voids and He nanobubbles throughout the pressure range examined. Analysis of the pressure and atomic displacement fields in the crystalline region that surrounds the He nanobubbles reveals that the significant reduction of tungsten lattice thermal conductivity in this region is due to phonon scattering from the nanobubbles, as well as lattice deformation around the nanobubbles and formation of lattice imperfections at higher bubble pressure.
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Livi, Kenneth J T; Villalobos, Mario; Leary, Rowan; Varela, Maria; Barnard, Jon; Villacís-García, Milton; Zanella, Rodolfo; Goodridge, Anna; Midgley, Paul
2017-09-12
Two synthetic goethites of varying crystal size distributions were analyzed by BET, conventional TEM, cryo-TEM, atomic resolution STEM and HRTEM, and electron tomography in order to determine the effects of crystal size, shape, and atomic scale surface roughness on their adsorption capacities. The two samples were determined by BET to have very different site densities based on Cr VI adsorption experiments. Model specific surface areas generated from TEM observations showed that, based on size and shape, there should be little difference in their adsorption capacities. Electron tomography revealed that both samples crystallized with an asymmetric {101} tablet habit. STEM and HRTEM images showed a significant increase in atomic-scale surface roughness of the larger goethite. This difference in roughness was quantified based on measurements of relative abundances of crystal faces {101} and {201} for the two goethites, and a reactive surface site density was calculated for each goethite. Singly coordinated sites on face {210} are 2.5 more dense than on face {101}, and the larger goethite showed an average total of 36% {210} as compared to 14% for the smaller goethite. This difference explains the considerably larger adsorption capacitiy of the larger goethite vs the smaller sample and points toward the necessity of knowing the atomic scale surface structure in predicting mineral adsorption processes.
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NASA Astrophysics Data System (ADS)
van Sebille, M.; Fusi, A.; Xie, L.; Ali, H.; van Swaaij, R. A. C. M. M.; Leifer, K.; Zeman, M.
2016-09-01
We report the effect of hydrogen on the crystallization process of silicon nanocrystals embedded in a silicon oxide matrix. We show that hydrogen gas during annealing leads to a lower sub-band gap absorption, indicating passivation of defects created during annealing. Samples annealed in pure nitrogen show expected trends according to crystallization theory. Samples annealed in forming gas, however, deviate from this trend. Their crystallinity decreases for increased annealing time. Furthermore, we observe a decrease in the mean nanocrystal size and the size distribution broadens, indicating that hydrogen causes a size reduction of the silicon nanocrystals.
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NASA Astrophysics Data System (ADS)
Belloul, M.; Bartolo, J.-F.; Ziraoui, B.; Coldren, F.; Taly, V.; El Abed, A. I.
2013-07-01
We investigate the effect of an applied ac high voltage on a confined stable nematic liquid crystal (LC) in a microfluidic device and show that this actuation leads to the formation of highly monodisperse microdroplets with an unexpected constant mean size over a large interval of the forcing frequency F and with a droplets production frequency f ≃2F. We show also that despite the nonlinear feature of the droplets formation mechanism, droplets size, and size distribution are governed simply by the LC flow rate Qd and the forcing frequency F.
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2013-06-01
project focuses on the theoretical study of suspensions of nano- particles of different nature (ferroelectric, ferromagnetic , multiferroic) with size ...SUBJECT TERMS EOARD, ferroelectric, ferromagnetic and multiferroic, new photorefractive effects in liquid crystal cell, new materials and systems...magnetic, mechanical, luminescence etc absent in a pure material . The idea of doping the liquid crystals with elongated ferromagnetic particles to
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On the influence of crystal size and wavelength on native SAD phasing.
Liebschner, Dorothee; Yamada, Yusuke; Matsugaki, Naohiro; Senda, Miki; Senda, Toshiya
2016-06-01
Native SAD is an emerging phasing technique that uses the anomalous signal of native heavy atoms to obtain crystallographic phases. The method does not require specific sample preparation to add anomalous scatterers, as the light atoms contained in the native sample are used as marker atoms. The most abundant anomalous scatterer used for native SAD, which is present in almost all proteins, is sulfur. However, the absorption edge of sulfur is at low energy (2.472 keV = 5.016 Å), which makes it challenging to carry out native SAD phasing experiments as most synchrotron beamlines are optimized for shorter wavelength ranges where the anomalous signal of sulfur is weak; for longer wavelengths, which produce larger anomalous differences, the absorption of X-rays by the sample, solvent, loop and surrounding medium (e.g. air) increases tremendously. Therefore, a compromise has to be found between measuring strong anomalous signal and minimizing absorption. It was thus hypothesized that shorter wavelengths should be used for large crystals and longer wavelengths for small crystals, but no thorough experimental analyses have been reported to date. To study the influence of crystal size and wavelength, native SAD experiments were carried out at different wavelengths (1.9 and 2.7 Å with a helium cone; 3.0 and 3.3 Å with a helium chamber) using lysozyme and ferredoxin reductase crystals of various sizes. For the tested crystals, the results suggest that larger sample sizes do not have a detrimental effect on native SAD data and that long wavelengths give a clear advantage with small samples compared with short wavelengths. The resolution dependency of substructure determination was analyzed and showed that high-symmetry crystals with small unit cells require higher resolution for the successful placement of heavy atoms.
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Khaleel, Maryam; Xu, Wenqian; Lesch, David A.
The effects of synthesis conditions on the FAU/EMT content and the size of nanocrystals, formed from inorganic aluminosilicate sols, were investigated. High resolution transmission electron microscopy imaging and comparison of experimental X-ray diffraction patterns with simulations demonstrated that all materials made starting from synthesis mixtures in the composition range (1.8-33) SiO2: 1 Al2O3: (2.7-33) Na2O: (41-1000) H2O contain FAU/EMT intergrowths. Compositions with low water content increase the FAU fraction up to 0.8 but the crystal size exceeds 100 nm. Extension of the higher FAU purity to nanocrystals was achieved only by first mixing the sol at high water content compositionsmore » that favor nanocrystal formation and then - after a certain time - lowering by freeze-drying the water to levels favoring the formation of FAU. Cryogenic transmission electron microscopy and small angle X-ray scattering from representative optically clear and colloidally stable precursor sols (aged and crystallized at ambient temperature) reveal the formation of amorphous aggregates before the detection of crystals, in agreement with earlier findings and an existing model for the aggregative growth of the zeolite MFI. The presence of these amorphous aggregates coincides with the aforementioned state of sol that preserves the original trajectory towards nano-crystals after the pronounced reduction of water content by freeze-drying. If water reduction by freeze-drying is applied earlier (before the detection of amorphous aggregates), the sol follows the low water content trajectory towards larger crystals. Despite this memory effect, the sol at this stage is still agnostic towards FAU or EMT formation, the relative content of which is dominantly determined by the final water content. These findings demonstrate that it is possible to combine the effects of pre-and post-nucleation sol composition to steer crystal size and crystal structure, respectively. They confirm precursor nanoparticle evolution, while they emphasize the importance of solution phase composition at both pre- and post-nucleation stages of aggregative crystal growth.« less
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NASA Astrophysics Data System (ADS)
Jiang, Jingkun; Chen, Da-Ren; Biswas, Pratim
2007-07-01
A flame aerosol reactor (FLAR) was developed to synthesize nanoparticles with desired properties (crystal phase and size) that could be independently controlled. The methodology was demonstrated for TiO2 nanoparticles, and this is the first time that large sets of samples with the same size but different crystal phases (six different ratios of anatase to rutile in this work) were synthesized. The degree of TiO2 nanoparticle agglomeration was determined by comparing the primary particle size distribution measured by scanning electron microscopy (SEM) to the mobility-based particle size distribution measured by online scanning mobility particle spectrometry (SMPS). By controlling the flame aerosol reactor conditions, both spherical unagglomerated particles and highly agglomerated particles were produced. To produce monodisperse nanoparticles, a high throughput multi-stage differential mobility analyser (MDMA) was used in series with the flame aerosol reactor. Nearly monodisperse nanoparticles (geometric standard deviation less than 1.05) could be collected in sufficient mass quantities (of the order of 10 mg) in reasonable time (1 h) that could be used in other studies such as determination of functionality or biological effects as a function of size.
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Zinc-Nucleated D 2 and H 2 Crystal Formation from Their Liquids
DOE Office of Scientific and Technical Information (OSTI.GOV)
Bernat, T. P.; Petta, N.; Kozioziemski, B.
Calorimetric measurements at University of Rochester Laboratory for Laser Energetics of D 2 crystallization from the melt indicate that zinc can act as a heterogeneous nucleation seed with suppressed supercooling. We further studied in this paper this effect for a variety of zinc substrates using the optical-access cryogenic sample cell at Lawrence Livermore National Laboratory. Small supercoolings are observed, some as low as 5 mK, but results depend on the zinc history and sample preparation. In general, thin samples prepared by physical vapor deposition were not effective in nucleating crystal formation. Larger (several-millimeter) granules showed greater supercooling suppression, depending onmore » surface modification and granule size. Surfaces of these granules are morphologically varied and not uniform. Scanning electron microscope images were not able to correlate any particular surface feature with enhanced nucleation. Finally, application of classical nucleation theory to the observed variation of supercooling level with granule size is consistent with nucleation features with sizes <100 nm and with wetting angles of a few degrees.« less
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Zinc-Nucleated D 2 and H 2 Crystal Formation from Their Liquids
Bernat, T. P.; Petta, N.; Kozioziemski, B.; ...
2016-09-01
Calorimetric measurements at University of Rochester Laboratory for Laser Energetics of D 2 crystallization from the melt indicate that zinc can act as a heterogeneous nucleation seed with suppressed supercooling. We further studied in this paper this effect for a variety of zinc substrates using the optical-access cryogenic sample cell at Lawrence Livermore National Laboratory. Small supercoolings are observed, some as low as 5 mK, but results depend on the zinc history and sample preparation. In general, thin samples prepared by physical vapor deposition were not effective in nucleating crystal formation. Larger (several-millimeter) granules showed greater supercooling suppression, depending onmore » surface modification and granule size. Surfaces of these granules are morphologically varied and not uniform. Scanning electron microscope images were not able to correlate any particular surface feature with enhanced nucleation. Finally, application of classical nucleation theory to the observed variation of supercooling level with granule size is consistent with nucleation features with sizes <100 nm and with wetting angles of a few degrees.« less
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Convection effects in protein crystal growth
NASA Technical Reports Server (NTRS)
Roberts, Glyn O.
1988-01-01
Protein crystals for X-ray diffraction study are usually grown resting on the bottom of a hanging drop of a saturated protein solution, with slow evaporation to the air in a small enclosed cell. The evaporation rate is controlled by hanging the drop above a reservoir of water, with its saturation vapor pressure decreased by a low concentration of a passive solute. The drop has a lower solute concentration, and its volume shrinks by evaporation until the molecular concentrations match. Protein crystals can also be grown from a seed crystal suspended or supported in the interior of a supersaturated solution. The main analysis of this report concerns this case because it is less complicated than hanging-drop growth. Convection effects have been suggested as the reason for the apparent cessation of growth at a certain rather small crystal size. It seeems that as the crystal grows, the number of dislocations increases to a point where further growth is hindered. Growth in the microgravity environment of an orbiting space vehicle has been proposed as a method for obtaining larger crystals. Experimental observations of convection effects during the growth of protein crystals have been reported.
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Synergistic Measurement of Ice Cloud Microphysics using C- and Ka-Band Radars
NASA Astrophysics Data System (ADS)
Ewald, F.; Gross, S.; Hagen, M.; Li, Q.; Zinner, T.
2017-12-01
Ice clouds play an essential role in the climate system since they have a large effect on the Earth's radiation budget. Uncertainties associated with their spatial and temporal distribution as well as their optical and microphysical properties still account for large uncertainties in climate change predictions. Substantial improvement of our understanding of ice clouds was achieved with the advent of cloud radars into the field of ice cloud remote sensing. Here, highly variable ice crystal size distributions are one of the key issues remaining to be resolved. With radar reflectivity scaling with the sixth moment of the particle size, the assumed ice crystal size distribution has a large impact on the results of microphysical retrievals. Different ice crystal sizes distributions can, however, be distinguished, when cloud radars of different wavelength are used simultaneously.For this study, synchronous RHI scans were performed for a common measurement range of about 30 km between two radar instruments using different wavelengths: the dual-polarization C-band radar POLDIRAD operated at DLR and the Mira-36 Ka-band cloud radar operated at the University of Munich. For a measurement period over several months, the overlapping region for ice clouds turned out to be quite large. This gives evidence on the presence of moderate-sized ice crystals for which the backscatter is sufficient high to be visible in the C-band as well. In the range between -10 to +10 dBz, reflectivity measurements from both radars agreed quite well indicating the absence of large ice crystals. For reflectivities above +10 dBz, we observed differences with smaller values at the Ka-band due to Mie scattering effects at larger ice crystals.In this presentation, we will show how this differential reflectivity can be used to gain insight into ice cloud microphysics on the basis of electromagnetic scattering calculations. We will further explore ice cloud microphysics using the full polarization agility of the C-band radar and compare the results to simultaneous linear depolarization measurements with the Ka-band radar. In summary, we will explore if the scientific understanding of ice cloud microphysics can be advanced by the combination of C- and Ka-band radars.
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Ice recrystallization inhibition in ice cream by propylene glycol monostearate.
Aleong, J M; Frochot, S; Goff, H D
2008-11-01
The effectiveness of propylene glycol monostearate (PGMS) to inhibit ice recrystallization was evaluated in ice cream and frozen sucrose solutions. PGMS (0.3%) dramatically reduced ice crystal sizes in ice cream and in sucrose solutions frozen in a scraped-surface freezer before and after heat shock, but had no effect in quiescently frozen solutions. PGMS showed limited emulsifier properties by promoting smaller fat globule size distributions and enhanced partial coalescence in the mix and ice cream, respectively, but at a much lower level compared to conventional ice cream emulsifier. Low temperature scanning electron microscopy revealed highly irregular crystal morphology in both ice cream and sucrose solutions frozen in a scraped-surface freezer. There was strong evidence to suggest that PGMS directly interacts with ice crystals and interferes with normal surface propagation. Shear during freezing may be required for its distribution around the ice and sufficient surface coverage.
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Crystal growth and annealing method and apparatus
Gianoulakis, Steven E.; Sparrow, Robert
2001-01-01
A method and apparatus for producing crystals that minimizes birefringence even at large crystal sizes, and is suitable for production of CaF.sub.2 crystals. The method of the present invention comprises annealing a crystal by maintaining a minimal temperature gradient in the crystal while slowly reducing the bulk temperature of the crystal. An apparatus according to the present invention includes a thermal control system added to a crystal growth and annealing apparatus, wherein the thermal control system allows a temperature gradient during crystal growth but minimizes the temperature gradient during crystal annealing. An embodiment of the present invention comprises a secondary heater incorporated into a conventional crystal growth and annealing apparatus. The secondary heater supplies heat to minimize the temperature gradients in the crystal during the annealing process. The secondary heater can mount near the bottom of the crucible to effectively maintain appropriate temperature gradients.
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NASA Astrophysics Data System (ADS)
Nanev, Christo N.; Petrov, Kostadin P.
2017-12-01
The use of the classical nucleation-growth-separation principle (NGSP) was restricted hitherto to nucleation kinetics studies only. A novel application of the NGSP is proposed. To reduce crystal polydispersity internal seeding of equally-sized crystals is suggested, the advantage being avoidance of crystal grinding, sieving and any introduction of impurities. In the present study, size distributions of grown insulin crystals are interpreted retrospectively to select the proper nucleation stage parameters. The conclusion is that when steering a crystallization process aimed at reducing crystal polydispersity, the shortest possible nucleation stage duration has to be chosen because it renders the closest size distribution of the nucleated crystal seeds. Causes of inherent propensity to increasing crystal polydispersity during prolonged growth are also explored. Step sources of increased activity, present in some crystals while absent in others, are pointed as the major polydispersity cause. Insulin crystal morphology is also considered since it determines the dissolution rate of a crystalline medicine.
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NASA Astrophysics Data System (ADS)
Xuan, Weidong; Lan, Jian; Liu, Huan; Li, Chuanjun; Wang, Jiang; Ren, Weili; Zhong, Yunbo; Li, Xi; Ren, Zhongming
2017-08-01
High magnetic fields are widely used to improve the microstructure and properties of materials during the solidification process. During the preparation of single-crystal turbine blades, the microstructure of the superalloy is the main factor that determines its mechanical properties. In this work, the effects of a high magnetic field on the microstructure of Ni-based single-crystal superalloys PWA1483 and CMSX-4 during directional solidification were investigated experimentally. The results showed that the magnetic field modified the primary dendrite arm spacing, γ' phase size, and microsegregation of the superalloys. In addition, the size and volume fractions of γ/ γ' eutectic and the microporosity were decreased in a high magnetic field. Analysis of variance (ANOVA) results showed that the effect of a high magnetic field on the microstructure during directional solidification was significant ( p < 0.05). Based on both experimental results and theoretical analysis, the modification of microstructure was attributed to thermoelectric magnetic convection occurring in the interdendritic regions under a high magnetic field. The present work provides a new method to optimize the microstructure of Ni-based single-crystal superalloy blades by applying a high magnetic field.
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Effects of cirrus composition on atmospheric radiation budgets
NASA Technical Reports Server (NTRS)
Kinne, Stefan; Liou, Kuo-Nan
1988-01-01
A radiative transfer model that can be used to determine the change in solar and infrared fluxes caused by variations in the composition of cirrus clouds was used to investigate the importance of particle size and shape on the radiation budget of the Earth-atmosphere system. Even though the cloud optical thickness dominates the radiative properties of ice clouds, the particle size and nonsphericity of ice crystals are also important in calculations of the transfer of near-IR solar wavelengths. Results show that, for a given optical thickness, ice clouds composed of larger particles would produce larger greenhouse effects than those composed of smaller particles. Moreover, spherical particles with equivalent surface areas, frequently used for ice crystal clouds, would lead to an overestimation of the greenhouse effect.
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NASA Astrophysics Data System (ADS)
Tong, Huifen; Zhou, Yingying; Chang, Gang; Li, Pai; Zhu, Ruizhi; He, Yunbin
2018-06-01
Anatase TiO2 micro-crystals with 51% surface exposing highly active {0 0 1} facets are prepared by hydrothermal synthesis using TiF4 as Ti resource and HF as morphology control agent. In addition, anatase TiO2 single crystals exposing large {0 0 1} crystal facets are facilely synthesized with "green" NaF plus HCl replacing HF for the morphology control. A series of comparative experiments are carried out for separately studying the effects of F- and H+ concentrations on the growth of TiO2 crystals, which have not been understood very much in depth so far. The results indicate that both F- and H+ synergistically affect the synthesis of truncated anatase octahedrons, where F- is preferentially adsorbed on the {0 0 1} facets resulting in lateral growth of these facets and H+ adjusts the growth rate of anatase TiO2 along different orientations by tuning the hydrolysis rate. Based on this information, anatase TiO2 single crystals with small size (1.3 μm) and large exposure of {0 0 1} facets (45%) are successfully prepared under optimal conditions ([H+]/[F-] = 20:1). Photocatalytic activities of the as-prepared products toward methylene blue photo-degradation are further tested. It is revealed that both crystal size and percentage of {0 0 1} facets are decisive for the photocatalytic performance, and the crystals with a small size (1.3 μm) and large exposure of {0 0 1} facets (45%) are catalytically most active. This work has clarified the main factors that control the growth process and morphology of anatase TiO2 single crystals for achieving superior photocatalytic properties.
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Imaging transport phenomena during lysozyme protein crystal growth by the hanging drop technique
NASA Astrophysics Data System (ADS)
Sethia Gupta, Anamika; Gupta, Rajive; Panigrahi, P. K.; Muralidhar, K.
2013-06-01
The present study reports the transport process that occurs during the growth of lysozyme protein crystals by the hanging drop technique. A rainbow schlieren technique has been employed for imaging changes in salt concentration. A one dimensional color filter is used to record the deflection of the light beam. An optical microscope and an X-ray crystallography unit are used to characterize the size, tetragonal shape and Bravais lattice constants of the grown crystals. A parametric study on the effect of drop composition, drop size, reservoir height and number of drops on the crystal size and quality is reported. Changes in refractive index are not large enough to create a meaningful schlieren image in the air gap between the drop and the reservoir. However, condensation of fresh water over the reservoir solution creates large changes in the concentration of NaCl, giving rise to clear color patterns in the schlieren images. These have been analyzed to obtain salt concentration profiles near the free surface of the reservoir solution as a function of time. The diffusion of fresh water into the reservoir solution at the early stages of crystal growth followed by the mass flux of salt from the bulk solution towards the free surface has been recorded. The overall crystal growth process can be classified into two regimes, as demarcated by the changes in slope of salt concentration within the reservoir. The salt concentration in the reservoir equilibrates at long times when the crystallization process is complete. Thus, transport processes in the reservoir emerge as the route to monitor protein crystal growth in the hanging drop configuration. Results show that crystal growth rate is faster for a higher lysozyme concentration, smaller drops, and larger reservoir heights.
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Investigating the Effect of Impurities on Macromolecule Crystal Growth in Microgravity
NASA Technical Reports Server (NTRS)
Snell, Edward H.; Judge, Russell A.; Crawford, Lisa; Forsythe, Elizabeth L.; Pusey, Marc L.; Sportiello, Michael; Todd, Paul; Bellamy, Henry; Lovelace, Jeff; Cassanto, John M.;
2001-01-01
Chicken egg-white lysozyme (CEWL) crystals were grown in microgravity and on the ground in the presence of various amounts of a naturally occurring lysozyme dimer impurity. No significant favorable differences in impurity incorporation between microgravity and ground crystal samples were observed. At low impurity concentration the microgravity crystals preferentially incorporated the dimer. The presence of the dimer in the crystallization solutions in microgravity reduced crystal size, increased mosaicity and reduced the signal to noise ratio of the X-ray data. Microgravity samples proved more sensitive to impurity. Accurate indexing of the reflections proved critical to the X-ray analysis. The largest crystals with the best X-ray diffraction properties were grown from pure solution in microgravity.
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Thermodynamic aspects of cluster crystallization in cryoprotective solutions.
Osetsky, A I
2011-01-01
Crystallization of the solutions with quite a high intermolecular interaction of the components is analyzed. For the first time there has been considered the phenomenon of cluster crystallization of these solutions, enabling the reduction of total energy of intermolecular bonds, broken down during crystallization of the components has been discussed. A special priority is given to the cluster crystallization of aqueous solutions of cryoprotective substances close to vitrification temperature. Within this temperature range the mechanism of cluster crystallization is especially effective due to a sharp reduction of sizes of critical ice nucleation centers and diffusion mobility of molecules. This should be taken into account when designing the cryopreservation protocols for biological systems.
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de Bruyn, John R.; Goiko, Maria; Mozaffari, Maryam; Bator, Daniel; Dauphinee, Ron L.; Liao, Yinyin; Flemming, Roberta L.; Bramble, Michael S.; Hunter, Graeme K.; Goldberg, Harvey A.
2013-01-01
We study the effect of isoforms of osteopontin (OPN) on the nucleation and growth of crystals from a supersaturated solution of calcium and phosphate ions. Dynamic light scattering is used to monitor the size of the precipitating particles and to provide information about their concentration. At the ion concentrations studied, immediate precipitation was observed in control experiments with no osteopontin in the solution, and the size of the precipitating particles increased steadily with time. The precipitate was identified as hydroxyapatite by X-ray diffraction. Addition of native osteopontin (nOPN) extracted from rat bone caused a delay in the onset of precipitation and reduced the number of particles that formed, but the few particles that did form grew to a larger size than in the absence of the protein. Recombinant osteopontin (rOPN), which lacks phosphorylation, caused no delay in initial calcium phosphate precipitation but severely slowed crystal growth, suggesting that rOPN inhibits growth but not nucleation. rOPN treated with protein kinase CK2 to phosphorylate the molecule (p-rOPN) produced an effect similar to that of nOPN, but at higher protein concentrations and to a lesser extent. These results suggest that phosphorylations are critical to OPN’s ability to inhibit nucleation, whereas the growth of the hydroxyapatite crystals is effectively controlled by the highly acidic OPN polypeptide. This work also demonstrates that dynamic light scattering can be a powerful tool for delineating the mechanism of protein modulation of mineral formation. PMID:23457612
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NASA Astrophysics Data System (ADS)
Luo, Zhilong; Cui, Yingdan; Dong, Weibing; Xu, Qipeng; Zou, Gaoxing; Kang, Chao; Hou, Baohong; Chen, Song; Gong, Junbo
2017-12-01
Nitroguanidine (NQ) is a commonly used explosive, which has been widely used for both civilian and military explosive applications. However, the weak flowability and mechanical performance limit its application. In this work, mechanical performance and thermodynamic stability of NQ crystals were improved by controlling crystal morphologies in the crystallization process. Typical NQ crystals with multiple morphologies and single crystal form were obtained in the presence of additives during the cooling crystallization. The morphology controlled NQ crystals showed higher density, unimodal crystal size distribution and enhanced flowability. The additives showed the inhibitory effect on the nucleation of NQ crystals by in-situ FBRM and PVM determination, and the mechanism was analyzed by means of morphological prediction and molecular simulation. Furthermore, the morphology controlled NQ crystals suggested higher thermodynamic stability according to the calculation of entropy, enthalpy, Gibbs free energy and apparent activation energy on the basis of DSC results.
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NASA Astrophysics Data System (ADS)
Wang, Dong-Xu; Chen, Shu-Sen; Li, Yan-Yue; Yang, Jia-Yun; Wei, Tian-Yu; Jin, Shao-Hua
2014-07-01
Additives are one of the most important factors that greatly affect the crystal characteristics of the high energy compound hexahydro-1,3,5-trinitro-1,3,5-s-triazine (RDX, C3H6N6O6) and they have an influence on impact sensitivity. In this article, a growth morphology method was applied to obtain the crystal habit of RDX in a vacuum as well as the morphologically important faces, and molecular dynamics simulations were applied to calculate the interaction energy between these crystal faces and additive molecules for prediction of the additive-effect crystal habits of RDX. On this basis, crystal characteristics including crystal morphology, aspect ratio, and total surface charge were investigated. Then the particle size and surface electrostatic voltage of the samples from recrystallization were analyzed experimentally. The impact sensitivity test indicated that acrylamide, which could enhance the regularity and degree of sphericity of RDX crystals and effectively reduce the surface static electricity of RDX, was successful in reducing the impact sensitivity of RDX as an additive for crystallization. The above experimental results were in good agreement with the conclusions based on the theoretical calculations.
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Chemical vapor deposition of high-quality large-sized MoS 2 crystals on silicon dioxide substrates
Chen, Jianyi; Tang, Wei; Tian, Bingbing; ...
2016-03-31
Large-sized MoS 2 crystals can be grown on SiO 2/Si substrates via a two-stage chemical vapor deposition method. The maximum size of MoS 2 crystals can be up to about 305 μm. The growth method can be used to grow other transition metal dichalcogenide crystals and lateral heterojunctions. Additionally, the electron mobility of the MoS 2 crystals can reach ≈30 cm 2 V –1 s –1, which is comparable to those of exfoliated flakes.
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Chemical Vapor Deposition of High-Quality Large-Sized MoS2 Crystals on Silicon Dioxide Substrates.
Chen, Jianyi; Tang, Wei; Tian, Bingbing; Liu, Bo; Zhao, Xiaoxu; Liu, Yanpeng; Ren, Tianhua; Liu, Wei; Geng, Dechao; Jeong, Hu Young; Shin, Hyeon Suk; Zhou, Wu; Loh, Kian Ping
2016-08-01
Large-sized MoS 2 crystals can be grown on SiO 2 /Si substrates via a two-stage chemical vapor deposition method. The maximum size of MoS 2 crystals can be up to about 305 μm. The growth method can be used to grow other transition metal dichalcogenide crystals and lateral heterojunctions. The electron mobility of the MoS 2 crystals can reach ≈30 cm 2 V -1 s -1 , which is comparable to those of exfoliated flakes.
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NASA Astrophysics Data System (ADS)
Zhu, Z.; Liu, F. R.; Wang, Z. M.; Fan, Z. K.; Liu, F.; Sun, N. X.
2015-04-01
A comparative study on crystallization characteristics of amorphous Ge2Sb2Te5 (GST) films induced by an ultraviolet pulse laser and isothermal annealing was carried out by using transmission electron microscopy (TEM) and Raman scattering. TEM observations showed that the mean grain size induced by a pulse laser was in the nanoscale. A more complete crystallization in the 50 nm thick GST film was obtained which was ascribed to the effect of thermal convection produced in a thinner GST film, however, when the film thickness was over 70 nm, no significant decrease in the mean grain size was found because of the effect of heating mode, where a surface heat source by the ultraviolet laser radiation caused a quick temperature drop. The body heating mode at the isothermal annealing condition made the mean grain size increase remarkably with the increase of film thickness, which could be up to the submicron scale, relative to the size of film thickness. The Raman spectrum analysis showed that a red shift was observed in laser induced Ge2Sb2Te5 films as compared to the isothermal annealing samples, which was caused by the resultant stress of the thermal stress and phase transformation stress.
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Liou, K N; Ou, Szu-Cheng; Takano, Yoshihide; Cetola, Jeffrey
2006-09-10
A satellite remote sensing methodology has been developed to retrieve 3D ice water content (IWC) and mean effective ice crystal size of cirrus clouds from satellite data on the basis of a combination of the conventional retrieval of cloud optical depth and particle size in a horizontal plane and a parameterization of the vertical cloud profile involving temperature from sounding and/or analysis. The inferred 3D cloud fields of IWC and mean effective ice crystal size associated with two impressive cirrus clouds that occurred in the vicinity of northern Oklahoma on 18 April 1997 and 9 March 2000, obtained from the Department of Energy's Atmospheric Radiation Measurement Program, have been validated against the ice crystal size distributions that were collected independently from collocated and coincident aircraft optical probe measurements. The 3D cloud results determined from satellite data have been applied to the simulation of cw laser energy propagation, and we show the significance of 3D cloud geometry and inhomogeneity and spherical atmosphere on the transmitted and backscattered laser powers. Finally, we demonstrate that the 3D cloud fields derived from satellite remote sensing can be used for the 3D laser transmission and backscattering model for tactical application.
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NASA Astrophysics Data System (ADS)
Liou, K. N.; Ou, Szu-Cheng; Takano, Yoshihide; Cetola, Jeffrey
2006-09-01
A satellite remote sensing methodology has been developed to retrieve 3D ice water content (IWC) and mean effective ice crystal size of cirrus clouds from satellite data on the basis of a combination of the conventional retrieval of cloud optical depth and particle size in a horizontal plane and a parameterization of the vertical cloud profile involving temperature from sounding and/or analysis. The inferred 3D cloud fields of IWC and mean effective ice crystal size associated with two impressive cirrus clouds that occurred in the vicinity of northern Oklahoma on 18 April 1997 and 9 March 2000, obtained from the Department of Energy's Atmospheric Radiation Measurement Program, have been validated against the ice crystal size distributions that were collected independently from collocated and coincident aircraft optical probe measurements. The 3D cloud results determined from satellite data have been applied to the simulation of cw laser energy propagation, and we show the significance of 3D cloud geometry and inhomogeneity and spherical atmosphere on the transmitted and backscattered laser powers. Finally, we demonstrate that the 3D cloud fields derived from satellite remote sensing can be used for the 3D laser transmission and backscattering model for tactical application.
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The effect of sulfated polysaccharides on the crystallization of calcite superstructures
NASA Astrophysics Data System (ADS)
Fried, Ruth; Mastai, Yitzhak
2012-01-01
Calcite with unique morphology and uniform size has been successfully synthesized in the presence of classes of polysaccharides based on carrageenans. In the crystallization of calcite, the choice of different carrageenans, (iota, lambda and kappa), as additives concedes systematic study of the influence of different chemical structures and particularly molecular charge on the formation of CaCO 3 crystals. The uniform calcite superstructures are formed by assemblies and aggregation of calcite crystals. The mechanism for the formation of calcite superstructures was studied by a variety of techniques, SEM, TEM, XRD, time-resolved conductivity and light scattering measurements, focusing on the early stages of crystals' nucleation and aggregation.
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Theory of the intermediate stage of crystal growth with applications to insulin crystallization
NASA Astrophysics Data System (ADS)
Barlow, D. A.
2017-07-01
A theory for the intermediate stage of crystal growth, where two defining equations one for population continuity and another for mass-balance, is used to study the kinetics of the supersaturation decay, the homogeneous nucleation rate, the linear growth rate and the final distribution of crystal sizes for the crystallization of bovine and porcine insulin from solution. The cited experimental reports suggest that the crystal linear growth rate is directly proportional to the square of the insulin concentration in solution for bovine insulin and to the cube of concentration for porcine. In a previous work, it was shown that the above mentioned system could be solved for the case where the growth rate is directly proportional to the normalized supersaturation. Here a more general solution is presented valid for cases where the growth rate is directly proportional to the normalized supersaturation raised to the power of any positive integer. The resulting expressions for the time dependent normalized supersaturation and crystal size distribution are compared with experimental reports for insulin crystallization. An approximation for the maximum crystal size at the end of the intermediate stage is derived. The results suggest that the largest crystal size in the distribution at the end of the intermediate stage is maximized when nucleation is restricted to be only homogeneous. Further, the largest size in the final distribution depends only weakly upon the initial supersaturation.
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Preferred viewing distance of liquid crystal high-definition television.
Lee, Der-Song
2012-01-01
This study explored the effect of TV size, illumination, and viewing angle on preferred viewing distance in high-definition liquid crystal display televisions (HDTV). Results showed that the mean preferred viewing distance was 2856 mm. TV size and illumination significantly affected preferred viewing distance. The larger the screen size, the greater the preferred viewing distance, at around 3-4 times the width of the screen (W). The greater the illumination, the greater the preferred viewing distance. Viewing angle also correlated significantly with preferred viewing distance. The more deflected from direct frontal view, the shorter the preferred viewing distance seemed to be. Copyright © 2011 Elsevier Ltd and The Ergonomics Society. All rights reserved.
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Size effects under homogeneous deformation of single crystals: A discrete dislocation analysis
NASA Astrophysics Data System (ADS)
Guruprasad, P. J.; Benzerga, A. A.
Mechanism-based discrete dislocation plasticity is used to investigate the effect of size on micron scale crystal plasticity under conditions of macroscopically homogeneous deformation. Long-range interactions among dislocations are naturally incorporated through elasticity. Constitutive rules are used which account for key short-range dislocation interactions. These include junction formation and dynamic source and obstacle creation. Two-dimensional calculations are carried out which can handle high dislocation densities and large strains up to 0.1. The focus is laid on the effect of dimensional constraints on plastic flow and hardening processes. Specimen dimensions ranging from hundreds of nanometers to tens of microns are considered. Our findings show a strong size-dependence of flow strength and work-hardening rate at the micron scale. Taylor-like hardening is shown to be insufficient as a rationale for the flow stress scaling with specimen dimensions. The predicted size effect is associated with the emergence, at sufficient resolution, of a signed dislocation density. Heuristic correlations between macroscopic flow stress and macroscopic measures of dislocation density are sought. Most accurate among those is a correlation based on two state variables: the total dislocation density and an effective, scale-dependent measure of signed density.
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Thermal properties of poly(3-hydroxybutyrate)/vegetable fiber composites
NASA Astrophysics Data System (ADS)
Vitorino, Maria B. C.; Reul, Lízzia T. A.; Carvalho, Laura H.; Canedo, Eduardo L.
2015-05-01
The present work studies the thermal properties of composites of poly(3-hydroxybutyrate) (PHB) - a fully biodegradable semi-crystalline thermo-plastic obtained from renewable resources through low-impact biotechno-logical process, biocompatible and non-toxic - and vegetable fiber from the fruit (coconut) of babassu palm tree. PHB is a highly crystalline resin and this characteristic leads to suboptimal properties in some cases. Consequently, thermal properties, in particular those associated with the crystallization of the matrix, are important to judge the suitability of the compounds for specific applications. PHB/babassu composites with 0-50% load were prepared in an internal mixer. Two different types of babassu fibers with two different particle size ranges were compounded with PHB and test specimens molded by compression. Melting and crystallization behavior were studied by differential scanning calorimetry (DSC) at heating/cooling rates between 2 and 30°C/min. Several parameters, including melting point, crystallization temperature, crystallinity, and rate of crystallization, were estimated as functions of load and heating/cooling rates. Results indicate that fibers do not affect the melting process, but facilitate crystallization from the melt. Crystallization temperatures are 30 to 40°C higher for the compounds compared with the neat resin. However, the amount of fiber added has little effect on crystallinity and the degree of crystallinity is hardly affected by the load. Fiber type and initial particle size do not have a significant effect on thermal properties.
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35 GHz Measurements of CO2 Crystals for Simulating Observations of the Martian Polar Caps
NASA Technical Reports Server (NTRS)
Foster, J. L.; Chang, A. T. C.; Hall, D. K.; Tait, A. B.; Barton, J. S.
1998-01-01
In order to learn more about the Martian polar caps, it is important to compare and contrast the behavior of both frozen H2O and CO2 in different parts of the electromagnetic spectrum. Relatively little attention has been given, thus far, to observing the thermal microwave part of the spectrum. In this experiment, passive microwave radiation emanating from within a 33 cm snowpack was measured with a 35 GHz hand-held radiometer, and in addition to the natural snow measurements, the radiometer was used to measure the microwave emission and scattering from layers of manufactured CO2 (dry ice). A 1 m x 2 m plate of aluminum sheet metal was positioned beneath the natural snow so that microwave emissions from the underlying soil layers would be minimized. Compared to the natural snow crystals, results for the dry ice layers exhibit lower' microwave brightness temperatures for similar thicknesses, regardless of the incidence angle of the radiometer. For example, at 50 degree H (horizontal polarization) and with a covering of 21 cm of snow and 18 cm of dry ice, the brightness temperatures were 150 K and 76 K, respectively. When the snow depth was 33 cm, the brightness temperature was 144 K, and when the total thickness of the dry ice was 27 cm, the brightness temperature was 86 K. The lower brightness temperatures are due to a combination of the lower physical temperature and the larger crystal sizes of the commercial CO2 Crystals compared to the snow crystals. As the crystal size approaches the size of the microwave wavelength, it scatters microwave radiation more effectively, thus lowering the brightness temperature. The dry ice crystals in this experiment were about an order of magnitude larger than the snow crystals and three orders of magnitude larger than the CO2 Crystals produced in the cold stage of a scanning electron microscope. Spreading soil, approximately 2 mm in thickness, on the dry ice appeared to have no effect on the brightness temperatures.
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Effect of Frozen Storage Temperature on the Quality of Premium Ice Cream.
Park, Sung Hee; Jo, Yeon-Ji; Chun, Ji-Yeon; Hong, Geun-Pyo; Davaatseren, Munkhtugs; Choi, Mi-Jung
2015-01-01
The market sales of premium ice cream have paralleled the growth in consumer desire for rich flavor and taste. Storage temperature is a major consideration in preserving the quality attributes of premium ice cream products for both the manufacturer and retailers during prolonged storage. We investigated the effect of storage temperature (-18℃, -30℃, -50℃, and -70℃) and storage times, up to 52 wk, on the quality attributes of premium ice cream. Quality attributes tested included ice crystal size, air cell size, melting resistance, and color. Ice crystal size increased from 40.3 μm to 100.1 μm after 52 wk of storage at -18℃. When ice cream samples were stored at -50℃ or -70℃, ice crystal size slightly increased from 40.3 μm to 57-58 μm. Initial air cell size increased from 37.1 μm to 87.7 μm after storage at -18℃ for 52 wk. However, for storage temperatures of -50℃ and -70℃, air cell size increased only slightly from 37.1 μm to 46-47 μm. Low storage temperature (-50℃ and -70℃) resulted in better melt resistance and minimized color changes in comparison to high temperature storage (-18℃ and -30℃). In our study, quality changes in premium ice cream were gradually minimized according to decrease in storage temperature up to-50℃. No significant beneficial effect of -70℃ storage was found in quality attributes. In the scope of our experiment, we recommend a storage temperature of -50℃ to preserve the quality attributes of premium ice cream.
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Effect of Frozen Storage Temperature on the Quality of Premium Ice Cream
Park, Sung Hee; Jo, Yeon-Ji; Chun, Ji-Yeon; Hong, Geun-Pyo
2015-01-01
The market sales of premium ice cream have paralleled the growth in consumer desire for rich flavor and taste. Storage temperature is a major consideration in preserving the quality attributes of premium ice cream products for both the manufacturer and retailers during prolonged storage. We investigated the effect of storage temperature (−18℃, −30℃, −50℃, and −70℃) and storage times, up to 52 wk, on the quality attributes of premium ice cream. Quality attributes tested included ice crystal size, air cell size, melting resistance, and color. Ice crystal size increased from 40.3 μm to 100.1 μm after 52 wk of storage at −18℃. When ice cream samples were stored at −50℃ or −70℃, ice crystal size slightly increased from 40.3 μm to 57-58 μm. Initial air cell size increased from 37.1 μm to 87.7 μm after storage at −18℃ for 52 wk. However, for storage temperatures of −50℃ and −70℃, air cell size increased only slightly from 37.1 μm to 46-47 μm. Low storage temperature (−50℃ and −70℃) resulted in better melt resistance and minimized color changes in comparison to high temperature storage (−18℃ and −30℃). In our study, quality changes in premium ice cream were gradually minimized according to decrease in storage temperature up to−50℃. No significant beneficial effect of −70℃ storage was found in quality attributes. In the scope of our experiment, we recommend a storage temperature of −50℃ to preserve the quality attributes of premium ice cream. PMID:26877639
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Synthesis, characterization, and ion-exchange properties of colloidal zeolite nanocrystals
NASA Astrophysics Data System (ADS)
Jawor, Anna; Jeong, Byeong-Heon; Hoek, Eric M. V.
2009-10-01
Here, we present physical-chemical properties of Linde type A (LTA) zeolite crystals synthesized via conventional hydrothermal and microwave heating methods. Both heating methods produced LTA crystals that were sub-micron in size, highly negatively charged, super-hydrophilic, and stable when dispersed in water. However, microwave heating produced relatively narrow crystal size distributions, required much shorter heating times, and did not significantly change composition, crystallinity, or surface chemistry. Moreover, microwave heating allowed systematic variation of crystal size by varying heating temperature and time during the crystallization reaction, thus producing a continuous gradient of crystal sizes ranging from about 90 to 300 nm. In ion-exchange studies, colloidal zeolites exhibited excellent sorption kinetics and capacity for divalent metal ions, suggesting their potential for use in water softening, scale inhibition, and scavenging of toxic metal ions from water.
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Effect of roll hot press temperature on crystallite size of PVDF film
DOE Office of Scientific and Technical Information (OSTI.GOV)
Hartono, Ambran, E-mail: ambranhartono@yahoo.com; Sanjaya, Edi; Djamal, Mitra
2014-03-24
Fabrication PVDF films have been made using Hot Roll Press. Preparation of samples carried out for nine different temperatures. This condition is carried out to see the effect of Roll Hot Press temperature on the size of the crystallite of PVDF films. To obtain the diffraction pattern of sample characterization is performed using X-Ray Diffraction. Furthermore, from the diffraction pattern is obtained, the calculation to determine the crystallite size of the sample by using the Scherrer equation. From the experimental results and the calculation of crystallite sizes obtained for the samples with temperature 130 °C up to 170 °C respectivelymore » increased from 7.2 nm up to 20.54 nm. These results show that increasing temperatures will also increase the size of the crystallite of the sample. This happens because with the increasing temperature causes the higher the degree of crystallization of PVDF film sample is formed, so that the crystallite size also increases. This condition indicates that the specific volume or size of the crystals depends on the magnitude of the temperature as it has been studied by Nakagawa.« less
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NASA Astrophysics Data System (ADS)
Prywer, Jolanta; Olszynski, Marcin; Torzewska, Agnieszka; Mielniczek-Brzóska, Ewa
2014-06-01
Effect of disodium EDTA (salt of ethylenediamine tetraacetic acid) on the crystallization of struvite and carbonate apatite was studied. To evaluate such an effect we performed an experiment of struvite and carbonate apatite growth from artificial urine. The crystallization process was induced by Proteus mirabilis to mimic the real urinary tract infection, which usually leads to urinary stone formation. The results demonstrate that disodium EDTA exhibits the effect against P. mirabilis retarding the activity of urease - an enzyme produced by these microorganisms. The spectrophotometric results demonstrate that, with and without P. mirabilis, the addition of disodium EDTA increases the induction time and decreases the growth efficiency compared to the baseline (without disodium EDTA). These results are discussed from the standpoint of speciation of complexes formed in the solution of artificial urine in the presence of disodium EDTA. The size of struvite crystals was found to decrease in the presence of disodium EDTA. However, struvite crystals are larger in the presence of bacteria while the crystal morphology and habit remain unchanged.
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Crystallization kinetics of cocoa butter in the presence of sorbitan esters.
Sonwai, Sopark; Podchong, Pawitchaya; Rousseau, Dérick
2017-01-01
Cocoa butter crystallization in the presence of sorbitan mono- and triesters or canola oil was investigated. Solid-state surfactant esters accelerated early-stage cocoa butter solidification while suppressing later growth. Sorbitan tristearate showed the strongest effect, followed by sorbitan monostearate and sorbitan monopalmitate. Liquid-state surfactants suppressed cocoa butter crystallization at all time points, with sorbitan trioleate showing a stronger effect than sorbitan monooleate, which behaved in a similar fashion to canola oil. Via DSC, the palmitic and stearic-based surfactants only associated with cocoa butter's high-melting fraction, with the oleic acid-based surfactants and canola oil showing little influence. All sorbitan esters had little effect on polymorphism, whereas canola oil accelerated the form II-to-III-to-IV transition. The palmitic and stearic-based surfactants greatly reduced cocoa butter crystal size whereas the oleic acid-based surfactants and canola showed no notable effect. Overall, sorbitan esters impacted cocoa butter crystallization kinetics, though this depended on surfactant structure and concentration. Copyright © 2016 Elsevier Ltd. All rights reserved.
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Characteristics of nanolite crystallization in volcanic pyroclasts
NASA Astrophysics Data System (ADS)
Mujin, M.; Nakamura, M.; Miyake, A.
2017-12-01
Crystal nucleation and initial growth in silicate melt may control the number density and later stage growth of crystals, such as twinning and morphology, and are therefore fundamental but still poorly understood processes in magma crystallization. Petrographic and experimental studies on groundmass microlites shed light on their importance for understanding eruption dynamics, but most studies did not focus on nanometer scale crystals. Recently, we reported "nanolites (30 nm-1 µm in width)" and "ultrananolites (< 30 nm in diameter)", which are nanoscale crystals with extremely high number density, in the interstices of microlites in pyroclasts. In this presentation, we summarize their mineralogical and petrological characteristics in pyroclasts of the 2011 eruption of Shinmoedake (Kirishima volcano group)1. By covering a wide size-range of crystals (down to 1 nm in diameter) based on scanning electron microscopy with tungsten filament (W-SEM), field emission (FE)-SEM, and transmission electron microscopy (TEM), we found a clear size gap (hiatus) in the size distribution and presence of minimum crystal size. In a dense juvenile fragment, crystals were absent or their number densities were too low to measure the sizes of pyroxene with a diameter of < 20 nm and a width of 30-100 nm, plagioclase with a width of < 100 nm, and Fe-Ti oxide with a diameter of 2-10 nm and a width of 20-100 nm. In pumice clasts, crystals smaller than 100 nm were not found. These observations show that nucleation of nanoscale crystals almost paused (froze) in the late stage of crystallization, possibly due to a decrease in undercooling, increase in interfacial free energy, and decrease in diffusivity in a dehydrated melt, whereas crystal growth was mostly continuous. Ultrananolites were found in pyroxene and Fe-Ti oxide; notably, these were spherical, whereas nanolites and microlites were rectangular. The observed ultrananolite-sized particles might partly include "subcritical clusters", which are particles smaller than the critical nucleation size assumed in the transient nucleation models. References 1) Mujin and Nakamura, 2014, Geology, v.42, p.611-614, and Mujin et al, in revision, Am. Min.
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A flow-free droplet-based device for high throughput polymorphic crystallization.
Yang, Shih-Mo; Zhang, Dapeng; Chen, Wang; Chen, Shih-Chi
2015-06-21
Crystallization is one of the most crucial steps in the process of pharmaceutical formulation. In recent years, emulsion-based platforms have been developed and broadly adopted to generate high quality products. However, these conventional approaches such as stirring are still limited in several aspects, e.g., unstable crystallization conditions and broad size distribution; besides, only simple crystal forms can be produced. In this paper, we present a new flow-free droplet-based formation process for producing highly controlled crystallization with two examples: (1) NaCl crystallization reveals the ability to package saturated solution into nanoliter droplets, and (2) glycine crystallization demonstrates the ability to produce polymorphic crystallization forms by controlling the droplet size and temperature. In our process, the saturated solution automatically fills the microwell array powered by degassed bulk PDMS. A critical oil covering step is then introduced to isolate the saturated solution and control the water dissolution rate. Utilizing surface tension, the solution is uniformly packaged in the form of thousands of isolating droplets at the bottom of each microwell of 50-300 μm diameter. After water dissolution, individual crystal structures are automatically formed inside the microwell array. This approach facilitates the study of different glycine growth processes: α-form generated inside the droplets and γ-form generated at the edge of the droplets. With precise temperature control over nanoliter-sized droplets, the growth of ellipsoidal crystalline agglomerates of glycine was achieved for the first time. Optical and SEM images illustrate that the ellipsoidal agglomerates consist of 2-5 μm glycine clusters with inner spiral structures of ~35 μm screw pitch. Lastly, the size distribution of spherical crystalline agglomerates (SAs) produced from microwells of different sizes was measured to have a coefficient variation (CV) of less than 5%, showing crystal sizes can be precisely controlled by microwell sizes with high uniformity. This new method can be used to reliably fabricate monodispersed crystals for pharmaceutical applications.
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NASA Astrophysics Data System (ADS)
Zhou, Wei; Shijimaya, Chiko; Takahashi, Mari; Miyata, Masanobu; Mott, Derrick; Koyano, Mikio; Ohta, Michihiro; Akatsuka, Takeo; Ono, Hironobu; Maenosono, Shinya
2017-12-01
Uniform Cu2Sn1-xZnxS3 (x = 0-0.2) nanoparticles (NPs) with a characteristic size of about 40 nm were chemically synthesized. The primary crystal phase of the NPs was wurtzite (WZ) with a mean crystalline size of about 20 nm. The NPs were sintered to form nanostructured pellets with different compositions preserving the composition and grain size of the original NPs by the pulse electric current sintering technique. The pellets had a zinc blende (ZB) structure with a residual WZ phase, and the mean crystalline size was found to remain virtually unchanged for all pellets. Among all samples, the pellets of Cu2Sn0.95Zn0.05S3 and Cu2Sn0.85Zn0.15S3 exhibited the highest ZT value (0.37 at 670 K) which is 10 times higher than that of a non-nanostructured Cu2SnS3 bulk crystal thanks to effective phonon scattering by nanograins, the phase-pure ZB crystal structure, and the increase in hole carrier density by Zn doping.
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NASA Astrophysics Data System (ADS)
Jang, Jisun; Kim, Il Won
2016-01-01
Polymeric additives to induce competitive crystallization of pharmaceutical compounds were explored. A cocrystal of theophylline and oxalic acid was used as a model system, and poly(acrylic acid), poly(caprolactone), and poly(ethylene glycol) were the additives. The cocrystal formation was selectively hindered with addition of poly(acrylic acid). First the size of the cocrystals were reduced, and eventually the cocrystallization was inhibited to generate neat theophylline crystals. The theophylline crystals were of a distinctively different crystal structure from known polymorphs, based on powder X-ray diffraction. They were also obtained in nanoscale size, when millimeter-scale crystals formed without poly(acrylic acid). Polymeric additives that could form specific interactions with crystallizing compounds seem to be useful tools for the phase and size control of pharmaceutical crystals.
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Albakry, Mohammad; Guazzato, Massimiliano; Swain, Michael Vincent
2004-10-15
Empress 1 and Empress 2 are well-known pressable all-ceramic dental materials that have generated substantial interest for many clinicians and patients. These two materials are reputed to benefit from heat pressing during the laboratory fabrication procedures, leading to better crystal distribution within a glass matrix, and hence an improved strength. The present study aimed to evaluate the effect of heat pressing on fracture toughness, microstructural features, and porosity. Results showed that Empress 1 had similar fracture toughness values before the pressing procedure, after it, and after the repressing procedure. The microstructural features were also similar among these specimens, but a more uniform distribution of leucite crystals was observed following the pressing and repressing procedures. Empress 2 demonstrated two different fracture toughness values. This was associated with the alignment of lithium disilicate crystals that occurred after the pressing and repressing procedures, which led to different indentation induced crack lengths, depending upon whether cracks propagated parallel to or perpendicular to the aligned crystals, the former having lower toughness than those that propagated in the perpendicular direction. Porosity, in terms of both the size and number of pores, was found to decrease after the pressing and repressing procedures for both materials. Repressing resulted in significant growth of the lithium disilicate crystals in Empress 2, but there was no change for the leucite crystals in Empress 1. The change in the lithium disilicate crystals' size did not have a noticeable effect on the fracture toughness of Empress 2. It was concluded that heat pressing did not significantly affect the fracture toughness of Empress 1, but resulted in two different values for Empress 2. It also decreased the size and number of pores for both materials, which could contribute to the strength improvement found after heat pressing, which has been reported in previous studies.
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The Effect of Thermal Cycling on Crystal-Liquid Separation During Lunar Magma Ocean Differentiation
NASA Technical Reports Server (NTRS)
Mills, Ryan D.
2013-01-01
Differentiation of magma oceans likely involves a mixture of fractional and equilibrium crystallization [1]. The existence of: 1) large volumes of anorthosite in the lunar highlands and 2) the incompatible- rich (KREEP) reservoir suggests that fractional crystallization may have dominated during differentiation of the Moon. For this to have occurred, crystal fractionation must have been remarkably efficient. Several authors [e.g. 2, 3] have hypothesized that equilibrium crystallization would have dominated early in differentiation of magma oceans because of crystal entrainment during turbulent convection. However, recent numerical modeling [4] suggests that crystal settling could have occurred throughout the entire solidification history of the lunar magma ocean if crystals were large and crystal fraction was low. These results indicate that the crystal size distribution could have played an important role in differentiation of the lunar magma ocean. Here, I suggest that thermal cycling from tidal heating during lunar magma ocean crystallization caused crystals to coarsen, leading to efficient crystal-liquid separation.
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Effect of Anatase Synthesis on the Performance of Dye-Sensitized Solar Cells
NASA Astrophysics Data System (ADS)
Sánchez-García, Mario Alberto; Bokhimi, Xim; Maldonado-Álvarez, Arturo; Jiménez-González, Antonio Esteban
2015-07-01
Anatase nanoparticles were synthesized from a titanium isopropoxide solution using a hydrothermal process at different pressures in an autoclave system while keeping the volume of the solution constant. As the autoclave pressure was increased from 1 to 71 atm (23 to 210 °C), the crystal size in the nanoparticles increased from 9 to 13.8 nm. The anatase nanoparticles were used to build dye-sensitized solar cells (DSSC). Mesoporous films of this oxide were deposited over conducting SnO2:F substrates using the screen-printing technique and then annealed at 530 °C at 1 atm of air pressure. The morphology of the mesoporous film surface of anatase, studied using scanning electron microscopy, revealed that the crystal size and pore distribution were functions of the pressure conditions. The energy band gap of the films as a function of the crystal size exhibited quantum effects below 11.8 nm. The effects of the anatase synthesis conditions and properties of the mesoporous film on the DSSC-type solar cell parameters, η%, V OC, J SC, and FF, were also investigated: the mesoporous anatase films prepared at 200 °C (54 atm of pressure in the autoclave) and annealed at 530 °C in air generated the best solar cell, having the highest conversion efficiency.
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Propagation of Ince-Gaussian beams in uniaxial crystals orthogonal to the optical axis
NASA Astrophysics Data System (ADS)
Xu, Y. Q.; Zhou, G. Q.
2012-03-01
An analytical propagation expression of an Ince-Gaussian beam in uniaxial crystals orthogonal to the optical axis is derived. The uniaxial crystal considered here has the property of the extraordinary refractive index being larger than the ordinary refractive index. The Ince-Gaussian beam in the transversal direction along the optical axis spreads more rapidly than that in the other transversal direction. With increasing the ratio of the extraordinary refractive index to the ordinary refractive index, the spreading of the Ince-Gaussian beam in the transversal direction along the optical axis increases and the spreading of the Ince-Gaussian beam in the other transversal direction decreases. The effective beam size in the transversal direction along the optical axis is always larger than that in the other transversal direction. When the even and odd modes of Ince-Gaussian beams exist simultaneously, the effective beam size in the direction along the optical axis of the odd Ince-Gaussian beam is smaller than that of the even Ince-Gaussian beam in the corresponding direction, and the effective beam size in the transversal direction orthogonal to the optical axis of the odd Ince-Gaussian beam is larger than that of the even Ince-Gaussian beam in the corresponding direction.
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Light scattering by nonspherical particles: Remote sensing and climatic implications
NASA Astrophysics Data System (ADS)
Liou, K. N.; Takano, Y.
Calculations of the scattering and adsorption properties of ice crystals and aerosols, which are usually nonspherical, require specific methodologies. There is no unique theoretical solution for the scattering by nonspherical particles. Practically, all the numerical solutions for the scattering of nonspherical particles, including the exact wave equation approach, integral equation method, and discrete-dipole approximation, are applicable only to size parameters less than about 20. Thus, these methods are useful for the study of radiation problems involving nonspherical aerosols and small ice crystals in the thermal infrared wavelengths. The geometric optics approximation has been used to evaluate the scattering, absorption and polarization properties of hexagonal ice crystals whose sizes are much larger than the incident wavelength. This approximation is generally valid for hexagonal ice crystals with size parameters larger than about 30. From existing laboratory data and theoretical results, we illustrate that nonspherical particles absorb less and have a smaller asymmetry factor than the equal-projected area/volume spherical counterparts. In particular, we show that hexagonal ice crystals exhibit numerous halo and arc features that cannot be obtained from spherical particles; and that ice crystals scatter more light in the 60° to 140° scattering angle regions than the spherical counterparts. Satellite remote sensing of the optical depth and height of cirrus clouds using visible and IR channels must use appropriate phase functions for ice crystals. Use of an equivalent sphere model would lead to a significant overestimation and underestimation of the cirrus optical depth and height, respectively. Interpretation of the measurements for polarization reflected from sunlight involving cirrus clouds cannot be made without an appropriate ice crystal model. Large deviations exist for the polarization patterns between spheres and hexagonal ice crystals. Interpretation of lidar backscattering and depolarization signals must also utilize the scattering characteristics of hexagonal ice crystals. Equivalent spherical models substantially underestimate the broadband solar albedos of ice crystal clouds because of stronger forward scattering and larger absorption by spherical particles than hexagonal ice crystals. We illustrate that the net cloud radiative forcing at the top of the atmosphere involving most cirrus clouds is positive, implying that the IR greenhouse effect outweighs the solar albedo effect. If the radiative properties of equivalent spheres are used, a significant increase in cloud radiative forcing occurs. Using a one-dimensional cloud and climate model, we further demonstrate that there is sufficient model sensitivity, in terms of temperature increase, to the use of ice crystal models in radiation calculations.
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Patil, Vidya, E-mail: vidya.patil@ruparel.edu; Patki, Mugdha, E-mail: mugdha.patki@ruparel.edu
Many nonlinear optical (NLO) crystals have been identified as potential candidates in optical and electro-optical devices. Use of NLO organic crystals is expected in photonic applications. Hence organic nonlinear optical materials have been intensely investigated due to their potentially high nonlinearities, and rapid response in electro-optic effect compared to inorganic NLO materials. There are many methods to grow organic crystals such as vapor growth method, melt growth method and solution growth method. Out of these methods, solution growth method is useful in providing constraint free crystal. Single crystals of Dopamine have been grown by evaporating the solvents from aqueous solution.more » Crystals obtained were of the size of orders of mm. The crystal structure of dopamine was determined using XRD technique. Images of crystals were obtained using FEG SEM Quanta Series under high vacuum and low KV.« less
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Crystallization Methods for Preparation of Nanocrystals for Drug Delivery System.
Gao, Yuan; Wang, Jingkang; Wang, Yongli; Yin, Qiuxiang; Glennon, Brian; Zhong, Jian; Ouyang, Jinbo; Huang, Xin; Hao, Hongxun
2015-01-01
Low water solubility of drug products causes delivery problems such as low bioavailability. The reduced particle size and increased surface area of nanocrystals lead to the increasing of the dissolution rate. The formulation of drug nanocrystals is a robust approach and has been widely applied to drug delivery system (DDS) due to the significant development of nanoscience and nanotechnology. It can be used to improve drug efficacy, provide targeted delivery and minimize side-effects. Crystallization is the main and efficient unit operation to produce nanocrystals. Both traditional crystallization methods such as reactive crystallization, anti-solvent crystallization and new crystallization methods such as supercritical fluid crystallization, high-gravity controlled precipitation can be used to produce nanocrystals. The current mini-review outlines the main crystallization methods addressed in literature. The advantages and disadvantages of each method were summarized and compared.
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Growing Larger Crystals for Neutron Diffraction
NASA Technical Reports Server (NTRS)
Pusey, Marc
2003-01-01
Obtaining crystals of suitable size and high quality has been a major bottleneck in macromolecular crystallography. With the advent of advanced X-ray sources and methods the question of size has rapidly dwindled, almost to the point where if one can see the crystal then it was big enough. Quality is another issue, and major national and commercial efforts were established to take advantage of the microgravity environment in an effort to obtain higher quality crystals. Studies of the macromolecule crystallization process were carried out in many labs in an effort to understand what affected the resultant crystal quality on Earth, and how microgravity improved the process. While technological improvements are resulting in a diminishing of the minimum crystal size required, neutron diffraction structural studies still require considerably larger crystals, by several orders of magnitude, than X-ray studies. From a crystal growth physics perspective there is no reason why these 'large' crystals cannot be obtained: the question is generally more one of supply than limitations mechanism. This talk will discuss our laboratory s current model for macromolecule crystal growth, with highlights pertaining to the growth of crystals suitable for neutron diffraction studies.
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NASA Astrophysics Data System (ADS)
Roberto Viana, J.; Rodriguez Salmon, Octavio D.; Neto, Minos A.; Carvalho, Diego C.
2018-02-01
A new approximation technique is developed so as to study the quantum ferromagnetic spin-1 Blume-Capel model in the presence of a transverse crystal field in the square lattice. Our proposal consists of approaching the spin system by considering islands of finite clusters whose frontiers are surrounded by noninteracting spins that are treated by the effective-field theory. The resulting phase diagram is qualitatively correct, in contrast to most effective-field treatments, in which the first-order line exhibits spurious behavior by not being perpendicular to the anisotropy axis at low-temperatures. The effect of the transverse anisotropy is also verified by the presence of quantum phase transitions. The possibility of using larger sizes constitutes an advantage to other approaches where the implementation of larger sizes is computationally costly.
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Size control of Au NPs supported by pH operation
NASA Astrophysics Data System (ADS)
Ichiji, Masumi; Akiba, Hiroko; Hirasawa, Izumi
2017-07-01
Au NPs are expected to become useful functional particles, as particle gun used for plant gene transfer and also catalysts. We have studied PSD (particle size distribution) control of Au NPs by reduction crystallization. Previous study found out importance of seeds policy and also feeding profile. In this paper, effect of pH in the reduction crystallization was investigated to clarify the possibility of Au NPs PSD control by pH operation and also their growth process. Au NPs of size range 10-600 nm were obtained in single-jet system using ascorbic acid (AsA) as a reducing agent with adjusting pH of AsA. Au NPs are found to grow in the process of nucleation, agglomeration, agglomeration growth and surface growth. Au NPs tend to grow by agglomeration and become larger size in lower pH regions, and to grow only by surface growth and become smaller size in higher pH regions.
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The effect factors of potassium dihydrogen phosphate crystallization in aqueous solution
NASA Astrophysics Data System (ADS)
Zhou, Cun; Sun, Fei; Liu, Xuzhao
2017-01-01
The effects of cooling rate and pH on the potassium dihydrogen phosphate crystallization process were studied by means of batch crystallization process. The experiment shows that with the increase of cooling rate, the metastable zone width increase and the induction period decrease. When the pH is 3.0, the metastable zone width and induction period are both the minimum, while the crystallization rate is the highest. The crystallization products were characterized by scanning election microscope. Potassium Dihydrogen Phosphate (KDP) is a kind of excellent nonlinear optical materials, and belongs to tetragonal system, and ideal shape is aggregate of tetragonal prism and tetragonal dipyramid, the (100) cone is alternating accumulation by double positive ions and double negative ions [1-4]. The crystals of aqueous solution method to grow have large electro-optical nonlinear coefficient and high loser-damaged threshold, and it is the only nonlinear optical crystal could be used in inertial confinement fusion (ICF), KDP crystals are the ideal system to study the native defects of complex oxide insulating material [5-7]. With the development of photovoltaic technology, KDP crystals growth and performance have become a research focus worldwide [8, 9]. The merits of the crystallization process directly affect the quality of KDP products, so the study of the effect of crystallization conditions has an important significance on industrial production. This paper studied the change rule of metastable zone width, induction period, crystallization rate and particle size distribution in crystal process, and discussed the technical condition of KDP crystallization.
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Power laws for the backscattering matrices in the case of lidar sensing of cirrus clouds
NASA Astrophysics Data System (ADS)
Kustova, Natalia V.; Konoshonkin, Alexander V.; Borovoi, Anatoli; Okamoto, Hajime; Sato, Kaori; Katagiri, Shuichiro
2017-11-01
The data bank for the backscattering matrixes of cirrus clouds that was calculated earlier by the authors and was available in the internet for free access has been replaced in the case of randomly oriented crystals by simple analytic equations. Four microphysical ratios conventionally measured by lidars have been calculated for different shapes and the effective size of the crystals. These values could be used for retrieving shapes of the crystals in cirrus clouds.
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Meso-size Effect from Self-assembled Carbon Structures and Their Device Applications
2013-08-23
electrical photoresponse from pentacene 1D disks and 2D wires, and 3) dramatic increase of solubility in water of zinc phthalocyanine (ZnPc) nanowires...Hong, M.; Son, M.; Choi, H. C.* “Crystal Plane-Dependent Photoluminescence Activity of Pentacene 1D Wire and 2D Disk Crystals.” Angew. Chem. Int...Ed. 2013, 52, 5997-6001. [7] Park, J. E.; Hong, M.; Son, M.; Choi, H. C.* “Crystal Plane-Dependent Photoluminescence Activity of Pentacene 1D Wire
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Husser, Edgar; Bargmann, Swantje
2017-01-01
The mechanical behavior of single crystalline, micro-sized copper is investigated in the context of cantilever beam bending experiments. Particular focus is on the role of geometrically necessary dislocations (GNDs) during bending-dominated load conditions and their impact on the characteristic bending size effect. Three different sample sizes are considered in this work with main variation in thickness. A gradient extended crystal plasticity model is presented and applied in a three-dimensional finite-element (FE) framework considering slip system-based edge and screw components of the dislocation density vector. The underlying mathematical model contains non-standard evolution equations for GNDs, crystal-specific interaction relations, and higher-order boundary conditions. Moreover, two element formulations are examined and compared with respect to size-independent as well as size-dependent bending behavior. The first formulation is based on a linear interpolation of the displacement and the GND density field together with a full integration scheme whereas the second is based on a mixed interpolation scheme. While the GND density fields are treated equivalently, the displacement field is interpolated quadratically in combination with a reduced integration scheme. Computational results indicate that GND storage in small cantilever beams strongly influences the evolution of statistically stored dislocations (SSDs) and, hence, the distribution of the total dislocation density. As a particular example, the mechanical bending behavior in the case of a physically motivated limitation of GND storage is studied. The resulting impact on the mechanical bending response as well as on the predicted size effect is analyzed. Obtained results are discussed and related to experimental findings from the literature. PMID:28772657
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Modeling TiO2's refractive index function from bulk to nanoparticles
NASA Astrophysics Data System (ADS)
Jalava, Juho-Pertti; Taavitsainen, Veli-Matti; Lamminmäki, Ralf-Johan; Lindholm, Minna; Auvinen, Sami; Alatalo, Matti; Vartiainen, Erik; Haario, Heikki
2015-12-01
In recent decades, the use of nanomaterials has become very common. Different nanomaterials are being used in over 1600 consumer products. Nanomaterials have been defined as having at least one dimension in the range of 1-100 nm. Such materials often have unique properties. Despite some warnings of applying bulk optical constants for nano size materials, stated already in 1980s, bulk constants are still commonly used in the light scattering measurements of nano size particles. Titanium dioxide is one of the materials that is manufactured and used as an engineered nanomaterial in increasing quantities. Due to the aforementioned facts, it is quite crucial for successful research and production of nanoparticles to find out the dependence of the refractive index function (RIF) of the material on its crystal size. We have earlier performed several ab initio computations for obtaining the dependence of the RIF of TiO2 on the crystal or on the cluster size, for particles of size up to ca. 2 nm. Extending the calculations to greater sizes has turned out to be infeasible due to the unbearable increase in computational time. However, in this study we show how the crystal-size-dependent-RIF (CS-RIF), for both rutile and anatase can be modeled from measured extinction or turbidity spectra of samples with varying crystal and particle sizes. For computing the turbidity spectrum, we constructed a model including primary crystals whose distributions were parameterized by mean and standard deviation, and also including aggregates consisting of mean sized primary particles, parameterized just by mean aggregate size. Mainly because of the long computing times Mie calculation was used in the computation of extinction spectra. However, in practical process applications, the obtained RIF will be used together with the T-matrix method. We constructed the RIFs used in the model using generalized oscillator model (GOM) as expanded to crystal size dependence. The unknown parameters of the model were solved using nonlinear least squares estimation. When the crystal size becomes smaller than the bulk size the shape of the estimated CS-RIFs reveal two distinct regions for both rutile and anatase. In the first region, starting apparently already from ca. 200 nm, the height of both the real part and the imaginary part of CS-RIF decreases on crystal diameter. However, the band gap remains constant. In the second region, starting when the crystal diameter is decreased to ca. 3 nm, a blue shift starts to increase the band gap. The band gap dependence on crystal size is quite consistent with the existing experimental values. Consequently, it is of great importance to use CS-RIF in light scattering measurements for nanoparticle size determination. Neglecting this, the smaller particles in the size distribution will have too small values, already for sub-micrometer particles, naturally distorting also the mean value. To our knowledge, this is the first time ever that a CS-RIF from bulk to 1 nm size is determined for any material.
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Habit modification of epsomite in the presence of urea
NASA Astrophysics Data System (ADS)
Ramalingom, S.; Podder, J.; Narayana Kalkura, S.; Bocelli, G.
2003-01-01
The pure and urea doped epsomite (MgSO 4·7H 2O) crystals were grown at low temperature by the slow cooling technique. The effect of pH on the growth rate of pure MgSO 4·7H 2O was studied. It was found that the higher pH values increased the growth rate and the size of the crystals. The quantity of urea present in the doped magnesium sulphate crystals was estimated. The incorporation of urea into the mother solution was found to promote the growth rate. The habit of the crystals changed from orthorhombic to tetragonal. Further, there was an increase of microhardness of the crystals on doping of urea.
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NASA Astrophysics Data System (ADS)
Zandi, Pegah; Hosseini, Elham; Rashchi, Fereshteh
2018-01-01
Titanium dioxide Nano powder has been synthesized from titanium isopropoxide (TTIP) in chloride media by sol-gel method. In this research, the effect of the drying environment, from air to oven drying at 100 °C, calcination time and temperature on nano TiO2 grain size was investigated. The synthesized powder was analyzed by x-ray diffraction and scanning electron microscope. Based on the results, the powder has been crystallized in anatase and rutile phases, due to different calcination temperatures. At temperatures above 600 °C, the Titanium dioxide nano powder has been crystallized as rutile. The crystalline structure of titanium dioxide nano powder changed because of the different calcination temperatures and time applied. The average particle size of the powder dried in air was larger than the powder dried in oven. The minimum particle size of the powder dried in air was 50 nm and in the oven was 9 nm, observed and calculated Williamson-Hall equation. All in all, with overall increasing of calcination time and temperature the grain size increased. Moreover, in the case of temperature, after a certain temperature, the grain size became constant and didn't change significantly.
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Parametric interactions in presence of different size colloids in semiconductor quantum plasmas
DOE Office of Scientific and Technical Information (OSTI.GOV)
Vanshpal, R., E-mail: ravivanshpal@gmail.com; Sharma, Uttam; Dubey, Swati
2015-07-31
Present work is an attempt to investigate the effect of different size colloids on parametric interaction in semiconductor quantum plasma. Inclusion of quantum effect is being done in this analysis through quantum correction term in classical hydrodynamic model of homogeneous semiconductor plasma. The effect is associated with purely quantum origin using quantum Bohm potential and quantum statistics. Colloidal size and quantum correction term modify the parametric dispersion characteristics of ion implanted semiconductor plasma medium. It is found that quantum effect on colloids is inversely proportional to their size. Moreover critical size of implanted colloids for the effective quantum correction ismore » determined which is found to be equal to the lattice spacing of the crystal.« less
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Epitaxially influenced boundary layer model for size effect in thin metallic films
NASA Astrophysics Data System (ADS)
Bažant, Zdeněk P.; Guo, Zaoyang; Espinosa, Horacio D.; Zhu, Yong; Peng, Bei
2005-04-01
It is shown that the size effect recently observed by Espinosa et al., [J. Mech. Phys. Solids51, 47 (2003)] in pure tension tests on free thin metallic films can be explained by the existence of a boundary layer of fixed thickness, located at the surface of the film that was attached onto the substrate during deposition. The boundary layer is influenced by the epitaxial effects of crystal growth on the dislocation density and texture (manifested by prevalent crystal plane orientations). This influence is assumed to cause significantly elevated yield strength. Furthermore, the observed gradual postpeak softening, along with its size independence, which is observed in short film strips subjected to pure tension, is explained by slip localization, originating at notch-like defects, and by damage, which can propagate in a stable manner when the film strip under pure tension is sufficiently thin and short. For general applications, the present epitaxially influenced boundary layer model may be combined with the classical strain-gradient plasticity proposed by Gao et al., [J. Mech. Phys. Solids 47, 1239 (1999)], and it is shown that this combination is necessary to fit the test data on both pure tension and bending of thin films by one and the same theory. To deal with films having different crystal grain sizes, the Hall-Petch relation for the yield strength dependence on the grain size needs to be incorporated into the combined theory. For very thin films, in which a flattened grain fills the whole film thickness, the Hall-Petch relation needs a cutoff, and the asymptotic increase of yield strength with diminishing film thickness is then described by the extension of Nix's model of misfit dislocations by Zhang and Zhou [J. Adv. Mater. 38, 51 (2002)]. The final result is a proposal of a general theory for strength, size effect, hardening, and softening of thin metallic films.
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Coalescence growth mechanism of ultrafine metal particles
NASA Astrophysics Data System (ADS)
Kasukabe, S.
1990-01-01
Ultrafine particles produced by a gas-evaporation technique show clear-cut crystal habits. The convection of an inert gas makes distinct growth zones in a metal smoke. The coalescence stages of hexagonal plates and multiply twinned particles are observed in the outer zone of a smoke. A model of the coalescence growth of particles with different crystal habits is proposed. Size distributions can be calculated by counting the ratio of the number of collisions by using the effective cross section of collisions and the existence probability of the volume of a particle. This simulation model makes clear the effect on the growth rate of coalescence growth derived from crystal habit.
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Retrieval of Ice Cloud Properties Using Variable Phase Functions
NASA Astrophysics Data System (ADS)
Heck, Patrick W.; Minnis, Patrick; Yang, Ping; Chang, Fu-Lung; Palikonda, Rabindra; Arduini, Robert F.; Sun-Mack, Sunny
2009-03-01
An enhancement to NASA Langley's Visible Infrared Solar-infrared Split-window Technique (VISST) is developed to identify and account for situations when errors are induced by using smooth ice crystals. The retrieval scheme incorporates new ice cloud phase functions that utilize hexagonal crystals with roughened surfaces. In some situations, cloud optical depths are reduced, hence, cloud height is increased. Cloud effective particle size also changes with the roughened ice crystal models which results in varied effects on the calculation of ice water path. Once validated and expanded, the new approach will be integrated in the CERES MODIS algorithm and real-time retrievals at Langley.
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Evolution of Nano-structured Quasicrystals from Amorphous alloys
NASA Astrophysics Data System (ADS)
Xing, L. Q.; Kelton, K. F.
2002-03-01
Ta shows a significant effect on the precipitation of quasicrystals in (Zr_1-xTa_x)_64Cu_18Ni_8Al_10 amorphous alloys. The amorphous alloy made without Ta forms precipitates of tetragonal Zr_2Cu primary phases upon annealing. The addition of a small amount of Ta ( ~ 3 at%) to the alloy initiates the precipitation of primary icosahedral quasicrystal phases. Moreover, as the Ta concentration increases, the size of the precipitates decreases dramatically. To study the effect of Ta in this alloy system and to understand the mechanism for the precipitation of nano-structured quasicrystals, we have investigated the crystallization characteristics of the alloys made with different Ta concentration using DSC, checked the structures of the annealed samples with TEM and X-ray diffraction, and analyzed the kinetics of the crystallization processes. The kinetic parameter and the measured crystal size distribution will be compared with theoretical predictions from conventional nucleation and growth model and from a new model for nucleation that couples the long-range diffusion flux with the interfacial attachment processes.
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Optical properties of anisotropic 3D nanoparticles arrays
NASA Astrophysics Data System (ADS)
Santiago, E. Y.; Esquivel-Sirvent, R.
2017-07-01
The optical properties of 3D periodic arrays of spheroidal Au nanoparticles are calculated using a Bruggeman effective medium approximation. The optical response of the supra-crystal depends on the volume fraction of the nanoparticles and their aspect or size ratio (major/minor axis). All the nanoparticles have the same orientation, and this defines an anisotropic dielectric function of the crystal. As a function of the filling fraction, while keeping the size ratio fixed, the maximum in the extinction spectra along the major and minor axes does not show a significant change. However, for a fixed filling fraction, varying the aspect ratio of the particles induces a shift of several hundred of nanometers in the maximum of the extinction spectra along the major axis and almost no changes along the minor axis. Depending on the aspect ratio and the filling fraction, we show that the supra-crystal has three regimes with different values of an effective plasma frequency. Contribution to the Focus Issue Self-assemblies of Inorganic and Organic Nanomaterials edited by Marie-Paule Pileni.
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NASA Astrophysics Data System (ADS)
Xuan, Weidong; Lan, Jian; Zhao, Dengke; Li, Chuanjun; Shang, Xingfu; Zhong, Yunbo; Li, Xi; Ren, Zhongming
2018-05-01
The effect of a high magnetic field on the γ' phase of Ni-based single crystal superalloy during directional solidification is investigated experimentally. The results clearly indicate that the magnetic field significantly reduces the γ' phase size. Further, the quenching experiment is carried out, and the results found that the length of mushy zone is obviously decreased under a high magnetic field. Based on both experimental results and nucleation mechanism, it is found that the decrease of γ' phase size should be attributed to the fact that a high magnetic field causes the increase of temperature gradient in front of solid/liquid interface and leads to the increase of undercooling of γ' phase.
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Jiang, Hui; Ye, Jun; Hu, Peng; Wei, Fengxia; Du, Kezhao; Wang, Ning; Ba, Te; Feng, Shuanglong; Kloc, Christian
2014-01-01
The fluorination of p-type metal phthalocyanines produces n-type semiconductors, allowing the design of organic electronic circuits that contain inexpensive heterojunctions made from chemically and thermally stable p- and n-type organic semiconductors. For the evaluation of close to intrinsic transport properties, high-quality centimeter-sized single crystals of F16CuPc, F16CoPc and F16ZnPc have been grown. New crystal structures of F16CuPc, F16CoPc and F16ZnPc have been determined. Organic single-crystal field-effect transistors have been fabricated to study the effects of the central metal atom on their charge transport properties. The F16ZnPc has the highest electron mobility (~1.1 cm2 V−1 s−1). Theoretical calculations indicate that the crystal structure and electronic structure of the central metal atom determine the transport properties of fluorinated metal phthalocyanines. PMID:25524460
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Unravelling the physics of size-dependent dislocation-mediated plasticity
NASA Astrophysics Data System (ADS)
El-Awady, Jaafar A.
2015-01-01
Size-affected dislocation-mediated plasticity is important in a wide range of materials and technologies. Here we develop a generalized size-dependent dislocation-based model that predicts strength as a function of crystal/grain size and the dislocation density. Three-dimensional (3D) discrete dislocation dynamics (DDD) simulations reveal the existence of a well-defined relationship between strength and dislocation microstructure at all length scales for both single crystals and polycrystalline materials. The results predict a transition from dislocation-source strengthening to forest-dominated strengthening at a size-dependent critical dislocation density. It is also shown that the Hall-Petch relationship can be physically interpreted by coupling with an appropriate kinetic equation of the evolution of the dislocation density in polycrystals. The model is shown to be in remarkable agreement with experiments. This work presents a micro-mechanistic framework to predict and interpret strength size-scale effects, and provides an avenue towards performing multiscale simulations without ad hoc assumptions.
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Polymorphism, microstructure and rheology of butter. Effects of cream heat treatment.
Rønholt, Stine; Kirkensgaard, Jacob Judas Kain; Pedersen, Thomas Bæk; Mortensen, Kell; Knudsen, Jes Christian
2012-12-01
The effect of cream heat treatment prior to butter manufacturing, fluctuating temperatures during storage and presence of fat globules vs. no fat globules was examined in laboratory scale produced butter. X-ray diffraction and differential scanning calorimetry was used to study crystallization behaviour and nuclear magnetic resonance to measure solid fat content and water droplet size distribution. Furthermore, the crystal structure was linked to the rheological properties and microstructure of the butter using confocal laser scanning microscopy. Butter produced from non-matured cream mainly formed α- and β'-crystals with minor traces of β-crystals. Maturing of the cream caused a transition from α- to β'- and β-form. The rheological behaviour of slow cooled butter deviated from the matured ones by having a lower elastic modulus, caused by a weaker crystal network. Presence of fat globules did not affect the rheological properties significantly. Copyright © 2012 Elsevier Ltd. All rights reserved.
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Righettoni, Marco; Pratsinis, Sotiris E., E-mail: sotiris.pratsinis@ptl.mavt.ethz.ch
Highlights: • Flame-made WO{sub 3} nanoparticles with closely controlled crystal and grain size. • Dynamic phase transition of annealing of pure and Si-doped WO{sub 3} by in situ XRD. • Irreversible evolution of WO{sub 3} crystallinity by heating/cooling during its annealing. • Si-doping alters the WO{sub 3} crystallinity dynamics and stabilizes nanosized WO{sub 3}. • Flame-made nano-WO{sub 3} can sense NO at the ppb level. - Abstract: Tungsten trioxide is a semiconductor with distinct applications in gas sensors, catalysis, batteries and pigments. As such the transition between its different crystal structures during its annealing are of interest, especially for sensormore » applications. Here, WO{sub 3} nanoparticles with closely controlled crystal and grain size (9–15 nm) and phase composition are made by flame spray pyrolysis and the formation of different WO{sub 3} phases during annealing is investigated. Most notably, the dynamic phase transition and crystal size evolution of WO{sub 3} during heating and cooling is monitored by in situ X-ray diffraction revealing how metastable WO{sub 3} phases can be captured stably. The effect of Si-doping is studied since it is used in practise to control crystal growth and phase transition during metal oxide synthesis and processing. Finally the influence of annealing on the WO{sub 3} sensing performance of NO, a lung inflammation tracer in the human breath, is explored at the ppb-level.« less
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Single-crystal growth, structure refinement and the properties of Bis(glycine) Strontium Chloride
NASA Astrophysics Data System (ADS)
Balaji, S. R.; Balu, T.; Rajasekaran, T. R.
2018-02-01
Single crystals of Bis (glycine) Strontium Chloride (BGSC) were grown by means of slow evaporation process by using analar grade Glycine and Strontium Chloride Hexahydrate as a parent compound from its aqueous solution at room temperature. The final chemical composition, [{{Sr}}{({{{C}}}2{{{H}}}5{{{NO}}}2)}2{{{Cl}}}2].{{{H}}}4{{{O}}}3+{{{H}}}8{{{O}}}3, formed were metallic light colorless block, about the size of 28 mm × 9 mm × 8 mm. A single-crystal x-ray diffraction study revealed an ordered superstructure with orthorhombic symmetry that could be assigned to the space group Pbcn. The structure in BGSC, revealed in the electron density distribution was analyzed by the direct methods (SHELXS-2014) and refined by least squares full matrix method (SHELXL-2014). The crystal structure, including anisotropic atomic displacement parameters for each atom and isotropic atomic displacement parameters for hydrogen atom, was refined to R1 = 0.0395, wR2 = 0.0776 using 1097 independent reflections. The FTIR spectrum of BGSC confirms the protonation of amino groups and the different molecular groups present in BGSC vibrate in different modes. Reverse Indentation Size Effect (RISE) was revealed in BGSC in the micro-hardness analysis using Vicker’s micro-hardness analysis. DTA and DSC results ruled out the possibility of structural change independent of mass change. The AFM studies shows fine nano size fiber like structure of the grown crystals.
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Study of Polymer Crystallization by Physical Vapor Deposition
NASA Astrophysics Data System (ADS)
Jeong, Hyuncheol
When a polymer is confined under the submicron length scale, confinement size and interfaces can significantly impact the crystallization kinetics and resulting morphology. The ability to tune the morphology of confined polymer systems is of critical importance for the development of high-performance polymer microelectronics. The wisdom from the research on confined crystallization suggests that it would be beneficial to have a processing route in which the crystallization of polymers is driven by interface and temperature effects at a nanometer-scale confinement. In practice, for atomic and small-molecular systems, physical vapor deposition (PVD) has been recognized as the most successful processing route for the precise control of the film structure at surface utilizing confinement effects. While standard PVD technologies are not generally applicable to the deposition of the chemically fragile macromolecules, the development of matrix-assisted pulsed laser evaporation (MAPLE) now enables the non-destructive PVD of high-molecular weight polymers. In this thesis work, we investigated the use of MAPLE for the precise control of the crystallization of polymer films at a molecular level. We also sought to decipher the rules governing the crystallization of confined polymers, by using MAPLE as a tool to form confined polymer systems onto substrates with a controlled temperature. We first explored the early stages of film growth and crystallization of poly(ethylene oxide) (PEO) at the substrate surface formed by MAPLE. The unique mechanism of film formation in MAPLE, the deposition of submicron-sized polymer droplets, allowed for the manifestation of confinement and substrate effects in the crystallization of MAPLE-deposited PEO. Furthermore, we also focused on the property of the amorphous PEO film formed by MAPLE, showing the dependence of polymer crystallization kinetics on the thermal history of the amorphous phase. Lastly, we probed how MAPLE processing affected the semi-crystalline structure in MAPLE-deposited polyethylene (PE) films. Depositing PE at various temperatures remarkably allowed for the tunability of the melting temperature and crystallinity of the PE films, thus manipulating the semi-crystalline structure. By comparing the structure of PE formed by different processing routes, i.e., MAPLE and melt-crystallization, we discussed how processing routes affect the development of semi-crystalline phase in polymer films.
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Spray printing of organic semiconducting single crystals
NASA Astrophysics Data System (ADS)
Rigas, Grigorios-Panagiotis; Payne, Marcia M.; Anthony, John E.; Horton, Peter N.; Castro, Fernando A.; Shkunov, Maxim
2016-11-01
Single-crystal semiconductors have been at the forefront of scientific interest for more than 70 years, serving as the backbone of electronic devices. Inorganic single crystals are typically grown from a melt using time-consuming and energy-intensive processes. Organic semiconductor single crystals, however, can be grown using solution-based methods at room temperature in air, opening up the possibility of large-scale production of inexpensive electronics targeting applications ranging from field-effect transistors and light-emitting diodes to medical X-ray detectors. Here we demonstrate a low-cost, scalable spray-printing process to fabricate high-quality organic single crystals, based on various semiconducting small molecules on virtually any substrate by combining the advantages of antisolvent crystallization and solution shearing. The crystals' size, shape and orientation are controlled by the sheer force generated by the spray droplets' impact onto the antisolvent's surface. This method demonstrates the feasibility of a spray-on single-crystal organic electronics.
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Manipulating crystallization with molecular additives.
Shtukenberg, Alexander G; Lee, Stephanie S; Kahr, Bart; Ward, Michael D
2014-01-01
Given the importance of organic crystals in a wide range of industrial applications, the chemistry, biology, materials science, and chemical engineering communities have focused considerable attention on developing methods to control crystal structure, size, shape, and orientation. Tailored additives have been used to control crystallization to great effect, presumably by selectively binding to particular crystallographic surfaces and sites. However, substantial knowledge gaps still exist in the fundamental mechanisms that govern the formation and growth of organic crystals in both the absence and presence of additives. In this review, we highlight research discoveries that reveal the role of additives, either introduced by design or present adventitiously, on various stages of formation and growth of organic crystals, including nucleation, dislocation spiral growth mechanisms, growth inhibition, and nonclassical crystal morphologies. The insights from these investigations and others of their kind are likely to guide the development of innovative methods to manipulate crystallization for a wide range of materials and applications.
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Finite-size Scaling of the Density of States in Photonic Band Gap Crystals
NASA Astrophysics Data System (ADS)
Hasan, Shakeeb Bin; Mosk, Allard P.; Vos, Willem L.; Lagendijk, Ad
2018-06-01
The famous vanishing of the density of states (DOS) in a band gap, be it photonic or electronic, pertains to the infinite-crystal limit. In contrast, all experiments and device applications refer to finite crystals, which raises the question: Upon increasing the linear size L of a crystal, how fast does the DOS approach the infinite-crystal limit? We present a theory for finite crystals that includes Bloch-mode broadening due to the presence of crystal boundaries. Our results demonstrate that the DOS for frequencies inside a band gap has a 1 /L scale dependence for crystals in one, two and three dimensions.
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The role of the cubic structure in freezing of a supercooled water droplet on an ice substrate
NASA Astrophysics Data System (ADS)
Takahashi, T.; Kobayashi, T.
1983-12-01
The possibility of the formation of a metastable cubic (diamond) structure and its role in freezing of a supercooled water droplet on an ice substrate are discussed in terms of two-dimensional nucleation. The mode of stacking sequence of new layers formed by two-dimensional nucleation is divided into single and multi-nucleation according to the degree of supercooling and to the size of the supercooled droplet. In the case of single nucleation a frozen droplet develops into a complete hexagonal single crystal or an optically single crystal (containing discontinuous stacking faults). In the case of multi-nucleation attention is paid to the size effect and the stacking direction of the nucleus to calculate the waiting time in the nucleation. Then the frozen droplets are crystallographically divided into three categories: completely single crystals, optically single crystals (containing a small cubic structure, i.e. stacking faults) and polycrystals with a misorientation of 70.53° between the c-axes.
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Mechanism of two-step vapour-crystal nucleation in a pore
NASA Astrophysics Data System (ADS)
van Meel, J. A.; Liu, Y.; Frenkel, D.
2015-09-01
We present a numerical study of the effect of hemispherical pores on the nucleation of Lennard-Jones crystals from the vapour phase. As predicted by Page and Sear, there is a narrow range of pore radii, where vapour-liquid nucleation can become a two-step process. A similar observation was made for different pore geometries by Giacomello et al. We find that the maximum nucleation rate depends on both the size and the adsorption strength of the pore. Moreover, a poe can be more effective than a planar wall with the same strength of attraction. Pore-induced vapour-liquid nucleation turns out to be the rate-limiting step for crystal nucleation. This implies that crystal nucleation can be enhanced by a judicious choice of the wetting properties of a microporous nucleating agent.
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Rajesh, P., E-mail: rajeshp@ssn.edu.in; Charoen In, Urit; Manyum, Prapun
2014-11-15
Highlights: • Bulk size KDP crystal has been grown with higher growth rate. • Systematic study on the effect of starting materials has been done. • Crystalline perfection is maintained in the entire crystal. - Abstract: A systematic study on the effect of purity of starting materials on the growth and properties of potassium dihydrogen phosphate single crystals is crucial for the future study of the material for nonlinear optical applications. Potassium dihydrogen phosphate crystals were grown using high pure (99.999%) and ordinary (99.9%) starting raw materials using slow cooling method in identical conditions. Their optical transparency and crystalline perfectionmore » are studied by UV and high resolution X-ray diffraction analyses respectively. The results are checked with the help of etching analyses. The full width at half maximum is 8″ which is close to that expected from the plane wave theory of dynamical X-ray diffraction for an ideally perfect crystal. Results of those studies are correlated with each other. The quantitative results show that the raw material plays an important role in the growth of good quality crystals.« less
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Advances and new directions in crystallization control.
Nagy, Zoltan K; Braatz, Richard D
2012-01-01
The academic literature on and industrial practice of control of solution crystallization processes have seen major advances in the past 15 years that have been enabled by progress in in-situ real-time sensor technologies and driven primarily by needs in the pharmaceutical industry for improved and more consistent quality of drug crystals. These advances include the accurate measurement of solution concentrations and crystal characteristics as well as the first-principles modeling and robust model-based and model-free feedback control of crystal size and polymorphic identity. Research opportunities are described in model-free controller design, new crystallizer designs with enhanced control of crystal size distribution, strategies for the robust control of crystal shape, and interconnected crystallization systems for multicomponent crystallization.
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Stoichiometry of Cd(S,Se) nanocrystals by anomalous small-angle x-ray scattering
NASA Astrophysics Data System (ADS)
Ramos, Aline; Lyon, Olivier; Levelut, Claire
1995-12-01
In Cd(S,Se)-doped glasses the optical properties are strongly dependent on the size of the nanocrystals, but can be also largely modified by changes in the crystal stoichiometry; however, the information on both stoichiometry and size is difficult to obtain in crystals smaller than 10 nm. The intensity scattered at small angles is classically used to get information about nanoparticles sizes. Moreover the variation of amplitude of this intensity with the energy of the x ray—``the anomalous effect''—near the selenium edge is related to stoichiometry. Anomalous small-angle x-ray scattering has been used as a tentative method to get information about stoichiometry in nanocrystals with size lower than 10 nm. Experiments have been performed on samples treated for 2 days at temperatures in the range 540-650 °C. The samples treated at temperatures above 580 °C contain crystals with size larger than 4 nm. For all these samples the anomalous effect has nearly the same amplitude, and we found the stoichiometry x=0.4 for the CdSxSe1-x nanocrystals. This agrees with the previous results obtained by scanning electron microscopy and Raman spectroscopy. The results are also confirmed by measurements of the position of the optical absorption edge and by wide-angle x-ray scattering experiments. For the sample treated at 560 °C, the nanocrystal size is 3 nm and the stoichiometry x=0.6 is deduced from the anomalous effect. For samples treated at lower temperatures the anomalous effect is not observable, indicating an even lower selenium content in the nanocrystals (x≳0.7). We observed differences in the Se content of nanocrystals for different heat treatments of the same initial glass. These results may be very helpful to interpret the change in the optical properties when the temperature of the treatments decreases in the range 560-590 °C. In this temperature range, compositional effects seem to be of the same order of magnitude as the effects of the quantum confinement.
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NASA Technical Reports Server (NTRS)
Heinemann, K.
1985-01-01
The interaction of 100 and 200 keV electron beams with amorphous alumina, titania, and aluminum nitride substrates and nanometer-size palladium particulate deposits was investigated for the two extreme cases of (1) large-area electron-beam flash-heating and (2) small-area high-intensity electron-beam irradiation. The former simulates a short-term heating effect with minimum electron irradiation exposure, the latter simulates high-dosage irradiation with minimum heating effect. All alumina and titania samples responded to the flash-heating treatment with significant recrystallization. However, the size, crystal structure, shape, and orientation of the grains depended on the type and thickness of the films and the thickness of the Pd deposit. High-dosage electron irradiation also readily crystallized the alumina substrate films but did not affect the titania films. The alumina recrystallization products were usually either all in the alpha phase, or they were a mixture of small grains in a number of low-temperature phases including gamma, delta, kappa, beta, theta-alumina. Palladium deposits reacted heavily with the alumina substrates during either treatment, but they were very little effected when supported on titania. Both treatments had the same, less prominent localized crystallization effect on aluminum nitride films.
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Multiple electrokinetic actuators for feedback control of colloidal crystal size.
Juárez, Jaime J; Mathai, Pramod P; Liddle, J Alexander; Bevan, Michael A
2012-10-21
We report a feedback control method to precisely target the number of colloidal particles in quasi-2D ensembles and their subsequent assembly into crystals in a quadrupole electrode. Our approach relies on tracking the number of particles within a quadrupole electrode, which is used in a real-time feedback control algorithm to dynamically actuate competing electrokinetic transport mechanisms. Particles are removed from the quadrupole using DC-field mediated electrophoretic-electroosmotic transport, while high-frequency AC-field mediated dielectrophoretic transport is used to concentrate and assemble colloidal crystals. Our results show successful control of the size of crystals containing 20 to 250 colloidal particles with less than 10% error. Assembled crystals are characterized by their radius of gyration, crystallinity, and number of edge particles, and demonstrate the expected size-dependent properties. Our findings demonstrate successful ensemble feedback control of the assembly of different sized colloidal crystals using multiple actuators, which has broad implications for control over nano- and micro- scale assembly processes involving colloidal components.
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Effect of Phytosterols on the Crystallization Behavior of Oil-in-Water Milk Fat Emulsions.
Zychowski, Lisa M; Logan, Amy; Augustin, Mary Ann; Kelly, Alan L; Zabara, Alexandru; O'Mahony, James A; Conn, Charlotte E; Auty, Mark A E
2016-08-31
Milk has been used commercially as a carrier for phytosterols, but there is limited knowledge on the effect of added plant sterols on the properties of the system. In this study, phytosterols dispersed in milk fat at a level of 0.3 or 0.6% were homogenized with an aqueous dispersion of whey protein isolate (WPI). The particle size, morphology, ζ-potential, and stability of the emulsions were investigated. Emulsion crystallization properties were examined through the use of differential scanning calorimetry (DSC) and Synchrotron X-ray scattering at both small and wide angles. Phytosterol enrichment influenced the particle size and physical appearance of the emulsion droplets, but did not affect the stability or charge of the dispersed particles. DSC data demonstrated that, at the higher level of phytosterol addition, crystallization of milk fat was delayed, whereas, at the lower level, phytosterol enrichment induced nucleation and emulsion crystallization. These differences were attributed to the formation of separate phytosterol crystals within the emulsions at the high phytosterol concentration, as characterized by Synchrotron X-ray measurements. X-ray scattering patterns demonstrated the ability of the phytosterol to integrate within the milk fat triacylglycerol matrix, with a concomitant increase in longitudinal packing and system disorder. Understanding the consequences of adding phytosterols, on the physical and crystalline behavior of emulsions may enable the functional food industry to design more physically and chemically stable products.
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Jo, Sinae; Kang, Seunggu
2013-11-01
Low-melting zinc-borate glass was added to the cordierite/Al2O3 composite in order to improve the sintering facility of Al2O3 and formation of nano-sized spinel crystal of high thermal conductivity. Increasing the ZnO/B2O3 ratio in the zinc-borate glass increased the ZnAl2O4 spinel and decreased the Al4B2O9 crystal peak intensities in X-ray diffraction pattern. The XRD peak intensities of the ZnAl2O4 spinel and Al4B2O9 crystals in the specimen containing 10 wt% zinc-borate glass (10G series) are higher than that of the specimen containing 5 wt% zinc-borate glass (5G series). The microstructures of most 10G series specimens had the flower-shaped crystal which was composed of 50 nm wide and 250 nm long needle-like crystals and identified as ZnAl2O4 spinel phase. The thermal conductivity of the 10G series specimen was higher than that of the 5G series in any ZnO/B2O3 ratio due to the formation of plenty of nano-sized ZnAl2O4 spinel of high thermal conductivity. Particularly, the thermal conductivity of the cordierite/Al2O3 composite containing 10 wt% zinc-borate glass of ZnO/B2O3 weight ratio = 1.5 was 3.8 W/Km which is much higher than that of the published value (3.0 W/Km).
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Protein crystallization aboard the Space Shuttle and the Mir space station
NASA Technical Reports Server (NTRS)
Delbaere, Louis T. J.; Vandonselaar, Margaret; Prasad, Lata; Quail, J. W.; Birnbaum, George I.; Delucas, Lawrence J.; Moore, Karen; Bugg, Charles E.
1993-01-01
Two different protein crystallizations, namely ,the free Fab fragment of the Je142 monoclonal antibody and the complex of Fab fragment/HPr with antigen, were performed aboard the Discovery Space Shuttle flights and the Mir space station, respectively. Medium sized crystals of the Je142 Fab fragment were obtained. The Je142 Fab fragment/Hpr complex produced two medium-sized crystals after two months aboard the Mir space station. Microgravity was found to eliminate the tendency of these crystals to form clusters.
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NASA Astrophysics Data System (ADS)
Çakal, G. Ö.; Eroğlu, İ.; Özkar, S.
2006-04-01
Colemanite, one of the important boron minerals, is dissolved in aqueous sulfuric acid to produce boric acid. In this reaction, gypsum is obtained as a by-product. Gypsum crystals are in the shape of thin needles. These crystals should be grown to an easily filterable size in order to increase the production yield and purity of boric acid. In this paper, the particle size distributions and the volume-weighted mean diameters of the gypsum crystals obtained in batch and continuous flow systems were compared. Experiments in both batch and continuous reactors were performed at a temperature of 85 °C, a stirring rate of 400 rpm, and the inlet CaO to SO42- molar ratio of 1.0 using colemanite mineral in particle size smaller than 150 μm. The average diameter of the gypsum crystals obtained at 3.5 h from the batch reactor was found to be 37-41 μm. This value for the continuous system at steady state was observed to change between 44-163 μm. The particle size of the gypsum crystals was found to increase with the residence time of the solid in the continuous system.
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Colour Size Illusion on Liquid Crystal Displays and Design Guidelines for Bioinformatics Tools
ERIC Educational Resources Information Center
Yoo, Hyun Seung; Smith-Jackson, Tonya L.
2011-01-01
Although the influence of colour on size perception has been known for a century, there is only limited research on interventions that can reduce this effect. This study was therefore undertaken in order to identify appropriate interventions and propose design guidelines for information visualisation, especially in applications where size…
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A new route for the synthesis of submicron-sized LaB{sub 6}
DOE Office of Scientific and Technical Information (OSTI.GOV)
Lihong, Bao; Wurentuya,; Wei, Wei
Submicron crystalline LaB{sub 6} has been successfully synthesized by a solid-state reaction of La{sub 2}O{sub 3} with NaBH{sub 4} at 1200 °C. The effects of reaction temperature on the crystal structure, grain size and morphology were investigated by X-ray diffraction, scanning electron microscope and transmission electron microscope. It is found that when the reaction temperature is in the range of 1000–1100 °C, there are ultrafine nanoparticles and nanocrystals that coexist. When the reaction temperature elevated to 1200 °C, the grain morphology transformed from ultrafine nanoparticle to submicron crystals completely. High resolution transmission electron microscope images fully confirm the formation ofmore » LaB{sub 6} cubic structure. - Highlights: • Single-phased LaB{sub 6} have been synthesized by a solid-state reaction in a continuous evacuating process. • The reaction temperature has a important effect on the phase composition. • The grain size increase from nano-size to submicron with increasing reaction temperature.« less
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NASA Astrophysics Data System (ADS)
Ono, Hiroshi; Kawatsuki, Nobuhiro
1995-03-01
The relationship between the saponification rate of poly(vinyl alcohol) (PVA), and the electrooptical properties and morphology of the PVA/liquid crystal (LC) composite films was investigated. Light transmission clazing and the LC droplet size were varied by changing the saponification rate or the blend ratio of two kinds of PVA with different saponification rates because the refractive index and surface tension could be controlled by the saponification rate of PVA. The threshold voltage decreased with increasing saponification rate though the extrapolation length was decreased. It was suggested that the electrooptical properties were strongly dependent on the droplet size.
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Further Improvement of the RITS Code for Pulsed Neutron Bragg-edge Transmission Imaging
NASA Astrophysics Data System (ADS)
Sato, H.; Watanabe, K.; Kiyokawa, K.; Kiyanagi, R.; Hara, K. Y.; Kamiyama, T.; Furusaka, M.; Shinohara, T.; Kiyanagi, Y.
The RITS code is a unique and powerful tool for a whole Bragg-edge transmission spectrum fitting analysis. However, it has had two major problems. Therefore, we have proposed methods to overcome these problems. The first issue is the difference in the crystallite size values between the diffraction and the Bragg-edge analyses. We found the reason was a different definition of the crystal structure factor. It affects the crystallite size because the crystallite size is deduced from the primary extinction effect which depends on the crystal structure factor. As a result of algorithm change, crystallite sizes obtained by RITS drastically approached to crystallite sizes obtained by Rietveld analyses of diffraction data; from 155% to 110%. The second issue is correction of the effect of background neutrons scattered from a specimen. Through neutron transport simulation studies, we found that the background components consist of forward Bragg scattering, double backward Bragg scattering, and thermal diffuse scattering. RITS with the background correction function which was developed through the simulation studies could well reconstruct various simulated and experimental transmission spectra, but refined crystalline microstructural parameters were often distorted. Finally, it was recommended to reduce the background by improving experimental conditions.
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NASA Astrophysics Data System (ADS)
Kawano, H.; Morii, K.; Nakayama, Y.
1993-05-01
The possibilities for fabricating solid solutions of (Ba1-x,Srx)TiO3 (x≤0.5,1.0) by crystallization of amorphous films and for improving their dielectric properties by adjusting the Sr content were investigated. Thin amorphous films were prepared from powder targets consisting of mixtures of BaTiO3 and SrTiO3 by sputtering with a neutralized Ar-ion beam. The amorphous films crystallized into (Ba1-x, Srx)TiO3 solid solutions with a cubic perovskite-type structure after annealing in air at 923 K for more than 1 h. The Debye-type dielectric relaxation was observed for the amorphous films, whereas the crystallized films showed paraelectric behavior. The relative dielectric constants were of the order of 20 for the amorphous samples, but increased greatly after crystallization to about 60-200, depending on the composition; a larger increase in the dielectric constant was observed in the higher Sr content films, in the range x≤0.5, which could be correlated with an increase in the grain size of the crystallites. The crystallization processes responsible for the difference in the grain size are discussed based on the microstructural observations.
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NASA Astrophysics Data System (ADS)
Zhuang, Han; Lim, Siak Piang; Lee, Heow Pueh
2009-06-01
Droplet quartz crystal microbalance has been demonstrated to be a promising tool for accessing material properties of fluids as well as the diverse solid-fluid interface phenomena. However, a microliter droplet localized on the surface of the electrodes of finite lateral size may cause a nonuniform distribution of the plane velocity, which may lead to surface normal fluid flow and generate the compressional waves above the crystal surface. In the present article, we report systematical investigation on both resonance frequency and dissipation measurements with reference to the small droplets of silicone oils spreading on the surface of the quartz crystal microbalance. Significant cyclical variations in the resonant frequency and resistance of the crystal have been observed as the characteristic sizes of the silicone oil droplets are close to specific values known to favor compressional wave generation. The experimental results have been compared with the theoretical values predicted by the finite element computation associated with a simple hydrodynamic model. Good agreement between theory and experiment has been obtained. The finding indicates that the small droplets on the crystal surface can act as resonant cavities for the compressional wave generation and that the greatest propensity to exhibit periodical resonance behavior in the frequency and dissipation measurements is at droplet height of λc/2 above the crystal surface.
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Solid-state characterization of nevirapine.
Sarkar, Mahua; Perumal, O P; Panchagnula, R
2008-09-01
The purpose of this investigation is to characterize nevirapine from commercial samples and samples crystallized from different solvents under various conditions. The solid-state behavior of nevirapine samples was investigated using a variety of complementary techniques such as microscopy (optical, polarized, hot stage microscopy), differential scanning calorimeter, thermogravimetric analysis, Fourier transform infrared spectroscopy and powder X-ray diffractometry. The commercial samples of nevirapine had the same polymorphic crystalline form with an anhedral crystal habit. Intrinsic dissolution of nevirapine was similar for both the commercial batches. Powder dissolution showed pH dependency, with maximum dissolution in acidic pH and there was no significant effect of particle size. The samples recrystallized from different solvent systems with varying polarity yielded different crystal habits. Stirring and degrees of supersaturation influenced the size and shape of the crystals. The recrystallized samples did not produce any new polymorphic form, but weak solvates with varying crystal habit were produced. Recrystallized samples showed differences in the x-ray diffractograms. However, all the samples had the same internal crystal lattice as revealed from their similar melting points and heat of fusion. The intrinsic dissolution rate of recrystallized samples was lower than the commercial sample. It was found that the compression pressure resulted in desolvation and partial conversion of the crystal form. After compression, the recrystallized samples showed similar x-ray diffractograms to the commercial sample. Amorphous form showed slightly higher aqueous solubility than the commercial crystalline form.
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NASA Technical Reports Server (NTRS)
Ray, Chandra S.; Huang, Wenhai; Day, Delbert E.
1991-01-01
DTA and both isothermal and nonisothermal DSC techniques are presently used to investigate the crystallization kinetics of a 40 (mol) percent Li2O-60 percent SiO2 glass as a function of glass powder particle size, the use of either alumina or Pt as the crucible material, the use of N, O, or Ar atmospheres, and surface pretreatments of the glass powder with deionized water, HCl, or HF. Neither the furnace atmosphere nor the crucible material had a significant effect on activation energy, frequency factor, or Avrami exponent. Washings of the glass with the three different fluids decreased the crystallization temperature by 25 to 30 C.
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Anharmonic, dimensionality and size effects in phonon transport
NASA Astrophysics Data System (ADS)
Thomas, Iorwerth O.; Srivastava, G. P.
2017-12-01
We have developed and employed a numerically efficient semi- ab initio theory, based on density-functional and relaxation-time schemes, to examine anharmonic, dimensionality and size effects in phonon transport in three- and two-dimensional solids of different crystal symmetries. Our method uses third- and fourth-order terms in crystal Hamiltonian expressed in terms of a temperature-dependent Grüneisen’s constant. All input to numerical calculations are generated from phonon calculations based on the density-functional perturbation theory. It is found that four-phonon processes make important and measurable contribution to lattice thermal resistivity above the Debye temperature. From our numerical results for bulk Si, bulk Ge, bulk MoS2 and monolayer MoS2 we find that the sample length dependence of phonon conductivity is significantly stronger in low-dimensional solids.
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[Spectrum studies on titania photocatalysts].
Su, W; Fu, X; Wei, K; Zhang, H; Lin, H; Wang, X; Li, D
2001-02-01
The nano-sized TiO2 photocatalysts were prepared by sol-gel method and characterized by FTIR spectroscopy, FT-Raman spectroscopy and diffuse reflectance spectroscopy(DRS). Photocatalytic degradation of oleic acid over the TiO2 catalysts was investigated. The result showed that calcination temperature has strong effect on crystal structure, energy band structure, optical adsorption and photocatalytic activity of the TiO2 catalysts. It was found that the TiO2 photocatalyst calcined at 400 degrees C has the best apparent optical adsorption, the biggest band edge position and the highest photoactivity. The effect of calcination temperature on photocatalytic activity of TiO2 catalysts has been ascribed to the changes in structure and optical property of catalyst such as crystal size, content of rutile, residual NO3-, and band-edge position of light adsorption.
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The performance studies of DKDP crystals grown by a rapid horizontal growth method
NASA Astrophysics Data System (ADS)
Xie, Xiaoyi; Qi, Hongji; Wang, Bin; Wang, Hu; Chen, Duanyang; Shao, Jianda
2018-04-01
A deuterated potassium dihydrogen phosphate (DKDP) crystal with about 70% deuterium level was grown by a rapid horizontal growth method with independent design equipment, which includes a continuous filtration system. The cooling program during crystal growth was designed according to a self-developed software to catch the size of growing crystal in real time. The crystal structure, optical performance and laser induced damage threshold (LIDT) of this DKDP crystal were investigated in this paper. The deuterium concentration of the crystal was confirmed by the neutron diffraction technique, which was effective and available in determining a complete range of deuteration level. The dielectric property was measured to evaluate the perfection of the lattice. The transmittance and LIDT were carried out further to evaluate the optical and functional properties of this DKDP crystal grown in the rapid horizontal growth technique. All of the detailed characterization for DKDP figured out that the 70% deuterated KDP crystal grown in this way had relatively good qualities.
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Rahaman, Md Saifur; Mavinic, Donald S; Meikleham, Alexandra; Ellis, Naoko
2014-03-15
The cost associated with the disposal of phosphate-rich sludge, the stringent regulations to limit phosphate discharge into aquatic environments, and resource shortages resulting from limited phosphorus rock reserves, have diverted attention to phosphorus recovery in the form of struvite (MAP: MgNH4PO4·6H2O) crystals, which can essentially be used as a slow release fertilizer. Fluidized-bed crystallization is one of the most efficient unit processes used in struvite crystallization from wastewater. In this study, a comprehensive mathematical model, incorporating solution thermodynamics, struvite precipitation kinetics and reactor hydrodynamics, was developed to illustrate phosphorus depletion through struvite crystal growth in a continuous, fluidized-bed crystallizer. A thermodynamic equilibrium model for struvite precipitation was linked to the fluidized-bed reactor model. While the equilibrium model provided information on supersaturation generation, the reactor model captured the dynamic behavior of the crystal growth processes, as well as the effect of the reactor hydrodynamics on the overall process performance. The model was then used for performance evaluation of the reactor, in terms of removal efficiencies of struvite constituent species (Mg, NH4 and PO4), and the average product crystal sizes. The model also determined the variation of species concentration of struvite within the crystal bed height. The species concentrations at two extreme ends (inlet and outlet) were used to evaluate the reactor performance. The model predictions provided a reasonably good fit with the experimental results for PO4-P, NH4-N and Mg removals. Predicated average crystal sizes also matched fairly well with the experimental observations. Therefore, this model can be used as a tool for performance evaluation and process optimization of struvite crystallization in a fluidized-bed reactor. Crown Copyright © 2013. Published by Elsevier Ltd. All rights reserved.
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Coughlan, H. D.; Darmanin, C.; Kirkwood, H. J.
2016-03-14
Three-dimensional imaging of protein crystals during X-ray diffraction experiments opens up a range of possibilities for optimising crystal quality and gaining new insights into the fundamental processes that drive radiation damage. Obtaining this information at the appropriate lengthscales however is extremely challenging. One approach that has been recently demonstrated as a promising avenue for charactering the size and shape of protein crystals at nanometre lengthscales is Bragg Coherent Diffractive Imaging (BCDI). BCDI is a recently developed technique that is able to recover the phase of the continuous diffraction intensity signal around individual Bragg peaks. When data is collected at multiplemore » points on a rocking curve a Reciprocal Space Map (RSM) can be assembled and then inverted using BCDI to obtain a three-dimensional image of the crystal. The first demonstration of two-dimensional BCDI of protein crystals was reported by Boutet at al., recently this work was extended to the study of radiation damage of micron-sized crystals. Here we present the first three-dimensional reconstructions of a Lysozyme protein crystal using BDI. The results are validated against RSM and TEM data and have implications for both radiation damage studies and for developing new approaches to structure retrieval from micron-sized protein crystals.« less
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Calculation Of Clinopyroxene And Olivine Growth Rates Using Plagioclase Residence Time
NASA Astrophysics Data System (ADS)
Kilinc, A. I.; Borell, A.; Leu, A.
2012-12-01
According to the Crystal Size Distribution theory (CSD) in a plot of logarithm of number of crystals of a given size range per unit volume [ln(n)], against crystal size [L] shows a straight line. Slope of that line is given by where is the crystal residence time and G is the crystal growth rate. Therefore if is known then G can be calculated. We used thin sections of the Kilauea basalt from Hawaii where olivine, clinopyroxene and plagioclase crystallized within a small temperature range, and the crystal growth rate of plagioclase is known. Assuming that crystal residence times of these three minerals are the same, we plotted ln(n) against L and using the slope and the known crystal growth rate of plagioclase we calculated the crystal growth rates of clinopyroxene and olivine. For the clinopyroxene growth rate we report 10-10.9cm/sec, which is in good agreement with Congdon's data of 10-10 cm/sec. We also calculated the growth rate of olivine is a basaltic melt as 10-8.5 cm/sec which is comparable to < 10-10 to 10-7 cm/sec given by Donaldson and Jambon.
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Micropatterned photoalignment for wavefront controlled switchable optical devices
NASA Astrophysics Data System (ADS)
Glazar, Nikolaus
Photoalignment is a well-established technique for surface alignment of the liquid crystal director. Previously, chrome masks were necessary for patterned photoalignment but were difficult to use, costly, and inflexible. To extend the capabilities of photoalignment we built an automated maskless multi-domain photoalignment device based on a DMD (digital multimirror device) projection system. The device is capable of creating arbitrary photoalignment patterns with micron-sized features. Pancharatnam-Berry phase (PB-phase) is a geometric phase that arises from cyclic change of polarization state. By varying the azimuthal anchoring angle in a hybrid-aligned liquid crystal cell we can control the spatial variation of the PB-phase shift. Using our automated photoalignment device to align the liquid crystal arbitrary wave front manipulations are possible. The PB-phase shift effect is maximized when the cell is tuned to have a half-wave retardation and disappears at full-wave retardation, so the cell can be switched on and off by applying a voltage. Two wavefront controlled devices developed using this technique will be discussed: A switchable liquid crystal phase shift mask for creating sub-diffraction sized photolithographic features, and a transparent diffractive display that utilizes a switchable liquid crystal diffraction grating.
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Synthesis and characterization of colloidal CdTe nanocrystals
NASA Astrophysics Data System (ADS)
Semendy, Fred; Jaganathan, Gomatam; Dhar, Nibir; Trivedi, Sudhir; Bhat, Ishwara; Chen, Yuanping
2008-08-01
We synthesized CdTe nano crystals (NCs) in uniform sizes and in good quality as characterized by photoluminescence (PL), AFM, and X-ray diffraction. In this growth procedure, CdTe nano-crystal band gap is strongly dependent on the growth time and not on the injection temperature or organic ligand concentration. This is very attractive because of nano-crystal size can be easily controlled by the growth time only and is very attractive for large scale synthesis. The color of the solution changes from greenish yellow to light orange then to deep orange and finally grayish black to black over a period of one hour. This is a clear indication of the gradual growth of different size (and different band gap) of CdTe nano-crystals as a function of the growth time. In other words, the size of the nano-crystal and its band gap can be controlled by adjusting the growth time after injection of the tellurium. The prepared CdTe NCs were characterized by absorption spectra, photoluminescence (PL), AFM and X-ray diffraction. Measured absorption maxima are at 521, 560, 600 and 603 nm corresponding to band gaps of 2.38, 2.21,2,07 and 2.04 eV respectively for growth times of 15, 30, 45 and 60 minutes. From the absorption data nano-crystal growth size saturates out after 45 minutes. AFM scanning of these materials indicate that the size of these particles is between 4 - 10 nm in diameter for growth time of 45 minutes. XD-ray diffraction indicates that these nano crystals are of cubic zinc blende phase. This paper will present growth and characterization data on CdTe nano crystals for various growth times.
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Ninagawa, Takako; Kawamura, Yukio; Konishi, Tadashi; Narumi, Akira
2016-08-01
Cryopreservation techniques are expected to evolve further to preserve biomaterials and foods in a fresh state for extended periods of time. Long-term cryopreservation of living materials such as food and biological tissue is generally achieved by freezing; thus, intracellular freezing occurs. Intracellular freezing injures the cells and leads to cell death. Therefore, a dream cryopreservation technique would preserve the living materials without internal ice crystal formation at a temperature low enough to prevent bacterial activity. This study was performed to investigate the effect of micro electrical current loading during cooling as a new cryopreservation technique. The behavior of intracellular ice crystal formation in plant tissues with or without an electric current load was evaluated using the degree of supercooling, degree of cell deformation, and grain size and growing rate of intracellular ice crystal. Moreover, the transition of intracellular pH during plant tissue cooling with or without electric current loading was also examined using the fluorescence intensity ratio to comprehend cell activity at lower temperatures. The results indicated that micro electric current load did not only decrease the degree of cell deformation and grain size of intracellular ice crystal but also reduced the decline in intracellular pH due to temperature lowering, compared with tissues subjected to the same cooling rate without an electric current load. Thus, the effect of electric current load on cryopreservation and the potential of a new cryopreservation technique using electric current load were discussed based on these results. Copyright © 2016 Elsevier Inc. All rights reserved.
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The Effects of Impurities on Protein Crystal Growth and Nucleation: A Preliminary Study
NASA Technical Reports Server (NTRS)
Schall, Constance A.
1998-01-01
Kubota and Mullin (1995) devised a simple model to account for the effects of impurities on crystal growth of small inorganic and organic molecules in aqueous solutions. Experimentally, the relative step velocity and crystal growth of these molecules asymptotically approach zero or non-zero values with increasing concentrations of impurities. Alternatively, the step velocity and crystal growth can linearly approach zero as the impurity concentration increases. The Kubota-Mullin model assumes that the impurity exhibits Langmuirian adsorption onto the crystal surface. Decreases in step velocities and subsequent growth rates are related to the fractional coverage (theta) of the crystal surface by adsorbed impurities; theta = Kx / (I +Kx), x = mole fraction of impurity in solution. In the presence of impurities, the relative step velocity, V/Vo, and the relative growth rate of a crystal face, G/Go, are proposed to conform to the following equations: V/Vo approx. = G/Go = 1 - (alpha)(theta). The adsorption of impurity is assumed to be rapid and in quasi-equilibrium with the crystal surface sites available. When the value of alpha, an effectiveness factor, is one the growth will asymptotically approach zero with increasing concentrations of impurity. At values less than one, growth approaches a non-zero value asymptotically. When alpha is much greater than one, there will be a linear relationship between impurity concentration and growth rates. Kubota and Mullin expect alpha to decrease with increasing supersaturation and shrinking size of a two dimensional nucleus. It is expected that impurity effects on protein crystal growth will exhibit behavior similar to that of impurities in small molecule growth. A number of proteins were added to purified chicken egg white lysozyme, the effect on crystal nucleation and growth assessed.
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NASA Astrophysics Data System (ADS)
Ishibashi, H.; Sato, H.
2010-12-01
Datasets of one atmosphere high temperature rotational viscometry of the Fuji 1707 basalt (Ishibashi, 2009) were analyzed based on the Bingham fluid model, and both yield stress and Bingham viscosity were determined. Reproducibility of the dataset by the Bingham fluid model was slightly better than that by the power law fluid modes adopted in our previous study although both the fluid models well represent the dataset in practical perspective. The relation between Bingham viscosity and crystallinity was compared with the Krieger-Dougherty equation, and both the maximum packing fraction of crystals and intrinsic viscosity for Bingham viscosity were determined ca. 0.45 and ca. 5.25, respectively, revealing that the maximum packing fraction decreased and intrinsic viscosity increased concomitantly with the increase in shape-anisotropy of crystals. However, the obtained value of the product of the maximum packing fraction and intrinsic viscosity (= ca. 2.36) was similar to that of uniform, isotropic-shaped particles (= 2.5), indicating that the effect of crystal shape-anisotropy on Bingham viscosity might be predicted only by change of the maximum packing fraction. Finite yield stress was detected for crystallinity larger than 0.133; it increased with crystallinity which suggests that critical crystallinity for onset of yield stress is at least lower than 0.133. The upper limit value of the critical crystallinity resembles the value calculated numerically for randomly oriented uniform particles by Saar et al. (2001) (0.10-0.15 for width/length ratio of 0.1-0.2, which is similar to the ratios in the basalt) whereas crystals in the basalt were moderately parallel arranged and their sizes vary significantly. That fact might be explained as follows; effects of parallel arrangement and size variation of crystals on the critical crystallinity are offset by the effect of variation in crystal shape-anisotropy, which suggests that shape-anisotropy distribution of crystals must be a critical factor for the onset of yield stress. Keywords: magma, viscosity, Bingham fluid, yield stress, plagioclase
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NASA Astrophysics Data System (ADS)
Nowakowski, Pawel; Dallas, Jean-Pierre; Villain, Sylvie; Kopia, Agnieszka; Gavarri, Jean-Raymond
2008-05-01
Nanostructured powders of ruthenium dioxide RuO 2 were synthesized via a sol gel route involving acidic solutions with pH varying between 0.4 and 4.5. The RuO 2 nanopowders were characterized by X-ray diffraction, scanning and transmission electron microscopy (SEM and TEM). Rietveld refinement of mean crystal structure was performed on RuO 2 nanopowders and crystallized standard RuO 2 sample. Crystallite sizes measured from X-ray diffraction profiles and TEM analysis varied in the range of 4-10 nm, with a minimum of crystallite dimension for pH=1.5. A good agreement between crystallite sizes calculated from Williamson Hall approach of X-ray data and from direct TEM observations was obtained. The tetragonal crystal cell parameter (a) and cell volumes of nanostructured samples were characterized by values greater than the values of standard RuO 2 sample. In addition, the [Ru-O 6] oxygen octahedrons of rutile structure also depended on crystal size. Catalytic conversion of methane by these RuO 2 nanostructured catalysts was studied as a function of pH, catalytic interaction time, air methane composition, and catalysis temperature, by the way of Fourier transform infrared (FTIR) spectroscopy coupled to homemade catalytic cell. The catalytic efficiency defined as FTIR absorption band intensities I(CO 2) was maximum for sample prepared at pH=1.5, and mainly correlated to crystallite dimensions. No significant catalytic effect was observed from sintered RuO 2 samples.
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Miura, Hiroki; Bon, Volodymyr; Senkovska, Irena; Ehrling, Sebastian; Watanabe, Satoshi; Ohba, Masaaki; Kaskel, Stefan
2017-10-17
Controlled nucleation in a micromixer and further crystal growth were used to synthesize Ni 2 (2,6-ndc) 2 dabco (2,6-ndc - 2,6-naphthalenedicarboxylate, dabco - 1,4-diazabicyclo[2.2.2]octane), also termed DUT-8(Ni) (DUT = Dresden University of Technology), with narrow particle size distribution in a range of a few nm to several μm. The crystal size was found to significantly affect the switching characteristics, in particular the gate opening pressure in nitrogen adsorption isotherms at 77 K for this highly porous and flexible network. Below a critical size of about 500 nm, a type Ia isotherm typical of rigid MOFs is observed, while above approximately 1000 nm a pronounced gating behaviour is detected, starting at p/p 0 = 0.2. With increasing crystal size this transition gate becomes steeper indicating a more uniform distribution of activation energies within the crystal ensemble. At an intermediate size (500-1000 nm), the DUT-8(Ni) crystals close during activation but cannot be reopened by nitrogen at 77 K possibly indicating monodomain switching.
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Effects of some polymeric additives on the cocrystallization of caffeine
NASA Astrophysics Data System (ADS)
Chung, Jihae; Kim, Il Won
2011-11-01
Effects of polymeric additives on the model cocrystallization were examined. The model cocrystal was made from caffeine and oxalic acid, and poly(ethylene glycol) (PEG), poly( L-lactide) (PLLA), poly(ɛ-caprolactone) (PCL), and poly(acrylic acid) (PAA) were the additives. The cocrystals were formed as millimeter-sized crystals without additives, and they became microcrystals with PLLA and PCL, and nanocrystals with PAA. XRD and IR revealed that the cocrystal structure was unchanged despite the strong effects of the additives on the crystal morphology, although some decrease in crystallinity was observed with PAA as confirmed by DSC. The DSC study also showed that the cocrystal melted and recrystallized to form α-caffeine upon heating. The present study verified that the polymeric additives can be utilized to modulate the size and morphology of the cocrystals without interfering the intermolecular interactions essential to the integrity of the cocrystal structures.
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Crystallization processes in Ge{sub 2}Sb{sub 2}Se{sub 4}Te glass
DOE Office of Scientific and Technical Information (OSTI.GOV)
Svoboda, Roman, E-mail: roman.svoboda@upce.cz; Bezdička, Petr; Gutwirth, Jan
2015-01-15
Highlights: • Crystallization kinetics of Ge{sub 2}Sb{sub 2}Se{sub 4}Te glass was studied in dependence on particle size by DSC. • All studied fractions were described in terms of the SB autocatalytic model. • Relatively high amount of Te enhances manifestation of bulk crystallization mechanisms. • XRD analysis of samples crystallized under different conditions showed correlation with DSC data. • XRD analysis revealed a new crystallization mechanism indistinguishable by DSC. - Abstract: Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analysis were used to study crystallization in Ge{sub 2}Sb{sub 2}Se{sub 4}Te glass under non-isothermal conditions as a function of the particlemore » size. The crystallization kinetics was described in terms of the autocatalytic Šesták–Berggren model. An extensive discussion of all aspects of a full-scale kinetic study of a crystallization process was undertaken. Dominance of the crystallization process originating from mechanically induced strains and heterogeneities was confirmed. Substitution of Se by Te was found to enhance the manifestation of the bulk crystallization mechanisms (at the expense of surface crystallization). The XRD analysis showed significant dependence of the crystalline structural parameters on the crystallization conditions (initial particle size of the glassy grains and applied heating rate). Based on this information, a new microstructural crystallization mechanism, indistinguishable by DSC, was proposed.« less
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NASA Astrophysics Data System (ADS)
Moitra, Pranabendu; Gonnermann, Helge
2014-05-01
Magma often contains crystals of various shapes and sizes. We present experimental results on the effect of the shape- and size-distribution of solid particles on the rheological properties of solid-liquid suspensions, which are hydrodynamically analogous to crystal-bearing magmas. The suspensions were comprised of either a single particle shape and size (unimodal) or a mixture of two different particle shapes and sizes (bimodal). For each type of suspension we characterized the dry maximum packing fraction of the particle mixture using the tap density method. We then systematically varied the total volume fraction of particles in the suspension, as well as the relative proportion of the two different particle types in the bimodal suspensions. For each of the resultant mixtures (suspensions) we performed controlled shear stress experiments using a rotational rheometer in parallel-plate geometry spanning 4 orders of magnitude in shear stress. The resultant data curves of shear stress as a function of shear rate were fitted using a Herschel-Bulkley rheological model. We find that the dry maximum packing decreases with increasing particle aspect ratio (ar) and decreasing particle size ratio (Λ). The highest dry maximum packing was obtained at 60-75% volume of larger particles for bimodal spherical particle mixture. Normalized consistency, Kr, defined as the ratio of the consistency of the suspension and the viscosity of the suspending liquid, was fitted using a Krieger-Dougherty model as a function of the total solid volume fraction (φ). The maximum packing fractions (φm) obtained from the shear experimental data fitting of the unimodal suspensions were similar in magnitude with the dry maximum packing fractions of the unimodal particles. Subsequently, we used the dry maximum packing fractions of the bimodal particle mixtures to fit Kr as a function of φ for the bimodal suspensions. We find that Kr increases rapidly for suspensions with larger ar and smaller Λ. We also find that both the apparent yield stress and the shear thinning behavior of the suspensions increase with increasing ar and become significant at φ/φm ≥ 0.4.
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Wang, Lei; Bock, David C.; Li, Jing; ...
2018-02-20
Here, a series of one-dimensional CuFe 2O 4 nano/sub-micron wires possessing different diameters, crystal phases, and crystal sizes have been successfully generated using a facile template-assisted co precipitation reaction at room temperature, followed by a short post-annealing process. The diameter and the crystal structure of the resulting CuFe 2O4 (CFO) wires were judiciously tuned by varying the pore size of the template and the post-annealing temperature, respectively. Carbon nanotubes (CNTs) were incorporated to generate CFO-CNT binder-free anodes, and multiple characterization techniques were employed with the goal of delineating the relationships between electrochemical behavior and the properties of both the CFOmore » wires (crystal phase, wire diameter, crystal size) and the electrode architecture (binder-free vs. conventionally prepared approaches). The study reveals several notable findings. First, the crystal phase (cubic or tetragonal) did not influence the electrochemical behavior in this CFO system. Second, regarding crystallite size and wire diameter, CFO wires with larger crystallite sizes exhibit improved cycling stability, while wires possessing smaller diameters exhibiting higher capacities. Finally, the electrochemical behavior is strongly influenced by the electrode architecture, with CFO-CNT binder-free electrodes demonstrating significantly higher capacities and cycling stability compared to conventionally prepared coatings. The mechanism(s) associated with the high capacities under low current density but limited electrochemical reversibility of CFO electrodes under high current density were probed via x-ray absorption spectroscopy (XAS) mapping with sub-micron spatial resolution for the first time. Results suggest that the capacity of the binder-free electrodes under high rate is limited by the irreversible formation of Cu 0, as well as limited reduction of Fe 3+, to Fe 2+ not Fe 0. The results (1) shed fundamental insight into the reversibility of CuFe 2O 4 materials cycled at high current density and (2) demonstrate that a synergistic effort to control both active material morphology and electrode architecture is an effective strategy for optimizing electrochemical behavior.« less
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Wang, Lei; Bock, David C.; Li, Jing
Here, a series of one-dimensional CuFe 2O 4 nano/sub-micron wires possessing different diameters, crystal phases, and crystal sizes have been successfully generated using a facile template-assisted co precipitation reaction at room temperature, followed by a short post-annealing process. The diameter and the crystal structure of the resulting CuFe 2O4 (CFO) wires were judiciously tuned by varying the pore size of the template and the post-annealing temperature, respectively. Carbon nanotubes (CNTs) were incorporated to generate CFO-CNT binder-free anodes, and multiple characterization techniques were employed with the goal of delineating the relationships between electrochemical behavior and the properties of both the CFOmore » wires (crystal phase, wire diameter, crystal size) and the electrode architecture (binder-free vs. conventionally prepared approaches). The study reveals several notable findings. First, the crystal phase (cubic or tetragonal) did not influence the electrochemical behavior in this CFO system. Second, regarding crystallite size and wire diameter, CFO wires with larger crystallite sizes exhibit improved cycling stability, while wires possessing smaller diameters exhibiting higher capacities. Finally, the electrochemical behavior is strongly influenced by the electrode architecture, with CFO-CNT binder-free electrodes demonstrating significantly higher capacities and cycling stability compared to conventionally prepared coatings. The mechanism(s) associated with the high capacities under low current density but limited electrochemical reversibility of CFO electrodes under high current density were probed via x-ray absorption spectroscopy (XAS) mapping with sub-micron spatial resolution for the first time. Results suggest that the capacity of the binder-free electrodes under high rate is limited by the irreversible formation of Cu 0, as well as limited reduction of Fe 3+, to Fe 2+ not Fe 0. The results (1) shed fundamental insight into the reversibility of CuFe 2O 4 materials cycled at high current density and (2) demonstrate that a synergistic effort to control both active material morphology and electrode architecture is an effective strategy for optimizing electrochemical behavior.« less
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Generation of 1.5-octave intense infrared pulses by nonlinear interactions in DAST crystal
NASA Astrophysics Data System (ADS)
Vicario, C.; Monoszlai, B.; Arisholm, G.; Hauri, C. P.
2015-09-01
Infrared pulses with large spectral width extending from 1.2 to 3.4 μm are generated in the organic crystal DAST (4-N, N-dimethylamino-4‧-N‧-methylstilbazolium tosylate). The input pulse has a central wavelength of 1.5 μm and 65 fs duration. With 2.8 mJ input energy we obtained up to 700 μJ in the broadened spectrum. The output can be easily scaled up in energy by increasing the crystal size together with the energy and the beam size of the pump. The ultra-broad spectrum is ascribed to cascaded second order processes mediated by the exceptionally large effective χ 2 nonlinearity of DAST, but the shape of the spectrum indicates that a delayed χ 3 process may also be involved. Numerical simulations reproduce the experimental results qualitatively and provide an insight in the mechanisms underlying the asymmetric spectral broadening.
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Szcześ, Aleksandra, E-mail: aszczes@poczta.umcs.lublin.pl; Czemierska, Magdalena; Jarosz-Wilkołazka, Anna
Extracellular polymeric substance (EPS) extracted from Rhodococcus opacus bacterial strain was used as a matrix for calcium carbonate precipitation using the vapour diffusion method. The total exopolymer and water-soluble exopolymer fraction of different concentrations were spread on the mica surface by the spin-coating method. The obtained layers were characterized using the atomic force microscopy measurement and XPS analysis. The effects of polymer concentration, initial pH of calcium chloride solution and precipitation time on the obtained crystals properties were investigated. Raman spectroscopy and scanning electron microscopy were used to characterize the precipitated minerals. It was found that the type of precipitatedmore » CaCO{sub 3} polymorph and the crystal size depend on the kind of EPS fraction. The obtained results indicates that the water soluble fraction favours vaterite dissolution and calcite growth, whereas the total EPS stabilizes vaterite and this effect is stronger at basic pH. It seems to be due to different contents of the functional group of EPS fractions. - Highlights: • CaCO{sub 3} crystal size and polymorph can be controlled by EPS substance obtained from R. opacus. • The water soluble fraction favours vaterite dissolution and calcite growth. • The total EPS stabilizes vaterite. • This effect is stronger at basic pH.« less
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NASA Astrophysics Data System (ADS)
Ushakov, A. A.; Chizhov, P. A.; Bukin, V. V.; Garnov, S. V.; Savel'ev, A. B.
2018-05-01
Two 2D techniques for visualising the field of pulsed THz radiation ('shadow' and 'interferometric'), which are based on the linear electro-optical effect with application of a ZnTe detector crystal 1 × 1 cm in size, are compared. The noise level and dynamic range for the aforementioned techniques are analysed and their applicability limits are discussed.
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NASA Technical Reports Server (NTRS)
Gratz, Andrew J.; Bird, Peter; Quiro, Glenn B.
1990-01-01
A highly accurate method, called the negative crystal method, for determining the rate of dissolution on specific crystallographic faces of crystals was developed, in which the dissolution rates of nominally perfect crystal faces are obtained by measuring the size of individual negative crystals during a sequence of dissolution steps. The method was applied to determine the apparent activation energy and rate constants for the dissolution of quartz in 0.01 M KOH solutions at temperatures from 106 to 236 C. Also investigated were the effects of hydroxyl activity and ionic strength. The apparent activation energies for the dissolution of the prism and of the rhomb were determined.
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Design of integrated all optical digital to analog converter (DAC) using 2D photonic crystals
NASA Astrophysics Data System (ADS)
Moniem, Tamer A.; El-Din, Eman S.
2017-11-01
A novel design of all optical 3 bit digital to analog (DAC) converter will be presented in this paper based on 2 Dimension photonic crystals (PhC). The proposed structure is based on the photonic crystal ring resonators (PCRR) with combining the nonlinear Kerr effect on the PCRR. The total size of the proposed optical 3 bit DAC is equal to 44 μm × 37 μm of 2D square lattice photonic crystals of silicon rods with refractive index equal to 3.4. The finite different time domain (FDTD) and Plane Wave Expansion (PWE) methods are used to back the overall operation of the proposed optical DAC.
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NASA Astrophysics Data System (ADS)
Lesiak, Piotr; Budaszewski, Daniel; Bednarska, Karolina; Wójcik, Michał; Sobotka, Piotr; Chychłowski, Miłosz; Woliński, Tomasz R.
2017-05-01
In this work we studied a newly reported class of nonlinear effects observed in 5CB liquid crystals doped with gold nanoparticles (GNPs). The size of the GNP was determined by direct TEM imaging and by X-ray scattering of the diluted NP solution. GNPs was coated by thiols with the ratio of mesogenic to n-alkyl thiols varying from 1:2 to 1:1. The research involved comparing properties of both undoped and doped 5CB (nematic LC) by infiltrating LC cell and microholes of the photonic crystal fiber (PCF) separately. In our experiment the PCF fiber type LMA-10 made by NKT Photonics as host material has been used.
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Miao, Yu; Qiu, Yanxuan; Cai, Jiawei; Wang, Zizhou; Yu, Xinwei; Dong, Wen
2016-01-01
The in-situ nano-crystal-to-crystal transformation (SCCT) synthesis provides a powerful approach for tailoring controllable feature shapes and sizes of nano crystals. In this work, three nitrogen-rich energetic nano-crystals based on 5,5′-azotetrazolate(AZT2−) Cr(III) salts were synthesized by means of SCCT methodology. SEM and TEM analyses show that the energetic nano-crystals feature a composition- and structure-dependent together with size-dependent thermal stability. Moreover, nano-scale decomposition products can be obtained above 500 °C, providing a new method for preparing metallic oxide nano materials. PMID:27869221
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Human serum albumin crystals and method of preparation
NASA Technical Reports Server (NTRS)
Carter, Daniel C. (Inventor)
1989-01-01
Human serum albumin (HSA) crystals are provided in the form of tetragonal plates having the space groups P42(sub 1)2, the crystals being grown to sizes in excess of 0.5 mm in two dimensions and a thickness of 0.1 mm. Growth of the crystals is carried out by a hanging drop method wherein a precipitant solution containing polyethylene glycol (PEG) and a phosphate buffer is mixed with an HSA solution, and a droplet of mixed solution is suspended over a well of precipitant solution. Crystals grow to the desired size in 3 to 7 days. Concentration of reagents, pH and other parameters are controlled within prescribed limits. The resulting crystals exhibit a size and quality such as to allow performance of x ray diffraction studies and enable the conduct of drug binding studies as well as genetic engineering studies.
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Coughlan, H D; Darmanin, C; Phillips, N W; Hofmann, F; Clark, J N; Harder, R J; Vine, D J; Abbey, B
2015-07-01
For laboratory and synchrotron based X-ray sources, radiation damage has posed a significant barrier to obtaining high-resolution structural data from biological macromolecules. The problem is particularly acute for micron-sized crystals where the weaker signal often necessitates the use of higher intensity beams to obtain the relevant data. Here, we employ a combination of techniques, including Bragg coherent diffractive imaging to characterise the radiation induced damage in a micron-sized protein crystal over time. The approach we adopt here could help screen for potential protein crystal candidates for measurement at X-ray free election laser sources.
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Coughlan, H. D.; Darmanin, C.; Phillips, N. W.; Hofmann, F.; Clark, J. N.; Harder, R. J.; Vine, D. J.; Abbey, B.
2015-01-01
For laboratory and synchrotron based X-ray sources, radiation damage has posed a significant barrier to obtaining high-resolution structural data from biological macromolecules. The problem is particularly acute for micron-sized crystals where the weaker signal often necessitates the use of higher intensity beams to obtain the relevant data. Here, we employ a combination of techniques, including Bragg coherent diffractive imaging to characterise the radiation induced damage in a micron-sized protein crystal over time. The approach we adopt here could help screen for potential protein crystal candidates for measurement at X-ray free election laser sources. PMID:26798804
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Coughlan, H. D.; Darmanin, C.; Phillips, N. W.
For laboratory and synchrotron based X-ray sources, radiation damage has posed a significant barrier to obtaining high-resolution structural data from biological macromolecules. The problem is particularly acute for micron-sized crystals where the weaker signal often necessitates the use of higher intensity beams to obtain the relevant data. Here, we employ a combination of techniques, including Bragg coherent diffractive imaging to characterise the radiation induced damage in a micron-sized protein crystal over time. The approach we adopt here could help screen for potential protein crystal candidates for measurement at X-ray free election laser sources.
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Coughlan, H. D.; Darmanin, C.; Phillips, N. W.; ...
2015-04-29
For laboratory and synchrotron based X-ray sources, radiation damage has posed a significant barrier to obtaining high-resolution structural data from biological macromolecules. The problem is particularly acute for micron-sized crystals where the weaker signal often necessitates the use of higher intensity beams to obtain the relevant data. Here, we employ a combination of techniques, including Bragg coherent diffractive imaging to characterise the radiation induced damage in a micron-sized protein crystal over time. The approach we adopt here could help screen for potential protein crystal candidates for measurement at X-ray free election laser sources.
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Effect Of Milling Time on Particle Size of Forsterite (Mg2SiO4) from South Solok District
NASA Astrophysics Data System (ADS)
Sarimai, S.; Ratnawulan, R.; Ramli, R.; Fauzi, A.
2018-04-01
West Sumatra has considerable serpentine mineral resources, including the Jorong Sungai Padi Nagari Lubuak Gadang Sangir Subdistrict, South Solok District. Exploitation of minerals of serpentine is still processed in raw or semi-finished material so that it has a low selling value. Serpentine minerals contain forsterite minerals that have higher economic value if in the form of nanoparticles. The manufacture of forsterite nanoparticles has been done using synthetic materials, while synthetic materials are expensive and require a long process to make them. The treatment of temperature variations of calcination to serpentine minerals, obtained results found forsterite phase that dominates at a temperature of 800 °C. Serpentine minerals can be used as alternative ingredients for the nanoparticle makers of forsterite that are easy to find in the deep, and do not require expensive to make them. The purpose of this study was to investigate the effect of milling time on the microstructure and grain size of the serpentine forsterite mineral nanoparticles in the form of crystal structure, crystal size, and particle size. The results of the study showed grain size of 5, 10, 20, and 40 hours milling time are 579, 478, 451, and 385 nm respectively. Based on the research that has been done can be drawn conclusion Time milling effect on the grain size of forsterite mineral serpentine from South Solok District, the longer milling time the size of forsterite grains smaller. Optimum milling time to produce nano forsterite is 40 hours with a grain size of 385 nm.
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NASA Astrophysics Data System (ADS)
Thangaraja, Amutha; Shinde, Sachin M.; Kalita, Golap; Tanemura, Masaki
2016-02-01
The synthesis of large-area monolayer tungsten disulphide (WS2) single crystal is critical for realistic application in electronic and optical devices. Here, we demonstrate an effective approach to synthesize monolayer WS2 crystals using tungsten hexachloride (WCl6) as a solid precursor in atmospheric chemical vapor deposition process. In this technique, 0.05M solution of WCl6 in ethanol was drop-casted on SiO2/Si substrate to create an even distribution of the precursor, which was reduced and sulfurized at 750 °C in Ar atmosphere. We observed growth of triangular, star-shaped, as well as dendritic WS2 crystals on the substrate. The crystal geometry evolves with the shape and size of the nuclei as observed from the dendritic structures. These results show that controlling the initial nucleation and growth process, large WS2 single crystalline monolayer can be grown using the WCl6 precursor. Our finding shows an easier and effective approach to grow WS2 monolayer using tungsten halide solution-casting, rather than evaporating the precursor for gas phase reaction.
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Size Dependence of S-bonding on (111) Facets of Cu Nanoclusters
Boschen, Jeffery S.; Lee, Jiyoung; Windus, Theresa L.; ...
2016-04-21
We demonstrate a strong damped oscillatory size dependence of the adsorption energy for sulfur on the (111) facets of tetrahedral Cu nanoclusters up to sizes of ~300 atoms. This behavior reflects quantum size effects. Consistent results are obtained from density functional theory analyses utilizing either atomic orbital or plane-wave bases and using the same Perdew–Burke–Ernzerhof functional. Behavior is interpreted via molecular orbitals (MO), density of states (DOS), and crystal orbital Hamilton population (COHP) analyses.
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Modeling of monolayer charge-stabilized colloidal crystals with static hexagonal crystal lattice
NASA Astrophysics Data System (ADS)
Nagatkin, A. N.; Dyshlovenko, P. E.
2018-01-01
The mathematical model of monolayer colloidal crystals of charged hard spheres in liquid electrolyte is proposed. The particles in the monolayer are arranged into the two-dimensional hexagonal crystal lattice. The model enables finding elastic constants of the crystals from the stress-strain dependencies. The model is based on the nonlinear Poisson-Boltzmann differential equation. The Poisson-Boltzmann equation is solved numerically by the finite element method for any spatial configuration. The model has five geometrical and electrical parameters. The model is used to study the crystal with particles comparable in size with the Debye length of the electrolyte. The first- and second-order elastic constants are found for a broad range of densities. The model crystal turns out to be stable relative to small uniform stretching and shearing. It is also demonstrated that the Cauchy relation is not fulfilled in the crystal. This means that the pair effective interaction of any kind is not sufficient to proper model the elasticity of colloids within the one-component approach.
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NASA Astrophysics Data System (ADS)
Vasenko, Liubov; Qu, Haiyan
2017-02-01
In this work, the effects of operational parameters, initial phosphorus concentration and molar ratios of Ca/P and NH4-N/P (further in the text N/P), on the nature and purity of precipitated phosphorus products have been investigated in an artificial system that mimics the supernatant in wastewater treatment plants. Metastable zone width was determined for two target phosphorus products: DCPD (dicalcium phosphate dihydrate) and HAp (hydroxyapatite) in the range of pH 4.5 - 7. HAp crystallizes at final pH higher than 6.3 while DCPD crystallizes at the final pH in between 4.7 and 5.7. At the final pH 5.7 - 6.3 and at pH lower than 4.7 the mixtures of DCPD and HAp were obtained. It was observed that N/P ratio affects not only the metastable zone width but also the kinetics of crystal growth for both DCPD and HAp: the higher the N/P ratio, the lower is the growth rate for both P-products. Investigation of the effect of Ca/P and N/P ratios on the nucleation and crystal growth of DCPD in batch crystallization experiment was performed. It showed that at high supersaturation level, crystals with larger median size can be obtained at higher N/P ratio despite the negative effects of N/P ratio on the growth rate of the crystals.
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The Question of Impurities in Macromolecule Crystal Quality Improvement in Microgravity
NASA Technical Reports Server (NTRS)
Judge, Russell A.; Snell, Edward H.; Pusey, Marc L.; Sportiello, Michael G.; Todd, Paul; Bellamy, Henry; Borgstahl, Gloria E.; Pokros, Matthew; Cassanto, John M.
2000-01-01
While macromolecule impurities may affect crystal size and morphology the over-riding question is how do macromolecule impurities effect crystal X-ray quality and diffraction resolution. In the case of chicken egg white lysozyme previous researchers have reported that crystals grown in the presence of ovalbumin, ovotransferrin, and turkey egg white lysozyme show no difference in diffraction resolution compared to those grown in pure solutions. One impurity however, a naturally occurring lysozyme dimer, does negatively impact the X-ray crystal properties. For this impurity it has been reported that crystal quality improvement in microgravity may be due to improved impurity partitioning during crystallization. In this study we have examined the incorporation of the dimer into lysozyme crystals, both on the ground and in microgravity experiments, and have performed detailed X-ray analysis of the crystals using a new technique for finely probing the mosaicity of the crystal at the Stanford Synchrotron Radiation Laboratory. Dimer partitioning was not significantly different in microgravity compared to the ground based experiments, although it is significantly better than that previously reported in microgravity. Mosaicity analysis of pure crystals, 1422 indexed reflections (microgravity) and 752 indexed reflections (ground), gave average results of 0.0066 and 0.0092 degrees (FWHM) respectively. The microgravity crystals also provided an increased signal to noise. Dimer incorporation increased the average mosaicity in microgravity but not on the ground. However, dimer incorporation did greatly reduce the resolution limit in both ground and microgravity grown crystals. The data is being treated anisotropically to explore these effects. These results indicate that impurity effects in microgravity are complex and that the conditions or techniques employed may greatly affect the role of impurities.
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Scale effects in crystal plasticity
NASA Astrophysics Data System (ADS)
Padubidri Janardhanachar, Guruprasad
The goal of this research work is to further the understanding of crystal plasticity, particularly at reduced structural and material length scales. Fundamental understanding of plasticity is central to various challenges facing design and manufacturing of materials for structural and electronic device applications. The development of microstructurally tailored advanced metallic materials with enhanced mechanical properties that can withstand extremes in stress, strain, and temperature, will aid in increasing the efficiency of power generating systems by allowing them to work at higher temperatures and pressures. High specific strength materials can lead to low fuel consumption in transport vehicles. Experiments have shown that enhanced mechanical properties can be obtained in materials by constraining their size, microstructure (e.g. grain size), or both for various applications. For the successful design of these materials, it is necessary to have a thorough understanding of the influence of different length scales and evolving microstructure on the overall behavior. In this study, distinction is made between the effect of structural and material length scale on the mechanical behavior of materials. A length scale associated with an underlying physical mechanism influencing the mechanical behavior can overlap with either structural length scales or material length scales. If it overlaps with structural length scales, then the material is said to be dimensionally constrained. On the other hand, if it overlaps with material length scales, for example grain size, then the material is said to be microstructurally constrained. The objectives of this research work are: (1) to investigate scale and size effects due to dimensional constraints; (2) to investigate size effects due to microstructural constraints; and (3) to develop a size dependent hardening model through coarse graining of dislocation dynamics. A discrete dislocation dynamics (DDD) framework where the scale of analysis is intermediate between a fully discretized (e.g. atomistic) and fully continuum is used for this study. This mesoscale tool allows to address all the stated objectives of this study within a single framework. Within this framework, the effect of structural and the material length scales are naturally accounted for in the simulations and need not be specified in an ad hoc manner, as in some continuum models. It holds the promise of connecting the evolution of the defect microstructure to the effective response of the crystal. Further, it provides useful information to develop physically motivated continuum models to model size effects in materials. The contributions of this study are: (a) provides a new interpretation of mechanical size effect due to only dimensional constraint using DDD; (b) a development of an experimentally validated DDD simulation methodology to model Cu micropillars; (c) a coarse graining technique using DDD to develop a phenomenological model to capture size effect on strain hardening; and (d) a development of a DDD framework for polycrystals to investigate grain size effect on yield strength and strain hardening.
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NASA Astrophysics Data System (ADS)
Wang, W. S.; Aggarwal, M. D.; Choi, J.; Gebre, T.; Shields, Angela D.; Penn, Benjamin G.; Frazier, Donald O.
1999-03-01
Single crystals of a new promising nonlinear optical material for the tunable UV harmonic generation, L-pyroglutamic acid 60×20×20 mm 3 in size were obtained from aqueous solution by using the temperature-lowering method. Solubility of L-pyroglutamic acid in different solvents was measured. The single crystals showed different morphological characteristics and growth rate in different solvents with different crystallographic orientations. Methanol or ethanol solutions yielded needle-like crystals. In mixed solution such as methanol/H 2O or ethanol/ H 2O plate-like crystals with a thickness in the direction [0 1 0] were observed. The water as a good solvent, however, produced long prism-like crystals. The two polymorphs of L-pyroglutamic acid (α and β phases) were found for the first time. The growth shapes of α-phase is mainly a prism and β phases is a rhombic plate.The growth rate of α and β phases is mainly a function of the supersaturation of the L-pyroglutamic acid in solution.
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NASA Astrophysics Data System (ADS)
Purwanto, P.; Adi, WA; Yunasfi
2017-05-01
The Composite of Ba1,5Sr0,5Fe2O5 has been synthesized by using powder metallurgy technique. The Ba1.5Sr0.5Fe2O5 were prepared from BaCO3, SrCO3 and Fe2O3 raw materials with a specific weight ratio. The three materials were synthesized by powder metallurgy under heat treatment at 800 °C, 900 °C, and 1000 °C for 5 hours. All the three samples were characterized by using X-ray Diffraction (XRD) to determine the crystal structure and crystal size, LCR meter to determine the conductivity, and Scanning Electron Microscope (SEM) to observe the morphological of the composites. The phase analysis result showed that the composite consists of several minor phases such as BaO2, SrO2, and Fe2O3. The Crystal size of composite Ba1.5Sr0.5Fe2O5 decreased while increases the strain of crystal with increasing of sintering temperature. The crystal size of the Ba1.5Sr0.5Fe2O5 composite is 3.55 nm to 7.23 nm and value of strain is 8.47% until 3.90%. Based on the conductivity measurement, it was obtained that the conductivity of the Ba1.5Sr0.5Fe2O5 composite decreased with increasing sintering temperature. It was also noticed that the conductivity increased with increasing of frequency. The conductivity ranged from 6.619×10-7 S/cm to 65.659×10-7 S/cm. The energy dispersive spectroscopy (EDS) analysis showed that several dominant elements were a good agreement with the phase analysis.
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Hutnik, Nina; Kozik, Anna; Mazienczuk, Agata; Piotrowski, Krzysztof; Wierzbowska, Boguslawa; Matynia, Andrzej
2013-07-01
Continuous DT MSMPR (Draft Tube Mixed Suspension Mixed Product Removal) crystallizer was provided with typical wastewater from phosphorus mineral fertilizers industry (pH < 4, 0.445 mass % of PO4(3-), inorganic impurities presence), dissolved substrates (magnesium and ammonium chlorides) and solution alkalising the environment of struvite MgNH4PO4·6H2O reaction crystallization process. Research ran in constant temperature 298 K assuming stoichiometric proportions of substrates or 20% excess of magnesium ions. Influence of pH (8.5-10) and mean residence time (900-3600 s) on product size distribution, its chemical composition, crystals shape, size-homogeneity and process kinetics was identified. Crystals of mean size ca. 25-37 μm and homogeneity CV 70-83% were produced. The largest crystals, of acceptable homogeneity, were produced using 20% excess of magnesium ions, pH 9 and mean residence time 3600 s. Under these conditions nucleation rate did not exceed 9 × 10(7) 1/(s m(3)) according to SIG (Size Independent Growth) MSMPR kinetic model. Linear crystal growth rate was 4.27 × 10(-9) m/s. Excess of magnesium ions influenced struvite reaction crystallization process yield advantageously. Concentration of phosphate(V) ions decreased from 0.445 to 9.2 × 10(-4) mass %. This can be regarded as a very good process result. In product crystals, besides main component - struvite, all impurities from wastewater were detected analytically. Copyright © 2013 Elsevier Ltd. All rights reserved.
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Cryogenic motion performances of a piezoelectric single crystal micromotor
NASA Astrophysics Data System (ADS)
Li, Xiaotian; Wu, Yuting; Chen, Zhijiang; Wei, Xiaoyong; Luo, Haosu; Dong, Shuxiang
2014-04-01
This study investigates the cryogenic performances of a millimeter-size piezoelectric ultrasonic linear micromotor. The piezoelectric vibrator of the micromotor is made of Pb(In1/2Nb1/2)O3 -Pb(Mg1/3Nb2/3)-PbTiO3 single crystal and operated in first-bending wobbling mode. Experiments show that the piezoelectric single crystal micromotor works effectively even at extremely low temperature of -175 °C, although its resonance peaks vary with temperature significantly. This work confirms the feasibility of cryogenic operation of the piezo-micromotor, which is meaningful for aerospace or superconducting microwave application.
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Manipulation of spontaneous emission in a tapered photonic crystal fibre
NASA Astrophysics Data System (ADS)
Myers, S. J.; Fussell, D. P.; Dawes, J. M.; Mägi, E.; McPhedran, R. C.; Eggleton, B. J.; de Sterke, C. Martijn
2006-12-01
We characterize the spontaneous emission of dye that is introduced into the central core of a tapered photonic crystal fiber. Since the photonic crystal period in the fibre cladding varies along the taper, the transmission and spontaneous emission spectra over a wide range of relative frequencies can be observed. The spontaneous emission spectra of the fibre transverse to the fiber axis show suppression due to partial band-gaps of the structure, and also enhancement of spontaneous emission near the band edges. We associate these with van Hove features, as well as finite cluster size effects.
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Physical and Structural Studies on the Cryo-cooling of Insulin Crystals
NASA Technical Reports Server (NTRS)
Lovelace, J.; Bellamy, H.; Snell, E. H.; Borgstahl, G.
2003-01-01
Reflection profiles were analyzed from microgravity-(mg) and earth-grown insulin crystals to measure mosaicity (h) and to reveal mosaic domain structure and composition. The effects of cryocooling on single and multi-domain crystals were compared. The effects of cryocooling on insulin structure were also re-examined. Microgravity crystals were larger, more homogeneous, and more perfect than earth crystals. Several mg crystals contained primarily a single mosaic domain with havg of 0.005deg. The earth crystals varied in quality and all contained multiple domains with havg of 0.031deg. Cryocooling caused a 43-fold increase in h for mg crystals (havg=0.217deg) and an %fold increase for earth crystals (havg=0.246deg). These results indicate that very well-ordered crystals are not completely protected from the stresses associated with cryocooling, especially when structural perturbations occur. However, there were differences in the reflection profiles. For multi-mosaic domain crystals, each domain individually broadened and separated from the other domains upon cryo-cooling. Cryo-cooling did not cause an increase in the number of domains. A crystal composed of a single domain retained this domain structure and the reflection profiles simply broadened. Therefore, an improved signal-to-noise ratio for each reflection was measured from cryo-cooled single domain crystals relative to cryo-cooled multi-domain crystals. This improved signal, along with the increase in crystal size, facilitated the measurement of the weaker high- resolution reflections. The observed broadening of reflection profiles indicates increased variation in unit cell dimensions which may be linked to cryo-cooling-associated structural changes and disorder.
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Control of interface shape during high melting sesquioxide crystal growth by HEM technique
NASA Astrophysics Data System (ADS)
Hu, Kaiwei; Zheng, Lili; Zhang, Hui
2018-02-01
During crystal growth in heat exchanger method (HEM) system, the shape of the growth interface changes with the proceeding of the growth process, which limits the crystal size and reduces the quality of the crystal. In this paper, a modified HEM system is proposed to control the interface shape for growth of sesquioxide crystals. Numerical simulation is performed to predict heat transfer, melt flow and interface shape during growth of high melting sesquioxide crystals by the heat exchanger method. The results show that a flat or slightly convex interface shape is beneficial to reduce the solute pileup in front of the melt/crystal interface and decrease the radial temperature gradient inside the crystal during growth of sesquioxide crystals. The interface shape can be controlled by adjusting the gap size d and lower resistance heater power during growth. The growth rate and the melt/crystal interface position can be obtained by two measured temperatures.
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A Near-Global Survey of Cirrus Particle Size Using ISCCP
NASA Technical Reports Server (NTRS)
Han, Qingyuan; Rossow, William B.; Chou, Joyce; Welch, Ronald M.
1996-01-01
Cirrus is the most frequently occurring and widely distributed cloud type. The average annual frequency of occurrence for cirrus is 34% and its global coverage is about 20-30% (Warren et al. 1985). It strongly influences weather and climate processes through its effects on the radiation budget of the earth and the atmosphere (Liou 1986). Microphysics of cirrus is a critical component in understanding cloud-climate radiative interactions. For example, ice water content feedback is positive from a 1-D model study. But the feedback is substantially reduced upon the inclusion of small ice crystals (Sinha and Shine 1994). Due to the complexity caused by the non-spherical shape of ice crystals in cirrus, retrievals of cirrus properties are difficult. In recent years, advances have been made both in models and in case studies (e.g., Takano and Liou 1989, Young et al. 1994), but no global scale survey has been conducted. Similar to our previous near-global survey of droplet sizes of liquid water clouds (Han et al. 1994), a survey of cirrus ice crystal sizes is conducted over both continental and oceanic areas. We describe a method for retrieving cirrus particle size information on a near-global scale 50 deg S to 50 deg N using currently available satellite data from ISCCP. To retrieve cirrus particle size, we use a radiative transfer model that includes all major absorbing gases and cloud scattering/absorption to compute synthetic radiances as a function of satellite viewing geometry. Ice crystal shapes are assumed to be hexagonal columns and plates. The model results have been validated against clear sky observations and are consistent with the observed radiance range under cloudy conditions.
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Eberl, Dennis D.; Drits, V.A.; Srodon, J.
2000-01-01
GALOPER is a computer program that simulates the shapes of crystal size distributions (CSDs) from crystal growth mechanisms. This manual describes how to use the program. The theory for the program's operation has been described previously (Eberl, Drits, and Srodon, 1998). CSDs that can be simulated using GALOPER include those that result from growth mechanisms operating in the open system, such as constant-rate nucleation and growth, nucleation with a decaying nucleation rate and growth, surface-controlled growth, supply-controlled growth, and constant-rate and random growth; and those that result from mechanisms operating in the closed system such as Ostwald ripening, random ripening, and crystal coalescence. In addition, CSDs for two types weathering reactions can be simulated. The operation of associated programs also is described, including two statistical programs used for comparing calculated with measured CSDs, a program used for calculating lognormal CSDs, and a program for arranging measured crystal sizes into size groupings (bins).
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Du, Chengxiao; Wei, Tongbo; Zheng, Haiyang; Wang, Liancheng; Geng, Chong; Yan, Qingfeng; Wang, Junxi; Li, Jinmin
2013-10-21
Size-controllable p-GaN hexagonal nanopyramids (HnPs)-photonic crystal (PhC) structures were selectively grown on flat p-GaN layer for the elimination of total internal reflection of light-emitting diodes (LEDs). The LEDs with HnPs-PhC of 46.3% bottom fill factor (PhC lattice constant is 730 nm) showed an improved light output power by 99.9% at forward current of 350 mA compared to the reference LEDs with flat p-GaN layer. We confirmed the effect of HnPs-PhC with different bottom fill factors and the effect of nanopyramid-shaped and nanocolumn-shaped PhC on the light-extraction of LEDs was also investigated by using three-dimensional finite-difference time-domain simulations.
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Structural properties of a-Si films and their effect on aluminum induced crystallization
DOE Office of Scientific and Technical Information (OSTI.GOV)
Tankut, Aydin; Ozkol, Engin; Karaman, Mehmet
2015-10-15
In this paper, we report the influence of the structural properties of amorphous silicon (a-Si) on its subsequent crystallization behavior via the aluminum induced crystallization (AIC) method. Two distinct a-Si deposition techniques, electron beam evaporation and plasma enhanced chemical vapor deposition (PECVD), are compared for their effect on the overall AIC kinetics as well as the properties of the final poly-crystalline (poly-Si) silicon film. Raman and FTIR spectroscopy results indicate that the PECVD grown a-Si films has higher intermediate-range order, which is enhanced for increased hydrogen dilution during deposition. With increasing intermediate-range order of the a-Si, the rate of AICmore » is diminished, leading larger poly-Si grain size.« less
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Effect of storage temperature on quality of light and full-fat ice cream.
Buyck, J R; Baer, R J; Choi, J
2011-05-01
Ice cream quality is dependent on many factors including storage temperature. Currently, the industry standard for ice cream storage is -28.9 °C. Ice cream production costs may be decreased by increasing the temperature of the storage freezer, thus lowering energy costs. The first objective of this research was to evaluate the effect of 4 storage temperatures on the quality of commercial vanilla-flavored light and full-fat ice cream. Storage temperatures used were -45.6, -26.1, and -23.3 °C for the 3 treatments and -28.9 °C as the control or industry standard. Ice crystal sizes were analyzed by a cold-stage microscope and image analysis at 1, 19.5, and 39 wk of storage. Ice crystal size did not differ among the storage temperatures of light and full-fat ice creams at 19.5 or 39 wk. An increase in ice crystal size was observed between 19.5 and 39 wk for all storage temperatures except -45.6 °C. Coldness intensity, iciness, creaminess, and storage/stale off-flavor of the light and full-fat ice creams were evaluated at 39 wk of storage. Sensory evaluation indicated no difference among the different storage temperatures for light and full-fat ice creams. In a second study, light and full-fat ice creams were heat shocked by storing at -28.9 °C for 35 wk and then alternating between -23.3 and -12.2 °C every 24h for 4 wk. Heat-shocked ice creams were analyzed at 2 and 4 wk of storage for ice crystal size and were evaluated by the sensory panel. A difference in ice crystal size was observed for light and full-fat ice creams during heat-shock storage; however, sensory results indicated no differences. In summary, storage of light or full-fat vanilla-flavored ice creams at the temperatures used within this research did not affect quality of the ice creams. Therefore, ice cream manufacturers could conserve energy by increasing the temperature of freezers from -28.9 to -26.1 °C. Because freezers will typically fluctuate from the set temperature, usage of -26.1 °C allows for a safety factor, even though storage at -23.3 °C did not affect ice cream quality. Copyright © 2011 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.
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Resonant frequency function of thickness-shear vibrations of rectangular crystal plates.
Wang, Ji; Yang, Lijun; Pan, Qiaoqiao; Chao, Min-Chiang; Du, Jianke
2011-05-01
The resonant frequencies of thickness-shear vibrations of quartz crystal plates in rectangular and circular shapes are always required in the design and manufacturing of quartz crystal resonators. As the size of quartz crystal resonators shrinks, for rectangular plates we must consider effects of both length and width for the precise calculation of resonant frequency. Starting from the three-dimensional equations of wave propagation in finite crystal plates and the general expression of vibration modes, we obtained the relations between frequency and wavenumbers. By satisfying the major boundary conditions of the dominant thickness-shear mode, three wavenumber solutions are obtained and the frequency equation is constructed. It is shown the resonant frequency of thickness-shear mode is a second-order polynomial of aspect ratios. This conforms to known results in the simplest form and is applicable to further analytical and experimental studies of the frequency equation of quartz crystal resonators.
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Li, Chengfeng; Ge, Xiaolu; Li, Guochang; Bai, Jiahai; Ding, Rui
2014-08-01
The formations of non-metabolic stones, bones and teeth were seriously related to the morphology, size and surface reactivity of dicalcium phosphate dihydrate (DCPD). Herein, a facile biomimetic mineralization method with presence of glutamic acid and arginine was employed to fabricate DCPD with well-defined morphology and adjustable crystallite size. In reaction solution containing more arginine, crystallization of DCPD occurred with faster rate of nucleation and higher density of stacked layers due to the generation of more OH(-) ions after hydrolysis of arginine at 37 °C. With addition of fluorescein or acetone, the consumption of OH(-) ions or desolvation reaction of Ca(2+) ions was modulated, which resulted in the fabrication of DCPD with adjustable crystallite sizes and densities of stacked layers. In comparison with fluorescein-loading DCPD, dicalcium phosphate anhydrate was prepared with enhanced photoluminescence properties due to the reduction of self-quenching effect and regular arrangement of encapsulated fluorescein molecules. With addition of more acetone, DCPD was prepared with smaller crystallite size via antisolvent crystallization. The simulated process with addition of amino acids under 37 °C would shed light on the dynamic process of biomineralization for calcium phosphate compounds. Copyright © 2014 Elsevier B.V. All rights reserved.
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Theoretical model of hardness anisotropy in brittle materials
NASA Astrophysics Data System (ADS)
Gao, Faming
2012-07-01
Anisotropy is prominent in the hardness test of single crystals. However, the anisotropic nature is not demonstrated quantitatively in previous hardness model. In this work, it is found that the electron transition energy per unit volume in the glide region and the orientation of glide region play critical roles in determining hardness value and hardness anisotropy for a single crystal material. We express the mathematical definition of hardness anisotropy through simple algebraic relations. The calculated Knoop hardnesses of the single crystals are in good agreement with observations. This theory, extended to polycrystalline materials by including hall-petch effect and quantum size effect, predicts that the polycrystalline diamond with low angle grain boundaries can be harder than single-crystal bulk diamond. Combining first-principles technique and the formula of hardness anisotropy the hardness of monoclinic M-carbon, orthorhombic W-carbon, Z-carbon, and T-carbon are predicted.
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Dynamical effects in Bragg coherent x-ray diffraction imaging of finite crystals
NASA Astrophysics Data System (ADS)
Shabalin, A. G.; Yefanov, O. M.; Nosik, V. L.; Bushuev, V. A.; Vartanyants, I. A.
2017-08-01
We present simulations of Bragg coherent x-ray diffractive imaging (CXDI) data from finite crystals in the frame of the dynamical theory of x-ray diffraction. The developed approach is based on a numerical solution of modified Takagi-Taupin equations and can be applied for modeling of a broad range of x-ray diffraction experiments with finite three-dimensional crystals of arbitrary shape also in the presence of strain. We performed simulations for nanocrystals of a cubic and hemispherical shape of different sizes and provided a detailed analysis of artifacts in the Bragg CXDI reconstructions introduced by the dynamical diffraction. Based on our theoretical analysis we developed an analytical procedure to treat effects of refraction and absorption in the reconstruction. Our results elucidate limitations for the kinematical approach in the Bragg CXDI and suggest a natural criterion to distinguish between kinematical and dynamical cases in coherent x-ray diffraction on a finite crystal.
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THF water hydrate crystallization: an experimental investigation
NASA Astrophysics Data System (ADS)
Devarakonda, Surya; Groysman, Alexander; Myerson, Allan S.
1999-08-01
Supersaturated solutions of THF-water hydrate system were experimentally studied before and during crystallization, to examine the system's behavior in the metastable zone and observe any anomalies suggesting cluster formation. Nucleation induction time measurements, with and without additives, were performed to screen potential growth inhibitors. Shifts in the onset points of crystallization for water and THF-water mixtures with additives were measured using differential scanning calorimetry (DSC). Aspartame was among one of the few successfully screened inhibitors. Preliminary on-line crystal size distribution (CSD) measurements were performed on this system to monitor the crystal size during crystallization. The CSD data was also used to compute the hydrate crystal growth rates, which were found to be in the order of 145 μm/h.
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Effect of water on foaming properties of diglycerol fatty acid ester-oil systems.
Shrestha, Lok Kumar; Shrestha, Rekha Goswami; Solans, Conxita; Aramaki, Kenji
2007-06-19
We have studied the effect of added water on the nonaqueous foaming properties of diglycerol fatty acid ester nonionic surfactant systems. Diglycerol monomyristate (designated as DGM) could not foam in nonpolar oils squalane and hexadecane at normal room temperature. Nevertheless, addition of a small amount of water induces a dramatic change in foaming properties. Both the foamability and foam stability increases with the amount of added water within the studied concentration range. Phase behavior study showed that in the dilute regions there is dispersion of solid surfactant in the aforementioned oils in the DGM systems. The particle size of the dispersed solid phase was found to be several tens of microns in the water free system, and hence it tends to coagulate and precipitate. In the case of shorter alkyl chain length, diglycerol monolaurate (DGL) surfactant-oil systems, dispersion of lamellar liquid crystal (Lalpha) is observed at room temperature, and the poor foaming properties were attributed to the large particle size of the liquid crystal. In both the DGL and DGM-oil systems, we observed a tendency of the particle size to decrease with the increasing concentration of added water. At higher temperature, the solid surfactant transforms to lamellar liquid crystal phase, and foaming is improved in the DGM/squalane system. Foams are stable for several minutes. Judging from the foaming test and particle size distribution data it can be concluded that the poor foaming in the diglycerol fatty acid esters-oil systems may possibly be due to bigger particle size, which causes precipitation. Addition of water results in the dispersion of smaller particles and improves the foaming behavior.
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NASA Astrophysics Data System (ADS)
Chen, Shuai-Feng; Song, Hong-Wu; Zhang, Shi-Hong
2017-09-01
Shear bands is a kind of typical microstructure in magnesium alloy which has drawn much attention during recent years. The formation of shear bands during the isothermal differential speed rolling of Mg-3Al-1Zn sheets is analysed by experimental methods. In addition, results of Erichsen and tensile tests indicate that the shear bands have an obvious effect on the anisotropic fracture behaviour and formability of magnesium alloy. A represent volume element (RVE) method combined with crystal plasticity model is established to investigate the effect of shear bands on the anisotropic fracture behaviours systematically by considering the grain size, texture, width, and tilted angle. The simulation results disclose the above factors can induce discontinuous strain and stress between the shear band regions (SBRs) and non-shear band regions (NSBRs), but the grain size and tilted angle have much bigger effect than that of texture and width, leading to the fracture at the interface SBR and NSBR.
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A Study of Biomolecules as Growth Modifiers of Calcium Oxalate Crystals
NASA Astrophysics Data System (ADS)
Kwak, Junha John
Crystallization processes are ubiquitous in nature, science, and technology. Controlling crystal growth is pivotal in many industries as material properties and functions can be tailored by tuning crystal habits (e.g. size, shape, phase). In biomineralization, organisms exert excellent control over bottom-up synthesis and assembly of inorganic-organic structures (e.g. bones, teeth, exoskeletons). This is made possible by growth modifiers that range from small molecules to macromolecules, such as proteins. Molecular recognition of the mineral phase allows proteins to function as nucleation templates, matrices, and growth inhibitors or promoters. We are interested in taking a biomimetic approach to control crystallization via biomolecular growth modifiers. We investigated calcium oxalate monohydrate (COM), found in plants and kidney stones, as a model system of crystallization. We studied the effects of four common proteins on COM crystallization: bovine serum albumin (BSA), transferrin, lactoferrin, and lysozyme. Through kinetic studies of COM crystallization, we classified BSA and lysozyme as COM growth inhibitor and promoter respectively. Their inhibition and promotion effects were also evident in the macroscopic crystal habit. Through adsorption and microscopy experiments, we showed that BSA exhibits binding specificity for the apical surfaces of macroscopic COM crystals. Lysozyme, on the other, functions via a non-binding mechanism at the surface to accelerate the growth of the apical surfaces. We also synthesized and studied peptides derived from the protein primary sequences to identify putative domains responsible for these inhibition and promotion effects. Collectively, our study of physiologically relevant biomolecules suggests potential roles of COM modifiers in pathological crystallization and helps to develop guidelines for rational design of biomolecular growth modifiers for applications in crystal engineering.
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Matsuda, Nobuyuki; Kato, Takumi; Harada, Ken-Ichi; Takesue, Hiroki; Kuramochi, Eiichi; Taniyama, Hideaki; Notomi, Masaya
2011-10-10
We demonstrate highly enhanced optical nonlinearity in a coupled-resonator optical waveguide (CROW) in a four-wave mixing experiment. Using a CROW consisting of 200 coupled resonators based on width-modulated photonic crystal nanocavities in a line defect, we obtained an effective nonlinear constant exceeding 10,000 /W/m, thanks to slow light propagation combined with a strong spatial confinement of light achieved by the wavelength-sized cavities.
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Ninagawa, Takako; Eguchi, Akemi; Kawamura, Yukio; Konishi, Tadashi; Narumi, Akira
2016-08-01
Intracellular ice crystal formation (IIF) causes several problems to cryopreservation, and it is the key to developing improved cryopreservation techniques that can ensure the long-term preservation of living tissues. Therefore, the ability to capture clear intracellular freezing images is important for understanding both the occurrence and the IIF behavior. The authors developed a new cryomicroscopic system that was equipped with a high-speed camera for this study and successfully used this to capture clearer images of the IIF process in the epidermal tissues of strawberry geranium (Saxifraga stolonifera Curtis) leaves. This system was then used to examine patterns in the location and formation of intracellular ice crystals and to evaluate the degree of cell deformation because of ice crystals inside the cell and the growing rate and grain size of intracellular ice crystals at various cooling rates. The results showed that an increase in cooling rate influenced the formation pattern of intracellular ice crystals but had less of an effect on their location. Moreover, it reduced the degree of supercooling at the onset of intracellular freezing and the degree of cell deformation; the characteristic grain size of intracellular ice crystals was also reduced, but the growing rate of intracellular ice crystals was increased. Thus, the high-speed camera images could expose these changes in IIF behaviors with an increase in the cooling rate, and these are believed to have been caused by an increase in the degree of supercooling. Copyright © 2016 Elsevier Inc. All rights reserved.
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Zubiaga, Asier; Warringham, Robbie; Boltz, Marilyne; Cooke, David; Crivelli, Paolo; Gidley, David; Pérez-Ramírez, Javier; Mitchell, Sharon
2016-04-07
Recent studies demonstrated the power of positron annihilation lifetime spectroscopy (PALS) to characterise the connectivity and corresponding effectiveness of hierarchical pore networks in zeolites. This was based on the fractional escape of ortho-positronium (Ps), formed within the micropore framework, to vacuum. To further develop this technique, here we assess the impact of the positron implantation energy and of the zeolite crystal size and the particle morphology. Conventional measurements using fast positrons and beam measurements applying moderated positrons both readily distinguish purely microporous ZSM-5 zeolites comprised of single crystals or crystal aggregates. Unlike beam measurements, however, conventional measurements fail to discriminate model hierarchical zeolites with open or constricted mesopore architectures. Several steps are taken to rationalise these observations. The dominant contribution of Ps diffusion to the PALS response is confirmed by capping the external surface of the zeolite crystals with tetraethylorthosilicate, which greatly enhances the sensitivity to the micropore network. A one-dimensional model is constructed to predict the out-diffusion of Ps from a zeolite crystal, which is validated experimentally by comparing coffin-shaped single crystals of varying size. Calculation of the trends expected on the application of fast or moderated positrons indicates that the distinctions in the initial distribution of Ps at the crystal level cannot explain the limited sensitivity of the former to the mesopore architecture. Instead, we propose that the greater penetration of fast positrons within the sample increases the probability of Ps re-entry from intercrystalline voids into mesopores connected with the external surface of zeolite crystals, thereby reducing their fractional escape.
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Role of scanning electron microscopy in identifying drugs used in medical practice.
Fazil Marickar, Y M; Sylaja, N; Koshy, Peter
2009-10-01
Several plant preparations are administered for treatment of stone disease without scientific basis. This paper presents the results of in vitro and animal experimental studies using scanning electron microscopy (SEM) in the identification of the therapeutic properties of trial drugs in medicine. In the first set of the study, urinary crystals namely calcium oxalate monohydrate and calcium oxalate dehydrate were grown in six sets of Hane's tubes in silica gel medium. Trial drugs namely scoparia dulcis Lynn, musa sapiens and dolicos biflorus were incorporated in the gel medium to identify the dopant effect of the trial drugs on the size and extent of crystal column growth. The changes in morphology of crystals were studied using SEM. In the second set, six male Wistar rats each were calculogenised by administering sodium oxalate and ethylene glycol and diabetised using streptozotocin. The SEM changes of calculogenisation were studied. The rats were administered trial drugs before calculogenisation or after. The kidneys of the rats studied under the scanning electron microscope showed changes in tissue morphology and crystal deposition produced by calculogenisation and alterations produced by addition of trial drugs. The trial drugs produced changes in the pattern of crystal growth and in the crystal morphology of both calcium oxalate monohydrate and calcium oxalate dihydrate grown in vitro. Elemental distribution analysis showed that the crystal purity was not altered by the trial drugs. Scoparia dulcis Lynn was found to be the most effective anticalculogenic agent. Musa sapiens and dolicos biflorus were found to have no significant effect in inhibiting crystal growth. The kidneys of rats on calculogenisation showed different grades of crystals in the glomerulus and interstitial tissues, extrusion of the crystals into the tubular lumen, collodisation and tissue inflammatory cell infiltration. Scoparia dulcis Lynn exhibited maximum protector effect against the changes of calculogenisation. Musa sapiens and dolicos biflorus had only minimal effect in preventing crystal deposition, inflammatory cell infiltration and other changes of calculogenisation. SEM was found to be effective in assessing the effect of drugs on crystal growth morphology and tissue histology.
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Effect of Microstructural Interfaces on the Mechanical Response of Crystalline Metallic Materials
NASA Astrophysics Data System (ADS)
Aitken, Zachary H.
Advances in nano-scale mechanical testing have brought about progress in the understanding of physical phenomena in materials and a measure of control in the fabrication of novel materials. In contrast to bulk materials that display size-invariant mechanical properties, sub-micron metallic samples show a critical dependence on sample size. The strength of nano-scale single crystalline metals is well-described by a power-law function, sigma ∝ D-n, where D is a critical sample size and n is a experimentally-fit positive exponent. This relationship is attributed to source-driven plasticity and demonstrates a strengthening as the decreasing sample size begins to limit the size and number of dislocation sources. A full understanding of this size-dependence is complicated by the presence of microstructural features such as interfaces that can compete with the dominant dislocation-based deformation mechanisms. In this thesis, the effects of microstructural features such as grain boundaries and anisotropic crystallinity on nano-scale metals are investigated through uniaxial compression testing. We find that nano-sized Cu covered by a hard coating displays a Bauschinger effect and the emergence of this behavior can be explained through a simple dislocation-based analytic model. Al nano-pillars containing a single vertically-oriented coincident site lattice grain boundary are found to show similar deformation to single-crystalline nano-pillars with slip traces passing through the grain boundary. With increasing tilt angle of the grain boundary from the pillar axis, we observe a transition from dislocation-dominated deformation to grain boundary sliding. Crystallites are observed to shear along the grain boundary and molecular dynamics simulations reveal a mechanism of atomic migration that accommodates boundary sliding. We conclude with an analysis of the effects of inherent crystal anisotropy and alloying on the mechanical behavior of the Mg alloy, AZ31. Through comparison to pure Mg, we show that the size effect dominates the strength of samples below 10 microm, that differences in the size effect between hexagonal slip systems is due to the inherent crystal anisotropy, suggesting that the fundamental mechanism of the size effect in these slip systems is the same.
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Espinosa, J R; Young, J M; Jiang, H; Gupta, D; Vega, C; Sanz, E; Debenedetti, P G; Panagiotopoulos, A Z
2016-10-21
Direct coexistence molecular dynamics simulations of NaCl solutions and Lennard-Jones binary mixtures were performed to explore the origin of reported discrepancies between solubilities obtained by direct interfacial simulations and values obtained from the chemical potentials of the crystal and solution phases. We find that the key cause of these discrepancies is the use of crystal slabs of insufficient width to eliminate finite-size effects. We observe that for NaCl crystal slabs thicker than 4 nm (in the direction perpendicular to the interface), the same solubility values are obtained from the direct coexistence and chemical potential routes, namely, 3.7 ± 0.2 molal at T = 298.15 K and p = 1 bar for the JC-SPC/E model. Such finite-size effects are absent in the Lennard-Jones system and are likely caused by surface dipoles present in the salt crystals. We confirmed that μs-long molecular dynamics runs are required to obtain reliable solubility values from direct coexistence calculations, provided that the initial solution conditions are near the equilibrium solubility values; even longer runs are needed for equilibration of significantly different concentrations. We do not observe any effects of the exposed crystal face on the solubility values or equilibration times. For both the NaCl and Lennard-Jones systems, the use of a spherical crystallite embedded in the solution leads to significantly higher apparent solubility values relative to the flat-interface direct coexistence calculations and the chemical potential values. Our results have broad implications for the determination of solubilities of molecular models of ionic systems.
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NASA Astrophysics Data System (ADS)
Miyajima, Kensuke; Akatsu, Tatsuro; Itoh, Ken
2018-05-01
We evaluated the crystal size, shape, and alignment of the lattice planes of CuCl quantum dots (QDs) embedded in NaCl single crystals by optical measurements, X-ray diffraction (XRD) patterns, and transmission electron microscopy (TEM). We obtained, for the first time, an XRD pattern and TEM images for CuCl QDs in NaCl crystals. The XRD pattern showed that the lattice planes of the CuCl QDs were parallel to those of the NaCl crystals. In addition, the size of the QDs was estimated from the diffraction width. It was apparent from the TEM images that almost all CuCl QDs were polygonal, although some cubic QDs were present. The mean size and size distribution of the QDs were also obtained. The dot size obtained from optical measurements, XRD, and TEM image were almost consistent. Our new findings can help to reveal the growth mechanism of semiconductor QDs embedded in a crystallite matrix. In addition, this work will play an important role in progressing the study of optical phenomena originating from assembled semiconductor QDs.
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Effects of rare-earth size on the electronic structure of La1−xLuxVO3.
Chen, B; Laverock, J; Newby, D; McNulty, J F; Smith, K E; Glans, P-A; Guo, J-H; Qiao, R-M; Yang, W-L; Lees, M R; Tung, L D; Singh, R P; Balakrishnan, G
2015-03-18
The electronic structure of La(1-x)Lu(x)VO(3)(x = 0, 0.2, 0.6 and 1) single crystals has been investigated using soft x-ray absorption spectroscopy, soft x-ray emission spectroscopy, and resonant soft x-ray inelastic scattering to study the effects of rare-earth size. The x-ray absorption and emission spectra at the O K-edge present a progressive evolution with R-site cation, in agreement with local spin density approximation calculations. This evolution with R, together with the temperature dependence of the O K-edge spectra, is attributed to changes in the crystal structure of La(1-x)Lu(x)VO(3). The crystal-field dd. excitations probed by resonant inelastic x-ray scattering at the V L(3)-edge exhibit an increase in energy and enhanced intensity with the decrease of R-site ionic radius, which is mainly attributed to the increased tilting magnitude of the VO(6) octahedra. Upon cooling to ~95 K, the dd* excitations are prominently enhanced in relative Intensity, in agreement with the formation of the Jahn.Teller distortion int he orbital ordering phase. Additionally, the dd* transitions of the mixed compounds are noticeably suppressed with respect to those of the pure compounds, possibly owing to the formation of C-type orbital ordering induced by large R-site size variances.
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Jo, Sinae; Kang, Seunggu
2013-05-01
The effect of TiO2 on the degree of crystallization, thermal properties and microstructure for MgO-Al2O3-SiO2 glass-ceramics system containing 0-13 wt% TiO2 and 0-1.5 wt% B2O3 in which the cordierite is the main phase was studied. Using Kissinger and Augis-Bennett equations, the activation energy, 510 kJ/mol and Avrami constant, 1.8 were calculated showing the surface-oriented crystallization would be preferred. The alpha-cordierite phase was generated in the glass-ceramics of containing TiO2 of 0-5.6 wt%. However, for the glass-ceramics of TiO2 content above 7 wt%, an alpha-cordierite disappeared and micro-cordierite phase was formed. The glass-ceramics of no TiO2 added had spherical crystals of few tens nanometer size spread in the matrix. As TiO2 content increased up to 5.6 wt%, a lump of dendrite was formed. In the glass-ceramics containing TiO2 7-13 wt%, in which the main phase is micro-cordierite, the dendrite crystal disappeared and a few hundred nanometer sized crystal particles hold tightly each other were generated. The thermal conductivity of glass-ceramics of both a-cordierite and micro-cordierite base decreased with TiO2 contend added. The thermal conductivity of glass-ceramics of 1.5 wt% TiO2 added was 3.4 W/mK which is 36% higher than that of glass-ceramics of no TiO2 added. The sintering temperature for 1.5 wt% TiO2 glass-ceramics was 965 degrees C which could be concluded as to apply to LTCC process for LED packaging.
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Torad, Nagy L; Naito, Masanobu; Tatami, Junichi; Endo, Akira; Leo, Sin-Yen; Ishihara, Shinsuke; Wu, Kevin C-W; Wakihara, Toru; Yamauchi, Yusuke
2014-03-01
Nanometer-sized zeolite A with a large cesium (Cs) uptake capability is prepared through a simple post-milling recrystallization method. This method is suitable for producing nanometer-sized zeolite in large scale, as additional organic compounds are not needed to control zeolite nucleation and crystal growth. Herein, we perform a quartz crystal microbalance (QCM) study to evaluate the uptake ability of Cs ions by zeolite, to the best of our knowledge, for the first time. In comparison to micrometer-sized zeolite A, nanometer-sized zeolite A can rapidly accommodate a larger amount of Cs ions into the zeolite crystal structure, owing to its high external surface area. Nanometer-sized zeolite is a promising candidate for the removal of radioactive Cs ions from polluted water. Our QCM study on Cs adsorption uptake behavior provides the information of adsorption kinetics (e.g., adsorption amounts and rates). This technique is applicable to other zeolites, which will be highly valuable for further consideration of radioactive Cs removal in the future. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
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Design, development and evaluation of a resistor-based multiplexing circuit for a 20×20 SiPM array
NASA Astrophysics Data System (ADS)
Wang, Zhonghai; Sun, Xishan; Lou, Kai; Meier, Joseph; Zhou, Rong; Yang, Chaowen; Zhu, Xiaorong; Shao, Yiping
2016-04-01
One technical challenge in developing a large-size scintillator detector with multiple Silicon Photomultiplier (SiPM) arrays is to read out a large number of detector output channels. To achieve this, different signal multiplexing circuits have been studied and applied with different performances and cost-effective tradeoffs. Resistor-based multiplexing circuits exhibit simplicity and signal integrity, but also present the disadvantage of timing shift among different channels. In this study, a resistor-based multiplexing circuit for a large-sized SiPM array readout was developed and evaluated by simulation and experimental studies. Similarly to a multiplexing circuit used for multi-anode PMT, grounding and branching resistors were connected to each SiPM output channel. The grounding resistor was used to simultaneously reduce the signal crosstalk among different channels and to improve timing performance. Both grounding and branching resistor values were optimized to maintain a balanced performance of the event energy, timing, and positioning. A multiplexing circuit was implemented on a compact PCB and applied for a flat-panel detector which consisted of a 32×32 LYSO scintillator crystals optically coupled to 5×5 SiPM arrays for a total 20×20 output channels. Test results showed excellent crystal identification for all 1024 LYSO crystals (each with 2×2×30 mm3 size) with 22Na flood-source irradiation. The measured peak-to-valley ratio from typical crystal map profile is around 3:1 to 6.6:1, an average single crystal energy resolution of about 17.3%, and an average single crystal timing resolution of about 2 ns. Timing shift among different crystals, as reported in some other resistor-based multiplexing circuit designs, was not observed. In summary, we have designed and implemented a practical resistor-based multiplexing circuit that can be readily applied for reading out a large SiPM array with good detector performance.
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Controllable Growth of Monolayer MoS2 and MoSe2 Crystals Using Three-temperature-zone Furnace
NASA Astrophysics Data System (ADS)
Zheng, Binjie; Chen, Yuanfu
2017-12-01
Monolayer molybdenum disulfide (MoS2) and molybdenum diselenide (MoSe2) have attracted a great attention for their exceptional electronic and optoelectronic properties among the two dimensional family. However, controllable synthesis of monolayer crystals with high quality needs to be improved urgently. Here we demonstrate a chemical vapor deposition (CVD) growth of monolayer MoS2 and MoSe2 crystals using three-temperature-zone furnace. Systematical study of the effects of growth pressure, temperature and time on the thickness, morphology and grain size of crystals shows the good controllability. The photoluminescence (PL) characterizations indicate that the as-grown monolayer MoS2 and MoSe2 crystals possess excellent optical qualities with very small full-width-half-maximum (FWHM) of 96 me V and 57 me V, respectively. It is comparable to that of exfoliated monolayers and reveals their high crystal quality. It is promising that our strategy should be applicable for the growth of other transition metal dichalcogenides (TMDs) monolayer crystals.
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Jiang, Yanbo; Shi, Kai; Wang, Shuo; Li, Xuefeng; Cui, Fude
2010-12-01
This study presents a preliminary exploration on extending the half-life of therapeutic proteins by crystallization strategy without new molecular entities generation. Recombinant human interferon (rhIFN) α-2b, a model protein drug in this case, was crystallized using a hanging-drop vapor diffusion method. A novel chelating technique with metal ions was employed to promote crystals formation. The effects of key factors such as seeding protein concentration, pH of the hanging drop, ionic strength of the equilibration solution, and precipitants were investigated. Size-exclusion liquid chromatography, antiviral activity determination, and enzyme-linked immunosorbent assay indicated that both the molecular integrity and biological potency of rhIFN were not significantly affected by crystallization process. In addition, the in vitro release behavior of rhIFN from crystal lattice was characterized by an initial fast release, followed by a sustained release up to 48 hour. The work described here suggested an exciting possibility of therapeutic protein crystals as a long-acting formulation.
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Sublimation rate of molecular crystals - role of internal degrees of freedom
DOE Office of Scientific and Technical Information (OSTI.GOV)
Maiti, A; Zepeda-Ruiz, L A; Gee, R H
2007-01-19
It is a common practice to estimate site desorption rate from crystal surfaces with an Arrhenius expression of the form v{sub eff} exp(-{Delta}E/k{sub B}T), where {Delta}E is an activation barrier to desorb and v{sub eff} is an effective vibrational frequency {approx} 10{sup 12} sec{sup -1}. However, such a formula can lead to several to many orders of magnitude underestimation of sublimation rates in molecular crystals due to internal degrees of freedom. We carry out a quantitative comparison of two energetic molecular crystals with crystals of smaller entities like ice and Argon (solid) and uncover the errors involved as a functionmore » of molecule size. In the process, we also develop a formal definition of v{sub eff} and an accurate working expression for equilibrium vapor pressure.« less
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Cheraft-Bahloul, Nassima; Husson, Cécile; Ourtioualous, Meriam; Sinaeve, Sébastien; Atmani, Djebbar; Stévigny, Caroline; Nortier, Joëlle L; Antoine, Marie-Hélène
2017-09-14
The world prevalence of kidney stones is increasing and plants are frequently used to treat urolithiasis. Pistacia lentiscus L, a plant which freely grows around the Mediterranean basin areas, is widely used for various pathologies. P. lentiscus has an important impact as it has economical value on top of its pharmacological interest. Decoctions of its aerial parts and/or resin are used to treat kidney stones. To in vitro assess the potential nephroprotective effect of Pistacia lentiscus ethanolic fruit extract (PLEF) on proximal tubular cells in response to the adhesion of calcium oxalate monohydrate (COM) crystals. Human Kidney [HK]-2 cells were incubated with and without COM in the presence or absence of PLEF. Cell viability was measured by the resazurin assay. The expression of E-cadherin was analyzed by PCR. The extracellular production of H 2 O 2 was measured by Amplex® Red H 2 O 2 Assay. The numbers of detached or non-adherent COM crystals in the presence of PLEF were microscopically captured and counted using ImageJ software. The interaction of PLEF with COM and the effect of PLEF on crystal size were analyzed by flow cytometry. The spectrophotometric measurement of turbidity was performed for assessing the COM concentration. PLEF incubated with COM was able to increase the cell viability. The decrease of E-cadherin expression after incubation with COM was counteracted by PLEF. Overproduction of H 2 O 2 induced by COM was also inhibited by PLEF. Observations using flow cytometry showed that interactions between PLEF and the COM crystals occurred. PLEF was also effective in reducing the particles size and in lowering COM concentration. Our data show that COM tubulotoxicity can be significantly reversed by PLEF -at least in part- via an inhibition of COM crystals adhesion onto the apical membrane. This early beneficial effect of PLEF needs to be further investigated as a useful strategy in nephrolithiasis prevention. Copyright © 2017 Elsevier Ireland Ltd. All rights reserved.
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NASA Astrophysics Data System (ADS)
Omidvari, Negar; Schulz, Volkmar
2015-06-01
This paper evaluates the performance of a new type of PET detectors called sensitivity encoded silicon photomultiplier (SeSP), which allows a direct coupling of small-pitch crystal arrays to the detector with a reduction in the number of readout channels. Four SeSP devices with two separate encoding schemes of 1D and 2D were investigated in this study. Furthermore, both encoding schemes were manufactured in two different sizes of 4 ×4 mm2 and 7. 73 ×7. 9 mm2, in order to investigate the effect of size on detector parameters. All devices were coupled to LYSO crystal arrays with 1 mm pitch size and 10 mm height, with optical isolation between crystals. The characterization was done for the key parameters of crystal-identification, energy resolution, and time resolution as a function of triggering threshold and over-voltage (OV). Position information was archived using the center of gravity (CoG) algorithm and a least squares approach (LSQA) in combination with a mean light matrix around the photo-peak. The positioning results proved the capability of all four SeSP devices in precisely identifying all crystals coupled to the sensors. Energy resolution was measured at different bias voltages, varying from 12% to 18% (FWHM) and paired coincidence time resolution (pCTR) of 384 ps to 1.1 ns was obtained for different SeSP devices at about 18 °C room temperature. However, the best time resolution was achieved at the highest over-voltage, resulting in a noise ratio of 99.08%.
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Retrieving the properties of ice-phase precipitation with multi-frequency radar measurements
NASA Astrophysics Data System (ADS)
Mace, G. G.; Gergely, M.; Mascio, J.
2017-12-01
The objective of most retrieval algorithms applied to remote sensing measurements is the microphysical properties that a model might predict such as condensed water content, particle number, or effective size. However, because ice crystals grow and aggregate into complex non spherical shapes, the microphysical properties of interest are very much dependent on the physical characteristics of the precipitation such as how mass and crystal area are distributed as a function of particle size. Such physical properties also have a strong influence on how microwave electromagnetic energy scatters from ice crystals causing significant ambiguity in retrieval algorithms. In fact, passive and active microwave remote sensing measurements are typically nearly as sensitive to the ice crystal physical properties as they are to the microphysical characteristics that are typically the aim of the retrieval algorithm. There has, however, been active development of multi frequency algorithms recently that attempt to ameliorate and even exploit this sensitivity. In this paper, we will review these approaches and present practical applications of retrieving ice crystal properties such as mass- and area dimensional relationships from single and dual frequency radar measurements of precipitating ice using data collected aboard ship in the Southern Ocean and from remote sensors in the Rocky Mountains of the Western U.S.
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Effect of milling on particle shape and surface energy heterogeneity of needle-shaped crystals.
Ho, Raimundo; Naderi, Majid; Heng, Jerry Y Y; Williams, Daryl R; Thielmann, Frank; Bouza, Peter; Keith, Adam R; Thiele, Greg; Burnett, Daniel J
2012-10-01
Milling and micronization of particles are routinely employed in the pharmaceutical industry to obtain small particles with desired particle size characteristics. The aim of this study is to demonstrate that particle shape is an important factor affecting the fracture mechanism in milling. Needle-shaped crystals of the β polymorph of D-mannitol were prepared from recrystallization in water. A portion of the recrystallized materials was ball-milled. Unmilled and milled sieved fractions of recrystallized D-mannitol were analyzed by dynamic image analysis (DIA) and inverse gas chromatography (IGC) at finite concentration to explain the breakage/fracture behavior. In the process of ball-milling, D-mannitol preferentially fractured along their shortest axis, exposing (011) plane with increased hydrophilicity and increased bounding rectangular aspect ratio. This is in contrary to attachment energy modeling which predicts a fracture mechanism across the (010) plane with increased hydrophobicity, and small change in particle shape. Crystal size, and more importantly, crystal shape and facet-specific mechanical properties, can dictate the fracture/cleavage behavior of organic crystalline materials. Thorough understanding of the crystal slip systems, combining attachment energy prediction with particle shape and surface characterization using DIA and IGC, are important in understanding fracture behavior of organic crystalline solids in milling and micronization.
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Micromechanical models for the stiffness and strength of UHMWPE macrofibrils
NASA Astrophysics Data System (ADS)
Dong, Hai; Wang, Zheliang; O'Connor, Thomas C.; Azoug, Aurelie; Robbins, Mark O.; Nguyen, Thao D.
2018-07-01
Ultrahigh molecular weight polyethylene (UHMWPE) fibers have a complex hierarchical structure that at the micron-scale is composed of oriented chain crystals, lamellar crystals, and amorphous domains organized into macrofibrils. We developed a computational micromechanical modeling study of the effects of the morphological structure and constituent material properties on the deformation mechanisms, stiffness and strength of the UHMWPE macrofibrils. Specifically, we developed four representative volume elements, which differed in the arrangement and orientation of the lamellar crystals, to describe the various macrofibrillar microstructures observed in recent experiments. The stiffness and strength of the crystals were determined from molecular dynamic simulations of a pure PE crystal. A finite deformation crystal plasticity model was used to describe the crystals and an isotropic viscoplastic model was used for the amorphous phase. The results show that yielding in UHMWPE macrofibrils under axial tension is dominated by the slip in the oriented crystals, while yielding under transverse compression and shear is dominated by slips in both the oriented and lamellar crystals. The results also show that the axial modulus and strength are mainly determined by the volume fraction of the oriented crystals and are insensitive to the arrangements of the lamellar crystals when the modulus of the amorphous phase is significantly smaller than that of the crystals. In contrast, the arrangement and size of the lamellar crystals have a significant effect on the stiffness and strength under transverse compression and shear. These findings can provide a guide for new materials and processing design to improve the properties of UHMWPE fibers by controlling the macrofibrillar morphologies.
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Armstrong, Mitchell R; Senthilnathan, Sethuraman; Balzer, Christopher J; Shan, Bohan; Chen, Liang; Mu, Bin
2017-01-01
Systematic studies of key operating parameters for the sonochemical synthesis of the metal organic framework (MOF) HKUST-1(also called CuBTC) were performed including reaction time, reactor volume, sonication amplitude, sonication tip size, solvent composition, and reactant concentrations analyzed through SEM particle size analysis. Trends in the particle size and size distributions show reproducible control of average particle sizes between 1 and 4μm. These results along with complementary studies in sonofragmentation and temperature control were conducted to compare these results to kinetic crystal growth models found in literature to develop a plausible hypothetical mechanism for ultrasound-assisted growth of metal-organic-frameworks composed of a competitive mechanism including constructive solid-on-solid (SOS) crystal growth and a deconstructive sonofragmentation. Copyright © 2016 Elsevier B.V. All rights reserved.
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NASA Astrophysics Data System (ADS)
Zhang, Minghui; Wen, Haiqin; Pan, Xiuhong; Yu, Jianding; Jiang, Meng; Yu, Huimei; Tang, Meibo; Gai, Lijun; Ai, Fei
2018-03-01
Nd3+/Yb3+ co-doped La2O3-TiO2-ZrO2 glasses have been prepared by aerodynamic levitation method. The glasses show high refractive index of 2.28 and Abbe number of 18.3. Glass-ceramics heated at 880 °C for 50 min perform the strongest upconversion luminescence. X-ray diffraction patterns of glass-ceramics with different depths indicate that rare earth ions restrain crystallization. Body crystallization mechanism mixed with surface crystallization is confirmed in the heat treatment. Surface crystals achieve priority to grow, resulting in important effects on upconversion luminescence. The results of atomic force microscope and scanning electron microscope indicate that crystal particles with uniform size distribute densely and homogenously on the surface and large amount of glass matrix exists in the glass ceramics heated at 880 °C for 50 min. Crystals in the glass-ceramics present dense structure and strong boundaries, which can reduce the mutual nonradiative relaxation rate among rare earth ions and then improve upconversion luminescence effectively. Based on micro-structural study, the mechanism that upconversion luminescence can be improved by heat treatment has been revealed. The results of micro-structural analysis agree well with the spectra.
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Tetragonal Lysozyme Nucleation and Crystal Growth: The Role of the Solution Phase
NASA Technical Reports Server (NTRS)
Pusey, Marc L.; Forsythe, Elizabeth; Sumida, John; Maxwell, Daniel; Gorti, Sridhar
2002-01-01
Lysozyme, and most particularly the tetragonal form of the protein, has become the default standard protein for use in macromolecule crystal nucleation and growth studies. There is a substantial body of experimental evidence, from this and other laboratories, that strongly suggests this proteins crystal nucleation and growth is by addition of associated species that are preformed by standard reversible concentration-driven self association processes in the bulk solution. The evidence includes high resolution AFM studies of the surface packing and of growth unit size at incorporation, fluorescence resonance energy transfer measurements of intermolecular distances in dilute solution, dialysis kinetics, and modeling of the growth rate data. We have developed a selfassociation model for the proteins crystal nucleation and growth. The model accounts for the obtained crystal symmetry, explains the observed surface structures, and shows the importance of the symmetry obtained by self-association in solution to the process as a whole. Further, it indicates that nucleation and crystal growth are not distinct mechanistically, but identical, with the primary difference being the probability that the particle will continue to grow or dissolve. This model also offers a possible mechanism for fluid flow effects on the growth process and how microgravity may affect it. While a single lysozyme molecule is relatively small (M.W. = 14,400), a structured octamer in the 4(sub 3) helix configuration (the proposed average sized growth unit) would have a M.W. = 115,000 and dimensions of 5.6 x 5.6 x 7.6 nm. Direct AFM measurements of growth unit incorporation indicate that units as wide as 11.2 nm and as long as 11.4 nm commonly attach to the crystal. These measurements were made at approximately saturation conditions, and they reflect the sizes of species that both added or desorbed from the crystal surface. The larger and less isotropic the associated species the more likely that it will be oriented to some degree in a flowing boundary layer, even at the low flow velocities measured about macromolecule crystals. Flow-driven effects resulting in misorientation upon addition to and incorporation into the crystal need only be a small fraction of a percentage to significantly affect the resulting crystal. One Earth, concentration gradient driven flow will maintain a high interfacial concentration, i.e., a high level (essentially that of the bulk solution) of solute association at the interface and higher growth rate. Higher growth rates mean an increased probability that misaligned growth units are trapped by subsequent growth layers before they can be desorbed and try again, or that the desorbing species will be smaller than the adsorbing species. In microgravity the extended diffusive boundary layer will lower the interfacial concentration. This results in a net dissociation of aggregated species that diffuse in from the bulk solution, i.e., smaller associated species, which are more likely able to make multiple attempts to correctly bind, yielding higher quality crystals.
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Control of hydrodynamic cavitation using ultrasonic
NASA Astrophysics Data System (ADS)
Chatterjee, Dhiman; Arakeri, Vijay H.
2003-11-01
Hydrodynamic cavitation is known to have many harmful effects like surface damage and generation of noise. We investigated the use of ultrasonics to control traveling bubble cavitation. Ultrasonic pressure field, produced by a piezoelectric crystal, was applied to modify the nuclei size distribution. Effects of continuous-wave (CW) and pulsed excitations were studied. At low dissolved gas content the CW-mode performed better than the pulsed one, whereas for high gas content the pulsed one was more effective. The dominant mechanisms were Bjerknes force and rectified diffusion in these two cases. Simultaneous excitation by two crystals in CW and pulsed modes was seen to control cavitation better.
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NASA Astrophysics Data System (ADS)
Zhang, Jing; Tian, Yu; Ling, Lu-Ting; Yin, Su-Na; Wang, Cai-Feng; Chen, Su
2014-12-01
Versatile hydrogel-based nanocrystal (NC) microreactors were designed in this work for the construction of uniform fluorescence colloidal photonic crystal (CPC) supraballs. The hydrogel-based microspheres with sizes ranging from 150 to 300 nm were prepared by seeded copolymerization of acrylic acid and 2-hydroxyethyl methacrylate with micrometer-sized PS seed particles. As an independent NC microreactor, the as-synthesized hydrogel microsphere can effectively capture the guest cadmium ions due to the abundant carboxyl groups inside. Followed by the introduction of chalcogenides, in situ generation of higher-uptake NCs with sizes less than 5 nm was finally realized. Additionally, with the aid of the microfluidic device, the as-obtained NC-latex hybrids can be further self-assembled to bi-functional CPC supraballs bearing brilliant structural colors and uniform fluorescence. This research offers an alternative way to finely bind CPCs with NCs, which will facilitate progress in fields of self-assembled functional colloids and photonic materials.
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NASA Astrophysics Data System (ADS)
Zhang, Fangkun; Liu, Tao; Huo, Yan; Guan, Runduo; Wang, Xue Z.
2017-07-01
In this paper the effects of operating conditions including cooling rate, initial supersaturation, and seeding temperature were investigated on the morphology evolution of β-L-glutamic acid (β-LGA) during seeded cooling crystallization. Based on the results of in-situ image acquisition of the crystal morphology evolution during the crystallization process, it was found that the crystal products tend to be plate-like or short rod-like under a slow cooling rate, low initial supersaturation, and low seeding temperature. In the opposite, the operating conditions of a faster cooling rate, higher initial supersaturation, and higher seeding temperature tend to produce long rod-like or needle-like crystals, and meanwhile, the length and width of crystal products will be increased together with a wider crystal size distribution (CSD). The aspect ratio of crystals, defined by the crystal length over width measured from in-situ or sample images, was taken as a shape index to analyze the crystal morphologies. Based on comparative analysis of the experimental results, guidelines on these operating conditions were given for obtaining the desired crystal shapes, along with the strategies for obtaining a narrower CSD for better product quality. Experimental verifications were performed to illustrate the proposed guidelines on the operating conditions for seeded cooling crystallization of LGA solution.
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NASA Astrophysics Data System (ADS)
Guo, Yun-Zhu; Sun, Li-Hua; Oberthuer, Dominik; Zhang, Chen-Yan; Shi, Jian-Yu; di, Jiang-Lei; Zhang, Bao-Liang; Cao, Hui-Ling; Liu, Yong-Ming; Li, Jian; Wang, Qian; Huang, Huan-Huan; Liu, Jun; Schulz, Jan-Mirco; Zhang, Qiu-Yu; Zhao, Jian-Lin; Betzel, Christian; He, Jian-Hua; Yin, Da-Chuan
2014-12-01
High-quality protein crystals of suitable size are an important prerequisite for applying X-ray crystallography to determine the 3-dimensional structure of proteins. However, it is often difficult to obtain protein crystals of appropriate size and quality because nucleation and growth processes can be unsuccessful. Here, we show that by adsorbing proteins onto porous polystyrene-divinylbenzene microspheres (SDB) floating on the surface of the crystallisation solution, a localised high supersaturation region at the surface of the microspheres and a low supersaturation region below the microspheres can coexist in a single solution. The crystals will easily nucleate in the region of high supersaturation, but when they grow to a certain size, they will sediment to the region of low supersaturation and continue to grow. In this way, the probability of crystallisation and crystal quality can be simultaneously increased in a single solution without changing other crystallisation parameters.
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1992-06-25
Zeolites are crystalline aluminosilicates that have complex framework structures. However, there are several features of zeolite crystals that make unequivocal structure determinations difficult. The acquisition of reliable structural information on zeolites is greatly facilitated by the availability of high-quality specimens. For structure determinations by conventional diffraction techniques, large single-crystal specimens are essential. Alternatively, structural determinations by powder profile refinement methods relax the constraints on crystal size, but still require materials with a high degree of crystalline perfection. Studies conducted at CAMMP (Center for Advanced Microgravity Materials Processing) have demonstrated that microgravity processing can produce larger crystal sizes and fewer structural defects relative to terrestrial crystal growth. Principal Investigator: Dr. Albert Sacco
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NASA Technical Reports Server (NTRS)
1992-01-01
Zeolites are crystalline aluminosilicates that have complex framework structures. However, there are several features of zeolite crystals that make unequivocal structure determinations difficult. The acquisition of reliable structural information on zeolites is greatly facilitated by the availability of high-quality specimens. For structure determinations by conventional diffraction techniques, large single-crystal specimens are essential. Alternatively, structural determinations by powder profile refinement methods relax the constraints on crystal size, but still require materials with a high degree of crystalline perfection. Studies conducted at CAMMP (Center for Advanced Microgravity Materials Processing) have demonstrated that microgravity processing can produce larger crystal sizes and fewer structural defects relative to terrestrial crystal growth. Principal Investigator: Dr. Albert Sacco
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Effect of heat treatment on the crystal structure of deformed samples of chromium-manganese steel
NASA Astrophysics Data System (ADS)
Chezganov, D. S.; Chikova, O. A.; Borovykh, M. A.
2017-09-01
Results of studying microstructures and the crystal structure of samples of 35KhGF steel (0.31-0.38 wt % C, 0.17-0.37 wt % Si, 0.95-1.25 wt % Mn, 1.0-1.3 wt % Cr, 0.06-0.12 wt % V, and the remainder was Fe) have been presented. The samples have been selected from hot-rolled pipes subjected to different heat treatments. A study has been carried out in order to explain the choice of the heat-treatment regime based on determining the structure-properties relationship that provides an increase in the corrosion resistance of pipes to the effect of hydrocarbons. Methods of the energy-dispersive X-ray spectroscopy (EDS) and electron backscatter diffraction (EBSD) have been used. In the microstructure of samples, oxide inclusions and discontinuities with sizes of 1-50 μm that presumably consist of the scale were detected. The ferrite grain size and the orientations of crystals were determined; the data on the local mechanical stresses in the Taylor orientation- factor maps were obtained. The grain refinement; the increase in the fraction of the low-angle boundaries; and the decrease in the local mechanical stresses and, therefore, the highest corrosion resistance to the effect of hydrocarbons is achieved by normalizing at 910°C.
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Hattori, Kenji; Nakadate, Kazuhiko; Morii, Akane; Noguchi, Takumi; Ogasawara, Yuki; Ishii, Kazuyuki
2017-10-14
Exposure to nanoparticles such as carbon nanotubes has been shown to cause pleural mesothelioma similar to that caused by asbestos, and has become an environmental health issue. Not only is the percutaneous absorption of nano-size titanium dioxide particles frequently considered problematic, but the possibility of absorption into the body through the pulmonary route is also a concern. Nevertheless, there are few reports of nano-size titanium dioxide particles on respiratory organ exposure and dynamics or on the mechanism of toxicity. In this study, we focused on the morphology as well as the size of titanium dioxide particles. In comparing the effects between nano-size anatase and rutile titanium dioxide on human-derived pleural mesothelial cells, the anatase form was shown to be actively absorbed into cells, producing reactive oxygen species and causing oxidative damage to DNA. In contrast, we showed for the first time that the rutile form is not easily absorbed by cells and, therefore, does not cause oxidative DNA damage and is significantly less damaging to cells. These results suggest that with respect to the toxicity of titanium dioxide particles on human-derived mesothelial cells, the crystal form rather than the particle size has a greater effect on cellular absorption. Also, it was indicated that the difference in absorption is the primary cause of the difference in the toxicity against mesothelial cells. Copyright © 2017 Elsevier Inc. All rights reserved.
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Scanning electron microscope view of iron crystal growing on pyroxene crystal
NASA Technical Reports Server (NTRS)
1972-01-01
A scanning electron microscope photograph of a four-micron size iron crystal growing on a pyroxene crystal (calcium-magnesium-iron silicate) from the Apollo 15 Hadley-Apennino lunar landing site. The well developed crystal faces indicate that the crystal was formed from a hot vapor as the rock was cooling.
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NASA Astrophysics Data System (ADS)
Ren, Xiaodong; Yang, Zhou; Yang, Dong; Zhang, Xu; Cui, Dong; Liu, Yucheng; Wei, Qingbo; Fan, Haibo; Liu, Shengzhong (Frank)
2016-02-01
Regulating the temperature during the direction contact and intercalation process (DCIP) for the transition from PbI2 to CH3NH3PbI3 modulated the crystallinity, crystal grain size and crystal grain orientation of the perovskite films. Higher temperatures produced perovskite films with better crystallinity, larger grain size, and better photovoltaic performance. The best cell, which had a PCE of 12.9%, was obtained on a film prepared at 200 °C. Further open circuit voltage decay and film resistance characterization revealed that the larger grain size contributed to longer carrier lifetime and smaller carrier transport resistance, both of which are beneficial for solar cell devices.Regulating the temperature during the direction contact and intercalation process (DCIP) for the transition from PbI2 to CH3NH3PbI3 modulated the crystallinity, crystal grain size and crystal grain orientation of the perovskite films. Higher temperatures produced perovskite films with better crystallinity, larger grain size, and better photovoltaic performance. The best cell, which had a PCE of 12.9%, was obtained on a film prepared at 200 °C. Further open circuit voltage decay and film resistance characterization revealed that the larger grain size contributed to longer carrier lifetime and smaller carrier transport resistance, both of which are beneficial for solar cell devices. Electronic supplementary information (ESI) available: XRD patterns and statistic results of solar cell performance. See DOI: 10.1039/c5nr08935b
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Mesoscale crystallization of calcium phosphate nanostructures in protein (casein) micelles
NASA Astrophysics Data System (ADS)
Thachepan, Surachai; Li, Mei; Mann, Stephen
2010-11-01
Aqueous micelles of the multi-protein calcium phosphate complex, casein, were treated at 60 °C and pH 7 over several months. Although partial dissociation of the micelles into 12 nm sized amorphous calcium phosphate (ACP)/protein nanoparticles occurred within a period of 14 days, crystallization of the ACP nanoclusters into bundles of hydroxyapatite (HAP) nanofilaments was not observed until after 12 weeks. The HAP nanofilaments were formed specifically within the partially disrupted protein micelles suggesting a micelle-mediated pathway of mesoscale crystallization. Similar experiments using ACP-containing synthetic micelles prepared from β-casein protein alone indicated that co-aligned bundles of HAP nanofilaments were produced within the protein micelle interior after 24 hours at temperatures as low as 35 °C. The presence of Mg2+ ions in the casein micelles, as well as a possible synergistic effect associated with the multi-protein nature of the native aggregates, could account for the marked inhibition in mesoscale crystallization observed in the casein micelles compared with the single-component β-casein constructs.Aqueous micelles of the multi-protein calcium phosphate complex, casein, were treated at 60 °C and pH 7 over several months. Although partial dissociation of the micelles into 12 nm sized amorphous calcium phosphate (ACP)/protein nanoparticles occurred within a period of 14 days, crystallization of the ACP nanoclusters into bundles of hydroxyapatite (HAP) nanofilaments was not observed until after 12 weeks. The HAP nanofilaments were formed specifically within the partially disrupted protein micelles suggesting a micelle-mediated pathway of mesoscale crystallization. Similar experiments using ACP-containing synthetic micelles prepared from β-casein protein alone indicated that co-aligned bundles of HAP nanofilaments were produced within the protein micelle interior after 24 hours at temperatures as low as 35 °C. The presence of Mg2+ ions in the casein micelles, as well as a possible synergistic effect associated with the multi-protein nature of the native aggregates, could account for the marked inhibition in mesoscale crystallization observed in the casein micelles compared with the single-component β-casein constructs. Electronic supplementary information (ESI) available: Particle size histograms, TEM, EDX and electron diffraction data. See DOI: 10.1039/c0nr00158a
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NASA Astrophysics Data System (ADS)
Mauge-Lewis, Kevin
In response to the growing need for new crystallization techniques that afford for rapid processing times along with control over crystal size and distribution, the Aslan Research Group has recently demonstrated the use of Metal-Assisted and Microwave-Accelerated Evaporative Crystallization MA-MAEC technique in conjunction with metal nanoparticles and nanostructures for the crystallization of amino acids and organic small molecules. In this study, we have employed the newly developed MA-MAEC technique to the accelerated crystallization of chicken egg-white lysozyme on circular crystallization platforms in order to demonstrate the proof-of-principle application of the method for protein crystallization. The circular crystallization platforms are constructed in-house from poly (methyl methacrylate) (PMMA) and silver nanoparticle films (SNFs), indium tin oxide (ITO) and iron nano-columns. In this study, we prove the MA-MAEC method to be a more effective technique in the rapid crystallization of macromolecules in comparison to other conventional methods. Furthermore, we demonstrate the use of the novel iCrystal system, which incorporates the use of continuous, low wattage heating to facilitate the rapid crystallization of the lysozyme while still retaining excellent crystal quality. With the incorporation of the iCrystal system, we observe crystallization times that are even shorter than those produced by the MA-MAEC technique using a conventional microwave oven in addition to significantly improved crystal quality.
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In-Situ Microphysics from the MPACE IOP
McFarquhar, Greg
2008-01-15
Best estimates of the size distributions of supercooled water droplets and ice crystals for mixed-phase clouds measured during M-PACE for spiral ascents/descents over Barrow and Oliktok Point, and for ramped ascents/descents between Barrow and Oliktok Point. Our best estimates of the bulk microphysical properties such as ice water content (IWC), liquid water content (LWC), effective radius of ice crystals defined following Fu (1996) (rei), effective radius of supercooled water droplets (rew), total ice crystal number concentration (Ni), total water droplet number concentration (Nw) and total condensed water content (CWC), are also provided. The quantities were derived from the FSSP, 1DC, 2DC, HVPS and the CVI. Note HVPS data are only available after 10 Oct 2004 and some procedures have been developed to account for the missing data.
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Methods for growth of relatively large step-free SiC crystal surfaces
NASA Technical Reports Server (NTRS)
Neudeck, Philip G. (Inventor); Powell, J. Anthony (Inventor)
2002-01-01
A method for growing arrays of large-area device-size films of step-free (i.e., atomically flat) SiC surfaces for semiconductor electronic device applications is disclosed. This method utilizes a lateral growth process that better overcomes the effect of extended defects in the seed crystal substrate that limited the obtainable step-free area achievable by prior art processes. The step-free SiC surface is particularly suited for the heteroepitaxial growth of 3C (cubic) SiC, AlN, and GaN films used for the fabrication of both surface-sensitive devices (i.e., surface channel field effect transistors such as HEMT's and MOSFET's) as well as high-electric field devices (pn diodes and other solid-state power switching devices) that are sensitive to extended crystal defects.
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Lansiquot, Carisse; Boone-Kukoyi, Zainab; Shortt, Raquel; Thompson, Nishone; Ajifa, Hillary; Kioko, Bridgit; Constance, Edward Ned; Clement, Travis; Ozturk, Birol; Aslan, Kadir
2017-01-01
The use of indium tin oxide (ITO) and focused monomode microwave heating for the ultra-rapid crystallization of L-alanine (a model amino acid) is reported. Commercially available ITO dots (< 5 mm) attached to blank poly(methyl)methacrylate (PMMA, 5 cm in diameter with 21-well silicon isolators: referred to as the iCrystal plates) were found to withstand prolonged microwave heating during crystallization experiments. Crystallization of L-alanine was performed at room temperature (a control experiment), with the use of two microwave sources: a 2.45 GHz conventional microwave (900 W, power level 1, a control experiment) and 8 GHz (20 W) solid state, monomode microwave source with an applicator tip that focuses the microwave field to a 5-mm cavity. Initial appearance of L-alanine crystals and on iCrystal plates with ITO dots took 47 ± 2.9 min, 12 ± 7.6 min and 1.5 ± 0.5 min at room temperature, using a conventional microwave and focused monomode microwave heating, respectively. Complete evaporation of the solvent using the focused microwaves was achieved in 3.2 ± 0.5 min, which is ~52-fold and ~172-fold faster than that observed at room temperature and using conventional microwave heating, respectively. The size and number of L-alanine crystals was dependent on the type of the 21-well iCrystal plates and the microwave heating method: 33 crystals of 585 ± 137 μm in size at room temperature > 37 crystals of 542 ± 100 μm in size with conventional microwave heating > 331 crystals of 311 ± 190 μm in size with focused monomode microwave. FTIR, optical microscopy and powder X-ray diffraction analysis showed that the chemical composition and crystallinity of the L-alanine crystals did not change when exposed to microwave heating and ITO surfaces. In addition, theoretical simulations for the binding of L-alanine molecules to ITO and other metals showed the predicted nature of hydrogen bonds formed between L-alanine and these surfaces.
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Lansiquot, Carisse; Boone-Kukoyi, Zainab; Shortt, Raquel; Thompson, Nishone; Ajifa, Hillary; Kioko, Bridgit; Constance, Edward Ned; Clement, Travis; Ozturk, Birol; Aslan, Kadir
2018-01-01
The use of indium tin oxide (ITO) and focused monomode microwave heating for the ultra-rapid crystallization of L-alanine (a model amino acid) is reported. Commercially available ITO dots (< 5 mm) attached to blank poly(methyl)methacrylate (PMMA, 5 cm in diameter with 21-well silicon isolators: referred to as the iCrystal plates) were found to withstand prolonged microwave heating during crystallization experiments. Crystallization of L-alanine was performed at room temperature (a control experiment), with the use of two microwave sources: a 2.45 GHz conventional microwave (900 W, power level 1, a control experiment) and 8 GHz (20 W) solid state, monomode microwave source with an applicator tip that focuses the microwave field to a 5-mm cavity. Initial appearance of L-alanine crystals and on iCrystal plates with ITO dots took 47 ± 2.9 min, 12 ± 7.6 min and 1.5 ± 0.5 min at room temperature, using a conventional microwave and focused monomode microwave heating, respectively. Complete evaporation of the solvent using the focused microwaves was achieved in 3.2 ± 0.5 min, which is ~52-fold and ~172-fold faster than that observed at room temperature and using conventional microwave heating, respectively. The size and number of L-alanine crystals was dependent on the type of the 21-well iCrystal plates and the microwave heating method: 33 crystals of 585 ± 137 μm in size at room temperature > 37 crystals of 542 ± 100 μm in size with conventional microwave heating > 331 crystals of 311 ± 190 μm in size with focused monomode microwave. FTIR, optical microscopy and powder X-ray diffraction analysis showed that the chemical composition and crystallinity of the L-alanine crystals did not change when exposed to microwave heating and ITO surfaces. In addition, theoretical simulations for the binding of L-alanine molecules to ITO and other metals showed the predicted nature of hydrogen bonds formed between L-alanine and these surfaces. PMID:29657884
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Low voltage polymer network liquid crystal for infrared spatial light modulators.
Peng, Fenglin; Xu, Daming; Chen, Haiwei; Wu, Shin-Tson
2015-02-09
We report a low-voltage and fast-response polymer network liquid crystal (PNLC) infrared phase modulator. To optimize device performance, we propose a physical model to understand the curing temperature effect on average domain size. Good agreement between model and experiment is obtained. By optimizing the UV curing temperature and employing a large dielectric anisotropy LC host, we have lowered the 2π phase change voltage to 22.8V at 1.55μm wavelength while keeping response time at about 1 ms. Widespread application of such a PNLC integrated into a high resolution liquid-crystal-on-silicon (LCoS) for infrared spatial light modulator is foreseeable.
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Oriented attachment by enantioselective facet recognition in millimeter-sized gypsum crystals.
Viedma, Cristóbal; Cuccia, Louis A; McTaggart, Alicia; Kahr, Bart; Martin, Alexander T; McBride, J Michael; Cintas, Pedro
2016-09-22
Crystal growth by oriented attachment involves the spontaneous self-assembly of adjoining crystals with common crystallographic orientations. Herein, we report the oriented attachment of gypsum crystals on agitation to form stereoselective mesoscale aggregates.
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Effective Ice Particle Densities for Cold Anvil Cirrus
NASA Technical Reports Server (NTRS)
Heymsfield, Andrew J.; Schmitt, Carl G.; Bansemer, Aaron; Baumgardner, Darrel; Weinstock, Elliot M.; Smith, Jessica
2002-01-01
This study derives effective ice particle densities from data collected from the NASA WB-57F aircraft near the tops of anvils during the Cirrus Regional Study of Tropical Anvils and Cirrus Layers (CRYSTAL) Florida Area Cirrus Experiment (FACE) in southern Florida in July 2002. The effective density, defined as the ice particle mass divided by the volume of an equivalent diameter liquid sphere, is obtained for particle populations and single sizes containing mixed particle habits using measurements of condensed water content and particle size distributions. The mean effective densities for populations decrease with increasing slopes of the gamma size distributions fitted to the size distributions. The population-mean densities range from near 0.91 g/cu m to 0.15 g/cu m. Effective densities for single sizes obey a power-law with an exponent of about -0.55, somewhat less steep than found from earlier studies. Our interpretations apply to samples where particle sizes are generally below 200-300 microns in maximum dimension because of probe limitations.
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Donovan, David Patrick; Quante, Markus; Schlimme, Ingo; Macke, Andreas
2004-09-01
The effect of ice crystal size and shape on the relation between radar reflectivity and optical extinction is examined. Discrete-dipole approximation calculations of 95-GHz radar reflectivity and ray-tracing calculations are applied to ice crystals of various habits and sizes. Ray tracing was used primarily to calculate optical extinction and to provide approximate information on the lidar backscatter cross section. The results of the combined calculations are compared with Mie calculations applied to collections of different types of equivalent spheres. Various equivalent sphere formulations are considered, including equivalent radar-lidar spheres; equivalent maximum dimension spheres; equivalent area spheres, and equivalent volume and equivalent effective radius spheres. Marked differences are found with respect to the accuracy of different formulations, and certain types of equivalent spheres can be used for useful prediction of both the radar reflectivity at 95 GHz and the optical extinction (but not lidar backscatter cross section) over a wide range of particle sizes. The implications of these results on combined lidar-radar ice cloud remote sensing are discussed.
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Synthetic octacalcium phosphate: a possible carrier for mesenchymal stem cells in bone regeneration.
Suzuki, Osamu; Anada, Takahisa
2013-01-01
The present paper reviews biomaterial studies of synthetic octacalcium phosphate (OCP) as a scaffold of osteoblastic cells. OCP crystals have been suggested to be one of precursor phases in hydroxyapatite (HA) crystal formation in bone and tooth. The recent intensive biomaterials and tissue engineering studies using synthetic OCP disclosed the potential function of OCP as a bioactive material as well as synthetic HA materials due to its highly osteoconductive and biodegradable properties. In vitro studies showed that OCP crystals exhibit a positive effect on osteoblastic cell differentiation. In vivo studies confirmed that the materials of OCP in a granule forms and OCP-based composite materials with natural polymers, such as gelatin and collagen, enhance bone regeneration if implanted in various model bone defects with critical-sized diameters, defined as a defect which does not heal spontaneously throughout the lifetime of the animals. One of particular characteristics of OCP, found as a mechanism to enhance bone regeneration in vivo, is a process of progressive conversion from OCP to HA at physiological conditions. The OCP-HA conversion is accompanied by progressive physicochemical changes of the material properties, which affects the tissue reaction around the crystals where osteoblastic cells are encountered. Mesenchymal stem cells (MSCs) seeded in an OCP-based material enhanced bone regeneration in the rat critical-sized calvaria defect more than that by the material alone. The overall results reveal that OCP crystals have an effect on osteoblastic cell differentiation including the differentiation of MSCs in vivo. The evidence collected experimentally in the laboratory was presented.
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Size and habit evolution of PETN crystals - a lattice Monte Carlo study
DOE Office of Scientific and Technical Information (OSTI.GOV)
Zepeda-Ruiz, L A; Maiti, A; Gee, R
2006-02-28
Starting from an accurate inter-atomic potential we develop a simple scheme of generating an ''on-lattice'' molecular potential of short range, which is then incorporated into a lattice Monte Carlo code for simulating size and shape evolution of nanocrystallites. As a specific example, we test such a procedure on the morphological evolution of a molecular crystal of interest to us, e.g., Pentaerythritol Tetranitrate, or PETN, and obtain realistic facetted structures in excellent agreement with experimental morphologies. We investigate several interesting effects including, the evolution of the initial shape of a ''seed'' to an equilibrium configuration, and the variation of growth morphologymore » as a function of the rate of particle addition relative to diffusion.« less
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Structure and Growth of Rod-Shaped Mn Ultrafine Particle
NASA Astrophysics Data System (ADS)
Kido, Osamu; Suzuki, Hitoshi; Saito, Yoshio; Kaito, Chihiro
2003-09-01
The structure of rod-shaped Mn ultrafine particles was elucidated by electron microscopy. Mn ultrafine particles have characteristic tristetrahedron (α-Mn), rhombic dodecahedron (β-Mn) and rod-shape crystal habits. It was found that the rod-shaped particle resulted from the parallel coalescence of β-Mn particles with the size of 50 nm. Detailed analysis of the defects seen in large rod-shaped particles with the width of 100 nm indicated a mixture of α- and β-phases. A size effect on the phase transition from β to α was observed throughout the rod-shaped crystal structure. The structure and growth of Mn particles were discussed based on the outline of the smoke and the temperature distribution in the smoke.
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Influence of tartaric acid on linear-nonlinear optical and electrical properties of KH2PO4 crystal
NASA Astrophysics Data System (ADS)
Baig, M. I.; Anis, Mohd; Muley, G. G.
2017-10-01
KH2PO4 (KDOP) is widely demanded technological crystal for applications in laser driven photonic devices. Therefore, present article is focused to investigate the effect of tartaric acid (TA) on laser induced nonlinear optical properties of KDOP crystal. The optically transparent TA doped KDOP crystal of size 15 × 10 × 04 mm3 has been grown by slow solvent evaporation technique at 35 °C. The structural analysis of pure and TA doped KDOP crystal has been achieved by means of single crystal X-ray diffraction technique. The functional groups of TA doped KDOP crystal has been identified by means of Fourier transform infrared spectral analysis. The UV-visible studies have been performed to determine the optical transparency and evaluate the linear optical constants of pure and TA doped KDOP crystal. The Kurtz-Perry test has been employed to confirm the frequency doubling phenomenon of crystal and the SHG efficiency of TA doped KDOP crystal is found to be 5.68 times higher than that of standard KDP material. The Z-scan technique has been employed to explore the third order nonlinear optical (TONLO) refraction (n2), absorption (β) and susceptibility (χ3) of pure and TA doped KDOP crystal at 632.8 nm. The TA facilitated optical switching in TONLO response of KDOP crystal is found to be an interesting effect to examine. The laser damage threshold of TA doped KDOP crystal has been determined at 1064 nm using the Nd:YAG laser. The comparative electrical analysis on pure and TA doped KDOP crystal has been accomplished by means of dielectric and photoconductivity characterization studies.
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Glushko, O; Meisels, R; Kuchar, F
2010-03-29
The plane-wave expansion method (PWEM), the multiple-scattering method (MSM) and the 3D finite-difference time-domain method (FDTD) are applied for simulations of propagation of electromagnetic waves through 3D colloidal photonic crystals. The system investigated is not a "usual" artificial opal with close-packed fcc lattice but a dilute bcc structure which occurs due to long-range repulsive interaction between electrically charged colloidal particles during the growth process. The basic optical properties of non-close-packed colloidal PhCs are explored by examining the band structure and reflection spectra for a bcc lattice of silica spheres in an aqueous medium. Finite size effects and correspondence between the Bragg model, band structure and reflection spectra are discussed. The effects of size, positional and missing-spheres disorder are investigated. In addition, by analyzing the results of experimental work we show that the fabricated structures have reduced plane-to-plane distance probably due to the effect of gravity during growth.
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NASA Astrophysics Data System (ADS)
Xu, Weitai; Zhao, Yutao; Sun, Shaochun; Liu, Manping; Ma, Dexin; Liang, Xiangfeng; Wang, Cunlong; Tao, Ran
2018-04-01
The mold shell used for single-crystal turbine blades preparation was modified from conventional process to fiber reinforcement technology. The wall thickness was decreased by 32.3 percent (pct) than the conventional process. Then these two mold shells were used to produce single crystal samples of nickel-base superalloy in a Bridgman furnace. The local temperature curves were recorded in the process. The results show that the modified mold shell can increase the temperature gradient in the mushy zone than the conventional mold shell. The primary and secondary dendrite arm space were reduced by 8 pct and 12 pct, respectively. Moreover, both the area fraction and mean size of the γ‧/γ eutectic were declined, as well as the dendritic segregation tendency. Therefore it contributed to the lower residual eutectic and micro-porosity in the heat-treated microstructure. Further, fracture surface of the samples made by modified mold shell exhibited smaller facets and more uniform dimples in the size and shape.
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Elevated temperature deformation of thoria dispersed nickel-chromium
NASA Technical Reports Server (NTRS)
Kane, R. D.; Ebert, L. J.
1974-01-01
The deformation behavior of thoria nickel-chromium (TD-NiCr) was examined over the temperature range 593 C (1100 F) to 1260 C (2300 F) in tension and compression and at 1093 C (2000 F) in creep. Major emphasis was placed on: (1) the effects of the material and test related variables (grain size, temperature, stress and strain rate) on the deformation process; and (2) the evaluation of single crystal TD-NiCr material produced by a directional recrystallization process. Elevated temperature yield strength levels and creep activation enthalpies were found to increase with increasing grain size reaching maximum values for the single crystal TD-NiCr. Stress exponent of the steady state creep rate was also significantly higher for the single crystal TD-NiCr as compared to that determined for the polycrystalline materials. The elevated temperature deformation of TD-NiCr was analyzed in terms of two concurrent, parallel processes: diffusion controlled grain boundary sliding, and dislocation motion.
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On dewetting of thin films due to crystallization (crystallization dewetting).
Habibi, Mehran; Rahimzadeh, Amin; Eslamian, Morteza
2016-03-01
Drying and crystallization of a thin liquid film of an ionic or a similar solution can cause dewetting in the resulting thin solid film. This paper aims at investigating this type of dewetting, herein termed "crystallization dewetting", using PbI2 dissolved in organic solvents as the model solution. PbI2 solid films are usually used in X-ray detection and lead halide perovskite solar cells. In this work, PbI2 films are fabricated using spin coating and the effect of major parameters influencing the crystallization dewetting, including the type of the solvent, solution concentration, drying temperature, spin speed, as well as imposed vibration on the substrate are studied on dewetting, surface profile and coverage, using confocal scanning laser microscopy. Simplified hydrodynamic governing equations of crystallization in thin films are presented and using a mathematical representation of the process, it is phenomenologically demonstrated that crystallization dewetting occurs due to the absorption and consumption of the solution surrounding a growing crystal. Among the results, it is found that a low spin speed (high thickness), a high solution concentration and a low drying temperature promote crystal growth, and therefore crystallization dewetting. It is also shown that imposed vibration on the substrate can affect the crystal size and crystallization dewetting.
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Effect of Gravity Level on the Particle Shape and Size During Zeolite Crystal Growth
NASA Technical Reports Server (NTRS)
Song, Hong-Wei; Ilebusi, Olusegun J.; Sacco, Albert, Jr.
2003-01-01
A microscopic diffusion model is developed to represent solute transport in the boundary layer of a growing zeolite crystal. This model is used to describe the effect of gravity on particle shape and solute distribution. Particle dynamics and crystal growth kinetics serve as the boundary conditions of flow and convection-diffusion equations. A statistical rate theory is used to obtain the rate of solute transport across the growing interface, which is expressed in terms of concentration and velocity of solute species. Microgravity can significantly decrease the solute velocity across the growing interface compared to its earth-based counterpart. The extent of this reduction highly depends on solute diffusion constant in solution. Under gravity, the flow towards the crystal enhances solute transport rate across the growing interface while the flow away from crystals reduces this rate, suggesting a non-uniform growth rate and thus an elliptic final shape. However, microgravity can significantly reduce the influence of flow and obtain a final product with perfect spherical shape. The model predictions compare favorably with the data of space experiment of zeolites grown in space.
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Microstructure, crystallization and shape memory behavior of titania and yttria co-doped zirconia
Zeng, Xiao Mei; Du, Zehui; Schuh, Christopher A.; ...
2015-12-17
Small volume zirconia ceramics with few or no grain boundaries have been demonstrated recently to exhibit the shape memory effect. To explore the shape memory properties of yttria doped zirconia (YDZ), it is desirable to develop large, microscale grains, instead of submicron grains that result from typical processing of YDZ. In this paper, we have successfully produced single crystal micro-pillars from microscale grains encouraged by the addition of titania during processing. Titania has been doped into YDZ ceramics and its effect on the grain growth, crystallization and microscale elemental distribution of the ceramics have been systematically studied. With 5 mol%more » titania doping, the grain size can be increased up to ~4 μm, while retaining a large quantity of the desired tetragonal phase of zirconia. Finally, micro-pillars machined from tetragonal grains exhibit the expected shape memory effects where pillars made from titania-free YDZ would not.« less
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Nishiyama, Yoshiharu; Wada, Masahisa; Hanson, B. Leif
2012-01-01
Structural changes during the treatment of films of highly crystalline microfibers of Cladophora cellulose with ethylenediamine (EDA) have been studied by time-resolved X-ray microprobe diffraction methods. As EDA penetrates the sample and converts cellulose I to EDA-cellulose I, the measured profile widths of reflections reveal changes in the shapes and average dimensions of cellulose I and EDA-cellulose I crystals. The (200) direction of cellulose I is most resistant to EDA penetration, with EDA penetrating most effectively at the hydrophilic edges of the hydrogen bonded sheets of cellulose chains. Most of the cellulose chains in the initial crystals of cellulose I are incorporated into crystals of EDA-cellulose I. The size of the emerging EDA-cellulose I crystals is limited to about half of their size in cellulose I, most likely due to strains introduced by the penetration of EDA molecules. There is no evidence of any gradual structural transition from cellulose I to EDA-cellulose I involving a continuously changing intermediate phase. Rather, the results point to a rapid transition to EDA-cellulose I in regions of the microfibrils that have been penetrated by EDA. PMID:22693365
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State of the art of fine patterned Si TFT
NASA Astrophysics Data System (ADS)
Noguchi, Takashi
2003-05-01
Performance and relating subject for fine patterned Si TFT (Thin Film Transistor) are reviewed and discussed from a viewpoint of device and/or fabrication process based on reported results. Poly-Si TFTs fabricated on glass using low-temperature process are studied extensively for the application to LCD (Liquid Crystal Display) or OLED (Organic Light Emitting Diode) Display. Currently, the research target for the TFT application is emphasized on the highly functional system on glass or the display on flexible substrate by adopting an effective crystallizing technique of SPC (Solid Phase Crystallization) or ELC (Excimer Laser Crystallization). Improvement of device characteristics such as an enhancement of carrier mobility has been studied intensively by enlarging the grain size. Reduction of the voltage and shrinkage of the device size are the trend of Si LSI, which arise a peculiar issue of uniformity or an anisotropy problem for the device characteristics in the large grained poly-Si film. Some trial approaches for solving the issues such as nucleation control for the grain growth or lateral grain growth are proposed, so far. By overcoming the issues, coming SOP (System on Panel) era using the Si TFTs is expected.
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Insights Into the Solution Crystallization of Oriented Alq3 and Znq2 Microprisms and Nanorods.
Boulet, Joel; Mohammadpour, Arash; Shankar, Karthik
2015-09-01
Optimized solution-based methods to grow high quality micro- and nanocrystals of organic semi-conductors with defined size, shape and orientation are important to a variety of optoelectronic applications. In this context, we report the growth of single crystal micro- and nanostructures of the organic semiconductors Tris(8-hydroxyquinoline)aluminum (Alq3) and bis(8-hydroxyquinoline)zinc (Znq2) terminating in flat crystal planes using a combination of evaporative and antisolvent crystallization. By controlling substrate-specific nucleation and optimizing the conditions of growth, we generate vertically-oriented hexagonal prism arrays of Alq3, and vertical half-disks and sharp-edged rectangular prisms of Znq2. The effect of process variables such as ambient vapour pressure, choice of anti-solvent and temperature on the morphology and crystal habit of the nanostructures were studied and the results of varying them catalogued to gain a better understanding of the mechanism of growth.
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Exploring the zone of anisotropy and broken symmetries in DNA-mediated nanoparticle crystallization.
O'Brien, Matthew N; Girard, Martin; Lin, Hai-Xin; Millan, Jaime A; Olvera de la Cruz, Monica; Lee, Byeongdu; Mirkin, Chad A
2016-09-20
In this work, we present a joint experimental and molecular dynamics simulations effort to understand and map the crystallization behavior of polyhedral nanoparticles assembled via the interaction of DNA surface ligands. In these systems, we systematically investigated the interplay between the effects of particle core (via the particle symmetry and particle size) and ligands (via the ligand length) on crystallization behavior. This investigation revealed rich phase diagrams, previously unobserved phase transitions in polyhedral crystallization behavior, and an unexpected symmetry breaking in the ligand distribution on a particle surface. To understand these results, we introduce the concept of a zone of anisotropy, or the portion of the phase space where the anisotropy of the particle is preserved in the crystallization behavior. Through comparison of the zone of anisotropy for each particle we develop a foundational roadmap to guide future investigations.
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The Nucleation and Growth of Protein Crystals
NASA Technical Reports Server (NTRS)
Pusey, Marc
2004-01-01
Obtaining crystals of suitable size and high quality continues to be a major bottleneck in macromolecular crystallography. Currently, structural genomics efforts are achieving on average about a 10% success rate in going from purified protein to a deposited crystal structure. Growth of crystals in microgravity was proposed as a means of overcoming size and quality problems, which subsequently led to a major NASA effort in microgravity crystal growth, with the agency also funding research into understanding the process. Studies of the macromolecule crystal nucleation and growth process were carried out in a number of labs in an effort to understand what affected the resultant crystal quality on Earth, and how microgravity improved the process. Based upon experimental evidence, as well as simple starting assumptions, we have proposed that crystal nucleation occurs by a series of discrete self assembly steps, which 'set' the underlying crystal symmetry. This talk will review the model developed, and its origins, in our laboratory for how crystals nucleate and grow, and will then present, along with preliminary data, how we propose to use this model to improve the success rate for obtaining crystals from a given protein.
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Deposition and characterization of silicon thin-films by aluminum-induced crystallization
NASA Astrophysics Data System (ADS)
Ebil, Ozgenc
Polycrystalline silicon (poly-Si) as a thin-film solar cell material could have major advantages compared to non-silicon thin-film technologies. In theory, thin-film poly-Si may retain the performance and stability of c-Si while taking advantage of established manufacturing techniques. However, poly-Si films deposited onto foreign substrates at low temperatures typically have an average grain size of 10--50 nm. Such a grain structure presents a potential problem for device performance since it introduces an excessive number of grain boundaries which, if left unpassivated, lead to poor solar cell properties. Therefore, for optimum device performance, the grain size of the poly-Si film should be at least comparable to the thickness of the films. For this project, the objectives were the deposition of poly-Si thin-films with 2--5 mum grain size on glass substrates using in-situ and conventional aluminum-induced crystallization (AIC) and the development of a model for AIC process. In-situ AIC experiments were performed using Hot-Wire Chemical Vapor Deposition (HWCVD) both above and below the eutectic temperature (577°C) of Si-Al binary system. Conventional AIC experiments were performed using a-Si layers deposited on aluminum coated glass substrates by Electron-beam deposition, Plasma Enhanced Chemical Vapor Deposition (PECVD) and HWCVD. Continuous poly-Si films with an average grain size of 10 mum on glass substrates were achieved by both in-situ and conventional aluminum-induced crystallization of Si below eutectic temperature. The grain size was determined by three factors; the grain structure of Al layer, the nature of the interfacial oxide, and crystallization temperature. The interface oxide was found to be crucial for AIC process but not necessary for crystallization itself. The characterization of interfacial oxide layer formed on Al films revealed a bilayer structure containing Al2O3 and Al(OH)3 . The effective activation energy for AIC process was determined to be 0.9 eV and depended on the nature of the interfacial oxide layer. Poly-Si layers prepared by AIC technique can be used as seed layers for epitaxial growth of bulk Si layer or as back contacts in c-Si based solar cells.
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The strength and dislocation microstructure evolution in superalloy microcrystals
NASA Astrophysics Data System (ADS)
Hussein, Ahmed M.; Rao, Satish I.; Uchic, Michael D.; Parthasarathay, Triplicane A.; El-Awady, Jaafar A.
2017-02-01
In this work, the evolution of the dislocations microstructure in single crystal two-phase superalloy microcrystals under monotonic loading has been studied using the three-dimensional discrete dislocation dynamics (DDD) method. The DDD framework has been extended to properly handle the collective behavior of dislocations and their interactions with large collections of arbitrary shaped precipitates. Few constraints are imposed on the initial distribution of the dislocations or the precipitates, and the extended DDD framework can support experimentally-obtained precipitate geometries. Full tracking of the creation and destruction of anti-phase boundaries (APB) is accounted for. The effects of the precipitate volume fraction, APB energy, precipitate size, and crystal size on the deformation of superalloy microcrystals have been quantified. Correlations between the precipitate microstructure and the dominant deformation features, such as dislocation looping versus precipitate shearing, are also discussed. It is shown that the mechanical strength is independent of the crystal size, increases linearly with increasing the volume fraction, follows a near square-root relationship with the APB energy and an inverse square-root relationship with the precipitate size. Finally, the flow strength in simulations having initial dislocation pair sources show a flow strength that is about one half of that predicted from simulations starting with single dislocation sources. The method developed can be used, with minimal extensions, to simulate dislocation microstructure evolution in general multiphase materials.
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Mn Impurity in Bulk GaAs Crystals
NASA Astrophysics Data System (ADS)
Pawłowski, M.; Piersa, M.; Wołoś, A.; Palczewska, M.; Strzelecka, G.; Hruban, A.; Gosk, J.; Kamińska, M.; Twardowski, A.
2006-11-01
Magnetic and electron transport properties of GaAs:Mn crystals grown by Czochralski method were studied. Electron spin resonance showed the presence of Mn acceptor A in two charge states: singly ionized A- in the form of Mn2+(d5), and neutral A0 in the form of Mn2+(d5) plus a bound hole (h). It was possible to determine the relative concentration of both types of centers from intensity of the corresponding electron spin resonance lines. Magnetization measured as a function of magnetic field (up to 6 T) in the temperature range of 2-300 K revealed overall paramagnetic behavior of the samples. Effective spin was found to be about 1.5 value, which was consistent with the presence of two types of Mn configurations. In most of the studied samples the dominance of Mn2+(d5)+h configuration was established and it increased after annealing of native donors. The total value of Mn content was obtained from fitting of magnetization curves with the use of parameters obtained from electron spin resonance. In electron transport, two mechanisms of conductivity were observed: valence band transport dominated above 70 K, and hopping conductivity within Mn impurity band at lower temperatures. From the analysis of the hopping conductivity and using the obtained values of the total Mn content, the effective radius of Mn acceptor in GaAs was estimated as a = 11 ± 3 Å.
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Electron Scattering at Surfaces of Epitaxial Metal Layers
NASA Astrophysics Data System (ADS)
Chawla, Jasmeet Singh
In the field of electron transport in metal films and wires, the 'size effect' refers to the increase in the resistivity of the films and wires as their critical dimensions (thickness of film, width and height of wires) approach or become less than the electron mean free path lambda, which is, for example, 39 nm for bulk copper at room temperature. This size-effect is currently of great concern to the semiconductor industry because the continued downscaling of feature sizes has already lead to Cu interconnect wires in this size effect regime, with a reported 2.5 times higher resistivity for 40 nm wide Cu wires than for bulk Cu. Silver is a possible alternate material for interconnect wires and titanium nitride is proposed as a gate metal in novel field-effect-transistors. Therefore, it is important to develop an understanding of how the growth, the surface morphology, and the microstructure of ultrathin (few nanometers) Cu, Ag and TiN layers affect their electrical properties. This dissertation aims to advance the scientific knowledge of electron scattering at surfaces (external surfaces and grain boundaries), that are, the primary reasons for the size-effect in metal conductors. The effect of surface and grain boundary scattering on the resistivity of Cu thin films and nanowires is separately quantified using (i) in situ transport measurements on single-crystal, atomically smooth Cu(001) layers, (ii) textured polycrystalline Cu(111) layers and patterned wires with independently varying grain size, thickness and line width, and (iii) in situ grown interfaces including Cu-Ta, Cu-MgO, Cu-vacuum and Cu-oxygen. In addition, the electron surface scattering is also measured in situ for single-crystal Ag(001), (111) twinned epitaxial Ag(001), and single-crystal TiN(001) layers. Cu(001), Ag(001), and TiN(001) layers with a minimum continuous thickness of 4, 3.5 and 1.8 nm, respectively, are grown by ultra-high vacuum magnetron sputter deposition on MgO(001) substrates with and without thin epitaxial TiN(001) wetting layers and are studied for structure, crystalline quality, surface morphology, density and composition by a combination of x-ray diffraction theta-2theta scans, o-rocking curves, pole figures, reciprocal space mapping, Rutherford backscattering, x-ray reflectometry and transmission electron microscopy. The TiN(001) surface suppresses Cu and Ag dewetting, yielding lower defect density, no twinning, and smaller surface roughness than if grown on MgO(001). Textured polycrystalline Cu(111) layers 25-50-nm-thick are deposited on a stack of 7.5-nm-Ta on SiO2/Si(001), and subsequent in situ annealing at 350°C followed by sputter etching in Ar plasma yields Cu layers with independently variable thickness and grain size. Cu nanowires, 75 to 350 nm wide, are fabricated from Cu layers with different average grain size using a subtractive patterning process. In situ electron transport measurements at room temperature in vacuum and at 77 K in liquid nitrogen for single-crystal Cu and Ag layers is consistent with the Fuchs-Sondheimer (FS) model and indicates specular scattering at the metal-vacuum boundary with an average specularity parameter p = 0.8 and 0.6, respectively. In contrast, layers measured ex situ show diffuse surface scattering due to sub-monolayer oxidation. Also, addition of Ta atoms on Cu(001) surface perturbs the smooth interface potential and results in completely diffuse scattering at the Cu-Ta interface, and in turn, a higher resistivity of single-crystal Cu layers. In situ exposure of Cu(001) layers to O2 between 10 -3 and 105 Pa-s results in a sequential increase, decrease and increase of the electrical resistance which is attributed to specular surface scattering for clean Cu(001) and for surfaces with a complete adsorbed monolayer, but diffuse scattering at partial coverage and after chemical oxidation. Electron transport measurements for polycrystalline Cu layers and wires show a 10-15% and 7-9% decrease in resistivity, respectively, when increasing the average lateral grain size by a factor of 1.8. The maximum resistivity decrease that can be achieved by increasing the grain size of polycrystalline Cu layers with an average grain size approximately ˜2.5x the layer thickness is 20-26%.
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Tin induced a-Si crystallization in thin films of Si-Sn alloys
NASA Astrophysics Data System (ADS)
Neimash, V.; Poroshin, V.; Shepeliavyi, P.; Yukhymchuk, V.; Melnyk, V.; Kuzmich, A.; Makara, V.; Goushcha, A. O.
2013-12-01
Effects of tin doping on crystallization of amorphous silicon were studied using Raman scattering, Auger spectroscopy, scanning electron microscopy, and X-ray fluorescence techniques. Formation of silicon nanocrystals (2-4 nm in size) in the amorphous matrix of Si1-xSnx, obtained by physical vapor deposition of the components in vacuum, was observed at temperatures around 300 °C. The aggregate volume of nanocrystals in the deposited film of Si1-xSnx exceeded 60% of the total film volume and correlated well with the tin content. Formation of structures with ˜80% partial volume of the nanocrystalline phase was also demonstrated. Tin-induced crystallization of amorphous silicon occurred only around the clusters of metallic tin, which suggested the crystallization mechanism involving an interfacial molten Si:Sn layer.
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Novel ZIF-300 Mixed-Matrix Membranes for Efficient CO2 Capture.
Yuan, Jianwei; Zhu, Haipeng; Sun, Jiajia; Mao, Yangyang; Liu, Gongping; Jin, Wanqin
2017-11-08
Because of the high separation performance and easy preparation, mixed-matrix membranes (MMMs) consisting of metal-organic frameworks have received much attention. In this article, we report a novel ZIF-300/PEBA MMM consisting of zeolite imidazolate framework (ZIF-300) crystals and polyether block amide (PEBA) matrix. The ZIF-300 crystal size was effectively reduced by optimizing the hydrothermal reaction condition from ∼15 to ∼1 μm. The morphology and physicochemical and sorption properties of the synthesized ZIF-300 crystals and as-prepared ZIF-300/PEBA MMMs were systematically studied. The results showed that ZIF-300 crystals with a size of ∼1 μm maintained excellent preferential CO 2 sorption over N 2 without degradation of the crystal structure in the MMMs. As a result, uniformly incorporated ZIF-300 crystals highly enhanced both the CO 2 permeability and the CO 2 /N 2 selectivity of pure PEBA membrane. The optimized ZIF-300-PEBA MMMs with a ZIF-300 loading of 30 wt % exhibited a high and stable CO 2 permeability of 83 Barrer and CO 2 /N 2 selectivity of 84, which are 59.2% and 53.5% higher than pure PEBA membrane, respectively. The obtained performance surpassed the upper bound of state-of-the-art membranes for CO 2 /N 2 separation. This work demonstrated that the proposed ZIF-300/PEBA MMM could be a potential candidate for an efficient CO 2 capture process.
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Microstructural control and superconducting properties of YBCO melt textured single crystals
NASA Astrophysics Data System (ADS)
Jongprateep, Oratai
The high temperature superconductor has great potential for practical applications such as superconducting energy storage systems. Since the levitation force, required specifically for these applications, largely depends on the critical current density and loop size of the superconducting current, large-sized single crystals with high critical current density are desired. To achieve the goal in fabricating YBa2Cu3O 7-delta (Y123) samples suitable for the applications, detailed and systematic studies are required to gain further understanding of the crystal growth and flux pinning mechanisms. This research is aimed at constituting a contribution to the knowledge base for the Y123 high temperature superconductor field by extending the study of processing conditions involved in controlling the microstructure of the Y123 superconductors for the enhancement of crystal growth and superconductor properties. Relations among processing parameters, microstructure, crystal growth, and critical current density of Y123 superconductors have been established. The experimental results reveal that low heating rate and short holding time can lead to refinement of Y2BaCuO5 (Y211) particles, which is strongly favorable to enhancement of the crystal growth and electrical properties of the Y123 superconductors. It was observed that relatively large Y123 crystals (17-22 mm in size) can be obtained with fine needle-shaped Y211 particles, processed with low heating rate and short holding time at the maximum temperatures. Additionally, the research also formulated a technique to fabricate Y123 superconductors with improved electrical properties required for the practical applications. By incorporating additives such as BaCeO3, BaSnO 3, Pt and Nd2O3 into Y123 superconductors, refinement of Y211 particles occurs. In addition, secondary phase particles with sizes in sub-micrometer and nanometer range can be formed in the Y123 superconductors. The interfaces between the Y123 matrix and these Y211 or secondary phase particles are believed to act as flux pinning sites and to enhance the critical current density (Jc) in the superconductor. The results showed that formation of secondary phase inclusions in Y123 by doping with BaCeO3, BaSnO 3, Pt or Nd2O3 result in enhancement of J c due to the effective flux pinning.
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Saadi, S; Ariffin, A A; Ghazali, H M; Miskandar, M S; Abdulkarim, S M; Boo, H C
2011-01-01
The ability of palm oil (PO) to crystallize as beta prime polymorph has made it an attractive option for the production of margarine fat (MF). Palm stearin (PS) expresses similar crystallization behavior and is considered one of the best substitutes of hydrogenated oils due to its capability to impart the required level of plasticity and body to the finished product. Normally, PS is blended with PO to reduce the melting point at body temperature (37 °C). Lipid phase, formulated by PO and PS in different ratios were subjected to an emulsification process and the following analyses were done: triacylglycerols, solid fat content (SFC), and thermal behavior. In addition, the microstructure properties, including size and number of crystals, were determined for experimental MFs (EMFs) and commercial MFs (CMFs). Results showed that blending and emulsification at PS levels over 40 wt% significantly changed the physicochemical and microstructure properties of EMF as compared to CMF, resulting in a desirable dipalmitoyl-oleoyl-glycerol content of less than 36.1%. SFC at 37 °C, crystal size, crystal number, crystallization, and melting enthalpies (ΔH) were 15%, 5.37 μm, 1425 crystal/μm(2), 17.25 J/g, and 57.69J/g, respectively. All data reported indicate that the formation of granular crystals in MFs was dominated by high-melting triacylglycerol namely dipalmitoyl-oleoyl-glycerol, while the small dose of monoacylglycerol that is used as emulsifier slowed crystallization rate. Practical Application: Most of the past studies were focused on thermal behavior of edible oils and some blends of oils and fats. The crystallization of oils and fats are well documented but there is scarce information concerning some mechanism related to crystallization and emulsification. Therefore, this study will help to gather information on the behavior of emulsifier on crystallization regime; also the dominating TAG responsible for primary granular crystal formations, as well as to determine the best level of stearin to impart the required microstructure properties and body to the finished products.
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Inference of Ice Cloud Properties from High-spectral Resolution Infrared Observations. Appendix 4
NASA Technical Reports Server (NTRS)
Huang, Hung-Lung; Yang, Ping; Wei, Heli; Baum, Bryan A.; Hu, Yongxiang; Antonelli, Paolo; Ackerman, Steven A.
2005-01-01
The theoretical basis is explored for inferring the microphysical properties of ice crystal from high-spectral resolution infrared observations. A radiative transfer model is employed to simulate spectral radiances to address relevant issues. The extinction and absorption efficiencies of individual ice crystals, assumed as hexagonal columns for large particles and droxtals for small particles, are computed from a combination of the finite- difference time-domain (FDTD) technique and a composite method. The corresponding phase functions are computed from a combination of FDTD and an improved geometric optics method (IGOM). Bulk scattering properties are derived by averaging the single- scattering properties of individual particles for 30 particle size distributions developed from in situ measurements and for additional four analytical Gamma size distributions for small particles. The non-sphericity of ice crystals is shown to have a significant impact on the radiative signatures in the infrared (IR) spectrum; the spherical particle approximation for inferring ice cloud properties may result in an overest&ation of the optical thickness and an inaccurate retrieval of effective particle size. Furthermore, we show that the error associated with the use of the Henyey-Greenstein phase function can be as larger as 1 K in terms of brightness temperature for larger particle effective size at some strong scattering wavenumbers. For small particles, the difference between the two phase functions is much less, with brightness temperatures generally differing by less than 0.4 K. The simulations undertaken in this study show that the slope of the IR brightness temperature spectrum between 790-960/cm is sensitive to the effective particle size. Furthermore, a strong sensitivity of IR brightness temperature to cloud optical thickness is noted within the l050-1250/cm region. Based on this spectral feature, a technique is presented for the simultaneous retrieval of the visible optical thickness and effective particle size from high spectral resolution infrared data under ice cloudy con&tion. The error analysis shows that the uncertainty of the retrieved optical thickness and effective particle size has a small range of variation. The error for retrieving particle size in conjunction with an uncertainty of 5 K in cloud'temperature, or a surface temperature uncertainty of 2.5 K, is less than 15%. The corresponding e m r in the uncertainty of optical thickness is within 5-2096, depending on the value of cloud optical thickness. The applicability of the technique is demonstrated using the aircraft-based High- resolution Interferometer Sounder (HIS) data from the Subsonic Aircraft: Contrail and Cloud Effects Special Study (SUCCESS) in 1996 and the First ISCCP Regional Experiment - Arctic Clouds Experiment (FIRE-ACE) in 1998.
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The Effect of Solution Thermal History on Chicken Egg White Lysozyme Nucleation
NASA Technical Reports Server (NTRS)
Burke, Michael W.; Judge, Russell A.; Pusey, Marc L.
2001-01-01
Proteins are highly flexible molecules and often exhibit defined conformational changes in response to changes in the ambient temperature. Chicken egg white lysozyme has been previously shown to undergo an apparent structural change when warmed above the tetragonal/orthorhombic phase transition temperature. This is reflected by a change in the habit of the tetragonal and orthorhombic crystals so formed. In this study, we show that possible conformational changes induced by heating are stable and apparently non-reversible by simple cooling. Exposure of protein solutions to temperatures above the phase change transition temperature, before combining with precipitant solution to begin crystallization, reduces final crystal numbers. Protein that is briefly warmed to 37 C, then cooled shows no sign of reversal to the unheated nucleation behavior even after storage for four weeks at 4 C. The change in nucleation behavior of tetragonal lysozyme crystals, attributed to a structural shift, occurs faster the greater the exposure to temperature above the equi-solubility point for the two phases. Heating for 2 hours at 48 C reduces crystal numbers by 20 fold in comparison to the same solution heated for the same time at 30 C. Thermal treatment of solutions is therefore a possible tool to reduce crystal numbers and increase crystal size. The effects of a protein's previous thermal history are now shown to be a potentially critical factor in subsequent macromolecule crystal nucleation and growth studies.
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The Effect of Solution Thermal History on Chicken Egg White Lysozyme Nucleation
NASA Technical Reports Server (NTRS)
Burke, Michael W.; Judge, Russell A.; Pusey, Marc L.; Rose, M. Franklin (Technical Monitor)
2000-01-01
Proteins are highly flexible molecules and often exhibit defined conformational changes in response to changes in the ambient temperature. Chicken egg white lysozyme has been previously shown to undergo an apparent structural change when warmed above the tetragonal/orthorhombic phase transition temperature. This is reflected by a change in the habit of the tetragonal and orthorhombic crystals so formed. In this study we show that possible conformational changes induced by heating are stable and apparently non- reversible by simple cooling. Exposure of protein solutions to temperatures above the phase change transition temperature, before combining with precipitant solution to begin crystallization, reduces final crystal numbers. Protein that is briefly warmed to 37 C, then cooled shows no sign of reversal to the unheated nucleation behavior even after storage for 4 weeks at 4 C. The change in nucleation behavior of tetragonal lysozyme crystals, attributed to a structural shift, occurs faster the greater the exposure to temperature above the equi-solubility point for the two phases. Heating for 2 h at 48 C reduces crystal numbers by 20 fold in comparison to the same solution heated for the same time at 30 C. Thermal treatment of solutions is therefore a possible tool to reduce crystal numbers and increase crystal size. The effects of a protein's previous thermal history are now shown to be a potentially critical factor in subsequent macromolecule crystal nucleation and growth studies.
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Crystalline silicon growth in nickel/a-silicon bilayer
NASA Astrophysics Data System (ADS)
Mohiddon, Md Ahamad; Naidu, K. Lakshun; Dalba, G.; Rocca, F.; Krishna, M. Ghanashyam
2013-02-01
The effect of substrate temperature on amorphous Silicon crystallization, mediated by metal impurity is reported. Bilayers of Ni(200nm)/Si(400nm) are deposited on fused silica substrate by electron beam evaporator at 200 and 500 °C. Raman mapping shows that, 2 to 5 micron size crystalline silicon clusters are distributed over the entire surface of the sample. X-ray diffraction and X-ray absorption spectroscopy studies demonstrate silicon crystallizes over the metal silicide seeds and grow with the annealing temperature.
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Yamaya, Taiga; Mitsuhashi, Takayuki; Matsumoto, Takahiro; Inadama, Naoko; Nishikido, Fumihiko; Yoshida, Eiji; Murayama, Hideo; Kawai, Hideyuki; Suga, Mikio; Watanabe, Mitsuo
2011-11-07
We are developing a novel, general purpose isotropic-3D PET detector X'tal cube which has high spatial resolution in all three dimensions. The research challenge for this detector is implementing effective detection of scintillation photons by covering six faces of a segmented crystal block with silicon photomultipliers (SiPMs). In this paper, we developed the second prototype of the X'tal cube for a proof-of-concept. We aimed at realizing an ultimate detector with 1.0 mm(3) cubic crystals, in contrast to our previous development using 3.0 mm(3) cubic crystals. The crystal block was composed of a 16 × 16 × 16 array of lutetium gadolinium oxyorthosilicate (LGSO) crystals 0.993 × 0.993 × 0.993 mm(3) in size. The crystals were optically glued together without inserting any reflector inside and 96 multi-pixel photon counters (MPPCs, S10931-50P, i.e. six faces each with a 4 × 4 array of MPPCs), each having a sensitive area of 3.0 × 3.0 mm(2), were optically coupled to the surfaces of the crystal block. Almost all 4096 crystals were identified through Anger-type calculation due to the finely adjusted reflector sheets inserted between the crystal block and light guides. The reflector sheets, which formed a belt of 0.5 mm width, were placed to cover half of the crystals of the second rows from the edges in order to improve identification performance of the crystals near the edges. Energy resolution of 12.7% was obtained at 511 keV with almost uniform light output for all crystal segments thanks to the effective detection of the scintillation photons.
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Solution Growth of a Novel Nonlinear Optical Material: L-Histidine Tetrafluoroborate
NASA Technical Reports Server (NTRS)
Aggarwal, M. D.; Choi, J.; Wang, W. S.; Bhat, K.; Lal, R. B.; Shields, Angela D.; Penn, Benjamin G.; Frazier, Donald O.
1998-01-01
Single crystals of L-Histidine tetrafluoroborate (L-HFB), a semiorganic nonlinear optical (NLO) material have been successfully grown by the temperature lowering and evaporation methods in our laboratory. Solubility curves of L-HFB have been determined in different solvents, such as water, ethanol and acetone. The solubility of L-HFB is very low in acetone, and ethanol, therefore, it is not feasible to grow L-HFB single crystals using these solvents. Good quality single crystals of a novel nonlinear optical material L-HFB have been grown from aqueous solution. Effects of seed orientation on morphologies of L-HFB crystals were studied. The advantages and disadvantage of both the evaporation and the temperature lowering techniques are compared. The single crystals in size 20 x 20 x 10 cubic mm were grown with deionized water as solvent in two weeks with an approximate growth rate of 1.4mm/day. The transmission range for these crystals has been found to be from 250 nm to 1500 nm.
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Li, Gang; Chen, Qiang; Li, Junjun; Hu, Xiaojian; Zhao, Jianlong
2010-06-01
A centrifuge-based microfluidic system has been developed that enables automated high-throughput and low-volume protein crystallizations. In this system, protein solution was automatically and accurately metered and dispensed into nanoliter-sized multiple reaction chambers, and it was mixed with various types of precipitants using a combination of capillary effect and centrifugal force. It has the advantages of simple fabrication, easy operation, and extremely low waste. To demonstrate the feasibility of this system, we constructed a chip containing 24 units and used it to perform lysozyme and cyan fluorescent protein (CyPet) crystallization trials. The results demonstrate that high-quality crystals can be grown and harvested from such a nanoliter-volume microfluidic system. Compared to other microfluidic technologies for protein crystallization, this microfluidic system allows zero waste, simple structure and convenient operation, which suggests that our microfluidic disk can be applied not only to protein crystallization, but also to the miniaturization of various biochemical reactions requiring precise nanoscale control.
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Boonna, Sureeporn; Tongta, Sunanta
2018-07-01
Structural transformation of crystallized debranched cassava starch prepared by temperature cycling (TC) treatment and then subjected to annealing (ANN), heat-moisture treatment (HMT) and dual hydrothermal treatments of ANN and HMT was investigated. The relative crystallinity, lateral crystal size, melting temperature and resistant starch (RS) content increased for all hydrothermally treated samples, but the slowly digestible starch (SDS) content decreased. The RS content followed the order: HMT → ANN > HMT > ANN → HMT > ANN > TC, respectively. The HMT → ANN sample showed a larger lateral crystal size with more homogeneity, whereas the ANN → HMT sample had a smaller lateral crystal size with a higher melting temperature. After cooking at 50% moisture, the increased RS content of samples was observed, particularly for the ANN → HMT sample. These results suggest that structural changes of crystallized debranched starch during hydrothermal treatments depend on initial crystalline characteristics and treatment sequences, influencing thermal stability, enzyme digestibility, and cooking stability. Copyright © 2018 Elsevier Ltd. All rights reserved.
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Analysis of stochastic crystallization in micron-sized droplets of undercooled liquid l-arabitol.
Guinet, Yannick; Carpentier, Laurent; Paccou, Laurent; Derollez, Patrick; Hédoux, Alain
2016-11-29
Kinetics of isothermal crystallization of l-arabitol were analyzed from the undercooled liquid state within micron-sized droplets from micro-Raman spectroscopy. This study reveals that crystallization slightly above T g is controlled by stochastic heterogeneous nucleation inherent to the droplet size. Microscopic Raman investigations performed in droplets give the unique opportunity to analyze the pure metastable Form II of l-arabitol. It was found that Form II is characterized by a molecular packing more compact than that of the stable Form I, inherent to strong intermolecular hydrogen bonding. Kinetics laws obtained by analyzing several droplets at different temperatures, reveal the transient character of Form II, quasi systematically detected during the crystallization process of form I. Form II appears as the first step of crystallization prior to successive short-living metastable states which is necessary to achieve a complete crystallization in Form I. It was found that the kinetics of conversion between the metastable states (Form II) into Form I is dependent on the amount of strong hydrogen bonding distinctive of Form II. Copyright © 2016 Elsevier Ltd. All rights reserved.
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NASA Astrophysics Data System (ADS)
Shao, Hui; Chen, Jingjing; Chen, Xia; Leng, Yixin; Zhong, Jing
2015-04-01
An experimental design was applied to the synthesis of AlPO4-21 molecular sieve (AWO structure) by vapor phase transport (VPT) method, using tetramethylguanidine (TMG) as the template. In this study, the effects of crystallization time, crystallization temperature, phosphor content, template content and water content in the synthesis gel were investigated. The materials obtained were characterized by X-ray diffraction, scanning electron microscopy and fourier transform infrared spectroscopy (FT-IR). Microstructural analysis of the crystal growth in vapor synthetic conditions revealed a revised crystal growth route from zeolite AlPO4-21 to AlPO4-15 in the presence of the TMG. Homogenous hexagonal prism AlPO4-21 crystals with size of 7 × 3 μm were synthesized at a lower temperature (120 °C), which were completely different from the typical tabular parallelogram crystallization microstructure of AlPO4-21 phase. The crystals were transformed into AlPO4-21 phase with higher crystallization temperature, longer crystallization time, higher P2O5/Al2O3 ratio and higher TMG/Al2O3 ratio.
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Ash, B J; Worsfold, S R; Vukusic, P; Nash, G R
2017-08-02
Surface acoustic wave (SAW) devices are widely used for signal processing, sensing and increasingly for lab-on-a-chip applications. Phononic crystals can control the propagation of SAW, analogous to photonic crystals, enabling components such as waveguides and cavities. Here we present an approach for the realisation of robust, tailorable SAW phononic crystals, based on annular holes patterned in a SAW substrate. Using simulations and experiments, we show that this geometry supports local resonances which create highly attenuating phononic bandgaps at frequencies with negligible coupling of SAWs into other modes, even for relatively shallow features. The enormous bandgap attenuation is up to an order-of-magnitude larger than that achieved with a pillar phononic crystal of the same size, enabling effective phononic crystals to be made up of smaller numbers of elements. This work transforms the ability to exploit phononic crystals for developing novel SAW device concepts, mirroring contemporary progress in photonic crystals.The control and manipulation of propagating sound waves on a surface has applications in on-chip signal processing and sensing. Here, Ash et al. deviate from standard designs and fabricate frequency tailorable phononic crystals with an order-of-magnitude increase in attenuation.
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Agrawal, Ravi; Espinosa, Horacio D
2011-02-09
Nanowires made of materials with noncentrosymmetric crystal structure are under investigation for their piezoelectric properties and suitability as building blocks for next-generation self-powered nanodevices. In this work, we investigate the size dependence of piezoelectric coefficients in nanowires of two such materials - zinc oxide and gallium nitride. Nanowires, oriented along their polar axis, ranging from 0.6 to 2.4 nm in diameter were modeled quantum mechanically. A giant piezoelectric size effect is identified for both GaN and ZnO nanowires. However, GaN exhibits a larger and more extended size dependence than ZnO. The observed size effect is discussed in the context of charge redistribution near the free surfaces leading to changes in local polarization. The study reveals that local changes in polarization and reduction of unit cell volume with respect to bulk values lead to the observed size effect. These results have strong implication in the field of energy harvesting, as piezoelectric voltage output scales with the piezoelectric coefficient.
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Nasi, Sonia; Ea, Hang-Korng; Lioté, Frédéric; So, Alexander; Busso, Nathalie
2016-01-01
Objectives Calcium-containing crystals participate in the pathogenesis of OA. Sodium thiosulfate (STS) has been shown to be an effective treatment in calcification disorders such as calciphylaxis and vascular calcification. This study investigated the effects and mechanisms of action of STS in a murine model of OA and in chondrocyte calcification. Methods Hydroxyapatite (HA) crystals-stimulated murine chondrocytes and macrophages were treated with STS. Mineralization and cellular production of IL-6, MCP-1 and reactive oxygen species (ROS) were assayed. STS's effects on genes involved in calcification, inflammation and cartilage matrix degradation were studied by RT-PCR. STS was administered in the menisectomy model of murine OA, and the effect on periarticular calcific deposits and cartilage degeneration was investigated by micro-CT-scan and histology. Results In vitro, STS prevented in a dose-dependent manner calcium crystal deposition in chondrocytes and inhibited Annexin V gene expression. In addition, there was a reduction in crystal-induced IL-6 and MCP-1 production. STS also had an antioxidant effect, diminished HA-induced ROS generation and abrogated HA-induced catabolic responses in chondrocytes. In vivo, administration of STS reduced the histological severity of OA, by limiting the size of new periarticular calcific deposits and reducing the severity of cartilage damage. Conclusions STS reduces the severity of periarticular calcification and cartilage damage in an animal model of OA via its effects on chondrocyte mineralization and its attenuation of crystal-induced inflammation as well as catabolic enzymes and ROS generation. Our study suggests that STS may be a disease-modifying drug in crystal-associated OA. PMID:27391970
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Nasi, Sonia; Ea, Hang-Korng; Lioté, Frédéric; So, Alexander; Busso, Nathalie
2016-01-01
Calcium-containing crystals participate in the pathogenesis of OA. Sodium thiosulfate (STS) has been shown to be an effective treatment in calcification disorders such as calciphylaxis and vascular calcification. This study investigated the effects and mechanisms of action of STS in a murine model of OA and in chondrocyte calcification. Hydroxyapatite (HA) crystals-stimulated murine chondrocytes and macrophages were treated with STS. Mineralization and cellular production of IL-6, MCP-1 and reactive oxygen species (ROS) were assayed. STS's effects on genes involved in calcification, inflammation and cartilage matrix degradation were studied by RT-PCR. STS was administered in the menisectomy model of murine OA, and the effect on periarticular calcific deposits and cartilage degeneration was investigated by micro-CT-scan and histology. In vitro, STS prevented in a dose-dependent manner calcium crystal deposition in chondrocytes and inhibited Annexin V gene expression. In addition, there was a reduction in crystal-induced IL-6 and MCP-1 production. STS also had an antioxidant effect, diminished HA-induced ROS generation and abrogated HA-induced catabolic responses in chondrocytes. In vivo, administration of STS reduced the histological severity of OA, by limiting the size of new periarticular calcific deposits and reducing the severity of cartilage damage. STS reduces the severity of periarticular calcification and cartilage damage in an animal model of OA via its effects on chondrocyte mineralization and its attenuation of crystal-induced inflammation as well as catabolic enzymes and ROS generation. Our study suggests that STS may be a disease-modifying drug in crystal-associated OA.
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Actinide/beryllium neutron sources with reduced dispersion characteristics
Schulte, Louis D.
2012-08-14
Neutron source comprising a composite, said composite comprising crystals comprising BeO and AmBe.sub.13, and an excess of beryllium, wherein the crystals have an average size of less than 2 microns; the size distribution of the crystals is less than 2 microns; and the beryllium is present in a 7-fold to a 75-fold excess by weight of the amount of AmBe.sub.13; and methods of making thereof.
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Kevorkyants, Ruslan; Wang, Xiqiao; Close, David M; Pavanello, Michele
2013-11-14
We present an application of the linear scaling frozen density embedding (FDE) formulation of subsystem DFT to the calculation of isotropic hyperfine coupling constants (hfcc's) of atoms belonging to a guanine radical cation embedded in a guanine hydrochloride monohydrate crystal. The model systems range from an isolated guanine to a 15,000 atom QM/MM cluster where the QM region is comprised of 36 protonated guanine cations, 36 chlorine anions, and 42 water molecules. Our calculations show that the embedding effects of the surrounding crystal cannot be reproduced by small model systems nor by a pure QM/MM procedure. Instead, a large QM region is needed to fully capture the complicated nature of the embedding effects in this system. The unprecedented system size for a relativistic all-electron isotropic hfcc calculation can be approached in this work because the local nature of the electronic structure of the organic crystals considered is fully captured by the FDE approach.
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Influence of diffusion and convective transport on dendritic growth in dilute alloys
NASA Technical Reports Server (NTRS)
Glicksman, M. E.; Singh, N. B.; Chopra, M.
1982-01-01
Experimentation has been carried out in which the kinetics and morphology of dendritic growth were measured as a function of thermal supercooling, solute concentration, and spatial orientation of the dendritic growth axis. The crystal growth system studied is succinonitrile, NC(CH2)2CN, with additions of argon (up to 0.1 mole percent). This system is especially useful as a model for alloy studies because kinetic data are available for high purity (7-9's) succinonitrile. The influence of the solute, at fixed thermal supercooling, is to increase the growth velocity and correspondingly decrease intrinsic crystal dimensions. Morphological measurements are described in detail relating tip size, perturbation wavelength, supercooling, and solute concentration. The analysis of these effects based on morphological stability theory is also discussed, and experiments permitting the separation of convective and diffusive heat transport during crystal growth of succinonitrile are described. The studies underscore the importance of gravitationally-induced buoyancy effects on crystal growth.
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Controlling ZIF-67 crystals formation through various cobalt sources in aqueous solution
DOE Office of Scientific and Technical Information (OSTI.GOV)
Guo, Xiangli; Jiangsu Key Laboratory of Advanced Metallic Materials, Nanjing 211189; Xing, Tiantian
2016-03-15
Zeolitic imidazolate frameworks ZIF-67 were prepared under hydrothermal (120 °C) and non-hydrothermal (room temperature) from various cobalt sources and 2-methylimidazolate (Hmim) in aqueous solution within 30 min. The particle size and morphology were found to be related to the reactivity of the cobalt salt, Hmim/Co{sup 2+} molar ratios and experimental condition. Using Co(NO{sub 3}){sub 2} as cobalt source, small-sized ZIF-67 crystals with agglomeration were formed. For CoCl{sub 2}, small-sized rhombic dodecahedron were obtained. While large-sized crystals of rhombic dodecahedron structure were obtained from CoSO{sub 4} and Co(OAc){sub 2}. Under hydrothermal condition, the size of ZIF-67 crystals tended to be moremore » uniform and the morphology were more regular comparing to non-hydrothermal condition. This study provides a simple way to control the size and morphology of ZIF-67 crystals prepared in aqueous solution. - Graphical abstract: Zeolitic imidazolate frameworks ZIF-67 were prepared under hydrothermal (120 °C) and non-hydrothermal (room temperature) from four different cobalt sources (Co(NO{sub 3}){sub 2}, CoCl{sub 2}, CoSO{sub 4} and Co(OAc){sub 2}) in aqueous solution within 30 min. The particle size and morphology were found to be related to the reactivity of the cobalt salt, Hmim/Co{sup 2+} molar ratios and experimental condition. - Highlights: • The particle size and morphology were determined by the reactivity of cobalt salt. • ZIF-67 could be prepared from CoSO{sub 4} and Co(OAc){sub 2} at Hmim/Co{sup 2+} molar ratio of 10. • Uniform and regular particles were obtained under hydrothermal condition.« less
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Cai, Fei; Jiang, Chuanhai, E-mail: chuanhaijiang1963@163.com; Zhao, Yuantao
2015-05-15
Highlights: • The novel NiCo–Zr coatings were prepared by electro-deposition. • Surface morphology, crystal structure, grain size and microstrain were examined. • Texture, residual stress and corrosion resistance were investigated. • Addition of Co increased the hardness and corrosion resistance of the coatings. - Abstract: In this study, the NiCo–Zr composite coatings were prepared from the electrolytes with different Co{sup 2+} concentrations by electrodeposition method. The effects of Co contents on the crystal structure, surface morphology, grain size, microstrain and residual stress were examined by X-ray diffractometer (XRD), field emission scanning electron microscopy (FESEM), Energy dispersive X-ray spectroscopy (EDX) andmore » atomic force microscope (AFM). The corrosion resistance of the composite coatings was also examined by the potentiodynamic polarization and electrochemical impedance (EIS) measurements. The results revealed that the crystal structures of the coatings were dependent on the Co contents and addition of Co content of 58 wt% resulted in the formation of hexagonal (hcp) Co. The increasing Co contents in the NiCo–Zr composite coatings resulted in the smoother and more compact surface, decreased the grain size and increased the microstrain. The micro-hardness and residual stress also increased with increasing Co contents. The addition of Co increased the corrosion resistance of the NiCo–Zr composite coatings compared with the Ni–Zr coating while the corrosion resistance of the NiCo–Zr composite coatings decreased as the Co contents increased.« less
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Gradient and size effects on spinodal and miscibility gaps
NASA Astrophysics Data System (ADS)
Tsagrakis, Ioannis; Aifantis, Elias C.
2018-05-01
A thermodynamically consistent model of strain gradient elastodiffusion is developed. Its formulation is based on the enhancement of a robust theory of gradient elasticity, known as GRADELA, to account for a Cahn-Hilliard type of diffusion. Linear stability analysis is employed to determine the influence of concentration and strain gradients on the spinodal decomposition. For finite domains, spherically symmetric conditions are considered, and size effects on spinodal and miscibility gaps are discussed. The theoretical predictions are in agreement with the experimental trends, i.e., both gaps shrink as the grain diameter decreases and they are completely eliminated for crystals smaller than a critical size.
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ERIC Educational Resources Information Center
Lange, Catherine
2008-01-01
In this inquiry-based, integrative art and science activity, Grade 5-8 students use multicolored Epsom salt (magnesium sulfate) crystallizing solutions to reveal beautiful, cylindrical, 3-dimensional, needle-shaped structures. Through observations of the crystal art, students analyze factors that contribute to crystal size and formation, compare…
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Low field magnetocaloric effect in bulk and ribbon alloy La(Fe0.88Si0.12)13
NASA Astrophysics Data System (ADS)
Vuong, Van-Hiep; Do-Thi, Kim-Anh; Nguyen, Duy-Thien; Nguyen, Quang-Hoa; Hoang, Nam-Nhat
2018-03-01
Low-field magnetocaloric effect occurred in itinerant metamagnetic materials is at core for magnetic cooling application. This works reports the magnetocaloric responses obtained at 1.35 T for the silicon-doped iron-based binary alloy La(Fe0.88Si0.12)13 in the bulk and ribbon form. Both samples possess a same symmetry but with different crystallite sizes and lattice parameters. The ribbon sample shows a larger maximum entropy change (nearly 8.5 times larger) and a higher Curie temperature (5 K higher) in comparison with that of the bulk sample. The obtained relative cooling power for the ribbon is also larger and very promising for application (RCP = 153 J/kg versus 25.2 J/kg for the bulk). The origin of the effect observed is assigned to the occurrence of negative magnetovolume effect in the ribbon structure with limit crystallization, caused by rapid cooling process at the preparation, which induced smaller crystallite size and large lattice constant at the overall weaker local crystal field.
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NASA Astrophysics Data System (ADS)
Dalton, D. A.; Worthington, D. L.; Sherek, P. A.; Pedrazas, N. A.; Quevedo, H. J.; Bernstein, A. C.; Rambo, P.; Schwarz, J.; Edens, A.; Geissel, M.; Smith, I. C.; Taleff, E. M.; Ditmire, T.
2011-11-01
Experiments investigating fracture and resistance to plastic deformation at fast strain rates (>106 s-1) were performed via laser ablation on thin sheets of aluminum and aluminum alloys. Single crystal high purity aluminum (Al-HP) and a single crystal 1100 series aluminum alloy (AA1100) were prepared to investigate the role of impurity particles. Specimens of aluminum alloy +3 wt. % Mg (Al+3Mg) at three different grain sizes were also studied to determine the effect of grain size. In the present experiments, high purity aluminum (Al-HP) exhibited the highest spall strength over 1100 series aluminum alloy (AA1100) and Al+3Mg. Fracture characterization and particle analysis revealed that fracture was initiated in the presence of particles associated with impurity content in the AA1100 and at both grain boundaries and particles in Al+3Mg. The Al+3Mg specimens exhibited the greatest resistance to plastic deformation likely resulting from the presence of magnesium atoms. The Al-HP and AA1100, both lacking a strengthening element such as Mg, were found to have the same Hugoniot elastic limit (HEL) stress. Within the single crystal specimens, orientation effects on spall strength and HEL stress appear to be negligible. Although the fracture character shows a trend with grain size, no clear dependence of spall strength and HEL stress on grain size was measured for the Al+3Mg. Hydrodynamic simulations show how various strength and fracture models are insufficient to predict material behavior at fast strain rates, and a revised set of Tuler-Butcher coefficients for spall are proposed.
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Sakamoto, Takeshi; Nagao, Daisuke; Noba, Masahiro; Ishii, Haruyuki; Konno, Mikio
2014-06-24
Submicrometer-sized amorphous titania spheres incorporating Au nanoparticles (NPs) were prepared in a one-pot synthesis consisting of a sol-gel reaction of titanium(IV) isopropoxide in the presence of chloroauric acid and a successive reduction with sodium borohydride in a mixed solvent of ethanol/acetonitrile. The synthesis was allowed to prepare monodisperse titania spheres that homogeneously incorporated Au NPs with sizes of ca. 7 nm. The Au NP-loaded titania spheres underwent different crystallization processes, including 500 °C calcination in air, high-temperature hydrothermal treatment (HHT), and/or low-temperature hydrothermal treatment (LHT). Photocatalytic experiments were conducted with the Au NP-loaded crystalline titania spheres under irradiation of UV and visible light. A combined process of LHT at 80 °C followed by calcination at 500 °C could effectively crystallize titania spheres maintaining the dispersion state of Au NPs, which led to photocatalytic activity higher than that of commercial P25 under UV irradiation. Under visible light irradiation, the Au NP-titania spheres prepared with a crystallization process of LHT at 80 °C for 6 h showed photocatalytic activity much higher than a commercial product of visible light photocatalyst. Structure analysis of the visible light photocatalysts indicates the importance of prevention of the Au NPs aggregation in the crystallization processes for enhancement of photocatalytic activity.
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Choudhary, Muhammad Ajmal; Kundin, Julia; Emmerich, Heike; Oettel, Martin
2014-08-01
Phase-field-crystal (PFC) modeling has emerged as a computationally efficient tool to address crystal growth phenomena on atomistic length and diffusive time scales. We use a two-dimensional phase-field-crystal model for a binary system based on Elder et al. [Phys. Rev. B 75, 064107 (2007)] to study critical nuclei and their liquid-solid phase boundaries, in particular the nucleus size dependence of the liquid-solid interface tension as well as of the nucleation barrier. Critical nuclei are stabilized in finite systems of various sizes, however, the extracted interface tension as function of the nucleus radius r is independent of system size. We suggest a phenomenological expression to describe the dependence of the extracted interface tension on the nucleus radius r for the liquid-solid system. Moreover, the numerical PFC results show that this dependency can not be fully described by the nonclassical Tolman formula.
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GCSS Cirrus Parcel Model Comparison Project
NASA Technical Reports Server (NTRS)
Lin, Ruei-Fong; Starr, David OC.; DeMott, Paul J.; Cotton, Richard; Jensen, Eric; Sassen, Kenneth; Einaudi, Franco (Technical Monitor)
2000-01-01
The Cirrus Parcel Model Comparison Project, a project of GCSS Working Group on Cirrus Cloud Systems (WG2), involves the systematic comparison of current models of ice crystal nucleation and growth for specified, typical, cirrus cloud environments. The goal of this project is to document and understand the factors resulting in significant inter-model differences. The intent is to foment research leading to model improvement and validation. In Phase 1 of the project reported here, simulated cirrus cloud microphysical properties are compared for situations of "warm" (-40 C) and "cold" (-60 C) cirrus subject to updrafts of 4, 20 and 100 cm/s, respectively. Five models participated. These models employ explicit microphysical schemes wherein the size distribution of each class of particles (aerosols and ice crystals) is resolved into bins. Simulations are made including both homogeneous and heterogeneous ice nucleation mechanisms. A single initial aerosol population of sulfuric acid particles is prescribed for all simulations. To isolate the treatment of the homogeneous freezing (of haze drops) nucleation process, the heterogeneous nucleation mechanism is disabled for a second parallel set of simulations. Qualitative agreement is found for the homogeneous-nucleation-only simulations, e.g., the number density of nucleated ice crystals increases with the strength of the prescribed updraft. However, non-negligible quantitative differences are found. Detailed analysis reveals that the homogeneous nucleation formulation, aerosol size, ice crystal growth rate (particularly the deposition coefficient), and water vapor uptake rate are critical components that lead to differences in predicted microphysics. Systematic bias exists between results based on a modified classical theory approach and models using an effective freezing temperature approach to the treatment of nucleation. Each approach is constrained by critical freezing data from laboratory studies, but each includes assumptions that can only be justified by further laboratory data. Consequently, it is not yet clear if the two approaches can be made consistent. Large haze particles may deviate considerably from equilibrium size in moderate to strong updrafts (20-100 cm/s) at -60 C when the commonly invoked equilibrium assumption is lifted. The resulting difference in particle-size-dependent solution concentration of haze particles may significantly affect the ice nucleation rate during the initial nucleation interval. The uptake rate for water vapor excess by ice crystals is another key component regulating the total number of nucleated ice crystals. This rate, the product of ice number concentration and ice crystal diffusional growth rate, which is sensitive to the deposition coefficient when ice particles are small, partially controls the peak nucleation rate achieved in an air parcel and the duration of the active nucleation time period. The effects of heterogeneous nucleation are most pronounced in weak updraft situations. Vapor competition by the nucleated (heterogeneous) ice crystals limits the achieved ice supersaturation and thus suppresses the contribution of homogeneous nucleation. Correspondingly, ice crystal number density is markedly reduced. Definitive laboratory and atmospheric benchmark data are needed for the heterogeneous nucleation process. Inter-model differences are correspondingly greater than in the case of the homogeneous nucleation process acting alone.
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Study of Etching Pits in a Large-grain Single Cell Bulk Niobium Cavity
DOE Office of Scientific and Technical Information (OSTI.GOV)
Zhao, Xin; Ciovati, Gianluigi; Reece, Charles E.
2009-11-01
Performance of SRF cavities are limited by non-linear localized effects. The variation of local material characters between "hot" and "cold" spots is thus of intense interest. Such locations were identified in a BCP-etched large-grain single-cell cavity and removed for examination by high resolution electron microscopy (SEM), electron-back scattering diffraction microscopy (EBSD), optical microscopy, and 3D profilometry. Pits with clearly discernable crystal facets were observed in both "hotspot" and "coldspot" specimens. The pits were found in-grain, at bi-crystal boundaries, and on tri-crystal junctions. They are interpreted as etch pits induced by surface crystal defects (e.g. dislocations). All "coldspots" examined had qualitativelymore » low density of etching pits or very shallow tri-crystal boundary junction. EBSD revealed crystal structure surrounding the pits via crystal phase orientation mapping, while 3D profilometry gave information on the depth and size of the pits. In addition, a survey of the samples by energy dispersive X-ray analysis (EDX) did not show any significant contamination of the samples surface.« less
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Grain Boundaries Act as Solid Walls for Charge Carrier Diffusion in Large Crystal MAPI Thin Films.
Ciesielski, Richard; Schäfer, Frank; Hartmann, Nicolai F; Giesbrecht, Nadja; Bein, Thomas; Docampo, Pablo; Hartschuh, Achim
2018-03-07
Micro- and nanocrystalline methylammonium lead iodide (MAPI)-based thin-film solar cells today reach power conversion efficiencies of over 20%. We investigate the impact of grain boundaries on charge carrier transport in large crystal MAPI thin films using time-resolved photoluminescence (PL) microscopy and numerical model calculations. Crystal sizes in the range of several tens of micrometers allow for the spatially and time resolved study of boundary effects. Whereas long-ranged diffusive charge carrier transport is observed within single crystals, no detectable diffusive transport occurs across grain boundaries. The observed PL transients are found to crucially depend on the microscopic geometry of the crystal and the point of observation. In particular, spatially restricted diffusion of charge carriers leads to slower PL decay near crystal edges as compared to the crystal center. In contrast to many reports in the literature, our experimental results show no quenching or additional loss channels due to grain boundaries for the studied material, which thus do not negatively affect the performance of the derived thin-film devices.
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NASA Astrophysics Data System (ADS)
Yuan, Nana; Huo, Hong
2016-02-01
The addition of 1,2,3,4-bis(p-methylbenzylidene sorbitol) (MDBS) does not change the nucleation mechanism or the crystal form of poly(3-hexylthiophene) (P3HT), but its presence increases the crystallization temperature (T c) of P3HT, decreases the crystallization half-time (t 1/2) and accelerates P3HT crystallization, which indicates that MDBS is an effective nucleating agent for P3HT. An acceleration of P3HT crystallization by the addition of MDBS decreases the crystalline size and crystallinity of P3HT, and enhances the connectivity between ordered regions of P3HT, leading to the hole mobility rising from 1.99 × 10-6 to 7.57 × 10-5 cm2 V-1s-1 in P3HT:PCBM blend based hole-only devices with sandwich configurations. Our results suggest that accelerating P3HT crystallization by adding a nucleating agent might be an important factor to improve the hole mobility and balance the electron and hole mobility in a photovoltaic blend.
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Size effect on multiferroic TbMn{sub 2}O{sub 5} nanorods
DOE Office of Scientific and Technical Information (OSTI.GOV)
Yang, Chun-Chuen, E-mail: chunchuenyang@cycu.edu.tw; Tung, Yung-Hsiang; Hsu, Ting-Wei
2015-05-07
The effect of the size of TbMn{sub 2}O{sub 5} on their magnetoelectric properties is studied using a field emission transmission electron microscope, ac magnetic susceptibility, relative dielectric constant, specific heat capacity, and x-ray diffraction at various temperatures. A bulk sample and nanorods with two axial lengths, 〈L{sub C}〉, are investigated. Nanorods with 〈L{sub C}〉 of 216 nm and 64 nm crystallize with orthorhombic Pbam symmetry as the bulk material. The axial direction of the two sizes of nanorod is parallel to the c axis of the crystal. No particular radial direction is observed. The critical size for the magnetic ordering of TbMn{submore » 2}O{sub 5} is found to be between 〈L{sub C}〉 = 64 nm and 216 nm. Experiments on specific heat capacity verified these results. No similar phenomenon concerning the ferroelectric property is observed. At T = 30 K and 35 K, the 〈L{sub C}〉 = 216 nm sample yields a charge-ordering-like x-ray diffraction peak, which may be associated with the magnetically induced charge ordering superlattice.« less
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Design of a novel multi channel photonic crystal fiber polarization beam splitter
NASA Astrophysics Data System (ADS)
Zhao, Yunyan; Li, Shuguang; Wang, Xinyu; Wang, Guangyao; Shi, Min; Wu, Junjun
2017-10-01
A kind of multi channel dual-core photonic crystal fiber polarization beam splitter is designed. We analyze the effects of the lattice parameters and the thickness of gold layer on the beam splitting by the finite element method. Numerical results show that the thickness of metal layer and the size of the air holes near the fiber cores are closely linked with the nature of the polarization beam splitter. We also obtain that extinction ratio can reach -73.87 dB at 1 . 55 μm wavelength and at 1 . 41 μm, 1 . 65 μm extinction ratio can reach 30.8978 dB and 31.1741 dB, respectively. The comparison of the effect on the characteristic of the photonic crystal fiber with coating no gold is also taken into account.
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NASA Astrophysics Data System (ADS)
Falkner, Joshua Charles
The three projects within this work address the difficulties of controlling biomolecular crystal formats (i.e. size and shape), producing 3-D ordered composite materials from biomolecular crystal templates, and understanding the mechanism of a practical iron oxide synthesis. The unifying thread consistent throughout these three topics is the development of methods to manipulate nanomaterials using a bottom-up approach. Biomolecular crystals are nanometer to millimeter sized crystals that have well ordered mesoporous solvent channels. The overall physical dimensions of these crystals are highly dependent on crystallization conditions. The controlled growth of micro- and nanoprotein crystals was studied to provide new pathways for creating smaller crystalline protein materials. This method produced tetragonal hen egg-white lysozyme crystals (250--100,000 nm) with near monodisperse size distributions (<15%). With this degree of control, existing protein crystal applications such as drug delivery and analytical sensors can reach their full potential. Applications for larger crystals with inherently ubiquitous pore structures could extend to materials used for membranes or templates. In this work, the porous structure of larger cowpea mosaic virus crystals was used to template metal nanoparticle growth within the body centered cubic crystalline network. The final composite material was found to have long range ordering of palladium and platinum nonocrystal aggregates (10nm) with symmetry consistent to the virus template. Nanoparticle synthesis itself is an immense field of study with an array of diverse applications. The final piece of this work investigates the mechanism behind a previously developed iron oxide synthesis to gain more understanding and direction to future synthesis strategies. The particle growth mechanism was found to proceed by the formation of a solvated iron(III)oleate complex followed by a reduction of iron (III) to iron (II). This unstable iron(II) nucleates to form a wustite (FeO) core which serves as an epitaxial surface for the magnetite (Fe3O4) shell growth. This method produces spherical particles (6-60nm) with relative size distributions of less than 15%.
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Sugamura, Yuka; Fujii, Makiko; Nakanishi, Sayaka; Suzuki, Ayako; Shibata, Yusuke; Koizumi, Naoya; Watanabe, Yoshiteru
2011-01-01
The effect of particle size on amorphization of drugs in a solid dispersion (SD) was investigated for two drugs, indomethacin (IM) and nifedipine (NP). The SD of drugs were prepared in a mixture with crospovidone by a variety of mechanical methods, and their properties investigated by particle sizing, thermal analysis, and powder X-ray diffraction. IM, which had an initial particle size of 1 µm and tends to aggregate, was forced through a sieve to break up the particles. NP, which had a large initial particle size, was jet-milled. In both cases, reduction of the particle size of the drugs enabled transition to an amorphous state below the melting point of the drug. The reduction in particle size is considered to enable increased contact between the crospovidone and drug particles, increasing interactions between the two compounds. © 2011 Pharmaceutical Society of Japan
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Synthesis of nanometer-sized sodalite without adding organic additives.
Fan, Wei; Morozumi, Kazumasa; Kimura, Riichiro; Yokoi, Toshiyuki; Okubo, Tatsuya
2008-06-01
Aggregates (80 nm) of sodalite nanocrystals with crystallite sizes ranging from 20 to 40 nm have been synthesized from a sodium aluminosilicate solution at low temperature, without adding any organic additives, while paying attention to the key factors for the synthesis of nanosized zeolite crystals. The physical properties of nanosized sodalite crystals were characterized by X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, 29Si solid-state magic-angle spinning (MAS) NMR, and N2 adsorption. As expected, the external surface area of nanosized sodalite crystals is significantly increased compared with that of microsized sodalite crystals. The size of synthesized sodalite crystals can be controlled from 20 nm to 10 microm. It is found that the preparation of a homogeneous aluminosilicate solution followed by the formation of an aluminosilicate hard gel by adjusting the initial composition, for example, SiO2/Al2O3 and Na2O/H2O ratios, is critical for synthesis.
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NASA Astrophysics Data System (ADS)
Kakiuchida, Hiroshi; Ogiwara, Akifumi
2018-04-01
Polymer network liquid crystals (PNLCs) whose optical transmittance state switches between transparence at low temperatures and haze at high temperatures were fabricated from mixtures of nematic liquid crystals (LCs) and reactive mesogens (RMs). This PNLC structure is simple but effective, namely, consists of micro-scale domains of orientation-ordered LCs and anisotropically polymerized RMs. The domains form through photopolymerization induced phase separation with inhomogeneous irradiation projected by laser speckling techniques. This irradiation method enables you to control the size and shape of phase-separation domains, and these PNLCs can be applied to novel thermoresponsive optical devices; optical isolators, thermometric sheets, and smart windows.
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NASA Technical Reports Server (NTRS)
Mackay, R. A.; Nathal, M. V.
1986-01-01
Some of the microstructural features which influence the creep properties of directionally solidified and single crystal nickel-base superalloys are discussed. Gamma precipitate size and morphology, gamma-gamma lattice mismatch, phase instability, alloy composition, and processing variations are among the factors considered. Recent experimental results are reviewed and related to the operative deformation mechanisms and to the corresponding mechanical properties. Special emphasis is placed on the creep behavior of single crystal superalloys at high temperatures, where directional gamma coarsening is prominent, and at lower temperatures, where gamma coarsening rates are significantly reduced. It can be seen that very subtle changes in microstructural features can have profound effects on the subsequent properties of these materials.
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Preparation of fine single crystals of magnetic superconductor RuSr2GdCu2O8-δ by partial melting
NASA Astrophysics Data System (ADS)
Yamaki, Kazuhiro; Bamba, Yoshihiro; Irie, Akinobu
2018-03-01
In this study, fine uniform RuSr2GdCu2O8-δ (RuGd-1212) single crystals have been successfully prepared by partial melting. Synthesis temperature could be lowered to a value not exceeding the decomposition temperature of RuGd-1212 using the Sr-Gd-Cu-O flux. The crystals grown by alumina boats are cubic, which coincides with the result of a previous study of RuGd-1212 single crystals using platinum crucibles. The single crystals were up to 15 × 15 × 15 µm3 in size and their lattice constants were consistent with those of polycrystalline samples reported previously. Although the present size of single crystals is not sufficient for measurements, the partial melting technique will be beneficial for future progress of research using RuGd-1212 single crystals. Appropriate nominal composition, sintering atmosphere, and temperature are essential factors for growing RuGd-1212 single crystals.
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Microfluidic sorting of protein nanocrystals by size for X-ray free-electron laser diffraction
Abdallah, Bahige G.; Zatsepin, Nadia A.; Roy-Chowdhury, Shatabdi; Coe, Jesse; Conrad, Chelsie E.; Dörner, Katerina; Sierra, Raymond G.; Stevenson, Hilary P.; Camacho-Alanis, Fernanda; Grant, Thomas D.; Nelson, Garrett; James, Daniel; Calero, Guillermo; Wachter, Rebekka M.; Spence, John C. H.; Weierstall, Uwe; Fromme, Petra; Ros, Alexandra
2015-01-01
The advent and application of the X-ray free-electron laser (XFEL) has uncovered the structures of proteins that could not previously be solved using traditional crystallography. While this new technology is powerful, optimization of the process is still needed to improve data quality and analysis efficiency. One area is sample heterogeneity, where variations in crystal size (among other factors) lead to the requirement of large data sets (and thus 10–100 mg of protein) for determining accurate structure factors. To decrease sample dispersity, we developed a high-throughput microfluidic sorter operating on the principle of dielectrophoresis, whereby polydisperse particles can be transported into various fluid streams for size fractionation. Using this microsorter, we isolated several milliliters of photosystem I nanocrystal fractions ranging from 200 to 600 nm in size as characterized by dynamic light scattering, nanoparticle tracking, and electron microscopy. Sorted nanocrystals were delivered in a liquid jet via the gas dynamic virtual nozzle into the path of the XFEL at the Linac Coherent Light Source. We obtained diffraction to ∼4 Å resolution, indicating that the small crystals were not damaged by the sorting process. We also observed the shape transforms of photosystem I nanocrystals, demonstrating that our device can optimize data collection for the shape transform-based phasing method. Using simulations, we show that narrow crystal size distributions can significantly improve merged data quality in serial crystallography. From this proof-of-concept work, we expect that the automated size-sorting of protein crystals will become an important step for sample production by reducing the amount of protein needed for a high quality final structure and the development of novel phasing methods that exploit inter-Bragg reflection intensities or use variations in beam intensity for radiation damage-induced phasing. This method will also permit an analysis of the dependence of crystal quality on crystal size. PMID:26798818
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Microfluidic sorting of protein nanocrystals by size for X-ray free-electron laser diffraction
Abdallah, Bahige G.; Zatsepin, Nadia A.; Roy-Chowdhury, Shatabdi; ...
2015-08-19
We report that the advent and application of the X-ray free-electron laser (XFEL) has uncovered the structures of proteins that could not previously be solved using traditional crystallography. While this new technology is powerful, optimization of the process is still needed to improve data quality and analysis efficiency. One area is sample heterogeneity, where variations in crystal size (among other factors) lead to the requirement of large data sets (and thus 10–100 mg of protein) for determining accurate structure factors. To decrease sample dispersity, we developed a high-throughput microfluidic sorter operating on the principle of dielectrophoresis, whereby polydisperse particles canmore » be transported into various fluid streams for size fractionation. Using this microsorter, we isolated several milliliters of photosystem I nanocrystal fractions ranging from 200 to 600 nm in size as characterized by dynamic light scattering, nanoparticle tracking, and electron microscopy. Sorted nanocrystals were delivered in a liquid jet via the gas dynamic virtual nozzle into the path of the XFEL at the Linac Coherent Light Source. We obtained diffraction to ~4 Å resolution, indicating that the small crystals were not damaged by the sorting process. We also observed the shape transforms of photosystem I nanocrystals, demonstrating that our device can optimize data collection for the shape transform-based phasing method. Using simulations, we show that narrow crystal size distributions can significantly improve merged data quality in serial crystallography. From this proof-of-concept work, we expect that the automated size-sorting of protein crystals will become an important step for sample production by reducing the amount of protein needed for a high quality final structure and the development of novel phasing methods that exploit inter-Bragg reflection intensities or use variations in beam intensity for radiation damage-induced phasing. Ultimately, this method will also permit an analysis of the dependence of crystal quality on crystal size.« less
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Loiola, A R; Andrade, J C R A; Sasaki, J M; da Silva, L R D
2012-02-01
Zeolite 4A (LTA) has been successfully synthesized by a hydrothermal method, where kaolin was used as silica and alumina source. The synthesized zeolite was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), laser granulometry, and FTIR spectroscopy. XRD data from the Rietveld refinement method confirmed only one crystallographic phase. Zeolite A morphology was observed by SEM analysis, and it showed well-defined crystals with slightly different sizes but with the same cubic shape. Particle size distribution of the crystals was confirmed by laser granulometry, whereas FTIR spectroscopy revealed significant structural differences between the starting material and the final zeolite product used as water softener. Copyright © 2010 Elsevier Inc. All rights reserved.
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Controlled morphology and size of curcumin using ultrasound in supercritical CO2 antisolvent.
Jia, Jingfu; Wang, Wucong; Gao, Yahui; Zhao, Yaping
2015-11-01
Controllable morphology and size of crystal materials prepared by using a supercritical antisolvent (SAS) technique is still challenge. In this study, ultrasound was introduced into the SAS process to produce the particles of curcumin, a model compound. The effects of ultrasound power on the particle morphology and size were investigated in the range of 0 and 240 W at three different pressures. The observation of jet flow indicated ultrasound could accelerate the mixing speed between the liquid solution and the CO2, and thus reduced the gaseous region and the local saturation gradient. Mixed polymorphic and uniform particles of the curcumin were produced at a low and high mixing speed, respectively, confirmed by scanning electron microscopy. The needle- or rod-like particle, irregular lumpy particle and nano spherical particle were generated with the increase of the ultrasound power, attributed to the changes of the degree of supersaturation. Therefore, the ultrasound can be potentially applied to adjust the morphology and size of the crystal materials in supercritical CO2 antisolvent. Copyright © 2015 Elsevier B.V. All rights reserved.
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Chaikuad, Apirat; Knapp, Stefan; von Delft, Frank
2015-01-01
The quest for an optimal limited set of effective crystallization conditions remains a challenge in macromolecular crystallography, an issue that is complicated by the large number of chemicals which have been deemed to be suitable for promoting crystal growth. The lack of rational approaches towards the selection of successful chemical space and representative combinations has led to significant overlapping conditions, which are currently present in a multitude of commercially available crystallization screens. Here, an alternative approach to the sampling of widely used PEG precipitants is suggested through the use of PEG smears, which are mixtures of different PEGs with a requirement of either neutral or cooperatively positive effects of each component on crystal growth. Four newly defined smears were classified by molecular-weight groups and enabled the preservation of specific properties related to different polymer sizes. These smears not only allowed a wide coverage of properties of these polymers, but also reduced PEG variables, enabling greater sampling of other parameters such as buffers and additives. The efficiency of the smear-based screens was evaluated on more than 220 diverse recombinant human proteins, which overall revealed a good initial crystallization success rate of nearly 50%. In addition, in several cases successful crystallizations were only obtained using PEG smears, while various commercial screens failed to yield crystals. The defined smears therefore offer an alternative approach towards PEG sampling, which will benefit the design of crystallization screens sampling a wide chemical space of this key precipitant. PMID:26249344
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Chaikuad, Apirat; Knapp, Stefan; von Delft, Frank
2015-08-01
The quest for an optimal limited set of effective crystallization conditions remains a challenge in macromolecular crystallography, an issue that is complicated by the large number of chemicals which have been deemed to be suitable for promoting crystal growth. The lack of rational approaches towards the selection of successful chemical space and representative combinations has led to significant overlapping conditions, which are currently present in a multitude of commercially available crystallization screens. Here, an alternative approach to the sampling of widely used PEG precipitants is suggested through the use of PEG smears, which are mixtures of different PEGs with a requirement of either neutral or cooperatively positive effects of each component on crystal growth. Four newly defined smears were classified by molecular-weight groups and enabled the preservation of specific properties related to different polymer sizes. These smears not only allowed a wide coverage of properties of these polymers, but also reduced PEG variables, enabling greater sampling of other parameters such as buffers and additives. The efficiency of the smear-based screens was evaluated on more than 220 diverse recombinant human proteins, which overall revealed a good initial crystallization success rate of nearly 50%. In addition, in several cases successful crystallizations were only obtained using PEG smears, while various commercial screens failed to yield crystals. The defined smears therefore offer an alternative approach towards PEG sampling, which will benefit the design of crystallization screens sampling a wide chemical space of this key precipitant.
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Er3+-doped transparent glass ceramics containing micron-sized SrF2 crystals for 2.7 μm emissions
Jiang, Yiguang; Fan, Jintai; Jiang, Benxue; Mao, Xiaojian; Tang, Junzhou; Xu, Yinsheng; Dai, Shixun; Zhang, Long
2016-01-01
Er3+-doped transparent glass ceramics containing micron-sized SrF2 crystals were obtained by direct liquid-phase sintering of a mixture of SrF2 powders and precursor glass powders at 820 °C for 15 min. The appearance and microstructural evolution of the SrF2 crystals in the resulting glass ceramics were investigated using X-ray diffraction, field-emission scanning electron microscopy and transmission microscopy. The SrF2 crystals are ~15 μm in size and are uniformly distributed throughout the fluorophosphate glass matrix. The glass ceramics achieve an average transmittance of 75% in the visible region and more than 85% in the near-IR region. The high transmittance of the glass ceramics results from matching the refractive index of the SrF2 with that of the precursor glass. Energy dispersive spectroscopy, photoluminescence spectra, and photoluminescence lifetimes verified the incorporation of Er3+ into the micron-sized SrF2 crystals. Intense 2.7 μm emissions due to the 4I11/2 → 4I13/2 transition were observed upon excitation at 980 nm using a laser diode. The maximum value of the emission cross section of Er3+ around 2.7 μm is more than 1.2 × 10−20 cm2, which indicates the potential of using transparent glass ceramics containing micron-sized SrF2 crystals for efficient 2.7 μm lasers and amplifiers. PMID:27430595
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Er(3+)-doped transparent glass ceramics containing micron-sized SrF2 crystals for 2.7 μm emissions.
Jiang, Yiguang; Fan, Jintai; Jiang, Benxue; Mao, Xiaojian; Tang, Junzhou; Xu, Yinsheng; Dai, Shixun; Zhang, Long
2016-07-19
Er(3+)-doped transparent glass ceramics containing micron-sized SrF2 crystals were obtained by direct liquid-phase sintering of a mixture of SrF2 powders and precursor glass powders at 820 °C for 15 min. The appearance and microstructural evolution of the SrF2 crystals in the resulting glass ceramics were investigated using X-ray diffraction, field-emission scanning electron microscopy and transmission microscopy. The SrF2 crystals are ~15 μm in size and are uniformly distributed throughout the fluorophosphate glass matrix. The glass ceramics achieve an average transmittance of 75% in the visible region and more than 85% in the near-IR region. The high transmittance of the glass ceramics results from matching the refractive index of the SrF2 with that of the precursor glass. Energy dispersive spectroscopy, photoluminescence spectra, and photoluminescence lifetimes verified the incorporation of Er(3+) into the micron-sized SrF2 crystals. Intense 2.7 μm emissions due to the (4)I11/2 → (4)I13/2 transition were observed upon excitation at 980 nm using a laser diode. The maximum value of the emission cross section of Er(3+) around 2.7 μm is more than 1.2 × 10(-20) cm(2), which indicates the potential of using transparent glass ceramics containing micron-sized SrF2 crystals for efficient 2.7 μm lasers and amplifiers.
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Protein-free formation of bone-like apatite: New insights into the key role of carbonation
Deymier, Alix C.; Nair, Arun K.; Depalle, Baptiste; Qin, Zhao; Arcot, Kashyap; Drouet, Christophe; Yoder, Claude H.; Buehler, Markus J.; Thomopoulos, Stavros; Genin, Guy M.; Pasteris, Jill D.
2017-01-01
The nanometer-sized plate-like morphology of bone mineral is necessary for proper bone mechanics and physiology. However, mechanisms regulating the morphology of these mineral nanocrystals remain unclear. The dominant hypothesis attributes the size and shape regulation to organic-mineral interactions. Here, we present data supporting the hypothesis that physicochemical effects of carbonate integration within the apatite lattice control the morphology, size, and mechanics of bioapatite mineral crystals. Carbonated apatites synthesized in the absence of organic molecules presented plate-like morphologies and nanoscale crystallite dimensions. Experimentally-determined crystallite size, lattice spacing, solubility and atomic order were modified by carbonate concentration. Molecular dynamics (MD) simulations and density functional theory (DFT) calculations predicted changes in surface energy and elastic moduli with carbonate concentration. Combining these results with a scaling law predicted the experimentally observed scaling of size and energetics with carbonate concentration. The experiments and models describe a clear mechanism by which crystal dimensions are controlled by carbonate substitution. Furthermore, the results demonstrate that carbonate substitution is sufficient to drive the formation of bone-like crystallites. This new understanding points to pathways for biomimetic synthesis of novel, nanostructured biomaterials. PMID:28279923
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Kim, Minjeong; Choi, Myoung Gil; Ra, Ho Won; Park, Seung Bin; Kim, Yong-Joo; Lee, Kyubock
2018-02-13
The encapsulation of living cells is appealing for its various applications to cell-based sensors, bioreactors, biocatalysts, and bioenergy. In this work, we introduce the encapsulation of multiple microalgal cells in hollow polymer shells of rhombohedral shape by the following sequential processes: embedding of microalgae in CaCO₃ crystals; layer-by-layer (LbL) coating of polyelectrolytes; and removal of sacrificial crystals. The microcapsule size was controlled by the alteration of CaCO₃ crystal size, which is dependent on CaCl₂/Na₂CO₃ concentration. The microalgal cells could be embedded in CaCO₃ crystals by a two-step process: heterogeneous nucleation of crystal on the cell surface followed by cell embedment by the subsequent growth of crystal. The surfaces of the microalgal cells were highly favorable for the crystal growth of calcite; thus, micrometer-sized microalgae could be perfectly occluded in the calcite crystal without changing its rhombohedral shape. The surfaces of the microcapsules, moreover, could be decorated with gold nanoparticles, Fe₃O₄ magnetic nanoparticles, and carbon nanotubes (CNTs), by which we would expect the functionalities of a light-triggered release, magnetic separation, and enhanced mechanical and electrical strength, respectively. This approach, entailing the encapsulation of microalgae in semi-permeable and hollow polymer microcapsules, has the potential for application to microbial-cell immobilization for high-biomass-concentration cultivation as well as various other bioapplications.
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Baghdasaryan, Tigran; Geernaert, Thomas; Chah, Karima; Caucheteur, Christophe; Schuster, Kay; Kobelke, Jens; Thienpont, Hugo; Berghmans, Francis
2018-04-03
It is common belief that photonic crystals behave similarly to isotropic and transparent media only when their feature sizes are much smaller than the wavelength of light. Here, we counter that belief and we report on photonic crystals that are transparent for anomalously high normalized frequencies up to 0.9, where the crystal's feature sizes are comparable with the free space wavelength. Using traditional photonic band theory, we demonstrate that the isofrequency curves can be circular in the region above the first stop band for triangular lattice photonic crystals. In addition, by simulating how efficiently a tightly focused Gaussian beam propagates through the photonic crystal slab, we judge on the photonic crystal's transparency rather than on isotropy only. Using this approach, we identified a wide range of photonic crystal parameters that provide anomalous transparency. Our findings indicate the possibility to scale up the features of photonic crystals and to extend their operational wavelength range for applications including optical cloaking and graded index guiding. We applied our result in the domain of femtosecond laser micromachining, by demonstrating what we believe to be the first point-by-point grating inscribed in a multi-ring photonic crystal fiber.
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Radiative Properties of Cirrus Clouds in the Infrared (8-13 microns) Spectral Region
NASA Technical Reports Server (NTRS)
Yang, Ping; Gao, Bo-Cai; Baum, Bryan A.; Hu, Yong X.; Wiscombe, Warren J.; Tsay, Si-Chee; Winker, Dave M.; Einaudi, Franco (Technical Monitor)
2000-01-01
Atmospheric radiation in the infrared (IR) 8-13 microns spectral region contains a wealth of information that is very useful for the retrieval of ice cloud properties from aircraft or space-borne measurements. To provide the scattering and absorption properties of nonspherical ice crystals that are fundamental to the IR retrieval implementation, we use the finite-difference time domain (FDTD) method to solve for the extinction efficiency, single-scattering albedo, and the asymmetry parameter of the phase function for ice crystals smaller than 40 microns. For particles larger than this size, the improved geometric optics method (IGOM) can be employed to calculate the asymmetry parameter with an acceptable accuracy, provided that we properly account for the inhomogeneity of the refracted wave due to strong absorption inside the ice particle. A combination of the results computed from the two methods provides the asymmetry parameter for the entire practical range of particle sizes between 1 micron and 10000 microns over wavelengths ranging from 8 microns to 13 microns. For the extinction and absorption efficiency calculations, several methods including the IGOM, Mie solution for equivalent spheres (MSFES), and the anomalous diffraction theory (ADT) can lead to a substantial discontinuity in comparison with the FDTD solutions for particle sizes on the order of 40 microns. To overcome this difficulty, we have developed a novel approach called the stretched scattering potential method (SSPM). For the IR 8-13 microns spectral region, we show that SSPM is a more accurate approximation than ADT, MSFES, and IGOM. The SSPM solution can be further refined numerically. Through a combination of the FDTD and SSPM, we have computed the extinction and absorption efficiency for hexagonal ice crystals with sizes ranging from 1 to 10000 microns at 12 wavelengths between 8 and 13 microns Calculations of the cirrus bulk scattering and absorption properties are performed for 30 size distributions obtained from various field campaigns for midlatitude and tropical cirrus cloud systems. Parameterization of these bulk scattering properties is carried out by using second-order polynomial functions for the extinction efficiency and the single-scattering albedo and the power law expression for the asymmetry parameter. We note that the volume-normalized extinction coefficient can be separated into two parts: one is inversely proportional to effective size and is independent of wavelength, and the other is the wavelength-dependent effective extinction efficiency. Unlike conventional parameterization efforts, the present parameterization scheme is more accurate because only the latter part of the volume-normalized extinction coefficient is approximated in terms of an analytical expression. After averaging over size distribution, the single-scattering albedo is shown to decrease with an increase in effective size for wavelengths shorter than 10.0 microns whereas the opposite behavior is observed for longer wavelengths. The variation of the asymmetry parameter as a function of effective size is substantial when the effective size is smaller than 50 microns. For effective sizes larger than 100 microns, the asymmetry parameter approaches its asymptotic value. The results derived in this study can be useful to remote sensing applications involving IR window bands under cirrus cloud conditions.
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NASA Astrophysics Data System (ADS)
Mitchell, Niall A.; Ó'Ciardhá, Clifford T.; Frawley, Patrick J.
2011-08-01
This work details the estimation of the growth kinetics of paracetamol in ethanol solutions for cooling crystallisation processes, by means of isothermal seeded batch experiments. The growth kinetics of paracetamol crystals were evaluated in isolation, with the growth rate assumed to be size independent. Prior knowledge of the Metastable Zone Width (MSZW) was required, so that supersaturation ratios of 1.7-1.1 could be induced in solution without the occurrence of nucleation. The technique involved the utilisation of two in-situ Process Analytical Techniques (PATs), with a Focused Beam Reflectance Measurement (FBRM ®) utilised to ensure that negligible nucleation occurred and an Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) probe employed for online monitoring of solute concentration. Initial Particle Size Distributions (PSDs) were used in conjunction with desupersaturation profiles to determine the growth rate as a function of temperature and supersaturation. Furthermore, the effects of seed loading and size on the crystal growth rate were investigated. A numerical model, incorporating the population balance equation and the method of moments, was utilised to describe the crystal growth process. Experimental parameters were compared to the model simulation, with the accuracy of the model validated by means of the final product PSDs and solute concentration.
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Crystal growth and annealing for minimized residual stress
Gianoulakis, Steven E.
2002-01-01
A method and apparatus for producing crystals that minimizes birefringence even at large crystal sizes, and is suitable for production of CaF.sub.2 crystals. The method of the present invention comprises annealing a crystal by maintaining a minimal temperature gradient in the crystal while slowly reducing the bulk temperature of the crystal. An apparatus according to the present invention includes a thermal control system added to a crystal growth and annealing apparatus, wherein the thermal control system allows a temperature gradient during crystal growth but minimizes the temperature gradient during crystal annealing.
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Influence of nano-size inclusions on spall fracture of copper single crystals
DOE Office of Scientific and Technical Information (OSTI.GOV)
Razorenov, S. V.; Ivanchihina, G. E.; Kanel, G. I.
2007-12-12
Spall experiments have been carried out for copper in different structural states. The samples were copper single crystals, crystals of Cu+0.1% Si, copper crystals with silica particles of 180 nm average size, and polycrystalline copper. In experiments, the free surface velocity histories were recorded with the VISAR. The recovered samples were studied using optical microscopy and SEM. Solid solution Cu+0.1% Si demonstrates slower spall process than pure copper crystals. At longer pulse durations its spall strength is slightly less than that of pure crystals but approaches the latter with decreasing pulse duration. Fracture of copper with silica inclusions is completedmore » much faster. The spall strength of this material is close to that of Cu+0.1% Si crystals at longer pulse duration and approaches the strength of polycrystalline copper with decreasing the load duration. Fractography of the spall surfaces correlates with the free surface velocity histories. The main fracture surface of the Cu+0.1% Si grains consists of net of dimples {approx}4 {mu}m to 40 {mu}m mean diameter. The fracture surfaces of copper with silica inclusions is covered by a net of dimples of 1 {mu}m to 5 {mu}m size.« less
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NASA Astrophysics Data System (ADS)
Sun, F. Z.; Zhang, P.; Liang, Y. C.; Lu, L. H.
2014-09-01
In the non-critical phase-matching (NCPM) along the Θ =90° direction, ADP and DKDP crystals which have many advantages, including a large effective nonlinear optical coefficient, a small PM angular sensitivity and non beam walk-off, at the non-critical phase-matching become the competitive candidates in the inertial confinement fusion(ICF) facility, so the reasonable temperature control of crystals has become more and more important .In this paper, the fluid-solid coupling models of ADP crystal and DKDP crystal which both have anisotropic thermal conductivity in the states of vacuum and non-vacuum were established firstly, and then simulated using the fluid analysis software Fluent. The results through the analysis show that the crystal surface temperature distribution is a ring shape, the temperature gradients in the direction of the optical axis both the crystals are 0.02°C and 0.01°C due to the air, the lowest temperature points of the crystals are both at the center of surface, and the temperatures are lower than 0.09°C and 0.05°C compared in the vacuum and non-vacuum environment, then propose two designs for heating apparatus.
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Sorbitol crystallization-induced aggregation in frozen mAb formulations.
Piedmonte, Deirdre Murphy; Hair, Alison; Baker, Priti; Brych, Lejla; Nagapudi, Karthik; Lin, Hong; Cao, Wenjin; Hershenson, Susan; Ratnaswamy, Gayathri
2015-02-01
Sorbitol crystallization-induced aggregation of mAbs in the frozen state was evaluated. The effect of protein aggregation resulting from sorbitol crystallization was measured as a function of formulation variables such as protein concentration and pH. Long-term studies were performed on both IgG1 and IgG2 mAbs over the protein concentration range of 0.1-120 mg/mL. Protein aggregation was measured by size-exclusion HPLC (SE-HPLC) and further characterized by capillary-electrophoresis SDS. Sorbitol crystallization was monitored and characterized by subambient differential scanning calorimetry and X-ray diffraction. Aggregation due to sorbitol crystallization is inversely proportional to both protein concentration and formulation pH. At high protein concentrations, sorbitol crystallization was suppressed, and minimal aggregation by SE-HPLC resulted, presumably because of self-stabilization of the mAbs. The glass transition temperature (Tg ') and fragility index measurements were made to assess the influence of molecular mobility on the crystallization of sorbitol. Tg ' increased with increasing protein concentration for both mAbs. The fragility index decreased with increasing protein concentration, suggesting that it is increasingly difficult for sorbitol to crystallize at high protein concentrations. © 2014 Wiley Periodicals, Inc. and the American Pharmacists Association.
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Compositional and microstructural design of highly bioactive P2O5-Na2O-CaO-SiO2 glass-ceramics.
Peitl, Oscar; Zanotto, Edgar D; Serbena, Francisco C; Hench, Larry L
2012-01-01
Bioactive glasses having chemical compositions between 1Na(2)O-2CaO-3SiO(2) (1N2C3S) and 1.5Na(2)O-1.5CaO-3SiO(2) (1N1C2S) containing 0, 4 and 6 wt.% P(2)O(5) were crystallized through two stage thermal treatments. By carefully controlling these treatments we separately studied the effects on the mechanical properties of two important microstructural features not studied before, crystallized volume fraction and crystal size. Fracture strength, elastic modulus and indentation fracture toughness were measured as a function of crystallized volume fraction for a constant crystal size. Glass-ceramics with a crystalline volume fraction between 34% and 60% exhibited a three-fold improvement in fracture strength and an increase of 40% in indentation fracture toughness compared with the parent glass. For the optimal crystalline concentration (34% and 60%) these mechanical properties were then measured for different grain sizes, from 5 to 21 μm. The glass-ceramic with the highest fracture strength and indentation fracture toughness was that with 34% crystallized volume fracture and 13 μm crystals. Compared with the parent glass, the average fracture strength of this glass-ceramic was increased from 80 to 210 MPa, and the fracture toughness from 0.60 to 0.95 MPa.m(1/2). The increase in indentation fracture toughness was analyzed using different theoretical models, which demonstrated that it is due to crack deflection. Fortunately, the elastic modulus E increased only slightly; from 60 to 70 GPa (the elastic modulus of biomaterials should be as close as possible to that of cortical bone). In summary, the flexural strength of our best material (215 MPa) is significantly greater than that of cortical bone and comparable with that of apatite-wollastonite (A/W) bioglass ceramics, with the advantage that it shows a much lower elastic modulus. These results thus provide a relevant guide for the design of bioactive glass-ceramics with improved microstructure. Copyright © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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NASA Astrophysics Data System (ADS)
Tirmizi, Shakeel H.; Gill, William N.
1989-06-01
The dynamics of spontaneous pattern formation are studied experimentally by observing and recording the evolution of ice crystal patterns which grow freely in a supercooled melt. The sequence of evolution to dendrites is recorded in real time using cine-micrography. In the range of subcoolings from 0.06 to 0.29°C, all the patterns evolved as follows: Smooth disk → Perturbed disk → Disk dendrite → Partially developed dendrite → Fully developed dendrite. The initial smooth disk, the main branch and the side branches all developed perturbations beyond a critical size which depends on the subcooling. The combined effect of the destabilizing thermal gradients ahead of the growing crystal and the stabilizing Gibbs-Thompson capillarity effect dictates the critical size of the unstable structures in terms of the mean curvature of the interface. Detailed analysis of the evolving patterns was done using digital image analysis on the PRIME computer to determine both the manner in which the dendritic growth process replicates itself and the role which the shape and the movement of the interface play in the pattern formation process. Total arc length ST, total area A and the complexity ratio ξ = ST⧸√ A of evolving patterns were computed as a function of time and undercooling for each crystal image. These results permitted us to make some comparisons with theoretical models on pattern evolution. Three distinct phases of evolution were identified: the initial phase when the crystal structure is smooth and free of any perturbations and the complexity ratio is almost a constant, an intermediate phase when the crystal structure develops perturbations which grow quickly in number and in size and the complexity ratio increases rapidly and a final phase when the pattern approaches that of a fully developed dendrite which, on a global scale grows in a shape-perserving manner and has a slowly increasing complexity ratio which seems to approach an asymptote. Two factors were found to be responsible for the symmetric dendritic patterns. These are: first, hexagonal symmetry due to the hexagonal closed packed structure, leads to strong anisotropy in molecular attachment kinetics and in surface free energy; second, the competition among side branches causes smaller side branches to melt when they are trapped between larger ones which generate latent heat and prevent the small branches from gaining access to the fresh cold fluid ahead of them. These two factors lead to a channelling effect which prevents the growth of perturbations from occurring randomly and thus directs the evolving crystal structure into patterns which are regular and reproducible. Theoretical models which are local in nature fail to take into account side branch competition, and this is one of their major weaknesses.
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Ferroelectric size effects in multiferroic BiFeO3 thin films
NASA Astrophysics Data System (ADS)
Chu, Y. H.; Zhao, T.; Cruz, M. P.; Zhan, Q.; Yang, P. L.; Martin, L. W.; Huijben, M.; Yang, C. H.; Zavaliche, F.; Zheng, H.; Ramesh, R.
2007-06-01
Ferroelectric size effects in multiferroic BiFeO3 have been studied using a host of complementary measurements. The structure of such epitaxial films has been investigated using atomic force microscopy, transmission electron microscopy, and x-ray diffraction. The crystal structure of the films has been identified as a monoclinic phase, which suggests that the polarization direction is close to ⟨111⟩. Such behavior has also been confirmed by piezoforce microscopy measurements. That also reveals that the ferroelectricity is down to at least 2nm.
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Dependence of crystal size on the catalytic performance of a porous coordination polymer.
Kiyonaga, Tomokazu; Higuchi, Masakazu; Kajiwara, Takashi; Takashima, Yohei; Duan, Jingui; Nagashima, Kazuro; Kitagawa, Susumu
2015-02-14
Submicrosized MOF-76(Yb) exhibits a higher catalytic performance for esterification than microsized MOF-76(Yb). Control of the crystal size of porous heterogeneous catalysts, such as PCP/MOFs, offers a promising approach to fabricating high-performance catalysts based on accessibility to the internal catalytic sites.
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Defect formation energy in pyrochlore: the effect of crystal size
NASA Astrophysics Data System (ADS)
Wang, Jianwei; Ewing, Rodney C.; Becker, Udo
2014-09-01
Defect formation energies of point defects of two pyrochlores Gd2Ti2O7 and Gd2Zr2O7 as a function of crystal size were calculated. Density functional theory with plane-wave basis sets and the projector-augmented wave method were used in the calculations. The results show that the defect formation energies of the two pyrochlores diverge as the size decreases to the nanometer range. For Gd2Ti2O7 pyrochlore, the defect formation energy is higher at nanometers with respect to that of the bulk, while it is lower for Gd2Zr2O7. The lowest defect formation energy for Gd2Zr2O7 is found at 15-20 Å. The different behaviors of the defect formation energies as a function of crystal size are caused by different structural adjustments around the defects as the size decreases. For both pyrochlore compositions at large sizes, the defect structures are similar to those of the bulk. As the size decreases, for Gd2Ti2O7, additional structure distortions appear at the surfaces, which cause the defect formation energy to increase. For Gd2Zr2O7, additional oxygen Frenkel pair defects are introduced, which reduce the defect formation energy. As the size further decreases, increased structure distortions occur at the surfaces, which cause the defect formation energy to increase. Based on a hypothesis that correlates the energetics of defect formation and radiation response for complex oxides, the calculated results suggest that at nanometer range Gd2Ti2O7 pyrochlore is expected to have a lower radiation tolerance, and those of Gd2Zr2O7 pyrochlore to have a higher radiation tolerance. The highest radiation tolerance for Gd2Zr2O7 pyrochlore is expected to be found at ˜2 nanometers.
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Determining ice water content from 2D crystal images in convective cloud systems
NASA Astrophysics Data System (ADS)
Leroy, Delphine; Coutris, Pierre; Fontaine, Emmanuel; Schwarzenboeck, Alfons; Strapp, J. Walter
2016-04-01
Cloud microphysical in-situ instrumentation measures bulk parameters like total water content (TWC) and/or derives particle size distributions (PSD) (utilizing optical spectrometers and optical array probes (OAP)). The goal of this work is to introduce a comprehensive methodology to compute TWC from OAP measurements, based on the dataset collected during recent HAIC (High Altitude Ice Crystals)/HIWC (High Ice Water Content) field campaigns. Indeed, the HAIC/HIWC field campaigns in Darwin (2014) and Cayenne (2015) provide a unique opportunity to explore the complex relationship between cloud particle mass and size in ice crystal environments. Numerous mesoscale convective systems (MCSs) were sampled with the French Falcon 20 research aircraft at different temperature levels from -10°C up to 50°C. The aircraft instrumentation included an IKP-2 (isokinetic probe) to get reliable measurements of TWC and the optical array probes 2D-S and PIP recording images over the entire ice crystal size range. Based on the known principle relating crystal mass and size with a power law (m=α•Dβ), Fontaine et al. (2014) performed extended 3D crystal simulations and thereby demonstrated that it is possible to estimate the value of the exponent β from OAP data, by analyzing the surface-size relationship for the 2D images as a function of time. Leroy et al. (2015) proposed an extended version of this method that produces estimates of β from the analysis of both the surface-size and perimeter-size relationships. Knowing the value of β, α then is deduced from the simultaneous IKP-2 TWC measurements for the entire HAIC/HIWC dataset. The statistical analysis of α and β values for the HAIC/HIWC dataset firstly shows that α is closely linked to β and that this link changes with temperature. From these trends, a generalized parameterization for α is proposed. Finally, the comparison with the initial IKP-2 measurements demonstrates that the method is able to predict TWC values larger than 0.3g/m3 with an error close to 20%. Fontaine, E., A. Schwarzenboeck, J. Delanoë, W. Wobrock, D. Leroy, R. Dupuy, C. Gourbeyre, and A. Protat, 2014: Constraining mass-diameter relations from hydrometeor images and cloud radar reflectivities in tropical continental and oceanic convective anvils. Atmos Chem Phys, 14, 11367-11392, doi:10.5194/acp-14-11367-2014. Leroy, D., E. Fontaine, A. Schwarzenboeck and J.W. Strapp : Ice Crystal Sizes in High Ice Water Content Clouds. Part 1: Mass-size Relationships Derived from Particle Images and TWC for Various Crystal Diameter Definitions and Impact on Median Mass Diameter. Submitted to Journal of Atmospheric and Oceanic Technology, 2015.
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Matyas, Josef; Amonette, James E.; Kukkadapu, Ravi K.
2014-10-31
Precipitation of large crystals/agglomerates of spinel and their accumulation in the pour spout riser of a Joule-heated ceramic melter during idling can plug the melter and prevent pouring of molten glass into canisters. Thus, there is a need to understand the effects of spinel-forming components, temperature, and time on the growth of crystals in connection with an accumulation rate. In our study, crystals of spinel [Fe, Ni, Mn, Zn, Sn][Fe, Cr]₂O₄ were precipitated from simulated high-level waste borosilicate glasses containing different concentrations of Ni, Fe, and Cr by heat treating at 850 and 900°C for different times. These crystals weremore » extracted from the glasses and analyzed with scanning electron microscopy and image analysis for size and shape, with inductively coupled plasma-atomic emission spectroscopy and atom probe tomography for concentration of spinel-forming components, and with wet colorimetry and Mössbauer spectroscopy for Fe²⁺/Fe total ratio. High concentrations of Ni, Fe, and Cr in glasses resulted in the precipitation of crystals larger than 100 µm in just two days. Crystals were a solid solution of NiFe₂O₄, NiCr₂O₄, and -Fe₂O₃ (identified only in the high-Ni-Fe glass) and also contained small concentrations of less than 1 at% of Li, Mg, Mn, and Al.« less
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Effect of particle size on the photochromic response of PWA/SiO2 nanocomposite
NASA Astrophysics Data System (ADS)
Huang, Feng-Hsi; Chen, Ching-Chung; Lin, Dar-Jong; Don, Trong-Ming; Cheng, Liao-Ping
2010-10-01
A series of photochromic phosphotungstic acid (PWA)/SiO2 composites were synthesized using the sol-gel method. Depending on the feeding schedule of PWA during synthesis, the size of the formed PWA/SiO2 particles varied considerably from as small as 1.2 nm to ca. 10 nm. With decreasing silica particle size, the total contact area/interaction between SiO2 and PWA increases, as revealed by FT-IR and solid-state 29Si-NMR analyses. Particularly, when the size of PWA/SiO2 is 1 nm, crystallization of PWA is inhibited, and PWA presents as amorphous molecular entities distributing uniformly in the SiO2 host, which is in evidence in the XRD spectroscopy and HR-TEM imaging. In contrast, substantial crystallization of PWA takes place when PWA/SiO2 particles are as large as 10 nm, in which case less amount of surface free Si-OH is available for PWA to make bonds with. Photochromism occurs activated by ultraviolet light irradiation. The rate of coloration/bleaching is found to depend strongly on the particle size of PWA/SiO2; specifically, the rate increases twice when the particle size is reduced from 10 nm to 1.2 nm.
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Lee, Sang-Jin; Jung, Choong-Hwan
2012-01-01
Nano-sized yttria (Y2O3) powders were successfully synthesized at a low temperature of 400 degrees C by a simple polymer solution route. PVA polymer, as an organic carrier, contributed to an atom-scale homogeneous precursor gel and it resulted in fully crystallized, nano-sized yttria powder with high specific surface area through the low temperature calcination. In this process, the content of PVA, calcination temperature and heating time affected the microstructure and crystallization behavior of the powders. The development of crystalline phase and the final particle size were strongly dependant on the oxidation reaction from the polymer burn-out step and the PVA content. In this paper, the PVA solution technique for the fabrication of nano-sized yttria powders is introduced. The effects of PVA content and holding time on the powder morphology and powder specific surface area are also studied. The characterization of the synthesized powders is examined by using XRD, DTA/TG, SEM, TEM and nitrogen gas adsorption. The yttria powder synthesized from the PVA content of 3:1 ratio and calcined at 400 degrees C had a crystallite size of about 20 nm or less with a high surface areas of 93.95-120.76 m2 g(-1).
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Chaikuad, Apirat, E-mail: apirat.chaikuad@sgc.ox.ac.uk; Knapp, Stefan; Johann Wolfgang Goethe-University, Building N240 Room 3.03, Max-von-Laue-Strasse 9, 60438 Frankfurt am Main
An alternative strategy for PEG sampling is suggested through the use of four newly defined PEG smears to enhance chemical space in reduced screens with a benefit towards protein crystallization. The quest for an optimal limited set of effective crystallization conditions remains a challenge in macromolecular crystallography, an issue that is complicated by the large number of chemicals which have been deemed to be suitable for promoting crystal growth. The lack of rational approaches towards the selection of successful chemical space and representative combinations has led to significant overlapping conditions, which are currently present in a multitude of commercially availablemore » crystallization screens. Here, an alternative approach to the sampling of widely used PEG precipitants is suggested through the use of PEG smears, which are mixtures of different PEGs with a requirement of either neutral or cooperatively positive effects of each component on crystal growth. Four newly defined smears were classified by molecular-weight groups and enabled the preservation of specific properties related to different polymer sizes. These smears not only allowed a wide coverage of properties of these polymers, but also reduced PEG variables, enabling greater sampling of other parameters such as buffers and additives. The efficiency of the smear-based screens was evaluated on more than 220 diverse recombinant human proteins, which overall revealed a good initial crystallization success rate of nearly 50%. In addition, in several cases successful crystallizations were only obtained using PEG smears, while various commercial screens failed to yield crystals. The defined smears therefore offer an alternative approach towards PEG sampling, which will benefit the design of crystallization screens sampling a wide chemical space of this key precipitant.« less
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NASA Astrophysics Data System (ADS)
Coutris, Pierre; Leroy, Delphine; Fontaine, Emmanuel; Schwarzenboeck, Alfons; Strapp, J. Walter
2016-04-01
A new method to retrieve cloud water content from in-situ measured 2D particle images from optical array probes (OAP) is presented. With the overall objective to build a statistical model of crystals' mass as a function of their size, environmental temperature and crystal microphysical history, this study presents the methodology to retrieve the mass of crystals sorted by size from 2D images using a numerical optimization approach. The methodology is validated using two datasets of in-situ measurements gathered during two airborne field campaigns held in Darwin, Australia (2014), and Cayenne, France (2015), in the frame of the High Altitude Ice Crystals (HAIC) / High Ice Water Content (HIWC) projects. During these campaigns, a Falcon F-20 research aircraft equipped with state-of-the art microphysical instrumentation sampled numerous mesoscale convective systems (MCS) in order to study dynamical and microphysical properties and processes of high ice water content areas. Experimentally, an isokinetic evaporator probe, referred to as IKP-2, provides a reference measurement of the total water content (TWC) which equals ice water content, (IWC) when (supercooled) liquid water is absent. Two optical array probes, namely 2D-S and PIP, produce 2D images of individual crystals ranging from 50 μm to 12840 μm from which particle size distributions (PSD) are derived. Mathematically, the problem is formulated as an inverse problem in which the crystals' mass is assumed constant over a size class and is computed for each size class from IWC and PSD data: PSD.m = IW C This problem is solved using numerical optimization technique in which an objective function is minimized. The objective function is defined as follows: 2 J(m)=∥P SD.m - IW C ∥ + λ.R (m) where the regularization parameter λ and the regularization function R(m) are tuned based on data characteristics. The method is implemented in two steps. First, the method is developed on synthetic crystal populations in order to evaluate the behavior of the iterative algorithm, the influence of data noise on the quality of the results, and to set up a regularization strategy. Therefore, 3D synthetic crystals have been generated and numerically processed to recreate the noise caused by 2D projections of randomly oriented 3D crystals and by the discretization of the PSD into size classes of predefined width. Subsequently, the method is applied to the experimental datasets and the comparison between the retrieved TWC (this methodology) and the measured ones (IKP-2 data) will enable the evaluation of the consistency and accuracy of the mass solution retrieved by the numerical optimization approach as well as preliminary assessment of the influence of temperature and dynamical parameters on crystals' masses.
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2 inch size Czochralski growth and scintillation properties of Li+ co-doped Ce:Gd3Ga3Al2O12
NASA Astrophysics Data System (ADS)
Kamada, Kei; Shoji, Yasuhiro; Kochurikhin, Vladimir V.; Yoshino, Masao; Okumura, Satoshi; Yamamoto, Seiichi; Yeom, Jung Yeol; Kurosawa, Shunsuke; Yokota, Yuui; Ohashi, Yuji; Nikl, Martin; Yoshino, Masao; Yoshikawa, Akira
2017-03-01
The 2 inch size Li 0.15 and 1.35 mol% co-doped Ce:Gd3Al2Ga3O12 single crystals were prepared by the Czochralski (Cz) method. Absorption and luminescence spectra were measured together with several other scintillation characteristics, namely the scintillation decay and light yield to reveal the effect of Li co-doping. Ce4+ CT absorption below 350 nm is clearly enhanced by Li co-doping as same as divalent ions co-doping. By 1.35 at.% Li co-doping, light yield was decrease to 88% of the Ce: GAGG standard and decay time was accelerated to 34.3ns 21.0%, 84.6ns 68.7%, 480ns 10.3%. The timing resolution measurement for a pair of 3 × 3 × 3mm3 size Li,Ce:GAGG scintillator crystals was performed using Si-PMs and the timing resolution of the 1.35 at.% Li co-doped Ce:GAGG was 218ps.
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Bio-inspired routes for synthesizing efficient nanoscale platinum electrocatalysts
DOE Office of Scientific and Technical Information (OSTI.GOV)
Cha, Jennifer N.; Wang, Joseph
2014-08-31
The overall objective of the proposed research is to use fundamental advances in bionanotechnology to design powerful platinum nanocrystal electrocatalysts for fuel cell applications. The new economically-viable, environmentally-friendly, bottom-up biochemical synthetic strategy will produce platinum nanocrystals with tailored size, shape and crystal orientation, hence leading to a maximum electrochemical reactivity. There are five specific aims to the proposed bio-inspired strategy for synthesizing efficient electrocatalytic platinum nanocrystals: (1) isolate peptides that both selectively bind particular crystal faces of platinum and promote the nucleation and growth of particular nanocrystal morphologies, (2) pattern nanoscale 2-dimensional arrays of platinum nucleating peptides from DNA scaffolds,more » (3) investigate the combined use of substrate patterned peptides and soluble peptides on nanocrystal morphology and growth (4) synthesize platinum crystals on planar and large-area carbon electrode supports, and (5) perform detailed characterization of the electrocatalytic behavior as a function of catalyst size, shape and morphology. Project Description and Impact: This bio-inspired collaborative research effort will address key challenges in designing powerful electrocatalysts for fuel cell applications by employing nucleic acid scaffolds in combination with peptides to perform specific, environmentally-friendly, simultaneous bottom-up biochemical synthesis and patterned assembly of highly uniform and efficient platinum nanocrystal catalysts. Bulk synthesis of nanoparticles usually produces a range of sizes, accessible catalytic sites, crystal morphologies, and orientations, all of which lead to inconsistent catalytic activities. In contrast, biological systems routinely demonstrate exquisite control over inorganic syntheses at neutral pH and ambient temperature and pressures. Because the orientation and arrangement of the templating biomolecules can be precisely controlled, the nanocrystals boast a defined shape, morphology, orientation and size and are synthesized at benign reaction conditions. Adapting the methods of biomineralization towards the synthesis of platinum nanocrystals will allow effective control at a molecular level of the synthesis of highly active metal electrocatalysts, with readily tailored properties, through tuning of the biochemical inputs. The proposed research will incorporate many facets of biomineralization by: (1) isolating peptides that selectively bind particular crystal faces of platinum (2) isolating peptides that promote the nucleation and growth of particular nanocrystal morphologies (3) using two-dimensional DNA scaffolds to control the spatial orientation and density of the platinum nucleating peptides, and (4) combining bio-templating and soluble peptides to control crystal nucleation, orientation, and morphology. The resulting platinum nanocrystals will be evaluated for their electrocatalytic behavior (on common carbon supports) to determine their optimal size, morphology and crystal structure. We expect that such rational biochemical design will lead to highly uniform and efficient platinum nanocrystal catalysts for fuel cell applications.« less
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Polymer-induced phase separation and crystallization in immunoglobulin G solutions.
Li, Jianguo; Rajagopalan, Raj; Jiang, Jianwen
2008-05-28
We study the effects of the size of polymer additives and ionic strength on the phase behavior of a nonglobular protein-immunoglobulin G (IgG)-by using a simple four-site model to mimic the shape of IgG. The interaction potential between the protein molecules consists of a Derjaguin-Landau-Verwey-Overbeek-type colloidal potential and an Asakura-Oosawa depletion potential arising from the addition of polymer. Liquid-liquid equilibria and fluid-solid equilibria are calculated by using the Gibbs ensemble Monte Carlo technique and the Gibbs-Duhem integration (GDI) method, respectively. Absolute Helmholtz energy is also calculated to get an initial coexisting point as required by GDI. The results reveal a nonmonotonic dependence of the critical polymer concentration rho(PEG) (*) (i.e., the minimum polymer concentration needed to induce liquid-liquid phase separation) on the polymer-to-protein size ratio q (equivalently, the range of the polymer-induced depletion interaction potential). We have developed a simple equation for estimating the minimum amount of polymer needed to induce the liquid-liquid phase separation and show that rho(PEG) (*) approximately [q(1+q)(3)]. The results also show that the liquid-liquid phase separation is metastable for low-molecular weight polymers (q=0.2) but stable at large molecular weights (q=1.0), thereby indicating that small sizes of polymer are required for protein crystallization. The simulation results provide practical guidelines for the selection of polymer size and ionic strength for protein phase separation and crystallization.
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Lu, Wenfu; Zhou, Dan; Freeman, John J; Thalmann, Isolde; Ornitz, David M; Thalmann, Ruediger
2010-09-01
Otoconia are biomineral particles of microscopic size essential for perception of gravity and maintenance of balance. Millions of older Americans are affected in their mobility, quality of life and in their health by progressive demineralization of otoconia. Currently, no effective means to prevent or counteract this process are available. Because of prohibitive anatomical and biological constraints, otoconial research is lagging far behind other systems such as bone and teeth. We have overcome these obstacles by generating otoconial matrix proteins by recombinant techniques. In the present study, we evaluated the effects of recombinant Otoconin 90 (OC90), the principal soluble matrix protein upon calcite crystal growth patterns in vitro. Our findings highlight multiple effects, including facilitation of nucleation, and inhibition of crystal growth in a concentration-dependent manner. Moreover, OC90 induces morphologic changes characteristic of native otoconia. OC90 is considerably less acidic than the prototypical invertebrate CaCO(3) -associated protein, but is nevertheless an effective modulator of calcite crystal growth. Based on homology modeling of the sPLA2-like domains of OC90, we propose that the lower density of acidic residues of the primary sequence is compensated by formation of major anionic surface clusters upon folding into tertiary conformation. Copyright (c) 2010 Elsevier B.V. All rights reserved.
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NASA Astrophysics Data System (ADS)
Mann, Nishan; Hughes, Stephen
2018-02-01
We present the analytical and numerical details behind our recently published article [Phys. Rev. Lett. 118, 253901 (2017), 10.1103/PhysRevLett.118.253901], describing the impact of disorder-induced multiple scattering on counterpropagating solitons in photonic crystal waveguides. Unlike current nonlinear approaches using the coupled mode formalism, we account for the effects of intraunit cell multiple scattering. To solve the resulting system of coupled semilinear partial differential equations, we introduce a modified Crank-Nicolson-type norm-preserving implicit finite difference scheme inspired by the transfer matrix method. We provide estimates of the numerical dispersion characteristics of our scheme so that optimal step sizes can be chosen to either minimize numerical dispersion or to mimic the exact dispersion. We then show numerical results of a fundamental soliton propagating in the presence of multiple scattering to demonstrate that choosing a subunit cell spatial step size is critical in accurately capturing the effects of multiple scattering, and illustrate the stochastic nature of disorder by simulating soliton propagation in various instances of disordered photonic crystal waveguides. Our approach is easily extended to include a wide range of optical nonlinearities and is applicable to various photonic nanostructures where power propagation is bidirectional, either by choice, or as a result of multiple scattering.
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Melo, E. G., E-mail: emerdemelo@usp.br; Alvarado, M. A.; Carreño, M. N. P.
2016-01-14
Photonic crystal slabs with a lower-index material surrounding the core layer are an attractive choice to circumvent the drawbacks in the fabrication of membranes suspended in air. In this work we propose a photonic crystal (PhC) slab structure composed of a triangular pattern of air holes in a multilayer thin film of aluminum nitride embedded in silicon dioxide layers designed for operating around 450 nm wavelengths. We show the design of an ideal structure and analyze the effects of material dispersion based on a first-order correction perturbation theory approach using dielectric functions obtained by experimental measurements of the thin film materials.more » Numerical methods were used to investigate the effects of fabrication induced disorder of typical nanofabrication processes on the bandgap size and spectral response of the proposed device. Deviation in holes radii and positions were introduced in the proposed PhC slab model with a Gaussian distribution profile. Impacts of slope in holes sidewalls that might result from the dry etching of AlN were also evaluated. The results show that for operation at the midgap frequency, slope in holes sidewalls is more critical than displacements in holes sizes and positions.« less
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Morphology Controls on Calcite Recrystallization.
Heberling, Frank; Paulig, Leonie; Nie, Zhe; Schild, Dieter; Finck, Nicolas
2016-11-01
Environmental scientists and geoscientists working in different fields regard the reactivity of calcite and corresponding changes in its trace elemental- or isotopic composition from diametrically opposed points of view. As one extreme, calcite based environmental remediation strategies rely on the fast recrystallization of calcite and the concurrent uptake and immobilization of pollutants. Paleo-ecological investigations denote the other extreme, and rely on the invariability of calcite composition over geological periods of time. We use long-term radiotracer experiments to quantify recrystallization rates of seven types of calcite powder with diverse morphology and particle size distribution. On the one hand our results demonstrate the long-term metastability of calcite with equilibrated crystal surfaces even at isotopic dis-equilibrium. On the other hand, we document the extremely high reactivity and interfacial free energy of freshly ground, rough calcite. Our results indicate that bulk calcite recrystallization is an interfacial free energy driven Ostwald-ripening process, in which particle roughness effects dominate over the effect of crystal habitus and particle size. We confirm that the dynamic equilibrium exchange of crystal constituents between kink sites involves an activation barrier of about 25 kJ/mol. At room temperature the equilibrium exchange is limited to a near surface region and proceeds at a rate of (3.6 ± 1.4)·10 -13 mol/(m 2 ·s).
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Diez-Berart, Sergio; López, David O.; Sebastián, Nerea; de la Fuente, María Rosario; Salud, Josep; Robles-Hernández, Beatriz; Pérez-Jubindo, Miguel Ángel
2014-01-01
We report an experimental study on confined systems formed by butyloxybenzylidene octylaniline liquid crystal (4O.8) + γ-alumina nanoparticles. The effects of the confinement in the thermal and dielectric properties of the liquid crystal under different densities of nanoparticles is analyzed by means of high resolution Modulated Differential Scanning Calorimetry (MDSC) and broadband dielectric spectroscopy. First, a drastic depression of the N-I and SmA-N transition temperatures is observed with confinement, the more concentration of nanoparticles the deeper this depression is, driving the nematic range closer to the room temperature. An interesting experimental law is found for both transition temperatures. Second, the change in shape of the heat capacity peaks is quantified by means of the full width half maximum (FWHM). Third, the confinement does not noticeably affect the molecular dynamics. Finally, the combination of nanoparticles and the external applied electric field tends to favor the alignment of the molecules in metallic cells. All these results indicate that the confinement of liquid crystals by means of γ-alumina nanoparticles could be optimum for liquid crystal-based electrooptic devices. PMID:28788528
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NASA Astrophysics Data System (ADS)
Wang, Jingcheng; Luo, Jingrun
2018-04-01
Due to the extremely high particle volume fraction (greater than 85%) and damage feature of polymer bonded explosives (PBXs), conventional micromechanical methods lead to inaccurate estimates on their effective elastic properties. According to their manufacture characteristics, a multistep approach based on micromechanical methods is proposed. PBXs are treated as pseudo poly-crystal materials consisting of equivalent composite particles (explosive crystals with binder coating), rather than two-phase composites composed of explosive particles and binder matrix. Moduli of composite spheres are obtained by generalized self-consistent method first, and the self-consistent method is modified to calculate the effective moduli of PBX. Defects and particle size distribution are considered by Mori-Tanaka method. Results show that when the multistep approach is applied to PBX 9501, estimates are far more accurate than the conventional micromechanical results. The bulk modulus is 5.75% higher, and shear modulus is 5.78% lower than the experimental values. Further analyses discover that while particle volume fraction and the binder's property have significant influences on the effective moduli of PBX, the moduli of particles present minor influences. Investigation of another particle size distribution indicates that the use of more fine particles will enhance the effective moduli of PBX.
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X-ray spectrometer having 12 000 resolving power at 8 keV energy
NASA Astrophysics Data System (ADS)
Seely, John F.; Hudson, Lawrence T.; Henins, Albert; Feldman, Uri
2017-10-01
An x-ray spectrometer employing a thin (50 μm) silicon transmission crystal was used to record high-resolution Cu Kα spectra from a laboratory x-ray source. The diffraction was from the (331) planes that were at an angle of 13.26° to the crystal surface. The components of the spectral lines resulting from single-vacancy (1s) and double-vacancy (1s and 3d) transitions were observed. After accounting for the natural lifetime widths from reference double-crystal spectra and the spatial resolution of the image plate detector, the intrinsic broadening of the transmission crystal was measured to be as small as 0.67 eV and the resolving power 12 000, the highest resolving power achieved by a compact (0.5 m long) spectrometer employing a single transmission crystal operating in the hard x-ray region. By recording spectra with variable source-to-crystal distances and comparing to the calculated widths from various geometrical broadening mechanisms, the primary contributions to the intrinsic crystal broadening were found to be the source height at small distances and the crystal apertured height at large distances. By reducing these two effects, using a smaller source size and vignetting the crystal height, the intrinsic crystal broadening is then limited by the crystal thickness and the rocking curve width and would be 0.4 eV at 8 keV energy (20 000 resolving power).
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Effect of the microstructure on electrical properties of high-purity germanium
NASA Astrophysics Data System (ADS)
Podkopaev, O. I.; Shimanskii, A. F.; Molotkovskaya, N. O.; Kulakovskaya, T. V.
2013-05-01
The interrelation between the electrical properties and the microstructure of high-purity germanium crystals has been revealed. The electrical conductivity of polycrystalline samples increases and the life-time of nonequilibrium charge carriers in them decreases with a decrease in the crystallite sizes.
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Compression deformation of WC: atomistic description of hard ceramic material
NASA Astrophysics Data System (ADS)
Feng, Qing; Song, Xiaoyan; Liu, Xuemei; Liang, Shuhua; Wang, Haibin; Nie, Zuoren
2017-11-01
The deformation characteristics of WC, as a typical hard ceramic material, were studied on the nanoscale using atomistic simulations for both the single-crystal and polycrystalline forms under uniaxial compression. In particular, the effects of crystallographic orientation, grain boundary coordination and grain size on the origin of deformation were investigated. The deformation behavior of the single-crystal and polycrystalline WC both depend strongly on the orientation towards the loading direction. The grain boundaries play a significant role in the deformation coordination and the potential high fracture toughness of the nanocrystalline WC. In contrast to conventional knowledge of ceramics, maximum strength was obtained at a critical grain size corresponding to the turning point from a Hall-Petch to an inverse Hall-Petch relationship. For this the mechanism of the combined effect of dislocation motion within grains and the coordination of stress concentration at the grain boundaries were proposed. The present work has moved forward our understanding of plastic deformability and the possibility of achieving a high strength of nanocrystalline ceramic materials.
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Ji Shidong; Murakami, Setsuaki; Kamitakahara, Masanobu
The titania/hydroxyapatite composite granular photo-catalyst with novel microstructure was fabricated by the process based on the liquid immiscibility effect and followed by precalcination and hydrothermal treatment from commercially available powders of {alpha}-Tri-calcium phosphate and TiO{sub 2}. XRD, SEM, BET, optical microscopy and UV-vis spectrophotometer were applied to characterize the prepared photo-catalyst. Microstructure analysis indicated that the granule was weaved by rod-shaped hydroxyapatite crystals whose surface was covered by nano-sized TiO{sub 2}. In the composite granules, the active surface of anatase was retained effectively. With the hybridization of TiO{sub 2} and HAp, a 16-nm blue-shift of absorption edge could be observedmore » and the crystallinity of anatase could be enhanced by precalcination. The granules with the rod-shaped hydroxyapatite crystals performing as scaffold work as three-dimensional high porous, size-controllable small reactor. The phase and microstructure transformation of the granule before and after hydrothermal treatment was investigated and its decomposition ability was evaluated by using Methylene blue as a target pollutant compound.« less
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Interacting effects of strengthening and twin boundary migration in nanotwinned materials
NASA Astrophysics Data System (ADS)
Joshi, Kartikey; Joshi, Shailendra P.
Twin boundaries play a governing role in the mechanical characteristics of nanotwinned materials. They act as yield strengthening agents by offering resistance to non-coplanar dislocation slip. Twin boundary migration may cause yield softening while also enhancing the strain hardening response. In this work, we investigate the interaction between strengthening and twin boundary migration mechanisms by developing a length-scale dependent crystal plasticity framework for face-centered-cubic nanotwinned materials. The crystal plasticity model incorporates strengthening mechanisms due to dislocation pile-up via slip and slip-rate gradients and twin boundary migration via source-based twin partial nucleation and lattice dislocation-twin boundary interaction. The coupled effect of the load orientation and initial twin size on the speed of twin boundary is discussed and an expression for the same is proposed in terms of relevant material parameters. The efficacy of finite element simulations and the analytical expression in predicting evolution of nanotwinned microstructures comprising size and spatial distributions of twins is demonstrated.
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Compression deformation of WC: atomistic description of hard ceramic material.
Feng, Qing; Song, Xiaoyan; Liu, Xuemei; Liang, Shuhua; Wang, Haibin; Nie, Zuoren
2017-11-24
The deformation characteristics of WC, as a typical hard ceramic material, were studied on the nanoscale using atomistic simulations for both the single-crystal and polycrystalline forms under uniaxial compression. In particular, the effects of crystallographic orientation, grain boundary coordination and grain size on the origin of deformation were investigated. The deformation behavior of the single-crystal and polycrystalline WC both depend strongly on the orientation towards the loading direction. The grain boundaries play a significant role in the deformation coordination and the potential high fracture toughness of the nanocrystalline WC. In contrast to conventional knowledge of ceramics, maximum strength was obtained at a critical grain size corresponding to the turning point from a Hall-Petch to an inverse Hall-Petch relationship. For this the mechanism of the combined effect of dislocation motion within grains and the coordination of stress concentration at the grain boundaries were proposed. The present work has moved forward our understanding of plastic deformability and the possibility of achieving a high strength of nanocrystalline ceramic materials.
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Shock Initiation Characteristics of an Aluminized DNAN/RDX Melt-Cast Explosive
NASA Astrophysics Data System (ADS)
Cao, Tong-Tang; Zhou, Lin; Zhang, Xiang-Rong; Zhang, Wei; Miao, Fei-Chao
2017-10-01
Shock sensitivity is one of the key parameters for newly developed, 2,4-dinitroanisole (DNAN)-based, melt-cast explosives. For this paper, a series of shock initiation experiments were conducted using a one-dimensional Lagrangian system with a manganin piezoresistive pressure gauge technique to evaluate the shock sensitivity of an aluminized DNAN/cyclotrimethylenetrinitramine (RDX) melt-cast explosive. This study fully investigated the effects of particle size distributions in both RDX and aluminum, as well as the RDX's crystal quality on the shock sensitivity of the aluminized DNAN/RDX melt-cast explosive. Ultimately, the shock sensitivity of the aluminized DNAN/RDX melt-cast explosives increases when the particle size decreases in both RDX and aluminum. Additionally, shock sensitivity increases when the RDX's crystal quality decreases. In order to simulate these effects, an Ignition and Growth (I&G) reactive flow model was calibrated. This calibrated I&G model was able to predict the shock initiation characteristics of the aluminized DNAN/RDX melt-cast explosive.
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The development of a super-fine-grained nuclear emulsion
NASA Astrophysics Data System (ADS)
Asada, Takashi; Naka, Tatsuhiro; Kuwabara, Ken-ichi; Yoshimoto, Masahiro
2017-06-01
A nuclear emulsion with micronized crystals is required for the tracking detection of submicron ionizing particles, which are one of the targets of dark-matter detection and other techniques. We found that a new production method, called the PVA—gelatin mixing method (PGMM), could effectively control crystal size from 20 nm to 50 nm. We called the two types of emulsion produced with the new method the nano imaging tracker and the ultra-nano imaging tracker. Their composition and spatial resolution were measured, and the results indicate that these emulsions detect extremely short tracks.
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Optimal fusion offset in splicing photonic crystal fibers
NASA Astrophysics Data System (ADS)
Jin, Wa; Bi, Weihong; Fu, Guangwei
2013-08-01
Heat transfer is very complicate in fusion splicing process of photonic crystal fibers (PCFs) due to different structures and sizes of air hole, which requires different fusion splicing power and offsets of heat source. Based on the heat transfer characteristics, this paper focus on the optimal splicing offset splicing the single mode fiber and PCFs with a CO2 laser irradiation. The theory and experiments both show that the research results can effectively calculate the optimal fusion splicing offset and guide the practical splicing between PCFs and SMFs.
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Numerical simulation of flow and mass transfer for large KDP crystal growth via solution-jet method
NASA Astrophysics Data System (ADS)
Yin, Huawei; Li, Mingwei; Hu, Zhitao; Zhou, Chuan; Li, Zhiwei
2018-06-01
A novel technique of growing large crystals of potassium dihydrogen phosphate (KDP) named solution-jet method is proposed. The aim is to increase supersaturation on the pyramidal face, especially for crystal surface regions close to the rotation axis. The fluid flow and surface supersaturation distribution of crystals grown under different conditions were computed using the finite-volume method. Results indicate that the time-averaged supersaturation of the pyramidal face in the proposed method significantly increases and the supersaturation difference from the crystal center to edge clearly decreases compared with the rotating-crystal method. With increased jet velocity, supersaturation on the pyramidal face steadily increases. Rotation rate considerably affects the magnitude and distribution of the prismatic surface supersaturation. With increased crystal size, the mean value of surface supersaturation averaged over the pyramid gradually decreases; conversely, standard deviation increases, which is detrimental to crystal growth. Moreover, the significant roles played by natural and forced convection in the process of mass transport are discussed. Results show that further increased jet velocity to 0.6 m/s renders negligible the effects of natural convection around the pyramid. The simulation for step propagation indicates that solution-jet method can promote a steady step migration and enhance surface morphology stability, which can improve the crystal quality.
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The effect of a solid surface on the segregation and melting of salt hydrates.
Zhang, Yu; Anim-Danso, Emmanuel; Dhinojwala, Ali
2014-10-22
Considering the importance of salt and water on earth, the crystallization of salt hydrates next to solid surfaces has important implications in physical and biological sciences. Heterogeneous nucleation is driven by surface interactions, but our understanding of hydrate formation near surfaces is limited. Here, we have studied the hydrate formation of three commonly prevalent salts, MgCl2, CaCl2, and NaCl, next to a sapphire substrate using surface sensitive infrared-visible sum frequency generation (SFG) spectroscopy. SFG spectroscopy can detect the crystallization and melting of salt hydrates at the interface by observing the changes in the intensity and the location of the cocrystallized water hydroxyl peaks (3200-3600 cm(-1)). The results indicate that the surface crystal structures of these three hydrates are similar to those in the bulk. For the NaCl solution, the brine solution is segregated next to the sapphire substrate after the formation of the ice phase. In contrast, the MgCl2 and CaCl2 surface hydrate crystals are interdispersed with nanometer-size ice crystals. The nanosize ice crystals melt at much lower temperatures than bulk ice crystals. For NaCl and MgCl2 solution, the NaCl hydrates prefer to crystallize next to the sapphire substrate instead of the ice crystals and MgCl2 hydrates.
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NASA Technical Reports Server (NTRS)
Regnault, W. F.; Yoo, K. C.; Soltani, P. K.; Johnson, S. M.
1984-01-01
Silicon ingot growth technologies like the Ubiquitous Crystallization Process (UCP) are solidified within a shaping crucible. The rate at which heat can be lost from this crucible minus the rate at which heat is input from an external source determines the rate at which crystallization will occur. Occasionally, when the process parameters for solidification are exceeded, the normally large multi-centimeter grain size material assocated with the UCP will break down into regions containing extremely small, millimeter or less, grain size material. Accompanying this breakdown in grain growth is the development of so called sinuous grain boundaries. The breakdown in grain growth which results in this type of small grain structure with sinuous boundaries is usually associated with the rapid crystallization that would accompany a system failure. This suggests that there are limits to the growth velocity that one can obtain and still expect to produce material that would possess good photovoltaic properties. It is the purpose to determine the causes behind the breakdown of this material and what parameters will determine the best rates of solidification.
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Ion beam radiation effects on natural halite crystals
NASA Astrophysics Data System (ADS)
Arun, T.; Ram, S. S.; Karthikeyan, B.; Ranjith, P.; Ray, D. K.; Rout, B.; Krishna, J. B. M.; Sengupta, Pranesh; Parlapalli, Venkata Satyam
2017-10-01
Halites are one of the interesting material due to its color variations. Natural halites whose color ranges from transparent to dark blue were studied by UV-VIS and Raman spectroscopy. The halite crystals were irradiated with 3 MeV proton micro-beam (∼20 μm beam width with ∼80 PA beam current) for 10 and 90 min to study the radiation damage. After 10 mins of irradiation, small spot developed on the surface of transparent halite crystal whereas after 90 mins of irradiation the spot spread inside the bulk leading to a brown coloration (20 μm initial size to ∼2.0 mm final size). The irradiated portion and the un-irradiated portion of the halites was characterized by Raman spectroscopic technique. The variation in the population density was observed from the UV-Vis spectra. The change in the Raman band intensities was observed for transparent, blue colored and proton beam irradiation halites. Such variation of spectroscopic characteristics due to proton irradiation suggests that the halite can be used for the radiation monitoring.
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An Alternative Hypothesis for How Microgravity Improves Macromolecular Crystal Quality
NASA Technical Reports Server (NTRS)
Pusey, Marc
2003-01-01
There is a substantial body of experimental evidence, from this and other laboratories, that strongly suggests that for many proteins crystal nucleation and growth is by addition of associated species that are preformed by reversible concentration-driven self association processes in the bulk solution. We have developed a self-association model for the crystal nucleation and growth of the protein chicken egg lysozyme. The model accounts for the obtained crystal symmetry, explains the observed surface structures, and shows the importance of the symmetry obtained by self-association in solution to the process as a whole. This model also offers a possible mechanism for fluid flow effects on the growth process and how microgravity may affect it. While a single lysozyme molecule is relatively small an octamer in the 43 helix configuration (the proposed average sized growth unit) would have a M.W. approx. 115,000 and dimensions of 5.6 x 5.6 x 7.6 nm. Direct AFM measurements of growth unit incorporation indicate that units as wide as 11.2 nm and as long as 11.4 nm (a 24-mer) commonly attach to the crystal. AFM results from Weichmann et al. (Ultramicroscopy 86, 159-166, 2001) suggest that associated species of up to 40-mers in size add to the (101) faces. These measurements reflect the sizes of units that both added and desorbed from the crystal surface. The larger and less isotropic the associated species the more likely that it will be oriented to some degree in a flowing boundary layer, even at the low flow velocities measured about macromolecule crystals. On Earth, concentration gradient driven flow will maintain a high interfacial concentration, i.e., a high level (essentially that of the bulk solution) of solute association at the interface and higher growth rate. Higher growth rates mean an increased probability that misaligned growth units are trapped by subsequent growth layers before they can be desorbed and try again, or that the desorbing species is more likely to be smaller than the adsorbing species. In microgravity the extended diffusive boundary layer will lower the interfacial concentration. This results in a net dissociation of aggregated species that diffuse in from the bulk solution, i.e., smaller associated species, which are more likely able to make multiple attempts to correctly bind, yielding higher quality crystals.
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Zu, Shuchong; Yang, Lei; Huang, Jinming; Ma, Chunhui; Wang, Wenjie; Zhao, Chunjian; Zu, Yuangang
2012-01-01
The aim of this study was to prepare micronized taxifolin powder using the supercritical antisolvent precipitation process to improve the dissolution rate of taxifolin. Ethanol was used as solvent and carbon dioxide was used as an antisolvent. The effects of process parameters, such as temperature (35–65 °C), pressure (10–25 MPa), solution flow rate (3–6 mL/min) and concentration of the liquid solution (5–20 mg/mL) on the precipitate crystals were investigated. With a lower temperature, a stronger pressure and a lower concentration of the liquid solution, the size of crystals decreased. The precipitation temperature, pressure and concentration of taxifolin solution had a significant effect. However, the solution flow rate had a negligible effect. It was concluded that the physicochemical properties and dissolution rate of crystalline taxifolin could be improved by physical modification such as particle size reduction using the supercritical antisolvent (SAS) process. Further, the SAS process was a powerful methodology for improving the physicochemical properties and radical scavenging activity of taxifolin. PMID:22942740
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NASA Astrophysics Data System (ADS)
Prabhakaran, SP.; Ramesh Babu, R.; Sukumar, M.; Bhagavannarayana, G.; Ramamurthi, K.
2014-03-01
Growth of bulk single crystal of 4-Aminobenzophenone (4-ABP) from the vertical dynamic gradient freeze (VDGF) setup designed with eight zone furnace was investigated. The experimental parameters for the growth of 4-ABP single crystal with respect to the design of VDGF setup are discussed. The eight zones were used to generate multiple temperature gradients over the furnace, and video imaging system helped to capture the real time growth and solid-liquid interface. 4-ABP single crystal with the size of 18 mm diameter and 40 mm length was grown from this investigation. Structural and optical quality of grown crystal was examined by high resolution X-ray diffraction and UV-visible spectral analysis, respectively and the blue emission was also confirmed from the photoluminescence spectrum. Microhardness number of the crystal was estimated at different loads using Vicker's microhardness tester. The size and quality of single crystal grown from the present investigation are compared with the vertical Bridgman grown 4-ABP.
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Liu, Lifeng; Ding, Xiangdong; Li, Ju; Lookman, Turab; Sun, Jun
2014-02-21
Martensitic transformation usually creates hierarchical internal structures beyond mere change of the atomic crystal structure. Multi-stage nucleation is thus required, where nucleation (level-1) of the underlying atomic crystal lattice does not have to be immediately followed by the nucleation of higher-order superstructures (level-2 and above), such as polysynthetic laths. Using in situ transmission electron microscopy (TEM), we directly observe the nucleation of the level-2 superstructure in a Cu-Al-Ni single crystal under compression, with critical super-nuclei size L2c around 500 nm. When the sample size D decreases below L2c, the superelasticity behavior changes from a flat stress plateau to a continuously rising stress-strain curve. Such size dependence definitely would impact the application of shape memory alloys in miniaturized MEMS/NEMS devices.
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Thomas g. Shelton; Laurent Cartier; Terence L. Wagner; Christian Becker
2007-01-01
We examined the efficacy of termiticidal baits comprised of powdered acellulose and a mineral insecticide, cryolite crystals, in laboratory bioassays against pseudergates of Eastern subterranean termites [Reticulitermes flavipes (Kollar)]. The influence of cryolite crystal size [0 (control), 0.2, and 20 pm diameter particles] on the overall mortality...
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NASA Astrophysics Data System (ADS)
Bertinotti, A.; Viallet, V.; Colson, D.; Marucco, J.-F.; Hammann, J.; Forget, A.; Le Bras, G.
1996-02-01
Single crystals of HgBa2CuO4+δ of submillimetric sizes were grown with the same one step, low pressure, gold amalgamation technique used to obtain single crystals of HgBa2Ca2Cu3O8+δ. Remarkable superconducting properties are displayed by the samples which are optimally doped as grown. The sharpness of the transition profiles of the magnetic susceptibility, its anisotropy dependence and the volume fraction exhibiting the Meissner effect exceed the values obtained with the best crystal samples of Hg-1223. X-rays show that no substitutional defects have been found in the mercury plane, in particular no mixed occupancy of copper at the mercury site. The interstitial oxygen content at (1/2, 1/2, 0) δ = 0.066+/-0.008 is about one third that observed in optimally doped Hg-1223, resulting in an identical doping level per CuO2 plane in both compounds.
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NASA Astrophysics Data System (ADS)
Walcher, H.; Diehl, R.; Baars, J.
The technical importance of the mixed-crystal system Hg(1-x)Cd(x)Te (MCT) is related to a growing interest in detector devices for the infrared spectral ranges of the two atmospheric 'windows'. Applications are not restricted to the military sector, but are also related to astronomy, archeology, medicine, construction engineering, fire fighting, and the determination of pollutants in the atmosphere. It is found that MCT is uniquely qualified for the considered applications, because no other material combines, in the same way, all the required characteristics. However, problems arise in connection with the need for pure, homogeneous, single crystals of adequate size, which are free of any defects. The best results in attempts to grow such crystals have been obtained in experiments utilizing the traveling heater method (THM). Remaining difficulties are caused by effects of gravity. It is, therefore, expected that the crystals needed can be produced under conditions of microgravity. Suitable experiments for exploring this possibility are discussed.
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Scintillation properties of a 2-inch diameter KCa0.8Sr0.2I3:Eu2+ single crystal
NASA Astrophysics Data System (ADS)
Wu, Yuntao; Lindsey, Adam C.; Loyd, Matthew; Stand, Luis; Zhuravleva, Mariya; Koschan, Merry; Melcher, Charles L.
2017-09-01
Inch-sized scintillating crystals are required for practical radiation detectors such as hand-held radio-isotope identification devices. In this work, a transparent and colorless 2-inch diameter KCa0.8Sr0.2I3: 0 . 5 mo% Eu2+ single crystal was grown by the vertical Bridgman method, and the scintillation properties of a ∅ 50 mm × 45 mm long sample were evaluated. The Eu2+ 5d1- 4 f emission under X-ray excitation is centered at 472 nm. Its scintillation decay time under 137 Cs source irradiation is 2 . 37 μs, and the absolute light output is 51,000 ± 3000 photons/MeV. The energy resolution at 662 keV was evaluated for different orientations of the crystals with respect to the PMT, and the effect of 40 K background subtraction on energy resolution was evaluated. The performance of the packaged crystal was also investigated.
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Wang, Xuping, E-mail: wangxp@sdas.org; Liu, Bing; Yang, Yuguo
2014-08-04
An abnormal laser deflection phenomenon in a copper-doped KTa{sub 1−x}Nb{sub x}O{sub 3} (Cu:KTN) crystal is demonstrated in this Letter. A near-50 mrad beam deflection angle was observed when a voltage of 1.2 kV was applied to a Cu:KTN block with size of 2.8 mm × 1.2 mm × 7.5 mm at room temperature. The special features of this deflection phenomenon are that the laser beam deflection direction is perpendicular to the electric field direction, and the beam deflection angle remains unchanged when the electric field direction is reversed. The operating principle of the phenomenon is investigated and the origin of the deflection phenomenon is attributed to an interactionmore » between the graded refractivity effect and the quadratic electro-optic effect of the crystal.« less
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The crystallization of tough thermoplastic resins in the presence of carbon fibers
NASA Technical Reports Server (NTRS)
Theil, Michael H.
1988-01-01
The presence of carbon fibers increased the crystallization rates of both PEEK and PPS thermoplastic polymers. The effect was most pronounced at higher crystallization temperatures. Isothermal crystallization rates were analyzed by applying classical phenomenological nucleation theory. Unusually high values of the so-called Avrami exponent were found for neat PEEK. Isothermal crystallization of PEEK and PPS polymers produced crystalline samples having a wide variety of melting temperatures. The melting as observed by differential scanning calorimetry occurred as dual endotherms which were called primary (higher temperature) and secondary melting peaks. Each primary peak accounted for most of the crystallinity present. The secondary peaks represented the melting of crystallites formed later than those attributable to the primary endotherms. The presence of carbon fibers increased the thermal stability of both PEEK and PPS crystallites as manifested by higher temperatures for the primary melting peaks. This may be attributable to increased crystallite size, greater crystallite perfection, and/or favorable modification of the crystallite interface. Over the range studied, crystallization temperature strongly influenced the positions of the secondary peaks but not the primary peaks.
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NASA Astrophysics Data System (ADS)
Svoboda, Martin; Lísal, Martin
2018-06-01
To address a high salinity of flow-back water during hydraulic fracturing, we use molecular dynamics (MD) simulations and study the thermodynamics, structure, and diffusion of concentrated aqueous salt solution in clay nanopores. The concentrated solution results from the dissolution of a cubic NaCl nanocrystal, immersed in an aqueous NaCl solution of varying salt concentration and confined in clay pores of a width comparable to the crystal size. The size of the nanocrystal equals to about 18 Å which is above a critical nucleus size. We consider a typical shale gas reservoir condition of 365 K and 275 bar, and we represent the clay pores as pyrophyllite and Na-montmorillonite (Na-MMT) slits. We employ the Extended Simple Point Charge (SPC/E) model for water, Joung-Cheatham model for ions, and CLAYFF for the slit walls. We impose the pressure in the normal direction and the resulting slit width varies from about 20 to 25 Å when the salt concentration in the surrounding solution increased from zero to an oversaturated value. By varying the salt concentration, we observe two scenarios. First, the crystal dissolves and its dissolution time increases with increasing salt concentration. We describe the dissolution process in terms of the number of ions in the crystal, and the crystal size and shape. Second, when the salt concentration reaches a system solubility limit, the crystal grows and attains a new equilibrium size; the crystal comes into equilibrium with the surrounding saturated solution. After crystal dissolution, we carry out canonical MD simulations for the concentrated solution. We evaluate the hydration energy, density profiles, orientation distributions, hydrogen-bond network, radial distribution functions, and in-plane diffusion of water and ions to provide insight into the microscopic behaviour of the concentrated aqueous sodium chloride solution in interlayer galleries of the slightly hydrophobic pyrophyllite and hydrophilic Na-MMT pores.
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Primary and secondary fragmentation of crystal-bearing intermediate magma
NASA Astrophysics Data System (ADS)
Jones, Thomas J.; McNamara, Keri; Eychenne, Julia; Rust, Alison C.; Cashman, Katharine V.; Scheu, Bettina; Edwards, Robyn
2016-11-01
Crystal-rich intermediate magmas are subjected to both primary and secondary fragmentation processes, each of which may produce texturally distinct tephra. Of particular interest for volcanic hazards is the extent to which each process contributes ash to volcanic plumes. One way to address this question is by fragmenting pyroclasts under controlled conditions. We fragmented pumice samples from Soufriere Hills Volcano (SHV), Montserrat, by three methods: rapid decompression in a shock tube-like apparatus, impact by a falling piston, and milling in a ball mill. Grain size distributions of the products reveal that all three mechanisms produce fractal breakage patterns, and that the fractal dimension increases from a minimum of 2.1 for decompression fragmentation (primary fragmentation) to a maximum of 2.7 by repeated impact (secondary fragmentation). To assess the details of the fragmentation process, we quantified the shape, texture and components of constituent ash particles. Ash shape analysis shows that the axial ratio increases during milling and that particle convexity increases with repeated impacts. We also quantify the extent to which the matrix is separated from the crystals, which shows that secondary processes efficiently remove adhering matrix from crystals, particularly during milling (abrasion). Furthermore, measurements of crystal size distributions before (using x-ray computed tomography) and after (by componentry of individual grain size classes) decompression-driven fragmentation show not only that crystals influence particular size fractions across the total grain size distribution, but also that free crystals are smaller in the fragmented material than in the original pumice clast. Taken together, our results confirm previous work showing both the control of initial texture on the primary fragmentation process and the contributions of secondary processes to ash formation. Critically, however, our extension of previous analyses to characterisation of shape, texture and componentry provides new analytical tools that can be used to assess contributions of secondary processes to ash deposits of uncertain or mixed origin. We illustrate this application with examples from SHV deposits.
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Svoboda, Martin; Lísal, Martin
2018-06-14
To address a high salinity of flow-back water during hydraulic fracturing, we use molecular dynamics (MD) simulations and study the thermodynamics, structure, and diffusion of concentrated aqueous salt solution in clay nanopores. The concentrated solution results from the dissolution of a cubic NaCl nanocrystal, immersed in an aqueous NaCl solution of varying salt concentration and confined in clay pores of a width comparable to the crystal size. The size of the nanocrystal equals to about 18 Å which is above a critical nucleus size. We consider a typical shale gas reservoir condition of 365 K and 275 bar, and we represent the clay pores as pyrophyllite and Na-montmorillonite (Na-MMT) slits. We employ the Extended Simple Point Charge (SPC/E) model for water, Joung-Cheatham model for ions, and CLAYFF for the slit walls. We impose the pressure in the normal direction and the resulting slit width varies from about 20 to 25 Å when the salt concentration in the surrounding solution increased from zero to an oversaturated value. By varying the salt concentration, we observe two scenarios. First, the crystal dissolves and its dissolution time increases with increasing salt concentration. We describe the dissolution process in terms of the number of ions in the crystal, and the crystal size and shape. Second, when the salt concentration reaches a system solubility limit, the crystal grows and attains a new equilibrium size; the crystal comes into equilibrium with the surrounding saturated solution. After crystal dissolution, we carry out canonical MD simulations for the concentrated solution. We evaluate the hydration energy, density profiles, orientation distributions, hydrogen-bond network, radial distribution functions, and in-plane diffusion of water and ions to provide insight into the microscopic behaviour of the concentrated aqueous sodium chloride solution in interlayer galleries of the slightly hydrophobic pyrophyllite and hydrophilic Na-MMT pores.
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NASA Technical Reports Server (NTRS)
Yang, P.; Gao, B.-C.; Baum, B. A.; Wiscombe, W.; Hu, Y.; Nasiri, S. L.; Soulen, P. F.; Heymsfield, A. J.; McFarquhar, G. M.; Miloshevich, L. M.
2000-01-01
A common assumption in satellite imager-based cirrus retrieval algorithms is that the radiative properties of a cirrus cloud may be represented by those associated with a specific ice crystal shape (or habit) and a single particle size distribution. However, observations of cirrus clouds have shown that the shapes and sizes of ice crystals may vary substantially with height within the clouds. In this study we investigate the sensitivity of the top-of-atmosphere bidirectional reflectances at two MODIS bands centered at 0.65 micron and 2.11 micron to the cirrus models assumed to be either a single homogeneous layer or three distinct but contiguous, layers. First, we define the single- and three-layer cirrus cloud models with respect to ice crystal habit and size distribution on the basis of in situ replicator data acquired during the First ISCCP Regional Experiment (FIRE-II), held in Kansas during the fall of 1991. Subsequently, fundamental light scattering and radiative transfer theory is employed to determine the single scattering and the bulk radiative properties of the cirrus cloud. Regarding the radiative transfer computations, we present a discrete form of the adding/doubling principle by introducing a direct transmission function, which is computationally straightforward and efficient an improvement over previous methods. For the 0.65 micron band, at which absorption by ice is negligible, there is little difference between the bidirectional reflectances calculated for the one- and three-layer cirrus models, suggesting that the vertical inhomogeneity effect is relatively unimportant. At the 2.11 micron band, the bidirectional reflectances computed for both optically thin (tau = 1) and thick (tau = 10) cirrus clouds show significant differences between the results for the one- and three-layer models. The reflectances computed for the three-layer cirrus model are substantially larger than those computed for the single-layer cirrus. Finally, we find that cloud reflectance is very sensitive to the optical properties of the small crystals that predominate in the top layer of the three-layer cirrus model. It is critical to define the most realistic geometric shape for the small "quasi-spherical" ice crystals in the top layer for obtaining reliable single-scattering parameters and bulk radiative properties of cirrus.
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Understanding Crystal Populations; Looking Towards 3D Quantitative Analysis
NASA Astrophysics Data System (ADS)
Jerram, D. A.; Morgan, D. J.
2010-12-01
In order to understand volcanic systems, the potential record held within crystal populations needs to be revealed. It is becoming increasingly clear, however, that the crystal populations that arrive at the surface in volcanic eruptions are commonly mixtures of crystals, which may be representative of simple crystallization, recycling of crystals and incorporation of alien crystals. If we can quantify the true 3D population within a sample then we will be able to separate crystals with different histories and begin to interrogate the true and complex plumbing within the volcanic system. Modeling crystal populations is one area where we can investigate the best methodologies to use when dealing with sections through 3D populations. By producing known 3D shapes and sizes with virtual textures and looking at the statistics of shape and size when such populations are sectioned, we are able to gain confidence about what our 2D information is telling us about the population. We can also use this approach to test the size of population we need to analyze. 3D imaging through serial sectioning or x-ray CT, provides a complete 3D quantification of a rocks texture. Individual phases can be identified and in principle the true 3D statistics of the population can be interrogated. In practice we need to develop strategies (as with 2D-3D transformations), that enable a true characterization of the 3D data, and an understanding of the errors and pitfalls that exist. Ultimately, the reproduction of true 3D textures and the wealth of information they hold, is now within our reach.
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Monitoring and modeling of ultrasonic wave propagation in crystallizing mixtures
NASA Astrophysics Data System (ADS)
Marshall, T.; Challis, R. E.; Tebbutt, J. S.
2002-05-01
The utility of ultrasonic compression wave techniques for monitoring crystallization processes is investigated in a study of the seeded crystallization of copper II sulfate pentahydrate from aqueous solution. Simple models are applied to predict crystal yield, crystal size distribution and the changing nature of the continuous phase. A scattering model is used to predict the ultrasonic attenuation as crystallization proceeds. Experiments confirm that modeled attenuation is in agreement with measured results.
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Rice-like hollow nano-CaCO3 synthesis
NASA Astrophysics Data System (ADS)
Ulkeryildiz, Eda; Kilic, Sevgi; Ozdemir, Ekrem
2016-09-01
We have shown that Ca(OH)2 solution is a natural stabilizer for CaCO3 particles. We designed a CO2 bubbling crystallization reactor to produce nano-CaCO3 particles in homogenous size distribution without aggregation. In the experimental set-up, the crystallization region was separated from the stabilization region. The produced nanoparticles were removed from the crystallization region into the stabilization region before aggregation or crystal growth. It was shown that rice-like hollow nano-CaCO3 particles in about 250 nm in size were produced with almost monodispersed size distribution. The particles started to dissolve through their edges as CO2 bubbles were injected, which opened-up the pores inside the particles. At the late stages of crystallization, the open pores were closed as a result of dissolution-recrystallization of the newly synthesized CaCO3 particles. These particles were stable in Ca(OH)2 solution and no aggregation was detected. The present methodology can be used in drug encapsulation into inorganic CaCO3 particles for cancer treatment with some modifications.
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NASA Astrophysics Data System (ADS)
Zhong, Mianzeng; Zhou, Ke; Wei, Zhongming; Li, Yan; Li, Tao; Dong, Huanli; Jiang, Lang; Li, Jingbo; Hu, Wenping
2018-07-01
Orthorhombic MoO3 (α-MoO3) is a typical layered n-type semiconductor with optical band gap over 2.7 eV, which have been widely studied in catalysis, gas sensing, lithium-ion batteries, field-emission, photoelectrical, photochromic and electrochromic devices, supercapacitors and organic solar cells. However, the bottleneck of generation large size atomic thin two-dimensional (2D) α-MoO3 crystals remain challenging this field (normally several micrometers size). Herein, we developed a facile vapor–solid (VS) process for controllable growth of large-size 2D α-MoO3 single crystals with a few nanometers thick and over 300 μm in lateral size. High-performance solar-blind photodetectors were fabricated based on individual 2D α-MoO3 single crystal. The detectors demonstrate outstanding optoelectronic properties under solar-blind UV light (254 nm), with a photoresponsivity of 67.9 A W‑1, external quantum efficiency of 3.3 × 104%. More important, the devices showed strong in-plane anisotropy in optoelectronic response and transport properties, e.g. the photocurrent along b-axis was found to be 5 times higher than the values along c-axis under 254 nm UV light, and current ON/OFF ratio and mobility anisotropy is about 2 times high. Our work suggests an optimized synthesis routine for 2D crystals, and the great potential of 2D oxides in functional optoelectronics.
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Amador, Julia; Hartel, Rich; Rankin, Scott
2017-08-01
The purpose of this work was to investigate iciness perception and other sensory textural attributes of ice cream due to ice and fat structures and mix viscosity. Two studies were carried out varying processing conditions and mix formulation. In the 1st study, ice creams were collected at -3, -5, and -7.5 °C draw temperatures. These ice creams contained 0%, 0.1%, or 0.2% emulsifier, an 80:20 blend of mono- and diglycerides: polysorbate 80. In the 2nd study, ice creams were collected at -3 °C draw temperature and contained 0%, 0.2%, or 0.4% stabilizer, a blend of guar gum, locust bean gum, and carrageenan. Multiple linear regressions were used to determine relationships between ice crystal size, destabilized fat, and sensory iciness. In the ice and fat structure study, an inverse correlation was found between fat destabilization and sensory iciness. Ice creams with no difference in ice crystal size were perceived to be less icy with increasing amounts of destabilized fat. Destabilized fat correlated inversely with drip-through rate and sensory greasiness. In the ice cream mix viscosity study, an inverse correlation was found between mix viscosity and sensory iciness. Ice creams with no difference in ice crystal size were perceived to be less icy when formulated with higher mix viscosity. A positive correlation was found between mix viscosity and sensory greasiness. These results indicate that fat structures and mix viscosity have significant effects on ice cream microstructure and sensory texture including the reduction of iciness perception. © 2017 Institute of Food Technologists®.
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Kim, Minjeong; Choi, Myoung Gil; Ra, Ho Won; Park, Seung Bin; Kim, Yong-Joo; Lee, Kyubock
2018-01-01
The encapsulation of living cells is appealing for its various applications to cell-based sensors, bioreactors, biocatalysts, and bioenergy. In this work, we introduce the encapsulation of multiple microalgal cells in hollow polymer shells of rhombohedral shape by the following sequential processes: embedding of microalgae in CaCO3 crystals; layer-by-layer (LbL) coating of polyelectrolytes; and removal of sacrificial crystals. The microcapsule size was controlled by the alteration of CaCO3 crystal size, which is dependent on CaCl2/Na2CO3 concentration. The microalgal cells could be embedded in CaCO3 crystals by a two-step process: heterogeneous nucleation of crystal on the cell surface followed by cell embedment by the subsequent growth of crystal. The surfaces of the microalgal cells were highly favorable for the crystal growth of calcite; thus, micrometer-sized microalgae could be perfectly occluded in the calcite crystal without changing its rhombohedral shape. The surfaces of the microcapsules, moreover, could be decorated with gold nanoparticles, Fe3O4 magnetic nanoparticles, and carbon nanotubes (CNTs), by which we would expect the functionalities of a light-triggered release, magnetic separation, and enhanced mechanical and electrical strength, respectively. This approach, entailing the encapsulation of microalgae in semi-permeable and hollow polymer microcapsules, has the potential for application to microbial-cell immobilization for high-biomass-concentration cultivation as well as various other bioapplications. PMID:29438340
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Li, Z Y; Lam, W M; Yang, C; Xu, B; Ni, G X; Abbah, S A; Cheung, K M C; Luk, K D K; Lu, W W
2007-03-01
Recently, strontium (Sr) as ranelate compound has become increasingly popular in the treatment of osteoporosis. However, the lattice structure of bone crystal after Sr incorporation is yet to be extensively reported. In this study, we synthesized strontium-substituted hydroxyapatite (Sr-HA) with different Sr content (0.3%, 1.5% and 15% Sr-HA in mole ratio) to simulate bone crystals incorporated with Sr. The changes in chemical composition and lattice structure of apetite after synthetic incorporation of Sr were evaluated to gain insight into bone crystal changes after incorporation of Sr. X-ray diffraction (XRD) patterns revealed that 0.3% and 1.5% Sr-HA exhibited single phase spectrum, which was similar to that of HA. However, 15% Sr-HA induced the incorporation of HPO4(2-) and more CO3(2-), the crystallinity reduced dramatically. Transmission electron microscopy (TEM) images showed that the crystal length and width of 0.3% and 1.5% Sr-HA increased slightly. Meanwhile, the length and width distribution were broadened and the aspect ratio decreased from 10.68+/-4.00 to 7.28+/-2.80. The crystal size and crystallinity of 15% Sr-HA dropped rapidly, which may suggest that the fundamental crystal structure is changed. The findings from this work indicate that current clinical dosage which usually results in Sr incorporation of below 1.5% may not change chemical composition and lattice structure of bone, while it will broaden the bone crystal size distribution and strengthen the bone.
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Historical and New Perspective of Moissanite in the Canyon Diablo Meteorite
NASA Astrophysics Data System (ADS)
Leung, I. S.; Winston, R.
2004-12-01
Silicon carbide (SiC) was reportedly found in the residue of a 50-kg sample of the Canyon Diablo meteorite dissolved in acid by Henri Moissan, and, in his honor, George F. Kunz coined the mineral name moissanite in 1904. Scholars of the same meteorite, unable to find SiC, believed that Moissan's sample might have been contaminated by synthetic SiC used in tools and abrasives. Thus, an intriguing mineralogical controversy ensued to this day. Recently, occurrence of SiC in carbonaceous chondrites has been confirmed. We present in this paper our finding of three varieties of SiC crystals in the Canyon Diablo meteorite. We found 5 crystals of SiC (size 70-150 microns) in a black nodule (1 cm in size), composed mostly of disordered graphite and diamond/lonsdaleite. The crystals are pale blue, but some have dark overgrowths of uneven thickness, and black spotty or feathery inclusions. Their forms are rounded and resorbed. Our second specimen is oxidized and friable, bearing a 2-cm nodule showing sandy and black magnetic layers. We found 3 apple-green crystals, up to 200 microns in size. Scattered over two of the sandy layers are many minute emerald-green SiC crystals. Carbon in these crystals might have a terrestrial origin. As Moissan's crystals are no longer available for re-examination, a study of large carbon nodules housed in museums might at least lend credence that meteoritic SiC crystals could be as large as ones reported by Moissan.
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Huang, Kuo-Chen; Yeh, Po-Chan
2007-04-01
The present study investigated the effects of numeral size, spacing between targets, and exposure time on the discrimination performance by elderly and younger people using a liquid crystal display screen. Analysis showed size of numerals significantly affected discrimination, which increased with increasing numeral size. Spacing between targets also had a significant effect on discrimination, i.e., the larger the space between numerals, the better their discrimination. When the spacing between numerals increased to 4 or 5 points, however, discrimination did not increase beyond that for 3-point spacing. Although performance increased with increasing exposure time, the difference in discrimination at an exposure time of 0.8 vs 1.0 sec. was not significant. The accuracy by the elderly group was less than that by younger subjects.
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Thangaraja, Amutha; Shinde, Sachin M.; Kalita, Golap, E-mail: kalita.golap@nitech.ac.jp
2016-02-01
The synthesis of large-area monolayer tungsten disulphide (WS{sub 2}) single crystal is critical for realistic application in electronic and optical devices. Here, we demonstrate an effective approach to synthesize monolayer WS{sub 2} crystals using tungsten hexachloride (WCl{sub 6}) as a solid precursor in atmospheric chemical vapor deposition process. In this technique, 0.05M solution of WCl{sub 6} in ethanol was drop-casted on SiO{sub 2}/Si substrate to create an even distribution of the precursor, which was reduced and sulfurized at 750 °C in Ar atmosphere. We observed growth of triangular, star-shaped, as well as dendritic WS{sub 2} crystals on the substrate. The crystalmore » geometry evolves with the shape and size of the nuclei as observed from the dendritic structures. These results show that controlling the initial nucleation and growth process, large WS{sub 2} single crystalline monolayer can be grown using the WCl{sub 6} precursor. Our finding shows an easier and effective approach to grow WS{sub 2} monolayer using tungsten halide solution-casting, rather than evaporating the precursor for gas phase reaction.« less
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Glassy phases and driven response of the phase-field-crystal model with random pinning.
Granato, E; Ramos, J A P; Achim, C V; Lehikoinen, J; Ying, S C; Ala-Nissila, T; Elder, K R
2011-09-01
We study the structural correlations and the nonlinear response to a driving force of a two-dimensional phase-field-crystal model with random pinning. The model provides an effective continuous description of lattice systems in the presence of disordered external pinning centers, allowing for both elastic and plastic deformations. We find that the phase-field crystal with disorder assumes an amorphous glassy ground state, with only short-ranged positional and orientational correlations, even in the limit of weak disorder. Under increasing driving force, the pinned amorphous-glass phase evolves into a moving plastic-flow phase and then, finally, a moving smectic phase. The transverse response of the moving smectic phase shows a vanishing transverse critical force for increasing system sizes.
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NASA Astrophysics Data System (ADS)
Prakash, J. Thomas Joseph; Gnanaraj, J. Martin Sam; Dhavud, S. Shek; Ekadevasena, S.
2015-09-01
Undoped and amino acid (L-Arginine and L-Valine) doped KAP crystals were grown by slow evaporation solution growth technique. The changes in the structural, spectral, optical, mechanical and thermal properties were observed. The sharp prominent peaks in the indexed powder XRD pattern confirms the crystalline nature of the sample. Optical studies reveal that the crystal is transparent in the entire visible light region. Thermal stability was checked by TG/DTA analysis. The mechanical stability was evaluated from Vicker's microhardness test. The SHG efficiency for the title materials was tested with different particle sizes by the Kurtz and Perry powder method, which established the existence of phase matching.
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NASA Astrophysics Data System (ADS)
Kavanagh, John P.; Rao, P. Nagaraj
2007-04-01
The stone farm is a system for measuring macroscopic stone growth of 12 calcium stones simultaneously. It is based on mixed suspension, mixed product removal continuous crystallization principles and the stones are grown continuously for about 500 hours or more. The growth of the stones follows a surface area dependent pattern and the growth rate constants are very similar irrespective of whether the stating materials are fragments of human stone or pieces of marble chip. Increasing citrate from 2mM to 6mM caused a significant growth inhibition which persisted in the presence of urinary macromolecules. Phytate was a very effective inhibitor (about 50% at sub-μM concentrations) but the effective concentration was increased by an order of magnitude in the presence of urinary macromolecules. The effective concentration for inhibition in a crystallization assay was a further two orders of magnitude higher. Urinary macromolecules or almost whole urine were also strongly inhibitory although neither human serum albumin nor bovine mucin had any great effect. The relationship between the size distribution of crystals in suspension and the stone enlargement rate suggests that the primary enlargement mechanism for these in vitro stones is through aggregation. The stone farm is a powerful tool with which to study crystallization inhibitors in a new light. Some differences between inhibition of crystallization and inhibition of stone growth have emerged and we have obtained quantitative evidence on the mechanism of stone enlargement in vitro. Our findings suggest that the interface between crystals in suspension and the stone surface is the key to controlling stone enlargement.
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Influence of Crystal Expansion/Contraction on Zeolite Membrane Permeation
DOE Office of Scientific and Technical Information (OSTI.GOV)
Sorenson, Stephanie G; Payzant, E Andrew; Noble, Richard D
X-ray diffraction was used to measure the unit cell parameters of B-ZSM-5, SAPO-34, and NaA zeolite powders as a function of adsorbate loading at 303 K, and in one case, at elevated temperatures. Most adsorbates expanded the zeolite crystals below saturation loading at 303 K: n-hexane and SF6 in B-ZSM-5, methanol and CO2 in SAPO-34, and methanol in NaA zeolite. As the loadings increased, the crystals expanded more. Changes in the unit cell volumes of B-ZSM-5 and SAPO-34 zeolite powders correlated with changes in permeation through zeolite membranes defects. When the zeolite crystals expanded or contracted upon adsorption, the defectmore » sizes decreased or increased. In B-ZSM-5 membranes, the fluxes through defects decreased dramatically when n-hexane or SF6 adsorbed. In contrast, i-butane adsorption at 303 K contracted B-ZSM-5 crystals at low loadings and expanded them at higher loadings. Correspondingly, the flux through B-ZSM-5 membrane defects increased at low i-butane loadings and decreased at high loading because the defects increased in size at low loading and decreased at high loadings. At 398 K and 473 K, n-hexane expanded the B-ZSM-5 unit cell more as the temperature increased from 303 to 473 K. The silicalite-1 and B-ZSM-5 unit cell volumes expanded similarly upon n-hexane adsorption at 303 K; boron substitution had little effect on volume expansion.« less
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Su, Xin; Chang, Jie; Wu, Suli; Tang, Bingtao; Zhang, Shufen
2016-03-21
Monodisperse semiconductor colloidal spheres with a high refractive index hold great potential for building photonic crystals with a strong band gap, but the difficulty in separating the nucleation and growth processes makes it challenging to prepare highly uniform semiconductor colloidal spheres. Herein, real monodisperse Cu2O spheres were prepared via a hot-injection & heating-up two-step method using diethylene glycol as a milder reducing agent. The diameter of the as prepared Cu2O spheres can be tuned from 90 nm to 190 nm precisely. The SEM images reveal that the obtained Cu2O spheres have a narrow size distribution, which permits their self-assembly to form photonic crystals. The effects of precursor concentration and heating rates on the size and morphology of the Cu2O spheres were investigated in detail. The results indicate that the key points of the method include the burst nucleation to form seeds at a high temperature followed by rapid cooling to prevent agglomeration, and appropriate precursor concentration as well as a moderate growth rate during the further growth process. Importantly, photonic crystal films exhibiting a brilliant structural color were fabricated with the obtained monodisperse Cu2O spheres as building blocks, proving the possibility of making photonic crystals with a strong band gap. The developed method was also successfully applied to prepare monodisperse CdS spheres with diameters in the range from 110 nm to 210 nm.
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NASA Astrophysics Data System (ADS)
Park, Il Song; Bae, Tae Sung; Seol, Kyeong Won
2006-10-01
Titanium is widely used as an implant material due to its good mechanical properties and the excellent biocompatibility of the oxide film on the surface. To modify the unstable oxide surface of pure titanium, plasma electrolytic oxidation was applied in this study. The electrolyte used for anodizing was a mixture of GP (glycerophosphate disodium salt) and CA (calcium acetate). In addition, a hydrothermal treatment was performed to precipitate a calcium phosphate crystal on the titanium oxide layer for bioactivity. The effect of the CA concentration of the electrolyte on the surface of titanium was investigated, with CA concentrations at 0.1 M, 0.2 M, and 0.3 M. A high concentration of CA results in a low breakdown voltage; hence many large micropores were formed on the anodized surface. Moreover, the size of the HA crystals was more minute in proportion to the increasing concentration of CA. The crystal phase of titanium dioxide was mainly anatase, and a rutile phase was also observed. As the size and/or amount of HA crystals increased, the surface roughness increased. However, the surface roughness could be decreased by fully and uniformly covering the surface with HA crystals. The corrosion resistance in the saline solution was increased by anodic spark oxidation. In addition, it was slightly increased by a hydrothermal treatment. It is considered that a more stable and thicker titanium oxide layer is formed by anodic oxidation and a hydrothermal treatment.