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Crystal Size (crystal + size)
Terms modified by Crystal Size Selected AbstractsStorage stability study of margarines produced from enzymatically interesterified fats compared to margarines produced by conventional methods.EUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 7-8 2005Physical properties Abstract In this study, margarine hardstocks were produced from two enzymatically interesterified fats at conversion degrees of 80 and 100%, a chemically randomized fat and a physically mixed fat, respectively. These four hardstocks blended with 50% of sunflower oil were mainly used for the production of table margarines in a pilot plant. Storage stability studies were carried out at storage temperatures of 5 and 25,°C during 12,wk. Margarines from the enzymatically interesterified fats were compared to the margarines produced by conventional methods and to selected commercial products. The changes in the physical properties of margarines, including hardness, dropping point, crystal form, and sensory evaluation, were examined during storage. It was observed that margarine storage stability increased with increasing conversion degree. The color of margarines made from the enzymatically interesterified fats was more similar to that of the physically mixed fat than that of the margarine from the chemically randomized fat, which had less color. Crystal transformation was accelerated at high storage temperature. Crystal size was not only related to the types of crystals, but also to the driving force of temperature difference. A larger crystal size was observed at 5,°C than at 25,°C for the margarine made from the blend. Margarines produced from interesterified fats had better physical properties than the blend. Overall, the margarine produced from the enzymatically fully converted fat had physical properties similar to the margarine produced from the chemically interesterified fat. [source] Feasibility of one-shot-per-crystal structure determination using Laue diffractionACTA CRYSTALLOGRAPHICA SECTION D, Issue 1 2010Sterling Cornaby Crystal size is an important factor in determining the number of diffraction patterns which may be obtained from a protein crystal before severe radiation damage sets in. As crystal dimensions decrease this number is reduced, eventually falling to one, at which point a complete data set must be assembled using data from multiple crystals. When only a single exposure is to be collected from each crystal, the polychromatic Laue technique may be preferable to monochromatic methods owing to its simultaneous recording of a large number of fully recorded reflections per image. To assess the feasibility of solving structures using single Laue images from multiple crystals, data were collected using a `pink' beam at the CHESS D1 station from groups of lysozyme crystals with dimensions of the order of 20,30,µm mounted on MicroMesh grids. Single-shot Laue data were used for structure determination by molecular replacement and correct solutions were obtained even when as few as five crystals were used. [source] Optimization of process parameters by Taguchi method in the recovery of lactose from whey using sonocrystallizationCRYSTAL RESEARCH AND TECHNOLOGY, Issue 7 2010S. R. Patel Abstract Anti-solvent crystallization of lactose in the presence of ultrasound will reduce crystal size and the level of agglomeration as compared to the commercial cooling crystallization. It offers a potential route to enhance the physical properties as well as the rapid recovery of lactose. Since lactose recovery itself can reduce biological oxygen demand of whey by more then 80%, recovery of lactose from dairy waste stream (whey) solves the problems of dairy industries by improving economics of whey utilization and pollution reduction. In the present study, recovery of lactose from partially deproteinated whey using an anti-solvent (acetone) by sonocrystallization was optimized for finding the most influencing operating parameters; such as sonication time, anti-solvent concentration, initial lactose concentration in the whey and initial pH of sample mixture at three levels using L9 -orthogonal method. The responses were analyzed for recovery of lactose from whey. The anti-solvent concentration and the sonication time were found to be most influencing parameters for the recovery of lactose and the recovery of lactose was found to be 89.03% at the identified optimized level. The crystal size distribution of recovered lactose was found to be narrower (2.5 , 6.5 ,m) as compared to the commercial lactose crystals (3.5 , 9.5 ,m). (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Flux growth and characterization of Ti- and Ni-doped forsterite single crystalsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 5 2009A. Bloise Abstract Forsterite monocrystals doped with Ti and Ni were grown by the flux growth technique. A suitable mixture of flux (MoO3, V2O5, Li2CO3) and nutrient was slowly cooled down to 750 °C from 1250 °C or 1350 °C. The crystals were then characterized by powder and single-crystal X-ray diffraction, scanning electron microscopy and differential scanning calorimetry (DSC). Variations observed in crystal size were attributed by both the varying experimental conditions in which they had been obtained, and to the amount of Ni substituted for Mg in the structure. High abundances of doped forsterite required a cooling rate of 1.8 K h -1. These synthetic, well-characterized Ti and Ni doped forsterite crystals may have potential for exploitation in industrial fields. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Kinetic studies on the influence of temperature and growth rate history on crystal growthCRYSTAL RESEARCH AND TECHNOLOGY, Issue 12 2008P. M. Martins Abstract Crystallization experiments of sucrose were performed in a batch crystallizer to study the effect of temperature and growth rate history on the crystal growth kinetics. In one of the growth methods adopted, the isothermal volumetric growth rate (RV) is determined as a function of supersaturation (S) at 35, 40 and 45 ºC. In the other, crystals are allowed to grow at constant supersaturation by automatically controlling the solution temperature as the solute concentration decreased. Using the latter method RV is calculated as the solution is cooled. The obtained results are interpreted using empirical, engineering and fundamental perspectives of crystal growth. Firstly, the overall activation energy (EA) is determined from the empirical growth constants obtained in the isothermal method. The concept of falsified kinetics, widely used in chemical reaction engineering, is then extended to the crystal growth of sucrose in order to estimate the true activation energy (ET) from the diffusion-affected constant, EA. The differences found in the isothermal and constant supersaturation methods are explained from the viewpoint of the spiral nucleation mechanism, taking into account different crystal surface properties caused by the growth rate history in each method. Finally, the crystal growth curve obtained in the batch crystallizer at 40 ºC is compared with the one obtained in a fluidized bed crystallizer at the same temperature. Apparently divergent results are explained by the effects of crystal size, hydrodynamic conditions and growth rate history on the crystallization kinetics of sucrose. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Geometrical aspects of solid solution separation by evaporation-condensation driven in a closed system by a small temperature differenceCRYSTAL RESEARCH AND TECHNOLOGY, Issue 5 2004A. Szczerbakow Abstract Evaporation-condensation driven in a closed system by a small temperature difference has demonstrated its ability to deliver semiconducting IV-VI and II-VI solid solution crystals of highest compositional uniformity. Geometrical aspects of solution component distribution emerging in the crystals grown in the near equilibrium evaporation/condensation systems are considered in this paper. The conclusion is drawn that no increase in the range of compositional variations with increase in the crystal size is to be anticipated. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Storage stability study of margarines produced from enzymatically interesterified fats compared to margarines produced by conventional methods.EUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 7-8 2005Physical properties Abstract In this study, margarine hardstocks were produced from two enzymatically interesterified fats at conversion degrees of 80 and 100%, a chemically randomized fat and a physically mixed fat, respectively. These four hardstocks blended with 50% of sunflower oil were mainly used for the production of table margarines in a pilot plant. Storage stability studies were carried out at storage temperatures of 5 and 25,°C during 12,wk. Margarines from the enzymatically interesterified fats were compared to the margarines produced by conventional methods and to selected commercial products. The changes in the physical properties of margarines, including hardness, dropping point, crystal form, and sensory evaluation, were examined during storage. It was observed that margarine storage stability increased with increasing conversion degree. The color of margarines made from the enzymatically interesterified fats was more similar to that of the physically mixed fat than that of the margarine from the chemically randomized fat, which had less color. Crystal transformation was accelerated at high storage temperature. Crystal size was not only related to the types of crystals, but also to the driving force of temperature difference. A larger crystal size was observed at 5,°C than at 25,°C for the margarine made from the blend. Margarines produced from interesterified fats had better physical properties than the blend. Overall, the margarine produced from the enzymatically fully converted fat had physical properties similar to the margarine produced from the chemically interesterified fat. [source] Performance of a confocal multilayer X-ray opticJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 1 2002J. Kusz In recent years, several companies have developed the technique of arranging two multilayer mirrors in confocal optics for monochromatizing X-rays. In this study, a focusing device of Osmic Inc., with a source-to-focus distance of 1005,mm, has been used. The goal was to measure the homogeneity of the beam, the cross section at various distances from the focus and the efficiency of the optic when it is operated with vacuum and with air in the beam path. A small crystal sphere set at various distances is used to compare the intensities and the widths of reflections with those of a flat graphite monochromator. In a standard diffraction experiment (crystal size 0.25,mm), the gain factor with respect to graphite is roughly ten at a position where the beam plateau is 0.5,mm. The suppression of the Cu K, radiation and of higher harmonics of K, is very good. [source] Polyaniline-multiwalled carbon nanotube composites: Characterization by WAXS and TGAJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008T. Jeevananda Abstract Polyaniline/carboxylated multi-walled carbon nanotube (PAni/c-MWNT) nanocomposites have been synthesized by micellar aided emulsion polymerization with various c-MWNTs compositions, viz., 0.5, 1, 5, and 10 wt %. The microcrystalline parameters such as the nanocrystal size (,N,), lattice strain (g), interplanar distance (dhkl), width of the crystallite size distribution, surface weighted crystal size (Ds), and volume of the ordered regions were calculated from the X-ray data by using two mathematical models, namely the Exponential distribution and Reinhold distribution methods. The effects of heat ageing on the microcrystalline parameters of the PAni/c-MWNT nanocomposites were also studied and the results are correlated. The thermal stability and electrical resistivity of the PAni/c-MWNT nanocomposites were examined with thermogravimetric analysis (TGA) and a conventional two-probe method. The TGA data indicate that the thermal stability of the nanocomposites improved after the incorporation of c-MWNTs. The influence of temperature on the resistivity of the nanocomposites was also measured. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008 [source] Investigating the jet stretch in the wet spinning of PAN fiberJOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2007Xiaomei Zeng Abstract The jet stretch of wet-spun PAN fiber and its effects on the cross-section shape and properties of fibers were investigated for the PAN-DMSO-H2O system. Evidently, the spinning parameters, such as dope temperature, bath concentration, and bath temperature, influenced the jet stretch. Also, under uniform conditions, the postdrawing ratio changed as well as that of jet stretch. When coagulation temperature was 35°C simultaneously with bath concentration of 70%, jet stretch impacted obviously the cross-section shapes of PAN fiber, but had little effect when the temperature was below 10°C or above 70°C. As the jet stretch ratio increased, the crystallinity, crystal size, sonic orientation, and mechanical properties of the as-spun fiber changed rapidly to a major value for jet stretch ratio of 0.9 where the cross section of as-spun fiber was circular. With further increasing of jet stretch ratio, the properties changed slightly but the fiber shape was not circular. The results indicated that appropriate jet stretch, under milder formation conditions in wet-spinning, could result in the higher postdrawing ratio and circular profile of PAN fiber, which were helpful to produce round PAN precursor with minor titer and perfect properties for carbon fiber. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 [source] Process control and monitoring of reactive crystallization of L -glutamic acidAICHE JOURNAL, Issue 8 2010Hannu Alatalo Abstract The aim of the present study was to investigate feedback control of a reactive crystallization process. The present study built up a control structure needed to control the driving force of reactive crystallization using the feed rate of added acid. The concentration of the crystallizing compound and pH was used to compute feedback in the closed-loop control of semi-batch precipitation. The concentration of L -glutamic acid was determined from measured MID-IR ATR-FTIR spectra based on a multivariate model. Dynamic change of set value was based on the mass of added sulfuric acid and pH. The studied properties of the product crystals were polymorphism and crystal size. The polymorphic composition was analyzed with a Raman spectrometer and was expressed by mass fraction of the ,-polymorph. The obtained results showed that the developed feedback process control system allows effective control of forming of polymorphs. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Preferential crystallization: Multi-objective optimization frameworkAICHE JOURNAL, Issue 2 2009Shrikant A. Bhat Abstract A four objective optimization framework for preferential crystallization of D-L threonine solution is presented. The objectives are maximization of average crystal size and productivity, and minimization of batch time and the coefficient of variation at the desired purity while respecting design and operating constraints. The cooling rate, enantiomeric excess of the preferred enantiomer, and the mass of seeds are used as the decision variables. The optimization problem is solved by using adaptation of the nondominated sorting genetic algorithm. The results obtained clearly distinguish different regimes of interest during preferential crystallization. The multi-objective analysis presented in this study is generic and gives a simplified picture in terms of three zones of operations obtained because of relative importance of nucleation and growth. Such analysis is of great importance in providing better insight for design and decision making, and improving the performance of the preferential crystallization that is considered as a promising future alternative to chromatographic separation of enantiomers. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Crystal growth rate dispersion modeling using morphological population balanceAICHE JOURNAL, Issue 9 2008Cai Y. Ma Abstract Crystal growth in solution is a surface-controlled process. The variation of growth rates of different crystal faces is considered to be due to the molecular arrangement in the crystal unit cell as well as the crystal surface structures of different faces. As a result, for some crystals, the growth rate for a specific facet is not only a function of supersaturation, but also dependent on some other factors such as its size and the lattice spread angle. This phenomenon of growth rate dispersion (GRD) or fluctuation has been described in literature to have attributed to the formation of some interesting and sophisticated crystal structures observed in experimental studies. In this article, GRD is introduced to a recently proposed morphological population balance model to simulate the dynamic evolution of crystal size distribution in each face direction for the crystallization of potash alum, a chemical that has been reported to show GRD phenomenon and sophisticated crystal structures. The GRD is modeled as a function of the effective relative supersaturation, which is directly related to crystal size, lattice spread angle, relative supersaturation, and solution temperature. The predicted results clearly demonstrated the significant effect of GRD on the shape evolution of the crystals. © 2008 American Institute of Chemical Engineers AIChE J, 2008 [source] Investigation of impinging-jet crystallization with a calcium oxalate model systemAICHE JOURNAL, Issue 9 2003Jean M. Hacherl An impinging-jet crystallizer was investigated in this work to assess its operational sensitivity and reproducibility for the production of small, monodisperse crystals using calcium oxalate, a model system capable of forming multiple hydrates. The impinging-jet mixer provides rapid mixing of the reactant solutions through the impingement of two narrow reactant streams at high velocity. Impinging jet linear velocity and postjetting conditions were studied, with the jet operated in nonsubmerged mode. Hydrate form and crystal-size distribution (CSD) were determined using optical microscopy and image analysis techniques. The impinging jet consistently produced small, monodisperse crystals. However, at a high level of supersaturation, slight variations in the CSD were observed for apparently identical conditions, suggesting a degree of sensitivity in the system that could lead to difficulty in its application. An apparent trend between impinging-jet linear velocity and crystal size and number was observed, with more small crystals produced at higher linear velocity. [source] Relevance of Osteoinductive Biomaterials in Critical-Sized Orthotopic DefectJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 5 2006Pamela Habibovic Abstract Several publications have shown the phenomenon of osteoinduction by biomaterials to be real. However, whether the ability of a biomaterial to initiate bone formation in ectopic implantation sites improves the performance of such osteoinductive biomaterial in clinically relevant orthotopic sites remains unclear. No studies have been published in which osteoinductive potential of a biomaterial is directly related to its performance orthotopically. In this study, we compared osteoinductive and nonosteoinductive biphasic calcium,phosphate (BCP) ceramics ectopically and in a clinically relevant critical-sized orthotopic defect in goats. The two materials, BCP1150 and BCP1300, had similar chemical compositions, crystallinities, and macrostructures, but their microstructures differed significantly. BCP1150, sintered at a lower temperature, had a large amount of micropores, small average crystal size, and hence a high specific surface area. In contrast, BCP1300, with few micropores, had a significantly lower specific surface area as compared to BCP1150. Twelve-week intramuscular implantation in goats (n,=,10) showed that bone was induced in all BCP1150 implants, while no signs of bone formation were found in any of the BCP1300 implants. After 12 weeks of implantation in a bilateral critical-sized iliac wing defect in the same goats, BCP1150 showed significantly more bone than BCP1300. In addition, the analysis of fluorochrome markers, which were administered to the animals 4, 6, and 8 weeks after implantation to follow the bone growth dynamics, showed an earlier start of bone formation in BCP1150 as compared to BCP1300. Significantly better performance of an osteoinductive ceramic in a critical-sized orthotopic defect in a large animal model in comparison to a nonosteoinductive ceramic suggests osteoinduction to be clinically relevant. Further improvement of material osteoinductive properties is thus a significant step forward in the search for alternatives for autologous bone graft. © 2006 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res [source] Crystallization conditions and formation of orthorhombic paracetamol from ethanolic solutionJOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 3 2002N. Al-Zoubi Orthorhombic paracetamol exhibits far better tabletability than the monoclinic form and its bulk crystallization from solution attracts much interest. In this study, temperature changes in supersaturated ethanolic solution have been recorded after seeding with orthorhombic crystals under different cooling temperatures (TC) and agitation rates (AR). Average cooling rate (CR), time for maximum temperature deviation (tmax) and area confined between curves of measured and reference temperature plots (AUC) were calculated and correlated with crystal yield (Y). The micromeritic (size and shape) and the compression properties, the density and the orthorhombic content of the crystalline product were evaluated and related to the main crystallization conditions applied (TC and AR). Conditions for optimal crystal yield and orthorhombic content were elucidated. It was found that crystal yield (Y) increased with AR and decreased with TC. The ratio tmax/CR provided good prediction of crystal yield (Y = 58.92 ,1.386 tmax/CR, r2 = 0.964 and P = 0.0001). TC and AR linearly affected crystal size and the size distribution, probably due to alterations in supersaturation, but they did not affect the crystal shape significantly. Density and compression properties (yield pressure and elastic recovery) were determined by the content of the orthorhombic form, which increased linearly with AR (P = 0.009) and with TC (P = 0.039) when agitation was between 300 and 500 rev min,1, while tmax decreased. At 700 rev min,1 orthorhombic content was maximized and became independent to TC. Higher orthorhombic content and crystal yield was expected for lower TC and for lower tmax, which corresponded to higher AR and might have also been affected by alteration of seeding and harvesting procedure. [source] µGISAXS and protein nanotemplate crystallization: methods and instrumentationJOURNAL OF SYNCHROTRON RADIATION, Issue 6 2005Eugenia Pechkova Microbeam grazing-incidence small-angle X-ray scattering (µGISAXS) has been used and the technique has been improved in order to investigate protein nucleation and crystal growth, assisted by a protein nanotemplate. The aim is to understand the protein nanotemplate method in detail, as this method has been proved capable of accelerating and increasing crystal size and quality as well as inducing crystallization of proteins that are not crystallizable by classical methods. The nanotemplate experimental setup was used for drops containing growing lysozyme crystals at three different stages of growth. [source] Nanopowder Preparation and Dielectric Properties of a Bi2O3,Nb2O5 Binary System Prepared by the High-Energy Ball-Milling MethodJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2008Di Zhou The high-energy ball-milling (HEM) method was used to synthesize the compositions of BiNbO4, Bi5Nb3O15, and Bi3NbO7 in a Bi2O3,Nb2O5 binary system. Reagent Bi2O3 and Nb2O5 were chosen as the starting materials. The X-ray diffraction patterns of the three compositions milled for different times were studied. Only the cubic Bi3NbO7 phase, Nb2O5, and amorphous matters were observed in powders after being milled for 10 h. After heating at proper temperatures the amorphous matters disappeared and the proleptic phases of BiNbO4 and Bi5Nb3O15 could be obtained. The Scherrer formula was used to calculate the crystal size and the results of nanopowders are between 10 and 20 nm. The scanning electron microscopy photos of Bi3NbO7 powders showed drastic aggregation, and the particle size was about 100 nm. The dielectric properties of ceramics sintered from the nanopowders prepared by HEM at 100,1 MHz and the microwave region were measured. Bi3NbO7 ceramics showed a good microwave permittivity ,r of about 80 and a Q×f of about 300 at 5 GHz. The triclinic phase of BiNbO4 ceramics reached its best properties with ,r=24 and Q×f=14 000 GHz at about 8 GHz. [source] Crystallization of Silicate Magmas Deciphered Using Crystal Size DistributionsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2007Bruce D. Marsh The remoteness and inhospitable nature of natural silicate magma make it exceedingly difficult to study in its natural setting deep beneath volcanoes. Although laboratory experiments involving molten rock are routinely performed, it is the style and nature of crystallization under natural conditions that is important to understand. This is where the crystal size distributions (CSD) method becomes fundamentally valuable. Just as chemical thermodynamics offers a quantitative macroscopic means of investigating chemical processes that occur at the atomic level, crystal size distribution theory quantitatively relates the overall observed spectrum of crystal sizes to both the kinetics of crystallization and the physical processes affecting the population of crystals themselves. Petrography, which is the qualitative study of rock textures, is the oldest, most comprehensively developed, and perhaps most beautiful aspect of studying magmatic rocks. It is the ultimate link to the kinetics of crystallization and the integrated space,time history of evolution of every magma. CSD analysis offers a quantitative inroad to unlocking and quantifying the observed textures of magmatic rocks. Perhaps the most stunning feature of crystal-rich magmatic rocks is that the constituent crystal populations show smooth and often quasi-linear log-normal distributions of negative slope when plotted as population density against crystal size. These patterns are decipherable using CSD theory, and this method has proven uniquely valuable in deciphering the kinetics of crystallization of magma. The CSD method has been largely developed in chemical engineering by Randolph and Larson,1,2 among many others, for use in understanding industrial crystallization processes, and its introduction to natural magmatic systems began in 1988. The CSD approach is particularly valuable in its ease of application to complex systems. It is an aid to classical kinetic theory by being, in its purest form, free of any atomistic assumptions regarding crystal nucleation and growth. Yet the CSD method provides kinetic information valuable to understanding the connection between crystal nucleation and growth and the overall cooling and dynamics of magma. It offers a means of investigating crystallization in dynamic systems, involving both physical and chemical processes, independent of an exact kinetic theory. The CSD method applied to rocks shows a systematic and detailed history of crystal nucleation and growth that forms the foundation of a comprehensive and general model of magma solidification. [source] Phases in Ceria,Zirconia Binary Oxide (1,x)CeO2,xZrO2 Nanoparticles: The Effect of Particle SizeJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2006Feng Zhang The phases of ceria,zirconia nanoparticles observed in air are studied as a function of particle size and composition by X-ray diffraction, transmission electron microscopy, and Raman spectroscopy. The emergence of two tetragonal phases t, and t monotonically moves toward higher zirconia concentrations with decreasing particle size. A smaller particle size increases the solubility of zirconia in cubic ceria, while higher zirconia content in ceria stabilizes against coarsening. In particular, the cubic Ce1,xZrxO2,y is persistent and is 8% in phase amount even at 90% zirconia with 33 nm crystal size. Neither the monoclinic phase m nor the tetragonal phase t, is observed in the present nanoparticles (<40 nm). The effectiveness of these nanoparticles as oxygen source-and-sink in catalytic support is largely due to the persistence of the cubic and the t, phases. [source] Relationship between ice recrystallisation rates and the glass transition in frozen sugar solutionsJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 15 2002Steve Ablett Abstract The increase in ice crystal size that occurs through recrystallisation when many frozen products such as ice cream and frozen desserts are stored is one of the major factors contributing to the perceived deterioration of the product by the consumer. In order to reduce the rate of deterioration, a detailed understanding of the fundamental mechanism is needed. This study demonstrates that ice recrystallisation rates in a series of frozen sugar solutions are strongly correlated with the molecular mobilities of the water and solute molecules as measured by time domain nuclear magnetic resonance. The study also demonstrates that the proximity to the glass transition temperature as described by state diagrams correlates well with the measured ice recrystallisation rates. The temperature dependence in these systems is described by Williams, Landel and Ferry theory. © 2002 Society of Chemical Industry [source] Enhancement of Electrochromic Contrast by Tethering Conjugated Polymer Chains onto Polyhedral Oligomeric Silsesquioxane NanocagesMACROMOLECULAR RAPID COMMUNICATIONS, Issue 3 2007Shanxin Xiong Abstract Copolymerization of aniline with octa(aminophenyl) silsesquioxane (OAPS) was performed, which resulted in polyaniline-tethered, polyhedral oligomeric silsesquioxane (POSS-PANI), with star-like molecular geometry. The spectro-electrochemical studies show that the electrochromic contrast of POSS-PANI is much higher than that of polyaniline (PANI). The great improvement can be attributed to the more accessible doping sites and the facile ion movement during the redox switching, brought by the loose packing of the PANI chains. This was evidenced by a drastic increase in ionic conductivity, a decrease in the electrical conductivity, and a decrease in the crystallinity and crystal size, with the increase of the OAPS concentration in the POSS-PANI. [source] The clay mineralogy of sediments related to the marine Mjølnir impact craterMETEORITICS & PLANETARY SCIENCE, Issue 10 2003Henning DYPVIK It was formed about 142 ± 2.6 Myr ago by the impact of a 1,2 km asteroid into the shallow shelf clays of the Hekkingen Formation and the underlying Triassic to Jurassic sedimentary strata. A core recovered from the central high within the crater contains slump and avalanche deposits from the collapse of the transient crater and central high. These beds are overlain by gravity flow conglomerates, with laminated shales and marls on top. Here, impact and post-impact deposits in this core are studied with focus on clay mineralogy obtained from XRD decomposition and simulation analysis methods. The clay-sized fractions are dominated by kaolinite, illite, mixed-layered clay minerals and quartz. Detailed analyses showed rather similar composition throughout the core, but some noticeable differences were detected, including varying crystal size of kaolinite and different types of illites and illite/smectite. These minerals may have been formed by diagenetic changes in the more porous/fractured beds in the crater compared to time-equivalent beds outside the crater rim. Long-term post-impact changes in clay mineralogy are assumed to have been minor, due to the shallow burial depth and minor thermal influence from impact-heated target rocks. Instead, the clay mineral assemblages, especially the abundance of chlorite, reflect the impact and post-impact reworking of older material. Previously, an ejecta layer (the Sindre Bed) was recognized in a nearby well outside the crater, represented by an increase in smectite-rich clay minerals, genetically equivalent to the smectite occurring in proximal ejecta deposits of the Chicxulub crater. Such alteration products from impact glasses were not detected in this study, indicating that little, if any, impact glass was deposited within the upper part of the crater fill. Crater-fill deposits inherited their mineral composition from Triassic and Jurassic sediments underlying the impact site. [source] First principles calculation of isolated intermediate bands formation in a transition metal-doped chalcopyrite-type semiconductorPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2006P. Palacios Abstract Density Functional Theory (DFT) calculations at the GGA level have been carried out for Ti-substituted chalcopyrite-type CuGaS2, as it might constitute an intermediate band material of the kind that has been proposed to lead to enhanced efficiency photovoltaic cells. According to these calculations an intermediate band appears when Ti substitutes Ga at a 25% level in this structure, resulting in a magnetic half-metallic compound. This intermediate band slightly overlaps the conduction band and, when a higher accuracy calculation approach like the introduction of a Hubbard-type empirical correction is used (GGA + U method), it splits leaving a filled narrow band, well isolated inside the band gap. Considering the nanocrystalline form in which these chalcopyrite-type compounds are used in solar cells, an assessment of the effects of a small crystal size in this system have been carried out with a slab model. In this calculation a decreased bandgap width is observed, which can be as a result of surface termination effects. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] High efficiency violet to blue light emission in porous SiC produced by anodic methodPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2010T. Nishimura Abstract Porous fluorescent (f-) SiC containing N and B was produced by anodic oxidation. The average crystal size can be controlled by adding K2S2O8 as an oxidant to dilute HF solution during the anodic process. With the reduction of the average crystal size of the porous crystal, the PL peak wavelength becomes shorter, and its intensity increases. Such behavior can be explained by the quantum size effect of donor-acceptor-pair recombination. Finally, we confirmed the superior fluorescent property of blue light emission in porous f-SiC crystal (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Vapor-induced crystallization behavior of bisphenol-A polycarbonatePOLYMER ENGINEERING & SCIENCE, Issue 6 2006Zhongyong Fan The effects of exposure time and vapor pressure on the crystallization behaviors of bisphenol-A polycarbonate (BAPC) films were investigated at 25°C by using differential scanning calorimetry (DSC). Double melting peaks were observed for various BAPC samples after vapor-induced crystallization. The low temperature melting peak shifted to higher temperature and became sharper with increasing exposure time, and could be assigned to defective crystals with smaller crystal size. Crystallinity and average crystal dimension normal to (020) were calculated from wide-angle X-ray diffraction spectra. A good agreement was obtained between crystallinity values obtained from WAXD and those from DSC. The morphology of crystallized samples after various exposure time periods was examined by means of polarized optical microscopy. Nucleation occurred at the initial stage of vapor-induced crystallization. Poor crystals become perfect through segment reorganization with increasing exposure time, and spherulites' growth was observed. The average diameter of spherulites increased from 2 ,m for 1 h, to 7 and 16 ,m after 3 and 56 h, respectively. POLYM. ENG. SCI., 46:729,734, 2006. © 2006 Society of Plastics Engineers [source] The effect of lanthanum oxide (La2O3) on the structure and crystallization of poly(vinylidene fluoride)POLYMER INTERNATIONAL, Issue 7 2010Jianbin Song Abstract Rare earth polymers, due to their excellent luminescence, fluorescence, laser protective, optical and magnetic properties, have attracted much research attention in recent years. However, little attention has been paid to the effect of rare earths on the structure and crystallization of polymers, which is of important significance in the development of functional polymers. X-ray diffraction and differential scanning calorimetry were used to investigate the structure and crystallization behavior of a poly(vinylidene fluoride) (PVDF)/lanthanum oxide (La2O3) composite. The results showed that the degree of perfection, crystal size, crystallization rate and isothermal crystallization activation energy of PVDF in the composite decreased, compared with pure PVDF. The spherulite nucleation and growth for PVDF and PVDF composite were analyzed in detail using the Lauritzen-Hoffman equation. The modified Avrami equation and the Mo equation were used to study the non-isothermal crystallization kinetics. The addition of La2O3 did not change the crystal structure and nucleation process for PVDF, but it decreased markedly the crystal growth rate and led to the formation of unstable crystals. This was attributed to the fact that too much La2O3 prevented PVDF molecular chains from moving and arranging in an orderly manner into crystals. Copyright © 2010 Society of Chemical Industry [source] Thermal analysis of poly(3-hydroxybutyrate- co -3-hydroxyvalerate) irradiated under vacuumPOLYMER INTERNATIONAL, Issue 11 2004Huili Yang Abstract Poly(3-hydroxybutyrate- co -3-hydroxyvalerate) (PHBV) was irradiated by 60Co ,-rays (doses of 50, 100 and 200 kGy) under vacuum. The thermal analysis of control and irradiated PHBV, under vacuum was carried out by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The tensile properties of control and irradiated PHBV were examined by using an Instron tensile testing machine. In the thermal degradation of control and irradiated PHBV, a one-step weight loss was observed. The derivative thermogravimetric curves of control and irradiated PHBV confirmed only one weight-loss step change. The onset degradation temperature (To) and the temperature of maximum weight-loss rate (Tp) of control and irradiated PHBV were in line with the heating rate (°C min,1). To and TP of PHBV decreased with increasing radiation dose at the same heating rate. The DSC results showed that 60Co ,-radiation significantly affected the thermal properties of PHBV. With increasing radiation dose, the melting temperature (Tm) of PHBV shifted to a lower value, due to the decrease in crystal size. The tensile strength and fracture strain of the irradiated PHBV decreased, hence indicating an increased brittleness. Copyright © 2004 Society of Chemical Industry [source] Simulation of fine particle formation by precipitation using computational fluid dynamicsTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2000Damien Piton Abstract The 4-environment generalized micromixing (4-EGM) model is applied to describe turbulent mixing and precipitation of barium sulfate in a tubular reactor. The model is implemented in the commercial computational fluid dynamics (CFD) software Fluent. The CFD code is first used to solve for the hydrodynamic fields (velocity, turbulence kinetic energy, turbulent energy dissipation). The species concentrations and moments of the crystal size distribution (CSD) are then computed using user-defined transport equations. CFD simulations are performed for the tubular reactor used in an earlier experimental study of barium sulfate precipitation. The 4-EGM CFD results are shown to compare favourably to CFD results found using the presumed beta PDF model. The latter has previously been shown to yield good agreement with experimental data for the mean crystal size at the outlet of the tubular reactor. On a appliqué un modéle de micromélange généralisé à 4 environnements (4-EGM) afin de décrire le mélange turbulent et la précipitation du sulfate de baryum dans un réacteur tubulaire. Ce modéle a été implanté dans le logiciel de CFD commercial Fluent. Le programme de CFD est d'abord utilisé pour calculer les champs hydrodynamiques (vitesse, énergie cinétique de turbulence, dissipation d'énergie turbulente). Les concentrations d'espéces et les moments de la distribution de taille des cristaux (CSD) sont ensuite calculés par ordinateur à l'aide des équations de transport définies par l'usager. Des simulations de CFD sont réalisées pour le réacteur tubulaire utilisé dans une étude expérimentale antérieure de la précipitation du sulfate de baryum. On montre que les prédictions du 4-EGM se comparent favorablement à celles du modéle béta PDF. II a été montré antérieurement que ce dernier présentait un bon accord avec les donnés expérimentales pour la taille moyenne des cristaux à la sortie du récteur tubulaire. [source] The minimum crystal size needed for a complete diffraction data setACTA CRYSTALLOGRAPHICA SECTION D, Issue 4 2010James M. Holton In this work, classic intensity formulae were united with an empirical spot-fading model in order to calculate the diameter of a spherical crystal that will scatter the required number of photons per spot at a desired resolution over the radiation-damage-limited lifetime. The influences of molecular weight, solvent content, Wilson B factor, X-ray wavelength and attenuation on scattering power and dose were all included. Taking the net photon count in a spot as the only source of noise, a complete data set with a signal-to-noise ratio of 2 at 2,Å resolution was predicted to be attainable from a perfect lysozyme crystal sphere 1.2,µm in diameter and two different models of photoelectron escape reduced this to 0.5 or 0.34,µm. These represent 15-fold to 700-fold less scattering power than the smallest experimentally determined crystal size to date, but the gap was shown to be consistent with the background scattering level of the relevant experiment. These results suggest that reduction of background photons and diffraction spot size on the detector are the principal paths to improving crystallographic data quality beyond current limits. [source] | ||||||||||||||||||||||||||||||||||