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Seed Crystals (seed + crystal)
Selected AbstractsInduction and Inhibition of Preferential Enrichment by Controlling the Mode of the Polymorphic Transition with Seed CrystalsCHEMISTRY - A EUROPEAN JOURNAL, Issue 13 2006Rui Tamura Prof. Abstract Both induction and inhibition of "preferential enrichment", an unusual symmetry-breaking enantiomeric-resolution phenomenon observed upon simple recrystallization of a certain kind of racemic crystals from organic solvents, have been successfully achieved by controlling the mode of the polymorphic transition during crystallization with appropriate seed crystals. Such control of the polymorphic transition can be interpreted in terms of a novel phenomenon consisting of 1) the adsorption of prenucleation aggregates, 2) the heterogeneous nucleation and crystal growth of a metastable crystalline form, and 3) the subsequent polymorphic transition into the more stable form; these three processes occur on the same surface of a seed crystal. We refer to this phenomenon as an "epitaxial transition", which has been confirmed by means of in situ attenuated total reflection (ATR) FTIR spectroscopy in solution and the solid state, differential scanning calorimetry (DSC) measurements of the deposited crystals, and X-ray crystallographic analysis of the single crystals or the direct-space approach employing the Monte Carlo method with the Rietveld refinement for the structure solution from the powder X-ray diffraction data. [source] Screen Printing to Achieve Highly Textured Bi4Ti3O12JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2010Michael R. Winter The focus of this paper is to explore the efficacy of screen printing to generate crystalline texture in bismuth titanate through the orientation of highly anisotropic seed crystals. Seed crystals were grown through a molten salt flux technique with aspect ratios of ,100:1, mixed with equiaxed powder of the same composition and oriented using screen printing, a high shear process. By printing on a flexible polymer substrate and using multiple print/dry cycles, it was possible to create pads with a thickness of several hundred micrometers and to remove the dried pads, creating free-standing samples. Upon sintering, the seed crystals grew at the expense of the matrix powder, a process known as templated grain growth. The degree of texture was analyzed using a variety of techniques including scanning electron microscopy, X-ray diffraction and electron backscatter diffraction. [source] Rapid growth of KDP crystals in the coniform bottom device and their characterizationCRYSTAL RESEARCH AND TECHNOLOGY, Issue 6 2009Bing Teng Abstract The coniform bottom device was designed and used in the rapid growth process of KDP crystal. A seed support rack was also designed to be used in rapid growth of KDP crystal to avoid spontaneous nucleation on the interface of seed crystal and rack. The KDP crystals were fast grown at the growth rate of up to 25 mm/day. The optical scatter centers in KDP crystals were observed and their transmissions of different parts were measured. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Numerical investigation of heat transport and fluid flow during the seeding process of oxide Czochralski crystal growth Part 1: non-rotating seedCRYSTAL RESEARCH AND TECHNOLOGY, Issue 6 2007M. H. Tavakoli Abstract For the seeding process of oxide Czochralski crystal growth, the flow and temperature field of the system as well as the seed-melt interface shape have been studied numerically using the finite element method. The configuration usually used initially in a real Czochralski crystal growth process consists of a crucible, active afterheater, induction coil with two parts, insulation, melt, gas and non-rotating seed crystal. At first the volumetric distribution of heat inside the metal crucible and afterheater inducted by the RF coil was calculated. Using this heat source the fluid flow and temperature field were determined in the whole system. We have considered two cases with respect to the seed position: (1) before and (2) after seed touch with the melt. It was observed that in the case of no seed rotation (,seed = 0), the flow pattern in the bulk melt consists of a single circulation of a slow moving fluid. In the gas domain, there are different types of flow motion related to different positions of the seed crystal. In the case of touched seed, the seed-melt interface has a deep conic shape towards the melt. It was shown that an active afterheater and its location with respect to the crucible, influences markedly the temperature and flow field of the gas phase in the system and partly in the melt. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Grain Growth Control and Solid-State Crystal Growth by Li2O/PbO Addition and Dislocation Introduction in the PMN,35PT SystemJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2006Min-Soo Kim Grain growth behavior and solid-state single crystal growth (SSCG) in the Pb(Mg1/3Nb2/3)O3,35 mol% PbTiO3 (PMN,35PT) system have been investigated with varying Li2O/PbO ratios. The effect of dislocation density on crystal growth has also been studied. For SSCG, a BaTiO3 single-crystal seed was embedded in a polycrystalline PMN,PT matrix. During annealing, a PMN,PT single crystal grew from the seed at the cost of the small matrix grains. Addition of Li2O dopant first enhanced and then reduced abnormal grain growth in the matrix. In the 2 mol% Li2O and 6 mol% PbO excess PMN,PT samples annealed at 1200°C, considerable single-crystal growth occurred without formation of abnormally large grains in the matrix. Increasing the dislocation density in the BaTiO3 seed crystal resulted in enhanced growth of single crystals. These results were explained in terms of interface reaction-controlled nucleation and growth, based on crystal growth theories. [source] Induction and Inhibition of Preferential Enrichment by Controlling the Mode of the Polymorphic Transition with Seed CrystalsCHEMISTRY - A EUROPEAN JOURNAL, Issue 13 2006Rui Tamura Prof. Abstract Both induction and inhibition of "preferential enrichment", an unusual symmetry-breaking enantiomeric-resolution phenomenon observed upon simple recrystallization of a certain kind of racemic crystals from organic solvents, have been successfully achieved by controlling the mode of the polymorphic transition during crystallization with appropriate seed crystals. Such control of the polymorphic transition can be interpreted in terms of a novel phenomenon consisting of 1) the adsorption of prenucleation aggregates, 2) the heterogeneous nucleation and crystal growth of a metastable crystalline form, and 3) the subsequent polymorphic transition into the more stable form; these three processes occur on the same surface of a seed crystal. We refer to this phenomenon as an "epitaxial transition", which has been confirmed by means of in situ attenuated total reflection (ATR) FTIR spectroscopy in solution and the solid state, differential scanning calorimetry (DSC) measurements of the deposited crystals, and X-ray crystallographic analysis of the single crystals or the direct-space approach employing the Monte Carlo method with the Rietveld refinement for the structure solution from the powder X-ray diffraction data. [source] Crystal growth by the travelling heater method using tapered crucibles and applied rotating magnetic fieldCRYSTAL RESEARCH AND TECHNOLOGY, Issue 8 2010J. Roszmann Abstract Crystal growth experiments were carried out by the Travelling Heater Method using tapered growth ampoules with and without the application of a rotating magnetic field. The objective was to enhance its commercial potential by reducing the size of required seed crystals and increasing the growth rate. To this end, a number of GaSb crystals were grown using either 25 mm diameter straight, or 10 mm to 25 mm tapered growth ampoules. Growth rates of 2 mm/day and 5 mm/day were employed. The effect of rotating magnetic fields of several strengths and frequencies was examined. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Morphological study of Czochralski-grown lanthanide orthovanadate single crystals and implications on the mechanism of bulk spiral formationJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2 2010Hengjiang Cong Single crystals of monoclinic Nd:LaVO4 with dimensions up to Ø28 × 21,mm have been grown from the near-stoichiometric melt by the Czochralski method, making use of various seed orientations that are perpendicular to the (010), (10), (001) and (00) crystal planes. A sample was also prepared with the seed orientation in an arbitrary direction relative to the crystal. The anisotropic properties of the crystal are manifested in the growth morphology of the as-grown crystals, where different degrees of bulk spiral growth were observed. It was also found that employing the (001) or (00) seed faces severely suppressed the bulk spiral growth, and thus high quality and large-scale Nd:LaVO4 crystals were obtained. The constituent segregation coefficients and high-temperature stability, including the melting point, were determined and evaluated. Based on the attachment energy model of Hartman,Perdok theory, morphology predictions were made for monoclinic LaVO4 and tetragonal YVO4 orthovanadate single crystals. Correlating with the as-grown morphology of both crystals developed along different seed orientations, a theoretical explanation is provided for the influences of seed crystals on bulk spiral formation, crystal quality and utilization ratio. It suggests that breaking the axial symmetry of the ideal atomic level interface between crystal and melt plays a crucial triggering role in bulk spiral formation in the Czochralski growth of lanthanide orthovanadate single crystals. Selecting a proper seed orientation that yields such a highly axially symmetric surface structure consisting of a series of large-area facets with similar growth velocities can greatly reduce bulk spiral formation and thus is preferable in the Czochralski growth of large-sized low-symmetry oxide crystals. [source] Solidification in heat packs: III.AICHE JOURNAL, Issue 2 2003Metallic trigger The metallic trigger used in commercial heat packs initiates solidification by releasing minute crystals of solid sodium acetate trihydrate into the subcooled solution. These crystals are harbored in submicron cracks on the disk's surface and are released when the disk is flexed. Using scanning electron microscopy, such seed crystals are observed on the surface of a disk after flexing it. Classic nucleation theory is used to investigate the behavior of crystals residing in the cracks on the metallic disk's surface during heating and cooling. Sodium acetate trihydrate crystals are capable of surviving in a 1-nm crack or smaller at regeneration temperatures of the order of 353 K. These seed crystals grow to the mouth of the crack at temperatures below the liquidus, but can only promote solidification of the whole solution surrounding the disk at temperatures below 256 K or when the disk is flexed. [source] Screen Printing to Achieve Highly Textured Bi4Ti3O12JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2010Michael R. Winter The focus of this paper is to explore the efficacy of screen printing to generate crystalline texture in bismuth titanate through the orientation of highly anisotropic seed crystals. Seed crystals were grown through a molten salt flux technique with aspect ratios of ,100:1, mixed with equiaxed powder of the same composition and oriented using screen printing, a high shear process. By printing on a flexible polymer substrate and using multiple print/dry cycles, it was possible to create pads with a thickness of several hundred micrometers and to remove the dried pads, creating free-standing samples. Upon sintering, the seed crystals grew at the expense of the matrix powder, a process known as templated grain growth. The degree of texture was analyzed using a variety of techniques including scanning electron microscopy, X-ray diffraction and electron backscatter diffraction. [source] Anatase Titanium Dioxide Crystallization by a Hydrolysis Reaction of Titanium Alkoxide without AnnealingJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2006Kunio Funakoshi The crystallization of anatase titanium dioxide (TiO2) was achieved by a hydrolysis reaction of titanium alkoxide without annealing. The hydrolysis reaction rates of tetraethyl orthotitanate were indicated by a function of the concentration of acetylacetone added. The degree of crystallinity of the product particles was influenced by the amounts of acetylacetone and seed crystals. Anatase TiO2 was crystallized by restraining the rapid increase in supersaturation of TiO2 and the consequent nucleation of amorphous TiO2. The degree of crystallinity of the product particles also changed with the types of seed crystals used, and was strongly influenced by the specific surface areas of the seed crystals. [source] Induction and Inhibition of Preferential Enrichment by Controlling the Mode of the Polymorphic Transition with Seed CrystalsCHEMISTRY - A EUROPEAN JOURNAL, Issue 13 2006Rui Tamura Prof. Abstract Both induction and inhibition of "preferential enrichment", an unusual symmetry-breaking enantiomeric-resolution phenomenon observed upon simple recrystallization of a certain kind of racemic crystals from organic solvents, have been successfully achieved by controlling the mode of the polymorphic transition during crystallization with appropriate seed crystals. Such control of the polymorphic transition can be interpreted in terms of a novel phenomenon consisting of 1) the adsorption of prenucleation aggregates, 2) the heterogeneous nucleation and crystal growth of a metastable crystalline form, and 3) the subsequent polymorphic transition into the more stable form; these three processes occur on the same surface of a seed crystal. We refer to this phenomenon as an "epitaxial transition", which has been confirmed by means of in situ attenuated total reflection (ATR) FTIR spectroscopy in solution and the solid state, differential scanning calorimetry (DSC) measurements of the deposited crystals, and X-ray crystallographic analysis of the single crystals or the direct-space approach employing the Monte Carlo method with the Rietveld refinement for the structure solution from the powder X-ray diffraction data. [source] | ||||||||||