Papers by Keyword: Crystal Growth

Abstract: Sheet nacre is a promising natural bioceramic, which consists on the internal lustrous “mother of pearl” layer of many molluscan shells, e.g. Pinctada, our model. The aim of this work is to study the structure of the flat polygonal tablets of nacre, in order to understand the multi-scale organization of this composite material and the role of the organic template during the growth of the biocrystal. We studied the organic matrix, in situ with techniques such as darkfield transmission electronic microscopy (TEM) on small cross-sections of nacre of Pinctada maxima, or intermittent-contact atomic force microscopy coupled with phase imaging on samples of nacre of Pinctada margaritifera polished parallel to the surface of the tablets. In this study, we demonstrate the continuity of the organic framework and the crystallographic orientation in the biocrystal at 2 relevant levels : nano- and micro-scale.

Abstract: The relationships between the morphologies of primary silicon and undissolved silicon particles in melt of Al-Si hypereutectic alloys are studied by holding the melt from 600 to 1100°C and then quench interrupting. The variation of growth process and mechanism of primary silicon is also investigated. The results show that undissolved silicon particles in the melt would become the nuclei of primary silicon precipitated in solidification and there is a close relationship between the shape of primary silicon and undissolved silicon particles. The growth of silicon would follow not only twin plane re-entrant edge (TPRE), but also layer mechanism as well. Meanwhile, the shape of primary silicon also relied on kinetic surroundings, such as solute transportation. At higher overheating temperatures of the melt, the primary silicon takes star-like and tree-like shapes.

Abstract: The bulk crystal growth of II-VI compounds, such as HgCdTe, CdZnTe etc., is usually carried out by Bridgman and modified Bridgman methods. Optimizing the growth process relies mainly on the understanding of the fundamental problems of solute and thermal transportation principles, which determines the composition segregations and other defects, including point defects, dislocations, precipitates, stacking faults, etc. In the last few years, the present author studied the coupling effects of the convection, thermal and solute transportation phenomena during the growth processes through both theoretical modeling and experimental methods. Several important phenomena, such as effects of ACRT forced convection on the thermal and solute field and the growth interface morphology, the shift of the growth interface due to the solute redistributions, solute segregation behaviors during the growth process, etc, are discussed. Based on these researches, technologies for growing high quality CdZnTe and other II-VI compounds have been developed.

Abstract: The effects of a series of polyphosphonate and poly-carboxylate additives have been investigated in the crystallization of various inorganic salts. Systematic variation of the additive structure has been used to provide insight into the dominant factors in additive-crystal interactions. The results obtained for barium sulfate and hematite (α-Fe2O3) show that the morphological effects do not necessarily follow the trend one might expect on the basis of the structural features of the additives. Molecular modeling, coupled with in-situ AFM imaging is being used to develop an approach that will allow more informed systematic design of crystal growth modifiers.

Abstract: Docetaxel (form A), a stoichiometric hydrate containing three water molecules per molecule of drug substance (Taxotere^®), is thermodynamically stable under ambient conditions of pressure, temperature and relative humidity. In order to gain a better understanding of docetaxel system at the atomic scale a structural study was performed. Due to strong anisotropy of crystals (thin plates), the crystal structure of docetaxel (29 degrees of freedom) was solved and refined using high resolution XRPD data applying an ab initio direct space method. In parallel, an in-depth crystal growth study was carried out until single crystals suitable for XRSCD structural resolution were obtained: surprisingly, a new polymorph of docetaxel, called form B, was isolated.