Home About us Contact
|
Home About us Contact | ||
|
|
||
Synchrotron X-ray Powder Diffraction (synchrotron + x-ray_powder_diffraction)
Terms modified by Synchrotron X-ray Powder Diffraction Selected AbstractsHigh-Temperature Processing of Ba3ZnTa2O9: An in situ Study Using Synchrotron X-Ray Powder Diffraction.CHEMINFORM, Issue 48 2007Phillip M. Mallinson Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Hydrolysis of Pure and Sodium Substituted Calcium Aluminates and Cement Clinker Components Investigated by in Situ Synchrotron X-ray Powder DiffractionJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2004Axel Nørlund Christensen The hydrolysis of pure and sodium-substituted calcium aluminates and cement clinker phases was investigated in situ in the temperature range 25°,170°C, using the angle dispersive powder synchrotron powder X-ray diffraction technique. The final hydrolysis product in all cases was Ca3Al2(OH)12. The intermediate phase Ca4Al2O7·19H2O was formed from the pure calcium aluminates, and the intermediate phases Ca4Al2O7·xH2O, x= 11, 13, or 19, were formed from the cement clinker phases. [source] The Microstructure of Biogenic Calcite: A View by High-Resolution Synchrotron Powder Diffraction,ADVANCED MATERIALS, Issue 18 2006B. Pokroy Biogenic calcite obtained from different mollusk shells is subjected to heat treatments at elevated temperatures and structurally analyzed by high-resolution synchrotron X-ray powder diffraction. Remarkable broadening of diffraction peaks in samples annealed at temperatures above 200,°C is observed (see figure), indicating heat-induced degradation of intra-crystalline proteins occluded in the mineral lattice during biomineralization. [source] Structural study of ferroelectric and paraelectric phases in PbK2LiNb5O15PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 11 2004Y. Gagou Abstract The structures of PbK2LiNb5O15 showing the ferroelectricity below about 640 K have been studied in the paraelectric and ferroelectric phases by means of synchrotron X-ray powder diffraction. The data are analyzed with a Rietveld refinement method. It is found that the paraelectric structure and the ferroelectric one are of tetragonal and orthorhombic symmetry with P4/mbm and Pba2, respectively. The Pba2 structure gives a polar displacement along c -axis, whose direction is consistent with that deduced from dielectric measurements. The refined chemical occupancies of the cations Pb, K and Nb give the site-situation of these ions in the tunnels with square sections and pentagonal sections in each phase. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Crystal structures and cation ordering in Cs2MgSi5O12, Rb2MgSi5O12 and Cs2ZnSi5O12 leucitesACTA CRYSTALLOGRAPHICA SECTION B, Issue 4 2009A. M. T. Bell The crystal structures of the leucite analogues Cs2MgSi5O12, Cs2ZnSi5O12 and Rb2MgSi5O12 have been determined by synchrotron X-ray powder diffraction using Rietveld refinement in conjunction with 29Si MAS NMR spectroscopy. These leucites are framework structures with distinct tetrahedral sites (T sites) occupied by Si and a divalent cation (either Mg or Zn in these samples); there is also a monovalent extra-framework cation (either Cs or Rb in these samples). The refined crystal structures were based on the Pbca leucite structure of Cs2CdSi5O12, thus a framework with five ordered Si T sites and one ordered Cd T site was used as the starting model for refinement. 29Si MAS NMR shows five distinct Si T sites for Cs2MgSi5O12 and Rb2MgSi5O12, but six Si T sites for Cs2ZnSi5O12. The refined structures for Cs2MgSi5O12 and Rb2MgSi5O12 were determined with complete T -site ordering, but the refined structure for Cs2ZnSi5O12 was determined with partial disorder of Mg and Si over two of the T sites. [source] Polymorphism of microcrystalline urate oxidase from Aspergillus flavusACTA CRYSTALLOGRAPHICA SECTION D, Issue 5 2010Ines Collings Different polymorphs of rasburicase, a recombinant urate oxidase enzyme (Uox) from Aspergillus flavus, were obtained as a series of polycrystalline precipitates. Different crystallization protocols were followed in which the salt type, pH and polyethylene glycol 8000 (PEG 8000) concentration were varied. The related crystalline phases were characterized by means of high-resolution synchrotron X-ray powder diffraction. In all cases, Uox complexed with the inhibitor 8-azaxanthine (AZA) was not altered from its robust orthorhombic I222 phase by variation of any of the factors listed above. However, in the absence of AZA during crystallization ligand-free Uox was significantly affected by the type of salt, resulting in different crystal forms for the four salts tested: sodium chloride, potassium chloride, ammonium chloride and ammonium sulfate. Remarkable alterations of some of these phases were observed upon gradual increase of the exposure time of the sample to the synchrotron beam in addition to variation of the PEG 8000 concentration. When Uox was crystallized in Tris buffer or pure water in the absence of salt, a distinct polymorph of orthorhombic symmetry (P21212) was obtained that was associated with significantly altered lattice dimensions in comparison to a previously reported isosymmetrical structure. The latter form of Uox exhibits enhanced stability to variation of pH and PEG 8000 concentration accompanied by minor modifications of the unit-cell dimensions in the ranges under study. Accurate lattice parameters were extracted for all crystalline phases. This study reveals the rich phase diagram of Uox, a protein of high pharmaceutical importance, which is associated with an enhanced degree of polymorphism. The outcome of our analysis verifies previously reported results as well as demonstrating polymorphs that have altered unit-cell dimensions with respect to known structural models. [source] | |||||||||||||