Powder X-ray Diffraction Of Samples Research Articles

Solubility and Pseudopolymorphic Transitions in Mixed Solvents: Sodium Naproxen in Methanol−Water and Ethanol−Water Solutions

The solubility of sodium naproxen in methanol−water and ethanol−water solutions was determined as functions of temperature and solvent composition over a temperature range of 10−40 °C and the entire range of alcohol water compositions. Data were correlated using an expression in the form of the van’t Hoff equation, which allowed estimation of heats and entropies of dissolution. In addition, the correlations indicated that different forms (hydrates and alcohol solvates) existed in different regions of the temperature−solvent composition space. Thermal analysis and powder X-ray diffraction of samples of the equilibrated solids confirmed the existence of the different pseudopolymorphic forms. Conditions at which the more stable form of the sodium naproxen became the less stable form were determined and are referred to as transition points; at such conditions, the solution and two solid forms were in equilibrium. The activity of water at the transition points was estimated from the Wilson equations and found ...

On the solid solution of the spinel phase in the system NiO–Al 2O 3

The solid solubility of Al 2O 3 in NiAl 2O 4 spinel has been investigated by powder X-ray diffraction of samples prepared by solid state synthesis. The solid solution region found was in agreement with a previous report. The cubic cell parameter of the spinel solid solution was observed to decrease with increasing alumina content. Spinel with high alumina content was shown to be close to an inverse spinel as previously reported for stoichiometric NiAl 2O 4 and the inversion parameter proved to be relatively independent of the overall composition.

High-temperature transformations of Cu-rich hydrotalcites

Cu M(II)Al ternary hydrotalcites ( M(II) = Ni, Co and Mg) with a (Cu+ M(II))/Al atomic ratio of 3.0 and Cu/ M(II) atomic ratio of 5.0 were synthesized by coprecipitation under low supersaturation. Powder X-ray diffraction of the as-synthesized samples showed a pattern characteristic of hydrotalcite-like (HT-like) structure (JCPDS: 41-1428). Thermal analyses of these samples showed four stages of weight loss/heat change when recorded in nitrogen. Analysis of the evolved gases characterized the nature of these transformations. The thermoanalytical effects differed significantly especially for the high-temperature transformations, when the treatment was performed in oxygen. In situ powder X-ray diffraction of the samples was carried out to elucidate the phase evolution of these compounds. Surprisingly formation of CuO was noted at temperatures around 200°C well below the destruction of the layered network. The nature of the resulting phases varied with both the nature of the co-bivalent metal ion and the heating atmosphere. FT-IR spectroscopy confirmed the retention of carbonate ions at higher temperatures (above 700°C), although the concentration of carbonate anion (most likely unidentate) varied with the calcination temperature. The crystallinity of CuO increased significantly above 600°C, probably through dissociation of copper oxycarbonate. Significant differences in the thermal transformation temperatures (for the third and the fourth transformations) of these samples containing different co-bivalent metal ions were not observed. This suggests that an association of the co-bivalent metal ions and/or trivalent metal ion in this phase is unlikely. A plausible thermal evolution scheme of these hydrotalcites is proposed.

Phase Relations at 1500°C in the Ternary System ZrO2–Gd2O3–TiO2

Phase relations at 1500°C in the ternary system ZrO2–Gd2O3–TiO2 have been determined by the powder X-ray diffraction of samples prepared by standard solid state reaction. A large area of this ternary oxide system centered on the Gd2Ti2O7–Gd2Zr2O7 join was shown to exhibit the pyrochlore and defect fluorite structures. The pyrochlore structure was observed for stoichiometries as far from the ideal M4O7 as M4O6.7 and M4O7.4, although the degree of disorder seemed much higher at these stoichiometries. On further deviation from the ideal M4O7 stoichiometry a smooth transition to fluorite average structure was observed for Zr-rich compositions. None of the other binary phases were observed to show significant extent of solid solution into the ternary region.

Phase Relations at 1500°C in the Ternary System ZrO2–Y2O3–TiO2

Phase relations at 1500°C in the ternary system ZrO2– Y2O3–TiO2have been determined by powder X-ray diffraction of samples prepared by standard solid state mixing and also by ball milling. A large region of this ternary oxide system was shown to exhibit the defect cubic fluorite structure and to encompass compositions containing very high oxygen vacancy concentrations up to 16%, e.g., Zr0.21Y0.62Ti0.17O1.69. We have accurately determined the maximum extent of the defect fluorite phase, at low concentrations of yttrium/high concentrations of titanium. From previous studies this region of the solid solution is expected to yield compositions which exhibit the optimum mixed ionic and electronic conducting properties for electrochemical applications. We have determined that at 1500°C up to 18 atom% Ti4+can be dissolved into ZrO2stabilized in the cubic fluorite structure by the presence of 14 to 20 atom% Y. Trends in composition and unit cell parameter are discussed.

Lattice Constants of Boron Carbides

The lattice constants of boron carbides have been determined by powder X‐ray diffraction for samples with compositions between about 7.7 and 20.5 at.% carbon. The boundaries of the single‐phase region are at about 9 at.% carbon and near, but likely somewhat less than, 20 at.% carbon. The composition dependence of the lattice constants thus established provides a method of assessing the carbon concentration of unknown materials. In particular, assignment of the approximate composition of single crystals used in previous studies allows for a systematic examination of changes in interatomic separation as a function of composition. These changes are discussed in terms of a structural model of the boron carbide solid solution.