High-temperature X-ray Diffraction Method Research Articles

Phase equilibria at low oxygen partial pressure in the YBaCuO system

The phase equilibria around YBa 2Cu 3O 7− x (123) and YBa 2Cu 4O 8 (124) phases at low oxygen partial pressure (≦1 atm) were investigated by X-ray diffraction and thermal analysis. The coexistence of 123 and 124 phase was confirmed under 1 atm oxygen pressure. By using the high temperature X-ray diffraction method, the univariant reaction YBa 2Cu 3O 7− x +Cu 2O⇆Y 2BaCu 2 O 2+O 2 was identified. The oxygen partial pressure dependence of several univariant reactions has been investigated and the existence of two invariant reactions of L+O 2⇆YBa 2Cu 3O 7− x + BaCuO 2+CuO+Cu 2O and L+Y 2BaCuO 5+O 2⇆YBa 2Cu 3O 7− x +CuO+Cu 2O was deduced to occur at 1103 K under 0.0032 atm O 2 and at 1143 K under 0.0085 atm O 2, respectively.

KINETICS OF SECOND PHASE Ba6Ti17O40 FORMATION

Kinetics of second phase Ba6Ti17O40 formation in the mixture of BaTiO3 and excess TiO2 were studied by high-temperature X-ray diffraction method. The reaction curves were obtained at various temperatures for the formation of Ti-rich phase Ba6Ti17O40, and the reaction rate constant K and the activation energy Q were calculated. Finally, the mechanism of second phase Ba6Ti17O40 formation and the effect of excess TiO2 are discussed.

High temperature X-ray diffraction studies of the compound YBa2Cu3Ox

Ambient and high temperature X-ray diffraction methods were used to determine the unit cell parameters of the orthorhombic and tetragonal phases of the YBa2Cu3Ox compound, as a function of oxygen stoichiometry and temperature. The total oxygen content was obtained by the thermogravimetric method (TGA) by determining the weight loss in hydrogen up to 1000 degrees C. Reduction reactions in hydrogen were also performed in situ using a high temperature X-ray unit. Using the TGA method the oxygen content in the structure was obtained by weight loss in 100% oxygen. Thermal expansion coefficients of the lattice parameters were determined for both orthorhombic and tetragonal materials with different, constant x values.

Studies of the silicon dioxide-dolomite system by thermal analysis

A study of the processes occurring in the SiO 2-dolomite system at a temperature in the range 25–1500 °C was carried cut with the use of thermoanalytical and high temperature X-ray diffraction methods. The purpose of this study was to reveal the effect of the composition on the transformation processes applied to similar mixtures which are frequently used in the silicate and glass industries.

Etude par diffraction des rayons X a haute temperature en atmosphere controlee de la transformation structurale de L'YBa 2Cu 3O z

A high temperature X-ray diffraction method, under a controlled atmosphere, is used to determine the composition dependence of the lattice parameters of YBa 2Cu 3O z . The phase transition occurs near the oxygen composition Z = 6.65, and near 680 °C in pure oxygen, 620 °C in air. Its structural transformation is reversible, without hysteresis and is of higher than first order.

Effects of some admixtures on the decomposition of calcium sulphate

The by-product phosphogypsum contains CaHPO4, H3PO4, Ca5(PO4)3F, Al2O3, Fe2O3, SiO2 etc. besides the main product CaSO4. By means of TG-DTA the thermochemical decomposition of pure phosphogypsum and phosphogypsum containing CaO, Al2O3, Fe2O3 and SiO2 in a reductive atmosphere was studied. The solid phase was examined by high-temperature thermomicroscopy, scanning electronmicroscopy, X-ray diffraction and other methods. It could be confirmed, that most of the admixtures undergo secondary reactions with CaO and CaS, modifying the decomposition rate of CaSO4.

In situ X-ray diffraction studies of structural transformations in V-P-O catalysts

Structural transformations of V-P-O catalysts have been studied in situ in oxidative, inert and reducing atmosphere by the high-temperature X-ray diffraction method. Formation of vanadyl phosphates is shown to depend on the P/V ratio in the initial sample. It has been established that transformations in the phase composition of catalysts is independent of the reaction media at P/V=2. The effect of catalyst composition on catalytic properties is discussed.

Phase equilibria in the system CoMnTiO in air

Abstract Studies of the system CoMnTiO in air have been made using high temperature X-ray diffraction methods and X-ray phase analysis of quenched samples. To illustrate the evolution of phase equilibria with temperature, isothermal sections of the phase equilibrium diagram of the system at 1470, 1370, 1270 and 1170 K have been constructed. Solid solutions with pseudobrookite, ilmenite, spinel, β-Mn 3 O 4 - and α-Mn 2 O 3 -type structures were formed. The spinel solid solution underwent tetragonal distortion due to the cooperative Jahn-Teller effect.

Chemical form of iron catalysts during the CO 2-gasification of carbon

The chemical form of iron catalysts during the gasification of carbon with a CO 2 CO mixture was examined in situ by a controlled atmosphere high temperature X-ray diffraction method. Several iron compounds, Fe 3 O 4, Fe 1 − x O, Fe 3 C, α- Fe and γ- Fe, were identified between 700–1000 °C. Both the gasification temperature and the ratio of CO 2 CO affect the chemical form. The gasification reactivity was determined by thermogravimetry under the same experimental conditions as the X-ray study, and considered in relation to the chemical form of the catalyst.

Étude du système FeCoO À 700 et 1000 °C par diffraction des rayons X en atmosphère contrôlée

A high-temperature X-ray diffraction method is used under controlled pressure to evaluate dependence of the lattice parameter of various oxides at 700 and 1000 °C on the partial pressures of oxygen. Fe 1− x O and CoO have complete mutual solubility at 1000 °C. Two monoxides are observed at 700 °C. The solubility of cobalt in iron protoxide is weak; the solubility of iron decreases with increasing oxygen partial pressures in cobalt monoxide. They are respectively in the c.c. alloy and spinel phase.

An in situ X-ray diffraction study of precipitation from a supersaturated solid solution: The γ' precipitate in a Ni-12.5% Si alloy

The kinetic behavior of precipitation in a supersaturated Ni-12.5 at.% Si alloy single crystal has been studied by an in situ high-temperature X-ray diffraction method for the first time. Experimental and analytic techniques have been developed to simultaneously determine the interfacial free energy, γ, the solute diffusivity, D, and the equilibrium solubility, C e , from a single type of X-ray measurement The principle of analysis entailed a diffusion-controlled coarsening model put forth by Lifshitz and Slyozov, and independently by Wagner. The kinetic parameters, i.e. rate constants, governing the growth of the particle size and the volume fraction of the γ' precipitate are derived from the line width and the integrated intensity of a superlattice reflection of the γ' phase, respectively. Results for D in the temperature range from 400° to 550°C are in good agreement with the extrapolated values obtained from the high-temperature data. Enhanced diffusion is noticed at temperatures below 500°C. Reasonable values for the interfacial free energy (about 11 ergs/cm 2) are found for all temperatures considered. The equilibrium solubility is found to be consistent with the published phase diagram values.

STUDY OF THE HIGH TEMPERATURE X-RAY DIFFRACTION OF A Fe-Cr-Co PERMANENT MAGNETIC ALLOY

A deformable permanent magnetic alloy, with composition of 62Pe-23Cr-15Co (in wt %), has been studied by high-temperature X-ray diffraction method. Debye-Scher-rer photographs of samples treated with aging in magnetic field and also of those treated without magnetic field were taken. It has been observed that the transformation process with rising temperature up to 800℃ is different in the two classes of samples. The lattice parameters of the samples without a treatment in magnetic field have been measured at various temperatures; and it has been found that in these samples a transitional phase unknown before appeared at 610℃, which was unstable at other temperatures.

The eutectic and liquidus in the Al2O3-ZrO2 system

A high-temperature X-ray diffraction method was employed to establish,in situ, the eutectic temperature (1910±20° C) and the liquidus line in the Al2O3-ZrO3 binary system. The eutectic composition was determined by optical microscopy to be 42.5±1 wt% ZrO2. No evidence was found for the existence of a reportede-Al2O2 high temperature phase.

The thermal expansion of staurolite, Fe4Al18Si8O44(OH)4

AbstractThe thermal expansion of iron end-member staurolite has been studied by high-temperature powder X-ray diffraction methods and by modelling with the Distance Least Squares (DLS) computer program. The X-ray approach was complicated by dehydroxylation of the staurolite. Mean linear expansion coefficients for the a, b, and c cell edges of dehydroxylated staurolite determined by the X-ray method are (× 10−6 °C−1); 20–500 °C, 8.93, 8.23, and 7.95, respectively, and 20–800 °C, 7.85, 9.43, and 9.13, respectively. Expansion coefficients of a, b, and c calculated for hydroxylated staurolite using the DLS program over the same temperature ranges are (7.86, 7.18, and 7.55 × 10−6 °C−1) and (7.87, 7.17, and 7.57 × 10−6 °C−1). The good agreement between the results from the two methods supports the use of computer modelling in estimating the thermal expansion behaviour of complex structures. The latter approach could be preferable for studying hydrated minerals.

Étude du système FeCoO à 900 °C par thermogravimétrie et diffraction des rayons X à haute température

The method of physicochemical equilibria between a gaseous phase and an oxide was used to determine the partial pressures of oxygen in equilibrium with non-stoichiometric oxides (Fe 0,5Co 0.5) 1− x O. The oxide composition evolution was recorded by means of a thermobalance; log P o 2 as a function of O Me was determined at 900 °C. A high temperature X-ray diffraction method under controlled pressure was used to evaluate the composition dependence of the lattice parameter of various oxides at 900 °C. Three varieties of cobaltowüstite (Fe 1− y Co y ) 1− x O were characterized. The phase initially consisted of wüstite and finally became a solution mainly of CoO. When P o 2 increased these three varieties were respectively in equilibrium with a c.c. or f.c.c. alloy, with the spinel (Fe 2.6Co 0.4)O 4 and with a spinel of variable composition Fe Co . The compositions of solid phases at the phase boundaries and the nature of predominant defects in the three varieties of monoxide were considered.

ChemInform Abstract: EFFECT OF SURROUNDING ATMOSPHERE IN THE TRANSFORMATION OF GERMANIUM DIOXIDE

AbstractMittels Hochtemperatur‐Röntgenbeugungsuntersuchungen wird der Einfluß der Atmosphäre auf die Phasenumwandlungvon GeO, in Gegenwart von Alkalimetallgermanat‐Katalysatoren untersucht.

ChemInform Abstract: ROLE OF GERMANATE CATALYST IN THE TRANSFORMATION OF GERMANIUM DIOXIDE

AbstractDurch Hochtemperatur‐Röntgenbeugungsuntersuchungen wird die Bedeutung der Alkalimetallgermanate als Katalysatoren bei der polymorphen Umwandlung von Geü, untersucht.

Effect of Surrounding Atmosphere in the Transformation of Germanium Dioxide

Abstract The effect of surrounding atmosphere on the phase transformation of germanium dioxide with alkali germanate catalysts was investigated by high temperature X-ray diffraction method. The catalysts were Li2O·7GeO2, 3K2O·11GeO2, K2O·7GeO2 and 2Na2O·9GeO2. The ambient atmospheres were dry or wet nitrogen and oxygen. The effect of atmosphere was found to be not so large as that of the catalyst. Water vapor has prominent effects upon the transformation as in other solid state reactions.

Role of Germanate Catalyst in the Transformation of Germanium Dioxide

Abstract The role of alkali germanates as catalysts in the polymorphic transformation of germanium dioxide was investigated by high-temperature X-ray diffraction method. Lithium germanate and sodium germanate catalyze the transformation in a solid state, the activation energies being larger than 80 kcal/mol. Potassium germanate catalyst plays its role in a liquid state, the activation energy being smaller than that of other catalysts.

Lattice expansions of two boron carbides between 12 and 940°C

High-temperature X-ray diffraction methods have been used to determine unit-cell parameters of two boron carbide compositions from 12° to about 940°C. One composition was at the carbon-rich end of the phase field (i.e. B4C), the second at the boron-rich end (5 at. % C by chemical analysis). The lattice expansion of both substances was isotropic in the temperature range studied. The mean linear thermal expansion coefficient for the carbon-rich composition is 5.65 x 10−6°C−1, while that of the boron-rich composition is 5"87 x 10−6°C−1.