Showing papers on "Solid solution published in 1987"

Systematics of chlorite alteration at the Phelps Dodge massive sulfide deposit, Matagami, Quebec

Abstract: Hydrothermal alteration at the Phelps Dodge Archcan volcanogenic massive sulfide deposit has converted rhyodacite and rhyolite footwall rocks into the following mineral assemblages: quartz-chlorite-albite-epidote + or - sericite, quartz-chlorite + or - sericite, chlorite + or - sericite, and chlorite-talc + or - stilpnomelane. Alteration at constant Al was initiated by hydration, addition of Fe + Mg, silicification, and leaching of Ca + Na which produced Al-saturated chlorites with a wide range of Fe/Fe + Mg ratios within the assemblage quartz-chlorite-albite-epidote + or - sericite. With continued addition of Fe and less Mg, combined with extensive leaching of quartz, the chlorite became Al-undersaturated (quartz-chlorite-talc assemblage), and ultimately formed a rock composed essentially of chlorite. The chlorite-talc + or - stilpnomelane assemblage is stable in late crosscutting veinlets and in the ore zone.Chlorites in the Si-Al-Mg-Fe system form a rectangular solid solution plane with limited substitution of Al for Si and extensive substitution of Fe for Mg. In Si-Al space the solid solution plane is outlined by Al saturation (presence of other Al-rich mineral) and Al undersaturation (presence of Al-poor or Al-free mineral) boundaries. Al iv substitution for Si in the chlorites increases from 2.3 to 3.01 formula units (based on 8 Si + Al iv ) with Fe/Fe + Mg, whereas Al iv occupancy decreases from 2.88 to 2.65. The valence charge balance is compensated by octahedral site vacancies or by the conversion of Fe (super +2) to Fe (super +3) . The Al iv content of chlorite also increases with temperature. Chlorites on the Al-saturated boundary of the solid solution field form a potentially useful geothermometer: T degrees C = 106 Al iv + 18; Al iv is corrected for changes with the Fe/Fe + Mg ratio as: Al iv corrected = Al iv + 0.7 Fe/Fe + Mg.The Fe/Fe + Mg ratios of bulk rock and contained chlorite correlate well. Birefringence colors of the chlorite change from green to brown, violet, and Berlin Blue as Fe/Fe + Mg changes from 0.18 to 0.64. The Fe/Fe + Mg variation apparently depends largely on the proportions of Mg-rich seawater and Fe-rich hydrothermal fluid in the altering brine.

Alumina‐Silica Phase Diagram in the Mollite Region

Abstract: The alumina-silica phase relations of samples annealed in oxygen and quenched were studied by optical microscopy, image analysis, X-ray diffraction, and the electron microprobe. The solid solution boundaries of mullite changed with increasing temperature and joined at 1890°C and a composition of 77.15 wt% alumina. The melting point of mullite was 189°C with a peritectic between 76.5 and 77.0 wi% alumina.

Phase diagram and superconductivity in the Y‐Ba‐Cu‐O system

Abstract: We have determined the phase diagram of the Y‐Ba‐Cu‐O system through structural, superconducting critical temperature and critical current density characterization. Our results show that a single‐phase compound with a stoichiometry YBa2Cu3Oy is responsible for the high‐temperature superconductivity (92.5 K) in this system.

Synthesis and Thermal Stability of Aluminum Titanate Solid Solutions

Abstract: Aluminum titanate solid solutions with empirical formulas of Al2Ti1-xZrxO5, Al6(2-x)(6+x)Si6x/(6+x)□6x/(6+x)TiO5, and Al2(1-x)MgxTi1+xO5 were synthesized by reaction sintering and annealed at 900° to 1300°C in air to evaluate the thermal stability. Substitution of Al in Al2TiO5 by Si and 2Al by Mg and Ti ions to form solid solutions such as AI6(2-x)/(6+x)l-Si6x/(6+x)□6x/(6+x)TiO5, and Al2(1-x)MgxTi1+xO5 was effective in controlling the thermal decomposition, but substitution of Ti by Zr had little effect.

Determination of the glass-forming concentration range in binary alloys from a semiempirical theory: Application to Zr-based alloys

Abstract: A semiempirical theory is presented to calculate free-energy diagrams of glass-forming alloys. The theory is based on the enthalpy of formation of the solid solution expressed as a sum of two contributions: (a) a chemical contribution due to electronic redistribution in forming the alloy, and (b) an elastic contribution arising from the difference in size between solute and solvent atoms. The enthalpy of formation of the amorphous phase has only the chemical contribution. The theory is used to successfully describe the glass-forming concentration range of some Zr-based alloys, which have been experimentally analyzed by several distinct techniques.

Phase transitions in AgTaxNb1−xO3 solid solutions

Abstract: X-ray diffraction has been used to determine the temperature of phase transitions and the existing distortions of the pseudoperovskite cells throughout the whole range of concentrations of AgTaxNb1−xO3 solid solutions. From the data obtained a phase diagram was constructed. Also plotted were the temperature dependences of the lattice parameters for a few selected concentrations of the solid solutions and also the curve of lattice parameters versus concentration at room temperature. Coexistence of phases was also studied. The existence of a morphotropic region in the concentration range 0.9 1 was ascertained for the AgTaxNb1−xO3 solution.

The Effect of Metallurgical Variables on the Electrocatalytic Properties of PtCr Alloys

Abstract: In this investigation, the effect of alloying on catalysis, especially with respect to oxygen and the ORR, was examined. A series of PtCr alloys allowed four major aspects of alloying to be investigated: (i) effect of decreasing lattice parameter with increasing Cr content in the Pt terminal solid solution, (ii) effect of an order/disorder transition, (iii) difference between intermetallic and solid solution structures, and (iv) effect of dendritic segregation. Results indicated that contrary to the findings of previous investigators, decreased lattice spacing did not correlate with an increase in ORR activity. Atomic ordering in low Cr content specimens, however, was found to generally increase catalysis. Results also indicated that disordered structures interact more strongly with impurities than the ordered structures. ORR Tafel slopes, however, were unaffected by atomic ordering although additional chromium, up to at least 35 atom percent (a/o), caused a decrease in Tafel slope apparently due to oxide reduction effects. At higher Cr concentrations, catalysis decreased due to the passive nature of chromium oxide. The change in crystal structure which occurs for the 80 a/o Cr sample and the dendritic structure, had little effect on most of the electrochemical parameters studied relative simply to the additional Cr content.more » The results of this work also indicated that, in general, no alloy in the PtCr system is more catalytic than pure Pt. This result is in contrast to gas diffusion cell studies which have shown significant increases in catalysis due to PtCr alloying.« less

The superconductive properties and crystal-structure of ba2(y1-xprx)cu3o9-y solid-solutions

Abstract: A series of Ba2(Y1−x Pr x )Cu3O9−y solid solutions were prepared with the orthorhombic distorted perovskite structure. The compound Ba2PrCu3O9−y belonging to tetragonal system is a good semiconductor. The superconductivity is observed for samples withx<0.6. With the increase of Y content, the distortion of crystal structure is greater and the superconductive transition temperature of zero resistanceTc(0) raises.

Superconductivity in HxYBa

Abstract: The preparation of H/sub x/YBa/sub 2/Cu/sub 3/O/sub 7/ by the direct reaction with hydrogen gas is described. The expansion of the original orthorhombic unit cell, as determined by x-ray diffraction, indicates that the system forms a hydrogen solid solution up to x--0.2; at higher H contents a hydrogen-rich phase is precipitated. The solid-solution phase exhibits a superconducting transition at --94 K, which was usually slightly higher than the original oxide. The H-rich phase(s), are not superconducting at 4 K or above. The maximum H content so far achieved corresponds to x = 5.9. The H-rich phases are stable at room temperature, at elevated temperatures (>473 K) they will decompose slowly under vacuum to form water and various solid products. They also slowly react upon exposure to room air.

New High Temperature Superconducting Oxides. (La1−xSrx)2CuO4−δ and (La1−xCax)2CuO4−δ

Abstract: Solid solution systems of (La1−xSrx)2CuO4−δ and (La1−xCax)2CuO4−δ with x=0.05, 0.075, and 0.10 were found to exhibit the superconductivity through a.c. magnetic susceptibility and electrical resistivity measurements. The onset critical temperature for (La0.90Sr0.10)2CuO4−δ was 37 K, the highest among all the superconducting materials ever known, while that for (La0.95Ca0.05)2CuO4−δ was 18 K.

A new hydride phase of LaNi5H3

Abstract: A new hydride phase in the LaNi5-H2 system has been found by precise pressure-composition isotherm measurements. Two plateaux on the isotherms have been clearly observed at temperatures higher than 353 K. The gap between the two plateaux that indicates the existence of the new phase appeared at the composition LaNi5H3. Results of in situ X-ray diffraction measurements show that the new phase LaNi5H3 has hexagonal structure which is the same as the solid solution phase (α phase) and the full hydride phase. The new phase is named β phase and the full hydride phase (LaNi5H6) which has been called β phase is named here γ phase. It was found that the β phase formed after reactions were carried out at temperatures higher than 343 K in desorption and 367 K in absorption. However, once the β phase appeared it formed even at room temperature. Change in lattice parameters has also been measured along the phase transformations. It was found that the lattice expansion accompanying hydride formation was anisotropic. The structure of the β-phase hydride is discussed.

Role of symmetry in the formation of n-paraffin solid solutions

Abstract: Analyse des spectres de diffraction electronique de solides binaires cristallises par epitaxie, de C 32 H 66 /nC 36 H 74 et nC 33 H 68 /nC 36 H 74

The Microstructure of Selective Palladium Hydrogenation Catalysts Supported on Calcium Carbonate and Modified by Lead (Lindlar Catalysts), Studied by Photoelectron Spectroscopy, Thermogravimetry, X‐Ray Diffraction, and Electron Microscopy

Abstract: A detailed analysis of the system Pd + Pb on CaCO3 is presented. This system known as Lindlar catalyst is used for selective hydrogenations of CC bonds to CC bonds. It was found to consist of seven distinct chemical phases. Essential ingredients are solid solutions of hydrogen and oxygen in Pd. The latter phase enables the metal particles to be attached to the support via an orientational relationship calcite (113)∥Pd + O (111). The addition of Pb neither changes the micromorphology of the disk-shaped Pd particles nor does it modify the electronic structure of Pd as studied by chemisorption experiments. The addition of Pb seems to block certain active sites and, thus, to enhance the selectivity. The support was found to be a multi-domain mixture of calcite and aragonite with domain sites of several hundred A. The free surface of the pore-free solid is covered by a calcium-hydroxide carbonate. This phase as well as several other Pb phases seem to represent only spectator materials. Verification of this as well as finding the correlation between structure and function of the various components requires a kinetic analysis which is outside the scope of this paper. It is demonstrated that a variety of analytical techniques is required to unravel the complex nature of such a ‘simple' catalyst’ as it is Pd on CaCO3.

The oxygen-deficient perovskite solid solution Nd1+xBa2-xCu3Oy and its superconductivity

Abstract: The Nd1+xBa2-xCu3Oy system and its superconductivity were studied. This system forms a solid solution within the x range of 0.00 to 0.80. At room temperature, it has orthorhombic symmetry for x ranging from 0.00 to 0.14 and tetragonal symmetry for x not less than 0.20. All specimens at 900°C in air have tetragonal symmetry. It is a superconductor in the region of x less than 0.50. The superconducting onset temperature decreases from 93.5 to 40.0 K with increasing x. In comparison with the superconductivity of the La1+xBa2-xCu3Oy system, there appears to be little influence of the magnetic ion Nd3+ on the Tc in the Nd1+xBa2-xCu3Oy system.

Crystal Structure of Tetragonal YBa2Cu3-δCoδO7-γ (δ=0, 0.3)

Abstract: Crystal structures of tetragonal YBa2Cu2.7Co0.3O7-γ and tetragonal YBa2Cu3O7-γ are determined by X-ray and TOF neutron powder diffractometries. Structural parameters are obtained by the Rietveld profile refinement method. In YBa2Cu2.7Co0.3O7-γ', cobalt atoms preferentially occupy one of the copper sites at 1a(0 0 0) rather than the 2g(0 0 z) site with z~0.36. The lattice constants are a = 3.8644(2)A and c = 11.7881(9)A for the quenched YBa2Cu3O6.15 and a = 3.8752(2)A and c = 11.6851(9)A for the furnace-cooled YBa2Cu2.7Co0.3O6.81.