Electromotive force (EMF) measurements using ZrO2 solid electrolyte were carried out in the Ba–Y–Cu–O system. Gibbs free energies for the reaction in the cell electrodes were summarized in the equations with linear temperature dependency. The standard free energies of the formation of Y2Cu2O5 and YCuO2 were derived from EMF data and compared with published informations on the stability of Y2Cu2O5.From the results of the X-ray diffraction measurements for the quenched specimens, the phase equilibria in Y–Cu–O system were determined in the temperature range 923 K to 1223 K. Based on the experimental results, YCuO2 was stable above 1115 K and at the oxygen partial pressure higher than 7.18×10−4 Pa. In the quaternary Ba–Y–Cu–O system, only a few cell could show the stable EMF. The solubilities of barium in both Y2Cu2O5 and YCuO2 were negligibly small.
The phase relationship in the liquid Cu-O system was determined by modifying the sampling method and oxygen analysis. The miscibility gap was seemed to disappear at higher temperature than 1620 K. Using the following cells, the emf’s of the cells were measured in the oxygen composition range from 0.8 to 11.5% and the temperature range from 1430 to 1600 K.(1) Pt/Ni, NiO/ZrO2(+CaO)/Cu-O liq. alloy/LaCrO3, Pt(2) Pt/Ni, NiO/ZrO2(+CaO)/Cu-O Liq. alloy, Cu2O(s)/LaCrO3, Pt(3) Pt/Ni, NiO/ZrO2(+CaO)/Cu-O liq. alloy, Cu-O liq. oxide/LaCrO3, Pt(4) Pt/Ni, NiO/ZrO2(+CaO)/Cu-O liq. oxide/LaCrO3, Pt.\ oindentThe samples were taken at 1593 K and analysed for oxygen. The activity curves of oxygen and copper were drawn at 1573 K, and the standard free energies of formation of the solid and liquid Cu2O were determined from 1370 to 1600 K. The partial molal entropy of oxygen in the liquid Cu-O system showed its minimum at the Cu2O composition.The oxygen potential-temperature-composition diagram for the Cu-O system were determined from the results of this study.
The carbothermic reduction-electron beam melting combination method has made it possible to produce the pure niobium metal. In the present investigation, the relationship between the pressure, the temperature and the concentration of carbon and oxygen in the Nb-C-O solid solutions has been determined as the base for the carbothermic reduction of niobium in vacuum.The niobium metal with arbitrary contents of carbon and oxygen was equilibrated with the CO-CO2 gas mixture of the CO2 content below 1000 ppm, at 2073∼2273 K and the reduced pressure. The reduced pressure from 0.13 to 13 Pa was realized in a vacuum furnace with a tantalum heating element by balancing the introducing rate of gas through a slow leak valve with the evacuating rate by a diffusion pump.The thermodynamic equilibrium between the Nb-C-O solid solution and the CO-CO2 gas mixture can be described by the following equations:(This article is not displayable. Please see full text pdf.) The total pressure must be reduced even at the temperature as high as 2273 K and the CO2 concentration must be very small for the Nb-C-O solid solution to be stable, so that the reaction (1) is predominant and the reaction (2) may be negligible. The following expression relating the pressure, the temperature and the concentration of carbon and oxygen in niobium has been derived:(This article is not displayable. Please see full text pdf.) \ oindentwhere PCO is the pressure in Pa, CC and CO the atomic percents of carbon and oxygen and T the absolute temperature.
Isothermal degassing of the Nb-C-O solid solutions under vacuum and low CO-pressures has been studied by measuring the carbon and oxygen contents as a function of degassing time at 2073∼2473 K. Carbon is removed by degassing as CO and oxygen is eliminated as CO and volatile suboxides such as NbO and NbO2.The observed degassing curves were compared with the theoretical laws which had been deduced from the kinetic analysis of certain elementary steps of the degassing process. In the case of low carbon contents, the diffusion via interstitials was supposed to be rate-determining for the complete process. For relatively higher oxygen contents, the rate-determining step for elimination of oxygen was supposed to be a combination of oxygen in the adsorbed state and carbon or niobium atoms to form molecules and leave the surface.At low CO-pressures, the degassing was well expressed by straight lines indicating that the most part of the adsorption sites on the surface are occupied by the gaseous molecules.
The thermodynamic activities of iron in iron-nickel alloys have been determined by e.m.f. measurements on solid-electrolyte oxygen concentration cells over the temperature range 750°∼1150°C.The activity of iron in the alloy system exhibits slightly positive departures from ideal solution behavior in iron-rich alloys and negative departures in nickel-rich alloys. The activities of nickel, deduced from the Gibbs-Duhem equation, indicate negative departures from ideality in all compositions.The relative integral molar excess entropies are positive for all the composition studied. However, consideration of magnetic factors suggests that the configurational excess entropies are negative and that the solid solutions are non-random.The heats of mixing vary from endothermic values to exothermic values with increasing nickel content; inferring that the non-random behavior suggested by the presumed configurational excess entropies is clustering at iron-rich compositions and short-range ordering at nickel-rich compositions.
Possibilities and conditions for preparing homogeneous Nb-W alloys by the carbothermic reduction-electron beam melting combination method have been examined with regard to the following items: (1) Determination of the relationship among the CO-pressure, the temperature and the concentration of carbon and oxygen in the Nb-W-C-O solid solutions by the low-pressure gas equilibrium method at 2173 K. (2) Simultaneous reduction of the Nb-W alloys from mixtures of constituent metal oxides, Nb2O5 and WO3, by carbon in vacuum at about 2200 K. (3) Elimination of carbon and oxygen in the carbon-reduced Nb-W alloys by the electron beam melting.In this process alloying would proceed and be completed at the first reduction stage. Subsequent melting in an electron-beam furnace lowers the carbon and oxygen contents to a commercial grade and consolidates the alloys into ingot. The evaporation deoxidation as in volatile oxides of niobium and tungsten plays an important role in this process.The purity and homogeneity of the alloys thus prepared have been assured to be a sufficient degree.
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