Toshio Oishi

Electrochemical deoxidation of titanium

Removal of oxygen in titanium using an electrochemical technique was examined at temperatures around 1223 K with the purpose of obtaining nearly oxygen-free titanium. Titanium and carbon electrodes, immersed in molten CaCl2, served as cathode and anode, respectively, with an external DC source. CaCl2 was employed to produce the deoxidant calcium and to facilitate the reaction by decreasing the activity of the by-product CaO. By applying about 3 V between the electrodes, the calcium potential in CaCl2 was increased at the titanium cathode surface and titanium samples of the cathode could be deoxidized by the electrolytically produced deoxidant calcium or by calcium of high activity in the CaCl2 flux. Resulting O2− species, mainly present as the deoxidation product CaO in the flux, reacted at the carbon anode to form CO (or CO2) gas which was removed from the system. Titanium wires containing 1400 mass ppm oxygen were deoxidized to less than 100 mass ppm, whereas the carbon concentration increased by about 50 mass ppm. In some cases, the oxygen concentration in titanium samples was lowered to a level less than 10 mass ppm that could be determined by conventional inert gas fusion analysis. The behavior of contaminants, such as carbon and nitrogen, is also discussed.

Preparation and characterization of extra-low-oxygen titanium

Abstract Removal of oxygen in titanium by reaction with chemically active calcium dissolved in CaCl2 was examined between 1273 and 1473 K with the purpose of obtaining extra low-oxygen titanium. CaCl2 was used as a flux to facilitate the reaction by decreasing the activity of the by-product CaO. Titanium wires and small pieces of titanium were deoxidized to 20–60 mass ppm oxygen by use of calcium-saturated CaCl2 at a temperature of 1273 K. Trace element analysis (e.g. glow discharge mass spectrometry), micro Vickers hardness measurements, and electrical resistivity measurements were carried out to characterize the deoxidized titanium. The deoxidation of electrolytically refined titanium wire produced titanium with a high residual resistivity ratio ( ga 298 /α 4.2 ⋍100 ). The “ideal resistivities”, or hypothetical resistivities of pure titanium, at 77 and 298 K were determined to be 40 and 440 nΩm respectively. The influence of oxygen on resistivity at 4.2 K was also measured by using titanium containing 30 and 500 mass ppm O, and was determined to be 88 nΩm (mol.% O)−1.

Electrochemical deoxidation of yttrium-oxygen solid solutions

Oxygen was removed from yttrium by an electrochemical method in which the metal is made the cathode in a cell consisting of a carbon anode and molten CaCl2 electrolyte. At 1223 K yttrium containing 5700 ppm oxygen was deoxidized down to less than 100 ppm. The method can be used to deoxidize other highly reactive metals. Furthermore, in principle it should be possible to remove other impurities besides oxygen.

Deoxidation of titanium aluminide by Ca-Al alloy under controlled aluminum activity

Removal of oxygen in titanium aluminide (TiAl) by chemically active calcium-aluminum (Ca-AI) alloy was carried out around 1373 K with the purpose of obtaining extra-low-oxygen TiAl. The deoxidation experiments were preceded by an investigation of the phase equilibria of the system Ti-Al-Ca at 1273 and 1373 K. The compositions of the Ca-AI alloy deoxidant, which equilibrates with TiAl, and the experimental conditions suitable for the deoxidation were of particular interest. In experiments in which Ti-Al samples were submerged in liquid Ca-AI alloys at 1373 K, the surfaces of the samples severely deteriorated and became nodular. When TiAl powders were mixed with CaO and the deoxidant was supplied in vapor form, powders which initially contained 510, 1100, and 4200 ppm O were deoxidized to about 160, 490, and 670 ppm O after deoxidation at 1373 K in 86.4 ks (1 day). Among many conditions tested, the use of TiAl powders mixed with CaCl2 was most effective for deoxidation at 1373 K. CaCl2 was used as a flux to facilitate the deoxidation by decreasing the activity of the deoxidation product CaO. In the case that TiAl powders mixed with CaCl2 and reacted with Ca-AI vapor at 1373 K for 86.4 ks, the powders initially containing 510, 1100, and 4200 mass ppm O were deoxidized to a level of 62, 140, and 190 mass ppm O, respectively. No significant change in morphology of the particle after deoxidation was observed. The titanium and nitrogen concentrations in the powders remained constant, whereas calcium, which was present only in trace amounts initially, increased up to 160 mass ppm after the deoxidation treatment.

Activity determinator for the automatic measurements of the chemical potentials of FeO in metallurgical slags

An automatic system for rapid determinations of the activities of FeO in metallurgical slags has been developed. With this facility, one datum is obtainable within 5 minutes. The facility was applied for the activity measurements in the system CaO + SiO2 + FeO, while activity data obtained were consistent with those deduced from the phase diagram.

Thermodynamic Properties of Oxygen in Yttrium-Oxygen Solid Solutions

The oxygen potential in yttrium-oxygen (Y-O) solid solutions was measured by equilibration with titanium-oxygen (Ti-O) solid solutions. Yttrium and titanium samples were immersed in calcium-saturated CaCl2 melts at temperatures between 1108 and 1438 K, and oxygen levels in the two metals were measured. With the Ti-O system acting as a reference, oxygen potentials in Y-O solid solutions were determined. By this technique, it was possible to make reliable measurements of extremely low oxygen potentials (as low as 10−44 atm at 1273 K), far beyond the range of solid oxide electrolyte sensors.

Another unusual phenomenon for Zr7Ni10: structural change in hydrogen solid solution and its conditions

Zr7Ni10 has three hydrogen occlusion phases, α, β and γ, and the following unusual features are known for the phase transitions in the Zr7Ni10–H2 system: (1) The intermediate hydride phase (β) appears only during dehydrogenation but not during hydrogenation, and (2) The continuous hydrogen solid solution phase (α) exhibits a much higher hydrogen solubility during hydrogenation than during dehydrogenation. In order to clarify the mechanism about the difference in the hydrogen solubility of the α phase, the relation between the pressure-composition isotherms and corresponding structural change has been examined by a conventional volumetric method and X-ray diffraction. Through the examination, we discovered that the crystal structure of the α phase, which undergoes hydrogenation followed by dehydrogenation, is different from that of its pure metal phase, where the crystal structure of the dehydrogenated α phase changes from an orthorhombic structure to a tetragonal structure. The conditions causing the structural change were then examined, and it has been found that the α phase maintains its original orthorhombic structure as long as it is hydrogenated so as not to absorb enough hydrogen to change it to the hydride with a higher hydrogen content (γ). The phenomenon can be understood as one of the hydrogen-assisted phase transitions such as hydrogen-induced amorphization (HIA) in the sense that the phase transition requires hydrogenation under special conditions.

Thermodynamics and local atomic arrangements of gold-nickel alloys

Abstract An e.m.f. apparatus with an oxygen-ion conducting solid electrolyte, differential thermal analysis, powder diffractometry, density measurements, and transmission electron microscopy (TEM) were used to determine thermodynamic quantities, the phase boundaries in the solid and liquid, and the microstructure of gold-rich solid solutions. Alloys with x Ni = 0.03, 0.06, 0.10, 0.15, 0.21, 0.35, 0.55, 0.73, 0.87 and 0.93 were investigated. The thermodynamic activities deviate positively from Raoults law in the liquid and solid states. The heats of formation and excess entropies exhibit positive values. This causes a large miscibility gap in the solid state. TEM, however, reveals short-range order in the alloys annealed above the miscibility gap.

Measurements on galvanic cells involving solid-sulphide electrolytes

Abstract It has been shown that emf measurements on galvanic cells involving solid-sulphide electrolytes may yield valuable thermodynamic data. CaSY2S3 and CaSZrS2 solid solutions were expected to satisfy the conditions as solid electrolyte. Emf measurements on the cells MoMo2S3(3 + s)/electrolyte/CuCu2S(1 + 1) (I), MoMo2S3(s + s)/electrolyte/Fe FeS(s + 1) (II), MoMo2S3(s + s)/electrolyte/WWS2(s + s) (III), WWS2(s + s)/electrolyte/CuCu2S(1 + 1) (IV), and WSW2(s + s)/ electrolyte/FeFeS(s + 1) (V) have been made using sulphide sensors in the temperature range 1000–1285°C. Observed emf values were compared with those calculated from the H2H2S gas equilibrium investigations. The sensor tubes were also dipped into liquid copper with sulphur concentration from 0.43 to 1.06 at% 1180–1312°C and the emf data were checked by the values deduced from the gas equilibrium experiments.

Disproportionation of CaNi3 hydride: formation of new hydride, CaNiH3

Abstract The hydrogenation properties of CaNi 3 were investigated at temperatures ranging from 298 to 773 K by differential thermal analysis (DTA). This compound exhibited four exothermic peaks at 373, 498, 543 and 653 K followed by an endothermic peak at 748 K when the compound was heated to 773 K under a hydrogen atmosphere of 3 MPa, and its final products were CaH 2 and Ni. However, the formation of a new ternary hydride was observed in the X-ray diffraction (XRD) profiles below the endothermic reaction temperature at which the final products were formed. The Rietveld refinement of the obtained XRD profiles and a volumetric measurement of the hydrogen content based on the Sieverts’ method indicated that this new phase was CaNiH 3 with a cubic CsCl type structure for the metal constituents. The experimental data obtained by XRD and DTA were discussed from the viewpoint of the disproportionation of CaNi 3 in the hydrogen atmosphere.