質量分析法による溶融Ti-Co合金の熱力学的研究

Abstract

The thermodynamic properties of the liquid Ti-Co alloys have been determined over the entire composition range at 1873 and 1973 K. A Y2O3 Knudsen cell-mass spectrometric technique was used to carry out the measurements of the ionic intensity ratios for the alloy components. The thermodynamic activities show negative deviations from Raoult’s law. The activity coefficients at infinite dilution are γTi°=0.011 and γCo°=0.014 at 1873 K and γTi°=0.021 and γCo°=0.028 at 1973 K. The minimum values of the molar free energies of mixing ΔGM are, respectively, −32.1 kJ·mol−1 at 1873 K and −30.9 kJ·mol−1 at 1973 K (NCo=0.49). The molar enthalpies of mixing ΔHM and the molar entropies of mixing ΔSM are negative. The minimum value of ΔHM is −50.5 kJ·mol−1 (NCo=0.48) and the minimum value of ΔSM is −9.9 J·mol−1K−1 (NCo=0.48). The partial molar enthalpies of mixing Δ\barHTi and Δ\barHCo at infinite dilution are −152.2 kJ·mol−1 and −195.7 kJ·mol−1, respectively. The oxygen concentrations in the alloys were determined by analysis, and the effect of dissolved oxygen on the activity of the alloy and the selection of oxide crucible material for the alloy have been discussed.