Yukitomi Ueda1, Takayuki Nishi2, Toshio Oishi1 and Katsutoshi Ono1
1Department of Metallurgy, Faculty of Engineering, Kyoto University, Kyoto
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 γ Ti°=0.011 and γ Co°=0.014 at 1873 K and γ Ti°=0.021 and γ Co°=0.028 at 1973 K. The minimum values of the molar free energies of mixing Δ GM 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 Δ HM and the molar entropies of mixing Δ SM are negative. The minimum value of Δ HM is -50.5 kJ • mol-1 (NCo=0.48) and the minimum value of Δ SM 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.
thermodynamics, activity, titanium-cobalt alloy, liquid alloy, high temperature, yttria, Knudsen cell, mass spectrometry, enthalpy of mixing, entropy of mixing
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