抄録
The activity coefficients of oxygen γO in Sn-Te melts in the dilute region of oxygen have been measured at 1123 and 1223 K utilizing the modified coulometric titration technique with the electrochemical cell: O in Sn-Te melts/ZrO2(+CaO)/air, Pt. The measured lnγO values decrease gradually with the addition of tellurium to tin, and increase rapidly in the vicinity of NTe=0.50. The enthalpy and entropy values for the oxygen dissolution also increase rapidly around this composition. The variation of lnγO reasonably agrees with that predicted from Otsuka’s PCC model. Since the saturation solubility of oxygen is expected to be a maximum around NTe=0.40∼0.50, the variation of γO values in the high oxygen concentratin range for NTe=0.40 was measured. The melt-oxide equilibrium was examined by electrochemically pumping oxygen into the melt until a constant emf was observed. The phase precipitated was found to be SnO2. Combining the both data, the saturation solubility of oxygen in Sn-Te melt of NTe=0.40 was determined to be 1.3 mol% at 1123 K. This experimental value is approximately 10 times larger than that in liquid Sn. When referring to the data for γO in other metal-chalcogen melts, it is quite feasible that there are metal-chalcogen melts whose saturation solubility of oxygen is more than ten times larger than that in the liquid metal solvent. The melts having high satuation solubility of oxygen and possessing electronic conduction may be useful as electrode materials for oxygen-related reaction.
