| Research Abstract |
1. The equilibrium oxygen partial pressures for the oxidation of pure metals (MO, Tc, Ru, Rh, Pd) and alloys (Mo-Ru-Pd, Mo-Ru-Rh, Mo-Tc-Pd), and the vapor pressures of the gaseous species during oxidative vaporization of the metals and alloys were calculated as a function of temperature based on the regular solution model. At high temperature, Pd and Rh in the alloys vaporize preferentially in vacuum and similarly Mo and Ru in the alloys in air. In the oxidative atmosphere at low temperature below 385 K, Ru and Tc in the alloy vaporize preferentially by oxidation, assuming the oxidation rates of Tc and Ru in the alloy are enough high.
2. The oxidation behaviors of the fine powders of Mo, Ru, Rh, Pd and Mo-Ru-Pd alloy were studied in the range of 673-973 K in air. The weight gain due to oxidation was observed with time for all samples below 773 K. It was concluded that Mo-Ru-Pd alloy was oxidized by the preferential oxidation of Mo and Ru below 773 K.
3. The oxidation behavior of the Mo-Ru-Pd and MO-Ru-Rh-Pd alloys were studied in the range of 1023-1373 K. The weight loss due to oxidative vaporization was seen with time. Two steps of the linear weight loss with time were observed and Mo and Ru were found to be lost preferentially in both steps, although the vaporization rate of Mo was larger than Ru in the first step.
4. The solubilities of Pd,, Rh, Ru in the alloy recovered in a lead button after lead extraction experiments in nitric acid (3N, 383 K) were measured as a function of time (3-12 h). The solubility of Ru was seen to be extremely lowcompared with Rh and Pd
5. Based on these results above mentioned, the new methods by using lead extraction or oxidative vaporization for the recovery and mutual separation of each element in the alloy were proposed.
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