<報文>酸化ウランに関する基礎的研究(第4報) : U_yTh_<1-y>O_<2+x>の酸化還元平衡の測定

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  • サンカ ウラン ニ カンスル キソテキ ケンキュウ 4
  • <Original Papers>Fundamental Studies on Uranium Oxides. (IV) : Oxygen Pressures in Equilibria with U_yTh_<1-y>O_<2+x>

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Oxygen partial pressures in equilibria with nonstoichiometric solid solutions having the general formula U_yTh_<1-y>O_<2+x> were measured by means of a flow method. Measurements were made at values of y 0.8 to 0.2 in the temperatue range up to 1200℃. The absolute value of nonstoichiometric oxygen increased with decreasing thorium content. The experimental results were discussed by using the O_<(U)>/U ratio calculated from x showing the nonstoichimetric oxygen originated from UO_2. Where the O_<(U)>/U is below 2.25,there are homogeneous and heterogeneous regions like those in the UO_2-U_4O_9 system. In the latter region where the O_<(U)>/U is 2.25,the temperature dependence of oxygen partial pressures in equilibria are as follows : [numerical formula] In the former, the temperature and the O_<(U)>/U dependence of oxygen partial pressure in equilibria and partial molar free energies, and partial molar free energies, and partial molar enthalpies and entropies of solution of oxygen in the solid solutions were calculated from the experimental results. The partial molar free energy increases with decreasing y where y is below 0.4. The partial molar entropy is affected by y with decreasing O_<(U)>/U ratio from 2.25. Calcium fluoride structnre remained stable over a wide range of O_<(U)>/U ratio larger than 2.25. These O_<(U)>/U ratios are affected by y, and the compositions in equilibria with air at 600℃ were found to be U_<0.8>Th_<0.2>O_<2.352>, U_<0.6>Th_<0.4>O_<2.306>, U_<0.4>Th_<0.6>O_<2.220> and U_<0.2>Th_<0.8>O_<2.095>. Converting x into O_<(U)>/U ratio, it was found that the O_<(U)>/U ratio attained the maximum when y was 0.4. The same tendensy was found to be applicable to other oxygen partial pressures and temperatures in equilibria.

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