著者

Kingo SUDO Akiichi KIGOSHI

出版者

Tohoku University

雑誌

東北大学研究所報告. A集, 物理学・化学・冶金学 = Science reports of the Research Institutes, Tohoku University. Ser. A, Physics, chemistry and metallurgy (ISSN:00408808)

巻号頁・発行日

no.13, pp.31-38, 1961

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Oxidation and reduction equilibria of the composition range of UO_2-U_3O_8 were measured with a flow method at 360~580℃ and the results are summarized as follows : In the composition range of UO_2-U_4O_9 there are two regions : homogeneous region in which oxygen dissolves in UO_2, and heterogeneous region containing UO_2 saturated with oxygen and U_4O_9. The former was found to exist also at lower temperature as Willardson et al. had suggested. In this region Henry's law can be adapted between oxygen potential and solubility of oxygen in solid. The temperature dependence of equilibrium constant is as follows : O[UO_2]=1/2O_2(g), logK=-10, 387/T+19.95logT+0.0391T-86.31. The empirical formula expressing the solubility limit of oxygen in UO_2 phase is given as a function of temperature, [O]= 0.11176 ・ 10^<-4>T^2-1.9465・10^<-2>T+8.479, and the temperature dependence of oxygen potential is given by the following equation 2U_4O_9=8UO_2 (saturated with O)+O_2, logPo_2=-26, 814/ T+19.51 logT+0.02151T-61.18. The composition range of U_4O_9-U_3O_8 can be regarded as a homogeneous solid solution. By using the activities of U_3O_8 and U_4O_9 in solid phase, the temperature function of equilibrium constant is calculated as follows : 8/5U_3O_8 (in solid solution)=6/5U_4O_9 (in solid solution)+O_2, logK=-12, 581/T-6.592logT+0.0627T-35.69. Furthermore, an equilibrium diagram of the uranium oxide-oxygen system was given in this temperature range.