The oxidation behavior of uranium monocarbide was investigated at moderate temperatures at various partial pressures of oxygen from 5 to 152 mmHg. The oxidation of uranium monocarbide began between 225° and 250°C with a slight dependence on the oxygen pressure.
Analysis of the oxidation curves and by X-rav diffraction patterns indicates that the final product U₃O₈ is formed in one-step. The present data agree well with the expression representing rate-controlling reaction at the surface:
(1-c)^1/3=1-kt,
where c is the fraction of oxidation in time t, and k the reaction rate constant.
The activation energy detemined for the oxidation process is 5.0 kcal/mol for low oxygen partial pressures (510 mmHg).

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Breakthrough experiments were carried out to study ion exchange separation of uranium isotopes. Four kinds of solutions containing natural uranium (mole fraction of ²³⁵U 0.720₀×10^-2),
(1) 0.05M TnOA/benzene solution saturated with U (IV)-chloro complex,
(2) mixture of 0.05M TnOA/benzene solution saturated with U (IV)-chloro complex and 0.05M TnOA/benzene solution saturated with U (VI)-chloro complex,
(3) 0.05M TBP/benzene solution with U (IV)-chloro complex,
(4) mixture of 0.05M TBP/benzene solution saturated with U (IV)-chloro complex and 0.05M TBP/benzene solution saturated with U (VI)-chloro complex, were passed through 100 cm long, 1.3cm diameter anion exchange resin columns until the composition of the effluents became equal to that of the feed solutions.
Near the front of the breakthrough of the solution (4) above, the ²³⁵U was found enriched to 0.732₄×10^-2 (enrichment factor 1.017), while in the case of the solution (2), ²³⁵U was depleted to 0.710₇×10^-2 (enrichment factor 0.987).
From the total amounts of ²³⁵U enriched or depleted by these breakthrough experiments, single process ion exchange separation factors of uranium isotopes were estimated to be 1.000000 for the solution (1), 1.00033 for the solution (2), 0.99989 for the solution (3), and 0.99988 for the solution (4).
Based on these data, the apparent equilibrium coefficients of the electron exchange reaction,
²³⁵U (VI)+²³⁸U (IV)_??_²³⁸U (VI)+²³⁵U (IV)
were estimated to be 1.0010 and 1.0013 for TnOA/benzene and TBP/benzene systems, respectively. These values are smaller than the value of 1.0020 obtained for 8M hydrochloric acid in the previous paper. The apparent equilibrium coefficient of the electron exchange reaction in the anion exchange resin (Dowex 21 K) was estimated to be 1.00101.0013.

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Uranium phosphides were prepared by direct reaction of uranium with red phosphorus vapor. Formation of U₃P₄ began at 430°C, and the optimum temperature for the reaction was found to be 450°C. By successive decomposition of U₃P₄ in vacuum at 1, 050°C, monophase UP was obtained.
Thorium phosphides were also prepared by the same method. The composition of ThP obtained by the decomposition of Th₃P₄ was determined by chemical analysis to be ThP_0.62. By heating ThP_0.62 and some Th-ThP_0.62 mixtures to higher temperatures, monophosphides with lower contents of phosphorus were obtained. The monophase range of ThP_χ was estimated to be about ThP_0.4-0.7.
From X-ray analysis, a complete solid solution was found to be formed between UP and ThP, and the lattice parameter of the solid solutions followed Vegard's law with a slight positive deviation.

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