A study was made of the oxidizing behavior at high temperature (800 0 ~ 1,800 0 C) in vacuum of UC, UN and U(C,N) samples containing added oxygen in excess amounts, through observations of gas release, X-ray diffraction analysis, and microphotography. The oxidation in vacuum of UC and U (C,N) was found to proceed above 1,200 0 C by stepwise reactions from one temperature interval to the next, the process differing however according to the chemical state of the oxygen present in the samples. In the temperature range below 1,200 0 C, the UC and U (C,N) samples reacted violently with the free oxygen present in dissolved state, to form U0 2 • Between 1,200 0 and 1,400 0 C the U0 2 thus produced reacted with the UC or U (C,N) , forming solid solutions of U (C,O) and U (C,N,O) respectively: Above 1,600 0 C, these solid solutions gradually decomposed back into UC and U(C,N) , and U. In all stages of oxidation, large amounts of CO-and N 2 in the case of U (C,N)-evolved from the samples as reaction products. In the case of UN, no reaction was observed below 1,200 0 C, and only oxidized above that temperature to form U0 2 and N 2 by the action of the dissolved oxygen present. These results indicate that in the case of UC and U (C,N) , the quantity of gases evolving from the oxidation is dictated by the total amount of oxygen contained in the samples, while that from UN is dependent on the amount of molecular oxygen alone.
