518. UC-UN固溶体のVegardの法則の成立性

The validity of Vegard's law for UC-UN solid solutions is still in dispute. A discussion is given on the possible causes of this disagreement among published papers on this subject. The factors taken up include oxygen contamination, errors of chemical analysis in determining the composition of solid solution, slower than expected reaction rate, non-stoichiometry of solid solution, coexisting second phase, and the state of distribution of carbon and nitrogen atoms in the UC-UN lattice.Experiments were performed in vacuo and in nitrogen gas in order to obtain the relation between the lattice parameter and the composition of solid solution, and to determine the effects brought upon this rebtion by the factors cited above.The lattice parameters of UC-UN solid solution obtained by vacuum sintering at 1, 700° and 1, 800°C showed a positive deviation from Vegard's law. The same parameters when the solid solution coexisted with UC2 deviated similarly from Vegard's law. The presence of oxygen in the UC-UN solid solution caused little change of lattice parameters in the vicinity of a composition of UC0.5N0.5.