Decomposition pressure of YN and UN-YN solid solutions

Abstract

Decomposition pressure-temperature relations have been determined experimentally for YN and U 1− x Y x N ( x = 0.25, 0.5, 0.75). The results are: log PN 2[ YN] = 12.8 − 3.51 × 10 4/ T, 2400–2750 K; log pN 2[ U 0.25 Y 0.75 N] = 12.6 − 3.54 × 10 4/ T, 2450–2800 K; log pN 2[ U 0.5 Y 0.5 N] = 12.3 − 3.61 × 10 4/ T, 2550–2850 K; log pN 2[ U 0.75 Y 0.25 N] = 12.1 − 3.65 × 10 4/ T, 2600–3000 K. These results agree well with the theoretical equation: log pN 2[ U 1− x Y x N] = (1 − x) log PN 2 [ UN] + x logPN 2[ YN], which may be derived from thermodynamic considerations of the decomposition reaction of U 1− x Y x N based on the reaction: U 1−xY xN(s) = U 1−xY x(1) + 1 2 N 2(g) . Statistical thermodynamic calculations based on the linearity of the isotherms in the log PN 2[ U 1− x Y x N] vs. YN mole fraction show that the interaction between U and N and that between Y and N in U 1− x Y x N may be attractive, having the same order of magnitude.