The Uranium-Carbon-Nitrogen System

In the previous work⁽¹⁾ dealing with the equilibrium phase relations in the ternary system U-C-N, a qualitative phase diagram was constructed from thermodynamical calculations and experiments. In the thermodynamical calculations, it was assumed that the free energy of formation of the solid solution between UC and UN, i.e., UC_1-x N _x , is the sum of (1-x)ΔG ⁰(UC), xΔG ⁰ and a term for the entropy of mixing RT{x logx+(1-x)log(1-x)}, neglecting the heat of mixing.

The purpose of the present work is to consider the same U-C-N system statistico-thermodynamically, and to evaluate the heat of mixing from the results of several experiments. A value of about ?1.3 kcal/mole was obtained as the heat of mixing corresponding to {2φ(C-N)-φ(C-C)-φ(N-N)}N, where φ(C-N), φ(C-C) and φ(N-N) are the bond energies of C-N, C-C and N-N respectively.