THE CONSTITUTION OF THE URANIUM-TIN-PALLADIUM SYSTEM

The Pd-rich region of the isothermal section of the ternary U-Sn-Pd sy stem at 1050 degrees C was investigated by metallography, X-ray microa nalysis and X-ray diffraction. The fcc alpha-Pd(Sn, U) solid solution dissolves up to 16 at.% Sn and 15 at.% U. The AuCu3 type phases SnPd3 and UPd4 are the end members of a single-phase region. SnPd2 and UPd3 are in equilibrium with this solid solution of the composition U0.68Sn 0.32Pd3 and with the ternary phase USnPd2. The Gibbs energies of forma tion of SnPd2, SnPd3 and UPd4 were used and ideal behaviour of the (Sn , U) Pd-3 + x solid solution was assumed to calculate the Gibbs energy of formation of UPd3 which gives Delta(f)G degrees = -312 kJ/mol at 1 050 degrees C. In addition, the annealing experiments in the Pd-rich r egion of the binary U-Pd system were extended to 950 degrees C which c onfirm the phase-field distribution established at 1050 degrees C in e arlier work.