PHASE-EQUILIBRIA IN THE CO-NI-F SYSTEM AND ACTIVITIES IN (COXNI1-X)F2 SOLID-SOLUTIONS AT 1373-K

The tie-lines delineating equilibria between CoF2-NiF2 and Co-Ni solid solutions in the ternary Co-Ni-F system at 1373 K have been determined by electron microprobe and EDAX point count analysis of the equilibrated phases. Activities in the fluoride solid solution have been derived from the knowledge of activity-composition relation in the metallic solid solution and tie-line data, using a modified form of the Gibbs-Duhem integration. The fluorine potentials corresponding to the tie-line compositions have been calculated. The excess Gibbs' energy of mixing for the fluoride solid solution derived from the present data can be represented by the expression DELTA-G(E) = 3080 X(NiF2)X(CoF2) J/mol