A NEUTRON-DIFFRACTION INVESTIGATION OF SOLUTIONS OF NICKEL IN MOLTEN NICKEL IODIDE AND MOLTEN NICKEL BROMIDE

The short-range chemical order of solutions of nickel in molten NiBr2 and NiI2 at 9 mol% concentration has been investigated by neutron diffraction. By using isotopically enriched samples, the three partial structure factors for NiBr2 + Ni have been determined by measurements made using the steady-state reactor source at the Institute Laue-Langevin. For NiI2 + Ni, the partial structure factor relating to I-I correlations has been determined and information on the other two structure factors has been obtained by the time-of-flight method using the intense pulsed neutron source at Argonne National Laboratory. The results are compared with those of previous diffraction studies of the pure salts. No evidence for the formation of subhalide complex ions has been found. It is proposed that nickel dissolves according to the equation Ni --> Ni2+ + 2e-, with the excess nickel ions occupying tetrahedrally coordinated sites within the liquid structure indistinguishable from those in the pure salt.