ELECTROMOTIVE FORCE MEASUREMENTS ON SOLUTIONS OF RARE EARTH METALS IN THEIR MOLTEN HALIDES .I. CERIUM-CERIUM CHLORIDE PRASEODYMIUM-PRASEODYMIUM CHLORIDE AND NEODYMIUM-NEODYMIUM CHLORIDE SOLUTIONS

A recently developed metal cell technique eliminated the need of ceramic materials and permitted the investigation of the emf of the rare earth metal-rare earth halide solutions in a corrosion-free system. The emf of solutions of Ce-CeCl3, Pr-PrCl3, and Nd-NdCl3 was measured as a function of metal concentration in the cell Ta | MCl3(1 - X), M0(X) ∥ KCl | glassVycor | KCl | Cl2, graphite The metal cell containing the rare earth metal-halide solutions was a cylindrical tantalum cup with communication to the bridging liquid by means of a sintered tantalum pellet of extremely fine porosity welded into the side of the cup. The potential measurements indicate the presence of a subion M2+ from the reaction M0 + 2M3+ → 3M2+ in all three systems. Saturation concentrations determined by the present technique are in agreement with those obtained by conductivity and phase equilibria studies where the solutions were not in contact with ceramic material.