BEHAVIOR OF NICKEL ANODE IN CSF-NH4F-HF MELTS

The chemical composition and the electrochemical properties of the oxi de layer formed on a nickel anode in molten CsF . NH4F . 4HF at 50 and 100-degrees-C were studied. Nickel compounds of high oxidation state such as NiF4, Ni3O4, and Ni2O3 were formed on the anode at potentials more positive than 3 V vs. the hydrogen evolution potential in the mel t. NiO1+x (0 < x < 0.5), especially Ni3O4, was conductive and electroc hemically active in contrast with the passive layer of divalent compou nds (NiO and NiF2) formed at low potentials. It is estimated that thes e layers are less than several tens of angstroms thick depending on th e polarization potentials and the time of electrolysis. It is also est imated that the thickness of these layers formed in molten CsF . NH4F . 4HF containing water is larger than that formed in a well-dehydrated melt.