Electrochemical Measurement of Oxide Formation

Measurements have been made of the potential developed between a metal wire covered with its oxide and a platinum wire over which air or oxygen was passed. The electrolyte was the eutectic mixture of Li/sub 2/SO/sub 4/ and K/sub 2/SO/sub 4/, containing dissolved CaO and operated at various temperatures between 550 deg and75O deg C. Heavy metal oxides are only very slightly soluble in this melt, so that the measured potential corresponds to the formation of metal oxide from the elements. Iron probably formed FeO, nickel formed NiO below 658 deg and probably a solid solution of LiNiO/sub 2/ in NiO at higher temperatures, while copper formed Cu/sub 2/O. Gold showed only the thermoelectric potential expected. The values found are in agreement with the free energy of formation of the oxides as determined by other methods.