Cathode Potentials during the Electrodeposition of Molybdenum Alloys from Aqueous Solutions

Abstract

Cathode potential measurements are used to explain the cathode reactions that result in the electrodeposition of molybdenum alloys. Potentials were measured by the direct method during the electrolysis of aqueous ammoniacal citrate solutions containing sodium molybdate and the sulfate of a codepositing metal, iron, nickel, or cobalt. The results indicate that the reduction of molybdate ion in this type of bath is probably not accomplished in one step with six electrons, but with one, two, or three electrons depending on the codepositing metal and its oxidation state in the bath. The results also indicate that hydrogen is involved in the molybdate reduction process. A two‐step mechanism for the reduction of molybdate ion in the presence of a codepositing metal is proposed and an explanation of why this metal must be iron, cobalt, or nickel rather than such metals as chromium, manganese, copper, or zinc is presented.