Role of ethylamines on the electrochemical behaviour of Fe-Ni alloy films

Cyclic voltammetric experiments were carried out on platinum in acidic solu tion (pH 3) containing ferrous sulfate, nickel sulfate and ethylamines (EtN H2, Et2NH, Et3N). Spectral ultraviolet absorption studies indicate the comp lexation of both Fe2+ and Ni2+ ions with ethylamines. The results under tra nsient polarisation conditions indicate the reduction of Fe2+ ions through the intermediate species FeOH+, with second electron transfer as a slow ste p. The higher charge transfer rate of FeOH+ over NiOH+ reduction causes the anomalous codeposition of Fe-Ni alloy film. Among the ethylamines, Et3N co nsiderably assists the alloy deposition process. A gradual variation in fre e energy of alloy formation with Fe2+:Ni2+ (mol:mol) in the bath suggests t he formation of an alloy intermediate phase rich in iron. Stripping voltamm etric curves indicate the preferential dissolution of iron from iron rich a lloy intermediate phase. X-ray diffraction studies further confirm the phas e to be b.c.c. Fe-Ni alloy. The extent of corrosion of the Fe-Ni alloy film in the presence of ethylamines is in the following order: Et3N > Et2NH > E tNH2.