アンモニア性酒石酸塩浴からのＮｉ‐Ｍｏ合金電着に及ぼすＳ‐，Ｎ‐化合物添加の影響について

Abstract

Effects of S- and N-compounds such as sodium thiosulfate, nicotinic acid, thiourea, glycin, etc. on the codeposition of molybdenum in the electrodeposition of Ni-Mo alloys were studied by measuring the partial cathode current efficiencies of nickel and molybdenum. The bath used contained 0.22M of nickel sulfate, 0.05M of acid molybdate, 0.27M of potassium sodium tartrate, and ammonium hydroxide (for adjusting the pH of the solution to 10.5). S- and N-compounds used in this work (except urea and glycin) prevented the codeposition of molybdenum with nickel. Further, polarographic behavior of nickel ion in the presence of S- and N-compounds was studied, and it was indicated that the additive compounds which prevented molybdenum codeposition facilitated discharge of nickel and hydrogen ions on mercury. Double layer capacity decreased when 40mM of nicotinic acid was added to the bath. This indicated that the adsorption of nicotinic acid occurred at nickel cathode during the electrodeposition of nickel. The adsorbed species appeared to electrocatalyse the deposition of nickel and hydrogen by the same mechanism proposed by Mark et al. on mercury electrode. Adsorbed S- and N-compound species also appeared to occupy the sites of hydrogen to bring about the reduction of intermediate molybdenum lower oxides formed on the cathode.