Parameters influencing the electrodeposition of Ni-Fe alloys

The present work consists of an experimental analysis of the effects of electrolyte composition and various other operation variables on the electrodeposition of Ni-Fe alloys. Two kinds of electrolytic solutions were used: sulphates and chlorides. Boric acid, citric acid and L-ascorbic acid were added to the solutions, and the FH was fixed at either of two values: 2.0 or 3.0. The alloys were electrodeposited at different current densities (0.5, 1.0, 1.5 and 2.0 A dm(-2)) and for all the conditions investigated the deposits with larger iron content were carried out with lower cathodic efficiency. From these experiments and from the decomposition of polarisation plots it was observed that the anomalous codeposition occurs preferentially for the same conditions (SO4-2 media, pH 2.0 and lower current densities), in that the presence of a hydroxide film at the surface would be favoured, which could both enable the reduction of iron to occur at more noble potentials and allow the iron to discharge through its thickness whilst hindering the movement of nickel ions. Concerning the role of the additives, citric acid containing solutions produced deposits with the largest iron contents, while the presence of ascorbic acid had no pronounced effect. The iron content is lower in deposits from boric acid solutions. (C) 1997 Elsevier Science S.A.