Abstract
Films of NiFe alloys were deposited under galvanostatic conditions from solutions containing no stress-relieving additives and no surfactants. The composition of the films and the deposition efficiency were determined as a function of current density, pH, the identity of the anion (S042- or CI-), and the boric acid content of tne solution. The Fe content is lower in deposits from chloride solution than from sulfate solution and is increased by the addition of H3BO3. The efficiency increases with increasing current density and increasing pH, is higher in deposits from chloride solution, and is little affected by H3BO3. The observations are interpreted in terms of suppression of Ni deposition by a surface iron hydroxide precipitated when the local surface pH rises during deposition. The way in which the solution components and conditions of deposition influence the formation of this hydroxide determines their effect on deposit properties. Increasing current density causes greater hydroxide precipitation and thus increases the Fe content of the film up to the point where ionic diffusion in the hydroxide limits the rate of Fe deposition. Chloride ion forms a weak complex with Fe2+ and thereby limits hydroxide formation, lowering the percentage Fe in the deposits. Boric acid has its greatest effect under conditions where hydroxide formation is most extensive. It does not act as a buffer, but apparently adsorbs on the hydroxide-covered surface. © 1981, The Electrochemical Society, Inc. All rights reserved.