Electrolytic Ni-Pb-P alloys

The conditions required for obtaining electrolytic Ni-Pb-P alloy layers were investigated. Alkaline citrate-ammonia solutions typical of those used in electroless nickel plating containing less than 10 mM lead(II) were used. The electrolysis of these solutions at temperatures of 25–85 °C and current densities of 25–400 A m^-2 produced smooth Ni-Pb-P films containing 4–50 wt.% Pb and 2–8 wt.% P. The films containing 5–8 wt.% and 2–4 wt.% P were very bright and exhibited good corrosion resistance.

Investigations of the effect of changes in the concentration of the solution components and in other Ni-Pb-P deposition parameters showed that lead was deposited preferentially. Under these conditions the cathodic deposition of lead was diffusion controlled. The lead(II) inhibited the partial deposition of nickel and phosphorus. The efficiency of the current depended strongly on the deposition temperature and varied from 30% to 50% at 25 °C and from 100% to 150% at 75 °C. These results proved that the contribution of electroless nickel and phosphorus deposition increased with increasing temperature. Electroless nickel and phosphorus deposition at the cathode in the presence of such strong inhibitors as lead(II) salts proved that a continuous renewal of the catalyst surface, i.e. metallic nickel, was the most important factor in simultaneous electroless processes.