2013 Volume 54 Issue 3 Pages 337-343
An electroless Ni–Co–P plating solution, which composed of lactate-citrate-ammonia as buffering and complexing agents, has been prepared. Various electroless Ni–Co–P coatings were deposited from this solution to investigate the effects of ion concentrations, pH and bath temperatures on the chemical composition of the deposited coating. The results showed that the present electroless Ni–Co–P plating solution has a potential for depositing Ni–Co–P coatings with an average composition of 71 mass% Ni, 17 mass% Co and 12 mass% P. The plating solution showed a good stability to deposit the coatings with a small deviation in compositions over wide ranges of pH values in acid region, bath temperatures, cobalt-ion and hypophosphite-ion concentrations. The nickel content of the Ni–Co–P coating could be tailored by varying nickel-ion concentrations of plating bath. The Ni content increased with increasing nickel-ion concentration while the opposite trend was observed for Co content. However, plating in the alkaline region showed significant changes in coating composition and plating behavior. Systematic UV–visible absorption measurement showed the change of complex ions from acid to alkaline regions, which could explain the different plating behavior in those regions.