Protonated Nickel Bis-Glycine Chelate: Effective Precursor for Electroless Deposition of Nickel-Phosphorus Alloy

The ionic equilibria in the NiSO4-H(2)Suc-HGly system were calculated using the Brinkley algorithm to assess the true composition of the glycinate-succinate solution for electroless nickel plating. In weakly acidic solutions, the protonated bis-glycinate complex cation prevails, which serves as a precursor in the electroless deposition of nickel-phosphorus coatings. The pH of weak acid solutions is stabilized by succinate ions and protonated nickel glycinate complexes. In alkaline solutions, nickel bis- and tris-glycinate complexes prevail. The assumptions about the role of the components of the electroless nickel plating solution were confirmed by the experimental data on the effect of acid concentrations and pH on the coating deposition rate and reaction zone acidity maintained at the optimum level. The optimum composition of the electroless nickel plating solution was determined (M): nickel sulfate 0.12, sodium hypophosphite 0.36, aminoacetic acid 0.2-0.3, succinic acid 0.2-0.4, and lead acetate 10(-5). At pH 4.8-6.8, 70-95 degrees C, and specific loading area of 1 dm(2)/L, high-quality nickel-phosphorus coatings of stable composition were obtained, which can be used as protective and strengthening coatings deposited at a rate of up to 38-40 mu m/h.