Gluconate solutions for nickel electrodeposition and nickel electroless plating

Nickel electroplating has found a wide range of industrial applications as a technique for creating protective and decorative coatings of metallic and non-metallic surfaces, protecting materials against corrosion at elevated temperatures in both alkaline environments and organic acid solutions, forming a sublayer for obtaining coatings of other metals on steel, enhancing the hardness and wear resistance of surfaces, as well as for improving solderability. Such coatings can be obtained from weakly acidic aqueous and weakly alkaline complex electrolytes. In this review, we analyze the available literature on complexation of nickel(+2) with D-gluconate ion CH2OH(CHOH)4COO‾, along with that on compositions and some technological characteristics of complex D-gluconate solutions for nickel electrodeposition and electroless plating. Thus, a corrosion-resistant smooth light-colored nickel coating, tightly adhered to a copper substrate, was obtained from an electrolyte with a pH level of 8, containing 53 g/dm 3 of NiSO 4 •6H 2 O, 44 g/dm 3 of D-C 6 H 11 O 7 Na, 25 g/dm 3 of H 3 BO 3 , 53 g/dm 3 of (NH4) 2 SO 4 , and 0.5–3 g/dm 3 of CO(NH 2 ) 2 , at a temperature of 25 °C, a cathodic current density of 2.5 A/dm 2 with a current efficiency of 96.4%. An electroless Ni-P(3–18 wt%) alloy coating on copper was obtained from a solution with a pH level of 9, containing 5–30 g/dm 3 of NiSO 4 •6H 2 O, 10–60 g/dm 3 of D-C 6 H 11 O 7 Na, 5–40 g/dm 3 of NaH 2 PO 2 •H 2 O, 3 g/dm 3 of HOOCCH 2 CH 2 COOH, 0.5 g/dm 3 of CH 3 (CH 2 ) 11 OSO 3 Na, 0.002 g/dm 3 of Pb(CH 3 COO)2•3H 2 O, at a temperature of 90 °C and a deposition rate of up to 0.75 μm/min. The review also discusses methods for preparing D-gluconate electrolytes for nickel plating using sodium D-gluconate, D-glucono-1,5-lactone, and nickel D-gluconate. One advantage of D-gluconate nickel plating solutions consists in the absence of toxicity and low cost of D-gluconates.