Electroforming and electrodeposition of stress-free nickel from the sulfamate bath

摘要

In electro-deposition of nickel from an aqueous acid bath containing 55 to 110 g/l Ni as nickel sulphamate with or without nickel sulphate, the molar content of sulphate ion being not more than that corresponding to the provision of half the nickel content as nickel sulphate, up to 25 g/l chloride ion, and boric acid as a buffer at a temperature between 38 DEG and 77 DEG C. with a cathode current density up to 300 amps/sq.ft., the electrolyte is subjected to anodic oxidation with a subsidiary polarized anode of insoluble material operated at a potential sufficient to liberate oxygen from the electrolyte and so that at least 0.25% of the total plating current passes through the subsidiary anode. The subsidiary anode may be located in the nickel deposition bath or in a subsidiary tank through which the deposition bath solution passes in an external circulation path. The subsidiary anode may be of Pt or platinized Ti or Ta, or of activated Ni containing 0.02 to 0.04% by weight of sulphur. The bath pH is maintained in the range of 4 to 4.5. The stress resulting in the nickel deposits for different operating conditions is specified. Semi-bright deposits of zero stress may be produced. By increasing the anodic oxidation, brighter stressed deposits are obtained.