CONTINUOUS IN-SITU REGENERATION OF ELECTROLESS NICKEL BATHS DURING POWDER PLATING

Continuous addition of nickel to an electroless nickel plating bath, equivalent to similar to 18 turnovers of the original nickel content, was made without performance deterioration. Plating was conducted on 118-mu m powders at loadings of 100 g/dm(3) or similar to 2 m(2)/dm(3). The formation and precipitation of nickel orthophosphite was prevented by continuous addition of lactic acid to control the free nickel ion activity, Nickel activities with lactic acid additions mere determined from EMF measurements on nickel substrates. Stress and toughness measurements of the deposits showed that addition of lactic acid increased the tensile stress in the deposit and decreased the toughness. These effects were overcome by lowering the operating pH of the electroless process.