Abstract
Electroless nickel-copper-phosphorus alloy platings from ammonia alkaline citrate bath (A-C bath) and caustic alkaline citrate bath (C-C bath) containing sodium hypophosphite as a reducing agent were investigated to determine the effect of copper ion concentration on the deposition rate, corrosion resistance and structure of the deposits. The basic bath composition was found to be: nickel sulfate +copper sulfate 0.1M, sodium hypophosphite 0.2M, sodium citrate 0.2M, pH10 (adjusted with NH4OH or NaOH); bath temperature was 80±2°C. The copper content in the nickel-copper deposits were found to be 0% to 44.5% in A-C bath and 0% to 69.0% in C-C bath, respectively, depending on the copper ion ratio in the plating bath. In A-C bath, the deposition rate increased considerably with the copper ion concentration in the bath, but in C-C bath, this effect was very small. The corrosion resistance of the deposits, containing 16.5% copper and 4.7% phosphorus, from A-C bath, and of the deposits containing 8.0% phosphorus, from C-C bath was excellent for a 0.5M sulfuric acid solution at 30°C.
