Effects of surfactants in an electroless nickel-plating bath on the properties of Ni-P alloy deposits

Effects of added surfactants in the acidic hypophosphite plating baths on the properties of the resulting electroless nickel-phosphorus (Ni-P) deposits on the brass substrates were studied. The surface appearance and microstructures were examined under a reflective optical microscope and a scanning electron microscope equipped with an in situ energy-dispersive X-ray spectroscopy with which the phosphorus contents were measured. The deposition rate and the corrosion rate of the Ni-P deposits were estimated respectively from the weight gains and losses after a period of time. It is found that the addition of suitable amounts of surfactants can increase the deposition rate up to 25% and reduce the formation of the pores on the surface of Ni-P alloys, as well as enhance the corrosion resistance of the deposits. The corrosion rate of the Ni-P alloys in 10 wt % HCl was determined. The corresponding corrosion rate fits well as an empirical power function having an order of near 1/3 in the amount of dissolved Ni-P deposits, equivalent to the concentration of nickel ions present in the acidic corrosive solution. The corrosion mechanism is discussed in line with the experimental discoveries.