Electrodeposition of nickel-zinc alloy from a sulfamate bath

The electrodeposition of Ni-Zn alloy coatings having high nickel content (74-97 wt%) from a sulfamate bath was studied. The investigation was performed by means of cyclic voltammetry, potentiostatic electrodeposition, X-ray diffraction, scanning electron microscopy and energy dispersive X-ray analysis. The effect of the experimental parameters (deposition potential, zinc concentration, addition of sodiumdodecylsulphate) on the coating composition, morphology and structure was studied. The obtained results show that the addition of Zn2+ to the deposition bath leads to a strong decrease in the cathodic current density, indicating a remarkable inhibition of Ni reduction. Even if anomalous codeposition was observed for all the studied experimental conditions, nickel rich alloys were obtained due to the mass transport control. A sudden decrease in the current efficiency, indicating a decrease in the hydrogen overvoltage, was found on increasing zinc percentage in the alloy over than about 15 wt%. The incorporation of Zn in the cfc Ni lattice up to about 20 wt% leads to a grain refinement and to an increase in hardness.