Optimization of electroless Ni-Zn-P deposition process: experimental study and mathematical modeling

A mathematical model based on mixed potential theory was developed which was used to optimize a non-anomalous Ni-Zn-P electroless deposition process developed by us at USC. The model was developed by assuming an adsorption step in addition to the electrochemical steps. The concentrations of the Zn and Ni complex were estimated by solving the material balances in addition to the electroneutrality condition and the equilibrium relations. The composition of the coating was estimated from the partial current densities of all charge transfer reactions, which occur at the electrode-electrolyte interface. The model results showed that the adsorption plays a significant role in the alloy deposition process. From the model results, it was seen that the addition of Zn ions to the bath inhibits the deposition rate by changing the surface coverage of the adsorbed electroactive species on the electrode surface. The model indicated that an increase of pH of the bath increases the alloy deposition rate.