Optimization study on hardness of gold film through supercritical electroplating process by response surface methodology

A non-cyanide gold bath has been used to deposit gold film on a brass substrate through electroplating process using supercritical carbon dioxide emulsion. The hardness of deposited gold film was considered as a response variable to optimize the process parameters of electroplating operation by statistical experimental methods. Effects of current density, pressure temperature, and chemical composition of the solution were investigated to select the optimal operation factors. Scanning electron microscopy and micro-hardness tester were applied to determine the characteristics of metallic film. The screening of significant variables was examined by a 25-1 fractional factorial design with V resolution method. The experimental result showed that the significant variables affecting the deposition of gold film were current density, pressure and temperature. Based on Box-Behnken design and response surface methodology (RSM), a regression model was built by fitting the experimental results with a polynomial equation. The optimal operating variable conditions can be searched at a specified hardness for industrial hard and soft gold application ranged from 83.8 to 157.7 HV.