Based on cyanide-free electroplating technology for hard gold plating, with ethanol as an anti-solvent for precipitation of sodium gold sulfite (Na₃Au(SO₃)₂), a process was developed for preparing Na₃Au(SO₃)₂, consisting of non-aqua regia gold dissolution and sodium sulfite complexation and precipitation with ethanol. Then, a cyanide-free formula for hard gold electroplating with good comprehensive performance was optimized. With the sodium gold sulfite-sodium sulfite-EDTA-2Na as the plating system, the effects of different additives on bath and plating properties were investigated, and the metal turnovers (MTO) of the bath was also verified. The results show that an addition of sodium dihydrogen phosphate can increase the limiting current density but greatly reduce the electroplating efficiency; while an addition of ethylenediamine can obviously improve the deposition rate, and the obtained plating remains bright at the current density of 3 mA/cm². In an experiment by employing the proposed electroplating technology with two addititives, a plating was prepared with a microhardness of 100HV-140HV, presenting dense structure with low porosity. The current efficiency of electroplating was above 98% and the MTO of bath exceeded 6. The bath system exhibited weak cathodic reaction.

gold-plating  /  cyanide-free electroplating  /  sodium gold sulfite  /  hard gold planting  /  additive  /  MTO