チオ尿素添加した研磨液におけるAu-Ag-Cu合金の電解研磨挙動

Abstract

To elucidate the electropolishing behavior of Au-Ag-Cu alloys in solutions containing thiourea, which forms stable complexes with gold, we investigated the effects of electrolytes, concentrations, and stirring conditions on electropolished surfaces. The concentrations of electrolytes and thiourea were fixed at 0.5 mol dm－3. Electropolishing was done using various electrolytes. Electropolishing at 0.6 V (vs. Ag/AgCl) using sulfuric acid as an electrolyte induced a high gloss surface with surface roughness of Ra=53 nm and Rz=391 nm. The dissolution of gold alloys was promoted by the increase in the concentrations of sulfuric acid and thiourea. Glossy surfaces were obtained using sulfuric acid and thiourea with respective concentrations of ≧0.2 mol dm－3 and ≧0.5 mol dm－3. During the rotating electrode process, the electrode potential at which the electropolished surface was sulfurated became more positive by increasing the rotation rate of the rotating disk electrode. Under a no-stirring condition, the surface was sulfurated at 1.0 V, although stirring the surface exhibited high gloss at 1.0 V. Moreover, electropolishing at 1.0 V under stirring conditions produced a polished surface with surface roughness (Ra=47 nm, Rz=369 nm) and glossiness (Gs (60°)=730) comparable to those of a buff-polished surface, and did so in a shorter time than electropolishing at 0.6 V under the no-stirring condition.