ピロリン酸浴からの銀-スズ合金電析

抄録

Alloy electrodeposition was made in aqueous solution of K₄P₂O₇ containing KAg (CN)₂ and Sn₂P₂O₇ to put silver-tin alloy plating to practical use. Cathode potential on silver-tin alloy deposit was -0.55V, and limiting current density was at nearly -1.10V. Limiting current density on silvertin alloy deposit shifted about 6.3 times that of Ag⁺ solution and about 2.5 times that of Sn²⁺ solution to the higher current density. Compared with alloy deposit pontential, the electrodeposition potential of silver in Ag⁺ solution was more noble and that of tin in Sn²⁺ solution was less noble. Silver content in silver-tin electrodeposited alloys was always higher than Ag⁺ concentration in an electrolyte, and tin deposit quantity tended to increase with a small molar ratio of silver concentration in the bath, or with high K₄P₂O₇ concentration and high bath temperature. Tin content increased with increasing a pH in the bath and cathode current density. Cathode current efficiency was 95% without pH effect, but increasing current density tended to decrease current efficiency. An adhesive, smooth and silver white semi-bright surface was observed in silver-tin alloy coats under the electrolytic conditions of the Ag/Sn molar ratio being 0.093/0.126, 0.7mol·l^-1 K₄P₂O₇ concentration, at pH 9.0, 25°C and a current density of 10mA·cm^-2.