Cyanide-Free Displacement Silver Plating Using Highly Concentrated Aqueous Solutions of Metal Chloride Salts

We report a novel, cyanide-free, and low-cost displacement silver (Ag) plating bath, i.e., AgCl-dissolved highly concentrated CaCl2/LiCl aqueous solution. Compared to dilute CaCl2/LiCl solutions, this aqueous solution exhibited much higher AgCl solubility because of the high activity of Cl–; the maximum AgCl solubility was achieved at 44.4 mmol dm–3 (i.e., [Ag(I)] = 8.07 g kg−1 H2O). Smooth Ag deposits with a lusterless gray-colored appearance were successfully obtained by displacement plating on a Cu substrate. The mechanism of smooth Ag plating is discussed in terms of its electrochemical and diffusive properties.