1. Formulation

In the mineral skeleton of an alkaline copper-plating electrolyte, the soluble copper in the mother phase is in the monovalent state (Cu ⁺ ). The formulation involves dissolving copper cyanide powder (CuCN) in an excess of potassium cyanide (KCN), in the presence of a slight excess of potassium hydrogen carbonate (KHCO ₃ ) and potash (KOH), which provide the alkalinity required for the mixture's chemical stability. Potassium-based products are more expensive than their sodium-based counterparts, but they feature better solubility as well as lower kinematic viscosity and higher ionic conductivity, properties that notably extend the average life of a bath (solubility of KHCO ₃ ) and facilitate rinsing of parts.

The passivity of iron...