The possible use of tin ion discharge inhibition in bronze electroplating from an electrolyte based on nitrilotrimethylphosphonic acid

Abstract

The joint electrodeposition of copper and tin from an alkali cyanide-free electrolyte was studied. It was found that the variation in the coating composition with an increase in pH cannot be due to stability constants of copper and tin complexes with nitrilotrimethylphosphonic acid. The electrochemical impedance method was used to study the mechanism of joint discharge of copper and tin. The difference between the expected and observed dependence of the alloy composition on рН of bronze-plating electrolyte is due to the cathode passivation as a result of the reaction with copper-containing complexes. The film formed on the cathode surface inhibits the incorporation of tin into the coating, thus controlling the tin content in the alloy. The strength of the passive film increases with an increase in рН.