Formulation of Electroplating salts: Part-I Alkaline Copper-plating salt

Abstract

Copper-plating from an alkaline bath is extensively used in plating of steel surfaces and zinc base alloys. Copper undercoats usually improve lustre and brightness of protective and decorative nickel plates. Alkaline copper-plating salt generally contain cuprous cyanide, sodium or potassium cyanide, sodium sulphate and sodium carbonate. Cuprous cyanide dissolves in NaCN giving a soluble complex Na2Cu (CN)3 which serves as an electrolyte in the copper plating process. The influence of each and every ingredient added in the electrolyte has been studied and the optimum concentration ascertained leading to salts- factory electro-deposited coatings of copper. The optimum concentration of cuprous cyanide in the electrolyte is maintained within the concentration of 25 gms/1CuCN beyond which the corresponding current efficiency is not appreciably increased at moderate current density. The effect of free cyanide in the electrolyte has been observed to increase the conductivity, anodic efficiency and decrease the anodic polarization. The optimum concentration of free NaCN in the two working concentration of CuCN in the electrolyte viz. 10 gms/1 and 25 gms/1 has been observed to be 7.5 gms/1 and 9gms/1 respectively to obtain the maximum efficiency. Sodium sulphate, to the extent of 4.5 gms/1has been added to the bath which exerts a reducing effect on the cyanide copper complex increasing metal ion concentration and thereby the current efficiency. Sodium carbonate in the cyanide copper plating bath serves as a good conductor and effective depolarizer. It has been worked out that sodium carbonate in the formulated salt should not be exceeded more than 8 gms/1 minimum. More addition makes the replenishment of the bath complicated.