APPLICATION OF FREQUENCY-RESPONSE ANALYSIS TO THE DETERMINATION OF CATHODIC DISCHARGE MECHANISM DURING SILVER ELECTROPLATING

The ac impedance data generated from the frequency response analysis technique were used to establish the mechanism of silver electroplating from the industrial cyanide plating bath. The deposition process involves parallel and concurrent charge-transfer reactions from more than one silver complex. Depending on the cyanide concentration in the silver plating bath, the electrode reaction seems to proceed mostly through one of the silver species/complexes: AgCN, Ag(CN)(2)(-), or Ag(CN)(3)(2-), which are in equilibrium with each other. The discharge of Ag(CN)(2)(-) complex appears the predominant process, especially for bath concentrations in the range of commercial silver cyanide plating systems. The complex plane ac impedance diagrams of the plating system, at steady state, consist of two capacitive loops at the lower frequencies, preceded by a high frequency spectrum which corresponds to the faradaic charge-transfer process. The lower frequency features are a manifestation of the surface adsorption and coverage processes by specific intermediate species like cyanide and carbonate ions in the plating bath.