On the Causes of the Formation of Rejected Silver Coatings

Free cyanide ions should be replaced by thiocyanate ions to decrease the toxicity of a cyanic silver-plating electrolyte. This allows the process to occur at high working current densities with the formation of a fine-grained deposit. This structure is shown to be formed due to the discharge of a mixed cyanide–thiocyanate complex. However, black or yellow spots causing article rejection form on the silver coating surface after washing and subsequent drying at elevated temperature. The spots are insoluble silver products, which further worsen the physicochemical characteristics of the coating. These spots can be removed by both chemical and electrochemical methods. The final elemental analysis of the coating composition after product removal shows no elements except for silver. The deposit structure has also been improved.