On reasons of defects of silver coatings

To reduce the toxicity of a cyanide electrolyte for silvering, it is necessary to replace free cyanide ions with rhodanide ions. It made possible to conduct the process at high operating current densities and obtain a fine-grained sediment structure. It is shown that such a structure has been obtained due to a discharge of a mixed cyanide-rhodanide complex. However, during washing and subsequent drying at elevated temperatures, black or yellow spots are formed on the surface of the silver coating, due to which parts are discarded. These spots are insoluble silver products which further lead to deterioration of the physical-chemical characteristics of the coating. It is shown that it is possible to remove these spots both chemical and electrochemical ways. The final elemental analysis of the coating composition after the removal of the products shows the absence of any other elements excepting silver. Some improvement in the sediment structure was also observed.