Silver plating is mostly processed on copper and copper alloy workpieces. In order to obtain a good adhesion of the silver coating, whether cyanide silver plating or any other, it is necessary to have it pre-plated or amalgamated. This is determined by the special properties of metallic silver.
Silver is a precious metal with strong positive electricity. According to the order in the electrochemical sequence, copper is in front of silver, so the potential of copper is more negative than that of silver..
When the copper part is in contact with the silver plating solution, the copper reacts with the silver particles in the electrolyte. As a result, the copper is transformed into copper ions into the solution and the silver ions acquire electrons from the solution to precipitate and deposit on the copper part.
This reaction is not only due to the contamination of the silver plating tank with copper ions, but more seriously because the resulting silver layer is loose and the copper adhesion is not strong.
If plating is applied to this loose replacement silver coating, the resulting coating will not meet the adhesion index and quality requirements. Therefore, in addition to degreasing and acid corrosion, copper and copper alloy parts require special pre-treatment before being placed in the plating tank..The simplest method of production is amalgamation of mercury.
A dense coating of copper-mercury alloy forms on the surface of the copper parts after amalgamation with mercury. The alloy's potential is more positive than that of silver, thus preventing the substitution of coatings that can easily be produced during silver plating.
Due to the mercuric treatment having a certain corrosive, mercury toxic, for tableware and high precision parts should not be used, some enterprises use copper cyanide pre-plating or silver pre-plating in cyanide bath solution with low silver ion concentration to change the surface potential of the parts to improve the adhesion of the silver plating coating.
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