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What is Involved in Cadmium Plating?

Paul Scott
Paul Scott

Cadmium plating is a material deposition process which coats articles with a thin protective layer of cadmium metal. The coatings are applied in several ways including electroplating which involves submerging recipient items in vats of cadmium salt solution through which an electric current is passed. Other cadmium plating processes include mechanical and vacuum methods for smaller items and to impart coatings of high uniformity. Cadmium is a popular plating material because it lends recipient items excellent corrosion resistance, low friction coefficients, and a high degree electrical conductivity. The use of cadmium as a plating material has, however, come under intense scrutiny due to the environmental issues.

Metal plating is a commonly used method of coating one material with thin layers of another to protect or enhance the recipient's characteristics or appearance. These processes are used to deposit metal coatings on other metals, and some processes may even be used to coat paper products and plastic films. Cadmium plating is a popular and widely applied form of metal plating and is used to coat a wide variety of items ranging from tiny springs and clips to substantial machine parts. Cadmium lends plated items outstanding conventional and galvanic corrosion resistance and even gives a degree of sacrificial protection. It has excellent friction coefficient values and electrical conductivity, is tough, easily soldered, and has good torque characteristics.

Man with a drill
Man with a drill

Cadmium plating is achieved in a number of ways, the most common of which is the electroplating method. This process involves suspending recipient items in a bath filled with a cadmium salt solution with an alkaline cyanide base. A cadmium anode is inserted into the bath, and a current is passed from it through the solution and to the recipient items which serve as a cathode or negative point. Cadmium is attracted to and deposited on the recipient items from the solution and replaced by material from the anode which is forced into solution. The cadmium electroplating method is characterized by good film thickness control, excellent brightness in the finish, and good covering characteristics.

Other cadmium plating methods include mechanical plating which involves tumbling recipient items in a drum with cadmium powder, glass beads, and specially formulated chemicals. Although effective, this process is only suitable for items which can be agitated in this way. One of the most specialized methods of cadmium plating is the vacuum deposition method where cadmium is heated in a vacuum until it vaporizes. A recipient substrate is exposed to the vapor where cadmium atoms adhere to its surface imparting a very thin, accurate, and high quality cadmium coating. Notwithstanding its many benefits and continued use, however, cadmium as a plating material has attracted considerable negative attention recently due to environmental issues surrounding its high toxicity.

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