IMMERSION PLATING

摘要

Immersion (displacement) plating is the deposition of a metallic coating on a base metal from a solution that contains the coating metal. One metal is displaced by a metal ion that has a lower oxidation potential than the displaced metal ion. This differs from electroless plating because, in immersion plating, reducing agents are not required to reduce the metal ions to metal, as the base metal acts as a reducing agent. When a steel part is immersed in a copper sulfate solution, the following reaction occurs: Fe + Cu~(+2) → Cu + Fe~(+2) The iron displaces the copper from its solution and the copper coats the steel part. The thickness of deposits obtained by immersion plating is limited because deposition stops when the entire surface of the base metal is coated. Higher temperatures increase reaction rates of immersion baths and stirring is sometimes beneficial. Parts must be properly cleaned prior to immersion. Immersion baths are usually inexpensive and have excellent coverage. They permit plating on difficult surfaces such as on the inside of tubing or in cases where there is difficulty in making electrical connections to isolated areas of the base metal. Immersion deposits are used for decorative purposes or as lubricants in drawing steel wire or shapes. The accepted safety rules for handling acids, bases, cyanides, and other solutions should be followed when operating an immersion bath. Fume hoods should be used when a process involves the liberation of hazardous or annoying fumes. Table I gives the ingredients and operating temperatures for a variety of immersion deposits on different substrates.