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is the process in which a layer of copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
is deposited on the item to be plated by using an electric current.
Three basic types of processes are commercially available based upon the complexing system utilized:
- alkaline-(several modifications of cyanide
A cyanide is a chemical compound that contains the cyano group, -C≡N, which consists of a carbon atom triple-bonded to a nitrogen atom. Cyanides most commonly refer to salts of the anion CN−. Most cyanides are highly toxic....
and non-cyanide) complexed bath
An acid is a substance which reacts with a base. Commonly, acids can be identified as tasting sour, reacting with metals such as calcium, and bases like sodium carbonate. Aqueous acids have a pH of less than 7, where an acid of lower pH is typically stronger, and turn blue litmus paper red...
-(sulfate and fluoborate) complexed bath
- mildly alkaline-(pyro phosphate) complexed bath
With a higher current, hydrogen bubbles will form on the item to be plated, leaving surface imperfections. Often various other chemicals are added to improve plating uniformity and brightness. Without some form of additive, it is almost impossible to obtain a smooth plated surface. These additives can be anything from dish soap to proprietary compounds.
Copper is an active metal and so difficult to plate onto a passivated surface, making direct plating of iron based metals difficult. Such surfaces often require a nickel strike base coat for the copper to adhere to.
The plating seen in chemistry classes, often obtained with a coin and copper sulphate bath, is in fact deposition as opposed to plating. Subjecting the surface to any wear causes the unstuck deposit to come away. Running such a bath for longer periods, one can often see the grainy like texture of deposition as opposed to the smooth surface of plating.
Commercial platers often use a copper cyanide-based solution to ensure a high level of copper remains in solution. These solutions are inherently dangerous due to the highly toxic nature of cyanide.
Effects of bath chemistry on finish
Cyanide based bath chemistry produces a matte finish favored for its diffusion blocking character. If a bright surface is required, such as one required for decoration or soldering upon, an acid bath chemistry is used.