Electroplating << ih LEHK truh `play` tihng >> is the process of putting a metallic coating on a metal or other conducting surface by using an electric current. It is used to improve the appearance of materials, for protection against corrosion, and to make plates for printing.
The article to be plated is thoroughly cleaned of grease and dirt by dipping it in acid and alkaline cleaning solutions. It is then put in a solution of the metal with which it is to be coated. The metal exists in the form of positive ions (atoms that have lost one or more electrons). The article is connected to the cathode (negative end of a source of electric current). The anode (positive electric terminal) is connected to another conductor which is also dipped into the solution. The electric current acts on the metallic ions in the solution. The ions are attracted to the cathode, and the coating is deposited on the article’s metal surface. If the metal in the solution and the metal of the positive terminal are the same, the electric current may remove metal from the terminal to replace metal taken from the solution.
The thickness of the layer deposited on the article depends on the strength of the electric current, the concentration of metallic ions, and the length of time the article has been in the solution. The terms triple-plated and quadruple-plated indicate various thicknesses of plating, not separate layers deposited on the surface.
Ornamental and protective platings are very thin, usually from 1/1,000 to 2/1,000 of an inch (0.03 to 0.05 millimeter) thick. For plating gold, silver, copper, zinc, and cadmium, cyanide solutions of the same metals are often used. Copper and zinc may also be plated by acid-sulfate solutions. Chromium is plated with a chromic-acid solution and nickel is plated with nickel sulfate. Other metals plated for commercial use include platinum, lead, and tin. Alloys of two or more metals may be deposited by using a solution of salts of the metals that make up the alloy. Examples of alloys used for plating are brass, black nickel, lead-tin, and bronze.
Electroplating is also used to reproduce medals or other objects in a process called electroforming. This process was formerly known as galvanoplasty. One kind of electroforming, called electrotyping, is the reproduction of type forms and engravings for the printing industry.
See also Alloy; Electrolysis.
