Plating Metals
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Plating Metals Metal coatings are added to base parts for protection and decoration. In some circumstances, thin metal platings are used to provide specific material properties such as high optical reflectivity (as in the case of telescope mirrors), low toxicity (protection against dust from beryllium metal), or high electrical conductivity. Screws, nuts, and other small parts are economically coated in large drums filled with plating solution. In the manufacture of tin cans, a layer of tin only 0.000015 inch (0.4 micron) thick can be electroplated onto steel strips at rates up to 2000 feet (610 m) per minute. Today, most metal coatings are deposited through the electroplating process. Before the development of reliable sources of direct-current electricity, however, metalworkers had to develop other techniques. One crude method was to fabricate the base article in its desired shape and then solder a thin sheet of plating onto its surface; obviously, coating complex surfaces was extremely difficult, if not impossible, with this technique. The first popular and economical plating method was the use of the "Sheffield plate" to place silver on the surface of serving dishes, candle sticks, buttons, snuff boxes, and tea urns. In 1743, Thomas Boulsover—a cutlery craftsman in Sheffield, England—discovered, while repairing a copper and silver knife handle, that the two metals could be fused. Boulsover then made a second important discovery: when the fused metals were rolled on a rolling mill, they expanded together like a single metal. Boulsover's technique was rapidly adopted by other Sheffield metal workers, and also gained popularity in the town of Birmingham. The metal fusion process of Sheffield plate was popular from 1750 to about 1880, when it was superseded by electroplating. In the early 1800s, Alessandro Volta's new battery made reliable amounts of electric current available for the first time. Later in that century, the availability of electricity was an important factor in the development of electroplating. In the electroplating process, a piece of the metal to be deposited acts as the anode and the object to be plated acts as the cathode; both are submerged in an electrolyte solution, usually containing ions of the metal to be deposited. When an electric voltage is applied between the anode and cathode, metal ions are attracted from the electrolyte and deposited on the cathode; the anode
metal dissolves to replace ions lost from the electrolyte solution. \folta's battery was first applied to deposit zinc, copper, and silver onto themselves, as well as onto other base metals such as iron and gold. Electroplating began on a commercial scale in 1840, and was soon enhanced by the discovery of cyanide electrolyte solutions for plating copper, gold, silver, and brass directly onto iron or steel—with excellent adherence. Earlier solutions, such as copper sulfate, corroded iron and steel, leaving nonadherent deposits of the plated metal. Finely buffed nickel-silver alloy electroplated with a silver coating, or brass
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