Palladium

Palladium, chemical element, symbol Pd; forphysical constants see Periodic Table. Palladium was discovered by William H. Wollaston in 1803. It occurs native associated with platinum, gold, and silver and also as a selenide. Commercially, it is obtained as a byproduct in the production of platinum, nickel, and copper. It is prepared in sponge form by the thermal decomposition of palladium dichlorodiamine. Palladium is a steel-white, malleable, soft, ductile metal. It is a member of the platinum group of metals and is the least dense, lowest melting, and most readily fused. Palladium metal resists oxidation. It absorbs up to 900 times its volume of hydrogen at ordinary temperatures. Hydrogen gas is purified by diffusing it through heated palladium. Palladium is used in the finely divided state as a catalyst for hydro-genation and dehydrogention reactions. Palladium is used in jewelry, dentistry, surgical instruments, electrical contacts, and high temperature solders. It is the least expensive of the platinum metals.