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   Pd

PALLADIUM

(named after the asteroid Pallas, discovered about the same time; Gr. Pallas, goddess of wisdom)

Pd  at. wt. 106.4
     at. no. 46 
     m.p.   1552°C 
     b.p. 3140°C
     sp. gr. 12.02 (20°C)
     valence 2, 3, or 4.

Palladium was discovered in 1803 by Wollaston. Palladium is found along with platinum and other metals of the platinum group in placer deposits of the U.S.S.R, South and North America, Abyssinia, and Australia. It is also found associated with the nickel-copper deposits of South Africa and Ontario. Its separation from the platinum metals depends upon the type of ore in which it is found. It is a steel-white metal, does not tarnish in air, and is the least dense and lowest melting of the platinum group of metals. When annealed, it is soft and ductile; cold working greatly increases its strength and hardness. Pal- ladium is attacked by nitric and sulfuric acid. At room temperatures the metal has the unusual property of absorb- mg up to 900 times its own volume of hydrogen, possibly forming Pd2H. It is not yet clear if this is a true compound. Hydrogen readily diffuses through heated palladium and this provides a means of purifying the gas. Finely divided palladium is a good catalyst and is used for hydrogenation and dehydrogenation reactions. It is alloyed and used in jewelry trades. White gold is an alloy of gold decolorized by the addition of palladium. Like gold, palladium can be beaten into leaf as thin as 1/250,000 inch. The metal is used in dentistry, watchmaking, and in making surgical instruments and electrical contacts. The metal sells for about $40/troy ounce.

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