Palladium
Palladium
For dental crowns.
History
Palladium was named after the asteroid Pallas, which was discovered at about the same time. Pallas was the Greek goddess of wisdom.
Sources
Discovered in 1803 by Wollaston, Palladium is found with platinum and other metals of the platinum group in placer deposits of Russia, South America, North America, Ethiopia, and Australia. It is also found associated with the nickel-copper deposits of South Africa and Ontario. Palladium's separation from the platinum metals depends upon the type of ore in which it is found.
Properties
The element is a steel-white metal, it does not tarnish in air, and it 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. Palladium is attacked by nitric and sulfuric acid.
At room temperatures, the metal has the unusual property of absorbing 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, providing a means of purifying the gas.
Uses
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 in. The metal is used in dentistry, watchmaking, and
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Palladium
in making surgical instruments and electrical contacts.
Cost
The metal sells for about $150/troy oz.
Sources: CRC Handbook of Chemistry and Physics and the American Chemical Society.
Last Updated: 12/19/97, CST Information Services Team
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Cadmium
Cadmium
For rechargeable batteries.
History
(L. cadmia; Gr. kadmeia - ancient name for calamine, zinc carbonate) Discovered by Stromeyer in 1817 from an impurity in zinc carbonate. Cadmium most often occurs in small quantities associated with zinc ores, such as sphalerite (ZnS). Greenockite (CdS) is the only mineral of any consequence bearing cadmium. Almost all cadmium is obtained as a by-product in the treatment of zinc, copper, and lead ores. It is a soft, bluish-white metal which is easily cut with a knife. It is similar in many respects to zinc. Failure to appreciate the toxic properties of cadmium may cause workers to be unwittingly exposed to dangerous fumes. Silver solder, for example, which contains cadmium, should be handled with care. Serious toxicity problems have been found from long-term exposure and work with cadmium plating baths. Exposure to cadmium dust should not exceed 0.01 mg/m3 (8-hour time-weighted average, 40-hour week). The ceiling concentration (maximum), for a period of 15 min, should not exceed 0.14 mg/m3. Cadmium oxide fume exposure (8-hour, 40-hour week) should not exceed 0.05 mg/m3, and the maximum concentration should not exceed 0.05 mg/m3. These values are presently being restudied and recommendations have been made to reduce the exposure. In 1927 the International Conference on Weights and Measures redefined the meter in terms of the wavelength of the red cadmium spectral line (i.e. 1m = 1.553,164.13 wavelengths). This definition has been changed (see under Krypton).
Uses
Cadmium is a component of some of the lowest melting alloys; it is used in bearing alloys with low coefficients of friction and great resistance to fatigue; it is used extensively in electroplating, which accounts for about 60% of its use. It is also used in many types of solder, for standard E.M.F. cells, for Ni-Cd batteries, and as a barrier to control nuclear fission. Cadmium compounds are used in black and white television phosphors and in blue and green phosphors for color TV tubes. It forms a number of salts, of which the sulfate is most common; the sulfide is used as a yellow pigment. Cadmium and solutions of its compounds are toxic.
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Cadmium
Cost
The current price of cadmium is about $12/lb. It is available in high purity form.
Isotope
Sources: CRC Handbook of Chemistry and Physics and the American Chemical Society.
Last Updated: 12/19/97, CST Information Services Team
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