Chemical Fact Sheet
Palladium
| Chemical Abstract Number (CAS #) | 7440-05-3 |
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| Analytical Methods | 200.8 - 6020 |
| Molecular Formula | Pd |
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Synopsis
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Palladium - (named after the asteroid Pallas, discovered about the same time; Gr. Pallas, goddess of wisdom), Pd; at. wt. 106.42(l) at. no. 46; m.p. 1554.9 deg C; b.p. 2963 deg C; sp. gr. 1202 (20 deg C); valence 2, 3, or 4. Discovered in 1803 by Wollaston. Palladium is found along with platinum and other metals of the platinum group in placer deposits of Russia, South and North America, Ethiopia, and Australia. Natural palladium contains six stable isotopes. Twenty five other isotopes are recognized, all of which are radioactive. 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. 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 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 in. The metal is used in dentistry, watchmaking, and in making surgical instruments and electrical contacts. The metal sells for about $140/troy oz. ($4.50/g). |
| Use | Palladium is used in gold, silver and copper alloys in dentistry. Alloys are also used for bearings, strings, and balance wheels in watches. Palladium is used as a catalyst in the manufacture of sulfuric acid. In powder form it is used as a catalyst in hydrogeneration. The sponge form is used for separation of hydrogen from a mixture of gases. Silver alloys are used for electrical contacts. The automotive industry has used palladium in catalytic converters since 1974. In jewelry, palladium hardened with 4-5% ruthenium provides a light, white, strong, tarnish-free alloy for watch cases, brooches, and settings for gems. For alloy bearings, springs, balance wheels of watches; for mirrors in astronomical instruments; as catalyzer in manufacture of sulfuric acid and in other oxidizing processes. Alloys for electrical relays and switching systems in telecommunication equipment, catalyst for reforming cracked petroleum fractions and hydrogenation, metallizing ceramics, "white gold" in jewelry, aircraft spark plugs, protective coatings. Palladium is used extensively in industry in alloys, as a catalyst in hydrogen purification, and in dental inlays with platinum and gold. A colloidal form of palladium has been used therapeutically for tuberculosis, gout, and obesity. When palladium is alloyed with 40% silver it becomes much tougher and wear-resistant and is used in electrical contact materials. Palladium-bearing thick-film pastes are used in miniature solid-state devices and integrated circuits. Palladium is widely used in dentistry, often alloyed with gold, and in jewelry, alloyed with platinum. Palladium dispersed on carbon or alumina has outstanding catalytic properties. Platinum-palladium catalysts are used to control emissions from automobile exhausts. Palladium-silver diffusion membranes are used in the purification of hydrogen. |
| Apparent Color | Silver-white, ductile metal |
| Boiling Point | 3167 deg C |
| Melting Point | 1555 deg C |
| Molecular Weight | 106.40 |
| Density | 12.02 g/cu cm |
| Sensitivity Data | Contact dermatitis has been associated with metallic palladium, especially with palladium alloys. |
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Chemical and Physical Properties |
Palladium is the lightest of the platinum group and very malleable and ductile when pure. It resists oxidation at ordinary temperatures. It absorbs a considerable amount of hydrogen gas. It is appreciably volatile at high temperatures. At red heat it is converted to the oxide. A property unique to palladium is its ability to absorb and retain over 800 times its volume of hydrogen, which results in an expansion of several percent. Palladium dissolves anodically in warm acidic chloride solutions. |
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Environmental Fate |
Palladium (Pd) is found with platinum, gold, and nickel ores. |
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