palladium (redirected from palladia)

palladium, chemical element

palladium [Gr. Pallas, goddess of wisdom], metallic chemical element; symbol Pd; at. no. 46; at. wt. 106.42; m.p. 1,554°C;; b.p. 2,970°C;; sp. gr. 12.02 at 20°C;; valence +2, +3, or +4. Palladium is a lustrous silver-white metal with a face-centered cubic crystalline structure. Directly above platinum, it is one of the platinum metals in Group 10 of the periodic table. It is strongly resistant to corrosion in air and to the action of acids (except nitric acid) at ordinary temperatures. However, it is attacked by hot acids, and it dissolves in aqua regia. It forms many compounds, including oxides, chlorides, fluorides, sulfides, phosphides, and several complex salts. Palladium has a great ability to absorb hydrogen; when finely divided, one volume of palladium absorbs as many as 900 volumes of the gas. When heated, it allows hydrogen to diffuse rapidly through it; it is thus used to purify hydrogen gas. Palladium is found in nature with platinum minerals and in association with the nickel ores mined near Sudbury, Ont., Canada. Because of its corrosion resistance, a major use of palladium is in alloys used in low voltage electrical contacts. Palladium is used extensively in jewelry-making in certain alloys called "white gold." It may be alloyed with platinum or substituted for it. It is used in watch bearings, springs, and balance wheels and also for mirrors in scientific instruments. For use in dentistry it is alloyed with silver, gold, and copper. In chemistry it is a catalyst in sulfuric acid manufacture and in hydrogenation processes. Palladium salts are used in electroplating. Although palladium is not as abundant as platinum, it is less expensive. Palladium was discovered in 1803 by W. H. Wollaston.

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Palladium, in Greek religion

Palladium (pəlā`dēəm), in Greek religion, sacred image kept in the temple of Athena at Troy. It was either an image of Athena or an image made by Athena of her unfortunate playmate Pallas (see Pallas (1)). According to legend, the image was sent by Zeus to Dardanus, the founder of Troy, and it was believed that the city could not be taken while it possessed the Palladium. Thus during the Trojan War two Greeks, Diomed and Odysseus, stole it. Another legend says that during the sack of Troy, Ajax the Lesser carried it off. The Romans, who later claimed to have the true Palladium in their temple of the vestal virgins, said that Aeneas took it when he fled Troy. But many cities, including Argos, Athens, and Luceria, owned such images, all of which came to be known as Palladia.

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palladium

Metallic chemical element, one of the transition elements, chemical symbol Pd, atomic number 46. A precious, silver-white metal that resembles platinum chemically, it is extremely ductile and easily worked and can be beaten into thin leaf. It is an excellent catalyst for chemical reactions involving hydrogen and oxygen, such as the hydrogenation of unsaturated organic compounds. Because it does not tarnish in air at ordinary temperatures, palladium and its alloys serve as substitutes for platinum in jewelry and in electrical contacts in telecommunications equipment. Small amounts of palladium alloyed with gold yield the best white gold. Palladium is used also in dental alloys. Because hydrogen passes rapidly through the metal at high temperatures, heated palladium tubes impervious to other gases function as semipermeable membranes and are used for hydrogen purification.

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palladium

A silvery metal similar to platinum. Palladium was the original name of Microsoft's security platform (see NGSCB).

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palladium

a ductile malleable silvery-white element of the platinum metal group occurring principally in nickel-bearing ores: used as a hydrogenation catalyst and, alloyed with gold, in jewellery. Symbol: Pd; atomic no.: 46; atomic wt.: 106.42; valency: 2, 3, or 4; relative density: 1202; melting pt.: 1555°C; boiling pt.: 2964°C

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palladium

a “safeguard”; Troy believed safe while statue of Pallas Athene remained. [Gk. Lit.: Iliad; Espy, 40]

See : Guardianship

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Palladium

colossal statue whose presence insured Troy’s safety. [Rom. Legend: Brewer Dictionary, 796]

See : Protectiveness