Palladium

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	Palladium

Notable Characteristics

Palladium is a soft steel-white metal that resembles platinum, doesn't tarnish in air, and is the least dense and has the lowest melting point of the platinum group[?] metals. It is soft and ductile when annealed and greatly increases its strength and hardness when it is cold-worked. Palladium is chemically attacked by sulfuric and nitric acid but dissolves slowly in hydrochloric acid. This metal also doesn't react with oxygen at normal temperatures.

This metal has the uncommon ability to absorb up to 900 times its own volume of hydrogen at room temperatures. It is thought that this possibly forms Pd₂H but it isn't yet clear if this is a true chemical compound.

Common oxidation states of palladium are +2, +3 and +4. Recently, palladium compounds in which palladium has oxidation state +6 were synthesized.

Applications

When it is finely divided, palladium forms a good catalyst and is used to speed-up hydrogenation and dehydrogenation reactions and also used in petroleum refinery reactions. This metal is also alloyed and used in jewelry. Other uses;

White gold[?] is an alloy of gold that is decolorized by the addition of palladium.
Similar to gold, palladium can be beaten into a thin leaf form as thin as 1/250,000 in.
Hydrogen easily diffuses through heated palladium and provides a means of purifying the gas.
Telecommunications switching system equipment employs palladium.
Palladium is also used in dentistry, watchmaking[?], in aircraft sparkplugs and in the production of surgical instruments[?] and electrical contacts[?].

History

Palladium was discovered by William Hyde Wollaston in 1803. This element was named by Wollaston in 1804 after the asteroid Pallas, which was discovered two years earlier.

Wollaston found element 46 in crude platinum ore from South America. He did this by dissolving the ore in aqua regia, neutralizing the solution with sodium hydroxide, Na OH[?], precipitating platinum as ammonium chloroplatinate[?] through treatment with ammonium chloride[?], N H₄Cl, then he added mercuric cyanide[?] to form the compound palladium cyanide[?]. Finally, he heated the resulting compound in order to extract palladium metal.

The compound palladium chloride[?] was at one time prescribed as a tuberculosis treatment at the rate of 0.065 g per day (approximately 1 mg per kg of body weight). This treatment did not have too many ill side effects but was later replaced by more effected drugs.

Derivation

Traditionally, a palladium is a statue of Pallas Athena, especially, the one that Odysseus took from the citadel of Troy and upon which the city's security was believed to depend. The word is a Latinization of the Greek παλλαδιον, which can be transliterated as "palladion".

Occurrence

Palladium is found as a free metal and alloyed with platinum and gold with platinum group metals in placer[?] deposits of the Ural Mountains, Australia, Ethiopia, South and North America. However it is commercially produced from nickel-copper deposits found in South Africa and Ontario (the huge volume of ore processed makes this extraction profitable in spite of its low concention in these ores).

Isotopes

Naturally occurring palladium is composed of six isotopes. The most stable radioisotopes are Pd-107 with a half-life of 6.5 million years, Pd-103 with a half-life of 17 days, and Pd-100 with a half-life of 3.63 days. Eighteen other radioisotopes have been characterized with atomic weights ranging from 92.936 amu (Pd-93) to 119.924 amu (Pd-120). Most of these have half-lifes that are less than a half an hour except Pd-101 (half-life: 8.47 hours), Pd-109 (half-life: 13.7 hours), and Pd-112 (half-life: 21 hours).

The primary decay mode before the most abundant stable isotope, Pd-106, is electron capture and the primary mode after is beta decay. The primary decay product before Pd-106 is rhodium and the primary product after is silver.

Radiogenic Ag-107 is a decay product of Pd-107 and was first discovered in the Santa Clara, California meteorite of 1978. The discoverers suggest that the coalescence and differentiation of iron-cored small planets may have occurred 10 million years after a nucleosynthetic event. Pd-107 versus Ag correlations observed in bodies, which have clearly been melted since accretion of the solar system, must reflect the presence of live short-lived nuclides in the early solar system.

External Links

WebElements.com - Palladium (http://www.webelements.com/webelements/elements/text/Pd/index.html)
EnvironmentalChemistry.com - Palladium (http://environmentalchemistry.com/yogi/periodic/Pd.html)

Nay, had I power, I should Uproar the universal peace, confound MACDUFF. O Scotland, Scotland! I am as I have spoken. No, not to live. O nation miserable! When shalt thou see thy wholesome days again, By his own interdiction stands accursed Was a most sainted king; the queen that bore thee, Died every day she lived. Fare thee well! Have banish'd me from Scotland. O my breast, MALCOLM. Macduff, this noble passion, Wiped the black scruples, reconciled my thoughts By many of these trains hath sought to win me From over-credulous haste. But God above I put myself to thy direction and The taints and blames I laid upon myself, Unknown to woman, never was forsworn, At no time broke my faith, would not betray No less in truth than life. My first false speaking Is thine and my poor country's to command. Old Siward, with ten thousand warlike men Now we'll together, and the chance of goodness MACDUFF. Such welcome and unwelcome things at once DOCTOR. Ay, sir, there are a crew of wretched souls The great assay of art, but at his touch, They presently amend. MACDUFF. What's the disease he means? A most miraculous work in this good King, I have seen him do. How he solicits heaven, All swol'n and ulcerous, pitiful to the eye, Hanging a golden stamp about their necks To the succeeding royalty he leaves He hath a heavenly gift of prophecy, That speak him full of.

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