Palladium

Palladium is a chemical element with the symbol Pd and atomic number 46. It is a rare and lustrous silvery-white metal discovered in 1803 by William Hyde Wollaston. He named it after the asteroid Pallas, which was itself named after the epithet of the Greek goddess Athena, acquired by her when she slew Pallas. Palladium, platinum, rhodium, ruthenium, iridium and osmium form a group of elements referred to as the platinum group metals (PGMs). These have similar chemical properties, but palladium has the lowest melting point and is the least dense of them.Palladium belongs to group 10 in the periodic table, but the configuration in the outermost electrons are in accordance with Hund's rule. Electrons in the s-shell migrate to fill the d orbitals because they have less energy. Palladium compounds primarily exist in the 0 and +2 oxidation state. Other less common states are also recognized. Generally the compounds of palladium are more similar to those of platinum than those of any other element.William Hyde Wollaston noted the discovery of a new noble metal in July 1802 in his lab book and named it palladium in August of the same year. Wollaston purified a quantity of the material and offered it, without naming the discoverer, in a small shop in Soho in April 1803. After harsh criticism from Richard Chenevix that palladium is an alloy of platinum and mercury, Wollaston anonymously offered a reward of £20 for 20 grains of synthetic palladium alloy. Chenevix received the Copley Medal in 1803 after he published his experiments on palladium. Wollaston published the discovery of rhodium in 1804 and mentions some of his work on palladium. He disclosed that he was the discoverer of palladium in a publication in 1805.As overall mine production of palladium reached 208,000 kilograms in 2016, Russia was the top producer with 82,000 kilograms, followed by South Africa, Canada and the U.S. Russia's company Norilsk Nickel ranks first among the largest palladium producers globally, it accounts for 39% of the world’s production.The largest use of palladium today is in catalytic converters. Palladium is also used in jewelry, dentistry, watch making, blood sugar test strips, aircraft spark plugs, surgical instruments, and electrical contacts. Palladium is also used to make professional transverse (concert or classical) flutes. As a commodity, palladium bullion has ISO currency codes of XPD and 964. Palladium is one of only four metals to have such codes, the others being gold, silver and platinum. Because it absorbs hydrogen, palladium is a key component of the controversial cold fusion experiments that began in 1989.Palladium is a metal with low toxicity as conventionally measured (eg. Ld50). Recent research on the mechanism of palladium toxicity suggests high toxicity if measured on a longer timeframe and at the cellular level in the liver and kidney. Mitochondria appear to have a key role in palladium toxicity via mitochondrial membrane potential collapse and depletion of the cellular glutathione (GSH) level. Until that recent work, it had been thought that palladium was poorly absorbed by the human body when ingested. Plants such as the water hyacinth are killed by low levels of palladium salts, but most other plants tolerate it, although tests show that, at levels above 0.0003%, growth is affected. High doses of palladium could be poisonous; tests on rodents suggest it may be carcinogenic, though until the recent research cited above, no clear evidence indicated that the element harms humans.Like other platinum-group metals, bulk Pd is quite inert. Although contact dermatitis has been reported, data on the effects are limited. It has been shown that people with an allergic reaction to palladium also react to nickel, making it advisable to avoid the use of dental alloys containing palladium on those so allergic.