User:MYfarrrrr/sandbox

鈀 是一種化學元素， 化學符號 Pd，原子序46. 鈀是在1803年由威廉·海德·沃拉斯頓所發現的一種罕見的、有光澤的銀白色金屬. 他以智神星（Pallas）命名，帕拉斯本身在被希臘女神雅典娜（Athena）殺死後獲得這個稱號. 鈀與鉑、銠、釕、銥、鋨形成一組鉑族金屬（PGM）. 它們具有相似的化學性質，但鈀的熔點最低，密度也最低.

超過一半用量的鈀及同類的鉑用於催化轉化器，將汽車排氣（碳氫化合物，一氧化碳和二氧化氮）中90％的有害氣體轉化為較少有害的物質（氮氣，二氧化碳和水蒸氣）. 還用於電子，牙科，醫藥，氫氣純化，化學應用，地下水處理和珠寶. 鈀是燃料電池的關鍵組成部分，它將氫氣與氧氣反應產生電，熱和水.

鈀和其他鉑金屬的礦床很少見. 分布最廣泛的礦床在南非德蘭士瓦盆地流域覆蓋的布什維爾德火成岩複合體的白雲帶、美國蒙大拿州的斯蒂爾沃特火成岩複合體、加拿大安大略省索德柏立盆地和雷灣區和俄羅斯的諾里爾斯克火成岩複合體，而最近發現的是菲律賓米沙鄢群島的北部. 回收也是一種來源，主要來自廢棄的催化轉化器. 眾多應用和有限的供應來源讓許多人產生了相當大的投資興趣.

特性
鈀屬於元素週期表中的第10族，但最外層電子中的配置符合洪德定則. s殼中的電子遷移以填充具有較少的能量的d軌域.

鈀是一種類似鉑金的柔軟銀白色金屬. 它的密度和熔點在鉑金屬族中都是最低的. 鈀在退火時柔軟且具有延展性，冷加工時強度和硬度大大提高. 將鈀置於濃硝酸或熱的濃硫酸中，還有精細研磨後在鹽酸中都會緩慢溶解. 它在室溫下易於在王水中溶解.

Palladium does not react with oxygen at standard temperature (and thus does not tarnish in air). Palladium heated to 800 °C will produce a layer of palladium(II) oxide (PdO). It tarnishes lightly in a moist atmosphere containing sulfur.

Palladium films with defects produced by alpha particle bombardment at low temperature exhibit superconductivity having Tc=3.2 K.

Isotopes
Naturally occurring palladium is composed of seven isotopes, six of which are stable. The most stable radioisotopes are 107Pd with a half-life of 6.5 million years (found in nature), 103Pd with 17 days, and 100Pd with 3.63 days. Eighteen other radioisotopes have been characterized with atomic weights ranging from 90.94948(64) u (91Pd) to 122.93426(64) u (123Pd). These have half-lives of less than thirty minutes, except 101Pd (half-life: 8.47 hours), 109Pd (half-life: 13.7 hours), and 112Pd (half-life: 21 hours).

For isotopes with atomic mass unit values less than that of the most abundant stable isotope, 106Pd, the primary decay mode is electron capture with the primary decay product being rhodium. The primary mode of decay for those isotopes of Pd with atomic mass greater than 106 is beta decay with the primary product of this decay being silver.

Radiogenic 107Ag is a decay product of 107Pd and was first discovered in 1978 in the Santa Clara meteorite of 1976. The discoverers suggest that the coalescence and differentiation of iron-cored small planets may have occurred 10 million years after a nucleosynthetic event. 107Pd versus Ag correlations observed in bodies, which have been melted since accretion of the solar system, must reflect the presence of short-lived nuclides in the early solar system.

Compounds


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.

Palladium(II)
Palladium(II) chloride is the principal starting material for other palladium compounds. It arises by the reaction of palladium with chlorine. It is used to prepare heterogeneous palladium catalysts such as palladium on barium sulfate, palladium on carbon, and palladium chloride on carbon. Solutions of PdCl2 in nitric acid react with acetic acid to give palladium(II) acetate, also a versatile reagent. PdCl2 reacts with ligands (L) to give square planar complexes of the type PdCl2L2. One example of such complexes is the benzonitrile derivative PdX2(PhCN)2.
 * PdCl2 + 2 L → PdCl2L2 (L = PhCN, PPh3, NH3, etc)

The complex bis(triphenylphosphine)palladium(II) dichloride is a useful catalyst.



Palladium(0)
Palladium forms a range of zerovalent complexes with the formula PdL4, PdL3 and PdL2. For example, reduction of a mixture of PdCl2(PPh3)2 and PPh3 gives tetrakis(triphenylphosphine)palladium(0):
 * 2 PdCl2(PPh3)2 + 4 PPh3 + 5 N2H4 → 2 Pd(PPh3)4 + N2 + 4 N2H5+Cl−

Another major palladium(0) complex, tris(dibenzylideneacetone)dipalladium(0) (Pd2(dba)3), is prepared by reducing sodium tetrachloropalladate in the presence of dibenzylideneacetone.

Palladium(0), as well as palladium(II), are catalysts in coupling reactions, as has been recognized by the 2010 Nobel Prize in Chemistry to Richard F. Heck, Ei-ichi Negishi, and Akira Suzuki. Such reactions are widely practiced for the synthesis of fine chemicals. Prominent coupling reactions include the Heck, Suzuki, Sonogashira coupling, Stille reactions, and the Kumada coupling. Palladium(II) acetate, tetrakis(triphenylphosphine)palladium(0) (Pd(PPh3)4, and tris(dibenzylideneacetone)dipalladium(0) (Pd2(dba)3) serve either as catalysts or precatalysts.

Other oxidation states
Although Pd(IV) compounds are comparatively rare, one example is sodium hexachloropalladate(IV), Na2[PdCl6]. A few compounds of palladium(III) are also known. Palladium(VI) was claimed in 2002, but subsequently disproven.

Mixed valence palladium complexes exist, e.g. Pd4(CO)4(OAc)4Pd(acac)2 forms an infinite Pd chain structure, with alternatively interconnected Pd4(CO)4(OAc)4 and Pd(acac)2 units.

History
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.

It was named by Wollaston in 1802 after the asteroid 2 Pallas, which had been discovered two months earlier. Wollaston found palladium in crude platinum ore from South America by dissolving the ore in aqua regia, neutralizing the solution with sodium hydroxide, and precipitating platinum as ammonium chloroplatinate with ammonium chloride. He added mercuric cyanide to form the compound palladium(II) cyanide, which was heated to extract palladium metal.

Palladium chloride was at one time prescribed as a tuberculosis treatment at the rate of 0.065 g per day (approximately one milligram per kilogram of body weight). This treatment had many negative side-effects, and was later replaced by more effective drugs.

Most palladium is used for catalytic converters in the automobile industry. In the run up to year 2000, the Russian supply of palladium to the global market was repeatedly delayed and disrupted; for political reasons, the export quota was not granted on time. The ensuing market panic drove the price to an all-time high of $1340 per troy ounce in January 2001. Around that time, the Ford Motor Company, fearing that automobile production would be disrupted by a palladium shortage, stockpiled the metal. When prices fell in early 2001, Ford lost nearly US$1 billion.

World demand for palladium increased from 100 tons in 1990 to nearly 300 tons in 2000. The global production of palladium from mines was 222 tonnes in 2006 according to the United States Geological Survey. Many were concerned about a steady supply of palladium in the wake of Russia's military maneuvers in Ukraine, partly as sanctions could hamper Russian palladium exports; any restrictions on Russian palladium exports would exacerbate what is already expected to be a large palladium deficit in 2014. Those concerns pushed palladium prices to their highest level since 2001. In September 2014 they soared above the $900 per ounce mark. In 2016 however palladium cost around $614 per ounce as Russia managed to maintain stable supplies. In January 2019 palladium futures climbed past $1,344 per ounce for the first time on record, mainly due to the strong demand from the automotive industry.

Occurrence
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.

Palladium can be found as a free metal alloyed with gold and other platinum-group metals in placer deposits of the Ural Mountains, Australia, Ethiopia, North and South America. For the production of palladium, these deposits play only a minor role. The most important commercial sources are nickel-copper deposits found in the Sudbury Basin, Ontario, and the Norilsk–Talnakh deposits in Siberia. The other large deposit is the Merensky Reef platinum group metals deposit within the Bushveld Igneous Complex South Africa. The Stillwater igneous complex of Montana and the Roby zone ore body of the Lac des Îles igneous complex of Ontario are the two other sources of palladium in Canada and the United States. Palladium is found in the rare minerals cooperite and polarite. Many more Pd minerals are known, but all of them are very rare.

Palladium is also produced in nuclear fission reactors and can be extracted from spent nuclear fuel (see synthesis of precious metals), though this source for palladium is not used. None of the existing nuclear reprocessing facilities are equipped to extract palladium from the high-level radioactive waste.

Applications
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.

Catalysis
When it is finely divided, as with palladium on carbon, palladium forms a versatile catalyst; it speeds heterogeneous catalytic processes like hydrogenation, dehydrogenation, and petroleum cracking. Palladium is also essential to the Lindlar catalyst, also called Lindlar's Palladium. A large number of carbon–carbon bonding reactions in organic chemistry are facilitated by palladium compound catalysts. For example:


 * Heck reaction
 * Suzuki coupling
 * Tsuji-Trost reactions
 * Wacker process
 * Negishi reaction
 * Stille coupling
 * Sonogashira coupling

(See palladium compounds and palladium-catalyzed coupling reactions.)

When dispersed on conductive materials, palladium is an excellent electrocatalyst for oxidation of primary alcohols in alkaline media. Palladium is also a versatile metal for homogeneous catalysis, used in combination with a broad variety of ligands for highly selective chemical transformations.

In 2010, palladium-catalysed organic reactions were recognized by the Nobel Prize in Chemistry. A 2008 study showed that palladium is an effective catalyst for carbon-fluorine bonds.

Palladium catalysis is primarily employed in organic chemistry and industrial applications, although its use is growing as a tool for synthetic biology; in 2017, effective in vivo catalytic activity of palladium nanoparticles was demonstrated in mammals to treat disease.

Electronics
The second greatest application of palladium in electronics is in multi-layer ceramic capacitors in which palladium (and palladium-silver alloy) is used for electrodes. Palladium (sometimes alloyed with nickel) is used for component and connector plating in consumer electronics and in soldering materials. The electronic sector consumed 1.07 million troy ounces (33.2 tonnes) of palladium in 2006, according to a Johnson Matthey report.

Technology
Hydrogen easily diffuses through heated palladium, and membrane reactors with Pd membranes are used in the production of high purity hydrogen. Palladium is used in palladium-hydrogen electrode s in electrochemical studies. Palladium(II) chloride readily catalyzes carbon monoxide gas to carbon dioxide and is useful in carbon monoxide detectors.

Hydrogen storage
Palladium readily absorbs hydrogen at room temperatures, forming palladium hydride PdHx with x less than 1. While this property is common to many transition metals, palladium has a uniquely high absorption capacity and does not lose its ductility until x approaches 1. This property has been investigated in designing an efficient, inexpensive, and safe hydrogen fuel storage medium, though palladium itself is currently prohibitively expensive for this purpose. The content of hydrogen in palladium can be linked to magnetic susceptibility, which decreases with the increase of hydrogen and becomes zero for PdH0.62. At any higher ratio, the solid solution becomes diamagnetic.

Dentistry
Palladium is used in small amounts (about 0.5%) in some alloys of dental amalgam to decrease corrosion and increase the metallic lustre of the final restoration.

Jewelry
Palladium has been used as a precious metal in jewelry since 1939 as an alternative to platinum in the alloys called "white gold", where the naturally white color of palladium does not require rhodium plating. Palladium is much less dense than platinum. Similar to gold, palladium can be beaten into leaf as thin as 100 nm ($1/250,000$ in). Unlike platinum, palladium may discolor at temperatures above 400 C; it is relatively brittle.

Prior to 2004, the principal use of palladium in jewelry was the manufacture of white gold. Palladium is one of the three most popular alloying metals in white gold (nickel and silver can also be used). Palladium-gold is more expensive than nickel-gold, but seldom causes allergic reactions (though certain cross-allergies with nickel may occur).

When platinum became a strategic resource during World War II, many jewelry bands were made out of palladium. Palladium was little used in jewelry because of the technical difficulty of casting. With the casting problem resolved the use of palladium in jewelry increased, originally because platinum increased in price while the price of palladium decreased. In early 2004, when gold and platinum prices rose steeply, China began fabricating volumes of palladium jewelry, consuming 37 tonnes in 2005. Subsequent changes in the relative price of platinum lowered demand for palladium to 17.4 tonnes in 2009. Demand for palladium as a catalyst has increased the price of palladium to about 50% higher than that of platinum in January 2019.

In January 2010, hallmarks for palladium were introduced by assay offices in the United Kingdom, and hallmarking became mandatory for all jewelry advertising pure or alloyed palladium. Articles can be marked as 500, 950, or 999 parts of palladium per thousand of the alloy.

Fountain pen nibs made from gold are sometimes plated with palladium when a silver (rather than gold) appearance is desired. Sheaffer has used palladium plating for decades, either as an accent on otherwise gold nibs or covering the gold completely.

Photography
In the platinotype printing process, photographers make fine-art black-and-white prints using platinum or palladium salts. Often used with platinum, palladium provides an alternative to silver.

Toxicity
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.

Precautions
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.

Some palladium is emitted with the exhaust gases of cars with catalytic converters. Between 4 and 108 ng/km of palladium particulate is released by such cars, while the total uptake from food is estimated to be less than 2 µg per person a day. The second possible source of palladium is dental restoration, from which the uptake of palladium is estimated to be less than 15 µg per person per day. People working with palladium or its compounds might have a considerably greater uptake. For soluble compounds such as palladium chloride, 99% is eliminated from the body within 3 days.

The median lethal dose (LD50) of soluble palladium compounds in mice is 200 mg/kg for oral and 5 mg/kg for intravenous administration.