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Palladium is a
chemical element 400px, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same numbers of protons in their atomic nuclei. Unlike chemical compounds, chemical elements cannot be br ...
with the
symbol A symbol is a mark, sign, or word that indicates, signifies, or is understood as representing an idea, object, or relationship. Symbols allow people to go beyond what is known or seen by creating linkages between otherwise very different concep ...
 Pd and
atomic number 300px, The Rutherford–Bohr model of the hydrogen atom () or a hydrogen-like ion (). In this model it is an essential feature that the photon energy (or frequency) of the electromagnetic radiation emitted (shown) when an electron jumps from one ...
46. It is a rare and lustrous silvery-white metal discovered in 1803 by the English chemist
William Hyde Wollaston William Hyde Wollaston (; 6 August 1766 – 22 December 1828) was an English chemist and physicist who is famous for discovering the chemical elements palladium and rhodium. He also developed a way to process platinum ore into malleable ingots. ...
. He named it after the
asteroid Pallas
asteroid Pallas
, which was itself named after the
epithet An epithet (from el, ἐπίθετον, , neuter of , , "attributed, added") is a word or phrase, accompanying or occurring in place of a name and having entered common usage. It has various shades of meaning when applied to seemingly real or fict ...
of the Greek goddess
Athena Athena or Athene, often given the epithet Pallas, is an ancient Greek goddess associated with wisdom, handicraft, and warfare who was later syncretized with the Roman goddess Minerva. Athena was regarded as the patron and protectress of var ...
, acquired by her when she slew
Pallas Pallas may refer to: Astronomy * 2 Pallas asteroid ** Pallas family, a group of asteroids that includes 2 Pallas * Pallas (crater), a crater on Earth's moon Mythology * Pallas (Giant), a son of Uranus and Gaia, killed and flayed by Athena * Palla ...
. Palladium,
platinum Platinum is a chemical element with the symbol Pt and atomic number 78. It is a dense, malleable, ductile, highly unreactive, precious, silverish-white transition metal. Its name is derived from the Spanish term ''platino'', meaning "little si ...
,
rhodium Rhodium is a chemical element with the symbol Rh and atomic number 45. It is an extraordinarily rare, silvery-white, hard, corrosion-resistant, and chemically inert transition metal. It is a noble metal and a member of the platinum group. It has ...
,
ruthenium Ruthenium is a chemical element with the symbol Ru and atomic number 44. It is a rare transition metal belonging to the platinum group of the periodic table. Like the other metals of the platinum group, ruthenium is inert to most other chemicals ...
,
iridium Iridium is a chemical element with the symbol Ir and atomic number 77. A very hard, brittle, silvery-white transition metal of the platinum group, iridium is considered to be the second-densest metal (after osmium) with a density of as define ...
and
osmium Osmium (from Greek ὀσμή ''osme'', "smell") is a chemical element with the symbol Os and atomic number 76. It is a hard, brittle, bluish-white transition metal in the platinum group that is found as a trace element in alloys, mostly in platin ...
form a group of elements referred to as the
platinum group The platinum-group metals (abbreviated as the PGMs; alternatively, the platinoids, platinides, platidises, platinum group, platinum metals, platinum family or platinum-group elements (PGEs)) are six noble, precious metallic elements clustered toget ...
metals (PGMs). They have similar chemical properties, but palladium has the lowest melting point and is the least dense of them. More than half the supply of palladium and its congener platinum is used in
catalytic converter A catalytic converter is an exhaust emission control device that reduces toxic gases and pollutants in exhaust gas from an internal combustion engine into less-toxic pollutants by catalyzing a redox reaction (an oxidation and a reduction reaction ...
s, which convert as much as 90% of the harmful gases in automobile exhaust (
hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons from which one hydrogen atom has been removed are functional groups called hydrocarb ...
s,
carbon monoxide#REDIRECT Carbon monoxide#REDIRECT Carbon monoxide {{Redirect category shell, 1= {{R from other capitalisation ...
{{Redirect category shell, 1= {{R from other capitalisation ...
, and
nitrogen dioxide Nitrogen dioxide is a chemical compound with the formula .It is one of several nitrogen oxides. is an intermediate in the industrial synthesis of nitric acid, millions of tons of which are produced each year for use primarily in the production ...
) into less noxious substances (
nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. It was first discovered and isolated by Scottish physician Daniel Rutherford in 1772. Although Carl Wilhelm Scheele and Henry Cavendish had independently done so at about t ...
,
carbon dioxide Carbon dioxide (chemical formula ) is a colorless gas with a density about 53% higher than that of dry air. Carbon dioxide molecules consist of a carbon atom covalently double bonded to two oxygen atoms. It occurs naturally in Earth's atmospher ...

carbon dioxide
and
water vapor (99.9839 °C) , - , Boiling point , , - , specific gas constant , 461.5 J/(kg·K) , - , Heat of vaporization , 2.27 MJ/kg , - , Heat capacity , 1.864 kJ/(kg·K) Water vapor, water vapour or aqueous vapor is the gaseous phase of water. It is ...
). Palladium is also used in electronics,
dentistry Dentistry, also known as dental medicine and oral medicine, is a branch of medicine that consists of the study, diagnosis, prevention, and treatment of diseases, disorders, and conditions of the oral cavity, commonly in the dentition but also ...
,
medicine Medicine is the art, science, and practice of caring for a patient and managing the diagnosis, prognosis, prevention, treatment or palliation of their injury or disease. Medicine encompasses a variety of health care practices evolved to maintain ...
,
hydrogen purificationA hydrogen purifier is a device to purify hydrogen if hydrogen production is done from hydrocarbon sources, the ultra-high purified hydrogen is needed for applications like PEM fuel cells . Palladium membrane hydrogen purifiers The palladium membran ...
, chemical applications, groundwater treatment, and jewelry. Palladium is a key component of
fuel cell A fuel cell is an electrochemical cell that converts the chemical energy of a fuel (often hydrogen) and an oxidizing agent (often oxygen) into electricity through a pair of redox reactions. Fuel cells are different from most batteries in requir ...
s, which react hydrogen with oxygen to produce electricity, heat, and water. Ore
deposits A deposit account is a bank account maintained by a financial institution in which a customer can deposit and withdraw money. Deposit accounts can be savings accounts, current accounts or any of several other types of accounts explained below. Tr ...
of palladium and other PGMs are rare. The most extensive deposits have been found in the norite belt of the
Bushveld Igneous Complex The Bushveld Igneous Complex (BIC) is the largest layered igneous intrusion within the Earth's crust. It has been tilted and eroded forming the outcrops around what appears to be the edge of a great geological basin: the Transvaal Basin. It is app ...

Bushveld Igneous Complex
covering the
Transvaal Basin The Transvaal Basin is one of three basins of the Transvaal Supergroup on the Kaapvaal craton. The evolution of this 2.65–2.05 Ga Neoarchaean–Palaeoproterozoic basin is thought to have been derived largely from magmatism, palaeoclimate and eust ...
in South Africa, the Stillwater Complex in
Montana Montana () is a state in the Mountain West region of the United States. It is bordered by Idaho to the west; North Dakota and South Dakota to the east; Wyoming to the south; and by the Canadian provinces of Alberta, British Columbia, and Sa ...
, United States; the
Sudbury Basin The Sudbury Basin (), also known as Sudbury Structure or the Sudbury Nickel Irruptive, is a major geological structure in Ontario, Canada. It is the third-largest known impact crater or astrobleme on Earth, as well as one of the oldest. The crat ...
and
Thunder Bay District Thunder Bay District is a district and census division in Northwestern Ontario in the Canadian province of Ontario. The district seat is Thunder Bay. In 2016, the population was 146,048. The land area is ; the population density was . Most of th ...
of
Ontario , Label_map = yes , image_map = Ontario in Canada 2.svg , map_alt = Map showing Ontario's location east/central of Canada. , coordinates = , capital = Toronto , largest_city ...
, Canada, and the Norilsk Complex in Russia.
Recycling Recycling is the process of converting waste materials into new materials and objects. The recovery of energy from waste materials is often included in this concept. The recyclability of a material depends on its ability to reacquire the pro ...
is also a source, mostly from scrapped catalytic converters. The numerous applications and limited supply sources result in considerable
investment To invest is to allocate money in the expectation of some benefit/return in the future. In other words, to invest means owning an asset or an item with the goal of generating income from the investment or the appreciation of your investment whic ...
interest.


Characteristics

Palladium belongs to group 10 in the periodic table, but the configuration in the outermost electrons is in accordance with
Hund's ruleHund's rule of maximum multiplicity is a rule based on observation of atomic spectra, which is used to predict the ground state of an atom or molecule with one or more open electronic shells. The rule states that for a given electron configuration, t ...
. Electrons in the 5 ''s'' orbital migrate to fill the 4 ''d'' orbitals, as it is more energetically favorable to have a completely filled 4d10 shell instead of the 5s2 4d8 configuration. This 5s0 configuration, unique in period 5, makes palladium the heaviest element having only ''one'' incomplete
electron shell In chemistry and atomic physics, an electron shell may be thought of as an orbit followed by electrons around an atom's nucleus. The closest shell to the nucleus is called the " shell" (also called the "K shell"), followed by the " shell" (or "L ...
, with all shells above it empty. Palladium is a soft silver-white metal that resembles platinum. It is the least dense and has the lowest
melting point#REDIRECT Melting point#REDIRECT Melting point {{Redirect category shell, 1= {{R from other capitalisation ...
{{Redirect category shell, 1= {{R from other capitalisation ...
of the platinum group metals. It is soft and
ductile Ductility is a mechanical property commonly described as a material's amenability to drawing (e.g. into wire). In materials science, ductility is defined by the degree to which a material can sustain plastic deformation under tensile stress befo ...

ductile
when annealed and is greatly increased in strength and hardness when cold-worked. Palladium dissolves slowly in concentrated
nitric acid Nitric acid (), also known as ''aqua fortis'' (Latin for "strong water") and spirit of niter, is a highly corrosive mineral acid. The pure compound is colorless, but older samples tend to acquire a yellow cast due to decomposition into oxides of ...
, in hot, concentrated
sulfuric acid Sulfuric acid (American spelling) or sulphuric acid (Commonwealth spelling), also known as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with molecular formula H2SO4. It is a colorless, odorless and vis ...

sulfuric acid
, and when finely ground, in
hydrochloric acid Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid. It is a component of the gastric acid in the digestive ...
. It dissolves readily at room temperature in
aqua regia ''Aqua regia'' (; from Latin, "regal water" or "Royal water") is a mixture of nitric acid and hydrochloric acid, optimally in a molar ratio of 1:3.The relative concentrations of the two acids in water differ; values could be 65% w/v for nitric ac ...

aqua regia
. Palladium does not react with
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as well a ...
at standard temperature (and thus does not tarnish in
air
air
). Palladium heated to 800 °C will produce a layer of palladium(II) oxide (PdO). It may slowly develop a slight brownish coloration over time, likely due to the formation of a surface layer of its monoxide. Palladium films with defects produced by alpha particle bombardment at low temperature exhibit superconductivity having ''T''c=3.2 K.


Isotopes

Naturally occurring palladium is composed of seven
isotope Isotopes are variants of a particular chemical element which differ in neutron number, and consequently in nucleon number. All isotopes of a given element have the same number of protons but different numbers of neutrons in each atom. The term ...
s, six of which are stable. The most stable
radioisotope A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is an atom that has excess nuclear energy, making it unstable. This excess energy can be used in one of three ways: emitted from the nucleus as gamma radiation; transferred ...
s are 107Pd with a
half-life Half-life (symbol ''t''1⁄2) is the time required for a quantity to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable atoms sur ...
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 weight Relative atomic mass (symbol: ''A'') or atomic weight is a dimensionless physical quantity defined as the ratio of the average mass of atoms of a chemical element in a given sample to the atomic mass constant. The atomic mass constant (symbol: ''m ...
s 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 Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is conside ...
is
electron capture Electron capture (K-electron capture, also K-capture, or L-electron capture, L-capture) is a process in which the proton-rich nucleus of an electrically neutral atom absorbs an inner atomic electron, usually from the K or L electron shells. This ...

electron capture
with the primary
decay product The decay chain from lead-212 down to lead-208, showing the intermediate decay products. In nuclear physics, a decay product (also known as a daughter product, daughter isotope, radio-daughter, or daughter nuclide) is the remaining nuclide left ...
being rhodium. The primary mode of decay for those isotopes of Pd with atomic mass greater than 106 is
beta decay (the accompanying antineutrino is omitted). The inset shows beta decay of a free neutron. Neither of these depictions shows the intermediate virtual boson. In nuclear physics, beta decay (''β''-decay) is a type of radioactive decay in which a ...
with the primary product of this decay being
silver Silver is a chemical element with the symbol Ag (from the Latin ', derived from the Proto-Indo-European ''h₂erǵ'': "shiny" or "white") and atomic number 47. A soft, white, lustrous transition metal, it exhibits the highest electrical cond ...
.
Radiogenic A radiogenic nuclide is a nuclide that is produced by a process of radioactive decay. It may itself be radioactive (a radionuclide) or stable (a stable nuclide). Radiogenic nuclides (more commonly referred to as radiogenic isotopes) form some of t ...
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 The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar ...

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. File:Alpha-palladium(II)-chloride-xtal-3D-balls.png, Structure of ''α''-PdCl2 File:Pd6Cl12-from-xtal-1996-CM-3D-ellipsoids.png,
Structure of ''β''-PdCl2


Palladium(II)

Palladium(II) chloride Palladium(II) chloride, also known as palladium dichloride and palladous chloride, are the chemical compounds with the formula PdCl2. PdCl2 is a common starting material in palladium chemistry – palladium-based catalysts are of particular value i ...
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 Acetic acid , systematically named ethanoic acid , is a colourless liquid organic compound with the chemical formula CH3COOH (also written as CH3CO2H, C2H4O2, or HC2H3O2). Vinegar is no less than 4% acetic acid by volume, making acetic acid ...

acetic acid
to give
palladium(II) acetate Palladium(II) acetate is a chemical compound of palladium described by the formula d(O2CCH3)2sub>n, abbreviated d(OAc)2sub>n. It is more reactive than the analogous platinum compound. Depending on the value of n, the compound is soluble in many or ...
, 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 Benzonitrile is the chemical compound with the formula , abbreviated PhCN. This aromatic organic compound is a colorless liquid with a sweet bitter almond odour. It is mainly used as a precursor to the resin benzoguanamine. Production It is prep ...
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) Tetrakis(triphenylphosphine)palladium(0) (sometimes called quatrotriphenylphosphine) is the chemical compound d(P(C6H5)3)4 often abbreviated Pd(PPh3)4, or rarely PdP4. It is a bright yellow crystalline solid that becomes brown upon decomposition in ...
: :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) Tris(dibenzylideneacetone)dipalladium(0) or d2(dba)3is an organopalladium compound. The compound is a complex of palladium(0) with dibenzylideneacetone (dba). It is a dark-purple/brown solid, which is modestly soluble in organic solvents. Because ...

tris(dibenzylideneacetone)dipalladium(0)
(Pd2(dba)3), is prepared by reducing
sodium tetrachloropalladate Sodium tetrachloropalladate is an inorganic compound with the chemical formula Na2PdCl4. This salt, and the analogous alkali metal salts of the form M2PdCl4, may be prepared simply by reacting palladium(II) chloride with the appropriate alkali metal ...
in the presence of
dibenzylideneacetone Dibenzylideneacetone or dibenzalacetone, often abbreviated dba, is an organic compound with the formula C17H14O. It is a pale-yellow solid insoluble in water, but soluble in ethanol. Dibenzylideneacetone is used as a component in sunscreens and as a ...
. Palladium(0), as well as palladium(II), are catalysts in palladium-catalyzed coupling reactions, coupling reactions, as has been recognized by the 2010 Nobel Prize in Chemistry to Richard F. Heck, Ei-ichi Negishi, and Akira Suzuki (chemist), Akira Suzuki. Such reactions are widely practiced for the synthesis of fine chemicals. Prominent coupling reactions include the Heck reaction, Heck, Suzuki reaction, Suzuki, Sonogashira coupling, Stille reactions, and the Kumada coupling. Palladium(II) acetate,
tetrakis(triphenylphosphine)palladium(0) Tetrakis(triphenylphosphine)palladium(0) (sometimes called quatrotriphenylphosphine) is the chemical compound d(P(C6H5)3)4 often abbreviated Pd(PPh3)4, or rarely PdP4. It is a bright yellow crystalline solid that becomes brown upon decomposition in ...
(Pd(PPh3)4, and
tris(dibenzylideneacetone)dipalladium(0) Tris(dibenzylideneacetone)dipalladium(0) or d2(dba)3is an organopalladium compound. The compound is a complex of palladium(0) with dibenzylideneacetone (dba). It is a dark-purple/brown solid, which is modestly soluble in organic solvents. Because ...

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 the chemical elements, 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 (chemist), 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 Rhodium is a chemical element with the symbol Rh and atomic number 45. It is an extraordinarily rare, silvery-white, hard, corrosion-resistant, and chemically inert transition metal. It is a noble metal and a member of the platinum group. It has ...
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 ''Aqua regia'' (; from Latin, "regal water" or "Royal water") is a mixture of nitric acid and hydrochloric acid, optimally in a molar ratio of 1:3.The relative concentrations of the two acids in water differ; values could be 65% w/v for nitric ac ...

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 Adverse effect (medicine), side-effects, and was later replaced by more effective drugs. Most palladium is used for
catalytic converter A catalytic converter is an exhaust emission control device that reduces toxic gases and pollutants in exhaust gas from an internal combustion engine into less-toxic pollutants by catalyzing a redox reaction (an oxidation and a reduction reaction ...
s 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 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 United States dollar, 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 Annexation of Crimea by the Russian Federation, annexation of Crimea, partly as sanctions could hamper Russian palladium exports; any restrictions on Russian palladium exports could have exacerbated what was 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 contract, futures climbed past $1,344 per ounce for the first time on record, mainly due to the strong demand from the automotive industry. Palladium reached on 6 January 2020, passing $2,000 per troy ounce the first time.


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, accounting 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 mining, placer deposits of the Ural Mountains, Australia, Ethiopia, North America, 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 The Sudbury Basin (), also known as Sudbury Structure or the Sudbury Nickel Irruptive, is a major geological structure in Ontario, Canada. It is the third-largest known impact crater or astrobleme on Earth, as well as one of the oldest. The crat ...
,
Ontario , Label_map = yes , image_map = Ontario in Canada 2.svg , map_alt = Map showing Ontario's location east/central of Canada. , coordinates = , capital = Toronto , largest_city ...
, and the Norilsk, Norilsk–Talnakh deposits in Siberia. The other large deposit is the Merensky Reef
platinum group The platinum-group metals (abbreviated as the PGMs; alternatively, the platinoids, platinides, platidises, platinum group, platinum metals, platinum family or platinum-group elements (PGEs)) are six noble, precious metallic elements clustered toget ...
metals deposit within the
Bushveld Igneous Complex The Bushveld Igneous Complex (BIC) is the largest layered igneous intrusion within the Earth's crust. It has been tilted and eroded forming the outcrops around what appears to be the edge of a great geological basin: the Transvaal Basin. It is app ...

Bushveld Igneous Complex
South Africa. The Stillwater igneous complex of
Montana Montana () is a state in the Mountain West region of the United States. It is bordered by Idaho to the west; North Dakota and South Dakota to the east; Wyoming to the south; and by the Canadian provinces of Alberta, British Columbia, and Sa ...
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 (mineral), 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 Dentistry, also known as dental medicine and oral medicine, is a branch of medicine that consists of the study, diagnosis, prevention, and treatment of diseases, disorders, and conditions of the oral cavity, commonly in the dentition but also ...
, watch making, blood sugar test strips, aircraft spark plugs, surgical instruments, and electrical contacts. Palladium is also used to make professional transverse flute, 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 Silver is a chemical element with the symbol Ag (from the Latin ', derived from the Proto-Indo-European ''h₂erǵ'': "shiny" or "white") and atomic number 47. A soft, white, lustrous transition metal, it exhibits the highest electrical cond ...
and platinum. Because it Adsorption, adsorbs hydrogen, palladium was a key component of the controversial cold fusion experiments of the late 1980s.


Catalysis

When it is finely divided, as with palladium on carbon, palladium forms a versatile catalyst; it speeds Heterogeneous catalysis, heterogeneous catalytic processes like hydrogenation, dehydrogenation, and cracking (chemistry), 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 reaction, Tsuji-Trost reactions * Wacker process * Negishi coupling, Negishi reaction * Stille coupling * Sonogashira coupling (See #Compounds, 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 the Nobel Prize in Chemistry was awarded "for palladium-catalyzed cross couplings in organic synthesis" to Richard F. Heck, Ei-ichi Negishi and Akira Suzuki (chemist), Akira Suzuki. 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 or can be used for component and connector plating in consumer electronics and in soldering materials. The electronic sector consumed 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 electrodes in electrochemical studies.
Palladium(II) chloride Palladium(II) chloride, also known as palladium dichloride and palladous chloride, are the chemical compounds with the formula PdCl2. PdCl2 is a common starting material in palladium chemistry – palladium-based catalysts are of particular value i ...
readily catalyzes carbon monoxide gas to carbon dioxide and is useful in carbon monoxide detectors.


Hydrogen storage

Palladium readily Adsorption, adsorbs 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 Lustre (mineralogy)#Metallic lustre, 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 "Colored gold#White gold, white gold", where the naturally white color of palladium does not require Plating#Rhodium plating, rhodium plating. Palladium is much less dense than platinum. Similar to gold, palladium can be beaten into Metal leaf, leaf as thin as 100 nm ( in). Unlike platinum, palladium may discolor at temperatures above due to oxidation, making it more brittle and thus less suitable for use in jewelry; to prevent this, palladium intended for jewelry is heated under controlled conditions. 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 (metalworking), 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 nib (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 (e.g. Median lethal dose, 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 converter A catalytic converter is an exhaust emission control device that reduces toxic gases and pollutants in exhaust gas from an internal combustion engine into less-toxic pollutants by catalyzing a redox reaction (an oxidation and a reduction reaction ...
s. 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 administration, oral and 5 mg/kg for intravenous administration.


See also

* 2000s commodities boom * Palladium as an investment * Pseudo palladium


References


External links


Palladium
at ''The Periodic Table of Videos'' (University of Nottingham)
Current and Historical Palladium Price


* {{Authority control Palladium, Chemical elements Noble metals Transition metals Precious metals Native element minerals