Palladium

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Palladium,  46Pd
Palladium (46 Pd).jpg
Palladium
Pronunciation /pəˈldiəm/ (pə-LAY-dee-əm)
Appearancesilvery white
Standard atomic weight Ar, std(Pd)106.42(1) [1]
Palladium in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson
Ni

Pd

Pt
rhodiumpalladiumsilver
Atomic number (Z)46
Group group 10
Period period 5
Block d-block
Element category   Transition metal
Electron configuration [ Kr ] 4d10
Electrons per shell
2, 8, 18, 18
Physical properties
Phase at  STP solid
Melting point 1828.05  K (1554.9 °C,2830.82 °F)
Boiling point 3236 K(2963 °C,5365 °F)
Density (near r.t.)12.023 g/cm3
when liquid (at m.p.)10.38 g/cm3
Heat of fusion 16.74  kJ/mol
Heat of vaporization 358 kJ/mol
Molar heat capacity 25.98 J/(mol·K)
Vapor pressure
P (Pa)1101001 k10 k100 k
at T (K)172118972117239527533234
Atomic properties
Oxidation states 0, +1, +2, +3, +4 (a mildly basic oxide)
Electronegativity Pauling scale: 2.20
Ionization energies
  • 1st: 804.4 kJ/mol
  • 2nd: 1870 kJ/mol
  • 3rd: 3177 kJ/mol
Atomic radius empirical:137  pm
Covalent radius 139±6 pm
Van der Waals radius 163 pm
Color lines in a spectral range Palladium spectrum visible.png
Color lines in a spectral range
Spectral lines of palladium
Other properties
Natural occurrence primordial
Crystal structure face-centered cubic (fcc)
Cubic-face-centered.svg
Speed of sound thin rod3070 m/s(at 20 °C)
Thermal expansion 11.8 µm/(m·K)(at 25 °C)
Thermal conductivity 71.8 W/(m·K)
Electrical resistivity 105.4 nΩ·m(at 20 °C)
Magnetic ordering paramagnetic [2]
Magnetic susceptibility +567.4·10−6 cm3/mol(288 K) [3]
Young's modulus 121 GPa
Shear modulus 44 GPa
Bulk modulus 180 GPa
Poisson ratio 0.39
Mohs hardness 4.75
Vickers hardness 400–600 MPa
Brinell hardness 320–610 MPa
CAS Number 7440-05-3
History
Namingafter asteroid Pallas, itself named after Pallas Athena
Discovery and first isolation William Hyde Wollaston (1802)
Main isotopes of palladium
Iso­tope Abun­dance Half-life (t1/2) Decay mode Pro­duct
100Pd syn 3.63 d ε 100Rh
γ
102Pd1.02% stable
103Pdsyn16.991 dε 103Rh
104Pd11.14%stable
105Pd22.33%stable
106Pd27.33%stable
107Pd trace 6.5×106 y β 107Ag
108Pd26.46%stable
110Pd11.72%stable
| references

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.

Chemical element a species of atoms having the same number of protons in the atomic nucleus

A chemical element is a species of atom having the same number of protons in their atomic nuclei. For example, the atomic number of oxygen is 8, so the element oxygen consists of all atoms which have 8 protons.

Symbol (chemistry) an arbitrary or conventional sign used in chemical science to represent a chemical element

In chemistry, a symbol is an abbreviation for a chemical element. Symbols for chemical elements normally consist of one or two letters from the Latin alphabet and are written with the first letter capitalised.

Atomic number number of protons found in the nucleus of an atom

The atomic number or proton number of a chemical element is the number of protons found in the nucleus of every atom of that element. The atomic number uniquely identifies a chemical element. It is identical to the charge number of the nucleus. In an uncharged atom, the atomic number is also equal to the number of electrons.

Contents

More than half the supply of palladium and its congener platinum is used in catalytic converters, which convert as much as 90% of the harmful gases in automobile exhaust (hydrocarbons, carbon monoxide, and nitrogen dioxide) into less noxious substances (nitrogen, carbon dioxide and water vapor). Palladium is also used in electronics, dentistry, medicine, hydrogen purification, chemical applications, groundwater treatment, and jewelry. Palladium is a key component of fuel cells, which react hydrogen with oxygen to produce electricity, heat, and water.

Congener (chemistry) related chemicals

In chemistry, congeners are related chemical substances "related to each other by origin, structure, or function".

Catalytic converter an exhaust emission control device that reduces toxic gases and pollutants in exhaust gas from an engine into less toxic pollutants by catalyzing a redox reaction

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. Catalytic converters are usually used with internal combustion engines fueled by either gasoline or diesel—including lean-burn engines as well as kerosene heaters and stoves.

Hydrocarbon organic compound consisting entirely of hydrogen and carbon

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 hydrocarbyls. Because carbon has 4 electrons in its outermost shell carbon has exactly four bonds to make, and is only stable if all 4 of these bonds are used.

Ore deposits of palladium and other PGMs are rare. The most extensive deposits have been found in the norite belt of the Bushveld Igneous Complex covering the Transvaal Basin in South Africa, the Stillwater Complex in Montana, United States; the Sudbury Basin and Thunder Bay District of Ontario, Canada, and the Norilsk Complex in Russia. Recycling is also a source, mostly from scrapped catalytic converters. The numerous applications and limited supply sources result in considerable investment interest.

Ore rock with valuable metals, minerals and elements

Ore is natural rock or sediment that contains desirable minerals, typically metals, that can be extracted from it. Ore is extracted from the earth through mining and refined, often via smelting, to extract the valuable element or elements.

Bushveld Igneous Complex mountain range

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 approximately 2 billion years old and is divided into four different limbs: the northern, southern, eastern, and western limbs. The Bushveld Complex comprises the Rustenburg Layered suite, the Lebowa Granites and the Rooiberg Felsics, that are overlain by the Karoo sediments. The site was first discovered around 1897 by Gustaaf Molengraaff.

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 eustasy, while plate tectonics played an intermittent role. The supergroup is made up of basal ‘protobasinal’ rocks, upon which followed the Black Reef Formation, Chuniespoort Group and the uppermost Pretoria Group.

Characteristics

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 orbital [ clarification needed ] migrate to fill the d orbitals because they have less energy.[ clarification needed ]

Group 10 element group of chemical elements

Group 10, numbered by current IUPAC style, is the group of chemical elements in the periodic table that consists of nickel (Ni), palladium (Pd), platinum (Pt), and perhaps also the chemically uncharacterized darmstadtium (Ds). All are d-block transition metals. All known isotopes of darmstadtium are radioactive with short half-lives, and are not known to occur in nature; only minute quantities have been synthesized in laboratories.

Atomic orbital A wave function for one electron in an atom having certain n and ℓ quantum numbers

In atomic theory and quantum mechanics, an atomic orbital is a mathematical function that describes the wave-like behavior of either one electron or a pair of electrons in an atom. This function can be used to calculate the probability of finding any electron of an atom in any specific region around the atom's nucleus. The term atomic orbital may also refer to the physical region or space where the electron can be calculated to be present, as defined by the particular mathematical form of the orbital.

Z Element No. of electrons/shell
28 nickel 2, 8, 16, 2 (or 2, 8, 17, 1)
46palladium2, 8, 18, 18, 0
78 platinum 2, 8, 18, 32, 17, 1
110 darmstadtium 2, 8, 18, 32, 32, 16, 2 (predicted)

This 5s0 configuration, unique in period 5, makes palladium the heaviest element having only one incomplete electron shell, with all shells above it empty.

The periodic table is laid out in rows to illustrate recurring (periodic) trends in the chemical behaviour of the elements as their atomic number increases: a new row is begun when chemical behaviour begins to repeat, meaning that elements with similar behaviour fall into the same vertical columns. The fifth period contains 18 elements, beginning with rubidium and ending with xenon. As a rule, period 5 elements fill their 5s shells first, then their 4d, and 5p shells, in that order; however, there are exceptions, such as rhodium.

In chemistry and atomic physics, an electron shell, or a principal energy level, may be thought of as an orbit followed by electrons around an atom's nucleus. The closest shell to the nucleus is called the "1 shell", followed by the "2 shell", then the "3 shell", and so on farther and farther from the nucleus. The shells correspond with the principal quantum numbers or are labeled alphabetically with letters used in the X-ray notation.

Palladium is a soft silver-white metal that resembles platinum. It is the least dense and has the lowest melting point of the platinum group metals. It is soft and ductile when annealed and is greatly increased in strength and hardness when cold-worked. Palladium dissolves slowly in concentrated nitric acid, in hot, concentrated sulfuric acid, and when finely ground, in hydrochloric acid. [4] It dissolves readily at room temperature in aqua regia.

Melting point temperature at which a solid turns liquid

The melting point of a substance is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends on pressure and is usually specified at a standard pressure such as 1 atmosphere or 100 kPa.

Ductility Material ability to undergo significant plastic deformation before rupture

Ductility is a measure of a material's ability to undergo significant plastic deformation before rupture, which may be expressed as percent elongation or percent area reduction from a tensile test. According to Shigley's Mechanical Engineering Design significant denotes about 5.0 percent elongation. See also Eq. 2–12, p. 50 for definitions of percent elongation and percent area reduction. Ductility is often characterized by a material's ability to be stretched into a wire.

In metallurgy and materials science, annealing is a heat treatment that alters the physical and sometimes chemical properties of a material to increase its ductility and reduce its hardness, making it more workable. It involves heating a material above its recrystallization temperature, maintaining a suitable temperature for a suitable amount of time, and then cooling.

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 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 Tc=3.2 K. [5]

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). [6] 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). [7]

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. [7]

Radiogenic 107Ag is a decay product of 107Pd and was first discovered in 1978 [8] in the Santa Clara [9] 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. [10]

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.

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

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. [11] 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. [12] [13]

PdCl2 + 2 L → PdCl2L2 (L = PhCN, PPh3, NH3, etc)

The complex bis(triphenylphosphine)palladium(II) dichloride is a useful catalyst. [14]

Palladium(II) acetate Palladium(II) acetate.jpg
Palladium(II) acetate

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): [15]

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. [16]

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. [17]

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. [18] Palladium(VI) was claimed in 2002, [19] [20] but subsequently disproven. [21] [22]

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. [23]

History

William Hyde Wollaston Wollaston William Hyde Jackson color.jpg
William Hyde Wollaston

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. [24] 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. [25] [26] He disclosed that he was the discoverer of palladium in a publication in 1805. [24] [27]

It was named by Wollaston in 1802 after the asteroid 2 Pallas, which had been discovered two months earlier. [4] 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. [25]

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. [28]

Most palladium is used for catalytic converters in the automobile industry. [29] 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. [30] The ensuing market panic drove the price to an all-time high of $1340 per troy ounce in January 2001. [31] 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. [32]

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. [33] Many were concerned about a steady supply of palladium in the wake of Russia's 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. [34] Those concerns pushed palladium prices to their highest level since 2001. [35] 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. [36] 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. [37]

Occurrence

Palladium output in 2005 2005palladium (mined).PNG
Palladium output in 2005

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. [38] Russia's company Norilsk Nickel ranks first among the largest palladium producers globally, accounting for 39% of the world’s production. [39]

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. [33] [40] Palladium is found in the rare minerals cooperite [41] and polarite. [42] Many more Pd minerals are known, but all of them are very rare. [43]

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. [44]

Applications

Cross section of a metal-core catalytic converter Aufgeschnittener Metall Katalysator fur ein Auto.jpg
Cross section of a metal-core catalytic converter
The Soviet 25-rouble commemorative palladium coin is a rare example of the monetary usage of palladium. 25 rubles palladium 1989 Ivan III.jpg
The Soviet 25-rouble commemorative palladium coin is a rare example of the monetary usage of palladium.

The largest use of palladium today is in catalytic converters. [45] Palladium is also used in jewelry, dentistry, [45] [46] watch making, blood sugar test strips, aircraft spark plugs, surgical instruments, and electrical contacts. [47] Palladium is also used to make professional transverse (concert or classical) flutes. [48] 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. [49] Because it adsorbs 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. [50] A large number of carbon–carbon bonding reactions in organic chemistry are facilitated by palladium compound catalysts. For example:

(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. [51] 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. [52]

Catalytic cycle for Kumada cross coupling reaction, which is widely used in the synthesis of fine chemicals. Kumada Catalytic Cycle.png
Catalytic cycle for Kumada cross coupling reaction, which is widely used in the synthesis of fine chemicals.

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. [53]

Electronics

The second greatest application of palladium in electronics is in multi-layer ceramic capacitors [54] in which palladium (and palladium-silver alloy) is used for electrodes. [45] Palladium (sometimes alloyed with nickel) is used for component and connector plating in consumer electronics [55] [56] 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. [57]

Technology

Hydrogen easily diffuses through heated palladium, [4] and membrane reactors with Pd membranes are used in the production of high purity hydrogen. [58] 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. [59]

Hydrogen storage

Palladium readily adsorbs hydrogen at room temperatures, forming palladium hydride PdHx with x less than 1. [60] 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. [61] 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. [62] 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. [63]

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. [64]

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 (1250,000 in). [4] Unlike platinum, palladium may discolor at temperatures above 400 °C (752 °F) [65] 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.[ citation needed ]

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). [45] Palladium-gold is more expensive than nickel-gold, but seldom causes allergic reactions (though certain cross-allergies with nickel may occur). [66]

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[ citation needed ] the use of palladium in jewelry increased, originally because platinum increased in price while the price of palladium decreased. [67] 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. [68] [69] Demand for palladium as a catalyst has increased the price of palladium to about 50% higher than that of platinum in January 2019. [70]

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. [71]

Toxicity

Palladium
Hazards
GHS pictograms GHS-pictogram-exclam.svg
GHS Signal word Warning
H317
P261, P273, P280, P302+352, P321, P333+313, P363, P501 [72]
NFPA 704 (fire diamond)
Flammability code 0: Will not burn. E.g. waterHealth code 0: Exposure under fire conditions would offer no hazard beyond that of ordinary combustible material. E.g. sodium chlorideReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no codePalladium
0
0
0

Palladium is a metal with low toxicity as conventionally measured (e.g. 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. [73] 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. [74]

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. [29] [75] [76] [77] [78]

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. [29]

The median lethal dose (LD50) of soluble palladium compounds in mice is 200 mg/kg for oral and 5 mg/kg for intravenous administration. [29]

See also

Related Research Articles

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Nickel is a chemical element with the symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile. Pure nickel, powdered to maximize the reactive surface area, shows a significant chemical activity, but larger pieces are slow to react with air under standard conditions because an oxide layer forms on the surface and prevents further corrosion (passivation). Even so, pure native nickel is found in Earth's crust only in tiny amounts, usually in ultramafic rocks, and in the interiors of larger nickel–iron meteorites that were not exposed to oxygen when outside Earth's atmosphere.

Osmium Chemical element with atomic number 76

Osmium 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 platinum ores. Osmium is the densest naturally occurring element, with an experimentally measured density of 22.59 g/cm3. Manufacturers use its alloys with platinum, iridium, and other platinum-group metals to make fountain pen nib tipping, electrical contacts, and in other applications that require extreme durability and hardness. The element's abundance in the Earth's crust is among the rarest.

Platinum Chemical element with atomic number 78

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 silver".

Rhodium Chemical element with atomic number 45

Rhodium is a chemical element with the symbol Rh and atomic number 45. It is a 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 only one naturally occurring isotope, 103Rh. Naturally occurring rhodium is usually found as free metal, as an alloy with similar metals, and rarely as a chemical compound in minerals such as bowieite and rhodplumsite. It is one of the rarest and most valuable precious metals.

Hydrogenation Chemical reaction between molecular hydrogen and another compound or element

Hydrogenation – meaning, to treat with hydrogen – is a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a catalyst such as nickel, palladium or platinum. The process is commonly employed to reduce or saturate organic compounds. Hydrogenation typically constitutes the addition of pairs of hydrogen atoms to a molecule, often an alkene. Catalysts are required for the reaction to be usable; non-catalytic hydrogenation takes place only at very high temperatures. Hydrogenation reduces double and triple bonds in hydrocarbons.

The platinum-group metals are six noble, precious metallic elements clustered together in the periodic table. These elements are all transition metals in the d-block.

The Heck reaction is the chemical reaction of an unsaturated halide with an alkene in the presence of a base and a palladium catalyst to form a substituted alkene. It is named after Tsutomu Mizoroki and Richard F. Heck. Heck was awarded the 2010 Nobel Prize in Chemistry, which he shared with Ei-ichi Negishi and Akira Suzuki, for the discovery and development of this reaction. This reaction was the first example of a carbon-carbon bond-forming reaction that followed a Pd(0)/Pd(II) catalytic cycle, the same catalytic cycle that is seen in other Pd(0)-catalyzed cross-coupling reactions. The Heck reaction is a way to substitute alkenes.

The Suzuki reaction is an organic reaction, classified as a cross-coupling reaction, where the coupling partners are a boronic acid and an organohalide catalyzed by a palladium(0) complex. It was first published in 1979 by Akira Suzuki and he shared the 2010 Nobel Prize in Chemistry with Richard F. Heck and Ei-ichi Negishi for their effort for discovery and development of palladium-catalyzed cross couplings in organic synthesis. In many publications this reaction also goes by the name Suzuki–Miyaura reaction and is also referred to as the Suzuki coupling. It is widely used to synthesize poly-olefins, styrenes, and substituted biphenyls. Several reviews have been published describing advancements and the development of the Suzuki Reaction. The general scheme for the Suzuki reaction is shown below where a carbon-carbon single bond is formed by coupling an organoboron species (R1-BY2) with a halide (R2-X) using a palladium catalyst and a base.

The Sonogashira reaction is a cross-coupling reaction used in organic synthesis to form carbon–carbon bonds. It employs a palladium catalyst as well as copper co-catalyst to form a carbon–carbon bond between a terminal alkyne and an aryl or vinyl halide.

Transition metal pincer complex

In chemistry, a transition metal pincer complex is a type of coordination complex with a pincer ligand. Pincer ligands are chelating agents that binds tightly to three adjacent coplanar sites in a meridional configuration. The inflexibility of the pincer-metal interaction confers high thermal stability to the resulting complexes. This stability is in part ascribed to the constrained geometry of the pincer, which inhibits cyclometallation of the organic substituents on the donor sites at each end. In the absence of this effect, cyclometallation is often a significant deactivation process for complexes, in particular limiting their ability to effect C-H bond activation. The organic substituents also define a hydrophobic pocket around the reactive coordination site. Stoichiometric and catalytic applications of pincer complexes have been studied at an accelerating pace since the mid-1970s. Most pincer ligands contain phosphines. Reactions of metal-pincer complexes are localized at three sites perpendicular to the plane of the pincer ligand, although in some cases one arm is hemi-labile and an additional coordination site is generated transiently. Early examples of pincer ligands were anionic with a carbanion as the central donor site and flanking phosphine donors; these compounds are referred to as PCP pincers.

Organopalladium chemistry is a branch of organometallic chemistry that deals with organic palladium compounds and their reactions. Palladium is often used as a catalyst in the reduction of alkenes and alkynes with hydrogen. This process involves the formation of a palladium-carbon covalent bond. Palladium is also prominent in carbon-carbon coupling reactions, as demonstrated in tandem reactions.

Palladium(II) chloride chemical compound

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 in organic synthesis. It is prepared by the reaction of chlorine with palladium metal at high temperatures.

Nanomaterial-based catalysts are usually heterogeneous catalysts broken up into metal nanoparticles in order to speed up the catalytic process. Metal nanoparticles have a higher surface area so there is increased catalytic activity because more catalytic reactions can occur at the same time. Nanoparticle catalysts can also be easily separated and recycled with more retention of catalytic activity than their bulk counterparts. These catalysts can play two different roles in catalytic processes: they can be the site of catalysis or they can act as a support for catalytic processes. They are typically used under mild conditions to prevent decomposition of the nanoparticles at extreme conditions.

Palladium on carbon, often referred to as Pd/C, is a form of palladium used as a catalyst. The metal is supported on activated carbon in order to maximize its surface area and activity.

The Negishi coupling is a widely employed transition metal catalyzed cross-coupling reaction. The reaction couples organic halides or triflates with organozinc compounds, forming carbon-carbon bonds (c-c) in the process. A palladium (0) species is generally utilized as the metal catalyst, though nickel is sometimes used:

In organic chemistry, the Kumada coupling is a type of cross coupling reaction, useful for generating carbon–carbon bonds by the reaction of a Grignard reagent and an organic halide. The procedure uses transition metal catalysts, typically nickel or palladium, to couple a combination of two alkyl, aryl or vinyl groups. The groups of Robert Corriu and Makoto Kumada reported the reaction independently in 1972.

A cross-coupling reaction in organic chemistry is a reaction where two fragments are joined together with the aid of a metal catalyst. In one important reaction type, a main group organometallic compound of the type R-M reacts with an organic halide of the type R'-X with formation of a new carbon-carbon bond in the product R-R'. Cross-coupling reaction are a subset of coupling reactions. It is often used in arylations.

Organoplatinum chemistry is the chemistry of organometallic compounds containing a carbon to platinum chemical bond, and the study of platinum as a catalyst in organic reactions. Organoplatinum compounds exist in oxidation state 0 to IV, with oxidation state II most abundant. The general order in bond strength is Pt-C (sp) > Pt-O > Pt-N > Pt-C (sp3). Organoplatinum and organopalladium chemistry are similar, but organoplatinum compounds are more stable and therefore less useful as catalysts.

Metal phosphine complex

In coordination chemistry phosphines are L-type ligands. Unlike most metal ammine complexes, metal phosphine complexes tend to be lipophilic, displaying good solubility in organic solvents. They also are compatible with metals in multiple oxidation states. Because of these two features, metal phosphine complexes are useful in homogeneous catalysis. Prominent examples of metal phosphine complexes include Wilkinson's catalyst (Rh(PPh3)3Cl), Grubbs' catalyst, and tetrakis(triphenylphosphine)palladium(0).

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