Palladium
Encyclopedia
Palladium is a chemical element
with the chemical symbol
Pd and an atomic number
of 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.
The unique properties of palladium and other platinum group metals account for their widespread use. A quarter of all goods manufactured today either contain PGMs or have a significant part in their manufacturing process played by PGMs. Over half of the supply of palladium and its congener
platinum goes into catalytic converter
s, which convert up to 90% of harmful gases from auto exhaust (hydrocarbons, carbon monoxide
, and nitrogen dioxide
) into less-harmful substances (nitrogen
, carbon dioxide
and water vapor
). Palladium is also used in electronics, dentistry
, medicine
, hydrogen purification, chemical applications, and groundwater treatment. Palladium plays a key role in the technology used for fuel cell
s, which combine hydrogen and oxygen to produce electricity, heat, and water.
Ore
deposits of palladium and other PGMs are rare, and 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 Thunder Bay District
of Ontario
, Canada, and the Norilsk Complex
in Russia. Recycling
is also a source of palladium, mostly from scrapped catalytic converters. The numerous applications and limited supply sources of palladium result in the metal attracting considerable investment
interest.
in the periodic table:
but has a very atypical configuration in its outermost electron shells compared to the other members of group 10 (see also niobium
(41), ruthenium
(44), and rhodium
(45)).
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 greatly increases its strength and hardness when it is cold-worked. Palladium dissolves slowly in sulfuric
, nitric
and hydrochloric acid
. This metal also does not react with oxygen
at normal temperatures (and thus does not tarnish in air
). Palladium heated to 800°C will produce a layer of palladium(II) oxide (PdO). It lightly tarnishes in moist atmosphere containing sulfur.
The metal has the uncommon ability to absorb up to 900 times its own volume of hydrogen at room temperatures. It is thought that this possibly forms palladium hydride
(PdH2) but it is not yet clear if this is a true chemical compound
. When palladium has absorbed large amounts of hydrogen, it will expand slightly in size.
Common oxidation state
s of palladium are 0, +1, +2 and +4. Although originally +3 was thought of as one of the fundamental oxidation states of palladium, there is no evidence for palladium occurring in the +3 oxidation state; this has been investigated via X-ray diffraction for a number of compounds, indicating a dimer of palladium(II) and palladium(IV) instead. In 2002, palladium(VI) was first reported.
s, which includes six stable isotopes. The most stable radioisotopes are 107Pd with a half-life
of 6.5 million years (found in nature), 103Pd with a half-life of 17 days, and 100Pd with a half-life of 3.63 days. Eighteen other radioisotopes have been characterized with atomic weight
s ranging from 90.94948(64) u
(91Pd) to 122.93426(64) u (123Pd). Most of these have half-lives that are less than a half-hour, except 101Pd (half-life: 8.47 hours), 109Pd (half-life: 13.7 hours), and 112Pd (half-life: 21 hours).
The primary decay mode before the most abundant stable isotope, 106Pd, is electron capture
and the primary mode after is beta decay
. The primary decay product
before 106Pd is rhodium and the primary product after is 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.
Elemental palladium reacts with chlorine to give palladium(II) chloride
; it dissolves in nitric acid and precipitates palladium(II) acetate
on addition of acetic acid
. These two compounds and the bromide
are reactive and relatively inexpensive, making them convenient entry points to palladium chemistry. All three are not monomeric; the chloride and bromide often must be refluxed in acetonitrile
to obtain the more reactive acetonitrile complex monomers, for example:
Palladium(II) chloride is the principal starting material for many other palladium catalysts. It is used to prepare heterogeneous palladium catalysts: palladium on barium sulfate, palladium on carbon, and palladium chloride on carbon. It reacts with triphenylphosphine in coordinating solvents to give bis(triphenylphosphine)palladium(II) dichloride
, a useful catalyst. Where desired, the catalyst may be formed in situ.
Reduction of this phosphine complex with hydrazine
with more phosphine gives tetrakis(triphenylphosphine)palladium(0)
, one of the two major palladium(0) complexes:
The other major palladium(0) complex, tris(dibenzylideneacetone)dipalladium(0)
(Pd2(dba)3), is prepared by reducing sodium tetrachloropalladate
in the presence of dibenzylideneacetone
.
The great many reactions in which palladium compounds serve as catalysts are collectively known as palladium-catalyzed coupling reactions
. Prominent examples include the Heck
, Suzuki
and Stille reaction
s. Palladium(II) acetate
, tetrakis(triphenylphosphine)palladium(0)
(Pd(PPh3)4, and tris(dibenzylideneacetone)dipalladium(0)
(Pd2(dba)3) are useful in this regard, either as catalysts or as starting points to catalysts.
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 enough of the material and offered it, without naming the discoverer, in a small shop in Soho
in April 1803. After harsh criticism that palladium is an alloy of platinum and mercury by Richard Chenevix
, Wollaston anonymously offered a reward of 20 British pounds 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 to be the discoverer of palladium in a publication in 1805.
It was named by Wollaston in 1802 after the asteroid Pallas, which had been discovered two years 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 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.
Palladium's affinity for hydrogen led it to play an essential role in the Fleischmann–Pons experiment in 1989.
In the run up to 2000, the Russian supply of palladium to the global market was repeatedly delayed and disrupted because the export quota was not granted on time, for political reasons. The ensuing market panic drove the price to an all-time high of $1100 per troy ounce
in January 2001. Around this time, the Ford Motor Company
, fearing auto vehicle production disruption due to a possible palladium shortage, stockpiled large amounts of the metal purchased near the price high. When prices fell in early 2001, Ford lost nearly US$
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 tonne
s in 2006 according to the United States Geological Survey
. Most palladium is used for catalytic converter
s in the automobile industry.
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In 2007, Russia was the top producer of palladium, with a 44% world share, followed by South Africa with 40%. Canada with 6% and the U.S. with 5% are the only other substantial producers of palladium.
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
.
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.
The largest use of palladium today is in catalytic converters. Palladium is also used in jewelry, in dentistry
, watch
making, in blood sugar test strips, in aircraft spark plug
s and in the production of surgical instruments and electrical contacts. Palladium is also used to make professional transverse flute
s. 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
.
, palladium forms a versatile catalyst and speeds up hydrogenation
and dehydrogenation
reactions, as well as in petroleum cracking
. A large number of carbon-carbon bond
forming reactions in organic chemistry
(such as the Heck and Suzuki coupling) are facilitated by catalysis with palladium compounds. (see #Compounds and palladium-catalyzed coupling reactions
) In addition, palladium, when dispersed on conductive materials, proves to be an excellent electrocatalyst for oxidation of primary alcohols in alkaline media. In 2010, palladium-catalysed organic reactions were recognised by the Nobel Prize in Chemistry
. Palladium is also a versatile metal for homogeneous catalysis
. It is used in combination with a broad variety of ligands for highly selective chemical transformations. A 2008 study showed that palladium is an effective catalyst for making carbon-fluoride bonds. Palladium is found in the Lindlar catalyst
, also called Lindlar's Palladium.
It is also used in plating of electronic components 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.
s with Pd membranes are therefore used for the production of high purity hydrogen. Palladium is a part of the palladium-hydrogen electrode
in electrochemical studies. Palladium(II) chloride
can oxidize large amounts of carbon monoxide gas, and is used in carbon monoxide detectors.
is metallic palladium that contains a substantial quantity of hydrogen within its crystal lattice. At room temperature
and atmospheric pressure
, palladium can absorb up to 900 times its own volume of hydrogen in a reversible process. This property has been investigated because hydrogen storage is of such interest and a better understanding of what happens at the molecular level could give clues to designing improved metal hydrides. A palladium-based store, however, would be prohibitively expensive owing to the cost of the metal.
Palladium itself has been used as a precious metal in jewelry since 1939, as an alternative to platinum for making white gold. This use resulted from the naturally white color of palladium, which required no rhodium plating. Palladium is proportionally much lighter than platinum. Similar to gold, palladium can be beaten into a thin leaf form as thin as 100 nm (1/250,000 in). Unlike platinum, palladium may discolor upon heating to above 400 °C; it is relatively brittle and reacts with strong acids such as nitric acid
.
Palladium is one of the three most popular metals used to make white gold alloys (nickel
and silver can also be used). Palladium-gold is a more expensive alloy than nickel-gold, but seldom causes allergic reactions (though certain cross-allergies with nickel may occur).
When platinum was declared a strategic government resource during World War II, many jewelry bands were made out of palladium. As recently as September 2001, palladium was more expensive than platinum and rarely used in jewelry also due to the technical obstacle of casting. However, the casting problem has been resolved and its use in jewelry has increased because of a large spike in the price of platinum and a drop in the price of palladium.
Prior to 2004, the principal use of palladium in jewelry was the manufacture of white gold. In early 2004, when gold and platinum prices rose steeply, China began fabricating significant volumes of palladium jewelry and used 37 tonne
s of palladium for this purpose in 2005. Changes of the relative price between palladium and platinum after 2008 lowered demand for palladium to 17.4 tonnes in 2009.
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.
has been reported, the amount of data on the effects of exposure to palladium is limited. It has been shown that people with an allergic reaction to palladium also react to nickel, making it possible to avoid the use of dental alloys containing palladium on those so allergic.
A considerable amount of palladium is distributed by the exhausts of cars with catalytic converter
s. Between 4 and 108 ng/km of palladium particulate is released by such cars. The total uptake of from food is estimated to be lower than 2 µg per person and day. The second possible source for palladium is alloys for dental restoration, there the possible uptake of palladium is estimated to be lower than 15 µg per person and day. People working with palladium or its compounds might have a considerably higher uptake. For soluble compounds like 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.
Chemical element
A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. Familiar examples of elements include carbon, oxygen, aluminum, iron, copper, gold, mercury, and lead.As of November 2011, 118 elements...
with the chemical symbol
Chemical symbol
A chemical symbol is a 1- or 2-letter internationally agreed code for a chemical element, usually derived from the name of the element, often in Latin. Only the first letter is capitalised...
Pd and an atomic number
Atomic number
In chemistry and physics, the atomic number is the number of protons found in the nucleus of an atom and therefore identical to the charge number of the nucleus. It is conventionally represented by the symbol Z. The atomic number uniquely identifies a chemical element...
of 46. It is a rare and lustrous silvery-white metal discovered in 1803 by William Hyde Wollaston
William Hyde Wollaston
William Hyde Wollaston FRS was an English chemist and physicist who is famous for discovering two chemical elements and for developing a way to process platinum ore.-Biography:...
. He named it after the asteroid Pallas
2 Pallas
Pallas, formally designated 2 Pallas, is the second asteroid to have been discovered , and one of the largest. It is estimated to constitute 7% of the mass of the asteroid belt, and its diameter of 530–565 km is comparable to, or slightly larger than, that of 4 Vesta. It is however 20%...
, which was itself named after the epithet
Epithet
An epithet or byname is a descriptive term 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 fictitious people, divinities, objects, and binomial nomenclature. It is also a descriptive title...
of the Greek
Greek mythology
Greek mythology is the body of myths and legends belonging to the ancient Greeks, concerning their gods and heroes, the nature of the world, and the origins and significance of their own cult and ritual practices. They were a part of religion in ancient Greece...
goddess Athena
Athena
In Greek mythology, Athena, Athenê, or Athene , also referred to as Pallas Athena/Athene , is the goddess of wisdom, courage, inspiration, civilization, warfare, strength, strategy, the arts, crafts, justice, and skill. Minerva, Athena's Roman incarnation, embodies similar attributes. Athena is...
, acquired by her when she slew Pallas
Pallas (daughter of Triton)
In Greek mythology, Pallas was the daughter of Triton. Acting as a foster parent to Zeus’s daughter Athena, Triton raised her alongside his own daughter. During a friendly fight between the two goddesses, Athena was protected from harm by Zeus but mortally wounded Pallas. Out of sadness and...
. Palladium, platinum
Platinum
Platinum is a chemical element with the chemical symbol Pt and an atomic number of 78. Its name is derived from the Spanish term platina del Pinto, which is literally translated into "little silver of the Pinto River." It is a dense, malleable, ductile, precious, gray-white transition metal...
, rhodium
Rhodium
Rhodium is a chemical element that is a rare, silvery-white, hard and chemically inert transition metal and a member of the platinum group. It has the chemical symbol Rh and atomic number 45. It is composed of only one isotope, 103Rh. Naturally occurring rhodium is found as the free metal, alloyed...
, ruthenium
Ruthenium
Ruthenium is a chemical element with 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 chemicals. The Russian scientist Karl Ernst Claus discovered the element...
, iridium
Iridium
Iridium is the chemical element with atomic number 77, and is represented by the symbol Ir. A very hard, brittle, silvery-white transition metal of the platinum family, iridium is the second-densest element and is the most corrosion-resistant metal, even at temperatures as high as 2000 °C...
and osmium
Osmium
Osmium is a chemical element with the symbol Os and atomic number 76. Osmium is a hard, brittle, blue-gray or blue-blacktransition metal in the platinum family, and is the densest natural element. Osmium is twice as dense as lead. The density of osmium is , slightly greater than that of iridium,...
form a group of elements referred to as the platinum group
Platinum group
The platinum group metals is a term used sometimes to collectively refer to six metallic elements clustered together in the periodic table.These elements are all transition metals, lying in the d-block .The six...
metals (PGMs). These have similar chemical properties, but palladium has the lowest melting point and is the least dense of them.
The unique properties of palladium and other platinum group metals account for their widespread use. A quarter of all goods manufactured today either contain PGMs or have a significant part in their manufacturing process played by PGMs. Over half of the supply of palladium and its congener
Congener
Congener has several different meanings depending on the field in which it is used. Colloquially, it is used to mean a person or thing like another, in character or action.-Biology:In biology, congeners are organisms within the same genus...
platinum goes into catalytic converter
Catalytic converter
A catalytic converter is a device used to convert toxic exhaust emissions from an internal combustion engine into non-toxic substances. Inside a catalytic converter, a catalyst stimulates a chemical reaction in which noxious byproducts of combustion are converted to less toxic substances by dint...
s, which convert up to 90% of harmful gases from auto exhaust (hydrocarbons, carbon monoxide
Carbon monoxide
Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...
, and nitrogen dioxide
Nitrogen dioxide
Nitrogen dioxide is the 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. This reddish-brown toxic gas has a characteristic sharp, biting odor and is a prominent...
) into less-harmful substances (nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
, carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
and water vapor
Water vapor
Water vapor or water vapour , also aqueous vapor, is the gas phase of water. It is one state of water within the hydrosphere. Water vapor can be produced from the evaporation or boiling of liquid water or from the sublimation of ice. Under typical atmospheric conditions, water vapor is continuously...
). Palladium is also used in electronics, dentistry
Dentistry
Dentistry is the branch of medicine that is involved in the study, diagnosis, prevention, and treatment of diseases, disorders and conditions of the oral cavity, maxillofacial area and the adjacent and associated structures and their impact on the human body. Dentistry is widely considered...
, medicine
Medicine
Medicine is the science and art of healing. It encompasses a variety of health care practices evolved to maintain and restore health by the prevention and treatment of illness....
, hydrogen purification, chemical applications, and groundwater treatment. Palladium plays a key role in the technology used for fuel cell
Fuel cell
A fuel cell is a device that converts the chemical energy from a fuel into electricity through a chemical reaction with oxygen or another oxidizing agent. Hydrogen is the most common fuel, but hydrocarbons such as natural gas and alcohols like methanol are sometimes used...
s, which combine hydrogen and oxygen to produce electricity, heat, and water.
Ore
Ore
An ore is a type of rock that contains minerals with important elements including metals. The ores are extracted through mining; these are then refined to extract the valuable element....
deposits of palladium and other PGMs are rare, and the most extensive deposits have been found in the norite belt of the Bushveld Igneous Complex
Bushveld igneous complex
The Bushveld Igneous Complex is a large layered igneous intrusion within the Earth's crust which has been tilted and eroded and now outcrops around what appears to be the edge of a great geological basin, the Transvaal Basin. Located in South Africa, the BIC contains some of the richest ore...
covering the Transvaal Basin
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 eustasy, while plate tectonics played an intermittent role...
in South Africa, the Stillwater Complex
Stillwater igneous complex
The Stillwater igneous complex is a large layered intrusion located in southern Montana in Stillwater, Sweet Grass and Park Counties. The complex is exposed across 30 miles of the north flank of the Beartooth Mountain Range. The complex has extensive reserves of chromium ore and has a history of...
in Montana
Montana
Montana is a state in the Western United States. The western third of Montana contains numerous mountain ranges. Smaller, "island ranges" are found in the central third of the state, for a total of 77 named ranges of the Rocky Mountains. This geographical fact is reflected in the state's name,...
, United States, the Thunder Bay District
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....
of Ontario
Ontario
Ontario is a province of Canada, located in east-central Canada. It is Canada's most populous province and second largest in total area. It is home to the nation's most populous city, Toronto, and the nation's capital, Ottawa....
, Canada, and the Norilsk Complex
Norilsk
Norilsk is an industrial city in Krasnoyarsk Krai, Russia, located between the Yenisei River and the Taymyr Peninsula. Population: It was granted city status in 1953. It is the northernmost city in Siberia and the world's second largest city north of the Arctic Circle...
in Russia. Recycling
Recycling
Recycling is processing used materials into new products to prevent waste of potentially useful materials, reduce the consumption of fresh raw materials, reduce energy usage, reduce air pollution and water pollution by reducing the need for "conventional" waste disposal, and lower greenhouse...
is also a source of palladium, mostly from scrapped catalytic converters. The numerous applications and limited supply sources of palladium result in the metal attracting considerable investment
Palladium as an investment
Like other precious metals, palladium may be used as an investment. Palladium price peaked near US$1,100 per troy ounce in January 2001 driven mainly on speculation of the catalytic converter demand from the automobile industry. Palladium is traded in the spot market with the code "XPD"...
interest.
Characteristics
Palladium belongs to group 10Group 10 element
A Group 10 element is one in the series of elements in group 10 in the periodic table, which consists of the transition metals nickel , palladium , platinum , and darmstadtium ....
in the periodic table:
| Z Atomic number In chemistry and physics, the atomic number is the number of protons found in the nucleus of an atom and therefore identical to the charge number of the nucleus. It is conventionally represented by the symbol Z. The atomic number uniquely identifies a chemical element... | Element Chemical element A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. Familiar examples of elements include carbon, oxygen, aluminum, iron, copper, gold, mercury, and lead.As of November 2011, 118 elements... | No. of electrons/shell Electron shell 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 "1 shell" , followed by the "2 shell" , then the "3 shell" , and so on further and further from the nucleus. The shell letters K,L,M,..... |
|---|---|---|
| 28 | nickel Nickel Nickel is a chemical element with the chemical 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... |
2, 8, 16, 2 or 2, 8, 17, 1 |
| 46 | palladium | 2, 8, 18, 18 |
| 78 | platinum Platinum Platinum is a chemical element with the chemical symbol Pt and an atomic number of 78. Its name is derived from the Spanish term platina del Pinto, which is literally translated into "little silver of the Pinto River." It is a dense, malleable, ductile, precious, gray-white transition metal... |
2, 8, 18, 32, 17, 1 |
| 110 | darmstadtium Darmstadtium Darmstadtium is a chemical element with the symbol Ds and atomic number 110. It is placed as the heaviest member of group 10, but no known isotope is sufficiently stable to allow chemical experiments to confirm its placing in that group... |
unknown |
but has a very atypical configuration in its outermost electron shells compared to the other members of group 10 (see also niobium
Niobium
Niobium or columbium , is a chemical element with the symbol Nb and atomic number 41. It's a soft, grey, ductile transition metal, which is often found in the pyrochlore mineral, the main commercial source for niobium, and columbite...
(41), ruthenium
Ruthenium
Ruthenium is a chemical element with 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 chemicals. The Russian scientist Karl Ernst Claus discovered the element...
(44), and rhodium
Rhodium
Rhodium is a chemical element that is a rare, silvery-white, hard and chemically inert transition metal and a member of the platinum group. It has the chemical symbol Rh and atomic number 45. It is composed of only one isotope, 103Rh. Naturally occurring rhodium is found as the free metal, alloyed...
(45)).
Palladium is a soft silver-white metal that resembles platinum. It is the least dense and has the lowest melting point
Melting point
The melting point of a solid 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 standard atmospheric pressure...
of the platinum group metals. It is soft and ductile when annealed
Annealing (metallurgy)
Annealing, in metallurgy and materials science, is a heat treatment wherein a material is altered, causing changes in its properties such as strength and hardness. It is a process that produces conditions by heating to above the recrystallization temperature, maintaining a suitable temperature, and...
and greatly increases its strength and hardness when it is cold-worked. Palladium dissolves slowly in sulfuric
Sulfuric acid
Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...
, nitric
Nitric acid
Nitric acid , also known as aqua fortis and spirit of nitre, is a highly corrosive and toxic strong acid.Colorless when pure, older samples tend to acquire a yellow cast due to the accumulation of oxides of nitrogen. If the solution contains more than 86% nitric acid, it is referred to as fuming...
and hydrochloric acid
Hydrochloric acid
Hydrochloric acid is a solution of hydrogen chloride in water, that is a highly corrosive, strong mineral acid with many industrial uses. It is found naturally in gastric acid....
. This metal also does not react with oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
at normal temperatures (and thus does not tarnish in air
Earth's atmosphere
The atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...
). Palladium heated to 800°C will produce a layer of palladium(II) oxide (PdO). It lightly tarnishes in moist atmosphere containing sulfur.
The metal has the uncommon ability to absorb up to 900 times its own volume of hydrogen at room temperatures. It is thought that this possibly forms palladium hydride
Palladium hydride
Palladium hydride is metallic palladium that contains a substantial quantity of hydrogen within its crystal lattice. At room temperature and atmospheric pressure, palladium can absorb up to 900 times its own volume of hydrogen. This process is reversible...
(PdH2) but it is not yet clear if this is a true chemical compound
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
. When palladium has absorbed large amounts of hydrogen, it will expand slightly in size.
Common oxidation state
Oxidation state
In chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. The formal oxidation state is the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic. Oxidation states are typically represented by...
s of palladium are 0, +1, +2 and +4. Although originally +3 was thought of as one of the fundamental oxidation states of palladium, there is no evidence for palladium occurring in the +3 oxidation state; this has been investigated via X-ray diffraction for a number of compounds, indicating a dimer of palladium(II) and palladium(IV) instead. In 2002, palladium(VI) was first reported.
Isotopes
Naturally occurring palladium is composed of seven isotopeIsotope
Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...
s, which includes six stable isotopes. The most stable radioisotopes are 107Pd with a half-life
Half-life
Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to...
of 6.5 million years (found in nature), 103Pd with a half-life of 17 days, and 100Pd with a half-life of 3.63 days. Eighteen other radioisotopes have been characterized with atomic weight
Atomic weight
Atomic weight is a dimensionless physical quantity, the ratio of the average mass of atoms of an element to 1/12 of the mass of an atom of carbon-12...
s ranging from 90.94948(64) u
Atomic mass unit
The unified atomic mass unit or dalton is a unit that is used for indicating mass on an atomic or molecular scale. It is defined as one twelfth of the rest mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state, and has a value of...
(91Pd) to 122.93426(64) u (123Pd). Most of these have half-lives that are less than a half-hour, except 101Pd (half-life: 8.47 hours), 109Pd (half-life: 13.7 hours), and 112Pd (half-life: 21 hours).
The primary decay mode before the most abundant stable isotope, 106Pd, is electron capture
Electron capture
Electron capture is a process in which a proton-rich nuclide absorbs an inner atomic electron and simultaneously emits a neutrino...
and the primary mode after is beta decay
Beta decay
In nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted from an atom. There are two types of beta decay: beta minus and beta plus. In the case of beta decay that produces an electron emission, it is referred to as beta minus , while in the case of a...
. The primary decay product
Decay product
In nuclear physics, a decay product is the remaining nuclide left over from radioactive decay. Radioactive decay often involves a sequence of steps...
before 106Pd is rhodium and the primary product after is silver
Silver
Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...
.
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
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
, must reflect the presence of short-lived nuclides in the early solar system.
Compounds
Palladium primarily exists in the 0, +2, +4 oxidation states; the +4 oxidation state is comparatively rare. One major example of palladium(IV) is hexachloropalladate(IV), [PdCl6]2−.Elemental palladium reacts with chlorine to give palladium(II) chloride
Palladium(II) chloride
Palladium chloride, also known as palladium dichloride, 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 chlorination of...
; it dissolves in nitric acid and precipitates palladium(II) acetate
Palladium(II) acetate
Palladium acetate is a chemical compound of palladium described by the formula Pd2 or Pd2. It is considered more reactive than the analogous platinum compound...
on addition of acetic acid
Acetic acid
Acetic acid is an organic compound with the chemical formula CH3CO2H . It is a colourless liquid that when undiluted is also called glacial acetic acid. Acetic acid is the main component of vinegar , and has a distinctive sour taste and pungent smell...
. These two compounds and the bromide
Palladium(II) bromide
Palladium bromide is an inorganic compound of palladium and bromine. It is a commercially available, though less common than palladium chloride, the usual entry point to palladium chemistry. Like the chloride, palladium bromide is insoluble in water, but dissolves when heated in acetonitrile to...
are reactive and relatively inexpensive, making them convenient entry points to palladium chemistry. All three are not monomeric; the chloride and bromide often must be refluxed in acetonitrile
Acetonitrile
Acetonitrile is the chemical compound with formula . This colourless liquid is the simplest organic nitrile. It is produced mainly as a byproduct of acrylonitrile manufacture...
to obtain the more reactive acetonitrile complex monomers, for example:
- PdX2 + 2 MeCN → PdX2(MeCN)2 (X = Cl, Br)
Palladium(II) chloride is the principal starting material for many other palladium catalysts. It is used to prepare heterogeneous palladium catalysts: palladium on barium sulfate, palladium on carbon, and palladium chloride on carbon. It reacts with triphenylphosphine in coordinating solvents to give bis(triphenylphosphine)palladium(II) dichloride
Bis(triphenylphosphine)palladium(II) dichloride
Bispalladium dichloride is a coordination compound of palladium containing two triphenylphosphine and two chloride ligands. This yellow complex is often used for palladium-catalyzed coupling reactions, e.g. the Sonogashira–Hagihara reaction. The complex is square planar...
, a useful catalyst. Where desired, the catalyst may be formed in situ.
- PdCl2 + 2 PPh3 → PdCl2(PPh3)2
Reduction of this phosphine complex with hydrazine
Hydrazine
Hydrazine is an inorganic compound with the formula N2H4. It is a colourless flammable liquid with an ammonia-like odor. Hydrazine is highly toxic and dangerously unstable unless handled in solution. Approximately 260,000 tons are manufactured annually...
with more phosphine gives tetrakis(triphenylphosphine)palladium(0)
Tetrakis(triphenylphosphine)palladium(0)
Tetrakispalladium is the chemical compound Pd[P3]4, often abbreviated Pd4, or even PdP4. It is a bright yellow crystalline solid that becomes brown upon decomposition in air.-Structure and properties:...
, one of the two major palladium(0) complexes:
- 2 PdCl2(PPh3)2 + 4 PPh3 + 5 N2H4HydrazineHydrazine is an inorganic compound with the formula N2H4. It is a colourless flammable liquid with an ammonia-like odor. Hydrazine is highly toxic and dangerously unstable unless handled in solution. Approximately 260,000 tons are manufactured annually...
→ 2 Pd(PPh3)4 + N2 + 4 N2H5+Cl−
The other major palladium(0) complex, tris(dibenzylideneacetone)dipalladium(0)
Tris(dibenzylideneacetone)dipalladium(0)
Trisdipalladium or Pd23 is an organometallic complex based on palladium and dibenzylideneacetone used in organic chemistry. It was discovered in 1970.-Preparation and structure:...
(Pd2(dba)3), is prepared by reducing sodium tetrachloropalladate
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 chloride with the appropriate alkali metal chloride in aqueous solution...
in the presence of dibenzylideneacetone
Dibenzylideneacetone
Dibenzylideneacetone or dibenzalacetone, often abbreviated dba, is an organic compound with the formula C17H14O. It is a bright-yellow solid insoluble in water, but soluble in ethanol. Dibenzylideneacetone is used as a sunscreen component and as a ligand in organometallic chemistry, for instance in...
.
The great many reactions in which palladium compounds serve as catalysts are collectively known as palladium-catalyzed coupling reactions
Palladium-catalyzed coupling reactions
Palladium compounds are used as a catalyst in many coupling reactions, usually as a homogeneous catalyst. Examples include:* Heck reaction between alkenes and aryl halides* Suzuki reaction between aryl halides and boronic acids...
. Prominent examples include the Heck
Heck reaction
The Heck reaction is the chemical reaction of an unsaturated halide with an alkene and a base and palladium catalyst to form a substituted alkene. Together with the other palladium-catalyzed cross-coupling reactions, this reaction is of great importance, as it allows one to do substitution...
, Suzuki
Suzuki reaction
The Suzuki reaction is the organic reaction of an aryl- or vinyl-boronic acid with an aryl- or vinyl-halide catalyzed by a palladium complex. It is widely used to synthesize poly-olefins, styrenes, and substituted biphenyls, and has been extended to incorporate alkyl bromides...
and Stille reaction
Stille reaction
The Stille reaction is a chemical reaction coupling an organotin compound with an sp2-hybridized organic halide catalyzed by palladium. The reaction is widely used in organic synthesis....
s. Palladium(II) acetate
Palladium(II) acetate
Palladium acetate is a chemical compound of palladium described by the formula Pd2 or Pd2. It is considered more reactive than the analogous platinum compound...
, tetrakis(triphenylphosphine)palladium(0)
Tetrakis(triphenylphosphine)palladium(0)
Tetrakispalladium is the chemical compound Pd[P3]4, often abbreviated Pd4, or even PdP4. It is a bright yellow crystalline solid that becomes brown upon decomposition in air.-Structure and properties:...
(Pd(PPh3)4, and tris(dibenzylideneacetone)dipalladium(0)
Tris(dibenzylideneacetone)dipalladium(0)
Trisdipalladium or Pd23 is an organometallic complex based on palladium and dibenzylideneacetone used in organic chemistry. It was discovered in 1970.-Preparation and structure:...
(Pd2(dba)3) are useful in this regard, either as catalysts or as starting points to catalysts.
History
Soho
Soho is an area of the City of Westminster and part of the West End of London. Long established as an entertainment district, for much of the 20th century Soho had a reputation for sex shops as well as night life and film industry. Since the early 1980s, the area has undergone considerable...
in April 1803. After harsh criticism that palladium is an alloy of platinum and mercury by Richard Chenevix
Richard Chenevix (chemist)
Richard Chenevix FRS was an Irish chemist.Chenevix was a chemist who played a role in the discovery of the elemental nature of the metal palladium. Disbelieving this solid to be an element, in 1803 he published his opinions that it was a combination of mercury and platinum...
, Wollaston anonymously offered a reward of 20 British pounds for 20 grains of synthetic palladium alloy. Chenevix received the Copley Medal
Copley Medal
The Copley Medal is an award given by the Royal Society of London for "outstanding achievements in research in any branch of science, and alternates between the physical sciences and the biological sciences"...
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 to be the discoverer of palladium in a publication in 1805.
It was named by Wollaston in 1802 after the asteroid Pallas, which had been discovered two years earlier. Wollaston found palladium in crude platinum ore from South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
by dissolving the ore in aqua regia
Aqua regia
Aqua regia or aqua regis is a highly corrosive mixture of acids, fuming yellow or red solution, also called nitro-hydrochloric acid. The mixture is formed by freshly mixing concentrated nitric acid and hydrochloric acid, usually in a volume ratio of 1:3, respectively...
, neutralizing the solution with sodium hydroxide, and precipitating platinum as ammonium chloroplatinate with ammonium chloride
Ammonium chloride
Ammonium chloride NH4Cl is an inorganic compound with the formula NH4Cl. It is a white crystalline salt that is highly soluble in water. Solutions of ammonium chloride are mildly acidic. Sal ammoniac is a name of natural, mineralogical form of ammonium chloride...
. He added mercuric cyanide to form the compound palladium cyanide, which was heated to extract palladium metal.
Palladium chloride was at one time prescribed as a tuberculosis
Tuberculosis
Tuberculosis, MTB, or TB is a common, and in many cases lethal, infectious disease caused by various strains of mycobacteria, usually Mycobacterium tuberculosis. Tuberculosis usually attacks the lungs but can also affect other parts of the body...
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
Adverse effect (medicine)
In medicine, an adverse effect is a harmful and undesired effect resulting from a medication or other intervention such as surgery.An adverse effect may be termed a "side effect", when judged to be secondary to a main or therapeutic effect. If it results from an unsuitable or incorrect dosage or...
, and was later replaced by more effective drugs.
Palladium's affinity for hydrogen led it to play an essential role in the Fleischmann–Pons experiment in 1989.
In the run up to 2000, the Russian supply of palladium to the global market was repeatedly delayed and disrupted because the export quota was not granted on time, for political reasons. The ensuing market panic drove the price to an all-time high of $1100 per troy ounce
Troy ounce
The troy ounce is a unit of imperial measure. In the present day it is most commonly used to gauge the weight of precious metals. One troy ounce is nowadays defined as exactly 0.0311034768 kg = 31.1034768 g. There are approximately 32.1507466 troy oz in 1 kg...
in January 2001. Around this time, the Ford Motor Company
Ford Motor Company
Ford Motor Company is an American multinational automaker based in Dearborn, Michigan, a suburb of Detroit. The automaker was founded by Henry Ford and incorporated on June 16, 1903. In addition to the Ford and Lincoln brands, Ford also owns a small stake in Mazda in Japan and Aston Martin in the UK...
, fearing auto vehicle production disruption due to a possible palladium shortage, stockpiled large amounts of the metal purchased near the price high. When prices fell in early 2001, Ford lost nearly US$
United States dollar
The United States dollar , also referred to as the American dollar, is the official currency of the United States of America. It is divided into 100 smaller units called cents or pennies....
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 tonne
Tonne
The tonne, known as the metric ton in the US , often put pleonastically as "metric tonne" to avoid confusion with ton, is a metric system unit of mass equal to 1000 kilograms. The tonne is not an International System of Units unit, but is accepted for use with the SI...
s in 2006 according to the United States Geological Survey
United States Geological Survey
The United States Geological Survey is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, and the natural hazards that threaten it. The organization has four major science disciplines, concerning biology,...
. Most palladium is used for catalytic converter
Catalytic converter
A catalytic converter is a device used to convert toxic exhaust emissions from an internal combustion engine into non-toxic substances. Inside a catalytic converter, a catalyst stimulates a chemical reaction in which noxious byproducts of combustion are converted to less toxic substances by dint...
s in the automobile industry.
Occurrence
Palladium can be found as a free metal alloyed with gold and other platinum-group metals in placer
Placer mining
Placer mining is the mining of alluvial deposits for minerals. This may be done by open-pit or by various surface excavating equipment or tunneling equipment....
deposits of the Ural Mountains
Ural Mountains
The Ural Mountains , or simply the Urals, are a mountain range that runs approximately from north to south through western Russia, from the coast of the Arctic Ocean to the Ural River and northwestern Kazakhstan. Their eastern side is usually considered the natural boundary between Europe and Asia...
, Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
, Ethiopia
Ethiopia
Ethiopia , officially known as the Federal Democratic Republic of Ethiopia, is a country located in the Horn of Africa. It is the second-most populous nation in Africa, with over 82 million inhabitants, and the tenth-largest by area, occupying 1,100,000 km2...
, North
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
and South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
. For the production of palladium these deposits play only a minor role. The most important commercial sources are nickel
Nickel
Nickel is a chemical element with the chemical 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...
-copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
deposits found in the Sudbury Basin
Sudbury Basin
The Sudbury Basin, also known as Sudbury Structure or the Sudbury Nickel Irruptive, is a major geologic structure in Ontario, Canada. It is the second-largest known impact crater or astrobleme on Earth, as well as one of the oldest....
, Ontario
Ontario
Ontario is a province of Canada, located in east-central Canada. It is Canada's most populous province and second largest in total area. It is home to the nation's most populous city, Toronto, and the nation's capital, Ottawa....
, and the Norilsk–Talnakh
Norilsk
Norilsk is an industrial city in Krasnoyarsk Krai, Russia, located between the Yenisei River and the Taymyr Peninsula. Population: It was granted city status in 1953. It is the northernmost city in Siberia and the world's second largest city north of the Arctic Circle...
deposits in Siberia
Siberia
Siberia is an extensive region constituting almost all of Northern Asia. Comprising the central and eastern portion of the Russian Federation, it was part of the Soviet Union from its beginning, as its predecessor states, the Tsardom of Russia and the Russian Empire, conquered it during the 16th...
. The other large deposit is the Merensky Reef
Merensky Reef
The Merensky Reef, is a layer of igneous rock in the Bushveld Igneous Complex in the Transvaal which together with an underlying layer, the Upper Group 2 Reef , contains most of the world's known reserves of platinum group metals or platinum group elements - platinum, palladium, rhodium,...
platinum group
Platinum group
The platinum group metals is a term used sometimes to collectively refer to six metallic elements clustered together in the periodic table.These elements are all transition metals, lying in the d-block .The six...
metals deposit within the Bushveld Igneous Complex
Bushveld igneous complex
The Bushveld Igneous Complex is a large layered igneous intrusion within the Earth's crust which has been tilted and eroded and now outcrops around what appears to be the edge of a great geological basin, the Transvaal Basin. Located in South Africa, the BIC contains some of the richest ore...
South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
. The Stillwater igneous complex
Stillwater igneous complex
The Stillwater igneous complex is a large layered intrusion located in southern Montana in Stillwater, Sweet Grass and Park Counties. The complex is exposed across 30 miles of the north flank of the Beartooth Mountain Range. The complex has extensive reserves of chromium ore and has a history of...
of Montana
Montana
Montana is a state in the Western United States. The western third of Montana contains numerous mountain ranges. Smaller, "island ranges" are found in the central third of the state, for a total of 77 named ranges of the Rocky Mountains. This geographical fact is reflected in the state's name,...
and the Roby zone ore body of the Lac des Îles igneous complex
Lac des Îles igneous complex
The Lac des Îles igneous complex of northwestern Ontario, Canada is a layered gabbroic intrusion which is the host for the largest palladium orebody in Canada...
of Ontario are the two other sources of palladium in Canada and the United States. Palladium is found in the rare minerals cooperite
Cooperite
Cooperite is a grey mineral consisting of platinum sulfide , generally in combinations with sulfides of other elements such as palladium and nickel . Its general formula is S. It is a dimorph of braggite....
and polarite
Polarite
Polarite , is an opaque, yellow-white mineral. Its crystals are orthorhombic pyramidal, but can only be seen through a microscope. It has a metallic luster and leaves a white streak. Polarite is rated 3.5 to 4 on the Mohs Scale....
.
Palladium is also produced in nuclear fission
Nuclear fission
In nuclear physics and nuclear chemistry, nuclear fission is a nuclear reaction in which the nucleus of an atom splits into smaller parts , often producing free neutrons and photons , and releasing a tremendous amount of energy...
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
Nuclear reprocessing
Nuclear reprocessing technology was developed to chemically separate and recover fissionable plutonium from irradiated nuclear fuel. Reprocessing serves multiple purposes, whose relative importance has changed over time. Originally reprocessing was used solely to extract plutonium for producing...
facilities are equipped to extract palladium from the high-level radioactive waste.
Applications
Dentistry
Dentistry is the branch of medicine that is involved in the study, diagnosis, prevention, and treatment of diseases, disorders and conditions of the oral cavity, maxillofacial area and the adjacent and associated structures and their impact on the human body. Dentistry is widely considered...
, watch
Watch
A watch is a small timepiece, typically worn either on the wrist or attached on a chain and carried in a pocket, with wristwatches being the most common type of watch used today. They evolved in the 17th century from spring powered clocks, which appeared in the 15th century. The first watches were...
making, in blood sugar test strips, in aircraft spark plug
Spark plug
A spark plug is an electrical device that fits into the cylinder head of some internal combustion engines and ignites compressed fuels such as aerosol, gasoline, ethanol, and liquefied petroleum gas by means of an electric spark.Spark plugs have an insulated central electrode which is connected by...
s and in the production of surgical instruments and electrical contacts. Palladium is also used to make professional transverse flute
Transverse flute
A transverse flute or side-blown flute is a flute which is held horizontally when played. The player blows "across" the embouchure hole, in a direction perpendicular to the flute's body length....
s. 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
Gold
Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...
, silver
Silver
Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...
and platinum
Platinum
Platinum is a chemical element with the chemical symbol Pt and an atomic number of 78. Its name is derived from the Spanish term platina del Pinto, which is literally translated into "little silver of the Pinto River." It is a dense, malleable, ductile, precious, gray-white transition metal...
.
Catalysis
When it is finely divided, such as in palladium on carbonPalladium on carbon
Palladium on carbon, often referred to as Pd/C, is a form of palladium used for catalysis. It is usually used for catalytic hydrogenations in organic chemistry...
, palladium forms a versatile catalyst and speeds up hydrogenation
Hydrogenation
Hydrogenation, to treat with hydrogen, also a form of chemical reduction, is a chemical reaction between molecular hydrogen and another compound or element, usually in the presence of a catalyst. The process is commonly employed to reduce or saturate organic compounds. Hydrogenation typically...
and dehydrogenation
Dehydrogenation
Dehydrogenation is a chemical reaction that involves the elimination of hydrogen . It is the reverse process of hydrogenation. Dehydrogenation reactions may be either large scale industrial processes or smaller scale laboratory procedures....
reactions, as well as in petroleum cracking
Cracking (chemistry)
In petroleum geology and chemistry, cracking is the process whereby complex organic molecules such as kerogens or heavy hydrocarbons are broken down into simpler molecules such as light hydrocarbons, by the breaking of carbon-carbon bonds in the precursors. The rate of cracking and the end products...
. A large number of carbon-carbon bond
Carbon-carbon bond
A carbon–carbon bond is a covalent bond between two carbon atoms. The most common form is the single bond: a bond composed of two electrons, one from each of the two atoms. The carbon–carbon single bond is a sigma bond and is said to be formed between one hybridized orbital from each...
forming reactions in organic chemistry
Organic chemistry
Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, composition, reactions, and preparation of carbon-based compounds, hydrocarbons, and their derivatives...
(such as the Heck and Suzuki coupling) are facilitated by catalysis with palladium compounds. (see #Compounds and palladium-catalyzed coupling reactions
Palladium-catalyzed coupling reactions
Palladium compounds are used as a catalyst in many coupling reactions, usually as a homogeneous catalyst. Examples include:* Heck reaction between alkenes and aryl halides* Suzuki reaction between aryl halides and boronic acids...
) In addition, palladium, when dispersed on conductive materials, proves to be an excellent electrocatalyst for oxidation of primary alcohols in alkaline media. In 2010, palladium-catalysed organic reactions were recognised by the Nobel Prize in Chemistry
Nobel Prize in Chemistry
The Nobel Prize in Chemistry is awarded annually by the Royal Swedish Academy of Sciences to scientists in the various fields of chemistry. It is one of the five Nobel Prizes established by the will of Alfred Nobel in 1895, awarded for outstanding contributions in chemistry, physics, literature,...
. Palladium is also a versatile metal for homogeneous catalysis
Homogeneous catalysis
In chemistry, homogeneous catalysis is a sequence of reactions that involve a catalyst in the same phase as the reactants. Most commonly, a homogeneous catalyst is codissolved in a solvent with the reactants.-Acid catalysis:...
. It is used in combination with a broad variety of ligands for highly selective chemical transformations. A 2008 study showed that palladium is an effective catalyst for making carbon-fluoride bonds. Palladium is found in the Lindlar catalyst
Lindlar catalyst
A Lindlar catalyst is a heterogeneous catalyst that consists of palladium deposited on calcium carbonate and treated with various forms of lead. The lead additive serves to deactivate the palladium sites. A variety of "catalyst poisons" have been used including lead acetate and lead oxide. The...
, also called Lindlar's Palladium.
Electronics
The second-biggest application of palladium in electronics is in the manufacture of multilayer ceramic capacitors, in which palladium (and palladium-silver alloys) are used as electrodes. Palladium (sometimes alloyed with nickel) is used in connector platings in consumer electronics.It is also used in plating of electronic components 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
Johnson Matthey
Johnson Matthey plc is multinational chemicals and precious metals company headquartered in London, United Kingdom.It is listed on the London Stock Exchange and is a constituent of the FTSE 100 Index.-History:...
report.
Technology
Hydrogen easily diffuses through heated palladium; thus, it provides a means of purifying the gas. Membrane reactorMembrane reactor
A membrane reactor is a piece of chemical equipment that combines a catalyst-filled reaction chamber with a membrane to add reactants or remove products of the reaction.Chemical reactors making use of membranes are usually referred to as membrane reactors...
s with Pd membranes are therefore used for the production of high purity hydrogen. Palladium is a part of the palladium-hydrogen electrode
Palladium-Hydrogen electrode
The palladium-hydrogen electrode is one of the common reference electrodes used in electrochemical study. Most of its characteristics are similar to the standard hydrogen electrode...
in electrochemical studies. Palladium(II) chloride
Palladium(II) chloride
Palladium chloride, also known as palladium dichloride, 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 chlorination of...
can oxidize large amounts of carbon monoxide gas, and is used in carbon monoxide detectors.
Hydrogen storage
Palladium hydridePalladium hydride
Palladium hydride is metallic palladium that contains a substantial quantity of hydrogen within its crystal lattice. At room temperature and atmospheric pressure, palladium can absorb up to 900 times its own volume of hydrogen. This process is reversible...
is metallic palladium that contains a substantial quantity of hydrogen within its crystal lattice. At room temperature
Room temperature
-Comfort levels:The American Society of Heating, Refrigerating and Air-Conditioning Engineers has listings for suggested temperatures and air flow rates in different types of buildings and different environmental circumstances. For example, a single office in a building has an occupancy ratio per...
and atmospheric pressure
Pressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...
, palladium can absorb up to 900 times its own volume of hydrogen in a reversible process. This property has been investigated because hydrogen storage is of such interest and a better understanding of what happens at the molecular level could give clues to designing improved metal hydrides. A palladium-based store, however, would be prohibitively expensive owing to the cost of the metal.
Jewelry
Nitric acid
Nitric acid , also known as aqua fortis and spirit of nitre, is a highly corrosive and toxic strong acid.Colorless when pure, older samples tend to acquire a yellow cast due to the accumulation of oxides of nitrogen. If the solution contains more than 86% nitric acid, it is referred to as fuming...
.
Palladium is one of the three most popular metals used to make white gold alloys (nickel
Nickel
Nickel is a chemical element with the chemical 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...
and silver can also be used). Palladium-gold is a more expensive alloy than nickel-gold, but seldom causes allergic reactions (though certain cross-allergies with nickel may occur).
When platinum was declared a strategic government resource during World War II, many jewelry bands were made out of palladium. As recently as September 2001, palladium was more expensive than platinum and rarely used in jewelry also due to the technical obstacle of casting. However, the casting problem has been resolved and its use in jewelry has increased because of a large spike in the price of platinum and a drop in the price of palladium.
Prior to 2004, the principal use of palladium in jewelry was the manufacture of white gold. In early 2004, when gold and platinum prices rose steeply, China began fabricating significant volumes of palladium jewelry and used 37 tonne
Tonne
The tonne, known as the metric ton in the US , often put pleonastically as "metric tonne" to avoid confusion with ton, is a metric system unit of mass equal to 1000 kilograms. The tonne is not an International System of Units unit, but is accepted for use with the SI...
s of palladium for this purpose in 2005. Changes of the relative price between palladium and platinum after 2008 lowered demand for palladium to 17.4 tonnes in 2009.
Photography
With the platinotypePlatinotype
Platinum prints, also called platinotypes, are photographic prints made by a monochrome printing process that provides the greatest tonal range of any printing method using chemical development....
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.
Precautions
Finely divided palladium metal can be pyrophoric. As a platinum-group metal, the bulk material is quite inert. Although contact dermatitisContact dermatitis
Contact dermatitis is a term for a skin reaction resulting from exposure to allergens or irritants . Phototoxic dermatitis occurs when the allergen or irritant is activated by sunlight....
has been reported, the amount of data on the effects of exposure to palladium is limited. It has been shown that people with an allergic reaction to palladium also react to nickel, making it possible to avoid the use of dental alloys containing palladium on those so allergic.
A considerable amount of palladium is distributed by the exhausts of cars with catalytic converter
Catalytic converter
A catalytic converter is a device used to convert toxic exhaust emissions from an internal combustion engine into non-toxic substances. Inside a catalytic converter, a catalyst stimulates a chemical reaction in which noxious byproducts of combustion are converted to less toxic substances by dint...
s. Between 4 and 108 ng/km of palladium particulate is released by such cars. The total uptake of from food is estimated to be lower than 2 µg per person and day. The second possible source for palladium is alloys for dental restoration, there the possible uptake of palladium is estimated to be lower than 15 µg per person and day. People working with palladium or its compounds might have a considerably higher uptake. For soluble compounds like 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.
See also
- 2000s commodities boom2000s commodities boomThe 2000s commodities boom is the rise in many physical commodity prices which occurred during the decade of the 2000s , following the Great Commodities Depression of the 1980s and 1990s...
- Palladium as an investmentPalladium as an investmentLike other precious metals, palladium may be used as an investment. Palladium price peaked near US$1,100 per troy ounce in January 2001 driven mainly on speculation of the catalytic converter demand from the automobile industry. Palladium is traded in the spot market with the code "XPD"...
- Palladium coinPalladium coinPalladium coins are a form of coinage made out of the rare silver-white transition metal palladium. Palladium is internationally recognised as a form of currency under ISO 4217. Sierra Leone issued the first palladium coins in 1966. Tonga commenced issuing palladium coins a year later in 1967,...
- Periodic tablePeriodic tableThe periodic table of the chemical elements is a tabular display of the 118 known chemical elements organized by selected properties of their atomic structures. Elements are presented by increasing atomic number, the number of protons in an atom's atomic nucleus...
- PlatinumPlatinumPlatinum is a chemical element with the chemical symbol Pt and an atomic number of 78. Its name is derived from the Spanish term platina del Pinto, which is literally translated into "little silver of the Pinto River." It is a dense, malleable, ductile, precious, gray-white transition metal...
- Precious metalPrecious metalA precious metal is a rare, naturally occurring metallic chemical element of high economic value.Chemically, the precious metals are less reactive than most elements, have high lustre, are softer or more ductile, and have higher melting points than other metals...