Palladium

For other uses, see Palladium (disambiguation).

46 rhodium ← palladium → silver Ni ↑ Pd ↓ Pt periodic table
General
Name, Symbol, Number	palladium, Pd, 46
Chemical series	transition metals
Group, Period, Block	10, 5, d
Appearance	silvery white metallic
Atomic mass	106.42(1) g/mol
Electron configuration	[Kr] 4d10
Electrons per shell	2, 8, 18, 18, 0
Physical properties
Phase	solid
Density (near r.t.)	12.023 g/cm³
Liquid density at m.p.	10.38 g/cm³
Melting point	1828.05 K (1554.9 °C, 2830.82 °F)
Boiling point	3236 K (2963 °C, 5365 °F)
Heat of fusion	16.74 kJ/mol
Heat of vaporization	362 kJ/mol
Heat capacity	(25 °C) 25.98 J/(mol·K)
Vapor pressure P/Pa 1 10 100 1 k 10 k 100 k at T/K 1721 1897 2117 2395 2753 3234
Atomic properties
Crystal structure	cubic face centered
Oxidation states	±1 (mildly basic oxide)
Electronegativity	2.20 (Pauling scale)
Ionization energies	1st: 804.4 kJ/mol
	2nd: 1870 kJ/mol
	3rd: 3177 kJ/mol
Atomic radius	140 pm
Atomic radius (calc.)	169 pm
Covalent radius	131 pm
Van der Waals radius	163 pm
Miscellaneous
Magnetic ordering	no data
Electrical resistivity	(20 °C) 105.4 nΩ·m
Thermal conductivity	(300 K) 71.8 W/(m·K)
Thermal expansion	(25 °C) 11.8 µm/(m·K)
Speed of sound (thin rod)	(20 °C) 3070 m/s
Speed of sound (thin rod)	(r.t.) 121 m/s
Shear modulus	44 GPa
Bulk modulus	180 GPa
Poisson ratio	0.39
Mohs hardness	4.75
Vickers hardness	461 MPa
Brinell hardness	37.3 MPa
CAS registry number	7440-05-3
Notable isotopes
Main article: [[Isotopes of {{{isotopesof}}}]] iso NA half-life DM DE (MeV) DP 100Pd syn 3.63 d ε - 107Rh γ 0.084, 0.074, 0.126 - 102Pd 1.02% Pd is stable with 56 neutrons 103Pd syn 16.991 d ε - 103Rh 104Pd 11.14% Pd is stable with 58 neutrons 105Pd 22.33% Pd is stable with 59 neutrons 106Pd 27.33% Pd is stable with 60 neutrons 107Pd syn 6.5×106 y β- 0.033 107Ag 108Pd 26.46% Pd is stable with 62 neutrons 110Pd 11.72% Pd is stable with 64 neutrons

Palladium (chemical symbol Pd, atomic number 46) is a rare, silver-white metal. It is a member of the platinum group of elements and resembles platinum chemically. It is extracted from some copper and nickel ores. It is primarily used as an industrial catalyst and in jewelry.

Occurrence

Palladium occurs in nature as a free metal and alloyed with gold, platinum, and other platinum group metals. It has been found in placer deposits in the Ural Mountains of western Russia, and in some parts of Australia, Ethiopia, and South and North America. In addition, it is commercially produced from nickel-copper deposits in South Africa, Ontario, and Siberia. Although the proportion of palladium in the nickel-copper ores is low, the processing of large volumes of ore makes this extraction profitable.

History

Palladium was discovered by William Hyde Wollaston in 1803 in England. Using a platinum ore that presumably came from South America, he performed a series of chemical reactions and obtained the compound palladium cyanide. Finally, by heating palladium cyanide, he was able to isolate palladium metal. He named the element in 1804, deriving the word from Pallas, the name of an asteroid discovered two years earlier.

The compound palladium chloride was at one time prescribed as a tuberculosis treatment at the rate of 0.065g per day (approximately one milligram per kilogram of body weight). This treatment did not have many negative side effects, but was later replaced by more effective drugs.

The element played an important role in the "cold fusion" experiments of Fleischmann and Pons.

In 2000, Ford Motor Company created a price bubble in palladium by stockpiling large amounts of the metal, fearing interrupted supplies from Russia. As prices fell in early 2001, Ford lost nearly 1 billion U.S. dollars.

Notable characteristics

Palladium

• transition metal

Palladium is a soft, silver-white metal that resembles platinum. Among the platinum group metals, it has the lowest density and melting point. It is soft and ductile when annealed and greatly increases its strength and hardness when it is cold-worked. Palladium is chemically attacked by sulfuric, nitric acid and hydrochloric acid in which it dissolves slowly. 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.

This metal has the uncommon ability to absorb up to 900 times its own volume of hydrogen at room temperatures. Upon absorbing large amounts of hydrogen, it swells up like a sponge full of water, visible to the naked eye. It is thought that this possibly forms palladium hydride (PdH₂), but it is not yet clear if this is a true chemical compound.

Common oxidation states 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. Recently, compounds with an oxidation state of +6 were synthesised.

Isotopes

Naturally occurring palladium is composed of six isotopes. The most stable radioisotopes are ¹⁰⁷Pd with a half-life of 6.5 million years, 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 weights ranging from 92.936 u (⁹³Pd) to 119.924 u (¹²⁰Pd). Most of these have half-lifes that are less than a half an 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 the Santa Clara, California meteorite of 1978. 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 clearly been melted since accretion of the solar system, must reflect the presence of short-lived nuclides in the early solar system.

Applications

• Finely divided palladium forms a good catalyst for various chemical reactions, such as 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 Suzuki coupling) are facilitated by catalysis with palladium compounds. It is also alloyed and used in jewelry.
• The largest use of palladium today is in catalytic converters. Much research is in progress to discover ways to replace the much more expensive platinum with palladium in this application.
• Palladium is one of the two metals which can be alloyed with gold to produce White gold. (Nickel can also be used.)
• Similar to gold, palladium can be beaten into a thin leaf form as thin as 100 nm (1/250,000 in).
• Since 1939 palladium itself has occasionally been used as a precious metal in jewelry, often as a replacement for platinum. ([1]).
• Hydrogen easily diffuses through heated palladium; thus, it provides a means of purifying the gas. Also, hydrogen dissolved in palladium is highly reactive, allowing it to be used in various chemical reductions.
• Palladium (and palladium-silver alloys) are used as electrodes in multi-layer ceramic capacitors. [2]
• Palladium (sometimes alloyed with nickel) is used in connector platings in consumer electronics.
• Palladium is also used in dentistry[3], watch making, in aircraft spark plugs and in the production of surgical instruments and electrical contacts.
• Palladium is also used to make professional transverse flutes.
• It is also used as Palladium-Hydrogen electrode in electrochemical studies.
• Palladium dichloride can absorb large amounts of carbon monoxide gas, and is used in carbon monoxide detectors.

References

ISBN links support NWE through referral fees

• Los Alamos National Laboratory – Palladium

See also

• Chemical element
• Periodic table
• Transition metal

External links

• Palladium in depth - Online Encyclopedia
• Current Palladium Price
• WebElements.com – Palladium
• Palladium Discovery History Uses & Investments
• Palladium Events Surrounding Its Discovery
• Platinum Metals Review E-Journal
• The Platinum Group Metals Database
• Palladium Coins
• Stillwater Palladium
• MMC Norilsk Nickel, world's largest Pd producer

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