Encyclopedia
Palladium is a
chemical element with symbol
Pd and atomic number 46. A rare silver-white
transition metal of the platinum group, palladium resembles
platinum chemically and is extracted from some
copper and
nickel ores. It is primarily used as an industrial
catalyst and in
jewelry.
Notable characteristics
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 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 . Palladium heated to 800°C produce layer of palladium-oxide . 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. It is thought that this possibly forms palladium hydride but it is not yet clear if this is a true chemical compound.
When palladium has absorbed large amounts of hydrogen, it can swell up, like a sponge full of water, visible to the naked eye.
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 and palladium instead. Recently, compounds with an oxidation state of +6 were synthesised.
Applications
When it is finely divided, palladium forms a good
catalyst and is used to speed up hydrogenation and dehydrogenation reactions, as well as in
petroleum cracking. A large number of carbon-carbon bond forming reactions in
organic chemistry are facilitated by catalysis with palladium compounds. It is also
alloyed and used in
jewelry. Other uses;
- 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.
- Similar to gold, palladium can be beaten into a thin leaf form as thin as 100 nm .
- Since 1939 palladium itself has occasionally been used as a precious metal in jewelry, often as a replacement for platinum. .
- Hydrogen easily diffuses through heated palladium; thus, it provides a means of purifying the gas. Also, hydrogen
| Triple point [i] || 13.8033 K, 7.042 kPa
...
dissolved in palladium is highly reactive, allowing it to be used in various chemical
reductions.
- Palladium are used as electrodes in multi-layer ceramic capacitors.
- Palladium is used in connector platings in consumer electronics.
- Palladium is also used in dentistry, watch making, in aircraft spark plugs and in the production of surgical instruments and electrical contact
...
s.
- 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.
History
Palladium was discovered by
William Hyde Wollaston in 1803. This element was named by Wollaston in 1804 after the asteroid
Pallas, which was discovered two years earlier.
Wollaston found element 46 in crude platinum ore from
South America. He did this by dissolving the ore in
aqua regia, neutralizing the solution with
sodium hydroxide,
NaOH, precipitating platinum as ammonium chloroplatinate through treatment with
ammonium chloride,
NH4Cl, and then adding mercuric cyanide to form the compound palladium cyanide. Finally, he heated the resulting compound in order to extract palladium metal.
The compound
palladium chloride was at one time prescribed as a
tuberculosis treatment at the rate of 0.065g per day . This treatment did not have many negative side effects, but was later replaced by more effective drugs.
The element played an essential role in the
Fleischmann-Pons experiment, also known as
cold fusion.
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.
Occurrence
Palladium is found as a free metal and alloyed with platinum and gold with platinum group metals in
placer deposits of the
Ural Mountains,
Australia,
Ethiopia,
South and
North America. However it is commercially produced from
nickel-
copper deposits found in
South Africa and
Ontario; the huge volume of ore processed makes this extraction profitable in spite of the low proportion of palladium in these ores.
About the possibility of producing palladium in reactors or extracting it from spent nuclear fuel, see Synthesis of noble metals.
See also .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 to 119.924 u . Most of these have half-lifes that are less than a half an hour except
101Pd ,
109Pd , and
112Pd .
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.
References
See also
...
External links
