Platinum

Platinum (IPA: /ˈplætɪnəm/) is a chemical element in the periodic table that has the symbol Pt and atomic number 78. A heavy, malleable, ductile, precious, grey-white transition metal, platinum is resistant to corrosion and occurs in some nickel and copper ores along with some native deposits. Platinum is used in jewelry, laboratory equipment, electrical contacts, dentistry, and automobile emissions control devices.

Notable characteristics

When pure, the metal appears greyish-white and firm. The metal is corrosion-resistant. The catalytic properties of the six platinum family metals are outstanding. For this catalytic property, platinum is used in catalytic converters, incorporated in automobile exhaust systems, as well as tips of spark plugs.

Platinum's wear- and tarnish-resistance characteristics are well suited for making fine jewelry. Platinum is more precious than gold. The price of platinum changes along with its availability, but it normally costs slightly less than twice the price of gold. In the 18th century, platinum's rarity made King Louis XV of France declare it the only metal fit for a king.^[1]

Platinum possesses high resistance to chemical attack, excellent high-temperature characteristics, and stable electrical properties. All these properties have been exploited for industrial applications. Platinum does not oxidize in air at any temperature, but can be corroded by cyanides, halogens, sulfur, and caustic alkalis. This metal is insoluble in hydrochloric and nitric acid, but does dissolve in the mixture known as aqua regia (forming chloroplatinic acid). Common oxidation states of platinum include +2, and +4. The +1 and +3 oxidation states are less common, and are often stabilized by metal bonding in bimetallic (or polymetallic) species.

Applications

As a catalyst in the catalytic converter, an optional (though often mandatory by law) component of the gasoline-fueled automobile exhaust system (see "Notable characteristics" in this article).
As a catalyst in fuel cells. Reducing the amount of platinum required (and thus cost) is a major focus of fuel cell research.
Certain platinum-containing compounds are capable of crosslinking DNA and kill cells by similar pathways to alkylating chemotherapeutic agents. Cisplatin, carboplatin and oxaliplatin are licensed examples of this class of drugs.
Platinum resistance thermometers.
Electrodes for use in electrolysis.
In the Clark polarographic electrode for measuring oxygen tension.
A wide range of jewelery
As a catalyst in the curing of silicone elastomers.
As a catalyst in glow plugs in some model engines.
Crucibles for high temperature melting of glass (for example) up to 1500°C,

better if alloyed with rhodium (10-40% of Rh).

In photography, it is used for archival printmaking.

History

Naturally-occurring platinum and platinum-rich alloys have been known for a long time. Though the metal was used by pre-Columbian Native Americans, the first European reference to platinum appears in 1557 in the writings of the Italian humanist Julius Caesar Scaliger (1484-1558) as a description of a mysterious metal found in Central American mines between Darién (Panama) and Mexico ("up until now impossible to melt by any of the Spanish arts"). The word platinum comes from the Spanish word platina, meaning "little silver."

Platinum was discussed by astronomer Antonio de Ulloa and Don Jorge Juan y Santacilia (1713–1773), both appointed by King Philip V to join a geographical expedition in Peru that lasted from 1735 to 1745. Among other things, Ulloa observed the platina del pinto, the unworkable metal found with gold in New Granada (Colombia). British privateers intercepted Ulloa's ship on the return voyage. Though he was well-treated in England, and even made a member of the Royal Society he was prevented from publishing a reference to the unknown metal until 1748. Before that could happen Charles Wood independently isolated the element in 1741.

Alchemical symbol for platinum

The alchemical symbol for platinum (shown left) was made by joining the symbols of silver and gold.

Occurrence

Platinum is often found chemically uncombined as native platinum and alloyed with iridium as platiniridium. The platinum arsenide, sperrylite (PtAs₂), is a major source of platinum associated with nickel ores in the Sudbury Basin deposit in Ontario, Canada. The rare sulfide mineral cooperite, (Pt,Pd,Ni)S, contains platinum along with palladium and nickel. Cooperite occurs in the Merensky Reef within the Bushveld complex, Transvaal, South Africa. South Africa is the largest producer of platinum in the world.

Platinum, often accompanied by small amounts of other platinum family metals, occurs in alluvial placer deposits in the Witwatersrand of South Africa, Colombia, Ontario, the Ural Mountains, and in certain western American states.

Platinum is produced commercially as a by-product of nickel ore processing in the Sudbury deposit. The huge quantities of nickel ore processed makes up for the fact that platinum is present as only 0.5 ppm in the ore.

Platinum exists in relatively higher abundances on the Moon and in asteroids - much terrestrial Platinum is mined where asteroids have hit.

Precautions

According to the Centers for Disease Control and Prevention, short-term exposure to platinum salts "may cause irritation of the eyes, nose, and throat" and long-term exposure "may cause both respiratory and skin allergies." The current OSHA standard is 0.002 milligram per cubic meter of air averaged over an 8-hour work shift.^[2]

Certain platinum complexes are used in chemotherapy and show good anti-tumor activity for some tumours. Cisplatin is particularly effective against testicular cancer; cure rate was improved from 10 % to 85 %.^[3] However, the side effects are severe. Cisplatin causes cumulative, irreversible kidney damage and deafness.^[4]

As platinum is a catalyst in the manufacture of the silicone rubber and gel components of several types of medical implants (breast implants, joint replacement prosthetics, artificial lumbar discs, vascular access ports), the possibility that platinum free radicals could enter the body and cause adverse effects has merited study. The FDA and other countries have reviewed the issue and found no evidence to suggest toxicity in vivo.^[5]

Rarity and color

Platinum's rarity as a metal has caused advertisers to associate it with exclusivity and wealth. "Platinum" credit cards have greater privileges than do "gold" ones. "Platinum awards" are the second highest possible, ranking above gold, silver and bronze, but below "Diamond". For example, a musical album that has sold more than 1,000,000 copies, will be credited as "platinum." And some products, such as blenders and vehicles, with a silvery-white colour are identified as "platinum". Platinum is considered a precious metal, although its use is not as common as the use of gold or silver. The frame of the Crown of Queen Elizabeth the Queen Mother, manufactured for her Coronation as Consort of King George VI, is made of platinum. It was the first British crown to be made of that metal.

Production

In order to obtain pure platinum, the ore is crushed, made into a slurry, and then mixed with a detergent containing 'collector' molecules. Air is then blown through the mixture, enabling the grains of metal minerals to be separated from the rest of the mixture.

World supply of platinum is around 40 million troy ounces (158,000 kg) per year.^[6]^[7] Platinum's cost fluctuates around USD $1250 per troy ounce ($40/g). [1]

References

^ "Platinum". Minerals Zone. Retrieved 2007-04-05.
^ Centers for Disease Control and Prevention
^ Einhorn, 1990
^ Von Hoff, et al. 1979
^ FDA
^ Johnson Matthey 2009 supply and demand charts
^ BBC 2002 article on supply and demand

Los Alamos National Laboratory — Platinum
Nuclides and Isotopes Fourteenth Edition: Chart of the Nuclides, General Electric Company, 1989.
Einhorn LH. "Treatment of testicular cancer: a new and improved model" J. Clin. Oncol. 1990 Vol 8, pp1777-81.
Von Hoff DD, et al. "Toxic effects of cis-dichlorodiammineplatinum(II) in man." Cancer Treat. Rep. 1979 Sep-Oct; 63(9-10), pp1527-31.

Jefferson Lab — The Element Platinum

External links

Template:Jewellery Materials

[mineralszone-1] "Platinum". Minerals Zone. Retrieved 2007-04-05.

[2] Centers for Disease Control and Prevention

[3] Einhorn, 1990

[4] Von Hoff, et al. 1979

[5] FDA

[6] Johnson Matthey 2009 supply and demand charts

[7] BBC 2002 article on supply and demand

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