Platinum

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This page is about platinum the chemical element. For other uses, see Platinum (disambiguation).

Platinum (IPA: /ˈplætɪnəm/) is a chemical element in the periodic table that has the atomic symbol Pt and an atomic number of 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 jewellery, laboratory equipment, electrical contacts, dentistry, and automobile emissions control devices. Platinum bullion has the ISO currency code of XPT.

[edit] 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 jewellery. Platinum is more precious than gold. The price of platinum changes along with its availability, but its price is normally slightly less than twice that 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.

[edit] 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 sometimes used for archival printmaking. Platinum prints display a greater range of tones than other Black and White printing methods. Additionally platinum's chemical stability makes for extremely long-lasting prints. The disadvantage of this method, in addition to the high cost, is that platinum is less light sensitive and prints must be contact printed at the same size as the negative. Therefore, enlargements can only be made by making an enlarged negative.

[edit] 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. Amongst 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. Major finds were discovered in Russia in 1819, which produced around 90% of the global Platinum production at the turn of the 20th century.^[2]

Due to its rarity, greater difficulty to work with and the need to alloy it with (at the time) an even more expensive metal iridium, platinum was only used in a limited way in jewelry at the end of the 19th century. This changed at beginning of the 20th century when most diamond ring mountings and most exclusive jewelry were almost completely made of platinum.^[2]

[edit] Occurrence

Platinum is an extremely rare metal, occurring as only 5 ppb in the Earth's crust. In 2005, South Africa was the top producer of platinum with almost 80% world share followed by Russia, and Canada, reports the British Geological Survey.^[3]

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, Gauteng, South Africa.

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.^{[citation needed]}

[edit] 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.^[4]

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%.^[5] However, the side effects are severe. Cisplatin causes cumulative, irreversible kidney damage and deafness.^[6]

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.^[7]

[edit] 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,” whereas an album that sold more than 10,000,000 copies will be certifed as “diamond.” And some products, such as blenders and vehicles, with a silvery-white color 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.

[edit] 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. This process is called "flotation" or "mineral beneficialness". The next step is smelting.

In 2006, world supply of platinum was of about 217,700 kg or 7 million troy ounces.^[8][9] Average Platinum price in 2006 was of US$1200 per troy ounce (~$40/g), representing a significant increase from the 2005 average of US$900 per troy oz.^[3][10]