Platinum
Platinum 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
jewellery, laboratory equipment,
electrical contacts, dentistry, and
automobile emissions control devices.
|
An assortment of native platinum nuggets |
The
metal appears silvery-white when pure, and firm. The metal is
corrosion-resistant. The
catalytic properties of the six
platinum family metals are outstanding (a mixture of
hydrogen and
oxygen explodes in the presence of platinum). 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.
Platinum possesses remarkable resistance to chemical attack, excellent high-temperature characteristics, and stable electrical properties. All these properties have been exploited for industrial applications. Platinum does not
oxidise 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, +3, and +4.
* As a catalyst in the
catalytic converter, an optional 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 (or alkylating) with
DNA and are
chemotherapeutic agents owing to this capability. For example,
cisplatin,
Carboplatin and
oxaliplatin belong to this class of drugs.
*
Platinum resistance thermometers.
*
Electrodes for use in
electrolysis.
*
Grills (decorative plates on the teeth).
* As a catalyst in the curing of
silicone elastomers.
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 Spaniards named the metal "platina," or little silver, when they first encountered it in Colombia. They regarded platinum as an unwanted impurity in the
silver they were mining, and often discarded it.
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.
The
alchemical symbol for platinum (shown below) was made by joining the symbols of silver and gold.
|
Alchemical symbol for platinum |
The definition of a
metre for a long time was based on the distance between two marks on a bar of a platinum-
iridium alloy housed at the
Bureau International des Poids et Mesures in
Sèvres,
France. A platinum-iridium cylinder serves to this day as the standard of the
kilogram and is housed in the same facility as the metre bar. Platinum is also used in the definition of the
Standard hydrogen electrode.
Platinum is an extremely rare metal, occurring as only 5
ppb in the
Earth's
crust.
Platinum is often found free in areas of the
Americas and
alloyed with
iridium as
platiniridium. The platinum
arsenide,
sperrylite (PtAs
2), 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.
Naturally occurring platinum is composed of five stable
isotopes and one
radioisotope, Pt-190, which has a very long
half-life (over 6 billion years or 190
Ps). There are also many other
radioisotopes with the most stable being Pt-193 with a half-life of 50 years.
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.
[Centers for Disease Control and Prevention] Certain platinum complexes (cis-platin) have been used in chemotherapy, as they have very good anti-tumor activity, particularly when used to combat testicular cancer, although they also cause cumulative, irreversible kidney damage.
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 has reviewed the issue and found no evidence to suggest toxicity in vivo. [
1].
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 highest possible, ranking above gold,
silver and
bronze. For example, a musical album that has sold more than 1,000,000 copies, will be credited as "platinum" (a higher certification of "
Diamond" does exist, however). 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 as such is much more rare than 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. Due to its rarity, platinum is a highly priced metal, more so than gold or silver.
World supply of platinum is around 6m
troy ounces per year.
[Johnson Matthey 2004 supply and demand analysis][BBC 2002 article on supply and demand]Platinum's cost fluctuates around USD 1200 per ounce. [
2]
*
Los Alamos National Laboratory â€" Platinum*
Nuclides and Isotopes Fourteenth Edition: Chart of the Nuclides, General Electric Company, 1989
*
Jefferson Lab â€" The Element Platinum*
Platinum coin*
Precious metal*
Platinum compounds*
Platinum group*
Kitco Platinum prices*
The Platinum Group Metals Database*
A balanced historical account of the sequence of discoveries of platinum; illustrated.*
WebElements.com â€" Platinum*
Platinum Metals Review E-Journal*
Platinum Guild International*
Platinum Today: Current and historical prices*
Video of Platinum (Uses
Java)
*
The Role of Near-Earth Asteroids in Long-Term Platinum Supplyzh-yue:鉑
