Platinum: Characteristics & Applications

Platinum is a chemical element in the periodic table that has the symbol Pt and atomic number 78. A heavy, malleable, ductile, precious, gray-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

The metal is a beautiful silvery-white when pure, and malleable and ductile. 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.

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 about twice as much as gold. In the 18th century, platinum's rarity made King Louis XV of France declare it the only metal fit for a king.

Other distinctive properties include 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, +3, and +4.

Applications

• catalyst utilized in the catalytic converter, an optional component of the gasoline-fueled automobile exhaust system (see "Notable characteristics" in this article)
• certain platinum-containing compounds are capable of intercalating into DNA and are chemotherapeutic agents owing to this capability. For example, cisplatin and carboplatin belong to this class of drugs.
• platinum resistance thermometers
• electrodes for use in electrolysis

History

The name platinum mainly derives from the Spanish platina meaning "little silver".

Naturally-occurring platinum and platinum-rich alloys have been known for a long time. Though the metal was used by pre-Columbian Indians, 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 "platino," 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 discovered 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.

The standard 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 Sevres, 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.

Occurrence

Platinum is often found as native platinum and alloyed with iridium as platiniridium. The platinum arsenide, sperrylite, is a major source of platinum associated with nickel ores in the Sudbury Basin deposit. 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.

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.

Isotopes

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.

Precautions
This metal doesn't normally cause health problems due to its unreactive nature but all compounds of platinum should be considered to be highly toxic. Platinum compounds rarely occur in nature.

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 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". And some products, such as blenders and vehicles, with a silvery-white color are identified as "platinum".