PLATINUM

As a pure metal, platinum is silvery-white in appearance, lustrous, ductile, and malleable. It does not oxidize at any temperature, although it is corroded by halogens, cyanides, sulfur, and caustic alkalis. Platinum is insoluble in hydrochloric and nitric acid, but dissolves in aqua regia to form chloroplatinic acid, H2PtCl6. platinum's wear- and tarnish-resistance characteristics are well suited for making fine jewelry. Platinum is more precious than gold or silver. Platinum possesses high resistance to chemical attack, excellent high-temperature characteristics, and stable electrical properties. All of these properties have been exploited for industrial applications.

Platinum has six naturally occurring isotopes: 190Pt, 192Pt, 194Pt, 195Pt, 196Pt, and 198Pt. The most abundant of these is 195Pt, comprising 33.83% of all platinum. 190Pt is the least abundant at only .01%. Of the naturally occurring isotopes, only 190Pt is unstable, though it decays with a half-life of 650 × 109 years. 198Pt undergoes alpha decay, but because its half-life is estimated as being greater than 320 × 1012 years, it is considered stable. Platinum also has 31 synthetic isotopes ranging in atomic mass from 166 to 202, making the total number of known isotopes 37. The least stable of these is 166Pt with a half-life of 300 µs, while the most stable is 193Pt with a half-life of 50 years. Most of platinum's isotopes decay by some combination of beta decay and alpha decay. 188Pt, 191Pt, and 193Pt decay primarily by electron capture. 190Pt and 198Pt have double beta decay paths.

If pure platinum is found in placer deposits or other ores it is isolated from them by various methods of subtracting impurities. Because platinum is significantly denser than many of its impurities, the lighter impurities can be removed by simply floating them away in a water bath. Platinum is also non-magnetic, while nickel and iron are both magnetic. These two impurities are thus removed by running an electromagnet over the mixture. Because platinum has a higher melting point than most other substances, many impurities can be burned or melted away without melting the platinum. Finally, platinum is resistant to hydrochloric and sulfuric acids, while other substances are readily attacked by them. Metal impurities can be removed by stirring the mixture in either of the two acids and recovering the remaining platinum.

The most common use of platinum is as catalyst in chemical reactions. It has been employed in this application since the early 1800s, when platinum powder was used to catalyze the ignition of hydrogen. The most important application of platinum is in automobiles as a catalytic converter, which allows the complete combustion of low concentrations of unburned hydrocarbon from the exhaust into carbon dioxide and water vapor. Platinum is also used in the petroleum industry as a catalyst in a number of separate processes, but especially in catalytic reforming of straight run naphthas into higher octane gasoline which becomes rich in aromatic compounds. PtO2, also known as Adams' catalyst, is used as a hydrogenation catalyst, specifically for vegetable oils. Platinum metal also strongly catalyzes the decomposition of hydrogen peroxide into water and oxygen gas.