For dental crowns.

History

(Sp. platina, silver) Discovered in South America by Ulloa in 1735 and by Wood in 1741. The metal was used by pre-Columbian Indians.

Sources

Platinum occurs native, accompanied by small quantities of iridium, osmium, palladium, ruthenium, and rhodium, all belonging to the same group of metals. These are found in the alluvial deposits of the Ural mountains, of Columbia, and of certain western American states. Sperrylite, occurring with the nickel-bearing deposits of Sudbury, Ontario, is the source of a considerable amount of metal.

The large production of nickel makes up for the fact that is only one part of the platinum metals in two million parts of ore.

Properties

Platinum is a beautiful silvery-white metal, when pure, and is malleable and ductile. It has a coefficient of expansion almost equal to that of soda-lime-silica glass, and is therefore used to make sealed electrodes in glass systems. The metal does not oxidize in air at any temperature, but is corroded by halogens, cyanides, sulfur, and caustic alkalis.

It is insoluble in hydrochloric and nitric acid, but dissolves when they are mixed as aqua regia, forming chloroplatinic acid.

Uses

The metal is extensively used in jewelry, wire, and vessels for laboratory use, and in many valuable instruments including therocouple elements. It is also used for electrical contacts, corrosion-resistant apparatus, and in dentistry.

Platinum-cobalt alloys have magnetic properties. One such alloy made of 76.7% Pt and 23.3% Co, by weight, is an extremely powerful magnet that offers a B-H (max) almost twice that of Alnico V. Platinum resistance wires are used for constructing high-temperature electric furnaces.

The metal is used for coating missile nose cones, jet engine fuel nozzles, etc., which must perform reliably at high temperatures for long periods of time. The metal, like palladium, absorbs large volumes, of hydrogen, retaining it at ordinary temperatures but giving it up when heated.

In the finely divided state platinum is an excellent catalyst, having long been used in the contact process for producing sulfuric acid. It is also used as a catalyst in cracking petroleum products. Much interest exists in using platinum as a catalyst in fuel cells and in antipollution devices for automobiles.

Platinum anodes are extensively used in cathodic protection systems for large ships and ocean-going vessels, pipelines, steel piers, etc. Fine platinum wire will glow red hot when placed in the vapor of methyl alcohol. It acts here as a catalyst, converting the alcohol to formaldehyde. The phenomenon has been used commercially to produce cigarette lighters and hand warmers. Hydrogen and oxygen explode in the presence of platinum.

Costs

The price of platinum has varied widely. More than a century ago platinum was used to adulterate gold and was worth nearly eight times more than gold in 1920. The price in January 1990 was about $500/troy oz.