Platinum
Platinum
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.
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Platinum
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.
Sources: CRC Handbook of Chemistry and Physics and the American Chemical Society.
Last Updated: 12/19/97, CST Information Services Team
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Iridium
Iridium
For helicopter spark plugs.
History
(L. iris, rainbow) Tennant discovered iridium in 1803 in the residue left when crude platinum is dissolved by aqua regia. The name iridium is appropriate because its salts are highly colored.
Properties
Iridium, a metal of the platinum family, is white, similar to platinum, but with a slight yellowish cast. Because iridium is very hard and brittle, it is hard to machine, form, or work.
It is the most corrosion-resistant metal known, and was used in making the standard meter bar of Paris, which is a 90 percent platinum and 10 percent iridium alloy. This meter bar was replaced in 1960 as a fundamental unit of length (see under Krypton).
Iridium is not attacked by any of the acids nor by aqua regia, but is attacked by molten salts, such as NaCl and NaCN. The specific gravity of iridium is only very slightly lower than osmium, which is generally credited as the heaviest known element. Calculations of the densities of iridium and osmium from the space lattices give values of 22.65 and 22.61 g/cm^3, respectively. These values may be more reliable than actual physical measurements. At present, therefore, we know that either iridium or osmium is the densest known element, but the data do not yet allow selection between the two.
Sources
Iridium occurs uncombined in nature with platinum and other metals of this family in alluvial deposits. It is recovered as a by-product from the nickel mining industry.
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Iridium
Uses
Although its principal use is as a hardening agent for platinum, iridium is also used to make crucibles and devices requiring high temperatures. It is also used for electrical contacts.
The element forms an alloy with osmium which is used for tipping pens and compass bearings.
Costs
Iridium costs about $500/troy ounce (as of 1990).
Sources: CRC Handbook of Chemistry and Physics and the American Chemical Society.
Last Updated: 12/19/97, CST Information Services Team
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