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For dental crowns.
(Sp. platina, silver) Discovered in South America by Ulloa in 1735 and by Wood in 1741.
The metal was used by pre-Columbian Indians.
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.
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
It is insoluble in hydrochloric and nitric acid, but dissolves when they are mixed as
aqua regia, forming chloroplatinic acid.
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
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.
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.