What is platinum used for

Platinum is a useful catalyst for a wide range of chemical reactions, both organic and inorganic. For example, it catalyzes the oxidation of ammonia in the production of a nitric acid, its efficiency being increased by the addition of 10 per cent rhodium. Both platinum and palladium catalysts are used extensively in the pharmaceutical industry, where they enable highly specific chemical reactions to be carried out in the building of particular molecules. In the manufacture of margarine, hydrogenation is brought about by a palladium catalyst.

In recent years, the use of palladium in ientistry has greatly increased, mainly because the metal is strong and highly resistant to corrosion.

The metals are often most effective as catalysts when in the Form of finely divided powders known as blacks. The ability of platinum to initiate low-temperature oxidation reactions was first exploited by Dobereiner to produce a lighter before the invention of friction matches. The principle is used today in ignition devices for domestic gas stoves. Platinum metals are also used to catalyze both the oxidation of unburnt hydrocarbons and the reduction of nitro-;en oxides in antipollution units incorporated in car .xhaust systems. Such devices, known as catalytic xonverters, can therefore transform toxic exhaust ;uses into harmless water vapor and carbon dioxide. Their effectiveness, though, is drastically reduced Dy lead derived from the tetraethyl lead component of high-octane fuels. The high cost of platinum metal limits its use in catalysts, where cheaper alternatives may be substituted.

An important property of platinum metals is their outstanding resistance to chemical attack. Platinum itself is used for analytical apparatus such as crucibles, combustion boats, and grids for metal deposition in electrochemical techniques. Other industrial applications include spinnerets in the artificial fiber industry and crucibles for the manufacture of optical glass, where contamination From nonmetallic refractories must be avoided. Often platinum is alloyed with up to 20 per cent rhodium to improve its strength. Palladium has a unique affinity for hydrogen, absorbing up to 850 times its own volume of hydrogen, and is employed as a diffusion medium for the purification of the gas.
In this application it is alloyed with silver to reduce the shape changes which would otherwise occur during thermal cycling.

The refractory properties of the platinum metals once made them candidates for electric light bulb filaments. Tungsten is now universally used, but formerly osmium was often used. The thermal expansion coefficient of platinum is very similar to that of glass, which makes it an ideal material for glass-to-metal seals, although a copper-coated nickel – iron alloy has been developed which is also suitable and much cheaper. Thermocouples made from platinum, and a platinum – rhodium alloy, operate reliably up to 3100° F (1700° C) and are widely used in the steel industry. For very accurate temperature measurement, the platinum resistance thermometer is a standard measuring instrument. The platinum metals are suitable materials for relay contacts which are required to switch reliably for nany years without attention, and for electrodes in ;park plugs for high-performance internal combus;ion engines.

Platinum and palladium are used extensively in ;he jewelry industry for setting diamonds and other )recious stones, palladium having the additional advantages that it is not under such heavy demand rom the chemical industry and is about half the density. Like gold, both metals are seldom used pure as they are too soft. A thin layer of rhodium  – ;he easiest of the group to electrodeposit  –  electroplated onto silver, prevents tarnishing through sulfide formation. The tips of fountain pen nibs are isually made from alloys of platinum, osmium and ridium, where the combination of hardness and resistance to corrosion by ink is especially valuable.