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Platinum

Background

Ulloa in 1735 and Wood in 1741 discovered platinum. Platinum (Pt) occurs native, accompanied by small quantities of iridium, osmium, palladium, ruthenium and rhodium, all belonging to the same group of metals. It has no commercial ore and exists in two rare minerals Sperrylite (PtAs2) and cupperite (PtS).

Pure platinum is beautiful silvery-white metal. It is malleable and is more ductile than silver, gold, or copper. It is heavier than gold.

The metal does not oxidise in air at any temperature, but is corroded by halogens, cyanides, sulphur and caustic alkalis. It is insoluble in hydrochloric and nitric acid, however, when they are mixed together to form aqua regia, platinum is dissolved forming chloroplatinic acid (H2PtCl6). Hydrogen and oxygen explode in the presence of platinum.

The metal has a face-centred-cubic lattice structure, leading to its high ductility and malleability. Because it is generally too soft to use alone it is alloyed with harder metals of the same group, namely osmium, rhodium and iridium.

Fine platinum wire placed in the vapour of methyl alcohol will glow red-hot.

Applications

Platinum is widely used in:

        Jewellery

        Electrical contacts

        Resistance wire

        Instrumentation devices

        Thermocouples

        Standard weights

        Laboratory dishes and vessels

        Corrosion resistant devices

        As an anode for cathodic protection systems for large ships and ocean-going vessels, pipelines, steel piers and the like.

        In dentistry as foil (99.99% pure) for maximum softness

        Platinum wire is used in high-temperature electric furnaces

It can be produced in several forms including, gauze, foil, powder, flake and coating.

In the gauze form is it used as a catalyst for the contact process, producing sulphuric acid, to a lesser extent in cracking petroleum products, an example of which is converting alcohol vapour to formaldehyde. This has seen commercial success in producing cigarette lighters and hand warmers, as a catalyst in fuel cells and in antipollution devices for automobiles.

In coating form platinum is used on missile nose cones, jet engine fuel nozzles and the like where performance reliability for long periods of time at high temperatures are required and/or resistance to atmospheric corrosion, even in sulphur environments.

Platinum is sometimes alloyed with other elements such as:

        Cobalt- To produce an extremely powerful magnet that offers a B-H (max) almost twice that of Alnico V

        Tungsten- For use in aircraft-engine spark plug electrodes, radar-tube grids, strain gauges, switches and heating elements.

Primary author: AZoM.com

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