Gold's place on the periodic table (Credit: Science Photo Library)

Gold's unique mix of malleability, ductility, conductivity and resistance to corrosion, plus its ability to reflect heat and act as a radiation shield in space make it a highly versatile metal in our age of high technology. In many applications, from electronics to rocket engines, "nothing is as good as gold". Over 400 tonnes (12.9 million oz) of gold is used annually in industry, decorative jewellery and ceramics, dentistry and medicine.

Electronics
	Gold-plated contacts in computers, telecommunications and household goods such as televisions and washing machines.
	Gold 'bonding' wire to bond or connect parts of semi-conductors, such as transistors and integrated circuits.
	'Thick' and 'thin' film for micro-circuitry, which puts an ink-like gold paste on a ceramic base.
	60% of electronic products are made in Japan and the United States.

Aviation/Space
	Gold plating in jet or rocket engines reflects heat.
	Gold-covered film acts as a radiation shield on lunar modules and astronauts' suits in space.
	Components of the Hubble space telescope's electronic camera are gold-coated.

Energy Conservation
	Gold reflective glass reflects summer heat, but retains heat in winter, cutting building maintenance costs.

Decoration
	Gold potassium cyanide and rolled gold are used in costume jewellery, cigarette lighters, cufflinks, pens and lipstick cartridges.
	Gold thread is used in Indian saris - this accounts for 20% of all decorative gold.
	Gold leaf outlasts paint by many years on the roofs and ceilings of public buildings. Twelve kilos (386 oz) is used every generation on the dome over Napoleon's tomb in Paris.
	Liquid gold is a gold solution used in the decoration of ceramics and glass.

Medicine
	A gold solution is used in the treatment of rheumatoid arthritis, and 'seeds' of radioactive gold-198 are used in treating cancer.
	Gold has been used in dental work for over 3,000 years, because of its malleability and resistance to corrosion in the mouth.

	Gold is malleable; it can be hammered cold into a translucent wafer five-millionths of an inch thick (0.000013 cm). One ounce can be beaten into a sheet covering 100 square feet (9.3 square metres).
	Gold is ductile; one ounce can be drawn into 62 miles (100 km) of thin gold wire to make electrical contacts.
	Gold does not tarnish; it is corroded only by a mixture of nitric and hydrochloric acid (aqua regia).
	Gold dissolves only in cyanide.
	Gold is a superb conductor of electricity, making it indispensable for semi-conductors and connectors in computer technology.

The purity of gold is described by its 'fineness' (parts per 1,000) or by the carat (karat in US) scale.

Fine Gold	Carat
1,000	24
995 (London 'good delivery')
916	22
750	18 (high quality jewellery)
583.3	14 (medium quality jewellery)
417.7	10 (broad jewellery range in US)
375	9 (common for jewellery in UK)
333.3	8 (normally lowest acceptable purity for jewellery in Europe)

25 gram bar	10 gram bar
5 gram bar	1 gram bar

Different gold bar sizes (Credit: courtesy PAMP S.A.)

For many years it was assumed that gold did not possess any catalytic properties. However, it has recently been demonstrated that carefully prepared and supported gold catalysts possess some quite remarkable and unique properties. In addition, for gold to be an effective catalyst, it has to be very carefully prepared and deposited onto the support material, or substrate. Substrates are often oxides of the transition series of metals, such as chromium, aluminium, iron and copper (amongst others). It is essential that the gold particles deposited onto the substrate are extremely small i.e. in the nanometer size range, yielding gold particles with a very large surface area.

Some areas where gold has demonstrated potential as a catalyst are:
	The oxidation of carbon monoxide to carbon dioxide. This reaction is catalysed by gold at temperatures below 0°C, well below the lowest temperature possible with other currently used catalysts. The reaction has significant positive environmental control potential
	The reduction of nitrogen oxides to nitrogen. With stricter European automotive pollution control regulations due to be enforced in 2005, which call for a 50% reduction in NOx emissions for passenger cars, the automotive industry faces a serious challenge to meet these requirements. Whilst gold catalysts will not find application in petrol engine emission control, because the operating temperature of the exhaust system is too high (above 550°C), it could well be applied in lower temperature diesel exhaust systems (the so-called lean-burn systems).

Both of the above reactions have also importance in air purification systems for mine workings, buildings and aircraft cabins.

The use of gold catalysts in the emerging technology of fuel cells is also being investigated. Fuel cells are an electro-chemical device that generates electricity from hydrogen. The hydrogen is sourced from the reforming of hydrocarbon fuels (such as methanol) and the electrical energy is produced without actually burning the fuel. They are most definitely the energy source of the future, for both vehicles and stationary power generation plants. Major advantages of fuel cells are that they are energy efficient and environmentally friendly. The only emissions from a fuel cell are water, carbon dioxide and heat.

AngloGold and Mintek, the leading South African metallurgical research organisation, have embarked on a joint venture called Project Autek to develop industrial uses for gold, and in particular gold catalyst systems. Agreements have also been concluded with LERCSI in France and the University of Leiden in the Netherlands.

These catalytic properties have yet to be exploited commercially.