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Science Innovation Centre · 090 · Thorium

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When pure, thorium is a silvery white metal which is air-stable and retains its lustre for several months. When contaminated with the oxide, thorium slowly tarnishes in air, becoming grey and finally black. Thorium oxide has a melting point of 3300°C, the highest of all oxides.

Thorium was discovered by Jöns Jacob Berzelius, a Swedish chemist, in 1828. He discovered it in a sample of a mineral that was given to him by the Reverend Has Morten Thrane Esmark, who suspected that it contained an unknown substance. Esmark’s mineral is now known as thorite (ThSiO4).

Thorium is named for Thor, the Scandinavian god of war. It is found in thorite and thorianite in New England (USA) and other sites.

Thorium is a source of nuclear power. There is probably more untapped energy available for use from thorium in the minerals of the earth’s crust than from combined uranium and fossil fuel sources. Much of the internal heat the earth has been attributed to thorium and uranium.

Until the inherent dangers associated with its radioactivity were realized, thorium and its compounds found some important retail uses, the best known of which was in gas mantles, and in toothpaste. Thorium is still used as an alloying element in magnesium, to coat tungsten wire used in electronic equipment, to control the grain size of plutonium used for electric lamps. In the manufacture of refractory materials for the metallurgical industries. Thorium oxide is used for high-temperature laboratory crucibles, it is added to glass to create glasses with a high refractive index and low dispersion (lenses for cameras and scientific instruments). Like uranium, thorium could be a source if nuclear fuel. Thorium can be burnt in a nuclear reactor, without generating plutonium. Uranium and thorium has been used to date hominid fossils.