Thorium

Thorium is used mainly to prepare the Welsbach mantle for portable gas lights.   It is alloyed with magnesium to give it strength and creep resistance at high temperatures.   It has a low work function and high electron emission, so it is used to coat tungsten wire in electronic equipment.   Thorium oxide, ThO₂, is used to control tungsten grain size in electric lamps, in high-temperature laboratory crucibles, high refractive index, low dispersion glass for high quality lenses in camera and scientific instruments, and as a catalyst in converting ammonia to nitric acid, in petroleum refining, and in producing sulfuric acid. ^{Lide 4-30}

Thorium is an alpha particle emitter, so it is a hazardous material.

Thorium, like uranium, can be used as fuel in a nuclear reactor.   Although not fissile itself, 232Th will absorb slow neutrons to produce uranium-233 (233U), which like 238U, is fissile.   The 232Th absorbs a neutron to become 233Th which normally decays to protactinium-233 (233Pa) and then 233U.   The irradiated fuel can then be unloaded from the reactor, the 233U separated from the thorium and fed back into another reactor as part of a closed nuclear fuel cycle.   Problems include the high cost of fuel fabrication due partly to the high radioactivity of 233U which is a result of its contamination with traces of the short-lived 232U; the similar problems in recycling thorium due to highly radioactive 228Th; some weapons proliferation risk of 233U; and the technical problems in reprocessing.   Much development work is still required before the thorium fuel cycle can be commercialised, and the effort required seems unlikely while abundant uranium is available.   Thorium is significantly more abundant than uranium, and is a key factor in sustainable nuclear energy. ^{Wiki n.p.}

Thorium was discovered by Jöns Jakob Berzelius, a Swedish chemist, in 1828.   Thorium is found in thorite, ThSiO₄, thorianite, ThO₂ + UO₂.   It is recovered commercially as ThO₂ from monazite, from which it is reduced to the metal with calcium by electrolysis of anhydrous thorium chloride in a fused mixture of sodium and potassium chlorides, by calcium reduction of thorium tetrachloride mixed with anhydrous zinc chloride, and by reduction of thorium tetrachloride with an alkali metal. ^{Lide 4-30}