Thorium

In 1815 Berzelius analyzed a rare mineral from the Falun district. He assumed that the mineral contained a new element, which he named thorium after the ancient Scandinavian god of thunder and weather, Thor (Weeks and Leicester, 1968).

Unfortunately, 10 years later the mineral turned out to be simply xenotime, e.g. yttrium phosphate. However, in 1828, Berzelius was given a mineral by the Reverend Hans Morten Thrane Esmark. In that mineral Berzelius really discovered a new element and gave it the same name (Berzelius, 1829; Gmelin, 1955, 1986a; Weeks and Leicester, 1968). Consequently, he called the mineral from which he isolated the new element thorite. It is a silicate that contains significant amounts of uranium and should therefore be written as (Th,U)SiO₄. Although thorium was discovered in 1828, it virtually had no application until the invention of the incandescent gas mantle in 1885 by C. Auer von Welsbach. Thereafter the application of thorium developed into a wide array of products and processes (Gmelin, 1988b). Besides the above-mentioned incandescent gas mantles, the production of ceramics, carbon arc lamps, and strong alloys may serve as examples. To be mentioned is also its use as coating for tungsten welding rods, because it provides a hotter arc. Furthermore, when added to refractive glass, it allows for smaller and more accurate camera lenses. As minor important applications, the use of ThO₂ in producing more heat-resistant laboratory crucibles and its occasional use as a catalyst for the oxidation of ammonia to nitric acid and other industrial chemical reactions can be mentioned. Nevertheless, during the last decade the demand for thorium in nonnuclear applications has sharply decreased due to environmental concerns related to its radioactivity. The radioactivity of thorium is helpful for the dating of very old materials, e.g. seabeds or mountain ranges.