Thoriumdioxid

VerwendenThorium was discovered in 1828, and its radioactivity was discovered in 1898. In the early 1900s, the only commercial use for thorium was in gas lamp mantles. Although demand for gas mantles declined with the advent of electric lights, mantle manufacturing still accounted for 92% of thorium’s non-fuel use as late as 1950 (Hedrick 2000). The use of thorium in the United States has decreased substantially because of concerns over its naturally occurring radioactivity (Hedrick 2002). Principal uses for thorium dioxide are in high-temperature ceramics, gas mantles, nuclear fuel, flame spraying, crucibles, medicines, nonsilica optical glass, and thoriated tungsten filaments, and as a catalyst. It has also been used as a diagnostic aid (radiopaque medium) in feline medication (HSDB 2009). Thorotrast was used as a contrast agent in medical radiology. It was used extensively as an intravascular contrast agent for cerebral and limb angiography in Europe, the United States, and Japan. It was also injected directly into the nasal cavity, paranasal sinus, spleen, brain, and other sites. Thorotrast treatment led to deposition of thorium and its decay products in body tissues and organs, especially reticuloendothelial tissue and bone, which resulted in continuous lifelong alpha-particle irradiation (BEIR IV 1988). Use of Thorotrast was discontinued in the 1950s, when harmful latent effects were observed (Grampa 1971, IARC 2001).

synthetischeThorium dioxide is obtained as an intermediate in the production of thorium metal from monazite sand (See Thorium).The compound also can be prepared by many other methods including thermal decomposition of thorium oxalate, hydroxide, carbonate, or nitrate. Heating thorium metal in oxygen or air, and hydrolysis of thorium halides also yield thorium dioxide.