トリウム(IV)

解説酸化トリウム(Ⅳ)，天然には，方トリウム鉱に主成分として含まれている．白色の粉末で蛍石型構造．融点3390 ℃ は金属酸化物中で最高，沸点4400 ℃．密度10.001 g cm－3(25 ℃)．非常に安定で，水，アルカリ，希酸に不溶，熱濃硫酸に可溶．高温で生成したものほど酸に溶けにくい．四塩化炭素やホスゲンなどの塩素化剤と反応して塩化トリウムに，また金属カルシウムやマグネシウムによって還元されて金属トリウムになる．硝酸，硫酸製造，石油化学工業などで触媒として，また，タングステンに少量添加すると熱電子を放出しやすくなるため，アーク溶接用電極，放電灯陰極に使われる．ニッケルに約2％ ThO2を加えたニッケル合金は，耐腐食性および強度が増加するため，ロケット，化学装置，炉などに使われる．発がん性物質．森北出版「化学辞典（第2版）

使用Thorium 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).

一般的な説明White powder. Density 9.7 g / cm3. Not soluble in water. Used in high-temperature ceramics, gas mantles, nuclear fuel, flame spraying, crucibles, non-silicia optical glass, catalysis, filaments in incandescent lamps, cathodes in electron tubes and arc-melting electrodes.

製造方法Thorium 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.