Thorium dioxide

Cubic

Th, O

Thorium ( IV) oxide

White crystalline solid

Fixed

10 g · cm -3

3390 ° C

4400 ° C

Insoluble in water and acids

Risk

400 mg · kg -1 ( LD50, mouse, oral)

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Thorium dioxide ( ThO2 ) is the only stable oxide of the radioactive element and the actinide thorium. In nature, the connection occurs as mineral thorianite.

Production

Thorium dioxide can be produced by oxidation of thorium and subsequent purification ( liberation of thorium residues).

Properties

Thorium dioxide is an odorless white powder. The mineral thorianite crystallizes in cubic Fluoritgitter. It has the highest melting point of all oxides, has a high refractive index and a high density of 9.86 g · cm -3. The water solubility of thoria is very low. Only in the strongly acidic pH range below pH = 4, the solubility increases slightly.

Applications

Thorium dioxide serves as an additional optical glass in order to increase the refraction. Earlier it was part of mantles. Further comprise tungsten electrodes 2 to 3% thoria, for stabilizing the electrical spark in electric welding. Due to the radioactivity of thorium civilian applications is limited. Thorium dioxide is also used as breeding material in breeder reactors.

Thorium dioxide can be used as a catalyst for the decarboxylation of carboxylic acids.

Hazards

Thorium dioxide is irritating to skin and eyes. In case of injury, it can enter the body and become toxic when inhaled it can be deposited in the lungs and irradiate them. Also it is very toxic if swallowed. The extremely durable material increases the risk of cancer. The X-ray contrast medium Thorotrast, which served to highlight details in X-ray images by the end of the 1940s, was no longer used because of the risk of cancer after the Second World War.