This mineral of thorium oxide, ThO2, is isomorphous with uraninite and occurs in black, nearly opaque cubic crystals in Ceylon and in Madagascar. Often containing rareearth metals and uranium, the ore is strongly radioactive. Because of its radioactivity, it is valuable in helping to date the relative ages of rocks in which it occurs.
Heavy white powder. Mohs hardness
6.5, very refractory. Soluble in sulfuric acid; insoluble
in water.
White cubic crystals; refractive index 2.200 (thorianite); density 10.0 g/cm3; hardness 6.5 Mohs; melts at 3,390°C; vaporizes at 4,400°C; insoluble in water or alkalis; soluble in acids with difficulties.
Ceramics (high temperature), gas mantles,
nuclear fuel, flame spraying, crucibles, medicine,
nonsilica optical glass, catalyst, thoriated tungsten
filaments.
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).
For example, thorium oxide (ThO2) has several uses,
including in the Welsbach lantern mantle that glows with a bright flame when heated by a
gas burner. Because of the oxide’s high melting point, it is used to make high-temperature
crucibles, as well as glass with a high index of refraction in optical instruments. It is also
used as a catalyst in the production of sulfuric acid (H2SO4), in the cracking procedures in
the petroleum industry, and in the conversion of ammonia (NH3) into nitric acid (HNO3).
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.
A white insoluble compound, used
as a refractory, in gas mantles, and as a replacement for silica in some types of optical glass.
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.
Has only weak oxidizing powers. Redox reactions can however still occur. Not water-reactive. Soluble in sulfuric acid.
Thoria, the most chemically stable oxideceramic, is only attacked by some earth alkalimetals under some conditions. It has the highestmelting point (3315°C) of the oxide ceramics.Like beryllia, it is costly. Also, it has highthermal expansion and poor thermal shockresistance.
Confirmed human
carcinogen producing angiosarcoma, liver
and kidney tumors, lymphoma and other
tumors of the blood system, and tumors at
the application site. See also THORIUM.
Thorium dioxide is known to be a human carcinogen based on sufficient evidence of carcinogenicity from studies in humans.
