Thorium is a chemical element with symbol Th and atomic number 90.



  • Many applications of thorium are becoming obsolete due to environmental concerns largely stemming from the radioactivity of thorium and its decay products. Thorium is thus being phased out of many of its uses.
  • Thorium is used in gas tungsten arc welding (GTAW) to increase the high-temperature strength of tungsten electrodes and improve arc stability. In electronic equipment, thorium coating of tungsten wire improves the electron emission of heated cathodes.
  • Many applications of thorium use the dioxide (commonly called “thoria” in the industry), rather than the metal.
  • When added to glass, thoria helps increase refractive index and decrease dispersion. Such glass finds application in high-quality lenses for cameras and scientific instruments. The radiation from these lenses can darken them and turn them yellow over a period of years and degrade film, but the health risks are minimal. Yellowed lenses may be restored to their original colourless state with lengthy exposure to intense ultraviolet radiation.
  • Thoria has been used as a chemical catalyst in the conversion of ammonia to nitric acid, in petroleum cracking and in producing sulfuric acid.
  • Thorium tetrafluoride is used as an antireflection material in multilayered optical coatings.




  • The chemical toxicity of thorium is low because thorium and its most common compounds (mostly the dioxide) are poorly soluble in water. Nevertheless, some thorium compounds are chemically moderately toxic. People who work with thorium compounds are at a risk of dermatitis. It can take as much as thirty years after the ingestion of thorium for symptoms to manifest themselves


Unknown, please consult with your doctor.

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