Barium sulfate
Template:Chembox new Barium sulfate is a white crystalline solid with the chemical formula BaSO4. It is poorly soluble in water and other traditional solvents but is soluble in concentrated sulfuric acid. The mineral barite is composed largely of barium sulfate and is a common ore of barium.
Uses
Catalyst support
Barium sulfate is a low surface area material used as a support for selectively hydrogenating functional groups sensitive to overreduction. With a low surface area, the contact time of the substrate with the catalyst is shorter. A supported palladium catalyst on barium sulfate, and doped (poisoned) with quinoline hydrogenates alkynes into cis-alkenes. Alkenes are liable to be hydrogenated further into alkanes, which reaction the special support and poison prevent.
Radiocontrast agent
Barium sulfate is frequently used clinically as a radiocontrast agent for X-ray imaging and other diagnostic procedures. It is most often used in imaging of the GI tract during what is colloquially known as a 'Barium meal'.
It is administered, orally or by enema, as a suspension of fine particles in an aqueous solution (often with sweetening agents added). Although barium is a heavy metal, and its water-soluble compounds are often highly toxic, the extremely low solubility of barium sulfate protects the patient from absorbing harmful amounts of the metal. Barium sulfate is also readily removed from the body, unlike Thorotrast, which it replaced. Due to the relatively high atomic number (Z = 56) of barium, its compounds absorb X-rays more strongly than compounds derived from lighter nuclei.
Pigment
Barium sulfate mixtures are used as white pigment for paints. The combination of barium sulfate and zinc sulfide (ZnS) is called lithopone. Barium sulfate itself is called blanc fixe. It replaced white lead due to the latter's toxicity.
Pyrotechnics
Barium sulfate is also used as a high temperature oxidizer in certain pyrotechnic formulas, as barium compounds emit a green colored light when burned. Barium nitrate is more common in green pyrotechnic formulas, as it contains an oxidizer while still producing green colored light.
Other uses
Barium sulfate is used as a filler in plastics and as a component of oil well drilling fluid to increase the density. It is used in Episal salt.
It is used in brake linings, anacoustic foams and powder coatings
Barium sulfate is also used during the procedure of the soil pH test. In this test it is used so that it precipitates out any particles (usually clay particles) which would otherwise 'cloud' solution preventing one from seeing the colour of the pH indicator i.e. the result of the test.
It is used in root canal filling.
In colorimetry barium sulfate is used as a near-perfect diffuser when measuring light sources.
In photography it is used as a coating for certain photographic papers.
In metal casting, the moulds used are often coated with barium sulfate in order to prevent the molten metal from bonding with the mould.
History
Barium sulfate is reduced to barium sulfide by carbon. The accidental discovery of this conversion many centuries ago led to the discovery of the first synthetic phosphor (Hollman and Wiberg, 2001). The sulfide, unlike the sulfate, is water soluble.
Etymology
Barium, 1808, Mod.L., from Gk. barys "heavy;" so called by its discoverer, British chemist Sir Humphrey Davy (1778-1829) because it was present in the mineral barytes "heavy spar," from Gk. barys "heavy" (see grave (adj.)).
References
- Holleman, A. F. and Wiberg, E. (2001) Inorganic Chemistry, San Diego, CA : Academic Press, ISBN 0-12-352651-5