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Barium sulfate and barite

Amoebiasis as seen in radiograph of barium-filled colon

Barium sulfate (the mineral barite, BaSO₄) is important to the petroleum industry, for example, as adrilling fluid in oil and gas wells.^[3]:4–5 The precipitate of the compound (called "blanc fixe", from a French expression meaning "permanent white") is used in paints and varnishes, and also as a filler in ringing ink, plastics, and rubbers. It is also a paper coating pigment. In the form of nanoparticles, it can improve physical properties of some polymers, such as epoxies.

Barium sulfate has a low toxicity and relatively high density of ca. 4.5 g·cm⁻³ (and thus opacity to X-rays). For this reason it is used as a radiocontrast agent in X-ray imaging of the digestive system ("barium meals" and "barium enemas"). Lithopone, a pigment that contains barium sulfate and zinc sulfide, is a permanent white that has good covering power, and does not darken when exposed to sulfides.

Other barium compounds

Green barium fireworks

Aside from the sulfate, other compounds of barium find only niche applications. Applications are limited by the toxicity of Ba²⁺ ions (barium carbonate is a rat poison), which is not a problem for the insoluble BaSO₄.

·         Barium oxide is used in a coating for the electrodes of fluorescent lamps, which facilitates the release of electrons.

·         Barium carbonate is used in glassmaking. Being a heavy element, barium increases the refractive indexand luster of the glass. The compound is also used to reduce leaks of X-rays from cathode ray tubes (CRT) TV sets.

·         Barium, typically as barium nitrate, is added to fireworks to impart them a green color. The species responsible for the brilliant green is barium monochloride; in the absence of chlorine a yellow or "apple" green is produced instead.

·         Barium peroxide can be used as a catalyst to start an aluminothermic reaction when welding rail tracks together. It can also be used in green tracer ammunition and as a bleaching agent.

·         Barium titanate is a promising electroceramic.

·         Barium fluoride is used for optics in infrared applications because of its wide transparency range of 0.15–12 micrometers.

·         YBCO was the first high-temperature superconductor that could be cooled by liquid nitrogen, as its transition temperature of 93 K (−180.2 °C; −292.3 °F) exceeded the boiling point of nitrogen (77 K or −196.2 °C or −321.1 °F).

• [Editor:Yueleilei]