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3D model (JSmol) | |||
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| DrugBank | |||
| ECHA InfoCard | 100.028.896 | ||
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| UNII | |||
| UN number | 1564 | ||
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| Properties | |||
| BaSO4 | |||
| Molar mass | 233.39 g/mol | ||
| Appearance | white crystalline | ||
| Odor | odorless | ||
| Density | 4.49 g/cm3 | ||
| Melting point | 1,580 °C (2,880 °F; 1,850 K) | ||
| Boiling point | 1,600 °C (2,910 °F; 1,870 K) (decomposes) | ||
| 0.2448 mg/100 mL (20 °C) 0.285 mg/100 mL (30 °C) | |||
Solubility product (Ksp) | 1.0842 × 10−10 (25 °C) | ||
| Solubility | insoluble inalcohol,[1] soluble in concentrated, hotsulfuric acid | ||
| −71.3·10−6 cm3/mol | |||
Refractive index (nD) | 1.636 (alpha) | ||
| Structure | |||
| orthorhombic | |||
| Thermochemistry | |||
| 101.7 J/(mol K) | |||
Std molar entropy(S⦵298) | 132 J/(mol·K)[2] | ||
Std enthalpy of formation(ΔfH⦵298) | −1465 kJ/mol[2] | ||
| Pharmacology | |||
| V08BA01 (WHO) | |||
| by mouth, rectal | |||
| Pharmacokinetics: | |||
| negligible by mouth | |||
| rectal | |||
| Legal status | |||
| Hazards | |||
| GHS labelling: | |||
| P260,P264,P270,P273,P314,P501 | |||
| NFPA 704 (fire diamond) | |||
| Flash point | noncombustible[3] | ||
| NIOSH (US health exposure limits): | |||
PEL (Permissible) | TWA 15 mg/m3 (total) TWA 5 mg/m3 (resp)[3] | ||
REL (Recommended) | TWA 10 mg/m3 (total) TWA 5 mg/m3 (resp)[3] | ||
IDLH (Immediate danger) | N.D.[3] | ||
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |||
Barium sulfate (orsulphate) is theinorganic compound with the chemical formulaBaSO4. It is a white crystalline solid that is odorless andinsoluble inwater. It occurs in nature as the mineralbarite, which is the main commercial source ofbarium and materials prepared from it. Its opaque white appearance and its high density are exploited in its main applications.[4]
About 80% of the world's barium sulfate production, mostly purified mineral, is consumed as a component ofoil welldrilling fluid. It increases the density of the fluid,[5] increasing the hydrostatic pressure in the well and reducing the chance of ablowout.
Barium sulfate in suspension is often used medically as aradiocontrast agent forX-rayimaging and other diagnostic procedures. It is most often used in imaging of theGI tract during what is colloquially known as a "barium meal". It is administered orally, or byenema, as asuspension of fine particles in a thick milk-like solution (often with sweetening and flavoring agents added). Although barium is aheavy metal, and its water-soluble compounds are often highly toxic, the low solubility of barium sulfate protects the patient from absorbing harmful amounts of the metal. Barium sulfate is also readily removed from the body, unlikeThorotrast, which it replaced. Due to the relatively highatomic number (Z = 56) of barium, its compounds absorb X-rays more strongly than compounds derived from lighter nuclei.
The majority of synthetic barium sulfate is used as a component of white pigment for paints. In oil paint, barium sulfate is almost transparent[citation needed], and is used as a filler or to modify consistency. One major manufacturer of artists' oil paint sells "permanent white" that contains a mixture of titanium white pigment (TiO2) and barium sulfate. The combination of barium sulfate andzinc sulfide (ZnS) is the inorganic pigment calledlithopone. In photography it is used as a coating for certain photographic papers.[5]It is also used as a coating to diffuse light evenly.
Barium sulfate is highly reflective, of both visible and ultraviolet light.[6] Researchers used it as an ingredient in paint that reflects 98.1% ofsolar radiation, allowing surfaces to which it has been applied to stay cooler in sunlit conditions. Commercially available white paints only reflect 80 - 90% of solar radiation.[7] By using hexagonal nanoplateletboron nitride, the thickness of a coat of this type of paint was reduced to 0.15 mm.[6]
A thin layer of barium sulfate called baryta is first coated on the base surface of mostphotographic paper to increase thereflectiveness of the image, with the first such paper introduced in 1884 inGermany.[8] The light-sensitivesilver halide emulsion is then coated over the baryta layer. The baryta coating limits the penetration of the emulsion into the fibers of the paper and makes the emulsion more even, resulting in more uniform blacks.[9] Further coatings may then be present for fixing and protection of the image. Baryta has also been used to brighten papers intended forink-jet printing.[10]
Barium sulfate is commonly used as afiller for plastics to increase the density of the polymer in vibrational mass damping applications. Inpolypropylene andpolystyrene plastics, it is used as a filler in proportions up to 70%. It has an effect of increasing acid and alkali resistance and opacity. Such composites are also used as X-ray shielding materials due to their enhanced radio-opacity.[11] In cases where machinability and weight are a concern, composites with high mass fraction (70–80%) of barium sulfate may be preferred to the more commonly used steel shields.[12]
Barium sulfate can also be used to enhance the material properties ofHDPE,[13] although typically in relatively low concentrations, and often in combination with other fillers likecalcium carbonate ortitanium oxide.
Barium sulfate is used in soil testing. Tests forsoil pH and other qualities of soil use colored indicators, and small particles (usually clay) from the soil can cloud the test mixture and make it hard to see the color of the indicator. Barium sulfate added to the mixture binds with these particles, making them heavier so they fall to the bottom, leaving a clearer solution.
Incolorimetry, barium sulfate is used as a near-perfectdiffuser when measuring light sources.
In metal casting, the moulds used are often coated with barium sulfate in order to prevent the molten metal from bonding with the mould.
It is also used inbrake linings,anacoustic foams,powder coatings, androot canal filling.
Barium sulfate is an ingredient in the"rubber" pellets used byChilean police.[14] This together with silica helps the pellet attain a 96.5Shore A hardness.[14]
Barium sulfate is used as acatalyst support when selectivelyhydrogenating functional groups that are sensitive tooverreduction. With a low surface area, the contact time of the substrate with the catalyst is shorter and thus selectivity is achieved. Palladium on barium sulfate is also used as a catalyst in theRosenmund reduction.
As barium compounds emit a characteristic green light when heated at high temperature, barium salts are often used in green pyrotechnic formulas, althoughnitrate andchlorate salts are more common. Barium sulfate is commonly used as a component of "strobe" pyrotechnic compositions.
As barium sulfate has a highmelting point and isinsoluble in water, it is used as a release material in casting ofcopper anode plates. Theanode plates are cast in copper molds, so to avoid the direct contact of the liquid copper with the solid copper mold, a suspension of fine barium sulfate powder in water is used as a coating on the mold surface. Thus, when the molten copper solidifies in form of an anode plate it can be easily released from its mold.
Barium sulfate is sometimes used, besidespolytetrafluoroethylene (PTFE), to coat the interior of integrating spheres due to the high reflectance of the material and nearLambertian characteristics.
Barium sulfate is listed among the materials acceptable to theBureau of Alcohol, Tobacco, Firearms and Explosives (BATFE) for the manufacturing of firearms and/or components that are made of plastic, to achieve compliance with the U.S. federal requirement that an X-ray machine must be able to accurately depict the shape of the plastic firearm or component.[15]
Almost all of the barium consumed commercially is obtained frombarite, which is often highly impure. Barite is processed by thermo-chemical sulfate reduction (TSR), also known as carbothermal reduction (heating withcoke) to givebarium sulfide:
In contrast to barium sulfate, barium sulfide is soluble in water and readily converted to the oxide, carbonate, and halides. To produce highly pure barium sulfate, the sulfide or chloride is treated withsulfuric acid or sulfate salts:
Barium sulfate produced in this way is often calledblanc fixe, which is French for "permanent white". Blanc fixe is the form of barium encountered in consumer products, such as paints.[5]
In the laboratory barium sulfate is generated by combining solutions of barium ions and sulfate salts. Because barium sulfate is the least toxic salt of barium due to its insolubility, wastes containing barium salts are sometimes treated withsodium sulfate to immobilize (detoxify) the barium. Barium sulfate is one of the most insoluble salts of sulfate. Its low solubility is exploited inqualitative inorganic analysis as a test for Ba2+ ions, as well as for sulfate.
Untreated raw materials such as naturalbaryte formed underhydrothermal conditions may contain many impurities, a.o.,quartz, or even amorphoussilica.[16]
Barium sulfate is reduced tobarium sulfide by carbon. The accidental discovery of this conversion many centuries ago led to the discovery of the first syntheticphosphor.[4] The sulfide, unlike the sulfate, is water-soluble.
During the early part of the 20th century, during the Japanese colonization period,hokutolite was found to exist naturally in the Beitou hot-springs area near Taipei City, Taiwan. Hokutolite is a radioactive mineral composed mostly ofPbSO4 and BaSO4, but also containing traces of uranium, thorium and radium. The Japanese harvested these elements for industrial uses, and also developed dozens of “therapeutic hot-spring baths” in the area.[17]
Although soluble salts of barium are moderately toxic to humans, barium sulfate is nontoxic due to its insolubility. The most common means of inadvertent barium poisoning arises from the consumption of soluble barium salts mislabeled as BaSO4. In theCelobar incident (Brazil, 2003), nine patients died from improperly prepared radiocontrast agent. In regards to occupational exposures, theOccupational Safety and Health Administration set apermissible exposure limit at 15 mg/m3, while theNational Institute for Occupational Safety and Health has arecommended exposure limit at 10 mg/m3. For respiratory exposures, both agencies have set an occupational exposure limit at 5 mg/m3.[18]
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