Barium sulfate
| Crystal structure | ||||||||||||||||||||||
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| __ Ba 2+ __ S 6+ __ O 2− | ||||||||||||||||||||||
| Crystal system |
orthorhombic |
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| Space group |
Pnma (No. 62) |
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| Lattice parameters |
a = 8.884 Å , b = 5.456 Å and c = 7.157 Å |
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| General | ||||||||||||||||||||||
| Surname | Barium sulfate | |||||||||||||||||||||
| other names |
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| Ratio formula | BaSO 4 | |||||||||||||||||||||
| Brief description |
colorless, rhombic crystals |
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| properties | ||||||||||||||||||||||
| Molar mass | 233.39 g mol −1 | |||||||||||||||||||||
| Physical state |
firmly |
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| density |
4.5 g cm −3 |
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| Melting point |
1580 ° C (decomposition) |
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| solubility |
practically insoluble in water (2.2 mg l −1 at 18 ° C) |
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| safety instructions | ||||||||||||||||||||||
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| MAK |
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| Thermodynamic properties | ||||||||||||||||||||||
| ΔH f 0 |
−1465.2 kJ mol −1 |
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| As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . | ||||||||||||||||||||||
Barium sulfate (BaSO 4 ) is the barium - salt of sulfuric acid .
Occurrence
In nature, barium sulfate occurs in the mineral barite (barite), which is the main raw material for the production of other barium compounds. In some algae, such as B. the cells of Closterium , barium sulfate occurs in the normal orthorhombic barite form. In the ciliate Loxodes it could be proven that the barium sulfate crystals serve as gravity receptors due to their high density.
properties
Barium (ordinal number 56 in PSE ) is derived from the Greek βαρύς / barys / "heavy". The natural mineral takes its name from this meaning of the word. Due to the high electron density, barium sulfate can be used as a positive X-ray contrast medium. Barium sulfate is a white powder that is practically insoluble in water, acids and alkalis, while it can be dissolved up to 12% in hot concentrated sulfuric acid. At high temperatures (> 1400 ° C) barium sulfate decomposes into barium oxide , sulfur dioxide and oxygen :
Due to its poor solubility, the mineral, unlike all other barium compounds, is not a hazardous substance.
It crystallizes orthorhombically , space group Pnma (space group no. 62) with the lattice parameters a = 8.884 Å , b = 5.456 Å and c = 7.157 Å.
Extraction and presentation
Barium sulfate is mainly obtained by breaking down the mineral barite. The two largest supplier countries are China and India . In 2019, the estimated global production was 9.5 million tons.
| country | 2018 | 2019, estimated |
|---|---|---|
| China | 2,900 | 2,900 |
| India | 2,390 | 2,200 |
| Iran | 490 | 490 |
| Kazakhstan | 620 | 620 |
| Laos | 90 | 420 |
| Morocco | 940 | 1,100 |
| Mexico | 380 | 400 |
| Pakistan | 110 | 110 |
| Russia | 163 | 160 |
| Turkey | 245 | 250 |
| United States of America | 366 | 390 |
| remaining countries | 482 | 480 |
| total | 9,180 | 9,500 |
The ore extracted is washed, crushed and ground and the barium sulfate is separated from the gangue by sedimentation . Further physical processing ( flotation ) and chemical processing ( oxidation , reduction ) further increase the purity and whiteness . Blanc fix is a synthetic barium sulphate produced by precipitation , which is used in particular as a filler . The precipitation of barium sulfide with sodium sulfate leads to a product that can be processed in a very fine-grained manner.
The precipitated barium sulfate is filtered off, dried and ground. The pure white barium sulfate usually has a particle size in the single-digit micrometer range.
To produce Blanc-fix pastes with a 25 to 30 percent solids content, barium chloride is reacted with sodium sulfate to form insoluble barium sulfate.
The barium chloride solution usually comes from the lithopone production or is produced by reacting barium sulfide with hydrochloric acid.
In the past, barium sulfate was produced when hydrogen peroxide was produced from barium peroxide when it was reacted with sulfuric acid .
use
Natural barium sulfate is used as a raw material for the technical production of other barium compounds, including barium metal. Barium sulfate is used as a filler in plastics , plastic masses, varnishes and paints , as well as in paper production. In addition, due to its physical properties, it is used in raw material extraction and in heavy concrete as well as due to the absorption of gamma and X-rays in radiation protection concrete and in radiology.
In the oil and gas industry
The most important application of barium sulphate - in terms of quantity - is its use in drilling mud . The high density of the barium sulfate results in suspensions whose density is so high that rocks float in the drilling mud and the borehole can be flushed free.
As a filler
Barite is used in the production of plastics for leveling compounds in the automotive repair sector, as a filler in clutch and brake linings, in carpet coatings and in sewer pipes. Due to its high density, it increases the density of the plastic, has a sound-absorbing effect and, thanks to its low oil number, improves processability and flow . It also increases the surface hardness and scratch resistance of plastics. Due to its temperature stability, it can also be used where other fillers such as calcium carbonate can no longer be used. In the manufacture of paper , barium sulfate is used as a filler to improve its spreadability (see Baryta paper for photo paper ).
As a white pigment
As blanc fixe , Blanc fixe , artist White , dolls White is precipitated barium sulfate , the white filler in many artists' paints and varnishes . It can also be found in opaque white . In the Color Index , barium sulphate is listed as synthetic BaSO 4 under the name CI Pigment White 21 and as “natural” barite under CI Pigment White 22. It is extremely lightfast and chemically stable. That is why it was also called permanent white . The effect as a white pigment is created by scattering at the interface between the filler and the surrounding binder . Therefore, barium sulfate appears almost transparent in binders that themselves have a refractive index close to that of barium sulfate (1.64). This small difference in the refractive indices is advantageous for use as an extender . In systems that are formulated above the critical pigment volume concentration , e.g. in emulsion paints , additional interfaces between barium sulfate and air are added. At this the difference of the refractive indices is greater, so that the opacity is significantly increased ( Dry-hiding effect ). When using organic pigments of strong color strength in small amounts, it is customary to produce so-called burns with barium sulfate as the carrier substance. The pigment and barium sulfate are ground together. The color location does not change, but the color strength is significantly reduced. This simplifies the dosage of small amounts of pigment. This method is needed for the production of glazes . Even with a nuance of pure white tones , it is advantageous to weigh larger amounts with reduced color strength. It was first marketed as Blanc fixe in 1830 by Kuhlmann in Lille . Natural, ground barite may have been used earlier. However , the barium sulfate produced by precipitation is finer and more brilliant and therefore better suited as a filler. The white pigment Lithopone is obtained as a mixture of barium sulfate and zinc sulfide by chemical reaction of BaS and ZnSO 4 in an aqueous medium .
In 1968, F. Grum and W. Luckey (Kodak) introduced barium sulfate as a white for coating integrating spheres . Due to its extremely low light absorption in the range between 250 nm and 2500 nm, barium sulfate is still used today, with a reflectivity of more than 90%, as the de facto standard for diffuse white reflectors. Teflon standards, which are more abrasion-resistant, are a replacement . Titanium dioxide is only suitable to a limited extent because of its noticeable absorption in the ultraviolet .
X-ray contrast media
In medicine, barium sulfate is given to patients as an X-ray contrast medium in the form of a milky suspension to drink in order to contrast the course of the digestive tract during an X-ray examination (positive X-ray contrast medium with high X-ray absorption). In lower concentrations, usually 1–1.5%, it is also used in computed tomography to mark the gastrointestinal tract.
Analytics
Sulphates are detected qualitatively by acidifying a sample solution with hydrochloric acid and adding barium chloride. The barium sulfate precipitates as a sparingly soluble, white precipitate. The barium sulphate precipitation is suitable both for the gravimetric determination of sulphate and for the determination of soluble barium with added sulphate.
Individual evidence
- ↑ Entry on BARIUM SULFATES in the CosIng database of the EU Commission, accessed on February 18, 2020.
- ↑ a b c d e f g Entry on barium sulfate. In: Römpp Online . Georg Thieme Verlag, accessed on November 26, 2016.
- ↑ a b c d data sheet Barium sulfate, Puratronic®, 99.998% (metals basis) from AlfaAesar, accessed on December 6, 2019 ( PDF )(JavaScript required) .
- ↑ a b List of MAK and BAT Values 2013
- ↑ G.Kortüm, H.Lachmann; Introduction to chemical thermodynamics; 7th, supplemented and revised edition; Page 465; Verlag Chemie; Weinheim; Vandenhoeck & Ruprecht; Göttingen; 1981; ISBN 3-527-25881-7 (Verlag Chemie); ISBN 3-525-42310-1 (Vandenhoeck & Ruprecht).
- ↑ D. Neugebauer et al. Evidence of central and peripheral gravireception in the ciliate Loxodes striatus, J. Comp. Physiol. A (1998) 183, 303-311.
- ^ RJ Hill: A further refinement of the barite structure. In: The Canadian Mineralogist , 15, 1977, pp. 522-526.
- ↑ a b c d BARITE. (pdf) USGS , January 2020, accessed April 10, 2020 .
- ↑ T. Brock, M. Groteklaes, P. Mischke; Paint technology textbook; 2nd Edition; Page 123; Vincentz Network; Hanover; 2000; ISBN 3-87870-569-7 .
- ^ F. Grum, GW Luckey; Optical Sphere Paint and a Working Standard of Reflectance; Applied Optics, Vol. 7, Issue 11, pp. 2289-2294 (1968), doi : 10.1364 / AO.7.002289 .