Properties and Use
Barium sulfate (BaSO4) is the barium salt of sulfuric acid. The term “barium” is derived from the Greek word barys = heavy, which indicates the element’s high atomic weight. Barium sulfate is practically insoluble in water, acids (an exception being hot concentrated sulfuric acid), and bases. Due to its extremely low water solubility, barium sulfate, as compared to other barium compounds, is non-toxic.
Occurrence and Production
In nature, barium sulfate is found as crystals which due to their high density are referred to as barite (heavy spar). Intergrowth of the crystals causes the formation of so-called barite roses. One of the rare manifestations of such barite roses in desert sand is called “desert rose”. The main heavy-spar deposits in Germany are located in Westphalia near the small town of Meggen . Considerably larger deposits are found in China which, in addition, ranks first in barium sulfate mining. The naturally occurring type of barium sulfate is used most commonly. For applications that require very pure white colors, barium sulfate is obtained by precipitation as “blanc-fixe” (permanent white).
Today, barite (heavy spar) is the only technically used base material for all barium compounds and for barium metal . The major quantity of the barium sulfate that is won by mining is used in oil and natural gas production to obtain high-density drilling fluids for flotation which keeps the boreholes free of rock. Barium sulfate, moreover, serves as filler (filling spar) in the plastics and the paint and varnish industries. It increases the plasticity and weight of plastic materials that are used for sound insulation in e.g., car mats, carpet coatings, or plastic sewage pipes. The chemical inertness and high temperature stability of barium sulfate are made use of in friction linings. Clutch and brake linings, for example, may contain up to 40 % barium sulfate. In the paint and varnish industry, high-quality barium sulfate is used as filler mainly due to its inertness and high density. It improves the volume and consistency, viscosity and workability of e.g., fillers, surfacers, and primers. Blanc-fixe is added for easy glazing of glossy papers and photographic papers (barite papers). Burning of such papers leaves whitish barium sulfate deposits. In the textile industry, barium sulfate is found as a finish for linen goods and an agent for rayon matting during etching and printing. Due to its high coefficient of absorption for gamma radiation and X-radiation, barium sulfate is used in concrete (barite concrete, barite cement) that screens nuclear reactors. It is contained, in addition, in numerous radio-opaque substances (radio-opaque barite).
About 70 % of the blanc-fixe produced is used in coating compounds. Blanc-fixe is brighter than barite. It comes in different particle sizes for use in e.g., primers and fillers for automobile finishing, industrial varnishes, building paints and construction coatings, wood varnishes, and printing inks. In covering coats and enamels, it is used as “spacer” to improve titanium dioxide pigment scattering or to avoid flocculation of organic or inorganic colored pigments. Compounds that consist of zinc sulfide and barium sulfate as a white pigment (lithopone) have become less important.
Blanc-fixe is used to improve the plasticity of plastics and serves as “spacer” (see above) for white pigments and colored pigments. Moreover, it is applied to increase the surface hardness and scratch resistance of polyolefins, to produce tintless white films or translucent plastics and to enhance the plasticity of many types of semi-crystalline thermoplastics. Medical devices such as catheters or drainage pipes, and toys which may be swallowed by children benefit from the powder’s capability to absorb X-radiation. Likewise, blanc-fixe improves the frictional behavior of particular synthetic-fiber surfaces.
The substance plays a secondary role today as filler in the paper industry.
NanoCare data sheet for download
Data sheet Barium sulphate.pdf