Barium carbonate

Barium carbonate

Chembox new
Name = Barium carbonate
ImageFile=Barium carbonate.png ImageSize=120px
OtherNames = witherite
Section1 = Chembox Identifiers
CASNo = 513-77-9
Section2 = Chembox Properties
Formula = BaCO3
MolarMass = 197.336 g/mol
Appearance = white crystals
Density = 4.2865 g/cm3, solid
Solubility = .0001 mol/l (25 °C)
MeltingPt = 811 °C
BoilingPt = 1555 °C

Barium carbonate (BaCO3), also known as witherite, is a chemical compound used in rat poison, bricks, ceramic glazes and cement.

Witherite crystallizes in the orthorhombic system. The crystals are invariably twinned together in groups of three, giving rise to pseudo-hexagonal forms somewhat resembling bipyramidal crystals of quartz, the faces are usually rough and striated horizontally.

The mineral is named after William Withering, who in 1784 recognized it to be chemically distinct from barytes. It occurs in veins of lead ore at Hexham in Northumberland, Alston in Cumbria, Anglezarke, near Chorley in Lancashire and a few other localities. Witherite is readily altered to barium sulfate by the action of water containing calcium sulfate in solution and crystals are therefore frequently encrusted with barytes. It is the chief source of barium salts and is mined in considerable amounts in Northumberland. It is used for the preparation of rat poison, in the manufacture of glass and porcelain, and formerly for refining sugar. It is also used for controlling the chromate to sulfate ratio in chromium electroplating baths. [cite web
last = Whitelaw
first = G.P.
coauthors =
title = Standard Chrome Bath Control
work =
pages =
publisher = finishing.com
date = 2003-10-25
url = http://www.finishing.com/Library/Whitelawchrome.html
accessdate = 2006-11-29 ]

Reactions

Barium carbonate reacts with many acids to soluble barium salts, for example barium chloride:

:BaCO3(s) + 2 HCl(aq) → BaCl2(aq) + CO2(g) + H2O(l)

However the reaction with sulfuric acid is poor, because barium sulfate is highly insoluble.

Uses

Barium carbonate is widely used in the ceramics industry as an ingredient in glazes. It acts as a flux, a matting and crystallizing agent and combines with certain coloring oxides to produce unique colors not easily attainable by other means. Its use is somewhat controversial since it can leach from glazes into food and drink. To provide a safe means of use, BaO is often used in fritted form.

In the brick, tile, earthenware and pottery industries barium carbonate is added to clays to precipitate soluble salts (calcium and magnesium sulfates) that cause efflorescence.

References

[http://ceramic-materials.com/cermat/material/86.html Barium Carbonate at CeramicMaterials.Info]

[http://ceramic-materials.com/cermat/education/138.html The use of barium in clay bodies]

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Look at other dictionaries:

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