Barium carbonate

Barium carbonate
Other names	Witherite
Identifiers
CAS number	513-77-9 Y
EC number	208-167-3
UN number	1564
RTECS number	CQ8600000
SMILES	[Ba+2].[O-]C([O-])=O
InChI	1/CH2O3.Ba/c2-1(3)4;/h(H2,2,3,4);/q;+2/p-2
InChI key	AYJRCSIUFZENHW-NUQVWONBAT
ChemSpider ID	10121
Properties
Molecular formula	BaCO3
Molar mass	197.34 g/mol
Appearance	white crystals
Density	4.286 g/cm3
Melting point	811 °C
Boiling point	1360 °C (decomp)
Solubility in water	0.0024 g/100 mL (20 °C)
Solubility	soluble in HCl, HNO3, ammonia, ethanol insoluble in H2SO4
Refractive index (nD)	1.60
Hazards
MSDS	ICSC 0777
EU Index	056-003-00-2
EU classification	Harmful (Xn)
R-phrases	R22
S-phrases	(S2), S24/25
NFPA 704	0 2 0
Flash point	Non-flammable
LD50	418 mg/kg, oral (rat)
Related compounds
Other cations	Magnesium carbonate Calcium carbonate Strontium carbonate
Y (what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

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.^[1]

Preparation

Barium carbonate is made commercially from barium sulfide either by treatment with sodium carbonate at 60 to 70 °C (soda ash method) or by passing carbon dioxide at 40 to 90 °C.

In the soda ash process, solid or dissolved sodium carbonate is added to barium sulfide solution, and the barium carbonate precipitate is filtered, washed and dried. ^[2]

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 some claim that 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

• Barium Carbonate at CeramicMaterials.Info
• The use of barium in clay bodies

1. ^ Whitelaw, G.P. (2003-10-25). "Standard Chrome Bath Control". finishing.com. http://www.finishing.com/Library/Whitelawchrome.html. Retrieved 2006-11-29. 
2. ^ Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002, ISBN 0070494398

• This article incorporates text from the Encyclopædia Britannica, Eleventh Edition, a publication now in the public domain.