Boron carbide

Boron carbide

Names
IUPAC name Boron carbide
Other names Tetrabor
Identifiers
CAS Number	12069-32-8 Y
3D model (Jmol)	Interactive image
ChemSpider	109889 Y
ECHA InfoCard	100.031.907
PubChem	123279
InChI InChI=1S/CB4/c2-1-3(2)5(1)4(1)2 Y Key: INAHAJYZKVIDIZ-UHFFFAOYSA-N Y InChI=1/CB4/c2-1-3(2)5(1)4(1)2 Key: INAHAJYZKVIDIZ-UHFFFAOYAS
SMILES B12B3B4B1C234
Properties
Chemical formula	B4C
Molar mass	55.255 g/mol
Appearance	dark gray or black powder, odorless
Density	2.52 g/cm3, solid.
Melting point	2,763 °C (5,005 °F; 3,036 K)
Boiling point	3,500 °C (6,330 °F; 3,770 K)
Solubility in water	insoluble
Acidity (pKa)	6–7 (20 °C)
Structure
Crystal structure	Rhombohedral
Hazards
Safety data sheet	External MSDS
Related compounds
Related compounds	Boron nitride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Y  (what is YN ?)
Infobox references

Boron carbide (chemical formula approximately B₄C) is an extremely hard boron–carbon ceramic, and covalent material used in tank armor, bulletproof vests, engine sabotage powders, as well as numerous industrial applications. With a Vickers Hardness of >30 GPa, it is one of the hardest known materials, behind cubic boron nitride and diamond.

Boron carbide was discovered in 19th century as a by-product of reactions involving metal borides, however, its chemical formula was unknown. It was not until the 1930s that the chemical composition was estimated as B₄C. There remained, however, controversy as to whether or not the material had this exact 4:1 stoichiometry, as in practice the material is always slightly carbon-deficient with regard to this formula, and X-ray crystallography shows that its structure is highly complex, with a mixture of C-B-C chains and B₁₂icosahedra. These features argued against a very simple exact B₄C empirical formula. Because of the B₁₂ structural unit, the chemical formula of "ideal" boron carbide is often written not as B₄C, but as B₁₂C₃, and the carbon deficiency of boron carbide described in terms of a combination of the B₁₂C₃ and B₁₂CBC units.

The ability of boron carbide to absorb neutrons without forming long-lived radionuclides makes it attractive as an absorbent for neutron radiation arising in nuclear power plants and from anti-personnel neutron bombs. Nuclear applications of boron carbide include shielding, control rod and shut down pellets. Within control rods, boron carbide is often powdered, to increase its surface area.