Boron carbide
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IUPAC name
Boron carbide
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Other names
Tetrabor
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Identifiers | |
3D model (
JSmol ) |
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ChemSpider | |
ECHA InfoCard
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100.031.907 |
PubChem CID
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UNII | |
CompTox Dashboard (EPA)
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Properties | |
B4C | |
Molar mass | 55.255 g/mol |
Appearance | dark gray or black powder, odorless |
Density | 2.50 g/cm3, solid.[1] |
Melting point | 2,350 °C (4,260 °F; 2,620 K)[1] |
Boiling point | >3500 °C[1] |
insoluble | |
Structure | |
Rhombohedral
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Hazards | |
Safety data sheet (SDS) | External MSDS |
Related compounds | |
Related compounds
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Boron nitride |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Boron carbide (chemical formula approximately B4C) is an extremely hard
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.[3]History
Boron carbide was discovered in the 19th century as a by-product of reactions involving metal borides, but its chemical formula was unknown. It was not until the 1930s that the chemical composition was estimated as B4C.[4] Controversy remained 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 B12 icosahedra.
These features argued against a very simple exact B4C empirical formula.[5] 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.
Crystal structure
Boron carbide has a complex crystal structure typical of
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 B12C2 units.[5][7] Some studies indicate the possibility of incorporation of one or more carbon atoms into the boron icosahedra, giving rise to formulas such as (B11C)CBC = B4C at the carbon-heavy end of the stoichiometry, but formulas such as B12(CBB) = B14C at the boron-rich end. "Boron carbide" is thus not a single compound, but a family of compounds of different compositions. A common intermediate, which approximates a commonly found ratio of elements, is B12(CBC) = B6.5C.[8] Quantum mechanical calculations have demonstrated that configurational disorder between boron and carbon atoms on the different positions in the crystal determines several of the materials properties – in particular, the crystal symmetry of the B4C composition[9] and the non-metallic electrical character of the B13C2 composition.[10]
Properties
Boron carbide is known as a robust material having extremely high hardness (about 9.5 up to 9.75 on
As of 2015[update], boron carbide is the third hardest substance known, after
Semiconductor properties
Boron carbide is a semiconductor, with electronic properties dominated by hopping-type transport.[8] The energy band gap depends on composition as well as the degree of order. The band gap is estimated at 2.09 eV, with multiple mid-bandgap states which complicate the photoluminescence spectrum.[8] The material is typically p-type.
Preparation
Boron carbide was first synthesized by
- 2 B2O3 + 7 C → B4C + 6 CO
If magnesium is used, the reaction can be carried out in a graphite crucible, and the magnesium byproducts are removed by treatment with acid.[17]
Applications
For its hardness :
- Padlocks
- Personal and vehicle ballistic armor plating
- Grit blasting nozzles
- High-pressure water jet cutter nozzles
- Scratch and wear resistant coatings
- Cutting tools and dies
- Abrasives
- Metal matrix composites
- In brake linings of vehicles
For other properties :
- nuclear reactors(see below)
- ramjets
Nuclear applications
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[18] and from anti-personnel neutron bombs. Nuclear applications of boron carbide include shielding.[11]
See also
References
- ^ ISBN 9781498754293.
- ^
Gray, Theodore (2012-04-03). The Elements: A Visual Exploration of Every Known Atom in the Universe. Black Dog & Leventhal Publishers. ISBN 9781579128951. Retrieved 6 May 2014.
- ^
"Rutgers working on body armor". Asbury Park Press. Asbury Park, N.J. August 11, 2012. Retrieved 2012-08-12.
... boron carbide is the third-hardest material on earth.
- ^ Ridgway, Ramond R "Boron Carbide", European Patent CA339873 (A), publication date: 1934-03-06
- ^ a b
Balakrishnarajan, Musiri M.; Pancharatna, Pattath D.; Hoffmann, Roald (2007). "Structure and bonding in boron carbide: The invincibility of imperfections". New J. Chem. 31 (4): 473. doi:10.1039/b618493f.
- ^ .
- ^ ISBN 978-0-08-037941-8.
- ^ doi:10.1111/j.1551-2916.2011.04865.x. Archived from the original(PDF) on 27 December 2014. Retrieved 23 July 2015.
- S2CID 39400050.
- S2CID 11805838.
- ^ a b Weimer, p. 330
- .
- PMID 19257210.
- ^ "Boron Carbide". Precision Ceramics. Archived from the original on 2015-06-20. Retrieved 2015-06-20.
- .
- ^ Weimer, p. 131
- ISBN 0-07-049439-8
- American Society for Testing Materials, 1959
Bibliography
- Weimer, Alan W. (1997). Carbide, Nitride and Boride Materials Synthesis and Processing. Chapman & Hall (London, New York). ISBN 0-412-54060-6.