Boron carbide is characterized by a unique combination of properties that make it a material of choice for a wide range of engineering applications. Boron carbide is used in refractory applications due to its high melting point and thermal stability; it is used as abrasive powders and coatings due to its extreme abrasion resistance; it excels in ballistic performance due to its high hardness and low density; and it is commonly used in nuclear applications as neutron radiation absorbent.
In addition, boron carbide is a high temperature semiconductor that can potentially be used for novel electronic applications.
Elastic and mechanical properties of boron carbide are derivative of such characteristics of atomic bonding as localization and delocalization, ionicity and covalence of the bonds and electron density in inter-atomic regions. In particular, higher stiffness and hardness is associated with more localized covalent bonds and higher inter-atomic electron density.
The hardest substances are all covalent solids, mainly based on carbon, boron and nitrogen.1 Boron carbide, long known,2 with an extreme hardness of about 30 GPa,3 is inferior only to diamond and cubic-BN, but is less expensive and easier to prepare. At temperatures above 1200 1C its hardness is reported to even exceed that of diamond.4 Coupled with its high thermodynamic stability (m.p. B2500 1C),5 low density (2.5 g cm 3 ) and remarkable chemical inertness,5 boron carbide serves as an ideal choice for a variety of important applications.
Among boron-rich materials, boron carbide has become the most extensively used technically;6 it is being used in abrasive/ shielding materials that sustain extreme conditions, such as light weight armor, and in nuclear reactors as a neutron absorber. It is also a promising material in high efficiency direct thermoelectric conversion7 and in special purpose doped semiconductors8 (though, so far, all doped boron carbides are only p-type semiconductors). The possibility of making superconducting materials9 and solid state neutron detectors10 based on the boron carbide family is also being explored.
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