Properties of Boron Carbide

The physical and chemical properties of boron carbide have been reviewed by Lipp [159], Thevenot and Bouchacourt [256], Thevenot [164,165], and Schwetz (1999) [223]. Special problems while presenting the physical properties arise from the large homogeneity range of boron carbide. Furthermore, its poor sinterability requests additives that are usually unspecified and results in residual porosity and various grain sizes which are often also not considered in the publications. Most variation and discrepancies in the properties reported come from the undefined composition of the materials studied. 

Thevenot [71] with those of Si-doped both single crystalline and polycrystalline B4C [83]. 

At room temperature the hardness of B4C is only inferior to diamond and cubic boron nitride, which tend to weaken above 500-600°C due to the beginning of the transformation from the diamond structure into the graphite structure. Above 

1100°C, and in a non-oxidizing atmosphere, B4C is the hardest compound known up to now. B4C is thus used for wear-resistant parts and inserts for mortars and ball mills, wear plates, sand blasting nozzles, dressing tools for grinding wheels, lightweight armor plates for helicopters, tanks, and in composites of glass fiber-reinforced plastics as bullet-proof protection for personnel. 

The large cross section for thermal neutrons makes boron carbide an interesting candidate for absorption or retardation of neutron radiation in power plants and as first-wall coating in fusion reactors. The cross section for °B is approximately 4000 barn, which is naturally present in boron carbide at 19.9%. 

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Maruyama, T., S. Onose, andT. Kaito. 1997. Effect of fast neutron irradiation on the properties of boron carbide pellet. J. Nucl Sci. Technol. 34 1006-1114. 

Such high concentrations of gap states attached to the valence band essentially affect the electronic charge transport in particular, they are responsible for the p-type character and the very low electrical conductivity. Aside from the electric conductivity in extended band states, a hopping-type conduction must be expected in localized gap states. The electronic properties of boron carbide can be consistently described by a band scheme, which highlights deep energy levels in the band gap (2.09 eV) at 0.065, 0.18, 0.47, 0.77, 0.92 and 1.2 eV (values based on optical measurements), related to the valence band edge. This allows the largely consistent description of all reliable experimental results [537]. 

Table 4.9 Physical properties of boron carbide ceramics used in armor applications. After Karandikar et al. [576]. 

The characteristics and properties of boron carbide are summarized in Table 8.2 (for structural data, see Table 7.5 of Ch. 7). They are reviewed in more detail in Secs. 4-8. The material has outstanding hardness and excellent nuclear properties (see Sec. 7.0). 

Table 8.2 Summary of Characteristics and Properties of Boron Carbide. Note Test temperature is 20°C unless otherwise stated.

Wood, C., Transport Properties of Boron Carbide, in Boron-Rich Solids, AIP Conf. Proc. 140 (D. Aselage, et al., eds.). Am Inst, of Physics, New York (1986)... 

Various results to furtiier develop these materials as TE materials have been obtained such as the densification of these materials through usage of sintering additives, doping with transition metals,and modification of the [B]/[C] composition, which previously had led to significant improvement in the TE properties of boron carbide. 

Baharvandi H. Hadian A Alizadeh A. (2006). Processing and Mechanical Properties of Boron Carbide-titanium Diboride Ceramic Matrix Composites. Applied Composite Materials, Vol. 13, No. 3, May, 2006, pp. 191-198, ISSN0929189X Basu B. Vleugels J. Biest O. (2005). Processing and Mechanical Properties of Zr02-TiB2 Composites. Journal of the European Ceramic Society, Vol. 25, No.l6, May,2005, pp.3629- 3637, ISSN 09552219... 

Recently, photoluminescence properties of boron carbide nanowires were being studied and reported. Photoluminescence spectrum of a thin film made out of B4C nanowires exhibited a broad band at 638 nm, which strongly suggests the potential application of boron nanowires in visible optical devices. Nonetheless, nanowire and nanorod structures based on boron carbide find their application in different areas, including field emission devices and thermoelectric energy converters, neutron adsorbent in nuclear industries, and especially in composite materials as reinforcing agents. ... 

Li-Hong, B. Chen, L. Yuan, T. Ji-Fa, T. Chao, H. Xing-Jun,W. Cheng-Min, S. and Hong-Jun, G. Synthesis and photoluminescence property of boron carbide nanowires. Chin. Phys. B, 2008,17,4585-4591. 

Another concept for describing the electronic properties of the boron-rich solids was developed by Emin et al. (13-16) on boron carbide. It is based on the assumption of hole bipolarons in BiiC icosahedra, and the essential basis of this theory is the experimental fact of a very low electron spin resonance (ESR) spin density. These authors were able to describe some uncommon electronic properties of boron carbide with their model. 

H Werheit. On the electronic transport properties of boron carbide. In R Freer, ed. The Physics and Chemistry of Carbides, Nitrides and Borides. Dordrecht Kluwer, 1990, p 677. 

U Kuhhnann, H Werheit. Properties of boron carbide related to the carbon distribution in the unit cell. Proceedings of the 11th International Symposium on Boron, Borides and Related Compounds, Tsukuha, 1993. JJAP Series 10 84, 1994. 

H Werheit, H Binnenbruck, A Hausen. Optical properties of boron carbide and comparison with P-rhombohedral boron. Phys Status Solidi (b) 47 153, 1971. 

H Werheit, U Kuhlmann, R Eranz, W Winkelbauer, B Herstefl, D Fister, H Neisius. Electronic transport properties of boron carbide within the homogeneity range. In D Emin, T Aselage, AC Switendick, B Morosin, CL Beckel, eds. Boron-Rich Solids, AIP Conference Proceedings 231. Albuquerque AIP, 1990, p 104. 

AK Bandyopadhyay, F Beuneu, L Zuppiroli, M Beauvy. The role of free carbon in the transport and magnetic properties of boron carbide. J Phys Chem Solids 45 207, 1984. 

Gibby, R.L., 1973, Thermal Properties of Boron Carbide and Europium (HI) Oxide, in ... 

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