Boron carbide, which has a high melting point, outstanding hardness, good mechanical properties, low specific weight, great resistance to chemical agents and high neutron absorption cross-section (10BxC, x>4) is currently used in high-technology industries—fast-breeders, lightweight armors and high-temperature thermoelectric conversion.

The contents of this review are: (1) introduction; (2) preparations—industrial preparative routes, powders, sintering (additives, pressureless, hot pressing, HIP); laboratory methods of synthesis (CVD, PVD, plasma, crystal growth); (3) analytical characterization; (4) phase diagram—a peritectic, nearly pure boron, and a wide phase homogeneity range (B4C-B10·5C); (5) rhombohedral crystal structure—a comprehensive model of the whole solid solution is proposed; (6) chemical properties; (7) physical properties—density, mechanical (strength, hardness, toughness) and thermo-electrical properties; (8) main industrial applications; (9) conclusion.

Boron carbide ― a comprehensive review

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. This paper provides a comprehensive review of the recent advances in understanding of structural and chemical variations in boron carbide and their influence on electronic, optical, vibrational, mechanical, and ballistic properties. Structural instability of boron carbide under high stresses associated with external loading and the nature of the resulting disordered phase are also discussed.

Boron Carbide: Structure, Properties, and Stability under Stress

Boron carbide is a strategic material, finding applications in nuclear industry, armour for personnel and vehicle safety, rocket propellant, etc. Its high hardness makes it suitable for grinding and cutting tools, ceramic bearing, wire drawing dies, etc. Boron carbide is commercially produced either by carbothermic reduction of boric acid in electric furnaces or by magnesiothermy in presence of carbon. Since many specialty applications of boron carbide require dense bodies, its densification is of great importance. Hot pressing and hot isostatic pressing are the main processes employed for densification. In the recent past, various researchers have made attempts to improve the existing methods and also invent new processes for synthesis and consolidation of boron carbide. All the techniques on synthesis and consolidation of boron carbide are discussed in detail and critically reviewed.

Synthesis and consolidation of boron carbide: a review

A method of forming (and apparatus for forming) refractory metal nitride layers (including silicon nitride layers), such as a tantalum (silicon) nitride barrier layer, on a substrate by using a vapor deposition process with a refractory metal precursor compound, a disilazane, and an optional silicon precursor compound.

Systems and methods of forming refractory metal nitride layers using disilazanes

In order to produce polycrystalline oxygen-terminated boron-doped diamond (BDD) electrodes suitable for electroanalysis (i.e., widest solvent window, lowest capacitive currents, stable and reproducible current responses, and capable of demonstrating fast electron transfer) for outer sphere redox couples, the following factors must be considered. The material must contain enough boron that the electrode shows metal-like conductivity; electrical measurements demonstrate that this is achieved at [B] > 1020 B atoms cm–3. Even though BDD contains a lower density of states than a metal, it is not necessary to use extreme doping levels to achieve fast heterogeneous electron transfer (HET). An average [B] ∼ 3 × 1020 B atoms cm–3 was found to be optimal; increasing [B] results in higher capacitive values and increases the likelihood of nondiamond carbon (NDC) incorporation. Hydrogen-termination causes a semiconducting BDD electrode to behave metal-like due to the additional surface conductivity hydrogen terminatio...

Examination of the factors affecting the electrochemical performance of oxygen-terminated polycrystalline boron-doped diamond electrodes.

We have obtained and analyzed Raman spectra of single-crystal, hot-pressed, and chemical-vapor-deposited boron carbide materials over their single-phase region (from {similar to}9 to {similar to}20 at. % carbon). These spectra provide insight into the substitutional disorder that characterizes these structurally ordered solids. In particular, although icosahedra and chain structures occupy regular lattice positions, there is local substitutional disorder resulting from the occupancy of certain sites within the icosahedra and chains by either boron or carbon atoms. Comparison of boron carbide Raman spectra with the Raman spectra of {alpha}-rhombohedral boron, boron phosphide, and boron arsenide has confirmed the following structural model derived from theoretical considerations and electrical and thermal transport data. The boron carbide composition with nearly 20 at. % carbon is composed of B{sub 11}C icosahedra linked by carbon-boron-carbon chains. As the carbon content is reduced toward approximately 13 at. %, carbon-boron-carbon chains are progressively replaced by carbon-boron-boron chains. Further reduction in the carbon content results in the replacement of B{sub 11}C icosahedra with B{sub 12} icosahedra.

Boron carbide structure by Raman spectroscopy

A Raman spectroscopic study confirms a structural model for boron carbides that was inferred from theory, transport data, and magnetic measurements. In this model substitutional disorder occurs within the icosahedra and chains that make up the boron carbide structure.

A. N. Campbell

Papers

Boron carbide structure by Raman spectroscopy

Boron carbides: Evidence for molecular level disorder