Preparation of Boron Carbide

Boron carbide powder is produced on a technical scale by the carbothermic reduction of boron oxide with graphite or petroleum coke 

The process is carried out in huge electric arc or resistance furnaces and is comparable to the Acheson process. The reaction takes place between 1500 and 2500°C, is strongly endothermic and requires 1812kJ/mol, i.e., 9.1 kWh/kg [159, 160]. Since large quantities of carbon monoxide (approximately 2.3m /kg) are formed, the reaction of Eq. (2) is accelerated to the benefit of B4C. Both volatilized boron oxides and carbon monoxide generate an internal Boudouard equilibrium within the raw material mixture and thus contribute to a self-propagating purification process, which can be expressed by 

The furnace is usually cooled externally to limit the toss of volatile materials and hence the outer mantle stays unreacted. The core contains blocky boron carbide of relatively high purity (total metallic impurities 0.5 mass-%), reproducible stoichiometry (B/C ratio = 4.3) [50], and several percent of residual graphite. The chunks are crushed and milled to the final grain size. 

A similar process with lower productivity is used for the synthesis of high-purity B4C of controlled stoichiometry. At temperatures of 1600-1800 C, hydroboric acid reacts with acetylene black, high purity sugar, or ethylene glycol in a vented tube furnace  

Boron oxide can also be converted to boron carbide by exothermic magnesio-thermic reduction in the presence of carbon black at 1000-1800°C [162], 

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S.3.2.2. Laboratory Preparation of Boron Carbide (from the Eiements or Boron Haiides)... 

Some routes for the preparation of boron carbide ceramics were investigated recently. 

Joly [21] reported the preparation of boron carbide in 1883, labeling the product as B3C, whilst in 1899 Moisson [22] labeled the compound as BeC. Yet, another 50 years passed until Ridgeway [23] suggested the stoichiometry to be 4 to 1. Today, it is well established that the composition of boron carbide has no exact stoichiometric composition but ranges from B4 3C to B10.4C. The composition of commercially produced boron carbide, using the carbothermal reduction of boron oxide in arc furnaces, is usually close to B4C, which corresponds to the stoichiometric limit on the high-carbon side. 

Welna, D. T. Bender, J. D. Wei, X. Sneddon, L. G. and AUcock, H. R. Preparation of boron-carbide/ carbon nanofibers from a poly(norbornenyldecaborane) single-source precursor via electrostatic spinning. Adv. Mater, 2005,17, 859-862. 

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