boron carbide

B4C powder is most often produced through the high temperature carbothermal reduction of anhydrous boric oxide (B2O3) in graphite furnaces (tube, electric arc, or batch). The reaction goes around 1750 C, but is difficult to achieve with the high vaporization pressure of the boron source at temperatures well below that, which means that most B4C contains excess soluble boron. It is not a stoichiometric material, having numerous ranges of boron to carbon ratios.

Due to its high hardness and strongly covalent bonding, B4C is a difficult powder to sinter; fine particle sizes are difficult to produce without impurities due to its hardness, and there is no stable glassy phase formed in inert atmospheres to assist in pressureless sintering. Prohaszka of General Electric demonstrated pressureless sintering using additions of very fine carbon. The sintering takes place generally above 2000 Centigrade in argon atmosphere.

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