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
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