Invariant B to C Ratio in B‐rich Boron Carbide Powders Synthesized From Carbothermal Reduction Over a Wide Precursor Composition

ABSTRACT

Boron‐rich boron carbide (B _5.25 C) rather than stoichiometric B ₄ C powder was synthesized via vacuum carbothermal reduction at 1400°C from boric acid and sorbitol. This value (5.25) remains constant even when the ratio of carbon to boron source (C/B) molar ratio in the raw materials varies in a large range from 1 to 3; furthermore, the C/B value could affect the particle size of as‐synthesized powders obviously. The maximum boron utilization efficiency was achieved at a C/B ratio of 1.75, yielding B _5.25 C powders with an average particle size of 1.80 ± 0.25 µm, free carbon and oxygen contents of 0.38 wt.% and 0.46 wt.%, respectively. The powders prepared under optimal conditions show good sinterability; after sintering at 1900°C under 60 MPa for 15 min by spark plasma sintering, fully dense boron carbide ceramics were obtained, in which ∼42% of their grains exhibit twins with a misorientation angle of 74.7° <01>, demonstrating good mechanical properties.