Abstract:

: Raw material is one of the most decisive factors for the quality of sintered boron carbide (B 4C) products, in the past, there were relatively successful efforts for the synthesis of B 4C powders via carbothermal reduction approaches. To prepare high-quality powder, a deeper understanding of the relationship between technological manufacturing parameters and resulting powder properties is required. In this paper, pure B 4C powders were synthesized by rapid carbothermal reduction (RCR) under B 2O 3 excess conditions using boric acid and a carbonizing binder as B 2O 3 and carbon source, respectively. The molar ratio of B 2O 3/C of starting mixtures was varied from 0.75:1 to 4:1. The effects of heat-treating temperature and starting composition on phase constitution, morphology as well as stoichiometry of the prepared powders were investigated. The studies show that the starting composition has no effect on the stoichiometry of the powders, all boron carbides synthesized at 1900 °C have a stoichiometric composition of B 4C. With increasing heating temperature and B 2O 3 content in the starting composition, the particle size of B 4C was reduced. Uniform B 4C powders with an average grain size of 300 nm were synthesized at 1900 °C from a starting powder mixture with a molar ratio of B 2O 3/C = 4. A formation mechanism is proposed under large B 2O 3 excess conditions. For the starting powder mixtures with a molar ratio of B 2O 3/C < 2, the formation of boron carbide occurs through both liquid–solid reaction and gas–solid reaction. Accordingly, the synthesized powders exhibit a morphology with mixed elongated platelets and small polyhedral particles. For the starting powder mixtures with a molar ratio of B 2O 3/C ≥ 2, fine-sized B 4C particles were formed by a liquid–solid reaction.

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