Carbothermal route for preparation of boron carbide powder from boric acid–citric acid gel precursor

Boron carbide (B4C) powder has been prepared by carbothermal process using boric acid and citric acid as raw materials. Aqueous solution of boric acid in presence of citric acid forms a stable gel under controlled pH condition. The gel on subsequent pyrolysis under vacuum yields a precursor powder consisting of boron oxide and carbon. The precursor is heated under vacuum at 50 °C/h up to 1450 °C and the product obtained has been characterized by X-ray diffraction (XRD), chemical analysis, particle size analysis and scanning electron microscopy. XRD pattern shows that the product consists of B4C and carbon (graphite). Presence of free carbon (11.1 wt%) indicates boron loss in the carbothermal reaction. Boron loss has been calculated to be 11.3 wt%. Boron carbide powder obtained is composed of near equiaxial particles of narrow size distribution having a median size of 2.25 μm.