Optimum pyrolysis conditions to prepare the most crystalline boron carbide powder from boric acid-mannitol complex ester.

Abstract

A weak acidic complex ester (CE) in solid form was prepared by a condensation reaction between very weak boric acid (BA: H₃BO₃) and (D)-mannitol (MA: C₆H₁₄O₆) by the molar ratio of BA/MA = 2. A boron carbide (B₄C) precursor was obtained from heating of the CE at 400 °C for 4 h. The precursor was pyrolyzed under argon flow in the interval of 1300-1550 °C for 4 h and at 1400 °C for 1-4 h, respectively. The materials were examined using several techniques such as X-ray diffraction analysis, thermal analysis, scanning electron microscopy, particle size distribution, and nitrogen adsorption/desorption. The optimum pyrolysis temperature and duration were 1400 °C and 4 h, respectively. The most crystalline B₄C particles were distributed between 1 and 100 μm with a mean particle size of 20 μm. The specific surface area and specific pore volume were 13.5 m² g^-1 and 0.09 cm³ g^-1, respectively. The size of the pores was between 2 and 36 nm with a mean size of 14 nm.