Morphological evolution of boron carbide particles: Sol-gel synthesis of nano/micro B4C fibers

Herein we present a novel non-catalytic sol-gel route to synthesize nano/micro boron carbide fibers. By in-situ decoration of the precursor surface with boric acid crystals during the thermal decomposition stage, the growth kinetics of boron carbide particles was manipulated. Therefore, the formation of anisotropic crystals instead of polyhedral-equiaxed ones was successfully enabled. The results indicated that highly crystalline boron carbide (B4C) particles with a low amount (<1 ± 5 wt%) of free carbon were obtained. The SEM and HR-FESEM micrographs revealed that B4C particles with fully polyhedral-equiaxed morphology were obtained from the precursors, which were thermally decomposed with 2 h holding time at 675 °C. As a result of increased thermal decomposition duration of precursor, B4C particles with various morphologies, such as rhomboid-plate, nanobelt, and fiber were formed beside the polyhedral-equiaxed particles. The yield of boron carbide fiber formation was increased, and polyhedral-equiaxed particles were decreased in the final products by tailoring the structure of the preceramic precursor. The products containing at least 50% of boron carbide fiber were achieved using 12 h of thermally decomposed precursors. The formation and growth mechanisms of boron carbide particles were speculated and comprehensively discussed.