A New Route to High Yield Mesostructure Boron Carbide Powder from SiC/Si₃N₄ Whiskers

Abstract

Boric acid/Mg (magnesiothermic or metal sintering aid)/C (activated carbon)/N 2 or Ar (atmosphere)/ additives (mesoporous SiO 2 or mesoporous SiC or SiC/Si 3 N 4 whiskers) systems were used in the onestep synthesis of mesostructured B 4 C (221.04 m 2 /g). In this study, a mixture of the active precursors was allowed to react via a self-sustaining reaction (high-energy ball milling process). Also, the properties of the samples prepared using powdered activated carbon (PAC) and SiC/Si 3 N 4 whiskers (concentration in the range 5-10 wt%) as sources of carbon were investigated. X-ray diffraction results proved the presence of crystalline boron carbide in the peak positions of B 4 C (B 12 C 3 ). The advantage of the present route for yielding mesostructured B 4 C powder seems to be limited by the growth of carbide crystals. This restriction is believed to be imposed by a lack of whisker additives around the pores where B 4 C crystals grow. The results also show that the best mesoporous additive for the synthesis of nanoscale boron carbide is mesoporous SiC. The effect of the concentration of CO (reduction of α-Fe 2 O 3 to Fe by CO) on the B 4 C synthesis suggests that, in addition to the concentration of CO, the pressure of the N 2 atmosphere is an important factor in the synthesis of mesostructured B 4 C.