Mesoporous silicon nitride synthesis via the carbothermal reduction and nitridation of carbonized Silica/RF gel composite

Silicon nitride (Si3N4), a high-temperature structural ceramic, was synthesized in a mesoporous form by a simple approach. At first, silica/resorcinol-formaldehyde (RF) gel was formed via sol-gel polycondensation process, using resorcinol and formaldehyde as sources for porous RF structure and amino propyl trimethoxysilane as a precursor for silica. Pyrolysis of the dried gel at 250 degrees C for 2 h following by at 750 degrees C for 4 h resulted in silica/carbon composite that could be converted into mesoporous Si3N4 or Si3N4/silicon carbide composite via the carbothermal reduction and nitridation process at 1450 degrees C. Significant increase in surface area of the products, comparing with that of the conventional Si3N4 granules, was observed. The content of silica in the starting composite was found to be a critical factor influencing both phase and porosity of the obtained product.