Incorporation of silica into RF gel for the synthesis of porous Si₃ N₄/SiC composite via the carbothermal reduction and nitridation

Abstract

Incorporation of silica into RF solution, which was prepared via the sol-gel polycondensation of resorcinol and formaldehyde with sodium carbonate as catalyst was investigated. The reaction between silica precursor and RF solution is quite violent and strongly exothermic. The addition of acetic acid into RF solution damages methylene and methylene ether bridges of the RF clusters, which enables the incorporation of increased amount of silica into the RF clusters. According to the experimental results, silica precursor (APTMS, MPTMS) incorporates into RF clusters at positions of hydroxyl group. Then, the silica/RF gel was converted into silica/carbon composite by pyrolysis before subjected to the carbothermal reduction and nitridation to synthesize silicon nitride/silicon carbide. The results indicated that temperature and porosity of silica/carbon composite does not affect the formation of silicon nitride or silicon carbide. Phase of the product depends upon chemical structure of silica/RF gel formed by polycondensation