In-situ preparation of SiC reinforced Si3N4 ceramics aerogels by foam-gelcasting method

High strength SiC reinforced Si3N4 ceramics aerogels (SCSNCAs) were fabricated via foam-gelcasting and subsequent catalytic reaction, utilizing industrial Si and melamine as raw materials, a small amount of incidental Fe impurities in Si powder as the catalyst and cetyltrimethylammonium bromide (CTAB, the amount of 0.075 wt%) as foaming agent. The effects of solid loading level and reaction temperature on phase composition, microstructure and mechanical properties of the as-prepared SCSNCAs were examined. The aerogels prepared at 1423 K using a slurry of solid loading level of 30 wt% (Si:melamine = 3:1, mass ratio) had porosity of 91.9%, having compressive and specific strength of 0.8 MPa and 3.8 MPa center dot cm3 center dot g 1 exhibited the lowest thermal conductivity of 0.066 W/(m center dot K) at 473 K. Compared with the control sample (without melamine, i.e., Si3N4 aerogels without the formation of SiC), the specific strength of the SCSNCAs increased by about 10%, which was attributed to the additional reinforcement from SiC whiskers formed in the Si3N4 matrix of the aerogels.