Fabrication of pure SiC ceramic foams using SiO2 as a foaming agent via high-temperature recrystallization

A novel method was developed to produce the pure silicon carbide foams via the high-temperature recrystallization with the presence of a novel foaming agent-SiO2. In this method, SiO2 reacts with SiC to produce the gases in the silica liquid at high temperature, which leads to the formation of foams. The foams consist of the directional and interconnecting SiC crystals, and numerous intercommunicating pores that are located between them. The phase of foams was identified as 6H–SiC without the presence of SiO2 since SiO2 particles could react completely with SiC particles and vaporize from the sample at high temperature. The total porosity, weight loss and volume expansion rate can be increased with increasing SiO2 contents while the three-point bending strength decreasing. The porosity of SiC foam with 25 wt.% SiO2 as a foaming agent exhibits the maximum value while the three-point bending strength shows minimum value correspondingly. The sintered samples presented the porosities of 61–81%, the bending strength from 1.5 MPa to 4.8 MPa, and the volume expansion rate from 17.4% to 65%. This research can develop the theory for the preparation of SiC ceramics foams with controlled structure.