Low-temperature fabrication of SiC/geopolymer cellular composites

Hierarchically porous SiC-geopolymer foams were synthesized by using geopolymerization, which is a low temperature method (75 °C) that allows to replace the high temperature treatment process. The porosity was developed by a novel saponification/peroxide combined route, with H2O2 and olive oil used as foaming agents. The in-situ formation of the water-soluble soap and glycerol molecules generated by the saponification reaction and the decomposition of hydrogen peroxide enabled to obtain a large volume of interconnected macro-porosity. The reaction bonding behavior, phase composition, porosity characteristics, microstructure and mechanical strength of porous SiC-geopolymer ceramics were investigated. The combination of peroxide and oil enabled the production of open celled SiC-geopolymer composite foams in a rather large range of total porosity and strength values, with an optimal sample possessing a total porosity of up to ∼84 vol%, an open porosity of ∼83 vol%, a thermal conductivity of 0.15 W/mK, and a compression strength of ∼1.1 MPa.