Preparation of fully stabilized cubic-leucite composite through heat-treating Cs-substituted K-geopolymer composite at high temperatures

Cf/cubic-leucite composite was prepared through heat-treating carbon fiber reinforced 20 at.% cesium substituted geopolymer precursor composite (Cf/CsKGP) at high temperatures. The thermal evolution, microstructure, mechanical and thermal expansion properties of the obtained composite were investigated, together with its non-isothermal oxidation behavior and high-temperature mechanical property. Post treatment at 1200 °C for 30 min in argon atmosphere, Cf/CsKGP was completely transformed into Cf/cubic-leucite composite, showing a better carbon fiber–matrix interfacial bonding and greatly improved mechanical properties as compared to Cf/tetragonal-leucite composite. Sol-SiO2 repeated impregnation process proved to be an efficient method to seal the cracks in Cf/cubic-leucite formed during the heat treatment, and the impregnated composite showed good oxidation resistance and excellent mechanical properties at elevated temperature range from 700 °C to 1200 °C in the air. It was therefore concluded that the cesium-substituted potassium-based geopolymer precursor technique and the sol-SiO2 impregnation process provide an alternative route for the preparation of ceramic composites for potential high-temperature applications.