Preparation of eco-friendly porous ceramic with low thermal conductivity by high-temperature treatment of foamed solid waste based geopolymer with cenospheres.

[Display omitted] • Porous ceramic was prepared by foamed cenosphere/geopolymer technology. • Compressive strength of the foamed composites was improved after crystallization. • Lowest thermal conductivity was obtained after crystallization. In order to enrich the porosity and high-temperature performance of geopolymer, a facile synthesis of foamed fly ash/slag-based cenosphere/geopolymer composite and its in-situ formation of porous ceramic via heat treatment were provided. The synergistic effects of H 2 O 2 and fly ash cenospheres (FACs) on the phase evolution, pore distribution and properties were investigated. Results showed that the foamed samples with amorphous structure could be synthesized at room temperature and fully crystallized to porous ceramics containing mullite and leucite after treated above 1000 °C. Porosity of the samples was enhanced with the increase of H 2 O 2 ratio (1–6 wt%) and treated temperature (600–1200 °C). Compressive strength of the whole composites was improved after treatment, which was attributed to the crystallization, good interface combination (between FACs and matrix), fractured spheres and crack deflection. The samples also showed lowest thermal conductivity of 0.115 W/(m⋅K) and 0.107 W/(m⋅K) before and after high-temperature treatment, respectively. It provided a strategy to prepare porous foam using solid waste and had the application to be used in insulation fields. [ABSTRACT FROM AUTHOR]