Geopolymer foams by gelcasting

Highly porous geopolymers, with homogeneous microstructure, open cells and porosity up to 80 vol%, were fabricated by gel-casting, a process commonly used to produce ceramic foams. Geopolymer foams were prepared by stirring an activated blend of metakaolin and fly ash with a mixture of potassium hydroxide and potassium silicate with Si/K=1.66. The cell size and size distribution of the geopolymer foams could be efficiently adjusted by the control of some parameters such as solid content, surfactant type and content and mixing speed. The influence of each parameter on the porosity and other characteristics of the geopolymer foams were investigated. The foams were evaluated only after heat treatment at 80 °C, which was conducted in order to complete the geopolymerization reactions. The produced components could be heat treated up to 1200 °C in air without melting, if desired.The characteristics (morphology, strength, chemical and thermal resistance) of the geopolymer foams suggest that they could be employed as low cost replacement for highly porous ceramics in applications such as catalysis supports, adsorption and separation, filtration of hot gases and refractory insulation of furnaces. In addition, these components could be considered sustainable, because they reach their final properties after processing at temperatures not exceeding 100 °C and part of the raw materials employed are industrial waste.