Open-cell cordierite-based foams from eco-friendly geopolymer precursors via replica route

Open-cell cordierite-based foams with high porosity were synthesized by a facile replica route, using geopolymers as precursors and polyurethane foams as polymer templates. The geopolymer precursors, incorporating MgO as an additional magnesium source, were prepared using metakaolin and fly ash under activation of NaOH solution and sodium silicate solution. Polyurethane foams with geopolymer were obtained by an impregnation method. The hybrid foams comprising polyurethane foam and geopolymer were cured/solidified at 75 °C for 24 h. Subsequently, the hybrid foams were subjected to ammonium ion-exchange followed by sintering at 1200 °C for 2 h to produce porous cordierite-based ceramics. The resulting foamed ceramics were characterized in terms of bulk density, porosity, structural evolution, and mechanical properties. Porous cordierite-based ceramic foams exhibiting a total porosity of approximately 88.64 vol% and a compressive strength of around 0.47 MPa were successfully fabricated by the replica route.