Preparation of phosphoric acid-based porous geopolymers

We report a porous geopolymer synthesized from metakaolin, α-Al2O3, Al powder and phosphoric acid at 80 °C for 5 h. The Al powder served as a foaming agent to control porosity, pore size and pore distribution producing a porosity ranging from 40% to 83% and a pore size of approximately 1 mm .The compressive strength was > 6 MPa. The phases of the geopolymers were determined by X-ray diffraction and their thermal properties investigated by TG-DTA and thermal shrinkage analysis. The porous geopolymer consisted of an amorphous phase and minor amounts of quartz, and showed an excellent thermal stability at a high temperature, with a linear shrinkage of only 5.3% at 1450 °C.