Effect of sintering temperature and ccalcium oxide content on microstructure and properties of geopolymer porous ceramics

Geopolymer porous ceramics with high porosity were prepared using casting process with metakaolin as the main raw material and coconut diethanolamide as the blowing agent. The effects of sintering temperature and calcium oxide content on the phase composition, microstructure and physical properties of geopolymer porous ceramics were investigated through X-ray diffraction, scanning electron microscopy, etc. The results show that for the samples without calcium oxide, the compressive strength and volume shrinkage gradually increase, while the open porosity gradually decreases with the sintering temperature increases. After the green body was sintered at 1200 degrees C for 2 hours, porous ceramic product with compressive strength of 22.9 MPa, open porosity of 41.8%, and leucite as the main phase was obtained. The addition of calcium oxide in the preparation process not only accelerate the solidification of geopolymer gel slurries and make the pores distribute in the height direction more evenly, but also acts as a modifier to lower the crystallization temperature of leucite in the sintering process. When the relative mass of calcium oxide to metakaolin is 6%, after sintering at 1000 degrees C for 2 hours, porous ceramic products with uniform pore size distribution containing leucite phase can be obtained. In addition, the potential of geopolymer porous ceramics as adsorbing material was validated by adsorption experiment of Pb(II) solution.