Foamed geopolymer with customized pore structure

Geopolymer foams, due to their favorable production conditions and promising properties (e.g. low shrinkage after foaming, mechanical and chemical stability, high temperature resistance) are suitable for use as heat- and sound insulating as well as refractory building materials. Another promising field of application may be their use as catalyst supports in water treatment. Metakaolin based foams were prepared by direct foaming process with high total porosity (> 75 vol%), low bulk density (< 500 kg/m3), approximately 1 MPa compressive strength and low thermal conductivity (0.095 W/mK). By varying the concentration of foaming agent (H2O2 solution) and stabilizing agent (sodium oleate), it is possible to produce foams with designed porosity and pore size distribution. Foams with mainly closed pores are suitable for thermal insulation, while those with significantly open pores can use as catalyst supports. The computed tomography images showed that the concentration of stabilizing agent is a key parameter in the formation of a homogeneous pore structure and open pores; up to 24 vol% open porosity can be achieved without significantly affecting other properties. The physical properties of the foams are equally influenced by the thickness of cell walls and the size of the cells themselves.