The geopolymer group at ANSTO (Dr. Dan S. Perera), Australian Nuclear Science and Technology Organisation, has released a paper on the geopolymer-kalsilite-leucite heat transformation. It is available for free download
A geopolymer was prepared by dissolving metakaolinite in a solution of K2SiO3 and KOH and curing at 80°C for 24 h. It was progressively heated from ambient to 1400°C in air and the phase changes were studied by X-ray diffraction analysis, scanning electron microscopy and energy dispersive X-ray spectroscopy. Only an amorphous geopolymer phase was observed on heating up to 800°C. Kalsilite was the major phase at 1000°C and 1250-1400°C. At 1200°C leucite was the major phase formed. At 1400°C there was no sign of significant melting. The open porosity of the material was ~ 38% at 1000°C, which is sufficiently porous for it to be used as a heat insulation material for continuous use at this temperature.