Production of nepheline/quartz ceramics from geopolymer mortars

This research has investigated the mechanical properties and microstructure of metakaolin derived geopolymer mortars containing 50% by weight of silica sand, after exposure to temperatures up to 1200 degrees C. The compressive strength, porosity and microstructure of the geopolymer mortar samples were not significantly affected by temperatures up to 800 degrees C. Nepheline (NaAlSiO4) and carnegieite (NaAlSiO4) form at 900 degrees C in the geopolymer phase and after exposure to 1000 C the mortar samples were transformed into polycrystalline nepheline/quartz ceramics with relatively high compressive strength (similar to 275 MPa) and high Vickers hardness (similar to 350 HV). Between 1000 and 1200 degrees C the samples soften with gas evolution causing the formation of closed porosity that reduced sample density and limited the mechanical properties. (C) 2012 Elsevier Ltd. All rights reserved.