Dehydration, dehydroxylation, densification and deformation during sintering of geopolymers based on the K2O-Al2O3-SiO2 system

Based on the principle of stability of geopolymer gel as refractory binder, a geopolymeric paste in the K2O-Al2O3-SiO2 system was developed and used to produce refractory concretes by adding various amount of α-quartz sand (grain size in the range 0.1μm-1mm) and fine powder alumina (grain size in the range 0.1-100 μm). The consolidated samples were characterized before and after sintering using optical dilatometer, DSC, XRD and SEM. The total shrinkage in the range of 25-900°C was less than 3%, reduced with respect to the most diffused potassium or sodium based systems, which generally records a >5% shrinkage. The maximum shrinkage of the base geopolymer was recorded at 1000°C with a 17% shrinkage which is reduced to 12% by alumina addition. The maximum densification temperature was shifted from 1000°C to 1150°C or 1200°C by adding 75wt% α-quartz sand or fine powder alumina respectively. The sequences of sintering of geopolymer concretes could be resumed as dehydration, dehydroxylation, densification and finally plastic deformation due to liquid phase appearance. The geopolymer formulations developed in this study appeared as promising candidates for high temperature applications. © 2009 Copyright