The composition range of aluminosilicate geopolymers

Aluminosilicate geopolymers with SiO(2)/Al(2)O(3) ratios ranging from 0.5 to 300 have been prepared from mixtures of dehydroxylated kaolinite with either p-Al(2)O(3) or fine Aerosil SiO(2), with the ratios Na(2)O/SiO(2) and H(2)O/SiO(2) kept constant throughout the series. All the compositions hardened at ambient temperature, but the high-alumina compositions were of low strength and did not display typical XRD and NMR geopolymer characteristics, by contrast with the compositions of S/A between 2 and 300 which showed typical amorphous geopolymer XRD traces and (27)Al, (29)Si and (23)Na NMR spectra. The samples with increasing SiO(2) content (S/A > 24) showed increasingly elastic behaviour, deforming rather than crushing in brittle fashion, and upon heating at 100-250 degrees C, their hydration water was expelled as bubbles, forming stable foamed materials at about 300 degrees C. (c) 2004 Elsevier Ltd. All rights reserved.