Formation of inorganic polymers (geopolymers) from 2 : 1 layer lattice alumino silicates

Attempts to produce fully reacted aluminosilicate inorganic polymers (judged on the basis of their hardening at ambient temperatures, amorphous XRD patterns and their Al-27 and Si-21 NMR spectra) from the crystalline 2:1 layer lattice mineral pyrophyllite were unsuccessful. Although dehydroxylation of this pyrophyllite at 800 degrees C produces significant changes in the Al coordination, the dehydroxylate does not form a viable geopolymer, probably because of its retention of a crystalline 2:1 layer structure which encloses the Al-O sheet by Si-O sheets and prevents alkaline attack to form soluble aluminate species. Disruption of the crystalline 2:1 layer lattice structure by severe mechanochemical processing (ball-milling for 60 h or vibro-milling for 15 min) leads to the formation of four-, five- and sixfold coordinated Al as in metakaolinite, and enables viable inorganic polymers to be formed at 60 degrees C which show the characteristic XRD, Al-27 and Si-29 MAS NMR spectra. These results illustrate the important role of the aluminate species in the formation of aluminosilicate inorganic polymers. (c) 2007 Elsevier Ltd. All rights reserved.