Authors: L Weng K SagoeCrentsil
Publish Date: 2007/01/09
Volume: 42, Issue: 9, Pages: 2997-3006
Abstract
Initial geopolymeric reaction processes governing dissolution of solid aluminosilicate particles in alkali solutions have been investigated using conventional experimental techniques and the data analysed by speciation predictions of the partial charge model PCM For metakaolin powders activated with 50 M NaOH solidstate nuclear magnetic resonance NMR spectra disclose the existence of monomeric AlOH4− species after two hours of dissolution consistent with PCM predictions However no equivalent monomeric silicate species were observed for 50–100 M NaOH activator solutions characteristic of systems with nominal Si/Al ≤ 1 The apparent absence of monomeric silicate species suggest rapid condensation of silicate units with AlOH4− to generate aluminosilicate species as indicated by the evolution of the shoulder at around −87 ppm in the 29Si NMR spectra Of the two possible stable silicate species SiO2OH22− and SiOOH3− the latter appears most likely to condense with AlOH4− to produce aluminosilicate oligomers from which larger oligomers subsequently form through further condensation with AlOH4− leading to a gradual build up of aluminosilicate networks and a lowering of system alkalinity This dissolution and hydrolysis sequence at the early stages of synthesis suggests a reaction path wholly consistent with predictions of the partial charge model
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