Callaghan Innovation Research Papers

Back to Research Papers

TitleCrystalline phase formation in metakaolinite geopolymers activated with NaOH and sodium silicate
Publication TypeJournal Article
Year of Publication2009
AuthorsZhang, B., Mackenzie K.J.D., and Brown I.W.M.
JournalJournal of Materials Science
Pagination4668 - 4676
Date Published2009
ISSN00222461 (ISSN)
KeywordsAluminium atoms, aluminum, Bridging oxygen, Coordination reactions, Crystalline materials, Crystalline phase, Crystalline phasis, Crystallinity, Geopolymerization, Geopolymers, Inorganic polymers, MAS NMR, Metakaolinite, Nano-sized crystals, Oxygen, Reaction routes, Rietveld, SEM, Silicon compounds, Sodium, Sodium silicate, Templating, X ray diffraction, X ray diffraction analysis, XRD, Zeolites
AbstractThe effect of the NaOH content and the presence of sodium silicate activators on the formation of crystalline phases from metakaolinite-based geopolymers were studied by X-ray powder diffraction (XRD), Rietveld quantitative XRD, solid-state MAS NMR and SEM in samples synthesized with varying NaOH contents and different curing times at 40°C. Geopolymers activated with NaOH alone with Si/Na ratios of 4/4 or less formed the crystalline zeolite Na-A (Na96Al96Si96O 384•216H2O), but at ratios >4/4 nanosized crystals of another zeolite (Na6[AlSiO4]6•4H 2O) were formed. The Si/Na ratio of 4/4 produces a product of greatest crystallinity. The addition of sodium silicate in addition to NaOH significantly reduces crystallite formation. The network units of all the materials containing NaOH and sodium silicate are essentially the same, namely, tetrahedral [SiO4] units coordinated through four bridging oxygens to four aluminium atoms [denoted as Q4 Si(4Al) units]. A templating function of the various silicate units of the sodium silicate molecules is suggested to occur in geopolymerization, which differs from the reaction route operating when NaOH alone is used as the activator. This templating function is responsible for the suppression of crystallization and the increase in strength of the geopolymers activated with sodium silicate. © 2009 Springer Science+Business Media, LLC.

Back to top