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Journal of Materials Science

, Volume 44, Issue 17, pp 4668–4676 | Cite as

Crystalline phase formation in metakaolinite geopolymers activated with NaOH and sodium silicate

  • Bo ZhangEmail author
  • Kenneth J. D. MacKenzie
  • Ian W. M. Brown
Article

Abstract

The 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 (Na96Al96Si96O384·216H2O), but at ratios >4/4 nanosized crystals of another zeolite (Na6[AlSiO4]6·4H2O) 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.

Keywords

Zeolite Geopolymer Sodium Silicate Sodium Silicate Solution Metakaolinite 

Notes

Acknowledgement

We are indebted to Martin Ryan for his assistance with the XRD quantitative analysis.

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Copyright information

© Springer Science+Business Media, LLC 2009

Authors and Affiliations

  • Bo Zhang
    • 1
    Email author
  • Kenneth J. D. MacKenzie
    • 1
  • Ian W. M. Brown
    • 1
  1. 1.Industrial Research Ltd.Lower HuttNew Zealand

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