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The Effect of the SiO₂/Na₂O Ratio in the Structural Modification of Metakaolin-Based Geopolymers Studied by XRD, FTIR and MAS-NMR

G.M. Nasab, F. Golestanifard, F. Golestanifard, K.J.D. MacKenzie

Journal of Ceramic Science and Technology, Vol. 5, No. 3 (2014), pp. 185-192

DOI: 10.4416/JCST2014-00007

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Abstract

A series of metakaolin-based geopolymers with different SiO2/Na2O compositions were synthesized to investigate the influence of the activator on the molecular nature and microstructure of the geopolymers. The structures and microstructures of the resulting products were systematically studied by means of XRD, FTIR, MASNMR, and SEM. The results show that the chemical composition of the activator and hence the ratios SiO2/Na2O and SiO2/Al2O3 exert a significant effect on the structure of the geopolymers. The XRD diffractograms indicated that the higher the concentration of silicate species in the activating solution, the higher the amorphous content of the geopolymer. Zeolite formation was observed in samples with low SiO2/Na2O ratios. The MAS NMR spectra of the cured materials showed that as the reaction progressed, the coordination of Al in the metakaolin changed almost completely to IV but the SiO2/Na2O ratio affects the position of the Q4(mAl) peaks.

Keywords

Geopolymer, alkali activation, NMR spectroscopy, composition design, metakaolin

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