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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. Nasab1, F. Golestanifard1,2, K.J.D. MacKenzie3
1 School of Metallurgy and Materials Engineering, Iran University of Science and Technology, P.O. Box 16845 – 161, Tehran, Iran
2 Center of Excellence for Advanced Materials, Iran University of Science and Technology, P.O. Box 16845 – 195, Tehran, Iran
3 MacDiarmid Institute for Advanced Materials and Nanotechnology, School of Chemical and Physical Sciences, Victoria University of Wellington, P.O. Box 600, Wellington, New Zealand
received February 22, 2014, received in revised form June 3, 2014, accepted June 16, 2014
Vol. 5, No. 3, Pages 185-192 DOI: 10.4416/JCST2014-00007
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.
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Keywords
Geopolymer, alkali activation, NMR spectroscopy, composition design, metakaolin
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