Abstract
Based on the wet chemical analysis, we measured and modeled the kinetics of reactions between fly ash and KOH at various temperatures and water-to-solid mass ratios (W/S). We find that three consecutive rate-limiting processes control reaction progress: (1) dissolution or alteration of the glass phase in the fly ash, (2) classical Fick diffusion through a surface layer, and (3) diffusive transport through a more complex gel structure (interstitial gel). This sequence of processes is independent of W/S (0.35–40), temperature (22–75 °C), and KOH concentration (5–10 M). The relative contribution of each process to the overall reaction progress changes with experimental conditions. Only if and when the third process is rate limiting, a fly ash geopolymer forms and develops mechanical strength (sufficiently low W/S ratio provided). The rate of reaction progress decreases significantly, due to slow transport of reacting species to the surface of the glass particles.
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Acknowledgements
The authors are grateful for financial support of this project from the Vitreous State Laboratory (VSL) of the Catholic University of America (CUA). Chen Chen thanks the Chinese Overseas Fellowship Commission for financial support of his visit to VSL/CUA. The authors thank Drs. Hong Zhao, Andrew Buechele, and David McKeown (all VSL) for discussions and experimental support.
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Chen, C., Gong, W., Lutze, W. et al. Kinetics of fly ash geopolymerization. J Mater Sci 46, 3073–3083 (2011). https://doi.org/10.1007/s10853-010-5186-9
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DOI: https://doi.org/10.1007/s10853-010-5186-9