Journal
JOURNAL OF MATERIALS SCIENCE
Volume 46, Issue 9, Pages 3073-3083Publisher
SPRINGER
DOI: 10.1007/s10853-010-5186-9
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Funding
- Vitreous State Laboratory (VSL) of the Catholic University of America (CUA)
- Chinese Overseas Fellowship Commission
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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 A degrees 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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