期刊
JOURNAL OF SOL-GEL SCIENCE AND TECHNOLOGY
卷 96, 期 3, 页码 589-603出版社
SPRINGER
DOI: 10.1007/s10971-020-05360-6
关键词
Geopolymer gel; Alkali; Sol-gel method; Condensation mechanism
资金
- NSF [1538432]
- civil engineering department at University of Delaware
- Directorate For Engineering
- Div Of Civil, Mechanical, & Manufact Inn [1538432] Funding Source: National Science Foundation
To balance cost and performance of geopolymers, alkalinity of activating solution is critical. Alkalinity affects condensation that determines the final gel structures, but this effect is confounded by dissolution and is not understood from direct experimental evidence. In this study, we investigated effects of alkalinity on condensation for gels synthesized via a sol-gel method that eliminates dissolution process. As alkalinity increased, particle sizes of the gels increased as indicated by SEM, Si/Al ratios of the gels decreased but polymerization extent increased as supported by FTIR,Al-27 and(23)Na NMR, and composition analysis. The mechanism for the effects of alkalinity was proposed accordingly: (1) increasing alkalinity lowers the Si/Al ratio (i.e., more incorporation of Al) of the resulting products probably by affecting charging conditions of the Si and Al units; (2) the presence of Al(OH)(4)(-)units promotes their condensation with nearby species to increase the extent of polymerization; (3) enhanced condensation increases particle sizes of the gels even at microstructural level. This understanding on condensation independent of dissolution provides ways to control gel structures and Si/Al ratios and thus tailor properties accordingly, as well as to suggest a strategy (by altering Si/Al ratios during condensation) to develop kinetics-controlling admixtures. [GRAPHICS] .
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