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Open AccessArticle

Insights into the Microstructure of Hydrothermal Synthesized Nanoscale K2O-Al2O3-SiO2-H2O Particles

by Bao Liu 1,2,3, Chunyan Zhu 1,2, Kunde Zhuang 1,2, Le Shuai 1,2, Dongxu Li 1,2,3, Wujian Long 1,2, Feng Xing 1,2 and Yuan Fang 1,2,*
1
College of Civil and Transportation Engineering, Shenzhen University, Shenzhen 518060, China
2
Guangdong Provincial Key Laboratory of Durability for Marine Civil Engineering, Shenzhen 518060, China
3
Jiangsu National Synergetic Innovation Center for Advanced Materials (SICAM), Nanjing Tech University, Nanjing 210009, China
*
Author to whom correspondence should be addressed.
Nanomaterials 2020, 10(1), 63; https://doi.org/10.3390/nano10010063
Received: 28 November 2019 / Revised: 19 December 2019 / Accepted: 24 December 2019 / Published: 26 December 2019
K-A-S-H (K2O-Al2O3-SiO2-H2O) gel is a key phase that forms in most alkali-activated binders (eco-friendly binders which utilize a substantial amount of industrial by-product). An in-depth understanding of the microstructure and performance of this nano-sized key phase facilitates better application to alkali-activated binders. However, such studies remain little and undetailed. Therefore, our research aims to provide insights into the microstructure of K-A-S-H particles synthesized with accurate stoichiometric control by the hydrothermal method through thermogravimetric analysis (TG), Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and BET surface area. The results show that for materials prepared at the curing temperature lower than 80 °C, the K-A-S-H products were completely amorphous. With increased curing temperature and time, the K-A-S-H products were transformed from the amorphous phase to the crystalline zeolite phase structure, with a reduction in the specific surface area. The TG results indicate that the crystalline phase contains more non-evaporated water or zeolite water for structural rearrangement. The degree of tetrahedral polymerization slightly decreased with an increase of the K2O/SiO2 ratio as the amount of non-bridged oxygen atoms increased, whereas it gradually increased with an increase of curing temperature and time, as suggested by the FTIR and NMR results. Various K2O/SiO2 ratios resulted in the formation of zeolite K-H and K-G zeolite, both of which exhibited highly polymerized three-dimensional network structures. However, there was no significant effect of the SiO2/Al2O3 ratio on the structure of K-A-S-H products. Overall, these results provide insight into understanding the chemical stability of K-A-S-H. View Full-Text
Keywords: K-A-S-H; zeolite; nuclear magnetic resonance; polymerization degree; phase composition K-A-S-H; zeolite; nuclear magnetic resonance; polymerization degree; phase composition
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Liu, B.; Zhu, C.; Zhuang, K.; Shuai, L.; Li, D.; Long, W.; Xing, F.; Fang, Y. Insights into the Microstructure of Hydrothermal Synthesized Nanoscale K2O-Al2O3-SiO2-H2O Particles. Nanomaterials 2020, 10, 63.

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