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

Abstract

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.

The state of Fe3+ in the C–F–A–S–H system with varying Fe/Si and Ca/Si ratios

“…13a, C 1.0 F 1/8 ASH), indicating a transformation to a branched aluminosilicate structure, as a similar profile was observed in the cases of N–A–S–H and K–A–S–H. 35,45,46 This also corresponded to the evolutions of XRD patterns and SEM images (Fig. 4 and 6), namely from the layered C–A–S–H to the hydroandradite and disordered gel.…”

Eco-friendly Nano-adsorbents for Pollutant Removal from Wastewaters

“…Other method for ash modification is fusion method [57,74]. The main types of new materials that are obtained are presented in Table 4.…”

“…The researches have been shown that materials synthesized from ash using the fusion method have higher crystallinity, cation exchange, and adsorption capacities compared with materials synthesized using the conventional hydrothermal method [7,74].…”

Geopolymer Composites—In Environmentally Friendly Aspects

“…Nowadays, besides the classic geopolymerization method, several new synthesis routes have been developed. New preparation techniques include co-precipitation [ 25 ] and hydrothermal methods [ 26 ]; and the most promising route is the low-energy-consuming sol–gel technique [ 27 , 28 , 29 , 30 , 31 , 32 ]. The aluminosilicate materials prepared by the sol–gel method can be characterized by high purity and homogeneity, good uniformity, and good reactivity to other components.…”

“…The aluminosilicate materials prepared by the sol–gel method can be characterized by high purity and homogeneity, good uniformity, and good reactivity to other components. The typical starting materials in sol–gel chemistry are alkoxides (Al iso propoxide, tetraethoxysilane, TEOS) and ethanol as a solvent [ 27 , 28 , 29 , 30 , 31 ]. The fundamental reactions are hydrolysis and condensation, resulting in 3D aluminosilicate networks.…”