Influence of hydrothermal treatment parameters on the phase composition of zeolites
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Influence of hydrothermal treatment parameters on the phase composition of zeolites Eva Kuzielová1,2 · Matúš Žemlička1 · Jiří Másilko3 · Pavol Hudec2 · Martin T. Palou1,2,3 Received: 18 July 2019 / Accepted: 4 May 2020 © Akadémiai Kiadó, Budapest, Hungary 2020
Abstract Analcime was prepared by hydrothermal transformation of metakaolin-based geopolymer activated by means of sodium water glass. Gradual transformation of geopolymer through primary and unstable zeolitic phases up to final analcime was studied as a function of hydrothermal treatment duration (6–48 h) and access of water vapour under the selected conditions (165 °C, 0.5 MPa). Composition, microstructure, and thermal stability of the prepared samples were assessed using simultaneous thermogravimetry and differential scanning calorimetry, X-ray diffraction and high-temperature XRD analyses, and scanning electron microscopy. In the case of shorter autoclaving and access of water vapour, the mix of different zeolitic phases was formed: analcime, zeolite P2 gmelinite-Na, and chabazite-Na. From the time of 24 h and autoclaving in the closed moulds, pure cubic analcime was detected. Uniform microstructure of these samples comprised of trapezoid particles with the diameter between 50 and 60 µm. Prolongation of autoclaving time did not lead to the significant change of particle size and their composition. Dehydration of detected zeolites took place through the formation of defect or unknown zeolitic structures before the structural collapse happened. Keywords Metakaolin · Analcime · Hydrothermal curing · Thermal stability of zeolites
Introduction Analcime NaAl(Si2O6)·(H2O) is one of the microporous zeolites with irregular channels that occurs in nature. In dependence on the conditions of its formation and present impurities, it can possess different crystallographic systems (cubic, tetragonal, orthorhombic, monoclinic, or triclinic). Because of its compact structure and resulting resistance to diffusion of either molecules or cations, applications of analcime as microporous material were delimited for a long time in comparison with other zeolites. Nowadays, its * Eva Kuzielová [email protected] 1
Institute of Construction and Architecture, Slovak Academy of Sciences, Dúbravská cesta 9, 845 03 Bratislava, Slovak Republic
2
Faculty of Chemical and Food Technology, Slovak University of Technology, Radlinského 9, 812 37 Bratislava, Slovak Republic
3
Materials Research Centre, Faculty of Chemistry, Brno University of Technology, Purkyňova 118, 612 00 Brno, Czech Republic
applications are expanding. Analcime is used as an absorbent in the treatment of wastewater or, in the case of the metals-modified analcime, also as a heterogeneous catalyst in the selective adsorption reactions, e.g. in the nanoelectronics applications. Although natural analcime occurs in different kinds of environment (cavities of altered mafic volcanic rocks, in some undersaturated volcanic rocks, in both open and closed hydrologic systems, in low-temperature hydrothermal v
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