Phase composition of ceramic-based alkali-activated polymers: combination of X-ray diffraction and thermal analysis
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Phase composition of ceramic‑based alkali‑activated polymers: combination of X‑ray diffraction and thermal analysis Martin Keppert1 · Lenka Scheinherrová1 · Magdaléna Doleželová1 · Eva Vejmelková1 · Robert Černý1 Received: 17 August 2019 / Accepted: 20 January 2020 © Akadémiai Kiadó, Budapest, Hungary 2020
Abstract Alkali-activated aluminosilicate polymers (AAP, geopolymers) are potentially able to replace partially the Portland cement production—and thus related energy consumption and CO2 emissions. Another benefit of AAP lies in possibility to prepare AAP from numerous aluminosilicate wastes. Besides the widely studied fly ash and blast furnace slag, also waste ceramic materials can be used. The present paper deals with preparation of AAP from alkali-activated red-clay ceramics. This material is specific, when compared to other AAP precursors, with lower amount of amorphous phase. The ceramic waste was activated by sodium silicate solution of various silicate moduli. The composition of the prepared materials was examined with the help of thermogravimetry and X-ray diffraction. Activated aluminosilicates are roentgen-amorphous, and thus, they are not directly detected by XRD; nevertheless, XRD can quantify the content of crystalline minerals and amorphous portion of material. Thermogravimetry was used in order to determine the amount of chemically bound water. Combination of these methods enabled to determine empirical formula of the activated material. Mixture of N–A–S–H and C–A–S–H products was identified; amount of C–A–S–H positively influenced the compressive strength of the prepared materials. Keywords Alkali-activated polymers · Ceramic precursor · XRD · TG
Introduction Alkali-activated inorganic polymers, known also as geopolymer binders, are attracting scientific and technical attention for last six decades, since the alkaline activation of aluminosilicates was described [1]. The term geopolymer was later introduced by Davidovits, who proposed general poly(sialates) empirical formula (1) [2, 3]; Al and Si atoms (AlO4 and SiO4 tetrahedrons) are alternately linked by oxygen bridges. The negative charge of this structure is balanced by a cation M. The Si/Al ratio can be 1 (poly(sialate)), 2 (poly(sialate-siloxo)) or 3 (poly(sialate-disiloxo)): } ) { ( Mn − SiO2 z − AlO2 n ⋅ wH2 O. (1) The resulting polycondensate is a roentgen-amorphous matter which can be considered as “amorphous zeolite”. * Martin Keppert [email protected] 1
Department of Materials Engineering and Chemistry, Faculty of Civil Engineering, Czech Technical University in Prague, Thákurova 7, 166 29 Praha 6, Czech Republic
Fundamental physical properties of aluminosilicate inorganic polymers predetermine their potential applications to be analogous to Portland cement or to conventional claybased ceramic, but without a direct need for a high-temperature process [4] what may reduce the C O2 emissions, compared to Portland cement-based materials, by 40–80% [5]. Later the concept of activated inorganic polymers was broadened
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