Synthesis and characterization of pure sol-gel Al2O3.2SiO2 as raw material in geopolymer preparation

Geopolymers are inorganic polymers obtained from the alkalination of aluminosilicate powders [1]. The mineralogy, the chemical composition and the reactivity of the precursor powders (metakaolins, fly ashes, sands, etc.) influence the properties of the final product. To shed new light on geopolymers based on uncontaminated silica and alumina, the sol-gel method [2] is used for the synthesis of the amorphous Al2O3.2SiO2, which is used for the geopolymer production, after the calcination at 750°C in muffle. Four EtOH:H2O ratios (1:9, 1:13, 1:17 and 1:24, respectively) were used to synthesize the aluminosilicate precursors. The Figure 1 reports the flow-chart procedure for the geopolymer synthesis. XRD analyses assessed the amorphous phase of the synthesized precursors, while FT-IR and NMR were used to follow the geopolymerization occurrence and the features of the MK and pure aluminosilicate-based geopolymers [3]. Leaching test and different NaOH solutions were also used to understand the reactivity of the synthesized precursors evaluating the Si and Al release [4]. Figure 1. Flow-chart procedure of the geopolymers from pure Al2O3.2SiO2. [1] Davidovits, J. 2020, Geopolymer Chemistry and Application (5th edition) [2] Brinker, C., Scherer, g. 1990, Sol-Gel Science, The Physics and Chemistry of Sol-Gel Processing [3] Catauro, M., Bollino, F., Cattaneo, A.s., Mustarelli, P. Al2O3.2SiO2 powders synthesized via sol-gel as pure raw material in geopolymer preparation, Journal of America Ceramic Society [4] Catauro, M., Bollino, F., Dell’Era, A., Vecchio Ciprioti, S. 2016, Pure Al2O3.2SiO2 synthesized via a sol-gel technique as a raw material to replace metakaolin: Chemical and structural characterization and thermal behaviour, Ceramic International