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Tailoring fly ash geopolymer ceramics: The influence of alkaline activation and thermal treatment on structure and phase transformation.

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Title: Tailoring fly ash geopolymer ceramics: The influence of alkaline activation and thermal treatment on structure and phase transformation.
Authors: Kljajević, Ljiljana1 (AUTHOR) ljiljana@vin.bg.ac.rs, Marković, Smilja2 (AUTHOR) smarkovic@itn.sanu.ac.rs, Mladenović Nikolić, Nataša1 (AUTHOR) natasa.nikolic@vin.bg.ac.rs, Nenadović, Miloš3 (AUTHOR) milosn@vin.bg.ac.rs, Mirković, Miljana1 (AUTHOR) miljanam@vin.bg.ac.rs, Pavlović, Vladimir2,4 (AUTHOR) vlaver@agrif.bg.ac.rs, Bučevac, Dušan1 (AUTHOR) bucevac@vin.bg.ac.rs, Nenadović, Snežana1 (AUTHOR) msneza@vin.bg.ac.rs
Source: Ceramics International. Feb2026, Vol. 52 Issue 5, p6342-6355. 14p.
Subjects: Heat treatment, Alkalinization, X-ray powder diffraction, Ceramics, Fourier transform infrared spectroscopy, Phase transitions, Fly ash, Sodium hydroxide
Abstract: In this study, fly ash, an industrial waste material, was used as a solid precursor for geopolymer synthesis. The sodium silicate to sodium hydroxide volume ratio was maintained at 1.6, with NaOH molarities of 2M, 4M, 6M, and 12M, and a liquid-to-solid ratio of 0.9. Thermal analysis demonstrated good stability of the geopolymer samples up to 900 °C, with major mass loss below 200 °C due to water evaporation and structural dehydroxylation between 200 and 650 °C. XRD analysis confirmed the presence of quartz, albite, and mullite in all samples, while increasing NaOH molarity led to the formation of faujasite. When these samples were heated, their internal structure became more organized and stable, leading to the formation of the mineral nepheline. This suggests that the thermal treatment was effective in promoting a more defined arrangement of atoms within the material, with this effect being particularly pronounced in samples produced using alkaline activators of higher molarity. FTIR spectroscopy identified vibrational bands corresponding Si–O/Al–O structures, with shifts in Si–O–T bands (T is Si, Al, Na) toward lower wavenumbers as alkalinity increased. Thermal exposure resulted in the disappearance of water-related signals and the emergence of carbonate band, confirming further phase transformation. These findings demonstrate the successful conversion of fly ash into geopolymer ceramics with tunable properties through controlled alkaline activation and heat treatment. [ABSTRACT FROM AUTHOR]
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Database: Engineering Source
Description
Abstract:In this study, fly ash, an industrial waste material, was used as a solid precursor for geopolymer synthesis. The sodium silicate to sodium hydroxide volume ratio was maintained at 1.6, with NaOH molarities of 2M, 4M, 6M, and 12M, and a liquid-to-solid ratio of 0.9. Thermal analysis demonstrated good stability of the geopolymer samples up to 900 °C, with major mass loss below 200 °C due to water evaporation and structural dehydroxylation between 200 and 650 °C. XRD analysis confirmed the presence of quartz, albite, and mullite in all samples, while increasing NaOH molarity led to the formation of faujasite. When these samples were heated, their internal structure became more organized and stable, leading to the formation of the mineral nepheline. This suggests that the thermal treatment was effective in promoting a more defined arrangement of atoms within the material, with this effect being particularly pronounced in samples produced using alkaline activators of higher molarity. FTIR spectroscopy identified vibrational bands corresponding Si–O/Al–O structures, with shifts in Si–O–T bands (T is Si, Al, Na) toward lower wavenumbers as alkalinity increased. Thermal exposure resulted in the disappearance of water-related signals and the emergence of carbonate band, confirming further phase transformation. These findings demonstrate the successful conversion of fly ash into geopolymer ceramics with tunable properties through controlled alkaline activation and heat treatment. [ABSTRACT FROM AUTHOR]
ISSN:02728842
DOI:10.1016/j.ceramint.2025.12.390