Phosphate-Activated Fayalite-Based Geopolymer Foam

Nikolov, Aleksandar; Tarassov, Mihail; Tsvetanova, Liliya; Delcheva, Zlatka; Jordanov, Nicolai; Velinov, Nikolay; Rostovsky, Ivan

doi:10.3390/ceramics9070071

Open AccessArticle

Phosphate-Activated Fayalite-Based Geopolymer Foam

by

Aleksandar Nikolov

^1,*

,

Mihail Tarassov

¹

,

Liliya Tsvetanova

¹

,

Zlatka Delcheva

¹,

Nicolai Jordanov

²

,

Nikolay Velinov

³

and

Ivan Rostovsky

⁴

¹

Institute of Mineralogy and Crystallography, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., bl. 107, 1113 Sofia, Bulgaria

²

Institute for Physical Chemistry, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 11, 1113 Sofia, Bulgaria

³

Institute of Catalysis, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., bl. 11, 1113 Sofia, Bulgaria

⁴

Department of Building Materials and Insulations, Faculty of Civil Engineering, University of Architecture, Civil Engineering and Geodesy, blvd. “Hristo Smirnenski” 1, 1046 Sofia, Bulgaria

^*

Author to whom correspondence should be addressed.

Ceramics 2026, 9(7), 71; https://doi.org/10.3390/ceramics9070071

Submission received: 11 June 2026 / Revised: 10 July 2026 / Accepted: 14 July 2026 / Published: 17 July 2026

(This article belongs to the Special Issue The Production Processes and Applications of Geopolymers, 2nd Edition)

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Abstract

This study presents the development of a one-part phosphate-activated geopolymer foam based on fayalite flotation residue from the copper industry. The solid activator consisted of triple superphosphate, enabling a dry-mix binder that requires only water addition prior to use. Foamed materials were characterized by XRD, FTIR, Mössbauer spectroscopy, DSC-TG, hot-stage microscopy, SEM-EDX and physical and mechanical testing. The foaming of the geopolymer reduced the densities between 0.753 and 2.15 g/cm³, relative porosities up to 73.6%, and compressive strengths ranging from 1.4 to 28.8 MPa. The foamed geopolymer maintained dimensional stability up to about 1000 °C. The thermal conductivity coefficient measured on large-sized specimen blocks was 0.099 W/mK at a density of 0.753 g/cm³. These results demonstrate that fayalite slag can be effectively utilized as a precursor for sustainable geopolymer foams combining low thermal conductivity, high thermal stability, and the utilization of industrial by-products.

Keywords: phosphate geopolymer; one-part; foam; fayalite slag; iron silicate fines; thermal insulation; fire-resistant; sustainable construction materials

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MDPI and ACS Style

Nikolov, A.; Tarassov, M.; Tsvetanova, L.; Delcheva, Z.; Jordanov, N.; Velinov, N.; Rostovsky, I. Phosphate-Activated Fayalite-Based Geopolymer Foam. Ceramics 2026, 9, 71. https://doi.org/10.3390/ceramics9070071

AMA Style

Nikolov A, Tarassov M, Tsvetanova L, Delcheva Z, Jordanov N, Velinov N, Rostovsky I. Phosphate-Activated Fayalite-Based Geopolymer Foam. Ceramics. 2026; 9(7):71. https://doi.org/10.3390/ceramics9070071

Chicago/Turabian Style

Nikolov, Aleksandar, Mihail Tarassov, Liliya Tsvetanova, Zlatka Delcheva, Nicolai Jordanov, Nikolay Velinov, and Ivan Rostovsky. 2026. "Phosphate-Activated Fayalite-Based Geopolymer Foam" Ceramics 9, no. 7: 71. https://doi.org/10.3390/ceramics9070071

APA Style

Nikolov, A., Tarassov, M., Tsvetanova, L., Delcheva, Z., Jordanov, N., Velinov, N., & Rostovsky, I. (2026). Phosphate-Activated Fayalite-Based Geopolymer Foam. Ceramics, 9(7), 71. https://doi.org/10.3390/ceramics9070071

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Phosphate-Activated Fayalite-Based Geopolymer Foam

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