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A geopolymer is a vague pseudo-chemical term used to describe inorganic, typically bulk ceramic-like material that forms covalently bonded, non-crystalline (amorphous) networks, often intermingled with other phases. Many geopolymers may also be classified as alkali-activated cements or acid-activated binders. They are mainly produced by a chemical reaction between a chemically reactive aluminosilicate powder e.g. metakaolin or other clay-derived powders, natural pozzolan, or suitable glasses, and an aqueous solution (alkaline or acidic) that causes this powder to react and re-form into a solid monolith. The most common pathway to produce geopolymers is by the reaction of metakaolin with sodium silicate, which is an alkaline solution, but other processes are also possible.[1]
Commercially produced geopolymers may be used for fire- and heat-resistant coatings and adhesives, medicinal applications, high-temperature ceramics, new binders for fire-resistant fiber composites, toxic and radioactive waste encapsulation, and as cementing components in making or repairing concretes. The properties and uses of geopolymers are being explored in many scientific and industrial disciplines such as modern inorganic chemistry, physical chemistry, colloid chemistry, mineralogy, geology, and in other types of engineering process technologies.
The term geopolymer was coined by Joseph Davidovits in 1978 due to the rock-forming minerals of geological origin used in the synthesis process.[2] These materials and associated terminology were popularized over the following decades via his work with the Institut Géopolymère (Geopolymer Institute).
Geopolymers are synthesized in one of two conditions:
- in alkaline medium (Na+, K+, Li+, Cs+, Ca2+…)
- in acidic medium (phosphoric acid: H3PO4)
The alkaline route is the most important in terms of research and development and commercial applications. Details on the acidic route have also been published.[3][4]
- ^ W.M. Kriven, C. Leonelli, J.L. Provis, A.R. Boccaccini, C. Attwell, V.S. Ducman, C. Ferone, S. Rossignol, T. Luukkonen, J.S.J. van Deventer, J.V. Emiliano, J.E. Lombardi (2024), Why geopolymers and alkali-activated materials are key components of a sustainable world: A perspective contribution. Journal of the American Ceramic Society, https://doi.org/10.1111/jace.19828
- ^ An article published by the Commission of the European Communities in 1982 outlines the reasons why the generic term geopolymer was chosen for this new chemistry. See: J. Davidovits, The Need to Create a New Technical Language For the Transfer of Basic Scientific Information, in Transfer and Exploitation of Scientific and Technical Information, Proceedings of the symposium, Luxemburg, 10–12 June 1981, pp. 316-320. http://bookshop.europa.eu/en/transfer-and-exploitation-of-scientific-and-technical-information-pbCD3381271/
- ^ Wagh, A.S. (2004). Chemically Bonded Phosphate Ceramics – A Novel Class of Geopolymers. Proceedings of the 106th annual meeting of the American Ceramic Society, Indianapolis. See also, Chapter 13, Phosphate-based Geopolymers, in J. Davidovits' book Geopolymer Chemistry and Applications.
- ^ Perera, D.S., Hanna, J.V., Davis, J., Blackford, M.G., Latella, B.A., Sasaki, Y. and Vance E.R. (2008). Relative strengths of phosphoric acid-reacted and alkali-reacted metakaolin materials. J. Mater. Sci., 43, 6562–6566.