What is "geopolymer"

n. Any of a class of synthetic aluminosilicate materials with potential use in construction and other areas.

Geopolymers are inorganic, typically ceramic, materials that form long-range, covalently bonded, non-crystalline ( amorphous) networks . Obsidian is an example of naturally-occurring geopolymer. 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 to make concrete. The properties and uses of geopolymers are being explored in many scientific and industrial disciplines: modern inorganic chemistry, physical chemistry, colloid chemistry, mineralogy, geology, and in other types of engineering process technologies. Raw materials used in the synthesis of silicon-based polymers are mainly rock-forming minerals of geological origin, hence the name: geopolymer. Joseph Davidovits coined the term in 1978 and created the non profit French scientific institution (Association Loi 1901) Institut Géopolymère (Geopolymer Institute).

According to T.F. Yen geopolymers can be classified into two major groups: pure inorganic geopolymers and organic containing geopolymers, synthetic analogues of naturally occurring macromolecules. In the following presentation, a geopolymer is essentially a mineral chemical compound or mixture of compounds consisting of repeating units, for example silico-oxide (-Si-O-Si-O-), silico-aluminate (-Si-O-Al-O-), ferro-silico-aluminate (-Fe-O-Si-O-Al-O-) or alumino-phosphate (-Al-O-P-O-), created through a process of geopolymerization. This mineral synthesis (geosynthesis) was first presented at an IUPAC symposium in 1976.

The microstructure of geopolymers is essentially temperature dependent:

• It is X-ray amorphous at room temperature,
• But evolves into a crystalline matrix at temperatures above 500 °C.

One can distinguish between two synthesis routes:

• In alkaline medium (Na, K, Li, Ca, Cs and the like);
• In acidic medium with phosphoric acid and humic acids.

The alkaline route is the most important in terms of R&D and commercial applications and will be described below. Details on the acidic route are to be found at the references and