Geopolymers are new materials 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 new cements for 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. Geopolymers are part of polymer science, chemistry and technology that forms one of the major areas of materials science. Polymers are either organic material, i.e. carbon-based, or inorganic polymer, for example silicon-based. The organic polymers comprise the classes of natural polymers (rubber, cellulose), synthetic organic polymers (textile fibers, plastics, films, elastomers, etc.) and natural biopolymers (biology, medicine, pharmacy). 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-for 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 presented at an IUPAC symposium in 1976 . However, very often, scientists are taking the 1991 publication as starting reference.
The microstructure of geopolymers is essentially temperature dependent:
- It is X-rays amorphous at room temperature,
- But evolved 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
Read more about Geopolymers: The Need For Standardization: What Is A Geopolymer?, Commercial Applications, Geopolymer Resins and Binders, Geopolymer Cements, Geopolymer Applications To Arts and Archaeology