08-16-2017, 09:24 PM
Geopolymers are inorganic, typically ceramic, materials that form long-range, covalently bonded, non-crystalline (amorphous) networks . Obsidian is an example of naturally-occurring geopolymer.[citation needed] 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[1] and created the non profit French scientific institution (Association Loi 1901) Institut G opolym re (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+, Ca2+, 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[6] and
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+, Ca2+, 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[6] and