Geopolymeric fluoro-alumino-silicate binder and process for obta

Details Geopolymeric fluoro-alumino-silicate binder and process for obta Geopolymeric fluoro-alumino-silicate binder and process for obta

1992-09-02

1994-10-04

McFarlane, Anthony

Chemistry of inorganic compounds

Silicon or compound thereof

Oxygen containing

4233271, 423332, 1062865, 1062871, C01B 3326

Patent

active

053524276

DESCRIPTION:

BRIEF SUMMARY
FIELD OF INVENTION

The present invention relates to fluoro-alumino-silicate geopolymers and a method for obtaining such geopolymers.


BACKGROUND OF THE INVENTION

The geopolymeric alumino-silicates have been grouped in three families depending on the atomic ratio Si/Al which may be 1, 2 or 3. With the most commonly used simplified notation, a distinction is made between


__________________________________________________________________________ poly(sialate) M.sub.n (--Si--O--Al--O--).sub.n or (M)-PS, poly(sialate-siloxo) M.sub.n (--Si--O--Al--O--Si--O--).sub.n or (M)-PSS, poly(sialate-disiloxo) M.sub.n (--Si--O--Al--O--Si--O--Si--O--).sub.n or (M)-PSDS. __________________________________________________________________________
In several scientific papers, for instance "Geopolymer: room temperature ceramic matrix composites" published in Ceram. Eng. Sci. Proc., 1988, Vol. 9 (7-8), pp. 835-41, cf. Chemical Abstracts 110-080924, or "Geopolymer Chemistry and Properties" published in Geopolymer '88, Vol. 1, pp. 18-23, University ,of Technology, Compiegne, France, and the international patent publication WO 88/02741 (U.S. Pat. No. 4,888,311), the prior art discloses the uses of date herewith, describes a process for producing,
Alumino-silicate geopolymers have a tridimensional structure and belong to the category of zeolites and feldspathoids. For these materials it is known that thermal stability is a function of the ratio Si/Al. The higher this ratio, the higher their stability. Therefore, any worker in the field will understand the interest provided by the use of geopolymers of the type Si/Al.gtoreq.3


SUMMARY OF THE INVENTION

The object of the invention is to provide a geopolymeric fluoro-alumino-silicate binder making it possible to manufacture items with excellent mechanical and heat resistance at temperatures between 250.degree. C. and 650.degree. C.
The geopolymeric binder of this invention is a fluoro-alumino-silicate geopolymer whose composition expressed in terms of oxides and in dehydrated form is: and 75 "y" has a value between 1.0 and 20, "w" has a value between 0.5 and 50. After curing, the geopolymeric compound thus obtained is a solid solution comprising: (M,F)-PSDS of formula ##STR3## (b) an alkaline-alumino-fluoride M.sub.3 AlF.sub.6 such as elpasolite K.sub.2 NaAlF.sub.6 ; polymerization.
In the description of this invention, the term "geopolymer binder" or "hardening or a geopolymeric resin" relates to a hardening process which results from an internal polycondensation or hydrothermal reaction, as opposed to the hardening of alkaline-silicate-based binders which generally harden by simple drying.
The main object of this invention is to provide geopolymeric compounds with the ratio Si/Al.gtoreq.3, with some examples where the ratio is as high as Si/Al=75.
The prior art tells us that silicon rich zeolites are, like all zeolites, produced in hydrothermal conditions and in very dilute reactive solutions. Molar ratio M.sub.2 O:H.sub.2 O ranges from 1:50 to 1:100 and the zeolites obtained are very porous powders.
In contrast, geopolymers are binders which are used to agglomerate fillers or impregnate fibers and fabrics for the manufacture of ceramic-like items; the prior art concerning the fabrication of geopolymers, for instance the patents U.S. Pat. No. 4,349,386 (EP 026.687), U.S. Pat. No. 4,472,199 (EP 066.571), U.S. Pat. No. 4,888,311 (EP 288.502), tells us that the production of geopolymers is carried out in highly concentrated reactive medium and with a molar ratio M.sub.2 O:H.sub.2 O which is higher than 1:15.5 for Na.sub.2 O and in the order of 1:12.0 for K.sub.2 O.
There has been, so far, no known method for the production of a reactive mixture providing a ratio Si/Al.gtoreq.3 associated with a molar ratio M.sub.2 O:H.sub.2 O higher than 1:17.5. In this invention, the silicon involved in the chemical reaction comes from soluble alkaline silicate whose molar ratio M.sub.2 O:SiO.sub.2 is lower than 1.0:4.0 and whose dry solid matter concentration is higher than 60

REFERENCES:
patent: 4509985 (1985-04-01), Davidovits et al.
patent: 4888311 (1989-12-01), Davidovits et al.
patent: 5194091 (1993-03-01), Laney

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