Process for obtaining a geopolymeric alumino-silicate and produc

Details Process for obtaining a geopolymeric alumino-silicate and produc Process for obtaining a geopolymeric alumino-silicate and produc

1992-09-02

1994-08-30

McFarlane, Anthony G.

Chemistry of inorganic compounds

Silicon or compound thereof

Oxygen containing

4233271, 423332, 1062865, C01B 3326

Patent

active

053425952

DESCRIPTION:

BRIEF SUMMARY
FIELD OF INVENTION

The invention relates to a process for obtaining a geopolymer of the alkaline poly(sialate-disiloxo) family (M)-PSDS of formula ##STR1## where "M" represents at least one alkaline cation and "n" the degree of polymerisation.


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 M.sub.n --(Si--O--Al--O) .sub.n-- or (M)--PS, (sialate) poly M.sub.n --(Si--O--Al--O--Si--O) .sub.n-- or (M)--PSS, (sialate- siloxo) poly M.sub.n --(Si--O--Al--O--Si--O--Si--O) .sub.n-- or (sialate- (M)--PSDS disiloxo). ______________________________________
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 11O-080924, or "Geopolymer Chemistry and Properties" published in Geopolymer '88, Vol. 1, pp. 18-23, University of Technology, Compiegne, France, or the international patent publication WO 88/02741 (U.S. Pat. No. 4,888,311), the prior art discloses the uses of poly(sialates) Mn(--Si--O--Al--O), (Na)-PS/(K)-PS and poly(sialate-siloxo) Mn(--Si--O--Al--O--Si--O--), i.e. (Na)-PSS/(K)-PSS. It does not deal with any process for producing poly(sialate-disiloxo) Mn(--Si--O--Al--O--Si--O--Si--O--)n, i.e. (M)-PSDS.


SUMMARY OF INVENTION

The present invention provides a method for the preparation of this geopolymer type.
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
(M)-PSDS, i.e. Mn(--Si--O--Al--O--Si--O--Si--O--), with the ratio Si/Al=3 in comparison with
(M)-PSS, i.e. Mn(--Si--O--Al--O--Si--O--), with the ratio Si/Al=2 and
(M)-PS, i.e. Mn(--Si--O--Al--O--), with the ratio Si/Al=1.
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 high 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.
In the description of this invention, the term "geopolymer binder" or "hardening of 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.
There has been, so far, no known method for the production of a reactive mixture providing a ratio Si/Al=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 SiO.sub.2 :M.sub.2 O is higher than 4.0:1.0 and whose dry solid matter concentration is higher than 60% by weight. In contrast, industrial alkaline silicates are usually highly diluted with a dry matter concentration lower than 25% by weight and do not enable the production of the reactional mixture claimed in the present invention.
The second object of this invention is to provide a method for obtaining an alkaline s

REFERENCES:
patent: 4509985 (1985-04-01), Davidovits et al.
patent: 4888311 (1989-12-01), Davidovits et al.
patent: 5194091 (1993-03-01), Laney
Weldes et al,. "Properties of Soluble Silicates", Industrial & Engineering Chemistry, vol. 61, No. 4 (Apr. 1969) pp. 29-32.
Davidovits et al,. "Geopolymer: Room Temperature Ceramic Matrix for Composites", Ceram. Eng. Sci. Proc., vol. 9, pp. 835-842 (1988).
"Aluminum-27 and Silicon-29 Magic Angle Spinning Nuclear Magnetic Resonance Study of the Kaolinite-Mullite Transformation", Sanz et al, J. Am. Ceram. Soc. vol. 71, C-418-C-422, 1988.
Davidovits et al, "Structural Characterization of Geopolymeric Materials with X-ray Diffractometry and MAS-NMR Spectroscopy", Geopolymer, vol. 2, pp. 149-166 (1988).

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