Alkaline alumino-silicate geopolymeric matrix for composite mate

Details Alkaline alumino-silicate geopolymeric matrix for composite mate Alkaline alumino-silicate geopolymeric matrix for composite mate

1997-04-29

1998-08-25

Marcantoni, Paul

Compositions: ceramic

Ceramic compositions

Refractory

4233281, C01B 3326

Patent

active

057983070

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

This application is a 371 of PCT/FR96/00388 filed Mar. 13, 1996.
Composite materials composed of a ceramic fiber reinforcement and a geopolymeric matrix are already known. Thus European Patent EP 0 288 502 (WO 88/02741) and its equivalent U.S. Pat. No. 4,888,311 describe fiber reinforced composite materials with a geopolymer matrix containing a geopolymer poly(sialate) M(--Si--O--Al--O--), with a ratio (SiO.sub.4):(AlO.sub.4)=1, or poly(sialate-siloxo) M(--Si--O--Al--O--Si--O--), with a ratio (SiO.sub.4):(AlO.sub.4)=2, and with fillers of dimension less than 5 microns and preferably less than 2 microns. Other geopolymers used as a matrix for fibrous composites are described in patent EP 0 518 980 (WO 91/13830), U.S. Pat. No. 5,342,595, for a geopolymer poly(sialate-disiloxo) M(--Si--O--Al--O--Si--O--Si--O--), with a ratio (SiO.sub.4):(AlO.sub.4)=3. Patent EP 0 518 962 (WO 91/13840), U.S. Pat. No. 5,352,427, describes a geopolymeric matrix poly(sialate-disiloxo) M(--Si--O--Al--O--Si--O--Si--O--), with a ratio (SiO.sub.4):(AlO.sub.4)=3, which contains a siliceous phase SiO.sub.2,H.sub.2 O of the Opal CT type and an alkali alumino-fluoride M.sub.3 AlF.sub.6. According to the quantities of the Opal CT type siliceous phase SiO.sub.2,H.sub.2 O and of the alkali alumino-fluoride, the total ratio SiO.sub.2 /Al.sub.2 O.sub.3 varies between 5.5 and 75, but the ratio (SiO.sub.4):(AlO.sub.4) of the polymeric matrix poly(sialate-disiloxo) M(--Si--O--Al--O--Si--O--Si--O--) remains at all times equal to 3. In these two patents, the raw material used is a special silica dust called thermal silica. As can be seen in the publication PCT/WO 91/13840, page 3 lines 1 to 17 (U.S. Pat. No. 5,352,427, column 3, lines 2-22), for overall values of Si and Al such as the ratio Si:Al>6.5, the geopolymeric compound obtained is unstable at high temperature. It swells, showing the existence of a pure, highly fusible silicate phase, which has not been involved in the three-dimensional cross-linking. In the prior art, this serious drawback is remedied by adding certain products to allow hardening of the alkali silicate solutions, such as sodium fluosilicate Na.sub.2 SiF.sub.6. Similarly, it can be seen in PCT WO 91/13830, page 7, line 40 and page 8 lines 1-11 (U.S. Pat. No. 5,342,595, column 7, lines 25-37) that a linear soluble (and fusible) alumino-silicate forms when K.sub.2 O/Al.sub.2 O.sub.3 >1.30. This is a major drawback which is eliminated by the addition of a stabilizing agent or any other hardening agent utilized in alkali silicate-based binders, in this particular case, zinc oxide ZnO in the proportions of 2.5% to 3.5% by weight of the matrix.
Certain ceramic fibers, and in particular those containing carbon, cannot be used at temperatures higher than 424.degree. C. in air. Above this temperature, the carbon oxidizes and the mechanical strength of the reinforcement diminishes considerably. This phenomenon is well known in the previous art, as can be seen in the article "Fiber Reinforced Glasses and Glass-Ceramics for High Performance Applications", by K. M Prewo et al., American Ceramic Society Ceramic Bulletin, Vol. 65, n.degree. 2, page 305, (1986). Similarly, for geopolymeric matrices in the prior art (WO 88/02741, WO 91/13830, WO 91/13840, U.S. Pat. No. 4,888,311, U.S. Pat. No. 5,342,595, U.S. Pat. No. 5,352,427), it is known that use of carbon fiber is limited to temperatures lower than 450.degree. C., as can be seen in the article "Geopolymer: Ultra-High Temperature Tooling Material for the Manufacture of Advanced Composites", by J. Davidovits et al., 36th International SAMPE Symposium Proceedings (1991), USA, Vol. 36, page 1943 , together with FIG. 8, page 1946.
In the prior art, in order to obtain a composite material which would be temperature-stable up to 1000.degree. C., one of two techniques had to be employed: either special treatment of the carbon fiber by vapor phase deposition techniques (silicon carbide or silicon nitride vapor), or use of a SiC fiber reinforcement, for example

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