Fiber reinforced composites and process for manufacture

In a process for manufacturing fiber reinforced composites made or inorganic sinterable material and inorganic fibers the fibers are continuously passed through a bath which works acccording to the fluidized bed principle and which contains a solution of at least one metal alkoxide of the elements of the first to the fourth main groups of the periodic table and the forth and fifth subgroups of the periodic table, which solution already comprises products of hydrolysis and their condensation products, and the fibers moistened with the solution are wound one upon the other to form layers, the moistened and wound fibers are dried, the metal alkoxides on the fibers are completely hydrolyzed and the products of hydrolysis are polycondensated, and the layers of the fibers being adhered by the powder and the polycondensation products of the products of hydrolysis of the metal alkoxides are hot pressed.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to fiber reinforced composites made of 
inorganic sinterable material and inorganic fibers and a process for the 
manufacture thereof. 
2. Description of the Prior Art 
In search of materials suitable for heat resistant structural components 
which are especially used in aeronautics and astronautics, and engine and 
turbine manufacturing, one meets with limitations in developing alloy 
materials. On the one hand, it is difficult to achieve the desired heat 
resistance at temperatures above 800.degree. C. On the other hand, for 
these materials, raw materials are required which are rare and expensive, 
so that the ratio of costs to yield becomes more and more unfavorable. 
Furthermore, since alloys on the basis of Fe, Ni and Co have a high 
specific weight and are often used in moving parts, there is beyond that a 
general interest in developing heat resistant materials with less specific 
weight. 
As materials which can substitute for the alloys in the mentioned fields of 
application in principle ceramic materials are taken into consideration 
which excel by having low specific weight and superior temperature 
resistance under a great variety of atmospheres. In addition, these 
materials often possess a superior wear resistance as well as a good 
chemical resistance. Finally, the raw materials involved are available in 
a sufficient extent and moderately priced. 
The fact that ceramic materials are rarely used in spite of these 
outstanding combinations of properties in the considered fields of 
application, is due to their typical brittle fracture behavior. The risk 
that a structural unit will suddenly break catastrophically is regarded as 
too high. 
On grounds of this situation, for 20 years attempts have been made to 
reduce the brittleness of ceramic materials by the development of 
composites. In this connection, the development of fiber reinforced 
glasses and glass ceramics has become an important field of technology. 
Thereby, increases in bending strength and fraction toughness up to values 
of about 1000 MPa and 20 MPa.times..sqroot.m, respectively (m=meter) were 
achieved. The increase of the values of fracture toughness, which is of 
special significance for the reduction of the brittle fracture behavior, 
has resulted up to now mainly from experimental experience. The knowledge 
how fracture development influences the value of the fracture toughness is 
still lacking. 
Up to now in the relevant literature two basically different methods for 
the manufacture of composites with a glassy or glass ceramic matrix, 
respectively, are known. 
Two methods are suspension technique and the sol gel technique. 
In case of the relatively simple, predominantly used suspension method, a 
matrix powder is mixed with a binder, mostly a mixture of alcohol(s) and a 
latex binder. The fibers are passed through the matrix/binder bath and 
thereby impregnated with matrix material, as was first described in 1972 
(Sambell et al. (1972), J. Mat. Sci. 7, p. 676 to 681). 
In U.S. Pat. No. 4,256,378, a mirror with particularly good properties made 
of a composite of C-fibers and borosilicate glass is described. The 
particularly good properties are especially the low relative deformation 
in extension and the specific rigidity. The production proceeds via the 
production of a prepreg. Generally, a prepreg is a half finished layer of 
a multitude of fibers being impregnated with matrix material and being 
deposited side-by-side in mutual contact with each other. Also a few fiber 
layers can be deposited one upon the other by passing the C-fibers through 
a suspension consisting of glass in propanol or glass in propanol, 
polyvinylalcohol and a wetting agent. Densification of the prepreg is 
performed by hot pressing under vacuum or an argon protective gas 
atmosphere at temperatures of 1050.degree. to 1450.degree. C. and 
pressures between 6.9 and 13.8 MPa. Burning out of binders is not 
necessary. However, the solvents do not contribute to the properties of 
the composite material. With respect to a bidirectional reinforced 
material in a three point transverse bending test, bending strengths up to 
387 MPa are described. In a later publication, obviously as a result of 
process optimization, in a three point transverse bending test bending 
strengths up to 520 MPa for 35 vol. % SiC-fibers and up to 840 MPa for 50 
vol. % SiC-fibers are reported (K. M. Prewo, J. J. Brennan, J. Mat. Sci. 
17 (1982), pp. 1201). 
In U.S. Pat. No. 4,314,852, the manufacture of composite materials made of 
SiC-fiber reinforced glasses is described. As glasses, a borosilicate 
glass, an alkaline earth aluminosilicate glass and a high silica content 
glass are quoted. The production proceeds via two process steps which are, 
except for modified amounts of single components, identical with those 
described in U.S. Pat. No. 4,256,378. With respect to the composite 
materials very good thermomechanical properties are obtained. With respect 
to the SiC-fiber reinforced borosilicate glass (SiC-fibers from Nippon 
Carbon Company, Japan), at room temperature bending strengths of just 
under 500 MPa for unidirectional and 350 MPa for bidirectional 
reinforcement are observed. The room temperature bending strength values 
of SiC-fiber reinforced alkaline earth aluminosilicate glass with a fiber 
loading of 50 vol. % are about 1000 MPa for bidirectional and just 1400 
MPa for unidirectional reinforcement. With respect to the SiC-fiber 
reinforced high silica content glass, the bending strength values at a 
fiber loading of 30 to 40 vol. % are between 400 and 550 MPa. With respect 
to the SiC-fiber reinforced alkaline earth aluminosilicate composites, 
fracture toughnesses of 16 MPa.times..sqroot.m for bidirectional and 27 
MPa.times..sqroot.m for unidirectional reinforcement are reported. 
In U.S. Pat. No. 4,485,179, the manufacture of composite materials made of 
SiC-fiber reinforced glass ceramics is described. As a preferred matrix 
material, the starting glass (precursor glass) of a Li.sub.2 O--Al.sub.2 
O.sub.3 --SiO.sub.2 -glass ceramic with Nb.sub.2 O.sub.5, Ta.sub.2 O.sub.5 
and ZrO.sub.2 as nucleation agents is quoted. The production process 
proceeds as described in U.S. Pat. No. 4,256,378, the suspension 
consisting of glass, water and latex binder which has to be burned out 
prior to hot pressing. The conversion of the starting glass (precursor 
glass) into a glass ceramic can take place either during hot pressing or 
during an additional temperature treatment. As a particularly important 
result of material selection, the use of Nb.sub.2 O.sub.5 and/or Ta.sub.2 
O.sub.5 is emphasized because during the production process NbC or TaC 
layers, respectively, form on the fibers at the interface. These layers 
prevent further reaction between the fibers and the matrix at high 
temperatures and under oxidative conditions. Furthermore, it is stated 
that the use of TiO.sub.2, which is preferably used as nucleation agent in 
Li.sub.2 O--Al.sub.2 O.sub.3 --SiO.sub.2 -glass ceramics, should be 
completely avoided or at least only used in very small amounts. This is 
due to the fact that TiO.sub.2 also reacts with SiC-fibers from which, 
contrary to the reactions between SiC and Nb.sub.2 O.sub.5 or Ta.sub.2 
O.sub.5, a strong degradation of the SiC-fiber properties results. With 
respect to composite materials with a fiber loading of 50 vol. %, in a 
three point transverse bending test at room temperature bending strengths 
of at most just under 1000 MPa are obtained. Fracture toughnesses are not 
measured, but values above 11 MPa.times..sqroot.m are expected. 
The EP 0 126 017 represents a further development of U.S. Pat. No. 
4,485,179, in that excellent bending strengths and a good oxidation 
resistance up to temperatures of 1200.degree. C. are achieved by 
utilization of another matrix material. The improvements are obtained by 
using a Ba-modified cordierite or a Ba-osumilite glass ceramic, 
respectively, instead of the Li.sub.2 O--Al.sub.2 O.sub.3 --SiO.sub.2 
-glass ceramic. Powders of the corresponding starting glasses are used as 
matrix materials, while the conversion of the glass into glass ceramics 
either takes place during or after hot pressing. As nucleation agents 
Na.sub.2 O.sub.5 and/or Ta.sub.2 O.sub.5 are again used because of their 
positive effect on the formation of an interface fiber/matrix. At room 
temperature in a three point transverse bending test bending strengths up 
to 700 MPa are measured. In especially one example (number 4) wherein a 
Ba-osumilite glass ceramic matrix is employed, a linear run of the stress 
strain curve is obtained which is explained by the fact that the matrix 
has completely crystallized. 
The manufacture of fiber reinforced glass ceramics on the basis of 
stoichiometric cordierite has as yet not been described. Presumably, this 
is due to the strong tendency of the powders of the starting glasses to 
crystallize just above the transformation temperature and also due to the 
difficulties during condensation which result therefrom. 
In the state of the art here described as well as in other publications, 
the suspension bath mostly works according to the fluidized bed principle, 
as it has been described by Bowen et al. in 1969 (Brit. Pat. Spec. 
1,279,252). 
Compressed air is injected into the suspension to prevent sedimentation of 
the powder and to expand the fiber bundles so that they are also 
impregnated with matrix material in the interior thereof. 
The NASA Contr. Reports 158 946 (1978) and 165 711 (1981) mention the 
addition of 2% LUDOX.RTM. (Trademark of Du Pont) to the binders already 
described, i.e., the addition of colloidal SiO.sub.2 which leads to an 
increase in strength. 
If binders are used in the above described process, they have to be burnt 
out after the preparation of the fibers and prior to prepreg densification 
by means of hot pressing. This means an additional process step. 
Furthermore, there is a risk that [rests] residues of "alien" binders will 
remain and contaminate the material. In the case where alcohol is used as 
the sole binder, the adhesion of the powder to the fibers is poor after 
its evaporation. This can lead to matrix losses by part of the matrix 
material dropping off the fibers. 
A second method which is quoted in the literature, the sol-gel-technique, 
is described in the following publications: 
Walker et al., Am. Cer. Soc. Bull. 62 (8) (1983), pages 916 to 923; 
Rice, Mat. Res. Soc. Sym. Proc. Vol. 32 (1984), pages 337 to 345; 
Lannutti, Clark, ebd, pages 369 to 375; and 
Lannutti, Clark, ebd, pages 375 to 381. 
In this method, the reinforcing fiber is either passed through a sol gel 
solution of matrix material and then wound up, or it is laid up dry and 
subsequently impregnated with solution during the course of which the 
impregnating process can be performed several times. 
If composites are to be formed which are non-porous and free of cracks, the 
partly protracted and complicated drying process of the prepreg 
(hydrolysis, pyrolysis) represents a disadvantage of this method. High 
volume shrinkage of the solution is the main problem of the method. In 
converting the sol into the gel state, the vaporization of the alcohols, 
normally present in the solution, becomes more and more difficult. If the 
fibers are laid up wet, there is a risk that in continuously processing 
the fibers the solution will start to hydrolyze, due to atmospheric 
moisture, resulting in changes in viscosity. 
If the protracted drying process should be avoided, hot pressing can be 
used for final densification as described by: 
Haluska, European Pat. Appl. 0 125 772 (1984); 
Fitzer, Schlichting, High Temp. Sci. 13 (1980) pages 149 to 172; 
Fitzer, Proc. Int. Fac. in Densification and Sintering of Oxide and 
Non-Oxide Cer., 1978, Japan; and 
Schubert, Diss., University Karlsruhe (1977). 
BRIEF SUMMARY OF THE INVENTION 
An object of the present invention is to provide a composite in which the 
adhesion between fiber and matrix can be optimally adjusted; especially, 
to provide a process by which such a composite can be fabricated more 
easily than by known processes. 
Upon further study of the specification and appended claims, further 
objects and advantages of this invention will become apparent to those 
skilled in the art. 
These objects are achieved by providing a process for manufacturing fiber 
reinforced composites made of inorganic sinterable material and inorganic 
fibers comprising the steps of: passing the inorganic fibers continuously 
through a suspension of inorganic sinterable silicate powder in a 
fluidized bed; winding the fibers, moistened with the suspension, one upon 
another in layers; drying; and hot pressing the layers of fibers; 
characterized in that a suspension is used which contains, to promote the 
adhesion between the fibers and the inorganic material, a solution of at 
least one metal alkoxide, which solution already comprises products of 
hydrolysis as well as their polycondensation products, and that the metal 
alkoxides are completely hydrolyzed on the fiber and the inorganic 
material, and the products of hydrolysis are polycondensated, in course of 
which surface layers are formed on the fiber and the inorganic material 
which, on the one hand, facilitate the sintering process and hot pressing 
due to their high reactivity, and, on the other hand, act as a reaction 
barrier between fiber and inorganic material. 
In the inventive process, by manufacturing fiber reinforced glasses and 
glass ceramics, fibers are coated with a binder and glass powder by being 
continuously passed through a suspension. The suspension contains a powder 
of glass and a sol gel solution. The glass powder forms the matrix of the 
fiber reinforced material and the sol gel solution acts as a binder and 
promotes the adhesion between the fiber and the matrix material as well as 
between the individual powder particles of the matrix material. The fibers 
being impregnated in this way are wound up on a drum to form a layer 
package which is subsequently subjected to hydrolysis and polycondensation 
of the sol. Densification of the resultant prepreg takes place during hot 
pressing. 
In the inventive composite adhesion between fibers and matrix can be 
adjusted to obtain an optimal adhesion. The inventive process especially 
renders such adjustment possible in that the composition of the matrix 
material as well as of the sol gel solution can be varied within wide 
ranges and can be reconciled with each other. 
Besides adjusting the adhesion between the fibers and the matrix, the sol 
gel solution can simultaneously serve as a reaction barrier between the 
matrix and the fibers. This is because the sol gel solution covers the 
fibers as well as the glass or glass ceramic powder. 
DETAILED DESCRIPTION OF THE INVENTION 
According to the invention, the alkoxides of the elements of the first to 
the fourth main group (groups Ia-IVa), as well as the fourth and the fifth 
sub groups (groups IVb and Vb) of the periodic table can be used alone or 
in combination. The alkoxides of sodium, potassium, magnesium, calcium, 
barium, aluminum, silicon, titanium, zirconium, hafnium and tantalum 
especially can be used. 
The following statements concerning silicic acid ester also apply to the 
other metal alkoxides which are suitable for the present invention. 
The disadvantages of the suspension method, such as either the poor 
adhesion of the powder to the fiber or the necessity of burning out the 
binders, and those of the sol gel method, high volume shrinkage and very 
protracted processing times, can be overcome by mixing defined 
anhydrolyzed silicic acid esters with a glass powder mixture and 
subsequently coating them on the SiC fibers. The anhydrolyzed silicic acid 
esters simultaneously act as a "chemical coupler" between the individual 
glass powder particles and as an adhesion agent for the fibers. In 
particular, the polycondensation of the utilized silicic acid esters, 
especially silicic acid tetramethyl- or -ethylester, decisively influences 
the coating ability, because both materials, fiber and matrix, have to be 
moistened by this solution. It has become apparent that the viscosity of 
the utilized sol gel solution has to be in the range of 2.0 to 2.4 cSt to 
achieve a good moistening of the glass powder particles and the SiC 
fibers. The coating thicknesses are determined, on the one hand, by the 
velocity with which the fibers are passed through the bath, and, on the 
other hand, by the adjusted viscosity of the coating solution. A 
particular advantage of the utilized sol gel solution is the possibility 
of adjusting the solution to be hydrophobic or hydrophilic. 
In the following, the production of a sol gel solution is described by 
means of the example of silicic acid tetramethyl ester. The utilized sol 
gel solutions are prepared prior to admixing the glass powder particles as 
follows: silicic acid tetramethyl ester is mixed with distilled water and 
acetic acid (glacial acetic acid) in a ratio of 1:1-10:1-3. The velocity 
of hydrolysis is determined by the concentration of water and acetic acid, 
but can also, with a great variety of solvents, by advantageously 
controlled by the degree of dilution. As a rule lower alcohols such as 
methanol, ethanol, n-propanol, i-propanol, n-butanol, etc., ketones such 
as acetone, methyl ethyl ketone, etc., and carboxylic acid esters such as 
methyl acetate, ethyl acetate, butyl acetate, etc., are used. 
The hydrolysis firstly takes place in concentrated solutions, the degree of 
dilution approximately corresponding to a ratio of silicic acid ester to 
solvent of 1:1-10. After hydrolysis, the viscosity of such a concentrate 
is between 2.4 and 3.2 cSt. Subsequently, the concentrate is diluted with 
the selected solvent until the viscosity is between 2.0 to 2.4 cSt. Glass 
powder particles are admixed to this sol gel solution in such an amount 
that the weight ratio of inorganic sinterable silicate powder and solution 
is in the range of 1:5 to 1:1. A particular advantage of the described sol 
gel solution is its ability to be used for a time period of up to three 
months. 
By adapting the sol gel solution to the chemical composition of the glass 
powder being utilized, it is possible, especially by controlling the 
reactivity of the sol gel solution via the degree of hydrolysis of the 
silicic acid ester, and by the possible use of polar-nonpolar, 
protic-aprotic solvents, and mixtures thereof, to optimize the bonding 
between the fiber and the glass powder. This means that, by chemically 
varying the sol gel solution, specified surfaces can be produced which are 
adapted to the fibers as well as to the glass powder particles and 
establish contact between the fibers and the glass powder particles. These 
surfaces lead to an essential improvement in the bonding between the glass 
powder particles and the fibers. 
After the fiber has been passed through the suspension, it is wound onto a 
drum. In the course of which, the threads are laid up side-by-side. 
Several layers are then laid one upon another to achieve thicker prepregs. 
To obtain a homogeneous distribution between the fibers and the matrix, 
the amount of adhering glass is regulated by a squeezing device. 
After the winding process, the prepreg is removed from the drum. The 
anhydrolyzed solution is completely hydrolyzed by a temperature treatment 
at 20.degree. to 250.degree. C. and an atmospheric moisture of 10 to 13 
g/m.sup.3. Subsequently, the final oxide layer is formed by a temperature 
treatment at 250.degree. to 450.degree. C. in 0.05 to 24 hours. 
After these process steps, a prepreg is obtained which is quite strong and, 
hence, can be subsequently well worked. The cylindrically shaped prepreg 
is cut into planar prepregs. Subsequently, the prepregs are optionally 
either immediately hot pressed, or they are stacked to obtain thicker 
specimens. The individual layers can be oriented in the same direction to 
obtain unidirectional reinforcement, or they can be oriented in different 
directions to obtain a more or less isotropic reinforcement. 
After inserting the prepreg layers into the hot press, hot pressing 
proceeds in several process steps. Firstly, the specimen is heated up to 
the glass transition temperature, T.sub.g, under vacuum. Approximately at 
T.sub.g of the glass, the press die is layed upon the specimen leading to 
a pressure of approximately 0.2 MPa. Subsequently, the specimen is heated 
up to the pressing temperature either under vacuum or a protective gas 
atmosphere. Depending on the high reactivity of the sol gel and upon the 
crystallization tendency of the matrix glass, a more or less strong 
densification occurs during heating up in the course of which in some 
matrix material/sol gel combinations two thirds of the final densification 
is achieved. At the press temperature, which for the materials used 
according to the invention is between 1150.degree. and 1400.degree. C., 
the densification takes place, in the course of which press pressures up 
to 10 MPa and press times of 5 to 10 min. are sufficient in most cases. 
Thus, lower pressures and shorter press times (at comparable temperatures) 
compared to the suspension method can be used. According to current 
knowledge this is due to the high reactivity of the sol gel which covers 
each fiber and each matrix grain. The sol gel has a double function in 
this process step, insofar as it protects, on the one hand, the fiber from 
a possible destabilizing reaction between the fiber and the matrix or the 
fiber and the atmosphere, and, on the other hand, shortens the process 
times. The importance of the second point is due to the fact that some 
fibers, especially the SiC fibers, are unstable independently from the 
atmosphere at temperatures of approximately 1300.degree. C. and more (see 
for example A. S. Fareed et al., Amer. Cer. Soc. Bull., 66 (1987), pages 
353 to 358), and thus should be subjected to these temperatures for as 
short a time as necessary. 
The invention process has the following advantages. 
No alien binders in the form of waxes, moistening agents, etc. are used so 
that the step of burning out these materials is omitted and the risk that 
contaminating residues remain in the prepreg is eliminated. A uniform 
distribution of powder bonded to the fibers is achieved even without the 
binding agents mentioned above by the adjustable bonding forces between 
the matrix and the fiber. Due to this bonding, the problem of 
homogeneously embedding the fibers is reduced to precisely controlling the 
winding procedure, i.e., merely a technological problem. The good 
homogeneity of the prepreg is not lost even when sawing through with a 
diamond saw; no matrix loss and no local enrichment arises. Compared with 
the sol gel technique, the inventive process has the advantage that the 
sol gel contributes only a small volume portion to the matrix material in 
which the fibers are embedded, because the matrix is formed by the glass 
powder. The strong shrinkage of the sol during hydrolysis and 
polycondensation is thus only of minor importance with respect to the 
inventive composite. 
The compatibility of the fiber and the matrix is increased by coating both 
components with a sol gel solution, even if the fiber and the matrix 
material are not very compatible. Hence, in most cases it is not necessary 
to cover the fibers with a protective coating. Also the process atmosphere 
during hot pressing is not limited by a possible reaction between the 
fiber and the process atmosphere. The "Grundichte" (density of the 
prepreg) is higher in comparison to other methods which use alien binders 
and/or alcohols, because the sol gel contributes to the material in which 
the fibers are embedded. 
Due to the high reactivity of the surface of the condensed sol, hot 
pressing is facilitated and can take place at lower temperatures. 
The inventive process is largely independent from the materials mentioned 
and thus allows the use of a wide range of glasses for manufacturing 
composites. In the manufacture of composites, the properties thereof can 
be directly varied, and an adaption of the glass to the fiber material is 
possible by selecting the composition of the sol gel solution as well as 
the glass composition. Optimization of especially such properties as 
strength, fracture toughness, thermal expansion, etc., can be carried out 
more quickly and are more easily surveyed. By the sole use of a pure 
anhydrolyzed silicic acid ester, for example, the SiO.sub.2 content of the 
glassy material in which the fibers are embedded is increased and in this 
way an increase in the glass transition temperature is observed. In 
addition, the decrease which occurs in bending strength at higher 
temperatures is shifted to higher values. 
Also all types of inorganic fibers comprising SiC, Si.sub.3 N.sub.4, 
Al.sub.2 O.sub.3, ZrO.sub.2, SiO.sub.2, mullite and/or C as main 
components, and optionally Si, Ti, Zr, Al, C, O, N as additional 
components, such as, for example, SiC--, SiC--Si.sub.3 N.sub.4 --, 
Si.sub.3 N.sub.4 --, Al.sub.2 O.sub.3 --, ZrO.sub.2 --, mullite and 
C-fibers can be used. Moreover, ceramizing of the glass can take place 
after hot pressing or during hot pressing in a glass ceramic. 
With the inventive process, composite materials can be produced with 
properties which clearly excel the prior art. With respect to SiC fiber 
reinforced borosilicate glass produced by use of a SiO.sub.2 -containing 
sol gel solution, for example, with unidirectional reinforcement and a 
fiber volume loading of 40%, bending strengths up to 800 MPa are observed 
in a three point transverse bending test. The fracture toughness values 
amount to 20 MPa.times..sqroot.m. In measuring stress strain diagrams, the 
linear portion of the stress strain curve extends nearly up to the 
ultimate strength. This has not been observed up to now with comparable 
composite materials, and thus attracts attention. Probably, this is due 
to, among other things, the formation of the SiO.sub.2 -containing 
interface between matrix and fiber. 
In the production of SiC fiber reinforced alkaline earth aluminosilicate 
glasses by use of SiO.sub.2 -containing sol gel solutions, not only high 
bending strengths of, for example, approximately 1300 MPa are achieved, 
but also high fracture toughnesses of, for example, 36.+-.7 
MPa.times..sqroot.m which clearly excel the prior art. Since the increase 
in fracture toughness is itself an essential aspect of material 
development, values of 36 MPa.times..sqroot.m and more represent clear 
progress in comparison to the prior art in which values of maximally 27 
MPa.times..sqroot.m are stated. 
Furthermore, the inventive process allows production of fiber reinforced 
glass ceramics on the basis of stoichiometric cordierite. The difficulties 
in densification previously mentioned which result from the strong 
crystallization tendency of the powders of the starting glasses are 
overcome by use of the sol gel solutions. Also, the properties obtained 
reach up to the values achieved by SiC fiber reinforced borosilicate 
glasses. 
While the best mechanical properties in using alkaline earth 
aluminosilicate glasses as matrix material are achieved with SiC fiber 
reinforcement, with C fiber reinforcement the best values are observed 
with borosilicate glasses and B.sub.2 O.sub.3 -modified alkaline earth 
aluminosilicate glasses as matrix material. In both cases, maximal bending 
strengths above 1200 MPa are achieved. The maximal fracture toughnesses 
are approximately 35 MPa.times..sqroot.m with respect to the borosilicate 
glass and approximately 25 MPa.times..sqroot.m with respect to the B.sub.2 
O.sub.3 -modified alkaline earth aluminosilicate glass. 
The following are examples of glasses suitable for use as the matrix 
material: 
1. borosilicate glass having the following physical properties: 
______________________________________ 
Density = 2.23 g/cm.sup.3 
Expansion coefficient .alpha..sub.20-300 
= 3.25 .times. 10.sup.-6 K.sup.-1 
Modulus of elasticity = 63 kN/mm.sup.2 
Dielectric constant at 1 MHz 
= 4.7 
Loss angle tan .delta. at 1 MHz 
= 55 .times. 10.sup.-4 
Transition temperature T.sub.g 
= 530.degree. C. 
Working temperature at 10.sup.4 dPa .multidot. s 
= 1270.degree. C.; and 
______________________________________ 
2. P.sub.2 O.sub.5 -containing alkaline earth aluminosilicate glass with 
the following physical properties: 
______________________________________ 
Density = 2.56 g/cm.sup.3 
Expansion coefficient .alpha..sub.20-300 
= 4.l .times. 10.sup.-6 K.sup.-1 
Modulus of elasticity = 90 kN/mm.sup.2 
Dielectric constant at 1 MHz 
= 6.1 
Loss angle tan .delta. at 1 MHz 
= 23 .times. 10.sup.-4 
Transition temperature T.sub.g 
= 730.degree. C. 
Working temperature at 10.sup.4 dPa .multidot. s 
= 1235.degree. C. 
______________________________________ 
The following are examples of fiber reinforced composites according to the 
invention: 
1. a composite of borosilicate glass as matrix material with the physical 
properties: 
______________________________________ 
Density = 2.23 g/cm.sup.3 
Expansion coefficient .alpha..sub.20-300 
= 3.25 .times. 10.sup.-6 K.sup.-1 
Modulus of elasticity = 63 kN/mm.sup.2 
Dielectric constant at 1 MHz 
= 4.7 
Loss angle tan .delta. at 1 MHz 
= 55 .times. 10.sup.-4 
Transition temperature T.sub.g 
= 530.degree. C. 
Working temperature at 10.sup.4 dPa .multidot. s 
= 1270.degree. C. 
______________________________________ 
and a SiC fiber loading of about 42-54 vol. %; the matrix material as well 
as the fibers are covered by a binding agent layer obtained by thermal 
hydrolysis and polycondensation of at least one silicic acid ester; and 
the composite has a bending strength of about 671-921 MPa and a fracture 
toughness of about 16-27 MPa.times..sqroot.m; 
2. a composite of P.sub.2 O.sub.5 -containing alkaline earth 
aluminosilicate glass as matrix material with the physical properties: 
______________________________________ 
Density = 2.56 g/cm.sup.3 
Expansion coefficient .alpha..sub.20-300 
= 4.1 .times. 10.sup.-6 K.sup.-1 
Modulus of elasticity = 90 kN/mm.sup.2 
Dielectric constant at 1 MHz 
= 6.1 
Loss angle tan .delta. at 1 MHz 
= 23 .times. 10.sup.-4 
Transition temperature T.sub.g 
= 730.degree. C. 
Working temperature at 10.sup.4 dPa .multidot. s 
= 1235.degree. C. 
______________________________________ 
and a SiC fiber loading of about 45 vol. %; the matrix material as well as 
the fibers are covered by a binding agent layer obtained by thermal 
hydrolysis and polycondensation of at least one silicic acid ester; and 
the composite has a bending strength of greater than about 1200 MPa and a 
fracture toughness of up to 43 MPa.times..sqroot.m; 
3. a composite of borosilicate glass as matrix material with the physical 
properties: 
______________________________________ 
Density = 2.23 g/cm.sup.3 
Expansion coefficient .alpha..sub.20-300 
= 3.25 .times. 10.sup.-6 K.sup.-1 
Modulus of elasticity = 63 kN/mm.sup.2 
Dielectric constant at 1 MHz 
= 4.7 
Loss angle tan .delta. at 1 MHz 
= 55 .times. 10.sup.-4 
Transition temperature T.sub.g 
= 530.degree. C. 
Working temperature at 10.sup.4 dPa .multidot. s 
= 1270.degree. C. 
______________________________________ 
and a C fiber loading of about 30-50 vol. %; the matrix material as well as 
the fibers are covered by a binding agent layer obtained by thermal 
hydrolysis and polycondensation of at least one silicic acid ester; and 
the composite has a bending strength of about 634-1328 MPa and a fracture 
toughness of about 17-39 MPa.times..sqroot.m; and 
4. a composite of B.sub.2 O.sub.3 -containing alkaline earth 
aluminosilicate glass as matrix material and a loading of about 42 vol. % 
C fibers which have a tensile strength of up to 7000 MPa and a modulus of 
elasticity of approximately 300 GPa; the matrix material as well as the 
fibers are covered by a binding agent layer obtained by thermal hydrolysis 
and polycondensation of at least one silicic acid ester; and the composite 
has an average bending strength of about 1200 MPa and an average fracture 
toughness of about 19 MPa.times..sqroot.m. 
Independently from the inorganic fibers matrix materials, and sol gel 
compositions used, with the inventive process high fiber volume loadings 
up to 65% can be reached while the mechanical properties remain constantly 
good. 
From this outline it follows that in using a sol gel solution as an 
additional component in a suspension solution the optimization of the 
fiber reinforced glasses and glass ceramics is decisively improved. The 
conversion of the solution surface layers on the matrix material and the 
fibers into coatings during the production process renders the production 
of protective coatings for the fibers largely superfluous. 
The glasses and glass ceramics, fibers and sol gel solutions herein 
described have only an exemplary character. It is self-evident that for 
one of ordinary skill in the art, a multitude of further combinations for 
manufacturing fiber reinforced composites according to the present 
invention are possible. 
Without further elaboration, it is believed that one skilled in the art 
can, using the preceding description, utilize the present invention to its 
fullest extent. The following preferred specific embodiments are, 
therefore, to be construed as merely illustrative, and not limitative of 
the remainder of the disclosure in any way whatsoever. 
In the foregoing and in the following examples, all temperatures are set 
forth uncorrected in degrees Celsius and unless otherwise indicated, all 
parts and percentages are by weight. 
The entire texts of all applications, patents and publications cited above 
and of corresponding German application P 37 31 650.8 (the priority 
document), are hereby incorporated by reference.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
In the table several different inventive fiber reinforced composites with 
different compositions and their mechanical properties are listed. For 
these examples, SiC fibers from Nippon Carbon Company, Japan, and C 
fibers, T 800 and T 1000, from Torayca, Japan, are used as fiber 
materials. T 800 is a fiber with a tensile strength of approximately 5800 
MPa, a modulus of elasticity of approximately 300 GPa and an ultimate 
strain of 1.9%. The C fiber with the name T 1000 has the same modulus of 
elasticity and a tensile strength of 7000 MPa. As matrix materials, 
glasses and glass ceramic starting glasses of Schott Glaswerke, Mainz, 
were utilized. Specifically, the borosilicate glass DURAN.RTM. with the 
type number 8330, the P.sub.2 O.sub.5 -containing alkaline earth 
aluminosilicate glass SUPREMAX with the type number 8409, a B.sub.2 
O.sub.3 -containing alkaline earth aluminosilicate glass with the type 
number 8252, the starting glass GM 30870 for a stoichiometric cordierite 
glass ceramic as well as a 3 wt. % Ba- and a 3.5 wt. % TiO.sub.2 
-containing GM 30870 glass are used. The sol gel solutions were selected 
to form SiO.sub.2 -, TiO.sub.2 - or DURAN glasses. In synthesizing of the 
multicomponent glass DURAN, the alkoxides of the single elements are used 
in matching amounts. The single alkoxides can be admixed in an arbitrary 
sequence and then, as described in connection with the SiO.sub.2 sol gel, 
converted into an oxide glass, which has the properties of conventionally 
produced DURAN glass, in an analogous way by joint hydrolysis, 
polycondensation and temperature treatment. 
In the following, the inventive process is described in detail with respect 
to three different composite compositions from the table (examples 1, 10 
and 24). 
EXAMPLE 1 
The production of a composite of DURAN glass with embedded SiC fibers as 
reinforcement components is described. 
For the production of the prepreg, the fibers, in the state they were 
supplied (provided with a facing), are continuously removed from the 
supply drum and passed through a tube furnace (temperature 600.degree. C.) 
to burn off the facing. Subsequently, the fiber bundle is guided via guide 
rollers into the fluidized bed, in which the glass powder/sol gel bath is 
located. The compressed air injected into the bath from below serves two 
purposes: 
a) to prevent sedimentation of the glass powder in the solution; 
b) to expand the fiber bundle consisting of approximately 400 monofilaments 
by the flow and thus rendering possible an intimate impregnation of the 
bundle with matrix material. 
Excess suspension is retained by a squeezing device and recycled to the 
fluidized bed. 
An example of the composition of the suspension is a mixture of 100 g glass 
powder (grain size&lt;40 .mu.m) and 250 g sol gel solution on the basis of a 
SiO.sub.2 composition. The anhydrolyzed silicic acid tetramethyl ester 
containing sol gel solution is in a way stabilized. It has an almost 
constant viscosity over a time period of three months at room temperature. 
The coated fibers guided by controls are laid up side-by-side on a drum 
being made of teflon. The drum has a hexagonal cross-section to obtain 
plane prepregs being as large as possible with minimal material losses and 
minimal fiber bending. The fiber bundles impregnated with matrix material 
remain on the winding drum till dry. When the desired dryness is obtained, 
the fiber bundles are removed and stored for 24 h at 80.degree. C. and an 
atmospheric moisture of 10 to 13 g/cm.sup.3 till complete hydrolysis of 
the sol has taken place. The subsequent polycondensation takes place at 
250.degree. C. also over a time period of 24 h. The finished prepregs are 
sawn by a diamond saw to the format needed for hot pressing. 
Hot pressing of the specimens takes place at 1200.degree. C. and a press 
pressure of 10 MPa. The pressing time is 5 min. Pressing takes place under 
nitrogen atmosphere. 
The determination of the expansion coefficient .alpha. in fiber direction 
yielded for .alpha..sub.20/300 a value of 1.6.times.10.sup.-6 K.sup.-1 and 
for .alpha..sub.20/600 a value of 2.2.times.10.sup.-6 K.sup.-1. DURAN 
glass has an expansion coefficient .alpha..sub.20/300 of 
3.25.times.10.sup.-6 K.sup.-1. The dilatometer curves of the composites 
showed merely a weak bending at approximately 620.degree. C. Consequently, 
the bending is 90.degree. C. above T.sub.g of the pure glass matrix 
(T.sub.g of DURAN: 530.degree. C.). The lowering of the expansion 
coefficient and the increase of T.sub.g of the composite are explained by 
the increased SiO.sub.2 content which is due to the sol gel solution. 
EXAMPLE 10 
The described process can also be used to produce a composite with a matrix 
consisting of SUPREMAX and the reinforcement component being again 
continuous SiC fibers. 
The fabrication of the prepreg proceeds according to example 1, also using 
a mixture of 100 g glass powder (grain size &lt;40 .mu.m) and 250 g sol gel 
solution as the composition of the suspension. 
The prepregs are hot pressed at 1250.degree. C. The pressure amounts to 5 
MPa, and the pressing time is 5 min. The hot pressing process is performed 
under nitrogen atmosphere. 
EXAMPLE 24 
As the matrix component, the stoichiometric cordierite glass GM 30870 is 
used for infiltration of the SiC fiber bundle a suspension of a mixture of 
100 g glass powder (grain size &lt;40 .mu.m) and 300 g sol gel solution is 
used. 
The production of the prepreg proceeds again according to example 1. The 
hot pressing process differs from that of examples 1 and 10 and involves 
the following steps. Firstly, the specimen is heated up to 850.degree. C. 
without applying pressure. After applying a pressure of 2 MPa, the 
temperature is increased up to 1310.degree. C. At that temperature, the 
pressure is further increased up to 5 MPa for a time period of 5 min. The 
conversion of the glass into the glass ceramic takes place during heating 
up to the maximal temperature. 
The mechanical properties, i.e., bending strength and fracture toughness of 
the three composites, the production of which is described above in 
detail, are listed in the table together with other preferred embodiments 
of the invention which had been manufactured with equivalent procedures. 
The examples 6 and 8 in the table are not covered by the teachings of the 
present invention. Example 6 was produced with a prior art process to show 
the superior properties of the inventive composites by comparison. Example 
8 serves to demonstrate the effect of the reaction barrier between the 
fiber and the matrix and, due to its very low mechanical strength is not 
to be reckoned among the inventive composites. 
The bending strengths in the table were mostly measured with a three point 
transverse bending test. Specimens with the following dimensions were 
used: length 90 to 100 mm, width 3.5 to 8 mm, and height 2.5 to 3.5 mm; 
the span between the supports was in the range of 75 to 80 mm, the ratio 
of support span/height always being larger than 18. In examples 1, 10 and 
24, four point bending strengths were measured. In these cases, rods with 
the dimension 43.0.times.4.6.times.3.5 mm.sup.3 were used; the inner and 
the outer spans were 20 and 40 mm, respectively. 
The measurement of the fracture toughnesses was carried out with the same 
experimental arrangement, though notched rods with 1 to 2 mm deep notches, 
depending on the sample height, and of 100 .mu.m width were used. The 
calculated standard deviations are based on a series of measurements with 
five individual measurements in each case. 
Referring to the following table, the examples are explained in detail. 
The first nine examples relate to SiC fiber reinforced DURAN. Examples 1 
and 2 show that very high strengths can be obtained as well at room 
temperature as at 600.degree. C. In comparing examples 1 and 2 with the 
following examples and the prior art, one should keep in mind that the 
values listed in the table for examples 1 and 2 refer to four point 
bending strengths which are generally lower than three point bending 
strengths. A typical stress strain diagram for example 1 is shown in FIG. 
1. A comparison of Examples 1 and 3 shows that the pressing temperature is 
uncritical for the production of the composites. With respect to the 
material combinations selected in this case, it can be varied within a 
relatively wide range without substantially changing the properties. 
Examples 3 and 4 show that the bending strengths increase with an increase 
in fiber volume loading. At a fiber volume loading of 48% maximal 
strengths above 920 MPa are observed which clearly excel the prior art. In 
further increasing the fiber volume loading up to 54% the strengths drop 
again a little, while the average fracture toughness increases from 20 
MPa.times..sqroot.m up to 25 MPa.times..sqroot.m. The fracture toughnesses 
of the composite combinations SiC fiber/borosilicate glass, here reported, 
clearly excel the prior art. The drop in strength values when fiber volume 
loading increases from 48% to 54% in example 5 is, according to the 
current knowledge, due to the threads being laid up nonuniformly during 
the winding procedure. 
As described in the prior art, in example 6 a suspension being free of 
binders is used which contains propanol instead of the SiO.sub.2 sol gel 
solution as suspension solvent. In production of the composite the glass 
powder adheres relatively poorly to the fibers, so that an unhomogeneous 
embedding of the fibers is to be expected. This is also shown by the 
bending strengths which are on the average lower than the values of the 
comparable inventive composites and are strongly scattered as reflected in 
the standard deviation of 127 MPa. 
The comparison of examples 3 and 7 shows that different sol gel solutions 
can be used as long as no--or only minor--chemical reactions between the 
matrix, fiber and sol gel solution occur. The equality of the measured 
bending strength does not, however, mean that both composite materials are 
equal in every respect. From FIG. 2, it follows that SiC fiber reinforced 
DURAN produced with a DURAN sol gel solution has a completely different 
stress strain behavior in comparison to when a SiO.sub.2 sol gel solution 
is used (FIG. 1). The reasons for the different stress strain diagrams are 
not understood at the present. In any case, the material represented in 
FIG. 2 shows pronounced "plastic" behavior after the first fiber break. 
While in the examples 1 to 8, data for unidirectional reinforced composites 
are quoted, example 9 shows data for bidirectional reinforced DURAN. The 
fibers are alternately aligned in 0.degree. and 90.degree. orientation. 
The bending strengths listed in the table were determined parallel to one 
fiber orientation. Although by this procedure only half of the fibers are 
loaded, the average strength decreases merely by 30% compared to a 
unidirectional reinforced glass to 519.+-.74 MPa. 
The upper application temperature of fiber reinforced DURAN is about 
500.degree. C. because the glass transition temperature of DURAN is 
530.degree. C. Higher application temperatures are achieved with the 
alkaline earth aluminosilicate glass SUPREMAX, the T.sub.g of which is 
730.degree. C. 
In examples 10 to 13, the properties and process parameters of composites 
made of SiC fiber reinforced SUPREMAX are listed. It appears that 
composites with SUPREMAX as the matrix material achieve higher bending 
strengths than with DURAN. This is, above all, evident from the 
comparisons of example 3 with 12 and example 4 with 13, which in each case 
have approximately equal fiber volume loadings. 
According to current knowledge, a chemical reaction between the fiber, 
matrix and sol gel solution is less responsible for the increase in 
bending strength and fracture toughness, than the higher expansion 
coefficient of SUPREMAX glass (.alpha.=4.1.times.10.sup.-6 K.sup.-1) 
compared to DURAN glass (.alpha.=3.25.times.10.sup.-6 K.sup.-1). 
SUPREMAX glass shrinks more strongly onto the fibers 
(.alpha.=2.7.times.10.sup.-6 K.sup.-1) than DURAN glass and by that 
adheres better. 
Examples 10 and 11 show that even with relatively low fiber volume loadings 
of 36 or 37%, respectively, high values of bending strength are obtained. 
Optimization of the process parameters, especially of the pressure, has 
led to an obvious increase in bending strength in example 11 compared to 
example 10. Maximal fracture toughness values of 36 MPa.times..sqroot.m in 
example 13 go, as mentioned above, vastly beyond the prior art in which 
values of 27 MPa.times..sqroot.m are stated, although the fiber volume 
loading of 45% in example 13 is by 5% lower than that of the prior art. 
The typical stress strain diagram of example 13 is shown in FIG. 3. The 
diagram shows the characteristic feature of fiber-reinforced glasses an 
initial linear functional relationship and then a slowly decreasing slope 
up to the maximal stress. At the maximal stress, the first fibers break. 
However, since not all fibers break at the same time, the stress strain 
curve shows a type of plastic behavior with respect to even higher 
strains. 
In example 14, the alkaline earth aluminosilicate glass with the type 
number 8252 is used as matrix material. That glass has compared to 
SUPREMAX a somewhat higher expansion coefficient 
(.alpha.=4.5.times.10.sup.-6 K.sup.-1) and approximately the same glass 
transition temperature (T.sub.g =717.degree. C.). Hence, the glass is 
considered to shrink more strongly on the fibers than SUPREMAX. The 
results for example 14 show that compared to SiC reinforced SUPREMAX no 
further increase in bending strength is achieved. The reason for this is, 
according to current knowledge, due to the substitution of B.sub.2 O.sub.3 
for P.sub.2 O.sub.5 as well as the large difference in the expansion 
coefficients. The average strength value of 752 MPa is nevertheless very 
high and by it emphasizes that the inventive process allows a high 
flexibility in the selection of the matrix glasses. 
The examples 15 to 22 show results obtained for C fiber reinforced glasses. 
In usage of DURAN as matrix material, apparently higher bending strengths 
and fracture toughnesses are obtained as compared to SiC fiber reinforced 
DURAN. With increasing fiber volume loading in examples 15 to 17, average 
strength values of 774 MPa (30% fiber volume), 1129 MPa (35%), and 1210 
MPa (42%) are observed. The corresponding fracture toughnesses are 20 
MPa.times..sqroot.m, 25 MPa.times..sqroot.m, and 28 MPa.times..sqroot.m. 
As in the case of SiC fiber reinforced DURAN, the increase of the fiber 
volume loading up to 50% in example 18 of C fiber reinforced DURAN also 
does not lead to a further increase in bending strength. According to 
current knowledge, this behavior is due to the special winding procedure. 
On the other hand, the increase of the fiber volume loading entails a 
marked increase in fracture toughness up to average values of 35 
MPa.times..sqroot.m. The change from the C fiber T 800 (example 17) to T 
1000 (example 19) leads again to a slight increase in strength and 
fracture toughness. A characteristic stress strain diagram with respect to 
example 18 is shown in FIG. 4. 
Composites made of C fiber reinforced SUPREMAX are distinguished with 
respect to the mechanical properties mentioned above by lower values, 
example 20, than the SiC fiber reinforced composites, example 12. However, 
in using the B.sub.2 O.sub.3 -containing alkaline earth aluminosilicate 
glass with the type number 8252 as matrix material, improved properties 
with respect to the C fiber reinforced composites result compared to SiC 
fiber reinforced composites, if the C fiber T 1000 is used. In example 22, 
average strength values of 1148.+-.71 MPa are achieved. 
The examples 23 to 27 show the results for SiC fiber reinforced glass 
ceramics. Solely starting glasses for cordierite glass ceramics were used 
as matrix material. Example 24 shows that the production of SiC fiber 
reinforced cordierite glass ceramics raises problems. The average strength 
of 333 MPa is indeed markedly higher than that of pure cordierite glass 
ceramic (approximately 100 MPa), however, the value is markedly lower than 
those of the above-mentioned fiber reinforced glasses. One of the reasons 
for the relatively low strength values is the use of four point transverse 
bending tests for the determination of the bending strength, because from 
experience four point bending strengths are lower than three point bending 
strengths. Furthermore, it appears that in carefully controlling the 
process parameters, further improvements in the properties can be 
achieved. This is shown by example 23, where at a fiber volume loading of 
27% average bending strengths of 656 MPa are reached. Using fiber volume 
loadings of 51% and by increasing the pressure from 5 MPa to 10 MPa, 
average strength values of 751 MPa are obtained (example 25). These are 
excellent values with respect to fiber reinforced stoichiometric 
cordierite. Also, the average fracture toughness of 19 MPa.times..sqroot.m 
in example 24 is a superior improvement as compared to the monolithic 
material. 
Example 26 shows that, in adding 3 wt. % BaO to a stoichiometric cordierite 
and at a fiber volume loading of 34%, average strengths of 803 MPa and 
average fracture toughness of 24 MPa.times..sqroot.m are achieved. These 
cordierite composites clearly excel the currently known prior art. 
Finally, in example 27 the stoichiometric cordierite was modified by 3.5 
wt. % TiO.sub.2. When using a TiO.sub.2 -containing matrix, it is to be 
expected that a chemical reaction between the SiC fiber and the TiO.sub.2 
in the matrix takes place, as described in the U.S. Pat. No. 4,485,179. 
That effect appears also when using a TiO.sub.2 -containing sol gel 
solution in the production of a SiC fiber reinforced DURAN glass, as 
example 8 clearly demonstrates. In that example the strength values drop 
due to the reactive sol gel layer, to values which are comparable to those 
exhibited by the pure matrix. However, according to the inventive process 
in the case of example 27, it is to be expected that this reaction is 
prevented by coating each matrix grain as well as the SiC fibers with the 
TiO.sub.2 -free sol gel solution layer which during polycondensation forms 
a SiO.sub.2 layer. This is confirmed by the examples. The average 
strengths achieved in example 27 amount to 400 MPa and, thus, do not 
suggest a degradation of the fiber. That in this example the strength of, 
for example, example 23 has not been obtained may have several reasons: 
a) the achieved values date from the duty factor in which the process 
parameters have not been sufficiently accurately controlled; 
b) only a few tests have been performed without optimization of the process 
parameters temperature, time and pressure; and 
c) it is to be expected that TiO.sub.2 changes the crystallization--and 
therewith the densification behavior of the glass GM 30870. 
TABLE 
__________________________________________________________________________ 
Composite combinations and their properties 
__________________________________________________________________________ 
Example 
composite data 
1 2 3 4 5 6 7 8 9 10 
__________________________________________________________________________ 
matrix material 
DURAN 
= = = = = = = = SUPREMAX 
type of fiber 
SiC = = = = = = = = SiC 
sol gel solution 
SiO.sub.2 
= = = = none DURAN 
TiO.sub.2 
SiO.sub.2 
SiO.sub.2 
fiber volume 
42 = = 48 54 42 40 42 40 37 
loading in % 
pressing temper- 
1200 = 1265 1250 1260 1270 1255 1270 1260 1250 
ature in .degree.C. 
pressing time 
5 = = = = = = = = 5 
in min. 
pressure 10 = = = = = = = = 5 
in MPa 
test temperature 
20 600 20 = = = = = = 20 
in .degree.C. 
bending strength 
743 .+-. 42 
764 .+-. 11 
752 .+-. 81 
840 .+-. 81 
749 .+-. 35 
676 .+-. 127 
772 .+-. 72 
104 .+-. 71 
519 .+-. 74 
655 .+-. 32 
in MPa 
fracture toughness 20 .+-. 1 
18 .+-. 2 
25 .+-. 2 
in MPa .sqroot.m 
remarks 4 point * ** 4 point 
bending strength bidirectional 
bending 
reinforcement 
strength 
__________________________________________________________________________ 
Example 
composite data 
11 12 13 14 15 16 17 18 19 
__________________________________________________________________________ 
matrix material 
= = = 8252 DURAN = = = = 
type of fiber 
= = = = C/T800 
= = = C/T1000 
sol gel solution 
= = = = = = = = = 
fiber volume 
36 41 45 40 30 35 42 50 42 
loading in % 
pressing temper- 
1235 1200 1175 1260 1250 1250 1240 1250 1240 
ature in .degree.C. 
pressing time 
= = = = = = = = = 
in min. 
pressure 10 = = = 8 10 = = = 
in MPa 
test temperature 
20 20 20 20 20 20 20 20 20 
in .degree.C. 
bending strength 
845 .+-. 27 
950 .+-. 41 
1222 .+-. 74 
752 .+-. 50 
774 .+-. 140 
1129 .+-. 161 
1210 .+-. 62 
1164 .+-. 92 
1287 .+-. 41 
in MPa 
fracture toughness 
25 .+-. 5 
26 .+-. 4 
36 .+-. 7 20 .+-. 3 
25 .+-. 6 
28 .+-. 3 
35 .+-. 4 
30 .+-. 6 
in MPa .sqroot.m 
remarks 
__________________________________________________________________________ 
Example 
composite data 
20 21 22 23 24 25 26 27 
__________________________________________________________________________ 
matrix material 
SUPREMAX 
8252 = GM30870 
= = GM30870 
GM30870 
+3 wt 
+3.5 wt % 
BaO Ti 
type of fiber 
= C/T800 
C/T1000 
SiC = = = = 
sol gel solution 
= SiO.sub.2 
= = = = = = 
fiber volume 
42 42 = 27 51 = 34 32 
loading in % 
pressing temper- 
1190 1210 1215 1300 1310 = 1315 1350 
ature in .degree.C. 
pressing time 
= 5 = = = = = = 
in min. 
pressure = 10 = 2 5 10 = 5 
in MPa 
test temperature 
= 20 = = = = = = 
in .degree.C. 
bending strength 
810 .+-. 46 
768 .+-. 81 
1148 .+-. 71 
656 .+-. 122 
333 .+-. 29 
751 .+-. 60 
803 
400 51 
in MPa 
fracture toughness 
22 .+-. 5 19 .+-. 6 19 24 
in MPa .sqroot.m 
remarks 4 point 
bending 
strength 
__________________________________________________________________________ 
*method according to prior art 
**not disclosed by the present invention