JPH03232776A - Heat-resistant fiber-reinforced inorganic composite material - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an inorganic composite material reinforced with inorganic fibers and having excellent heat resistance, oxidation resistance, and thermal shock resistance.

(Prior art and its problems) Among carbonaceous inorganic composite materials reinforced with inorganic fibers, the so-called C/C composite, which uses carbon fiber as the reinforcing fiber and carbon as the inorganic matrix, has poor specific strength, specific elasticity, and non-oxidation. Excellent heat resistance, toughness, and friction properties in a harsh atmosphere,
Practical use is progressing as a heat-resistant structural material and brake material.

However, when considering the application to supersonic aircraft and space planes, which are expected to be used as future high-speed transportation systems, the maximum temperature of the aircraft surface due to aerodynamic heating is 1,200 yen for supersonic aircraft.
It is predicted that the temperature will reach 1,700 to 1,800 degrees Celsius for space planes, and ordinary C/C composites will burn and cannot be used.

As a means to solve this problem, a technique has been developed in the United States in which the surface of a C/C composite is coated with silicon carbide by CVI or CVD.

This oxidation-resistant C/C composite has been used for the nose cone and wing leading edge of the American Space Shuttle.

Recently, advances in coating technology have made it possible for the silicon carbide-coated C/C composite described above to be used in a high-temperature air atmosphere for long periods of time. Due to the difference in thermal expansion and contraction coefficients, peeling of the surface coating layer, pinholes, cranks, etc. occur. If even minute cracks occur in the coating layer, oxidative deterioration of the internal C/C composite will progress rapidly, making the material unusable as a structural material.

Both supersonic aircraft and space planes repeatedly take off and land, so destruction of the coating layer due to the thermal stress is unavoidable, and the oxidation-resistant C/C composite cannot be said to be a material that fully satisfies the required physical properties. In order to alleviate this thermal stress, research is being carried out on graded materials that are highly heat resistant and have many intermediate layers with small differences in thermal expansion coefficients between adjacent eyebrows, but this does not fully satisfy the requirements. No material has been obtained. Furthermore, the production of graded materials requires advanced technology and expensive equipment, resulting in very low productivity and very high costs.

On the other hand, as another method for improving the oxidation resistance of C/C composites, Japanese Patent Laid-Open No. 1-167290 discloses C/C composites.
After impregnating the C composite with an organosilicon compound that can be converted into silicon carbide by thermal decomposition, such as polycarbosilane or polysilastyrene, it is mineralized, and the surface is further coated with SiC or 5izNa.
A method of coating with a layer is disclosed. This method has been shown to alleviate the difference in thermal expansion and contraction rates between the carbon matrix and the surface coating layer due to the formation of the SiC layer through pyrolysis, and to reduce the occurrence of microcranks in the coating layer. ing.

However, in this method, the carbon layer and the SiC layer are in direct contact, and it is not possible to completely suppress the development of cracks due to thermal stress.When the -degree crank reaches the carbon layer, oxidative deterioration progresses rapidly. do. Further, if polycarbosilane or the like is directly applied to the carbon layer to make it inorganic, deterioration of the carbon layer due to the decomposed gas of polycarbosilane or the like cannot be avoided, causing new defects.

Also, in French patent FR2611198,
After coating the carbon fiber surface with carbon and SiC, impregnating it with a mixture of an organic polymer such as a phenolic resin and silicones that can be converted into carbon, baking it to produce a C/SiC matrix, and further applying a silicate polymer.
A SiC surface layer is provided by firing. Furthermore, Si
A method is disclosed in which surface glass flows into cracks caused by thermal stress and improves oxidation resistance by coating with an Ox layer or a SiO□10B z O:+ layer. This method is based on the assumption that cracks will occur, so it is ineffective unless the surface glass layer sufficiently fills the cracks.Also, since the matrix includes a glass layer with low heat resistance on the surface and inside, it has poor mechanical properties at high temperatures, e.g. It has an adverse effect on hot strength, etc.

(Means for Solving the Problems) An object of the present invention is to provide a novel heat-resistant fiber-reinforced inorganic composite material that solves the above problems.

Another object of the present invention is to provide a heat-resistant, oxidation-resistant, fiber-reinforced inorganic composite material that exhibits little deterioration in a high-temperature oxidizing atmosphere.

Another object of the present invention is to provide a fiber-reinforced inorganic composite material that generates less thermal stress and has excellent thermal shock resistance.

Another object of the present invention is to provide a low-cost fiber-reinforced inorganic composite material that has the above characteristics.

The fiber-reinforced inorganic composite material of the present invention is a composite material using inorganic fibers as a reinforcing material and an inorganic substance as a matrix,
The inorganic fiber is an inorganic fiber obtained from a silicon-containing polycyclic aromatic polymer, and the constituent components thereof are i) a radial structure derived from a polycyclic aromatic compound in a mesophase state constituting the polymer, and an onion. ii) an optically isotropic polycyclic aromatic compound constituting the polymer; ji) an amorphous phase consisting essentially of Si, C and 0;
Or, it is an aggregate consisting of crystalline ultrafine particles substantially consisting of β-SiC with a particle size of 500λ or less and amorphous 5iOX (0<x≦2), and the ratio of the constituent elements is Si; 30 to 70.
Weight %, C; 20-60 weight % and O; 0.5-10
5i-C-0 substance by weight, and the inorganic substance is mainly a) crystalline carbon derived from a polycyclic aromatic compound in a mesophase state constituting the polymer, or crystalline carbon and amorphous carbon, b) non-oriented crystalline carbon and/or amorphous carbon derived from the optically isotropic polycyclic aromatic compound constituting the polymer, and c) c+) S r, C and An amorphous phase consisting essentially of O and/or crystalline ultrafine particles having a particle size of 500 Å or less and consisting essentially of β-SiC and amorphous SiOx (0<x
≦2) and/or c2) (1) an amorphous material consisting essentially of Si, M, C and O, and/or ■ substantially consisting of β-SiCSMC, β-SiC and MC Crystalline ultrafine particles with a particle size of 500 Å or less consisting of a solid solution and MCr-, and amorphous SiOy and MO.

(In the above formula, M is at least one element selected from Ti, Zr and Hf, 0<x<1, O
<)l≦2, O<z≦2. ) is a heat-resistant fiber-reinforced inorganic composite material characterized by a matrix having a gradient structure in which the silicon content is controlled to increase as the distance from the reinforcing fiber surface increases.

First, the inorganic fiber in the present invention will be explained in detail.

In the following explanation, "part J" is "part by weight" and "%"
is "% by weight".

The inorganic fiber consists of the above-mentioned components i), ii) and ji), Si: 0.01-29%, C: 70-9
9.9% and O; 0.001-10%, preferably S
i; 0.1-25%, C; 74-99°8% and 0; 0
．． 01-8%.

Crystalline carbon, which is a component of this inorganic fiber, has a crystallite size of 500 Å or less, and is oriented in the fiber axis direction in a high-resolution electron microscope with a resolution of 1.5 people.
It is an ultrafine graphite crystal in which a fine lattice image corresponding to two (002) planes can be observed.

The crystalline carbon in the inorganic fibers can have a radial structure, an onion structure, a random structure, a core radial structure, a skin onion structure, a mosaic structure, a random structure including a partial radial structure, and the like. This is due to the presence of mesophase polycyclic aromatic compounds in the raw materials.

Total sum of constituent components 1) and 11) in this inorganic fiber 1
The ratio of component in) to 00 parts is 0.015 to 2
00 parts, and the ratio of constituent components i) and ii) is 1:
It is 0.02-4.

When the ratio of component ui) to 100 parts of the total of components i) and ii) is less than 0.015, the fiber is almost the same as pitch fiber, and the oxidation resistance and interfacial adhesion with the matrix are not improved. If the above ratio exceeds 200 parts, graphite fine crystals will not be effectively generated and fibers with a high elastic modulus will not be obtained.

In the continuous inorganic fiber of the present invention, microcrystals with a small interlayer spacing and three-dimensional arrangement are effectively generated,
Silicon atoms are distributed very uniformly so as to surround the microcrystals.

The inorganic fiber in the present invention includes: 1) a bonding unit (Si CH2) or a bonding unit (Si CH2);
-CH2) and a bonding unit (Si-3i), the silicon atom has a side chain group selected from the group consisting of a hydrogen atom, a lower alkyl group, a phenyl group, and a silyl group, and the bonding unit (Si-CHz) The total number of bonding units (Si-3i)
At least a part of the silicon atoms of the organosilicon polymer in which the ratio of the total number of is in the range of 140 to 20 is bonded to an aromatic ring of petroleum-based or coal-based pitch or a heat-treated product thereof through a silicon-carbon linking group. 100 parts of the precursor polymer and 2) a mesophase state obtained by heat-treating petroleum-based or coal-based pitch, or a polycyclic aromatic compound consisting of both mesophase and optically isotonic phase (hereinafter, both are collectively referred to as "
Sometimes referred to as ``mesophase polycyclic aromatic compounds''.

) 5 to 50,000 parts are heat-reacted and/or heat-melted at a temperature in the range of 200 to 500°C to obtain a silicon-containing polycyclic aromatic polymer.
a second step of preparing a spinning dope of the silicon-containing polycyclic aromatic polymer and spinning it; a third step of infusibleizing the spun yarn under tension or without tension;
and a fourth step of firing the infusible spun fiber bundle at a temperature in the range of 800 to 3000°C in vacuum or in an inert gas atmosphere.

Each of the above steps will be explained in more detail.

First step: The organosilicon polymer, which is one of the starting materials, can be synthesized by a known method. For example, polydimethylsilane obtained by the reaction of dimethyldichlorosilane and metallic sodium is heated at 400 °C in an inert gas. Obtained by heating above °C.

The organosilicon polymer has a bonding unit (Si CHz),
or bonding unit (Si-3i) and bonding unit (SiCH2)
The ratio of the total number of bonding units (SiCHz) to the total number of bonding units (Si-3i) is in the range of 1:0 to 20.

The weight average molecular weight (Ml) of the organosilicon polymer is 300 to
1000. In particular, it is preferably 400 to 800 in order to prepare the precursor polymer (1), which is an intermediate raw material for obtaining excellent inorganic fibers.

Another starting material, the polycyclic aromatic compound, is pi-soti obtained from petroleum and/or coal, and particularly preferred bichi is heavy oil obtained by fluid catalytic cracking of petroleum, and heavy oil thereof. These are distillate components or residual oils obtained by distilling and pitch obtained by heat-treating them.

The above pitch contains 5 to 9 components insoluble in organic solvents such as Hensen, toluene, xylene, and tetrahydrofuran.
The content is preferably 8%.

When pitch containing less than 5% of the above-mentioned insoluble components is used as a raw material, inorganic fibers with excellent strength and elastic modulus cannot be obtained.
In addition, when more than 98% pitch is used as a raw material,
The molecular weight of the copolymer increases rapidly, and coking may occur in some cases, making spinning difficult.

The weight average molecular weight (M) of this pitch is 100 to 30
It is 00.

The weight average molecular weight is a value determined as follows. That is, if the pitch does not contain organic solvent insoluble matter for gel permeation chromatography (CPC) measurement, such as henzene, toluene, xylene, tetrahydrofuran, chloroform, and dichlorohensen, it is directly measured by GPC, and the pitch is insoluble in the organic solvent. If it contains a component, it is hydrogenated under mild conditions and the organic solvent-insoluble component is changed to the organic solvent-soluble component, followed by GPC measurement. Below, the weight average molecular weight of the polymer containing the above organic solvent insoluble matter is:
This is a value obtained by performing the same processing as above. Precursor polymer (
1) Adds petroleum-based or coal-based pitch to an organosilicon polymer, and heats the mixture preferably at 250 to 500°C in an inert gas.
It is prepared by a heating reaction at a temperature in the range of .

The ratio of pitch used is 8 parts per 100 parts of organosilicon polymer.
It is preferable that it is 3-1900 parts.

If the ratio of pitch used is too small, the silicon carbide component in the resulting inorganic fiber will increase, making it impossible to obtain an inorganic fiber with a high modulus of elasticity. As a result, inorganic fibers with excellent interfacial adhesion with the matrix and oxidation resistance cannot be obtained.

If the reaction temperature of the above reaction is too low, it will be difficult to form bonds between silicon atoms and aromatic carbon, and if the reaction temperature is too high, the resulting precursor polymer (1) will be violently decomposed and its molecular weight will increase. Undesirable.

Mesophase polycyclic aromatic compounds can be prepared, for example, by heating petroleum-based or coal-based pitch to 300 to 500°C in an inert gas and subjecting it to condensation polymerization while removing the generated soft fraction. .

If the temperature of the condensation polymerization reaction is too low, the growth of the condensed ring will not be sufficient, and if the temperature is too high, an insoluble or infusible product will be produced due to coking.

Mesophase polycyclic aromatic compounds have a melting point of 200 to 4
00°C, and the weight average molecular weight is 200°C.
~10000.

Among mesophase polycyclic aromatic compounds, 20 to 10
Those having an optical anisotropy of 0% and containing 30 to 100% of insoluble matter in Hensen, toluene, xylene, or tetrahydrofuran are particularly preferred in order to obtain inorganic fibers with excellent mechanical performance.

In the first step, the precursor polymer (1) and the mesophase polycyclic aromatic compound are melted and/or heated to react in a temperature range of 200 to 500°C to produce a spun polymer made of a silicon-containing polycyclic aromatic polymer. Prepare.

The mesophase polycyclic aromatic compound is preferably used in an amount of 5 to 50,000 parts per 100 parts of the precursor polymer (1). If it is less than 5 parts, the mesophase content in the product will be insufficient, so high elasticity If yarn cannot be obtained, and if the amount exceeds 50,000 parts, the silicon component will be insufficient, making it impossible to obtain inorganic fibers with excellent interfacial adhesion with the matrix and oxidation resistance.

The weight average molecular weight of the silicon-containing polycyclic aromatic polymer is 200
~11,000 and a melting point of 200-400°C.

2nd step: The spinning polymer, which is a silicon-containing polycyclic aromatic polymer obtained in the 1st step, is heated and melted, and in some cases, it is filtered to remove substances that are harmful during spinning, such as microgels and impurities. This is then spun using a commonly used synthetic fiber spinning device.

The temperature of the spinning dope during spinning varies depending on the softening temperature of the raw material polymer, but a temperature in the range of 220 to 420°C is advantageous.

In the spinning device, a spinning tube is attached as necessary,
After setting the atmosphere in the spinning tube to one or more atmospheres selected from the group consisting of air, inert gas, hot air, hot inert gas, steam, and ammonia gas, the winding speed is increased to create a thin diameter. fibers can be obtained. The spinning speed in the melt spinning is determined by the average molecular weight of the raw materials,
Although it varies depending on the molecular weight distribution and molecular structure, 50 to 500
A range of 0 m/min is preferable.

Third step: The spun fibers obtained in the second step are made infusible under the action of tension or no tension.

A typical method for infusibility is to heat the spun fibers in an oxidizing atmosphere. The temperature of infusibility is preferably 50~
The temperature is in the range of 400°C. If the infusibility temperature is too low, the polymer constituting the spinning atoms will not be fused, and if the temperature is too high, the polymer will burn.

The purpose of infusibility is to make the polymer that makes up the spun fibers into a three-dimensional structure that is infusible and insoluble, so that it does not melt during the next firing process and does not fuse with adjacent fibers. It is. Gases constituting the oxidizing atmosphere during infusibility include air, ozone, oxygen, chlorine gas, bromine gas, ammonia gas, and mixed gases thereof.

As an infusible method different from the above, spun fibers are infusible by T-ray irradiation or electron beam irradiation in an oxidizing or non-oxidizing atmosphere, under tension or no tension, while heating at a low temperature as necessary. method can also be adopted.

The purpose of irradiating this T-ray or electron beam is to further polymerize the polymer that forms the spun fibers.
The purpose is to prevent the spun yarn from melting and losing its fiber shape.

The appropriate irradiation dose of T-rays or electron beams is 106 to 1010 rand.

Irradiation can be carried out in a vacuum, an inert gas atmosphere, or an oxidizing gas atmosphere such as air, ozone, oxygen, chlorine gas, bromine gas, ammonia gas, and mixtures thereof.

Infusibility by irradiation can be carried out at room temperature, or, if necessary, by heating in the temperature range of 50 to 200''C, infusibility can be achieved in a shorter time.

If infusibility is carried out without tension, the spun fibers will shrink and take on a wavy shape, but this can sometimes be corrected in the next firing process, and tension is not necessarily required. In this case, good results can be obtained if the tension is greater than that which can at least prevent the spun fibers from shrinking and becoming wavy during infusibility.

The tension to be applied during infusibility is 1 to 500
g/W" range is preferable; even if a tension of 1 g/l1l12 or less is applied, it is not possible to apply tension that will not cause the fibers to sag, and if a tension of 500 g/l112 or more is applied, the fibers will break. There are things to do.

Fourth step: By firing the infusible yarn obtained in the third step at a temperature in the range of 800 to 3000°C in a vacuum or inert gas atmosphere, inorganic fibers mainly composed of carbon, silicon, and oxygen are obtained. It will be done.

In the firing process, it is not necessarily necessary to apply tension, but if the fiber is fired at a high temperature while applying tension in the range of 0.001 to 100 kg/ml, a high-strength inorganic fiber with less bending can be obtained.

It is estimated that during the heating process, mineralization becomes intense from about 700°C and is almost completed at about 800°C. Therefore, the firing is preferably performed at a temperature of 800°C or higher. Furthermore, since obtaining a temperature higher than 3000°C requires expensive equipment, firing at a higher temperature than 3000″C is not practical from a cost standpoint.

However, when using the fibers as short fibers, infusible yarns or calcined yarns at 800°C or less are mixed with the matrix matrix material described later and fired together with the matrix matrix material to strengthen the adhesion with the matrix. methods are also adopted.

The distribution state of silicon in the inorganic fiber of the present invention can also be controlled by the atmosphere during firing and the size and concentration of mesophase in the raw material. For example, when the mesophase is grown to a large size, the silicon-containing polymer is easily extruded into the fiber surface phase, and a silicon-rich layer can be formed on the fiber surface after firing.

Next, a method for manufacturing the fiber-reinforced inorganic composite material of the present invention will be explained.

(1) Manufacture of fiber-containing molded article A method of adding powder of a matrix matrix material to various woven fabrics such as plain weave, satin weave, mosaic weave, twill weave, spiral weave, three-dimensional fabric, etc. of the inorganic fibers, heat pressing, and forming the said woven fabric. After impregnating with matrix matrix solution or slurry, remove the solvent,
A fiber-containing molded article is produced by a method of thermoforming a dried prepreg sheet, a method of melt-kneading the short fibers of the inorganic fibers or chopped fibers, and a matrix base material, followed by press molding or injection molding.

The content of inorganic fibers in the molded body is preferably 10 to 70% by volume.

The matrix matrix in the present invention is a silicon-containing polycyclic aromatic polymer which is a precursor polymer of the inorganic fibers and/or a metal-containing polycyclic polymer containing silicon and at least one element selected from titanium, zirconium, and hafnium. Aromatic polymers are suitable.

The silicon-containing polycyclic aromatic polymer can be produced by the first step of producing the inorganic fiber.

Moreover, the metal-containing polycyclic aromatic polymer can be obtained by the method described below.

First, the precursor polymer (
1) and a transition metal compound represented by the formula MX, from 100 to
The reaction is carried out at a temperature in the range of 500°C.

In the above MX, M is at least one element selected from Ti, Zr and Hf, and X is by condensation,
M may be anything as long as it can be bonded directly or via an oxygen atom to the silicon of the precursor polymer (1), and is preferably a halogen atom, an alkoxy group, or a complex-forming group such as β-diketone, although there is no particular limitation. .

If the reaction temperature is too low, the precursor polymer (1) and 2MX4
If the condensation reaction with M does not proceed and the reaction temperature is excessively high, M
The cross-linking reaction of the precursor polymer (1) via the reaction proceeds excessively and gelation occurs, the precursor polymer (1) itself condenses and becomes high in molecular weight, or in some cases MX may volatilize, which is undesirable. .

- For example, when M is Ti and X is 0C4H9, a suitable reaction temperature is 200-400°C.

Through this reaction, a random copolymer (2) in which at least some of the silicon atoms of the precursor polymer (1) are bonded to the metal M directly or via oxygen atoms is prepared.

The metal M can be bonded to the silicon atom of the precursor polymer (1) in the form of a side chain in a bonding mode such as -MX3 or 10-MX3, or can be bonded directly to the silicon atom of the precursor polymer (1) or by bonding with oxygen. A cross-linked bonding mode may also be used.

As a method for preparing the random copolymer (2), in addition to the above-mentioned method, it is also possible to prepare the random copolymer (2) by reacting an organosilicon polymer with MX and further reacting the resulting product with pitch. .

Using the random copolymer (2) instead of the precursor polymer (1), the metal-containing Polycyclic aromatic polymers can be prepared.

In addition, in producing the fiber-containing molded article, the above polymer may contain calcined powder of the above polymer and/or graphite, silicon carbide, titanium carbide, zirconium carbide, hafnium carbide, titanium boride, zirconium boride, hafnium boride. There is no problem in mixing and using a small amount of heat-resistant ceramic fine powder such as. Moreover, a binder can also be used for the purpose of improving the adhesion between the fibers and the matrix.

The binder includes organic silicon polymers such as diphenylsiloxane, dimethylsiloxane, polyborodiphenylsiloxane, polyborodimethylsiloxane, polycarbosilane, polydimethylsilazane, polytitanocarbosilane, polyzirconocarbosilane, and diphenylsilane diol. , hexamethyldisilazane and other organic silicon compounds.

(2) Infusibility of fiber-containing molded bodies Next, the molded body is subjected to an infusible treatment, if necessary.

As the method of infusibility treatment, the method of the third step of producing the inorganic fibers can be directly adopted.

(3) The fiber-containing molded product is fired and infusible in a vacuum or inert gas.
Calcining at temperatures in the range from 800 to 3000° C. yields mineralized, fiber-reinforced composite materials with a matrix of carbon, silicon and oxygen and/or carbon, M, silicon and oxygen.

In the heating process, it is estimated that mineralization becomes intense from about 700°C and is almost completed at about 800°C. Therefore, the firing is preferably performed at a temperature of 800°C or higher. Furthermore, since obtaining a temperature higher than 3000°C requires expensive equipment, firing at a higher temperature than 3000°C is not practical from a cost standpoint.

Note that the infusibility step can be omitted by extremely slowing down the temperature increase rate for mineralization in this step, or by using a shape-retaining means such as a molded object shape-retaining jig or a powder head. It is also possible to obtain a high-density composite material in one step by using high-temperature hot pressing as a molding method.

The composition of the matrix in the resulting composite material is preferably the same or similar to that of the reinforcing fibers.

If the reinforcing fiber composition and the matri lettuce composition are significantly different, the adhesion at the interface will be poor, and under severe mixing fluctuations, thermal stress will occur due to the difference in coefficient of thermal expansion and thermal contraction, which is undesirable.

(4) The fiber-reinforced composite material obtained by densification, high-strength firing, and mineralization of the composite material contains open pores, so the silicon-containing polycyclic aromatic polymer or the metal-containing polycyclic After being impregnated with a melt, solution, or slurry of an aromatic polymer, the composite can be made higher in density and strength by infusibility, firing, and inorganicization, if necessary. Impregnation may be performed using any of a melt, solution, or slurry of the silicon-containing polycyclic aromatic polymer, but
In order to penetrate into the fine open pores, this composite material is impregnated with the melt, solution or slurry of the polymer, and after promoting penetration into the fine pores under reduced pressure, the temperature is raised while the solvent is distilled off. 10~
By applying a pressure of 500 kg/c111, the pores are filled with the polymer melt.

The obtained impregnated body is made infusible in the same manner as in the third step,
Can be calcined and mineralized. By repeating this operation, a fiber-reinforced composite material with high density and high strength can be obtained. The number of impregnations and changes in bulk density and porosity at that time depend on the solution used for impregnation, the composition of the melt, the molecular weight distribution, the selection of impregnation, infusibility, and mineralization processes, and the residual mineralization rate associated with the selection of conditions. There are no specific regulations, but 2~
Preferably 10 times.

In this impregnation step, calcined powder of the polymer and/or fine heat-resistant ceramic powder may be added as in the production of the fiber-containing molded body.

In subsequent impregnations, the composition of the impregnated base material is changed so that the silicon or the ratio of silicon and M increases as the steps are repeated, and for the final impregnation, a base material that changes to almost component C) by sintering is selected. It is preferable.

In this way, the surface phase that is susceptible to oxidative impregnation has excellent oxidation resistance because it is rich in component C), and has a gradient structure toward the reinforcing fibers, so it is a fiber-reinforced composite that does not crack due to thermal stress. materials can be obtained.

In order to further improve the oxidation resistance of this composite material, the surface of the composite material may be coated with a heat-resistant ceramic layer.

Heat-resistant ceramics include silicon carbide, titanium carbide,
Zirconium carbide, hafnium carbide, vanadium carbide,
Carbide ceramics such as niobium carbide, tantalum carbide, boron carbide, chromium carbide, tungsten carbide, molybdenum carbide, silicon nitride, titanium nitride, zirconium nitride, vanadium nitride, niobium nitride, tantalum nitride, boron nitride, aluminum nitride, hafnium nitride, etc. Oxide ceramics such as nitride ceramics, alumina, silica, magnesia, boron oxide, mullite, and cordierite, titanium boride,
Although boride ceramics such as zirconium boride can be used, silicon carbide is particularly suitable because it has excellent heat resistance and oxidation resistance, and has a small difference in coefficient of thermal expansion with the internal matrix.

Examples of the coating method include a conventional coating method such as a CVD method and a thermal spraying method, and a method in which a precursor that can be converted into the ceramic by firing is applied to the surface and then fired. Note that polycarbosilane, polytitanocarbosilane, polysilazane, polycarbosilastyrene, and polysilastyrene may be used as the precursor.

(Effects of the Invention) In the heat-resistant fiber-reinforced inorganic composite material of the present invention, the SiC/C composition ratio of the matrix can be continuously controlled from the fiber surface, and the matrix layer is composed of a single silicon-containing layer as described below. Since it is manufactured from a polycyclic aromatic polymer and/or a metal-containing polycyclic aromatic polymer, S i
The uniformity of C/C is microscopically excellent, so there is almost no occurrence of cranks due to thermal stress, and both the matrix and reinforcing fibers are made of new materials that exhibit much better oxidation resistance than conventional technology. Therefore, even if oxygen reaches inside the matrix layer for some reason, it exhibits extremely excellent oxidation resistance.

The fiber-reinforced composite material of the present invention has excellent strength, elastic modulus, and toughness, as well as heat resistance, oxidation resistance, corrosion resistance, abrasion resistance, and thermal shock resistance. Not only can it be used as an alternative material to ordinary C/C composites, such as heat-resistant structural materials such as furnace materials, insulation materials, and heat-resistant belts, but also as external wall materials and engine peripheral materials for supersonic aircraft, space planes, space shuttle materials, etc. It can be used under extremely harsh conditions such as

(Example) The present invention will be explained below with reference to Examples.

Reference Example 1 (Production of Polymer I) 5! 2.5 of anhydrous xylene in a three-ring flask! and 400 g of sodium were added thereto, heated to the boiling point of xylene under a nitrogen gas stream, and dimethyldichlorosilane IIl was added dropwise over 1 hour. After the dropwise addition was completed, the mixture was heated under reflux for 10 hours to form a precipitate. The precipitate was filtered and washed with methanol and then water to obtain 420 g of white powder polydimethylsilane.

400 g of this polydimethylsilane was charged into a 31-hole flask equipped with a gas inlet tube, a stirrer, a condenser, and a distillation tube, and heated at 420 degrees under a nitrogen stream for 50-7 minutes while stirring.
C. to obtain 350 g of a colorless and transparent slightly viscous liquid in a distillation receiver.

The number average molecular weight of this liquid was 470 as measured by vapor pressure osmosis.

When the infrared absorption spectrum of this substance was measured, it was found that 6
SiC for 50~900c+n-' and 1250CI+-'
Absorption of H3, 2100a++-J:S i -HO:)
Absorption, Si near 102102O' and 1355cm-'
Absorption of CHzSi, 2900 cm-' and 2950 cm-
C-H absorption was observed at 380an-', and when the far-infrared absorption spectrum of this material was measured, 5.
Since absorption of i-3i is observed, the obtained liquid material mainly consists of (Si CHz) bond units and (Si
-3i) It was found to be an organosilicon polymer consisting of bonding units and having a hydrogen atom and a methyl group in the silicon side chain.

From the measurement results of nuclear magnetic resonance analysis and infrared absorption analysis, this organosilicon polymer is a polymer in which the ratio of the total number of (Si CH2) bond units to the total number of (Si-3i) bond units is approximately 1:3. This was confirmed.

300 g of the above organosilicon polymer was treated with ethanol to remove low molecular weight substances to obtain 40 g of a polymer having a number average molecular weight of 1200.

When the infrared absorption spectrum of this material was measured, absorption peaks similar to those above were observed, and this material mainly consists of (Si CHz) bond units and (Si-3i) bond units, and has hydrogen atoms and hydrogen atoms in the side chains of silicon. It turned out to be an organosilicon polymer with methyl groups.

From the measurement results of nuclear magnetic resonance analysis and infrared absorption analysis, this organosilicon polymer is a polymer in which the ratio of the total number of (Si-CH,) bond units to the total number of (Si-3i) bond units is approximately 7:1. It was confirmed that

On the other hand, among petroleum fractions, substances with a boiling point higher than that of light oil are removed using silica.
Fluid catalytic cracking and rectification were performed at a temperature of 500°C in the presence of an alumina-based cracking catalyst, and a residue was obtained from the bottom of the column. Hereinafter, this residue will be referred to as FCC slurry oil.

As a result of elemental analysis, this FCC slurry oil had an atomic ratio of carbon atoms to hydrogen atoms (C/H) of 0.75, and an aromatic carbon ratio of 0.55 as determined by nuclear magnetic resonance analysis.

200g of the above FCC slurry oil was added under a stream of nitrogen gas.
After heating to 50°C and distilling off the distillate at the same temperature, the residue was filtered while hot at 200°C to remove the infusible portion at the same temperature to obtain 57 g of light bone-removed pinches.

This light bone removal pitch contained 25% xylene insolubles.

Add 25 g of organosilicon polymer and 20 mm of xylene to 57 g of this light bone-removed pitch, raise the temperature with stirring, distill off the xylene, and react at 400"C for 6 hours to obtain 51 g of precursor polymer (1). Ta.

As a result of infrared absorption spectrum measurement, this precursor polymer (1) was found to contain 5i-H bonds (I R
: 2100CIm-') and new Si-
C (benzene ring carbon) bond (IR: 1135cm-'
), it was found that the organosilicon polymer was a copolymer in which some of the silicon atoms were directly bonded to the carbon atoms of the polycyclic aromatic ring.

This precursor polymer (1) contained no xylene-insoluble portion, had a weight average molecular weight of 1400, a melting point of 265'C, and a softening point of 310C.

On the other hand, 180 g of the light bone removal pitch was heated at 400°C under a nitrogen stream while removing light bones generated by the reaction.
Time-condensation polymerization was performed to obtain a heat-treated pitch of 97.2.

This heat-treated pitch has a melting point of 263°C and a softening point of 308°C.
It was a mesophase polycyclic aromatic compound containing 77% xylene insoluble matter and 31% quinoline soluble matter, and had an optical anisotropy of 75% when observed with a polarizing microscope on the polished surface.

90 g of this mesophase polycyclic aromatic compound and 6.4 g of the precursor polymer (1) were mixed at 380° under a nitrogen atmosphere.
The mixture was melted and heated at C for 1 hour to obtain a silicon-containing polycyclic aromatic polymer (Polymer I) in a uniform state.

The melting point of this polymer is 267°C and the softening point is 315°C.
It contained 70% xylene insoluble matter.

Reference Example 2 (Production of Polymer ■) A silicon-containing polycyclic aromatic compound was produced in the same manner as in Reference Example 1, except that 97 g of the mesophase polycyclic aromatic compound and 3 g of the precursor polymer (1) were mixed and melted and heated at 400'C. A group polymer (Polymer ■) was obtained.

The melting point of this polymer is 272°C, the softening point is 319"C,
It contained 71% xylene insoluble matter.

Reference Example 3 (Production of Polymer ■) A silicon-containing polycyclic aromatic compound was prepared in the same manner as in Reference Example 1, except that 66 g of the mesophase polycyclic aromatic compound and 34 g of the precursor polymer (1) were melted and heated at 360°C. Polymer (
Polymer ■) was obtained.

The melting point of this polymer is 266°C, and the softening point is 314°C.
It contained 57% xylene insoluble matter.

Reference Example 4 (Production of Polymer ■) Tetraoctoxytitanium (T i (QCs HI?) 4) 2.7 g was added to 39 g of the precursor polymer (1) obtained in Reference Example 1.
Add 5 g of xylene solution (11 g of 25% xylene solution), and after distilling off the xylene, react at 340 °C for 2 hours.
38.8 g of random copolymer (2) was obtained.

66 g of the mesophase polycyclic aromatic compound obtained in Reference Example 1 was added to 34 g of this random copolymer (2), and the mixture was melt-mixed at 380°C in a nitrogen atmosphere to form a metal-containing polycyclic aromatic polymer (polymer ■). Obtained.

The melting point of this polymer is 274°C, and the softening point is 322°C.
It contained 61% xylene insoluble matter.

Reference Example 5 (Manufacture of reinforcing fibers) Polymers ①, ② and ② obtained in Reference Examples 1.2 and 3 were used as raw materials for spinning, and melt-spun at 360°C using a metal nozzle with a nozzle diameter of 0.15 mm. The obtained spun yarn was oxidized and made infusible at 300° C. in air, and then fired at a predetermined temperature in an argon atmosphere to produce reinforcing fibers. The tensile strength and tensile modulus of the obtained reinforcing fibers were measured, and the silicon content in the fibers was measured by high-frequency plasma emission spectroscopy. The results of these measurements are shown in Table 1.

Table 1 Example 1 A two-dimensional plain woven fabric of the inorganic fiber ■ obtained in Reference Example 5 was made with a diameter of 7 cm.
It was cut into discs of 500 m in diameter, impregnated in a 30% xylene slurry of polymer (1), and dried to produce prepreg sheets. In the mold, fill the spaces between the prepreg sheets with fine powder of polymer
°Layering 30 sheets while shifting them one after another, 50kg/c+
Hot pressing was performed at 350° C. under pressure of 1 to obtain a disc-shaped molded product.

This molded body was buried in a powder bed of carbon powder to maintain its shape, and the temperature was raised to 800°C at a rate of 5°C/h in a nitrogen stream, and then further raised to 1300°C to inorganize the polymer (2).
A first matrix layer having a silicon content of 0.95% was formed.

The bulk density of the resulting composite material was 1.32 g/cIf!
Met.

This composite material was immersed in a 50% xylene slurry of polymer (III), heated to 350"C while distilling off the xylene under reduced pressure, and then impregnated under pressure at 100 kg/ciM at a rate of 5°C/h in air. The temperature was raised to 300''C to make it infusible and then mineralized at 1300°C to form a second matrix layer having the same silicon content as the first matrix layer.

Furthermore, the impregnated polymer was replaced with polymer
．． A third matrix layer of 8% was formed.

For the third impregnation, the precursor polymer (1
) to form a fourth matrix layer having a silicon content of 15.1%.

For the fourth impregnation, the precursor polymer (1) synthesized in Reference Example 1 with a charging ratio of organosilicon polymer and light fraction removed pitch of 70:30 was used, and impregnation and mineralization were performed in the same manner as above. A fifth matrix layer was formed with a silicon content of 27.1%.

For the fifth impregnation, 3 parts of polyporosiloxane was added to 100 parts of polydimethylsilane obtained in Reference Example 1,
Using polycarbosilane obtained by thermal condensation at 350° C. in nitrogen, impregnation and mineralization were performed in the same manner as above to form a sixth matrix layer having a silicon content of 50.8%.

The bulk density of the resulting composite was 1.70 g/cd and contained almost no open pores. Further, the fiber volume content (V) of the composite material was 61%.

The obtained composite material was coated with silicon tetrachloride and methane as raw materials and subjected to CVD coating at 1300° C. under a reduced pressure of 50 KHg to form a silicon carbide coating layer with a thickness of about 10 μm. The bending strength of the obtained composite material according to the three-point bending strength test method was 32 kg/mm''.

Example 2 Using the inorganic fiber (2) obtained in Reference Example 5 as a reinforcing material, a prepreg sheet was prepared by impregnating it with polymer (2) in the same manner as in Example 1. The obtained prepreg sheets were filled with fine powder of polymer (2) and the pressure was set to 20 kg/c1a, but the same procedure as in Example 1 was carried out, followed by mineralization, and finally calcined at 2500°C to obtain a bulk density of 1. A composite material of .20 g/cd was obtained.

This composite material was coated in the same manner as in Example 1, and the first time was polymer 1. The second time was polymer ①, the third time was the precursor polymer (1) in Reference Example 1, and the fourth time was the organosilicon polymer and the light weight removal pitch. The precursor polymer (1) obtained at a charging ratio of 70:30 was impregnated with polycarbosilane for the fifth time and mineralized. At that time, mineralization was performed at 1900°C.

As a result, a composite material with a bulk density of 1.90 g/cdl was obtained. Note that this composite material had a rating of 42%.

The obtained composite material was subjected to CVD coating in the same manner as in Example 1 to obtain a composite material covered with a silicon carbide coating layer of about 10 μm. The bending strength of this composite material is 35k
g/mm2.

Example 3 A two-dimensional plain woven fabric of the inorganic fiber (■) obtained in Reference Example 5 was impregnated with a 20% xylene solution of the polymer (■) and then dried, and this sheet and a fine powder of the polymer (■) were alternately laminated to form an example. Hot press molding was carried out in the same manner as in 1 to form a first matrix layer which was mineralized and had a silicon content of 4.8%.

The bulk density of the obtained composite material was 1.23 g/csa.

This composite material was removed in the same manner as in Example 1. First time: Polymer ■; Second time: Polymer ■; Third time: Random copolymer (2) in Reference Example 4; Fourth time: Organosilicon polymer and light adhesion removed. Tetraoctoxytitanium (T
i (QCs HI?) 4) Random copolymer (2) synthesized by adding 15 parts, fifth time, titanium tetrabutoxide was added to the polycarbosilane obtained in Example 1,
Impregnation using polytitanocarbosilane consisting of 100 parts of carbosilane units obtained by crosslinking polymerization at 340 ° C and 10 parts of titanoxane units of formula (T 1-0),
Mineralization was performed. At that time, the mineralization temperature was all 130
The temperature was 0°C. Note that the second
The silicon content of the matrix layer is 4.8%, and the silicon content of the third matrix layer formed in the second treatment is 5.
．． The silicon content of the fourth layer formed in the third treatment is 15.2%, and the silicon content of the fifth matrix layer formed in the fourth treatment is 27.2%. The silicon content of the sixth matrix layer formed by the treatment is 50.
It was 8%.

As a result, a composite material with a bulk density of 1.74 g/ci was obtained. Note that this composite material had a rating of 51%.

The obtained composite material was subjected to CVD coating in the same manner as in Example 1 to obtain a composite material having a silicon carbide coating layer of about 10 μm. The bending strength of this composite material is 29 kg
/mm”.

Comparative Example 1 As a reinforcing fiber, a plain weave fabric of Torayka M-40 (“Toreca” is a trade name of carbon fiber manufactured by Toshi Co., Ltd.), which is a commercially available PAN-based carbon fiber and a highly elastic type carbon fiber, was used.
A phenol resin was used as a matrix base material, hot-pressed and cured at 180°C, and further post-cured at 250°C for 4 hours to obtain a fiber-reinforced molded article. This molded body was mineralized at 900°C, impregnated with phenol resin, mineralized four times, and then fired at 1800″C to obtain a C/C composite. Coated with silicon carbide.

Comparative Example 2 A carbon fiber-reinforced carbon/silicon carbide composite material whose surface was coated with silicon carbide was obtained in the same manner as in Comparative Example 1, except that a phenol resin with 10% silicon added was used as the matrix base material. Ta.

Example 4 The composite materials of Examples 1 to 3 were placed in a furnace maintained at 1300°C in the air, heated for 20 minutes, taken out, and forced air cooled for 20 minutes, which was repeated 5 times, and then heated at 1500°C in the air.
The oxidative depletion rate was measured by holding at C. As a result, the oxidative consumption rate of each composite material was 0.0006 for the material of Example 1.
kg/m”/h, O, OO1B for the material of Example 2
kg/m”/h, 0.0012 for the material of Example 3
kg/m”/h.

Comparative Example 3 The oxidative consumption rate was measured in the same manner as in Example 4 using the materials of Comparative Example 1.2. As a result, the oxidative consumption rate of each composite material was 0.45 kg/m"/h for the material of Comparative Example 1, and 15 kg/m"/h for the material of Comparative Example 2.

Claims (1)

[Scope of Claims] A fiber-reinforced composite material having inorganic fibers as a reinforcing material and an inorganic substance as a matrix, wherein the inorganic fibers are inorganic fibers obtained from a silicon-containing polycyclic aromatic polymer, and the constituent components thereof i) at least one type of crystal selected from the group consisting of a radial structure, an onion structure, a random structure, a core radial structure, a skin onion structure, and a mosaic structure derived from a polycyclic aromatic compound in a mesophase state constituting the polymer; carbonaceous matter exhibiting an aligned state, ii) non-oriented crystalline carbon and/or amorphous carbon derived from an optically isotropic polycyclic aromatic compound constituting the polymer, and iii) Si, Amorphous phase consisting essentially of C and O and/or crystalline ultrafine particles consisting essentially of β-SiC with a particle size of 500 Å or less and amorphous SiO_x (0<x≦2)
It is an aggregate consisting of Si, and the proportion of the constituent elements is Si; 30 ~
70% by weight, C: 20-60% by weight and O: 0.5-1
0% by weight of Si-C-O material, and the inorganic material is mainly a) crystalline carbon derived from a polycyclic aromatic compound in a mesophase state constituting the polymer, or crystalline carbon and amorphous b) non-oriented crystalline carbon and/or amorphous carbon derived from the optically isotropic polycyclic aromatic compound constituting the polymer, and c) c_1) Si, C and An amorphous phase consisting essentially of O and/or crystalline ultrafine particles consisting essentially of β-SiC with a particle size of 500 Å or less and amorphous SiO_x (0<x≦
2) an aggregate consisting of and/or c_2) (1) an amorphous material consisting essentially of Si, M, C and O, and/or (2) essentially consisting of β-SiC, MC, β-SiC An aggregate of crystalline ultrafine particles with a particle size of 500 Å or less consisting of a solid solution of is an element with 0<x<1, 0
<y≦2, 0<z≦2. ) A heat-resistant fiber-reinforced inorganic composite material comprising a matrix having a gradient structure in which the silicon content is controlled to increase as the distance from the inorganic fiber surface increases.