JPH0977570A - Fiber reinforced ceramic composite - Google Patents

Abstract

PROBLEM TO BE SOLVED: To convert a ceramic material requiring a high-temp. process for production into a composite and to obtain a fiber reinforced ceramic composite excellent in fracture toughness by using specified boron nitride fibers having high tensile strength and a high degree of orientation as a filler for a composite. SOLUTION: This fiber reinforced ceramic composite contains boron nitride fibers made of boron nitride having a structure obtd. by stacking faces (C-faces) each formed by combining 6-membered rings each consisting of alternately bonded boron and nitrogen atoms in the surface direction of the rings in the matrix made of ceramics, glass or an inorg. single crystal. The boron nitride fibers have at least 1,400MPa tensile strength. At least a part of the C-faces of the boron nitride have been oriented practically parallel to the fiber axes of the boron nitride fibers and the degree of orientation of the C-faces is at least 0.74.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fiber-reinforced ceramic composite and a filling material used for the composite.

[0002]

2. Description of the Related Art Ceramics, glass, or inorganic single crystals (hereinafter also referred to as ceramic materials) have high strength and are stable up to high temperatures, so that they are used as high-temperature structural materials that cannot be replaced by plastics or metal materials. Applications are expected. However, these materials have, on the contrary, excellent thermal and mechanical properties and are inherently brittle and fragile. Therefore, these materials have not been widely used because they lack reliability as structural materials that are required to maintain a certain structure.

As a means of overcoming the brittleness of ceramics,
Strengthening of toughness by compounding with various filler materials is effective.
As the filling material to be compounded, spherical particles, plate-like particles,
Whiskers, continuous fibers, etc. have been investigated, but strengthening toughness by compounding with continuous fibers is particularly effective.
It is known that the fracture toughness can be increased to the same level as that of cemented carbide.

Ceramic fibers or carbon fibers typified by silicon carbide fibers and alumina fibers are considered as candidates for the fibers for composite reinforcement. However, both of them have their respective disadvantages and are not suitable as composite reinforcing fibers. For example, in the case of ceramic fibers, the structure is a polycrystalline body in which fine crystals are aggregated, but when exposed to high temperature, the constituent crystals become coarse, and the tensile strength of the fibers is significantly reduced. For example, in the case of silicon carbide fiber, when heated in an argon gas of 0.1 MPa (almost atmospheric pressure), silicon carbide microcrystals having a size of several nm before heating are 14
It is coarsened to about 100 nm by heating to 00 ° C. Along with this, the tensile strength of the silicon carbide fiber is about 16
Decrease from 00 MPa to 600 MPa [Journa of American Ceramic Society (Journa
l of the American Ceramic Society), Volume 72, 2
No., 192-97 (1989). ]. Generally, when compounding a fiber for composite reinforcement with a ceramic material,
It is necessary to heat at a high temperature of over one thousand and several hundred degrees Celsius. Therefore, the tensile strength of the ceramic fiber is reduced in the step of forming a composite with the ceramic material, and it becomes difficult to enhance the toughness.

Further, when the ceramic fiber is compounded with the ceramic material, the ceramic material of the base material and the fiber are often bonded relatively firmly. When the composite material is broken, the fiber is pulled out from the base material ( Also called pull-out)
May not occur easily. The fracture toughness of the ceramic-based material, which is a brittle material, is improved by compounding with the fiber because the reinforcing fiber is pulled out from the base material near the crack tip of the fracture part and added to the compounded material. It is believed that this is because mechanical energy is absorbed. Therefore, when pullout is unlikely to occur, it becomes difficult to improve the fracture toughness.

On the other hand, in the case of carbon fiber, the change in structure at high temperature is small and the tensile strength is maintained even when heated to about 2000 ° C. Therefore, even if high-temperature heat treatment is performed in the step of forming a composite with a ceramic material, the strength of the fiber is maintained, and thus it may be possible to form a composite and strengthen the toughness.
Further, since carbon easily pulls out due to its solid lubricity, the fracture toughness of the composite material may be significantly improved in some cases. However, in the case of carbon fiber, it may react with an oxide at a high temperature to be oxidized and consumed as carbon monoxide, and the material of the base material is limited. Further, since carbon fibers are consumed by oxidation when heated to about 400 ° C. or higher in air, the obtained carbon fiber reinforced ceramics material has a drawback that it cannot be used at high temperature in air or in an oxidizing atmosphere.

As described above, at present, brittle materials such as ceramic materials are used without impairing their useful characteristics.
There are no reinforcing inorganic fibers that can be reinforced or toughened. Therefore, ceramic-based materials, which are expected to be applied as high-temperature structural materials, have not been widely used because of their inherent characteristic of brittleness.

On the other hand, the boron nitride fiber is unlikely to undergo structural changes such as crystal coarsening even at high temperature due to the anisotropy of its crystal structure, and therefore the tensile strength of the fiber due to exposure to high temperature is high. Is estimated to be small. That is, it is considered that the decrease in strength of boron nitride fiber due to heat is smaller than that of ceramic fiber. Furthermore, boron nitride is stable against oxidation up to about 1000 ° C. in air, and has excellent oxidation resistance as compared with carbon fiber.

In addition to such excellent heat resistance and oxidation resistance, boron nitride fiber has excellent characteristics as a fiber for composite reinforcement. For example, boron nitride has low reactivity with other substances, as can be seen from the fact that it is also used for crucibles and mold release agents. Therefore, even if it is combined with various ceramic materials, it is considered that it is possible to form a composite without reacting with the matrix phase. Furthermore, since the boron nitride fiber has low reactivity with the matrix phase as described above, it often does not form a strong bond with the matrix phase. In addition, since boron nitride fiber is excellent in solid lubricity, it is considered that when boron nitride fiber is used as the fiber for composite reinforcement, pullout easily occurs and the effect of improving fracture toughness is great.

However, conventionally, the strength of boron nitride fiber is weak, and it has been difficult to obtain a toughness-reinforced composite material. For example, JP-B-53-37837 and JP-A-63-
195173, US Pat. No. 5,061,469, and US Pat. No. 3,668,059 have tensile strengths of 784 MPa, 500 MPa, and 1200 MP, respectively.
Although it is a, 580 MPa, the present situation is that these tensile strengths are very low compared to, for example, the tensile strength of carbon fiber of 3000 MPa.

[0011]

Thus, in the present situation,
Ceramic materials that are brittle materials, without impairing their useful properties, strengthening, there is no reinforcing inorganic fiber that enables high toughness, and ceramic materials that are expected to be applied as high-temperature structural materials are It has not been widely used.

[0012]

Means for Solving the Problems Accordingly, the present inventors have:
We have found a boron nitride fiber in which the C-plane of boron nitride is preferentially oriented in a direction parallel to the fiber axis, and as the degree of orientation of this boron nitride fiber increases, its tensile strength is dramatically improved. I found it for the first time. Furthermore, since this boron nitride fiber does not cause strength deterioration due to microstructural changes even when it is heated to a high temperature, it is possible to compound ceramic materials that require a high temperature process for fabrication, and the resulting composite material is a base material. It was found that the heat resistance and the oxidation resistance of No. 1 were not impaired and the brittleness of the base material was improved, that is, the fracture toughness was improved, and the present invention was completed here.

That is, according to the present invention, a 6-membered ring formed by alternately bonding boron and nitrogen in a base material made of ceramics, glass, or an inorganic single crystal is connected in the plane direction of the 6-membered ring. Fiber-reinforced ceramics-based composite comprising boron nitride fibers made of boron nitride having a structure in which the surfaces (C planes) formed by stacking the boron nitride fibers have a tensile strength of at least 1400 MPa. Is.

In another invention, a 6-membered ring formed by alternately bonding boron and nitrogen in a base material made of ceramics, glass, or an inorganic single crystal is connected in the plane direction of the 6-membered ring. A boron nitride fiber made of boron nitride having a structure in which the surfaces (C surfaces) formed by the above are laminated, and at least a part of the C surface is substantially parallel to the fiber axis of the boron nitride fiber. A fiber-reinforced ceramics-based composite that is oriented and contains boron nitride fibers having a degree of orientation of the C plane of at least 0.74.

Still another aspect of the present invention is a structure in which a 6-membered ring made by alternately bonding boron and nitrogen is connected in the plane direction of the 6-membered ring and the surface (C-plane) is laminated. A boron nitride fiber comprising boron nitride having at least 1400
It is a filling material for inorganic composites made of boron nitride fiber having a tensile strength of MPa.

Yet another invention is a structure in which a 6-membered ring formed by alternately bonding boron and nitrogen is connected in the plane direction of the 6-membered ring and the surface (C-plane) is laminated. Boron nitride fiber comprising boron nitride having at least a part of the C-plane oriented substantially parallel to the fiber axis of the boron nitride fiber, and the degree of orientation of the C-plane is at least 0. It is a filling material for ceramic composites composed of boron nitride fiber of 0.74.

The fiber-reinforced ceramic composite containing the boron nitride fiber of the present invention will be described in detail below.

Boron nitride is a substance formed by chemically bonding boron of group III of the periodic table and nitrogen of group V of the periodic table. Currently, (1) boron and nitrogen are three-dimensional. Known as boron nitride having a structure formed by mechanically bonding, and (2) boron nitride having a structure formed by two-dimensionally bonding boron and nitrogen.

As a boron nitride having a structure formed by two-dimensionally bonding boron and nitrogen, a 6-membered ring formed by alternately bonding boron and nitrogen is a 6-membered ring surface. BACKGROUND ART Boron nitride having a structure in which surfaces formed by connecting in a direction are laminated is known.

Further, as a boron nitride having a structure in which planes are laminated, (a) hexagonal boron nitride (h-BN) having a laminated structure having a two-layer structure as a period, and (b) a three-layer structure as a periodic structure. It is known that the rhombohedral boron nitride (r-BN) has a laminated structure of, and (c) turbostratic boron nitride (t-BN) has a non-regular laminated structure.

In the boron nitride of the present invention, the 6-membered ring formed by alternately bonding boron and nitrogen described above is connected in the plane direction of the 6-membered ring and the surfaces are laminated. It is composed of boron nitride having a structure.

Therefore, the boron nitride according to the present invention includes hexagonal boron nitride (h-BN), rhombohedral boron nitride (r-BN) and / or turbostratic boron nitride (t-BN). May be contained.

However, in the present invention, generally speaking, hexagonal boron nitride (h-BN) and / or turbostratic boron nitride (t-BN) form a main part of boron nitride. Often, rhombohedral boron nitride (r-BN), if present, is often present in a small proportion.

In the hexagonal crystal structure and the rhombohedral crystal structure, a plane (hereinafter also referred to as a C plane) formed by two-dimensionally connecting six-membered rings formed by alternately bonding boron and nitrogen is regularly formed. It is a laminated structure. Also, the turbostratic structure is
A structure in which the C planes are laminated without having regularity in the direction perpendicular to the planes is sometimes called a disordered layer structure.

The laminated structure of the boron nitride can be confirmed from the diffraction peak from the C plane by X-ray diffraction. This diffraction peak is 2θ = 24 to 26 ° when the X-ray is CuKα ray.
The distance between the laminated C-planes calculated from the position of the diffraction peak is about 3 to 4 angstroms.

The boron nitride fibers used in the present invention have a tensile strength of at least 1400 MPa, preferably at least 1700 MPa, most preferably at least 2300 M.
Pa. This tensile strength is JIS R 76
It can be measured according to the "Testing method for carbon fibers" defined in No. 01 (1986).

The degree of orientation of the C plane (hereinafter, also referred to as orientation degree) is used as an index showing the orientation distribution of the C plane of boron nitride with respect to the fiber axis of the boron nitride fiber. The tensile strength in the present invention is 1400 MPa. The degree of orientation of the above boron nitride fibers is about 0.74 or more. The degree of orientation of boron nitride fibers is determined by the method of measuring the degree of orientation of carbon fibers [Carbon Society of Japan, Ed.
9). ] Can be measured.

In practice, the inventor has found and can also produce boron nitride fibers with a degree of orientation of less than 0.74. For example, a boron nitride fiber having an orientation degree of less than 0.74 can be produced by heating a boron nitride precursor fiber without applying tensile stress. However, manufacturing boron nitride fibers with various degrees of orientation,
A systematic examination of the tensile strength of the boron nitride fiber with respect to the degree of orientation shows that the tensile strength of the boron nitride fiber having an orientation degree of less than 0.5 does not substantially depend on the degree of orientation, and its value is also low. In many cases. On the other hand, when the degree of orientation is 0.5 or more,
The tensile strength of boron nitride fibers shows a significant improvement. For example, when the typical values are shown, the boron nitride fibers having the orientation degrees of 0.26 and 0.46 both have a tensile strength of 440 MPa, whereas the boron nitride fibers having the orientation degree of 0.80 have a tensile strength of It was 1970 MPa.

When the degree of orientation is 0.7 or more, the tensile strength of the boron nitride fiber improves in proportion to the degree of orientation. For example, when the typical value is shown, the tensile strength is 8 when the degree of orientation is 0.70.
While it was 40 MPa, when the orientation degree was 0.74, the tensile strength was improved to 1400 MPa. Therefore, when the orientation degree is 0.70 or more, the tensile strength can be further improved by improving the orientation degree.

As described above, the boron nitride fiber according to the present invention has a high tensile strength comparable to that of conventionally produced ceramic fibers such as silicon carbide fiber. What is remarkably superior to fibers and the like is that the boron nitride fiber maintains high tensile strength even after history of high temperature. Conventional ceramic fiber is a polycrystalline body in which very fine crystals are aggregated, but the bonding of these substances is isotropic as compared with boron nitride, so if such fiber is exposed to high temperature, Often, the fine crystals that make up the fibers show significant growth.
As a result, the coarsening of the crystal causes the growth of defects that are the source of fracture, and the ceramic fiber causes a significant decrease in tensile strength. In the case of silicon carbide fiber, it has been confirmed that when it is heated to about 1300 ° C. or higher, the tensile strength is significantly reduced. On the other hand, in the case of boron nitride fiber, since the bond of boron nitride has strong anisotropy, it is difficult for structural changes such as grain growth to occur even at high temperatures. Therefore, the boron nitride fiber can maintain high tensile strength even after being exposed to high temperatures.
In fact, the boron nitride fiber in the embodiment of the present invention is 200
It was produced by heating to 0 ° C., and the excellent heat resistance of the boron nitride fiber in the present invention is clearly shown.

Further, since boron nitride has a high chemical stability of conventionally produced ceramic fibers, it can be compounded without reacting with various base materials.
Since boron nitride has solid lubricity, when boron nitride fiber is used as a composite reinforcing fiber, boron nitride fiber pull-out easily occurs when the composite is broken, and the breaking energy is absorbed efficiently. Therefore, a composite having improved fracture toughness can be obtained.

Furthermore, although boron nitride fibers having a tensile strength of 1400 MPa or more have a high degree of orientation, the effect of higher orientation is that the thermal conductivity in the fiber axis direction is improved. In the case of graphite having a structure similar to that of boron nitride, the thermal conductivity in the in-plane direction is higher than that in the in-plane direction and the in-plane direction of the single crystal carbon 6-membered ring. It is known to take. Similarly, in the case of boron nitride, boron nitride of boron nitride-
When the thermal conductivity of boron nitride obtained by regularly stacking planes composed of nitrogen 6-membered rings is measured, the thermal conductivity in the in-plane direction is close to 100 times that in the direction perpendicular to the plane. high. Further, it is known that in the case of carbon fibers in which the 6-membered carbon ring is preferentially oriented in the direction parallel to the fiber axis, the thermal conductivity improves as the degree of orientation improves. In graphite and boron nitride containing carbon fibers, the reason for the high thermal conductivity in the in-plane direction is that relatively light elements such as carbon, boron and nitrogen are bonded to each other by a strong covalent bond, It is thought that this is because heat is efficiently propagated by vibration. Therefore, as in the case of the carbon fiber, it is considered that the thermal conductivity in the fiber axis direction is improved as the orientation degree of the boron nitride fiber is improved.

Generally, the thermal conductivity of boron nitride is nearly 10 times higher than that of alumina, mullite, silicon nitride, etc., so that boron nitride particles and the like are used for the purpose of improving the thermal conductivity of the material. Although composite formation may be performed, the thermal conductivity of the composite can be efficiently improved by using the boron nitride fiber whose orientation improves the thermal conductivity in the fiber axis direction.

The method for producing the boron nitride fiber having a high tensile strength and a high degree of orientation used in the present invention is not particularly limited, but typically it can be produced as follows.

(A) First, an adduct of a boron trihalide and a nitrile compound is reacted with an ammonium halide or a primary amine hydrohalide in the presence of boron trihalide to produce a boron nitride precursor. Generate the body.

Examples of the boron trihalide include boron trifluoride, boron trichloride, boron tribromide and boron triiodide, which can be used without particular limitation.

As the nitrile compound, a known compound having a nitrile group can be used without particular limitation. Specifically, acetonitrile, propionitrile, capronitrile, acrylonitrile, crotonnitrile,
Tolunitrile, benzonitrile, i-butyronitrile,
Examples include n-butyronitrile, isovaleronitrile, malononitrile, succinonitrile, glutaronitrile, adiponitrile, pimeronitrile, suberonitrile and the like. When the number of carbon atoms contained in the nitrile compound increases,
Since the carbon contained in the boron nitride precursor increases and the elimination component increases when the boron nitride precursor is boronized by the heat treatment, it is possible to use acetonitrile, acrylonitrile or the like having a small number of carbon atoms. More preferable.

As ammonium halides, ammonium fluoride, ammonium chloride, ammonium bromide,
Ammonium iodide and the like can be mentioned. Preferred examples of the ammonium halide include ammonium chloride.

As the primary amine hydrohalide salt,
Primary amine hydrofluoride, primary amine hydrochloride,
Primary amine hydrobromide, primary amine hydroiodide and the like can be mentioned. Preferred examples of the primary amine hydrohalide include primary amine hydrochloride (hereinafter, referred to as primary amine hydrochloride).
Primary amine hydrochloride).

The primary amine hydrochloride has the general formula: RNH ₂ ·.
A compound represented by HCl, in which R is an alkyl group such as a methyl group, an ethyl group and a propyl group, and an aryl group such as a phenyl group, a tolyl group and a xylyl group is used without limitation.
When the carbon number of R increases, the carbon contained in the boron nitride precursor increases and the elimination component at the time of boron nitridation by heat treatment increases, so that R is a lower alkyl group such as a methyl group or an ethyl group. It is more preferred to use the group primary amine hydrochloride.

To obtain the boron nitride fiber of the present invention,
First, a boron nitride precursor is synthesized by reacting an adduct of the boron trihalide and the nitrile compound with an ammonium halide or a primary amine hydrohalide.

The adduct of the boron trihalide and the nitrile compound is a product in which the boron halide is additionally bonded to the non-bonded electron pair of the nitrogen atom of the nitrile group. It easily reacts with a nitrile compound to form an adduct. The method for producing the adduct is not particularly limited. For example, a method of dropping boron trihalide into a solution of a nitrile compound in an organic solvent at room temperature, a method of dissolving a nitrile compound in an organic solvent and then blowing boron trihalide, or a method of trihalogenating the organic solvent An adduct can be formed by dissolving boron and then dropping a nitrile compound.
Since boron trihalide and the nitrile compound easily react to form an adduct, they may be brought into contact with each other immediately before the reaction.

It is essential that boron trihalide be present during the reaction of the adduct with ammonium halide or primary amine hydrohalide. When boron trihalide is not present during the reaction, the yield of the boron nitride precursor of the present invention is low, and a spinning solvent for spinning as described later, such as N, N-dimethylformamide (hereinafter referred to as DMF).
(Also referred to as) insoluble reaction by-products are generated.

The boron trihalide may be present at least during the reaction between the boron trihalide / addition product of the nitrile compound and the ammonium halide or the primary amine hydrohalide. For example, when an adduct of a nitrile compound and boron trihalide is formed, excess boron trihalide may be used, and unreacted boron trihalide may be allowed to coexist in the adduct in advance. good. The amount of boron trihalide to be added to the nitrile compound is 1.05 to 5 in molar ratio (boron trihalide / nitrile compound).
It can be arbitrarily selected from the range of 2.00. But,
When the amount of boron trihalide added is small, a DMF-insoluble component is produced, and when the amount of boron trihalide added is large, the amount of boron trihalide that does not contribute to the reaction increases, so trihalogen for a more preferable nitrile compound is used. The addition molar ratio of boron bromide is 1.1 to 1.5. At this time, since the boron trihalide and the nitrile compound form a 1: 1 adduct, the amount of boron trihalide present during the reaction is in a molar ratio (boron trihalide / addition). In the range of 0.1) to 0.5).

The concentration of the nitrile compound in the reaction solvent is not particularly limited, but it is preferably in the range of 0.1 to 10 mol / l. When the concentration of the nitrile compound is less than 0.1 mol / l, the amount of the obtained boron nitride precursor is small, which is not preferable because it is not efficient.
On the other hand, if the concentration of the nitrile compound exceeds 10 mol / l, the amount of the adduct formed as a solid with respect to the solvent becomes too large, and the formation of the adduct becomes ununiform.

The amount of ammonium halide or primary amine hydrohalide salt added is 0.67 to a molar ratio to the nitrile compound (ammonium halide or primary amine hydrohalide salt / nitrile compound).
It is preferable to select from the range of 1.5. When the amount of ammonium halide or primary amine hydrohalide is large, a component insoluble in DMF is generated, and when the amount of nitrile compound is large, the amount of unreacted adduct tends to increase. What is necessary is just to choose from the range of -1.2.

The solvent used for synthesizing the boron nitride precursor of the present invention is not particularly limited, but when separating the reaction product boron nitride precursor, the reaction by-product borazine compound is dissolved. It is preferable that it is easy to remove. From such a viewpoint, an organic solvent such as benzene, toluene, xylene, chlorobenzene is preferably selected.

The heating temperature for reacting the adduct with the ammonium halide or the primary amine hydrohalide is generally low at a low temperature and D at a high temperature.
Components insoluble in MF increase and the reaction yield decreases. Therefore, the heating temperature may be selected from the range of 100 ° C to 160 ° C. The heating time varies depending on the temperature, but may be selected from the range of 3 to 30 hours.

By performing the above heat treatment, the boron nitride precursor is formed as an orange or brown precipitate.

As a reaction device for obtaining the boron nitride precursor, a known device can be used without particular limitation. However, since the adduct of boron trihalide with the nitrile compound and the boron nitride precursor are both hydrolyzed, the inside of the reaction system is sufficiently dried in advance with nitrogen gas or the like, and air is also supplied from outside the reaction system during the reaction. It is necessary to provide a moisture absorbent such as calcium chloride in the opening portion of the apparatus so that moisture in the apparatus does not enter.

(B) The boron nitride precursor produced in step (a) is dissolved in a solvent to prepare a boron nitride precursor solution.

This boron nitride precursor solution can be used as a spinning solution in the next step (c).

As a method for producing a boron nitride precursor fiber from this boron nitride precursor, a known method can be used without particular limitation. For example, when spinning a precursor fiber from a boron nitride precursor solution, the spinning solution is prepared by dissolving the boron nitride precursor in a soluble solvent. Examples of the precursor-soluble solvent include DMF, ε-caprolactam, chloronitrile, malonitrile, N-methyl-β-cyanoethylformamide, N, N-diethylformamide and the like. By dissolving the boron nitride precursor in the soluble solvent, an orange or brown transparent spinning solution can be obtained.

The viscosity of the spinning solution can be adjusted, if desired, by concentration or by adding, for example, an acrylonitrile polymer. When the molecular weight of the boron nitride precursor is relatively small, the viscosity of the spinning solution is increased by using an acrylonitrile polymer having a relatively large molecular weight together with the boron nitride precursor, and the spinnability of the spinning solution is improved. can do.

The acrylonitrile polymer used in the present invention can be used without particular limitation as long as it is soluble in a soluble solvent constituting the spinning solution and does not cause phase separation with the boron nitride precursor in the spinning solution. it can. Preferably, a polymer of acrylonitrile, or a polymerizable monomer other than acrylonitrile having a vinyl group such as vinyl acetate, acrylamide, methacrylic acid, methacrylic acid ester, acrylic acid, acrylate (hereinafter, simply referred to as vinyl monomer) and acrylonitrile Is used.
When a copolymer of acrylonitrile and a vinyl monomer is used, when the amount of the vinyl monomer constituting the copolymer increases, phase separation with the boron nitride precursor occurs in the spinning solution. Therefore, the composition of the acrylonitrile that constitutes the copolymer is 85% based on the total polymerizable monomer.
It is preferably at least mol%.

The weight average molecular weight of the acrylonitrile polymer used in the present invention is not particularly limited, but it is 10,000 to 20.
It is preferably in the range of 10,000.

The amount of the acrylonitrile polymer added to the spinning solution is not particularly limited, but the boron nitride precursor 100
It is preferably 0.01 to 5 parts by weight with respect to parts by weight.

(C) The boron nitride precursor solution prepared in step (b) is spun to form a boron nitride precursor fiber.

The preferred concentration range of the spinning solution depends on the spinning method, but is 0.01 to 3.0 g / ml, and the viscosity at that time is 10 to 100,000 poises. As a method for spinning the boron nitride precursor fiber from the obtained spinning solution, a widely known method can be used. For example, by rotating a container having a small hole containing a spinning solution, a method of discharging the spinning solution using centrifugal force, a method of discharging the spinning solution by gas pressure from the small hole, and using a gear pump from the small hole The boron nitride precursor fiber can be spun by using a method of discharging a spinning solution.

The spinning temperature may vary depending on the solvent used, but is, for example, -60 to 200 ° C, preferably -10 to 10.
The temperature is 180 ° C, more preferably 0 to 160 ° C.

As one of methods for obtaining a boron nitride fiber having a tensile strength of 1400 MPa or more, there is a method of heating a boron nitride precursor fiber while applying stress.

(D) The boron nitride precursor fiber is preheated in an inert gas atmosphere in the range of 100 to 600 ° C., and (e) the preheated fiber is heated in an ammonia gas atmosphere at 200 to 1300 ° C. Treat with ammonia.

That is, the boron nitride precursor fiber obtained in the above step (c) was used for 10 times in an inert gas atmosphere.
Heat treatment (preheating) at 0 to 600 ° C. and then heat treatment at 200 to 1300 ° C. in an ammonia gas atmosphere give a boron nitride fiber. The boron nitride fiber at this stage is called unoriented boron nitride fiber. When producing unoriented boron nitride fiber, if only heat treatment in an ammonia atmosphere is carried out, defects and scratches are generated on the fiber surface of the obtained boron nitride fiber, and high strength boron nitride fiber is obtained. I can't.

Nitrogen, argon, helium, or the like can be used as the atmospheric gas in the heat treatment in the inert gas atmosphere. The heat treatment temperature in the heat treatment under an inert gas atmosphere is 100 to 600 ° C., preferably 15 to
It can be arbitrarily selected from the range of 0 to 550 ° C, more preferably 160 to 500 ° C. This heat treatment is 100 ° C
If it is performed at a lower temperature, defects and scratches may be generated on the fiber surface of the boron nitride fiber in the subsequent heat treatment in an ammonia gas atmosphere, and the fiber strength may decrease. Further, when the heat treatment is performed at a temperature higher than 600 ° C., carbon derived from the precursor is likely to be graphitized, and it may be difficult to remove the carbon even if the subsequent heat treatment in an ammonia gas atmosphere is performed. is there.

The heating device for heat-treating the boron nitride precursor fiber in an inert gas atmosphere may have a structure capable of controlling the atmosphere with a chamber or a furnace core tube, and may be an electric furnace or a gas furnace. A known heating device such as the above can be used without particular limitation. As the heat treatment method, a batch-type heat treatment in which a certain amount of boron nitride precursor fibers are heat-treated at one time, and continuous boron nitride precursor fibers are sequentially fed into a heating device which has been heated to a heat treatment temperature in advance and heated. There is a continuous heat treatment in which treated and heat-treated fibers are wound and collected, and any heat treatment method may be used in the present invention. When performing batch heat treatment in an inert gas atmosphere, the boron nitride precursor fiber is introduced into the heat treatment device which has been preheated to the heat treatment temperature for heat treatment, or the heat treatment device is used for nitriding. After arranging the boron precursor fiber, the temperature can be raised to reach the heat treatment temperature for heat treatment.

In any of the heat treatment methods, when the boron nitride precursor fiber is rapidly heated, DMF, which is a solvent for preparing a spinning solution from the boron nitride precursor, is rapidly evaporated, Desorption of decomposition products may occur rapidly, resulting in defects such as voids and cracks in the obtained boron nitride fiber, leading to a decrease in strength. Therefore, the temperature rising rate until the boron nitride precursor fiber reaches the heat treatment temperature is 20 ° C.
/ Min or less, it is preferable to perform heat treatment. The holding time at the heat treatment temperature depends on the amount of boron nitride precursor fibers and the heat treatment temperature, but can be arbitrarily selected from the range of 0 to 10 hours. The holding time of 0 hours means that immediately after the boron nitride precursor fiber reaches the heat treatment temperature, the heating device is cooled down, or the boron nitride precursor fiber is removed from the heating device, and the heat treatment is completed. Indicates that

The heat treatment atmosphere in the heat treatment under an inert gas atmosphere may be any of the temperature rising process until reaching the heat treatment temperature, the holding process at the heat treatment temperature, and the temperature lowering process until the end of the heat treatment. That is, while the boron nitride precursor fiber is in the chamber of the heating device, the furnace core tube, or the like in an inert gas atmosphere, the inert gas atmosphere is preferable. In order to make the atmosphere of the inert gas, the chamber of the heating device replaced with the inert gas, the furnace tube or the like is sealed, or the chamber of the heating device,
An inert gas may be passed through a furnace tube or the like.

In some cases, the carbon component derived from the boron nitride precursor or the like can be efficiently removed by performing the heat treatment in the inert gas atmosphere and then the heat treatment in the ammonia gas atmosphere. . The heat treatment temperature in the atmosphere of ammonia gas is 200 to 1300.
℃, preferably 250 to 1250 ℃, more preferably 3
Since the carbon derived from the precursor is almost decomposed and removed by the heat treatment at a temperature of 00 to 1200 ° C, it is not particularly necessary to perform the heat treatment at a temperature higher than 1300 ° C in an ammonia gas atmosphere.

The heating device for performing the heat treatment of the boron nitride precursor fiber in the atmosphere of ammonia gas may have a structure capable of controlling the atmosphere by a chamber or a furnace core tube, and may be an electric furnace, a gas furnace or the like. A known heating device can be used without particular limitation. As the heat treatment method, either a batch heat treatment or a continuous heat treatment method may be used as in the heat treatment in an inert gas atmosphere. When performing batch type heat treatment, the boron nitride precursor fiber is introduced into the heat treatment device which has been preheated to the heat treatment temperature for heat treatment, or the boron nitride precursor fiber is added to the heat treatment device. After the arrangement, the temperature is raised to reach the heat treatment temperature and heat treatment is performed.

In any of the heat treatment methods, when the boron nitride precursor fiber is rapidly heated, the thermal decomposition products are rapidly desorbed, resulting in defects such as voids and cracks in the obtained boron nitride fiber. May occur, leading to a decrease in strength. Therefore, it is preferable to perform the heat treatment at a heating rate of 20 ° C./min or less until the boron nitride precursor fiber reaches the heat treatment temperature. The holding time at the heat treatment temperature depends on the amount of boron nitride precursor fibers and the heat treatment temperature, but can be arbitrarily selected from the range of 0 to 10 hours. The holding time of 0 hour means that the temperature of the heating device is lowered immediately after the boron nitride precursor fiber reaches the heat treatment temperature, or
This indicates that the heat treatment is completed by taking out the boron nitride precursor fiber from the heating device.

In the heat treatment under the ammonia gas atmosphere, it is necessary that the heat treatment atmosphere is the ammonia gas because the temperature of the heat treatment carried out under the inert gas atmosphere during the heating process is changed from the heat treatment under the ammonia gas atmosphere. It is the process of holding at the heat treatment temperature in the ammonia gas atmosphere until reaching the treatment temperature. In other heat treatment processes, that is, in the temperature raising process to the heat treatment temperature performed in an inert gas atmosphere and in the temperature lowering process from the heat treatment temperature in an ammonia gas atmosphere, an inert atmosphere such as nitrogen, argon, or helium or Any of the ammonia gas atmospheres may be used. In order to change the atmosphere of the heat treatment to ammonia gas, the chamber of the heating device, the furnace core tube, or the like, which is replaced with the ammonia gas, may be sealed, or the ammonia gas may be circulated through the chamber of the heating device, the furnace core tube, or the like.

In the present invention, it is preferable that the heat treatment (preheating) is first performed in an inert gas atmosphere, and then the heat treatment is performed in an ammonia gas atmosphere. As a method of sequentially performing heat treatment in an inert gas atmosphere and heat treatment in an ammonia gas atmosphere, first, heat treatment in an inert gas atmosphere is performed, and heat treatment in an inert gas atmosphere is completed. At this point, the atmosphere gas may be switched to ammonia and heat treatment may be subsequently performed in an ammonia gas atmosphere.After the heat treatment, the temperature may be lowered, or the boron nitride fiber may be taken out from the heating device, or the like in an inert gas atmosphere. The heat treatment below may be terminated and the heat treatment may be performed again in an ammonia gas atmosphere.

(F) The boron nitride fiber of the present invention is obtained by heating the ammonia-treated fiber obtained in the above step (e) at 1600 to 2300 ° C. under an inert gas atmosphere while applying tensile stress. can get.

That is, for the boron nitride fiber having a tensile strength of 1400 MPa or more, the unoriented boron nitride fiber is applied in an inert gas atmosphere while applying tensile stress to the fiber.
Heat treatment at 0 to 2300 ° C., preferably 1650 to 2250 ° C., more preferably 1700 to 2200 ° C. (hereinafter,
It can also be obtained by performing an orientation treatment).

The atmosphere in this orientation treatment is not particularly limited as long as boron nitride is not chemically altered such as by oxidation. Therefore, an inert gas such as nitrogen, argon, or helium can be used as the atmospheric gas in the orientation treatment path. Alternatively, the orientation treatment can be performed under vacuum.

The heat treatment temperature in the orientation treatment is 160
It can be arbitrarily selected from the range of 0 to 2300 ° C. When the heat treatment temperature is lower than 1600 ° C, the orientation does not proceed sufficiently even if tensile stress is applied, and the tensile strength is 1400MP.
It may not reach a. Further, since the decomposition reaction of boron nitride starts at 2300 ° C or higher, it is not preferable to perform the heat treatment at 2300 ° C or higher. The heating device for carrying out the orientation treatment may be any structure having a structure such that the atmosphere can be controlled by a chamber or a core tube, and a known heating device such as an electric furnace or a gas furnace can be used without particular limitation. The orientation treatment is a batch-type treatment in which a certain amount of unoriented boron nitride fibers are treated at a time, and continuous unoriented boron nitride fibers are continuously fed to a heating device which has been heated to a heat treatment temperature in advance. There is a continuous treatment in which treated and treated fibers are wound and collected, and any treatment method may be used in the present invention. When carrying out the orientation treatment in a batch system, the non-oriented boron nitride fiber is introduced into the heating device which has been preheated to the heat treatment temperature for heat treatment, or the non-oriented boron nitride fiber is heated. After being placed in the processing apparatus, the temperature is raised to reach the heat treatment temperature and heat treatment is performed.

When the unoriented boron nitride fiber is rapidly heated in the orientation treatment, defects may occur due to thermal stress and the strength of the obtained boron nitride fiber may be reduced. Therefore, the orientation treatment is preferably performed at a rate of 100 ° C./min or less until the unoriented boron nitride fiber reaches the heat treatment temperature. The holding time at the heat treatment temperature can be arbitrarily selected from the range of 0 to 10 hours, though it depends on the amount of unoriented boron nitride fibers to be heat treated and the heat treatment temperature. The holding time of 0 hours means that the heating device is cooled immediately after the unoriented boron nitride fiber reaches the heat treatment temperature, or the unoriented boron nitride fiber is taken out of the heating device and the heat treatment is completed. Indicates that.

The atmosphere in the orientation treatment is an inert gas atmosphere or a vacuum in any of the temperature raising process until reaching the heat treatment temperature, the holding process at the heat treatment temperature, and the temperature lowering process until the heat treatment is completed. Preferably. In order to obtain an inert gas atmosphere, the chamber of the heating device replaced with the inert gas, the furnace tube, or the like may be sealed, or the inert gas may be passed through the chamber of the heating device, the furnace tube, or the like.

In the orientation treatment, the method of applying tensile stress to the non-oriented boron nitride fiber is not particularly limited. For example, when the orientation treatment is carried out in a batch system, the unoriented boron nitride fiber is used. Can be applied in the vertical direction, and a tensile stress can be applied by adding a weight to the lower end. In addition, the unoriented boron nitride fiber is 1600 to 2300 ° C. in an inert gas atmosphere without applying a tensile stress.
When heat-treated, the fiber shrinks in the fiber axis direction depending on the heat-treatment temperature. Therefore, a non-oriented boron nitride fiber is attached to a form made of a material such as boron nitride that does not react with the non-oriented boron nitride fiber and the boron nitride fiber produced by the heat treatment, and it is inactive as it is. Under gas atmosphere, 160
If heat treatment is performed at 0 to 2300 ° C., the heat shrinkage of the unoriented boron nitride fiber due to the heat treatment is prevented by the mold, and as a result, the heat treatment is performed while applying tensile stress to the unoriented boron nitride fiber. be able to. When the orientation treatment is carried out in a continuous manner, it is possible to control the unorientation by controlling the feed rate of the unoriented boron nitride fiber to the heat treatment device and the winding speed of the fiber after the heat treatment. It is possible to control the thermal contraction of the boron nitride fiber during the heat treatment, and as a result, it is possible to perform the orientation treatment while applying tensile stress.

The tensile stress applied to the non-oriented boron nitride fiber in the orientation treatment varies depending on the heating treatment temperature and the heating treatment time of the heating treatment, but is 0. It can be arbitrarily selected within the range of 1 to 1000 MPa. If the applied stress is less than 0.1 MPa, the orientation may be insufficient and the tensile strength may not reach 1400 MPa. The applied stress is 1000M
If it is larger than Pa, the unoriented fiber may be broken. On the other hand, when the tensile stress is applied to the non-oriented boron nitride fiber by limiting the shrinkage of the non-oriented boron nitride fiber due to the heat treatment, or in the continuous treatment, the non-oriented boron nitride fiber is applied to the heat treatment device. When the tensile stress is applied to the non-oriented boron nitride fiber by controlling the rate of feeding the heat-treated fiber and the rate of winding the heat-treated fiber to limit the heat shrinkage due to the heat treatment, the draw ratio is 4%. It may be selected from the range of up to 32%.
However, the stretching ratio (E) is defined by the formula (1).

E = 100 × (Ls−Lf) / Lf (1) Lf is a heat treatment without limiting the heat shrinkage of the boron nitride fiber of unit length, that is, without applying tensile stress to the boron nitride fiber. Represents the fiber sample length when heat-treated at temperature (T ° C.), and Ls is the fiber sample length when heat-treated at a heat treatment temperature (T ° C.) by limiting thermal contraction of a unit length boron nitride fiber. Represent

If the stretching ratio is less than 4%, the tensile stress applied to the unoriented boron nitride fiber may be insufficient and the tensile strength may not reach 1400 MPa. If the stretching ratio is larger than 32%, the unoriented boron nitride fiber may be broken during the heat treatment.

The composite of the present invention is constituted by containing the boron nitride fiber having a high tensile strength and a high degree of orientation prepared as described above in a matrix material made of ceramics, glass or an inorganic single crystal. To be done.

As the ceramics in the base material in the present invention, known ceramics such as oxide ceramics, nitride ceramics, carbide ceramics and boride ceramics can be used without particular limitation.

The oxide ceramics include aluminum oxide, mullite, zinc oxide, uranium oxide, rare earth oxides (cerium oxide, yttrium oxide, lanthanum oxide, etc.), calcium oxide, chromium oxide, cobalt oxide,
Silicon oxide, silicate compounds (cordierite, spodumene, etc.), zirconium oxide, zirconate, tin oxide,
Tungsten oxide, tungsten bronze, tantalum oxide, titanium oxide, titanate, iron oxide, thorium oxide,
Phosphates such as niobium oxide, nickel oxide, hafnium oxide, vanadium oxide, barium oxide, bismuth oxide, beryllium oxide, magnesium oxide, molybdenum oxide, molybdenum bronze, and apatite, and solid solutions, mixtures, and complex oxides of these oxides. And a solid solution or mixture with carbides, nitrides, borides, metals and alloys containing these oxide ceramics as main components.

Examples of the nitride ceramics include aluminum nitride, silicon nitride, sialon, zirconium nitride, titanium nitride, boron nitride, and the like, and solid solutions, mixtures, and composite nitrides of these nitrides, as well as these nitride ceramics. Examples thereof include solid solutions or mixtures with oxides, carbides, borides, metals and intermetallic compounds, etc., which are main components.

As the carbide ceramics, silicon carbide,
Solid solutions or mixtures of tungsten carbide, titanium carbide, boron carbide, etc., and solid solutions, mixtures, complex carbides of these carbide ceramics, and oxides, nitrides, borides, metals and alloys containing these carbides as main components. The body etc. can be mentioned.

The boride ceramics include titanium boride, zirconium boride, hafnium boride, chromium boride, molybdenum boride, tungsten boride, nickel boride, and the like, and solid solutions, mixtures, and composites of these boride ceramics. Examples thereof include borides, and solid solutions or mixtures with oxides, nitrides, carbides, metals and alloys containing these borides as main components.

As the glass of the base material in the present invention, known glasses such as oxide glass, fluoride glass and chalcogen glass can be used without particular limitation, but it is called a high temperature structural material which is the object of the present invention. From the viewpoint, oxide glass is preferably used.

Specific examples of the oxide glass include silicate glass, alkali silicate glass, soda lime glass, potassium lime glass, lead alkali glass, barium glass, aluminosilicate glass, borosilicate glass, phosphate glass and boric acid. Examples thereof include salt glass, crystallized glass in which a crystal phase of a silicate compound is mainly deposited in these glasses, and a composite in which ceramics, metals and alloys are dispersed in these glasses.

As the inorganic single crystal in the present invention, the above-mentioned substances such as oxides, nitrides, carbides and borides as various ceramics can be used without particular limitation.

However, although it depends on the method of producing the single crystal, it may be difficult to produce the single crystal due to the fact that it does not melt with carbides, nitrides, borides, etc., or the melting point is extremely high, so it is more preferable. Oxides can be used. Even in oxides, the melting point is often as high as 2050 ° C. such as aluminum oxide, but in the case of aluminum oxide, for example, aluminum oxide is
By utilizing the eutectic composition of a composite oxide having a garnet structure in which aluminum oxide and some rare earth oxides such as yttrium oxide are reacted at a molar ratio of 5: 3, the melting point is lowered to about 1800 ° C. be able to.
At a temperature of about 1800 ° C., the boron nitride fiber of the present invention can maintain its strength without undergoing a structural change due to heat, so that the composite of the present invention can be produced. Of course, since the base material in this case has a eutectic composition, it has a structure in which the second phase is precipitated in the single crystal. That is, in the above example, the base material has a structure in which a complex oxide having a garnet structure is deposited in a single crystal of aluminum oxide.

On the other hand, in the conventional ceramic fiber,
There are no fibers that maintain strength at 1800 ° C., making it difficult to make such a composite material. In the case of carbon fiber, which is stable against heat, for example, in the aluminum oxide-yttrium oxide system given as an example, since carbon is oxidized by yttrium oxide and volatilized as carbon monoxide, It is difficult to produce a composite material in which a single crystal of the same type is used as a base material, and the applicable material of the base material is limited.

By including the boron nitride fiber in such a base material, the composite of the present invention is obtained. However, the boron nitride fiber contained in the base material made of ceramics, glass, or an inorganic single crystal is used. The form and sequence structure are not particularly limited. That is, it may be present in the base material as continuous boron nitride fibers (also called continuous fibers), or may be present in the base material in the form of being cut into short pieces (also called short fibers). . The length of the short fibers may be uniform or have a distribution. In addition, these continuous fibers and short fibers can be spatially irregularly present in the base material without having a specific arrangement structure, or can be present uniaxially or polyaxially. It is also possible to do so. When continuous fibers are used, they may be uniaxially or polyaxially arranged in the base material, and the boron nitride fibers form a three-dimensional structure composed of a three-dimensional woven fabric. May be.

In the composite of the present invention, the volume ratio of the boron nitride fiber contained in the base material is not particularly limited, but is preferably 10 to 90%, more preferably 20 to 70. %.

The composite of the present invention, in which the boron nitride fiber is contained in the base material made of ceramics, glass, or inorganic single crystal, is represented by a known method for producing an inorganic fiber-reinforced ceramic composite material. Specifically, it can be manufactured as follows.

When the composite of the present invention is produced using short fibers, a step of mixing the short fibers and the raw materials of the base material, a step of molding the mixture into a desired shape, and a step of heat-treating the molded body. After that, the composite of the present invention is produced.

First, the short fiber and the raw material of the base material are mixed. The short fiber mixed with the raw material of the base material is the boron nitride fiber having a short cut form, and its preferable average length is 10 μm to 50 mm, more preferably 20 μm.
To 30 mm, more preferably 30 μm to 10 mm
It is. In order to produce such short fibers, a method of cutting the boron nitride fiber into a desired length, a method of cutting the unoriented boron nitride fiber into a desired length, or a boron nitride precursor Any method such as a method of cutting the body fiber into a desired length can be used.

The raw material of the base material to be mixed with the short fibers is the above-mentioned material in the step of heat-treating the material itself which becomes the ceramic, glass, or inorganic single crystal constituting the above-mentioned base material, and / or the subsequent molded body. Any material that can be converted into a base material such as ceramics, glass, or an inorganic single crystal may be used.

When the raw material of the base material is ceramics, glass, or the substance itself which becomes the inorganic single crystal constituting the base material, the raw material of the base material is powder because it is uniformly mixed with the short fibers. It is preferable. The particle size of the powder is not particularly limited, but when the base material is ceramics or the like, in order to promote sintering and densification in the subsequent heat treatment process,
The particle size of the raw material powder of the base material is preferably 10 μm or less, and more preferably the particle size of the raw material powder of the base material is 1 μm or less.

As the raw material of the base material which can be converted into the base material ceramics, glass, or inorganic single crystal in the heat treatment step, an alkoxide or inorganic high-content material containing all or a part of the elements of the base material is used. Examples include molecules. When an alkoxide is used, in addition to forming the base material by thermal decomposition in heat treatment, sol-
It is also possible to form the base material by a gel method or the like.

As a method of mixing the raw material of the base material and the short fibers, a known method can be adopted, for example, a ball mill, a mortar or the like can be used for mixing. At this time, any of a wet method and a dry method may be used for mixing. In the case of mixing by a wet method, the suspension or solution of the raw material of the base material and short fibers are mixed, and after the mixing is completed, the dispersion medium or the solvent may be removed by drying or the like. Further, depending on the raw material of the base material, it is possible to mix the melt of the raw material of the base material and the short fibers at the glass point transfer or at a temperature equal to or higher than the melting point. Alternatively, the short fiber may be passed through a suspension, solution, or melt of the raw material of the base material to coat or adhere the raw material of the base material to the short fiber, so that the raw material of the base material and the short fiber are separated from each other. It can also be mixed. Further, it is also possible to coat the raw material of the base material on the surface of the short fibers by a vapor phase method such as a vapor deposition method or a chemical vapor deposition method.
The raw material of the base material and the short fibers can be mixed.

When the short fibers and the powder are mixed, it may be possible to improve the moldability of the mixture by appropriately adding and mixing a binder called a binder. When the base material is ceramics or the like, it may be possible to promote the densification of the obtained composite by appropriately adding and mixing a known sintering aid depending on the material of the base material.

The mixture of the short fibers and the raw material of the base material obtained as described above is molded into a desired shape. A known method can be adopted for molding the mixture, and for example, a molded body can be produced by uniaxial molding and / or cold isostatic pressing.

By subjecting the molded body to heat treatment, a composite body of the present invention in which a boron nitride fiber is contained in the base material made of ceramics, glass, or an inorganic single crystal is obtained. In the mixing step, when a binder is added, it may be necessary to remove the binder by heating (also referred to as degreasing) prior to the heat treatment. Since the purpose of the heat treatment for producing the composite differs depending on the type of the base material, each of ceramics, glass, and inorganic single crystal will be described below.

When the base material is ceramics, the heat treatment sinters the raw material of the base material mixed with the short fibers to obtain the composite object of the present invention. In the mixing process, if short fibers and alkoxides or inorganic polymers that can be converted to ceramics, which is the base material, are mixed, convert them to the target base material substance by thermal decomposition, etc. Is also done. The heating temperature of the heat treatment varies depending on the substance of the base material, the particle size of the base material in the mixture, the presence or absence of the sintering aid, and so cannot be uniformly determined, but in the range of 1000 to 2000 ° C. Heat treatment may be performed. In some cases, uniaxial pressure or hydrostatic pressure may be effective during the heat treatment in order to accelerate the sintering of the raw material of the base material and to produce a dense composite. If the atmosphere of the heat treatment is an oxidizing atmosphere, the nitride, carbide, boride or boron nitride fiber of the base material may be oxidized at a high temperature, so the heat treatment is performed in a non-oxidizing atmosphere. It is preferable. In order to perform heat treatment in a non-oxidizing atmosphere, heat treatment may be performed in an atmosphere of an inert gas such as nitrogen, argon, or helium, or may be performed in vacuum.

The case where the base material is glass is divided into the case where the base material is a uniform glass phase and the case where the base material is a sintered body of glass particles. When the base material has a uniform glass phase, the heat treatment may be performed at a melting temperature of the base material or higher, and then gradually cooled. Since the melting temperature of glass varies greatly depending on its composition and the like, the heating temperature of the heat treatment cannot be uniformly determined, but the heat treatment may be performed within the range of 800 to 2000 ° C. Further, if the entire molded body of the mixture is heated to the melting temperature or higher, it may be separated due to the difference in specific gravity from the boron nitride fiber of the base material. In such a case, a uniform composite can be formed by continuously melting and solidifying the raw material of the base material by the zone melting method or the floating zone method.

On the other hand, when the matrix is a sintered body of glass particles, the heat treatment is generally carried out near the glass transition temperature of the matrix. Since the glass transition temperature greatly varies depending on the composition of glass, heat history, etc., the heating temperature of the heat treatment cannot be uniformly determined, but 400 to 1600 ° C.
By heating within the range, the raw material of the base material mixed with the short fibers is sintered, and a composite body in which the base material is a sintered body of glass particles is obtained. At this time, as in the case of using ceramics as the base material, uniaxial pressure or hydrostatic pressure may be applied during the heat treatment to promote sintering and obtain a dense composite.

If the atmosphere for the heat treatment is an oxidizing atmosphere, the fluoride glass, chalcogen glass or boron nitride fiber as the base material may be oxidized at a high temperature. It is preferable to perform the heat treatment. In order to perform heat treatment in a non-oxidizing atmosphere,
The heat treatment may be performed under an atmosphere of an inert gas such as nitrogen, argon, or helium, or may be performed under vacuum.

In the case of using glass as the base material, it may be possible to form a composite and then perform heat treatment to precipitate a crystal phase from the glass of the base material to obtain crystallized glass.

When the base material is an inorganic single crystal, a molded body composed of a mixture of the base material and short fibers is heated to a melting temperature such as a melting point or a eutectic point of the base material and then cooled to form the base material. A composite can be manufactured by single crystallization.
Since the melting point of the base material depends on the substance and its combination,
Although the heating temperature of the heat treatment cannot be uniformly determined, the heat treatment may be performed within the range of 1000 ° C to 2300 ° C. When the heating temperature exceeds 2300 ° C., the decomposition of boron nitride begins, so it is not preferable to perform the heat treatment at a temperature higher than 2300 ° C. Further, if the entire molded body of the mixture is heated to a temperature equal to or higher than the melting point of the base material, the mixture may be separated due to the difference in specific gravity between the base material and the boron nitride fiber. In such a case, a uniform composite can be formed by continuously melting and crystallizing the raw material of the base material by the zone melting method or the floating zone method.

If the atmosphere of the heat treatment is an oxidizing atmosphere, the nitride, carbide, boride or boron nitride fiber of the base material may be oxidized at a high temperature, so heating in a non-oxidizing atmosphere is necessary. Treatment is preferred. In order to perform the heat treatment in a non-oxidizing atmosphere, the heat treatment may be performed in an atmosphere of an inert gas such as nitrogen, argon or helium, or the heat treatment may be performed in a vacuum. A publicly known method can be used for producing the composite. For example, I) The raw material of the base material is previously coated or adhered to the surface of the continuous fiber, and the coated fiber is molded and heat-treated to form a composite. Any method such as a method for producing a body, or II) a method for producing a composite by forming a structure with continuous fibers, then infiltrating the raw material of the base material into the structure, and performing heat treatment be able to.

In the method I), the coating or attachment of the raw material of the matrix to the surface of the continuous fiber can be achieved by a known method. For example, the continuous fiber is a suspension, solution or solution of the raw material of the matrix. It is achieved by passing it through a melt or the like. At this time, it may be possible to facilitate the molding in the next step by adding a binder called a binder at the same time as the raw material of the base material. When the base material is ceramics or the like, it may be possible to accelerate the densification of the obtained composite by appropriately adding a known sintering aid depending on the substance of the base material. Further, the raw material of the base material can be coated on the surface of the continuous fiber by a method utilizing a vapor phase such as a vapor deposition method and a chemical vapor deposition method. Hereinafter, the continuous fiber having the surface coated with or attached to the raw material of the base material is simply referred to as a coated fiber.

The molded body made of the coated fiber is prepared by laminating a sheet in which the coated fiber is arranged in one direction.
The molded body can be produced by a method of laminating as a three-dimensional woven fabric, a method of forming a coated fiber into a three-dimensional woven fabric, or the like.

By subjecting the molded body thus produced to heat treatment, the composite body of the present invention in which the boron nitride fiber is contained in the base material made of ceramics, glass, or an inorganic single crystal is obtained. When a binder is added when coating or adhering the base material and the raw material on the surface of the continuous fiber, it may be necessary to remove the binder by heating (also referred to as degreasing) prior to the heat treatment. Depending on the type of base material, the heat treatment performs the same heat treatment as when a composite material is made using short fibers, and thus creates a composite material containing boron nitride fibers that are continuous fibers in the base material. can do.

When the composite of the present invention is produced by the method of II), that is, after forming the structure with continuous fibers, the raw material of the base material is permeated into the structure and heat-treated to form the composite. In the case of manufacturing, for example, a composite is prepared as follows.

First, a continuous fiber is formed by a method of laminating a sheet in which continuous fibers are arranged in one direction, a method of forming continuous fibers into a two-dimensional woven fabric, a method of laminating continuous fibers into a three-dimensional woven fabric, or the like. Create a structure. The raw material of the base material is permeated into the spaces between the continuous fibers in this structure to form a molded body. As a method of infiltrating the base material, a structure is immersed in a suspension, solution or melt of the base material, or a chemical vapor infiltration method (chemical v
apor infiltration (hereinafter also referred to as CVI),
Examples include a method of supplying a base material as a gas phase and precipitating the base material in the gaps between continuous fibers in the structure.

The molded body produced in this manner is subjected to heat treatment in the same manner as described in the case of using short fibers, whereby the composite body of the present invention can be produced.
Further, it may be possible to further densify the composite by repeating the infiltration of the raw material of the base material and the heat treatment.
In the case of producing a molded product by CVI, there is a case where a dense base material has already been formed at the stage of finishing CVI, and therefore heat treatment may not be particularly required.

Further, in the same manner as the above-mentioned method, when a composite body using a ceramic material as a base material is prepared by using unoriented boron nitride fiber, during the heat treatment during the production of the composite body,
In some cases, tensile stress is applied to the fiber at high temperature due to the difference in coefficient of thermal expansion from the base material, and the boron nitride fiber may be oriented and strengthened. Therefore, the composite of the present invention can be produced also by this method.

[0120]

INDUSTRIAL APPLICABILITY The present invention provides a filling material for inorganic composites made of boron nitride fiber having both high heat resistance and oxidation resistance and high tensile strength. It has become possible to fabricate a composite having improved fracture toughness while maintaining its chemical properties, and it has become possible to use a ceramic material as a high temperature structural material.

[0121]

EXAMPLES The present invention will be described below in detail with reference to examples, but the present invention is not limited thereto.

Example 1 A stirrer was placed in the middle tube of a three-necked flask having a volume of 1 liter, a Dewar cold finger in which a cylinder containing boron trichloride was connected to one of the side tubes, and a ball containing cooling tube was attached to the remaining side tubes. I installed each. A dewar type cold finger was attached to the ball inlet cooling tube, and a calcium chloride tube was attached to the outlet of the cold finger. Dry nitrogen was passed through this device at 200 ml / min for 4 hours to dry the inside of the device.
Chlorobenzene 30 dried over anhydrous sodium sulfate overnight
0 ml and acetonitrile 16.4 g were added. Fill two cold fingers with dry ice-acetone and stir with a stirrer, 60 g of boron trichloride from the cold finger directly attached to the three-necked flask.
Was condensed and added dropwise over 2 hours. This produced a white boron trichloride-acetonitrile adduct. After the dropping of boron trichloride was completed, the cold finger directly attached to the three-necked flask was removed, and 21.5 g of ammonium chloride dried at 110 ° C. overnight was added. When this suspension was heated to 125 ° C. for 8 hours, generation of hydrogen chloride almost disappeared, and a brown precipitate was formed. The formed precipitate was filtered off, washed with 100 ml of chlorobenzene and dried under reduced pressure to obtain 24 g of boron nitride precursor (yield 83%).

After dissolving 10 g of this boron nitride precursor in 200 ml of N, N-dimethylformamide (DMF), 100 ml of DMF was removed by evaporation to obtain a uniform viscous solution. This solution was discharged from a spinning nozzle having a hole having a diameter of 60 μm and wound up to spin a continuous boron nitride precursor fiber having a diameter of about 20 μm.

The spun boron nitride precursor fiber was heated in a nitrogen stream at a heating rate of 1 ° C./min from room temperature to 400 ° C., and after reaching 400 ° C., it was left to cool to room temperature for heat treatment. It was Then, the temperature is raised from room temperature to 1000 ° C. at a heating rate of 2 ° C./min in an ammonia gas atmosphere, and
After reaching 00 ° C, 500 ° C at a cooling rate of 5 ° C / min
Then, the mixture was cooled to room temperature and then left to cool to room temperature for heat treatment. As a result, a white unoriented boron nitride fiber having a diameter of about 15 μm was obtained.

This unoriented boron nitride fiber was applied to the surrounding 12
Winding up into a 2mm loop, keeping the loop shape,
Place it on a boron nitride frame with a circumference of 103 mm, and in a nitrogen stream as it is, from room temperature to 1800 at a heating rate of 10 ° C / min.
The temperature was raised to 1800C, held at 1800C for 30 minutes, cooled to 500C at a cooling rate of 5C / min, and then allowed to cool to room temperature for crystal orientation treatment. After the treatment, the boron nitride fiber was kept in a state of being wrapped around the mold without breaking or unraveling. This stretch ratio was 12.7%. As a result, a boron nitride fiber having an orientation degree of 0.78 and a tensile strength of 1400 MPa was obtained. .

On the other hand, mixed powder 10 of aluminum nitride and yttrium oxide obtained by adding 5% by weight of yttrium oxide as a sintering aid to aluminum nitride having an average particle diameter of 0.2 μm.
0 g was added to 100 g of toluene. This mixed solution was mixed for 4 hours using a ball mill consisting of a polyethylene pot and coated balls to prepare a suspension of mixed powder of aluminum nitride and yttrium oxide.

This suspension is mixed with the above-mentioned boron nitride fiber 50.
After soaking a bundle of 0 bundles, the bundle was lifted up from the suspension, shaped into a sheet arranged in one direction, and toluene as a dispersion medium was dried and removed to prepare a coated fiber.

This sheet-shaped coated fiber was laminated with the fiber axis direction kept constant, molded into 50 mm × 50 mm × 10 mm, and heated at 1900 ° C. for 1 hour while uniaxially applying a pressure of 50 MPa in a nitrogen atmosphere. An aluminum nitride composite containing boron nitride fibers was obtained. In this composite, the ratio of boron nitride fibers was about 40% by volume.

The bending strength of the sintered body was 350 MPa, and fiber pullout was observed on the fracture surface.
(Single edge notched bend bar) method [ASTM Standard E
399-81 (Annual Book of ASTM Standards (1981) Part 10
Fracture toughness K _IC is 15.3M
Pa · m ^1/2 .

The fracture toughness K _IC of the aluminum nitride sintered body containing no boron nitride fiber was 3.5 MPa · m ^1/2 .

Example 2 100 g of a mixed powder of aluminum nitride and yttrium oxide obtained by adding 5% by weight of yttrium oxide as a sintering aid to aluminum nitride having an average particle size of 0.2 μm was added with 10 parts of toluene.
0 g. This mixed solution was mixed for 4 hours using a ball mill consisting of a polyethylene pot and coated balls to prepare a suspension of mixed powder of aluminum nitride and yttrium oxide.

On the other hand, the unoriented boron nitride fiber produced in the same manner as in Example 1 was wound around a loop having a circumference of 122 mm and hung on a boron nitride mold having a circumference of 107 mm while maintaining the loop shape. , As it is in nitrogen stream, heating rate 1
Increase the temperature from room temperature to 2000 ° C at 0 ° C / min, and
Hold at 0 ℃ for 30 minutes, 500 at a cooling rate of 5 ℃ / min
It was cooled to 0 ° C. and then allowed to cool to room temperature for crystal orientation treatment. After the treatment, the boron nitride fiber was kept in a state of being wrapped around the mold without breaking or unraveling. The stretch ratio at this time was 20.2%. The obtained boron nitride fiber had an orientation degree of 0.80 and a tensile strength of 1970 MPa.

Boron nitride fiber 5 produced in this way
A bundle of 00 pieces is dipped in the above-mentioned suspension, then lifted from the suspension and shaped into a sheet arranged in one direction to dry and remove toluene as a dispersion medium to obtain a coated fiber. It was made.

This sheet-shaped coated fiber was laminated with the fiber axis direction kept constant, molded into 50 mm × 50 mm × 10 mm, and heated at 1900 ° C. for 1 hour while uniaxially applying a pressure of 50 MPa in a nitrogen atmosphere. An aluminum nitride composite containing boron nitride fibers was obtained. In this composite, the ratio of boron nitride fibers was about 40% by volume.

The bending strength of the sintered body was 380 MPa, fiber pullout was observed on the fracture surface, and the fracture toughness K _IC measured by the SENB method was 17.6 MPa · m.
It was ^1/2 .

Example 3 100 g of a mixed powder of aluminum nitride and yttrium oxide obtained by adding 5% by weight of yttrium oxide as a sintering aid to aluminum nitride having an average particle size of 0.2 μm was added with 10 parts of toluene.
0 g. This mixed solution was mixed for 4 hours using a ball mill consisting of a polyethylene pot and coated balls to prepare a suspension of mixed powder of aluminum nitride and yttrium oxide.

On the other hand, the non-oriented boron nitride fiber produced in the same manner as in Example 1 was wound on a loop having a circumference of 122 mm and hung on a boron nitride mold having a circumference of 111 mm while keeping the loop shape. , As it is in nitrogen stream, heating rate 1
Increase the temperature from room temperature to 2000 ° C at 0 ° C / min, and
Hold at 0 ℃ for 30 minutes, 500 at a cooling rate of 5 ℃ / min
It was cooled to 0 ° C. and then allowed to cool to room temperature for crystal orientation treatment. After the treatment, the boron nitride fiber was kept in a state of being wrapped around the mold without breaking or unraveling. The stretching ratio at this time was 24.7%. The obtained boron nitride fiber had an orientation degree of 0.82 and a tensile strength of 2300 MPa.

Boron nitride fiber 5 produced in this way
A bundle of 00 pieces is dipped in the above-mentioned suspension, then lifted from the suspension and shaped into a sheet arranged in one direction to dry and remove toluene as a dispersion medium to obtain a coated fiber. It was made.

This sheet-shaped coated fiber was laminated with the fiber axis direction kept constant, molded into 50 mm × 50 mm × 10 mm, and heated at 1900 ° C. for 1 hour while uniaxially applying a pressure of 50 MPa in a nitrogen atmosphere. An aluminum nitride composite containing boron nitride fibers was obtained. In this composite, the ratio of boron nitride fibers was about 40% by volume.

The bending strength of the sintered body was 420 MPa, fiber pullout was observed on the fracture surface, and the fracture toughness K _IC measured by the SENB method was 20.1 MPa · m.
It was ^1/2 .

Example 4 100 g of a mixed powder of aluminum oxide and magnesium oxide obtained by adding 0.25% by weight of magnesium oxide as a sintering aid to aluminum oxide having an average particle size of 0.2 μm was added to 100 g of toluene. Using a ball mill consisting of polyethylene pots and coated balls, this mixed solution was
The mixture was mixed for a period of time to prepare a suspension of mixed powder of aluminum oxide and magnesium oxide.

A bundle of 500 boron nitride fibers manufactured in the same manner as in Example 1 was dipped in this suspension, which was then lifted from the suspension and shaped into a sheet arranged in one direction. Toluene as a dispersion medium was dried and removed to prepare a coated fiber.

This sheet-shaped coated fiber was laminated with the fiber axis direction kept constant, molded into 50 mm × 50 mm × 10 mm, and heated at 1700 ° C. for 1 hour while uniaxially applying a pressure of 50 MPa in a nitrogen atmosphere. An aluminum oxide composite containing boron nitride fibers was obtained. In this composite, the ratio of boron nitride fibers was about 40% by volume.

The bending strength of the sintered body was 400 MPa, fiber pullout was observed on the fracture surface, and the fracture toughness K _IC measured by the SENB method was 16.5 MPa · m.
It was ^1/2 .

The fracture toughness K _IC of the aluminum oxide sintered body containing no boron nitride fiber was 4.5 MPa · m ^1/2 .

Example 5 Mixed powder of α-type silicon carbide and boron carbide obtained by adding 5.0% by weight of boron carbide (B ₄ C) as a sintering aid to α-type silicon carbide having an average particle size of 0.2 μm. 100 g was added to 100 g toluene. This mixed solution was mixed for 4 hours using a ball mill consisting of a polyethylene pot and coated balls to prepare a suspension of a mixed powder of α-type silicon carbide and boron carbide.

A bundle of 500 boron nitride fibers manufactured in the same manner as in Example 1 was dipped in this suspension, which was then lifted from the suspension and shaped into a sheet arranged in one direction. Toluene as a dispersion medium was dried and removed to prepare a coated fiber.

This sheet-shaped coated fiber was laminated with the fiber axis direction kept constant and molded into 50 mm × 50 mm × 10 mm, and heated at 1950 ° C. for 1 hour while uniaxially applying a pressure of 70 MPa in a nitrogen atmosphere. Thus, a silicon carbide composite containing boron nitride fibers was obtained. In this composite, the ratio of boron nitride fibers was about 40% by volume.

The bending strength of the sintered body was 500 MPa, fiber pullout was observed on the fracture surface, and the fracture toughness K _IC measured by the SENB method was 18.9 MPa · m.
It was ^1/2 .

The fracture toughness K _IC of the silicon carbide sintered body containing no boron nitride fiber was 4.3 MPa · m ^1/2 .

Example 6 100 g of mixed powder of β-type silicon nitride and magnesium oxide obtained by adding 5.0% by weight of magnesium oxide as a sintering aid to β-type silicon nitride having an average particle diameter of 0.2 μm was added to 100 g of toluene.
Added. This mixed solution was mixed for 4 hours using a ball mill consisting of a polyethylene pot and coated balls to prepare a suspension of mixed powder of β-type silicon nitride and magnesium oxide.

A bundle of 500 boron nitride fibers manufactured in the same manner as in Example 1 was immersed in this suspension, which was then lifted from the suspension and shaped into a sheet arranged in one direction. Toluene as a dispersion medium was dried and removed to prepare a coated fiber.

This sheet-shaped coated fiber was laminated with the fiber axis direction kept constant, molded into 50 mm × 50 mm × 10 mm, and heated at 1900 ° C. for 1 hour while uniaxially applying a pressure of 50 MPa in a nitrogen atmosphere. A silicon nitride composite containing boron nitride fibers was obtained. In this composite, the ratio of boron nitride fibers was about 40% by volume.

The bending strength of the sintered body was 530 MPa, fiber pullout was observed on the fracture surface, and the fracture toughness K _IC measured by the SENB method was 21.8 MPa · m.
It was ^1/2 .

The fracture toughness K _IC of the silicon nitride sintered body containing no boron nitride fiber was 6.5 MPa · m ^1/2 .

Example 7 5% by weight of yttrium oxide was added as a sintering aid to aluminum nitride having an average particle size of 0.2 μm, and boron nitride fibers produced in the same manner as in Example 1 were made to have a length of about 5 mm. The cut short fibers were added so as to be 40% by volume with respect to aluminum nitride. Toluene 10 was added to 100 g of this mixture.
0 g was added and mixed for 4 hours using a ball mill consisting of a polyethylene pot and coated balls.

After the toluene, which is a dispersion medium, was dried and removed from the obtained suspension-like mixture, it was molded into a size of 50 mm × 50 mm × 10 mm by a pseudonym type press, and while uniaxially applying a pressure of 50 MPa under a nitrogen atmosphere. 1900 ° C
After heating for 1 hour, an aluminum nitride composite containing boron nitride fibers was obtained.

The bending strength of the sintered body was 300 MPa, fiber pullout was observed on the fracture surface, and the fracture toughness K _IC measured by the SENB method was 12.0 MPa · m.
It was ^1/2 .

Comparative Example 1 100 g of a mixed powder of aluminum nitride and yttrium oxide, which was obtained by adding 5% by weight of yttrium oxide as a sintering aid to aluminum nitride having an average particle diameter of 0.2 μm, was mixed with 10 parts of toluene.
0 g. This mixed solution was mixed for 4 hours using a ball mill consisting of a polyethylene pot and coated balls to prepare a suspension of mixed powder of aluminum nitride and yttrium oxide.

PAN having a tensile strength of 3 GPa was added to this suspension.
After immersing a bundle of 500 carbon fibers, the bundle was lifted from the suspension, shaped into a sheet arranged in one direction, and toluene as a dispersion medium was dried and removed to prepare a coated fiber.

This sheet-shaped coated fiber was laminated with the fiber axis direction kept constant, molded into 50 mm × 50 mm × 10 mm, and heated at 1900 ° C. for 1 hour while uniaxially applying a pressure of 50 MPa in a nitrogen atmosphere. . After firing, the carbon fibers were consumed by oxidation, and the production of yttrium nitride, which is a reaction product of the carbon fibers and yttrium oxide in a nitrogen atmosphere, was confirmed by X-ray diffraction.

Comparative Example 2 5% by weight of yttrium oxide as a sintering aid was added to aluminum nitride having an average particle size of 0.2 μm, and commercially available silicon carbide fibers were cut into short fibers having a length of about 5 mm. It was added to 40% by volume. Toluene 100g was added to this mixture 100g, and it mixed for 4 hours using the ball mill which consists of a polyethylene pot and a covered ball.

After the toluene, which is a dispersion medium, was dried and removed from the obtained suspension mixture, it was mixed with a die press to obtain 5
Molded into 0 mm x 50 mm x 10 mm, under a nitrogen atmosphere,
While uniaxially applying pressure of 50 MPa, 1 at 1900 ° C
It was heated for a period of time to obtain an aluminum nitride composite containing silicon carbide fibers.

The bending strength of the sintered body was 150 MPa, the fibers were broken in the coarser carbonaceous elementary particles as compared with those before firing, and no pullout was observed. SE
The fracture toughness K _IC measured by the NB method is 2.8 MPa
It was m ^1/2 .

Claims (4)

[Claims] 1. A 6-membered ring formed by alternately bonding boron and nitrogen is formed in a base material made of ceramics, glass, or an inorganic single crystal by connecting in the plane direction of the 6-membered ring. A fiber-reinforced ceramics-based composite, which is a boron nitride fiber made of boron nitride having a laminated structure of a flat surface (C surface), the boron nitride fiber having a tensile strength of at least 1400 MPa. 2. A 6-membered ring formed by alternately bonding boron and nitrogen is formed in a base material made of ceramics, glass, or an inorganic single crystal by connecting in the plane direction of the 6-membered ring. A boron nitride fiber made of boron nitride having a laminated structure of a flat surface (C surface), wherein at least a part of the C surface is oriented substantially parallel to the fiber axis of the boron nitride fiber. Cage,
A fiber-reinforced ceramic-based composite containing boron nitride fibers having a degree of orientation of the C-plane of at least 0.74. 3. A plane (C) formed by connecting a 6-membered ring formed by alternately bonding boron and nitrogen in the plane direction of the 6-membered ring.
A filling material for a ceramic-based composite body, which is a boron nitride fiber made of boron nitride having a laminated structure of (faces) and having a tensile strength of at least 1400 MPa. 4. A plane (C) formed by connecting a 6-membered ring formed by alternately bonding boron and nitrogen in the plane direction of the 6-membered ring.
Plane) is a boron nitride fiber made of boron nitride having a laminated structure, wherein at least a part of the C plane is oriented substantially parallel to the fiber axis of the boron nitride fiber.
A filling material for a ceramic-based composite body, which comprises a boron nitride fiber having a surface orientation of at least 0.74.