JP2001163671A - Silicon carbide-carbon composite material wherein boron nitride is dispersed - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a silicon carbide-carbon composite material wherein boron nitride is dispersed, which is capable of improving oxidation resistance of a carbon product and suppressing sticking of a material to be treated. SOLUTION: The silicon carbide-carbon composite material wherein boron nitride is dispersed is formed at the surface layer part of a graphite substrate by coating a slurry composed of a silicon powder, a boron carbide powder, a boron nitride powder and a thermoplastic resin onto the surface of a substrate of the carbon material and then heat treating the coated carbon substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a boron nitride-dispersed silicon carbide-carbon composite used in a high-temperature oxidizing atmosphere.

[0002]

2. Description of the Related Art Carbon materials have been used for various heat treatments such as crucibles for melting metals, crucibles for sintering ceramics, jigs for metal deposition, dies for continuous casting, casting molds, etc. because of their superior properties at higher temperatures than before. It is widely used as a heat-resistant material used for jigs and the like.

[0003] However, carbon materials have a disadvantage that they are easily oxidized and consumed in a high-temperature oxidizing atmosphere.
Even under a reducing atmosphere, when used in the above-mentioned various applications, there is a problem that the material reacts with the material to be treated, or the treated material dissolves and penetrates into the carbon material, and the carbon material is damaged. Various measures have been devised in the past to prevent oxidation of water and to prevent penetration of dissolved substances.

[0004] In order to make up for such a drawback of the carbon material, the inventors of the present invention provided a silicon (hereinafter, referred to as “Si”) powder and a boron carbide (hereinafter, referred to as “B”) on the surface of a substrate made of the carbon material.
₄ C "that. A) a slurry composed of a powder and a thermoplastic resin is applied and heat-treated to form a silicon carbide-carbon (hereinafter, referred to as “SiC-C”) composite layer on the surface of the base material, which is oxidation-resistant; And developed an application (Japanese Patent Application Laid-Open No. 10-212182).

[0005]

However, SiC-C is applied to a surface that comes into contact with an object to be processed, such as a metal or ceramic, such as a metal melting crucible, a ceramic sintering crucible, a continuous casting die, and a casting mold. When the composite layer is formed, there is a problem that the object to be processed is stuck to the surface of a heat treatment jig such as a tray, a crucible or a mold after cooling.

Accordingly, an object of the present invention is to provide a boron nitride-dispersed silicon carbide-carbon composite material capable of improving the oxidation resistance of a carbon product and suppressing sticking of an object to be treated.

[0007]

Means for Solving the Problems In order to solve this problem, the present inventors worked on improving the technology of the prior application, Japanese Patent Application Laid-Open No. 10-212182, and as a result of diligent research, they found that
The inventors have found that it is effective to disperse boron nitride (hereinafter, referred to as “BN”) in the surface layer of the CC composite layer, and have completed the present invention.

That is, the BN-dispersed SiC-C composite material of the present invention comprises an SiC-C composite layer formed on a surface layer of a substrate made of a carbon material, and is continuous with the SiC-C composite layer.
This is a BN-dispersed SiC-C composite material in which BN is dispersed over part or the entire surface of the outermost layer. In addition, the BN of the present invention
The dispersed SiC-C composite comprises BN powder, B ₄ C powder,
A slurry composed of a Si powder and a solvent is applied to the surface of the substrate, dried and heat-treated to form a SiC-
A C composite layer is formed, and BN is dispersed over part or the entire surface of the SiC-C composite layer.

Further, in the BN-dispersed SiC-C composite material according to the present invention, a SiC-C composite layer is formed on a surface layer of a base material made of a carbon material, and BN is formed in a concave portion on the surface of the SiC-C composite layer. BN is dispersed and formed at a rate of 30 to 80% of the surface of the surface layer portion.

The substrate made of the carbon material used in the present invention is not particularly limited, and examples thereof include a high-density isotropic graphite material. Among them, the average pore radius measured by a mercury intrusion method is used. It is preferable to use a graphite material having a particle size of 0.1 μm or more processed into a product shape.

When a graphite material having an average pore radius smaller than 0.1 μm is used as a base material, when a slurry of a mixture of Si, B ₄ C and BN is applied to the base material, the fine pores of the base material may be removed. This is not preferable because the slurry hardly permeates and the slurry coating layer easily peels off. In addition,
The upper limit of the average pore radius of the substrate is not particularly limited. If the average pore radius is large, the slurry permeates deep inside the substrate, and Si in the slurry reacts with the substrate after the heat treatment. The generated SiC-C composite layer is uniformly formed in the depth direction with a thickness of 1 mm or more. in this way,
Since the thickness of the SiC-C composite layer can be set to 1 mm or more, the oxidation resistance of the substrate made of a carbon material such as graphite can be improved.

The BN-dispersed SiC-C composite material of the present invention comprises a Si powder having an average particle size of 10 to 50 μm and an average particle size of 4 to 50 μm.
A slurry is prepared using 50 μm B ₄ C powder, BN powder having an average particle size of 1 to 5 μm, and a thermoplastic resin as a solvent for mixing them. Here, the thermoplastic resin used is preferably a thermoplastic resin having a high film-forming property and a low residual carbon ratio. For example, those selected from polyamide imide, polyvinyl alcohol, polycarbodiimide, and polyamide resin are particularly preferable. In some cases, a solvent can be used to dissolve these thermoplastic resins. By appropriately selecting and using dimethylacetamide, dimethylformamide, dimethylsulfoxide, N-2-pyrrolidone, or the like as the solvent, the thermoplastic resin can be deeply penetrated into the graphite base material.

[0013] Si powder, B ₄ C powder and mixing ratio in mixing the BN powder, Si powder 60-80 wt%, and BN powder 15 wt% or less, the remainder B ₄ for these
It is preferable to mix so as to obtain C powder. If the BN powder exceeds 15% by mass, the SiC—C layer is not formed uniformly and deeply in the depth direction, which is not preferable. When the content is less than 5% by mass, the amount of BN dispersed and formed in the depressions on the surface of the SiC-C layer is reduced, and the effect of adding BN is not sufficiently obtained, and the object to be treated is preferably fixed. Absent. Therefore, the BN powder content is preferably 5 to 15% by mass. A thermoplastic resin having a mass of 50 to 100% is mixed with the mixed powder. Here, if the amount of the resin exceeds 100% with respect to the mixed powder, the viscosity of the slurry decreases, it becomes difficult to apply the resin thickly to the surface of the substrate, and the SiC on the surface of the carbon substrate decreases, which is not preferable. . On the other hand, if it is less than 50%, the viscosity becomes high, and a portion where the slurry does not sufficiently adhere to the substrate surface is generated, and a portion where the SiC layer is not formed is not preferable.

By mixing the B ₄ C powder into the slurry, Si penetrates deeply into the pores of the carbon substrate by some catalytic action, and as a result, the SiC-C layer is uniformly and deeply formed in the depth direction. Can be formed.

The slurry prepared as described above is applied to the entire surface or a necessary portion by an appropriate means such as brushing and spatula coating. Moreover, you may immerse in a slurry. The thickness applied at this time can be any thickness, but is preferably about 0.1 to 2 mm from the surface of the carbon substrate. If the thickness is less than 0.1 mm, the formation of the composite layer becomes shallow and 2
It is not preferable to apply the coating in a thickness exceeding mm because the coating may be peeled off. After this, about 80-200 ° C,
The resin is completely cured by drying for about 1 to 2 hours. The material obtained in this way is 0.1 MPa or less,
Preferably, high-temperature heat treatment is performed under a non-oxidizing atmosphere pressure of 2 kPa or less. Pressure below 0.1MPa, preferably 2kP
By setting a or less, penetration of the molten Si into the inside of the base material is promoted. Further, the treatment temperature is maintained at 1500 ° C. or higher, preferably 1600 to 1800 ° C., for 1 to 2 hours.
The heating means is not particularly limited, and may be performed by an appropriate means. By this operation, the Si component is melted, penetrates into the pores of the base material through the carbonized layer of the resin, and reacts with carbon to form SiC. Thereafter, if necessary, the deposits on the surface are removed.

With the above series of treatments, the surface layer of the substrate corresponding to the portion where the slurry is applied becomes a dense layer converted into a SiC-C composite layer. This layer is formed substantially uniformly in the depth direction from the surface of the substrate at a depth of 1 mm or more. Then, BN is dispersedly formed on the surface layer at a depth of 30 μm or less from the surface. Since the BN on the surface enters into the depressions on the surface of the SiC-C composite layer and is formed continuously from the SiC-C composite layer, the anchor effect acts and adheres firmly. And it does not mean that it chemically reacts with and adheres to the SiC or carbon base material, but is dispersed and scattered in a fine powder state at a rate of 30 to 80% on the surface of the surface layer of the SiC-C composite layer. I have.

The BN-dispersed SiC-C composite material of the present invention is formed as described above, and is used as a spacer for a hot press die, a crucible for melting metal, a crucible for sintering ceramics, a jig for metal vapor deposition, Even when applied as a heat-resistant material used for a jig for heat treatment of various materials including a casting die, a casting mold, and the like, it is possible to prevent the contact portion from sticking to an object to be processed.

[0018]

The present invention will be described below in detail with reference to examples. (Example 1) As carbon substrate, bulk density 1.90 g / cm
³ , average pore radius 0.3μm, bending strength 68MPa
Isotropic graphite (manufactured by Toyo Tanso Co., Ltd.) with an outer diameter of 100 m
m, a crucible having an inner diameter of about 70 mm and a depth of 90 mm. Next, Si powder (average particle size of 40 μm), B ₄ C powder (average particle size of 30 μm), and BN powder (particle size of 1 to 5 μm)
m) was mixed at a weight ratio of 80: 12: 8, and mixed and dispersed in a polyvinyl alcohol (PVA) resin having the same weight as the mixed powder to obtain a slurry.

This slurry is applied to the entire inner surface of the crucible with a brush so as to have a thickness of 1 to 2 mm, and is then dried in a dryer.
The solvent was evaporated at 0 ° C. for 1 hour, and further heated from room temperature to 1800 in a vacuum heating furnace under a nitrogen gas atmosphere of 400 Pa.
The temperature was raised to about 4 hours, kept for 30 minutes, cooled, and taken out. Thereafter, by performing this series of treatments, a SiC-C composite material is formed uniformly at a depth of 2 mm from the surface of the graphite base material in the depth direction, and BN is dispersedly formed at a depth of 20 μm on the surface layer. You. The ingot was put in this crucible, heated to 1600 ° C., and a melting test of the cast iron was performed.

FIG. 1 shows that BN is dispersed in the surface layer.
3 shows a polarizing micrograph of the surface of the iC-C composite. In FIG. 1, the portion that looks white is BN. From FIG. 1, BN
Are dispersed and formed on the surface. As described above, since the SiC—C composite material can be dispersed and formed without being partially condensed, the release property of BN possessed by the SiC—C composite material can be sufficiently exhibited, and the fixation of the object to be processed is suppressed.

Example 2 Si powder in slurry (average particle size 40 μm) and B ₄ C powder (average particle size 30 μm)
And the mass ratio of BN powder (particle size: 1 to 5 μm) to 80: 1
A graphite substrate of the same quality as in Example 1 was processed into the same shape except that it was mixed at a ratio of 0:10, and a 1 mm thick SiC layer was formed on the inner surface of the crucible from the surface of the graphite substrate by the same procedure as in Example 1. A C composite material was formed, BN was dispersed and formed at a depth of 30 μm from the surface, and an ingot was put in the same manner as in Example 1 to perform a dissolution test.

Example 3 Si powder in slurry (average particle size 40 μm) and B ₄ C powder (average particle size 30 μm)
And the mass ratio of BN powder (particle size: 1 to 5 μm) to 80: 1
A graphite substrate of the same quality as in Example 1 was processed into the same shape, except that the mixture was mixed at a ratio of 5: 5, and the inner surface of the crucible was formed with a thickness of 3 mm from the surface of the graphite substrate in the same procedure as in Example 1. A C composite material was formed, BN was dispersed and formed at a depth of 15 μm from the surface, and an ingot was put in the same manner as in Example 1 to perform a dissolution test.

(Comparative Example 1) Without adding BN powder, the mass ratio of Si powder (average particle size: 40 μm) and B ₄ C powder (average particle size: 30 μm) in the slurry was mixed at a ratio of 80:20. A graphite substrate of the same quality as in Example 1 was processed into the same shape, and a SiC-C composite material was formed on the inner surface of the crucible with a thickness of 3 mm from the surface of the graphite substrate by the same procedure as in Example 1. As in Example 1, an ingot was placed and a dissolution test was performed.

The crucibles of Examples 1 to 3 hardly adhered to cast iron despite the 35 melting tests.
No problems that could cause the crucible to be replaced, such as cracking of the crucible or corrosion by cast iron, were found. On the other hand, B
The crucible of Comparative Example 1 in which N was not formed by dispersion was 2-3
In the dissolution test, sticking of the cast iron occurred. in this way,
The SiC-C composite material is formed on the surface layer of the graphite base material, and BN is continuously dispersed and formed on the surface layer of the SiC-C composite material. In addition to the properties, it is possible to obtain a material having excellent properties in the releasability of the object to be treated.

[0025]

The present invention is configured as described above.
It is possible to easily and inexpensively form a silicon carbide-carbon composite material in which boron nitride is dispersed at any place on the surface of a graphite substrate, and has excellent lubricity, abrasion resistance, and oxidation resistance. A smooth covering surface can be formed. In addition, the effect of extending the life of carbon products for various heat treatments, such as spacers for dies for hot pressing, crucibles for melting metals and sintering ceramics, dies for continuous casting, casting molds, and the like can be obtained.

[Brief description of the drawings]

FIG. 1 is a view showing a polarizing microscope photograph of the surface of a BN-dispersed SiC—C composite material.

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Claims (8)

[Claims] 1. A boron nitride-dispersed silicon carbide-carbon composite material in which a silicon carbide-carbon composite layer is formed on a surface layer of a carbon substrate, and boron nitride is dispersed on the surface layer of the silicon carbide-carbon composite layer. 2. The silicon carbide-carbon composite layer is uniformly formed in the depth direction from the surface of the carbon substrate to a thickness of 1 mm or more, and the dispersion depth of the boron nitride is 30 μm or less from the surface. Item 3. The boron nitride-dispersed silicon carbide-carbon composite material according to item 1. 3. The boron nitride-dispersed silicon carbide-carbon composite material according to claim 1, wherein the proportion of boron nitride on the surface of the carbon substrate is 30 to 80%. 4. A boron nitride powder, a boron carbide powder,
A slurry comprising silicon powder and a solvent is applied to the surface of a carbon substrate, dried and heat-treated to form a silicon carbide-carbon composite layer on the surface layer of the carbon substrate, and the silicon carbide-carbon composite A boron nitride-dispersed silicon carbide-carbon composite material in which boron nitride is dispersed in a surface layer of the layer. 5. A mixed powder comprising 15% by mass or less of boron nitride powder, 60 to 80% by mass of silicon powder, and a balance of boron carbide powder, and 50 to 100% by mass of the mixed powder. The boron nitride-dispersed silicon carbide-carbon composite according to claim 4, comprising a solvent by mass. 6. The boron nitride-dispersed silicon carbide-carbon composite according to claim 4, wherein the heat treatment is performed at a temperature of 1500 ° C. or higher in a non-oxidizing atmosphere of 0.1 MPa or lower. 7. The silicon carbide-carbon composite layer is uniformly formed in the depth direction from the surface of the carbon substrate to a thickness of 1 mm or more, and the dispersion depth of the boron nitride is 30 μm or less from the surface. Item 7. The boron nitride-dispersed silicon carbide-carbon composite material according to any one of Items 4 to 6. 8. The boron nitride-dispersed silicon carbide-carbon composite material according to claim 1, which is used as a jig for various heat treatments.