JP2017024923A - Ceramic composite material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ceramic composite material that has a heat resistant property and an anti-corrosion property to high temperature steam without the use of radioactive elements, elements having toxicity, or rare elements.SOLUTION: Provided is a ceramic composite material comprising a substrate made of a SiC/SiC composite material, and a carbon layer covering the substrate, and in which rare metals, toxic elements and radioactive elements are not used. The SiC/SiC composite material comprises SiC fibers and a matrix made of a CVD-SiC material, and since the CVD-SiC material is a material deposited while the raw material gas is being decomposed, pores are not likely to be formed and a dense and strong substrate can be formed, and because of this, when a carbon layer such as a pyrolytic carbon layer is formed on the top of it, a coat film that is difficult to be deformed and peeled off even when a force is applied from the outside can be obtained, and a ceramic composite material which is hard for a gas to penetrate, which can sufficiently separate the SiC/SiC composite material and water inside, and which has an anti-corrosion property to hot steam can be obtained.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a ceramic composite material.

  SiC, known as engineering ceramics, has excellent heat resistance, thermal shock resistance, wear resistance, and oxidation resistance, so it can be used in high-temperature environments as a structural material for semiconductor manufacturing equipment, crucibles in high-temperature furnaces, jigs, etc. Has been.

However, Patent Document 1 points out that silicon-containing ceramics such as SiC do not have corrosion resistance to high-temperature steam, and the ceramic is consumed so much that its life is short. In order to solve such a problem, Patent Document 1 discloses a substrate made of at least one silicon-containing ceramic selected from silicon nitride, silicon carbide, and sialon, and a surface layer provided on the surface of the substrate. In the corrosion-resistant ceramic provided, the surface layer is made of zirconium oxide stabilized with a group IIIa element of the periodic table, and the content of Al and Si in the surface layer is suppressed to 1% by mass or less in total. Corrosion resistant ceramics characterized by the above have been proposed.
According to such a corrosion-resistant ceramic, in the surface layer made of zirconium oxide stabilized with Group IIIa element of the periodic table (hereinafter, sometimes simply referred to as stabilized zirconia), the reaction with high-temperature water vapor causes It is described that the content of highly consumed Al and Si is suppressed to a small amount below a certain amount, and as a result, such a surface layer is resistant to high temperature steam corrosion and can protect the surface of ceramics containing silicon. ing.

  Further, in Patent Document 2, an SiC layer is formed on at least the outer surface of a tubular fiber-reinforced carbonaceous substrate made of an aggregate made of ceramic fibers and a carbonaceous material filled between the ceramic fibers, and the fiber-reinforced carbon A tubular body is described in which silicon atoms are diffused from the boundary region between the carbonaceous substrate and the SiC layer toward the inside of the fiber-reinforced carbonaceous substrate.

JP 2003-201191 A JP 2009-210266 A

In Patent Document 1, the Group IIIa elements of the periodic table used for stabilization of zirconium oxide are Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu. Since these elements are rare metals, corrosion-resistant ceramics using them are expensive materials. Further, mass production of corrosion-resistant ceramics using these rare metals consumes a large amount of rare metals and depletes resources, so a means for recovering rare metals must be established. Further, since Pm (promium) is a radioactive element, it must be strictly controlled when used in corrosion-resistant ceramics and must be recovered after use.
However, since the above corrosion-resistant ceramics have heat resistance and are chemically stable, rare metals cannot be easily separated and recovered.

  In Patent Document 2, since the base material is made of a carbon matrix and the outermost surface is made of SiC, SiC is eluted when used in hot water or high-temperature steam, and has no corrosion resistance in the first place.

  In view of the above problems, an object of the present invention is to provide a ceramic composite material having heat resistance and corrosion resistance to high-temperature steam without using radioactive elements, toxic elements, and rare elements.

In order to solve the above problems, the ceramic composite material of the present invention comprises:
(1) It consists of a base material made of SiC / SiC composite and a carbon layer covering the base material.

  According to the ceramic composite material of the present invention, since it consists of a base material made of SiC / SiC composite material and a carbon layer covering the base material, rare metals, toxic elements and radioactive elements are not used. Moreover, the Clark number of silicon is 25.8% (2nd place), and carbon is 0.08% (14th place). This is larger than 0.0045% (28th position) of Ce, which is the Group IIIa element of the periodic table having the largest Clark number, and these are easily available elements. For this reason, the necessity of collection | recovery and isolation | separation is also low. In addition, both the SiC / SiC composite material and the carbon layer have heat resistance, and the base material made of the SiC / SiC composite material is covered with the carbon layer. It protects and a base material does not contact | connect high temperature water vapor | steam, and consumption of SiC can be prevented.

Moreover, it is preferable that the ceramic composite material of this invention is the following aspect.
(2) The SiC / SiC composite material includes SiC fibers and a matrix made of a CVD-SiC material.

  Since the CVD-SiC material is a material that is deposited while the source gas is decomposed, it is difficult to form pores, and a dense and strong base material can be formed. For this reason, the carbon layer formed on this can obtain the film which is hard to deform | transform and to which it is hard to peel even if force is applied from the outside.

(3) The carbon layer is a pyrolytic carbon layer.

  When the carbon layer of the ceramic composite of the present invention is a pyrolytic carbon layer, a dense and strong ceramic layer can be obtained. In addition, pyrolytic carbon undergoes thermal decomposition at the same time as depositing on the substrate, and there is no desorption of atoms from the carbon layer due to generation of cracked gas after deposition. For this reason, it is difficult for gas to permeate, the internal SiC / SiC composite material and water can be sufficiently separated, and a ceramic composite material having corrosion resistance against thermal steam can be obtained.

(4) The carbon layer is a glassy carbon layer.

When the carbon layer of the ceramic composite of the present invention is a glassy carbon layer, a dense and strong ceramic layer can be obtained. Moreover, since the carbon precursor which is raw material arranges the carbon precursor which is a raw material in random order, it is difficult to be oriented, so the thermal expansion coefficient is 3-4 × 10 ⁻⁶ / ° C., and the SiC / SiC composite which is the base material It is equivalent to the material. For this reason, the glassy carbon layer is difficult to peel off even when heated, and a ceramic composite material having corrosion resistance against hot water vapor can be obtained.

(5) The carbon layer has a thickness of 5 to 200 μm.

  If the thickness of the carbon layer is 5 μm or more, the carbon layer has a sufficient thickness, so that even if an impact is applied from the outside, it can be made difficult to chip. When the thickness of the carbon layer is 200 μm or less, the stress with the base material due to the difference in thermal expansion coefficient can be reduced, so that deformation can be made difficult.

(6) The ceramic composite material has a pipe shape.

  When the ceramic composite material of the present invention is in a pipe shape, it can be suitably used as a pipe for circulating hot water and hot water vapor. Moreover, since a base material is a SiC / SiC composite material and is a high intensity | strength material, it can utilize suitably as a pressure piping and vacuum piping to which a pressure is applied from the inside or the exterior.

(7) The carbon layer is formed on an inner surface side and an outer surface side of the pipe-shaped ceramic composite material.

When the carbon layer is formed on the inner surface side and the outer surface side of the pipe-shaped ceramic composite material, a ceramic composite material corresponding to the use environment can be obtained.
In general, when the atmosphere oxygen concentration is high, SiC forms a SiO ₂ film and suppresses the progress of oxidation, and when the atmosphere oxygen concentration is low, it is difficult to form a SiO ₂ film and oxidation proceeds. To do. When exposed to hot water vapor or hot water, the oxygen concentration is low and oxidation tends to proceed.
In the ceramic composite material of the present invention, in the portion where the oxygen concentration is high, the carbon layer is oxidized to expose SiC, and the surface of SiC is rapidly oxidized to form a thin coating of SiO ₂ . On the other hand, when the oxygen concentration in the atmosphere such as hot water vapor or hot water is low, the carbon layer covering the surface of the base material made of the SiC / SiC composite material protects against oxidation. For this reason, the pipe-shaped ceramic composite material in which the carbon layers are formed on the inner surface side and the outer surface side can provide a protective film suitable for the environment in which it is used. Examples of the pipe-shaped ceramic composite include piping and casings for steam turbine equipment.

(8) The ceramic composite material is a heat exchange pipe.

In the heat exchange pipe, for example, heat exchange between hot water and high-temperature air is performed. Hot water is not able to form a SiO ₂ film on the surface of the SiC, it is possible to prevent the consumption of SiC by the carbon layer having a surface. On the other hand, on the side exposed to high-temperature air such as combustion gas, SiC is exposed by burning the carbon layer on the surface. When SiC is exposed to a combustion gas having a high oxygen content, a SiO ₂ film is formed on the surface, and the progress of oxidation is hindered.

(9) The ceramic composite is a nuclear reactor channel box or a nuclear fuel cladding.

Reactor channel boxes and nuclear fuel cladding are used in boiling water reactors, pressurized water reactors, and the like. In these nuclear reactors, they are used by being submerged in pressurized water. However, in the case of SiC alone, a coating of SiO ₂ cannot be formed against hot water, and corrodes, and SiC is gradually eluted. Happens. On the other hand, in the ceramic composite material of the present invention, since the surface is covered with the carbon layer, the elution of SiC can be prevented and corrosion can be prevented. In addition, since the base material is a SiC / SiC composite material, even if the atmosphere is opened to the atmosphere due to the trouble of the nuclear reactor, the combustion is limited to the carbon layer on the surface, and damage to the structural member can be prevented.

(10) The ceramic composite is a reaction vessel for supercritical water or subcritical water.

  The critical point temperature of water is 374 ° C., and the pressure is 22.1 MPa. At the critical point, water at high temperature and high pressure has an intermediate property between liquid and gas and becomes very reactive. Moreover, it has strong reactivity even in a subcritical state that does not reach such conditions. Since the ceramic composite of the present invention has a carbon layer on the surface, it can be suitably used as a reaction vessel for supercritical water or subcritical water.

  According to the ceramic composite material of the present invention, since it consists of a base material made of SiC / SiC composite material and a carbon layer covering the base material, rare metals, toxic elements and radioactive elements are not used. Moreover, the Clark number of silicon is 25.8% (2nd place), and carbon is 0.08% (14th place). This is larger than 0.0045% (28th position) of Ce, which is the Group IIIa element of the periodic table having the largest Clark number, and these are easily available elements. For this reason, the necessity of collection | recovery and isolation | separation is also low. In addition, both the SiC / SiC composite material and the carbon layer have heat resistance, and the base material made of the SiC / SiC composite material is covered with the carbon layer. It protects and a base material does not contact | connect high temperature water vapor | steam, and consumption of SiC can be prevented.

It is the photograph of the sample 1 used for the reaction test by the hot water of the pyrolytic carbon which comprises the surface of the ceramic composite material of this invention, (a) is the surface photograph before a test, (b) is the laser microscope photograph before a test. It is a partial area of the photograph of (a). (C) is a laser micrograph after the test, which is the same location as the photo of (b). It is the photograph of the sample 2 used for the reaction test by the hot water of the CVD-SiC material which is the surface equivalent to the comparative example 1 of this invention, (a) is the surface photograph before a test, (b) is the laser before a test. It is a micrograph and is a partial region of the photograph of (a). (C) is a laser micrograph after the test, which is the same location as the photo of (b). It is the photograph of the sample 3 used for the reaction test by the hot water of the polished CVD-SiC material which is the surface equivalent to the comparative example 2 of this invention, (a) is the surface photograph before a test, (b) is a test. It is a previous laser micrograph and is a partial region of the photograph of (a). (C) is a laser micrograph after the test, which is the same location as the photo of (b).

(1) The ceramic composite material of the present invention includes a base material made of a SiC / SiC composite material and a carbon layer covering the base material.

  According to the ceramic composite material of the present invention, since it consists of a base material made of SiC / SiC composite material and a carbon layer covering the base material, rare metals, toxic elements and radioactive elements are not used. Moreover, the Clark number of silicon is 25.8% (2nd place), and carbon is 0.08% (14th place). This is larger than 0.0045% (28th position) of Ce, which is the Group IIIa element of the periodic table having the largest Clark number, and these are easily available elements. For this reason, the necessity of collection | recovery and isolation | separation is also low. In addition, both the SiC / SiC composite material and the carbon layer have heat resistance, and the base material made of the SiC / SiC composite material is covered with the carbon layer. It protects and a base material does not contact | connect high temperature water vapor | steam, and consumption of SiC can be prevented.

  The SiC / SiC composite material is composed of an aggregate of SiC fibers and a matrix of SiC. The aggregate of SiC fiber may be used in any form. For example, a filament winding body obtained by bundling a plurality of strands to form a strand and winding the strand can be used. In addition, a braided body in which strands are knitted, a woven fabric in which strands are woven, a nonwoven fabric in which SiC fibers are randomly stacked, a papermaking body in which SiC fibers are made, and the like can be used. The SiC matrix is not particularly limited, and a PIP-SiC material matrix by a PIP (Polymer Implication and Pyrolysis) method in which a SiC precursor such as polycarbosilane is fired, a CVD-SiC material matrix by a CVD method, or the like can be used.

(2) The SiC / SiC composite material of the ceramic composite material of the present invention is preferably composed of SiC fibers and a matrix made of a CVD-SiC material.
Since the CVD-SiC material is a material that is deposited while the source gas is decomposed, it is difficult to form pores, and a dense and strong base material can be formed. For this reason, the carbon layer formed on this can obtain the film which is hard to deform | transform and to which it is hard to peel even if force is applied from the outside. In addition, rare metals, toxic elements, and radioactive elements are not used, and the SiC / SiC composite material and the carbon layer have heat resistance, and the base material made of the SiC / SiC composite material is covered with the carbon layer. Therefore, even if exposed to high temperature water vapor, the carbon layer is protected, the base material does not come into contact with high temperature water vapor, and consumption of SiC can be prevented.

  The CVD-SiC material can be obtained as follows. Aggregates made of SiC fibers are put in a CVD furnace, and the inside of the furnace is heated to 1000 to 1800 ° C., for example. Next, methane, which is a raw material gas, and silane gas are introduced into the furnace, and thermally decomposed SiC is deposited on the surface of the aggregate. The obtained SiC is a CVD-SiC material, and since SiC has already been obtained when it is deposited on the surface of the aggregate, it is not necessary to decompose after deposition, so that a dense film can be formed. .

(3) When the carbon layer of the ceramic composite of the present invention is a pyrolytic carbon layer, a dense and strong ceramic layer can be obtained. In addition, pyrolytic carbon undergoes thermal decomposition at the same time as it is deposited on the substrate, and there is no detachment of atoms from the carbon layer due to generation of decomposition gas. For this reason, it is difficult for gas to permeate, the internal SiC / SiC composite material and water can be sufficiently separated, and a ceramic composite material having corrosion resistance against thermal steam can be obtained. Further, since the CVD-SiC material is a material that is deposited while the source gas is decomposed, it is difficult to form pores, and a dense and strong base material can be formed. For this reason, the carbon layer formed on this can obtain the film which is hard to deform | transform and to which it is hard to peel even if force is applied from the outside. At the same time, both the SiC / SiC composite material and the carbon layer have heat resistance, and the base material made of the SiC / SiC composite material is covered with the carbon layer. It protects and a base material does not contact | connect high temperature water vapor | steam, and consumption of SiC can be prevented.

  The pyrolytic carbon layer can be obtained as follows. The SiC / SiC composite material is put in a CVD furnace, and the inside of the furnace is heated to 1000 to 2500 ° C., for example. Next, methane as a raw material gas is introduced into the furnace, and pyrolytic carbon is deposited on the surface of the SiC / SiC composite material. The obtained pyrolytic carbon becomes a pyrolytic carbon layer.

(4) When the carbon layer of the ceramic composite of the present invention is a glassy carbon layer, a dense and strong ceramic layer can be obtained. Moreover, since the carbon precursor which is raw material arranges the carbon precursor which is a raw material in random order, it is difficult to be oriented, so the thermal expansion coefficient is 3-4 × 10 ⁻⁶ / ° C., and the SiC / SiC composite which is the base material It is equivalent to the material. For this reason, the glassy carbon layer is difficult to peel off even when heated, and a ceramic composite material having corrosion resistance against hot water vapor can be obtained.

  The carbon precursor for obtaining the glassy carbon layer is not particularly limited as long as it is thermally decomposed to become glassy carbon. For example, phenol resin, furan resin, polyvinyl chloride, copna resin, polyvinylidene chloride, cellulose, furfuryl alcohol resin and the like can be mentioned.

(5) The carbon layer of the present invention preferably has a thickness of 5 to 200 μm.

  If the thickness of the carbon layer is 5 μm or more, the carbon layer has a sufficient thickness, so that even if an impact is applied from the outside, it can be made difficult to chip. When the thickness of the carbon layer is 200 μm or less, the stress with the base material due to the difference in thermal expansion coefficient can be reduced, so that deformation can be made difficult.

  If it is a pyrolytic carbon layer, the thickness of a carbon layer can be suitably adjusted with the film-forming time of a CVD process, the density | concentration of raw material gas, the film-forming temperature, etc. Moreover, if it is a glassy carbon layer, it can adjust suitably with the solute density | concentration of a carbon precursor, the frequency | count of application | coating, etc.

(6) The ceramic composite material of the present invention preferably has a pipe shape.

  When the ceramic composite material of the present invention is in a pipe shape, it can be suitably used as a pipe for circulating hot water and hot water vapor. Moreover, since a base material is a SiC / SiC composite material and is a high intensity | strength material, it can utilize suitably as a pressure piping and vacuum piping to which a pressure is applied from the inside or the exterior.

  The pipe shape is not particularly limited as long as it is a hollow pipe. Examples of the cross-sectional shape include a circle, an ellipse, a square, a rectangle, a hexagon, and a polygon. Both ends may be open, and both ends or one end may be closed.

  The pipe-shaped ceramic composite material of the present invention is a SiC / SiC composite material whose base material is composed of an aggregate of SiC fibers and a matrix of a CVD-SiC material, and the carbon layer is a pyrolytic carbon layer. preferable. Since the CVD-SiC material is a material that is deposited while the source gas is decomposed, it is difficult to form pores, and a dense and strong base material can be formed. For this reason, the carbon layer formed on this can obtain the film which is hard to deform | transform and to which it is hard to peel even if force is applied from the outside. In addition, rare metals, toxic elements, and radioactive elements are not used, and the SiC / SiC composite material and the carbon layer have heat resistance, and the base material made of the SiC / SiC composite material is covered with the carbon layer. Therefore, even if exposed to high temperature water vapor, the carbon layer is protected, the base material does not come into contact with high temperature water vapor, and consumption of SiC can be prevented.

(7) It is preferable that the carbon layer of the present invention is formed on the inner surface side and the outer surface side of the pipe-shaped ceramic composite material.

When the carbon layer is formed on the inner surface side and the outer surface side of the pipe-shaped ceramic composite material, a ceramic composite material corresponding to the use environment can be obtained.
In general, when the atmosphere oxygen concentration is high, SiC forms a SiO ₂ film and suppresses the progress of oxidation, and when the atmosphere oxygen concentration is low, it is difficult to form a SiO ₂ film and oxidation proceeds. To do. When exposed to hot water vapor or hot water, the oxygen concentration is low and oxidation tends to proceed.
In the ceramic composite material of the present invention, in the portion where the oxygen concentration is high, the carbon layer is oxidized to expose SiC, and the surface of SiC is rapidly oxidized to form a thin coating of SiO ₂ . On the other hand, when the oxygen concentration in the atmosphere such as hot water vapor or hot water is low, the carbon layer covering the surface of the base material made of the SiC / SiC composite material protects against oxidation. For this reason, the pipe-shaped ceramic composite material in which the carbon layers are formed on the inner surface side and the outer surface side can provide a protective film suitable for the environment in which it is used. Examples of the pipe-shaped ceramic composite include piping and casings for steam turbine equipment.

(8) The ceramic composite material of the present invention can be used as a heat exchange pipe.

In the heat exchange pipe, for example, heat exchange between hot water and high-temperature air is performed. Hot water is not able to form a SiO ₂ film on the surface of the SiC, it is possible to prevent the consumption of SiC by the carbon layer having a surface. On the other hand, on the side exposed to high-temperature air such as combustion gas, SiC is exposed by burning the carbon layer on the surface. When SiC is exposed to a combustion gas having a high oxygen content, a SiO ₂ film is formed on the surface, and the progress of oxidation is hindered.

As the heat exchange pipe, for example, a large number of circular pipe-shaped ceramic composite materials can be aligned in parallel and used in combination. A heat medium can be circulated inside and outside the pipe-shaped ceramic composite material, and heat can be exchanged through the ceramic composite material. Examples of the heat medium include water, steam, air, and oil. When the reactivity with the carbon layer is not known, it is preferable to have a carbon layer on the surface in contact with the heat medium. If there is no reactivity with the carbon layer, the carbon layer prevents corrosion of the ceramic composite, and if there is reactivity between the carbon layer and the heat medium, the carbon layer is oxidized and SiC is exposed. A protective film of SiO ₂ is quickly formed on the surface of SiC to prevent corrosion of the ceramic composite material.

(9) The ceramic composite material of the present invention can be used as a nuclear reactor channel box or a nuclear fuel cladding tube.

Reactor channel boxes and nuclear fuel cladding are used in boiling water reactors, pressurized water reactors, and the like. In these nuclear reactors, they are used by being submerged in pressurized water. However, in the case of SiC alone, a coating of SiO ₂ cannot be formed against hot water, and corrodes, and SiC is gradually eluted. Happens. On the other hand, in the ceramic composite material of the present invention, since the surface is covered with the carbon layer, the elution of SiC can be prevented and corrosion can be prevented. In addition, since the base material is a SiC / SiC composite material, even if the atmosphere is opened to the atmosphere due to the trouble of the nuclear reactor, the combustion is limited to the carbon layer on the surface, and damage to the structural member can be prevented.

(10) The ceramic composite material of the present invention can be used as a reaction vessel for supercritical water or subcritical water.

  The critical point temperature of water is 374 ° C., and the pressure is 22.1 MPa. At the critical point, water at high temperature and high pressure has an intermediate property between liquid and gas and becomes very reactive. Moreover, it has strong reactivity even in a subcritical state that does not reach such conditions. Since the ceramic composite of the present invention has a carbon layer on the surface, it can be suitably used as a reaction vessel for supercritical water or subcritical water.

Supercritical water is the state of water in an environment of 374 ° C. or higher and 22.1 MPa or higher. The subcritical water is the state of water under the environment in the range A excluding the following ranges B and C.
A: 100 ° C. or more and 0.1013 MPa or more B: 100 ° C. and 0.1013 MPa
C: 374 ° C. or higher and 22.1 MPa or higher

  Examples of the present invention and comparative examples will be described below.

<Example 1>
A strand is formed by bundling 1600 SiC fibers, and the obtained strand is woven to form a braided body. The braiding body has a pipe shape with an inner diameter of 10 mm and a thickness of 0.5 mm. The obtained braided body is used as an aggregate, and a CVD-SiC material is filled in the gap between the aggregates to obtain a base material.
The CVD-SiC material is formed using a CVD furnace. A braided body is placed in a CVD furnace, heated to 1200 ° C., silane gas and methane, which are raw material gases, are introduced, a matrix made of a CVD-SiC material is formed in the gap between the aggregates, and the base of the SiC / SiC composite material Get the material.

  Next, the source gas is switched to methane, and a pyrolytic carbon layer is formed on the surface of the substrate. The thickness of the pyrolytic carbon layer is 30 μm. The pyrolytic carbon layer can be deposited on both the inner and outer surfaces of the pipe-shaped substrate.

  The obtained ceramic composite is a ceramic composite in which a pyrolytic carbon layer is formed on the surface of a SiC / SiC composite base material.

<Example 2>
A strand is formed by bundling 1600 SiC fibers, and the obtained strand is wound to form a filament winding body. The filament winding body has a pipe shape with an inner diameter of 100 mm and a thickness of 2 mm. The obtained filament winding body is used as an aggregate, and a CVD-SiC material is filled in the gap between the aggregates to obtain a base material.
The CVD-SiC material is formed using a CVD furnace. A filament winding body is placed in a CVD furnace, heated to 1200 ° C., silane gas and methane as raw material gases are introduced, a matrix made of a CVD-SiC material is formed in the gap between the aggregates, and the substrate of the SiC / SiC composite material is formed. Get the material.

  Next, after immersing a base material in a phenol resin solution, it is dried and cured at 120 ° C., and then fired at 1000 ° C. to form a glassy carbon layer on the surface of the base material. The thickness of the glassy carbon layer is 30 μm. The glassy carbon layer can be coated on both the inner and outer surfaces of the pipe-shaped substrate.

  The obtained ceramic composite is a ceramic composite in which a glassy carbon layer is formed on the surface of a substrate made of a SiC / SiC composite.

<Example 3>
A strand is formed by bundling 1600 SiC fibers, and the obtained strand is woven to form a braided body. The braiding body has a pipe shape with an inner diameter of 10 mm and a thickness of 0.5 mm. The obtained braided body is used as an aggregate, and a PIP-SiC material is filled in the gap between the aggregates to obtain a base material.
The PIP-SiC material can be obtained by impregnating an SiC precursor (polycarbosilane) in the gap between the aggregates and firing. A matrix made of a PIP-SiC material is formed by immersing the aggregate in a solution of polycarbosilane, followed by drying and firing to obtain a SiC / SiC composite base material.

  The carbon layer is formed using a CVD furnace. A base material is put in a CVD furnace, heated to 1500 ° C., methane as a raw material gas is introduced, a pyrolytic carbon layer is formed on the surface of the base material, and a ceramic composite material is obtained. The thickness of the pyrolytic carbon layer is 30 μm. The pyrolytic carbon layer can be deposited on both the inner and outer surfaces of the pipe-shaped substrate.

<Comparative Example 1>
In Example 1, a SiC / SiC composite base material is used as it is without forming a carbon layer. In this comparative example, the surface is a CVD-SiC material.

<Comparative example 2>
A CVD-SiC material having a smooth surface obtained by polishing a flat plate of a CVD-SiC material obtained by the CVD-SiC method is referred to as Comparative Example 2.

<Evaluation test>
In order to verify the corrosion resistance of the ceramic composite of the present invention, pyrolytic carbon and SiC exposed on the surface in Examples 1 to 3 and Comparative Examples 1 and 2 were used as evaluation samples, and the evaluation sample was 300 ° C. and 8 MPa water. For 80 hours, and the changes before and after immersion were compared.
Sample 1 has a carbon layer formed on the surface of the substrate. In Sample 2, a CVD-SiC layer is formed on the surface of the base material. In Sample 3, the surface of the CVD-SiC layer is further polished. That is, Sample 1 and Sample 2 are surfaces whose surfaces are formed by film formation, and Sample 3 is smoothed by polishing.
In addition, the surface of the sample 1 is a carbon layer, and is the same material as Examples 1-3. Since it is especially pyrolytic carbon, it is the same material as Example 1 and 3 whose surface is a pyrolytic carbon layer.
Sample 2 is a CVD-SiC material whose surface is still formed by the CVD method, and is the same surface as Comparative Example 1.
Since the sample 3 is obtained by polishing and smoothing a CVD-SiC material whose surface is formed by the CVD method, it is the same surface as the comparative example 2.

  Sample 1 and sample 3 are 3 × 4 × 40 mm in size, and sample 2 is in the form of a pipe having a diameter of φ10 × 29 mm and a thickness of 0.5 mm.

  Table 1 shows the change in weight before and after the test. FIG. 1 is a photograph of Sample 1 used for a reaction test of pyrolytic carbon constituting the surface of the ceramic composite of the present invention using hot water, (a) is a surface photograph before the test, and (b) is a photograph before the test. It is a laser micrograph and is a partial region of the photograph of (a). (C) is a laser micrograph after the test, which is the same location as the photo of (b). FIG. 2 is a photograph of Sample 2 used in a reaction test with hot water of a CVD-SiC material equivalent to the surface of Comparative Example 1 of the present invention, (a) is a surface photograph before the test, and (b) is a test. It is a previous laser micrograph and is a partial region of the photograph of (a). (C) is a laser micrograph after the test, which is the same location as the photo of (b). FIG. 3 is a photograph of Sample 3 used in a reaction test with hot water of a polished CVD-SiC material equivalent to Comparative Example 2 of the present invention, (a) is a surface photograph before the test, and (b) is a test. It is a previous laser micrograph and is a partial region of the photograph of (a). (C) is a laser micrograph after the test, which is the same location as the photo of (b).

  Sample 1 consisting of the pyrolytic carbon layer had no weight change before and after the test. As shown in FIG. 1, there was no change in appearance between FIG. 1B before the test and FIG. 1C after the test. Samples 2 and 3 made of CVD-SiC were confirmed to increase in weight by testing. The amount of change in weight differs depending on the state of the surface, and the amount of increase in weight was larger for the film-formed surface having a large surface roughness. As shown in FIGS. 2 and 3, surface CVD-SiC was confirmed to drop off in both samples 2 and 3 after the hot water test.

  In Samples 2 and 3 made of CVD-SiC, the weight is increased despite the occurrence of surface detachment because of the oxidation reaction of the SiC surface by high-temperature and high-pressure water and the surface detachment reaction. This is probably because they are awake at the same time. If the test is continued for a long period of time, dropout will increase and the weight will decrease.

  As described above, it was confirmed that the coating of pyrolytic carbon, which is one form of carbon, has corrosion resistance against high-temperature and high-pressure water. For this reason, it can be seen from the results of Sample 1 that the composite material having a surface layer of pyrolytic carbon has high corrosion resistance against high-temperature and high-pressure water. Further, even glassy carbon, which is the same material as pyrolytic carbon, is considered to have high corrosion resistance to high-temperature and high-pressure water as well.

  Further, since the ceramic composite material of the present invention is composed of carbon and silicon, it was confirmed that the ceramic composite material has heat resistance and corrosion resistance to high-temperature steam without using radioactive elements, toxic elements, and rare elements.

Claims (10)

A ceramic composite material comprising a base material made of a SiC / SiC composite material and a carbon layer covering the base material. The ceramic composite material according to claim 1, wherein the SiC / SiC composite material includes SiC fibers and a matrix made of a CVD-SiC material. The ceramic composite material according to claim 1, wherein the carbon layer is a pyrolytic carbon layer. The ceramic composite material according to claim 1, wherein the carbon layer is a glassy carbon layer. The ceramic composite material according to claim 1, wherein the carbon layer has a thickness of 5 to 200 μm. The ceramic composite material according to claim 1, wherein the ceramic composite material has a pipe shape. The said carbon layer is formed in the inner surface side and outer surface side of the said pipe-shaped ceramic composite material, The ceramic composite material of Claim 6 characterized by the above-mentioned. The ceramic composite material according to claim 6, wherein the ceramic composite material is a heat exchange pipe. The ceramic composite material according to claim 6 or 7, wherein the ceramic composite material is a nuclear reactor channel box or a nuclear fuel cladding tube. The ceramic composite material according to claim 1, wherein the ceramic composite material is a reaction vessel for supercritical water or subcritical water.