Composite material and method for producing same

Abstract

Provided is a method that produces a composite material having excellent thermal conductivity without using, or only using a sufficiently reduced amount of, hydrides that may cause blowholes. This method includes heating contents at least including at least one type of inorganic particles composed of a material selected from the group consisting of diamond, boron nitride, graphite, SiC, AlN, Si3N4, B4C, MgB2, Mg3N2, MgCl2, CaCl2, Mg2Si, carbon fibers, carbon nanotubes, TiC, WC, and TaC; metal particles; and metal oxide particles having oxygen defects to a temperature higher than the melting point of the metal particles in a mold filled with the contents, to melt the metal particles; allowing oxygen released from a molten product of the metal particles to be absorbed by the metal oxide particles; and cooling the mold and then collecting a composite material containing the inorganic particles and a matrix metal which binds the inorganic particles.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a composite material and a method for producing the same, more particularly to a composite material containing inorganic particles and a matrix metal which binds the inorganic particles and a method for producing the same.BACKGROUND ART

[0002] Conventionally, there has been known a composite material composed of diamond particles and a matrix metal which binds the diamond particles. Patent Literature 1 discloses a “diamond composite material comprising: a coated diamond particle including a diamond particle and a carbide layer coating a surface of the diamond particle and including an element of group 4 of the periodic table; and silver or a silver alloy binding such coated diamond particles together, with an oxygen content of 0.1 mass % or less” (see claim 1 in Patent Literature 1).CITATION LISTPatent Literature

[0003] Patent Literature 1: JP6292688BSUMMARY OF INVENTION

[0004] According to Patent Literature 1, a diamond composite material that is exceptionally thermally conductive and dense can be obtained by having as small oxygen content as possible in the diamond composite material. The paragraph

[0118] of Patent Literature 1 presumes reasons for being able to obtain such a diamond composite material since “using a raw material of a powder of a group 4 compound including an element of group 4 of the periodic table can suppress oxidation of the element of group 4 of the periodic table in the production process and oxygen which may be present around a raw material can be reduced / removed by an effect of a particular element generated in a chemolysis of the above group 4 compound, and furthermore, the element of group 4 of the periodic table generated through the chemolysis can react with the diamond and thus efficiently form a carbide and thus enhance wettability with molten metal.”

[0005] According to the study by the present inventors, a thermal conductivity of a matrix metal of a composite material is likely to decrease if the addition amount of compounds including elements of group 4 of the periodic table (for example, titanium hydride) is increased in a production process of the composite material. Therefore, there is an upper limit to the amount of these elements to be added. In addition, when titanium hydride (TiH2) powders, for example, are used to reduce oxygen by hydrogen generated by decomposition of titanium hydride, H2O formed by the hydrogen and the oxygen or the hydrogen is incorporated into a molten metal, and due to this, blowholes may be formed in the matrix metal. The blowholes deteriorate performance of the composite material.

[0006] The present disclosure was developed in light of the above problems and provides a composite material having an excellent thermal conductivity and a method for producing the same without using, or only using a sufficiently reduced amount of, hydrides that may cause blowholes.

[0007] A method for producing a composite material according to the present disclosure comprises the steps of:

[0008] (a) at least filling a mold with at least one type of inorganic particles composed of a material selected from the group consisting of diamond, boron nitride (h-BN or c-BN), graphite, SiC, AlN, Si3N4, B4C, MgB2, Mg3N2, MgCl2, CaCl2, Mg2Si, carbon fibers, carbon nanotubes, TiC, WC, and TaC; metal particles; and metal oxide particles;

[0009] (b) heating contents comprising the inorganic particles, the metal particles, and the metal oxide particles in the mold in reducing atmosphere to a temperature lower than a melting point of the metal particles to release oxygen from the metal oxide particles;

[0010] (c) discharging the oxygen released from the metal oxide particles to the outside of the mold;

[0011] (d) heating the contents in the mold to a temperature higher than the melting point of the metal particles to melt the metal particles;

[0012] (e) allowing the oxygen released from a molten product of the metal particles to be absorbed by the metal oxide particles; and

[0013] (f) cooling the mold and then collecting a composite material comprising the inorganic particles and a matrix metal which binds the inorganic particles.

[0014] A method for producing a composite material according to the present disclosure may comprise the steps of:

[0015] (x) heating contents at least comprising at least one type of inorganic particles composed of a material selected from the group consisting of diamond, boron nitride (h-BN or c-BN), graphite, SiC, AlN, Si3N4, B4C, MgB2, Mg3N2, MgCl2, CaCl2, Mg2Si, carbon fibers, carbon nanotubes, TiC, WC, and TaC; metal particles; and metal oxide particles having oxygen defects to a temperature higher than a melting point of the metal particles in a mold filled with the contents, to melt the metal particles;

[0016] (y) allowing oxygen released from a molten product of the metal particles to be absorbed by the metal oxide particles; and

[0017] (z) cooling the mold and then collecting a composite material comprising the inorganic particles and a matrix metal which binds the inorganic particles.

[0018] According to the above production method, the metal oxide particles can function as an oxygen absorbent. In other words, the metal oxide particles can exhibit a gettering effect of trapping oxygen. As the oxygen is trapped by the metal oxide particles, it is possible to prevent a decrease in thermal conductivity of the matrix metal caused by oxygen. In addition, differing from the above-mentioned situation where the hydrogen generated by decomposition of titanium hydride is used to reduce oxygen, H2O or hydrogen is not generated and so the formation of blowholes can be prevented. Furthermore, as the metal oxide particles are thermally stable, it is possible to prevent deterioration in physical properties of the matrix metal caused by the metal oxide particles.

[0019] The composite material according to the present disclosure includes at least one type of inorganic particles selected from the group consisting of diamond particles and boron nitride particles (for example, h-BN particles or c-BN particles); a matrix metal which binds the inorganic particles; and metal oxide particles, and an oxygen content is higher than 0.1 mass % and a thermal conductivity is 300 W / m·K or more at room temperature.

[0020] Although the above composite material has the oxygen content higher than 0.1 mass %, the oxygen in the composite material is mainly derived from the metal oxide particles and so the decrease in the thermal conductivity of the matrix metal caused by oxygen is prevented thereby achieving a thermal conductivity of 300 W / m·K or more at room temperature. As the metal oxide particles are thermally stable, deterioration in physical properties of the matrix metal caused by the metal oxide particles is also prevented.

[0021] The present disclosure provides a composite material having an excellent thermal conductivity and a method for producing the same without using, or only using a sufficiently reduced amount of, hydrides, such as titanium hydride, that may cause blowholes.BRIEF DESCRIPTION OF DRAWINGS

[0022] FIG. 1 is a sectional view schematically illustrating an embodiment of a composite material according to the present disclosure.

[0023] FIG. 2 is a sectional view schematically illustrating other embodiment of a composite material according to the present disclosure.

[0024] FIG. 3 is a sectional view schematically illustrating other embodiment of a composite material according to the present disclosure.

[0025] FIG. 4A is a sectional view schematically illustrating a production process of the composite material illustrated in FIG. 1.

[0026] FIG. 4B is a sectional view schematically illustrating the production process of the composite material illustrated in FIG. 1.

[0027] FIG. 5 is a sectional view schematically illustrating a production process of the composite materials illustrated in FIGS. 2 and 3.

[0028] FIG. 6 is a sectional view schematically illustrating the state in which the mold is filled with the metal oxide particles having oxygen defects.DESCRIPTION OF EMBODIMENTS

[0029] The embodiments of the present disclosure are explained below. The following embodiments are examples to explain the present disclosure and are not aimed to limit the present disclosure to the following descriptions. The upper limit or the lower limit for the numerical range specified herein may be replaced with any values indicated in the examples. Also, the upper limit and the lower limit described individually may be combined optionally. Unless otherwise specified, the materials or the components described as examples herein may be used alone or in combination of two or more. In terms of explanation, like elements or elements with like function are represented with like symbols to avoid repeating of explanation. Moreover, unless otherwise specified, the vertical and horizontal positional relationships used in explanation are based on the positional relationships indicated on the drawings.[Composite Material]

[0030] FIG. 1 is a sectional view schematically illustrating an embodiment of a composite material according to the present disclosure. A composite material 10 illustrated in the figure has a plurality of inorganic particles 1, a plurality of metal oxide particles 3, and a matrix metal 5. In the composite material 10, the metal oxide particles 3 are dispersed, and the oxygen content of the composite material 10 is higher than 0.1 mass %, or it may be 0.2 mass % or more or 0.3 mass % or more. It should be noted that, in view of thermal conductivity, the upper limit for the oxygen content of the composite material 10 is, for example, 1.0 mass %, or it may be 0.8 mass % or 0.6 mass %.

[0031] Although the oxygen content of the composite material 10 is higher than 0.1 mass %, the thermal conductivity is 300 W / m·K or more. The composite material 10 may have a thermal conductivity of 500 W / m·K or more or 600 W / m·K or more. The upper limit for the thermal conductivity of the composite material 10 is, for example, 700 W / m·K, or it may be 800 W / m·K or 1,000 W / m·K. As the composite material 10 has an excellent thermal conductivity, it can be used for a heat dissipation member. The composite material 10 may be in a form of a plate, or it may be molded into a desirable shape depending on the intended use.

[0032] A material composing the inorganic particles 1 is a material selected from the group consisting of diamond, boron nitride (h-BN or c-BN), graphite, SiC, AlN, Si3N4, B4C, MgB2, Mg3N2, MgCl2, CaCl2, Mg2Si, carbon fibers, carbon nanotubes, TiC, WC, and TaC. The thermal conductivity of diamond is about 1,000 to 2,000 W / m·K. The thermal conductivity of c-BN is about 1,300 W / m·K. The thermal conductivity of SiC is about 150 to 500 W / m—K. Among the above materials, it is desirable to use diamond particles or c-BN particles as the inorganic particles 1 in view of thermal conductivity. In view of thermal conductivity, the average particle diameter (median diameter D50) of the inorganic particles 1 is preferably 10 μm or more, more preferably 20 μm or more, and even more preferably 50 μm or more. In view of workability of the composite material, the average particle diameter (median diameter D50) of the inorganic particles 1 is preferably 500 μm or less, more preferably 300 μm or less, and even more preferably 200 μm or less.

[0033] In view of thermal conductivity, the content rate of the inorganic particles 1 in the composite material 10 is preferably 35 volume % or more, more preferably 40 volume % or more, and even more preferably 45 volume % or more based on the volume of the composite material 10. In view of formability, this content rate is preferably 90 volume % or less, more preferably 85 volume % or less, and even more preferably 80 volume % or less.

[0034] Examples of the metal oxide particles 3 include titanium oxide particles, cerium oxide particles, calcium titanate particles, and niobium oxide particles. The metal oxide particles 3 may be perovskite-type oxide particles. The thermal conductivity of titanium oxide is about 7 W / m·K. The thermal conductivity of cerium oxide is about 14 W / m·K. The thermal conductivity of calcium titanate is about 2 W / m·K. The thermal conductivity of niobium oxide is about 2 W / m·K. In view of workability, the average particle diameter (median diameter D50) of the metal oxide particles 3 is preferably 0.1 μm or more, more preferably 0.5 μm or more, and even more preferably 1 μm or more. In view of mixability, the average particle diameter (median diameter D50) of the metal oxide particles 3 is preferably 200 μm or less, more preferably 100 μm or less, and even more preferably 50 μm or less.

[0035] The content rate of the metal oxide particles 3 in the composite material 10 is, for example, 0.01 volume % or more, or it may be 0.05 volume % or more or 0.1 volume % or more based on the volume of the composite material 10. In view of formability, this content rate is preferably 5 volume % or less, more preferably 2 volume % or less, and even more preferably 1 volume % or less.

[0036] The matrix metal 5 is present in between a plurality of the inorganic particles 1 and a plurality of the metal oxide particles 3 and binds these particles. Examples of a metal composing the matrix metal include copper, silver, aluminum, magnesium or an alloy of two or more metals selected from these. In view of formability, the content rate of the matrix metal 5 in the composite material 10 is preferably 10 volume % or more, more preferably 15 volume % or more, and even more preferably 20 volume % or more based on the volume of the composite material 10. In view of thermal conductivity, this content rate is preferably 65 volume % or less, more preferably 60 volume % or less, and even more preferably 55 volume % or less.

[0037] FIG. 2 is a sectional view schematically illustrating other embodiment of a composite material according to the present disclosure. A composite material 20 illustrated in the figure does not have the metal oxide particles 3 dispersed in the composite material 20 and has a region R3 where the metal oxide particles 3 exist in high concentration. The region R3 is formed on one surface 20a of the composite material 20.

[0038] FIG. 3 is a sectional view schematically illustrating other embodiment of a composite material according to the present disclosure. A composite material 30 illustrated in the figure has the region R3 removed from the composite material 20 illustrated in FIG. 2. For example, the region R3 can be removed by grinding the side of the surface 20a of the composite material 20. The oxygen content of the composite material 30 is, for example, 0.10 mass % or less, or it may be 0.07 mass % or less, or it may substantially be zero. The lower limit for the oxygen content of the composite material 30 is, for example, 0.01 mass %. The composite material 30 may have a thermal conductivity of 600 W / m·K or more or 700 W / m·K or more. The upper limit for the thermal conductivity of the composite material 30 is, for example, 800 W / m·K, or it may be 900 W / m·K or 1,000 W / m·K.[Method for Producing Composite Material]

[0039] Next, a method for producing the composite material 10 is explained with reference to FIGS. 4A and 4B. The production method includes the steps of:

[0040] (a) filling a mold 50 with contents 7 at least having the inorganic particles 1, metal particles 5p, and the metal oxide particles 3 (see FIG. 4A);

[0041] (b) heating the contents 7 in the mold 50 in reducing atmosphere to a temperature lower than the melting point of the metal particles 5p to release oxygen from the metal oxide particles 3;

[0042] (c) discharging the oxygen released from the metal oxide particles 3 to the outside of the mold 50;

[0043] (d) heating the contents 7 in the mold 50 to a temperature higher than the melting point of the metal particles 5p to melt the metal particles 5p (see FIG. 4B);

[0044] (e) allowing the oxygen released from the molten product of the metal particles to be absorbed by the metal oxide particles 3; and

[0045] (f) cooling the mold 50 and then collecting the composite material 10.

[0046] The composite material 10 is obtained by the above steps. In view of improving the wettability of the inorganic particles 1 to the matrix metal 5, various additives may be added into the mold 50 in the above step (a). Examples of the additives include a compound, such as a metal compound, including (i) an element of Ti, Cr, V, Mn, Nb, W, Mo, Fe, Co, Ni, Pd, Pt, Rh, Ta, Re, Zr, U, Ce, Si, B, Y, Mg, Zn, and / or a rare earth element (for example, an element that is a metal among these) and (ii) a specific element (specifically, at least one element of sulfur, nitrogen, hydrogen, or boron). By performing the above step (b), oxygen defects are formed on the metal oxide particles 3. The heating temperature in the step (b) is a temperature that is lower than the melting point of the metal particles 5p by, for example, 50 to 200° C. The heating duration is, for example, 5 to 60 minutes. To discharge oxygen to the outside of the mold 50 in the above step (c), the pressure in the mold 50 may be, for example, reduced by a vacuum pump. The heating temperature in the above step (d) is a temperature that is higher than the melting point of the metal particles 5p by, for example, 50 to 200° C. The heating duration is, for example, 5 to 60 minutes. Once melted, the metal particles 5p solidify to form a matrix metal 5.

[0047] The methods for producing the composite material 20 and the composite material 30 are explained with reference to FIG. 5. Firstly, in the above step (a), a first layer L1 is formed in the mold 50, and then a second layer L2 is formed on the first layer L1. The first layer L1 is composed of the inorganic particles 1. Meanwhile, the second layer L2 is composed of the metal particles 5p and the metal oxide particles 3. The above additive may be formulated into at least one of the first layer L1 and the second layer L2 as necessary. The metal oxide particles 3 included in the second layer L2 have a larger average particle diameter than that of the inorganic particles 1 included in the first layer L1. Therefore, when the molten product of the metal particles 5p enters the first layer L1 in the above step (d), at least some of the metal oxide particles 3 remain on the first layer L1. As a result, the composite material 20 having the region R3 is obtained. It should be noted that the average particle diameter of the metal oxide particles 3 may not necessarily be larger than the average particle diameter of the inorganic particles 1. In other words, as long as the particle diameter of the metal oxide particles 3 is larger than the space formed by a plurality of the adjacent inorganic particles 1, at least some of the metal oxide particles 3 remain on the first layer L1. The region R3 is removed from the composite material 20 to obtain the composite material 30.

[0048] Herein, a case in which the first layer L1 was composed of the inorganic particles 1 and the second layer L2 was composed of the metal particles 5p and the metal oxide particles 3 was demonstrated, but the first layer L1 may be composed of the inorganic particles 1 and the metal oxide particles 3, and the second layer L2 may be composed of the metal particles 5p. In the latter case, as the first layer L1 contains the metal oxide particles 3, the region containing a large amount of the metal oxide particles 3 cannot be removed afterwards as above. However, the oxygen contained in the matrix metal can be removed by the gettering effect of the metal oxide particles 3 when the molten product of the metal particles 5p enters the first layer L1. As a result, it is possible to obtain a composite material with high thermal conductivity despite the fact that the oxygen content thereof is relatively high (for example, see examples 3 and 4). It should be noted again that the above additive may be formulated into at least one of the first layer L1 and the second layer L2 as necessary.

[0049] The embodiments of the present disclosure were explained in detail above, but the present invention is not limited to the above embodiments. For example, the above embodiments illustrated the production method including the steps of heating the metal oxide particles 3 in the mold 50 in reducing atmosphere to release the oxygen from the metal oxide particles 3; however, metal oxide particles 3A having oxygen defects may be, for example, prepared beforehand to fill the mold 50 (see FIG. 6). In other words, the composite material 10 may be produced by the steps of:

[0050] (x) heating contents 7A at least including the inorganic particles 1, the metal particles 5p, and the metal oxide particles 3A having oxygen defects and filled in the mold 50 to a temperature higher than the melting point of the metal particles 5p to melt the metal particles 5p;

[0051] (y) allowing the oxygen released from the molten product of the metal particles 5p to be absorbed by the metal oxide particles 3A; and

[0052] (z) cooling the mold 50 and then collecting the composite material 10.

[0053] It should be noted that the metal oxide particles 3A may be obtained by subjecting the metal oxide particles 3 to reduction treatment. The metal oxide particles 3A may be used to produce the composite materials 20, 30.

[0054] In the above embodiments, diamond particles are illustrated as a preferred example for the inorganic particles 1, but the diamond particles may have a coated layer (not shown) composing the outermost layer of the diamond particles, or the diamond particles may be boron-doped. Examples of the coated layer include a titanium coated layer, a chromium coated layer, and a boron-doped layer (diamond particles with only the surface layer doped with boron). For example, in case of the titanium coated layer, having the titanium coated layer on the diamond particles further improves the wettability of the diamond particles to the matrix metal due to the titanium carbide layer present at the interface between the surface of the diamond particle body and the matrix metal.

[0055] The present disclosure relates to the following:

[0056] [1] A method for producing a composite material comprising the steps of:

[0057] at least filling a mold with at least one type of inorganic particles composed of a material selected from the group consisting of diamond, boron nitride, graphite, SiC, AlN, Si3N4, B4C, MgB2, Mg3N2, MgCl2, CaCl2, Mg2Si, carbon fibers, carbon nanotubes, TiC, WC, and TaC; metal particles; and metal oxide particles;

[0058] heating contents comprising the inorganic particles, the metal particles, and the metal oxide particles in the mold in reducing atmosphere to a temperature lower than a melting point of the metal particles to release oxygen from the metal oxide particles;

[0059] discharging the oxygen released from the metal oxide particles to the outside of the mold;

[0060] heating the contents in the mold to a temperature higher than the melting point of the metal particles to melt the metal particles;

[0061] allowing the oxygen released from a molten product of the metal particles to be absorbed by the metal oxide particles; and

[0062] cooling the mold and then collecting a composite material comprising the inorganic particles and a matrix metal which binds the inorganic particles.

[0063] [2]A method for producing a composite material comprising the steps of:

[0064] heating contents at least comprising at least one type of inorganic particles composed of a material selected from the group consisting of diamond, boron nitride, graphite, SiC, AlN, Si3N4, B4C, MgB2, Mg3N2, MgCl2, CaCl2, Mg2Si, carbon fibers, carbon nanotubes, TiC, WC, and TaC; metal particles; and metal oxide particles having oxygen defects to a temperature higher than a melting point of the metal particles in a mold filled with the contents, to melt the metal particles;

[0065] allowing oxygen released from a molten product of the metal particles to be absorbed by the metal oxide particles; and

[0066] cooling the mold and then collecting a composite material comprising the inorganic particles and a matrix metal which binds the inorganic particles.

[0067] [3] The method for producing a composite material according to [1] or [2], wherein the inorganic particles are diamond particles.

[0068] [4] The method for producing a composite material according to [3], wherein the diamond particles comprise a coated layer composing an outermost layer of the diamond particles.

[0069] [5] The method for producing a composite material according to [4], wherein the coated layer is a titanium coated layer.

[0070] [6] The method for producing a composite material according to any one of [1] to [5],

[0071] wherein the contents filled in the mold comprise a first layer and a second layer formed on the first layer,

[0072] wherein the first layer comprises the inorganic particles; and the second layer comprises the metal particles and the metal oxide particles.

[0073] [7] The method for producing a composite material according to [6], wherein in the step of melting the metal particles, when the molten product of the metal particles enters the first layer, at least some of the metal oxide particles remain on the first layer.

[0074] [8] The method for producing a composite material according to [7], further comprising a step of removing at least some of the metal oxide particles remaining on the surface layer part of the composite material collected from the mold.

[0075] [9]A composite material comprising at least one type of inorganic particles selected from the group consisting of diamond particles and boron nitride particles; a matrix metal which binds the inorganic particles; and metal oxide particles,

[0076] wherein an oxygen content is higher than 0.1 mass % and a thermal conductivity is 300 W / m·K or more at room temperature.

[0077]

[10] The composite material according to [9], wherein the metal oxide particles are at least one type selected from the group consisting of titanium oxide particles, cerium oxide particles, calcium titanate particles, and niobium oxide particles.

[0078]

[11] The composite material according to [9], wherein the metal oxide particles are perovskite-type oxide particles.EXAMPLES

[0079] The present disclosure is explained in more detail with examples and comparative examples below. It should be noted that the present invention is not limited to the following examples.

[0080] Following materials were prepared as the inorganic particles, the metal particles, the metal oxide particles, and the additive.(1) Inorganic ParticlesDiamond particles

[0082] Average particle size: 50 μm(2) Metal ParticlesSilver and copper alloy particles

[0084] Composition: Silver and copper alloy (silver: 72 mass %, copper: 28 mass %)

[0085] Average particle diameter: 5 μm

[0086] Melting point: 780° C.(3) Metal Oxide ParticlesTitanium oxide particles A (average particle diameter: 45 μm)

[0088] Titanium oxide particles B (average particle diameter: 2 μm)

[0089] Cerium oxide particles (average particle diameter: 1 μm)

[0090] Calcium titanate particles (average particle diameter: 1 μm)

[0091] Niobium oxide particles (average particle diameter: 1 μm)(4) AdditiveTitanium hydride particles (average particle diameter: 5 μm)

[0093] It should be noted that “average particle diameter” used in the present disclosure indicates a median diameter D50 obtained from a particle diameter distribution of particles, and the median diameter D50 indicates a particle diameter with the cumulative volume reaching at 50% from the small particle diameter side in the particle diameter distribution obtained by laser diffraction method.Example 1

[0094] Mixing 44 parts by volume of the diamond particles with 2 parts by volume of the titanium hydride particles obtained a first mixed powder. Meanwhile, mixing 54 parts by volume of the metal particles with 0.6 parts by volume of the titanium oxide particles A obtained a second mixed powder. The first mixed powder (46 parts by volume) was firstly added to a mold of 0.3 cc volume to form a first layer in the mold. Then, the second mixed powder (54 parts by volume), which was separately press molded under 200 MPa, was added to form a second layer on the first layer.

[0095] While operating a vacuum pump connected to the inside of the mold to vacuum the inside of the mold, the temperature inside the mold was increased to 600° C. and was kept at 600° C. for 10 minutes. By doing this, oxygen was released from the titanium oxide particles, and the oxygen released from the titanium oxide particles was discharged to the outside of the mold. Then, after increasing the temperature inside the mold from 600° C. to 780° C., the mold was sealed, and the contents were heated at 950° C. for 10 minutes. By doing this, the metal particles were melted, and the oxygen released from the molten product of the metal particles was absorbed by the titanium oxide particles. After decreasing the temperature inside the mold, a composite material for the example was collected from the mold. The resulting composite material had a diameter of 30 mm and a thickness of about 0.4 mm.Example 2

[0096] Apart from using the titanium oxide particles B instead of the titanium oxide particles A and mixing 54 parts by volume of the metal particles with 0.3 parts by volume of the titanium oxide particles B to obtain the second mixed powder, a composite material for the example was produced similarly to the example 1.Example 3

[0097] Apart from mixing 44 parts by volume of the diamond particles with 0.6 parts by volume of the titanium oxide particles A to obtain the first mixed powder and mixing 54 parts by volume of the metal particles with 2 parts by volume of the titanium hydride particles to obtain the second mixed powder, a composite material for the example was produced similarly to the example 1.Example 4

[0098] Apart from subjecting the titanium oxide particles A to reduction treatment in advance, a composite material for the example was produced similarly to the example 3. It should be noted that the titanium oxide particles A were heated at 1,000° C. for 4 hours under vacuum atmosphere to subject the titanium oxide particles A to reduction treatment.Example 5

[0099] Apart from using the cerium oxide particles instead of the titanium oxide particles A as the reduction treated metal oxide particles and mixing 44 parts by volume of the diamond particles with 0.6 parts by volume of the cerium oxide particles to obtain the first mixed powder, a composite material for the example was produced similarly to the example 4. It should be noted that the cerium oxide particles were heated at 1,000° C. for 8 hours under vacuum atmosphere to subject the cerium oxide particles to reduction treatment.Example 6

[0100] Apart from using the calcium titanate particles instead of the titanium oxide particles A as the reduction treated metal oxide particles and mixing 44 parts by volume of the diamond particles with 0.5 parts by volume of the calcium titanate particles to obtain the first mixed powder, a composite material for the example was produced similarly to the example 4. It should be noted that the calcium titanate particles were heated at 1,200° C. for 8 hours under vacuum atmosphere to subject the calcium titanate particles to reduction treatment.Example 7

[0101] Apart from using the niobium oxide particles instead of the titanium oxide particles A as the reduction treated metal oxide particles and mixing 44 parts by volume of the diamond particles with 0.2 parts by volume of the niobium oxide particles to obtain the first mixed powder, a composite material for the example was produced similarly to the example 4. It should be noted that the niobium oxide particles were heated at 1,000° C. for 8 hours under vacuum atmosphere to subject the niobium oxide particles to reduction treatment.Comparative Example 1

[0102] Apart from using the metal particles as such instead of the second mixed powder, a composite material for the comparative example was obtained similarly to the example 1. In other words, while operating the vacuum pump connected to the inside of the mold to vacuum the inside of the mold, the temperature inside the mold was increased to 600° C. and was kept at 600° C. for 10 minutes. Then, after increasing the temperature inside the mold from 600° C. to 780° C., the mold was sealed, and the contents were heated at 950° C. for 10 minutes. After decreasing the temperature inside the mold, a composite material for the comparative example was collected from the mold.[Measurement of Oxygen Content]

[0103] The composite materials for the examples and the comparative example were broken into small pieces, and a total weight of about 0.1 g was provided as a test piece for each measurement. The oxygen concentration of the test piece was measured using an oxygen / nitrogen analyzer (EMGA-930 manufactured by HORIBA, Ltd.) under the heating condition of a furnace temperature at 2,400° C. for 110 seconds. Tables 1 and 2 indicate the average values of the three test pieces for each of the examples and the comparative example.[Measurement of Thermal Conductivity]

[0104] A test piece (size: 30 mm diameter and 0.3 mm thickness) was produced from each of the composite materials for the examples and the comparative example. A thermal diffusion coefficient of the test piece at room temperature (25° C.) was measured by temperature wave method using a thermal diffusion coefficient measuring device (TA35 manufactured by Bethel Co., Ltd.) to calculate thermal conductivity of the test piece. Tables 1 and 2 indicate the average values of the three test pieces for each of the examples and the comparative example.TABLE 1ExampleExampleExampleExample1234Mixing ratio forDiamond particles44444444raw materialTitanium hydride particles2222powdersMetal particles54545454[parts by volume]Metal oxideTitanium oxide particles A0.6—0.60.6particlesTitanium oxide particles B—0.3——Oxygen content [mass %]0.110.110.300.33Thermal conductivity [W / m · K]600612632635TABLE 2ExampleExampleExample Comparative567example 1Mixing ratio forDiamond particles44444444raw materialTitanium hydride particles2222powdersMetal particles54545454[parts by volume]Metal oxideCerium oxide particles0.6———particlesCalcium titanate—0.5——particlesNiobium oxide——0.2—particlesOxygen content [mass %]0.220.290.150.12Thermal conductivity [W / m · K]630662618578REFERENCE SIGNS LIST1: inorganic particle, 3, 3A: metal oxide particle, 5: matrix metal, 5p: metal particle, 7, 7A: contents, 10, 20, 30: composite material, 20a, 20b: surface, 50: mold, L1: first layer, L2: second layer, R3: region

Claims

1. A method for producing a composite material comprising the steps of:at least filling a mold with at least one type of inorganic particles composed of a material selected from the group consisting of diamond, boron nitride, graphite, SiC, AlN, Si3N4, B4C, MgB2, Mg3N2, MgCl2, CaCl2), Mg2Si, carbon fibers, carbon nanotubes, TiC, WC, and TaC; metal particles; and metal oxide particles;heating contents comprising the inorganic particles, the metal particles, and the metal oxide particles in the mold in reducing atmosphere to a temperature lower than a melting point of the metal particles to release oxygen from the metal oxide particles;discharging the oxygen released from the metal oxide particles to the outside of the mold;heating the contents in the mold to a temperature higher than the melting point of the metal particles to melt the metal particles;allowing the oxygen released from a molten product of the metal particles to be absorbed by the metal oxide particles; andcooling the mold and then collecting a composite material comprising the inorganic particles and a matrix metal which binds the inorganic particles.

2. A method for producing a composite material comprising the steps of:heating contents at least comprising at least one type of inorganic particles composed of a material selected from the group consisting of diamond, boron nitride, graphite, SiC, AlN, Si3N4, B4C, MgB2, Mg3N2, MgCl2, CaCl2), Mg2Si, carbon fibers, carbon nanotubes, TiC, WC, and TaC; metal particles; and metal oxide particles having oxygen defects to a temperature higher than a melting point of the metal particles in a mold filled with the contents, to melt the metal particles;allowing oxygen released from a molten product of the metal particles to be absorbed by the metal oxide particles; andcooling the mold and then collecting a composite material comprising the inorganic particles and a matrix metal which binds the inorganic particles.

3. The method for producing a composite material according to claim 1, wherein the inorganic particles are diamond particles.

4. The method for producing a composite material according to claim 3, wherein the diamond particles comprise a coated layer composing an outermost layer of the diamond particles.

5. The method for producing a composite material according to claim 4, wherein the coated layer is a titanium coated layer.

6. The method for producing a composite material according to claim 1,wherein the contents filled in the mold comprise a first layer and a second layer formed on the first layer,wherein the first layer comprises the inorganic particles; and the second layer comprises the metal particles and the metal oxide particles.

7. The method for producing a composite material according to claim 6, wherein in the step of melting the metal particles, when the molten product of the metal particles enters the first layer, at least some of the metal oxide particles remain on the first layer.

8. The method for producing a composite material according to claim 7, further comprising a step of removing at least some of the metal oxide particles remaining on the surface layer part of the composite material collected from the mold.

9. A composite material comprising at least one type of inorganic particles selected from the group consisting of diamond particles and boron nitride particles; a matrix metal which binds the inorganic particles; and metal oxide particles,wherein an oxygen content is higher than 0.1 mass % and a thermal conductivity is 300 W / m·K or more at room temperature.

10. The composite material according to claim 9, wherein the metal oxide particles are at least one type selected from the group consisting of titanium oxide particles, cerium oxide particles, calcium titanate particles, and niobium oxide particles.

11. The composite material according to claim 9, wherein the metal oxide particles are perovskite-type oxide particles.

12. The method for producing a composite material according to claim 2, wherein the inorganic particles are diamond particles.

13. The method for producing a composite material according to claim 12, wherein the diamond particles comprise a coated layer composing an outermost layer of the diamond particles.

14. The method for producing a composite material according to claim 13, wherein the coated layer is a titanium coated layer.

15. The method for producing a composite material according to claim 2,wherein the contents filled in the mold comprise a first layer and a second layer formed on the first layer,wherein the first layer comprises the inorganic particles; and the second layer comprises the metal particles and the metal oxide particles.

16. The method for producing a composite material according to claim 15, wherein in the step of melting the metal particles, when the molten product of the metal particles enters the first layer, at least some of the metal oxide particles remain on the first layer.

17. The method for producing a composite material according to claim 16, further comprising a step of removing at least some of the metal oxide particles remaining on the surface layer part of the composite material collected from the mold.

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