JPH11130537A - Production of carbon composite material of particulate-dispersed type - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently produce a carbon composite material having high purity and strengthened with dispersed fine metal carbide grain having a particle diameter equal to or smaller than the preferred one at low cost by previously blending raw material powder having carbon as a matrix phase with metal oxide powder, and molding and calcining the blended product, followed by impregnating pitch into the calcined product and then calcining again the impregnated product. SOLUTION: This carbon composite material is prepared by adopting natural graphite, artificial graphite, coke powder, charcoal powder or the like, having a particle diameter of 5-200 μm as carbon materials and by usually blending the metal oxide powder into raw material powder having carbon materials as a matrix phase so as to make the metal carbide content in the carbon composite material come to the range of <=10 vol.%. Particle diameter of metal oxide is preferably in the range of about 0.2-1 μm. The uniform dispersion of fine metal oxide grain into carbon material powder is conducted by ball milling, attrition blending or the like using such a solvent as methyl alcohol, ethyl alcohol, acetone or the like. The usual blending portion of carbon material powder is 80-95 wt.% and that of fine metal oxide grain is 20-5 wt.%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for efficiently producing a high-performance carbon composite material.

[0002]

2. Description of the Related Art Carbon materials are self-lubricating (low friction),
Because of its excellent properties such as heat resistance, corrosion resistance and electric conductivity, it is used in various industrial fields. Sliding members, which are one of the typical applications, are widely used as brushes and bearings for electric motors. In addition,
Known applications include refractories utilizing heat resistance and corrosion resistance, furnace wall materials, applications in the field of nuclear power, and applications as arc furnace electrodes utilizing electrical conductivity.

[0003] However, although carbon materials are used in a wide range of fields, in terms of strength and wear resistance,
Inferior to metal and ceramic materials. Therefore, improvement of these characteristics is extremely important because it leads to downsizing of members, improvement of service life, and the like.

[0004] It is known that dispersion of fibers or second phase particles is effective for improving the performance of carbon materials.
For example, a carbon fiber / carbon composite material in which high-strength carbon fiber is composited is known as a C / C composite material, and has a higher specific strength (= strength / density) than a conventional metal material. Its use in the aerospace field is expanding. One example of its practical application is a brake shoe for a large aircraft for transportation.

[0005] Various attempts have been made to form a composite by dispersing the second phase particles in a carbon material for strengthening. However, although the addition of the dispersed particles improves the abrasion resistance of the composite material, the additive particles are destroyed. As a source, there is a case where the strength of the material is rather lowered. Therefore, in order to simultaneously improve the strength and wear resistance of the carbon material due to the presence of the second phase particles,
It is necessary to add a required amount of fine second phase particles that do not cause a decrease in strength. In order to achieve high strength, it is necessary to add fine second phase particles having an average particle size of 1 μm or less. As the second phase particles, since the parent phase is a carbon material, high-purity metal carbides such as tungsten carbide, titanium carbide, and silicon carbide which are stable without being changed even during the manufacturing process of the predetermined member are suitable. It is assumed that

[0006] However, it is technically extremely difficult to produce fine high-purity metal carbide particles at low cost. In addition, the smaller the particle size of the metal carbide particles becomes, the more difficult it is to disperse in the matrix carbon material due to agglomeration and the like. Therefore, it is technically difficult to uniformly mix the metal carbide particles with the matrix carbon material. Further, the surface of fine particles having an extremely large surface area is easily oxidized during the manufacturing process. Therefore, it is practically impossible to compound a carbon material with fine metal carbide particles having high purity.

[0007]

Accordingly, an object of the present invention is to provide a more efficient and inexpensive method for producing a carbon composite material dispersed and strengthened by high-purity fine metal carbide particles. The main purpose is.

[0008]

Means for Solving the Problems The present inventor has conducted various studies to achieve the above object, and as a result, paid attention to the reactivity between metal oxide and carbon. Then, when firing a molded body made of a carbon material powder mixed with metal oxide fine particles, the metal oxide particles and the carbon material powder react to form fine metal carbide fine particles, and as a result, The present inventors have found that a carbon composite material dispersion-reinforced by metal carbide fine particles can be efficiently produced, and have completed the present invention.

That is, the present invention provides the following method for producing a metal carbide particle dispersed material; The raw material powder of the matrix carbon and at least one metal oxide are pre-mixed, molded, fired, impregnated with pitch in a fired body, and fired again, the average particle diameter of 1 μm or less A method for producing a carbon composite material containing the metal carbide particles dispersedly contained as reinforcing particles.

[0010] 2. Item 2. The method for producing a carbon composite material according to Item 1, wherein the metal oxide powder is mixed with the matrix carbon material raw material powder such that the content of the metal carbide in the carbon composite material is 10% by volume or less.

[0011]

DETAILED DESCRIPTION OF THE INVENTION The present invention utilizes the reactivity between metal oxide and carbon. That is, a reaction is used in which the metal oxide fine particles mixed in the carbon material powder react with the carbon material powder at a high temperature to reduce the metal oxide to generate a metal carbide.

The carbon material is not particularly limited, and may be natural graphite, petroleum artificial graphite, coal artificial graphite, coke powder,
Charcoal powder is exemplified. The carbon material powder is pulverized when mixed with the metal oxide fine particles, and is not particularly limited. However, it is usually in a range of about 5 to 200 μm, and more preferably in a range of about 5 to 120 μm. In addition, the particle diameter of various particles in the present specification is a value measured by a laser scattering method.

The metal oxide used in the present invention may be selected according to the reactivity with the carbon material, the use of the carbon composite material, etc., and is not particularly limited. Examples include tungsten, niobium oxide, silicon oxide, zirconium oxide, hafnium oxide, tantalum oxide, molybdenum oxide, and vanadium oxide. These metal oxides form corresponding metal carbides by reaction with the carbon material. The particle size of the metal oxide is preferably about 0.2 to 1 μm. If the particle size of the metal oxide particles is too large, the particle size of the carbide generated by firing becomes coarse, whereas if it is too small, uniform mixing with the carbon material powder becomes difficult. The metal oxides may be used alone or in combination of two or more.

The metal oxide fine particles can be uniformly dispersed in the carbon material powder by a conventional method such as a ball mill mixing method or an attrition mixing method using a liquid medium such as methyl alcohol, ethyl alcohol or acetone. The ratio between the carbon material powder and the metal oxide fine particles varies depending on the type of the carbon material and the metal oxide used, the use of the carbon composite material, and the like.
About 80-95% and metal oxide fine particles about 20-5%,
More preferably, the former is about 90 to 95% and the latter is about 10 to 5%.

After the dispersing operation is completed, the mixture is dried in a hot-air drying oven or the like, and then the dried mass is crushed and sieved to obtain a mixed powder for molding. The particle size of the mixed powder for molding is usually about 300 μm to 1 mm.

Alternatively, a mixed powder having a predetermined particle size can be obtained by spray-drying a slurry containing a liquid medium after the above-described dispersion operation.

Next, the obtained mixed powder for molding is mixed with a binder and molded. As the binder, coal tar, coal tar pitch, petroleum pitch, or a synthetic resin (a phenol resin, a furan resin, or the like) that is commonly used in molding a carbon material may be used. The amount of the binder is usually about 5 to 30% of the weight of the mixed powder for molding,
More preferably, it is about 5 to 10%. The molding method is not particularly limited, and examples thereof include mold molding, rubber press (hydrostatic pressure molding), and extrusion molding. The molding may be performed by a two-stage molding method including primary molding (for example, mold molding) and secondary molding (for example, hydrostatic pressure molding).

Next, the obtained molded body is fired (primary sintering) in a non-oxidizing atmosphere. Primary firing conditions are more different, such as the type of metal oxide used, but are usually 700-1300
It is in the range of about 700C, more preferably in the range of about 700-1000C. By this firing, the carbon material reacts with the metal oxide to form a metal carbide, and the binder is thermally decomposed and removed. As a result, a porosity having a communication hole with the outside air is about 30 to 45%, more preferably
A primary sintered body of about 30 to 35% is obtained.

Next, after the primary sintered body is impregnated with the pitch, it is fired again. The amount of the pitch impregnated into the primary sintered body may be appropriately selected according to the raw material particle size, the porosity depending on the molding conditions, the use of the final product, and the like, but is usually 20 to 40% of the weight of the primary sintered body. Degree, more preferably 20 to
It is about 30%.

Next, the primary sintered body impregnated with the pitch is sintered again (secondary sintering). Secondary sintering is 1000 ~ 1400 ℃
It is performed at a temperature of the order of magnitude and higher than the primary sintering temperature. As a result, a secondary sintered body having a porosity of about 15 to 30%, more preferably about 15 to 20%, having continuous air holes with the outside air is obtained. In order to further improve the properties such as strength and wear resistance of the sintered body, pitch impregnation and sintering may be further repeated (higher order sintering). Alternatively, a graphitized composite material can be obtained by sintering a secondary or higher-order sintered body at a higher temperature.

In the present invention, a predetermined amount of metal oxide fine particles are uniformly mixed in advance with a carbon material raw material powder to be a matrix. Next, in the firing process of the mixture, a reaction (internal reaction) between the metal oxide fine particles and the carbon material powder occurs in the matrix carbon, and the desired metal carbide particles are uniformly dispersed in the matrix carbon. Generated by The use of the metal carbide fine particles generated by the internal reaction as the reinforcing particles of the carbon composite material has been realized for the first time by the present invention. Therefore, in the present invention, unlike the prior art, it is not necessary to mix the metal carbide fine particles prepared in advance and the matrix phase carbon material powder, and then fire them. In addition, since high-purity metal carbide fine particles are formed in one stage of the firing process of the matrix carbon material, the method is efficient as a method for producing a carbon composite material.

In this reaction, when titanium oxide is used as the metal oxide fine particles, the following reaction formula is used.
Titanium carbide is produced. TiO ₂ + 3C → TiC + 2CO When tungsten oxide is used, tungsten carbide is produced by the following reaction formula. WO ₃ + 4C → WC + 3CO The method of the present invention The particle size of the metal carbide particles generated by
It is almost the same as or slightly smaller than the metal oxide particles as the raw material. Since many types of metal oxides having a particle size of 1 μm or less are commercially available, by using this kind of commercially available raw material, a carbon composite material dispersed and strengthened by metal carbide fine particles having a particle size of 1 μm or less can be easily obtained. Can be manufactured.

In the conventional carbon material-metal carbide mixing method,
In view of the fact that metal carbide particles having a particle size of 1 μm or less are extremely expensive, and that it was difficult to prevent surface oxidation during the pulverization process and contamination of impurities from a pulverization jig and the like, the present invention The usefulness of is obvious.

The effect of improving the strength of the carbon material by dispersing the second-phase metal carbide fine particles having a particle size of 1 μm or less is because the matrix carbon material and the metal carbide particles have different coefficients of thermal expansion, so that the high temperature during the production is reduced. During the cooling process, a local residual stress field is generated around the particle.
The residual stress field acts to suppress the growth of defects with respect to minute defects that cause destruction. That is, even at a stress level at which defects usually grow easily and brittle fracture occurs, the residual stress field around the particles prevents the overall stress, particularly the stress concentration at the defect tip, so that the growth of defects is suppressed. You. As a result, the fracture toughness of the carbon material can be improved, and the brittle fracture load is also improved. That is, the fracture strength is improved by improving the fracture toughness. On the other hand, when the particle is large, a grain boundary between the particle and the matrix carbon material becomes a fracture source, and conversely, the strength of the carbon material is reduced.

Further, the effect of improving the wear resistance of the carbon material according to the present invention is that the residual stress field around the fine second phase particles prevents the detachment of the matrix carbon material particles due to friction and has a high hardness. This is because the metal carbide improves the hardness as a material.

[0026]

According to the present invention, it has become possible to economically produce a high-performance carbon composite material having excellent strength, fracture toughness, abrasion resistance and the like. As a result, the field of application of the carbon composite material is expanded, and effects such as miniaturization of various members and improvement of the life of the members are achieved.

[0027]

The following examples are provided to further clarify the features of the present invention.

Example 1 10% by volume of titanium carbide (Ti) was added to a carbon powder (particle size: 5 to 20 μm) made from petroleum coke by an internal reaction during firing.
To produce C), titanium oxide particles having an average particle size of 1.1 μm were mixed (carbon: TiO = 77: 23, weight ratio), and mixed for 24 hours by a ball mill using ethyl alcohol as a medium. The obtained homogeneous mixture was filtered, dried with hot air, and sieved to obtain a granulated mixture having a particle size of 300 to 500 µm.

Next, 20% by weight of petroleum pitch was added as a binder to the obtained granules, and the mixture was subjected to primary molding (pressure: 100 kgf / cm ² ) with a mold, and the obtained primary molded body was placed in a vacuum bag. By performing secondary molding at 3000 kgf / cm ² , a disk-shaped sample having a thickness of 8 mm × a diameter of 35 mm and a density of 1.8 g / cm ³ was obtained.

Next, the disk-shaped sample was fired in a nitrogen atmosphere at 1000 ° C. for 5 hours to obtain a primary sintered body having a density of 1.5 g / cm ³ .

Next, the primary sintered body was placed in an autoclave, impregnated with pitch at 250 ° C. and 100 kgf / cm ² , and then baked at 1200 ° C. for 1 hour to obtain a density of 1.7 g / cm ^3.
Was obtained (carbon composite material).

A part of the obtained carbon composite material is pulverized,
Using a powder obtained by passing through a mesh of 0 mesh, the structure was examined by an X-ray diffraction method.
Only the diffraction peak of titanium carbide was observed other than the matrix carbon, and it was found that the internal reaction had progressed completely as expected.

Further, a part of the obtained carbon composite material was embedded in resin, and after final lapping with 1 μm diamond by an automatic polishing machine, the fine structure was observed with a scanning electron microscope. Like, average particle size 0.8
It was found that μm titanium carbide particles were dispersed in the matrix carbonaceous material structure.

The bending strength of the carbon composite material according to the present embodiment,
Surface pressure 200 g / cm ² by Shore hardness and sliding wear tester
Table 1 shows the amount of wear per 1000 m measured in the above. In addition,
Table 1 also shows the same test results for the carbon composite materials obtained in Example 2 and Comparative Examples 1 to 4.

Comparative Example 1 10% by volume of titanium carbide having an average particle size of 5 μm was mixed with the same carbon powder as in Example 1 in a ball mill using ethyl alcohol as a medium. The carbon composite material was obtained by sequentially molding and firing according to the procedure.

Comparative Example 2 The same carbon powder as in Example 1 was molded and fired in the same procedure as in Example 1 to obtain a carbon material.

Example 2 Oxidation with an average particle size of 0.65 μm was performed on carbon powder (particle size: 5 to 20 μm) using natural graphite as a raw material so as to produce 10% by volume of silicon carbide by an internal reaction during firing. Silicon was mixed with a ball mill (carbon: SiO ₂ = 82: 18, weight ratio) and mixed with ethyl alcohol as a medium by a ball mill for 24 hours.

Using the mixed powder thus obtained, molding, primary baking, pitch impregnation, secondary baking and the like were sequentially performed in the same procedure as in Example 1 to obtain a carbon composite material.

When the structure of the obtained carbon composite material was examined by an X-ray diffraction method, only the diffraction peak of silicon carbide was observed except for the matrix carbon, and as expected, the internal reaction completely proceeded. I knew it was there.

Further, when the microstructure of the obtained carbon composite material was examined by an electron microscope, it was found that silicon carbide particles having an average particle diameter of 0.8 μm were dispersed in the structure of the matrix carbon material.

Comparative Example 3 10% by volume of silicon carbide having an average particle diameter of 5 μm was mixed with the same carbon powder as in Example 2 using ethyl alcohol as a medium in a ball mill, and the resulting mixture was subjected to the same method as in Example 2. The carbon composite material was obtained by sequentially molding and firing according to the procedure.

Comparative Example 4 The same carbon powder as in Example 2 was molded and fired in the same procedure as in Example 2 to obtain a carbon material.

[0043]

[Table 1]

[Brief description of the drawings]

FIG. 1 is a drawing-substituting electron micrograph showing the fine structure of the carbon composite material obtained in Example 1.

Claims (2)

[Claims] The present invention is characterized in that the raw material powder of the matrix carbon and at least one kind of metal oxide particles are preliminarily mixed, molded, fired, then impregnated with pitch in a fired body and fired again. And a method for producing a carbon composite material in which metal carbide particles having an average particle size of 1 μm or less are dispersed and contained as reinforcing particles. 2. The content of a metal carbide in a carbon composite material is as follows:
2. The method for producing a carbon composite material according to claim 1, wherein the metal oxide powder is mixed with the matrix carbon material raw material powder so as to be 10% by volume or less.