JPH0333064A - Powder composition for producing carbon/silicon carbide composite material, production of carbon/silicon carbide composite material and carbon/silicon carbide composite material - Google Patents

Abstract

PURPOSE:To improve moldability and sinterability and to improve density, bending strength, etc., by compounding >=1 kinds of sintering assistant powders selected from a group of boron (compd.) with a mixture composed of the fine particles of a self- sinterable spheroidal carbonaceous material and SiC powder. CONSTITUTION:The mixture (C) is obtd. by compounding 5 to 30 pts.wt. fine particles (A) of the self-sinterable spheroidal carbonaceous material which are mesocarbon microbeads of <=20mum average grain size contg. >=5wt.% binder component (beta-resin) made from a coal tar as a raw material and 95 to 70 pts.wt. SiC powder (B) having <=1mum average grain size. The powder compsn. (D) for producing the C/SiC composite material is then produced by mixing 100 pts.wt. component C and 0.5 to 5 pts.wt. sintering assistant powders of <=1mum average size selected from metal B, B4C, etc., for 30 minutes to one hour by a dry process. The component D is subjected to a pressurized molding and is temporally calcined in an nonoxidative atmosphere, following which the molding is subjected to regular calcination for 0.2 to 3 hours at 1900 to 2400 deg.C in a gaseous N2 atmosphere, by which the C/SiC composite material having >=20kgf/mm<2> bending strength is produced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a composition for producing a carbon-silicon carbide composite material and a carbon-silicon carbide composite material obtained using the composition.

Prior Art and its Problems Various methods have been proposed for producing composite materials made of carbon materials and ceramics, among which many use silicon carbide as the ceramic.

Silicon carbide is a ceramic that is difficult to sinter, and it is known that the presence of small amounts of boron and carbon promotes sintering, but if one or both are in excess, sintering may be accelerated. As a result, only low-strength materials can be obtained. Therefore, a large amount of carbonaceous content (for example, 10% by weight or more)
It is usually difficult to obtain a carbon-silicon carbide sintered body containing carbon and having high mechanical strength. That is, the obtained carbon-silicon carbide sintered body is mainly composed of silicon carbide or carbonaceous material, and its use is almost limited to sliding materials.

Conventionally, methods for manufacturing composite materials in which graphite is dispersed in silicon carbide have been proposed (for example, Japanese Patent Application Laid-Open No.
-131577). However, the method disclosed herein involves kneading a binder (such as a phenolic resin), carbon powder, and a dispersion medium, and although the process is complicated and requires a long time, the carbon powder is The problem is that it is difficult to disperse.

Furthermore, in order to uniformly disperse carbon powder, a method has been proposed in which raw coke powder and silicon carbide are mixed and ground (Japanese Patent Laid-Open No. 59-213674). However, even in this method, it is necessary to carry out mixing and grinding for a long time (5 hours in the example), and it lacks practicality. Furthermore, the bending strength of the obtained carbon-silicon carbide sintered body is 11
There is also a practical problem in that it is as low as about kg f/mm2.

A method of producing a carbon-silicon carbide sintered body using bulk mesophase powder without using a binder has also been proposed (Japanese Patent Application Laid-Open No. 61-275166), but this also has low bending strength ( In the examples, 14,
2 kgf/ff1m2) is a difficult point.

Means for Solving the Problems As a result of repeated research in view of the current state of the technology as described above, the present inventor found that the surface is covered with a viscous component (β-resin) and the particle size is uniform. When using spherical carbonaceous fine particles (e.g., mesocarbon microbeads; hereinafter referred to as MCMB) having self-sintering properties as a carbon raw material, conventional techniques for producing carbon-silicon carbide sintered bodies are used. It has been found that the problems can be practically eliminated or greatly reduced.

That is, the present invention provides the following powder composition for producing a carbon-silicon carbide composite material and a method for producing a carbon-silicon carbide composite material: ■ A composition for producing a carbon-silicon carbide composite material. A total of 100 parts of (a) 5 to 30 parts by weight of self-sintering spherical carbonaceous fine particles and (b) 95 to 70 parts by weight of silicon carbide powder.
(c) 0.5 of at least one sintering aid powder selected from the group consisting of boron and compounds thereof, based on part by weight;
A powder composition containing ~5 parts by weight.

■ In the composition for producing a carbon-silicon carbide composite material described in the above item ■, (a) the self-sintering spherical carbonaceous fine particles are mesocarbons made from coal tar and having an average particle size of 20 tt m or less; A powder composition which is microbeads, (b) silicon carbide powder having an average particle size of 1 μm or less, and (c) sintering aid powder comprising boron carbide having an average particle size of 1 μm or less.

■(a) 5 to 30 parts by weight of self-sintering spherical carbonaceous fine particles and (b) 95 to 70 parts by weight of silicon carbide powder, total 10
(c) at least one sintering aid powder selected from the group consisting of boron and compounds thereof;
A method for producing a carbon-silicon carbide composite material, which comprises molding a powder composition containing 5 to 5 parts by weight and firing it in an inert atmosphere.

■(a) 5 to 30 parts by weight of self-sintering spherical carbonaceous fine particles and (b) 95 to 70 parts by weight of silicon carbide powder, total 10
(c) at least one sintering aid powder selected from the group consisting of boron and its compounds, based on 0 parts by weight
A carbon-silicon carbide composite material obtained by molding and firing a powder composition containing 5 parts by weight.

(2) The carbon-silicon carbide composite material according to item (2) above, which has a bending strength of 20 kgf/mu2 or more.

As long as the surface of the spherical carbonaceous fine particles used in the present invention is covered with a viscous component (β-resin) that acts as a binder, and as a result has self-sintering properties,
Regardless of its origin, examples include those manufactured using coal tar, coal tar pitch, petroleum pitch, etc. as raw materials.

The average particle diameter of the spherical carbonaceous fine particles is preferably within a range of 20 μm or less. If the average particle size exceeds 20 μm, the graphite particles of the sintered body become large and the strength decreases, which is not preferable. Among the various types of carbonaceous particles, coal tar-based MCMB has a higher carbonization yield than petroleum-based MCMB, is close to a perfect sphere, and has a uniform particle size, so the structure of the sintered body is uniform. It is more preferable because its mechanical strength is further enhanced. That is, in the sintered body, S
Because the graphite dispersed in iC (which is produced from MCMB) is spherical, the stress at the graphite-5iC interface is evenly distributed, thereby increasing its strength. MCBC is also preferable because it has a significantly higher carbonization yield (80% or more) than phenol resins, generates fewer pores, and forms a high-density sintered body. From the viewpoint of moldability, MCMB preferably contains 5% or more of a viscous component (β-resin);
% or more is particularly preferred.

The average particle size of the silicon carbide powder is preferably 1 μm or less. When it exceeds 1 μm, sintering does not proceed quickly and abnormal grain growth tends to occur before sintering sufficiently proceeds.

Since silicon carbide is a covalently bonded ceramic material that is difficult to sinter, in the present invention, at least one of powders of boron and compounds thereof is used as a sintering aid. Boron and its compounds include metal B, B4
Examples include C, BN, TiB2, WB, NiB, and CoB, with 84C being particularly preferred. The average particle size of the sintering aid is preferably 1 μm or less. If it exceeds 1 μm, it is not suitable because it becomes difficult to function effectively as a sintering aid and silicon carbide is not dispersed in the powder.

When boron or a compound thereof is used as a sintering aid, it also promotes graphitization of carbonaceous fine particles, so that the sliding properties of the obtained sintered body are particularly improved. At this time, boron carbide and boron nitride are also generated in the sintered body, but
These also contribute to improving sliding characteristics.

In the composition of the present invention, sintering aid powder is added to a total of 100 parts by weight of 5 to 30 parts by weight of MCMB and 95 to 70 parts by weight of silicon carbide powder. It is preferable to mix about 5 to 5 parts by weight.

The composition for producing carbon-silicon carbide composite material of the present invention is
It can be easily prepared by dry mixing the above-mentioned spherical carbonaceous fine particles, silicon carbide powder, and sintering aid powder for a short time (about 30 minutes to 1 hour, depending on the amount). That is,
When a binder is used, a uniform powder composition can be obtained in a shorter time than when raw coke is used as a carbon source.

In order to produce a carbon-silicon carbide composite material using the composition according to the invention, the composition may be pressure molded and the molded body sintered in an inert atmosphere.

Molding and sintering may be carried out according to conventional methods, and the conditions are not particularly limited. For example, molding can be done at room temperature (
(or under heating if necessary) 5-30kgf/ll1m
Do this with about 2 degrees of pressure. As a molding device, any device such as a rubber press, CIP, HIP, etc. can be used. In addition, sintering can be performed using, for example, nitrogen, argon,
0.0 at a temperature of about 600 to 1400°C at normal pressure (or under pressure if necessary) in an inert gas atmosphere such as helium.
After calcination for about 5 to 2 hours, main firing is performed at a temperature of about 1900 to 2400° C. for about 0.2 to 3 hours. These molding and sintering conditions should be selected or modified as appropriate depending on the composition of the composition, the shape of the product, the performance required of the product, etc., and are of course not limited to the above ranges. do not have.

In the present invention, when N2 is used as the non-oxidizing atmospheric gas, at least 50% of 84C is converted to BN. Even if this material is used as a sliding material, its properties will not be impaired. The composite material usually has a bulk density of 80% or more of the theoretical density and 15 kgf/m
It has a bending strength of m2 or more, and furthermore, a bulk density of 90% or more of the theoretical density and a bending strength of 20 kgf/mm2 or more can be obtained.

The carbon-silicon carbide composite material according to the present invention can be used for mechanical parts such as bearings, mechanical seals, and molds; valves, heat exchanger parts; crucibles, electrodes, and heating elements (far-infrared heaters).
; Useful as other structural materials, sliding materials, etc.

Effects of the Invention According to the present invention, since spherical carbonaceous fine particles with uniform particle size and coated with a cohesive component are used as a carbon source, a binder such as a phenol resin is not separately blended. A uniform powder composition can be prepared by mixing for a short time.

Furthermore, the composition of the present invention has excellent moldability and sinterability.

Therefore, the carbon-silicon carbide composite material of the present invention obtained using such a composition has a uniform structure, high density, and excellent various mechanical properties such as bending strength.

Furthermore, since the composite material according to the present invention has a structure in which spherical graphite particles are dispersed in silicon carbide, it also has excellent toughness and friction properties.

EXAMPLES Examples and comparative examples are shown below to further clarify the features of the present invention.

(I) MCMB, (n) in the proportions (wt%) shown in Table 1 of Examples
β-3iC with an average particle size of 0.3 μm or (III) a-8iC with an average particle size of 0.5 μm, and (IV) β-3iC with an average particle size of 0.5 μm. The composition of the present invention was obtained by mixing 5 μm of B4C in a sieve machine for 30 minutes.

Table 1 (I) (II) (m) (IV) Particle size Quantity
Amount Amount Amount (μm) (%) (%) (%) (%) No.

1 6 30 69 0
12 6 20 79
0 13 6 10 89
0 14 6 30
0 B9 15 6 20
0 79 16 6
10 0 89 17 2
030 69 0 182020
7901 9 20 10 89 0
1. Next, the obtained composition was molded under a pressure of 20 kg/mn+2 to a size of 40 mm in diameter and 15 mm in length.

The obtained molded body was heated to 1000° C. at a temperature increase rate of 150° C./hour under normal pressure in a nitrogen atmosphere, and calcined at the same temperature for 1 hour.

Next, the obtained shaped calcined product was heated to (A) 2200°C under normal pressure.
or (B) 2 hours at 2400℃,
A carbon-silicon carbide composite material was obtained.

Table 2 shows the bending strength of the composite materials obtained under each sintering condition and the ratio (%) of the bulk density to the theoretical density. The test piece is
The composite material obtained above has a rectangular parallelepiped shape (8anX 8an
x 30 mm).

Further, the bending strength was determined by a three-point support strength test method under the conditions of a distance between fulcrums of 20 a+m and a crosshead speed of 0.5 mm/min.

Table 2 Bending strength Bulk density (kgf/mm2) (g/cm3) (A)
(B) (A) (B) No,
14.2 19.5 2.105 2.2B4
1 19.6 24.7 2.330 2.
53B2 30.5 33.3 2.549
2.8283 21.3
2.34B5 30.4 2
．． 8476 35.6 2.
9027-14.2 2.1
428-18.1 2.18
49 21.7 2.653
Example 2 A composition in which the amount of MCMB and the amount of B4C were proportionately combined, and β-3iC with a particle size of 0.3 μm as silicon carbide was used, and was fired at 2200"C for 2 hours. A carbon-silicon carbide composite material was obtained.The conditions during molding and calcination were the same as in Example 1.

The results are shown in FIG. In FIG. 1, the amount indicated by "vt%" attached to each line is the amount of MC in the composition.
Represents the amount of MB. Therefore, the amount of silicon carbide (wt%)
is "10100-MC amount-84C amount".

Example 3 A carbon-silicon carbide composite material was obtained in the same manner as in Example 2, except that the composition was fired at 2400° C. for 2 hours.

The results are shown in FIG. In FIG. 2, the amount indicated by "vt%" attached to each line is the amount of MC in the composition.
Represents the amount of MB.

[Brief explanation of drawings]

Figure 1 shows the results of molding and calcining various compositions of Example 2.
In the sintered body obtained by main firing at 200°C for 2 hours, M
It is a graph showing the relationship between CMBffi and B4Cm and rib strength. Figure 2 shows the bottom shapes of various compositions of Example 3, calcined, and 2
In the sintered body obtained by main firing at 400°C for 2 hours, M
It is a graph showing the relationship between the amount of CMB, the amount of B4C, and the bending strength. (And more) Fig. 2345 B4C wood weight (wt%) Fig. 2345 B4C'vl;nof (wt%)

Claims (5)

[Claims] (1) A composition for producing a carbon-silicon carbide composite material, comprising (a) 5 to 30 parts by weight of self-sintering spherical carbonaceous fine particles and (b) 95 to 70 parts by weight of silicon carbide powder. 100
(c) 0.5 of at least one sintering aid powder selected from the group consisting of boron and compounds thereof, based on part by weight;
A powder composition containing ~5 parts by weight. (2) In the composition for producing a carbon-silicon carbide composite material according to claim (1), (a) the self-sintering spherical carbonaceous particles are made from coal tar and have an average particle diameter of 20 μm or less. mesocarbon microbeads, (b) silicon carbide powder has an average particle size of 1 μm or less, and (c) sintering aid powder has an average particle size of 1 μm or less.
A powder composition which is boron carbide with a size of less than μm. (3) consisting of (c) boron and its compounds for a total of 100 parts by weight of (a) 5 to 30 parts by weight of self-sintering spherical carbonaceous fine particles and (b) 95 to 70 parts by weight of silicon carbide powder. A carbon-silicon carbide composite material characterized in that a powder composition containing 0.5 to 5 parts by weight of at least one sintering aid powder selected from the group is molded and fired in a non-oxidizing atmosphere. manufacturing method. (4) For a total of 100 parts by weight of (a) 5 to 30 parts by weight of self-sintering spherical carbonaceous fine particles and (b) 95 to 70 parts by weight of silicon carbide powder, (c) a group consisting of boron and its compounds. At least one sintering aid powder selected from 0.
A carbon-silicon carbide composite material obtained by molding and firing a powder composition containing 5 to 5 parts by weight. (5) The carbon-silicon carbide composite material according to claim 4, which has a bending strength of 20 kgf/mm^2 or more.