JPH0412072A - Production of high-strength porous sic sintered material - Google Patents

Abstract

PURPOSE:To obtain the title sintered material, by using SiC whiskers having formed a carbonaceous surface coating film as an aggregate raw material, blending the SiC whiskers with B powder and subjecting to hot press sintering under a specific condition. CONSTITUTION:A mixture of SiC whiskers having formed a carbonaceous surface coating film with 200-100Angstrom thickness and 0.3-1.0wt.% B powder is subjected to hot press sintering in an inert atmosphere at 1,950-2,100 deg.C under >=100kg/cm<2>. Whiskers are dispersed into a solution of phenol resin, etc., filtered, dried, the resin is cured, heat-treated in a nonoxidizing atmosphere and the thickness of the carbonaceous coating film is adjusted to 20-100Angstrom by controlling conditions such as solution concentration of resin, etc. When the amount of the B powder added is lower than the lower limit, blending effects are not shown and when the amount of the B powder exceeds the upper limit, excessive B remains on the bond interface of the whiskers and causes reduction in strength. When the sintering temperature is lower than the lower limit, the sintering is made unsmooth and when the temperature exceeds the upper limit, deformation can not be suppressed and the mixture is difficult to sinter. When sintering pressure is <100kg/cm<2>, bonding base points can not be formed in the whiskers and the mixture has difficulty in sintering.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention provides SiC with a porous structure that has excellent mechanical strength performance.
The present invention relates to a method for producing a sintered body.

[Prior art] Porous structures made of ceramic materials such as SiC have excellent heat resistance and chemical stability, so they can be used as filters for molten metals, high-temperature insulation materials, catalyst supports, and particulate traps. It is used for collecting wood, etc.

Conventionally, many manufacturing techniques have been proposed for porous ceramic structures, but the simplest method in terms of process is to apply a ceramic slurry on the skeletal surface of an organic porous body with a three-dimensional network structure, and then Drying and firing method (
JP-A-59-3059, JP-A No. 63-1.56084
Publications, etc.). As a process for SiC-based porous bodies using this type of means, a method is known in which an organic fiber molded body is impregnated with SiC slurry, solidified, and then sintered (Japanese Patent Laid-Open No. 71659/1983). [Problems to be Solved by the Invention] However, in the conventional method of impregnating an organic porous body with SiC slurry, drying and firing, the bonding force of the SiC porous structure formed is weak, so that sufficient strength performance cannot be achieved. There are some issues that are not covered.

In order to strengthen the framework of the porous structure and improve its strength performance, it is necessary to use microfibrous Si instead of SiC powder as the framework raw material.
Sintering using C whiskers is considered effective. However, when SiC whiskers are sintered at a high temperature of 1700° C. or higher, they undergo transformation due to recrystallization, resulting in shape deformation and difficulty in maintaining their original shape and strength.

The inventor conducted repeated research focusing on the fact that thermal transformation of SiC whiskers can be prevented by forming a thin carbonaceous film on the surface, and as a result, the SiC whiskers with the carbonaceous film formed thereon were mixed with B powder. It has been confirmed that hot press sintering under specific conditions converts the material into a high-strength porous SiC material.

The present invention was developed based on the above findings, and its purpose is to provide a method for producing a porous SiC sintered body having excellent mechanical strength and having a skeleton of SiC whiskers.

[Means to solve the problem]

In order to achieve the above object, the method for producing a high-strength porous SiC sintered body according to the present invention is based on SiC whiskers having a carbonaceous surface film formed thereon with a thickness of 0.3 to 1.0 mm.
0% by weight of B powder was mixed, and the mixture was heated in an inert atmosphere at a temperature of 1950-2100°C and a pressure of 100kg/cm.
The structural feature is that hot press sintering is performed under two or more conditions.

SiC whiskers have a diameter of 0.5 to 2 μm and a length of 10
A needle-like single crystal having an aspect property of ~100 μm is used. To form a carbonaceous surface film on the SiC whiskers, the SiC whiskers are dispersed in a solution of a carbonizable thermosetting resin such as a phenolic resin or a furan resin, and after filtration, drying, and resin curing, a non-oxidizing A method of heat treatment at a temperature of 800 to 1800"C in an atmosphere is applied. At this time, the carbonaceous film is formed by controlling conditions such as the solution concentration of the thermosetting resin used and the stirring and mixing time of the SiC whiskers. The thickness of 20~1
It can be adjusted to a range of 00 people.

The reason why the thickness of the carbonaceous film is set to 20 to 100 is as follows.
This is because if there are less than 20 people, thermal deformation of the SiC whiskers cannot be effectively prevented, and if more than 100 people, sinterability will deteriorate.

B powder is mixed into the SiC whiskers on which the carbonaceous surface coating has been formed. The B powder functions as a sintering aid, and is preferably mixed as a fine powder with an average particle size of 05 μm or less in an amount of 0.3 to 1.0% by weight based on the SiC whisker. If the amount added is less than 0.3% by weight, the mixing effect will not be exhibited and poor sintering will occur, while if the amount added is 1.0% by weight, excess B component will remain at the bonding interface of the SiC whiskers. Both cause a decrease in strength.

The SiC whiskers and the B powder are mixed, for example, by stirring and mixing in a ball mill with an appropriate organic solvent,
This is done until it is completely uniform. The mixture is subsequently dried to form a sintering material.

The sintering process was carried out using a hot press, and the sintering conditions were: in an inert atmosphere, temperature 1950-2100°C, pressure 10°C.
0 kg/cm” or more. Maintaining the inside of the sintering system in an inert atmosphere is a necessary condition to prevent oxidation of the carbonaceous surface film formed on the SiC whiskers. It is preferable to maintain the atmospheric pressure at a pressure higher than normal pressure, and in a vacuum or reduced pressure system, the deformation of the SiC iscar will proceed with sublimation.The sintering temperature is 19
If the temperature is less than 50°C, sintering will not be carried out smoothly and 21
If the temperature exceeds 00°C, recrystallization of the SiC whiskers will proceed rapidly, so that a thin carbonaceous surface coating will not be able to suppress the deformation. Furthermore, if the sintering pressure exceeds 100 kg/cm2, bonding points cannot be formed in the SiC whiskers (and sintering becomes difficult. Therefore, sintering is performed at a pressure of 100 kg/cm2 or more. The pressure conditions are adjusted to achieve the desired porosity in the area.

[Function] According to the present invention, SiC whiskers on which a carbonaceous surface film with a thickness of 20 to 100 mm has been formed are used as a skeleton component, and after being mixed with a small amount of sintering aid B powder, the whiskers are heated under specific conditions. A hot press sintering process is used. In this process, the carbonaceous film effectively suppresses transformation deterioration during sintering, and together with the inherent high strength of the SiC whiskers serving as the skeleton, it functions to form a strong structure. Bonding between SiC whiskers is achieved by a load of 100 kg/cm during the sintering process.
The carbonaceous film at the contact interface between the SiC whiskers peels off or the SiC whiskers break under pressure of 2 or more, forming countless bonding points, and sintering progresses through these bonding points, making the product extremely strong. Become.

The structure after sintering becomes a porous structure in which fine fibrous SiC whiskers are bonded together at bonding points, and the porosity can be adjusted mainly by the pressurizing conditions of the hot press.

(Example) Hereinafter, the present invention will be explained based on examples.

Example 1 Phenol resin [manufactured by Gunei Chemical Co., Ltd., "Resito Nobu PGA"
-4508'"] was dissolved in ethanol and allowed to stand for 7 days to prepare fully homogenized resin solutions with different concentrations. SiC whiskers with an average diameter of 0.4 μm and an average length of 30 μm were added to this solution. "Toka Whisker" (manufactured by Tokai Carbon ■) was dispersed and mixed with stirring, followed by filtration and drying to volatilize and remove ethanol. Next, the phenol resin was cured by heating at a temperature of 170°C for 2 hours, and then transferred to a high frequency furnace and fired at a temperature of 1000°C in an Ar flow to form carbonaceous films of different thicknesses on the surface of the SiC whiskers. Formed.

Each SiC whisker with a carbonaceous film has an average particle size of 0.
．． 1 micron of amorphous B powder was mixed at a ratio of 0.7% by weight, and the mixture was placed in a ball mill with an ethanol dispersion medium and rotated for 20 hours.

The formed mixed slurry was filtered and dried to remove the ethanol component. The obtained mixture was used as a sintering material, and 40 g of each was filled into a graphite mold, and the temperature was 2050° C. and the pressure was 500 kg/c while maintaining the system in an Ar atmosphere.
Hot press sintering was carried out under the conditions of ``m''.

The bulk density and bending strength of each of the obtained sintered bodies were measured, and the results are shown in FIG. 1 as a graph of the relationship with the thickness of the carbonaceous film formed on the surface of the SiC whisker.

From FIG. 1, when the thickness of the carbonaceous surface coating is in the range of 20 to 100%, it has a porosity of about 15% and 300%
High strength porous Si with bending strength exceeding MPa
Although a C sintered body was obtained, the bending strength was found to be extremely low in cases where the thickness of the carbonaceous coating was less than 20 or more than 100. In addition, when the SiC sintered body formed in the case of less than 10 carbonaceous coatings was observed under a microscope, it was found that Si
It was observed that the C whiskers were deformed into particles.

Example 2 50 SiC whiskers with a carbonaceous surface coating formed by the method of Example 1 were mixed with varying amounts of B powder by the same means as in Example 1, and sintered to form porous SiC. A body was produced.

The bulk density and bending strength of each SiC sintered body obtained were measured, and the relationship with the amount of B powder added is shown in a graph in FIG.

From the results shown in Figure 2, when the amount of B powder added is in the range of 0.3 to 1.0% by weight, the bulk density is stable at about 2.75 g/cm3, and the bending strength remains in the high strength range of 300 MPa or more. However, if the amount of B powder added is 0. When the amount of B powder added is less than 3% by weight, neither the bulk density nor the bending strength increases.
．． It can be seen that when the content exceeds 0% by weight, the bending strength is extremely reduced.

Example 3 A carbonaceous surface coating having a thickness of 50 μm was formed on SiC whiskers having an average diameter of 1 μm and an average length of 40 μm using the method of Example 1. A sintering material was prepared by adding and mixing 0.7% by weight of B powder to the SiC whiskers under the same conditions as in Example 1, and hot press sintered this material under different temperature and pressure conditions.

The bulk density and bending strength of each SiC sintered body obtained were measured, and the results are shown in Table 1 in comparison with the applied sintering conditions.

Table: RUN No. 1 to 5, which meet the requirements of the present invention, are approximately 1
It exhibited a porosity of 5% and a bending strength of over 300 MPa.

However, in RUN No. 6, the temperature drops below 1950°C, so sintering does not proceed smoothly, and the bulk density and bending strength are both low. In RUN No. 7, the temperature drops to 2100°C, so sintering does not proceed smoothly. The thickness of the surface coating (human) is exceeded, resulting in a decrease in bending strength. Also, IIUN
In No. 8, sintering did not proceed because the pressure was low, and the bending strength was low.

(Effects of the Invention) As described above, according to the present invention, strength properties are improved by using SiC whiskers with a carbonaceous surface coating formed on the skeletal raw material, mixing them with B powder, and real-breath sintering under selected conditions. An excellent porous SIC sintered body can be manufactured.

Therefore, it is expected to be useful as a porous structural member used in harsh environments.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between the thickness of the carbonaceous film of SiC whiskers and the bulk density and bending strength of the SjC sintered body in Example 1, and Figure 2 is a graph showing the relationship between the amount of B powder added and the bulk density in Example 2. It is a graph showing the relationship between density and bending strength. Applicant Tokai Carbon Co., Ltd. Agent Patent Attorney Masaya Takahata Figure 2 0.5 1. Amount of O B powder added (wt%)

Claims (1)

[Claims] 1. S with a carbonaceous surface coating of 20 to 100 Å thick
0.3-1.0 wt% B powder is mixed with iC whiskers, and the mixture is heated in an inert atmosphere at a temperature of 1950-210°C.
A method for producing a high-strength porous SiC sintered body, comprising hot press sintering at 0° C. and a pressure of 100 kg/cm^2 or more.