JPH0952780A - Production of porous silicon carbide sintered compact - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a porous silicon carbide sintered compact having high porosity and high strength and capable of easy control of pore diameter. SOLUTION: Silicon carbide whiskers are mixed with 30-50wt.% α-silicon carbide powder of <=30μm, preferably 0.5-10μm average particle diameter and the resultant mixture is compacted and sintered at 1,90O-2,100 deg.C in a nonoxidizing atmosphere.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a porous silicon carbide sintered body having a high porosity and a high strength and capable of easily controlling the pore diameter.

Since a silicon carbide sintered body is excellent in heat resistance, high temperature strength, chemical stability, etc., it has been widely used as various structural members for high temperature. In addition, the porous silicon carbide sintered body, which has a porous structure of sintered body, is expected to be put to practical use in various application fields such as molten metal filters, breathable high temperature heat insulating materials, catalyst carriers, and exhaust gas filters. Has been.

[0003]

2. Description of the Related Art As a method of producing a porous silicon carbide sintered body, an organic porous body having a three-dimensional network structure such as polyurethane foam is impregnated with a slurry of silicon carbide, dried and then heat-treated to form an organic body. There is known a method of incineration and removing (for example, JP-A-58-122016), but the silicon carbide porous body obtained by this method has a high porosity of 80% or more, but has an extremely low strength. There are drawbacks.

As a method for producing a porous silicon carbide sintered body, an organic resin binder is added to and mixed with a powder of silicon carbide, and the mixture is shaped into a predetermined shape and then fired to obtain powder particles of the silicon carbide. A method of growing grains is also known. For example, in Japanese Patent Application Laid-Open No. 3-215374, the average grain size is 100 to 150 μm, and the average grain size is within ± 20%.
After adding a molding binder and a plasticizer to silicon carbide granules having a particle size distribution such that 0% by weight or more is present and mixed, the surface layer portions of the granules are crushed and interconnected, and the inside thereof is not crushed. In this state, a method of molding under a molding pressure that remains in the molded body and then sintering is proposed.

Further, in Japanese Patent Application Laid-Open No. 3-215375, a molded body is molded from a raw material composition prepared by mixing a carbonaceous substance with silicon carbide powder, and the molded body is fired in a non-oxidizing atmosphere to give silicon carbide. A carbonaceous material in the sintered body is formed by sintering the powder to form a silicon carbide sintered body in which the carbonaceous material is dispersed and contained, and then heating the sintered body in an oxidizing atmosphere. A method for burning and eliminating the powder to form pores in the sintered body is disclosed in Japanese Patent Laid-Open No. 187578/1992 by using a raw silicon carbide powder obtained by mixing α silicon carbide powder with β silicon carbide powder. Has been proposed, in which the abnormal grain growth of β-type silicon carbide is suppressed by controlling the pore diameter by molding the molded body and firing the molded body.

However, while the porous silicon carbide sintered body produced by these methods has a porosity of about 50%, the bonding of the silicon carbide particles forming the porous body is the particle of silicon carbide fine particles. Since it is based only on growth, there is a problem that mechanical strength is small and it is not sufficient to achieve both pore characteristics and strength characteristics.

[0007]

In order to solve this problem, the present inventor has found that by using a raw material system in which silicon carbide whiskers are mixed with silicon carbide powder, both pore characteristics and strength characteristics can be achieved, Japanese Patent Application No. 6-11964
No. 9 silicon carbide whiskers with an average particle size of 30 μm
A method for producing a silicon carbide sintered body was proposed, in which the following silicon carbide powders were mixed in a ratio of 30 to 50% by weight and sintered after molding at a temperature of 1900 to 2100 ° C in a non-oxidizing atmosphere.

As a result of continuing research by the present inventor, the pore characteristics and strength characteristics of the silicon carbide sintered body obtained differ depending on the crystal form of the silicon carbide powder used, and when α-type silicon carbide powder is used, excellent strength characteristics are obtained. It has been found that it has pore characteristics and that the pore diameter can be easily controlled.

The present invention has been developed on the basis of the above findings, and its object is to provide a porous silicon carbide sintered body having a high porosity and a large material strength and capable of easily controlling the pore diameter. It is to provide a manufacturing method of.

[0010]

The method for producing a porous silicon carbide sintered body according to the present invention for achieving the above object comprises:
The α-type silicon carbide powder having an average particle diameter of 30 μm or less is mixed with silicon carbide whiskers in a proportion of 30 to 50% by weight, and after molding, sintering is performed at a temperature of 1900 to 2100 ° C. in a non-oxidizing atmosphere. Characterize.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Silicon carbide whiskers have a diameter of 0.
It is a fine fibrous substance having an extremely high strength, which is composed of a needle-shaped single crystal having a length of 1 to 2.0 μm and a length of 5 to 100 μm. To function as a skeleton for forming. Then, when silicon carbide powder is mixed with silicon carbide whiskers and heated and sintered, the silicon carbide powder promotes mutual bonding of the silicon carbide whiskers to form a strong bonded body.

The present invention mainly uses α-type silicon carbide powder as the silicon carbide powder to be mixed with the silicon carbide whiskers. Since β-type silicon carbide powder is prone to abnormal grain growth during sintering, it is difficult to control the pore diameter because the pore characteristics, especially the pore diameter, greatly change. On the other hand, the α-type silicon carbide powder has high stability even at a high temperature and it is difficult for the particles to grow, so that the change in the pore diameter can be suppressed to a small level.

In this case, the α-type silicon carbide powder having an average particle diameter of 30 μm or less is used, preferably 0.5 to
10 μm fine powder is used. Average particle size is 30μm
This is because if it exceeds 1.0, the sinterability is deteriorated and the material strength of the obtained porous silicon carbide sintered body is lowered.

The α-type silicon carbide powder is mixed in a proportion of 30 to 50% by weight with respect to the silicon carbide whiskers. If the mixing ratio exceeds 50% by weight, the α-type silicon carbide powder is filled in the voids formed by the intertwined silicon carbide whiskers and the porosity decreases. On the other hand, if the mixing ratio is less than 30% by weight, it becomes a skeleton. Since the whiskers are not sufficiently connected to each other, the material strength of the sintered body cannot be improved.

The α-type silicon carbide powder and the silicon carbide whiskers are dispersed together with a molding binder in water or an organic solvent such as alcohol or ether so as to have a predetermined ratio to prepare a uniform mixed slurry. Molded into a molded body. Methylcellulose, carboxymethylcellulose, etc. are used as the molding binder, and the total amount of α-type silicon carbide powder and silicon carbide whiskers is 10
It is mixed in a proportion of 1 to 30 parts by weight with respect to 0 parts by weight.
A molding aid such as glycerin may be added if necessary.

Next, the mixed slurry is molded into a molded body having a desired shape by a known molding means such as casting, extrusion molding, press molding, injection molding, etc., and after drying, it is heated to 1900 in a non-oxidizing atmosphere such as nitrogen or argon. 21
Sinter at a temperature of 00 ° C. When the sintering temperature is less than 1900 ° C, the silicon carbide whiskers are not sufficiently bonded to each other by the α-type silicon carbide powder, and when the sintering temperature exceeds 2100 ° C, sublimation of the silicon carbide whiskers occurs and the skeletons of the entangled whiskers collapse. This is because.

According to the invention, silicon carbide whiskers and α
By sintering the mixed compact of the silicon carbide powder of type α, a porous sintered body in which the entangled silicon carbide whiskers are firmly bonded to each other through the α type silicon carbide powder is formed, and voids inside the sintered body are formed. Since most of them are retained, a silicon carbide sintered body having a high porosity can be obtained.

Further, since the α-type silicon carbide powder has high stability at high temperature, abnormal grain growth does not occur even during high temperature treatment during sintering, so that it is possible to prevent abrupt changes in the formed pore size. it can. Therefore, the pore diameter can be easily controlled by adjusting the sintering temperature.

In this way, using α-type silicon carbide powder,
High porosity by specifying the average particle size and the mixing ratio with the silicon carbide whiskers and the sintering temperature,
It is possible to manufacture a porous silicon carbide sintered body having high strength characteristics and having a uniform average pore diameter.

[0020]

Hereinafter, examples of the present invention will be described in comparison with comparative examples.

Examples 1 to 8 and Comparative Examples 1 to 8 As raw materials, silicon carbide whiskers having an average diameter of 1.5 μm and an average length of 25 μm, α-type silicon carbide powder having an average particle size of 0.7 μm, and an average particle size of 0. A .beta.-type silicon carbide powder of 0.7 .mu.m was used, and the raw material slurry was prepared by dispersing the raw materials in water by changing the mixing ratio. 100 mixed raw materials
20 parts by weight of methyl cellulose as a binder for molding and 10 parts by weight of glycerin as a molding aid were added to parts by weight. After extruding this raw material slurry into a cylindrical shape with a diameter of 50 mm and a height of 100 mm,
The molded body was sintered in a nitrogen atmosphere at different temperatures for 1 hour.
The porosity characteristics (average porosity, porosity) of the obtained sintered body were measured by the mercury intrusion method and the three-point bending strength was measured by JISR1601, and the results are shown in Tables 1 and 2.

[0022]

[Table 1]

[0023]

[Table 2]

Examples 9 to 11 and Comparative Examples 9 to 13 Using silicon carbide whiskers having an average diameter of 1.5 μm and an average length of 25 μm, the α-type silicon carbide powder and β-type silicon carbide powder to be mixed have an average particle size and mixing. A molded body was prepared in the same manner as in Examples 1 to 8 except that the raw material slurries were prepared by changing the ratio, and the molded body was sintered in a nitrogen atmosphere at a temperature of 2000 ° C. for 1 hour. The pore characteristics and the three-point bending strength of the obtained sintered body were measured by the same methods as in Examples 1 to 8 and the results are shown in Table 3.

[0025]

[Table 3]

From the results shown in Tables 1 and 2, the porosity and the average pore diameter of the porous silicon carbide sintered bodies of Examples 1 to 8 using α-type silicon carbide powder gradually increased with the sintering temperature. On the other hand, in the porous silicon carbide sintered bodies of Comparative Examples 1 to 8 using β-type silicon carbide powder, the sintering temperature was 2100 to 220.
It is recognized that the temperature rapidly increases near 0 ° C. Further, all of the porous silicon carbide sintered bodies of Examples 1 to 8 have high bending strength characteristics and a porosity of about 70%,
It can be seen that the material strength is superior to the porous silicon carbide sintered bodies of Comparative Examples 1 to 8. Furthermore, from the results of Table 3, the porous silicon carbide sintered bodies of Examples 9 to 11 which satisfy the requirements of the present invention are compared with the porous silicon carbide sintered bodies of Comparative Examples 9 to 13 which deviate from the requirements of the present invention. It is clear that the pore characteristics and strength characteristics are superior.

[0027]

As described above, according to the present invention, by using a raw material obtained by mixing a predetermined amount of α-type silicon carbide powder having a specific particle size range with silicon carbide whiskers, a porous silicon carbide firing having high porosity and high strength is obtained. A bonded body can be manufactured, and the average pore size can be controlled by appropriately setting the sintering temperature. Therefore, it is extremely useful as a method for producing a molten metal filter, a breathable high-temperature heat insulating material, a catalyst carrier, an exhaust gas purifying filter, a porous ceramics heater, and the like.

Claims (2)

[Claims] 1. A silicon carbide whisker having an average particle size of 30.
The α-type silicon carbide powder having a particle size of μm or less is mixed in a proportion of 30 to 50% by weight, and after molding, in a non-oxidizing atmosphere, 1900 to 2100.
A method for producing a porous silicon carbide sintered body, which comprises sintering at a temperature of ° C. 2. The average particle diameter of the α-type silicon carbide powder is 0.5.
The method for producing a porous silicon carbide sintered body according to claim 1, which has a thickness of 10 μm.