JPH013083A - Silicon carbide porous material and its manufacturing method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a porous silicon carbide body used as a catalyst carrier, a filter for filtration, a member for a heat exchanger, etc., and a method for producing the same.

[Conventional technology]

Conventionally, the following prior art techniques have been known for silicon carbide porous bodies and methods for producing the same.

(1) A method of reacting silicon with a molded body made of carbon or carbon and silicon carbide (Japanese Unexamined Patent Publication No. 48-39515
No., JP-A-57-160971, JP-A-59-162
No. 178, JP-A-60-86074, JP-A-60-9
No. 0868, JP-A-61-10068, JP-A-615
No. 2107).

(2) A method of mixing β-type silicon carbide somen fine powder with polycrystalline silicon carbide powder, molding it, and baking it (Japanese Patent Application Laid-Open No. 61-1747
No. 2, Japanese Patent Publication No. 61-53163).

(3) Method of forming a cellular skeleton structure of silicon carbide using organic polymer foam (Japanese Patent Application Laid-Open No. 58-122016
No., JP-A-61-14181, JP-A-61-2572
No. 17).

(4) A method in which β-type silicon carbide powder is used as a starting material and is fired with or without adding a crystal growth aid (Unexamined Japanese Patent Publication No. 6
0-255671, JP-A-60-264365, JP-A-61-91076, JP-A-61-191575).

The structure of the silicon carbide porous body produced by these methods has a substantially three-dimensional network structure.

[Problem that the invention seeks to solve]

However, in the silicon carbide porous body produced by method (1), silicon carbide is synthesized and sintered by the reaction C+Si-*SiC, so it is not possible to control the particle size of the silicon carbide produced. Have difficulty. Further, the shape of the silicon carbide produced is granular, and a porous silicon carbide body is formed in which a part of the grain is combined with a part of another grain.

The porosity of this porous silicon carbide body is about 25 to 35%, which is relatively small. Therefore, the resistance when fluid passes through the porous body is extremely high.

On the other hand, in order to keep the resistance low when fluid passes through the porous body, the porosity must be increased. However, in order to increase the porosity, it is necessary to reduce the amount of silicon carbide produced, which significantly reduces the strength of the sintered body.

The silicon carbide porous body produced by method (2) uses β-type silicon carbide fine powder as a binding material between polycrystalline silicon carbide grains. In this case, the porosity is approximately determined by the arrangement of polycrystalline silicon carbide grains that serve as the aggregate. If the distance between grains of polycrystalline silicon carbide is small, a porous body can be obtained with a small amount of β-type silicon carbide fine powder binder, but the porosity will be small.

Furthermore, when the distance between grains of polycrystalline silicon carbide is increased, a large amount of β-type silicon carbide fine powder binder is required to bond the grains together. Since the binding material remains as it is even after sintering, in extreme cases, the binding material will fill the gaps (pores) between polycrystalline silicon carbide, resulting in a decrease in porosity.

The silicon carbide porous body produced by the method (3) is composed of large and small cellular skeletons. For this reason, a porous body with high porosity can be obtained, but only one with relatively low strength can be obtained.

The silicon carbide porous body produced by the method (4) has a three-dimensional network structure in which plate crystals are entangled.

This porous body somewhat improves the above problems.

However, since the starting material is granular, it is difficult to uniformly grow plate crystals throughout the interior of the porous body. In particular, when producing a large porous body, silicon carbide tends to remain in the form of particles without being able to grow into a plate shape in the center of the porous body.

The relatively high strength of this porous body is largely due to the granular silicon carbide remaining inside the porous body, and the surface layer in which the plate crystals are entangled does not have such high strength.

Therefore, there were problems such as the surface layer being heavily worn and easily worn away.

In order to solve the above-mentioned problems, the present invention provides a novel silicon carbide porous body that has both high strength and high porosity by making the porous body have a double structure, and a method for manufacturing the same. It is something to do.

[Means for solving problems]

That is, the silicon carbide porous body of the present invention is characterized in that an inner layer portion made of entangled silicon carbide whiskers and a surface layer portion made of particulate silicon carbide are integrally formed. The manufacturing method is to impregnate a molded silicon carbide whisker with a thermosetting resin, heat it to 800 to 1200°C in a non-oxidizing atmosphere to carbonize the thermosetting resin, and then heat it in an oxidizing atmosphere. After heating to 800°C in a non-oxidizing atmosphere to burn off the carbon in the surface layer,
There is a patent which is characterized in that the porous body is heat treated at 800 to 2200°C, and then heated to 800°C or lower in an oxidizing atmosphere to burn off free carbon in the porous body.

Next, the present invention will be explained with reference to the drawings. FIG. 1 is a cross-sectional view illustrating the silicon carbide porous body of the present invention.

In FIG. 1, 1 is a surface layer made of particulate silicon carbide, and 2 is an inner layer made of entangled silicon carbide whiskers.

Silicon carbide whiskers are fine fibrous substances made of needle-like single crystals with a diameter of 0.1 to 1.0 μm and a length of 30 to 100 μm. A porous silicon carbide body is obtained by intertwining molded bodies formed into a desired shape and porosity. However, since this molded body is formed by intertwining silicon carbide whiskers with each other, the strength itself is not sufficient. Therefore, by composing the surface layer of the molded body with sintered particulate silicon carbide,
This is intended to improve strength.

This porous silicon carbide body can be manufactured by the following method.

First, silicon carbide whiskers are uniformly dispersed in a suitable dispersion medium such as water or an organic solvent, and then filtered to obtain a molded body of a predetermined shape. At this time, the porosity of the molded body can be adjusted and controlled by changing the molding pressure during molding.

Next, the molded body is impregnated with a thermosetting resin and heated to 800 to 1200° C. in a non-oxidizing atmosphere such as argon or nitrogen to sinter and carbonize the thermosetting resin. In this way, a silicon carbide whisker molded body in which carbon is uniformly dispersed is obtained.

In this case, it is preferable to lower the viscosity by dissolving the thermosetting resin in an organic solvent such as alcohol or ether, since this facilitates the impregnation operation and enables uniform impregnation. The organic solvent is vaporized and removed by heating to around 100°C.

Next, heat treatment is performed at a temperature of 800°C or less in an oxidizing atmosphere for an appropriate time to burn off the carbon dispersed in the surface layer of the compact, and then heat treatment is performed at a temperature of 1800°C or less in a non-oxidizing atmosphere such as argon or nitrogen.
When heat-treated at 2200° C., the silicon carbide whiskers in the surface layer of the compact are converted into particles, and some of the particles come into contact and sinter, forming a high-strength surface layer. Since carbon suppresses silicon carbide from becoming particulate, the inner layer is kept whisker-like and only the surface part becomes particulate. In this case, if the amount of carbon present is less than 10% by weight, the effect of suppressing the formation of silicon carbide particles will not be sufficient, which is not preferable. The heat treatment temperature is set at 1,800 to 2,200°C.If the heat treatment temperature is lower than 1,800°C, the whiskers in the surface layer will not be sufficiently granulated.
This is because as the particle formation progresses to the inner layer portion, the porosity decreases and closed pores are likely to be formed which deteriorate the function of the porous body.

Next, a silicon carbide porous body can be obtained by heat treatment in an oxidizing atmosphere at a temperature of 800° C. or less for an appropriate time to burn off free carbon as a particulate inhibitor remaining in the porous body. can.

Further, by interposing a sintering accelerator such as boron or aluminum in the surface layer, the strength of the surface layer can be increased. The sintering accelerator can be present in the surface layer in the form of a solution or a dispersion.

[For production]

Based on the above structure, the silicon carbide porous body of the present invention is constructed such that the inner layer part is composed of a molded body in which intertwined whiskers are aggregated, and the surface layer part is composed of a sintered body in which some of the particles are in contact with each other. Since they are integrally formed, high porosity can be achieved by the whisker molded body, and high strength can be achieved by the sintered body in which some of the particles are in contact with each other. Further, the porosity of the porous body can be easily adjusted and controlled during molding of the whisker molded product. In this porous silicon carbide body, only the surface layer of the molded body can be sintered to form particles by skillfully utilizing the particle formation suppressing effect of carbon.

〔Example〕

Next, the present invention will be explained by examples.

Example 1 Silicon carbide whiskers with a diameter of 0.1 to 1.0μ and a length of 30 to 100μ are dispersed and mixed in ethanol, filtered and dried, and then molded to a size of 50m x 50xix 5.
A silicon carbide whisker molded body having a temperature of 0rix and a weight of 609 was obtained. The porosity of this silicon carbide whisker molded body is 85
%Met.

Phenol resin 25 is added to the silicon carbide whisker molded body.
It was impregnated with a solution prepared by dissolving 25 g of ethanol in 25 g of ethanol. Then, after drying and curing at 200°C, 900°C in an argon atmosphere.
'C was fired and carbonized for 1 hour. The carbon content at this time was 20% by weight based on the silicon carbide whisker molded body.

Next, the molded body was held at 700°C for 5 minutes in air to burn off the carbon on the surface layer, and then heated at 1900°C in an argon atmosphere for 1 hour.
It was heat treated and sintered for a period of time.

The porous body was then held at 700°C for 2 hours to burn off free carbon.

The obtained porous silicon carbide body had a porosity of 85% and a compressive strength of 300 kg/cx. When this porous silicon carbide body was cut and the cross section was observed, the thickness of the surface layer was It was granular silicon carbide with a diameter of 2.1 x m, and the inner layer was a porous silicon carbide body with a double structure intertwined with silicon carbide whiskers.

Example 2 In the same manner as in Example 1, a silicon carbide whisker molded body was impregnated with a phenol resin, dried, and hardened, and then fired and carbonized. Amorphous boron dispersed in ethanol was then applied.

After drying, it was sintered at 2000° C. for 1 hour in an argon atmosphere.

The obtained porous silicon carbide body had a porosity of 8.1% and a compressive strength of 410 kg/cm''. When this porous silicon carbide body was cut and the cross section was observed, the surface layer was It was made of granular silicon carbide with a thickness of 2.4 sIl, and the inside was a 2 m+rlt porous silicon carbide body intertwined with silicon carbide whiskers.

Comparative Example 1 A silicon carbide whisker molded body molded in the same manner as in Example 1 was sintered as it was at 1900° C. for 1 hour in an argon atmosphere without impregnating it with resin.

The obtained porous silicon carbide body had a porosity of 85% and a compressive strength of 63/cyt''. As a result of cross-sectional observation, granular silicon carbide was observed throughout the porous body.

Comparative Example 2 A porous silicon carbide body was obtained in the same manner as in Example 2 except that only the firing temperature was set to 2300°C.

The obtained porous silicon carbide material had a porosity of 75% and a compressive strength of 410 kg/cm''. As a result of cross-sectional observation, the thickness of the surface layer was 5 MR, which was preferable as a porous material with many closed pores. It wasn't.

〔Effect of the invention〕

As is clear from the above description, the silicon carbide porous material of the present invention has both high porosity and high strength, and is suitable for various fields such as filters for various filtration applications, catalyst carriers, heat exchanger members, and aeration members. Can be used for

As the uses of ceramic porous bodies expand in the future, the present invention will play a large role in industry.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view illustrating the silicon carbide porous body of the present invention. 1... Surface layer 2... Inner layer I Ward

Claims (1)

[Claims] 1. A silicon carbide characterized by integrally forming an inner layer made of intertwined silicon carbide whiskers and a surface layer made of particulate silicon carbide. Elementary porous body. 2. A molded body of silicon carbide whiskers is impregnated with a thermosetting resin, heated to 800 to 1200°C in a non-oxidizing atmosphere to carbonize the thermosetting resin, and then heated in an oxidizing atmosphere.
After heating to below 00℃ to burn off the carbon in the surface layer,
Heat treated at 1800-2200°C in a non-oxidizing atmosphere,
A method for producing a porous silicon carbide body, which comprises then heating the porous body to 800° C. or lower in an oxidizing atmosphere to burn off free carbon in the porous body. 3. The method for producing a porous silicon carbide body according to claim 2, wherein the amount of impregnation of the thermosetting resin is 10% by weight or more as carbon based on the silicon carbide whisker. 4. The method for producing a porous silicon carbide body according to claim 2, wherein a solution or dispersion containing a sintering accelerator such as boron or aluminum is applied to the silicon carbide whisker molded body.