JPH0782052A - Production of porous silicon carbide material - Google Patents

Abstract

PURPOSE:To produce a porous silicon carbide material having a high porosity and excellent in strength. CONSTITUTION:SiC whisker composed mainly of beta crystal form and having 0.3 to 1.5mum diameter and 10 to 100mum length is kneaded with a binder solution in which polycarbosilane is dissolved. The resultant kneaded material is shaped, dried and subsequently calcined in an inert atmosphere at a temperature at which the polycarbosilane is converted to silicon carbide. The calcined material is further heat-treated in a range of 1700 to 2000 deg.C in an inert 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 body which is substantially composed of silicon carbide and has a high porosity and excellent material strength.

[0002]

2. Description of the Related Art As a technique for manufacturing a porous silicon carbide body,
Although a method of forming granular silicon carbide into a predetermined shape with a binder and then performing a firing treatment has been known for a long time, this method cannot provide a material with a desired high porosity.
For this reason, a method of controlling the porosity by mixing and sintering α-type and β-type silicon carbide particles having different particle sizes (Japanese Patent Publication No. 4-187578) has been proposed. Obtaining porosity is difficult.

As a method for producing a porous silicon carbide body having a high porosity, a method is known in which a silicon carbide slurry is adhered to the skeleton surface of an organic porous foam having a three-dimensional network structure, followed by drying and firing. There is. The silicon carbide body produced by this method exhibits a highly porous structure having a porosity of as high as 75 to 95%, but has a drawback that the material strength is extremely lowered. As a means for improving this method, the amount of ceramics slurry deposited by one operation is reduced and the steps from deposition to drying are repeated (Japanese Patent Laid-Open No. 59-3059), or compression at a specified ratio. A method has been proposed in which a ceramic slurry is filled in the formed organic foam, and then the compressed body is restored to its original volume and dried and fired (Japanese Patent Laid-Open No. 63-156084). However, in these methods, since the organic component forming the skeleton after firing is thermally decomposed and lost, the pores remain in the tissue as they are, so that the lack of the tissue strength cannot be solved.

As a method of solving the above problems and obtaining a porous ceramic structure having a uniform vent hole without clogging and an excellent skeletal strength, an organic porous foam is impregnated with a ceramic slurry to form a surplus slurry. The present applicant has proposed a process comprising a first step of removing and removing, followed by drying and calcination, and a second step of re-impregnating the calcinated body with ceramics slurry and removing excess slurry, followed by drying and calcination. (JP-A-3-83875). According to this method, the voids of the organic component are filled with silicon carbide by re-impregnation, so that the material strength can be effectively improved. In this impregnation operation, however, the ceramic slurry is filled in all the pores inside the tissue. There is a difficulty in smooth and uniform penetration, and there are often problems that local clogging and uneven strength occur.

[0005]

Recently, in high temperature furnace materials (including heat insulating materials), structural materials, filter materials, etc. used in the field of semiconductors, porous materials having high purity and high porosity and excellent material strength Although there is a strong demand for the development of a porous ceramic structure, a manufacturing technique satisfying all of these requirements has not been developed so far.

An object of the present invention is to provide a method for producing a porous silicon carbide body which has a high purity, a high porosity, a high strength and can be adjusted to a desired porous structure within a range of a porosity of 75% or more. It is in.

[0007]

A method for producing a porous silicon carbide body according to the present invention for achieving the above object is a β type having a property of a diameter of 0.3 to 1.5 μm and a length of 10 to 100 μm. The main body of SiC whiskers is kneaded with a binder solution in which polycarbosilane is dissolved, and then the kneaded product is molded and dried, and then calcined under an inert atmosphere at a temperature at which the polycarbosilane is converted to silicon carbide, and further inert. The structural feature is that the heat treatment is performed in the temperature range of 1700 to 2000 ° C. in the atmosphere.

In the present invention, the SiC whiskers are used as an aggregate raw material, but the manufacturing history thereof is not particularly limited. Therefore, a method of reacting a decomposable silicon compound with hydrocarbon in a gas phase, a mixture of a solid silicon source material containing silica and carbon powder, or a substance containing a silicon source and a carbonaceous material component such as rice husk charcoal in a complex manner A SiC whisker produced by a method such as heat-treating and solid-phase reaction can be appropriately used. It is desirable that the SiC whiskers produced using a metal catalyst be purified before being subjected to acid treatment, if necessary, in order to remove impurities, and then used. However, the SiC whiskers have a diameter of 0.3 to 1.5 μm and a length of 10 to 10.
It is necessary to select and use a material having a shape of 100 μm and exhibiting a structure mainly of β crystal type. The reason for this selection is
This is because the SiC whiskers having the above-described properties and crystal system exhibit the most effective diameter increase by sublimation recrystallization in the final heat treatment step, and can impart a highly adjustable porosity to the structure.

The structure mainly composed of β crystal type means that the crystal system constituting the SiC whiskers is all β type, or even if α / β mixed type, β type is dominant. The crystal characteristics of the β type SiC whiskers most suitable for the purpose of the present invention are α degree of 20 or less according to the following formula, and half-width of (111) diffraction line is 0.
It is 14 deg or less, and it becomes easy to control at a porosity of 70% or more in this characteristic range. α degree = (H ₁ × 2 / H ₂ ) × 100 where H ₁ is a peak intensity of 2θ of about 33.6 deg when CuKα is used as a radiation source in X-ray diffraction, and H ₂ is 2θ3.
It is a peak intensity of 5.5 deg.

The SiC whiskers having the above-mentioned properties are prepared by mixing polycarbosilane with a binder solution prepared by dissolving a suitable organic solvent such as benzene, toluene, xylene, ether, alcohol or the like, and kneading the mixture into a slurry by a mechanical stirring operation. The amount ratio of the polycarbosilane used is preferably set in the range of 10 to 30% by weight based on the SiC whiskers. When this amount ratio is less than 10% by weight, it is not possible to impart a high degree of material strength to the obtained porous silicon carbide body, and when it exceeds 30% by weight, it becomes difficult to obtain a high porosity structure. .

Then, the kneaded product is molded into a desired shape by applying a molding method such as a casting method, a filtration molding method, or a slip casting method, and the solvent is volatilized and dried. The molded body is subjected to a firing treatment in an inert atmosphere such as argon or nitrogen at a temperature at which polycarbosilane as a binder component is converted into silicon carbide. This heating temperature is 100
It is preferable to set in the range of 0 to 1200 ° C.

The silicon carbide-based fired body thus obtained is then further heat-treated in an inert atmosphere in the temperature range of 1700 to 2000 ° C. This heating step increases the diameter by subliming and recrystallizing the SiC whiskers, and this action is an important factor that functions to control the porosity of the structure to a high porosity and a high porosity range. At this time, if the heating temperature is less than 1700 ° C., the diameter of the SiC whiskers will not be smoothly increased, and if the heating temperature exceeds 2000 ° C., the vaporization of SiC will be severe and the material strength will be significantly reduced.

The porous silicon carbide body produced in the above process has a controlled porosity with a porosity of 75 to 85% in which continuous pores having a pore diameter of 0.5 to 10 μm are uniformly distributed. The strength is a high-purity product consisting essentially of silicon carbide having a physical property of 100 kg / cm ² or more as bending strength.

[0014]

According to the process of the present invention, fine fiber SiC whiskers are used as an aggregate raw material, and polycarbosilane which is converted into silicon carbide by heat treatment is used as a binder. During the firing process, a precursor of a porous structure is formed through a strong, homogeneous and dense shape-retaining effect due to the entanglement of SiC whiskers and a binding effect due to silicon carbide converted from polycarbosilane. Then, when heat treatment is finally applied, S in the tissue is
The diameter of iC whiskers is increased based on the mechanism of sublimation recrystallization. Due to the effect of increasing the diameter, innumerable minute voids are formed in the tissue, and high porosity is imparted while maintaining practical material strength.

The improvement of the high porosity due to the diameter increasing effect is
This can be effectively achieved by selectively using a SiC whisker having a diameter of 0.3 to 1.5 μm and a length of 10 to 100 μm and mainly composed of β crystal type.
It is possible to adjust the porous structure in a region having a porosity of 75% or more by appropriately controlling in the range of 00 to 2000 ° C.

[0016]

EXAMPLES Examples of the present invention will be described in detail below in comparison with comparative examples.

Examples 1 to 3 and Comparative Examples 1 to 2 As raw materials for aggregate, they have a property of 0.5 μm in diameter and 50 μm in length, and the half value width of the (111) diffraction line is 0 at α degree 0.5. .13
SiC whiskers [TWS-100 manufactured by Tokai Carbon Co., Ltd.] exhibiting a β-type main crystal system of 75 were selectively used. This S
Polycarbosilane for iC whiskers [Shin-Etsu Chemical Co., Ltd., number average molecular weight: 1475, weight average molecular weight: 3365
] The xylene solution is mixed so that the amount ratio of polycarbosilane to SiC whiskers is 20% by weight,
The mixture was stirred until it became a uniform slurry. Then, add the slurry-like kneaded product to a plastic container (100 mm in length and width,
It was poured into a height of 50 mm), air-dried at room temperature for 2 days, and then vacuum-dried. The dried compact was placed in a heating furnace held by nitrogen gas, and fired at 1000 ° C. for 5 hours. The properties of the obtained fired body were a porous body of silicon carbide simple substance having a porosity of 73% and a bending strength of 300 kg / cm ² .

Next, the fired body was transferred to a high-frequency induction heating furnace maintained in an argon atmosphere and subjected to a heat treatment for 20 minutes in a temperature range of 1500 to 2200 ° C. With respect to each of the porous silicon carbide bodies thus produced, the porosity of the structure, the bending strength of the material, etc. were measured, and the results are shown in Table 1 in comparison with the heat treatment temperature.

[0019]

[Table 1]

From the results shown in Table 1, in Examples 1 to 3, it is possible to produce a porous silicon carbide body having a bending strength of 100 kg / cm ² or more, which has a porosity in the range of 75 to 81% and the porosity varies depending on the heat treatment temperature. Is recognized. On the other hand, in Comparative Example 1 in which the heat treatment temperature is 1500 ° C., the porosity does not increase because the diameter of the SiC whiskers does not increase, and in Comparative Example 2 in which the heat treatment temperature is 2200 ° C., the material strength is extremely high. It showed a declining result.

Comparative Examples 3 to 5 α crystalline SiC whiskers having a diameter of 0.7 μm and a length of 50 μm and an α degree of 100 were used as the raw material of the aggregate, and the other examples were used.
A silicon carbide based sintered body was obtained under the same conditions as above. This sintered body had a porosity of 70% and a bending strength of 300 kg / cm ² . This sintered body was processed in the same manner as in Example 1 at 1800 ° C., 1
Heat treatment was performed at each temperature of 900 ° C and 2000 ° C. As shown in Table 2, the properties of the obtained porous silicon carbide body did not show an effective increase in porosity.

[0022]

[Table 2]

[0023]

As described above, according to the present invention, a high purity product having a high porosity and material strength can be obtained by firing and heat treating a molded product of SiC whisker aggregate having a characteristic property and a polycarbosilane binder. It becomes possible to efficiently manufacture the above porous silicon carbide body. Moreover, by controlling the heat treatment temperature, the degree of porosity can be adjusted within the range of the porosity of 75% or more. Therefore, it is extremely useful as a member for semiconductors, a heat insulating material used under severe conditions, a filtering material, a particulate collecting material, and the like.

Claims (2)

[Claims] 1. A diameter of 0.3 to 1.5 μm and a length of 10 to 1
A β-crystal type SiC whisker having a property of 00 μm is kneaded with a binder solution in which polycarbosilane is dissolved, and then the kneaded product is molded and dried, and then the temperature at which the polycarbosilane is siliconized in an inert atmosphere. And a heat treatment in a temperature range of 1700 to 2000 ° C. in an inert atmosphere, a method for producing a porous silicon carbide body. 2. The SiC whisker has an α degree of 20 or less,
The method for producing a porous silicon carbide body according to claim 1, wherein the full width at half maximum of the (111) diffraction line is 0.14 deg or less.