JPH0826848A - Method for producing porous SiC compact - Google Patents

Abstract

(57) [Summary] [Object] To provide a method for producing a porous SiC compact having a high porosity and an excellent material strength, which is composed of a composite of SiC having whisker and fine particle properties, using an inexpensive raw material. [Structure] A crushing process of crushing the charcoal of rice husks to a maximum particle size of 40 μm 0 or less, a surface treatment process of applying a solution of a carbonizing thermosetting resin to the crushed rice husk carbide powder, and a surface treatment Molding process of molding the rice husk carbide powder into a predetermined shape, and the molded body in a non-oxidizing atmosphere at 1500-18
A reaction step of heat-treating in the temperature range of 00 ° C. and an incineration step of heat-treating the molded body after the reaction step in the atmosphere to burn off residual carbon components are sequentially performed. The strength of the material is further improved by treating the obtained porous SiC molded body with a solution containing polycarbosilane and then firing the polycarbosilane at a temperature at which the polycarbosilane becomes SiC.

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 SiC compact having a high porosity and an excellent material strength, which is composed of a composite of substantially whisker and fine particle SiC.

[0002]

2. Description of the Related Art As a technique for manufacturing a porous SiC compact, there has been known for a long time a method in which granular silicon carbide is molded into a predetermined shape with a binder and then subjected to a firing treatment. Porosity cannot be imparted. 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 SiC compact having a high porosity, a slurry of SiC is adhered to the skeleton surface of an organic porous foam having a three-dimensional network structure and then dried,
There is a method of baking. The SiC molded body produced by this method exhibits a highly porous structure having a porosity of 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 (JP-A-59-3059), or compression at a specified ratio. A method has been proposed in which a ceramics 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 obtain a surplus slurry. The present applicant has proposed a process comprising a first step of removing and removing, and then drying and calcination, and a second step of re-impregnating the calcinated body with ceramics slurry and removing excess slurry, and then drying and calcination. (JP-A-3-83875). According to this method, the voids of the organic component are filled with SiC by re-impregnation, so that the material strength can be effectively improved. However, in this impregnation operation, all the pores inside the tissue are smoothed with the ceramic slurry. In addition, it is difficult to uniformly permeate, and there is a problem that local clogging and uneven strength are often generated.

On the other hand, rice husk containing a large amount of SiO ₂ component is made of Si.
It has attracted attention as an inexpensive raw material system for producing C, and its carbides and ash are used as raw materials for SiC whiskers and SiC.
Many techniques for obtaining a molded body have been proposed. this house,
Examples of the technology for producing a SiC molded body include, for example, rice husks made of iron salt,
After immersing in an aqueous solution containing vanadium salt, nickel salt or chromium salt and drying, it is carbonized and pulverized at a temperature of 400 to 100 ° C, and oxidized as it is or once in air, then 100 to 400 kg / cm ² There is proposed a method (Japanese Patent Application Laid-Open No. 60-5072) in which a sintering treatment is performed at a temperature of 1800 ° C. or higher under the above pressure. According to this method, it is said that a porous and strong molded body substantially composed of a SiC structure can be obtained by using an inexpensive raw material system, but it is high because of the simultaneous reaction of molding and SiC formation by hot pressing. It was not possible to obtain a porous SiC compact with porosity, the atmosphere during sintering was not non-oxidizing, and the heating temperature was set to 1800 ° C. or higher, so the generated SiC became coarse grains, and There is a problem that it is difficult to obtain a high molded product.

[0006]

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.

The inventor of the present invention has conducted extensive studies on a manufacturing technique of a porous SiC compact which satisfies the above-mentioned required characteristics by using an inexpensive rice husk raw material system, and as a result, carbonizes the rice husk carbide crushed to a predetermined grain size or less. Surface treatment with a thermosetting thermosetting resin, and after molding this, it is 1500-180 in a non-oxidizing atmosphere.
When the reaction treatment is performed in the temperature range of 0 ° C. and the step of burning out the residual carbon content is sequentially performed, the SiC whiskers and the Si
C Porous S having a structure in which fine particles are compounded, has a high porosity, is excellent in material strength, and is useful as a preform for composite materials.
The present invention was developed after confirming that an iC molded body was obtained.

Therefore, an object of the present invention is to use substantially inexpensive raw material system to obtain substantially whisker-like and fine-particle-like Si.
It is an object of the present invention to provide a method for producing a porous SiC compact having a high porosity and excellent material strength, which is composed of a composite structure of C.

[0009]

Means for Solving the Problems In order to achieve the above object, a method for producing a porous SiC compact according to the present invention comprises a crushing step of crushing a charcoal of rice husks to a maximum particle size of 40 μm or less. A surface treatment step of adhering a solution of a carbonizing thermosetting resin to the crushed chaff carbide powder, a molding step of shaping the chaff carbide powder after surface treatment into a predetermined shape, and a molded body under a non-oxidizing atmosphere. At 1500-180
A structural feature is that a reaction step of heat-treating in a temperature range of 0 ° C. and an incineration step of heat-treating a molded body after the reaction step in the atmosphere to burn off residual carbon components are sequentially performed.

(1) Grinding process: The present invention selectively uses, as a starting material, inexpensive rice husk charcoal which is targeted for agricultural waste. Carbide of rice husks can be removed by heating the rice husks in a furnace with the air shielded or in an inert gas atmosphere.
It can be produced by heat treatment in a temperature range of 00 to 1000 ° C, preferably 700 to 800 ° C.
The chaff carbide is pulverized by a pulverizing device such as a ball mill into a fine powder having a maximum particle size of 40 μm or less. The maximum particle size of crushed chaff carbide powder is 4
When it exceeds 0 μm, a large amount of coarse SiC particles are mixed in the structure of the obtained SiC molded body, the structure becomes inhomogeneous, and the material strength decreases. A catalyst component such as Fe, Ni, or Co may be attached to the chaff carbide powder after the crushing treatment, if necessary. The operation of depositing the catalyst component is carried out by immersing the rice husk carbide powder in a solution in which the water-soluble compound of the metal is dissolved, or by spraying the solution on the surface of the rice husk carbide powder and then drying.

(2) Surface treatment step: The rice husk carbide powder after the pulverization treatment is subjected to a surface treatment with a carbonizing thermosetting resin. As the carbonizing thermosetting resin to be surface-treated, a phenol resin or a furan resin is preferably used, and is used in a solution state dissolved in an organic solvent such as ethanol. The surface treatment is carried out by a method in which the rice husk carbide powder is immersed in a carbonizing thermosetting resin solution, sufficiently stirred and dispersed, and excess solution is removed by filtration or the like, followed by drying.

(3) Molding step: The rice husk carbide powder after the surface treatment is molded into a predetermined shape. Molding is performed by filling chaff charcoal powder into a mold, and at room temperature 100-400 kg.
It is carried out by a method of compression molding by applying a pressure of / cm ² . At this time, it is possible to adjust the tissue density of the molded body by changing the applied pressure, but the pressure is 100 kg / cm ²
If it is less than 400, the material strength of the finally obtained porous SiC compact will be insufficient, and if it exceeds 400 kg / cm ² , it will be impossible to impart high porosity to the finally obtained porous SiC compact.

(4) Reaction step: Next, the molded body is heat-treated in a non-oxidizing atmosphere to convert the structure of the molded body into SiC. The heat treatment conditions are as follows: the molded body is set in a heating furnace kept in an N ₂ or Ar atmosphere and the temperature is set to 1500 to 1
The temperature is set in the range of 800 ° C, preferably 1550 to 1700 ° C. In the heating stage, SiO ₂ which is a compositional component in the chaff carbide constituting the molded body reacts with C and the C component generated by carbonization of the thermosetting resin, and a part thereof becomes a needle-shaped single crystal SiC whisker, In addition, a part is generated as SiC fine particles, and Si is contained in the void skeleton that is macroscopically finely entwined with the SiC whiskers and entwined in a non-directional manner.
It has a tissue morphology in which C microparticles are bonded and fixed. But,
If the heating temperature is less than 1500 ° C, SiC does not react and generate,
If the temperature exceeds 1800 ° C, the degree of formation of SiC whiskers is reduced, and instead, a large amount of coarse SiC particles are formed, resulting in a decrease in material strength and an inhomogeneous structure.

(5) Incineration step: Since unreacted carbon component remains in the molded body after the reaction step, it is removed by incineration. This burn-off treatment is performed by molding the molded body in the atmosphere at 600-80.
The heat treatment is performed in the temperature range of 0 ° C. 600 ° C
If the temperature is less than 80%, the residual carbon component will not be burned off smoothly.
When the temperature exceeds 0 ° C, SiC is oxidized and SiO ₂
It is not preferable because the degree of conversion to

By sequentially carrying out the above-mentioned crushing step, surface treatment step, molding step, reaction step and incineration step,
A porous SiC molding having a desired high porosity and material strength is manufactured.

In order to produce a porous SiC compact having a higher material strength, the porous SiC compact obtained through the above steps is treated with a solution containing polycarbosilane, and then the polycarbosilane is added. A method of performing a firing treatment at a temperature at which is converted to SiC is added. Specific treatment means, polycarbosilane, for example, benzene, toluene, xylene,
It is dissolved in an appropriate organic solvent such as ether or alcohol, and the porous SiC molded body obtained in the above step is immersed in this solution and dried, and then 1500 to 1800 ° C. under an inert atmosphere such as argon or nitrogen. The method of baking at the heating temperature of is adopted. The porous silicon carbide body produced in the above process has a regulated porous structure having a porosity of 75 to 85% in which continuous pores having a pore diameter of 0.5 to 10 μm are uniformly distributed, and the material strength is bent. It is a high-purity product consisting essentially of silicon carbide having a physical property of 100 kg / cm ² or more in strength.

[0017]

According to the process of the present invention, inexpensive rice husk carbide is used as a starting material, and coarse S is obtained by adjusting the particle size in the crushing step.
By suppressing the generation of iC particles and increasing the bondability of the rice husks carbide powder in the surface treatment step, the shaping in the next molding step is facilitated and the molding structure is strengthened and made uniform. In the subsequent reaction step, the SiO ₂ component and the carbon component in the rice husk carbide forming the compact react with each other to form acicular single crystal SiC whiskers and SiC fine particles in a macroscopically fine fibrous state. An SiC morphology in which SiC fine particles are bonded and fixed is formed inside the skeleton in which the SiC whiskers are entangled in a non-directional manner. This structure morphology has a high porosity while maintaining practical material strength by forming innumerable minute voids through an incineration step of finally burning out residual carbon components.

Furthermore, when the above-mentioned porous SiC compact is treated with a polycarbosilane solution and then post-treated to be SiC, the tissue skeleton is covered with the newly generated SiC and reinforced, and the material strength is further increased. To do. Therefore, the obtained porous SiC molded body has a porous structure in which continuous pores having a pore diameter of 0.5 to 10 μm are uniformly distributed and which has a porosity of more than 50%, and at the same time, is substantially silicon carbide excellent in material strength. It is a high-purity product consisting of a single substance.

[0019]

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

Examples 1 to 4 and Comparative Examples 1 to 2 Rice husks were filled in a graphite container, covered with a lid, placed in a heating furnace kept in an N ₂ gas atmosphere, and carbonized at 800 ° C. for 1 hour. The rice husk carbide was crushed by a ball mill for about 24 hours and then classified to obtain a fine powder having a maximum particle size of 38 μm (crushing step). The crushed rice husk charcoal powder is immersed in a solution of 50 parts by weight of a phenolic resin in 50 parts by weight of ethanol to be sufficiently stirred and dispersed, and then filtered to remove an excess solution, and vacuum dried for 10 hours. Phenolic resin was adhered to the surface of the rice husk carbide powder (surface treatment step). The rice husk carbide powder surface-treated in this manner was filled in a mold and molded at a normal temperature by applying a pressure of 400 kg / cm ² (molding step). Next, the molded body was set in a high-frequency induction heating furnace maintained in an N ₂ gas atmosphere, heated to a predetermined temperature at a temperature rising rate of 3 ° C./min, and heat-treated for 90 minutes to react (reaction step). . The molded body after the reaction step,
The residual carbon content was burned off by incineration at a temperature of 600 ° C. for 12 hours in the air (incineration step).

The compositional properties, porosity and compressive strength of the porous SiC compacts produced in the above steps were measured and shown in Table 1 in comparison with the varying generation conditions. In Table 1, the coarse particles are particles having a particle size of 5 μm or more, and the compression strength is shown as a strength value at a compression strain of 10% when a disk-shaped sample having a diameter of 30 mm and a height of 30 mm is used. .

Comparative Examples 3 to 4 All were the same as those in Examples 2 (reaction temperature 1600 ° C.) and 4 (reaction temperature 1800 ° C.) except that a husk carbide powder having a particle size of 75 μm was obtained in the crushing step. Porous S depending on conditions
An iC molded body was manufactured. The compositional properties, porosity, and compressive strength of the obtained porous SiC compact were measured, and are listed in Table 1 in comparison with the fluctuation generation conditions.

Examples 5 to 7 The molding pressure in the molding process was 100 kg / cm ² , 200 kg / cm ² , 3
A porous SiC compact was manufactured under the same conditions as in Example 3 except that the amount was changed to 00 kg / cm ² . Obtained porous Si
The compositional properties, porosity and compressive strength of the C molded body were measured,
It is also listed in Table 1 in comparison with the fluctuation generation conditions.

[0024]

[Table 1]

From the results shown in Table 1, the porous Si according to the example is
All C molded products have a high porosity of over 50% and 4.5 kg
It exhibits a compressive strength of / cm ² or more, and the porosity can be adjusted by controlling the molding pressure as seen in Examples 5 to 7. On the other hand, in Comparative Example 1 in which the reaction temperature is 1450 ° C., SiC is not generated, and in Comparative Example 2 in which the reaction temperature is 1900 ° C., the production rate of SiC whiskers is relatively small, so that the material strength is significantly reduced. Further, in Comparative Examples 3 and 4 in which the rice husk carbide powder at the time of crushing contained the maximum particle size exceeding 40 μm, a large amount of coarse SiC particles were formed, the material strength was lowered, and the structure was found to be heterogeneous. It was

Example 8 The porous SiC compact produced in Example 3 was treated with polycarbosilane (manufactured by Shin-Etsu Chemical Co., Ltd., number average molecular weight: 1475).
, Weight average molecular weight: 3365] xylene solution (concentration 20 wt
%), Air dried at room temperature, and then vacuum dried. The dried compact was placed in a heating furnace maintained with nitrogen gas and subjected to a firing treatment at 1700 ° C. for 5 hours. The obtained fired body was a porous body of simple substance of SiC whose porosity was slightly reduced to 67% but whose compressive strength was improved to 7.3 kg / cm ² .

[0027]

As described above, according to the present invention, it becomes possible to efficiently manufacture a high-purity porous SiC compact having a high porosity and material strength. Therefore, in addition to semiconductor materials, heat insulation materials used under severe conditions, filtration materials, particulate collection materials, etc., S
Since it has a composite composition containing a large amount of iC whiskers, it is expected to be useful as a preform for a composite material for infiltrating a metal or resin matrix.

Claims (2)

[Claims] 1. A crushing step of crushing a charcoal of rice husks to a maximum particle size of 40 μm or less, a surface treatment step of applying a solution of a carbonizing thermosetting resin to the crushed rice husk carbide powder, and a surface A molding step of molding the treated rice husk carbide powder into a predetermined shape, a reaction step of heat-treating the molded body in a temperature range of 1500 to 1800 ° C. in a non-oxidizing atmosphere, and a molded body after the reaction step in the atmosphere. A method for producing a porous SiC compact, which comprises sequentially performing an incineration step in which the residual carbon component is burned off by performing a heat treatment with. 2. A porous SiC molded body obtained according to claim 1 is treated with a solution containing polycarbosilane,
A method for producing a porous SiC compact, which is characterized by performing a baking treatment at a temperature at which the polycarbosilane becomes SiC.