JPH05132373A - Method for producing porous silicon carbide composite - Google Patents

Abstract

(57) [Abstract] [Purpose] A method for producing a porous silicon carbide composite having a composite structure in which a tissue surface of a porous carbon skeleton is formed by coating and having excellent tissue strength and air permeability. provide. [Structure] A sheet-shaped molded body of rayon fiber is impregnated with a phenol resin, laminated and hot-pressed, and then fired and carbonized to form a skeleton porous carbon body. Then, the skeleton porous carbon body is set in the reaction chamber, and the carbon texture surface is coated with silicon carbide by the pulse CVI method in which the halogenated organosilicon compound is intermittently charged while heating at 900 to 1000 ° C. to cause the reductive thermal decomposition reaction. Form the layers.

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 composite having a composite structure in which a silicon carbide layer is uniformly formed on the surface of a porous carbonaceous skeleton without clogging.

[0002]

2. Description of the Related Art A porous body made of silicon carbide is used for industrial filters and heat insulating materials by utilizing its excellent heat resistance and corrosion resistance. As a technique for producing this type of porous silicon carbide body, a slurry in which fine particles of silicon carbide and a binder are mixed in water is impregnated into a urethane foam having a three-dimensional network structure, and high-temperature heat treatment is performed to vaporize the urethane component and water. A method of recrystallizing residual silicon carbide (Japanese Patent Laid-Open No. 3-83875) is known. According to this method, a porous silicon carbide molded body can be obtained relatively easily, but since the silicon carbide structure formed by recrystallization has a low density and weak skeletal strength, it cracks in the material during use. However, there are defects in the material such as breakage and detachment of silicon carbide particles from the structure.

In the above method, depending on the impregnation condition of the slurry, the formed structure may be clogged to impair the air permeability, and when applied to the filter material, the sufficient function may not be exhibited. As a means for preventing such clogging, a method of lowering the slurry concentration and performing impregnation in several times has also been proposed (JP-A-59-3059),
Even in this method, weakening of the skeletal tissue still remains.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, which have been a bottleneck in the prior art for producing a porous silicon carbide body, and its object is excellent in material structure strength. Another object of the present invention is to provide a method for producing a porous silicon carbide composite body having a porous structure without clogging.

[0005]

The method for producing a porous silicon carbide composite according to the present invention for achieving the above object comprises:
A sheet-shaped molded body of rayon fiber is impregnated with a thermosetting resin liquid having a residual carbon ratio of 40% or more, laminated hot-press molding, and then firing carbonized to form a skeletal porous carbon body, and then reacting the skeletal porous carbon body. It is set in a chamber, and a silicon carbide coating layer is formed on the carbon texture surface by the pulse CVI method in which a halogenated organosilicon compound is intermittently charged while heating at 900 to 1000 ° C. to cause a reduction thermal decomposition reaction. It is a feature of.

The structure of the present invention is roughly divided into a carbon skeleton forming step of forming a skeleton porous carbon body and a silicon carbide coating step of forming a silicon carbide coating layer on the textured surface of the skeleton porous carbon body. Details of each of these steps are as follows.

(1) Carbon skeleton forming step It is preferable to apply a non-woven sheet of rayon fiber to the sheet-shaped molded article of rayon fiber as a raw material base material,
For example, a sheet-shaped molded product obtained by dispersing short fibers cut from rayon filaments in water and molding into paper is preferably used. The sheet-shaped molded product is sufficiently dried and then impregnated with a thermosetting resin liquid having a residual carbon rate of 40% or more. The residual carbon ratio of the thermosetting resin means that the resin is 800 in a non-oxidizing atmosphere.
Indicates the weight of carbon content remaining when calcined at a temperature of ℃, and when the residual carbon content is less than 40%, it is extremely difficult to improve the strength of the obtained skeletal porous carbon body to a practical level. Become.

Examples of the thermosetting resin having a residual carbon content of 40% or more include phenol resin, furan resin, polyimide resin, divinylbenzene, etc. For the purpose of the present invention, phenol resin is used. Resins are preferably used. These thermosetting resins are preferably dissolved in a suitable solvent in the initial condensation state to form a solution. For solution, low viscosity such as acetone and ethanol, high permeability,
It is preferable to select and use an organic solvent having a property of easily heat-volatilizing. When the resin concentration of the solution is less than 5% by weight, the strength characteristics are deteriorated, while when it exceeds 40% by weight, the viscosity is increased to impair the impregnating property and the pores are clogged. Therefore, it is preferable to set the resin concentration in the range of 5 to 40% by weight. The impregnation treatment is performed by immersing the sheet-shaped molded product in a thermosetting resin liquid, or by applying the thermosetting resin liquid to the sheet-shaped molded product by a method such as spraying or brushing.

After the impregnation treatment, the sheet-shaped compact is laminated in a desired number in a semi-cured state, and the impregnated resin is cured by molding under a hot-pressing condition in which the entire surface is compressed while being heated. A skeleton porous carbon body is obtained by carrying out a firing carbonization treatment at a temperature of ℃ or higher. In this step, by controlling the conditions such as the concentration of the thermosetting resin liquid and the impregnation amount, the porosity suitable for the skeletal structure is 25 to 70%, the average pore diameter is 5 to 55 μm.
It is possible to impart a property with good air permeability of m 2.

(2) Silicon Carbide Coating Step In this step, the skeletal porous carbon body is set in the reaction chamber and heated to 900 to 1000 ° C. in the reaction chamber while the halogenated organosilicon compound is entrained in hydrogen gas. This is performed by the pulse CVI method in which the operation of contacting the skeleton porous carbon body in a gas state is intermittently repeated in a short cycle. Examples of the halogenated organosilicon compound include trichloromethylsilane (CH ₃ SiCl ₃ ), trichlorophenylsilane (C ₆ H
₅ SiCl ₃ ), dichlorodimethylsilane (CH ₃ SiHCl ₂ ), chlorotrimethylsilane ((CH ₃ ) ₃ SiCl) and the like can be used.

Appropriate reaction conditions include heating the temperature of the skeletal porous carbon body set in the reaction chamber to 900 to 1100 ° C. to reduce the system internal pressure to 2 Torr or less, and adding trichloromethylsilane (CH _{3) to the system.} A cycle of introducing a mixed gas of SiCl ₃ ) and hydrogen so that the system pressure is 700 to 760 Torr and maintaining it for a certain period is repeated intermittently at intervals of a second. Is formed.

[0012]

According to the present invention, first, in the carbon skeleton forming step, the carbon volatile component is converted into a carbon compact having a porous structure by volatilization of the heat volatile component and carbonization of the thermosetting resin component. At this time, most of the thermal volatile components mainly composed of rayon fiber volatilize smoothly in the carbonization process and contribute to the formation of uniform pores, but at the same time, part of them remain carbonized to form the basic skeleton of the carbon fiber. ..
On the other hand, the thermosetting resin component is converted into strong glassy carbon by firing and carbonization, and is evenly distributed in a state of being fixed to the basic skeleton. Therefore, the obtained carbon body is provided with uniform fine air-permeable pores and a porous property excellent in tissue strength.

In the subsequent silicon carbide coating step, pulse C
Since the VI method is used, the reaction gas having a high degree of saturation surely reaches the inside of the texture of the porous carbon body, and the carbon texture plane is formed as an amorphous or fine polycrystalline homogeneous and strong silicon carbide layer without causing clogging. Cover completely.

The above actions synergistically produce a composite structure in which a silicon carbide layer is formed on the entire surface of a strong porous carbon body,
It is possible to manufacture a porous silicon carbide composite having both excellent tissue strength and air permeability.

[0015]

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

Example A rayon short fiber having an average diameter of 30 μm and a length of 5 mm is stirred and dispersed in water, paper-formed using a Fourdrinier paper machine, dried and weighed 70 g / m ² , a sheet having a thickness of 0.23 mm. A shaped body was obtained.
This sheet-shaped compact was immersed in a phenol resin acetone solution (concentration: 20% by weight) with a residual carbon rate of 45% and impregnated at 50 ° C
It was dried for 15 minutes and semi-cured. Laminate 14 semi-cured sheets and put them in a mold, heating temperature 140 ℃, applied pressure 0.5
The resin component was completely cured while being integrally molded under a heat / pressure condition of kg / cm ² . Then, it was transferred to an electric furnace maintained in a nitrogen atmosphere and heated up to 1000 ° C at a heating rate of 20 ° C / hr.
It was held for a time and carbonized by firing. The obtained skeleton porous carbon body is a plate having a length and width of 40 mm and a thickness of 2 mm, a bulk specific gravity of 0.45 g / cm ³ , a porosity of 65%, an average pore diameter of 35 μm, a bending strength of 220 kg / cm ² , and a bending elastic modulus of 450 kg / mm. ^{It had two} physical properties.

Next, the above-mentioned skeleton porous carbon body is pulsed with CVI.
Set it in the reaction chamber of the device and apply a reduced pressure of 2 Torr.
Heated to 1000 ° C. A mixed gas of trichloromethylsilane (CH ₃ SiCl ₃ ) and hydrogen (H ₂ ) with a molar ratio of 5: 100 was introduced into the system under the condition of 720 Torr in 1 second, held for 1 second, and then again in the system. Was reduced to 2 Torr in 2 seconds. This cycle of pressure reduction, introduction and holding was repeated 2000 times to form a silicon carbide coating layer on the entire surface of the texture of the skeleton porous carbon body. Various characteristics of the porous silicon carbide composite body thus formed were measured, and the results are shown in Table 1.

Comparative Example A three-dimensional reticulated urethane foam having a porosity of 98% was vacuum-impregnated with a slurry prepared by mixing 100 parts by weight of α-type silicon carbide powder having an average particle size of 10 μm, 20 parts by weight of water, 1.5 parts by weight of an organic binder and a dispersant. And dry it, then at 2100 ℃ in a nitrogen atmosphere.
The silicon carbide component was recrystallized by heating at the temperature. The characteristics of the porous silicon carbide body thus obtained are also listed in Table 1.

[0019]

[Table 1]

From the results shown in Table 1, the porous silicon carbide composites according to the examples have a porosity with good air permeability, and the strength performance is a comparative example of silicon carbide alone obtained by the prior art. The value is remarkably higher than that of the porous silicon carbide body according to.

[0021]

As described above, according to the present invention, a porous carbon skeleton has a composite structure in which a textured surface is covered with a silicon carbide layer, and has excellent texture strength and good air permeability without clogging. A porous silicon carbide composite can be manufactured.
Therefore, it is expected to be useful as a particularly high-performance industrial filter material.

Claims (1)

[Claims] 1. A residual carbon rate in a rayon fiber sheet-shaped molded product.
After 40% or more of thermosetting resin liquid is impregnated and laminated thermocompression molding is performed, firing carbonization is performed to form a skeleton porous carbon body, and then the skeleton porous carbon body is set in the reaction chamber, and 900 ~
A porous silicon carbide composite material, characterized in that a silicon carbide coating layer is formed on a carbon texture surface by a pulse CVI method in which a halogenated organosilicon compound is intermittently charged while being heated to 1000 ° C. to carry out a reductive thermal decomposition reaction. Production method.