JPH1067578A - Porous silicon carbide compact - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a porous silicon carbide compact, excellent in durability, hardly dusting and suitably usable in a heat insulating material, etc., of a high- temperature furnace by converting a part or all of a porous carbon compact into silicon carbide. SOLUTION: A thermosetting resin is mixed with a foaming agent, a curing agent and, as necessary, further a modifier, etc., and expanded and cured into a required shape to thereby provide a thermosetting resin foam, which is then carbonized at >=600 deg.C in a nonoxidizing atmosphere to afford a porous carbon compact. A part or all of the resultant porous carbon compact is subsequently converted into silicon carbide according to a method for reacting the porous carbon compact with silicon vapor or various silicon compounds at 1300-2300 deg.C temperature, etc., to thereby provide a porous silicon carbon compact. All or a part of the surface of the porous silicon carbide compact, as necessary, can be covered with a silicon carbide film or a carbon film by a method such as chemical vapor deposition(CVD) or physical vapor deposition(PVD).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a porous silicon carbide compact which can be suitably used as a heat insulator for a high temperature furnace such as a silicon single crystal pulling furnace.

[0002]

2. Description of the Related Art Porous carbon moldings obtained by firing thermosetting resin foams have excellent heat resistance and are lightweight, so that they can be used for aircraft, spacecraft, missiles, vapor deposition devices,
It has been widely used as a heat insulating material for various high-temperature furnaces, crucibles, various filters, and the like.

[0003] When such a porous carbon molded article is used as a heat insulating material, it has excellent shape retention properties and is easy to handle as compared with carbon fibers conventionally used as a heat insulating material. However, such a porous carbon molded body was inferior in durability because of insufficient mechanical strength and oxidation resistance. In addition, since powder is easily dropped from the surface, when used as a heat insulating material for a high-temperature furnace, the atmosphere in the furnace may be contaminated.

Japanese Patent Application Laid-Open Nos. 62-132716 and 1-122976 disclose a technique for solving the above-mentioned problem by forming a carbon film having a dense structure on the surface to prevent gas impermeability. Is disclosed.

However, in a semiconductor-related furnace having a precise function, such as a silicon single crystal pulling furnace, the performance required for a heat insulating material is extremely high. However, performance was not satisfactory. In particular, semiconductor-related furnaces are required to have a very high degree of cleanliness, and therefore are required to have less powder falling and not to be dusted.

When such a porous carbon compact is used in a silicon single crystal pulling furnace by the Czochralski method, the carbon component of the porous carbon compact and the carbon present in the furnace are reduced. Reaction with the silicon oxide gas produced carbon monoxide, a toxic gas, which was dangerous for the human body. The generated carbon monoxide is
It melts into the silicon single crystal to lower the quality and deteriorates the yield, or changes the dimensions of the member to form silicon carbide by altering the porous carbon constituting the member of the silicon single crystal pulling furnace. Was causing furnace destruction and damage.

[0007] Japanese Patent Publication No. 6-15808 discloses a vane obtained by converting a carbon material into silicon carbide. Japanese Patent Publication No. 3-3086 discloses a friction disk obtained by converting a carbon / carbon composite into silicon carbide. These techniques are intended to achieve improvement in abrasion resistance, oxidation resistance, etc. by converting a carbon component into silicon carbide, but are not intended to prevent the generation of carbon monoxide. Further, the technique is not intended to be used as a heat insulating material for a silicon single crystal pulling furnace or the like.

[0008]

SUMMARY OF THE INVENTION In view of the above, it is an object of the present invention to provide a porous silicon carbide molding which is excellent in durability, has less powder falling, and can be suitably used particularly as a heat insulating material for a silicon single crystal pulling furnace. It is intended to provide the body.

[0009]

SUMMARY OF THE INVENTION The present invention provides a porous carbon molded article obtained by carbonizing a thermosetting resin foam, and converting all or a part of the porous carbon molded article into silicon carbide. It is a porous silicon carbide molded body obtained by conversion. Hereinafter, the present invention will be described in detail.

In the present invention, first, a thermosetting resin foam is carbonized to obtain a porous carbon molded body. The above-mentioned thermosetting resin foam can be obtained by mixing a thermosetting resin with a foaming agent, a curing agent, and other modifiers as required, and foam-curing the mixture. The thermosetting resin is not particularly limited, and examples thereof include a phenol resin, a furan resin, an epoxy resin, a urethane resin, a coal pitch, and a petroleum pitch.

In the case where the thermosetting resin is foamed and cured, the thermosetting resin is a liquid raw material, so that it depends on the use to which the finally obtained porous silicon carbide molded article of the present invention is applied. Can be formed into an appropriate shape. For example, a cubic block shape can be obtained by curing using a cubic mold, or a shape matching the size of the heat insulating material of the furnace can be obtained by curing using a heat insulating material type mold.

The carbonization of the thermosetting resin foam is preferably performed in a non-oxidizing atmosphere, that is, under a reduced pressure or in an atmosphere of argon gas, helium gas, nitrogen gas, halogen gas or the like. The firing temperature is 600 ° C.
The above is preferred. When the temperature is lower than 600 ° C., the thermosetting resin foam is not sufficiently carbonized, so that the resulting porous carbon molded article has a low ignition temperature and is inferior in dimensional stability. More preferably, it is 800 ° C. or higher. Further, when the firing temperature is about 400 to 600 ° C., the thermal decomposition gas of the thermosetting resin foam is rapidly generated, and the dimensional shrinkage becomes large. Is preferred. Preferably, the heating rate is about 5 ° C./hour or less.

In the present invention, next, all or a part of the porous carbon compact is converted into silicon carbide (hereinafter referred to as "silicide").
) To obtain a porous silicon carbide molded body. The method for silicidizing the porous carbon molded body is not particularly limited, for example, a conversion method of reacting with silicon vapor or various silicon compounds; an object to be processed is embedded together with a filler same as a gas generation source of the conversion method. A method using pack cementation for heat treatment can be employed. Preferably, a conversion method in which a silicon monoxide gas is reacted with the porous carbon molded body by a silicidation reaction represented by the following formula: SiO (g) + 2C = SiC + CO According to the above conversion method, the reaction can be allowed to proceed while maintaining the shape of the porous carbon molded body.

The above silicidation reaction proceeds by heating in a temperature range of 1300 to 2300 ° C. Here, to generate silicon monoxide gas, for example, a mixture of silicon powder and silicon dioxide, a mixture of silicon carbide powder and silicon dioxide powder,
It can be carried out by heating a gas generating source such as a mixture of carbon powder and silicon dioxide powder and other various silicon mixtures to 1200 to 2300 ° C.

The porous silicon carbide molded article of the present invention may be obtained by silicifying only a part of the porous carbon molded article. For example, as shown in FIG. 1, in the case of the above-mentioned porous carbon molded body having a constant thickness and having a surface layer portion 11 and a central portion 12 on both surfaces, a portion excluding the central portion 12 is made of silicon carbide. After the conversion, the silicidation is stopped, and the carbonaceous matter remaining in the central portion 12 is removed.
A porous silicon carbide molded body having a hollow inside can be obtained. The method for removing the carbonaceous material remaining in the central portion 12 is not particularly limited.
A method of oxidizing and removing by heating to 00 ° C. can be adopted. In this case, the obtained cavity is preferably about が of the entire thickness of the porous silicon carbide molded body. Such a porous silicon carbide molded body having a hollow inside has a large amount of space therein, so it is lightweight, has excellent heat insulating effect, and can be particularly suitably used as a heat insulating material for a high-temperature furnace or the like.

As shown in FIG. 2, the inner layer 21 of the porous carbon molded body formed into a cylindrical shape is converted into silicon carbide so that the inner layer 21 is made of silicon carbide and the outer layer 22 is made of silicon carbide. A cylindrical porous carbon molded body having a two-layer structure, which is carbonaceous, can be obtained. A specific method for obtaining the cylindrical porous silicon carbide molded body having the two-layer structure is not particularly limited. For example, the outer peripheral surface 23 of the cylindrically formed porous carbon molded body is protected, A method in which only the surface is brought into contact with silicon monoxide and then the above silicidation reaction is performed can be employed. When such a cylindrical porous silicon carbide molded body having a two-layer structure is used as a heat insulating material for a silicon single crystal pulling furnace or the like, only the inner layer facing the furnace core is silicified. Generation of carbon oxide and the like can be effectively prevented.

The silicidation of only a part of the porous carbon compact can be performed by adjusting the reaction time while keeping the reaction temperature and the concentration of silicon monoxide constant in the silicidation reaction.

Generally, the silicon carbide molded body is made of alumina,
There is a method of sintering using a sintering aid such as silica to obtain a silicon carbide sintered body.
At a high temperature of not less than ℃, there is a disadvantage that the sintering aid is softened and the strength is reduced. Since the porous silicon carbide molded body of the present invention is so-called reaction sintering without using a general sintering method, it does not include a sintering aid and can exhibit extremely high strength.

The crystalline structure of the porous silicon carbide molded body of the present invention is preferably a cubic structure (cubic) β type. The β-type porous silicon carbide molded body having a cubic structure can be obtained by performing the silicidation reaction at 1400 to 2000 ° C. The β-type of the cubic structure has a strong tendency to increase in strength with an increase in temperature as compared with the α-type of a hexagonal structure (hexagonal) and a trigonal rhombohedral structure (rhombohedral),
It is highest at 1700 ° C. Since the pulling temperature of the silicon single crystal by the silicon single crystal pulling furnace is around 1500 ° C., the above-mentioned β-type porous silicon carbide molded body having a cubic structure exhibits extremely high strength and is powdered. Can be minimized.

The entire surface or a part of the porous silicon carbide molded body of the present invention can be covered with a silicon carbide film. Further, the entire surface or a part of the porous silicon carbide molded body of the present invention can be covered with a carbon coating. By coating the surface of the porous silicon carbide molded body of the present invention with the silicon carbide or the carbon coating, the gas impermeability of the porous silicon carbide molded body of the present invention can be significantly improved, Can be almost completely prevented. The porous silicon carbide molded body of the present invention has a surface layer formed by foaming and curing a resin, has a number of fine pores on its surface, and is coated with the silicon carbide film or the carbon film. In such a case, these coatings are rooted inside the porous material and exert a so-called anchor effect, so that an extremely firm surface coating can be obtained.

The surface of the porous silicon carbide molded body of the present invention is
The method for coating with the silicon carbide film or the carbon film is not particularly limited, and for example, a chemical vapor deposition method (CVD)
Method), a PVD method such as sputtering, or the like. In the present invention, among these, the above-mentioned CVD
It is preferable to form a thermal decomposition film by the method. Since the thermal decomposition film is very dense, the gas permeability is significantly lower than that of a film obtained by another method. Incidentally, the gas permeability (cm ² / sec) of the pyrolytic carbon is 1
In contrast to 0 ^-10 to 10 ^-12 , the high-density graphite fired body is 1 to 10 ^-1 .

As a specific method of the above-mentioned CVD method, in the case of coating with the above-mentioned silicon carbide film, for example, the porous silicon carbide molded body of the present invention is placed in a heating furnace having a reduced pressure vessel, and CH ₄ + H under an atmosphere of ₂ + SiCl _{4, 1700~}
Evaporate at 2000 ° C. or use CH ₃ SiCl ₄
A method of performing a vapor deposition treatment at 1400 to 1800 ° C. in an atmosphere of + H _{2 and} the like can be given. In the case of coating with the above carbon film, for example, a method in which the porous silicon carbide molded body of the present invention is placed in a heating furnace having a reduced-pressure vessel and subjected to a vapor deposition treatment at 1400 to 2000 ° C. in a CH ₄ + H ₂ atmosphere. And the like. In this case, the pressure in the heating furnace is 100
It is preferably equal to or less than Torr.

The porous silicon carbide molded body of the present invention can be suitably used as a heat insulating agent for high temperature furnaces such as a high temperature sintering furnace, a vacuum furnace, and a hot press furnace, particularly, a heat insulating material for a silicon single crystal pulling furnace. it can. Further, it can be suitably used as a heat insulating material in various fields such as the nuclear industry, the aircraft industry, the rocket industry, and the like. Furthermore, it is also used as a crucible for a silicon single crystal pulling furnace, a filter for exhaust gas treatment of automobiles, a bubbler for smelting metals such as aluminum, a filter for removing dust such as high-grade castings such as arts and crafts, and a whetstone. can do.

The porous silicon carbide compact of the present invention has a cell structure composed of a network in which solid columns or flat plates constituting the edges and surfaces of the cells are connected to each other. As the cell structure, an open cell type in which a solid portion is concentrated at a cell edge and an interface between cells is open, and a solid portion also exists at a cell boundary, and a cell and a cell There is a closed cell type that is separated. When the porous silicon carbide molded body of the present invention is used as a heat insulating material, the closed cell type is preferably used. In the case of a conventional heat insulating material using carbon fiber, its thermal conductivity (kcal / m
(Hr · ° C.) is 0.24, but in the closed-cell type heat insulating material using the porous silicon carbide molded body of the present invention,
The heat insulating effect is greatly improved to 0.11.

On the other hand, the porous silicon carbide molded body of the present invention is
Gas and liquid are poured into the inside, such as for gas smelting bubbler (plug) for metal smelting such as steel making, steel making, aluminum making, etc. for filtration filters of high-grade castings such as arts and crafts, etc. When used for the purpose of performing processing or physical processing, the above-mentioned open cell type can be suitably used. When the porous silicon carbide molded body of the present invention is used as a grindstone or the like, the above cell structure can be appropriately selected according to the object to be polished.

When the porous silicon carbide molded body of the present invention is used under a high temperature at which a certain force is applied, a carbon plate,
A sandwich structure using a face material such as a ceramic plate or a metal plate can be used as a panel. When the porous silicon carbide molded article of the present invention is applied as a heat insulating material for a square furnace or the like, the porous silicon carbide molded article of the present invention is made into a panel-like material, and the size and shape of the furnace to which these are applied It can be used by suitably joining with bolts or the like according to the requirements. Further, when the porous silicon carbide molded body of the present invention is applied as a furnace wall heat insulating material of a tunnel furnace, it can be used by suitably joining with bolts or the like according to the shape of the furnace wall.

The porous silicon carbide molded body of the present invention is hard and less powdered because all or a part of it is converted into silicon carbide. Further, when used as a heat insulating material for a silicon single crystal pulling furnace, since the layer facing the core portion is silicon carbide, it occurs in a silicon single crystal pulling furnace using a conventional carbon-based heat insulating material. No generation of carbon oxide occurs.
Furthermore, by coating the surface with a silicon carbide film or a carbon film, a dense surface layer having excellent gas impermeability can be obtained, and the mechanical strength and oxidation resistance are increased to further improve the durability, Further, powder drop can be minimized.

[0028]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Example 1 100 parts by weight of a phenol resin having a non-volatile content of 80% and a viscosity of 400 cps / 25 ° C. and 9 parts by weight of a foaming agent were stirred in a container for about 25 seconds, and then p-toluenesulfonic acid was used as a curing agent. 15 parts by weight of the aqueous solution was added and stirred for about 25 seconds to prepare a mixed liquid. This mixed liquid is heated at a surface temperature of 50 ° C.
Cylindrical mold (inner diameter 640 mm, outer diameter 800 mm,
(710 mm height). After foaming and curing for about 30 minutes, it was taken out of the mold to obtain a resol type phenol resin foam.

The obtained phenolic resin foam is heated in a non-oxidizing atmosphere to 900 ° C. at a rate of about 20 ° C./hour.
Further, it was fired at a temperature rising rate of 300 ° C./hour up to 2000 ° C. to obtain a porous carbon molded body having an apparent density of 0.15 g / cm ³ . The obtained porous carbon compact is put into a carbon container so as not to come into contact with a mixture of silicon powder and silicon dioxide, and is kept at 1900 ° C. for 2 hours to convert the whole into β-type silicon carbide. A molded article was obtained.

The obtained porous silicon carbide compact was used as a heat insulating material of a silicon single crystal pulling furnace to obtain a silicon single crystal. The obtained silicon single crystal was evaluated by comparing it with a silicon single crystal obtained from a conventional silicon single crystal pulling furnace using carbon fiber as a heat insulating material. It was 1/3. In addition, the life as a heat insulating material is 4 times longer than that of conventional carbon fiber.
It was twice.

Example 2 By setting the treatment time for converting to silicon carbide to 30 minutes, the cylindrical inner surface layer was converted to silicon carbide, and the other portion was formed of a carbonaceous porous silicon carbide molded body. except,
A porous silicon carbide molded body was obtained in the same manner as in Example 1, and a silicon single crystal was obtained and evaluated in the same manner as in Example 1. The content of carbon contained as an impurity was １ ／.
And the life as a heat insulating material was tripled.

Example 3 A silicon carbide coating was formed on the entire porous silicon carbide compact by CVD.
A porous silicon carbide molded body was obtained in the same manner as in Example 2 except that it was provided by the method, and a silicon single crystal was obtained and evaluated in the same manner as in Example 2. , 1/4, and the life as a heat insulating material was quadrupled.

Example 4 A pyrolytic carbon coating was applied to the entire surface of the porous silicon carbide molded body by CV.
A porous silicon carbide molded body was obtained in the same manner as in Example 2 except that it was provided by Method D, and a silicon single crystal was obtained and evaluated in the same manner as in Example 2. The content of carbon contained as an impurity was determined. Was 1/3, and the life as a heat insulating material was 4 times.

Example 5 A porous silicon carbide molded article was obtained in the same manner as in Example 1 except that a silicon carbide film was provided on the inner surface of the cylindrical porous silicon carbide molded article by the CVD method. When a silicon single crystal was obtained and evaluated in the same manner as in Example 1, the content of carbon contained as an impurity was 1/3, and the life as a heat insulating material was 5 times.

[0036]

The porous silicon carbide molded body of the present invention has the above-mentioned structure, and therefore has excellent heat insulating properties and durability, and has less powder falling. In addition, when used as a heat insulating material for a silicon single crystal pulling furnace, carbon monoxide is not generated, so that work safety is high and a high quality silicon single crystal can be obtained at a high yield. .

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a porous silicon carbide molded body of the present invention in which only a portion excluding a central portion is silicified.

FIG. 2 is a schematic view of a porous silicon carbide molded body of the present invention in which only an inner layer portion of a cylindrical molded body is silicided.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Surface layer part 12 Central part 21 Inner layer part 22 Outer layer part 23 Outer peripheral surface

Claims (5)

[Claims] 1. A method of using a porous carbon molding obtained by carbonizing a thermosetting resin foam to convert all or a part of the porous carbon molding into silicon carbide. Characteristic porous silicon carbide molded body. 2. When converting the porous carbon molded body into silicon carbide, a portion excluding a central portion of the porous carbon molded body is converted into silicon carbide, and carbonaceous material remaining in the central portion is removed. The porous silicon carbide molded body according to claim 1, which is obtained by the above method. 3. The method according to claim 1, wherein when converting the porous carbon molded body into silicon carbide, only the inner layer portion of the porous carbon molded body formed into a cylindrical shape is converted into silicon carbide. Porous silicon carbide molded body. 4. A porous silicon carbide molded body, characterized in that the porous silicon carbide molded body according to claim 1 is further covered with a silicon carbide coating on all or a part of its surface. 5. A porous silicon carbide molded body, characterized in that the porous silicon carbide molded body according to claim 1 is further covered with a carbon coating on all or a part of its surface.