JP2001089238A - Molded thermlly insulating material and heat shield - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a molded thermally insulating material which exhibits an excellent thermally insulating characteristic for a long period of time, has an excellent shape retaining property and is used for a high-temperature atmosphere furnace having excellent mechanical strength. SOLUTION: The molded thermally insulating material of a sandwich structure is contituted by laminating felt-like carbon fibers 13 and expanded graphite sheets 12 and sandwiching this laminate with C/C materials 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molded heat insulating material used in a high-temperature atmosphere furnace.

[0002]

2. Description of the Related Art Conventionally, as a heat insulating material used in a high-temperature atmosphere furnace, a molded article made of felt-like carbon fiber has been known.

[0003] However, molded articles made of felt-like carbon fibers have insufficient shape retention and mechanical strength.
Due to its large specific surface area, it easily reacts with the surrounding atmosphere,
For example, when used in a semiconductor single crystal pulling furnace, etc.,
Compared to a member made of graphite or a carbon fiber reinforced carbon composite material (hereinafter referred to as C / C material) used at the same time, silicon carbide is formed very quickly, the shape cannot be maintained, and some parts are missing. Or Further, there is a problem that the heat insulating property is deteriorated and the heat insulating material does not function sufficiently.

Japanese Utility Model Laid-Open No. 4-104434 proposes a molded heat insulating material in which a carbonaceous sheet is mechanically joined to a surface of a heat insulating material made of felt-like carbon fibers by a carbonaceous joining member. The purpose is to prevent the carbonaceous sheet bonded to the surface of the molded heat insulating material from being peeled off. Therefore, the carbonaceous sheet on the surface
Since it is mechanically joined by the carbonaceous joining member, it does not peel off, and it is a molded heat insulating material which is excellent in shape retention as compared with a heat insulating material consisting only of felt-like carbon fibers.
However, since the mechanical strength of the carbonaceous sheet itself is low, the mechanical strength of the entire molded heat insulating material has not been improved. Further, the molded heat insulating material from which the felt-like carbon fibers are exposed generates dust during use and contaminates the inside of the furnace. When used in the presence of an atmosphere (for example, SiO gas), it is further promoted. For this reason, there was a problem that the heat insulation characteristics changed.

[0005]

SUMMARY OF THE INVENTION Accordingly, the present invention has been made in view of the above circumstances, and has excellent heat insulating properties over a long period of time, excellent shape retention properties, and excellent mechanical strength. An object of the present invention is to provide a heat insulating material used in a high-temperature atmosphere furnace.

[0006]

Means for Solving the Problems In order to solve the above problems, the present inventors have conducted intensive studies, laminated felt carbon fibers and expanded graphite sheets, and sandwiched the laminate with a C / C material. By having a structure, and in some cases, a structure in which the laminate is entirely covered with the C / C material, it is possible to provide an excellent heat-insulating material having excellent mechanical strength, less contamination in the furnace, excellent durability, and excellent durability over a long period of time. We have found that we can do this and completed the present invention.

That is, in the molded heat insulating material of the present invention, felt-like carbon fibers and expanded graphite sheets are alternately laminated, and C
/ C material. Further, the carbon fiber sheet is characterized in that felt-like carbon fibers and expanded graphite sheets are alternately laminated and sandwiched by a C / C material, and the remaining surface is covered with the C / C material. Also,
The carbon fiber reinforced carbon composite material is two cylinders having different diameters, and the felt-like carbon fiber and the expanded graphite sheet are alternately laminated in the radial direction between the two cylinders, and It is preferable to be sandwiched by the carbon composite material. In that case, it is preferable that the upper and lower surfaces are covered with a C / C material. The bulk density of the laminate comprising the felt-like carbon fibers and the expanded graphite sheet is 0.1
It is preferably ~0.3g / cm ^3. Further, it is preferable that the ratio of the felt-like carbon fiber and the expanded graphite sheet is one layer of the expanded graphite sheet with respect to the felt-like carbon fiber thickness of 3 to 10 mm. In addition, the impurity content is 10 pp.
m or less. Further, it is preferable that the surface is coated with pyrolytic carbon or glassy carbon.

The felt-like carbon fiber heat insulating material is formed by alternately laminating a plurality of felt-like carbon fibers and expanded graphite sheets to form a laminate and sandwiching the laminate with a C / C material. , A material having both functions of each material such as gas impermeability, heat shielding property, and mechanical strength of C / C material of the expanded graphite sheet. In addition, by sandwiching the laminate between two C / C cylinders having different diameters, the felt-like carbon fibers can be easily maintained in a compressed state. That is,
A molded heat insulating material having excellent mechanical strength and capable of maintaining heat insulating properties for a long time can be obtained. Further, by covering the remaining surface not sandwiched by the C / C material, dust generation from these laminates can be completely prevented. here,
The remaining surfaces refer to upper and lower surfaces, for example, when the laminate has a hollow cylindrical shape. When the laminate is a rectangular parallelepiped, it refers to a plane parallel to the lamination direction.

Here, the C / C material used in the present invention is:
It may be manufactured by a general manufacturing method, for example, in advance,
A prepreg having a predetermined shape is produced, and the prepreg is laminated and then hot-pressed to form a molded product, or a molded product produced by a filament winding method. These match the shape of the desired insulation,
It can be manufactured by appropriately selecting the manufacturing method. Examples of the carbon fiber constituting the C / C material include a PAN type and a pitch type.

The felt-like carbon fiber may be manufactured by a general method. The felt-like carbon fiber may be made of only the felt-like carbon fiber, or the felt-like carbon fiber may be impregnated with a resin or the like, carbonized or graphitized. May be used. Examples of the carbon fibers constituting the felt-like carbon fibers include polyacrylonitrile, rayon, polymer fibers of cellulosic fibers, and carbon fibers made of pitch fibers. Is used. Further, the felt-like carbon fiber in the present invention,
The density is 0.05 to 0.15 g / cm ³ , preferably 0.1 to 0.1 g / cm ³ .
It is preferably from 0.7 to 0.12 g / cm ³ . With such a density range, C / C having different diameters, which will be described later, is used.
It becomes possible to compress and laminate between materials. Then, by adjusting the degree of compression and adjusting the number of layers to be laminated, it is possible to adjust the heat insulation properties.

The expanded graphite sheet is not particularly limited and has excellent gas impermeability, for example, a gas permeability of nitrogen gas at room temperature of 1 × 10 ⁻⁴ cm ² / s or less, preferably 5 × 10 ⁻⁴ cm ² / s. × 10 ^-5 cm ² / s that is less. By forming a laminate with the felt-like carbon fiber using such an expanded graphite sheet having excellent gas impermeability, it is possible to prevent gas convection inside the heat insulating material, Heat can be shielded.

When laminating the felt-like carbon fiber and the expanded graphite sheet, the felt-like carbon fiber is compressed and laminated with the expanded graphite sheet so that the bulk density of the laminate made of these is 0.1%. It can be adjusted to 0.3 g / cm ³ , preferably 0.15 to 0.25 g / cm ³ . By adjusting the density, the heat insulation properties can be adjusted.

Further, the heat insulating property can be adjusted by inserting one layer of the expanded graphite sheet with respect to the felt carbon fiber thickness of 3 to 10 mm in the ratio of the felt-like carbon fiber and the expanded graphite sheet.

Further, the treatment is carried out at a high temperature of 2,000 ° C. or more in a halogen gas atmosphere, and the impurity content is 1 ash content.
It is preferably at most 0 ppm. The amount of ash referred to here is determined by accurately measuring 20 g of a sample, loading the sample into a platinum crucible (volume: 50 cc), and placing it in an oxygen stream (2 to 3 l / min).
, After holding at a temperature of 950 ° C., ashing, cooling naturally in a desiccator, and measuring the remaining ash content.

The molded heat insulating material of the present invention is configured as described above, and can be suitably used in various high-temperature atmosphere furnaces, particularly, a semiconductor single crystal pulling furnace, a heat treatment furnace for manufacturing an optical fiber, and the like. Particularly, in a semiconductor single crystal pulling furnace (hereinafter, referred to as a CZ furnace), an inner shield, a lower ring, an upper ring, a heat shield, and the like, which are components of the CZ furnace, are conventionally provided separately from a heat insulating material. By using the molded heat insulating material of the present invention,
The combined characteristics of these two can be exhibited, and the effective processing range in the furnace can be expanded.

Hereinafter, the case where the molded heat insulating material of the present invention is used as a heat shield of a CZ furnace will be described in detail with reference to the drawings.

[0017]

FIG. 1 shows a molded heat insulating material of the present invention.
It is the schematic which shows one Example at the time of using as a heat shield of a Z furnace. Heat shield 1 of the present invention
Is composed of a C / C material 11 that sandwiches a laminate 14 composed of an expanded graphite sheet 12 and felt-like carbon fibers 13 from the outer peripheral side and the inner peripheral side.

The C / C materials 11a and 11b are made of a general C / C material.
According to the method of manufacturing the C material, the carbon fiber cloth prepreg is cured to form a molded body. Alternatively, a cylindrical molded body made of cylindrical C / C materials having different diameters is manufactured by, for example, forming into a cylindrical shape by a filament winding method, and a C / C material 11a having a small diameter on the inner peripheral side and an outer peripheral side are formed. A C / C material 11b having a large diameter is prepared. These molded bodies may be in a state of being baked, carbonized and graphitized, or in a state where a resin used in molding by prepreg, filament winding or the like is cured.

These C / C materials 11a and 11b have a thickness of 0.5 to 10.0 mm, preferably 1.0 to 2.0 mm.
It is preferable to keep Thereby, while maintaining shape retention, it can be set as the heat insulating material with high mechanical strength.

Next, the C / C material 1 having a small diameter on the inner peripheral side
The expanded graphite sheet 12 and the felt-like carbon fibers 13 are alternately laminated on the surface of the surface 1a in the order of concentric circles. And
The outermost layer, that is, the layer in contact with the C / C material 11b on the outer peripheral side is preferably laminated so as to form the expanded graphite sheet 12. In addition, first, felt-like carbon fiber 13 and then expanded graphite sheet 12 are applied to the surface of the inner peripheral side C / C material 11a.
, And the felt-like carbon fibers 13 may be in contact with the outer C / C material 11b. However, it is preferable to laminate the expanded graphite sheet 12 so as to be in contact with the C / C materials 11a and 11b on the inner and outer peripheries, since the felt-like carbon fibers 13 can be prevented from directly contacting the gas.

Here, the expanded graphite sheet 12 used is acceptable.
Flexible, gas permeability 1 × 10 ^-Fourcm^Two/ S or less,
Preferably 5 × 10^-Fivecm^Two/ S or less
New With such a gas permeability, the inside of the heat insulating material
Gas convection can be prevented.

The felt-like carbon fiber 13 has a density of 0.0
5 to 0.15 g / cm ³ , preferably 0.07 to 0.1
It is preferably 2 g / cm ³ . Thereby, the compression ratio can be adjusted.

The laminate 14 of the felt-like carbon fiber 13 and the expanded graphite sheet 12 is put in a plastic bag together with the C / C material 11a, and the air in the bag is evacuated from outside using a vacuum pump or the like. By adjusting the pressure in the bag, it is adjusted to a predetermined thickness.

Then, the laminate 14 in the bag in a vacuum state is
Is covered with the C / C material 11b on the outer peripheral side, and the vacuum bag is removed. When the vacuum is released, the felt-like carbon fibers 13 in the laminate 14 expand. Thereby, the felt-like carbon fibers 13 in the laminate 14 are compressed, and the C / C material 1
A state of being sandwiched by 1a and 11b is obtained.

In this state, it is possible to use the resin, but it is preferable to make resin penetrate into the internal laminate 14. Thereby, the bond between the C / C materials 11a and 11b, the expanded graphite sheet 12, and the felt-like carbon fiber 13 can be strengthened. Further, in some cases, the C / C material 11 is put on the upper and lower end faces. As a result, the felt-like carbon fibers 13 are not exposed, and the felt-like carbon fibers 13 are not exposed.
And the laminate made of the expanded graphite sheet 12 can be completely covered with the C / C material, and the generation of dust during use can be suppressed. It is preferable that the C / C material 11 used here has a thickness of 0.5 to 10 mm, like the C / C materials 11a and 11b used for the inner and outer circumferences.

After the resin is impregnated into the laminate 14, 15
Heat treatment at 0 to 200 ° C. to cure the resin. Then
Heat treatment at 800 to 1000 ° C. to carbonize the resin. Next, the molded body was subjected to an atmospheric pressure of halogen gas atmosphere for 18 hours.
The graphitization treatment and the high-purification treatment are performed at 00 to 2200 ° C. Here, the halogen gas is a gas of halogen or a compound thereof, for example, chlorine, a chlorine compound, fluorine, a fluorine compound, and a compound containing chlorine and fluorine in the same molecule (monochlorotrifluoro). Methane, trichloromonofluoromethane, dichlorofluoroethane, trichloromonofluoroethane, etc.). Then, by the reaction with these halogen-based gases, impurities contained in the compact, particularly metal impurities, are evaporated and vaporized as halides and removed. As a result, the impurity content is reduced to 10 ash content.
ppm or less, CZ that requires high purity
It can be used as a heat shield or a heat insulator for a furnace.

Next, it is preferable to impregnate and coat the pyrolytic carbon by the CVD method. The CVD method referred to here is a method including a so-called CVI method in which pyrolytic carbon is permeated and deposited from the open pores on the surface to the inside, and includes hydrocarbons, for example, hydrocarbons having 1 to 8 carbon atoms, particularly 3 carbon atoms. The operation is performed at a hydrocarbon concentration of 3 to 30%, preferably 5 to 15%, and a total pressure of 100 Torr or less, preferably 50 Torr or less, using a hydrocarbon gas or a hydrocarbon compound such as propane or methane gas. When such an operation is performed, the hydrocarbon forms a giant carbon compound near the surface of the base material by dehydrogenation, thermal decomposition, polymerization, etc., which deposits and precipitates on the base material, and the dehydrogenation reaction further proceeds, resulting in a dense body. A pyrolytic carbon layer is formed or penetrated and impregnated. The temperature range for the precipitation is generally 80
Although it is a wide range from 0 to 2500 ° C., it is preferable to perform the treatment in a relatively low temperature range of 1300 ° C. or less in order to impregnate as much pyrolytic carbon as possible. By setting the deposition time to 50 hours or more, and more preferably 100 hours or more, pyrolytic carbon can be formed inside. Further, by setting the deposition time at 50 hours or more, and more preferably at 100 hours or more, pyrolytic carbon can be formed at every corner of the inside, which contributes to suppressing generation of gas from the inside. Further, in order to increase the degree of impregnation, an isothermal method, a temperature gradient method, a pressure gradient method, or the like can be used, and a pulse method capable of shortening time and densifying may be used.

Further, glassy carbon can be coated instead of the above-mentioned pyrolytic carbon. The glassy carbon is immersed in a thermosetting resin such as a phenolic resin, or applied to the surface by any method such as brushing. Then, the resin is cured and fired in a nitrogen atmosphere to carbonize the resin. As a result, the entire surface can be covered with glassy carbon.

The molded heat insulating material of the present invention is not limited to a cylindrical shape, but has a sandwich structure in which a laminate formed by alternately laminating expanded graphite sheets and felt-like carbon fibers is sandwiched between C / C materials. If so, a plate-like molded body may be used. Then, it is preferable that the remaining surface not sandwiched by the C / C material is covered with the C / C material so that the felt-like carbon fiber is not exposed on the surface. Thereby, it is possible to suppress the carbon fibers constituting the felt-like carbon fibers from scattering into the furnace.

[0030]

The present invention will be described more specifically with reference to the following examples.

(Example 1) Bulk density 0.08 g / cm^Three
Felt carbon fiber with a gas permeability of 5 × 10 ^-Fivecm
^Two/ S expanded graphite sheet impregnated with phenolic resin
Alternately so that the layers of felted carbon fibers become 8 layers
Laminated, the bulk density of the laminated body is 0.2 g / cm^ThreeWill be
The laminate is compressed to 42 mm by hot pressing.
Was. Felt carbon fiber and expanded graphite sheet of laminate cross section
The ratio of felt is one layer of graphite sheet per 5.1 mm of felt
Met. The thickness of this laminated body is 1.2 m above and below.
m, sandwiched by C / C material impregnated with phenolic resin,
Sandwich structure, hot press molding, 200 ×
A plate-shaped compact having a thickness of 200 mm and a thickness of 42.4 mm was obtained.
After firing this molded body and carbonizing the resin etc., the halogen gas
High purity at the same time as graphitization under the conditions of a gas atmosphere and a temperature of 2000 ° C.
Ash content to reduce the ash content to 10 ppm or less.
The following high-purity molded insulation was obtained.

Example 2 Same as Example 1 except that the number of felt carbon fiber layers in the laminate was eight, and the laminate was compressed to a bulk density of 0.15 g / cm ³ . By the method, a plate-shaped molded heat insulating material having a size of 200 × 200 mm and a thickness of 56 mm was obtained. The ratio between the felt-like carbon fibers and the expanded graphite sheet in the cross section of the laminate was one layer of graphite sheet with respect to 6.8 mm of felt. Further, the same high-purification treatment as in Example 1 was performed to obtain a high-purity molded heat insulating material.

Example 3 Eight layers of felt-like carbon fibers in the laminate were compressed, and the laminate was compressed to a bulk density of 0.3 g / cm ³ , in the same manner as in Example 1. 200
× 200mm, 28mm thick plate-shaped molded heat insulating material,
Further, the end face was covered with a C / C material. The ratio of the felt-like carbon fiber and the expanded graphite sheet in the cross section of the laminate was one layer of the graphite sheet with respect to the felt of 3.3 mm. Further, the same high-purification treatment as in Example 1 was performed to obtain a high-purity molded heat insulating material.

Example 4 The high-purity molded heat insulating material obtained in Example 1 was coated with a 20 μm-thick pyrolytic carbon film by a CVD method to obtain a heat insulating material.

(Comparative Example 1) Bulk density 0.08 g / cm ³
Of the same shape and shape as in Example 1 using only
/ C material, sandwiched in the same manner as in Example 1,
A plate-like molded heat insulating material having a size of 200 mm and a thickness of 40 mm was obtained.

Each of the molded heat-insulating materials of Examples 1 to 3 and Comparative Example 1 was used in the range of room temperature to 1600 ° C.
The thermal conductivity was measured continuously. The thermal conductivity was measured by measuring the temperatures of the outermost layer of the heat insulating material exposed to a predetermined temperature in a vacuum and the outermost layer on the opposite side, and calculating the thermal conductivity. Also,
The reaction with SiO gas was observed with an electron microscope, and the degree of the reaction was evaluated by X-ray analysis in the stacking direction. In addition, the degree of dust generation was measured by sieving with a shaker for 5 minutes, and the amount of generated dust was measured.

FIG. 2 shows the measurement results of the thermal conductivity.

Table 1 summarizes the results of the degree of reaction with SiO gas and the degree of dust generation.

[0039]

[Table 1]

FIG. 2 shows that the heat insulating materials of Examples 1 to 4 have a thermal conductivity of 0.07 to 0.09 W /
(M · K), and the rise curve of the thermal conductivity was smoother than the molded heat insulating material of the comparative example. In other words, it indicates that the heat insulating property is excellent, in that heat is easily transferred at low temperatures and difficult to transfer at high temperatures.

[0041]

According to the present invention, a laminated structure in which felt-like carbon fibers and expanded graphite sheets are alternately laminated is sandwiched between C / C materials, and the density of the laminate and the lamination ratio of felt-like carbon fibers and expanded graphite sheets are adjusted. By doing so, it is possible to adjust the heat insulation properties. Further, by covering the felt-like carbon fiber with a C / C material so that the felt-like carbon fiber is not exposed on the surface, dust generation from the felt-like carbon fiber can be suppressed. In addition, since the surface is made of a C / C material having high mechanical strength, it is very easy to handle, it is possible to suppress the reaction with the surrounding atmosphere gas, and it has a long life and excellent shape retention. A molded heat insulating material having excellent heat insulating properties can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic view showing one embodiment of a molded heat insulating material according to the present invention.

FIG. 2 is a graph showing the relationship between the temperature of the molded heat insulating material and the room temperature in the example.
It is a figure which shows the measurement result of the thermal conductivity in ° C.

[Explanation of symbols]

 11 C / C material 11a, 11b C / C material 12 Expanded graphite sheet 13 Felt-like carbon fiber 14 Laminated body

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Naoto Ota 211-2-2 Nakahime, Onohara-cho, Mitoyo-gun, Kagawa Prefecture Toyo Carbon Co., Ltd. (72) Inventor Yasuhisa Ogita 211-2-2 Nakahime, Onohara-cho, Mitoyo-gun, Kagawa Toyo Carbon F term in reference (reference) 4G032 AA04 AA52 BA01 GA06

Claims (10)

[Claims] 1. A molded heat insulating material in which felt-like carbon fibers and expanded graphite sheets are alternately laminated and sandwiched by a carbon fiber reinforced carbon composite material. 2. A molded heat insulating material in which felt-like carbon fibers and expanded graphite sheets are alternately laminated and sandwiched by a carbon fiber reinforced carbon composite material, and the remaining surface is covered with the carbon fiber reinforced carbon composite material. . 3. The carbon fiber-reinforced carbon composite material is two cylinders having different diameters, and the felt-like carbon fibers and the expanded graphite sheet are alternately laminated in the radial direction between the two cylinders. The molded heat insulating material according to claim 1, which is sandwiched by said carbon fiber reinforced carbon composite material. 4. The carbon fiber reinforced carbon composite material is two cylinders having different diameters, and the felt-like carbon fibers and the expanded graphite sheet are alternately laminated in the radial direction between the two cylinders. The molded heat insulating material according to claim 2, which is sandwiched by the carbon fiber reinforced carbon composite material and has upper and lower surfaces covered with the carbon fiber reinforced carbon composite material. 5. The laminate comprising the felt-like carbon fiber and the expanded graphite sheet has a bulk density of 0.1 to 0.3 g / cm.
³ is claims 1 to 4 shaped heat insulating material according to any one. 6. The ratio of the felt-like carbon fiber and the expanded graphite sheet is such that the felt-like carbon fiber thickness is 3 to 10 mm.
The molded heat insulating material according to any one of claims 1 to 5, wherein the expanded graphite sheet has one layer. 7. The molded heat insulating material according to claim 1, which has an impurity content of 10 ppm or less. 8. The molded heat insulating material according to claim 1, which is coated with pyrolytic carbon. 9. The method according to claim 1, wherein the glassy carbon is coated.
8. The molded heat insulating material according to any one of claims 7 to 7. 10. A heat shield using the molded heat insulating material according to claim 1.