Stock material or miscellaneous articles – Self-sustaining carbon mass or layer with impregnant or...
Reexamination Certificate
2001-11-26
2004-02-03
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Self-sustaining carbon mass or layer with impregnant or...
C428S218000, C428S323000, C428S367000, C428S402000, C428S403000, C428S913000
Reexamination Certificate
active
06686048
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to carbonaceous heat insulators and, particularly, to a composite carbonaceous heat insulator suitable for use in a furnace such as a monocrystal pulling-up furnace or ceramic sintering furnace and a method of making the insulator.
BACKGROUND OF THE INVENTION
The carbonaceous fiber heat insulator has excellent heat insulation and low heat capacity and is used widely as a heat insulator for a high temperature furnace such as a monocrystal pulling-up furnace, vacuum deposition furnace, or ceramic sintering furnace.
Most of such a carbonaceous fiber heat insulator is made by molding. See Japanese patent application Kokai No.
50-35930
. The molded heat insulator is made by impregnating a carbonaceous fiber felt with a resin having a high carbonization rate, laminating and compressing the felt to form a molded material, and carbonizing the molded material to give it an independent shape.
The carbonaceous fiber heat insulator withstands high temperatures up to 3000 degrees C. in an inert atmosphere for its high heat resistance and low vapor pressure. In the practical atmosphere, however, the carbon fibers of the heat insulator wear and deteriorate by reaction with the oxidizing and/or metallic gases generated in the furnace. In the ceramics sintering or silicon monocrystal pulling-up furnace, for example, the carbonaceous fibers react with the gasses, such as silicon oxide (SiO), generated in the furnace and wear and become brittle and powder, with the metal adhering to the fiber surfaces. Under such conditions, the carbonaceous fiber heat insulator not only has poor heat insulation and useful life but also produces fine carbon dust in the furnace, contaminating the product.
For this reason, the heat insulator for the silicon monocrystal pulling-up furnace is housed in a graphite case to keep the generated gases from contacting with the heat insulator. The heat capacity of the graphite case, however, is so high that the thermal efficiency and operation rate of the furnace become low.
To solve such a problem, it has been proposed to form a thermally decomposed carbon film on the surface of porous carbonaceous felt or impregnating a carbonaceous felt with a thermally decomposed carbon to provide a carbonaceous fiber heat insulator. See Japanese patent application Kokai No. 1-167210.
In the method of JP210, however, if the amount of thermally decomposed carbon impregnated is too large, the carbonaceous fiber heat insulator has low heat insulation. Also, if a film of the thermally decomposed carbon is formed on the surface, the amount of carbon impregnated is so small that the depletion and pulverization of the heat insulator become large.
Accordingly, it is an object of the invention to provide a carbonaceous heat insulator with low depletion, deterioration, and pulverization in use and high heat insulation and a method of making it.
DISCLOSURE OF THE INVENTION
According to the invention there is provided a composite carbonaceous heat insulator comprising a carbonaceous heat-insulating member having a bulk density of 0.1 to 0.4 g/cm
3
; a carbonaceous protecting layer made by penetrating a thermally decomposed carbon into a carbon fiber structure and having a bulk density of 0.3 to 2.0 g/cm
3
; and a thermally decomposed carbon coating layer having a bulk density higher than that of the carbonaceous protecting layer, wherein the carbonaceous protecting layer is joined with at least part of a surface of the carbonaceous heat-insulating member to form a joined body; the thermally decomposed carbon coating layer is formed on at least a face of the carbonaceous heat-insulating member of the joined body.
It is preferred that the composite carbonaceous heat insulator further comprises a dense carbonaceous intermediate layer between the carbonaceous heat-insulating member and the carbonaceous protecting layer of the joined body.
Also, it is preferred that the composite carbonaceous heat insulator further comprises a dense carbonaceous surface layer between the thermally decomposed carbon coating layer and the carbonaceous heat-insulating member.
The dense carbonaceous intermediate and surface layers are made by forming a dense carbon forming composition consisting of a graphite flake and a binder component able to be carbonized by heat and carbonizing the composition.
According to another aspect of the invention there is provided a method of making the composite carbonaceous heat insulator, which comprises the steps of joining the carbonaceous protecting layer made by penetrating the thermally decomposed carbon into the carbon fiber structure to at least part of a surface of the carbonaceous heat-insulating member made of a carbon fiber molding to form a joined body; and form the thermally decomposed carbon coating layer on at least a face of the carbonaceous heat-insulating member or a face of the carbonaceous heat-insulating member and/or the carbonaceous protecting layer. Alternatively, the thermally decomposed coating layer is formed on the carbonaceous heat-insulating member after the dense carbon surface layer is formed.
According to still another aspect of the invention there is provided a method of making a composite carbonaceous heat insulator, comprising the steps of joining the carbonaceous heat-insulating member made of a carbon fiber molding and the carbon fiber structure to form a joined body, forming a dense carbonaceous surface layer on a surface of the carbonaceous heat-insulating member and forming the thermally decomposed carbon coating layer on a surface of the carbonaceous heat-insulating member while penetrating the terminally decomposed carbon into the carbon fiber structure.
According to the invention, the carbonaceous heat-insulating member with low bulk density maintains the heat insulation while the carbonaceous protecting layer with high bulk density suppresses the depletion, deterioration, and pulverization during the use. The thermally decomposed carbon penetrates into the carbonaceous protecting layer so that the reactive gases hardly enter and the reaction resistance is high. Since the thermally decomposed carbon coating layer covers the surface, the composite carbonaceous heat insulator is reduced in the depletion and deterioration and spread of the carbon powder is prevented.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The composite carbonaceous heat insulator according to the invention comprises a carbonaceous heat-insulating member, a carbonaceous protecting layer made by penetrating a carbon fiber structure with thermally decomposed carbon, and a thermally decomposed carbon coating layer having a bulk density higher than that of the carbonaceous protecting layer. The carbonaceous protecting layer is joined with at least a part of the carbonaceous heat-insulating member to form a joined body such that the thermally decomposed carbon coating layer is formed on at least the carbonaceous heat-insulating member.
It is preferred that the carbonaceous heat-insulating member and the carbonaceous protecting layer are joined via a dense carbonaceous intermediate layer having low gas permeability.
The carbonaceous heat-insulating member is any porous carbonaceous material having a low bulk density. A preferred example is a carbon fiber molded heat-insulating material.
The carbon fiber molded heat-insulating material is made by penetrating a felt of carbon fiber, such as pitch carbon fiber, rayon carbon fiber, or polyacrylonitrile carbon fiber, with a binder, such as phenol resin, or furan resin, and molding and hardening the felt, carbonizing the binder to join the carbon fibers with the binder carbide.
The carbonaceous heat-insulating member should have a bulk density of 0.1-0.4 g/cm
3
in view of the heat insulation, strength, and plasticity. If the bulk density is lower than-the lower limit, the strength and plasticity become poor while, if it is higher than the higher limit, the heat insulation is lowered. For the heat insulation and thermal capacity, it is preferred that the bulk density is in the range between
Arimoto Yoshihiro
Iwamoto Shigeki
Kobayashi Masanori
Sibuya Yukihiro
Bahta Abraham
Jones Deborah
Kanesaka & Takeuchi
Kureha Kagaku Kogyo K. K.
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