JPH08151282A - Ceramic coating on graphite - Google Patents

Abstract

PURPOSE: To provide a method for forming a stable ceramic coating film on the surface of graphite. CONSTITUTION: The surface of a graphite material is coated with a ceramic material as follows. A mixture of a graphite bonding agent 2 for bonding graphite pieces to each other and ceramic powder 1 is applied on the surface of a graphite 3 and subsequently this is heated to form a ceramic coating film consisting of the mixed layer 5 of ceramic powder.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a ceramic coating applied to reduce reactivity when molten metal and graphite are reactive, when graphite is used in a high temperature oxidizing atmosphere, and the like. Provide a construction method with excellent releasability.

[0002]

2. Description of the Related Art Graphite is one of the allotropes of carbon, is a smooth and good conductor of electricity, and is a heat-resistant material.
Alternatively, it is widely used as a heat resistant material.

However, since graphite is an allotrope of carbon, there is concern about oxidation and reaction with other metals. Therefore, when the metal to be melted reacts with graphite during melting, such as when it is used as a vessel (crucible or melting furnace) for melting metal, or when graphite is used in a high-temperature oxidizing atmosphere. In such cases, a ceramic coating is applied to graphite to protect it so as to suppress reactivity.

[0004] In general, this ceramic coating is formed by spraying melted ceramic particles so that a ceramic layer is adhered to the surface of the graphite material to form a ceramic film, or a ceramic powder is mixed with an inorganic or organic binder. A method such as a method (coating method) of forming a ceramic film by applying the formed material to the surface of a graphite material is used.

Here, FIG. 3 shows an example of a construction method by a thermal spraying method as a conventional embodiment. FIG. 3 shows a cross-sectional view of a graphite material on which a ceramic layer is formed, where g is the graphite material and h is the numerous pores on the surface of the graphite g. Also, sc is graphite g
It is a ceramic coating film formed on the surface of.

Graphite g is a material having releasability, and graphite g has innumerable pores h. The ceramic has a property that it is difficult for the ceramic to penetrate into the pores h of the graphite. Therefore, the graphite pores h
The inside remains empty, and the ceramic coating film sc is formed only on the surface of the graphite g.

Therefore, in the conventional spraying method, the adhesion between the graphite g and the ceramic coating film sc formed on the surface thereof is very weak, and
Due to the difference in thermal expansion between graphite and ceramics due to the temperature rise during use, and cooling during the suspension of operation, etc., both are likely to peel off.

There are also nitrides and carbides of ceramics, and a ceramic coating film s by a thermal spraying method.
When forming c, the ceramic powder is heated to such a high temperature that it becomes a molten state. Further, such a nitride or carbide-based ceramic may change into an oxide at a high temperature at a high temperature such that it is in a molten state, and therefore it may not be applicable to graphite, which is susceptible to oxidation.

On the other hand, in the case of the coating method, a mixture of an inorganic binder or an organic binder such as carboxymethyl cellulose and ceramic powder with water or alcohol (hereinafter referred to as a slurry) is applied to the surface of graphite with a brush, for example. As a result, a ceramic coating film is formed.

However, the binder basically has only an anchor effect for fixing the ceramic powder, and has no ability to bond the ceramic powder to graphite. That is, the binder that has penetrated into the pores of the graphite supports the entire layer of the binder as if it struck a pile, and this is not an adhesion but a so-called anchor effect that prevents it from coming off. is there.

[0011]

It has been attempted to protect a graphite material by forming a corrosion resistant film against molten metal or the like on the surface of the graphite material. Ceramics are usually used as such a corrosion-resistant coating of graphite.

Conventionally, when such a ceramic coating is applied to the surface of a graphite material, a method of spraying ceramic powder by a thermal spraying method or applying a mixture of an inorganic or organic binder and ceramic powder to the graphite surface And so on.

However, since graphite is a material having releasability and has numerous pores, and ceramics have a property of being difficult to penetrate into the pores of graphite, the conventional spraying method is used. When applied, the ceramic coating film is not a powder layer but a structure in which ceramic materials are welded to each other. The adhesion between the graphite and the ceramic coating film formed on the surface of the graphite is very weak,
Moreover, due to the difference in thermal expansion between graphite and ceramics due to the temperature rise during use and the cooling during the suspension of operation, etc., both are liable to cause separation and the like, and there is a problem that they do not last long.

There are also nitrides and carbides of ceramics. When a ceramic coating film is formed by a thermal spraying method, such nitrides or carbides of ceramics may change to oxides at high temperature. Therefore, there are cases where it cannot be applied to graphite, which is susceptible to oxidation.

There is also a method of forming a ceramic coating film by applying a mixture of an inorganic or organic binder and ceramic powder or the like to the surface of graphite material. In this case, the binder is basically ceramic powder. Since there is only an anchor effect to the above, and there is no ability to adhere ceramic powder to graphite, the coating method also has a weak side in peeling due to temperature changes.

Therefore, whichever ceramic coating method is adopted, the deterioration over time due to changes in the environment and temperature is large, and a sufficient protective effect cannot be maintained. Therefore, it is an object of the present invention to provide a graphite ceramic coating method which can form a stable ceramic coating film on the surface of graphite and can be applied easily and inexpensively.

[0017]

To achieve the above object, the present invention is as follows. That is, as a method of coating the surface of the graphite material with the ceramic material, a mixture of a graphite adhesive for adhering graphite to each other and ceramic powder is applied to the surface of graphite.

Further, thereafter, heating is performed to form a mixed layer of carbide of the graphite adhesive and ceramic powder, and thereby a ceramic film is formed. Furthermore, by overlaying on the mixed layer, by a spraying method or by applying a mixture of an inorganic binder or an organic binder and ceramic powder,
It is characterized in that an upper layer ceramics film is formed into a ceramics film.

[0019]

In the present invention, a mixture of a graphite adhesive for adhering graphite to each other and ceramic powder is applied to the surface of graphite to form a ceramic film.

Since the graphite adhesive is developed for the purpose of adhering graphite to each other, the adhesive force to graphite is strong. When this graphite adhesive and ceramic powder are mixed and applied to the graphite surface to form a film, the ceramic powder is firmly adhered to the graphite surface by the action of the adhesive and also inside the pores of the graphite. Penetrate and settle here. The present ceramic coating thus obtained can greatly improve the degree of adhesion as compared with the conventional one, due to the synergistic effect of the adhesive force of the adhesive and the anchor effect of the ceramic that has penetrated between the graphite pores.

Further, according to the present invention, a mixture of a graphite adhesive for adhering graphite to each other and ceramic powder is applied to the surface of graphite to form a ceramic film and then heated to form a carbide of the graphite adhesive. A mixed layer of ceramic powder is formed to form a ceramic film.

Since the graphite adhesive is developed for the purpose of adhering graphite to each other, the adhesive force to graphite is strong. When this graphite adhesive and ceramic powder are mixed and applied to the graphite surface to form a film, the ceramic powder is firmly adhered to the graphite surface by the action of the adhesive and also inside the pores of the graphite. Penetrate and settle here. Then, by performing a heat treatment at a temperature at which the adhesive is carbonized, the adhesive is carbonized and more firmly fixes the ceramic powder to the graphite. The ceramic film obtained in this manner can significantly improve the adhesion as compared with the conventional one by the synergistic effect of the adhesive force of the adhesive, the fixing force of carbonization, and the anchor effect of the ceramic that has penetrated between the graphite pores. it can.

Further, when a high-purity ceramic coating is required, the ceramic coating formed by the above-mentioned mixed layer may be superposed on the ceramic coating by a conventional thermal spraying method or by using an inorganic binder or an organic binder. If a high-purity ceramic film is formed by a method such as coating, the adhesiveness can be greatly improved due to the bonding effect of the ceramics between the two layers, and the surface of the mixed layer can be coated with the high-purity ceramic film. Since it covers, more graphite protection can be achieved. In addition, since the thermal spraying method is not used in the process of forming the mixed layer formed directly on the graphite, the ceramic powder does not enter a molten state in which it easily reacts with graphite, and the heat treatment temperature is much lower than that. Since the temperature is a level necessary for carbonization of the agent, the problem of graphite oxidation is eliminated even if a nitride or carbide type ceramic is used.

Then, a ceramic film made of a mixture of graphite adhesive carbide containing ceramic powder,
Adhesion between graphite and conventional thermal spraying method, inorganic or organic binder such as carboxymethyl cellulose (basically, there is no ability to bond graphite except for the anchor effect), ceramic powder and water Or, it is so strong that it is incomparable as compared with the adhesion force by a method of applying a mixture (slurry) mixed with alcohol or the like. Therefore, it is possible to form a stable ceramic film that is hard to peel off on the graphite, and to reliably protect the graphite.

In addition, the solvent of the adhesive evaporates during drying, and the remaining resin component is carbonized by the heat treatment to remain, and the other components are ceramic powders. Durability is significantly improved. Further, since it is sufficient to apply a mixture of ceramic powder and an adhesive for adhering graphite, dry and heat-treat, the process is simple and the construction cost is low.

[0026]

Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) A first embodiment of the present invention is shown in FIG. In the present invention, a graphite adhesive that has been developed for the purpose of adhering graphite to each other, for example, a graphite adhesive such as a Kopuna resin-based adhesive, is used. To form a film.

To explain in detail, the present invention first shows that, as shown in FIG. 1 (a), it is effective as a ceramic coating material for adhering graphite materials to each other and easily penetrates into the pores of graphite. An adhesive having the properties to be obtained, for example, a Copna resin-based adhesive 2 and a fine powdery ceramic powder 1 are prepared.
And an appropriate amount of ceramic powder 1 are mixed to prepare a ceramic coating stock solution. This ceramic coating stock solution is applied to the surface of the graphite 3 to be coated with a brush or a spray (FIG. 1 (b)).

The applied ceramic coating stock solution uses an adhesive that is easily compatible with graphite, so it is well compatible with the surface of graphite 3 and
Penetrate into the graphite pores 4.

After the application of the ceramics coating stock solution is completed, the step of drying the ceramics coating stock solution is started. In the drying process, high temperature treatment is performed by heating. However, the heating temperature of this high temperature treatment is not a temperature at which the graphite 3 is oxidized, but is an appropriate temperature at which the solvent of the adhesive evaporates and the remaining resin component is carbonized.

By this high-temperature treatment, the solvent of the adhesive 2 is evaporated and dried, and the resin component of the adhesive 2 is carbonized (carbide 2A) during the high-temperature treatment, and the adhesive 2 originally used is good with graphite. In combination with the familiar property, a good ceramic coating film 5 of ceramic powder is formed, which adheres well to the surface of the graphite 3.

The adhesive 2 is the pores 4 on the surface of the graphite 3.
Assuming that the ceramic coating stock solution is sufficiently agitated in such a manner that the ceramic powder 1 is evenly distributed in the adhesive 2, the ceramic powder 1 is in a proper distribution state. The pores 4 of the graphite 3 are filled, the surface of the graphite 3 is covered, and the graphite 3 is firmly adhered to the surface of the graphite 3. Further, the carbonization of the resin component of the adhesive 2 by the above high temperature treatment causes the ceramic coating film 5 to be formed. The degree of adhesion and the degree of fixation of the graphite 3 to the surface is extremely good, and a film having a uniform ceramic powder distribution state is obtained.

Since the carbonization of the resin component of the adhesive 2 is also carried out by raising the temperature of the graphite 3 in the use environment, the heat treatment in the drying step may be about drying the adhesive. In this case, since the drying process can be simplified, the process of applying the ceramic coating film 5 can be simplified,
The cost can be reduced.

As described above, according to the present invention, an undiluted ceramic coating solution prepared by mixing an appropriate amount of an adhesive agent such as a Copna resin system, which is well compatible with graphite, and ceramic powder is used. The ceramic coating film is formed by drying by a high-temperature treatment at a temperature at which the oxide does not oxidize.

According to this method, the ceramic powder, together with the adhesive, is made to adapt to the surface of the graphite and penetrates into the pores of the graphite, and the solvent of the adhesive 2 is evaporated in the drying step and the high temperature treatment or use in the drying step is performed. The resin component in the adhesive is carbonized by the temperature rise in the environment, and it is possible to form a ceramic coating film with a mixed layer of ceramics and carbon that strongly adheres to the graphite surface, and therefore it is difficult to peel off on the graphite surface. It is possible to provide a graphite ceramic coating method capable of forming an extremely stable ceramic coating film and easily and inexpensively applied.

Further, since the ceramic coating film 5 is a mixed layer of ceramic powder and carbon, there is no risk of oxidation unlike the thermal spraying method in which molten ceramic is brought into direct contact with the surface of graphite. However, it can be extended to nitrides and carbides, which were difficult with the conventional thermal spraying method. Further, since the ceramic coating film 5 is in the state of ceramic powder, unlike a thermal sprayed film in which ceramics are integrated, there is no fear of peeling due to a temperature difference. Further, since a simple construction method of mixing the adhesive and the ceramic powder, coating and drying is sufficient, this embodiment can be constructed at low cost.

As described above, a mixture of an adhesive and a ceramic powder that is well compatible with graphite is used, and this is applied to graphite and heat-treated to carbonize the adhesive to form a ceramic coating film of a mixed layer of ceramics and carbon. However, it is conceivable that the corrosion resistance may be impaired due to the fact that the resulting coating contains some carbon component due to the graphite adhesive. A coping method in this case will be described below as a second embodiment.

(Second Embodiment) By the method of the first embodiment,
For graphite 3 on which a ceramic coating film 5 formed of a mixed layer of ceramic powder and carbon is formed,
The following process is further added.

That is, as shown in the sectional view of FIG. 2 (a), the ceramic coating film 5 of FIG. 1 (c) is sprayed with a fine ceramic powder by a spraying method or a slurry coating method. A layer having a high purity of ceramic components is formed as the upper surface ceramic layer 6.

As a result, a protective upper surface ceramic layer 6 is formed on the ceramic coating film 5 according to the first embodiment so as to cover the film 5 ((b) of FIG. 2). The upper surface ceramic layer 6 for protection is formed by a conventional method, but since it is formed on the ceramic coating film 5 firmly formed on the graphite surface, it is stable on the ceramic coating film 5 as well. Also, from the two points that the ceramic component has a high purity and is formed so as to cover the entire surface of the ceramic coating film 5, the contact with the outside is suppressed and the corrosion resistance of the ceramic coating film 5 due to carbon is lowered. The effect of suppressing is obtained.

As described above, in the second embodiment, the ceramic component is formed on the mixed layer of the ceramic powder and carbon formed according to FIG. 1 (on the surface layer) by the thermal spraying method or the method of applying the slurry. By forming a layer with high purity, the mixed layer of ceramic powder and carbon formed on the surface of graphite is protected by the surface layer with high purity of ceramic components, so a stable ceramic coating that protects graphite The film can be easily formed.

Further, since the ceramic coating film 5 has an underlayer made of a mixed layer of ceramic powder and carbon, there is no concern that the molten ceramic is brought into direct contact with the graphite surface even if thermal spraying is performed. However, it can be extended to nitrides and carbides, which were difficult with the conventional thermal spraying method.

Also, an adhesive and a ceramic powder are mixed,
Since a simple construction method of coating and drying is sufficient, this embodiment can be constructed at low cost. It should be noted that the present invention is not limited to the above-described embodiments, and can be appropriately modified and implemented within the scope of the invention. Further, the present invention, various melting, for protecting the graphite used in processes such as casting, or for protecting the graphite used in the film forming process premised on the dissolution treatment of the metal, such as vacuum deposition, or, It can be used for protecting graphite as a heat resistant member used in the atmosphere.

[0043]

The various embodiments have been described above. In short, the method of the present invention impregnates the pores of graphite, and
Applying a mixture of ceramic powder to a graphite adhesive made of Copuna resin, which is an adhesive with good adhesion to graphite, is applied to the surface of graphite to form a ceramic coating film in which ceramics are distributed in the powder state. It was done like this. Further, this is used as a base ceramic film, and the protective ceramic film layer is formed by superimposing it on the base ceramic film and further applying it by a thermal spraying method or by applying a mixture of an inorganic binder or an organic binder and ceramic powder or the like. Are formed.

Therefore, due to the strong adhesive effect and anchor effect of the graphite adhesive, the powdery ceramics layer can be formed on the graphite layer in a strongly adhered state, and can be easily implemented. A ceramic film can be coated on the graphite layer. Further, since the ceramic component is present in the surface layer of the ceramic layer formed by the mixed layer of the ceramic powder and carbon, the purity of the ceramic component can be improved by applying the thermal spraying method or the method of applying slurry again to the surface layer. It is possible to form a high layer firmly and with good stability, and it can be easily formed.

Therefore, according to the present invention, it is possible to form a ceramic coating having excellent adhesion and resistance to molten metal or reactivity with the environment on the surface of graphite, as well as mixing and coating an adhesive and ceramic powder and drying. It is possible to provide a ceramics coating method that has a feature that it can be applied at low cost because it is a construction method that can be applied, and that the applied ceramics can be extended to nitrides and carbides that were difficult with the conventional thermal spraying method. .

[Brief description of drawings]

FIG. 1 is a diagram for explaining an embodiment of the present invention,
Sectional drawing for demonstrating the ceramic coating film forming method as 1st Example of this invention.

FIG. 2 is a diagram for explaining an embodiment of the present invention,
FIG. 5 is a process diagram showing an example of ceramic coating in which a protective upper surface ceramic layer having a high purity of ceramic components is formed on the surface layer of the ceramic coating film according to the first embodiment by a thermal spraying method or the like.

FIG. 3 is a view for explaining a conventional example and is a cross-sectional view showing an example in which a ceramic coating film is applied by a conventional thermal spraying method.

[Explanation of symbols]

 1 ... Ceramic powder 2 ... Adhesive 3 ... Graphite 4 ... Graphite pores 5 ... Ceramic coating film

Claims (3)

[Claims] 1. A method for coating a surface of a graphite material with a ceramic material, wherein a mixture of graphite adhesive for adhering graphite to each other and ceramic powder is applied to the surface of graphite to form a mixed layer of ceramic powder. A method for coating ceramics on graphite, which comprises forming a ceramics film by forming a film. 2. A method of coating a ceramic material on a surface layer of a graphite material, which comprises applying a mixture of a graphite adhesive for adhering graphite to each other and ceramic powder onto a surface of graphite,
A ceramic coating method for graphite, which comprises forming a ceramic film by heating to form a mixed layer of a carbide of a graphite adhesive and a ceramic powder. 3. A method of coating a ceramic material on a surface layer of a graphite material, which comprises applying a mixture of a graphite adhesive for adhering graphite to each other and ceramic powder onto a surface of graphite,
Heat to form a mixed layer of ceramic powder, then
A method of coating ceramics on graphite, which is characterized by forming an upper ceramics film by forming a ceramics film on the mixed layer by a thermal spraying method or by applying a mixture of an inorganic binder or an organic binder and ceramics powder.