KR102215074B1 - Carbon material coated by a layer having improved oxidation stability, and a method therefor - Google Patents

Abstract

According to the present invention, the carbon material having a homogeneous coating layer of SiOC network from polycarbosilane solves the problems of the prior art, so that not only excellent surface properties but also improved oxidation stability.

Description

Carbon material coated by a layer having improved oxidation stability, and a method therefor}

The present invention relates to a carbon material having a coating layer with improved oxidation stability and a method of manufacturing the same.

Graphite materials have high specific strength, are very resistant to thermal shock and corrosion, and are easy to process as a material with high thermal and electrical conductivity, so the amount of use is increased as parts such as heat treatment jigs (JIG), heating elements, and insulation materials in the semiconductor and solar cell industries. It is a trend.

However, when the graphite material is repeatedly used at a high temperature of 400° C. or higher as a heating element, a heat insulating material, etc., oxidation proceeds and physical properties are rapidly reduced. In order to compensate for these shortcomings, various methods of anti-oxidation treatment of graphite have been studied.

As a coating method for preventing the oxidation of graphite, a coating method such as silicon carbide (SiC), silicon nitride (Si ₃ N ₄ ), mullite using chemical vapor deposition (CVD), and magnesia (MgO) through plasma spraying, Coatings such as alumina (Al ₂ O ₃ ) and chromium oxide (Cr ₂ O ₃ ) are actively in progress.

However, the coating method by plasma spraying has a disadvantage in that the coating layer must be thickened because the adhesion with the material is poor and peeling is likely to occur.

On the other hand, since the graphite surface coated with silicon carbide has a strong covalent bond with silicon and carbide, it is a component that does not change in physical or chemical composition even at temperatures above 2000℃ and has superior strength, hardness, abrasion resistance, and oxidation resistance compared to existing graphite. Therefore, it is used as the main coating material.

In general, a method of coating silicon carbide on the surface of graphite includes a chemical vapor deposition method using an organosilicon compound, a method using penetration of molten silicon or silicon gas, and a gas-solid reaction method using a silicon monoxide (SiO ₂ ) gas.

When silicon carbide is coated by chemical vapor deposition, methyltrichlorosilane (MTS) is mainly used as a precursor. In this case, high temperature due to the process of flowing hydrogen gas together to remove the chlorine component from the methyltrichlorosilane precursor. When hydrogen gas is used, it has risk factors such as fire occurrence, and due to the corrosiveness of hydrochloric acid (HCl) gas, which is a by-product, it is difficult to handle due to corrosion of equipment and chlorine contamination in the final product.

SiC is one of the materials that can satisfy these oxidation-resistance properties, but it is a non-oxide ceramic, which cannot be coated by thermal spray coating, and the precursor material suitable for impregnation and spin coating is unknown. It has been limited.

Among the preceramic polymers, polycarbosilane is an environmentally friendly SiC precursor that does not contain chlorine. When it is heat-treated at 600°C to 800°C in an inert atmosphere, it is converted to SiC, and when dissolved in a solvent at room temperature, it becomes a liquid state. Since the presence of is possible, when a liquid phase is impregnated, coated on graphite using a spin method, or heat-treated, graphite coated with silicon carbide having excellent chemical resistance and abrasion resistance can be formed.

Korean Patent Publication Nos. 10-0776252, 10-0951633, and 10-1331403 describe the contents of improving the oxidation resistance of graphite by coating the surface of graphite using a polyphenylcarbosilane solution and then heat treatment.

However, since polyphenylcarbosilane has a yield of about 60% or less in the process of converting to ceramic through an organic-inorganic conversion process, cracking due to volume reduction is inevitable when heat-treated at 1200°C or higher. When there are cracks and peeling in the coating layer, there is a problem that it is difficult to maintain oxidation resistance for a long time.

Korean Patent Registration No. 10-0776252 Korean Patent Registration No. 10-0951633 Korean Patent Registration No. 10-1331403

An object of the present invention is to provide a carbon material having a coating layer having improved oxidation stability as well as excellent surface properties by forming a homogeneous coating layer of polycarbosilane by solving the problems of the prior art, and a method of manufacturing the same.

The carbon material having a coating layer having improved oxidation stability according to the present invention is a carbon material having a homogeneous coating layer of SiOC network formed from polycarbosilane and an organic solvent having a number average molecular weight (Mn) of 800 to 1400 g/mol.

It is preferable that the carbon material is a graphitized carbon foam, mat or felt.

The polycarbosilane preferably contains at least one selected from the group consisting of polymethylcarbosilane, polymethylphenylcarbosilane, polyvinylcarbosilane, and polymethylsilane.

It is preferable that the organic solvent is selected from cyclohexane, normal hexane, toluene, benzene or tetrahydrofuran.

It is preferable that the polycarbosilane solution has a concentration of 5 to 10% by weight of the polycarbosilane in the organic solvent.

The manufacturing method of a carbon material having a coating layer having improved oxidation stability according to the present invention comprises the steps of preparing a 5 to 10% by weight solution from polycarbosilane and an organic solvent having a number average molecular weight (Mn) of 800 to 1400 g/mol;

Applying a carbon material such as a foam, mat or felt of graphitized carbon to the polycarbosilane solution;

It is preferable to include the step of curing the carbon material coated with the polycarbosilane to form a SiOC network and heat treatment.

The curing step is preferably treated at 150 to 250 °C for 1 to 7 hours.

The heat treatment step is preferably carried out for 1 to 2 hours at 800 to 1200 ℃ under an inert gas atmosphere.

According to the present invention, the carbon material having a homogeneous coating layer of SiOC network from polycarbosilane solves the problems of the prior art, so that not only excellent surface properties but also improved oxidation stability.

1 is an SEM photograph of a carbon material according to an embodiment of the present invention.
2 is a SEM photograph of a carbon material coated according to an embodiment of the present invention.
3 is an SEM photograph for estimating the thickness of a carbon material coated according to an embodiment of the present invention.
4 is a diagram showing the weight loss due to oxidation of the coated carbon material according to an embodiment of the present invention by time.
5A and 5B are SEM photographs when the concentration of polycarbosilane is 20% by weight and 30% by weight according to Comparative Example 1.
6 is an SEM photograph of a surface peeling state of Comparative Example 1. FIG.
7A and 7B are SEM photographs of the interior and surface conditions of a carbon material when polycarbosilane is 30% by weight.
8A and 8B are SEM photographs when the heat treatment temperatures are 1400°C and 1800°C according to Comparative Example 2.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, embodiments of the present invention may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below.

In describing the present embodiments, the same names and symbols are used for the same configuration, and therefore, redundant additional descriptions are omitted below. In the drawings referred to below, the accumulation ratio is not applied.

The carbon material having a coating layer having improved oxidation stability according to the present invention is a carbon material having a homogeneous coating layer of SiOC network formed from polycarbosilane and an organic solvent having a number average molecular weight (Mn) of 800 to 1400 g/mol.

It is preferable that the polycarbosilane has a number average molecular weight of 800 to 1400 g/mol. The higher the molecular weight of the polycarbosilane, the thicker the silicon carbide coating film can be obtained after heat treatment, but if the molecular weight exceeds 1400, polycarbosilane is not completely dissolved in the organic solvent, and the viscosity of the solution is high, forming a heterogeneous coating. do. Conversely, when the molecular weight is less than 800, the thickness of the coating layer is thin and it is difficult to secure the amount of inorganic matter remaining in the heat treatment process, so that a coating layer that satisfies the desired antioxidant effect cannot be obtained.

The thickness of the silicon carbide coating layer prepared by using polycarbosilane as a precursor as described above is preferably 1 to 300 nm. When the thickness of the coating layer is less than 1 nm, it is too thin to secure oxidation resistance, and when it exceeds 300 nm, cracks in the coating layer cannot be avoided.

It is preferable that the carbon material is a graphitized carbon foam, mat, or felt, but is not limited thereto within the range apparent to those skilled in the art.

The polycarbosilane preferably contains at least one selected from the group consisting of polymethylcarbosilane, polymethylphenylcarbosilane, polyvinylcarbosilane, and polymethylsilane.

The organic solvent used as the solvent of the polyphenylcarbosilane in the present invention is not particularly limited, and may include normal hexane, cyclohexane, tetrahydrofuran, and benzene.

It is preferable that the polycarbosilane solution has a concentration of 5 to 10% by weight of the polycarbosilane in the organic solvent. When the concentration of the coating solution is less than 5% by weight, the thickness of the coating film available at one time is too thin, and when it exceeds 10% by weight, a heterogeneous coating is formed by the surface tension of the coating solution, and the film formed by the coating is formed by the carbon material. In addition to filling the voids, peeling or cracking of the coating film after heat treatment cannot be avoided.

The method of manufacturing a carbon material having a coating layer having improved oxidation stability according to the present invention comprises the steps of preparing a 5 to 10% by weight solution from polycarbosilane and an organic solvent having a number average molecular weight (Mn) of 800 to 1,400 g/mol;

Applying a carbon material such as a foam, mat or felt of graphitized carbon to the polycarbosilane solution;

It is preferable to include the step of curing the carbon material coated with the polycarbosilane to form a SiOC network and heat treatment.

In general, when applying a polycarbosilane solution to a carbon material, a known coating method such as an impregnation method, a spray coating method, or a spin coating method may be used. In the present invention, an impregnation method is preferred.

After the polycarbosilane is applied to the carbon material, it may be subjected to an ultrasonic treatment or a degassing process under vacuum, if necessary.

In addition, the carbon material coated with polycarbosilane may further include a drying step before the subsequent curing step. The drying is to remove the organic solvent of the coating agent impregnated with the carbon material, and may be performed at 100° C. or less for 12 to 24 hours. It is preferably carried out at 15 ~ 80 ℃.

In the present invention, a polycarbosilane is coated on a carbon material and then cured. In this case, the curing temperature is preferably 150 to 250°C. The curing process is preferably carried out for 1 to 7 hours in an air atmosphere. At this time, the polycarbosilane reacts with the carbon material to form a SiOC network.

The heat treatment step is preferably carried out for 1 to 2 hours at 800 to 1200 ℃ under an inert gas atmosphere. In this case, the cured coating layer maintains a homogeneous coating state in an amorphous state through heat treatment.

If the heat treatment temperature is less than 800°C, the organic/inorganic conversion reaction is not completed, and if it exceeds 1200°C, deformation occurs on the fiber due to the decomposition behavior of the coating layer or the SiC crystal phase develops largely, which is not preferable.

The heat treatment is performed in an inert gas or vacuum atmosphere, and the inert gas may be any one selected from the group consisting of argon, helium, and nitrogen.

<Example>

end. A 10% solution was prepared by using a solvent as cyclonucleic acid and adding polymethylcarbosilane having a number average molecular weight (Mn) of 1,200 g/mol.

I. A graphite felt (see FIG. 1) was immersed in the solution to apply polycarbosilane.

All. The graphite felt immersed in the solution was taken out at a rate of 1 mm/sec and dried at room temperature for 12 hours or longer.

la. The graphite felt was cured for 5 hours in an oven set at 200°C.

hemp. Subsequently, the cured graphite felt was heat-treated at 1000° C. for 1 hour under a nitrogen or argon atmosphere.

The coated graphite felt prepared according to the above example had a homogeneous coating layer as shown in FIG. 2.

In addition, as shown in Figure 3, the thickness of the coating layer was less than 300 nm.

<Coating layer oxidation test>

The coated graphite felt prepared according to the above example was exposed to the atmosphere at 400° C., and the weight loss due to oxidation was measured by time and presented in FIG. 4.

The graphite felt (bare) without coating has a weight loss at the same time as the oxidation test, and shows a weight loss of about 10% after 100 hours. However, when a homogeneous thin film was formed using 10% polycarbosilane, it showed a 1% weight loss even after exposure for 100 hours.

<Comparative Example 1>

The experiment was performed in the same manner as in Examples of the present invention except that the concentration of the polycarbosilane coating solution was changed to 20% by weight and 30% by weight.

5A and 5B, as the concentration of the coating solution increases, a heterogeneous coating is formed by the surface tension of the high viscosity coating solution, and the film formed by the coating fills the voids between fibers, which is not preferable. In addition, as shown in Figure 6, cracking and peeling of the coating layer was observed prominently.

On the other hand, when the concentration of the polycarbosilane is 30% by weight, as shown in Figs. 7A and 7B, it was observed that the polycarbosilane fills the voids of the felt with a heterogeneous coating on the inside and the surface of the graphite felt. .

<Comparative Example 2>

Experiments were performed in the same manner as in the examples of the present invention except that the heat treatment temperature was changed to 1400°C and 1800°C.

As observed in FIGS. 8A and 8B, deformation occurs in the fiber phase due to the decomposition behavior of the coating layer under 1400°C heat treatment conditions, and the phenomenon that the SiC crystal phase develops largely under the 1800°C heat treatment condition was an undesirable result. .

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and variations are possible without departing from the technical spirit of the present invention described in the claims. It will be obvious to those of ordinary skill in the field.

Claims (10)

Homogeneous coating layer of SiOC network with a thickness of 1 to 300 nm formed from a solution having a polycarbosilane having a number average molecular weight (Mn) of 800 to 1,400 g/mol and a polycarbosilane concentration of 5 to 10% by weight containing an organic solvent A carbon material having a coating layer having improved oxidation stability. The carbon material according to claim 1, wherein the carbon material is a graphitized carbon foam, mat, or felt. The carbon material according to claim 1, wherein the polycarbosilane comprises at least one selected from the group consisting of polymethylcarbosilane, polymethylphenylcarbosilane, polyvinylcarbosilane, and polymethylsilane. The carbon material according to claim 1, wherein the organic solvent is selected from cyclohexane, normal hexane, toluene, benzene or tetrahydrofuran. delete Preparing a solution having a number average molecular weight (Mn) of 5 to 10% by weight from a polycarbosilane having a number average molecular weight (Mn) of 800 to 1,400 g/mol and an organic solvent;
Applying a carbon material such as foam, mat or felt of graphitized carbon to the polycarbosilane solution;
A method of manufacturing a carbon material having a coating layer having improved oxidation stability of 1 to 300 nm in thickness, comprising curing and heat treating the carbon material coated with polycarbosilane to form a SiOC network. The method of claim 6, wherein the curing is performed at 150 to 250° C. for 1 to 7 hours. The method of manufacturing a carbon material having a coating layer having improved oxidation stability. The method of claim 6, wherein the heat treatment is performed in an inert gas atmosphere at 800 to 1200° C. for 1 to 2 hours, with improved oxidation stability. The method of claim 6, wherein the polycarbosilane comprises at least one selected from the group consisting of polymethylcarbosilane, polymethylphenylcarbosilane, polyvinylcarbosilane, and polymethylsilane. Manufacturing method. The method according to claim 6, wherein the organic solvent is selected from cyclohexane, normal hexane, toluene, benzene or tetrahydrofuran.

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