KR102058875B1 - Process for Forming High Density SiC Coating on Graphite Foam And Coating Agent For The Same - Google Patents

Abstract

Disclosed is a method of coating silicon carbide on a graphite foam surface using silica sol and organosilane. The present invention comprises the steps of coating a coating agent comprising a silica sol and an organic silane on the graphite foam; Drying the coated graphite foam; And it provides a method for producing a coating layer of silicon carbide on the graphite foam comprising the step of heat-treating the dried graphite foam to form a silicon carbide coating layer.

Description

Process for Forming Dense Silicon Carbide on Graphite Foams and Coatings Used Therein {Process for Forming High Density SiC Coating on Graphite Foam And Coating Agent For The Same}

The present invention relates to a method of forming a coating of silicon carbide on graphite foam, and more particularly, to a method of coating silicon carbide on the surface of graphite foam using silica sol and organic silane.

Graphite material has high specific strength, is extremely resistant to thermal shock and corrosion, and has high thermal conductivity and electrical conductivity, making it easy to process, increasing the use of components such as heat treatment jig, heating element, and heat insulating material in the semiconductor and solar cell industries. The trend is.

However, the graphite material has a disadvantage in that the oxidation proceeds at a temperature of 400 ° C. or higher, thereby rapidly decreasing physical properties. In order to make up for these drawbacks, various methods for preventing oxidation of graphite have been studied.

Coating methods for preventing oxidation of graphite include coating of silicon carbide (SiC), silicon nitride (Si ₃ N ₄ ) and mullite (CVD) 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 underway.

The coating method by plasma spraying has a disadvantage in that the coating layer has to be thickened because it is easy to peel off due to poor adhesion with the material.

On the other hand, since the surface of graphite coated with silicon carbide (SiC) has strong covalent bonds with silicon and carbide, it does not change physical properties or chemical composition even at temperatures above 2000 ℃, and it has strength, hardness, abrasion resistance, and resistance. It is used as the main coating material because of its excellent oxidation resistance.

In general, a method of coating silicon carbide on the graphite surface 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 silicon monoxide (SiO) gas.

In the case of coating silicon carbide by chemical vapor deposition, methyltrichlorosilane (MTS) is mainly used as a precursor. At this time, the methyl trichlorosilane precursor is flowed at a high temperature due to the flow of hydrogen gas to remove chlorine from the methyltrichlorosilane precursor. The use of hydrogen gas has risk factors such as fire occurrence, and due to the corrosion of hydrochloric acid (HCl) gas as a by-product, it is difficult to handle due to corrosion of equipment and chlorine pollution problem in the final product.

Korean Patent Publication No. 10-0951633 discloses a method of improving graphite oxidation resistance by coating and heat treating a graphite surface using a polyphenylcarbosilane solution.

However, since polyphenylcarbosilane has a yield of about 60% or less in the process of converting into a ceramic through an organic-inorganic conversion process, cracks due to volume reduction cannot be avoided when heat treatment is performed at 1200 ° C. or more. If there is a crack in the coating layer, there is a problem in that oxidation resistance is difficult to be maintained for a long time.

Korea Patent Publication No. 10-0951633 (2010.04.09. Notification)

In order to solve the above problems, the inventors of the present invention using a low concentration of the silica gel sol in the patent application No. 2017-138128 to provide a silicon carbide coated graphite foam having excellent surface properties as well as excellent oxidation resistance I have suggested how. The researchers of the present invention have found that when silica silica sol is used as the SiC precursor, the use of high concentrations of silacasol to obtain a dense and thick SiC coating layer causes oxidation of graphite foam, resulting in a decrease in strength.

Accordingly, an object of the present invention is to provide a method for producing a silicon carbide coated graphite foam which is not only excellent in surface properties but also excellent in oxidation resistance while forming a dense silicon carbide coating layer.

It is another object of the present invention to provide a coating agent suitable for the above-mentioned manufacturing method.

In order to achieve the above technical problem, the present invention comprises the steps of: coating a coating agent comprising a hydrophobic surface-treated silica sol and an organic silane on the graphite foam; Drying the coated graphite foam; And it provides a method for producing a coating layer of silicon carbide on the graphite foam comprising the step of heat-treating the dried graphite foam to form a silicon carbide coating layer.

The coating agent in the present invention 20 to 40% by weight silica sol; 20 to 40% by weight of organic silanes; And it is preferable to include 20 to 40% by weight of the organic solvent.

In addition, in the present invention, the silica content and the organic silane content in the silica sol in the coating agent are preferably 1: 0.5 to 1: 1.5 by weight.

After the drying step in the present invention, there is provided a method for producing a coating layer of silicon carbide on the graphite foam, further comprising the step of removing the silica in the graphite foam by a centrifugation method.

The present invention can use any one coating method selected from the impregnation method, spray coating method, and spin coating method.

In the present invention, the drying is preferably performed for 12-24 hours at 100 ℃ or less.

In the present invention, the heat treatment is preferably carried out at 1400-1800 ℃ in an inert gas or vacuum atmosphere.

In the present invention, the heat treatment is preferably carried out for 1 hour at 1,600 ℃ after maintaining for 2 hours at 1,400 ℃. .

In the present invention, the organosilane comprises at least one compound selected from the group consisting of DMDMS, MTMS, TEOS, and GPTMS or at least two compounds selected from the group consisting of silicon carbide on the graphite foam.

The present invention, 20 to 40% by weight silica sol in order to achieve the above another technical problem; 20 to 40% by weight of organic silanes; And it provides a coating agent for producing a coating layer of silicon carbide comprising 20 to 40% by weight of an organic solvent.

In the present invention, the silica content and the organic silane content in the silica sol in the coating agent are preferably 1: 0.5 to 1: 1.5 by weight.

According to the present invention, the method for forming a silicon carbide coating on the graphite foam is to form a silicon carbide coating on the graphite foam using silica sol and organic silane, it is possible to provide a graphite foam having excellent surface properties and oxidation resistance .

1 is a flow chart of a method for forming a coating of silicon carbide on a graphite foam according to an embodiment of the present invention.
FIG. 2 is an external image (FIG. 2A) of the graphiform foam of the present invention and an image taken with a field emission scanning electron microscope (FE-SEM) of the graphiform foam (FIG. 2B).

As the invention allows for various changes and numerous embodiments, particular embodiments will be illustrated in the drawings and described in detail in the written description. However, this is not intended to limit the present invention to specific embodiments, it should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

Throughout this specification, when a part is said to "include" a certain component, it means that it can further include other components, without excluding other components unless otherwise stated.

Hereinafter, a method for forming a coating of silicon carbide on the graphite foam according to an aspect of the present invention will be described in detail with reference to the accompanying drawings.

1 is a flow chart of a method of forming a coating of silicon carbide on a graphite foam in accordance with an aspect of the present invention. The present invention is characterized by forming a silicon carbide coating having excellent crystallinity using silica sol and organic silane in coating the graphite foam surface with silicon carbide by inducing a direct reaction between silicon and carbon. As a result, the graphite foam is coated without cracking to improve oxidation resistance, so that it can be used as a material exposed to an oxidizing atmosphere such as air at a high temperature of 1,200 ° C. or higher.

Coating formation method of silicon carbide on the graphite foam containing silicon according to an aspect of the present invention is a step of coating a coating agent comprising a silica sol and an organic silane on the graphite foam (S10) to dry the coated graphite foam Step S20 and heat-treating the dried graphite foam (S30).

The manufacturing method of the present invention will be described by dividing each step as follows.

First, a step (S10) of coating a coating agent including a silica sol and an organic silane on the graphite foam is performed. In the present invention, the coating agent may include 20 to 40% by weight of the hydrophobic silica sol, 20 to 40% by weight of the organic silane, and 20 to 40% by weight of the organic solvent.

It is preferable that the silica sol of this invention is an organic silica sol. Thereby, the wettability of the surface of silica and carbon fiber can be improved. The silica sol of the present invention may include 20 to 100 parts by weight of silica based on 100 parts by weight of the total silica sol.

In addition, the viscosity of the silica sol is not limited thereto, but may be 50 cps or less, for example, 5 to 10 cps. If the viscosity is greater than 50 cps, the excess silica particles are adsorbed on the surface, the oxygen contained therein may adversely affect.

In addition, the average particle diameter of the silica sol may be hundreds of nanometers at several nanometers smaller than the diameter of the carbon fiber because the adsorption may not be good when the diameter (similar to several micrometers) of the carbon fiber becomes larger. Preferably the average particle diameter is 10-20 nm.

As an example, the silica sol of the present invention can be used SNS-40 product of Diopaint, and may be used by adjusting the silica content coated by dilution with methanol, isopropanol, propylene glycol, and the like in the above range.

Various silanes may be used as the silane in the present invention. At least one silane selected from the group consisting of dimethyldimethoxysilane (DMDMS), methyltrimethoxysilane (MTMS), tetraethoxysilane (TEOS) and 3-glycidoloxypropyl-trimethoxysilane (GPTMS) Or a compound thereof.

In the present invention, methyltrimethoxysilane (MTMS), tetraethoxysilane (TEOS) and 3-glycidoloxypropyl-trimethoxysilane (GPTMS) among silanes which are hydrolyzable by water and have three or more alkyl group groups. It is preferable to use either or at least 2 types in combination. For example, the MTMS and TEOS can be used in combination.

In the present invention, the organic silane may be an organic silane compound prepared by hydrolyzing and condensing silanes such as MTMS and TEOS with water.

Silane as a raw material for the production of the organic silane or the organic silane compound is preferably contained in the coating agent 20 to 40% by weight. In addition, the distilled water for hydrolysis of the silane is preferably included 15 to 20% by weight. Preferably, the weight ratio of silane and distilled water is preferably maintained in the range of 1: 0.8 to 1: 1.5.

In the present invention, the organic solvent is preferably included in the range 20 to 40% by weight. If the organic solvent is less than 20% by weight, it is difficult to form a coating film because the viscosity of the coating agent is increased, and when the organic solvent is more than 40% by weight, there is a problem that the shrinkage of the coating film greatly occurs during the drying after forming the coating film.

In addition, the coating agent in the present invention may further include an additive. For example, a surfactant may be used as the additive in the present invention. The surfactant connects the hydrophobic surface-treated liquid nanocolloid sol and silane hydrolyzate to each other, and also improves the leveling property of the coating surface and defects that may appear in the coating film after coating, such as pinholes and craters. You can prevent creation. In the coating agent of the present invention, the surfactant is preferably included 0.01 to 1.0% by weight.

In the present invention, the content of the silica sol and the organosilane is set at an appropriate ratio such that the organosilane supplies a carbon source for the formation of SiC. For example, in the present invention, the silica solid content and the content of the organic silane in the silica sol may be 1: 0.5 to 1: 2 by weight. More preferably, the silica solid content and the content of the organic silane in the silica sol may be 1: 0.5 to 1: 1.5 by weight.

As shown in Figure 2, the graphite foam is composed of fine carbon short fibers of 0.5 ~ several ㎛.

In the present invention, the coating agent may be coated on the graphite foam using any one coating method selected from impregnation method, spray coating method, and spin coating method. At this time, the silica sol in the coating agent may be impregnated on the graphite foam in the range of about tens of nanometers to several hundred nanometers.

Then, the step of drying the coated graphite foam (S20) is performed.

The drying is to remove the dispersion medium or the organic solvent of the coating agent in the graphite foam, it can be carried out at 100 ℃ or less for 12-24 hours. Preferably it is carried out at 30 ~ 80 ℃.

The method of the present invention may optionally further include removing the coating accumulated in the graphite foam by the centrifugation method after the step S20. This removes the precipitated silica inside the graphite foam surface coating. Such centrifugation is preferably performed immediately after impregnation or before drying.

Finally, performing the heat treatment of the dried graphite foam (S30). In this step, the silica sol and the organic silane serve as the Si source for the reaction with SiC. In addition, the carbon of the organosilane serves as a carbon source of the SiC reaction. This suppresses the production of silicon oxide in the graphite foam, converts it into crystalline silicon carbide, and coats it. In addition, in the present invention, the coating layer can be formed at a high density by providing the organic silane as a source of the SiC reaction as compared with the case of using the silacasol alone.

The heat treatment may be performed at 1400-1800 ° C. in an inert gas or vacuum atmosphere, preferably at 1400-1600 ° C. The heat treatment process should be carried out at 1400 ° C. or higher, which is the minimum temperature at which the silica powder can react and convert to SiC in an inert gas or oxygen atmosphere that has been deoxygenated. In addition, the oxidizing properties of the object of the invention above 1800 ℃ may not be good.

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

Accordingly, the thickness of the coated silicon carbide may range from tens of nanometers to several hundred nanometers, and the thickness may be adjusted to a desired range according to process conditions.

<Example 1>

As a silica sol, SNS-40 manufactured by Diopaint (SiO 2 35-45%, viscosity 10 cps or less, average particle diameter 10-20 nm) was used. Coating samples were prepared for each coating by diluting to concentrations of 25 wt% and 50 wt% to control the amount of silica coated. On the other hand, undiluted coating (100 wt%) samples were prepared for comparison.

The 30 mm x 30 mm x 10 mm graphite foam to be impregnated was washed with ethanol and dried at 80 to 30 minutes. It was coated by impregnating the silica sol for 5 minutes using a dip coater. The coated graphite foam was then dried at 70 ° C. for 6 hours. The dried graphite foam was maintained at 1,400 ° C. for 2 hours, and then heat treated at 1600 ° C. for 1 hour to obtain a silicon carbide coated graphite foam having excellent crystallinity.

As a result of visual observation of the coated foam, the silicon carbide coating on the graphite was well formed when the silica powder of 25wt% concentration was used, and the foam was not collapsed after the heat treatment. However, when 50 wt% silica sol was used, the foam did not collapse, but the foam was weak due to the reaction of oxygen and graphite produced by decomposition of the silica sol. In addition, in the case of 100wt% silica sol, the coating layer did not completely cover the surface.

<Example 2>

Diospaint's SNS-40 product was diluted to 25 wt% as in Example 1. Subsequently, an organic silane (TEOS) having the same weight as the solid content (silica) content of the silica sol was added to prepare a mixed solution. Diluted silica sol and organosilane were mixed to prepare a coating agent.

The prepared coating was impregnated and coated in the same manner as in Example 1, and dried and heat-treated to prepare a graphite coated foam coated with silicon carbide.

As a result of visual observation, the coating of silicon carbide on the graphite was well performed, little oxidation of the foam was observed, and no foam collapse after heat treatment.

The present invention has been described above with reference to the preferred embodiments. Those skilled in the art will appreciate that the present invention can be implemented in a modified form without departing from the essential features of the present invention. Therefore, the disclosed embodiments should be considered in descriptive sense only and not for purposes of limitation. The scope of the present invention is shown in the claims rather than the foregoing description, and all differences within the scope will be construed as being included in the present invention.

Claims (11)

Coating a coating comprising a silica sol and an organosilane onto the graphite foam;
Drying the coated graphite foam; And
Heat treating the dried graphite foam to form a silicon carbide coating layer;
The silica content and the organic silane content in the silica sol in the coating agent is 1: 0.5 to 1: 1.5 in the weight ratio of the method for producing a coating layer of silicon carbide on the graphite foam. The method of claim 1,
The coating agent is 20 to 40% by weight silica sol; 20 to 40% by weight of organic silanes; And 20 to 40% by weight of an organic solvent. delete The method of claim 1,
After the drying step, the method of producing a coating layer of silicon carbide on the graphite foam characterized in that it further comprises the step of removing the silica in the graphite foam by a centrifugal separation method. The method of claim 1,
The coating is a method for producing a coating layer of silicon carbide on the graphite foam, characterized in that using any one coating method selected from impregnation method, spray coating method, and spin coating method. The method of claim 1,
The drying method for producing a coating layer of silicon carbide on the graphite foam, characterized in that carried out for 12-24 hours at 100 ℃ or less. The method of claim 1,
The heat treatment is a method for producing a coating layer of silicon carbide on the graphite foam, characterized in that carried out at 1400-1800 ℃ in an inert gas or vacuum atmosphere. The method of claim 1,
The heat treatment is a method for producing a coating layer of silicon carbide on the graphite foam, characterized in that for 1 hour at 1,600 ℃ after maintaining for 2 hours at 1,400 ℃. The method of claim 1,
The organic silane is at least one selected from the group consisting of DMDMS, MTMS, TEOS and GPTMS or at least two compounds selected from the group consisting of silicon carbide on the graphite foam.

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