KR100951633B1 - Process for SiC coating on graphite foam - Google Patents

Abstract

The present invention provides a method for forming a silicon carbide coating comprising a step of coating a silicon carbide prepared by using a polyphenyl carbosilane as a starting material on the graphite foam. The silicon carbide coated graphite foam manufactured by the present invention is light, has high thermal conductivity, and is about 5 times lighter than conventional aluminum foam, and can be used as a heat dissipation material and a high temperature heat exchanger material of electronic devices, which are becoming smaller and larger in size. .

Graphite Foam, Silicon Carbide, Heating Material

Description

A method of forming a silicon carbide coating on graphite foam. {Process for SiC coating on graphite foam}

The present invention relates to a method of coating silicon carbide on graphite foam.

As the industrial society evolves into a high information age, electronic devices equipped with high-speed CPUs, large LCDs, and large-capacity memories are increasing, and heating materials that can effectively release heat generated from such electronic devices are required.

Graphite foam materials are materials with high specific strength, extremely resistant to thermal shock and corrosion, and high thermal and electrical conductivity. In addition, due to the volatilization of low-boiling compounds during heat treatment in the reducing atmosphere and high thermal decomposition during the condensation and condensation, they have a low density foam form, which enables high specific surface area required for use as a thermal converter. It is an ideal material to meet the requirements of three heat dissipating materials: thermal conductivity, large specific surface area and low density. In addition, it is about 5 times lighter than the existing aluminum material, which has superior advantages in weight, and is being actively researched as a heat dissipation material for electronic devices, which is becoming smaller and larger in capacity.

However, graphite foam material has a disadvantage in that the oxidation proceeds at a temperature of 400 ° C. or more, and the physical properties rapidly decrease. In order to compensate for these disadvantages, various methods for treating antioxidants on graphite foam have been studied.

Coating method for oxidation prevention on graphite foam is magnesia by coating with silicon carbide (SiC), silicon nitride (Si ₃ N ₄ ), silicon bronze (SiBC), Mullite using chemical vapor deposition (CVD) and magnesia through plasma spraying Coatings such as (MgO), alumina (Al ₂ Cl ₃ ), and chromium oxide (Cr ₂ O ₃ ) are actively underway.

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

On the other hand, since silicon carbide-coated graphite foam has strong covalent bonds with silicon and carbide, there is no change in physical properties or chemical composition even at temperatures over 2000 ℃, and it has higher strength, hardness, abrasion resistance, and oxidation resistance than conventional graphite foam. It is excellent and is used as the main coating material. However, silicon carbide can not be coated, such as thermal spray coating using a non-oxide ceramic, and the precursor material suitable for impregnation and spin coating has not been known, and its use has been limited.

Generally, silicon carbide is coated on graphite foam by chemical vapor deposition using organosilicon compounds or by infiltration of molten silicon or silicon gas and gas-solid reaction by silicon monoxide (SiO ₂ ) gas. . In the case of coating silicon carbide by chemical vapor deposition, methyltrichlorosilane (MTS) is mainly used as a precursor. At this time, a high temperature is caused by flowing hydrogen gas together to remove chlorine from the methyltrichlorosilane precursor. Has risk factors such as fire when using hydrogen gas, and due to corrosion of hydrochloric acid (HCl) gas as a by-product, it is difficult to handle due to corrosion of equipment and chlorine pollution of end product.

 In order to solve the above problems of the prior art, the present invention is to provide a method for coating silicon carbide on the graphite foam through a safe and effective method.

In addition, the present invention is to provide a method that can be used as a heat dissipation material and a high temperature heat exchanger material of the electronic device has a high thermal conductivity and stable at high temperatures.

Accordingly, the present invention is to provide a method for forming a silicon carbide coating comprising the step of coating a polyphenyl carbosilane solution on the graphite foam as a preferred embodiment.

In the above embodiment, the coating process comprises applying the polyphenylcarbosilane solution on the graphite foam by using an impregnation, spray, or spin coating method; Curing at 200 ° C. to 400 ° C .; And a heat treatment at 600 ° C. to 1500 ° C.

In the above embodiment, the heat treatment step may be performed in an inert gas or a vacuum atmosphere.

In the above embodiment, the polyphenylcarbosilane solution may be one in which a polyphenylcarbosilane having a molecular weight of 2000 to 6000 is dissolved in a solvent.

The present invention can provide a method for easily coating silicon carbide on graphite foam by using polyphenylcarbosilane as a precursor of silicon carbide.

The present invention can provide a method of coating silicon carbide on the graphite foam that is light, high thermal conductivity and excellent oxidation resistance to be used as a heat release material and a high temperature heat exchanger material of the electronic device.

The present invention relates to a method of coating silicon carbide by coating a polyphenylcarbosilane solution on graphite foam.

In general, when coating the polyphenyl carbosilane solution on the graphite foam, a known coating method such as an impregnation method, a spray coating method, or a spin coating method may be used. The polyphenylcarbosilane solution is applied onto the graphite foam by impregnation, spray coating, and spin coating, followed by curing and heat treatment steps.

It does not specifically limit as a precursor of polyphenyl carbosilane, For example, it can manufacture using phenyl trichlorosilane, diphenyl dichlorosilane, polydimethylsilane, and polymethylphenylsilane. Among them, preferably, polymethylphenylsilane may be prepared, and the method for producing polyphenylcarbosilane is as follows.

Under an inert atmosphere such as nitrogen, phenylmethyldichlorosilane is condensed with an alkali metal, preferably sodium metal, to produce polymethylphenylsilane.

Specifically, in an inert atmosphere, the sodium metal is finely chopped in a solvent such as xylene, tetrahydrofuran (THF), toluene, and the like, followed by heating and stirring to disperse the sodium metal completely, where phenylmethyl Dichlorosilane can be prepared by injecting and heating to form a polymer and then removing residual metal sodium and solvent.

The polymethylphenylsilane thus prepared may be converted to polyphenylcarbosilane using a high temperature pressurization reactor. The conversion reaction temperature is preferably 300 to 350 ° C, and polyphenylcarbosilane having a molecular weight suitable for coating may be prepared by polymerization at 400 to 450 ° C.

The polyphenylcarbosilane preferably has a molecular weight of 2000 to 6000, more preferably 2500 to 4000. As the molecular weight of the polyphenyl carbosilane increases, a thick silicon carbide coating film may be obtained after the heat treatment. However, when the molecular weight exceeds 6000, the polyphenyl carbosilane may not be completely dissolved in an organic solvent such as nucleic acid. On the contrary, when the molecular weight is less than 2000, the thickness of the coating layer is thin so that a coating layer that satisfies the desired antioxidant effect cannot be obtained. As described above, the thickness of the silicon carbide coating layer prepared using polyphenylcarbosilane as a precursor is preferably 1 μm to 100 μm.

The organic solvent used as the solvent of the polyphenyl carbosilane in the present invention is not particularly limited and may include nucleic acids, cyclonucleic acid, tetrahydrofuran, benzene and the like. The polyphenyl carbosilane is preferably used diluted 10 to 30% in the organic solvent. When the concentration of the coating solution is less than 10%, the thickness of the coating film that is possible at one time is too thin. If the coating solution exceeds 30%, cracks in the coating film after coating and heat treatment cannot be avoided.

In the present invention, the polyphenyl carbosilane is coated on the graphite foam and then subjected to a curing process which is an insolubilization process, wherein the curing temperature is preferably 200 ° C. to 400 ° C., more preferably 250 ° C. to 300 ° C., which is made in air. desirable.

After the curing process, an organic-inorganic conversion reaction in which the polyphenylcarbosilane polymer is converted to silicon carbide is performed. The heat treatment temperature is preferably 600 ° C. to 1500 ° C., more preferably 800 ° C. to 1200 ° C., preferably in an inert gas such as nitrogen or argon helium or in a vacuum atmosphere. If the heat treatment temperature is less than 600 ℃, the organic / inorganic conversion reaction is not completed, if it exceeds 1500 ℃ will cause unnecessary waste of power.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the scope of the present invention is not limited to the following Examples.

<Example 1>

As a starting material, 500g of coal tar pitch (softening point 110 ℃, specific gravity 1.03, fixed carbon content 45wt%) (Dongyang Steel Chemical Coal Pitch) was heat treated at 300 ℃ for 1 hour, and then again at 450 ℃ for 30 minutes. After heat treatment, the ball mill was pulverized for 24 hours, pressurized at 500 psi for 1 hour at 500 ° C., and then heat treated at 2600 ° C. for 1 hour in an inert atmosphere to obtain 220 g of graphite foam.

20 g of polyphenylcarbosilane having a molecular weight of 3,000 was dissolved in 100 g of cyclonucleic acid to prepare a 20% polyphenylcarbosilane solution.

The surface of the graphite foam was washed with ethanol and dried at 80 ° C. for 30 minutes. The 20% polyphenylcarbosilane solution was impregnated with the dip coater for 5 minutes, the sample was pulled up to 1 mm / sec, and then thermally cured in air at 250 ° C. for 30 minutes and at 800 ° C. under an inert gas atmosphere for 1 hour. After heat treatment to obtain a silicon carbide coated graphite foam. Polyphenyl carbosilanes subjected to the heat treatment process were measured in an X-ray diffractometer, and are shown in FIG. 1, and the surface of the obtained graphite foam was photographed by electron microscopy.

<Example 2>

Except for changing the heat treatment temperature after thermal curing of the graphite foam impregnated in the polyphenyl carbosilane solution in Example 1 was prepared in the same conditions and methods. The obtained silicon carbide coated graphite foam was photographed with an electron microscope and shown in FIG. 4.

<Example 3>

Except for changing the heat treatment temperature after thermal curing of the graphite foam impregnated in the polyphenyl carbosilane solution in Example 1 was prepared in the same conditions and methods. The obtained silicon carbide coated graphite foam was photographed with an electron microscope and shown in FIG. 5.

<Example 4>

 Except for using a polyphenyl carbosilane having a molecular weight of 1000 or less was prepared in Example 1 and the method.

Comparative Example 1

Graphite foams were prepared under the same conditions and methods as in Example 1, but were not coated.

The physical property evaluation of the graphite foam prepared by the said Example and the comparative example was performed as follows.

(1) thermal conductivity (W / mk)

Thermal conductivity was measured according to the KSL4204 measurement method using a thermal conductivity meter (Netzch Co. LFA 4204), the results are shown in Table 1.

division Coating thickness (㎛) Thermal conductivity (w / mk) Example 1 3 160.63 Example 2 3 174.09 Comparative Example 1 - 148.24

(2) oxidation resistance (%)

In the oxidation resistance test, the graphite foams prepared in Examples and Comparative Examples were oxidized in an air atmosphere at 800 ° C. for 1 hour to compare the weight difference, and the oxidation resistance represented by Equation 1 was measured. The measurement results are shown in Table 2 and FIG. 6.

<Equation 1>

Degree of oxidation (%) = weight of graphite foam after oxidation (wt ^f ) / weight of initial graphite foam (wt ⁱ )

division Coating thickness (㎛) Oxidation degree (%) Example 1 3 82 Example 2 3 95 Example 3 3 90 Example 4 0.5 53 Comparative Example 1 - 10

(3) XRD analysis

XRD analysis was performed using an X-ray diffractometer (MAC Science Co. Ltd. MO3XMF, Japan), and the results are shown in FIG. 1.

As a result of the physical property evaluation, it can be seen that the graphite foam prepared in the embodiment of the present invention exhibits excellent thermal conductivity, and shows higher thermal conductivity than that of the comparative example in which the silicon carbide is not coated.

In addition, in the evaluation of the oxidation resistance, in the case of the uncoated graphite foam, most of the graphite was oxidized to CO ₂ and there was almost no residual amount. However, in the case of the example, the oxidation resistance was significantly increased.

1 is a graph measured by the X-ray diffractometer after the heat treatment process for the polyphenyl carbosilane used in the embodiment of the present invention,

2 is an electron micrograph taken at 50 times the surface of the graphite foam prepared in Example 1 of the present invention,

3 is an electron micrograph taken at 200 times the surface of the graphite foam prepared in Example 1 of the present invention,

4 is an electron micrograph taken at 500 times the surface of the graphite foam prepared in Example 2 of the present invention,

5 is an electron micrograph taken at 500 times the surface of the graphite foam prepared in Example 3 of the present invention,

6 is a photograph of a sample taken after the oxidation resistance test of the graphite foam prepared in Examples and Comparative Examples of the present invention.

Claims (4)

Applying a polyphenylcarbosilane solution containing 10 to 30% by weight of polyphenylcarbosilane on the graphite foam using any one of a coating method selected from an impregnation method, a spray coating method, and a spin coating method; Curing the graphite foam to which the polyphenylcarbosilane solution is applied at 200 ° C. to 400 ° C. for 30 minutes; And Method for forming a silicon carbide coating on the graphite foam comprising the step of heat-treating the cured graphite foam at 600 ℃ ~ 1500 ℃. delete The method of claim 1, Process for forming a silicon carbide coating on the graphite foam, characterized in that the heat treatment step is carried out in an inert gas or vacuum atmosphere. The method of claim 1, Polyphenyl carbosilane solution is a method of forming a silicon carbide coating on a graphite foam, characterized in that the polyphenyl carbosilane having a weight average molecular weight of 2000 ~ 6000 dissolved in a solvent.

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