Preparation method of silicon carbide coating on surface of graphite base

Abstract

The invention discloses a preparation method of a silicon carbide coating on the surface of a graphite base. The preparation method comprises the following steps: (1) carrying out ultrasonic cleaning on the graphite base; (2) dispersing graphite powder, silicon powder and silicon carbide powder into a polyvinylpyrrolidone aqueous solution to obtain a coating solution; (3) coating the surface of the graphite base with the coating liquid in the step (2), and drying; (4) placing the graphite sagger filled with the solid silicon material in a vacuum siliconizing furnace, placing the graphite base on a bracket in the graphite sagger, and carrying out gas-phase siliconizing treatment; the solid silicon material is a mixture of silicon and silicon dioxide; (5) the graphite base subjected to siliconing treatment is put into acid liquor to be etched; the preparation method is simple in process, the prepared silicon carbide coating is uniform in covering, excellent in adhesive force, high in density and low in cost, the oxidation resistance of the graphite base in a high-temperature environment is improved, and the service life of the graphite base in the high-temperature environment is prolonged.

Description

Technical Field

[0001] The invention belongs to the technical field of coating production, and in particular relates to a method for preparing a silicon carbide coating on the surface of a graphite base. Background Art

[0002] In the field of copper rod processing, graphite bases are widely used as support and heat transfer elements under high temperature conditions. However, because graphite is easily oxidized in high temperature environments, its mechanical properties and electrical conductivity are significantly reduced, limiting its service life and performance stability. Especially in the process of copper water processing, the oxidation problem of graphite bases is particularly serious, which directly affects the product stability and safety of copper rod processing.

[0003] In order to solve the oxidation problem of the graphite base, the prior art generally adopts a coating protection method, among which the silicon carbide (SiC) coating has become the most common coating because of its excellent high temperature resistance and oxidation resistance. However, the existing method for making the silicon carbide coating on the graphite base has poor coating adhesion, which is easy to peel off at high temperatures and cannot effectively protect the graphite base for a long time. Its manufacturing process usually also requires multiple steps, such as high temperature sintering, chemical vapor deposition, etc., and the process flow is cumbersome and the cost is high. In addition, there are often many micropores and cracks in the silicon carbide coating, and these defects will become channels for oxidizing gases, reducing the protective effect of the coating. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a method for preparing a silicon carbide coating on the surface of a graphite base. The preparation method has a simple process, and the prepared silicon carbide coating has uniform coverage, excellent adhesion and high density, which significantly improves the oxidation resistance of the coating, thereby improving the oxidation resistance and service life of the graphite base in a high temperature environment.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing a silicon carbide coating on the surface of a graphite base, the preparation method comprising the following steps:

[0007] (1) Ultrasonic cleaning of the graphite base;

[0008] (2) dispersing graphite powder, silicon powder and silicon carbide powder into a polyvinyl pyrrolidone aqueous solution to obtain a coating solution;

[0009] (3) coating the coating liquid in step (2) on the surface of the graphite base and drying;

[0010] (4) placing a graphite sagger containing solid silicon material in a vacuum siliconizing furnace, placing a graphite base on a bracket in the graphite sagger, and performing a vapor phase siliconizing treatment; the solid silicon material is a mixture of silicon and silicon dioxide;

[0011] (5) The siliconized graphite base is placed in an acid solution for etching.

[0012] In step (2), the mass concentration of the polyvinyl pyrrolidone aqueous solution is 0.5 to 2 g / mL.

[0013] In step (2), the mass ratio of graphite powder, silicon powder and silicon carbide powder is 30-45:15-35:20-55, and their total mass concentration in the polyvinyl pyrrolidone aqueous solution is 0.05-0.1 g / mL.

[0014] In step (3), the coating method is spin coating or dip coating.

[0015] In step (4), the mass ratio of silicon to silicon dioxide in the solid silicon material is 1:0.5-1.

[0016] In step (4), the conditions of the siliconizing treatment are: temperature 1450-1700°C, pressure 50-1000Pa, and time 2-4h.

[0017] In step (5), the acid solution is a hydrofluoric acid solution.

[0018] In step (5), the mass concentration of the hydrofluoric acid solution is 10-20%.

[0019] In step (5), the etching time is 2-4 hours.

[0020] The graphite base obtained by the preparation method provided by the present invention can be used in the copper rod processing process, and can ensure that the copper liquid can flow smoothly during the high-temperature processing, and the graphite base is fully protected.

[0021] The method for preparing a silicon carbide coating on the surface of a graphite base provided by the present invention sequentially comprises coating a coating liquid, siliconizing treatment, and acid etching. The process is simple, and the prepared silicon carbide coating has uniform coverage, excellent adhesion and high density, which significantly improves the oxidation resistance of the coating, thereby improving the oxidation resistance and service life of the graphite base in a high temperature environment.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. The preparation process is simple and the cost is low;

[0024] 2. Before siliconizing treatment, a PVP solution containing graphite powder, silicon powder and silicon carbide powder is first coated on the surface of the graphite base to form a porous carbon material coating. PVP is a water-soluble polymer material with good film-forming and thermal decomposition properties, and can be cured by drying at room temperature; the porous carbon material coating can increase the carbon source on the surface of the graphite base, increase the carbon source in the GSI reaction, increase the degree of reaction, and help to generate a dense silicon carbide coating on the surface of the graphite base. The presence of the porous carbon material coating helps to enhance the bonding strength between the silicon carbide coating and the surface of the graphite base and improve the adhesion of the coating.

[0025] 3. During the siliconizing treatment, a siliconizing sagger coated with a mixture of silicon and silicon dioxide is used for siliconizing treatment. Under high temperature and high pressure, silicon and silicon dioxide react to generate silicon monoxide, and silicon monoxide reacts with carbon to generate silicon carbide and carbon monoxide, forming a dense silicon carbide coating. The coating has few internal defects and low porosity, which can effectively prevent the penetration of oxygen and other corrosive gases, thereby improving the overall protection effect.

[0026] 4. After siliconization treatment, further etching is performed using an acid solution, preferably a hydrofluoric acid solution. Etching with a hydrofluoric acid solution can remove excess silicon residues on the surface of the silicon carbide coating, further optimize the surface structure of the coating, improve the density and adhesion of the coating, ensure that the coating surface is smooth and uniform, and further improve its antioxidant properties and mechanical strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a SEM image of the silicon carbide coating on the surface of the graphite base in Example 1;

[0028] Figure 2 This is the SEM image of the silicon carbide coating on the surface of the graphite base in Comparative Example 1. DETAILED DESCRIPTION

[0029] The present invention is described in detail below with reference to the embodiments.

[0030] Example 1

[0031] A method for preparing a silicon carbide coating on the surface of a graphite base comprises the following steps:

[0032] (1) Ultrasonic cleaning of the graphite base;

[0033] (2) dispersing graphite powder, silicon powder, and silicon carbide powder in a polyvinyl pyrrolidone aqueous solution with a concentration of 0.5 g / mL in a mass ratio of 30:35:20, wherein the total mass concentration of the graphite powder, silicon powder, and silicon carbide powder in the polyvinyl pyrrolidone aqueous solution is 0.6 g / mL, to obtain a coating solution;

[0034] (3) Apply the coating liquid on the surface of the graphite base and dry it at room temperature. The average amount of coating liquid used per square centimeter of the surface area of ​​the graphite base is 1.5 mL;

[0035] (4) placing a graphite sagger containing solid silicon material in a vacuum siliconizing furnace, placing a graphite base on a bracket in the graphite sagger, and siliconizing for 120 min at 1450° C. and 800 Pa; the solid silicon material is a mixture of silicon and silicon dioxide in a mass ratio of 1:0.5;

[0036] (5) The siliconized graphite base was placed in a 10% HF solution for etching for 120 min, and then washed with deionized water and dried, forming a 30 μm thick silicon carbide coating on the surface of the graphite base. The SEM image is shown in FIG. Figure 1 As shown in the figure, it can be seen that there is silicon carbide material in the graphite fault with a flaky structure, which is closely attached to the graphite matrix.

[0037] Example 2

[0038] A method for preparing a silicon carbide coating on the surface of a graphite base comprises the following steps:

[0039] (1) Ultrasonic cleaning of the graphite base;

[0040] (2) dispersing graphite powder, silicon powder, and silicon carbide powder in a polyvinyl pyrrolidone aqueous solution with a concentration of 1.0 g / mL in a mass ratio of 35:20:40, wherein the total mass concentration of the graphite powder, silicon powder, and silicon carbide powder in the polyvinyl pyrrolidone aqueous solution is 0.8 g / mL, to obtain a coating solution;

[0041] (3) coating the surface of the graphite base with a coating liquid of 1.5 mL per square centimeter of the surface area of ​​the graphite base, and drying at room temperature;

[0042] (4) placing a graphite sagger containing solid silicon material in a vacuum siliconizing furnace, placing a graphite base on a bracket in the graphite sagger, and siliconizing for 240 minutes at 1580° C. and 500 Pa; the solid silicon material is a mixture of silicon and silicon dioxide in a mass ratio of 1:0.6;

[0043] (5) The siliconized graphite base is placed in a 20% HF solution for etching for 120 minutes, and then washed with deionized water and dried.

[0044] Example 3

[0045] A method for preparing a silicon carbide coating on the surface of a graphite base comprises the following steps:

[0046] (1) Ultrasonic cleaning of the graphite base;

[0047] (2) dispersing graphite powder, silicon powder, and silicon carbide powder in a polyvinyl pyrrolidone aqueous solution with a concentration of 1.5 g / mL in a mass ratio of 45:15:55, wherein the total mass concentration of the graphite powder, silicon powder, and silicon carbide powder in the polyvinyl pyrrolidone aqueous solution is 0.1 g / mL, to obtain a coating solution;

[0048] (3) coating the surface of the graphite base with a coating liquid of 2 mL per square centimeter of the surface area of ​​the graphite base, and drying at room temperature;

[0049] (4) placing a graphite sagger containing solid silicon material in a vacuum siliconizing furnace, placing a graphite base on a bracket in the graphite sagger, and siliconizing for 150 minutes at 1700° C. and 100 Pa; the solid silicon material is a mixture of silicon and silicon dioxide in a mass ratio of 1:1;

[0050] (5) The siliconized graphite base is placed in a 15% HF solution for etching for 120 minutes, and then washed with deionized water and dried.

[0051] Comparative Example 1

[0052] The rest is the same as in Example 1, except that steps (2) and (3) are omitted. The SEM image of the silicon carbide coating formed on the surface of the graphite base is shown in FIG. Figure 2 As shown, it can be seen from the figure that a large number of silicon carbide particles are produced on the surface.

[0053] Comparative Example 2

[0054] The rest is the same as in Example 1, except that the solid silicon material used in step (4) is silicon.

[0055] Comparative Example 3

[0056] The rest is the same as in Example 1, except that the solid silicon material used in step (4) is a mixture of silicon and silicon dioxide in a mass ratio of 1:0.2.

[0057] The graphite bases prepared in the embodiments and comparative examples were used in the copper water processing process, and the service life of each graphite base was counted. At least 5 samples were selected for testing in each case, and the average service life results were counted as shown in Table 1.

[0058] Table 1

[0059] Graphite base service life / h Example 1 240 Example 2 210 Example 3 220 Comparative Example 1 120 Comparative Example 2 96 Comparative Example 3 102

[0060] From the above content, it can be seen that the silicon carbide coating on the surface of the graphite base prepared according to the method provided by the present invention is evenly covered, the coating has excellent adhesion and high density, thereby improving the oxidation resistance and service life of the graphite base in a high temperature environment.

[0061] The above-mentioned detailed description of a method for preparing a silicon carbide coating on the surface of a graphite base with reference to the embodiment is illustrative rather than restrictive, and several embodiments can be listed according to the limited scope. Therefore, changes and modifications without departing from the overall concept of the present invention should fall within the scope of protection of the present invention.

Claims

1. A method for preparing a silicon carbide coating on the surface of a graphite base, characterized in that: The preparation method comprises the following steps: (1) Ultrasonic cleaning of the graphite base; (2) dispersing graphite powder, silicon powder and silicon carbide powder into a polyvinyl pyrrolidone aqueous solution to obtain a coating solution; (3) coating the coating liquid in step (2) on the surface of the graphite base and drying; (4) placing a graphite sagger containing solid silicon material in a vacuum siliconizing furnace, placing a graphite base on a bracket in the graphite sagger, and performing a vapor phase siliconizing treatment; the solid silicon material is a mixture of silicon and silicon dioxide; (5) The siliconized graphite base is placed in an acid solution for etching.

2. The preparation method according to claim 1, characterized in that: In step (2), the mass concentration of the polyvinyl pyrrolidone aqueous solution is 0.5 to 2 g / mL.

3. The preparation method according to claim 1, characterized in that: In step (2), the mass ratio of graphite powder, silicon powder and silicon carbide powder is 30-45:15-35:20-55, and their total mass concentration in the polyvinyl pyrrolidone aqueous solution is 0.05-0.1 g / mL.

4. The preparation method according to claim 1, characterized in that: In step (3), the coating method is spin coating or dip coating.

5. The preparation method according to claim 1, characterized in that: In step (4), the mass ratio of silicon to silicon dioxide in the solid silicon material is 1:0.5-1.

6. The preparation method according to claim 1, characterized in that: In step (4), the conditions of the siliconizing treatment are: temperature 1450-1700°C, pressure 50-1000Pa, and time 2-4h.

7. The preparation method according to claim 1, characterized in that: In step (5), the acid solution is a hydrofluoric acid solution.

8. The preparation method according to any one of claims 1 to 7, characterized in that: In step (5), the mass concentration of the hydrofluoric acid solution is 10-20%.

9. The preparation method according to any one of claims 1 to 7, characterized in that: In step (5), the etching time is 2-4 hours.

10. The preparation method according to any one of claims 1 to 7, characterized in that: The graphite base is used in the copper rod processing process.

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