Graphite surface anti-oxidation coating and preparation method thereof

Abstract

The invention relates to a preparation method of a graphite surface anti-oxidation coating, and belongs to the technical field of coating preparation, and the preparation method comprises the following steps: 1, carrying out hot dipping on a graphite substrate by using a dipping solution, and sequentially drying and sintering after the dipping is completed to obtain a pretreated graphite substrate; 2, carrying out heat treatment on the residual steeping liquor in the step 1 to obtain a fixed product, grinding the solid product to obtain precursor powder, mixing the precursor powder, a fixed filler and an adhesive, and carrying out ball milling to obtain coating slurry; and 3, brushing the coating slurry obtained in the step 2 on the pretreated graphite substrate obtained in the step 1, and sequentially drying and sintering to obtain the anti-oxidation coating on the graphite surface. According to the method, steeping liquor is subjected to heat treatment at 400 DEG C to be converted into a solid product, the solid product is ground into powder, then the powder is mixed with an aluminum dihydrogen phosphate solution and boron nitride powder to prepare slurry, and the slurry is brushed on the surface of graphite to form a coating.

Description

Technical Field

[0001] The present invention relates to the technical field of coating preparation, and particularly relates to an antioxidant coating on the surface of graphite and a preparation method thereof. Background Art

[0002] As an allotrope of carbon, graphite has good thermal stability, chemical stability and processability, and due to its excellent electrical conductivity, it is widely used in the fields of petrochemical, metallurgy, microelectronics, aviation, etc. However, like other carbon materials, graphite has the disadvantage of being easily oxidized at high temperatures. Under air conditions, the mass of graphite begins to slowly decrease at 450°C, and when the ambient temperature exceeds 750°C, the mass loss of graphite shows an accelerating trend, which sharply shortens the service life of graphite under such conditions. Therefore, when working at high temperatures, it needs to be carried out in an inert gas or vacuum environment, which greatly limits the application of graphite molds. In order to enable graphite molds to still work normally in a high-temperature environment with the presence of oxygen, it is necessary to find a protection method for graphite molds to improve the application prospects of graphite molds.

[0003] At present, the methods to improve the antioxidant performance of graphite materials mainly include material modification, surface coating technology, chemical vapor deposition technology, impregnation treatment technology, etc. In the existing antioxidant coating processes, the solution impregnation method for preparing a graphite surface coating is a treatment method with relatively low cost and strong industrial operability. This method uses a specific impregnating solution to impregnate the graphite surface to form a protective antioxidant coating on the graphite surface, which can not only improve the density and mechanical strength of the material, but also improve the antioxidant and wear-resistant properties of the material surface.

[0004] Although the above methods can improve the antioxidant performance of graphite to a certain extent, a single method is difficult to achieve an ideal antioxidant effect. Simply using a phosphate or borate impregnating solution to treat graphite, the density and adhesion of the coating are insufficient, and cracks or coating peeling are likely to occur, resulting in a significant decrease in antioxidant performance. It is difficult to meet the actual application requirements in a long-term high-temperature working environment, and the durability of the coating is insufficient to significantly extend the service life of graphite molds in a high-temperature environment.

[0005] In summary, in view of these deficiencies in the existing graphite material antioxidant technology, there is an urgent need to develop a new preparation method for an antioxidant coating on the surface of graphite to improve the coating adhesion strength, density and antioxidant performance, extend the service life of graphite products, reduce production costs and improve industrial production efficiency. Summary of the Invention

[0006] The object of the present invention is to provide an antioxidant coating for the graphite surface and its preparation method so as to overcome at least one of the defects existing in the above-mentioned prior art. In the traditional impregnation process, graphite has hydrophobic and relatively inert surface properties, and the actual adsorption amount of the impregnating liquid during the impregnation process is still small. After the remaining impregnating liquid cools, it will form a white highly viscous solid, and this part of the substance is often difficult to reuse, resulting in waste of raw materials and treatment problems. The present invention converts the residue of the impregnating liquid treatment from "waste" into "functional raw materials", effectively improving the material utilization rate and constructing an efficient and low-consumption antioxidant coating preparation system.

[0007] The object of the present invention can be achieved by the following technical solutions:

[0008] A preparation method of an antioxidant coating for the graphite surface, comprising:

[0009] Step 1: Thermally impregnate a graphite substrate with an impregnating liquid, and after the impregnation is completed, perform drying and sintering in sequence to obtain a pretreated graphite substrate;

[0010] Step 2: Heat-treat the impregnating liquid used in Step 1 to obtain a fixed product, grind the solid product to obtain a precursor powder, mix the precursor powder, a fixed filler, and a binder, and then perform ball milling to obtain a coating slurry;

[0011] Step 3: Brush the coating slurry obtained in Step 2 on the pretreated graphite substrate obtained in Step 1, and perform drying and sintering in sequence to obtain an antioxidant coating on the graphite surface.

[0012] Further, the impregnating liquid is composed of water, phosphoric acid, disodium hydrogen phosphate, sodium tetraborate, and glycerol with a mass ratio of 1:(3 - 6):(5 - 7):(3 - 5):(1 - 3). Preferably, the mass ratio of water, phosphoric acid, disodium hydrogen phosphate, sodium tetraborate, and glycerol is 1:5:6:4:2.

[0013] Further, in Step 1, the impregnation temperature of the thermal impregnation is 150 - 200 °C, and the impregnation time is 30 - 60 min; the sintering procedure for the sintering is: heating to 150 - 200 °C at a rate of 2 - 5 °C / min and holding for 60 - 90 min, then heating to 250 - 300 °C at a rate of 2 - 5 °C / min and holding for 60 - 90 min, and finally heating to 400 - 450 °C at a rate of 3 - 5 °C / min and holding for 90 - 120 min.

[0014] Further, in Step 2, the ball milling time for the ball milling is 12 - 20 h.

[0015] Further, in Step 2, the mass ratio of the precursor powder, the fixed filler, and the binder is 8:(2 - 4):(4 - 7), and the preferred mass ratio of the three is 8:3:6.

[0016] Further, in step two, the fixed filler is boron nitride with a particle size of 2-5 μm.

[0017] Further, in step two, the binder is an aluminum dihydrogen phosphate solution, and the mass concentration of the solute in the solution is 20%.

[0018] Further, the sintering procedure in step three is as follows: heating to 90-120°C at a rate of 3-5°C / min and holding for 60-90 min, then heating to 200-250°C at a rate of 3-5°C / min and holding for 60-90 min, then heating to 600-700°C at a rate of 3-5°C / min and holding for 60-90 min, and finally heating to 750-800°C at a rate of 5-10°C / min and holding for 60-90 min.

[0019] Further, the sintering in step three is carried out in an inert atmosphere, and the inert atmosphere is selected from any one or more of vacuum, nitrogen, and argon.

[0020] The second object of the present invention is a graphite surface antioxidant coating, which is prepared by the preparation method described above.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) In the method of the present invention, the impregnating solution used in the traditional method is heat-treated at 400°C to be converted into a solid product and ground into powder, and then mixed with an aluminum dihydrogen phosphate solution and boron nitride powder to form a slurry, and a coating is formed on the graphite surface by brushing. After thermal impregnation, a solid product will be generated from the impregnating solution, making it only usable once. In the traditional method, only the used impregnating solution can be treated as waste. The present invention effectively utilizes the waste by heating the used impregnating solution to obtain a solid product.

[0023] (2) Compared with the traditional method, the method provided by the present invention is brushed at room temperature, the operation process is simpler and more controllable, a thicker and firmly attached coating can be formed, and the brushing process is convenient for realizing large-area uniform brushing, providing technical support for subsequent process automation and large-scale production.

[0024] (3) In the coating prepared by the present invention through improving the slurry method, aluminum dihydrogen phosphate generates a stable phosphate ceramic phase after high-temperature treatment; at the same time, the added boron nitride powder has excellent high-temperature resistance and oxygen isolation performance, and the two act synergistically at high temperature to form a dense protective layer, which can significantly improve the antioxidant ability of graphite and extend the service life of graphite in a high-temperature environment. Description of the Drawings

[0025] Figure 1 It is the XRD pattern of the aluminum dihydrogen phosphate prepared in Example 1 of the present invention;

[0026] Figure 2 XRD patterns of the precursor powder and boron nitride prepared in Example 1 of the present invention;

[0027] Figure 3 Graphite oxidation weight loss rate diagram of the graphite antioxidant coating prepared in Example 1 of the present invention.

[0028] Figure 4 SEM photograph of the graphite antioxidant coating prepared in Example 2 of the present invention;

[0029] Figure 5 SEM photograph of the graphite antioxidant coating prepared in Comparative Example 1 of the present invention;

[0030] Figure 6 SEM photograph of the graphite antioxidant coating prepared in Comparative Example 2 of the present invention. Detailed implementation manners

[0031] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented on the premise of the technical solution of the present invention, and the detailed implementation manners and specific operation processes are given, but the protection scope of the present invention is not limited to the following embodiments.

[0032] Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the protection scope of the present invention. Those not specified in specific conditions are carried out according to conventional conditions or conditions recommended by the manufacturer. Those reagents or instruments not specified in the manufacturer are all conventional products that can be obtained through commercial purchase.

[0033] In the ranges disclosed in the present invention, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in the present invention.

[0034] The present invention provides a method for preparing a graphite surface antioxidant coating, comprising the following steps:

[0035] 1. Pretreatment of graphite substrate

[0036] 1.1 Place the graphite substrate in a container filled with an impregnating solution and heat it to 150 - 200 °C. During the hot impregnation process, magnetic stirring is carried out, and the hot impregnation is carried out for 30 - 60 min until there are no obvious bubbles on the surface of the graphite substrate.

[0037] 1.2 After the impregnation is completed, the graphite substrate is transferred to a blast drying oven for preliminary drying treatment, and the temperature is raised to 60 - 80°C at a rate of 1 - 2°C / min and dried for 1 - 2 hours.

[0038] 1.3 The dried graphite substrate is placed in a tube furnace for heat treatment. The set program is: the temperature is raised to 150 - 200°C at a rate of 2 - 5°C / min, held for 60 - 90 minutes, then the temperature is raised to 250 - 300°C at a rate of 2 - 5°C / min, held for 60 - 90 minutes, and then the temperature is raised to 400 - 450°C at a rate of 3 - 5°C / min, held for 90 - 120 minutes.

[0039] 2. Preparation of coating slurry

[0040] 2.1 The hot impregnation used in 1.1 is heat-treated. The set program is: the temperature is raised to 150 - 200°C at a rate of 2 - 5°C / min, held for 60 - 90 minutes, then the temperature is raised to 250 - 300°C at a rate of 2 - 5°C / min, held for 60 - 90 minutes, and then the temperature is raised to 400 - 450°C at a rate of 3 - 5°C / min, held for 90 - 120 minutes. The solid product obtained after sintering is ground to obtain precursor powder.

[0041] 2.2 Solid fillers and binders are added to the precursor powder, and the mixture is ball-milled for 12 - 20 hours. After mixing evenly, the coating slurry is obtained.

[0042] 3. Preparation of coating by brushing method

[0043] 3.1 A soft and fine brush is dipped in the slurry to brush the coating on the pretreated graphite substrate. The brushing method uses the cross-cross method to ensure the uniformity of the coating and the coating thickness.

[0044] 3.2 The prepared coated graphite substrate is dried in an oven at 60 - 80°C for 1 - 2 hours.

[0045] 3.3 The dried coated graphite is heat-treated. The set program is: the temperature is raised to 90 - 120°C at a rate of 3 - 5°C / min, held for 60 - 90 minutes, then the temperature is raised to 200 - 250°C at a rate of 3 - 5°C / min, held for 60 - 90 minutes, and then the temperature is raised to 600 - 700°C at a rate of 3 - 5°C / min, held for 60 - 90 minutes, and then the temperature is raised to 750 - 800°C at a rate of 5 - 10°C / min, held for 60 - 90 minutes. Sintering is carried out under the protection of an inert atmosphere after the temperature is higher than 400°C.

[0046] In some embodiments of the present invention, the heating rate of the oven during the drying process is 1 - 2°C / min; the inert atmosphere includes one or more of vacuum, helium, or argon.

[0047] In some embodiments of the present invention, the impregnating solution is water, phosphoric acid, disodium hydrogen phosphate, sodium tetraborate, and glycerol; the solid filler is hexagonal boron nitride; and the binder is aluminum dihydrogen phosphate.

[0048] In some embodiments of the present invention, the mass ratio of water, phosphoric acid, disodium hydrogen phosphate, sodium tetraborate, and glycerol in the impregnating solution is 1:(3 - 6):(5 - 7):(3 - 5):(1 - 3), preferably 1:5:6:4:2.

[0049] In some embodiments of the present invention, the concentration of the binder aluminum dihydrogen phosphate is 20%; and the particle size of the solid filler hexagonal boron nitride is 2 - 5 μm.

[0050] In some embodiments of the present invention, when the slurry is precursor powder, hexagonal boron nitride, and disodium hydrogen phosphate solution, the mass ratio of the precursor powder, hexagonal boron nitride, and disodium hydrogen phosphate solution after heat treatment of the impregnating solution is 8:(2 - 4):(4 - 7), preferably 8:3:6.

[0051] Example 1

[0052] In this example, the carbon matrix is a graphite material, and the coating method is brush coating.

[0053] This example provides a method for preparing a graphite antioxidant coating, which includes the following steps:

[0054] (1) Select a graphite substrate with appropriate dimensions, polish, clean, dry it, and set it aside.

[0055] (2) Prepare the impregnating solution: The mass ratio of water, phosphoric acid, disodium hydrogen phosphate, sodium tetraborate, and glycerol in the impregnating solution is 1:5:6:4:2. Place the mixed solution on a heating platform, heat it to 180°C, add the graphite substrate when the mixed solution becomes transparent, perform magnetic stirring during the hot impregnation process, transfer it to an 80°C oven for drying for 1 h after 40 min of hot impregnation, and set the oven heating rate to 1°C / min. The dried graphite substrate is placed in a tubular furnace for heat treatment, and the set program is: heat up to 150°C at a rate of 2°C / min, hold for 60 min, then heat up to 250°C at a rate of 5°C / min, hold for 90 min, and then heat up to 400°C at a rate of 5°C / min, hold for 90 min.

[0056] (3) Preparation of the coating slurry: Heat-treat the impregnating solution used in (2), and the set program is: heat up to 150°C at a rate of 2°C / min, hold for 60 min, then heat up to 250°C at a rate of 5°C / min, hold for 90 min, and then heat up to 400°C at a rate of 5°C / min, hold for 120 min. Grind the solid product obtained after sintering to obtain the precursor powder.

[0057] Using hexagonal boron nitride as a solid filler and aluminum dihydrogen phosphate as a binder. The mass ratio of the precursor powder, hexagonal boron nitride, and disodium hydrogen phosphate solution is 8:3:6. The mixture is ball-milled for 16 h, and the coating slurry is obtained after uniform mixing.

[0058] (4) Preparation of the graphite antioxidant coating: Dip a soft and fine brush into the slurry and brush the coating on the pretreated graphite substrate. The brushing method uses the cross-cross method to ensure the uniformity of the coating and the coating thickness. The prepared coated graphite substrate is dried in an oven at 80 °C for 1 h, and the heating rate of the oven is 1 °C / min. The dried coated graphite is heat-treated, and the set program is: heated to 100 °C at 3 °C / min, held for 60 min, heated to 200 °C at 5 °C / min, held for 60 min, heated to 600 °C at 5 °C / min, held for 60 min, heated to 800 °C at 10 °C / min, held for 60 min. Sintering is carried out under the protection of an inert atmosphere after exceeding 400 °C.

[0059] The X-ray diffraction pattern of the graphite antioxidant coating prepared in this example is as Figure 1 、 Figure 2 shown. Figure 1 is the X-ray diffraction pattern of aluminum dihydrogen phosphate at 800 °C, indicating that aluminum dihydrogen phosphate can be transformed into a three-dimensional network structure of metaphosphoric acid aluminum at high temperature as an inorganic binder, forming an inorganic ceramic skeleton structure with extremely high thermal stability, providing high-temperature mechanical strength and thermal shock stability of the coating, avoiding the coating from peeling off or cracking during thermal expansion and cooling, and at the same time, it can also cooperate with the glass phase generated by the precursor powder, thereby improving the overall structural integrity of the coating. Figure 2 is the X-ray diffraction pattern of the precursor powder and boron nitride powder at 800 °C. After heat treatment at 800 °C, the precursor powder forms a composite structure with BPO4 as the main crystal phase. BPO4 has high-temperature stability, low oxygen permeability, and good interfacial bonding properties. Its dense crystal structure can effectively prevent oxygen penetration and avoid oxidation of the graphite matrix at high temperature; at the same time, the added boron nitride filler maintains its structural integrity during sintering and does not react, further playing an auxiliary function of heat insulation and oxygen resistance. Overall, it shows that this composite coating system has good thermal stability and functional synergy at high temperature. Figure 5 Shown is the antioxidant coating formed by single impregnation and sintering, which does not contain aluminum dihydrogen phosphate and boron nitride. Cracks appear on the surface and there is large-area peeling. Although the coating can be transformed into a molten phosphoborate glass phase at high temperature and has a certain repair ability, without the inorganic skeleton and inert filler formed by aluminum dihydrogen phosphate and boron nitride, the excessive fluidity will instead cause the surface coating of the graphite to be uneven after heating, and weak protection parts appear on the graphite surface.

[0060] The oxidation weight loss rate diagram of the graphite antioxidant coating prepared in this example is as Figure 3As shown. The test conditions were natural cooling after holding at 800 °C in air for a certain time; the first stage was held for 5 h and cycled 5 times; the second stage was held for 10 h and cycled 16 times; the third stage was held for 20 h and cycled 6 times. After a cumulative holding time of 315 h at 800 °C in air, the weight loss rate was only 7.768%, reflecting the good thermal shock resistance and oxidation resistance of the coating.

[0061] Example 2

[0062] In this example, the carbon matrix is a graphite material, and the coating method is brush coating.

[0063] This example provides a method for preparing a graphite oxidation-resistant coating, which includes the following steps:

[0064] (1) Select a graphite substrate with appropriate dimensions, polish, clean, dry it, and set it aside.

[0065] (2) Prepare the impregnating solution: The mass ratio of water, phosphoric acid, disodium hydrogen phosphate, sodium tetraborate, and glycerol in the impregnating solution is 1:6:6:3:2. Place the mixed solution on a heating platform and heat it to 200 °C. When the mixed solution becomes transparent, add the graphite substrate. During the hot impregnation process, perform magnetic stirring. After hot impregnation for 30 min, transfer it to an 80 °C oven and dry it for 1 h. The heating rate of the oven is set to 1 °C / min. The dried graphite substrate is placed in a tube furnace for heat treatment. The set program is: heat up to 180 °C at 2 °C / min, hold for 60 min, then heat up to 250 °C at 5 °C / min, hold for 90 min, and then heat up to 420 °C at 5 °C / min, hold for 90 min.

[0066] (3) Preparation of the coating slurry: Heat-treat the impregnating solution used in (2). The set program is: heat up to 120 °C at 2 °C / min, hold for 60 min, then heat up to 220 °C at 5 °C / min, hold for 90 min, and then heat up to 400 °C at 5 °C / min, hold for 120 min. Grind the solid product obtained after sintering to obtain the precursor powder.

[0067] Using hexagonal boron nitride as the solid filler and aluminum dihydrogen phosphate as the binder. The mass ratio of the precursor powder, hexagonal boron nitride, and disodium hydrogen phosphate solution is 8:3:6. Mix and perform ball milling for 16 h. After mixing evenly, the coating slurry is obtained.

[0068] (4) Preparation of the graphite antioxidant coating: Dip a soft and fine brush in the slurry and brush the coating on the pretreated graphite substrate. The brushing method uses the cross-cross method to ensure the uniformity and thickness of the coating. The prepared coated graphite substrate is dried in an oven at 80 °C for 1 h, and the heating rate of the oven is 1 °C / min. The dried coated graphite is heat-treated, and the set program is: heating to 100 °C at 3 °C / min, holding for 60 min, heating to 200 °C at 5 °C / min, holding for 60 min, heating to 600 °C at 5 °C / min, holding for 60 min, heating to 800 °C at 10 °C / min, holding for 60 min. After exceeding 400 °C, sintering is carried out under the protection of an inert atmosphere.

[0069] The graphite antioxidant coating prepared in this example is as Figure 4 shown. At high temperatures, the surface coating will transform into a molten phosphate borate glass phase, which has a certain viscosity and sealing ability in a high-temperature environment. It will soften and self-heal the cracks on the coating surface at high temperatures, seal the micropores and defects on the graphite surface, and can form a dense and continuous barrier layer to physically isolate the oxygen diffusion channel.

[0070] Comparative Example 1

[0071] In this Comparative Example 1, the carbon matrix is a graphite material.

[0072] This Comparative Example 1 provides a preparation method for a graphite antioxidant coating, and this preparation method includes the following steps:

[0073] (1) Select a graphite substrate with appropriate dimensions, and set it aside after grinding, cleaning and drying.

[0074] (2) Prepare the impregnating solution: The mass ratio of water, phosphoric acid, disodium hydrogen phosphate, sodium tetraborate, and glycerol in the impregnating solution is 1:6:6:3:2. Place the mixed solution on a heating platform and heat it to 200 °C. When the mixed solution becomes transparent, add the graphite substrate. Magnetic stirring is carried out during the hot impregnation process. After hot impregnation for 30 min, transfer it to an oven at 80 °C and dry for 1 h. The heating rate of the oven is set to 1 °C / min. The dried graphite substrate is placed in a tube furnace for heat treatment, and the set program is: heating to 180 °C at 2 °C / min, holding for 60 min, then heating to 250 °C at 5 °C / min, holding for 90 min, and then heating to 420 °C at 5 °C / min, holding for 90 min.

[0075] The graphite antioxidant coating prepared in this comparative example is as Figure 5As shown, the antioxidant coating formed after single impregnation and sintering is cracked and has large-area peeling. Although the coating can transform into a molten phosphoborate glass phase at high temperature and has a certain repair ability, there is still a large gap compared with the coating formed by the brushing method. The weight loss rate is 11.3% after holding at 800 °C for 10 h in air, and obvious pores appear on the surface.

[0076] Comparative Example 2

[0077] In this Comparative Example 2, the carbon matrix is a graphite material.

[0078] This Comparative Example 2 provides a preparation method of a graphite antioxidant coating, and the preparation method includes the following steps:

[0079] (1) Select a graphite substrate with appropriate size, and after grinding, cleaning and drying, reserve it for use.

[0080] (2) Preparation of the coating slurry: The mass ratio of water, phosphoric acid, disodium hydrogen phosphate, sodium tetraborate, and glycerol in the slurry precursor is 1:6:6:3:2. Heat-treat the mixed solution, and the set program is: heat up to 120 °C at a rate of 2 °C / min, hold for 60 min, then heat up to 220 °C at a rate of 5 °C / min, hold for 90 min, and then heat up to 400 °C at a rate of 5 °C / min, hold for 120 min. Grind the solid product obtained after sintering to obtain the precursor powder.

[0081] Using hexagonal boron nitride as the solid filler and aluminum dihydrogen phosphate as the binder. The mass ratio of the precursor powder, hexagonal boron nitride, and disodium hydrogen phosphate solution is 8:3:6. Mix and carry out ball milling for 16 h, and the coating slurry is obtained after mixing evenly.

[0082] (3) Preparation of the graphite antioxidant coating: Dip a soft and fine brush in the slurry and brush the coating on the pretreated graphite substrate. The brushing method uses the cross-cross method to ensure the uniformity and thickness of the coating. Dry the prepared coated graphite substrate in an oven at 80 °C for 1 h, and the heating rate of the oven is 1 °C / min. Heat-treat the dried coated graphite, and the set program is: heat up to 100 °C at a rate of 3 °C / min, hold for 60 min, heat up to 200 °C at a rate of 5 °C / min, hold for 60 min, heat up to 600 °C at a rate of 5 °C / min, hold for 60 min, and heat up to 800 °C at a rate of 10 °C / min, hold for 60 min. Sinter in an inert gas atmosphere after exceeding 400 °C.

[0083] The graphite antioxidant coating prepared in this comparative example is as Figure 6As shown, the graphite substrate was directly prepared with an antioxidant coating without pre-impregnation treatment. Since an intermediate layer was not formed on the graphite surface through thermal impregnation pretreatment, local bulges and peeling occurred on the surface after sintering. During the antioxidant test, due to incomplete local coating and lack of sealing of pores in the substrate, oxygen easily invaded through the graphite pore channels during the antioxidant test, resulting in the formation of an oxygen "breakthrough point" and increased oxidation.

[0084] The above are only the preferred embodiments of the present invention and do not limit the present invention in other forms. Any person skilled in the art may use the disclosed technical content to make changes or modifications into equivalent embodiments with equivalent changes. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the technical solution content of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing an antioxidant coating on the surface of graphite, characterized in that, Including: Step 1: Thermally impregnate the graphite substrate with an impregnating solution. After impregnation, perform drying and sintering in sequence to obtain a pretreated graphite substrate; Step 2: Heat-treat the impregnating solution used in Step 1 to obtain a fixed product. Grind the solid product to obtain a precursor powder. Mix the precursor powder, fixed filler, and binder and then perform ball milling to obtain a coating slurry; Step 3: Brush the coating slurry obtained in Step 2 onto the pretreated graphite substrate obtained in Step 1, and perform drying and sintering in sequence to obtain an antioxidant coating on the graphite surface.

2. The preparation method of an antioxidant coating on the graphite surface according to claim 1, characterized in that, The impregnating solution is composed of water, phosphoric acid, disodium hydrogen phosphate, sodium tetraborate, and glycerol with a mass ratio of 1:(3 - 6):(5 - 7):(3 - 5):(1 - 3).

3. The preparation method of an antioxidant coating on the graphite surface according to claim 1, characterized in that, In Step 1, the impregnation temperature for the thermal impregnation is 150 - 200°C, and the impregnation time is 30 - 60 min; the sintering procedure for the sintering is: heat up to 150 - 200°C at a rate of 2 - 5°C / min and hold for 60 - 90 min, then heat up to 250 - 300°C at a rate of 2 - 5°C / min and hold for 60 - 90 min, and finally heat up to 400 - 450°C at a rate of 3 - 5°C / min and hold for 90 - 120 min.

4. The preparation method of an antioxidant coating on the graphite surface according to claim 1, wherein, In Step 2, the ball milling time for the ball milling is 12 - 20 h.

5. The preparation method of an antioxidant coating on the graphite surface according to claim 1, characterized in that, In Step 2, the mass ratio of the precursor powder, fixed filler, and binder is 8:(2 - 4):(4 - 7).

6. The preparation method of an antioxidant coating on the graphite surface according to claim 1, wherein, In Step 2, the fixed filler is boron nitride with a particle size of 2 - 5 μm.

7. The preparation method of an antioxidant coating on the graphite surface according to claim 1, wherein, In Step 2, the binder is an aluminum dihydrogen phosphate solution, and the mass concentration of the solute in this solution is 20%.

8. The preparation method of an antioxidant coating on the graphite surface according to claim 1, characterized in that, The sintering procedure for the sintering in Step 3 is: heat up to 90 - 120°C at a rate of 3 - 5°C / min and hold for 60 - 90 min, then heat up to 200 - 250°C at a rate of 3 - 5°C / min and hold for 60 - 90 min, then heat up to 600 - 700°C at a rate of 3 - 5°C / min and hold for 60 - 90 min, and finally heat up to 750 - 800°C at a rate of 5 - 10°C / min and hold for 60 - 90 min.

9. The preparation method of an antioxidant coating on the graphite surface according to claim 1, wherein, The sintering in Step 3 is carried out in an inert atmosphere, and the inert atmosphere is selected from any one or more of vacuum, nitrogen, and argon.

10. An antioxidant coating on the graphite surface, characterized in that, It is obtained by the preparation method described in any one of claims 1 - 9.

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