A method for preparing a glassy carbon coating on the surface of isostatic graphite

Abstract

This invention provides a method for preparing a glassy carbon coating on the surface of isostatically pressed graphite, relating to the fields of special coatings and semiconductor materials. The method includes the following steps: after cleaning the isostatically pressed graphite workpiece, surface roughening is achieved by sandblasting with non-metallic abrasives, controlling the surface roughness Ra of the workpiece to be 0.8~6.4μm; one of phenolic resin and furan resin is selected as the first resin, and the workpiece is impregnated, pre-cured, and subjected to a stepwise initial pyrolysis under an inert atmosphere. This invention utilizes the differences in the pyrolysis properties of the two types of resins to achieve synergistic compensation of internal stress in the coating: phenolic resin has a high pyrolysis carbon yield and high hardness of the formed glassy carbon, but also high pyrolysis shrinkage stress and brittleness; furan resin has a low pyrolysis shrinkage rate and excellent toughness of the formed carbon layer; the alternating stacking of the two types of resin coatings can disperse and offset the shrinkage internal stress accumulated during multi-layer processing, fundamentally inhibiting the initiation of microcracks and macroscopic peeling of the thick film coating, and significantly improving the coating's thermal cycling resistance.

Description

Technical Field

[0001] This invention relates to the field of special coatings and semiconductor materials technology, and in particular to a method for preparing a glassy carbon coating on an isostatically pressed graphite surface. Background Technology

[0002] Isostatic graphite, with its excellent high-temperature mechanical strength, superior thermal and electrical conductivity, low coefficient of thermal expansion, and ease of machining, is now widely used in core processes such as semiconductor SiC / GaN crystal growth, epitaxial processing, high-temperature diffusion, and wafer annealing, serving as a semiconductor thermal field structure and wafer carrier substrate. The mainstream protection method in the industry is to prepare a glassy carbon protective coating on the surface of isostatic graphite workpieces. The conventional industrial preparation method is to use a single phenolic resin solution and form the glassy carbon protective coating through repeated impregnation and coating and stepwise pyrolysis carbonization.

[0003] However, in existing technologies, the pyrolysis volume shrinkage rate of single-component phenolic resin exceeds 20%. After multiple cycles of processing, the internal shrinkage stress of the coating continues to accumulate, easily causing micro-cracks and macro-peeling of the coating under thick film conditions, resulting in extremely poor thermal shock resistance. The carbon network structure formed by the pyrolysis of single resin is simple, and the multi-layer stacking process cannot seal the inherent micropores of the substrate and the micro-pinholes of the coating, resulting in a technical bottleneck in coating density. Corrosive process gases can easily penetrate the coating and erode the graphite substrate. Under multi-layer processing conditions, there is an inherent contradiction between coating thickness and interfacial bonding force. After the coating thickens, the interfacial thermal expansion mismatch stress intensifies, and the interlayer pretreatment process can easily damage the structure of the lower coating layer, ultimately leading to coating peeling and protective failure. Therefore, this invention proposes a method for preparing glassy carbon coatings on isostatically pressed graphite surfaces to solve the problems existing in the prior art. Summary of the Invention

[0004] To address the aforementioned problems, this invention proposes a method for preparing a glassy carbon coating on an isostatically pressed graphite surface. This method achieves a comprehensive improvement in coating adhesion, density, thickness integrity, and thermal shock resistance through alternating coating with two resins and a high-temperature fusion process.

[0005] To achieve the objectives of this invention, the invention is implemented through the following technical solution: a method for preparing a glassy carbon coating on the surface of isostatically pressed graphite, comprising the following steps:

[0006] S1: After cleaning the isostatic graphite workpiece, the surface roughening treatment is completed by sandblasting with non-metallic abrasives, and the surface roughness Ra of the workpiece is controlled to be 0.8~6.4μm.

[0007] S2: Select one of phenolic resin and furan resin as the first resin, and form the first glassy carbon substrate on the roughened matrix surface by impregnation coating, pre-curing, and stepwise initial pyrolysis under an inert atmosphere.

[0008] S3: Alternately coat with another type of resin and perform multiple rounds of intermediate pyrolysis to complete 1 to 5 cycles of alternating stacking of the two types of resins to prepare a multilayer heterogeneous composite glassy carbon intermediate layer;

[0009] S4: Under an inert atmosphere, the final high-temperature heat treatment is carried out at 1200~1800℃, and the temperature is held for 1~4 hours to complete the interlayer interface fusion, internal stress elimination and pore sealing, and obtain an overall dense composite glassy carbon coating.

[0010] The further improvement is as follows: In S1, the sandblasting roughening process parameters are: using 180~800 mesh non-metallic abrasive, sandblasting pressure 0.3~1.5MPa; after roughening, compressed air is used for blowing, organic solvent and deionized water are used for ultrasonic cleaning, and then dried at 80~150℃ for later use; the non-metallic abrasive is white corundum or silicon carbide.

[0011] A further improvement is made in the following: In S2, the phenolic resin preparation and processing parameters are as follows: a phenolic resin organic solution with a solid content of 10~50wt.% is prepared, and the organic solvent is any one of methanol, ethanol, acetone, and dimethylformamide; the pre-curing temperature is controlled at 80~220℃; the initial stepwise pyrolysis heating rate is 0.01~5℃ / min, and the temperature is raised to 350~750℃ and then held at 900~1300℃ for carbonization.

[0012] A further improvement is made in the following: In step S2, the furan resin preparation and processing parameters are as follows: prepare a furfuryl alcohol-based furan resin organic solution with a solid content of 40-60 wt.%; add an acidic catalyst with a solid phase mass ratio of 1-5 wt.% of furan resin; the acidic catalyst is any one of acetic acid, citric acid, oxalic acid, and p-toluenesulfonic acid; and control the maximum temperature of the initial pyrolysis at 900-1300℃.

[0013] Further improvements are made in the following aspects: In S3, the coating order of the two types of resins is adjustable; when phenolic resin is selected as the first resin, a phenolic-furan alternating stacked coating structure is formed; when furan resin is selected as the first resin, a furan-phenolic alternating stacked coating structure is formed; phenolic resin is preferentially selected as the bottom resin to enhance the adhesion of the graphite matrix interface.

[0014] A further improvement is made in S3, where the preceding pyrolytic carbon layer is surface activated before each round of resin coating; the activation treatment method is either a very light sandblasting with a fine abrasive of 600 mesh or higher or a low-temperature oxygen plasma treatment; this is used to improve the physical bonding strength between the heterogeneous carbon layers.

[0015] Further improvements are made in the following aspects: In S3, an inert high-purity nitrogen atmosphere is maintained throughout the intermediate pyrolysis process, and the highest temperature of a single round of intermediate pyrolysis is controlled at 800~1300℃; a segmented step heating process is adopted, with a heating rate range of 0.02~10℃ / min, and the segmented heat preservation time is matched according to the type of resin.

[0016] A further improvement is that, in S3, the overall film thickness of the multilayer heterogeneous composite glass carbon intermediate layer is controlled by adjusting the number of alternating stacking cycles of the resin, and the coating thickness increases linearly with the number of alternating cycles.

[0017] Further improvements are made in the following: In S4, the final high-temperature heat treatment adopts a segmented step heating program: first, the temperature is increased to 750~850℃ at 1~3℃ / min and held for 1h, and then the temperature is increased to the target 1200~1800℃ at 1~2℃ / min and held; the interface between heterogeneous coatings is eliminated by high-temperature carbon structure reforming, and the residual internal stress of multilayer stacking is compensated.

[0018] Further improvements are made in the following: In S4, the high-temperature heat treatment condition matches the number of resin alternation cycles in S3; when the number of resin alternation cycles increases, the final high-temperature heat treatment holding temperature is increased and the holding time is extended to achieve complete fusion of the multilayer heterogeneous coating interface.

[0019] The beneficial effects of this invention are as follows:

[0020] 1. This invention utilizes the differences in the pyrolysis properties of two types of resins to achieve synergistic compensation of internal stress in the coating: phenolic resin has a high pyrolysis carbon yield and high hardness of the formed glassy carbon, but it also has large pyrolysis shrinkage stress and high brittleness; furan resin has a low pyrolysis shrinkage rate and excellent toughness of the formed carbon layer; the alternating stacking of the two types of resin coatings can disperse and offset the shrinkage internal stress accumulated by multi-layer processing, thereby inhibiting the initiation of microcracks and macroscopic peeling of thick film coatings from the root, greatly improving the coating's thermal cycling resistance, and solving the problem of coating cracking caused by internal stress accumulation in existing processes.

[0021] 2. The amorphous carbon micro-network structure formed by the pyrolysis of precursor resins with different chemical structures in this invention has significant differences. Alternating stacking of heterogeneous glass carbon layers can form an interlaced sealing structure, which can accurately fill the micropores, pinholes and micro-defects of the lower coating. Combined with the final high-temperature interface fusion heat treatment process, the interlayer boundary interface is broken, the carbon structure is reorganized, and a near-monolithic interface-free dense coating is formed, which blocks the diffusion channels of small molecule process gases and metal impurities, and breaks through the inherent density limit of a single resin coating.

[0022] 3. This invention matches the substrate sandblasting roughening pretreatment process to construct a micro-anchored structure on the isostatic graphite surface, thereby improving the mechanical bonding strength between the underlying glassy carbon coating and the graphite substrate; the interlayer controllable mild activation treatment ensures the interlayer bonding force of heterogeneous carbon layers; the multi-layer alternating stacking process does not require damage to the mature coating structure of the lower layer, and can prepare a thick protective coating while ensuring ultra-high interfacial bonding force, thus solving the core contradiction of mutual constraint between coating thickness and interfacial bonding force in existing processes.

[0023] 4. This invention allows for free adjustment of the stacking order and number of processing cycles of the two types of resins, enabling directional control of the hardness, toughness, electrical and thermal conductivity of the composite coating; it can stably prepare complete protective coatings with a thickness of 50~200μm; the finished coating possesses comprehensive properties of high adhesion, low gas permeability, low porosity, and strong thermal shock resistance, making it suitable for complex working conditions of semiconductor high temperature and strong corrosion, reducing the risks of dust pollution, substrate corrosion, and poor migration of metal impurities in semiconductor graphite components, and improving the yield of wafer processing devices. Attached Figure Description

[0024] Figure 1 This is a flowchart of the present invention;

[0025] Figure 2 Metallographic image (500x) of a cross section of an embodiment of the present invention;

[0026] Figure 3 This is a cross-sectional metallographic image (1000x magnification) of an embodiment of the present invention. Detailed Implementation

[0027] To enhance understanding of the present invention, the present invention will be further described in detail below with reference to embodiments. These embodiments are only used to explain the present invention and do not constitute a limitation on the scope of protection of the present invention.

[0028] Example 1

[0029] according to Figure 1 , 2 As shown in Figure 3, this embodiment proposes a method for preparing a glassy carbon coating on an isostatically pressed graphite surface, involving alternating layers of phenolic resin followed by furan resin (a total of 3 composite coating layers):

[0030] S1. Matrix Pretreatment and Roughening

[0031] Isostatically pressed graphite workpieces were selected, with the grade being Donghai Graphite IG-15, and the bulk density of this graphite was ≥1.78 g / cm³. 3 The average particle size is ≤15μm, and the coefficient of thermal expansion is 4.5×10. -6 / ℃, ash content ≤30ppm. The workpiece specifications are a flat plate sample of 100mm×100mm×10mm and an actual semiconductor fixture workpiece of the same material.

[0032] The graphite workpiece was ultrasonically cleaned, then rinsed in acetone and ethanol for 15 minutes each to remove surface oil and adhering particles. Subsequently, a sandblasting process was used to uniformly roughen the surface. 240-mesh white corundum (Al₂O₃) was used as the abrasive, with a sandblasting pressure of 0.6 MPa, a sandblasting angle of 75°, a sandblasting distance of 150 mm, and a treatment time of 30 seconds. After roughening, residual abrasive was blown away with compressed air, followed by ultrasonic cleaning with deionized water for 20 minutes. The workpiece was then dried in an oven at 120°C for 2 hours. The surface roughness Ra after treatment was measured to be 2.8 μm using a stylus roughness meter.

[0033] S2. First coating layer (phenolic resin) and initial pyrolysis

[0034] The pretreated graphite workpiece was completely immersed in a phenolic resin ethanol solution with a solid content of 30 wt.%, using Shandong Shengquan PF-5012 phenolic resin. Immersion was carried out at room temperature and pressure for 30 minutes. After removal, the workpiece was allowed to drain in a ventilated area for 15 minutes, and then placed in a forced-air drying oven for pre-curing at 120℃ for 2 hours.

[0035] After pre-curing, the workpiece is transferred to a high-temperature tube furnace for step-by-step pyrolysis under a high-purity nitrogen atmosphere (purity ≥99.999%). The pyrolysis heating program is as follows: increase from room temperature to 400℃ at a rate of 1℃ / min and hold for 1 hour; then increase to 600℃ at a rate of 2℃ / min and hold for 1 hour; finally, increase to 1000℃ at a rate of 3℃ / min and hold for 2 hours. After pyrolysis, the furnace is allowed to cool naturally to room temperature, thus forming the first phenolic resin-based glassy carbon coating on the graphite substrate surface.

[0036] S3. Second coating (furan resin) and intermediate pyrolysis

[0037] The workpiece with the first coating layer was immersed in an acetone solution containing 50 wt.% furan resin. The furan resin used was industrial-grade furfuryl alcohol resin with a purity ≥98%. P-Toluenesulfonic acid (PTSA) was added to the immersion solution as an acidic catalyst at a concentration of 2 wt.% of the furan resin solid content. The immersion time was 20 minutes at room temperature and pressure, followed by 10 minutes of drainage. Pre-curing was performed using a stepped heating method: first, holding at 80℃ for 3 hours, then increasing the temperature to 150℃ and holding for 1 hour.

[0038] Intermediate pyrolysis was carried out under a high-purity nitrogen atmosphere. The pyrolysis procedure was as follows: the temperature was increased from room temperature to 350℃ at a rate of 0.5℃ / min and held for 1 hour; the temperature was increased to 550℃ at a rate of 1℃ / min and held for 1 hour; the temperature was increased to 1000℃ at a rate of 2℃ / min and held for 2 hours. After pyrolysis, the furnace was allowed to cool naturally to form a second layer of furan resin-based glassy carbon coating.

[0039] S4. Third coating layer (phenolic resin) and intermediate pyrolysis

[0040] Repeat the impregnation, pre-curing, and pyrolysis process of step S2, but shorten the impregnation time to 20 minutes. The maximum pyrolysis temperature remains at 1000℃. A third phenolic resin-based glassy carbon coating is formed.

[0041] S5. Final high-temperature heat treatment

[0042] After completing all three alternating coating layers (phenolic-furan-phenolic), a final high-temperature heat treatment is performed under a high-purity nitrogen atmosphere. The heating program is as follows: increase from room temperature to 800℃ at a rate of 2℃ / min and hold for 1 hour; then increase to 1500℃ at a rate of 1℃ / min and hold for 2 hours. After the holding period, the furnace is allowed to cool naturally to room temperature, yielding the final composite glassy carbon coating product.

[0043] Actual test results of coating performance:

[0044] Metallographic section measurements showed the total coating thickness to be approximately 20 μm. The surface roughness of the coating, measured using a stylus roughness tester, was Ra = 0.6 μm. The microhardness HV of the coating was measured using a Vickers microhardness tester under a load of 50 g. 0.05 The resistivity was 3.2 GPa. The coating resistivity, determined by the four-probe method, was 3.5 × 10⁻⁶. -4 The apparent density of the coating, measured by buoyancy method, was 1.52 g / cm³. 3 .

[0045] Example 2

[0046] according to Figure 1 , 2 As shown in Figure 3, this embodiment proposes a method for preparing a glassy carbon coating on an isostatically pressed graphite surface, involving alternating layers of furan followed by phenolic resin (a total of 4 composite coating layers):

[0047] SGL graphite R6510 isostatically pressed graphite was selected, with a bulk density ≥1.82 g / cm³. 3 The average particle size is ≤10μm. The workpiece dimensions are 150mm×150mm×15mm.

[0048] S1. Matrix Pretreatment and Roughening

[0049] The abrasive used for blasting was 320-mesh silicon carbide (SiC), the blasting pressure was 0.8 MPa, the treatment time was 25 s, and the remaining cleaning and drying conditions were the same as in Example 1. The surface roughness Ra after treatment was 3.5 μm.

[0050] S2. First coating layer (furan resin) and initial pyrolysis

[0051] The sample was impregnated in a methanol solution of furan resin (furfuryl alcohol resin) with a solid content of 55 wt.%, using oxalic acid as the catalyst at an addition amount of 3 wt.% of the furan resin solid content. The sample was impregnated at room temperature for 25 min, drained, and then pre-cured at 90℃ for 2 h, followed by curing at 160℃ for 1 h. The pyrolysis procedure was as follows: under a nitrogen atmosphere, the temperature was increased to 380℃ at 0.8℃ / min and held for 1 h, then increased to 580℃ at 1.5℃ / min and held for 1 h, and finally increased to 1050℃ at 2.5℃ / min and held for 2 h.

[0052] S3. Second coating (phenolic resin) and intermediate pyrolysis

[0053] The resin was impregnated in an ethanol solution of phenolic resin (Sumitomo Bakelite PR-51794) with a solid content of 35 wt.% for 25 min at room temperature, followed by pre-curing at 130°C for 1.5 h. The pyrolysis procedure was the same as that of phenolic resin in Example 1, with a maximum temperature of 1050°C.

[0054] S4. Third coating layer (furan resin) and intermediate pyrolysis

[0055] Repeat step S2 of the furan resin coating and pyrolysis process, with a maximum temperature of 1050℃.

[0056] S5. Fourth coating layer (phenolic resin) and intermediate pyrolysis

[0057] Repeat step S3 of the phenolic resin coating and pyrolysis process, with a maximum temperature of 1050℃.

[0058] S6. Final high-temperature heat treatment

[0059] The temperature is increased to 800℃ at a rate of 1.5℃ / min and held for 1 hour, then increased to 1600℃ at a rate of 1℃ / min and held for 3 hours, followed by natural cooling with the furnace.

[0060] Actual test results of coating performance:

[0061] The total coating thickness is approximately 30 μm. The surface roughness Ra is 0.5 μm. The microhardness HV is... 0.05 The pressure is 3.5 GPa, and the apparent density is 1.55 g / cm³. 3 .

[0062] Comparative Example 1 (Single phenolic resin coating, 6 impregnation-pyrolysis cycles)

[0063] The same Donghai graphite IG-15 matrix as in Example 1 was used, and the same sandblasting roughening process (Ra=2.8μm) and cleaning and drying steps were employed. Only phenolic resin (same as in Example 1, 30wt.% ethanol solution) was used for repeated impregnation-pyrolysis, with each impregnation time being 30 min. Each pyrolysis procedure was the same as step S2 in Example 1 (maximum temperature 1000℃). A total of 6 repeated cycles were performed without any furan resin coating. When the fourth layer was coated, obvious microcracks were visible in the cross-section; after the fifth and sixth layers were coated, the cracks further expanded, and localized coating peeling occurred.

[0064] Comparative Example 2 (Single furan resin coating, 4 impregnation-pyrolysis)

[0065] The same matrix and sandblasting roughening process as in Example 1 were used. Only furan resin (same as in Example 1, 50 wt.% acetone solution, 2 wt.% PTSA addition) was used for repeated impregnation-pyrolysis, with each impregnation lasting 20 minutes. Each pyrolysis procedure was the same as step S3 in Example 1 (maximum temperature 1000℃). A total of 4 repeated cycles were performed, followed by a final heat treatment at 1500℃.

[0066] The comparative coating showed no macroscopic cracks, but the cross-section revealed a large number of dispersed micropores inside the coating, indicating that the coating density was significantly insufficient.

[0067] Performance comparison between the examples and comparative examples

[0068] Adhesion strength tests: Scratch test (ASTM C1624) and pull-out test (ASTM D4541) results show that, for Example 1, Lc2 > 85 N and pull-out strength > 18 MPa; for Example 2, Lc2 > 90 N and pull-out strength > 20 MPa; for Comparative Example 1, Lc2 is approximately 35 N and pull-out strength is approximately 8 MPa; for Comparative Example 2, Lc2 is approximately 50 N and pull-out strength is approximately 11 MPa. The adhesion strength of this invention is 2.3 to 2.4 times that of a single phenolic resin coating.

[0069] Thermal shock performance: Cyclic testing from room temperature to 1000°C showed that Example 1 had a 98% integrity rate after 100 cycles, while Example 2 had a 99% integrity rate; Comparative Example 1 peeled off within 30 cycles, while Comparative Example 2 had only a 65% integrity rate after 100 cycles.

[0070] Tightness (helium permeability, ASTM D1434): Example 1 < 1.0 × 10⁻⁶ -10 cm 2 / s, Example 2 < 8.0 × 10 -11 cm 2 / s; Comparative Example 1: approximately 5.0 × 10⁻⁶ -8 cm2 / s, Comparative Example 2 is approximately 2.0 × 10 -9 cm 2 / s. This invention reduces the efficiency by 2 to 3 orders of magnitude compared to a single phenolic resin coating.

[0071] Porosity: Example 1 < 0.5%, Example 2 < 0.3%; Comparative Example 1 approximately 8%, Comparative Example 2 approximately 3%.

[0072] Coating integrity: The present invention is intact and crack-free at a thickness of 20-30μm.

[0073] This method for preparing glassy carbon coatings on isostatically pressed graphite surfaces utilizes the differences in the pyrolysis properties of two types of resins to achieve synergistic compensation of internal stress in the coating: phenolic resin has a high carbon yield from pyrolysis and high hardness in the formed glassy carbon, but it also has high pyrolysis shrinkage stress and is brittle; furan resin has a low pyrolysis shrinkage rate and excellent toughness in the formed carbon layer. The alternating stacking of the two types of resin coatings can disperse and offset the shrinkage stress accumulated during multi-layer processing, fundamentally inhibiting the initiation of microcracks and macroscopic peeling of thick film coatings, significantly improving the coating's thermal cycling resistance, and solving the problem of coating cracking caused by internal stress accumulation in existing processes. The amorphous carbon micro-network structure formed by the pyrolysis of precursor resins with different chemical structures in this invention has significant differences. The alternating stacking of heterogeneous glassy carbon layers can form an interlaced sealing structure, accurately filling the micropores, pinholes, and micro-defects of the lower coating layer; combined with the final high-temperature interface fusion heat treatment process, the interlayer boundary interface is broken, the carbon structure is reorganized, and a near-monolithic interface-free dense coating is formed, blocking the diffusion channels of small molecule process gases and metal impurities, and breaking through the inherent density limit of single resin coatings. This invention utilizes a substrate sandblasting and roughening pretreatment process to construct a microscopic uneven anchoring structure on the isostatically pressed graphite surface, enhancing the mechanical bonding strength between the underlying glassy carbon coating and the graphite substrate. Controllable mild activation treatment between layers ensures the interlayer bonding strength of the heterogeneous carbon layers. The multi-layer alternating stacking process does not damage the underlying mature coating structure, enabling the preparation of thick protective coatings while maintaining ultra-high interfacial bonding strength, thus resolving the core contradiction of existing processes where coating thickness and interfacial bonding strength are mutually constrained. This invention allows for free adjustment of the stacking order and cycle number of the two types of resins, enabling directional control of the composite coating's hardness, toughness, electrical and thermal conductivity. It can stably prepare complete protective coatings with a thickness of 50~200μm. The finished coating possesses high bonding strength, low gas permeability, low porosity, and strong thermal shock resistance, making it suitable for the complex high-temperature and high-corrosion conditions of semiconductors. It reduces the risks of dust contamination, substrate corrosion, and poor migration of metal impurities in semiconductor graphite components, improving the yield of wafer fabrication devices.

[0074] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a glassy carbon coating on the surface of isostatically pressed graphite, characterized in that, Includes the following steps: S1: After cleaning the isostatic graphite workpiece, the surface roughening treatment is completed by sandblasting with non-metallic abrasives, and the surface roughness Ra of the workpiece is controlled to be 0.8~6.4μm; S2: Select one of phenolic resin and furan resin as the first resin, and form the first glassy carbon substrate on the roughened matrix surface by impregnation coating, pre-curing, and stepwise initial pyrolysis under an inert atmosphere. S3: Alternately coat with another type of resin and perform multiple rounds of intermediate pyrolysis to complete 1 to 5 cycles of alternating stacking of the two types of resins to prepare a multilayer heterogeneous composite glassy carbon intermediate layer; S4: Under an inert atmosphere, the final high-temperature heat treatment is carried out at 1200~1800℃, and the temperature is held for 1~4 hours to complete the interlayer interface fusion, internal stress elimination and pore sealing, and obtain an overall dense composite glassy carbon coating.

2. The method for preparing a glassy carbon coating on an isostatically pressed graphite surface according to claim 1, characterized in that: In S1, the sandblasting roughening process parameters are as follows: using 180~800 mesh non-metallic abrasive, sandblasting pressure 0.3~1.5MPa; after roughening, the abrasive is sequentially purged with compressed air, ultrasonically cleaned with organic solvent and deionized water, and dried at 80~150℃ for later use; the non-metallic abrasive is white corundum or silicon carbide.

3. The method for preparing a glassy carbon coating on an isostatically pressed graphite surface according to claim 1, characterized in that: In step S2, the phenolic resin preparation and processing parameters are as follows: prepare an organic solution of phenolic resin with a solid content of 10~50wt.%, and the organic solvent is any one of methanol, ethanol, acetone, and dimethylformamide; the pre-curing temperature is controlled at 80~220℃; the initial step pyrolysis heating rate is 0.01~5℃ / min, and the temperature is raised to 350~750℃ and then held at 900~1300℃ for carbonization.

4. The method for preparing a glassy carbon coating on an isostatically pressed graphite surface according to claim 1, characterized in that: In step S2, the furan resin preparation and processing parameters are as follows: prepare a furfuryl alcohol-based furan resin organic solution with a solid content of 40~60 wt.%; add an acidic catalyst with a solid phase mass ratio of 1~5 wt.% of furan resin; the acidic catalyst is any one of acetic acid, citric acid, oxalic acid, and p-toluenesulfonic acid; and control the maximum temperature of the initial pyrolysis at 900~1300℃.

5. The method for preparing a glassy carbon coating on an isostatically pressed graphite surface according to claim 1, characterized in that: In S3, the coating order of the two types of resins is adjustable; when phenolic resin is selected as the first resin, a phenolic-furan alternating stacked coating structure is formed; when furan resin is selected as the first resin, a furan-phenolic alternating stacked coating structure is formed; phenolic resin is preferentially selected as the bottom resin to enhance the adhesion of the graphite matrix interface.

6. The method for preparing a glassy carbon coating on an isostatically pressed graphite surface according to claim 5, characterized in that: In S3, before each round of resin coating, the previous pyrolytic carbon layer is subjected to surface activation treatment. The activation treatment method is either a very light sandblasting with fine abrasive of 600 mesh or higher, or a low-temperature oxygen plasma treatment; it is used to improve the physical bonding strength between heterogeneous carbon layers.

7. The method for preparing a glassy carbon coating on an isostatically pressed graphite surface according to claim 6, characterized in that: In S3, the intermediate pyrolysis process is maintained in an inert high-purity nitrogen atmosphere, and the highest temperature of a single intermediate pyrolysis is controlled at 800~1300℃. A segmented step heating process is adopted, with a heating rate range of 0.02~10℃ / min, and the segmented holding time is matched according to the type of resin.

8. The method for preparing a glassy carbon coating on an isostatically pressed graphite surface according to claim 7, characterized in that: In step S3, the overall film thickness of the multilayer heterogeneous composite glass carbon intermediate layer is controlled by adjusting the number of alternating stacking cycles of the resin. The coating thickness increases linearly with the number of alternating cycles.

9. The method for preparing a glassy carbon coating on an isostatically pressed graphite surface according to claim 1, characterized in that: In S4, the final high-temperature heat treatment adopts a segmented step heating program: first, the temperature is increased to 750~850℃ at 1~3℃ / min and held for 1h, then the temperature is increased to the target 1200~1800℃ at 1~2℃ / min and held; the interface between heterogeneous coatings is eliminated by high-temperature carbon structure reforming, and the residual internal stress of multilayer stacking is compensated.

10. The method for preparing a glassy carbon coating on an isostatically pressed graphite surface according to claim 9, characterized in that: In S4, the high-temperature heat treatment condition matches the number of resin alternation cycles in S3; when the number of resin alternation cycles increases, the final high-temperature heat treatment holding temperature is increased and the holding time is extended to achieve complete fusion of the multilayer heterogeneous coating interface.

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