Composite coating aluminum oxide ceramic and preparation method thereof

Abstract

The invention provides a composite coating aluminum oxide ceramic and a preparation method thereof, and relates to the technical field of coating aluminum oxide ceramics, the composite coating aluminum oxide ceramic comprises a sealing aluminum oxide ceramic component and a composite coating on the surface of the sealing aluminum oxide ceramic component; the composite coating comprises the following preparation raw materials in percentage by mass: 10-25% of a charge dissipation agent, 5-10% of zirconium boride nano powder, 5-15% of silicon modified aluminum oxide nanowires and the balance of aluminum oxide; the charge dissipation agent is prepared from the following raw materials in parts by mass: 50 parts of flaky hexagonal boron nitride, 50-70 parts of rutile type nano titanium oxide powder, 3-10 parts of aluminum borate whiskers, 5-15 parts of tetrabutyl titanate, 1-2 parts of a dispersing agent, 0.5-1.5 parts of an interface modifier, 0.2-0.5 part of an electrostatic stabilizer and 20-50 parts of a solvent. The composite coating provided by the invention can provide a good charge dissipation effect for sealing an aluminum oxide ceramic assembly.

Description

Technical Field

[0001] The invention belongs to the technical field of coated alumina ceramics, in particular to a composite coated alumina ceramic and a preparation method thereof. Background Art

[0002] Vacuum high-pressure alumina ceramic sealing components have been widely used in vacuum devices, high-voltage electrical equipment, semiconductor equipment, aerospace and nuclear industries due to their excellent comprehensive performance. The components can withstand high pressure and high temperature environments while maintaining good airtightness, and have corrosion resistance, wear resistance and insulation properties.

[0003] Alumina ceramics have high vacuum breakdown strength. However, although traditional insulating coatings can achieve extremely high resistivity, their charge dissipation ability is poor, which easily leads to surface electrostatic deposition. This electrostatic deposition phenomenon will reduce the service life of the equipment, interfere with the normal operation of electronic equipment, and may even cause electrostatic breakdown. In addition, the coating materials in the prior art have the problem of excessive leakage current, which is difficult to meet the actual needs of high-voltage insulation. Summary of the invention

[0004] In order to overcome the above technical problems, the present invention provides a composite coating alumina ceramic and a preparation method thereof. The composite coating of the present invention can provide a good charge dissipation effect for sealing alumina ceramic components.

[0005] The present invention solves the above technical problems through the following technical solutions.

[0006] The present invention provides a composite coating alumina ceramic, which is composed of a sealed alumina ceramic component and a composite coating on its surface; The composite coating comprises the following raw materials in parts by weight: 10-25% of a charge dissipating agent, 5-10% of zirconium boride nanopowder, 5-15% of silicon-modified alumina nanowires and the balance of alumina; The charge dissipation agent comprises the following raw materials in parts by weight: 50 parts of flaky hexagonal boron nitride, 50-70 parts of rutile nano titanium oxide powder, 3-10 parts of aluminum borate whiskers, 5-15 parts of tetrabutyl titanate, 1-2 parts of a dispersant, 0.5-1.5 parts of an interface modifier, 0.2-0.5 parts of an electrostatic stabilizer and 20-50 parts of a solvent.

[0007] Preferably, the composite coating comprises the following raw materials in parts by weight: 12-20% of charge dissipation agent, 6-9% of zirconium boride nanopowder, 7-12% of silicon-modified alumina nanowires and the balance of alumina.

[0008] Preferably, the charge dissipator comprises the following raw materials in parts by weight: 50 parts of flaky hexagonal boron nitride, 50-60 parts of rutile nano-titanium oxide powder, 3-6 parts of aluminum borate whiskers, 5-9 parts of tetrabutyl titanate, 1-2 parts of dispersant, 0.5-1.5 parts of interface modifier, 0.2-0.5 parts of electrostatic stabilizer and 20-50 parts of solvent.

[0009] Among the raw materials for preparing the charge dissipation agent, flake hexagonal boron nitride has high in-plane thermal conductivity and interlayer insulation properties; the oxygen vacancies of rutile nano-titanium oxide powder are conductive, which can provide a bulk dissipation path, and nano-titanium oxide can also fill the gaps in flake hexagonal boron nitride to reduce the interfacial contact resistance. Aluminum borate whiskers bridge the flake hexagonal boron nitride layers, enhance toughness, and assist charge transfer. Tetrabutyl titanate is hydrolyzed to generate titanium oxide nanoparticles, which densify the coating and bond with the silane coupling agent.

[0010] In the present invention, the aluminum oxide D50=100~250nm.

[0011] In the present invention, the D50 of the zirconium boride nanopowder is 40-60 nm.

[0012] In the present invention, the D50 of the flaky hexagonal boron nitride is 0.5-1 μm.

[0013] In the present invention, the rutile nano-titanium oxide powder has a D50 of 20-40 nm.

[0014] In the present invention, the aluminum borate whisker has a length of 10-60 μm and a diameter of 0.3-3 μm.

[0015] In the present invention, the dispersant is polyvinyl pyrrolidone or polyether amine.

[0016] In the present invention, the electrostatic stabilizer is ammonium polyacrylate, sodium polystyrene sulfonate, polyethylene imine, sodium polyacrylate or sodium lignin sulfonate.

[0017] In the present invention, the solvents are ethanol and propylene glycol methyl ether.

[0018] In the present invention, the interface modifier is 3-chloropropyltriethoxysilane (CAS No.: 5089-70-3), 3-chloropropyltrimethoxysilane (CAS No.: 2530-87-2) or 3-chloropropylmethyldimethoxysilane (CAS No.: 18171-19-2).

[0019] In the present invention, the method for preparing the charge dissipator comprises: mixing and dispersing the raw materials to obtain slurry, casting the slurry into a film, hot pressing at low temperature and crushing to obtain the charge dissipator.

[0020] Furthermore, the dispersion process is to add flake hexagonal boron nitride, rutile nano-titanium oxide powder, aluminum borate whiskers, a dispersant and an electrostatic stabilizer to a solvent for ultrasonic dispersion, ball milling, and then adding tetrabutyl titanate and an interface modifier, adjusting the pH to 3-4, and aging to obtain a slurry; Furthermore, the knife gap of the film casting is 80-100 μm.

[0021] Furthermore, the base belt speed of the film casting is 0.3-0.6 m / min, for example 0.5 m / min.

[0022] Furthermore, the drying process of the cast film is first heated from 30-40°C to 75-85°C and maintained for 2-5 minutes, and then cooled to 55-65°C and maintained for 2-5 minutes; the heating / cooling rate in the drying process is 15-20°C / min.

[0023] Furthermore, the low-temperature hot pressing is pre-pressing at 80-120°C and 5-12MPa for 3-5min, hot pressing at 140-170°C and 13-18MPa for 8-12min, and then hot pressing at 280-320°C and 45-55MPa for 20-30min, and the pressure is maintained to cool to below 80°C for demolding.

[0024] Furthermore, the crushing adopts shear dispersion or air flow crushing, and the output particle size is D50=5~8μm.

[0025] In the present invention, the method for preparing the silicon-modified alumina nanowires is as follows: placing the alumina nanowires in a silane coupling agent solution, and then adding ammonia water to react for 0.5 to 2 hours.

[0026] In the present invention, the diameter of the aluminum oxide nanowire is 15-30 nm, and the length of the aluminum oxide nanowire is 1-3 μm.

[0027] In the present invention, the silane coupling agent is KH550 or KH560.

[0028] In the present invention, the mass concentration of the silane coupling solution is 1-5wt%.

[0029] In the present invention, the mass ratio of the aluminum oxide nanowires to the silane coupling solution is 10-30:100.

[0030] In the present invention, the concentration of the ammonia water is 5-8 wt %, and the concentration of the ammonia gas in the reaction kettle is controlled to be 0.5-1.0 vol %.

[0031] The present invention also discloses a method for preparing the composite coating alumina ceramic, comprising the following steps: S1. Preparing a coating slurry: mixing the raw materials for preparing the composite coating; S2. Spraying: Plasma spraying the coating slurry onto the surface of the sealed alumina ceramic component; S3. Sintering: Sinter at 280~350℃ for 0.5~1h, introduce nitrogen to raise the temperature to 750~850℃ and sinter for 1.5~2h, and raise the temperature to 1100~1200℃ under vacuum and sinter for 30~80min.

[0032] In S1, the solid content of the coating slurry is 40-50%.

[0033] In S2, the power of the plasma spraying is 35-40 kW.

[0034] In S2, the Ar flow rate of the plasma spraying is 30-40 L / min, H 2 The flow rate is 10~20L / min.

[0035] In S2, the powder feeding rate of the plasma spraying is 15-20 g / min.

[0036] In S3, the heating rate of the sintering process is 5-10°C / min.

[0037] In S3, the sintered product is cooled to ≤80° C. in a nitrogen atmosphere and then taken out of the furnace to obtain a composite coated alumina ceramic.

[0038] On the basis of being in accordance with the common sense in the art, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0039] Compared with the prior art, the present invention has the following beneficial effects: The composite coating alumina ceramic of the present invention has good charge dissipation performance on the surface, and can achieve high-efficiency and rapid static discharge under vacuum and high-pressure conditions. In the composite coating, the conductive network provided by the charge dissipator can achieve static dissipation; the zirconium boride nanopowder has strong antioxidant capacity at high temperature and can improve the thermal stability of the coating; the silicon-modified alumina nanowires can improve the fracture toughness of the coating and enhance the durability and adhesion of the coating.

[0040] The raw materials used in the preparation of the composite coating have a reasonable formula, which provides the coating with good charge dissipation performance, heat dissipation capacity and mechanical properties. Among them, the flake hexagonal boron nitride acts as an insulating skeleton, and together with the rutile nano-titanium oxide powder, it forms a conductive-insulating network to promote charge dissipation; the aluminum borate whiskers bridge the flake hexagonal boron nitride layers, thereby enhancing the toughness of the coating and simultaneously improving the mechanical and electrical properties.

[0041] The surface resistivity of the composite coating alumina ceramics in vacuum is 3-8× 1010Ω; leakage current under vacuum high voltage is 2.2~4.5 nA / cm 2 , in some preferred embodiments, 3.5-4.5 nA / cm 2 ; Adhesion ≥ 65MPa, in some preferred embodiments 70~80MPa. DETAILED DESCRIPTION

[0042] In order to facilitate the understanding of the present invention, the present invention will be described more comprehensively and carefully in combination with preferred embodiments below, but the protection scope of the present invention is not limited to the following specific embodiments.

[0043] Unless otherwise defined, all professional terms used below have the same meanings as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0044] The "range" disclosed in the present invention is defined in the form of a lower limit and an upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The range defined in this way can be inclusive or exclusive of end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 60-120 and 80-110 is listed for a specific parameter, it is understood that the range of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following ranges can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present invention, unless otherwise specified, the numerical range "ab" represents an abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" represents that all real numbers between "0-5" have been fully listed herein, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0045] If not otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form a new technical solution.

[0046] Unless otherwise specified, all technical features and optional technical features of the present invention can be combined with each other to form a new technical solution.

[0047] If not otherwise specified, all steps of the present invention may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0048] If there is no special explanation, the "include" and "comprising" mentioned in the present invention represent open-ended or closed-ended expressions. For example, the "include" and "comprising" may represent that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0049] If not specifically stated, in the present invention, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0050] The raw material information used in the following examples is as follows: The D50 of zirconium boride nanopowder is 50nm and the specific surface area is 45m 2 / g; Alumina was purchased from Yumu New Materials YM-A1203-N200, with alumina D50 = 200nm, alumina crystal form of α / γ phase, and a spherical micromorphology; Alumina nanowires were purchased from Zhongke Leiming, with a diameter of 20 nm and an average length of 1 μm; Flake hexagonal boron nitride was purchased from Zhejiang Yamei Nanotechnology Co., Ltd., D50 = 500 nm; Rutile nano-titanium oxide powder was purchased from Zhongke Keyou ZKKY-T220, with a content of 99.9%, D50 = 20nm, and a specific surface area of ​​60m 2 / g; Aluminum borate whiskers were purchased from Shanghai Fengzhu Composite New Materials. The composition of aluminum borate whiskers is 9Al 2 O 3 2B 2 O 3 The length of aluminum borate whiskers is 10~60μm, the diameter is 0.3~3μm, and the density is 2.93g / cm 3 ; Polyetheramine Mn (number average molecular weight) = 1000.

[0051] Example 1 1. The composite coated alumina ceramic of this embodiment is composed of a sealed alumina ceramic component and a composite coating on its surface.

[0052] The composite coating includes the following raw materials in parts by weight: 15% of charge dissipation agent, 7.5% of zirconium boride nanopowder, 11.5% of silicon-modified alumina nanowires and the balance of alumina.

[0053] The charge dissipation agent includes the following raw materials in parts by weight: 50 parts of flake hexagonal boron nitride, 55 parts of rutile nano-titanium oxide powder, 5 parts of aluminum borate whiskers, 8 parts of tetrabutyl titanate, 1.2 parts of a dispersant (polyvinyl pyrrolidone), 0.7 parts of an interface modifier (3-chloropropylmethyldimethoxysilane), 0.28 parts of an electrostatic stabilizer (ammonium polyacrylate), and 30 parts of a solvent (ethanol / propylene glycol methyl ether, volume ratio 7:3). Preparation method of charge dissipative agent: (1) Mixing and dispersing: Add flake hexagonal boron nitride, rutile nano-titanium oxide powder, aluminum borate whiskers, dispersant and electrostatic stabilizer to a solvent in the above proportions, perform ultrasonic dispersion, ball milling, and then add tetrabutyl titanate and an interface modifier. Adjust the pH to 3.5 with acetic acid, stir at 25°C for 24 hours, and then obtain a slurry. (2) Cast film: The slurry is cast into a film with a knife gap of 80 μm and a base belt speed of 0.5 m / min. The drying process of the cast film is a heating / cooling rate of 20 °C / min, first heating from 40 °C to 80 °C, maintaining at 80 °C for 2 min, and then cooling to 60 °C for 2 min; (3) Low temperature hot pressing: pre-press at 100°C and 10 MPa for 5 min, hot press at 150°C and 15 MPa for 10 min, and then hot press at 300°C and 50 MPa for 30 min. Keep the pressure and cool to below 80°C before unloading. (4) Crushing: Use shearing to disperse the material to a particle size of D50 = 7 μm.

[0054] Preparation method of silicon-modified alumina nanowires: The alumina nanowires were placed in a 2.5wt% silane coupling agent KH550 solution, and then 5wt% ammonia water was added to react for 1 hour, and the ammonia concentration in the reactor was controlled to be 0.5vol%; the mass ratio of alumina nanowires: silane coupling solution was 15:100.

[0055] 2. The preparation method of the composite coating alumina ceramic of this embodiment is as follows: S1. Preparation of coating slurry: The composite coating was mixed and water was added to prepare a coating slurry having a solid content of 45%; S2. Spraying: Plasma spray the coating slurry onto the surface of the sealed alumina ceramic component; the plasma spraying power is 35kW, the Ar flow rate during the plasma spraying process is 40L / min, and the H 2 The flow rate is 10L / min and the powder feeding rate is 20g / min; S3. Sintering: The heating rate of the sintering process is 10℃ / min, the temperature is raised from 20℃ to 300℃ and sintered for 1h, nitrogen is introduced to raise the temperature to 800℃ and sintered for 2h, the temperature is raised to 1200℃ under vacuum and sintered for 30min, nitrogen is introduced to cool down to below 80℃ and take out of the furnace.

[0056] Example 2 The difference between this embodiment and embodiment 1 is that: The composite coating includes the following raw materials in parts by weight: 20% of charge dissipation agent, 6.1% of zirconium boride nanopowder, 7.4% of silicon-modified alumina nanowires and the balance of alumina.

[0057] Other raw materials, steps and parameters are the same as in Example 1.

[0058] Example 3 The difference between this embodiment and embodiment 1 is that: The charge dissipator includes the following raw materials in parts by mass: 50 parts of flaky hexagonal boron nitride, 60 parts of rutile nano-titanium oxide powder, 6 parts of aluminum borate whiskers, 5 parts of tetrabutyl titanate, 1.8 parts of a dispersant (polyether amine), 1.4 parts of an interface modifier (3-chloropropyltrimethoxysilane), 0.49 parts of an electrostatic stabilizer (sodium polystyrene sulfonate) and 40 parts of a solvent.

[0059] Other raw materials, steps and parameters are the same as in Example 1.

[0060] Example 4 The difference between this embodiment and embodiment 1 is that: The charge dissipator includes the following raw materials in parts by mass: 50 parts of flaky hexagonal boron nitride, 30 parts of rutile nano-titanium oxide powder, 5 parts of aluminum borate whiskers, 7.2 parts of tetrabutyl titanate, 1.8 parts of dispersant, 1.1 parts of interface modifier, 0.44 parts of electrostatic stabilizer and 30 parts of solvent.

[0061] Other raw materials, steps and parameters are the same as in Example 1.

[0062] Example 5 The difference between this embodiment and embodiment 1 is that: Step (3) of the preparation method of the charge dissipative agent is low-temperature hot pressing: pre-pressing at 120°C and 10 MPa for 3 minutes, hot pressing at 160°C and 13 MPa for 8 minutes, and then hot pressing at 280°C and 50 MPa for 20 minutes. The pressure is maintained and the mold is cooled to below 80°C before demolding.

[0063] Other raw materials, steps and parameters are the same as in Example 1.

[0064] Example 6 The difference between this embodiment and embodiment 1 is that: Preparation method of silicon-modified alumina nanowires: The alumina nanowires were placed in a 3.0wt% silane coupling agent KH560 solution, and then 8wt% ammonia water was added to react for 0.5h, and the ammonia concentration in the reactor was controlled to be 0.5vol%; the mass ratio of alumina nanowires: silane coupling solution was 10:100.

[0065] Other raw materials, steps and parameters are the same as in Example 1.

[0066] Comparative Example 1 This comparative example does not add rutile nano titanium oxide powder. The difference between this comparative example and Example 1 is: The charge dissipation agent includes the following raw materials in parts by mass: 50 parts of flaky hexagonal boron nitride, 5 parts of aluminum borate whiskers, 5 parts of tetrabutyl titanate, 1.2 parts of a dispersant, 1.0 parts of an interface modifier, 0.2 parts of an electrostatic stabilizer and 25 parts of a solvent.

[0067] Other raw materials, steps and parameters are the same as in Example 1.

[0068] Comparative Example 2 Aluminum borate whiskers are not added in this comparative example. The difference between this comparative example and Example 1 is that: The charge dissipator comprises the following raw materials in parts by weight: 50 parts of flaky hexagonal boron nitride, 60 parts of rutile nano-titanium oxide powder, 6 parts of tetrabutyl titanate, 1.3 parts of a dispersant, 1.4 parts of an interface modifier, 0.28 parts of an electrostatic stabilizer and 35 parts of a solvent.

[0069] Other raw materials, steps and parameters are the same as in Example 1.

[0070] Comparative Example 3 The difference between this comparative example and Example 1 is: S3. Sintering: The heating rate of the sintering process is 10°C / min, and the temperature is raised to 1200°C and sintered for 40 minutes.

[0071] Other raw materials, steps and parameters are the same as in Example 1.

[0072] Test Case The composite coating alumina ceramics obtained in the above examples and comparative examples were tested for insulation performance and leakage performance. The test results are shown in Table 1.

[0073] The surface resistivity test method refers to GB / T 1410. -3 Pa vacuum environment; The leakage current test method refers to GB / T 5594.4. The test is carried out at 10 -3 Pa, under vacuum high pressure conditions of 20kV / mm; Adhesion test method refers to ISO 20502.

[0074] .

[0075] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods. The specific embodiments described above further describe the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. Composite coating alumina ceramics, characterized in that: It consists of a sealed alumina ceramic component and a composite coating on its surface; The composite coating comprises the following raw materials in parts by weight: 10-25% of a charge dissipating agent, 5-10% of zirconium boride nanopowder, 5-15% of silicon-modified alumina nanowires and the balance of alumina; The charge dissipation agent comprises the following raw materials in parts by weight: 50 parts of flaky hexagonal boron nitride, 50-70 parts of rutile nano titanium oxide powder, 3-10 parts of aluminum borate whiskers, 5-15 parts of tetrabutyl titanate, 1-2 parts of a dispersant, 0.5-1.5 parts of an interface modifier, 0.2-0.5 parts of an electrostatic stabilizer and 20-50 parts of a solvent.

2. The composite coating alumina ceramic according to claim 1, characterized in that: Meet at least one of the following conditions ①~⑤: ① The aluminum oxide D50=100~250nm; ② D50 of zirconium boride nanopowder = 40~60nm; ③ The D50 of the flake hexagonal boron nitride is 0.5-1 μm; ④ The rutile nano titanium oxide powder has a D50 of 20-40 nm; ⑤ The aluminum borate whisker has a length of 10-60 μm and a diameter of 0.3-3 μm.

3. The composite coating alumina ceramic according to claim 1, characterized in that: Meet at least one of the following conditions ①~④: ① The dispersant is polyvinyl pyrrolidone or polyether amine; ② The electrostatic stabilizer is ammonium polyacrylate, sodium polystyrene sulfonate, polyethyleneimine, sodium polyacrylate or sodium lignin sulfonate; ③ The solvent is ethanol and propylene glycol methyl ether; ④ The interface modifier is 3-chloropropyltriethoxysilane, 3-chloropropyltrimethoxysilane or 3-chloropropylmethyldimethoxysilane.

4. The composite coating alumina ceramic according to claim 1, characterized in that: The preparation method of the charge dissipating agent comprises the following steps: mixing and dispersing the raw materials to obtain slurry, casting the slurry into a film, hot pressing at low temperature and crushing the film to obtain the charge dissipating agent.

5. The composite coating alumina ceramic according to claim 4, characterized in that: Meet at least one of the following conditions ①~⑤: ① The dispersion process is to add flake hexagonal boron nitride, rutile nano-titanium oxide powder, aluminum borate whiskers, a dispersant and an electrostatic stabilizer to a solvent for ultrasonic dispersion, ball milling, and then adding tetrabutyl titanate and an interface modifier, adjusting the pH to 3-4, and aging to obtain a slurry; ② The knife gap of the cast film is 80-100 μm, and the base belt speed of the cast film is 0.3-0.6 m / min; ③ The drying process of the cast film is first heated from 30-40°C to 75-85°C and maintained for 2-5 minutes, and then cooled to 55-65°C and maintained for 2-5 minutes; the heating / cooling rate in the drying process is 15-20°C / min; ④ The low temperature hot pressing is pre-pressing at 80-120°C and 5-12MPa for 3-5min, hot pressing at 140-170°C and 13-18MPa for 8-12min, and then hot pressing at 280-320°C and 45-55MPa for 20-30min, and the pressure is maintained to cool to below 80°C for demolding; ⑤ The crushing adopts shear dispersion or air flow crushing, and the output particle size is D50=5~8μm.

6. The composite coating alumina ceramic according to claim 1, characterized in that: The method for preparing the silicon-modified alumina nanowires comprises placing the alumina nanowires in a silane coupling agent solution, and then adding ammonia water to react for 0.5 to 2 hours.

7. The composite coating alumina ceramic according to claim 6, characterized in that: Meet at least one of the following conditions ①~④: ① The diameter of the aluminum oxide nanowire is 15-30 nm, and the length of the aluminum oxide nanowire is 1-3 μm; ② The silane coupling agent is KH550 or KH560; ③The mass concentration of the silane coupling solution is 1~5wt%; ④ The mass ratio of the aluminum oxide nanowires to the silane coupling solution is 10-30:

100.

8. The method for preparing the composite coating alumina ceramic according to any one of claims 1 to 7, characterized in that: The following steps are involved: S1. Preparing a coating slurry: mixing the raw materials for preparing the composite coating; S2. Spraying: Plasma spraying the coating slurry onto the surface of the sealed alumina ceramic component; S3. Sintering: Sinter at 280~350℃ for 0.5~1h, introduce nitrogen to raise the temperature to 750~850℃ and sinter for 1.5~2h, and raise the temperature to 1100~1200℃ under vacuum and sinter for 30~80min.

9. The method for preparing the composite coating alumina ceramic according to claim 8, characterized in that: Meet at least one of the following conditions ①~④: ① The solid content of the coating slurry is 40-50%; ② The power of the plasma spraying is 35~40kW; ③ The Ar flow rate of the plasma spraying is 30~40 L / min, and the H2 flow rate is 10~20 L / min; ④ The powder feeding rate of the plasma spraying is 15~20g / min.

10. The method for preparing the composite coating alumina ceramic according to claim 8, characterized in that: Meet at least one of the following conditions ①~②: ① The heating rate of the sintering process is 5-10°C / min; ② After sintering, the temperature is lowered to ≤80°C in a nitrogen atmosphere and then taken out of the furnace.