Composite oxygen barrier coating and method of making same

Abstract

The application discloses a kind of composite oxygen barrier coating and preparation method thereof, comprising the following steps: cobalt salt and 2-methylimidazole are dissolved in solvent to form first mixed solution, after substrate is immersed in first mixed solution, the substrate removed is sequentially washed, dried, calcined and cooled, and transition layer is formed on the surface of substrate, to obtain first intermediate;Carboxylic acid and ammonium borate are dissolved in water to form second mixed solution, and second mixed solution is heated, and the above-mentioned first intermediate is immersed in heated second mixed solution, and then the first intermediate removed is heated in sections, to obtain second intermediate;Phosphoric acid and aluminum dihydrogen phosphate are dissolved in water to form third mixed solution, and the above-mentioned second intermediate is immersed in third mixed solution, and then the second intermediate removed is sequentially dried, calcined and cooled, to form oxygen barrier layer on the surface of transition layer, to obtain the required composite oxygen barrier coating.

Description

Technical Field

[0001] This invention relates to the field of oxygen barrier technology, and in particular to a composite oxygen barrier coating and its preparation method. Background Technology

[0002] In fields such as high-temperature protection, electronic packaging, and energy storage, the performance of oxygen barrier coatings directly affects the reliability and lifespan of devices. Traditional oxygen barrier materials (such as Al2O3 coatings and SiO2 coatings) face the following technical bottlenecks: poor interfacial adhesion with the substrate, making them prone to peeling during thermal cycling; and the inability to self-heal after microcracks form, leading to a sharp increase in oxygen permeability.

[0003] Taking graphene as an example, graphene has broad application prospects in fields such as heating plates, flexible electronic devices, heating elements, and smart wearable devices due to its excellent conductivity and electrothermal conversion efficiency. However, graphene is easily oxidized in high-temperature or humid environments, leading to increased resistivity, decreased heating efficiency, and reduced product quality. Summary of the Invention

[0004] In order to overcome the shortcomings and deficiencies of the existing technology, the present invention aims to provide a composite oxygen barrier coating and its preparation method, which realizes the organic combination of self-healing function and oxygen barrier performance, and solves the problems of low repair efficiency and poor oxygen barrier performance of traditional coatings.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A method for preparing a composite oxygen barrier coating for application on a substrate surface, the method comprising the following steps:

[0007] Cobalt salt and 2-methylimidazole are dissolved in a solvent to form a first mixed solution. The substrate is immersed in the first mixed solution, and then the removed substrate is washed, dried, calcined and cooled in sequence to form a transition layer on the surface of the substrate, thus obtaining a first intermediate.

[0008] Carboxylic acid and ammonium borate are dissolved in water to form a second mixed solution. The second mixed solution is heated, and the first intermediate is immersed in the heated second mixed solution. The first intermediate is then heated in stages to load the transition layer with boron trioxide to obtain the second intermediate.

[0009] Phosphoric acid and aluminum dihydrogen phosphate are dissolved in water to form a third mixture. The second intermediate is then immersed in the third mixture, and the extracted second intermediate is then dried, calcined, and cooled in sequence to form an oxygen barrier layer on the surface of the transition layer, thus obtaining the desired composite oxygen barrier coating.

[0010] Furthermore, the cobalt salt includes cobalt nitrate hexahydrate, wherein the molar ratio of cobalt nitrate hexahydrate to 2-methylimidazole is 1:3.

[0011] Furthermore, the specific process of calcining the substrate includes:

[0012] The dried substrate is placed in a heating furnace, a protective gas is introduced, and it is heated to 500-600°C at a heating rate of 2-5°C / min, and held at that temperature for 5-6 hours.

[0013] Furthermore, the second mixed solution is heated by a water bath to 75-85°C.

[0014] Furthermore, the carboxylic acid includes citric acid, and the molar ratio of citric acid to ammonium borate is (1.5:1) to (3:1).

[0015] Furthermore, the specific process of segmenting and heating the extracted first intermediate includes:

[0016] The first intermediate was placed in a vacuum oven and heated to 100-150°C for 1-2 hours, then heated to 200-250°C for 3-4 hours, and finally heated to 300-350°C for 2-3 hours.

[0017] Furthermore, the molar ratio of phosphoric acid to aluminum dihydrogen phosphate is 20:9.

[0018] Furthermore, the specific process of drying, calcining, and cooling the extracted second intermediate includes:

[0019] The second intermediate was placed in a vacuum drying oven and dried sequentially at 80–100°C and 150–200°C. Then, the second intermediate was placed in a heating furnace and heated to 250–300°C at a rate of 4–5°C / min, and then heated to 500–600°C at a rate of 2–3°C / min and held at that temperature for 1–3 hours. After that, it was allowed to cool naturally to room temperature.

[0020] Furthermore, before obtaining the first intermediate, the preparation method further includes cleaning the substrate. The specific cleaning process includes immersing the substrate in acetone and sonicating it for 5-10 minutes, and then rinsing it with deionized water.

[0021] The present invention also provides a composite oxygen barrier coating, which is prepared by the preparation method described above. The composite oxygen barrier coating includes a transition layer and an oxygen barrier layer. The transition layer is disposed on the surface of the substrate, and the oxygen barrier layer is disposed on the surface of the transition layer.

[0022] The beneficial effects of this invention are as follows: Based on a metal-organic framework, a transition layer (loaded with boron oxide) with self-healing function is designed and prepared. This transition layer comprises a porous carbon framework embedded with ultrafine nano-metal particles (cobalt particles) and nano-boron oxide particles contained within the pores of the porous carbon framework. The porous carbon framework is embedded in the pores of the substrate to improve physical adhesion, and the porous carbon framework can buffer volume changes caused by thermal expansion and contraction. The active sites of metal particles are controllably exposed in the transition layer, providing directional anchoring points for the self-healing material. Through chemical coordination, the self-healing design is guided, forming a uniformly dispersed system in the transition layer. This structural design not only improves the self-healing response efficiency of the transition layer, but its orderly distributed active sites can also effectively block oxygen diffusion paths, thereby significantly enhancing the oxygen barrier performance of the composite oxygen barrier coating (transition layer + oxygen barrier layer). Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of the composite oxygen barrier coating of the present invention covering the substrate;

[0025] Figure 2 This is a schematic diagram of the orderly arrangement of the metal-organic framework in the transition layer;

[0026] Figure 3 This is a schematic diagram of a porous carbon framework loaded with boron oxide.

[0027] Figure 4a This is a TEM image of cobalt particles embedded in a porous carbon framework in the transition layer of Example 1;

[0028] Figure 4b This is a SEM image of cobalt particles embedded in a porous carbon framework in the transition layer of Example 1;

[0029] Figure 5 This is an SEM image of the oxygen barrier layer surface in Example 1. Detailed Implementation

[0030] This invention provides a method for preparing a composite oxygen barrier coating, which is used to apply to the surface of a substrate to act as an oxygen barrier and prevent oxidation of the internal substrate. The preparation method includes the following steps:

[0031] Cobalt salt and 2-methylimidazole are dissolved in a solvent to form a first mixed solution. The substrate is immersed in the first mixed solution, and then the removed substrate is washed, dried, calcined and cooled in sequence to form a transition layer on the surface of the substrate, thus obtaining a first intermediate.

[0032] Carboxylic acid and ammonium borate are dissolved in water to form a second mixed solution. The second mixed solution is heated, and the first intermediate is immersed in the heated second mixed solution. The first intermediate is then heated in stages to load boron trioxide onto the transition layer, thus obtaining the second intermediate.

[0033] Phosphoric acid and aluminum dihydrogen phosphate are dissolved in water to form a third mixture. The second intermediate is then immersed in the third mixture, and the extracted second intermediate is then dried, calcined, and cooled in sequence to form an oxygen barrier layer on the surface of the transition layer, thus obtaining the desired composite oxygen barrier coating.

[0034] In this embodiment, a composite oxygen barrier coating was constructed using a three-step method. First, a metal-organic framework (MOF) was generated on the substrate surface through a coordination reaction between cobalt salt and 2-methylimidazole. During calcination, the MOF decomposed and carbonized at high temperature, yielding a porous carbon framework embedded with cobalt nanoparticles, forming a transition layer. Next, carboxylic acid and ammonium borate were further reacted on the transition layer surface by heating to generate boron oxide. The boron oxide nanoparticles were loaded into the pores of the porous carbon framework, repairing microcracks through capillary action with the assistance of cobalt active sites. Finally, phosphoric acid and aluminum dihydrogen phosphate were further reacted on the transition layer surface to form an oxygen barrier layer containing an aluminum phosphate (AlPO4) crystal structure. This resulted in a composite oxygen barrier coating that possesses both electrical conductivity and oxidation resistance.

[0035] Specifically, this embodiment designs and prepares a transition layer (loaded with boron oxide) with self-healing function based on a metal-organic framework. This transition layer comprises a porous carbon framework embedded with ultrafine nano-metal particles (cobalt particles) and nano-boron oxide particles contained within the pores of the porous carbon framework. The porous carbon framework is embedded within the substrate pores to improve physical adhesion, and it can buffer volume changes caused by thermal expansion and contraction. The transition layer controllably exposes active sites of the metal particles, providing directional anchoring points for the self-healing material. Through chemical coordination, it guides the self-healing design, forming a uniformly dispersed system within the transition layer. This structural design not only improves the self-healing response efficiency of the transition layer, but its orderly distributed active sites also effectively block oxygen diffusion paths, thereby significantly enhancing the oxygen barrier performance of the composite oxygen barrier coating (transition layer + oxygen barrier layer). The substrate is a material requiring antioxidant treatment, which can be graphene, carbon black, or metal oxides, and is not limited here.

[0036] Furthermore, before obtaining the first intermediate, the preparation method also includes cleaning the substrate. The specific cleaning process includes immersing the substrate in acetone and sonicating it for 5 to 10 minutes, and then rinsing it with deionized water 3, 4 or 5 times, which is not limited here.

[0037] Furthermore, the cobalt salt includes cobalt nitrate hexahydrate, with a molar ratio of cobalt nitrate hexahydrate to 2-methylimidazole of 1:3, ensuring Co... 2+ Complete coordination forms a metal-organic framework, avoiding the impact of residual free metal ions on performance. Of course, cobalt salts also include cobalt chloride or cobalt sulfate, which can be selected individually or in combination. Specifically, the cobalt salt and 2-methylimidazole are dissolved in a solvent to form a first mixed solution, which can be one or more of methanol, ethanol, or water; methanol is preferred.

[0038] Furthermore, the specific process of calcining the substrate includes:

[0039] The dried substrate is placed in a heating furnace, a protective gas is introduced, and it is heated to 500–600°C at a heating rate of 2–5°C / min, and held at that temperature for 5–6 hours. Calcination effectively removes the organic ligands (coordinated water molecules in 2-methylimidazole and cobalt nitrate), causing them to decompose and carbonize at high temperatures, forming a metal-carbon composite structure. In this structure, cobalt particles are anchored to the substrate surface, and the carbon skeleton of the organic ligands is transformed into a conductive carbon layer, enhancing the material's conductivity.

[0040] Specifically, the preparation of the transition layer includes:

[0041] The substrate is immersed in acetone and ultrasonically treated for 5–10 min, then rinsed three times with deionized water to remove solvent residue. Next, the substrate is immersed in methanol (first mixed solution) containing Co(NO3)2·6H2O and 2-methylimidazole (molar ratio 1:3) and allowed to stand for approximately 3–8 h (preferably 5 h). The substrate is then washed three times consecutively with deionized water and methanol. Finally, the substrate is dried in a freeze dryer for 24 h, and then calcined in a protective gas stream (preferably argon). The specific calcination steps are as follows: the substrate is placed in a heating furnace, and an argon stream is first introduced at room temperature for half an hour. Then, the furnace is heated to 500–600 °C at a heating rate of 2–5 °C / min (preferably 3 °C / min). After reaching the target temperature, it is held for 5–6 h; then cooled to room temperature to obtain a transition layer on the substrate surface; thus obtaining the first intermediate.

[0042] Furthermore, the second mixed solution is heated by a water bath to 75-85°C, wherein 75°C, 80°C or 85°C can be selected, and 80°C is preferred.

[0043] Furthermore, the carboxylic acid includes citric acid, with a molar ratio of citric acid to ammonium borate of (1.5:1) to (3:1). Excess citric acid ensures complete dissolution of ammonium borate and the formation of a boron-citric acid complex, which generates B₂O₃ at high temperature. Alternatively, tartaric acid or oxalic acid can be selected as the carboxylic acid, or a mixture of one or more of these can be used. Citric acid primarily functions as a chelating agent and reducing agent in this process, reacting with Co… 2+ Metal ions form stable complexes to uniformly disperse active sites, and at high temperatures, they can participate in reduction reactions and decompose to produce amorphous carbon; their function can be replaced by other polycarboxylic acids (such as tartaric acid and oxalic acid). Ammonium borate, as a boron source, transforms into molten B2O3 at high temperatures to achieve crack repair.

[0044] Further, the specific process of segmented heating of the extracted first intermediate includes: placing the first intermediate in a vacuum oven, heating to 100-150℃ and holding for 1-2 hours, then raising the temperature to 200-250℃ and holding for 3-4 hours, and finally raising the temperature to 300-350℃ and holding for 2-3 hours. Specifically, the 100-150℃ stage removes residual solvent and stabilizes the porous carbon framework; subsequently, the 200-250℃ stage promotes the decomposition of organic acid (citric acid) and initiates the initial pyrolysis of ammonium borate, while allowing ammonium borate to completely decompose into fluid B2O3 and release NH3 gas, and simultaneously repairing the microcracks in the transition layer through capillary action with the assistance of Co active sites; finally, under vacuum treatment at 300-350℃, the melt distribution of B2O3 is further optimized and residual gas is removed, ensuring the densification of the transition layer. Ammonium borate was chosen as the boron source because it can efficiently decompose into B2O3 and volatile NH3 in the 200–250℃ range (without affecting the oxygen barrier layer). Compared to boric acid (which decomposes prematurely), ammonium borate is more conducive to obtaining a pure and stable self-healing coating system. The exposure of cobalt particles can effectively provide active sites for the boron source. B2O3 melts and flows at high temperatures, repairing the transition layer cracks through capillary action.

[0045] Specifically, the preparation process of the transition layer loaded with boron trioxide includes:

[0046] Citric acid, tartaric acid, oxalic acid (preferably citric acid), and ammonium borate (boron source) are dissolved in water in a molar ratio (1.5:1 to 3:1). The mixture is heated in a water bath at 75–85°C (preferably 80°C) and stirred to form a second mixed solution. The second mixed solution is then impregnated onto the transition layer, which is then placed in a vacuum oven and heated in stages: first, it is kept at 100–150°C for 1–2 hours (preferably 1 hour), then raised to 200–250°C and kept at 200–250°C for 3–4 hours (preferably 4 hours), and finally, it is further kept at 300–350°C in a vacuum environment for 2–3 hours (preferably 2 hours) to obtain a transition layer with self-healing function, thus obtaining the second intermediate. The staged heating process is designed to gradually control the formation of the transition layer structure and its self-healing properties.

[0047] Furthermore, the molar ratio of phosphoric acid to aluminum dihydrogen phosphate is 20:9, which optimizes the ratio to form dense AlPO4 crystals, fills the pores of the transition layer, and improves the oxygen barrier performance.

[0048] Furthermore, the specific process of drying, calcining, and cooling the extracted second intermediate includes:

[0049] The second intermediate was placed in a vacuum drying oven and dried sequentially at 80–100°C and 150–200°C. Then, the second intermediate was placed in a heating furnace, first heated to 250–300°C at a rate of 4–5°C / min, then heated to 500–600°C at a rate of 2–3°C / min and held at that temperature for 1–3 hours, before naturally cooling to room temperature. During the high-temperature calcination at 500–600°C, the aluminum dihydrogen phosphate (Al(H2PO4)3) and phosphoric acid (H3PO4) system underwent decomposition and reconstruction reactions. First, upon heating, aluminum dihydrogen phosphate gradually lost bound water and hydroxyl groups, decomposing to generate intermediate aluminum metaphosphate (Al(PO3)3) and releasing H2O and P. x O y The gas undergoes further dehydration and condensation of phosphoric acid to form polyphosphoric acid or pyrophosphoric acid. When the temperature rises to 500℃, aluminum ions in the system undergo a deep reaction with phosphate ions, forming aluminum phosphate (AlPO4) crystal structure through PO-Al bonds. During this process, partial oxidation of aluminum may also occur to generate trace amounts of Al2O3, which forms a complex phase with aluminum phosphate.

[0050] Specifically, the preparation of the oxygen barrier layer includes:

[0051] Phosphoric acid and aluminum dihydrogen phosphate in a molar ratio of (20:9) are mixed with deionized water and magnetically stirred for 2 hours until transparent to obtain a third mixed solution. The second intermediate is immersed in this third mixed solution and allowed to stand in air for 1–3 hours (preferably 1 hour). Then, it is dried sequentially in a vacuum drying oven at 80–100°C and 150–200°C for 30 minutes each to remove residual moisture. Afterwards, the temperature is raised to 250–300°C in a heating furnace (tube furnace) at a rate of 4–5°C / min (preferably 5°C / min), then raised to 500–600°C at a rate of 2–3°C / min (preferably 3°C / min), held at this temperature for 1–3 hours (preferably 2 hours), and allowed to cool naturally to form an oxygen barrier layer; thus obtaining the final composite oxygen barrier coating.

[0052] like Figure 1 As shown, the present invention also provides a composite oxygen barrier coating, prepared by the above-described preparation method. The composite oxygen barrier coating includes a transition layer and an oxygen barrier layer. The transition layer is disposed on the surface of a substrate, and the oxygen barrier layer is disposed on the surface of the transition layer. The transition layer includes a porous carbon framework and cobalt particles (not shown in the figure) embedded in the pores of the porous carbon framework, and boron oxide (such as...). Figure 3As shown), the oxygen barrier layer 3 comprises an aluminum phosphate crystal structure (not shown in the figure). The metal-organic framework (such as...) Figure 2 (As shown) After high-temperature calcination, a porous carbon skeleton can be formed. This invention introduces a transition layer with a porous carbon skeleton, which provides directional anchoring points for boron oxide through the active sites of metal particles. B2O3 melts and flows at high temperature, repairing the cracks in the transition layer through capillary action. This achieves an organic combination of self-healing function and oxygen barrier performance, solving the problems of low repair efficiency and insufficient durability of traditional coatings.

[0053] The present invention will be further described below with reference to embodiments; wherein, the substrate is selected as a graphene substrate. Existing graphene heating films are prone to oxidation in high-temperature environments above 400°C, while existing self-healing coatings generally suffer from technical bottlenecks such as poor dispersion uniformity, low oxygen barrier efficiency, and lack of density.

[0054] Example 1

[0055] step:

[0056] (1) Preparation of transition layer:

[0057] The graphene substrate was immersed in acetone and sonicated for 8 min, then rinsed three times with deionized water to remove solvent residue. It was then immersed in a methanol solution containing Co(NO3)2·6H2O and 2-methylimidazole (molar ratio 1:3) and allowed to stand for 5 h. It was then washed three times alternately with deionized water and methanol, and freeze-dried for 24 h. Calcination was performed in an argon atmosphere: the temperature was increased to 600℃ at 3℃ / min, held for 5 h, and then naturally cooled to obtain a porous carbon framework embedded with cobalt nanoparticles (TEM analysis is shown below). Figure 4a As shown, the SEM analysis is as follows: Figure 4b As shown in the figure, a transition layer is formed.

[0058] (2) Boron oxide loaded in the transition layer:

[0059] Citric acid and ammonium borate (molar ratio 2:1) were dissolved in water and stirred in an 80°C water bath until transparent to obtain a second mixed solution.

[0060] After impregnating the transition layer with the second mixed solution, staged vacuum heating is performed:

[0061] Hold at 120℃ for 1 hour (to remove solvent and stabilize the skeleton);

[0062] Keep warm at 230℃ for 4 hours (decompose organic acids and generate B2O3);

[0063] Vacuum heat treatment at 320℃ for 2 hours (densification of molten B2O3).

[0064] (3) Preparation of oxygen barrier layer:

[0065] Phosphoric acid and aluminum dihydrogen phosphate (molar ratio 20:9) were dissolved in water and stirred for 2 hours to obtain a third mixed solution.

[0066] The third mixed solution impregnates the boron oxide-loaded transition layer, which is then allowed to stand for 1 hour before being dried in stages.

[0067] Vacuum dry at 90℃ for 30 min;

[0068] Vacuum dry at 180℃ for 30 minutes.

[0069] The temperature program in the tube furnace is as follows: 5℃ / min to 280℃, 3℃ / min to 550℃, and hold for 2 hours.

[0070] Test results: Through SEM analysis (e.g.) Figure 5 The prepared composite oxygen barrier coating exhibits a dense, crack-free morphology, and the transition layer is tightly bonded to the graphene matrix interface, forming a stable multilayer structure. Oxygen barrier performance testing shows that the oxygen diffusion rate of this composite oxygen barrier coating is significantly reduced to 0.12 cm⁻¹ at a high temperature of 450℃. 3 / (m 2 (day). Durability test data comparison shows that the composite oxygen barrier coating prepared in Example 1 decreased by 5% in oxygen barrier efficiency after 2300h test, proving that it has excellent long-term oxygen barrier stability.

[0071] Example 2 (Optimization of calcination temperature and time): In the preparation of the transition layer, the calcination temperature was adjusted to 550℃ and the holding time was extended to 6h (Example 1 was 600℃ for 5h); other steps were the same as in Example 1.

[0072] Test Results: By optimizing the calcination process (holding at 550℃ for 6 hours), the prepared transition layer material showed significant improvement: although the porosity of the porous carbon skeleton was basically the same as in Example 1, the uniformity of pore size distribution was significantly improved, and the material density was enhanced. Performance test data showed that in the long-term stability test at 450℃, the optimized composite oxygen barrier coating exhibited superior durability. The oxygen barrier efficiency of the sample in Example 2 decreased by 5% after 2500 hours of testing, proving that its high-temperature stability was substantially improved.

[0073] Comparative Example 1: Pure SiO2 oxygen barrier layer (without transition layer)

[0074] Procedure: In the preparation experiment of pure SiO2 oxygen barrier layer (without transition layer), the graphene substrate was first pretreated by ultrasonically cleaning it sequentially with acetone, ethanol, and deionized water for 10 min each, followed by vacuum drying at 80℃. The SiO2 coating was prepared using the sol-gel method. Tetraethoxysilane (TEOS) and anhydrous ethanol were mixed at a molar ratio of 1:4, and 0.1M hydrochloric acid was added to adjust the pH to 3-4. The mixture was magnetically stirred for 2 h to form a transparent sol. Graphene was immersed in the sol using an dip-coating method (coating speed 2 mm / s), and allowed to stand at room temperature for 30 min to allow preliminary gel formation. Subsequently, a staged heating and drying process was performed: vacuum drying at 80℃ for 1 h to remove the solvent, followed by densification at 300℃ in air atmosphere for 2 h.

[0075] Test results: Under the same test conditions (working environment at 450℃), the oxygen barrier efficiency of this coating decreased by 5% after 1530 hours.

[0076] Conclusion: Pure SiO2 coatings cannot meet the requirements for high-temperature oxygen barrier due to the lack of interfacial buffering effect of the transition layer. The transition layer plays a decisive role in improving interfacial adhesion and high-temperature stability.

[0077] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content without departing from the scope of the technical solution of the present invention, which are equivalent embodiments with equivalent changes. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the technical solution of the present invention shall still fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing a composite oxygen barrier coating for disposing on a surface of a substrate, characterized by, The preparation method comprises the following steps: dissolving a cobalt salt and 2-methyl imidazole in a solvent to form a first mixed solution, immersing a substrate in the first mixed solution, then taking out the substrate and sequentially performing washing, drying, calcination and cooling on the substrate to form a transition layer on the surface of the substrate, and obtaining a first intermediate; wherein the specific process of the calcination comprises: placing the dried substrate in a heating furnace, introducing a protective gas, heating at a heating rate of 2-5 ℃ / min to 500-600 ℃, and maintaining for 5-6 h; dissolving a carboxylic acid and ammonium borate in water to form a second mixed solution, heating the second mixed solution, immersing the first intermediate in the heated second mixed solution, then taking out the first intermediate and performing segmented heating to load boron trioxide on the transition layer, and obtaining a second intermediate; wherein the segmented heating specifically comprises: placing the first intermediate in a vacuum oven, heating to 100-150 ℃ for 1-2 h, then heating to 200-250 ℃ for 3-4 h, and finally heating to 300-350 ℃ for 2-3 h; dissolving phosphoric acid and aluminum dihydrogen phosphate in water to form a third mixed solution, immersing the second intermediate in the third mixed solution, then taking out the second intermediate and sequentially performing drying, calcination and cooling to form an oxygen barrier layer on the surface of the transition layer, and obtaining the required composite oxygen barrier coating.

2. The method of claim 1, wherein the composite oxygen barrier coating is prepared by a process comprising: The cobalt salt comprises cobalt nitrate hexahydrate, and the molar ratio of cobalt nitrate hexahydrate to 2-methyl imidazole is 1:

3.

3. The method of claim 1, wherein the composite oxygen barrier coating is prepared by a process comprising: The heating of the second mixed solution is performed by water bath heating, and the second mixed solution is heated to 75-85 ℃ by water bath heating.

4. The method of claim 1, wherein the composite oxygen barrier coating is prepared by a process comprising: The carboxylic acid comprises citric acid, and the molar ratio of citric acid to ammonium borate is (1.5:1)-(3:1).

5. The method of claim 1, wherein the composite oxygen barrier coating is prepared by a process comprising: The molar ratio of the phosphoric acid to aluminum dihydrogen phosphate is 20:

9.

6. The method of claim 1, wherein the composite oxygen barrier coating is prepared by a process comprising: The specific process of sequentially performing drying, calcination and cooling on the taken-out second intermediate comprises: placing the second intermediate in a vacuum drying oven, sequentially drying at 80-100 ℃ and 150-200 ℃, then placing the second intermediate in a heating furnace, first heating to 250-300 ℃ at a heating rate of 4-5 ℃ / min, then heating to 500-600 ℃ at a heating rate of 2-3 ℃ / min and maintaining for 1-3 h, and naturally cooling to room temperature.

7. The method of claim 1-6, wherein the composite oxygen barrier coating is prepared by, Before obtaining the first intermediate, the preparation method further comprises: cleaning the substrate, and the specific process of the cleaning comprises: immersing the substrate in acetone and ultrasonic treating for 5-10 min, and then washing with deionized water.

8. A composite oxygen barrier coating, characterized by, The composite oxygen barrier coating obtained by the preparation method of any one of claims 1-7 comprises a transition layer and an oxygen barrier layer, the transition layer is arranged on the surface of the substrate, and the oxygen barrier layer is arranged on the surface of the transition layer.

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