A high-temperature antioxidant protective coating material for nitride ceramics, its preparation method and application

Abstract

This invention proposes a high-temperature antioxidant protective coating material for nitride ceramics, its preparation method, and its application. It belongs to the field of functional materials technology. The coating is performed using silane coupling agents and borate esters. A membrane structure is formed by heating, curing, and heat treatment. The preparation process is simple and efficient, and can effectively improve the high-temperature antioxidant properties of nitride ceramics. It also has great advantages in production process.

Description

Technical Field

[0001] This invention belongs to the field of functional materials technology, and particularly relates to a high-temperature antioxidant protective coating material for nitride ceramics, its preparation method and application. Background Technology

[0002] Nitride ceramics possess excellent high-temperature mechanical properties and corrosion resistance, making them widely used in aerospace, energy, and automotive fields. However, under high-temperature environments, nitride ceramics are susceptible to oxidative damage, leading to performance degradation and reduced service life. The necessity of applying high-temperature anti-oxidation coatings to nitride ceramics is primarily due to the following factors: First, nitride ceramics are easily oxidized at high temperatures, reducing their performance and lifespan; second, high-temperature anti-oxidation coatings effectively improve the oxidation resistance of nitride ceramics, extending their service life; and finally, by applying high-temperature anti-oxidation coatings to nitride ceramics, their application range in aerospace, energy, and automotive fields can be expanded, improving the economic and social benefits of the materials. Therefore, research on high-temperature anti-oxidation coating technology for nitride ceramics has significant scientific and applied value.

[0003] Currently, commonly used methods for preparing high-temperature antioxidant coatings for nitride ceramics include physical vapor deposition, chemical vapor deposition, and the sol-gel method. Among these, the sol-gel method is a frequently used approach. Through sol treatment and gelation, a uniform and dense coating can be formed on the surface of nitride ceramics, improving the material's high-temperature antioxidant properties. However, this method still faces challenges such as high cost, weak coating adhesion, uneven coating thickness, complex preparation process, and poor environmental friendliness. In summary, current research methods still have some limitations in improving the performance and stability of high-temperature antioxidant coatings for nitride ceramics, requiring further improvement and optimization.

[0004] Therefore, there is an urgent need to provide a high-temperature antioxidant protective coating for nitride ceramics with excellent performance and its preparation method. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a high-temperature antioxidant protective coating material for nitride ceramics, its preparation method, and its application.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] One of the technical solutions of the present invention:

[0008] A method for preparing a high-temperature antioxidant protective coating material for nitride ceramics includes the following steps:

[0009] The silane coupling agent and the borate ester were dissolved separately in an organic solvent to form separate solutions;

[0010] The individual solutions are mixed together and stirred until homogeneous to form the final coating solution;

[0011] The coating solution is uniformly coated onto the surface of the nitride ceramic, and then dried and cured by heat to form an antioxidant film on the surface of the nitride ceramic.

[0012] The coating method is brushing, spraying, or dipping to ensure the formation of a uniform film; and before coating, the nitride ceramic surface needs to be cleaned and impurities removed with anhydrous ethanol to ensure that the nitride ceramic surface is clean and dust-free; the drying process allows the organic solvents in the coating to evaporate.

[0013] Nitride ceramics coated with an antioxidant film are preheated and heat-treated to form a high-temperature antioxidant protective coating material on the surface of the nitride ceramics.

[0014] The reaction principle involved in the technical solution defined in this invention is as follows: First, the oxidation process of nitrides, taking silicon nitride and boron nitride as examples, is characterized by deliquescence due to water absorption at room temperature, forming products such as silicon-oxygen hydrate and boron-oxygen hydrate in extremely small areas and thicknesses on its surface. Then, after being exposed to high temperature in the air, the water is first lost, and the silicon dioxide and boron anhydride (B2O3) formed by dehydration decompose at high temperature to form gaseous silicon dioxide and boron anhydride, which volatilize and leave the ceramic surface, exposing Si3N4 or BN to high temperature air. At the same time, because of the above hydration process, many tiny channels are formed inside and outside the ceramic, resulting in a larger area of ​​contact between the ceramic and high temperature oxygen, increasing its oxidation probability.

[0015] Therefore, this invention creatively utilizes the room-temperature film-forming property of organic materials, that is, the ability of organic materials to form a continuous thin film covering the surface of a certain substrate at room temperature. This film-forming property is usually due to the adhesiveness and fluidity of organic materials, which can form a uniform coating on the substrate surface and form a stable film after curing. Based on this, this invention uses silane coupling agents and borate esters to first arrange a uniform anti-oxidation film on the ceramic surface. Then, the treated ceramic is heated to further cure the anti-oxidation film. Finally, through heat treatment, a corresponding high-temperature resistant anti-oxidation continuous phase amorphous ceramic is formed inside the anti-oxidation film and on the surface of the ceramic substrate, while a low-temperature glassy phase generated from the remaining oxides is formed on the outside. The combination of the two forms a membrane structure from the inside out: nitride ceramic – continuous phase amorphous ceramic – low-temperature glassy phase. This structure can avoid the influence of high-temperature oxygen reaction on the internal ceramic, increasing its high-temperature resistance and stability.

[0016] Preferably, the silane coupling agent is KH550 and HPSO;

[0017] The organic solvent is anhydrous ethanol.

[0018] Furthermore, the KH550 and HPSO are dissolved separately in the anhydrous ethanol;

[0019] The mass-to-volume ratio of KH550 or HPSO to anhydrous ethanol is 15g:25-35mL.

[0020] The mass-to-volume ratio of the borate ester to anhydrous ethanol is 30g:50-70mL.

[0021] Preferably, the drying process is carried out under the following conditions: drying at 25°C for 2 hours.

[0022] Preferably, the preheating temperature is 150°C and the time is 1 hour.

[0023] Preferably, the heat treatment includes two stages, with the first stage heat treatment conditions being: a heat treatment temperature of 450°C and a time of 0.5 hours;

[0024] The second stage heat treatment conditions are as follows: when the nitride ceramic is silicon nitride ceramic, the heat treatment temperature is 800℃ and the time is 0.5h.

[0025] When the nitride ceramic is boron nitride ceramic, the temperature is 1250℃ and the time is 0.5h.

[0026] The second technical solution of the present invention:

[0027] A high-temperature antioxidant protective coating material for nitride ceramics is prepared by the above-described preparation method.

[0028] The third technical solution of the present invention:

[0029] The above-mentioned high-temperature antioxidant protective coating materials for nitride ceramics are used in the aerospace, energy and automotive fields.

[0030] Compared with the prior art, the present invention has the following advantages and technical effects:

[0031] (1) This invention provides a simple, efficient, and low-cost method for preparing a high-temperature antioxidant protective coating material for nitride ceramics. The coating is performed using a silane coupling agent and a borate ester, followed by heating, curing, and heat treatment to form a membrane structure. This preparation process is simple and efficient, effectively improving the high-temperature oxidation resistance of nitride ceramics, and exhibits significant advantages in production technology. Furthermore, this method can reduce material production costs and improve production efficiency, thereby better realizing the high-temperature antioxidant effect. Therefore, this invention has broad application prospects and is expected to become an important technology in the field of silicon nitride-based composite material preparation.

[0032] (2) This invention improves the high-temperature oxidation resistance of nitride ceramics by forming a membrane structure through the combination of continuous amorphous ceramic and low-temperature glass phase. That is, it can effectively prevent nitride ceramics from being affected by high-temperature oxygen, increase their high-temperature tolerance and stability, and extend their service life; moreover, the process is simple, low-cost, and can be mass-produced.

[0033] (3) The high-temperature antioxidant protective coating material provided by the present invention is applicable to various nitride ceramic materials that require high-temperature antioxidant protection and has broad application prospects. Attached Figure Description

[0034] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0035] Figure 1 The image shows a physical sample of the high-temperature antioxidant protective coating material for nitride ceramics prepared in Example 1.

[0036] Figure 2 The image shows the microstructure of the fracture surface of the high-temperature antioxidant protective coating material for nitride ceramics prepared in Example 1.

[0037] Figure 3 The XRD patterns of silicon nitride ceramic before and after coating with high-temperature antioxidant protective coating material are obtained by taking powder from the surface of both ceramics in Example 1. Detailed Implementation

[0038] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0039] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0040] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0041] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0042] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0043] The first aspect of this invention provides a method for preparing a high-temperature antioxidant protective coating material for nitride ceramics, comprising the following steps:

[0044] The silane coupling agent and the borate ester are dissolved separately in an appropriate amount of organic solvent to form separate solutions;

[0045] The individual solutions mentioned above are mixed together in a certain ratio and stirred evenly to form the final coating solution;

[0046] The mixed coating solution is evenly applied to the ceramic surface by brushing, spraying, or dipping to ensure the formation of a uniform film. Before applying the coating, the ceramic surface must be clean and dust-free. Organic solvents can be used to clean and remove impurities.

[0047] The coated ceramic sample was dried at room temperature for a period of time to allow the organic solvents in the coating to evaporate.

[0048] The dried ceramic sample was cured by heating, so that the silane coupling agent and borate ester formed a uniform and cured antioxidant film on the ceramic surface.

[0049] The ceramic sample coated with an antioxidant film was heat-treated to obtain a nitride ceramic with a high-temperature antioxidant coating having a diaphragm structure.

[0050] In a preferred embodiment of the present invention, the preferred experimental parameters are obtained using silicon nitride and boron nitride ceramics with a length and width of 15cm and a thickness of 1mm as examples.

[0051] In a preferred embodiment of the present invention, the silane coupling agent is KH550 and HPSO, and the organic solvent is anhydrous ethanol; the mass ratio of the silane coupling agent to the borate ester is KH550:HPSO:borate ester = 1:1:2; the organic solvent is added according to the above-mentioned amounts of both, specifically the mass-volume ratio of the silane coupling agent and the borate ester to the organic solvent is KH550 (or HPSO):anhydrous ethanol = 15g:(25-35)mL, and borate ester:anhydrous ethanol = 30g:(50-70)mL. Separate dispersion before mixing ensures that KH550, HPSO, and the borate ester are fully dissolved, making the effective content of the final coating closer to the expected level.

[0052] The aforementioned limits on the amounts of silane coupling agent and borate ester promote low-temperature forming and easy coating. The sintering result is a membrane structure consisting of nitride ceramic – continuous amorphous ceramic – low-temperature glassy phase, exhibiting high overall structural hardness and strength. Therefore, the above ratio was chosen. If the amount of silane coupling agent and borate ester is too small, the silane coupling agent decomposes during heat treatment to produce SiO2, and the borate ester becomes boron gangue, forming a liquid-phase thin film. Therefore, insufficient silane coupling agent and borate ester will result in an insufficient amount of the external continuous amorphous ceramic and low-temperature glassy phase, weakening high-temperature resistance and stability.

[0053] In a preferred embodiment of the present invention, the room temperature drying temperature is 25°C and the time is 2 hours;

[0054] In a preferred embodiment of the present invention, the heating and curing device is a drying oven with a temperature of 50°C and a time of 2 hours.

[0055] The heating process further evaporates the anhydrous ethanol in the coating and allows the silane coupling agent and borate ester to form a uniform, cured, antioxidant film on the ceramic surface.

[0056] In a preferred embodiment of the present invention, preheating is performed before the heat treatment process, set at 100-200°C. The purpose is to remove as much organic solvent and volatile metaboric acid from the borate ester as possible from the material, preventing the formation of rising gas within the coating during heat treatment and thus avoiding internal pore blockage. Preferably, the preheating temperature is 150°C for 1 hour, ensuring the coating material's effectiveness while saving energy. If the preheating temperature is too low or the time too short, residual organic solvent and metaboric acid will cause rising gas. Excessively high preheating temperatures will cause premature decomposition of the silane coupling agent and borate ester, which is detrimental to subsequent reactions.

[0057] In a preferred embodiment of the present invention, after the heat treatment preheating, the temperature is first raised to 380-500℃. The purpose is to allow HPSO and KH550 to decompose and generate SiO2 in the micro-regions of the film layer, while simultaneously causing the borate ester to decompose and generate B2O3. The two form a eutectic liquid phase near 400℃, namely an inorganic SiO2 and B2O3 liquid phase film layer. The present invention preferably maintains the temperature at 450℃ for 0.5 hours. Temperatures that are too high or too low, or holding times that are too short, will result in insufficient SiO2 and B2O3 content in the liquid phase film layer, preventing the formation of the final membrane structure.

[0058] In a preferred embodiment of the present invention, after the heat treatment in the first step is completed, the temperature is raised to a second step of heat treatment at a higher temperature. Taking silicon nitride ceramic as an example, the temperature needs to be raised to 750-800℃, and the present invention preferably holds at 800℃ for 0.5h; taking boron nitride ceramic as an example, the temperature needs to be raised to 1200-1300℃, and the present invention preferably holds at 1250℃ for 0.5h.

[0059] At temperatures above 730℃, silicon nitride ceramics react with B2O3 in the SiO2 and B2O3 liquid phase films on the substrate surface to form an amorphous SiBON phase (resistant to air temperatures above 1900℃). The remaining B2O3 in the external liquid phase maintains its compositional stability through partial volatilization, while the remaining SiO2-enriched film forms a low-temperature glassy phase. Boron nitride ceramics, on the other hand, at 1200℃, the substrate strips its internal SiO2 content to form an amorphous SiBON phase. Similarly, the B2O3 in the liquid phase maintains its compositional stability through partial volatilization, while the remaining SiO2-enriched film forms a low-temperature glassy phase. This ultimately results in a stable membrane structure that can withstand high-temperature oxidation.

[0060] A second aspect of the present invention provides a high-temperature antioxidant protective coating material for nitride ceramics prepared according to the above-described preparation method.

[0061] The third aspect of the present invention provides the application of the above-mentioned high-temperature antioxidant protective coating material with a diaphragm structure for nitride ceramics in the fields of aerospace, automotive, electronics, and functional materials.

[0062] Unless otherwise specified, all raw materials used in the embodiments and comparative examples of this invention can be obtained commercially. Specifically, the silicon nitride ceramics and boron nitride ceramics used in the embodiments and comparative examples of this invention were purchased from Guangwei Composite Materials Co., Ltd., KH550 and HPSO were purchased from Shandong Zhengji Chemical Co., Ltd., and borate esters and anhydrous ethanol were purchased from Hubei Yongkuo Technology Co., Ltd.

[0063] The instruments and equipment used in the embodiments and comparative examples of this invention are all commonly used instruments and equipment in the art.

[0064] The technical solution of the present invention will be further illustrated by the following embodiments.

[0065] Example 1

[0066] (1) Add 15g KH550, 15g HPSO and 30g borate to three beakers respectively, and then add 30mL, 30mL and 60mL of anhydrous ethanol in sequence to form separate solutions. After stirring the three separate solutions evenly, a coating solution with uniform material mixing is obtained.

[0067] (2) After ensuring that the silicon nitride ceramic surface is clean and dust-free, the mixed coating solution is uniformly coated on the ceramic surface by brushing to ensure the formation of a uniform film, and then dried at room temperature (25°C) for 2 hours.

[0068] (3) The dried ceramic sample was heated and cured. The heating temperature was set to 50°C and the holding time was 2h, so that the silane coupling agent and borate ester formed a uniform and cured antioxidant film on the ceramic surface.

[0069] (4) The ceramic coated with the anti-oxidation film is preheated to 150℃ for 1 hour. After the heat treatment preheating, the temperature is raised to 450℃ and held for 0.5 hours. After that, the temperature is raised to 800℃ and held for 0.5 hours to obtain a silicon nitride ceramic product with a high-temperature anti-oxidation protective coating material on the surface.

[0070] Example 2

[0071] The difference from Example 1 is that boron nitride ceramic is used in step (2); after step (4) is completed, the temperature is raised to 1250°C and held for 0.5 h; other conditions are the same as in Example 1.

[0072] Figure 1 The image shows a physical picture of the composite material prepared in Example 1. As can be seen from the image, the surface density of the prepared ceramic material is increased.

[0073] Figure 2 This is a microstructure diagram of the fracture surface of the coating prepared in Example 1. Figure 2 This proves the existence of the diaphragm structure.

[0074] Figure 3 The XRD patterns of silicon nitride ceramic before and after coating with the high-temperature antioxidant protective coating material are shown in Example 1. The surface layers of both ceramics were powdered and analyzed. Figure 3 It can be seen that the main crystal form of silicon nitride ceramic before treatment is β-Si3N4; in the surface of the treated ceramic, the main crystal phase is still β-Si3N4, and some amorphous phases (i.e., Figure 3 Amorphous), cristobalite phase (i.e.) Figure 3The results (in Quartz) indicate that B2O3 reacts in situ with β-Si3N4 to form the amorphous phase SiBON, while the remaining B2O3 completely decomposes and detaches from the structure. During the cooling process, SiO2 segregates and crystallizes, resulting in the appearance of the cristobalite phase.

[0075] Comparative Example 1

[0076] The only difference from Example 1 is that 20g KH550, 20g HPSO and 35g borate ester are added in step (1); other conditions are the same as in Example 1.

[0077] Comparative Example 2

[0078] The difference from Example 1 is that step (1) involves adding 10g KH550, 10g HPSO, and 25g borate ester; other conditions are the same as in Example 1.

[0079] Comparative Example 3

[0080] The only difference from Example 2 is that 20g KH550, 20g HPSO and 35g borate ester are added in step (1); other conditions are the same as in Example 2.

[0081] Comparative Example 4

[0082] The difference from Example 2 is that 10g KH550, 10g HPSO and 25g borate ester were added in step (1); other conditions were the same as in Example 2.

[0083] Comparative Example 5

[0084] The only difference from Example 1 is that the preheating process in step (4) is not included.

[0085] Effect verification

[0086] Antioxidant and deliquescence resistance tests were conducted on the products from Examples 1-2 and Comparative Examples 1-5. The antioxidant test involved treating the ceramics coated with a high-temperature antioxidant protective coating material at 1850°C and measuring their weight loss rate. The deliquescence resistance test involved boiling the ceramics coated with the high-temperature antioxidant protective coating material in 100°C water for 2.5 hours and measuring their water absorption rate. The results are shown in Tables 1 and 2.

[0087] Table 1. Antioxidant test results

[0088] weight loss rate Example 1 1.7％ Example 2 2.9％ Comparative Example 1 2.5％ Comparative Example 2 2.2％ Comparative Example 3 3.6％ Comparative Example 4 3.3％ Comparative Example 5 2.7％

[0089] Table 2 Results of Deliquescence Resistance Test

[0090]

[0091]

[0092] Conclusion: As shown in Tables 1 and 2, comparing Example 1 with Comparative Examples 1 and 2, and Example 2 with Comparative Examples 3 and 4, it can be seen that the appropriate amount of silane coupling agent and borate ester added is sufficient; too much or too little will affect the antioxidant capacity of the material. As shown in the comparison between Example 1 and Comparative Example 5, after the preheating step was removed, the weight loss rate and water absorption rate increased, which proves that the volatilization of the ethanol and metaboric acid involved will cause internal closed pores, affecting the formation of the membrane structure.

[0093] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for preparing a high-temperature antioxidant protective coating material for nitride ceramics, characterized in that, Includes the following steps: Separate solutions were prepared by dissolving silane coupling agent and borate ester in an organic solvent; the silane coupling agent was KH550 and HPSO; the organic solvent was anhydrous ethanol; KH550 and HPSO were dissolved separately in the anhydrous ethanol; wherein the mass-to-volume ratio of KH550 or HPSO to anhydrous ethanol was 15 g : (25-35) mL; the mass-to-volume ratio of borate ester to anhydrous ethanol was 30 g : (50-70) mL. The individual solutions are mixed and stirred until homogeneous to form a coating solution; The coating solution is uniformly coated onto the surface of the nitride ceramic, and then dried and cured by heating to form an antioxidant film on the surface of the nitride ceramic. Nitride ceramics coated with an antioxidant film are preheated and heat-treated to form a high-temperature antioxidant protective coating material on the surface of the nitride ceramics. The preheating temperature is 100-200℃; The heat treatment includes two stages. The first stage heat treatment conditions are: heat treatment temperature of 380-500℃. The second stage heat treatment conditions are as follows: when the nitride ceramic is silicon nitride ceramic, the heat treatment temperature is 750-800℃; When the nitride ceramic is boron nitride ceramic, the heat treatment temperature is 1200-1300℃.

2. The method for preparing a high-temperature antioxidant protective coating material for nitride ceramics according to claim 1, characterized in that, The drying conditions are as follows: drying at 25°C for 2 hours.

3. The method for preparing a high-temperature antioxidant protective coating material for nitride ceramics according to claim 1, characterized in that, The temperature during the heating and curing process is 50°C, and the time is 2 hours.

4. The method for preparing a high-temperature antioxidant protective coating material for nitride ceramics according to claim 1, characterized in that, The preheating temperature is 150℃ and the time is 1 hour.

5. The method for preparing a high-temperature antioxidant protective coating material for nitride ceramics according to claim 1, characterized in that, The heat treatment includes two stages. The first stage heat treatment conditions are: heat treatment temperature of 450 °C and time of 0.5 h. The second stage heat treatment conditions are as follows: when the nitride ceramic is silicon nitride ceramic, the heat treatment temperature is 800 ℃ and the time is 0.5 h; When the nitride ceramic is boron nitride ceramic, the heat treatment temperature is 1250 ℃ and the time is 0.5 h.

6. A high-temperature antioxidant protective coating material for nitride ceramics, characterized in that, It is prepared by the preparation method according to any one of claims 1-5.

7. The application of the high-temperature antioxidant protective coating material for nitride ceramics as described in claim 6 in the aerospace, energy and automotive fields.

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