A method for preparing an oxidation-resistant nanocoating of BN fibers

Abstract

This invention discloses a method for preparing an antioxidant nanocoating for BN fibers, belonging to the field of special ceramics technology. The preparation method involves mixing a patellae nanosheet dispersion with a surface grafting agent solution to obtain a patellae nanosheet dispersion grafted with highly active groups; surface modification of BN fibers using a surfactant solution to obtain organically modified BN fibers; immersing the organically modified BN fibers in the patellae nanosheet dispersion grafted with highly active groups, followed by high-temperature pyrolysis to synthesize the antioxidant nanocoating for BN fibers in situ. The synthesis process of this invention is simple and has a short preparation cycle. The prepared antioxidant nanocoating achieves the construction of an antioxidant layer for BN fibers at low temperatures through a unique surface grafting technique, and simultaneously utilizes the Si-Al-O system on the surface of the patellae nanosheets to realize the microscopic antioxidant mechanism of the fibers, providing a new approach for constructing an ideal antioxidant coating for BN fibers.

Description

Technical Field

[0001] This invention belongs to the field of special ceramics technology, specifically relating to a method for preparing a BN fiber antioxidant nanocoating. Background Technology

[0002] In recent years, with the rapid development of high-end fields such as aerospace, new energy, and special ceramics, boron (BN) fibers have been widely used in key applications such as high-temperature structural materials, thermal insulation materials, and electronic packaging materials due to their excellent high-temperature resistance, low dielectric constant, and good mechanical stability. However, under high-temperature oxidizing environments (especially above 400℃), BN fibers are prone to oxidation reactions on their surface, forming brittle B2O3 films. These films are easily volatilized or detached, leading to damage to the fiber structure and a sharp decline in mechanical and high-temperature resistance, severely limiting their long-term service capability in high-temperature oxidizing environments. Therefore, constructing an efficient anti-oxidation coating for BN fibers has become a core requirement for expanding their application range and improving their service reliability. An ideal anti-oxidation coating should have the characteristics of strong interfacial bonding with BN fibers, excellent anti-oxidation performance, good high-temperature stability, and no significant increase in fiber density. Among these, the technology for constructing anti-oxidation coatings under low-temperature conditions is particularly crucial, as it can avoid damage to the intrinsic properties of BN fibers caused by high-temperature treatment, while also reducing preparation costs and simplifying the process.

[0003] Currently, the existing BN fiber antioxidant coating preparation technologies on the market can be mainly divided into several categories, including chemical vapor deposition, sol-gel method, and plasma spraying method. Although chemical vapor deposition can prepare coatings with high density, it has problems such as high reaction temperature (usually exceeding 800℃), complex process, large equipment investment, and long preparation cycle. In addition, the coating is prone to high porosity and uneven bonding with the fiber interface. The sol-gel method produces coatings with better uniformity, but cracks are prone to occur during the coating curing process, and the temperature resistance is insufficient, making it easy to peel off after long-term use at high temperatures. Plasma spraying can achieve rapid coating preparation, but the coating thickness is difficult to control precisely, which can easily lead to increased fiber surface roughness. In addition, the bonding strength between the coating and the fiber matrix is ​​low, making it easy to peel off under complex stress environments.

[0004] Regarding publicly available oxide-based antioxidant modification technologies for BN fibers, such as the sol-gel method used in existing technologies to coat oxide precursors onto the BN fiber surface, followed by high-temperature sintering to form an antioxidant coating, while this method can improve the fiber's antioxidant capacity to some extent, the high-temperature sintering process (usually above 600℃) causes slight oxidation on the BN fiber surface, and there is a significant stress difference between the coating and fiber interface, making it prone to cracking under long-term high-temperature conditions. Another example is the use of chemical vapor deposition (CVD) to grow SiC coatings, which exhibit good high-temperature oxidation resistance. However, the preparation process involves complex gas ratio control and high-temperature reaction steps, resulting in high production costs and difficulty in ensuring coating thickness uniformity. Furthermore, SiC coatings are relatively brittle and prone to breakage during fiber bending or thermal cycling. In addition, while some existing technologies attempt to prepare antioxidant coatings at low temperatures, they suffer from problems such as a single antioxidant mechanism, weak interfacial bonding, and poor stability under extreme high-temperature or complex media environments, making it difficult to meet the stringent requirements of high-end applications.

[0005] Based on the above problems, developing a method for preparing a BN fiber antioxidant nanocoating that is simple in process, has a short preparation cycle, can be prepared under low temperature conditions, has a strong interface bond with BN fiber, has excellent antioxidant properties, and relies on a multi-dimensional microscopic antioxidant mechanism has important practical significance and application value. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention proposes a method for preparing an antioxidant nano-coating for BN fibers. The preparation method of this invention has the advantages of simple process, short preparation cycle, and preparation under low temperature conditions. The prepared antioxidant nano-coating is firmly bonded to the BN fiber interface and has excellent antioxidant properties.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A method for preparing an antioxidant nanocoating for BN fibers involves mixing a patellae nanosheet dispersion with a surface grafting agent solution to obtain a patellae nanosheet dispersion grafted with highly active groups; surface modification of BN fibers using a surfactant solution to obtain organically modified BN fibers; immersing the organically modified BN fibers in the patellae nanosheet dispersion grafted with highly active groups, followed by high-temperature pyrolysis to synthesize the antioxidant nanocoating for BN fibers in situ.

[0008] Preferably, the method for preparing the BN fiber antioxidant nanocoating includes the following steps: (1) Add natural attapulgite and intercalating agent to an organic solvent, perform ultrasonic crushing at room temperature, centrifuge, take the supernatant to obtain attapulgite nanosheet dispersion; mix attapulgite nanosheet dispersion with surface grafting agent solution, react to obtain attapulgite nanosheet dispersion with highly active groups grafted. (2) Pre-treat the BN fiber to obtain pre-treated BN fiber. Add the pre-treated BN fiber to a surfactant solution, soak, filter, and dry to obtain organically modified BN fiber. (3) Mix the organically modified BN fiber with a dispersion of attapulgite nanosheets grafted with highly active groups, react, filter, and dry to obtain BN fiber coated with attapulgite nanosheets. (4) The BN fibers coated with attapulgite nanosheets were subjected to high-temperature pyrolysis to obtain an antioxidant nano-coating for BN fibers. Preferably, in step (1), the natural raptorite is one of sodium-based raptorite powder and lithium-based raptorite powder; More preferably, in step (1), the natural rettosite is sodium-based rettosite powder.

[0009] Preferably, in step (1), the intercalating agent is one of polyvinylpyrrolidone, alkyl glycoside, and isotridecyl alcohol ether; More preferably, in step (1), the intercalating agent is polyvinylpyrrolidone.

[0010] Preferably, in step (1), the organic solvent is one of N-methylpyrrolidone, N,N-dimethylformamide, and dimethyl sulfoxide; More preferably, in step (1), the organic solvent is N-methylpyrrolidone; Preferably, in step (1), the mass ratio of natural attapulgite to intercalating agent is 1:1~3; More preferably, in step (1), the mass ratio of natural attapulgite to intercalating agent is 1:2; Preferably, in step (1), the ratio of natural attapulgite to organic solvent is 0.6~1.2g:30mL; More preferably, in step (1), the ratio of natural attapulgite to organic solvent is 0.9 g: 30 mL; Preferably, in step (1), the power of ultrasonic crushing is 200~700W and the time is 60~150min; More preferably, in step (1), the power of ultrasonic crushing is 500W and the time is 120min; Preferably, in step (1), the centrifugation speed is 2000~4000 rpm and the time is 5~20 min; More preferably, in step (1), the centrifugation speed is 3000 rpm and the time is 10 min; Preferably, in step (1), the surface grafting agent solution is an ethanol-water solution of the surface grafting agent, wherein the volume ratio of the surface grafting agent to ethanol is 10:40~80, and the volume ratio of ethanol to water is 40~80:20~60. More preferably, in step (1), the surface grafting agent solution is an ethanol-water solution of the surface grafting agent, wherein the volume ratio of the surface grafting agent to ethanol is 10:50, and the volume ratio of ethanol to water is 50:50. Preferably, in step (1), the surface grafting agent in the surface grafting agent solution is one of KH-550, KH-560, and KH-570; Further, preferably, in step (1), the surface grafting agent in the surface grafting agent solution is KH-560; Preferably, in step (1), the ratio of natural attapulgite to the surface grafting agent in the surface grafting agent solution is 0.9g:0.8~1.2mL; More preferably, in step (1), the ratio of the amount of natural attapulgite to the amount of surface grafting agent in the surface grafting agent solution is 0.9g:1mL; Preferably, in step (1), the reaction is a stirring reaction, and the reaction time is 20~40 min; More preferably, in step (1), the reaction is a stirring reaction, and the reaction time is 30 min; Preferably, in step (2), the pretreatment method is pre-oxidation or soaking in an alkaline solution; the temperature during pre-oxidation is 500~700℃ and the time is 90~150min; the alkaline solution during alkaline soaking is one of NaOH solution, LiOH solution, or Na2CO3 solution, the concentration of the alkaline solution is 5~30wt%, and the soaking time is 5~20min; More preferably, in step (2), the pretreatment method is pre-oxidation or immersion in an alkaline solution; the temperature for pre-oxidation is 600℃ and the time is 120min; the alkaline solution for immersion in an alkaline solution is NaOH solution with a concentration of 20wt% and an immersion time of 10min. More preferably, in step (2), the pretreatment method is pre-oxidation; the temperature during pre-oxidation is 600℃ and the time is 120min; Preferably, in step (2), the surfactant solution is a mixed solution of surfactant, organic solvent, and pH adjuster, wherein the surfactant is KH-550; the organic solvent is one of N-methylpyrrolidone, N,N-dimethylformamide, and dimethyl sulfoxide; the pH adjuster is glacial acetic acid or dilute hydrochloric acid, wherein the concentration of the dilute hydrochloric acid is 0.3~1wt%, and the mass ratio of surfactant, organic solvent, and pH adjuster is 1:10~100:0.05~0.2; More preferably, in step (2), the surfactant solution is a mixed solution of surfactant, organic solvent and pH adjuster, wherein the surfactant is one of KH-550, KH-560 and KH-570; the organic solvent is N,N-dimethylformamide; the pH adjuster is glacial acetic acid, and the mass ratio of surfactant, organic solvent and pH adjuster is 1:20:0.1; Preferably, in step (2), the mass ratio of BN fiber used in preparing the pretreated BN fiber to the surfactant in the surfactant solution is 0.002~0.005:0.8~1.2; More preferably, in step (2), the mass ratio of BN fiber used in preparing the pretreated BN fiber to the surfactant in the surfactant solution is 0.005:1; Preferably, in step (2), the soaking time is 20~40 min; More preferably, in step (2), the soaking time is 30 minutes; Preferably, in step (2), the drying temperature is 50~80℃; More preferably, in step (2), the drying temperature is 60°C; Preferably, in step (3), the mass ratio of BN fiber used in preparing organically modified BN fiber to natural attapulgite used in preparing attapulgite nanosheet dispersion with highly active groups is 0.002~0.005:0.8~1; More preferably, in step (3), the mass ratio of BN fiber used in preparing organically modified BN fiber to natural attapulgite used in preparing attapulgite nanosheet dispersion with highly active groups is 0.005:0.9. Preferably, in step (3), the reaction temperature is room temperature and the reaction time is 20~40 min; More preferably, in step (3), the reaction temperature is room temperature and the reaction time is 30 min; Preferably, in step (3), the drying temperature is 50~80℃; More preferably, in step (3), the drying temperature is 60°C; Preferably, in step (4), the temperature during high-temperature pyrolysis is 700~900℃ and the time is 90~150min; More preferably, in step (4), the temperature during high-temperature pyrolysis is 800℃ and the time is 120min.

[0011] The preparation method of the BN fiber antioxidant nanocoating is based on the following principle: efficient exfoliation of attapulgite is achieved through ultrasonic crushing, forming a nanosheet dispersion rich in a Si-Al-O system; a surface grafting agent solution is added to the attapulgite nanosheet dispersion to further build a link bridge with the BN fiber; the BN fiber is pretreated to introduce a small number of surface defects, and then organically modified by surfactant to enhance the surface reactivity of the fiber; with the bridging effect of the surface grafting agent, the modified BN fiber and attapulgite nanosheets are tightly assembled, thereby achieving uniform encapsulation of the attapulgite nanosheets; the surface grafting agent and silane coupling agents such as surfactants are pyrolyzed at high temperature to release the antioxidant factor Si, which synergistically with the attapulgite nanosheets to construct a uniform and dense nanocoating. The Si-Al-O system of attapulgite nanosheets and silane coupling agents can form a physical barrier layer, inhibiting the contact between oxygen and BN fiber, while the chemical bonds enhance the interfacial bonding force between the coating and the fiber matrix, achieving a synergistic effect of multiple microscopic antioxidant mechanisms.

[0012] Compared with the prior art, the present invention has the following advantages and technical effects: 1. The preparation process of this invention mainly involves ultrasonic exfoliation, liquid phase grafting, and room temperature soaking. The process is simple, the reaction conditions are mild, the equipment requirements are low, the preparation cycle is short, and it is easy to scale up for production.

[0013] 2. This invention uses surface modification and grafting technology to make the nano-coating firmly bonded to the BN fiber interface, and the coating thickness is uniform, which solves the problems of easy peeling and uneven bonding of traditional coatings; the Si-Al-O system of attapulgite nanosheets endows the coating with excellent antioxidant properties, which can effectively inhibit the oxidative degradation of BN fibers in high-temperature environments above 800℃.

[0014] 3. The antioxidant coating constructed in this invention relies on a multi-dimensional micro-antioxidant mechanism. It forms a physical barrier through attapulgite nanosheets, and utilizes the B2O3 formed by the oxidation of BN fibers to form a continuous borosilicate (B-Si-O) three-dimensional network glassy melt with the attapulgite nanosheets at high temperature, thereby achieving the self-healing function of defects. Compared with traditional single-mechanism coatings, the stability in extreme high temperature or complex media environments is significantly improved, providing a guarantee for the long-term service of BN fibers in high-end fields.

[0015] 4. The preparation method of the anti-oxidation nano-coating of BN fiber of the present invention involves the chemical reaction of attapulgite nanosheets, modified BN fiber, and surface grafting agent to form a uniform and dense nano-coating. The surface grafting agent bridges the attapulgite nanosheets and modified BN fiber to form a stable bonding interface. The Si-Al-O system of attapulgite constructs a physical barrier layer. This physical barrier layer not only utilizes the B2O3 formed by the oxidation of BN fiber to form a continuous borosilicate (B-Si-O) three-dimensional network glassy melt with attapulgite nanosheets at high temperature, but also inhibits the contact between oxygen and BN fiber to resist oxidation by physically blocking it. This forms a multi-dimensional micro-anti-oxidation mechanism, which significantly improves the service reliability and mechanical property retention rate of BN fiber in high-temperature oxidizing environments.

[0016] 5. The BN fiber antioxidant nano-coating prepared by the present invention has an antioxidant coating thickness of 80-140 nm. After a high-temperature oxidation test (air atmosphere, 1000℃ for 5 hours), the fiber oxidation weight loss rate is 2.1-3.1%, and the tensile strength retention rate is 85.6-91.5%. Detailed Implementation

[0017] The technical solution of the present invention is described below with reference to specific embodiments. It should be understood that one or more steps mentioned in the present invention do not preclude the existence of other methods and steps before or after the combined steps, or that other methods and steps may be inserted between these explicitly mentioned steps. It should also be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Unless otherwise stated, the numbering of each method step is only for the purpose of identifying each method step, and not for limiting the order of each method or limiting the scope of the present invention. Changes or adjustments to their relative relationships, without substantial changes to the technical content, can also be considered as within the scope of the present invention.

[0018] Unless otherwise specified, all raw materials used in this invention are obtained through commercial channels.

[0019] The natural attapulgite, BN fiber, surfactants, etc. used in the embodiments of this invention are all commercially available analytical grade products, and the glassware and equipment used are commonly used instruments and equipment in laboratories. The natural raptosite used in the embodiments of the present invention is sodium-based raptosite powder.

[0020] In the embodiments of the present invention, room temperature or ambient temperature refers to 25±2℃.

[0021] Example 1 A method for preparing a BN fiber antioxidant nanocoating specifically includes the following steps: 1. Preparation of a dispersion of attapulgite nanosheets grafted with highly active groups Take 0.9 g of natural attapulgite and 1.8 g of polyvinylpyrrolidone, add them to 30 mL of N-methylpyrrolidone, and sonicate at 500 W for 120 min at room temperature. After centrifugation at 3000 rpm for 10 min, separate and take out the supernatant to obtain an attapulgite nanosheet dispersion. Then take 1 mL of KH-560, 5 mL of anhydrous ethanol, and 5 mL of deionized water, mix thoroughly, and pre-hydrolyze for 10 min to obtain a surface grafting agent solution. Under stirring, slowly add the prepared surface grafting agent solution dropwise to the above attapulgite nanosheet dispersion, react for 30 min, and obtain an attapulgite nanosheet dispersion with highly active groups grafted on.

[0022] 2. Surface modification of BN fibers A bundle of BN fibers with a mass of 0.005g, a diameter of 0.5~1.5mm, and a length of 4~6cm was placed in a tube furnace and pretreated at 600℃ for 2 hours to obtain pretreated BN fibers. 1g of KH-550, 20g of N,N-dimethylformamide, and 0.1g of glacial acetic acid were mixed thoroughly to obtain a surfactant solution. The pretreated BN fibers were then immersed in the surfactant solution for 20min, filtered, washed, and dried at 60℃ to obtain organically modified BN fibers.

[0023] 3. Chemical grafting for nanosheet coating The organically modified BN fibers obtained in step 2 were added to the dispersion of attapulgite nanosheets grafted with highly active groups obtained in step 1. The mixture was reacted at room temperature for 30 min, filtered, washed, and dried at 60 °C to obtain BN fibers coated with attapulgite nanosheets.

[0024] 4. In-situ preparation of nano-coatings via high-temperature pyrolysis The BN fibers coated with rettosite nanosheets obtained in step 3 were placed in a tube furnace and kept at 800°C for 2 hours in an air atmosphere to synthesize an antioxidant nanocoating for BN fibers in situ.

[0025] The performance was characterized by high-temperature oxidation test (air atmosphere, 1000℃ for 5h) and tensile strength test. The results showed that the coating thickness was 120nm, the fiber oxidation weight loss rate was only 2.3%, and the tensile strength retention rate was 91.5%.

[0026] Example 2 Same as Example 1, except that in the surface modification of BN fibers, the pretreatment method is to soak in 20wt% NaOH solution for 10 minutes, otherwise the same as Example 1.

[0027] The performance was characterized by high-temperature oxidation test (air atmosphere, 1000℃ for 5h) and tensile strength test. The results showed that the coating thickness was 110nm, the fiber oxidation weight loss rate was 2.4%, and the tensile strength retention rate was 91.0%.

[0028] Example 3 Same as Example 1, except that the surface grafting agent solution is KH-550 and the surfactant solution is KH-560, otherwise the same as Example 1.

[0029] The performance was characterized by high-temperature oxidation test (air atmosphere, 1000℃ for 5h) and tensile strength test. The results showed that the coating thickness was 135nm, the fiber oxidation weight loss rate was 2.2%, and the tensile strength retention rate was 89.7%.

[0030] Example 4 Same as Example 1, except that the concentration of KH-550 in the surfactant solution is 10wt%, and the soaking time of the pretreated BN fiber in the surfactant solution is 40min. Otherwise, it is the same as Example 1.

[0031] Performance characterization was conducted using a high-temperature oxidation test (air atmosphere, 1000℃ for 5 hours) and tensile strength test. The results showed that the coating thickness was 140 nm, the fiber oxidation weight loss rate was 2.1%, and the tensile strength retention rate reached 87.8%. This may be because as the KH-550 concentration increased, the system viscosity increased and the molecular packing increased, leading to an increase in coating thickness. Simultaneously, excessive KH-550 can damage the coating's cross-linking network, increase internal defects, dilute the proportion of high-strength components, and generate internal stress due to uneven drying shrinkage, ultimately reducing the coating's tensile strength retention rate.

[0032] Example 5 Same as Example 1, except that the organic solvent in the surfactant solution is dimethyl sulfoxide, and the glacial acetic acid reagent is replaced with 0.36wt% dilute hydrochloric acid; otherwise, it is the same as Example 1.

[0033] The performance was characterized by high-temperature oxidation test (air atmosphere, 1000℃ for 5h) and tensile strength test. The results showed that the coating thickness was 115nm, the fiber oxidation weight loss rate was 2.3%, and the tensile strength retention rate was 90.3%.

[0034] Example 6 Same as Example 2, except that the alkaline solution is a 20wt% LiOH solution, otherwise the same as Example 1.

[0035] The performance was characterized by high-temperature oxidation test (air atmosphere, 1000℃ for 5h) and tensile strength test. The results showed that the coating thickness was 80nm, the fiber oxidation weight loss rate was 3.1%, and the tensile strength retention rate was 85.6%.

[0036] Example 7 Same as Example 1, except that the surface grafting agent solution is KH-570, and the volume ratio of the attapulgite nanosheet dispersion to the surface grafting agent solution is changed to 2:1. Otherwise, it is the same as Example 1.

[0037] The performance was characterized by high-temperature oxidation test (air atmosphere, 1000℃ for 5h) and tensile strength test. The results showed that the coating thickness was 95nm, the fiber oxidation weight loss rate was 2.8%, and the tensile strength retention rate was 87.3%.

[0038] Example 8 Same as Example 1, except that the intercalating agent in the preparation of the highly active group-grafted attapulgite nanosheet dispersion is changed from polyvinylpyrrolidone to alkyl glycoside 1214, otherwise the same as Example 1.

[0039] The performance was characterized by high-temperature oxidation test (air atmosphere, 1000℃ for 5h) and tensile strength test. The results showed that the coating thickness was 105nm, the fiber oxidation weight loss rate was 2.5%, and the tensile strength retention rate was 90.1%.

[0040] Comparative Example 1 The difference from Example 1 is that the BN fibers were not surface modified. Instead, a bundle of raw BN fibers with a mass of 0.005g, a diameter of 0.5~1.5mm, and a length of 4~6cm was directly added to a dispersion of attapulgite nanosheets grafted with highly active groups. The other process steps were the same as in Example 1.

[0041] The performance was characterized by high-temperature oxidation test (air atmosphere, 1000℃ for 5h) and tensile strength test. The results showed that the coating and fiber interface were loosely bonded and the thickness was uneven. The fiber oxidation weight loss rate was 8.7% and the tensile strength retention rate was only 62.3%. The surface of the unmodified BN fiber lacked active groups and could not achieve effective electrostatic assembly.

[0042] Comparative Example 2 The difference from Example 1 is that the bottom sol was prepared according to the method of Example 1 in CN114149700B. A bundle of raw BN fibers with a mass of 0.005g, a diameter of 0.5~1.5mm and a length of 4~6cm was added to the bottom sol and impregnated for 30min. Then, it was sintered and cured at a high temperature of 600℃. The remaining operations were the same as the performance test conditions of Example 1.

[0043] The properties were characterized by high-temperature oxidation test (air atmosphere, 1000℃ for 5h) and tensile strength test. The results showed that the fiber surface was slightly oxidized, the coating had micro-cracks, the thickness was 70nm, the oxidation weight loss rate was 4.5%, and the tensile strength retention rate was 75.8%. High-temperature sintering caused damage to the intrinsic properties of the fiber, and the coating was prone to stress cracking.

[0044] Comparative Example 3 The difference from Example 1 is that no surface grafting agent solution is used; instead, the attapulgite nanosheet dispersion is mixed and assembled with organically modified BN fibers. The other process steps are the same as in Example 1.

[0045] The performance was characterized by high-temperature oxidation test (air atmosphere, 1000℃ for 5h) and tensile strength test. The results showed that the coating had poor density, many pores, a thickness of only 60nm, fiber oxidation weight loss rate of 6.3%, tensile strength retention rate of 71.2%, and lack of bridging effect of grafting agent, resulting in insufficient bonding strength between coating and fiber.

[0046] Comparative Example 4 The difference from Example 1 is that the SiC coating is prepared according to the method of step (4) in Example 1 of patent CN109400168B, and the remaining operations are the same as the performance test conditions of Example 1.

[0047] The performance was characterized by high-temperature oxidation test (air atmosphere, 1000℃ for 5h) and tensile strength test. The results showed that the coating thickness was not uniform and was brittle. The coating broke when the fiber was bent. The oxidation weight loss rate was 3.8% and the tensile strength retention rate was 78.5%. The high-temperature preparation process increased the cost and the brittleness of the coating affected the mechanical stability of the fiber.

[0048] The results of Examples 1-8 and Comparative Examples 1-4 are statistically analyzed as follows:

[0049] 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 BN fiber antioxidant nanocoating, characterized in that, A raptosite nanosheet dispersion was mixed with a surface grafting agent solution to obtain a raptosite nanosheet dispersion with highly active groups grafted on it. BN fibers were surface modified using a surfactant solution to obtain organically modified BN fibers. The organically modified BN fibers were then immersed in a dispersion of attapulgite nanosheets grafted with highly active groups, followed by high-temperature pyrolysis to synthesize an antioxidant nanocoating for BN fibers in situ.

2. The method for preparing the BN fiber antioxidant nanocoating according to claim 1, characterized in that, The preparation method includes the following steps: (1) Add natural attapulgite and intercalating agent to an organic solvent, perform ultrasonic crushing at room temperature, centrifuge, take the supernatant to obtain attapulgite nanosheet dispersion; mix attapulgite nanosheet dispersion with surface grafting agent solution, react to obtain attapulgite nanosheet dispersion with highly active groups grafted. (2) Pre-treat the BN fiber to obtain pre-treated BN fiber. Add the pre-treated BN fiber to a surfactant solution, soak, filter, and dry to obtain organically modified BN fiber. (3) Mix the organically modified BN fiber with a dispersion of attapulgite nanosheets grafted with highly active groups, react, filter, and dry to obtain BN fiber coated with attapulgite nanosheets. (4) The BN fibers coated with attapulgite nanosheets were subjected to high-temperature pyrolysis to obtain an antioxidant nanocoating of BN fibers.

3. The method for preparing the BN fiber antioxidant nanocoating according to claim 2, characterized in that, In step (1), the natural raptorite is one of sodium-based raptorite powder or lithium-based raptorite powder; The intercalating agent is one of polyvinylpyrrolidone, alkyl glycoside, and isotridecyl alcohol ether; The organic solvent is one of N-methylpyrrolidone, N,N-dimethylformamide, and dimethyl sulfoxide.

4. The method for preparing the BN fiber antioxidant nanocoating according to claim 2, characterized in that, In step (1), the mass ratio of natural attapulgite to intercalating agent is 1:1~3; The ratio of natural attapulgite to organic solvent is 0.6~1.2g:30mL; The power during ultrasonic fragmentation is 200~700W, and the time is 60~150min; The centrifugation speed is 2000~4000 rpm, and the time is 5~20 min.

5. The method for preparing the BN fiber antioxidant nanocoating according to claim 2, characterized in that, In step (1), the surface grafting agent solution is an ethanol-water solution of the surface grafting agent, wherein the volume ratio of the surface grafting agent to ethanol is 10:40~80, and the volume ratio of ethanol to water is 40~80:20~60. The surface grafting agent in the surface grafting agent solution is one of KH-550, KH-560, and KH-570.

6. The method for preparing the BN fiber antioxidant nanocoating according to claim 2, characterized in that, In step (1), the ratio of natural attapulgite to the amount of surface grafting agent in the surface grafting agent solution is 0.9g:0.8~1.2mL; The reaction is a stirred reaction, and the reaction time is 20-40 minutes.

7. The method for preparing the BN fiber antioxidant nanocoating according to claim 2, characterized in that, In step (2), the pretreatment method is pre-oxidation or soaking in an alkaline solution; the temperature for pre-oxidation is 500~700℃ and the time is 90~150min; the alkaline solution for soaking in an alkaline solution is one of NaOH solution, LiOH solution, or Na2CO3 solution, the concentration of the alkaline solution is 5~30wt%, and the soaking time is 5~20min. The surfactant solution is a mixture of surfactant, organic solvent, and pH adjuster. The surfactant is KH-550; the organic solvent is one of N-methylpyrrolidone, N,N-dimethylformamide, and dimethyl sulfoxide; the pH adjuster is glacial acetic acid or dilute hydrochloric acid, wherein the concentration of the dilute hydrochloric acid is 0.3~1wt%, and the mass ratio of surfactant, organic solvent, and pH adjuster is 1:10~100:0.05~0.

2.

8. The method for preparing the BN fiber antioxidant nanocoating according to claim 2, characterized in that, In step (2), the mass ratio of BN fiber used in preparing the pretreated BN fiber to the surfactant in the surfactant solution is 0.002~0.005:0.8~1.2; Soaking time is 20-40 minutes; The drying temperature is 50~80℃.

9. The method for preparing the BN fiber antioxidant nanocoating according to claim 2, characterized in that, In step (3), the mass ratio of BN fiber used in preparing organically modified BN fiber to natural attapulgite used in preparing attapulgite nanosheet dispersion with highly active groups is 0.002~0.005:0.8~1; The reaction was carried out at room temperature for 20–40 minutes. The drying temperature is 50~80℃.

10. The method for preparing the BN fiber antioxidant nanocoating according to claim 2, characterized in that, In step (4), the temperature during high-temperature pyrolysis is 700~900℃ and the time is 90~150min.

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