Modified hexagonal boron nitride-based composite coating as well as preparation method and application thereof

Abstract

The invention provides a modified hexagonal boron nitride-based composite coating as well as a preparation method and application thereof, and belongs to the technical field of protective coatings. The aniline oligomer (AO) is adopted as a surface modifier, stable dispersion of the boron nitride nanosheets in an organic solvent is achieved, and the interfacial compatibility between the BNNSs and the polymer is enhanced through the hydrogen-bond interaction between the terminal amino group of the AO and the amide group in the resin. Due to the synergistic effects, the dispersion stability, the interfacial compatibility and the bonding strength of the BNNSs in the polyamide-imide are greatly improved, so that the wear resistance and the corrosion resistance of the coating are enhanced. Therefore, high barrier, wear resistance and corrosion resistance of the polyamide-imide coating are realized on the basis of the aniline oligomer modified hexagonal boron nitride-based nanofiller.

Description

Technical Field

[0001] The present invention relates to the technical field of protective coatings, and in particular to a modified hexagonal boron nitride-based composite coating, a preparation method thereof, and an application thereof. Background Art

[0002] In modern fields such as chemical industry, energy, aerospace and high-end equipment manufacturing, the problem of material failure under extreme service conditions is becoming increasingly prominent. Among various forms of failure, wear and corrosion are the most common forms of damage to the surface of materials, which not only greatly shorten the service life of the equipment, but also bring potential safety risks and lead to huge economic losses. Therefore, it is crucial to develop effective wear and corrosion protection technologies to extend the service life and reliability of marine and industrial equipment, while further reducing the economic losses, energy consumption and accident risks caused by corrosion and wear. Surface coating technology is considered to be one of the most effective solutions. Due to the complementary and synergistic effects between the polymer matrix and inorganic fillers, organic composite coatings have multifunctionality. Among them, the addition of nanofillers to organic coatings has become a promising method that can significantly improve the tribological properties and long-term corrosion resistance of the coatings.

[0003] In recent years, two-dimensional (2D) materials such as graphene oxide, MXene, and MMT have demonstrated the ability to form physical barriers in coatings, thereby improving the coating's resistance to penetration by corrosive media. In addition, nanofillers can enhance the mechanical properties of coatings. However, the high electrical conductivity of many 2D fillers may induce electrochemical corrosion, thereby accelerating the degradation of the underlying substrate. To address this issue, hexagonal boron nitride nanosheets (BNNSs) have attracted much attention due to their excellent chemical inertness, high thermal stability, self-lubricating properties, and excellent electrical insulation properties. The insulating properties of BNNSs can effectively block corrosion currents, while their layered structure can produce a maze effect, greatly extending the diffusion path of corrosive substances, thereby improving the barrier properties of the coating. In addition, BNNSs also have high mechanical strength and excellent wear resistance, making them promising in applications requiring lubrication and wear protection.

[0004] However, the strong π-π interactions between BNNSs often lead to severe agglomeration, making it difficult to disperse them uniformly in the coating matrix. These agglomerated areas may become corrosion channels, allowing corrosive media to penetrate into the coating, thereby affecting the protective properties of the coating and shortening its service life. Therefore, BNNSs are rarely used directly in coatings and usually require surface functionalization treatment to prevent rapid agglomeration and improve their dispersibility and interfacial compatibility in polymer matrices. Although existing research has made significant progress in improving the individual properties of BNNSs, systematic research on key issues such as the synergistic mechanism of corrosion resistance and wear resistance, the uniformity of filler dispersion, and the interfacial adhesion strength under complex usage conditions remains limited. In addition, challenges related to the inherent surface inertness of BNNSs continue to hinder the compatibility of BNNSs with polymer matrices, so it is necessary to further develop effective functionalization strategies. Summary of the Invention

[0005] The purpose of the present invention is to provide a modified hexagonal boron nitride-based composite coating and its preparation method and application, which can effectively improve the interfacial interaction between BNNSs and polymers.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing a modified hexagonal boron nitride-based composite coating, comprising the following steps:

[0008] Aniline, a surfactant, water and an initiator are mixed to carry out a polymerization reaction to obtain an aniline oligomer;

[0009] The aniline oligomer, the acid solution and the nitrite are mixed to carry out a diazotization reaction, and the obtained product is mixed with a hexagonal boron nitride nanosheet suspension to carry out modification to obtain aniline oligomer-modified hexagonal boron nitride;

[0010] The aniline oligomer modified hexagonal boron nitride is mixed and dispersed with a polyamide-imide resin, an epoxy resin and an organic solvent, and the obtained slurry is sprayed on a substrate and cured to obtain a modified hexagonal boron nitride-based composite coating.

[0011] Preferably, the surfactant is sodium dodecyl sulfate or dodecylbenzenesulfonic acid; the initiator is ammonium persulfate or ferric chloride; and the usage ratio of aniline, surfactant and initiator is 0.25-0.5 g:0.5-0.8 mmol:1-3 mmol.

[0012] Preferably, the polymerization reaction temperature is -5 to 25°C, and the time is 20 to 40 minutes.

[0013] Preferably, the usage ratio of the aniline oligomer to the nitrite is 0.025-0.05 g:0.1-0.3 mmol; the temperature of the diazotization reaction is 0-5° C., and the time is 30-60 min.

[0014] Preferably, the concentration of the hexagonal boron nitride nanosheet suspension is 0.01-0.1 wt %; the mass ratio of the aniline oligomer to the hexagonal boron nitride nanosheets in the hexagonal boron nitride nanosheet suspension is 0.01-0.1:0.01-0.05;

[0015] The modification temperature is 60-80° C. and the modification time is 2-6 hours.

[0016] Preferably, the mass ratio of the polyamide-imide resin, epoxy resin and aniline oligomer modified hexagonal boron nitride is (1-5):(0.1-0.5):(0.001-0.055); the organic solvent is a mixed solvent of N,N-dimethylformamide and N-methyl-2-pyrrolidone; the volume ratio of N,N-dimethylformamide and N-methyl-2-pyrrolidone is 1-3:1.

[0017] Preferably, the solid content of the slurry is 15-20 wt %; the spraying method is multiple spraying, and the total thickness of the coating after curing is 18-22 μm.

[0018] Preferably, the curing includes a first curing and a second curing performed sequentially; the first curing is performed at a temperature of 100 to 130° C. for 1 to 3 hours, and the second curing is performed at a temperature of 150 to 200° C. for 1 to 3 hours.

[0019] The present invention provides a modified hexagonal boron nitride-based composite coating prepared by the preparation method described in the above technical solution.

[0020] The present invention provides the application of the modified hexagonal boron nitride-based composite coating described in the above technical solution in the field of surface protection.

[0021] The present invention prepares a method for preparing a modified hexagonal boron nitride-based composite coating. Using aniline oligomer (AO) as a surface modifier, the stable dispersion of boron nitride nanosheets in an organic solvent is achieved. This enhanced dispersibility is attributed to the strong π-π interaction between the aromatic rings of AO and the hexagonal boron nitride surface. Furthermore, AO is chemically incorporated into the polyamide-imide (PAI) resin matrix through hydrogen bonding between its terminal amine groups (-NH2) and the amide groups in the resin, thereby enhancing the interfacial compatibility between BNNSs and the polymer. These synergistic effects significantly improve the dispersion stability, interfacial compatibility, and bonding strength of BNNSs in the polyamide-imide, thereby enhancing the wear resistance and corrosion resistance of the coating. When a corrosive medium enters the coating, the boron nitride nanosheets modified with the aniline oligomer are well dispersed in the coating. The two-dimensional layered structure of the boron nitride nanosheets can block the penetration of the corrosive medium, prolonging the penetration time of the corrosive medium and improving the barrier performance. Therefore, the present invention provides a novel coating based on aniline oligomer-modified hexagonal boron nitride-based nanofiller to achieve high barrier, wear resistance and corrosion resistance of polyamide-imide coating.

[0022] Furthermore, the aniline oligomer-modified hexagonal boron nitride filler in this invention, which provides high barrier, wear, and corrosion resistance, effectively enhances the mechanical strength of the solid matrix. The tensile strength and microhardness of pure polyamide-imide resin are 86.23 MPa and 27.32 Hv, respectively; the addition of this filler increases these strengths to 122.93 MPa and 40.73 Hv, respectively. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 SEM images of different coatings in Example 1 and Comparative Examples 1 to 3: (a) PAI, (b) h-BN / PAI, (c) BNNSs / PAI, and (d) AO-BN / PAI;

[0024] Figure 2 SEM and TEM images of h-BN, BNNSs, and AO-BN in Example 1, as well as their dispersions, (a–a1) h-BN, (b–b1) BNNSs, (c–c1) AO-BN, and (d–d1) dispersions.

[0025] Figure 3 Mechanical properties of different coatings in Example 1 and Comparative Examples 1 to 3, (a) stress-strain curve, (b) microhardness;

[0026] Figure 4 The friction coefficient and wear rate of different coatings in Example 1 and Comparative Examples 1 to 3 under a load of 10N and a frequency of 5Hz; (a) friction coefficient curve, (b) wear rate and wear life;

[0027] Figure 5 are the low-frequency impedance modulus values ​​of the four coatings in Example 1 and Comparative Examples 1 to 3;

[0028] Figure 6 Polarization test results of the four coatings and Q235 steel substrate in Example 1 and Comparative Examples 1 to 3: (a) polarization curves; (b) corrosion potential and corrosion current density. DETAILED DESCRIPTION

[0029] In the present invention, unless otherwise specified, all raw materials or reagents used are commercially available products well known in the art.

[0030] The present invention provides a method for preparing a modified hexagonal boron nitride-based composite coating, comprising the following steps:

[0031] Aniline, a surfactant, water and an initiator are mixed to carry out a polymerization reaction to obtain an aniline oligomer;

[0032] The aniline oligomer, the acid solution and the nitrite are mixed to carry out a diazotization reaction, and the obtained product is mixed with a hexagonal boron nitride nanosheet suspension to carry out modification to obtain aniline oligomer-modified hexagonal boron nitride;

[0033] The aniline oligomer modified hexagonal boron nitride is mixed and dispersed with a polyamide-imide resin, an epoxy resin and an organic solvent, and the obtained slurry is sprayed on a substrate and cured to obtain a modified hexagonal boron nitride-based composite coating.

[0034] The invention mixes aniline, a surfactant, water and an initiator, and performs polymerization reaction to obtain an aniline oligomer.

[0035] In the present invention, the surfactant is preferably sodium lauryl sulfate or dodecylbenzenesulfonic acid (DBSA).

[0036] The role of surfactant in the present invention is:

[0037] 1. Morphology Control and Template Effect: Micelles or microemulsions are formed in aqueous solution, providing a "soft template" for aniline polymerization, guiding the formation of specific nanostructures (such as nanofibers, nanotubes, or hollow spheres). By adjusting its concentration, the morphology and size of the product can be precisely controlled.

[0038] 2. Improve polymerization efficiency and reaction rate

[0039] During polymerization, the sodium dodecyl sulfate micelle system can shift the oxidation potential of aniline negatively, lower the reaction energy barrier, and increase polymerization efficiency. At the same time, it can reduce side reactions and improve product stability.

[0040] 3. Dispersion and stabilization

[0041] By adsorbing on the surface of polyaniline, electrostatic repulsion and steric hindrance are formed to prevent particle agglomeration.

[0042] In the present invention, the initiator preferably includes ammonium persulfate (APS) or ferric chloride; the usage ratio of the aniline, surfactant and initiator is preferably 0.25-0.5 g:0.5-0.8 mmol:1-3 mmol, more preferably 0.5 g:0.69 mmol:2 mmol.

[0043] In the present invention, the polymerization reaction temperature is preferably -5 to 25°C, more preferably 5°C, and the polymerization reaction time is preferably 20 to 40 minutes, more preferably 30 minutes. The polymerization reaction is carried out under the above temperature conditions to avoid excessively high temperatures that may lead to excessively rapid reaction rates, accelerate initiator decomposition, increase side reactions, and thus reduce product purity and yield. Furthermore, excessively high temperatures may prevent changes in the molecular structure of the aniline oligomer, thereby affecting its performance.

[0044] The present invention preferably dissolves a surfactant and an initiator in water, adds aniline to the resulting surfactant aqueous solution, and mechanically stirs for 30 minutes until a uniform solution is formed. The initiator aqueous solution is then added dropwise under continuous stirring, and the polymerization reaction continues for 30 minutes. The mixture is centrifuged at 8000 rpm for 10 minutes, and the brown-green precipitate is collected, washed at least four times with deionized water, and then dried in a vacuum drying oven at 40°C for 12 hours to obtain aniline oligomer (AO). The present invention does not specifically limit the concentrations of the surfactant aqueous solution and the initiator aqueous solution; they can be adjusted to meet the aforementioned ratio according to actual needs.

[0045] After obtaining the aniline oligomer, the present invention mixes the aniline oligomer, an acid solution and a nitrite to carry out a diazotization reaction, and mixes the obtained product with a hexagonal boron nitride nanosheet suspension to carry out modification to obtain aniline oligomer-modified hexagonal boron nitride.

[0046] In the present invention, the nitrite is preferably sodium nitrite or potassium nitrite, and the nitrite is used in the form of a nitrite aqueous solution; the concentration of the nitrite aqueous solution is preferably 0.14M; the usage ratio of the aniline oligomer to the nitrite is preferably 0.025-0.05g:0.1-0.3mmol, more preferably 0.05g:0.21mmol.

[0047] In the present invention, the acid solution is preferably a hydrochloric acid solution; the concentration of the hydrochloric acid solution is preferably 1 mol / L; and the ratio of the acid solution to the aniline oligomer is preferably 0.8 mL:0.05 g.

[0048] In the present invention, the preparation method of hexagonal boron nitride (h-BN) nanosheets in the hexagonal boron nitride nanosheet suspension is preferably as follows: h-BN powder (2.0 g) is dispersed in 100 mL of 2M NaOH aqueous solution, zirconium oxide balls are added at a mass ratio of 50:1 (balls: h-BN), the mixture is ball-milled at 250 rpm for 24 hours, the resulting slurry is collected, washed with 1M HCl solution (100 mL) to remove residual NaOH, and then repeatedly rinsed with deionized water until the pH value is neutral, and dried at 80°C for 12 hours; then the dried powder is dispersed in an isopropyl alcohol (IPA) aqueous solution with an initial concentration of 0.5 mg / mL, ultrasonically treated for 2 hours, and centrifuged at 8000 rpm for 10 minutes to remove unexfoliated particles, the supernatant is collected, filtered, and dried at 80°C for 12 hours to obtain exfoliated hexagonal boron nitride nanosheets BNNSs.

[0049] In the present invention, the acid solution and the aniline oligomer are preferably added to water and stirred, a nitrite aqueous solution is added dropwise, and the diazotization process is carried out in an ice bath; the BNNSs aqueous suspension that has been ultrasonically treated for 30 minutes is added to the diazotization product and stirred for modification.

[0050] In the present invention, the diazotization reaction temperature is preferably 0°C to 5°C, more preferably 0°C, and the reaction time is preferably 30 to 60 minutes, more preferably 45 minutes. Under acidic conditions, nitrite reacts with aniline oligomers to form diazonium salts. The resulting diazonium salts are relatively active and are favorable for binding to boron nitride nanosheets.

[0051] In the present invention, the dispersant used in the hexagonal boron nitride nanosheet suspension is water; the concentration of the hexagonal boron nitride nanosheet suspension is preferably 0.01-0.1wt%, more preferably 0.01-0.08wt%, and further preferably 0.05wt%; the mass ratio of the aniline oligomer to the hexagonal boron nitride nanosheets in the hexagonal boron nitride nanosheet suspension is preferably 0.01-0.1:0.01-0.05, more preferably 0.05-0.08:0.015-0.035, and further preferably 0.05:0.025.

[0052] In the present invention, the modification temperature is preferably 60 to 80° C., more preferably 70° C., and the modification time is preferably 2 to 6 hours, more preferably 4 hours.

[0053] After the modification reaction is completed, the present invention preferably filters the obtained product to collect the AO-functionalized BNNSs product, washes it with deionized water at least six times, and dries it in a vacuum oven at 40° C. for 12 hours to obtain aniline oligomer-modified hexagonal boron nitride, which is recorded as AO-BN.

[0054] After obtaining the aniline oligomer modified hexagonal boron nitride, the present invention mixes and disperses the aniline oligomer modified hexagonal boron nitride with a polyamide-imide resin, an epoxy resin and an organic solvent, sprays the obtained slurry on a substrate, and obtains a modified hexagonal boron nitride-based composite coating after curing.

[0055] In the present invention, the mass ratio of the polyamide-imide resin, the epoxy resin and the aniline oligomer modified hexagonal boron nitride is (1-5):(0.1-0.5):(0.001-0.055), more preferably (3-5):(0.3-0.5):(0.003-0.055), and further preferably 5:0.5:0.055; the present invention has no special limitation on the amount of the organic solvent, and it can be adjusted according to actual needs to ensure uniform mixing of the materials.

[0056] The present invention has no particular limitation on the type of the epoxy resin. Any epoxy resin known in the art having a curing temperature lower than that of polyamide-imide resin may be used. In an embodiment of the present invention, the epoxy resin is preferably AG80.

[0057] In the present invention, the organic solvent is preferably a mixed solvent of N,N-dimethylformamide and N-methyl-2-pyrrolidone; the volume ratio of N,N-dimethylformamide to N-methyl-2-pyrrolidone is preferably 1 to 3:1, more preferably 1:1.

[0058] The present invention preferably dissolves polyamide-imide resin and epoxy resin in part of organic solvent to obtain a resin system, ultrasonically disperses the AO-BN nanocomposite into the resin system, adds the remaining organic solvent, adjusts the solid content to the required slurry content, and performs high-speed shear dispersion to obtain a slurry.

[0059] The present invention has no special limitation on the type of the substrate, and any corresponding substrate well known in the art can be used. In an embodiment of the present invention, the substrate is preferably a Q235 low carbon steel substrate.

[0060] The present invention preferably sprays the slurry onto a substrate that has been sandblasted and cleaned with anhydrous ethanol, constructs a composite coating by repeating the spraying process, and then air-dries at room temperature and solidifies to obtain a modified hexagonal boron nitride-based composite coating.

[0061] In the present invention, the solid content of the slurry is preferably 15 to 20 wt%, more preferably 16 to 20 wt%.

[0062] The present invention has no special limitation on the spraying process, and spraying can be performed according to methods well known in the art; the spraying method is preferably multiple spraying, and the total thickness of the coating after curing is preferably 18 to 22 μm, more preferably 20 μm.

[0063] In the present invention, the curing preferably includes a first curing and a second curing carried out in sequence; the temperature of the first curing is preferably 100-130°C, more preferably 110-120°C, and the time is preferably 1-3 hours, more preferably 1-2 hours; the temperature of the second curing is preferably 150-200°C, more preferably 160-170°C, and the time is preferably 1-3 hours, more preferably 1-2 hours.

[0064] The present invention provides a modified hexagonal boron nitride-based composite coating prepared by the preparation method described in the above technical solution.

[0065] The present invention provides the application of the modified hexagonal boron nitride-based composite coating described in the above technical solution in the field of surface protection. The present invention has no particular limitation on the application method, and the application can be carried out according to methods well known in the art.

[0066] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited by the specific embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. The experimental methods described in the embodiments of the present invention are all conventional methods unless otherwise specified.

[0067] The following experimental methods and detection methods, unless otherwise specified, are conventional methods; the following reagents and raw materials, unless otherwise specified, are commercially available.

[0068] In the following examples, h-BN particles (particle size 1.5 μm) were purchased from Tianyuan Aerospace Materials Technology Co., Ltd. Aniline (99.5%) and ammonium persulfate (APS, 99.5%) were purchased from Xilong Chemical Co., Ltd. Sodium dodecyl sulfate (SDS, 98.0%) was purchased from Komei Chemical Reagent Co., Ltd., and sodium nitrite (NaNO2, 99.0%) was purchased from Komei Chemical Co., Ltd. Polyamide-imide (PAI) resin was provided by Beijing Huatong Ruichi Materials Technology Co., Ltd. AG80 epoxy resin (EP) was purchased from Huayi Resin Co., Ltd. N,N-dimethylformamide (DMF) was provided by Lianlong Bohua Pharmaceutical Chemical Co., Ltd. N-Methyl-2-pyrrolidone (NMP) was provided by Komei Chemical Reagent Co., Ltd. Hydrogen chloride (HCl) and sodium hydroxide (NaOH) were purchased from Lianlong Bohua Pharmaceutical Chemical Co., Ltd. All reagents were of analytical grade and used without further treatment.

[0069] Example 1

[0070] The coating of this embodiment is prepared from 5g of polyamide-imide resin (PAI), 0.5g of AG-80 epoxy resin, and 0.055g of nano-AO-BN:

[0071] (1) Exfoliation of hexagonal boron nitride: h-BN (boron nitride) powder (2.0 g) was dispersed in 100 mL of 2 M NaOH aqueous solution; zirconia balls were added at a mass ratio of 50:1 (balls: h-BN), and the mixture was ball-milled at 250 rpm for 24 h. The resulting slurry was collected and washed with 1 M HCl solution (100 mL), and then repeatedly rinsed with deionized water until the pH value was neutral. It was then dried at 80 °C for 12 h. The dried powder was dispersed in an isopropyl alcohol (IPA) aqueous solution with an initial concentration of 0.5 mg / mL, ultrasonicated for 2 h, and centrifuged at 8000 rpm for 10 min. The supernatant was collected, filtered, and dried at 80 °C for 12 h to obtain exfoliated BNNSs.

[0072] (2) Synthesis of aniline oligomers: Aniline (0.50 g) was added to 100 mL of sodium dodecyl sulfate (SDS) solution (0.0069 mol / L) and mechanically stirred for 30 min until a homogeneous solution was formed. 10 mL of ammonium persulfate (APS) solution (0.2 mol / L) was added dropwise under continuous stirring. The reaction was continued at 5°C for another 30 min. The resulting product was centrifuged at 8000 rpm for 10 min. The brown-green precipitate was collected, washed four times with deionized water, and dried in a vacuum drying oven at 40°C for 12 h to obtain aniline oligomers (AO).

[0073] (3) Aniline oligomer functionalized BNNSs: 0.8 mL of HCl (1 M) and 0.05 g of AO were added to 50 mL of deionized water and stirred. Then, 1.5 mL of sodium nitrite aqueous solution (0.14 M) was added dropwise. The reactants were placed in an ice bath for 45 min for diazotization. 50 mL of an aqueous suspension containing 0.025 g of BNNSs (concentration 0.05 wt%) that had been ultrasonically treated for 30 min was added to the diazotized product and stirred at 70 °C for 4 h. After the reaction was completed, the AO-functionalized BNNSs product was collected by filtration, thoroughly washed with deionized water six times, and dried in a vacuum oven at 40 °C for 12 h to obtain aniline oligomer modified hexagonal boron nitride nanocomposites (AO-BN).

[0074] (4) 5 g of PAI and 0.5 g of AG80 were dissolved in 10 g of a mixed solvent of N,N-dimethylformamide and N-methyl-2-pyrrolidone with a volume ratio of 1:1 to obtain a resin system. 0.055 g of AO-BN was ultrasonically dispersed into the resin system, and the solid content was adjusted to 20 wt% using the above-mentioned mixed solvent. The mixture was then sheared and dispersed at 1000000 rpm for 1 min. The obtained slurry was sprayed onto a Q235 low-carbon steel substrate that had been sandblasted and cleaned with anhydrous ethanol. The spraying was repeated multiple times. The obtained composite coating sample was air-dried at room temperature, cured at 120 ° C for 1 h, heated to 170 ° C and cured for another 1 h. The thickness of the cured coating was 20 μm, and a modified hexagonal boron nitride-based composite coating was obtained, which was recorded as AO-BN / PAI coating.

[0075] Results: The AO-BN prepared in Example 1 exhibited stable dispersion in the mixed solvent for up to 8 days. The coating exhibited a tensile strength of 122.93 MPa and a microhardness of 40.73 Hv. The resulting coating exhibited a friction coefficient of 0.15 in a ball-on-disk friction test at 10 N and 5 Hz, and a microhardness of 1.46×10 -7 mm 3 ·N -1 ·m -1 The wear rate of the coating was 6.01×10 9 Ω·cm 2 Low frequency impedance value, high corrosion potential (0.2229V) and low corrosion current (5.035×10 -13 A.cm -2 ), higher than 720h neutral salt spray performance.

[0076] Comparative Example 1

[0077] The coating is prepared from 5 g of polyamide-imide, 0.5 g of AG-80 epoxy resin, and 0.055 g of nano-BNNSs:

[0078] Nano-BNNSs were prepared by the following method:

[0079] (1) Preparation of BNNSs by peeling off hexagonal boron nitride: same as in Example 1;

[0080] (2) 5 g of PAI and 0.5 g of AG80 were dissolved in 10 g of a mixed solvent of N,N-dimethylformamide and N-methyl-2-pyrrolidone with a volume ratio of 1:1. 0.055 g of nano-BNNSs was ultrasonically dispersed into the resin system. The solid content was adjusted to 20 wt% using the above mixed solvent. The mixture was then dispersed at a high speed shear rate of 1,000,000 rpm / min for 1 min. The obtained slurry was sprayed onto a Q235 low-carbon steel substrate that had been sandblasted and cleaned with anhydrous ethanol. The spraying was repeated multiple times to construct a composite coating. The coating sample was air-dried at room temperature, cured at 120 °C for 1 h, and further heated to 170 °C for another 1 h. The total coating thickness was 20 μm, and a BNNSs / PAI coating was obtained.

[0081] Results: The BNNSs / PAI coating prepared in Comparative Example 1 exhibited a tensile strength of 116.04 MPa and a microhardness of 37.32 Hv. The resulting coating exhibited a friction coefficient of 0.24 in a ball-on-disc friction test at 10 N and 5 Hz, and a microhardness of 2.35×10 -7 mm 3 ·N -1 ·m -1 The wear rate of the coating was 1.14×10 7 Ω·cm 2 The low frequency impedance value, corrosion potential (-0.2524V) and corrosion current (9.186×10 -11 A.cm -2 ).

[0082] Comparative Example 2

[0083] The coating was prepared from 5 g of polyamide-imide resin, 0.5 g of AG-80 epoxy resin, and 0.055 g of h-BN:

[0084] 5 g of PAI and 0.5 g of AG80 were dissolved in 10 g of a mixed solvent of N,N-dimethylformamide and N-methyl-2-pyrrolidone with a volume ratio of 1:1. 0.055 g of h-BN powder was ultrasonically dispersed into the resin system, and the solid content was adjusted to 20 wt% using the above-mentioned mixed solvent. The mixture was then high-speed sheared and dispersed at 1,000,000 rpm / min for 1 min. The resulting slurry was sprayed onto a Q235 low-carbon steel substrate that had been sandblasted and cleaned with anhydrous ethanol. The spraying process was repeated multiple times to construct a composite coating. The coating sample was air-dried at room temperature, cured at 120°C for 1 h, and further heated to 170°C for another 1 h. The total coating thickness was 20 μm, resulting in an h-BN / PAI coating.

[0085] Results: The h-BN / PAI coating prepared in Comparative Example 2 exhibited a tensile strength of 78.14 MPa and a microhardness of 32.74 Hv. The obtained coating exhibited a friction coefficient of 0.29 in a ball-disc friction test at 10 N and 5 Hz, and a microhardness of 3.96×10 - 7 mm 3 ·N -1 ·m -1 The wear rate of the coating was 5.04×10 6 Ω·cm 2 The low-frequency impedance value, corrosion potential (-0.5195V) and corrosion current (9.79×10 -9 A.cm -2 ).

[0086] Comparative Example 3

[0087] The coating is made of 5g of polyamide-imide resin and 0.5g of AG-80 epoxy resin:

[0088] 5 g of PAI and 0.5 g of AG80 were dissolved in 10 g of a mixed solvent of N,N-dimethylformamide and N-methyl-2-pyrrolidone with a volume ratio of 1:1. The solid content was then adjusted to 20 wt% using the mixed solvent. The mixture was then dispersed at 1,000,000 rpm for 1 min. The resulting slurry was sprayed onto a Q235 low-carbon steel substrate that had been sandblasted and cleaned with anhydrous ethanol. The spraying was repeated multiple times to construct a composite coating. The coating sample was air-dried at room temperature, cured at 120°C for 1 h, and further heated to 170°C for another 1 h. The total coating thickness was 20 μm, resulting in a PAI coating.

[0089] Results: The PAI coating prepared in Comparative Example 3 exhibited a tensile strength of 86.23 MPa and a microhardness of 27.32 Hv. The resulting coating exhibited a friction coefficient of 0.41 in a ball-disc friction test at 10 N and 5 Hz, and a microhardness of 9.65 × 10 -7 mm 3 ·N -1· m -1 The wear rate of the coating was 6.66×10 4 Ω·cm 2 The low frequency impedance value, corrosion potential (-0.5229V) and corrosion current (1.971×10-8 A.cm -2 ).

[0090] Characterization and performance testing

[0091] 1) Figure 1 SEM images of different coatings in Example 1 and Comparative Examples 1 to 3: (a) PAI, (b) h-BN / PAI, (c) BNNSs / PAI, (d) AO-BN / PAI; Figure 1 As shown in (a), the pure PAI coating exhibits a relatively flat and smooth surface, while the composite coating containing fillers exhibits a relatively rough surface. In the h-BN / PAI and BNNSs / PAI coatings, the surface appears rough due to the aggregation of h-BN and BNNSs ( Figure 1 (b) and (c)). In contrast, the AO-BN / PAI coating in Example 1 ( Figure 1 Middle (d) shows a smoother and denser surface, and the AO-BN particles are uniformly embedded in the PAI matrix, indicating that the nanofiller AO-BN is well dispersed in the PAI matrix.

[0092] 2) The morphologies of the h-BN, BNNSs and AO-BN nanocomposites in Example 1 were characterized using SEM and TEM analysis. Figure 2 The SEM and TEM images of h-BN, BNNSs and AO-BN in Example 1, as well as their dispersion, are shown in Figures 1 to 2. (a to a1) are h-BN, (b to b1) are BNNSs, (c to c1) are AO-BN, and (d to d1) are their dispersions. (a, b, c) are SEM images, and (a1, b1, c1) are TEM images. Figure 2 As shown in (a-a1), h-BN exhibits a large size and smooth layered structure. After exfoliation, the average lateral size of the nanosheets is significantly reduced, as shown in Figure 2 As shown in (b-b1). For AO-BN nanocomposites ( Figure 2 (c) shows a flat sphere with a densely packed and clustered structure. Figure 2 The TEM image in (c1) shows that the light-colored flakes represent individual BNNSs, while the black areas represent AO materials. Figure 2 The dispersion stability of AO-BN in a 1:1 volume ratio DMF and NMP mixture is observed in (d) and (d1), where (d) represents the dispersion state at 0 days and (d1) represents the dispersion state at 8 days. The dispersion results show that AO-BN in DMF and NMP is more stable than h-BN and BNNSs, with no obvious sedimentation after 8 days of standing.

[0093] Figure 3The mechanical properties of different coatings in Example 1 and Comparative Examples 1 to 3 are (a) stress-strain curves and (b) microhardness. Figure 3 As shown in (a), the addition of h-BN and BNNSs increased the elongation at break of the PAI coating by 62.99% and 135.70%, respectively. It is worth noting that BNNSs significantly increased the tensile strength of the PAI coating from 86.23 MPa to 116.04 MPa, which can be attributed to its dispersion in the coating and the increase in the density of the composite coating. Similarly, the tensile strength of the AO-BN / PAI composite coating was 122.93 MPa, and the elongation at break was significantly improved by 232.80%, indicating excellent mechanical properties. Regarding microhardness ( Figure 3 In (b), the pure PAI coating exhibits a relatively low microhardness of 27.32 Hv. The hardness of the h-BN / PAI and BNNSs / PAI composites increases to 32.74 Hv and 37.32 Hv, respectively. However, the AO-BN / PAI composite achieves the highest microhardness of 40.73 Hv. This is attributed to the high hardness of the BNNSs, which act as a support, and the strong interfacial interaction between the AO-functionalized BNNSs and the PAI matrix.

[0094] Figure 4 The friction coefficient and wear rate of different coatings in Example 1 and Comparative Examples 1 to 3 under a load of 10N and a frequency of 5Hz are shown; wherein (a) the friction coefficient curve, (b) the wear rate (Wearrate) and the wear life (Lifetime); Figure 4 As shown in (a), the friction coefficients of h-BN / PAI and BNNSs / PAI composite coatings are 0.29 and 0.24, respectively, which are lower than the friction coefficient of pure PAI coating (0.41). It is worth noting that the AO-BN / PAI composite coating with excellent dispersion achieves the lowest friction coefficient of 0.15. Under the same friction conditions, further analysis of wear rate and wear life shows consistent trends. Figure 4 As shown in (b), the pure PAI coating has the highest wear rate of 9.65×10 -7 mm 3 ·N -1 ·m -1 and the shortest wear life of 158.5m. After adding h-BN, the wear rate was significantly reduced to 3.9×10 -7 mm 3 ·N -1 ·m -1 , and the wear life was extended to 264.87 m. The BNNSs / PAI coating showed a wear rate of 2.35×10 -7 mm 3 ·N -1 ·m -1, and the wear life is 353.19 m. It is worth noting that the AO-BN / PAI composite coating exhibits the best tribological performance and achieves the lowest wear rate of 1.46×10 -7 mm 3 ·N -1 ·m -1 and the longest wear life of 518.16 m. The excellent tribological performance of the AO-BN / PAI coating is attributed to the strong interfacial interaction and compatibility between the AO-BN nanofillers and the PAI matrix, which effectively improves the density and load-bearing capacity of the coating.

[0095] Figure 5 The low-frequency impedance modulus values ​​of the four coatings in Example 1 and Comparative Examples 1 to 3. The low-frequency part reflects the corrosion response of the substrate-coating interface. The low-frequency impedance modulus (|Z| f＝0.01Hz ) is a semi-quantitative indicator reflecting the anti-corrosion ability of coatings. Figure 5 The |Z| of different coatings is summarized. f＝0.01Hz |Z| of the PAI coating after immersion in 3.5wt% NaCl solution for 1 day f＝0.01Hz 6.17×10 9 Ω·cm 2 , decreased by about 4 orders of magnitude after immersion for 30 days, which means that the barrier effect is deteriorated. The h-BN / PAI coating showed a higher |Z| when immersed in 3.5wt% NaCl solution for 1 day. f＝0.01Hz (2.87×10 10 Ω·cm 2 ), but after immersion for 30 days, the value dropped to 5.04×10 6 Ω·cm 2 The incorporation of h-BN into the PAI matrix can extend the corrosion path and reduce the permeability of the corrosive medium. A similar trend was observed in the BNNSs / PAI coating, where the initial corrosion resistance improved but gradually decreased over time. In contrast, the |Z| f＝0.01Hz Significantly higher than the other three types of coatings. Especially after immersion for 30 days, |Z| f＝0.01Hz Maintained at 6.01×10 9 Ω·cm 2 The long-term anti-corrosion performance of AO-BN / PAI coating is better than that of the other three coatings.

[0096] Figure 6 Polarization test results of four coatings and Q235 steel substrate in Example 1 and Comparative Examples 1 to 3: (a) polarization curve; (b) corrosion potential and corrosion current density; the corrosion potential of the coating was evaluated by measuring the Tafel curve (E corr ) and corrosion current density (I corr), which demonstrates the relationship between overpotential and logarithmic current density ( Figure 6 After immersion in 3.5wt% NaCl solution for 30 days, the Q235 steel matrix showed E corr =-0.5874V corrosion potential and I corr =1.882×10 -5 A.cm -2 The slope of the curve increases with the increase of corrosion potential, which indicates that the corrosion process is intensified. In contrast, the corrosion potentials of PAI, h-BN / PAI and BNNSs / PAI are -0.5229V, -0.5195V and -0.2524V, respectively, and the corresponding corrosion currents are 1.971×10 -8 A.cm -2 , 9.79×10 -9 A.cm -2 and 9.186×10 - 11 A.cm -2 Nevertheless, the AO-BN / PAI composite coating exhibited a more positive corrosion potential (0.2229 V) and a lower corrosion current (5.035×10 -13 A.cm -2 ), showing good anti-corrosion effect

[0097] In summary, the present invention successfully prepared AO-BN nanosheets through ball milling and surface functionalization, thereby improving the dispersion of BNNSs within the PAI coating and enhancing interfacial interactions. The wear and corrosion resistance of the AO-BN / PAI composite coating are as follows:

[0098] (1) Stable dispersion: Due to the strong π-π* interaction between AO and BNNSs surfaces, AO-BN nanosheets exhibited dispersion stability for more than 8 days in a mixed solvent of DMF and NMP.

[0099] (2) Enhanced tribological properties: The AO-BN / PAI composite coating exhibits excellent tribological properties, with an average coefficient of friction (COF) of approximately 0.15 and a wear rate as low as 1.46×10 -7 mm 3 ·N -1 ·m -1 This is mainly attributed to the low shear resistance provided by the layered structure of BNNSs, which effectively disperses the shear stress during friction. In addition, the modified BNNSs are evenly dispersed in PAI, which improves the hardness and density of the AO-BN / PAI coating.

[0100] (3) Excellent corrosion resistance: AO-BN / PAI coating showed the best corrosion resistance. After immersion for 30 days, the low-frequency impedance modulus of AO-BN / PAI composite coating was the largest, 5 orders of magnitude higher than that of PAI coating. A lower corrosion current density (I corr =5.035×10 -13 A.cm -2 ) and a more corrected corrosion potential value. This is attributed to the uniform dispersion of AO-functionalized BNNSs and the formation of a tortuous physical barrier within the PAI matrix, which effectively hinders the diffusion of electrolytes.

[0101] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing a modified hexagonal boron nitride-based composite coating, characterized in that: The following steps are involved: Aniline, a surfactant, water and an initiator are mixed to carry out a polymerization reaction to obtain an aniline oligomer; The aniline oligomer, the acid solution and the nitrite are mixed to carry out a diazotization reaction, and the obtained product is mixed with a hexagonal boron nitride nanosheet suspension to carry out modification to obtain aniline oligomer-modified hexagonal boron nitride; The aniline oligomer modified hexagonal boron nitride is mixed and dispersed with a polyamide-imide resin, an epoxy resin and an organic solvent, and the obtained slurry is sprayed on a substrate and cured to obtain a modified hexagonal boron nitride-based composite coating.

2. The preparation method according to claim 1, characterized in that The surfactant is sodium dodecyl sulfate or dodecylbenzenesulfonic acid; the initiator is ammonium persulfate or ferric chloride; and the usage ratio of aniline, surfactant and initiator is 0.25-0.5 g:0.5-0.8 mmol:1-3 mmol.

3. The preparation method according to claim 1 or 2, characterized in that The polymerization reaction temperature is -5 to 25° C., and the reaction time is 20 to 40 minutes.

4. The preparation method according to claim 1, characterized in that The dosage ratio of the aniline oligomer to the nitrite is 0.025-0.05 g: 0.1-0.3 mmol; the temperature of the diazotization reaction is 0-5° C., and the time is 30-60 min.

5. The preparation method according to claim 1 or 4, characterized in that The concentration of the hexagonal boron nitride nanosheet suspension is 0.01-0.1 wt %; the mass ratio of the aniline oligomer to the hexagonal boron nitride nanosheets in the hexagonal boron nitride nanosheet suspension is 0.01-0.1:0.01-0.05; The modification temperature is 60-80° C. and the modification time is 2-6 hours.

6. The preparation method according to claim 1, characterized in that The mass ratio of the polyamide-imide resin, epoxy resin and aniline oligomer modified hexagonal boron nitride is (1-5):(0.1-0.5):(0.001-0.055); the organic solvent is a mixed solvent of N,N-dimethylformamide and N-methyl-2-pyrrolidone; the volume ratio of N,N-dimethylformamide and N-methyl-2-pyrrolidone is 1-3:

1.

7. The preparation method according to claim 6, characterized in that The solid content of the slurry is 15-20 wt %; the spraying method is multiple spraying, and the total thickness of the coating after curing is 18-22 μm.

8. The preparation method according to claim 1 or 7, characterized in that The curing includes a first curing and a second curing performed sequentially; the first curing temperature is 100-130° C. and the time is 1-3 hours, and the second curing temperature is 150-200° C. and the time is 1-3 hours.

9. The modified hexagonal boron nitride-based composite coating prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the modified hexagonal boron nitride-based composite coating according to claim 9 in the field of surface protection.

Images