A waterborne epoxy resin grafted polysilazane-based high-temperature-resistant ceramic coating and a preparation method thereof

Abstract

This invention provides a waterborne epoxy resin-grafted polysilazane high-temperature resistant ceramic coating and its preparation method. The preparation method includes: adding vinyl polysilazane and inorganic nanofillers to a waterborne epoxy resin dispersion, then adding a free radical initiator, and carrying out a grafting reaction under an inert atmosphere to obtain a grafted product of waterborne epoxy resin-grafted vinyl polysilazane; adding an amine curing agent to the grafted product, mixing evenly, coating it onto the surface of a substrate, and allowing it to cure at room temperature; subjecting the substrate to a stepped heating ceramicization treatment to obtain a ceramic coating. This invention, by grafting and modifying vinyl polysilazane with waterborne epoxy resin, endows the system with excellent waterborne coating performance. Combined with an amine curing agent, it achieves room temperature curing, and after high-temperature firing, a dense silicon nitride ceramic coating can be obtained. The ceramic coating provided by this invention combines environmental friendliness, ease of application, and excellent high-temperature resistance and corrosion resistance.

Description

Technical Field

[0001] This invention relates to the field of ceramic coating preparation technology, specifically to a waterborne epoxy resin grafted polysilazane alkyl high-temperature resistant ceramic coating and its preparation method. Background Technology

[0002] Silicon nitride (Si3N4) ceramics possess excellent high-temperature resistance, wear resistance, corrosion resistance, and insulation properties, making them promising candidates for applications in aerospace, electronics, machinery, and chemical industries. Vinyl polysilazane, an important precursor for silicon nitride ceramics, contains active groups such as Si-N bonds and C=C double bonds in its molecular structure. After curing and high-temperature pyrolysis, it can be in situ converted into silicon nitride ceramic coatings, making it one of the ideal materials for preparing silicon nitride ceramic coatings.

[0003] However, existing vinyl polysilazane coatings suffer from two major technical challenges: firstly, they are difficult to apply. Vinyl polysilazane is mostly a solvent-based system with high viscosity and poor compatibility with water-based systems, leading to problems such as sagging and poor adhesion during application, making it difficult to achieve large-area, uniform coating; secondly, they require high curing temperatures. Traditional polysilazane coatings need to be cured at temperatures above 200°C or under ultraviolet light, which are demanding and increase construction costs. CN117363154A discloses a light-moisture dual-curing epoxy polysilazane coating that utilizes the ring-opening reaction between the Si-N bonds of polysilazane and epoxy groups to generate a prepolymer, achieving room-temperature curing through light-moisture dual curing. However, this solution uses a solvent-based epoxy resin, failing to achieve water-based curing, and still suffers from difficulties in application and high VOC content. Furthermore, its final product is an organic-inorganic hybrid coating, which does not involve high-temperature sintering for ceramicization, making it impossible to obtain a silicon nitride ceramic coating.

[0004] Therefore, developing a method for preparing a water-based, easily coatable, room-temperature curing silicon nitride ceramic coating that can be obtained after high-temperature treatment has become a pressing technical problem in this field. Summary of the Invention

[0005] In view of the technical problems existing in the background art, the present invention provides a waterborne epoxy resin grafted polysilazane high-temperature resistant ceramic coating and its preparation method, aiming to solve the technical problems of the existing vinyl polysilazane coatings being difficult to apply, having high curing temperature, and being unable to balance ease of application and ceramicization performance.

[0006] In a first aspect, the present invention provides a method for preparing a waterborne epoxy resin grafted polysilazane alkyl high-temperature resistant ceramic coating, comprising the following steps: S1. Mix and stir the water-based epoxy resin with water to obtain an epoxy resin dispersion; S2. Add vinyl polysilazane and inorganic nanofiller to the epoxy resin dispersion and disperse to obtain a mixed dispersion. S3. Add a free radical initiator to the mixed dispersion, and carry out the grafting reaction under an inert atmosphere to obtain the grafted product of waterborne epoxy resin grafted with vinyl polysilazane. S4. Add an amine curing agent to the grafted product, mix well, coat it onto the substrate surface, and let it stand at room temperature to cure into a film. S5. The substrate after film formation is subjected to a stepped heating ceramicization treatment to obtain a ceramic coating. The conditions for the stepped heating ceramicization treatment are: the first stage temperature is 180~220℃, and the holding time is 20~40min; the second stage temperature is 750~850℃, and the holding time is 20~60min.

[0007] Preferably, in step S1, the mass ratio of waterborne epoxy resin to water is 1:(0.8~1.5), and the stirring temperature is 50~70℃; the waterborne epoxy resin includes bisphenol A type waterborne epoxy resin.

[0008] Preferably, in step S2, the dry mass ratio of the waterborne epoxy resin to the vinyl polysilazane is (1.5~3):1.

[0009] Preferably, in step S2, the inorganic nanofiller includes at least one of nano-titanium dioxide, nano-silica, and nano-alumina; the mass ratio of vinyl polysilazane to the inorganic nanofiller is (8~12):1.

[0010] Preferably, in step S3, the free radical initiator includes any one of organic peroxides and azo compounds; the amount of free radical initiator added is 0.01% to 0.1% of the total mass of the aqueous epoxy resin and vinyl polysilazane.

[0011] Preferably, in step S3, the inert atmosphere includes at least one of nitrogen and argon; the grafting reaction temperature is 80~90℃, and the reaction time is 4~6h.

[0012] Preferably, in step S4, the amount of amine curing agent is 15-20% of the dry weight of the waterborne epoxy resin; the amine curing agent includes any one of cashew phenol modified amine curing agent and polyamide curing agent.

[0013] Preferably, in step S4, the time for the film to solidify at room temperature is 24~48h.

[0014] Preferably, in step S5, the stepped heating ceramicization treatment specifically involves: heating from room temperature to 180-220°C at a rate of 1-3°C / min, holding at that temperature for 20-40 min, then heating to 750-850°C at a rate of 4-6°C / min, holding at that temperature for 20-40 min, and then cooling to room temperature with the furnace; the atmosphere for the ceramicization treatment includes at least one of nitrogen and argon.

[0015] In a second aspect, the present invention provides a high-temperature resistant ceramic coating, which is prepared by the preparation method described in the first aspect.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) This invention achieves covalent bonding between waterborne epoxy resin and vinyl polysilazane through molecular grafting reaction, which solves the problems of poor compatibility and phase separation in traditional physical compounding at the molecular level. The resulting grafted product has good film-forming properties, strong coating adhesion, and excellent stability.

[0017] (2) The present invention uses amine curing agents to construct a room temperature curing system, which does not require special high temperature or UV equipment. It can achieve coating curing at room temperature, and the construction process is simple. It is suitable for large and complex workpieces and breaks through the construction scenario limitations of ceramic coating preparation.

[0018] (3) The present invention adopts a stepped heating ceramicization process. The low temperature section realizes the full cross-linking of epoxy resin and avoids coating cracking during the high temperature heating process. The high temperature section realizes the ceramicization conversion of vinyl polysilazane. The high temperature insulation ensures the continuity and density of the ceramic phase and the ceramic yield is high.

[0019] (4) The present invention uses waterborne epoxy resin as the base material, and the whole system is a water-phase dispersion type with low VOC emissions, which is in line with the current green and environmentally friendly development trend of the coating industry.

[0020] (5) The ceramic coating obtained by the present invention has excellent high temperature resistance and corrosion resistance, and is suitable for aerospace, high-end equipment, metallurgy and chemical industry and other fields, with broad industrialization prospects. Detailed Implementation

[0021] The embodiments of the technical solution of the present invention will be described in detail below. These embodiments are only used to illustrate the technical solution of the present invention more clearly, and are therefore merely examples and should not be used to limit the scope of protection of the present invention.

[0022] To address the technical challenges of existing vinyl polysilazane coatings, such as high coating difficulty, high curing temperature, and inability to simultaneously achieve ease of application and ceramization performance, this invention provides a waterborne epoxy resin-grafted polysilazane high-temperature resistant ceramic coating and its preparation method. Specifically, by covalently grafting waterborne epoxy resin with vinyl polysilazane, a precursor system possessing both room-temperature application capability and high-temperature ceramization ability is constructed. Combined with room-temperature curing and stepped-temperature ceramization processes, this achieves efficient and stable conversion of organic coatings into high-performance inorganic ceramic coatings.

[0023] In a first aspect, embodiments of the present invention provide a method for preparing a waterborne epoxy resin-grafted polysilazane alkyl high-temperature resistant ceramic coating, comprising the following steps: S1. Mix and stir the water-based epoxy resin with water to obtain an epoxy resin dispersion; S2. Add vinyl polysilazane and inorganic nanofiller to the epoxy resin dispersion and disperse to obtain a mixed dispersion. S3. Add a free radical initiator to the mixed dispersion, and carry out the grafting reaction under an inert atmosphere to obtain the grafted product of waterborne epoxy resin grafted with vinyl polysilazane. S4. Add an amine curing agent to the grafted product, mix well, coat it onto the substrate surface, and let it stand at room temperature to cure into a film. S5. The substrate after film formation is subjected to a stepped heating ceramicization treatment to obtain a ceramic coating. The conditions for the stepped heating ceramicization treatment are: the first stage temperature is 180~220℃, and the holding time is 20~40min; the second stage temperature is 750~850℃, and the holding time is 20~60min.

[0024] In the technical solution of this invention embodiment, the technical solution mechanism is as follows: (I) The grafting of waterborne epoxy resin and vinyl polysilazane is achieved through free radical grafting polymerization: Under the action of free radical initiator, the vinyl groups on the vinyl polysilazane molecule are activated to generate alkyl free radicals; at the same time, the initiator abstracts hydrogen from the methylene and methine groups on the waterborne epoxy resin molecular chain to form epoxy macromolecular free radicals; the two free radicals undergo addition and chain transfer reactions, so that the vinyl polysilazane is covalently bonded to the main chain of the waterborne epoxy resin to form a graft copolymer. This structure solves the problem of large polarity difference and poor compatibility between epoxy resin and polysilazane at the molecular level. (ii) Curing at room temperature: The grafted product still retains reactive epoxy groups. After adding amine curing agents, the active hydrogen of the amine and the epoxy groups undergo a room temperature nucleophilic ring-opening addition reaction to rapidly form a three-dimensional cross-linked network, which uniformly anchors the polysilazane and inorganic nanofillers grafted on the molecular chain inside the coating. After being coated on the substrate, the system can complete cross-linking and curing at room temperature, providing the coating with excellent adhesion, flexibility and film-forming properties. (III) High-temperature ceramization: In the low-temperature stage (180~220℃), the epoxy resin network is further cross-linked and densified, while the pre-cross-linking of polysilazane is promoted to avoid blistering or cracking of the coating caused by subsequent rapid heating; In the high-temperature stage (750~850℃), vinyl polysilazane undergoes pyrolysis transformation, Si-N bond breaks and recombines, accompanied by dehydrogenation, deamination and other reactions, and finally generates a ceramic phase with Si3N4 as the main crystalline phase in situ. In this process, inorganic nanofillers form an intercalation with the ceramic matrix, which plays a role in strengthening the ceramic skeleton and refining the grains, thereby obtaining a dense, continuous and high-hardness silicon nitride-based ceramic coating.

[0025] Furthermore, in some embodiments, in step S1, the mass ratio of waterborne epoxy resin to water is 1:(0.8~1.5), and the stirring temperature is 50~70°C.

[0026] Furthermore, in some embodiments, in step S1, the waterborne epoxy resin includes a bisphenol A type waterborne epoxy resin.

[0027] In the technical solution of this invention embodiment, the waterborne epoxy resin is preferably a bisphenol A type waterborne epoxy resin, whose molecular structure contains a rigid benzene ring skeleton and a flexible ether bond, which gives the coating a good balance of mechanical strength and toughness.

[0028] Furthermore, in some embodiments, in step S1, the epoxy value of the waterborne epoxy resin is 0.40~0.55, and the solid content is 50~80%.

[0029] Furthermore, in some embodiments, in step S2, the dry mass ratio of the aqueous epoxy resin to the vinyl polysilazane is (1.5~3):1.

[0030] Furthermore, in some embodiments, in step S2, the inorganic nanofiller includes at least one of nano-titanium dioxide, nano-silica, and nano-alumina; the mass ratio of vinyl polysilazane to the inorganic nanofiller is (8~12):1.

[0031] In the technical solution of this invention embodiment, the introduction of inorganic nanofillers can significantly improve the density and mechanical properties of the final ceramic coating, but excessive addition can lead to dispersion difficulties and increased coating defects. The inorganic nanofillers are preferably at least one of nano-titanium dioxide, nano-silica, and nano-alumina. Nano-titanium dioxide can improve the coating's weather resistance and whiteness after ceramization, nano-silica, as an inert filler, can strengthen the ceramic skeleton, and nano-alumina helps improve the hardness and wear resistance of the ceramic layer. The three fillers can be used individually or in combination as needed.

[0032] Furthermore, in some embodiments, in step S3, the free radical initiator includes any one of organic peroxides and azo compounds; the amount of free radical initiator added is 0.01% to 0.1% of the total mass of the aqueous epoxy resin and vinyl polysilazane.

[0033] Furthermore, in some embodiments, in step S3, the inert atmosphere includes at least one of nitrogen and argon; the grafting reaction temperature is 80~90°C, and the reaction time is 4~6h.

[0034] Furthermore, in some embodiments, in step S4, the amount of amine curing agent is 15-20% of the dry weight of the waterborne epoxy resin; the amine curing agent includes any one of cashew phenol modified amine curing agent and polyamide curing agent.

[0035] Furthermore, in some embodiments, in step S4, the time for room temperature standing curing to form a film is 24~48h.

[0036] Furthermore, in some embodiments, in step S5, the stepped heating ceramicization treatment specifically involves: heating from room temperature to 180-220°C at a rate of 1-3°C / min, holding at that temperature for 20-40 min, then heating to 750-850°C at a rate of 4-6°C / min, holding at that temperature for 20-40 min, and then cooling to room temperature with the furnace; the atmosphere for the ceramicization treatment includes at least one of nitrogen and argon.

[0037] In the technical solution of this invention embodiment, the ceramic treatment atmosphere is preferably at least one of nitrogen and argon, wherein nitrogen and argon are used as inert atmospheres to prevent oxidation.

[0038] Secondly, embodiments of the present invention provide a high-temperature resistant ceramic coating, which is prepared by the preparation method described in the first aspect.

[0039] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0040] Example 1 A waterborne epoxy resin-grafted polysilazane alkyl high-temperature resistant ceramic coating, the raw materials and specific process steps of which are as follows: raw material: Waterborne epoxy resin (model E-44, epoxy value 0.44, solid content 60%); vinyl polysilazane (TC-P11, Hangzhou Qingci New Material Technology Co., Ltd.); curing agent (cashew phenol modified amine curing agent, Kramar brand ZY-A1); BPO initiator (benzoyl peroxide); nano titanium dioxide (particle size 20-50nm); deionized water.

[0041] The specific steps of the preparation process are as follows: (1) Mix waterborne epoxy resin and deionized water at a mass ratio of 1:1, heat to 60℃ and stir for 30 min until the system is homogeneous to obtain an epoxy resin aqueous dispersion. (2) Add vinyl polysilazane and nano titanium dioxide to the above epoxy resin aqueous dispersion (the mass ratio of epoxy resin dry mass to vinyl polysilazane is 2:1, and the mass ratio of vinyl polysilazane to nano titanium dioxide is 10:1), and ultrasonically disperse for 20 min to obtain a mixed dispersion. (3) Add 0.05% of BPO (benzoyl peroxide) initiator to the mixed dispersion, heat to 85°C under nitrogen protection, react at a constant temperature for 5 hours, and cool naturally to room temperature after the reaction to obtain the waterborne epoxy resin grafted with vinyl polysilazane. (4) Add cashew phenol modified amine curing agent to the grafted product. The amount of curing agent is 15% of the dry weight of waterborne epoxy resin. Stir at room temperature for 30 min until the system is uniform. Coat the substrate surface to be protected and let it stand at room temperature for 24 h to form a film. (5) The substrate after surface curing and film formation is subjected to step heating ceramicization treatment under nitrogen atmosphere. The heating program is as follows: from 25℃ to 200℃ (epoxy crosslinking stage) at a rate of 2℃ / min, hold for 20min, then heat to 800℃ (polysilazane ceramicization conversion stage) at a rate of 5℃ / min, and hold at 800℃ for 30min (ceramic phase densification stage), and then cool to room temperature with the furnace to obtain ceramic coating.

[0042] Example 2 A waterborne epoxy resin-grafted polysilazane alkyl high-temperature resistant ceramic coating, the raw materials and specific process steps of which are as follows: raw material: Waterborne epoxy resin (model E-51, epoxy value 0.51, solid content 75%); vinyl polysilazane (TC-P11, Hangzhou Qingci New Material Technology Co., Ltd.); polyamide curing agent type 650; BPO initiator (benzoyl peroxide); nano titanium dioxide (particle size 20-50nm); deionized water.

[0043] The specific steps of the preparation process are as follows: (1) Mix waterborne epoxy resin and deionized water at a mass ratio of 1:1, heat to 60℃ and stir for 30 min until the system is homogeneous to obtain an epoxy resin aqueous dispersion. (2) Add vinyl polysilazane and nano titanium dioxide to the above epoxy resin aqueous dispersion (the mass ratio of epoxy resin dry mass to vinyl polysilazane is 2:1, and the mass ratio of vinyl polysilazane to nano titanium dioxide is 10:1), and ultrasonically disperse for 20 min to obtain a mixed dispersion. (3) Add 0.05% of BPO (benzoyl peroxide) initiator to the mixed dispersion, heat to 85°C under nitrogen protection, react at a constant temperature for 5 hours, and cool naturally to room temperature after the reaction to obtain the waterborne epoxy resin grafted with vinyl polysilazane. (4) Add 650 type polyamide curing agent to the grafted product. The amount of curing agent is 20% of the dry weight of waterborne epoxy resin. Stir at room temperature for 30 minutes until the system is uniform. Coat it on the surface of the substrate to be protected and let it stand at room temperature for 24 hours to form a film. (5) The substrate after surface curing and film formation is subjected to step heating ceramicization treatment under nitrogen atmosphere. The heating program is as follows: from 25℃ to 200℃ (epoxy crosslinking stage) at a rate of 2℃ / min, hold for 20min, then heat to 800℃ (polysilazane ceramicization conversion stage) at a rate of 5℃ / min, and hold at 800℃ for 30min (ceramic phase densification stage), and then cool to room temperature with the furnace to obtain ceramic coating.

[0044] Example 3 A waterborne epoxy resin-grafted polysilazane alkyl high-temperature resistant ceramic coating, the raw materials and specific process steps of which are as follows: raw material: Waterborne epoxy resin (model E-44, epoxy value 0.44, solid content 60%); vinyl polysilazane (TC-P11, Hangzhou Qingci New Material Technology Co., Ltd.); curing agent (cashew phenol modified amine curing agent, Kramar brand ZY-A1); AIBN initiator (azobisisobutyronitrile); nano titanium dioxide (particle size 20-50nm); deionized water.

[0045] The specific steps of the preparation process are as follows: (1) Mix waterborne epoxy resin and deionized water at a mass ratio of 1:1, heat to 60℃ and stir for 30 min until the system is homogeneous to obtain an epoxy resin aqueous dispersion. (2) Add vinyl polysilazane and nano titanium dioxide to the above epoxy resin aqueous dispersion (the mass ratio of epoxy resin dry mass to vinyl polysilazane is 2:1, and the mass ratio of vinyl polysilazane to nano titanium dioxide is 10:1), and ultrasonically disperse for 20 min to obtain a mixed dispersion. (3) Add 0.08% of the total mass of waterborne epoxy resin and vinyl polysilazane to the mixed dispersion, heat to 85°C under nitrogen protection, react at a constant temperature for 5 hours, and cool naturally to room temperature after the reaction to obtain waterborne epoxy resin grafted vinyl polysilazane graft product. (4) Add cashew phenol modified amine curing agent to the grafted product. The amount of curing agent is 18% of the dry weight of waterborne epoxy resin. Stir at room temperature for 30 min until the system is uniform. Coat the substrate surface to be protected and let it stand at room temperature for 24 h to form a film. (5) The substrate after surface curing and film formation is subjected to step heating ceramicization treatment under nitrogen atmosphere. The heating program is as follows: from 25℃ to 200℃ (epoxy crosslinking stage) at a rate of 2℃ / min, hold for 20min, then heat to 800℃ (polysilazane ceramicization conversion stage) at a rate of 5℃ / min, and hold at 800℃ for 30min (ceramic phase densification stage), and then cool to room temperature with the furnace to obtain ceramic coating.

[0046] Comparative Example 1 (no grafting reaction performed) Raw materials: waterborne epoxy resin E-44, vinyl polysilazane, cashew phenol modified amine curing agent, nano titanium dioxide, deionized water; the specifications and models are the same as in Example 1.

[0047] The preparation process, specifically the following steps: (1) Mix waterborne epoxy resin and deionized water at a ratio of 1:1 and stir at 60°C for 30 min to obtain an epoxy resin aqueous dispersion. (2) Add vinyl polysilazane and nano titanium dioxide to the above dispersion (the mass ratio of epoxy resin dry weight to vinyl polysilazane is 2:1, and the mass ratio of vinyl polysilazane to nano titanium dioxide is 10:1), and ultrasonically disperse for 20 min to obtain a mixed dispersion (no initiator was added and no grafting reaction was carried out). (3) Add cashew phenol modified amine curing agent accounting for 15% of the total mass of waterborne epoxy resin and vinyl polysilazane, stir at room temperature for 30 min and then coat it onto the substrate, and let it stand at room temperature for 24 h to cure and form a film. (4) The substrate after surface curing is subjected to step heating ceramic treatment under nitrogen atmosphere. The heating program is as follows: from 25℃ to 200℃ at a rate of 2℃ / min, hold for 20min, then heat to 800℃ at a rate of 5℃ / min, hold at 800℃ for 30min, and then cool to room temperature with the furnace to obtain ceramic coating.

[0048] Comparative Example 2 (without nano titanium dioxide) The difference between this comparative example and Example 1 is that in step (2), no nano-titanium dioxide was added, while the parameters of the other steps are the same as those in Example 1.

[0049] Comparative Example 3 (Changing the ceramicization heating program) Compared with Example 1, the difference in this comparative example is that in step (5), the step heating is cancelled, and the temperature is directly increased from 25°C to 800°C at 5°C / min, and held for 30min (without the 200°C epoxy crosslinking stage).

[0050] Performance testing 1. Grafting rate test Test method: Quantitative analysis of Si-N bond characteristic peaks (1020 cm⁻¹) using Fourier transform infrared spectroscopy (FTIR). -1 ) and epoxy groups (915cm) -1 The peak area ratio of ).

[0051] Test results showed that the grafting rates of Examples 1-3 were 82%, 78%, and 80%, respectively.

[0052] 2. Coating performance test The ceramic yield was tested using a TG-DSC thermogravimetric analyzer; temperature resistance was tested by a 1500℃ thermal shock test in a muffle furnace; and salt spray resistance was tested according to GB / T 1771-2021 standard. The test results are shown in Table 1 below.

[0053] Table 1

[0054] Table 1 shows that Examples 1-3 of this invention significantly improved the overall performance of the coating by grafting vinyl polysilazane with water-based epoxy resin, combining it with polyamide curing agents to achieve room temperature curing, and using a stepped temperature-increasing ceramization process. All examples achieved high grafting rates, high ceramic yields, and excellent temperature and salt spray resistance. This indicates that the grafting reaction system has good compatibility with different types of epoxy resins and curing agents. It can be observed that the ceramic yield in each example is positively correlated with the grafting rate, indicating that in the high-temperature ceramization stage after covalent grafting, the epoxy phase and the polysilazane phase achieve synergistic thermal decomposition, and the organic components are efficiently converted into the inorganic ceramic phase, reducing the loss of small molecules through volatilization. The temperature and salt spray resistance results show that the homogeneous system and dense ceramic phase structure resulting from the high grafting rate endow the coating with excellent high-temperature stability and corrosion resistance. The uniform dispersion of nano-titanium dioxide further enhances the density of the ceramic coating, effectively preventing the penetration of corrosive media and the damage caused by high-temperature thermal stress.

[0055] Comparative Example 1 did not undergo grafting reaction, and the grafting rate was 0. The ceramic yield decreased significantly, and the temperature resistance and salt spray resistance were greatly reduced. This is because the physical compounding of waterborne epoxy resin and vinyl polysilazane resulted in severe phase separation. At high temperatures, the two phases decomposed independently, and a large amount of organic components were ineffectively volatilized. Furthermore, after ceramization, a loose and porous ceramic phase was formed, which could not resist high-temperature thermal stress and the penetration of corrosive media.

[0056] In Comparative Example 2, without the addition of nano-titanium dioxide, the ceramic yield and resistance to temperature and salt spray were reduced to some extent. Although nano-titanium dioxide does not participate in the grafting reaction, as a ceramic phase, it can further improve the density of the ceramic coating and reduce the formation of pores during the high-temperature ceramization stage.

[0057] In Comparative Example 3, directly heating to 800℃ resulted in a decrease in ceramic yield and the appearance of network cracks in the coating. This is because room temperature curing only completes the initial cross-linking of the epoxy resin and the curing agent, not the complete cross-linking of the epoxy system. Directly heating to 800℃ causes the residual active groups of the insufficiently cross-linked epoxy phase to decompose violently at high temperatures. At the same time, the sudden increase in thermal stress triggers coating cracking, ultimately leading to incomplete ceramicization, decreased ceramic yield, and deterioration of overall performance.

[0058] It should be noted that the present invention is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments that have the same structure and perform the same effects as the technical concept within the scope of the present invention are included within the scope of the present invention. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of the present invention, are also included within the scope of the present invention.

Claims

1. A method for preparing a waterborne epoxy resin grafted polysilazane alkyl high-temperature resistant ceramic coating, characterized in that, Includes the following steps: S1. Mix and stir the water-based epoxy resin with water to obtain an epoxy resin dispersion; S2. Add vinyl polysilazane and inorganic nanofiller to the epoxy resin dispersion and disperse to obtain a mixed dispersion. S3. Add a free radical initiator to the mixed dispersion, and carry out a grafting reaction under an inert atmosphere to obtain a grafted product of waterborne epoxy resin grafted with vinyl polysilazane. S4. Add an amine curing agent to the grafted product, mix well, coat it onto the substrate surface, and let it stand at room temperature to cure into a film. S5. The substrate after film formation is subjected to a stepped heating ceramicization treatment to obtain a ceramic coating. The conditions for the stepped heating ceramicization treatment are as follows: the first stage temperature is 180~220℃, and the holding time is 20~40min; the second stage temperature is 750~850℃, and the holding time is 20~60min.

2. The method for preparing a waterborne epoxy resin grafted polysilazane alkyl high-temperature resistant ceramic coating according to claim 1, characterized in that, In step S1, the mass ratio of the waterborne epoxy resin to water is 1:(0.8~1.5); the stirring temperature is 50~70℃. And / or, the waterborne epoxy resin includes bisphenol A type waterborne epoxy resin.

3. The method for preparing a waterborne epoxy resin grafted polysilazane alkyl high-temperature resistant ceramic coating according to claim 1, characterized in that, In step S2, the dry mass ratio of the waterborne epoxy resin to the vinyl polysilazane is (1.5~3):

1.

4. The method for preparing a waterborne epoxy resin grafted polysilazane alkyl high-temperature resistant ceramic coating according to claim 1, characterized in that, In step S2, the inorganic nanofiller includes at least one of nano titanium dioxide, nano silicon dioxide, and nano aluminum oxide. And / or, the mass ratio of the vinyl polysilazane to the inorganic nanofiller is (8~12):

1.

5. The method for preparing a waterborne epoxy resin grafted polysilazane alkyl high-temperature resistant ceramic coating according to claim 1, characterized in that, In step S3, the free radical initiator includes any one of organic peroxides and azo compounds; And / or, the amount of the free radical initiator added is 0.01% to 0.1% of the total mass of the aqueous epoxy resin and the vinyl polysilazane.

6. The method for preparing a waterborne epoxy resin grafted polysilazane alkyl high-temperature resistant ceramic coating according to claim 1, characterized in that, In step S3, the inert atmosphere includes at least one of nitrogen and argon. And / or, the grafting reaction is carried out at a temperature of 80-90°C for a reaction time of 4-6 hours.

7. The method for preparing a waterborne epoxy resin grafted polysilazane alkyl high-temperature resistant ceramic coating according to claim 1, characterized in that, In step S4, the amount of the amine curing agent is 15-20% of the dry weight of the waterborne epoxy resin; And / or, the amine curing agent includes any one of cashew phenol-modified amine curing agents and polyamide curing agents.

8. The method for preparing a waterborne epoxy resin grafted polysilazane alkyl high-temperature resistant ceramic coating according to claim 1, characterized in that, In step S4, the time for the film to be cured at room temperature is 24~48h.

9. The method for preparing a waterborne epoxy resin grafted polysilazane alkyl high-temperature resistant ceramic coating according to claim 1, characterized in that, In step S5, the stepped heating ceramicization treatment specifically involves: heating from room temperature to 180-220°C at a rate of 1-3°C / min, holding at that temperature for 20-40 minutes, then heating to 750-850°C at a rate of 4-6°C / min, holding at that temperature for 20-40 minutes, and then cooling to room temperature with the furnace. And / or, the atmosphere for the ceramicizing treatment includes at least one of nitrogen and argon.

10. A waterborne epoxy resin-grafted polysilazane alkyl high-temperature resistant ceramic coating, characterized in that, It is prepared by any one of the preparation methods described in claims 1 to 9.

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