Inorganic high-temperature-resistant heat-insulating coating as well as preparation method and application thereof

Abstract

The invention discloses an inorganic high-temperature-resistant heat-insulating coating and a preparation method and application thereof, and the inorganic high-temperature-resistant heat-insulating coating comprises the following raw materials in parts by mass: 45-55 parts of a composite inorganic film-forming system, 25-30 parts of gradient composite heat-insulating filler, 2-4 parts of a functional aid and 15-18 parts of deionized water, wherein the composite inorganic film forming system is composed of a ternary inorganic binder and a core-shell structure nano reinforcing agent modified by a bifunctional silane coupling agent; the gradient composite heat insulation filler is composed of lithium aluminosilicate glass beads, silicon dioxide aerogel and fumed silica; the functional additive is composed of a high-temperature dispersing agent, a thixotropic agent and a high-temperature coalescing agent. The coating can be cured by stages to obtain a Deou high-temperature-resistant heat-insulating coating, and the coating has flexibility, cracking resistance and heat-insulating performance.

Description

Technical Field

[0001] This invention belongs to the field of inorganic coating technology, specifically relating to an inorganic high-temperature resistant heat-insulating coating, its preparation method, and its application. Background Technology

[0002] In fields such as high-temperature protection of industrial equipment and protection of thermal structural components in aerospace, inorganic high-temperature resistant thermal insulation coatings have gradually replaced traditional organic thermal insulation materials as the mainstream choice due to their excellent high-temperature resistance, chemical stability and environmental friendliness. At present, most inorganic high-temperature resistant thermal insulation coatings commonly used in the industry are prepared by using single or binary inorganic binders (such as silica sol and alumina sol) as the film-forming base, combined with thermal insulation fillers such as hollow microspheres and silica powder.

[0003] However, existing inorganic high-temperature heat-insulating coatings still have significant shortcomings in addressing the issues of "flexibility and crack resistance." The inorganic film formed after the inorganic binder cures has poor toughness and high brittleness, and the heat-insulating fillers added to the system are mostly rigid particles, resulting in weak interfacial bonding. Once the coating cures, the overall flexibility of the coating is significantly insufficient. Simultaneously, the difference in thermal expansion coefficients between the coating and the metal substrate is substantial. During high-temperature service or thermal cycling, microcracks easily form within the coating due to thermal stress concentration. With prolonged use, these microcracks gradually expand, leading to coating cracking and detachment, ultimately resulting in the loss of heat insulation protection. Even though some technologies attempt to improve toughness by adding nanoparticles, nanoparticles tend to agglomerate and are difficult to disperse uniformly in the coating system, failing to form an effective "toughening network." This only slightly improves the toughness at room temperature; the coating is still prone to cracking due to internal stress release under high-temperature conditions, failing to meet the long-term high-temperature resistance and thermal cycling crack resistance requirements of industrial equipment and aerospace components. Summary of the Invention

[0004] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of the invention, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0005] In view of the problems existing in the above and / or prior art, the present invention is proposed.

[0006] Therefore, the purpose of this invention is to overcome the shortcomings of the prior art and provide an inorganic high-temperature resistant heat-insulating coating.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution: comprising, by mass parts of raw materials, 45-55 parts of composite inorganic film-forming system, 25-30 parts of gradient composite thermal insulation filler, 2-4 parts of functional additives, and 15-18 parts of deionized water; The composite inorganic film-forming system is composed of a ternary inorganic binder and a core-shell structured nano-reinforcing agent modified with a bifunctional silane coupling agent. The gradient composite thermal insulation filler is composed of lithium aluminum silicate glass microspheres, silica aerogel, and fumed silica. The functional additives consist of high-temperature dispersants, thixotropic agents, and high-temperature film-forming aids.

[0008] As a preferred embodiment of the inorganic high-temperature resistant heat-insulating coating of the present invention, the ternary inorganic binder is composed of silica sol, aluminum sol, and cerium oxide sol; the particle size of the silica sol is 8-15 nm, the particle size of the aluminum sol is 15-25 nm, and the particle size of the cerium oxide sol is 5-10 nm; the mass ratio of the ternary inorganic binder to the core-shell structured nano-reinforcing agent modified by the bifunctional silane coupling agent is 7-9:1.

[0009] As a preferred embodiment of the inorganic high-temperature heat-insulating coating of the present invention, the core-shell structure nano-reinforcing agent modified by the bifunctional silane coupling agent is composed of a nano-zirconia fiber core and a graphene shell, wherein the diameter of the nano-zirconia fiber is 60-80nm, the length is 6-8μm, and the thickness of the graphene shell is 5-10nm.

[0010] As a preferred embodiment of the inorganic high-temperature heat-insulating coating of the present invention, the amount of the bifunctional silane coupling agent is 2-2.5 wt% of the mass of the core-shell structure.

[0011] In a preferred embodiment of the inorganic high-temperature resistant thermal insulation coating of the present invention, the coefficient of thermal expansion of the lithium aluminum silicate glass microspheres in the gradient composite thermal insulation filler is ≤1.5×10⁻⁶. -6 / ℃, particle size is 80-120μm, silica aerogel particle size is 20-50μm, porosity ≥95%.

[0012] As a preferred embodiment of the inorganic high-temperature resistant heat-insulating coating of the present invention, the high-temperature dispersant is a polycarboxylate ammonium salt, and the molecular weight of the polycarboxylate ammonium salt is 8000-10000.

[0013] In a preferred embodiment of the inorganic high-temperature heat-insulating coating of the present invention, the amount of the high-temperature dispersant added is 4.81-5.36 wt% compared to the gradient composite heat-insulating filler.

[0014] As a preferred embodiment of the inorganic high-temperature heat-insulating coating of the present invention, the thixotropic agent is organically modified bentonite, and the particle size of the organically modified bentonite is 1-5 μm.

[0015] Another objective of this invention is to overcome the shortcomings of the prior art and provide a method for preparing an inorganic high-temperature resistant heat-insulating coating.

[0016] As a preferred embodiment of the preparation method of the inorganic high-temperature resistant heat-insulating coating of the present invention, it includes: Zirconia nanofibers, glucose, and nitric acid were dissolved in deionized water at a mass ratio of 9-11:5:1. The pH of the solution was adjusted to 2.0-2.2. The resulting mixture was reacted at 185-190℃ for 6.5-7 hours. After cooling to room temperature, the mixture was centrifuged to obtain a zirconia fiber-graphene core-shell structure. Zirconia fiber-graphene core-shell structure is mixed with a bifunctional silane coupling agent solution of 8-9 wt%, dispersed for 45-60 min, and then centrifuged and dried to obtain a bifunctional silane coupling agent modified core-shell structure nano-reinforcing agent; silica sol, aluminum sol and cerium oxide sol are mixed and stirred evenly in a mass ratio of 4-6:3:2 to obtain a ternary inorganic binder. By mass, 39.4-49.5 parts of ternary inorganic binder and 4.5-6.9 parts of core-shell structured nano-reinforcing agent modified with bifunctional silane coupling agent are stirred evenly to obtain a composite inorganic film-forming system. By mass, 5-7 parts of fumed silica, 5-6 parts of deionized water, and 0.6-0.8 parts of high-temperature dispersant are milled at 2500-3000 r / min for 10-15 min to complete the bottom layer dispersion. Then, 8-10 parts of silica aerogel, 10-12 parts of deionized water, and 0.6-0.8 parts of high-temperature dispersant are added and milled at 1500-2000 r / min for 25-30 min to complete the middle layer dispersion. Then, 11-14 parts of lithium aluminum silicate glass microspheres are added and physically stirred at 200-250 r / min for 10-15 min to complete the surface layer dispersion, thus obtaining a gradient dispersion. By mass fraction, the composite inorganic film-forming system and gradient dispersion are mixed, and then 0.6-0.8 parts of thixotropic agent and 0.6-0.8 parts of high-temperature film-forming aid are added. The mixture is dispersed at a low speed of 200-250 r / min for 15-20 min, dispersed at a medium speed of 400-450 r / min for 15-20 min, and homogenized at a high speed of 600-650 r / min for 15-20 min. After filtration, the coating is obtained.

[0017] Another objective of this invention is to overcome the shortcomings of the prior art and provide a method for preparing an inorganic high-temperature resistant heat-insulating coating.

[0018] To solve the above-mentioned technical problems, the present invention provides the following technical solution: including, The inorganic high-temperature heat-insulating coating is applied to the surface of a metal substrate and then subjected to drying at 20-25℃ for 2-3 hours, curing at 60-80℃ with forced air for 1-2 hours, curing at 200-220℃ for 1-2 hours, and curing at 400-450℃ for 30-40 minutes to obtain the high-temperature heat-insulating coating.

[0019] Beneficial effects of this invention: (1) The present invention achieves phased optimization of the film formation process through a ternary compound system. However, the existing technology cannot simultaneously achieve low-temperature film formation and high-temperature stability.

[0020] (2) In the prior art, the nano-reinforcing phase is mostly randomly dispersed particulate material, while the core-shell fiber structure of the present invention can be oriented to form a three-dimensional toughened network.

[0021] (3) Traditional processes use a uniform mixing method, while the gradient dispersion process of the present invention constructs a density gradient structure with continuous transition characteristics by controlling the particle size and dispersion sequence of the filler.

[0022] (4) Finally, through the synergistic effect of the composite inorganic film-forming system and the gradient composite thermal insulation filler, a coating structure with a continuous density gradient is formed, which significantly improves the flexibility and crack resistance of the coating, while the thermal insulation performance is also optimized, and a coating with flexibility, crack resistance and thermal insulation performance is prepared. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a flowchart illustrating the preparation process of the inorganic high-temperature heat-insulating coating of Embodiment 1 of the present invention. Detailed Implementation

[0025] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0026] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0027] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0028] The thixotropic agent used in this invention is organically modified bentonite, purchased from Shanghai Chenqi Chemical Technology Co., Ltd.

[0029] In this invention, the deionized water is ultrapure water with a resistivity ≥18.2 MΩ·cm.

[0030] This invention refers to GB / T 1731-2020 to test the flexural strength of the coating at 25°C.

[0031] This invention refers to GB / T 5210-2006 to test the coating adhesion at 25°C and the adhesion after burning at 800°C for 3 hours.

[0032] This invention refers to GB / T 2794-2013 to test the thixotropic index of coatings. The ratio of the viscosity of the coating at low speed (6 rpm) and high speed (60 rpm) is used as the thixotropic index.

[0033] The test method for the thermal insulation performance of the coating of the present invention is as follows: the temperature of the inner side of the coating is tested under a heat source condition of 800℃.

[0034] The test method for the crack resistance of the coating of the present invention is as follows: 5 cycles from 800℃ to 25℃, and the surface morphology of the coating is observed.

[0035] Example 1 This embodiment provides a method for preparing an inorganic high-temperature resistant heat-insulating coating, specifically as follows: (1) Preparation of core-shell structured nano-reinforcing agents modified with bifunctional silane coupling agents: Zirconia nanofibers, glucose, and nitric acid were dissolved in deionized water at a mass ratio of 10:5:1. The pH was adjusted to 2.0. The resulting mixture was heated to 185°C at a rate of 5°C / min and reacted at a constant temperature for 6.5 h. After cooling to room temperature, the mixture was centrifuged at 8000 r / min for 10 min to obtain a zirconia fiber-graphene core-shell structure. Among them, the nano-zirconia fibers have a diameter of 65nm and a length of 6.5μm; The core-shell structure was mixed with an ethanol-water solution of 8wt% γ-aminopropyltriethoxysilane, ultrasonically dispersed at 300W for 45min, and then vacuum dried at 90℃ for 2h to obtain a core-shell structure nano-reinforcing agent modified with a bifunctional silane coupling agent. (2) Preparation of composite inorganic film-forming system: Silica sol, aluminum sol and cerium oxide sol are mixed in a mass ratio of 5:3:2 and stirred at 400 r / min for 30 min to obtain a ternary inorganic binder; By mass, 42.35 parts of ternary inorganic binder and 5.65 parts of the reinforcing agent prepared in step (1) were stirred at 450 r / min for 1.5 h at 50 °C to obtain a composite inorganic film-forming system. The particle size of the silica sol is 10 nm, the particle size of the aluminum sol is 18 nm, the particle size of the cerium oxide sol is 7 nm, and the mass ratio of the ternary inorganic binder to the reinforcing agent is 7.5:1. (3) Preparation of gradient dispersion: By mass, 5.78 parts of fumed silica, 5.33 parts of deionized water, and 0.625 parts of maleic anhydride-acrylic acid copolyammonium salt (high-temperature dispersant) were added to a sand mill (zirconium bead particle size 0.5 mm) and milled at 2500 r / min for 15 min to complete the bottom layer dispersion. Then, 8.67 parts of silica aerogel, 0.625 parts of maleic anhydride-acrylic acid copolyammonium salt (high-temperature dispersant), and 10.67 parts of deionized water were added. The speed was reduced to 1500 r / min and milling continued for 30 min to complete the middle layer dispersion. Then, 11.56 parts of lithium aluminum silicate glass microspheres were added and physically stirred at 200 r / min for 10 min to complete the surface layer dispersion, thus obtaining the gradient dispersion. The mass ratio of lithium aluminum silicate glass microspheres, silica aerogel, and fumed silica is 4:3:2; the silica aerogel has a particle size of 30 μm and a porosity of 95.5%; the lithium aluminum silicate glass microspheres have a particle size of 90 μm and a coefficient of thermal expansion of 1.3 × 10⁻⁶. -6 / ℃; The amount of high-temperature dispersant added compared to gradient dispersion is 4.81wt% to obtain a coating with a suitable thixotropic index, and the molecular weight of the high-temperature dispersant is 8500. (4) Coating mixing and filtration: Mix the composite inorganic film-forming system obtained in step (2) and the gradient dispersion obtained in step (3), add 0.625 parts of organic modified bentonite (thixotropic agent) and 0.625 parts of silica sol (high temperature film-forming aid), disperse at a low speed of 250 r / min for 15 min, disperse at a medium speed of 450 r / min for 15 min, homogenize at a high speed of 650 r / min for 15 min, filter through a 100-mesh nylon filter to remove impurity particles, and obtain the coating. The mass ratio of the high-temperature dispersant in step (3), the thixotropic agent in step (4), and the high-temperature film-forming aid in step (4) is 2:1:1. The filtration pressure of the nylon filter is 0.2 MPa, and the particle size of the organic modified bentonite is 2 μm.

[0036] Figure 1This is a flowchart illustrating the preparation process of the inorganic high-temperature heat-insulating coating in Example 1.

[0037] The amount of core-shell coupling agent modified in step (1) of Example 1 was calculated by thermogravimetric analysis using the weight loss rate at 500℃. The modification amount of the bifunctional silane coupling agent relative to the mass of the core-shell structure was found to be 2.1%. The thickness of the graphene shell in the core-shell structure was found to be 7 nm by TEM testing.

[0038] The particle size distribution of fumed silica in step (3) of Example 3 was monitored by a laser particle size analyzer. After the bottom layer dispersion was completed, the particle size distribution of silica aerogel was D50=4.5μm≤5μm, which met the requirements. After the middle layer dispersion was completed, the particle size distribution of silica aerogel was D50=25μm.

[0039] Example 2 This embodiment uses the coating obtained in Example 1 to prepare a high-temperature resistant heat-insulating coating, as detailed below: The coating prepared in Example 1 was applied to the surface of an aluminum alloy and cured in four stages: the first stage was drying at 25°C for 2 hours, the second stage was curing at 80°C with forced air for 1 hour, the third stage was curing at 200°C for 1 hour, and the fourth stage was curing at 400°C for 30 minutes, thus obtaining the high-temperature heat-insulating coating of this example.

[0040] The coating thickness of Example 2 was approximately 1 mm, as measured at multiple points using a micrometer.

[0041] Example 3 This embodiment provides a method for preparing an inorganic high-temperature resistant heat-insulating coating, specifically as follows: (1) Preparation of core-shell structured nano-reinforcing agents modified with bifunctional silane coupling agents: Zirconia nanofibers, glucose, and nitric acid were dissolved in deionized water at a mass ratio of 10:5:1. The pH was adjusted to 2.2. The resulting mixture was heated to 190°C at a rate of 5°C / min and reacted at a constant temperature for 7 hours. After cooling to room temperature, the mixture was centrifuged at 8000 r / min for 10 minutes to obtain a zirconia fiber-graphene core-shell structure. Among them, the nano-zirconia fibers have a diameter of 70nm and a length of 7μm; The core-shell structure was mixed with an ethanol-water solution of 8wt% γ-aminopropyltriethoxysilane, ultrasonically dispersed at 300W for 45min, and then vacuum dried at 90℃ for 2h to obtain a core-shell structure nano-reinforcing agent modified with a bifunctional silane coupling agent. (2) Preparation of composite inorganic film-forming system: Silica sol, aluminum sol and cerium oxide sol are mixed in a mass ratio of 5:3:2 and stirred at 400 r / min for 30 min to obtain a ternary inorganic binder; By mass, 44.44 parts of ternary inorganic binder and 5.56 parts of the reinforcing agent prepared in step (1) were stirred at 450 r / min for 1.5 h at 50 °C to obtain a composite inorganic film-forming system. Among them, the particle size of silica sol is 12nm, the particle size of aluminum sol is 20nm, the particle size of cerium oxide sol is 8nm, and the mass ratio of ternary inorganic binder to reinforcing agent is 8:1. (3) Preparation of gradient dispersion: By mass fraction, 6.22 parts of fumed silica, 5.67 parts of deionized water, and 0.75 parts of maleic anhydride-acrylic acid copolyammonium salt (high-temperature dispersant) were added to a sand mill (zirconium bead particle size 0.5 mm) and milled at 2500 r / min for 30 min to complete the bottom layer dispersion. Then, 9.33 parts of silica aerogel, 0.75 parts of maleic anhydride-acrylic acid copolyammonium salt (high-temperature dispersant), and 11.33 parts of deionized water were added. The speed was reduced to 1500 r / min and milling continued for 15 min to complete the middle layer dispersion. Then, 12.44 parts of lithium aluminum silicate glass microspheres were added and physically stirred at 200 r / min for 10 min to complete the surface layer dispersion, thus obtaining the gradient dispersion. The mass ratio of lithium aluminum silicate glass microspheres, silica aerogel, and fumed silica is 4:3:2; the silica aerogel has a particle size of 35 μm and a porosity of 96%; the lithium aluminum silicate glass microspheres have a particle size of 100 μm and a coefficient of thermal expansion of 1.2 × 10⁻⁶. -6 / ℃; The amount of high-temperature dispersant added compared to gradient dispersion is 5.36wt% to obtain a coating with a suitable thixotropic index, and the molecular weight of the high-temperature dispersant is 9000. (4) Coating mixing and filtration: Mix the composite inorganic film-forming system obtained in step (2) and the gradient dispersion obtained in step (3), add 0.75 parts of organic modified bentonite (thixotropic agent) and 0.75 parts of silica sol (high temperature film-forming aid), disperse at a low speed of 250 r / min for 15 min, disperse at a medium speed of 450 r / min for 15 min, homogenize at a high speed of 650 r / min for 15 min, and filter through a 100-mesh nylon filter to remove impurity particles to obtain the coating. The mass ratio of the high-temperature dispersant in step (3), the thixotropic agent in step (4), and the high-temperature film-forming aid in step (4) is 2:1:1, the filtration pressure of the nylon filter is 0.2 MPa, and the particle size of the organic modified bentonite is 3 μm.

[0042] The amount of core-shell coupling agent modified in step (1) of Example 1 was calculated by thermogravimetric analysis using the weight loss rate at 500℃. The modification amount of the bifunctional silane coupling agent relative to the mass of the core-shell structure was found to be 2.2%. The thickness of the graphene shell in the core-shell structure was found to be 8 nm by TEM testing.

[0043] The particle size distribution of the reinforcing agent in the composite inorganic film-forming system of Example 1 (2) was monitored by a laser particle size analyzer, with a particle size distribution D50=75nm and no agglomeration. After the bottom layer dispersion was completed, the particle size distribution of the fumed silica was D50=4.2μm≤5μm, which met the requirements. After the middle layer dispersion was completed, the particle size distribution of the silica aerogel was D50=28μm.

[0044] Example 4 This embodiment uses the coating obtained in Example 3 to prepare a high-temperature resistant heat-insulating coating, as detailed below: The coating prepared in Example 3 was applied to the surface of an aluminum alloy and cured in four stages: drying at 25°C for 2 hours, curing at 80°C with forced air for 1 hour, curing at 200°C for 1 hour, and curing at 400°C for 30 minutes, thus obtaining the high-temperature heat-insulating coating of this example.

[0045] The coating thickness of Example 4 was approximately 1 mm, as measured at multiple points using a micrometer.

[0046] The mechanical and high-temperature properties of the coatings in Examples 2 and 4 were tested, and the results are shown in Tables 1 and 2.

[0047] Table 1 Comparison of mechanical properties of coatings

[0048] Table 2 Comparison of high temperature resistance of coatings

[0049] Comparing Tables 1 and 2, it can be seen that the coatings prepared in Examples 2 and 4 have a flexural strength higher than 7 MPa at room temperature. No cracks were observed after thermal cycling at 800℃, verifying the synergistic toughening effect of the "ternary binder + core-shell reinforcing agent," i.e., the "pull-out effect" of the core-shell fibers and the "stress dispersion effect" of graphene inhibit the initiation of microcracks.

[0050] The temperature difference was ≥560℃ under an 800℃ heat source, proving that the "dense-porous-low expansion" layered structure of the gradient filler effectively blocked heat conduction. The low expansion characteristics of the surface microspheres reduced thermal stress, and the high porosity of the middle aerogel reduced heat conduction.

[0051] After being burned at 800℃ for 3 hours, the adhesion retention rate was ≥95%. In Example 2, the adhesion retention rate reached 96.8%, and in Example 4, the adhesion retention rate reached 96.9%, demonstrating the high-temperature cross-linking stability of the ternary adhesive and the interfacial bonding effect of the coupling agent.

[0052] Comparative Example 1 The difference between this comparative example and Example 1 is that only the cerium oxide sol in step (2) is changed to titanium oxide sol, while the rest of the preparation process is the same as in Example 1, and the coating of this comparative example is obtained.

[0053] Comparative Example 2 The difference between this comparative example and Example 1 is that the particle size of the silica sol in step (2) is 20 nm, while the rest of the preparation process is the same as in Example 1, thus obtaining the coating of this comparative example.

[0054] Comparative Example 3 The difference between this comparative example and Example 1 is that the particle size of the silica sol, aluminum sol and cerium oxide sol in step (2) is adjusted to be the same, all being 10 nm. The rest of the preparation process is the same as in Example 1, and the coating of this comparative example is obtained.

[0055] Comparative Example 4 The coatings prepared in Comparative Examples 1-3 were applied to the surface of aluminum alloy and cured in four stages: the first stage was drying at 25°C for 2 hours, the second stage was curing at 80°C with forced air for 1 hour, the third stage was curing at 200°C for 1 hour, and the fourth stage was curing at 400°C for 30 minutes, thus obtaining the high-temperature heat-insulating coating of the comparative examples.

[0056] The thickness of all coatings in Comparative Example 4 was found to be approximately 1 mm by multi-point measurement using a micrometer.

[0057] The mechanical and high-temperature resistance properties of each coating in Comparative Example 4 were tested, and the results are shown in Tables 3 and 4.

[0058] Table 3. Effects of different bonding systems on the mechanical properties of the coating

[0059] Table 4. Effect of different bonding systems on the high-temperature resistance of the coating

[0060] As can be seen from Table 1, the coating obtained by using the ternary binder system of silica sol, aluminum sol and titanium oxide sol has a significantly reduced flexibility. This is because the high surface activity of cerium oxide sol in this invention can improve the dispersion uniformity of silica-alumina sol and avoid stress concentration caused by local agglomeration.

[0061] Meanwhile, when the particle size of the sol is the same, and is too large, the mechanical properties and high-temperature resistance of the material deteriorate significantly. Only by using a sol-bonded system with a suitable gradient particle size can a coating with good flexibility and resistance to cracking during high-temperature thermal cycling be obtained. This is because when silica sol constructs the main network structure, its 8-15nm particle size ensures the tight packing between nanoparticles; the 15-25nm particles of aluminum sol can be embedded in the gaps of the silica sol network to achieve secondary filling; and the 5-10nm ultrafine particles of cerium oxide sol further penetrate into the microporous structure of the silica-alumina sol, forming a tertiary densification filling. The particle size differences of the three sols create a complementary effect. During the film formation process, the stepwise intercalation of particles of different sizes effectively reduces interfacial porosity and enhances the cohesive strength of the binder system. Through the particle size gradient design of silica sol, aluminum sol, and cerium oxide sol, a film formation system with large-medium-small particle synergistic filling was constructed. Its multi-level filling effect significantly improves the density of the binder system and optimizes the interfacial bonding state with the thermal insulation filler.

[0062] Furthermore, the silicon, aluminum, and cerium sols in the ternary inorganic binder form a three-dimensional network structure through hydroxyl condensation, which can play a role in stages under staged curing conditions: the silicon sol preferentially forms a film at low temperatures, the aluminum sol enhances the network crosslinking degree at high temperatures, and the cerium oxide sol inhibits coating oxidation through the redox effect of cerium ions.

[0063] Therefore, only by using the ternary binder system in the embodiments of the invention and under the curing conditions of the present invention can a coating with high flexibility, high temperature resistance and crack resistance be prepared.

[0064] Comparative Example 5 The difference between this comparative example and Example 1 is that step (1) does not have a graphene shell, while the rest of the preparation process is the same as in Example 1, resulting in the coating of this comparative example.

[0065] Comparative Example 6 The difference between this comparative example and Example 1 is that the nano-zirconia fiber in step (1) is changed to nano-alumina fiber, while the rest of the preparation process is the same as in Example 1, so as to obtain the coating of this comparative example.

[0066] Comparative Example 7 The difference between this comparative example and Example 1 is that the diameter of the nano-zirconia fiber in step (1) is adjusted to 100 nm and the length is adjusted to 10 μm. The rest of the preparation process is the same as in Example 1, and the coating of this comparative example is obtained.

[0067] Comparative Example 8 The difference between this comparative example and Example 1 is that the reaction temperature for the preparation of the core-shell structure in step (1) is adjusted to 220°C and the reaction time is adjusted to 8h. The rest of the preparation process is the same as in Example 1, and the coating of this comparative example is obtained.

[0068] TEM testing showed that the thickness of the core-shell structured graphene shell in the coating prepared in Comparative Example 8 was 15 nm.

[0069] Comparative Example 9 The difference between this comparative example and Example 1 is that the concentration of the ethanol-water solution of γ-aminopropyltriethoxysilane in step (1) is adjusted to 3wt%, while the rest of the preparation process is the same as in Example 1, and the coating of this comparative example is obtained.

[0070] Comparative Example 10 The coatings prepared in Comparative Examples 5-9 were applied to the surface of an aluminum alloy and cured in four stages: the first stage was drying at 25°C for 2 hours, the second stage was curing at 80°C with forced air for 1 hour, the third stage was curing at 200°C for 1 hour, and the fourth stage was curing at 400°C for 30 minutes, thus obtaining the high-temperature heat-insulating coating of this comparative example.

[0071] The thickness of all coatings in Comparative Example 9 was found to be approximately 1 mm by multi-point measurement using a micrometer.

[0072] The mechanical and high-temperature properties of each coating in Comparative Example 10 were tested, and the results are shown in Tables 5 and 6.

[0073] Table 5. Effects of different reinforcing agents on the mechanical properties of the coating.

[0074] Table 6. Effects of different reinforcing agents on the high-temperature resistance of the coating.

[0075] As can be seen from Comparative Example 5 in Tables 5-6, the mechanical properties and high-temperature resistance of the shell-less reinforcing agent are significantly reduced. This is because the nanoparticles are prone to agglomeration and the interfacial bonding with the inorganic binder is weak, leading to easy cracking of the coating at high temperatures. Comparative Examples 6-7 show that the coatings made using nano-alumina fibers and zirconium oxide fibers with unsuitable aspect ratios have poor flexibility and high-temperature resistance.

[0076] As can be seen from Comparative Example 8, the thickness of the graphene shell should be within the range of 5-10 nm. This thickness range is sufficient to utilize the flexibility of graphene to buffer stress and avoid excessive thickness that would reduce the interfacial bonding force with the inorganic binder.

[0077] As can be seen from Comparative Example 9, under certain treatment conditions, if the concentration of the coupling agent solution is too high, the amount of grafting on the core-shell structure surface will be too high, the interfacial bonding strength between the nano-reinforcing agent and the inorganic binder will be reduced, and the flexibility and crack resistance of the coating under high temperature and cold cycling conditions will be reduced.

[0078] This invention utilizes a core-shell structure formed by nano-zirconia fibers with a suitable aspect ratio and graphene, along with interface modification, to create a directional three-dimensional network of nano-reinforcing agents within an inorganic binder. Simultaneously, gradient interfacial bonding enables the gradual release of stress from the inorganic to the organic phase, resolving the issue of poor compatibility between rigid fillers and the inorganic matrix. Specifically, when the coating is subjected to thermal stress, the zirconia fibers act as a rigid support, while the graphene shell forms a flexible connection through π-π stacking. The fibers dissipate energy through pull-out, while the graphene layers disperse stress through slippage.

[0079] Comparative Example 11 The difference between this comparative example and Example 1 is that the three layers of materials in step (3) are all made of silica aerogel, and the rest of the preparation process is the same as that in Example 1, so as to obtain the coating of this comparative example.

[0080] Comparative Example 12 The difference between this comparative example and Example 1 is that in step (3), lithium aluminum silicate glass microspheres are used for the bottom layer dispersion and fumed silica is used for the surface layer dispersion. The rest of the preparation process is the same as in Example 1, and the coating of this comparative example is obtained.

[0081] Comparative Example 13 The difference between this comparative example and Example 1 is that the amount of high-temperature dispersant added in step (3) is adjusted to 2.5% compared to the gradient dispersion. The rest of the preparation process is the same as in Example 1, and the coating of this comparative example is obtained.

[0082] Comparative Example 14 The difference between this comparative example and Example 1 is that the molecular weight of the high-temperature dispersant in step (3) is adjusted to 12000, while the rest of the preparation process is the same as in Example 1, thus obtaining the coating of this comparative example.

[0083] Comparative Example 15 The difference between this comparative example and Example 1 is that 5.78 parts of fumed silica, 1.25 parts of maleic anhydride-acrylic acid copolyammonium salt, 8.67 parts of silica aerogel, 16 parts of deionized water, and 11.56 parts of lithium aluminum silicate glass microspheres in step (3) are directly mechanically mixed without stepwise sand milling. The rest of the preparation process is the same as in Example 1, and the coating of this comparative example is obtained.

[0084] Comparative Example 16 The difference between this comparative example and Example 1 is that in step (3), the bottom layer dispersion, the middle layer dispersion and the surface layer dispersion are all subjected to sand milling, and the sand milling time is 30 min. The rest of the preparation process is the same as that in Example 1, and the coating of this comparative example is obtained.

[0085] Comparative Example 17 This comparative example uses the coatings prepared in Comparative Examples 11-16 to coat the surface of an aluminum alloy and cures them in four stages: the first stage is drying at 25°C for 2 hours, the second stage is curing at 80°C with forced air for 1 hour, the third stage is curing at 200°C for 1 hour, and the fourth stage is curing at 400°C for 30 minutes, thus obtaining the high-temperature heat-insulating coating of this comparative example.

[0086] The thickness of all coatings in Comparative Example 17 was found to be approximately 1 mm by multi-point measurement using a micrometer.

[0087] The mechanical and high-temperature properties of each coating in Comparative Example 17 were tested, and the results are shown in Tables 7 and 8.

[0088] Table 7. Effects of different gradient fillers and their preparation processes on the mechanical properties of the coating.

[0089] Table 8. Effects of different gradient fillers and their preparation processes on the high-temperature resistance of the coating.

[0090] As can be seen from Comparative Examples 11-12 in Tables 7-8, using thermal insulation fillers with a single particle size or random distribution results in a significant density interface within the coating, which easily leads to stress concentration points during thermal cycling. This solution, however, constructs a composite structure with a continuously transitioning coefficient of thermal expansion by precisely controlling the particle size gradient and distribution of the three fillers, effectively dispersing thermal stress and inhibiting crack propagation. Specifically, this invention uses lithium aluminum silicate glass microspheres as the surface filler, whose low coefficient of expansion matches the thermal expansion of the metal substrate, reducing interfacial stress differences caused by temperature changes. Silica aerogel serves as the middle layer filler, utilizing its high porosity structure to undergo reversible compression under thermal stress, absorbing and dispersing the stress wave transmission path. Fumed silica powder serves as the bottom layer filler, filling the microscopic voids between the coating and the substrate with the high surface activity of nanoparticles, forming a continuous and dense transition layer. The three-layer material, with its gradient particle size distribution from micrometers to nanometers, forms a composite structure with continuously varying density within the coating. This allows for a gradual transition in the coefficient of thermal expansion from the substrate to the coating surface, avoiding stress concentration caused by abrupt changes in physical properties.

[0091] Furthermore, based on Comparative Examples 13-14, we found that high-temperature dispersants play a crucial role in the preparation of gradient filler dispersions. Ammonium polycarboxylate salts, with molecular weights only in the range of 8000-10000, can only effectively cover thermal insulation fillers of different particle size gradients at high temperatures through the adsorption of carboxylate groups onto the hydroxyl groups on the filler surface. The molecular chains adsorb onto the filler surface through a combination of electrostatic repulsion and steric hindrance, preventing agglomeration of thermal insulation fillers with different particle size gradients and ensuring uniform dispersion of the filler in the coating. However, excessively high molecular weights and dosages result in poor adsorption selectivity for fillers of different particle sizes, leading to uneven dispersion, lower coating adhesion under high-temperature conditions, increased susceptibility to cracking, and consequently, reduced thermal insulation performance.

[0092] As can be seen from Comparative Examples 15-16, the single sand milling process for gradient composite thermal insulation fillers, which treats all fillers, leads to damage to the aerogel structure or breakage of hollow microspheres, failing to form an effective gradient structure. This invention, however, controls the sand milling time gradient: the bottom layer is sand-milled for 30 minutes, the middle layer for an additional 15 minutes, and the surface layer is not sand-milled. This allows the bottom layer silica powder to form a dense dispersed phase through prolonged sand milling, the middle layer aerogel to maintain its porous structure through short-time sand milling, and the surface layer hollow microspheres to be physically mixed only to retain their complete spherical structure. This creates a continuous transition structure from dense to porous. While ensuring the functional integrity of each filler, it achieves interlayer interface fusion. The fine particles formed by the bottom layer sand milling enhance interfacial bonding, the middle layer aerogel maintains pores to buffer thermal stress, and the surface layer microspheres form a thermal insulation barrier with their intact morphology. This solves the problem of internal stress concentration in the coating caused by uneven filler dispersion in traditional processes, improving the coating's flexibility and crack resistance.

[0093] Comparative Example 18 The difference between this comparative example and Example 1 is that the thixotropic agent organic modified bentonite in step (4) is changed to fumed silica, while the rest of the preparation process is the same as in Example 1, and the coating of this comparative example is obtained.

[0094] Comparative Example 19 The difference between this comparative example and Example 1 is that the particle size of the thixotropic agent organic modified bentonite in step (4) is adjusted to 10 μm, while the rest of the preparation process is the same as in Example 1, thus obtaining the coating of this comparative example.

[0095] Comparative Example 20 The coatings prepared in Comparative Examples 18-19 were applied to the surface of an aluminum alloy and cured in four stages: the first stage was drying at 25°C for 2 hours, the second stage was curing at 80°C with forced air for 1 hour, the third stage was curing at 200°C for 1 hour, and the fourth stage was curing at 400°C for 30 minutes, thus obtaining the high-temperature heat-insulating coating of this comparative example.

[0096] The thickness of all coatings in Comparative Example 20 was found to be approximately 1 mm by multi-point measurement using a micrometer.

[0097] The mechanical and high-temperature properties of each coating in Comparative Example 20 were tested, and the results are shown in Tables 9 and 10.

[0098] Table 9. Effects of different thixotropic agents on the mechanical properties of the coating.

[0099] Table 10. Effect of different thixotropic agents on the high-temperature resistance of the coating.

[0100] According to Comparative Example 18 in Tables 1-2, compared with organically modified bentonite, thixotropic silica exhibits reduced flexural strength and adhesion. After high-temperature burning, the adhesion decreases to below 90%, and surface cracks appear. This is because silica, as a thixotropic agent, has a wide thixotropic index range, making it difficult to precisely match the dispersion requirements of gradient fillers. In contrast, the lamellar structure of organically modified bentonite forms a network structure through hydrogen bonds and van der Waals forces at low shear rates, increasing the system viscosity to suppress filler sedimentation. At high shear rates, the network structure is destroyed, reducing viscosity to improve coating leveling. Controlling the thixotropic index within the range of 3.0-4.0 can prevent filler sedimentation during storage through viscosity changes and avoid coating sagging or uneven coating thickness due to excessive thixotropy during application.

[0101] This invention addresses the challenge of matching the dispersion and rheological properties of gradient fillers by limiting the molecular weight range and addition ratio of ammonium polycarboxylate salts with the particle size and thixotropic index of organically modified bentonite, thus forming a synergistic mechanism. This effectively suppresses the agglomeration and sedimentation of gradient composite insulation fillers, ensuring a continuous density gradient structure within the coating. Simultaneously, it optimizes the leveling and anti-sagging properties during coating application, ultimately improving the coating's crack resistance and service stability.

[0102] According to Comparative Example 19 in Tables 1-2, excessively large particle size of the thixotropic organic-modified bentonite also led to a decrease in the high-temperature resistance of the coating and slight surface cracking. Only when the particle size is within the range of this invention can a crack-resistant coating be obtained.

[0103] Comparative Example 21 The difference between this comparative example and Example 2 is that the coating was directly cured at 200°C for 4.5 hours. The preparation process was the same as in Example 1, resulting in the coating of this comparative example.

[0104] The coating thickness in Comparative Example 21 was approximately 1 mm, as measured at multiple points using a micrometer.

[0105] The mechanical and high-temperature properties of the coating in Comparative Example 21 were tested, and the results are shown in Tables 11-12.

[0106] Table 11 Effect of different thixotropic agents on the mechanical properties of the coating

[0107] Table 12 Effect of different thixotropic agents on the high-temperature resistance of coatings

[0108] Comparing Example 2 and Comparative Example 21 in Tables 11-12, it can be seen that the single-stage high-temperature curing process leads to stress concentration within the coating and insufficient interfacial bonding, making it prone to cracking and peeling during thermal cycling. This solution, however, uses a segmented curing process. At 80℃, it promotes the volatilization of organic components and the initial cross-linking of the inorganic binder; at 200℃, it accelerates the inorganic sol-gel condensation reaction to form a dense network structure; and finally, at 400℃, it eliminates residual stress and strengthens the stability of the inorganic skeleton. This staged heating allows for the gradual release of internal stress in the coating, preventing the propagation of microcracks due to sudden temperature changes. The cured thickness is controlled within the range of 0.8-1.5 mm, ensuring thermal insulation performance while avoiding stress accumulation due to excessive thickness. The synergistic effect of flexural strength and adhesion effectively inhibits coating cracking and interfacial failure, significantly improving the long-term stability of the coating and meeting the long-term stability requirements of industrial equipment and aerospace components.

[0109] Furthermore, existing technologies often employ forced air cooling or water cooling to accelerate cooling after high-temperature treatment, leading to stress concentration at the coating-metal substrate interface due to differences in cooling rates. This invention, by limiting the burning temperature and time parameters and combining them with a specific process of natural cooling at room temperature, achieves synergistic control of coating structural stability and interfacial stress release. This solves the problem of decreased adhesion caused by differences in the coefficients of thermal expansion of traditional inorganic coatings. The coating maintains stable interfacial bonding strength even after undergoing high-temperature treatment at 800℃, avoiding the risk of peeling caused by microcrack propagation during thermal cycling, and significantly improving the reliability of the coating in high-temperature protection applications.

[0110] In summary, this application effectively improves the flexibility and resistance to thermal cycling cracking of inorganic coatings. Specifically, by designing a particle size gradient of silica sol, alumina sol, and cerium oxide sol, a film-forming system with large-medium-small particle synergistic filling is constructed. The multi-level filling effect significantly improves the density of the binder system while optimizing the interfacial bonding with the thermal insulation filler. The three-dimensional network formed by the core-shell structured nano-reinforcing agent can alleviate stress concentration. The gradient composite filler structure can buffer the internal stress caused by thermal expansion differences. The staged dispersion process ensures the structural integrity of each functional component. After staged curing, the resulting coating forms a coating structure with a continuous density gradient, which can maintain stable interfacial bonding under high temperature conditions and significantly reduce the probability of microcrack formation.

[0111] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. An inorganic high-temperature resistant heat-insulating coating, characterized in that: Based on the mass fractions of raw materials, including, 45-55 parts of composite inorganic film-forming system, 25-30 parts of gradient composite thermal insulation filler, 2-4 parts of functional additives, and 15-18 parts of deionized water; The composite inorganic film-forming system is composed of a ternary inorganic binder and a core-shell structured nano-reinforcing agent modified with a bifunctional silane coupling agent. The gradient composite thermal insulation filler is composed of lithium aluminum silicate glass microspheres, silica aerogel, and fumed silica. The functional additives consist of high-temperature dispersants, thixotropic agents, and high-temperature film-forming aids.

2. The inorganic high-temperature resistant heat-insulating coating as described in claim 1, characterized in that: The ternary inorganic binder is composed of silica sol, aluminum sol, and cerium oxide sol; the particle size of the silica sol is 8-15 nm, the particle size of the aluminum sol is 15-25 nm, and the particle size of the cerium oxide sol is 5-10 nm; the mass ratio of the ternary inorganic binder to the core-shell structured nano-reinforcing agent modified with a bifunctional silane coupling agent is 7-9:

1.

3. The inorganic high-temperature resistant heat-insulating coating as described in claim 1, characterized in that: The core-shell structured nano-reinforcing agent modified with the bifunctional silane coupling agent consists of a zirconia nanofiber core and a graphene shell. The zirconia nanofiber has a diameter of 60-80 nm, a length of 6-8 μm, and a graphene shell thickness of 5-10 nm.

4. The inorganic high-temperature resistant heat-insulating coating as described in claim 3, characterized in that: The amount of modification of the bifunctional silane coupling agent is 2-2.5 wt% of the mass of the core-shell structure.

5. The inorganic high-temperature resistant heat-insulating coating as described in claim 1, characterized in that: In the gradient composite thermal insulation filler, the coefficient of thermal expansion of lithium aluminum silicate glass microspheres is ≤1.5×10⁻⁶. -6 / ℃, particle size is 80-120μm, silica aerogel particle size is 20-50μm, porosity ≥95%.

6. The inorganic high-temperature resistant heat-insulating coating as described in claim 1, characterized in that: The high-temperature dispersant is a polycarboxylic acid ammonium salt with a molecular weight of 8000-10000.

7. The inorganic high-temperature resistant heat-insulating coating as described in claim 1, characterized in that: The amount of the high-temperature dispersant added is 4.81-5.36 wt% compared to the gradient composite thermal insulation filler.

8. The inorganic high-temperature resistant heat-insulating coating as described in claim 1, characterized in that: The thixotropic agent is organically modified bentonite, and the particle size of the organically modified bentonite is 1-5 μm.

9. The method for preparing the inorganic high-temperature resistant heat-insulating coating as described in any one of claims 1 to 8, characterized in that: include, Zirconia nanofibers, glucose, and nitric acid were dissolved in deionized water at a mass ratio of 9-11:5:

1. The pH of the solution was adjusted to 2.0-2.

2. The resulting mixture was reacted at 185-190℃ for 6.5-7 hours. After cooling to room temperature, the mixture was centrifuged to obtain a zirconia fiber-graphene core-shell structure. Zirconia fiber-graphene core-shell structure is mixed with a bifunctional silane coupling agent solution of 8-9 wt%, dispersed for 45-60 min, and then centrifuged and dried to obtain a bifunctional silane coupling agent modified core-shell structure nano-reinforcing agent; silica sol, aluminum sol and cerium oxide sol are mixed and stirred evenly in a mass ratio of 4-6:3:2 to obtain a ternary inorganic binder. By mass, 39.4-49.5 parts of ternary inorganic binder and 4.5-6.9 parts of core-shell structured nano-reinforcing agent modified with bifunctional silane coupling agent are stirred evenly to obtain a composite inorganic film-forming system. By mass, 5-7 parts of fumed silica, 5-6 parts of deionized water, and 0.6-0.8 parts of high-temperature dispersant are milled at 2500-3000 r / min for 10-15 min to complete the bottom layer dispersion. Then, 8-10 parts of silica aerogel, 10-12 parts of deionized water, and 0.6-0.8 parts of high-temperature dispersant are added and milled at 1500-2000 r / min for 25-30 min to complete the middle layer dispersion. Then, 11-14 parts of lithium aluminum silicate glass microspheres are added and physically stirred at 200-250 r / min for 10-15 min to complete the surface layer dispersion, thus obtaining a gradient dispersion. By mass fraction, the composite inorganic film-forming system and gradient dispersion are mixed, and then 0.6-0.8 parts of thixotropic agent and 0.6-0.8 parts of high-temperature film-forming aid are added. The mixture is dispersed at a low speed of 200-250 r / min for 15-20 min, dispersed at a medium speed of 400-450 r / min for 15-20 min, and homogenized at a high speed of 600-650 r / min for 15-20 min. After filtration, the coating is obtained.

10. A method for preparing an inorganic high-temperature resistant heat-insulating coating, characterized in that: include, The inorganic high-temperature heat-insulating coating of claim 1 is applied to the surface of a metal substrate and then subjected to drying at 20-25℃ for 2-3 hours, curing at 60-80℃ with forced air for 1-2 hours, curing at 200-220℃ for 1-2 hours, and curing at 400-450℃ for 30-40 minutes to obtain the high-temperature heat-insulating coating.

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