Aqueous inorganic nanoceramic thermal barrier coating and method of making same

Abstract

This invention belongs to the field of thermal insulation coating technology, specifically relating to a water-based inorganic nano-ceramic thermal insulation coating and its preparation method. It uses boron-aluminum dual-doped lithium silicate inorganic resin as the film-forming matrix, amorphous Al2O3-SiO2 nano-coated mullite hollow ceramic microspheres as thermal insulation fillers, and combines modified nanoporous zirconium dioxide and titanium dioxide to form a multi-level thermal insulation system. Specifically, the boron-aluminum dual-doped lithium silicate enhances structural density by embedding aluminum elements into the silicon-oxygen network framework, while boron elements introduce flexible sites to form an inorganic hybrid network, achieving low-temperature dense curing and enhancing the coating's high-temperature service stability. The mullite hollow ceramic microspheres, after nano-coating modification, form covalent bonds with the matrix, avoiding interface defects and reducing interface thermal resistance. The modified nanoporous zirconium dioxide and the microsphere cavities constitute a multi-level porous synergistic thermal insulation structure, combined with the infrared thermal radiation reflection effect of titanium dioxide, achieving all-round thermal insulation and adapting to the coating application needs of various high-temperature thermal insulation scenarios.

Description

Technical Field

[0001] This invention relates to the field of heat insulation coating technology, and in particular to a water-based inorganic nano-ceramic heat insulation coating and its preparation method. Background Technology

[0002] High-temperature thermal insulation coatings are core functional materials in the fields of industrial kilns, thermal pipelines, new energy equipment, building energy conservation, and thermal protection of high-end equipment. They play a vital role in reducing heat transfer loss, ensuring the safe and stable operation of high-temperature equipment, and improving overall energy utilization efficiency. With the continuous development of high-end manufacturing and green energy-saving industries, the market has put forward more stringent application requirements for thermal insulation coatings in terms of high-temperature resistance, interfacial bonding strength, thermal insulation efficiency, environmental protection characteristics, and adaptability to complex working conditions. Currently, thermal insulation coatings on the market are mainly divided into two categories: organic and inorganic systems. While organic thermal insulation coatings offer advantages such as convenient construction and good flexibility, their upper temperature resistance is relatively low, and they are prone to softening, aging, decomposition, and even failure under high-temperature environments, failing to meet the requirements of long-term high-temperature operation. Furthermore, some organic coatings have environmental drawbacks related to volatile organic compound emissions. Inorganic thermal insulation coatings, with silicates, aluminates, and other inorganic film-forming matrices as their core, have become the mainstream technology in the field of high-temperature thermal insulation due to their advantages such as high temperature resistance, non-flammability, strong weather resistance, and environmental friendliness. Among them, lithium silicate-based inorganic coatings are widely used due to their excellent film-forming properties and high-temperature resistance. The application of thermal insulation fillers such as hollow ceramic microspheres and porous inorganic powders has also provided more pathways for achieving thermal insulation in inorganic coatings. However, existing inorganic high-temperature thermal insulation coatings generally suffer from poor interfacial compatibility and insufficient interfacial bonding between the thermal insulation filler and the inorganic film-forming matrix, and their single thermal insulation structure limits overall thermal insulation efficiency, failing to meet the integrated application requirements for high-performance thermal insulation protection under harsh high-temperature environments. Summary of the Invention

[0003] To address the shortcomings of existing technologies, the present invention aims to provide a water-based inorganic nano-ceramic thermal insulation coating and its preparation method. The coating uses boron-aluminum dual-doped lithium silicate inorganic resin as the film-forming matrix, amorphous Al2O3-SiO2 nano-coated mullite hollow ceramic microspheres as the thermal insulation filler, and combines modified nanoporous zirconium dioxide and titanium dioxide to form a multi-level thermal insulation system. Specifically, the boron-aluminum dual-doped lithium silicate enhances structural density by embedding aluminum elements into the silicon-oxygen network framework, while boron elements introduce flexible sites to form an inorganic hybrid network, achieving low-temperature densification and curing and enhancing the coating's high-temperature service stability. The mullite hollow ceramic microspheres, after nano-coating modification, form covalent bonds with the matrix, avoiding interface defects and reducing interface thermal resistance. The modified nanoporous zirconium dioxide and the microsphere cavities constitute a multi-level porous synergistic thermal insulation structure. Combined with the infrared thermal radiation reflection effect of titanium dioxide, it achieves all-round thermal insulation, adapting to the coating application needs of various high-temperature thermal insulation scenarios.

[0004] To achieve the above objectives, the present invention employs the following technical solution:

[0005] In a first aspect, the present invention provides an aqueous inorganic nano-ceramic heat insulation coating, the coating being prepared from the following raw materials: boron-aluminum dual-doped lithium silicate inorganic resin, amorphous Al2O3-SiO2 nano-coated mullite hollow ceramic microspheres, modified nanoporous zirconium dioxide slurry, titanium dioxide slurry, and defoamer.

[0006] The boron-aluminum dual-doped lithium silicate inorganic resin is obtained by reacting sodium aluminate and boric acid pre-complexed with lithium silicate inorganic resin.

[0007] The amorphous Al2O3-SiO2 nano-coated mullite hollow ceramic microspheres were obtained by KH-550 activation of mullite hollow ceramic microspheres followed by coating with boehmite sol and silica sol.

[0008] The modified nanoporous zirconium dioxide slurry was obtained by dispersing nanoporous zirconium dioxide with sodium polyacrylate, complexing with aluminum nitrate nonahydrate, and neutralizing and modifying with sodium bicarbonate buffer solution.

[0009] The titanium dioxide slurry is obtained by dispersing rutile titanium dioxide with sodium polyphosphate.

[0010] The defoamer is polysiloxane.

[0011] Further, the mass ratio of the boron-aluminum dual-doped lithium silicate inorganic resin, amorphous Al2O3-SiO2 nano-coated mullite hollow ceramic microspheres, modified nanoporous zirconium dioxide slurry, titanium dioxide slurry, and defoamer is (313.5-344.1):(240-260):(101.1-121.5):(33.2-45.4):(3.5-4.5); the mass-to-volume ratio of sodium aluminate, boric acid, and lithium silicate inorganic resin is (3.0-3.4) g:(0.5-0.7) g. The mass-volume ratio of the mullite hollow ceramic microspheres, KH-550, boehmite sol and silica sol is (240-260) g: (2-3) g: (45-55) mL: (45-55) mL; the mass ratio of the nanoporous zirconium dioxide, sodium polyacrylate and aluminum nitrate nonahydrate is (55-65): (0.4-0.6): (0.7-0.9); the mass ratio of the rutile titanium dioxide and sodium polyphosphate is (25-35): (0.2-0.4).

[0012] Furthermore, the lithium silicate inorganic resin has a solid content of 22 wt%; the mullite hollow ceramic microspheres have an average particle size of 20-50 μm; the boehmite sol has a boehmite content of 20 wt% and a particle size of 10-40 nm; the silica sol is alkaline sodium type, with a SiO2 content of 30 wt% and a particle size of 8-15 nm; the sodium bicarbonate buffer solution has a mass fraction of 0.4 wt%-0.55 wt%; the nanoporous zirconium dioxide has a particle size of 20-30 nm; and the rutile titanium dioxide has an average particle size of 0.2-0.3 μm.

[0013] Secondly, the present invention provides a method for preparing an aqueous inorganic nano-ceramic heat-insulating coating, comprising the following steps:

[0014] S1. Sodium aluminate, boric acid and deionized water are mixed and placed in a water bath to obtain a boron-aluminum pre-complexed solution. This solution is then added dropwise to lithium silicate inorganic resin and stirred to react, resulting in boron-aluminum dual-doped lithium silicate inorganic resin.

[0015] S2. Prepare a sodium bicarbonate buffer solution and add it dropwise to a mixture of KH-550 and deionized water to adjust the pH, thus obtaining a pre-hydrolyzed KH-550 solution. After drying the mullite hollow ceramic microspheres, add deionized water and the pre-hydrolyzed KH-550 solution, adjust the pH, and perform a first heating reaction to obtain activated microspheres. Add a mixture of boehmite sol and silica sol, perform a second heating reaction, filter, and vacuum dry to obtain amorphous Al2O3-SiO2 nano-coated mullite hollow ceramic microspheres.

[0016] S3. Mix nanoporous zirconium dioxide, sodium polyacrylate, aluminum nitrate nonahydrate and deionized water, and add sodium bicarbonate buffer solution to adjust the pH to obtain modified nanoporous zirconium dioxide slurry; mix rutile titanium dioxide, sodium polyphosphate and deionized water to obtain titanium dioxide slurry;

[0017] S4. Modified nanoporous zirconium dioxide slurry is added to boron-aluminum dual-doped lithium silicate inorganic resin and dispersed at high speed. Titanium dioxide slurry and polysiloxane are added, and amorphous Al2O3-SiO2 nano-coated mullite hollow ceramic microspheres are added. The viscosity of the system is adjusted to obtain a coating. The coating is sprayed onto a metal substrate, pre-cured at room temperature, dried, cured at elevated temperature, and naturally cooled to obtain a water-based inorganic nano-ceramic heat insulation coating.

[0018] In one feasible implementation, in S1, the mass-to-volume ratio of sodium aluminate to deionized water is (3.0-3.4) g: (20-30) mL; the temperature of the water bath is 55-65℃, and the water bath time is 10-20 min; the dropping rate is 1.5-2.5 mL / min; the stirring speed is 750-850 r / min, and the stirring time is 15-25 min.

[0019] A boron-aluminum pre-complex structure is formed by sodium aluminate and boric acid in an aqueous environment: sodium aluminate dissociates in water to form tetrahydroxyaluminate anions, while boric acid exists in the water as hydroxylated boric acid molecules. The hydroxyl groups in tetrahydroxyaluminate can undergo dehydration condensation with the hydroxyl groups in boric acid molecules to form a stable BO-Al coordination pre-complex structure. This structure exists in a soluble ionic state, which can avoid the problems of agglomeration and uneven distribution that occur when boron and aluminum components are added to the lithium silicate system alone, thus laying a solid structural foundation for subsequent uniform doping.

[0020] After introducing a boron-aluminum pre-complexed structure into lithium silicate inorganic resin, aluminum element is embedded in the silicon-oxygen tetrahedral network framework of lithium silicate in a four-coordinate aluminum-oxygen tetrahedral configuration. By isomorphically replacing some silicon-oxygen structural units, it significantly increases the crosslinking density and structural compactness of the silicon-oxygen network, enhancing the overall stiffness and high-temperature structural stability of the film substrate. Furthermore, the embedding of aluminum-oxygen tetrahedra activates residual silanol and aluminum hydroxyl groups in the matrix, significantly improving the inorganic bonding reaction activity between the film substrate and the inorganic filler. Boron element is uniformly dispersed in the silicon-oxygen network in a hybrid state with coordinated three-coordinate and four-coordinate configurations. By breaking the continuous rigid long chains in the silicon-oxygen network, flexible structural units are introduced into the inorganic network, effectively alleviating the internal stress generated during curing and thermal cycling of the coating. Simultaneously, the hybrid structure of boron can also seal the hydrophilic groups in the matrix, improving the water and alkali resistance of the coating. The two elements, aluminum and boron, work together to construct a continuous and stable silicon-oxygen-aluminum-boron inorganic hybrid network. This can also reduce the activation energy of resin cross-linking and curing, promote the full cross-linking of the hybrid network, and make the coating more compact. This provides the coating with excellent high-temperature service stability and interfacial bonding foundation from the film-forming matrix level.

[0021] In one feasible implementation, in step S2, the step of preparing the sodium bicarbonate buffer solution is as follows: 0.4-0.5g of anhydrous sodium bicarbonate is mixed with 90-100mL of deionized water and stirred at 300r / min until completely dissolved to obtain the sodium bicarbonate buffer solution; the mass-to-volume ratio of KH-550 to deionized water is (2-3)g:(20-30)mL; the dropping rate is 0.8-1.2mL / min; the pH is adjusted to 8.4-8.6; and the mass-to-volume ratio of mullite hollow ceramic microspheres to deionized water is (240-260)g:(1200-1300)mL.

[0022] Mullite hollow ceramic microspheres, relying on their closed internal cavity structure, can efficiently block heat conduction and convection, making them the core heat-insulating filler for coatings. Their surface naturally contains active groups such as silanol and aluminol, providing ample reaction sites for surface coating modification. KH-550 silane coupling agent undergoes a pre-hydrolysis reaction in a weakly alkaline aqueous environment, converting the alkoxy groups in the molecule into active silanol groups. These silanol groups can undergo dehydration condensation with the hydroxyl groups on the surface of the mullite microspheres, forming Si-O-Si covalent bonds. This achieves chemical grafting and activation modification of the silane coupling agent on the microsphere surface, providing stable anchoring points for the subsequent growth of inorganic coating layers.

[0023] In one feasible implementation, in step S2, the drying temperature is 100-110℃, and the drying time is 1.5-2.5h; the pH adjustment step is as follows: sodium bicarbonate buffer solution is added dropwise at a rate of 0.8-1.2mL / min to adjust the pH to 8.0-9.0; the temperature of the first heating reaction is 45-55℃, and the time of the first heating reaction is 25-35min; the dropwise addition rate is 2.5-3.5mL / min; the temperature of the second heating reaction is 60-70℃, and the time of the second heating reaction is 1.5-2.5h; the vacuum drying temperature is 100-110℃, and the vacuum drying time is 1.5-2.5h.

[0024] Boehmite sol, primarily composed of hydroxylated alumina hydrate, and silica sol, with active silanol groups as its core functional groups, can undergo simultaneous condensation reactions with the active groups on the surface of activated microspheres under weakly alkaline conditions. The aluminol groups in the boehmite sol form Si-O-Al covalent bonds with the silanol groups on the microsphere surface and the silanol groups of the silane coupling agent, while the silanol groups in the silica sol form Si-O-Si covalent bonds. These two types of covalent bonds intertwine, growing in situ on the mullite microsphere substrate, continuously spreading and gradually densifying, ultimately forming a uniform and continuous amorphous structure on the microsphere surface. Nano-coating layer. This coating layer forms covalent bonds with the boron-aluminum dual-doped lithium silicate matrix through abundant active hydroxyl groups on its surface, eliminating physical interface gaps between the filler and the matrix, avoiding interface debonding and the formation of micropore defects, and significantly reducing interface thermal resistance. This allows the intrinsic thermal insulation performance of the mullite hollow ceramic microspheres to be maximized, thus both strengthening the coating interface adhesion and ensuring the core thermal insulation effect.

[0025] In one feasible implementation, in step S3, the mass-to-volume ratio of the nanoporous zirconium dioxide to deionized water is (55-65) g: (45-55) mL; the dropping rate of the sodium bicarbonate buffer solution is 0.4-0.6 mL / min; the pH is adjusted to 8.0-9.0; and the mass-to-volume ratio of the rutile titanium dioxide to deionized water is (25-35) g: (8-10) mL.

[0026] Nanoporous zirconium dioxide possesses a rich nanoporous structure, making it a key component in constructing hierarchical porous thermal insulation systems. Its high surface energy makes it prone to aggregation in aqueous systems, leading to pore blockage and functional failure. The surface of nanoporous zirconium dioxide naturally contains a large number of zirconium hydroxyl groups, which are the core active sites for surface chemical modification. In this system, aluminum nitrate nonahydrate is used as the aluminum source. Under a weakly alkaline aqueous environment, this source first dissociates into aluminum cations, which further form hydrated aluminum ions and undergo stepwise hydrolysis to generate amorphous aluminum hydroxyl oxide active species. These species exist in an oligomeric form, with their molecular chains rich in reactive aluminum hydroxyl groups. These aluminum hydroxyl oxide active species can undergo dehydration condensation reactions with the zirconium hydroxyl groups on the surface of nanoporous zirconium dioxide, forming stable Zr-O-Al covalent bonds. Through chemical bonding, the amorphous aluminum hydroxyl oxides are uniformly anchored and spread on the surface of the nanoporous zirconium dioxide particles and the inner walls of the pores, forming a continuous, ultrathin aluminum hydroxyl complex layer that is firmly bonded to the matrix.

[0027] Sodium polyacrylate, acting as a dispersant, adsorbs onto the surface of nanoporous zirconia particles, initially inhibiting particle aggregation through electrostatic repulsion and steric hindrance. The in-situ generated aluminum hydroxyl complex layer further enhances the dispersion effect at the chemical bonding level, suppressing nanoparticle aggregation and fully preserving the nanoporous structure of the zirconia. Simultaneously, the abundant active aluminum hydroxyl groups retained within the layer improve the compatibility and bonding ability between zirconia and the inorganic film-forming matrix, ensuring uniform dispersion within the coating system. The modified nanoporous zirconia can form a hierarchical synergistic thermal insulation structure with the micron-sized cavities of mullite hollow ceramic microspheres. This hierarchical pore structure extends the heat conduction path and suppresses gas convection heat transfer within the pores, further improving the coating's thermal insulation performance from both thermal conduction and convection perspectives.

[0028] Rutile titanium dioxide, with its extremely high refractive index, is a core functional filler for reflecting infrared thermal radiation. Inorganic titanium dioxide particles are prone to agglomeration in aqueous systems due to van der Waals forces, thus reducing their scattering and reflection capabilities. Sodium polyphosphate, as an inorganic dispersant, can adsorb onto the surface of titanium dioxide particles, stabilizing them uniformly in the aqueous system through an electrostatic stabilization mechanism, forming a stable and homogeneous slurry and preventing functional degradation caused by particle agglomeration. The dispersed rutile titanium dioxide can be evenly distributed between the inorganic film-forming matrix and the thermal insulation filler in the coating. Its high refractive index allows for efficient reflection and scattering of infrared thermal radiation in high-temperature scenarios, blocking the transmission path of heat radiation and compensating for the shortcomings of hollow ceramic microspheres and nanoporous zirconium dioxide in heat radiation blocking. Together with the first two types of fillers, it forms a comprehensive thermal insulation mechanism encompassing heat conduction, heat convection, and heat radiation, comprehensively improving the thermal insulation effect of the coating.

[0029] In one feasible implementation, in step S4, the high-speed dispersion rotation speed is 950-1050 r / min, and the high-speed dispersion time is 8-12 min; the rate of adding amorphous Al2O3-SiO2 nano-coated mullite hollow ceramic microspheres is 1.5-2.5 g / s; and the step of adjusting the viscosity of the system is to adjust the viscosity to 2500-3000 mPa·s with deionized water.

[0030] Modified nanoporous zirconium dioxide slurry and titanium dioxide slurry were sequentially added to boron-aluminum dual-doped lithium silicate inorganic resin for compounding and mixing. The functional components were uniformly dispersed at the molecular level under high-speed stirring. Subsequently, amorphous materials were added... Nano-coated mullite hollow ceramic microspheres are used to achieve uniform distribution of large-particle-size thermal insulation fillers through gentle stirring, avoiding damage to the hollow structure and ultimately forming a coating system in which the functions of each component are synergistic and the dispersion is stable.

[0031] In one feasible implementation, in step S4, the wet film thickness of the sprayed coating is controlled to be 1-2 mm; the pre-curing time is 25-35 min; the drying temperature is 120-130℃, and the drying time is 25-35 min; the heating and curing step is as follows: heating to 145-155℃ at a heating rate of 4-6℃ / min and then maintaining the temperature for 1.5-2.5 h.

[0032] The coating employs a staged curing method. Room temperature pre-curing removes free moisture from the coating, preventing bubble defects during high-temperature curing. Medium-temperature drying further removes bound water from the system. After reaching the isothermal curing stage, the silicon-oxygen-aluminum-boron inorganic hybrid network of boron-aluminum dual-doped lithium silicate fully cross-links and densifies, while the amorphous surface of the filler... The coating layer and the film-forming substrate are tightly bonded by covalent bonds, forming a defect-free, high-bonding integral coating structure. This curing process ensures both the structural integrity and interfacial bonding strength of the coating, while also fully preserving the core characteristics of each functional component. Ultimately, the coating possesses excellent interfacial bonding strength, low thermal conductivity, high-temperature service stability, and water and alkali resistance, making it suitable for various coating applications in high-temperature insulation scenarios.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] This scheme uses boron-aluminum dual-doped lithium silicate inorganic resin as the film-forming substrate, and amorphous... A water-based inorganic nano-ceramic thermal insulation coating is obtained by using nano-coated mullite hollow ceramic microspheres as the core thermal insulation filler, combined with modified nanoporous zirconium dioxide and titanium dioxide. This coating exhibits excellent interfacial bonding strength, low thermal conductivity, and high-temperature service stability. In boron-aluminum dual-doped lithium silicate, aluminum is embedded in the silicon-oxygen network framework of lithium silicate in a four-coordinate aluminum-oxygen tetrahedral configuration, replacing some silicon-oxygen structural units. This increases the crosslinking density and structural compactness of the network, enhancing the overall stiffness and structural stability of the coating. Furthermore, it activates hydroxyl groups in the matrix, improving the inorganic bonding reaction activity with the filler. Boron is uniformly dispersed in the silicon-oxygen network in a three-coordinate and four-coordinate synergistic hybrid state, breaking continuous rigid long chains and introducing inorganic flexible sites. This effectively alleviates the internal stress of the coating during curing and thermal cycling, while also improving the coating's water and alkali resistance. Furthermore, by constructing a silicon-oxygen-aluminum-boron inorganic hybrid network, the activation energy for crosslinking and curing is reduced, ensuring full crosslinking of the hybrid network and a denser coating curing, thus endowing the coating with excellent high-temperature service stability.

[0035] Mullite hollow ceramic microspheres, with their internal closed cavity structure, efficiently block heat conduction and convection, providing a core low-thermal-conductivity support for the coating. Their surface hydroxyl groups condense with the active silanol groups in KH-550 to form Si-O-Si covalent bonds, achieving chemical anchoring. These further condense with the aluminum hydroxyl groups of boehmite sol and the silanol groups of silica sol, forming a network structure interwoven with Si-O-Al and Si-O-Si covalent bonds. This network grows in situ on the microsphere substrate, continuously spreads, and becomes fully densified, thus forming a continuous and dense amorphous structure. Nano-coating layer. This coating layer forms covalent bonds with the matrix through surface-active hydroxyl groups, strengthening interfacial adhesion, preventing interfacial debonding and the formation of micropore defects, and reducing interfacial thermal resistance, allowing the intrinsic thermal insulation performance of the filler to be fully utilized. To further improve the thermal insulation effect, modified nanoporous zirconium dioxide effectively inhibits nanoparticle aggregation and retains the nanoporous structure through a surface aluminum hydroxyl complex layer. It forms a multi-level porous synergistic thermal insulation system with the micron-scale cavities of the microspheres, extending the heat conduction path and inhibiting gas convection heat transfer. At the same time, titanium dioxide, with its high refractive index, efficiently reflects infrared thermal radiation. It comprehensively improves the thermal insulation performance of the coating from three dimensions: thermal conduction, thermal convection, and thermal radiation, adapting to the coating application needs of various high-temperature thermal insulation scenarios. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the preparation process of an aqueous inorganic nano-ceramic heat-insulating coating according to the present invention.

[0037] Figure 2 This is a physical image of an aqueous inorganic nano-ceramic heat-insulating coating prepared in Example 1 of the present invention. Detailed Implementation

[0038] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the application will be further described in detail below with reference to embodiments. However, this should not be construed as limiting the scope of this application to the following examples. All other embodiments obtained by those skilled in the art without creative effort without departing from the above-described methodological spirit of this application are within the scope of protection of this application.

[0039] The singular forms “for,” “or,” “a,” “any,” and “described” used in this application are intended to include the plural forms unless the context clearly indicates otherwise. Furthermore, the terms “first” and “second” are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0040] Example 1

[0041] like Figure 1 As shown, a method for preparing a water-based inorganic nano-ceramic heat-insulating coating includes the following steps:

[0042] S1. Weigh 3.2g sodium aluminate and 0.6g boric acid, add them together to 25mL of deionized water, and stir in a 60℃ water bath at 500r / min for 15min to obtain a boron-aluminum pre-complexed solution. Under high-speed stirring at 800r / min, add the boron-aluminum pre-complexed solution dropwise to 300mL of lithium silicate inorganic resin with a solid content of 22wt% at a rate of 2mL / min, and continue stirring for 20min to obtain boron-aluminum dual-doped lithium silicate inorganic resin.

[0043] S2. Weigh 0.5g of anhydrous sodium bicarbonate, add 100mL of deionized water, and stir at 300r / min until completely dissolved to obtain a sodium bicarbonate buffer solution; weigh 2.5g of KH-550 silane coupling agent, add 25mL of deionized water, and adjust the pH to 8.5 by adding sodium bicarbonate buffer solution dropwise at a rate of 1mL / min, and stir at 300r / min for 10min to obtain a pre-hydrolyzed KH-550 solution; weigh 250g of mullite hollow ceramic microspheres with a particle size of 30nm, dry at 105℃ for 2h, transfer to a stirred tank, add 1250mL of deionized water, stir at 400r / min for 15min to disperse evenly, add the pre-hydrolyzed KH-550 solution, and adjust the pH to 8.5 by adding sodium bicarbonate buffer solution dropwise at a rate of 1mL / min, raise the temperature to 50℃, and stir at 400r / min for 30 minutes. After a period of time, activated microspheres were obtained. 50 mL of boehmite sol and 50 mL of silica sol were measured. The boehmite sol contained 20 wt% boehmite with a particle size of 30 nm. The silica sol was an alkaline sodium type with a SiO2 content of 30 wt% and a particle size of 10 nm. After mixing evenly, the mixture was added dropwise to the activated microspheres at a rate of 3 mL / min. The mixture was stirred at a low speed of 400 r / min, and the pH was adjusted to 8.5 with a buffer solution every 30 min. The mixture was heated to 65 °C and stirred at a constant temperature for 2 h. After filtration, the filter cake was washed three times with deionized water and dried at 105 °C for 2 h to obtain amorphous Al2O3-SiO2 nano-coated mullite hollow ceramic microspheres.

[0044] S3. Weigh 60g of 25nm porous zirconium dioxide, 0.5g of sodium polyacrylate, and 0.8g of aluminum nitrate nonahydrate. Add 50mL of deionized water, ultrasonically disperse at 300W for 15min, stir at 500r / min for 10min, and add the prepared sodium bicarbonate buffer solution dropwise at a rate of 0.5mL / min while stirring. Adjust the pH of the slurry to 8.5, and continue stirring at 500r / min for 5min to obtain the modified nano-zirconia slurry. Weigh 30g of rutile titanium dioxide with an average particle size of 0.25μm and 0.3g of sodium polyphosphate. Add 9mL of deionized water, ultrasonically disperse at 300W for 10min, and stir at 500r / min for 5min to obtain the titanium dioxide slurry.

[0045] S4. Add all of the modified nano-zirconia slurry to the boron-aluminum dual-doped lithium silicate inorganic resin, stir at 1000 r / min for 10 min, add titanium dioxide slurry, stir at 1000 r / min for 5 min, add 4 g of polysiloxane, stir at 400 r / min for 2 min, add 250 g of amorphous Al2O3-SiO2 nano-coated mullite hollow ceramic microspheres at a rate of 2 g / s, stir gently at 500 r / min for 15 min, adjust the viscosity to 2800 mPa·s with deionized water to obtain a water-based inorganic nano-ceramic heat insulation coating; spray the coating onto the substrate, control the wet film thickness to 1-2 mm, pre-cur at room temperature for 30 min, first transfer to a 125℃ oven to dry for 30 min, then heat to 150℃ at a heating rate of 5℃ / min and maintain the temperature for 2 h, and naturally cool to room temperature to obtain a water-based inorganic nano-ceramic heat insulation coating.

[0046] A physical image of the water-based inorganic nano-ceramic heat-insulating coating prepared in this embodiment is shown below. Figure 2 As shown.

[0047] Example 2

[0048] like Figure 1 As shown, a method for preparing a water-based inorganic nano-ceramic heat-insulating coating includes the following steps:

[0049] S1. Weigh 3g of sodium aluminate and 0.5g of boric acid, add them together to 20mL of deionized water, and stir in a 55℃ water bath at 500r / min for 10min to obtain a boron-aluminum pre-complexed solution. Under high-speed stirring at 750r / min, add the boron-aluminum pre-complexed solution dropwise to 290mL of lithium silicate inorganic resin with a solid content of 22wt%, and continue stirring for 15min to obtain boron-aluminum dual-doped lithium silicate inorganic resin.

[0050] S2. Weigh 0.4g of anhydrous sodium bicarbonate, add 100mL of deionized water, and stir at 300r / min until completely dissolved to obtain a sodium bicarbonate buffer solution; weigh 2g of KH-550 silane coupling agent, add 20mL of deionized water, and adjust the pH to 8.4 by adding sodium bicarbonate buffer solution dropwise at a rate of 0.8mL / min, stirring at 300r / min for 10min to obtain a pre-hydrolyzed KH-550 solution; weigh 240g of mullite hollow ceramic microspheres with a particle size of 10nm, dry at 100℃ for 1.5h, transfer to a stirred tank, add 1200mL of deionized water, stir at 300-500r / min for 15min to disperse evenly, add the pre-hydrolyzed KH-550 solution, and add sodium bicarbonate buffer solution dropwise at a rate of 0.8mL / min. The pH was adjusted to 8.0 with sodium buffer solution, the temperature was raised to 45℃, and the mixture was stirred at 400 rpm for 25 min to obtain activated microspheres. 45 mL of boehmite sol and 45 mL of silica sol were measured. The boehmite sol contained 20 wt% boehmite with a particle size of 10 nm. The silica sol was alkaline sodium type with a SiO2 content of 30 wt% and a particle size of 8 nm. After mixing evenly, the mixture was added dropwise to the activated microspheres at a rate of 2.5 mL / min and stirred at a low speed of 400 rpm. The pH was adjusted to 8.0 with buffer solution every 30 min. The temperature was raised to 60℃ and stirred at a constant temperature for 1.5 h. After filtration, the filter cake was washed three times with deionized water and dried at 100℃ for 1.5 h to obtain amorphous Al2O3-SiO2 nano-coated mullite hollow ceramic microspheres.

[0051] S3. Weigh 55g of 20nm porous zirconium dioxide, 0.4g of sodium polyacrylate, and 0.7g of aluminum nitrate nonahydrate. Add 45mL of deionized water, ultrasonically disperse at 300W for 15min, stir at 500r / min for 10min, and add the prepared sodium bicarbonate buffer solution dropwise at a rate of 0.4mL / min while stirring. Adjust the pH of the slurry to 8.0, and continue stirring at 500r / min for 5min to obtain the modified nano-zirconia slurry. Weigh 25g of rutile titanium dioxide with an average particle size of 0.2μm and 0.2g of sodium polyphosphate. Add 8mL of deionized water, ultrasonically disperse at 300W for 10min, and stir at 500r / min for 5min to obtain the titanium dioxide slurry.

[0052] S4. Add all of the modified nano-zirconia slurry to the boron-aluminum dual-doped lithium silicate inorganic resin, stir at 950 r / min for 8 min, add titanium dioxide slurry, stir at 950 r / min for 5 min, add 3.5 g of polysiloxane, stir at 400 r / min for 2 min, add 240 g of amorphous Al2O3-SiO2 nano-coated mullite hollow ceramic microspheres at a rate of 1.5 g / s, stir gently at 500 r / min for 15 min, adjust the viscosity to 2500 mPa·s with deionized water to obtain a water-based inorganic nano-ceramic heat insulation coating; spray the coating onto the substrate, control the wet film thickness to 1 mm, pre-cur at room temperature for 25 min, first transfer to a 120℃ oven to dry for 25 min, then heat to 145℃ at a heating rate of 4℃ / min and maintain the temperature for 1.5 h, and naturally cool to room temperature to obtain a water-based inorganic nano-ceramic heat insulation coating.

[0053] Example 3

[0054] like Figure 1 As shown, a method for preparing a water-based inorganic nano-ceramic heat-insulating coating includes the following steps:

[0055] S1. Weigh 3.4g sodium aluminate and 0.7g boric acid, add them together to 30mL of deionized water, and stir in a 65℃ water bath at 500r / min for 20min to obtain a boron-aluminum pre-complexed solution. Under high-speed stirring at 850r / min, add the boron-aluminum pre-complexed solution dropwise to 310mL of lithium silicate inorganic resin with a solid content of 22wt%, and continue stirring for 25min to obtain boron-aluminum dual-doped lithium silicate inorganic resin.

[0056] S2. Weigh 0.5g of anhydrous sodium bicarbonate, add 90mL of deionized water, and stir at 300r / min until completely dissolved to obtain a sodium bicarbonate buffer solution; weigh 3g of KH-550 silane coupling agent, add 30mL of deionized water, and adjust the pH to 8.6 by adding sodium bicarbonate buffer solution dropwise at a rate of 1.2mL / min, stirring at 300r / min for 10min to obtain a pre-hydrolyzed KH-550 solution; weigh 260g of mullite hollow ceramic microspheres with a particle size of 40nm, dry at 110℃ for 2.5h, transfer to a stirred tank, add 1300mL of deionized water, stir at 400r / min for 15min to disperse evenly, add the pre-hydrolyzed KH-550 solution, and add sodium bicarbonate buffer solution dropwise at a rate of 1.2mL / min. The solution was adjusted to pH 9.0, heated to 55℃, and stirred at 400 rpm for 35 min to obtain activated microspheres. 55 mL of boehmite sol and 55 mL of silica sol were measured. The boehmite sol contained 20 wt% boehmite with a particle size of 40 nm. The silica sol was an alkaline sodium type with a SiO2 content of 30 wt% and a particle size of 15 nm. After mixing thoroughly, the mixture was added dropwise to the activated microspheres at a rate of 3.5 mL / min, stirred at 400 rpm, and the pH was adjusted to 9.0 with a buffer solution every 30 min. The mixture was heated to 70℃ and stirred at a constant temperature for 2.5 h. After filtration, the filter cake was washed three times with deionized water and dried at 110℃ for 2.5 h to obtain amorphous Al2O3-SiO2 nano-coated mullite hollow ceramic microspheres.

[0057] S3. Weigh 65g of 30nm porous zirconium dioxide, 0.6g of sodium polyacrylate, and 0.9g of aluminum nitrate nonahydrate. Add 55mL of deionized water, ultrasonically disperse at 300W for 15min, stir at 500r / min for 10min, and add the prepared sodium bicarbonate buffer solution dropwise at a rate of 0.6mL / min while stirring. Adjust the pH of the slurry to 9.0, and continue stirring at 500r / min for 5min to obtain the modified nano-zirconia slurry. Weigh 35g of rutile titanium dioxide with an average particle size of 0.3μm and 0.3g of sodium polyphosphate. Add 10mL of deionized water, ultrasonically disperse at 300W for 10min, and stir at 500r / min for 5min to obtain the titanium dioxide slurry.

[0058] S4. Add all of the modified nano-zirconia slurry to the boron-aluminum dual-doped lithium silicate inorganic resin, stir at 1050 r / min for 12 min, add titanium dioxide slurry, maintain high-speed stirring at 1050 r / min for 5 min, add 4.5 g of polysiloxane, stir at 400 r / min for 2 min, add 260 g of amorphous Al2O3-SiO2 nano-coated mullite hollow ceramic microspheres at a rate of 2.5 g / s, stir gently at 500 r / min for 15 min, adjust the viscosity to 3000 mPa·s with deionized water to obtain a water-based inorganic nano-ceramic heat insulation coating; spray the coating onto the substrate, control the wet film thickness to 2 mm, pre-cur at room temperature for 35 min, first transfer to a 130℃ oven to dry for 35 min, then heat to 155℃ at a heating rate of 6℃ / min and maintain the temperature for 2.5 h, and naturally cool to room temperature to obtain a water-based inorganic nano-ceramic heat insulation coating.

[0059] Comparative Example 1

[0060] A method for preparing an aqueous inorganic nano-ceramic thermal insulation coating differs from Example 1 in that the boron-aluminum pre-complexed solution is not prepared in step S1, and boron-aluminum doping is not performed; that is, lithium silicate inorganic resin is used directly. The remaining steps and parameters are the same.

[0061] Comparative Example 2

[0062] A method for preparing an aqueous inorganic nano-ceramic thermal insulation coating differs from Example 1 in that step S2 does not involve coating mullite hollow ceramic microspheres; instead, mullite hollow ceramic microspheres are used directly. The remaining steps and parameters are the same.

[0063] Comparative Example 3

[0064] A method for preparing an aqueous inorganic nano-ceramic heat-insulating coating differs from Example 1 in that modified nano-zirconia slurry is not prepared in step S3, while the remaining steps and parameters are the same.

[0065] Comparative Example 4

[0066] A method for preparing an aqueous inorganic nano-ceramic heat-insulating coating differs from Example 1 in that titanium dioxide slurry is not prepared in step S3, while the remaining steps and parameters are the same.

[0067] Performance testing:

[0068] Thermal conductivity test: The water-based inorganic nano-ceramic thermal insulation coatings prepared in Examples 1-3 and Comparative Examples 1-4 were processed into standard square samples of 50mm×50mm×2mm to ensure that the sample surface was flat and free of defects and that the thickness was uniform. The sample was placed in the central test chamber of the protective hot plate test device. After the device was closed, the test environment temperature was controlled to be stable at 25℃, and the temperature difference between the hot plate and the cold plate was adjusted to 5℃. The device was turned on and the system was run until it reached thermal equilibrium. The temperature was maintained for 30 minutes. The heat flux density, hot surface temperature and cold surface temperature data of the sample were collected in real time by the built-in sensor of the device. The thermal conductivity of the coating was automatically calculated by the instrument according to the standard formula. Each sample was tested in parallel 3 times. After removing abnormal data, the arithmetic mean was taken as the final thermal conductivity result.

[0069] Adhesion test: The test was conducted according to GB / T9286-1998 "Cross-cut test of paint and varnish film". Three test areas without scratches or bubbles were selected on the dry and intact coating surface of the water-based inorganic nano-ceramic heat insulation coatings prepared in Examples 1-3 and Comparative Examples 1-4 using a cross-cut tester. The cross-cut tester was pressed vertically against the coating surface and cut a 1mm×1mm square grid at a uniform speed. The cutting depth was ensured to penetrate the coating to the bottom layer of the metal substrate. After cutting, the surface was cleaned 5 times along the diagonal of the grid with a soft brush to remove surface debris and coating fragments. 3M 600 test tape was tightly adhered to the grid area. The tape was repeatedly pressed with fingers to remove internal air bubbles and ensure that the tape was in complete contact with the coating. After standing for 5 minutes, the tape was quickly peeled off at a 180° angle. The coating peeling within the grid was observed. The adhesion level was determined according to the standard rating rules, with level 0 being the best (no peeling) and level 5 being the worst (large-area peeling). The average rating of the three test sites for each sample was taken.

[0070] High-temperature service stability test: The water-based inorganic nano-ceramic thermal insulation coatings prepared in Examples 1-3 and Comparative Examples 1-4 were processed into standard samples of 100mm × 50mm, respectively. The sample surfaces were undamaged, scratch-free, and the coating thickness was uniform. The above samples were placed in a constant temperature forced-air drying oven, and the oven temperature was set at 180℃ for continuous constant temperature baking for 500h. During the baking period, the surface condition of the sample was observed and recorded every 100h. After baking, the sample was removed and allowed to cool naturally to room temperature at 25℃. The presence of defects such as yellowing, blistering, cracking, powdering, peeling, and delamination on the coating surface was observed and recorded. This was used as the evaluation basis for high-temperature service stability. The absence of obvious defects indicated that the coating had good high-temperature service stability.

[0071] Water resistance test: The water-based inorganic nano-ceramic heat insulation coatings prepared in Examples 1-3 and Comparative Examples 1-4 were marked with water-immersed and non-water-immersed areas, respectively. Two-thirds of the sample area was vertically immersed in a sealed container filled with 25°C deionized water, ensuring that the water surface completely covered the marked water-immersed area. The container was sealed to prevent dust and impurities from falling in. After continuous immersion for 96 hours, the sample was removed and the surface moisture was immediately gently absorbed with dust-free filter paper. The water-immersed area of ​​the coating was observed to see if whitening, blistering, swelling, peeling, wrinkling, or other phenomena occurred. After standing for 2 hours, the adhesion grade of the coating after immersion was tested according to GB / T9286-1998. The changes in adhesion grade and surface condition before and after immersion were compared to comprehensively evaluate the water resistance performance of the coating.

[0072] Thermal cycling performance test: The water-based inorganic nano-ceramic thermal insulation coatings prepared in Examples 1-3 and Comparative Examples 1-4 were processed into standard samples of 100mm×50mm and placed in a thermal cycling test chamber. The cycling program was set as follows: the temperature was lowered to -40℃ at a rate of 10℃ / min and held at a constant temperature for 30min, and then the temperature was raised to 150℃ at a rate of 10℃ / min and held at a constant temperature for 30min to complete one thermal cycle. The test was carried out continuously for 50 cycles. The appearance of the sample was monitored in real time during the cycle. After all cycles were completed, the sample was taken out and placed at room temperature of 25℃ for 2h. The surface of the coating was observed to see whether there were failure phenomena such as cracking, peeling, flaking, powdering, or delamination. If there were no obvious defects, the thermal cycling performance was judged to be qualified. If defects appeared, the type and degree of defects were recorded.

[0073] Fire resistance rating test: The water-based inorganic nano-ceramic heat insulation coatings prepared in Examples 1-3 and Comparative Examples 1-4 were processed into standard samples of 100mm × 50mm and tested for fire resistance rating according to GB8624-2012 "Classification of Combustion Performance of Building Materials and Products". This standard classifies the combustion performance of materials into four levels from high to low: Class A (non-combustible materials), Class B1 (flame-retardant materials), Class B2 (combustible materials), and Class B3 (flammable materials). Class A has no ignition, no flame spread, no dripping, and no continuous combustion, which is the highest fire resistance rating; Class B1 is difficult to ignite when exposed to fire and extinguishes immediately after the fire source is removed; Class B2 can be ignited and continues to burn; Class B3 is very easy to ignite and has a fast burning rate. During the test, the samples were placed in the test device, and their combustion performance was measured. It was observed whether the samples ignited, whether there was flame spread, whether there were dripping, and whether there was continuous combustion. The corresponding combustion performance rating was determined according to the standard.

[0074] Table 1. Performance test results of the waterborne inorganic nano-ceramic thermal insulation coatings prepared in Examples 1-3 and Comparative Examples 1-4

[0075]

[0076] As shown in Table 1, the thermal conductivity of the water-based inorganic nano-ceramic thermal insulation coatings prepared in Examples 1-3 is lower than that of Comparative Examples 1-4, and the adhesion and fire resistance are higher than those of Comparative Examples 1-4. This indicates that the thermal insulation performance, interfacial bonding strength, environmental service stability and fire resistance of the water-based inorganic nano-ceramic thermal insulation coatings prepared in Examples 1-3 are all better than those of Comparative Examples 1-4.

[0077] Comparative Example 1 uses pure lithium silicate inorganic resin without boron-aluminum dual doping. Lacking the silicon-oxygen-aluminum-boron inorganic hybrid network structure, the absence of aluminum prevents the improvement of the crosslinking density and compactness of the lithium silicate network. The absence of boron also prevents the introduction of flexible sites to alleviate internal stress, leading to severe cracking and peeling of the coating during thermal cycling. After high-temperature aging, significant yellowing and cracking occur, resulting in extremely poor high-temperature service stability. Furthermore, the high resin curing activation energy and insufficient crosslinking result in an overall porous coating, increasing thermal conductivity and significantly reducing thermal insulation performance. On the other hand, insufficient hydroxyl activity in the matrix prevents the formation of efficient inorganic bonds with the filler, resulting in weak interfacial bonding and an initial adhesion level of only 2. After water immersion, the resin exhibits poor water resistance, turning white and blistering, further reducing adhesion to level 3. Moreover, the coating's structural defects limit its fire resistance to only B1 grade flame retardant, significantly degrading its overall performance.

[0078] Comparative Example 2 did not involve coating the mullite hollow ceramic microspheres. The microspheres could not be chemically anchored to the film-forming matrix via covalent bonds, resulting in numerous micropore defects at the filler-matrix interface. This significantly increased interfacial thermal resistance, preventing the microspheres from fully utilizing their intrinsic thermal insulation properties and leading to an increased coating thermal conductivity. Furthermore, it directly weakened interfacial adhesion, reducing the initial adhesion to level 3. During water immersion, moisture easily penetrated along these defects, causing coating swelling and localized detachment. After water immersion, the adhesion dropped to level 4. During thermal cycling, the interface easily debonded, resulting in localized detachment and blistering. High-temperature aging also caused blistering and localized detachment due to interfacial failure. Simultaneously, the interfacial defects damaged the overall density of the coating, failing to meet the Class A non-combustible standard and only achieving Class B1 flame retardancy. This demonstrates the crucial role of the nano-coating layer in interfacial bonding, thermal insulation performance, and stability.

[0079] Comparative Example 3, without the addition of modified nanoporous zirconium dioxide, lacked a multi-level porous synergistic insulation system composed of nanopores and micron-sized cavities of mullite microspheres. This resulted in an inability to effectively extend the heat conduction path and suppress gas convection heat transfer. Relying solely on single microspheres for insulation led to an increased thermal conductivity and a significant reduction in insulation effectiveness. Furthermore, the lack of structural support from modified nanoporous zirconium dioxide and the auxiliary dispersion from the surface aluminum hydroxyl complex layer resulted in decreased coating density and structural integrity. Initial adhesion was only Grade 1, and slight whitening occurred after water immersion. Minor cracking occurred during thermal cycling due to uneven internal stress distribution, and slight yellowing occurred after high-temperature aging. Insufficient coating density also reduced fire resistance to Grade B1. This fully demonstrates the core value of modified nanoporous zirconium dioxide in constructing a multi-level insulation system and improving coating structural stability.

[0080] Comparative Example 4, without the addition of rutile titanium dioxide, lacks the efficient reflection of infrared thermal radiation by the high-refractive-index filler. The coating can only achieve thermal insulation from the dimensions of heat conduction and heat convection, failing to form a comprehensive thermal insulation mechanism. This results in an increased thermal conductivity and decreased thermal insulation performance. Furthermore, the absence of titanium dioxide, a functional filler, reduces the coating's filling density and structural reinforcement effect. The initial adhesion is only Grade 1. After water immersion, there are no obvious appearance defects, but the adhesion remains at Grade 1. After thermal cycling, slight powdering occurs due to insufficient structural toughness of the coating. Slight powdering also occurs after high-temperature aging. Moreover, the overall coating lacks a dense and compact structure, weakening it and preventing it from achieving Grade A non-combustible performance, only reaching Grade B1 flame retardant. This demonstrates the important synergistic role of rutile titanium dioxide in thermal radiation reflection and assisting in improving the coating's structural performance.

[0081] Comparative Examples 1-4, due to the lack of boron-aluminum dual-doping modification, amorphous Al2O3-SiO2 nano-coating, modified nanoporous zirconium dioxide, and rutile titanium dioxide, resulted in defects in the coating film matrix structure, weak interfacial bonding of fillers, lack of a multi-level synergistic thermal insulation system, and insufficient thermal radiation reflection capacity. Consequently, the thermal conductivity increased, the adhesion decreased, and the water resistance, thermal cycling performance, and high-temperature service stability all deteriorated significantly. The fire rating also failed to meet the Class A non-combustible standard. All of these factors manifested as varying degrees of deterioration in thermal insulation performance, interfacial bonding strength, environmental service stability, and fire resistance.

[0082] The above results demonstrate and describe the basic principles and main features of this application, as well as its advantages.

[0083] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. A water-based inorganic nano-ceramic heat-insulating coating, characterized in that, The coating is prepared from the following raw materials: boron-aluminum dual-doped lithium silicate inorganic resin, amorphous Al2O3-SiO2 nano-coated mullite hollow ceramic microspheres, modified nanoporous zirconium dioxide slurry, titanium dioxide slurry, and defoamer. The boron-aluminum dual-doped lithium silicate inorganic resin is obtained by reacting sodium aluminate and boric acid pre-complexed with lithium silicate inorganic resin. The amorphous Al2O3-SiO2 nano-coated mullite hollow ceramic microspheres were obtained by KH-550 activation of mullite hollow ceramic microspheres followed by coating with boehmite sol and silica sol. The modified nanoporous zirconium dioxide slurry was obtained by dispersing nanoporous zirconium dioxide with sodium polyacrylate, complexing with aluminum nitrate nonahydrate, and neutralizing and modifying with sodium bicarbonate buffer solution. The titanium dioxide slurry is obtained by dispersing rutile titanium dioxide with sodium polyphosphate. The defoamer is polysiloxane.

2. The water-based inorganic nano-ceramic heat-insulating coating according to claim 1, characterized in that, The mass ratio of the boron-aluminum dual-doped lithium silicate inorganic resin, amorphous Al2O3-SiO2 nano-coated mullite hollow ceramic microspheres, modified nanoporous zirconium dioxide slurry, titanium dioxide slurry, and defoamer is (313.5-344.1):(240-260):(101.1-121.5):(33.2-45.4):(3.5-4.5); the mass-to-volume ratio of sodium aluminate, boric acid, and lithium silicate inorganic resin is (3.0-3.4) g:(0.5-0.7) g. (290-310) mL; the mass-to-volume ratio of the mullite hollow ceramic microspheres, KH-550, boehmite sol and silica sol is (240-260) g: (2-3) g: (45-55) mL: (45-55) mL; the mass ratio of the nanoporous zirconium dioxide, sodium polyacrylate and aluminum nitrate nonahydrate is (55-65): (0.4-0.6): (0.7-0.9); the mass ratio of the rutile titanium dioxide and sodium polyphosphate is (25-35): (0.2-0.4).

3. The water-based inorganic nano-ceramic heat-insulating coating according to claim 1, characterized in that, The lithium silicate inorganic resin has a solid content of 22 wt%; the mullite hollow ceramic microspheres have an average particle size of 20-50 μm; the boehmite sol has a boehmite content of 20 wt% and a particle size of 10-40 nm; the silica sol is alkaline sodium type, with a SiO2 content of 30 wt% and a particle size of 8-15 nm; the sodium bicarbonate buffer solution has a mass fraction of 0.4 wt%-0.55 wt%; the nanoporous zirconium dioxide has a particle size of 20-30 nm; and the rutile titanium dioxide has an average particle size of 0.2-0.3 μm.

4. A method for preparing an aqueous inorganic nano-ceramic heat-insulating coating as described in any one of claims 1-3, characterized in that, Includes the following steps: S1. Sodium aluminate, boric acid and deionized water are mixed and placed in a water bath to obtain a boron-aluminum pre-complexed solution. This solution is then added dropwise to lithium silicate inorganic resin and stirred to react, resulting in boron-aluminum dual-doped lithium silicate inorganic resin. S2. Prepare a sodium bicarbonate buffer solution and add it dropwise to a mixture of KH-550 and deionized water to adjust the pH, thus obtaining a pre-hydrolyzed KH-550 solution. After drying the mullite hollow ceramic microspheres, add deionized water and the pre-hydrolyzed KH-550 solution, adjust the pH, and perform a first heating reaction to obtain activated microspheres. Add a mixture of boehmite sol and silica sol, perform a second heating reaction, filter, and vacuum dry to obtain amorphous Al2O3-SiO2 nano-coated mullite hollow ceramic microspheres. S3. Mix nanoporous zirconium dioxide, sodium polyacrylate, aluminum nitrate nonahydrate and deionized water, and add sodium bicarbonate buffer solution to adjust the pH to obtain modified nanoporous zirconium dioxide slurry; mix rutile titanium dioxide, sodium polyphosphate and deionized water to obtain titanium dioxide slurry; S4. Modified nanoporous zirconium dioxide slurry is added to boron-aluminum dual-doped lithium silicate inorganic resin and dispersed at high speed. Titanium dioxide slurry and polysiloxane are added, and amorphous Al2O3-SiO2 nano-coated mullite hollow ceramic microspheres are added to adjust the viscosity of the system to obtain a coating. The coating is sprayed onto the substrate, pre-cured at room temperature, dried, cured at elevated temperature, and naturally cooled to obtain a water-based inorganic nano-ceramic heat insulation coating.

5. The method for preparing an aqueous inorganic nano-ceramic heat-insulating coating according to claim 4, characterized in that, In step S1, the mass-to-volume ratio of sodium aluminate to deionized water is (3.0-3.4) g : (20-30) mL; the temperature of the water bath is 55-65℃, and the water bath time is 10-20 min; the dropping rate is 1.5-2.5 mL / min; the stirring speed is 750-850 r / min, and the stirring time is 15-25 min.

6. The method for preparing an aqueous inorganic nano-ceramic heat-insulating coating according to claim 4, characterized in that, In S2, the step of preparing the sodium bicarbonate buffer solution is as follows: 0.4-0.5g of anhydrous sodium bicarbonate is mixed with 90-100mL of deionized water and stirred at 300r / min until completely dissolved to obtain the sodium bicarbonate buffer solution; the mass-volume ratio of KH-550 to deionized water is (2-3)g:(20-30)mL; the dropping rate is 0.8-1.2mL / min; the pH is adjusted to 8.4-8.6; and the mass-volume ratio of mullite hollow ceramic microspheres to deionized water is (240-260)g:(1200-1300)mL.

7. The method for preparing an aqueous inorganic nano-ceramic heat-insulating coating according to claim 4, characterized in that, In step S2, the drying temperature is 100-110℃, and the drying time is 1.5-2.5h; the pH adjustment step is as follows: sodium bicarbonate buffer solution is added dropwise at a rate of 0.8-1.2mL / min to adjust the pH to 8.0-9.0; the temperature of the first heating reaction is 45-55℃, and the time of the first heating reaction is 25-35min; the dropwise addition rate is 2.5-3.5mL / min; the temperature of the second heating reaction is 60-70℃, and the time of the second heating reaction is 1.5-2.5h; the vacuum drying temperature is 100-110℃, and the vacuum drying time is 1.5-2.5h.

8. The method for preparing an aqueous inorganic nano-ceramic heat-insulating coating according to claim 4, characterized in that, In step S3, the mass-to-volume ratio of the nanoporous zirconium dioxide to deionized water is (55-65) g: (45-55) mL; the dropping rate of the sodium bicarbonate buffer solution is 0.4-0.6 mL / min; the pH is adjusted to 8.0-9.0; and the mass-to-volume ratio of the rutile titanium dioxide to deionized water is (25-35) g: (8-10) mL.

9. The method for preparing an aqueous inorganic nano-ceramic heat-insulating coating according to claim 4, characterized in that, In step S4, the high-speed dispersion rotation speed is 950-1050 r / min, and the high-speed dispersion time is 8-12 min; the rate of adding amorphous Al2O3-SiO2 nano-coated mullite hollow ceramic microspheres is 1.5-2.5 g / s; the step of adjusting the viscosity of the system is to adjust the viscosity to 2500-3000 mPa·s with deionized water.

10. The method for preparing an aqueous inorganic nano-ceramic heat-insulating coating according to claim 4, characterized in that, In step S4, the thickness of the wet film sprayed is controlled to be 1-2 mm; the pre-curing time is 25-35 min; the drying temperature is 120-130℃ and the drying time is 25-35 min; the heating and curing step is: heating to 145-155℃ at a heating rate of 4-6℃ / min and then curing at a constant temperature for 1.5-2.5 h.

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