High-temperature-resistant zirconia-based nanoporous thermal insulation composite material and preparation method thereof

Abstract

The application relates to the technical field of aerospace heat insulation materials, and discloses a high-temperature-resistant zirconia-based nano-porous heat insulation composite material and a preparation method thereof. Low-density nano zirconia powder, second-phase oxide powder, a light shielding agent and short-cut high-temperature-resistant fibers are uniformly mixed through mechanical mixing, a zirconia-based blank body with a required shape is obtained through a die molding process, and the zirconia-based blank body is obtained by adjusting a die pressure and / or adopting a limiting device; the zirconia-based blank body is placed in a sealed tank, and silanolate steam and water vapor are respectively introduced into the sealed tank through separate steam conveying pipelines, the zirconia-based blank body after steam treatment is obtained by controlling a steam treatment environment temperature and a holding time; the zirconia-based blank body after steam treatment is subjected to drying treatment, is heated to a temperature higher than a boiling point of the silanolate and is held, the sample is cooled to room temperature, and the high-temperature-resistant zirconia-based nano-porous heat insulation composite material is obtained.

Description

Technical Field

[0001] This invention relates to the field of aerospace thermal insulation materials technology, and in particular, to a high-temperature resistant zirconia-based nanoporous thermal insulation composite material and its preparation method. Background Technology

[0002] In recent years, with the rapid development of aerospace technology, the flight speed of new aircraft has been continuously increasing, and the flight time within the atmosphere has been significantly extended. This has led to more extreme high-temperature environments and complex aerodynamic loads posing challenges to the thermal protection systems (TPS) of aircraft. Therefore, developing lightweight thermal insulation materials with excellent temperature resistance, ultra-low thermal conductivity, and good mechanical strength has become a key technical challenge that urgently needs to be solved in this field.

[0003] Traditional thermal insulation materials, such as ceramic fiber felt and quartz wool felt, can meet the thermal insulation requirements of medium and low temperature ranges to a certain extent. However, when faced with the above-mentioned extreme working conditions, their thermal insulation efficiency often drops significantly due to their high solid thermal conductivity and structural degradation at high temperatures, making it difficult to meet the thermal protection design requirements of the next generation of aircraft.

[0004] Among numerous candidate materials, oxide aerogels are considered highly promising next-generation high-temperature insulation materials due to their extremely high porosity, nanoscale porous structure, extremely low intrinsic thermal conductivity, and high specific surface area. Common oxide aerogels mainly include silica (SiO2), alumina (Al2O3), and zirconium oxide (ZrO2). Among them, zirconium oxide (ZrO2), due to its extremely high melting point (approximately 2700℃) and relatively low intrinsic thermal conductivity at high temperatures (e.g., approximately 2.29 W / (m·K) at 1000℃), is theoretically best suited for ultra-high temperature insulation applications.

[0005] However, pure zirconia aerogel faces two major technological bottlenecks in practical applications, which severely restrict its engineering application: Structural failure due to high-temperature crystal transformation: Under normal pressure, zirconia exists in three crystal forms: monoclinic (m-ZrO2), tetragonal (t-ZrO2), and cubic (c-ZrO2). The low-temperature stable monoclinic phase undergoes a reversible martensitic transformation to the tetragonal phase when the temperature rises to approximately 1170℃. This phase transformation is accompanied by a volume shrinkage of approximately 7%–9%. This drastic volume change causes the collapse and cracking of the nanoframework within the zirconia aerogel, thereby destroying its fine nanoporous structure and leading to a sharp decline or even complete failure of the material's thermal insulation performance.

[0006] Fragile mechanical properties: Zirconia aerogels are typically composed of nanoparticles linked by weak physical or chemical bonds, resulting in weak interparticle bonding. This leads to the material exhibiting extremely brittle characteristics and very low mechanical strength, making it difficult to withstand the vibrations, impacts, and thermal stresses generated during takeoff, landing, and flight of aircraft. It is highly susceptible to pulverization or peeling.

[0007] To address the aforementioned issues, existing technologies typically employ a composite reinforcement strategy. For instance, Chinese invention patent ZL201310139544.1 discloses a zirconia-silica composite aerogel, which suppresses the phase transformation and shrinkage of zirconia by introducing a silica component; Chinese invention patent ZL201310498274.3 discloses a method for preparing an alumina-silica-zirconia ternary composite aerogel, aiming to improve the overall mechanical properties of the material.

[0008] However, the aforementioned existing technologies still have significant limitations: First, due to the introduction of components with low melting points or those that are prone to phase transformation at high temperatures (such as SiO2, which has a melting point of 1670℃ and reacts with ZrO2 at high temperatures to form a eutectic), the upper limit of the long-term service temperature of these composite materials is usually limited to around 1000℃. This makes it impossible to truly leverage the advantages of zirconium oxide in resisting ultra-high temperatures and to meet more stringent thermal protection requirements.

[0009] Secondly, most existing aerogel preparation processes follow the traditional sol-gel method, which is complex and has a long production cycle. In particular, to achieve amorphous state or specific microstructures, a large amount of organic solvent is often required for the reaction, and expensive and dangerous supercritical drying equipment is needed for solvent removal. This not only significantly increases production costs and safety risks, but also makes it difficult to rapidly prepare large-sized, complex-shaped components.

[0010] In summary, there is a lack of zirconia-based thermal insulation materials in the current technology that can work stably for a long time in high-temperature environments of 1200℃ and above while maintaining high strength and low thermal conductivity. Moreover, the existing preparation process is complex and costly, which is not conducive to large-scale application. Summary of the Invention

[0011] This invention provides a high-temperature resistant zirconia-based nanoporous thermal insulation composite material and its preparation method. The fiber-reinforced zirconia-based porous preform is constructed by compression molding, and a silicon oxide coating layer is constructed in situ on the surface of the nanoframework by hydrolysis-condensation reaction of gas-phase silanol to suppress high-temperature phase transformation shrinkage. This solves the technical problems of existing zirconia-based thermal insulation materials, such as structural failure due to high-temperature crystal transformation, insufficient mechanical strength, complex preparation process, and limited operating temperature (only about 1000℃).

[0012] According to one aspect of the present invention, a method for preparing a high-temperature resistant zirconia-based nanoporous thermal insulation composite material is provided, comprising the following steps: S100, using low-density nano-zirconia powder as the matrix component, adding second-phase oxide powder and a light-blocking agent, and short-cut high-temperature resistant fibers, mixing them uniformly by mechanical mixing, pouring the mixed raw materials into a customized mold, obtaining a zirconia-based preform of the desired shape by compression molding, and obtaining a 0.50 g·cm³ preform by adjusting the molding pressure and / or using a limiting device. -3 - 0.86 g·cm -3 S200: The zirconia-based preform is placed in a sealed container. Silica alkoxide vapor and water vapor are introduced into the container through separate steam delivery pipelines. By controlling the temperature and holding time of the steam treatment environment, the silica alkoxide vapor and water vapor are allowed to fully contact the surface and pores of the zirconia-based preform in a closed steam environment, and a hydrolysis-condensation reaction occurs, thereby forming a silicon oxide coating layer on the surface of the zirconia framework, thus obtaining a steam-treated zirconia-based preform. S300: The steam-treated zirconia-based preform is dried by heating to a temperature higher than the boiling point of the silica alkoxide and holding for 1-12 hours. Then, the sample is cooled to room temperature to obtain a high-temperature resistant zirconia-based nanoporous thermal insulation composite material.

[0013] Furthermore, the low-density nano-zirconia powder in step S100 is one or a mixture of several of the following: monoclinic zirconia, tetragonal zirconia powder, cubic zirconia powder, or yttrium-stabilized zirconia powder, with a specific surface area of ​​25 m². 2 ·g -1 -65m 2 ·g -1 Preferably, the specific surface area is 40 m². 2 ·g -1 -65 m 2 ·g -1 .

[0014] Furthermore, the second phase oxide powder in step S100 is one or a mixture of several of silicon oxide, aluminum oxide or yttrium oxide; the amount of the second phase oxide powder added is 10 wt%-50 wt%.

[0015] Further, the light-blocking agent in step S100 is one or a mixture of several of silicon carbide, titanium oxide, or potassium hexatitanate whiskers; the particle size of the light-blocking agent is 2μm-5μm; and the amount of light-blocking agent added is 5 wt%~20 wt%. Preferably, the light-blocking agent is silicon carbide.

[0016] Further, in step S100, the chopped high-temperature resistant fiber is one or a mixture of several of the following: chopped alumina fiber, chopped mullite fiber, chopped zirconia fiber, and chopped polycrystalline alumina fiber; the fiber length of the chopped high-temperature resistant fiber is 1 mm to 20 mm; and the amount of chopped high-temperature resistant fiber added is 5 wt% to 20 wt%. Preferably, the fiber length of the chopped high-temperature resistant fiber is 2 mm to 8 mm.

[0017] Further, the silanolate in step S200 is one or a mixture of several of tetraethyl orthosilicate, methyltriethoxysilane, methyl orthosilicate, methyltrimethoxysilane, dimethyldiethoxysilane, or dimethyldimethoxysilane; the mass ratio of the silanolate to the zirconia-based preform is 20 wt%-100 wt%, and the mass ratio of water to the silanolate is 5 wt%-70 wt%.

[0018] Further, the steam treatment process in step S200 is specifically as follows: the pressed zirconia-based blank is placed in a sealed container, and silanol salt vapor and water vapor are introduced into the sealed container through separate steam delivery pipelines. The silanol salt and water are placed in the evaporation devices of the corresponding steam delivery pipelines, and after heating, they form silanol salt vapor and water vapor and are delivered into the sealed container. The steam treatment ambient temperature is close to the boiling point of the silanol salt reactant used, and the heat preservation time is 12 hours to 24 hours.

[0019] Furthermore, in step S300, the temperature above the boiling point of the silanol salt refers to a temperature 10°C to 50°C higher than the boiling point of the silanol salt reactant used.

[0020] According to another aspect of the present invention, a high-temperature resistant zirconia-based nanoporous thermal insulation composite material is also provided, which is prepared by the above-described method for preparing the high-temperature resistant zirconia-based nanoporous thermal insulation composite material.

[0021] Furthermore, the density of the zirconia-based nanoporous thermal insulation composite material is 0.50 g·cm³. -3 -0.90 g·cm -3 The compressive strength at 10% strain is 0.50 MPa-0.70 MPa, the temperature resistance is 1200℃, and the thermal conductivity at 1200℃ is 0.04 W·m. -1 ·K -1 -0.07 W·m -1 ·K -1 .

[0022] The present invention has the following beneficial effects: 1. The effect of compression molding on the microstructure and mechanical properties: By introducing chopped high-temperature resistant fibers, second-phase oxide powder, and opacifiers, and combining mechanical mixing with compression molding, the precise construction of the material's macroscopic morphology and microstructure is achieved; the compression molding process, combined with a limiting device, can precisely control the preform density to 0.50 g·cm³. -3 - 0.86 g·cm -3 Within a certain range, the material is ensured to have a suitable porosity to maintain low thermal conductivity; the short-cut high-temperature resistant fibers form a three-dimensional randomly distributed reinforcing network in the matrix, which plays a significant role in toughening and crack resistance, effectively improving the brittleness of the pure oxide matrix, and enhancing the compressive strength and flexural strength of the material, enabling it to withstand mechanical loads and thermal stresses during service; at the same time, the introduction of the second-phase oxide powder plays a role in inhibiting the abnormal growth of zirconia grains in the initial stage, while the uniform dispersion of the light-blocking agent helps to scatter infrared radiation in high-temperature environments and reduce radiative heat transfer efficiency.

[0023] 2. Mechanism of improving high-temperature phase transformation stability through gas-phase steam treatment: Separate steam delivery pipelines are used to introduce silanol salt vapor and water vapor into the sealed tank. Combined with specific ambient temperature control, in-situ coating and modification of silicon oxide on the surface of the zirconia framework are achieved. The separate pipeline design ensures that the precursor vapor and water vapor remain independent before entering the reaction zone, avoiding homogeneous nucleation reactions in the gas phase in advance, thus ensuring that the silanol salt vapor can penetrate deeply into the internal pores of the green body. Without the need for external catalysts, the active sites and adsorbed water on the zirconia surface promote the hydrolysis-condensation reaction of silanol salt. This process not only forms a continuous silicon oxide coating layer on the surface and neck region of zirconia particles, but also forms stable zirconium-oxygen-silicon chemical bonds on the surface of zirconia particles through chemical reactions. This chemical bond greatly enhances the connection strength between particles and acts as a diffusion barrier layer, effectively inhibiting the migration of oxygen ions and grain boundary movement at high temperatures, thereby blocking the volume shrinkage caused by the transformation of the monoclinic phase to the tetragonal phase and maintaining the integrity of the nanoporous structure.

[0024] 3. The effect of heat treatment process on structural stability and purity: By heating the steam-treated blank to a temperature higher than the boiling point of siloxane and holding it at that temperature, unreacted adsorbates and excess products remaining in the pores can be completely removed, preventing them from volatilizing or decomposing during subsequent high-temperature use and causing the pore structure to collapse. This heat treatment process promotes further densification and network improvement of the silicon oxide coating layer, while eliminating residual stress inside the material, making the bond between the zirconia skeleton and the silicon oxide coating layer stronger, and finally obtaining a composite material with excellent high-temperature phase transformation stability, low thermal conductivity and high mechanical strength.

[0025] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. The invention will now be described in further detail with reference to the figures. Attached Figure Description

[0026] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a process flow diagram of the preparation method of the high-temperature resistant zirconia-based nanoporous thermal insulation composite material according to a preferred embodiment of the present invention; Figure 2 This is a diagram of a zirconium oxide-based nanoporous thermal insulation composite material sequentially doped with silicon oxide, yttrium oxide, and aluminum oxide, according to a preferred embodiment of the present invention. Figure 3 This is an XPS image of a zirconia-based nanoporous thermal insulation composite material according to a preferred embodiment of the present invention; Figure 4 This is a stress-strain curve diagram of the zirconium oxide nanoporous thermal insulation composite material before and after tetraethyl orthosilicate steam treatment according to a preferred embodiment of the present invention, wherein... Figure 4 (a) shows the compressive stress-strain curves before and after steam treatment. Figure 4 (b) shows the bending stress-strain curves before and after steam treatment. Detailed Implementation

[0027] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, the present invention can be implemented in many different ways as defined and covered below. Unless otherwise stated, the raw materials and reagents used in the following embodiments are commercially available or can be prepared by known methods.

[0028] like Figure 1 As shown, the preparation method of the high-temperature resistant zirconia-based nanoporous thermal insulation composite material in this embodiment includes the following steps: S100, using low-density nano-zirconia powder as the matrix component, adding second-phase oxide powder and a light-blocking agent, as well as short-cut high-temperature resistant fibers, and mixing them uniformly by mechanical mixing, pouring the mixed raw materials into a customized mold, and obtaining a zirconia-based preform of the desired shape through a compression molding process, and obtaining a 0.50 g·cm³ preform by adjusting the compression molding pressure and / or using a limiting device. -3 -0.86 g·cm -3S200: The zirconia-based preform is placed in a sealed container. Silica alkoxide vapor and water vapor are introduced into the container through separate steam delivery pipelines. By controlling the temperature and holding time of the steam treatment environment, the silica alkoxide vapor and water vapor are allowed to fully contact the surface and pores of the zirconia-based preform in a closed steam environment, and a hydrolysis-condensation reaction occurs, thereby forming a silicon oxide coating layer on the surface of the zirconia framework, thus obtaining a steam-treated zirconia-based preform. S300: The steam-treated zirconia-based preform is dried by heating to a temperature higher than the boiling point of the silica alkoxide and holding for 1-12 hours. Then, the sample is cooled to room temperature to obtain a high-temperature resistant zirconia-based nanoporous thermal insulation composite material. This invention discloses a method for preparing a high-temperature resistant zirconia-based nanoporous thermal insulation composite material. By introducing short-cut high-temperature resistant fibers, second-phase oxide powder, and a light-blocking agent, and combining mechanical mixing with compression molding, the precise construction of the material's macroscopic morphology and microstructure is achieved. The compression molding process, coupled with a limiting device, enables precise control of the preform density to within 0.50 g·cm³. -3 - 0.86 g·cm -3Within a certain range, the material is ensured to have a suitable porosity to maintain low thermal conductivity; the short-cut high-temperature resistant fibers form a three-dimensional randomly distributed reinforcing network in the matrix, which plays a significant role in toughening and crack resistance, effectively improving the brittleness of the pure oxide matrix, and enhancing the compressive strength and flexural strength of the material, enabling it to withstand mechanical loads and thermal stresses during service; at the same time, the introduction of the second-phase oxide powder plays a role in inhibiting the abnormal growth of zirconia grains in the initial stage, while the uniform dispersion of the light-blocking agent helps to scatter infrared radiation in high-temperature environments and reduce radiative heat transfer efficiency. Separate steam delivery pipelines were used to introduce silanol salt vapor and water vapor into a sealed container. Combined with specific ambient temperature control, in-situ coating and modification of silicon oxide on the surface of the zirconia framework were achieved. The separate pipeline design ensured that the precursor vapor and water vapor remained independent before entering the reaction zone, avoiding premature homogeneous nucleation reactions in the gas phase, thus ensuring that the silanol salt vapor could penetrate deeply into the internal pores of the green body. Without the need for an external catalyst, the active sites and adsorbed water on the zirconia surface promoted the hydrolysis-condensation reaction of the silanol salt. This process not only formed a continuous silicon oxide coating layer on the surface and neck region of the zirconia particles, but also formed stable zirconium-oxygen-silicon chemical bonds on the surface of the zirconia particles through chemical reactions. This chemical bond greatly enhanced the connection strength between particles and, as a diffusion barrier layer, effectively suppressed the migration of oxygen ions and grain boundary movement at high temperatures, thereby blocking the volume shrinkage caused by the transformation of the monoclinic phase to the tetragonal phase and maintaining the integrity of the nanoporous structure. By heating the steam-treated preform to a temperature higher than the boiling point of the siloxane and holding it at that temperature, unreacted adsorbates and excess products remaining in the pores can be completely removed, preventing them from volatilizing or decomposing during subsequent high-temperature use and causing the pore structure to collapse. This heat treatment process promotes further densification and network improvement of the silicon oxide coating layer, while eliminating residual stress inside the material, making the bond between the zirconia skeleton and the silicon oxide coating layer stronger, and finally obtaining a composite material with excellent high-temperature phase transformation stability, low thermal conductivity and high mechanical strength. Short-cut high-temperature resistant fibers provide macroscopic mechanical support, solving the problem of aerogel fragility; the second-phase oxide powder stabilizes the zirconia phase from a crystal structure perspective, delaying phase transformation shrinkage; while the silicon oxide coating layer formed by vapor deposition strengthens particle connections and blocks high-temperature mass transfer channels at the microscale through zirconium-oxygen-silicon bonding. This multi-synergistic mechanism of "fiber reinforcement-phase stabilization-surface coating" enables the material to maintain structural integrity even in extreme environments up to 1200℃, overcoming the volume instability and strength reduction problems caused by crystal transformation in traditional zirconia aerogels; the process eliminates the complex sol preparation, gel aging, solvent replacement, and dangerous supercritical drying steps in the traditional sol-gel method, and has significant advantages such as simple process flow, moderate equipment requirements, and suitability for large-scale production.This invention discloses a method for preparing a high-temperature resistant zirconia-based nanoporous thermal insulation composite material. By organically combining compression molding and vapor phase surface modification technology, a zirconia-based nanoporous thermal insulation composite material with low density, high strength, and high temperature resistance is successfully prepared. This method not only fundamentally inhibits the high-temperature phase transformation shrinkage and grain growth of zirconia, significantly improving the structural stability and thermal insulation efficiency of the material under extreme high-temperature environments, but also provides a safe, efficient, and easily industrialized preparation route, offering a novel technical solution for the preparation of high-performance thermal insulation materials.

[0029] like Figure 1 As shown, in this embodiment, the low-density nano-zirconia powder in step S100 is one or a mixture of several of the following: monoclinic zirconia, tetragonal zirconia powder, cubic zirconia powder, or yttrium-stabilized zirconia powder, with a specific surface area of ​​25 m². 2 ·g -1 -65 m 2 ·g -1 Preferably, the specific surface area is 40 m². 2 ·g -1 -65 m 2 ·g -1 By selecting one or more of monoclinic zirconia, tetragonal zirconia, cubic zirconia, or yttrium-stabilized zirconia as the matrix component, active control of the matrix's thermophysical behavior was achieved. The introduction of yttrium-stabilized zirconia powder utilizes the stabilizing effect of yttrium ions on the zirconia lattice to suppress the reversible transformation from monoclinic to tetragonal phase at the microscopic level, thereby reducing the 7%–9% volume shrinkage stress caused by the crystal transformation at its source. Simultaneously, retaining some monoclinic or tetragonal zirconia helps utilize the phase transformation toughening mechanism to absorb energy under stress, improving the material's toughness. This multiphase composite design ensures that the stability of the microscopic lattice and the integrity of the macroscopic structure are balanced during high-temperature service. The specific surface area of ​​the nano-zirconia powder was controlled at 25 m². 2 ·g -1 -65 m 2 ·g -1 The preferred interval is 40 m. 2 ·g -1 -65 m 2 ·g -1A high specific surface area means that the powder per unit mass has higher surface energy and more active sites. In the subsequent steam treatment step S200, this high surface activity can significantly reduce the activation energy of the silanol steam hydrolysis-condensation reaction, promote the uniform heterogeneous nucleation and growth of the silicon oxide coating layer on the surface of the zirconia particles, and ensure the formation of a continuous and dense silicon oxide modified layer. In the molding process of step S100, the high specific surface area nanoparticles can form a large number of nanoscale pores through random stacking between particles. These nanoscale pores are the core structure that hinders the thermal motion of gas molecules and reduces gaseous heat conduction, providing a structural basis for the material to obtain a low thermal conductivity. The appropriate high specific surface area provides a suitable sintering driving force, so that in the heat treatment of step S300, the contact (neck) area between particles can be strengthened through mass migration without causing excessive grain growth or pore closure, thereby maintaining the stability of the nanoporous structure. The powder characteristics defined in step S100 form a tight process chain with subsequent steps. The porous preform formed by the high specific surface area zirconia powder after molding has excellent capillary effect and permeability, ensuring that the silanol vapor and water vapor in step S200 can smoothly penetrate into the depth of the preform, achieving uniform modification across the entire thickness range. The zirconium-oxygen-silicon chemical bonds generated by the reaction of the highly active hydroxyl groups on the powder surface with the silanol vapor further anchor the zirconia particles, enabling them to resist grain growth and phase transformation shrinkage even at high temperatures up to 1200℃.

[0030] like Figure 1 and Figure 2As shown, in this embodiment, the second-phase oxide powder in step S100 is a mixture of one or more of silicon oxide, aluminum oxide, or yttrium oxide; the amount of the second-phase oxide powder added is 10 wt%-50 wt%. By introducing yttrium oxide as the second-phase oxide, the solid solution effect of yttrium ions in the zirconia lattice can significantly improve the high-temperature stability of tetragonal or cubic zirconia and suppress the formation of monoclinic phase, thereby offsetting the 7%-9% volume shrinkage stress caused by the martensitic phase transformation from the crystal structure perspective. The introduction of silicon oxide and aluminum oxide can form a dispersed second-phase barrier layer on the surface of zirconia particles and at grain boundaries. In a high-temperature environment of up to 1200℃, these dispersed phases can effectively pin the grain boundaries, hinder the movement of grain boundaries and the migration of oxygen ions, thereby inhibiting the abnormal growth and aggregation of zirconia grains and maintaining the microstructural stability of the nanoporous framework. The selection and dosage (10 wt%-50 wt%) of the second-phase oxide have a significant impact on the thermal transport behavior of the material. Silica and alumina themselves have low thermal conductivity. When uniformly dispersed in the zirconium oxide matrix, they can increase phonon scattering centers and reduce the mean free path of phonons, thereby effectively weakening solid-state thermal conduction. In particular, the silica component, at the interface with zirconium oxide, can assist the hydrolysis and condensation reaction of silanol vapor in the subsequent step S200, promoting the formation of a continuous silicon oxide coating layer, further enhancing interfacial thermal resistance, and achieving even lower thermal conductivity. An appropriate amount of second-phase oxide (10 wt%-50 wt%) fills the voids between nano-zirconia particles during the compression molding process, which not only improves the packing density and uniformity of the preform, but also enhances the mechanical interlocking effect between particles. In the subsequent steam treatment step S200, these second-phase oxide particles (especially silicon oxide) can react with the gaseous precursor or form chemical bonds, strengthening the connection strength between particles. This dual modification strategy of "solid phase doping + gas phase coating" enables the material to maintain a high specific surface area and complete pore structure after high-temperature heat treatment, solving the technical problem of structural collapse caused by sintering of single zirconia aerogel at high temperature.

[0031] like Figure 1As shown, in this embodiment, the light-shielding agent in step S100 is one or a mixture of silicon carbide, titanium oxide, or potassium hexatitanate whiskers; the particle size of the light-shielding agent is 2μm-5μm; and the amount of light-shielding agent added is 5 wt%~20 wt%. Preferably, the light-shielding agent is silicon carbide. The introduction of the light-shielding agent is mainly aimed at the significant radiative heat transfer phenomenon inside the material under high temperature environment; by selecting inorganic non-metallic materials with high refractive index and high infrared extinction coefficient, such as silicon carbide, titanium oxide, or potassium hexatitanate whiskers, and utilizing their specific band structure or whisker structure, strong scattering and absorption effects are generated on infrared thermal radiation; the particle size of the light-shielding agent is limited to between 2μm and 5μm, which matches the peak wavelength of high-temperature blackbody radiation, thereby maximizing the Mie scattering efficiency, effectively cutting off the radiative heat transfer path in the pores, and significantly reducing the effective thermal conductivity of the material in the high-temperature range (such as 1200℃). Limiting the amount of light-shielding agent added to the range of 5 wt% to 20 wt% ensures its appropriate filling in the matrix. Too low a doping amount cannot form an effective radiation shielding network, while too high a doping amount may lead to particle agglomeration, increase the solid-state thermal bridging effect and degrade mechanical properties. This doping range ensures that the light-shielding agent forms a uniform and diffuse distribution in the nano-zirconia framework, while avoiding pore blockage or abnormal increase in density due to excessive filling, thus maintaining the integrity of the nanoporous structure of the material. Silicon carbide is preferably selected as the light-shielding agent. Silicon carbide not only has excellent infrared shielding ability, but also has extremely high high-temperature oxidation resistance and chemical stability. In the subsequent steam treatment in step S200 and heat treatment in step S300, silicon carbide can maintain chemical inertness and will not have adverse interfacial reactions with the silanol precursor or zirconium oxide matrix, thereby ensuring the smooth formation of the silicon oxide coating layer and the interfacial bonding strength. In addition, the high hardness and high modulus of silicon carbide enable it to assist in the transmission of pressure during the compression molding process, and together with chopped high-temperature resistant fibers, it plays a role in strengthening and toughening, further improving the overall mechanical properties of the composite material.

[0032] like Figure 1As shown, in this embodiment, the chopped high-temperature resistant fibers in step S100 are one or a mixture of several of the following: chopped alumina fibers, chopped mullite fibers, chopped zirconia fibers, and chopped polycrystalline alumina fibers; the fiber length of the chopped high-temperature resistant fibers is 1mm-20mm; and the amount of chopped high-temperature resistant fibers added is 5 wt%-20 wt%. Preferably, the fiber length of the chopped high-temperature resistant fibers is 2mm-8mm. By introducing one or a combination of chopped alumina fibers, chopped mullite fibers, chopped zirconia fibers, or chopped polycrystalline alumina fibers, these fibers are randomly distributed in the nano-zirconia matrix and form a three-dimensional network reinforcement structure during the compression molding process. When the material is subjected to external loads (such as compression, bending, or thermal shock), the fibers can effectively bridge cracks, hinder crack propagation, and consume fracture energy through the fiber pull-out mechanism, thereby improving the defects of high brittleness and easy pulverization of pure zirconia aerogel, and significantly improving the compressive strength, flexural strength, and toughness of the composite material. The length of the chopped high-temperature resistant fibers is limited to between 1mm and 20mm, preferably between 2mm and 8mm. Fibers that are too thin are prone to breakage during molding, reducing reinforcement efficiency; while fibers that are too thick will occupy too much space, disrupting the continuity of the nanoporous structure and increasing the solid-state thermal bridging effect. The preferred length range ensures that the fibers maintain a good aspect ratio in the matrix to achieve effective stress transfer, without causing excessive compression or blockage of the nanopores. The appropriate fiber length is beneficial for the silanol salt vapor to fully wet and coat the fiber surface in the subsequent steam treatment step S200, further strengthening the bonding strength between the fiber and the matrix interface by forming a ceramic bonding phase (such as aluminosilicate or zirconium silicate). By limiting the addition of short-cut high-temperature resistant fibers to the range of 5 wt%-20 wt%, the optimal balance between mechanical properties and thermal insulation properties is achieved. This dosage is sufficient to form a continuous and effective reinforcing network in the matrix, avoiding poor reinforcement due to insufficient fibers or excessive fiber content leading to over-segmentation of matrix components, abnormal increase in overall material density, and increase in thermal conductivity. This ensures that the composite material can maintain its essential characteristics of low density and low thermal conductivity while achieving significant mechanical reinforcement. The selected high-temperature resistant oxide fibers have similar coefficients of thermal expansion to the zirconium oxide matrix, effectively alleviating the internal stress caused by thermal mismatch during heating and cooling, and improving the thermal shock stability of the material. During the steam treatment in step S200, the active groups on the fiber surface can react with the silanol salt vapor, and the resulting silicon oxide coating layer not only covers the zirconium oxide particles but also wraps the fiber surface, thereby forming a strong chemical bonding interface between the fiber and the matrix, further consolidating the structural stability of the entire nanoporous framework. Furthermore, by optimizing the interfacial bonding between the fiber and the matrix, a synergistic reinforcement effect is formed with the vapor phase coating modification process, ensuring that the composite material has both excellent load-bearing capacity and thermal insulation efficiency under extreme high-temperature environments.

[0033] like Figure 1As shown, in this embodiment, the silanolate in step S200 is one or a mixture of several of tetraethyl orthosilicate, methyltriethoxysilane, methyl orthosilicate, methyltrimethoxysilane, dimethyldiethoxysilane, or dimethyldimethoxysilane; the mass ratio of the silanolate to the zirconia-based preform is 20 wt%-100 wt%, and the mass ratio of water to the silanolate is 5 wt%-70 wt%. By selecting one or more of tetraethyl orthosilicate, methyltriethoxysilane, methyl orthosilicate, methyltrimethoxysilane, dimethyldiethoxysilane, or dimethyldimethoxysilane as the silicon source, this invention utilizes the characteristic of organosilicon alkoxides having suitable saturated vapor pressure at specific temperatures. These compounds can vaporize in a closed environment and disperse uniformly in molecular form, ensuring that vapor can penetrate into the internal pores of the zirconia-based preform. Different silanolates have different hydrolysis rates and steric hindrance effects. By using them in combination, the degree of polymerization and crosslinking density of the hydrolysis-condensation products can be adjusted, thereby controlling the density and chemical structure of the generated silicon oxide coating layer to meet different high-temperature protection requirements. The mass ratio of silanolate to zirconia-based preform is limited to 20 wt%-100 wt%, and the mass ratio of water to silanolate is limited to 5 wt%-70 wt%, thereby ensuring a complete and uniform reaction. The proportion of silanols ensures sufficient silicon source for the reaction on the surface and within the pores of the preform; too low a proportion leads to discontinuous coating layers, failing to form an effective diffusion barrier layer; too high a proportion may cause pore blockage or excessive surface deposition, increasing the solid-state thermal conductivity of the material. The amount of water introduced directly determines the completeness of the silanol hydrolysis reaction; the mass ratio range of water to silanols ensures that silanol molecules can fully hydrolyze to generate silanol intermediates, and also undergo condensation reactions with the hydroxyl groups on the zirconium oxide surface to form stable zirconium-oxygen-silicon chemical bonds; an appropriate amount of water can also regulate the humidity of the reaction atmosphere, avoiding premature pre-hydrolysis or nucleation of precursors in the gas phase due to lack of water. Through steam treatment with the above-mentioned proportions, silicon oxide grows in situ on the surface and neck region of zirconia nanoparticles via chemical bonding, forming a continuous amorphous nanocrystalline coating layer. This coating layer acts as a physical and chemical barrier at high temperatures, hindering material migration at zirconia grain boundaries, inhibiting grain growth and high-temperature sintering, altering the energy state of the zirconia surface, and suppressing the driving force for the transformation from monoclinic to tetragonal phase. This significantly reduces the linear shrinkage rate of the material at temperatures up to 1200℃, maintaining the integrity of the nanoporous structure. The silicon oxide coating layer formed in step S200 has good chemical compatibility with the second-phase oxides (such as silicon oxide and aluminum oxide) and light-blocking agents introduced in step S100. At the interface between zirconia particles and fibers, the silicon oxide coating layer acts as a "welding" agent, enhancing the bonding force between heterogeneous interfaces through chemical bonding, further improving the overall mechanical strength and thermal shock resistance of the composite material.

[0034] like Figure 1As shown in this embodiment, the steam treatment process in step S200 specifically involves: placing the pressed zirconia-based preform into a sealed container, and introducing silanol salt vapor and water vapor into the sealed container through separate steam delivery pipelines. The silanol salt and water are respectively placed in evaporation devices within their respective steam delivery pipelines, and after heating, form silanol salt vapor and water vapor, which are then transported into the sealed container. The steam treatment ambient temperature is close to the boiling point of the silanol salt reactant used (e.g., if tetraethyl orthosilicate is used as the silanol salt, this temperature is 140℃-160℃; if dimethyldiethoxysilane is used, this temperature is 100℃-130℃), and the holding time is 12-24 hours. By using separate steam delivery pipelines to transport silanol salt vapor and water vapor respectively, homogeneous nucleation reactions of the precursors in the gas phase are avoided. Silanol salt and water are placed in independent evaporation devices, heated and vaporized, and then simultaneously enter a sealed container. This ensures that the two reactants remain in an independent gas phase state before contacting the surface of the zirconia-based preform, preventing premature hydrolysis-condensation reactions in the delivery pipelines or gas phase space that would generate free silica particles. This ensures that the silanol salt vapor can carry the water vapor to fully penetrate into the internal pores of the preform, and that heterogeneous nucleation and growth occur on the surface and neck region of the zirconia particles, thereby forming a continuous, dense, and firmly bonded silicon oxide coating layer, rather than a loosely piled powder. Controlling the steam treatment environment temperature to near the boiling point of the silanol reactant offers dual technical benefits. This temperature condition ensures that the silanol has a suitable saturated vapor pressure, maintaining a continuous and stable steam flow. This drives the reactant gas to diffuse into the micro-nano pores deep within the billet, overcoming the mass transfer resistance of deep penetration and achieving uniform modification of the interior of large-sized or thick-walled components. The near-boiling temperature provides sufficient thermal energy to overcome the activation energy barrier of the hydrolysis-condensation reaction, accelerating the condensation reaction rate of the silanol molecules and the hydroxyl groups on the zirconium oxide surface. This promotes the rapid formation of zirconium-oxygen-silicon chemical bonds, thereby strengthening the interfacial bonding strength between particles while ensuring production efficiency. Setting the holding time within the range of 12-24 hours ensures that the reaction system reaches thermodynamic and kinetic equilibrium. The sufficiently long reaction time allows the silanol salt vapor to fully wet and react completely, eliminating coating defects (such as pinholes or exposed points) caused by incomplete reaction. This not only ensures the uniformity of the silicon oxide coating thickness at the microscale, but also allows the coating to fully fill the micro gaps between particles, further passivating the grain boundaries. This effectively suppresses oxygen ion migration and grain boundary movement during subsequent high-temperature service, significantly improving the material's ability to resist high-temperature sintering and phase transformation shrinkage.The steam treatment process synergizes well with the preform structure in step S100 and the heat treatment process in step S300. The high-porosity preform prepared by compression molding provides a channel for steam permeation, while the prolonged near-boiling point treatment constructs a robust chemical protective barrier on the surface of the zirconia framework. This barrier further hinders the growth and phase transformation of zirconia grains during the high-temperature drying process in step S300, ensuring that the composite material maintains the integrity of its nanoporous structure even at temperatures as high as 1200℃. By precisely controlling the pipeline design, reaction temperature, and holding time in the steam treatment process, in-situ, uniform, and strongly bonded growth of the silicon oxide coating layer on the zirconia-based nanoporous framework is achieved. This not only fundamentally solves the structural instability problem caused by weak particle bonding in traditional aerogels but also strengthens the microstructure through chemical bonding, providing core process support for the preparation of composite materials with high-temperature stability, low thermal conductivity, and excellent mechanical properties.

[0035] like Figure 1As shown in this embodiment, the temperature above the boiling point of the silanolyte in step S300 refers to a temperature 10°C-50°C higher than the boiling point of the silanolyte reactant used (e.g., 110°C-160°C for methyltrimethoxysilane, or 130°C-170°C for methyl orthosilicate). Setting the processing temperature within the range of 10°C-50°C above the boiling point of the silanolyte ensures that unreacted adsorbates and excess products remaining in the pores of the zirconia-based preform and the micropores of the silicon oxide coating layer are completely vaporized. This temperature gradient provides sufficient vapor pressure driving force, prompting these volatile organic compounds to diffuse from the deep interior of the material and be discharged. This effectively avoids the formation of carbon residues in the pores due to carbonization or decomposition of residual organic compounds during subsequent high-temperature service, thereby preventing pore structure collapse, increased thermal conductivity, or high-temperature oxidation failure caused by these factors, and ensuring the purity and integrity of the nanoporous structure. Although this temperature range is above the boiling point of silanols, it is generally below the phase transition temperature of the zirconia matrix, making it a suitable heat treatment window. At this temperature, the incompletely condensed silicon oxide coating layer after steam treatment can undergo further dehydration condensation reaction, eliminating silanol groups and promoting the transition of the silicon-oxygen network from a loose state to a dense state. This in-situ thermal densification process further strengthens the neck connections between zirconia particles and increases the bonding area between particles, thereby significantly improving the macroscopic mechanical strength and thermal shock resistance of the composite material. By holding the material at this specific temperature for 1 to 12 hours, the residual stress generated by molding and steam treatment is fully released, which helps maintain the dimensional stability of the material under subsequent extreme high-temperature environments (such as 1200°C). This step is essentially a low-temperature annealing process, which fixes the amorphous or metastable structure of the silicon oxide coating layer and inhibits its potential over-crystallization or phase separation at higher temperatures, thus ensuring the microstructural stability of the material during long-term thermal cycling. The drying temperature and the near-boiling-point steam treatment in step S200 form a perfect process connection. Step S200 completes the deposition and initial bonding of silicon oxide at a temperature close to the boiling point, while step S300 completes the removal of residues and the final curing of the coating layer at a temperature slightly above the boiling point. This stepwise heating strategy avoids cracking or blistering of the coating layer caused by excessively rapid heating, and ensures that the final product has extremely low volatile substance content and excellent high-temperature structural stability. By precisely limiting the drying temperature to 10℃-50℃ above the boiling point of siloxides, effective removal of internal impurities and deep optimization of the microstructure of the composite material are achieved. This not only eliminates potential thermal failure hazards, but also further consolidates the structural integrity and thermal insulation performance of the material under high-temperature extreme environments by promoting the densification and stress release of the silicon oxide coating layer, ensuring that the composite material reaches a temperature resistance rating of 1200℃ and achieves long-term stable service.

[0036] The high-temperature resistant zirconia-based nanoporous thermal insulation composite material of this embodiment was prepared using the above-described preparation method for high-temperature resistant zirconia-based nanoporous thermal insulation composite material.

[0037] In this embodiment, the density of the zirconia-based nanoporous thermal insulation composite material is 0.50 g·cm³. -3 -0.90 g·cm -3 The compressive strength at 10% strain is 0.50 MPa-0.70 MPa, the temperature resistance is 1200℃, and the thermal conductivity at 1200℃ is 0.04 W·m. -1 ·K -1 -0.07 W·m -1 ·K -1 The density of the composite material is controlled at 0.50 g·cm³. -3 -0.90 g·cm -3 Between these two values, it belongs to a typical lightweight nanoporous material. At this low density, the compressive strength of the material under 10% strain conditions can still reach 0.50 MPa-0.70 MPa. This combination of properties indicates that the three-dimensional reinforcement of short-cut high-temperature resistant fibers in step S100, the zirconium-oxygen-silicon chemical bonding reinforcement formed by the silicon oxide coating layer in step S200, and the reinforcement of the neck region between particles have successfully overcome the defects of low mechanical strength and easy pulverization of traditional aerogel materials. This "low density-high strength" matching characteristic enables the material to meet the requirements of lightweight design while having the ability to withstand aerodynamic loads and mechanical vibrations. The material's maximum withstand temperature reaches 1200℃, significantly superior to existing zirconia-based composites typically limited to around 1000℃. This technological advantage is primarily attributed to the stabilizing effect of the second-phase oxide (such as yttrium oxide) introduced in step S100, and the physical and chemical barrier effect of the silicon oxide coating layer in step S200 on grain boundary migration. This coating layer effectively suppresses abnormal grain growth of zirconia at high temperatures and the volume shrinkage caused by the monoclinic-to-tetragonal phase transformation, thus ensuring the integrity of the material's microstructure under extreme high-temperature conditions. This solves the technical problem that traditional zirconia aerogels cannot be applied to high-temperature environments due to phase transformation instability. Even in extreme environments up to 1200℃, the material's thermal conductivity remains at 0.04 W·m. -1 ·K -1 -0.07 W·m -1 ·K -1The low density of the material is achieved through a multi-scale synergistic thermal insulation mechanism. The low-density nanoporous structure greatly suppresses gaseous and solid-state heat conduction. The light-shielding agent (such as silicon carbide) introduced in step S100 strongly scatters high-temperature infrared radiation, weakening radiative heat transfer. The silicon oxide coating layer formed in step S200 further optimizes the phonon transport path of the framework. This synergistic effect of multiple mechanisms enables the material to maintain excellent thermal insulation efficiency at high temperatures. The listed performance indicators (low density, high strength, resistance to 1200℃ high temperature, low thermal conductivity) are a highly coupled system engineering result. This not only verifies the rationality of the component ratios (such as the dosage of second-phase oxide, light-shielding agent, and fiber) and process parameters (such as steam treatment and heat treatment regime) in the preparation method, but also proves that the material prepared by this invention can meet the stringent requirements of modern high-speed aircraft and near-space aircraft for thermal protection systems, that is, to provide reliable thermal protection in extreme thermal environments without significantly increasing structural weight. This invention presents a high-temperature resistant zirconia-based nanoporous thermal insulation composite material. Through the deep integration of component design and process innovation, it successfully achieves a perfect balance of lightweight, high strength, high-temperature stability, and low thermal conductivity. The material performance data not only confirms the effectiveness and advancement of the aforementioned preparation method, but also signifies a substantial breakthrough in solving the core technical challenges of high-temperature phase transformation instability and mechanical fragility in zirconia-based materials. This provides a material solution with significant technological advancements for the design and application of thermal protection systems in extreme environments.

[0038] In response to the problem that "single zirconia aerogels, due to crystal-induced phase transformation and grain growth at high temperatures, experience a significant decrease in specific surface area, shrinkage, and limit their service temperature to below 1000℃," this invention provides a high-temperature resistant zirconia-based nanoporous thermal insulation composite material and its preparation method. This invention introduces a second-phase oxide powder into a zirconia-based nanoporous framework and forms a nano-silica oxide coating layer on the surface of the zirconia framework to inhibit sintering and crystal transformation of the material under high-temperature conditions, thereby improving its high-temperature structural stability and thermal insulation performance. During the steam reaction, a separate pipeline steam supply method is used, introducing silanol salt steam and water steam into the sealed tank respectively. Without the participation of a catalyst, the active sites on the zirconia surface promote the hydrolysis and condensation reaction of the silanol salt precursor, which further reacts with the hydroxyl groups on the surface of the zirconia particles to form Zr-O-Si bonds. After the sample has fully reacted, it is dried to obtain the high-temperature resistant zirconia-based nanoporous thermal insulation composite material.

[0039] This invention relates to a high-temperature resistant zirconia-based nanoporous material. It is a lightweight nanoporous thermal insulation composite material with zirconia as the main solid-phase framework, short-cut high-temperature resistant fibers as reinforcement, and containing oxide regulating components and light-blocking components. Macroscopically, it exhibits a porous bulk structure; microscopically, it consists of interconnected nanoscale zirconia particles forming a porous framework containing numerous nanoscale pores. Oxide powder and light-blocking agents are dispersed within the framework. Simultaneously, a silicon oxide coating layer, produced by the hydrolysis-condensation reaction of silanol salt vapor, is formed on the surface of the zirconia framework, thereby improving the material's thermal stability and suppressing heat conduction and radiation transfer under high-temperature conditions. The material's density is 0.50 g·cm³. -3 -0.90 g·cm -3 The compressive strength at 10% strain is 0.50 MPa-0.70 MPa, the temperature resistance is 1200℃, and the thermal conductivity at 1200℃ is 0.04 W·m. -1 ·K -1 -0.07 W·m -1 ·K -1 .

[0040] Compared with existing technologies, the high-temperature resistant zirconia-based nanoporous thermal insulation composite material and its preparation method of this invention have the following technical advantages: This invention is based on the hydrolysis-condensation reaction of silanol precursors, using nano-zirconia powder as the matrix component, short-cut high-temperature resistant fibers as the reinforcement, and introducing an appropriate amount of second-phase oxide powder and opacifier. Zirconia-based preforms are prepared by mechanical mixing and molding, and then the preforms are steam-surface-treated with silanol vapor and water vapor. Finally, high-temperature resistant zirconia-based nanoporous thermal insulation composite material is obtained by drying.

[0041] (1) The zirconia-based nanoporous thermal insulation composite material prepared by this invention exhibits high high-temperature stability and a wide applicable temperature range. By introducing second-phase oxide powders such as silicon oxide, aluminum oxide, or yttrium oxide during the preform preparation process, and subsequently performing steam surface treatment to form a SiO2-modified layer on the surface of the zirconia nanoframework, grain growth, structural densification, and framework shrinkage under high-temperature conditions can be effectively suppressed. After heat treatment at 1200℃ for 2 hours, the specific surface area of ​​the material remains at 36.89 m². 2 ·g -1 -33.70 m 2 ·g -1 The linear shrinkage rate is 1.98%-3.32%, indicating that the material can still maintain good pore structure and dimensional stability under high temperature environment.

[0042] (2) The zirconia-based nanoporous thermal insulation composite material prepared by the present invention exhibits low high-temperature thermal conductivity and good thermal insulation effect. The light-blocking agent added during the first step of preform preparation effectively weakens high-temperature radiative heat transfer. The introduction of the second-phase oxide and the silicon oxide coating layer formed by the second step of steam treatment are beneficial to optimizing the nanoskeleton structure and reducing solid-phase heat transfer, thereby enabling the material to maintain low thermal conductivity in the high-temperature region. The thermal conductivity of the material obtained by the present invention at 1200℃ is only 0.042 W·m. -1 ·K -1 -0.053 W·m -1 ·K -1 It has excellent high-temperature thermal insulation properties.

[0043] (3) The zirconia-based nanoporous thermal insulation composite material prepared by the present invention exhibits good mechanical strength. The short-cut alumina fibers added during the first step of preform preparation play a reinforcing and supporting role within the material, while the Zr-O-Si chemical bonds formed during the second step of steam treatment further enhance the interparticle bonding strength, thereby improving the overall structural stability. The resulting composite material exhibits a compressive strength of 0.456 MPa to 0.685 MPa and a flexural strength of 0.164 MPa to 0.225 MPa at 10% strain, demonstrating good mechanical properties.

[0044] (4) The preparation method of this invention has the advantages of simple process, mild conditions and easy scale-up. The method first obtains a green body with a certain shape and strength through mechanical mixing and molding, then steam treatment is carried out by introducing silanol salt steam and water steam through separate pipelines, and finally the material structure is stabilized by drying. Compared with the traditional sol-gel method, this method does not require complicated sol preparation, gel aging, solvent replacement and special drying process, the process is shorter and the equipment requirements are lower, which is more conducive to continuous and large-scale preparation.

[0045] Example 1: (1) Preparation of zirconia-based preforms: With a specific surface area of ​​40 m² 2 ·g -1 ~65 m 2 ·g -1 Monoclinic nano-zirconia powder was used as the matrix component, with 10 wt% silica powder, 10 wt% silicon carbide opacifier with a particle size of 2 μm, and 5 wt% short-cut alumina fibers with a length of 4 mm added. The mixture was mechanically mixed until homogeneous, then poured into a custom mold and press-molded to obtain a cylindrical zirconia preform. The density was approximately 0.52 g·cm³ by adjusting the pressing pressure or using a limiting device. -3 Zirconia-based preform; (2) Steam treatment of zirconia-based preforms: A pressed zirconia preform is placed in a sealed container, and silanol vapor and water vapor are introduced into the reaction vessel through separate steam delivery pipelines. The amounts of silanol and water added to the evaporation devices in the corresponding pipelines are 100 wt% and 40 wt% of the zirconia preform, respectively. After heating, the vapor is generated and transported into the sealed container. During the steam treatment process, the steam treatment environment is heated to 160℃ and held for 24 hours, allowing the silanol vapor and water vapor to fully contact the surface and pores of the zirconia preform in a closed steam environment, resulting in a hydrolysis-condensation reaction. This forms a silicon oxide coating layer on the surface of the zirconia framework, yielding the steam-treated zirconia preform. (3) Drying treatment: The surface-treated zirconia-based material was placed in a regular drying oven, heated to 120°C, and kept at that temperature for 6 hours. After the sample cooled to room temperature, the zirconia-based nanoporous thermal insulation composite material was obtained. The density of the zirconia-based nanoporous thermal insulation composite material prepared in this embodiment was 0.752 g·cm³. -3 Its thermal conductivity at 1200℃ is 0.047 W·m. -1 ·K -1 The linear shrinkage rate is 3.21%, and the compressive strength (at 10% strain) and flexural strength are 0.628 MPa and 0.215 MPa, respectively.

[0046] Example 2-Example 184 In Example 1, during the first step of preparing the zirconia-based preform, the chopped fibers mainly serve to support and reinforce the nanoskeleton. When the fiber length is too small, it is difficult to effectively support the preform skeleton, while excessive fiber length increases the internal solid-state heat transfer channels, leading to higher thermal conductivity. Therefore, controlling the fiber length between 2mm and 8mm effectively balances the preform forming support function with the thermal insulation performance requirements, resulting in better overall material performance. Furthermore, among the available high-temperature resistant fibers, chopped alumina fibers offer a superior balance between temperature resistance and formability, meeting the requirements for skeleton support stability at high temperatures while also being economical. Therefore, chopped alumina fibers were selected as the reinforcing component in subsequent examples. When the opacifier particle size is selected as 2μm-5μm, it effectively inhibits radiative heat transfer under high-temperature conditions, meeting the requirements for use in thermal insulation composite materials. In the second step of steam treatment, the ambient temperature is mainly related to the volatility of the silanol. When the steam treatment temperature is controlled at a difference of about 10°C from the boiling point of the silanol reactant, the silanol can volatilize sufficiently and participate in the surface reaction. After 24 hours of heat treatment, the hydrolysis products of the silanol and the nano-zirconia framework have fully completed the hydrolysis-condensation reaction, thus meeting the process requirements for surface modification. In the third step of drying treatment, heat treatment at a temperature 10°C-50°C higher than the boiling point of the silanol reactant for 6 hours has been sufficient to remove unreacted adsorbates and excess products from the composite material. Therefore, the above process conditions are mainly used to ensure the smooth implementation of each step and achieve the corresponding process objectives. Under the premise of meeting the above conditions, the relevant parameters do not constitute key limiting factors affecting the performance of the zirconia-based nanoporous thermal insulation composite material. Therefore, the main process parameters used in Examples 2-184 are shown in Table 1. Experimental process parameters not listed in the table are the same as those in Example 1.

[0047]

[0048]

[0049]

[0050]

[0051]

[0052]

[0053]

[0054]

[0055]

[0056] As shown in the table above, the comprehensive performance of the zirconia-based nanoporous thermal insulation composite material is closely related to factors such as the type and amount of siloxane reactant, the type and amount of second-phase oxide doping, and the amount of water. Specifically, under conditions where the steam treatment environment temperature is controlled and close to the boiling point of the siloxane reactant (approximately 10°C), the compressive strength of the resulting composite material is generally positively correlated with the molecular weight of the siloxane in the reactant, and the compressive strength increases with increasing reactant and fiber dosages. The introduction of a light-blocking agent is mainly used to improve the high-temperature thermal insulation performance of the material. When the amount of light-blocking agent increases from 5 wt% to 20 wt%, it can effectively reduce the high-temperature thermal conductivity of the material and simultaneously reduce the linear shrinkage rate under high-temperature conditions. Second-phase oxide doping can effectively suppress the sintering shrinkage of the material under high-temperature conditions, resulting in a significant reduction in the linear shrinkage rate. Among the three oxides—silicon oxide, yttrium oxide, and aluminum oxide—aluminum oxide has the most significant effect on improving the high-temperature resistance of the material, followed by yttrium oxide, while silicon oxide is relatively weaker. Furthermore, as the doping concentration gradually increases from 10 wt% to 50 wt%, the linear shrinkage of the material further decreases, allowing the material to reach a maximum operating temperature of 1200℃. In addition, Examples 31-60 investigated the effect of water dosage on the material properties, with water dosages of 1.25 times, 1.50 times, and 2.00 times the theoretical value, respectively. The results show that when the water dosage is 1.25-1.50 times the theoretical value, the compressive strength of the material is high; when the water dosage is only the theoretical value or higher than 1.50 times the theoretical value, the mechanical properties of the material are relatively poor. This is because when the water dosage is only the theoretical value, the degree of hydrolysis of the silanol is insufficient, which is not conducive to the formation of a sufficient silicon oxide coating layer. Conversely, excessive water dosage may adversely affect the hydrolysis-condensation reaction equilibrium, thereby affecting the final performance of the material.

[0057] like Figure 3The image shows the X-ray photoelectron spectroscopy (XPS) spectra of zirconia-based nanoporous thermal insulation composite materials (including samples in two states: "treated (ZA)" and "untreated (ZA-untreated)"). The figure identifies the characteristic peak positions of oxygen (O 1s), carbon (C 1s), zirconium (Zr 3d), and silicon (Si 2p). Comparing the "ZA" and "ZA-untreated" spectra, the ZA-untreated sample shows no obvious peak signal in the Si 2p region, while the ZA sample exhibits a clear peak in the Si 2p region. Furthermore, the relative intensities of the O 1s, C 1s, and Zr 3d peaks also differ. This indicates that after the process of the present invention (such as the silanol vapor treatment in step S200), silicon (Si) is introduced into the surface / bulk phase of the composite material (corresponding to the appearance of the Si 2p peak), and the changes in the signal intensity of carbon, oxygen, and zirconium also reflect the regulation of the chemical state or content of the elements by the treatment process. This is consistent with the mechanism of "the formation of a silicon oxide coating layer after silanol vapor treatment", which verifies the deposition and reaction of silicon source (silanol) on the surface / pores of the material in the process, and corroborates the modification effect of the preparation method on the chemical composition of the composite material.

[0058] like Figure 4 Figures (a) and (b) show the stress-strain curves of zirconia nanoporous thermal insulation composite materials before and after treatment with tetraethyl orthosilicate (TEOS) (i.e., “ZA” and “ZA-TEOS” samples), respectively: like Figure 4 As shown in (a), the compressive stress-strain curves before and after treatment are: comparing "ZA" (solid line) and "ZA-TEOS" (dashed line), the compressive stress of "ZA-TEOS" increases with strain at a significantly faster rate than that of "ZA"; at 40% strain, the compressive stress of "ZA-TEOS" is approximately 1.5 MPa (or higher), while that of "ZA" is only about 0.8 MPa; and in the low strain (~10%) stage, the stress of "ZA-TEOS" is already significantly higher than that of "ZA". This indicates that TEOS treatment significantly improves the compressive strength and resistance to compressive deformation of the material.

[0059] like Figure 4 As shown in (a), the bending stress-strain curves before and after treatment are: comparing "ZA" (solid line) and "ZA-TEOS" (dashed line), the peak bending stress of "ZA-TEOS" (~0.21 MPa) is much higher than that of "ZA" (~0.09 MPa), and the strain corresponding to the peak value is also better; at the same time, "ZA-TEOS" still maintains a higher stress level after the strain >10%, while the stress of "ZA" decreases faster. This indicates that TEOS treatment significantly enhances the bending strength and bending deformation toughness of the material.

[0060] In conclusion, Figure 4 (a) and Figure 4 The stress-strain behavior in (b) together demonstrates that the vapor phase treatment of tetraethyl orthosilicate (TEOS) can effectively improve the mechanical properties (compressive strength, flexural strength and deformation toughness) of zirconia-based nanoporous thermal insulation composites. This effect is consistent with the mechanism of "the formation of a silicon oxide coating layer on the particle surface after TEOS treatment, which strengthens the neck connection between particles", providing performance support for the material to withstand mechanical loads (such as aerodynamic pressure and vibration) in the field of aerospace thermal insulation.

[0061] Matters not covered in this invention are common knowledge.

[0062] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0063] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

[0064] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a high-temperature resistant zirconia-based nanoporous thermal insulation composite material, characterized in that, Includes the following steps: S100 uses low-density nano-zirconia powder as the matrix component, adds second-phase oxide powder and opacifier, as well as short-cut high-temperature resistant fibers, and mixes them evenly by mechanical mixing. The mixed raw materials are poured into a customized mold, and a zirconia-based preform of the desired shape is obtained through a compression molding process. By adjusting the molding pressure and / or using a limiting device, a preform of 0.50 g·cm³ is obtained. -3 - 0.86 g·cm -3 High density zirconia-based preform; S200. The zirconia substrate is placed in a sealed tank. Silica alkoxide vapor and water vapor are introduced into the sealed tank through separate steam delivery pipelines. By controlling the temperature and holding time of the steam treatment environment, the silica alkoxide vapor and water vapor are allowed to fully contact the surface and pores of the zirconia substrate in a closed steam environment, and a hydrolysis-condensation reaction occurs, thereby forming a silicon oxide coating layer on the surface of the zirconia framework, and obtaining the steam-treated zirconia substrate. S300. The steam-treated zirconia-based preform is dried, heated to a temperature higher than the boiling point of silanol, and kept at that temperature for 1-12 hours. Then, the sample is cooled to room temperature to obtain a high-temperature resistant zirconia-based nanoporous thermal insulation composite material.

2. The method for preparing the high-temperature resistant zirconia-based nanoporous thermal insulation composite material according to claim 1, characterized in that, The low-density nano-zirconia powder in step S100 is one or a mixture of several of the following: monoclinic zirconia, tetragonal zirconia powder, cubic zirconia powder, or yttrium-stabilized zirconia powder, with a specific surface area of ​​25 m². 2 ·g -1 -65 m 2 ·g -1 .

3. The method for preparing the high-temperature resistant zirconia-based nanoporous thermal insulation composite material according to claim 1, characterized in that, The second phase oxide powder in step S100 is one or a mixture of several of silicon oxide, aluminum oxide or yttrium oxide; The amount of second-phase oxide powder added is 10 wt%-50 wt%.

4. The method for preparing the high-temperature resistant zirconia-based nanoporous thermal insulation composite material according to claim 1, characterized in that, The light-blocking agent in step S100 is one or a mixture of several of silicon carbide, titanium oxide, or potassium hexatitanate whiskers; The particle size of the opacifier is 2μm-5μm; The amount of opaque agent added is 5 wt% to 20 wt%.

5. The method for preparing the high-temperature resistant zirconia-based nanoporous thermal insulation composite material according to claim 1, characterized in that, The chopped high-temperature resistant fiber in step S100 is one or a mixture of several of the following: chopped alumina fiber, chopped mullite fiber, chopped zirconia fiber, and chopped polycrystalline alumina fiber. The length of chopped high-temperature resistant fiber is 1mm-20mm; The amount of short-cut high-temperature resistant fiber added is 5 wt%-20 wt%.

6. The method for preparing the high-temperature resistant zirconia-based nanoporous thermal insulation composite material according to claim 1, characterized in that, The silanol salt in step S200 is one or a mixture of several of tetraethyl orthosilicate, methyltriethoxysilane, methyl orthosilicate, methyltrimethoxysilane, dimethyldiethoxysilane, or dimethyldimethoxysilane. The mass ratio of silanol to zirconia-based preform is 20 wt%-100 wt%, and the mass ratio of water to silanol is 5 wt%-70 wt%.

7. The method for preparing the high-temperature resistant zirconia-based nanoporous thermal insulation composite material according to claim 1, characterized in that, The steam treatment process in step S200 is as follows: The pressed zirconia-based preform is placed in a sealed container, and silanol salt vapor and water vapor are introduced into the sealed container through separate steam delivery pipelines. The silanol salt and water are placed in the evaporation devices of the corresponding steam delivery pipelines, and after heating, they form silanol salt vapor and water vapor and are delivered into the sealed container. The steam treatment environment temperature is close to the boiling point of the silanol salt reactant used, and the holding time is 12-24 hours.

8. The method for preparing the high-temperature resistant zirconia-based nanoporous thermal insulation composite material according to claim 1, characterized in that, In step S300, the temperature above the boiling point of the silanol salt refers to a temperature 10°C to 50°C higher than the boiling point of the silanol salt reactant used.

9. A high-temperature resistant zirconia-based nanoporous thermal insulation composite material, characterized in that, The high-temperature resistant zirconia-based nanoporous thermal insulation composite material was prepared using any one of claims 1 to 8.

10. The high-temperature resistant zirconia-based nanoporous thermal insulation composite material according to claim 9, characterized in that, The density of the zirconia-based nanoporous thermal insulation composite material is 0.50 g·cm³. -3 -0.90 g·cm -3 The compressive strength at 10% strain is 0.50 MPa-0.70 MPa, the temperature resistance is 1200℃, and the thermal conductivity at 1200℃ is 0.04 W·m. -1 ·K -1 -0.07W·m -1 ·K -1 .

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