Alumina aerogel composite and method for preparing the same

Abstract

The application discloses an alumina aerogel composite material and a preparation method thereof, and belongs to the technical field of aerogel preparation. The method comprises the following steps: adding light-shielding agent particles into deionized water containing a surfactant, uniformly stirring to form a light-shielding agent dispersion liquid, pre-dispersing the light-shielding agent dispersion liquid into a fiber preform through an impregnation method, drying, and then performing alumina sol impregnation, gel aging and drying treatment to prepare the alumina aerogel composite material. The light-shielding agent can be uniformly distributed in the composite material, and the shielding effect of the composite material on infrared radiation is improved. The application provides a complete preparation process of the alumina aerogel composite material, and the alumina aerogel composite material can meet the requirement of long-time use in an extremely high-temperature environment.

Description

Technical Field

[0001] This invention belongs to the field of aerogel preparation technology, specifically relating to an alumina aerogel composite material and its preparation method. Background Technology

[0002] Compared to conventional high-speed aircraft, reusable high-speed aircraft are characterized by their ability to serve multiple times and lower maintenance costs, making them a crucial development direction in the current aerospace field. When high-speed aircraft fly at high Mach numbers (approximately Mach 25) in the atmosphere, their fuselage surfaces generate intense aerodynamic heat, reaching temperatures exceeding 1200°C. Thermal insulation layers are essential to prevent heat transfer to the aircraft's interior, ensuring the normal operation of electronic components. Furthermore, these insulation layers must be as thin and lightweight as possible, without significantly impacting the aircraft's weight or usable space. This creates an urgent need for lightweight thermal insulation materials that are resistant to long-term high temperatures, have low thermal conductivity, and possess excellent mechanical properties. Existing high-temperature insulation materials such as ceramic fibers and thermal insulation tiles suffer from problems such as high thermal conductivity (requiring thicker insulation layers), insufficient load-bearing capacity, and difficulty in molding large-sized components, thus failing to meet the requirements of reusable high-speed aircraft.

[0003] Alumina aerogel is a novel nanoporous material with superior temperature resistance and thermal insulation performance compared to existing insulation materials, showing promising application prospects in the thermal insulation of high-speed aircraft. However, alumina aerogel exhibits strong transmittance to near-infrared thermal radiation with wavelengths of 3–8 μm. Under high-temperature conditions, infrared radiation heat transfer dominates, leading to a significant increase in the thermal conductivity of alumina aerogel at high temperatures, thus affecting its overall thermal insulation performance. Current technologies improve the specific extinction coefficient and infrared radiation blocking ability by adding infrared-shielding materials, but this often results in uneven dispersion of the shielding agent. This defect is particularly pronounced in the manufacture of large-size components, rendering existing doping methods unsuitable for improving the high-temperature thermal insulation performance of large-size components. Furthermore, existing alumina aerogel materials are prone to sintering and phase transformation at temperatures above 1100℃, leading to pore structure collapse, decreased thermal insulation performance, and difficulty in repeated use at 1200℃ and above. Therefore, existing alumina aerogel materials cannot meet the requirements for use in extreme high-temperature environments and cannot be used for extended periods at extremely high temperatures. Summary of the Invention

[0004] The problem to be solved by the present invention is to provide an alumina aerogel composite material and its preparation method. The method uses a hydrothermal method to prepare alumina aerogel with high crystallinity and its composite material, which significantly improves the service temperature of the alumina aerogel material and makes the light-shielding agent uniformly distributed in the composite material, thereby improving the shielding effect of the composite material on infrared radiation and meeting the requirements of alumina aerogel composite material for long-term use in extreme high-temperature environments.

[0005] The present invention includes a method for preparing an alumina aerogel composite material, comprising adding opaque agent particles to deionized water containing a surfactant, stirring evenly to form an opaque agent dispersion, pre-dispersing the opaque agent dispersion into a fiber preform by impregnation, drying, and then performing modified alumina sol impregnation, gel aging and drying treatment to prepare an alumina aerogel composite material.

[0006] Furthermore, the mass fraction ratio of the opaque agent to deionized water is 0.5% to 4%, the particle size of the opaque agent is 0.2 μm to 5 μm, and the opaque agent includes any one of zirconium oxide, silicon carbide, titanium oxide, boron carbide, or boron nitride.

[0007] Furthermore, the mass fraction ratio of surfactant to deionized water is 0.2% to 3%, and the surfactant includes any one of sodium oleate, sodium alkyl succinic anhydride, sodium cocoate, sodium dodecylbenzene sulfonate, sodium dodecyl sulfate, sodium secondary alkyl sulfonate, dodecyl trimethyl ammonium chloride, dodecyl dimethyl benzyl ammonium chloride, bis(dodecyl dimethyl) ammonium chloride, dodecyl glucoside, fatty alcohol polyoxyethylene ether glucoside, dodecyl betaine, dodecyl dimethyl ammonium chloride, dodecyl dimethylamine oxide, fatty alcohol polyoxyethylene ether, and dodecylphenol polyoxyethylene ether.

[0008] Furthermore, the specific steps include:

[0009] S1. Preparation and molding of ceramic fiber preforms: Ceramic fiber cotton of a certain thickness is laid flat along the fiber axis to form a ceramic fiber cotton layer. Ceramic fiber threads are used to needle-punch the ceramic fiber cotton layer in the thickness direction to form an integral whole. Then, it is compressed and molded to obtain a ceramic fiber preform.

[0010] S2, Pre-dispersion of opaque agent: The opaque agent dispersion is pre-dispersioned into the ceramic fiber preform obtained in step S1 by impregnation under normal pressure;

[0011] S3, Preparation of modified alumina sol, including:

[0012] S3.1 Preparation of alumina sol: After mixing deionized water and aluminum source precursor in a molar ratio of (20-100):1, the mixture is naturally cooled to obtain precursor hydrolysate. Acid is added and stirred evenly. The mixture is then placed in an autoclave, stirred, heated to a certain temperature and kept warm for a period of time, and then naturally cooled to obtain alumina sol.

[0013] S3.2 Alumina sol modification: The modification component precursor is added to an alcohol solvent containing acid and deionized water, and the reaction is carried out to obtain a modified solution; the modified solution is added to the alumina sol in step S3.1, stirred evenly, and then the coagulant is added and stirred thoroughly to dissolve, thus obtaining modified alumina sol;

[0014] S4. Sol impregnation and gel pre-aging: The alumina sol obtained in step S3 is impregnated into the ceramic fiber preform after step S2. After full impregnation, gel pre-aging is performed to obtain fiber / gel composite material.

[0015] S5, Solvent replacement: The fiber / gel composite material obtained in step S4 is immersed in an alcohol solvent at 10℃~70℃, and the alcohol solvent is replaced every 12 hours, with the number of replacements being 2 to 5 times.

[0016] S6. High-temperature and high-pressure aging and supercritical drying: The fiber / gel composite material treated in step S5 is placed in a supercritical drying kettle and subjected to high-temperature and high-pressure aging and supercritical drying to obtain an alumina aerogel composite material blank.

[0017] S7. Heat treatment to remove impurities: The alumina aerogel composite material blank obtained in step S6 is subjected to heat treatment to remove impurities, and the alumina aerogel composite material is obtained.

[0018] Furthermore, in step S1:

[0019] The chemical composition of ceramic fiber yarn and / or ceramic fiber cotton includes any one of zirconium oxide, alumina or mullite;

[0020] The ceramic fiber layup is compressed along its thickness direction until the density of the ceramic fiber preform is 0.18 g / cm³. 3 ~0.40g / cm 3 ;

[0021] The ceramic fiber cotton can be in any of the following forms: loose fiber cotton, fiber felt (in its natural state or peeled in the thickness direction), or fiber blanket (in its natural state or peeled in the thickness direction). The mass fraction of the slag balls is 0-5%, and the thickness is 0.5mm-3mm.

[0022] The mass fraction of ceramic fiber yarn in ceramic fiber preforms is 4% to 22%.

[0023] Furthermore, step S3 specifically includes:

[0024] In step S3.1: the aluminum source precursor includes any one of aluminum isopropoxide, aluminum n-propoxide, aluminum sec-butoxide, aluminum n-butoxide, or aluminum tert-butoxide; the aluminum source precursor is added to deionized water at 50℃~95℃ and reacted for 1h. After natural cooling, acid is added at a molar ratio of acid to aluminum source precursor (0.005~0.3):1 and stirred evenly. The resulting mixture is heated to 180℃~240℃ in an autoclave and held for 0.5h~24h.

[0025] In step S3.2: the reaction time between the modified component precursor and the alcohol solution containing acid and deionized water is 0.5 h to 4 h. The modified component precursor includes any one or a combination of several of tetraethyl orthosilicate, methyltriethoxysilane, ethyltriethoxysilane, dimethyldiethoxysilane, diethyldiethoxysilane, trimethylethoxysilane, triethylethoxysilane, methyltrimethoxysilane, ethyltrimethoxysilane, dimethyldimethoxysilane, and diethyldimethoxysilane. The coagulant includes any one of urea or hexamethylenetetramine. The molar ratio of the modified component precursor to the aluminum source precursor is (0.05 to 0.4):1, and the molar ratio of the coagulant to the aluminum source precursor is (0.05 to 0.3):1. The molar ratio of acid, deionized water, alcohol solvent to the modified component precursor is (0.001 to 0.1):(2 to 6):(1 to 4):1.

[0026] Furthermore, in step S4:

[0027] Modified alumina sol was immersed in ceramic fiber preforms at a pressure of -0.1 MPa to atmospheric pressure and kept for 0.5 h to 4 h.

[0028] The gel pre-aging temperature is 40℃~95℃, and the time is 10~48h.

[0029] Furthermore, in step S6: an alcohol equivalent to 5% to 50% of the volume of the supercritical drying vessel is added to the vessel, and nitrogen gas is pre-charged at 0.1 MPa to 3 MPa. The vessel is heated to an internal temperature of 260°C to 295°C and an internal pressure of 12 MPa to 20 MPa. After maintaining the temperature and pressure for 8 to 24 hours, the fluid inside the vessel is slowly released until the internal pressure is at atmospheric pressure. Finally, the vessel is purged with nitrogen gas for 10 to 60 minutes to obtain an alumina aerogel composite material blank.

[0030] Furthermore, in step S7: the alumina aerogel composite material blank is placed in a high-temperature furnace and heat-treated at 500℃~1100℃ for 6h~24h to remove impurities.

[0031] An alumina aerogel composite material is obtained by any of the above-mentioned methods for preparing alumina aerogel composite materials.

[0032] The beneficial effects of this invention are:

[0033] This invention uses safe, environmentally friendly, non-toxic, and non-flammable water as the dispersion medium for opacifier particles. A surfactant and opacifier particles are added to form an opacifier dispersion. The addition of the surfactant reduces the surface tension of the dispersion, allowing it to effectively wet the fiber preform during subsequent impregnation, thus ensuring uniform dispersion within the preform. The surfactant molecules, composed of both hydrophilic and oleophilic ends, significantly improve the compatibility and uniformity of the polar and non-polar mixture, ensuring the opacifier particles are stably and uniformly suspended in the dispersion. The fiber preform is then immersed in the opacifier dispersion, and the dispersion is pre-dispersed into the preform using a simple atmospheric pressure impregnation method. After the dispersion fully penetrates the fiber, it is dried to obtain a fiber preform doped with opacifier. This preform is then impregnated and composited with alumina sol, thus introducing the opacifier into the alumina aerogel composite material. The preparation method of the present invention can avoid the aggregation and sedimentation of the light-blocking agent particles caused by directly mixing the light-blocking agent with the sol in conventional methods, so that the light-blocking agent is uniformly distributed in the composite material, which significantly improves the shielding effect of the composite material on infrared radiation and reduces the high-temperature thermal conductivity. This method can effectively introduce the light-blocking agent uniformly into large-sized irregular fiber preforms, thereby enabling the preparation of large-sized irregular components of alumina aerogel composite material uniformly doped with light-blocking agent. Attached Figure Description

[0034] Appendix Figure 1 The images show actual photographs of the alumina aerogel composite material plate and components from Example 1.

[0035] Appendix Figure 2 This is a photograph of the alumina aerogel composite material of Example 1 after heat treatment at 1500℃ for 72 hours;

[0036] Appendix Figure 3 The bending stress-displacement curve of the alumina aerogel composite material in Example 1 is shown.

[0037] Appendix Figure 4 The thermal conductivity curves of the alumina aerogel composite material in Example 2 are shown in the range of room temperature to 1400°C. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0039] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items. Furthermore, the technical solutions of the various embodiments of this invention can be combined with each other, but only on the basis of being achievable by one of ordinary skill in the art. When a combination of technical solutions is contradictory or impossible to implement, such a combination should be considered non-existent and not within the scope of protection claimed by this invention.

[0040] This invention provides a method for preparing an alumina aerogel composite material, comprising adding opacifier particles to deionized water containing a surfactant, stirring to form an opacifier dispersion, pre-dispersing the opacifier dispersion into a fiber preform under normal pressure, drying, and then performing alumina sol impregnation, gel aging, and drying treatments to obtain the alumina aerogel composite material. This invention uses safe, environmentally friendly, non-toxic, and non-flammable water as the dispersion medium for the opacifier particles, adding a surfactant and opacifier particles to form the opacifier dispersion. By adding a surfactant, the surface tension of the opacifier dispersion is reduced, allowing it to effectively wet the fiber preform during subsequent impregnation, thus achieving uniform dispersion within the fiber preform. Furthermore, the surfactant molecules consist of hydrophilic and lipophilic ends, significantly improving the compatibility of polar and non-polar substances in the mixture. The compatibility and uniformity of the opacifier ensure that the opacifier particles are stably and uniformly suspended in the dispersion. The fiber preform is immersed in the opacifier dispersion, and the opacifier dispersion is pre-dispersed into the fiber preform through a simple atmospheric pressure impregnation method. After the opacifier dispersion fully penetrates the fiber, it is dried to obtain the fiber preform doped with opacifier. Then, it is impregnated and compounded with alumina sol to realize the introduction of opacifier into alumina aerogel composite material. The preparation method of this invention can avoid the aggregation and sedimentation of opacifier particles caused by direct mixing of opacifier and sol in conventional methods. It makes the opacifier uniformly distributed in the composite material, significantly improving the opacifier's shielding effect against infrared radiation and reducing high-temperature thermal conductivity. This method can effectively introduce opacifier uniformly into large-sized irregular fiber preforms, thereby enabling the preparation of large-sized irregular components of alumina aerogel composite material uniformly doped with opacifier.

[0041] In a preferred embodiment, the mass fraction ratio of the opaque agent to deionized water is 0.5% to 4%, which ensures optimal infrared radiation blocking effect without significantly increasing solid-state thermal conductivity, resulting in the alumina aerogel composite material with the lowest overall thermal conductivity. Preferably, the particle size of the opaque agent is 0.2 μm to 5 μm. Within this range, the opaque agent has the best blocking effect on infrared radiation waves corresponding to the temperature range of 500℃ to 1500℃, which can significantly reduce the overall thermal conductivity of the composite material in this temperature range. The opaque agent is any one of zirconium oxide, silicon carbide, titanium oxide, boron carbide, or boron nitride.

[0042] In a preferred embodiment, the mass fraction ratio of surfactant to deionized water is 0.2% to 3%, which ensures good dispersion of the opacifier in water, while the amount and cost of surfactant raw materials are low. The surfactant is any one of sodium oleate, sodium alkyl succinic anhydride, sodium cocoate, sodium dodecylbenzene sulfonate, sodium dodecyl sulfate, sodium secondary alkyl sulfonate, dodecyl trimethyl ammonium chloride, dodecyl dimethyl benzyl ammonium chloride, bis(dodecyl dimethyl) ammonium chloride, dodecyl glucoside, fatty alcohol polyoxyethylene ether glucoside, dodecyl betaine, dodecyl dimethyl ammonium chloride, dodecyl dimethylamine oxide, fatty alcohol polyoxyethylene ether, and dodecylphenol polyoxyethylene ether.

[0043] The method for preparing alumina aerogel composite material provided in this embodiment of the invention specifically includes the following steps:

[0044] S1. Preparation and molding of ceramic fiber preforms: A certain thickness of ceramic fiber cotton is laid flat along the fiber axis to form a ceramic fiber cotton layer. Ceramic fiber threads are used to needle the ceramic fiber cotton layer in the thickness direction, so that the ceramic fiber cotton layers overlap and entangle with each other to form a whole. Then, the ceramic fiber cotton layer is compressed to a certain density along the thickness direction to form a ceramic fiber preform.

[0045] S2. Pre-dispersion of opaque agent: The opaque agent dispersion is pre-dispersioned into the ceramic fiber preform under normal pressure. Preferably, the mass fraction ratio of opaque agent to deionized water is 0.5% to 4%. Preferably, the particle size of the opaque agent particles used to prepare the opaque agent dispersion is 0.2 μm to 5 μm. Preferably, the mass fraction ratio of surfactant to deionized water in the opaque agent dispersion is 0.2% to 3%.

[0046] S3. Preparation of modified alumina sol, specifically including the following steps:

[0047] S3.1 Preparation of alumina sol: The aluminum source precursor is uniformly added to deionized water at a certain temperature, and the reaction is maintained at the temperature for 1 hour. After natural cooling, the precursor hydrolysate is obtained. The molar ratio of deionized water to aluminum source precursor is (20-100):1. When the molar ratio is less than 20:1, the solid content in the precursor hydrolysate is too high, and the particles are prone to agglomeration and precipitation, making it impossible to form a uniform and stable sol. When the molar ratio is greater than 100:1, the solid content in the precursor hydrolysate is too low, and the resulting alumina aerogel has poor bulking and mechanical properties, and the mechanical properties of the composite material are also poor. Then, acid is added to the precursor hydrolysate and stirred evenly to obtain a mixed solution. The mixed solution is placed in a high-pressure reactor, stirred, heated to a certain temperature and kept at that temperature for a period of time, and then naturally cooled to obtain alumina sol.

[0048] S3.2 Alumina sol modification: The modifying component precursor is added to an alcohol solvent containing acid and deionized water, and the reaction is carried out to obtain a modified solution; the modified solution is added to the alumina sol in step S3.1, stirred evenly, and then a coagulant is added and stirred thoroughly to dissolve, thereby obtaining modified alumina sol; wherein, the acid used in this step is any one of nitric acid, hydrochloric acid, acetic acid, sulfuric acid or hydrofluoric acid, and the alcohol solvent used in this step is any one of ethanol, isopropanol, n-propanol, n-butanol, sec-butanol or tert-butanol;

[0049] S4. Sol impregnation and gel pre-aging: Under pressure conditions of -0.1MPa to normal pressure, the alumina sol obtained in step S3 is impregnated into the ceramic fiber preform after step S2. After full impregnation, gel pre-aging is performed to obtain fiber / gel composite material.

[0050] S5. Solvent Replacement: The fiber / gel composite material obtained in step S4 is immersed in an alcohol solvent at 10℃~70℃. The alcohol solvent is replaced every 12 hours, and the number of replacements is 2 to 5 times. When the alcohol solvent temperature is below 10℃, the solvent molecules diffuse slowly, resulting in incomplete replacement. When the alcohol solvent temperature is above 70℃, it is prone to evaporation, requiring an additional sealing device, which increases the complexity of the replacement process. If the alcohol solvent is replaced less than 2 times, the replacement is incomplete, while if the alcohol solvent is replaced more than 5 times, the complexity of the replacement process increases, the alcohol solvent consumption increases, and the cost is high. The alcohol solvent used in this step is any one of ethanol, isopropanol, n-propanol, n-butanol, sec-butanol, or tert-butanol.

[0051] During the drying process of wet gel, the main reason for the shrinkage and collapse of wet gel is that the capillary force is too large. The magnitude of the capillary force depends on the surface tension of the solvent in the gel network. Therefore, solvent replacement is performed on the alumina gel before supercritical drying to replace the water and by-products in the pores of the fiber / gel composite material with alcohols. During the subsequent supercritical drying process, the surface tension is close to zero, thus maintaining a good pore structure.

[0052] S6. High-temperature and high-pressure aging and supercritical drying: The fiber / gel composite material treated in step S5 is placed in a supercritical drying kettle and subjected to high-temperature and high-pressure aging and supercritical drying to obtain an alumina aerogel composite material blank.

[0053] S7. Heat treatment to remove impurities: The alumina aerogel composite material blank obtained in step S6 is subjected to heat treatment to remove impurities, and the alumina aerogel composite material is obtained.

[0054] Heat treatment removes the hydroxyl groups from the alumina aerogel matrix in the composite material, so that the chemical composition of the composite material is entirely composed of high-temperature resistant inorganic components (mainly alumina and silicon dioxide), ensuring the stability of the aerogel composite material at high temperatures.

[0055] This invention uses high-temperature resistant ceramic fibers as raw materials, employing ceramic fiber cotton layering and ceramic fiber needle punching. This transverse layering and longitudinal needle punching weaving method can improve the overlap and entanglement between ceramic fibers, providing a high-strength, high-toughness, and high-temperature resistant reinforcing phase for the preparation of alumina aerogel composites. By compressing along the thickness direction of the layers, the density of the ceramic fiber preforms is increased, serving as the skeleton of the composite material. This further improves the mechanical properties of the alumina aerogel and its ability to resist sintering at high temperatures, ensuring that the composite material can withstand high temperatures for a long time. Furthermore, transverse layering can maximally suppress heat transfer in the thickness direction of the fibers in the composite material, thereby reducing the overall thermal conductivity of the composite material. Appropriate longitudinal needle punching can significantly improve the interlaminar shear strength of the composite material, enabling the molding of large-sized complex irregular components. The size of a single piece can reach 1.5m in length, 1.2m in width, and 3mm to 150mm in thickness.

[0056] The superior thermal insulation properties of alumina aerogel are primarily due to its low density, nanoparticle framework, and nanoporous structure. Therefore, a crucial prerequisite for the long-term use of alumina aerogel at high temperatures is its ability to maintain this low density, nanoparticle framework, and nanoporous structure. A typical preparation method for alumina aerogel is the sol-gel method, which involves the formation of alumina sol and gel through the hydrolysis and condensation reactions of precursors. This process is very mild (low temperature, low pressure), and the hydrolysis and condensation reactions are incomplete. Consequently, the prepared alumina aerogel is amorphous and contains a large number of unreacted chemical groups. The nanoparticle structure of the aerogel... The aerogel contains numerous defects and active sites, making it prone to sintering growth and α-phase transformation at high temperatures. This leads to densification and shrinkage (increased density) of the aerogel, collapse of the nanoporous structure, and decreased thermal insulation performance. In this embodiment, excess water is added to completely hydrolyze the aluminum source precursor, forming a precursor hydrolysate. This hydrolysate is then placed in a high-pressure autoclave for sealed stirring and heating. During this process, both temperature and pressure increase simultaneously. The precursor particles in the hydrolysate continuously grow under high temperature and pressure conditions, forming highly crystalline boehmite grains with anisotropic morphology. The addition of a modified precursor component further enhances the process. After reacting with a catalyst, an alumina gel is formed, which is then subjected to supercritical drying to obtain a highly crystalline alumina aerogel. The alumina aerogel prepared in this embodiment of the invention has two advantages: firstly, its framework is formed by stacked highly crystalline, large-grain-size nanoparticle units, resulting in a significantly lower surface energy than conventional amorphous alumina aerogels and a significantly reduced sintering activity at high temperatures; secondly, because the nanoparticles constituting the alumina aerogel have an anisotropic morphology, such as flat rods, the number and contact area of ​​their neck contacts are reduced, making atomic diffusion and neck fusion sintering less likely to occur at high temperatures, thus significantly increasing its α-phase transformation temperature. Finally, a modified component is introduced into the alumina sol to combine with the surface of the alumina sol particles, forming a core-shell structured alumina particles. The modified component particles act as an insulator between the alumina particles and react with the alumina on the particle surface at high temperature to generate a thermally stable phase, inhibiting the sintering and α-phase transformation of the alumina particles. Therefore, the alumina aerogel of this invention has significantly improved resistance to sintering and shrinkage at high temperatures, and can maintain low density and good nanoparticle framework and nanopore structure at high temperatures. The operating temperature is 200℃~300℃ higher than that of conventional alumina aerogel.

[0057] This invention improves the mechanical properties of alumina aerogel by using supercritical fluid high-temperature and high-pressure aging. In the high-temperature and high-pressure supercritical fluid, the atomic diffusion ability and reactivity of the nanoparticle surface of the alumina wet gel are improved, and further physical connection and chemical cross-linking reactions occur, thereby further improving the strength of the aerogel skeleton structure and enhancing the comprehensive mechanical properties of the alumina aerogel composite material.

[0058] This invention provides a complete preparation process for alumina aerogel composite materials, including ceramic fiber preform preparation and molding, light-blocking agent pre-dispersion, modified alumina sol preparation, sol impregnation and gel pre-aging, solvent replacement, high-temperature and high-pressure aging and supercritical drying, and heat treatment for impurity removal. The raw materials are readily available and the process is simple. The prepared alumina aerogel composite material can withstand high temperatures of 1200℃ to 1500℃ for a long time, while having very low high-temperature thermal conductivity. The typical thickness shrinkage rates after treatment at 1300℃ and 1500℃ for 72 hours are 0.2% and 1.4%, respectively. The thermal conductivity at 1400℃ is as low as 0.062 W / (m·K). The compressive strength at 3% deformation can reach more than 0.2 MPa, and the flexural strength can reach more than 1.1 MPa.

[0059] In a preferred embodiment, in step S1:

[0060] The chemical composition of ceramic fiber yarn and / or ceramic fiber cotton includes any one of zirconium oxide, alumina, or mullite; the form of ceramic fiber cotton includes any one of loose fiber, fiber felt (in its natural state or peeled in the thickness direction), or fiber blanket (in its natural state or peeled in the thickness direction); the ceramic fiber layup is compressed in the thickness direction to a density of 0.18 g / cm³ for the ceramic fiber preform. 3 ~0.40g / cm 3 The fiber density is less than 0.18 g / cm³. 3 At this stage, the fiber skeleton provides poor reinforcement to alumina aerogel, and its ability to resist sintering and shrinkage at high temperatures is insufficient, leading to inadequate mechanical properties and temperature resistance of the composite material. Furthermore, fiber densities exceeding 0.40 g / cm³ are problematic. 3 When the density and overall thermal conductivity of the composite material are too high, the mass fraction of ceramic fiber wire in the ceramic fiber preform is 4% to 22%. When the mass fraction of ceramic fiber wire is less than 4%, the fiber preform is difficult to form completely. When the mass fraction of ceramic fiber wire is higher than 22%, the longitudinal thermal conductivity of the fiber preform will increase significantly.

[0061] In a preferred embodiment, the mass fraction of slag balls in the ceramic fiber cotton in step S1 is 0-5%. When the slag ball content in the fiber is higher than 5%, it will lead to an increase in the thermal conductivity of the composite material and a decrease in temperature resistance. The thickness of the ceramic fiber cotton is 0.5mm-3mm. Ceramic fibers are obtained by laying multiple layers of ceramic fiber cotton flat. When the thickness of the ceramic fiber cotton is less than 0.5mm, the flat laying process is more difficult. When the thickness is greater than 3mm, the formability and uniformity of the obtained ceramic fiber preform are insufficient.

[0062] In a preferred embodiment, step S3 specifically includes:

[0063] In step S3.1:

[0064] The aluminum source precursor includes any one of aluminum isopropoxide, aluminum n-propoxide, aluminum sec-butoxide, aluminum n-butoxide, or aluminum tert-butoxide;

[0065] The aluminum source precursor is added to deionized water at 50℃~95℃ and reacted for 1 hour to obtain the precursor hydrolysate. When the temperature of the deionized water is below 50℃, the aluminum source precursor is difficult to completely hydrolyze. When the temperature is above 95℃, a reflux device is required, which increases the complexity of the equipment.

[0066] Acid was added to the precursor hydrolysate and stirred until homogeneous to obtain a mixed solution. The molar ratio of acid to aluminum source precursor was (0.05–0.3):1. When the molar ratio was below 0.05:1, the double layer charge on the surface of the particles in the sol was unstable outside this range, making it difficult to obtain a stable sol. The obtained mixed solution was heated in an autoclave to 180°C–240°C for 0.5 h–24 h. When the heating temperature was below 180°C and the heating time was less than 0.5 h, the alumina sol had a small grain size, and the resulting alumina aerogel had insufficient temperature resistance. When the heating temperature was above 240°C and the heating time was more than 24 h, the alumina sol was prone to precipitation, and its stability decreased.

[0067] In step S3.2:

[0068] The reaction time between the modified component precursor and the alcohol solution containing acid and deionized water is 0.5 h to 4 h. Within this time range, the reaction is complete and the reaction cycle is relatively short.

[0069] The molar ratio of the modified component precursor to the aluminum source precursor is (0.05~0.4):1. When the molar ratio is too low, the modification effect of the modified component on the alumina aerogel is insufficient and the resistance to sintering is not significantly improved. When the molar ratio is too high, the content of the modified component in the alumina aerogel is high and it is easy for it to sinter and agglomerate, which has an adverse effect on the temperature resistance of the alumina aerogel.

[0070] The molar ratio of coagulant to aluminum source precursor is (0.05-0.3):1. When the amount of coagulant is too low, the sol cannot gel; when it is too high, the gelation time is short, which affects the uniformity of the network structure and pore structure of alumina aerogel.

[0071] The molar ratio of acid to modified component precursor is (0.001-0.1):1. When the molar ratio of acid is too low, the catalytic reaction effect is poor; when it is too high, the catalytic reaction rate is too fast, causing uneven reaction. The molar ratio of deionized water to modified component precursor is (2-6):1. When the molar ratio of deionized water is too low, the hydrolysis reaction is incomplete; when it is too high, the reaction rate is too fast, which can easily cause precipitation in the modified solution.

[0072] The molar ratio of alcohol solvent to modified component precursor is (1-4):1. When the molar ratio of alcohol solvent is too low, the precursor and water cannot be completely miscible, affecting the uniformity of the modified solution. When it is too high, the reactant concentration is reduced, the degree of reaction decreases, and the reaction cycle is prolonged.

[0073] The modified component precursor is any one or a combination of several of tetraethyl orthosilicate, methyltriethoxysilane, ethyltriethoxysilane, dimethyldiethoxysilane, diethyldiethoxysilane, trimethylethoxysilane, methyltrimethoxysilane, ethyltrimethoxysilane, dimethyldimethoxysilane, and diethyldimethoxysilane; the coagulant includes any one of urea or hexamethylenetetramine.

[0074] In a preferred embodiment, in step S4: the modified alumina sol is immersed in the ceramic fiber preform under pressure of -0.1 MPa to atmospheric pressure for 0.5 h to 4 h to achieve sufficient impregnation effect and a short impregnation cycle; the gel pre-aging temperature is 40 °C to 95 °C and the time is 10 to 48 h to achieve complete gelation and a short aging cycle.

[0075] In a preferred embodiment, in step S6: An alcoholic substance, equivalent to 5% to 50% of the vessel's volume, is added to a supercritical drying vessel. Nitrogen gas is pre-charged at 0.1 MPa to 3 MPa. The vessel is heated to an internal temperature of 260°C to 295°C and an internal pressure of 12 MPa to 20 MPa. After maintaining this temperature and pressure for 8 to 24 hours, the fluid inside the vessel is slowly released until the internal pressure returns to atmospheric pressure. Finally, the vessel is purged with nitrogen gas for 10 to 60 minutes to obtain an alumina aerogel composite material blank. Adding 5% to 50% alcohol to the vessel makes heat and mass transfer more uniform and temperature and pressure more stable. Adding more than 50% will significantly affect the filling volume ratio. Pre-charging with 0.1 MPa to 3 MPa nitrogen aims to minimize air content inside the vessel. The concentration ensures safety while providing pressure for the high-temperature, high-pressure aging and supercritical drying processes. Maintaining the reactor temperature at 260℃~295℃ and the reactor pressure at 10MPa~18MPa allows the fluid inside the reactor to reach a supercritical state, resulting in alumina aerogel with good bulking and porous structure, and a non-shrinking aerogel composite material. The purpose of maintaining the temperature and pressure for 8h~24h is to allow the alumina gel to undergo further physicochemical cross-linking under high-temperature and high-pressure conditions, increasing the aerogel particle size and improving the strength of the aerogel's skeletal structure, thereby enhancing the aerogel's resistance to high-temperature sintering and the comprehensive mechanical properties of the composite material. In this embodiment, the alcohol is any one of ethanol, isopropanol, n-propanol, n-butanol, sec-butanol, or tert-butanol.

[0076] In a preferred embodiment, in step S7: the alumina aerogel composite material blank is placed in a high-temperature furnace and heat-treated at 500℃~1100℃ for 6h~24h to remove impurities; if the heat treatment temperature is lower than 500℃ and the time is less than 6h, the hydroxyl groups on the surface of the alumina aerogel particles will not be completely removed, making it difficult to completely convert into alumina and silicon oxide components, which will lead to a decrease in the heat resistance of the composite material. If the heat treatment temperature is too high and the time is too long, it will increase the design difficulty of the high-temperature furnace and the preparation cycle will be too long.

[0077] This invention also provides an alumina aerogel composite material, obtained by the alumina aerogel composite material preparation method described above. It can withstand high temperatures of 1200℃ to 1500℃ for extended periods, while exhibiting very low high-temperature thermal conductivity. Typical thickness shrinkage values ​​after treatment at 1300℃ and 1500℃ for 72 hours are 0.2% and 1.2%, respectively. The lowest thermal conductivity at 1400℃ is 0.062 W / (m·K). The compressive strength at 3% deformation is 0.26 MPa, and the flexural strength is 1.12 MPa.

[0078] Example 1

[0079] This embodiment provides a method for preparing alumina aerogel composite material, including the following steps:

[0080] S1. Preparation and molding of ceramic fiber preforms: A 2mm thick layer of alumina fiber felt is laid flat along the fiber axis to form a fiber layup. Alumina fiber threads are then needle-punched along its thickness direction to form a whole. The slag ball mass fraction in the alumina fiber felt is 2%, and the needle-punched fiber threads account for 14% of the total fiber mass fraction. Then, it is compressed along its thickness direction to 0.30g / cm². 3 Alumina fiber preforms are obtained by molding.

[0081] S2. Pre-dispersion of opacifier: Zirconia particles with an average particle size of 1.2 μm are added to deionized water containing sodium dodecylbenzene sulfonate and stirred evenly to form a zirconia dispersion, wherein the mass fraction ratio of zirconia particles to deionized water is 2.5% and the mass fraction ratio of sodium dodecylbenzene sulfonate to deionized water is 1.2%; the zirconia dispersion is pre-dispersed into alumina fiber preforms by impregnation under normal pressure and dried at 150℃ for 8 hours;

[0082] S3. Preparation of modified alumina sol, specifically including the following steps:

[0083] S3.1 Preparation of alumina sol: Aluminum sec-butoxide is uniformly added to deionized water at 85°C, and the reaction is maintained at the temperature for 1 hour. After natural cooling, an aluminum sec-butoxide hydrolysate is obtained. The molar ratio of deionized water to aluminum sec-butoxide is 50:1. Nitric acid is added to the aluminum sec-butoxide hydrolysate, and the molar ratio of nitric acid to aluminum sec-butoxide is 0.15:1. After stirring evenly, the mixture is poured into a high-pressure reactor, stirred, heated to a certain temperature of 220°C, and kept at that temperature for 16 hours. After natural cooling, an alumina sol is obtained.

[0084] S3.2 Alumina sol modification: Tetraethyl orthosilicate was added to sec-butanol containing nitric acid and deionized water, wherein the molar ratio of tetraethyl orthosilicate to aluminum sec-butoxide was 0.15:1, and the molar ratio of nitric acid, deionized water, sec-butanol to tetraethyl orthosilicate was 0.01:3:3:1. After stirring and reacting for 2 hours, a modified solution was formed. The modified solution was added to the alumina sol from step S3.1, stirred evenly, and then urea was added and stirred thoroughly to dissolve, wherein the molar ratio of urea to aluminum sec-butoxide was 0.18:1, to obtain the modified alumina sol.

[0085] S4. Sol impregnation and gel pre-aging: Under normal pressure, the modified alumina sol obtained in step S3 is impregnated into the ceramic fiber preform obtained in step S1 and kept for 1 hour. Then, it is kept at 90°C for 24 hours for gel pre-aging to obtain fiber / gel composite.

[0086] S5, Solvent replacement: Immerse the fiber / gel composite obtained in step S4 in sec-butanol at 60°C, and replace the sec-butanol every 12 hours for a total of 3 times.

[0087] S6. High-temperature and high-pressure aging and supercritical drying: The fiber / gel composite material treated in step S5 is placed in a supercritical drying kettle, and ethanol with a volume fraction of 30% of the kettle volume is added as a drying medium. Nitrogen gas is pre-charged at 1.8 MPa, and the kettle is heated to a temperature of 290°C and a pressure of 16 MPa. After maintaining the temperature and pressure for 14 hours, the fluid in the kettle is slowly released until the pressure inside the kettle is normal. Finally, the kettle is purged with nitrogen gas for 30 minutes to obtain an alumina aerogel composite material blank.

[0088] S7. Heat treatment to remove impurities: The alumina aerogel composite material blank obtained in step S6 is placed in a high-temperature furnace and heat-treated at 1100℃ for 12 hours to remove impurities from the composite material and obtain the alumina aerogel composite material.

[0089] As attached Figure 1 As shown in Example 1, the alumina aerogel composite material plate has dimensions of 200×200×20mm, and the component has dimensions of 350×100×30mm, exhibiting good formability, dimensional accuracy, and uniformity. (See attached...) Figure 2As shown, after heat treatment at 1300℃ and 1500℃ for 72 hours, the alumina aerogel composite material did not exhibit delamination or deformation, with thickness shrinkage of only 0.2% and 1.4%, respectively, demonstrating excellent long-term high-temperature resistance. The alumina aerogel composite material also exhibits a very low thermal conductivity of 0.068 W / (m·K) at 1400℃. (See attached image.) Figure 3 As shown, the alumina aerogel composite exhibits a slow decreasing stress trend after failure under bending load, which is a typical ductile fracture. The bending strength reaches 1.12 MPa, indicating that the composite has good toughness and will not fail instantaneously under load. The composite also has good compressive strength, with a compressive strength (3% deformation) of 0.26 MPa.

[0090] Example 2

[0091] This embodiment provides a method for preparing alumina aerogel composite material, including the following steps:

[0092] S1. Preparation and molding of ceramic fiber preforms: 1.5mm thick zirconia fiber loose cotton is laid flat along the fiber axis to form a fiber layup. Zirconia fiber threads are then needle-punched along its thickness direction to form a whole. The slag ball mass fraction of the zirconia fiber is 0.2%, and the needle-punched fiber threads account for 8% of the total fiber mass fraction. Then, it is compressed along its thickness direction to 0.28g / cm³. 3 The zirconia fiber preform is obtained by molding.

[0093] S2. Pre-dispersion of opacifier: Zirconia particles with an average particle size of 1.0 μm are added to deionized water containing fatty alcohol polyoxyethylene ether glucoside and stirred evenly to form a zirconia dispersion, wherein the mass fraction ratio of zirconia particles to deionized water is 1.8% and the mass fraction ratio of fatty alcohol polyoxyethylene ether glucoside to deionized water is 1.5%; the zirconia dispersion is pre-dispersed into alumina fiber preforms by impregnation under normal pressure and dried at 150℃ for 8 hours;

[0094] S3. Preparation of modified alumina sol, specifically including the following steps:

[0095] S3.1 Preparation of alumina sol: Aluminum isopropoxide is uniformly added to deionized water at 75°C, and the reaction is maintained at this temperature for 1 hour. After natural cooling, an aluminum isopropoxide hydrolysate is obtained. The molar ratio of deionized water to aluminum isopropoxide is 50:1. Hydrochloric acid is added to the aluminum isopropoxide hydrolysate, and the molar ratio of hydrochloric acid to aluminum isopropoxide is 0.12:1. After stirring evenly, the mixture is poured into a high-pressure reactor, stirred, heated to a certain temperature of 200°C, and kept at this temperature for 8 hours. After natural cooling, an alumina sol is obtained.

[0096] S3.2 Alumina sol modification: Methyltrimethoxysilane was added to isopropanol containing hydrochloric acid and deionized water, wherein the molar ratio of methyltrimethoxysilane to aluminum isopropoxide was 0.25:1, and the molar ratio of hydrochloric acid, deionized water, isopropanol and methyltrimethoxysilane was 0.03:3.5:3:1. After stirring and reacting for 3.5 h, a modified solution was formed. The modified solution was added to the alumina sol from step S3.1, stirred evenly, and then urea was added and stirred thoroughly to dissolve, wherein the molar ratio of urea to aluminum sec-butoxide was 0.25:1, to obtain the modified alumina sol.

[0097] S4. Sol impregnation and gel pre-aging: Under normal pressure, the modified alumina sol obtained in step S3 is immersed in the ceramic fiber preform obtained in step S1 and kept for 1 hour. Then, it is kept at 90°C for 30 hours for gel pre-aging to obtain fiber / gel composite.

[0098] S5, Solvent replacement: Immerse the fiber / gel composite obtained in step S4 in isopropanol at 55°C, and replace the isopropanol every 12 hours for a total of 3 times.

[0099] S6. High-temperature and high-pressure aging and supercritical drying: The fiber / gel composite material treated in step S5 is placed in a supercritical drying kettle, and isopropanol with a volume fraction of 24% of the kettle volume is added as a drying medium. Nitrogen gas is pre-charged at 2.5 MPa, and the kettle is heated to a temperature of 285℃ and a pressure of 15 MPa. After maintaining the temperature and pressure for 10 hours, the fluid in the kettle is slowly released until the pressure inside the kettle is normal. Finally, the kettle is purged with nitrogen gas for 30 minutes to obtain an alumina aerogel composite material blank.

[0100] S7. Heat treatment to remove impurities: The alumina aerogel composite material blank obtained in step S6 is placed in a high-temperature furnace and heat-treated at 1000℃ for 6 hours to remove impurities from the composite material, thus obtaining the alumina aerogel composite material.

[0101] The alumina aerogel composite material of Example 2, after heat treatment at 1300℃ and 1500℃ for 72 hours, showed a thickness shrinkage of only 0.8% and 3.7%, respectively, demonstrating excellent long-term high-temperature resistance. (See attached diagram.) Figure 4 As shown, the thermal conductivity of alumina aerogel composite material at room temperature is 0.032 W / (m·K). With the increase of temperature, the increase of thermal conductivity is very gradual. The thermal conductivity at 1200℃ and 1400℃ is only 0.050 and 0.062 W / (m·K), respectively, indicating that it has excellent comprehensive thermal insulation performance.

[0102] Example 3

[0103] This embodiment provides a method for preparing alumina aerogel composite material, including the following steps:

[0104] S1. Preparation and molding of ceramic fiber preforms: A 1.8 mm thick mullite fiber mat layer is laid flat along the fiber axis to form a fiber layup. Mullite fiber threads are then needle-punched along its thickness direction to form a whole. The slag ball mass fraction of the mullite fiber mat is 3%, and the needle-punched fiber threads account for 11% of the total fiber mass fraction. Then, it is compressed along its thickness direction to 0.34 g / cm³. 3 The process involves molding to obtain mullite fiber preforms.

[0105] S2. Pre-dispersion of opacifier: Silicon carbide particles with an average particle size of 1.5 μm are added to deionized water containing sodium dodecylbenzene sulfonate and stirred evenly to form a silicon carbide dispersion, wherein the mass fraction ratio of silicon carbide particles to deionized water is 2.0% and the mass fraction ratio of sodium dodecylbenzene sulfonate to deionized water is 1.5%; the silicon carbide dispersion is pre-dispersed into mullite fiber preforms by impregnation under normal pressure and dried at 150℃ for 8 hours;

[0106] S3. Preparation of modified alumina sol, specifically including the following steps:

[0107] S3.1 Preparation of alumina sol: Aluminum sec-butoxide is uniformly added to deionized water at 80°C, and the reaction is maintained at this temperature for 1 hour. After natural cooling, an aluminum sec-butoxide hydrolysate is obtained. The molar ratio of deionized water to aluminum sec-butoxide is 40:1. Nitric acid is added to the aluminum sec-butoxide hydrolysate, and the molar ratio of nitric acid to aluminum sec-butoxide is 0.15:1. After stirring evenly, the mixture is poured into a high-pressure reactor, stirred, heated to a certain temperature of 240°C, and kept at this temperature for 20 hours. After natural cooling, an alumina sol is obtained.

[0108] S3.2 Alumina sol modification: Tetraethyl orthosilicate was added to sec-butanol containing nitric acid and deionized water, wherein the molar ratio of tetraethyl orthosilicate to aluminum sec-butoxide was 0.15:1, and the molar ratio of nitric acid, deionized water, sec-butanol to tetraethyl orthosilicate was 0.01:3:3:1. After stirring and reacting for 2 hours, a modified solution was formed. The modified solution was added to the alumina sol from step S3.1, stirred evenly, and then urea was added and stirred thoroughly to dissolve, wherein the molar ratio of urea to aluminum sec-butoxide was 0.12:1, to obtain the modified alumina sol.

[0109] S4. Sol impregnation and gel pre-aging: Under normal pressure, the modified alumina sol obtained in step S3 is immersed in the ceramic fiber preform obtained in step S1 and kept for 1 hour. Then, it is kept at 80°C for 36 hours for gel pre-aging to obtain fiber / gel composite.

[0110] S5, Solvent replacement: Immerse the fiber / gel composite obtained in step S4 in sec-butanol at 70°C, and replace the sec-butanol every 12 hours, for a total of 2 replacements.

[0111] S6. High-temperature and high-pressure aging and supercritical drying: The fiber / gel composite material treated in step S5 is placed in a supercritical drying kettle, and sec-butanol with a volume fraction of 42% of the kettle volume is added as a drying medium. Nitrogen gas is pre-charged at 1.0 MPa, and the kettle is heated to a temperature of 290℃ and a pressure of 18 MPa. After maintaining the temperature and pressure for 20 hours, the fluid in the kettle is slowly released until the pressure inside the kettle is normal. Finally, the kettle is purged with nitrogen gas for 30 minutes to obtain an alumina aerogel composite material blank.

[0112] S7. Heat treatment to remove impurities: The alumina aerogel composite material blank obtained in step S6 is placed in a high-temperature furnace and heat-treated at 1100℃ for 20 hours to remove impurities from the composite material, thus obtaining the alumina aerogel composite material.

[0113] The alumina aerogel composite material of Example 3, after heat treatment at 1300℃ and 1500℃ for 72 hours, showed a thickness shrinkage of only 0.1% and 0.5%, respectively, demonstrating good long-term high-temperature resistance. The compressive strength (3% deformation) of the composite material was 0.24 MPa.

[0114] Example 4

[0115] This embodiment provides a method for preparing alumina aerogel composite material, including the following steps:

[0116] S1. Preparation and molding of ceramic fiber preforms: A 2.5mm thick layer of alumina fiber felt is laid flat along the fiber axis to form a fiber layup. Alumina fiber threads are then needle-punched along its thickness direction to form a whole. The slag ball mass fraction of the alumina fiber felt is 2%, and the needle-punched fiber threads account for 14% of the total fiber mass fraction. The preform is then compressed along its thickness direction to 0.30g / cm². 3 Alumina fiber preforms are obtained by molding.

[0117] S2. Pre-dispersion of opacifier: Zirconia particles with an average particle size of 1.2 μm are added to deionized water containing sodium dodecylbenzene sulfonate and stirred evenly to form a zirconia dispersion, wherein the mass fraction ratio of zirconia particles to deionized water is 2.5% and the mass fraction ratio of sodium dodecylbenzene sulfonate to deionized water is 1.2%; the zirconia dispersion is pre-dispersed into alumina fiber preforms by impregnation under normal pressure and dried at 150℃ for 8 hours;

[0118] S3. Preparation of modified alumina sol, specifically including the following steps:

[0119] S3.1 Preparation of alumina sol: Aluminum sec-butoxide is uniformly added to deionized water at 85°C, and the reaction is maintained at the temperature for 1 hour. After natural cooling, an aluminum sec-butoxide hydrolysate is obtained. The molar ratio of deionized water to aluminum sec-butoxide is 50:1. Nitric acid is added to the aluminum sec-butoxide hydrolysate, and the molar ratio of nitric acid to aluminum sec-butoxide is 0.15:1. After stirring evenly, the mixture is poured into a high-pressure reactor, stirred, heated to a certain temperature of 200°C, and kept at that temperature for 2 hours. After natural cooling, an alumina sol is obtained.

[0120] S3.2 Alumina sol modification: Tetraethyl orthosilicate was added to sec-butanol containing nitric acid and deionized water, wherein the molar ratio of tetraethyl orthosilicate to aluminum sec-butoxide was 0.15:1, and the molar ratio of nitric acid, deionized water, sec-butanol to tetraethyl orthosilicate was 0.01:3:3:1. After stirring and reacting for 2 hours, a modified solution was formed. The modified solution was added to the alumina sol from step S3.1, stirred evenly, and then urea was added and stirred thoroughly to dissolve, wherein the molar ratio of urea to aluminum sec-butoxide was 0.18:1, to obtain the modified alumina sol.

[0121] S4. Sol impregnation and gel pre-aging: Under normal pressure, the modified alumina sol obtained in step S3 is impregnated into the ceramic fiber preform obtained in step S1 and kept for 1 hour. Then, it is kept at 90°C for 24 hours for gel pre-aging to obtain fiber / gel composite.

[0122] S5, Solvent replacement: Immerse the fiber / gel composite obtained in step S4 in sec-butanol at 60°C, and replace the sec-butanol every 12 hours for a total of 3 times.

[0123] S6. High-temperature and high-pressure aging and supercritical drying: The fiber / gel composite material treated in step S5 is placed in a supercritical drying kettle, and ethanol with a volume fraction of 30% of the kettle volume is added as a drying medium. Nitrogen gas is pre-charged at 1.8 MPa, and the kettle is heated to a temperature of 290°C and a pressure of 16 MPa. After maintaining the temperature and pressure for 14 hours, the fluid in the kettle is slowly released until the pressure inside the kettle is normal. Finally, the kettle is purged with nitrogen gas for 30 minutes to obtain an alumina aerogel composite material blank.

[0124] S7. Heat treatment to remove impurities: The alumina aerogel composite material blank obtained in step S6 is placed in a high-temperature furnace and heat-treated at 1100℃ for 12 hours to remove impurities from the composite material and obtain the alumina aerogel composite material.

[0125] The alumina aerogel composite material of Example 4 exhibits good formability and uniformity. After heat treatment at 1300℃ and 1500℃ for 72 hours, it does not delaminate or deform, with thickness shrinkage of 0.7% and 2.4%, respectively, demonstrating good long-term high-temperature resistance. The composite material also exhibits good compressive strength, with a compressive strength (3% deformation) of 0.28 MPa.

[0126] Comparative Example 1

[0127] The preparation method of this comparative example is the same as that of Example 1, except that the ceramic fiber needle punching was not used in step S1. After heat treatment at 1300℃ and 1500℃ for 72 h, the alumina aerogel composite material showed a thickness shrinkage of 0.9% and 2.8%, respectively, a flexural strength of 0.92 MPa, and a compressive strength (3% deformation) of 0.18 MPa. This indicates that the needle punching method can improve the temperature resistance and mechanical properties of the composite material.

[0128] Comparative Example 2

[0129] The preparation method of this comparative example is the same as that of Example 1, except that the light-blocking agent is introduced in step S2 using a conventional method. The thermal conductivity of the alumina aerogel composite material at 1400℃ is 0.084 W / (m·K). Conventional methods are difficult to uniformly introduce the light-blocking agent into the alumina aerogel composite material, making it difficult to effectively utilize the light-blocking agent to block infrared radiation. At the same time, it may increase solid-state heat conduction, resulting in a higher overall thermal conductivity.

[0130] Comparative Example 3

[0131] The preparation method of this comparative example is the same as that of Example 1, except that step S3 uses a conventional method to prepare alumina sol. After heat treatment at 1300℃ and 1500℃ for 72 hours, the thickness shrinkage of the alumina aerogel composite material was 3.4% and 7.9%, respectively. The alumina aerogel obtained by the conventional method is amorphous and is prone to sintering and phase transformation at high temperatures, thus reducing the temperature resistance of the composite material.

[0132] Comparative Example 4

[0133] The preparation method of this comparative example is the same as that of Example 1, except that the alumina aerogel in step S3 was not modified. After heat treatment at 1300℃ and 1500℃ for 72 hours, the thickness shrinkage of the alumina aerogel composite material was 0.6% and 3.5%, respectively. The unmodified alumina aerogel still undergoes a certain degree of sintering at 1500℃, thus the shrinkage of the composite material is relatively increased.

[0134] Comparative Example 5

[0135] The preparation method of this comparative example is the same as that of Example 1, except that the heat treatment in step S6 was not extended after supercritical drying. After heat treatment at 1300℃ and 1500℃ for 72 hours, the thickness shrinkage of the alumina aerogel composite material was 0.5% and 2.7%, respectively. Extending the heat treatment and pressure treatment time further increased the particle size of the alumina aerogel and the strength of the skeleton, thereby improving its heat resistance at higher temperatures to a certain extent.

[0136] Comparative Example 6

[0137] The preparation method of this comparative example is the same as that of Example 1, except that step S7 was not performed. After heat treatment at 1300℃ and 1500℃ for 72 h, the thickness shrinkage of the alumina aerogel composite material was 0.4% and 1.8%, respectively, and the thermal conductivity at 1400℃ was 0.072 W / (m·K). After heat treatment, unstable components were removed from the composite material, the thermal stability of the composite material was improved, and the thermal conductivity was reduced.

[0138] Comparative Example 7

[0139] The preparation method of this comparative example is the same as that of Example 1, except that in step S1, the density of the compressed ceramic fiber preform is less than 0.18 g / cm³. 3 After heat treatment at 1300℃ and 1500℃ for 72 hours, the thickness shrinkage of the alumina aerogel composite material was 0.8% and 3.7%, respectively. When the fiber density is low, its strength as a skeleton decreases, and the composite material's ability to resist sintering at high temperatures is relatively weak.

[0140] Comparative Example 8

[0141] The preparation method of this comparative example is the same as that of Example 1, except that in step S1, the density of the compressed ceramic fiber preform is higher than 0.40 g / cm³. 3 After heat treatment at 1300℃ and 1500℃ for 72 hours, the thickness shrinkage of the alumina aerogel composite material was 0.0% and 0.3%, respectively, and the thermal conductivity at 1400℃ was 0.078 W / (m·K). When the fiber density is high, its strength as a skeleton is very high, the composite material has relatively strong resistance to sintering at high temperatures, and lower thickness shrinkage; the solid-state thermal conductivity is high, resulting in high-temperature thermal conductivity.

[0142] Comparative Example 9

[0143] The preparation method of this comparative example is the same as that of Example 1, except that in step S1, the mass fraction of ceramic fiber threads in the ceramic fiber preform is greater than 20%. The thermal conductivity of the alumina aerogel composite material at 1400℃ is 0.077 W / (m·K). When the mass fraction of ceramic fiber threads is high, the solid-state thermal conductivity in the thickness direction is high, resulting in a higher high-temperature thermal conductivity.

[0144] Comparative Example 10

[0145] The preparation method of this comparative example is the same as that of Example 1, except that in step S2, the mass fraction ratio of the opaque agent to deionized water is less than 0.5%. The thermal conductivity of the alumina aerogel composite material at 1400℃ is 0.080 W / (m·K). When the opaque agent content in the composite material is low, the blocking effect on infrared radiation is poor, resulting in a high thermal conductivity at high temperatures.

[0146] Comparative Example 11

[0147] The preparation method of this comparative example is the same as that of Example 1, except that in step S2, the mass fraction ratio of the opaque agent to deionized water is greater than 4%. The thermal conductivity of the alumina aerogel composite material at 1400℃ is 0.082 W / (m·K). When the opaque agent content in the composite material is high, the solid thermal conductivity of the opaque agent itself increases significantly, resulting in a higher high-temperature thermal conductivity.

[0148] Comparative Example 12

[0149] The preparation method of this comparative example is the same as that of Example 1, except that in step S2, the mass fraction ratio of surfactant to deionized water is less than 0.2%. The thermal conductivity of the alumina aerogel composite material at 1400℃ is 0.075 W / (m·K). When the surfactant content is too low, the light-blocking agent is difficult to suspend uniformly in the dispersion and is difficult to wet well with the fiber preform, thus making it difficult to disperse uniformly in the composite material, resulting in poor light-blocking effect and high thermal conductivity.

[0150] Comparative Example 13

[0151] The preparation method of this comparative example is the same as that of Example 1, except that in step S2, the mass fraction ratio of surfactant to deionized water is greater than 3%. The thermal conductivity of the alumina aerogel composite material at 1400℃ is 0.069 W / (m·K). When the surfactant content is too high, the effect of increasing the dispersibility of the opacifier and the wettability of the dispersion is not obvious, and the raw material cost increases.

[0152] Comparative Example 14

[0153] The preparation method of this comparative example is the same as that of Example 1, except that in step S2, the average particle size of the opaque agent particles is less than 0.2 μm. The thermal conductivity of the alumina aerogel composite material at 1400℃ is 0.079 W / (m·K). When the average particle size of the opaque agent is smaller, the blocking effect on infrared radiation is weakened, and the high-temperature thermal conductivity increases.

[0154] Comparative Example 15

[0155] The preparation method of this comparative example is the same as that of Example 1, except that in step S2, the average particle size of the opaque agent particles is greater than 5 μm. The thermal conductivity of the alumina aerogel composite material at 1400℃ is 0.086 W / (m·K). When the average particle size of the opaque agent is larger, the blocking effect on infrared radiation is weakened, and the solid-state thermal conductivity of the large-particle opaque agent is higher, resulting in a more significant increase in thermal conductivity at high temperatures.

[0156] Comparative Example 16

[0157] The preparation method of this comparative example is the same as that of Example 1, except that in step S3, the molar ratio of the modified precursor to the aluminum source precursor is less than 0.05:1. After heat treatment at 1300℃ and 1500℃ for 72 h, the thickness shrinkage of the alumina aerogel composite material is 0.4% and 3.1%, respectively. When the content of the modified component in the aerogel is low, its effect on inhibiting alumina aerogel is limited, and the thickness shrinkage of the composite material increases.

[0158] Comparative Example 17

[0159] The preparation method of this comparative example is the same as that of Example 1, except that in step S3, the molar ratio of the modified component precursor to the aluminum source precursor is greater than 0.4:1. After heat treatment at 1300℃ and 1500℃ for 72 h, the thickness shrinkage of the alumina aerogel composite material is 1.4% and 3.8%, respectively. When the content of the modified component in the aerogel is too high, it is prone to agglomeration and sintering at high temperatures, which in turn increases the thickness shrinkage of the composite material.

[0160] The properties of the alumina aerogel composite materials prepared in Examples 1-4 and Comparative Examples 1-17 were tested and are shown in Table 1.

[0161] Table 1. Properties of the alumina aerogel composite materials prepared in Examples 1-4 and Comparative Examples 1-17

[0162]

[0163] 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.

[0164] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. 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 all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

[0165] The contents not described in detail in this specification are existing technologies known to those skilled in the art.

Claims

1. A method for preparing an alumina aerogel composite material, characterized in that, Includes the following steps: S1. Preparation and molding of ceramic fiber preforms: Ceramic fiber cotton is laid flat to form a ceramic fiber cotton layer. Ceramic fiber threads are needle-punched in the thickness direction of the ceramic fiber cotton layer to form a whole. Then, it is compressed and molded to obtain ceramic fiber preforms. S2, Pre-dispersion of opaque agent: Add opaque agent particles to deionized water containing surfactant, stir evenly to form opaque agent dispersion, and pre-dispersion the opaque agent dispersion into the ceramic fiber preform obtained in step S1 by impregnation under normal pressure. S3, Preparation of modified alumina sol, including: S3.1 Preparation of alumina sol: Add the aluminum source precursor to deionized water at 50℃~95℃ and react for 1h. The molar ratio of deionized water to aluminum source precursor is (20~100):

1. After natural cooling, the precursor hydrolysate is obtained. Add acid at a molar ratio of acid to aluminum source precursor of (0.005~0.3):1 and stir evenly. Heat the resulting mixture in an autoclave to 180℃~240℃ and hold for 0.5h~24h. After natural cooling, alumina sol is obtained. The aluminum source precursor includes any one of aluminum isopropoxide, aluminum n-propoxide, aluminum sec-butoxide, aluminum n-butoxide, or aluminum tert-butoxide; S3.2 Alumina sol modification: The modification component precursor is added to an alcohol solvent containing acid and deionized water, and the reaction is carried out for 0.5h~4h to obtain the modified solution; Add the modified liquid to the alumina sol from step S3.1, stir evenly, then add the coagulant and stir thoroughly to dissolve, thus obtaining the modified alumina sol. The modified component precursor includes any one or a combination of several of the following: tetraethyl orthosilicate, methyltriethoxysilane, ethyltriethoxysilane, dimethyldiethoxysilane, diethyldiethoxysilane, trimethylethoxysilane, triethylethoxysilane, methyltrimethoxysilane, ethyltrimethoxysilane, dimethyldimethoxysilane, and diethyldimethoxysilane; the coagulant includes any one of urea or hexamethylenetetramine; the molar ratio of the modified component precursor to the aluminum source precursor is (0.05~0.4):1, the molar ratio of the coagulant to the aluminum source precursor is (0.05~0.3):1; the molar ratio of acid, deionized water, alcohol solvent to the modified component precursor is (0.001~0.1):(2~6):(1~4):1; S4. Sol impregnation and gel pre-aging: The alumina sol obtained in step S3 is impregnated into the ceramic fiber preform after step S2. After impregnation, gel pre-aging is performed to obtain fiber / gel composite material. S5, Solvent replacement: The fiber / gel composite material obtained in step S4 is immersed in an alcohol solvent at 10℃~70℃, and the alcohol solvent is replaced every 12 hours, with the number of replacements being 2 to 5 times. S6. High-temperature and high-pressure aging and supercritical drying: The fiber / gel composite material treated in step S5 is placed in a supercritical drying kettle and subjected to high-temperature and high-pressure aging and supercritical drying to obtain an alumina aerogel composite material blank. S7. Heat treatment to remove impurities: The alumina aerogel composite material blank obtained in step S6 is subjected to heat treatment to remove impurities, and the alumina aerogel composite material is obtained.

2. The method for preparing alumina aerogel composite material as described in claim 1, characterized in that, The mass fraction ratio of the light-blocking agent to deionized water is 0.5% to 4%, the particle size of the light-blocking agent is 0.2 μm to 5 μm, and the light-blocking agent includes any one of zirconium oxide, silicon carbide, titanium oxide, boron carbide, or boron nitride.

3. The method for preparing alumina aerogel composite material as described in claim 1, characterized in that, The surfactant has a mass fraction ratio of 0.2% to 3% with deionized water, and the surfactant includes any one of sodium oleate, sodium alkyl succinic anhydride, sodium cocoate, sodium dodecylbenzene sulfonate, sodium dodecyl sulfate, sodium secondary alkyl sulfonate, dodecyl trimethyl ammonium chloride, dodecyl dimethyl benzyl ammonium chloride, bis(dodecyl dimethyl) ammonium chloride, dodecyl glucoside, fatty alcohol polyoxyethylene ether glucoside, dodecyl betaine, dodecyl dimethyl ammonium chloride, dodecyl dimethylamine oxide, fatty alcohol polyoxyethylene ether, and dodecylphenol polyoxyethylene ether.

4. The method for preparing alumina aerogel composite material as described in claim 1, characterized in that, In step S1: The chemical composition of ceramic fiber yarn and / or ceramic fiber cotton includes any one of zirconium oxide, alumina or mullite; The ceramic fiber layup is compressed along its thickness direction until the density of the ceramic fiber preform is 0.18 g / cm³. 3 ~0.40g / cm 3 ; The ceramic fiber cotton can be in any form, including loose fiber cotton, fiber felt or fiber blanket in its natural state or separated in the thickness direction, with a slag ball mass fraction of 0~5% and a thickness of 0.5mm~3mm. The mass fraction of ceramic fiber yarn in ceramic fiber preforms is 4% to 22%.

5. The method for preparing alumina aerogel composite material as described in claim 1, characterized in that, In step S4: Modified alumina sol was immersed in ceramic fiber preforms at -0.1 MPa to atmospheric pressure and kept for 0.5 h to 4 h. The gel pre-aging temperature is 40℃~95℃, and the time is 10~48h.

6. The method for preparing alumina aerogel composite material as described in claim 1, characterized in that, In step S6: Add alcoholic substances of 5% to 50% of the volume of the supercritical drying vessel, pre-charge with nitrogen gas at 0.1 MPa to 3 MPa, heat to the temperature inside the vessel at 260℃ to 295℃ and the pressure inside the vessel at 12 MPa to 20 MPa, maintain the temperature and pressure for 8 to 24 hours, slowly release the fluid inside the vessel until the pressure inside the vessel is at atmospheric pressure, and finally purge with nitrogen gas for 10 to 60 minutes to obtain an alumina aerogel composite material blank.

7. The method for preparing alumina aerogel composite material as described in claim 1, characterized in that, In step S7: the alumina aerogel composite material blank is placed in a high-temperature furnace and heat-treated at 500℃~1100℃ for 6h~24h to remove impurities.

8. An alumina aerogel composite material, characterized in that, The alumina aerogel composite material is obtained by the preparation method according to any one of claims 1 to 7.

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