Wave-transparent high-strength ablation-resistant element hybrid branched polysiloxane nano aerogel composite material and preparation method thereof

Abstract

The invention discloses a wave-transparent high-strength ablation-resistant element hybrid branched nano aerogel composite material and a preparation method thereof, the material takes boron / zirconium hybrid branched polysiloxane as a matrix, a sol-gel method is combined with a resin transfer molding process, and an inorganic fiber reinforced part and a nanoscale functional filler are subjected to multi-scale compounding. By regulating and controlling various reaction factors, complete molding of the material under a normal-pressure drying process is realized, a nanoscale porous network structure is successfully constructed, and large-scale production can be realized. The composite material has the following characteristics: the wave transmission performance is excellent, and the dielectric constant in the frequency band of 8-20GHz is less than or equal to 3.0; the extreme ablation resistance is high, and the structural integrity is still kept after the material is ablated by oxyacetylene flame at 1650 DEG C for 30 minutes; the comprehensive performance is outstanding, the density is low, the specific strength is high, and the heat insulation property is excellent.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of hybrid polysiloxane aerogels, in particular to a wave-transparent high-strength ablation-resistant element hybrid branched polysiloxane nanometer aerogel composite material and a preparation method thereof. BACKGROUND

[0002] With the development of aerospace vehicles and hypersonic weapons towards extreme speed and long endurance, the thermal protection system is facing the limit challenge of synergistic performance of high temperature resistance (1400-1600℃), wave transmission and lightweight (density <0.5g / cm 3 In the current technical system, alumina-based ceramics (temperature resistance 1500-1600℃) have a dielectric loss tangent (tanδ) of 0.015 at 1200℃, which is increased from 0.001 at room temperature, resulting in a wave transmission efficiency of less than 50%; nickel-based high-temperature alloy relies on an active cooling system (density 8.0-8.9g / cm 3 ), which is difficult to meet the lightweight demand. Existing solutions such as ablation layer + wave-transparent window stacking design (such as the Orion spacecraft TPS system) result in a thermal protection structure accounting for 18%-22% of the launch mass, and the multi-material interface is prone to delamination failure under thermal stress. In summary, the existing materials can only compromise and balance in the ablation-resistant-wave-transparent-lightweight triangle index, and it is urgent to break through the bottleneck of multi-physical field synergistic design to support the research and development of new generation aerospace equipment.

[0003] Aerogel, as a kind of nano-porous solid material, has shown revolutionary potential in the aerospace field with its ultra-low density (0.01-0.4g / cm 3 ), ultra-high porosity (>95%), good wave transmission performance and cross-scale designability: its three-dimensional continuous network skeleton (such as SiO2, SiC-based) realizes ultra-low thermal conductivity through limited gas film effect. Its high porosity brings low dielectric constant, which brings excellent wave transmission performance. However, traditional aerogels still face serious bottlenecks, such as poor mechanical properties, insufficient high-temperature stability, and high difficulty in industrialization.

[0004] In order to improve the mechanical properties of aerogels, in recent years, researchers have introduced reinforcing fibers to construct aerogel-fiber composites. This composite effectively improves the brittleness and mechanical strength of aerogel, making it more durable and adaptable in application. The current mature preparation method of aerogel-fiber is mainly the sol-gel method. In the aging and drying stage of the preparation process, solvent exchange, supercritical drying method and other complex processes are often used to ensure the smooth discharge of the solvent and the integrity of the structure. These methods are not suitable for large-scale production. Direct atmospheric drying often leads to excessive capillary force, and traditional SiCO aerogel skeletons have high brittleness, which will collapse during atmospheric drying, causing structural damage and other problems.

[0005] In addition to improving the mechanical properties of aerogels, high-temperature resistance is also a key factor for high-end applications. Traditional SiOC aerogels based on polysiloxane as the base material will decompose at about 350°C, and will be converted to inorganic silicon-oxygen-carbon aerogels at 600°C. Traditional carbon-oxygen-silicon ceramics face problems such as low yield and large size shrinkage. At the same time, most SiOC aerogels have poor high-temperature resistance and will lose functionality at about 1000°C in an air atmosphere. To further improve the high-temperature resistance of aerogels, researchers will place the prepared aerogels or aerogel composites into a tube furnace or an atmosphere furnace after the sol-gel drying is completed, and will heat them under inert gas protection to convert them into inorganic ceramic materials to withstand high temperatures above 1000°C. However, most tube furnaces and atmosphere furnaces have very small internal spaces and are expensive, and the overall time during the ceramic conversion process is 12-48h, which cannot meet the needs of large-scale production. At the same time, after high-temperature treatment, SiOC aerogels will start to undergo eutectic reaction and form cristobalite structure when the temperature rises to 1300°C in an oxygen-containing environment. When the temperature further rises to 1400°C, cristobalite starts to melt, resulting in structural damage and loss of thermal protection performance.

[0006] Domestic patent CN102910926B discloses a silicon carbide aerogel thermal insulation composite material, which uses organosiloxane as the silicon source and fiber cotton as the reinforcing material, and is prepared by a sol-gel method, normal pressure drying, and high-temperature pyrolysis process in an inert gas atmosphere. The obtained material can withstand high temperatures of 1400°C. However, the preparation process requires pyrolysis in a tube furnace filled with inert gas, which has high requirements for equipment and cannot be prepared on a large scale.

[0007] Domestic patent CN102276236B discloses a SiCO aerogel thermal insulation composite material, which uses organosiloxane as the raw material and fiber felt as the reinforcing material, and is prepared by a sol-gel method, aging, supercritical drying, and high-temperature pyrolysis process. The obtained material can be used at temperatures up to 1200°C, with a minimum thermal conductivity of 0.051 W / m·K at 1200°C and a bending strength of up to 2.6 MPa. However, the use of supercritical drying and pyrolysis in an inert gas atmosphere requires high equipment and process requirements, and cannot be prepared on a large scale.

[0008] The domestic patent CN104261798B introduces a kind of high-temperature-resistant SiCOB aerogel heat-insulating composite material and its preparation method. By using silicon source, carbon source is hydrolyzed to generate SiCOB precursor sol under the action of acidic catalyst, then impregnated, aged, supercritical drying, and pyrolysis under inert gas atmosphere. The patent technology successfully introduces B element into traditional SiCO aerogel, and the use temperature is increased to 1500 DEG C. However, the supercritical drying method and pyrolysis under inert gas atmosphere require high equipment and process, and cannot be prepared on a large scale.

[0009] The domestic patent application CN116239817A discloses a high-strength ablation-resistant nanoporous organic silicon aerogel composite material and its preparation method and application. By using RTM forming process, the fiber preform is used as the reinforcing body, and the organic silicon aerogel is used as the matrix to obtain the composite material, which avoids the traditional complicated preparation process, but the reported test temperature is 800 DEG C.

[0010] The domestic patent application CN117843335A discloses an alumina aerogel composite material and its preparation method. By using organic aluminum source precursor, alumina-silica sol is prepared, and ceramic fiber is used as reinforcing material. It can withstand 1600 DEG C heat treatment, and has excellent mechanical and wave-transparent properties. The wave-transparent rate of the composite material plate is greater than or equal to 85% at 8~32 GHz. However, the preparation process involves supercritical drying, high-temperature and high-pressure aging, heat treatment and other processes, which is complex and requires high equipment, and cannot be prepared on a large scale. The domestic patents CN109607551B and CN112592149B also have such problems. SUMMARY

[0011] The present application provides a wave-transparent high-strength ablation-resistant element hybrid branched polysiloxane nanometer aerogel composite material and its preparation method. The composite material has the characteristics of ultra-high temperature resistance (structure does not collapse after 1650 DEG C flame ablation for 30 minutes), light weight, excellent heat insulation, wave-transparent performance and mechanical properties. In the preparation process, RTM process and sol-gel method can be combined, and the structure integrity can be ensured during normal pressure drying process, and the demand of large-scale preparation can also be met.

[0012] The specific technical solutions are as follows: In the first aspect, the present application provides a preparation method of a wave-transparent high-strength ablation-resistant element hybrid branched polysiloxane nanometer aerogel composite material, comprising the following steps: (1) mixing element hybrid branched polysiloxane, solvent, amine curing agent and surface amino group grafted nano filler according to the mass ratio of 1:(1~8):(0.01~0.5):(0.01~0.5) to prepare silicon sol; The hybrid element in the element hybrid branched polysiloxane includes one or both of boron and zirconium; the element hybrid branched polysiloxane contains one or both of siloxane-boron bond (Si-O-B) and siloxane-zirconium bond (Si-O-Zr); the main chain of the element hybrid branched polysiloxane contains a plurality of ring structures connected by siloxane bonds; and the element hybrid branched polysiloxane is terminated by an epoxy functional group; The solvent includes two or more of toluene, xylene, ethanol, isopropanol, n-hexane and petroleum ether, and must include at least one of ethanol, isopropanol, n-hexane and petroleum ether; (2) The silica sol is infiltrated into the fiber preform, and then gel aging, normal pressure drying are performed to obtain the wave-transparent high-strength ablation-resistant element hybrid branched polysiloxane nanometer aerogel composite material.

[0013] Preferably, the branching degree of the element hybrid branched polysiloxane is 0.4-0.75.

[0014] Preferably, the molar ratio of the hybrid element to the silicon element in the element hybrid branched polysiloxane is 0.1-0.4:1.

[0015] Preferably, the plurality of ring structures include one or both of eight-membered ring structures and ten-membered ring structures.

[0016] Preferably, the proportion of the epoxy functional group in the element hybrid branched polysiloxane is 0.15-0.3 mmol / g.

[0017] Preferably, the viscosity of the element hybrid branched polysiloxane at 25°C is 800-25000 cp, and further 1000-10000 cp.

[0018] Preferably, the preparation method of the element hybrid branched polysiloxane includes the following steps: S1, the vinyl siloxane, the organosilicon poly-membered ring body and the platinum catalyst are mixed to react to obtain a polysiloxane precursor; S2, the polysiloxane precursor, the hybrid element precursor, the epoxy functional group silane coupling agent, the optional acidic catalyst and the optional water are mixed to react to obtain the element hybrid branched polysiloxane.

[0019] Preferably, in step S1, the vinyl siloxane includes one or more of methyl vinyl dimethoxysilane, vinyl trimethoxysilane and vinyl methyl diethoxysilane.

[0020] Preferably, in step S1, the organosilicon poly-membered ring body includes one or both of 1,3,5,7 tetramethylcyclotetrasiloxane and 1,3,5,7,9-pentamethylcyclopentasiloxane.

[0021] Preferably, in step S1, the molar ratio of the vinyl siloxane and the organosilicon polybasic ring body is 1:0.1-5.

[0022] Preferably, in step S1, the amount of the platinum catalyst, in terms of platinum, is 1-100 ppm, based on the total mass of the vinyl siloxane and the organosilicon polybasic ring body. Preferably, in step S1, the platinum catalyst comprises a Karstedt platinum catalyst.

[0023] Preferably, in step S1, the temperature of the mixing reaction is 40-90°C.

[0024] Preferably, in step S2, the hybrid element precursor comprises one or more of boric acid, trimethyl borate, triethyl borate, diethyl methyl boron, n-butyl borate, tetrabutyl zirconate, n-butyl zirconium, tetraethoxy zirconium, acetylacetone zirconium, and zirconium oxychloride.

[0025] Preferably, in step S2, the epoxy functional silane coupling agent comprises one or more of KH560, KH561, and KH562.

[0026] Preferably, in step S2, the acid catalyst comprises one or more of boric acid, sulfuric acid, hydrochloric acid, nitric acid, and acetic acid.

[0027] In the present application, when boric acid is used as the hybrid element precursor, it can function as an acid catalyst, and in this case, the acid catalyst can be omitted.

[0028] In the present application, the silicon-oxygen-boron bond can be formed by the hybrid element precursor or the acid catalyst boric acid.

[0029] Preferably, in step S2, the temperature of the mixing reaction is room temperature-45°C.

[0030] Preferably, in step S2, the molar ratio of the polysiloxane precursor and the hybrid element precursor is 1:0.01-10.

[0031] Preferably, in step S2, the molar ratio of the polysiloxane precursor and the epoxy functional silane coupling agent is 1:0.01-10.

[0032] Preferably, in step S2, the molar ratio of the polysiloxane precursor and the acid catalyst is 1:0-0.01.

[0033] Preferably, in step S2, the molar ratio of the polysiloxane precursor and the water is 1:0-10. When the hybrid element comprises zirconium, the water can be omitted.

[0034] Preferably, the surface active agent includes one or more of potassium perfluorohexylethyl sulfonate, polyoxyethylene perfluoroalkyl ether, and trifluoropropylmethylsiloxane.

[0035] Preferably, the mass percentage of the surface active agent in the solvent is 0.001% to 0.1%.

[0036] Preferably, the mass percentage of at least one of ethanol, isopropanol, n-hexane, and petroleum ether in the solvent is 30% to 80%.

[0037] Preferably, the amine curing agent includes one or more of ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, isophorone diamine, N,N-dimethyl-p-toluidine, and triethanolamine.

[0038] Preferably, the nanofiller includes one or more of nanotubular filler and nanofiber filler.

[0039] Preferably, the nanofiller includes one or more of zirconium oxide fiber, aluminum oxide fiber, silicon carbide fiber, and halloysite nanotube.

[0040] Preferably, one or more of the zirconium oxide fiber, aluminum oxide fiber, silicon carbide fiber, and halloysite nanotube has a length of 80 to 1500 nm and an aspect ratio of 3 to 30.

[0041] Preferably, the nanofiller is modified by one or more of silane coupling agents KH540, KH550, KH602, and KH792 to achieve surface amino grafting.

[0042] Preferably, the mass ratio of the nanofiller to one or more of the silane coupling agents KH540, KH550, KH602, and KH792 is 1:0.01 to 1.

[0043] Preferably, the fiber in the fiber preform includes one or more of quartz fiber, zirconium oxide fiber, mullite fiber, and aluminum oxide fiber.

[0044] Preferably, the fiber preform is modified by at least one of silane coupling agents KH540, KH550, KH602, and KH792 to achieve surface amino grafting.

[0045] Preferably, the mass ratio of the fiber preform to at least one of the silane coupling agents KH540, KH550, KH602, and KH792 is 1:0.01 to 1.

[0046] Preferably, the density of the fiber preform is less than 0.3 g·cm -3 .

[0047] Preferably, in step (2), the silica sol is infiltrated into the fiber preform by using the RTM process. Further, the specific process of the RTM process comprises: placing the fiber preform into a mold; closing the mold and sealing; applying positive pressure or negative pressure to the inside of the mold to reduce voids and bubbles and promote the flow of the silica sol; and injecting the silica sol into the mold through an injection system so that the silica sol completely infiltrates the fiber preform.

[0048] Preferably, in step (2), the fiber preform comprises a fiber felt.

[0049] Preferably, in step (2), the mass ratio of the fiber preform to the silica sol is 1:2-7.

[0050] Preferably, in step (2), the temperature for the gel aging is 40-140℃, and the time is 6-24h.

[0051] Preferably, in step (2), the temperature for the atmospheric drying is 80-200℃, and the time is 6-24h.

[0052] In a second aspect, the present application provides a wave-transparent high-strength ablation-resistant element hybrid branched polysiloxane nanometer aerogel composite material prepared by the preparation method of the first aspect. The composite material can be applied to the field of thermal protection and thermal insulation, and the use temperature can be up to 1650℃ or above.

[0053] The wave-transparent high-strength ablation-resistant element hybrid branched polysiloxane nanometer aerogel composite material of the present application takes boron / zirconium hybrid branched polysiloxane as the matrix, is combined by the sol-gel method and the resin transfer molding (RTM) process, and is multi-scale compounded by using inorganic fiber reinforced preforms and nanoscale functional fillers. By adjusting various reaction factors, the material is completely formed under the atmospheric drying process, a nanoscale porous network structure is successfully constructed, and large-scale production can be realized. The composite material has the following characteristics: excellent wave-transparent performance, dielectric constant ≤3.0 in the 8-20GHz frequency band; strong extreme ablation resistance, still maintaining structural integrity after 1650℃ oxygen acetylene flame ablation for 30 minutes; outstanding comprehensive performance, low density, high specific strength, and excellent heat insulation. The composite material of the present application can be applied to the fields of aerospace, national defense and military industry, and can simultaneously meet multiple engineering requirements such as structural bearing, electromagnetic wave transmission, thermal protection and light weight under extreme thermal coupling environment.

[0054] Compared with the prior art, the present application has the following beneficial effects: 1) The application of a wave-transparent high-strength ablation-resistant element hybrid branched polysiloxane aerogel composite material innovatively uses ablation-resistant element boron / zirconium hybrid hyperbranched polysiloxane as a substrate for the preparation of aerogel composite material. By introducing organosilicon rings into the polysiloxane main chain, the crosslinking density of the system can be significantly improved. This structural change enhances the material performance through three synergistic effects: first, the highly crosslinked network structure effectively inhibits the high-temperature slippage or rupture of molecular chains, greatly improving the thermal decomposition temperature; second, the tight crosslinked network hinders the high-temperature volatilization of small molecules, significantly reducing the mass loss rate; third, the high crosslinking density strengthens the material skeleton strength, effectively resisting the capillary shrinkage stress during drying. At the same time, the organosilicon ring itself is rich in high-energy Si-O-Si structural units, which provides additional strengthening for the resin's high-temperature resistance, ultimately synergistically improving the material's thermal decomposition resistance and structural stability. By introducing epoxy groups, the crosslinking sites of the system are increased, and the skeleton strength is enhanced. By introducing ablation-resistant elements boron and zirconium, new chemical bonds can be formed in polysiloxane, avoiding eutectic reaction to form cristobalite near 1400°C, further improving its ablation resistance and residual weight after ablation to improve its dimensional stability. At the same time, due to its nano-porous structure, the polysiloxane has good wave-transparent performance (8-20GHz, dielectric constant ≤3.0). The aerogel composite material prepared by this method can be converted to ceramic in an oxygen-containing environment, and the structure remains intact without collapse after ablation for 30min at a high temperature of 1650°C.

[0055] 2) In the method for preparing a wave-transparent high-strength ablation-resistant element hybrid branched polysiloxane aerogel composite material, the mixture of solvents and the control of solid content ensure the sufficient dissolution of polysiloxane and curing agent, and the uniform dispersion of fillers, effectively avoiding defects caused by excessive crosslinking density or filler agglomeration, as well as the poor solubility of single solvent leading to large pore size or large surface tension, strong capillary force leading to structural damage. The mixed solvent with surfactant has good solubility for each component, which makes the prepared aerogel composite material have high porosity, small pore size (pore size 50nm~5µm), low surface tension, and reduces the capillary force generated during drying, making the overall structure complete.

[0056] 3) In the method for preparing a wave-transparent high-strength ablation-resistant element hybrid branched polysiloxane aerogel composite material, the nanofiller is modified by using silane coupling agent KH540, KH550, etc., the amino group contained on the surface of the modified filler cooperates to initiate the curing of the polysiloxane, and enhances the interfacial action between the filler and the polysiloxane. The modified filler can provide certain support to the element hybrid branched polysiloxane aerogel composite material, so that the structure remains stable during the normal pressure drying process, and the high-temperature resistance of the filler itself also cooperatively improves the high-temperature resistance of the element hybrid branched polysiloxane aerogel composite material as a whole.

[0057] 5) In the method for preparing a wave-transparent high-strength ablation-resistant element hybrid branched polysiloxane aerogel composite material, the fiber preform such as fiber felt is introduced by the RTM process for reinforcement, and the mechanical properties of the aerogel (tensile strength 4~19MPa, compressive strength 35~90MPa) are improved.

[0058] 6) The wave-transparent high-strength ablation-resistant element hybrid branched polysiloxane nanometer aerogel composite material prepared by the present application can be applied in extreme thermal environment conditions in the fields of aviation, aerospace, military industry, etc. The overall preparation method of the material is simple, avoiding the traditional complex preparation process (supercritical drying, solvent displacement, etc.), and is suitable for large-scale industrial production. BRIEF DESCRIPTION OF DRAWINGS

[0059] Figure 1 The actual photos of the wave-transparent high-strength ablation-resistant element hybrid branched polysiloxane aerogel composite material prepared in Example 1 before and after ablation at 1650℃.

[0060] Figure 2 The scanning electron microscope (SEM) photos of the wave-transparent high-strength ablation-resistant element hybrid branched polysiloxane aerogel composite material prepared in Example 1. DETAILED DESCRIPTION

[0061] The present application will be further described below in conjunction with the drawings and specific examples. It should be understood that these examples are only used to illustrate the present application and are not used to limit the scope of the present application. The operation methods not specified in the following examples are usually carried out according to the conventional conditions, or according to the conditions recommended by the manufacturers.

[0062] The preparation method of the surface amino grafted nanofiller used in the following examples includes: the nanofiller with a length of 80-1500 nm and an aspect ratio of 3-30 is added to an ethanol aqueous solution with pH=5, 40 kHz ultrasonic treatment is performed for 30 min, then KH550 is added, 50℃ water bath is performed for 2 h, hydrolysis reaction is performed, after the hydrolysis is completed, centrifugal separation is performed to pour out the upper liquid, it is placed in an oven for drying at 70℃ for 6 h, after complete drying, the surface amino grafted nanofiller is obtained; the mass ratio of the nanofiller, ethanol, water and KH550 is 1:32:3:0.1.

[0063] The fiber preform used in the following examples is pre-modified, specifically including: the fiber preform with a density lower than 0.3 g·cm -3 is completely immersed in an ethanol aqueous solution with pH=5, 25℃ ultrasonic (40 kHz) treatment is performed for 30 min, then KH550 is added, 50℃ water bath is performed for 2 h, hydrolysis reaction is performed, after the hydrolysis is completed, it is placed in an oven for drying at 70℃ for 12 h, after complete drying, the pretreated modified fiber preform is obtained; the mass ratio of the fiber preform, ethanol, water and KH550 is 1:32:3:0.1.

[0064] In the following examples, the preparation method of the polysiloxane precursor includes: mixing vinyltrimethoxysilane and 1,3,5,7-tetramethylcyclotetrasiloxane at a molar ratio of 1:0.8, then adding 20 ppm (calculated based on platinum and based on the total mass of vinyltrimethoxysilane and 1,3,5,7-tetramethylcyclotetrasiloxane) of Karstedt platinum catalyst, stirring and reacting at 75℃ for 1 hour to obtain the polysiloxane precursor.

[0065] In the following examples, the preparation method of the element hybrid branched polysiloxane containing silicon-oxygen-boron (Si-O-B) bonds includes: reacting the polysiloxane precursor, the hybrid element precursor boric acid, water and KH560 at a molar ratio of 1:0.3:0.6:0.1 at 25℃ for 4 h to obtain the element hybrid branched polysiloxane containing silicon-oxygen-boron bonds.

[0066] In the following examples, the preparation method of the element hybrid branched polysiloxane containing silicon-oxygen-zirconium (Si-O-Zr) bonds includes: reacting the polysiloxane precursor, zirconium n-butoxide, hydrochloric acid and KH560 at a molar ratio of 1:3:0.001:0.1 at 25℃ for 4 h to obtain the element hybrid branched polysiloxane containing silicon-oxygen-zirconium bonds.

[0067] In the following examples, the preparation method of the element hybrid branched polysiloxane containing silicon-oxygen-boron bonds and silicon-oxygen-zirconium bonds includes: reacting the polysiloxane precursor, tetrabutyl zirconate, the acidic catalyst boric acid and KH560 at a molar ratio of 1:2:0.001:0.1 at 25℃ for 4 h to obtain the element hybrid branched polysiloxane containing silicon-oxygen-boron bonds and silicon-oxygen-zirconium bonds.

[0068] Example 1: First, the element hybrid branched polysiloxane containing silicon-oxygen-boron bond, ethanol, dimethylbenzene, potassium perfluorohexylethyl sulfonate, and surface amino grafted nanofiller halloysite nanotube were mixed at room temperature for 5 min. Then, ethylenediamine was added and mixed at room temperature for 5 min to prepare a silica sol. The mass ratio of the element hybrid branched polysiloxane containing silicon-oxygen-boron bond, ethanol, dimethylbenzene, potassium perfluorohexylethyl sulfonate, surface amino grafted nanofiller halloysite nanotube, and ethylenediamine was 1:1.2:1.2:0.0002:0.1:0.05.

[0069] The pretreated modified fiber preform quartz fiber felt was placed into a mold, and the silica sol was injected under positive pressure. After the mold was completely filled with the silica sol, the mold was sealed. The mass ratio of the fiber preform and the silica sol was 1:3.

[0070] The mold was placed in an oven at 60°C for gel aging for 18 h.

[0071] The fiber felt composite material after sufficient aging was taken out of the mold and placed in an oven at 120°C for atmospheric pressure drying for 24 h to obtain a high-strength ablation-resistant wave-transparent element hybrid branched polysiloxane nanoaerogel composite material.

[0072] The element hybrid branched polysiloxane containing silicon-oxygen-boron bond used in this example had a branching degree DB of 0.62, a viscosity of 2050 cp at 25°C, and contained silicon-oxygen-boron bonds in the structure.

[0073] The element hybrid branched polysiloxane nanoaerogel composite material prepared had a complete structure, a density of 389 mg / cm 3 , an average pore size of 94 nm, a thermal conductivity of 0.038 W / m·K, a tensile strength of 4.0 MPa, a compressive strength of 43 MPa, a dielectric constant of 1.7, and a structure that was not destroyed after ablation at 1650°C for 30 min.

[0074] Example 2: The difference from Example 1 was that the element hybrid branched polysiloxane containing silicon-oxygen-zirconium bond was used instead of the element hybrid branched polysiloxane containing silicon-oxygen-boron bond, and the rest were the same.

[0075] The element hybrid branched polysiloxane containing silicon-oxygen-zirconium bond used in this example had a branching degree DB of 0.61, a viscosity of 3270 cp at 25°C, and contained silicon-oxygen-zirconium bonds in the structure.

[0076] The element hybrid branched polysiloxane nanoaerogel composite material prepared had a complete structure, a density of 374 mg / cm 3 , an average pore size of 123 nm, a thermal conductivity of 0.042 W / m·K, a tensile strength of 4.5 MPa, a compressive strength of 48 MPa, a dielectric constant of 1.9, and a structure that was not destroyed after ablation at 1650°C for 30 min.

[0077] Example 3: The difference from Example 1 is that the element hybrid branched polysiloxane containing siloxaboron bond and siloxazirconium bond is replaced by the element hybrid branched polysiloxane containing siloxaboron bond, and the rest is the same.

[0078] The element hybrid branched polysiloxane containing siloxaboron bond and siloxazirconium bond used in this example has a branching degree DB of 0.55; a viscosity of 2830 cp at 25℃; and contains siloxaboron bond and siloxazirconium bond in the structure.

[0079] The prepared element hybrid branched polysiloxane nanogel composite material has a complete structure, a density of 433 mg / cm 3 , an average pore size of 83 nm, a thermal conductivity of 0.039 W / m·K, a dielectric constant of 1.9, a tensile strength of 5.3 MPa, a compressive strength of 58 MPa, and a structure not damaged after ablation at 1650℃ for 30 min.

[0080] Example 4: The difference from Example 1 is that the mass ratio of the element hybrid branched polysiloxane containing siloxaboron bond, ethanol, dimethylbenzene, potassium perfluorohexylethyl sulfonate, surface amino grafted nanofiller halloysite nanotube and ethylenediamine is 1:0.75:0.75:0.0002:0.1:0.05, and the rest is the same.

[0081] The prepared element hybrid branched polysiloxane nanogel composite material has a complete structure, a density of 518 mg / cm 3 , an average pore size of 77 nm, a thermal conductivity of 0.049 W / m·K, a tensile strength of 6.6 MPa, a compressive strength of 65 MPa, a dielectric constant of 2.3, and a structure not damaged after ablation at 1650℃ for 30 min.

[0082] Example 5: The difference from Example 1 is that the mass ratio of the element hybrid branched polysiloxane containing siloxaboron bond, ethanol, dimethylbenzene, potassium perfluorohexylethyl sulfonate, surface amino grafted nanofiller halloysite nanotube and ethylenediamine is 1:0.5:0.5:0.0002:0.1:0.05, and the rest is the same.

[0083] The prepared element hybrid branched polysiloxane nanogel composite material has a complete structure, a density of 633 mg / cm 3 , an average pore size of 62 nm, a thermal conductivity of 0.056 W / m·K, a tensile strength of 7.8 MPa, a compressive strength of 74 MPa, a dielectric constant of 2.8, and a structure not damaged after ablation at 1650℃ for 30 min.

[0084] Table 1 summarizes Examples 1-5.

[0085] Table 1 Examples 1-3 differ mainly in that the difference between the selected ablation-resistant element hybrid branched polysiloxanes in the synthesis of the element hybrid branched polysiloxane nanometer aerogel composite material, since the selected polysiloxanes are all hybridized with ablation-resistant elements, their structures remain intact under 1650℃ flame impact for 30 min, without structural collapse and destruction, but their wave-transparent performance is affected by the introduction of polar bonds and interface polarization and changes. At the same time, due to the design and regulation of the element hybrid branched polysiloxane, filler, fiber felt, and solvent, the overall structure of the prepared element hybrid branched polysiloxane nanometer aerogel composite material is good.

[0086] Examples 1, 4, and 5 differ mainly in that the difference between the solid contents (the ratio of element hybrid branched polysiloxane to solvent) in the synthesis of the element hybrid branched polysiloxane nanometer aerogel composite material, with the increase of the solid content, the overall density of the material increases, the pore size decreases, the mechanical properties improve, the dielectric constant increases, and the wave-transparent performance decreases. The solid content can be adjusted within a certain range according to different needs, and the overall structure of the prepared element hybrid branched polysiloxane nanometer aerogel composite material is good.

[0087] Comparative Example 1: The difference between Example 1 and Comparative Example 1 is only that polysiloxane I is used instead of the element hybrid branched polysiloxane containing siloxane-boron bonds, and the rest are the same.

[0088] The polysiloxane I used in this comparative example is prepared by reacting polysiloxane precursor, water, and KH560 at a molar ratio of 1:0.6:0.1 at 25℃ for 4h.

[0089] The polysiloxane I used in this comparative example is not hybridized with ablation-resistant elements, and the branching degree DB is 0.42; the viscosity at 25℃ is 3430cp.

[0090] The prepared polysiloxane nanometer aerogel composite material has a complete structure, a density of 376mg / cm 3 , an average pore size of 114nm, a thermal conductivity of 0.037W / m·K, a dielectric constant of 1.4, a tensile strength of 4.2MPa, and a compressive strength of 47MPa. The overall structure cracks and is destroyed after ablation at 1650℃ for 30 min. This is because the polysiloxane structure used in Comparative Example 1 is not hybridized with ablation-resistant elements, which cannot inhibit the occurrence of eutectic reaction at high temperature, and thus cannot resist the flame impact at 1650℃, resulting in structural damage.

[0091] Comparative Example 2: The difference between Example 1 and Comparative Example 2 is only that polysiloxane II is used instead of the element hybrid branched polysiloxane containing siloxane-boron bonds, and the rest are the same.

[0092] The polysiloxane II used in the present comparative example was prepared by reacting vinyltrimethoxysilane, boron acid as a hybrid element precursor, water, and KH560 at a molar ratio of 1:0.3:0.6:0.1 at 25°C for 4h.

[0093] The polysiloxane II used in the present comparative example contains siloxane-boron bonds, but does not contain a silicone ring structure in the main chain, and has a branching degree DB of 0.29; the viscosity at 25°C is 5100cp.

[0094] During the preparation process, the structure of the polysiloxane nanometer aerogel composite material was damaged and cracked. This is because the polysiloxane structure used in Comparative Example 2 does not contain a silicone ring structure, resulting in low overall crosslinking density and weak strength of the material, which cannot withstand the capillary force during the drying process, thereby causing the material to crack and the structure to be damaged.

[0095] Comparative Example 3: The difference from Example 1 is only that the amount of potassium perfluorohexylethyl sulfonate is 0 and the same amount of dimethylbenzene is used instead of ethanol, and the rest are the same.

[0096] During the preparation process, the structure of the polysiloxane nanometer aerogel composite material was damaged and cracked. This is because the surface energy of dimethylbenzene is high, and the capillary force caused by solvent evaporation during normal pressure drying is greater, resulting in structural damage.

[0097] Comparative Example 5: The difference from Example 1 is only that the mass ratio of the polysiloxane containing siloxane-boron bonds, ethanol, dimethylbenzene, potassium perfluorohexylethyl sulfonate, surface amino-grafted nanofiller halloysite nanotubes, and ethylenediamine is 1:4.5:4.5:0.0002:0.1:0.05, and the rest are the same.

[0098] During the preparation process, the structure of the polysiloxane nanometer aerogel composite material was damaged and the whole collapsed. This is because the solid content (the ratio of the element-hybrid branched polysiloxane to the solvent) is too low, resulting in too little overall polysiloxane content, incomplete structure, and collapse and fragmentation.

[0099] Figure 1 The photos of the actual object before and after ablation of the wave-transparent high-strength ablation-resistant element-hybrid branched polysiloxane aerogel composite material prepared in Example 1 are shown.

[0100] Figure 2 The scanning electron microscope (SEM) photos of the wave-transparent high-strength ablation-resistant element-hybrid branched polysiloxane aerogel composite material prepared in Example 1 are shown.

[0101] Furthermore, it should be understood that after reading the above description of the present invention, those skilled in the art can make various alterations or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims.

Claims

1. A method for preparing a high-strength, ablation-resistant, elementally hybridized branched polysiloxane nano-aerogel composite material, characterized in that, Including the following steps: (1) Element-hybridized branched polysiloxane, solvent, amine curing agent and surface amino-grafted nanofiller are mixed in a mass ratio of 1:(1~8):(0.01~0.5):(0.01~0.5) to prepare silica sol; The hybrid elements in the element-hybridized branched polysiloxane include one or two of boron and zirconium; the element-hybridized branched polysiloxane contains one or two of silicon-oxygen-boron bonds and silicon-oxygen-zirconium bonds; the main chain of the element-hybridized branched polysiloxane contains a multi-ring structure formed by silicon-oxygen bonds; the element-hybridized branched polysiloxane is end-capped with epoxy functional groups. The solvent includes two or more of toluene, xylene, ethanol, isopropanol, n-hexane, and petroleum ether, as well as a surfactant, and must include at least one of ethanol, isopropanol, n-hexane, and petroleum ether. (2) The silica sol is used to impregnate the fiber preform, and then gel aging and drying are carried out at normal pressure to obtain the high-strength, ablation-resistant hybrid branched polysiloxane nano-aerogel composite material.

2. The preparation method of the high-strength, ablation-resistant, elementally hybridized branched polysiloxane nano-aerogel composite material according to claim 1, characterized in that, The degree of branching of the element-hybridized branched polysiloxane is 0.4~0.75; The molar ratio of the hybrid element to silicon in the element-hybridized branched polysiloxane is 0.1~0.4:1; The multi-ring structure includes one or both of the octagonal ring structure and the deca-ring structure; The epoxy functional group content in the element-hybridized branched polysiloxane is 0.15~0.3 mmol / g; The element-hybridized branched polysiloxane has a viscosity of 800~25000cp at 25°C, and more specifically 1000~10000cp. The preparation method of the element-hybridized branched polysiloxane includes the following steps: S1, vinylsiloxane, organosilicon polycyclic ring and platinum catalyst are mixed and reacted to obtain polysiloxane precursor; S2, the polysiloxane precursor, hybrid element precursor, epoxy functional group silane coupling agent, selectively added acidic catalyst and selectively added water are mixed and reacted to obtain the element hybrid branched polysiloxane.

3. The preparation method of the high-strength, ablation-resistant, elementally hybridized branched polysiloxane nano-aerogel composite material according to claim 2, characterized in that, In step S1, the vinylsiloxane includes one or more of methylvinyldimethoxysilane, vinyltrimethoxysilane, and vinylmethyldiethoxysilane; In step S1, the organosilicon polycyclic ring includes one or two of 1,3,5,7-tetramethylcyclotetrasiloxane and 1,3,5,7,9-pentamethylcyclopentasiloxane. In step S1, the molar ratio of the vinylsiloxane to the organosilicon polycyclic ring is 1:0.1~5; In step S1, based on the total mass of the vinylsiloxane and the organosilicon polycyclic ring, the amount of platinum catalyst used, calculated as platinum, is 1~100 ppm. In step S1, the platinum catalyst includes a caster platinum catalyst; In step S1, the temperature of the mixing reaction is 40~90℃.

4. The preparation method of the high-strength, ablation-resistant, elementally hybridized branched polysiloxane nano-aerogel composite material according to claim 2, characterized in that, In step S2, the hybrid element precursor includes one or more of the following: boric acid, trimethyl borate, triethyl borate, diethylmethoxyborane, n-butyl borate, tetrabutyl zirconate, zirconium n-butoxide, tetraethoxyzirconium, zirconium acetylacetonate, and zirconium oxychloride. In step S2, the epoxy functional group silane coupling agent includes one or more of KH560, KH561, and KH562. In step S2, the acidic catalyst includes one or more of boric acid, sulfuric acid, hydrochloric acid, nitric acid, and acetic acid; In step S2, the temperature of the mixing reaction is room temperature to 45°C; In step S2, the molar ratio of the polysiloxane precursor to the hybrid element precursor is 1:0.01~10; In step S2, the molar ratio of the polysiloxane precursor to the epoxy functional group silane coupling agent is 1:0.01~10; In step S2, the molar ratio of the polysiloxane precursor to the acidic catalyst is 1:0~0.01; In step S2, the molar ratio of the polysiloxane precursor to the water is 1:0~10.

5. The preparation method of the high-strength, ablation-resistant, elementally hybridized branched polysiloxane nano-aerogel composite material according to claim 1, characterized in that, In the solvent, the surfactant accounts for 0.001% to 0.1% by mass, and at least one of ethanol, isopropanol, n-hexane, and petroleum ether accounts for 30% to 80% by mass. The surfactant includes one or more of potassium perfluorohexyl ethyl sulfonate, polyoxyethylene perfluoroalkyl ether, and trifluoropropyl methylsiloxane.

6. The method for preparing the high-strength, ablation-resistant, elementally hybridized branched polysiloxane nano-aerogel composite material according to claim 1, characterized in that, The amine curing agent includes one or more of the following: ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, isophorone diamine, N,N-dimethyl-p-toluidine, and triethanolamine.

7. The method for preparing the high-strength, ablation-resistant, elementally hybridized branched polysiloxane nano-aerogel composite material according to claim 1, characterized in that, The nanofiller includes one or more of zirconium oxide fibers, alumina fibers, silicon carbide fibers, and halloysite nanotubes. The zirconium oxide fiber, alumina fiber, silicon carbide fiber, halloysite nanotubes, or one or more of these materials have a length of 80-1500 nm and an aspect ratio of 3-30. The nanofiller is modified by one or more of the following silane coupling agents: KH540, KH550, KH602, and KH792 to achieve surface amino grafting. The mass ratio of the nanofiller to one or more of the silane coupling agents KH540, KH550, KH602, and KH792 is 1:0.01~0.

1.

8. The method for preparing the high-strength, ablation-resistant, elementally hybridized branched polysiloxane nano-aerogel composite material according to claim 1, characterized in that, The fibers in the fiber preform include one or more of the following: quartz fiber, zirconium oxide fiber, mullite fiber, and alumina fiber. The fiber preform is pre-modified with at least one of the silane coupling agents KH540, KH550, KH602, and KH792 to achieve surface amino grafting. The mass ratio of the fiber preform to at least one of the silane coupling agents KH540, KH550, KH602, and KH792 is 1:0.01~1; The density of the fiber preform is less than 0.3 g·cm³. -3 .

9. The method for preparing the high-strength, ablation-resistant, elementally hybridized branched polysiloxane nano-aerogel composite material according to claim 1, characterized in that, In step (2): The silica sol is used to impregnate the fiber preform using the RTM process; The fiber preform includes fiber felt; The mass ratio of the fiber preform to the silica sol is 1:2~7; The gel aging temperature is 40~140℃, and the time is 6~24h; The temperature for atmospheric pressure drying is 80~200℃, and the time is 6~24h.

10. The high-strength, ablation-resistant, element-hybridized branched polysiloxane nano-aerogel composite material prepared by the preparation method according to any one of claims 1 to 9.

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