A fiber-reinforced silicon-boron modified phenolic aerogel multiphase composite material with anti-ablation and thermal management functions and a preparation method thereof

Abstract

The present application belongs to the technical field of heat protection materials, and particularly relates to a fiber-reinforced silicon-boron modified phenolic aerogel multiphase composite material with ablation resistance and heat management functions and a preparation method thereof. The method comprises the following steps: (1) preparing a silicon modified phenolic resin; (2) synthesizing a silicon boroxine prepolymer modified phenolic resin solution; (3) preparing a reaction precursor solution; (4) vacuum impregnating a fiber preform; (5) sol-gel and phase separation; and (6) drying and filling a phase change material. The present application controls the reaction parameters in the modification process of the phenolic resin, forms a silicon boroxine oligomer under mild conditions, and inhibits the hydrolysis of silicon and boron components from the molecular level, so as to realize the stable introduction of high content silicon and boron components into the molecular chain of the phenolic resin. The filling of a high-enthalpy phase change material makes the heat transfer in the thickness direction of the material present a nonlinear delay, and can effectively inhibit the temperature rise rate on the back surface of the material within a given heating time.

Description

Technical Field

[0001] This invention belongs to the field of thermal protection materials technology, specifically relating to a fiber-reinforced silicon-boron modified phenolic aerogel multiphase composite material with both ablation resistance and thermal management functions, and its preparation method. Background Technology

[0002] Advanced engines are key power sources for long-range operations. Their combustion chambers / nozzles operate under extreme environments (≥400 s) of ultra-high temperature (>2000 ℃), high pressure, and strong oxidation due to propellant combustion, and their compact structure presents significant challenges for thermal protection design. Traditional insulation materials often fail to meet these requirements, necessitating the development of novel materials with higher service temperatures, longer lifespans, high thermal efficiency, high load-bearing capacity, and low density. Phenolic aerogels, using phenolic resin as a precursor and constructed with a sol-gel process to create a three-dimensional nanoporous structure, possess excellent properties such as low density, low thermal conductivity, and high carbon residue, making them an ideal candidate material for combustion chamber / nozzle insulation. However, their nanoporous structure also presents performance bottlenecks: the framework is prone to oxidation and pulverization in high-temperature (>600 ℃) aerobic environments; simultaneously, the material exhibits significant intrinsic brittleness, resulting in insufficient resistance to ablation and insufficient mechanical load-bearing capacity, making it difficult to meet the demands of harsh operating conditions. Therefore, current methods primarily employ silicon-boron doping for modification and optimization. Boron forms a molten B₂O₃ glass phase in situ at high temperatures, covering the carbon framework and sealing nanopores to create a physical oxygen barrier, significantly improving oxidation and ablation resistance. Silicon enhances mechanical strength and thermal stability by constructing a hybrid structure that interpenetrates the organic framework with an -Si-O-Si- inorganic network. Crucially, the synergistic effect of silicon and boron at high temperatures generates borosilicate glass, forming a dense, self-healing ceramic protective layer, achieving a synergistic improvement in oxidation resistance, ablation resistance, and mechanical properties.

[0003] Achieving high, stable, and uniform dispersion of silicon and boron in phenolic resin is the core challenge of the aforementioned modification. The difficulty lies in the inherent mismatch between the two: the phenolic skeleton is mainly composed of C-C bonds, belonging to an organic system; while silicon and boron precursors tend to form Si-O-Si and BOB inorganic networks. Their compatibility is poor, and direct blending easily leads to phase separation during gelation, disrupting material homogeneity. Furthermore, simply increasing the amount of feedstock is insufficient for effective doping; excessive inorganic sources accelerate gelation, introduce defects, and leave incomplete residues in the pores, which volatilize and decompose upon heating, causing the aerogel pore structure to collapse. Existing patents have proposed different solutions to these problems. CN120098406A uses boron-phenolic resin with a limited molecular weight as the matrix, and uses acid catalysis to match the silicon source hydrolysis rate to resin curing, followed by gradient drying to construct a three-dimensional ordered network. However, this method has a theoretical upper limit on the amount of silicon and boron introduced to maintain the ordered structure, and the actual effective introduction amount is limited by the degree of reaction. CN118978703A synthesizes a boron-containing polysilicon silsesquioxane precursor and uses its organic groups to chemically copolymerize with phenolic resin to achieve uniform introduction of silicon and boron elements. However, this synthesis and subsequent copolymerization process involves harsh reaction conditions (the highest reaction temperature reaches 180 °C, and the longest reaction time requires 96 h), and suffers from drawbacks such as complex synthesis processes, high raw material costs, and significant dependence on organic solvents. In summary, although existing technologies have achieved stable introduction of silicon and boron elements through controlled hydrolysis matching or precursor copolymerization strategies, they generally face limitations such as limited introduction efficiency, harsh reaction conditions, or complex processes. There is an urgent need to develop more efficient, milder, and more compatible doping methods.

[0004] The thermal insulation performance of aerogel materials primarily stems from their low thermal conductivity due to their low density and high porosity structure. Traditional optimization approaches focus on further reducing density as an effective way to improve insulation performance. However, this approach has two limitations: first, the material's density has a physical lower limit, making it unsustainable to improve insulation efficiency solely by reducing thermal conductivity; second, excessive density reduction inevitably weakens the material's ablation resistance, creating an inherent contradiction between insulation and ablation resistance. Therefore, it is crucial to break through the limitations of traditional density control thinking and introduce novel thermal management-based insulation mechanisms. This involves further improving the insulation efficiency while ensuring the material's ablation resistance, achieving an integrated design of ablation resistance and high-efficiency insulation, and ultimately providing key technical support and material solutions for the thermal protection systems of advanced engine combustion chambers / nozzles. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a fiber-reinforced silicon-boron modified phenolic aerogel multiphase composite material with both ablation resistance and thermal management functions, as well as its preparation method. The resulting composite material overcomes the technical bottleneck of traditional aerogels in achieving a balance between thermal insulation, high strength, and ablation resistance, realizing a synergistic unity of mechanical load-bearing capacity, efficient thermal insulation, and long-term ablation resistance, and is expected to be applied to advanced engine thermal protection systems.

[0006] This invention proposes a method for preparing a fiber-reinforced silicon-boron modified phenolic aerogel multiphase composite material with both ablation resistance and thermal management functions, comprising the following steps: (1) Preparation of silicon-modified phenolic resin: Linear phenolic resin is mixed with a first siloxane, a first acidic catalyst is added, and transesterification reaction is carried out; after the reaction is completed, the phenolic resin is obtained by vacuum distillation. (2) Synthesis of silboroxane prepolymer modified phenolic resin solution: The silicon-modified phenolic resin obtained in step (1) is mixed with an alcohol solvent, a boron source and a second acidic catalyst are added, and the mixture is refluxed at normal pressure to allow the boron source to undergo a condensation reaction with the residual silanol groups in the silicon-modified phenolic resin to form a silboroxane prepolymer, thereby obtaining a silboroxane prepolymer modified phenolic resin solution with high silicon boron content. (3) Preparation of reaction precursor solution: Take the siloxane prepolymer modified phenolic resin solution obtained in step (2), mix it with the second siloxane, surfactant and curing agent to obtain the reaction precursor solution; (4) Vacuum impregnation of fiber preform: Place the fiber preform in a vacuum impregnation mold, evacuate to a predetermined pressure, and then introduce the reaction precursor solution obtained in step (3). Vacuum pressure is maintained to fully impregnate the fiber preform. (5) Sol-gel and phase separation: The mold containing the impregnated fiber preform in step (4) is heated and kept warm to carry out the sol-gel reaction. After naturally cooling to room temperature, fiber-reinforced silicon boron modified phenolic resin wet gel composite material is obtained. (6) Drying and phase change material filling: The wet gel composite material obtained in step (5) is dried under normal pressure to obtain fiber-reinforced silicon boron modified phenolic resin dry gel composite material; the phase change material is heated to a molten state and impregnated with silicon boron modified phenolic resin dry gel composite material. After vacuum pressure holding, it is taken out and cooled to obtain fiber-reinforced silicon boron modified phenolic aerogel multiphase composite material with both ablation resistance and thermal management functions.

[0007] Further, in step (1), the first siloxane is one or more of methyltrimethoxysilane, methyltriethoxysilane, 3-aminopropyltriethoxysilane, phenyltrimethoxysilane and phenyltriethoxysilane; the first acidic catalyst is one or more of acetic acid, p-toluenesulfonic acid, oxalic acid, dilute hydrochloric acid and sulfuric acid; The mass ratio of the linear phenolic resin to the first siloxane is 1:(0.5~2.5), and the mass ratio of the first acidic catalyst to the linear phenolic resin is 1:(10~200); the reaction temperature is 80~120℃, and the reaction time is 0.5~4 h; the vacuum distillation temperature is 80~150℃, the absolute pressure is 1~20 kPa, and the time is 2~6 h.

[0008] Further, in step (2), the alcohol solvent is one or more of ethanol, ethylene glycol, diethylene glycol, propylene glycol, and 1,4-butanediol; the boron source is one or more of boric acid, phenylboronic acid, 4-aminophenylboronic acid, 2-aminophenylboronic acid, and borocyclopentane; and the second acidic catalyst is one or more of citric acid, acetic acid, p-toluenesulfonic acid, phosphoric acid, and dilute hydrochloric acid. The mass ratio of the silicon-modified phenolic resin to the alcohol solvent is 1:(0.5~8), the mass ratio of the boron source to the silicon-modified phenolic resin is 1:(2~10), and the mass ratio of the second acidic catalyst to the silicon-modified phenolic resin is 1:(10~100); the reaction temperature is 80~150℃, and the reaction time is 0.5~3 h.

[0009] Further, in step (3), the second siloxane is one or more of methyltrimethoxysilane, methyltriethoxysilane, phenyltrimethoxysilane, methylphenyldimethoxysilane, and tetraethyl orthosilicate; the surfactant is one or more of polyether-modified polysiloxane, polyoxyethylene ether-modified trisiloxane, Span-80, Tween-80, OP-10, Pluronic F127, and Pluronic P123; and the curing agent is one or more of paraformaldehyde, hexamethylenetetramine, benzenesulfonyl chloride, p-toluenesulfonic acid, p-toluenesulfonyl chloride, and propylene carbonate. The mass ratio of the siloxane prepolymer modified phenolic resin solution to the second siloxane is 1:(0.5~3), the mass ratio of the surfactant to the siloxane prepolymer modified phenolic resin solution is 1:(50~200), and the mass ratio of the curing agent to the siloxane prepolymer modified phenolic resin solution is 1:(10~100).

[0010] Further, in step (4), the fiber preform is one or more of the following: carbon fiber preform, quartz fiber preform, high-silica fiber preform, alumina fiber preform, zirconia fiber preform, mullite fiber preform, and basalt fiber preform, and the fiber preform density is 0.1~1.2 g / cm³. 3 The fiber preform is dried at 80-120℃ for 2-6 hours before use; the absolute pressure of the vacuum is 1-10 kPa and the holding time is 16-48 hours.

[0011] Furthermore, in step (5): the temperature for heat preservation is 60~180 ℃, and the heat preservation time is 18~48 h.

[0012] Further, in step (6): the drying temperature is 80~160 ℃, the drying time is 24~72 h; the phase change material is one or more of erythritol, stearic acid, lauric acid, myristic acid, palmitic acid, trimethylolpropane and polyethylene glycol; the absolute pressure of the vacuum pressure holding is 1~10 kPa; the pressure holding time is 1-4 h.

[0013] A fiber-reinforced silicon-boron modified phenolic aerogel multiphase composite material with both ablation resistance and thermal management functions, prepared by the above method, has the following performance indicators: density ≤ 1.6 g / cm³. 3 Its compressive strength is ≥ 400 MPa according to GB / T 1448-2005; it is evaluated by oxyacetylene ablation test at a heat flux density of 1.5 MW / m³. 2 Under the condition of an ablation time of 600 s, the back surface temperature of the 18 mm thick composite material sample is ≤ 200℃ and the linear ablation rate is ≤ 5 μm / s.

[0014] The effects and advantages of this invention are as follows: 1. This invention achieves precise molecular-level introduction of heteroatoms through stepwise chemical anchoring. By controlling reaction parameters under mild conditions, silylboroxane oligomers are formed, suppressing the hydrolysis of silicon and boron components at the molecular level and ensuring their high content and stable existence in phenolic resin solutions. The stepwise doping strategy introduces silicon atoms into the phenolic molecule chain via chemical bonds to form active anchor points, thereby capturing boron atoms to form a stable Si-OB bond structure, effectively avoiding the competitive reactions and segregation risks associated with the co-introduction of multiple elements. Since heteroatoms are embedded in the molecular framework via chemical bonds rather than being physically dispersed, high doping content can be achieved without migration and aggregation, laying the foundation for excellent ablation resistance.

[0015] 2. This invention proposes a novel thermal management strategy by introducing a phase change material (PCM) into the pores of a phenolic aerogel to improve thermal insulation efficiency. Under the influence of heat flow, a temperature gradient is formed along the thickness direction within the composite material. When the local temperature reaches the PCM point, the PCM absorbs heat and undergoes an isothermal PCM transition. The temperature in this region is then stably maintained near the PCM point until the PCM is depleted, allowing heat to continue to transfer inward. This process constructs a dynamic heat sink along the heat conduction path, slowing down heat transfer, reconstructing the heat flow path, and significantly reducing the instantaneous heat flux density. This effectively suppresses the back-side temperature rise within a specified heating time, laying the foundation for high-efficiency thermal insulation performance. Attached Figure Description

[0016] Figure 1The infrared spectra of the phenolic resin modified with siliboxane prepolymer prepared in step (2) of Example 1 are compared with those of the unmodified phenolic resin. Figure 2 The XPS spectrum of the silicon boron modified phenolic resin dry gel prepared in step (6) of Example 1; Figure 3 The TG-DSC curve of the silicon-boron modified phenolic dry gel prepared in step (6) of Example 1; Figure 4 The TG-DSC curve of the silicon-boron modified phenolic dry gel prepared in step (6) of Example 2; Figure 5 The pore size distribution curve of the silicon-boron modified phenolic dry gel prepared in step (6) of Example 1; Figure 6 The pore size distribution curve of the silicon-boron modified phenolic dry gel prepared in step (6) of Example 2; Figure 7 The image shows the microstructure of the silicon-boron modified phenolic dry gel composite material prepared in step (6) of Example 1. Figure 8 The image shows the microstructure of the silicon-boron modified phenolic dry gel composite material prepared in step (6) of Example 2; Figure 9 The fiber-reinforced silicon-boron modified phenolic aerogel multiphase composite material in Example 1, which combines ablation resistance and thermal management functions; Figure 10 The material after high-temperature thermal insulation performance testing: Figure 10 (a) is the front view after ablation in Comparative Example 1; Figure 10 (b) shows the side view after ablation in Comparative Example 1; Figure 10 (c) is the front view after ablation in Example 1; Figure 10 (d) shows the side surface after ablation in Example 1; Figure 11 The material after high-temperature thermal insulation performance testing: Figure 11 (a) The overall state after ablation in Example 1; Figure 11 (b) shows the overall state after ablation in Comparative Example 3; Figure 12 The back temperature rise curves of Example 1 and Comparative Example 1 during the high-temperature thermal insulation performance test are shown. Figure 13 The back temperature rise curves of Example 1 and Comparative Example 4 during the high-temperature thermal insulation performance test are shown. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be described clearly and completely below. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. The following embodiments are composite materials with different properties prepared according to different raw materials and proportions.

[0018] Example 1: (1) 100 g of linear phenolic resin and 150 g of methyltrimethoxysilane were added to a reaction vessel and mixed. The mixture was stirred until the linear phenolic resin was completely dissolved. 1 g of p-toluenesulfonic acid was added as a catalyst, and the temperature was raised to 100 °C. The mixture was stirred at a constant temperature for 2 h to carry out the transesterification reaction. After the reaction was completed, the system temperature was raised to 120 °C, and the mixture was distilled under reduced pressure for 4 h at an absolute pressure of 5 kPa to remove the byproduct methanol and unreacted siloxanes, thus obtaining silicon-modified phenolic resin.

[0019] (2) Take 50 g of the silicon-modified phenolic resin obtained in step (1) and dissolve it in 100 g of ethylene glycol. Stir until completely dissolved. Add 10 g of boric acid and 0.5 g of citric acid to the solution as a second acidic catalyst. Heat the mixture to 120°C and reflux it under normal pressure for 1.5 h to allow the boric acid to undergo a condensation reaction with the residual silanol groups in the silicon-modified phenolic resin, forming a solution containing silboroxane prepolymer, thus obtaining a phenolic resin solution modified with silboroxane prepolymer of high silicon boron content.

[0020] (3) Take 80 g of the siloboroxane prepolymer modified phenolic resin solution obtained in step (2) and mix it with 80 g of phenyltrimethoxysilane. Add 1 g of polyether modified polysiloxane and 4 g of paraformaldehyde to the mixture and stir evenly at room temperature to obtain a homogeneous reaction precursor solution.

[0021] (4) The density is 0.6 g / cm³ 3 The quartz fiber preform (purchased from Jiangsu Tianniao High-Tech Co., Ltd., 50mm×50mm×20mm) was dried in an oven at 110 ℃ for 4 h, and then placed in a vacuum impregnation mold (aluminum, 60mm×60mm×50mm). The mold was sealed, and a vacuum was drawn to an absolute pressure of 5 kPa. Then, the reaction precursor solution prepared in step (3) was introduced, and the quartz fiber preform was completely immersed in the reaction precursor solution. The pressure was maintained at 5 kPa for 24 h to ensure that the fiber preform was fully impregnated by the reaction precursor solution. In order to ensure that the liquid level of the reaction precursor solution always exceeded the quartz fiber preform during the entire pressure holding process, the volume of the reaction precursor solution was set to be 1.5 times the volume of the quartz fiber preform.

[0022] (5) Place the impregnated mold in an oven and heat it to 120 °C at a heating rate of 1 °C / min. Keep it at this temperature for 24 h to carry out the sol-gel reaction and promote phase separation of the system. After the reaction is completed, allow it to cool naturally to room temperature to obtain fiber-reinforced silicon boron modified phenolic resin wet gel composite material.

[0023] (6) Remove the obtained wet gel composite material from the mold, manually remove excess wet gel, and place it in a forced-air drying oven. Dry it at 120 °C under normal pressure for 48 h to obtain fiber-reinforced silicon boron modified phenolic resin dry gel composite material. Heat erythritol to 150 °C to completely melt it, and completely immerse the dry gel composite material in the molten erythritol. Maintain it under vacuum conditions of 5 kPa absolute pressure for 2 h to ensure that the phase change material is fully filled into the pores of the dry gel. Remove the filled composite material, quickly blow or wipe the surface with a hot air gun to remove residual phase change material, and then allow it to cool naturally to room temperature to obtain fiber-reinforced silicon boron modified phenolic aerogel multiphase composite material with both ablation resistance and thermal management functions.

[0024] Example 2: (1) 100 g of linear phenolic resin and 250 g of phenyltriethoxysilane were added to a reaction vessel and mixed. The mixture was stirred until the linear phenolic resin was completely dissolved. 0.5 g of oxalic acid was added as a catalyst, and the temperature was raised to 120 °C. The mixture was stirred at a constant temperature for 4 h to carry out the transesterification reaction. After the reaction was completed, the system temperature was raised to 150 °C, and the mixture was distilled under reduced pressure for 2 h at an absolute pressure of 1 kPa to remove byproducts and unreacted siloxanes, thereby obtaining silicon-modified phenolic resin.

[0025] (2) Take 50 g of the silicon-modified phenolic resin obtained in step (1) and dissolve it in 400 g of diethylene glycol. Stir until completely dissolved. Add 25 g of phenylboronic acid and 5 g of phosphoric acid as a second acidic catalyst to the solution. Heat the mixture to 150 °C and reflux at normal pressure for 3 h to allow the boron source to fully condense with the residual silanol groups in the silicon-modified phenolic resin, forming a solution rich in siloboroxane prepolymer, thus obtaining the siloboroxane prepolymer modified phenolic resin solution.

[0026] (3) Take 50 g of the siloxane prepolymer modified phenolic resin solution obtained in step (2) and mix it with 150 g of a mixture of methyltrimethoxysilane and tetraethyl orthosilicate (mass ratio 1:1) to further increase the silicon content. Add 1 g of polyoxyethylene ether modified trisiloxane and 5 g of hexamethylenetetramine to the mixture and stir evenly at room temperature to obtain a homogeneous reaction precursor solution.

[0027] (4) The density is 0.2 g / cm³ 3The carbon fiber preform (purchased from Jiangsu Tianniao High-Tech Co., Ltd., 50mm×50mm×20mm) was dried in an oven at 80 ℃ for 6 h, and then placed in a vacuum impregnation mold (aluminum, 60mm×60mm×50mm). The mold was sealed, and a vacuum was drawn to an absolute pressure of 1 kPa. Then, the reaction precursor solution prepared in step (3) was introduced, and the carbon fiber preform was completely immersed in the reaction precursor solution. The pressure was maintained at 1 kPa for 48 h to ensure that the fiber preform was fully impregnated by the reaction precursor solution.

[0028] (5) Place the impregnated mold in an oven and heat it to 80 °C. Keep it at this temperature for 48 h to carry out a sol-gel reaction, which promotes phase separation of the system. After the reaction is completed, allow it to cool naturally to room temperature to obtain a fiber-reinforced silicon boron modified phenolic resin wet gel composite material.

[0029] (6) The obtained wet gel composite material was removed from the mold, and after manually removing excess wet gel, it was placed in a forced-air drying oven and dried at 80 °C under normal pressure for 72 h to obtain fiber-reinforced silicon boron modified phenolic resin dry gel composite material. Polyethylene glycol was heated to 120 °C to completely melt it, and the dry gel composite material was completely immersed in the molten polyethylene glycol and kept under vacuum conditions of 1 kPa absolute pressure for 3 h to ensure that the phase change material was fully filled into the pores of the dry gel. The filled composite material was removed, the residual phase change material on the surface was quickly removed, and then it was naturally cooled to room temperature to obtain a fiber-reinforced silicon boron modified phenolic aerogel multiphase composite material with both ablation resistance and thermal management functions.

[0030] Example 3: (1) 100 g of linear phenolic resin and 50 g of 3-aminopropyltriethoxysilane were added to a reaction vessel and mixed. The mixture was stirred until the linear phenolic resin was completely dissolved. 10 g of acetic acid was added as a catalyst, and the temperature was raised to 80 °C. The mixture was stirred at a constant temperature for 0.5 h to carry out the transesterification reaction. After the reaction was completed, the system temperature was raised to 80 °C, and the mixture was distilled under reduced pressure for 6 h at an absolute pressure of 20 kPa to remove byproducts and unreacted siloxanes, thereby obtaining silicon-modified phenolic resin.

[0031] (2) Take 50 g of the silicon-modified phenolic resin obtained in step (1) and dissolve it in 25 g of ethanol. Stir until completely dissolved. Add 5 g of 4-aminophenylboronic acid to the solution and add 0.5 g of hydrochloric acid (1 mol / L) as a second acidic catalyst. Heat the mixture to 80 °C and reflux it under normal pressure for 0.5 h to allow the boron source to undergo a condensation reaction with the residual silanol groups in the silicon-modified phenolic resin, forming a solution containing silboroxane prepolymer, thus obtaining the silboroxane prepolymer modified phenolic resin solution.

[0032] (3) Take 100 g of the silaboroxane prepolymer modified phenolic resin solution obtained in step (2) and mix it with 50 g of a mixture of phenyltrimethoxysilane and methylphenyldimethoxysilane (mass ratio 1:1). Add 2 g of a mixture of Span-80 and Tween-80 (mass ratio 1:1) and 1 g of p-toluenesulfonic acid to the mixture and stir evenly at room temperature to obtain a homogeneous reaction precursor solution.

[0033] (4) The density is 1.2 g / cm³ 3 The alumina fiber preform (purchased from Jiangsu Tianniao High-Tech Co., Ltd., 50mm×50mm×20mm) was dried in an oven at 120 ℃ for 2 h, and then placed in a vacuum impregnation mold (aluminum, 60mm×60mm×50mm). The mold was sealed, and a vacuum was drawn to an absolute pressure of 10 kPa. Then, the reaction precursor solution prepared in step (3) was introduced, and the alumina fiber preform was completely immersed in the reaction precursor solution. The pressure was maintained at 10 kPa for 16 h to ensure that the fiber preform was fully impregnated by the reaction precursor solution.

[0034] (5) Place the impregnated mold in an oven and heat it to 180 °C. Keep it at this temperature for 18 h to carry out a sol-gel reaction, which promotes phase separation of the system. After the reaction is completed, allow it to cool naturally to room temperature to obtain a fiber-reinforced silicon boron modified phenolic resin wet gel composite material.

[0035] (6) Remove the obtained wet gel composite material from the mold, manually remove excess wet gel, and place it in a forced-air drying oven. Dry it at 160 °C under normal pressure for 24 h to obtain fiber-reinforced silicon boron modified phenolic resin dry gel composite material. Heat a mixture of stearic acid and lauric acid (mass ratio 1:1) to 130 °C to completely melt it. Completely immerse the dry gel composite material in the molten phase change material and maintain it under a vacuum of 10 kPa for 1.5 h to ensure that the phase change material fully fills the pores of the dry gel. Remove the filled composite material, quickly remove the residual phase change material from the surface, and then allow it to cool naturally to room temperature to obtain fiber-reinforced silicon boron modified phenolic aerogel multiphase composite material with both ablation resistance and thermal management functions.

[0036] Example 4: (1) 100 g of linear phenolic resin and a mixture of 200 g of phenyltrimethoxysilane and methyltriethoxysilane (mass ratio 1:1) were added to a reaction vessel and stirred until the linear phenolic resin was completely dissolved. A mixture of 5 g of p-toluenesulfonic acid and acetic acid (mass ratio 1:1) was added as a catalyst, and the temperature was raised to 110 °C. The transesterification reaction was carried out by stirring at a constant temperature for 3 h. After the reaction was completed, the system temperature was raised to 130 °C, and the system was distilled under reduced pressure at an absolute pressure of 10 kPa for 4 h to remove byproducts and unreacted siloxanes, thereby obtaining silicon-modified phenolic resin.

[0037] (2) Take 50 g of the silicon-modified phenolic resin obtained in step (1) and dissolve it in a mixture of 200 g of propylene glycol and 1,4-butanediol (mass ratio 1:1), stirring until completely dissolved. Add 8 g of a mixture of boric acid and borocyclopentane (mass ratio 1:1) to the solution, and add 2 g of p-toluenesulfonic acid as a second acidic catalyst. Heat the mixture to 130 °C and reflux at atmospheric pressure for 2 h to allow the boron source to undergo a condensation reaction with the residual silanol groups in the silicon-modified phenolic resin, forming a solution containing siloboroxane prepolymer, thus obtaining the siloboroxane prepolymer modified phenolic resin solution.

[0038] (3) Take 80 g of the silaboroxane prepolymer modified phenolic resin solution obtained in step (2) and mix it with 120 g of a mixture of tetraethyl orthosilicate and phenyltrimethoxysilane (mass ratio 2:1). Add 0.8 g of a mixture of Pluronic F127 and OP-10 (mass ratio 1:1) and 4 g of a mixture of propylene carbonate and benzenesulfonyl chloride (mass ratio 1:1) to the mixture and stir evenly at room temperature to obtain a homogeneous reaction precursor solution.

[0039] (4) The density is 0.8 g / cm³ 3 The mullite fiber and basalt fiber hybrid preform (mass ratio 1:1, purchased from Jiangsu Tianniao High-Tech Co., Ltd., 50mm×50mm×20mm) was dried in an oven at 100 ℃ for 4 h, and then placed in a vacuum impregnation mold (aluminum, 60mm×60mm×50mm). The mold was sealed, and a vacuum was drawn to an absolute pressure of 3 kPa. Then, the reaction precursor solution prepared in step (3) was introduced, and the mullite fiber and basalt fiber hybrid preform was completely immersed in the reaction precursor solution. The pressure was maintained at 3 kPa for 30 h to ensure that the fiber preform was fully impregnated by the reaction precursor solution.

[0040] (5) Place the impregnated mold in an oven and heat it to 150 °C. Keep it at this temperature for 30 h to carry out a sol-gel reaction, which promotes phase separation of the system. After the reaction is completed, allow it to cool naturally to room temperature to obtain a fiber-reinforced silicon boron modified phenolic resin wet gel composite material.

[0041] (6) Remove the obtained wet gel composite material from the mold, manually remove excess wet gel, and place it in a forced-air drying oven. Dry it at 140 °C under normal pressure for 48 h to obtain a fiber-reinforced silicon boron modified phenolic resin dry gel composite material. Heat a mixture of trimethylolpropane and myristic acid (mass ratio 1:2) to 140 °C to completely melt it. Completely immerse the dry gel composite material in the molten phase change material and maintain it under a vacuum of 5 kPa for 2 h to ensure that the phase change material fully fills the pores of the dry gel. Remove the filled composite material, quickly remove the residual phase change material from the surface, and then allow it to cool naturally to room temperature to obtain a fiber-reinforced silicon boron modified phenolic aerogel multiphase composite material with both ablation resistance and thermal management functions.

[0042] Comparative Example 1: The conventional commercially available density is 1.75 g / cm³. 3 The high-silica / phenolic heat-resistant composite material is made by molding process and has the characteristics of being lightweight and high-strength.

[0043] Comparative Example 2: The conventional commercially available density is 1.80 g / cm³. 3 The high-silica / phenolic heat-resistant composite material is made by molding process and has the characteristics of being lightweight and high-strength.

[0044] Comparative Example 3: (1) Add 100 g of linear phenolic resin and 100 g of ethylene glycol to the reaction vessel and stir until the linear phenolic resin is completely dissolved to obtain a phenolic resin solution.

[0045] (2) Take 80 g of the phenolic resin solution obtained in step (1), add 4 g of paraformaldehyde, stir evenly at room temperature to obtain a homogeneous reaction precursor solution.

[0046] (3) The density is 0.6 g / cm³ 3 The quartz fiber preform (purchased from Jiangsu Tianniao High-Tech Co., Ltd., 50 mm × 50 mm × 20 mm) was dried in an oven at 110 ℃ for 4 h, and then placed in a vacuum impregnation mold (aluminum, 60 mm × 60 mm × 50 mm). The mold was sealed, and a vacuum was drawn to an absolute pressure of 5 kPa. Then, the reaction precursor solution prepared in step (2) was introduced, and the quartz fiber preform was completely immersed in the reaction precursor solution. The pressure was maintained at 5 kPa for 24 h to ensure that the fiber preform was fully impregnated by the reaction precursor solution. To ensure that the liquid level of the reaction precursor solution always exceeded the quartz fiber preform during the entire pressure holding process, the volume of the reaction precursor solution was set to be 1.5 times the volume of the quartz fiber preform.

[0047] (4) Place the impregnated mold in an oven and heat it to 120 ℃ at a heating rate of 1 ℃ / min, and keep it at that temperature for 24 h to carry out the curing reaction. After the reaction is completed, allow it to cool naturally to room temperature to obtain a fiber-reinforced phenolic resin wet gel composite material.

[0048] (5) The obtained wet gel composite material was removed from the mold and placed in a forced-air drying oven and dried at 120 °C under normal pressure for 48 h to obtain fiber-reinforced phenolic resin dry gel composite material.

[0049] (6) Heat erythritol to 150 °C until it is completely melted, immerse the dry gel composite material completely in the molten erythritol, and maintain it under vacuum conditions of 5 kPa for 2 h to ensure that the phase change material is fully filled into the pores of the dry gel. Take out the filled composite material, quickly blow or wipe the surface with a hot air gun to remove the residual phase change material, and then let it cool naturally to room temperature to obtain the fiber-reinforced phenolic aerogel multiphase composite material.

[0050] Comparative Example 4: (1) 100 g of linear phenolic resin and 150 g of methyltrimethoxysilane were added to a reaction vessel and mixed. The mixture was stirred until the linear phenolic resin was completely dissolved. 1 g of p-toluenesulfonic acid was added as a catalyst, and the temperature was raised to 100 °C. The mixture was stirred at a constant temperature for 2 h to carry out the transesterification reaction. After the reaction was completed, the system temperature was raised to 120 °C, and the mixture was distilled under reduced pressure for 4 h at an absolute pressure of 5 kPa to remove the byproduct methanol and unreacted siloxanes, thus obtaining the silicon-modified phenolic resin.

[0051] (2) Take 50 g of the silicon-modified phenolic resin obtained in step (1) and dissolve it in 100 g of ethylene glycol. Stir until completely dissolved. Add 10 g of boric acid and 0.5 g of citric acid to the solution as a second acidic catalyst. Heat the mixture to 120°C and reflux it under normal pressure for 1.5 h to allow the boric acid to undergo a condensation reaction with the residual silanol groups in the silicon-modified phenolic resin, forming a solution containing silboroxane prepolymer, thus obtaining a phenolic resin solution modified with silboroxane prepolymer of high silicon boron content.

[0052] (3) Take 80 g of the siloboroxane prepolymer modified phenolic resin solution obtained in step (2) and mix it with 80 g of phenyltrimethoxysilane. Add 1 g of polyether modified polysiloxane and 4 g of paraformaldehyde to the mixture and stir evenly at room temperature to obtain a homogeneous reaction precursor solution.

[0053] (4) The density is 0.6 g / cm³ 3The quartz fiber preform (purchased from Jiangsu Tianniao High-Tech Co., Ltd., 50mm×50mm×20mm) was dried in an oven at 110 ℃ for 4 h, and then placed in a vacuum impregnation mold (aluminum, 60mm×60mm×50mm). The mold was sealed, and a vacuum was drawn to an absolute pressure of 5 kPa. Then, the reaction precursor solution prepared in step (3) was introduced, and the quartz fiber preform was completely immersed in the reaction precursor solution. The pressure was maintained at 5 kPa for 24 h to ensure that the fiber preform was fully impregnated by the reaction precursor solution. In order to ensure that the liquid level of the reaction precursor solution always exceeded the quartz fiber preform during the entire pressure holding process, the volume of the reaction precursor solution was set to be 1.5 times the volume of the quartz fiber preform.

[0054] (5) Place the impregnated mold in an oven and heat it to 120 °C at a heating rate of 1 °C / min. Keep it at this temperature for 24 h to carry out the sol-gel reaction and promote phase separation of the system. After the reaction is completed, allow it to cool naturally to room temperature to obtain fiber-reinforced silicon boron modified phenolic resin wet gel composite material.

[0055] (6) The obtained wet gel composite material was removed from the mold and placed in a forced-air drying oven and dried at 120 °C under normal pressure for 48 h to obtain fiber-reinforced silicon boron modified phenolic resin dry gel composite material.

[0056] The solvent in the silboroxane prepolymer-modified phenolic resin solution obtained in step (2) of Example 1 was removed by vacuum distillation. The bonding mode of silicon in the silboroxane prepolymer-modified phenolic resin was analyzed using Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). Thermogravimetric analysis (TG-DSC) was performed on the obtained silboroxane-modified phenolic resin dry gel under a nitrogen atmosphere and a heating rate of 10 °C / min. The pore structure of the silboroxane-modified phenolic resin dry gel composite material was analyzed using an automated mercury porosimeter. The microstructure of the fiber-reinforced silboroxane-modified phenolic resin dry gel composite material was analyzed using scanning electron microscopy.

[0057] The density of the composite material was tested according to the national standard GB / T 1463-2005 "Test Methods for Density and Relative Density of Fiber Reinforced Plastics". The compressive strength of the composite material was tested according to the national standard GB / T 1448-2005 "Test Methods for Compressive Properties of Fiber Reinforced Plastics". The oxygen-acetylene ablation test method in the national standard GJB 323B-2018 "Test Methods for Ablation of Ablation Materials" was used at 1.5 MW / m³. 2 The thermal insulation and ablation properties of the composite material were tested under a heat flux density and a test duration of 600 s.

[0058] The specific implementation process for the thermal insulation performance test is as follows: 1) Cut the sample into composite material specimens with dimensions of 40 mm × 40 mm × 18 mm; 2) Simultaneously adjust the gas flow rate and the initial distance from the specimen surface to the flame nozzle surface to stabilize the heat flux density at 1.5 ± 0.1 MW / m². 2 3) An oxyacetylene flame is vertically sprayed onto the surface of the composite material, and the temperature on the back of the heat-insulating composite material flat plate sample is recorded simultaneously by a thermocouple. The total heating time is 600 s. 4) The back temperature rise curve of the heat-insulating composite material sample during the test is recorded. The high-temperature heat insulation performance of different heat-insulating composite material samples is evaluated by comparing the back temperature peak at 600 s.

[0059] The results of tests on different sample densities, compressive strengths, peak back temperatures, and linear ablation rates are shown in Table 1.

[0060] Table 1. Comparison of density, compressive strength, peak back temperature, and fire resistance of different samples.

[0061] The silicon-boron modified phenolic resin aerogel multiphase composite material prepared in this invention, which combines ablation resistance and thermal management functions, achieves a comprehensive breakthrough in mechanical, thermal insulation, and ablation resistance properties while maintaining lightweight properties. As shown in Table 1, compared with commercially available high-silica / phenolic heat-resistant composite materials, the density of this material is reduced by more than 14% (based on the average of 1.78 g / cm³ of Comparative Examples 1 and 2). 3 The concentration decreased to an average of 1.52 g / cm³ compared to Examples 1-4. 3 The compressive strength increased by more than 40% (from the average of 290 MPa in Comparative Examples 1 and 2 to the average of 410 MPa in Examples 1-4), the peak back temperature decreased by more than 130°C (from the average of 289.5°C in Comparative Examples 1 and 2 to the average of 158°C in Examples 1-4), and the average linear ablation rate decreased by 12% (from the average of 5.4 μm / s in Comparative Examples 1 and 2 to the average of 4.7 μm / s in Examples 1-4). These superior properties are attributed to the synergistic effect of its unique chemical composition, microstructure design, and thermal management strategy.

[0062] In terms of chemical composition, this invention employs a stepwise introduction strategy to achieve uniform doping of high-content silicon and boron elements, effectively avoiding competitive reactions and segregation risks associated with the co-introduction of multiple elements. For example... Figure 1 As shown, the modified phenolic resin is in the range of 915–930 cm⁻¹ -1 The B–O–Si vibrational absorption peak appears at the point, and the Si 2p spectrum of its dry gel ( Figure 2The presence of Si–O–B characteristic peaks in the sample confirms the successful formation of the siloboroxane prepolymer. This structure not only ensures the stable introduction of silicon and boron elements into the resin matrix through chemical bonds, but also constructs an organic-inorganic interpenetrating network, providing the material with a high pyrolysis residual weight. (See...) Figure 3 and Figure 4 The pyrolysis residual weight of the material was measured using a comprehensive thermal analyzer. Under N2 atmosphere and a heating rate of 10 °C / min, it reached 70.13% (Example 1) to 81.65% (Example 2), far exceeding the 45% to 55% of traditional phenolic resins, thus laying a solid foundation for excellent ablation resistance. Simultaneously, the interpenetrating network structure helps refine pores and enhance matrix strength, further contributing to the improvement of mechanical properties.

[0063] In terms of microstructure, the obtained boron-modified phenolic dry gel exhibits a uniform single-peak pore size distribution. Figure 5 , Figure 6 The average pore size is 27.5 nm (Example 2) to 66.3 nm (Example 1). These nanopores below 100 nm not only effectively disperse local stress and improve the mechanical strength of the material, but also simultaneously reduce both solid-state thermal conductivity (by limiting solid-phase heat transfer paths) and gaseous thermal conductivity (by suppressing gas molecule collisions), thus endowing the material with intrinsic thermal insulation capabilities. The fiber-aerogel matrix interface in the composite material exhibits good bonding (…). Figure 7 , Figure 8 Macroscopically, the material is dense and uniform, without interlayer cracks. Figure 9 This ensures stable overall performance. After high-temperature testing, commercially available materials exhibited significant warping, cracking, and thickness-direction expansion. Figure 10 (a) and Figure 10 (b); The central region of the phenolic aerogel multiphase composite material without modification by introducing silicon-boron components shows obvious ablation marks. Figure 11 (b) The resin matrix was completely oxidized and decomposed, leaving only white quartz fiber reinforcement; while the material of the present invention had an intact structure, with only localized oxidation and erosion, further verifying its excellent structural stability and ablation resistance. Figure 10 (c) Figure 10 (d) and Figure 11 (a).

[0064] This invention further endows the material with unique thermal management functions by introducing a phase change agent into the nanopores. Under the action of heat flow, a temperature gradient is formed along the thickness direction inside the composite material. When the local temperature reaches the phase change point, the phase change material undergoes an isothermal phase change, absorbing a large amount of heat and converting sensible heat into latent heat for storage, thereby constructing a dynamic heat sink in the heat conduction path and locking the material temperature near the phase change point until the phase change agent is consumed before heat transfer can continue. This mechanism, combined with the ultra-low solid and gaseous thermal conductivity brought about by the material's well-developed porous structure, can significantly reconstruct the heat flow path, reduce the instantaneous heat flux density, and greatly delay the temperature rise on the back side. In the thermal insulation performance evaluation, commercially available high-silica / phenolic thermal insulation composite materials (Comparative Example 1) were compared. Figure 12 The back heating rate was approximately 28 °C / min; the fiber-reinforced silicon-boron modified phenolic resin dry gel composite material (Comparative Example 4) without the introduction of a phase change agent for thermal management... Figure 13 The back heating rate of the original material is approximately 19 °C / min; while the composite material of this invention has a heating rate of only 15 °C / min, exhibiting extremely high thermal insulation efficiency. In summary, this invention, through the synergistic effect of chemical composition design and thermal management strategies, successfully prepared a silicon-boron modified phenolic resin aerogel multiphase composite material with both excellent thermal insulation and ablation resistance, showing broad application prospects in the field of thermal protection.

Claims

1. A method for preparing a fiber-reinforced silicon-boron modified phenolic aerogel multiphase composite material with both ablation resistance and thermal management functions, characterized in that, Includes the following steps: (1) Preparation of silicon-modified phenolic resin: Linear phenolic resin is mixed with a first siloxane, a first acidic catalyst is added, and transesterification reaction is carried out; after the reaction is completed, the phenolic resin is obtained by vacuum distillation. (2) Synthesis of silboroxane prepolymer modified phenolic resin solution: The silicon-modified phenolic resin obtained in step (1) is mixed with an alcohol solvent, a boron source and a second acidic catalyst are added, and the mixture is refluxed under normal pressure to obtain a silboroxane prepolymer modified phenolic resin solution with high silicon and boron content. (3) Preparation of reaction precursor solution: Take the siloxane prepolymer modified phenolic resin solution obtained in step (2), mix it with the second siloxane, surfactant and curing agent to obtain the reaction precursor solution; (4) Vacuum impregnation of fiber preform: Place the fiber preform in a vacuum impregnation mold, evacuate to a predetermined pressure, and then introduce the reaction precursor solution obtained in step (3). Vacuum pressure is maintained to fully impregnate the fiber preform. (5) Sol-gel and phase separation: The mold containing the impregnated fiber preform in step (4) is heated and kept warm to carry out the sol-gel reaction. After naturally cooling to room temperature, fiber-reinforced silicon boron modified phenolic resin wet gel composite material is obtained. (6) Drying and phase change material filling: The wet gel composite material obtained in step (5) is dried under normal pressure to obtain fiber-reinforced silicon boron modified phenolic resin dry gel composite material; the phase change material is heated to a molten state and impregnated with silicon boron modified phenolic resin dry gel composite material. After vacuum pressure holding, it is taken out and cooled to obtain fiber-reinforced silicon boron modified phenolic aerogel multiphase composite material with both ablation resistance and thermal management functions.

2. The method for preparing the fiber-reinforced silicon-boron modified phenolic aerogel multiphase composite material with both ablation resistance and thermal management functions according to claim 1, characterized in that: In step (1), the first siloxane is one or more of methyltrimethoxysilane, methyltriethoxysilane, 3-aminopropyltriethoxysilane, phenyltrimethoxysilane, and phenyltriethoxysilane; the first acid catalyst is one or more of acetic acid, p-toluenesulfonic acid, oxalic acid, dilute hydrochloric acid, and sulfuric acid. The mass ratio of the linear phenolic resin to the first siloxane is 1:(0.5~2.5), and the mass ratio of the first acidic catalyst to the linear phenolic resin is 1:(10~200); the reaction temperature is 80~120℃, and the reaction time is 0.5~4 h; the vacuum distillation temperature is 80~150℃, the absolute pressure is 1~20 kPa, and the time is 2~6 h.

3. The method for preparing the fiber-reinforced silicon-boron modified phenolic aerogel multiphase composite material with both ablation resistance and thermal management functions according to claim 1, characterized in that: In step (2), the alcohol solvent is one or more of ethanol, ethylene glycol, diethylene glycol, propylene glycol, and 1,4-butanediol; the boron source is one or more of boric acid, phenylboronic acid, 4-aminophenylboronic acid, 2-aminophenylboronic acid, and borocyclopentane; and the second acidic catalyst is one or more of citric acid, acetic acid, p-toluenesulfonic acid, phosphoric acid, and dilute hydrochloric acid. The mass ratio of the silicon-modified phenolic resin to the alcohol solvent is 1:(0.5~8), the mass ratio of the boron source to the silicon-modified phenolic resin is 1:(2~10), and the mass ratio of the second acidic catalyst to the silicon-modified phenolic resin is 1:(10~100); the reaction temperature is 80~150℃, and the reaction time is 0.5~3 h.

4. The method for preparing the fiber-reinforced silicon-boron modified phenolic aerogel multiphase composite material with both ablation resistance and thermal management functions according to claim 1, characterized in that: In step (3), the second siloxane is one or more of methyltrimethoxysilane, methyltriethoxysilane, phenyltrimethoxysilane, methylphenyldimethoxysilane, and tetraethyl orthosilicate; the surfactant is one or more of polyether-modified polysiloxane, polyoxyethylene ether-modified trisiloxane, Span-80, Tween-80, OP-10, Pluronic F127, and Pluronic P123; and the curing agent is one or more of paraformaldehyde, hexamethylenetetramine, benzenesulfonyl chloride, p-toluenesulfonic acid, p-toluenesulfonyl chloride, and propylene carbonate. The mass ratio of the siloxane prepolymer modified phenolic resin solution to the second siloxane is 1:(0.5~3), the mass ratio of the surfactant to the siloxane prepolymer modified phenolic resin solution is 1:(50~200), and the mass ratio of the curing agent to the siloxane prepolymer modified phenolic resin solution is 1:(10~100).

5. The method for preparing the fiber-reinforced silicon-boron modified phenolic aerogel multiphase composite material with both ablation resistance and thermal management functions according to claim 1, characterized in that: In step (4), the fiber preform is one or more of the following: carbon fiber preform, quartz fiber preform, high-silica fiber preform, alumina fiber preform, zirconia fiber preform, mullite fiber preform, and basalt fiber preform, and the fiber preform density is 0.1~1.2 g / cm³. 3 The fiber preform is dried at 80-120℃ for 2-6 hours before use; the absolute pressure of the vacuum is 1-10 kPa and the holding time is 16-48 hours.

6. The method for preparing the fiber-reinforced silicon-boron modified phenolic aerogel multiphase composite material with both ablation resistance and thermal management functions according to claim 1, characterized in that, In step (5): the temperature for heat preservation is 60~180 ℃, and the heat preservation time is 18~48 h.

7. The method for preparing the fiber-reinforced silicon-boron modified phenolic aerogel multiphase composite material with both ablation resistance and thermal management functions according to claim 1, characterized in that, In step (6): the drying temperature is 80~160 ℃, the drying time is 24~72 h; the phase change material is one or more of erythritol, stearic acid, lauric acid, myristic acid, palmitic acid, trimethylolpropane and polyethylene glycol; the absolute pressure of the vacuum pressure holding is 1~10 kPa; the pressure holding time is 1-4 h.

8. A fiber-reinforced silicon-boron modified phenolic aerogel multiphase composite material with both ablation resistance and thermal management functions, prepared by the preparation method according to any one of claims 1 to 7, characterized in that, The performance indicators of the composite material are as follows: density ≤ 1.6 g / cm³ 3 Its compressive strength is ≥ 400 MPa according to GB / T 1448-2005; it is evaluated by oxyacetylene ablation test at a heat flux density of 1.5 MW / m³. 2 Under the condition of an ablation time of 600 s, the back surface temperature of the 18 mm thick composite material sample is ≤200℃ and the linear ablation rate is ≤5 μm / s.

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