Thermal response type Ti-Si-B ternary hybrid phenolic aerogel composite material with excellent thermal protection performance

Abstract

The invention discloses a thermal response type Ti-Si-B ternary hybrid phenolic aerogel composite material with excellent thermal protection performance, and belongs to the technical field of aerospace special materials and high-temperature protection. Phenolic resin (PR) is synergistically modified by introducing polyborosilazane (PBSZ) and tetrabutyl titanate (TBT), and a triple crosslinking interpenetrating network structure is constructed by taking high-temperature-resistant fiber felt as a rigid reinforcing framework. The design solves the problems of dispersity and interfacial compatibility of the inorganic filler in a resin matrix, and meanwhile, thermal response conversion of material performance is realized through molecular structure design. The prepared composite material has the advantages of ultra-light weight, high elasticity, efficient heat insulation and excellent ablation resistance.

Description

Technical Field

[0001] This invention relates to a thermally responsive Ti-Si-B ternary hybrid phenolic aerogel composite material with excellent thermal protection performance, belonging to the field of aerospace special materials and high-temperature protection technology. Background Technology

[0002] With the development of cutting-edge technologies such as deep space exploration and hypersonic vehicles, spacecraft are facing severe challenges from extreme thermo-electromagnetic coupling environments during flight. On the one hand, the aerodynamic heat and engine heat generated by high-speed flight require materials with excellent thermal insulation and ablation resistance. On the other hand, the complex electromagnetic environment of deep space and the high sensitivity of electronic systems require materials to provide effective electromagnetic interference (EMI) shielding to ensure communication quality and equipment safety. In addition, the enormous vibrations and shocks generated during launch and orbit changes require materials to have a certain degree of elasticity and deformation adaptability to meet the requirements of lightweight and vibration-resistant design.

[0003] However, traditional aerospace materials, such as rigid ceramic tiles, dense carbon-carbon composites, or metal matrix composites, typically suffer from high density, brittleness, and limited functionality. They cannot simultaneously meet the three conflicting yet crucial performance requirements of thermal protection, structural elasticity, and electromagnetic shielding in a single material. Therefore, developing a novel material that integrates these multiple functions is of great significance for improving the reliability and safety of aircraft in extreme environments and has become an urgent technological bottleneck in this field.

[0004] Against this backdrop, phenolic aerogels, due to their inherent low density, low thermal conductivity, excellent thermal stability, and the ability to achieve electrical conductivity through high-temperature carbonization, are considered ideal matrix materials for integrating thermal protection and electromagnetic shielding functions, attracting widespread research interest. However, intrinsic phenolic aerogels exhibit inherent brittleness, and their rigid network structure leads to poor strain tolerance, making it difficult to meet elasticity and vibration resistance requirements. Furthermore, the electromagnetic shielding effectiveness after carbonization still has significant room for improvement, and their oxidation and ablation resistance at high temperatures also need further enhancement.

[0005] Studies have shown that introducing inorganic or metal hybrid elements (such as Mo, Si, Zr, etc.) through covalent bonding can effectively improve the thermal stability and ablation resistance of phenolic resins. These hybrid elements construct a more stable chemical structure, delay the pyrolysis process of the resin, and ultimately form a carbon / ceramic composite structure that can effectively resist thermal erosion. Despite numerous studies, reported modified phenolic aerogels are usually limited to one or two functional elements, and the deep integration of their multifunctional properties has not yet been achieved. A key bottleneck lies in the complexity of material synthesis, making the preparation of hybrid phenolic precursors containing three or more functional elements and their three-dimensional aerogels extremely difficult, resulting in few related reports.

[0006] Among various functional modifying elements, boron-modified phenolic precursors stand out, significantly improving the thermal properties and mechanical toughness of phenolic aerogels. Similarly, silicon-modified phenolic aerogels, which combine good thermal stability, ablation resistance, and flexibility, have also attracted considerable attention. However, at high temperatures, the B2O3 in boron-modified phenolic aerogels is prone to volatilization, leading to the failure of the protective layer. Silicon-modified materials also experience a decrease in oxidation resistance due to SiO2 evaporation at temperatures exceeding 1800°C. Introducing transition metal elements such as Ti and Zr into the phenolic backbone or side chains can further enhance the oxidation resistance and thermal stability of organosilicon, and improve the electrical and dielectric properties of the carbonized material.

[0007] Patents such as CN115678090A (an ablation-resistant phenolic aerogel and its preparation method) and CN118165353A (an organic-inorganic-metal hybrid thermosetting phenolic aerogel and its preparation method, a carbon aerogel and its application) have prepared ablation-resistant aerogels. Among them, the aerogel of CN118165353A also has excellent heat resistance, thermal insulation, compression performance and electromagnetic shielding ability, but its electromagnetic shielding effectiveness is still only 31.6 dB and can be further improved, and its thermal stability also has room for improvement.

[0008] Overall, although the introduction of elements such as boron, silicon, and transition metals has significantly improved the thermal stability, mechanical properties, and functional diversity of phenolic aerogels, current research mainly focuses on single or binary systems. The design, synthesis, and synergistic mechanism research of ternary and multi-component systems are still in their early stages. Especially under extreme high-temperature environments, the long-term stability of the materials, the uniform dispersion of elements, and the optimization of the balance between multifunctionality remain the core challenges for achieving large-scale applications in hypersonic vehicles, deep space exploration, and other fields. Summary of the Invention

[0009] To address the limitations of existing technologies, such as the single function of materials, the inability to simultaneously achieve extreme thermal protection, mechanical elasticity, and efficient electromagnetic shielding, as well as the trade-offs in mechanical properties and the irreversible nature of static performance in traditional materials, this invention synergistically modifies phenolic resin (PR) by introducing polyborosilazane (PBSZ) and tetrabutyl titanate (TBT), and constructs a triple-crosslinked interpenetrating network structure using a high-temperature resistant fiber preform as a rigid reinforcing skeleton. This design solves the problems of dispersion and interfacial compatibility of inorganic fillers in the resin matrix, and simultaneously achieves thermal response conversion of material properties through molecular structure design. The composite material prepared by this invention not only possesses ultra-lightweight, high elasticity, efficient thermal insulation, and excellent ablation resistance, but also transforms in situ into a carbon-ceramic composite material with excellent electromagnetic shielding performance after exposure to extreme high temperatures, thus achieving multifunctional integrated design.

[0010] This invention is achieved through the following technical solution: The first objective of this invention is to provide a method for preparing fiber-reinforced Si-B hybrid phenolic aerogel composite materials, comprising the following steps: (1) Under a protective atmosphere, methylvinyl dichlorosilane, dichloromethylsilane, hexamethyl dichlorosilane and boron trichloride were mixed and subjected to ammonolysis reaction. After heating to remove volatile products, PBSZ was obtained after cooling. (2) Dissolve phenolic resin in an organic solvent, add PBSZ and stir, then add hexamethyltetramine and stir to mix evenly to obtain Si-B phenolic resin precursor solution. (3) The high-temperature resistant fiber preform is immersed in the above-mentioned Si-B phenolic resin precursor solution and heated to cure. Then the cured wet gel composite material is immersed in an organic solvent for solvent exchange and finally dried to obtain fiber-reinforced Si-B hybrid phenolic aerogel composite material.

[0011] Furthermore, the protective gas mentioned in step (1) is nitrogen or argon.

[0012] Furthermore, in step (1), the molar ratio of methylvinyldichlorosilane and dichloromethylsilane is 1:0.5~1.5.

[0013] Furthermore, in step (1), the molar ratio of methylvinyldichlorosilane to boron trichloride is 1:3~6.

[0014] Furthermore, in step (1), the molar ratio of methylvinyldichlorosilane and hexamethyldichlorosilane is 1:0.5~1.5.

[0015] Furthermore, the temperature of the ammonolysis reaction in step (1) is -20 ~ -15℃, and the time is 10-18h.

[0016] Furthermore, in step (1), the heating is carried out at 100~220℃ for 2~10h.

[0017] Specifically, in step (1), the heating is carried out by heating the temperature to 100~130℃ and holding it for 2-4 hours, then heating it to 180~220℃ and holding it for 2-4 hours, with a heating rate of 1-5℃ / min.

[0018] Furthermore, the organic solvent in step (2) includes one or more of ethylene glycol, ethanol, methanol, isopropanol, toluene, and xylene.

[0019] Furthermore, in step (2), the concentration of phenolic resin in the Si-B phenolic resin precursor solution is 5~15wt%.

[0020] Furthermore, in step (2), the amount of PBSZ added is 10 to 80 wt% of the mass of the solute (PR + PBSZ).

[0021] Preferably, the amount of PBSZ added in step (2) is 40-50 wt% of the mass of the solute (PR+PBSZ).

[0022] Furthermore, in step (2), the proportion of organic solvent in the Si-B phenolic resin precursor solution is 50~90wt%.

[0023] Furthermore, in step (2), the amount of hexamethyltetramine added is 1 to 5 wt% of the phenolic resin mass.

[0024] Furthermore, the material of the high-temperature resistant fiber preform in step (3) includes one or two of the following high-performance fibers as reinforcing fibers: aluminosilicate fiber, carbon fiber felt, glass fiber, quartz fiber, mullite fiber, aramid fiber, and polyimide fiber.

[0025] Furthermore, the impregnation process in step (3) can be carried out by vacuum circulation; the vacuum circulation is to evacuate to -0.1 MPa and maintain it for 5 to 15 minutes before restoring it to normal pressure; the number of vacuum circulations is 3 to 7 times until complete impregnation.

[0026] Furthermore, in step (3), the heating and curing process involves heating at 100~110°C for 0.5~2 hours, at 120~130°C for 2~4 hours, at 140~160°C for 2~4 hours, and at 170~210°C for 1~3 hours.

[0027] Furthermore, the organic solvent in step (3) includes ethanol or acetone.

[0028] Furthermore, in step (3), the solvent exchange process involves soaking in an organic solvent for 40 to 60 hours, during which the organic solvent is replaced every 5 to 10 hours to continue soaking.

[0029] Furthermore, the drying process in step (3) includes vacuum drying and heat drying.

[0030] The second objective of this invention is to provide a method for preparing fiber-reinforced Ti-Si-B hybrid phenolic aerogel composite materials, comprising the following steps: S1. Under a protective atmosphere, methylvinyldichlorosilane, dichloromethylsilane, hexamethyldichlorosilane and boron trichloride are mixed and subjected to ammonolysis. After heating to remove volatile products, the mixture is cooled to obtain PBSZ. S2. Dissolve phenolic resin in an organic solvent, add PBSZ obtained in step S1 and stir, then add tetrabutyl titanate, then add hexamethyltetramine and stir to mix evenly to obtain Ti-Si-B phenolic resin precursor solution. S3. The reinforcing fibers are impregnated in the above-mentioned Ti-Si-B phenolic resin precursor solution and cured by heating. Then, the cured reinforcing fibers are immersed in ethanol for organic solvent exchange and finally dried to obtain fiber-reinforced Ti-Si-B hybrid phenolic aerogel composite material.

[0031] Furthermore, the protective gas mentioned in step S1 is nitrogen or argon.

[0032] Furthermore, in step S1, the molar ratio of methylvinyldichlorosilane to dichloromethylsilane is 1:0.5~1.5.

[0033] Furthermore, in step S1, the molar ratio of methylvinyldichlorosilane to boron trichloride is 1:3~6.

[0034] Furthermore, in step S1, the molar ratio of methylvinyldichlorosilane to hexamethyldichlorosilane is 1:0.5~1.5.

[0035] Furthermore, the ammonolysis reaction in step S1 is carried out at a temperature of -20 ~ -15℃ for 10-18 hours.

[0036] Furthermore, in step S1, the heating is carried out at 100~220℃ for 2~10 hours.

[0037] Specifically, in step S1, the heating process involves heating the temperature to 100~130℃ and holding it for 2-4 hours, then heating it to 180~220℃ and holding it for 2-4 hours, with a heating rate of 1-5℃ / min.

[0038] Furthermore, the organic solvent in step S2 includes one or more of ethylene glycol, ethanol, methanol, isopropanol, toluene, and xylene.

[0039] Furthermore, in step S2, the concentration of phenolic resin in the Ti-Si-B phenolic resin precursor solution is 5~15wt%.

[0040] Furthermore, in step S2, the amount of PBSZ added is 10-80 wt% of the mass of the solute (PR+PBSZ).

[0041] Preferably, the amount of PBSZ added in step S2 is 40-50 wt% of the mass of the solute (PR+PBSZ).

[0042] Furthermore, in step S2, the proportion of organic solvent in the Ti-Si-B phenolic resin precursor solution is 50~90wt%.

[0043] Furthermore, in step S2, the amount of tetrabutyl titanate added is 5 to 30 wt% of the solute (PR+PBSZ+TBT).

[0044] Preferably, the amount of tetrabutyl titanate added in step S2 is 10-15 wt% of the solute (PR+PBSZ+TBT).

[0045] Furthermore, in step S2, the amount of hexamethyltetramine added is 1 to 5 wt% of the phenolic resin mass.

[0046] Furthermore, the material of the high-temperature resistant fiber preform in step S3 includes one or two of the following high-performance fibers as reinforcing fibers: aluminosilicate fiber, carbon fiber felt, glass fiber, quartz fiber, mullite fiber, aramid fiber, and polyimide fiber.

[0047] Furthermore, the impregnation process in step S3 can be performed by vacuum cycling; the vacuum cycling is to evacuate to -0.1 MPa and maintain it for 5 to 15 minutes before restoring it to normal pressure; the number of vacuum cycles is 3 to 7 times until complete impregnation.

[0048] Furthermore, in step S3, the heating and curing process involves heating at 100~110°C for 0.5~2 hours, at 120~130°C for 2~4 hours, at 140~160°C for 2~4 hours, and at 170~210°C for 1~3 hours.

[0049] Furthermore, the organic solvent in step S3 includes ethanol or acetone.

[0050] Furthermore, the solvent exchange process in step S3 involves soaking in an organic solvent for 40 to 60 hours, during which the organic solvent is replaced every 5 to 10 hours to continue soaking.

[0051] Furthermore, the drying process in step S3 includes vacuum drying and heat drying.

[0052] The third objective of this invention is to provide a method for preparing fiber-reinforced Ti-Si-B hybrid carbon aerogel composite materials, wherein the preparation method is based on the preparation method of the second objective, with the following additional steps: The obtained fiber-reinforced Ti-Si-B hybrid phenolic aerogel composite material was heated to 700-1500℃ at a heating rate of 2-5℃ / min under an inert atmosphere and held at that temperature for 0.5-3h for high-temperature carbonization treatment, finally obtaining fiber-reinforced Ti-Si-B hybrid carbon aerogel composite material.

[0053] Furthermore, the inert atmosphere includes nitrogen, argon, and xenon.

[0054] A fourth objective of the present invention is to provide a fiber-reinforced Ti-Si-B hybrid carbon aerogel composite material obtained by the preparation method of the third objective.

[0055] The fifth objective of this invention is to provide the application of the fiber-reinforced Ti-Si-B hybrid phenolic aerogel composite material or the fiber-reinforced titanium-silicon-boron hybrid carbon aerogel composite material in integrated thermal protection-structure-function components in the aerospace field.

[0056] Beneficial effects Synergistic Enhancement: This invention utilizes polyborosilazane (PBSZ) and tetrabutyl titanate (TBT) to synergistically modify phenolic resin (PR), and uses high-temperature resistant fiber felt as a reinforcing skeleton. By constructing a triple cross-linked interpenetrating network structure, a fiber-reinforced titanium-silicon-boron hybrid phenolic aerogel composite material is prepared. PBSZ constructs a flexible secondary cross-linked network through BOC and Si-OC covalent bonds, while TBT constructs a rigid tertiary reinforcing phase through Ti-OC coordination bonds and Ti-O-Ti nanoclusters. These components form a multi-scale synergistic effect with the main network of phenolic resin and the fiber skeleton, achieving high compressive strength and interfacial bonding strength between the organic and inorganic phases. This increases the compressive strength to over 8 MPa and the strain value to over 60%, effectively solving the problems of high brittleness, limited functionality, and performance degradation at high temperatures in traditional aerogel materials.

[0057] Comprehensive performance: The composite material obtained by this invention integrates ultra-lightweight, high elasticity, high-efficiency heat insulation, excellent ablation resistance and excellent electromagnetic shielding performance. It can achieve high mechanical properties while maintaining excellent electromagnetic interference shielding performance. Moreover, it can undergo thermally driven in-situ phase change under extreme high temperature environment, realizing the functional transformation from "elastic heat insulation body" to "robust electromagnetic shielding body". It breaks through the technical bottleneck of traditional materials that are difficult to balance mechanical properties, thermal protection performance and electromagnetic function. Attached Figure Description

[0058] Figure 1 The image shows the FTIR spectrum of the aerogel composite material.

[0059] Figure 2 The XPS spectra of T1-BS4-PRA aerogel are shown in (a) for the full spectrum, (b) for c1s, (c) for o1s, (d) for b1s, (e) for si2p, and (f) for ti2p.

[0060] Figure 3 The compressive stress-strain (σ-ε) curves of BS-PRf composites with different PBSZ contents are shown.

[0061] Figure 4(a) FTIR spectra at different depths after T-BS-PRf ablation, (b) XRD spectra at different depths, (c) magnified XRD view of the ablated surface.

[0062] Figure 5 The top image is a SEM image of the ablated surface, and the bottom image is an EDS image.

[0063] Figure 6 (a) shows the EMI SE and frequency curves of carbon aerogel composite material in the X-band (8.2-12.4 GHz, 1 cm thickness), and (b) shows the average SET, SEA, and SER.

[0064] Figure 7 (a) shows the absorption (A) and reflection (R) coefficients of the carbon aerogel composite in the X-band (12.4–18 GHz, 1 cm thickness), and (b) shows the EMI SE and thickness compared with the reported composite.

[0065] Figure 8 (a) shows the compressive stress-strain (σ-ε) curve of the carbon aerogel composite material, and (b) shows the maximum strain and fracture strength.

[0066] Figure 9 The image shows the XRD pattern of the carbon aerogel composite material.

[0067] Figure 10 The Raman spectrum of Cf is shown.

[0068] Figure 11 The Raman spectrum of BS4-Cf is shown.

[0069] Figure 12 The Raman spectrum of T1-BS4-Cf is shown.

[0070] Figure 13 The Raman spectrum of T2-BS4-Cf is shown.

[0071] Figure 14 The Raman spectrum of T3-BS4-Cf is shown. Detailed Implementation Plan The technical solution of the present invention will be described in detail below with reference to specific embodiments. In the following embodiments, unless otherwise specified, the reagents, materials and equipment used can be purchased commercially, prepared by conventional methods, or commonly used in the industry.

[0072] Source of raw materials Phenolic resin (PR, analytical grade) and methyl vinyl dichlorosilane (MVDCS, analytical grade) were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; hexamethyldisilazane (HMDZ, analytical grade), dichloromethylsilane (MDCS, analytical grade), boron trichloride (BTC, analytical grade), and tetrabutyl titanate (TBT, analytical grade) were purchased from China Anaiji Chemical Co., Ltd.; ethylene glycol (EG, analytical grade) and ethanol (GA, analytical grade) were purchased from Sinopharm Chemical Reagent Co., Ltd.; and needle-punched aluminosilicate fiber felt (AF) was purchased from Langfang Debin Environmental Protection Technology Co., Ltd.

[0073] Test methods Fourier transform infrared spectroscopy (FTIR): using a Nicolet 6700 spectrometer (Thermo Electron, USA) in the range of 400-4000 cm⁻¹. -1 Characterize the chemical structure of the sample within a specified range.

[0074] X-ray photoelectron spectroscopy (XPS): performed on an ESCALAB MK-II instrument (VG Scientific, UK), with all spectra charged to the C 1s peak (284.8 eV).

[0075] Field emission scanning electron microscope (FESEM) and energy dispersive spectroscopy (EDS): Hitachi SU-8100 FESEM was used to observe microstructure and elemental distribution.

[0076] Bulk density and shrinkage rate: Bulk density is calculated by mass-to-volume ratio; volume shrinkage rate S = (V0 - Vd) / V0 × 100%, where V0 and Vd are the initial and dried volumes, respectively.

[0077] Mechanical properties: Compression tests were conducted using an Instron 3385H electronic universal testing machine at a loading rate of 0.5 mm / min. Elastic recovery rate Re = hr / h0 × 100%, where h0 and hr are the initial height and recovered height, respectively.

[0078] Thermogravimetric analysis (TGA): Using a Q500 thermogravimetric analyzer (TA Instruments, USA) under N2 atmosphere, the temperature was increased from room temperature to 800°C at a rate of 20°C / min.

[0079] Thermal insulation performance: Thermal conductivity was measured using a TC3000E thermal conductivity meter (Xi'an Xiaxi). The back temperature was recorded using a Hikmicro H16 Pro infrared thermal imager, with a heating platform and an alcohol burner as the heat source.

[0080] Ablation performance: Ablation tests were conducted using a butane flame. Mass ablation rate Rm = (M0 - Ma) / t, linear ablation rate Rl = (L0 - La) / t, where M0, Ma and L0, La are the mass and thickness before and after ablation, respectively, and t is the time.

[0081] Electromagnetic interference shielding performance (EMI SE): Measured in the X-band (8.2-12.4 GHz) using an Agilent E5071C vector network analyzer via the waveguide method.

[0082] Example 1: Preparation of fiber-reinforced Si-B modified phenolic aerogel composite material (1) In a three-necked flask under N2 protection, methylvinyl dichlorosilane (MVDCS), dichloromethylsilane (MDCS), hexamethyl dichlorosilane (HMDZ), and boron trichloride (BTC) were subjected to ammonolysis at -20°C for 4 hours in a molar ratio of 1:1:6:1. The mixture was then gradually heated to room temperature and further heated to 200°C to remove volatile byproducts. After cooling to room temperature, a viscous liquid PBSZ was obtained.

[0083] (2) Dissolve 10g of phenolic resin (PR) in 90g of ethylene glycol (EG) to prepare a 10 wt% PR solution. Then, add PBSZ at 0-70 wt% of the total mass of solute (PR+PBSZ), and sonicate at 60°C for 40 minutes to allow it to react and mix fully, forming a homogeneous boron-silicon phenolic resin precursor (BS-PR) solution. Finally, add 0.2g of hexamethyltetramine (HMTA) as a catalyst and stir thoroughly to mix evenly.

[0084] (3) The needle-punched aluminum silicate fiber felt (AF) was immersed in the above-mentioned BS-PR precursor solutions with different ratios and placed in a polytetrafluoroethylene mold. Then, five vacuum cycles (10 minutes each) were performed to ensure that the precursor solution fully penetrated into the fiber felt.

[0085] (4) After sealing the mold, perform step heating curing: heat at 100°C for 1 hour, at 120°C for 3 hours, at 150°C for 3 hours, and at 180°C for 2 hours.

[0086] (5) Demold the cured wet gel and immerse it in ethanol for solvent exchange. Replace the ethanol every 8 hours for 6 times. Finally, obtain the final fiber-reinforced Si-B hybrid phenolic aerogel composite material by vacuum drying, denoted as BSx-PRf (x=1 to 7).

[0087] The obtained fully bio-based epoxy resin composite material was subjected to performance testing, and the test results are shown in Table 1 below: Table 1

[0088] The results show FTIR analysis confirmed the presence of C=C skeleton vibrations in the aromatic ring of the phenolic skeleton (1600 cm⁻¹). -1 After the introduction of PBSZ, the transition from BS4-PRA to BS6-PRA occurred at 1352 cm⁻¹. -1 The presence of characteristic B–O–C peaks indicates that boron forms a covalent bond with the phenolic skeleton; simultaneously, Si–CH3 and Si–O–C related peaks (1230, 1100 cm⁻¹) are observed. -1 This confirmed the covalent interface between the silicon-oxygen chain and the phenolic group. Furthermore, 1148 cm⁻¹ - The Si–O–Si vibration at position ¹ indicates the formation of a permeable inorganic reinforcing phase. XPS results systematically show that PBSZ constructs a flexible cross-linked network in the phenolic system through B–O–C and Si–O–C bonds, while some Si–N bonds are retained, forming a secondary reinforcing phase together with the formed Si–O–Si network. This provides direct evidence for the realization of a rigid-flexible coupled interfacial structure in the material. In summary, FTIR and XPS characterization confirm the successful synthesis of PBSZ and its covalent bonding (BOC, Si-OC) with phenolic resin.

[0089] With increasing PBSZ content, the bulk density of the composite material decreased significantly, and the volume shrinkage rate decreased sharply before stabilizing. When the PBSZ content reached approximately 40% (BS4-PRf), the composite material achieved an ultra-low density (approximately 0.204–0.210 g / cm³). 3 The low shrinkage rate (approximately 2.41–2.53%) indicates that the flexible cross-linked network of PBSZ effectively inhibits skeletal shrinkage and promotes the formation of nanopores.

[0090] Mechanical tests showed that the PRf composite material underwent brittle fracture at a stress of 24 MPa and a strain of 60%. The addition of PBSZ significantly altered the material's mechanical properties; the breaking stress and strain of BS1-PRf increased to 38 MPa and 74%, respectively, indicating that the flexible network of PBSZ effectively enhanced the matrix toughness. With increasing PBSZ content (from BS2-PRf to BS4-PRf), the breaking strain further increased to 77%-80%, with BS4-PRf reaching a maximum breaking stress of 39 MPa, demonstrating that crosslinking density optimized the balance between toughness and strength. When the PBSZ content continued to increase (from BS5-PRf to BS7-PRf), the composite material maintained structural integrity at 80% strain without fracture, with BS5-PRf exhibiting a stress of 34 MPa and BS7-PRf 29 MPa, indicating good compressive stability. However, excessive PBSZ addition also led to a gradual decrease in the maximum stress, suggesting that excessive flexible phase weakens the material's rigid load-bearing capacity. Furthermore, the introduction of PBSZ fundamentally alters the material's response mechanism, transforming it from brittle fracture of PRf to highly elastic deformation. The elastic recovery rate increases significantly with the amount of PBSZ added, with BS4-PRf achieving a recovery rate as high as 93.09% at 50% strain. Simultaneously, the maximum compressive stress reaches a peak of 1.97 MPa with BS4-PRf; excessive PBSZ slightly sacrifices rigidity due to the excessive flexible phase.

[0091] With increasing PBSZ content, the thermal conductivity of the composite material decreased significantly, reaching a minimum of 0.0526 W / (m·K) when the PBSZ content reached approximately 40% (BS4-PRf). This is attributed to the formation of a nanoparticle stack structure by the flexible cross-linked network of PBSZ, which significantly prolonged the phonon transport path and limited solid-phase heat conduction. However, when excessive PBSZ was added, the thermal conductivity showed an increasing trend. This may be because excessive PBSZ induced molecular chain entanglement, shortening the effective phonon scattering path, and may also partially block the pores, weakening the Knudsen effect.

[0092] Therefore, it can be considered that when the amount of PBSZ added reaches about 40% to 50% (BS4-PRf to BS5-PRf), the composite material exhibits good comprehensive performance in terms of lightweight, low shrinkage, high elasticity and excellent thermal insulation properties.

[0093] Example 2: Preparation of fiber-reinforced T-Si-B hybrid phenolic aerogel composite material (1) The synthesis of PBSZ is the same as in Example 1.

[0094] (2) Based on the optimized PBSZ addition amount (40 wt%, i.e., BS4 formulation), 10 g of phenolic resin was dissolved in 90 g of ethylene glycol to prepare a 10 wt% PR solution. Subsequently, 6.67 g of PBSZ was added, and the mixture was ultrasonically stirred at 60 °C for 40 minutes to obtain a BS-PR precursor solution. Then, tetrabutyl titanate (TBT) at a mass of 10~30 wt% relative to the total mass of the solute (PR+PBSZ+TBT) was added dropwise to the BS-PR precursor solution to initiate coordination and self-assembly, forming a T-BS-PR precursor solution. Finally, 0.2 g of HMTA catalyst was added and mixed thoroughly.

[0095] (3) to (5) are the same as in Example 1, using aluminum silicate fiber felt (AF) to finally obtain T-BS-PRf composite material, denoted as Ty-BS4-PRf (y=1, 2, 3).

[0096] The obtained T-BS-PRf composite material was subjected to performance testing, and the test results are shown in Table 2 below: Table 2

[0097] The results show FTIR analysis showed that after introducing TBT, the T-BS-PRA was obtained at 600 cm⁻¹. -1 A broad peak at 925 cm⁻¹ corresponds to the stretching vibration of Ti-O-Ti, confirming the formation of TiO₂ nanoclusters. Furthermore, a distinct new peak appears at 925 cm⁻¹, which is attributed to the interaction of phenolic CO groups and Ti. 4+ The characteristic coordination bonds between (Ti-O-C) provide direct evidence for the covalent interfacial bonds between the titanium dioxide nanoclusters and the phenolic framework. XPS analysis detected the characteristic Ti 2p peak in the T-BS-PRf spectrum, and fitted the Ti-O-Ti and CO-Ti peaks in the O 1s spectrum, confirming the successful introduction of TiO2 nanoclusters and their coordination effect with the phenolic framework (third network).

[0098] By introducing TBT after optimizing the amount of PBSZ added, the bulk density of the ternary composite system (T-BS-PRf) was maintained at 0.203–0.210 g / cm³. 3 The ultra-low level is comparable to that of the binary BS4-PRf system. In the early stage, the volume shrinkage rate of the titanium-doped (T1-BS4-PRf) increased slightly to 3.42% due to the disturbance of the sol-gel process; however, as the TBT content increased (T2 / T3-BS4-PRf), the shrinkage rate dropped back to about 2.53–2.57%, indicating that the TiO2 nanoclusters are uniformly dispersed in the framework through CO-Ti bonds, and their rigidity enhancement effect complements the flexible cross-linked network, realizing an ultra-stable hierarchical porous structure with controllable shrinkage rate.

[0099] Compression test results show that the binary system BS4-PRf, after the introduction of 40% PBSZ, achieved a good balance between elasticity (92.18% recovery rate) and strength (1.97 MPa). Furthermore, the introduction of 10% TBT to form a ternary system (T1-BS4-PRf) successfully achieved a synergistic improvement in both strength and elasticity: while maintaining an ultra-high elastic recovery rate of 92.34%, both compressive modulus and strength remained at excellent levels (modulus 2.39 GPa, strength 1.88 GPa). This demonstrates that TiO2 nanoclusters, as rigid reinforcing elements, effectively strengthen the cross-linked network without sacrificing, and even further optimize, the material's elasticity, thus compensating for the insufficient strength of purely flexible networks.

[0100] The introduction of TBT has a slight effect on thermal conductivity. The thermal conductivity of T1-BS4-PRf (0.0559 W / (m·K)) is slightly higher than that of BS4-PRf (0.0526 W / (m·K)). This is mainly attributed to the solid-phase thermal conductivity of TiO2 nanoclusters. However, its value is still better than that of traditional ceramic fiber felt, and the infrared shielding ability enhanced by TiO2 compensates for the conduction loss.

[0101] The introduction of TBT significantly improved the ablation resistance. After ablation at 1300°C in a butane flame for 30 minutes, T1-BS4-PRf exhibited extremely low linear ablation rate (0.00279 mm / s) and mass ablation rate (0.00152 g / s). FTIR, XRD, and SEM-EDS analyses of the ablated samples showed that the organic components decomposed during heating, promoting material densification and amorphous network shrinkage. Under continuous ablation, Si–O–C transformed into Si–O–Si, forming a glassy phase. Simultaneously, boron catalyzed phenolic carbonization promoted the formation of ordered graphite microcrystals. Anatase TiO2 and β-SiC crystal phases also formed on the surface, indicating that the material ultimately transformed into a carbon / ceramic composite structure. SEM / EDS analysis showed that the fiber skeleton remained intact after ablation, with approximately 200 μm blocky aerogel monomers forming within the voids. These monomers had ~5 μm spherical TiO2 particles and a B2O3–SiO2 glassy phase distributed on their surface. The material surface forms a dense ceramic layer composed of anatase TiO2, B2O3-SiO2 glass phase and β-SiC, which is the fundamental reason for its excellent ablation resistance.

[0102] Therefore, it can be considered that when the TBT addition is about 10% (T1-BS4-PRf), the composite material significantly improves its ablation resistance and maintains excellent thermal insulation while maintaining ultra-low density and good elasticity, thus exhibiting the best overall performance balance.

[0103] Example 3: Preparation of carbon aerogel composite materials and their electromagnetic shielding and mechanical properties The BS4-PRf and Ty-BS4-PRf composite materials obtained in Examples 1 and 2 were heated to 1000℃ at a rate of 5℃ / min and held at that temperature for 1h for high-temperature pyrolysis conversion, and finally the corresponding carbon aerogel composite materials were obtained, which were labeled as BS4-Cf and Ty-BS4-Cf, respectively.

[0104] And prepare samples Cf and T1-Cf according to the following steps: Cf: The PRf in Example 1 is heated to 1000℃ at a rate of 5℃ / min and held at that temperature for 1 hour to carry out high-temperature pyrolysis conversion; T1-Cf: 10g of phenolic resin was dissolved in 90g of ethylene glycol to prepare a 10 wt% PR solution. Then, 1.11g of TBT was added, and the mixture was ultrasonically stirred at 60℃ for 40 minutes to obtain the T1-PR precursor solution. Finally, 0.2g of HMTA catalyst was added and mixed evenly. The curing-washing-drying steps were the same as those in Example 1 (3) to (5), and aluminum silicate fiber felt (AF) was used to finally obtain the T-PRf composite material. The temperature was then increased to 1000℃ at a rate of 5℃ / min and held for 1h for high-temperature pyrolysis conversion to finally obtain the T1-Cf composite material.

[0105] The obtained carbon aerogel composite material was subjected to performance testing, and the test results are shown in Table 3 below: Table 3

[0106] The results show After high-temperature carbonization, all samples exhibited excellent electromagnetic interference shielding performance in the X-band (8.2-12.4 GHz, 1 cm thickness), with absorption loss (SEA) being the main contributor to the total shielding effectiveness (SET) (accounting for over 89.6%), indicating that the material employs an absorption-dominated shielding mechanism. After PBSZ modification, the SET of BS4-Cf increased by 19.0% compared to unmodified Cf, reaching 89.3 dB, thanks to the flexible cross-linked network of PBSZ promoting polarization relaxation. Further introduction of TBT to form a ternary system (T-BS-Cf) further improved the SET to 91.8-92.8 dB, with SEA contributing over 92.5%. Simultaneously, the reflection coefficient (R) decreased from 83% for BS0-Cf to 77% for T1-BS4-Cf, indicating that titanium incorporation optimized the impedance matching at the material-air interface, allowing more electromagnetic waves to enter the material and be absorbed, thereby improving shielding efficiency.

[0107] This superior shielding performance extends into the Ku band (12.4–18 GHz, 1 cm thickness), with SET values ​​of 70.0, 80.0, and 88.0 dB for Cf, BS4-Cf, and T1-BS4-Cf, respectively. This is consistent with the trend in the X band and reflects the effectiveness of PBSZ and TBT modifications. Furthermore, the absorption coefficient (A) gradually increases from 0.26 (Cf) to 0.32 (T1-BS4-Cf), while the reflectivity (R) decreases accordingly. This trend indicates that impedance matching and absorption dominance mechanisms are also improved over a wider frequency range (Ku band).

[0108] Furthermore, the effect of sample thickness on shielding performance was investigated. Reducing the sample thickness from 1 cm to 4 mm resulted in a decrease in the shielding effectiveness of the optimal sample, T1-BS4-Cf, primarily due to the shortened absorption path of electromagnetic waves within the material. Specifically, in the X-band, the shielding effectiveness decreased from 92.8 dB at 10 mm thickness to 71.7 dB at 4 mm thickness; in the Ku-band, it decreased from 88.0 dB to 60.4 dB. Although this trend of performance degradation with decreasing thickness is expected, the composite material still exhibits excellent shielding effectiveness even when thinned to 4 mm. In conclusion, this composite material demonstrates superior broadband (X-band and Ku-band) shielding capabilities, which are maintained even with reduced thickness. This further confirms its significant advantages and potential for practical applications.

[0109] The mechanical properties of the carbonized composite material underwent a significant transformation compared to the unmodified elastomer, exhibiting characteristics of ceramic-carbon materials. However, the structural integrity, superior to the unmodified system, was maintained through modification with PBSZ and TBT. Unmodified Cf exhibited typical brittle fracture, with low compressive strength (2.37 MPa) and minimal fracture strain (9.03%). After introducing PBSZ, BS4-Cf achieved a 98% increase in strength (reaching 4.7 MPa) and a strain exceeding 57.44% through the retained B–O–C / Si–O–C network memory effect. The appropriately titanium-doped T1-BS4-Cf achieved peak compressive strength (8.62 MPa) and excellent strain (66.59%), attributed to the reinforcing synergy between TiO2 nanoclusters and the carbon framework.

[0110] Microstructural analysis using XRD and Raman spectroscopy revealed that all carbonized samples exhibited a broad peak at approximately 25° on the graphite (002) crystal plane. After the introduction of PBSZ and TBT, the D-band to G-band intensity ratio (ID / IG) in the Raman spectra decreased from 3.72 for Cf to 3.44 for BS4-Cf, and further to 3.32 for T1-BS4-Cf. This indicates that boron atoms in PBSZ have a catalytic graphitization effect, while Ti atoms in TBT... 4+It inhibited the formation of defects during the pyrolysis process and jointly promoted the growth of sp. 2 The increased orderliness of the carbon domain. More ordered graphite microcrystals act as effective electron transport channels, improving electrical conductivity and thus enhancing electromagnetic wave reflection and absorption losses. Simultaneously, this enhanced ordered structure also contributes to the mechanical properties of the material after carbonization.

[0111] Therefore, it can be considered that the T1-BS4-Cf carbon aerogel composite material obtained by synergistic modification of PBSZ with an appropriate amount of TBT (about 10%) and high-temperature carbonization achieves the best balance in terms of electromagnetic interference shielding effectiveness (with both high absorption and low reflection characteristics) and mechanical robustness, demonstrating great potential as a high-performance lightweight electromagnetic shielding material.

[0112] In summary, considering the balance of lightweight, elasticity, thermal insulation, and ablation resistance, the T1-BS4-PRf composite material in Example 2 exhibits the best overall performance.

[0113] The embodiments provided above are not intended to limit the scope of the invention, nor are the described steps intended to limit the order of execution. Any obvious modifications made to the invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined by the claims.

Claims

1. A method for preparing a fiber-reinforced Ti-Si-B hybrid phenolic aerogel composite, characterized in that, The method comprises the following steps: S1, mixing methylvinyl dichlorosilane, dichloromethylsilane, hexamethyldichlorosilane and boron trichloride in a protective atmosphere, and then performing an ammonolysis reaction, and then removing volatile products by heating, and then cooling to obtain PBSZ; The molar ratio of methylvinyl dichlorosilane to dichloromethylsilane is 1:0.5-1.5; the molar ratio of methylvinyl dichlorosilane to boron trichloride is 1:3-6; and the molar ratio of methylvinyl dichlorosilane to hexamethyldichlorosilane is 1:0.5-1.5; S2, dissolving the phenolic resin in an organic solvent, adding the PBSZ obtained in step S1, stirring, then adding tetrabutyl titanate, and then adding hexamethyltetramine, and then stirring to obtain a Ti-Si-B phenolic resin precursor solution; The concentration of the phenolic resin in the Ti-Si-B phenolic resin precursor solution is 5-15wt%; the addition amount of the PBSZ is 10-80wt% of the mass of the phenolic resin and the PBSZ; and the addition amount of the tetrabutyl titanate is 5-30wt% of the mass of the phenolic resin, the PBSZ and the tetrabutyl titanate; S3, immersing the reinforcing fibers in the Ti-Si-B phenolic resin precursor solution, performing heat curing, then immersing the cured reinforcing fibers in ethanol to perform solvent exchange, and finally drying to obtain fiber-reinforced Ti-Si-B hybrid phenolic aerogel composite materials.

2. The production method according to claim 1, characterized by, The temperature of the ammonolysis reaction in step S1 is -20 to -15°C, and the time is 10-18h; and the heating is performed at 100-220°C for 2-10h.

3. The preparation method according to claim 1, characterized in that, The addition amount of the PBSZ in step S2 is 40-50wt% of the mass of the phenolic resin and the PBSZ.

4. The preparation method according to claim 1, characterized in that, The addition amount of the tetrabutyl titanate in step S2 is 10-15wt% of the mass of the phenolic resin, the PBSZ and the tetrabutyl titanate.

5. The preparation method according to claim 1, characterized in that, The addition amount of the hexamethyltetramine in step S2 is 1-5wt% of the mass of the phenolic resin.

6. The preparation method according to claim 1, characterized in that, The material of the high-temperature resistant fiber preform in step S3 comprises one or two of high-performance fibers such as aluminum silicate fibers, carbon fiber mats, glass fibers, quartz fibers, mullite fibers, aramid fibers and polyimide fibers.

7. The preparation method according to claim 1, characterized in that, The heat curing in step S3 is heating at 100-110°C for 0.5-2h, heating at 120-130°C for 2-4h, heating at 140-160°C for 2-4h, and heating at 170-210°C for 1-3h.

8. The preparation method according to claim 1, characterized in that, The solvent exchange in step S3 is soaking in an organic solvent for 40-60h, wherein the organic solvent is replaced every 5-10h to continue the soaking; and the organic solvent comprises ethanol or acetone.

9. A method for preparing a fiber-reinforced Ti-Si-B hybrid carbon aerogel composite, characterized by, The preparation method is as follows: The fiber-reinforced Ti-Si-B hybrid phenolic aerogel composite material prepared by the preparation method of any one of claims 1-8 is heated to 700-1500°C at a heating rate of 2-5°C / min under the protection of an inert atmosphere, and is kept at the temperature for 0.5-3h to perform high-temperature carbonization treatment, and finally a fiber-reinforced Ti-Si-B hybrid carbon aerogel composite material is obtained.

10. A fiber-reinforced Ti-Si-B hybrid carbon aerogel composite, characterized by, The fiber-reinforced Ti-Si-B hybrid carbon aerogel composite material is prepared by the preparation method of claim 9.

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