A high-temperature heat protection sandwich structure with phase change heat absorption and skeleton support

Abstract

This invention belongs to the field of aircraft thermal protection technology, and specifically relates to a phase-change heat-absorbing high-temperature thermal protection sandwich structure with a skeleton support. The sandwich structure, from the outside to the inside, includes an outer thermal protection layer, a skeleton support-functional filling layer, and an inner thermal protection layer. Both the outer and inner thermal protection layers are made of ablation-resistant ultra-high-temperature ceramic matrix composite materials coated with an anti-oxidation and anti-ablation coating, providing structural load-bearing capacity and thermal insulation protection, ensuring overall mechanical integrity and high-temperature stability. The skeleton support-functional filling layer includes a spatial support skeleton and a functional filling layer. The spatial support skeleton is rigidly connected to the inner surfaces of the outer and inner thermal protection layers along the entire contact length. The functional filling layer is made of hydrogel, metal-organic framework, and phenolic resin, and fills a closed cavity formed by the spatial support skeleton, the outer thermal protection layer, and the inner thermal protection layer. This invention improves the thermal protection performance and service life of hypersonic aircraft.

Description

Technical Field

[0001] This invention belongs to the field of aircraft thermal protection technology, and specifically relates to a phase change heat absorption type high temperature thermal protection sandwich structure with skeleton support. Background Technology

[0002] Hypersonic vehicles and reentry vehicles currently operate under extremely complex thermal environments, with surface temperatures reaching thousands of degrees Celsius in a short period. The high-temperature heat flux generated by aerodynamic heating is characterized by its transient nature, large gradient, and uneven distribution, making it difficult for traditional single-material protection systems to simultaneously meet the comprehensive requirements of heat absorption, insulation, and structural strength. Most existing thermal protection structures employ ceramic-based or phenolic-based ablation materials, relying on high-temperature carbonization or thermal barrier to achieve thermal protection. However, these structures generally suffer from severe heat accumulation, high thermal conductivity, and poor reusability. Furthermore, single-layer thermal insulation coatings or passive ablation layers lack adaptive adjustment capabilities in complex thermal environments, making it difficult to balance thermal protection and structural reliability, resulting in low overall efficiency and limited lifespan of the thermal protection system.

[0003] To address these issues, multi-layered gradient thermal protection structures have become a research hotspot in recent years. These structures typically achieve graded protection through an outer layer resisting high-temperature airflow, a middle layer insulating heat conduction, and an inner layer providing mechanical support. However, existing multi-layered structures are mostly static, passive systems, lacking the ability to actively respond to transient heat flows. This results in common technical problems in hypersonic vehicle thermal protection structures, such as slow thermal response, low thermal protection efficiency, and insufficient reusability. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a phase-change heat-absorbing high-temperature thermal protection sandwich structure with a skeletal support, which can solve the technical problems commonly found in existing hypersonic vehicle thermal protection systems, such as slow thermal response, low thermal protection efficiency, poor structural stability, and insufficient reusability. The present invention achieves an organic combination of structural load-bearing and active thermal management by introducing a spatial skeletal support system and a hydrogel-MOF-phenolic composite functional layer, allowing heat flow to be dispersed spatially and released gradually over time, thereby significantly improving thermal protection performance and service life.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: This invention provides a phase change heat-absorbing high-temperature thermal protection sandwich structure with a skeleton support. The sandwich structure includes, from the outside to the inside, an outer heat-protecting surface layer, a skeleton support-functional filling layer, and an inner heat-protecting surface layer. The outer and inner heat-protecting surface layers are both ultra-high temperature ceramic matrix composite materials coated with an anti-oxidation and anti-ablation coating, providing structural load-bearing and thermal insulation protection, ensuring overall mechanical integrity and high-temperature stability. The skeleton support-functional filling layer includes a spatial support skeleton and a functional filling layer. The spatial support skeleton is rigidly connected to the inner surfaces of the outer and inner heat-protecting surface layers along the entire contact length. The functional filling layer is made of hydrogel, metal-organic framework, and phenolic resin, and fills a closed cavity formed by the spatial support skeleton, the outer heat-protecting surface layer, and the inner heat-protecting surface layer.

[0006] Preferably, the outer heat-resistant surface layer is provided with multiple steam-conducting microchannels for releasing water vapor. These microchannels are connected to the sealed cavity to prevent interlayer bulging and delamination. The pore size of these steam-conducting microchannels is 50μm~300μm. When the pore size is too small, the flow resistance of the microchannels increases significantly and they are easily blocked by carbonized residues / ablation particles, making it difficult to release water vapor in time and easily causing interlayer bulging and delamination. When the pore size is too large, it will significantly weaken the mechanical strength of the outer heat-resistant surface layer and form obvious channels for heat leakage and oxidizing media intrusion. The spacing between the multiple steam-conducting microchannels is 5mm~15mm to facilitate the rapid release of water vapor and maintain pressure balance, further addressing the problem of insufficient reusability. The steam-conducting microchannels have a pressure-adaptive exhaust threshold characteristic. The exhaust threshold design is based on the critical saturated vapor pressure of the internal sealed cavity. Specifically, when the external heat load causes a phase change in the hydrogel within the functional filling layer, the pressure inside the cavity increases with the steam output. The pressure threshold for exhaust opening is set to 0.1MPa~0.3MPa. The selection of this threshold is based on the following criteria: the internal pressure must be sufficient to overcome the flow resistance of the microchannels, allowing water vapor to be discharged smoothly, while the pressure value must be lower than the shear failure threshold of the rigid interface connection.

[0007] Preferably, the mass fraction ratio of hydrogel dry matter, metal-organic framework, and phenolic resin in the functional filler layer is 10%–35%: 5%–20%: 45%–80%; the water content of the hydrogel is 50%–300% of the dry matter mass of the hydrogel. The mass percentage of hydrogel dry matter in the functional filler layer is limited to 10%–35% to control the amount of vapor production and volume change during phase change while providing sufficient latent heat of vaporization to avoid excessively high pressure peaks. The MOF content is limited to 5%–20% to form controllable microporous migration channels and improve the uniformity of water migration and the nucleation of aerogel pore structures. Too low a content makes it difficult to exert a regulatory effect, while too high a content easily introduces embrittlement and interface defects. The phenolic resin, as a continuous phase and high-temperature carbonization matrix, must ensure sufficient wetting and bonding between the hydrogel and MOF, as well as the residual structural strength after carbonization. Too low a content leads to insufficient support for molding and carbonization, while too high a content will compress the hydrogel proportion, thereby reducing the phase change heat absorption effect and potentially increasing heat conduction pathways. The water content of the hydrogel is limited to 50%–300% of its dry matter. If the water content is too low, the heat absorption capacity is insufficient; if the water content is too high, the phase change vapor production is too intense, the exhaust burden increases, and interlayer pressure instability may be induced. The functional filler layer, composed of 10%–35% hydrogel dry matter, 5%–20% metal-organic framework, and 45%–80% phenolic resin, can, to some extent, improve the problems of slow thermal response and low thermal protection efficiency.

[0008] Preferably, the spatial support skeleton is a three-dimensional lattice structure, honeycomb structure, through-pillar structure, or rib structure, used to connect the outer heat shield layer and the inner heat shield layer. All of the above structures can form a stable three-dimensional / two-dimensional load-bearing skeleton in the sandwich structure, providing a clear interlayer force transmission path and high specific stiffness, thereby suppressing core layer collapse and interface instability during the phase change heat absorption, water loss shrinkage, and high-temperature carbonization processes of the functional filling layer. At the same time, the above topological structure can form a connected pore / cavity network, which facilitates the filling of the functional filling layer by vacuum injection or in-situ polymerization, and provides channel conditions for water vapor migration and pressure equalization, thereby improving the thermal cycling reliability of the structure.

[0009] Preferably, the spatial support skeleton is made of SiC ceramic, C / C composite ceramic or ultra-high temperature ceramic, which can maintain sufficient high-temperature mechanical properties and morphological stability under high heat flux density and strong thermal shock conditions. The relative density of the spatial support skeleton is 5% to 25%. If the relative density is too low, the skeleton will not be able to bear enough load and it will be difficult to restrain the volume change caused by phase change. If the relative density is too high, thermal bridges will easily form and increase the mass. At the same time, the volume fraction of the functional filler layer will be compressed, thereby reducing the heat absorption and insulation effect of phase change.

[0010] Preferably, the ablation-resistant ultra-high temperature ceramic matrix composite material is at least one of carbon / carbon composite material, silicon carbide-based ceramic matrix composite material, and ultra-high temperature ceramic matrix composite material containing hafnium or zirconium; the anti-oxidation and anti-ablation coating is one of silicon carbide coating, hafnium oxide coating, HfB2-SiC composite coating, or silicon-containing glass transition coating. This ensures that the outer / inner surface layer still has structural load-bearing capacity and thermal shock resistance under high temperature conditions, while taking into account lightweight and high temperature dimensional stability, thus forming an integrated surface-core-surface load-bearing structure together with the intermediate skeleton support system. In order to ensure continuous coating coverage and oxidation resistance life, while controlling the residual stress and peeling risk caused by thermal cycling due to coating thickness, the thickness of each coating is 50μm~300μm.

[0011] Preferably, the spatial support frame is connected to the outer heat-insulating surface layer and the inner heat-insulating surface layer through co-curing, inorganic high-temperature adhesive, ceramic precursor bonding or diffusion reaction bonding, respectively. The inorganic connecting phase remains stable under high temperature and thermal cycling conditions, avoiding the softening, decomposition or creep of the connecting layer at high temperature, which would lead to interface slippage and failure.

[0012] Preferably, the latent heat of vaporization of the hydrogel is 2000 J / g to 2500 J / g. If the latent heat is too low, the heat absorption capacity of the phase change is insufficient, making it difficult to effectively slow down the release of transient thermal shock. If the latent heat is too high, it often exceeds the level of achievable latent heat based on water vaporization, which is not conducive to the feasibility and stability control of the material system. After the hydrogel loses water, it forms an aerogel with a thermal conductivity of 0.01 W / (m·K) to 0.05 W / (m·K).

[0013] This invention provides a phase change heat absorption type high temperature thermal protection sandwich structure with skeleton support for use in the nose of hypersonic vehicles and the high heat flux region of hypersonic vehicles.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: In the phase change heat-absorbing high-temperature thermal protection sandwich structure with skeleton support provided by this invention, the outer heat-resistant surface layer is made of load-bearing heat-resistant material, which can be used to bear a certain structural load and block the transfer of heat to the interior of the structure. An anti-oxidation and anti-ablation coating is applied to the outer surface of the outer heat-resistant surface layer to reduce the adverse effects of high-temperature airflow impact and oxidative environment on the outer surface, thus forming an outer protective barrier together with the outer heat-resistant surface layer, which helps to reduce the coupling of external thermal effects to the interior of the structure. The inner heat-resistant surface layer is made of the same material as the outer heat-resistant surface layer, providing inner load-bearing and thermal insulation support. The skeleton support-functional filling layer of this invention consists of a spatial support skeleton and a functional filling layer within its cavity. The spatial support skeleton is positioned between the outer and inner heat-resistant surface layers and is rigidly connected to both surface layers to form an integrated surface-core-surface load-bearing structure. The spatial support skeleton provides clear geometric constraints and load-bearing paths, making it easier for the functional filling layer to maintain its shape and interlayer matching during high-temperature phase change, thereby reducing the risk of core layer instability. The functional filler layer consists of hydrogel, metal-organic framework (MOF), and phenolic resin. The hydrogel undergoes a phase change / evaporation to absorb heat in the early stages of high temperature, thus absorbing heat and reducing transient thermal peaks during the initial thermal shock phase. After dehydration, the hydrogel forms a porous framework to provide continuous insulation. The phenolic resin carbonizes at high temperatures to form a supporting phase, which works synergistically with the spatial support framework to help maintain the core layer morphology and delay further heat transfer during subsequent high-temperature stages. This forms a continuous thermal protection process of phase change heat absorption, porous insulation, and carbonized support, which can improve the problems of slow thermal response and low thermal protection efficiency to some extent, and is beneficial in reducing the backsheet temperature rise.

[0015] In summary, this invention, through an integrated design of external surface anti-oxidation and ablation protection, core layer phase change heat absorption and porous insulation, and frame support, enables the structure to balance thermal protection and load-bearing stability in high-temperature environments. Simultaneously, by reducing the risk of external surface ablation / oxidation damage and core layer instability, it helps improve the structure's ability to maintain function and integrity under repeated thermal exposure, thereby enhancing its reusability. The overall structure achieves an integrated high-temperature protection system encompassing ablation prevention, phase change heat absorption, heat insulation and slow release, and structural load-bearing, possessing both active thermal response and high-temperature mechanical stability. This provides a lightweight and reliable thermal protection solution for hypersonic vehicles, significantly improving their safety and service life in extreme thermal environments. Attached Figure Description

[0016] Figure 1 This is a three-dimensional schematic diagram of a phase change heat absorption type high-temperature thermal protection sandwich structure with a skeleton support.

[0017] Figure 2 This is a cross-sectional view of a phase change heat-absorbing high-temperature thermal protection sandwich structure with a skeleton support.

[0018] Figure 3This is a schematic diagram of a phase change heat absorption type high-temperature thermal protection sandwich structure with skeleton support.

[0019] Figure Labels 1. Head unit; 2. Body connectors; 3. External heat shield layer; 4. Frame support-functional filling layer; 5. Internal heat shield layer; 6. Anti-oxidation and anti-ablation layer; 7. Spatial support frame; 8. Steam guide microchannel. Detailed Implementation

[0020] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention. Unless otherwise specified, the experimental methods described in the embodiments of the present invention are conventional methods.

[0021] like Figures 1-3 As shown, this invention provides a phase change heat-absorbing high-temperature thermal protection sandwich structure with skeleton support. The sandwich structure includes, from the outside to the inside, an outer heat-protecting surface layer 3, a skeleton support-functional filling layer 4, and an inner heat-protecting surface layer 5. The outer heat-protecting surface layer 3 and the inner heat-protecting surface layer 5 are both ablation-resistant ultra-high temperature ceramic matrix composite materials coated with an anti-oxidation and anti-ablation coating 6. The skeleton support-functional filling layer 4 includes a spatial support skeleton 7 and a functional filling layer. The spatial support skeleton 7 is rigidly connected to the inner surfaces of the outer heat-protecting surface layer 3 and the inner heat-protecting surface layer 5 along the entire contact length. The functional filling layer is made of hydrogel, metal-organic framework, and phenolic resin, and the functional filling layer fills the closed cavity formed by the spatial support skeleton 7, the outer heat-protecting surface layer 3, and the inner heat-protecting surface layer 5.

[0022] The space support frame 7 is made of SiC ceramic, C / C composite ceramic or ultra-high temperature ceramic, and the relative density of the space support frame 7 is 5% to 25%.

[0023] The latent heat of vaporization of the hydrogel is 2000 J / g to 2500 J / g, and the hydrogel forms an aerogel with a thermal conductivity of 0.01 W / (m·K) to 0.05 W / (m·K) after water loss.

[0024] This invention provides a phase change heat absorption high-temperature thermal protection sandwich structure with a skeleton support. Its core lies in the physical decoupling and spatial layering of structural load-bearing and thermal management functions: the outer thermal protection layer 3 and the inner thermal protection layer 5 serve as dual load-bearing surfaces, absorbing flight loads and thermal stresses; the skeleton support-functional filling layer 4 acts as an independent functional layer, not participating in the main load-bearing path, and is specifically designed for phase change heat absorption and gradient insulation. This design avoids the problem of a sudden drop in overall stiffness caused by the softening of the core material at high temperatures in traditional sandwich structures. Simultaneously, the spatial support skeleton 7 applies three-dimensional constraints to the functional filling layer, effectively suppressing the volumetric abrupt changes and interface instability caused by the thermal expansion of the hydrogel. The functional filling layer is made of a ternary composite system of hydrogel, metal-organic framework, and phenolic resin, which sequentially triggers a three-stage response under thermal load: vaporization heat absorption, microporous aerogel formation, and carbonization matrix reinforcement, forming continuous thermal protection capabilities over time.

[0025] like Figure 1 and Figure 2 As shown, this sandwich structure is used for the nose section 1 and high heat flux region of the hypersonic vehicle. The nose section 1 of the hypersonic vehicle is integrally formed using this sandwich structure. The integrally formed nose section 1 has a cavity in which the nose section 1, connected to the fuselage of the hypersonic vehicle, is connected to the fuselage via a fuselage connector 2. The nose section 1 is an integral curved surface structure adapted to the aerodynamic shape of the leading edge of the hypersonic vehicle. Its geometric profile can be optimized into a pointed cone, blunt cone, or ellipsoidal shape according to different Mach number conditions. The overall thickness is gradually distributed along the axial direction to match the local heat flux density and structural stiffness requirements. The fuselage connector 2 can be a ring flange or an embedded tenon and groove structure made of titanium alloy or nickel-based high-temperature alloy. The integrally formed nose section 1 matches the fuselage connector 2. The fuselage connector 2 and the nose section 1 are integrally connected by mechanical fastening or diffusion welding to ensure that the nose section 1 with thermal protection structure has sufficient force transmission stiffness and thermal barrier capability with the fuselage. Since the outer heat-insulating layer 3 and the inner heat-insulating layer 5 of the machine head 1 are both made of ablation-resistant ultra-high temperature ceramic matrix composite material coated with an anti-oxidation and anti-ablation coating 6, this type of material refers to high temperature structural material that can maintain a bending strength of not less than 50 MPa and an elastic modulus of not less than 0.5 GPa at temperatures above 1500℃, its function is to form the first thermal-chemical dual barrier.

[0026] The skeleton support-functional filling layer 4 includes two parts: a spatial support skeleton 7 and a functional filling layer. The spatial support skeleton 7 is a through-type three-dimensional support structure, which is rigidly connected to the inner surfaces of the outer heat shield layer 3 and the inner heat shield layer 5 along the entire contact length, ensuring that the thermal load can be efficiently transferred along the skeleton axis and synchronously constraining the thermal deformation of the outer layer and the displacement of the inner layer structure. This rigid connection method differs from traditional adhesive or spot welding connections, avoiding interface slippage and shear failure caused by high-temperature creep. The functional filling layer is made of hydrogel, metal-organic framework (MOF), and phenolic resin. The hydrogel provides initial phase change endothermic capacity, the MOF acts as a nano-porous control medium to regulate the water migration rate and heat diffusion path, and the phenolic resin acts as a high-temperature carbonization matrix to impart residual structural strength. This functional filling layer is not independently molded and then placed, but is filled into the closed cavity formed by the spatial support skeleton 7, the outer heat-insulating surface layer 3, and the inner heat-insulating surface layer 5 through vacuum infusion or in-situ polymerization after the spatial support skeleton 7 and the two surface layers are assembled, ensuring dense filling, no macroscopic bubbles, and sufficient interface wetting. The shape of this cavity dynamically changes with the topology of the skeleton and the curvature of the surface layers.

[0027] Hydrogels are hydrophilic polymer network materials. They undergo vigorous vaporization in the initial heating stage (100°C–200°C), with a latent heat of vaporization of 2000 J / g–2500 J / g. This rapid absorption of the heat flux peak penetrating the outer layer significantly slows down the rate of temperature transfer inwards. Metal-organic frameworks (MOFs) are crystalline porous materials with high specific surface area and controllable micropore size. Typical examples include MOF-74 and ZIF-8. In these systems, they do not solely bear the load-bearing function but rather regulate it through adsorption-desorption cycles. The transport dynamics of water molecules within the gel network prevent boiling and bulging caused by localized vapor pressure accumulation, and serve as nucleation sites for the aerogel framework after the hydrogel loses water, promoting the ordering of the porous structure. Phenolic resin is a thermosetting resin that carbonizes after heat treatment, generating a continuous carbon network that coats the MOF particles and aerogel pore walls, forming a carbon shell-aerogel-framework composite thermal insulation interface. This ensures that the final residual structure maintains structural integrity and low thermal conductivity (≤0.05 W / (m·K)) even above 1000°C.

[0028] The outer heat shield layer 3 is adapted to the shape of the aircraft and arranged on its surface. It is made of silicon carbide-based or carbon / carbon composite material, and its outer surface is coated with a silicon carbide-hafnium oxide anti-oxidation and anti-ablation coating 6 with a thickness of 0.05mm to 0.3mm to resist the impact of high-temperature airflow and oxidation corrosion. The skeleton support-functional filling layer 4 is located between the outer heat shield layer 3 and the inner heat shield layer 5. It is composed of a space support skeleton 7 and a hydrogel-metal-organic framework (MOF)-phenolic resin composite system. The space support skeleton 7 is a three-dimensional lattice that is connected to the outer heat shield layer 3 and the inner heat shield layer 5 to bear the interlayer load and maintain the geometric stability of the intermediate layer. The space support skeleton 7 can be SiC ceramic or C / C composite. The porosity of the space support skeleton 7 is 5% to 25%, and the unit cell edge length is 2mm to 15mm. In the functional filler system, the hydrogel reduces the thermal peak through vaporization and heat absorption at high temperatures, and transforms into a porous aerogel framework after water loss to achieve continuous thermal insulation. MOF materials (such as MOF-74 or ZIF-8) provide microporous channels to regulate moisture migration and enhance the endothermic response. Phenolic resin carbonizes at even higher temperatures to form a dense carbon layer, maintaining the overall structural strength. The inner thermal insulation layer 5 uses the same or similar thermal insulation material as the outer thermal insulation layer 3 to provide backplate support and thermal insulation protection.

[0029] In the above embodiments, the anti-oxidation and anti-ablation coating 6 of the outer heat-insulating surface layer 3 is the first thermal protection barrier. Its high emissivity (0.7~0.8) can reflect 30%~40% of the incident radiative heat flux. In an oxidizing environment above 1500 °C, the SiC component forms a dense SiO2 glass phase, while HfO2 provides extremely high high-temperature stability due to its melting point of 2810 °C. The two work together to form a self-healing oxidation barrier, effectively blocking oxygen diffusion. In the initial stage of heating, the hydrogel in the functional filling layer 4 rapidly vaporizes and absorbs heat, absorbing 2000 J / g~2500 J / g of latent heat, which significantly reduces the peak heat flux. As the temperature rises, the thermal conductivity of the aerogel structure remaining after water evaporation is only 0.01 W / (m·K)~0.05 W / (m·K), providing continuous thermal insulation over time. The spatial support skeleton 7 ensures the dimensional stability of the hydrogel layer during the phase transition process, avoiding expansion-collapse problems. At the same time, the skeleton ribs guide part of the heat flux circumferentially, promoting spatial heat diffusion. The phenolic matrix is ​​carbonized in the range of 400℃ to 600℃ to generate a dense carbon layer that adheres to the surface of the skeleton and forms a high thermal resistance composite interface together with the pore walls of the aerogel.

[0030] Specifically, the mass fraction ratio of hydrogel dry matter, metal-organic framework and phenolic resin in the functional filling layer is 10%~35%: 5%~20%: 45%~80%; the water content of the hydrogel is 50%~300% of the dry matter of the hydrogel.

[0031] Specifically, the ablation-resistant ultra-high temperature ceramic matrix composite material is at least one of carbon / carbon composite material, silicon carbide-based ceramic matrix composite material, and ultra-high temperature ceramic matrix composite material containing hafnium or zirconium. The anti-oxidation and ablation layer is a silicon carbide, hafnium oxide, HfB2-SiC composite coating or a silicon-containing glass transition coating, and the coating thickness is 50μm~300μm.

[0032] Specifically, the spatial support frame 7 is connected to the outer heat-insulating layer 3 and the inner heat-insulating layer 5 through co-curing, inorganic high-temperature adhesives, ceramic precursor bonding, or diffusion reaction bonding. This structure forms a bonding zone at the interlayer interface through bonding or co-curing with a high-temperature resistant ceramic precursor. To prevent moisture accumulation that could cause bulging or delamination, specifically, as shown... Figure 3 As shown, the outer heat-resistant surface layer 3 is provided with multiple steam-conducting microchannels 8 for releasing water vapor. The steam-conducting microchannels 8 are connected to the sealed cavity, and the pore size of the steam-conducting microchannels 8 is 50μm~300μm. Each steam-conducting microchannel 8 is connected to the outer layer to discharge water vapor and maintain pressure balance.

[0033] Working principle: During thermal protection operations, when high-temperature airflow impacts the aircraft surface, the outer heat shield layer 3 and the anti-oxidation and anti-ablation layer 4 first reflect and dissipate most of the heat flux. After some heat penetrates into the skeleton support-functional filling layer 4, the hydrogel in the functional filling layer of the skeleton support-functional filling layer 4 undergoes phase change heat absorption, rapidly reducing the temperature rise rate. At the same time, the porous structure of the space support skeleton 7 and the metal-organic framework (MOF) promotes heat diffusion along the surface, achieving spatial heat flow dispersion. The subsequently formed aerogel-carbonized layer structure provides long-term thermal insulation, while the inner heat shield layer 5 further blocks residual heat and maintains mechanical support. This is achieved through the synergistic effect of multiple mechanisms: anti-ablation reflection, phase change heat absorption, porous thermal insulation, and structural load-bearing.

[0034] By introducing a skeleton support-functional filling layer 4, the technical bottlenecks of insufficient load-bearing capacity of the core layer and its tendency to collapse or delaminate at high temperatures in traditional sandwich structures are solved. The spatial support skeleton in the skeleton support-functional filling layer 4 is rigidly connected to the inner surfaces of the outer heat-insulating layer 3 and the inner heat-insulating layer 5 along the entire contact length, forming a three-dimensional mechanical framework. This framework ensures the overall rigidity and dimensional stability of the structure while providing support and constraint for the intermediate functional material, enabling it to maintain a stable shape during phase change heat absorption. Compared to traditional foam or honeycomb sandwich structures, this skeleton system not only improves interlaminar shear strength but also significantly extends the service life of the structure under thermal cycling conditions.

[0035] Secondly, the functional filling layer employs a hydrogel-MOF-phenolic composite material made of hydrogel, metal-organic framework, and phenolic resin, constructing a controllable multi-stage thermal response mechanism. At high temperatures, the hydrogel first reduces the peak heat flux through vaporization and heat absorption, rapidly mitigating surface thermal shock. As the temperature further increases, the hydrogel loses water to form a porous aerogel framework, maintaining extremely low thermal conductivity and achieving continuous insulation. At even higher temperatures, the phenolic resin carbonizes to form a dense carbon layer, further blocking heat transfer and enhancing antioxidant properties. The MOF material permeates the entire system, promoting moisture migration and heat diffusion through its highly tunable pore structure and excellent thermal diffusivity, making the heat absorption and release processes more uniform and controllable. This continuous transformation of phase change heat absorption, aerogel insulation, and carbonization barrier overcomes the limitations of traditional materials' single and irreversible thermal response.

[0036] Furthermore, the anti-oxidation and anti-ablation coating of the outer heat-resistant layer 5 constitutes the first high-temperature barrier, maintaining a stable structure at temperatures above 1500℃. The silicon carbide component in the coating oxidizes to form a self-healing SiO2 glass phase, while hafnium oxide, with its ultra-high melting point, provides long-lasting high-temperature stability. These two components synergistically form a dense oxide film, significantly reducing the oxygen diffusion rate and material ablation rate, effectively protecting the substrate material from oxidation and corrosion. Simultaneously, the coating's high emissivity gives it excellent radiation reflection properties, reflecting approximately one-third of the incident heat flow, thus reducing the heat load at its source.

[0037] In summary, the three-layer synergistic effect of the entire phase change heat-absorbing high-temperature thermal protection sandwich structure (outer thermal protection layer 3, skeleton support-functional filling layer 4, and inner thermal protection layer 5) achieves heat dispersion and slow release on both spatial and temporal scales. The outer layer reduces heat input through ablation prevention and radiation reflection; the middle layer stores and delays heat transfer through phase change heat absorption and porous insulation; and the inner layer balances residual heat through carbonization support and thermal diffusion. This results in heat flow being weakened and delayed multiple times before entering the interior of the structure, forming an effective multi-level energy barrier.

[0038] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A phase change heat-absorbing high-temperature thermal protection sandwich structure with a skeleton support, characterized in that, The sandwich structure comprises, from the outside to the inside, an outer heat-insulating surface layer (3), a skeleton support-functional filling layer (4), and an inner heat-insulating surface layer (5). The outer heat-insulating surface layer (3) and the inner heat-insulating surface layer (5) are both ablation-resistant ultra-high temperature ceramic matrix composite materials coated with an anti-oxidation and anti-ablation coating (6). The skeleton support-functional filling layer (4) includes a spatial support skeleton (7) and a functional filling layer. The spatial support skeleton (7) is rigidly connected to the inner surfaces of the outer heat-insulating surface layer (3) and the inner heat-insulating surface layer (5) along the entire contact length. The functional filling layer is made of hydrogel, metal-organic framework, and phenolic resin, and the functional filling layer fills the closed cavity formed by the spatial support skeleton (7), the outer heat-insulating surface layer (3), and the inner heat-insulating surface layer (5).

2. The phase change heat absorption type high-temperature thermal protection sandwich structure with skeleton support as described in claim 1, characterized in that, The outer heat-resistant surface layer (3) is provided with multiple steam-conducting microchannels (8) for releasing water vapor. The steam-conducting microchannels (8) are connected to the closed cavity, and the pore size of each steam-conducting microchannel (8) for releasing water vapor is 50μm~300μm.

3. The phase change heat absorption type high-temperature thermal protection sandwich structure with skeleton support as described in claim 1, characterized in that, The ablation-resistant ultra-high temperature ceramic matrix composite material is at least one of carbon / carbon composite material, silicon carbide-based ceramic matrix composite material, and ultra-high temperature ceramic matrix composite material containing hafnium or zirconium.

4. The phase change heat absorption type high-temperature thermal protection sandwich structure with skeleton support as described in claim 1, characterized in that, The antioxidant and ablation-resistant coating (6) is one of silicon carbide coating, hafnium oxide coating, HfB2-SiC composite coating or silicon-containing glass transition coating, and the thickness of each coating is 50μm~300μm.

5. The phase change heat absorption type high-temperature thermal protection sandwich structure with skeleton support as described in claim 1, characterized in that, The mass fraction ratio of hydrogel dry matter, metal-organic framework and phenolic resin in the functional filling layer is 10%~35%: 5%~20%: 45%~80%; the water content of the hydrogel is 50%~300% of the dry matter of the hydrogel.

6. The phase change heat absorption type high-temperature thermal protection sandwich structure with skeleton support as described in claim 1, characterized in that, The spatial support framework (7) is a three-dimensional lattice structure, honeycomb structure, through-column structure or rib structure.

7. The phase change heat-absorbing high-temperature thermal protection sandwich structure with skeleton support as described in claim 1 or 6, characterized in that, The space support frame (7) is made of SiC ceramic, C / C composite ceramic or ultra-high temperature ceramic, and the relative density of the space support frame (7) is 5% to 25%.

8. The phase change heat absorption type high-temperature thermal protection sandwich structure with skeleton support as described in claim 1, characterized in that, The spatial support frame (7) is connected to the outer heat-insulating layer (3) and the inner heat-insulating layer (5) through co-curing, inorganic high-temperature adhesive, ceramic precursor bonding or diffusion reaction bonding.

9. The phase change heat absorption type high-temperature thermal protection sandwich structure with skeleton support as described in claim 1, characterized in that, The latent heat of vaporization of the hydrogel is 2000 J / g to 2500 J / g, and the hydrogel forms an aerogel with a thermal conductivity of 0.01 W / (m·K) to 0.05 W / (m·K) after water loss.

10. The phase change heat absorption type high temperature thermal protection sandwich structure with skeleton support as described in claim 1 is used for the nose (1) of a hypersonic vehicle and the high heat flux region of a hypersonic vehicle.

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