Gradient self-heating material based on phase change-oxidation synergistic regulation and preparation method and application thereof

Abstract

This invention relates to a gradient self-heating material based on phase change-oxidation synergistic regulation, its preparation method, and its application. The gradient self-heating material based on phase change-oxidation synergistic regulation comprises a core layer, a transition layer, and a shell layer connected sequentially; wherein the core layer is a reduced iron powder-phenolic resin composite layer; the transition layer is a gradient transition structure of iron powder, CNT-graphite composite material, and resin; and the shell layer is a catalytic phase change material particle-resin composite layer; the volume percentages of the shell layer, transition layer, and core layer are 20%-30%, 20%-30%, and 40%-60%, respectively. The problem this invention aims to solve is overcoming the interfacial failure challenge between the oxidant and the phase change material through chemical bonding reconstruction, breaking through the thermal accumulation bottleneck by employing a gradient thermal conductivity structure design, and achieving cross-scale synergy across four dimensions: exothermic reaction, heat storage phase change, heat conduction, and dynamic regulation. The final product's thermal response time (temperature greater than 50℃) is <30 seconds.

Description

Technical Field

[0001] This invention relates to a gradient self-heating material based on phase change-oxidation synergistic regulation, its preparation method and application, belonging to the fields of self-heating material technology, functional materials and energy conversion technology. Background Technology

[0002] With the widespread application of self-heating materials in special packaging, polar equipment, and other fields, existing technologies have revealed a core contradiction: insufficient precision in heat control and an imbalance in thermal inertia management. Traditional self-heating systems generally suffer from technical bottlenecks such as delayed thermal start-up, unstable continuous heating (fluctuation amplitude > ±8℃), and disordered thermal gradient distribution when dealing with sudden low-temperature shocks or dynamic thermal environments. Especially in scenarios such as self-heating and self-insulating individual field rations, existing materials struggle to simultaneously meet the dual requirements of rapid thermal activation and thermal inertia compensation.

[0003] In recent years, research on self-heating material systems has mainly focused on the coupling mechanism between metal oxidation exothermics and phase change thermal storage. The technical approach achieves basic thermal regulation through the physical mixing of oxidants and phase change materials, and optimizes thermal management performance with auxiliary components such as catalysts and high thermal conductivity materials. However, existing solutions still face significant challenges in terms of thermal response efficiency, dynamic regulation capability, and long-term stability. Existing improvement methods, such as multilayer encapsulation and microencapsulation technologies, still have inherent limitations: the former reduces thermal conductivity by 55%-70% due to the physical isolation layer; the latter, while increasing the encapsulation rate of phase change materials to 85%, suffers from contact thermal resistance (≥10⁻³) between the shell material (silica, etc.) and the oxidizing exothermic agent. m 2 The heat transfer efficiency is severely limited by the K / W ratio. More importantly, existing technologies have failed to establish a dynamic matching mechanism between heat release intensity and heat storage capacity. When encountering a sudden change from a -30°C environment to a humid and warm 5°C environment, the probability of system thermal inertia compensation failure is as high as 78%. Therefore, there is an urgent need to develop an intelligent self-heating material system that combines controllable oxidation heat release, adaptive phase change heat storage, and gradient heat conduction. Summary of the Invention

[0004] In view of this, the main objective of this invention is to provide a gradient self-heating material based on phase change-oxidation synergistic regulation, which features high-efficiency energy release, precise temperature control, rapid response, and cycle stability, as well as its preparation method and application. The problem to be solved is to overcome the interfacial failure problem between oxidant and phase change material through chemical bonding reconstruction, and to break through the thermal accumulation bottleneck by adopting a gradient thermal conduction structure design, so as to achieve cross-scale synergy in four dimensions: exothermic reaction, thermal storage phase change, thermal conduction, and dynamic regulation.

[0005] The objective of this invention and the technical problem it solves are achieved through the following technical solution. This invention proposes a gradient self-heating material based on phase change-oxidation synergistic regulation, comprising a core layer, a transition layer, and a shell layer connected sequentially; wherein,

[0006] The core layer is a reduced iron powder-phenolic resin composite layer;

[0007] The transition layer is a gradient transition structure of iron powder, CNT-graphite composite material and resin;

[0008] The shell layer is a catalytic phase change material particle-resin composite layer;

[0009] The volume percentages of the shell, transition layer, and core layer are 20%-30%, 20%-30%, and 40%-60%, respectively.

[0010] The objectives of this invention and the technical problems it addresses can be further achieved by the following technical measures.

[0011] Preferably, in the aforementioned gradient self-heating material based on phase change-oxidation synergistic regulation, the core layer comprises 70 wt% reduced iron powder and 30 wt% phenolic resin by mass percentage; the transition layer comprises 50 wt% iron powder, 30 wt% CNT-graphite composite material and 20 wt% resin by mass percentage; and the shell layer comprises 60 wt% catalytic phase change material particles and 40 wt% resin by mass percentage.

[0012] Preferably, in the aforementioned gradient self-heating material based on phase change-oxidation synergistic regulation, the particle size of the reduced iron powder is ≤50μm.

[0013] Preferably, in the aforementioned gradient self-heating material based on phase change-oxidation synergistic regulation, the particle size of the catalytic phase change material particles is 100-200 μm.

[0014] The objective of this invention and the technical problem it solves are achieved through the following technical solution. This invention proposes a method for preparing a gradient self-heating material based on phase change-oxidation synergistic regulation, comprising the following steps:

[0015] a) Preparation of catalytic phase change precursor: Construction of ferric stearate and lauric acid eutectic system → ultrasonic dispersion of graphene oxide → directional crystallization;

[0016] b) Hierarchical framework construction: Vertical CNT array grown by CVD catalytic metal ion solution → Fe 3+ Solution impregnation modification;

[0017] c) Centrifugal gradient molding: sequential perfusion of shell-transition layer-core layer at 2000-3000 rpm;

[0018] d) Three-stage gradient curing: 75-85℃ / 1-3h → 110-130℃ / 0.5-1.5h → 180-220℃ / 0.4-0.6h programmed curing to obtain the gradient self-heating material based on phase change-oxidation synergistic regulation.

[0019] The objectives of this invention and the technical problems it addresses can be further achieved by the following technical measures.

[0020] Preferably, in the aforementioned method for preparing gradient self-heating materials based on phase change-oxidation synergistic regulation, step a) involves the preparation of the catalytic phase change precursor, which includes:

[0021] Ferric stearate and lauric acid were melt-eutectic at a mass ratio of 3:7 to 4:6 under nitrogen atmosphere at 100-120℃. 0.5-1wt% of graphene oxide was added as a nucleating agent, and the crystal orientation was controlled by ultrasonic treatment at 40kHz / 300W for 20-30 minutes.

[0022] Preferably, in the aforementioned method for preparing gradient self-heating materials based on phase change-oxidation synergistic regulation, in step b), the hierarchical framework construction satisfies the following conditions: the substrate is expanded graphite with a porosity ≥85%; the CVD process parameters are: acetylene / argon volume ratio of 1:(4.5-5.5); growth at 600℃-800℃ for 10-30 minutes; impregnation concentration of FeCl3 solution of 0.1-0.5 mol / L; and drying at 70-90℃ to form Fe... 3+ Preload layer.

[0023] Preferably, in the aforementioned method for preparing gradient self-heating materials based on phase change-oxidation synergistic regulation, in step b), the metal is Fe, Co, or a combination thereof; the metal ion solution is a metal ion coordination solution; and the vertical CNT array satisfies the following conditions: aspect ratio ≥ 500, and bonding strength with the expanded graphite matrix ≥ 15 MPa.

[0024] Preferably, in the aforementioned method for preparing gradient self-heating materials based on phase change-oxidation synergistic regulation, in step c), the centrifugal gradient molding includes: the volume ratio of the shell layer / transition layer / core layer is 20%-30% / 20%-30% / 40%-60%, and the viscosity gradient of the slurry during the centrifugal gradient molding process is controlled as follows: shell layer 800cP → transition layer 1200cP → core layer 1500cP.

[0025] Preferably, in the aforementioned method for preparing gradient self-heating materials based on phase change-oxidation synergistic regulation, step d) of the three-stage gradient curing includes: firstly, pre-curing at 75-85℃ for 1-3 hours, then raising the temperature to 110-130℃ and holding for 0.5-1.5 hours, and finally curing at 180-220℃ for 0.4-0.6 hours; under the protection of a N2 / H2 / CH4 mixed gas with a volume ratio of (70-80):(1-22):(4-6), raising the temperature to 400-500℃ at 3-7℃ / min and holding for 2-3 hours to form an interlocking interface of phase change material crystals-carbonized resin-metal particles.

[0026] The objective of this invention and the technical problem it solves are achieved through the following technical solution. This invention proposes an industrial self-heating device, wherein the industrial self-heating device employs the aforementioned gradient self-heating material based on phase change-oxidation synergistic regulation; the thermal response time of the gradient self-heating material based on phase change-oxidation synergistic regulation is less than or equal to 30 seconds, and the heat release density per unit mass is greater than or equal to 450 kJ / kg.

[0027] By employing the above technical solution, the present invention provides a gradient self-heating material based on phase change-oxidation synergistic regulation, its preparation method, and its application, which has at least the following advantages:

[0028] 1. High-efficiency energy conversion and rapid thermal response capabilities

[0029] By synergistically designing composite phase change materials and catalytically active components, a dynamic equilibrium system for energy storage and release is constructed. Combined with a three-dimensional high thermal conductivity network structure, energy density and conversion efficiency are significantly improved. A unique vertically oriented carbon nanotube array and an expanded graphite substrate form a rapid heat transfer channel, enabling directional heat conduction and precise control, greatly shortening the system response time and meeting the requirements of transient high heat flux scenarios.

[0030] 2. Gradient structure reinforcement and stability in extreme environments

[0031] The multi-layered composite structure design based on centrifugal molding effectively disperses thermal stress and suppresses delamination failure of the material under high-temperature cycling through density gradient transition and interface interlocking technology. The chemical stability of the carbonized resin-metal particle composite interface combined with the catalytic framework enables the material to maintain structural integrity over a wide temperature range.

[0032] 3. Intelligent adaptive thermal management features

[0033] The synergistic effect of the gradient thermal conductivity distribution within the material and the phase change triggering mechanism endows it with dynamic heat flow regulation capabilities. The directional heat conduction network achieves axial / radial thermal conductivity difference control through its orientation structure. Combined with the temperature sensitivity of the phase change material, it can autonomously adjust the heat transfer path and rate, adapting to the needs of multi-condition intelligent temperature control systems.

[0034] 4. Compatibility and cost advantages for industrial mass production

[0035] The core process parameters are deeply adapted to standard production equipment. The gradient slurry viscosity classification design and multi-stage curing process overcome the limitations of laboratory preparation, achieving consistent performance control of mass-produced products. Low-cost iron-based materials are used to replace precious metal components, combined with a short-process manufacturing process, reducing production costs.

[0036] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below. Detailed Implementation

[0037] To further illustrate the technical means and effects adopted by the present invention to achieve its intended purpose, the following detailed description, in conjunction with preferred embodiments, details a gradient self-heating material based on phase change-oxidation synergistic regulation, its preparation method, and its application, as well as its specific implementation methods, structures, features, and effects. In the following description, different "embodiments" or "embodiments" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable manner.

[0038] Unless otherwise specified, all materials or reagents listed below are commercially available.

[0039] Some embodiments of the present invention provide a gradient self-heating material based on phase change-oxidation synergistic regulation, comprising the following components by volume ratio:

[0040] Core layer: It is a composite layer of 70wt% reduced iron powder and 30wt% phenolic resin;

[0041] Transition layer: It is a gradient transition structure consisting of 50wt% iron powder, 30wt% CNT-graphite composite material and 20wt% resin;

[0042] Shell: It consists of 40 wt% catalytic phase change material particles, 20 wt% resin composite layer and 40 wt% iron powder;

[0043] The volume percentages of the shell, transition layer, and core layer are 20%-30%, 20%-30%, and 40%-60%, respectively.

[0044] The shell layer serves as both an ignition and thermal buffer; too much of it can easily release heat, which is then suppressed by the phase change material. The transition layer provides thermal buffering (but does not constitute the majority of the heat). The core layer is the key component for providing heat generation; to ensure continuous energy supply, it needs to account for a relatively large proportion. Too much of it can make the heat difficult to control, while too little can result in insufficient heat generation.

[0045] In some optional embodiments, the reduced iron powder has a particle size ≤50μm. Reduced iron powder, due to its high purity, porous structure, and controllable activity, becomes the core heating medium for self-heating materials. Its synergistic oxidation effect with phenolic resin is the cornerstone supporting the "rapid start-up - sustained high temperature" performance. In contrast, ordinary iron powder is limited by impurities and low activity, making it difficult to overcome technical bottlenecks. The essential difference between the two lies in the oxidation reaction kinetics and thermodynamic efficiency, which directly determines whether the self-heating material can achieve gradient control design. When the particle size is higher than 50μm, the particle size is larger, and the overall specific surface area of ​​the activated material will be relatively small. This smaller particle size allows for greater contact with oxygen, faster heating, and more thorough activation.

[0046] In some optional embodiments, the particle size of the catalytic phase change material is 100-200 μm. When the particle size is greater than 200 μm, the particles are too large, resulting in sluggish heat transfer, incomplete phase change, and cracking caused by interfacial stress; when the particle size is less than 100 μm, the particles are too small and melt, blocking oxygen channels.

[0047] Some embodiments of the present invention also provide a method for preparing a gradient self-heating material based on phase change-oxidation synergistic regulation, comprising the following steps:

[0048] a) Preparation of catalytic phase change precursor: Construction of a ferric stearate / lauric acid eutectic system → ultrasonic dispersion of graphene oxide → directional crystallization; Specifically, the preparation of the catalytic phase change precursor includes: firstly, ferric stearate and lauric acid are mixed at a mass ratio of 3:7 to 4:6, and melt-stirred at 100-120°C for 2 hours under nitrogen protection to form a eutectic mixture. Subsequently, 0.5-1.0 wt% of graphene oxide (GO) is added as a nucleating agent. Its surface oxygen-containing functional groups provide heterogeneous nucleation sites, inducing directional crystallization of the ferric stearate / lauric acid eutectic system. If the mass ratio of ferric stearate to lauric acid is lower than 3:7 to 4:6, insufficient iron catalysis will occur; if the mass ratio is higher than 3:7 to 4:6, iron cluster agglomeration is likely to occur. When the amount of graphene oxide added is less than 0.5 wt%, nucleation will be uncontrolled, while when the amount of graphene oxide added is greater than 1 wt%, diffusion channels will be easily blocked. Uniform dispersion and crystal orientation control were achieved by ultrasonic treatment at a frequency of 40kHz and a power of 300W for 20-30 minutes. Finally, the resulting mixture was injected into a polytetrafluoroethylene (PTFE) mold, and the PTFE mold was dried in an oven at 75-85℃ for 22-26 hours before demolding to obtain a blocky catalytic phase change material with a regular crystal structure.

[0049] b) Hierarchical framework construction: Fe, Co, or Fe-Co bimetallic ion-catalyzed CVD growth of vertical CNT→Fe 3+Solution impregnation modification; specifically, the hierarchical framework construction includes: selecting expanded graphite with a porosity ≥85% as a substrate material and placing it in a container; adding 0.4-0.6 mol / L of iron ions, cobalt ions, or iron ion solution (including its coordination solution), cobalt ion solution (including its coordination solution), or a solution of both (including its coordination solution) to wet the expanded graphite; subsequently, placing the container in a chemical vapor deposition (CVD) reaction chamber, and introducing an acetylene / argon gas mixture with a volume ratio of 1:(4.5-5.5). A acetylene ratio greater than 1:4.5 can easily lead to amorphous carbon encapsulation, while a ratio less than 1:5.5... Insufficient acetylene leads to insufficient carbon source. Using Fe / Co bimetallic nanoparticles (5nm particle size) as a catalyst, vertically oriented carbon nanotube structures are formed within 10-30 minutes at 600-800℃. Below 600℃, catalyst activation is insufficient; above 800℃, the temperature is too high, damaging the bonding strength of the carbon nanotubes. Growth within 10 minutes results in insufficient length, numerous structural defects, poor orientation, and inadequate catalyst activation. Above 30 minutes, catalyst deactivation occurs, with carbon encapsulation and sintering leading to loss of activity, subsequently causing amorphous carbon deposition, decreased carbon nanotube quality, and array structure destruction (bending / collapse). The prepared CNT-graphite composite framework is then impregnated in a 0.1-0.5mol / L FeCl3 solution and dried at 70-90℃ to achieve Fe... 3+ The pre-loading of ions ultimately yielded a CNT-graphite composite material possessing both high thermal conductivity and catalytic activity. The increased material mass and brownish-red color (characteristic color of Fe3+) after impregnation, along with the significant enhancement of its activity in the catalytic reaction, indirectly demonstrate that Fe... + Successful loading. When the catalyst concentration is less than 0.1 mol / L, the catalytic activity is too low, the active sites are few, and the carbon nanotubes are few; when the concentration is greater than 0.5 mol / L, the concentration is too high and too dense; when the temperature is higher than 90℃, the temperature is too high and hydrolysis is easy to produce a ferrite passivation layer.

[0050] c) Centrifugal gradient molding: Shell-transition layer-core layer sequential pouring at 2000-3000 rpm; insufficient centrifugal force at speeds below 2000 rpm results in residual bubbles and uneven density, leading to large exothermic fluctuations; excessive centrifugal force at speeds above 3000 rpm causes component stratification (iron powder / PCM separation); specifically, the centrifugal gradient molding includes: the core layer slurry (viscosity 800 cP) is composed of 70 wt% reduced iron powder (particle size ≤ 50 μm) and 30 wt% phenolic resin; the transition layer slurry is prepared according to the ratio of 50 wt% iron powder, 30 wt% CNT-graphite composite material and 20 wt% resin; and the shell layer slurry is composed of 40 wt% catalytic phase change material particles (particle size 100-200 μm), 20 wt% resin composite layer and 40 wt% iron powder. During the molding process, centrifugal force is used to sequentially inject slurry into the shell, transition layer, and core layer, with the injection thickness accounting for 20%-30%, 20%-30%, and 40%-60% of the total volume, respectively (centrifugal speed 2000-3000 rpm). The shell layer serves as both an ignition and heat buffer; if its proportion is too high, heat release may be suppressed by the phase change material. The transition layer acts as a heat buffer. The core layer is the key component providing heat generation, and its proportion is relatively high to ensure continuous energy supply. The viscosity gradient of the slurry is controlled during centrifugal molding: shell layer 800 cP → transition layer 1200 cP → core layer 1500 cP. In centrifugal casting molding, a shell layer (<20%) that is too thin can easily lead to unstable combustion or structural damage, while a shell layer that is too thick (>30%) inhibits the reaction and makes ignition difficult. A core layer (<40%) has insufficient energy, while a core layer that is too thick (>60%) is prone to runaway combustion and deflagration. An inaccurate transition layer proportion can lead to poor interfacial stress or energy coupling. At speeds below 2000 rpm, the density is too low, resulting in a blurred interface; at speeds above 3000 rpm, the components separate. The ranges of these parameters are designed to balance energy output, stability, and structural integrity.

[0051] d) Three-stage gradient curing: 75-85℃ / 1-3h → 110-130℃ / 0.5-1.5h → 180-220℃ / 0.4-0.6h programmed curing to obtain the gradient self-heating material based on phase change-oxidation synergistic regulation; specifically, the three-stage gradient curing includes: firstly, pre-curing at 75-85℃ for 1-3h to achieve initial cross-linking of the resin, then raising the temperature to 110-130℃ and holding for 0.5-1.5h to form an interlocking structure at the interface, and finally curing at 180-220℃ for 0.4-0.6h to complete the overall densification of the material. The cured preform is placed in a tube furnace for calcination. Under the protection of a N2 / H2 / CH4 mixed gas (volume ratio of (70-80):(1-22):(4-6)), the temperature is raised to 400-500℃ at a rate of 3-7℃ / min and held for 2-3 hours to form an interlocking interface between the phase change material crystal, the carbonized resin, and the metal particles, thus obtaining the gradient self-heating material based on phase change-oxidation synergistic regulation. A volume ratio of N2 / H2 / CH4 mixed gas that is less than the lower limit or greater than the upper limit will result in interfacial carbon layer defects (insufficient CH4). The following factors can cause problems: metal deactivation (excess H2) or incomplete reaction (excess N2), disrupting the "phase change-oxidation synergistic" gradient structure; a heating rate of less than 3℃ / min leads to prolonged exposure of the precursor's low-temperature region, causing premature resin cleavage and damage to structural integrity; a heating rate greater than 7℃ / min may result in asynchronous metal reduction and resin carbonization reactions; insufficient hydrogen leads to inadequate iron ion reduction, while slightly high methane levels can cause cracked carbon to clog pores; incomplete resin carbonization below 400℃ leads to decreased interfacial bonding; and decomposition of the phase change material occurs above 500℃. A time of less than 2 hours results in insufficient carbonization, while a time of more than 3 hours leads to metal sintering, reducing active sites, and thickening of the interfacial carbon layer, hindering contact with the phase change material.

[0052] In some optional embodiments, the vertical CNT array satisfies the following conditions: aspect ratio ≥ 500 (to ensure a certain axial thermal conductivity) and bonding strength with the expanded graphite matrix ≥ 15 MPa (to ensure interfacial bonding).

[0053] Some embodiments of the present invention also provide an industrial self-heating device, which employs a gradient self-heating material based on phase change-oxidation synergistic regulation.

[0054] In some optional embodiments, the thermal response time of the gradient self-heating material based on phase change-oxidation synergistic regulation is less than or equal to 30 seconds, and the heat release density per unit mass is greater than or equal to 450 kJ / kg.

[0055] In the above technical solution, the present invention overcomes the interface failure problem between oxidant and phase change material by chemical bonding reconstruction, breaks through the thermal accumulation bottleneck by adopting gradient thermal conduction structure design, and realizes cross-scale synergy in four dimensions: exothermic reaction, thermal storage phase change, thermal conduction and dynamic control.

[0056] The specific embodiments of the present invention will be described in further detail below with reference to examples, but this should not be construed as a limitation on the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention still fall within the scope of protection of the present invention.

[0057] Unless otherwise specified, all materials and reagents mentioned below are commercially available products well known to those skilled in the art; unless otherwise specified, all methods described are methods known in the art. Unless otherwise defined, the technical or scientific terms used should have the ordinary meaning understood by those skilled in the art to which this invention pertains.

[0058] Example 1

[0059] This embodiment provides a method for preparing a gradient self-heating material based on phase change-oxidation synergistic regulation, including the following steps:

[0060] 1) First, ferric stearate and lauric acid were mixed at a mass ratio of 3:7 and melted and stirred at 120°C for 2 hours under nitrogen protection (purity of 99.999%, i.e., 5N grade) to form a eutectic mixture. Then, 0.5wt% GO was added as a nucleating agent, and the mixture was ultrasonically treated at a frequency of 40kHz and a power of 300W for 30 minutes to achieve uniform dispersion. The resulting mixture was injected into a polytetrafluoroethylene mold, and the polytetrafluoroethylene mold was dried in an oven at 80°C for 24 hours before demolding to obtain a blocky catalytic phase change material with a regular crystal structure.

[0061] 2) Expanded graphite with a porosity of 85% was selected as the substrate material (100g) and placed in a container. 300mL (0.5mol / L) of iron ion coordination solution was added to wet the expanded graphite. The container was then placed in a CVD reaction chamber, and a 1:5 volume ratio acetylene / argon mixture was introduced. Carbon nanotubes (CNTs) were induced to grow at 700℃ using the iron ion coordination solution for 20min. The resulting CNT composite framework was then immersed in a 0.1mol / L FeCl3 solution and dried at 80℃ for 6h to achieve Fe... 3+ The preloading of ions ultimately yields the CNT-graphite composite material. The iron ion coordination solution is prepared through the following steps: ferric nitrate nonahydrate is selected as the precursor, 202g of ferric nitrate nonahydrate is dissolved in 1L of water, and 0.5mol of urea complexing agent is added. A homogeneous and transparent solution is formed by stirring.

[0062] 3) Gradient Material Molding Process: Slurry Preparation First, prepare dry powder mixtures of three components (each based on 100g of solid powder): Core layer: weigh reduced iron powder and phenolic resin powder at a mass ratio of 7:3; Transition layer: weigh reduced iron powder, CNT-graphite composite material obtained in step 2), and phenolic resin powder at a mass ratio of 5:3:2; Shell layer: weigh catalytic phase change material obtained in step 1) and phenolic resin powder at a mass ratio of 6:4. After preliminary grinding and mixing of each layer's dry powder mixture in separate containers, add an appropriate amount of anhydrous ethanol as a solvent (80mL for the core layer, 90mL for the transition layer, and 100mL for the shell layer). First add 80% of the volume of solvent, then place the mixture on a magnetic stirrer and stir at 300rpm until the solid powder is fully dispersed to form a slurry. Slowly add the remaining ethanol dropwise using a dropper until the slurry is easy to pour and has no obvious particle texture. When the viscosity reaches a certain level, stop adding solvent; after mixing evenly, transfer to an ultrasonic instrument and treat at a frequency of 40kHz and a power of 200W for 20 minutes to ensure sufficient dispersion and degassing, finally obtaining a uniformly mixed slurry with a core layer (800cP), a transition layer (1200cP), and a shell layer (1500cP) of the corresponding viscosity; after the slurry preparation is completed, centrifugal casting molding is immediately performed: the prepared shell layer slurry is injected into a centrifugal mold and centrifuged at 2500rpm for 3 minutes to form a uniform shell layer accounting for 25% of the total volume around the mold; then, while maintaining the centrifugation state, the transition layer slurry (25%) is slowly injected through the injection channel in the center of the mold and centrifuged for 2 minutes; finally, the core layer slurry (50%) is injected while maintaining the speed and centrifuged for 3 minutes; finally, a preform with a distinct three-dimensional structure of shell-transition layer-core layer (thickness of 10mm) is obtained, followed by subsequent curing processes.

[0063] 4) The preform with a distinct shell-transition layer-core layer three-dimensional structure obtained in step 3) is first pre-cured at 80℃ for 2 hours to achieve initial cross-linking of the resin. Then, the temperature is raised to 120℃ and held for 1 hour to form an interlocking structure at the interface. Finally, it is cured at 200℃ for 0.5 hours to complete the overall densification of the material. The cured preform is placed in a tube furnace for calcination treatment. Under the protection of a N2 / H2 / CH4 mixed gas (volume ratio of 75:20:5), the temperature is raised to 450℃ at a rate of 5℃ / min and held for 2.5 hours to finally form the gradient self-heating material based on phase change-oxidation synergistic regulation.

[0064] Example 2

[0065] The difference between this embodiment and Example 1 is that in step 1), the mass ratio of ferric stearate to lauric acid is 4:6, and the amount of GO added is 0.75wt%; in step 2), the CNT skeleton is grown at 800℃ for 30 minutes; in step 3), gradient centrifugation is performed at 3000rpm (shell layer 20% (v / v) / transition layer 20% (v / v) / core layer 60% (v / v)); calcination is performed at 500℃ for 3 hours; the remaining steps and parameters are the same as in Example 1.

[0066] Example 3

[0067] The difference between this embodiment and Example 1 is that in step 1), the amount of GO added is 1.0 wt%; in step 2), the CNT framework is grown at 600℃ for 10 minutes; in step 3), gradient centrifugation is performed at 2000 rpm (shell 30% (v / v) / transition layer 30% (v / v) / core layer 40% (v / v)); calcination is performed at 400℃ for 2 hours. The remaining steps and parameters are the same as in Example 1.

[0068] Example 4

[0069] The difference between this embodiment and Example 1 is that in step 1) of this embodiment, the mass ratio of ferric stearate to lauric acid is 4:6, the CNT skeleton is grown at 750°C for 25 minutes, and then subjected to gradient centrifugation at 2800 rpm (shell 20% (v / v) / transition 25% (v / v) / core 55% (v / v)); followed by calcination at 480°C for 2.5 hours. The remaining steps and parameters are the same as in Example 1.

[0070] Example 5

[0071] The difference between this embodiment and Example 1 is that in step 1) of this embodiment, the mass ratio of ferric stearate to lauric acid is 3.5:6.5, 0.8wt% GO is added, the CNT skeleton is grown at 650℃ for 15 minutes, and then subjected to gradient centrifugation at 2200rpm (shell 30% (v / v) / transition 25% (v / v) / core 45% (v / v)); calcination is performed at 420℃ for 2.2 hours. The remaining steps and parameters are the same as in Example 1.

[0072] Example 6

[0073] The difference between this embodiment and Example 1 is that in step 1), the mass ratio of ferric stearate to lauric acid is 4:6, and the amount of GO added is 1.0 wt%; in step 2), the CNT skeleton is grown at 780℃ for 28 minutes; in step 3), gradient centrifugation is performed at 2900 rpm (shell layer 25% (v / v) / transition layer 22% (v / v) / core layer 53% (v / v)); calcination is performed at 490℃ for 2.8 hours. The remaining steps and parameters are the same as in Example 1.

[0074] Example 7

[0075] The difference between this embodiment and Example 1 is that in step 1), the mass ratio of ferric stearate to lauric acid is 4:6, and the amount of GO added is 0.5wt%; in step 2), the CNT framework is grown at 700℃ for 20 minutes; in step 3), gradient centrifugation is performed at 2500 rpm (shell layer 25% (v / v) / transition layer 25% (v / v) / core layer 50% (v / v)); calcination is performed at 450℃ for 2.5 hours. The remaining steps and parameters are the same as in Example 1.

[0076] Example 8

[0077] The difference between this embodiment and Example 1 is that in step 1), the mass ratio of ferric stearate to lauric acid is 3:7, and the amount of GO added is 0.8wt%; in step 2), the CNT framework is grown at 700℃ for 20 minutes; in step 3), gradient centrifugation is performed at 2500 rpm (shell layer 25% (v / v) / transition layer 25% (v / v) / core layer 50% (v / v)); calcination is performed at 450℃ for 2.5 hours. The remaining steps and parameters are the same as in Example 1.

[0078] Example 9

[0079] The difference between this embodiment and Example 1 is that in step 1), the mass ratio of ferric stearate to lauric acid is 3:7, and the amount of GO added is 0.5wt%; in step 2), the CNT framework is grown at 800℃ for 20 minutes; in step 3), gradient centrifugation is performed at 2500 rpm (shell layer 25% (v / v) / transition layer 25% (v / v) / core layer 50% (v / v)); calcination is performed at 450℃ for 2.5 hours. The remaining steps and parameters are the same as in Example 1.

[0080] Example 10

[0081] The difference between this embodiment and Example 1 is that in step 1), the mass ratio of ferric stearate to lauric acid is 3:7, and the amount of GO added is 0.5wt%; in step 2), the CNT skeleton is grown at 700℃ for 20 minutes; in step 3), gradient centrifugation is performed at 2500rpm (shell layer 25% (v / v) / transition layer 25% (v / v) / core layer 50% (v / v)); calcination is performed at 450℃ for 3.0h (originally 2.5h). The remaining steps and parameters are the same as in Example 1.

[0082] Example 11

[0083] The difference between this embodiment and Example 1 is that in step 1), the mass ratio of ferric stearate to lauric acid is 3:7, and the amount of GO added is 0.5wt%; in step 2), the CNT skeleton is grown at 700℃ for 20 minutes; in step 3), gradient centrifugation is performed at 2500 rpm (shell 30% (v / v) / transition layer 20% (v / v) / core layer 50% (v / v) (originally 25% / 25% / 50%); calcination is performed at 450℃ for 2.5 hours. The remaining steps and parameters are the same as in Example 1.

[0084] Example 12 (Ratio of high core layer to Example 1)

[0085] The difference between this embodiment and Example 1 is that in step 1), the mass ratio of ferric stearate to lauric acid is 3:7, and the amount of GO added is 0.5wt%; the CNT skeleton is grown at 700℃ for 20 minutes; in step 3), gradient centrifugation is performed at 2500 rpm (shell layer 20% (v / v) / transition layer 20% (v / v) / core layer 60% (v / v)) (originally 25% / 25% / 50%); calcination is performed at 450℃ for 2.5 hours. The remaining steps and parameters are the same as in Example 1.

[0086] Comparative Example 1

[0087] The difference between this comparative example and Example 1 is that GO was not added in the preparation of the phase variant in this comparative example, while the remaining steps and parameters are the same as in Example 1.

[0088] Comparative Example 2

[0089] The difference between this comparative example and Example 1 is that ordinary graphite is used instead of expanded graphite in the skeleton construction of this comparative example, while the other steps and parameters are the same as in Example 1.

[0090] Comparative Example 3

[0091] The difference between this comparative example and Example 1 is that the transition layer (shell / core layer in direct contact) is omitted in the gradient molding of this comparative example, while the remaining steps and parameters are the same as in Example 1.

[0092] Comparative Example 4

[0093] The difference between this comparative example and Example 1 is that the shell ratio in this comparative example exceeds the upper limit, with the shell accounting for 50%, the transition layer for 20%, and the core layer for 30%. The remaining steps and parameters are the same as in Example 1.

[0094] Comparative Example 5

[0095] The difference between this comparative example and Example 1 is that this comparative example does not use graded gradient molding, but selects a core layer with a single core heating component (composed of 70 wt% reduced iron powder and 30 wt% phenolic resin). The remaining steps and parameters are the same as in Example 1.

[0096] Table 1. Key performance comparison of Examples 1-12 and Comparative Examples 1-5

[0097] Case Peak temperature (°C) Thermal response rate (°C / s) Duration at 200℃ (min) Example 1 488 4.1 42 Example 2 503 4.7 38 Example 3 478 3.8 46 Example 4 495 4.4 40 Example 5 485 4.0 44 Example 6 500 4.6 37 Example 7 498 4.3 36 Example 8 482 4.5 44 Example 9 502 4.8 35 Example 10 492 4.0 46 Example 11 475 3.7 49 Example 12 502 4.9 32 Comparative Example 1 458 2.8 32 Comparative Example 2 423 1.9 18 Comparative Example 3 469 3.1 25 Comparative Example 4 321 2.3 28 Comparative Example 5 685 / 25

[0098] As can be seen from the data in Table 1, compared with Comparative Examples 1-5, the peak temperature of Examples 1-12 of the present invention is 475-503℃, the thermal response rate is 3.7-4.9℃ / s, and the duration of 200℃ is 32-49min.

[0099] This invention achieves a revolutionary breakthrough in self-heating materials in the high-temperature range by synergistically optimizing three core parameters: GO nucleation control (0.5-0.8wt%), CNT framework growth temperature (700-800℃), and gradient structure core layer ratio (40-60%). It also relies on the triple coupling of core layer thermal inertia design, interface stress elimination, and GO crystal stabilization technologies. Experiments show that: CNT growth temperature directly dominates the upper limit of peak temperature - when the temperature increases from 700℃ (Example 1: 488℃) to 800℃ (Example 9: 502℃; Example 2: 503℃), the peak temperature increases due to the high temperature promoting the increase of the aspect ratio of carbon nanotubes and the optimization of the three-dimensional thermal conductivity network; the amount of GO added precisely controls the thermal response kinetics - an appropriate increase of 0.5wt% GO (Example 1: 4.1℃ / s) to 0.8wt% GO (Example 8: 4.5℃ / s) enhances the nucleation density and the thermal conductivity of the crystal interface, increasing the response rate by 9.8%, but excessive GO (Example 3: 1.0wt% → 3.8℃ / s) will have a negative effect due to the obstruction of molecular ordering; the core-layer ratio of the gradient structure determines the thermal sustainability - when the core-layer ratio decreases from 50% (v / v) (Example 1: 42min) to 40% (v / v) (Example 3: 46min), the shell thermal accumulation effect extends the duration by 9.5%, while when the core-layer ratio increases to 60% (v / v)...

[0100] Example 12: Although the response rate was increased to 4.9℃ / s (32 min), the duration was sharply reduced by 23.8% due to the release of high thermal inertia.

[0101] The deep synergy of three technologies creates a performance leap: In Example 2 (0.75wt% GO + 800℃ CNT + 60% (v / v) core layer), the crystal ordering induced by GO nucleation, the rapid heat conduction of high aspect ratio CNTs, and the release of high thermal inertia of the core layer form a positive cycle, enabling the peak temperature to exceed 503℃ and the response rate to reach 4.7℃ / s; while the combined strategy of core layer ratio control (40-50%) + stress dissipation of the interface transition layer + enhancement of the thermal stability of GO crystal (such as the core layer 5 in Example 1) creates a performance leap. 0% (v / v) / duration 42 min; core layer of Example 10 50% (v / v) / duration 46 min), successfully solved the problem of thermal sustainability in the high temperature range of 480–500℃ - the duration of all examples (1 / 3 / 5 / 8 / 10 / 11) with core layer ≤50% exceeded 40 min, with Example 10 reaching 46 min, which is 155.6% higher than the traditional homogeneous material (comparative example 2: 18 min), achieving a technical leap from "short peak" to "long steady state".

[0102] The comparative examples demonstrate the irreplaceable nature of the technology: In Comparative Example 1, the absence of the GO nucleating agent led to a sharp increase in grain boundary thermal resistance, causing the peak temperature to plummet to 458°C (30°C lower than Example 1); in Comparative Example 2, the lack of pore structure resulted in CNT network fracture, resulting in a response rate of only 1.9°C / s; and the removal of the gradient transition layer (Comparative Example 3) caused interfacial thermal stress concentration, drastically reducing the duration to 25 minutes (40%). These failure cases confirm that GO crystal stabilization is the foundation for high-temperature nucleation, the high thermal conductivity CNT network is the core carrier for rapid response, and gradient interface design is the structural guarantee for long-term operation.

[0103] In summary, this invention, through a three-level synergistic mechanism of "nucleation-heat transfer-heat storage," achieves long-term continuous operation within a high-temperature window of 400-500℃, breaking through the inherent contradiction of "high response but short lifespan" in traditional materials, and providing a brand-new material paradigm for high-temperature self-heating systems.

[0104] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0105] The numerical range described in this invention includes all values ​​within this range, and also includes any range value composed of any two values ​​within this range. Different values ​​of the same indicator appearing in all embodiments of this invention can be arbitrarily combined to form a range value.

[0106] The technical features in the claims and / or specification of this invention can be combined, and the combination is not limited to the combinations obtained through reference in the claims. Technical solutions obtained by combining the technical features in the claims and / or specification are also within the scope of protection of this invention.

[0107] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A gradient self-heating material based on phase change-oxidation synergistic regulation, characterized in that, It includes a core layer, a transition layer, and a shell layer connected in sequence; among which, The core layer is a reduced iron powder-phenolic resin composite layer; The transition layer is a gradient transition structure of iron powder, CNT-graphite composite material and resin; The shell layer is a catalytic phase change material particle-resin composite layer; The volume percentages of the shell, transition layer, and core layer are 20%-30%, 20%-30%, and 40%-60%, respectively. The core layer comprises 70 wt% reduced iron powder and 30 wt% phenolic resin by weight percentage; the transition layer comprises 50 wt% iron powder, 30 wt% CNT-graphite composite material and 20 wt% resin by weight percentage; and the shell layer comprises 60 wt% catalytic phase change material particles and 40 wt% resin by weight percentage.

2. The gradient self-heating material based on phase change-oxidation synergistic regulation as described in claim 1, characterized in that, The particle size of the reduced iron powder is ≤50 micrometers; the particle size of the catalytic phase change material particles is 100-200 micrometers.

3. A method for preparing a gradient self-heating material based on phase change-oxidation synergistic regulation as described in claim 1 or 2, characterized in that, Includes the following steps: a) Preparation of catalytic phase change precursor: Construction of ferric stearate and lauric acid eutectic system → ultrasonic dispersion of graphene oxide → directional crystallization; b) Hierarchical framework construction: vertical CNT array grown by CVD catalyzed by metal ion solution → Fe³⁺ solution impregnation modification; c) Centrifugal gradient molding: sequential infusion of shell-transition layer-core layer at 2000-3000 rpm, with the volume ratio of shell / transition layer / core layer being 20%-30% / 20%-30% / 40%-60%; d) Three-stage gradient curing: 75-85℃ / 1-3h → 110-130℃ / 0.5-1.5h → 180-220℃ / 0.4-0.6h programmed curing to obtain the gradient self-heating material based on phase change-oxidation synergistic regulation.

4. The method for preparing gradient self-heating materials based on phase change-oxidation synergistic regulation as described in claim 3, characterized in that, In step a), the preparation of the catalytic phase change precursor includes: Ferric stearate and lauric acid were melt-eutectic at a mass ratio of 3:7 to 4:6 under nitrogen atmosphere at 100-120℃. 0.5-1wt% of graphene oxide was added as a nucleating agent, and the crystal orientation was controlled by ultrasonic treatment at 40kHz / 300W for 20-30 minutes.

5. The method for preparing gradient self-heating materials based on phase change-oxidation synergistic regulation as described in claim 3, characterized in that, In step b), the hierarchical framework construction meets the following requirements: the substrate uses expanded graphite with a porosity ≥85%, and the CVD process parameters are: acetylene / argon volume ratio of 1:(4.5-5.5), growth at 600℃-800℃ for 10-30 minutes. The impregnation concentration of the solution is 0.1-0.5 mol / L, and it is dried at 70-90℃ to form... Preload layer.

6. The method for preparing gradient self-heating materials based on phase change-oxidation synergistic regulation as described in claim 3, characterized in that, In step b), the metal is Fe, Co, or a combination thereof; the metal ion solution is a metal ion coordination solution; the vertical CNT array satisfies the following conditions: aspect ratio ≥ 500, and bonding strength with the expanded graphite matrix ≥ 15 MPa.

7. The method for preparing gradient self-heating materials based on phase change-oxidation synergistic regulation as described in claim 3, characterized in that, In step c), the viscosity gradient of the slurry during the centrifugal gradient molding process is controlled as follows: shell layer 800 cP → transition layer 1200 cP → core layer 1500 cP.

8. The method for preparing gradient self-heating materials based on phase change-oxidation synergistic regulation as described in claim 3, characterized in that, In step d), the three-stage gradient curing includes: first, pre-curing at 75-85℃ for 1-3 h, then raising the temperature to 110-130℃ and holding for 0.5-1.5 h, and finally curing at 180-220℃ for 0.4-0.6 h; in a volume ratio of (70-80): (1-22): (4-6) Under mixed gas protection, the temperature is increased to 400-500℃ at 3-7℃ / min and held for 2-3 hours to form an interlocking interface between phase change material crystals, carbide resin, and metal particles.

9. An industrial self-heating device, characterized in that, The industrial self-heating device uses the gradient self-heating material based on phase change-oxidation synergistic regulation as described in claim 1 or 2; the thermal response time of the gradient self-heating material based on phase change-oxidation synergistic regulation is less than or equal to 30 seconds, and the heat release density per unit mass is greater than or equal to 450 kJ / kg.