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

Abstract

The invention relates to a gradient self-heating material based on phase change-oxidation cooperative regulation and a preparation method and application thereof. The gradient self-heating material based on phase change-oxidation cooperative regulation comprises a core layer, a transition layer and a shell layer which are connected in sequence, wherein the core layer is a reduced iron powder-phenolic resin composite layer; the transition layer is of a gradient transition structure of iron powder, a CNT-graphite composite material and resin; the shell layer is a catalytic phase change material particle-resin composite layer; the volume ratios of the shell layer, the transition layer and the core layer are 20%-30%, 20%-30% and 40%-60% respectively. The problem to be solved by the invention is that the interface failure problem of an oxidant and a phase change material is solved through chemical bonding reconstruction, a gradient heat conduction structure design is adopted to break through a heat accumulation bottleneck, cross-scale cooperation of four dimensions of exothermic reaction, heat storage phase change, heat conduction and dynamic regulation and control is realized, and the thermal response (the temperature is greater than 50 DEG C) time of a final product is less than 30 seconds.

Description

TECHNICAL FIELD

[0001] The present application relates to a gradient self-heating material based on phase change-oxidation synergistic regulation and its preparation method and application, and belongs to the technical field of self-heating materials, functional materials and energy conversion. BACKGROUND

[0002] With the wide application of self-heating materials in special packaging, polar equipment and other fields, the existing technology exposes the core contradiction of insufficient heating control precision and unbalanced thermal inertia management. When dealing with sudden low temperature impact or dynamic thermal environment, the traditional self-heating system generally has technical bottlenecks such as thermal start-up lag, unstable continuous heating (fluctuation amplitude > ± 8℃) and disorderly thermal gradient distribution. Especially in the scene of single soldier field food self-heating and self-temperature preservation, the existing materials are difficult to achieve the dual needs of rapid thermal activation and thermal inertia compensation.

[0003] In recent years, the research of self-heating material system mainly focuses on the coupling mechanism of metal oxidation exothermic and phase change heat storage. Its technical path realizes basic heat regulation through physical mixing of oxidizing agent and phase change material, and optimizes the heat management performance with the help of catalyst, high thermal conductivity material and other auxiliary components. However, the existing scheme still faces significant challenges in terms of thermal response efficiency, dynamic regulation ability and long-term stability. The existing improvement schemes such as multi-layer packaging joint and microencapsulation technology still have essential limitations: the former causes a 55%-70% decrease in thermal conductivity due to the physical isolation layer; the latter increases the encapsulation rate of phase change material to 85%, but the contact thermal resistance (≥10-3 m 2 ·K / W) between shell material (silicon dioxide, etc.) and oxidizing exothermic agent seriously restricts the heat transfer efficiency. More importantly, the existing technology fails to build a dynamic matching mechanism between exothermic intensity and heat storage capacity. When the environment suddenly changes from-30℃ to 5℃ humid warm environment, the system thermal inertia compensation failure probability is as high as 78%. Therefore, it is urgent to develop an intelligent self-heating material system with controllable oxidation exothermic, adaptive phase change heat storage and gradient heat conduction. SUMMARY

[0004] Therefore, the main purpose of the present application is to provide a gradient self-heating material based on phase change-oxidation synergistic regulation, which has high energy release efficiency, precise temperature control, fast response and cycle stability, and its preparation method and application. The problem to be solved is to overcome the interface failure problem of oxidizing agent and phase change material by chemical bonding reconstruction, to break the heat accumulation bottleneck by gradient heat conduction structure design, and to realize the cross-scale synergy of four dimensions of exothermic reaction, heat storage phase change, heat conduction and dynamic regulation.

[0005] The purpose of the present application and the technical problems thereof are realized by adopting the following technical scheme. The gradient self-heating material based on phase change-oxidation synergistic regulation provided by the present application comprises a core layer, a transition layer and a shell layer connected in sequence; 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 ratios of the shell layer, the transition layer and the core layer are 20%-30%, 20%-30% and 40%-60%, respectively.

[0010] The purposes of the present application and the technical problems thereof can be further achieved by the following technical measures.

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

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

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

[0014] The purposes of the present application and the technical problems thereof are achieved by the following technical solutions. The present application provides a preparation method of a gradient self-heating material based on phase change-oxidation synergistic regulation, which comprises the following steps:

[0015] a) preparation of catalytic phase change precursor: construction of eutectic system of iron stearate and lauric acid → ultrasonic dispersion of graphene oxide → directional crystallization molding;

[0016] b) hierarchical skeleton construction: CVD growth of vertical CNT array catalyzed by metal ion solution → Fe 3+ solution immersion modification;

[0017] c) centrifugal gradient molding: shell layer-transition layer-core layer sequential perfusion under a rotation speed of 2000-3000rpm;

[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 purposes and technical problems of the present application can also be further achieved by the following technical measures.

[0020] Preferably, the preparation method of the gradient self-heating material based on phase change-oxidation synergistic regulation, wherein in step a), the preparation of the catalytic phase change precursor comprises:

[0021] Iron stearate and lauric acid are melt eutectic at 100-120℃ in a nitrogen environment, 0.5-1wt% graphene oxide is added as a nucleating agent, and crystal orientation control is achieved by 40kHz / 300W ultrasonic treatment for 20-30 minutes.

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

[0023] Preferably, the preparation method of the gradient self-heating material based on phase change-oxidation synergistic regulation, wherein 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 aspect ratio is ≥500, and the bonding strength with the expanded graphite matrix is ≥15MPa.

[0024] Preferably, the preparation method of the gradient self-heating material based on phase change-oxidation synergistic regulation, wherein in step c), the centrifugal gradient forming comprises: the volume ratio of shell / transition layer / core layer is 20%-30% / 20%-30% / 40%-60%, and the slurry viscosity gradient control during the centrifugal gradient forming process is: 800cP for the shell layer→1200cP for the transition layer→1500cP for the core layer.

[0025] Preferably, the preparation method of the gradient self-heating material based on phase change-oxidation synergistic regulation, wherein in step d), the three-stage gradient curing comprises: first pre-curing at 75-85 DEG C for 1-3 h, then increasing the temperature to 110-130 DEG C for 0.5-1.5 h, and finally curing at 180-220 DEG C for 0.4-0.6 h; under the protection of N2 / H2 / CH4 mixed gas with a volume ratio of (70-80):(1-22):(4-6), the temperature is increased to 400-500 DEG C at a rate of 3-7 DEG C / min and kept for 2-3 h to form an interlocking interface of phase change material crystal-carbonized resin-metal particles.

[0026] The purpose of the present application and the technical problems thereof are realized by adopting the following technical solutions. The industrial self-heating device provided by the present application adopts the gradient self-heating material based on phase change-oxidation synergistic regulation described above; the gradient self-heating material based on phase change-oxidation synergistic regulation has a heat response time of less than or equal to 30 seconds and a unit mass heat release density of greater than or equal to 450 kJ / kg.

[0027] Through the above technical solutions, the gradient self-heating material based on phase change-oxidation synergistic regulation, the preparation method and the application thereof provided by the present application have at least the following advantages:

[0028] 1. High energy conversion efficiency and fast heat response capability

[0029] Through the synergistic design of the composite phase change material and the catalytically active component, a dynamic balance system for energy storage and release is constructed, and combined with the three-dimensional high-thermal-conductivity network structure, the energy density and conversion efficiency are significantly improved. The unique vertically oriented carbon nanotube array and the expanded graphite substrate form a rapid heat transfer channel, realizing directional conduction and precise regulation of heat, greatly shortening the system response time and meeting the needs of transient high heat flow scenarios.

[0030] 2. Gradient structure strengthening and extreme environmental stability

[0031] Based on the multi-layer composite structure design of the centrifugal forming process, the thermal stress is effectively dispersed through the density gradient transition and the interface interlocking technology, and the delamination failure of the material under high temperature cycling is inhibited. The chemical stability of the carbonized resin-metal particle composite interface combined with the catalytic skeleton enables the material to maintain structural integrity in a wide temperature range.

[0032] 3. Intelligent self-adaptive thermal management characteristics

[0033] The gradient thermal conductivity distribution inside the material and the phase change triggering mechanism work together to give the dynamic heat flow regulation capability. The directional heat conduction network realizes the difference control of axial / radial thermal conductivity through the orientation structure, and combined with the temperature sensitivity of the phase change material, the heat transfer path and rate can be automatically adjusted to adapt to the needs of the multi-working-condition intelligent temperature control system.

[0034] 4. Industrialization production compatibility and cost advantage

[0035] The core process parameters are deeply adapted to the standard production equipment, the gradient slurry viscosity grading design and the multi-stage curing program break through the laboratory preparation limitation, and the batch product performance consistency control is realized. Low-cost iron-based materials are used to replace noble metal components, and a short process manufacturing process is combined to reduce production cost.

[0036] The above description is only a summary of the technical solutions of the present application. In order to more clearly understand the technical means of the present application, and can be implemented according to the content of the specification, the following will be described in detail as follows. DETAILED DESCRIPTION

[0037] In order to further illustrate the technical means and effects adopted by the present application to achieve the predetermined invention purpose, the following will be described in detail as follows by combining the preferred embodiments, the specific implementation, structure, characteristics and effects of the gradient self-heating material based on phase change-oxidation synergistic regulation and its preparation method and application thereof according to the present application. In the following description, different "an embodiment" or "embodiments" do not necessarily refer to the same embodiment. In addition, the specific features, structures or characteristics in one or more embodiments can be combined in any suitable form.

[0038] The following materials or reagents, unless otherwise specified, are commercially available.

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

[0040] The core layer is a composite layer of 70wt% reduced iron powder and 30wt% phenolic resin;

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

[0042] The shell layer includes 40wt% catalytic phase change material particles, 20wt% resin composite layer and 40wt% iron powder;

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

[0044] The shell layer has the functions of ignition and heat buffering, and too much heat release is inhibited by the phase change material; the transition layer is a heat buffer (the proportion does not occupy the main part); the core layer is a key component for providing heat, and a larger proportion is needed to ensure continuous energy supply, too much heat is not easy to control, and too little heat is not enough.

[0045] In some optional embodiments, the particle size of the reduced iron powder is ≤ 50 μm. The reduced iron powder is the core heating medium of the self-heating material due to its high purity, porous structure, and controllable activity. The synergistic effect of the reduced iron powder and the oxidation of phenolic resin is the cornerstone supporting the performance of "fast start-high temperature persistence". However, the general iron powder is limited by impurities and low activity, and it is difficult to break through the technical bottleneck. The essential difference between the two is the oxidation reaction kinetics and thermodynamic efficiency, which directly determines whether the self-heating material can realize gradient regulation design. When the particle size is greater than 50 μm, the particle size is relatively large, and the specific surface area of the material after activation is relatively small. The setting of the particle size makes the contact with oxygen more, the temperature rises faster, and the activation is more thorough.

[0046] In some optional embodiments, the particle size of the catalytic phase change material particle is 100-200 μm. When the particle size is greater than 200 μm, the particle is too large, which causes heat transfer delay, incomplete phase change, and interface stress-induced cracking; when the particle size is less than 100 μm, the small particle size causes the melting to block the oxygen channel.

[0047] Some embodiments of the present application also provide a preparation method of 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 iron stearate and lauric acid eutectic system → ultrasonic dispersion of graphene oxide → directional crystallization molding; specifically, the preparation of the catalytic phase change precursor comprises: first, mixing iron stearate and lauric acid in a mass ratio of 3:7 to 4:6, melting and stirring at 100-120°C under nitrogen protection for 2 hours to form a eutectic mixture, then adding 0.5-1.0wt% of graphene oxide (GO) as a nucleating agent, which provides heterogeneous nucleation sites on the surface of the oxygen-containing functional groups, inducing directional crystallization of the iron stearate / lauric acid eutectic system. If the mass ratio of iron stearate to lauric acid is less than 3:7 to 4:6, the iron catalysis is insufficient, and if the mass ratio of iron stearate to lauric acid is greater than 3:7 to 4:6, iron clusters are easily aggregated. When the addition amount of graphene oxide is less than 0.5wt%, the nucleation is out of control, and when the addition amount of graphene oxide is greater than 1wt%, the diffusion channel is easily blocked. The uniform dispersion and crystal orientation control are achieved by ultrasonic treatment at a frequency of 40 kHz and a power of 300 W for 20-30 minutes. Finally, the obtained mixture is injected into a polytetrafluoroethylene mold, and the polytetrafluoroethylene mold is placed in an oven at 75-85°C for 22-26h to dry and demold, thereby obtaining a block-shaped catalytic phase change material with regular crystal structure.

[0049] b) hierarchical skeleton construction: Fe, Co or Fe-Co bimetallic ion catalytic CVD growth of vertical CNT → Fe 3+Solution immersion modification; specifically, the hierarchical skeleton construction comprises: selecting expanded graphite with porosity ≥ 85% as a base material and placing it in a container, adding 0.4-0.6 mol / L iron ion, cobalt ion or iron ion solution (containing its coordination solution), cobalt ion solution (containing its coordination solution) or solution of both (containing its coordination solution) to wet the expanded graphite; then placing the container in a chemical vapor deposition (CVD) reaction chamber, and introducing acetylene / argon mixed gas with a volume ratio of 1:(4.5-5.5), too much acetylene is easy to be wrapped in amorphous carbon when the volume ratio is greater than 1:4.5, and too little acetylene leads to insufficient carbon source when the volume ratio is less than 1:5.5; using Fe / Co bimetallic nanoparticles (particle size 5 nm) as catalyst at 600-800℃, growing for 10-30 minutes to form vertically oriented carbon nanotube structure, the catalyst is not fully activated when the temperature is lower than 600℃, and the carbon nanotube growth bonding strength is damaged when the temperature is higher than 800℃; the growth is insufficient when the time is less than 10 minutes, the length is insufficient, the structure has many defects, the orientation is poor, and the catalyst is not activated enough, and the catalyst is deactivated when the time is greater than 30 minutes, leading to carbon wrapping and sintering, resulting in loss of activity, and further causing amorphous carbon deposition, carbon tube quality decline, and array structure damage (bending / falling). Then immerse the prepared CNT-graphite composite skeleton in a 0.1-0.5 mol / L FeCl3 solution, dry at 70-90℃ to achieve pre-loading of Fe 3+ ions, and finally obtain CNT-graphite composite materials with high thermal conductivity and catalytic activity; the successful loading of Fe + ions can be indirectly proved by the increase in material mass after immersion, the color change to brown (Fe3+ characteristic color), and the significant increase in activity in catalytic reactions. When the concentration of the catalyst is less than 0.1 mol / L, the catalytic activity is insufficient, the active sites are few, and the carbon tubes 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 easy to hydrolyze to produce ferrite passivation layer.

[0050] c) centrifugal gradient forming: shell-transition layer-core layer sequential perfusion at a rotation speed of 2000-3000 rpm; less than 2000 rpm, the centrifugal force is insufficient, bubbles remain, density is uneven, resulting in large exothermic fluctuation; more than 3000 rpm, the centrifugal force is too strong to cause component separation (iron powder / PCM separation); specifically, the centrifugal gradient forming includes: the core layer slurry (viscosity of 800 cP) is composed of 70wt% of reduced iron powder (particle size ≤50 μm) and 30wt% of phenolic resin, the transition layer slurry is prepared according to the proportion of 50wt% of iron powder, 30wt% of CNT-graphite composite material and 20wt% of resin, and the shell layer slurry is mixed by 40wt% of catalytic phase change material particles (particle size of 100-200 μm), 20wt% of resin composite layer and 40wt% of iron powder. In the forming process, the shell layer, the transition layer and the core layer slurry are sequentially injected by using centrifugal force, the perfusion thickness accounts for 20%-30%, 20%-30% and 40%-60% of the total volume (centrifugal rotation speed of 2000-3000 rpm), respectively. The shell layer has the functions of ignition and heat buffering, and too much proportion is easy to be inhibited by the phase change material; the transition layer has the function of heat buffering; the core layer is the key component for providing heat, and a larger proportion is needed to ensure continuous energy supply; the slurry viscosity gradient control in the centrifugal forming process is: shell layer 800 cP→transition layer 1200 cP→core layer 1500 cP. In the centrifugal perfusion forming, the shell layer (<20%) is too thin to cause unstable combustion or structural damage, and the shell layer (>30%) is too thick to inhibit the reaction and cause ignition difficulty; the core layer (<40%) is insufficient in energy, and the core layer (>60%) is easy to lose control and cause deflagration; the proportion of the transition layer is inaccurate, which can cause interface stress or poor energy coupling. Less than 2000 rpm, the rotation speed is too low to cause poor density and unclear interface, and more than 3000 rpm, the rotation speed is too high to cause component separation. The parameter range is aimed at balancing 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 comprises: first, pre-curing at 75-85℃ for 1-3h to achieve initial crosslinking of the resin, then heating to 110-130℃ for 0.5-1.5h to form an interfacial interlocking structure, and finally curing at 180-220℃ for 0.4-0.6h to complete the densification of the whole material. The cured green body is placed in a tube furnace for calcination treatment, heated to 400-500℃ at a rate of 3-7℃ / min under the protection of N2 / H2 / CH4 mixed gas (volume ratio (70-80):(1-22):(4-6)) and kept for 2-3 hours, to form an interlocking interface of phase change material crystal-carbonized resin-metal particle, to obtain the gradient self-heating material based on phase change-oxidation synergistic regulation; if the volume ratio of the three N2 / H2 / CH4 mixed gases is less than the lower limit value or greater than the upper limit value, it will cause interface carbon layer defects (insufficient CH4), metal deactivation (excessive H2) or incomplete reaction (excessive N2), which will destroy the "phase change-oxidation synergistic" gradient structure; if the rate is less than 3℃ / min, the heating is too slow, the precursor is exposed to low temperature for a long time, the resin is broken down too early, and the structural integrity is destroyed; if the rate is greater than 7℃ / min, the heating is too fast, which may cause the reduction of metal and the carbonization of resin to be out of sync; too little hydrogen will cause insufficient reduction of iron ions, and slightly higher methane will cause the cracked carbon to block the pores; less than 400℃ will result in incomplete carbonization of the resin, leading to a decrease in interface bonding strength, and greater than 500℃ will cause the phase change material to decompose. Less than 2 hours will result in insufficient carbonization reaction, and greater than 3 hours will cause the metal to sinter, reducing the active sites; the interface carbon layer thickens, hindering contact with the phase change material.

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

[0053] Some embodiments of the present application also provide an industrial self-heating device using the gradient self-heating material based on phase change-oxidation synergistic regulation.

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

[0055] In the technical solution described above, the application overcomes the interface failure problem of oxidizing agent and phase change material by chemical bonding reconstruction, breaks the heat accumulation bottleneck by using a gradient heat conduction structure design, and realizes the cross-scale cooperation of four dimensions of heat release reaction, heat storage phase change, heat conduction and dynamic regulation.

[0056] The specific embodiments of the application are further described in detail below with reference to the examples, but it should not be understood as limiting the scope of protection of the application. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the application described above still belong to the protection scope of the application.

[0057] Unless otherwise specified, the materials, reagents, etc. involved below are commercially available goods well known to those skilled in the art; unless otherwise specified, the methods described are well-known methods in the art. Unless otherwise defined, the technical terms or scientific terms used should be the usual meaning understood by those skilled in the art in the field to which the application belongs.

[0058] Example 1

[0059] The present embodiment provides a preparation method of gradient self-heating material based on phase change-oxidation synergistic regulation, comprising the following steps:

[0060] 1) First, mix iron stearate and lauric acid at a mass ratio of 3:7, melt and stir at 120℃ for 2 hours under a nitrogen (purity 99.999% (i.e. 5N grade)) protection environment to form a eutectic mixture, then add 0.5wt% GO as a nucleating agent, and use ultrasonic treatment at a frequency of 40kHz and a power of 300W for 30 minutes to achieve uniform dispersion; pour the obtained mixture into a polytetrafluoroethylene mold, and after the polytetrafluoroethylene mold is placed in an oven at 80℃ for drying for 24h, demold to obtain a blocky catalytic phase change material with regular crystal structure.

[0061] 2) Select expanded graphite with a porosity of 85% as a base material (take 100g) and place it in a container, add 300mL (0.5mol / L) iron ion complex solution to the container to wet the expanded graphite; then place the container in a CVD reaction chamber, introduce a mixture of acetylene / argon gas with a volume ratio of 1:5, and induce the growth of carbon nanotubes (CNT) at 700℃ for 20min using the iron ion complex solution; then immerse the obtained CNT composite framework in a 0.1mol / L FeCl3 solution, and after drying treatment at 80℃ for 6h, realize the preloading of Fe 3+ ions, and finally obtain a CNT-graphite composite material. The iron ion complex solution is prepared by the following steps: selecting iron nitrate nonahydrate as a precursor, dissolving 202g of iron nitrate nonahydrate in 1L of water, and adding urea complexing agent (0.5mol) to form a uniform transparent solution by stirring.

[0062] 3) Gradient material forming process: The slurry preparation firstly prepared three kinds of dry powder mixture of components respectively (three kinds of configuration basis on 100 g solid powder): the core layer was weighed with the mass ratio of 7:3 of reduced iron powder and phenolic resin powder; the transition layer was weighed with the mass ratio of 5:3:2 of reduced iron powder, CNT-graphite composite material obtained in step 2) and phenolic resin powder; the shell layer was weighed with the mass ratio of 6:4 of catalytic phase change material obtained in step 1) and phenolic resin powder; the dry powder mixture of each layer was placed in a container and initially ground and mixed uniformly, then an appropriate amount of anhydrous ethanol was added as a solvent (core layer 80 mL, transition layer 90 mL, shell layer 100 mL), 80% by volume of the solvent was added first, then placed on a magnetic stirrer with a stirring speed of 300 rpm until the solid powder was fully dispersed to form a slurry, the remaining ethanol was slowly added drop by drop with a dropper, and when the slurry reached a thick consistency that was easy to pour and had no obvious particle feeling, the addition of solvent was stopped; after mixing uniformly, it was transferred to an ultrasonic instrument for treatment at a frequency of 40 kHz and a power of 200 W for 20 minutes to ensure full dispersion and defoaming, and finally a uniform mixed slurry of the core layer (800 cP), the transition layer (1200 cP) and the shell layer (1500 cP) with corresponding viscosity was obtained; then after the completion of the slurry preparation, centrifugal casting forming was immediately carried out: the prepared shell layer slurry was injected into a centrifugal mold, and the slurry was formed into a uniform shell layer with a volume fraction of 25% on the periphery of the mold under a centrifugal speed of 2500 rpm for 3 minutes; then the transition layer slurry (25%) was slowly injected through the injection channel in the center of the mold under the centrifugal state for 2 minutes; finally, the core layer slurry (50%) was injected under the centrifugal speed for 3 minutes; finally, a preform with a clear shell-transition-core three-dimensional structure (thickness of 10 mm) was obtained, and then subsequent curing process was carried out.

[0063] 4) The preform with a clear shell-transition-core three-dimensional structure obtained in step 3) was firstly pre-cured at 80℃ for 2 hours to realize the initial crosslinking of the resin, then the temperature was raised to 120℃ and kept for 1 hour to form an interfacial interlocking structure, and finally the whole material was densified at 200℃ for 0.5 hour. The cured blank was placed in a tube furnace for calcination treatment, and the temperature was raised to 450℃ at a rate of 5℃ / min under the protection of N2 / H2 / CH4 mixed gas (volume ratio of 75:20:5) and kept for 2.5 hours, and finally the gradient self-heating material based on phase change-oxidation synergistic regulation was formed.

[0064] Example 2

[0065] The difference between this embodiment and Example 1 is that the mass ratio of iron stearate to lauric acid in step 1) of this embodiment is 4:6, and the amount of GO added is 0.75 wt%; in step 2), the CNT skeleton is grown at 800°C for 30 minutes; in step 3), gradient centrifugation is performed at 3000 rpm (shell layer 20% (v / v) / transition layer 20% (v / v) / core layer 60% (v / v)); calcination is performed at 500°C for 3h; 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 the amount of GO added in step 1) of this embodiment is 1.0 wt%; in step 2), the CNT skeleton is grown at 600°C for 10 minutes; in step 3), gradient centrifugation is performed at 2000 rpm (shell layer 30% (v / v) / transition layer 30% (v / v) / core layer 40% (v / v)); calcination is performed at 400°C for 2h. 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 the mass ratio of iron stearate to lauric acid in step 1) of this embodiment is 4:6, the CNT skeleton is grown at 750°C for 25 minutes, and gradient centrifugation is performed at 2800 rpm (shell 20% (v / v) / transition 25% (v / v) / core 55% (v / v)); calcination is performed at 480°C for 2.5h. 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 the mass ratio of iron stearate to lauric acid in step 1) of this embodiment is 3.5:6.5, the amount of GO added is 0.8 wt%, the CNT skeleton is grown at 650°C for 15 minutes, and gradient centrifugation is performed at 2200 rpm (shell layer 30% (v / v) / transition layer 25% (v / v) / core layer 45% (v / v)); calcination is performed at 420°C for 2.2h. 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 the mass ratio of iron stearate to lauric acid in step 1) of this embodiment is 4:6, and the amount of GO added is 1.0 wt%; in step 2), the CNT skeleton is grown at 780°C 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°C for 2.8h. The remaining steps and parameters are the same as in Example 1.

[0074] Example 7

[0075] The difference between this example and Example 1 is that in step 1) of this example, the mass ratio of iron stearate to lauric acid is 4:6, and the amount of GO added is 0.5 wt%; in step 2), the CNT skeleton is grown at 700°C 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)); and calcination is performed at 450°C for 2.5 h. The remaining steps and parameters are the same as in Example 1.

[0076] Example 8

[0077] The difference between this example and Example 1 is that in step 1) of this example, the mass ratio of iron stearate to lauric acid is 3:7, and the amount of GO added is 0.8 wt%; in step 2), the CNT skeleton is grown at 700°C 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)); and calcination is performed at 450°C for 2.5 h. The remaining steps and parameters are the same as in Example 1.

[0078] Example 9

[0079] The difference between this example and Example 1 is that in step 1) of this example, the mass ratio of iron stearate to lauric acid is 3:7, and the amount of GO added is 0.5 wt%; in step 2), the CNT skeleton is grown at 800°C 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)); and calcination is performed at 450°C for 2.5 h. The remaining steps and parameters are the same as in Example 1.

[0080] Example 10

[0081] The difference between this example and Example 1 is that in step 1) of this example, the mass ratio of iron stearate to lauric acid is 3:7, and the amount of GO added is 0.5 wt%; in step 2), the CNT skeleton is grown at 700°C 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)); and calcination is performed at 450°C for 3.0 h (originally 2.5 h). 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 the mass ratio of iron stearate to lauric acid in step 1) of this embodiment is 3:7, and the amount of GO added is 0.5wt%; the CNT framework is grown at 700℃ for 20 minutes in step 2); the gradient centrifugation is 2500rpm (shell layer 30%(v / v) / transition layer 20%(v / v) / core layer 50%(v / v)) (originally 25% / 25% / 50%) in step 3); and calcination is at 450℃ for 2.5h. The remaining steps and parameters are the same as in Example 1.

[0084] Example 12 (high core layer ratio compared to Example 1)

[0085] The difference between this embodiment and Example 1 is that the mass ratio of iron stearate to lauric acid in step 1) of this embodiment is 3:7, and the amount of GO added is 0.5wt%; the CNT framework is grown at 700℃ for 20 minutes; the gradient centrifugation is 2500rpm (shell layer 20%(v / v) / transition layer 20%(v / v) / core layer 60%(v / v)) (originally 25% / 25% / 50%) in step 3); and calcination is at 450℃ for 2.5h. 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 no GO is added in the preparation of the phase change body in this comparative example, and 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 framework construction of this comparative example, and the remaining 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 is omitted in the gradient formation of this comparative example (the shell layer directly contacts the core layer), and 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 layer ratio in this comparative example exceeds the upper limit, with a shell layer of 50% / transition layer of 20% / core layer of 30%, and 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 no hierarchical gradient formation is used in this comparative example, and the core layer is selected as a single core heating component (70wt% of reduced iron powder and 30wt% of phenolic resin), and the remaining steps and parameters are the same as in Example 1.

[0096] Table 1 Comparison of key properties of Examples 1-12 and Comparative Examples 1-5

[0097] Case Peak temperature (°C) Thermal response rate (°C / s) Duration at 200 °C (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, the peak temperature of the inventive Examples 1-12 is 475-503℃, the thermal response rate is 3.7-4.9℃ / s, and the 200℃ duration is 32-49min, as compared to Comparative Examples 1-5.

[0099] The present application realizes a revolutionary breakthrough of self-heating materials in the high temperature range by synergistically optimizing three core parameters of GO nucleation regulation (0.5-0.8wt%), CNT skeleton growth temperature (700-800℃) and gradient structure core layer proportion (40-60%), and relying on the triple technical coupling of core layer thermal inertia design, interface stress elimination and GO crystal stabilization. Experiments show that: the CNT growth temperature directly dominates the upper limit of the 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 promotion of high temperature to the growth of carbon nanotube aspect ratio and the optimization of three-dimensional heat conduction network; the GO addition amount precisely regulates the thermal response dynamics - the 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 crystal interface heat conduction, and the response rate increases by 9.8%, but excessive GO (Example 3: 1.0wt%→3.8℃ / s) will have a negative effect due to hindered molecular ordering; the proportion of the core layer of the gradient structure determines the thermal duration - when the core layer proportion decreases from 50% (v / v) (Example 1: 42min) to 40% (v / v) (Example 3: 46min), the shell layer thermal accumulation effect prolongs the duration by 9.5%, and when the core layer increases to 60% (v / v) (Example 12: 32min), although the response rate increases to 4.9℃ / s, the duration sharply decreases by 23.8% due to the release of high thermal inertia.

[0100] Example 12: 32min) although the response rate increases to 4.9℃ / s, the duration sharply decreases by 23.8% due to the release of high thermal inertia.

[0101] The deep synergy of the triple technology creates a performance leap: in embodiment 2 (0.75wt% GO + 800℃ CNT + 60% (v / v) core layer), the GO nucleation-induced crystal ordering, the rapid heat conduction of high aspect ratio CNT and the high thermal inertia release of the core layer form a positive cycle, making the peak temperature break through 503℃ and the response rate reach 4.7℃ / s; and through the combination strategy of core layer proportion control (40-50%) + interface transition layer stress dissipation + GO crystal thermal stability reinforcement (such as the core layer 50% (v / v) / duration 42min of embodiment 1; the core layer 50% (v / v) / duration 46min of embodiment 10), the problem of thermal persistence in the high temperature range of 480-500℃ is successfully solved - all the embodiments with core layer ≤50% (1 / 3 / 5 / 8 / 10 / 11) have a duration of more than 40min, among which embodiment 10 reaches 46min, which is 155.6% higher than the traditional homogeneous material (comparative example 2: 18min), realizing the technical leap from "short peak" to "long steady state".

[0102] The reverse verification of the comparative example proves the irreplaceability of the technology: the absence of GO nucleating agent (comparative example 1) causes the peak temperature to drop to 458℃ (↓30℃ compared with embodiment 1) due to the sharp increase of grain boundary thermal resistance; the ordinary graphite substrate (comparative example 2) causes the CNT network to break due to the lack of pore structure, with a response rate of only 1.9℃ / s; and the cancellation of the gradient transition layer (comparative example 3) causes the interface thermal stress to concentrate, with a duration of only 25min (↓40%). These failure cases confirm that GO crystal stabilization is the basis of high-temperature nucleation, CNT high-thermal-conductivity network is the core carrier of rapid response, and gradient interface design is the structural guarantee of long-term work.

[0103] In summary, the present application realizes long-term and continuous work in the high-temperature window of 400-500℃ through the "nucleation-heat storage-heat storage" three-level synergy mechanism, breaks through the inherent contradiction of "high response and short life" of traditional materials, and provides a new material paradigm for high-temperature self-heating systems.

[0104] In the above embodiments, the description of each embodiment has its own focus, and the parts not described in detail in a certain embodiment can be referred to the related description of other embodiments.

[0105] The numerical range described in the present application includes all numerical values within the range, and includes the range value composed of any two numerical values within the range. Different numerical values of the same index appearing in all embodiments of the present application can be combined to form a range value.

[0106] The technical features in the claims and / or description of the present application can be combined, and the combination manner is not limited to the combination obtained by reference relationship in the claims. The technical solutions obtained by combining the technical features in the claims and / or description are also within the protection scope of the present application.

[0107] The above merely describes preferred embodiments of the present application, and is not intended to limit the present application in any form. Any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present application still falls within the scope of the technical solutions of the present application.

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.

2. The gradient self-heating material based on phase change-oxidation synergistic regulation as described in claim 1, characterized in that, 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.

3. 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 ≤50μm; the particle size of the catalytic phase change material particles is 100-200μm.

4. A method for preparing a gradient self-heating material based on phase change-oxidation synergistic regulation, 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 catalytic metal ion solution → Fe3+ + Solution impregnation modification; c) Centrifugal gradient molding: sequential perfusion of shell-transition layer-core layer at 2000-3000 rpm; 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.

5. The method for preparing gradient self-heating materials based on phase change-oxidation synergistic regulation as described in claim 4, 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.

6. The method for preparing gradient self-heating materials based on phase change-oxidation synergistic regulation as described in claim 4, characterized in that, In step b), the hierarchical framework construction meets the following requirements: 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.

7. The method for preparing gradient self-heating materials based on phase change-oxidation synergistic regulation as described in claim 4, 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.

8. The method for preparing gradient self-heating materials based on phase change-oxidation synergistic regulation as described in claim 4, characterized in that, 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 800 cP → transition layer 1200 cP → core layer 1500 cP.

9. The method for preparing gradient self-heating materials based on phase change-oxidation synergistic regulation as described in claim 4, characterized in that, In step d), the three-stage gradient curing includes: first, 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), the temperature is raised to 400-500℃ at 3-7℃ / min and held for 2-3 hours to form an interlocking interface of phase change material crystal-carbonized resin-metal particles.

10. 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 any one of claims 1-4; 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.