A TiO2-foamed carbon composite microwave absorbing material, its preparation method and application

Abstract

The application discloses a TiO2-foam carbon composite wave-absorbing material and a preparation method and application thereof, and comprises the following steps: performing a hydroxymethylation reaction on melamine and a formaldehyde aqueous solution under alkaline conditions to obtain a melamine-formaldehyde resin prepolymer solution; adding dropwise di(acetylacetonyl) titanium diisopropyl titanate and stirring to react to obtain a titanium-doped colloid; adding a non-ionic surfactant, a physical foaming agent and a curing agent, and then performing shear homogenization treatment to obtain a foaming slurry; performing step-by-step curing to obtain a titanium-doped organic foam block; and performing carbonization and crushing to obtain the TiO2-foam carbon composite wave-absorbing material. The wave-absorbing material effectively utilizes the dielectric loss capacity of TiO2 and the electric conduction loss characteristics of foam carbon, and further introduces a large number of heterogeneous interfaces, pore structures and defects, so that the interface polarization, multiple scattering and dipole polarization effects are enhanced, and the impedance matching and electromagnetic wave loss capacity of the material are improved.

Description

Technical Field

[0001] This invention belongs to the technical field of electromagnetic wave absorption and shielding functional materials, and particularly relates to a TiO2-foamed carbon composite wave absorbing material, its preparation method and application. Background Technology

[0002] With the rapid development of modern electronic information technology and wireless communication technology, the application of electromagnetic waves is becoming increasingly widespread, and the resulting problems such as electromagnetic radiation pollution and electromagnetic interference (EMI) are becoming more and more prominent. Developing efficient, lightweight, broadband, and strongly absorbing electromagnetic wave materials has become key to solving these problems. An ideal absorbing material should possess excellent impedance matching characteristics, enabling it to maximize the penetration of incident electromagnetic waves into the material's interior and efficiently convert them into heat energy through mechanisms such as dielectric loss and magnetic loss.

[0003] Titanium dioxide (TiO2) is considered a promising microwave absorbing material due to its high dielectric constant and good dielectric loss capability. However, TiO2 alone exhibits poor impedance matching and lacks an effective loss synergy mechanism, often resulting in its absorption performance failing to meet the requirements of broadband and strong absorption. Therefore, TiO2 is often composited with carbon materials, utilizing the excellent conductivity and loss characteristics of carbon to enhance the overall loss capability of the material. However, in traditional composite methods, the interfacial bonding between TiO2 and the carbon phase is weak and the dispersion is uneven, limiting the interfacial polarization and multiple scattering effects of the composite material and hindering further improvement in its absorption performance.

[0004] In the preparation of carbon-based composite materials, organometallic precursors (such as metal acetylacetone) are often used in methods such as chemical vapor deposition to prepare carbon-coated metal nanocomposites. For example, iron acetylacetone and cobalt acetylacetone are solids at room temperature with moderate evaporation temperatures (140~230℃). During pyrolysis, the generated oxides such as Fe and Co are easily reduced by carbon to elemental metals and can dissolve carbon, ultimately forming metals. The TiO2 produced by pyrolysis exhibits high chemical stability and is difficult to reduce with carbon (reduction temperature exceeds 900℃). Furthermore, TiO2 has extremely weak carbon solubility, making it difficult to achieve effective carbon coating or uniform composite formation of TiO2 using traditional methods. This limits the effectiveness of TiO2 coating. Structural design and performance optimization of carbon composite microwave absorbing materials. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the background art above, and to provide a TiO2-foamed carbon composite microwave absorbing material, its preparation method and application, which has good microwave absorption performance.

[0006] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows:

[0007] A method for preparing a TiO2-foamed carbon composite microwave absorbing material includes the following steps:

[0008] (1) Melamine and formaldehyde aqueous solution were subjected to hydroxymethylation reaction under alkaline conditions to obtain melamine-formaldehyde resin prepolymer solution;

[0009] (2) Diisopropyl di(acetylacetonyl)titanate was added dropwise to the melamine-formaldehyde resin prepolymer solution and stirred to react, thus obtaining titanium-doped colloid;

[0010] (3) Add nonionic surfactant, physical foaming agent and curing agent to titanium doped colloid, and then perform shear homogenization treatment to obtain foamed slurry;

[0011] (4) The foaming slurry is subjected to step curing to obtain titanium-doped organic foam blocks; the step curing includes: keeping the temperature at 50-65℃, raising the temperature to 120-150℃ and keeping the temperature, raising the temperature to 180-220℃ and keeping the temperature.

[0012] (5) Carbonize and crush the titanium-doped organic foam block to obtain the TiO2-foam carbon composite microwave absorbing material; the carbonization includes: heating to 700-900℃ at a heating rate of 1-4℃ / min and holding under an inert atmosphere.

[0013] Furthermore, in step (1), the molar ratio of melamine to formaldehyde is 1:(2-3).

[0014] Furthermore, the conditions for the hydroxymethylation reaction in step (1) are: pH 8-9 and reaction temperature 60-85℃.

[0015] Furthermore, in step (2), the molar ratio of diisopropyl di(acetylacetonyl)titanate to melamine is (1-4):1.

[0016] Furthermore, the reaction conditions in step (2) are: react at a temperature of 60-80℃, and continue to keep warm and stir for 0.5-2 hours after the addition is completed.

[0017] Furthermore, in step (3), the amounts of nonionic surfactant, physical foaming agent and curing agent added are 0.5-1.5%, 8-15% and 3-6% of the mass of titanium-doped colloid, respectively.

[0018] Furthermore, the nonionic surfactant in step (3) is selected from at least one of fatty alcohol polyoxyethylene ether, alkylphenol polyoxyethylene ether, Tween series or Span series; the physical foaming agent is selected from at least one of n-pentane, isopentane or cyclopentane; and the curing agent is selected from at least one of ammonium chloride, ammonium sulfate, ammonium phosphate, oxalic acid, citric acid, p-toluenesulfonic acid or benzenesulfonic acid.

[0019] Furthermore, the step-by-step curing in step (4) includes: holding at 50-65℃ for 1-3 hours, raising the temperature to 120-150℃ and holding for 2-4 hours, raising the temperature to 180-220℃ and holding for 2-4 hours; the carbonization holding time is 2-4 hours.

[0020] The present invention provides a TiO2-foamed carbon composite microwave absorbing material, which is prepared by the preparation method described above.

[0021] This invention provides an application of a TiO2-foamed carbon composite microwave absorbing material, which is applied to the field of electromagnetic wave absorption.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] This invention proposes a highly dispersed TiO2-foam carbon composite material based on organic titanium precursor blending and slow-release carbonization, and its preparation method. This method involves uniformly blending the organic titanium precursor and the carbon source precursor in the liquid phase, followed by a programmed slow-release carbonization process. This allows the titanium species and the carbon matrix to interact at the molecular scale, achieving uniform dispersion and strong bonding of TiO2 nanoparticles within the three-dimensional network structure of the foam carbon. The resulting TiO2-foam carbon composite microwave absorbing material possesses a three-dimensional interpenetrating network porous structure derived from foam gel, with nano-TiO2 crystals uniformly dispersed within the amorphous carbon matrix. This structure not only effectively utilizes the dielectric loss capability of TiO2 and the conductive loss characteristics of foam carbon, but also enhances interfacial polarization, multiple scattering, and dipole polarization effects by introducing numerous heterogeneous interfaces, pore structures, and defects. This synergistically improves the impedance matching and electromagnetic wave loss capability of the material, providing a new approach for the design of high-performance, lightweight, broadband microwave absorbing materials. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is an optical photograph of the TiO2-foamed carbon composite material after being crushed in Example 1.

[0026] Figure 2 This is a model structural diagram of the TiO2-foamed carbon composite material of Example 1.

[0027] Figure 3This is a TEM image of the TiO2-foamed carbon composite material from Example 1.

[0028] Figure 4 The image shows the microwave absorption performance of the TiO2-foamed carbon composite material (Example 1).

[0029] Figure 5 The image shows the microwave absorption performance of the TiO2-foamed carbon composite material (Example 2).

[0030] Figure 6 The image shows the microwave absorption performance of the TiO2-foamed carbon composite material (Example 3). Detailed Implementation

[0031] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0032] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0033] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0034] This invention uses melamine, formaldehyde, and liquid titanium acetylacetonate as raw materials. By precisely controlling the molar ratio of the raw materials, a titanium-doped resin colloid is first prepared. Then, a specific surfactant, a low-boiling-point physical foaming agent, and a curing agent are introduced, and a homogeneous foaming slurry is formed by high-speed shearing. Finally, through an integrated process of "stepped foaming curing-programmed temperature-controlled carbonization", foam gelation, deep resin curing, organic-inorganic hybridization, and controllable carbonization and crystallization are completed sequentially in an inert atmosphere.

[0035] The liquid acetylacetone titanium described in this invention refers to diisopropyl di(acetylacetone)titanate. It can be titanium acetylacetone LD-801 from Yangzhou Lida Resin Co., Ltd., whose main component is diisopropyl di(acetylacetone)titanate, or it can be a corresponding foreign brand: TILCOM PI-2 from Tioxide UK Limited, or ICI P-12.

[0036] In some embodiments, the preparation method of the TiO2-foamed carbon composite microwave absorbing material of the present invention includes the following steps:

[0037] Step 1: Preparation of titanium-doped melamine-formaldehyde resin colloid

[0038] S1.1 Raw material feeding and reaction: Melamine powder and formaldehyde aqueous solution are added to the reaction vessel at a melamine to formaldehyde molar ratio of 1:(2-3). Under pH 8-9 conditions (with the addition of an alkaline catalyst, such as triethanolamine), the temperature is raised to 60-85℃ and the mixture is stirred at 300-500 rpm to carry out the hydroxymethylation reaction for 30-45 minutes to form a clear and transparent basic melamine-formaldehyde resin prepolymer solution.

[0039] In this invention, the chemical structure advantage of the melamine-formaldehyde resin prepolymer is key to its successful construction of a high-performance microwave absorbing material precursor. Its core molecule, melamine, possesses a rigid triazine ring structure and can connect up to six highly reactive hydroxymethyl groups, forming a prepolymer with extremely high functionality. This characteristic brings two core advantages: First, during the curing and foaming stage, the high-density hydroxymethyl groups can rapidly undergo cross-linking condensation to form a rigid three-dimensional network, thereby promptly capturing and fixing the pores generated by the foaming agent, forming a stable and uniformly porous foam skeleton, providing a perfect template for the final porous carbon. Second, the triazine ring itself is a nitrogen-rich structure; after high-temperature carbonization, nitrogen atoms can be retained in the carbon skeleton as dopant, forming nitrogen-doped carbon. This doping not only enhances the material's conductivity loss but also introduces dipole polarization, significantly improving dielectric loss-type microwave absorption capability—a unique performance source not possessed by other non-nitrogen-rich hydroxymethyl polymers.

[0040] S1.2 Introduction of the organotitanium precursor: Maintaining the temperature of the prepolymer reaction system at 60-80℃, and under continuous stirring (300-500 rpm), slowly and uniformly add a measured amount of liquid titanium acetylacetonate using a constant-pressure dropping funnel. The amount of liquid titanium acetylacetonate added should be such that its molar ratio with melamine is (1-4):1. The dropping time should be controlled within 1-2 hours to ensure sufficient coordination between the organotitanium precursor molecules and the active groups such as hydroxymethyl groups in the prepolymer. After the dropping is complete, continue stirring at the temperature for 0.5-2 hours to obtain a homogeneous, stable pale yellow to amber titanium-doped colloid. Then, cool the colloid to room temperature.

[0041] The dropping rate of the liquid acetylacetone titanium is controlled within a range that ensures the temperature fluctuation of the system does not exceed ±2℃, so as to guarantee the uniform dispersion of titanium species at the molecular level.

[0042] Liquid titanium acetylacetonate can coordinate or undergo preliminary reactions with active groups such as hydroxymethyl groups in the system, thereby achieving uniform introduction and dispersion of titanium species at the molecular level.

[0043] In the preparation process of this invention, the unique chelate structure of liquid acetylacetone titanium plays an irreplaceable role. Its most prominent advantages lie in its excellent hydrolytic stability and controllable reactivity. As a strong chelating ligand, acetylacetone can form a stable six-membered ring with the titanium center, allowing it to be directly and stably added to the aqueous resin prepolymer system, achieving uniform dispersion of titanium species at the molecular level and avoiding the problems of violent hydrolysis and instantaneous aggregation of ordinary titanate esters upon contact with water. This controllability is fully demonstrated in the subsequent stepped heating process: in the lower-temperature foaming-gel stage, it can partially decompose and promote resin crosslinking, helping to stabilize the foam prototype; in the higher-temperature curing and carbonization stage, it can be transformed into nano-titanium dioxide in a mild and gradual manner and uniformly dispersed in situ within the carbon skeleton. This slow and controlled transformation process, combined with the carefully designed slow heating program in the process, effectively prevents the high-temperature sintering and aggregation of nanoparticles, ensuring that TiO2 in the final composite material remains at the nanoscale and highly dispersed, laying the foundation for the formation of a large number of effective heterogeneous interfaces, thereby enhancing the key microwave absorption mechanism of interfacial polarization loss.

[0044] Step 2: Preparation and homogenization of foaming slurry

[0045] S2.1 Additives: To the cooled titanium-doped colloid, add sequentially 0.5-1.5% by weight of a nonionic surfactant, 8-15% by weight of a physical foaming agent with a boiling point of 25-50℃ (such as pentanes), and 3-6% by weight of a curing agent (which can be pre-prepared as a 10 wt% aqueous solution). The surfactant is used to stabilize the subsequently formed foam, the physical foaming agent is used to generate bubbles, and the curing agent is used to catalyze the cross-linking and curing of the resin.

[0046] The nonionic surfactant is selected from at least one of fatty alcohol polyoxyethylene ether, alkylphenol polyoxyethylene ether, Tween series (such as Tween-80) or Span series; the physical foaming agent is selected from n-pentane, isopentane, cyclopentane or mixtures thereof; the curing agent is selected from at least one of ammonium chloride, ammonium sulfate, ammonium phosphate, oxalic acid, citric acid, p-toluenesulfonic acid or benzenesulfonic acid.

[0047] S2.2 High-speed shear homogenization: Place the above mixture in a high-speed shear homogenizer and homogenize it at a speed of 10,000-15,000 rpm for 3-5 minutes to ensure that the physical foaming agent is uniformly dispersed in the slurry as micron-sized droplets. Through high-speed shear emulsification, all components are homogenized and dispersed, and finally a stable, uniform, fine and fluid emulsion foaming slurry is formed.

[0048] Step 3: Step-by-step curing and foam shaping

[0049] S3.1 Low-Temperature Foaming and Gelation: The homogenized foaming slurry is rapidly transferred to an open mold or heat-resistant flat plate, and then placed in a preheated drying oven or tube furnace (under an inert atmosphere such as N2) at 50-65℃. It is held at 50-65℃ for 1-3 hours. During this stage, the physical foaming agent (such as n-pentane) vaporizes upon heating, causing the slurry to expand in volume. Simultaneously, the resin begins to gel under acidic conditions. These two processes work synergistically to form a preliminary, moist foam structure. Liquid titanium acetylacetonate partially hydrolyzes or pyrolyzes during this process, promoting local cross-linking of the system and helping to stabilize the foam structure.

[0050] S3.2 Medium-temperature cross-linking and curing: Increase the temperature to 120-150℃ at a rate of 1-2℃ / min and hold for 2-4 hours. This stage is the key process for deep cross-linking and curing of melamine-formaldehyde resin, where the foam skeleton is permanently fixed. Simultaneously, titanium species undergo further hydrolysis / pyrolysis transformation within the organic skeleton, generating amorphous titanium oxides or nano-TiO2, which are uniformly dispersed within the formed organic foam skeleton.

[0051] S3.3 High-Temperature Post-Cure and Impurity Removal: Continue heating to 180-220℃ and hold at this temperature for 2-4 hours. This stage aims to thoroughly remove residual free formaldehyde, water, and other small volatile molecules from the resin curing process, and to promote the formation of a more stable hybrid structure between the titanium species and the organic framework before carbonization, resulting in a dry, hard titanium-doped organic foam block.

[0052] Step 4: Programmed slow-release carbonization

[0053] The fully cured titanium-doped organic foam block was broken into small pieces and placed in a quartz boat in a tube furnace. Under the protection of a continuous flow of high-purity argon gas (Ar, purity ≥99.999%), a programmed temperature-increasing carbonization treatment was carried out.

[0054] S4.1 Slow Heating Carbonization: The furnace temperature is raised from room temperature to the preset carbonization final temperature of 700-900℃ at a slow heating rate of 1-4℃ / min. The slow heating rate is the core of "slow-release carbonization," ensuring that the organic foam releases small-molecule gases gradually during thermal decomposition into carbon, thereby maximizing the preservation of its porous foam structure and promoting the slow crystallization and good dispersion of TiO2 nanoparticles. The slow heating process aims to ensure that the titanium-doped foam carbonizes smoothly, avoiding the destruction of the formed porous structure due to the large amount of gas generated by the rapid decomposition of organic matter in a short time, while effectively preventing the formation of large-sized TiO2 particles due to excessively high-temperature sintering.

[0055] The preferred heating rate is 1.5-2.5℃ / min to achieve gradual carbonization of the organic framework and uniform development of TiO2 nanocrystals, preventing the collapse of the porous structure and excessive sintering of particles.

[0056] During the carbonization stage, the flow rate of high-purity argon is typically controlled at 50-100 sccm. This flow rate is sufficient to maintain an inert protective atmosphere, expel decomposition gases, and prevent excessive gas flow from blowing away the porous foam powder or affecting temperature uniformity.

[0057] S4.2 Final Temperature Holding and Crystallization: After reaching the target temperature (700-900℃), maintain the temperature for 2-4 hours to ensure complete carbonization and full crystallization of TiO2 (mainly forming anatase phase, possibly containing a small amount of rutile phase). After the holding period, allow the furnace to cool naturally to room temperature.

[0058] Step 5: Product Post-processing

[0059] S5.1 Crushing and Classification: The carbonized foam block product is placed in a mortar or a small pulverizer for preliminary crushing. Subsequently, it is sieved using a standard sieve to collect the micron-sized powder that passes through a 500-mesh sieve (corresponding to an aperture of approximately 25 micrometers), ultimately yielding a TiO2-carbon composite material with a foam-like porous structure.

[0060] S5.2 Storage: Store the obtained powder in a desiccator for characterization and performance testing.

[0061] Product characteristics: The final product consists of a three-dimensional interconnected foam carbon network, in which nano-TiO2 particles (typically 10-50 nm in diameter) are highly dispersed and firmly embedded in the pore walls or nodes of the carbon framework. The foam carbon itself is rich in micropores and mesopores, with low density and high specific surface area.

[0062] During the step-curing stage, the organic titanium precursor undergoes hydrolysis in an acidic environment and integrates with the resin crosslinking network, achieving uniform dispersion of titanium species at the molecular scale. In the subsequent slow-release carbonization process, the organic framework gradually pyrolyzes into conductive foamed carbon, while the in-situ generated titanium oxide is "fixed" by the carbon matrix and crystallizes into TiO2 at medium to high temperatures. This integrated strategy of "mixing-curing-slow-release carbonization" overcomes the challenge of effective carbon coating of TiO2 by vapor deposition, constructing a unique microstructure with strong interfacial bonding between TiO2 and the carbon phase. This structure achieves efficient attenuation and broadband absorption of incident electromagnetic waves through the synergistic effects of multiple mechanisms, including the conductive loss of foamed carbon, the dielectric loss of TiO2, interfacial polarization caused by abundant heterogeneous interfaces, and multiple scattering and dipole polarization resulting from the porous structure.

[0063] This invention introduces a titanium source uniformly at the molecular level before resin foaming, and utilizes the synergistic effect of the foaming process and the hydrolysis / pyrolysis of titanium species to achieve highly uniform dispersion of nano-TiO2 in a three-dimensional carbon framework. The resulting composite material possesses a unique foam-derived interpenetrating network porous structure with a high specific surface area, showing promising application prospects in the field of electromagnetic wave absorption and shielding.

[0064] Example 1

[0065] First, melamine, formaldehyde, and liquid titanium acetylacetone (LD-801 from Yangzhou Lida Resin Co., Ltd., whose main component is diisopropyl di(acetylacetone)titanate) were accurately weighed according to a molar ratio of melamine, formaldehyde, and liquid titanium acetylacetone of 1:2.5:1. Melamine powder and formaldehyde aqueous solution were reacted at 80°C for 30 minutes under alkaline conditions (pH 8) to synthesize a melamine-formaldehyde resin prepolymer. Then, liquid titanium acetylacetone was slowly added dropwise (dropping time 1.5 hours) and the reaction was continued for 1 hour to obtain a uniform titanium-doped colloid.

[0066] Subsequently, 1% Tween-80 surfactant, 10% n-pentane foaming agent and 5% oxalic acid curing agent were added to the colloid in sequence, and the mixture was homogenized at 15,000 rpm for 5 minutes to obtain a homogeneous foamed slurry.

[0067] The slurry was initially foamed and gelled at 55°C for 2 hours under N2 atmosphere, then cured at 130°C for 3 hours and 200°C for 3 hours to obtain shaped titanium-doped foam.

[0068] Finally, the foam was placed in an argon atmosphere and carbonized to 800°C at a slow heating rate of 2°C / min and held for 3 hours. After crushing and sieving, a foam carbon composite material with uniform TiO2 dispersion was obtained.

[0069] Example 2

[0070] Except for the following conditions, this embodiment is the same as embodiment 1:

[0071] The molar ratio of melamine, formaldehyde, and liquid titanium acetylacetonate was 1:2:2. After forming the titanium-doped colloid, citric acid was used as a curing agent to prepare the foaming slurry. The step-curing process was carried out in a nitrogen atmosphere, successively at 60℃ / 2h, 140℃ / 3h, and 180℃ / 3h. In the critical slow-release carbonization stage, the heating rate was reduced to 1℃ / min, and the temperature was held at a relatively low final temperature of 700℃ for 4 hours to obtain more dispersed nano-TiO2 and a more developed carbon framework pore structure.

[0072] Example 3

[0073] Except for the following conditions, this embodiment is the same as embodiment 1:

[0074] The amount of liquid acetylacetone titanium was further increased to achieve a molar ratio of melamine, formaldehyde, and titanium precursor of 1:2.7:3. The foaming slurry used p-toluenesulfonic acid as the curing agent. The curing process was completed in an air-circulating oven (50℃ / 2h, 120℃ / 3h, 220℃ / 3h). The carbonization process employed a relatively rapid heating rate of 4℃ / min and a relatively high final temperature of 900℃, held for 2 hours, to promote TiO2 crystallization and investigate the effect of high temperature on the stability of the foam structure.

[0075] Figure 1 This is an optical photograph of the TiO2-foamed carbon composite material after being pulverized in Example 1, showing it in powder form.

[0076] Figure 2 This is a model structural diagram of the TiO2-foamed carbon composite material of Example 1, with TiO2 particles distributed on the surface of the foamed carbon.

[0077] Figure 3 The image shows a TEM image of the TiO2-foamed carbon composite material from Example 1, in which TiO2 particles are clearly visible, embedded in a porous carbon layer.

[0078] Figure 4 The image shows the microwave absorption performance of the TiO2-foamed carbon composite material (Example 1). The lowest reflection loss is -41.2dB and the effective bandwidth is 10.2dB.

[0079] Figure 5 The image shows the microwave absorption performance of the TiO2-foamed carbon composite material (Example 2). The lowest reflection loss is -36.5dB and the effective bandwidth is 11.2dB.

[0080] Figure 6 The image shows the microwave absorption performance of the TiO2-foamed carbon composite material (Example 3), with a minimum reflection loss of -21.4 dB and an effective bandwidth of 9.7 dB. Increasing the reaction temperature leads to an increase in the degree of crystallization of TiO2 and graphitization of carbon, thereby deteriorating the microwave absorption performance. On the one hand, both processes significantly increase the dielectric constant of the material, causing severe impedance mismatch, resulting in most microwaves being reflected at the surface and unable to penetrate. On the other hand, the crystallization and graphitization processes eliminate internal defects and interfaces in the material, weakening the key polarization loss mechanism. Although this may increase conductivity, it creates an unfavorable situation of "strong reflection and weak absorption."

[0081] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Therefore, any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention should fall within the protection scope of the present invention.

Claims

1. A method for preparing a TiO2-foamed carbon composite microwave absorbing material, characterized in that, The steps include the following: (1) Melamine and formaldehyde aqueous solution were subjected to hydroxymethylation reaction under alkaline conditions to obtain melamine-formaldehyde resin prepolymer solution; the molar ratio of melamine to formaldehyde was 1:(2-3); (2) Diisopropyl di(acetylacetonate) titanate was added dropwise to a melamine-formaldehyde resin prepolymer solution and stirred to obtain a titanium-doped colloid; the molar ratio of diisopropyl di(acetylacetonate) titanate to melamine was (1-4):

1. (3) Add nonionic surfactant, physical foaming agent and curing agent to titanium doped colloid, and then perform shear homogenization treatment to obtain foamed slurry; (4) The foaming slurry is subjected to step curing to obtain titanium-doped organic foam blocks; the step curing includes: keeping the temperature at 50-65℃, raising the temperature to 120-150℃ and keeping the temperature, raising the temperature to 180-220℃ and keeping the temperature. (5) Carbonize and crush the titanium-doped organic foam block to obtain the TiO2-foam carbon composite microwave absorbing material; the carbonization includes: heating to 700-900℃ at a heating rate of 1-4℃ / min and holding under an inert atmosphere.

2. The preparation method of the TiO2-foamed carbon composite microwave absorbing material according to claim 1, characterized in that, The conditions for the hydroxymethylation reaction in step (1) are: pH 8-9 and reaction temperature 60-85℃.

3. The preparation method of the TiO2-foamed carbon composite microwave absorbing material according to claim 1, characterized in that, The reaction conditions in step (2) are: react at a temperature of 60-80℃, and continue to keep warm and stir for 0.5-2 hours after the addition is complete.

4. The preparation method of the TiO2-foamed carbon composite microwave absorbing material according to claim 1, characterized in that, In step (3), the amounts of nonionic surfactant, physical foaming agent and curing agent added are 0.5-1.5%, 8-15% and 3-6% of the mass of titanium-doped colloid, respectively.

5. The preparation method of the TiO2-foamed carbon composite microwave absorbing material according to claim 1, characterized in that, The nonionic surfactant in step (3) is selected from at least one of fatty alcohol polyoxyethylene ether, alkylphenol polyoxyethylene ether, Tween series or Span series; the physical foaming agent is selected from at least one of n-pentane, isopentane or cyclopentane; the curing agent is selected from at least one of ammonium chloride, ammonium sulfate, ammonium phosphate, oxalic acid, citric acid, p-toluenesulfonic acid or benzenesulfonic acid.

6. The preparation method of the TiO2-foamed carbon composite microwave absorbing material according to claim 1, characterized in that, Step (4) of the step curing includes: holding at 50-65℃ for 1-3 hours, raising the temperature to 120-150℃ and holding for 2-4 hours, raising the temperature to 180-220℃ and holding for 2-4 hours; the holding time for carbonization is 2-4 hours.

7. A TiO2-foamed carbon composite microwave absorbing material, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 6.

8. An application of a TiO2-foamed carbon composite microwave absorbing material, characterized in that, The TiO2-foamed carbon composite microwave absorbing material described in claim 7 is applied to the field of electromagnetic wave absorption.

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