Epoxy resin-based composite material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of electromagnetic wave absorbing materials, in particular to an epoxy resin-based composite material as well as a preparation method and application thereof. Comprising the following steps: immersing balsa wood chips into an anionic surfactant solution for pretreatment to obtain pretreated balsa wood chips; mixing the pretreated balsa wood chips with a cobalt-iron solution, and reacting to obtain a CoFe-LDH precursor loaded balsa wood composite material; the CoFe-LDH precursor loaded bala wood composite material is sequentially subjected to pre-oxidation treatment and carbonization treatment, and a Fe2O3 / Co3O4 loaded carbon material is obtained; and mixing the Fe2O3 / Co3O4-loaded carbon material with an epoxy resin solution, and curing to obtain the epoxy resin-based composite material. The epoxy resin-based composite material provided by the invention can realize high electromagnetic wave absorptivity in a broadband range of 11.8 GHz-18 GHz under the condition of low thickness of the composite material, and has the characteristics of light weight and high strength.

Description

Technical Field

[0001] The invention relates to the technical field of electromagnetic wave absorbing materials, and in particular to an epoxy resin-based composite material and a preparation method and application thereof. Background Art

[0002] Due to the widespread application of electronic technology, the rapid development and popularization of radio broadcasting, mobile phones, televisions, new energy vehicles, and microwave technology, the power of radio frequency equipment has increased exponentially, and the electromagnetic radiation on the ground has increased significantly. Electromagnetic waves not only cause electronic equipment to malfunction, but also harm human health. At present, the impact of electromagnetic waves on human society has attracted the attention of countries around the world and has been listed as one of the environmental protection projects. Using absorbing materials as the shell packaging material of electronic equipment or devices, using their characteristics of absorbing electromagnetic waves, limiting electromagnetic waves to a certain range, reducing or avoiding electromagnetic wave radiation from causing harm to the human body, is currently a more commonly used method for controlling electromagnetic wave pollution.

[0003] Epoxy resin is a polymer composite material with good physical and chemical properties. It is widely used as a packaging material for electronic devices and devices. The balsa sandwich composite material prepared by compounding epoxy resin with balsa wood has the advantages of good environmental sustainability, low raw material cost, light weight and high strength, and good thermal insulation performance. It is widely used in the field of electronic equipment and device packaging materials. However, the composite material has poor wave absorption effect and can only be used for wave absorption in a lower frequency range.

[0004] Researchers usually use the method of adding fillers, porous materials or metal powders to improve the wave absorption performance of epoxy resin-based composite materials. For example, adding fillers such as coke and graphite to epoxy resin can improve the wave absorption performance of epoxy resin; adding porous materials with fine pore structures can increase the surface area of ​​the material and further improve the wave absorption performance; adding metal powders such as iron powder and copper powder can absorb high-frequency signals, thereby improving the wave absorption performance of epoxy resin. However, these methods will result in poor self-sustaining power and high viscosity of the film-forming resin of the wave-absorbing layer, which seriously affects the manufacturing processability of the wave-absorbing composite material layer. Due to poor interlayer adhesion, it will also affect the mechanical properties of the composite material structure; and most of the materials obtained are narrow-band wave-absorbing materials with limited wave absorption effects. Designing and preparing lightweight, high-strength composite materials with broadband and strong wave absorption functions is an urgent problem to be solved. Summary of the invention

[0005] In order to solve the above problems, the present invention provides an epoxy resin-based composite material and a preparation method and application thereof. The epoxy resin-based composite material provided by the present invention can achieve a higher electromagnetic wave absorption rate in a wide frequency range of 11.8GHz to 18GHz under the condition of lower composite material thickness, and has the characteristics of light weight and high strength.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing an epoxy resin-based composite material, comprising the following steps:

[0008] 1) immersing balsa wood chips in an anionic surfactant solution for pretreatment to obtain pretreated balsa wood chips;

[0009] 2) mixing the pretreated balsa wood chips obtained in step 1) with a cobalt-iron solution and reacting them to obtain a balsa wood composite material loaded with a CoFe-LDH precursor;

[0010] The components of the cobalt-iron solution include urea, soluble cobalt salt, soluble iron salt and water;

[0011] 3) subjecting the CoFe-LDH precursor-loaded balsa wood composite material obtained in step 2) to a pre-oxidation treatment and a carbonization treatment in sequence to obtain a Fe2O3 / Co3O4-loaded carbon material;

[0012] 4) mixing the Fe2O3 / Co3O4 loaded carbon material obtained in step 3) with an epoxy resin solution, and curing the mixture to obtain an epoxy resin-based composite material;

[0013] The components of the epoxy resin solution include epoxy resin, epoxy resin curing agent and epoxy resin accelerator.

[0014] Preferably, the method for obtaining the balsa wood chips in step 1) comprises: cutting along the growth direction of the balsa wood to obtain pieces with a size of 1×2×0.3 cm 3 of balsa wood chips.

[0015] Preferably, the anionic surfactant in the anionic surfactant solution in step 1) comprises one or more of sodium polyacrylate, sodium alkylbenzene sulfonate and sodium alkyl sulfate;

[0016] The mass percentage of the anionic surfactant solution is 1-3%.

[0017] Preferably, the pretreatment conditions in step 1) include: a temperature of 50-80° C. and a time of 0.5-2 h.

[0018] Preferably, in step 2), the volume ratio of the moles of urea, the moles of soluble cobalt salt, the moles of soluble iron salt and water is 7.5-15 mmol: 0.75-7.5 mmol: 0.25 mmol: 60 mL;

[0019] The soluble cobalt salt includes one or more of cobalt nitrate, cobalt chloride, cobalt sulfate and cobalt carbonate;

[0020] The soluble iron salt includes one or more of ferric nitrate, ferric chloride, ferric sulfate and ferric nitrate.

[0021] Preferably, the volume ratio of the pretreated balsa wood chips in step 2) to the cobalt-iron solution is 1 chip: 60 mL;

[0022] The reaction conditions include: temperature of 100-160° C. and time of 4-10 h.

[0023] Preferably, the conditions of the pre-oxidation treatment in step 3) include: a temperature of 200-300° C. and a time of 2-4 hours;

[0024] The carbonization treatment conditions include: carbonization in a nitrogen atmosphere at a temperature of 600-800° C. for 2-4 hours.

[0025] Preferably, in step 4), the mass ratio of the carbon material loaded with Fe2O3 / Co3O4 to the epoxy resin solution is 1:19;

[0026] The mass ratio of the epoxy resin, epoxy resin curing agent and epoxy resin accelerator is 10:3:1;

[0027] The epoxy resin curing agent includes diethylmethylphenylenediamine;

[0028] The epoxy resin accelerator includes (2,4,6-tris(dimethylamino)methyl)phenol.

[0029] The present invention also provides an epoxy resin-based composite material prepared by the preparation method described in the above technical solution.

[0030] The present invention also provides the use of the epoxy resin-based composite material described in the above technical solution as a broadband wave absorbing material.

[0031] Beneficial effects of the present invention:

[0032] The present invention uses the oriented porous structure obtained by carbonizing balsa wood as a matrix, generates Fe2O3 / Co3O4 heterojunction particles in situ thereon, and uses them as absorbing units to prepare lightweight absorbing materials in combination with epoxy resin. This method not only effectively suppresses the agglomeration of Fe2O3 / Co3O4 heterojunction particles, but also significantly optimizes the impedance matching characteristics, thereby effectively extending the propagation path of electromagnetic waves. Based on this unique structure and the synergistic effect of multiple components, when the mass ratio of the absorbing unit in the composite material is only 5%, the minimum reflection loss of the material at a bandwidth of 9.92GHz reaches 51.5 dB, and its effective reflection loss reaches 6.2GHz (11.8-18GHz) in the microwave range when the thickness is 2.5mm. Moreover, since the absorbing unit is a porous structure, its apparent density is only 0.157g / cm3 , which is much smaller than the apparent density of epoxy resin (1.6~2.3 g / cm 3 ), when compounded with epoxy resin, the weight of the material can be significantly reduced to obtain a lightweight epoxy resin-based absorbing material. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required to be used in the embodiments are briefly introduced below.

[0034] Figure 1 The SEM morphology of natural balsa wood in the growth direction (a) and cross-section direction (b);

[0035] Figure 2 is a SEM morphology image of the wave absorbing element prepared in Example 1;

[0036] Figure 3 This is the XRD pattern of the absorbing element obtained in Example 1;

[0037] Figure 4 This is a diagram of the wave absorption performance of the lightweight epoxy resin-based composite material obtained in Example 1. DETAILED DESCRIPTION

[0038] The present invention provides a method for preparing an epoxy resin-based composite material, comprising the following steps:

[0039] 1) immersing balsa wood chips in an anionic surfactant solution for pretreatment to obtain pretreated balsa wood chips;

[0040] 2) mixing the pretreated balsa wood chips obtained in step 1) with a cobalt-iron solution and reacting them to obtain a balsa wood composite material loaded with a CoFe-LDH precursor;

[0041] The components of the cobalt-iron solution include urea, soluble cobalt salt, soluble iron salt and water;

[0042] 3) subjecting the CoFe-LDH precursor-loaded balsa wood composite material obtained in step 2) to a pre-oxidation treatment and a carbonization treatment in sequence to obtain a Fe2O3 / Co3O4-loaded carbon material;

[0043] 4) mixing the Fe2O3 / Co3O4 loaded carbon material obtained in step 3) with an epoxy resin solution, and curing the mixture to obtain an epoxy resin-based composite material;

[0044] The components of the epoxy resin solution include epoxy resin, epoxy resin curing agent and epoxy resin accelerator.

[0045] The present invention immerses balsa wood chips in an anionic surfactant solution for pretreatment to obtain pretreated balsa wood chips.

[0046] In the present invention, the method for obtaining the balsa wood chips preferably comprises: cutting along the growth direction of the balsa wood to obtain balsa wood chips with a size of 1×2×0.3 cm 3 of balsa wood chips. In the present invention, the balsa wood chips have the natural oriented cellular pore structure of balsa wood. In the present invention, the anionic surfactant in the anionic surfactant solution preferably includes one or more of sodium polyacrylate, sodium alkylbenzene sulfonate and sodium alkyl sulfate. In the present invention, the mass percentage of the anionic surfactant solution is preferably 1~3%. In the present invention, the pretreatment conditions preferably include: temperature of 50~80℃, time of 0.5~2h. In the present invention, the purpose of pretreatment of the balsa wood chips with anionic surfactants is to make their surface negatively charged, so as to facilitate the adsorption of more positively charged cobalt and iron cations, thereby generating CoFe-LDH precursor in situ on the balsa wood surface.

[0047] The present invention mixes and reacts the obtained pretreated balsa wood chips with a cobalt-iron solution to obtain a balsa wood composite material loaded with a CoFe-LDH precursor; the components of the cobalt-iron solution include urea, a soluble cobalt salt, a soluble iron salt and water.

[0048] In the present invention, the volume ratio of the mole of urea, the mole of soluble cobalt salt, the mole of soluble iron salt and water is preferably 7.5~15mmol:0.75~7.5mmol:0.25mmol:60mL. In the present invention, the soluble cobalt salt preferably includes one or more of cobalt nitrate, cobalt chloride, cobalt sulfate and cobalt carbonate. In the present invention, the soluble iron salt preferably includes one or more of ferric nitrate, ferric chloride, ferric sulfate and ferric nitrate. In the present invention, the volume ratio of the number of pretreated balsa wood chips to the cobalt iron solution is preferably 1 piece:60mL. In the present invention, the reaction conditions preferably include: a temperature of 100~160°C and a time of 4~10h.

[0049] The present invention sequentially performs pre-oxidation treatment and carbonization treatment on the obtained balsa wood composite material loaded with CoFe-LDH precursor to obtain a carbon material loaded with Fe2O3 / Co3O4.

[0050] In the present invention, the conditions of the pre-oxidation treatment preferably include: a temperature of 200-300°C and a time of 2-4 hours. In the present invention, the role of the pre-oxidation is to carbonize the balsa wood, increase its conductivity, and improve its conductivity loss capacity. In the present invention, the conditions of the carbonization treatment preferably include: carbonization for 2-4 hours in a nitrogen atmosphere and a temperature of 600-800°C. In the present invention, the carbon material loaded with Fe2O3 / Co3O4 has an oriented pore structure. When a material with an oriented pore structure is used as the matrix of the absorbing material, when the electromagnetic wave is radiated perpendicular to the pore orientation direction, the purpose of absorbing waves will be achieved due to multiple reflections, thereby increasing the intensity of the material's absorption and achieving broadband absorption. If it is not cut along the growth direction, there will be no "multiple reflection" effect.

[0051] The present invention mixes the obtained Fe2O3 / Co3O4 loaded carbon material with an epoxy resin solution and solidifies them to obtain an epoxy resin-based composite material; the components of the epoxy resin solution include epoxy resin, epoxy resin curing agent and epoxy resin accelerator.

[0052] In the present invention, the mass ratio of the carbon material loaded with Fe2O3 / Co3O4 to the mass ratio of the epoxy resin solution is preferably 1:19. In the present invention, the mass ratio of the epoxy resin, epoxy resin curing agent and epoxy resin accelerator is preferably 10:3:1. In the present invention, the epoxy resin curing agent preferably includes diethylmethylphenylenediamine. In the present invention, the epoxy resin accelerator preferably includes (2,4,6-tris(dimethylamino)methyl)phenol. In the present invention, the epoxy resin is preferably a bisphenol F type epoxy resin.

[0053] The present invention also provides an epoxy resin-based composite material prepared by the preparation method described in the above technical solution.

[0054] The present invention also provides the use of the epoxy resin-based composite material described in the above technical solution as a broadband wave absorbing material.

[0055] In order to further illustrate the present invention, the present invention is described in detail below in conjunction with embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0056] Example 1

[0057] Using natural balsa wood as raw material, the wood was cut along the growth direction of the balsa wood to obtain 1×2×0.3cm 3 The balsa wood flakes are immersed in an aqueous solution containing 2% by mass of sodium polyacrylate, the solution is heated to 60° C., and reacted for 1 hour to obtain pretreated balsa wood;

[0058] 15mmol urea, 0.75mmol cobalt nitrate and 0.25mmol ferric nitrate were dissolved in 60ml deionized water, and after stirring for 0.5h, the mixed solution was transferred to a 100ml polytetrafluoroethylene-lined sealed autoclave, and the pretreated balsa wood was added, and the reaction was carried out at 120℃ for 8h. After cooling to room temperature, the mixture was washed alternately with water and ethanol for multiple times, and dried at 60℃ to obtain a balsa wood composite material loaded with CoFe-LDH precursor;

[0059] The balsa wood composite material loaded with CoFe-LDH precursor was placed in a tube furnace, pre-oxidized at 260 °C for 2 h, and then carbonized at 800 °C for 2 h in a nitrogen atmosphere to obtain a porous carbon material loaded with Fe2O3 / Co3O4.

[0060] The prepared porous carbon material loaded with Fe2O3 / Co3O4 was placed in a 1.5×2.5cm 2 The mold was prepared by mixing bisphenol F epoxy resin, diethylmethylphenylenediamine and (2,4,6-tris(dimethylamino)methyl)phenol in a mass ratio of 10:3:1 to obtain an epoxy resin solution, which was poured into the mold and cured under vacuum conditions to obtain a sample. The mass ratio of the porous carbon material of Fe2O3 / Co3O4 to the epoxy resin solution in the sample was 1:19. The microwave absorption performance was tested, and the results are shown in Table 1.

[0061] Example 2

[0062] Using natural balsa wood as raw material, the wood was cut along the growth direction of the balsa wood to obtain 1×2×0.3cm 3 The balsa wood flakes are immersed in an aqueous solution containing 1% by mass of sodium alkylbenzene sulfonate, the solution is heated to 50° C., and reacted for 2 hours to obtain pretreated balsa wood;

[0063] 7.5mmol urea, 2.5mmol cobalt chloride and 0.25mmol ferric chloride were dissolved in 60ml deionized water, and after stirring for 0.5h, the mixed solution was transferred to a 100ml polytetrafluoroethylene-lined sealed autoclave, and the pretreated balsa wood was added, and the mixture was reacted at 100°C for 10h. After cooling to room temperature, the mixture was washed alternately with water and ethanol for multiple times, and dried at 60°C to obtain a balsa wood composite material loaded with CoFe-LDH precursor;

[0064] The balsa wood composite material loaded with CoFe-LDH precursor was placed in a tube furnace, pre-oxidized at 200 °C for 4 h, and then carbonized at 600 °C for 4 h in a nitrogen atmosphere to obtain a porous carbon material loaded with Fe2O3 / Co3O4.

[0065] The prepared porous carbon material loaded with Fe2O3 / Co3O4 was placed in a 1.5×2.5cm 2 The mold was prepared by mixing bisphenol F epoxy resin, diethylmethylphenylenediamine and (2,4,6-tris(dimethylamino)methyl)phenol in a mass ratio of 10:3:1, pouring them into the mold, and curing them under vacuum to obtain a sample. The mass ratio of the porous carbon material of Fe2O3 / Co3O4 to the epoxy resin solution in the sample was 1:19. The results of testing its wave absorption performance are shown in Table 1.

[0066] Example 3

[0067] Using natural balsa wood as raw material, the wood was cut along the growth direction of the balsa wood to obtain 1×2×0.3cm 3 The balsa wood flakes are immersed in an aqueous solution containing 3% by mass of sodium alkyl sulfate, the solution is heated to 80°C, and the reaction is carried out for 0.5h to obtain pretreated balsa wood;

[0068] 15mmol urea, 7.5mmol cobalt sulfate and 0.25mmol ferric sulfate were dissolved in 60ml deionized water, and after stirring for 0.5h, the mixed solution was transferred to a 100ml polytetrafluoroethylene-lined sealed autoclave, and the pretreated balsa wood was added, and the mixture was reacted at 160°C for 4h. After cooling to room temperature, the mixture was washed alternately with water and ethanol for multiple times, and dried at 60°C to obtain a balsa wood composite material loaded with CoFe-LDH precursor;

[0069] The balsa wood composite material loaded with CoFe-LDH precursor was placed in a tube furnace, pre-oxidized at 300 °C for 2 h, and then carbonized at 800 °C for 2 h in a nitrogen atmosphere to obtain a porous carbon material loaded with Fe2O3 / Co3O4.

[0070] The prepared porous carbon material loaded with Fe2O3 / Co3O4 was placed in a 1.5×2.5cm 2 The mold was prepared by mixing bisphenol F epoxy resin, diethylmethylphenylenediamine and (2,4,6-tris(dimethylamino)methyl)phenol in a mass ratio of 10:3:1 to obtain an epoxy resin solution, which was poured into the mold and cured under vacuum conditions to obtain a sample. The mass ratio of the porous carbon material of Fe2O3 / Co3O4 to the epoxy resin solution in the sample was 1:19. The microwave absorption performance was tested, and the results are shown in Table 1.

[0071] Example 4

[0072] Using natural balsa wood as raw material, cut the wood along the growth direction of balsa wood to obtain 1×2×0.3cm 3The balsa wood flakes are immersed in an aqueous solution containing 3% by mass of sodium alkyl sulfate, the solution is heated to 70° C., and reacted for 1 hour to obtain pretreated balsa wood;

[0073] 10mmol urea, 3.75mmol cobalt carbonate and 0.25mmol ferric nitrate were dissolved in 60ml deionized water, and after stirring for 0.5h, the mixed solution was transferred to a 100ml polytetrafluoroethylene-lined sealed autoclave, and the pretreated balsa wood was added, and the mixture was reacted at 120°C for 8h. After cooling to room temperature, the mixture was washed alternately with water and ethanol for multiple times, and dried at 60°C to obtain a balsa wood composite material loaded with CoFe-LDH precursor;

[0074] The balsa wood composite material loaded with CoFe-LDH precursor was placed in a tube furnace, pre-oxidized at 250 °C for 3 h, and then carbonized at 700 °C for 3 h under nitrogen to obtain a porous carbon material loaded with Fe2O3 / Co3O4.

[0075] The prepared porous carbon material loaded with Fe2O3 / Co3O4 was placed in a 1.5×2.5cm 2 The mold was prepared by mixing bisphenol F epoxy resin, diethylmethylphenylenediamine and (2,4,6-tris(dimethylamino)methyl)phenol in a mass ratio of 10:3:1 to obtain an epoxy resin solution, which was poured into the mold and cured under vacuum conditions to obtain a sample. The mass ratio of the porous carbon material of Fe2O3 / Co3O4 to the epoxy resin solution in the sample was 1:19. The microwave absorption performance was tested, and the results are shown in Table 1.

[0076] The microwave network parameters were measured using a vector network analyzer (Rohde & Schwarz, ZVA24). The APC-7mm coaxial air line was used to test the wave absorption performance of the material. The test sample was cut into concentric rings with an outer diameter of 7mm and an inner diameter of 3.04mm. The wave absorption performance of the four samples prepared in Example 1 (denoted as a), 2 (denoted as b), 3 (denoted as c), and 4 (denoted as d) was measured. Table 1 shows the wave absorption performance characterization results of the lightweight epoxy resin-based composite materials prepared by Examples 1, 2, 3, and 4. It can be seen from the data in the table that the minimum reflection losses of the epoxy resin-based composite materials obtained by the preparation method of the present invention are 51.5 (3.5mm), 42.1 (4.5mm), 49.6 (3.8mm), and 48.7 (3.0mm) GHz, respectively, and their effective absorption bandwidths are 6.2, 4.3, 5.7, and 4.7 GHz, respectively.

[0077] Table 1 Microwave absorption properties of lightweight epoxy resin-based composites

[0078]

[0079] like Figure 1 From the scanning electron microscope photos of balsa wood, it can be seen that along its growth direction, the wood presents an oriented porous structure, but the pores in the cross-sectional direction are not oriented;

[0080] like Figure 2 From the field emission scanning electron microscope photograph of the absorbing element prepared in Example 1, it can be seen that a large number of dispersed particles are generated on the surface, and the particle size is about 1 micron.

[0081] like Figure 3 From the XRD diagram of the absorbing element prepared in Example 1, it can be seen that its main crystal phases are Fe2O3 and Co3O4.

[0082] like Figure 4 The microwave absorption performance of the lightweight epoxy resin-based composite material prepared in Example 1 is as follows: the minimum reflection loss reaches 51.5 dB (3.5 mm) and the bandwidth is 9.92 GHz; the effective reflection loss reaches 6.2 GHz (11.8-18 GHz) in the microwave range when the thickness is 2.5 mm.

[0083] Comparative Example 1

[0084] The balsa wood without CoFe-LDH precursor was used as an absorbing unit and compounded with epoxy resin. Its absorbing performance was measured and it was found that it did not show absorbing ability.

[0085] Comparative Example 2

[0086] The balsa wood loaded with CoFe-LDH precursor was directly used as an absorbing unit (without carbonization treatment). After compounding with epoxy resin, its absorbing performance was measured. Its minimum reflection loss was only 11.2 (4.5mm) and the bandwidth was only 0.9 GHz.

[0087] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention, not all of the embodiments. People can also obtain other embodiments based on this embodiment without creativity, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing an epoxy resin-based composite material, It is characterized in that The following steps are involved: 1) immersing balsa wood chips in an anionic surfactant solution for pretreatment to obtain pretreated balsa wood chips; 2) mixing the pretreated balsa wood chips obtained in step 1) with a cobalt-iron solution and reacting them to obtain a balsa wood composite material loaded with a CoFe-LDH precursor; The components of the cobalt-iron solution include urea, soluble cobalt salt, soluble iron salt and water; 3) The balsa wood composite material loaded with CoFe-LDH precursor obtained in step 2) is subjected to pre-oxidation treatment and carbonization treatment in sequence to obtain a loaded Fe 2 O 3 / Co 3 O 4 Carbon materials; 4) The loaded Fe obtained in step 3) 2 O 3 / Co 3 O 4 The carbon material is mixed with an epoxy resin solution and cured to obtain an epoxy resin-based composite material; The components of the epoxy resin solution include epoxy resin, epoxy resin curing agent and epoxy resin accelerator.

2. The preparation method according to claim 1, It is characterized in that The method for obtaining the balsa wood chips in step 1) comprises: cutting along the growth direction of the balsa wood to obtain pieces with a size of 1×2×0.3 cm 3 of balsa wood chips.

3. The preparation method according to claim 1, It is characterized in that In the step 1), the anionic surfactant in the anionic surfactant solution comprises one or more of sodium polyacrylate, sodium alkylbenzene sulfonate and sodium alkyl sulfate; The mass percentage of the anionic surfactant solution is 1-3%.

4. The preparation method according to claim 1, It is characterized in that The pretreatment conditions in step 1) include: a temperature of 50-80° C. and a time of 0.5-2 h.

5. The preparation method according to claim 1, It is characterized in that In the step 2), the volume ratio of the moles of urea, the moles of soluble cobalt salt, the moles of soluble iron salt and water is 7.5-15 mmol: 0.75-7.5 mmol: 0.25 mmol: 60 mL; The soluble cobalt salt includes one or more of cobalt nitrate, cobalt chloride, cobalt sulfate and cobalt carbonate; The soluble iron salt includes one or more of ferric nitrate, ferric chloride, ferric sulfate and ferric nitrate.

6. The preparation method according to claim 1 or 2, It is characterized in that In the step 2), the volume ratio of the pretreated balsa wood chips to the cobalt-iron solution is 1 chip: 60 mL; The reaction conditions include: temperature of 100-160° C. and time of 4-10 h.

7. The preparation method according to claim 1, It is characterized in that The conditions of the pre-oxidation treatment in step 3) include: a temperature of 200-300° C. and a time of 2-4 hours; The carbonization treatment conditions include: carbonization in a nitrogen atmosphere at a temperature of 600-800° C. for 2-4 hours.

8. The preparation method according to claim 1, It is characterized in that Step 4) Loading Fe 2 O 3 / Co 3 O 4 The mass ratio of the carbon material to the epoxy resin solution is 1:19; The mass ratio of the epoxy resin, epoxy resin curing agent and epoxy resin accelerator is 10:3:1; The epoxy resin curing agent includes diethylmethylphenylenediamine; The epoxy resin accelerator includes (2,4,6-tris(dimethylamino)methyl)phenol.

9. An epoxy resin-based composite material prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the epoxy resin-based composite material according to claim 9 as a broadband wave absorbing material.

Images