Silicon carbide composite wave-absorbing and heat-conducting bifunctional material and preparation method thereof

Abstract

The invention relates to the technical field of wave-absorbing material preparation, and particularly discloses a silicon carbide composite wave-absorbing and heat-conducting bifunctional material and a preparation method thereof.The preparation method comprises the steps that high-purity graphite powder, high-purity silicon powder and stainless steel balls are weighed and placed in a stainless steel ball milling tank, absolute ethyl alcohol is added for ball milling treatment, and composite powder is obtained; placing the composite powder in a central temperature zone of a PECVD furnace, firstly introducing inert gas, then raising the temperature to 700-900 DEG C, finally introducing acetylene and opening a plasma generator for reaction, and finally obtaining the silicon carbide composite wave-absorbing and heat-conducting dual-function material, namely Si-coated SiC-coated Fe3O4 / C. The invention also discloses a preparation method of the silicon carbide composite wave-absorbing and heat-conducting dual-function material. The silicon carbide-based composite wave-absorbing material is prepared on the basis of mechanical ball milling combined with the plasma chemical vapor deposition method, energy conservation and emission reduction are achieved, and the technological method is simple; and the prepared material has efficient wave-absorbing performance and high-temperature stability.

Description

Technical Field

[0001] The present invention relates to the technical field of preparation of microwave absorbing materials, and particularly to a silicon carbide composite microwave absorbing and heat conducting dual-functional material and a preparation method thereof. Background Art

[0002] Microwave absorbing materials have broad application prospects in the fields of electromagnetic compatibility, electromagnetic interference prevention, radar stealth, etc. The core lies in reducing the electromagnetic characteristics of the target in the corresponding frequency band by absorbing or dissipating electromagnetic wave energy. With the rapid development of modern electronic technology, the demand for microwave absorbing materials with high-efficiency broadband absorption performance, environmental friendliness, and structural designability is increasing continuously.

[0003] Silicon carbide (SiC) has always attracted much attention due to its excellent high-temperature stability, chemical inertness, and adjustable dielectric properties. Microwave absorbing materials based on SiC can not only meet the application requirements at higher temperatures or under harsh conditions, but also have good feasibility in electromagnetic parameter design and structural regulation. However, traditional processes for preparing SiC (such as high-temperature sintering method, hot pressing sintering method, etc.) often have problems such as high preparation temperature (usually above 1000 °C) and large energy consumption, and the controllability of the structure and morphology of the SiC microwave absorbing materials prepared by the existing technology is poor, and the difficulty of composite modification is large, resulting in poor microwave absorbing performance and high-temperature stability of the materials.

[0004] Therefore, the existing technology still needs to be improved and developed. Summary of the Invention

[0005] In view of the above deficiencies of the existing technology, the purpose of the present invention is to provide a silicon carbide composite microwave absorbing and heat conducting dual-functional material and a preparation method thereof, aiming to solve the problems of high preparation temperature, large energy consumption in the existing process for preparing SiC microwave absorbing materials, and poor microwave absorbing performance and high-temperature stability of the prepared microwave absorbing materials.

[0006] The technical solution of the present invention is as follows:

[0007] A preparation method of a silicon carbide composite microwave absorbing and heat conducting dual-functional material, which includes the steps of:

[0008] Weigh high-purity graphite powder and high-purity silicon powder with a purity greater than 99.9% and place them in a stainless-steel ball milling tank, then weigh stainless-steel balls and place them in the stainless-steel ball milling tank, add absolute ethanol, and perform ball milling treatment at a rotation speed of 300 - 500 r / min to obtain a composite powder, where the composite powder includes silicon powder and graphite powder and Fe3O4 particles distributed on the surface of the silicon powder;

[0009] Place the composite powder in the central temperature zone of the PECVD furnace. First, introduce an inert gas into the PECVD furnace, then heat the central temperature zone of the PECVD furnace to 700 - 900 °C, and finally introduce acetylene and turn on the plasma generator for reaction, so that silicon carbide is formed on the surface of the silicon powder, and at the same time, a C layer formed by the cracking of acetylene partially coats the surface of the silicon carbide, and finally a silicon carbide composite wave-absorbing and heat-conducting dual-functional material, namely Si@SiC@Fe3O4 / C, is obtained.

[0010] The preparation method of the silicon carbide composite wave-absorbing and heat-conducting dual-functional material, wherein the molar ratio of the high-purity graphite powder to the high-purity silicon powder is 1:1.

[0011] The preparation method of the silicon carbide composite wave-absorbing and heat-conducting dual-functional material, wherein stainless steel balls are placed in the stainless steel ball mill tank according to the ratio of the ball-to-material mass ratio of 15 - 20:1.

[0012] The preparation method of the silicon carbide composite wave-absorbing and heat-conducting dual-functional material, wherein the inert gas is one of argon, nitrogen and helium.

[0013] The preparation method of the silicon carbide composite wave-absorbing and heat-conducting dual-functional material, wherein the flow rate of the inert gas is 50 - 80 mL / min.

[0014] The preparation method of the silicon carbide composite wave-absorbing and heat-conducting dual-functional material, wherein in the step of heating the central temperature zone of the PECVD furnace to 800 - 900 °C, the heating rate is 8 - 15 °C / min.

[0015] The preparation method of the silicon carbide composite wave-absorbing and heat-conducting dual-functional material, wherein in the step of finally introducing acetylene and turning on the plasma generator for reaction, the acetylene flow rate is 10 - 30 mL / min, the power of the plasma generator is 150 - 250 W, and the reaction time is 20 - 40 min.

[0016] A silicon carbide composite wave-absorbing and heat-conducting dual-functional material, which is prepared by using the preparation method of the silicon carbide composite wave-absorbing and heat-conducting dual-functional material of the present invention.

[0017] Beneficial effects: The present invention provides a method for preparing a silicon carbide-based composite microwave absorbing material at a relatively low temperature based on mechanical ball milling combined with plasma-induced chemical vapor deposition, achieving the dual functions of microwave absorption and heat conduction. In the present invention, the carbon and silicon sources are empowered through a mechanical ball milling process and magnetic particles are introduced. On the one hand, the magnetic particles play a catalytic role in the subsequent plasma-induced preparation of silicon carbide, and on the other hand, they serve as heterogeneous interfaces of the material to improve the multi-interface loss ability of electromagnetic waves and provide the magnetic loss ability of the material. The plasma-induced chemical vapor deposition method in-situ grows silicon carbide at the Si-C interface, and acetylene grows a dense carbon layer on the surface of silicon carbide under the action of plasma. As a tunable dielectric material, it optimizes the impedance matching of the Si / C system and fully improves the microwave absorption performance of the material. In addition, due to the high-temperature stability and excellent thermal conductivity of silicon carbide itself, the composite structure is stable at high temperatures and can transfer the heat energy converted from the absorbed electromagnetic waves to the outside of the absorber in time, keeping the temperature inside the absorber stable and greatly improving the service life of the absorber in extreme temperature environments. Therefore, the present invention prepares a silicon carbide-based composite microwave absorbing material based on mechanical ball milling combined with plasma chemical vapor deposition, which saves energy and reduces emissions, and the process method is simple, laying an important application foundation for the large-scale and low-cost production of microwave absorbing materials serving in high-temperature environments. Description of the Drawings

[0018] Figure 1 It is a flow chart of a preparation method of a silicon carbide composite microwave absorbing and heat conducting dual-functional material of the present invention.

[0019] Figure 2 In it, a is the morphology diagram of the powder SC2 obtained after simple mixing, b is the morphology diagram of the powder SC1 obtained by mechanical ball milling empowerment, and d, e, g are the morphology diagrams of the powders SC3-SC5 respectively; Figure 2 In it, c, f, i are the particle size distribution diagrams of the corresponding powders of SC3-SC5, Figure 2 In it, h is the energy spectrum diagram of the powder obtained by the mechanical ball milling / PECVD combined technology at 900 °C.

[0020] Figure 3 In it, (a-d) is the fitting peak splitting diagram of Si@SiC@Fe3O4 / C obtained in Example 1; (e-h) is the fitting peak splitting diagram of Si / C without PECVD treatment in Comparative Example 1.

[0021] Figure 4 It is the XRD diagram obtained by analyzing SC1-SC5 in the examples and comparative examples through X-ray diffraction technology.

[0022] Figure 52D / 3D reflection loss diagrams of samples prepared under different reaction conditions. Among them, (a) and (b) are the 2D / 3D reflection loss diagrams of C / Si / powder obtained by simple mixing; (c-d), (e-f), and (g-h) are the 2D / 3D reflection loss diagrams of the powders obtained after PECVD at 700 °C, 800 °C, and 900 °C, respectively. Detailed implementation manners

[0023] The present invention provides a silicon carbide composite wave-absorbing and heat-conducting dual-functional material and a preparation method thereof. To make the objectives, technical solutions, and effects of the present invention clearer and more definite, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0024] Please refer to Figure 1 , Figure 1 which is a flowchart of a preparation method of a silicon carbide composite wave-absorbing and heat-conducting dual-functional material provided by the present invention. As shown in the figure, it includes the following steps:

[0025] S10. Weigh high-purity graphite powder and high-purity silicon powder with a purity greater than 99.9% and place them in a stainless-steel ball-milling tank. Then, weigh stainless-steel balls and place them in the stainless-steel ball-milling tank. Add anhydrous ethanol and perform ball-milling treatment at a rotation speed of 300 - 500 r / min to obtain a composite powder, where the composite powder includes silicon powder and graphite powder and Fe3O4 particles distributed on the surface of the silicon powder;

[0026] S20. Place the composite powder in the central temperature zone of a PECVD furnace. First, introduce an inert gas into the PECVD furnace, then heat the central temperature zone of the PECVD furnace to 700 - 900 °C, and finally introduce acetylene and turn on the plasma generator for reaction, so that silicon carbide is formed on the surface of the silicon powder, and at the same time, a C layer formed by the cracking of acetylene partially coats the surface of the silicon carbide, and finally a silicon carbide composite wave-absorbing and heat-conducting dual-functional material, namely Si@SiC@Fe3O4 / C, is obtained.

[0027] To further improve the microwave absorption performance of SiC-based materials, in this implementation, by introducing magnetic media and hetero-interfaces into the SiC material, the synergistic effect of dielectric loss and magnetic loss is enhanced, thereby obtaining higher absorption intensity and wider effective absorption bandwidth. As a technology with high energy density and low temperature gradient, plasma induction can promote the reaction at a lower substrate temperature or in a shorter time, and effectively regulate the crystal morphology and structure of SiC; while mechanical ball milling can fully mix, activate and introduce defects to the reactants by mechanical force, further improving their reaction activity and interface characteristics. In addition, the ball milling process can also achieve the controllable introduction of some functional components such as metals or oxides, enhancing the ability to regulate the electromagnetic parameters of the material. By using the combined technology of mechanical ball milling and plasma-induced chemical vapor deposition to prepare SiC-based composite microwave absorbing materials in this example, a dual-functional microwave absorbing material with high microwave absorption performance and high-temperature stability can be rapidly prepared at a lower temperature, which has important research significance and practical value.

[0028] Specifically, in step S10, the collision and shear force of stainless steel balls fully mix high-purity graphite powder (C) and Si powder, and induce defects and nanosizing through mechanical force to improve the reaction activity; Fe particles are released from the stainless steel balls (containing Fe) during the ball milling process due to frictional wear, and then Fe3O4 particles (magnetite) are generated in the micro-oxidizing environment in the presence of ethanol. Finally, a composite powder with C and Fe3O4 particles attached to the surface of Si particles (denoted as Si@C / Fe3O4) is obtained, where the Fe3O4 particles are evenly distributed on the surface of Si particles; in this step, mechanical energy is converted into chemical energy to activate the surface activity of C and Si, and at the same time, the introduced Fe3O4 particles, as magnetic media, can not only enhance the magnetic loss ability of the subsequent material, but also provide catalytic sites for the formation of SiC.

[0029] In step S20, acetylene is cracked into active carbon (C*) and other high-energy charged particles (such as hydrogen radicals H*, etc.) under the bombardment of plasma high-energy ions. The high-energy environment provided by the plasma can reduce the reaction activation energy, enabling the activated C and Si to undergo a solid-phase reaction at the C-Si interface to form SiC under the catalysis of Fe3O4 particles and at a reaction temperature of 7800 - 900 °C; and the active carbon cracked from acetylene will deposit on the surface of SiC to form a uniform carbon layer (C), optimizing the dielectric properties, and finally forming a similar multi-layer core-shell structure as follows: Si (core) → SiC (intermediate layer) → Fe3O4 particles / C (outer layer), that is, Si@SiC@Fe3O4 / C; the SiC composite microwave absorbing and heat-conducting dual-functional material (Si@SiC@Fe3O4 / C) can achieve the synergistic loss of dielectric loss and magnetic loss, that is, the difference in dielectric constants between SiC and the carbon layer induces interface polarization, thereby causing dielectric loss; at the same time, the surface Fe3O4 can bring about magnetic hysteresis loss and eddy current effect.

[0030] In this embodiment, through two-step coordination, a SiC-based composite material with both wave absorption and heat conduction functions is prepared at low temperature and high efficiency. The high thermal conductivity of SiC can quickly export the heat energy converted by electromagnetic waves, while the carbon layer protects the high-temperature stability of the material.

[0031] In some embodiments, the molar ratio of the high-purity graphite powder to the high-purity silicon powder is preferably 1:1, but is not limited thereto.

[0032] In some embodiments, stainless steel balls are placed in the stainless steel ball mill tank according to the ratio of the mass of the balls to the mass of the material of 15-20:1. In this embodiment, the introduction of Fe element on the surface of the powder helps the magnetic loss of Si@SiC@Fe3O4 / C, which greatly improves the subsequent wave absorption performance. Second, it can play a catalytic role in the preparation of SiC by PECVD. This embodiment requires a ball-to-material mass ratio. A smaller ball-to-material ratio will result in less introduction of Fe element, leading to ineffective synthesis of SiC in the subsequent process. An excessive ball-to-material ratio will result in excessive energy and may also cause uneven enrichment of Fe and the generation of impurities.

[0033] In some embodiments, an inert gas is introduced into the PECVD furnace for exhaust. The inert gas serves as a protective gas and is continuously introduced from the start until the reaction ends and the temperature cools down to room temperature. The inert gas is one of argon, nitrogen, and helium; the flow rate of the inert gas is 50-80 mL / min, but is not limited thereto. By way of example, the flow rate can be 50 mL / min, 60 mL / min, 70 mL / min, 80 mL / min, etc.

[0034] In some embodiments, in the step of heating the central temperature zone of the PECVD furnace to 700-900 °C, the heating rate is 8-15 °C / min, but is not limited thereto. By way of example, the heating rate can be 8 °C / min, 9 °C / min, 10 °C / min, 11 °C / min, 12 °C / min, 13 °C / min, 14 °C / min, 15 °C / min, etc.

[0035] In some embodiments, in the step of finally introducing acetylene and turning on the plasma generator for reaction, the flow rate of acetylene is 10-30 mL / min, the power of the plasma generator is 150-250 W, and the reaction time is 20-40 min, but is not limited thereto. By way of example, the flow rate of acetylene is 10 mL / min, 20 mL / min, 30 mL / min, etc.; the power of the plasma generator is 150 W, 160 W, 170 W, 180 W, 190 W, 200 W, 210 W, 220 W, 230 W, 240 W, 250 W, etc.; the reaction time is 20 min, 23 min, 25 min, 28 min, 30 min, 32 min, 35 min, 38 min, 40 min, etc.

[0036] In some embodiments, a silicon carbide composite wave-absorbing and heat-conducting dual-functional material is further provided, which is prepared by using the preparation method of the silicon carbide composite wave-absorbing and heat-conducting dual-functional material of the present invention. The present invention uses a mechanical ball milling process to mix, empower, and introduce magnetic particles (Fe) into high-purity carbon powder and silicon powder. The introduction of magnetic particles enhances the multiple heterogeneous interface loss, conductive loss, and magnetic loss of the composite structure, and can catalyze the effective synthesis of silicon carbide in subsequent processes. Subsequently, an acetylene plasma induction technique is used to promote the further reaction of carbon powder and silicon powder to generate silicon carbide, and at the same time, a uniform carbon layer is coated on the surface to form a multi-layer structure. The synthesis of silicon carbide helps to improve the dielectric loss ability of the material, thereby improving the wave-absorbing performance of the composite structure, and at the same time enhancing the high-temperature stability and heat-conducting ability of the material.

[0037] The following further explains the present invention through specific examples:

[0038] Example 1

[0039] A preparation method of a silicon carbide composite wave-absorbing and heat-conducting dual-functional material includes the following steps:

[0040] Step 1: Weigh 12 g of high-purity graphite powder (purity > 99.9%) and 28 g of high-purity silicon powder (purity > 99.9%), place them in a stainless-steel ball milling tank, weigh 600 g of stainless-steel balls according to a ball-to-material ratio of 15:1, place them in the tank, add 20 mL of absolute ethanol, and simply stir and mix; install the ball milling tank filled with fillers on a mechanical ball mill, set the machine speed to 400 r / min, and the time to 6 h; after ball milling, collect the powder in the tank to obtain a mechanically ball mill-empowered Si@C / Fe3O4 composite powder, denoted as SC1.

[0041] Step 2: Place the Si@C / Fe3O4 composite powder obtained in Step 1 in the central temperature zone of a PECVD furnace, exhaust for 30 min in an argon environment; after the air in the tube is exhausted, start the reaction heating program, set the argon gas flow rate to 60 mL / min, and the heating rate to 10 °C / min; after heating to 700 °C, open the acetylene flowmeter, set the gas flow rate to 20 mL / min, and turn on the plasma generator, set the plasma power to 200 W, and after the reaction proceeds for 30 min, finally obtain a silicon carbide composite wave-absorbing and heat-conducting dual-functional material, namely Si@SiC@Fe3O4 / C-700, denoted as SC3.

[0042] Example 2

[0043] A preparation method of a silicon carbide composite wave-absorbing and heat-conducting dual-functional material includes the following steps:

[0044] Step 1: Weigh 12 g of high-purity graphite powder (purity > 99.9%) and 28 g of high-purity silicon powder (purity > 99.9%), place them in a stainless-steel ball-milling tank, weigh 600 g of stainless-steel balls according to the ball-to-material ratio of 18:1 and place them in the tank, add 20 mL of anhydrous ethanol, and stir and mix them simply; install the ball-milling tank filled with materials on a mechanical ball mill, set the machine speed to 300 r / min, and the time to 6 h; after ball milling, collect the powder in the tank to obtain the mechanically ball-milled and energy-enabled Si@C / Fe3O4 composite powder.

[0045] Step 2: Place the Si@C / Fe3O4 composite powder obtained in Step 1 in the central temperature zone of a PECVD furnace, evacuate for 30 min in an argon environment; after the air in the tube is exhausted, start the reaction heating program, set the argon gas flow rate to 50 mL / min, and the heating rate to 8 °C / min; after heating to 800 °C, open the acetylene flowmeter, set the gas flow rate to 10 mL / min, and turn on the plasma generator, set the plasma power to 150 W, and after the reaction proceeds for 40 min, finally obtain the silicon carbide composite wave-absorbing and heat-conducting dual-functional material, namely Si@SiC@Fe3O4 / C-800, denoted as SC4.

[0046] Example 3

[0047] A preparation method of a silicon carbide composite wave-absorbing and heat-conducting dual-functional material, which comprises the following steps:

[0048] Step 1: Weigh 12 g of high-purity graphite powder (purity > 99.9%) and 28 g of high-purity silicon powder (purity > 99.9%), place them in a stainless-steel ball-milling tank, weigh 600 g of stainless-steel balls according to the ball-to-material ratio of 20:1 and place them in the tank, add 20 mL of anhydrous ethanol, and stir and mix them simply; install the ball-milling tank filled with materials on a mechanical ball mill, set the machine speed to 500 r / min, and the time to 6 h; after ball milling, collect the powder in the tank to obtain the mechanically ball-milled and energy-enabled Si@C / Fe3O4 composite powder.

[0049] Step 2: Place the Si@C / Fe3O4 composite powder obtained in Step 1 in the central temperature zone of a PECVD furnace, evacuate for 30 min in an argon environment; after the air in the tube is exhausted, start the reaction heating program, set the argon gas flow rate to 80 mL / min, and the heating rate to 15 °C / min; after heating to 900 °C, open the acetylene flowmeter, set the gas flow rate to 30 mL / min, and turn on the plasma generator, set the plasma power to 250 W, and after the reaction proceeds for 20 min, finally obtain the silicon carbide composite wave-absorbing and heat-conducting dual-functional material, namely Si@SiC@Fe3O4 / C-900, denoted as SC5.

[0050] Comparative Example 1

[0051] Preparation of a simple mixture C / Si, which comprises the following steps:

[0052] Weigh 12 g of high-purity graphite powder (purity > 99.9%) and 28 g of high-purity silicon powder (purity > 99.9%), stir and mix them to obtain the mixture C / Si, denoted as SC2.

[0053] Perform electron microscopy observations on SC1 - SC5 prepared in Examples 1 - 3 and Comparative Example 1. The microscopic morphology results are as Figure 2 shown in a, b, d, e, g in it. Among them, a is the morphology diagram of the powder SC2 obtained after simple mixing, b is the morphology diagram of the powder SC1 obtained by mechanical ball milling for energy imparting, and d, e, g are the morphology diagrams of the powders SC3 - SC5 respectively; Figure 2 c, f, i in it are the particle size distribution diagrams of the corresponding powders of SC3 - SC5. By observing the microscopic morphology and particle size of the samples, it is found that the simply mixed powder SC1 has a larger particle size and is in irregular block shape, with an average particle size of 4.52 μm; while the particle size of the powder SC2 after mechanical ball milling is significantly reduced, and its morphology presents irregular flakes, and relatively fine Fe3O4 particles with an average particle size of 3.8 μm are attached to the flakes; the powders SC3 - SC5 obtained by the combined technology of mechanical ball milling / PECVD at 700 - 900 °C all present regular polygon morphologies, with an average particle size of 2.1 μm. Figure 2 h in it is the energy spectrum diagram of the powder obtained by the combined technology of mechanical ball milling / PECVD at 900 °C. The energy spectrum shows that Fe is evenly distributed on the particle surface, confirming the introduction of Fe3O4.

[0054] Analyze the simply mixed powder SC2 in Comparative Example 1 and the silicon carbide composite microwave absorbing and heat conducting dual-functional material Si@SiC@Fe3O4 / C - 700 (i.e., SC3) prepared in Example 1 by X-ray photoelectron spectroscopy technology to obtain the XPS diagram as Figure 3 shown. Among them, (a - d) are the fitting peak splitting diagrams of the obtained Si@SiC@Fe3O4 / C; (e - h) are the fitting peak splitting diagrams of Si / C without PECVD treatment. By comparing the fitting peak splitting diagrams of the C element, no obvious C - Si covalent bond is found in the powder before the reaction, and the C - Si covalent bond is generated in the powder after PECVD treatment. By comparing the fitting peak splitting diagrams of the Si element, the corresponding peak positions of the Si - C covalent bond that did not appear in the powder before the reaction are found, and there is a strong Si - C covalent bond peak position in the powder after PECVD treatment. By peak splitting of the Fe element, it can be found that the simply mixed C / Si powder does not have the valence state peak of Fe, and the powder after the reaction has Fe 3+ 、Fe 2+, the peak position of the Fe-O bond indicates that mechanical ball milling deposits uniform Fe3O4 on the surface of the C / Si powder. In summary, through XPS comparative analysis, the powder prepared by mechanical ball milling combined with plasma-induced chemical vapor deposition technology has a C-Si covalent bond, directly proving the in-situ synthesis of SiC; during mechanical ball milling, Fe is released from the wear of stainless steel balls and subsequently oxidized to form Fe3O4, and its uniform distribution is verified by XPS, and the mixed valence state of Fe (Fe 2+ / Fe 3+ ) indicates the presence of Fe3O4, enhancing the magnetic loss ability of the material, which indicates the successful preparation of Si@SiC@Fe3O4 / C in Example 1.

[0055] Analyze SC1-SC5 in the examples and comparative examples by X-ray diffraction technology, and obtain the XRD patterns as shown in Figure 4 . Among them, through the analysis of the diffraction peaks, SC1 (the powder Si@C / Fe3O4 obtained after mechanical ball milling) has the corresponding diffraction peaks of C, Si, and Fe3O4, and SC2 (the simply mixed C / Si powder) only has the corresponding diffraction peaks of C and Si. This further proves that the introduction of Fe3O4 magnetic particles during ball milling can effectively enhance the magnetic loss ability of the Si@SiC@Fe3O4 / C powder and greatly improve the microwave loss ability. It can be found from the diffraction peak patterns of the powders SC3-SC5 prepared at reaction temperatures of 700 °C, 800 °C, and 900 °C respectively that a weak SiC diffraction peak appears at 700 °C. As the temperature increases, the peak intensity of the SiC diffraction peak also increases and reaches the highest at 900 °C. This indicates that after PECVD treatment, SiC begins to appear in the powder at 700 °C, and the SiC content also increases continuously with the increase of the reaction temperature. This shows that at a temperature far lower than the conventional reaction temperature (1400 °C), SiC was successfully prepared in this example by mechanical ball milling combined with plasma-induced chemical vapor deposition method, which effectively reduces the reaction temperature and time of the traditional SiC preparation process, greatly reduces the reaction energy consumption and cost, and at the same time the introduction of SiC can effectively improve the dielectric loss ability of the Si@SiC@Fe3O4 / C powder.

[0056] Figure 5 are the 2D / 3D reflection loss diagrams of the samples prepared under different reaction conditions. Among them, (a) and (b) are the 2D / 3D reflection loss diagrams of the simply mixed C / Si powder; (c-d), (e-f), and (g-h) are the 2D / 3D reflection loss diagrams of the powders obtained after PECVD at 700 °C, 800 °C, and 900 °C respectively. From Figure 5It can be seen that the maximum reflection loss of the powder prepared without plasma-induced chemical vapor deposition technology is -32 dB, and the absorption bandwidth is 5 GHz. When the PECVD technology is used for treatment at 700 °C, the reflection loss of the sample is significantly improved, and the maximum reflection loss reaches -40 dB. As the reaction temperature increases, the reflection loss of the sample continues to increase. When treated at 800 °C, the reflection loss reaches -50 dB, and when treated at 900 °C, the reflection loss reaches -54 dB, with an effective absorption bandwidth of 6 GHz, showing good wave absorption performance and a relatively large effective absorption bandwidth. The results in the figure show that in the range of 700-900 °C, as the temperature increases, the SiC content increases, the interfacial polarization is enhanced, and the reflection loss is significantly improved; moreover, the multi-heterogeneous interface (Si / SiC / Fe3O4 / C) causes multiple losses (dielectric, magnetic, and conductive losses), broadening the effective absorption bandwidth.

[0057] It should be understood that the application of the present invention is not limited to the above examples. For those of ordinary skill in the art, improvements or transformations can be made according to the above description, and all such improvements and transformations shall fall within the protection scope of the appended claims of the present invention.

Claims

1. A method for preparing a silicon carbide composite wave absorbing and heat conducting dual-functional material, characterized in that: Includes steps: Weighing high-purity graphite powder and high-purity silicon powder with a purity greater than 99.9% and placing them in a stainless steel ball mill, then weighing stainless steel balls and placing them in the stainless steel ball mill, adding anhydrous ethanol, and performing ball milling at a speed of 300-500 r / min to obtain a composite powder, wherein the composite powder includes silicon powder and graphite powder and Fe3O4 particles distributed on the surface of the silicon powder; The composite powder is placed in the central temperature zone of a PECVD furnace. An inert gas is first introduced into the PECVD furnace, and then the central temperature zone of the PECVD furnace is heated to 800-900°C. Finally, acetylene is introduced and a plasma generator is turned on for reaction, so that the surface of the silicon powder reacts to generate silicon carbide. At the same time, a C layer generated by the decomposition of acetylene forms a partial coating on the surface of the silicon carbide, and finally a silicon carbide composite wave absorbing and thermal conductive dual-functional material, i.e., Si@SiC@Fe3O4 / C, is obtained.

2. The method for preparing the silicon carbide composite wave absorbing and thermally conductive dual-functional material according to claim 1, characterized in that: The molar ratio of the high-purity graphite powder to the high-purity silicon powder is 1:

1.

3. The method for preparing the silicon carbide composite wave absorbing and heat conducting dual-functional material according to claim 1, characterized in that: The stainless steel balls are placed in the stainless steel ball mill according to a ball-to-material mass ratio of 15-20:

1.

4. The method for preparing the silicon carbide composite wave absorbing and heat conducting dual-functional material according to claim 1, characterized in that: The inert gas is one of argon, nitrogen and helium.

5. The method for preparing the silicon carbide composite wave absorbing and heat conducting dual-functional material according to claim 4, characterized in that: The flow rate of the inert gas is 50-80 mL / min.

6. The method for preparing the silicon carbide composite wave absorbing and heat conducting dual-functional material according to claim 1, characterized in that: In the step of heating the central temperature zone of the PECVD furnace to 800-900°C, the heating rate is 8-15°C / min.

7. The method for preparing the silicon carbide composite wave absorbing and heat conducting dual-functional material according to claim 1, characterized in that: In the step of introducing acetylene and turning on the plasma generator for reaction, the acetylene flow rate is 10-30 mL / min, the power of the plasma generator is 150-250 W, and the reaction time is 20-40 min.

8. A silicon carbide composite wave absorbing and heat conducting dual-functional material, characterized in that: The material is prepared by the method for preparing the silicon carbide composite wave absorbing and heat conducting dual-functional material according to any one of claims 1 to 7.

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