A preparation method of a carbon-based core-shell structure composite microwave absorber

Abstract

The application belongs to the technical field of inorganic composite materials, and particularly relates to a preparation method of a carbon-based core-shell structure composite microwave absorber. The method comprises the following steps: uniformly laying magnetic absorber powder with a screened particle size on a stainless steel plate with a movable frame arranged on the periphery, and fixing the powder by using the magnetic attraction; horizontally and uniformly passing the powder through a candle flame with one side of the powder downward, so that the exposed part of the powder is coated with a layer of carbon nanoparticles; then, placing the powder on another stainless steel plate with the same size with one side of the powder downward, fixing the movable frame on the stainless steel plate, fixing the powder on the other side of the stainless steel plate by using the magnetic attraction, and horizontally and uniformly passing the powder through the candle flame again with one side of the powder downward; and finally, performing heat treatment under a nitrogen atmosphere. The application has the advantages of simple process, low cost, excellent wave-absorbing performance of the carbon-based core-shell structure composite microwave absorber, super-hydrophobic characteristics, and strong environmental stability.

Description

Technical Field

[0001] This invention belongs to the field of inorganic composite materials technology, specifically relating to a method for preparing a carbon-based core-shell structured composite microwave absorber. Background Technology

[0002] With the widespread use of various electronic products, while bringing convenience to people's work and life, they also bring serious electromagnetic pollution, endangering human health and affecting the safe operation of equipment. Utilizing absorbing materials to absorb and attenuate electromagnetic wave energy is an important way to reduce and protect against electromagnetic pollution. Furthermore, absorbing materials can also be used in military vehicles, aircraft, ships, and other equipment to reduce the probability of being detected by radar, thereby improving their stealth performance and battlefield survivability.

[0003] Currently, carbon materials possess advantages such as lightweight, high conductivity, high specific surface area, and strong dielectric loss, and are often used as electromagnetic wave absorbing materials. However, when carbon materials are used as microwave absorbers alone, they suffer from poor impedance matching performance and a single loss mechanism, limiting their application in electromagnetic protection. Therefore, carbon materials are often combined with magnetic absorbing agents to prepare carbon-based composite absorbing agents, in order to improve the impedance matching performance of carbon materials and introduce diversified loss mechanisms to solve the aforementioned problems of single carbon material absorbing agents. For example, patent CN114684802A discloses a method for preparing magnetic iron-cobalt-nickel alloy / carbon series composite absorbing materials, patent CN112449568A discloses a method for preparing hollow cobalt-nickel alloy / porous carbon composite absorbing materials, and patent CN112225950A proposes a method for preparing environmentally friendly Fe@C composite absorbing materials. These carbon-based composite microwave absorbing materials effectively enhance the microwave absorption performance of carbon materials. However, these methods typically involve pretreatment using wet chemical reactions such as hydrothermal or sol-gel methods, followed by high-temperature carbonization or pyrolysis to obtain the product. The problems are: 1. Product collection during pretreatment is cumbersome, resulting in complex and time-consuming processes; 2. High-temperature carbonization or pyrolysis requires high temperatures and sometimes necessitates the addition of inert gases, placing high demands on equipment, consuming large amounts of energy, and increasing production costs; 3. The magnetic materials in the composite absorber are easily oxidized and have poor corrosion resistance, making them unsuitable for applications requiring high resistance to salt spray corrosion, such as marine environments; 4. Due to the complexity of the composite process and the numerous process parameters that need to be controlled, the composite effect is difficult to guarantee. Therefore, it is necessary to develop new methods for preparing carbon-based microwave absorbing materials to address the many shortcomings of existing methods. Summary of the Invention

[0004] This invention provides a simple preparation method for a carbon-based core-shell composite microwave absorber, which solves the problems of complex processing, long cycle, high production cost, insufficient salt spray corrosion resistance, and difficulty in guaranteeing the composite effect in the prior art.

[0005] To achieve the objectives of this invention, the technical solution provided by this invention is: a method for preparing a carbon-based core-shell structured composite microwave absorber, comprising the following steps:

[0006] (1) Screening magnetic absorber powder with uniform particle size: First, the magnetic absorber powder is screened using a sieve to obtain magnetic absorber powder with an average particle size difference within 1 μm. Then, the powder is placed in a vacuum drying oven and dried at 60-80℃ for 1-3 hours.

[0007] (2) Adsorption of absorbent core material: The magnetic absorbent powder is spread on a stainless steel plate with a movable frame around it. The thickness of the magnetic absorbent powder is flush with the height of the frame. A magnet of the same size is provided on the other side of the stainless steel plate.

[0008] (3) Surface coating: Set up a row of candles close together, with one side of the magnetic absorber powder facing down, so that the stainless steel plate passes through the candle flame below at a uniform speed;

[0009] (4) Transfer and surface coating: Place it horizontally on another stainless steel plate of the same size, and fix the movable frame on this stainless steel plate. Then remove the magnet and stainless steel plate from the top in sequence, and place the other side of the stainless steel plate on the magnet. Repeat step (3) to collect absorbent powder with carbon nanoparticles completely coated on the surface.

[0010] (5) Heat treatment: The collected absorbent powder with carbon nanoparticles on the surface is heat-treated at a suitable temperature for 1-2 hours to obtain a carbon-based core-shell structure microwave absorber.

[0011] Furthermore, the aforementioned stainless steel plate passed through the outer layer of the flame at a uniform speed.

[0012] Furthermore, the stainless steel plate passes through the candle flame at a speed of 0.0005 m / s to 0.005 m / s.

[0013] Furthermore, the stainless steel plate passed through the candle flame at a speed of 0.001 m / s.

[0014] Furthermore, the thickness of the aforementioned stainless steel plate is 0.1~0.5mm.

[0015] Furthermore, the heat treatment temperature is 100℃~300℃.

[0016] Furthermore, the heat treatment temperature is 200℃.

[0017] Furthermore, the thickness of the aforementioned stainless steel rectangular movable frame corresponds to the particle size of the powder. The thickness of the rectangular movable frame used for magnetic absorber powders with particle sizes of 2~5um, 5~7um, and 7~10um is 0.005~0.008mm, 0.006~0.01mm, and 0.008~0.014mm, respectively.

[0018] Furthermore, the aforementioned magnetic absorber powder is one or more of Co powder, Ni powder, Ti powder, Al powder, Fe powder and their alloy powders, and ferrite powder, with a particle size of 2~10 μm.

[0019] Furthermore, the particle size of the pretreated magnetic absorber powder is 2~3 μm.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] (1) The carbon source used in the candle of the present invention is inexpensive, and the temperature used in the heat treatment is relatively low, so there is no need for expensive production equipment and the production cost is low.

[0022] (2) The present invention uses a dry method to directly process the magnetic absorber powder. During this process, the carbon nanoparticles generated by the candle directly coat the surface of the magnetic absorber powder. Then, after heat treatment, its electromagnetic parameters are improved. The preparation process is simple, and the prepared carbon-based composite absorbing material has excellent absorption performance. When the thickness is 2mm, the maximum reflection loss in the frequency range of 2~18GHz reaches -67.8dB, and the effective absorption bandwidth reaches 10.3GHz.

[0023] (3) Since the carbon nanoparticles produced by candle combustion have strong superhydrophobic properties, when they are coated on the surface of magnetic absorber, the resulting carbon-based core-shell structure microwave absorber also has good hydrophobic properties, with a water contact angle of up to 165°. The strong superhydrophobic properties significantly enhance the corrosion resistance of the carbon-based core-shell structure microwave absorber, with a salt spray resistance of over 3000 hours. It has good environmental stability and can meet the application requirements of high corrosion resistance in marine, lake and other environments. Detailed Implementation

[0024] The technical solutions provided by the present invention will be further described in detail below with reference to specific embodiments. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0025] The design concept of this invention is as follows: The magnetic absorbent powder, after particle size screening, is evenly spread on a stainless steel plate with a movable frame around its perimeter, and the powder is fixed in place using magnetic attraction. The powder is then passed horizontally and at a constant speed through a candle flame with one side facing down, the exposed part of the powder being coated with a layer of carbon nanoparticles. Next, the powder is placed horizontally and at a constant speed on another stainless steel plate of the same size with the powder side facing down, and the movable frame is fixed to this stainless steel plate. The powder is then fixed in place on the other side of the stainless steel plate using magnetic attraction. The powder is again passed horizontally and at a constant speed through the candle flame with the powder side facing down. Finally, heat treatment is performed.

[0026] Specifically, the present invention provides a method for preparing a carbon-based core-shell structured composite microwave absorber, comprising the following steps:

[0027] (1) Screening magnetic absorber powder with uniform particle size: First, the magnetic absorber powder is screened using a sieve to obtain magnetic absorber powder with an average particle size difference within 1 μm. For example, magnetic absorber powder with particle sizes of 2~3 μm, 3~4 μm, 4~5 μm, 5~6 μm, 6~7 μm, 7~8 μm, 8~9 μm, or 9~10 μm. Then, the powder is placed in a vacuum drying oven and dried at 60-80℃ for 1-3 hours. The magnetic absorber powder is one or a mixture of magnetic absorber powders such as Co powder, Ni powder, Ti powder, Al powder, Fe powder and their alloy powders, and ferrite powder, with a particle size of 2~10 μm, preferably 2~3 μm.

[0028] (2) Absorbent core material adsorption: Magnetic absorbent powder is spread evenly on a stainless steel plate with a movable frame around its perimeter. The thickness of the magnetic absorbent powder is flush with the height of the frame. A magnet of the same size is placed on the other side of the stainless steel plate. The thickness of the stainless steel plate is 0.1~0.5mm to obtain a suitable magnetic adsorption strength while ensuring rigidity. The thickness of the rectangular movable frame can correspond to the particle size of the powder so that the appropriate powder spreading thickness can be controlled by scraping to prevent the powder from being too thick and not completely covered. The thickness of the rectangular movable frame used for magnetic absorbent powder with particle sizes of 2~5um, 5~7um and 7~10um is 0.005~0.008mm, 0.006~0.01mm and 0.008~0.014mm, respectively.

[0029] In practice, firstly, a detachable rectangular stainless steel frame is fixed to the four edges of the upper surface of a smooth rectangular stainless steel plate, creating a groove in the center of the plate. Then, a scraper is used to evenly spread a layer of magnetic absorbent powder into the groove on the horizontally placed stainless steel plate, ensuring the powder thickness is flush with the height of the rectangular frame at the edge of the groove. Next, the other side of the stainless steel plate is placed flat on a magnet of the same size, using the magnet's attraction to fix the magnetic absorbent powder within the groove on the stainless steel plate surface.

[0030] (3) Surface coating: A row of candles are arranged closely together, with one side of the magnetic absorber powder facing downwards. In this embodiment, the stainless steel plate is rectangular, and the length of the candle arrangement is the same as the width of the rectangular stainless steel plate. The rectangular stainless steel plate is initially located on one side of a row of candles, so that the stainless steel plate passes through the candle flame below at a uniform speed, so that the exposed surface of the magnetic absorber powder is uniformly coated with a layer of black carbon nanoparticles. The part of the candle flame includes the inner layer, middle layer or outer layer of the flame. In this embodiment, the stainless steel plate passes through the outer layer of the flame at a uniform speed. The speed at which the stainless steel plate passes through the candle flame is 0.0005m / s to 0.005m / s. Preferably, the speed at which the stainless steel plate passes through the candle flame is 0.001m / s.

[0031] (4) Transfer and surface coating: Place the magnetic absorbent powder with the side facing down on another stainless steel plate of the same size, and move and fix the movable frame to this stainless steel plate, or take another movable frame and fix it to this stainless steel plate. Then remove the magnet and stainless steel plate in sequence, and place the other side of the stainless steel plate on the magnet of the same size. Use the magnetic attraction to fix the magnetic absorbent powder in the groove on the surface of the stainless steel plate. Repeat step (3) to make the exposed surface of the magnetic absorbent powder uniformly coated with a layer of black carbon nanoparticles. Remove the magnet and collect the absorbent powder with the surface completely coated with carbon nanoparticles.

[0032] (5) Heat treatment: The collected absorbent powder with carbon nanoparticles on its surface is heat-treated at a suitable temperature for 1-2 hours to obtain a carbon-based core-shell structured microwave absorber. The heat treatment temperature is 100℃~300℃, preferably 200℃.

[0033] Example 1: A method for preparing a carbon-based core-shell composite microwave absorber, comprising the following steps:

[0034] (1) Pretreatment of absorbent core material: Carbonyl iron powder with a particle size of 2~10um is screened using a sieve to obtain powder with a particle size of 2~3um, and then placed in a vacuum drying oven at 60℃ for 1 hour.

[0035] (2) Absorbent core material adsorption: A rectangular movable frame with a width of 1 mm and a height of 0.005 mm is fixed around the upper surface of a smooth 0.2 mm thick rectangular stainless steel plate, forming a groove in the middle of the stainless steel plate surface. Then, a layer of pretreated carbonyl iron powder is evenly spread in the groove on the horizontally placed stainless steel plate surface using a scraper. The thickness of the powder is controlled to be flush with the height of the rectangular movable frame at the edge of the groove. Then, the other side of the stainless steel plate is placed flat on a magnet of the same size, and the magnetic absorbent powder is fixed in the groove on the surface of the stainless steel plate by the attraction of the magnet.

[0036] (3) Surface coating: Place the stainless steel plate with the side adsorbing the magnetic absorbent powder facing down, and place a row of candles directly below it, with the candles flush with the end face of the stainless steel plate and the length of the candles matching the width of the stainless steel plate. Pass the stainless steel plate through the outer layer of the candle flame at a uniform speed of 0.001 m / s, so that the exposed surface of the powder is coated with a layer of carbon nanoparticles. Then, place the side adsorbing the magnetic absorbent powder horizontally on another stainless steel plate of the same size, and fix the rectangular movable frame to this stainless steel plate. Then, remove the magnet and stainless steel plate from the top in sequence, and place the other side of the stainless steel plate flat on the magnet of the same size. Use the magnetic attraction to fix the magnetic absorbent powder in the groove on the surface of the stainless steel plate. Then, using the same method as above, pass the stainless steel plate through the outer layer of the candle flame at a uniform speed of 0.001 m / s, remove the magnet, and collect the absorbent powder with the surface completely coated with carbon nanoparticles.

[0037] (4) Heat treatment: The carbonyl iron powder with carbon nanoparticles on the surface collected is heat treated at 200℃ for 1 hour to obtain a carbon-based core-shell structure microwave absorber.

[0038] (5) The water contact angle of the above-mentioned carbon-based core-shell structure microwave absorber is 163° and the salt spray test is more than 3000 hours. When mixed with paraffin, the amount added is 23wt% and the thickness is 2mm. The maximum reflection loss in the frequency range of 2~18GHz reaches -67.8dB and the effective absorption bandwidth is 10.3GHz.

[0039] Example 2: A method for preparing a carbon-based core-shell composite microwave absorber, comprising the following steps:

[0040] (1) Pretreatment of absorbent core material: Carbonyl iron powder with a particle size of 2~10 μm is screened using a sieve to obtain powder with a particle size of 4~5 μm, and then placed in a vacuum drying oven at 60°C for 1 hour.

[0041] (2) Absorbent core material adsorption: A rectangular movable frame with a width of 1 mm and a height of 0.008 mm is fixed around the four edges of the upper surface of a 0.1 mm thick rectangular stainless steel plate with a smooth surface. Then, a layer of pretreated carbonyl iron powder is evenly spread in the groove formed on the surface of the horizontally placed stainless steel plate using a scraper. The thickness of the powder is controlled to be flush with the height of the rectangular movable frame. Then, the other side of the stainless steel plate is placed flat on a magnet of the same size as the plate, and the magnetic absorbent powder is fixed in the groove on the surface of the stainless steel plate by the attraction of the magnet.

[0042] (3) Surface coating: Place the stainless steel plate with the side that adsorbs the magnetic absorbent powder facing down, and place a row of candles directly below it, with the candles flush with the end face of the stainless steel plate and the length of the candles matching the width of the stainless steel plate. Pass the stainless steel plate through the inner layer of the candle flame below at a uniform speed of 0.002 m / s, so that the exposed surface of the powder is coated with a layer of carbon nanoparticles.

[0043] (4) Place one side of the magnetic absorbent powder horizontally on another stainless steel plate of the same size, and fix the rectangular movable frame to the stainless steel plate. Then remove the magnet and stainless steel plate from the top in sequence. Place the other side of the stainless steel plate on the magnet of the same size. Use the magnetic attraction to fix the magnetic absorbent powder in the groove on the surface of the stainless steel plate. Then, using the same method as above, pass the stainless steel plate through the inner layer of the candle flame below at a uniform speed of 0.002 m / s. Remove the magnet and collect the absorbent powder with carbon nanoparticles completely coated on the surface.

[0044] (5) Heat treatment: The carbonyl iron powder with carbon nanoparticles on the surface of the collected carbon was heat-treated at 150°C for 1 hour to obtain a carbon-based core-shell structure microwave absorber.

[0045] Testing revealed that the aforementioned carbon-based core-shell structured microwave absorber has a water contact angle of 160° and withstands salt spray tests for over 2800 hours. When mixed with paraffin at an addition amount of 25 wt% and a thickness of 2 mm, it achieves a maximum reflection loss of -57.2 dB in the 2–18 GHz frequency range and an effective absorption bandwidth of 8.1 GHz.

[0046] Example 3: A method for preparing a carbon-based core-shell composite microwave absorber, comprising the following steps:

[0047] (1) Pretreatment of absorbent core material: Co powder with a particle size of 2~10 μm is screened using a sieve to obtain powder with a particle size of 3~4 μm, and then placed in a vacuum drying oven at 60℃ for 1 hour.

[0048] (2) Absorbent core material adsorption: A rectangular movable frame with a width of 1 mm and a height of 0.006 mm is fixed around the upper surface of a 0.1 mm thick rectangular stainless steel plate with a smooth surface. Then, a layer of pre-treated Co powder is evenly spread in the groove formed on the surface of the horizontally placed stainless steel plate using a scraper. The thickness of the powder is controlled to be flush with the height of the rectangular movable frame. Then, the other side of the stainless steel plate is placed flat on a magnet of the same size as the plate. The magnetic absorbent powder is fixed in the groove on the surface of the stainless steel plate by the attraction of the magnet.

[0049] (3) Surface coating: Place the stainless steel plate with the side that adsorbs the magnetic absorbent powder facing down, and place a row of candles directly below it, with the candles flush with the end face of the stainless steel plate and the length of the candles matching the width of the stainless steel plate. Pass the stainless steel plate through the outer layer of the candle flame below at a uniform speed of 0.0015 m / s, so that the exposed surface of the powder is coated with a layer of carbon nanoparticles.

[0050] (4) Place one side of the magnetic absorbent powder horizontally on another stainless steel plate of the same size, and fix the rectangular movable frame to the stainless steel plate. Then remove the magnet and stainless steel plate from the top in sequence. Place the other side of the stainless steel plate on the magnet of the same size. Use the magnetic attraction to fix the magnetic absorbent powder in the groove on the surface of the stainless steel plate. Then, using the same method as above, pass the stainless steel plate through the outer layer of the candle flame below at a uniform speed of 0.0015 m / s. Remove the magnet and collect the absorbent powder with carbon nanoparticles completely coated on the surface.

[0051] (5) Heat treatment: The collected Co powder with carbon nanoparticles on the surface was heat-treated at 200℃ for 1 hour to obtain a carbon-based core-shell structure microwave absorber.

[0052] Testing revealed that the aforementioned carbon-based core-shell structure microwave absorber has a water contact angle of 161° and withstands salt spray tests for over 3000 hours. When mixed with paraffin at an addition amount of 30wt% and a thickness of 1.3mm, the maximum reflection loss reaches -48.9dB in the frequency range of 2~18GHz, and the effective absorption bandwidth is 6.3GHz.

[0053] Example 4: A method for preparing a carbon-based core-shell composite microwave absorber, comprising the following steps:

[0054] (1) Pretreatment of absorbent core material: Ferrite powder with a particle size of 2~10 μm is screened using a sieve to obtain powder with a particle size of 2~3 μm, and then placed in a vacuum drying oven at 60°C for 1 hour.

[0055] (2) Absorbent core material adsorption: A rectangular movable frame with a width of 1 mm and a height of 0.005 mm is fixed around the four edges of the upper surface of a 0.2 mm thick rectangular stainless steel plate with a smooth surface. Then, a layer of pre-treated ferrite powder is evenly spread in the groove formed on the surface of the horizontally placed stainless steel plate using a scraper. The thickness of the powder is controlled to be flush with the height of the rectangular movable frame. Then, the other side of the stainless steel plate is placed flat on a magnet of the same size as the plate, and the magnetic absorbent powder is fixed in the groove on the surface of the stainless steel plate by the attraction of the magnet.

[0056] (3) Surface coating: Place the stainless steel plate with the side that adsorbs the magnetic absorbent powder facing down, and place a row of candles directly below it, with the candles flush with the end face of the stainless steel plate and the length of the candles matching the width of the stainless steel plate. Pass the stainless steel plate through the outer layer of the candle flame below at a uniform speed of 0.001 m / s, so that the exposed surface of the powder is coated with a layer of carbon nanoparticles.

[0057] (4) Place one side of the magnetic absorbent powder horizontally on another stainless steel plate of the same size, and fix the rectangular movable frame to the stainless steel plate. Then remove the magnet and stainless steel plate from the top in sequence. Place the other side of the stainless steel plate on the magnet of the same size. Use the magnetic attraction to fix the magnetic absorbent powder in the groove on the surface of the stainless steel plate. Then, using the same method as above, pass the stainless steel plate through the outer layer of the candle flame below at a uniform speed of 0.001 m / s. Remove the magnet and collect the absorbent powder with carbon nanoparticles completely coated on the surface.

[0058] (5) Heat treatment: The collected ferrite powder with carbon nanoparticles on the surface is heat-treated at 150°C for 1 hour to obtain a carbon-based core-shell structure microwave absorber.

[0059] Testing revealed that the aforementioned carbon-based core-shell structure microwave absorber has a water contact angle of 165° and withstands salt spray tests for over 3000 hours. When mixed with paraffin at an addition amount of 20wt% and a thickness of 2.2mm, the maximum reflection loss reaches -52.2dB in the frequency range of 2~18GHz, and the effective absorption bandwidth is 8.9GHz.

[0060] Example 5: A method for preparing a carbon-based core-shell composite microwave absorber, comprising the following steps:

[0061] (1) Pretreatment of absorbent core material: Co3Fe7 magnetic alloy powder with a particle size of 2~10 μm is screened using a sieve to obtain powder with a particle size of 5~6 μm, and then placed in a vacuum drying oven at 60℃ for 1 hour.

[0062] (2) Absorbent core material adsorption: A rectangular movable frame with a width of 1mm and a height of 0.01mm is fixed around the four edges of the upper surface of a 0.2mm thick rectangular stainless steel plate with a smooth surface. Then, a layer of pre-treated Co3Fe7 alloy powder is evenly spread in the groove formed on the surface of the horizontally placed stainless steel plate using a scraper. The thickness of the powder is controlled to be flush with the height of the rectangular movable frame. Then, the other side of the stainless steel plate is placed flat on a magnet of the same size as the plate, and the magnetic absorbent powder is fixed in the groove on the surface of the stainless steel plate by the attraction of the magnet.

[0063] (3) Surface coating: Place the stainless steel plate with the side that adsorbs the magnetic absorbent powder facing down, and place a row of candles directly below it, with the candles flush with the end face of the stainless steel plate and the length of the candles matching the width of the stainless steel plate. Pass the stainless steel plate through the outer layer of the candle flame below at a uniform speed of 0.0007 m / s, so that the exposed surface of the powder is coated with a layer of carbon nanoparticles.

[0064] (4) Place one side of the magnetic absorbent powder horizontally on another stainless steel plate of the same size, and fix the rectangular movable frame to the stainless steel plate. Then remove the magnet and stainless steel plate from the top in sequence. Place the other side of the stainless steel plate on the magnet of the same size. Use the magnetic attraction to fix the magnetic absorbent powder in the groove on the surface of the stainless steel plate. Then, using the same method as above, pass the stainless steel plate through the outer layer of the candle flame below at a uniform speed of 0.0007 m / s. Remove the magnet and collect the absorbent powder with carbon nanoparticles completely coated on the surface.

[0065] (5) Heat treatment: The collected Co3Fe7 alloy powder with carbon nanoparticles on the surface was heat-treated at 270℃ for 1 hour to obtain a carbon-based core-shell structure microwave absorber.

[0066] Testing revealed that the aforementioned carbon-based core-shell structure microwave absorber has a water contact angle of 155° and withstands over 3000 hours of salt spray testing. When mixed with paraffin at an addition amount of 32wt% and a thickness of 1.7mm, it achieves a maximum reflection loss of -56.7dB in the 2~18GHz frequency range and an effective absorption bandwidth of 8.1GHz.

[0067] Of the above embodiments, Embodiment 1 is the best embodiment.

[0068] The above description is only a part of the embodiments of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a carbon-based core-shell structure composite microwave absorber, characterized in that: It comprises the following steps: (1) screening the magnetic absorbent powder with uniform particle size: first, screen the magnetic absorbent powder by using a screen, to obtain the magnetic absorbent powder with an average particle size difference within 1 um, and then dry the powder in a vacuum drying oven at 60-80℃ for 1-3 hours; (2) adsorption of the absorbent core material: spread the magnetic absorbent powder on a stainless steel plate with a movable frame arranged around the periphery, and the thickness of the magnetic absorbent powder is flush with the height of the frame, and the other side of the stainless steel plate is provided with a magnet with the same size as the stainless steel plate; (3) surface coating: set a row of adjacent candles, and horizontally place one side of the magnetic absorbent powder downward, and make the stainless steel plate pass through the candle flame below at a uniform speed; (4) transfer and surface coating: horizontally place the side of the magnetic absorbent powder adsorbed downward on another stainless steel plate with the same size, and fix the movable frame on the stainless steel plate, then sequentially remove the magnet and the stainless steel plate above, and then horizontally place the other side of the stainless steel plate below on the magnet, and repeat step (3), to collect the absorbent powder with complete surface coating of carbon nanoparticles; (5) heat treatment: heat treat the collected absorbent powder with surface coating of carbon nanoparticles for 1-2 hours, to obtain the carbon-based core-shell structure microwave absorber; The stainless steel plate passes through the outer layer of the flame at a uniform speed; The speed of the stainless steel plate passing through the candle flame is 0.0005 m / s-0.005 m / s; The heat treatment temperature is 100℃-300℃; The thickness of the stainless steel rectangular movable frame corresponds to the particle size of the powder, and the thickness of the rectangular movable frame used for the magnetic absorbent powder with a particle size of 2-5 um, 5-7 um and 7-10 um is 0.005-0.008 mm, 0.006-0.01 mm and 0.008-0.014 mm, respectively.

2. The method for preparing a carbon-based core-shell structured composite microwave absorber according to claim 1, characterized in that: The speed of the stainless steel plate passing through the candle flame is 0.001 m / s.

3. The method for preparing a carbon-based core-shell structured composite microwave absorber according to claim 2, characterized in that: The thickness of the stainless steel plate is 0.1-0.5 mm.

4. The method for preparing a carbon-based core-shell structured composite microwave absorber according to claim 3, characterized in that: The heat treatment temperature is 200℃.

5. The method for preparing a carbon-based core-shell structured composite microwave absorber according to claim 4, characterized in that: The magnetic absorbent powder is a mixture of one or more of Co powder, Ni powder, Ti powder, Al powder, Fe powder and alloy powder, and ferrite powder, and the particle size is 2-10 um.

6. The method for preparing a carbon-based core-shell structured composite microwave absorber according to claim 5, characterized in that: The particle size of the magnetic absorbent powder after pretreatment in step (1) is 2-3 um.