Lightweight concrete wave-absorbing material based on carbon-based magnetic material and preparation method thereof

Abstract

The application discloses a lightweight concrete wave-absorbing material based on carbon-based magnetic materials and a preparation method thereof, relates to the technical field of lightweight building materials, and replaces conductive carbon black, graphene, carbon nanotubes and other materials in traditional carbon-based magnetic materials by using natural plant fibers; after instant carbonization by using high-voltage electricity, the natural plant fibers form carbonized fiber networks; the conductive wave-absorbing performance of the carbonized fibers is not inferior to that of traditional carbon materials; due to the long length and good cross-linking of the plant fibers, the overall conductivity of the plant fibers is much higher than that of traditional carbon materials; and due to the effect of the current, a large number of originally non-contact fiber networks are broken through and connected, further enhancing the conductive performance of the material; meanwhile, the magnetic phase attached to the surface of the plant fibers is also melted due to the current and fused with the carbonized fiber networks, further improving the conductive performance and magnetic permeability of the plant fibers, increasing the electric loss and magnetic loss of the material to electromagnetic waves, thereby improving the wave-absorbing performance of the material and reducing the production cost.

Description

Technical Field

[0001] This invention relates to the technical field of microwave absorbing materials, specifically to lightweight concrete microwave absorbing materials based on carbon-based magnetic materials and their preparation methods. Background Technology

[0002] With the continuous development of modern technology, the application of microwave absorbing materials in military, electronics, and communications fields is becoming increasingly widespread. Although traditional microwave absorbing materials have certain microwave absorption performance, they often have disadvantages such as high density, heavy weight, and difficulty in processing, which limit their application range. Therefore, the development of lightweight, high-strength, and easy-to-process microwave absorbing materials has become one of the hot topics in the field of materials science. Carbon-based magnetic materials, as a new type of microwave absorbing material, have received widespread attention due to their excellent properties such as lightweight, high conductivity, and high magnetic permeability. When combined with aerated lightweight concrete, they can have advantages such as light weight, high strength, high efficiency microwave absorption, and good stability.

[0003] Currently, the carbon component in carbon-based magnetic materials is typically made of conductive carbon black, graphene, carbon nanotubes, etc. These materials are expensive and their structures are usually quite fragile. When mixed with concrete, they can damage the fiber structure, resulting in fibers that are too short and have less contact with each other after being encased in concrete. This leads to poor connection of the conductive phase in the concrete and affects the microwave absorption effect. The only way to improve the microwave absorption performance is to increase the proportion of carbon-based magnetic materials added, but this will increase the material cost. Summary of the Invention

[0004] The purpose of this invention is to provide a lightweight concrete microwave absorbing material based on carbon-based magnetic materials and its preparation method, so as to solve the problem of poor continuity of the conductive phase in traditional microwave absorbing materials mentioned in the background above.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a lightweight concrete microwave absorbing material based on carbon-based magnetic materials, comprising carbon-based magnetic materials and an aerated concrete substrate, wherein the carbon-based magnetic materials are composed of magnetic materials and dielectric carbon materials, the magnetic materials are magnetic material powder, and the dielectric carbon materials are plant fibers instantaneously carbonized by high voltage. The magnetic materials and dielectric carbon materials are mixed in the following proportions by weight: 1-5 parts magnetic materials and 20-100 parts dielectric carbon materials.

[0006] The aerated concrete substrate is made of the following components by weight: 10-15 parts cement, 60-70 parts fly ash, 15-20 parts quicklime, 0.5-1 parts aluminum powder, and 50-60 parts water.

[0007] Furthermore, the particle size of the aluminum powder is selected to be between 100 mesh and 325 mesh, that is, the diameter of the aluminum powder particles is between approximately 150 micrometers and 45 micrometers. Particle size within this range can provide better reactivity and foaming effect. At the same time, the particle size distribution of the aluminum powder should be as uniform as possible to avoid too many excessively large or small particles, as this will affect the uniformity and stability of foaming.

[0008] This invention provides another technical solution: a method for preparing lightweight concrete microwave absorbing material based on carbon-based magnetic materials, comprising the following steps:

[0009] S1. Premixing of carbon-based magnetic materials: Select magnetic materials with high magnetic permeability and good dispersibility, including Mn-ZnFe2O4; select lightweight and high-strength plant fibers, including long-staple cotton fibers; use spray drying to uniformly spray the magnetic material powder into the plant fibers in the form of tiny droplets, and then promote adsorption by mechanical stirring. The premixing time is controlled between 5 and 10 minutes to ensure uniform mixing.

[0010] S2. Aerated concrete mixing: First, prepare cement, fly ash, quicklime, aluminum powder and water, then mix them according to the design ratio and pour them into the mixer to mix evenly;

[0011] S3. Add carbon-based magnetic material: After the concrete is mixed evenly, add the premixed carbon-based magnetic material continuously while stirring constantly to ensure that the carbon-based magnetic material is fully and evenly mixed with the concrete. After the carbon-based magnetic material is added, continue stirring for 5 to 10 minutes to ensure that the material is evenly distributed.

[0012] S4. Pouring: Apply a release agent to the surface of the mold beforehand, and then pour the well-mixed concrete material into the mold, maintaining a constant speed during the pouring process;

[0013] S5. Static foaming: Place the mold in a stable environment and let it stand for 24 hours to allow the aluminum powder to react with water to produce hydrogen gas and form a uniform bubble structure. During the static foaming process, add water as needed according to the temperature and humidity to keep the concrete surface moist.

[0014] S6. Surface grinding: After the concrete has solidified, the upper and lower surfaces of the aerated concrete block are ground to expose the plant fibers in the concrete. The grinding depth is 2-5mm.

[0015] S7. Electro-organic carbonization: First, wet the solidified concrete, then evenly arrange electrodes on the planed upper and lower surfaces with a spacing of 5-10 cm. Then, apply electricity and use instantaneous high-voltage current to carbonize the plant fibers. Ensure ventilation during the carbonization process to remove the gases produced by the carbonization of the plant fibers, and monitor temperature changes to prevent overheating and damage to the structure.

[0016] Furthermore, in step S1, the purity of the magnetic material used is greater than 99%, and the magnetic material is ground before premixing the carbon-based magnetic material to ensure that the particle size of the magnetic material is less than 100 mesh.

[0017] Furthermore, in S1, a carding machine is used to finely comb the plant fibers before premixing, breaking down the aggregated fiber clumps into individual fibers and removing larger fiber impurities.

[0018] In one example, the method of spray drying magnetic material powder onto plant fibers in S1 includes the following steps:

[0019] S401. Preparation of magnetic material suspension: Mix magnetic material powder with an appropriate amount of water to prepare a suspension, and stir thoroughly with a stirrer to ensure that the magnetic material is evenly dispersed in the liquid;

[0020] S402. Adjust spray parameters: Based on the characteristics of the magnetic material suspension and the properties of the plant fiber, adjust the sprayer parameters, including spray pressure, flow rate and spray angle, to obtain appropriate droplet size and spray pattern;

[0021] S403. Preheating Drying Chamber: Activate the hot air system to preheat the drying chamber to the predetermined temperature. The temperature should be determined based on the thermal sensitivity of the magnetic material and plant fibers.

[0022] S404. Spray drying: The prepared magnetic material suspension is fed into the sprayer, and then the sprayer is turned on so that the suspension is evenly sprayed into the drying chamber in the form of tiny droplets. Hot air enters from the bottom of the drying chamber and comes into countercurrent contact with the droplets, rapidly evaporating the liquid and causing the magnetic material powder to adhere evenly to the plant fiber.

[0023] In one example, the process of mixing aerated concrete in S2 includes the following steps:

[0024] S701. Raw Material Preparation: Cement: Ordinary Portland cement conforming to national standards, with a strength grade of not less than 42.5; Fly ash: Grade II or above fly ash, with a fineness of less than 45μm and a loss on ignition of less than 5%; Quicklime: Quicklime with an effective calcium oxide content of more than 70% and a fineness of less than 10mm; Aluminum powder: Aluminum powder with a purity of more than 90% and a fineness of less than 45μm; Water: Clean fresh water with a pH value between 6 and 8.

[0025] S702. Raw material measurement: Weigh out 10-15 parts of cement, 60-70 parts of fly ash, 15-20 parts of quicklime, 0.5-1 parts of aluminum powder, and 50-60 parts of water by weight.

[0026] S703. Raw material mixing: First, pour cement, fly ash and quicklime into the mixer and dry mix for 1 to 2 minutes. Then add aluminum powder and continue to dry mix for 1 to 2 minutes to make the aluminum powder evenly distributed in the cement, fly ash and quicklime.

[0027] S704. Concrete mixing: Add water to the well-mixed dry materials and start mixing. Control the mixing time to 3-5 minutes to ensure that the concrete is mixed evenly and has good workability. During the mixing process, pay attention to the consistency of the concrete. If adjustment is needed, add or reduce the amount of water as appropriate to adjust to a suitable consistency so that dielectric carbon material can be added.

[0028] Furthermore, when adding carbon-based magnetic material in S3, the carbon-based magnetic material is added in batches according to the size of the upper surface area of ​​the aerated concrete in the mixer, ensuring that the carbon-based magnetic material added each time is loosely covering the surface of the aerated concrete with a coverage thickness of less than 5mm, ensuring uniform thickness without accumulation, and continuing to stir for 2-3 minutes after each addition of carbon-based magnetic material.

[0029] Furthermore, in step S5, during the static foaming of concrete, the ambient temperature is controlled between 20 and 30°C, and the relative humidity is controlled between 60% and 80%, which promotes the reaction between aluminum powder and water to produce hydrogen gas, thereby forming a uniform and dense bubble structure in the concrete.

[0030] Furthermore, during the electrochemical carbonization process in S7, a high-voltage direct current is used as the power source, with the voltage controlled between 3kV and 5kV for a duration of 0.3s, to ensure that the plant fibers are effectively carbonized in a short time.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] This invention proposes a lightweight concrete microwave absorbing material based on carbon-based magnetic materials and its preparation method. By utilizing natural plant fibers to replace traditional carbon-based magnetic materials such as conductive carbon black, graphene, and carbon nanotubes, the natural plant fibers are mixed with lightweight concrete. These natural plant fibers possess significantly higher strength and toughness than conductive carbon black, graphene, and carbon nanotubes, and will not break during mixing with concrete. Furthermore, their fiber length is much longer than traditional carbon materials, making it easier to form cross-linked networks. Moreover, after instantaneous carbonization using high-voltage electricity, substances such as fats in the natural plant fibers disappear. The carbonized fiber network is formed, and its conductive and microwave absorption properties after carbonization are comparable to those of traditional carbon materials. Moreover, due to the long length of plant fibers and their good cross-linking, its overall conductivity is much higher than that of traditional carbon materials. Furthermore, due to the action of electric current, a large number of originally unconnected fiber networks are broken down and connected, further enhancing the conductivity of the material. At the same time, the magnetic phase attached to the surface of the plant fibers will melt due to the electric current and fuse with the carbon fiber network, further improving its conductivity and permeability. This increases the material's electrical and magnetic losses to electromagnetic waves, thereby improving the material's microwave absorption performance and reducing its production cost. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the carbonized fiber network inside the microwave absorbing material of the present invention;

[0034] Figure 2 This is a schematic diagram of the cross-section pores of the microwave absorbing material of the present invention;

[0035] Figure 3 This is a table showing the carbonization effects of different fiber materials in this invention. Detailed Implementation

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] like Figures 1-3 As shown, the lightweight concrete microwave absorbing material based on carbon-based magnetic materials is composed of carbon-based magnetic materials and an aerated concrete substrate. The carbon-based magnetic materials consist of magnetic materials and dielectric carbon materials. The magnetic materials are made of magnetic material powder, and the dielectric carbon materials are made of plant fibers through high-voltage instantaneous carbonization treatment. The magnetic materials and dielectric carbon materials are mixed in the following proportions by weight:

[0038] 1-5 parts of magnetic material;

[0039] 20-100 parts of dielectric carbon material.

[0040] Magnetic materials are primarily used to improve the impedance matching of carbon materials, allowing electromagnetic waves to penetrate the absorbing material more effectively. Simultaneously, magnetic materials can also create a synergistic effect with carbon materials, further enhancing the material's ability to dissipate electromagnetic waves. Dielectric carbon materials form a conductive network within the concrete, improving the material's conductivity. These conductive materials not only contribute to the transmission and dissipation of electromagnetic waves but also absorb electromagnetic wave energy through resistive loss, magnetic loss, and dielectric loss.

[0041] The aerated concrete substrate is made of the following components by weight:

[0042] 10-15 parts cement;

[0043] 60-70 parts fly ash;

[0044] 15-20 parts quicklime;

[0045] 0.5 to 1 part aluminum powder;

[0046] 50-60 parts water.

[0047] Cement plays a role in reinforcing the framework, increasing strength and stability;

[0048] Fly ash, as a siliceous material, can replace part of the cement, reduce the cost of concrete, improve the later strength of concrete, and expand the range of concrete types and strength grades.

[0049] Quicklime can provide effective CaO, which reacts hydrothermally with SiO2 and AlO3 in fly ash to produce hydrated silicates and hydrated aluminosilicates, thereby increasing the strength of concrete.

[0050] Aluminum powder acts as a foaming agent, promoting bubble formation. Through oxidation, it generates gas, producing tiny bubbles that create a porous structure in the concrete. These bubbles reduce the density of the concrete, making it lighter. The particle size of the aluminum powder is selected to be between 100 and 325 mesh, meaning the particle diameter is approximately 150 to 45 micrometers. This particle size range provides good reactivity and foaming effect. Simultaneously, the particle size distribution should be as uniform as possible, avoiding an excessive number of overly large or small particles, as this will affect the uniformity and stability of the foaming process.

[0051] Example 1: The preparation method of lightweight concrete microwave absorbing material based on carbon-based magnetic materials includes the following steps:

[0052] Step 1: Premixing of carbon-based magnetic materials: Select magnetic materials with high magnetic permeability and good dispersibility, including Mn-ZnFe2O4, with a purity greater than 99%. Before premixing the carbon-based magnetic materials, grind the magnetic materials to ensure that the particle size is less than 100 mesh. Select lightweight, high-strength plant fibers, using long-staple cotton fibers. Long-staple cotton fibers are fine and have high strength, which allows them to better play a reinforcing and supporting role in concrete, forming a uniform fiber network in the concrete, and also helping to improve the microstructure and performance of concrete.

[0053] Before premixing, the long-staple cotton fibers are finely combed using a carding machine to break down loose knots into single fibers, while removing larger knots and impurities, which facilitates uniform dispersion in the concrete. Then, Mn-ZnFe2O4 powder is sprayed evenly onto the long-staple cotton fibers in the form of tiny droplets using a spray-drying method. Mechanical stirring is then used to promote adsorption. The premixing time is controlled between 5 and 10 minutes to ensure uniform mixing. The specific steps of spray-drying Mn-ZnFe2O4 powder onto long-staple cotton fibers include:

[0054] 1. Prepare Mn-ZnFe2O4 suspension: Mix Mn-ZnFe2O4 powder with an appropriate amount of water to prepare a suspension. Stir thoroughly with a stirrer to ensure that Mn-ZnFe2O4 is evenly dispersed in the liquid.

[0055] 2. Adjust spray parameters: Based on the characteristics of the Mn-ZnFe2O4 suspension and the properties of long-staple cotton fibers, adjust the sprayer parameters, including spray pressure, flow rate, and spray angle, to obtain appropriate droplet size and spray pattern;

[0056] 3. Preheating the drying chamber: Activate the hot air system to preheat the drying chamber to the predetermined temperature. The temperature should be determined based on the heat sensitivity of Mn-ZnFe2O4 and long-staple cotton fibers.

[0057] 4. Spray drying: The prepared Mn-ZnFe2O4 suspension is fed into the sprayer, and then the sprayer is turned on so that the suspension is evenly sprayed into the drying chamber in the form of tiny droplets. Hot air enters from the bottom of the drying chamber and comes into countercurrent contact with the droplets, rapidly evaporating the liquid and allowing the magnetic material powder to be evenly attached to the long-staple cotton fibers.

[0058] Step 2: Aerated Concrete Mixing: First, prepare cement, fly ash, quicklime, aluminum powder, and water. Then, mix them according to the designed proportions and pour them into a mixer to stir evenly. The specific mixing method includes the following steps:

[0059] 1. Raw material preparation: Cement: Ordinary Portland cement conforming to national standards, with a strength grade of not less than 42.5; Fly ash: Grade II or above fly ash, with a fineness of less than 45μm and a loss on ignition of less than 5%; Quicklime: Quicklime with an effective calcium oxide content of more than 70% and a fineness of less than 10mm; Aluminum powder: Aluminum powder with a purity of more than 90% and a fineness of less than 45μm; Water: Clean fresh water with a pH value between 6 and 8.

[0060] 2. Raw material measurement: Weigh out 10-15 parts cement, 60-70 parts fly ash, 15-20 parts quicklime, 0.5-1 part aluminum powder, and 50-60 parts water by weight.

[0061] 3. Raw material mixing: First, pour cement, fly ash and quicklime into the mixer and dry mix for 1 to 2 minutes. Then add aluminum powder and continue to dry mix for 1 to 2 minutes to make the aluminum powder evenly distributed in the cement, fly ash and quicklime.

[0062] 4. Concrete mixing: Add water to the mixed dry materials and start mixing. Control the mixing time to 3-5 minutes to ensure that the concrete is mixed evenly and has good workability. During the mixing process, pay attention to the consistency of the concrete. If adjustment is needed, add or reduce the amount of water as appropriate to adjust to a suitable consistency so that dielectric carbon material can be added.

[0063] Step 3: Adding carbon-based magnetic material: After the concrete is evenly mixed, continuously add the premixed carbon-based magnetic material while stirring constantly to ensure that the carbon-based magnetic material is fully and evenly mixed with the concrete. When adding the carbon-based magnetic material, add it in batches according to the surface area of ​​the aerated concrete in the mixer, ensuring that each addition of carbon-based magnetic material loosely covers the surface of the aerated concrete, with a coverage thickness of less than 5mm, ensuring uniform thickness and no accumulation. After each addition of carbon-based magnetic material, continue stirring for 2-3 minutes before adding the next addition. After all the carbon-based magnetic material has been added, continue stirring for 5-10 minutes to ensure that the material is evenly distributed.

[0064] Step 4, Pouring: Apply release agent to the surface of the mold beforehand, and then pour the well-mixed concrete material into the mold, maintaining a uniform pouring speed during the process.

[0065] Step 5, Static Foaming: Place the mold in a stable environment and let it stand for 24 hours. During the static foaming of the concrete, control the ambient temperature between 20 and 30°C and the relative humidity between 60% and 80% to promote the reaction between aluminum powder and water to produce hydrogen gas, thereby forming a foam in the concrete. Figure 2 The uniform and fine bubble structure shown allows for appropriate replenishment of moisture during the settling process, based on temperature and humidity, to keep the concrete surface moist.

[0066] Step 6: Surface planing: After the concrete has solidified, plan the upper and lower surfaces of the aerated concrete block to expose the long-staple cotton fibers in the concrete. The planing depth is 2-5mm.

[0067] Step 7, Electrochemical Carbonization: First, wet the solidified concrete. Then, evenly arrange electrodes on the planed upper and lower surfaces, with an electrode spacing of 5-10 cm. Then, apply electricity. After multiple tests, controlling the power supply voltage at around 3kV yields the best carbonization effect and is also relatively safe. The energizing duration should be less than 0.3 seconds to prevent excessively high current flow from causing the concrete temperature to rise too high and affecting its structural performance.

[0068] Mn-ZnFe2O4 attached to plant fibers can increase the conductivity of the plant fibers. Using a transient high-voltage current to carbonize long-staple cotton fibers causes the loss of fatty components, leaving only biochar, thus forming a... Figure 1 The diagram shows an interlinked hollow carbon nanotube network. Mn-ZnFe2O4 is instantly melted by a high-voltage current and solidified onto the hollow carbon nanotube network. Compared to traditional microwave absorbing materials, this hollow carbon nanotube network structure exhibits superior electrical conductivity due to the longer and more continuous fiber structure of the hollow carbon nanotubes. It is also important to ensure ventilation during the carbonization process to remove gases generated during the carbonization of the long-staple cotton fibers, and to monitor temperature changes to prevent overheating and structural damage.

[0069] Example 2: The preparation method of lightweight concrete microwave absorbing material based on carbon-based magnetic materials includes the following steps:

[0070] Step 1: Premixing of carbon-based magnetic materials: Select magnetic materials with high magnetic permeability and good dispersibility, including Mn-ZnFe2O4, with a purity greater than 99%. Before premixing the carbon-based magnetic materials, grind them to ensure that the particle size is less than 100 mesh. Select lightweight, high-strength plant fibers. The plant fibers are wood fibers made from recycled waste paper. The advantages are that they are widely available, inexpensive, and in line with the concept of environmental protection and sustainable development. In addition, the fine fiber structure of recycled waste paper wood fibers helps to enhance the strength and hardness of concrete.

[0071] Before premixing, the wood fibers are soaked and washed to remove impurities, and then dried. Magnetic material powder is sprayed evenly onto the wood fibers in the form of tiny droplets using a spray drying method. Adsorption is then promoted by mechanical stirring. The premixing time is controlled between 5 and 10 minutes to ensure uniform mixing. The specific steps of spray drying Mn-ZnFe2O4 powder onto wood fibers include:

[0072] 1. Prepare Mn-ZnFe2O4 suspension: Mix Mn-ZnFe2O4 powder with an appropriate amount of water to prepare a suspension. Stir thoroughly with a stirrer to ensure that Mn-ZnFe2O4 is evenly dispersed in the liquid.

[0073] 2. Adjust spray parameters: Based on the characteristics of the Mn-ZnFe2O4 suspension and the properties of the wood fiber, adjust the sprayer parameters, including spray pressure, flow rate, and spray angle, to obtain appropriate droplet size and spray pattern;

[0074] 3. Preheating the drying chamber: Activate the hot air system to preheat the drying chamber to the predetermined temperature. The temperature should be determined based on the heat sensitivity of Mn-ZnFe2O4 and wood fibers.

[0075] 4. Spray drying: The prepared Mn-ZnFe2O4 suspension is fed into the sprayer, and then the sprayer is turned on so that the suspension is evenly sprayed into the drying chamber in the form of tiny droplets. Hot air enters from the bottom of the drying chamber and comes into countercurrent contact with the droplets, rapidly evaporating the liquid and allowing the magnetic material powder to be evenly attached to the wood fiber.

[0076] Step 2: Aerated Concrete Mixing: First, prepare cement, fly ash, quicklime, aluminum powder, and water. Then, mix them according to the designed proportions and pour them into a mixer to stir evenly. The specific mixing method includes the following steps:

[0077] 1. Raw material preparation: Cement: Ordinary Portland cement conforming to national standards, with a strength grade of not less than 42.5; Fly ash: Grade II or above fly ash, with a fineness of less than 45μm and a loss on ignition of less than 5%; Quicklime: Quicklime with an effective calcium oxide content of more than 70% and a fineness of less than 10mm; Aluminum powder: Aluminum powder with a purity of more than 90% and a fineness of less than 45μm; Water: Clean fresh water with a pH value between 6 and 8.

[0078] 2. Raw material measurement: Weigh out 10-15 parts cement, 60-70 parts fly ash, 15-20 parts quicklime, 0.5-1 part aluminum powder, and 50-60 parts water by weight.

[0079] 3. Raw material mixing: First, pour cement, fly ash and quicklime into the mixer and dry mix for 1 to 2 minutes. Then add aluminum powder and continue to dry mix for 1 to 2 minutes to make the aluminum powder evenly distributed in the cement, fly ash and quicklime.

[0080] 4. Concrete mixing: Add water to the mixed dry materials and start mixing. Control the mixing time to 3-5 minutes to ensure that the concrete is mixed evenly and has good workability. During the mixing process, pay attention to the consistency of the concrete. If adjustment is needed, add or reduce the amount of water as appropriate to adjust to a suitable consistency so that dielectric carbon material can be added.

[0081] Step 3: Adding carbon-based magnetic material: After the concrete is evenly mixed, continuously add the premixed carbon-based magnetic material while stirring constantly to ensure that the carbon-based magnetic material is fully and evenly mixed with the concrete. When adding the carbon-based magnetic material, add it in batches according to the surface area of ​​the aerated concrete in the mixer, ensuring that each addition of carbon-based magnetic material loosely covers the surface of the aerated concrete, with a coverage thickness of less than 5mm, ensuring uniform thickness and no accumulation. After each addition of carbon-based magnetic material, continue stirring for 2-3 minutes before adding the next addition. After all the carbon-based magnetic material has been added, continue stirring for 5-10 minutes to ensure that the material is evenly distributed.

[0082] Step 4, Pouring: Apply release agent to the surface of the mold beforehand, and then pour the well-mixed concrete material into the mold, maintaining a uniform pouring speed during the process.

[0083] Step 5, Static Foaming: Place the mold in a stable environment and let it stand for 24 hours. During the static foaming of the concrete, control the ambient temperature between 20 and 30°C and the relative humidity between 60% and 80% to promote the reaction between aluminum powder and water to produce hydrogen gas, thereby forming a foam in the concrete. Figure 2 The uniform and fine bubble structure shown allows for appropriate replenishment of moisture during the settling process, based on temperature and humidity, to keep the concrete surface moist.

[0084] Step 6: Surface planing: After the concrete has solidified, plan the upper and lower surfaces of the aerated concrete block to expose the wood fibers in the concrete. The planing depth is 2-5mm.

[0085] Step 7, Electrochemical Carbonization: First, wet the solidified concrete. Then, evenly arrange electrodes on the planed upper and lower surfaces, with an electrode spacing of 5-10 cm. Then, apply electricity. After multiple tests, controlling the power supply voltage between 3kV and 5kV yields the best carbonization effect and is also relatively safe. The energizing duration should be less than 0.3 seconds to prevent excessively high current flow from causing the concrete temperature to rise too high and affecting its structural performance.

[0086] Mn-ZnFe2O4 attached to plant fibers can increase their conductivity. By carbonizing the wood fibers with a transient high-voltage current, components such as fats in the plant fibers disappear, leaving only bio-carbon, which forms a network of interconnected hollow carbon nanotubes. The Mn-ZnFe2O4 is then melted and solidified on the hollow carbon nanotube network by the instantaneous high-voltage current. Compared to traditional microwave absorbing materials, the hollow carbon nanotube network structure has longer fibers and better continuity, resulting in superior conductivity. It is also important to ensure ventilation during the carbonization process to remove gases generated during the carbonization of the wood fibers, and to monitor temperature changes to prevent overheating and structural damage.

[0087] Example 3: The preparation method of lightweight concrete microwave absorbing material based on carbon-based magnetic materials includes the following steps:

[0088] Step 1: Premixing of Carbon-Based Magnetic Materials: Select magnetic materials with high permeability and good dispersibility, including Mn-ZnFe2O4, with a purity greater than 99%. Before premixing the carbon-based magnetic materials, grind them to ensure the particle size is less than 100 mesh. Select lightweight, high-strength plant fibers, specifically bamboo fiber, which is derived from processed moso bamboo. Moso bamboo grows quickly and is highly renewable, making it a green and environmentally friendly source of fiber materials. Bamboo fibers have a moderate length and a unique fiber structure with numerous micropores and grooves on the surface. After premixing, they can adsorb a large amount of magnetic material, resulting in a finished product with good conductivity and strong absorption of electromagnetic waves.

[0089] Before premixing, the bamboo fiber needs to be cleaned and dried to remove impurities and increase its surface roughness, which is beneficial for the adsorption of Mn-ZnFe2O4. Mn-ZnFe2O4 powder is sprayed evenly onto the bamboo fiber in the form of tiny droplets using a spray drying method. Adsorption is then promoted by mechanical stirring. The premixing time is controlled between 5 and 10 minutes to ensure uniform mixing. The specific steps of spray drying Mn-ZnFe2O4 powder onto bamboo fiber include:

[0090] 1. Prepare Mn-ZnFe2O4 suspension: Mix Mn-ZnFe2O4 powder with an appropriate amount of water to prepare a suspension. Stir thoroughly with a stirrer to ensure that Mn-ZnFe2O4 is evenly dispersed in the liquid.

[0091] 2. Adjust spray parameters: Based on the characteristics of the Mn-ZnFe2O4 suspension and the properties of bamboo fiber, adjust the sprayer parameters, including spray pressure, flow rate, and spray angle, to obtain appropriate droplet size and spray pattern;

[0092] 3. Preheating the drying chamber: Activate the hot air system to preheat the drying chamber to the predetermined temperature. The temperature should be determined based on the heat sensitivity of Mn-ZnFe2O4 and bamboo fiber.

[0093] 4. Spray drying: The prepared Mn-ZnFe2O4 suspension is fed into the sprayer, and then the sprayer is turned on so that the suspension is evenly sprayed into the drying chamber in the form of tiny droplets. Hot air enters from the bottom of the drying chamber and comes into countercurrent contact with the droplets, rapidly evaporating the liquid and allowing the magnetic material powder to be evenly attached to the bamboo fiber.

[0094] Step 2: Aerated Concrete Mixing: First, prepare cement, fly ash, quicklime, aluminum powder, and water. Then, mix them according to the designed proportions and pour them into a mixer to stir evenly. The specific mixing method includes the following steps:

[0095] 1. Raw material preparation: Cement: Ordinary Portland cement conforming to national standards, with a strength grade of not less than 42.5; Fly ash: Grade II or above fly ash, with a fineness of less than 45μm and a loss on ignition of less than 5%; Quicklime: Quicklime with an effective calcium oxide content of more than 70% and a fineness of less than 10mm; Aluminum powder: Aluminum powder with a purity of more than 90% and a fineness of less than 45μm; Water: Clean fresh water with a pH value between 6 and 8.

[0096] 2. Raw material measurement: Weigh out 10-15 parts cement, 60-70 parts fly ash, 15-20 parts quicklime, 0.5-1 part aluminum powder, and 50-60 parts water by weight.

[0097] 3. Raw material mixing: First, pour cement, fly ash and quicklime into the mixer and dry mix for 1 to 2 minutes. Then add aluminum powder and continue to dry mix for 1 to 2 minutes to make the aluminum powder evenly distributed in the cement, fly ash and quicklime.

[0098] 4. Concrete mixing: Add water to the mixed dry materials and start mixing. Control the mixing time to 3-5 minutes to ensure that the concrete is mixed evenly and has good workability. During the mixing process, pay attention to the consistency of the concrete. If adjustment is needed, add or reduce the amount of water as appropriate to adjust to a suitable consistency so that dielectric carbon material can be added.

[0099] Step 3: Adding carbon-based magnetic material: After the concrete is evenly mixed, continuously add the premixed carbon-based magnetic material while stirring constantly to ensure that the carbon-based magnetic material is fully and evenly mixed with the concrete. When adding the carbon-based magnetic material, add it in batches according to the surface area of ​​the aerated concrete in the mixer, ensuring that each addition of carbon-based magnetic material loosely covers the surface of the aerated concrete, with a coverage thickness of less than 5mm, ensuring uniform thickness and no accumulation. After each addition of carbon-based magnetic material, continue stirring for 2-3 minutes before adding the next addition. After all the carbon-based magnetic material has been added, continue stirring for 5-10 minutes to ensure that the material is evenly distributed.

[0100] Step 4, Pouring: Apply release agent to the surface of the mold beforehand, and then pour the well-mixed concrete material into the mold, maintaining a uniform pouring speed during the process.

[0101] Step 5, Static Foaming: Place the mold in a stable environment and let it stand for 24 hours. During the static foaming of the concrete, control the ambient temperature between 20 and 30°C and the relative humidity between 60% and 80% to promote the reaction between aluminum powder and water to produce hydrogen gas, thereby forming a foam in the concrete. Figure 2 The uniform and fine bubble structure shown allows for appropriate replenishment of moisture during the settling process, based on temperature and humidity, to keep the concrete surface moist.

[0102] Step 6: Surface planing: After the concrete has solidified, plan the upper and lower surfaces of the aerated concrete block to expose the bamboo fibers in the concrete. The planing depth is 2-5mm.

[0103] Step 7, Electrochemical Carbonization: First, wet the solidified concrete. Then, evenly arrange electrodes on the planed upper and lower surfaces, with an electrode spacing of 5-10 cm. Then, apply electricity. After multiple tests, controlling the power supply voltage at around 5kV yields the best carbonization effect and is also relatively safe. The energizing duration should be less than 0.3 seconds to prevent excessively high current flow from causing the concrete temperature to rise too high and affecting its structural performance.

[0104] Mn-ZnFe2O4 attached to plant fibers can increase their conductivity. By carbonizing bamboo fibers with a transient high-voltage current, components such as fats in the plant fibers disappear, leaving only bio-carbon, which forms a network of interconnected hollow carbon nanotubes. The Mn-ZnFe2O4 is then melted and solidified on the hollow carbon nanotube network by the instantaneous high-voltage current. Compared to traditional microwave absorbing materials, the hollow carbon nanotube network structure has longer fibers and better continuity, resulting in superior conductivity. It is also important to ensure ventilation during the carbonization process to remove gases generated during bamboo fiber carbonization, and to monitor temperature changes to prevent overheating and structural damage.

[0105] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0106] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing lightweight concrete microwave absorbing material based on carbon-based magnetic materials, characterized in that: The microwave absorbing material is composed of carbon-based magnetic material and an aerated concrete substrate. The carbon-based magnetic material is composed of magnetic material and dielectric carbon material. The magnetic material is made of magnetic material powder, and the dielectric carbon material is made of plant fiber through high-voltage instantaneous carbonization treatment. The magnetic material and dielectric carbon material are mixed in the following proportions by weight: magnetic material 1-5 parts, dielectric carbon material 20-100 parts. The aerated concrete substrate is made of the following components by weight: cement 10-15 parts, fly ash 60-70 parts, quicklime 15-20 parts, aluminum powder 0.5-1 parts, water 50-60 parts. The particle size of the aluminum powder is selected between 100 mesh and 325 mesh. The preparation method includes the following steps: S1. Premixing of carbon-based magnetic materials: Mn-ZnFe2O4 is selected as the magnetic material, and long-staple cotton fiber is selected as the plant fiber. The magnetic material powder is evenly sprayed onto the plant fiber in the form of tiny droplets by spray drying. Then, mechanical stirring is used to promote adsorption. The premixing time is controlled between 5 and 10 minutes. S2. Aerated concrete mixing: First, prepare cement, fly ash, quicklime, aluminum powder and water, then mix them according to the design ratio and pour them into the mixer to mix evenly; S3. Add carbon-based magnetic material: After the concrete is mixed evenly, add the premixed carbon-based magnetic material continuously while stirring constantly to ensure that the carbon-based magnetic material is fully and evenly mixed with the concrete. After the carbon-based magnetic material is added, continue stirring for 5 to 10 minutes. S4. Pouring: Apply a release agent to the surface of the mold beforehand, and then pour the well-mixed concrete material into the mold, maintaining a constant speed during the pouring process; S5. Static foaming: Place the mold in a stable environment and let it stand for 24 hours to allow the aluminum powder to react with water to produce hydrogen gas, forming a uniform bubble structure in the concrete. During the static foaming process, add water according to the temperature and humidity to keep the concrete surface moist. S6. Surface grinding: After the concrete has solidified, the upper and lower surfaces of the aerated concrete block are ground to expose the plant fibers in the concrete. The grinding depth is 2-5mm. S7. Electro-organic carbonization: First, wet the solidified concrete, then evenly arrange electrodes on the planed upper and lower surfaces with a spacing of 5-10 cm. Then, apply electricity to carbonize the plant fibers using a momentary high-voltage current. Ensure ventilation during the carbonization process to remove the gases produced by the carbonization of the plant fibers, and monitor temperature changes to prevent overheating from damaging the structure.

2. The method for preparing lightweight concrete microwave absorbing material based on carbon-based magnetic materials as described in claim 1, characterized in that: In step S1, the purity of the magnetic material used is greater than 99%, and the magnetic material is ground before premixing the carbon-based magnetic material so that the particle size of the magnetic material is less than 100 mesh.

3. The method for preparing lightweight concrete microwave absorbing material based on carbon-based magnetic materials as described in claim 1, characterized in that: In step S1, a carding machine is used to finely comb the plant fibers before premixing, breaking down the aggregated fiber clumps into individual fibers and removing larger fiber impurities.

4. The method for preparing lightweight concrete microwave absorbing material based on carbon-based magnetic materials as described in claim 1, characterized in that: In step S1, the method of spraying magnetic material powder onto plant fibers using spray drying includes the following steps: S401. Preparation of magnetic material suspension: Mix magnetic material powder with water to prepare a suspension, and stir thoroughly with a stirrer to ensure that the magnetic material is evenly dispersed in the liquid; S402. Adjust spray parameters: Adjust the sprayer parameters, including spray pressure, flow rate and spray angle, according to the characteristics of the magnetic material suspension and the properties of the plant fiber; S403. Preheating drying chamber: Start the hot air system to preheat the temperature of the drying chamber to a predetermined value. The temperature is determined based on the thermal sensitivity of the magnetic material and plant fiber. S404. Spray drying: The prepared magnetic material suspension is fed into the sprayer, and then the sprayer is turned on so that the suspension is evenly sprayed into the drying chamber in the form of tiny droplets. Hot air enters from the bottom of the drying chamber and comes into countercurrent contact with the droplets, rapidly evaporating the liquid and causing the magnetic material powder to adhere evenly to the plant fiber.

5. The method for preparing lightweight concrete microwave absorbing material based on carbon-based magnetic materials as described in claim 1, characterized in that: The process of mixing aerated concrete in S2 includes the following steps: S701. Raw Material Preparation: Cement: Ordinary Portland cement with a strength grade of not less than 42.5; Fly ash of grade II or above with a fineness of less than 45μm and a loss on ignition of less than 5%; Quicklime with an effective calcium oxide content of more than 70% and a fineness of less than 10mm; Aluminum powder with a purity of more than 90% and a fineness of less than 45μm; Clean fresh water with a pH value between 6 and 8. S702. Raw material measurement: Weigh out 10-15 parts of cement, 60-70 parts of fly ash, 15-20 parts of quicklime, 0.5-1 parts of aluminum powder, and 50-60 parts of water by weight. S703. Raw material mixing: First, pour cement, fly ash and quicklime into the mixer and dry mix for 1 to 2 minutes. Then add aluminum powder and continue to dry mix for 1 to 2 minutes to make the aluminum powder evenly distributed in the cement, fly ash and quicklime. S704. Concrete mixing: Add water to the mixed dry materials and start mixing. The mixing time should be controlled at 3 to 5 minutes.

6. The method for preparing lightweight concrete microwave absorbing material based on carbon-based magnetic materials as described in claim 1, characterized in that: When adding carbon-based magnetic material in step S3, the carbon-based magnetic material is added in batches according to the size of the upper surface area of ​​the aerated concrete in the mixer, so that the carbon-based magnetic material added each time is loosely covered on the surface of the aerated concrete, with a single layer thickness of less than 5mm, ensuring uniform thickness and no accumulation. After each addition of carbon-based magnetic material, continue stirring for 2 to 3 minutes.

7. The method for preparing lightweight concrete microwave absorbing material based on carbon-based magnetic materials as described in claim 1, characterized in that: In S5, when the concrete is allowed to stand and foam, the ambient temperature is controlled between 20 and 30°C, and the relative humidity is controlled between 60% and 80%.

8. The method for preparing lightweight concrete microwave absorbing material based on carbon-based magnetic materials as described in claim 1, characterized in that: During the electrochemical carbonization process in S7, a high-voltage direct current is used as the power source, with the voltage controlled between 3kV and 5kV, and the duration is less than 0.3s.

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