Electromagnetic interference shielding material based on multi-component regenerated carbon short fiber / silicon carbide matrix and preparation method thereof

Abstract

The invention discloses an electromagnetic interference shielding material based on a multi-component regenerated carbon short fiber / silicon carbide matrix and a preparation method of the electromagnetic interference shielding material. A carbon matrix recovered in a photovoltaic thermal field is used as a raw material, 8-12% of SiC and 2-5% of Si are reserved through selective pickling and compounded with 5-10% of exogenous modified short carbon fibers and 3-8% of nano-graphite flakes, and the material is prepared through gradient hot pressing and 2400 DEG C graphitization. The density is less than or equal to 2.0 g / cm < 3 >, the shielding effectiveness at the frequency band of 8-18GHz is greater than or equal to 110dB, the absorption loss proportion is greater than or equal to 88%, the raw material cost is reduced by 72%, the energy consumption is reduced by 40%, the CO2 emission is reduced by 4.8 tons per ton of material, and an efficient environment-friendly scheme is provided for high-frequency electromagnetic protection.

Description

Technical Field

[0001] The present invention relates to the technical field of electromagnetic shielding functional materials, and in particular to an electromagnetic interference shielding material based on a multi-component regenerated carbon short fiber / silicon carbide matrix and a preparation method thereof. Background Art

[0002] With the rapid development of electronic information technology and the widespread use of various electronic devices and communications devices, electromagnetic radiation is becoming increasingly serious. Electromagnetic interference not only affects the normal operation of electronic devices but also poses potential risks to human health. Therefore, efficient electromagnetic shielding materials have become a hot topic and a key research topic.

[0003] Carbon materials have great potential for application in the field of electromagnetic shielding due to their advantages such as light weight, corrosion resistance, and strong designability, and have attracted widespread attention. However, traditional carbon / carbon composites have significant technical bottlenecks in practical applications. Traditional carbon / carbon composites usually rely on high-purity virgin carbon fibers and resin matrices. Although they can achieve a certain range of electrical conductivity (1.0×10 4 -1.0×10 5 S / m), but at high-frequency electromagnetic fields (>6 GHz), the shielding effectiveness (SE) decreases dramatically due to insufficient dielectric loss. Research has shown that the SE value of pure carbon-based materials is typically less than 60 dB at 10 GHz. This is because a single carbon phase struggles to form a multi-scale electromagnetic wave dissipation mechanism, and defects at the fiber-matrix interface easily cause phase mismatch in electromagnetic wave reflection.

[0004] At the same time, the rapid development of the photovoltaic industry has brought about a large number of problems in the recycling of retired thermal field carbon / carbon composite materials. There are serious technical misunderstandings in the current recycling process. In order to pursue the purity of the carbon phase, high-temperature incineration (>1500°C) is usually used to remove the inherent silicon carbide (SiC) and silicon (Si) components in the material. This method will not only cause damage to the short carbon fiber structure and cause the conductivity loss to exceed 50%, but also produce a large amount of CO2 and silicon oxide dust during the incineration process, which seriously violates the concept of green manufacturing. More importantly, the removed SiC (dielectric constant ε'=9.5-10.5@1GHz) and Si (carrier mobility ≥1400cm 2 / V·s) is precisely the potential functional phase that enhances dielectric loss and interface polarization. Removing these components will cause the electromagnetic shielding performance of the recycled material to further deteriorate compared with the original material, forming a technical dilemma of "recycling means degradation".

[0005] At present, in the research on high-frequency electromagnetic shielding materials, some technologies attempt to improve the shielding effectiveness by adding metal particles, etc., but this often increases the weight of the material and sacrifices the lightweight advantage of the material. In addition, the dispersion problem of metal particles in composite materials is difficult to solve, which easily leads to uneven material performance. Some studies focus on the modification of single carbon materials. Although the dielectric properties have been improved to a certain extent, they still cannot break through the bottleneck of high-frequency shielding effectiveness and it is difficult to achieve efficient multi-scale electromagnetic wave dissipation. Summary of the Invention

[0006] In response to the above technical problems, the present application solves the problem that existing shielding materials cannot take into account high-frequency SE, lightweight and low cost, and the functional components in waste carbon / carbon materials are not effectively utilized.

[0007] In order to achieve the above-mentioned purpose, the technical solution adopted in this application is: an electromagnetic interference shielding material based on a multi-component regenerated carbon short fiber / silicon carbide matrix, comprising the following components:

[0008] After pickling, the photovoltaic thermal field recovers the carbon matrix.

[0009] After pickling, the SiC content in the photovoltaic thermal field recovered carbon matrix is 8-12% and the Si content is 2-5%;

[0010] Exogenously modified short carbon fibers 5-10%;

[0011] 3-8% graphite nanosheets;

[0012] Phenolic resin binder 4-6%;

[0013] After graphitization treatment at 2400℃, the material conductivity is ≥1.3×10 5 S / m, shielding effectiveness ≥110dB in the 8-18GHz frequency band.

[0014] In order to better realize the present invention, further, the surface of the SiC particles in the recycled carbon matrix is coated with a cracked carbon layer to form a C / SiC / C sandwich structure with a thickness of 100-300 nm.

[0015] In order to better implement the present invention, further, a Schottky barrier is formed at the interface between the silicon particles and the graphitized carbon, and the barrier height is ≥0.35 eV.

[0016] In order to better implement the present invention, further, the short carbon fibers are oriented and distributed in the XY plane, with an orientation degree of ≥80% and a porosity of ≤0.5%.

[0017] A method for preparing the aforementioned electromagnetic interference shielding material includes selective pickling, gradient hot pressing and high-temperature graphitization processes.

[0018] In order to better realize the present invention, further, the selective pickling purification is specifically as follows:

[0019] The recycled material crushed to 0.5-2mm is immersed in a mixture of hydrofluoric acid (5wt%) and oxalic acid (3wt%).

[0020] Ultrasonic treatment was performed at 60°C for 45 minutes to control the SiC retention rate to 60-70%.

[0021] The SiC surface oxide layer is partially dissolved, and the Si purity is ≥99%.

[0022] In order to better implement the present invention, further, the gradient hot pressing molding includes:

[0023] In the first stage, pre-curing was performed at 200°C and 10 MPa for 30 min;

[0024] In the second stage, the temperature was raised to 800 °C and the pressure was increased to 30 MPa for densification treatment for 60 min;

[0025] In the third stage, the product is cooled to 200℃ under nitrogen protection and demoulded. The density of the green body is ≥1.9g / cm 3 .

[0026] In order to better realize the present invention, further, the high temperature graphitization is carried out in an argon environment, heating the temperature to 2400°C at a heating rate of 20°C / min and keeping the temperature for 1 hour, thereby obtaining a conductivity of ≥1.3×10 5 The final product of S / m.

[0027] In order to better realize the present invention, further, the exogenously modified short carbon fibers are oxidized with nitric acid and treated with a silane coupling agent;

[0028] The thickness of the nanographite sheet is 10-50 nm.

[0029] The electromagnetic interference shielding material based on multi-component recycled carbon short fibers / silicon carbide matrix provided by this application has a significant innovative composition design. The SiC content in the photovoltaic thermal field recovered carbon matrix after pickling is precisely controlled at 8-12%, and the Si content is controlled at 2-5%. This ratio is not a simple choice, but is obtained after a large number of experiments and theoretical analysis. The retention of SiC and Si not only makes full use of the functional components in the waste materials, but more importantly, they form a synergistic composite system with exogenous modified short carbon fibers (5-10%), nanographite sheets (3-8%) and phenolic resin binder (4-6%).

[0030] Exogenously modified short carbon fibers undergo nitric acid oxidation and silane coupling agent treatment. Nitric acid oxidation increases the number of active groups on the fiber surface, enhancing the interfacial bonding between the fiber and the matrix. Silane coupling agent treatment further optimizes the chemical compatibility between the fiber and the matrix, allowing the fibers to better enhance their reinforcing properties within the composite material. The nanographene flakes, with a thickness of 10-50nm, form a continuous conductive network within the composite material, interweaving with the short carbon fibers to enhance the material's electrical conductivity. Furthermore, the large surface area of the nanographene flakes provides more areas for electromagnetic wave absorption.

[0031] The surface of the SiC particles in the recycled carbon matrix is coated with a cracked carbon layer, forming a C / SiC / C sandwich structure with a thickness of 100-300nm. This unique structural design, not previously reported in the prior art, not only strengthens the bonding between the SiC particles and the carbon matrix but also has a unique impact on the propagation of electromagnetic waves. Under high-frequency electromagnetic fields, the interfaces between the different materials in the sandwich structure produce an interfacial polarization effect, effectively dissipating electromagnetic wave energy and enhancing the dielectric loss of the material.

[0032] A Schottky barrier is formed at the interface between silicon particles and graphitized carbon, with a barrier height of ≥0.35eV. The formation of the Schottky barrier is another key innovation of this material. It can regulate the transmission behavior of electrons at the interface, allowing the material to produce a unique electrical response under high-frequency electromagnetic fields, further enhancing the absorption loss of electromagnetic waves. The short carbon fibers are oriented in the XY plane, with an orientation degree of ≥80% and a porosity of ≤0.5%. This highly oriented fiber distribution and extremely low porosity design give the material excellent electrical conductivity and mechanical properties in the planar direction, while reducing the reflection loss of electromagnetic waves within the material and improving absorption efficiency.

[0033] The preparation method includes selective pickling, gradient hot pressing and high-temperature graphitization process, and each process step contains innovative thinking. The selective pickling purification is specifically to immerse the recycled material crushed to 0.5-2mm in a mixture of hydrofluoric acid (5wt%) and oxalic acid (3wt%), and ultrasonically treat it at 60°C for 45 minutes, control the SiC retention rate to 60-70%, partially dissolve the SiC surface oxide layer, and the Si purity is ≥99%. This pickling method is different from the traditional single acid treatment method. Hydrofluoric acid can effectively remove the oxide layer on the SiC surface, and oxalic acid has a good complexing effect on metal impurities. The synergistic effect of the two realizes the precise purification of the recycled material, while retaining SiC and Si, improving the purity of the raw material. The introduction of ultrasonic treatment further enhances the pickling effect, promotes full contact between the acid solution and the recycled material through ultrasonic vibration, and improves the pickling efficiency and uniformity.

[0034] The gradient hot pressing process is divided into three stages. The first stage is pre-curing at 200°C and 10 MPa for 30 minutes. This stage allows the phenolic resin to initially solidify, laying the foundation for subsequent molding and also facilitates the initial uniform distribution of the components at a lower temperature. The second stage is densification treatment by increasing the temperature to 800°C and the pressure to 30 MPa for 60 minutes. In this stage, high temperature and high pressure promote the close integration of the internal structure of the material, reduce porosity, and increase material density. At the same time, physical and chemical reactions occur between the components, further enhancing the performance of the material. The third stage is cooling to 200°C under nitrogen protection for demolding. Nitrogen protection prevents oxidation of the material during the cooling process. The resulting green body density is ≥1.9g / cm 3 Compared with the traditional single temperature and pressure forming method, this gradient hot pressing process can better control the microstructure and properties of the material, allowing the material to achieve different changes at different stages, ultimately achieving the ideal densification effect and performance.

[0035] High temperature graphitization is carried out in an argon environment by heating the sample to 2400℃ at a heating rate of 20℃ / min and keeping the temperature for 1h to obtain a conductivity of ≥1.3×10 5 The final product is S / m. Precisely controlled heating rates and high-temperature holding times fully graphitize the carbon structure within the material, forming a highly ordered graphite crystal structure, significantly improving the material's electrical conductivity and electromagnetic shielding properties. Argon protection provides an inert environment for the graphitization process, preventing the material from reacting with oxygen in the air at high temperatures and ensuring the stability of its properties.

[0036] The technical solution provided by the present invention has the following beneficial effects compared with the prior art:

[0037] 1. The electromagnetic interference shielding material prepared in this invention achieves a shielding effectiveness (SE) of 110-125dB in the 8-18GHz frequency band, with absorption loss accounting for ≥88%. This is due to the synergistic effect of the dielectric loss of SiC in the material and the polarization effect of the Si / carbon heterojunction, which effectively enhances the absorption loss of electromagnetic waves and forms a multi-scale electromagnetic wave dissipation mechanism, overcoming the insufficient shielding effectiveness of traditional carbon-based materials in high-frequency bands.

[0038] 2. The material density of the present invention is ≤2.0g / cm 3 Compared with metal-based materials with equivalent shielding effectiveness, the weight can be reduced by up to 50%. The lightweight feature gives it significant application advantages in fields such as aerospace and electronic equipment where weight requirements are strict.

[0039] 3. This invention reduces raw material costs by 72% because the recycled matrix accounts for ≥65% of the material, making full use of discarded photovoltaic thermal field carbon / carbon composite materials; energy consumption is reduced by 40%, with the pickling process energy consumption being only 15kWh / ton; and CO emissions are reduced by 4.8 tons / ton of material, conforming to the concept of green manufacturing and achieving the goals of efficient resource utilization and environmental friendliness.

[0040] 4. The electromagnetic interference shielding material prepared by the present invention has a shielding effectiveness (SE) of 110-125dB in the 8-18GHz frequency band, and the absorption loss accounts for ≥88%. Compared with the SE value of pure carbon-based materials in the prior art, which is usually less than 60dB at 10GHz, this has achieved a qualitative leap. This excellent performance is due to the synergistic effect of various innovative designs in the material. The dielectric loss of SiC works synergistically with the polarization effect of the Si / carbon heterojunction, effectively enhancing the absorption loss of electromagnetic waves and forming a multi-scale electromagnetic wave dissipation mechanism.

[0041] 5. In high-frequency electromagnetic fields, the dielectric loss properties of SiC particles enable them to convert electromagnetic wave energy into heat, thereby dissipating it. The polarization effect at the Si / carbon heterojunction generates polarization currents, further absorbing electromagnetic wave energy. Furthermore, the C / SiC / C sandwich structure and Schottky barrier also play a positive role in the propagation and absorption of electromagnetic waves. The interfacial polarization and Schottky barrier in the sandwich structure regulate electron transmission, enabling the material to more effectively absorb and dissipate electromagnetic waves at high frequencies. This overcomes the insufficient shielding effectiveness of traditional carbon-based materials at high frequencies and provides a novel solution for high-frequency electromagnetic protection.

[0042] 6.Material density ≤2.0g / cm 3 Compared with metal-based materials with equivalent shielding effectiveness, the weight reduction can reach 50%. In the aerospace field, every bit of weight reduction in equipment can bring significant economic benefits and performance improvements, such as reduced fuel consumption and increased payload. In the field of electronic equipment, lightweight electromagnetic shielding materials can make equipment thinner and more portable, improving the user experience. This lightweight property makes the material of the present invention have irreplaceable application advantages in fields with strict weight requirements, filling the gap in the lightweighting of existing high-frequency electromagnetic shielding materials.

[0043] 7. Raw material costs were reduced by 72%. This is due to the fact that recycled matrix accounts for ≥65% of the material, fully utilizing discarded photovoltaic thermal field carbon / carbon composite materials, converting waste into high-value electromagnetic shielding materials and achieving resource recycling. Energy consumption was reduced by 40%, with the pickling process consuming only 15kWh / ton, significantly reducing energy consumption compared to traditional high-temperature incineration regeneration processes. CO2 emissions were reduced by 4.8 tons per ton of material, in line with green manufacturing concepts and effectively reducing environmental pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without paying any creative labor.

[0045] Figure 1 The figure is a flow chart of the process for preparing the material of the present invention. DETAILED DESCRIPTION

[0046] To make the objectives, technical solutions, and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Generally, the components of the embodiments of the present application described and shown in the drawings herein can be arranged and designed in various different configurations.

[0047] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the present application for protection, but merely represents selected embodiments of the present application. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments in the present application without making any creative efforts shall fall within the scope of protection of the present application.

[0048] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings.

[0049] In the description of this application, it should be noted that if the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. appear, the orientation or position relationship indicated is based on the orientation or position relationship shown in the accompanying drawings, or the orientation or position relationship in which the product of the application is usually placed when in use. It is only for the convenience of describing this application and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, it cannot be understood as a limitation on this application. In addition, if the terms "first", "second", etc. appear in the description of this application, they are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0050] Furthermore, the use of terms such as "horizontal" and "vertical" in the description of this application does not necessarily imply that a component must be absolutely horizontal or suspended, but rather that it can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical" and does not mean that the structure must be completely horizontal, but rather that it can be slightly tilted.

[0051] It should also be noted that, unless otherwise expressly specified or limited, the terms "disposed," "installed," "connected," and "connected" should be understood broadly. For example, they may refer to fixed connections, detachable connections, or integral connections; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and internal connections between two components. A person of ordinary skill in the art will understand the specific meanings of the above terms in this application based on the specific circumstances.

[0052] The electromagnetic interference shielding material provided by the present invention has the following composition and process characteristics:

[0053] Raw material composition (mass percentage)

[0054] The recycled carbon matrix comprises 20-28% short carbon fibers, 50-58% cracked carbon, 8-12% SiC, and 2-5% Si, and is obtained by selective pickling to retain the corresponding components; 5-10% exogenously modified short carbon fibers, which are oxidized by nitric acid and treated with a silane coupling agent; 3-8% nanographite sheets, with a thickness of 10-50 nm; and 4-6% phenolic resin binder.

[0055] Preparation method:

[0056] Selective acid wash purification: The recycled material, crushed to 0.5-2 mm, is immersed in a mixture of hydrofluoric acid (5wt%) and oxalic acid (3wt%) and ultrasonically treated at 60°C for 45 minutes. This treatment controls the SiC retention rate to 60-70%, partially dissolves the SiC surface oxide layer, and ensures Si purity ≥99%.

[0057] Multiphase compounding and molding:

[0058] Mixing: The acid-washed matrix, exogenous fibers and nanographite sheets were three-dimensionally mixed under argon protection for 120 minutes to ensure uniform mixing of the components.

[0059] Gradient hot pressing: In the first stage, pre-curing is carried out at 200°C and 10MPa for 30 minutes to initially solidify the phenolic resin and lay the foundation for subsequent molding. In the second stage, the temperature is raised to 800°C and the pressure is increased to 30MPa for densification treatment for 60 minutes to promote the close bonding of the internal structure of the material and increase the material density. In the third stage, the mold is demoulded after cooling to 200°C under nitrogen protection. The density of the obtained green body is ≥1.9g / cm 3 .

[0060] High temperature graphitization: In an argon environment, the temperature was raised to 2400℃ at a heating rate of 20℃ / min and kept at this temperature for 1h to further graphitize the internal structure of the material and obtain a conductivity of ≥1.3×10 5 The final product of S / m.

[0061] The prepared electromagnetic interference shielding material achieves a shielding effectiveness (SE) of 110-125dB in the 8-18GHz frequency band, with absorption loss accounting for ≥88%. This is due to the synergistic effect of the dielectric loss of SiC in the material and the polarization effect of the Si / carbon heterojunction, which effectively enhances the absorption loss of electromagnetic waves and forms a multi-scale electromagnetic wave dissipation mechanism, overcoming the problem of insufficient shielding effectiveness of traditional carbon-based materials in high-frequency bands.

[0062] Material density ≤2.0g / cm 3 Compared with metal-based materials with equivalent shielding effectiveness, the weight can be reduced by up to 50%. The lightweight feature gives it significant application advantages in fields such as aerospace and electronic equipment where weight requirements are strict.

[0063] Raw material costs were reduced by 72% because the recycled matrix accounts for ≥65% of the material, making full use of discarded photovoltaic thermal field carbon / carbon composite materials; energy consumption was reduced by 40%, with the pickling process consuming only 15kWh / ton; CO emissions were reduced by 4.8 tons / ton of material, in line with the green manufacturing concept and achieving the goals of efficient resource utilization and environmental friendliness.

[0064] like Figure 1 As shown, the following examples are given for analysis:

[0065] Example 1: Material preparation and performance testing

[0066] 1. Raw material processing:

[0067] Crushing: A jaw crusher is used to perform primary crushing on the photovoltaic thermal field recovered carbon / carbon composite material to obtain granular materials with a particle size of 0.5-2mm;

[0068] Acid cleaning and activation: Place the crushed material in a hydrofluoric acid-oxalic acid mixed cleaning solution (hydrofluoric acid concentration 5wt%, oxalic acid concentration 3wt%) and use ultrasonic cleaning equipment to treat it at 60±2℃ for 45±5min to selectively remove the surface silicon oxide layer and retain the internal silicon carbide structure. The silicon carbide retention rate is controlled at 60-70%;

[0069] Cleaning and drying: After acid washing, the material is rinsed with three-stage countercurrent deionized water to a pH value of 6.5-7.5, and then dried in a vacuum drying oven at 120°C ± 5°C for 4 hours to obtain a pretreated carbon matrix material with a silicon particle purity of ≥99%.

[0070] Exogenous short carbon fibers (grade T700) were oxidized with concentrated nitric acid.

[0071] 2. Compounding and molding:

[0072] Raw material ratio: recycled matrix 68% + exogenous fiber 8% + nanographite flakes 8% + phenolic resin 6%;

[0073] Gradient hot pressing parameters: 200℃ / 10MPa→800℃ / 30MPa;

[0074] Graphitization temperature: 2400℃ / 1h.

[0075] 3. Performance data:

[0076] Frequency (GHz) SE(dB) <![CDATA[Density (g / cm 3 )]]> Conductivity (S / m) 2.4 102 1.98 <![CDATA[1.25×10 5 ]]> 10 122 1.98 <![CDATA[1.31×10 5 ]]> 18 118 1.97 <![CDATA[1.28×10 5 ]]>

[0077] Example 1: Shielding Effectiveness Calculation

[0078] Test Method

[0079] According to ASTM D4935-18, a coaxial flange fixture and a vector network analyzer (Keysight N5227B) were used to measure the scattering parameters (S11: reflection coefficient, S21: transmission coefficient) of the material in the 1-18 GHz frequency band with a measurement accuracy of ±0.5 dB.

[0080] Calculation formula

[0081] The total shielding effectiveness (SE) is composed of reflection loss (SER) and absorption loss (SEA). The multiple reflection factor (SEM) can be ignored when the material thickness is ≥1.5mm. The calculation formula is simplified to:

[0082]

[0083] in:

[0084] Reflection loss ratio:

[0085]

[0086] Absorption loss ratio:

[0087] A(%)=100-R

[0088] Skin depth calculation

[0089] The material conductivity (σ) is measured by the four-probe method, and the relationship between skin depth (δ) and frequency (f) is:

[0090] (μ is the magnetic permeability, which is taken as the vacuum value 4π×10 -7 H / m)

[0091] Measured σ = 1.3 × 10 5 When S / m, δ=0.92μm at 10GHz.

[0092] Example 2: Dielectric Loss Calculation

[0093] Test Method

[0094] The complex dielectric constant (ε' is the real part and ε" is the imaginary part) is measured using the resonant cavity method (ASTM D5568).

[0095] Calculate the dielectric loss tangent:

[0096]

[0097] Separation of SiC contribution

[0098] By comparing the material data before and after pickling:

[0099] When SiC is not retained: ε' = 18.2, tanδ = 0.09 (@10GHz);

[0100] When retaining 10% SiC: ε' = 26.5, tanδ = 0.17 (@10GHz);

[0101] It shows that SiC increases dielectric loss by 88.9%.

[0102] Data processing

[0103] All data were measured 5 times to eliminate outliers according to the 3σ criterion, and the uncertainty was ≤±3%.

[0104] Currently, existing research on electromagnetic shielding materials focuses on either modifying a single material, failing to achieve high-frequency shielding efficiency, or using methods such as adding metal particles, sacrificing the material's lightweight advantages. This invention aims to address the problems of existing shielding materials failing to achieve high-frequency SE, lightweightness, and low cost, as well as the ineffective utilization of functional components in waste carbon / carbon materials.

[0105] Retention of SiC and Si is achieved through a selective pickling process, which enhances dielectric loss and interfacial polarization, thereby achieving efficient electromagnetic shielding. The C / SiC / C sandwich structure and Schottky barrier, both not seen in existing technologies, enhance the material's electromagnetic wave absorption losses through interfacial polarization and regulation of electron transport behavior, respectively. The preparation method utilizes a hydrofluoric acid-oxalic acid mixture in the selective pickling process, introduces ultrasonic treatment, employs a three-stage gradient hot pressing process, and precisely controls high-temperature graphitization, ultimately resulting in a material with ideal performance.

[0106] The synergistic effect between the C / SiC / C sandwich structure, Schottky barrier and other material components together form a multi-scale electromagnetic wave dissipation mechanism, achieving efficient electromagnetic shielding in the high-frequency band; the combination of gradient hot pressing and high-temperature graphitization processes enables the material to form an ideal microstructure and performance. These synergistic effects and overall performance advantages are the important distinguishing features of the present invention.

[0107] The technical problem actually solved by the present invention is to develop an electromagnetic shielding material that can take into account high-frequency shielding effectiveness, light weight and low cost, while effectively utilizing functional components in waste carbon / carbon materials.

[0108] In the field of high-frequency electromagnetic shielding, pure carbon-based materials in the existing technology have insufficient shielding effectiveness in high-frequency bands. However, the present invention, through a unique material composition design and preparation method, has achieved a shielding effectiveness (SE) of 110-125dB in the 8-18GHz frequency band, with an absorption loss ratio of ≥88%, far exceeding the existing technical level and producing a "quantity" change that exceeds people's expectations. At the same time, while achieving efficient shielding, it also takes into account lightweight (density ≤2.0g / cm 3 , weight reduction can reach 50%) and green manufacturing (raw material costs reduced by 72%, energy consumption reduced by 40%, CO2 emissions reduced by 4.8 tons / ton of material), achieving a "qualitative" change in technical effects.

[0109] The above description is merely a preferred embodiment of the present application and is not intended to limit the present application. Various modifications and variations are possible for those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. An electromagnetic interference shielding material based on a multi-component regenerated carbon short fiber / silicon carbide matrix, characterized by: Contains the following components: After pickling, the photovoltaic thermal field recovers the carbon matrix. After pickling, the SiC content in the photovoltaic thermal field recovered carbon matrix is 8-12% and the Si content is 2-5%; Exogenously modified short carbon fibers 5-10%; 3-8% graphite nanosheets; Phenolic resin binder 4-6%; After graphitization treatment at 2400℃, the material conductivity is ≥1.3×10 5 S / m, shielding effectiveness ≥110dB in the 8-18GHz frequency band.

2. The electromagnetic interference shielding material based on a multi-component regenerated carbon short fiber / silicon carbide matrix according to claim 1, characterized in that: The surfaces of the SiC particles in the recycled carbon matrix are coated with a cracked carbon layer to form a C / SiC / C sandwich structure with a thickness of 100-300 nm.

3. The electromagnetic interference shielding material based on a multi-component regenerated carbon short fiber / silicon carbide matrix according to claim 1, characterized in that: A Schottky barrier is formed at the interface between silicon particles and graphitized carbon, and the barrier height is ≥0.35eV.

4. The electromagnetic interference shielding material based on a multi-component regenerated carbon short fiber / silicon carbide matrix according to claim 1, characterized in that: The short carbon fibers are oriented and distributed in the XY plane, with an orientation degree of ≥80% and a porosity of ≤0.5%.

5. A method for preparing the electromagnetic interference shielding material according to any one of claims 1 to 4, characterized in that: Including selective pickling, gradient hot pressing and high-temperature graphitization processes.

6. The preparation method according to claim 5, characterized in that: The selective pickling purification is specifically as follows: The recycled material crushed to 0.5-2mm is immersed in a mixture of hydrofluoric acid (5wt%) and oxalic acid (3wt%). Ultrasonic treatment was performed at 60°C for 45 minutes to control the SiC retention rate to 60-70%. The SiC surface oxide layer is partially dissolved, and the Si purity is ≥99%.

7. The preparation method according to claim 5, characterized in that: The gradient hot pressing molding comprises: In the first stage, pre-curing was performed at 200°C and 10 MPa for 30 min; In the second stage, the temperature was raised to 800 °C and the pressure was increased to 30 MPa for densification treatment for 60 min; In the third stage, the product is cooled to 200℃ under nitrogen protection and demoulded. The density of the green body is ≥1.9g / cm 3 .

8. The preparation method according to claim 5, characterized in that: The high temperature graphitization is carried out in an argon environment, heating the temperature to 2400°C at a heating rate of 20°C / min and keeping the temperature for 1 hour, thereby obtaining a conductivity of ≥1.3×10 5 The final product of S / m.

9. The electromagnetic interference shielding material according to any one of claims 1 to 4, characterized in that: The exogenously modified short carbon fibers are oxidized with nitric acid and treated with a silane coupling agent; The thickness of the nanographite sheet is 10-50 nm.

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