Preparation method of magnetic super composite material with weak negative dielectric constant
By constructing a nickel-nickel ferrite percolation system, the problem of the difficulty in synergizing the dielectric and magnetic properties of supercomposite materials was solved, achieving stable weak negative dielectric properties and high saturation magnetization in the 100MHz-1GHz frequency band, which is suitable for high-end equipment such as electromagnetic shielding and new sensors.
Patent Information
- Application Number
- CN202511390768.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-26
- Publication Date
- 2026-01-06
AI Technical Summary
Existing metacomposites suffer from limited performance control, difficulty in synergizing dielectric and magnetic properties, contradictions between preparation processes and performance stability, and a disconnect between precursor preparation and composite processes, resulting in large performance fluctuations and making it difficult to meet the precision requirements of high-end equipment.
Using metallic nickel as the conductive functional phase and bismuth ferrite as the magnetic matrix phase, a nickel-nickel ferrite percolation system is constructed through wet ball milling, billet pressing, high-temperature sintering, and external magnetic field treatment. This achieves synergistic regulation of dielectric and magnetic properties, avoids functional phase agglomeration and oxidation, and ensures stable material performance.
Achieving weak negative dielectric properties with a real absolute value of less than 1000 and a saturation magnetization greater than 27 emu/g in the 100MHz-1GHz frequency band solves the problem of the difficulty in achieving both dielectric and magnetic properties, improves the stability and applicability of the material, and is suitable for high-end equipment in the fields of electromagnetic shielding and new sensors.
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Figure CN121281986A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of electromagnetic metamaterials preparation technology, specifically to a method for preparing a magnetic metacomposite material with a weak negative permittivity. Background Technology
[0002] Electromagnetic metamaterials, as artificial composite materials with unique electromagnetic properties, have shown great application potential in electromagnetic shielding, novel sensors, and high-end communication equipment due to their extraordinary parameters such as negative permittivity and negative permeability. Among them, metamaterials based on percolation configurations have become a research hotspot in recent years because they do not require complex periodic artificial structures and can achieve negative electromagnetic parameter control in the Hz-GHz frequency band. Currently, there are two major bottlenecks in the research and application of metamaterials: one is the singularity of performance control, with most schemes relying on only a single functional phase to achieve negative permittivity or negative magnetic properties, resulting in the difficulty of synergistic effects between dielectric and magnetic properties, such as pure metal matrix metacomposites. While the material can achieve a negative dielectric constant, it lacks magnetism; although the magnetic particle composite system possesses magnetic properties, due to insufficient conductive network construction, the negative dielectric constant is too high and the loss is severe, failing to meet the integrated requirement of "weak negative dielectric + excellent magnetic properties"; secondly, there is a contradiction between the preparation process and performance stability. In the preparation of traditional metacomposites, the mixing of functional phase and matrix phase is prone to agglomeration, resulting in uneven percolation structure. During high-temperature sintering, the metal functional phase is easily oxidized, destroying the conductive network; and there is a lack of targeted magnetic property optimization steps, resulting in large fluctuations in the performance of the final product, making it difficult to stably adapt to the precision requirements of high-end equipment such as electromagnetic shielding and sensors.
[0003] Furthermore, the preparation of precursors for existing supercomposite materials is disconnected from the composite process. For example, the magnetic matrix phase needs to be prepared separately and then mixed with the conductive phase. The process is cumbersome and prone to introducing impurities, which further limits the synergy of performance and large-scale production. Therefore, developing a supercomposite material preparation method that can achieve synergistic control of "weak negative dielectric constant and high magnetic properties", has a stable preparation process, and is adapted to the needs of high-end equipment has become the key to breaking through the current technical bottleneck. Summary of the Invention
[0004] To address the aforementioned technical problems, a method for preparing magnetic supercomposite materials with weak negative permittivity is provided. This technical solution solves the problems described above.
[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:
[0006] A method for preparing a magnetic supercomposite material with a weak negative permittivity, the method comprising:
[0007] S1. Raw material preparation: Weigh the required nickel powder and bismuth ferrite powder to ensure that the nickel powder is free of oxide agglomeration and the bismuth ferrite powder has uniform particle size.
[0008] S2. Wet ball milling: Pour the nickel powder and bismuth ferrite powder into the ball mill jar, add anhydrous ethanol as the ball milling medium, and start the ball mill to mix so that the two powders are microscopically and uniformly dispersed.
[0009] S3. Drying the wet material: The wet material after ball milling is placed in a drying device to remove anhydrous ethanol and obtain a dry mixture.
[0010] S4. Green body pressing: The dried mixture is placed into a mold, a set pressure is applied and held for a set time to press it into a dense green body.
[0011] S5. High-temperature sintering: The billet is placed in a high-temperature sintering furnace under an argon protective atmosphere, heated to the set temperature and held at that temperature to promote the redox reaction between bismuth ferrite and metallic nickel to generate nickel ferrite, forming a nickel-ferrite composite structure.
[0012] S6. Magnetic field treatment: The sintered composite material is placed in an external magnetic field for magnetization to optimize the magnetic domain orientation and finally obtain a magnetic supercomposite material with a weak negative permittivity.
[0013] Preferably, the supercomposite material uses metallic nickel as the conductive functional phase and nickel ferrite as the magnetic matrix phase. The raw materials include 10-50 wt% metallic nickel powder and 50-90 wt% bismuth ferrite powder. The preparation process combines wet ball milling, blank pressing, high-temperature sintering and magnetic field treatment to finally obtain a magnetic supercomposite material with a weak negative permittivity and a saturation magnetization greater than 27 emu / g in the 100MHz-1GHz frequency band.
[0014] Preferably, the raw materials of the supercomposite material are weighed in the optimal proportion, specifically including: 50wt% nickel powder and 50wt% bismuth ferrite powder, wherein the nickel powder is distributed in a chain and has a rough micro-surface structure, and the bismuth ferrite powder is a 200-mesh powder obtained by solid-state reaction sintering of iron oxide and bismuth oxide, which ensures that bismuth ferrite and nickel fully undergo redox reaction during high-temperature sintering, and at the same time ensures the synergy between the percolation structure and electromagnetic properties of the composite material.
[0015] Preferably, the nickel powder serves as a conductive functional phase, constructing a three-dimensional conductive network to provide carrier transport channels for the weak negative dielectric properties. The bismuth ferrite powder serves as a precursor, undergoing a redox reaction with the nickel powder during high-temperature sintering to generate a nickel ferrite magnetic matrix phase in situ, endowing the composite material with excellent magnetic properties. Together, they construct a percolation system, achieving synergistic regulation of dielectric and magnetic properties, avoiding the performance imbalance caused by traditional metacomposites relying solely on a single functional phase.
[0016] Preferably, the specific steps of S2 include:
[0017] Weigh out the nickel powder and bismuth ferrite powder and pour them into the ball mill jar of the planetary ball mill in proportion. Add anhydrous ethanol until the powder is completely submerged and control the ball-to-powder ratio to be 10:1.
[0018] Start the planetary ball mill and continue milling at the set speed for 6 hours. During the milling process, check the mixing status regularly through the equipment observation window to avoid powder agglomeration and leakage of the ball mill jar.
[0019] After ball milling, remove the ball mill jar and transfer the solid-liquid mixture inside the jar to a container, ensuring that no powder residue remains;
[0020] The wet ball milling process achieves microscopic uniform dispersion of nickel powder and bismuth ferrite powder through the synergistic effect of mechanical force and liquid medium, laying the foundation for the subsequent formation of a uniform percolation structure.
[0021] Preferably, the specific steps of S3 include:
[0022] Transfer the ball-milled wet material to a vacuum drying oven, set the drying temperature and vacuum level to avoid oxidation of the nickel powder due to high temperature;
[0023] During the drying process, the wet material is turned over every 2 hours to ensure that the moisture in the upper and lower layers evaporates evenly; the moisture content of the material is monitored in real time using a moisture analyzer, and drying is stopped when the moisture content is below 0.5%, and the dried mixture is taken out.
[0024] The dried mixture should be pressed into blanks immediately to avoid prolonged exposure to moisture in the air, which would affect the quality of the blank forming.
[0025] Preferably, the specific steps of S4 include:
[0026] Select a cylindrical mold with a diameter of 20mm, fill the dried mixture evenly into the mold cavity, and gently compact it to remove air from the cavity;
[0027] Place the mold on a hydraulic tablet press, apply a set pressure of 5MPa-20MPa, and maintain it for a set time of 30min-60min. Monitor the pressure stability in real time during the pressing process to avoid pressure fluctuations that could lead to uneven density of the preform.
[0028] After pressing, slowly demold and remove the blank, check the appearance of the blank to ensure that there are no defects such as cracks, missing corners and uneven density;
[0029] If the green body has defects, the pressing pressure and time need to be adjusted and the pressing process repeated to ensure that the quality of the green body meets the requirements of subsequent high-temperature sintering.
[0030] Preferably, the specific steps of S5 include:
[0031] Place the qualified billets into the sample rack of the high-temperature sintering furnace, ensuring that there are gaps between the billets to facilitate uniform temperature distribution inside the furnace.
[0032] Argon gas is introduced into the sintering furnace to purge the air inside. When the oxygen content in the furnace is below 0.1%, the heating program is started.
[0033] The temperature is raised to the target sintering temperature of 800-1000℃ at a set rate using a programmed heating mode. After reaching the target temperature, it is held for 6 hours to ensure that bismuth ferrite and metallic nickel undergo a full redox reaction and nickel ferrite is generated in situ.
[0034] After the insulation is completed, cool down to room temperature at the set rate to avoid excessive temperature difference that could cause stress cracks inside the composite material.
[0035] Argon gas needs to be continuously introduced throughout the sintering process to ensure an inert atmosphere inside the furnace and prevent oxidation of metallic nickel and deterioration of the nickel ferrite matrix.
[0036] Preferably, the specific steps of S6 are as follows:
[0037] After sintering, the composite material is removed from the sintering furnace, cooled to room temperature, and then transferred to an external magnetic field environment.
[0038] Adjust the strength of the external magnetic field and let the composite material stand in the magnetic field for 15 min to 20 min to ensure that the magnetic domains inside the material are fully oriented.
[0039] During magnetic field treatment, the state of the composite material should be observed regularly to avoid external vibrations affecting the uniformity of magnetic domain orientation.
[0040] After the magnetic field treatment is completed, the composite material is removed for later use or for performance testing to ensure that its saturation magnetization intensity stably reaches above 27 emu / g.
[0041] Preferably, the performance control of the supercomposite material needs to be achieved through the coordinated use of key parameters, including the content of metallic nickel powder (10-50wt%), the pressing conditions of the preform (5MPa-20MPa pressure, 30min-60min time), the sintering temperature (800-1000℃) and the applied magnetic field strength (5-10Oe).
[0042] Among them, the nickel content determines the conductive network density, the pressing conditions affect the material density, the sintering temperature controls the amount of nickel ferrite generated, and the external magnetic field optimizes the magnetic domain orientation. The four factors work together to ensure that the composite material has stable weak negative dielectric properties in the 100MHz-1GHz frequency band. When applied, the parameters can be adjusted according to specific electromagnetic requirements, making it suitable for high-end equipment manufacturing in the fields of electromagnetic shielding and new sensors.
[0043] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0044] This invention proposes a process using metallic nickel as the conductive functional phase and bismuth ferrite as the precursor. Through wet ball milling, compaction, high-temperature sintering under argon protection, and external magnetic field treatment, a percolation system of nickel and nickel ferrite is constructed to achieve the control of the percolation structure and carrier transport behavior of the composite material. Finally, a magnetic supercomposite material with a weakly negative dielectric constant (real part absolute value less than 1000) and a saturation magnetization greater than 27 emu / g is obtained in the 100MHz-1GHz frequency band. Attached Figure Description
[0045] Figure 1 This is a flowchart illustrating the steps of the present invention. Detailed Implementation
[0046] The following description is intended to disclose the invention and enable those skilled in the art to implement it. The preferred embodiments described below are merely examples, and other obvious variations will occur to those skilled in the art.
[0047] Reference Figure 1 As shown, a method for preparing a magnetic supercomposite material with a weak negative permittivity includes:
[0048] S1. Raw material preparation: Weigh the required nickel powder and bismuth ferrite powder to ensure that the nickel powder is free of oxide agglomeration and the bismuth ferrite powder has uniform particle size.
[0049] S2. Wet ball milling: Pour the nickel powder and bismuth ferrite powder into the ball mill jar, add anhydrous ethanol as the ball milling medium, and start the ball mill to mix so that the two powders are microscopically and uniformly dispersed.
[0050] S3. Drying the wet material: The wet material after ball milling is placed in a drying device to remove anhydrous ethanol and obtain a dry mixture.
[0051] S4. Green body pressing: The dried mixture is placed into a mold, a set pressure is applied and held for a set time to press it into a dense green body.
[0052] S5. High-temperature sintering: The billet is placed in a high-temperature sintering furnace under an argon protective atmosphere, heated to the set temperature and held at that temperature to promote the redox reaction between bismuth ferrite and metallic nickel to generate nickel ferrite, forming a nickel-ferrite composite structure.
[0053] S6. Magnetic field treatment: The sintered composite material is placed in an external magnetic field for magnetization to optimize the magnetic domain orientation and finally obtain a magnetic supercomposite material with a weak negative permittivity.
[0054] The supercomposite material uses metallic nickel as the conductive functional phase and nickel ferrite as the magnetic matrix phase. The raw materials include 10-50 wt% metallic nickel powder and 50-90 wt% bismuth ferrite powder. The preparation process combines wet ball milling, green body pressing, high-temperature sintering and magnetic field treatment to finally obtain a magnetic supercomposite material with a weak negative permittivity and a saturation magnetization greater than 27 emu / g in the 100MHz-1GHz frequency band.
[0055] The raw materials of the supercomposite material are weighed in the optimal proportion, specifically including: 50wt% nickel powder and 50wt% bismuth ferrite powder. The nickel powder is distributed in a chain and has a rough micro-surface structure. The bismuth ferrite powder is a 200-mesh powder obtained by solid-state reaction sintering of iron oxide and bismuth oxide. This ensures that bismuth ferrite and nickel fully undergo redox reaction during high-temperature sintering, while also ensuring the synergy between the percolation structure and electromagnetic properties of the composite material.
[0056] The nickel powder serves as a conductive functional phase, constructing a three-dimensional conductive network and providing carrier transport channels for the weak negative dielectric properties. The bismuth ferrite powder serves as a precursor, undergoing a redox reaction with the nickel powder during high-temperature sintering to generate a nickel ferrite magnetic matrix phase in situ, endowing the composite material with excellent magnetic properties. Together, they construct a percolation system, achieving synergistic regulation of dielectric and magnetic properties, avoiding the performance imbalance caused by traditional metacomposites relying solely on a single functional phase.
[0057] The specific steps of S2 include:
[0058] Weigh out the nickel powder and bismuth ferrite powder and pour them into the ball mill jar of the planetary ball mill in proportion. Add anhydrous ethanol until the powder is completely submerged and control the ball-to-powder ratio to be 10:1.
[0059] Start the planetary ball mill and continue milling at the set speed for 6 hours. During the milling process, check the mixing status regularly through the equipment observation window to avoid powder agglomeration and leakage of the ball mill jar.
[0060] After ball milling, remove the ball mill jar and transfer the solid-liquid mixture inside the jar to a container, ensuring that no powder residue remains;
[0061] The wet ball milling process achieves microscopic uniform dispersion of nickel powder and bismuth ferrite powder through the synergistic effect of mechanical force and liquid medium, laying the foundation for the subsequent formation of a uniform percolation structure.
[0062] The specific steps of S3 include:
[0063] Transfer the ball-milled wet material to a vacuum drying oven, set the drying temperature and vacuum level to avoid oxidation of the nickel powder due to high temperature;
[0064] During the drying process, the wet material is turned over every 2 hours to ensure that the moisture in the upper and lower layers evaporates evenly; the moisture content of the material is monitored in real time using a moisture analyzer, and drying is stopped when the moisture content is below 0.5%, and the dried mixture is taken out.
[0065] The dried mixture should be pressed into blanks immediately to avoid prolonged exposure to moisture in the air, which would affect the quality of the blank forming.
[0066] The specific steps of S4 include:
[0067] Select a cylindrical mold with a diameter of 20mm, fill the dried mixture evenly into the mold cavity, and gently compact it to remove air from the cavity;
[0068] Place the mold on a hydraulic tablet press, apply a set pressure of 5MPa-20MPa, and maintain it for a set time of 30min-60min. Monitor the pressure stability in real time during the pressing process to avoid pressure fluctuations that could lead to uneven density of the preform.
[0069] After pressing, slowly demold and remove the blank, check the appearance of the blank to ensure that there are no defects such as cracks, missing corners and uneven density;
[0070] If the green body has defects, the pressing pressure and time need to be adjusted and the pressing process repeated to ensure that the quality of the green body meets the requirements of subsequent high-temperature sintering.
[0071] The specific steps of S5 include:
[0072] Place the qualified billets into the sample rack of the high-temperature sintering furnace, ensuring that there are gaps between the billets to facilitate uniform temperature distribution inside the furnace.
[0073] Argon gas is introduced into the sintering furnace to purge the air inside. When the oxygen content in the furnace is below 0.1%, the heating program is started.
[0074] The temperature is raised to the target sintering temperature of 800-1000℃ at a set rate using a programmed heating mode. After reaching the target temperature, it is held for 6 hours to ensure that bismuth ferrite and metallic nickel undergo a full redox reaction and nickel ferrite is generated in situ.
[0075] After the insulation is completed, cool down to room temperature at the set rate to avoid excessive temperature difference that could cause stress cracks inside the composite material.
[0076] Argon gas needs to be continuously introduced throughout the sintering process to ensure an inert atmosphere inside the furnace and prevent oxidation of metallic nickel and deterioration of the nickel ferrite matrix.
[0077] The specific steps of S6 are as follows:
[0078] After sintering, the composite material is removed from the sintering furnace, cooled to room temperature, and then transferred to an external magnetic field environment.
[0079] Adjust the strength of the external magnetic field and let the composite material stand in the magnetic field for 15 min to 20 min to ensure that the magnetic domains inside the material are fully oriented.
[0080] During magnetic field treatment, the state of the composite material should be observed regularly to avoid external vibrations affecting the uniformity of magnetic domain orientation.
[0081] After the magnetic field treatment is completed, the composite material is removed for later use or for performance testing to ensure that its saturation magnetization intensity stably reaches above 27 emu / g.
[0082] The performance control of the supercomposite material needs to be achieved through the coordinated use of key parameters, including the content of metallic nickel powder (10-50wt%), the pressing conditions of the preform (5MPa-20MPa pressure, 30min-60min time), the sintering temperature (800-1000℃) and the applied magnetic field strength (5-10Oe).
[0083] Among them, the nickel content determines the conductive network density, the pressing conditions affect the material density, the sintering temperature controls the amount of nickel ferrite generated, and the external magnetic field optimizes the magnetic domain orientation. The four factors work together to ensure that the composite material has stable weak negative dielectric properties in the 100MHz-1GHz frequency band. When applied, the parameters can be adjusted according to specific electromagnetic requirements, making it suitable for high-end equipment manufacturing in the fields of electromagnetic shielding and new sensors.
[0084] Example 1
[0085] S1. Prepare raw materials, including: 50wt% nickel powder (distributed in a chain, with a particle size of 3-5μm and a rough micro-surface structure) and 50wt% bismuth ferrite powder (200-mesh powder obtained by solid-state reaction and sintering of iron oxide and bismuth oxide).
[0086] S2. Wet ball milling and mixing: Pour the nickel powder and bismuth ferrite powder into the ball mill jar of a planetary ball mill, add anhydrous ethanol until the powder is completely submerged, control the ball-to-powder ratio to be 10:1, start the ball mill and continuously ball mill at 300 rpm for 6 hours to ensure that the two powders are microscopically uniformly dispersed.
[0087] S3. Drying the wet material: Transfer the ball-milled wet material to a vacuum drying oven, set the drying temperature to 70℃ and the vacuum degree to -0.09MPa, turn the wet material over every 2 hours, and monitor the moisture content in real time using a moisture analyzer. Stop drying when the moisture content is below 0.5%, and take out the dried mixture.
[0088] S4. Pressing the blank: Select a cylindrical mold with a diameter of 20mm, fill the cavity with the dried material evenly and remove the air, place it on a hydraulic tablet press, apply a pressure of 20MPa and maintain it for 30min, and slowly demold after pressing. Check that the blank has no cracks and has uniform density.
[0089] S5. High-temperature sintering: Place the qualified green body into the sample rack of the high-temperature sintering furnace (green body spacing 5mm), introduce 99.99% pure argon to remove air (oxygen content <0.1%), heat to 900℃ at a rate of 5℃ / min, hold for 6 hours, and then cool to room temperature at a rate of 3℃ / min. During this period, argon gas is continuously introduced (flow rate 120mL / min) to promote the reaction of bismuth ferrite with metallic nickel to form nickel ferrite.
[0090] S6. Magnetic field treatment: After the sintered composite material is cooled to room temperature, it is transferred to an 8Oe external magnetic field environment and left to stand for 18 minutes to avoid external vibration. After the treatment is completed, it is taken out for use and testing.
[0091] Example 2
[0092] S1. Prepare raw materials, including: 40wt% nickel powder (same morphology and particle size as in Example 1) and 60wt% bismuth ferrite powder (same preparation process and particle size as in Example 1).
[0093] S2. Wet ball milling: Pour the two powders into a ball milling jar, add anhydrous ethanol until the powder is submerged, with a ball-to-powder ratio of 10:1, and ball mill at 280 rpm for 6 hours. During the process, check regularly to avoid agglomeration and leakage.
[0094] S3. Wet material drying: Set the temperature of the vacuum drying oven to 65℃ and the vacuum degree to -0.08MPa. Turn the wet material over every 2 hours. Take out the dried material when the moisture content is lower than 0.5%.
[0095] S4. Pressing the billet: Select a mold of the same specification, fill in the material, apply a pressure of 15MPa and hold for 40 minutes. After demolding, check the billet for defects.
[0096] S5. High-temperature sintering: The green body is placed in a sintering furnace, and argon gas is introduced until the oxygen content is <0.1%. The temperature is increased to 850℃ at 5℃ / min, held for 6 hours, and then cooled to room temperature at 3℃ / min. The argon gas flow rate is 110mL / min.
[0097] S6. Magnetic field treatment: Place the composite material in an external magnetic field of 7 Oe and let it stand for 16 minutes to ensure that the magnetic domains are fully oriented. After completion, remove it.
[0098] Example 3
[0099] S1. Prepare raw materials, including: 30wt% nickel powder (same morphology and particle size as in Example 1) and 70wt% bismuth ferrite powder (same preparation process and particle size as in Example 1).
[0100] S2. Wet ball milling: Pour the two powders into a ball milling jar, add anhydrous ethanol to submerge them, with a ball-to-powder ratio of 10:1, and ball mill at 250 rpm for 6 hours.
[0101] S3. Drying wet materials: Vacuum drying oven temperature 60℃, vacuum degree -0.1MPa, turn the wet materials until the moisture content is <0.5%, and take out the dried materials;
[0102] S4. Pressing the billet: Fill the mold of the same specification with the material, apply 10MPa pressure and hold for 50 minutes. After demolding, confirm that the billet is intact.
[0103] S5. High-temperature sintering: After the billet is put into the furnace, argon gas is introduced to remove oxygen (<0.1%), the temperature is increased to 800℃ at 5℃ / min, held for 6 hours, and then cooled down at 3℃ / min with an argon gas flow rate of 100mL / min.
[0104] S6. Magnetic field treatment: The composite material is placed in an external magnetic field of 6 Oe and left to stand for 15 minutes. After magnetization is completed, it is taken out.
[0105] Comparative Example 1
[0106] S1. Prepare raw materials, including: 20wt% nickel powder (same morphology and particle size as in Example 1) and 80wt% bismuth ferrite powder (same preparation process and particle size as in Example 1).
[0107] S2. Wet ball milling: Pour the two powders into a ball mill jar, add anhydrous ethanol to immerse them, with a ball-to-powder ratio of 10:1, and ball mill at 200 rpm for 4 hours (shorten the ball milling time).
[0108] S3. Wet material drying: using a regular oven (non-vacuum) at 80℃, the wet material was not turned over periodically, and was taken out after the surface was dry (moisture content was not monitored).
[0109] S4. The blank is pressed and filled with material in a mold of the same specification. A pressure of 5MPa is applied and held for 20 minutes (reduce the pressure and shorten the time). After demolding, the blank has slight cracks.
[0110] S5. High-temperature sintering: The green body is placed in a sintering furnace without argon protection (air atmosphere), and the temperature is rapidly increased to 900℃ at 8℃ / min, held for 4 hours (shorten the holding time), and then cooled naturally to room temperature.
[0111] S6. Magnetic field treatment: Without applying an external magnetic field for magnetization, the sintered composite material is directly taken out for use.
[0112] The table below compares the properties of the supercomposite materials from different embodiments and comparative examples.
[0113]
[0114]
[0115] In summary, the advantages of this invention are:
[0116] This invention innovatively constructs a percolation system of conductive functional phase of metallic nickel and magnetic matrix phase of nickel ferrite. Using bismuth ferrite as a precursor, it generates a nickel ferrite matrix through an in-situ redox reaction with metallic nickel via high-temperature sintering. This eliminates the need for separate preparation of the magnetic phase, simplifying the process while ensuring a tight bond between the conductive and magnetic phases. The final product achieves a weakly negative dielectric property with an absolute real part of the dielectric constant of less than 1000 in the 100MHz-1GHz frequency band, and a saturation magnetization greater than 27 emu / g. This solves the problem of traditional supercomposite materials struggling to achieve both dielectric and magnetic properties, providing core material support for scenarios requiring "dual electromagnetic properties" such as electromagnetic shielding and novel sensors.
[0117] To optimize the preparation process and improve the stability of material performance, the following measures were taken: First, a wet ball milling process was adopted, combined with the dispersion effect of anhydrous ethanol medium and mechanical shear force, to achieve microscopic uniform dispersion of metallic nickel and bismuth ferrite powder, effectively avoiding functional phase agglomeration and laying the foundation for the subsequent formation of a uniform percolation structure. Second, an argon protective atmosphere was introduced during the high-temperature sintering stage to prevent the oxidation of metallic nickel from damaging the conductive network, while ensuring the purity and chemical stability of the nickel ferrite matrix. Third, a magnetic field treatment step was added to optimize the orientation of magnetic domains inside the material, so that the saturation magnetization intensity could be stably met. The whole process control reduced the fluctuation of product performance by more than 30%, meeting the stringent requirements of high-end equipment for material consistency.
[0118] With simplified processes and controllable parameters, this invention combines precursor preparation, composite, and performance optimization into one, generating nickel ferrite through the in-situ reaction of bismuth ferrite and metallic nickel. This eliminates the traditional separate preparation step of magnetic matrix, shortening the process flow by 30%. At the same time, it clarifies key control parameters, which can be flexibly adjusted according to different application scenarios, enabling customized production of multiple products with one process, and adapting to the high-end equipment manufacturing needs of multiple fields such as electromagnetic shielding and new sensors.
[0119] To promote industrial application, the raw materials used in this invention are conventional metallic nickel powder and bismuth ferrite powder, which do not require rare metals or complex artificial structural units, and the raw material cost is lower than that of supercomposite materials containing precious metals.
[0120] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention. The scope of protection claimed by the appended claims and their equivalents is defined.
Claims
1. A method for preparing a magnetic super-composite of low negative dielectric permittivity, characterized in that, The preparation method comprises: S1, raw material preparation, weighing the required metal nickel powder and bismuth ferrite powder, ensuring that the metal nickel powder is not oxidized and the bismuth ferrite powder is uniform in particle size; S2, wet ball milling mixing, pouring the metal nickel powder and bismuth ferrite powder into the ball mill tank, adding anhydrous ethanol as the ball milling medium, starting the ball mill for mixing, and making the two powders microscopically uniformly dispersed; S3, drying the wet material, placing the wet material after ball milling in a drying device to remove anhydrous ethanol, and obtaining a dry mixture; S4, green body pressing, placing the dried mixture into a mold, applying a set pressure and maintaining a set time, and pressing to form a green body with a dense structure; S5, high-temperature sintering, placing the green body in a high-temperature sintering furnace in an argon protective atmosphere, heating to a set temperature and maintaining the temperature, promoting the redox reaction of bismuth ferrite and metal nickel to form nickel ferrite, and forming a nickel-iron nickel ferrite composite structure; S6, magnetic field treatment, placing the sintered composite material in an external magnetic field for magnetization, optimizing the magnetic domain orientation, and finally obtaining a magnetic super composite material with weak negative dielectric constant.
2. The method for preparing a magnetic supercomposite material with a weak negative permittivity according to claim 1, characterized in that, The super composite material uses metal nickel as the conductive functional phase and nickel ferrite as the magnetic matrix phase, and the raw materials include: 10-50wt% metal nickel powder and 50-90wt% bismuth ferrite powder. The preparation process combines wet ball milling, green body pressing, high-temperature sintering, and magnetic field treatment processes, and finally obtains a magnetic super composite material with weak negative dielectric constant in the 100MHz-1GHz frequency band and a saturation magnetization greater than 27emu / g.
3. The method of claim 1, wherein the magnetic super-composite material has a low dielectric constant. The raw materials of the super composite material are weighed according to the optimal ratio, specifically including: 50wt% metal nickel powder and 50wt% bismuth ferrite powder. The metal nickel powder is chain-shaped and has a rough micro-surface structure, and the bismuth ferrite powder is a 200-mesh powder obtained by solid-phase reaction sintering of iron oxide and bismuth oxide, ensuring that the bismuth ferrite and metal nickel fully undergo the redox reaction during high-temperature sintering, while ensuring the percolation structure and electromagnetic performance of the composite material.
4. The method of claim 2, wherein the magnetic super-composite material has a low dielectric constant. The metal nickel powder serves as the conductive functional phase, constructing a three-dimensional conductive network to provide a carrier transport channel for the weak negative dielectric performance. The bismuth ferrite powder serves as a precursor and undergoes a redox reaction with metal nickel during high-temperature sintering to generate nickel ferrite magnetic matrix phase in situ, giving the composite material excellent magnetic properties. Together, they construct a percolation system to achieve the synergistic regulation of dielectric and magnetic properties, avoiding the performance imbalance problem caused by relying solely on a single functional phase in traditional super composite materials.
5. The method for preparing a magnetic supercomposite material with a weak negative permittivity according to claim 1, characterized in that, The specific steps of S2 include: Pour the weighed metal nickel powder and bismuth ferrite powder into the ball mill tank of the planetary ball mill according to the proportion, add anhydrous ethanol to completely immerse the powder, and control the ball-to-material ratio to be 10:1; Start the planetary ball mill at a set speed for 6 hours. During the ball milling process, the mixing state is observed through the equipment observation window regularly to avoid powder agglomeration and ball mill tank leakage; After the ball milling is completed, the ball mill tank is taken out, and the solid-liquid mixture in the tank is transferred to a container to ensure that there is no powder residue; The wet ball milling process realizes the micro-uniform dispersion of metal nickel powder and bismuth ferrite powder through the synergistic effect of mechanical force and liquid medium, laying a foundation for the formation of a uniform percolation structure.
6. The method for preparing a magnetic supercomposite material with a weak negative permittivity according to claim 1, characterized in that, The specific steps of S3 include: After ball milling, the wet material is transferred to a vacuum drying oven, and the drying temperature and vacuum degree are set to avoid oxidation of the metal nickel powder caused by high temperature; During the drying process, the wet material is turned over every 2 hours to ensure uniform evaporation of moisture in the upper and lower layers of the material; the moisture content of the material is detected in real time by a moisture meter, and the drying process is stopped when the moisture content is less than 0.5%, and the dried mixture is taken out; The dried mixture needs to be immediately pressed into a green body to avoid absorbing moisture in the air for a long time, which affects the quality of the green body.
7. The method of claim 1, wherein the magnetic super-composite material has a low dielectric constant. The specific steps of S4 include: A cylindrical mold with a diameter of 20 mm is selected, and the dried mixture is evenly filled into the mold cavity and gently compacted to remove air from the cavity; The mold is placed on a hydraulic tablet press, and a set pressure of 5-20 MPa is applied for 30-60 minutes; the pressure stability is monitored in real time during the pressing process to avoid fluctuations in the pressure, which may cause uneven density of the green body; After pressing is completed, the green body is slowly removed from the mold, and the appearance of the green body is checked to ensure that there are no cracks, missing corners, or uneven density defects; If the green body has defects, the pressing pressure and time need to be adjusted, and the pressing process needs to be repeated to ensure that the quality of the green body meets the requirements of subsequent high-temperature sintering.
8. The method of claim 1, wherein the magnetic super-composite material has a low dielectric constant. The specific steps of S5 include: The qualified green body is placed in the sample holder of the high-temperature sintering furnace, ensuring that there is a gap between the green bodies to facilitate uniform temperature distribution in the furnace; Argon gas is introduced into the sintering furnace to remove air from the furnace; when the oxygen content in the furnace is less than 0.1%, the temperature rising program is started; The program temperature rising mode is adopted, and the target sintering temperature is reached at a set rate; the target sintering temperature is 800-1000℃, and the temperature is maintained for 6 hours after reaching the target temperature to ensure that the bismuth ferrite and the metal nickel fully undergo oxidation-reduction reaction to generate nickel ferrite in situ; After the holding period ends, the temperature is lowered to room temperature at a set rate to avoid stress cracks in the composite material caused by large temperature differences; Throughout the sintering process, argon gas is continuously introduced to ensure an inert atmosphere in the furnace to prevent oxidation of the metal nickel and deterioration of the nickel ferrite matrix.
9. The method of claim 1, wherein the magnetic super-composite material has a low dielectric constant. The specific steps of S6 are: After the sintered composite material is removed from the sintering furnace and cooled to room temperature, it is transferred to an external magnetic field environment; The strength of the external magnetic field is adjusted, and the composite material is left in the magnetic field for 15-20 minutes to ensure that the internal magnetic domains of the material are fully oriented; During the magnetic field treatment process, the state of the composite material is observed regularly to avoid external vibrations affecting the uniformity of the magnetic domain orientation; After the magnetic field treatment is completed, the composite material is removed and is ready for use or performance testing to ensure that its saturation magnetization is stable and reaches more than 27emu / g.
10. The method of claim 9, wherein the magnetic super-composite material has a low dielectric constant. The performance control of the super composite material needs to be achieved through the coordination of key parameters, including the content of metal nickel powder, the pressing conditions of the green body, the sintering temperature, and the strength of the external magnetic field; Among them, the content of metal nickel determines the density of the conductive network, the pressing conditions affect the density of the material, the sintering temperature controls the amount of nickel ferrite generated, and the external magnetic field optimizes the orientation of the magnetic domains; the four work together to ensure that the composite material has stable weak negative dielectric properties in the frequency range of 100MHz-1GHz; when applied, the parameters can be adjusted according to specific electromagnetic requirements, and it is suitable for high-end equipment manufacturing in the fields of electromagnetic shielding and new sensors.