A method for preparing a phosphoric acid / graphene / silicon nitride coated iron-silicon-aluminum magnetic powder core

Abstract

This invention discloses a method for preparing a phosphoric acid / graphene / silicon nitride-coated iron-silicon-aluminum magnetic powder core, relating to the fields of soft magnetic materials and powder surface treatment. The method for preparing the phosphoric acid / graphene / silicon nitride-coated iron-silicon-aluminum magnetic powder core includes the following steps: powder preparation, phosphoric acid / graphene / silicon nitride coating, addition of lubricant, pressing and molding, and annealing. This invention uses a phosphoric acid / graphene / silicon nitride composite coating of iron-silicon-aluminum magnetic powder core, which can improve microwave absorption and high-temperature resistance, effectively avoiding the increase in loss and decrease in permeability of the iron-silicon-aluminum magnetic powder core caused by high-temperature treatment and improved microwave absorption performance. While ensuring high permeability, a low-loss, high-absorption-performance iron-silicon-aluminum magnetic powder core can be prepared.

Description

Technical Field

[0001] This invention belongs to the field of soft magnetic materials and powder surface treatment, and specifically relates to a method for preparing a phosphoric acid / graphene / silicon nitride coated iron-silicon-aluminum magnetic powder core. Background Technology

[0002] With the rapid development of the electronics and information industry, there is a growing demand for new electronic components that are miniaturized, low-loss, highly sensitive, high-capacity, and high-power. This also places new demands on the preparation of soft magnetic metal materials widely used in various electronic products. The application and development of soft magnetic metal powder cores are precisely to meet these requirements. Among the development of soft magnetic metal materials, iron-silicon-aluminum magnetic powder cores, with their advantages of high resistivity, low coercivity, high permeability, wear resistance, and excellent cost-effectiveness, are widely used in electronic components such as transformers, inductors, and choke coils.

[0003] In the fabrication of magnetic powder cores, insulating coating is extremely important. It is the most critical step in the preparation of iron-silicon-aluminum soft magnetic powder cores, affecting their magnetic and mechanical properties. The coating layer of the iron-silicon-aluminum magnetic powder isolates the contact between the powder particles, blocking the eddy current path between them, reducing the formation of large eddy currents, increasing the resistivity of the magnetic powder core, and reducing eddy current losses. Simultaneously, the coating layer improves the surface morphology and adhesion between the powder particles, which is beneficial for improving the mechanical strength of the magnetic powder core. In addition, the coating layer can also act as an absorbing coating, weakening electromagnetic wave and electromagnetic radiation interference and improving the microwave absorption performance of the magnetic powder core. Currently, the coating methods for iron-silicon-aluminum magnetic powder are divided into organic coating and inorganic coating. Although the organic coating process is simple, the resins are prone to aging, reducing the service life of the magnetic powder core; moreover, the resin is prone to decomposition at high temperatures, increasing the demagnetizing field and reducing the density and effective permeability of the powder core. Inorganic coating is further divided into chemical coating and physical coating, depending on whether it reacts with the magnetic powder. Chemical coating often uses phosphate passivation of magnetic powder particles, resulting in a uniform and dense coating layer. The coating process is simple and the production cost is low. However, the phosphate insulating layer decomposes at around 600℃, reducing the magnetic properties and mechanical strength of the magnetic powder core. Physical coating mainly involves coating the magnetic powder with inorganic oxides, which has high resistivity and good high-temperature resistance. However, it suffers from problems such as uneven oxide coating and the tendency for simple oxide coatings to detach during pressing and molding.

[0004] Therefore, existing coating methods for iron-silicon-aluminum magnetic powder cores still have many shortcomings in terms of the high-temperature resistance of the coating layer, as well as the permeability, loss, and microwave absorption performance of the magnetic powder core. To obtain good microwave absorption and high-temperature resistance, and to avoid increased loss and decreased permeability of the iron-silicon-aluminum magnetic powder core due to high-temperature treatment and improved microwave absorption performance, it is urgently necessary to develop a novel composite coating process for iron-silicon-aluminum magnetic powder cores. Summary of the Invention

[0005] To overcome the shortcomings of the existing technology, this invention provides a method for preparing a phosphoric acid / graphene / silicon nitride-coated iron-silicon-aluminum magnetic powder core. This invention uses a phosphoric acid / graphene / silicon nitride composite coating on the iron-silicon-aluminum magnetic powder core, which improves microwave absorption and high-temperature resistance, effectively avoiding increased losses and decreased permeability of the iron-silicon-aluminum magnetic powder core caused by high-temperature treatment and improved microwave absorption performance. While ensuring high permeability, a low-loss, high-absorption-performance iron-silicon-aluminum magnetic powder core can be prepared.

[0006] The method for preparing a phosphoric acid / graphene / silicon nitride-coated iron-silicon-aluminum magnetic powder core of the present invention includes the following steps:

[0007] S1. Powder preparation: FeSiAl magnetic powder is prepared by high-energy ball milling. FeSiAl powder is placed in an inert atmosphere and annealed at 800℃~900℃ for 1~3h.

[0008] S2, Phosphoric acid coating: Dilute phosphoric acid with anhydrous ethanol, add the diluted phosphoric acid solution to the FeSiAl powder obtained in S1 for preliminary surface treatment, and then heat and stir in a constant temperature water bath of 50℃~70℃ until dry.

[0009] S3, Graphene / Silicon Nitride Coating: Graphene powder, silicon nitride powder and S2 phosphoric acid coated FeSiAl magnetic powder are mixed evenly in proportion, and 0.2-0.6 wt% binder is added and mixed evenly; the uniformly stirred powder is heated in the range of 70-160℃ and continuously stirred until dry;

[0010] S4. Add lubricant: Add 0.6-1.0% of the powder weight of lubricant and mix evenly;

[0011] S5. Press molding: The powder is pressed into shape under a press to form a magnetic powder core;

[0012] S6. Annealing: Under an inert atmosphere, the magnetic powder core is first placed in a furnace at 750℃~950℃ for annealing. The holding time is set to 1~2h, the heating rate is 9℃ / min, and the core is cooled with the furnace.

[0013] Further, in step S1, the FeSiAl magnetic powder is composed of the following composition by mass percentage: Si 9.0–10.0%, Al 5.0–6.0%, with the balance being Fe; the powder particle size distribution is as follows by mass percentage: 5% -150 to +200 mesh, 70% -200 to +400 mesh, and 25% -400 mesh. Here, "-150 to +200 mesh" means that the powder can pass through a 150-mesh sieve but cannot pass through a 200-mesh sieve, and so on.

[0014] Furthermore, in the preparation process of this invention, the inert atmosphere is argon or nitrogen.

[0015] Furthermore, in step S2, the amount of phosphoric acid added is 0.3 wt% (this concentration refers to the concentration of H3PO4 in the system after the addition of phosphoric acid, the same below), and the reaction time is 10-30 min.

[0016] Furthermore, in step S3, the graphene powder has a purity greater than 95%, a sheet diameter of 5–50 μm, a thickness of 3.4–8 nm, a number of layers of 5–10, and a specific surface area of ​​less than 50 m². 2 / g; the particle size of the silicon nitride powder is 200 mesh.

[0017] Further, in step S3, the mass ratio of graphene powder, silicon nitride powder and FeSiAl powder obtained in S1 is 1:(1~2):(19~25).

[0018] Further, in step S3, the adhesive is a sodium silicate solution, and the amount of adhesive added mentioned above, 0.2 to 0.6 wt%, is based on the amount of sodium silicate added.

[0019] Further, in step S4, the lubricant is zinc stearate.

[0020] The design basis of the method of this invention is:

[0021] Graphene: As a novel two-dimensional material, graphene possesses advantages such as high strength, high thermal conductivity, high specific surface area, good lubrication properties, dielectric properties, and interfacial polarization. Loading magnetic particles onto graphene sheets can enhance interfacial polarization, adjust impedance matching, and achieve a synergistic effect between dielectric and magnetic losses. This results in graphene-incorporated iron-silicon-aluminum magnetic powder cores exhibiting excellent microwave absorption performance.

[0022] Silicon nitride: On the one hand, silicon nitride is an important structural ceramic material with high hardness, wear resistance, and strong resistance to high temperature creep. Adding silicon nitride can improve the high temperature resistance and mechanical properties of iron-silicon-aluminum magnetic powder cores. On the other hand, silicon nitride is also a dielectric material with low dielectric constant and dielectric loss. After coating iron-silicon-aluminum magnetic powder, it can effectively prevent the magnetic powder from being oxidized and block the eddy current path between magnetic powders, which is beneficial to reducing eddy current loss.

[0023] In the present invention, after the phosphoric acid / graphene / silicon nitride composite coating, during the subsequent high-temperature annealing process, the graphene and Si3N4 in the coating layer partially react at the interface to form SiC. At this time, the SiC is dispersed, playing a role in dispersion strengthening. When the magnetic powder core is subjected to external force, dislocation lines cut through or circle through the SiC, which increases the lattice distortion energy in the dislocation-affected region, thereby increasing the resistance to dislocation movement and improving the mechanical properties of the magnetic powder core. Furthermore, the amount of graphene added also affects the mechanical properties. When the ratio of graphene to silicon nitride is less than 1:1, and the sum of their amounts is less than 2:25 compared to the ratio of phosphoric acid-coated FeSiAl powder (note: corresponding to a ratio of graphene, silicon nitride, and phosphoric acid-coated FeSiAl powder less than 1:1:25), the coating layer is thin and cannot be uniformly coated. The proportion of the contact surface between silicon nitride and graphene decreases, and the proportion of SiC generated is less than 0.5%. The SiC dispersion strengthening effect is not significant, resulting in low mechanical properties that do not meet the requirements. When the ratio of graphene to silicon nitride is greater than 1:2, and the sum of their amounts is greater than 3:19 compared to the ratio of graphene, silicon nitride, and phosphoric acid-coated FeSiAl powder greater than 1:2:19, the mechanical properties decrease because graphene cannot be well and uniformly dispersed and agglomerates. When the ratio of graphene to silicon nitride is in the range of 1:(1-2), and the ratio of the sum of the two to the phosphoric acid-coated FeSiAl powder is between 2:25 and 3:19 (note: corresponding to a ratio of graphene, silicon nitride, and phosphoric acid-coated FeSiAl powder in the range of 1:(1-2):(19-25)), a core-shell layer of 0.5-0.8 μm thickness is formed between Si3N4, SiC, and graphene, with the shell layer containing 0.5% to... The 1.5% SiC dispersed particles hinder dislocation movement during plastic deformation, thus strengthening the magnetic powder core. Furthermore, the uniform distribution of Si3N4 and SiC on the attached graphene surface, along with the uniform dispersion of the graphene itself, results in optimal mechanical properties for the magnetic powder core. The tensile strength of the coated FeSiAl magnetic powder core after annealing increases from 221.35 MPa under phosphate coating to 323.22–333.73 MPa. Therefore, the graphene-Si3N4 composite coating layer formulated according to this scheme significantly enhances the mechanical properties of the magnetic powder core, and the uniform dispersion of graphene further improves the reinforcing effect.

[0024] The phosphoric acid / graphene / silicon nitride composite coating process of this invention forms a shell structure between the composite coating layer and FeSiAl magnetic powder. It uses FeSiAl magnetic powder as the core and a 0.5μm–0.8μm thick graphene-Si3N4 composite coating layer as the shell, effectively improving the integrity of the coating through diffusion and chemical reaction. First, the magnetic powder core undergoes high-temperature annealing. Through high-temperature diffusion and the chemical reaction between graphene and silicon nitride, a core-shell structure FeSiAl / graphene / Si3N4 / SiC composite magnetic powder core is obtained. Because graphene and silicon nitride react chemically at their interface at high temperature to form silicon carbide, the coating layer forms a graphene / Si3N4 / SiC composite structure. The excellent thermal stability and dispersed distribution of Si3N4-SiC give the coating layer good high-temperature resistance. Secondly, graphene (under oxygen-free conditions) and silicon nitride have high-temperature properties, and during high-temperature annealing, the reaction between graphene and Si3N4 is relatively mild and not violent. The composite coating layer can maintain a good morphology and will not decompose even when annealed at a temperature not exceeding 1000℃. This greatly improves the stability of the phosphate / graphene / silicon nitride composite coating layer, which can maintain the magnetic properties and mechanical strength of the magnetic powder core. This avoids the situation where, when coated with phosphate alone, the phosphate insulating layer Al(PO3)3 decomposes at 600℃ to generate Al2O3 and P2O5, which destroys the stability of the magnetic powder coating layer and reduces the magnetic properties and mechanical strength of the magnetic powder core.

[0025] The phosphoric acid / graphene / silicon nitride composite coating process of this invention forms various heterogeneous interfaces with a thickness of 0.5 μm to 0.8 μm between Si3N4 and SiC generated by the reaction and graphene in the composite coating layer. These heterogeneous interfaces are composed of irregularly shaped Si3N4 and SiC particles uniformly distributed within the graphene sheets, including both graphene-Si3N4 and graphene-SiC types. The interface is a location where defects concentrate. When the magnetic powder core is in an electromagnetic field, unneutralized positive and negative charges begin to move and accumulate at the interface. Once the charges are pinned by defects, they become a pair of dipoles. When the rotation of these dipoles cannot keep up with the changes in the electromagnetic field, polarization relaxation occurs, enhancing the attenuation capability of the magnetic powder core against electromagnetic waves. Furthermore, the graphene, Si3N4, and SiC in the graphene-Si3N4 composite coating layer are cross-distributed, forming a large number of conductive micronetworks. When external electromagnetic waves enter the interior of a material, the electromagnetic field induces conduction currents and a large number of displacement microcurrents, resulting in strong conductivity losses and converting the electromagnetic waves into heat energy. The combined effect of these two factors gives the magnetic powder core good electromagnetic wave absorption performance. However, related research shows that the better the absorption properties of the magnetic powder, the greater the loss.

[0026] In the phosphoric acid / graphene / silicon nitride composite coating process of this invention, silicon nitride possesses a low dielectric constant, low dielectric loss, and high resistivity. According to this scheme, the mass ratio of graphene powder, silicon nitride powder, and phosphoric acid coating is 1:(1-2):(19-25). After coating FeSiAl magnetic powder, the eddy current path between magnetic powder particles can be blocked, which helps reduce eddy current loss. Furthermore, the appropriate amount of SiC generated at high temperature has good thermal conductivity and insulation properties, which can act as a heat conduction channel and increase the resistivity of FeSiAl magnetic powder, thereby reducing the problem of core loss and heat generation in FeSiAl magnetic powder. In addition, the added graphene has a scaly structure and good lubricity; the added Si3N4, under pressure, undergoes slight decomposition on the friction surface to form a thin gas film, thereby reducing the sliding resistance between the friction surfaces. Therefore, the more friction occurs, the lower the resistance, and it also possesses good lubricity. Therefore, during the pressing process, the dual effect of graphene and silicon nitride enhances the interfacial interaction between the composite coating layer and FeSiAl magnetic powder, resulting in a tight bond between FeSiAl magnetic powder particles, reducing the voids in the magnetic powder core, increasing the density of the magnetic powder core, and thus increasing the resistivity of the magnetic powder core. As can be seen from P=U2 / R, the loss of the magnetic powder core is reduced.

[0027] Compared with the prior art, the beneficial effects of the present invention are reflected in:

[0028] (1) This invention employs a phosphoric acid / graphene / silicon nitride composite coating process, in which graphene and Si3N4 in the coating layer partially react at the interface to generate SiC. At this time, SiC is dispersed, which plays a role in dispersion reinforcement and improves the mechanical properties of the magnetic powder core.

[0029] (2) The present invention adopts a phosphoric acid / graphene / silicon nitride composite coating process. First, a core-shell structure with FeSiAl magnetic powder as the core and an insulating coating layer as the core and shell is formed. Second, through diffusion at high temperature and chemical reaction at the interface between graphene and silicon nitride, a FeSiAl / graphene / Si3N4 / SiC composite magnetic powder core with a core and shell structure is obtained, which improves the high temperature resistance of the magnetic powder core and avoids the problem of poor high temperature resistance of single phosphoric acid coating.

[0030] (3) The present invention uses a phosphoric acid / graphene / silicon nitride composite coating process to prepare FeSiAl magnetic powder cores. Irregular silicon nitride covers the graphene surface, and a large number of heterogeneous interfaces with a thickness of 0.5μm to 0.8μm and conductive micronetworks are formed between Si3N4, SiC and graphene, which improves the wave absorption of magnetic powder cores and effectively reduces the influence of electromagnetic interference and electromagnetic radiation.

[0031] (4) This invention employs a phosphoric acid / graphene / silicon nitride composite coating process to form a dense, uniform, and highly lubricated composite coating layer on the surface of the magnetic powder. During pressing, the good lubricity of the coating layer ensures that the FeSiAl magnetic powder particles are tightly bonded together, increasing the density of the magnetic powder core and reducing losses. Simultaneously, the uniform distribution of Si3N4 in the coating layer, with its high resistivity, reduces eddy current losses, thereby reducing the loss of the magnetic powder core. Attached Figure Description

[0032] Figure 1 X-ray diffraction analysis of the composite powder obtained by heating graphene and silicon nitride powders at 850°C for 1 hour under a protective atmosphere, according to the present invention. Figure 1 As can be seen, SiC is generated after being kept at 850℃ for 1 hour.

[0033] Figure 2 The images show the electron microscopy (SEM) analysis results of the composite-coated magnetic powder core, where (a) is the SEM image and (b) is the scanning electron microscope (SEM) cross-sectional image. Figure 2 As can be seen, a shell structure is formed between the composite coating layer and the FeSiAl magnetic powder, with the FeSiAl magnetic powder as the core and the 0.5μm to 0.8μm thick graphene-Si3N4 composite coating layer as the shell. Detailed Implementation

[0034] The exemplary embodiments, features, and aspects of the present invention will be described below with reference to specific examples.

[0035] Specifically, the present invention provides a method for preparing a phosphoric acid / graphene / silicon nitride coated iron-silicon-aluminum magnetic powder core, which includes the following steps:

[0036] S1. Powder preparation: FeSiAl magnetic powder is prepared by high-energy ball milling. FeSiAl powder is placed in an inert atmosphere and annealed at 800℃~900℃ for 1~3h.

[0037] S2, Phosphoric acid coating: Dilute phosphoric acid with anhydrous ethanol, add the diluted phosphoric acid solution to the FeSiAl powder obtained in S1 for preliminary surface treatment, and then heat and stir in a constant temperature water bath of 50℃~70℃ until dry.

[0038] S3, Graphene / Silicon Nitride Coating: Graphene powder, silicon nitride powder and S2 phosphoric acid coated FeSiAl magnetic powder are mixed evenly in proportion, and 0.2-0.6 wt% binder is added and mixed evenly; the uniformly stirred powder is heated in the range of 70-160℃ and continuously stirred until dry;

[0039] S4. Add lubricant: Add 0.6-1.0% of the powder weight of lubricant and mix evenly;

[0040] S5. Press molding: The powder is pressed into shape under a press to form a magnetic powder core;

[0041] S6. Annealing: Under an inert atmosphere, the magnetic powder core is first placed in a furnace at 750℃~950℃ for annealing. The holding time is set to 1~2h, the heating rate is 9℃ / min, and the core is cooled with the furnace.

[0042] The protective atmosphere is argon or nitrogen.

[0043] The composition of FeSiAl magnetic powder by mass percentage is: Si 9.0-10.0%, Al 5.0-6.0%, with the balance being Fe; the powder particle size distribution is: 5% -150 to +200 mesh, 70% -200 to +400 mesh, and 25% -400 mesh.

[0044] The adhesive in step S3 is a sodium silicate solution.

[0045] The lubricant in step S4 is zinc stearate.

[0046] Table 1 shows the composition of the raw materials for the alloys in Examples 1-7 by mass percentage.

[0047]

[0048] Example 1:

[0049] FeSiAl powder was prepared using a high-energy ball mill. The composition by mass percentage was: Si 9.5%, Al 5.8%, and the balance Fe. The FeSiAl powder was placed in an argon atmosphere and annealed at 850℃ for 1.5h. After annealing, 250g of powder was weighed. The required powder particle size distribution was: 5% -150 to +200 mesh, 70% -200 to +400 mesh, and 25% -400 mesh.

[0050] Dilute phosphoric acid with 100 ml of anhydrous ethanol. The amount of phosphoric acid added is 0.75 g, which accounts for 0.3% of the powder weight. Add the diluted phosphoric acid solution to the FeSiAl powder obtained in the above process for preliminary surface treatment. Then, heat and stir in a constant temperature water bath at 60°C until dry.

[0051] After the FeSiAl powder cools to room temperature, add 1.5g of zinc stearate lubricant, which accounts for 0.6% of the powder weight; mix the powder evenly through an 80-mesh sieve to obtain a pressed powder.

[0052] The composite coated powder is pressed into shape. The pressure is 20.3 t / cm2, and the dimensions of the magnetic ring blank are: outer diameter 26.92 mm, inner diameter 14.73 mm, and height 11.18 mm.

[0053] The magnetic powder core was placed in an argon atmosphere heat treatment furnace, held at 850℃ for 1 hour, with a heating rate of 9℃ / min, and then cooled with the furnace.

[0054] Example 2:

[0055] The ingredients for this embodiment are shown in Table 1. FeSiAl powder was prepared using a high-energy ball mill. The FeSiAl powder was placed in an argon atmosphere and annealed at 850°C for 1.5 hours. After annealing, 250g of powder was weighed. The required powder particle size distribution was: 5% -150 to +200 mesh, 70% -200 to +400 mesh, and 25% -400 mesh.

[0056] Dilute phosphoric acid with 100 ml of anhydrous ethanol. The amount of phosphoric acid added is 0.75 g, which accounts for 0.3% of the powder weight. Add the diluted phosphoric acid solution to the FeSiAl powder obtained in the above process for preliminary surface treatment. Then, heat and stir in a constant temperature water bath at 60°C until dry.

[0057] Add 10g of 200-mesh graphene powder and 10g of silicon nitride powder to the phosphoric acid-coated powder, accounting for 4% of the powder weight, and mix evenly; add 1.5g of sodium silicate to the mixed powder, accounting for 0.6% of the powder weight, and dilute with deionized water before use; mix the mixed powder with the added graphene, silicon nitride and sodium silicate solution evenly and react for 10 minutes; heat the evenly stirred mixed powder to 85°C and stir continuously until dry.

[0058] After the FeSiAl powder cools to room temperature, add 1.5g of zinc stearate lubricant, which accounts for 0.6% of the powder weight; mix the powder evenly through an 80-mesh sieve to obtain a pressed powder.

[0059] The composite coated powder is pressed into shape. The pressure is 20.3 t / cm2, and the dimensions of the magnetic ring blank are: outer diameter 26.92 mm, inner diameter 14.73 mm, and height 11.18 mm.

[0060] The magnetic powder core was placed in an argon atmosphere heat treatment furnace, held at 850℃ for 1 hour, with a heating rate of 9℃ / min, and then cooled with the furnace.

[0061] Example 3:

[0062] The ingredients for this embodiment are shown in Table 1.

[0063] The preparation method in this embodiment is the same as in Embodiment 2.

[0064] Example 4:

[0065] The ingredients for this embodiment are shown in Table 1.

[0066] The preparation method in this embodiment is the same as in Embodiment 2.

[0067] Example 5:

[0068] The ingredients for this embodiment are shown in Table 1.

[0069] The preparation method in this embodiment is the same as in Embodiment 2.

[0070] Example 6:

[0071] The ingredients for this embodiment are shown in Table 1.

[0072] The preparation method in this embodiment is the same as in Embodiment 2.

[0073] Example 7:

[0074] The ingredients for this embodiment are shown in Table 2. FeSiAl powder was prepared using a high-energy ball mill. The FeSiAl powder was placed in an argon atmosphere and annealed at 850°C for 1.5 hours. After annealing, 250g of powder was weighed. The required powder particle size distribution was: 5% -150 to +200 mesh, 70% -200 to +400 mesh, and 25% -400 mesh.

[0075] Dilute phosphoric acid with 100 ml of anhydrous ethanol. The amount of phosphoric acid added is 0.75 g, which accounts for 0.3% of the powder weight. Add the diluted phosphoric acid solution to the FeSiAl powder obtained in the above process for preliminary surface treatment. Then, heat and stir in a constant temperature water bath at 60°C until dry.

[0076] Add 10g of 200-mesh MnZn ferrite powder (4% of the powder weight) to the phosphoric acid-coated powder and mix thoroughly. Add 1.5g of sodium silicate (0.6% of the powder weight) to the mixed powder and dilute with deionized water before use. Mix the powder with the added MnZn ferrite and sodium silicate solution thoroughly and react for 10 minutes. Heat the well-stirred powder to 85°C and stir continuously until dry.

[0077] After the FeSiAl powder cools to room temperature, add 1.5g of zinc stearate lubricant, which accounts for 0.6% of the powder weight; mix the powder evenly through an 80-mesh sieve to obtain a pressed powder.

[0078] The composite coated powder is pressed into shape. The pressure is 20.3 t / cm2, and the dimensions of the magnetic ring blank are: outer diameter 26.92 mm, inner diameter 14.73 mm, and height 11.18 mm.

[0079] The magnetic powder core was placed in an argon atmosphere heat treatment furnace, held at 850℃ for 1 hour, with a heating rate of 9℃ / min, and then cooled with the furnace.

[0080] The mechanical and magnetic properties of the samples obtained by this invention are shown in Table 2 below.

[0081] Table 2 Mechanical and magnetic properties of magnetic powder cores

[0082]

[0083] *The effective absorption bandwidth is the bandwidth with a reflectivity of less than -10dB.

[0084] This invention improves the mechanical properties of FeSiAl magnetic powder cores through a phosphoric acid / graphene / silicon nitride composite coating process, increasing the tensile strength after annealing from 221.35 MPa to 344.15 MPa. By simply changing the amount of Si3N4 added, increasing the amount of Si3N4 enhances the magnetic properties of the FeSiAl magnetic powder, raising the permeability to 122 H / m. The resistivity of the magnetic powder core also significantly increases, while the power loss decreases to 192 mW / cm². 3 The high-temperature resistance is enhanced; the phosphate / graphene / silicon nitride coating does not decompose at 1000℃. The microwave absorption performance is improved; the effective absorption bandwidth with a reflectivity of less than -10dB is increased to 1.35GHz, achieving excellent microwave absorption performance.

[0085] Finally, it should be noted that the above-described embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; all process solutions that are not substantially different from the concept of the present invention are within the protection scope of the present invention.

Claims

1. A method for preparing a phosphoric acid / graphene / silicon nitride-coated iron-silicon-aluminum magnetic powder core, characterized in that... Includes the following steps: S1. Powder preparation: FeSiAl powder is prepared by high-energy ball mill. The FeSiAl powder is placed in an inert atmosphere and annealed at 800℃~900℃ for 1~3h. S2, Phosphoric acid coating: Dilute phosphoric acid with anhydrous ethanol, add the diluted phosphoric acid solution to the FeSiAl powder obtained in S1, and perform preliminary surface treatment; S3, Graphene / Silicon Nitride Coating: Graphene powder, silicon nitride powder and S2 phosphoric acid coated FeSiAl powder are mixed evenly in proportion, a binder is added and mixed evenly; the evenly mixed powder is heated in the range of 70~160℃ and continuously stirred until dry; S4. Add lubricant: Add lubricant and mix evenly; S5. Press molding: The mixture obtained in S4 is pressed into shape under a press to form a magnetic powder core; S6. Annealing: Under an inert atmosphere, the magnetic powder core is first placed in a furnace at 750℃~950℃ for annealing. The holding time is set to 1~2h, the heating rate is 9℃ / min, and the core is cooled with the furnace. In step S3, the mass ratio of graphene powder, silicon nitride powder and FeSiAl powder obtained in S1 is 1:(1~2):(19~25).

2. The preparation method according to claim 1, characterized in that: In step S1, the FeSiAl powder has the following composition by mass percentage: Si 9.0~10.0%, Al 5.0~6.0%, with the balance being Fe; the powder particle size distribution by mass percentage is: 5% -150~+200 mesh, 70% -200~+400 mesh, and 25% -400 mesh.

3. The preparation method according to claim 1, characterized in that: In step S2, the amount of phosphoric acid added is 0.3 wt%.

4. The preparation method according to claim 3, characterized in that: The surface treatment temperature is 50℃~70℃, and the reaction time is 10-30min.

5. The preparation method according to claim 1, characterized in that: In step S3, the graphene powder has a purity greater than 95%, a sheet diameter of 5-50 μm, a thickness of 3.4-8 nm, a number of layers of 5-10, and a specific surface area of ​​less than 50 m². 2 / g; the particle size of the silicon nitride powder is 200 mesh.

6. The preparation method according to claim 1, characterized in that: In step S3, the adhesive is a sodium silicate solution, and the amount of adhesive added is 0.2~0.6wt%, based on the amount of sodium silicate added.

7. The preparation method according to claim 1, characterized in that: In step S4, the lubricant is zinc stearate, and the amount added is 0.6~1.0% of the weight of the FeSiAl powder.

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