CN116364405A - Preparation method of phosphoric acid/graphene/silicon nitride coated sendust core - Google Patents

Abstract

The invention discloses a method for preparing a phosphoric acid/graphene/silicon nitride coated sendust magnetic powder core, and relates to the field of soft magnetic materials and powder surface treatment. The preparation method of the phosphoric acid/graphene/silicon nitride coated sendust magnetic powder core comprises the following steps: powder making, phosphoric acid/graphene/silicon nitride coating, adding lubricant, compression molding, and annealing. The present invention adopts phosphoric acid/graphene/silicon nitride composite coated sendust magnetic powder core, which can improve the wave absorption and high temperature resistance, and effectively avoid the increase of sendust magnetic powder core loss due to high temperature treatment and improvement of wave absorption performance. And the decrease of magnetic permeability, under the condition of ensuring high magnetic permeability, sendust magnetic powder core with low loss and high absorbing performance can be prepared.

Description

A preparation method of phosphoric acid/graphene/silicon nitride coated sendust magnetic powder core

technical field

The invention belongs to the field of soft magnetic materials and powder surface treatment, in particular to a method for preparing a phosphoric acid/graphene/silicon nitride coated sendust magnetic powder core.

Background technique

With the rapid development of the electronic information industry, new electronic components are required to develop toward the trend of miniaturization, low loss, high sensitivity, large capacity, and high power. This is also the preparation of metal soft magnetic materials widely used in various electronic products. New requirements were raised. The application and development of metal soft magnetic powder cores are just to meet this requirement. In the development of metal soft magnetic materials, sendust magnetic powder cores are widely used in transformers, inductors, choke coils and other electronic products due to their advantages of high resistivity, low coercive force, high magnetic permeability, wear resistance and excellent cost performance. in components.

Insulation coating is very important in the preparation process of magnetic powder core. It is the most critical step in the preparation process of sendust soft magnetic powder core, which affects the magnetic and mechanical properties of magnetic powder core. The coating layer of sendust magnetic powder isolates the mutual contact between the magnetic powder particles, blocks the eddy current path between the magnetic powder particles, reduces the formation of large eddy currents, increases the resistivity of the magnetic powder core, and reduces the eddy current loss. At the same time, the cladding layer formed by coating can improve the surface morphology of the magnetic powder particles and the cohesion between the magnetic powder particles, which is beneficial to improving the mechanical strength of the magnetic powder core. In addition, the cladding layer can also act as a wave-absorbing coating to reduce the interference of electromagnetic waves and electromagnetic radiation and improve the wave-absorbing performance of the magnetic powder core. At present, the coating methods of sendust magnetic powder are divided into two methods: organic coating and inorganic coating. Although the organic coating process is simple, these resins are easy to age, which reduces the service life of the magnetic powder core; and the resin is easy to decompose at high temperature, which increases the demagnetization field and reduces the density and effective magnetic permeability of the powder core. Inorganic coating is divided into chemical coating and physical coating according to whether it reacts with magnetic powder. Phosphoric acid passivation magnetic powder particles are often used for chemical coating, the coating layer is uniform and dense, the coating process is simple, and the production cost is low. However, the phosphate insulating layer decomposes at about 600°C, which reduces the magnetic properties and mechanical strength of the magnetic powder core. Physical coating is mainly the coating of magnetic powder by inorganic oxides, which has high resistivity and good high temperature resistance. However, there are problems such as uneven oxide coating, and simple oxide coating is easy to fall off during compression molding.

Therefore, the sendust magnetic powder core prepared by the existing coating method still has many deficiencies in the high temperature resistance of the coating layer, and the magnetic permeability, loss and wave absorption performance of the magnetic powder core. In order to obtain good wave absorption and high temperature resistance, avoid the increase of sendust magnetic powder core loss and the decrease of magnetic permeability due to high temperature treatment and improvement of wave absorption performance, it is urgent to develop a new type of sendust magnetic powder core composite Coating preparation process.

Contents of the invention

In order to overcome the shortcomings of the prior art above, the present invention provides a method for preparing a phosphoric acid/graphene/silicon nitride coated sendust magnetic powder core. The present invention adopts phosphoric acid/graphene/silicon nitride composite coated sendust magnetic powder core, which can improve wave absorption and high temperature resistance, and effectively avoid the increase of sendust magnetic powder core loss due to high temperature treatment and improvement of wave absorbing performance. And the decrease of magnetic permeability, under the condition of ensuring high magnetic permeability, sendust magnetic powder core with low loss and high absorbing performance can be prepared.

The preparation method of phosphoric acid/graphene/silicon nitride coated sendust magnetic powder core of the present invention comprises the following steps:

S1. Powder making: FeSiAl magnetic powder is prepared by using a high-energy ball mill to prepare FeSiAl powder, and the FeSiAl powder is placed in an inert atmosphere, and annealed at a high temperature of 800 ° C to 900 ° C for 1 to 3 hours;

S2. Phosphoric acid coating: dilute phosphoric acid with absolute ethanol, add the phosphoric acid diluent to the FeSiAl powder obtained in S1 for preliminary surface treatment, and then heat and stir in a constant temperature water bath at 50°C to 70°C until dry;

S3, graphene/silicon nitride coating: uniformly mix graphene powder, silicon nitride powder and FeSiAl magnetic powder coated with S2 phosphoric acid in proportion, add 0.2-0.6wt% binder, and mix uniformly; The homogeneous powder is heated in the range of 70-160°C and continuously stirred until dry;

S4, add lubricant: add lubricant accounting for 0.6-1.0% of powder weight, and mix evenly;

S5, compression molding: the powder is pressed and molded under a press to form a magnetic powder core;

S6. Annealing: In an inert atmosphere, first put the magnetic powder core into a furnace at 750°C to 950°C for annealing, set the holding time to 1 to 2h, and heat up at a rate of 9°C/min, cooling with the furnace.

Further, in step S1, the composition of the FeSiAl magnetic powder is constituted by mass percentage: Si9.0-10.0%, Al5.0-6.0%, and the balance is Fe; the powder particle size distribution is constituted by mass percentage: 5% -150～+200 mesh, 70% of -200～+400 mesh and 25% of -400 mesh. The meaning of "-150～+200 mesh" here means that the powder can pass through the mesh of the 150 mesh sieve, but cannot pass through the mesh of the 200 mesh sieve, and so on.

Further, in the preparation process of the present invention, the inert atmosphere is argon or nitrogen.

Further, in step S2, the amount of phosphoric acid added is 0.3wt% (this concentration refers to the concentration of H ₃ PO ₄ in the system after adding phosphoric acid, the same below), and the reaction time is 10-30 min.

Further, 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 layers, and a specific surface area of less than 50 m ² /g; the particle size of the silicon nitride powder is 200 head.

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).

Further, in step S3, the binder is a sodium silicate solution, and the amount of the binder mentioned above is 0.2-0.6 wt%, based on the amount of sodium silicate added.

Further, in step S4, the lubricant is zinc stearate.

The design basis of the inventive method is:

Graphene: As a new type of two-dimensional material, graphene has the advantages of high strength, high thermal conductivity, high specific surface area, good lubricating properties, dielectric properties and interface polarization. The magnetic particles loaded on the graphene sheet can not only enhance the interface polarization, adjust the impedance matching, but also realize the synergistic effect of dielectric loss and magnetic loss. The sendust magnetic powder core added with graphene has good wave-absorbing performance.

Silicon nitride: On the one hand, silicon nitride is an important structural ceramic material with high hardness, wear resistance, and high temperature creep resistance. Adding silicon nitride can improve the high temperature resistance and mechanical properties of the sendust magnetic powder core On the other hand, silicon nitride is also a dielectric material with low dielectric constant and dielectric loss. After coating the sendust magnetic powder, it can not only effectively prevent the magnetic powder from being oxidized, but also block the eddy current between the magnetic powder The passage is beneficial to reduce eddy current loss.

After the composite coating of phosphoric acid/graphene/silicon nitride of the present invention, in the subsequent high-temperature annealing treatment, graphene and Si ₃ N ₄ in the coating layer partially react at the interface to form SiC. At this time, SiC is in a dispersed distribution, which plays a role of dispersion strengthening. When the magnetic powder core is subjected to external force, the dislocation line cuts or wraps through SiC, which increases the lattice distortion energy of the dislocation-affected area, thereby increasing the resistance of dislocation movement and improving the mechanical properties of the magnetic powder core. In addition, the addition of graphene also has an impact on the mechanical properties. When the ratio of graphene to silicon nitride addition is lower than 1:1, and the ratio of the sum of the two additions to phosphoric acid-coated FeSiAl powder is lower than 2 : 25 (note: the ratio of FeSiAl powder coated with graphene, silicon nitride, and phosphoric acid is lower than 1:1:25), the thickness of the coating layer is thin and cannot be uniformly coated, and silicon nitride and graphite The proportion of graphene contact surface is reduced, and the proportion of SiC generated by the reaction is less than 0.5%, and the dispersion strengthening effect of SiC is not obvious, resulting in low mechanical properties, which do not meet the requirements; when the ratio of graphene to silicon nitride addition is higher than 1 : 2, and the ratio of the sum of the two additions to the phosphoric acid-coated FeSiAl powder is higher than 3:19 (Note: corresponding to the ratio of graphene, silicon nitride, and phosphoric acid-coated FeSiAl powder higher than 1:2 : 19), because graphene can not be well dispersed evenly, agglomeration occurs, and the mechanical properties decrease instead. When the ratio of graphene to silicon nitride addition is in the range of 1: (1~2), and the ratio of the sum of the two additions to phosphoric acid-coated FeSiAl powder is between 2:25 and 3:19 (Note: The ratio corresponding to graphene, silicon nitride, and phosphoric acid-coated FeSiAl powder is in the range of 1:(1~2):(19~25)), Si ₃ N ₄ , SiC and graphene are formed 0.5-0.8μm thick core-shell, with 0.5%-1.5% SiC dispersed particles in the shell, when plastic deformation occurs, these dispersed particles will hinder the dislocation movement, thereby strengthening the magnetic powder core; and Si ₃ N ₄ and SiC are evenly distributed on the attached graphene surface, and the graphene itself is also uniformly dispersed, so that the magnetic powder core exhibits the best mechanical properties. The tensile strength of the coated FeSiAl magnetic powder core after annealing is lower than that of phosphoric acid 221.35MPa increased to 323.22 ~ 333.73MPa. It can be seen that the graphene-Si ₃ N ₄ composite coating layer according to the proportion of this scheme greatly enhances the mechanical properties of the magnetic powder core, and the uniform dispersion of graphene can better achieve the enhancement effect.

In the phosphoric acid/graphene/silicon nitride composite coating process of the present invention, a shell structure is formed between the composite coating layer and the FeSiAl magnetic powder, which uses FeSiAl magnetic powder as the core, and graphene-Si with a thickness of 0.5 μm to 0.8 μm _{The 3} N ₄ composite coating is the shell, which effectively improves the integrity of the coating through diffusion and chemical reactions. First, the magnetic powder core is annealed at high temperature, and through the diffusion at high temperature and the chemical reaction of graphene and silicon nitride, a composite magnetic powder core with a core-shell structure of FeSiAl/graphene/Si ₃ N ₄ /SiC is obtained. Since graphene and silicon nitride form silicon carbide through chemical reaction at the interface at high temperature, the cladding layer forms a graphene/Si ₃ N ₄ /SiC composite structure, and the excellent thermal stability of Si ₃ N ₄ -SiC, And dispersed distribution, so that the cladding layer has good high temperature resistance. Secondly, graphene (oxygen-free condition) and silicon nitride have high-temperature characteristics, and during the high-temperature annealing process, the reaction between graphene and Si ₃ N ₄ is relatively mild and not violent, and the composite coating layer can maintain a good shape. It will not decompose when annealing is not higher than 1000°C, which greatly improves the stability of the phosphoric acid/graphene/silicon nitride composite coating, and can maintain the magnetic properties and mechanical strength of the magnetic powder core, while avoiding the single phosphoric acid coating. When coating, the formed phosphate insulating layer Al(PO ₃ ) ₃ decomposes to generate Al ₂ O ₃ and P ₂ O ₅ at 600°C, which destroys the stability of the magnetic powder coating layer and reduces the magnetic properties and mechanical properties of the magnetic powder core. strength.

In the phosphoric acid/graphene/silicon nitride composite coating process of the present invention, in the composite coating layer, Si ₃ N ₄ and SiC formed by the reaction and graphene form a variety of heterogeneous layers with a thickness of 0.5 μm to 0.8 μm. The heterogeneous interface is composed of irregular Si ₃ N ₄ and SiC particles uniformly distributed in graphene sheets, including graphene- _{Si 3} N ₄ and graphene-SiC. The interface is the place where the defects are concentrated. When the magnetic powder core is in the electromagnetic field, the unneutralized positive and negative charges start to move and gather at the interface. Once the charges are pinned by the defects, they become a pair of dipoles. When the rotation of the poles cannot keep up with the change of the electromagnetic field, a polarization relaxation phenomenon occurs, which enhances the attenuation ability of the magnetic powder core to electromagnetic waves. On the other hand, graphene, Si ₃ N ₄ , and SiC in the graphene-Si ₃ N ₄ composite cladding layer are cross-distributed to form a large number of conductive micro-networks. When external electromagnetic waves enter the interior of the material, the electromagnetic field induces the formation of conduction current and a large number of displacement micro-currents, resulting in strong conductance loss and converting electromagnetic waves into heat energy. The combined effect of the two makes the magnetic powder core have better electromagnetic wave absorption performance. However, relevant studies have shown that the better the absorbing property of the magnetic powder, the greater the loss.

In the phosphoric acid/graphene/silicon nitride composite coating process of the present invention, silicon nitride possesses lower dielectric constant, dielectric loss and higher resistivity, according to this scheme, namely graphene powder, silicon nitride powder and The mass ratio of phosphoric acid coating is 1:(1~2):(19~25). After coating the FeSiAl magnetic powder, it can block the eddy current path between the magnetic powder particles, which is beneficial to reduce the eddy current loss. Moreover, an appropriate amount of SiC formed at high temperature has good thermal conductivity and insulation, which can act as a heat conduction channel and increase the resistivity of FeSiAl magnetic powder, thereby reducing the problem of FeSiAl magnetic powder core loss and heat generation. In addition, the added graphene has a scaly structure and has good lubricity; under the action of pressure, the added Si ₃ N ₄ decomposes in a small amount on the friction surface to form a thin gas film, thereby reducing the sliding resistance between the friction surfaces. Therefore, the more friction, the smaller the resistance, and it also has good lubricity. Therefore, during compression molding, the dual effects of graphene and silicon nitride enhance the interfacial interaction between the composite cladding layer and FeSiAl magnetic powder, resulting in a tight combination of FeSiAl magnetic powder particles, reducing the gaps in the magnetic powder core, and increasing the density of the magnetic powder core. , thereby increasing the resistivity of the magnetic powder core, and it can be known from P=U2/R that the loss of the magnetic powder core is reduced.

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

(1) The present invention adopts phosphoric acid/graphene/silicon nitride composite coating process, and graphene and Si ₃ N ₄ in the coating layer partially react at the interface to form SiC. At this time, SiC is in a dispersed distribution, which plays a role of dispersion strengthening and improves the mechanical properties of the magnetic powder core.

(2) The present invention adopts phosphoric acid/graphene/silicon nitride composite coating process, at first, forms the core-shell structure with FeSiAl magnetic powder as the core, insulating cladding layer as core-shell; The chemical reaction on the contact surface of ene and silicon nitride can obtain FeSiAl/graphene/Si ₃ N ₄ /SiC composite magnetic powder core with core-shell structure, which improves the high temperature resistance of the magnetic powder core and avoids the poor high temperature resistance of single phosphoric acid coating. The problem.

(3) The present invention adopts the phosphoric acid/graphene/silicon nitride composite coating process to prepare the FeSiAl magnetic powder core. The irregular silicon nitride is covered on the graphene surface, and a thick layer is formed between Si ₃ N ₄ , SiC and graphene. A large number of heterogeneous interfaces with a diameter of 0.5 μm to 0.8 μm and a conductive micro-network improve the wave-absorbing properties of the magnetic powder core and greatly reduce the influence of electromagnetic interference and electromagnetic radiation.

(4) The present invention adopts the phosphoric acid/graphene/silicon nitride composite coating process to form a dense and uniform composite coating layer with good lubricity on the surface of the magnetic powder. During compression molding, due to the good lubricity of the coating layer, The FeSiAl magnetic powder particles are closely combined to increase the density of the magnetic powder core and reduce the loss. At the same time, Si ₃ N ₄ is evenly distributed in the cladding layer, which has high resistivity and reduces eddy current loss, thereby reducing the loss of the magnetic powder core.

Description of drawings

Fig. 1 is the X-ray diffraction analysis of the composite powder obtained by graphene and silicon nitride powder of the present invention kept at 850° C. for 1 h under a protective atmosphere. It can be seen from Figure 1 that SiC is formed after 850°C heat preservation for 1h.

Figure 2 shows the electron microscope analysis results of the composite coated magnetic powder core, where (a) is the SEM image, and (b) is the scanning electron microscope cross-sectional view. It can be seen from Figure 2 that a shell structure is formed between the composite cladding layer and the FeSiAl magnetic powder, which uses the FeSiAl magnetic powder as the core, and the graphene-Si ₃ N ₄ composite cladding layer with a thickness of 0.5 μm to 0.8 μm is shell.

Detailed ways

Exemplary embodiments, features and aspects of the present invention will be described below with reference to specific embodiments.

Specifically, the present invention provides a method for preparing a phosphoric acid/graphene/silicon nitride coated sendust magnetic powder core, which comprises the following steps:

S1. Powder making: FeSiAl magnetic powder is prepared by using a high-energy ball mill to prepare FeSiAl powder, and the FeSiAl powder is placed in an inert atmosphere, and annealed at a high temperature of 800 ° C to 900 ° C for 1 to 3 hours;

S2. Phosphoric acid coating: dilute phosphoric acid with absolute ethanol, add the phosphoric acid diluent to the FeSiAl powder obtained in S1 for preliminary surface treatment, and then heat and stir in a constant temperature water bath at 50°C to 70°C until dry;

S3, graphene/silicon nitride coating: uniformly mix graphene powder, silicon nitride powder and FeSiAl magnetic powder coated with S2 phosphoric acid in proportion, add 0.2-0.6wt% binder, and mix uniformly; The homogeneous powder is heated in the range of 70-160°C and continuously stirred until dry;

S4, add lubricant: add lubricant accounting for 0.6-1.0% of powder weight, and mix evenly;

S5, compression molding: the powder is pressed and molded under a press to form a magnetic powder core;

S6. Annealing: In an inert atmosphere, first put the magnetic powder core into a furnace at 750°C to 950°C for annealing, set the holding time to 1 to 2h, and heat up at a rate of 9°C/min, cooling with the furnace.

The protective atmosphere is argon or nitrogen.

The composition of FeSiAl magnetic powder is composed by mass percentage: Si9.0～10.0%, Al5.0～6.0%, and the balance is Fe; the powder particle size distribution is: 5% -150～+200 mesh, 70% -200～ +400 mesh and 25% -400 mesh.

The binder in step S3 is sodium silicate solution.

The lubricant in step S4 is zinc stearate.

The raw material of alloy in the embodiment 1-7 of table 1 constitutes by mass percentage

Example 1:

The FeSiAl powder was prepared by a high-energy ball mill, and the composition was composed by mass percentage: Si9.5%, Al5.8%, and the balance was Fe; the FeSiAl powder was placed in an argon atmosphere, annealed at 850°C for 1.5h, and weighed after annealing. Take 250g of powder, and the particle size distribution of the powder is required to be: 5% of -150～+200 mesh, 70% of -200～+400 mesh and 25% of -400 mesh.

Dilute phosphoric acid with 100ml of absolute ethanol, the amount of phosphoric acid added is 0.75g, accounting 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, and then use a 60°C constant temperature water bath to heat Stir until dry.

After the FeSiAl powder is cooled to room temperature, 1.5 g of zinc stearate as a lubricant is added, accounting for 0.6% of the powder weight; the mixed powder is uniformly mixed with an 80-mesh sieve to obtain a compacted powder.

Composite coating powder compression molding. The pressure is 20.3t/cm2, and the size of the magnetic ring blank is: outer diameter 26.92mm, inner diameter 14.73mm, height 11.18mm.

Place the magnetic powder core in an argon atmosphere heat treatment furnace, keep it at 850°C for 1h, and heat up at a rate of 9°C/min, then cool with the furnace.

Example 2:

The ingredients of this example are shown in Table 1. The FeSiAl powder was prepared by a high-energy ball mill. The FeSiAl powder was placed under an argon atmosphere and annealed at a high temperature of 850°C for 1.5h. After annealing, 250g of the powder was weighed. 150～+200 mesh, 70% of -200～+400 mesh and 25% of -400 mesh.

Dilute phosphoric acid with 100ml of absolute ethanol, the amount of phosphoric acid added is 0.75g, accounting 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, and then use a 60°C constant temperature water bath to heat Stir until dry.

Add 200 mesh graphene powders and silicon nitride powders to the phosphoric acid-coated powder, and the addition amount is 10g each, accounting for 4% of the powder weight, and uniformly mixing; adding 1.5g sodium silicate to the mixed powder, accounting for 4% of the powder weight 0.6%, dilute with deionized water before use; uniformly mix the mixed powder with graphene, silicon nitride and sodium silicate solution, and react for 10 minutes; heat the evenly mixed mixed powder to 85°C, and continue stirring until dry .

After the FeSiAl powder is cooled to room temperature, 1.5 g of zinc stearate as a lubricant is added, accounting for 0.6% of the powder weight; the mixed powder is uniformly mixed with an 80-mesh sieve to obtain a compacted powder.

Composite coating powder compression molding. The pressure is 20.3t/cm2, and the size of the magnetic ring blank is: outer diameter 26.92mm, inner diameter 14.73mm, height 11.18mm.

Place the magnetic powder core in an argon atmosphere heat treatment furnace, keep it at 850°C for 1h, and heat up at a rate of 9°C/min, then cool with the furnace.

Example 3:

The ingredients of this embodiment are shown in Table 1.

The preparation method of this embodiment is the same as that of Example 2.

Example 4:

The ingredients of this embodiment are shown in Table 1.

The preparation method of this embodiment is the same as that of Example 2.

Example 5:

The ingredients of this embodiment are shown in Table 1.

The preparation method of this embodiment is the same as that of Example 2.

Embodiment 6:

The ingredients of this embodiment are shown in Table 1.

The preparation method of this embodiment is the same as that of Example 2.

Embodiment 7:

The ingredients of this example are shown in Table 2. The FeSiAl powder is prepared by a high-energy ball mill. The FeSiAl powder is placed under an argon atmosphere and annealed at a high temperature of 850°C for 1.5h. After annealing, 250g of the powder is weighed, and the particle size distribution of the powder is required: 150～+200 mesh, 70% of -200～+400 mesh and 25% of -400 mesh.

Dilute phosphoric acid with 100ml of absolute ethanol, the amount of phosphoric acid added is 0.75g, accounting 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, and then use a 60°C constant temperature water bath to heat Stir while stirring until dry.

Add 200 mesh MnZn ferrite powder to the phosphoric acid-coated powder, the addition amount is 10g, 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, use Dilute with deionized water; mix the mixed powder added with MnZn ferrite and sodium silicate solution evenly, and react for 10 minutes; heat the evenly mixed mixed powder to 85°C, and continue stirring until dry.

After the FeSiAl powder is cooled to room temperature, 1.5 g of zinc stearate as a lubricant is added, accounting for 0.6% of the powder weight; the mixed powder is uniformly mixed with an 80-mesh sieve to obtain a compacted powder.

Composite coating powder compression molding. The pressure is 20.3t/cm2, and the size of the magnetic ring blank is: outer diameter 26.92mm, inner diameter 14.73mm, height 11.18mm.

Place the magnetic powder core in an argon atmosphere heat treatment furnace, keep it at 850°C for 1h, and heat up at a rate of 9°C/min, then cool with the furnace.

The mechanical properties and magnetic properties of the samples prepared by the present invention are shown in Table 2 below.

Table 2 Mechanical properties and magnetic properties of magnetic powder cores

*Effective absorption bandwidth is the frequency bandwidth with reflectivity less than -10dB.

In the present invention, the mechanical properties of the sendust magnetic powder core are improved through the phosphoric acid/graphene/silicon nitride composite coating process, and the tensile strength after annealing is increased from 221.35MPa to 344.15MPa; only changing the amount of Si ₃ N ₄ Under certain conditions, increasing the addition of Si ₃ N ₄ improves the magnetic properties of FeSiAl magnetic powder, and the magnetic permeability increases to 122H/m; the resistivity of the magnetic powder core increases significantly, and the power loss decreases to 192mW/cm ³ . Enhanced high temperature resistance, the phosphoric acid/graphene/silicon nitride coating will not decompose at a high temperature of 1000°C; the wave absorption performance is improved, and the effective absorption bandwidth with reflectivity less than -10dB is increased to 1.35GHz, obtaining good absorption wave performance.

Finally, it should be noted that the above-described embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; various technical solutions without substantial differences with the concept of the present invention are all within the protection scope of the present invention .

Claims (8)

1. The preparation method of the phosphoric acid/graphene/silicon nitride coated sendust core is characterized by comprising the following steps of:

s1, pulverizing: preparing FeSiAl powder from FeSiAl magnetic powder by adopting a high-energy ball mill, and placing the FeSiAl powder in an inert atmosphere and annealing at a high temperature of 800-900 ℃ for 1-3 h;

s2, phosphoric acid coating: diluting phosphoric acid with absolute ethyl alcohol, adding phosphoric acid diluent into FeSiAl powder obtained in the step S1, and performing primary surface treatment;

s3, graphene/silicon nitride coating: uniformly mixing graphene powder, silicon nitride powder and FeSiAl magnetic powder coated by S2 phosphoric acid according to a proportion, adding a binder, and uniformly mixing; heating the uniformly stirred powder within the range of 70-160 ℃, and continuously stirring until the powder is dried;

s4, adding a lubricant: adding a lubricant, and uniformly mixing;

s5, press forming: pressing and forming the powder under a press to form a magnetic powder core;

s6, annealing: under inert atmosphere, the magnetic powder core is put into a furnace at 750-950 ℃ for annealing, the heat preservation time is set to be 1-2 h, the heating rate is 9 ℃/min, and the magnetic powder core is cooled along with the furnace.

2. The method of manufacturing according to claim 1, characterized in that:

in the step S1, the FeSiAl magnetic powder comprises the following components in percentage by mass: 9.0 to 10.0 percent of Si, 5.0 to 6.0 percent of Al and the balance of Fe; the powder particle size distribution comprises the following components in percentage by mass: 5% of-150- +200 meshes, 70% of-200- +400 meshes and 25% of-400 meshes.

3. The method of manufacturing according to claim 1, characterized in that:

in step S2, the amount of phosphoric acid added was 0.3wt%.

4. A method of preparation according to claim 3, characterized in that:

the surface treatment temperature is 50-70 ℃ and the reaction time is 10-30min.

5. The method of manufacturing according to claim 1, characterized in that:

in the step S3, the purity of the graphene powder is more than 95%, the diameter of a sheet layer is 5-50 mu m, the thickness is 3.4-8 nm, the number of layers is 5-10, and the specific surface area is less than 50m ² /g; the particle size of the silicon nitride powder was 200 mesh.

6. The method of manufacturing according to claim 1, characterized in that:

in the step S3, the mass ratio of the graphene powder to the silicon nitride powder to the FeSiAl powder obtained in the step S1 is 1: (1-2): (19-25).

7. The method of manufacturing according to claim 1, characterized in that:

in the step S3, the binder is sodium silicate solution, and the addition amount of the binder is 0.2-0.6wt% based on the addition amount of sodium silicate.

8. The method of manufacturing according to claim 1, characterized in that:

in the step S4, the lubricant is zinc stearate, and the addition amount is 0.6-1.0% of the weight of the powder.

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