CN111584223B - Preparation method of high-resistance flaky soft magnetic powder - Google Patents
Preparation method of high-resistance flaky soft magnetic powder Download PDFInfo
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Abstract
The invention provides a preparation method of high-resistance flaky soft magnetic powder, which comprises the following steps: providing an oxidizing atmosphere by using mixed gas containing oxygen, and keeping the flaky soft magnetic powder at the temperature of between 100 and 250 ℃ for 10 to 60 minutes in a reaction area filled with the mixed gas to perform vapor deposition reaction so as to form an oxide film on the surface of the flaky soft magnetic powder; in the process of carrying out vapor deposition reaction, the flaky soft magnetic powder is kept in a suspension motion state in a reaction area. The flaky soft magnetic powder keeping the suspension motion state can be fully contacted with the oxidizing atmosphere in a dispersion state, so that a complete and uniform oxide film can be formed on the surface of the flaky soft magnetic powder, the reaction condition of the related vapor deposition reaction is mild, the controllability is strong, the thickness of the oxide film can be accurately controlled by controlling the heat treatment process and the oxygen partial pressure, the use of a large amount of reagents is not involved, the operation is simple and convenient, the flaky soft magnetic powder is suitable for large-scale production, and the environment-friendly degree is high.
Description
Technical Field
The invention belongs to the field of magnetic materials, and particularly relates to a preparation method of high-resistance flaky soft magnetic powder.
Background
The soft magnetic composite material is a magnetic component with high saturation magnetic induction intensity, high magnetic permeability and low loss prepared by mixing and molding soft magnetic powder and a small amount of adhesive, and is widely applied to the fields of electric power, electronics, communication, energy and the like. Common product forms of the soft magnetic composite material comprise a magnetic powder core and a wave-absorbing material, and the material comprises iron base (Fe, Fe-Si-Al, Fe-Si-Cr, Fe-Ni-Mo) crystalline state, amorphous state and nanocrystalline. Wherein, the magnetocrystalline anisotropy constant and the magnetostriction coefficient of the Fe-Si-Al series soft magnetic alloy are close to zero, thereby having very beneficial comprehensive magnetic performance. The main advantages of the Fe-Si-Al soft magnetic composite material are that the coercive force is very low and is only 1.6A/m, and therefore, higher magnetic permeability is obtained; due to the addition of alloy elements of silicon and aluminum, the volume resistivity of the alloy is improved, so that the alloy still can obtain lower eddy current loss at high frequency; the reserves of silicon and aluminum are large, and the price is low, so the Fe-Si-Al type soft magnetic composite material has lower cost. The flaky Fe-Si-Al powder prepared by the prior invention patent (CN 105838117B) has super-strong magnetic property, is easy to orient in a magnetic field, and can be used for preparing a high-performance soft magnetic composite material.
Recent rapid development of information and communication technologies has put higher demands on soft magnetic composite materials. The soft magnetic alloy powder is insulated and coated, so that the eddy current loss among particles can be effectively isolated, and the application requirement of the soft magnetic composite material under high frequency is met. In general, the insulating coating can be classified into two major categories, organic coating and inorganic coating, depending on the substance used for the insulating coating.
Organic coating adopts organic substances as insulating layer substances, and the selected organic substances can be divided into thermosetting resin and thermoplastic resin according to the difference of molecular frameworks. However, the organic solvent used for organic coating is easily dissolved in industrial solution, and has the hidden danger of environmental pollution. In addition, because of the poor thermal stability of the resin, decomposition generally occurs at about 200 ℃, so that the soft magnetic composite material cannot be annealed at high temperature in the annealing process after pressing, the internal stress introduced in the pressing process cannot be effectively removed, and the optimization of the magnetic performance of the soft magnetic composite material is limited. Generally, the organic coating layer has weak bonding force with magnetic powder and is not compact, and the organic coating layer is easy to lose efficacy when encountering organic solvent.
The inorganic coating is generally to form a passivation film of aluminum oxide on the surface of the powder by using a strong oxidant such as chromic anhydride and the like aiming at the soft magnetic alloy powder containing Al, thereby improving the surface resistance. The chromic anhydride passivation process relates to the use of heavy metal chromium, which has certain toxicity, serious environmental pollution and great influence on human bodies. In addition, the oxidation property of the chromic anhydride is too strong, the controllability of the reaction is low, while the thickness direction of the flaky powder is generally only from hundreds of nanometers to several micrometers, if the flaky powder is oxidized by the chromic anhydride, the magnetic property is easily greatly reduced due to excessive reaction, and even the flaky powder is possibly completely oxidized.
Furthermore, the conventional organic coating method and inorganic coating method for coating flaky powder generally have the following defects:
(1) the flaky powder has large diameter-thickness ratio and small apparent density, and has serious bridging phenomenon during natural accumulation, poor surface treatment effect on the materials, incomplete coating, non-uniform coating and the like;
(2) the use of a large amount of industrial reagents can increase the powder surface treatment cost;
(3) the preparation method is carried out after the powder is prepared, and comprises the procedures of wetting, mixing, drying and the like, and the preparation method is complex and long in process and is not suitable for large-scale production.
Disclosure of Invention
The invention aims to provide a preparation method of high-resistance flaky soft magnetic powder, which is used for optimizing the oxidation coating effect on the surface of the flaky soft magnetic powder and enabling the flaky soft magnetic powder to have higher resistivity.
According to one aspect of the invention, the preparation method of the high-resistance flaky soft magnetic powder comprises the following steps: providing an oxidizing atmosphere by using mixed gas containing oxygen, and keeping the flaky soft magnetic powder at the temperature of between 100 and 250 ℃ for 10 to 60 minutes in a reaction area filled with the mixed gas to perform vapor deposition reaction so as to form an oxide film on the surface of the flaky soft magnetic powder; in the process of carrying out vapor deposition reaction, the flaky soft magnetic powder is kept in a suspension motion state in a reaction area. Optionally, the oxidizing atmosphere is provided by air.
The flaky soft magnetic powder keeping the suspension motion state can be fully contacted with the oxidizing atmosphere in a dispersion state, so that the oxidation reaction can be uniformly carried out, and the utilization rate of the oxidizing atmosphere is improved. On the other hand, the flaky soft magnetic powder in suspension motion can avoid the stacking of the powder to a great extent, the specific surface area participating in the reaction is increased, the area of the modified surface is increased, the full and uniform adsorption on the surface of the flaky soft magnetic powder is promoted, in addition, the agglomeration of the flaky soft magnetic powder due to heating is avoided, and the flaky soft magnetic powder can keep uniform granularity and smooth surface. The preparation method provided by the invention can coat a complete and uniform oxide film on the surface of the flaky soft magnetic powder, wherein the related vapor deposition reaction has mild reaction conditions and strong controllability, the thickness of the oxide film can be accurately controlled by controlling the heat treatment process and the oxygen partial pressure, the use of a large amount of reagents is not involved, the operation is simple and convenient, the preparation method is suitable for large-scale production, and the preparation method has high environmental friendliness.
Optionally, during the vapor deposition reaction, the flaky soft magnetic powder is kept in a suspension motion state by means of gas flow agitation and/or equipment rotation and/or equipment vibration and/or component stirring and/or magnetic field application. In the method of imparting momentum to the sheet-shaped soft magnetic powder by using the apparatus for providing a reaction region, any apparatus that heats in motion, such as a double cone dryer, a rake dryer, and the like, may be used as the apparatus for providing a reaction region.
Preferably, in the process of carrying out the vapor deposition reaction, the flaky soft magnetic powder is kept in a suspension motion state by applying a magnetic field; the magnetic field intensity of the magnetic field is 0.01T-1.0T. The flaky soft magnetic powder is controlled to move along a certain track through the magnetic field, so that the movement controllability of the flaky soft magnetic powder is improved.
Preferably, at the same time, the magnetic field is a uniform magnetic field.
Preferably, in the process of carrying out vapor deposition reaction, injecting the mixed gas into the reaction region at a certain speed, so that the flaky soft magnetic powder obtains a first initial speed under the acceleration of the mixed gas and enters the magnetic field at the first initial speed; the first initial velocity is at an angle to the magnetic field direction of the magnetic field.
After the mixed gas is accelerated, the flaky soft magnetic powder enters the alternating magnetic field along the direction perpendicular to the magnetic field direction of the magnetic field or at a certain angle with the magnetic field direction of the magnetic field, based on the fact that the magnetic field is a uniform magnetic field, under an ideal state, the flaky soft magnetic powder with the first initial speed direction perpendicular to the magnetic field direction performs uniform circular motion under the action of Lorentz force, the first initial speed direction forms a certain angle with the magnetic field direction, and the flaky soft magnetic powder entering the alternating magnetic field performs uniform-radius spiral motion under the action of the Lorentz force. In practical situations, the radius of the circular or spiral motion of the flaky soft magnetic powder may be changed under the influence of the airflow.
Preferably, the angle formed by the direction of the initial velocity and the gravity action direction of the flaky soft magnetic powder is not less than 90 degrees, and the magnetic field direction of the magnetic field and the gravity action direction of the flaky soft magnetic powder form a certain angle; in the process of carrying out vapor deposition reaction, the flaky soft magnetic powder accelerated by the mixed gas passes through a magnetic field, obtains a second initial speed under the action of gravity and returns to the magnetic field at the second initial speed. .
Preferably, at the same time, the magnetic field direction of the magnetic field is perpendicular to the gravitational action direction of the flaky soft magnetic powder.
The flaky soft magnetic powder entering the magnetic field at a certain angle with the direction of the magnetic field possibly passes through the magnetic field, the flaky soft magnetic powder is under the action of gravity in the whole moving process, and the flaky soft magnetic powder leaving the magnetic field moves towards the magnetic field under the action of the self gravity and enters the magnetic field at a second initial speed by arranging the inlet and outlet positions of the alternating magnetic field. Under an ideal state, the flaky soft magnetic powder with the second initial speed in the speed direction perpendicular to the magnetic field direction performs uniform circular motion under the action of the Lorentz force, and the flaky soft magnetic powder with the second initial speed in the speed direction forming a certain angle with the magnetic field direction performs equal-radius spiral motion under the action of the Lorentz force. In practical situations, the radius of the circular or spiral motion of the flaky soft magnetic powder may be changed under the influence of the airflow. Therefore, the flaky soft magnetic powder is always restricted to reciprocate in the alternating magnetic field.
Alternatively, the mixed gas is injected into the reaction region in a jet motion manner, and the motion direction of the mixed gas when entering the reaction region is opposite to the gravity action direction of the sheet-shaped soft magnetic powder.
Optionally, the mixed gas is injected into the reaction zone in a swirling vortex motion.
Optionally, the magnetic field is an alternating magnetic field.
Preferably, the soft magnetic powder is a flaky Fe-Si-Al series magnetic powder.
The flaky Fe-Si-Al series magnetic powder has the characteristics of good adhesive force, obvious shielding effect, strong light reflection capability and other excellent physical properties, and can be widely applied to different fields, such as coating, printing ink, electromagnetic shielding and the like. After the sheet-shaped Fe-Si-Al alloy magnetic body is subjected to the oxidation coating treatment, Al with high resistivity, lightness, thinness, compactness and high thermal stability can be formed on the surface2O3Oxidation film to make Fe-Si-Al alloy magneticThe resistivity of the body is obviously improved.
Optionally, the composition of the Fe-Si-Al system magnetic powder is, in mass percent: 9.4 to 10.0 weight percent of Si; 5.4 to 6.0 weight percent of Al; the balance being Fe.
Optionally, the Fe-Si-Al series magnetic powder has average particle size of 10 μm-100 μm and loose packed density of 0.3g/cm3–0.8g/cm3The ratio of diameter to thickness is 10-100. The Fe-Si-Al series magnetic powder with the above dimension specification is processed by the preparation method provided by the invention, the original shape and dimension of the alloy magnetic body can be completely maintained, and the material is not damaged because the material has the excellent performance peculiar to the dimension specification. The magnetic powder has average grain size of 10-100 microns, high magnetic permeability, high anisotropy, high color effect, small rotation resistance and easy orientation. The apparent density is 0.3g/cm3–0.8g/cm3The Fe-Si-Al series magnetic powder with the diameter-thickness ratio of 10-100 is obviously flaky, has moderate filling power and higher filling rate, and also has better magnetic property and glossiness.
Alternatively, the Fe-Si-Al system magnetic powder is held at 200 ℃ for 10 minutes to 60 minutes in the reaction zone to perform the vapor deposition reaction. The temperature of 200 ℃ is the optimal oxidation temperature of the Fe-Si-Al series magnetic powder, and the product obtained by carrying out oxidation coating at the temperature has the best magnetic performance. And the thickness of the oxide film can be effectively controlled by controlling the reaction time so as to adapt to different application requirements.
Drawings
Fig. 1 is a schematic view of a furnace structure of an apparatus for manufacturing a high-resistance flaky soft magnetic powder in example 1, in which a dotted line indicates a length orientation of a magnetic induction line, and a dividing line between a first acceleration region, a magnetic field region, and a second acceleration region is only a virtual dividing line to clearly distinguish the regions;
FIG. 2 is a schematic view of the hearth structure of the apparatus for producing a high-resistance flaky soft magnetic powder in example 2, in which the dotted lines indicate the length orientation of the magnetic induction lines;
FIG. 3 is a schematic view of the hearth structure of the apparatus for producing a high-resistance flaky soft magnetic powder in example 3;
FIG. 4 is a schematic view of a furnace structure of an apparatus for manufacturing a high-resistance flaky soft magnetic powder in a comparative example.
Detailed Description
In order to make the technical solutions of the present invention better understood by those skilled in the art, the technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments.
In the following examples, the same batch of the sheet-shaped Fe-Si-Al system magnetic powder was used as the raw material sheet-shaped soft magnetic powder to be coated, and the material characteristics of the batch of the Fe-Si-Al system magnetic powder were as follows:
comprises the following components: 9.4 to 10.0 weight percent of Si, 5.4 to 6.0 weight percent of Al and the balance of Fe;
the average particle size is 55-60 μm;
the apparent density is 0.35g/cm3–0.4g/cm3；
The diameter-thickness ratio is 20-80.
Example 1
In this embodiment, the apparatus for preparing the high-resistance flaky soft magnetic powder is obtained by improving an existing tube furnace, a hearth 1-1 of the apparatus is made of corundum, and is in an elongated hollow cylindrical shape as a whole, the hearth 1-1 is arranged in a direction parallel to a vertical direction (in a direction of gravity applied to an object) along an axial direction of the hearth 1-1, the bottom of the hearth 1-1 is dense, an air tap 1-3 is connected to the bottom of the hearth 1-1, except for a connection part of the air tap 1-3, the bottom of the hearth 1-1 is in a dense structure, the top of the hearth 1-1 is in an open structure communicated with the outside, and a flange 1-4 matched with the open structure covers the top of the hearth 1-1. As shown in figure 1, along the axial direction of a hearth 1-1, from bottom to top, a reaction area in the hearth 1-1 is divided into a first acceleration area 1-11, a magnetic field area 1-12 and a second acceleration area 1-13 which are sequentially communicated, an air outlet of an air nozzle 1-3 is positioned in the first acceleration area 1-11, and in the axial direction of the hearth 1-1, the length and size relations of the three areas are as follows: magnetic field region 1-12 > second acceleration region 1-13 > first acceleration region 1-11. Two parallel metal polar plates 1-2 are arranged around the outer surface of the side wall of the hearth 1-1 corresponding to the reaction area, and the metal polar plates 1-2 are connected with current to generate a uniform magnetic field with the magnetic field direction oriented horizontally between the metal polar plates 1-2.
This embodiment utilizes the air to provide the oxidizing atmosphere, and according to the air cock 1-3 kinds difference that adopt, sets up two sets of processing groups, marks respectively and handles IA group and handle IB group: the air nozzle 1-3 adopted by the processing group IA is a direct injection type air nozzle 1-3, and air passes through the direct injection type air nozzle 1-3 and then is injected into the reaction area along the vertical upward direction; the air nozzle 1-3 adopted by the treatment group IB is a rotational flow type air nozzle 1-3, and air is injected into the reaction area in a rotary vortex motion mode after passing through the rotational flow type air nozzle 1-3.
The oxidation coating reaction steps of the treatment IA group and the treatment IB group are the same, and the specific operation is as follows:
s1, sample introduction, opening of a flange 1-4, placing the flaky soft magnetic powder to be coated into a first acceleration area 1-11 and enabling the flaky soft magnetic powder to be positioned near an air outlet of an air tap 1-3, and then covering the flange 1-4.
S2, enabling the metal polar plate 1-2 to be connected with current, and generating a uniform magnetic field with the magnetic field direction parallel to the horizontal direction and the magnetic field intensity of 0.1T in the magnetic field area 1-12.
S3, ventilating to enable air to be injected into the first acceleration area 1-11 through the air nozzle 1-3 at a certain speed, enabling the air entering the first acceleration area 1-11 to accelerate the flaky soft magnetic powder located in the first acceleration area 1-11, enabling the flaky soft magnetic powder to obtain a first initial speed, enabling the flaky soft magnetic powder with the first initial speed in a vertically upward direction (circular motion in the magnetic field area 1-12) or enabling the speed direction of the first initial speed and the vertically upward direction to form an acute angle (spiral motion in the magnetic field area 1-12) to enter the magnetic field area 1-12; part of flaky soft magnetic powder passes through the magnetic field area 1-12 to reach a second acceleration area 1-13, the flaky soft magnetic powder in the second acceleration area 1-13 tends to move downwards under the action of gravity and reenters the magnetic field area 1-12 at a second initial speed, and the flaky soft magnetic powder with the second initial speed in a vertically downward direction (circular motion in the magnetic field area 1-12) or with an acute angle between the speed direction of the second initial speed and the vertically downward direction (spiral motion in the magnetic field area 1-12) enters the magnetic field area 1-12; thereby, the sheet-like soft magnetic powder can reciprocate in the magnetic field regions 1 to 12.
And S4, starting a heating system of the equipment, raising the temperature in the reaction area to 200 ℃, and preserving the heat for 40 minutes to enable the flaky soft magnetic powder and the air to generate vapor deposition reaction.
And S5, after the reaction is finished, naturally cooling the reaction area.
S6, cutting off the current of the metal polar plate 1-2, and enabling the magnetic field to disappear.
S7, after the reaction area is cooled to the room temperature, finished product sedimentation is completed, and the flange 1-4 is opened to take out the finished product.
Example 2
In the embodiment, the equipment for preparing the high-resistance flaky soft magnetic powder is obtained by improving the existing tube furnace, a hearth 2-1 of the equipment is made of corundum materials and is in an elongated hollow cylindrical shape, an inner cavity of the hollow cylindrical shape is used as a reaction area 2-11, the hearth 2-1 is arranged in a manner that the axial direction of the hearth is parallel to the horizontal direction, two ends of the hearth 2-1 are both open structures communicated with the outside, and two ends of the hearth 2-1 are covered by flanges 2-3 matched with the open structures respectively. As shown in figure 2, two parallel metal polar plates 2-2 are arranged around the side wall of a hearth 2-1 corresponding to a reaction area 2-11, alternating current is connected into the metal polar plates 2-2 to generate an alternating magnetic field with uniform spatial distribution and periodically changing size along with time among the metal polar plates 2-2, and the alternating magnetic field is a uniform magnetic field with the magnetic field direction parallel to the vertical direction at the same moment.
This example utilizes air to provide an oxidizing atmosphere and sets up a set of treatment groups, labeled treatment group ii. The specific operation of treatment group II was as follows:
s1, sample introduction, opening of a flange 2-3, placing the flaky soft magnetic powder to be coated into a reaction area 2-11 and enabling the flaky soft magnetic powder to be positioned near an air outlet of an air tap, and then covering of the flange 2-3.
S2, enabling the metal polar plate 2-2 to be connected with alternating current, generating an alternating magnetic field with a magnetic field direction being vertically upward or vertically downward in a magnetic field area, wherein at the same moment, the magnetic field intensity of the alternating magnetic field is 0.1T, and the flaky soft magnetic powder body reciprocates in the vertical direction along with the change of the magnetic field direction.
And S3, starting a heating system of the equipment, raising the temperature in the reaction area 2-11 to 200 ℃, and keeping the temperature for 40 minutes to enable the flaky soft magnetic powder and air to generate vapor deposition reaction.
And S4, after the reaction is finished, naturally cooling the reaction area 2-11.
S5, cutting off the current of the metal polar plate 2-2, and enabling the magnetic field to disappear.
S6, after the reaction area 2-11 is cooled to the room temperature, finished product sedimentation is completed, and the flange 2-3 is opened to take out the finished product.
Example 3
In the embodiment, the equipment for preparing the high-resistance flaky soft magnetic powder is obtained by improving the existing tube furnace, a hearth 3-1 of the equipment is made of corundum materials and is in an elongated hollow cylindrical shape, an inner cavity of the hollow cylindrical shape is used as a reaction area 3-11, the hearth 3-1 is arranged in a manner that the axial direction of the hearth is parallel to the horizontal direction, two ends of the hearth 3-1 are both open structures communicated with the outside, and two ends of the hearth 3-1 are covered by flanges 3-3 matched with the open structures respectively. As shown in figure 3, a spiral stirring paddle 3-2 extending into the reaction area 3-11 is also arranged at one end of the hearth 3-1, and the rotating shaft of the spiral stirring paddle 3-2 is electrically connected with a rotation driving device positioned outside the hearth 3-1.
This example uses air to provide an oxidizing atmosphere and sets up a set of treatment groups, labeled treatment group iii. The specific operation for group III treatment is as follows:
s1, sample introduction, opening of a flange 3-3, placing the flaky soft magnetic powder to be coated into a reaction area 3-11 and enabling the flaky soft magnetic powder to be positioned near an air outlet of an air tap, and then covering the flange 3-3.
And S2, starting the rotation driving device to drive the spiral stirring paddle 3-2 to rotate, wherein the part of the spiral stirring paddle 3-2, which is positioned in the reaction area 3-11, stirs the flaky soft magnetic powder, so that the flaky soft magnetic powder is fully stirred.
And S3, starting a heating system of the equipment, raising the temperature in the reaction area 3-11 to 200 ℃, and keeping the temperature for 40 minutes to enable the flaky soft magnetic powder and air to generate vapor deposition reaction.
And S4, after the reaction is finished, naturally cooling the reaction area 3-11.
And S5, closing the rotation driving device, and stopping rotation of the spiral stirring paddle 3-2.
S6, after the reaction area 3-11 is cooled to the room temperature, finished product sedimentation is completed, the flange 3-3 is opened, and the finished product is taken out.
Comparative examples
In this embodiment, the apparatus for preparing the high-resistance sheet-like soft magnetic powder is an existing tube furnace, a hearth 4-1 of the apparatus is made of corundum, as shown in fig. 4, the whole hearth 4-1 is in an elongated hollow cylindrical shape, an inner cavity of the hollow cylindrical shape is used as a reaction region 4-11, the hearth 4-1 is arranged in parallel to a horizontal direction according to an axial direction of the hearth 4-1, two ends of the hearth 4-1 are both open structures communicated with the outside, and two ends of the hearth 4-1 are covered with flanges 4-2 matched with the open structures respectively.
This example uses air to provide an oxidizing atmosphere and sets up a set of control treatment groups, labeled control I.
The specific operation of control group I was as follows:
s1, sampling, opening a flange 4-2, placing the flaky soft magnetic powder to be coated into a reaction area 4-11 and enabling the flaky soft magnetic powder to be positioned near an air outlet of an air tap, and then covering the flange 4-2.
S2, starting a heating system of the equipment, raising the temperature in the reaction area 4-11 to 200 ℃, and keeping the temperature for 40 minutes to enable the flaky soft magnetic powder and air to generate vapor deposition reaction.
And S3, after the reaction is finished, naturally cooling the reaction area 4-11.
S4, after the reaction area 4-11 is cooled to the room temperature, finished product sedimentation is completed, and the flange 4-2 is opened to take out the finished product.
Example 4
In this example, four treatment groups were set up to investigate the influence of the reaction temperature on the oxidation-coated flaky soft magnetic powder, with the treatment group ib in example 1 as a reference and the reaction temperature of the vapor deposition reaction as a variable. The four groups of contrast treatment groups constructed in this example are respectively labeled as a treatment group iva, a treatment group ivb, a treatment group ivc, and a treatment group ivd, and the vapor deposition reaction temperatures corresponding to the groups are respectively: group IVA was treated at 100 ℃; treating group IVB at 150 deg.C; group IVC was treated at 225 ℃; group IVD was treated at 250 ℃. All steps and parameters during the specific operations of treatment group IVA, treatment group IVB, treatment group IVC and treatment group IVD, except for the variables set forth in this example, were strictly consistent with treatment group IB in example 1.
Example 5
In this example, five treatment groups were set up to investigate the influence of the reaction time on the oxidation-coated flaky soft magnetic powder, with the treatment group ib in example 1 as a reference and the reaction time of the vapor deposition reaction as a variable. The four comparative processing groups constructed in this example are labeled processing group va, processing group vb, processing group vc, processing group vd, and processing group ve, respectively, and the vapor deposition reaction times for each group are: treatment group VA for 10 minutes; treatment of group VB for 20 minutes; treatment of group V C for 30 minutes; treatment of group VD for 50 minutes; treat group VE for 60 minutes. All steps and parameters in the specific operations for treatment group VA, treatment group VB, treatment group VC, treatment group VD and treatment group VE were strictly identical to those for treatment group IB in example 1, except for the variables set forth in this example.
Test example
(I) Performance testing and sample characterization
The magnetic paste was prepared by mixing the finished products obtained in each of examples and comparative examples with a binder solution containing polyurethane as a main component. The filling ratio of the magnetic particles in the paste was 85 wt%. Coating the magnetic body paste on a PET substrate to be 100 mu m thick, and then pressurizing, heating and curing for 10 minutes at 150 ℃ in a flat vulcanizing machine to obtain a wave-absorbing sheet with the thickness of 50 mu m as a test sample.
The Q value of the quality factor of the test sample was measured as the magnetic properties of the finished product, and the Q value was measured using an Agilent E4991A radio frequency impedance/material analyzer manufactured by Agilent Technology corporation, and HP16454A was used as a fixing device. In the data table, the Q value of the finished product obtained from the example raw material sheet-like Fe-Si-Al system magnetic powder is expressed in terms of 100, and the Q values of the other examples and comparative examples are expressed in terms of ratios to the Q value of the example.
As a measurement of the resistivity of the finished product, the surface resistance (IR) of the test sample was measured in such a manner that both terminals were brought into contact with the front and back surfaces of the sheet having a thickness of 100 μm or less. For IR measurement, HIGH RESISTANCE METER4339B manufactured by Agilent Technology was used.
The thickness of the oxide film on the surface of the finished product was measured by auger electron spectroscopy. For the measurement, SAM680 type Auger manufactured by ULVAC-PHI was used. The number of flat magnetic particles for measuring the thickness of the oxygen film was 5 per magnetic sheet, and the average thickness was calculated.
Influence of (II) disturbance mode on oxidation coating effect
Compared with a finished sheet directly made of the flaky Fe-Si-Al series magnetic powder, the Q value and the resistivity of the finished product made in each embodiment are obviously improved after oxidation coating. By comparing the finished products obtained by the treatment groups in examples 1 to 3 with the finished products obtained by the comparative treatment group in the comparative example, it can be proved that the raw material flaky soft magnetic powder can keep a suspension motion state in the process of carrying out vapor deposition, and the effect of oxidation coating can be effectively improved. In examples 1 to 3, the raw material sheet-like soft magnetic powder was effectively dispersed during the vapor deposition reaction to increase the contact area with the oxidizing atmosphere, and repeated stirring allowed the sheet-like soft magnetic powder to contact the oxidizing atmosphere multiple times, and finally allowed the sheet-like soft magnetic powder to sufficiently react with the oxygen atmosphere to form a uniform and dense oxide film on the surface of the sheet-like soft magnetic powder. Compared with various disturbance modes, the controllability of stirring (processing III groups) of the traditional equipment is poor, and the flaky soft magnetic powder can collide the inner wall of the hearth for many times, so that adverse effects are brought to the reaction. In the embodiment of disturbing the powder by applying the magnetic field (processing IA group, processing IB group and processing II group), the controllability of the motion trail of the flaky soft magnetic powder is stronger, and the invalid collision between the flaky soft magnetic powder and the inner wall of the hearth can be reduced by controlling the direction of the magnetic field or the intensity of the magnetic field. Among the various treatment groups, the oxidation coating effect corresponding to the treatment group IB was the best.
TABLE 1 Effect of perturbation mode on oxidative coating Effect
(III) influence of reaction temperature on Oxidation coating Effect
With the increase of the reaction temperature, the thickness of the oxide film and the IR both tend to increase, the Q value tends to increase and then decrease, and when the reaction temperature is 200 ℃, the Q value corresponding to the finished product of the oxidation coating is the highest. Because the reaction temperature is relatively low and the reaction conditions are relatively mild, the oxide films on the surfaces of finished products prepared by treating the group I B, the group IVA, the group IVB, the group IVC and the group IVD are relatively uniform.
TABLE 2 influence of reaction temperature on the effect of oxidative coating
| Kind of sample | Reaction temperature | Thickness of oxide film | Q value | IR(Ω) |
| Treatment of IVA compositions | 100℃ | 3.8nm | 108.4 | 7.47E+05 |
| Treatment of IVB compositions | 150℃ | 5.3nm | 125.2 | 1.01E+06 |
| Processing IB compositions | 200℃ | 7.8nm | 149.4 | 1.26E+06 |
| Treatment of IVC compositions | 225℃ | 8.9nm | 117.2 | 1.36E+06 |
| Treatment of IV D compositions | 250℃ | 10.2nm | 105.2 | 1.48E+06 |
(IV) Effect of reaction time on Oxidation coating Effect
As the reaction time is prolonged, the thickness of the oxide film, the Q value and the IR value all tend to increase, so that after the optimal reaction temperature is determined, the reaction time is adjusted, and the high-resistance flaky soft magnetic powder material with the required thickness, Q value or IR can be obtained.
TABLE 3 Effect of reaction time on oxidative coating Effect
Although the present invention has been described in detail with reference to the preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the true spirit and scope of the present invention.
Claims (7)
1. A preparation method of high-resistance flaky soft magnetic powder is characterized by comprising the following steps:
providing an oxidizing atmosphere by using mixed gas containing oxygen, and keeping the temperature of the flaky soft magnetic powder at 100-250 ℃ for 10-60 minutes in a reaction area filled with the mixed gas to perform vapor deposition reaction so as to form an oxide film on the surface of the flaky soft magnetic powder; the method comprises the steps of carrying out the vapor deposition reaction, enabling the flaky soft magnetic powder to be in a state of keeping suspension motion in a reaction area by applying a magnetic field, injecting mixed gas into the reaction area at a certain speed, enabling the flaky soft magnetic powder to obtain a first initial speed under acceleration of the mixed gas, and enabling the flaky soft magnetic powder to enter the magnetic field at the first initial speed, wherein the magnetic field is a uniform magnetic field, the magnetic field strength of the uniform magnetic field is 0.01T-1.0T, and the first initial speed and the magnetic field direction of the magnetic field form a certain angle.
2. The method for preparing high-resistance flaky soft magnetic powder according to claim 1, characterized in that:
the angle formed by the direction of the first initial speed and the gravity action direction of the flaky soft magnetic powder is not less than 90 degrees, and the magnetic field direction of the magnetic field and the gravity action direction of the flaky soft magnetic powder form a certain angle;
in the process of carrying out the vapor deposition reaction, the flaky soft magnetic powder accelerated by the mixed gas passes through the magnetic field, obtains a second initial speed under the action of gravity and returns to the magnetic field at the second initial speed.
3. The method for preparing high-resistance flaky soft magnetic powder according to claim 2, characterized in that: at the same moment, the magnetic field direction of the magnetic field is perpendicular to the gravity action direction of the flaky soft magnetic powder.
4. The method for preparing a high-resistance flaky soft magnetic powder according to any one of claims 1 to 3, characterized in that: and the mixed gas is injected into the reaction area in a jet motion mode, and the motion direction of the mixed gas when entering the reaction area is opposite to the gravity action direction of the flaky soft magnetic powder.
5. The method for preparing a high-resistance flaky soft magnetic powder according to any one of claims 1 to 3, characterized in that: the mixed gas is injected into the reaction zone in a swirling vortex motion.
6. The method for preparing high-resistance flaky soft magnetic powder according to claim 1, characterized in that: the magnetic field is an alternating magnetic field.
7. The method for preparing high-resistance flaky soft magnetic powder according to claim 1, characterized in that: the flaky soft magnetic powder is Fe-Si-Al soft magnetic alloy.
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