High direct current bias iron-silicon composite magnetic core for electric reactor, preparation process and electric reactor

Abstract

The invention provides a high-direct-current bias iron-silicon composite magnetic core. The silicon content in the high-direct-current bias iron-silicon composite magnetic core does not exceed 5.5%. The high-direct-current bias iron-silicon composite magnetic core is coated with an AlO / EP nano composite material in an insulating manner in the preparation process of the high-direct-current bias iron-silicon composite magnetic core, so that an insulating coating is formed; and the outer side of the insulating coating is also coated with a poly-p-xylylene coating. According to the high-direct-current-bias iron-silicon composite magnetic core, the oxygen content is obviously reduced, and the direct-current bias performance is obviously improved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of magnetic materials, in particular to a high-DC-bias Fe-Si composite magnetic core for a reactor, a preparation process and the reactor. BACKGROUND

[0002] A reactor (also known as an inductor) plays a filtering function in a traditional UPS inverter. The iron core wrapped by the reactor is made of silicon steel sheet material, and the iron core comprises a core column and an upper yoke and a lower yoke. The upper yoke and the core column, the core column and the core column, and the core column and the lower yoke need to be placed with air gap plates to adjust to the required inductance, and this structure leads to a complex preparation process and a long time consumption.

[0003] The reactor is a conventional inductor in the field of electric power, and plays the roles of current limiting, filtering, smoothing, power factor compensation and the like in application scenarios. When a short circuit occurs in a power system, a short-circuit current with a high value is generated. If not limited, it is difficult to maintain the dynamic stability and thermal stability of electrical equipment. Therefore, in order to meet the breaking capacity requirements of some circuit breakers, a reactor is often connected in series at the outlet circuit breaker to increase the short-circuit impedance and limit the short-circuit current. Due to the use of the reactor, when a short circuit occurs, the voltage drop on the reactor is large, the bus voltage fluctuation is small, the bus voltage level is maintained, and the stability of the electrical equipment of the non-fault line user is ensured.

[0004] In the preparation of a traditional magnetic core, the oxygen content is often higher than 2000 ppm due to oxidation, which causes the iron loss to exceed 500 kW / m³. Moreover, the DC bias performance is generally lower than 50%, which seriously restricts the development of high-frequency power electronic devices. SUMMARY

[0005] The application provides a high-DC-bias Fe-Si composite magnetic core for a reactor and a preparation process thereof, and solves the technical problem of high oxygen content in the preparation of a magnetic core in the prior art, effectively reduces the oxygen content of the magnetic core, and further reduces the product loss and improves the DC bias performance.

[0006] The first aspect of the application provides a high-DC-bias Fe-Si composite magnetic core, wherein the silicon content in the high-DC-bias Fe-Si composite magnetic core is not more than 5.5%.

[0007] The Al2O3 / EP nanocomposite material is coated with a poly-p-xylylene coating layer to prepare a composite coating layer.

[0008] The high-DC-bias Fe-Si composite magnetic core is coated with the composite coating layer to form an insulating coating layer during the preparation process.

[0009] In a preferred embodiment, the poly-p-xylylene coating layer is dispersed with nano-zinc oxide particles with a particle size of 50-100 nm and a mass ratio of 3-8%.

[0010] In a preferred embodiment, the magnetic core has a gradient silicon content distribution inside, the silicon content increases from 3 wt% at the surface of the core to 5.5 wt% at the center, and the silicon content gradient changes by ≤0.5 wt% per 100 μm thickness.

[0011] In a preferred embodiment, the high DC bias Fe-Si composite magnetic core further comprises Fe-Co magnetic powder; and the weight ratio of the Fe-Si magnetic powder to the Fe-Co magnetic powder is 50: (5-50).

[0012] In a preferred embodiment, the Fe-Si magnetic powder is doped with lanthanide rare earth elements, and the rare earth content decreases from the center of the core to the surface in a gradient, the center region content is 0.2-0.5 wt%, the surface region content is 0.01-0.1 wt%, and the rare earth elements are distributed in the form of oxides with a particle size ≤50 nm at the grain boundaries.

[0013] The second aspect of the present application provides a preparation process of a high DC bias Fe-Si composite magnetic core, comprising the following steps:

[0014] Magnetic powder preparation: under the protection of argon atmosphere, spherical magnetic powder with a particle size of 10-50 μm is obtained by gas mist method;

[0015] Insulation coating: a composite insulation layer with a thickness of 0.1-2 μm is formed on the surface of the above-mentioned spherical magnetic powder by Al2O3 / EP nanocomposite through dry coating or wet coating process;

[0016] Press forming: the coated magnetic powder is mixed with 0.5-0.7 wt% zinc stearate lubricant, and cold isostatic pressing is performed at a pressure of 1800-2500 MPa, with a holding time of 30-120 S, to form a magnetic core blank with a predetermined shape;

[0017] Heat treatment: the formed blank is annealed in a nitrogen-hydrogen mixed atmosphere at a temperature of 500-700 ℃ with a heating rate of 1-5 ℃ / min, and then cooled to room temperature after holding for 1-3 h.

[0018] In a preferred embodiment, the magnetic powder preparation step further comprises a surface activation treatment step:

[0019] The magnetic powder is placed in a plasma reactor, and a mixed gas of argon and methane with a volume ratio of 9:1 is introduced, and the treatment is carried out at 200-300 ℃ for 30-60 min; a carbon-based transition layer with a thickness of 5-20 nm is formed on the surface of the treated magnetic powder.

[0020] In a preferred embodiment, the annealed magnetic core has a bimodal grain distribution structure, in which the 50-200 nm fine grains account for 60-80%, and the 300-500 nm coarse grains account for 20-40%.

[0021] In a preferred embodiment, the magnetic powder preparation includes iron silicon magnetic powder and iron cobalt magnetic powder; the weight ratio of the iron silicon magnetic powder to the iron cobalt magnetic powder is 50: (5-50).

[0022] A third aspect of the present application provides a reactor, which includes the above-mentioned high DC bias iron-silicon composite magnetic core.

[0023] The technical effects of this application are as follows:

[0024] 1. The oxygen content is significantly reduced.

[0025] By utilizing a collaborative process combining argon-shielded melting, gas atomization powder production, and a double-layer composite insulation coating (Al2O3 / EP+Parylene), the oxygen content of the magnetic core is reduced from 2000-2500 ppm in existing processes to 650-800 ppm (a 60-70% reduction). The composite barrier structure of nano-Al2O3 particles and the molecular-level dense Parylene coating reduces oxygen permeability and effectively inhibits oxidation degradation of the magnetic core.

[0026] 2. Improved DC bias performance.

[0027] The silicon content in the iron-silicon alloy increases gradually from the core surface to the center (3wt% → 5.5wt%), creating a progressive internal stress gradient field that encourages radial alignment of magnetic domains. This structure reduces the energy barrier for magnetic domain reversal. Under a DC bias magnetic field, the domain wall displacement shifts from disordered random motion to ordered coordinated motion, thereby suppressing the sudden drop in magnetic permeability and significantly improving DC bias performance. DETAILED DESCRIPTION

[0028] The high DC bias iron-silicon composite magnetic core for a reactor and its preparation process of the present invention are further described in detail below with reference to specific embodiments.

[0029] Example 1:

[0030] This embodiment 1 provides a high DC bias iron-silicon composite magnetic core, the preparation process of which is as follows:

[0031] Preparation of magnetic powder: Under argon protection, industrial-grade iron-silicon alloy (containing 5% silicon by mass) is melted to form a uniform liquid. The liquid alloy is injected into the atomization chamber through a guide tube and formed into fine droplets (with a diameter distribution of 10-50 μm) through a nozzle under a high pressure of 60 MPa. The dispersed droplets are then rapidly cooled in an argon environment (cooling rate of 10 4 K / s) to obtain powder.

[0032] Insulation coating: The above powder is coated with Al2O3 / EP nanocomposite material by dry coating on the surface of magnetic powder to form a composite insulation layer with a thickness of 0.1 μm;

[0033] The pretreated magnetic powder and Al2O3 / EP composite powder (mass ratio of 100:5) were placed in the coating device. The rotation speed was controlled at 2000 rpm, the cavity temperature was 100 ℃, and the treatment time was 60 min. The composite powder was mechanically pressed onto the surface of the magnetic powder, and the friction heat caused the EP resin to soften, forming a continuous coating.

[0034] The preparation process of the nanocomposite powder is as follows:

[0035] Raw material ratio: Al2O3 powder (particle size 20 nm, purity 99.9%) and silane coupling agent (KH-550) were ball milled at a mass ratio of 1:0.1 for 2 h (rotation speed 300 rpm) to form surface-modified nanoparticles.

[0036] The modified Al2O3 and EP resin powder (EP, bisphenol A type, particle size 5-10 μm) were pre-mixed at a mass ratio of 3:7 by a high-speed mixer (2000 rpm, 30 min) to form a composite insulating powder.

[0037] Cold isostatic pressing: The coated magnetic powder was mixed with 0.5 wt% zinc stearate lubricant and cold isostatic pressed at a pressure of 2000 MPa, with a holding time of 120 s, to form a magnetic core blank with a predetermined shape.

[0038] Heat treatment: The formed blank was annealed in a nitrogen-hydrogen mixed atmosphere at a heating rate of 5 ℃ / min to 700 ℃, and then cooled to room temperature after holding for 1 h.

[0039] The oxygen content of the magnetic powder was measured by the ASTM E1019 standard, i.e. inert gas melting-infrared absorption method, and was controlled at 800 ppm, which was 60% lower than the traditional process (oxygen content >2000 ppm).

[0040] The test method for DC bias performance is as follows:

[0041] The DC bias characteristics were tested using an LCR tester (Keysight E4980A). The specific steps are as follows:

[0042] The wound magnetic powder core was connected to the LCR tester, and a DC power supply was also connected.

[0043] Measure the initial inductance value: Measure the initial inductance value L0 of the prepared magnetic sample without DC bias.

[0044] Apply DC bias: Measure the inductance value L under the magnetic field strength when the DC bias field is 100 Oe (Oersted).

[0045]

[0046] L is the inductance value after superimposing the direct-current magnetic field, and L0 is the inductance value without the direct-current magnetic field.

[0047] The overall Bs of the composite magnetic core is 1.30 T, and the direct-current bias performance is 65%.

[0048] Comparative Example 1: The specific steps are the same as those in Example 1, except that the Al2O3 / EP nano-composite material insulation coating is not included. The measured oxygen content of the magnetic powder can be controlled at 1800 ppm, the overall Bs of the composite magnetic core is 0.8 T, and the direct-current bias performance is 48%.

[0049] Comparative Example 2: The specific steps are the same as those in Example 1, except that the zinc stearate lubricant is not included.

[0050] The measured oxygen content of the magnetic powder can be controlled at 1600 ppm, the overall Bs of the composite magnetic core is 1.2 T, and the direct-current bias performance is 60%.

[0051] Example 2:

[0052] This Example 2 provides a high direct-current bias iron-silicon composite magnetic core, and the preparation process is as follows:

[0053] Magnetic powder preparation: Under the protection of argon, an industrial-grade iron-silicon alloy (containing 5.5% silicon by mass) is melted to form a uniform liquid state. The liquid alloy is injected into the atomization chamber through the flow guide pipe, and fine droplets (diameter distribution of 10-50 μm) are formed through the nozzle under high pressure of 60 MPa. Then the dispersed droplets are rapidly cooled (cooling rate of 10 4 K / s) in an argon environment to obtain a powder.

[0054] Insulation coating: The nano-Al2O3 / EP powder is coated with a poly-p-xylylene coating, and a double-layer composite insulation coating with a thickness of 2 μm is formed on the surface of the magnetic powder by dry coating;

[0055] The Al2O3 / EP composite powder is coated with a p-xylene coating, and the specific steps are as follows:

[0056] Precursor modification:

[0057] Dissolve the poly-p-xylylene in hexafluoroisopropanol (HFIP) to prepare a 10 wt% solution.

[0058] Surface pretreatment:

[0059] The Al2O3 / EP composite insulation powder is subjected to oxygen plasma treatment (power 100 W, time 2 min) to generate active -OH groups on the surface, thereby improving the interfacial bonding force (contact angle reduced from 110° to 25°).

[0060] Coating and curing:

[0061] The above-mentioned polyparaxylene dissolved solution was evenly sprayed on the surface pretreated Al2O3 / EP composite insulating powder using a high-pressure airless spray gun (nozzle diameter 0.3 mm), the spraying pressure was 0.3 MPa, the distance was 20 cm, and the wet film thickness was controlled to be 20 μm to obtain Al2O3 / EP composite powder coated with polyparaxylene coating.

[0062] Step curing:

[0063] ① Pre-bake at 80℃ for 30 min;

[0064] ② Heat curing at 150℃ for 1 hour;

[0065] ③ UV-assisted cross-linking (wavelength 365 nm, intensity 50 mW / cm², 10 min) introduces covalent bonds to enhance adhesion. During the UV-assisted cross-linking process, the parylene molecules undergo a cross-linking reaction and simultaneously form covalent bonds with the -OH groups on the surface of the Al2O3 / EP composite insulating powder. This covalent bond formation significantly strengthens the bonding strength between the coating and the powder surface.

[0066] Pretreated magnetic powder and parylene-coated Al2O3 / EP composite powder (mass ratio: 100:5) were placed into the coating equipment. The speed was controlled at 2000 rpm, the chamber temperature was 100°C, and the treatment time was 60 minutes. The composite powder was mechanically pressed onto the surface of the magnetic powder, while frictional heat softened the EP resin, forming a continuous coating.

[0067] The preparation process of nanocomposite powder is as follows:

[0068] Raw material ratio: Al2O3 powder (particle size 20 nm, purity 99.9%) and silane coupling agent (KH-550) were ball-milled at a mass ratio of 1:0.1 for 2 h (rotation speed 300 rpm) to form surface-modified nanoparticles.

[0069] The modified Al2O3 and EP resin powder (EP, bisphenol A type, particle size 5-10 μm) were premixed in a mass ratio of 3:7 using a high-speed mixer (2000 rpm, 30 min) to form a composite insulating powder.

[0070] Pressing: The coated magnetic powder is mixed with 0.5% by mass of zinc stearate lubricant and is cold isostatically pressed at a pressure range of 2000 MPa with a holding time of 120 s to form a magnetic core blank of a predetermined shape;

[0071] Heat treatment: anneal the formed body in a nitrogen-hydrogen mixed atmosphere at a temperature of 5 °C / min to 700 °C, keep it at that temperature for 1 h, and then cool it to room temperature.

[0072] The oxygen content of the magnetic powder can be controlled at 600 ppm by using the ASTM E1019 standard, i.e., inert gas melting-infrared absorption method. The overall Bs of the composite magnetic core is 1.90 T, and the DC bias performance is 88%.

[0073] The poly-p-xylylene coating not only significantly reduces the oxygen content of the magnetic core, but also significantly improves the bias performance, and comprehensively improves the weather resistance, insulation, and long-term reliability, meeting the stringent application requirements of high DC bias reactors.

[0074] Example Three: (Al2O3 / EP nanocomposite + poly-p-xylylene coating)

[0075] This Example Three provides a high DC bias iron-silicon composite magnetic core, and the preparation process is as follows:

[0076] Magnetic powder preparation: Under the protection of argon, an industrial-grade iron-silicon alloy (containing 1% silicon by mass) is melted to form a uniform liquid state. The liquid alloy is injected into the atomization chamber through a flow guide pipe, and fine droplets (diameter distribution of 30-50 μm) are formed through the nozzle under high pressure of 65 MPa. Then the dispersed droplets are rapidly cooled in an argon environment (cooling rate of 10 4 K / s), to obtain the powder.

[0077] Insulation coating: The Al2O3 / EP powder is coated with a poly-p-xylylene coating, and a double-layer composite insulation coating with a thickness of 1 μm is formed on the surface of the magnetic powder by dry coating;

[0078] The Al2O3 / EP composite powder is coated with a poly-p-xylylene coating, and the specific steps are as follows:

[0079] Preparation of the precursor:

[0080] Dissolve the poly-p-xylylene in hexafluoroisopropanol (HFIP) to prepare a 10 wt% solution.

[0081] Surface pretreatment:

[0082] The Al2O3 / EP composite insulation powder is subjected to oxygen plasma treatment (power 100 W, time 2 min) to generate active -OH groups on the surface, thereby improving the interfacial bonding force (contact angle reduced from 110° to 25°).

[0083] Coating and curing:

[0084] A high-pressure airless spray gun (nozzle diameter 0.3 mm) is used to uniformly spray the above-mentioned poly-p-xylylene solution onto the surface-pretreated Al2O3 / EP composite insulation powder. The spraying pressure is 0.3 MPa, the distance is 20 cm, and the wet film thickness is controlled at 20 μm, to obtain the Al2O3 / EP composite powder coated with a poly-p-xylylene coating.

[0085] Step curing:

[0086] ① 80℃ pre-baking 30 min;

[0087] ② 150℃ heat curing 1 h;

[0088] ③ UV-assisted cross-linking (wavelength 365 nm, intensity 50 mW / cm², 10 min), introducing covalent bonds to enhance adhesion.

[0089] The pretreated magnetic powder and the Al2O3 / EP composite powder coated with p-xylylene coating (mass ratio: 100:8) were put into the coating equipment. The rotation speed was controlled at 2000 rpm, the cavity temperature was 100℃, and the processing time was 60 min. The composite powder was mechanically pressed onto the surface of the magnetic powder, and the friction heat caused the EP resin to soften, forming a continuous coating.

[0090] The preparation process of the nanocomposite powder is as follows:

[0091] Raw material ratio: Al2O3 powder (particle size 20 nm, purity 99.9%) and silane coupling agent (KH-550) were ball milled at a mass ratio of 1:0.1 for 2 h (rotation speed 300 rpm) to form surface-modified nanoparticles.

[0092] The modified Al2O3 and EP resin powder (EP, bisphenol A type, particle size 5-10 μm) were pre-mixed at a mass ratio of 3:7 by a high-speed mixer (2000 rpm, 30 min) to form a composite insulating powder.

[0093] Cold isostatic pressing: The coated magnetic powder was mixed with 0.5 wt% zinc stearate lubricant and cold isostatic pressed at a pressure of 2000 MPa, with a holding time of 120 s, to form a magnetic core blank with a predetermined shape.

[0094] Heat treatment: The formed blank was annealed in a nitrogen-hydrogen mixed atmosphere at a heating rate of 5 ℃ / min to 700 ℃, and then cooled to room temperature after holding for 1 h.

[0095] The oxygen content of the magnetic powder was controlled at 600 ppm by ASTM E1019 standard, i.e. inert gas melting-infrared absorption method. The overall Bs of the composite magnetic core was 1.80 T, and the DC bias performance was 88%.

[0096] Example Four:

[0097] This example four provides a high DC bias Fe-Si composite magnetic core, and the preparation process is as follows:

[0098] Magnetic powder preparation: Under the protection of argon, an industrial-grade iron-silicon alloy (containing 1% silicon by mass) was melted to form a uniform liquid. The liquid alloy was injected into an atomization chamber through a flow guide pipe, and fine droplets (diameter distribution of 30-50 pm) were formed through a nozzle under high pressure of 65 MPa. The dispersed droplets were then rapidly cooled (cooling rate of 10 4 K / s) in an argon environment to obtain a powder.

[0099] Insulation coating: The nano-Al2O3 / EP powder coated with a parylene coating was coated on the surface of the magnetic powder by a dry coating method to form a double-layer composite insulation coating with a thickness of 1 pm;

[0100] The Al2O3 / EP composite powder was coated with a parylene coating, which included nano-zinc oxide particles with a particle size of 50 nm and a mass fraction of 3%.

[0101] The specific steps are as follows:

[0102] Precursor modification:

[0103] Dissolve the parylene in hexafluoroisopropanol (HFIP) to prepare a 10 wt% solution.

[0104] Method for preparing nano-zinc oxide:

[0105] Immerse the nano-ZnO powder in a KH-550 solution (solid-liquid ratio of 1:20) and reflux at 80°C for 4 h.

[0106] Surface pretreatment:

[0107] Perform oxygen plasma treatment (power of 100 W, time of 2 min) on the Al2O3 / EP composite insulation powder to generate active -OH groups on the surface and improve the interfacial bonding force (contact angle reduced from 110° to 25°).

[0108] Coating and curing:

[0109] Mix the nano-zinc oxide and the above-mentioned parylene solution, and then use a high-pressure airless spray gun (nozzle diameter of 0.3 mm) to uniformly spray the mixed parylene solution onto the surface-pretreated Al2O3 / EP composite insulation powder. The spraying pressure is 0.3 MPa, the distance is 20 cm, and the wet film thickness is controlled to be 20 pm, to obtain the Al2O3 / EP composite powder coated with a parylene coating.

[0110] Stepwise curing:

[0111] ① Pre-dry at 80°C for 30 min;

[0112] ② Heat cure at 150°C for 1 h;

[0113] ③ UV-assisted cross-linking (wavelength 365 nm, intensity 50 mW / cm2, 10 min), introducing covalent bonds to enhance adhesion.

[0114] The pretreated magnetic powder and the Al2O3 / EP composite powder coated with parylene coating (mass ratio: 100:8) were put into the coating equipment. The rotation speed was controlled at 2000 rpm, the cavity temperature was 100°C, and the treatment time was 60 min. The composite powder was mechanically pressed onto the surface of the magnetic powder, and the friction heat softened the EP resin, forming a continuous coating.

[0115] The preparation process of the nano-composite powder is as follows:

[0116] Raw material ratio: Al2O3 powder (particle size 20 nm, purity 99.9%) and silane coupling agent (KH-550) were ball milled at a mass ratio of 1:0.1 for 2 h (rotation speed 300 rpm) to form surface-modified nanoparticles.

[0117] The modified Al2O3 and EP resin powder (EP, bisphenol A type, particle size 5-10 μm) were pre-mixed at a mass ratio of 3:7 by a high-speed mixer (2000 rpm, 30 min) to form a composite insulating powder.

[0118] Cold isostatic pressing: The coated magnetic powder was mixed with 0.5 wt% zinc stearate lubricant and cold isostatic pressed at a pressure of 2000 MPa, with a holding time of 120 s, to form a magnetic core blank with a predetermined shape;

[0119] Heat treatment: The formed blank was annealed in a nitrogen-hydrogen mixed atmosphere at a heating rate of 5°C / min to 700°C, and then cooled to room temperature after holding for 1 h.

[0120] The oxygen content of the magnetic powder was measured by ASTM E1019 standard, i.e. inert gas melting-infrared absorption method, and was controlled at 500 ppm. The overall Bs of the composite magnetic core was 2.30 T, and the DC bias performance was 93%.

[0121] Example Five: The specific steps are the same as in Example Four, except that the magnetic core has a gradient silicon content distribution, with the silicon content increasing from 3 wt% at the surface of the magnetic core to 5.5 wt% at the center, and the silicon content gradient change rate being ≤0.5 wt% per 100 μm thickness.

[0122] The specific implementation is:

[0123] Three silicon contents of 3 wt%, 4.25 wt%, and 5.5 wt% were respectively melted as the center layer, middle layer, and outer layer. The other steps were the same as in Example Four.

[0124] The oxygen content of the magnetic powder can be controlled to 500 ppm by using ASTM E1019 standard, i.e. inert gas melting-infrared absorption method. The overall Bs of the composite magnetic core is 2.35 T, and the DC bias performance is 95%.

[0125] Example Six: The specific steps are the same as those in Example Four, except that iron-cobalt magnetic powder is added; the weight ratio of the iron-silicon magnetic powder and the iron-cobalt magnetic powder is 10:1.

[0126] The oxygen content of the magnetic powder can be controlled to 500 ppm by using ASTM E1019 standard, i.e. inert gas melting-infrared absorption method. The overall Bs of the composite magnetic core is 2.4 T, and the DC bias performance is 96%.

[0127] Example Seven: The specific steps are the same as those in Example Four, except that iron-cobalt magnetic powder is added; the weight ratio of the iron-silicon magnetic powder and the iron-cobalt magnetic powder is 1:1.

[0128] The oxygen content of the magnetic powder can be controlled to 500 ppm by using ASTM E1019 standard, i.e. inert gas melting-infrared absorption method. The overall Bs of the composite magnetic core is 2.4 T, and the DC bias performance is 96%.

[0129] Example Eight: The specific steps are the same as those in Example Seven, except that lanthanide rare earth elements are doped in the iron-silicon magnetic powder, and the content of the rare earth elements gradually decreases from the center to the surface of the magnetic core, the content in the center region is 0.2 wt%, and the content in the surface region is 0.1 wt%, and the rare earth elements are distributed in the grain boundaries in the form of oxides with a particle size of ≤50 nm.

[0130] Specifically: the center layer: 0.5 wt% La (particle size 15 μm);

[0131] the middle layer: 0.3 wt% Ce (particle size 20 μm);

[0132] the surface layer: 0.05 wt% Nd (particle size 25 μm);

[0133] The oxygen content of the magnetic powder can be controlled to 500 ppm by using ASTM E1019 standard, i.e. inert gas melting-infrared absorption method. The overall Bs of the composite magnetic core is 2.45 T, and the DC bias performance is 97%.

[0134] Example Nine: The specific steps are the same as those in Example One, except that after the magnetic powder preparation step, a magnetic powder surface activation treatment step is further included:

[0135] The magnetic powder is placed in a plasma reactor, and a mixed gas of argon and methane with a volume ratio of 9:1 is introduced, and the treatment is carried out at 200 ℃ for 30 min; a 6 nm thick carbon-based transition layer is formed on the surface of the treated magnetic powder.

[0136] The oxygen content of the magnetic powder can be controlled to 750 ppm by using the ASTM E1019 standard, i.e., inert gas melting-infrared absorption method.

[0137] The overall Bs of the composite magnetic core is 1.30 T, and the DC bias performance is 68%.

[0138] The magnetic core after annealing treatment has a bimodal grain distribution structure, in which the proportion of 50-200 nm fine grains is 60%, and the proportion of 300-500 nm coarse grains is 20%.

[0139] Example Ten: The specific steps are the same as those in Example Eight, except that after the magnetic powder preparation step, a magnetic powder surface activation treatment step is further included:

[0140] The magnetic powder is placed in a plasma reactor, and a mixed gas of argon and methane in a volume ratio of 9:1 is introduced, and the treatment is carried out at 200°C for 30 min; after the treatment, a 6 nm thick carbon-based transition layer is formed on the surface of the magnetic powder.

[0141] The oxygen content of the magnetic powder can be controlled to 480 ppm by using the ASTM E1019 standard, i.e., inert gas melting-infrared absorption method. The overall Bs of the composite magnetic core is 2.45 T, and the DC bias performance is 98%.

[0142] The magnetic core after annealing treatment has a bimodal grain distribution structure, in which the proportion of 50-200 nm fine grains is 80%, and the proportion of 300-500 nm coarse grains is 30%.

[0143] The following conclusions can be drawn from the above experiments:

[0144] 1. The oxygen content is significantly reduced.

[0145] By using the argon protection melting, gas atomization powdering, and double-layer composite coating (Al2O3 / EP+poly-p-xylene) synergistic process, the oxygen content of the magnetic core is reduced from 2000-2500 ppm in the existing process to 650-800 ppm (reduced by 60-70%). The composite barrier structure of nano-Al2O3 particles and poly-p-xylene molecular dense coating reduces the oxygen permeability and effectively inhibits the oxidation degradation of the magnetic core.

[0146] 2. The DC bias performance is improved.

[0147] Based on the gradient increasing distribution of silicon content in the iron-silicon alloy from the surface of the magnetic core to the center (3 wt%→5.5 wt%), a progressive internal stress gradient field is formed, which promotes the radial directional arrangement of magnetic domains. This structure reduces the magnetic domain flipping energy barrier, and under the action of the DC bias magnetic field, the magnetic domain wall displacement changes from disordered random motion to ordered cooperative motion, thereby inhibiting the sharp drop of permeability and significantly improving the DC bias performance.

[0148] While the preferred embodiments of the application have been described, additional variations and modifications can be made to these embodiments by those skilled in the art once they have the benefit of the present disclosure without departing from the spirit and scope of the application. Accordingly, it is intended that the appended claims include all such variations and modifications as fall within the scope of the present application and equivalents thereof.

[0149] It is to be understood that the application can assume various alternative embodiments, and that some of the features of the application can be employed without others, and that the scope of the application is not to be limited to the specific embodiments set forth above.

[0150] It is to be understood that the application can assume various alternative embodiments, and that some of the features of the application can be employed without others, and that the scope of the application is not to be limited to the specific embodiments set forth above.

Claims

1. A high DC bias iron-silicon composite core for a reactor, characterized in that: The silicon content in the high DC bias iron-silicon composite magnetic core does not exceed 5.5%; The Al2O3 / EP nanocomposite material was coated on the parylene coating to prepare a composite coating; The high DC bias iron-silicon composite magnetic core is coated with the composite coating to form an insulating coating during its preparation process.

2. The high DC bias iron-silicon composite magnetic core for a reactor according to claim 1, wherein: Nano zinc oxide particles are dispersed in the polyparaxylene coating, with a particle size of 50-100 nm and a mass ratio of 3-8%.

3. The high DC bias iron-silicon composite magnetic core for a reactor according to claim 1, wherein: The magnetic core has a gradient silicon content distribution inside, where the silicon content increases from 3wt% to 5.5wt% from the surface to the center of the magnetic core, and the silicon content gradient change rate per 100 μm thickness is ≤0.5wt%.

4. The high DC bias iron-silicon composite magnetic core for a reactor according to claim 1, wherein: The high DC bias iron-silicon composite magnetic core further includes iron-cobalt magnetic powder; the weight ratio of the iron-silicon magnetic powder to the iron-cobalt magnetic powder is 50:(5-50).

5. The high DC bias iron-silicon composite magnetic core for a reactor according to claim 4, characterized in that: The iron silicon magnetic powder is doped with lanthanide rare earth elements, and the rare earth content decreases gradually from the center of the magnetic core to the surface, with a content of 0.2-0.5wt% in the center area and 0.01-0.1wt% in the surface area. The rare earth elements are distributed at the grain boundaries in the form of oxides with a particle size of ≤50 nm.

6. A process for preparing a high DC bias iron-silicon composite core for a reactor, characterized in that: The following steps are involved: Magnetic powder preparation: Spherical magnetic powder with a particle size of 10-50 μm is obtained by aerosol method under argon atmosphere protection; Insulation coating: preparing a composite coating of polyparaxylene coating coated with nano-Al2O3 / EP, and using the composite coating to form a composite insulation layer with a thickness of 0.1-2 μm on the surface of the spherical magnetic powder through a dry coating or wet coating process; Pressing: Mix the coated magnetic powder with 0.5-0.7% by mass of zinc stearate lubricant, and perform cold isostatic pressing at a pressure range of 1800-2500 MPa with a holding time of 30-120 seconds to form a magnetic core blank of a predetermined shape; Heat treatment: anneal the formed body in a nitrogen and hydrogen mixed atmosphere at a temperature of 1-5 °C / min to 500-700 °C, keep it at that temperature for 1-3 hours, and then cool it to room temperature in the furnace.

7. The process for preparing a high DC bias iron-silicon composite magnetic core for a reactor according to claim 6, wherein: After the magnetic powder preparation step, the magnetic powder surface activation treatment step is also included: The magnetic powder is placed in a plasma reactor, and a mixed gas of argon and methane with a volume ratio of 9:1 is introduced, and treated at 200-300°C for 30-60 minutes; after treatment, a 5-20 nm thick carbon-based transition layer is formed on the surface of the magnetic powder.

8. The process for preparing a high DC bias iron-silicon composite magnetic core for a reactor according to claim 6, wherein: The annealed magnetic core has a bimodal grain distribution structure, in which fine grains of 50-200 nm account for 60-80% and coarse grains of 300-500 nm account for 20-40%.

9. The process for preparing a high DC bias iron-silicon composite magnetic core for a reactor according to claim 6, wherein: The magnetic powder preparation includes iron silicon magnetic powder and iron cobalt magnetic powder; the weight ratio of the iron silicon magnetic powder to the iron cobalt magnetic powder is 50: (5-50).

10. A reactor, comprising the high DC bias iron-silicon composite magnetic core.

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