High direct current biasing ferrosilicon composite magnetic core for electric reactor, preparation process and electric reactor

Abstract

This invention provides a high DC bias iron-silicon composite magnetic core, wherein the silicon content of the high DC bias iron-silicon composite magnetic core does not exceed 5.5%; the high DC bias iron-silicon composite magnetic core is insulatingly coated with Al₂O₃ / EP nanocomposite material during its preparation process to form an insulating coating; the insulating coating is further coated with a parylene coating. The high DC bias iron-silicon composite magnetic core of this application has a significantly reduced oxygen content and a significantly improved DC bias performance.

Description

Technical Field

[0001] This invention relates to the field of magnetic materials technology, and in particular to a high DC bias iron-silicon composite magnetic core for reactors, its preparation process, and the reactor itself. Background Technology

[0002] Reactors (also known as inductors) function as filters in traditional inverters such as UPS systems. The core of a typical reactor is made of silicon steel sheets and consists of a core column, an upper yoke, and a lower yoke. Air gaps are required between the upper yoke and the core column, between the core columns, and between the core column and the lower yoke to adjust the required inductance. This structure makes the manufacturing process complex and time-consuming.

[0003] Reactors are a type of conventional inductor in the power industry, serving functions such as current limiting, filtering, smoothing, and power factor compensation in various applications. When a short circuit occurs in a power system, a high short-circuit current is generated. Without limitation, maintaining the dynamic and thermal stability of electrical equipment becomes difficult. Therefore, to meet the breaking capacity requirements of certain circuit breakers, reactors are often connected in series at the outgoing circuit breakers to increase short-circuit impedance and limit the short-circuit current. Because of the use of reactors, the voltage drop across the reactor is significant during a short circuit, resulting in smaller bus voltage fluctuations, maintaining the bus voltage level, and ensuring the stability of electrical equipment operation for users on non-faulty lines.

[0004] In traditional magnetic core manufacturing, the oxygen content due to oxidation often exceeds 2000 ppm, resulting in iron losses exceeding 500 kW / m³. Furthermore, the DC bias performance is generally below 50%, severely hindering the development of high-frequency power electronic devices. Summary of the Invention

[0005] This application provides a high DC bias iron-silicon composite magnetic core for reactors and its preparation process, which solves the technical problem of high oxygen content in the preparation of magnetic cores in the prior art, effectively reduces the oxygen content of the magnetic core, thereby reducing product loss and improving DC bias performance.

[0006] The first aspect of this application provides a high DC bias iron-silicon composite magnetic core, wherein the silicon content in the high DC bias iron-silicon composite magnetic core does not exceed 5.5%;

[0007] A composite coating was prepared by coating Al2O3 / EP nanocomposite material with a poly(p-xylene) coating.

[0008] The high DC bias iron-silicon composite magnetic core is coated with the above-mentioned composite coating during its preparation process to form an insulating coating.

[0009] In a preferred embodiment, the parylene coating contains dispersed zinc oxide nanoparticles with a particle size of 50-100 nm and a mass percentage of 3-8%.

[0010] In a preferred embodiment, the magnetic core has a gradient silicon content distribution, with the silicon content increasing from 3 wt% to 5.5 wt% from the surface to the center of the magnetic core, and the rate of change of silicon content gradient per 100 μm thickness is ≤0.5 wt%.

[0011] In a preferred embodiment, 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).

[0012] In a preferred embodiment, 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 0.2-0.5 wt% in the central region and 0.01-0.1 wt% in the surface region. The rare earth elements are distributed at the grain boundaries in the form of oxides with a particle size ≤50 nm.

[0013] The second aspect of this application provides a fabrication process for a high DC bias iron-silicon composite magnetic core, comprising the following steps:

[0014] Magnetic powder preparation: Spherical magnetic powder with a particle size of 10-50 μm was obtained by aerosol method under argon atmosphere protection;

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

[0016] Compression molding: The coated magnetic powder is mixed with 0.5-0.7 wt% zinc stearate lubricant and cold isostatically pressed in a pressure range of 1800-2500MPa for a holding time of 30-120 s to form a magnetic core blank of a predetermined shape.

[0017] Heat treatment: The formed preform is annealed in a nitrogen-hydrogen mixed atmosphere, heated to 500-700 ℃ at a rate of 1-5 ℃ / min, held at that temperature for 1-3 h, and then cooled to room temperature in the furnace.

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

[0019] The magnetic powder was placed in a plasma reactor and a mixture of argon and methane at a volume ratio of 9:1 was introduced. The mixture was then treated at 200-300℃ for 30-60 min. After treatment, a 5-20 nm thick carbon-based transition layer was formed on the surface of the magnetic powder.

[0020] In a preferred embodiment, the annealed magnetic core has a bimodal grain distribution structure, wherein 60-80% of the grains are fine (50-200 nm) and 20-40% are coarse (300-500 nm).

[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 this application provides a reactor comprising the aforementioned high DC bias iron-silicon composite magnetic core.

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

[0024] 1. Oxygen content is significantly reduced.

[0025] By employing a synergistic process of argon-protected melting, gas atomization powder production, and a double-layer composite insulating 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 reduction of 60-70%). The composite barrier structure of nano-Al2O3 particles and the dense parylene molecular-level coating reduces oxygen permeability and effectively inhibits the oxidation and degradation of the magnetic core.

[0026] 2. Improved DC bias performance.

[0027] Based on the gradient increase of silicon content from the surface to the center of the magnetic core in the iron-silicon alloy (3wt%→5.5wt%), a progressive internal stress gradient field is formed, which promotes the radial orientation of the magnetic domains. This structure reduces the domain flipping energy barrier. Under the action of a DC bias magnetic field, the domain wall displacement changes from disordered random motion to ordered cooperative motion, thereby suppressing the sudden drop in permeability and significantly improving DC bias performance. Detailed Implementation

[0028] The following detailed description of the high DC bias iron-silicon composite magnetic core for reactors and its fabrication process of the present invention, with reference to specific embodiments, is provided in further detail.

[0029] Example 1:

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

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

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

[0033] Pretreated magnetic powder and Al2O3 / EP composite powder (mass ratio 100:5) were placed into a coating device. The rotation speed was controlled at 2000 rpm, the chamber temperature at 100 ℃, and the processing time at 60 min. The composite powder was mechanically pressed onto the surface of the magnetic powder, while frictional heat softened the EP resin, 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 (300 rpm) to form surface-modified nanoparticles.

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

[0037] Compression molding: The coated magnetic powder is mixed with 0.5 wt% zinc stearate lubricant and cold isostatically pressed at a pressure of 2000 MPa for 120 s to form a magnetic core blank of the predetermined shape.

[0038] Heat treatment: The formed preform is annealed in a nitrogen-hydrogen mixed atmosphere, heated to 700℃ at 5℃ / min, held at that temperature for 1 h, and then cooled to room temperature in the furnace.

[0039] Using the ASTM E1019 standard, specifically the inert gas melting-infrared absorption method, the oxygen content of the magnetic powder can be controlled at 800 ppm, which is 60% lower than that of traditional processes (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 meter (Keysight E4980A). The specific steps are as follows:

[0042] Connect the wound magnetic powder core to the LCR tester and connect it to a DC power supply.

[0043] Measure the initial inductance value: Measure the initial inductance value L0 of the prepared magnetic sample under no DC bias.

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

[0045]

[0046] L is the inductance value after superimposed DC magnetic field, and L0 is the inductance value without DC magnetic field.

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

[0048] Comparative Example 1: The specific steps are the same as in Example 1, except that the Al2O3 / EP nanocomposite 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 DC bias performance is 48%.

[0049] Comparative Example 2: The specific steps are the same as in Example 1, except that 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 DC bias performance is 60%.

[0051] Example 2:

[0052] This second embodiment provides a high DC bias iron-silicon composite magnetic core, the fabrication process of which is as follows:

[0053] Magnetic powder preparation: Under argon protection, industrial-grade iron-silicon alloy (containing 5.5% silicon by mass) is melted to form a homogeneous liquid. The liquid alloy is injected into the atomization chamber through a guide tube and formed into fine droplets (10-50 μm in diameter) through a nozzle under a high pressure of 60 MPa. The dispersed droplets are then rapidly cooled in an argon environment (cooling rate up to 10⁻⁶ m / s). 4 K / s), to obtain powder.

[0054] Insulation coating: Nano-Al2O3 / EP powder is coated with parylene coating, and a 2 μm thick double-layer composite insulation coating is formed on the surface of magnetic powder by dry coating.

[0055] The specific steps for coating Al2O3 / EP composite powder with xylene are as follows:

[0056] Precursor modification:

[0057] Prepare a 10 wt% solution by dissolving parylene in hexafluoroisopropanol (HFIP).

[0058] Surface pretreatment:

[0059] Oxygen plasma treatment (100 W power, 2 min) was applied to Al2O3 / EP composite insulating powder to generate active -OH groups on the surface, thereby improving the interfacial bonding force (the contact angle decreased from 110° to 25°).

[0060] Coating and curing:

[0061] The above-mentioned parylene solution was uniformly sprayed onto the 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, thus obtaining Al2O3 / EP composite powder coated with parylene.

[0062] Stepped curing:

[0063] ① Pre-bake at 80℃ for 30 min;

[0064] ② Heat cure at 150 ℃ for 1 h;

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

[0066] Pretreated magnetic powder and Al2O3 / EP composite powder coated with parylene (mass ratio: 100:5) were fed into a coating equipment. The rotation speed was controlled at 2000 rpm, the chamber temperature at 100 ℃, and the processing time at 60 min. 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 the 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 (300 rpm) to form surface-modified nanoparticles.

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

[0070] Compression molding: The coated magnetic powder is mixed with 0.5% zinc stearate lubricant by mass, and cold isostatically pressed at a pressure of 2000 MPa for 120 seconds to form a magnetic core blank of the predetermined shape.

[0071] Heat treatment: The formed preform is annealed in a nitrogen-hydrogen mixed atmosphere, heated to 700℃ at 5℃ / min, held at that temperature for 1 h, and then cooled to room temperature in the furnace.

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

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

[0074] Example 3: (Al2O3 / EP nanocomposite material + parylene coating)

[0075] This embodiment three provides a high DC bias iron-silicon composite magnetic core, the fabrication process of which is as follows:

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

[0077] Insulation coating: Nano-Al2O3 / EP powder is coated with parylene coating, and a 1 μm thick double-layer composite insulation coating is formed on the surface of magnetic powder by dry coating.

[0078] The specific steps for coating Al2O3 / EP composite powder with xylene are as follows:

[0079] Precursor modification:

[0080] Prepare a 10 wt% solution by dissolving parylene in hexafluoroisopropanol (HFIP).

[0081] Surface pretreatment:

[0082] Oxygen plasma treatment (100 W power, 2 min) was applied to Al2O3 / EP composite insulating powder to generate active -OH groups on the surface, thereby improving the interfacial bonding force (the contact angle decreased from 110° to 25°).

[0083] Coating and curing:

[0084] The above-mentioned parylene solution was uniformly sprayed onto the 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, thus obtaining Al2O3 / EP composite powder coated with parylene.

[0085] Stepped curing:

[0086] ① Pre-bake at 80℃ for 30 minutes;

[0087] ② Heat cure at 150℃ for 1 hour;

[0088] ③ Ultraviolet-assisted crosslinking (wavelength 365 nm, intensity 50 mW / cm², 10 min) introduces covalent bonds to enhance adhesion.

[0089] Pretreated magnetic powder and Al2O3 / EP composite powder coated with parylene (mass ratio: 100:8) were fed into a coating equipment. The rotation speed was controlled at 2000 rpm, the chamber temperature at 100℃, and the processing time at 60 min. The composite powder was mechanically pressed onto the surface of the magnetic powder, while frictional heat softened the EP resin, 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 (300 rpm) to form surface-modified nanoparticles.

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

[0093] Compression molding: The coated magnetic powder is mixed with 0.5 wt% zinc stearate lubricant and cold isostatically pressed at a pressure of 2000 MPa for 120 s to form a magnetic core blank of the predetermined shape.

[0094] Heat treatment: The formed preform is annealed in a nitrogen-hydrogen mixed atmosphere, heated to 700℃ at 5℃ / min, held at that temperature for 1 h, and then cooled to room temperature in the furnace.

[0095] The oxygen content of the magnetic powder, measured using the ASTM E1019 standard (inert gas melting-infrared absorption method), can be controlled at 600 ppm. The overall Bs of the composite magnetic core is 1.80 T, and the DC bias performance is 88%.

[0096] Example 4:

[0097] This embodiment four provides a high DC bias iron-silicon composite magnetic core, the fabrication process of which is as follows:

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

[0099] Insulation coating: Nano-Al2O3 / EP powder coated with parylene is dry coated onto the surface of magnetic powder to form a 1 μm thick double-layer composite insulation coating;

[0100] The p-xylene coating is used to coat Al2O3 / EP composite powder, wherein the p-xylene coating includes nano zinc oxide particles with a particle size of 50 nm and a mass percentage of 3%.

[0101] The specific steps are as follows:

[0102] Precursor modification:

[0103] Prepare a 10 wt% solution by dissolving parylene in hexafluoroisopropanol (HFIP).

[0104] Preparation method of nano zinc oxide:

[0105] The nano-ZnO powder was immersed in KH-550 solution (solid-liquid ratio 1:20) and refluxed at 80 °C for 4 h.

[0106] Surface pretreatment:

[0107] Oxygen plasma treatment (100 W power, 2 min) was applied to Al2O3 / EP composite insulating powder to generate active -OH groups on the surface, thereby improving the interfacial bonding force (the contact angle decreased from 110° to 25°).

[0108] Coating and curing:

[0109] After mixing nano zinc oxide and the above-mentioned parylene solution, the parylene solution was uniformly sprayed onto the 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, thus obtaining Al2O3 / EP composite powder coated with parylene.

[0110] Stepped curing:

[0111] ① Pre-bake at 80℃ for 30 minutes;

[0112] ② Heat cure at 150℃ for 1 hour;

[0113] ③ Ultraviolet-assisted crosslinking (wavelength 365 nm, intensity 50 mW / cm², 10 min) introduces covalent bonds to enhance adhesion.

[0114] Pretreated magnetic powder and Al2O3 / EP composite powder coated with parylene (mass ratio: 100:8) were fed into a coating equipment. The rotation speed was controlled at 2000 rpm, the chamber temperature at 100 ℃, and the processing time at 60 min. The composite powder was mechanically pressed onto the surface of the magnetic powder, while frictional heat softened the EP resin, forming a continuous coating.

[0115] The preparation process of the nanocomposite 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 (300 rpm) to form surface-modified nanoparticles.

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

[0118] Compression molding: The coated magnetic powder is mixed with 0.5 wt% zinc stearate lubricant and cold isostatically pressed at a pressure of 2000 MPa for 120 s to form a magnetic core blank of the predetermined shape.

[0119] Heat treatment: The formed preform is annealed in a nitrogen-hydrogen mixed atmosphere, heated to 700℃ at 5℃ / min, held at that temperature for 1 h, and then cooled to room temperature in the furnace.

[0120] The oxygen content of the magnetic powder, measured using the ASTM E1019 standard (inert gas melting-infrared absorption method), can be controlled within 500 ppm. The overall Bs of the composite magnetic core is 2.30 T, and the DC bias performance is 93%.

[0121] Example 5: The specific steps are the same as in Example 4, except that there is a gradient silicon content distribution inside the magnetic core. The silicon content increases from 3 wt% to 5.5 wt% from the surface of the magnetic core to the center, and the gradient change rate of silicon content per 100 μm thickness is ≤0.5 wt%.

[0122] The specific implementation is as follows:

[0123] Three silicon contents of 3 wt%, 4.25 wt%, and 5.5 wt% were respectively melted to serve as the core layer, intermediate layer, and outer layer. All other steps were the same as in Example 4.

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

[0125] Example 6: The specific steps are the same as in Example 4, except that iron-cobalt magnetic powder is added; the weight ratio of iron-silicon magnetic powder to iron-cobalt magnetic powder is 10:1.

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

[0127] Example 7: The specific steps are the same as in Example 4, except that iron-cobalt magnetic powder is added; the weight ratio of iron-silicon magnetic powder to iron-cobalt magnetic powder is 1:1.

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

[0129] Example 8: The specific steps are the same as in Example 7, except that lanthanide rare earth elements are doped into the iron-silicon magnetic powder, and the rare earth content decreases in a gradient from the center of the magnetic core to the surface, with a content of 0.2 wt% in the central region and 0.1 wt% in the surface region. The rare earth elements are distributed at the grain boundaries in the form of oxides with a particle size ≤50 nm.

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

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

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

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

[0134] Example 9: The specific steps are the same as in Example 1, except that after the magnetic powder preparation step, a magnetic powder surface activation treatment step is also included:

[0135] The magnetic powder was placed in a plasma reactor and a mixture of argon and methane at a volume ratio of 9:1 was introduced. The mixture was then treated at 200 °C for 30 min. After treatment, a 6 nm thick carbon-based transition layer was formed on the surface of the magnetic powder.

[0136] The oxygen content of the magnetic powder, measured using the ASTM E1019 standard (inert gas melting-infrared absorption method), can be controlled at 750 ppm.

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

[0138] The annealed magnetic core has a bimodal grain distribution structure, in which 60% of the grains are fine (50-200 nm) and 20% are coarse (300-500 nm).

[0139] Example 10: The specific steps are the same as in Example 8, except that after the magnetic powder preparation step, a magnetic powder surface activation treatment step is also included:

[0140] The magnetic powder was placed in a plasma reactor and a mixture of argon and methane at a volume ratio of 9:1 was introduced. The mixture was then treated at 200°C for 30 min. After treatment, a 6 nm thick carbon-based transition layer was formed on the surface of the magnetic powder.

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

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

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

[0144] 1. Oxygen content is significantly reduced.

[0145] By employing an argon-protected melting process, gas atomization powder production, and a synergistic process of a double-layer composite 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 reduction of 60-70%). The composite barrier structure of nano-Al2O3 particles and the dense parylene molecular-level coating reduces oxygen permeability and effectively inhibits the oxidation and degradation of the magnetic core.

[0146] 2. Improved DC bias performance.

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

[0148] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0149] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from the scope of the invention.

[0150] The spirit and scope of the invention are as follows: Thus, if these modifications and variations of the invention fall within the scope of the claims of the invention and their equivalents, the invention is also intended to include these modifications and variations.

Claims

1. A high DC bias iron-silicon composite magnetic core for reactors, characterized in that, The silicon content in the high DC bias iron-silicon composite magnetic core does not exceed 5.5%; A composite coating was prepared by coating alumina / EP nanocomposite material with a poly(p-xylene) coating. The high DC bias iron-silicon composite magnetic core is coated with the above-mentioned composite coating during its preparation process to form an insulating coating. The parylene coating contains dispersed zinc oxide nanoparticles with a particle size of 50-100 nm and a mass percentage of 3-8%. The magnetic core has a gradient silicon content distribution, with the silicon content increasing from 3wt% to 5.5wt% from the surface to the center, and the rate of change of silicon content gradient per 100μm thickness is ≤0.5wt%. The high DC bias iron-silicon composite magnetic core also includes iron-cobalt magnetic powder; the weight ratio of iron-silicon magnetic powder to iron-cobalt magnetic powder is 50:(5-50). 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 0.2-0.5 wt% in the central region and 0.01-0.1 wt% in the surface region. The rare earth elements are distributed at the grain boundaries in the form of oxides with a particle size ≤50 nm.

2. A fabrication process for a high DC bias iron-silicon composite magnetic core for reactors as described in claim 1, characterized in that, Includes the following steps: Magnetic powder preparation: Spherical magnetic powder with a particle size of 10-50 μm was obtained by aerosol method under argon atmosphere protection; Insulation coating: Prepare a composite coating of parylene coating on nano-alumina / EP, and form a composite insulating layer with a thickness of 0.1-2μm on the surface of the above spherical magnetic powder by dry coating or wet coating process. Press molding: The coated magnetic powder is mixed with 0.5-0.7% zinc stearate lubricant by mass, and cold isostatically pressed in a pressure range of 1800-2500MPa for 30-120 seconds to form a magnetic core blank of the predetermined shape. Heat treatment: The formed blank is annealed in a nitrogen-hydrogen mixed atmosphere, heated to 500-700 ℃ at 1-5℃ / min, held at the temperature for 1-3h, and then cooled to room temperature in the furnace. Following the magnetic powder preparation step, a magnetic powder surface activation treatment step is also included: The magnetic powder was placed in a plasma reactor and a mixture of argon and methane at a volume ratio of 9:1 was introduced. The mixture was then treated at 200-300℃ for 30-60 min. After treatment, a 5-20 nm thick carbon-based transition layer was formed on the surface of the magnetic powder.

3. The fabrication process of the high DC bias iron-silicon composite magnetic core for reactors as described in claim 2, characterized in that, 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%.

4. The fabrication process of the high DC bias iron-silicon composite magnetic core for reactors as described in claim 2, characterized in that, 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).

5. A reactor comprising the high DC bias iron-silicon composite core for reactors as described in claim 1.

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