Method for preparing nitride insulating layer soft magnetic powder through ball milling in ammonia atmosphere and application of method

Abstract

The invention relates to a method for preparing nitride insulating layer soft magnetic powder through ball milling in an ammonia atmosphere and application of the method, and provides the method for preparing nitride insulating layer soft magnetic powder through ball milling in the ammonia atmosphere in order to meet the high-end requirement of the ai field for an integrated inductor and the defects of an existing process, and the nitride insulating layer soft magnetic powder is obtained through the synergistic effect of the mechanochemical effect, the ammonia atmosphere and precise temperature control. Uniform in-situ coating of a nitride insulating layer on the surface of soft magnetic powder (iron-nickel powder, carbonyl iron powder, iron-silicon-aluminum powder and the like) is achieved, the insulation uniformity, the magnetic conductivity stability under 1MHz, the 100Oe direct current bias performance and the high temperature resistance of the magnetic core are improved, and the high-frequency, high-power and miniaturized development tendency of ai equipment is adapted.

Description

Technical Field

[0001] This invention relates to the field of soft magnetic material preparation technology for integrated inductors, specifically to a modification method for uniformly coating soft magnetic powder (including iron-nickel powder, carbonyl iron powder, iron-silicon-aluminum powder, etc.) with an in-situ nitride insulating layer using an ammonia atmosphere ball milling process. Background Technology

[0002] With the rapid popularization of artificial intelligence (AI) technology in fields such as AI chips, servers, and terminal devices, AI integrated inductors, as core energy conversion components, face stringent requirements of "high frequency, miniaturization, and high power density": they need to have characteristics such as ultra-high permeability, extremely low eddy current loss, high temperature resistance, uniform and stable insulation performance, and adaptability to mass production, which directly affects the computing speed, energy consumption control, and operational reliability of AI devices.

[0003] Currently, the mainstream core material used in AI integrated inductors is soft magnetic powder (including iron-nickel powder, carbonyl iron powder, iron-silicon-aluminum powder, etc.). Its surface insulation treatment is the core link that determines the performance of the inductor, but the existing coating process has significant bottlenecks and cannot meet the high-end needs of the AI ​​field.

[0004] Resin coating process: Applicable to various soft magnetic powders, but the insulation layer has extremely poor uniformity (thickness deviation ≥20%) and poor thermal stability. Under long-term high-temperature and high-frequency operation of AI integrated inductors, it is very easy to cause insulation layer failure and a sharp increase in core loss, which seriously affects the operational stability of AI devices. Oxide coating process: For soft magnetic powders with high activity such as carbonyl iron powder and iron-silicon-aluminum powder, the bonding force between the coating layer and the matrix is ​​weaker, which easily leads to local exposure, pinhole defects, and uneven dielectric properties. It cannot meet the requirements of low loss and performance consistency in high-frequency (above 0.5MHz) and high-power scenarios of AI devices. Traditional nitride coating methods (such as high-temperature nitriding and ammonolysis): Require additional high-temperature equipment, have high energy consumption and long process, and have poor adaptability to different types of soft magnetic powders such as iron-nickel powder, carbonyl iron powder, and iron-silicon-aluminum powder. The nitride layer generally has problems such as high generation temperature, agglomeration coating, and uneven thickness, making it difficult to achieve the mass production requirement of "one process adapting to multiple types of soft magnetic powders".

[0005] Therefore, developing a low-cost, high-efficiency, and compatible uniform nitride insulation coating technology for various soft magnetic powders such as iron-nickel powder, carbonyl iron powder, and iron-silicon-aluminum powder is crucial for overcoming the performance bottleneck of AI integrated inductors and supporting technological upgrades in the AI ​​field. Summary of the Invention

[0006] To address the high-end demands for integrated inductors in the AI ​​field and the shortcomings of existing processes, this invention provides a ball milling method in an ammonia atmosphere. Through the synergistic effect of mechanochemical effects, ammonia atmosphere, and precise temperature control, a uniform in-situ coating of nitride insulating layer on the surface of soft magnetic powder (iron-nickel powder, carbonyl iron powder, iron-silicon-aluminum powder, etc.) is achieved, improving the insulation uniformity of the magnetic core, the permeability stability at 1MHz, the DC bias performance at 100Oe, and the high-temperature resistance performance, thus adapting to the development trend of high frequency, high power, and miniaturization in AI devices.

[0007] This invention provides a method for preparing nitride insulating layer soft magnetic powder, the preparation method comprising the following steps: (1) Raw material pretreatment: Select soft magnetic powder (including iron-nickel powder, carbonyl iron powder, iron-silicon-aluminum powder, etc.), wherein: Iron-nickel powder: Fe content 70-90 wt.%, Ni content 10-30 wt.%; Carbonyl iron powder: purity ≥ 99.5%, carbon content ≤ 0.05 wt.%; Iron-silicon-aluminum powder: Fe-Si-Al alloy, Si content 5-10 wt.%, Al content 3-8 wt.%; All soft magnetic powders have a particle size D50 of 500-20000nm and are vacuum dried (80-120℃, 2-4h) to remove surface adsorbed water and ensure powder dispersibility. (2) Preparation of ball milling equipment: A planetary ball mill equipped with a built-in temperature control module is used (temperature control accuracy ±5℃, temperature control range 100-300℃). The ball mill jar is made of silicon nitride (to avoid contaminating the powder). The ball milling media is silicon nitride balls (particle size 3-10mm). The ball-to-material ratio is 5:1-15:1 (to ensure that the powder is fully activated by mechanical force, rather than crushed). (3) Ammonia atmosphere construction: The pretreated soft magnetic powder is loaded into a ball mill jar, sealed and evacuated to a pressure ≤10Pa. High-purity ammonia (purity ≥99.99%) is introduced and the ammonia pressure in the jar is controlled at 0.1-0.6MPa and the ammonia flow rate is 10-100mL / min. The gas is continuously ventilated to maintain a uniform atmosphere and ensure that the ammonia is in full contact with each powder particle. (4) Mechanochemical uniform coating ball milling: Set the ball mill temperature control temperature to 100-300℃, the rotation speed to 200-500r / min, and the ball milling time to 1-10 days; maintain a stable reaction temperature through the temperature control module, and activate the soft magnetic powder surface atoms with the gentle mechanical energy generated by the collision of the media balls (without destroying the particle size structure of the powder), so that ammonia molecules are uniformly chemically adsorbed on the powder surface and react efficiently, and generate a continuous and dense nitride insulating layer in situ (Fe4N for iron-based soft magnetic powder, Ni3N for nickel-based components, and aluminum-silicon components do not participate in the nitriding reaction, but only form surface passivation auxiliary insulation), to achieve "atomic-level uniform coating"; (5) Post-processing: After ball milling, stop the gas supply and temperature control. After the equipment cools down to room temperature, introduce an inert gas (argon or nitrogen) to replace the residual ammonia. Collect the product to obtain soft magnetic powder uniformly coated with nitride.

[0008] Further optimization of key process parameters: (1) Temperature control parameters: preferably 150-250℃, to adapt to the differences in surface activity of different soft magnetic powders, promote reaction uniformity, and avoid incomplete reaction caused by low temperature or powder agglomeration caused by high temperature. (2) The ball-to-powder ratio is preferably 8:1-12:1, and the rotation speed is preferably 300-400 r / min: to ensure that mechanical energy and thermal energy are transferred to the surface of various soft magnetic powders in a coordinated manner, to activate atoms while avoiding powder agglomeration or breakage, and to ensure uniform coating. (3) The ammonia pressure is preferably 0.2-0.4MPa and the flow rate is preferably 30-60mL / min: to maintain a uniform ammonia concentration in the tank, improve reaction efficiency in combination with temperature conditions, and avoid incomplete local coating or accumulation of nitrides. (4) The ball milling time is preferably 3-7 days (72-168h): to ensure that the thickness of the insulating layer on the surface of various soft magnetic powders reaches 5-50nm (10-30nm is optimal) and the thickness deviation is ≤±5%, so as to achieve uniform coverage of the entire powder surface without dead corners.

[0009] Among them, temperature and time are optimized in synergy: at high temperatures (250-300℃), the time can be shortened to 3-5 days, and at low temperatures (100-150℃), the time can be extended to 5-7 days, balancing production efficiency and coating quality.

[0010] Application of the nitride insulating layer soft magnetic powder of this invention in integrated inductors: The soft magnetic powder (iron-nickel powder, carbonyl iron powder, iron-silicon-aluminum powder, etc.) uniformly coated with the above-mentioned nitrides is mixed with silicone resin (5-10% by mass), pressed into magnetic rings by a mold (pressing pressure 1000-1800MPa), and sintered at 400-500℃ for 0.5-2h. This magnetic ring has the following advantages: (1) Excellent insulation uniformity: The volume resistivity deviation of different regions of the magnetic ring is ≤±30%, and the insulation withstand voltage performance is stable, which is suitable for the high-frequency working requirements of AI equipment. (2) Stable permeability: The permeability is 50 to 100 at 1MHz and 50mT. The permeability deviation of the same batch of magnetic rings is ≤±5%, ensuring the consistency of the inductor energy conversion efficiency. (3) Excellent DC bias performance: Under a 100Oe bias magnetic field, the permeability retention rate is ≥50%, supporting the high power density design of AI integrated inductors; (4) The working temperature range is widened to -50℃~400℃. It maintains insulation uniformity and magnetic stability at high temperatures, meeting the requirements of extreme working conditions such as AI servers and vehicle AI driving systems.

[0011] The core characteristic of the nitride insulating layer soft magnetic powder of this invention is that a continuous, dense, and uniform nitride composite insulating layer is formed on the surface of various modified soft magnetic powders, wherein: (1) Insulation layer characteristics: thickness 5-50nm, thickness uniformity deviation ≤±5%, no local exposure, pinholes or accumulation defects, and adaptable to the matrix structure of different soft magnetic powders; (2) Insulation performance: Volume resistivity ≥10 10 Ω・m, and the resistivity deviation of different areas of the same batch of powder is ≤±8% (excellent uniformity). (3) Magnetic properties: Under the conditions of 1MHz and 50mT, the magnetic permeability is ≥50 (iron-nickel powder ≥90, carbonyl iron powder ≥50, iron-silicon-aluminum powder ≥80), and the magnetic permeability deviation of the same batch of powder is ≤±3% (due to uniform coating leading to stable performance). (4) DC bias performance: Under a bias magnetic field of 100Oe, the permeability retention rate is ≥50% (iron-nickel powder ≥65%, carbonyl iron powder ≥70%, iron-silicon-aluminum powder ≥50%). (5) High-frequency loss (1MHz, 50mT): ≤1500mW / cm³.

[0012] The beneficial effects of this invention are: The innovative achievement of "one process adapting to multiple types of soft magnetic powders + precise temperature control": The addition of a 100-300℃ temperature control device, through the synergistic effect of temperature and mechanical force, can uniformly coat commonly used soft magnetic powders for AI integrated inductors, such as iron-nickel powder, carbonyl iron powder, and iron-silicon-aluminum powder, with an insulation layer thickness deviation of ≤±10%, solves the core defects of traditional processes that require separate formula adjustments for different soft magnetic powders and have poor uniformity. The nitride insulating layer bonds more tightly with various soft magnetic powder matrices: temperature control promotes full interface reaction, avoiding the problems of easy peeling of traditional oxide coatings and easy cracking of resin coatings. At the same time, it provides uniform coverage without dead corners, adapting to the application needs of soft magnetic powders of various materials. Dual optimization of high-frequency performance and DC bias performance: permeability ≥50 at 1MHz, bias retention rate ≥50% at 100Oe, precisely matching the high-frequency and high-power requirements of AI devices; Significantly improved product performance consistency: the permeability deviation of the same batch is ≤±5%, and the DC bias performance is stable, which improves the energy conversion efficiency of AI integrated inductors and meets the core requirements of high frequency, high power and miniaturization in the AI ​​field.

[0013] Instruction manual illustrations Figure 1 The image shown is an SEM image of Example 1 after coating (testing equipment used: Hitachi SU 5000, magnification 1000x). Figure 2This is a SEM image of Example 2 after coating (testing equipment used: Hitachi SU 5000, magnification 1000x). Figure 3 This is a SEM image of Example 3 after coating (testing equipment used: Hitachi SU 5000, magnification 1000x). Figure 4 This is a TEM image of the iron-nickel powder coating in Example 1 (testing equipment used was Talos F200X G2 TEM). Detailed Implementation

[0014] Example 1 (1) Pretreatment: Raw material: iron-nickel powder (Fe-80Ni, particle size D50=5000nm), air-drying to remove surface moisture.

[0015] (2) Ammonia atmosphere ball milling: A planetary ball mill equipped with a built-in temperature control module was used to load the pretreated soft magnetic powder into the silicon nitride ball milling jar; ball milling parameters: ball-to-material ratio 10:1, silicon nitride ball particle size 5mm, temperature control temperature 200℃, rotation speed 350r / min, ammonia pressure 0.3MPa, flow rate 50mL / min, ball milling time 3 days (72h); after coating, the residual ammonia was replaced with inert gas, and the soft magnetic powder with a uniform nitride insulating layer formed on the surface was collected.

[0016] (3) Preparation of magnetic rings: Mix with 2wt.% silicone resin, press at 1500MPa, sinter at 500℃ for 0.5h under nitrogen atmosphere to make magnetic rings (specifications: outer diameter 20mm × inner diameter 10mm × height 5mm), test performance (test standards refer to GB / T1408.1-2016; GB / T 3658-2022; SJ / T 11559-2016; IEC 60404-2-3:2021) ◦ Nitride insulation layer thickness 9.5nm, thickness deviation ±5%, no exposed area on the entire powder surface ( Figure 1 , Figure 4 ); ◦ Insulation withstand voltage: ≥5.2kV / mm; ◦ Magnetic properties: Magnetic permeability of 98 at 1MHz, with a permeability deviation of ±2.5% for the same batch of powder; ◦ DC bias performance: Permeability retention of 60% under 100Oe bias; ◦Loss at high frequency (1MHz, 50mT): 975mW / cm³.

[0017] Example 2 (1) Pretreatment: Raw material: carbonyl iron powder (purity 99.6%, particle size D50=10000nm, carbon content 0.03wt.%). (2) Ammonia atmosphere ball milling: A planetary ball mill equipped with a built-in temperature control module was used to load the pretreated soft magnetic powder into the silicon nitride ball milling jar; ball milling parameters: ball-to-material ratio 12:1, silicon nitride ball particle size 6mm, temperature control temperature 220℃, rotation speed 380r / min, ammonia pressure 0.35MPa, flow rate 45mL / min, ball milling time 4 days (96h); after coating, the residual ammonia was replaced with inert gas, and the soft magnetic powder with a uniform nitride insulating layer formed on the surface was collected.

[0018] Magnetic ring preparation: Mixed with 2 wt.% silicone resin, pressed at a pressure of 1500 MPa, and sintered at 450℃ for 0.5 h under a nitrogen atmosphere to produce a magnetic ring (specifications: outer diameter 20 mm × inner diameter 10 mm × height 5 mm). Performance testing: The nitride insulating layer is 18 nm thick with a thickness deviation of ±8.8%, and there are no exposed areas on the entire powder surface. Figure 2 ); Insulation withstand voltage: ≥4.8kV / mm; Magnetic properties: Permeability 53 at 1MHz, with a permeability deviation of ±2.8% for the same batch of powder; DC bias performance: 70% permeability retention under 100Oe bias; Loss at high frequencies (1MHz, 50mT): 1483mW / cm³; Example 3 (1) Pretreatment: Raw material: iron-silicon-aluminum powder (Fe-8Si-5Al, particle size D50=15000nm); (2) Ammonia atmosphere ball milling: A planetary ball mill equipped with a built-in temperature control module was used to load the pretreated soft magnetic powder into the silicon nitride ball milling jar; ball milling parameters: ball-to-material ratio 9:1, silicon nitride ball particle size 8mm, temperature control temperature 180℃, rotation speed 320r / min, ammonia pressure 0.25MPa, flow rate 55mL / min, ball milling time 5 days (120h); after coating, the residual ammonia was replaced with inert gas, and the soft magnetic powder with a uniform nitride insulating layer formed on the surface was collected.

[0019] Magnetic ring preparation: Mixed with 2 wt.% silicone resin, pressed at a pressure of 1500 MPa, and sintered at 450℃ for 0.5 h under a nitrogen atmosphere to produce a magnetic ring (specifications: outer diameter 20 mm × inner diameter 10 mm × height 5 mm). Performance testing: The nitride insulating layer is 25 nm thick, with a thickness deviation of ±9.5%. Figure 3 ); Insulation withstand voltage: ≥5.0kV / mm; Magnetic properties: Permeability of 65 at 1MHz and 50mT; permeability deviation of the same batch of powder is ±2.2%. DC bias performance: Permeability retention of 51% under 100Oe bias; Loss at high frequency (1MHz, 50mT): 1350mW / cm³.

Claims

1. A method for preparing nitride insulating layer soft magnetic powder by ball milling in an ammonia atmosphere, characterized in that, The preparation method includes the following steps: (1) Raw material pretreatment: Select soft magnetic powder with a particle size D50 of 500-20000nm. Remove surface adsorbed water by vacuum drying to ensure powder dispersibility. The drying temperature is 80-120℃. (2) Preparation of ball milling equipment: A planetary ball mill equipped with a built-in temperature control module is used. The ball milling jar is made of silicon nitride, the ball milling media is silicon nitride balls with a particle size of 3-10mm and a ball-to-material ratio of 5:1-15:

1. (3) Ammonia atmosphere construction: The pretreated soft magnetic powder is loaded into the ball mill jar, sealed and evacuated to a pressure ≤10Pa. Ammonia gas is introduced and the pressure of ammonia gas in the jar is controlled at 0.1-0.6MPa and the flow rate of ammonia gas is 10-100mL / min. The gas is continuously introduced to maintain a uniform atmosphere and ensure that ammonia gas is in full contact with each powder particle. (4) Mechanochemical uniform coating ball milling: set the ball mill temperature control temperature to 100-300℃, the rotation speed to 200-500r / min, and the ball milling time to 1-10 days; (5) Post-processing: After the ball milling is completed, stop the gas supply and temperature control. After the equipment cools down to room temperature, introduce inert gas to replace the residual ammonia gas and collect the product to obtain soft magnetic powder uniformly coated with nitride.

2. The method for preparing nitride insulating layer soft magnetic powder by ball milling in an ammonia atmosphere as described in claim 1, characterized in that, The soft magnetic powder includes one or more of iron-nickel powder, carbonyl iron powder, and iron-silicon-aluminum powder; wherein, Iron-nickel powder: Fe content 70-90 wt.%, Ni content 10-30 wt.%; Carbonyl iron powder: purity ≥ 99.5%, carbon content ≤ 0.05 wt.%; Iron-silicon-aluminum powder: Fe-Si-Al alloy, with Si content of 5-10 wt.% and Al content of 3-8 wt.%.

3. The method for preparing nitride insulating layer soft magnetic powder by ball milling in an ammonia atmosphere as described in claim 1, characterized in that, In step (4), the temperature of the ball mill is controlled at 150-250℃, the rotation speed is selected as 300-400r / min, and the ball milling time is preferably 3-7 days.

4. The method for preparing nitride insulating layer soft magnetic powder by ball milling in an ammonia atmosphere as described in claim 1, characterized in that, In step (2), the ball-to-material ratio is selected as 8:1-12:

1.

5. The method for preparing nitride insulating layer soft magnetic powder by ball milling in an ammonia atmosphere as described in claim 1, characterized in that, In step (3), the ammonia pressure is selected as 0.2-0.4 MPa and the flow rate is selected as 30-60 mL / min.

6. The application of the soft magnetic powder prepared by the method for preparing nitride insulating layer soft magnetic powder by ball milling in an ammonia atmosphere as described in claim 1, characterized in that, The soft magnetic powder is used to manufacture the magnetic ring of an integrated inductor.

7. The application of the soft magnetic powder prepared by the method for preparing nitride insulating layer soft magnetic powder by ball milling in an ammonia atmosphere as described in claim 6, characterized in that, The magnetic ring preparation method is as follows: nitride-coated soft magnetic powder is mixed with silicone resin, pressed into a magnetic ring by a mold, and then sintered at 400-500℃ for 0.5-2h; wherein the mass ratio of silicone resin is 5-10%, and the pressing pressure is 1000-1800MPa.

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