Fe4n@tio2 composite double-layer insulating coated magnetic powder based on ti-n-o interface cross-linking and preparation method thereof

Abstract

The application discloses a kind of Fe4N@TiO2 Composite Double-layer Insulation Coated Magnetic Powder based on Ti-N-O interface crosslinking and preparation method thereof, comprising the following steps: (1) dry pretreatment of carbonyl iron powder, to obtain magnetic powder A;(2) magnetic powder A is heated and treated under the atmosphere of mixed gas of N2 and NH3, to obtain single-layer coated magnetic powder B of surface in-situ growth γ'-Fe4N layer;(3) magnetic powder B is added to tetrabutyl titanate and anhydrous ethanol solution and stirred, the solution is adjusted to basicity and hydrolysis condensation reaction is carried out, to form Ti-N-O crosslinking bond, to obtain magnetic powder C;(4) magnetic powder C is added to resin acetone solution, ultrasonic stirring is carried out until acetone is completely volatilized, vacuum drying, sieving, to obtain granulation magnetic powder D;After pressing and curing, Fe4N@TiO2 Composite Double-layer Insulation Coated Magnetic Powder core is obtained.The application can realize the significant reduction of high-frequency magnetic loss on the basis of maintaining high saturation magnetization.

Description

Technical Field

[0001] This invention relates to the field of soft magnetic composite materials technology, and more specifically, to a soft magnetic composite material with carbonyl iron powder surface nitrided composite oxide insulating coating and its preparation method. Background Technology

[0002] Soft magnetic composite materials (magnetic powder cores) are metal-based composite materials made from insulating, soft magnetic metal powder as raw material, supplemented with binders, and then pressed into shape using powder metallurgy processes. They are commonly used to manufacture core magnetic components such as high-frequency inductors, transformers, filters, and chokes, and are widely applied in fields such as communications, computers, new energy vehicles, power electronics, and national defense.

[0003] With the rapid development of third-generation semiconductor technology, the operating frequency of power electronic components is gradually moving from the kHz level to the MHz level. However, under high-frequency alternating magnetic field conditions, the eddy current effect inside the material is significantly enhanced, resulting in extremely high eddy current losses. Carbonyl iron powder with high saturation magnetization is the preferred material to adapt to the trend of high current and miniaturization, but its low intrinsic resistivity leads to a surge in high-frequency eddy current losses, becoming a core bottleneck limiting its high-frequency applications.

[0004] In recent years, inorganic insulating coating has gradually become a research hotspot for magnetic powder core coating due to its excellent insulation and thermal stability. The most commonly used inorganic insulating agents are phosphates and inorganic oxides, with phosphate coating being the most widely used method due to its simple processing. To address the magnetic dilution problem caused by the insulating layer, patent CN115579233A discloses an electrochemical phosphating method to prepare an extremely thin phosphate layer for coating, reducing the impact of magnetic dilution on the magnetic permeability of the powder core by decreasing the coating thickness. However, phosphate coatings obtained using the phosphate passivation method gradually decompose at heat treatment temperatures exceeding 500℃, leading to a sharp decrease in resistivity and a significant increase in the loss of the magnetic powder core. Therefore, the use of inorganic oxides such as SiO2, MgO, and Al2O3 as insulating layers has emerged. These inorganic oxide insulating layers generally possess high-temperature stability, overcoming the defects of organic insulating materials and phosphate coatings in thermal decomposition. Patent CN109786100A discloses a TiO2-coated iron-based soft magnetic composite material and its preparation method. The material exhibits a high permeability of 35% and excellent DC bias performance, achieving 70% DC bias performance under a 100 Oe applied field. Simultaneously, it reduces magnetic loss; at 0.05 T / 100 kHz, the loss of the TiO2-coated iron-based amorphous magnetic powder is 320 mW / cm. 3 However, most of these oxide layers are merely surface deposits, resulting in weak adhesion of the coating layer, which makes them prone to coating failure under high pressure.

[0005] To balance magnetic properties with mechanical / insulating performance, researchers have attempted to introduce surface nitriding, as illustrated in patent CN108057878A, which generates a single-layer nitride layer with high resistivity on the particle surface. However, traditional nitriding processes often struggle to precisely control phase composition, easily leading to the formation of non-magnetic high-nitrogen phases (such as ε-Fe3N and ζ-Fe2N) or the precipitation of free α-Fe impurities. This not only significantly reduces the material's saturation magnetization but also substantially increases its magnetic anisotropy, thus raising losses. Furthermore, conventional nitriding often uses NH3 / H2 mixtures, which not only pose an explosion risk at high temperatures but also, due to the excessively high nitrogen potential and violent kinetic processes, make it extremely difficult to precisely control the nitrided layer thickness to the nanometer scale, easily resulting in deterioration of magnetic properties due to excessive layer thickness.

[0006] Therefore, how to effectively improve the bonding force between the carbonyl iron powder matrix and the insulating coating layer, avoid the cracking and detachment of the originally intact but extremely thin insulating layer due to plastic deformation, and construct a high-performance insulating coating layer with both high resistivity and high magnetic permeability without causing a serious magnetic dilution effect, so as to comprehensively improve the overall electromagnetic performance of high-frequency soft magnetic composite materials, has become a key problem that urgently needs to be solved in this field. Summary of the Invention

[0007] To address the problems existing in the prior art mentioned above, this invention provides a Fe4N@TiO2 composite double-layer insulating coated magnetic powder based on Ti-NO interfacial crosslinking and its preparation method.

[0008] The technical solution of the present invention is as follows:

[0009] A method for preparing Fe4N@TiO2 composite double-layer insulating coated magnetic powder based on Ti-NO interfacial crosslinking includes the following steps:

[0010] (1) Raw material preparation: Carbonyl iron powder was selected as raw material and dried and pretreated to obtain magnetic powder A;

[0011] (2) Gas phase surface nitriding: Magnetic powder A is heated in a mixed gas atmosphere of N2 and NH3, and cooled after the reaction is completed to obtain a single layer of magnetic powder B with an in-situ grown γ'-Fe4N layer on the surface.

[0012] (3) TiO2 coating and interfacial crosslinking: Magnetic powder B was added to a solution of tetrabutyl titanate (TBOT) and anhydrous ethanol and stirred. The solution was adjusted to alkaline and a hydrolysis condensation reaction was carried out. The inner γ'-Fe4N and the outer TiO2 underwent an in-situ chemical reaction at the interface to form Ti-NO crosslinking bonds. After washing and drying, Fe4N@TiO2 composite double-layer magnetic powder C with a double core-shell structure was obtained.

[0013] (4) Organic coating granulation: Fe4N@TiO2 composite double-layer magnetic powder C is added to resin acetone solution, ultrasonically stirred until acetone is completely volatilized, vacuum dried, and sieved using a 40-120 mesh sieve to obtain granulated magnetic powder D.

[0014] (5) Pressing and curing: The granulated magnetic powder D is pressed into shape, and after pressing, it is heat-treated and cured to obtain Fe4N@TiO2 composite double-layer insulating coated magnetic powder core.

[0015] Preferably, the carbonyl iron powder in step (1) is spherical carbonyl iron powder with an average particle size in the range of 1μm-20μm and a purity of not less than 99.5%.

[0016] Preferably, in step (2), the volume percentage of NH3 in the mixed gas is 20%~30%, the volume percentage of N2 is 70%~80%, and the total flow rate of the mixed gas is controlled at 50~100 sccm.

[0017] Preferably, the nitriding reaction temperature in step (2) is 450-550°C, the heating rate is 10-20°C / min, and the nitriding reaction time is 20-90min.

[0018] Preferably, in step (3), the mass of magnetic powder B in step (2) is used as the basis for calculation, the mass percentage of tetrabutyl titanate is 0.01 wt.%~0.5 wt.%, the mass percentage of anhydrous ethanol is 80 wt.%~100 wt.%, and the pH of the solution is adjusted to 8~12 using ammonia water with a mass concentration of 25%~28%.

[0019] Preferably, the reaction conditions in step (3) are: temperature of 40~60℃, mechanical stirring time of 30~60 min, drying temperature after cleaning of 60~80℃, and drying time of 2~6 h.

[0020] Preferably, the resin used in step (4) is one or two of epoxy resin and silicone resin. The overall mass percentage of the resin is 1 wt.% to 3 wt.% based on the mass of Fe4N@TiO2 composite double-layer magnetic powder C in step (3), and the mass percentage of the acetone used is 10 wt.% to 30 wt.%.

[0021] Preferably, the vacuum drying temperature in step (4) is 50-80°C and the drying time is 60-180 min.

[0022] Preferably, in step (5), the pressing pressure of the granulated magnetic powder D is 600-1500 MPa, the holding time is 5-8 s, the heat treatment curing temperature is 100-120℃, and the curing holding time is 1-2 h.

[0023] The method yields Fe4N@TiO2 composite double-layer insulating coated magnetic powder based on Ti-NO interface crosslinking.

[0024] The principle of this invention is as follows: First, under an NH3 / N2 mixed atmosphere, active nitrogen atoms [N] diffuse into the body-centered cubic (BCC) α-Fe lattice, inducing a phase transformation and generating a dense face-centered cubic (FCC) γ'-Fe4N magnetic layer. Subsequently, an amorphous TiO2 insulating coating layer is constructed on the surface of the nitride layer using a sol-gel method to prepare a Ti-OR precursor. The specific chemical reaction formula is as follows:

[0025] Hydrolysis of tetrabutyl titanate:

[0026]

[0027] On the Fe4N surface, N undergoes dehydration condensation with Ti(OH)4 to form Ti-NO bonds:

[0028]

[0029] Further carboxyl condensation forms Ti-O-Ti and Ti-NO networks:

[0030]

[0031] This cross-interface chemical bonding replaces traditional physical adsorption, establishing a strong interfacial bond. This not only effectively prevents the insulation layer from peeling off under complex service environments, but also significantly enhances the mechanical stability of the composite double-layer insulation coating structure.

[0032] Compared with the prior art, the present invention has the following significant advantages:

[0033] (1) This invention breaks through the limitations of traditional physical coating. First, a uniform and dense γ'-Fe4N magnetic insulating inner layer is prepared on the surface of iron powder by in-situ nitriding. When coating the amorphous TiO2 outer layer, the precursor and the nitrided layer undergo an in-situ interfacial reaction to generate Ti-NO chemical crosslinking bonds, realizing the chemical bonding and locking of the outer layer to the inner layer, and significantly improving the interfacial bonding force. This crosslinking effect, together with the high hardness of the Fe4N layer, enables the Fe4N@TiO2 magnetic powder to deform synchronously without peeling during high-pressure molding, solving the problem of insulation layer cracking and falling off.

[0034] (2) This invention constructs a stable and dense double-layer insulating network by using an outer layer locked by Ti-NO bonds and an inner layer of ferromagnetic nitride, which cuts off the microscopic eddy current path, significantly reduces eddy current loss, and endows the final Fe4N@TiO2 composite double-layer insulating coated magnetic powder core with excellent magnetic permeability and low magnetic loss characteristics. Compared with P@TiO2, the Fe4N@TiO2 composite double-layer insulating coated magnetic powder core can still maintain the integrity of the coating layer under increased pressing pressure, and the magnetic loss decreases with increasing pressing pressure. Conversely, the magnetic loss of the P@TiO2 composite double-layer insulating coated magnetic powder core first decreases and then increases with increasing pressing pressure, indicating that the coating layer is damaged.

[0035] (3) This invention uses an NH3 / N2 mixed gas for soft nitriding treatment. The dilution effect of N2 effectively reduces the atmospheric nitrogen potential and slows down the diffusion rate of nitrogen atoms into the matrix. This mild kinetic environment allows the nitrided layer to spread uniformly on the particle surface, thereby stabilizing the thickness of the γ'-Fe4N layer at 10~15 nm. This not only avoids the problem of uncontrolled layer thickness and safety hazards under the high nitrogen potential of traditional NH3 / H2, but also maximizes the suppression of magnetic dilution effect while ensuring the acquisition of a dense magnetic nitrided layer. The nitrogen carrier gas of this invention eliminates the risk of hydrogen embrittlement and precisely controls the nitrogen potential, growing a high-hardness ferromagnetic γ'-Fe4N inner insulating layer in situ on the iron powder surface. This not only effectively avoids the magnetic dilution effect caused by the thick insulating layer, but also retains the high saturation magnetization and high effective permeability of the matrix, making it suitable for high-frequency, high-current power electronics applications. Attached Figure Description

[0036] Figure 1 Hysteresis loops of TiO2-coated carbonyl iron powder after different nitriding times and ordinary phosphating treatment.

[0037] Figure 2 The magnetic properties of TiO2-coated carbonyl iron powder cores after different nitriding times and ordinary phosphating treatments are shown as the relationship between magnetic properties and frequency: (a) magnetic permeability; (b) quality factor.

[0038] Figure 3 Comparison of magnetic losses of TiO2-coated carbonyl iron powder cores after different nitriding times and ordinary phosphating treatment: (a) total loss; (b) hysteresis loss; (c) eddy current loss; (d) loss separation histogram.

[0039] Figure 4 The magnetic loss diagrams under molding pressure of 600MPa~1500MPa are as follows: (a) TiO2 carbonyl iron powder magnetic powder coated with nitrided TiO2 carbonyl iron powder coated with nitrided TiO2 carbonyl iron powder magnetic powder (b) (c) and (d) are the magnetic loss curves of Example 1 and Ratio 1 at 50mT100kHz as a function of pressing pressure.

[0040] Figure 5 The XPS total spectrum (a) and detailed elemental spectra (bd) of Example 1 are shown.

[0041] Figure 6 The XPS total spectrum (a) and the detailed elemental spectra (bd) of Fe, Si, and O are shown in Comparative Example 3.

[0042] Figure 7 SEM microstructure images of the double-layer composite magnetic powder: (a, a1) Example 1, (b, b1) Example 2, (c, c1) Example 3, (d, d1) Comparative Example 1; where ad is a low magnification image and a1-d1 are high magnification images.

[0043] Figure 8 Example 1: Cross-sectional microstructure characterization of composite magnetic powder: (a, d) cross-sectional TEM images; (b, c) high-resolution HRTEM images of regions b and c in Figure (a), respectively (inset shows the FFT pattern of the corresponding region); (e) magnified image of the interface; (f) HRTEM image of region f; (g) STEM-EDS elemental distribution map of region g.

[0044] Figure 9 This is a schematic diagram of the technical principle of the present invention. Detailed Implementation

[0045] The present invention will be further described in detail below with reference to embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto. All raw materials involved in the present invention can be purchased directly from the market. For process parameters not specifically specified, conventional techniques can be referred to.

[0046] Carbonyl iron powder was purchased from Jiangsu Tianyi Ultrafine Metal Powder Co., Ltd., model RZE. KR5235 silicone resin and TT310 epoxy resin were purchased from Shin-Etsu Chemical Co., Ltd. (Japan) and Guangzhou Tiantai Chemical Co., Ltd., respectively.

[0047] Example 1

[0048] A method for preparing a high-frequency soft magnetic composite material with carbonyl iron powder surface nitrided composite oxide insulation, wherein the magnetic powder used is carbonyl iron powder, and the preparation method includes the following steps:

[0049] (1) Raw material pretreatment: Commercial carbonyl iron powder with an average particle size of 6 μm was selected and placed in a vacuum drying oven for pretreatment to obtain original magnetic powder A;

[0050] (2) Gas phase surface nitriding: Magnetic powder A is placed in a tubular reactor and a mixture of N2 and NH3 with a volume ratio of 4:1 is introduced. The total flow rate is 100 sccm. The mixture is kept at 500℃ for 30 min. After cooling with the furnace, nitrided monolayer coated magnetic powder B is obtained.

[0051] (3) TiO2 coating: Prepare a tetrabutyl titanate-anhydrous ethanol solution with a mass fraction of 0.01 wt.%, then mix 30 g of magnetic powder B with 30 ml of the above solution, add ammonia solution with a mass fraction of 25% to adjust the pH of the solution to alkaline (pH≈10), stir at a constant speed for 60 min under a 50℃ water bath, and after washing and drying with deionized water and anhydrous ethanol multiple times, obtain composite magnetic powder C with a double core-shell structure coating;

[0052] (4) Preparation of organic binder: Dissolve 0.7 wt.% KR5235 silicone resin and 0.3 wt.% tt310 epoxy resin in 9 ml acetone solvent and sonicate for 15 min to obtain organic resin solution;

[0053] (5) Organic coating granulation: 30 g of magnetic powder C was added to 9 ml of organic resin solution and stirred at a constant speed until the acetone was completely evaporated. Then, it was vacuum dried at 60°C for 60 min and passed through a 40-120 mesh sieve to obtain granulated magnetic powder D.

[0054] (6) Pressing and curing: The magnetic powder D is pressed into a magnetic powder core ring with an outer diameter of 20 mm, an inner diameter of 16 mm, and a height of 5 mm. The pressing pressure is 600 MPa. After holding the pressure for 7 s, the formed magnetic powder core is placed in a heating furnace and cured at 120°C for 60 min to obtain the final carbonyl iron powder-based high-frequency soft magnetic composite material.

[0055] Example 2

[0056] This embodiment provides a method for preparing an insulating carbonyl iron powder magnetic core. The difference between this method and Example 1 is that the nitriding time is 60 min, while the rest of the preparation method and parameters are the same as in Example 1.

[0057] Example 3

[0058] This embodiment 3 provides a method for preparing an insulating coated carbonyl iron powder magnetic core. The difference between this method and embodiment 1 is that the nitriding time is 90 min, while the rest of the preparation method and parameters are the same as in embodiment 1.

[0059] Comparative Example 1

[0060] Comparative Example 1 provides a method for preparing an insulating coated carbonyl iron powder magnetic core. The difference between this method and Example 1 is that it does not undergo nitriding treatment. Instead, it is treated with a common 0.5 wt.% acetone phosphating solution for 10 minutes and then coated with TiO2. The remaining preparation methods and parameters are the same as in Example 1.

[0061] Comparative Example 2

[0062] Comparative Example 2 provides a method for preparing an insulating coated carbonyl iron powder magnetic core. The difference between this method and Example 1 is that the nitriding temperature is 450°C, while the other preparation methods and parameters are the same as in Example 1.

[0063] Comparative Example 3

[0064] Comparative Example 3 provides a method for preparing an insulating coated carbonyl iron powder magnetic core. The difference from Example 1 is that, after a 30-minute nitriding treatment, SiO2 is coated using a sol-gel method: a 0.05 wt.% tetraethyl silicate-anhydrous ethanol solution is prepared, and 30 g of magnetic powder B is mixed with 30 ml of the above solution. A 25% ammonia solution is added to adjust the pH of the solution to alkaline (pH≈10). The solution is stirred uniformly for 60 minutes in a 50°C water bath. After repeated washing with deionized water and anhydrous ethanol, and drying, a composite magnetic powder with a double-layer core-shell structure is obtained. The remaining preparation methods and parameters are the same as in Example 1.

[0065] The magnetic properties of the samples from Examples 1, 2, 3, Comparative Example 1, and Comparative Example 2 were tested, and the test results are recorded in Table 1.

[0066] Table 1. Saturation magnetization M of magnetic powder s and the effective permeability μ of the magnetic powder core e Quality factor Q, magnetic loss P cv

[0067]

[0068] Depend on Figure 1 As shown in Table 1, with the extension of nitriding time, the saturation magnetization M in Examples 1 to 3 decreases. s The values ​​showed a decreasing trend, but were all significantly higher than those in Comparative Example 1. This indicates that the introduction of the γ'-Fe4N ferromagnetic phase effectively alleviated the magnetic dilution effect caused by non-magnetic materials. However, the thickness of the γ′-Fe4N layer should be limited to keep it at a low level.

[0069] Depend on Figure 2 It can be seen that the effective permeability μ of Examples 1-3 eIt exhibits excellent frequency stability in the range of 100 kHz to 10 MHz, with values ​​higher than those in Comparative Example 1. This confirms that the in-situ grown ferromagnetic γ'-Fe4N inner layer effectively enhances the magnetic coupling between particles and alleviates the magnetic dilution effect induced by the insulating layer. Comparative Example 2, due to insufficient nitrogen potential caused by low temperature, failed to undergo phase transition to generate Fe4N, thus maintaining the permeability at the level of the α-Fe matrix, but its magnetic loss was significantly too high (Table 1).

[0070] Figure 3 The variation law of magnetic powder core loss with frequency and the results of loss separation were revealed. Figure 3 (ac) shows that under a magnetic induction intensity of 50mT, the total loss P in Examples 1-3 is... cv The loss was significantly lower than that of the comparison sample, and this advantage became more pronounced with increasing frequency. Loss separation showed that the embodiment effectively suppressed hysteresis loss P. h At the same time, it significantly reduced eddy current loss P e .Depend on Figure 3 (c)(d) It can be seen that, in Comparative Example 2, due to the failure to form a dense Fe4N layer at the interface under the nitriding temperature of 450℃, it is unable to form an effective chemical cross-link with the outer TiO2 layer, resulting in the highest eddy current loss at high frequencies.

[0071] Figure 4 The loss characteristics of the magnetic powder core under different molding pressures were compared, further verifying the mechanical reliability of the coating layer of this invention. Figure 4 As shown in (a, c), the total loss in Example 1 continuously decreases with increasing pressing pressure (600-1500 MPa). This is attributed to the Ti-NO interfacial crosslinking network, which endows the coating layer with extremely strong adhesion and mechanical stability, allowing it to maintain the integrity of the insulation structure during ultra-high pressure molding. In contrast, the loss from... Figure 4 (b, d) As can be seen, the loss of Comparative Example 1 (phosphating sample) increased significantly after the pressure exceeded 900 MPa, indicating that the traditional physical coating layer is prone to peeling failure under high pressure shearing, leading to the destruction of insulation between particles. The experimental results confirm that the Fe4N@TiO2 composite coated magnetic powder prepared in this invention not only has excellent electromagnetic properties, but also has excellent pressure resistance processing performance, which can meet the molding requirements of higher density, thereby effectively suppressing high-frequency loss while improving magnetic flux density.

[0072] Figure 5 XPS energy dispersive spectroscopy analysis of the composite magnetic powder in Example 1, by Figure 5The N 1s fine spectrum in (c) shows that, in addition to the Fe-N bond at 397.1 eV, a distinct Ti-ON binding energy peak was detected at 399.9 eV. This result strongly confirms that at the heterogeneous interface between the Fe4N magnetic inner layer and the TiO2 insulating outer layer, nitrogen atoms, titanium, and oxygen atoms form a strongly covalently bonded cross-linked network through in-situ chemical reactions.

[0073] Figure 6 XPS energy dispersive spectroscopy analysis of the composite magnetic powder in Comparative Example 3. Figure 6 The fine spectra of Fe2p and N1s in (a, b) show significant Fe-N binding energy peaks at 707.83 eV and 399.71 eV, confirming the in-situ growth of a dense magnetic γ'-Fe4N inner layer on the iron powder surface. Figure 6 (c, d) show the compositional characteristics of the insulating outer layer, including the characteristic SiO2 peak at 103.14 eV in the Si2p spectrum and the Si-O-Si bond at 532.71 eV in the O1s spectrum. However, unlike the XPS in Example 1, no bonding bonds are formed with the substrate, indicating that SiO2 and Fe4N are deposited on the outer layer via surface adhesion. This surface adhesion coating is prone to cracking and detachment during subsequent high-pressure pressing, compromising the integrity of the coating layer and causing electrical contact between the substrates, significantly increasing losses.

[0074] Figure 7 SEM morphology analysis of the composite magnetic powder was performed. Low-magnification images show that all samples maintained the spherical morphology characteristic of carbonyl iron powder, which is beneficial for improving the filling rate of the magnetic powder core. High-magnification morphology revealed that continuous, smooth, and dense composite coating layers were grown in situ on the particle surfaces of Examples 1-3. This dense shell structure demonstrates that the low nitrogen potential atmosphere of NH3 / N2 can induce uniform nucleation and growth of nitrogen atoms on the particle surface. Combined with the amorphous TiO2 formed by the sol-gel method, a high-quality heterogeneous coating layer was constructed. In contrast, Comparative Example 1 exhibited obvious roughness and granular accumulation on its surface, with poor coating uniformity.

[0075] Figure 8 Atomic-scale structural evidence of the composite magnetic powder cross-section in Example 1 is provided. HRTEM and its FFT patterns clearly confirm the successful in-situ growth of a γ'-Fe4N crystal layer on the iron powder matrix surface, with clear lattice fringes and a thickness of approximately 10-15 nm, effectively verifying the precise control of nitriding kinetics in this invention. Subsequent EDS mapping confirmed that N, Ti, and O elements are distributed in continuous layers on the matrix surface. High-resolution images further reveal that the outer TiO2 coating exhibits a typical amorphous structure and forms an atomically tightly bonded heterogeneous interface with the inner Fe4N layer.

[0076] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing Fe4N@TiO2 composite double-layer insulating coated magnetic powder based on Ti-NO interfacial crosslinking, characterized in that, Includes the following steps: (1) Raw material preparation: Carbonyl iron powder was selected as raw material and dried and pretreated to obtain magnetic powder A; (2) Gas phase surface nitriding: Magnetic powder A is heated in a mixed gas atmosphere of N2 and NH3, and cooled after the reaction is completed to obtain a single layer of magnetic powder B with an in-situ grown γ'-Fe4N layer on the surface. (3) TiO2 coating and interfacial crosslinking: Magnetic powder B was added to a solution of tetrabutyl titanate and anhydrous ethanol and stirred. The solution was adjusted to alkaline and a hydrolysis condensation reaction was carried out. The inner γ'-Fe4N and the outer TiO2 were subjected to an in-situ chemical reaction at the interface to form Ti-NO crosslinking bonds. After washing and drying, Fe4N@TiO2 composite double-layer magnetic powder C with a double core-shell structure was obtained. (4) Organic coating granulation: Fe4N@TiO2 composite double-layer magnetic powder C is added to resin acetone solution, ultrasonically stirred until acetone is completely volatilized, vacuum dried, and sieved using a 40-120 mesh sieve to obtain granulated magnetic powder D. (5) Pressing and curing: The granulated magnetic powder D is pressed into shape, and after pressing, it is heat-treated and cured to obtain Fe4N@TiO2 composite double-layer insulating coated magnetic powder core.

2. The preparation method according to claim 1, characterized in that, The carbonyl iron powder mentioned in step (1) is spherical carbonyl iron powder with an average particle size in the range of 1μm-20μm and a purity of not less than 99.5%.

3. The preparation method according to claim 1, characterized in that, In step (2), the volume percentage of NH3 in the mixed gas is 20%~30%, the volume percentage of N2 is 70%~80%, and the total flow rate of the mixed gas is controlled at 50~100 sccm.

4. The preparation method according to claim 1, 2, or 3, characterized in that, The nitriding reaction temperature in step (2) is 450-550℃, the heating rate is 10-20℃ / min, and the nitriding reaction time is 20-90min.

5. The preparation method according to claim 1, 2, or 3, characterized in that, In step (3), the mass of magnetic powder B in step (2) is used as the basis for calculation. The mass percentage of tetrabutyl titanate is 0.01 wt.%~0.5 wt.%, the mass percentage of anhydrous ethanol is 80 wt.%~100 wt.%, and the pH of the solution is adjusted to 8~12 using ammonia water with a mass concentration of 25%~28%.

6. The preparation method according to claim 1, 2, or 3, characterized in that, The reaction conditions in step (3) are: temperature of 40~60℃, mechanical stirring time of 30~60 min, drying temperature after cleaning of 60~80℃, and drying time of 2~6 h.

7. The preparation method according to claim 1, 2, or 3, characterized in that, The resin used in step (4) is one or two of epoxy resin and silicone resin. The overall mass percentage of the resin is 1 wt.% to 3 wt.% based on the mass of Fe4N@TiO2 composite double-layer magnetic powder C in step (3), and the mass percentage of the acetone used is 10 wt.% to 30 wt.%.

8. The preparation method according to claim 1, 2, or 3, characterized in that, The vacuum drying temperature in step (4) is 50-80℃, and the drying time is 60-180 min.

9. The preparation method according to claim 1, 2, or 3, characterized in that, In step (5), the pressing pressure of the granulated magnetic powder D is 600-1500 MPa, the holding time is 5-8 s, the heat treatment curing temperature is 100-120℃, and the curing holding time is 1-2 h.

10. Fe4N@TiO2 composite double-layer insulating magnetic powder based on Ti-NO interfacial crosslinking prepared by the method of any one of claims 1 to 9.

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