A core-shell structured iron-based nanocrystalline alloy composite powder, its preparation method and application

Abstract

This invention provides a core-shell structured iron-based nanocrystalline alloy composite powder, its preparation method, and its applications. The alumina coating layer has a thickness of 60-100 nm, and the alumina accounts for 2-5% of the mass percentage of the composite powder. The carbon coating layer has a thickness of 40-60 nm, and the carbon accounts for 4-15% of the mass percentage of the composite powder. This invention uses an iron-based nanocrystalline alloy as the core, surrounded by an alumina and carbon composite coating layer. The resulting composite powder is lightweight, highly corrosion-resistant, and possesses excellent magnetic properties such as high saturation magnetization and high permeability.

Description

Technical Field

[0001] This invention belongs to the field of nanocrystalline composite magnetic powder manufacturing technology, and particularly relates to a core-shell structured iron-based nanocrystalline alloy composite powder, its preparation method and application. Background Technology

[0002] With the development of the electronics and power industry and the advancement of wireless communication technology, the application of modern electronic devices in various industries is increasing, and they are developing towards miniaturization, high frequency, and integration. Against this backdrop, electromagnetic radiation is also increasing at a rate of about 10% per year. A series of electromagnetic wave absorbing materials have emerged, becoming an effective way to solve the hazards of electromagnetic radiation.

[0003] Based on the loss mechanism of electromagnetic waves, absorbing materials can be classified into magnetic loss type and dielectric loss type. Currently, ferrite absorbing materials, which are mainly magnetic loss materials, are widely used at relatively low frequencies due to their large magnetic loss and good absorption performance. However, due to their poor temperature stability and the limitations imposed by the Snoek relationship, the permeability of ferrites decreases sharply with increasing electromagnetic wave frequency, resulting in poor absorption performance that cannot meet the requirements of high-frequency applications. In addition to ferrites, traditional iron-based alloy powders such as FeNi, FeCo, and FeSiAl are also typical magnetic absorbing materials. However, because their dielectric constants are still relatively large, they weaken the impedance matching of the absorber at high frequencies, reducing the absorption performance of electromagnetic waves.

[0004] In recent years, iron-based nanocrystalline soft magnetic alloys have exhibited excellent soft magnetic properties due to their mixed microstructure consisting of nanoscale α-Fe phase and residual amorphous phase, such as high saturation magnetization (Ms) and permeability (μ), low coercivity (Hc), and low magnetostriction. Nanocrystalline soft magnetic alloys show a significant advantage in permeability at high frequencies compared to traditional magnetic materials, and also possess high resistivity and low dielectric constant, attracting increasing attention in the field of electromagnetic wave absorption.

[0005] CN113628823A discloses a highly corrosion-resistant iron-based nanocrystalline soft magnetic alloy and its preparation method. The iron-based nanocrystalline soft magnetic alloy has the following expression: Fe a Si b B c P d Cu e Cr fWhere a is 74–84, b is 3.2–4.5, c is 7.1–8.5, d is 3.2–4.5, e is 0.6–0.72, and f is 1–10, and a+b+c+d+e+f=100. The alloy exhibits excellent overall soft magnetic properties, high corrosion resistance, good formability, relaxed heat treatment requirements, and low production costs. However, it suffers from only single characteristics: high magnetic loss, high density, and susceptibility to corrosion, making it difficult to meet the comprehensive requirements of modern high-performance microwave absorbing materials.

[0006] Carbon materials such as graphite possess excellent dielectric loss properties, low density, and resistance to high temperatures and corrosion. However, carbon materials alone also suffer from drawbacks such as a narrow absorption frequency range and low absorption intensity. Composite modification of iron-based nanocrystalline alloys and carbon materials holds promise for leveraging the synergistic effect of magnetic and dielectric losses, while simultaneously improving absorption performance, reducing absorber density, and enhancing stability. Therefore, inventing an electromagnetic wave absorber with superior overall absorption performance and a simple and efficient preparation process is of great significance. Summary of the Invention

[0007] The purpose of this invention is to provide a core-shell structured iron-based nanocrystalline alloy composite powder, its preparation method, and its application. The prepared composite powder has a spherical core-shell structure, with an iron-based nanocrystalline alloy as the matrix and an outer layer of a composite coating of alumina and carbon. The magnetic-dielectric synergistic effect of the coating layer further improves the microwave absorption performance of the material, while also compensating for the shortcomings of high alloy density and easy corrosion, resulting in a nanocrystalline composite material with excellent microwave absorption and magnetic properties.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a core-shell structured iron-based nanocrystalline alloy composite powder, wherein the composite powder comprises, from the inside to the outside, a core, an aluminum hydride coating layer and a carbon coating layer;

[0010] The thickness of the alumina coating layer is 60-100 nm, and the alumina accounts for 2-5% of the mass percentage of the composite powder.

[0011] The thickness of the carbon coating layer is 40-60 nm, and the carbon accounts for 4-15% of the mass percentage of the composite powder.

[0012] The composite powder of the present invention has a spherical core-shell structure, with an iron-based nanocrystalline alloy as the matrix and an outer layer of alumina and carbon composite coating. The magnetic-dielectric synergistic effect of the coating further improves the microwave absorption performance of the material, while also compensating for the shortcomings of the alloy's high density and susceptibility to corrosion, resulting in a nanocrystalline composite material with excellent microwave absorption and magnetic properties.

[0013] The thickness of the alumina coating layer is 60-100nm, for example, 60nm, 70nm, 80nm, 90nm or 100nm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0014] The alumina accounts for 2-5% of the mass of the composite powder, for example, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0015] The thickness of the carbon coating layer is 40-60nm, for example, 40nm, 45nm, 50nm, 55nm or 60nm, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0016] The carbon content in the composite powder is 4-15% by mass, for example, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14% or 15%, etc., but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0017] As a preferred embodiment of the present invention, the core is an iron-based nanocrystalline alloy.

[0018] Preferably, the chemical formula of the iron-based nanocrystalline alloy is Fe. a Si b B c P d Cu e RE f , where RE is any one or at least two of Nd, Gd, Ce, Sm, and Gd, a, b, c, d, e, and f represent the atomic percentage content of the corresponding elements, satisfying 0≤b≤15, 0≤c≤9, 0≤d≤5, 0≤e≤1, 0≤f≤3, with the balance being Fe, and satisfying a+b+c+d+e+f=100.

[0019] Preferably, the iron-based nanocrystalline alloy has an amorphous / α-Fe nanocrystalline dual-phase structure.

[0020] In this invention, the electromagnetic wave absorbing coating, which is formed by mixing the composite powder and the wave-transparent substrate at a mass ratio of 3:2, has a reflection loss of less than -10dB in the frequency range of 4 to 15 GHz and a minimum reflection loss of -60dB when the layer thickness is 1.2 to 2 mm.

[0021] Secondly, the present invention also provides a method for preparing the composite powder described in the first aspect, the method comprising the following steps:

[0022] (1) The iron-based nanocrystalline alloy strip prepared according to the formula was heat-treated and crushed to obtain iron-based nanocrystalline alloy powder.

[0023] (2) Mix the alumina powder with the iron-based nanocrystalline alloy powder described in step (1) and press them to obtain a disc.

[0024] (3) The disc obtained in step (2) is heat-treated and then magnetically separated to obtain alumina powder and preliminary alumina-coated iron-based nanocrystalline magnetic powder.

[0025] (4) After mixing graphite carbon powder, surfactant and magnetic powder described in step (3), high-energy ball milling and heat treatment are performed sequentially to obtain the core-shell structured iron-based nanocrystalline alloy composite powder.

[0026] In this invention, the preparation process is simple. By changing the heat treatment and ball milling processes, the morphology, particle size and microstructure of the matrix nanocrystalline alloy of the composite powder can be controlled, thereby achieving the regulation of the electromagnetic wave absorption performance of the composite powder; the core-shell structure of the prepared composite powder is uniformly distributed.

[0027] As a preferred technical solution of the present invention, the heat treatment in step (1) includes sequential heating and cooling stages.

[0028] Preferably, the heat treatment in step (1) is carried out under an inert gas protective atmosphere.

[0029] Preferably, the heating rate is 8-12℃ / min, for example, it can be 8℃ / min, 9℃ / min, 10℃ / min, 11℃ / min or 12℃ / min, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0030] Preferably, the endpoint temperature of the heating is 400-500℃, for example, it can be 400℃, 420℃, 440℃, 460℃, 480℃ or 500℃, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0031] Preferably, the holding time for heating is 10-30 minutes, for example, it can be 10 minutes, 12 minutes, 14 minutes, 16 minutes, 18 minutes, 20 minutes, 22 minutes, 24 minutes, 26 minutes, 28 minutes or 30 minutes, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0032] Preferably, the cooling stage includes a first cooling and a second cooling performed sequentially.

[0033] Preferably, the cooling rate of the first cooling is 13-18℃ / min, for example, it can be 13℃ / min, 14℃ / min, 15℃ / min, 16℃ / min, 17℃ / min or 18℃ / min, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0034] Preferably, the endpoint temperature of the first cooling is 320-370℃, for example, it can be 320℃, 330℃, 340℃, 350℃, 360℃ or 370℃, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0035] Preferably, the holding time for the first cooling is 20-40 minutes, for example, it can be 20 minutes, 22 minutes, 24 minutes, 26 minutes, 28 minutes, 30 minutes, 32 minutes, 34 minutes, 36 minutes, 38 minutes or 40 minutes, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0036] Preferably, the second cooling is furnace-side cooling.

[0037] Preferably, the iron-based nanocrystalline alloy powder obtained in step (1) is sieved.

[0038] Preferably, the sieving is performed through a 100-200 mesh sieve. The mesh size of the sieve is 100-200 mesh, such as 100 mesh, 120 mesh, 140 mesh, 160 mesh, 180 mesh, or 200 mesh, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0039] As a preferred technical solution of the present invention, the particle size of the alumina powder in step (2) is 400-600nm, for example, 400nm, 420nm, 440nm, 460nm, 480nm, 500nm, 520nm, 540nm, 560nm, 580nm or 600nm, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0040] Preferably, the pressing pressure in step (2) is 15-25 MPa, for example, 15 MPa, 16 MPa, 17 MPa, 18 MPa, 19 MPa, 20 MPa, 21 MPa, 22 MPa, 23 MPa, 24 MPa or 25 MPa, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0041] In this invention, step (2) yields a disc with a radius of 35-45 mm and a height of 7-12 mm.

[0042] As a preferred technical solution of the present invention, the heat treatment in step (3) is carried out under an inert gas protective atmosphere.

[0043] Preferably, the heat treatment in step (3) includes a first heating and a second heating in sequence.

[0044] Preferably, the heating rate of the first heating is 8-12℃ / min, for example, it can be 8℃ / min, 9℃ / min, 10℃ / min, 11℃ / min or 12℃ / min, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0045] Preferably, the endpoint temperature of the first heating is 850-950℃, for example, it can be 850℃, 860℃, 870℃, 880℃, 890℃, 900℃, 910℃, 920℃, 930℃, 940℃ or 950℃, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0046] Preferably, the holding time for the first heating is 10-30 min, for example, it can be 10 min, 12 min, 14 min, 16 min, 18 min, 20 min, 22 min, 24 min, 26 min, 28 min or 30 min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0047] Preferably, the heating rate of the second heating is 13-17℃ / min, for example, it can be 13℃ / min, 14℃ / min, 15℃ / min, 16℃ / min or 17℃ / min, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0048] Preferably, the endpoint temperature of the second heating is 1170-1210℃, for example, it can be 1170℃, 1175℃, 1180℃, 1185℃, 1190℃, 1195℃ or 1210℃, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0049] Preferably, the holding time for the second heating is 3-10 minutes, for example, it can be 3 minutes, 4 minutes, 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes or 10 minutes, but it is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0050] Preferably, after the heat treatment in step (3), the sample is removed from the furnace and placed in liquid nitrogen for cooling.

[0051] In this invention, the cooled mixed powder is placed in a vibratory mill for vibratory grinding.

[0052] As a preferred technical solution of the present invention, the preliminary alumina-coated iron-based nanocrystalline magnetic powder in step (3) is ball-milled, dried and sieved in sequence to obtain alumina-coated iron-based nanocrystalline magnetic powder with a particle size of 8-12μm.

[0053] This invention involves ball milling the initially alumina-coated iron-based nanocrystalline magnetic powder, which can better remove excess alumina from the outside of the alumina coating layer.

[0054] Preferably, the rotational speed of the ball mill is 100-200 r / min, for example, it can be 100 r / min, 120 r / min, 140 r / min, 160 r / min, 180 r / min or 200 r / min, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0055] Preferably, the ball milling time is 17-22 hours, for example, 17 hours, 18 hours, 19 hours, 20 hours, 21 hours or 22 hours, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0056] In this invention, the solvent for ball milling includes ethanol, and the milling balls are zirconium oxide balls.

[0057] As a preferred technical solution of the present invention, the particle size of the graphite carbon powder in step (4) is 3-8μm, for example, it can be 3μm, 4μm, 5μm, 6μm, 7μm or 8μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0058] Preferably, the surfactant in step (4) includes any one of oleic acid, sucrose fatty acid ester or polysorbate.

[0059] Preferably, the mass ratio of magnetic powder to surfactant in step (4) is (18-22):1, for example, it can be 18:1, 19:1, 20:1, 21:1 or 22:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0060] Preferably, the high-energy ball milling process in step (4) specifically includes: stopping the ball milling and cooling after each high-energy ball milling, and then repeating the high-energy ball milling process again.

[0061] Preferably, the rotational speed of the high-energy ball mill is 900-1100 r / min, for example, it can be 900 r / min, 920 r / min, 940 r / min, 960 r / min, 980 r / min, 1000 r / min, 1020 r / min, 1040 r / min, 1060 r / min, 1080 r / min or 1100 r / min, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0062] Preferably, the total time for high-energy ball milling is 4-8 hours, for example, it can be 4 hours, 5 hours, 6 hours, 7 hours or 8 hours, but it is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0063] Preferably, the single-stage ball milling time in the high-energy ball mill is 2-6 minutes, for example, it can be 2 minutes, 3 minutes, 4 minutes, 5 minutes or 6 minutes, but it is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0064] Preferably, the cooling time in the high-energy ball mill is 15-20 min, for example, it can be 15 min, 16 min, 17 min, 18 min, 19 min or 20 min, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0065] Preferably, the heat treatment in step (4) is carried out under an inert gas protective atmosphere.

[0066] Preferably, the heating rate of the heat treatment in step (4) is 5-10℃ / min, for example, it can be 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min or 10℃ / min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0067] Preferably, the endpoint temperature of the heat treatment in step (4) is 350-450℃, for example, it can be 350℃, 370℃, 390℃, 400℃, 420℃, 440℃ or 450℃, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0068] Preferably, the heat treatment holding time in step (4) is 6-10h, for example, it can be 6h, 7h, 8h, 9h or 10h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0069] Preferably, the heat treatment described in step (4) is followed by furnace cooling.

[0070] As a preferred technical solution of the present invention, the preparation method includes the following steps:

[0071] (1) The iron-based nanocrystalline alloy strip prepared according to the formula is heat-treated under an inert gas protective atmosphere, crushed, and passed through a 100-200 mesh sieve to obtain iron-based nanocrystalline alloy powder.

[0072] The heat treatment includes sequential heating, a first cooling, and a second cooling; the heating is performed by heating to 400-500℃ at a rate of 8-12℃ / min and holding for 10-30min; the first cooling is performed by cooling to 320-370℃ at a rate of 13-18℃ / min and holding for 20-40min; the second cooling is furnace cooling.

[0073] (2) Alumina powder with a particle size of 400-600nm is mixed with the iron-based nanocrystalline alloy powder described in step (1) and pressed under a pressure of 15-25MPa to obtain a disc.

[0074] (3) The disc obtained in step (2) is heat-treated under an inert gas protective atmosphere, taken out of the furnace, cooled in liquid nitrogen, and obtained by magnetic separation. Alumina powder and preliminary alumina-coated iron-based nanocrystalline magnetic powder are then obtained. The preliminary alumina-coated iron-based nanocrystalline magnetic powder is ball-milled at 100-200 r / min for 17-22 h, dried and sieved to obtain alumina-coated iron-based nanocrystalline magnetic powder with a particle size of 8-12 μm.

[0075] The heat treatment includes a first heating and a second heating in sequence; the first heating is to heat to 850-950℃ at a heating rate of 8-12℃ / min and hold for 10-30min; the second heating is to heat to 1170-1210℃ at a heating rate of 13-17℃ / min and hold for 3-10min.

[0076] (4) Graphite carbon powder with a particle size of 3-8 μm, surfactant and magnetic powder from step (3) are mixed and subjected to high-energy ball milling at a speed of 900-1100 r / min for a total time of 4-8 h. After each high-energy ball milling for 2-6 min, the ball milling is stopped and cooled for 15-20 min. Then, heat treatment is carried out under an inert gas protective atmosphere. After furnace cooling, the core-shell structured iron-based nanocrystalline alloy composite powder is obtained.

[0077] The mass ratio of the magnetic powder to the surfactant is (18-22):1;

[0078] The heat treatment involves heating to 350-450℃ at a heating rate of 5-10℃ / min and holding at that temperature for 6-10 hours.

[0079] Thirdly, the present invention provides an application of the composite powder as described in the first aspect, wherein the composite powder is used as an electromagnetic wave absorber.

[0080] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0081] Compared with the prior art, the present invention has the following beneficial effects:

[0082] (1) The iron-based nanocrystalline alloy composite powder with core-shell structure provided by the present invention has good sphericity and a spherical core-shell structure. The powder has excellent impedance matching performance and realizes the synergistic effect of magnetic-dielectric loss. Its absorption performance is significantly better than that of single magnetic loss or dielectric loss type absorbers. It also has excellent absorption performance in the G Hertz band and has a wide effective absorption band.

[0083] (2) The iron-based nanocrystalline alloy provided by the present invention is composed of an alumina and a carbon composite coating layer in sequence. The resulting composite powder has a light density, strong corrosion resistance, and excellent magnetic properties such as high saturation magnetization and high permeability.

[0084] (3) The preparation method provided by the present invention is simple, efficient and industrially feasible for mass production; the morphology, particle size and microstructure of the matrix nanocrystalline alloy of the composite powder can be controlled by changing the ball milling and heat treatment processes, thereby achieving the regulation of the electromagnetic wave absorption performance of the composite powder. Attached Figure Description

[0085] Figure 1 This is a SEM image of the core-shell structured iron-based nanocrystalline alloy composite powder prepared in Example 1 of this invention;

[0086] Figure 2 This is a SEM image of the core-shell structured iron-based nanocrystalline alloy composite powder prepared in Example 1 of this invention;

[0087] Figure 3 The image shows the XRD pattern of the core-shell structured iron-based nanocrystalline alloy composite powder prepared in Example 1 of this invention.

[0088] Figure 4 The image shows the XRD pattern of the untreated iron-based nanocrystalline alloy strip in step (1) of Embodiment 1 of the present invention.

[0089] Figure 5 The image shows the XRD pattern of the iron-based nanocrystalline alloy strip after crystallization heat treatment in step (1) of Embodiment 1 of the present invention. Detailed Implementation

[0090] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0091] Example 1

[0092] This embodiment provides a method for preparing a core-shell structured iron-based nanocrystalline alloy composite powder, wherein the chemical formula of the iron-based nanocrystalline alloy in the composite powder is Fe. 78 .Si 15 B3P3Cu1, wherein the thickness of the alumina coating layer is 80 nm, and the alumina accounts for 3% of the mass percentage of the composite powder; the thickness of the carbon coating layer is 50 nm, and the carbon accounts for 10% of the mass percentage of the composite powder.

[0093] The preparation method includes the following steps:

[0094] (1) The iron-based nanocrystalline alloy strip prepared according to the formula is heat-treated in a nitrogen atmosphere. The heat-treated strip is put into a wall-breaking machine for repeated mechanical crushing and passed through a 100-200 mesh sieve to obtain iron-based nanocrystalline alloy powder.

[0095] The heat treatment includes sequential heating, a first cooling, and a second cooling; the heating is performed by heating to 450°C at a rate of 10°C / min and holding for 20 min; the first cooling is performed by cooling to 350°C at a rate of 15°C / min and holding for 30 min; the second cooling is performed by furnace cooling.

[0096] (2) Alumina powder with a particle size of 500nm is uniformly mixed with the iron-based nanocrystalline alloy powder in step (1), and the resulting mixed powder is placed in a servo press and pressed into a round cake with a radius of 40mm and a height of 10mm under a pressure of 20MPa.

[0097] (3) The disc obtained in step (2) is heat-treated under a nitrogen atmosphere, taken out of the furnace, placed in liquid nitrogen for cooling, and the cooled mixed powder is placed in a vibratory mill for 3 minutes and then taken out. After magnetic separation, alumina powder and preliminary alumina-coated iron-based nanocrystalline magnetic powder are obtained. Then, the preliminary alumina-coated iron-based nanocrystalline magnetic powder is ball-milled in a ball mill. The ball milling solvent is alcohol, which just submerges the material surface. The ball milling balls are zirconia balls with a ball-to-material ratio of 5:1. The ball milling is carried out at a speed of 150 r / min for 20 hours. After drying and sieving, alumina-coated iron-based nanocrystalline magnetic powder with a particle size of 8-12 μm is obtained.

[0098] The heat treatment includes a first heating and a second heating in sequence; the first heating is to heat to 900°C at a heating rate of 10°C / min and hold for 20 min; the second heating is to heat to 1180°C at a heating rate of 15°C / min and hold for 5 min.

[0099] (4) Graphite carbon powder with a particle size of 5 μm, oleic acid and the magnetic powder in step (3) are mixed and subjected to high-energy ball milling at a speed of 1000 r / min for a total time of 6 h. After each high-energy ball milling for 3 min, the ball milling is stopped and cooled for 17 min. The forward and reverse rotation program is used to ensure that the powder is ball milled uniformly. Then, heat treatment is carried out in a nitrogen atmosphere. After furnace cooling, the core-shell structured iron-based nanocrystalline alloy composite powder is obtained.

[0100] The mass ratio of the magnetic powder to the surfactant is 20:1;

[0101] The heat treatment involves heating to 400°C at a heating rate of 8°C / min and holding at that temperature for 8 hours.

[0102] Example 2

[0103] This embodiment provides a method for preparing a core-shell structured iron-based nanocrystalline alloy composite powder, wherein the chemical formula of the iron-based nanocrystalline alloy in the composite powder is Fe. 73.5 .Si 13.5 B9Cu1Nd3.

[0104] The alumina coating layer, carbon coating layer, and process parameters of the preparation method are the same as in Example 1.

[0105] Example 3

[0106] This embodiment provides a method for preparing a core-shell structured iron-based nanocrystalline alloy composite powder, wherein the chemical formula of the iron-based nanocrystalline alloy in the composite powder is Fe. 73.5 .Si 13.5 B9P3Cu1.

[0107] The alumina coating layer, carbon coating layer, and process parameters of the preparation method are the same as in Example 1.

[0108] Example 4

[0109] This embodiment provides a method for preparing core-shell structured iron-based nanocrystalline alloy composite powder. Except for the final temperature of heating in step (1) being 350°C, the rest is the same as in Example 1.

[0110] Example 5

[0111] This embodiment provides a method for preparing core-shell structured iron-based nanocrystalline alloy composite powder. Except for the final temperature of heating in step (1) being 550°C, the rest is the same as in Example 1.

[0112] Example 6

[0113] This embodiment provides a method for preparing iron-based nanocrystalline alloy composite powder with a core-shell structure. Except for the endpoint temperature of the first cooling step (1) being 300°C, the rest is the same as in Example 1.

[0114] Example 7

[0115] This embodiment provides a method for preparing a core-shell structured iron-based nanocrystalline alloy composite powder. Except for the endpoint temperature of the first cooling step (1) being 420°C, the rest is the same as in Embodiment 1.

[0116] Example 8

[0117] This embodiment provides a method for preparing core-shell structured iron-based nanocrystalline alloy composite powder. Except for the endpoint temperature of the first heating step (3), which is 800°C, the rest is the same as in Example 1.

[0118] Example 9

[0119] This embodiment provides a method for preparing iron-based nanocrystalline alloy composite powder with a core-shell structure. Except for the endpoint temperature of the first heating in step (3) being 1000℃, the rest is the same as in embodiment 1.

[0120] Example 10

[0121] This embodiment provides a method for preparing core-shell structured iron-based nanocrystalline alloy composite powder. Except for the endpoint temperature of the second heating step (3), which is 1150°C, the rest is the same as in Example 1.

[0122] Example 11

[0123] This embodiment provides a method for preparing iron-based nanocrystalline alloy composite powder with a core-shell structure. Except for the endpoint temperature of the second heating step (3) being 1250°C, the rest is the same as in Example 1.

[0124] Example 12

[0125] This embodiment provides a method for preparing core-shell structured iron-based nanocrystalline alloy composite powder. Except for the heating rate of 10℃ / min in step (3), the rest is the same as in embodiment 1.

[0126] Example 13

[0127] This embodiment provides a method for preparing core-shell structured iron-based nanocrystalline alloy composite powder. Except for step (4), which is not heat-treated in a nitrogen atmosphere, the rest is the same as in Example 1.

[0128] Comparative Example 1

[0129] This comparative example provides a method for preparing a core-shell structured iron-based nanocrystalline alloy composite powder, wherein the chemical formula of the iron-based nanocrystalline alloy in the composite powder is Fe. 73.5 .Si 13.5 B9Nb3Cu1.

[0130] The alumina coating layer, carbon coating layer, and process parameters of the preparation method are the same as in Example 1.

[0131] Comparative Example 2

[0132] This comparative example provides a method for preparing a core-shell structured iron-based nanocrystalline alloy composite powder, wherein the chemical formula of the iron-based nanocrystalline alloy in the composite powder is Fe. 78 .Si 15 B3P3Cu1, wherein the thickness of the alumina coating layer is 150 nm, and the alumina accounts for 3% of the mass percentage of the composite powder.

[0133] The carbon coating layer and the process parameters for its preparation method are the same as in Example 1.

[0134] Comparative Example 3

[0135] This comparative example provides a method for preparing a core-shell structured iron-based nanocrystalline alloy composite powder, wherein the chemical formula of the iron-based nanocrystalline alloy in the composite powder is Fe. 78 .Si 15 B3P3Cu1, wherein the thickness of the alumina coating layer is 40 nm, and the alumina accounts for 1% of the mass percentage of the composite powder.

[0136] The carbon coating layer and the process parameters for its preparation method are the same as in Example 1.

[0137] Comparative Example 4

[0138] This comparative example provides a method for preparing a core-shell structured iron-based nanocrystalline alloy composite powder, wherein the chemical formula of the iron-based nanocrystalline alloy in the composite powder is Fe. 78 .Si 15 B3P3Cu1, wherein the thickness of the carbon coating layer is 100 nm, and the carbon accounts for 5% of the mass percentage of the composite powder.

[0139] The alumina coating and the process parameters for its preparation are the same as in Example 1.

[0140] Comparative Example 5

[0141] This comparative example provides a method for preparing a core-shell structured iron-based nanocrystalline alloy composite powder, wherein the chemical formula of the iron-based nanocrystalline alloy in the composite powder is Fe. 78 .Si 15 B3P3Cu1, wherein the thickness of the carbon coating layer is 20 nm, and the carbon accounts for 2% of the mass percentage of the composite powder.

[0142] The alumina coating and the process parameters for its preparation are the same as in Example 1.

[0143] Comparative Example 6

[0144] This comparative example provides a method for preparing a core-shell structured iron-based nanocrystalline alloy composite powder, wherein the chemical formula of the iron-based nanocrystalline alloy in the composite powder is Fe. 78 .Si 15 B3P3Cu1.

[0145] The alumina coating and the process parameters of the preparation method are the same as in Example 1, but carbon coating is not performed.

[0146] Comparative Example 7

[0147] This comparative example provides a method for preparing a core-shell structured iron-based nanocrystalline alloy composite powder, wherein the chemical formula of the iron-based nanocrystalline alloy in the composite powder is Fe. 78 .Si 15 B3P3Cu1.

[0148] The carbon coating layer and the process parameters of the preparation method are the same as those in Example 1, but the alumina coating is not performed. The iron-based nanocrystalline alloy powder obtained in step (1) is directly processed in step (3).

[0149] The core-shell structured iron-based nanocrystalline alloy composite powder prepared in Example 1 was characterized by SEM and XRD. The SEM characterization results are as follows: Figure 1-2 As shown, the composite powder has good sphericity; the XRD characterization results are as follows. Figure 3-5 As shown, the composite powder has a nanocrystalline / amorphous dual-phase structure.

[0150] Performance testing:

[0151] The morphology, average particle size, saturation magnetization, minimum reflection loss of the composite powder / paraffin composite sample at the optimal matching thickness, and frequency range with reflection loss below -10dB obtained from the above examples and comparative examples were tested. The saturation magnetization was measured using a VSM. The composite powder and paraffin were mixed uniformly at a weight ratio of 3:2 and pressed into a ring-shaped sample. The complex permeability μ=μ'-jμ" and complex permittivity ε=ε'-jε" of the composite powder sample in the frequency range of 4~15GHz were tested using a vector network analyzer. The RL curve was calculated based on the transmission line principle and the measured electromagnetic parameters. The test results are shown in Table 1.

[0152] Table 1

[0153]

[0154]

[0155] The following points can be drawn from Table 1:

[0156] (1) The present invention uses an iron-based nanocrystalline alloy with an outer layer of aluminum oxide and carbon composite coating, which makes the resulting composite powder light in density, strong in corrosion resistance, and also has excellent magnetic properties such as high saturation magnetization and high permeability.

[0157] (2) By comparing Examples 1 and Examples 4-5, it can be seen that when the final temperature of the heat treatment of the iron-based nanocrystalline alloy strip in step (1) is too low, the residual stress of the strip leads to a larger particle size of the nanocrystalline powder obtained by ball milling, resulting in an increase in the magnetic permeability of the final composite powder but a decrease in its microwave absorption performance; when the final temperature of the heat treatment of the iron-based nanocrystalline alloy strip in step (1) is too high, the strip partially crystallizes due to the high temperature, resulting in the destruction of the amorphous structure, and a decrease in the microwave absorption performance of the final composite powder; by comparing Examples 1 and Examples 6-7, it can be seen that when the final temperature of the first cooling of the heat treatment of the iron-based nanocrystalline alloy strip in step (1) is too low, the residual stress of the strip leads to a larger particle size of the nanocrystalline powder obtained by ball milling, resulting in an increase in the magnetic permeability of the final composite powder but a decrease in its microwave absorption performance; when the final temperature of the first cooling of the heat treatment of the iron-based nanocrystalline alloy strip in step (1) is too high, the strip partially crystallizes due to the high temperature, resulting in the destruction of the amorphous structure, and a decrease in the microwave absorption performance of the final composite powder.

[0158] (3) By comparing Examples 1 and Examples 8-9, it can be seen that when the final temperature of the first heating in the heat treatment of alumina powder and iron-based nanocrystalline alloy powder in step (3) is too low, the nanocrystalline powder is not completely melted, resulting in uneven initial coating of alumina and ultimately reducing the microwave absorption performance; when the final temperature of the first heating in the heat treatment of alumina powder and iron-based nanocrystalline alloy powder in step (3) is too high, the nanocrystalline powder is over-melted, resulting in poor sphericity of the powder after coating and reducing the microwave absorption performance of the composite powder; by comparing Examples 1 and Examples 10-11, it can be seen that when the final temperature of the second heating in step (3) is too low, the alumina coating layer is not uniform due to the decrease in annealing temperature, resulting in a decrease in the microwave absorption performance of the composite powder; when the final temperature of the second heating in step (3) is too high, the nanocrystalline powder is over-melted, resulting in poor sphericity of the powder after coating and reducing the microwave absorption performance of the composite powder.

[0159] (4) As can be seen from the comparison between Example 1 and Comparative Example 1, the addition of Nb element to iron-based nanocrystals reduces the saturation magnetization of the material and affects the coupling structure between the nanocrystals and the alumina / carbon coating layer, which further reduces the overall performance of the composite powder.

[0160] (5) The microwave absorption performance originates from the good impedance matching and electromagnetic synergy provided by the shell (dielectric)-core (magnetic) structure of the composite powder. The microwave absorption performance of the composite powder can be controlled by adjusting the alumina and carbon content (alumina shell thickness and carbon shell thickness). A comparison of Example 1 and Comparative Examples 2-3 shows that when the alumina content is too high and the coating layer thickness is also too thick, the microwave absorption performance decreases due to the disruption of the impedance matching and electromagnetic synergy between the core and shell. When the alumina content is too low and the coating layer thickness is also too thin, the microwave absorption performance decreases due to the disruption of the impedance matching and electromagnetic synergy between the core and shell. A comparison of Example 1 and Comparative Examples 4-5 shows that when the carbon content is too high and the coating layer thickness is also too thick, the microwave absorption performance decreases due to the disruption of the impedance matching and electromagnetic synergy between the core and shell. When the carbon content is too low and the coating layer thickness is also too thin, the microwave absorption performance decreases due to the disruption of the impedance matching and electromagnetic synergy between the core and shell.

[0161] (6) As can be seen from the comparison between Example 1 and Comparative Example 6, if carbon coating is not performed, the saturation magnetization of the obtained powder will increase, but at the same time the magnetic-dielectric coupling effect of the coating layer will be weakened, and the microwave absorption performance of the obtained powder will decrease significantly. As can be seen from the comparison between Example 1 and Comparative Example 7, if the iron-based nanocrystals are not mixed with alumina, and the crushed iron-based nanocrystal powder is directly annealed and then carbon coated, the resulting composite powder will not have a spherical morphology, but will be a flake or fragmented powder, which will also reduce the saturation magnetization of the material, resulting in a decrease in the microwave absorption performance of the powder.

[0162] The applicant declares that the detailed structural features of the present invention are illustrated through the above embodiments, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the components selected in the present invention, additions of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

[0163] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0164] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0165] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A core-shell structured Fe-based nanocrystalline alloy composite powder having excellent wave-absorbing properties and magnetic properties, characterized by comprising a core-shell structure in which a core is composed of a Fe-based nanocrystalline alloy powder and a shell is composed of a magnetic material. The composite powder comprises, from inside to outside, a core, an alumina coating layer and a carbon coating layer; the core is an iron-based nanocrystalline alloy; the chemical formula of the iron-based nanocrystalline alloy is Fe a Si b B c P d Cu e RE f , wherein RE is any one or a combination of at least two of Nd, Gd, Ce, Sm and Gd, a, b, c, d, e and f respectively represent the atomic percentage content of the corresponding element, and satisfy 0≤b≤15, 0≤c≤9, 0≤d≤5, 0≤e≤1, 0≤f≤3, the balance is Fe, and satisfy a+b+c+d+e+f=100. The thickness of the alumina coating layer is 60-100 nm, and the mass percentage of the alumina in the composite powder is 2-5%. The thickness of the carbon coating layer is 40-60 nm, and the mass percentage of the carbon in the composite powder is 4-15%.

2. The composite powder according to claim 1, wherein The iron-based nanocrystalline alloy is in an amorphous / α-Fe nanocrystalline dual-phase structure.

3. A method for producing the composite powder according to any one of claims 1 or 2, characterized by, The preparation method comprises the following steps: (1) performing heat treatment on the iron-based nanocrystalline alloy strip prepared according to the formula amount, crushing to obtain an iron-based nanocrystalline alloy powder; (2) mixing alumina powder with the iron-based nanocrystalline alloy powder in step (1), and performing pressing to obtain a round cake; (3) performing heat treatment on the round cake in step (2), and obtaining alumina powder and a preliminary alumina-coated iron-based nanocrystalline magnetic powder after magnetic separation; (4) mixing graphite carbon powder, a surfactant, and the magnetic powder in step (3), and sequentially performing high-energy ball milling and heat treatment to obtain the iron-based nanocrystalline alloy composite powder with a core-shell structure.

4. The production method according to claim 3, characterized by, The heat treatment in step (1) comprises sequentially performed heating and cooling stages.

5. The preparation method according to claim 3, characterized in that, The heat treatment in step (1) is performed in an inert gas protective atmosphere.

6. The preparation method according to claim 4, characterized in that, The heating rate of the heating is 8-12 ℃ / min.

7. The preparation method according to claim 4, characterized in that, The terminal temperature of the heating is 400-500 ℃.

8. The preparation method according to claim 4, characterized in that, The holding time of the heating is 10-30 min.

9. The preparation method according to claim 4, characterized in that, The cooling stage comprises sequentially performed first cooling and second cooling.

10. The method of claim 9, wherein, The cooling rate of the first cooling is 13-18 ℃ / min.

11. The preparation method according to claim 9, characterized in that, The terminal temperature of the first cooling is 320-370 ℃.

12. The method of claim 9, wherein, The holding time of the first cooling is 20-40 min.

13. The preparation method according to claim 9, characterized in that, The second cooling is furnace cooling.

14. The method of claim 3, wherein, The iron-based nanocrystalline alloy powder obtained in step (1) is sieved.

15. The method of claim 14, wherein, The sieving is sieving through a 100-200 mesh sieve.

16. The preparation method according to claim 3, characterized in that, The particle size of the alumina powder in step (2) is 400-600 nm.

17. The preparation method according to claim 3, characterized in that, The pressure of the pressing in step (2) is 15-25 MPa.

18. The method of claim 3, wherein, The heat treatment in step (3) is performed in an inert gas protective atmosphere.

19. The method of claim 3, wherein, The heat treatment in step (3) comprises sequentially performed first heating and second heating.

20. The method of claim 19, wherein, The heating rate of the first heating is 8-12 ℃ / min.

21. The method of claim 19, wherein, The terminal temperature of the first heating is 850-950 ℃.

22. The preparation method according to claim 19, characterized in that, The holding time of the first heating is 10-30 min.

23. The preparation method according to claim 19, characterized in that, The heating rate of the second heating is 13-17 ℃ / min.

24. The method of claim 19, wherein, The terminal temperature of the second heating is 1170-1210 ℃.

25. The preparation method according to claim 19, characterized in that, The holding time of the second heating is 3-10 min.

26. The method of claim 3, wherein, The heat treatment in step (3) is taken out from the furnace and cooled in liquid nitrogen.

27. The preparation method according to claim 3, characterized in that, The preliminary alumina-coated iron-based nanocrystalline magnetic powder in step (3) is sequentially subjected to ball milling, drying, and sieving to obtain alumina-coated iron-based nanocrystalline magnetic powder with a particle size of 8-12 μm.

28. The method of claim 27, wherein, The rotation speed of the ball milling is 100-200 r / min.

29. The preparation method according to claim 27, characterized in that, The ball milling time is 17-22 h.

30. The method of claim 3, wherein, The particle size of the graphite carbon powder in step (4) is 3-8 μm.

31. The method of claim 3, wherein, The surfactant in step (4) comprises any one of oleic acid, sucrose fatty acid ester, or polysorbate.

32. The method of claim 3, wherein, The mass ratio of the magnetic powder to the surfactant in step (4) is (18-22):

1.

33. The method of claim 3, wherein the method further comprises: The high-energy ball milling process of step (4) comprises: stopping the ball milling and cooling after each high-energy ball milling, and then repeating the high-energy ball milling again.

34. The method of claim 3, wherein, The rotation speed of the high-energy ball milling is 900-1100 r / min.

35. The preparation method according to claim 3, characterized in that, The total time of the high-energy ball milling is 4-8 h.

36. The preparation method according to claim 33, characterized in that, The time of each single ball milling in the high-energy ball milling is 2-6 min.

37. The preparation method according to claim 33, characterized in that, The cooling time in the high-energy ball milling is 15-20 min.

38. The preparation method according to claim 3, characterized in that, The heat treatment of step (4) is carried out in an inert gas protective atmosphere.

39. The method of claim 3, wherein, The heating rate of the heat treatment of step (4) is 5-10 ℃ / min.

40. The method of claim 3, wherein, The terminal temperature of the heat treatment of step (4) is 350-450 ℃.

41. The method of claim 3, wherein, The holding time of the heat treatment of step (4) is 6-10 h.

42. The method of claim 3, wherein, The heat treatment of step (4) is followed by furnace cooling.

43. The method of claim 3, wherein the method is carried out at a temperature of about 20°C to about 30°C. The preparation method comprises the following steps: (1) preparing an iron-based nanocrystalline alloy strip according to the formula quantity, carrying out heat treatment in an inert gas protective atmosphere, crushing, and sieving through a 100-200 mesh sieve to obtain an iron-based nanocrystalline alloy powder; The heat treatment of step (1) comprises sequentially carried out heating, first cooling and second cooling; the heating is heating to 400-500 ℃ at a heating rate of 8-12 ℃ / min and holding for 10-30 min; the first cooling is cooling to 320-370 ℃ at a cooling rate of 13-18 ℃ / min and holding for 20-40 min; and the second cooling is furnace cooling; (2) mixing alumina powder with a particle size of 400-600 nm and the iron-based nanocrystalline alloy powder of step (1), and pressing at a pressure of 15-25 MPa to obtain a round cake; (3) carrying out heat treatment on the round cake of step (2) in an inert gas protective atmosphere, taking it out of the furnace, cooling it in liquid nitrogen, and obtaining alumina powder and preliminary alumina-coated iron-based nanocrystalline magnetic powder after magnetic separation, and then ball milling the preliminary alumina-coated iron-based nanocrystalline magnetic powder at a rotation speed of 100-200 r / min for 17-22 h, drying and sieving to obtain alumina-coated iron-based nanocrystalline magnetic powder with a particle size of 8-12 μm; The heat treatment of step (3) comprises sequentially carried out first heating and second heating; the first heating is heating to 850-950 ℃ at a heating rate of 8-12 ℃ / min and holding for 10-30 min; and the second heating is heating to 1170-1210 ℃ at a heating rate of 13-17 ℃ / min and holding for 3-10 min; (4) mixing graphite carbon powder with a particle size of 3-8 μm, a surfactant and the magnetic powder of step (3), and carrying out high-energy ball milling at a rotation speed of 900-1100 r / min and a total time of 4-8 h, stopping the ball milling and cooling for 15-20 min after each high-energy ball milling for 2-6 min, and then carrying out heat treatment in an inert gas protective atmosphere, to obtain the core-shell structure iron-based nanocrystalline alloy composite powder after furnace cooling; The mass ratio of the magnetic powder to the surfactant is (18-22):1; The heat treatment of step (4) is heating to 350-450 ℃ at a heating rate of 5-10 ℃ / min and holding for 6-10 h.

44. Use of the composite powder according to claim 1 or 2, wherein The composite powder is used for electromagnetic wave absorbers. The composite powder is used for electromagnetic wave absorbers.

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