Pr-doped SmFeN powder and preparation method thereof

Abstract

The application relates to the technical field of magnetic materials, and discloses a praseodymium-coated samarium iron nitride powder and a preparation method thereof. The praseodymium-coated samarium iron nitride powder comprises a samarium iron nitride powder and a coating layer coated on the outer surface of the samarium iron nitride powder; and the material of the coating layer is pure metal. The praseodymium-coated samarium iron nitride powder material is obtained through process steps of pretreatment, target material feeding, target surface pretreatment, coating and post-treatment. The praseodymium-coated samarium iron nitride powder is prepared by a magnetron sputtering device under airtight and oxygen-free conditions, the oxidation degree of the powder is reduced from the source, the oxygen content of the obtained product is significantly lower than that of a product prepared by a traditional process, the dense praseodymium coating layer prevents oxygen and water from invading and avoids process pollution and powder agglomeration, and the praseodymium and the samarium iron nitride produce a magnetic performance synergistic effect, so that the comprehensive magnetic performance of the powder, such as residual magnetism, intrinsic coercive force and magnetic energy product, is effectively improved.

Description

Technical Field

[0001] This invention relates to the field of magnetic materials technology, and more specifically, to a praseodymium-coated samarium iron nitrogen powder and its preparation method. Background Technology

[0002] Rare earth permanent magnet materials, as core functional materials in modern industry, are increasingly widely used in electric vehicles, wind turbines, precision electronic components, aerospace equipment, and other fields. Their performance directly determines the energy efficiency and reliability of end products. In recent years, the prices of rare earth elements Nd and Pr have risen rapidly. How to utilize relatively abundant rare earth resources such as Sm and Ce, which are cheaper, has become a hot topic in the field of magnetic materials. Therefore, samarium iron nitrogen materials, which do not contain heavy rare earth elements or neodymium, have more significant economic advantages and application prospects.

[0003] Samarium iron nitrogen ( Samarium iron nitride (SFeNi) permanent magnets are considered a next-generation permanent magnet material after NdFeB due to their high saturation magnetization, high Curie temperature, high intrinsic coercivity, and excellent oxidation resistance. They hold irreplaceable potential, especially in high-temperature, miniaturized applications—their magnetocrystalline anisotropy field can reach over 20T, far exceeding that of NdFeB (approximately 7.3T), theoretically possessing superior demagnetization resistance. However, SFeNi magnets are prone to decomposition at high temperatures, making them difficult to apply in environments with high temperature requirements. To address this instability issue, in powder metallurgy processes (such as the preparation of bonded magnets or hot-pressed magnets), a layer of praseodymium (usually achieved through nanoparticles, thin films, or surface alloying) is typically coated to improve powder flowability and pressing density. The praseodymium layer can interact with… Forming a better interfacial bond helps improve the overall thermal stability of the material and partially offsets [the effects of the previous method]. The disadvantage of easy decomposition at high temperatures is addressed by expanding the operating temperature range.

[0004] Traditional "praseodymium-plated samarium-iron-nitrogen" materials are mainly prepared through a smelting-crushing-nitriding process, which is currently the mainstream method in the industry. The process is as follows: Sm, Fe, and Pr metal raw materials are smelted into alloy ingots in a certain proportion → crushed into micron-sized powder → nitrided at high temperature in a nitrogen atmosphere to form "Pr solid solution type" materials. "Powder. This process has inherent drawbacks: it cannot construct an independent and uniform functional coating layer on the surface of powder particles, the product is prone to oxidation, and the process flexibility is poor. In addition, magnetron sputtering, as a mature surface modification technology, has advantages such as high coating purity, strong adhesion to the substrate, and controllable thickness, and is theoretically the best method for preparing 'Pr shell-'" While samarium iron nitrogen (SMR) is an ideal method for producing composite powders, it still faces technical challenges: 1) Throughout the process, the refined SMR powder has high surface activity and is easily oxidized during washing, drying, and subsequent treatment. If the surface is not effectively protected, the oxidation reaction will erode the interior of the material, severely affecting its magnetic properties; 2) Target failure can prevent the subsequent processes from operating normally. Direct DC sputtering can lead to "target poisoning"—a sudden drop in sputtering current, unstable glow discharge, and frequent arcing, ultimately causing the deposition process to be interrupted and continuous coating to be impossible.

[0005] Therefore, there is a need to develop a preparation method that can solve the oxidation of active materials, achieve three-dimensional uniform coating of powder, and has a stable and controllable process. Summary of the Invention

[0006] To address at least one of the aforementioned problems, this invention employs an inclined magnetron sputtering device and combines target pretreatment with sputtering coating processes to provide a method for dry preparation of praseodymium-coated samarium iron nitrogen powder by magnetron sputtering.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A method for preparing praseodymium-coated samarium iron nitrogen powder includes the following steps:

[0009] S1. Pretreatment: The samarium iron nitrogen powder is pretreated by cleaning and drying;

[0010] S2, Feeding: Install the high-purity praseodymium target on the cathode target holder of the tilting magnetron sputtering equipment, and load the pretreated samarium iron nitrogen powder into the tilting self-rotating powder loading tray;

[0011] S3. Target surface pretreatment: Under vacuum conditions, the praseodymium target is surface treated to remove the surface oxide layer and obtain a pure praseodymium target.

[0012] S4. Coating: Turn off the target surface pretreatment mode, turn on the DC magnetron sputtering power supply, and use the magnetron sputtering process to coat the surface of the samarium iron nitrogen powder with praseodymium metal material to obtain coated samarium iron nitrogen powder.

[0013] S5. Post-processing: After vacuum cooling, the vacuum is broken to remove the coated samarium iron nitrogen powder, and the powder is immediately sealed with inert gas.

[0014] Optionally, the target pretreatment method in step S3 is either the assisted cathode excited ion bombardment method or the radio frequency power supply assisted ignition method.

[0015] Optionally, in step S3, the power supply of the auxiliary cathode-excited ion bombardment method is 200-3000W, the bombardment time is 10-30min, and the powder loading tray is blocked by a baffle during the bombardment process.

[0016] Optionally, in step S3, the power supply for RF power-assisted ignition is 200-3000W, the bombardment time is 15-25min, and after the discharge stabilizes, it is switched to DC sputtering.

[0017] Optionally, in step S2, the tilt angle of the tilting self-rotating powder loading tray is 10° to 45°, and the rotation speed is 1 to 10 rpm.

[0018] Optionally, the median particle size D50 of the samarium iron nitrogen powder in step S1 is 1–50 μm. D50 is obtained using a laser particle size analyzer and refers to the particle size corresponding to a cumulative percentage of 50% of the samarium iron nitrogen powder based on its volumetric particle size distribution; it characterizes the average particle size level of the overall samarium iron nitrogen powder, with particles smaller than this value accounting for 50% of the volume and particles larger than this value accounting for 50% of the volume.

[0019] Optionally, the environment in steps S3 and S4 is a vacuum condition, and the vacuum degree is <5×10⁻⁶. -3 Pa, the working gas is argon with a purity ≥ 99.999%.

[0020] Optionally, the conditions for depositing the praseodymium coating in step S4 are: working gas pressure 0.1-1.0 Pa, praseodymium target power 300-2000 W, and sputtering time 5-100 min.

[0021] Another objective of this invention is to provide a praseodymium-coated samarium iron nitrogen powder prepared by the above-described preparation method.

[0022] Optionally, the praseodymium-coated samarium-iron-nitrogen powder includes samarium-iron-nitrogen powder and a coating layer covering the samarium-iron-nitrogen powder; the coating layer is made of pure metal.

[0023] This invention provides a praseodymium-coated samarium iron nitrogen powder and its preparation method, which has at least the following beneficial effects:

[0024] 1. This application constructs a uniform and dense praseodymium metal coating layer on the surface of samarium iron nitrogen powder using a magnetron sputtering dry process. This coating layer effectively blocks the intrusion of oxygen and moisture, inhibiting powder oxidation at its source and significantly reducing the oxygen content of the product (see Table 1). Simultaneously, the coating layer forms a strong physical-metallurgical bond with the substrate, exhibiting strong adhesion and resistance to peeling. The process is carried out in a closed, oxygen-free environment, avoiding the risk of praseodymium target oxidation and ensuring the stability of the preparation process. Furthermore, the dense praseodymium coating layer may... The powder generates interfacial coupling, which synergistically optimizes the magnetic properties of the material. This results in a significant improvement in key magnetic properties such as intrinsic coercivity, remanence, and energy product compared to products produced by traditional wet processes (see Table 1), thereby expanding its application potential under harsh conditions such as high temperature and high humidity.

[0025] 2. In response to the easy oxidation of praseodymium metal targets, this application innovatively designs a target surface pretreatment scheme (assisted cathode ion bombardment or RF power supply assisted ignition), which can efficiently remove the oxide layer on the target surface. This fundamentally solves the key technical problems caused by target surface oxidation in traditional sputtering processes, such as "target poisoning", sputtering arcing, and deposition rate decay. It ensures stable glow and controllable parameters throughout the DC magnetron sputtering main process, and significantly improves process repeatability and product consistency in mass production.

[0026] 3. This invention adopts a completely dry magnetron sputtering process, which generates and emits no wastewater or waste gas throughout the process. It completely avoids the environmental governance pressure and pollutant treatment costs associated with wet coating processes, meets the development requirements of green, low-carbon and clean production in modern manufacturing, and has significant environmental benefits and industrial sustainability. Attached Figure Description

[0027] Figure 1 A process flow diagram for preparing praseodymium-coated samarium iron nitrogen powder is provided in the embodiments of this application;

[0028] Figure 2 A schematic diagram illustrating the coating device according to an embodiment of the present invention;

[0029] Figure 3 A top view of the tray and agitator blades.

[0030] Reference numerals in the attached drawings: 1. Powder; 2. Cavity; 21. Mounting position; 3. Tray; 31. Receiving tank; 4. Stirring blade; 5. Rotation structure; 6. Station switching structure; 7. Target material. Detailed Implementation

[0031] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0032] The following is a detailed description of a method for preparing praseodymium-coated samarium iron nitrogen powder according to an embodiment of this application.

[0033] This invention provides a method for preparing praseodymium-coated samarium iron nitrogen powder, the process flow of which can be found in [reference needed]. Figure 1 It mainly includes the following steps:

[0034] S1. Pretreatment: The samarium iron nitrogen powder is pretreated by cleaning and drying;

[0035] S2, Feeding: Install the high-purity praseodymium target on the cathode target holder of the tilting magnetron sputtering equipment, and load the pretreated samarium iron nitrogen powder into the tilting self-rotating powder loading tray;

[0036] S3. Target surface pretreatment: Under vacuum conditions, the praseodymium target is surface treated to remove its surface oxide layer and obtain a pure praseodymium target.

[0037] S4. Coating: Turn off the target surface pretreatment mode, turn on the DC magnetron sputtering power supply, and use the magnetron sputtering process to coat the surface of the samarium iron nitrogen powder with praseodymium metal to obtain coated samarium iron nitrogen powder.

[0038] S5. Post-processing: After vacuum cooling, the vacuum is broken to remove the coated samarium iron nitrogen powder, and the powder is immediately sealed with inert gas.

[0039] This invention employs magnetron sputtering dry technology to construct a uniform and dense praseodymium-based coating layer, which effectively blocks the intrusion of media such as oxygen and moisture, fundamentally preventing the oxidation and degradation of the samarium iron nitrogen powder surface, while also avoiding the risk of process failure caused by praseodymium target oxidation. This coating layer forms a strong physical-metallurgical bond with the powder matrix, exhibiting significantly improved adhesion compared to traditional wet coatings, and is less prone to peeling or detachment.

[0040] like Figure 2 and Figure 3 As shown, the coating equipment used in this embodiment of the invention includes a cavity 2, a tray 3, a stirring blade 4, a driving element (not shown in the figure), a rotation structure 5, and a station switching structure 6. The cavity 2 has multiple spaced mounting positions 21 for mounting a target material 7 connected to the cathode. The tray 3 has a receiving groove 31, and the tray 3 is inclinedly disposed in the cavity 2. The bottom of the tray 3 is used to connect to the anode, and the receiving groove 31 of the tray 3 is used to hold powder 1. The stirring blade 4 is disposed on one side of the bottom wall of the receiving groove 31 for stirring the powder 1, and the driving element is used to drive the stirring blade 4 to rotate. The tray 3 is mounted on the station switching structure 6, which is used to change the position of the tray 3 so that the tray 3 can be aligned with one of the mounting positions 21. The rotation structure 5 is used to drive the tray 3 to rotate around its own axis.

[0041] The tray 3 is tilted inside the cavity 2 (the axis of the tray 3 is not 90° to the horizontal plane). During operation, the rotating structure 5 allows the tray 3 to rotate around its own axis. This allows the powder 1 to be tumbled in the tray 3 not only by the mechanical tumbling of the stirring blades 4, but also by the tumbling caused by its own gravity under the influence of the tilt angle. This allows the powder 1 to be mixed three-dimensionally on the basis of planar mixing, resulting in more uniform coating of the powder 1. The station switching structure 6 can drive the tray 3 to move, so that the tray 3 can be aligned with the target material 7 at different installation positions 21. That is, through this structure design of continuous preparation of different target materials 7 in multiple online stages, multiple sets of powder coating production can be carried out continuously. Compared with the previous single-stage production, the production time is shortened and the production efficiency is improved.

[0042] Specifically, the target surface pretreatment method described in step S3 is either assisted cathode ion bombardment or RF power supply assisted ignition. This invention innovatively designs a target surface pretreatment scheme (assisted cathode ion bombardment or RF power supply assisted ignition), which can efficiently remove the oxide layer on the target surface. This fundamentally solves key technical problems in traditional sputtering processes such as "target poisoning," sputtering arcing, and deposition rate attenuation caused by target surface oxidation. It ensures stable glow discharge and controllable parameters throughout the DC magnetron sputtering main process, significantly improving process repeatability and product consistency in mass production.

[0043] Specifically, in step S3, the power supply for the auxiliary cathode-excited ion bombardment method is 200-3000W, and the bombardment time is 10-30 minutes. During the bombardment process, the powder loading tray is shielded by a baffle. On the one hand, before the main DC sputtering process begins, the plasma generated by the auxiliary cathode is used to bombard the praseodymium target surface with high-energy ions to physically remove the surface oxide layer and restore the metallic conductivity of the target material. On the other hand, the powder loading tray needs to be shielded by a baffle during this process to prevent powder contamination, ensure powder cleanliness, and facilitate uniform coating.

[0044] Specifically, in step S3, the power supply for RF-assisted ignition is 200-3000W, and the bombardment time is 15-25 minutes. After the discharge stabilizes, the process switches to DC sputtering. During pretreatment, the plasma is first ignited using an RF power supply. Taking advantage of the ability of RF sputtering to treat insulating / semi-insulating targets, the oxide layer on the praseodymium target surface is "removed." After the target surface regains its metallic properties and the discharge stabilizes, the process switches to DC power for efficient and stable body sputtering coating.

[0045] Specifically, in step S2, the tilt angle of the inclined rotating powder loading disc is 10° to 45°, and the rotation speed is 1 to 10 rpm. As an example, the rotating disc has a specific tilt angle of 10° to 45°, such as, but not limited to, any value or a range between 10°, 12°, 15°, 18°, 20°, 22°, 25°, 27°, 30°, 32°, 35°, and 45°; the rotation speed of the rotating disc is 1 to 10 rpm, such as, but not limited to, any value or a range between 1 rpm, 3 rpm, 4 rpm, 5 rpm, 7 rpm, 9 rpm, and 10 rpm. The tilted rotating disc achieves dynamic tumbling of the powder. This specific tilt angle and rotation speed ensure that the powder can continuously and uniformly tumble under gravity, allowing the samarium iron nitrogen powder to obtain a uniform and dense coating layer.

[0046] Specifically, in step S1, the median particle size D50 of the samarium iron nitrogen powder is 1–50 μm. The samarium iron nitrogen powder obtained by this invention has a controllable particle size distribution, and its median particle size D50 is controlled within the range of 1 μm–50 μm, which can meet the requirements of subsequent coating. If the particle size of the samarium iron nitrogen powder is less than 1 μm, it is prone to forming micro agglomerates under the influence of van der Waals forces when tumbling on the rotating disk, which may affect the uniformity of the coating layer and is not conducive to obtaining the optimal coating effect.

[0047] Specifically, the environment in steps S3 and S4 is under vacuum conditions, and the vacuum level is <5×10⁻⁶. -3 Pa, the working gas is argon with a purity ≥99.999%. The vacuum environment can effectively block the intrusion of oxygen, moisture and other media, fundamentally avoiding the oxidation and degradation of the samarium iron nitrogen powder surface, while avoiding the risk of process failure caused by the oxidation of praseodymium target material.

[0048] Specifically, the conditions for depositing the praseodymium coating in step S4 are: working gas pressure 0.1-1.0 Pa, praseodymium target sputtering power 300-2000 W, and sputtering time 5-100 min.

[0049] As an example, the deposition conditions for the praseodymium coating of this invention are as follows: working gas pressure 0.1–1.0 Pa, for example, the working gas pressure can be any value or a range between 0.1 Pa, 0.2 Pa, 0.3 Pa, 0.4 Pa, 0.5 Pa, 0.6 Pa, 0.8 Pa, 0.9 Pa, and 1.0 Pa; and praseodymium target sputtering power 300–2000 W, for example, the praseodymium target sputtering power can be any value or a range between 300 W, 500 W, 800 W, 1000 W, 1200 W, 1500 W, and 2000 W. Specifically, in the actual magnetron sputtering process, the thickness of the praseodymium coating is controlled by adjusting the sputtering power of the praseodymium target and the deposition time, thus obtaining praseodymium-coated samarium iron nitrogen powder. This invention uses a dry magnetron sputtering process, which produces no wastewater or waste gas emissions throughout the entire preparation process, making it quite environmentally friendly. In addition, the preparation process has good repeatability and strong controllability, making it suitable for large-scale preparation of praseodymium-encapsulated samarium iron nitrogen powder, which has good prospects for engineering applications.

[0050] Specifically, praseodymium-coated samarium-iron-nitrogen powder includes samarium-iron-nitrogen powder and a coating layer covering the samarium-iron-nitrogen powder; the coating layer is made of pure metal.

[0051] As an example, the coating layer can be prepared using a single pure metal material, or it can use praseodymium and other pure metals as coating materials for sputtering targets, wherein the other pure metals can be at least one of copper, aluminum, and zinc. The powder coated by the composite coating has higher intrinsic coercivity and lower oxygen content. The main function of the other metal layers is to physically isolate oxygen, form a low-melting-point interface layer with the praseodymium material, improve the density of the coating, and have good conductivity, providing a new approach for the design of multilayer / composite functional coatings.

[0052] Example 1

[0053] This embodiment includes the following steps:

[0054] With an average particle size of 1.0 μm The powder particles are sequentially subjected to ultrasonic cleaning with acetone, cleaning with anhydrous ethanol, rinsing with deionized water, and vacuum drying to remove surface organic contaminants and impurities. Then, they are loaded into a tilted self-rotating powder loading tray with an inclination angle of 20° and a rotation speed of 8 rpm to ensure that the powder can be continuously and evenly turned over under the action of gravity.

[0055] A high-purity praseodymium target (purity ≥ 99.9%) is mounted on the cathode target holder of the tilting magnetron sputtering equipment. The vacuum chamber is closed, and the system is evacuated to a background vacuum of 4 × 10⁻⁶. -3 The vacuum chamber pressure was adjusted to 0.8 Pa, and high-purity argon gas (purity ≥99.999%) was continuously introduced for protection. The target surface was then bombarded with particles excited by an auxiliary cathode. The auxiliary cathode (an independently controllable anode or hot cathode electron emission source) was activated to generate high-density plasma for ion bombardment cleaning of the praseodymium target surface. Specifically, the bombardment power was 320 W, and the target surface was bombarded for 15 minutes. During this process, a baffle shielded the powder loading tray.

[0056] Under vacuum conditions, the auxiliary cathode was turned off, the DC magnetron sputtering power supply was turned on, and the DC sputtering power intensity was adjusted to 320W with an argon flow rate of 50 sccm to obtain a higher deposition rate and maintain a stable discharge. Then, the baffle was removed, and the deposition rate in the rotating disk was increased. The powder was coated by magnetron sputtering for 10 minutes to obtain a relatively thin but dense praseodymium coating. After sputtering, the argon gas supply was stopped, and the powder was allowed to cool naturally under vacuum. The vacuum was then broken to remove the coated "praseodymium-coated samarium iron nitrogen" powder, which was immediately encapsulated with argon gas.

[0057] The performance of the "praseodymium-coated samarium iron nitrogen" powder prepared in the above steps was tested using a vibrating sample magnetometer (VSM), and the oxygen content of the powder was tested using an inert melting-infrared absorption analyzer. The test results are shown in Table 1.

[0058] Example 2

[0059] This embodiment includes the following steps:

[0060] With an average particle size of 1.0 μm The powder particles are sequentially subjected to ultrasonic cleaning with acetone, cleaning with anhydrous ethanol, rinsing with deionized water, and vacuum drying to remove surface organic contaminants and impurities. Then, they are loaded into a tilted self-rotating powder loading tray with an inclination angle of 20° and a rotation speed of 8 rpm to ensure that the powder can be continuously and evenly turned over under the action of gravity.

[0061] A high-purity praseodymium target (purity ≥ 99.9%) is mounted on the cathode target holder of the tilting magnetron sputtering equipment. The vacuum chamber is closed, and the system is evacuated to a background vacuum of 4 × 10⁻⁶. -3 The vacuum chamber pressure was adjusted to 0.8 Pa, and high-purity argon gas (purity ≥99.999%) was continuously introduced for protection. The target surface was then bombarded with particles excited by an auxiliary cathode. The auxiliary cathode (an independently controllable anode or hot cathode electron emission source) was activated to generate high-density plasma for ion bombardment cleaning of the praseodymium target surface. Specifically, the bombardment power was 320 W, and the target surface was bombarded for 15 minutes. During this process, a baffle shielded the powder loading tray.

[0062] Under vacuum conditions, the auxiliary cathode was turned off, the DC magnetron sputtering power supply was turned on, and the DC sputtering power intensity was adjusted to 320W with an argon flow rate of 50 sccm to obtain a higher deposition rate and maintain a stable discharge. Then, the baffle was removed, and the deposition rate in the rotating disk was increased. The powder was coated by magnetron sputtering for 50 minutes to obtain a composite material with a relatively thin but dense praseodymium coating. After sputtering, the argon gas supply was stopped, and the powder was allowed to cool naturally under vacuum. The vacuum was then broken to remove the coated "praseodymium-coated samarium iron nitrogen" powder, which was immediately encapsulated with argon gas.

[0063] The performance of the "praseodymium-coated samarium iron nitrogen" powder prepared in the above steps was tested using a vibrating sample magnetometer (VSM), and the oxygen content of the powder was tested using an inert melting-infrared absorption analyzer. The test results are shown in Table 1.

[0064] Example 3

[0065] This embodiment includes the following steps:

[0066] With an average particle size of 2.5 μm The powder particles are sequentially subjected to ultrasonic cleaning with acetone, cleaning with anhydrous ethanol, rinsing with deionized water, and vacuum drying to remove surface organic contaminants and impurities. Then, they are loaded into a tilted self-rotating powder loading tray with an inclination angle of 30° and a rotation speed of 3 rpm to ensure that the powder can be continuously and evenly turned over under the action of gravity.

[0067] A high-purity praseodymium target (purity ≥ 99.9%) is mounted on the cathode target holder of the tilting magnetron sputtering equipment. The vacuum chamber is closed, and the system is evacuated to a background vacuum of 4 × 10⁻⁶. -3 The vacuum chamber pressure was adjusted to 0.5 Pa, and high-purity argon gas (purity ≥99.999%) was continuously introduced for protection. The target surface was then bombarded with particles excited by an auxiliary cathode. The auxiliary cathode (an independently controllable anode or hot cathode electron emission source) was activated to generate high-density plasma for ion bombardment cleaning of the praseodymium target surface. Specifically, the bombardment power was 300 W, and the target surface was bombarded for 20 minutes. During this process, a baffle shielded the powder loading tray.

[0068] Under vacuum conditions, the auxiliary cathode was turned off, the DC magnetron sputtering power supply was turned on, the DC sputtering power was adjusted to 320W, the argon flow rate was 50sccm, and a stable discharge was maintained. Then the baffle was removed to discharge the Sm2Fe in the rotating disk. 17 N3 powder was magnetron sputtered for 5 minutes to obtain a praseodymium-coated samarium iron nitrogen composite material. After sputtering, the argon gas supply was stopped, and the material was allowed to cool naturally under vacuum. The vacuum was then broken to remove the coated "praseodymium-coated samarium iron nitrogen" powder, which was immediately encapsulated with argon gas.

[0069] The performance of the "praseodymium-coated samarium iron nitrogen" powder prepared in the above steps was tested using a vibrating sample magnetometer (VSM), and the oxygen content of the powder was tested using an inert melting-infrared absorption analyzer. The test results are shown in Table 1.

[0070] Example 4

[0071] This embodiment includes the following steps:

[0072] With an average particle size of 2.5 μm The powder particles are sequentially subjected to ultrasonic cleaning with acetone, cleaning with anhydrous ethanol, rinsing with deionized water, and vacuum drying to remove surface organic contaminants and impurities. Then, they are loaded into a tilted self-rotating powder loading tray with an inclination angle of 20° and a rotation speed of 8 rpm to ensure that the powder can be continuously and evenly turned over under the action of gravity.

[0073] A high-purity praseodymium target (purity ≥ 99.9%) is mounted on the cathode target holder of the tilting magnetron sputtering equipment. The vacuum chamber is closed, and the system is evacuated to a background vacuum of 4 × 10⁻⁶. -3 The vacuum chamber pressure was adjusted to 0.8 Pa, and high-purity argon gas (purity ≥99.999%) was continuously introduced for protection. The target surface was then bombarded with particles excited by an auxiliary cathode. The auxiliary cathode (an independently controllable anode or hot cathode electron emission source) was activated to generate high-density plasma for ion bombardment cleaning of the praseodymium target surface. Specifically, the bombardment power was 320 W, and the target surface was bombarded for 15 minutes. During this process, a baffle shielded the powder loading tray.

[0074] Under vacuum conditions, the auxiliary cathode was turned off, the DC magnetron sputtering power supply was turned on, the DC sputtering power intensity was adjusted to 320W, and the argon flow rate was 50sccm to obtain a higher deposition rate and maintain a stable discharge. Then the baffle was removed, and the powder in the rotating disk was magnetron sputtered for 30 minutes to obtain a composite material with a relatively thin but dense praseodymium coating. After sputtering, the argon gas supply was stopped, and the material was allowed to cool naturally under vacuum conditions. The vacuum was then broken to remove the coated "praseodymium-coated samarium iron nitrogen" powder, and it was immediately encapsulated with argon gas.

[0075] The performance of the "praseodymium-coated samarium iron nitrogen" powder prepared in the above steps was tested using a vibrating sample magnetometer (VSM), and the oxygen content of the powder was tested using an inert melting-infrared absorption analyzer. The test results are shown in Table 1.

[0076] Example 5

[0077] This embodiment includes the following steps:

[0078] With an average particle size of 5 μm The powder particles are sequentially subjected to ultrasonic cleaning with acetone, cleaning with anhydrous ethanol, rinsing with deionized water, and vacuum drying to remove surface organic contaminants and impurities. Then, they are loaded into a tilted self-rotating powder loading tray with an inclination angle of 40° and a rotation speed of 2 rpm to ensure that the powder can be continuously and evenly turned over under the action of gravity.

[0079] A high-purity praseodymium target (purity ≥ 99.9%) is mounted on the cathode target holder of the tilting magnetron sputtering equipment. The vacuum chamber is closed, and the system is evacuated to a background vacuum of 4 × 10⁻⁶. -3 The vacuum chamber pressure was adjusted to 0.2 Pa, and high-purity argon gas (purity ≥99.999%) was continuously introduced for protection. The surface treatment of the target material was performed by bombardment using an RF power supply-assisted ignition method. Specifically, the RF power supply connected to the target material was first turned on, set to 200W, and the surface oxide layer was treated for 25 minutes. Then, the power supply was switched to DC.

[0080] Under vacuum conditions, the RF power supply was turned off, and the DC magnetron sputtering power supply was turned on. The DC sputtering power was adjusted to 400W, and the argon flow rate was 40 sccm to perform fine, low-stress deposition. The baffle was removed, and the deposition was carried out on the rotating disk. The powder was coated by magnetron sputtering for 50 minutes. The argon gas supply was stopped, and the powder was allowed to cool naturally under vacuum. The vacuum was then broken to remove the coated "praseodymium-coated samarium iron nitrogen" powder, which was immediately sealed with argon gas.

[0081] The performance of the "praseodymium-coated samarium iron nitrogen" powder prepared in the above steps was tested using a vibrating sample magnetometer (VSM), and the oxygen content of the powder was tested using an inert melting-infrared absorption analyzer. The test results are shown in Table 1.

[0082] Example 6

[0083] This embodiment includes the following steps:

[0084] With an average particle size of 10 μm The powder particles are sequentially subjected to ultrasonic cleaning with acetone, cleaning with anhydrous ethanol, rinsing with deionized water, and vacuum drying to remove surface organic contaminants and impurities. Then, they are loaded into a tilted self-rotating powder loading tray with an inclination angle of 25° and a rotation speed of 5 rpm to ensure that the powder can be continuously and evenly turned over under the action of gravity.

[0085] High-purity praseodymium (purity ≥ 99.9%) and aluminum targets are mounted on the cathode target holder of the tilting magnetron sputtering equipment. The vacuum chamber is closed, and the system is evacuated to a background vacuum of 4 × 10⁻⁶. -3 The vacuum chamber pressure was adjusted to 0.5 Pa, and high-purity argon gas (≥99.999%) was continuously introduced for protection, providing a low-pressure sputtering environment. Surface treatment of the target material was performed by particle bombardment using an auxiliary cathode (an independently controllable anode or hot cathode electron emission source). High-density plasma was generated to perform ion bombardment cleaning on the praseodymium and aluminum target surfaces. Specifically, the bombardment power density was 300 W, and the target surface was bombarded for 40 minutes, during which the powder loading tray was shielded by a baffle.

[0086] Under vacuum conditions, the auxiliary cathode was turned off, and the DC magnetron sputtering power supply was turned on. The DC sputtering power was 400W, and the argon flow rate was 50sccm to obtain a higher deposition rate and maintain a stable discharge. Then, the baffle was removed, and the discharge was carried out on the rotating disk. The powder was coated by magnetron sputtering, with praseodymium target sputtering first for 30 minutes. After sputtering, aluminum target sputtering was started for 20 minutes to obtain a composite material with praseodymium / aluminum coating. After sputtering, the argon gas supply was stopped and the powder was naturally cooled under vacuum. The vacuum was then broken and the coated "praseodymium / aluminum coated samarium iron nitrogen" powder was taken out and immediately encapsulated with argon gas.

[0087] The performance of the "praseodymium / aluminum-coated samarium iron nitrogen" powder prepared in the above steps was tested using a vibrating sample magnetometer (VSM), and the oxygen content of the powder was tested using an inert melting-infrared absorption analyzer. The test results are shown in Table 1.

[0088] Example 7

[0089] This embodiment uses the same process conditions as Example 2 to prepare the praseodymium coating layer, obtaining praseodymium-coated samarium iron nitrogen powder. The difference lies in the type of powder used in this embodiment. The particle size of the powder differs from that in Example 2; this example uses 20 μm. The powder was then subjected to the same performance tests as in Example 2, and the specific parameters are shown in Table 1.

[0090] Example 8

[0091] This embodiment uses the same process conditions as Example 2 to prepare the praseodymium coating layer, obtaining praseodymium-coated samarium iron nitrogen powder. The difference lies in the type of powder used in this embodiment. The particle size of the powder and the sputtering time of the praseodymium target differ from those in Example 2. In this example, a 30 μm powder is used. The powder was sputtered and coated for 60 minutes. Finally, the powder was subjected to the same performance tests as in Example 2. The specific parameters are shown in Table 1.

[0092] Example 9

[0093] This embodiment uses the same process conditions as Example 2 to prepare the praseodymium coating layer, obtaining praseodymium-coated samarium iron nitrogen powder. The difference lies in the type of powder used in this embodiment. The particle size of the powder and the sputtering time of the praseodymium target differ from those in Example 2. In this example, a 40 μm target was selected. The powder was sputtered and coated for 80 minutes. Finally, the powder was subjected to the same performance tests as in Example 2. The specific parameters are shown in Table 1.

[0094] Example 10

[0095] This embodiment uses the same process conditions as Example 2 to prepare the praseodymium coating layer, obtaining praseodymium-coated samarium iron nitrogen powder. The difference lies in the type of powder used in this embodiment. The particle size of the powder and the sputtering time of the praseodymium target differ from those in Example 2. In this example, a 50 μm target was selected. The powder was sputtered and coated for 100 minutes. Finally, the powder was subjected to the same performance tests as in Example 2. The specific parameters are shown in Table 1.

[0096] Comparative Example 1

[0097] This embodiment uses the same process conditions as Example 1 to prepare the praseodymium coating layer, obtaining praseodymium-coated samarium iron nitrogen powder. The difference lies in the type of powder used in this embodiment. The particle size of the powder differs from that in Example 2; in this example, a particle size of 0.5 μm is used. The powder was then subjected to the same performance tests as in Example 1, and the specific parameters are shown in Table 1.

[0098] Comparative Example 2

[0099] This embodiment uses the same process conditions as Example 10 to prepare the praseodymium coating layer, obtaining praseodymium-coated samarium iron nitrogen powder. The difference lies in the selection of... The particle size of the powder differs from that in Example 10; this example uses 60 μm. The powder was then subjected to the same performance tests as in Example 10, and the specific parameters are shown in Table 1.

[0100] Comparative Example 3

[0101] This embodiment uses the same process conditions as Example 9 to prepare the praseodymium coating layer, obtaining praseodymium-coated samarium iron nitrogen powder. The difference lies in the selection of... The particle size of the powder differs from that in Example 10; this example uses 100 μm. The powder was then subjected to the same performance tests as in Example 9, and the specific parameters are shown in Table 1.

[0102] Comparative Example 4

[0103] Batching and Smelting: Using 100kg as a standard, high-purity metals Sm, Pr, and Fe are mixed evenly in a mass ratio of 13.5:1.5:85 and smelted in a vacuum induction furnace. Rapid cooling is required to obtain a homogeneous mixture. Main phase, avoiding the precipitation of rare earth-rich phases or α-Fe;

[0104] Powdering: First, "hydrogen crushing" is carried out at 300℃ to crack the alloy ingot by utilizing the "hydrogen embrittlement" effect of hydrogen; then, an air jet mill is used to strictly control the powder particle size D50 to 1.0μm.

[0105] Nitriding: carried out in a pure N2 atmosphere at 480℃;

[0106] Powder pretreatment: The qualified nitrided powder is discharged in an inert glove box to avoid premature oxidation. Then anhydrous ethanol / petroleum ether inert organic solvent is added and dispersed by low-speed stirring to remove surface micro powder and dust.

[0107] Wet coating: The coating solution of silane coupling agent and praseodymium powder is slowly dripped into the powder suspension, stirred at low speed at room temperature for 30-60 minutes. After coating is completed, the coated powder is separated by centrifugation and filtration or vacuum filtration, and excess solvent and unadsorbed coating agent are discarded.

[0108] Curing and Packaging: The powder is dried at low temperature in a vacuum oven at 60-80℃, cooled under an inert atmosphere, slightly dispersed and agglomerated, sieved, and vacuum-sealed to obtain a finished powder with complete coating, oxidation resistance, and long-term storage.

[0109] The performance of the "praseodymium-coated samarium iron nitrogen" powder prepared in the above steps was tested using a vibrating sample magnetometer (VSM), and the oxygen content of the powder was tested using an inert melting-infrared absorption analyzer. The test results are shown in Table 1.

[0110] Comparative Example 5

[0111] Comparative Example 5 used the same process conditions as Comparative Example 4 to prepare the praseodymium coating, obtaining praseodymium-coated samarium iron nitrogen powder. The difference lies in the process conditions used in this comparative example. The particle size of the powder is different from that of Comparative Example 4; this comparative example uses 10 μm. The powder was then subjected to the same performance tests as in Comparative Example 4, and the specific parameters are shown in Table 1.

[0112] Comparative Example 6

[0113] Comparative Example 6 used the same process conditions as Comparative Example 4 to prepare the praseodymium coating, obtaining praseodymium-coated samarium iron nitrogen powder. The difference lies in the process conditions used in this comparative example. The particle size of the powder is different from that of Comparative Example 4; this comparative example uses 30 μm. The powder was then subjected to the same performance tests as in Comparative Example 4, and the specific parameters are shown in Table 1.

[0114] Comparative Example 7

[0115] Comparative Example 7 used the same process conditions as Comparative Example 4 to prepare the praseodymium coating, obtaining praseodymium-coated samarium iron nitrogen powder. The difference lies in the process conditions used in this comparative example. The particle size of the powder is different from that of Comparative Example 4; this comparative example uses a particle size of 50 μm. The powder was then subjected to the same performance tests as in Comparative Example 4, and the specific parameters are shown in Table 1.

[0116] Table 1 shows the powder performance parameters obtained in Examples 1-10 and Comparative Examples 1-7. This invention employs a magnetron sputtering dry method to complete the coating preparation in a closed, oxygen-free environment, thus suppressing powder oxidation from the source of the process. Combining the performance test results of Examples 1-10 and Comparative Examples 1-7 in Table 1, it can be seen that the oxygen content of the praseodymium-coated samarium iron nitrogen powder prepared by this invention is controlled below 200 ppm, and in some cases even below 100 ppm; while the oxygen content of powders prepared by traditional wet processes is generally higher than 1000 ppm. This indicates that the dense praseodymium coating layer in the praseodymium-coated samarium iron nitrogen powder prepared by the magnetron sputtering dry process of this application not only effectively isolates oxygen and moisture throughout the entire process, but also avoids the pollution and oxidation risks associated with wet processes.

[0117] As can be seen from Examples 1-10 and Comparative Examples 4-7 in Table 1, compared with the problems of powder agglomeration and interface performance degradation easily caused by traditional wet processes, the dry process of the present invention can maintain good powder dispersibility and interface integrity; praseodymium, as a light rare earth metal, is compatible with... The synergistic effect of magnetic properties produced by the powder results in powders that are significantly superior to traditional wet-process products in key magnetic property indicators such as remanence, intrinsic coercivity, and magnetic energy product, thus significantly improving overall magnetic properties.

[0118] This invention adopts a completely dry magnetron sputtering process, which generates and emits no wastewater or waste gas throughout the entire process. It completely avoids the environmental governance pressure and pollutant treatment costs associated with wet coating processes, meets the development requirements of green, low-carbon and clean production in modern manufacturing, and has significant environmental benefits and industrial sustainability.

[0119] While the disclosure is as stated above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of this disclosure, and all such changes and modifications will fall within the protection scope of this invention.

Claims

1. A method for preparing praseodymium-coated samarium iron nitrogen powder, characterized in that, Includes the following steps: S1. Pretreatment: The samarium iron nitrogen powder is pretreated by cleaning and drying; S2, Feeding: Install the high-purity praseodymium target on the cathode target holder of the tilting magnetron sputtering equipment, and load the pretreated samarium iron nitrogen powder into the tilting self-rotating powder loading tray; S3. Target surface pretreatment: Under vacuum conditions, the praseodymium target is surface treated to remove the surface oxide layer and obtain a pure praseodymium target. S4. Coating: Turn off the target surface pretreatment mode, turn on the DC magnetron sputtering power supply, and use the magnetron sputtering process to coat the surface of the samarium iron nitrogen powder with praseodymium metal material to obtain coated samarium iron nitrogen powder. S5. Post-processing: After vacuum cooling, the vacuum is broken to remove the coated samarium iron nitrogen powder, and the powder is immediately sealed with inert gas.

2. The preparation method according to claim 1, characterized in that, The target pretreatment method in step S3 is either the assisted cathode excited ion bombardment method or the radio frequency power supply assisted ignition method.

3. The preparation method according to claim 2, characterized in that, In step S3, the power supply for the auxiliary cathode-excited ion bombardment method is 200-3000W, the bombardment time is 10-30min, and the powder loading tray is blocked by a baffle during the bombardment process.

4. The preparation method according to claim 2, characterized in that, In step S3, the power supply for RF power-assisted ignition is 200-3000W, the bombardment time is 15-25min, and after the discharge stabilizes, it switches to DC sputtering.

5. The preparation method according to claim 1, characterized in that, In step S2, the tilt angle of the tilting self-rotating powder loading tray is 10° to 45°, and the rotation speed is 1 to 10 rpm.

6. The preparation method according to claim 1, characterized in that, The median particle size D50 of the samarium iron nitrogen powder in step S1 is 1-50 μm.

7. The preparation method according to claim 1, characterized in that, In steps S3 and S4, the environment is under vacuum conditions, and the vacuum level is <5×10⁻⁶. -3 Pa, the working gas is argon with a purity ≥ 99.999%.

8. The preparation method according to claim 1, characterized in that, The conditions for depositing the praseodymium metal coating in step S4 are: working gas pressure 0.1-1.0 Pa, praseodymium target sputtering power 300-2000 W, and sputtering time 5-100 min.

9. A praseodymium-coated samarium iron nitrogen powder, characterized in that, The praseodymium-containing samarium-iron-nitrogen powder is prepared by the preparation method according to any one of claims 1-8.

10. The praseodymium-coated samarium iron nitrogen powder according to claim 9, characterized in that, The praseodymium-coated samarium-iron-nitrogen powder includes samarium-iron-nitrogen powder and a coating layer covering the samarium-iron-nitrogen powder; the coating layer is made of pure metal.

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