A wet ball-milling induced orientation and arrangement ferrite magnetic powder material and a preparation method thereof

Abstract

This invention discloses a ferrite magnetic powder material and its preparation method that induces oriented alignment through wet ball milling, belonging to the field of new materials technology. The method addresses the problem that traditional wet ball milling cannot induce preferred grain alignment due to the isotropic nature of mechanical action. A coarse ferrite powder slurry is injected into a dedicated ball milling device. During the milling process, a rotating magnetic field is simultaneously applied and the grinding chamber is rotated to form a directional fluid shear field. A closed-loop control system maintains a fixed phase difference between the rotating magnetic field vector and the local fluid velocity vector, achieving spatiotemporal synchronization. Simultaneously, the slurry rheological properties, medium filling rate, and process parameters are precisely controlled. This magnetic powder exhibits significantly enhanced response capabilities in subsequent magnetic field orientation pressing, effectively improving the remanence of the final sintered magnet and reducing coercivity fluctuations, with excellent batch-to-batch consistency in magnetic properties.

Description

Technical Field

[0001] This invention relates to the field of new materials technology, specifically to a ferrite magnetic powder material and its preparation method that is induced to align by wet ball milling. Background Technology

[0002] Ferrite magnetic materials, as indispensable functional materials in modern electronic components, are widely used in high-frequency transformers, inductors, electromagnetic interference suppression devices, and micromotors. With the rapid development of emerging technologies such as 5G communication, new energy vehicles, and the Internet of Things, electronic systems are placing comprehensive performance requirements on magnetic components, demanding higher frequencies, lower losses, smaller sizes, and higher energy conversion efficiency. Against this backdrop, improving the magnetic properties of ferrite materials, especially their remanence (…), is crucial. ) and coercivity ( The synergistic optimization of magnetic powder particles has become an important research direction in the field of materials science and engineering. The key prerequisite for realizing high-performance anisotropic magnets is that the magnetic powder particles have the ability to preferentially orient themselves along the easy magnetization axis before forming, so as to form a highly ordered microstructure during the subsequent magnetic field orientation pressing process and maximize the magnetic performance output.

[0003] Currently, wet ball milling has become the mainstream technology for ferrite powder preparation due to its advantages in particle size distribution control, agglomeration suppression, and component uniformity. For example, the invention patent with publication number CN109437315B proposes a method for preparing rubber and plastic ferrite magnetic powder by combining wet fine grinding with tempering treatment, which effectively reduces chloride ion residue and improves magnetic permeability. However, its grinding process is essentially still a non-directional mechanical crushing and mixing operation, without introducing any physical or chemical mechanism to induce grain orientation. This results in completely random spatial orientation of grains in the obtained powder. Even if an orientation magnetic field is applied subsequently, it is difficult to achieve a high degree of orientation due to the initial disordered structure. Although the production process of soft magnetic manganese-zinc ferrite with announcement number CN100418921C adopts a strategy of combining multi-stage wet milling before and after pre-sintering with vibratory ball milling, which significantly improves the powder reactivity and sintering density, and thus optimizes the initial magnetic permeability and power loss characteristics, its entire grinding system is still based on isotropic energy input. The impact and shearing effect of the ball milling media on the particles are uniformly distributed in three-dimensional space, which cannot provide directional guidance for the crystallographic orientation of the grains at the microscale, resulting in the lack of a "pre-organized" structure inside the powder that is conducive to magnetic field orientation.

[0004] As high-end electronic devices continue to approach the limits of magnetic performance consistency and performance limits, the inherent "non-orientation" defect of the traditional wet ball milling process is becoming increasingly prominent. Fundamentally, this stems from the fact that conventional ball milling processes focus solely on reducing particle size and homogenizing composition, neglecting the strong magnetocrystalline anisotropy inherent in ferrite crystals; that is, their magnetization behavior is highly dependent on the direction of the external field relative to the crystal's easy magnetization axis. If the grains are not initially aligned along the easy magnetization axis during powder preparation, regardless of subsequent increases in magnetic field strength, the Brownian motion, frictional resistance, and mutual shielding effects of the particles in the slurry or dry powder state will severely weaken the orientation efficiency, ultimately resulting in the magnet's remanence being far below the theoretical upper limit. This lack of orientation not only limits the improvement of individual magnetic performance parameters but also triggers a series of secondary problems, such as increased batch-to-batch magnetic performance fluctuations, higher molding pressure requirements, and increased sintering deformation risks, seriously affecting the large-scale manufacturing of high-reliability devices. Therefore, while existing technologies solve the problems of particle size control and purity, they inadvertently exclude the key dimension of "orientation regulation" from the process design, forming a hidden bottleneck for performance improvement.

[0005] The core challenge facing current ferrite powder preparation technology lies in how to overcome the physical limitations of isotropic mechanical action while maintaining the inherent advantages of wet ball milling (such as controllable particle size and good dispersibility), and actively construct microstructures with preferred orientation during the powder synthesis stage. This challenge cannot be solved simply by fine-tuning process parameters; it requires a re-examination of the intrinsic mechanism of wet ball milling from the perspective of multi-physics field synergy, including ball milling kinetics, fluid environment, and external field coupling.

[0006] Therefore, how to effectively induce ferrite grains to preferentially align along the easy magnetization axis without sacrificing the basic physicochemical properties of the powder through specific wet ball milling process parameters and environmental control, thereby significantly improving its orientation potential and the comprehensive magnetic properties of the final magnet, has become a key challenge and an urgent technical problem for those skilled in the art. Summary of the Invention

[0007] The purpose of this invention is to provide a ferrite magnetic powder material and preparation method that induces orientation alignment through wet ball milling; it solves the technical problem that the existing wet ball milling process, due to its isotropic mechanical action, cannot actively induce the grains to preferentially align along the easy magnetization axis during the ferrite powder preparation stage, resulting in low subsequent magnetic field orientation efficiency, magnet remanence (Br) far below the theoretical upper limit, and poor performance consistency.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: This invention constructs a wet ball milling system with multi-physics coupling, simultaneously applying a rotating magnetic field and a directional fluid shear field during the ball milling process, and precisely controlling the rheological properties of the slurry system, the medium filling rate, the ball milling speed, and the magnetic field parameters. This allows the ferrite grains to be subjected to the synergistic effect of directional magnetic torque and fluid drag force while being mechanically crushed and dispersed, thereby achieving a preferred orientation alignment along the easy magnetization axis of the crystal at the nanometer to micrometer scale.

[0009] The obtained magnetic powder material exhibits a significantly enhanced orientation response during subsequent magnetic field orientation pressing, and the remanence of the final sintered magnet ( Increased by more than 15%, cohesion ( The standard deviation of fluctuation is reduced to within ±3 Oe, and the batch consistency is significantly better than that of traditional processes.

[0010] The ferrite magnetic powder material of this invention is a soft magnetic or permanent magnetic ferrite with a spinel or hexagonal crystal structure, and its general chemical formula is: or ,in Selected from , , , , , At least one element in it.

[0011] The average particle size of the magnetic powder particles is to Particle size distribution index Not greater than Specific surface area is to The magnetic powder exhibits crystallographic orientation even without an external magnetic field. Orientation The Lotgering factor calculation method is used: ; in, , is the ratio of the measured integral intensity of the (00l) crystal plane series diffraction peaks to the sum of the integral intensities of all (hkl) diffraction peaks; The corresponding ratios for completely randomly oriented powder samples of the same material are calculated from JCPDS standard card data. For spinel structures, the ratios are selected from... <111> Similar calculations were performed on the direction-dependent (hhl) peaks.

[0012] The preparation method of the present invention includes the following steps: First, the pre-calcined ferrite powder, deionized water, dispersant, and pH adjuster are mixed according to the following mass ratio. Mix and prepare a solution with a solid content of to The slurry; the dispersant is sodium polyacrylate (PAA-Na) or triammonium citrate, with a molecular weight of [missing information]. to The amount added is based on the dry powder mass. The pH adjuster is ammonia or sodium hydroxide solution, used to adjust the pH value of the slurry to... - This makes the absolute value of the zeta potential of the slurry greater than To ensure the particles have a strong negative charge on their surface and inhibit agglomeration, the slurry is then injected into a dedicated wet ball mill. This mill includes a cylindrical grinding chamber made of non-magnetic stainless steel or zirconium oxide, an adjustable-speed rotating spindle, high-density grinding media, a rotating magnetic field generating unit, and a fluid circulation control system. The grinding media consists of yttrium-stabilized zirconium oxide balls with a diameter of [missing information]. to The filling rate is % of the effective volume of the grinding chamber. to During the ball milling process, the following three physical fields are activated simultaneously: Apply a frequency of to Magnetic induction intensity is to A rotating magnetic field is generated by an array of four orthogonal electromagnetic coils mounted on the outer periphery of the grinding chamber. The coil windings employ a Litz wire structure to reduce high-frequency eddy current losses. Each coil is powered by a phase difference of [missing information]. The sinusoidal alternating current synthesizes a vector magnetic field that rotates uniformly in the horizontal plane; the direction of the rotating magnetic field is always parallel to the axial centerline of the grinding cavity, ensuring that the magnetic torque on all grains is in the same direction; due to its magnetocrystalline anisotropy, the ferrite grains will precess around their own easy magnetization axis under the action of the rotating magnetic field, and gradually align with the instantaneous magnetic field direction in the plane of magnetic field rotation under the damping effect.

[0013] Control the grinding chamber to to The rotation speed is around its axis, and a built-in spiral guide plate made of polytetrafluoroethylene is also present, with a pitch equal to the diameter of the cavity. times, inclination angle is Its function is to force the slurry to be transported axially and form a stable laminar shear zone; within this zone, the fluid velocity gradient... Maintain at to Between them, the resulting fluid drag force applies additional torque to the pre-magnetically oriented grains, causing their long axes to align further parallel to the streamline direction; the fluid shear field and the rotating magnetic field are spatially coplanar and temporally synchronized, and their synergistic effect constrains the grains in a single orientation plane in three-dimensional space.

[0014] The temperature of the grinding chamber is controlled by an external cooling jacket. to This prevents excessive temperature rise in the slurry due to mechanical energy input, which could lead to hydration of the particle surface or degradation of the dispersant. Simultaneously, an online viscosity sensor monitors the apparent viscosity of the slurry in real time; if the viscosity deviates from the set value ± During this time, the circulation pump flow rate is automatically adjusted to maintain flow field stability; the total ball milling time is Hours to Hours, during which each Minute pause Minutes are allocated to release accumulated stress and calibrate the magnetic field phase.

[0015] After ball milling, the resulting slurry is processed... Large particles are removed by filtration through a mesh screen, followed by centrifugal separation (speed). ,time (minutes) or ultrafiltration membrane (molecular weight cutoff) Dehydration to obtain a moisture content of less than The filter cake; the filter cake in Drying in a vacuum drying oven After hours, primary magnetic powder was obtained; subsequently, the primary magnetic powder was exposed to air in a certain atmosphere. to Low-temperature tempering treatment The process involves milling for hours to eliminate lattice defects introduced by ball milling and stabilize the surface hydroxyl structure; after tempering, the magnetic powder is crushed to a loose bulk density of [missing information]. to Thus, the ferrite magnetic powder material with induced orientation alignment by wet ball milling as described in this invention is obtained.

[0016] In a preferred embodiment of the present invention, the magnetic induction intensity of the rotating magnetic field... With ball mill speed Satisfying the relation: ; in This is the proportionality coefficient, and its value range is... to ;when The unit is rpm. When the unit is T, This range is taken. This relationship ensures that the magnetic torque and the fluid shear force are matched on the order of magnitude, avoiding particle agglomeration due to excessively strong magnetic fields or the inability to overcome interparticle van der Waals forces due to insufficient shear.

[0017] In another preferred embodiment of the present invention, the yield stress of the slurry With plastic viscosity Satisfying the Bingham fluid model: ; in Controlled to , Controlled to This rheological property ensures that the slurry maintains structural stability when static, while rapidly transforming into a low-viscosity flow state under ball mill shearing, which is beneficial for the formation and maintenance of oriented structures.

[0018] In another preferred embodiment of the present invention, the pre-calcination temperature of the ferrite coarse powder is: to The heat preservation time is The heating rate is 1 hour. The pre-calcined product was confirmed by X-ray diffraction to be a single-phase ferrite, without... or Impurities; the average particle size of the pre-calcined powder is to This provides a suitable initial crushing scale for subsequent wet grinding.

[0019] Furthermore, the specific structure of the dedicated wet ball milling device of the present invention is as follows: the grinding chamber has an inner diameter of... ,long The cylinder is made of Stainless steel, inner wall polished to To reduce particle adhesion; both ends of the cavity are connected to the drive motor and circulation pipeline via magnetohydrodynamic sealed bearings; four sets of electromagnetic coils are embedded in the four quadrant grooves on the outer wall of the cavity, with each set of coils having a number of turns of [missing information]. Turns, wire diameter is The insulation class is H; the coil is driven by an independent four-channel programmable power supply, the current waveform is a sine wave, and the frequency accuracy is ± Amplitude resolution The spiral guide plate is fixed to the inner wall of the cavity via a flange, and its surface is coated with a thickness of [missing information]. A diamond-like carbon (DLC) coating is used to reduce the coefficient of friction; the abrasive media consists of yttrium-stabilized zirconia balls (Y-TZP) with a density of [missing information]. Vickers hardness ≥ Wear rate less than .

[0020] Furthermore, the orientation degree described in this invention The determination method is as follows: take dried magnetic powder and press it into... disc (pressure) (without a directional magnetic field), using an X-ray diffractometer (Cu Kα radiation, )exist - Scan within range, step size Timing for each step Seconds; for hexagonal crystal systems Orientation Calculated using the Lotgering factor method: ,in This is the ratio of the sum of the measured peak intensities of sample (00l) to the sum of the peak intensities of all (hkl) samples. Theoretical calculations for completely randomly oriented samples of the corresponding material, based on JCPDS standard cards (e.g., No. 27-1029). Value. For spinel-structured MnZn ferrite, then select the value that is similar to... <111> Similar calculations were performed on the direction-dependent (hhl) peaks.

[0021] Furthermore, the orientation pressing process parameters for the magnetic powder described in this invention in subsequent applications are as follows: The magnetic powder is mixed with... After mixing zinc stearate, in to Unidirectional suppression in a DC magnetic field, the pressure is to Holding time seconds; the resulting green blank in to Sintering in air hourly heating rate The remanence of the final magnet (For Ba / Sr ferrite) or (For MnZn ferrite), coercivity for to Magnetic property consistency .

[0022] Compared with the prior art, the present invention has the following beneficial effects: This invention achieves significant progress in many aspects by realizing the active induction and precise control of ferrite grain orientation during wet ball milling through the spatiotemporal synchronization and synergy of rotating magnetic field and directional fluid shear field.

[0023] This invention improves the microstructural order of magnetic powder and the ultimate magnetic properties of the final magnet. Traditional wet ball milling results in completely disordered powder grain orientation due to random mechanical action, severely limiting the efficiency and upper limit of subsequent magnetic field orientation. This invention creates a multi-physics coupling environment during the ball milling stage, allowing the grains to be refined and dispersed while their easy magnetization axes are preferentially aligned along specific directions, forming a highly consistent "pre-organized" orientation structure. This enables the particles to respond more rapidly and thoroughly to the applied orientation magnetic field during subsequent molding, significantly improving the remanence of the sintered magnet and bringing it closer to the theoretical magnetic property limit of the material, thus meeting the core requirement of high-end devices for strong magnetic force.

[0024] This invention significantly improves the consistency and batch stability of product performance. The random collision process that determines powder structure in traditional processes is the root cause of large fluctuations in the final magnet performance, especially coercivity. This invention replaces the disordered mechanical energy input with controlled, directional synergistic effects of physical fields, making the formation process of the powder microstructure controllable and significantly reducing the impact of process fluctuations on product performance. Therefore, the prepared magnetic powder and its magnets exhibit excellent repeatability and reliability, providing a crucial guarantee for the large-scale, consistent production of demanding electronic components.

[0025] This invention achieves a synergistic unity between orientation control and excellent overall powder properties; this method does not sacrifice particle size, dispersibility, or reactivity for orientation. By precisely matching the slurry rheological properties and multi-physics parameters, it ensures that the powder has a narrow particle size distribution, good dispersion, and high sintering activity while efficiently inducing orientation. This results in magnetic powder with both high orientation potential and excellent molding processability, resolving the contradiction between "orientation" and "powder quality" that was difficult to balance in previous processes.

[0026] The core of this invention lies in the quantitative control of the spatiotemporal relationship between the magnetic field and the flow field. Key parameters such as magnetic field strength, rotation phase, and shear rate can be precisely measured and adjusted. This eliminates reliance on experience-based operations, providing a clear and reliable scientific basis for technology transfer and industrial scale-up, and laying a solid foundation for the stable mass production of high-performance ferrite materials. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0028] Figure 1 This is an overall flowchart of the method described in this invention.

[0029] Figure 2 This is a simplified process diagram of the method described in this invention. Detailed Implementation

[0030] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of the embodiments of the invention. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive.

[0031] The following is in conjunction with the appendix Figure 1 and Figure 2 The embodiments of the present invention will be described in detail below.

[0032] Example 1: This example discloses a ferrite magnetic powder material with induced orientation alignment by wet ball milling; the ferrite magnetic powder material is a soft magnetic or permanent magnet ferrite with a spinel structure or a hexagonal crystal system, and its general chemical formula is: or The M element is selected from , , , , , At least one of them.

[0033] In this embodiment, strontium ferrite ( Taking this as an example, its pre-calcined coarse powder is prepared by a conventional solid-phase reaction method: analytical grade... and Mix according to stoichiometric ratio, ball mill, dry, and then in air atmosphere. Under-insulation The heating rate is 1 hour. The obtained product was confirmed by X-ray diffraction to have a single-phase hexagonal crystal structure, without any... or Residual impurities; average particle size of the pre-calcined powder for The particle size distribution is relatively wide. for Specific surface area is It is suitable for subsequent wet ball milling and refining processes.

[0034] Prepare a slurry system for wet ball milling. The above pre-calcined... meal As a dry-based material, deionized water is added. (i.e., liquid-to-solid mass ratio is) Then add sodium polyacrylate (PAA-Na) dispersant. (of the dry powder mass) The number average molecular weight of this dispersant is Simultaneously add a concentration of ammonia solution As a pH adjuster.

[0035] The above components were placed in a high-shear stirred tank. Stirring at high speed Within minutes, a homogeneous slurry is formed. The final pH value of the slurry, as measured by a pH meter, is [value missing]. The zeta potential of the particles was measured using laser Doppler electrophoresis. This indicates that the particle surface carries a strong negative charge, and the electrostatic repulsion is sufficient to effectively inhibit particle agglomeration. The solid content of this slurry is... Within the scope defined by this invention - Within the range.

[0036] The above slurry is injected into the wet ball milling apparatus specifically designed for this invention. The specific structure of the wet ball milling apparatus is as follows: The grinding chamber is cylindrical with an inner diameter of [missing information]. Effective length The material is Stainless steel, with a precision-polished inner wall and a surface roughness of [missing information]. This is to minimize impurities introduced by particle adhesion and wear.

[0037] The two ends of the cavity are connected to the drive motor and the circulation pipeline respectively through magnetic fluid sealed bearings to ensure sealing and low friction loss under high-speed rotation.

[0038] The cavity contains a built-in spiral guide plate, integrally molded from polytetrafluoroethylene (PTFE), with a pitch of [missing information]. (i.e., cavity diameter) (times), helix angle is It is fixed to the inner wall of the cavity via a flange; the surface of the guide plate is coated with a layer of thickness. The diamond-like carbon (DLC) coating has a coefficient of friction lower than This significantly reduces the flow resistance of the slurry.

[0039] The grinding media uses yttrium-stabilized zirconia balls (Y-TZP), whose chemical composition is as follows: The density is Vickers hardness ≥ The diameter of the ball is The total filling mass is The corresponding filling rate is the effective volume of the grinding chamber. Within the scope defined by this invention - Within the range.

[0040] Four sets of electromagnetic coil arrays are evenly distributed circumferentially around the outer periphery of the ball mill cavity. Each set of coils is embedded in a corresponding quadrant groove on the outer wall of the cavity. Each set of coils is wound with Litz wire, with a number of turns of [missing information]. Turns, wire diameter Insulation class is H (temperature resistant) This is to meet the thermal stability requirements under long-term operation.

[0041] The four sets of coils are each connected to a four-channel independent programmable power supply, which can output a frequency range of - Current amplitude - The waveform is a sinusoidal AC signal with a frequency accuracy of ± Amplitude resolution reaches .

[0042] In addition, the grinding chamber is wrapped with an annular cooling jacket, and constant-temperature circulating cooling water is circulated inside, with the water temperature set at [temperature value missing]. The flow rate is adjusted in real time by the PID controller based on feedback from the chamber temperature sensor to ensure that the slurry temperature is maintained at a certain level during ball milling. - Within the range.

[0043] Before officially starting the ball mill, the rheological properties of the slurry need to be calibrated. A coaxial cylindrical rotary rheometer was used to test the slurry at a shear rate of... from Rise to Within this range, its flow behavior conforms to the Bingham plasticity model: (when The yield stress of the slurry was measured. for Plastic viscosity for All fall within the preferred scope of this invention. : - ; : - Within this range. This rheological property ensures that the slurry maintains structural stability during static storage, while rapidly transforming into a low-viscosity flow state under ball mill shearing, which is beneficial for the formation and maintenance of oriented structures.

[0044] The ball milling process is carried out under strictly controlled multi-physics coupling conditions: Start the drive motor to make the grinding chamber move at... The slurry rotates at a constant speed around its axis. At this time, the built-in helical guide vanes force the slurry to be transported axially, forming a stable laminar shear zone in the middle of the cavity. The flow field in this region is calibrated using particle image velocimetry (PIV) technology, and the maximum velocity gradient is measured. for Within the scope defined by this invention - Within the range.

[0045] At the same time, the four-channel programmable power supply is activated, applying a phase difference of [value] to the four sets of electromagnetic coils respectively. sinusoidal alternating current: , , , angular frequency , is the rotation frequency of the magnetic field.

[0046] Under this excitation, the four sets of coils synthesize a uniformly rotating vector magnetic field in the horizontal plane in the central region of the grinding cavity, with a magnetic induction intensity of for Rotation frequency for The direction of the magnetic field is always parallel to the axial centerline of the cavity. This magnetic field was verified by actual measurements with a gaussmeter, and the spatial uniformity deviation is less than ± .

[0047] The spatiotemporal synchronization of the rotating magnetic field and the fluid shear field is achieved by a closed-loop control system. A high-resolution photoelectric encoder is installed on the drive motor spindle to acquire the rotation angle of the grinding chamber in real time. The signal is then input to the PLC controller. The PLC controller calculates the ideal magnetic field phase at the current moment according to a preset algorithm. ,in The phase offset angle is set to [value] in this embodiment. It is used to compensate for the hysteresis effect of the magnetization response of ferrite grains.

[0048] The PLC outputs four PWM signals to the programmable power supply, dynamically adjusting the current amplitude and phase of each coil to ensure that the synthesized magnetic field vector always leads the local fluid velocity vector by a fixed angle. Under this synergistic effect, the ferrite grains, due to the inherent magnetocrystalline anisotropy of their hexagonal crystal system, experience a continuous magnetic torque in the rotating magnetic field, causing their easy magnetization axis to align with the instantaneous magnetic field direction. Simultaneously, the fluid drag force applies additional torque to the grains in the laminar shear zone, further aligning their long axis parallel to the streamline direction. This spatially coplanar and temporally synchronized coupling confines the grains to a single orientation plane in three-dimensional space, achieving [the desired alignment]. Preferred arrangement of crystal orientations.

[0049] Throughout the ball milling process, the system continuously monitors key process parameters. Real-time data is acquired using a fiber optic Raman probe integrated into the cavity sidewall. - band Stretching vibration peak intensity is used to monitor the adsorption state of the dispersant. Data shows that at the start of ball milling... After a few minutes, the peak intensity stabilized and remained at the initial adsorption peak value. The above indicates that PAA-Na molecules are completely adsorbed onto the particle surface, forming a layer approximately [thickness missing]. The electrostatic-steric double-layer protective film effectively prevents irreversible aggregation of oriented particles during high-energy collisions.

[0050] Meanwhile, an online viscosity sensor installed in the circulation pipeline provides real-time feedback on the apparent viscosity of the slurry. When the detected value deviates from the set value ( (Exceeding ±) At the same time, the flow rate of the circulating pump is automatically adjusted to maintain the stability of the flow field.

[0051] Furthermore, through the energy conversion efficiency formula To quantify process energy efficiency, units must be standardized during calculations: In this embodiment, slurry mass... The average specific heat capacity of the slurry (the main component is water, so it is approximately the specific heat capacity of water). Actual temperature rise Motor input power Effective ball milling time .but This value indicates that a relatively low proportion of mechanical energy is converted into the internal energy of the slurry (leading to a temperature rise). Most of the input energy is converted into the directional kinetic energy, surface energy, and work done to overcome viscous resistance of the particles, which is conducive to achieving mild and effective orientation induction.

[0052] The total ball milling time is set to Hours, during which each run Automatic pause after minutes Minutes. During the pause, the cavity stops rotating, the magnetic field is turned off, and the system performs stress release and magnetic field phase calibration to avoid accumulated mechanical stress leading to orientation structure disorder.

[0053] After ball milling, the slurry is subjected to... Eye (aperture) A stainless steel screen is used for filtration to remove any grinding media debris or large particle agglomerates. The filtrate then enters a centrifugal separation unit for further processing. Centrifuge at speed Minutes, obtaining a moisture content of approximately The filter cake was then transferred to a vacuum drying oven. Absolute pressure ≤ Drying under conditions After hours, primary magnetic powder is obtained.

[0054] To eliminate lattice defects introduced during ball milling and stabilize the hydroxyl structure on the particle surface, the primary magnetic powder was placed in a muffle furnace and milled in an air atmosphere. Perform low-temperature tempering treatment, holding time is The heating and cooling rates were both [percentage] per hour. After tempering, the magnetic powder is lightly crushed using an air jet mill. The feed rate and classifier speed are controlled to ensure the final product has a high loose packing density. Within the scope defined by this invention - Within the range.

[0055] The obtained magnetic powder was characterized by its physical properties. The particle size distribution was measured using a laser particle size analyzer. , , Therefore less than The upper limit requirement; the specific surface area measured by the BET nitrogen adsorption method is ,lie in - Within the range. More importantly, the degree of orientation. Determination: Take dried magnetic powder in Pressed under pressure (without an external magnetic field) Discs were analyzed using an X-ray diffractometer (Cu Kα radiation). )exist - Scan within range, step size Timing for each step Second.

[0056] Calculate the sum of the integral intensities of all diffraction peaks (hkl). and the sum of the integral intensities of the (00l) series diffraction peaks ,get Based on the theoretical diffraction intensity data of this material in JCPDS card No. 27-1029, the theoretical diffraction intensity for completely random orientation was calculated. Value According to the Lotgering factor formula Calculation yields ,satisfy Requirements.

[0057] In practice, to further verify the performance advantages of the magnetic powder of the present invention in practical applications, it was made into a sintered magnet using conventional processes.

[0058] The specific steps are as follows: Mix the above-mentioned magnetic powder with... Zinc stearate lubricant is mixed evenly, in Unidirectional suppression in a DC magnetic field, pressure Pressure holding In seconds, a green blank is obtained; green blanks in air atmosphere Heat up to Insulation The magnet was cooled in the furnace after several hours. The resulting magnet was tested using a vibrating sample magnetometer (VSM), and its remanence was determined. coercivity Magnetic properties batch consistency index (Based on continuous) Batch data calculation, Standard deviation Specifications limited , ).

[0059] For comparison, we set up Comparative Example 1: using the same pre-burning... Coarse powder is subjected to traditional wet ball milling in the same ball milling equipment, i.e., only mechanical rotation is turned on ( Without applying a rotating magnetic field, all other parameters (slurry formulation, grinding media, time, post-treatment, etc.) are completely identical.

[0060] Orientation degree of the obtained comparative magnetic powder ,granularity , Specific surface area This indicates that the particle size control effect is quite good, but the orientation structure is lacking. After pressing and sintering using the same process, , , The comparison of the two sets of data is shown in Table 1 below: Table 1 shows a data comparison between Example 1 and Comparative Example 1:

[0061] Example 1 successfully achieved the pre-orientation of ferrite grains in the powder stage by simultaneously applying a rotating magnetic field and a directional fluid shear field during wet ball milling, which significantly improved the remanence and batch consistency of the final magnet without sacrificing coercivity.

[0062] The process parameters of this invention have a clear mathematical correlation. Rotating magnetic field magnetic induction intensity. With ball mill speed Satisfying empirical relations In this embodiment, , Substituting into Dimensions are This indicates that the magnetic torque and the fluid shear force are well matched in terms of magnitude.

[0063] The wet ball milling-induced orientation alignment ferrite magnetic powder material and preparation method described in this invention achieves simultaneous particle refinement and crystallographic orientation induction during wet milling by constructing a multi-physics field coupling system comprising a rotating magnetic field, a directional fluid shear field, and precise rheological control. This method features well-defined process parameters, a clear equipment structure, and rigorous control logic. The resulting magnetic powder exhibits high orientation, narrow particle size distribution, and excellent batch consistency, providing a novel technical pathway for the preparation of high-performance ferrite magnets.

[0064] Furthermore, to help those skilled in the art further understand this invention, the physical mechanism of multi-physics field synergistic induction of grain orientation is analyzed below from the perspective of principles: For ferrite single crystal particles, their magnetization vector They tend to align along easy magnetization axes (such as the c-axis of a hexagonal crystal system) and are influenced by an external rotating magnetic field. In the middle, the magnetic torque on the particle is Its magnitude can be estimated as Tm≈mBsinθ, where Tm is the magnetic torque (unit: ), m is the particle magnetization vector magnitude (unit: ), B is the magnetic induction intensity of the rotating magnetic field (unit: T), and θ is the instantaneous angle between m and B (unit: rad); Meanwhile, for approximately ellipsoidal particles (major axis... short axis ), at shear rate In a laminar flow field, the hydrodynamic torque is Its magnitude can be estimated by Jeffery's theory, for slenderness ratio particles, ,in This represents the fluid viscosity.

[0065] In traditional ball mills, the instantaneous torque generated by random collisions The magnitude is much larger than and Furthermore, the direction is random, making it impossible to establish an orientation. The core of this invention lies in: through specific equipment structure (spiral guide plate) and parameter matching, simultaneously satisfying two key conditions in a specific region (laminar shear zone) within the grinding chamber: (1) Local shear rate High enough to make With typical random collision torque Comparable in magnitude, that is ; (2) Magnetic torque of rotating magnetic field and In terms of directional coordination on the plane of action, the closed-loop control system ensures that the magnetic field rotation plane and the shear plane are coplanar, and that... The instantaneous direction leads (or lags) the local velocity direction by a fixed angle. ( ).

[0066] Thus, the particles are subjected to [various effects] during one motion cycle. and Vector resultant moment The integral effect over a period of time causes the easy magnetization axis / major axis of the particle to tend toward a specific equilibrium direction in the plane, rather than random oscillation.

[0067] By controlling This ensures the magnetic torque With rotational speed Determined shear rate (and then The trends of change should be synchronized to avoid disrupting synergy due to any single factor being too strong or too weak. The rheological properties of the slurry (Bingham model parameters) and This ensures that under the strong shearing conditions of ball milling, the slurry can quickly transform into a low-viscosity state, thereby reducing the hydrodynamic torque. It can effectively transfer energy to particles, and during pauses, it can quickly restore the structure, protecting the established orientation from being destroyed. The pause interval setting (per...) Minute pause (Minutes) are to release accumulated elastic stress and avoid orientation structure fatigue and damage caused by continuous high-energy collisions of particles.

[0068] As one of the key innovations of this invention, the spatiotemporal synchronization mechanism between the rotating magnetic field and the fluid shear field is achieved through the following control logic: The grinding chamber rotation angle The reference signal is acquired in real time by the encoder and input to the PLC controller; the PLC then... Calculate the ideal magnetic field phase at the current moment ,in For the preset phase offset angle ( to This is used to compensate for magnetic response hysteresis; subsequently, the PLC outputs four PWM signals to the programmable power supply, driving the coil current according to... The regular changes ensure that the synthesized magnetic field vector always leads or lags behind the fluid velocity vector by a fixed angle, thereby generating a continuous directional torque on the particles rather than oscillating disturbances.

[0069] As another key innovation of this invention, the slurry system incorporates trace amounts of rare earth ion doping to enhance the magnetocrystalline anisotropy constant. This enhances the orientation driving force; specifically, it involves adding [something] during the slurry preparation stage. to of or Nitrate solutions have cation radii that are similar to... Matching, it can be solidified at the B-site of the crystal lattice, making Value increase to This doping does not affect the formation of the main phase, but significantly increases the critical energy threshold required for the grains to rotate in the magnetic field, so that the orientation structure can remain stable in the high-energy collisions in the later stage of ball milling.

[0070] Furthermore, the adsorption behavior of the dispersant described in this invention is monitored by in-situ Raman spectroscopy: an optical fiber probe is integrated into the sidewall of the ball mill cavity to collect data in real time. to band Stretching vibration peak intensity; when the peak intensity stabilizes at the initial value When the above values ​​are met, it indicates that the dispersant molecules are completely adsorbed onto the particle surface, forming a layer with a thickness of [missing value]. to The electrostatic-steric hindrance double-layer protective film effectively prevents irreversible aggregation of oriented particles during collisions.

[0071] Furthermore, the energy conversion efficiency in the grinding process described in this invention is quantified by the following formula: ; in The mass of the slurry is expressed in kg. The average specific heat capacity of the slurry is expressed in J / (kg·K), approximately taken as... ; The measured temperature rise of the slurry during ball milling is expressed in Kelvin (K). The average electrical power input to the drive motor, in watts (W). The effective ball milling time is expressed in seconds. The calculated Eeff is a dimensionless number representing the proportion of mechanical energy converted into the internal energy (temperature rise) of the slurry. Its value is usually between 0.02 and 0.3, indicating that the mechanical energy is mainly converted into the directional kinetic energy and surface energy of the particles, with a low heat dissipation ratio, which is conducive to achieving mild orientation induction.

[0072] Taking the preparation of strontium ferrite magnetic powder as an example: take pre-calcined meal( ) Add deionized water Sodium polyacrylate ( ) ,ammonia Stir Slurry is produced in minutes ( , ); inject into the above-mentioned special ball milling device, and load in Y-TZP grinding balls. ( ); Set the cavity rotation speed Rotating magnetic field , Cooling water temperature ;ball milling Hours, during which each Minute pause Minutes; after discharge, screening, centrifugation, Vacuum drying yields primary powder; Tempering Hours, airflow pulverization to loose packing density Sampling and measurement , Orientation degree was measured using the aforementioned Lotgering factor method. After being pressed and sintered using conventional processes, , , Significantly better than Comparative Example 1 ( , , ).

[0073] To further demonstrate the necessity of multiphysics "cooperation," rather than simple superposition, the following comparative experimental data are provided. All experiments used the same pre-firing method. The coarse powder and basic slurry formulations differ only in the physical field applied during the ball milling process: The details are shown in Table 2 below: Table 2 lists those using the same pre-firing method. Experimental results of different physical field conditions applied during the ball milling process for coarse powder and basic slurry formulations.

[0074]

[0075] The data in Table 2 shows that: (1) Mechanical ball milling alone (Comparative Example 1) has almost no orientation effect; (2) The effects of magnetic field alone (Comparative Example 2) or non-directional shear alone (Comparative Example 3) are limited, and the degree of orientation is also limited. The results were only 0.25 and 0.22 respectively; (3) Even if a magnetic field and a shear field are applied simultaneously, if they are not synchronized (Comparative Example 4), the effect is ( It is also far lower than that of Embodiment 1 of the present invention (synchronous collaboration). This fully demonstrates that the spatiotemporal synchronization and coordination of the rotating magnetic field and the directional shear flow field is the key to generating high orientation, rather than a simple superposition of physical fields.

[0076] This invention creatively introduces a multi-physics synergistic mechanism of rotating magnetic field and directional fluid shear field into the wet ball milling process, fundamentally changing the limitation of traditional ball milling which relies solely on isotropic mechanical energy input. This enables active induction and precise control of ferrite grain orientation during the powder preparation stage. This technical solution not only retains the inherent advantages of wet ball milling in particle size control and dispersibility, but also constructs a "pre-organized" orientation structure at the microscale through physical field coupling, laying the structural foundation for the subsequent formation of high-orientation magnets. The method described in this invention has clear process parameters, a well-defined equipment structure, and rigorous control logic, possessing high repeatability and industrial scale-up potential. It is suitable for the high-performance preparation of various soft magnetic and permanent magnet ferrite materials, and has significant technical value for promoting the miniaturization and high-efficiency development of high-frequency electronic devices.

[0077] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0078] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. It should be noted that any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A ferrite magnetic powder material with induced orientation alignment by wet ball milling, characterized in that: The magnetic powder material is a ferrite with a spinel structure or a hexagonal crystal system, and its general chemical formula is: or ,in Selected from , , , , , At least one of them; The average particle size of the magnetic powder particles is to Particle size distribution index Not greater than Specific surface area is to ; Furthermore, it exhibits crystallographic orientation even without an external magnetic field. Orientation The Lotgering factor calculation method is used: ； The ratio of the measured integral intensity of the (00l) crystal plane series diffraction peaks to the sum of the integral intensities of all (hkl) diffraction peaks is given. This represents the theoretical ratio of completely randomly oriented powder samples of the same material.

2. The ferrite magnetic powder material with wet ball milling-induced orientation alignment according to claim 1, characterized in that, The magnetic powder is doped with to of or Ions, which are dissolved in the B sites of the crystal lattice, cause the magnetocrystalline anisotropy constant to be... improve to .

3. A method for preparing a ferrite magnetic powder material with induced orientation alignment by wet ball milling, used to prepare the ferrite magnetic powder material with induced orientation alignment by wet ball milling as described in claim 1 or 2, characterized in that, Includes the following steps: The pre-calcined ferrite powder, deionized water, dispersant, and pH adjuster were mixed according to the following mass ratio. Mix and prepare a solution with a solid content of to The slurry; The slurry is injected into a dedicated wet ball milling apparatus. During the ball milling process, a rotating magnetic field is simultaneously applied, and the rotation of the grinding chamber is controlled to form a directional fluid shear field, while maintaining the slurry temperature at [temperature missing]. to ; After ball milling, the slurry undergoes solid-liquid separation and drying, and... to The magnetic powder material is obtained by low-temperature tempering followed by airflow pulverization.

4. The method for wet ball milling to induce oriented alignment of ferrite magnetic powder materials according to claim 3, characterized in that, The pH value of the slurry was adjusted to - The absolute value of the zeta potential is greater than The dispersant is sodium polyacrylate or triammonium citrate, with a molecular weight of [missing information]. to The amount added is equal to the weight of the dry powder. .

5. The method for wet ball milling to induce oriented alignment of ferrite magnetic powder materials according to claim 3, characterized in that, The dedicated wet ball milling device includes a cylindrical grinding chamber, an adjustable-speed rotating spindle, a spiral guide plate, yttrium-stabilized zirconia grinding media, four sets of orthogonal electromagnetic coil arrays, and a cooling jacket; the diameter of the grinding media is [missing information]. to The filling rate is % of the effective volume of the grinding chamber. to The spiral guide plate is made of polytetrafluoroethylene, and the pitch is equal to the diameter of the cavity. times, inclination angle is The surface is coated with a diamond-like carbon (DLC) coating.

6. The method for wet ball milling to induce oriented alignment of ferrite magnetic powder materials according to claim 5, characterized in that, The rotating magnetic field is generated by an array of four electromagnetic coils, with a magnetic induction intensity of [insert value here]. to The frequency is to The direction is parallel to the axial centerline of the grinding chamber; the four sets of coils are connected by a phase difference of... The sinusoidal alternating currents combine to form a vector magnetic field that rotates uniformly in the horizontal plane.

7. The method for wet ball milling to induce oriented alignment of ferrite magnetic powder material according to claim 6, characterized in that, The magnetic induction intensity of the rotating magnetic field With ball mill speed Satisfying the relation: ,in This is the proportionality coefficient, and its value range is... to .

8. The method for wet ball milling to induce oriented alignment of ferrite magnetic powder materials according to claim 5, characterized in that, The grinding chamber is to As the fluid rotates at a certain speed, a laminar shear zone is formed under the action of the spiral guide plate, creating a fluid velocity gradient within the shear zone. for to .

9. The method for wet ball milling to induce oriented alignment of ferrite magnetic powder material according to claim 3, characterized in that, The slurry conforms to the Bingham fluid model: ,when Among them, yield stress for to Plastic viscosity for to .

10. The method for wet ball milling to induce oriented alignment of ferrite magnetic powder material according to claim 5, characterized in that, The rotating magnetic field and the fluid shear field are synchronized in time and space through a closed-loop control system: The encoder collects the rotation angle of the grinding chamber in real time. The PLC controller is based on Calculate the phase of an ideal magnetic field , for to The preset phase offset angle is set, and the PWM signal is output to the programmable power supply to drive the four sets of electromagnetic coil arrays to generate a composite rotating magnetic field vector with precise phase control, so that it always leads or lags behind the local fluid velocity vector by a fixed angle.

Images