Rare earth doped ferrite magnetic powder and preparation method thereof, injection ferrite and application

Abstract

The invention provides rare earth doped ferrite magnetic powder and a preparation method thereof, injection ferrite and application, the chemical formula of the ferrite magnetic powder is Sr < 1-x > LaxFe < 12-y > CoyO19, 0 lt; x is less than or equal to 0.5, 0lt; y < = 0.35, 1 < = x / y < = 1.5; the D50 particle size of the ferrite magnetic powder is 3-5 [mu] m, and the length-diameter ratio L / D is 1.0-2.5. The invention provides ferrite magnetic powder with a relatively large particle size, although the ferrite magnetic powder is of a polycrystalline structure, the length-diameter ratio L / D of the ferrite magnetic powder is 1.0-2.5, and the ferrite magnetic powder has a high orientation degree similar to that of single crystal particles, so that the ferrite magnetic powder has high residual magnetism; moreover, the ferrite magnetic powder with the polycrystalline structure has a grain boundary, so that the ferrite magnetic powder also has relatively high coercive force.

Description

Technical Field

[0001] The present invention belongs to the technical field of magnetic materials, and relates to rare earth doped ferrite magnetic powder, in particular to rare earth doped ferrite magnetic powder and a preparation method, injected ferrite and application. Background Art

[0002] Injected ferrite is a type of permanent magnet produced by mixing ferrite powder with a binder and then producing it through magnetic field injection molding. Compared to sintered ferrite, injected ferrite has the advantages of superior strength, the ability to be integrally molded with other components, and the ability to create magnet structures with complex shapes. However, a disadvantage of injected ferrite is its low magnetic performance, with a magnetic energy product generally below 2.3 MGOe. In recent years, with the increasing miniaturization and lightweighting of magnetic devices, the market has placed higher demands on the magnetic properties of magnetic materials. Therefore, the preparation of high-performance injected ferrite has become a hot topic in the field of magnetic materials research.

[0003] In order to obtain high-performance injected ferrite magnets, the key is to obtain a high-performance ferrite / binder composite material. There are many factors that affect the magnetic properties of ferrite / binder composite materials, but the most important ones are: (1) how to prepare ferrite powder with high magnetic properties; (2) how to fill it with more ferrite powder while ensuring the strength of the composite material; (3) how to make the composite material have good fluidity so that the ferrite powder can obtain a higher degree of orientation in the magnetic field. In order to meet the above conditions, the ferrite powder is required to have higher intrinsic magnetic properties, better particle size distribution and better surface condition.

[0004] In the field of sintered ferrite permanent magnets, a common method to enhance the magnetic properties of the material is to dope it with rare earth ions and transition elements, such as La and Co ions. However, this method is difficult to implement with existing bonded ferrite powders. This is because La and Co ion doping requires sufficiently high temperatures (above 1200°C) to allow the La and Co ions to diffuse within the ferrite lattice. To maintain a good morphology, bonded ferrite powders are typically sintered at relatively low temperatures, not exceeding 1200°C. Therefore, the performance of existing bonded ferrite powders still has room for further improvement.

[0005] CN113889309A discloses a bonded ferrite powder for injection molding, its preparation method, and application. The bonded ferrite powder for injection molding is prepared by adding fine-grained ferrite powder with an average particle size of 0.5 to 1.2 microns and coarse-grained ferrite powder with an average particle size of 3.0 to 6.0 microns to a ball mill, with the fine-grained ferrite powder accounting for 10 to 35 weight percent. The resulting coarse-fine mixed magnetic powder is then ball-milled. The bonded ferrite powder for injection molding can be mixed with a rubber binder, a plasticizer, and a stabilizer to produce an injection-molded flexible bonded magnet. This invention significantly improves the fluidity of the magnetic powder and the magnetic properties of the magnet, exceeding the levels of existing similar products. It also increases the upper operating temperature limit of the injection-molded flexible bonded magnet from 80°C to 125°C, broadening its application and enhancing the stability and reliability of the injection-molded flexible bonded magnet.

[0006] CN109574083A discloses a rubber-plastic ferrite magnetic powder, wherein the ferrite magnetic powder is SrFe with a magnetoplumbite structure. 12 O 19 The ferrite magnetic powder contains a mass fraction of 0.35-0.75% Mn element. The particles of the ferrite magnetic powder are flaky, with a particle diameter-to-thickness ratio of 2.0-5.0, and the distribution of the particle shape is relatively uniform. The ferrite magnetic powder has high jHc and high Br. The invention uses iron red and strontium carbonate as the main raw materials, with a molar ratio of iron red to strontium carbonate of 5.5-5.9:1, and adds manganese carbonate and 4.5-6.5% mass fraction of SrCl2. After uniform mixing, it is pre-sintered at 1050-1150°C, and then subjected to processes such as coarse crushing, fine grinding, and tempering to obtain the rubber-plastic ferrite magnetic powder.

[0007] CN104446427A discloses a rare earth-doped spinel ferrite magnetic powder produced based on NdFeB waste and its preparation method. The structural formula of the spinel ferrite is AB2O4, and the non-ferrous substitution elements at position A of the structural formula are all or partially derived from NdFeB waste, and the doping substitution elements at position B of the structural formula are all or partially derived from NdFeB waste. The production process of this invention makes full use of the "secondary process waste" that is produced in large quantities during the process of hydrometallurgical recovery of rare earth elements from NdFeB waste and has not yet realized its due resource value. In terms of the implementation of the technical solution, the technology of this invention achieves "seamless connection" with the currently industrialized process flow of recycling rare earths from NdFeB waste resources, and realizes an organic and reasonable combination of the resource utilization and doping substitution of secondary waste to improve the performance of spinel magnets and the simplicity of process implementation.

[0008] Currently, the publicly available ferrite magnetic powders and their preparation methods all have certain defects. There are problems such as the doping effects of La and Co ions being unsatisfactory due to process limitations, and the magnetic properties of the rare-earth-doped ferrite magnetic powders being poor. Therefore, it is crucial to develop and design a new type of rare-earth-doped ferrite magnetic powder, its preparation method, and injection ferrite. Summary of the Invention

[0009] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a rare-earth-doped ferrite magnetic powder, its preparation method, injection ferrite, and applications. The present invention provides a ferrite magnetic powder with a relatively coarse particle size. Although the ferrite magnetic powder has a polycrystalline structure, the aspect ratio L / D of the ferrite magnetic powder is 1.0 - 2.5, and it has a high degree of orientation similar to that of single crystal particles. Therefore, it has a high remanence. Moreover, due to the presence of grain boundaries in the polycrystalline structure of the ferrite magnetic powder, the ferrite magnetic powder also has a relatively high coercive force.

[0010] To achieve this purpose, the present invention adopts the following technical solutions: [[ID=IO]]

[0011] In the first aspect, the present invention provides a rare-earth-doped ferrite magnetic powder, and the chemical formula of the ferrite magnetic powder is Sr 1-x La x Fe 12-y Co y O 19 , where 0 < x ≤ 0.5, 0 < y ≤ 0.35, and 1 ≤ x / y ≤ 1.5;

[0012] The D50 particle size of the ferrite magnetic powder is 3 - 5 μm, and the aspect ratio L / D is 1.0 - 2.5.

[0013] In the present invention, 0 < x ≤ 0.5, and the value of x can be, for example, 0.05, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, or 0.5, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0014] In the present invention, 0 < y ≤ 0.35, and the value of y can be, for example, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, or 0.35, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0015] In the present invention, 1 ≤ x / y ≤ 1.5, and the value of x / y can be, for example, 1, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, or 1.5, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0016] The D50 particle size of the ferrite magnetic powder described in the present invention is 3 to 5 μm, for example, it can be 3 μm, 3.2 μm, 3.4 μm, 3.6 μm, 3.8 μm, 4 μm, 4.2 μm, 4.4 μm, 4.6 μm, 4.8 μm or 5 μm, but is not limited to the listed values. Other values not listed within this numerical range are also applicable.

[0017] The aspect ratio L / D of the ferrite magnetic powder described in the present invention is 1.0 to 2.5, for example, it can be 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4 or 2.5, but is not limited to the listed values. Other values not listed within this numerical range are also applicable.

[0018] In traditional ferrite magnetic powder, in order to ensure high orientation of magnetic powder, magnetic powder particles are generally turned into single crystal particles. Therefore, the magnetic powder needs to be crushed to a very fine particle size (2μm). This kind of magnetic powder has relatively high magnetic properties, but the overly fine magnetic powder increases the surface area, so it requires more binder to ensure that the prepared composite material has good strength and fluidity. However, too much binder makes the magnetic properties of the composite permanent magnet material less than ideal.

[0019] Therefore, the present invention provides a ferrite magnetic powder with a relatively coarse particle size. Although the ferrite magnetic powder has a polycrystalline structure, the aspect ratio L / D of the ferrite magnetic powder is 1.0 to 2.5, and it has a high orientation degree close to that of single crystal particles, and therefore has high remanence. Moreover, due to the presence of grain boundaries in the ferrite magnetic powder with a polycrystalline structure, the ferrite magnetic powder also has a relatively high coercive force.

[0020] Preferably, the proportion of the ferrite powder with a size of 1 to 10 μm is not less than 90%, for example, it can be 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99%, but is not limited to the listed values, and other unlisted values within this numerical range are also applicable.

[0021] Preferably, the proportion of ferrite powder with a size less than 1 μm is less than 5%, for example, it can be 4.9%, 4.5%, 4%, 3.5%, 3%, 2.5%, 2%, 1.5%, 1% or 0.5%, but is not limited to the listed values, and other unlisted values within this numerical range are also applicable.

[0022] Preferably, the proportion of the ferrite powder with a size greater than 10 μm is less than 5%, for example, it can be 4.9%, 4.5%, 4%, 3.5%, 3%, 2.5%, 2%, 1.5%, 1% or 0.5%, but is not limited to the listed values, and other unlisted values within this numerical range are also applicable.

[0023] In a second aspect, the present invention provides a method for preparing the ferrite magnetic powder according to the first aspect, the preparation method comprising:

[0024] (1) mixing a Sr source, a La source, an Fe source, and a Co source and sintering the mixture to obtain a first mixed material;

[0025] (2) mixing the first mixed material obtained in step (1) with water to obtain a slurry, pressing the obtained slurry in a magnetic field and simultaneously draining the slurry, and then sintering the slurry to obtain a second mixed material;

[0026] (3) crushing the second mixed material obtained in step (2), and then performing heat treatment to obtain ferrite magnetic powder.

[0027] Preferably, the mixing in step (1) further includes mixing with water.

[0028] The mixing method in step (1) of the present invention includes a first ball milling, the rotation speed of the first ball milling can be, for example, 60 rpm, the time can be, for example, 5 hours, and the mass ratio of material, grinding balls and water can be, for example, 1:10:1.5.

[0029] Preferably, the Sr source includes SrO and / or SrCO3.

[0030] Preferably, the La source includes La(OH)3 and / or La2O3.

[0031] Preferably, the Fe source comprises Fe(OH)3 and / or Fe2O3.

[0032] Preferably, the Co source includes Co(OH)3 and / or Co2O3.

[0033] Preferably, step (1) further includes a first drying process between the mixing and the sintering.

[0034] In the present invention, the temperature of the first drying may be, for example, 120° C., and the time may be, for example, 2 hours.

[0035] In the present invention, the sintering temperature in step (1) may be, for example, 1250° C., and the sintering time may be, for example, 1 hour.

[0036] In the present invention, the sintering in step (1) is carried out at a temperature not lower than 1200° C., so that the rare earth ions La and the rare metal ions Co are fully diffused, thereby making the ferrite magnetic powder have higher intrinsic magnetic properties.

[0037] Preferably, the mixing method in step (2) includes a second ball milling, the rotation speed of the second ball milling can be, for example, 60 rpm, the time is 25 to 35 hours, and the mass ratio of material, grinding balls and water can be, for example, 1:10:1.5.

[0038] The second ball milling time of the present invention is 25 to 35 hours, for example, it can be 25 hours, 26 hours, 27 hours, 28 hours, 29 hours or 30 hours, but is not limited to the listed values. Other values not listed within the numerical range are also applicable.

[0039] The magnetic induction intensity of the magnetic field in step (2) of the present invention can be, for example, 1.0T.

[0040] Preferably, a cylindrical material is obtained after the pressing.

[0041] Preferably, the sintering temperature in step (2) is 1200-1300° C., and the sintering time is 1-3 hours.

[0042] The sintering temperature in step (2) of the present invention is 1200-1300°C, for example, it can be 1200°C, 1220°C, 1240°C, 1260°C, 1280°C or 1300°C, but is not limited to the listed values. Other values not listed within this numerical range are also applicable.

[0043] In the present invention, the sintering time in step (2) is 1 to 3 hours, for example, it can be 1 hour, 1.2 hours, 1.4 hours, 1.6 hours, 1.8 hours, 2 hours, 2.2 hours, 2.4 hours, 2.6 hours, 2.8 hours or 3 hours, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

[0044] Preferably, the crushing in step (3) includes performing a first crushing and a second crushing in sequence.

[0045] Preferably, the first crushing method is vibration crushing.

[0046] In the present invention, the D50 particle size of the material obtained after the first crushing is less than 20 μm, for example, it can be 19 μm, 17 μm, 15 μm, 10 μm, 5 μm or 3 μm, but is not limited to the listed values. Other values not listed within this numerical range are also applicable.

[0047] Preferably, an Sr-containing additive is added between the first crushing and the second crushing, and the Sr-containing additive includes SrCl2.

[0048] In the present invention, the Sr-containing additive is supplemented between the first crushing and the second crushing before heat treatment, which is beneficial to eliminating the residual stress generated by the material during the first crushing and the second crushing process, thereby improving the coercive force of the finally obtained ferrite magnetic powder.

[0049] The Sr-containing additive in the present invention is SrCl2 with a relatively low melting point, which is already in a molten state within the temperature range of the heat treatment, forming a liquid environment surrounding the solid material. Sharp protrusions or ultrafine materials generated during the crushing process of the material are in a relatively high energy state and will melt into the liquid phase in the liquid environment. After diffusion-recrystallization, they will combine with the surrounding coarse particles to form a material with a larger particle size. Therefore, after the heat treatment, the ultrafine powder and sharp protrusions in the material will be greatly reduced, so that the final ferrite magnetic powder has better fluidity. In addition, the liquid SrCl2 can also act as an isolating agent, which can prevent multiple materials from forming overly coarse particles due to contact and mutual diffusion at high temperatures.

[0050] In the present invention, the mass ratio of the Sr-containing additive to the material obtained after the first crushing can be, for example, 2:10.

[0051] Preferably, the second crushing method is the third ball milling, and the D50 particle size of the material obtained after the third ball milling is 2.5 to 4.5 μm, for example, it can be 2.5 μm, 2.7 μm, 3 μm, 3.2 μm, 3.5 μm, 3.7 μm, 4 μm, 4.2 μm or 4.5 μm, but is not limited to the listed values, and other unlisted values within this numerical range are also applicable.

[0052] Preferably, step (3) further includes a second drying step between the crushing and the heat treatment.

[0053] Preferably, the heat treatment in step (3) includes keeping warm at 950-1100°C, for example, it can be 950°C, 960°C, 970°C, 980°C, 990°C, 1000°C, 1010°C, 1020°C, 1030°C, 1040°C, 1050°C, 1060°C, 1070°C, 1080°C, 1090°C or 1100°C, but is not limited to the listed values, and other unlisted values within this numerical range are also applicable.

[0054] The holding time in the heat treatment in step (3) of the present invention can be, for example, 2 hours.

[0055] Preferably, the preparation method further comprises sequentially washing and third drying the material after the heat treatment.

[0056] Preferably, the cleaning includes placing the heat-treated material into a mixer with ceramic balls, adding water to soak and stir, and then rinsing with water, the purpose of which is to wash away the non-magnetic SrCl2, and at the same time use the slight impact of the ceramic balls to disperse some of the materials that have "agglomerated" together due to the heat treatment.

[0057] Preferably, the third drying temperature is 110-120°C.

[0058] The temperature of the third drying in the present invention is 110-120°C, for example, it can be 110°C, 111°C, 112°C, 113°C, 114°C, 115°C, 116°C, 117°C, 118°C, 119°C or 120°C, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

[0059] As a preferred technical solution of the preparation method of the present invention, the preparation method comprises:

[0060] (1) mixing a Sr source, a La source, a Fe source, a Co source, and water, drying, and sintering to obtain a first mixed material;

[0061] (2) mixing the first mixture obtained in step (1) with water to obtain a slurry, pressing the obtained slurry in a magnetic field and simultaneously draining the slurry, and then sintering it at 1200-1300° C. for 1-3 hours to obtain a second mixture;

[0062] (3) The second mixed material obtained in step (2) is crushed by vibration crushing, an Sr-containing additive is added, and the material is crushed by ball milling to obtain a material with a D50 particle size of 2.5 to 4.5 μm. The material is dried and then heat-treated, wherein the heat treatment includes heat preservation at 950 to 1100° C. The heat-treated material is placed in a mixer with ceramic balls, soaked and stirred in water, and then rinsed with water. After drying, ferrite magnetic powder is obtained.

[0063] In a third aspect, the present invention provides an injected ferrite, comprising a binder and the injected ferrite magnetic powder according to the first aspect.

[0064] In a fourth aspect, the present invention provides an application of the injected ferrite according to the third aspect, wherein the injected ferrite is used in a magnetic device.

[0065] Compared with the prior art, the present invention has the following beneficial effects:

[0066] The present invention provides a ferrite magnetic powder with a relatively coarse particle size. Although the ferrite magnetic powder has a polycrystalline structure, the aspect ratio L / D of the ferrite magnetic powder is 1.0 to 2.5, and it has a high degree of orientation similar to that of single crystal particles, and therefore has high remanence. Moreover, due to the presence of grain boundaries in the polycrystalline ferrite magnetic powder, the ferrite magnetic powder also has a relatively high coercive force. DETAILED DESCRIPTION

[0067] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0068] Example 1

[0069] This embodiment provides a rare earth doped ferrite powder, the chemical formula of which is Sr 0.75 La 0.25 Fe 11.8 Co 0.2 O 19 .

[0070] The preparation method of the ferrite magnetic powder comprises:

[0071] (1) SrCO3, La2O3, Fe2O3, Co2O3, and water were mixed by ball milling at a speed of 60 rpm and a mass ratio of material, grinding balls, and water of 1:10:1.5 for 5 h, dried at 115°C for 2 h, and sintered at 1250°C for 1 h to obtain a first mixed material;

[0072] (2) The first mixture obtained in step (1) was mixed with water by ball milling at a rotation speed of 60 rpm and a mass ratio of material, grinding balls and water of 1:10:1.5 for 30 hours to obtain a slurry, and the obtained slurry was pressed in a magnetic field with a magnetic induction intensity of 1.0 T and drained simultaneously to obtain a cylindrical material, which was then sintered at 1250° C. for 2 hours to obtain a second mixture;

[0073] (3) The second mixed material obtained in step (2) is crushed by vibration crushing to obtain a material with a D50 particle size of 15 μm, SrCl2 is added in a mass ratio of 2:10 to the material obtained after the first crushing, and then crushed by ball milling at a speed of 60 rpm and a mass ratio of material to grinding balls of 1:10 for 30 hours to obtain a material with a D50 particle size of 3.5 μm, and then dried at 115°C and heat treated, wherein the heat treatment includes keeping warm at 1050°C for 2 hours, and then placing the heat-treated material in a stirrer with ceramic balls, adding water to soak and stir, and then rinsing with water, and then drying at 115°C to obtain ferrite magnetic powder.

[0074] Example 2

[0075] This embodiment provides a rare earth doped ferrite powder, the chemical formula of which is Sr 0.9 La 0.1 Fe 11.9 Co 0.1 O 19 .

[0076] The preparation method of the ferrite magnetic powder comprises:

[0077] (1) SrO, La(OH)3, Fe2O3, Co2O3, and water were mixed by ball milling at a speed of 60 rpm and a mass ratio of material, grinding balls, and water of 1:10:1.5 for 3 h, dried at 120°C for 2 h, and sintered at 1250°C for 1 h to obtain a first mixed material;

[0078] (2) The first mixture obtained in step (1) was mixed with water by ball milling at a rotation speed of 60 rpm and a mass ratio of material, grinding balls and water of 1:10:1.5 for 35 hours to obtain a slurry, and the obtained slurry was pressed in a magnetic field with a magnetic induction intensity of 1.0 T and drained simultaneously to obtain a cylindrical material, which was then sintered at 1200° C. for 3 hours to obtain a second mixture;

[0079] (3) The second mixed material obtained in step (2) is crushed by vibration crushing to obtain a material with a D50 particle size of 12 μm, SrCl2 is added in a mass ratio of 2:10 to the material obtained after the first crushing, and then crushed by ball milling at a speed of 60 rpm and a mass ratio of material to grinding balls of 1:10 for 30 hours to obtain a material with a D50 particle size of 2.5 μm, and then dried at 110°C and heat treated, wherein the heat treatment includes keeping warm at 1100°C for 2 hours, and then placing the heat-treated material in a stirrer with ceramic balls, adding water to soak and stir, and then rinsing with water, and then drying at 110°C to obtain ferrite magnetic powder.

[0080] Example 3

[0081] This embodiment provides a rare earth doped ferrite powder, the chemical formula of which is Sr 0.5 La 0.5 Fe 11.65 Co 0.35 O 19 .

[0082] The preparation method of the ferrite magnetic powder comprises:

[0083] (1) SrCO3, La2O3, Fe(OH)3, Co(OH)3 and water were mixed by ball milling at a speed of 60 rpm and a mass ratio of material, grinding balls and water of 1:10:1.5 for 7 hours, dried at 110°C for 2 hours, and sintered at a temperature of 1250°C for 1 hour to obtain a first mixed material;

[0084] (2) The first mixture obtained in step (1) was mixed with water by ball milling at a rotation speed of 60 rpm and a mass ratio of material, grinding balls and water of 1:10:1.5 for 25 hours to obtain a slurry, and the obtained slurry was pressed in a magnetic field with a magnetic induction intensity of 1.0 T and drained simultaneously to obtain a cylindrical material, which was then sintered at 1300° C. for 1 hour to obtain a second mixture;

[0085] (3) The second mixed material obtained in step (2) is crushed by vibration crushing to obtain a material with a D50 particle size of 18 μm, SrCl2 is added at a mass ratio of 2:10 to the material obtained after the first crushing, and then crushed by ball milling at a speed of 60 rpm and a mass ratio of material to grinding balls of 1:10 for 30 hours to obtain a material with a D50 particle size of 4.5 μm, and then dried at 120°C and heat treated, wherein the heat treatment includes keeping warm at 950°C for 2 hours, and then the heat-treated material is placed in a stirrer with ceramic balls, soaked and stirred with water, and then rinsed with water, and then dried at 120°C to obtain ferrite magnetic powder.

[0086] Example 4

[0087] This embodiment provides a rare earth-doped ferrite magnetic powder, which is the same as that of Example 1 except that the sintering temperature in step (2) of the preparation method of the ferrite magnetic powder is 1100°C.

[0088] Example 5

[0089] This embodiment provides a rare earth-doped ferrite magnetic powder, which is the same as that of Example 1 except that the sintering temperature in step (2) of the preparation method of the ferrite magnetic powder is 1500°C.

[0090] Example 6

[0091] This embodiment provides a rare earth-doped ferrite magnetic powder, which is the same as Example 1 except that the addition of SrCl2 in step (3) of the preparation method of the ferrite magnetic powder is omitted.

[0092] Example 7

[0093] This embodiment provides a rare earth-doped ferrite magnetic powder, which is the same as that of Example 1 except that the holding temperature in the heat treatment in step (3) of the preparation method of the ferrite magnetic powder is 800°C.

[0094] Example 8

[0095] This embodiment provides a rare earth-doped ferrite magnetic powder, which is the same as that of Example 1 except that the holding temperature in the heat treatment in step (3) of the preparation method of the ferrite magnetic powder is 1200°C.

[0096] Comparative Example 1

[0097] This comparative example provides a rare earth doped ferrite powder, except that the chemical formula of the ferrite powder is Sr 0.4 La 0.6 Fe 11.65 Co 0.35 O 19 Except for this, the rest are the same as in Example 1.

[0098] Comparative Example 2

[0099] This comparative example provides a rare earth doped ferrite powder, except that the chemical formula of the ferrite powder is Sr 0.8 La 0.2 Fe 11.75 Co 0.25 O 19 Except for this, the rest are the same as in Example 1.

[0100] Comparative Example 3

[0101] This comparative example provides a rare earth doped ferrite powder, except that the chemical formula of the ferrite powder is Sr 0.7 La 0.3 Fe 11.85 Co 0.15 O 19 Except for this, the rest are the same as in Example 1.

[0102] Comparative Example 4

[0103] The present invention provides a ferrite powder with a single crystal structure, wherein the chemical formula of the ferrite powder is Sr1Fe 12 O 19 ;

[0104] The preparation method of the ferrite magnetic powder comprises:

[0105] (1) SrCO 3 , Fe 2 O 3 , and water were mixed by ball milling at a rotation speed of 60 rpm and a mass ratio of material, grinding balls, and water of 1:10:1.5 for 5 h, dried at 115° C. for 2 h, and sintered at 1250° C. for 1 h to obtain a first mixed material;

[0106] (2) The first mixture obtained in step (1) was mixed with water by ball milling at a rotation speed of 60 rpm and a mass ratio of material, grinding balls and water of 1:10:1.5 for 30 hours to obtain a slurry, and the obtained slurry was pressed in a magnetic field with a magnetic induction intensity of 1.0 T and drained simultaneously to obtain a cylindrical material, which was then sintered at 1250° C. for 2 hours to obtain a second mixture;

[0107] (3) The second mixed material obtained in step (2) is crushed by vibration crushing to obtain a material with a D50 particle size of 15 μm, SrCl2 is added in a mass ratio of 2:10 to the material obtained after the first crushing, and then crushed by ball milling at a speed of 60 rpm and a mass ratio of material to grinding balls of 1:10 for 30 hours to obtain a material with a D50 particle size of 3.5 μm, and then dried at 115°C and heat treated, wherein the heat treatment includes keeping warm at 1050°C for 2 hours, and then placing the heat-treated material in a stirrer with ceramic balls, adding water to soak and stir, and then rinsing with water, and then drying at 115°C to obtain ferrite magnetic powder.

[0108] The rare earth-doped ferrite powders of Examples 1 to 8 and Comparative Examples 1 to 3, and the ferrite powder of Comparative Example 4 were subjected to particle size testing, aspect ratio testing, saturation magnetic induction testing, residual magnetic induction testing, and coercive force testing;

[0109] The particle size test method is: using a laser particle size tester to test, the particle size of the ferrite magnetic powder, the proportion of particles with a size of 1 to 10 μm K1, the proportion of particles with a size less than 1 μm K2, and the proportion of particles with a size greater than 10 μm K3 are shown in Table 1;

[0110] The aspect ratio test method is: using SEM electron microscopy to select particles in different areas for comparative analysis and calculation, and then calculating the average value after statistics. The aspect ratio of the ferrite magnetic powder obtained by the test is shown in Table 1;

[0111] The saturation magnetic induction intensity, residual magnetic induction intensity, and coercive force test method is: using a vibrating sample magnetometer (VSM) test, the saturation magnetic induction intensity Ms, residual magnetic induction intensity Mr, and coercive force Hcj of the ferrite magnetic powder are tested and shown in Table 2;

[0112] Table 1

[0113]

[0114] Table 2

[0115]

[0116]

[0117] From Table 1 and Table 2, we can get:

[0118] (1) The rare earth-doped ferrite magnetic powder provided in Examples 1 to 3 has a D50 particle size of 3 to 5 μm, a proportion of particles with a particle size of 1 to 10 μm of not less than 90%, a proportion of particles with a particle size of less than 1 μm of less than 5%, a proportion of particles with a particle size of greater than 10 μm of less than 5%, and an aspect ratio L / D of 1.0 to 2.5. Furthermore, the rare earth-doped ferrite magnetic powder provided in Examples 1 to 3 also has relatively high saturation magnetic induction, residual magnetic induction, and coercive force.

[0119] (2) By comparing Example 1 with Examples 4 and 5, it can be seen that the sintering temperature in step (2) of the method for preparing ferrite magnetic powder of the present invention will affect the performance of the ferrite magnetic powder; when the sintering temperature is low, the saturation magnetic induction intensity and the residual magnetic induction intensity will be low, because the lower temperature causes the ferrite grains to not grow fully and there are tiny defects, which makes the saturation magnetic induction intensity and the residual magnetic induction intensity both low; when the sintering temperature is high, the coercive force will be low, because the high temperature causes the ferrite grains to grow rapidly, and the grains are larger and the aspect ratio L / D becomes larger, which leads to a lower coercive force;

[0120] (3) By comparing Example 1 with Example 6, it can be seen that the supplementary Sr source added in step (3) of the preparation method of ferrite magnetic powder of the present invention will affect the performance of the ferrite magnetic powder; in the present invention, the supplementation of the Sr source between the first crushing and the second crushing before the heat treatment is beneficial to eliminate the residual stress generated by the material in the first crushing and the second crushing process, thereby improving the coercive force of the ferrite magnetic powder finally obtained; in the present invention, the supplementary Sr source is SrCl2 with a lower melting point, which is already in a molten state within the temperature range of the heat treatment, forming a liquid environment surrounding the solid material, and the sharp protrusions or ultrafine materials generated in the crushing process of the material will melt into the liquid phase in the liquid environment due to being in a higher energy state, and after diffusion-recrystallization, they will combine with the surrounding coarse particles to form a material with a larger particle size. Therefore, after the heat treatment, the ultrafine powder and the sharp protrusions in the material will be greatly reduced, so that the ferrite magnetic powder finally obtained has better fluidity; in addition, the liquid SrCl2 can also act as an isolating agent, which can prevent multiple materials from forming overly coarse particles due to contact-interdiffusion at high temperature;

[0121] (4) By comparing Example 1 with Examples 7 and 8, it can be seen that the terminal temperature of the heating process in step (3) of the preparation method of ferrite magnetic powder of the present invention, that is, the holding temperature, will affect the performance of the ferrite magnetic powder; when the holding temperature is too low, the saturation magnetic induction intensity and the residual magnetic induction intensity will become smaller. This is because when the holding temperature is too low, the ultrafine powder particles in the magnetic powder are too many and the average grain size is too small, thereby affecting the magnetic properties of the magnetic powder; when the holding temperature is too high, the coercive force will become smaller. This is because when the holding temperature is too high, although the ultrafine powder particles in the magnetic powder can be significantly reduced, the average grain size will also be too large, resulting in a decrease in the coercive force of the magnetic powder;

[0122] (5) By comparing Example 1 with Comparative Examples 1 to 3, it can be seen that the chemical formula provided by the present invention is Sr 1-x La x Fe 12- y Co y O 19 The x / y ratio in the ferrite powder affects the performance of the ferrite powder. When the x / y ratio deviates from the range of the present invention, the saturation magnetic induction intensity, residual magnetic induction intensity and coercive force will all decrease. This is because when the ratio of La to Co is not appropriate, a soft magnetic impurity phase will appear in the material, reducing the magnetic properties of the magnetic powder.

[0123] (6) By comparing Example 1 with Comparative Example 4, it can be seen that although the rare earth-doped ferrite powder provided by the present invention is a polycrystalline structure, the aspect ratio L / D of the ferrite powder is 1.0 to 2.5, and it has a high orientation degree similar to that of single crystal particles, and therefore has high remanence; moreover, due to the presence of grain boundaries in the polycrystalline ferrite powder, the ferrite powder also has a relatively high coercive force.

[0124] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and disclosure scope of the present invention.

Claims

1. A rare earth doped ferrite magnetic powder, characterized in that: The chemical formula of the ferrite powder is Sr 1-x La x Fe 12- y Co y O 19 , where 0 <x≤0.5,0<y≤0.35,1≤x / y≤1.5; The D50 particle size of the ferrite magnetic powder is 3 to 5 μm, and the aspect ratio L / D is 1.0 to 2.

5.

2. The ferrite powder according to claim 1, characterized in that The proportion of the ferrite powder with a size of 1 to 10 μm is not less than 90%; Preferably, the proportion of ferrite powder with a size less than 1 μm is less than 5%; Preferably, the proportion of ferrite powder with a size larger than 10 μm is less than 5%.

3. A method for preparing the ferrite magnetic powder according to claim 1 or 2, characterized in that: The preparation method comprises: (1) mixing a Sr source, a La source, an Fe source, and a Co source and sintering the mixture to obtain a first mixed material; (2) mixing the first mixed material obtained in step (1) with water to obtain a slurry, pressing the obtained slurry in a magnetic field and simultaneously draining the slurry, and then sintering the slurry to obtain a second mixed material; (3) crushing the second mixed material obtained in step (2), and then performing heat treatment to obtain ferrite magnetic powder.

4. The preparation method according to claim 3, characterized in that The mixing in step (1) further includes mixing with water; Preferably, the Sr source comprises SrO and / or SrCO3; Preferably, the La source comprises La(OH)3 and / or La2O3; Preferably, the Fe source comprises Fe(OH)3 and / or Fe2O3; Preferably, the Co source comprises Co(OH)3 and / or Co2O3; Preferably, step (1) further includes a first drying process between the mixing and the sintering.

5. The preparation method according to claim 3 or 4, characterized in that The sintering temperature in step (2) is 1200-1300° C. and the sintering time is 1-3 hours.

6. The preparation method according to any one of claims 3 to 5, characterized in that The crushing in step (3) includes sequentially performing a first crushing and a second crushing; Preferably, the first crushing method is vibration crushing; Preferably, an Sr-containing additive is added between the first crushing and the second crushing, and the Sr-containing additive includes SrCl2; Preferably, the second crushing method is a third ball milling, and the D50 particle size of the material obtained after the third ball milling is 2.5 to 4.5 μm; Preferably, step (3) further includes a second drying step between the crushing and the heat treatment; Preferably, the heat treatment in step (3) includes keeping the temperature at 950-1100°C.

7. The preparation method according to any one of claims 3 to 6, characterized in that: The preparation method further comprises washing and third drying the material after the heat treatment in sequence; Preferably, the cleaning comprises placing the heat-treated material into a mixer with ceramic balls, adding water to soak and stir, and then rinsing with water.

8. The preparation method according to any one of claims 3 to 7, characterized in that The preparation method comprises: (1) mixing a Sr source, a La source, a Fe source, a Co source, and water, drying, and sintering to obtain a first mixed material; (2) mixing the first mixture obtained in step (1) with water to obtain a slurry, pressing the obtained slurry in a magnetic field and simultaneously draining the slurry, and then sintering it at 1200-1300° C. for 1-3 hours to obtain a second mixture; (3) The second mixed material obtained in step (2) is crushed by vibration crushing, an Sr-containing additive is added, and the material is crushed by ball milling to obtain a material with a D50 particle size of 2.5 to 4.5 μm. The material is dried and then heat-treated, wherein the heat treatment includes heat preservation at 950 to 1100° C. The heat-treated material is placed in a mixer with ceramic balls, soaked and stirred in water, and then rinsed with water. After drying, ferrite magnetic powder is obtained.

9. An injection ferrite, characterized in that: The injected ferrite comprises a binder and the injected ferrite magnetic powder according to claim 1 or 2.

10. An application of the injected ferrite according to claim 9, characterized in that: The injected ferrite is used for magnetic devices.

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