CN110204326B - Ferrite permanent magnet material with core-shell structure and preparation method thereof - Google Patents

Ferrite permanent magnet material with core-shell structure and preparation method thereof Download PDF

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CN110204326B
CN110204326B CN201910410429.0A CN201910410429A CN110204326B CN 110204326 B CN110204326 B CN 110204326B CN 201910410429 A CN201910410429 A CN 201910410429A CN 110204326 B CN110204326 B CN 110204326B
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slurry
core
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shell
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李玉平
包大新
何震宇
李军华
吴云飞
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Hengdian Group DMEGC Magnetics Co Ltd
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Abstract

The invention relates to the field of ferrite materialsThe ferrite permanent magnet material is prepared by mixing a core component and a shell component, and then magnetizing, molding and sintering the mixture; the mass content of each element in the nuclear component is Sr1‑xLaxFe12‑yCoyO19Wherein x =0-0.08, y = 0-0.05; the mass content of each element in the shell component is Sr1‑w‑ vLawCavFe12‑zCozO19Wherein w =0.2-0.45, v =0.2-0.45, z = 0.15-0.35; the crystal grains of the obtained ferrite permanent magnetic material are in a core-shell structure, and the contents of the La element and the Co element in the crystal grains are increased in an uneven gradient mode from inside to outside. The invention can ensure that the ferrite permanent magnetic material can still keep higher magnetic performance under the condition of reducing the usage amount of the La-Co element.

Description

Ferrite permanent magnet material with core-shell structure and preparation method thereof
Technical Field
The invention relates to the field of ferrite materials, in particular to a ferrite permanent magnet material with a core-shell structure and a preparation method thereof.
Background
Strontium ferrite permanent magnet material (SrFe)12O19) Because of good chemical stability, environmental friendliness, high magnetic performance and low price, the magnetic material is widely applied to the fields of motors and sensors. In recent years, as magnetic devices are more and more miniaturized and lightened, the market has made higher demands on the magnetic performance of ferrite permanent magnetic materials. On the other hand, in order to control the production cost of the magnetic device, it is desired that the price of the ferrite material is not greatly increased by the improvement of the performance.
The traditional method for improving the permanent magnetic material of ferrite generally adopts ion substitution, such as La3+、Nd3+、Sm3+、Pr3+、Ce3+Isosubstituted for Sr2+Using Al3+、Cu2+、Zn2+、Co2+Isosubstitution of Fe3+. Wherein, La3+-Co2+The combined substitution is proved to be a very effective method, which can greatly improve the intrinsic magnetic property of the material, thus being widely applied to the batch production of high-performance ferrite permanent magnetic materials. However, this method requires a large consumption of La and Co. As is well known, La belongs to rare earth elements and has a limited earth reserve; cobalt is a strategic resource, mainly produced in south america, africa and oceania, and is very expensive. Thus using La3+-Co2+The ion substitution method can cause the price of the ferrite material to be greatly increased. Therefore, it is desirable to find a method that can improve the magnetic properties of the material without greatly increasing the material cost, i.e., a method that can reduce the usage of La and Co while maintaining the magnetic properties of the material.
On the other hand, by optimizing the microstructure of the ferrite material, the magnetic properties of the material can also be improved. According to the related magnetic theory, the coercive force can be greatly improved by refining the crystal grains of the ferrite permanent magnetic material to make the size of the crystal grains smaller than the size of a magnetic domain. At present, in order to refine the microstructure of a material, a common method is to perform ball milling on a pre-sintered material for a long time to prepare magnetic powder particles with a fine particle size, and then perform sintering. However, long-term ball milling usually brings many impurities, which degrade the magnetic properties of the material. In addition, the fine magnetic powder particles can make the material difficult to form in the subsequent process, and the sintered product is easy to crack.
In addition, the magnetic performance of the material can also be adjusted by controlling the grain growth of the material in the sintering process to keep the length-diameter ratio of the material grains in a certain range. For example, in the ball milling process, some compounds containing Ca and Si ions are added, and the ratio of Ca/Si is controlled, so that the remanence and the coercive force of the magnet present a trade-off relationship, namely, one performance index is lost, and the other performance index is improved. In general, when the value of Ca/Si is increased, the remanence of the material is increased and the coercivity is decreased, whereas when the value is increased, the coercivity is increased and the remanence is decreased. However, the improvement of the magnetic properties of the material is limited only by the Ca/Si adjustment. Furthermore, excessive addition of compounds containing Ca and Si ions increases the amount of nonmagnetic phases in the material, which adversely reduces the magnetic properties of the material.
Several prior art solutions are exemplified below:
1. chinese patent publication No. CN 1658340a discloses that by adding La — Co element to a material, the magnetic properties of the material can be greatly improved. However, the technology adopts the traditional ion adding method, the content of La-Co element is higher, and the cost of the material is greatly increased.
2. The Chinese patent with publication number CN 1767087A proposes to add a small amount of Pr/Nd on the basis of the traditional La-Co element substitution, and can improve the magnetic performance of the material on the premise of not adding Co element. However, this method is limited to improve the magnetic properties of the material, and cannot significantly reduce the amount of the La — Co element used.
3. Chinese patent publication No. CN 104261811B, CN 104003707B, CN 101542646A, CN102471162A and other Chinese patent application propose Ca-La-Co ion combined substitution technology based on traditional La-Co element substitution, and the method can greatly improve the magnetic property of the material. However, in this method, the amount of solid solution of La and Co in the ferrite lattice is increased by adding Ca ions, so as to improve the magnetic properties of the material. Therefore, although the magnetic properties of the material are greatly improved, the performance is essentially improved by increasing the addition amount of the La and Co elements, and the cost is greatly increased.
Disclosure of Invention
In order to overcome the defects and shortcomings of the prior art, the invention aims to provide a ferrite permanent magnetic material with a core-shell structure and a method thereof.
The specific technical scheme of the invention is as follows: a ferrite permanent magnetic material with a core-shell structure is composed ofMixing the core component and the shell component, and then magnetizing, molding and sintering the mixture to obtain the core-shell composite material; the molar content of each element in the nuclear component is Sr1-xLaxFe12-yCoyO19Wherein x is 0-0.08 and y is 0-0.05; the molar content of each element in the shell component is Sr1-w- vLawCavFe12-zCozO19Wherein w is 0.2-0.45, v is 0.2-0.45, and z is 0.15-0.35.
The crystal grains of the obtained ferrite permanent magnetic material are in a core-shell structure, and the contents of the La element and the Co element in the crystal grains are increased in an uneven gradient mode from inside to outside.
In order to prepare a ferrite permanent magnet material with high magnetic property and low cost, the invention carries out detailed research on the correlation between the microstructure and the magnetic property of the ferrite material, finds that through component design and process innovation, the crystal grains of the material have a core-shell structure, and can reduce the usage amount of Co element while ensuring the magnetic property of the material. In the core-shell structure, as shown in FIG. 1, the core layer of the crystal grains is Sr with little or no Co1-xLaxFe12-yCoyO19(x is 0-0.08; y is 0-0.05) and the shell (shaded part) of the crystal grain is Co-rich Sr1-w-vLawCavFe12-zCozO19(w ═ 0.2 to 0.45; v ═ 0.2 to 0.45; z ═ 0.15 to 0.35). Wherein the thickness of the shell layer is 0.2-0.5 μm. In the core-shell structure of the present invention, the components of the crystal grains are not uniform from inside to outside but distributed in a gradient manner, and the concentrations of La and Co increase with the increase of the distance from the core portion.
As a technology known in the industry, the coercive force of the ferrite permanent magnetic material can be improved by adding La and Co elements, and the coercive force of the material is improved along with the increase of the contents of the La and Co elements in a certain composition range. The ferrite permanent magnetic material with the core-shell structure has good magnetic property although the total La and Co content is reduced, and the principle is as follows: the La and Co element concentration of the core part of the material grain is low, so that the magnetic moment of the part is easy to turn, but the La and Co element concentration of the grain shell is high, and the magnetic moment is difficult to turn. Under the action of a counter magnetic field, although the magnetic moment of the core part of the crystal grain is easy to turn, the magnetic moment is difficult to expand to the shell of the crystal grain, namely the Co-rich shell outside the crystal grain plays a role in pinning the expansion of the magnetic domain of the material, and finally the ferrite material has high coercive force macroscopically.
Preferably, the thickness of the grain mesoshell layer is 0.2 to 0.5 μm.
The thickness of the shell layer can be controlled by adjusting the ratio of the core component to the shell component.
A preparation method of a ferrite permanent magnetic material comprises the following steps:
1) weighing each initial raw material of the nuclear components according to the proportion, and uniformly mixing the raw materials in a wet ball milling mode;
2) pre-burning the material obtained in the step 1) at the temperature of 1200-1300 ℃ to obtain a pre-burnt material;
3) coarsely crushing the pre-sintered material, and performing wet ball milling until the particle size of the powder is 0.6-1 mu M to obtain slurry M1;
4) obtaining slurry M2 according to the method of the steps 1) to 3), wherein the difference is that the materials are mixed according to the proportion of shell components, the presintering temperature is 900-;
5) mixing the slurry M1 with the slurry M2, and adding CaCO according to the mass of 0.8-1.2% and 0.5-0.7% of the total mass of the powder in the slurry3And SiO2Continuing ball milling;
6) pressing and molding under a magnetic field;
7) and (5) sintering.
The core-shell structure can be formed by the above process, and the principle can be explained as follows: due to different pre-sintering temperatures and ball milling times, the particle sizes of the M1 slurry and the M2 slurry are greatly different; after the two slurries are mixed, a plurality of fine M2 particles are adsorbed on the M1 particles; when sintering, elements of M1 particles and M2 particles mutually diffuse, and due to the difference of particle sizes, M2 particles are easily adsorbed and phagocytized by M1 particles to form an outer layer structure of M1 particles, and a plurality of M2 particles are phagocytized to form a shell-shaped outer layer structure. Moreover, the mutual diffusion of the two materials during the sintering process can lead to the uneven gradient distribution of La and Co elements in the newly formed crystal grains.
The sintered ferrite prepared by the invention has a core-shell structure, so that high coercive force can be obtained even if the usage amount of La and Co is reduced.
Preferably, the initial raw material is Fe2O3Powder, SrCO3Powder, La2O3Powder, Co2O3Powder, CaCO3And (3) powder.
Preferably, in the step 1), the ball milling solvent is deionized water or tap water, and the ball milling time is 4-6 h.
Preferably, in the step 2), the pre-burning time is 1.5 to 2.5 hours.
Preferably, slurry M1 is prepared by pre-sintering and ball-milling for 15-25h, and slurry M2 is prepared by pre-sintering and ball-milling for 50-100 h.
Under the different ball milling time, slurry M1 and M2 with different particle sizes can be obtained.
Preferably, in the step 5), the mass ratio of the slurry M1 to the slurry M2 is 1:1-5:1, and the ball milling time is 0.5-1.5 h.
The thickness of the shell layer can be controlled by adjusting the ratio of the core component to the shell component.
Preferably, in step 6), the magnetic field strength is 1.3-1.7T.
Preferably, in step 7), sintering is carried out at 1100-1300 ℃ for 50-70 min.
Under the magnetic field intensity and the sintering process, the ferrite material with better performance can be prepared.
Compared with the prior art, the invention has the beneficial effects that: the crystal grain of the ferrite permanent magnetic material is in a core-shell structure, the concentration of La and Co elements at the core part of the crystal grain in the material is low, so that the magnetic moment of the part is easy to turn, but the concentration of the La and Co elements at the shell layer of the crystal grain is high, and the magnetic moment is difficult to turn. Under the action of a counter magnetic field, although the magnetic moment of the core part of the crystal grain is easy to turn, the magnetic moment is difficult to expand to the shell of the crystal grain, namely the Co-rich shell outside the crystal grain plays a role in pinning the expansion of the magnetic domain of the material, and finally the ferrite material has high coercive force macroscopically. Therefore, although the total La and Co content of the ferrite permanent magnetic material is reduced, the ferrite permanent magnetic material still has good magnetic performance and can greatly reduce the cost.
Drawings
FIG. 1 is a schematic view of a core-shell structure of ferrite grains;
FIG. 2 is a composition analysis of ferrite grains and inner and outer layers thereof in the present invention.
The reference signs are: core layer A and shell layer B.
Detailed Description
The present invention will be further described with reference to the following examples.
General examples
A ferrite permanent magnetic material with a core-shell structure is prepared by mixing a core component and a shell component, and then magnetizing, molding and sintering the mixture; the molar content of each element in the nuclear component is Sr1-xLaxFe12-yCoyO19Wherein x is 0-0.08 and y is 0-0.05; the molar content of each element in the shell component is Sr1-w-vLawCavFe12-zCozO19Wherein w is 0.2-0.45, v is 0.2-0.45, and z is 0.15-0.35.
As shown in FIG. 1, the crystal grains of the obtained ferrite permanent magnetic material are in a core-shell structure, the core layer A is a component with little Co or no Co, the shell layer B (shaded part) is a component with rich Co, and the contents of La and Co in the crystal grains are increased in an uneven gradient from inside to outside.
Preferably, the thickness of the grain mesoshell layer is 0.2 to 0.5 μm.
A preparation method of a ferrite permanent magnetic material comprises the following steps:
1) weighing each initial raw material (Fe) of nuclear component according to the proportion2O3Powder, SrCO3Powder, La2O3Powder, Co2O3Powder and CaCO3Powder) and uniformly mixing by a wet ball milling mode; wherein the ball milling solvent is deionized water or tap water, and the ball milling time is 4-6h；
2) Pre-burning the material obtained in the step 1) at the temperature of 1200-1300 ℃ for 1.5-2.5h to obtain a pre-burnt material;
3) coarsely crushing the pre-sintered material, and performing wet ball milling for 15-25h until the particle size of the powder is 0.6-1 μ M to obtain slurry M1;
4) obtaining slurry M2 according to the method of the steps 1) to 3), wherein the difference is that the materials are mixed according to the proportion of shell components, the presintering temperature is 900-;
5) mixing the slurry M1 and M2 according to the mass ratio of 1:1-5:1, and adding CaCO according to the mass of 0.8-1.2% and 0.5-0.7% of the total mass of the powder in the slurry3And SiO2Continuing ball milling for 0.5-1.5 h;
6) pressing and molding under a magnetic field of 1.3-1.7T;
7) sintering at 1100-1300 deg.C for 50-70 min.
Example 1
1) The following starting materials were prepared: fe2O3Powder, SrCO3Powder, La2O3Powder, Co2O3Powder, CaCO3And (3) powder.
2) Are weighed according to Sr1-xLaxFe12-yCoyO19And (x is 0.02, y is 0-0.02) and uniformly mixing by a wet ball milling method, wherein the ball milling time is 5 hours, and the solvent is deionized water.
3) And pre-burning the uniformly mixed material at 1250 ℃ for 2 hours to obtain a pre-burned material.
4) The pre-sintering material is coarsely crushed and subjected to wet ball milling for 20 hours to obtain powder D50Slurry M1 having a particle size of about 0.6 μ M.
5) Repeating steps 2) -4) to obtain slurry M2, except that the composition of the material in step 2) is changed to Sr1-w- vLawCavFe12-zCozO19(w ═ 0.45; v ═ 0.45; z ═ 0.25), the presintering temperature in step 2 was 1000 ℃ and the ball milling time in step 3 was 100 hours, with the powder particle diameter D50The thickness became about 0.05. mu.m.
6. Mixing the slurry M1 and M2 according to the mass ratio of 1:1, and adding CaCO according to 1 percent and 0.6 percent of the total mass of the powder in the slurry respectively3And SiO2And continuing ball milling for 1 h.
7. Pressing and molding under a magnetic field of 1.5T.
8. Sintering at 1200 deg.C for 1 hr.
The magnetic properties of the magnet obtained in this example were as follows: the thickness of the shell layer is 0.3-0.5 μm, and the remanence Br4455Gs, coercive force Hcj4420Oe, maximum magnetic energy product (BH)max＝4.75MGOe。
Example 2
The present embodiment is different from embodiment 1 in that: x is 0; y is 0.
The magnetic properties of the magnet obtained in this example were as follows: the thickness of the shell layer is 0.3-0.5 μm, and the remanence Br4407Gs, coercive force Hcj4328Oe, maximum magnetic energy product (BH)max＝4.63MGOe。
Example 3
The present embodiment is different from embodiment 1 in that: x is 0.08; y is 0.05.
The magnetic properties of the magnet obtained in this example were as follows: the thickness of the shell layer is 0.3-0.5 μm, and the remanence Br4475Gs, coercive force Hcj4528Oe, maximum magnetic energy product (BH)max＝4.87MGOe。
Example 4
The present embodiment is different from embodiment 1 in that: w is 0.2; v is 0.2; and z is 0.15.
The magnetic properties of the magnet obtained in this example were as follows: the thickness of the shell layer is 0.3-0.5 μm, and the remanence Br4275Gs, coercive force Hcj4028Oe, maximum magnetic energy product (BH)max＝4.12MGOe。
Example 5
The present embodiment is different from embodiment 1 in that: in step 5), the ball milling time was 50 hours, and the particle size of the M2 powder was about 0.1. mu.m.
The magnetic properties of the magnet obtained in this example were as follows: the thickness of the shell layer is 0.3-0.5 μm, and the remanence Br4412Gs, coercive force Hcj4431Oe, maximum magnetic energy product (BH)max＝4.69MGOe。
Example 6
The present embodiment is different from embodiment 1 in that: in step 5), the ball milling time was changed to 75 hours, and the particle size of the M2 powder was changed to about 0.08. mu.m.
The magnetic properties of the magnet obtained in this example were as follows: the thickness of the shell layer is 0.3-0.5 μm, and the remanence Br4432Gs, coercive force Hcj4531Oe, maximum magnetic energy product (BH)max＝4.76MGOe。
Example 7
A ferrite permanent-magnet material with core-shell structure has the crystal grains in core-shell structure and the core layer containing less or no Co Sr component1-xLaxFe12-yCoyO19(x is 0, y is 0), and the shell layer B is a Co-rich component Sr1-w-vLawCavFe12-zCozO19(w is 0.2, v is 0.2, z is 0.15), and the content of the La element and the Co element in the crystal grains increases in a non-uniform gradient from inside to outside.
The preparation method comprises the following steps:
1) weighing each initial raw material (Fe) of nuclear component according to the proportion2O3Powder, SrCO3Powder, La2O3Powder, Co2O3Powder and CaCO3Powder) and uniformly mixing by a wet ball milling mode; wherein the ball milling solvent is deionized water, and the ball milling time is 4 hours;
2) pre-burning the material obtained in the step 1) at 1200 ℃ for 2.5h to obtain a pre-burnt material;
3) coarsely crushing the pre-sintered material, and performing wet ball milling until the particle size D of the powder50The particle size is 0.6 mu M, and slurry M1 is obtained;
4) obtaining slurry M2 according to the method of the steps 1) to 3), wherein the difference is that the materials are mixed according to the proportion of shell components, the presintering temperature is changed to 900 ℃, and the ball milling is carried out after presintering until the particle size D of the powder is achieved500.05 μm;
5) mixing the slurry M1 and M2 according to the mass ratio of 2: 1, and adding CaCO according to 0.8 percent and 0.5 percent of the total mass of the powder in the slurry respectively3And SiO2Continuing ball milling for 0.5 h;
6) pressing and molding under a 1.3T magnetic field;
7) sintering at 1100 deg.C for 70 min.
The magnetic properties of the magnet obtained in this example were as follows: the thickness of the shell layer is 0.15-0.3 μm, and the remanence Br4321Gs, coercive force Hcj4131Oe, maximum magnetic energy product (BH)max＝4.46MGOe。
Example 8
A ferrite permanent-magnet material with core-shell structure has the crystal grains in core-shell structure and the core layer containing less or no Co Sr component1-xLaxFe12-yCoyO19(x is 0.04 and y is 0.025), and the shell layer B is Co-rich Sr1-w-vLawCavFe12- zCozO19And the content of the La element and the Co element in the crystal grains increases in a non-uniform gradient from inside to outside (w is 0.325, v is 0.325, and z is 0.25).
The preparation method comprises the following steps:
1) weighing each initial raw material (Fe) of nuclear component according to the proportion2O3Powder, SrCO3Powder, La2O3Powder, Co2O3Powder and CaCO3Powder) and uniformly mixing by a wet ball milling mode; wherein the ball milling solvent is deionized water, and the ball milling time is 5 hours;
2) pre-burning the material obtained in the step 1) at 1250 ℃ for 2h to obtain a pre-burnt material;
3) coarsely crushing the pre-sintered material, and performing wet ball milling until the particle size D of the powder50The particle size is 0.8 mu M, and slurry M1 is obtained;
4) obtaining slurry M2 according to the method of the steps 1) to 3), wherein the difference is that the materials are mixed according to the proportion of shell components, the presintering temperature is 1000 ℃, and the particle size D of ball-milled powder after presintering is D500.08 μm;
5) mixing the slurry M1 and M2 according to the mass ratio of 3: 1, and adding CaCO according to 1 percent and 0.6 percent of the total mass of the powder in the slurry respectively3And SiO2Continuing ball milling for 1 h;
6) pressing and molding under a magnetic field of 1.5T;
7) sintering at 1200 deg.C for 60 min.
The magnetic properties of the magnet obtained in this example were as follows: the thickness of the shell layer is 0.15-0.2 μm, and the remanence Br4281Gs, coercive force Hcj4061Oe, maximum magnetic energy product (BH)max＝4.40MGOe。
Example 9
A ferrite permanent-magnet material with core-shell structure has the crystal grains in core-shell structure and the core layer containing less or no Co Sr component1-xLaxFe12-yCoyO19(x is 0.08 and y is 0.05), and the shell layer B is a Co-rich component Sr1-w-vLawCavFe12- zCozO19And the content of the La element and the Co element in the crystal grains is increased in a non-uniform gradient manner from inside to outside (w is 0.45, v is 0.45, and z is 0.35).
The preparation method comprises the following steps:
1) weighing each initial raw material (Fe) of nuclear component according to the proportion2O3Powder, SrCO3Powder, La2O3Powder, Co2O3Powder and CaCO3Powder) and uniformly mixing by a wet ball milling mode; wherein the ball milling solvent is tap water, and the ball milling time is 6 hours;
2) pre-burning the material obtained in the step 1) at 1300 ℃ for 1.5h to obtain a pre-burnt material;
3) coarsely crushing the pre-sintered material, and performing wet ball milling until the particle size D of the powder50Is 1 mu M, and slurry M1 is obtained;
4) obtaining slurry M2 according to the method of the steps 1) to 3), wherein the difference is that the materials are mixed according to the proportion of shell components, the presintering temperature is 1100 ℃, and the particle size D of ball-milled powder after presintering is D500.1 μm;
5) mixing the slurry M1 and M2 according to the mass ratio of 5:1, and adding CaCO according to the mass ratio of 1.2 percent and 0.7 percent of the total mass of the powder in the slurry3And SiO2Continuing ball milling for 1.5 h;
6) pressing and molding under a magnetic field of 1.7T;
7) sintering at 1300 deg.C for 50 min.
Obtained in this exampleThe magnetic properties of the magnet were as follows: the thickness of the shell layer is 0.05-0.15 μm, and the remanence Br4269Gs, coercive force Hcj3852Oe, maximum magnetic energy product (BH)max＝4.35MGOe。
Comparative example 1
1) Preparing a starting material: fe2O3Powder, SrCO3Powder, La2O3Powder, Co2O3Powder, CaCO3And (3) powder.
2) Are weighed according to Sr1-xLaxFe12-yCoyO19And (x is 0.02, y is 0-0.02) and uniformly mixing by a wet ball milling method, wherein the ball milling time is 5 hours, and the solvent is deionized water.
3) And pre-burning the uniformly mixed material at 1250 ℃ for 2 hours to obtain a pre-burned material.
4) The pre-sintering material is coarsely crushed and subjected to wet ball milling for 20 hours to obtain powder with the particle diameter D50Slurry M of 0.6 μ M1。
5) Pressing and molding under a magnetic field of 1.5T.
6) Sintering at 1200 deg.C for 1 hr.
The magnetic properties of the magnet obtained in this comparative example were as follows: remanence Br4355Gs, coercive force Hcj3220Oe, maximum magnetic energy product (BH)max＝4.1MGOe。
Comparative example 2
The present comparative example differs from comparative example 1 in that: in step 2), according to Sr1-w-vLawCavFe12-zCozO19(w-0.45; v-0.45; z-0.25).
The magnetic properties of the magnet obtained in this comparative example were as follows: remanence Br4461Gs, coercive force Hcj4420Oe, maximum magnetic energy product (BH)max＝4.67MGOe。
As shown in FIG. 2, it is a composition analysis chart of the crystal grain of the ferrite obtained in example 1 of the present invention and each point of the inner and outer layers thereof. As can be seen from the data in the figure, the contents of La and Co in the crystal grains increase in a non-uniform gradient from inside to outside.
The data for examples 1-9 and comparative examples 1-2 were compared and the results are shown in the following table:
Figure BDA0002061618730000081
Figure BDA0002061618730000091
by comparing the data in the above table, it is understood that the overall magnetic properties of comparative example 1 are much weaker than those of the ferrite materials of examples 1 to 9, although the contents of La and Co are small. In comparative example 2, the overall magnetic performance was comparable to examples 1 to 9, but the added amounts of La and Co were significantly increased, resulting in an increase in cost.
In conclusion, the ferrite permanent magnet material can still keep higher magnetic performance under the condition of reducing the usage amount of the La-Co element.
The raw materials and equipment used in the invention are common raw materials and equipment in the field if not specified; the methods used in the present invention are conventional in the art unless otherwise specified.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and all simple modifications, alterations and equivalents of the above embodiments according to the technical spirit of the present invention are still within the protection scope of the technical solution of the present invention.

Claims (10)

1. A ferrite permanent magnetic material with a core-shell structure is prepared by mixing a core component and a shell component, and then magnetizing, molding and sintering the mixture; the method is characterized in that: the molar content of each element in the nuclear component is Sr1-xLaxFe12- yCoyO19Wherein x =0-0.08, y = 0-0.05; the molar content of each element in the shell component is Sr1-w-vLawCavFe12- zCozO19Wherein w =0.2-0.45, v =0.2-0.45,z=0.15-0.35；
the crystal grains of the obtained ferrite permanent magnetic material are in a core-shell structure, and the contents of the La element and the Co element in the crystal grains are increased in an uneven gradient mode from inside to outside.
2. The ferrite permanent magnetic material with a core-shell structure as claimed in claim 1, wherein the thickness of the shell layer in the crystal grains is 0.05-0.5 μm.
3. A method for preparing a ferrite permanent magnetic material as claimed in claim 1 or 2, characterized by comprising the steps of:
1) weighing each initial raw material of the nuclear components according to the proportion, and uniformly mixing the raw materials in a wet ball milling mode;
2) pre-burning the material obtained in the step 1) at the temperature of 1200-1300 ℃ to obtain a pre-burnt material;
3) coarsely crushing the pre-sintered material, and performing wet ball milling until the particle size of the powder is 0.6-1 mu M to obtain slurry M1;
4) obtaining slurry M2 according to the method of the steps 1) to 3), wherein the difference is that the materials are mixed according to the proportion of shell components, the presintering temperature is 900-;
5) mixing the slurry M1 with the slurry M2, and adding CaCO according to the mass of 0.8-1.2% and 0.5-0.7% of the total mass of the powder in the slurry3And SiO2Continuing ball milling;
6) pressing and molding under a magnetic field;
7) and (5) sintering.
4. The preparation method of claim 3, wherein in the step 1), the ball milling solvent is deionized water or tap water, and the ball milling time is 4-6 h.
5. The method of claim 3, wherein in step 2), the pre-firing time is 1.5 to 2.5 hours.
6. The preparation method according to claim 3, wherein the slurry M1 is prepared by presintering and then ball-milling for 15-25h, and the slurry M2 is prepared by presintering and then ball-milling for 50-100 h.
7. The preparation method of claim 3, wherein in the step 5), the mass ratio of the slurry M1 to the slurry M2 is 1:1-5:1, and the ball milling time is 0.5-1.5 h.
8. The method of claim 3, wherein in step 6), the magnetic field strength is 1.3 to 1.7T.
9. The method as claimed in claim 3, wherein in step 7), the sintering is performed at 1100-1300 ℃ for 50-70 min.
10. The method of claim 3, wherein the starting material is Fe2O3Powder, SrCO3Powder, La2O3Powder, Co2O3Powder, CaCO3And (3) powder.
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