Strontium permanent magnetic ferrite and preparation process thereof

Abstract

The invention discloses a strontium permanent magnetic ferrite and a preparation process thereof, and belongs to the technical field of permanent magnets, and the preparation process comprises the following steps: weighing strontium carbonate, lanthanum oxide, cobalt oxide and iron oxide with corresponding molar weights according to a main formula LaxSr1-xO.n [(Fe1-yCoy) 2O3]; uniformly mixing strontium carbonate, lanthanum oxide, cobalt oxide and iron oxide, transferring the mixture into a ball mill, and carrying out wet ball milling until the particle size of slurry is less than or equal to 8.0 microns to obtain a premix; sintering, and naturally cooling to room temperature to obtain pre-sintered powder; uniformly mixing the pre-sintered powder with calcium carbonate, silicon dioxide and an organic auxiliary agent, carrying out secondary ball milling until the particle size of the slurry is less than or equal to 7.5 microns, and dehydrating to obtain wet slurry; carrying out compression molding on the wet material to obtain a green body; and sintering the green body, and naturally cooling to room temperature to obtain the strontium permanent magnetic ferrite. The product produced by the invention has high magnetic performance, the residual magnetism Br is greater than or equal to 4300Gs, and the magnetic induction coercive force Hcb is greater than or equal to 5000e.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of permanent magnets, and particularly relates to a strontium permanent magnet ferrite and a preparation process thereof. BACKGROUND

[0002] With the rapid development of the electronic information industry and the increasing demand of people for the quality of life, the demand for magnetic materials is increasing. The performance of the ferrite raw materials produced by domestic raw material manufacturers is generally low according to the conventional process, with Br being 4000GS and HCJ being about 3500Oe.

[0003] Strontium permanent magnet ferrite is an important magnetic functional material in the electronic information industry, and is widely used in the fields of automobile motor, household appliances, electric tools and toy design and manufacturing. It has the advantages of simple structure, reliable work, light weight, small size, convenient use, high temperature resistance, high coercive force, high remanence and high magnetic energy product, and the like. In addition, the raw material is cheap and easy to purchase in large quantities. The automobile starting motor requires high remanence, high coercive force, high intrinsic coercive force and anti-demagnetization, and it is imperative to develop a material for high-performance starting motor magnetic tile.

[0004] The magnetic performance indicators of strontium permanent magnet ferrite mainly include remanence (Br) and intrinsic coercive force (Hcj), and the higher the two indicators, the better the material performance of the magnet. The remanence is proportional to the density, grain orientation degree and saturation magnetization (MS) of the magnet, and the intrinsic coercive force is related to the grain size, single magnetic domain particle ratio and magnetic crystal anisotropy parameter of the magnet. At present, in the production of high-performance permanent magnets, high-purity iron red raw materials and strontium oxide or strontium carbonate are used as basic raw materials, and a series of related ceramic processes such as pre-sintering, molding, ball milling and sintering are used to obtain the products, which have poor magnetic properties. Current research shows that Al 3+ Doped strontium permanent magnet ferrite is an effective way to improve its coercive force. For example, a preparation method of high-performance permanent magnet ferrite is disclosed in Chinese Patent No. 202011129056.9, in which aluminum oxide is added as a doping additive to the magnet pre-sintering material. However, the melting point of aluminum oxide is very high, reaching 2054℃. Strontium permanent magnet ferrite forms a strontium ferrite phase at 1200-1300℃. A too low calcination temperature makes it difficult for aluminum ions in aluminum oxide to play an effective doping role, and a too high calcination temperature leads to excessive growth of magnet grains, which is not conducive to the improvement of coercive force. Therefore, how to better utilize Al 3+ Doped strontium permanent magnet ferrite to improve the coercive force is a technical problem to be solved at present. SUMMARY

[0005] The application provides a strontium permanent magnet ferrite and a preparation process thereof, which can solve the problem of poor Al 3+ doping effect in the prior art.

[0006] The object of the present application can be achieved by the following technical solutions:

[0007] A preparation process of a strontium permanent magnet ferrite, comprising the following steps:

[0008] S1, preparing pre-sintering material: according to the main formula La x Sr 1-x O·n[(Fe 1-y Co y )2O3], the corresponding molar amount of strontium carbonate, lanthanum oxide, cobalt oxide and iron oxide is weighed, wherein n=5.9-6.1, x=0.1-0.3, and y=0.08-0.3; first, design the main formula raw material containing rare earth elements, and the doping substitution of La and Co rare earth elements can greatly improve the intrinsic properties of magnetic materials;

[0009] S2, after mixing strontium carbonate, lanthanum oxide, cobalt oxide and iron oxide uniformly, transferring to a ball mill, wet ball milling to a slurry particle size of ≤8.0um, obtaining a premix; drying the premix and then sintering, and naturally cooling to room temperature to obtain a pre-sintering powder;

[0010] S3, mixing the pre-sintering powder with calcium carbonate, silicon dioxide and organic additives uniformly, and performing secondary ball milling to a slurry particle size of ≤7.5um, and then dehydrating to obtain a wet material;

[0011] S4, pressing the wet material into a green body; sintering the green body and naturally cooling to room temperature to obtain a strontium permanent magnet ferrite.

[0012] In some embodiments, the mass ratio of material, water and steel balls in the S2 ball milling process is 1:1.5-3:15-20, the rotation speed is 80-100r / min, and the steel ball diameter is 5-8mm.

[0013] In some embodiments, the sintering temperature in S2 is 1200-1300℃, and the sintering time is 2-3h.

[0014] In some embodiments, the amount of calcium carbonate in S3 is 0.7-0.9% of the mass of the pre-sintering powder, the amount of silicon dioxide is 0.1-0.4% of the mass of the pre-sintering powder, and the amount of organic additives is 0.2-0.5% of the mass of the pre-sintering powder.

[0015] In some embodiments, the organic additive is composed of triethanolamine and aluminum carboxylate compound, and the mass ratio of triethanolamine to aluminum carboxylate compound is 1:1-1.5.

[0016] In some embodiments, the aluminum carboxylate compound is at least one of aluminum stearate, aluminum distearate and aluminum oleate.

[0017] In the secondary ball milling process, calcium carbonate, silicon dioxide and organic additives are introduced as additives, wherein the calcium carbonate can promote the solid phase reaction and increase the density of the sintered magnet, and the addition amount of the calcium carbonate is controlled to avoid abnormal growth of the crystal grains caused by excessive calcium carbonate, thereby reducing the magnetic performance; in the sintering process, the silicon dioxide can react with the iron oxide to generate a low-melting-point substance (FeSiO3), so that the temperature of the solid phase reaction of the ferrite is reduced, liquid phase sintering is formed, the reaction temperature range is widened, the density of the ferrite is improved, the remanence is improved, the silicon dioxide is segregated at the grain boundaries in the strontium ferrite, the low-melting-point substance (FeSiO3) produced in the grain boundaries inhibits the grain growth and can refine the grains to improve the coercive force;

[0018] The triethanolamine in the organic additive is a dispersant, and the triethanolamine aqueous solution is alkaline, which is beneficial to improve the Zeta potential between the slurry particles, so that the particles obtain stronger electrostatic repulsion, thereby improving the dispersity of the magnetic powder particles, and further improving the stability of the slurry; the added aluminum carboxylate compound acts as an additive, and the aluminum carboxylate compound can interact with the particles in the slurry to further improve the dispersity of the magnetic powder particles; and in the sintering process, the Al 3+ Tend to enrich on the surface of the crystal grains and replace Fe 3+ , and form an epitaxial layer. The epitaxial layer pins the magnetic domain wall in the crystal grain, hinders the movement of the domain wall under the reverse magnetic field, and thus improves the coercive force of the magnetic material; therefore, the triethanolamine and the aluminum carboxylate compound synergistically improve the uniformity of the green body, the uniform green body shrinks more uniformly during sintering, reduces internal stress and microcracks, improves the density and uniformity of the final product, which is beneficial to the improvement of the remanence and the coercive force.

[0019] In some embodiments, the moisture content of the wet slurry in S3 is 25-30%.

[0020] In some embodiments, the pressing forming in S4 is performed by using a wet forming hydraulic press in a magnetic field, the pressing pressure is 100-300 MPa, and the magnetic field strength is 8000-14000 Gs.

[0021] Further, the sintering in S4 is performed by using a programmed heating method, first, the temperature is raised to 500 DEG C at a heating rate of 1-2 DEG C / min, and then the temperature is raised to 1150-1200 DEG C at a heating rate of 5-8 DEG C / min, and the temperature is maintained for 1-3 h.

[0022] A strontium permanent magnet ferrite is prepared by the above preparation process.

[0023] The beneficial effects of the present application are as follows:

[0024] 1. The invention is designed by substituting lanthanum and cobalt in low content as main formula, and high performance permanent ferrite is prepared by introducing multiple trace additives through suitable process. The product has high magnetic performance, remanence Br≥4315Gs, magnetic induction coercivity Hcb≥5021Oe.

[0025] 2. The triethanolamine in the organic auxiliary agent is a dispersant, and the triethanolamine aqueous solution is alkaline, which is beneficial to improve the Zeta potential between slurry particles. The improvement of Zeta potential makes the particles obtain stronger electrostatic repulsion, thereby improving the dispersity of magnetic powder particles and further improving the stability of the slurry. The added aluminum carboxylate compound acts as an auxiliary agent, and the aluminum carboxylate compound can interact with the particles in the slurry, further improving the dispersity of the magnetic powder particles. In the sintering process, the Al 3+ Tend to enrich on the surface of the grain and replace Fe 3+ Form a layer with an epitaxial layer. This epitaxial layer pins the domain wall inside the grain, hindering the movement of the domain wall under the reverse magnetic field, thereby improving the coercivity of the magnetic material. Therefore, triethanolamine and aluminum carboxylate compound have synergistic effect, improve the uniformity of the green body, the uniform green body shrinks more uniformly during sintering, reduces internal stress and microcracks, improves the density and uniformity of the final product, which is beneficial to the improvement of remanence and coercivity. DETAILED DESCRIPTION

[0026] In order to make the technical problems, technical solutions and beneficial effects of the present application more clear, the following embodiments are further described. It should be understood that the specific embodiments described herein are only used to explain the present application, and are not used to limit the present application.

[0027] It should be understood that in various embodiments of the present application, the size of the serial number of each process does not mean the order of execution, and part or all of the steps can be executed in parallel or in sequence, and the execution order of each process should be determined according to its function and inherent logic, and should not constitute any limitation on the implementation process of the present application.

[0028] The weight of the related components mentioned in the specification of the embodiments of the present application can not only refer to the specific content of each component, but also represent the proportional relationship between the weights of each component. Therefore, as long as the content of the related components in the specification of the embodiments of the present application is enlarged or reduced in proportion, it is within the scope disclosed in the specification of the embodiments of the present application. Specifically, the mass mentioned in the specification of the embodiments of the present application can be μg, mg, g, kg and other mass units commonly known in the chemical industry.

[0029] Unless otherwise defined, all terms used in the description herein, including technical and scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art. The terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the scope of the present application.

[0030] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present application can be purchased from the market or prepared by existing methods.

[0031] The technical solutions of the present application will be illustrated below through specific examples and comparative examples.

[0032] Example 1

[0033] A preparation process of a strontium permanent ferrite, comprising the following steps:

[0034] S1, preparing pre-sintering material: according to the main formula La x Sr 1-x O·n[(Fe 1-y Co y )2O3], the corresponding molar amounts of strontium carbonate, lanthanum oxide, cobalt oxide and iron oxide are weighed, wherein n=5.9, x=0.1, y=0.08;

[0035] S2, after mixing strontium carbonate, lanthanum oxide, cobalt oxide and iron oxide uniformly, transferring them to a ball mill, the mass ratio of material, water and steel ball is 1:1.5:15, the rotating speed is 80r / min, the diameter of steel ball is 5-8mm, wet ball milling to slurry particle size≤8.0um, obtaining premix; drying the premix and sintering, the sintering temperature is 1200℃, the sintering time is 3h, natural cooling to room temperature, obtaining pre-sintering powder;

[0036] S3, mixing the pre-sintering powder with calcium carbonate, silicon dioxide and organic additives uniformly, the amount of calcium carbonate is 0.7% of the mass of pre-sintering powder, the amount of silicon dioxide is 0.1% of the mass of pre-sintering powder, the amount of organic additives is 0.2% of the mass of pre-sintering powder, secondary ball milling, ball milling to slurry particle size≤7.5um, then dehydrating to obtain wet material, the water content of wet slurry is 25%;

[0037] S4, pressing the wet material into green body, the pressing is carried out in a magnetic field using a wet forming hydraulic press, the pressing pressure is 100MPa, the magnetic field strength is 8000Gs, obtaining green body with size φ30mm×15mm; sintering the green body, the sintering is carried out in a programmed heating way, first heating to 500℃ at a heating rate of 1℃ / min, keeping for 1h, then heating to 1150℃ at a heating rate of 5℃ / min, keeping for 1h, natural cooling to room temperature, obtaining strontium permanent ferrite.

[0038] The organic auxiliary agent is composed of triethanolamine and aluminum stearate according to a mass ratio of 1:1.

[0039] Example 2

[0040] A preparation process of a strontium permanent magnet ferrite includes the following steps:

[0041] S1, preparing a pre-sintering material: according to a main formula La x Sr 1-x O·n[(Fe 1-y Co y )2O3], corresponding molar amounts of strontium carbonate, lanthanum oxide, cobalt oxide and iron oxide are weighed, wherein n=6.0, x=0.2, and y=0.1;

[0042] S2, after the strontium carbonate, the lanthanum oxide, the cobalt oxide and the iron oxide are uniformly mixed, the pre-mixed material is transferred to a ball mill, the mass ratio of the material, water and steel balls is 1:2:18, the rotating speed is 90 r / min, the diameter of the steel balls is 5-8 mm, and the wet ball milling is performed until the particle size of the slurry is less than or equal to 8.0 um, so as to obtain the pre-sintering powder;

[0043] S3, the pre-sintering powder is uniformly mixed with calcium carbonate, silicon dioxide and an organic auxiliary agent, the amount of the calcium carbonate is 0.8% of the mass of the pre-sintering powder, the amount of the silicon dioxide is 0.2% of the mass of the pre-sintering powder, and the amount of the organic auxiliary agent is 0.3% of the mass of the pre-sintering powder, and then secondary ball milling is performed until the particle size of the slurry is less than or equal to 7.5 um, and then the wet material is obtained by dehydration, and the water content of the wet slurry is 28%;

[0044] S4, the wet material is pressed and formed, the pressing and forming are performed in a magnetic field by using a wet forming hydraulic machine, the pressing pressure is 200 MPa, and the magnetic field strength is 10000 Gs, so as to obtain a green body with a size of φ30 mm*15 mm; the green body is sintered by using a programmed heating mode, first, the temperature is raised to 500 DEG C at a heating rate of 1.5 DEG C / min, and then the temperature is raised to 1180 DEG C at a heating rate of 7 DEG C / min, and the temperature is maintained for 2 h, and then the green body is naturally cooled to room temperature, so as to obtain the strontium permanent magnet ferrite.

[0045] The organic auxiliary agent is composed of triethanolamine and aluminum stearate according to a mass ratio of 1:1.2.

[0046] Example 3

[0047] A preparation process of a strontium permanent magnet ferrite includes the following steps:

[0048] S1, preparing a pre-sintering material: according to a main formula La x Sr 1-x O·n[(Fe 1-y Co y)2O3]Take the corresponding molar amount of strontium carbonate, lanthanum oxide, cobalt oxide and iron oxide, wherein n = 6.1, x = 0.2, y = 0.3;

[0049] S2, after the strontium carbonate, lanthanum oxide, cobalt oxide and iron oxide are uniformly mixed, they are transferred to a ball mill, the mass ratio of the material, water and steel balls is 1:3:20, the rotating speed is 100r / min, the diameter of the steel balls is 5-8mm, the wet ball milling is carried out until the slurry particle size is ≤8.0um, and the premix is obtained; the premix is dried and then sintered, the sintering temperature is 1300℃, the sintering time is 2h, and the natural cooling is carried out until room temperature, and the presintered powder is obtained;

[0050] S3, the presintered powder is uniformly mixed with calcium carbonate, silicon dioxide and organic additives, the amount of calcium carbonate is 0.9% of the mass of the presintered powder, the amount of silicon dioxide is 0.4% of the mass of the presintered powder, and the amount of organic additives is 0.5% of the mass of the presintered powder, secondary ball milling is carried out until the slurry particle size is ≤7.5um, and then the wet material is obtained by dehydration, and the water content of the wet slurry is 30%;

[0051] S4, the wet material is pressed into a green body, the pressing is carried out in a magnetic field by using a wet molding hydraulic press, the pressing pressure is 300MPa, and the magnetic field strength is 14000Gs, and the green body with the size of φ30mm*15mm is obtained; the green body is sintered, the sintering is carried out in a programmed heating mode, first, the temperature is raised to 500℃ at a rate of 2℃ / min, and then the temperature is raised to 1200℃ at a rate of 8℃ / min, and the temperature is kept for 3h, and then the natural cooling is carried out until room temperature, and the strontium permanent magnet ferrite is obtained.

[0052] The organic additives are composed of triethanolamine and aluminum stearate according to the mass ratio of 1:1.5.

[0053] Example 4

[0054] A preparation process of a strontium permanent magnet ferrite, compared with example 1, the difference is that the aluminum stearate in example 1 is replaced by the same amount of aluminum distearate.

[0055] Example 5

[0056] A preparation process of a strontium permanent magnet ferrite, compared with example 1, the difference is that the aluminum stearate in example 1 is replaced by the same amount of aluminum oleate.

[0057] Comparative example 1

[0058] A preparation process of a strontium permanent magnet ferrite, compared with example 1, the difference is that the aluminum stearate in example 1 is replaced by the same amount of aluminum oxide.

[0059] Comparative example 2

[0060] A preparation process of strontium permanent magnet ferrite, compared with example 1, the only difference is that the aluminum stearate in example 1 is replaced by the same mass of triethanolamine.

[0061] Comparative example 3

[0062] A preparation process of strontium permanent magnet ferrite, compared with example 1, the only difference is that the triethanolamine in example 1 is replaced by the same mass of aluminum stearate.

[0063] Comparative example 4

[0064] A preparation process of strontium permanent magnet ferrite, compared with example 4, the only difference is that the aluminum distearate in example 4 is replaced by the same mass of triethanolamine.

[0065] Comparative example 5

[0066] A preparation process of strontium permanent magnet ferrite, compared with example 4, the only difference is that the triethanolamine in example 4 is replaced by the same mass of aluminum distearate.

[0067] Comparative example 6

[0068] A preparation process of strontium permanent magnet ferrite, compared with example 5, the only difference is that the aluminum oleate in example 5 is replaced by the same mass of triethanolamine.

[0069] Comparative example 7

[0070] A preparation process of strontium permanent magnet ferrite, compared with example 5, the only difference is that the triethanolamine in example 5 is replaced by the same mass of aluminum oleate.

[0071] The magnetic material prepared by example 1 to example 5 and comparative example 1 to comparative example 7 is measured by NIM-2000F permanent magnet ferrite measuring instrument, the remanence and magnetic induction coercive force of the permanent magnet ferrite are measured, and the results are shown in table 1:

[0072] Table 1

[0073]

[0074] It can be seen from the data recorded in table 1 that the remanence Br of the permanent magnet ferrite prepared by example 1 to example 5 is greater than or equal to 4315Gs, and the magnetic induction coercive force Hcb is greater than or equal to 5021Oe, which shows that the strontium permanent magnet ferrite obtained by the preparation process has better magnetic properties.

[0075] It can be seen from the test results of example 1 and comparative example 1 that compared with using aluminum oxide, using aluminum stearate as an aluminum-based additive is more conducive to obtaining high-performance permanent magnet ferrite.

[0076] From the test results in example 1, comparative example 2 and comparative example 3, the test results in example 4, comparative example 4, comparative example 4, the test results in example 5, comparative example 6, comparative example 7, it can be seen that the triethanolamine in the organic additive of the application is a dispersant, the triethanolamine aqueous solution is alkaline, which is beneficial to improve the Zeta potential between the particles of the slurry, the improvement of the Zeta potential, the stronger electrostatic repulsion between the particles, thereby improving the dispersity of the magnetic powder particles, and further improving the stability of the slurry, the addition of the aluminum carboxylate compound as an additive, the aluminum carboxylate compound can interact with the particles in the slurry, further improving the dispersity of the magnetic powder particles, and in the sintering process, the Al 3+ Tend to enrich and replace Fe on the surface of the crystal grain 3+ Form a layer with an epitaxial layer. This epitaxial layer plays a pinning effect on the magnetic domain wall inside the crystal grain, hindering the movement of the domain wall under the reverse magnetic field, thereby improving the coercivity of the magnetic material; therefore, the triethanolamine and the aluminum carboxylate compound synergistically improve the uniformity of the green body, the uniform green body shrinks more uniformly during sintering, reduces internal stress and microcracks, and improves the density and uniformity of the final product, which is beneficial to the improvement of the remanence and coercivity.

[0077] It should be noted that, in this text, relational terms such as first and second are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "contain" or any other variant thereof are intended to cover non-exclusive inclusion, so that the process, method, article or equipment including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such process, method, article or equipment.

[0078] Although the embodiments of the application have been shown and described, it can be understood by those of ordinary skill in the art that various changes, modifications, replacements and variations can be made to these embodiments without departing from the principles and spirits of the application, and the scope of the application is defined by the appended claims and their equivalents.

Claims

1. A process for producing a strontium permanent ferrite, characterized by, The method comprises the following steps: S1, according to the main formula La x Sr 1-x O·n[(Fe 1-y Co y )2O3]Take the corresponding molar amount of strontium carbonate, lanthanum oxide, cobalt oxide and iron oxide; S2, after mixing strontium carbonate, lanthanum oxide, cobalt oxide and iron oxide uniformly, transferring to a ball mill, wet ball milling to slurry particle size ≤8.0um, obtaining a premix; drying the premix, sintering, and naturally cooling to room temperature to obtain a presintered powder; S3, mixing the presintered powder with calcium carbonate, silicon dioxide and organic additives uniformly, secondary ball milling to slurry particle size ≤7.5um, then dehydrating to obtain a wet material; S4, pressing the wet material to obtain a green body; sintering the green body, and naturally cooling to room temperature to obtain a strontium permanent magnet ferrite.

2. The preparation process of a strontium permanent magnet ferrite according to claim 1, characterized in that, n=5.9-6.1, x=0.1-0.3, y=0.08-0.

3.

3. The preparation process of a strontium permanent magnet ferrite according to claim 1, characterized in that, In the S2 ball milling process, the mass ratio of material, water and steel ball is 1:1.5-3:15-20, the rotating speed is 80-100r / min, and the diameter of steel ball is 5-8mm.

4. The process for preparing a strontium permanent ferrite according to claim 1, wherein the step of adding the strontium compound is performed after the step of adding the iron compound. In S2, the sintering temperature is 1200-1300℃, and the sintering time is 2-3h.

5. The process for preparing a strontium permanent ferrite according to claim 1, wherein the step of adding the strontium compound is performed after the step of adding the iron compound. In S3, the amount of calcium carbonate is 0.7-0.9% of the mass of the presintered powder, the amount of silicon dioxide is 0.1-0.4% of the mass of the presintered powder, and the amount of organic additives is 0.2-0.5% of the mass of the presintered powder.

6. The process for preparing a strontium permanent ferrite according to claim 5, wherein the step of adding the strontium compound is performed after the step of adding the iron compound. The organic additives are composed of triethanolamine and aluminum carboxylate compounds, and the mass ratio of triethanolamine and aluminum carboxylate compounds is 1:1-1.

5.

7. The preparation process of a strontium permanent magnet ferrite according to claim 6, characterized in that, The aluminum carboxylate compound is at least one of aluminum stearate, aluminum distearate and aluminum oleate.

8. The preparation process of a strontium permanent magnet ferrite according to claim 1, characterized in that, In S4, the pressing is performed in a magnetic field using a wet forming hydraulic press, the pressing pressure is 100-300MPa, and the magnetic field strength is 8000-14000Gs.

9. The preparation process of a strontium permanent magnet ferrite according to claim 1, characterized in that, In S4, the sintering is performed in a programmed heating manner, first heating to 500℃ at a heating rate of 1-2℃ / min for 1h, then heating to 1150-1200℃ at a heating rate of 5-8℃ / min for 1-3h.

10. A strontium permanent magnet ferrite, characterized by, Prepared by the preparation process of any one of claims 1-9.

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