A permanent magnet strontium ferrite and a preparation method and application thereof

Abstract

This invention relates to a permanent magnet strontium ferrite, its preparation method, and its application, belonging to the field of ferrite material preparation technology. The chemical formula of the permanent magnet strontium ferrite provided by this invention is: SrCu. x / 2 Si x / 2Fe 11.8‑x O 19 Where 0 < x ≤ 0.3; the preparation method includes: ball milling, drying, pre-calcining, crushing and sieving the raw materials to obtain pre-calcined particles; ball milling the pre-calcined particles a second time to obtain a second ball milling slurry; applying a magnetic field for orientation, wet pressing to form a green body; drying, and then sintering at a gradient temperature to obtain the permanent magnet strontium ferrite. The permanent magnet ferrite provided by this invention has excellent magnetic properties at room temperature and a low temperature coefficient, which can maintain the stability of the operating point and high-efficiency output in motors, reduce losses, and has high application value.

Description

Technical Field

[0001] This invention relates to the field of ferrite material preparation technology, and in particular to a permanent magnet strontium ferrite, its preparation method and application. Background Technology

[0002] The largest application of ferrite magnetic materials is in the field of electric motors. To meet the requirements of the permanent magnet motor market, the performance of ferrite permanent magnet materials must be comprehensively improved. Currently, in addition to their magnetic properties at room temperature, people are also concerned about the ability of ferrites to maintain stable magnetic properties under varying temperatures. Permanent magnet ferrites have a negative remanence temperature coefficient; if the remanence decreases too rapidly with temperature changes, it will reduce the output torque of the permanent magnet motor. Permanent magnet ferrites also have a positive coercivity temperature coefficient, making them less prone to demagnetization at high temperatures; however, if the coercivity increases too rapidly with temperature changes, it will increase the torque pulsation of the permanent magnet motor. Achieving control over the temperature coefficient of permanent magnet ferrites can expand the reliable operating range of permanent magnet motors and avoid demagnetization, which is of great significance to the development of permanent magnet motors.

[0003] Currently, in reducing the temperature coefficient of coercivity of ferrites, Yang, Z. et al. have replaced barium ferrites with Zn-Ti, Ni-Ti, and Ni-Zn-Ti (Yang, Z.; Wang, CS; Li, XH; Zeng, HX). (BaFe) 10.8-2x Ni x Ti x O 19 Ni-Ti substitution can effectively reduce the coercivity temperature coefficient α(Hc), but it will reduce the saturation magnetization σ of BaM. s Regarding reducing the remanence temperature coefficient of ferrite, Haneda, K. et al. used (Cu) 2+ ,Ge 4+ ) etc. to replace Fe 3+ Barium and strontium ferrites. The remanence temperature coefficient can be reduced to about 0.1%, but the ferrite prepared by this method has low magnetic properties at room temperature, Br = 2.65 kG and Hcj = 2.87 kOe.

[0004] Therefore, developing a high-temperature-stability strontium ferrite material and its preparation method, while ensuring high magnetic properties, improves the temperature characteristics of strontium ferrite and addresses the problem of strontium ferrite's tendency to demagnetize under varying temperature environments. This is of great significance for broadening the application range of permanent magnet strontium ferrites. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a permanent magnet strontium ferrite, its preparation method, and its applications. The permanent magnet strontium ferrite provided by this invention exhibits good magnetic properties at room temperature and high temperature stability, making it highly valuable for applications.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] In a first aspect, the present invention provides a permanent magnet strontium ferrite, wherein the chemical formula of the permanent magnet strontium ferrite is: SrCu x / 2 Si x / 2 Fe 11.8-x O 19 , where 0 < x ≤ 0.3.

[0008] This invention, based on the chemical composition of permanent magnet strontium ferrite, incorporates specific amounts of Cu and Si elements, and utilizes non-magnetic Cu ions. 2+ and Si 4+ The combination of Fe substitution in the strontium ferrite lattice 3+ Cu 2+ and Si 4+ It can weaken the Fe in ferrite 3+ The superexchange interaction between the grains allows Fe to be deposited in the grains. 3+ The parallel alignment of the spin magnetic moments of ions makes them less susceptible to temperature changes, thus improving the temperature characteristics of the material's magnetism.

[0009] Within the aforementioned chemical formula range, at doping ratios of Cu and Si, permanent magnet strontium ferrite materials exhibiting good magnetic properties at room temperature and high temperature stability can be obtained. Compared to undoped Cu and Si strontium ferrite, the permanent magnet strontium ferrite provided by this invention shows a significantly lower absolute value of its coercivity temperature coefficient and less susceptibility to temperature changes when temperature varies; simultaneously, the absolute value of its remanence temperature coefficient decreases, resulting in a comprehensive improvement in the high-temperature stability of the ferrite's magnetic properties. Further increasing the Cu and Si doping amounts may significantly reduce the ferrite's magnetic properties at room temperature.

[0010] The permanent magnet strontium ferrite provided by this invention has high-temperature stability, and its coercivity and remanence temperature coefficient change little with temperature. It can also ensure good magnetic properties at room temperature and can be used in permanent magnet motors to reduce torque loss.

[0011] Preferably, in the chemical formula of the permanent magnet strontium ferrite, 0.1 ≤ x ≤ 0.2. With this Cu and Si doping ratio, the permanent magnet strontium ferrite at room temperature exhibits Br above 3.959 kG, Hcj above 3.902 kOe, and Hcb above 3.512 kOe, significantly improving temperature stability compared to undoped ferrite while preventing a decrease in room temperature magnetic properties.

[0012] Secondly, the present invention provides a method for preparing the above-mentioned permanent magnet strontium ferrite, characterized by comprising the following steps:

[0013] (1) The raw materials are mixed with water and ball-milled once to obtain a ball-milled slurry; the raw materials include iron source, strontium source, copper source and silicon source;

[0014] (2) The ball mill slurry is dried, pre-calcined, then crushed and sieved to obtain pre-calcined particles; the pre-calcination temperature is 1200-1240℃;

[0015] (3) The pre-burned material particles, additives, and water are mixed and subjected to secondary ball milling to obtain a secondary ball mill slurry; the particle size of the secondary ball mill slurry is D. 50 =0.8-0.9μm;

[0016] (4) The secondary ball milling slurry is oriented by a magnetic field and wet-pressed to obtain a green body;

[0017] (5) The green blank is dried and then sintered at a gradient temperature of 1100-1150℃ to obtain the permanent magnet strontium ferrite.

[0018] The present invention optimizes the preparation method of the permanent magnet strontium ferrite: the raw materials are ball-milled once, pre-fired at a specific temperature to allow the raw materials to react initially, crushed and sieved to obtain pre-fired particles; then ball-milled a second time to further refine the particles in the product slurry to achieve a specific size range, and then shaped by magnetic field orientation, pressed into green blanks, sintered, and sintered at a specific temperature to obtain the permanent magnet strontium ferrite.

[0019] Controlling the pre-firing temperature in step (1) to 1200-1240℃ ensures the magnetic properties of the permanent magnet strontium ferrite. If the pre-firing temperature is too low, the prepared material cannot form a pure phase, and 2% to 3% Fe2O3 remains. The presence of the non-magnetic phase deteriorates the magnetic properties. If the pre-firing temperature is too high, the magnetic powder will show orientation along the c-axis, the magnetic properties will decrease, and it will be impossible to further prepare it into a bulk material.

[0020] Controlling the particle size in the secondary ball milling slurry within D 50Within the range of 0.8-0.9μm, the coercivity and squareness of permanent magnet strontium ferrite can be improved, and the anti-demagnetization ability is strong; if the particle size of the secondary ball milling slurry is too large or too small, it will not be conducive to the magnetic properties of permanent magnet strontium ferrite.

[0021] The final sintering temperature is controlled at 1100-1150℃ to ensure a full reaction and obtain permanent magnet strontium ferrite with good magnetic properties; if the sintering temperature is too high, the coercivity will be significantly reduced; if the temperature is too low, the reaction will be insufficient.

[0022] Preferably, in step (1), the raw materials include iron oxide red, strontium carbonate, copper oxide and silicon oxide; more preferably, in step (1), the molar ratio of iron oxide red, strontium carbonate, copper oxide and silicon oxide is 5.9:1:(0.1-0.3):(0.1-0.3).

[0023] Preferably, in step (1), during one ball milling, the mass ratio of the milling media, the raw material, and water is milling media: raw material: water = (14-18):(0.9-1.1):(1-1.5), and the milling time is 1.5-2.5 hours. The diameter of the milling media used is 3 mm.

[0024] More preferably, in step (1), during one ball milling, the mass ratio of the ball milling media, the raw material to the water is ball milling media: raw material to water = 16:1:1.2, and the ball milling time is 2 hours.

[0025] Ball milling was performed using a horizontal ball mill, followed by microwave drying: power 400W, drying temperature 80℃, drying time 1-3 hours, and pre-calcination after drying.

[0026] Preferably, in step (2), the preheating time is 6-6.5 hours and the holding time is 0.5-1 hour.

[0027] More preferably, in step (2), the preheating time is 6.5 hours and the holding time is 0.5 hours.

[0028] After heating to the pre-firing temperature for 6.5 hours, the temperature is maintained for another 0.5 hours to complete the pre-firing. Then, the material is cooled to room temperature with the furnace and crushed and sieved to obtain pre-fired material particles.

[0029] Preferably, in step (2), the mesh size of the sieve used for crushing and screening is 100 mesh.

[0030] Preferably, in step (3), the additives are calcium gluconate, SiO2, H3BO3, and CaCO3. The amounts of calcium gluconate and SiO2 added are 0.5% of the mass of the pre-calcined material, respectively; the amount of H3BO3 added is 0.08% of the mass of the pre-calcined material; and the amount of CaCO3 added is 1.5% of the mass of the raw materials.

[0031] After the pre-burned material particles are crushed, they are subjected to secondary ball milling: In this invention, calcium gluconate, SiO2, H3BO3 and CaCO3 are added as secondary additives during secondary ball milling. After ball milling, the material is oriented and pressed into a green blank by magnetic field, and a gradient sintering method with variable heating rate is adopted to control the grain / grain boundary characteristics of ferrite and realize the densification growth of hexagonal ferrite single domain.

[0032] Preferably, in step (3), during the secondary ball milling, the mass ratio of the milling media, pre-burnt particles, and water is milling media: pre-burnt particles: water = (15.5-16.5):(0.9-1.1):(1-1.5), and the milling time is 15.5-16.5 hours. The diameter of the milling media used is 3 mm.

[0033] More preferably, in step (3), during the secondary ball milling, the mass ratio of the ball milling media, pre-burned material particles, and water is ball milling media: pre-burned material particles: water = 16:1:1.2, and the ball milling time is 16h.

[0034] If the secondary ball milling time is too long, the slurry particle size will be too small, reducing the coercivity and squareness of the permanent magnet strontium ferrite; if the ball milling time is insufficient, the particles will be too large, which may lead to a decrease in magnetic properties.

[0035] After ball milling, the green body is oriented by a magnetic field and then wet-pressed to form a green body with a diameter of 20-22 mm and a height of 8-12 mm.

[0036] Preferably, in step (4), the green blank is dried in an oven at 70°C for 3-5 hours before sintering.

[0037] Preferably, in step (5), the gradient heating includes the following stages: a first stage, heating from room temperature to 400℃ at a rate of 1.5-2.5℃ / min; a second stage, heating from 400℃ to 800℃ at a rate of 4.5-5.5℃ / min; and a third stage, heating from 800℃ to the sintering temperature at a rate of 4.5-5.5℃ / min.

[0038] More preferably, in step (5), the sintering temperature is 1120℃ and the sintering holding time is 1h.

[0039] This invention employs a variable-speed gradient sintering process, starting slowly and gradually increasing the speed, to prevent cracking and failure to form the desired shape during sintering. The temperature is raised from room temperature to a sintering temperature of 1120℃ in three stages, and held for 1 hour to achieve dense growth of single domains in hexagonal ferrite. If the temperature is raised rapidly at a constant rate, it is impossible to obtain a formed permanent magnet strontium ferrite.

[0040] Thirdly, the present invention provides the application of the above-mentioned permanent magnet strontium ferrite in permanent magnet motors.

[0041] The permanent magnet strontium ferrite prepared by this invention has excellent magnetic properties at room temperature and a low temperature coefficient, which is crucial for maintaining the stability of the operating point and high-efficiency output of ferrite in motors, thus broadening its application in permanent magnet motors.

[0042] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0043] This invention uses non-magnetic Cu ions 2+ and Si 4+ The combination partially replaces Fe in the permanent magnet strontium ferrite lattice 3+ Furthermore, the preparation method was optimized to obtain permanent magnet strontium ferrite with high temperature stability and excellent magnetic properties at room temperature. It can be applied to permanent magnet motors to maintain the stability of the operating point and high-efficiency output. Attached Figure Description

[0044] Figure 1 The XRD patterns of the permanent magnet strontium ferrites in Examples 1-3 are shown below.

[0045] Figure 2 The image shows the XRD pattern of the magnetic powder product from Comparative Example 2.

[0046] Figure 3 The image shows the XRD pattern of the magnetic powder product from Comparative Example 3. Detailed Implementation

[0047] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments. Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods; the materials and reagents used, unless otherwise specified, are commercially available reagents and materials.

[0048] Example 1

[0049] One embodiment of the permanent magnet strontium ferrite of the present invention, wherein the chemical formula of the permanent magnet strontium ferrite in this embodiment is SrCu 0.05 Si 0.05 Fe 11.7 O 19 .

[0050] The method for preparing the permanent magnet strontium ferrite described in this embodiment is as follows:

[0051] (1) First ball milling: Weigh the raw materials SrCO3, Fe2O3, SiO2 and CuO according to the chemical formula ratio, add water and mix, and ball mill using a horizontal ball mill. The mass ratio of ball milling media, raw materials and water is ball milling media: raw materials: water = 16:1:1.2, the rotation speed is 1500 r / min, and the ball milling is 2h to obtain the first ball milling slurry.

[0052] (2) Drying, pre-calcining, crushing and sieving: After filtering water from the ball mill slurry with filter cloth, microwave drying is performed. The dried slurry is crushed into fine particles and then placed in a box furnace for sintering. The temperature is raised to 1220℃ in 6.5 hours and held for 30 minutes. Then, the furnace is cooled to room temperature and crushed using a laboratory crusher. The particles are then passed through a 100-mesh sieve to obtain pre-calcined particles.

[0053] (3) Secondary ball milling: Weigh the pre-fired material particles, add 0.5 wt% calcium gluconate, 0.5 wt% SiO2, 0.08 wt% H3BO3, and 1.5 wt% CaCO3 relative to the pre-fired material particles, and mix with water; ball mill using a horizontal ball mill, with the mass ratio of ball milling media: pre-fired material particles: water = 16:1:1.2, rotation speed 1500 r / min, ball milling for 16 h to obtain secondary ball milling slurry; the particle size D of the secondary ball milling slurry is measured by a laser particle size analyzer. 50 It is 0.85μm.

[0054] (4) Wet pressing: The secondary ball mill slurry is magnetically oriented and pressed to obtain a green blank with a diameter of 20-22 mm and a height of 8-12 mm.

[0055] (5) Sintering: Before sintering, the green blank is dried in an oven at 70°C and then placed in a box furnace. It is heated to 400°C at room temperature for 188 minutes, then to 800°C for 80 minutes, then to 1120°C for 64 minutes, held for 60 minutes, and finally cooled to room temperature with the furnace to obtain permanent magnet strontium ferrite.

[0056] The obtained permanent magnet strontium ferrite was ground into powder, and XRD was measured. The results are as follows: Figure 1 .

[0057] Depend on Figure 1 It can be seen that the XRD pattern matches the standard card for strontium ferrite, indicating the formation of a single M-phase strontium ferrite.

[0058] Example 2

[0059] The only difference between Example 2 and Example 1 is that, using the chemical formula SrCu 0.1 Si 0.1 Fe 11.6 O 19The raw materials were weighed and prepared according to the specified proportions to obtain SrCu. 0.1 Si 0.1 Fe 11.6 O 19 Permanent magnet strontium ferrite.

[0060] The obtained permanent magnet strontium ferrite was ground into powder, and XRD was measured. The results are as follows: Figure 1 .

[0061] Depend on Figure 1 It can be seen that the XRD pattern matches the standard card for strontium ferrite, indicating the formation of a single M-phase strontium ferrite.

[0062] Example 3

[0063] The only difference between Example 3 and Example 1 is that, using the chemical formula SrCu 0.15 Si 0.15 Fe 11.5 O 19 The raw materials were weighed and prepared according to the specified proportions to obtain SrCu. 0.15 Si 0.15 Fe 11.5 O 19 Permanent magnet strontium ferrite.

[0064] The obtained permanent magnet strontium ferrite was ground into powder, and XRD was measured. The results are as follows: Figure 1 .

[0065] Depend on Figure 1 It can be seen that the XRD pattern matches the standard card for strontium ferrite, indicating the formation of a single M-phase strontium ferrite.

[0066] Example 4

[0067] The only difference between Example 4 and Example 1 is that the pre-firing temperature was 1200℃ and the sintering temperature was 1150℃, yielding a product with the chemical formula SrCu. 0.05 Si 0.05 Fe 11.7 O 19 Permanent magnet strontium ferrite.

[0068] Example 5

[0069] The only difference between Example 5 and Example 1 is that the pre-firing temperature was 1240℃ and the sintering temperature was 1100℃, resulting in the preparation of SrCu. 0.05 Si 0.05 Fe 11.7 O 19 Permanent magnet strontium ferrite.

[0070] Comparative Example 1

[0071] The only difference between Comparative Example 1 and Example 1 is that, using the chemical formula SrFe 11.8 O 19 The raw materials were weighed and prepared according to the specified proportions to obtain SrFe. 11.8 O 19 Permanent magnet strontium ferrite.

[0072] Comparative Example 2

[0073] The only difference between Comparative Example 2 and Example 1 is that the preheating temperature is 1180°C.

[0074] The obtained block was ground into powder, and XRD was measured. The results are as follows: Figure 2 .

[0075] Depend on Figure 2 It can be seen that the XRD pattern of the magnetic powder, compared with the standard card of strontium ferrite, contains 2% to 3% Fe2O3 impurity phase. The presence of this impurity phase will deteriorate the magnetic properties of the magnet.

[0076] Comparative Example 3

[0077] The only difference between Comparative Example 3 and Example 1 is that the preheating temperature is 1250°C.

[0078] Using this pre-calcination temperature, it is impossible to prepare a bulk product. The XRD results of the prepared product are as follows... Figure 3 .

[0079] Depend on Figure 3 It can be seen that, compared with the standard card for strontium ferrite, the XRD pattern of the magnetic powder shows a significant increase in peak intensity along the c-axis, indicating an orientation along the c-axis. This is because, at excessively high pre-calcination temperatures, the liquefaction of Cu leads to excessive growth of the main phase particles, resulting in the magnetic powder exhibiting an orientation along the c-axis, a decrease in magnetic properties, and an inability to be further prepared into a bulk form.

[0080] Comparative Example 4

[0081] The only difference between Comparative Example 4 and Example 1 is that the secondary ball milling time was 18 hours. The particle size D of the secondary ball-milled slurry was measured by a laser particle size analyzer. 50 =0.68μm.

[0082] Comparative Example 5

[0083] The only difference between Comparative Example 5 and Example 1 is that the third stage of gradient heating sintering is changed to heating to 1170°C at a heating rate of 5°C / min, holding at that temperature for 60 min, and finally cooling to room temperature with the furnace.

[0084] Comparative Example 6

[0085] The only difference between Comparative Example 6 and Example 1 is that gradient heating sintering is not used. Instead, the temperature is directly increased from room temperature to 1120°C at a heating rate of 5°C / min, held for 60 minutes, and finally cooled to room temperature in the furnace.

[0086] Due to excessively rapid heating, the bulk material cracked during sintering, and after sintering, it was impossible to form a complete permanent magnet ferrite.

[0087] Example 1

[0088] To investigate the room-temperature magnetic properties of permanent magnet strontium ferrite, the top and bottom surfaces of the permanent magnet strontium ferrite blocks prepared in Examples 1-3 and Comparative Examples 1, 4, and 5 were polished smooth. The room-temperature magnetic properties of the blocks were tested using BH: remanent magnetic flux density Br, coercivity Hcb, and intrinsic coercivity Hcj. The results are shown in Table 1.

[0089] Table 1. Room temperature magnetic performance test data of Examples 1-3 and Comparative Examples 1, 4, and 5

[0090] Br / kG Hcb / kOe Hcj / kOe Example 1 3.985 3.625 4.091 Example 2 3.959 3.512 3.902 Example 3 3.9 3.455 3.815 Comparative Example 1 4.012 3.778 4.397 Comparative Example 4 3.903 1.569 2.719 Comparative Example 5 3.805 0.797 1.043

[0091] Example 2

[0092] To investigate the temperature stability of the magnetic properties of permanent magnet strontium ferrite, the top and bottom surfaces of the permanent magnet strontium ferrite blocks prepared in Examples 1-3 and Comparative Example 1 were polished smooth, and the temperature coefficients of remanence and coercivity were measured.

[0093] The magnetic properties were tested at 20°C intervals within the range of 25°C to 140°C, and the temperature coefficients of remanence and coercivity were calculated according to the following formulas (where the starting temperature T0 is 25°C). The results are shown in Table 2.

[0094]

[0095]

[0096] Table 2 Temperature coefficients of remanence and coercivity in Examples 1-3 and Comparative Example 1

[0097]

[0098] From Tables 1 and 2, we can see that:

[0099] (1) Comparison of Examples 1-3 with Comparative Example 1: Introducing appropriate amounts of copper and silicon into the formulation can improve the remanence and coercivity temperature stability of strontium ferrite. With increasing doping amount, the absolute value of the coercivity temperature coefficient decreases significantly, and the influence of temperature becomes significantly smaller; the absolute value of the remanence temperature coefficient also decreases slightly, meaning that temperature stability is improved. Too low a doping amount does not significantly improve temperature stability; however, the addition of non-magnetic ions reduces the magnetic properties of the ferrite at room temperature, and the higher the doping amount, the greater the decrease in magnetic properties. The optimal formulation conforms to the chemical formula SrCu. x / 2 Si x / 2 Fe 11.8-x O 19 , permanent magnet strontium ferrite with a ratio of 0.1≤x≤0.2.

[0100] (2) As can be seen from the examples and comparative examples 4 and 5: if the secondary ball milling time exceeds the limit of the present invention, the particle size of the slurry will be too small, D 50 Beyond 0.8-0.9 μm, the coercivity and squareness of the prepared permanent magnet strontium ferrite will be significantly reduced; when the sintering temperature is 1170℃, the sintering temperature is too high, and the coercivity and squareness of the prepared permanent magnet strontium ferrite will also be significantly reduced, and the magnetic properties will be significantly worse.

[0101] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A permanent magnet strontium ferrite, characterized in that, The chemical formula of the permanent magnet strontium ferrite is: SrCu x / 2 Si x / 2 Fe 11.8- x O 19 Where 0.1≤x≤0.2; The method for preparing the permanent magnet strontium ferrite includes the following steps: (1) The raw materials are mixed with water and ball-milled once to obtain a ball-milled slurry; the raw materials include an iron source, a strontium source, a copper source and a silicon source; (2) The ball mill slurry is dried, pre-calcined, and then crushed and sieved to obtain pre-calcined particles; the pre-calcination temperature is 1200-1240℃; (3) The pre-burned material particles, additives, and water are mixed and subjected to secondary ball milling to obtain a secondary ball mill slurry; the particle size of the secondary ball mill slurry is D. 50 =0.8-0.9μm; the additives are calcium gluconate, SiO2, H3BO3 and CaCO3; (4) The secondary ball milling slurry is oriented by a magnetic field and wet-pressed to obtain a green body; (5) The green blank is dried and then sintered at a gradient temperature of 1100-1150℃ to obtain the permanent magnet strontium ferrite.

2. The permanent magnet strontium ferrite according to claim 1, characterized in that, In step (1), during one ball milling, the mass ratio of the ball milling media, the raw materials to water is ball milling media: raw materials to water = (14-18): (0.9-1.1): (1-1.5), and the ball milling time is 1.5-2.5h.

3. The permanent magnet strontium ferrite according to claim 1, characterized in that, In step (2), the preheating time is 6-6.5 hours and the holding time is 0.5-1 hour.

4. The permanent magnet strontium ferrite according to claim 1, characterized in that, In step (2), the mesh size of the sieve used for crushing and screening is 100 mesh.

5. The permanent magnet strontium ferrite according to claim 1, characterized in that, In step (3), during the secondary ball milling, the mass ratio of the ball milling media, pre-burned material particles and water is ball milling media: pre-burned material particles: water = (15.5-16.5): (0.9-1.1): (1-1.5), and the ball milling time is 15.5-16.5h.

6. The application of permanent magnet strontium ferrite according to any one of claims 1-5 in permanent magnet motors.

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