Preparation process of high-performance high-resistance seven-system permanent magnet ferrite and product prepared by the process

Abstract

The application discloses a preparation process of high-performance high-resistance seven-system permanent magnet ferrite and a product prepared by the process, and belongs to the technical field of permanent magnet ferrite. The method comprises the following steps: mixing nine-system pre-sintered materials and high-resistance iron red in proportion, pre-oxidizing the mixed materials to form permanent magnet ferrite pre-sintered materials, and then crushing the pre-sintered materials; mixing the pre-sintered materials obtained in the step a with auxiliary materials in proportion, ball milling, and twice sintering to obtain the high-resistance seven-system permanent magnet ferrite, so that the resistance of the permanent magnet ferrite can be effectively improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of permanent ferrites, and more specifically, relates to a preparation process of a high-performance and high-resistance seventh-series permanent ferrite and a product obtained therefrom. Background Art

[0002] Permanent ferrite, also known as hard ferrite, is a new type of non-metallic magnetic material. It only requires a single external magnetizing energy to generate a stable magnetic field, thereby continuously providing magnetic energy. Permanent ferrites are made from abundant and inexpensive raw materials, have simple and controllable production processes, and exhibit strong corrosion resistance. They also offer advantages such as a low price per unit magnetic energy product, corrosion resistance, and suitability for harsh operating environments. For these reasons, permanent ferrite is currently the most widely used permanent magnetic material.

[0003] Resistance is a key factor in evaluating ferrites. Different ferrite materials have different resistances. The low resistance of existing heptad permanent ferrites stems primarily from the presence of divalent iron ions surrounding oxygen ions. These ions lose electrons due to the lack of oxygen ions, forming oxygen vacancies and iron cations. These conduction charges, creating a current in the material and reducing resistance. Furthermore, the presence of interface and grain boundary defects in multiphase ferrites effectively scatters electron transport, further reducing resistance.

[0004] Patent CN108455981A discloses a permanent ferrite material made from raw materials such as SrCO3, BaCO3, CaCO3, La2O3, Fe2O3, and ZnO, to which an additive consisting of at least one of silicate, carbonate, aluminum oxide, bismuth oxide, or silicon dioxide may be added. The invention also discloses a method for preparing the permanent ferrite material, which includes the steps of batching, primary ball milling, pre-sintering, secondary ball milling, molding, sintering, and post-processing. However, the permanent ferrite disclosed in this patent has a low resistance value and can generate eddy currents in specific magnetic fields, resulting in eddy current losses. Summary of the Invention

[0005] 1. Problem to be solved

[0006] Aiming at the problem that the existing seven-series permanent magnet ferrite has low resistance, the present invention provides a preparation process of high-performance and high-resistance seven-series permanent magnet ferrite and the product obtained. The permanent magnet ferrite obtained by the method has high resistance.

[0007] 2. Technical solution

[0008] In order to solve the above problems, the technical solutions adopted by the present invention are as follows:

[0009] The first object of the present invention is to provide a preparation process of high performance and high resistance seven-series permanent ferrite, which specifically comprises the steps of:

[0010] Step a, mixing: mixing the nine series pre-burned material and the high resistance iron red in proportion, pre-oxidizing after mixing to form a permanent magnet ferrite pre-burned material, and then crushing the pre-burned material;

[0011] Step b, secondary batching: mixing the pre-burned material obtained in step a with the auxiliary materials in proportion;

[0012] Step c, secondary ball milling: adding the ingredients in step b and water in a ratio of 1:(1.2-1.5) by weight to a ball mill, mixing, and ball milling for 10-12 hours. Preferably, the ball milling medium is zirconia ceramic balls;

[0013] Step d, secondary sintering: The slurry obtained in step c after secondary ball milling is subjected to secondary sintering at 1175° C.-1235° C.

[0014] Furthermore, in step a, the nine series pre-sintered materials include, by mass percentage: Fe2O3: 85%-88%; SrCO3: 1.5%-1.8%; CaCO3: 2.5%-3.8%; La2O3: 4.5%-6.0%; Co2O3: 1.8%-2.5%; and H3BO3: 0.5%.

[0015] The high-resistance iron oxide comprises the following components by mass percentage: Fe2O3 content is greater than 98%, SiO2 content is 0.05%-0.25%, and the rest are inevitable impurities. The resistance of the high-resistance iron oxide is greater than 1.8MΩ.

[0016] Furthermore, the ratio of the nine series pre-fired material to the high-resistance iron red is 7:3.

[0017] Furthermore, the pre-oxidation step is: calcining the iron red and the nine series pre-sintered materials in proportion at a temperature of 700° C. to 800° C. in an air atmosphere for pre-oxidation.

[0018] Among them, iron red with higher Fe2O3 purity and lower SiO2 content is selected to be sand-ground with the nine series pre-sintered materials, and then pre-oxidized to reduce the Fe in the raw materials. 2+ and Fe by reacting with oxygen and oxidizing to Fe 3+ , Fe in the material 2+ , Fe reduction and Fe 3+ The increase in will reduce the number of free electrons and increase the resistance value.

[0019] Furthermore, the auxiliary materials include SrCO3: 1.0%; Al2O3: 0.14%; La2O3: 1.5%-3.0%; Co2O3: 0.6%-1.5%; H3BO3 0.5%; BaCO3: 0.3% and white carbon black 0.12% in weight percentage of the pre-burned material.

[0020] By adding BaCO3, Ba 2+ The addition of BaSi2O5 is beneficial to improving the resistance of permanent magnet ferrite. It can generate BaSi2O5 with Si in the component, and generate liquid glass at 1200℃, so that Si is enriched in the grain boundary, which can prevent grain growth, refine the grains, ensure the grain refinement and uniformity, and improve the Hcj of the material.

[0021] Furthermore, white carbon black is added to the auxiliary materials, including SiO2 with a content higher than 85%. The present application adds white carbon black to the auxiliary materials. Compared with the existing SiO2, white carbon black has a larger specific surface area, better wear resistance and electrical insulation. When added to the pre-sintered material, the white carbon black can better change the particle size distribution during the secondary ball milling, making the slurry particle size distribution more concentrated and reducing the ball milling time. Furthermore, since the main component of white carbon black is SiO2, Si acts as a flux in M-type hexagonal ferrite, which can effectively reduce the sintering temperature and refine the grain particles at a lower sintering temperature; improve magnetic properties, increase magnetic permeability and saturation magnetization, and improve dielectric properties.

[0022] Furthermore, the Al content in the auxiliary material is controlled to be less than 0.5 wt % to increase Hcj while maintaining Br.

[0023] Furthermore, the ball milling medium in step c is zirconia ceramic balls, which are used instead of steel balls; zirconia balls have non-magnetic conductivity and electrical insulation properties, which can reduce Fe 2+ The entry of Fe 2+ The presence of will reduce the resistance, prevent friction electrification, and reduce the generation and accumulation of electrons. In addition, during the ball milling process, the Zr in the zirconia ceramic ball 4+ Ion doping of the seven-series permanent ferrite at the B site can not only regulate the magnetic structure and magnetic properties of the material, but also 4+ The unequal doping of ions at the B site of the seven-series permanent ferrite can also produce related defects, carriers and variable valence Fe ions, thereby changing the electrical properties of the material. It should be noted that zirconia ceramic balls, as ball milling media, will have losses during the ball milling process and enter the raw materials. The length of ball milling time will affect the Zr 4+ The longer the ball milling time, the more Zr 4+ The higher the ion doping amount, the shorter the ball milling time, and the 4+ The lower the ion doping amount, the 4+When the ion doping amount is less than 0.06%, it is easier to replace the Fe in the upper spin lattice. 3+ ions, whose magnetization intensity decreases with the increase of Zr doping amount; 4+ As the ion doping amount increases, the Fe 3+ The ions will also be gradually replaced, and at this time, the saturation magnetization increases with the increase of doping amount.

[0024] This application changes the amount of Si white carbon black and Al, and adds an appropriate amount of BaCO3 to the auxiliary materials. During the reaction process, Si can reduce the reaction temperature, allowing BaCO3 to 2+ It is easier to enter the particle lattice to obtain high-resistance seven-series ferrite. The high-performance and high-resistance seven-series permanent magnet ferrite obtained meets the requirements of Br≥420mT, Hcb≥320KA / m, Hcj≥375KA / m, (BH) max ≥30kJ / m 3 , resistance ≥ 24MΩ.

[0025] 3. Beneficial effects

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) The present invention adds BaCO3, Ba 2+ The addition of is beneficial to improve the resistance of permanent magnet ferrite, change the amount of Si, reduce the reaction temperature, make BaCO3 react with Si in the component to generate BaSi2O5, refine the grains, improve the Hcj of the material, and obtain high performance and high resistance seventh series permanent magnet ferrite;

[0028] (2) The present invention adds high-resistance iron oxide to the pre-fired material to prepare the seventh series pre-fired material. The addition of high-resistance iron oxide can improve the resistance of the pre-fired material;

[0029] (3) The present invention adds white carbon black to the auxiliary material. Compared with the existing SiO2, white carbon black has a larger specific surface area, better wear resistance and electrical insulation. When added to the pre-burned material, the white carbon black can better change the particle size distribution in the secondary ball milling, making the slurry particle size distribution more concentrated and reducing the ball milling time;

[0030] (4) The ball milling medium of the present invention is zirconia ceramic balls, which reduce Fe 2+ The entry of Zr in zirconia ceramic balls improves resistance and 4+ Ions are used to dope the B-site of the seven-series permanent ferrite to regulate the magnetic structure and magnetic properties of the material and change the electrical properties of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The technical solutions of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. However, it should be understood that these drawings are designed for illustrative purposes only and are not intended to limit the scope of the present invention. Furthermore, unless otherwise specified, these drawings are intended only to conceptually illustrate the structures described herein and are not necessarily drawn to scale.

[0032] Figure 1 This is a scanning electron microscope image of the permanent ferrite prepared in Example 1. DETAILED DESCRIPTION

[0033] The following detailed description of exemplary embodiments of the present invention refers to the accompanying drawings, which form a part of the description, and in which exemplary embodiments of the present invention that can be implemented are shown as examples. Although these exemplary embodiments are described in sufficient detail to enable those skilled in the art to implement the present invention, it should be understood that other embodiments can be implemented and various changes can be made to the present invention without departing from the spirit and scope of the present invention. The following more detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but is merely for illustration and does not limit the description of the features and characteristics of the present invention, so as to propose the best way to perform the present invention and be sufficient to enable those skilled in the art to implement the present invention. Therefore, the scope of the present invention is limited only by the appended claims.

[0034] It should be understood that the following text is only used to describe one or more specific embodiments of the present invention and does not strictly limit the scope of protection of the specific claims of the present invention. As used herein, the terms "parallel" and "perpendicular" are not limited to their strict geometric definitions, but include reasonable and inconsistent tolerances for machining or human errors.

[0035] In Examples 1-4 of the present invention, the components and contents of high-resistance iron oxide are shown in Table 1:

[0036] Table 1 Composition and content of high resistance iron oxide (wt%)

[0037]

[0038] In the embodiment, the components of white carbon black include SiO2 content of 88.30wt%;

[0039] The components of the ninth series pre-sintered material include: Fe2O3: 87.56%; SrCO3: 1.72%; CaCO3: 3.28%; La2O3: 5.10%; Co2O3: 1.96%; and H3BO3: 0.38%.

[0040] Example 1

[0041] The preparation process of a high-performance and high-resistance seven-series permanent ferrite according to Example 1 specifically comprises the following steps:

[0042] Step a, mixing: stirring and mixing the nine series pre-sintered material and high-resistance iron oxide at a weight ratio of 7:3, pre-oxidizing after mixing to form a permanent magnet ferrite pre-sintered material, and then crushing the pre-sintered material; wherein the components and proportions of the high-resistance iron oxide are shown in Table 1;

[0043] Step b, secondary batching: mixing the permanent magnet ferrite pre-sintered material obtained in step a with auxiliary materials, wherein the auxiliary materials include, by weight percentage of the permanent magnet ferrite pre-sintered material: SrCO3 1.0%; Al2O3 0.14%; La2O3 1.8%; Co2O3 1.5%; H3BO3 0.5%; BaCO3 0.3%; and white carbon black 0.12%;

[0044] Step c, secondary ball milling: adding the ingredients in step b and water into a ball mill, mixing, and ball milling for 11 hours at a speed of 35 rpm, using zirconia ceramic steel balls as the ball milling medium;

[0045] Step d, secondary sintering: The slurry obtained after secondary ball milling in step c is subjected to secondary sintering at 1216°C.

[0046] The scanning electron microscope image of the high performance and high resistance seven-series permanent ferrite prepared is as follows: Figure 1 As shown, its performance meets the following requirements: Br422.3mT, Hcb 318.3KA / m, Hcj 377.3KA / m, resistance 24.2Ω·m, (BH) max 33.2kJ / m 3 .

[0047] Example 2

[0048] The preparation process of a high-performance and high-resistance seven-series permanent ferrite according to Example 2 specifically comprises the following steps:

[0049] Step a, mixing: stirring and mixing the nine series pre-sintered material and the high resistance iron oxide at a weight ratio of 7:3, pre-oxidizing after mixing to form a permanent magnet ferrite pre-sintered material, and then crushing the pre-sintered material; wherein the components and proportions of the high resistance iron oxide are shown in Table 1;

[0050] Step b, secondary batching: mixing the permanent magnet ferrite pre-sintered material obtained in step a with auxiliary materials, wherein the auxiliary materials include, by weight percentage of the permanent magnet ferrite pre-sintered material: SrCO3 0.8%; Al2O3 0.2%; La2O3 2.5%; Co2O3 1.5%; H3BO3 0.5%; BaCO3 0.3%; and white carbon black 0.15%;

[0051] Step c, secondary ball milling: adding the ingredients in step b and water into a ball mill, mixing, and ball milling for 11 hours at a speed of 35 rpm, using zirconia ceramic steel balls as the ball milling medium;

[0052] Step d, secondary sintering: The slurry obtained after secondary ball milling in step c is subjected to secondary sintering at 1216°C.

[0053] The high performance and high resistance seven series permanent ferrite prepared has the following properties: Br 423.7mT, Hcb 322.1KA / m, Hcj 379.3KA / m, resistance 28.4MΩ, (BH) max 32.9kJ / m 3 .

[0054] Example 3

[0055] The preparation process of a high-performance and high-resistance seven-series permanent ferrite according to Example 3 specifically comprises the following steps:

[0056] Step a, mixing: stirring and mixing the nine series pre-sintered material and the high resistance iron oxide at a weight ratio of 7:3, pre-oxidizing after mixing to form a permanent magnet ferrite pre-sintered material, and then crushing the pre-sintered material; wherein the components and proportions of the high resistance iron oxide are shown in Table 1;

[0057] Step b, secondary batching: mixing the permanent magnet ferrite pre-sintered material obtained in step a with auxiliary materials, wherein the auxiliary materials include, by weight percentage of the permanent magnet ferrite pre-sintered material: SrCO3 0.8%; Al2O3 0.14%; La2O3 2.8%; Co2O3 1.5%; H3BO3 0.5%; BaCO3 0.3%; and white carbon black 0.2%;

[0058] Step c, secondary ball milling: adding the ingredients in step b and water into a ball mill, mixing, and ball milling for 11 hours at a speed of 35 rpm, using zirconia ceramic steel balls as the ball milling medium;

[0059] Step d, secondary sintering: The slurry obtained after secondary ball milling in step c is subjected to secondary sintering at 1216°C.

[0060] The high performance and high resistance seven series permanent ferrite prepared has the following properties: Br 425.3mT, Hcb 326.4KA / m, Hcj 381.4KA / m, resistance 56.4MΩ, (BH) max 32.6kJ / m 3 .

[0061] Example 4

[0062] The preparation process of a high-performance and high-resistance seven-series permanent ferrite according to Example 4 specifically comprises the following steps:

[0063] Step a, mixing: stirring and mixing the nine series pre-sintered material and the high resistance iron oxide at a weight ratio of 7:3, pre-oxidizing after mixing to form a permanent magnet ferrite pre-sintered material, and then crushing the pre-sintered material; wherein the components and proportions of the high resistance iron oxide are shown in Table 1;

[0064] Step b, secondary batching: mixing the permanent magnet ferrite pre-sintered material obtained in step a with auxiliary materials, wherein the auxiliary materials include, by weight percentage of the permanent magnet ferrite pre-sintered material: SrCO3 0.8%; Al2O3 0.18%; La2O3 2.5%; Co2O3 1.2%; H3BO3 0.5%; BaCO3 0.3%; and white carbon black 0.15%;

[0065] Step c, secondary ball milling: adding the ingredients in step b and water into a ball mill and mixing, and ball milling for 11 hours at a speed of 35 rpm, the ball milling medium being zirconia ceramic steel balls;

[0066] Step d, secondary sintering: The slurry obtained after secondary ball milling in step c is subjected to secondary sintering at 1216°C.

[0067] The high performance and high resistance seven series permanent ferrite prepared has the following properties: Br 420.3mT, Hcb 320.3KA / m, Hcj 376.7KA / m, resistance 65.2MΩ, (BH) max 33.5kJ / m 3 .

[0068] Comparative Example 1

[0069] Comparative Example 1 is a preparation process of a high-performance seven-series permanent magnetic ferrite, which specifically includes the following steps:

[0070] Step a, mixing: nine series pre-sintered material and common iron oxide with a resistance value of less than 1.8 MΩ are stirred and mixed in a weight ratio of 7:3, wherein the common iron oxide with a resistance value of less than 1.8 MΩ is commercially available AT6.1. After mixing, the mixture is pre-oxidized to form a permanent magnet ferrite pre-sintered material, and then the pre-sintered material is crushed; wherein the components and proportions of the high resistance iron oxide are shown in Table 1;

[0071] Step b, secondary batching: mixing the permanent magnet ferrite pre-sintered material obtained in step a with auxiliary materials, wherein the auxiliary materials include, by weight percentage of the permanent magnet ferrite pre-sintered material: SrCO3 1.0%; Al2O3 0.14%; La2O3 1.8%; Co2O3 1.5%; H3BO3 0.5%; BaCO3 0.3%; and white carbon black 0.12%;

[0072] Step c, secondary ball milling: adding the ingredients in step b and water into a ball mill, mixing, and ball milling for 11 hours at a speed of 35 rpm, using zirconia ceramic steel balls as the ball milling medium;

[0073] Step d, secondary sintering: The slurry obtained after secondary ball milling in step c is subjected to secondary sintering at 1216°C.

[0074] The high performance seven-series permanent magnet ferrite obtained has the following properties: Br 420.1mT, Hcb 313.2KA / m, Hcj 356.3KA / m, resistance 0.01MΩ, (BH) max 31.2kJ / m 3 .

[0075] Comparative Example 2

[0076] Comparative Example 2 is a preparation process of a high-performance seven-series permanent magnetic ferrite, which specifically includes the following steps:

[0077] Step a, mixing: stirring and mixing the nine series pre-sintered material and the high resistance iron oxide at a weight ratio of 7:3, pre-oxidizing after mixing to form a permanent magnet ferrite pre-sintered material, and then crushing the pre-sintered material; wherein the components and proportions of the high resistance iron oxide are shown in Table 1;

[0078] Step b, secondary batching: mixing the permanent magnet ferrite pre-sintered material obtained in step a with auxiliary materials, wherein the auxiliary materials do not contain BaCO3 and comprise, by weight percentage of the permanent magnet ferrite pre-sintered material: SrCO3 0.8%; Al2O3 0.2%; La2O3 2.5%; Co2O3 1.5%; H3BO3 0.5%; and white carbon black 0.15%;

[0079] Step c, secondary ball milling: adding the ingredients in step b and water into a ball mill, mixing, and ball milling for 11 hours at a speed of 35 rpm, using zirconia ceramic steel balls as the ball milling medium;

[0080] Step d, secondary sintering: The slurry obtained after secondary ball milling in step c is subjected to secondary sintering at 1216°C.

[0081] The high performance seven-series permanent magnet ferrite obtained has the following properties: Br 418.5mT, Hcb 305.3KA / m, Hcj 363.6KA / m, resistance 0.01MΩ, (BH) max 30.59kJ / m 3 .

[0082] Comparative Example 3

[0083] Comparative Example 3 is a preparation process of a high-performance seven-series permanent magnetic ferrite, which specifically includes the following steps:

[0084] Step a, mixing: stirring and mixing the nine series pre-sintered material and the high resistance iron oxide at a weight ratio of 7:3, pre-oxidizing after mixing to form a permanent magnet ferrite pre-sintered material, and then crushing the pre-sintered material; wherein the components and proportions of the high resistance iron oxide are shown in Table 1;

[0085] Step b, secondary batching: mixing the permanent magnet ferrite pre-sintered material obtained in step a with auxiliary materials, wherein the auxiliary materials include, by weight percentage of the permanent magnet ferrite pre-sintered material: SrCO3 0.8%; Al2O3 0.14%; La2O3 2.8%; Co2O3 1.5%; H3BO3 0.5%; BaCO3 0.3%; and white carbon black 0.2%;

[0086] Step c, secondary ball milling: adding the ingredients in step b and water into a ball mill, mixing, and ball milling for 11 hours at a speed of 35 rpm, using zirconia ceramic steel balls as the ball milling medium;

[0087] Step d, secondary sintering: The slurry obtained after secondary ball milling in step c is subjected to secondary sintering at 1216°C.

[0088] The high performance seven-series permanent magnet ferrite obtained has the following properties: Br 422.5mT, Hcb 318.5KA / m, Hcj 369.6KA / m, resistance 0.01MΩ, (BH) max 32.9kJ / m 3 .

[0089] Comparative Example 4

[0090] Comparative Example 4 is a preparation process of a high-performance seven-series permanent magnetic ferrite, which specifically includes the following steps:

[0091] Step a, mixing: stirring and mixing the nine series pre-sintered material and the high resistance iron oxide at a weight ratio of 7:3, pre-oxidizing after mixing to form a permanent magnet ferrite pre-sintered material, and then crushing the pre-sintered material; wherein the components and proportions of the high resistance iron oxide are shown in Table 1;

[0092] Step b, secondary batching: mixing the permanent magnet ferrite pre-sintered material obtained in step a with auxiliary materials, wherein the auxiliary materials include, by weight percentage of the permanent magnet ferrite pre-sintered material: SrCO3 0.8%; Al2O3 0.18%; La2O3 2.5%; Co2O3 1.2%; H3BO3 0.5%; BaCO3 0.3%; and white carbon black 0.15%;

[0093] Step c, secondary ball milling: adding the ingredients in step b and water into a ball mill and mixing, and ball milling for 11 hours at a speed of 35 rpm, the ball milling medium being zirconia ceramic steel balls;

[0094] Step d, secondary sintering: The slurry obtained after secondary ball milling in step c is subjected to secondary sintering at 1216°C.

[0095] The high performance seven-series permanent magnet ferrite obtained has the following properties: Br 417.6mT, Hcb 330.2KA / m, Hcj385.2KA / m, resistance 0.01MΩ, (BH) max 33.8kJ / m 3 .

[0096] Table 2 Properties of high performance and high resistance seven series permanent ferrites prepared in the examples of the present invention and the comparative examples

[0097]

[0098] The above description is only a preferred embodiment of the present application and an explanation of the technical principles used. Those skilled in the art should understand that the scope involved in the present application is not limited to the technical solutions formed by a specific combination of the above-mentioned technical features, but should also cover other technical solutions formed by any combination of the above-mentioned technical features or their equivalent features without departing from the inventive concept, such as the technical solutions formed by replacing the above-mentioned features with (but not limited to) technical features with similar functions disclosed in this application.

[0099] Except for the technical features described in the specification, the remaining technical features are known technologies to those skilled in the art. In order to highlight the innovative features of the present invention, the remaining technical features will not be described here in detail.

Claims

1. A process for preparing high performance and high resistance seven-series permanent ferrite, characterized in that: Including steps: Step a, mixing: mixing the nine series pre-burned material and the high resistance iron red in proportion, pre-oxidizing after mixing to form a permanent magnet ferrite pre-burned material, and then crushing the pre-burned material; The nine series pre-sintered materials include, by mass percentage: Fe2O3: 85%-88%; SrCO3: 1.5%-1.8%; CaCO3: 2.5%-3.8%; La2O3: 4.5%-6.0%; Co2O3: 1.8%-2.5%; H3BO3: 0.3%-0.5%; The high-resistance iron oxide comprises the following components by mass percentage: Fe2O3 content greater than 98%, SiO2 content 0.05%-0.25%, and its resistance is greater than 1.8 MΩ; The weight ratio of the nine series pre-sintered material to the high-resistance iron red is 7:3; Step b, secondary batching: the pre-calcined material obtained in step a is mixed with auxiliary materials in proportion, wherein the auxiliary materials include SrCO3: 0.8%-1.0%; Al2O3: 0.14%-0.35%; La2O3: 1.5%-3.0%; Co2O3: 0.6%-1.5%; H3BO3 0.3%-0.5%; BaCO3: 0.3-0.9% and SiO2 0.1%-0.2% by weight of the pre-calcined material; Step c, secondary ball milling: add the ingredients in step b and water into a ball mill, mix, and ball mill for 10-12 hours; Step d, secondary sintering: The slurry obtained after secondary ball milling in step c is subjected to secondary sintering at 1175-1235°C.

2. The preparation process according to claim 1, characterized in that The pre-oxidation step comprises: calcining the high-resistance iron red and the nine-series pre-sintered material at a temperature of 700° C. to 800° C. in an air atmosphere for pre-oxidation.

3. The preparation process according to claim 1, characterized in that The raw material of the SiO2 is white carbon black, and the SiO2 content in the white carbon black is greater than 85%.

4. The preparation process according to claim 1, characterized in that The ball milling medium in step c is zirconia ceramic balls.

5. The product obtained by the preparation process according to any one of claims 1 to 4, characterized in that The resistance of the prepared seven-series permanent ferrite is ≥24MΩ.

6. The product according to claim 5, characterized in that The performance of the seven series permanent ferrites meets the following requirements: Br≥420mT, Hcb≥318.3 KA / m, Hcj≥375 KA / m, (BH) max ≥30 kJ / m 3 .

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