Preparation process of high-resistance M-type hexaferrite and product prepared thereby

Abstract

The application discloses a preparation process of high-resistance M-type hexagonal ferrite and a prepared product, and belongs to the technical field of permanent magnet ferrite. The method comprises the following steps: step a, dosing: dosing pre-sintered materials and auxiliary materials according to a weight ratio, wherein the auxiliary materials include SiO2 0.05%-0.2%, CaCO3 0.5%, Al2O3 0.14% and HBO3 0.3% according to the mass percentage of the pre-sintered materials; step b, ball milling: putting the dosed materials and water in the step a into a ball mill and ball milling; and step c, sintering: sintering the mixture after the ball milling in the step b at 1175 DEG C.-1235 DEG C. The high-resistance M-type hexagonal ferrite prepared by the method has the following performances: Br 390-420 mT, Hcb 270-300 KA / m, Hcj 240-380 KA / m, (BH) max 31-33 kJ / m 3 , and the resistance is greater than 21 MΩ.

Description

Technical Field

[0001] The present invention belongs to the technical field of permanent ferrites, and more particularly relates to a preparation process of high-resistance M-type hexagonal ferrite and the prepared product. Background Art

[0002] M-type ferrites have high coercivity, high saturation magnetization, and good chemical stability, and are widely used in permanent magnet materials. However, existing M-type hexagonal ferrites have low resistance. This is primarily due to 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, thus generating 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.

[0003] Patent CN107056270A discloses a hexagonal sintered permanent ferrite magnet and its preparation method. The composition formula of the hexagonal sintered permanent ferrite magnet of the invention is A 2+ 1-x-y B 1+ y La 3+ x Fe 3+ n-z Co 2+ z O 2- 19 The invention states that A is at least one of the divalent alkaline earth metals calcium, strontium, and barium; B is at least one of the monovalent alkali metals lithium, sodium, and potassium; and x, y, z, and n are the addition ratios of the elements, where x is 0.24-0.45, y is 0.03-0.10, z is 0.20-0.33, and n is 10.0-12.0, and 1.1z≤x≤1.8z, and y+z≤x. The ingredient mix also includes one or a mixture of primary additives: silicon dioxide, boric acid, alkali metal chloride, and alkaline earth metal chloride, with the addition ratio being 0.05-0.5wt% silicon dioxide. This patent incorporates monovalent alkali metals lithium, sodium, potassium, and alkaline earth metal chlorides. During the high-temperature sintering stage, the alkali metal chlorides produce HCl and other substances that are highly corrosive to equipment, causing certain environmental pollution.

[0004] Patent CN102701721A discloses a low-cost sintered calcium permanent magnet ferrite and its preparation method. The sintered calcium permanent magnet ferrite includes a hexagonal M-type ferrite main phase containing calcium, lanthanum, iron and zinc, and has the following characteristic molecular formula: Ca 1-x La x Fe 2n-z Zn z O 19; Wherein, x, z, and n represent the molar ratio of calcium, lanthanum, iron, and zinc, and x is 0.2 to 0.6, z is 0.2 to 0.4, n is 4 to 6, and x / z is 1.0 to 3.0. The secondary additives include calcium carbonate powder, silicon oxide powder, aluminum oxide powder, and boric acid powder. The addition amounts of the secondary additives are: CaCO3: 0.3 to 1.5 wt%, SiO2: 0.1 to 1.0 wt%, Al2O3: 0.1 to 1.5 wt%, H3BO3: 0.05 to 0.2 wt%, and the sintering temperature is 1150°C to 1250°C. However, the addition of lanthanum and zinc metal elements in this patent results in excessive grain boundaries, which affects the density of the ferrite and thus the resistance of the ferrite.

[0005] Patent CN117658645A discloses a method for removing silicon impurities from high-silicon iron red used in permanent magnet ferrites. The method uses additives such as strontium carbonate, silicon dioxide, aluminum oxide, calcium carbonate, and boric acid, or a mixture thereof. The sintering temperature is 1220-1270°C, and the holding time is 1-2 hours. The excessive silicon content in this patent results in high electrical conductivity and low resistance in the ferrite. Summary of the Invention

[0006] 1. Problem to be solved

[0007] Aiming at the problem of low resistance of existing M-type hexagonal ferrite, the present invention provides a method for preparing high-resistance M-type hexagonal ferrite. The M-type hexagonal ferrite prepared by the method has higher resistance.

[0008] 2. Technical solution

[0009] In order to solve the above problems, the technical solutions adopted by the present invention are as follows:

[0010] The present invention provides a method for preparing high-resistance M-type hexagonal ferrite, which specifically comprises the steps of:

[0011] Step a, mixing ingredients: mixing pre-sintered material and auxiliary materials in a certain weight ratio in proportion, wherein the pre-sintered material comprises, by mass percentage, the following: Fe2O3 90.0% to 92.2%, SiO2 0.126% to 0.152%, Al2O3 0.094% to 0.108%, CaO 0.056% to 0.075%, SrO 7.5% to 9.5%, and the remainder being unavoidable impurities;

[0012] The auxiliary materials include SiO2 0.05%-0.2%, CaCO3 0.5%, Al2O3 0.14%, and HBO3 0.3% according to the mass percentage of the pre-sintered material;

[0013] Step b, ball milling: Add the ingredients in step a and water in a weight ratio of 1: (1.2-1.5) into a ball mill, mix, and ball mill for 10-12 hours;

[0014] Step c, sintering: sinter the ball-milled mixture obtained in step b at 1175° C.-1235° C. for 2 hours.

[0015] It should be noted that the presence of Si crystals in ferrite is equivalent to the presence of semiconductors. Under the action of an external electric field, the two carriers, electrons and holes, in the semiconductor material move in opposite directions. Therefore, this application reduces the transition of electrons and reduces its conductivity by reducing the content of SiO2. When the SiO2 content is lower than 0.2%, the resistance of the ferrite is significantly improved. Furthermore, SiO2 is a flux in M-type hexagonal ferrite, which can effectively reduce the sintering temperature. At a lower sintering temperature, it can effectively inhibit grain growth and refine grain particles; improve magnetic properties, increase magnetic permeability and saturation magnetization, and improve dielectric properties.

[0016] Among the auxiliary materials of this component and proportion, SiO2 is a flux. During the reaction, it can reduce the reaction temperature from 1300℃ to 1175℃~1230℃ by fluxing ferrite grains; CaCO3 mainly provides Ca 2+ , Ca 2+ Substitute Fe in the ferrite lattice 2+ and Co 2+ , effectively improve the residual magnetic properties; Al2O3 mainly provides Al 3+ , replacing Fe in the ferrite lattice 3+ and La 3+ , effectively improving the intrinsic coercive force performance; HBO3 is a dispersant, which reduces particle agglomeration and makes ball milling more uniform. The particle size after ball milling is more uniform, and the particle size is concentrated in the range of 0.75 to 0.85 microns.

[0017] Furthermore, the sintering temperature is controlled between 1175°C and 1235°C. The sintering temperature is related to the degree of densification of the ferrite, which in turn affects its resistance. As shown in Table 1, when the sintering temperature is below 1175°C, the ferrite resistance remains essentially unchanged as the temperature increases. At 1175°C, the resistance increases significantly, and the resistance continues to rise as the temperature rises. This is because densification proceeds rapidly with the liquid phase flow of the additives, with the densification change initially increasing and then decreasing. At 1235°C, the density change rate reaches its highest point, and the resistance is relatively high. When the temperature exceeds 1235°C, the grains grow excessively, crystallization becomes severe, the density change rate decreases, and the resistance drops sharply.

[0018] Table 1 Density and resistance of ferrite at different sintering temperatures

[0019]

[0020] 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 M-type hexagonal 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 hexagonal 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.

[0021] Therefore, the present invention improves the resistance of M-type hexagonal ferrite by changing the content of SiO2 in the auxiliary material and selecting the sintering temperature according to the degree of densification of the ferrite. The high-resistance M-type hexagonal ferrite finally obtained has the following properties: Br390-420mT, Hcb 270-300KA / m, Hcj 280-330KA / m, (BH) max 31-33 kJ / m 3 , resistance is greater than 21MΩ.

[0022] 3. Beneficial effects

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) The present invention controls the content of SiO2 in the auxiliary material so that it acts as a flux, reduces the sintering temperature, and simultaneously controls the sintering temperature so that when the density change rate reaches the highest, the resistance is relatively high, which can effectively improve the magnetic properties, increase the magnetic permeability and saturation magnetization, and improve the dielectric properties;

[0025] (2) The present invention uses zirconia ceramic balls instead of steel balls in the ball milling process. 4+ Ion doping of M-type hexagonal ferrite at the B site can not only regulate the magnetic structure and magnetic properties of the material, but also 4+ Unequal doping of ions at the B site of hexagonal ferrite can also produce related defects, carriers and variable valence Fe ions, thereby changing its electrical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] 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.

[0027] Figure 1 This is a scanning electron microscope image of the high-resistance M-type hexagonal ferrite in Example 1. DETAILED DESCRIPTION

[0028] 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.

[0029] 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.

[0030] The components and contents of the auxiliary materials in the examples of the present invention and the comparative examples are shown in Table 2.

[0031] Table 2 Components and contents of excipients in the examples of the present invention and comparative examples

[0032]

[0033] Example 1

[0034] A method for preparing high-resistance M-type hexagonal ferrite, which specifically comprises the steps of:

[0035] Step a, mixing ingredients: mixing the pre-sintered material and the auxiliary materials in proportion, wherein the components of the pre-sintered material include, by weight percentage: Fe2O3 90.25%; SiO2 0.142%; Al2O3 0.098%; CaO 0.069%; MgO 0.004%; MnO 0.353%; SO3 <0.005%; P2O5 0.005%; K2O <0.005%; Na2O 0.014%; V2O5 <0.005%; TiO2 <0.005%; CuO 0.020%; ZnO <0.005%; Cr2O3 0.029%; NiO <0.005%; BaO 0.124%; SrO 8.89%;

[0036] The auxiliary materials include SiO2 0.1wt%, CaCO3 0.5wt%, Al2O3 0.14wt%, H3BO3 0.3wt%, La2O3 0.4wt%, and Co2O3 0.2wt% by weight;

[0037] Step b, ball milling: the pre-sintered material and auxiliary materials in step a are placed in a ball mill with water and ball milled for 11 hours, with the weight ratio of the pre-sintered material and auxiliary materials to water being 1:1.2; the ball milling medium is zirconia ceramic balls;

[0038] Step c, sintering: After discharging and filtering the water, the slurry is pressed into a round cake blank in a press, and then placed in a roller kiln for sintering at a sintering temperature of 1216°C.

[0039] After sintering, the ferrite sintered product is taken out, both sides are ground smooth and then dried to obtain permanent ferrite.

[0040] Place the ferrite on a voltage withstand tester to test the breakdown voltage, and then test the magnetic properties.

[0041] The scanning electron microscope image of the high resistance M-type hexagonal ferrite is as follows: Figure 1 As shown in Table 2, the performance meets the following requirements: Br412.3mT, Hcb 283KA / m, Hcj 296.4KA / m, (BH) max 31.2kJ / m 3 .

[0042] Example 2

[0043] The preparation method and process of the high-resistance M-type hexagonal ferrite in Example 2 are basically the same as those in Example 1, except that the content of SiO2 in the auxiliary material is 0.05 wt%.

[0044] The properties of the obtained high resistance M-type hexagonal ferrite are shown in Table 2, which meet the following requirements: Br 418.7mT, Hcb 275.1KA / m, Hcj 283.5.4KA / m, (BH) max 32.9kJ / m 3 .

[0045] Example 3

[0046] The preparation method and process of the high-resistance M-type hexagonal ferrite of Example 3 are basically the same as those of Example 1, except that the content of SiO2 in the auxiliary material is 0.2%.

[0047] The properties of the obtained high resistance M-type hexagonal ferrite are shown in Table 2, which meet the following requirements: Br 406.2mT, Hcb 293.2KA / m, Hcj 306.1KA / m, (BH) max 32.6kJ / m 3 .

[0048] Example 4

[0049] The preparation method and process of the high-resistance M-type hexagonal ferrite of Example 4 are basically the same as those of Example 3, except that the secondary sintering temperature is 1195°C.

[0050] The properties of the obtained high resistance M-type hexagonal ferrite are shown in Table 2, which meet the following requirements: Br 400.1mT, Hcb 295.2KA / m, Hcj 312.1KA / m, (BH) max 31.9kJ / m 3 .

[0051] Comparative Example 1

[0052] The preparation method and process of the M-type hexagonal ferrite of Comparative Example 1 are basically the same as those of Example 1, except that synthetic steel balls are used as the ball milling media.

[0053] The properties of the obtained high resistance M-type hexagonal ferrite are shown in Table 2, which meet the following requirements: Br 413.7mT, Hcb 286.5KA / m, Hcj 299.7KA / m, (BH) max 32.1kJ / m 3 .

[0054] Comparative Example 2

[0055] The preparation method and process of the M-type hexagonal ferrite in Comparative Example 2 are basically the same as those in Example 1, except that the content of SiO2 in the auxiliary material is 0.3%.

[0056] The properties of the obtained high resistance M-type hexagonal ferrite are shown in Table 2, which meet the following requirements: Br 403.8mT, Hcb 297.2KA / m, Hcj 312.4KA / m, (BH) max 33.7kJ / m 3 .

[0057] Comparative Example 3

[0058] The preparation method of M-type hexagonal ferrite in Comparative Example 3 is basically the same as that in Example 1, except that the content of SiO2 in the auxiliary material is 0.25%, and synthetic steel balls are used as the ball milling medium.

[0059] The properties of the obtained high resistance M-type hexagonal ferrite are shown in Table 3, which meet the following requirements: Br 405.3mT, Hcb 281.2KA / m, Hcj 302.3KA / m, (BH) max 33.5kJ / m 3 .

[0060] Table 3 Performance parameters of M-type hexagonal ferrite in the embodiments of the present invention and the comparative examples

[0061]

[0062] The present application improves the resistance of M-type hexagonal ferrite by changing auxiliary materials and ball milling methods.

[0063] 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.

[0064] 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-resistance M-type hexagonal ferrite, characterized in that: Including steps: Step a, mixing ingredients: pre-sintered material and auxiliary materials are mixed in proportion, wherein the auxiliary materials include SiO2 0.05%-0.2%, CaCO3 0.5%, Al2O3 0.14%, HBO3 0.3%, La2O3 0.4%, and Co2O3 0.2% by mass percentage of the pre-sintered material; the pre-sintered material includes: Fe2O3 90.0%-92.2%, SiO2 0.126%-0.152%, Al2O3 0.094%-0.108%, CaO 0.056%-0.075%, SrO 7.5%-9.5%, and the rest are unavoidable impurities; Step b, ball milling: adding water to the ingredients in step a and then ball milling; the ball milling medium is zirconia ceramic balls; Step c, sintering: sinter the mixture obtained in step b after secondary ball milling at 1175° C. to 1230° C. for 2 hours.

2. The preparation process according to claim 1, characterized in that In step b, the ball milling time is 10 to 12 hours.

3. The preparation process according to claim 2, characterized in that In step b, the mass ratio between the ingredients and water is 1:(1.2~1.5).

4. The ferrite obtained by the preparation process according to any one of claims 1 to 3, characterized in that: The resistance of the prepared high-resistance M-type hexagonal ferrite is greater than 21 MΩ.

5. The ferrite according to claim 4, characterized in that The high resistance M-type hexagonal ferrite meets Br 390-420mT, Hcb 270-300 KA / m, Hcj 240-380KA / m, (BH) max 31-33 kJ / m 3 .

6. The ferrite according to claim 5, characterized in that The density of the high-resistance M-type hexagonal ferrite is 5.10-5.20 g / cm 3 .

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