Modified ferrite pre-sintering material and preparation method thereof, permanent magnetic ferrite and preparation method thereof

Abstract

The invention discloses a modified ferrite pre-sintering material and a preparation method thereof, and permanent magnetic ferrite and a preparation method thereof, and belongs to the technical field of magnetic materials. The preparation method of the modified ferrite pre-sintering material comprises the following steps: step 1, mixing a ferrite pre-sintering material base material, a silicon source and a solvent to obtain a mixture; the mass ratio of the ferrite pre-sintering material base material to the silicon source is (500-3000): (10-100); 2, mixing the mixture with a catalyst, and carrying out ball milling; the catalyst comprises an aqueous solution of acid or an aqueous solution of alkali; and step 3, carrying out solid-liquid separation to obtain the modified ferrite pre-sintered material. The magnetic performance of the permanent magnetic ferrite is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of magnetic materials, and in particular relates to a modified ferrite pre-sintered material and a preparation method thereof, a permanent ferrite and a preparation method thereof. Background Art

[0002] Ferrite raw materials are abundant and ferrite has excellent chemical stability. Since its application as a magnetic material, it has developed rapidly. Among them, permanent ferrite has high magnetic permeability and stable magnetic properties, and is widely used in automobiles, home appliances, aerospace and other fields. At present, the preparation processes of permanent ferrites at home and abroad include dry and wet methods. Magnets prepared by the dry method are widely used in magnetic devices with complex shapes such as multi-pole magnetic rings and magnetic tiles due to low raw material costs, simple equipment and stable performance. Magnets prepared by the wet method can obtain higher magnetic properties, mainly because the magnetic domains are easy to move, resulting in better orientation, but the dispersion medium needs to be removed during forming, which is time-consuming, has low productivity, and high operating costs. Therefore, the dry process will be more widely applicable.

[0003] Permanent ferrite has the characteristics of abundant raw materials, low price, simple preparation process, excellent oxidation resistance, and large residual magnetization. After decades of development and improvement, ferrite materials have become a kind of functional material with wide applications and a wide variety, and are the preferred materials in many fields. How to further improve the magnetic properties of permanent ferrite is the focus of current research. Summary of the invention

[0004] Therefore, the present invention provides a modified ferrite pre-sintered material and a preparation method thereof, a permanent magnet ferrite and a preparation method thereof, which further improve the magnetic properties of the permanent magnet ferrite.

[0005] To this end, the present invention provides the following technical solutions.

[0006] In a first aspect, the present invention provides a method for preparing a modified ferrite pre-sintered material, comprising the following steps:

[0007] Step 1, mixing a ferrite pre-sintered material substrate, a silicon source and a solvent to obtain a mixture;

[0008] The mass ratio of the ferrite pre-sintered material substrate to the silicon source is (500-3000): (10-100); for example, it can be 500:10, 500:40, 500:70, 500:100, 1000:10, 1000:40, 1000:70, 1000:100, 2000:10, 2000:40, 2000:70, 2000:100, 3000:10, 3000:40, 3000:70 or 3000:100, but it is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable, preferably (1500-2500): (25-90);

[0009] Step 2, mixing the mixture with a catalyst and ball milling;

[0010] The catalyst includes an aqueous acid solution or an aqueous base solution;

[0011] Step 3: solid-liquid separation to obtain modified ferrite pre-sintered material.

[0012] Furthermore, step 1 satisfies at least one of the following conditions:

[0013] (1) The mass ratio of the silicon source to the solvent is (10-100): (3000-6000); for example, it can be 10:3000, 10:4000, 10:5000, 10:6000, 40:3000, 40:4000, 40:5000, 40:6000, 70:3000, 70:4000, 70:5000, 70:6000, 100:3000, 100:4000, 100:5000 or 100:6000, but is not limited to the values ​​listed, and other values ​​not listed within the numerical range are also applicable, preferably (25-90): (4000-5000);

[0014] (2) mixing a ferrite pre-sintered material substrate, a silicon source and a solvent, and performing ultrasonic dispersion to obtain a mixture;

[0015] (3) The silicon source includes one or more of methyl orthosilicate, ethyl orthosilicate and sodium silicate; preferably ethyl orthosilicate;

[0016] (4) The solvent includes water and / or an organic solvent;

[0017] Optionally, the organic solvent includes one or more of anhydrous ethanol, acetone and toluene, preferably anhydrous ethanol.

[0018] Furthermore, step 2 satisfies at least one of the following conditions:

[0019] (1) The mass ratio of the silicon source to the catalyst is (10-100): (1-10), for example, 10:1, 10:4, 10:7, 10:10, 40:1, 40:4, 40:7, 40:10, 70:1, 70:4, 70:7, 70:10, 100:1, 100:4 or 100:7, but is not limited to the listed values, and other values ​​not listed in the numerical range are also applicable, preferably (25-90): (4-8);

[0020] (2) The aqueous acid solution includes one or more of hydrochloric acid and selenic acid;

[0021] Exemplarily, it may be 1 mol / L hydrochloric acid;

[0022] (3) the aqueous solution of the alkali comprises aqueous ammonia;

[0023] Exemplarily, it may be aqueous ammonia with a concentration of 12 mol / L;

[0024] (4) The rotation speed of the ball mill is 200 to 600 r / min, for example, 200 r / min, 250 r / min, 300 r / min, 350 r / min, 400 r / min, 450 r / min, 500 r / min, 550 r / min or 600 r / min, but is not limited to the listed values. Other values ​​not listed in the numerical range are also applicable, preferably 250 to 450 r / min;

[0025] (5) The ball milling time is 6 to 10 hours, for example, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, but not limited to the listed values. Other values ​​not listed in the numerical range are also applicable, preferably 7 to 8 hours.

[0026] Furthermore, the step 3 includes drying the liquid product after solid-liquid separation;

[0027] Optionally, the drying method is air drying;

[0028] Optionally, step 3 also includes crushing and screening the dried product; optionally, a sieve of 10 to 100 mesh is used for screening, for example, it can be 10 mesh, 20 mesh, 30 mesh, 40 mesh, 50 mesh, 60 mesh, 70 mesh, 80 mesh, 90 mesh or 100 mesh, but is not limited to the listed values, other unlisted values ​​within the numerical range are also applicable, preferably a sieve of 20 to 50 mesh.

[0029] In a second aspect, the present invention provides a modified ferrite pre-sintered material, which is prepared according to the above preparation method.

[0030] In a third aspect, the present invention provides a method for preparing permanent ferrite, which is prepared by using the above-mentioned modified ferrite pre-sintered material.

[0031] Furthermore, the method for preparing the permanent ferrite comprises the following steps:

[0032] Step A, blending the modified ferrite pre-sintered material, flux and lubricant to obtain a blend;

[0033] Step B, dry pressing the blend and sintering it.

[0034] Furthermore, step A satisfies at least one of the following conditions:

[0035] (1) The mass ratio of the modified ferrite pre-sintered material to the flux is (500-3000): (10-18), for example, it can be 500:10, 500:14, 500:18, 1000:10, 1000:14, 1000:18, 2000:10, 2000:14, 2000:18, 3000:10, 3000:14 and 3000:18, but it is not limited to the listed values, and other values ​​not listed in the numerical range are also applicable, preferably (1500-2500): (12-16);

[0036] (2) The mass ratio of the lubricant to the modified ferrite pre-sintered material is (1-25):(500-3000), for example, it can be 1:500, 1:1000, 1:1500, 1:2000, 1:2500, 1:3000, 7:500, 7:1000, 7:1500, 7:2000, 7:2500, 7:3000, 13:500, 13:1000, 13:1500, 13:2000, 13: 2500, 13:3000, 19:500, 19:1000, 19:1500, 19:2000, 19:2500, 19:3000, 25:500, 25:1000, 25:1500, 25:2000, 25:2500 or 25:3000, but are not limited to the values ​​listed, and other values ​​not listed within the numerical range are also applicable, preferably (8-16):(1500-2500);

[0037] (3) The flux includes one or more of La2O3, Al2O3 and CaCO3;

[0038] (4) The lubricant includes one or more of zinc stearate, magnesium stearate and calcium stearate, preferably zinc stearate.

[0039] Furthermore, step B satisfies at least one of the following conditions:

[0040] (1) The dry pressing is performed in a magnetic field. Optionally, the magnetic field strength is 1000 to 1400 Oe, for example, 1000 Oe, 1050 Oe, 1100 Oe, 1150 Oe, 1200 Oe, 1250 Oe, 1300 Oe, 1350 Oe or 1400 Oe, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0041] (2) The pressure of the dry pressing is 40 to 80 MPa, for example, 40 MPa, 45 MPa, 50 MPa, 55 MPa, 60 MPa, 65 MPa, 70 MPa, 75 MPa or 80 MPa, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable;

[0042] (3) The sintering includes a first heating, a first heat preservation, a second heating, a second heat preservation, a third heating, a third heat preservation, a fourth heating and a fourth heat preservation performed in sequence;

[0043] Optionally, the first heating rate is 2 to 10°C / min, for example, 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min or 10°C / min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable, preferably 5 to 8°C / min;

[0044] Optionally, the endpoint temperature of the first heating is 300-500° C., for example, 300° C., 320° C., 340° C., 360° C., 380° C., 400° C., 420° C., 440° C., 460° C., 480° C. or 500° C., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable;

[0045] Optionally, the first insulation time is 1 to 6 hours, for example, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours or 6 hours, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable, preferably 2 to 3 hours;

[0046] Optionally, the second heating rate is 3 to 9°C / min, for example, 3°C / min, 3.5°C / min, 4°C / min, 4.5°C / min, 5°C / min, 5.5°C / min, 6°C / min, 6.5°C / min, 7°C / min, 7.5°C / min, 8°C / min, 8.5°C / min or 9°C / min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable, preferably 4 to 6°C / min;

[0047] Optionally, the end temperature of the second heating is 600-800°C, for example, 600°C, 620°C, 640°C, 660°C, 680°C, 700°C, 720°C, 740°C, 760°C, 780°C or 800°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable;

[0048] Optionally, the second insulation time is 1 to 8 hours, for example, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours or 8 hours, but is not limited to the listed values, and other values ​​not listed in the numerical range are also applicable, preferably 2 to 6 hours;

[0049] Optionally, the third heating rate is 2 to 7°C / min, for example, 2°C / min, 2.5°C / min, 3°C / min, 3.5°C / min, 4°C / min, 4.5°C / min, 5°C / min, 5.5°C / min, 6°C / min, 6.5°C / min or 7°C / min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable, preferably 3 to 6°C / min;

[0050] Optionally, the endpoint temperature of the third heating is 900-1100° C., for example, it may be 900° C., 920° C., 940° C., 960° C., 980° C., 1000° C., 1020° C., 1040° C., 1060° C., 1080° C. or 1100° C., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable;

[0051] Optionally, the third insulation time is 1 to 5 hours, for example, 1 hour, 2 hours, 3 hours, 1 hour, 4 hours or 5 hours, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable, preferably 2 to 4 hours;

[0052] Optionally, the fourth heating rate is 1 to 5°C / min, for example, 1°C / min, 2°C / min, 3°C / min, 4°C / min or 5°C / min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable, preferably 2 to 4°C / min;

[0053] Optionally, the endpoint temperature of the fourth heating is 1200-1300° C., for example, 1200° C., 1210° C., 1220° C., 1230° C., 1240° C., 1250° C., 1260° C., 1270° C., 1280° C., 1290° C. or 1300° C., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable;

[0054] Optionally, the fourth insulation time is 1 to 12 hours, for example, it can be 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h or 12h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable, preferably 3 to 10 hours.

[0055] Furthermore, the permanent magnet ferrite blank after being cooled in the furnace is ground and cleaned.

[0056] In a fourth aspect, the present invention provides a permanent ferrite prepared according to the above preparation method.

[0057] Optionally, the step of mixing the ferrite pre-sintered material substrate, the silicon source and the solvent in step 1 includes stirring.

[0058] Optionally, the step of blending the modified ferrite pre-sintered material, flux and lubricant in step A includes stirring.

[0059] After sintering, the furnace is cooled.

[0060] The technical solution of the present invention has the following advantages:

[0061] 1. The preparation method of the modified ferrite pre-sintered material of the present invention comprises the following steps: step 1, mixing a ferrite pre-sintered material substrate, a silicon source and a solvent to obtain a mixture; the mass ratio of the ferrite pre-sintered material substrate to the silicon source is (500-3000): (10-100); step 2, mixing the mixture with a catalyst and ball milling; the catalyst comprises an aqueous solution of an acid or an aqueous solution of an alkali; step 3, solid-liquid separation to obtain a modified ferrite pre-sintered material.

[0062] The silicon source is catalyzed by a catalyst to hydrolyze and condense on the surface of the ferrite pre-sintered material substrate to form a nano silicon dioxide surface layer. The present invention uses a simple in-situ growth method to generate nano silicon dioxide on the surface of the ferrite pre-sintered material substrate. Nano silicon dioxide modifies a single ferrite pre-sintered material substrate grain, improves the uniformity of the grain, increases the specific surface area of ​​the grain, increases the grain boundary strength during dry pressing and sintering, reduces the void ratio between the grains, avoids cracking caused by excessive stress in the region during sintering, and improves the magnetic properties of the permanent ferrite.

[0063] The mass ratio of the ferrite pre-sintered material substrate to the silicon source is (500-3000): (10-100). Within this range, insufficient modification of the grains by nano-silicon dioxide can be avoided, while the adverse effect of excessive nano-silicon dioxide on the performance can be avoided.

[0064] 2. The mass ratio of modified ferrite pre-sintered material to flux is (500-3000): (10-18).

[0065] In the process of preparing permanent ferrite by dry pressing, in order to ensure that the permanent ferrite has high magnetic properties, it is necessary to solve the problems of poor uniformity of grain morphology and disordered growth of grains during sintering, which leads to reduced magnetic properties. At present, in actual large-scale production, only screening and other processes are used to control the uniformity of grains, and certain additives are added to control the disordered growth of grains, so as to finally achieve the purpose of regulating the change of pores inside the magnet and improving the strength of grain boundaries. Although screening the ferrite pre-sintered material particles can improve the uniformity of the ferrite pre-sintered material grains to a certain extent, from the perspective of a single grain, the grains have uneven convex and concave morphologies, and there are still certain gaps between the grains. Adding flux can make up for some gaps to a certain extent when forming a liquid phase, but as the grains grow, it will cause excessive stress in some areas, and eventually the magnet will have defects and reduced magnetic properties.

[0066] The present invention gives each ferrite grain a certain degree of high melting point nano-silicon dioxide shell, and regulates the growth of nano-silicon dioxide by regulating the amount of silicon source added and the processing technology, which can not only better modify the morphology of the ferrite grain, but also improve the strength of each ferrite grain, and prevent disordered growth from causing excessive stress in the region. At the same time, it can also reduce the use of other additives (fluxing agents and lubricants) to improve production efficiency.

[0067] The present invention aims at preparing permanent ferrite magnets. Based on the dry preparation process, the ferrite pre-sintered material is modified by in-situ growth of nano-silicon dioxide, and the surface of the ferrite pre-sintered material is modified and strengthened, aiming to further improve the magnetic properties of the magnet and enhance the competitiveness of the product.

[0068] The modified ferrite pre-sintered material is mixed, dry pressed and sintered to finally prepare a magnet with excellent magnetic properties. The magnet prepared by the modified ferrite pre-sintered material can better solve the problems of reduced magnetic properties and cracking caused by excessive pores in the internal structure of the magnet, low grain boundary strength and uneven internal stress. It has a high application prospect in the field of dry pressed permanent ferrite. DETAILED DESCRIPTION

[0069] The following examples are provided for a better understanding of the present invention, but are not intended to limit the best mode of implementation, nor to limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior arts shall fall within the protection scope of the present invention.

[0070] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in the field can be used. If no manufacturer is specified for the reagents or instruments used, they are all conventional reagent products that can be obtained commercially.

[0071] Example 1

[0072] This embodiment provides a method for preparing a permanent magnetic ferrite, comprising the following steps:

[0073] (1) Preparation of modified ferrite pre-sintered material:

[0074] Step 1: Pre-sinter the ferrite substrate Sr 0.86 La 0.14 Fe 11.86 Co 0.14 O 19 , tetraethyl orthosilicate and anhydrous ethanol are mixed and ultrasonically dispersed, wherein the mass ratio of the ferrite pre-sintered material substrate to tetraethyl orthosilicate is 2000:70, and the mass ratio of the ferrite pre-sintered material substrate to anhydrous ethanol is 2000:4500.

[0075] Step 2: The mixture was placed in a ball mill for ball milling. After half an hour of ball milling, a catalyst of dilute hydrochloric acid (1 mol / L) was added.

[0076] The mass ratio of ferrite pre-sintered material to dilute hydrochloric acid is 2000:5, the ball milling speed is 300r / min, and the ball milling time is 8h.

[0077] Step 3: solid-liquid separation, spreading the solid product flat for air drying, and sieving it with a 30-mesh sieve to obtain a modified ferrite pre-sintered material.

[0078] (2) Preparation of permanent ferrite:

[0079] Step A: Blending the modified ferrite pre-sintered material prepared above, flux La2O3 and lubricant zinc stearate to obtain a blend.

[0080] The mass ratio of the modified ferrite pre-sintered material, La2O3 and zinc stearate is 2000:15:14.

[0081] Step B, dry pressing and sintering the blend:

[0082] After dry pressing at a pressure of 50 MPa in a magnetic field with a magnetic field strength of 1200Oe, the temperature is increased to 400°C at a rate of 6°C / min and kept warm for 2 hours, then increased to 700°C at a rate of 5°C / min and kept warm for 4 hours, then increased to 1000°C at a rate of 4°C / min and kept warm for 3 hours, then increased to 1260°C at a rate of 3°C / min and kept warm for 6 hours, and then cooled with the furnace to obtain permanent ferrite.

[0083] Example 2

[0084] This embodiment provides a method for preparing a permanent magnetic ferrite, which is basically the same as that of Embodiment 1, except that the mass ratio of the ferrite pre-sintered material substrate to tetraethyl orthosilicate is 500:100.

[0085] Example 3

[0086] This embodiment provides a method for preparing a permanent magnetic ferrite, which is basically the same as that of Embodiment 1, except that the mass ratio of the ferrite pre-sintered material substrate to tetraethyl orthosilicate is 3000:10.

[0087] Example 4

[0088] This embodiment provides a method for preparing permanent magnetic ferrite, which is basically the same as that of Embodiment 1, except that the ball milling speed is 600 r / min.

[0089] Example 5

[0090] This embodiment provides a method for preparing permanent magnetic ferrite, which is basically the same as that of Embodiment 1, except that the ball milling speed is 200 r / min.

[0091] Example 6

[0092] This embodiment provides a method for preparing permanent magnetic ferrite, which is basically the same as that of Embodiment 1, except that the ball milling time is 10 hours.

[0093] Example 7

[0094] This embodiment provides a method for preparing permanent magnetic ferrite, which is basically the same as that of Embodiment 1, except that the ball milling time is 6 hours.

[0095] Example 8

[0096] This embodiment provides a method for preparing permanent magnetic ferrite, which is basically the same as that of Embodiment 1, except that the mass ratio of the modified ferrite pre-sintered material to La2O3 is 500:18.

[0097] Example 9

[0098] This embodiment provides a method for preparing permanent magnetic ferrite, which is basically the same as that of Embodiment 1, except that the mass ratio of the modified ferrite pre-sintered material to La2O3 is 3000:10.

[0099] Example 10

[0100] This embodiment provides a method for preparing permanent magnetic ferrite, which is basically the same as that of Embodiment 1, except that the mass ratio of the modified ferrite pre-sintered material to zinc stearate is 500:25.

[0101] Embodiment 11

[0102] This embodiment provides a method for preparing permanent magnetic ferrite, which is basically the same as that of Embodiment 1, except that the mass ratio of the modified ferrite pre-sintered material to zinc stearate is 3000:1.

[0103] Example 12

[0104] This embodiment also provides a method for preparing a permanent ferrite, comprising the following steps:

[0105] (1) Preparation of modified ferrite pre-sintered material:

[0106] Step 1: Pre-sinter the ferrite substrate Sr 0.86 La 0.14 Fe 11.86 Co 0.14 O 19 , tetraethyl orthosilicate and anhydrous ethanol are mixed and ultrasonically dispersed, wherein the mass ratio of the ferrite pre-sintered material substrate to tetraethyl orthosilicate is 2000:70, and the mass ratio of the ferrite pre-sintered material substrate to anhydrous ethanol is 2000:4500.

[0107] Step 2: The mixture is placed in a ball mill for ball milling, and a catalyst, dilute hydrochloric acid (1 mol / L), is added during the ball milling process.

[0108] The mass ratio of ferrite pre-sintered material to dilute hydrochloric acid is 2000:5, the ball milling speed is 300r / min, and the ball milling time is 8h.

[0109] Step 3: solid-liquid separation, spreading the solid product flat for air drying, and sieving it with a 30-mesh sieve to obtain a modified ferrite pre-sintered material.

[0110] (2) Preparation of permanent ferrite:

[0111] Step A: Blending the modified ferrite pre-sintered material prepared above, flux Al2O3 and lubricant calcium stearate to obtain a blend.

[0112] The mass ratio of the modified ferrite pre-sintered material, Al2O3 and calcium stearate is 2000:15:14.

[0113] Step B, dry pressing and sintering the blend:

[0114] After dry pressing at a pressure of 50 MPa in a magnetic field with a magnetic field strength of 1200Oe, the temperature is increased to 400°C at a rate of 6°C / min and kept warm for 2 hours, then increased to 700°C at a rate of 5°C / min and kept warm for 4 hours, then increased to 1000°C at a rate of 4°C / min and kept warm for 3 hours, then increased to 1260°C at a rate of 3°C / min and kept warm for 6 hours, and then cooled with the furnace to obtain permanent ferrite.

[0115] Example 13

[0116] This embodiment also provides a method for preparing a permanent ferrite, comprising the following steps:

[0117] (1) Preparation of modified ferrite pre-sintered material:

[0118] Step 1: Pre-sinter the ferrite substrate Sr 0.86 La 0.14 Fe 11.86 Co 0.14 O 19 , tetraethyl orthosilicate and anhydrous ethanol are mixed and ultrasonically dispersed, wherein the mass ratio of the ferrite pre-sintered material substrate to tetraethyl orthosilicate is 2000:70, and the mass ratio of the ferrite pre-sintered material substrate to anhydrous ethanol is 2000:4500.

[0119] Step 2: The mixture is placed in a ball mill for ball milling, and ammonia water (concentration 12 mol / L) is added as a catalyst during the ball milling process.

[0120] The mass ratio of ferrite pre-sintered material to dilute hydrochloric acid is 2000:5, the ball milling speed is 300r / min, and the ball milling time is 8h.

[0121] Step 3: solid-liquid separation, spreading the solid product flat for air drying, and sieving it with a 30-mesh sieve to obtain a modified ferrite pre-sintered material.

[0122] (2) Preparation of permanent ferrite:

[0123] Step A: Blending the modified ferrite pre-sintered material prepared above, flux La2O3 and lubricant zinc stearate to obtain a blend.

[0124] The mass ratio of the modified ferrite pre-sintered material, La2O3 and zinc stearate is 2000:15:14.

[0125] Step B, dry pressing and sintering the blend:

[0126] After dry pressing at a pressure of 50 MPa in a magnetic field with a magnetic field strength of 1200Oe, the temperature is increased to 400°C at a rate of 6°C / min and kept warm for 2 hours, then increased to 700°C at a rate of 5°C / min and kept warm for 4 hours, then increased to 1000°C at a rate of 4°C / min and kept warm for 3 hours, then increased to 1260°C at a rate of 3°C / min and kept warm for 6 hours, and then cooled with the furnace to obtain permanent ferrite.

[0127] Comparative Example 1

[0128] This comparative example provides a method for preparing a permanent magnetic ferrite, comprising the following steps:

[0129] Step A: pre-sinter the ferrite substrate Sr 0.86 La 0.14 Fe 11.86 Co 0.14 O 19, flux La2O3 and lubricant zinc stearate are blended to obtain a blend.

[0130] The mass ratio of the ferrite pre-sintered material substrate, La2O3 and zinc stearate is 2000:15:14.

[0131] Step B, dry pressing and sintering the blend:

[0132] After dry pressing at a pressure of 50 MPa in a magnetic field with a magnetic field strength of 1200Oe, the temperature is increased to 400°C at a rate of 6°C / min and kept warm for 2 hours, then increased to 700°C at a rate of 5°C / min and kept warm for 4 hours, then increased to 1000°C at a rate of 4°C / min and kept warm for 3 hours, then increased to 1260°C at a rate of 3°C / min and kept warm for 6 hours, and then cooled with the furnace to obtain permanent ferrite.

[0133] Comparative Example 2

[0134] This comparative example provides a method for preparing a permanent magnetic ferrite, comprising the following steps:

[0135] (1) Preparation of modified ferrite pre-sintered material:

[0136] Step 1: Pre-sinter the ferrite substrate Sr 0.86 La 0.14 Fe 11.86 Co 0.14 O 19 Mix with tetraethyl orthosilicate and anhydrous ethanol and disperse by ultrasonic. The mass ratio of ferrite pre-sintered material base material to tetraethyl orthosilicate is 2000:500, and the mass ratio of ferrite pre-sintered material base material to anhydrous ethanol is 2000:4500.

[0137] Step 2: The mixture was placed in a ball mill for ball milling. After half an hour of ball milling, a catalyst of dilute hydrochloric acid (1 mol / L) was added.

[0138] The mass ratio of ferrite pre-sintered material to dilute hydrochloric acid is 2000:5, the ball milling speed is 300r / min, and the ball milling time is 8h.

[0139] Step 3: solid-liquid separation, spreading the solid product flat for air drying, and sieving it with a 30-mesh sieve to obtain a modified ferrite pre-sintered material.

[0140] (2) Preparation of permanent ferrite:

[0141] Step A: Blending the modified ferrite pre-sintered material, flux La2O3 and lubricant zinc stearate to obtain a blend.

[0142] The mass ratio of the modified ferrite pre-sintered material, La2O3 and zinc stearate is 2000:15:14.

[0143] Step B, dry pressing and sintering the blend:

[0144] After dry pressing at a pressure of 50 MPa in a magnetic field with a magnetic field strength of 1200Oe, the temperature is increased to 400°C at a rate of 6°C / min and kept warm for 2 hours, then increased to 700°C at a rate of 5°C / min and kept warm for 4 hours, then increased to 1000°C at a rate of 4°C / min and kept warm for 3 hours, then increased to 1260°C at a rate of 3°C / min and kept warm for 6 hours, and then cooled with the furnace to obtain permanent ferrite.

[0145] The magnetic properties of the permanent ferrites prepared in the embodiment and the comparative example were tested on a BH performance tester, and the X-ray diffraction patterns of the modified ferrite pre-sintered materials prepared in the embodiment and the comparative example 2 and the ferrite pre-sintered material substrate of the comparative example 1 were measured on a particle size tester. 50 The test results are shown in Table 1.

[0146] Table 1

[0147]

[0148] B r is the remanence, H cb is the coercive force, H cj is the intrinsic coercivity, (BH) max is the maximum magnetic energy product, X 50 It is the particle size corresponding to when the cumulative particle size distribution percentage reaches 50%.

[0149] As shown in Table 1, the magnetic properties of the permanent ferrite prepared by the method of the present invention are significantly improved. In Comparative Example 1, the ferrite pre-sintered material substrate is not modified. Due to the different regularity of the grains, it is often difficult to move or rotate the grains during the dry preparation process, resulting in a low orientation degree. In addition, during the crystal growth, the interface strength between the grains is not high, and certain gaps appear, resulting in a decrease in the performance of the magnet. In Comparative Example 2, the amount of tetraethyl orthosilicate used is too much, which also leads to a poor coating effect. 50 The size of the magnet increases significantly, and the grain uniformity deteriorates, resulting in a decrease in magnet performance.

[0150] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the scope of protection of the invention.

Claims

1. A method for preparing a modified ferrite pre-sintered material, characterized in that: The following steps are involved: Step 1, mixing a ferrite pre-sintered material substrate, a silicon source and a solvent to obtain a mixture; The mass ratio of the ferrite pre-sintered material substrate to the silicon source is (500-3000): (10-100); Step 2, mixing the mixture with a catalyst and ball milling; The catalyst includes an aqueous acid solution or an aqueous base solution; Step 3: solid-liquid separation to obtain modified ferrite pre-sintered material.

2. The method for preparing the modified ferrite pre-sintered material according to claim 1, characterized in that: The step 1 satisfies at least one of the following conditions: (1) The mass ratio of the silicon source to the solvent is (10-100): (3000-6000); (2) mixing a ferrite pre-sintered material substrate, a silicon source and a solvent, and performing ultrasonic dispersion to obtain a mixture; (3) The silicon source includes one or more of methyl orthosilicate, ethyl orthosilicate and sodium silicate; (4) The solvent includes water and / or an organic solvent; Optionally, the organic solvent includes one or more of anhydrous ethanol, acetone and toluene.

3. The method for preparing the modified ferrite pre-sintered material according to claim 1, characterized in that: The step 2 satisfies at least one of the following conditions: (1) The mass ratio of the silicon source to the catalyst is (10-100): (1-10); (2) the aqueous acid solution comprises one or more of hydrochloric acid and selenic acid; (3) The aqueous solution of the alkali includes aqueous ammonia; (4) The rotation speed of the ball mill is 200 to 600 r / min; (5) The ball milling time is 6 to 10 hours.

4. The method for preparing the modified ferrite pre-sintered material according to any one of claims 1 to 3, characterized in that: The step 3 comprises drying the liquid product after solid-liquid separation; Optionally, the drying method is air drying; Optionally, step 3 further comprises crushing and screening the dried product; optionally, a sieve of 10 to 100 mesh is used for screening.

5. A modified ferrite pre-sintered material, characterized in that: Prepared according to the preparation method according to any one of claims 1 to 4.

6. A method for preparing a permanent magnetic ferrite, characterized in that: It is prepared by using the modified ferrite pre-sintered material described in claim 5.

7. The method for preparing permanent ferrite according to claim 6, characterized in that: The following steps are involved: Step A, blending the modified ferrite pre-sintered material, flux and lubricant to obtain a blend; Step B, dry pressing the blend and sintering it.

8. The method for preparing permanent ferrite according to claim 7, characterized in that: The step A satisfies at least one of the following conditions: (1) The mass ratio of the modified ferrite pre-sintered material to the flux is (500-3000): (10-18); (2) The mass ratio of the lubricant to the modified ferrite pre-sintered material is (1-25): (500-3000); (3) The flux includes one or more of La2O3, Al2O3 and CaCO3; (4) The lubricant includes one or more of zinc stearate, magnesium stearate and calcium stearate.

9. The method for preparing a permanent magnetic ferrite according to claim 7 or 8, characterized in that: The step B satisfies at least one of the following conditions: (1) The dry pressing is performed in a magnetic field, and optionally, the strength of the magnetic field is 1000 to 1400 Oe; (2) The pressure of the dry pressing molding is 40 to 80 MPa; (3) The sintering includes a first heating, a first heat preservation, a second heating, a second heat preservation, a third heating, a third heat preservation, a fourth heating and a fourth heat preservation performed in sequence; Optionally, the first heating rate is 2 to 10°C / min; Optionally, the endpoint temperature of the first heating is 300-500° C.; Optionally, the first insulation time is 1 to 6 hours; Optionally, the second heating rate is 3 to 9°C / min; Optionally, the end temperature of the second heating is 600-800° C.; Optionally, the second insulation time is 1 to 8 hours; Optionally, the third heating rate is 2-7°C / min; Optionally, the end temperature of the third heating is 900-1100° C.; Optionally, the third insulation time is 1 to 5 hours; Optionally, the fourth heating rate is 1 to 5°C / min; Optionally, the end temperature of the fourth heating step is 1200-1300° C.; Optionally, the fourth insulation time is 1 to 12 hours.

10. A permanent magnetic ferrite, characterized in that: Prepared according to the preparation method according to any one of claims 6 to 9.

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