Slurry for preparing permanent magnetic ferrite as well as preparation method and application of slurry

Abstract

The invention relates to slurry for preparing permanent magnetic ferrite as well as a preparation method and application of the slurry. The preparation method comprises the following steps: providing a pre-sintered material, and carrying out primary dry grinding treatment on the pre-sintered material to obtain primary powder; performing second-stage dry grinding treatment on the first-stage powder to obtain second-stage powder; mixing the second-stage powder with a solvent and a dispersing agent, and carrying out third-stage wet grinding treatment to obtain slurry with the sediment density of less than 0.9 g / cm < 3 >; wherein the particle size difference between the first-stage powder and the second-stage powder is smaller than or equal to 4.5 microns, the particle size difference between the second-stage powder and the precipitate is smaller than or equal to 1.5 microns, and the dispersing agent is selected from sodium citrate and boric acid. According to the preparation method disclosed by the invention, the granularity of the precipitate in the slurry has approximate normal distribution through a three-stage grinding process, the precipitate density of less than 0.9 g / cm < 3 > can be achieved, and the cohesive force of the slurry is reduced, so that the orientation degree of crystal grains is improved, the magnetic performance is improved, and meanwhile, the forming qualification rate of the magnet can be ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of permanent ferrite, and particularly to a slurry for preparing permanent ferrite, a preparation method thereof, and an application thereof. Background Art

[0002] The main magnetic performance indexes of anisotropic permanent ferrite include coercivity (Hcj) and remanent magnetic induction intensity (Br). Among them, the coercivity of the magnet can be improved by adopting appropriate additives and controlling the growth of grains; while the main factors affecting the remanent magnetic induction intensity include the saturation magnetization intensity of the magnet and the degree of grain orientation in the magnet. Selecting high-purity raw materials is the key to improving the saturation magnetization intensity, and the key to improving the degree of grain orientation is the degree of grain alignment during the wet magnetic field pressing of the slurry for preparing permanent ferrite.

[0003] In traditional preparation methods, calcium gluconate dispersant is usually added to the slurry to improve the degree of grain alignment during the wet magnetic field pressing of the slurry. However, the effect of calcium gluconate dispersant is limited. Moreover, due to the strong water retention of calcium gluconate, it is not easy to discharge during the forming stage, and a large amount of calcium gluconate will remain inside the green body, resulting in cracking of the magnet during the sintering process due to the decomposition of calcium gluconate, which will instead reduce the forming qualification rate of the magnet. Summary of the Invention

[0004] Based on this, in view of the above problems, it is necessary to provide a slurry for preparing permanent ferrite, a preparation method thereof, and an application thereof; the preparation method enables the particle size of the precipitate in the slurry to have an approximate normal distribution through a three-stage abrasive process, and can achieve a precipitate density of less than 0.9 g / cm 3 , reducing the cohesion of the slurry, thereby improving the degree of grain alignment during the wet magnetic field pressing of the slurry, improving the magnetic properties, and ensuring the forming qualification rate of the magnet at the same time.

[0005] A preparation method of a slurry for preparing permanent ferrite, comprising the following steps:

[0006] Providing a pre-sintered material, and performing a first-stage dry grinding treatment on the pre-sintered material to obtain a first-stage powder;

[0007] Performing a second-stage dry grinding treatment on the first-stage powder to obtain a second-stage powder;

[0008] Mixing the second-stage powder with a solvent and a dispersant for a third-stage wet grinding treatment to obtain a slurry, and the density of the precipitate in the slurry is less than 0.9 g / cm 3 ;

[0009] Among them, the particle size difference between the primary powder and the secondary powder is less than or equal to 4.5 μm, the particle size difference between the secondary powder and the precipitate is less than or equal to 1.5 μm, and the dispersant is selected from sodium citrate and boric acid.

[0010] In one embodiment, the particle size difference between the primary powder and the secondary powder is 2.5 μm - 4.5 μm;

[0011] And / or, the particle size difference between the secondary powder and the precipitate is 0.2 μm - 1.5 μm.

[0012] In one embodiment, the particle size of the primary powder is 4.5 μm - 5.5 μm;

[0013] And / or, the particle size of the secondary powder is 1 μm - 2 μm;

[0014] And / or, the particle size of the precipitate is 0.6 μm - 0.8 μm.

[0015] In one embodiment, the method of primary dry grinding treatment is selected from vibration pulverization;

[0016] And / or, the method of secondary dry grinding treatment is planetary ball milling, the rotation speed is 280 r / min - 320 r / min, and the time is 4 h - 8 h;

[0017] And / or, the method of tertiary wet grinding treatment is ball milling, the rotation speed is 78 r / min - 85 r / min, and the time is 6 h - 12 h.

[0018] In one embodiment, the mass ratio of sodium citrate to boric acid is 3:1 - 1.5:1;

[0019] And / or, the mass of the dispersant is 0.05% - 0.4% of the mass of the secondary powder.

[0020] In one embodiment, the main phase molecular formula of the pre-sintered material is Ca y La x Sr 1-x-y Fe 2n-z Co z O 19 , where 0.25 ≤ x ≤ 0.6, 0.1 ≤ y ≤ 0.5, 4.0 ≤ n ≤ 6.0, 0.18 ≤ z ≤ 0.36.

[0021] In one embodiment, the preparation method of the pre-sintered material includes the following steps:

[0022] According to Ca y La x Sr 1-x-y Fe2n-z Co z O 19 where 0.25 ≤ x ≤ 0.6, 0.1 ≤ y ≤ 0.5, 4.0 ≤ n ≤ 6.0, 0.18 ≤ z ≤ 0.36, prepare the raw material powder, and perform primary wet grinding with an additive to obtain a mixed powder;

[0023] Pre - sinter the mixed powder to obtain a pre - sintered material.

[0024] In one embodiment, the additive is selected from nano - quartz sand, and the mass of the additive is 0.05% - 0.1% of the mass of the raw material powder;

[0025] and / or, the particle size of the mixed powder is 0.7 μm - 1.0 μm;

[0026] and / or, the pre - sintering temperature is 1190 °C - 1220 °C, and the time is 1 h - 3 h.

[0027] A slurry prepared by the method for preparing a slurry for preparing permanent ferrite as described above, the density of the precipitate in the slurry is less than 0.9 g / cm 3 .

[0028] A permanent ferrite made of the slurry as described above.

[0029] In the preparation method of the present invention, on the one hand, through a three - stage abrasive process, a specific particle size gradient is formed between the powders obtained in each step, so as to synergistically control the particle size of the precipitate in the slurry to have an approximate normal distribution, and the density of the precipitate can reach less than 0.9 g / cm 3 , which is beneficial to improving the uniform dispersion effect of the precipitate, reducing the slurry cohesion, and further improving the degree of alignment of the grains during the wet magnetic field pressing forming, thereby improving the magnetic properties; on the other hand, in the three - stage wet grinding treatment, sodium citrate and boric acid are used as dispersants, which is not only beneficial to further reducing the density of the precipitate in the slurry, making the precipitate more dispersed, but also easy to discharge and not easy to remain in the forming stage, which can ensure the forming qualification rate of the magnet.

[0030] Therefore, the permanent ferrite made of the slurry provided by the present invention has a high degree of orientation and excellent magnetic properties such as residual magnetic induction intensity, coercivity, and magnetic energy product, and can be effectively used in devices such as motors. Detailed implementation mode

[0031] To facilitate the understanding of the present invention, the present invention will be described in more detail below. However, it should be understood that the present invention can be implemented in many different forms and is not limited to the embodiments or examples described herein. On the contrary, the purpose of providing these embodiments or examples is to make the understanding of the disclosure content of the present invention more thorough and comprehensive.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this invention belongs. The terms used in the description of the present invention herein are for the purpose of describing specific embodiments or examples only and are not intended to limit the present invention. The optional scope of the term "and / or" used herein includes any one of two or more related listed items, and also includes any and all combinations of the related listed items. The any and all combinations include any two related listed items, any more than two related listed items, or the combination of all related listed items.

[0033] The present invention provides a method for preparing a slurry for preparing a permanent magnet ferrite, comprising the following steps:

[0034] S1, providing a pre-sintered material, performing a first-stage dry grinding treatment on the pre-sintered material to obtain a first-stage powder;

[0035] S2, performing a second-stage dry grinding treatment on the first-stage powder to obtain a second-stage powder;

[0036] S3, mixing the second-stage powder with a solvent and a dispersant to perform a third-stage wet grinding treatment to obtain a slurry, and the density of the precipitate in the slurry is less than 0.9 g / cm 3 ;

[0037] Wherein, the particle size difference between the first-stage powder and the second-stage powder is less than or equal to 4.5 μm, the particle size difference between the second-stage powder and the precipitate is less than or equal to 1.5 μm, and the dispersant is selected from sodium citrate and boric acid.

[0038] In step S1, through the first-stage dry grinding treatment, the pre-sintered material is coarsely pulverized, so that the first-stage powder can reach a certain particle size distribution. Considering the preparation efficiency, it is preferably to adopt the vibration pulverization method for the first-stage dry grinding treatment.

[0039] In one embodiment, the powder after the first-stage dry grinding treatment is sieved through a 60-mesh sieve to remove the pre-sintered material blocks that are not sufficiently pulverized.

[0040] In one embodiment, the main phase molecular formula of the pre-sintered material is Ca y La x Sr 1-x-y Fe 2n-z Co z O 19 , wherein, 0.25 ≤ x ≤ 0.6, 0.1 ≤ y ≤ 0.5, 4.0 ≤ n ≤ 6.0, 0.18 ≤ z ≤ 0.36.

[0041] In one embodiment, the method for preparing the pre-sintered material comprises the following steps:

[0042] According to Ca y La x Sr 1-x-y Fe 2n-z Co z O 19 ,0.25 ≤ x ≤ 0.6, 0.1 ≤ y ≤ 0.5, 4.0 ≤ n ≤ 6.0, 0.18 ≤ z ≤ 0.36, prepare the raw material powder, and conduct primary wet grinding with an additive to obtain a mixed powder;

[0043] Pre-calcine the mixed powder to obtain a pre-calcined material.

[0044] By selecting an appropriate molar ratio and with the combined action of the additive, wet grinding first and then pre-calcining are beneficial to obtaining a ferrite pre-calcined material with high-purity magnetic phase, good grain growth, and low coercivity.

[0045] Among them, the additive at least includes nano silica sand, and may also include calcium carbonate. The present invention does not limit this, and preferably uses nano silica sand.

[0046] Preferably, the mass of the additive is 0.05% - 0.1% of the mass of the raw material powder.

[0047] Preferably, the particle size of the mixed powder is 0.7 μm - 1.0 μm.

[0048] Preferably, the pre-calcination temperature is 1190°C - 1220°C, and the time is 1 h - 3 h.

[0049] In steps S2 to S3, compared with the traditional technology, the present invention also sets up a secondary dry grinding treatment, constituting a three-stage abrasive process, so that there is a specific particle size gradient between the powders obtained in each step, thereby synergistically regulating the particle size of the precipitate in the slurry to have an approximate normal distribution, and being able to achieve a precipitate density less than 0.9 g / cm 3 , which is beneficial to improving the uniform dispersion effect of the precipitate, reducing the slurry cohesion, and further improving the alignment degree of the grains during the wet magnetic pressing forming of the slurry, and improving the magnetic properties.

[0050] Moreover, in the three-stage wet grinding treatment, the present invention uses sodium citrate and boric acid as dispersants, which is not only beneficial to further reducing the density of the precipitate in the slurry, making the precipitate more dispersed, but also easy to discharge and not easy to remain in the forming stage, and can ensure the forming qualification rate of the magnet.

[0051] Preferably, the particle size difference between the primary powder and the secondary powder is 2.5 μm - 4.5 μm, and / or the particle size difference between the secondary powder and the precipitate is 0.2 μm - 1.5 μm.

[0052] More preferably, the particle size difference between the primary powder and the secondary powder is 2.5 μm - 4.5 μm, and the particle size difference between the secondary powder and the precipitate is 0.2 μm - 1.5 μm.

[0053] In one embodiment, the particle size of the primary powder is 4.5 μm - 5.5 μm;

[0054] and / or, the particle size of the secondary powder is 1 μm - 2 μm;

[0055] and / or, the particle size of the precipitate is 0.6 μm - 0.8 μm.

[0056] In one embodiment, the method of secondary dry grinding is selected from planetary ball milling, at 280 r / min - 320 r / min, for 4 h - 8 h;

[0057] In one embodiment, the method of tertiary wet grinding is selected from ball milling, at a rotation speed of 78 r / min - 85 r / min, for 6 h - 12 h.

[0058] Specifically, when the method of tertiary wet grinding is selected from ball milling, by reasonably preparing grinding balls of different sizes, it is beneficial to improve the grinding effect and efficiency, and the present invention does not limit this.

[0059] In one embodiment, the mass ratio of sodium citrate to boric acid is 3:1 - 1.5:1, and / or, the mass of the dispersant is 0.05% - 0.4% of the mass of the secondary powder, which is beneficial to further improve the dispersion effect of the precipitate in the slurry, thereby reducing the slurry cohesion and improving the grain orientation degree.

[0060] In one embodiment, the slurry after tertiary wet grinding is subjected to ultrasonic dispersion treatment for 0.5 min - 2 min, which can break the aggregates in the slurry, so that the precipitate in the slurry can be better dispersed in the solvent, thereby improving the uniformity and stability of the slurry.

[0061] In one embodiment, the solvent includes but is not limited to water, preferably deionized water, which not only makes the preparation method green and environmentally friendly, but also helps to reduce costs.

[0062] The present invention provides a slurry prepared by the preparation method of the slurry for preparing permanent ferrite as described above, and the density of the precipitate in the slurry is less than 0.9 g / cm 3 。

[0063] The present invention also provides a permanent ferrite made of the slurry as described above.

[0064] The permanent magnet ferrite made from the slurry provided by the present invention has a high degree of orientation and excellent magnetic properties such as remanent magnetic induction intensity, coercivity, and magnetic energy product, and can be effectively used in devices such as motors.

[0065] It should be noted that the present invention does not limit the specific method for preparing permanent magnet ferrite from the slurry, and existing processes can be used for preparation. For example: centrifugally dehydrating the slurry to adjust the slurry to a relatively high concentration, then subjecting the relatively high-concentration slurry to ultrasonic treatment and pressing it into a shape, and applying a magnetic field in the pressing direction while pressing it into a shape to obtain a green body; heat-treating the green body under the temperature condition of 100°C - 600°C to completely remove the solvent, and then sintering it in the air to obtain the permanent magnet ferrite.

[0066] Hereinafter, the slurry for preparing permanent magnet ferrite, its preparation method and application will be further described through the following specific examples. However, those skilled in the art will understand that the following examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. For those not specified in the examples, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. For the reagents or instruments not specified for the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0067] The powder raw materials used include: Fe 2 O 3 (purity ≥ 99.4 wt%, Cl - ≤ 0.1 wt%, the original average particle size of the particles ≤ 1.5 μm), CaCO 3 (purity ≥ 98.5 wt%, the original average particle size of the particles ≤ 1.0 μm), La 2 O 3 (purity ≥ 99.2 wt%, the original average particle size of the particles ≤ 5 μm), Co 2 O 3 (Co content ≥ 72.2%, the original average particle size of the particles ≤ 3 μm), SrCO 3 purity ≥ 97.2 wt%, the original average particle size of the particles ≤ 1.5 μm).

[0068] Example 1

[0069] According to Ca 0.36 La 0.42 Sr 0.22 Fe 10.68 Co 0.28 O 19Weigh the powder raw materials according to the ratio, mix them with nano quartz sand and conduct primary wet ball milling. Among them, the dosage of nano quartz sand is 0.07 wt% of the mass of all powder raw materials. After ball milling for 5 hours, a mixed powder with an average particle size of about 0.8 μm is obtained. The mixed powder is first dried in an oven and then pre-fired in a pit-type sintering furnace at 1200 °C for 3 hours to obtain a pre-fired material.

[0070] The obtained pre-fired material is subjected to primary dry grinding treatment by a dry vibrating mill, and then the crushed powder is sieved through a 60-mesh sieve to obtain a primary powder with an average particle size of about 5.2 μm.

[0071] Transfer the primary powder into a high-speed planetary mill for secondary dry grinding treatment. Among them, the rotation speed is 300 r / min, the grinding balls are zirconia balls with a diameter of 2 mm, the time is 6 hours, and after crushing, a secondary powder with an average particle size of about 1.3 μm is obtained.

[0072] Weigh 500 g of the secondary powder, add 1.5 g of silicon dioxide, 7.15 g of calcium carbonate, 0.5 g of sodium citrate, 0.25 g of boric acid and 800 mL of deionized water for tertiary wet ball milling treatment. Among them, the grinding balls are prepared with bearing steel balls with a diameter of 6.35 mm and bearing steel balls with a diameter of 3.85 mm according to a mass ratio of 1:1, and the total weight of the grinding balls is 10 kg, the rotation speed is 80 r / min, and ball milling is carried out for 8 hours to obtain a slurry. Among them, the average particle size of the precipitate in the slurry is about 0.65 μm, and the density of the precipitate is about 0.75 g / cm 3 。

[0073] Example 2

[0074] According to Ca 0.36 La 0.42 Sr 0.22 Fe 10.68 Co 0.28 O 19 Weigh the powder raw materials according to the ratio, mix them with nano quartz sand and conduct primary wet ball milling. Among them, the dosage of nano quartz sand is 0.05 wt% of the mass of all powder raw materials. After ball milling for 5 hours, a mixed powder with an average particle size of about 0.79 μm is obtained. The mixed powder is first dried in an oven and then pre-fired in a pit-type sintering furnace at 1220 °C for 2 hours to obtain a pre-fired material.

[0075] The obtained pre-fired material is subjected to primary dry grinding treatment by a dry vibrating mill, and then the crushed powder is sieved through a 60-mesh sieve to obtain a primary powder with an average particle size of about 4.9 μm.

[0076] Transfer the primary powder into a high-speed planetary mill for secondary dry grinding treatment. Among them, the rotation speed is 305 r / min, the time is 5.5 hours, and after crushing, a secondary powder with an average particle size of about 1.5 μm is obtained.

[0077] Weigh 500 g of the secondary powder, add 1.0 g of silicon dioxide, 2.5 g of calcium carbonate, 0.75 g of sodium citrate, 0.4 g of boric acid, and 800 mL of deionized water, and perform three-stage wet ball milling. Among them, the grinding balls are prepared with bearing steel balls with a diameter of 6.35 mm and bearing steel balls with a diameter of 3.85 mm according to a mass ratio of 1:1, and the total weight of the grinding balls is 10 kg, the rotation speed is 78 r / min, and ball milling is carried out for 10 hours to obtain a slurry. Among them, the average particle size of the precipitate in the slurry is about 0.68 μm, and the density is about 0.8 g / cm 3 .

[0078] Example 3

[0079] According to the ratio of Ca 0.36 La 0.42 Sr 0.22 Fe 10.68 Co 0.28 O 19 Weigh the powder raw materials according to the ratio, mix them with nano quartz sand and perform one-stage wet ball milling. Among them, the dosage of nano quartz sand is 0.1 wt% of the mass of all powder raw materials. After ball milling for 5 hours, a mixed powder with an average particle size of about 0.83 μm is obtained. The mixed powder is first dried in an oven and then pre-sintered in a vertical sintering furnace at 1230 °C for 2 hours to obtain a pre-sintered material.

[0080] Perform primary dry grinding on the obtained pre-sintered material with a dry vibratory mill, and then screen the crushed powder through a 60-mesh sieve to obtain a primary powder with an average particle size of about 4.8 μm.

[0081] Transfer the primary powder to a high-speed planetary mill for secondary dry grinding. Among them, the rotation speed is 280 r / min and the time is 8 hours. After crushing, a secondary powder with an average particle size of about 1.15 μm is obtained.

[0082] Weigh 500 g of the secondary powder, add 1.0 g of silicon dioxide, 5 g of calcium carbonate, 1.5 g of sodium citrate, 0.5 g of boric acid, and 800 mL of deionized water, and perform three-stage wet ball milling. Among them, the grinding balls are prepared with bearing steel balls with a diameter of 6.35 mm and bearing steel balls with a diameter of 3.85 mm according to a mass ratio of 1:1, and the total weight of the grinding balls is 10 kg, the rotation speed is 82 r / min, and ball milling is carried out for 10 hours to obtain a slurry. Among them, the average particle size of the precipitate in the slurry is about 0.7 μm, and the density is about 0.81 g / cm 3 .

[0083] Example 4

[0084] According to the ratio of Ca 0.3 La 0.42 Sr 0.28Fe 10.74 Co 0.26 O 19 Weigh the powder raw materials according to the ratio, mix them with nano quartz sand and carry out primary wet ball milling. Among them, the dosage of nano quartz sand is 0.07 wt% of the mass of all powder raw materials. After ball milling for 5 hours, a mixed powder with an average particle size of about 0.72 μm is obtained. The mixed powder is first dried in an oven and then pre-sintered in a pit type sintering furnace at 1200 °C for 3 hours to obtain a pre-sintered material.

[0085] The obtained pre-sintered material is subjected to primary dry grinding treatment by a dry vibrating mill, and then the pulverized powder is sieved through a 60-mesh sieve to obtain a primary powder with an average particle size of about 4.95 μm.

[0086] Transfer the primary powder into a high-speed planetary mill for secondary dry grinding treatment. Among them, the rotation speed is 300 r / min and the time is 6 hours. After pulverization, a secondary powder with an average particle size of about 1.28 μm is obtained.

[0087] Weigh 500 g of the secondary powder, add 2 g of silicon dioxide, 7.15 g of calcium carbonate, 0.5 g of sodium citrate, 0.25 g of boric acid and 800 mL of deionized water for tertiary wet ball milling treatment. Among them, the grinding balls are prepared from bearing steel balls with a diameter of 6.35 mm and bearing steel balls with a diameter of 3.85 mm according to a mass ratio of 1:1, and the total weight of the grinding balls is 10 kg, the rotation speed is 80 r / min, and the ball milling time is 8 hours to obtain a slurry. Among them, the average particle size of the precipitate in the slurry is about 0.68 μm and the density is about 0.78 g / cm 3 。

[0088] Comparative Example 1

[0089] According to Ca 0.36 La 0.42 Sr 0.22 Fe 10.68 Co 0.28 Weigh the powder raw materials according to the ratio, mix them with nano quartz sand and carry out primary wet ball milling. Among them, the dosage of nano quartz sand is 0.07 wt% of the mass of all powder raw materials. After ball milling for 5 hours, a mixed powder with an average particle size of about 0.8 μm is obtained. The mixed powder is first dried in an oven and then pre-sintered in a pit type sintering furnace at 1200 °C for 3 hours to obtain a pre-sintered material.

[0090] The obtained pre-sintered material is subjected to primary dry grinding treatment by a dry vibrating mill, and then the pulverized powder is sieved through a 60-mesh sieve to obtain a primary powder with an average particle size of about 4.9 μm.

[0091] Weigh 500 g of first-grade powder, add 1.5 g of silicon dioxide, 7.15 g of calcium carbonate, 0.5 g of sodium citrate, 0.25 g of boric acid, and 800 mL of deionized water, and perform three-stage wet ball milling. Among them, the grinding balls are prepared with bearing steel balls with a diameter of 6.35 mm and bearing steel balls with a diameter of 3.85 mm according to a mass ratio of 1:1. The total weight of the grinding balls is 10 kg, the rotation speed is 80 r / min, and ball milling is carried out for 18 hours to obtain a slurry. Among them, the average particle size of the precipitate in the slurry is about 0.78 μm, and the density is about 0.95 g / cm 3 .

[0092] Comparative Example 2

[0093] The difference between Comparative Example 2 and Example 1 is that 0.75 g of calcium gluconate is used instead of 0.5 g of sodium citrate and 0.25 g of boric acid.

[0094] The average particle size of the precipitate in the prepared slurry is about 0.68 μm, and the density is about 0.97 g / cm 3 .

[0095] The slurries or powders prepared in Examples 1 to 4 and Comparative Examples 1 to 2 are used to prepare permanent ferrite magnets. The specific preparation method is as follows:

[0096] Centrifuge the prepared slurry to adjust the concentration of the slurry to 68%, or mix the prepared powder with water to prepare a slurry with a concentration of 68%; then perform ultrasonic treatment on the high-concentration slurry for 1 minute and then press it into shape. While applying a molding pressure of 5 MPa, apply a molding magnetic field of 15,000 Oe in the pressing direction. The formed green body sample is a cylinder with a diameter of 45 mm and a height of 10 mm.

[0097] Heat-treat the green body sample at a temperature of 300 °C to completely remove moisture, and then sinter it in air. The heating rate is 150 °C / hour, and it is kept at 1200 °C for 60 minutes to obtain a permanent ferrite magnet sample. Grind the upper and lower surfaces of the permanent ferrite magnet sample and measure its remanence (Br), coercivity (Hcb), intrinsic coercivity (Hcj), and maximum magnetic energy product (BH)max. The results are shown in Table 1.

[0098] Table 1

[0099]

[0100] As can be seen from Table 1, the permanent magnet ferrite prepared from the slurries provided in Examples 1 to 4 has an orientation degree of 98.9% - 99.1%. Compared with Comparative Examples 1 to 2, the remanent magnetic induction intensity, coercivity, intrinsic coercivity, and maximum magnetic energy product of the permanent magnet ferrite prepared in Examples 1 to 4 are all improved.

[0101] Comparative Example 1 uses the traditional two-stage segmented abrasive process, which not only takes a long time to prepare and is not conducive to improving the preparation efficiency, but also has poor dispersion effect of the prepared slurry, resulting in a decrease in the orientation degree, thus affecting the magnetic properties; Comparative Example 2 uses calcium gluconate as a dispersant, and the improvement effect of the orientation degree is limited, and the molding qualification rate is the worst.

[0102] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0103] The above-described embodiments only represent several implementation manners of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A preparation method of slurry for preparing permanent magnet ferrite, characterized in that, it includes the following steps: Provide a pre-sintered material, perform primary dry grinding on the pre-sintered material to obtain primary powder; Perform secondary dry grinding on the primary powder to obtain secondary powder; Mix the secondary powder with a solvent and a dispersant for tertiary wet grinding to obtain a slurry, wherein the density of the precipitate in the slurry is less than 0.9 g / cm 3 ; Wherein, the particle size difference between the primary powder and the secondary powder is less than or equal to 4.5 μm, the particle size difference between the secondary powder and the precipitate is less than or equal to 1.5 μm, and the dispersant is selected from sodium citrate and boric acid.

2. The preparation method of slurry for preparing permanent magnet ferrite according to claim 1, characterized in that, the particle size difference between the primary powder and the secondary powder is 2.5 μm - 4.5 μm; and / or, the particle size difference between the secondary powder and the precipitate is 0.2 μm - 1.5 μm.

3. The preparation method of slurry for preparing permanent magnet ferrite according to claim 2, characterized in that, the particle size of the primary powder is 4.5 μm - 5.5 μm; and / or, the particle size of the secondary powder is 1 μm - 2 μm; and / or, the particle size of the precipitate is 0.6 μm - 0.8 μm.

4. The preparation method of slurry for preparing permanent magnet ferrite according to claim 1, characterized in that, the method of primary dry grinding is selected from vibration crushing; and / or, the method of secondary dry grinding is selected from planetary ball mill, the rotation speed is 280 r / min - 320 r / min, and the time is 4 h - 8 h; and / or, the method of tertiary wet grinding is selected from ball mill, the rotation speed is 78 r / min - 85 r / min, and the time is 6 h - 12 h.

5. The preparation method of slurry for preparing permanent magnet ferrite according to claim 1, characterized in that, the mass ratio of sodium citrate to boric acid is 3:1 - 1.5:1; and / or, the mass of the dispersant is 0.05% - 0.4% of the mass of the secondary powder.

6. The preparation method of slurry for preparing permanent magnet ferrite according to claim 1, characterized in that, The main phase molecular formula of the pre-sintered material is Ca y La x Sr 1-x-y Fe 2n-z Co z O 19 , where 0.25 ≤ x ≤ 0.6, 0.1 ≤ y ≤ 0.5, 4.0 ≤ n ≤ 6.0, 0.18 ≤ z ≤ 0.

36.

7. The preparation method of slurry for preparing permanent magnet ferrite according to claim 6, characterized in that, the preparation method of the pre-sintered material includes the following steps: According to Ca y La x Sr 1-x-y Fe 2n-z Co z O 19 , prepare raw material powder with 0.25 ≤ x ≤ 0.6, 0.1 ≤ y ≤ 0.5, 4.0 ≤ n ≤ 6.0, 0.18 ≤ z ≤ 0.36, and conduct primary wet grinding with an additive to obtain mixed powder; Perform pre-sintering on the mixed powder to obtain a pre-sintered material.

8. The preparation method of slurry for preparing permanent magnet ferrite according to claim 7, characterized in that, the additive is selected from nano quartz sand, and the mass of the additive is 0.05% - 0.1% of the mass of the raw material powder; and / or, the particle size of the mixed powder is 0.7 μm - 1.0 μm; and / or, the pre-sintering temperature is 1190 °C - 1220 °C, and the time is 1 h - 3 h.

9. A slurry prepared by the preparation method of slurry for preparing permanent magnet ferrite according to any one of claims 1 - 8, characterized in that, The density of the precipitate in the slurry is less than 0.9 g / cm 3 .

10. A permanent magnet ferrite made from the slurry according to claim 9.

Images