CN113087513A - High-coercivity ferrite and preparation method thereof - Google Patents

High-coercivity ferrite and preparation method thereof Download PDF

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CN113087513A
CN113087513A CN202110273920.0A CN202110273920A CN113087513A CN 113087513 A CN113087513 A CN 113087513A CN 202110273920 A CN202110273920 A CN 202110273920A CN 113087513 A CN113087513 A CN 113087513A
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ferrite
powder
ball
milling
coercive force
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CN113087513B (en
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白国华
张雪峰
张振华
严密
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Hangzhou Dianzi University
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Abstract

The invention discloses a high-coercivity ferrite and a preparation method thereof. The intrinsic coercive force Hcj of the ferrite is more than 430kA/m, the remanence Br is more than 460mT, and the maximum magnetic energy product is more than 41kJ/m3. The preparation method comprises the steps of material preparation, primary ball milling, pre-sintering, secondary ball milling, flash firing treatment, refined ball milling and pulping, wet pressing forming and two-stage sintering. The innovation of the invention is that through flash firing treatment, refined ball milling pulping and two-stage sintering process, the crystal grains smaller than 1 mu m can be obtained, simultaneously, the size distribution of the crystal grains is effectively narrowed, and the powder agglomeration and the magnetic interaction among the crystal grains are reduced, so thatThereby improving the coercive force of the permanent magnetic ferrite.

Description

High-coercivity ferrite and preparation method thereof
Technical Field
The invention belongs to the technical field of electronic materials and components, and particularly relates to a high-coercivity ferrite and a preparation method thereof.
Background
The M-type ferrite is a magnetoplumbite type ferrite of hexagonal crystal type, can obtain very high magnetocrystalline anisotropy, and is widely applied to the preparation of various permanent magnet materials. The permanent magnet material prepared from the M-type ferrite has the advantages of rich raw materials, low price, high temperature resistance, corrosion resistance and the like, and is a core material of electronic components such as motors, generators, acoustic devices, sensors and the like. However, due to defects caused in the preparation process of the material, the coercive force of the M-type permanent magnetic ferrite is far lower than a theoretical value, so that related electronic components are easy to demagnetize under the action of a reverse magnetization field, and the stability of the components is greatly reduced. Therefore, it is required to develop an M-type permanent magnetic ferrite having a high coercive force.
At present, technicians usually adopt an ion replacement method to improve the coercive force of the M-type permanent magnetic ferrite. Chinese patent publication No. CN1658340A discloses a hexagonal ferrite, which is substituted by La-Co to greatly improve the magnetic properties of the material, but La-Co is expensive and not suitable for addition in large quantities. Chinese patent publication No. CN104003703A discloses a method for preparing a high-performance permanent magnetic ferrite material, which adopts a molten salt method to prepare the high-performance magnetic ferrite, effectively improves the microstructure and improves the magnetic performance, but the method needs to add a molten salt cleaning process, and is not suitable for large-scale production and use. Chinese patent publication nos. CN104900363A, 104380403a relate to a method for preparing M-type ferrite, which obtains high permanent magnetic properties by adding alkali metal compounds such as potassium salt, sodium salt, and zinc compound at the time of sintering ferrite. However, in the current technical scheme, the microstructure of the M-type permanent magnetic ferrite is difficult to improve, the single domain structure crystal grain is ensured to be obtained, and the adjacent M-type main phase crystal grains in the sintered ferrite are in contact and easy to generate reverse magnetization nucleation, so that the coercive force is still far smaller than the theoretical value.
Disclosure of Invention
In view of the above problems, an object of the present invention is to provide a high coercive force ferrite and a method for preparing the same, in which a ferrite microstructure having a single domain uniform grain and being magnetically isolated is obtained by controlling the particle size distribution, surface state and sintering method of ferrite particles in a molding slurry, and the coercive force of a sintered M-type ferrite is finally improved.
In order to achieve the purpose, the invention is realized by the following technical scheme:
a high coercive force ferrite has a magnet grain size distribution of 1 + -0.2 μ M and a grain having M phase @ SiO2The core-shell structure of (1); intrinsic coercive force HcjGreater than 430kA/m, residual magnetism Br greater than 460mT, and maximum magnetic energy product greater than 41kJ/m3。
A preparation method of high-coercivity ferrite comprises the following steps:
1) preparing materials: according to component A1-x-yCaxLay(Fe12-u-vCou)O19Proportioning and calculating the mass of each raw material to weigh Fe2O3Powder, CaCO3Powder, La2O3Powder, Co2O3Powder, SrCO3Powder and/or BaCO3Powder and mixed. Wherein, A represents at least one of Sr and Ba, x, y, u and v are molar ratio, x is more than or equal to 0.01 and less than or equal to 0.3, y is more than or equal to 0.1 and less than or equal to 0.5, u is more than or equal to 0.1 and less than or equal to 0.3, and v is more than or equal to 0.1 and less than or equal to 0.5
2) Primary ball milling: ball-milling the powder mixture obtained in the step 1) in a ball-milling tank;
3) pre-burning: preserving the heat of the mixture obtained in the step 2) at 1100-;
4) secondary ball milling: ball-milling and drying the pre-sintered material obtained in the step 3) in a ball-milling tank to obtain a dried material;
5) flash burning treatment: putting the dried material obtained in the step 4) into a rapid heating furnace for flash combustion treatment, wherein the heating rate is 20-50 ℃/s, and keeping the temperature to obtain flash combustion treatment powder;
6) refining ball milling and pulping: carrying out ball milling on the flash-burned treatment powder obtained in the step 5) in a ball milling tank, then sequentially adding a grinding aid, a coating agent, a pH regulator and a dispersing agent, and continuing ball milling to obtain slurry, wherein the particle size distribution of ferrite in the slurry is 1 +/-0.3 mu m;
7) wet pressing and forming: precipitating and filtering the slurry obtained in the step 6) until the water content is 20-45%, and forming under a 1.0-1.6T magnetic field to obtain a biscuit;
8) two-stage sintering: sintering the biscuit obtained in the step 7) in a sintering furnace, preserving heat at the temperature of 400 ℃ of 250-.
Preferably, in the step 2), the ratio of the material balls to the water is 1:10:2, and the rotating speed is 100-.
Preferably, in the step 4), the ratio of the material balls to the water is 1:12:2, and the rotating speed is 250-.
Preferably, in the step 6), the ratio of the material balls to the water is 1:10:2, and the rotating speed is 100-.
The invention can effectively narrow the size distribution of crystal grains while obtaining the crystal grains with the granularity less than 1 mu m and reduce the agglomeration of powder and the magnetic interaction among the crystal grains by flash firing treatment, refining ball milling pulping and two-stage sintering process, thereby improving the coercive force of the permanent magnetic ferrite.
Preferably, the grinding aid is one of sodium metaphosphate, sodium hexametaphosphate, polyacrylate, triethanolamine and ethylene glycol, and the addition amount of the grinding aid is 0.1-1% of the weight of the pre-sintering material; the coating agent is ethyl orthosilicate, and the addition amount of the coating agent is 0.5-4% of the weight of the pre-sintering material; the pH regulator is ammonia water, and the addition amount of the pH regulator is 0.3-1.5% of the weight of the pre-sintering material; the dispersing agent is one of calcium gluconate and sorbitol, and the addition amount is 1-2% of the weight of the pre-sintering material; the pH value of the slurry is 5-11.
The M-type permanent magnetic ferrite pre-sintering material obtained by the invention has small particle size and narrow distribution, and the particles are coated with SiO2After coating, the magnetostatic effect among particles is reduced, the agglomeration phenomenon is weakened, and the orientation degree during molding is improved. The grain size of the finally obtained sintered ferrite is lower than the single domain size limit, the grain size is uniform, and the grains are magnetically isolated, so that the coercive force of the M-type ferrite is effectively improved.
Detailed Description
The following description of the preferred embodiments of the present invention is provided for the purpose of illustrating and explaining the features of the present invention, and is not intended to limit the scope of the present invention in any way, since the contents of the present invention will be understood and appreciated by those skilled in the art.
Example 1:
according to the component Sr0.6Ca0.1La0.3(Fe11.7Co0.15)O19Proportioning and calculating the mass of each raw material to weigh Fe2O3Powder, CaCO3Powder, La2O3Powder, Co2O3Powder and SrCO3Powder and mixed. And (3) putting the powder mixture into a ball milling tank, ball milling for 2 hours at a ball milling water ratio of 1:10:2 and a rotating speed of 150 r/min. Keeping the temperature at 1350 ℃ for 2h to obtain a pre-sintered material. And (3) ball-milling the pre-sintered material in a ball-milling tank for 8 hours at a material ball-water ratio of 1:12:2 and a rotating speed of 400r/min, and drying to obtain a dried material. And (3) putting the dried material into a rapid heating furnace for flash combustion treatment, wherein the heating rate is 50 ℃/s, and the heat preservation time is 5min, so as to obtain flash combustion treatment powder. Putting the flash-burned powder into a ball-milling tank, wherein the ball-milling water ratio is 1:10:2, the rotating speed is 100r/min, after ball milling is carried out for 0.5h, sequentially adding 0.1% of sodium metaphosphate, 1.5% of ethyl orthosilicate, 1.2% of ammonia water and 1.2% of calcium gluconate, adjusting the pH value to 8, and then continuing ball milling for 0.5h to obtain slurry, wherein the average particle size of ferrite in the slurry is 0.9 mu m. And precipitating and filtering the slurry to obtain a slurry with the water content of 45%, and forming under a 1.0T magnetic field to obtain a biscuit. And (2) placing the biscuit in a sintering furnace for sintering, preserving heat for 3h at 250 ℃, then heating to 900 ℃ at 1 ℃/min, then rapidly heating to 1100 ℃ at 10 ℃/min, preserving heat for 20min, then heating to 1300 ℃ at 0.8 ℃/min, and preserving heat for 2 h.
The obtained ferrite magnet was tested for magnet grain size d500.8 μm, d900.9 μm; intrinsic coercive force Hcj432kA/m, remanence Br 465mT, maximum magnetic energy product 41.5kJ/m3。
Example 2:
according to the composition Ba0.5Ca0.15La0.35(Fe11.5Co0.2)O19Proportioning and calculating the mass of each raw material to weigh Fe2O3Powder, CaCO3Powder, La2O3Powder, Co2O3Powder and BaCO3Powder and mixed. And (3) putting the powder mixture into a ball milling tank, ball milling for 2 hours at a ball milling water ratio of 1:10:2 and a rotating speed of 200 r/min. Maintaining the temperature at 1300 ℃ for 2.5h to obtain pre-sinteringAnd (5) feeding. And (3) ball-milling the pre-sintered material in a ball-milling tank for 6h at a ball-milling-water ratio of 1:12:2 and a rotating speed of 380r/min, and drying to obtain a dried material. And (3) putting the dried material into a rapid heating furnace for flash combustion treatment, wherein the heating rate is 40 ℃/s, and the heat preservation time is 7min, so as to obtain flash combustion treatment powder. And putting the flash-burned powder into a ball milling tank, wherein the ball-ball water ratio is 1:10:2, the rotating speed is 150r/min, ball milling is carried out for 0.5h, then 0.3% of sodium hexametaphosphate, 2.5% of ethyl orthosilicate, 0.5% of ammonia water and 1% of sorbitol are sequentially added, the PH value is adjusted to 7.5, ball milling is carried out for 1h, and slurry is obtained, wherein the average particle size of ferrite in the slurry is 0.8 mu m. And precipitating and filtering the slurry to obtain a slurry with the water content of 35%, and forming under a 1.3T magnetic field to obtain a biscuit. And (2) sintering the biscuit in a sintering furnace, preserving heat for 2h at 350 ℃, then heating to 900 ℃ at 1 ℃/min, then rapidly heating to 1050 ℃ at 8 ℃/min and preserving heat for 30min, then heating to 1280 ℃ at 1 ℃/min and preserving heat for 2.5 h.
The obtained ferrite magnet was tested for magnet grain size d500.9 μm, d901.0 μm; intrinsic coercive force Hcj438kA/m, residual magnetism Br 467mT, maximum magnetic energy product 41.8kJ/m3。
Example 3:
according to the component Sr0.3Ba0.3Ca0.2La0.2(Fe11.6Co0.1)O19Proportioning and calculating the mass of each raw material to weigh Fe2O3Powder, CaCO3Powder, La2O3Powder, Co2O3Powder, SrCO3Powder and BaCO3Powder and mixed. And (3) putting the powder mixture into a ball milling tank, ball milling for 2 hours at a ball milling water ratio of 1:10:2 and a rotating speed of 150 r/min. And preserving the heat for 4 hours at 1150 ℃ to obtain the pre-sintered material. And (3) ball-milling the pre-sintered material in a ball-milling tank for 5h at a material ball-water ratio of 1:12:2 and a rotating speed of 400r/min, and drying to obtain a dried material. And (3) putting the dried material into a rapid heating furnace for flash combustion treatment, wherein the heating rate is 35 ℃/s, and the heat preservation time is 9min, so as to obtain flash combustion treatment powder. Placing the flash-burned powder in a ball-milling tank at a ball-milling water ratio of 1:10:2 and a rotation speed of 100r/min, and sequentially adding 0.6% polyacrylate, 3.5% ethyl orthosilicate, 0.8% ammonia water and 1.2% sorb after ball milling for 0.5hAdjusting the pH of the sugar alcohol to 9, and continuing ball milling for 1h to obtain slurry, wherein the average particle size of ferrite in the slurry is 1.1 mu m. And precipitating and filtering the slurry to obtain a slurry with the water content of 30%, and forming under a 1.4T magnetic field to obtain a biscuit. And (2) placing the biscuit in a sintering furnace for sintering, preserving heat for 3h at 280 ℃, then heating to 900 ℃ at 1 ℃/min, then rapidly heating to 1000 ℃ at 5 ℃/min and preserving heat for 60min, then heating to 1250 ℃ at 1.5 ℃/min and preserving heat for 3 h.
The obtained ferrite magnet was tested for magnet grain size d500.8 μm, d901.0 μm; intrinsic coercive force Hcj440kA/m, a remanence Br of 470mT and a maximum magnetic energy product of 42.1kJ/m3。
While the preferred embodiments and principles of this invention have been described in detail, it will be apparent to those skilled in the art that variations may be made in the embodiments based on the teachings of the invention and such variations are considered to be within the scope of the invention.

Claims (10)

1. A preparation method of high coercivity ferrite is characterized by comprising the following steps:
1) according to component A1-x-yCaxLay(Fe12-u-vCou)O19Proportioning and calculating the mass of each raw material to weigh Fe2O3Powder, CaCO3Powder, La2O3Powder, Co2O3Powder, SrCO3Powder and/or BaCO3Powder and mixing; wherein A represents at least one of Sr and Ba, x, y, u and v are molar ratios, x is more than or equal to 0.01 and less than or equal to 0.3, y is more than or equal to 0.1 and less than or equal to 0.5, u is more than or equal to 0.1 and less than or equal to 0.3, and v is more than or equal to 0.1 and less than or equal to 0.5;
2) ball-milling the powder mixture obtained in the step 1) in a ball-milling tank;
3) preserving the heat of the mixture obtained in the step 2) at 1100-;
4) ball-milling and drying the pre-sintered material obtained in the step 3) in a ball-milling tank to obtain a dried material;
5) putting the dried material obtained in the step 4) into a rapid heating furnace for flash combustion treatment, wherein the heating rate is 20-50 ℃/s, and keeping the temperature to obtain flash combustion treatment powder;
6) ball-milling the flash-burned treatment powder obtained in the step 5) in a ball-milling tank, sequentially adding a grinding aid, a coating agent, a pH regulator and a dispersing agent after ball-milling, and continuing ball-milling to obtain slurry, wherein the particle size distribution of ferrite in the slurry is 1 +/-0.3 mu m;
7) precipitating and filtering the slurry obtained in the step 6) to obtain a slurry with a water content of 20-45%, and forming the slurry under a 1.0-1.6T magnetic field to obtain a biscuit;
8) sintering the biscuit obtained in the step 7) in a sintering furnace, preserving heat at the temperature of 400 ℃ of 250-.
2. The method of preparing a high coercivity ferrite as claimed in claim 1, wherein: in the step 2), the ratio of the material balls to the water is 1:10:2, and the rotating speed is 100-.
3. The method of preparing a high coercivity ferrite as claimed in claim 1, wherein: in the step 4), the ratio of the material balls to the water is 1:12:2, and the rotating speed is 250-400 r/min.
4. The method of preparing a high coercivity ferrite as claimed in claim 1, wherein: in the step 6), the ratio of the material balls to the water is 1:10:2, and the rotating speed is 100-.
5. A method of preparing a high coercive force ferrite as claimed in any one of claims 1 to 4, wherein: the grinding aid is one of sodium metaphosphate, sodium hexametaphosphate, polyacrylate, triethanolamine and ethylene glycol, and the addition amount of the grinding aid is 0.1-1% of the weight of the pre-sintering material.
6. A method of preparing a high coercive force ferrite as claimed in any one of claims 1 to 4, wherein: the coating agent is ethyl orthosilicate, and the addition amount of the coating agent is 0.5-4% of the weight of the pre-sintering material.
7. A method of preparing a high coercive force ferrite as claimed in any one of claims 1 to 4, wherein: the pH regulator is ammonia water, and the addition amount of the pH regulator is 0.3-1.5% of the weight of the pre-sintering material.
8. A method of preparing a high coercive force ferrite as claimed in any one of claims 1 to 4, wherein: the dispersing agent is one of calcium gluconate and sorbitol, and the addition amount is 1-2% of the weight of the pre-sintering material.
9. A method of preparing a high coercive force ferrite as claimed in any one of claims 1 to 4, wherein: the pH value of the slurry is 5-11.
10. A high coercivity ferrite characterized by: the magnetic body has a grain size distribution of 1 + -0.2 μ M, and the grains have M phase @ SiO2The core-shell structure of (1); intrinsic coercive force HcjGreater than 430kA/m, residual magnetism Br greater than 460mT, and maximum magnetic energy product greater than 41kJ/m3。
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