CN113620700A - Short-process for preparing permanent magnetic ferrite - Google Patents
Short-process for preparing permanent magnetic ferrite Download PDFInfo
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Abstract
A process for preparing a permanent magnetic ferrite by a short process comprises the following steps: according to SrO. nFe2O3，5.6<n<6.1, mixing the ultrapure magnetite concentrate and the strontium carbonate, and then carrying out wet-process mixed grinding and water filtration; drying, granulating and pre-oxidizing the filtered slurry in a first rotary kiln, and then pre-burning in a second rotary kiln; and (3) crushing the pre-sintered materials, adding an additive for secondary proportioning, and then carrying out wet mixing grinding, water filtration, magnetizing, press forming, sintering and grinding processing to obtain the permanent magnetic ferrite. The invention provides a two-section rotary kiln process in the preparation process of the permanent magnetic ferrite, wherein the first rotary kiln is used for drying, granulating and pre-oxidizing a pre-sintered material, and the second rotary kiln is used for completing the pre-sintering reaction, so that the oxidation of the ultrapure magnetite concentrate is closely linked with the solid-phase sintering reaction process of the iron strontium oxideThe links of drying, cooling, pelletizing, strong mixing and chain impediment machine pre-oxidation in the prior art are omitted, so that the production is more efficient and smooth.
Description
Technical Field
The invention belongs to the field of permanent magnetic ferrite material preparation, and particularly relates to a short-process permanent magnetic ferrite preparation process.
Background
The permanent magnetic material is an important component of the magnetic material, and plays an important role in the industries such as the electronic industry, the information industry, motorcycles, electric tools industry, automobile industry and the like. The permanent magnetic ferrite material has the advantages of high comprehensive cost performance and convenient use, and is widely applied to automobile motors, loudspeakers, earphones and various instruments. Compared with an alternating current motor, the direct current motor with the same power can reduce the energy consumption by 30-50%. Under the support and guidance of national policies, the direct current motor must replace a high-energy-consumption alternating current motor in a large scale. The permanent ferrite magnetic shoe is indispensable to a direct current motor, which brings new opportunities for the development of permanent ferrite and also puts higher requirements on the performance of permanent ferrite materials. At present, more than 60 percent of domestic permanent magnetic ferrite products are produced by using iron scale as a raw material to produce middle-low grade ferrite materials, the rest of the domestic permanent magnetic ferrite products are produced by using iron oxide red as a raw material to produce middle-high grade products, and a small amount of high-purity magnetite concentrate (TFe is greater than 71.5 percent and the purity is 99 percent) is used as a raw material to prepare the middle-low grade ferrite materials, and the product performance is equivalent to the FB5 series level. Iron oxide red for producing ferrite materials depends on import, strict control on the imported iron oxide red is increased in the countries in recent years, the productivity level of the iron oxide red in China cannot meet the requirement of the ferrite industry for a while, the price of the iron oxide red continuously rises, and the supply is short. Iron scale is a steel rolling byproduct in iron and steel plants, short steel smelting process is advocated in China, and the iron scale is used as an iron-containing raw material and a coolant to return to a converter and an electric furnace for steelmaking.
High purity magnetite concentrates are limited by the raw material purity (> 0.2% of elemental impurities containing silicon and aluminium) and can only produce medium and low grade ferrite products. Moreover, the existing process for preparing ferrite material by using high-purity magnetite concentrate (TFe > 71.5%) as a raw material is a traditional curdlan rotary kiln process, as shown in fig. 1, the process comprises the steps of drying and pre-oxidizing the raw material, cooling, fine grinding, weighing and batching once, strong mixing, pelletizing and the like, and is long in process and low in production efficiency.
Disclosure of Invention
The technical problem to be solved by the invention is to overcome the defects and shortcomings mentioned in the background technology and provide a short-flow process for preparing the permanent magnetic ferrite.
In order to solve the technical problems, the technical scheme provided by the invention is as follows:
a process for preparing permanent magnetic ferrite in a short process comprises the following steps:
(1) according to the chemical formula SrO. nFe2O3，5.6<n<6.1, carrying out primary batching on the ultrapure magnetite concentrate and the strontium carbonate;
(2) performing wet-process mixed grinding and water filtering on the material obtained in the step (1);
(3) drying, granulating and pre-oxidizing the primary slurry after water filtration in a first rotary kiln, and then pre-burning in a second rotary kiln;
(4) crushing the materials subjected to the pre-sintering in the step (3), and adding calcium carbonate, silicon dioxide, boric acid, aluminum oxide and a dispersing agent for secondary burdening;
(5) and (4) carrying out wet-process mixed grinding, water filtration, magnetizing, compression molding, sintering and grinding on the material obtained in the step (4) to obtain the permanent magnetic ferrite.
Preferably, in the step (1), the moisture of the ultrapure magnetite concentrate is detected on line and fed back to a primary batching system in real time.
Preferably, in the step (3), the slurry enters a first rotary kiln, is heated to 200-500 ℃ for drying, is subjected to heat preservation for 3-4 hours, is heated to 800-900 ℃ for pre-oxidation, is subjected to heat preservation for 2-3 hours, a blast device is arranged at the mouth of the kiln, the oxygen content in the kiln is ensured to be more than 9%, and the material powder rolls in the rotary kiln to be automatically prepared into pellets.
Preferably, in the step (3), the kiln temperature of the second rotary kiln is 1260-1310 ℃, and the oxygen content in the kiln is controlled to be more than 5%.
Preferably, in the step (1), the purity of the ultrapure magnetite concentrate is more than 99.5%, the contents of Si and Al are both lower than 0.1%, the Fisher average particle size of the ultrapure magnetite concentrate is 8-15 micrometers, and the water content is 5-15%; the purity of the strontium carbonate is more than 98%, and the average particle size is 1-2 microns.
In the above process, preferably, in the step (2), the average particle size of the primary slurry after wet mixing and grinding is 1-5 microns; the water content of the filtered primary slurry is 10-20%.
Preferably, in the step (4), the average particle size of the calcium carbonate is 1-2 microns, and the addition amount of the calcium carbonate is 0.2-1.2 wt% of the mass of the sintering powder;
the average particle size of the silicon dioxide is 1-2 microns, and the addition amount of the silicon dioxide is 0.1-0.4 wt% of the mass of the sintering powder;
the boric acid has an average particle size of 1-2 microns, and the addition amount is 0.05-0.55 wt% of the mass of the sintering powder;
the average grain size of the aluminum oxide is 1-2 microns, and the addition amount of the aluminum oxide is 0.05-0.55 wt% of the mass of the sintering powder;
the dispersing agent is calcium gluconate and sorbitol, the addition amount of the calcium gluconate is 0.02-0.50 wt% of the mass of the sintering powder, and the addition amount of the sorbitol is 0.02-0.50 wt% of the mass of the sintering powder.
Preferably, in the step (5), the average particle size of the secondary slurry after wet mixing and grinding is 0.55-1.05 microns, and the water content of the secondary slurry after water filtration is 30-40%.
Preferably, in the step (5), the molding magnetic field for magnetizing and press molding is 6000Gs to 10000Gs, and the molding pressure is 100 kg/cm to 400kg/cm2。
In the above process, preferably, in the step (5), the sintering temperature is 1150-1250 ℃.
Compared with the prior art, the invention has the advantages that:
(1) the invention provides a two-section rotary kiln process in the preparation process of the permanent magnetic ferrite, wherein the first rotary kiln is used for drying, granulating and pre-oxidizing a pre-sintered material, and the second rotary kiln is used for completing the pre-sintering reaction, so that the oxidation of the ultrapure magnetite concentrate is closely linked with the solid-phase sintering reaction process of the iron strontium oxide, and the links of drying, cooling, pelletizing, strong mixing and chain impediment machine pre-oxidation in the prior art are omitted, and the production of the permanent magnetic ferrite is more efficient and smooth; compared with the traditional preparation process of the permanent magnetic ferrite of the high-purity magnetite concentrate, the preparation process of the invention does not add new equipment, but performs the functions of granulation and full oxidation of the ultrapure magnetite concentrate on the basis of the original drying function by adjusting the position of the rotary kiln, thereby realizing the short-flow preparation of the permanent magnetic ferrite.
(2) The method takes the ultrapure magnet concentrate with the purity of more than 99.5 percent as the raw material for preparing the ferrite material, and the ultrapure magnet concentrate does not contain manganese and chlorine impurities which have negative effects on the ferrite material, so that accurate proportioning is facilitated, and the consistency and the stability of the performance of the ferrite product are ensured; meanwhile, the ultrapure magnetite concentrate adopted by the invention can be obtained by a simple ore dressing and purification method from high-quality magnetite concentrate, large magnetite mines in Sichuan, Anhui and inner Mongolia provinces in China can supply a large amount of high-quality magnetite concentrate, the product performance is stable, no waste gas and waste residue is generated in the production process, and the method is green, environment-friendly and economic and sustainable compared with the iron oxide red production process.
(3) The invention adopts the ultrapure magnetite concentrate to prepare the ferrite material, and the expensive transition element Co and rare earth elements Nd, Sm, Pr and the like do not need to be added in the preparation process, so that the process flow is simple and compact, and the production cost is economic and controllable.
(4) The invention provides a method for detecting the water content of ultrapure magnetite concentrate on line, the error value of water content detection can be controlled within 0.5%, the complex procedures of manual sampling, sample setting, assay and the like of the traditional drying method are avoided, the water content of the ultrapure magnetite concentrate is detected in real time and quickly fed back to a primary batching system, and the accurate batching of ferrite pre-sintering materials can be ensured, so that the links of drying and cooling raw materials can be eliminated, the production flow is further simplified, and the production cost is reduced.
(5) The sintered permanent magnetic ferrite material prepared by the invention has the performance reaching TDK FB6 series and above, and has considerable market popularization and application value.
Drawings
FIG. 1 is a flow chart of a prior art process for preparing ferrite material from high purity magnetite concentrate;
FIG. 2 is a process flow chart of the short-flow preparation of permanent magnetic ferrite of the present invention.
Detailed Description
In order to facilitate an understanding of the invention, the invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of the invention is not limited to the specific embodiments below.
Unless otherwise defined, all terms of art used hereinafter have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of the present invention.
Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment and the like used in the present invention are commercially available or can be prepared by existing methods.
Example 1 (this example was carried out in three parallel runs at 1155 ℃, 1160 ℃ and 1165 ℃):
the invention discloses a process for preparing a permanent magnetic ferrite by a short process, which has a flow chart shown in figure 2 and comprises the following steps:
(1) conveying ultrapure magnetite concentrate with the purity of 99.6%, the content of Si impurities of 0.08%, the content of Al impurities of 0.09%, the Fisher average particle size of 9 microns and the water content of 9% into a batching bin by a belt, detecting the water content of the material by a microwave online detection probe, and feeding back the analysis value of the water content of the material to a primary batching system in real time; referring to the water content of the ultrapure magnetite concentrate detected in real time according to the chemical formula SrO.5.85 Fe2O3Adding strontium carbonate with purity of 98% and average grain size of 1.5 micron;
(2) adding water into the material obtained in the step (1) to perform wet mixing grinding, wherein the average particle size of primary slurry after wet mixing grinding is 3 microns, and then filtering water, wherein the water content of the filtered primary slurry is 15%;
(3) drying, granulating and pre-oxidizing the filtered primary slurry in a first rotary kiln, heating the first rotary kiln to 300 ℃ for drying, preserving heat for 3 hours, then heating to 850 ℃ for oxidizing, preserving heat for 2 hours, wherein the oxygen content in the kiln is more than 9%; after falling from the kiln head of a first rotary kiln, small balls with the diameter of 5-8 microns are transferred to the kiln tail of a second rotary kiln through a high-temperature belt, the falling height between the belt and the rotary kiln is less than 0.5m, the highest temperature of the kiln head of the second rotary kiln is 1290 ℃, the oxygen content in the kiln is controlled to be more than 5%, so that solid-phase sintering reaction is fully carried out, the small balls are cooled to room temperature after presintering, and the small balls are crushed to 4mm through a ball mill, so that presintering material powder is obtained;
(4) performing secondary burdening on the pre-sintering material powder, calcium carbonate with the average particle size of 1.5 micrometers, silicon dioxide with the average particle size of 1.0 micrometer, boric acid with the average particle size of 1.2 micrometers, aluminum oxide with the average particle size of 1.5 micrometers, calcium gluconate serving as a dispersant and sorbitol, wherein the addition amount of calcium carbonate is 1.0 wt%, the addition amount of silicon dioxide is 0.2 wt%, the addition amount of boric acid is 0.3 wt%, the addition amount of aluminum oxide is 0.2 wt%, the addition amount of calcium gluconate is 0.05 wt% and the addition amount of sorbitol is 0.05 wt%; finely grinding the secondary ingredients in a roller ball mill (ball: material: water: 15:1:1.5) for 15h, wherein the average particle size of secondary slurry is 0.85 micron, and then standing and filtering to control the water content to be 35%;
(5) wet pressing the secondary slurry after water filtration in 7000Gs magnetic field at 250kg/cm2Pressing under the pressure of the pressure to obtain a magnetic cake with the diameter of 40cm multiplied by the height of 13cm, preserving the temperature of the green body for 3 hours in electric kilns at 1155 ℃, 1160 ℃ and 1165 ℃ respectively in batches, and detecting the magnetic property after grinding, wherein the result is shown in table 1.
TABLE 1 comparison of the magnetic properties of the high performance ferrite material of the present invention with FB6 series products
As can be seen from Table 1, the residual magnetism and the magnetic energy product of the ferrite magnetic cake of the invention are improved along with the increase of the sintering temperature, the intrinsic coercive force and the magnetic induction coercive force are slightly reduced, the squareness ratio of the product is 0.91 or more, and the detection indexes reach the requirements of TDK FB6 series products.
Example 2 (three parallel tests were carried out simultaneously in this example, the maximum temperatures of the kiln head of the second rotary kiln were 1280 ℃, 1290 ℃ and 1300 ℃):
the invention discloses a process for preparing a permanent magnetic ferrite by a short process, which has a flow chart shown in figure 2 and comprises the following steps:
(1) the ultrapure magnetite concentrate with the purity of 99.5 percent, the content of Si impurities of 0.07 percent, the content of Al impurities of 0.08 percent, the Fisher average grain diameter of 10 microns and the water content of 8 percent is conveyed by a beltConveying the materials into a batching bin, checking the water content of the materials by a microwave online detection probe, and feeding back the analyzed value of the water content of the materials to a primary batching system in real time; referring to the water content detected in real time by the ultrapure magnetite concentrate according to the chemical formula SrO.5.95 Fe2O3Adding strontium carbonate with purity of 98% and average grain size of 1.5 micron;
(2) adding water into the material obtained in the step (1) to perform wet mixing grinding, wherein the average particle size of primary slurry after wet mixing grinding is 3 microns, and then filtering water, wherein the water content of the filtered primary slurry is 16%;
(3) drying, granulating and pre-oxidizing the filtered primary slurry in a first rotary kiln, heating the first rotary kiln to 300 ℃ for drying, drying and preserving heat for 2.5 hours, then heating to 850 ℃ for oxidizing, and preserving heat for 2 hours, wherein the oxygen content in the kiln is more than 9%; after falling from the kiln head of the first rotary kiln, small balls with the diameter of 5-8 microns are transferred to the kiln tail of the second rotary kiln through a high-temperature belt, the falling height between the belt and the rotary kiln is less than 0.5m, the maximum temperature of the kiln head of the second rotary kiln is 1280 ℃, 1290 ℃ and 1300 ℃, the oxygen content in the kiln is controlled to be more than 5 percent, so that the solid-phase sintering reaction is fully carried out, the small balls are cooled to the room temperature after presintering, and the small balls are crushed to 4mm through a ball mill to obtain presintering material powder;
(4) performing secondary burdening on the pre-sintering material powder, calcium carbonate with the average particle size of 1.5 micrometers, silicon dioxide with the average particle size of 1.0 micrometer, boric acid with the average particle size of 1.2 micrometers, aluminum oxide with the average particle size of 1.5 micrometers, calcium gluconate serving as a dispersant and sorbitol, wherein the addition amount of calcium carbonate is 1.0 wt%, the addition amount of silicon dioxide is 0.2 wt%, the addition amount of boric acid is 0.3 wt%, the addition amount of aluminum oxide is 0.2 wt%, the addition amount of calcium gluconate is 0.05 wt% and the addition amount of sorbitol is 0.05 wt%; finely grinding the secondary ingredients in a roller ball mill (ball: material: water: 15:1:1.5) for 15h, wherein the average particle size of secondary slurry is 0.85 micron, and then standing and filtering to control the water content to be 35%;
(5) wet pressing the secondary slurry after water filtration in 7000Gs magnetic field at 250kg/cm2Pressing under the pressure of the pressure to obtain a magnetic cake with the diameter of 40cm and the height of 13cm, and keeping the temperature of a green body in an electric kiln at 1160 ℃ for 3hThe magnetic properties were measured after grinding, and the results are shown in Table 2.
TABLE 2 magnetic properties of the high performance ferrite material of this example are compared with FB6 series products
As can be seen from Table 2, the remanence of the ferrite magnetic cake is improved with the increase of the pre-sintering temperature, the intrinsic coercive force and the magnetic induction coercive force are improved and then reduced, the magnetic energy product presents the optimal value at 1290 ℃, the squareness ratio of the product is 0.92 or more, and the detection indexes all meet the requirements of TDK FB6 products.
Example 3:
the invention discloses a process for preparing a permanent magnetic ferrite by a short process, which has a flow chart shown in figure 2 and comprises the following steps:
(1) conveying ultrapure magnetite concentrate with the purity of 99.6 percent, the contents of Si impurities and Al impurities of 0.08 percent, the Fisher average particle size of 10 microns and the water content of 10 percent into a batching bin by a belt, feeding the material back to a primary batching system in real time by a microwave online detection probe, and feeding back the analysis value of the water content of the material; referring to the water content detected by the ultrapure magnetite concentrate in real time according to the chemical formula SrO. nFe2O3Adding strontium carbonate (purity 98%, average grain size 1.5 micron);
(2) adding water into the material obtained in the step (1) to perform wet mixing grinding, wherein the average particle size of primary slurry after wet mixing grinding is 3 microns, and then filtering water, wherein the water content of the filtered primary slurry is 15%;
(3) drying, granulating and pre-oxidizing the filtered primary slurry in a first rotary kiln, heating the first rotary kiln to 400400 ℃, preserving heat for 3 hours, heating to 850 ℃, preserving heat for 2 hours, wherein the oxygen content in the kiln is more than 9%; after falling from the kiln head of a first rotary kiln, small balls with the diameter of 5-8 microns are transferred to the kiln tail of a second rotary kiln through a high-temperature belt, the falling height between the belt and the rotary kiln is less than 0.5m, the highest temperature of the kiln head of the second rotary kiln is 1290 ℃, the oxygen content in the kiln is controlled to be more than 5%, so that solid-phase sintering reaction is fully carried out, the small balls are cooled to room temperature after presintering, and the small balls are crushed to 4mm through a ball mill to obtain presintering material powder;
(4) and (3) mixing the pre-sintering material powder with calcium carbonate with the average particle size of 1.5 microns, silicon dioxide with the average particle size of 1.0 micron, boric acid with the average particle size of 1.2 microns, aluminum oxide with the average particle size of 1.5 microns, calcium gluconate serving as a dispersant and sorbitol for the second time. Wherein the addition amount of calcium carbonate is 1.0 wt%, the addition amount of silicon dioxide is 0.2 wt%, the addition amount of boric acid is 0.3 wt%, the addition amount of aluminum oxide is 0.2 wt%, the addition amount of calcium gluconate is 0.2 wt%, and the addition amount of sorbitol is 0.3 wt%; finely grinding the secondary ingredients in a roller ball mill (ball: material: water: 15:1:1.5) for 15h, wherein the average particle size of secondary slurry is 0.85 micron, and then standing and filtering to control the water content to be 35%;
(5) wet pressing the filtered secondary slurry in 8000Gs magnetic field at 250kg/cm2Pressing under the pressure of the pressure to obtain a magnetic cake with the diameter of 40cm multiplied by the height of 13cm, keeping the temperature of a green body in an electric kiln at 1165 ℃ for 3 hours, and detecting the magnetic property after grinding, wherein the result is shown in Table 3.
Comparative example 1:
the comparative example adopts the existing ferrite preparation process to prepare the permanent magnetic ferrite, the flow chart is shown in figure 1, and the specific process is as follows:
(1) completely drying and partially pre-oxidizing ultrapure magnet concentrate with the purity of 99.6 percent, the contents of Si impurities and Al impurities of 0.08 percent, the Fisher average particle size of 10 micrometers and the water content of 10 percent in a drying kiln, wherein the highest temperature of the drying kiln is 850 ℃, the heat preservation time is 3 hours, cooling the dried material to room temperature in a waterproof way, and then finely grinding the material until the average particle size is 3.5 micrometers;
(2) reference chemical formula SrO.5.95 Fe2O3Adding strontium carbonate with purity of 98% and average particle diameter of 1.5 μm, dry-milling, mixing in a forced mixer, adding 9% water, preparing green pellets with diameter of 8mm in a disc pelletizer, oxidizing and presintering the green pellets in a rotary kiln at 1290 deg.C, controlling oxygen content in the kiln at above 5%, allowing solid-phase sintering reaction to proceed fully, presintering, and mixingCooling the pellets to room temperature, and crushing the pellets to 4mm by using a ball mill to obtain pre-sintered material powder;
(3) then, a permanent magnetic ferrite was prepared according to the same protocol as in step (3) and step (4) in example 3, and the detection properties of the prepared ferrite are shown in Table 3.
TABLE 3 comparison of the conventional ferrite preparation process with the short-flow preparation process of the present invention
As can be seen from Table 3, the short-flow preparation process of the invention is shorter in time consumption than the existing ferrite preparation process, and the product has certain advantages in terms of magnetic coercivity, intrinsic coercivity and magnetic energy product, thereby demonstrating certain innovativeness and value of the short-flow preparation process of the invention.
Claims (10)
1. A process for preparing a permanent magnetic ferrite by a short process is characterized by comprising the following steps:
(1) according to the chemical formula SrO. nFe2O3，5.6<n<6.1, carrying out primary batching on the ultrapure magnetite concentrate and the strontium carbonate;
(2) performing wet-process mixed grinding and water filtering on the material obtained in the step (1);
(3) drying, granulating and pre-oxidizing the primary slurry after water filtration in a first rotary kiln, and then pre-burning in a second rotary kiln;
(4) crushing the materials subjected to the pre-sintering in the step (3), and adding calcium carbonate, silicon dioxide, boric acid, aluminum oxide and a dispersing agent for secondary burdening;
(5) and (4) carrying out wet-process mixed grinding, water filtration, magnetizing, compression molding, sintering and grinding on the material obtained in the step (4) to obtain the permanent magnetic ferrite.
2. The process of claim 1, wherein in step (1), the moisture of the ultrapure magnetite concentrate is detected on-line and fed back to a primary batching system in real time.
3. The process as claimed in claim 1, wherein in the step (3), the slurry enters the first rotary kiln, the temperature is raised to 200-500 ℃ firstly, the temperature is kept for 2-6 h, then the temperature is raised to 800-900 ℃ and the temperature is kept for 1-4 h, and the oxygen content in the kiln is more than 9%.
4. The process as claimed in claim 1, wherein in the step (3), the temperature of the kiln of the second rotary kiln is 1260-1310 ℃, and the oxygen content in the kiln is controlled to be more than 5%.
5. The process according to any one of claims 1 to 4, wherein in the step (1), the purity of the ultrapure magnetite concentrate is more than 99.5%, the Si and Al contents are both lower than 0.1%, the Fisher average particle size of the ultrapure magnetite concentrate is 8-15 microns, and the water content is 5-15%; the purity of the strontium carbonate is more than 98%, and the average particle size is 1-2 microns.
6. The process according to any one of claims 1 to 4, wherein in the step (2), the average particle size of the primary slurry after wet mixing and grinding is 1 to 5 micrometers; the water content of the filtered primary slurry is 10-20%.
7. The process according to any one of claims 1 to 4, wherein in step (4), the calcium carbonate has an average particle size of 1 to 2 μm and is added in an amount of 0.2 to 1.2 wt%;
the average particle size of the silicon dioxide is 1-2 micrometers, and the addition amount of the silicon dioxide is 0.1-0.4 wt%;
the boric acid has an average particle size of 1-2 micrometers, and the addition amount of 0.05-0.55 wt%;
the average grain size of the aluminum oxide is 1-2 micrometers, and the addition amount is 0.05-0.55 wt%;
the dispersing agent is calcium gluconate and sorbitol, the addition amount of the calcium gluconate is 0.02 wt% -0.50 wt%, and the addition amount of the sorbitol is 0.02 wt% -0.50 wt%.
8. The process according to any one of claims 1 to 4, wherein in the step (5), the average particle size of the secondary slurry after wet mixing and grinding is 0.55 to 1.05 microns, and the water content of the secondary slurry after water filtration is 30 to 40 percent.
9. The process according to any one of claims 1 to 4, wherein in the step (5), the molding magnetic field for magnetizing and press molding is 6000Gs to 10000Gs, and the molding pressure is 100 kg/cm to 400kg/cm2。
10. The process according to any one of claims 1 to 4, wherein in the step (5), the sintering temperature is 1150 to 1250 ℃.
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