CN112876231A - Preparation method of permanent magnetic ferrite and permanent magnetic ferrite - Google Patents
Preparation method of permanent magnetic ferrite and permanent magnetic ferrite Download PDFInfo
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Abstract
The invention discloses a preparation method of a permanent magnetic ferrite and the permanent magnetic ferrite, wherein the preparation method comprises the following steps: step (1): weighing and proportioning an iron source, strontium carbonate, a rare earth oxide and a transition metal oxide, and uniformly mixing and grinding the materials to obtain a primary mixed material; step (2): preparing the primary uniformly mixed material into green balls, drying the green balls, and then oxidizing and presintering the green balls to obtain a presintering material; and (3): crushing the pre-sintering material into powder to obtain pre-sintering material powder; and (5): mixing the pre-sintering material powder with calcium carbonate, silicon dioxide, boric acid, kaolin and a dispersing agent, and finely grinding and uniformly mixing to obtain a secondary mixed material; and (6): and (4) pressing and molding the secondary mixed material in a magnetic field, and then roasting to obtain the permanent magnetic ferrite. The preparation method can not only reduce the production cost of the middle and high-end permanent magnetic ferrite, but also effectively ensure and improve the magnetic performance of the magnet.
Description
Technical Field
The invention relates to the technical field of ferrite magnetic material preparation, in particular to a permanent magnetic ferrite preparation method and a permanent magnetic ferrite.
Background
The ferrite permanent magnet material has the advantages of low price, high temperature resistance and corrosion resistance, and has a wide application range, and industries such as electronics, information, electric tools, automobiles, household appliances and the like have wide requirements on the ferrite permanent magnet material. Energy conservation, environmental protection and green development are advocated in the current country, permanent magnet materials are more and more widely applied in new energy, electric vehicles, smart cities, smart earth and other emerging fields, and the market demand is increased at a speed of about 15% every year.
China is a big country for producing permanent magnetic ferrite materials, middle and low-end FB5 series and FB6 series materials prepared by taking iron scale as raw materials account for more than half of the ferrite material market, and middle and high-end magnetic materials of FB9 series and FB12 series prepared by taking iron oxide red as raw materials and mixing a small amount of rare earth elements and transition metal elements only account for a small part of the market share. With the promotion of industrial 4.0 and intelligent manufacturing in China, the domestic market has more and more large demand on medium-high-end permanent magnetic ferrite materials. Therefore, how to effectively solve the contradiction between supply and demand of the middle-high end permanent magnetic ferrite material, namely, how to effectively ensure the excellent magnetic performance of the magnetic material while reducing the production cost of the middle-high end permanent magnetic ferrite material becomes an industry research hotspot.
The pre-sintering material is used as a precursor for producing the ferrite material, and the quality of the pre-sintering material has substantial influence on the quality of a finished ferrite material product. The mainstream production process of the high-performance ferrite material is based on an iron oxide red pre-sintered material, a small amount of rare earth elements and transition metal elements are added in the secondary mixing and fine grinding process, the ferrite material is sintered after magnetizing and compression molding, and a ferrite material finished product is obtained after grinding.
The defects of the mainstream production process of the prior middle-high-end ferrite material are as follows: (1) a small amount of rare earth elements and transition metal elements added in the secondary mixed grinding process are difficult to realize effective dispersion in the mixed grinding process, the energy consumption is increased if the mixed grinding time is too long, and meanwhile, the over grinding can be caused to influence the particle size distribution of slurry, and finally, the magnetic property of a ferrite finished product is reduced; (2) the iron oxide red has high external dependence, and the production cost of the iron oxide red pre-sintering material is high; (3) the grain size distribution of the secondary mixed grinding slurry has important influence on the secondary generation and perfection of ferrite crystals, and the traditional method for controlling the grain size distribution of the slurry by singly controlling the secondary mixed grinding time has the problem of wide grain size distribution of the slurry.
Disclosure of Invention
The invention mainly aims to provide a preparation method of a permanent magnetic ferrite and the permanent magnetic ferrite, so as to at least solve the problems that in the prior art, rare earth elements and transition metal elements are difficult to effectively disperse in the secondary mixed grinding process, the mixed grinding time is long, and the magnetic performance of a product is reduced.
In order to achieve the above object, according to one aspect of the present invention, there is provided a method for preparing a permanent magnetic ferrite, comprising the steps of:
step (1): weighing and proportioning an iron source, strontium carbonate, a rare earth oxide and a transition metal oxide, and uniformly mixing and grinding the materials to obtain a primary mixed material;
step (2): preparing the primary uniformly mixed material into green balls, drying the green balls, and then oxidizing and presintering the green balls to obtain a presintering material;
and (3): crushing the pre-sintering material into powder to obtain pre-sintering material powder;
and (5): mixing the pre-sintering material powder with calcium carbonate, silicon dioxide, boric acid, kaolin and a dispersing agent, and finely grinding and uniformly mixing to obtain a secondary mixed material;
and (6): and (4) pressing and molding the secondary mixed material in a magnetic field, and then roasting to obtain the permanent magnetic ferrite.
In the traditional preparation process of the permanent magnetic ferrite, rare earth elements and transition metal elements are used as secondary additives and are mixed and ground with pre-sintering materials in secondary mixing ingredients. Because the strontium ferrite crystal is formed in the pre-sintering process, rare earth elements and transition metal elements are difficult to completely enter strontium ferrite crystal lattices to be subjected to atomic substitution with strontium and iron, and part of the rare earth elements and the transition metal elements can be retained at crystal boundaries, so that high-valence element loss in a certain proportion is caused, and the production cost is increased. Rare earth elements and transition metal elements are difficult to effectively disperse in the secondary mixing and grinding process, so that the mixing and grinding time is too long, the energy consumption is increased, meanwhile, the over-grinding can be caused to influence the particle size distribution of slurry, and finally, the magnetic property of a ferrite finished product is reduced.
According to the invention, the rare earth element and the transition metal element are added in the production of the pre-sintered material (during primary mixing and batching), so that the rare earth element and the transition metal element are replaced while the ferrite crystal is formed, and the expensive rare earth element and the transition metal element can more easily enter the ferrite crystal lattice, thereby being beneficial to improving the utilization rate of the expensive rare earth element and the expensive transition metal element, shortening the secondary mixing and grinding time, improving the magnetic performance of the ferrite product, reducing the energy consumption and reducing the production cost.
Further, in the step (1), the iron source, strontium carbonate, rare earth oxide and transition metal oxide are weighed and mixedSpecifically, the method comprises the following steps: converting the ratio of Sr, R, Fe and T in the chemical structural formula of the permanent magnetic ferrite to the mass ratio of the corresponding raw materials; wherein R represents rare earth elements, the rare earth oxide is one or more of oxides of La, Pr, Dy, Tb and Ce, T represents transition metal elements, and the transition metal oxide is one or more of oxides of Co, Ni and Cr. For example according to the formula Sr1-XRXO·6(Fe2-YTYO3) The strontium carbonate, the rare earth oxide, the iron source and the transition metal oxide are weighed and proportioned according to the proportion of the elements of Sr, R, Fe and T, wherein the value range of X is 0.03-0.5%, and the value range of Y is 0.005-0.05%.
Further, the iron source is the ultra-pure magnet fine powder, the total iron grade of the ultra-pure magnet fine powder is more than 72%, the purity of the ultra-pure magnet fine powder is more than 99.5%, and the mass fraction of silicon dioxide in the ultra-pure magnet fine powder is less than 0.3%; the ultra-pure magnet fine powder is obtained by mineral separation and purification of iron concentrate, or is obtained by further mineral separation and purification of commercially available magnet fine powder, and the particle size of the ultra-pure magnet fine powder after mixed grinding is less than 3 mu m, preferably 1 to 2 mu m.
The existing middle-high end permanent magnetic ferrite usually takes iron oxide red as an iron source, and has the problems of high dependence of the iron oxide red on the outside and high production cost of an iron oxide red pre-sintering material. The invention adopts the ultra-pure magnet fine powder as the raw material, and the cost of the ultra-pure magnet fine powder product obtained by deep processing, mineral separation and purification of the iron fine powder is lower than that of the iron oxide red, thereby reducing the cost of the raw material end for processing and preparing the ferrite material.
Further, after the step (3) is completed and before the step (5) is started, the preparation method further comprises the following steps:
and (4): sieving the pre-sintering material powder, wherein the diameter of a mesh of a screen mesh is 2-4 mu m, feeding the pre-sintering material on the screen into a crushing cycle, and feeding the pre-sintering material under the screen into secondary mixing and proportioning.
The grain size distribution of the secondary uniform mixing slurry has important influence on the secondary generation and perfection of ferrite crystals. In the traditional process, the slurry particle size distribution is controlled by singly controlling the secondary mixing and grinding time in the secondary mixing and grinding process, the method not only ensures that the secondary mixing and grinding time is overlong, but also has the problem of wider slurry particle size distribution, thus causing higher production energy consumption, low densification degree of the sintered magnet and reduced magnetic performance.
According to the invention, the pre-sintering material powder is sieved before secondary mixing and proportioning, the pre-sintering material on the sieve is sent to a crushing cycle, the pre-sintering material under the sieve is sent to secondary mixing and proportioning, the pre-sintering material is sieved after fine grinding for particle size control, the secondary mixing and grinding time is greatly shortened, the production energy consumption is reduced, and meanwhile, the particle size distribution of secondary mixing slurry can be effectively controlled, so that the densification degree of a magnet obtained by sintering is higher, and the magnetic performance is more excellent.
Further, in the step (1), the average grain diameters of the strontium carbonate, the rare earth oxide and the transition metal oxide after mixed grinding are all 1-2 μm, and the mass fractions of the rare earth oxide and the transition metal oxide in the primary mixed material are both 0.05-0.10%; the mixing and grinding are wet ball milling and mixing, and the ball milling time is 2-4 h.
Further, in the step (2), the primary uniformly mixed material is prepared into green balls, which specifically means: the primary mixed material is made into raw balls with the diameter of 8mm to 10mm by a disc pelletizer and water with the mass percent of 8 percent to 10 percent, and the density of the raw balls is 1.112g/cm3～1.212g/cm3。
Further, in the step (2), the drying operation specifically means: drying and preheating the green pellets in a chain grate machine, wherein the preheating temperature is preferably 100-150 ℃, and the preheating time is preferably 20-30 min.
Further, in the step (2), the pre-firing operation specifically includes: putting the dried green pellets into a rotary kiln of a chain grate machine, and pre-oxidizing for 0.5 h-1 h at the temperature of 850-900 ℃ in air atmosphere to ensure that Fe in the materials3O4Fully oxidized into Fe2O3Then roasting at 1260-1280 ℃ for 2-3 h to obtain the strontium ferrite pre-sintered material.
Further, in the step (6), the roasting temperature is 1160-1180 ℃, and the roasting time is 1-2 hours, so that the high-temperature liquid phase reaction is fully performed; the molding magnetic field intensity in the magnetic field compression molding is 8000 Gs-10000 Gs.
Further, in the step (5), the average particle size of the calcium carbonate is 2 to 3 μm, and the average particle sizes of the silicon dioxide, the boric acid and the kaolin are all 1 to 2 μm; the mass fraction of the calcium carbonate in the secondary mixing material is 0.1-0.5%, and the mass fractions of the silicon dioxide, the boric acid and the kaolin in the secondary mixing material are all 0.05-0.10%; the dispersant is calcium gluconate and sorbitol, and the mass fractions of the calcium gluconate and the sorbitol in the secondary mixing material are both 0.025-0.05%.
According to another aspect of the present invention, there is provided a permanent magnetic ferrite prepared by the above preparation method.
Compared with the prior art, the invention has the beneficial effects that:
(1) according to the invention, rare earth elements and transition metal oxides are added in a primary mixing and blending process, and expensive rare earth elements and transition metal elements are added in a pre-sintering material preparation process, so that the rare earth elements and the transition metal elements can enter ferrite crystal lattices in the strontium ferrite crystal forming process, the utilization rate of the rare earth elements and the transition metal elements is improved, and the production cost of the ferrite material is reduced.
(2) According to the invention, rare earth elements and transition metal oxides are added in the primary mixing and blending process, so that the rare earth elements and the transition metal elements can more easily enter ferrite lattices, the secondary mixing and milling time can be shortened, the energy consumption of the secondary mixing and milling is reduced, the particle size distribution of the secondary mixing and milling slurry is improved, and the magnetic performance of ferrite finished products is improved.
(3) The invention takes the ultra-pure magnet fine powder as the raw material, and the cost of the ultra-pure magnet fine powder product obtained by deep processing, mineral separation and purification of the iron fine powder is lower than that of the iron oxide red, thereby reducing the cost of the raw material end for processing and preparing the ferrite material.
(4) According to the invention, the pre-sintering material powder is sieved after the pre-sintering material is crushed to prepare powder, the pre-sintering material on the sieve enters a crushing cycle, and the pre-sintering material under the sieve enters secondary ingredients to be uniformly mixed, so that the secondary mixing and grinding time is greatly shortened, the particle size distribution of the secondary mixed and homogenized material can be effectively controlled while the energy consumption is reduced, the densification degree of a magnet obtained by sintering is improved, and the magnetic performance of the product is more excellent.
(5) The invention can also reduce the addition of the dispersing agent in the secondary blending process, thereby greatly reducing the formation of micro-cracks on the surface of the magnet caused by carbon dioxide and water vapor generated by the decomposition of the dispersing agent.
Detailed Description
In order to facilitate an understanding of the present invention, the present invention will be described more fully and in detail with reference to the preferred embodiments, but the scope of the present invention is not limited to the specific embodiments described 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.
The iron source used in the following examples of the present invention was ultra-pure fine magnet powder, which was purified by reverse flotation. The reverse flotation adopts cationic collector dodecylamine and inhibitor caustic starch. The total iron grade of the ultra-pure magnet fine powder product is more than 72 percent, the purity of the ultra-pure magnet fine powder product reaches more than 99.7 percent, and the content of silicon dioxide is less than 0.2 percent.
Example 1:
the preparation method of the permanent magnetic ferrite provided by the embodiment of the invention comprises the following steps:
(1) one-time mixing material
According to the chemical formula Sr of the permanent magnetic ferrite material0.92R0.08O·6(Fe1.99T0.01O3) The molar ratio of the elements of Sr, R, Fe and T is converted into the mass of strontium carbonate, rare earth oxide, super-pure magnet fine powder and transition metal oxide, and the materials are weighed and mixed. Wherein the average particle of the ultra-pure fine magnet powder, strontium carbonate, praseodymium oxide and cobalt oxideThe diameter is 1-2 μm. And (3) putting the raw materials into a wet ball mill for mixing and grinding for 2 hours to obtain a primary mixed material.
(2) Pelletizing
Mixing the primary uniformly mixed material with 8 percent of water by mass, preparing raw balls with the diameter of 8-10 mm by using a disc pelletizer, wherein the density of the raw balls is 1.182g/cm3。
(3) Pre-firing
Placing the green ball into a chain grate machine, drying and preheating at about 100 ℃ for 20min in air atmosphere, and then pre-oxidizing at about 850 ℃ for 30 min; then roasting in a rotary kiln for 120min (the highest temperature in the kiln is 1260 ℃), thereby preparing the ferrite pre-sintered material.
(4) Crushing and pulverizing
And further crushing the pre-sintered material by adopting a ball mill to prepare powder, sieving the pre-sintered material powder, performing closed cycle by using a sieve plate with the diameter of 2 mu m (the diameter of a sieve mesh is 2 mu m), feeding the pre-sintered material on the sieve into crushing cycle, and feeding the pre-sintered material under the sieve into secondary mixing and batching.
(5) Secondary mixing material
The pre-sintered material below 2 mu m under the sieve is matched with calcium carbonate (0.2 wt%, average grain diameter is 2 mu m-3 mu m), silicon dioxide (0.05 wt%, average grain diameter is 1 mu m-2 mu m), boric acid (0.05 wt%, average grain diameter is 1 mu m-2 mu m), kaolin (0.05 wt%, average grain diameter is 1 mu m-2 mu m), a small amount of dispersant calcium gluconate (0.025 wt%) and sorbitol (0.025 wt%), and the pre-sintered material is fully and finely ground and uniformly mixed to obtain secondary uniform material.
(6) Magnetizing and pressing for forming
And standing the secondary uniform slurry, filtering out the dispersing agent, and performing magnetic field wet-pressing molding to obtain a preset shape, wherein the molding magnetic field intensity of the magnetic field wet-pressing molding is 8000 Gs.
(7) Roasting
And roasting the formed material for 1.5 hours at 1160 ℃ in the air atmosphere to obtain the sintered magnet.
And grinding the surface of the sintered magnet until the surface is smooth and burr-free, and then detecting the magnetic property of the prepared ferrite material by using a magnetic property tester.
Magnetic properties of ferrite materials prepared from ultrapure magnet fine powder, praseodymium oxide and cobalt oxide were added to the primary and secondary mixing ingredients, respectively, and compared (the preparation process and conditions of the two magnetic materials are as in example 1), and the results are shown in table 1.
TABLE 1 comparison of magnetic properties of ferrite materials prepared by adding rare earth elements and transition metal elements in primary blending ingredients and secondary blending ingredients, respectively
As can be seen from table 1, compared with the magnetic properties of the magnet prepared by adding praseodymium oxide and cobalt oxide during the primary mixing, the properties of the magnet prepared by adding praseodymium oxide and cobalt oxide during the secondary mixing are respectively improved by 1.0%, 0.4%, 1.7% and 4.8% in terms of remanence, intrinsic coercivity, magnetic induction coercivity and magnetic energy product, and the radial shrinkage ratio is basically unchanged. Therefore, the method for adding praseodymium oxide and cobalt oxide during primary mixing and proportioning is beneficial to improving the magnetic property of the ferrite material.
Example 2:
the preparation method of the permanent magnetic ferrite provided by the embodiment of the invention comprises the following steps:
(1) one-time mixing material
According to the chemical formula Sr of the permanent magnetic ferrite material0.82R0.18O·6(Fe1.98T0.02O3) The molar ratio of the elements of Sr, R, Fe and T is converted into the mass of strontium carbonate, rare earth oxide, super-pure magnet fine powder and transition metal oxide, and the materials are weighed and mixed. Wherein the average grain sizes of the ultra-pure magnet fine powder, the strontium carbonate, the praseodymium oxide and the cobalt oxide are all 1-2 mu m. And (3) putting the raw materials into a wet ball mill for mixing and grinding for 2 hours to obtain a primary mixed material.
(2) Pelletizing
Mixing the primary uniformly-mixed material with 8% of water by mass, and preparing raw balls with the diameter of 8-10 mm by using a disc pelletizer, wherein the density of the raw balls is 1.186g/cm3。
(3) Pre-firing
Placing the green ball into a chain grate machine, drying and preheating at about 100 ℃ for 20min in air atmosphere, and then pre-oxidizing at about 850 ℃ for 30 min; then roasting in a rotary kiln for 120min (the highest temperature in the kiln is 1260 ℃), thereby preparing the ferrite pre-sintered material.
(4) Crushing and pulverizing
And further crushing the pre-sintered material by adopting a ball mill to prepare powder, sieving the pre-sintered material powder, performing closed circulation by using a sieve plate with the diameter of 2 mu m, feeding the pre-sintered material on the sieve into crushing circulation, and feeding the pre-sintered material below the sieve into secondary mixing and proportioning.
(5) Secondary mixing material
The pre-sintered material below 2 mu m under the sieve is matched with calcium carbonate (0.2 wt%, average grain diameter is 2 mu m-3 mu m), silicon dioxide (0.05 wt%, average grain diameter is 1 mu m-2 mu m), boric acid (0.05 wt%, average grain diameter is 1 mu m-2 mu m), kaolin (0.05 wt%, average grain diameter is 1 mu m-2 mu m), a small amount of dispersant calcium gluconate (0.025 wt%) and sorbitol (0.025 wt%), and the pre-sintered material is fully and finely ground and uniformly mixed to obtain secondary uniform material.
(6) Magnetizing and pressing for forming
And standing the secondary uniform slurry, filtering out the dispersing agent, and performing magnetic field wet-pressing molding to obtain a predetermined shape, wherein the molding magnetic field intensity of the magnetic field wet-pressing molding is 9000 Gs.
(7) Roasting
And roasting the formed material for 1h at 1180 ℃ in an air atmosphere to obtain the sintered magnet.
And grinding the surface of the sintered magnet until the surface is smooth and burr-free, and then detecting the magnetic property of the prepared ferrite material by using a magnetic property tester.
The magnetic properties of the prepared magnetic materials were compared by adding terbium oxide and nickel oxide to the ferrite material prepared from the ultrapure magnet fine powder as a raw material in the first blending batch and in the second blending batch, respectively (the preparation processes and conditions of the two magnetic materials were as in example 2), and the results are shown in table 2.
TABLE 2 comparison of magnetic properties of ferrite materials prepared by adding rare earth elements and transition metal elements in the primary blending ingredients and the secondary blending ingredients, respectively
As can be seen from table 2, compared with the magnetic properties of the magnet prepared by adding terbium oxide and nickel oxide during the primary mixing, the properties of the magnet prepared by adding terbium oxide and nickel oxide during the secondary mixing are respectively improved by 1.0%, 0.8%, 1.5% and 4.7% in terms of remanence, intrinsic coercivity, magnetic induction coercivity and magnetic energy product, and the radial shrinkage ratio is basically unchanged. Therefore, the method for adding terbium oxide and nickel oxide during the primary mixing and proportioning is beneficial to improving the magnetic property of the ferrite material.
Example 3:
the preparation method of the permanent magnetic ferrite provided by the embodiment of the invention comprises the following steps:
(1) one-time mixing material
According to the chemical formula Sr of the permanent magnetic ferrite material0.7R0.3O·6(Fe1.975T0.025O3) The molar ratio of the elements of Sr, R, Fe and T is converted into the mass of strontium carbonate, rare earth oxide, super-pure magnet fine powder and transition metal oxide, and the materials are weighed and mixed. Wherein the average grain sizes of the ultra-pure magnet fine powder, the strontium carbonate, the praseodymium oxide and the cobalt oxide are all 1-2 mu m. And (3) putting the raw materials into a wet ball mill for mixing and grinding for 2 hours to obtain a primary mixed material.
(2) Pelletizing
Mixing the primary mixed material with 8 percent of water by mass percent, and preparing the mixture into green pellets with the diameter of 8-10 mm by using a disc pelletizer, wherein the density of the green pellets is 1.178g/cm3。
(3) Pre-firing
Placing the green ball into a chain grate machine, drying and preheating at about 100 ℃ for 20min in air atmosphere, and then pre-oxidizing at about 850 ℃ for 30 min; then roasting in a rotary kiln for 120min (the highest temperature in the kiln is 1260 ℃), thereby preparing the ferrite pre-sintered material.
(4) Crushing and pulverizing
And further crushing the pre-sintered material by adopting a ball mill to prepare powder, sieving the pre-sintered material powder, performing closed cycle by using a sieve plate with the diameter of 2 mu m (the diameter of a sieve mesh is 2 mu m), feeding the pre-sintered material on the sieve into crushing cycle, and feeding the pre-sintered material under the sieve into secondary mixing and batching.
(5) Secondary mixing material
The pre-sintered material below 2 mu m under the sieve is matched with calcium carbonate (0.2 wt%, average grain diameter is 2 mu m-3 mu m), silicon dioxide (0.05 wt%, average grain diameter is 1 mu m-2 mu m), boric acid (0.05 wt%, average grain diameter is 1 mu m-2 mu m), kaolin (0.05 wt%, average grain diameter is 1 mu m-2 mu m), a small amount of dispersant calcium gluconate (0.025 wt%) and sorbitol (0.025 wt%), and the pre-sintered material is fully and finely ground and uniformly mixed to obtain secondary uniform material.
(6) Magnetizing and pressing for forming
And standing the secondary uniform slurry, filtering out the dispersing agent, and performing magnetic field wet pressing to obtain a predetermined shape, wherein the magnetic field intensity of the formed magnetic field wet pressing is 10000 Gs.
(7) Roasting
And roasting the formed material for 2 hours at 1170 ℃ in an air atmosphere to obtain the sintered magnet.
And grinding the surface of the sintered magnet until the surface is smooth and burr-free, and then detecting the magnetic property of the prepared ferrite material by using a magnetic property tester.
The magnetic properties of the ferrite material prepared from the ultra-pure fine magnet powder, cerium oxide and chromium oxide were compared by adding the materials in the first blending and the second blending (the preparation process and conditions of the two magnetic materials are as in example 3), and the results are shown in table 3.
TABLE 3 comparison of magnetic properties of ferrite materials prepared by adding rare earth elements and transition metal elements in the primary blending ingredients and the secondary blending ingredients, respectively
As can be seen from table 3, compared with the magnetic properties of the magnet prepared by adding cerium oxide and chromium oxide during the primary mixing, the properties of the magnet prepared by adding cerium oxide and chromium oxide during the secondary mixing are respectively improved by 1.3%, 0.9%, 1.3% and 4.9% in terms of remanence, intrinsic coercivity, magnetic induction coercivity and magnetic energy product, and the radial shrinkage ratio is basically unchanged. Therefore, the method for adding cerium oxide and chromium oxide during primary mixing is beneficial to improving the magnetic property of the ferrite material.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. The preparation method of the permanent magnetic ferrite is characterized by comprising the following steps of:
step (1): weighing and proportioning an iron source, strontium carbonate, a rare earth oxide and a transition metal oxide, and uniformly mixing and grinding the materials to obtain a primary mixed material;
step (2): preparing the primary uniformly mixed material into green balls, drying the green balls, and then oxidizing and presintering the green balls to obtain a presintering material;
and (3): crushing the pre-sintering material into powder to obtain pre-sintering material powder;
and (5): mixing the pre-sintering material powder with calcium carbonate, silicon dioxide, boric acid, kaolin and a dispersing agent, and finely grinding and uniformly mixing to obtain a secondary mixed material;
and (6): and (4) pressing and molding the secondary mixed material in a magnetic field, and then roasting to obtain the permanent magnetic ferrite.
2. The method for preparing a permanent magnetic ferrite according to claim 1, wherein in the step (1), the iron source, the strontium carbonate, the rare earth oxide and the transition metal oxide are weighed and proportioned, specifically:
converting the proportions of Sr, R, Fe and T in the chemical structural formula of the permanent magnetic ferrite to corresponding raw material mass proportions according to the required proportion, and respectively weighing and proportioning strontium carbonate, rare earth oxide, iron source and transition metal oxide; wherein R represents rare earth elements, the rare earth oxide is one or more of oxides of La, Pr, Dy, Tb and Ce, T represents transition metal elements, and the transition metal oxide is one or more of oxides of Co, Ni and Cr.
3. The method for preparing a permanent magnetic ferrite according to claim 1, wherein the iron source is ultra-pure magnet fine powder, the total iron grade of the ultra-pure magnet fine powder is 72% or more, the purity of the ultra-pure magnet fine powder is 99.5% or more, and the mass fraction of silicon dioxide in the ultra-pure magnet fine powder is 0.3% or less; the ultra-pure magnet fine powder is obtained by mineral separation and purification of iron concentrate, or is obtained by further mineral separation and purification of commercially available magnet fine powder, and the particle size of the ultra-pure magnet fine powder after mixed grinding is less than 3 mu m.
4. The method for preparing a permanent magnetic ferrite according to claim 1, wherein after the completion of the step (3) and before the start of the step (5), the method further comprises:
and (4): sieving the pre-sintering material powder, wherein the diameter of a mesh of a screen mesh is 2-4 mu m, feeding the pre-sintering material on the screen into a crushing cycle, and feeding the pre-sintering material under the screen into secondary mixing and proportioning.
5. The preparation method of the permanent magnetic ferrite according to any one of claims 1 to 4, characterized in that in the step (1), the average particle diameters of the strontium carbonate, the rare earth oxide and the transition metal oxide after mixed grinding are all 1 μm to 2 μm, and the mass fractions of the rare earth oxide and the transition metal oxide in the primary mixed material are both 0.05% to 0.10%; the mixing and grinding are wet ball milling and mixing, and the ball milling time is 2-4 h.
6. The preparation method of the permanent magnetic ferrite according to any one of claims 1 to 4, characterized in that in the step (2), the primary mixed material is prepared into a green ball, specifically: the primary mixed material passes through a disc pelletizer to be matched with 8 to 10 mass percent of water to prepare the productPreparing green balls with the diameter of 8 mm-10 mm and the density of 1.112g/cm3～1.212g/cm3。
7. The method for preparing a permanent magnetic ferrite according to any one of claims 1 to 4, wherein in the step (2), the pre-sintering operation specifically comprises: putting the dried green pellets into a rotary kiln of a chain grate machine, pre-oxidizing for 0.5 h-1 h at 850-900 ℃ in air atmosphere, and then roasting at 1260-1280 ℃ for 2 h-3 h.
8. The method for preparing a permanent magnetic ferrite according to any one of claims 1 to 4, wherein in the step (6), the calcination temperature is 1160 ℃ to 1180 ℃, the calcination time is 1h to 2h, and the molding magnetic field strength in the magnetic field compression molding is 8000Gs to 10000 Gs.
9. The method for preparing a permanent magnetic ferrite according to any one of claims 1 to 4, wherein in the step (5), the average particle size of calcium carbonate is 2 μm to 3 μm, and the average particle sizes of silica, boric acid and kaolin are all 1 μm to 2 μm; the mass fraction of the calcium carbonate in the secondary mixing material is 0.1-0.5%, and the mass fractions of the silicon dioxide, the boric acid and the kaolin in the secondary mixing material are all 0.05-0.10%; the dispersant is calcium gluconate and sorbitol, and the mass fractions of the calcium gluconate and the sorbitol in the secondary mixing material are both 0.025-0.05%.
10. The permanent magnetic ferrite prepared by the preparation method according to any one of claims 1 to 9.
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