High intrinsic coercive force permanent magnetic ferrite and preparation method and application thereof

Abstract

The invention discloses a high intrinsic coercive force permanent magnetic ferrite and a preparation method and application thereof, and belongs to the technical field of permanent magnetic ferrites.The cerium and manganese are introduced in a limited range to partially replace lanthanum and cobalt oxides, Ce can form Ce < 4 + > and Ce < 3 + > more easily, charge offset of Fe < 2 + > and Fe < 3 + > can be compensated, meanwhile, Ce can inhibit overgrowth of crystal grains, Mn adjusts magnetic domain distribution, and therefore the permanent magnetic ferrite with the high intrinsic coercive force can be obtained. The sintering temperature is reduced and ferrite compactness is promoted. In the process of preparing the ferrite, the green body is sintered in a staged gradient heating and cooling mode, through cooling sintering after first heating, overgrowth of crystal grains at a high temperature is inhibited, the crystal grains grow to a reasonable size, and the number of crystal boundaries is controlled, so that magnetic domain migration is hindered, and meanwhile, excessive precipitation of a non-magnetic phase at the crystal boundaries is inhibited; the ferrite can be uniformly heated through rapid cooling, and the uniformity of the grain size is ensured.

Description

Technical Field

[0001] This invention belongs to the field of permanent magnet ferrite technology, and particularly relates to a high intrinsic coercivity permanent magnet ferrite, its preparation method and application. Technical Background

[0002] Ferrite magnets are permanent magnets primarily made from SrO, BaO, or Fe2O3. Besides their strong resistance to demagnetization, these magnetic materials are also cost-effective. In recent years, with industrial development and increasing demands for miniaturization, lightweighting, thinning, and energy conservation in permanent magnets, there is a growing demand for higher performance in permanent magnet ferrite materials. M-type permanent magnet ferrites belong to the hexagonal crystal system. Due to their high uniaxial magnetocrystalline anisotropy, excellent cost-effectiveness, high Curie temperature, and chemical stability, they are widely used as important permanent magnet and magnetic recording materials in various fields such as home appliances, computers, automobiles, and communications. Exploring and developing high-performance permanent magnet ferrite materials and their preparation technologies is of significant innovative importance for improving the structural composition of current high-end ferrite products and has always been a key focus in the field of magnetic materials research.

[0003] In existing technologies, to improve the magnetic properties of permanent magnet ferrites, breakthroughs are typically achieved through elemental doping modification, controlling the particle size of raw materials, and high-temperature sintering processes, aiming to obtain permanent magnet materials with superior intrinsic coercivity. For example, Chinese patent CN 104446418 A discloses a method for improving the remanence and intrinsic coercivity of permanent magnet ferrites. This involves adding calcium carbonate and calcium chloride to pre-calcined powder, ball milling it to an average particle size below 0.95 μm, obtaining a slurry, pressing it into shape, and sintering it at 1100-1200℃ to obtain permanent magnet ferrites. Calcium carbonate and sodium chloride are used to enhance intrinsic coercivity. For instance, Chinese patent CN 103896571 A discloses a high-energy permanent magnet ferrite material that improves magnetic properties by incorporating iron oxide, lanthanum oxide, silicon dioxide, barium oxide, cobalt oxide, etc., and through pre-calcination, crushing, blanking, and sintering. However, excessive introduction of lanthanum can easily generate lattice defects such as vacancies and dislocations; while Co... 3+ The anisotropy is lower than that of Fe 3+ Doping reduces overall anisotropy, leading to a decrease in its Hcj. Furthermore, cobalt oxide is too expensive and is a strategic metal, making it uneconomical.

[0004] Therefore, how to combine elemental doping modification with high-temperature sintering process to synergistically improve the magnetic properties of ferrite materials by incorporating modifying substances has become a problem that needs to be solved. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a high intrinsic coercivity permanent magnet ferrite, its preparation method and application, so as to solve the problems mentioned in the background art or achieve better technical effects.

[0006] To solve the above-mentioned technical problems, the inventors, through practice and summarization, derived the technical solution of this invention. This invention discloses a high intrinsic coercivity permanent magnet ferrite, the composition of which, by weight percentage, is as follows: 92-98% pre-calcined material, 0.2-1.5% lanthanum oxide, 0.1-0.3% strontium carbonate, 0.05-0.2% cerium oxide, 0.01-0.15% manganese oxide, 0.05-0.5% cobalt oxide, 0.12-0.28% aluminum oxide, 0.02-0.3% boric acid, and 0.05-0.3% nano-silica.

[0007] The purity of the lanthanum oxide is ≥99.3%, the purity of the strontium carbonate is ≥99.5%, the purity of the cerium oxide is ≥99.9%, the purity of the manganese oxide is ≥99.5%, the purity of the cobalt oxide is ≥99.9%, the purity of the aluminum oxide is ≥99%, the purity of the boric acid is ≥99%, and the purity of the nano-silica is ≥99.5%.

[0008] Furthermore, the composition of each component by weight percentage is as follows: 97.82% pre-fired material, 0.8% lanthanum oxide, 0.2% strontium carbonate, 0.2% cerium oxide, 0.1% manganese oxide, 0.35% cobalt oxide, 0.18% aluminum oxide, 0.15% boric acid, and 0.20% nano-silica.

[0009] Furthermore, the pre-fired material is a series 9 pre-fired material, with a composition including 85%~88% Fe2O3; 1.5%~1.8% SrCO3; 2.5%~3.8% CaCO3; 4.5%~6.0% La2O3; 1.8%~2.5% Co2O3 and 0.3%~0.5% H3BO3; and is prepared by mixing, pre-firing and crushing processes.

[0010] Furthermore, the preparation method of any of the above-mentioned high intrinsic coercivity permanent magnet ferrites includes the following steps:

[0011] S1: First, put lanthanum oxide and strontium oxide into a sand mill and mill them at 400~600 r / min for 20~35 min to obtain auxiliary material A;

[0012] S2: Cerium oxide and manganese oxide are placed in a sand mill and milled at 400~600 r / min for 1.5~2 h to obtain auxiliary material B;

[0013] S3: The pre-burned material, cobalt oxide, alumina and boric acid are put into a ball mill and ball-milled to obtain a mixed powder with a particle size of 0.8~1.0μm;

[0014] S4: Mix and stir the auxiliary material A in S1, the auxiliary material B in S2, and the mixed powder in S3. After stirring evenly, press and shape the mixture at 13~16MPa to obtain a green body.

[0015] S5: The green body is placed in the pusher kiln and sintered in stages with gradient heating and cooling to obtain high intrinsic coercivity permanent magnet ferrite.

[0016] Furthermore, in S1, the particle size of excipient A is 0.6~0.8μm.

[0017] Furthermore, in S2, the particle size of excipient B is 0.6~0.8μm.

[0018] Furthermore, in S5, the staged gradient heating and cooling sintering procedure is as follows: first, heat to 1200~1250℃, then cool to 1000~1050℃, hold for 2~3 hours, then heat to 1200~1250℃ again, hold for 5~15 minutes, and then water-cool rapidly to 750℃, and cool with the furnace.

[0019] Furthermore, the first heating rate is 3~5℃ / min; the second heating rate is 5~10℃ / min.

[0020] Furthermore, the first cooling rate is 15~25℃ / min; the second cooling rate is 5~10℃ / min.

[0021] Furthermore, the application of any of the aforementioned high intrinsic coercivity permanent magnet ferrites in permanent magnet materials.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] (1) In the formulation of the present invention, cerium and manganese are introduced to partially replace the oxides of lanthanum and cobalt within a limited range. Compared with lanthanum and cobalt, the introduction of cerium and manganese will replace part of the Fe. 3+ Due to cerium, manganese and Fe 3+ The radius is closer, compared to Co. 3+ A more stable crystal structure is obtained, and lattice defects are reduced; while La 3+ The ionic radius is much larger than that of Fe. 3+ Doping can easily introduce lattice defects such as vacancies and dislocations; Co 3+ The anisotropy is lower than that of Fe 3+ Doping reduces overall anisotropy, leading to a decrease in its Hcj. Furthermore, cobalt oxide is too expensive and, being a strategic metal, is not economically viable. In addition, Ce readily forms Ce. 4+ and Ce 3+ It can compensate for Fe 2+ and Fe 3+The charge shift is achieved, while Ce can suppress excessive grain growth, and Mn can adjust the magnetic domain distribution, reduce the sintering temperature, and promote ferrite densification.

[0024] (2) In the process of preparing ferrite, the present invention adopts a staged gradient heating and cooling method for sintering the billet. Compared with the high temperature sintering process of the prior art, the cooling sintering after the first heating suppresses the excessive growth of grains at high temperature, so that the grains grow to a reasonable size, controls the number of grain boundaries and thus hinders the migration of magnetic domains, while suppressing the excessive precipitation of non-magnetic phases at the grain boundaries. Rapid cooling can make the ferrite heat evenly and ensure the uniformity of grain size.

[0025] (3) After being kept at a relatively low temperature, the temperature is raised again to improve the densification of the ferrite. The temperature rise leads to an increase in atomic activity at the grain boundaries, resulting in grain boundary migration, squeezing out micropores, enhancing interface fusion, eliminating gaps, and densifying the ferrite. After densification, the grains are tightly bonded, making the magnetocrystalline anisotropy distribution uniform and improving coercivity.

[0026] (4) After sintering, water cooling is used to quickly cool down the ferrite to stop grain growth and prevent excessive grain growth. The ferrite is cooled with the furnace to prevent the temperature difference between the inside and outside of the ferrite from expanding rapidly, so that the internal stress cannot be released and the ferrite will not crack or delaminate. Attached Figure Description

[0027] Figure 1 This is a scanning electron microscope image of the ferrite prepared in Example 1 of the present invention. Detailed Implementation

[0028] To make the above-mentioned objectives, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to specific examples.

[0029] Unless otherwise specified, the raw materials or reagents used in the following examples and comparative examples are commercially available products or products prepared using conventional techniques.

[0030] The source of the pre-fired material of this invention is as follows: it adopts the nine-series pre-fired material, and the components by mass percentage include: iron oxide 85%~88%; strontium carbonate 1.5%~1.8%; calcium carbonate 2.5%~3.8%; lanthanum oxide 4.5%~6.0%; cobalt oxide 1.8%~2.5% and boric acid 0.3%~0.5%; the pre-fired material is obtained by mixing, pre-firing and crushing process;

[0031] In the following embodiments, the purity of strontium carbonate is ≥99.5%, the purity of alumina is ≥99%, the purity of lanthanum oxide is ≥99.3%, the purity of cobalt oxide is ≥99.9%, the purity of boric acid is ≥99%, and the purity of nano-silica is ≥99.5%.

[0032] A high intrinsic coercivity permanent magnet ferrite, with the following composition by weight percentage:

[0033] The pre-burned material contains 92-98% lanthanum oxide, 0.2-1.5% strontium carbonate, 0.1-0.3% cerium oxide, 0.05-0.2% manganese oxide, 0.01-0.15% cobalt oxide, 0.05-0.5% aluminum oxide, 0.12-0.28% boric acid, and 0.05-0.3% nano-silica.

[0034] The preparation method of the above-mentioned high intrinsic coercivity permanent magnet ferrite includes the following steps:

[0035] (1) Ingredients: Prepare the ingredients according to the above formula and set aside;

[0036] (2) First, put lanthanum oxide and strontium carbonate into a sand mill and mill them at 400~600 r / min for 20~35 min to obtain auxiliary material A. The particle size of auxiliary material A is 0.6~0.8 μm.

[0037] (3) Cerium oxide and manganese oxide are placed in a sand mill and milled at 400~600 r / min for 1.5~2 h to obtain auxiliary material B, the particle size of auxiliary material B is 0.6~0.8 μm;

[0038] (4) The pre-burned material, cobalt oxide, alumina and boric acid are put into a ball mill for ball milling to obtain a mixed powder with a particle size of 0.8~1.0μm;

[0039] (5) Mix and stir the auxiliary materials A and B with the mixed powder. After stirring evenly, press the mixture into shape at 13~16MPa to obtain a green body.

[0040] (6) Place the green body into the pusher kiln, first heat it to 1200~1250℃ at 3~5℃ / min, then cool it down to 1000~1050℃ at 15~25℃ / min, and hold it for 2~3 hours (cooling down for sintering, inhibiting excessive grain growth at high temperature, allowing the grains to grow to a reasonable size, controlling the number of grain boundaries to hinder magnetic domain migration, and at the same time inhibiting the excessive precipitation of non-magnetic phases at the grain boundaries. Rapid cooling can make the ferrite heat up evenly and ensure the uniformity of grain size). Then heat it again at 5~10℃ / min. The temperature is raised to 1200-1250℃ and held for 5-15 minutes. (Heating after holding at low temperature improves the densification of the ferrite. The increased temperature leads to increased atomic activity at grain boundaries, causing grain boundary migration, squeezing out micropores, enhancing interface fusion, eliminating gaps, and densifying the ferrite. After densification, the grains are tightly bonded, resulting in a uniform distribution of magnetocrystalline anisotropy and improved coercivity.) Then, the temperature is rapidly reduced to 750℃ by water cooling at a rate of 5-10℃ / min, followed by furnace cooling, yielding a high intrinsic coercivity permanent magnet ferrite. (Rapid cooling stops grain growth and prevents overgrowth; furnace cooling prevents a rapid increase in the temperature difference between the inside and outside of the ferrite, preventing internal stress from being released and avoiding cracks or delamination in the ferrite.)

[0041] Example 1

[0042] A high intrinsic coercivity permanent magnet ferrite, with the following composition by weight percentage:

[0043] The pre-burned material contains 97.82% lanthanum oxide, 0.8% strontium carbonate, 0.2% cerium oxide, 0.1% manganese oxide, 0.35% cobalt oxide, 0.18% aluminum oxide, 0.15% boric acid, and 0.20% nano-silica.

[0044] The preparation method of the above-mentioned high intrinsic coercivity permanent magnet ferrite includes the following steps:

[0045] (1) Ingredients: Prepare the ingredients according to the above formula and set aside;

[0046] (2) First, put lanthanum oxide and strontium carbonate into a sand mill and mill them at 500 r / min for 30 min to obtain auxiliary material A. The particle size of auxiliary material A is 0.75 μm.

[0047] (3) Cerium oxide and manganese oxide were put into a sand mill and milled at 500 r / min for 1.5 h to obtain auxiliary material B with a particle size of 0.79 μm;

[0048] (4) The pre-burned material, cobalt oxide, alumina and boric acid were put into a ball mill and ball milled to obtain a mixed powder with a particle size of 0.83 μm;

[0049] (5) Mix and stir the auxiliary materials A and B with the mixed powder. After stirring evenly, press the mixture at 14 MPa to obtain a green body.

[0050] (6) The green body is placed in a pusher kiln, heated to 1230℃ at 5℃ / min, then cooled to 1050℃ at 20℃ / min, and held for 2.5h. The temperature is then increased to 1200℃ at 10℃ / min and held for 5min. Finally, the temperature is rapidly reduced to 750℃ by water cooling at 10℃ / min, and cooled with the furnace to obtain a high intrinsic coercivity permanent magnet ferrite with the following microstructure: Figure 1 As shown.

[0051] Example 2

[0052] A high intrinsic coercivity permanent magnet ferrite, with the following composition by weight percentage:

[0053] The pre-burned material contains 97.82% lanthanum oxide, 0.9% strontium carbonate, 0.2% cerium oxide, 0.1% manganese oxide, 0.05% cobalt oxide, 0.40% aluminum oxide, 0.18% boric acid, and 0.20% nano-silica.

[0054] The preparation method of the above-mentioned high intrinsic coercivity permanent magnet ferrite includes the following steps:

[0055] (1) Ingredients: Prepare the ingredients according to the above formula and set aside;

[0056] (2) First, put lanthanum oxide and strontium carbonate into a sand mill and mill them at 500 r / min for 30 min to obtain auxiliary material A. The particle size of auxiliary material A is 0.75 μm.

[0057] (3) Cerium oxide and manganese oxide were put into a sand mill and milled at 500 r / min for 1.5 h to obtain auxiliary material B with a particle size of 0.79 μm;

[0058] (4) The pre-burned material, cobalt oxide, alumina and boric acid were put into a ball mill and ball milled to obtain a mixed powder with a particle size of 0.83 μm;

[0059] (5) Mix and stir the auxiliary materials A and B with the mixed powder. After stirring evenly, press the mixture at 14 MPa to obtain a green body.

[0060] (6) Place the green billet into the pusher kiln, first heat it to 1230℃ at 5℃ / min, then cool it to 1050℃ at 20℃ / min, hold it for 2.5h, then heat it to 1200℃ at 10℃ / min again, hold it for 5min, and then cool it down rapidly to 750℃ with water at 10℃ / min, and cool it with the furnace to obtain high intrinsic coercivity permanent magnet ferrite.

[0061] Example 3

[0062] A high intrinsic coercivity permanent magnet ferrite, with the following composition by weight percentage:

[0063] The pre-burned material contains 97.82% lanthanum oxide, 0.6% strontium carbonate, 0.3% cerium oxide, 0.2% manganese oxide, 0.15% cobalt oxide, 0.40% aluminum oxide, 0.18% boric acid, and 0.20% nano-silica.

[0064] The preparation method of the above-mentioned high intrinsic coercivity permanent magnet ferrite includes the following steps:

[0065] (1) Ingredients: Prepare the ingredients according to the above formula and set aside;

[0066] (2) First, put lanthanum oxide and strontium carbonate into a sand mill and mill them at 500 r / min for 30 min to obtain auxiliary material A. The particle size of auxiliary material A is 0.75 μm.

[0067] (3) Cerium oxide and manganese oxide were put into a sand mill and milled at 500 r / min for 1.5 h to obtain auxiliary material B with a particle size of 0.79 μm;

[0068] (4) The pre-burned material, cobalt oxide, alumina and boric acid were put into a ball mill and ball milled to obtain a mixed powder with a particle size of 0.83 μm;

[0069] (5) Mix and stir the auxiliary materials A and B with the mixed powder. After stirring evenly, press the mixture at 14 MPa to obtain a green body.

[0070] (6) Place the green billet into the pusher kiln, first heat it to 1230℃ at 5℃ / min, then cool it to 1050℃ at 20℃ / min, hold it for 2.5h, then heat it to 1200℃ at 10℃ / min again, hold it for 5min, and then cool it down rapidly to 750℃ with water at 10℃ / min, and cool it with the furnace to obtain high intrinsic coercivity permanent magnet ferrite.

[0071] Example 4

[0072] A high intrinsic coercivity permanent magnet ferrite, with the following composition by weight percentage:

[0073] The pre-burned material contains 97.82% lanthanum oxide, 0.8% strontium carbonate, 0.2% cerium oxide, 0.1% manganese oxide, 0.35% cobalt oxide, 0.18% aluminum oxide, 0.15% boric acid, and 0.20% nano-silica.

[0074] The preparation method of the above-mentioned high intrinsic coercivity permanent magnet ferrite includes the following steps:

[0075] (1) Ingredients: Prepare the ingredients according to the above formula and set aside;

[0076] (2) First, put lanthanum oxide and strontium carbonate into a sand mill and mill them at 500 r / min for 30 min to obtain auxiliary material A. The particle size of auxiliary material A is 0.75 μm.

[0077] (3) Cerium oxide and manganese oxide were put into a sand mill and milled at 500 r / min for 1.5 h to obtain auxiliary material B with a particle size of 0.79 μm;

[0078] (4) The pre-burned material, cobalt oxide, alumina and boric acid were put into a ball mill and ball milled to obtain a mixed powder with a particle size of 0.83 μm;

[0079] (5) Mix and stir the auxiliary materials A and B with the mixed powder. After stirring evenly, press the mixture at 14 MPa to obtain a green body.

[0080] (6) Place the green billet into the pusher kiln, first heat it to 1220℃ at 5℃ / min, then cool it down to 1050℃ at 15℃ / min, keep it at the temperature for 2.5h, then heat it up to 1200℃ at 5℃ / min again, keep it at the temperature for 5min, and then cool it down rapidly to 750℃ with water at 5℃ / min, and cool it with the furnace to obtain high intrinsic coercivity permanent magnet ferrite.

[0081] Example 5

[0082] A high intrinsic coercivity permanent magnet ferrite, with the following composition by weight percentage:

[0083] The pre-burned material contains 97.82% lanthanum oxide, 0.8% strontium carbonate, 0.2% cerium oxide, 0.1% manganese oxide, 0.35% cobalt oxide, 0.18% aluminum oxide, 0.15% boric acid, and 0.20% nano-silica.

[0084] The preparation method of the above-mentioned high intrinsic coercivity permanent magnet ferrite includes the following steps:

[0085] (1) Ingredients: Prepare the ingredients according to the above formula and set aside;

[0086] (2) First, put lanthanum oxide and strontium carbonate into a sand mill and mill them at 500 r / min for 30 min to obtain auxiliary material A. The particle size of auxiliary material A is 0.75 μm.

[0087] (3) Cerium oxide and manganese oxide were put into a sand mill and milled at 500 r / min for 1.5 h to obtain auxiliary material B with a particle size of 0.79 μm;

[0088] (4) The pre-burned material, cobalt oxide, alumina and boric acid were put into a ball mill and ball milled to obtain a mixed powder with a particle size of 0.83 μm;

[0089] (5) Mix and stir the auxiliary materials A and B with the mixed powder. After stirring evenly, press the mixture at 14 MPa to obtain a green body.

[0090] (6) Place the green billet into the pusher kiln, first heat it to 1220℃ at 5℃ / min, then cool it to 1050℃ at 25℃ / min, keep it at the temperature for 2.5h, then heat it to 1200℃ at 5℃ / min again, keep it at the temperature for 5min, and then cool it down rapidly to 750℃ with water at 8℃ / min, and cool it with the furnace to obtain high intrinsic coercivity permanent magnet ferrite.

[0091] Comparative Example 1

[0092] A type of permanent magnet ferrite, with the following composition by weight percentage:

[0093] The pre-burned material contains 97.82% lanthanum oxide, 0.8% strontium carbonate, 0.2% cerium oxide, 0.1% manganese oxide, 0.35% cobalt oxide, 0.18% aluminum oxide, 0.15% boric acid, and 0.20% nano-silica.

[0094] The preparation method of the above-mentioned permanent magnet ferrite includes the following steps:

[0095] (1) Ingredients: Prepare the ingredients according to the above formula and set aside;

[0096] (2) First, put lanthanum oxide and strontium carbonate into a sand mill and mill them at 500 r / min for 30 min to obtain auxiliary material A. The particle size of auxiliary material A is 0.75 μm.

[0097] (3) Cerium oxide and manganese oxide were put into a sand mill and milled at 500 r / min for 1.5 h to obtain auxiliary material B with a particle size of 0.79 μm;

[0098] (4) The pre-burned material, cobalt oxide, alumina and boric acid were put into a ball mill and ball milled to obtain a mixed powder with a particle size of 0.83 μm;

[0099] (5) Mix and stir the auxiliary materials A and B with the mixed powder. After stirring evenly, press the mixture at 14 MPa to obtain a green body.

[0100] (6) Place the green billet into the pusher kiln, heat it to 1200~1250℃ at 5℃ / min, keep it at that temperature for 2.5h, and then cool it with the furnace to obtain permanent magnet ferrite.

[0101] Comparative Example 2

[0102] A type of permanent magnet ferrite, with the following composition by weight percentage:

[0103] The pre-burned material contains 98.12% lanthanum oxide, 0.8% strontium carbonate, 0.2% cobalt oxide, 0.35% alumina, 0.18% boric acid, and 0.20% nano-silica.

[0104] The preparation method of the above-mentioned high intrinsic coercivity permanent magnet ferrite includes the following steps:

[0105] (1) Ingredients: Prepare the ingredients according to the above formula and set aside;

[0106] (2) First, put lanthanum oxide and strontium carbonate into a sand mill and mill them at 500 r / min for 30 min to obtain auxiliary material A. The particle size of auxiliary material A is 0.75 μm.

[0107] (3) The pre-burned material, cobalt oxide, alumina and boric acid were put into a ball mill for ball milling to obtain a mixed powder with a particle size of 0.83 μm;

[0108] (4) Mix and stir the auxiliary material A with the mixed powder. After stirring evenly, press it into shape at 14MPa to obtain a green body;

[0109] (5) Place the green billet into the pusher kiln, first heat it to 1230℃ at 5℃ / min, then cool it down to 1050℃ at 20℃ / min, keep it at the temperature for 2.5h, then heat it up to 1200℃ at 10℃ / min again, keep it at the temperature for 5min, and then cool it down rapidly to 750℃ with water at 10℃ / min, and cool it with the furnace to obtain permanent magnet ferrite.

[0110] Comparative Example 3

[0111] A high intrinsic coercivity permanent magnet ferrite, with the following composition by weight percentage:

[0112] The pre-burned material contains 97.82% lanthanum oxide, 0.4% strontium carbonate, 0.2% cerium oxide, 0.4% manganese oxide, 0.35% cobalt oxide, 0.3% aluminum oxide, 0.18% boric acid, and 0.20% nano-silica.

[0113] The preparation method of the above-mentioned high intrinsic coercivity permanent magnet ferrite includes the following steps:

[0114] (1) Ingredients: Prepare the ingredients according to the above formula and set aside;

[0115] (2) First, put lanthanum oxide and strontium carbonate into a sand mill and mill them at 500 r / min for 30 min to obtain auxiliary material A. The particle size of auxiliary material A is 0.75 μm.

[0116] (3) Cerium oxide and manganese oxide were put into a sand mill and milled at 500 r / min for 1.5 h to obtain auxiliary material B with a particle size of 0.79 μm;

[0117] (4) The pre-burned material, cobalt oxide, alumina and boric acid were put into a ball mill and ball milled to obtain a mixed powder with a particle size of 0.83 μm;

[0118] (5) Mix and stir the auxiliary materials A and B with the mixed powder. After stirring evenly, press the mixture at 14 MPa to obtain a green body.

[0119] (6) Place the green billet into the pusher kiln, first heat it to 1230℃ at 5℃ / min, then cool it down to 1050℃ at 20℃ / min, keep it at the temperature for 2.5h, then heat it up to 1200℃ at 10℃ / min again, keep it at the temperature for 5min, and then cool it down rapidly to 750℃ with water at 10℃ / min, and cool it with the furnace to obtain high intrinsic coercivity permanent magnet ferrite.

[0120] Comparative Example 4

[0121] A high intrinsic coercivity permanent magnet ferrite, with the following composition by weight percentage:

[0122] The pre-burned material contains 98.52% lanthanum oxide, 0.4% strontium carbonate, 0.2% cerium oxide, 0.04% manganese oxide, 0.01% cobalt oxide, 0.3% aluminum oxide, 0.18% boric acid, and 0.20% nano-silica.

[0123] The preparation method of the above-mentioned high intrinsic coercivity permanent magnet ferrite includes the following steps:

[0124] (1) Ingredients: Prepare the ingredients according to the above formula and set aside;

[0125] (2) First, put lanthanum oxide and strontium carbonate into a sand mill and mill them at 500 r / min for 30 min to obtain auxiliary material A. The particle size of auxiliary material A is 0.75 μm.

[0126] (3) Cerium oxide and manganese oxide were put into a sand mill and milled at 500 r / min for 1.5 h to obtain auxiliary material B with a particle size of 0.79 μm;

[0127] (4) The pre-burned material, cobalt oxide, alumina and boric acid were put into a ball mill and ball milled to obtain a mixed powder with a particle size of 0.83 μm;

[0128] (5) Mix and stir the auxiliary materials A and B with the mixed powder. After stirring evenly, press the mixture at 14 MPa to obtain a green body.

[0129] (6) Place the green billet into the pusher kiln, first heat it to 1230℃ at 5℃ / min, then cool it down to 1050℃ at 20℃ / min, keep it at the temperature for 2.5h, then heat it up to 1200℃ at 10℃ / min again, keep it at the temperature for 5min, and then cool it down rapidly to 750℃ with water at 10℃ / min, and cool it with the furnace to obtain high intrinsic coercivity permanent magnet ferrite.

[0130] The permanent magnet ferrites prepared in Examples 1-5 and Comparative Examples 1-4 were subjected to remanence B tests. r (mT), magnetic coercivity H cb (kA / m), intrinsic coercivity H cj (kA / m) and maximum energy product (BH) max (kJ / m 3 The test was conducted using the NIM-62000 equipment; the test results are shown in Table 1 below.

[0131] Table 1. Magnetic performance test results of permanent magnet ferrites prepared in Examples 1-5 and Comparative Examples 1-4

[0132]

[0133] Analysis of Table 1 shows that the magnetic coercivity H in Examples 1-5 of the present invention cb With intrinsic coercivity H cj The intrinsic coercivity of the samples was significantly higher than that of comparative examples 1-4, and the intrinsic coercivity of comparative examples 3-4 was also better than that of comparative examples 1-2. This is because the introduction of cerium and manganese will replace part of the Fe. 3+ And because of its relationship with Fe 3+ Its ionic radius is closer than that of Co. 3+ A more stable crystal structure is obtained, reducing lattice defects; Ce is more easily formed. 4+ and Ce 3+ It can compensate for Fe 2+ and Fe 3+The charge shift, Ce can suppress excessive grain growth, Mn adjusts the magnetic domain distribution, lowers the sintering temperature, and promotes ferrite densification. In the sintering process of this invention, a staged gradient heating and cooling method is adopted (first, slowly heat up and quickly sinter at 1200~1250℃, then rapidly cool down to 1000~1050℃ for sintering, then heat up to 1200~1250℃, rapidly water-cool to 750℃, and finally cool with the furnace). On the one hand, it can lower the temperature for sintering, suppress excessive grain growth at high temperature, allow the grains to grow to a reasonable size, control the number of grain boundaries to hinder magnetic domain migration, and suppress excessive precipitation of non-magnetic phases at grain boundaries. Rapid cooling can make the ferrite heat evenly and ensure uniform grain size. On the other hand, heating up after holding at low temperature can improve the densification of ferrite. Heating increases the activity of atoms at grain boundaries, causing grain boundary migration, squeezing out micropores, enhancing interface fusion, eliminating gaps, and densifying the ferrite. After densification, the grains are tightly bonded, resulting in a uniform distribution of magnetocrystalline anisotropy and improved coercivity. In addition, rapid cooling stops grain growth, prevents excessive grain growth, and furnace cooling prevents a sharp increase in the temperature difference between the inside and outside of the ferrite, which would prevent internal stress from being released and avoid cracking or delamination of the ferrite.

[0134] Comparing Examples 1-5 with Comparative Examples 3 and 4, it can be seen that when the content of cerium and manganese oxides in the formula exceeds or falls below the range defined by the present invention, the improvement of magnetic performance is actually reduced. This is because when the content exceeds the defined range, there will be excess cerium oxide and manganese oxide crystals, which will reduce the magnetic performance; when the content falls below the defined range, it is easy to produce uneven ion distribution and local aggregation, which will destroy the continuity of the magnetic circuit and lead to a decrease in performance.

Claims

1. A high intrinsic coercivity permanent magnet ferrite, characterized in that, The composition of each component, by weight percentage, is as follows: 92-98% pre-calcined material, 0.2-1.5% lanthanum oxide, 0.1-0.3% strontium carbonate, 0.05-0.2% cerium oxide, 0.01-0.15% manganese oxide, 0.05-0.5% cobalt oxide, 0.12-0.28% aluminum oxide, 0.02-0.3% boric acid, and 0.05-0.3% nano-silica. The purity of the lanthanum oxide is ≥99.3%, the purity of the strontium carbonate is ≥99.5%, the purity of the cerium oxide is ≥99.9%, the purity of the manganese oxide is ≥99.5%, the purity of the cobalt oxide is ≥99.9%, the purity of the aluminum oxide is ≥99%, the purity of the boric acid is ≥99%, and the purity of the nano-silica is ≥99.5%.

2. The high intrinsic coercivity permanent magnet ferrite according to claim 1, characterized in that, The composition of each component by weight percentage is as follows: 97.82% pre-fired material, 0.8% lanthanum oxide, 0.2% strontium carbonate, 0.2% cerium oxide, 0.1% manganese oxide, 0.35% cobalt oxide, 0.18% aluminum oxide, 0.15% boric acid, and 0.20% nano-silica.

3. The high intrinsic coercivity permanent magnet ferrite according to claim 1 or 2, characterized in that, The pre-fired material is a series 9 pre-fired material, and its composition includes 85%~88% Fe2O3; 1.5%~1.8%SrCO3; 2.5%~3.8%CaCO3; 4.5%~6.0%La2O3; 1.8%~2.5% Co2O3 and 0.3%~0.5% H3BO3; prepared by mixing, pre-calcining and crushing process.

4. A method for preparing a high intrinsic coercivity permanent magnet ferrite as described in any one of claims 1 to 3, characterized in that, The steps are as follows: S1: First, put lanthanum oxide and strontium oxide into a sand mill and mill them at 400~600 r / min for 20~35 min to obtain auxiliary material A; S2: Cerium oxide and manganese oxide are placed in a sand mill and milled at 400~600 r / min for 1.5~2 h to obtain auxiliary material B; S3: The pre-burned material, cobalt oxide, alumina and boric acid are put into a ball mill and ball-milled to obtain a mixed powder with a particle size of 0.8~1.0μm; S4: Mix and stir the auxiliary material A in S1, the auxiliary material B in S2, and the mixed powder in S3. After stirring evenly, press and shape the mixture at 13~16MPa to obtain a green body. S5: The green body is placed in the pusher kiln and sintered in stages with gradient heating and cooling to obtain high intrinsic coercivity permanent magnet ferrite.

5. The method for preparing high intrinsic coercivity permanent magnet ferrite according to claim 4, characterized in that, In S1, the particle size of excipient A is 0.6~0.8μm.

6. The method for preparing high intrinsic coercivity permanent magnet ferrite according to claim 4, characterized in that, In S2, the particle size of excipient B is 0.6~0.8μm.

7. The method for preparing high intrinsic coercivity permanent magnet ferrite according to claim 4, characterized in that, In S5, the staged gradient heating and cooling sintering procedure is as follows: first, heat to 1200~1250℃, then cool to 1000~1050℃, hold for 2~3 hours, then heat to 1200~1250℃ again, hold for 5~15 minutes, then water-cool rapidly to 750℃, and cool with the furnace.

8. The method for preparing high intrinsic coercivity permanent magnet ferrite according to claim 7, characterized in that, The first heating rate is 3~5℃ / min; the second heating rate is 5~10℃ / min.

9. The method for preparing high intrinsic coercivity permanent magnet ferrite according to claim 7, characterized in that, The first cooling rate is 15~25℃ / min; the second cooling rate is 5~10℃ / min.

10. The application of the high intrinsic coercivity permanent magnet ferrite as described in any one of claims 1 to 3 in permanent magnet materials.

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