A permanent magnet strontium ferrite material, a preparation method and application thereof

Abstract

The application relates to a permanent magnet strontium ferrite material and a preparation method and application thereof, and the preparation method comprises the following steps: after rare earth oxide, additives and a first solvent are mixed for the first time, the obtained composite additives are mixed with strontium ferrite pre-sintering materials and a second solvent for the second time to obtain mixed powder, after molding, a magnetic blank is obtained, and after sintering, the permanent magnet strontium ferrite material is obtained. The rare earth oxide and the additives are mixed first, the composite additive powder which is mixed uniformly, has small particle size and is uniform is formed first, the problem that the components in the composite additives are not mixed uniformly due to direct addition in the secondary adding process is avoided, and then the composite additive powder is mixed with the strontium ferrite pre-sintering materials. In the secondary adding process, the composite additive powder which is mixed uniformly can be uniformly distributed in the pre-sintering materials, the rare earth oxide in the composite additives and the additives can more favorably play a synergistic role, and then the magnetic performance of the whole permanent magnet strontium ferrite material is improved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of permanent magnet strontium ferrite preparation, and particularly relates to a permanent magnet strontium ferrite material and a preparation method and application thereof. BACKGROUND

[0002] The permanent magnet strontium ferrite with a hexaferrite structure has become a widely used permanent magnet material due to its excellent stability and high cost performance, and with the expansion of application fields and strict requirements on material performance, how to further improve the magnetic performance has become the focus of current research.

[0003] Research shows that in addition to changing the intrinsic properties of strontium ferrite through ion substitution, improving the corresponding preparation process also helps to improve the density, orientation degree and single-domain particle existence rate of strontium ferrite, thereby improving the remanence and coercivity of strontium ferrite. Among the ways to improve the process, the use of additives is an effective method, and different additives can play different roles, for example, some additives can form a liquid phase at high temperatures to promote sintering, thereby improving the sintering density to improve the remanence; some additives can adhere to the grain boundaries to inhibit the growth of the grains, thereby improving the existence rate of single-domain particles to improve the coercivity; some additives can also modify the grain boundaries to make the grain surface smooth, reduce the sharp corners, and improve the squareness and orientation degree.

[0004] Rare earth elements have a unique 4f electron layer structure, and are widely used as additives to improve material performance due to their high activity, large radius and their own structure and chemical properties, especially in the field of ceramic sintering. However, in the production of sintered permanent magnet strontium ferrite, more rare earth oxides are directly mixed with raw materials Fe2O3 and SrCO3 for sintering, so that rare earth ions enter the strontium ferrite lattice to replace Fe and Sr ions. For example, CN114195502A discloses a rare earth doped permanent magnet ferrite and a preparation method thereof, which discloses a preparation method including using Fe2O3, SrCO3, Al2O3, CaCO3, SiO2, and a nano cerium oxide compound, mixing the above materials, then adding water for wet ball milling, pressing into a green body after ball milling, and sintering the green body twice to obtain a rare earth doped permanent magnet ferrite after cooling. However, few people add rare earth oxides as secondary additives to observe their influence on the magnetic performance of strontium ferrite. At the same time, in the production process of strontium ferrite, the secondary addition process usually involves sequentially adding CaCO3, SiO2 and H3BO3, and mixing with strontium ferrite premix, which is usually not conducive to the uniform dispersion of the additives, thereby affecting the joint action of the additives.

[0005] In the magnetic properties of permanent strontium ferrite, the remanence and coercivity are a pair of contradictory properties. The increase of remanence benefits from the oriented growth of grains and the densification of the magnet during the sintering process. If the density is to be increased, the sintering temperature has to be moderately increased, but the increase of the sintering temperature will cause the grains to grow excessively, resulting in the gradual decrease of the proportion of single-domain particles, and further resulting in the decrease of coercivity. Therefore, although the remanence can be slightly increased by simply increasing the sintering temperature, the coercivity will decrease sharply. It is generally believed in the industry that when the remanence is increased by 1Gs, the decrease of the coercivity should be controlled within 3-5Oe, or the M value is used as the evaluation standard of the comprehensive magnetic properties, wherein M=B r +H cJ / 3, the higher the M value, the higher the comprehensive magnetic properties of the permanent strontium ferrite.

[0006] Therefore, how to realize the uniform dispersion of the additives in the secondary adding process, fully exert the role of each additive, and how to realize the increase of the remanence of the permanent strontium ferrite material while the coercivity is also increased or not greatly decreased, and further improve the overall magnetic properties of the permanent strontium ferrite material, have become the problems to be solved at present. SUMMARY

[0007] To solve the above technical problems, the application provides a kind of permanent strontium ferrite material and its preparation method and application, the application first mixes rare earth oxides and additives, first forms a composite additive powder with uniform mixing, small particle size and uniformity, directly avoids the problem of uneven mixing caused by direct addition of each component in the composite additive during the secondary adding process, and then mixes it with strontium ferrite pre-sintering material. In the secondary adding process, the uniformly mixed composite additive powder can be uniformly distributed in the pre-sintering material, which is more conducive to the synergistic effect of rare earth oxides and each additive in the composite additive, and further improves the overall magnetic properties of the permanent strontium ferrite material.

[0008] To achieve this purpose, the application adopts the following technical solutions:

[0009] In the first aspect, the application provides a preparation method of a permanent strontium ferrite material, which comprises the following steps:

[0010] (1) First mix rare earth oxides, additives and a first solvent to obtain a composite additive;

[0011] (2) Second mix strontium ferrite pre-sintering material, the composite additive of step (1) and a second solvent to obtain a mixed powder. After compression molding, a magnetic blank is obtained, and after sintering, a permanent strontium ferrite material is obtained.

[0012] In the present application, the rare earth oxide and the additive are mixed in advance, which can make the components mix uniformly, the synergistic effect of the components is easier to play in the secondary addition, thereby effectively improving the magnetic properties of the permanent magnet strontium ferrite material, avoiding the direct addition of the components, and the problem of uneven mixing of the components and the strontium ferrite pre-fired material, secondly, the particle size of the composite additive is small and uniform, and after mixing with the strontium ferrite pre-fired material, it is beneficial to its adhesion and movement on the grain boundary, which can inhibit the abnormal growth of the grain, improve the sintering efficiency, and thirdly, the rare earth oxide is directly mixed with the conventional additive, which can further improve the reaction activity of the conventional additive, and is beneficial to the orientation of the grain and the increase of the magnet density in the sintering process.

[0013] As a preferred technical solution of the present application, the additive in step (1) comprises a calcium source, a silicon source, a boron source and a strontium source.

[0014] Preferably, the calcium source comprises Ca 12 H 22 O 14 Ca and an inorganic calcium-containing compound.

[0015] Preferably, the inorganic calcium-containing compound comprises any one or a combination of at least two of CaCO3, CaO or Ca(OH)2.

[0016] Preferably, the silicon source comprises SiO2 or H2SiO3.

[0017] Preferably, the boron source comprises any one or a combination of at least two of H3BO3, HBO2 or B2O3.

[0018] Preferably, the strontium source comprises any one or a combination of at least two of SrCO3, SrO or Sr(OH)2.

[0019] Preferably, the rare earth oxide in step (1) comprises La2O3 and / or CeO2.

[0020] In the present application, the rare earth oxide is mixed with the conventional additive, because the rare earth element has an unfilled 4f electron layer structure, corresponding to a variety of electronic energy levels, so it has many special and excellent physical and chemical properties, which can further improve the reaction activity of the conventional additive, and is beneficial to the orientation of the grain and the increase of the magnet density in the sintering process.

[0021] Preferably, in the composite additive in step (1), the inorganic calcium-containing compound, C 12 H 22 O 14The mass ratio of Ca, silicon source, boron source, strontium source, La2O3 and CeO2 is (9-12):(3-6):(3-5):(1-2):(3-5):(0-4):(0-4), and is not 0 at the same time, for example, 9:5:3:1:3:4:0, 9:5:3:1:3:0:4, 12:5:5:1:5:2:2 or 12:5:3:1:3:2:2, 12:5:3:1:4:2:2, etc., preferably (9-12):5:(3-5):1:(3-5):(0-4):(0-4), and is not 0 at the same time.

[0022] As a preferred technical solution of the present application, the first solvent in step (1) comprises deionized water.

[0023] Preferably, the mass ratio of the first solvent to the whole of the rare earth oxide and the additive is (5-9):1, for example 5:1, 6:1, 7:1, 8:1 or 9:1, etc.

[0024] Preferably, the mixing method of step (1) comprises ball milling.

[0025] In the present application, the mixing method of ball milling can further refine the particle size of the composite additive on the basis of uniform mixing, which is beneficial to its adhesion and movement on the grain boundary, thereby improving the sintering efficiency.

[0026] Preferably, the ball milling time is 2h-8h, for example 2h, 3h, 4h, 5h, 6h, 7h or 8h, etc., preferably 4h-6h.

[0027] Preferably, the ball milling speed is 60rpm-100rpm, for example 60rpm, 70rpm, 80rpm, 90rpm or 100rpm, etc.

[0028] Preferably, after the first mixing of step (1), it further comprises the steps of dehydration, drying and grinding.

[0029] Preferably, the dehydration time is ≥12h, for example 12h, 15h, 18h, 20h, 22h, 25h, 28h or 30h, etc., preferably 16h-24h.

[0030] Preferably, the drying temperature is 70℃-90℃, for example 70℃, 80℃ or 90℃, etc.

[0031] Preferably, the drying time is ≥12h, for example 12h, 15h, 18h, 20h, 22h, 25h, 28h or 30h, etc., preferably 20h-24h.

[0032] As a preferred technical solution of the present application, the second solvent in step (2) comprises deionized water.

[0033] Preferably, in step (2), the mass ratio of the strontium ferrite pre-sintering material, the composite additive and the second solvent is (80-120):(1-4):(100-300), such as 100:1:100, 100:2:200, 100:3:300, 100:3:200, 100:4:200, 100:4:100, 100:3:100 or 100:4:300, etc., preferably 100:(2-3):(140-200).

[0034] Preferably, the second mixing in step (2) is by ball milling.

[0035] Preferably, the ball milling time is ≥12h, such as 12h, 15h, 18h, 20h, 22h, 25h, 28h or 30h, etc.

[0036] Preferably, the ball milling speed is 60rpm-100rpm, such as 60rpm, 70rpm, 80rpm, 90rpm or 100rpm, etc.

[0037] Preferably, after the second mixing, the average particle size of the powder in the mixed slurry is ≤1μm, such as 0.99μm, 0.95μm, 0.90μm, 0.85μm, 0.80μm, 0.75μm, 0.70μm, 0.65μm, 0.60μm or 0.50μm, etc., preferably 0.85μm-0.95μm.

[0038] In the present application, by controlling the average particle size of the powder in the mixed slurry to be ≤1μm, the proportion of single-domain particles can be increased, and the problem of excessive particle size leading to a decrease in coercivity and poor improvement in magnetic properties can be avoided.

[0039] Preferably, after the second mixing in step (1), a step of dewatering is further included to obtain a mixed powder.

[0040] Preferably, the dewatering time is ≥12h, such as 12h, 15h, 18h, 20h, 22h, 25h, 28h or 30h, etc.

[0041] Preferably, the solid content of the mixed powder is >60%, such as 65%, 70%, 75% or 80%, etc.

[0042] In the present application, by controlling the solid content of the mixed powder to be >60%, the powder can be more easily pressed into a shape.

[0043] As a preferred technical solution of the present application, the pressing pressure for the pressing into a shape is 300kg / cm 3 -600kg / cm 3for example 300 kg / cm 3 , 350 kg / cm 3 , 400 kg / cm 3 , 450 kg / cm 3 , 500 kg / cm 3 , 550 kg / cm 3 or 600 kg / cm 3 , preferably 400 kg / cm 3 - 500 kg / cm 3 .

[0044] Preferably, during the press forming process, an orientation magnetic field is also added.

[0045] Preferably, the magnetizing current of the orientation magnetic field is 200A-400A, for example 200A, 250A, 300A, 350A or 400A, etc., preferably 250A-350A.

[0046] Preferably, the demagnetizing current of the orientation magnetic field is 30A-60A, for example 30A, 35A, 40A, 45A, 50A, 55A or 60A, etc., preferably 45A-55A.

[0047] In the present application, the pressure of the press forming and the orientation magnetic field are matched together to improve the orientation degree of the permanent magnet strontium ferrite material, and the green body with better orientation degree will also have higher orientation degree after sintering, which helps to improve the magnetic properties of the strontium ferrite, especially to improve the remanence of the strontium ferrite.

[0048] Preferably, after the press forming, a drying step is also included.

[0049] As a preferred technical solution of the present application, the sintering temperature is 1180℃-1230℃, for example 1180℃, 1185℃, 1190℃, 1195℃, 1200℃, 1205℃, 1210℃, 1215℃, 1220℃, 1225℃ or 1230℃, etc.

[0050] In the present application, the sintering temperature is controlled to be 1180℃-1230℃, which can increase the density of the permanent magnet strontium ferrite material, and obtain a magnetic body with a density ≥4.9g / cm 3 , so that the permanent magnet strontium ferrite material has high overall magnetic properties.

[0051] Preferably, the holding time of the sintering is 30min-60min, for example 30min, 35min, 40min, 45min, 50min, 55min or 60min, etc.

[0052] Preferably, the sintering temperature rising rate is 3℃ / min-10℃ / min, for example, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min or 10℃ / min, etc.

[0053] As a preferred technical solution of the present application, the preparation method comprises the following steps:

[0054] (1) ball-milling La2O3 and / or CeO2, C 12 H 22 O 14 Ca, the inorganic calcium-containing compound, the silicon source, the boron source, the strontium source and the first solvent at a rotating speed of 60rpm-100rpm for 2h-8h to perform first mixing, and then after the steps of dehydrating the mixed slurry for ≥12h, drying at 70℃-90℃ for ≥12h and grinding, a composite additive is obtained;

[0055] In the composite additive, the mass ratio of the inorganic calcium-containing compound, C 12 H 22 O 14 Ca, the silicon source, the boron source, the strontium source, La2O3 and CeO2 is (9-12):(3-6):(3-5):(1-2):(3-5):(0-4):(0-4), and is not 0 at the same time;

[0056] (2) ball-milling the strontium ferrite pre-sintered material, the composite additive in step (1) and the second solvent at a rotating speed of 60rpm-100rpm for ≥12h to perform second mixing, the average particle size of the powder in the obtained mixed slurry is ≤1μm, and after dehydrating for ≥12h, a mixed powder with a solid content of >60% is obtained, which is press-formed under a pressure of 300kg / cm 2 -600kg / cm 2 The press-forming process further adds an orientation magnetic field, the magnetizing current of the orientation magnetic field is 200A-400A, the demagnetizing current is 30A-60A, and after drying, a magnetic blank is obtained, which is sintered at a temperature rising rate of 3℃ / min-10℃ / min to 1180℃-1230℃ for 30min-60min to obtain a permanent magnet strontium ferrite material;

[0057] The mass ratio of the strontium ferrite pre-sintered material, the composite additive and the second solvent is (80-120):(1-4):(100-300).

[0058] In a second aspect, the present application further provides a permanent magnet strontium ferrite material, which is prepared according to the preparation method in the first aspect.

[0059] As a preferred technical scheme of the present application, the density of the permanent magnet strontium ferrite material is greater than or equal to 4.9 g / cm 3 , preferably 4.95 g / cm 3 -5.00 g / cm 3 .

[0060] In a third aspect, the present application further provides a use of the permanent magnet strontium ferrite material according to the second aspect, or the permanent magnet strontium ferrite material prepared by the preparation method according to the first aspect, in the field of consumer electronics or automotive electronics.

[0061] Compared with the prior art, the present application has at least the following beneficial effects:

[0062] In the present application, rare earth oxides are introduced as additives into the production of the permanent magnet strontium ferrite material, and the additives of various components are uniformly mixed in advance to obtain a composite additive, which is then mixed with strontium ferrite pre-fired material. Under the same raw material and the same process conditions, compared with directly mixing the strontium ferrite pre-fired material with each additive component, the remanence of the permanent magnet strontium ferrite material prepared by the preparation method of the present application can be maintained at 4050Gs-4099Gs, the coercive force can be maintained at 3852Oe-4054Oe, the remanence and the coercive force can both reach a relatively optimal standard, the M value is in the range of 5383-5415, and the overall magnetic performance is relatively optimal. BRIEF DESCRIPTION OF DRAWINGS

[0063] Figure 1 is a flowchart of the preparation method of Example 1 of the present application.

[0064] Figure 2 is an SEM image of the completely dried mixed powder and the powder sintered at 1220℃ in Example 1 of the present application.

[0065] Figure 3 is an SEM image of the completely dried mixed powder and the powder sintered at 1220℃ in Example 2 of the present application.

[0066] Figure 4 is an SEM image of the completely dried mixed powder and the powder sintered at 1220℃ in Example 3 of the present application.

[0067] Figure 5 is an SEM image of the completely dried mixed powder and the powder sintered at 1150℃ in Example 7 of the present application.

[0068] Figure 6 is an SEM image of the completely dried mixed powder and the powder sintered at 1250℃ in Example 8 of the present application.

[0069] Figure 7This is a SEM image of the mixed powder in Comparative Example 1 of the present invention after it has been completely dried and sintered at 1220°C.

[0070] Figure 8 This is a schematic flowchart of the preparation method of Comparative Example 2 of the present invention.

[0071] Figure 9 These are XRD patterns of the permanent magnet strontium ferrite materials prepared in Examples 1-3 and Comparative Examples 1-2 of this invention. Detailed Implementation

[0072] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0073] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0074] The chemical formula of the strontium ferrite pre-sintered material described in the specific embodiment of this invention is SrFe. 12 O 19 The preparation method of the strontium ferrite pre-sintered material includes the following steps:

[0075] SrCO3 and Fe2O3 were weighed at a molar ratio of 1:6 and added to deionized water to cover the raw materials. The mixture was ball-milled at 80 rpm for 12 hours (ball-to-material ratio of 10:1). After washing, the mixed powder was thoroughly dried and sintered at 1220℃ for 30 minutes at a heating rate of 5℃ / min. After crushing, strontium ferrite pre-sintered material was obtained.

[0076] Example 1

[0077] This embodiment provides a method for preparing a permanent magnet strontium ferrite material, the method comprising the following steps:

[0078] (1) Weigh out 45g of CaCO3 and 25g of C according to a mass ratio of 9:5:5:1:5:2:2. 12 H 22 O 14 Ca, 25g SiO2, 5g H3BO3, 25g SrCO3, 10g La2O3 and 10g CeO2 were ball-milled with 750g deionized water (ball-to-material ratio of 10:1) at a frequency of 40Hz and a speed of 80rpm for 4 hours. After ball milling, the mixture was poured onto a filter cloth and dehydrated for 18 hours. The water was drained, and the mixture was dried at 70℃ for 20 hours. The mixture was then ground evenly with an agate mortar to obtain a composite additive.

[0079] (2) Take 14.5 g of the composite additive, 500 g of the strontium ferrite pre-fired material and 850 g of deionized water for ball milling (ball-to-material ratio of 10:1), ball mill for 14 h at a frequency of 40 Hz and a rotation speed of 80 rpm, after the ball milling, dry the mixed slurry naturally for 18 h, after the dehydration, obtain the mixed powder with a solid content of 63.7%, use the hydraulic press for orientation forming, the forming pressure is 500 kg / cm 3 , magnetize the magnetic blank at a magnetizing current of 300 A, demagnetize the magnetic blank at a demagnetizing current of 50 A, dry the magnetic blank at 70 ℃ for 4 h, sinter the magnetic blank at a sintering temperature of 1220 ℃ with a temperature increasing rate of 5 ℃ / min and a holding time of 30 min, and cool down in the furnace, obtain the permanent magnet strontium ferrite material with a density of 4.96 g / cm 3 .

[0080] Figure 1 The flowchart of the preparation method of Example 1 is shown, as shown in the figure, the method is to first mix CaCO3, C 12 H 22 O 14 Ca, SiO2, H3BO3, SrCO3, La2O3 and CeO2 uniformly to obtain the composite additive, and then mix the composite additive with the strontium ferrite pre-fired material.

[0081] Figure 2 The SEM image of the mixed powder after completely dried and sintered at 1220 ℃ in Example 1 is shown, as shown in the figure, most of the permanent magnet strontium ferrite grains are uniform in size and smooth in corners and edges.

[0082] Example 2

[0083] The preparation method of the permanent magnet strontium ferrite material is provided in this embodiment, and the difference between the preparation method and Example 1 is that in step (1), 45 g of CaCO3, 25 g of C 12 H 22 O 14 Ca, 25 g of SiO2, 5 g of H3BO3, 25 g of SrCO3 and 20 g of La2O3 are weighed according to a mass ratio of 9:5:5:1:5:4:0, and the remaining preparation method and parameters remain the same as those in Example 1.

[0084] Figure 3 The SEM image of the mixed powder after completely dried and sintered at 1220 ℃ in Example 2 is shown, as shown in the figure, the particle size of the permanent magnet strontium ferrite powder is less than 1 μm, and the size is uniform and appropriate.

[0085] Example 3

[0086] The embodiment provides a preparation method of a permanent magnet strontium ferrite material, which is different from the embodiment 1 in that in step (1), 45g of CaCO3, 25g of C 12 H 22 O 14 25g of SiO2, 5g of H3BO3, 25g of SrCO3 and 20g of CeO2 are taken according to a mass ratio of 9:5:5:1:5:0:4, and the remaining preparation method and parameters remain unchanged.

[0087] Figure 4 The SEM diagram of the mixed powder after complete drying and sintering at 1220 DEG C in the embodiment 3 is shown, and it can be known from the diagram that many small particles are distributed on larger particles, and the existence of the small particles has a better influence on the coercive force of the permanent magnet strontium ferrite.

[0088] Embodiment 4

[0089] The embodiment provides a preparation method of a permanent magnet strontium ferrite material, which comprises the following steps:

[0090] (1) 45g of CaCO3, 25g of C 12 H 22 O 14 15g of SiO2, 5g of H3BO3, 15g of SrCO3, 5g of La2O3 and 5g of CeO2 are taken according to a mass ratio of 9:5:3:1:3:1:1, 690g of deionized water is added for ball milling (a ball-to-material ratio is 10:1), and ball milling is carried out at a frequency of 40Hz and a rotating speed of 60rpm for 2h. After the ball milling is completed, the mixture is poured on filter cloth, dehydrated for 16h, and then dried at 70 DEG C for 24h, and the mixture is uniformly ground by using a corundum mortar to obtain a composite additive;

[0091] (2) 10g of the composite additive, 500g of strontium ferrite pre-sintered material and 700g of deionized water are taken for ball milling (a ball-to-material ratio is 10:1), and ball milling is carried out at a frequency of 40Hz and a rotating speed of 60rpm for 14h. After the ball milling is completed, the mixed slurry is naturally air-dried for 18h, and then dehydrated to obtain mixed powder with a solid content of 80%, and the mixed powder is oriented and formed by using a hydraulic machine, a forming pressure is 300kg / cm 3 , a magnetizing current is 200A, a demagnetizing current is 30A, and the mixture is dried at 70 DEG C for 4h to obtain a magnetic blank with a diameter of 26.5mm and a thickness of 13mm, and the magnetic blank is sintered by increasing the temperature to 1180 DEG C at a temperature increasing rate of 3 DEG C / min, and then kept for 60min, and then cooled in the furnace to obtain a permanent magnet strontium ferrite material with a density of 4.95g / cm 3 .

[0092] Embodiment 5

[0093] The embodiment provides a preparation method of a permanent magnet strontium ferrite material, and the preparation method comprises the following steps:

[0094] (1) 60 g of CaCO3, 25 g of C 12 H 22 O 14 g of H3BO3, 25 g of SrCO3, 10 g of La2O3 and 10 g of CeO2 are weighed according to a mass ratio of 12:5:5:1:5:2:2, 1440 g of deionized water is added for ball milling (a ball-to-material ratio is 10:1), and ball milling is carried out at a frequency of 40 Hz and a rotating speed of 100 rpm for 8 h. After the ball milling is completed, the mixture is poured on filter cloth, dehydrated for 24 h, and then dried at 70 DEG C for 22 h, and the mixture is uniformly ground by using a garnet mortar to obtain a composite additive;

[0095] (2) 15 g of the composite additive, 500 g of strontium ferrite pre-sintered material and 1000 g of deionized water are weighed for ball milling (a ball-to-material ratio is 10:1), and ball milling is carried out at a frequency of 40 Hz and a rotating speed of 100 rpm for 16 h. After the ball milling is completed, the mixed slurry is naturally air-dried for 20 h, and then dehydrated to obtain mixed powder with a solid content of 60%, and the mixed powder is oriented and formed by using a hydraulic machine, a forming pressure is 600 kg / cm 3 , a magnetizing current is 400 A, a demagnetizing current is 60 A, and the mixture is dried at 70 DEG C for 4 h to obtain a magnetic blank with a diameter of 26.5 mm and a thickness of 13 mm, the magnetic blank is sintered by increasing the temperature to 1230 DEG C at a temperature increasing rate of 10 DEG C / min, and the mixture is kept for 45 min, and then the mixture is cooled in the furnace to obtain a permanent magnet strontium ferrite material with a density of 5.00 g / cm 3 .

[0096] Embodiment 6

[0097] The embodiment provides a preparation method of a permanent magnet strontium ferrite material, and the preparation method is different from that of embodiment 1, in step (2), the ball milling time is 10 h, and after the ball milling is completed, the average particle size of the powder in the mixed slurry is 1.134 mu m, and the rest of the preparation method and parameters are consistent with those of embodiment 1.

[0098] Embodiment 7

[0099] The embodiment provides a preparation method of a permanent magnet strontium ferrite material, and the preparation method is different from that of embodiment 1, in step (2), the sintering temperature is 1150 DEG C, and the rest of the preparation method and parameters are consistent with those of embodiment 1.

[0100] Figure 5 An SEM diagram of the mixed powder after being completely dried and sintered at 1150 DEG C in embodiment 7 is shown, and it can be known from the diagram that the grain size is small and the edges and corners are relatively sharp under the sintering temperature of 1150 DEG C.

[0101] Example 8

[0102] The embodiment provides a preparation method of a permanent magnet strontium ferrite material, and the preparation method is different from that of the example 1 in that in step (2), the sintering temperature is 1250 DEG C, and the rest of the preparation method and parameters are consistent with those of the example 1.

[0103] Figure 6 The SEM diagram of the mixed powder completely dried and sintered at 1250 DEG C in the example 8 is shown, and it can be known from the diagram that the crystal grains are closely fused together, connected into a piece, the size is large, and the whole is more compact.

[0104] Example 9

[0105] The embodiment provides a preparation method of a permanent magnet strontium ferrite material, and the preparation method is different from that of the example 1 in that in step (2), the pressure of the press forming is 280 kg / cm 3 , and the rest of the preparation method and parameters are consistent with those of the example 1.

[0106] Example 10

[0107] The embodiment provides a preparation method of a permanent magnet strontium ferrite material, and the preparation method is different from that of the example 1 in that in step (2), the pressure of the press forming is 620 kg / cm 3 , and the rest of the preparation method and parameters are consistent with those of the example 1.

[0108] Comparative Example 1

[0109] The comparative example provides a preparation method of a permanent magnet strontium ferrite material, and the preparation method is different from that of the example 1 in that in step (1), La2O3 and CeO2 are omitted, 45g of CaCO3, 25g of C 12 H 22 O 14 , 5g of H3BO3 and 25g of SrCO3 are weighed according to a mass ratio of 9:5:5:1:5:0:0, and the rest of the preparation method and parameters are consistent with those of the example 1.

[0110] Figure 7 The SEM diagram of the mixed powder completely dried and sintered at 1220 DEG C in the comparative example 1 is shown, and it can be known from the diagram that there are many large particles with a size of about 2um, which can cause the coercive force of the magnet to be poor.

[0111] Comparative Example 2

[0112] The comparative example 2 provides a preparation method of a permanent magnet strontium ferrite material, which is different from the example 1 in that the process of step (1) is omitted, and in step (2), 4.5 g of CaCO3, 2.5 g of C 12 H 22 O 14 2.5 g of SiO2, 0.5 g of H3BO3, 2.5 g of SrCO3, 1 g of La2O3, 1 g of CeO2, 500 g of strontium ferrite pre-fired material and 850 g of water are directly weighed and ball milled, and the rest of the preparation method and parameters remain the same as those of the example 1.

[0113] Figure 8 The flowchart of the preparation method of the comparative example 2 is shown, and it can be seen from the figure that the method of directly mixing CaCO3, C 12 H 22 O 14 SiO2, H3BO3, SrCO3, La2O3, CeO2 and strontium ferrite pre-fired material is used.

[0114] The permanent magnet strontium ferrite materials prepared in the examples 1-10 and the comparative examples 1-2 are measured by a B-H instrument to measure the coercive force H cJ and the remanence B r , and the M value is calculated, M = B r + H cJ / 3; the average particle size of the powder in the mixed slurry obtained after the second mixing in the examples 1-10 and the comparative examples 1-2 is tested by a particle size analyzer; the XRD patterns of the permanent magnet strontium ferrite materials prepared in the examples 1-10 and the comparative examples 1-2 are tested, and then the orientation degree of each is calculated by using the texture factor formula , and the specific data are shown in Table 1.

[0115] Figure 9 The XRD patterns of the permanent magnet strontium ferrite materials prepared in the examples 1-3 and the comparative examples 1-2 are shown, and it can be seen from the figure that the diffraction peak intensity of the crystal face (004), (006), (008) and (0014) is high, which indicates that the strontium ferrite has obvious C-axis preferred orientation during the pressing and sintering process, and the higher the degree of C-axis preferred orientation of the crystal grain, the better the macroscopic magnetic properties such as remanence and coercive force.

[0116] Table 1

[0117] Item Residual magnetism B r (Gs) Coercivity H cJ (Oe)]]> M value Degree of orientation Average particle size (μm) Example 1 4061 4022 5402 0.612 0.891 Example 2 4060 3992 5391 0.593 0.896 Example 3 4081 4003 5415 0.609 0.880 Example 4 4050 4054 5401 0.540 0.843 Example 5 4099 3852 5383 0.604 0.821 Example 6 4073 3821 5347 0.527 1.134 Example 7 4043 4007 5379 0.518 0.876 Example 8 4115 3650 5332 0.626 0.882 Example 9 4045 3980 5372 0.670 0.889 Example 10 4028 3930 5338 0.501 0.885 Comparative Example 1 4032 3890 5329 0.587 0.893 Comparative Example 2 4015 3894 5313 0.581 0.902

[0118] It can be seen from the test results that:

[0119] (1) As can be seen from Example 1 to Example 5, the present application can improve the magnetic properties of the permanent magnet strontium ferrite material by first mixing the rare earth oxide and the additive to form a uniformly mixed composite additive powder, and then mixing the composite additive powder with the strontium ferrite pre-sintering material. The remanence can be maintained at 4050Gs-4099Gs, the coercive force can be maintained at 3852Oe-4054Oe, and the remanence and coercive force can both reach a relatively optimal standard, and the M value is in the range of 5383-5415, so that the overall magnetic properties are relatively optimal.

[0120] (2) As can be seen from Example 1 and Example 6, the present application can further improve the coercive force by further regulating the ball milling time to control the average particle size of the powder in the mixed slurry obtained after the second mixing to be ≤1μm, so as to avoid the decrease of the initial single-domain particles due to the excessively large particle size, and to make the improvement of the coercive force not obvious.

[0121] (3) As can be seen from Example 1 and Example 7 to Example 8, the present application can make the permanent magnet strontium ferrite material have a relatively high density by further regulating the sintering temperature to be in the range of 1180℃-1230℃, so as to make the magnet show good magnetic properties, prevent the magnet from having a low remanence and a high coercive force due to insufficient density, and prevent the magnet from having an increased particle size due to over-sintering, although a larger remanence can be obtained but the coercive force decreases sharply.

[0122] (4) As can be seen from Example 1 and Example 9 to Example 10, the present application can make the permanent magnet strontium ferrite material have a relatively high orientation degree by further regulating the pressing forming pressure to be in the range of 300kg / cm 2 -600kg / cm 2 , in combination with an orientation magnetic field, so as to improve the remanence. Although a lower pressing forming pressure is more conducive to the orientation of the green body, it will lead to a decrease of the green body density and affect the remanence, and a higher pressing forming pressure will lead to a poor orientation of the green body and affect the improvement of the orientation degree in the sintering process.

[0123] (5) As can be seen from Example 1 and Comparative Example 1, the present application can improve the orientation degree of the strontium ferrite, promote the mass transfer efficiency in the sintering process and inhibit the excessive growth of the crystal grains to some extent, so as to improve the magnetic properties of the permanent magnet strontium ferrite material, and the addition of the rare earth oxide will not affect the particle size of the mixed slurry, which verifies that it plays a role at the grain boundary in the subsequent sintering process; and when the rare earth oxide is not added, it cannot achieve the effect of inhibiting the excessive growth of the crystal grains, so as to cause the magnetic properties of the permanent magnet strontium ferrite material to decrease;

[0124] In addition, the remanence is improved while the coercivity is also improved to some extent, thereby comprehensively improving the remanence and coercivity of the strontium ferrite material, and the overall magnetic performance is better.

[0125] (6) It can be seen from Example 1 and Comparative Example 2 that, by mixing the rare earth oxide and the additive first, the composite additive powder with uniform mixing, small particle size and uniformity is formed first, on the one hand, the mass transfer rate in the sintering process is improved, so that the sintering of the magnet is more sufficient, on the other hand, the small particles adhere to the grain boundaries of the strontium ferrite, play a pinning effect, inhibit the abnormal growth of the grains, and it can be seen from the XRD pattern and the texture factor that the addition of the composite additive promotes the preferred orientation of the particles along the C axis, the SEM micro-morphology diagram also shows that the grain agglomeration in Example 1 is reduced, the dispersibility is better, and the particle size is more uniform, and the comprehensive magnetic performance of the strontium ferrite is improved in all aspects.

[0126] When all the additives are directly added to the strontium ferrite pre-sintering material, the synergistic effect between the additives is difficult to play, and the non-uniform growth of the grains is easy to cause, and the modification effect cannot be better.

[0127] In summary, the rare earth oxide and the additive are mixed first in the present application, and the composite additive powder with uniform mixing, small particle size and uniformity is formed first, which directly avoids the problem of uneven mixing of the components in the composite additive in the secondary addition process due to direct addition, and then the composite additive powder is mixed with the strontium ferrite pre-sintering material, in the secondary addition process, the uniformly mixed composite additive powder can be uniformly distributed in the pre-sintering material, which is more conducive to the synergistic effect of the rare earth oxide and the additives in the composite additive, and the magnetic performance of the permanent magnet strontium ferrite material is improved.

[0128] The applicant declares that the above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto, and those skilled in the art should understand that any changes or replacements within the technical scope disclosed by the present application can be easily thought of by those skilled in the art, and all fall within the protection scope and disclosure scope of the present application.

Claims

1. A method of producing a permanent magnet strontium ferrite material, characterized by, The preparation method comprises the following steps: (1) first mixing a rare earth oxide, an additive and a first solvent to obtain a composite additive; The rare earth oxide comprises La2O3 and / or CeO2; The first mixing mode comprises ball milling; The inorganic calcium-containing compound, C 12 H 22 O 14 The mass ratio of Ca, silicon source, boron source, strontium source, La2O3 and CeO2 is (9-12):(3-6):(3-5):(1-2):(3-5):(0-4):(0-4), and is not 0 at the same time; (2) second mixing strontium ferrite pre-sintering material, the composite additive in step (1) and a second solvent to obtain a mixed powder, and after compression molding, a magnetic blank is obtained, and after sintering, a permanent magnet strontium ferrite material is obtained.

2. The production method according to claim 1, characterized by, The additive in step (1) comprises a calcium source, a silicon source, a boron source and a strontium source.

3. The preparation method according to claim 1, characterized in that, The inorganic calcium-containing compound comprises any one or a combination of at least two of CaCO3, CaO or Ca(OH)2.

4. The preparation method according to claim 2, characterized in that, The silicon source comprises SiO2 or H2SiO3.

5. The preparation method according to claim 2, characterized in that, The boron source comprises any one or a combination of at least two of H3BO3, HBO2 or B2O3.

6. The preparation method according to claim 2, characterized in that, The strontium source comprises any one or a combination of at least two of SrCO3, SrO or Sr(OH)2.

7. The preparation method according to claim 1, characterized in that, The inorganic calcium-containing compound, C 12 H 22 O 14 The mass ratio of Ca, the silicon source, the boron source, the strontium source, La2O3, and CeO2 is (9-12):5:(3-5):1:(3-5):(0-4):(0-4), and none of them is 0.

8. The method of claim 1, wherein, The first solvent in step (1) comprises deionized water.

9. The method of claim 1, wherein, The mass ratio of the first solvent to the rare earth oxide and the additive as a whole is (5-9):

1.

10. The method of claim 1, wherein, The ball milling time is 2h-8h.

11. The method of claim 1, wherein, The ball milling time is 4h-6h.

12. The method of claim 1, wherein, The ball milling speed is 60rpm-100rpm.

13. The method of claim 1, wherein, After the first mixing in step (1), the steps of dehydration, drying and grinding are further included.

14. The method of claim 13, wherein, The dehydration time is ≥12h.

15. The method of claim 14, wherein, The dehydration time is 16h-24h.

16. The method of claim 13, wherein, The drying time is ≥12h.

17. The method of claim 16, wherein, The drying time is 20h-24h.

18. The method of claim 1, wherein, The second solvent in step (2) comprises deionized water.

19. The method of claim 1, wherein, In step (2), the mass ratio of the strontium ferrite pre-sintering material, the composite additive and the second solvent is (80-120):(1-4):(100-300).

20. The method of claim 19, wherein, In step (2), the mass ratio of the strontium ferrite pre-sintering material, the composite additive and the second solvent is 100:(2-3):(140-200).

21. The method of claim 1, wherein, The second mixing mode in step (2) comprises ball milling.

22. The method of claim 21, wherein, The ball milling time is ≥12h.

23. The preparation method according to claim 21, characterized in that, The ball milling speed is 60rpm-100rpm.

24. The method of claim 1, wherein, After the second mixing is completed, the average particle size of the powder in the mixed slurry is ≤1μm.

25. The method of claim 24, wherein, After the second mixing is completed, the average particle size of the powder in the mixed slurry is 0.85μm-0.95μm.

26. The method of claim 1, wherein, After the second mixing in step (1), the step of dehydration is further included to obtain a mixed powder.

27. The method of claim 26, wherein, The dehydration time is ≥12h.

28. The method of claim 1, wherein, The solid content of the mixed powder is >60%.

29. The method of claim 1, wherein, The pressure of the press forming is 300 kg / cm 2 - 600 kg / cm 2 .

30. The preparation method according to claim 29, characterized in that, The pressure of the press molding is 400 kg / cm 2 - 500 kg / cm 2 .

31. The method of claim 1, wherein, During the compression molding process, an orientation magnetic field is further added.

32. The method of claim 31, wherein, The magnetizing current of the orientation magnetic field is 200A-400A.

33. The method of claim 32, wherein the method further comprises, The magnetizing current of the orientation magnetic field is 250A-350A.

34. The method of claim 31, wherein the step of forming the first and second layers is performed by a method selected from the group consisting of: 5 extrusion, injection molding, and compression molding. The demagnetizing current of the orientation magnetic field is 30A-60A.

35. The method of claim 34, wherein the method is performed in a single step. The demagnetizing current of the orientation magnetic field is 45A-55A.

36. The method of claim 1, wherein, After the compression molding, the step of drying is further included.

37. The method of claim 1, wherein, The sintering temperature is 1180℃-1230℃.

38. The method of claim 1, wherein, The holding time of the sintering is 30min-60min.

39. The method of claim 1, wherein, The heating rate of the sintering is 3℃ / min-10℃ / min.

40. The method of claim 1, wherein, The preparation method comprises the following steps: (1) La2O3and / or CeO2, C 12 H 22 O 14 Ca, inorganic calcium-containing compound, silicon source, boron source, strontium source and first solvent are ball milled at a rotation speed of 60 rpm-100 rpm for 2 h-8 h for first mixing, and then after the steps of dehydrating the first mixed slurry for > 12 h, drying at 70 °C-90 °C for > 12 h and grinding, a composite additive is obtained; The inorganic calcium-containing compound, C 12 H 22 O 14 The mass ratio of Ca, the silicon source, the boron source, the strontium source, La2O3, and CeO2 is (9-12):(3-6):(3-5):(1-2):(3-5):(0-4):(0-4), and is not simultaneously 0. (2) the strontium ferrite pre-sintering material, the composite additive of step (1) and the second solvent are ball-milled at a rotating speed of 60 rpm-100 rpm for ≥12 h to perform a second mixing, the average particle size of the powder in the obtained mixed slurry is ≤1 μm, after dehydration for ≥12 h, a mixed powder with a solid content of >60% is obtained, and the mixed powder is formed by pressing under a pressure of 300 kg / cm 2 -600 kg / cm 2 The pressing forming process further comprises adding an orientation magnetic field, the magnetizing current of the orientation magnetic field is 200 A-400 A, the demagnetizing current is 30 A-60 A, and after drying, a magnetic blank is obtained. The magnetic blank is sintered at a temperature of 1180 ℃-1230 ℃ for 30 min-60 min at a temperature increasing rate of 3 ℃ / min-10 ℃ / min to obtain a permanent magnet strontium ferrite material. The mass ratio of the strontium ferrite pre-sintering material, the composite additive and the second solvent is (80-120):(1-4):(100-300).

41. A permanent magnet strontium ferrite material, characterized by, The permanent magnet strontium ferrite material is prepared according to the preparation method in any one of claims 1-40.

42. The permanent magnet strontium-ferrite material of claim 41, wherein, The density of the permanent magnet strontium ferrite material is ≥ 4.9 g / cm 3 .

43. The permanent magnet strontium-ferrite material of claim 42, wherein, The density of the permanent magnet strontium ferrite material is 4.95 g / cm 3 - 5.00 g / cm 3 .

44. Use of a permanent magnet strontium-ferrite material according to any one of claims 41 to 43, or a permanent magnet strontium-ferrite material produced according to the production method of any one of claims 1 to 40, characterized in that, The permanent magnet strontium ferrite material is applied to the field of consumer electronics or the field of automobile electronics.

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