Preparation method of anisotropic decagonal nickel-manganese-neodymium ferrite wave-absorbing material and application thereof

Abstract

The application relates to a preparation method of an anisotropic ten-faced nickel-manganese-neodymium ferrite wave-absorbing material and application thereof, and belongs to the technical field of wave-absorbing materials. The method solves the problem that the existing ferrite has a relatively thick matching thickness when absorbing low-frequency electromagnetic waves. The method comprises the following steps: adding magnetic particles into a nickel-manganese-neodymium ferrite-containing nitrate aqueous solution and uniformly mixing, adding citric acid, and adjusting the PH value to obtain a mixed solution; the mixed solution is vacuum dried after heating, and then is heated, ground, high-temperature calcined and ground to obtain the anisotropic ten-faced nickel-manganese-neodymium ferrite wave-absorbing material. The anisotropic ten-faced nickel-manganese-neodymium ferrite wave-absorbing material prepared by the method has a ten-faced crystal structure and multiple crystal structures, has excellent anisotropy, generates high magnetic loss, is beneficial to widening the effective absorption bandwidth of the material under a thinner matching thickness, realizes the lightness of the material, the process has the effect of enhancing the magnetic loss of the material, the method is simple, raw materials are rich in sources, and is suitable for the preparation of most low-frequency wave-absorbing materials.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of wave-absorbing materials, and particularly relates to a preparation method of an anisotropic decagonal nickel-manganese-neodymium ferrite wave-absorbing material and application thereof. BACKGROUND

[0002] In this fast developing era, the emergence of mobile phone communication, satellite navigation, WiFi, Bluetooth, etc. is accompanied by the emergence of 2-8 GHz electromagnetic waves, and electromagnetic radiation comes with it. Compared with high-frequency electromagnetic waves, the harm of low-frequency electromagnetic waves is more insidious. Not only will it interfere with other electronic devices, but also it will interfere with the inherent weak electromagnetic field of the human body in the long-term use process, and even affect the functions and organs of the human body, especially children. Therefore, the research on 2-8 GHz low-frequency electromagnetic wave-absorbing materials is urgent.

[0003] Low-frequency waveband wave-absorbing materials generally use magnetic wave-absorbing materials or composite materials based on magnetic wave-absorbing materials. In most cases, magnetic metal powder, ferrite, etc. are candidates for low-frequency wave-absorbing materials. The existing ferrite has high permeability and relatively small dielectric constant, good impedance matching, and is favored by researchers. However, ferrite also has a fatal disadvantage, that is, the limitation of low-frequency electromagnetic waves, that is, long wavelength and low frequency, which leads to an increase in the corresponding matching thickness, and the material thickness is difficult to meet the requirements. SUMMARY

[0004] The application aims to solve the problem of thick matching thickness of the existing ferrite in absorbing low-frequency electromagnetic waves, and provides a preparation method of an anisotropic decagonal nickel-manganese-neodymium ferrite wave-absorbing material and application thereof.

[0005] A preparation method of an anisotropic decagonal nickel-manganese-neodymium ferrite wave-absorbing material is realized according to the following steps:

[0006] I. Magnetic microparticles are added to a nickel-manganese-neodymium iron-containing nitrate aqueous solution and mixed, then citric acid is added and mixed, and then ammonia water is used to adjust the pH value to 7 to obtain a mixed solution;

[0007] II. The above mixed solution is heated to form a dry gel under water bath, and then a brown porous solid gel is obtained after vacuum drying, and then the brown porous solid gel is placed in a muffle furnace to obtain a fluffy ferrite powder, which is ground and then high-temperature calcined, and then ground to obtain an anisotropic decagonal nickel-manganese-neodymium ferrite wave-absorbing material, that is, the preparation method is completed.

[0008] Further, the configuration of the nickel-manganese-neodymium iron-containing nitrate aqueous solution in step I is as follows: nickel nitrate hexahydrate, manganese nitrate hexahydrate, neodymium nitrate nonahydrate, iron nitrate nonahydrate and deionized water are mixed in a molar ratio of 0.5:0.5:0.04:1.96:(1-3), and a glass rod is used for stirring until dissolution.

[0009] Further, the molar ratio of metal ions in the aqueous solution of nickel-manganese-neodymium iron nitrate to citric acid in step one is 1:(1-3).

[0010] Further, the magnetic microparticles in step one are nickel-manganese-neodymium iron spinel ferrite.

[0011] Further, the molar ratio of each atom of nickel-manganese-neodymium iron in the aqueous solution of nickel-manganese-neodymium iron nitrate to each atom of nickel-manganese-neodymium iron in the magnetic microparticles in step one is 10:(3-1).

[0012] Further, the heating in the water bath in step two is at a temperature of 80-110 DEG C.

[0013] Further, the vacuum drying in step two is in a vacuum drying oven with a vacuum degree of 0.01-0.5 MPa and a temperature of 110-120 DEG C for 10-24 h.

[0014] Further, the heating in the muffle furnace in step two is at a temperature of 200-300 DEG C for 1-3 h.

[0015] Further, the high-temperature calcination in step two is in a high-temperature tube furnace, with a temperature rising rate of 1-5 DEG C / min to 1100-1200 DEG C and a temperature holding time of 1-2 h, and then a temperature falling rate of 1-2 DEG C / min to room temperature.

[0016] Further, the grinding in step two is with an agate mortar until no obvious particles are felt.

[0017] The application of the above-mentioned anisotropic ten-faced nickel-manganese-neodymium ferrite wave-absorbing material is to use the anisotropic ten-faced nickel-manganese-neodymium ferrite wave-absorbing material for microwave absorption in S, C and X wave bands.

[0018] Further, the S wave band is 2-4 GHz, the C wave band is 4-8 GHz, and the X wave band is 2-12 GHz.

[0019] Advantages of the present application:

[0020] 1. The present application uses the sol-gel method with the addition of magnetic ferrite secondary microparticles to promote nucleation, adds magnetic particles in a uniform solution to promote the formation of nickel-manganese-neodymium ferrite microparticles with anisotropy and mainly ten-faced crystal structure, thereby having a wider and stronger low-frequency electromagnetic wave absorption performance in a thinner matching thickness.

[0021] 2. The anisotropic decahedral nickel-manganese-neodymium ferrite microwave absorbing material prepared by the present invention has a decahedral crystal structure and various crystal structures, exhibiting excellent anisotropy, thereby generating high magnetic loss. This is beneficial for broadening the effective absorption bandwidth of the material with a thinner matching thickness, and realizing the lightweighting of the material.

[0022] 3. With an absorber thickness of 1-6mm, the effective absorption bandwidth (absorbing 90% of electromagnetic waves) of the decahedral nickel-manganese-neodymium ferrite covers 2.56-9.52GHz, achieving the goal of broadband absorption.

[0023] 4. At the corresponding frequency of 8.4 GHz, when the thickness of the decahedral nickel-manganese-neodymium ferrite absorption layer is 5.5 mm, the reflection loss reaches -40.489 dB, and the material achieves a strong absorption effect of 99.99% for electromagnetic waves.

[0024] 5. Due to its strong anisotropy, exhibiting decahedral crystals and various crystal structures at the microscopic level, nickel-manganese-neodymium ferrite is suitable as an electromagnetic wave absorbing material for microwave absorption in the S, C, and X bands. Attached Figure Description

[0025] Figure 1 The image shows the XRD pattern of the anisotropic decahedral nickel-manganese-neodymium ferrite microwave absorbing material in the embodiment.

[0026] Figure 2 Parts a and b are SEM images of the anisotropic decahedral nickel-manganese-neodymium ferrite absorbing material in the embodiment; part c is a TEM image of the anisotropic decahedral nickel-manganese-neodymium ferrite absorbing material in the embodiment; part d is a high-resolution image of the anisotropic decahedral nickel-manganese-neodymium ferrite absorbing material in the embodiment; and part e is an elemental surface scan of the anisotropic decahedral nickel-manganese-neodymium ferrite absorbing material in the embodiment.

[0027] Figure 3 The image shows the VSM diagram of the anisotropic decahedral nickel-manganese-neodymium ferrite microwave absorbing material in the embodiment.

[0028] Figure 4 The graph shows the real and imaginary parts of the complex permeability and the tangent of the magnetic loss factor of the anisotropic decahedral nickel-manganese-neodymium ferrite absorbing material in the coaxial ring sample when the filling mass ratio is 75%. In the example, ● represents the real part, ■ represents the imaginary part, and ▲ represents the tangent of the magnetic loss factor.

[0029] Figure 5 The graph shows the reflection loss curves of the anisotropic decahedral nickel-manganese-neodymium ferrite absorbing material in the embodiments. ■ indicates 1mm, ■ indicates 2mm, ◆ indicates 3mm. This indicates 3.5mm. Indicates 4mm, denotes 4.5 mm, denotes 5 mm, denotes 5.5 mm, and denotes 6 mm. DETAILED DESCRIPTION

[0030] The technical solution of the present application is not limited to the following specific embodiments, but also includes any combination of the specific embodiments.

[0031] Specific embodiment one: a preparation method of an anisotropic ten-faced nickel-manganese-neodymium ferrite wave-absorbing material, which is realized according to the following steps:

[0032] I. magnetic microparticles are added to a nickel-manganese-neodymium ferrite-containing nitrate aqueous solution and mixed, then citric acid is added and mixed, and then ammonia water is used to adjust the pH value to 7, to obtain a mixed solution;

[0033] II. the mixed solution is heated under water bath to form a dry gel, and after vacuum drying, a brown porous solid gel is obtained, which is then placed in a muffle furnace to be heated to obtain a fluffy ferrite powder, which is ground and then high-temperature calcined, and then ground to obtain an anisotropic ten-faced nickel-manganese-neodymium ferrite wave-absorbing material, i.e., the preparation method is completed.

[0034] In the present embodiment, the heating under water bath to form a dry gel is to first generate a green sol, and then continue to heat to remove water to form a dry gel.

[0035] In the present embodiment, the purpose of vacuum drying is to completely remove the water in the dry gel to obtain a brown porous solid gel.

[0036] Specific embodiment two: different from specific embodiment one, the configuration of the nickel-manganese-neodymium ferrite-containing nitrate aqueous solution in step I is that nickel nitrate hexahydrate, manganese nitrate hexahydrate, neodymium nitrate nonahydrate, iron nitrate nonahydrate and deionized water are mixed in a molar ratio of 0.5:0.5:0.04:1.96:(1-3), and stirred with a glass rod until dissolved. The other steps and parameters are the same as those of specific embodiment one.

[0037] Specific embodiment three: different from specific embodiment one, the molar ratio of metal ions to citric acid in the nickel-manganese-neodymium ferrite-containing nitrate aqueous solution in step I is 1:(1-3). The other steps and parameters are the same as those of specific embodiment one.

[0038] Specific embodiment four: different from specific embodiment one, the magnetic microparticles in step I are nickel-manganese-neodymium ferrite spinel ferrite. The other steps and parameters are the same as those of specific embodiment one.

[0039] Embodiment five: the embodiment is different from embodiment one in that the molar ratio of each atom of the nickel-manganese-neodymium-iron in the aqueous solution of the nickel-manganese-neodymium-iron nitrate in step one to each atom of the nickel-manganese-neodymium-iron in the magnetic microparticles is 10:(3-1). The other steps and parameters are the same as those in embodiment one.

[0040] Embodiment six: the embodiment is different from embodiment one in that the heating in the water bath in step two is at a temperature of 80-110℃. The other steps and parameters are the same as those in embodiment one.

[0041] Embodiment seven: the embodiment is different from embodiment one in that the vacuum drying in step two is in a vacuum drying oven with a vacuum degree of 0.01-0.5MPa and a temperature of 110-120℃ for 10-24h. The other steps and parameters are the same as those in embodiment one.

[0042] Embodiment eight: the embodiment is different from embodiment one in that the heating in the muffle furnace in step two is at a temperature of 200-300℃ for 1-3h. The other steps and parameters are the same as those in embodiment one.

[0043] Embodiment nine: the embodiment is different from embodiment one in that the high-temperature calcination in step two is in a high-temperature tube furnace, the temperature is increased to 1100-1200℃ at a rate of 1-5℃ / min and kept for 1-2h, and then decreased to room temperature at a rate of 1-2℃ / min. The other steps and parameters are the same as those in embodiment one.

[0044] Embodiment ten: the embodiment is different from embodiment one in that the grinding in step two is with an agate mortar until no obvious particle feeling. The other steps and parameters are the same as those in embodiment one.

[0045] Embodiment eleven: the application of the anisotropic decagonal nickel-manganese-neodymium-iron oxide wave-absorbing material is to use the anisotropic decagonal nickel-manganese-neodymium-iron oxide wave-absorbing material for microwave absorption in the S, C and X wave bands.

[0046] In the embodiment, the S wave band is 2-4GHz, the C wave band is 4-8GHz, and the X wave band is 2-12GHz.

[0047] The beneficial effects of the present application are verified by the following examples:

[0048] Example:

[0049] A preparation method of an anisotropic decagonal nickel-manganese-neodymium-iron oxide wave-absorbing material is realized according to the following steps:

[0050] I. Add magnetic particles to the aqueous solution of nickel-manganese-neodymium-iron nitrate and mix, then add citric acid and mix, and then adjust the pH value to 7 with ammonia water to obtain a mixed solution;

[0051] II. Heat the mixed solution to form a xerogel under water bath, and obtain a brown porous solid gel after vacuum drying, then heat in a muffle furnace to obtain a fluffy ferrite powder, and then grind, high-temperature calcine, and grind again to obtain an anisotropic dodecahedral nickel-manganese-neodymium-iron ferrite wave-absorbing material, thereby completing the preparation method.

[0052] The aqueous solution of nickel-manganese-neodymium-iron nitrate in step I of the embodiment is prepared by mixing 0.727 g of nickel nitrate hexahydrate, 0.717 g of manganese nitrate hexahydrate, 0.088 g of neodymium nitrate nonahydrate, 3.958 g of iron nitrate nonahydrate, and 18 ml of deionized water, and stirring with a glass rod until dissolved.

[0053] The molar ratio of metal ions to citric acid in the aqueous solution of nickel-manganese-neodymium-iron nitrate in step I of the embodiment is 1:2.

[0054] The magnetic particles in step I of the embodiment are nickel-manganese-neodymium-iron spinel ferrite.

[0055] The molar ratio of nickel-manganese-neodymium-iron atoms in the aqueous solution of nickel-manganese-neodymium-iron nitrate to nickel-manganese-neodymium-iron atoms in the magnetic particles in step I of the embodiment is 10:1.

[0056] The heating under water bath in step II of the embodiment is at a temperature of 100℃.

[0057] The vacuum drying in step II of the embodiment is in a vacuum drying box with a vacuum degree of 0.2 MPa and a temperature of 110℃ for 12 h.

[0058] The heating in the muffle furnace in step II of the embodiment is at 260℃ for 2 h.

[0059] The high-temperature calcination in step II of the embodiment is in a high-temperature tube furnace, with a temperature rising rate of 4℃ / min to 1200℃ and a temperature holding time of 1 h, and then a temperature falling rate of 2℃ / min to room temperature.

[0060] The grinding in step II of the embodiment is with an agate mortar until no obvious particles are felt.

[0061] The prepared anisotropic ten-faced nickel-manganese-neodymium ferrite wave-absorbing material in the embodiment is in ten-faced structure and flaky structure, and irregular structure such as spherical structure, the size of the ten-faced crystal material is 3 μm, and the grain size is micron level; under the micro-morphology, the ten-faced grain distribution state is disordered, the anisotropy of the material is increased, the Snoek limit is broken through, and greater magnetic permeability is exhibited.

[0062] The obtained anisotropic ten-faced nickel-manganese-neodymium ferrite wave-absorbing material is subjected to X-ray diffraction phase analysis (XRD). The characterization instrument used is a DX-2700 type X-ray diffractometer produced by Dandong Haoyuan Analysis Instrument Co., Ltd., China, the scanning speed is set to 10° / min, and the scanning range is 10°-90°. The characterization test result is shown in Table 1. Figure 1 As shown in Table 1 and compared with the standard PDF card, the diffraction angle of the prepared nickel-manganese-neodymium ferrite wave-absorbing material with anisotropic ten-faced crystal structure is matched with the standard Fe3O4 PDF card 88-0866, and there is a clear diffraction peak at about 2θ = 32.68° in the XRD diagram, the second phase FeNd2O3 is generated at this position, and the (1 1 1), (2 2 0), (3 1 1), (22 2), (4 0 0), (3 31), (4 2 2), (5 1 1), (4 4 0), (5 3 1), (4 4 2), (6 2 0), (5 3 3), (6 2 2), (4 4 4), (55 1), (6 4 2), (7 3 1) reflection plane diffraction peaks prove that the cubic spinel ferrite phase is generated.

[0063] The obtained anisotropic ten-faced nickel-manganese-neodymium ferrite wave-absorbing material is subjected to scanning (SEM) and energy spectrum area scanning analysis of elements and transmission (TEM) electron microscope characterization, and TESCAN MIRA LMS type scanning electron microscopes of Czech and FEI Talos F200x type transmission electron microscopes of the United States are used. As shown in Table 2, Figure 2 As shown in Table 2 and (a, b), the microstructure of the nickel-manganese-neodymium ferrite wave-absorbing material with anisotropic ten-faced crystal structure presents a plurality of crystal structures with ten-faced crystal structure as the main crystal structure, such as irregular crystal structures like spherical and flaky structures. The TEM diagram of the nickel-manganese-neodymium ferrite wave-absorbing material with anisotropic ten-faced crystal structure is shown in Table 2. Figure 2 As shown in Table 2 and (c), the microstructure is still adhered together at a smaller scale, and it can be seen that the ten-faced crystal structure is adhered together with other crystal structures. At the same time, high-resolution shooting is performed on the selected area under the TEM, as shown in Table 2. Figure 2(d) shows, the lattice fringes of 0.4864 nm corresponding to the (111) plane of the nickel manganese neodymium ferrite material are marked. The element surface scan of the nickel manganese neodymium ferrite wave-absorbing material with an anisotropic ten-faced crystal structure is shown in Figure 2 (e) shows that each element is uniformly distributed, and the prepared spinel ferrite is a pure nickel manganese neodymium ferrite.

[0064] The magnetic properties of the nickel manganese neodymium ferrite wave-absorbing material with an anisotropic ten-faced crystal structure are analyzed at room temperature by using a Lake Shore 7404 instrument from the United States, as shown in Figure 3 As shown in (f), it can be seen that the material prepared by us is a soft magnetic ferrite, the saturation magnetization is 56.456 emu / g, the coercive force is 21.488 Oe, and Mr / Ms is 0.068, indicating that the material obtained is a single domain structure.

[0065] The dielectric properties of the nickel manganese neodymium ferrite wave-absorbing material with an anisotropic ten-faced crystal structure are as follows: the anisotropic ten-faced nickel manganese neodymium ferrite wave-absorbing material is mixed with melted paraffin wax at a mass ratio of 7.5:2.5, and then poured into a mold (i.e., the filling degree mass ratio is 75%), and then pressurized at 100-125°C under 1-10 MPa for 5 min, and then cooled to room temperature to form a coaxial ring sample with an outer diameter of 7 mm, an inner diameter of 3 mm, and a height of 2-3 mm. After that, the electromagnetic parameters of the wave-absorbing material are tested. During the test, the electromagnetic parameters are obtained by using a vector network analyzer, and the test frequency range is 2-18 GHz. Due to the submagnetic property of the ferrite, the relative magnetic permeability is used to summarize the change rule of the electromagnetic parameters, and further reflects the wave-absorbing performance of the material to a certain extent. The real part of the relative magnetic permeability represents the storage capacity of the material to electromagnetic energy, and the imaginary part represents the dielectric loss capacity of the material to electromagnetic energy. As shown in Figure 4 The larger real and imaginary parts of the relative magnetic permeability show the high magnetic energy storage and loss capacity of the nickel manganese neodymium ferrite wave-absorbing material with an anisotropic ten-faced crystal structure, and the high magnetic loss is the magnetic loss loss tangent above 1, which is beneficial to the low-frequency band (2-8 GHz) wave-absorbing capacity of the material.

[0066] The reflection loss values of the nickel manganese neodymium ferrite wave-absorbing material with an anisotropic ten-faced crystal structure under the thickness of 1-6.0 mm are calculated, as shown in Figure 5The effective absorption bandwidth, i.e. the range of reflection loss values <-10 dB, is 0.08 GHz (4.16-4.24 GHz) when the thickness of the absorber is 3.5 mm, and the minimum reflection loss value is -10.32 dB, corresponding to the frequency point of 4.24 GHz. The effective absorption bandwidth is 2.64 GHz (3.76-6.32 GHz) when the thickness of the absorber is 4.0 mm, and the minimum reflection loss value is -13.0 dB, corresponding to the frequency point of 4.24 GHz. The effective absorption bandwidth is 5.92 GHz (3.36-9.36 GHz) when the thickness of the absorber is 4.5 mm, and the maximum reflection loss value is -13.66 dB, corresponding to the frequency of 4.24 GHz. The effective absorption bandwidth is 6.56 GHz (2.96-9.52 GHz) when the thickness of the absorber is 5.0 mm, and the maximum reflection loss value is -21.86 dB, corresponding to the frequency of 4.08 GHz. The effective absorption bandwidth is 6.56 GHz (2.8-9.36 GHz) when the thickness of the absorber is 5.5 mm, and the maximum reflection loss value is -40.49 dB, corresponding to the frequency of 8.4 GHz. The effective absorption bandwidth is 6.4 GHz (2.56-8.96 GHz) when the thickness of the absorber is 6 mm, and the maximum reflection loss value is -36.78 dB, corresponding to the frequency of 3.76 GHz. Thus, when the thickness of the absorber changes from 1.0 to 6.0 mm, the effective absorption frequency band of the material almost covers the 2-10 GHz band. The nickel-manganese-neodymium ferrite wave-absorbing material with an anisotropic ten-faced crystal structure realizes the wide-frequency absorption (6.56 GHz) at a thickness of 5.0 mm, and the strong absorption (-40.49 dB) at a thickness of 5.5 mm.

[0067] In summary, the reasons for the excellent wave-absorbing performance of the nickel-manganese-neodymium ferrite wave-absorbing material with an anisotropic ten-faced crystal structure are as follows. Firstly, in the preparation and design of the nickel-manganese-neodymium ferrite wave-absorbing material with an anisotropic ten-faced crystal structure, the sol-gel method with magnetic particle addition is adopted to generate microparticles with a ten-faced crystal structure, increase the anisotropy of the material, and effectively improve the magnetic permeability of the material, thereby giving the nickel-manganese-neodymium ferrite wave-absorbing material greater absorption of low-frequency electromagnetic waves. Secondly, the generation of the ten-faced crystal structure and the multiple crystal structures of the nickel-manganese-neodymium ferrite wave-absorbing material effectively improves the magnetic permeability of the material, thereby giving the nickel-manganese-neodymium ferrite wave-absorbing material greater absorption of low-frequency electromagnetic waves.

Claims

1. A preparation method of an anisotropic decagonal nickel-manganese-neodymium ferrite wave-absorbing material, characterized in that It is carried out in the following steps: I. To the aqueous solution of nickel-manganese-neodymium-iron nitrate, magnetic particles are added and mixed, then citric acid is added and mixed, and then the pH value is adjusted to 7 with ammonia water to obtain a mixed solution; II. The mixed solution is heated to form a dry gel under water bath, and then a brown porous solid gel is obtained after vacuum drying, and then the brown porous solid gel is heated in a muffle furnace to obtain a fluffy ferrite powder, which is ground and then high-temperature calcined, and then ground to obtain an anisotropic dodecahedral nickel-manganese-neodymium-iron ferrite wave-absorbing material, i.e. the preparation method is completed; The aqueous solution of nickel-manganese-neodymium-iron nitrate in step I is prepared by mixing nickel nitrate hexahydrate, manganese nitrate hexahydrate, neodymium nitrate nonahydrate, iron nitrate nonahydrate and deionized water in a molar ratio of 0.5:0.5:0.04:1.96:(1-3), and stirring with a glass rod until dissolved; The molar ratio of metal ions in the aqueous solution of nickel-manganese-neodymium-iron nitrate in step I to citric acid is 1:(1-3); The magnetic particles in step I are nickel-manganese-neodymium-iron spinel ferrite; The molar ratio of each atom of nickel-manganese-neodymium-iron in the aqueous solution of nickel-manganese-neodymium-iron nitrate in step I to each atom of nickel-manganese-neodymium-iron in the magnetic particles is 10:(3-1); The heating under water bath in step II is at a temperature of 80-110℃; The vacuum drying in step II is carried out in a vacuum drying oven at a vacuum degree of 0.01-0.5MPa and a temperature of 110-120℃ for 10-24h; The heating in the muffle furnace in step II is at a temperature of 200-300℃ for 1-3h; The high-temperature calcination in step II is carried out in a high-temperature tube furnace at a rate of 1-5℃ / min to a temperature of 1100-1200℃ and maintained for 1-2h, and then reduced to room temperature at a rate of 1-2℃ / min.

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