A dual-rare-earth co-substituted M-type barium ferrite wave-absorbing material and a preparation method thereof

Abstract

The application relates to the technical field of electromagnetic wave absorbing materials, and discloses a double-rare-earth co-substituted M-type barium ferrite wave absorbing material and a preparation method thereof, wherein the structural formula of the wave absorbing material is Ba 0.8 La 0.2‑ x Nd x Fe 12 O 19 , wherein x=0.05-0.15. The preparation method comprises the following steps: mixing barium salt, lanthanum salt, neodymium salt, iron salt and citric acid monohydrate, adding deionized water to fully dissolve and stir to obtain a transparent sol, then adjusting the pH value to 7.5-8.5, and obtaining a viscous wet gel after heating; the wet gel is subjected to high-temperature drying to form a porous and fluffy bread-shaped dry gel, which is ground and then pressed into shape and subjected to high-temperature calcination. The double-rare-earth co-substituted M-type barium ferrite wave absorbing material has good wave absorbing performance in the 2-18 GHz and 26.5-40 GHz wave bands.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic wave absorbing materials technology, specifically to a dual rare earth co-substituted M-type barium ferrite absorbing material and its preparation method. Background Technology

[0002] The rapid development of electronic information technology has driven the widespread adoption of high-frequency intelligent electromagnetic devices in the GHz band, leading to a significant increase in demand for high-performance microwave absorbing materials within this band. M-type ferrites, due to their chemical stability, high saturation magnetization, high resistivity, and large magnetocrystalline anisotropy, exhibit excellent microwave absorption performance. Therefore, hexagonal barium ferrites, with their magnetic and dielectric loss mechanisms and a natural resonant frequency close to 45 GHz, have become promising candidates for efficient millimeter-wave absorption. However, the inherent strong magnetism and low dielectric properties of ferrites often lead to poor impedance matching, typically resulting in larger thicknesses and narrow absorption bandwidths. Therefore, researchers frequently modify ferrites to achieve a more balanced electromagnetic property.

[0003] Ion substitution is one of the most common modification methods for barium ferrites, as it can alter the crystal structure to precisely control the intrinsic electromagnetic properties of barium ferrites. However, single-ion substitution struggles to achieve the optimal balance between magnetic and dielectric properties, leading researchers to increasingly focus on strategies involving multiple metal elements. Dual-ion co-substitution can overcome the limitations of single-ion control, enabling more flexible synergistic optimization of multiple electrical and magnetic properties.

[0004] While existing barium ferrite dual-ion co-substitution techniques can improve the magnetic properties of materials to some extent, they still suffer from problems such as limited solid solubility of substituent ions, easy generation of impurity phases, complex charge compensation mechanisms, and difficulties in synergistic optimization of magnetic properties. Especially for rare-earth ion co-substitution systems, the differences in the radii and electronic structures of different rare-earth ions easily lead to lattice distortion and rare-earth segregation, resulting in a decrease in material phase purity and magnetic property stability. Therefore, developing a barium ferrite material that can achieve stable rare-earth ion co-substitution, improve crystal structure stability, and simultaneously improve magnetic properties remains a pressing technical problem to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to provide a dual rare earth co-substituted M-type barium ferrite absorbing material and its preparation method, which can improve the electromagnetic parameters of barium ferrite, reduce the matching thickness of the material, broaden the effective absorption frequency band, and obtain a high-efficiency absorbing material that can be used in both frequency bands.

[0006] In one aspect of the invention, a dual rare-earth co-substituted M-type barium ferrite microwave absorbing material is proposed. According to an embodiment of the invention, the rare-earth elements are lanthanum and neodymium, and the structural formula of the microwave absorbing material is Ba. 0.8 La 0.2-x Nd x Fe 12 O 19 , where x = 0.05~0.15.

[0007] In another aspect, the present invention provides a method for preparing the aforementioned dual rare-earth co-substituted M-type barium ferrite microwave absorbing material. According to an embodiment of the present invention, rare-earth elements lanthanum and neodymium are co-doped into barium ferrite, while simultaneously affecting the Ba content in the barium ferrite. 2+ Substitution was carried out to obtain a dual rare earth co-substituted M-type barium ferrite microwave absorbing material.

[0008] In addition, the preparation method of the dual rare earth co-substituted M-type barium ferrite microwave absorbing material according to the above embodiments of the present invention may also have the following additional technical features: the method includes the following steps:

[0009] (1) Mix barium salt, lanthanum salt, neodymium salt, iron salt and citric acid monohydrate, add deionized water and stir to fully dissolve and obtain a transparent sol;

[0010] (2) Adjust the pH of the transparent sol to 7.5~8.5, and then heat it to obtain a viscous wet gel;

[0011] (3) The wet gel is dried at high temperature to form a porous and fluffy bread-like dry gel, which is then ground to obtain precursor powder;

[0012] (4) The precursor powder is pressed into shape, calcined at high temperature, cooled to room temperature, and then ground thoroughly to obtain the dual rare earth co-substituted M-type barium ferrite microwave absorbing material.

[0013] In some embodiments of the present invention, in step (1), the barium salt, lanthanum salt, neodymium salt, and iron salt are soluble metal salts, with nitrates being preferred.

[0014] Based on the reaction mechanism of the sol-gel method, any soluble metal salt that can be fully dissolved in the solvent and form a homogeneous system with the complexing agent can be used as a precursor, such as nitrates, acetates, and chlorides. In this embodiment of the invention, nitrates are used as the precursor because they have good solubility, few impurities, and are easy to obtain into a homogeneous sol; therefore, nitrates are preferred.

[0015] In some embodiments of the present invention, in step (1), the molar ratio of the barium salt, lanthanum salt, neodymium salt, iron salt and citric acid monohydrate is 0.8:(0.05~0.15):(0.05~0.15):12:13.

[0016] In step (1), barium salt, lanthanum salt, neodymium salt, and iron salt respectively provide Ba 2+ La 3+ 、Nd3+ and Fe 3+ Source, of which La 3+ and Nd 3+ Used to partially replace Ba 2+ At specific sites, synergistic substitution modification of rare earth ions is achieved; iron ions are used to construct the main crystal structure of M-type barium ferrite. Citric acid monohydrate acts as a complexing agent, forming stable coordination complexes with various metal ions, ensuring uniform dispersion of Ba, La, Nd, and Fe elements at the molecular level and suppressing local component segregation. Through complexation, a stable and uniform sol system is formed, providing a uniform precursor for subsequent gelation and heat treatment processes. This step helps to lower the barium ferrite formation temperature, improve the purity of the product phase, reduce grain size, and promote the uniform entry of La and Nd ions into the barium ferrite lattice, thus laying the foundation for obtaining high-performance lanthanum-neodymium co-substituted barium ferrite materials.

[0017] In some embodiments of the present invention, in step (2), the heating is carried out by an oil bath, the heating temperature is 110~140℃, and the heating time is 2~4 h.

[0018] In step (2), the sol system is maintained at 110-140℃ and heated for 2-4 hours using an oil bath. This allows the water in the system to gradually evaporate, increasing the concentration of metal ion complexes and promoting further cross-linking and aggregation of the citric acid complex network, thereby achieving the transformation from sol to gel. The resulting gel structure can uniformly fix Ba, La, Nd, and Fe elements in a three-dimensional network, preventing local segregation of components during subsequent heat treatment. When the heating temperature is below 110℃, the gelation process is slow and incomplete; when it is above 140℃, organic components such as citric acid are prone to premature thermal decomposition or carbonization, which is not conducive to the formation of a uniform gel structure. Therefore, controlling the heating temperature at 110-140℃ and the heating time at 2-4 hours is beneficial for obtaining a gel precursor with a uniform structure and stable component distribution, providing conditions for the subsequent formation of high-purity lanthanum-neodymium co-substituted barium ferrite materials.

[0019] In some embodiments of the present invention, in step (3), the drying temperature is 150~180°C and the drying time is 4~8 h.

[0020] In step (3), the wet gel obtained in step (2) is dried at 150~180℃ for 4~8 h to fully remove free water, adsorbed water and some bound water from the gel, and to promote further shrinkage and solidification of the gel network, thereby realizing the transformation from wet gel to dry gel. During this process, the metal ions remain uniformly dispersed, which is beneficial to maintaining the uniformity of the precursor composition. When the drying temperature is below 150℃, the residual water inside the gel is difficult to remove completely, affecting the subsequent heat treatment process; when it is above 180℃, the organic complexing agent is prone to rapid thermal decomposition or local carbonization, resulting in the destruction of the gel structure. By controlling the drying temperature at 150~180℃ and the drying time at 4~8 h, a dry gel precursor with stable structure and uniform composition can be obtained, which provides favorable conditions for the formation of high-purity lanthanum-neodymium co-substituted barium ferrite in the subsequent calcination process, and at the same time helps to reduce particle agglomeration and improve the stability of material properties.

[0021] In some embodiments of the present invention, in step (4), the material is pressed into a circular sheet with a diameter of 10-20 mm and a thickness of 3-10 mm.

[0022] In some embodiments of the present invention, in step (4), the heating rate of the high-temperature calcination is 5~10℃ / min.

[0023] In some embodiments of the present invention, the high-temperature calcination is first heated to 400-500°C and held for 2-3 hours, then heated to 1300-1400°C and held for 4-6 hours.

[0024] When the calcination temperature is low, the solid-phase diffusion reaction between the components is insufficient, and impurity phases such as α-Fe₂O₃ are easily left behind. As the calcination temperature increases, the reaction between Ba, La, Nd, and Fe elements becomes more complete, and the M-type barium ferrite main phase gradually forms and its crystallinity increases, thereby reducing the impurity content and improving the material properties. Experimental results show that a material with M-type lanthanum-neodymium co-substituted barium ferrite as the main phase can be obtained at 1400℃, with a significant reduction in impurity content. Therefore, high-temperature calcination at 1400℃ is preferred.

[0025] Compared with the prior art, the beneficial effects of the present invention are:

[0026] 1) This invention incorporates the rare earth elements lanthanum and neodymium simultaneously into barium ferrite, thereby increasing the rare earth ion La 3+ and Nd 3+ It simultaneously replaced the Ba in barium ferrite. 2+ A double rare-earth lanthanum-neodymium co-substituted barium ferrite powder material was obtained. Ion substitution with different ionic radii causes changes in the crystal lattice structure. 3+ and Nd 3+ Mainly by replacing BaFe 12 O 19Ba in the crystal lattice 2+ The position is inserted into the M-type barium ferrite structure. Due to La 3+ and Nd 3+ The ionic radii are all smaller than Ba. 2+ Substitution with rare earth ions leads to changes in lattice parameters and cell volume, causing a certain degree of lattice shrinkage. Furthermore, oxygen vacancies are generated in the system, increasing conductivity, dielectric constant, and loss, thereby reducing the matching thickness. In addition, dual rare earth ion substitution allows the material to broaden its effective absorption band under the influence of natural and exchange resonances, enabling it to exhibit certain electromagnetic wave attenuation capabilities in both the 2–18 GHz and 26.5–40 GHz frequency bands.

[0027] 2) This invention combines the sol-gel method with a pressing and sintering process. The sol-gel method achieves uniform dispersion of Ba, La, Nd, and Fe elements at the molecular level, yielding a precursor powder with uniform composition. Subsequently, the dry gel powder is pressed to form a green body with a fixed shape and thickness. During pressing, a denser and more uniform contact network forms between particles, which is beneficial for uniform heat transfer and element diffusion during subsequent calcination. Compared to direct calcination of the powder, the thickness of the pressed green body is more controllable, shortening the gas diffusion path, promoting the discharge of residual organic components and decomposition products, and reducing local component segregation and incomplete reactions. Simultaneously, the increased contact area between particles facilitates solid-phase diffusion reactions between Ba, La, Nd, and Fe components, thereby promoting the formation of the M-type barium ferrite main phase, reducing the content of impurity phases such as α-Fe₂O₃, and improving the crystallinity and phase purity of the material.

[0028] 3) To address the problems of uneven ion dispersion, easy formation of impurity phases, rare earth element segregation, and insufficient calcination in existing dual rare earth ion-substituted barium ferrites, this invention employs a sol-gel method combined with a pressing and sintering process. First, barium salts, lanthanum salts, neodymium salts, and iron salts are used as metal ion sources, and citric acid monohydrate is introduced as a complexing agent to make Ba... 2+ La 3+ 、Nd 3+ and Fe 3+ Uniform dispersion at the molecular level overcomes the problem of uneven mixing in traditional solid-phase methods. Subsequently, a uniform and stable precursor network structure is constructed through gelation and drying, reducing the possibility of rare earth ion segregation and enrichment during subsequent heat treatment.

[0029] 4) This invention employs a process route combining compression molding and two-stage calcination. Compression molding creates a uniformly thick preform structure in the precursor, increasing interparticle contact and facilitating subsequent solid-phase diffusion reactions. The 400-500℃ pre-calcination stage thoroughly removes organic components and nitrate ions, reducing the impact of residual impurities on the phase formation process. The high-temperature calcination stage promotes the formation of the M-type barium ferrite main phase, increasing the material's crystallinity and reducing the content of impurity phases such as α-Fe2O3. Simultaneously, La... 3+ and Nd 3+ Synergistic replacement of Ba 2+ The site causes changes in lattice parameters and the local crystal field environment, regulating the Fe-O-Fe superexchange interaction and magnetic moment coupling state. Through the synergistic effect of the above-mentioned techniques, this invention improves the main phase content and structural uniformity of the material, thereby effectively overcoming the problems of easy formation of impurity phases, insufficient phase formation, and insufficient performance stability in existing technologies. Attached Figure Description

[0030] Figure 1 BaFe obtained as Comparative Example 1 of the present invention 12 O 19 XRD diffraction pattern of the material (X-ray diffraction pattern).

[0031] Figure 2 BaFe obtained as Comparative Example 1 of the present invention 12 O 19 SEM image of the material -1 (scanning electron microscope image);

[0032] Figure 3 BaFe obtained as Comparative Example 1 of the present invention 12 O 19 -1 Absorption performance of the material in the frequency range of 2~18 GHz;

[0033] Figure 4 BaFe obtained as Comparative Example 1 of the present invention 12 O 19 -1 Absorption performance of the material in the frequency range of 26.5~40 GHz;

[0034] Figure 5 Ba obtained in Embodiment 1 of the present invention 0.8 La 0.1 Nd 0.1 Fe 12 O 19 XRD diffraction pattern of the material;

[0035] Figure 6 Ba obtained in Embodiment 1 of the present invention 0.8 La 0.1 Nd 0.1 Fe 12 O19 SEM images of the materials;

[0036] Figure 7 Ba obtained in Embodiment 1 of the present invention 0.8 La 0.1 Nd 0.1 Fe 12 O 19 Wave absorption performance of the material in the frequency range of 2~18 GHz;

[0037] Figure 8 Ba obtained in Embodiment 1 of the present invention 0.8 La 0.1 Nd 0.1 Fe 12 O 19 Absorption performance of the material in the frequency range of 26.5~40 GHz;

[0038] Figure 9 Ba obtained in Embodiment 1 of the present invention 0.8 La 0.1 Nd 0.1 Fe 12 O 19 Materials, Ba obtained in Example 2 0.8 La 0.15 Nd 0.05 Fe 12 O 19 Materials and Ba obtained in Example 3 0.8 La 0.05 Nd 0.15 Fe 12 O 19 A comparative schematic diagram of the X-ray diffraction patterns of the materials;

[0039] Figure 10 Ba obtained in Embodiment 1 of the present invention 0.8 La 0.1 Nd 0.1 Fe 12 O 19 Materials and BaFe obtained from Comparative Example 1 12 O 19 A comparison of electromagnetic parameters of the material, where a is the complex permittivity and b is the complex permeability;

[0040] Figure 11 BaFe obtained as Comparative Example 2 of the present invention 12 O 19 -2 Absorption performance of the material in the frequency range of 26.5~40 GHz. Detailed Implementation

[0041] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0042] Example 1

[0043] A method for preparing a dual rare earth co-substituted M-type barium ferrite microwave absorbing material includes the following steps:

[0044] (1) Barium nitrate, lanthanum nitrate, neodymium nitrate, ferric nitrate and citric acid monohydrate were mixed in a molar ratio of 0.8:0.1:0.1:12:13, and deionized water was added and stirred for 40 min to dissolve and obtain a sol.

[0045] (2) Add an appropriate amount of ammonia to the sol obtained in step (1) to adjust the pH value to 8, and then place the sol in an oil bath at 130°C and continue to stir and heat for 4 hours to obtain a wet gel.

[0046] (3) The wet gel obtained in step (2) is placed in a 160℃ forced-air drying oven and dried for 6 h to form a dry gel;

[0047] (4) Grind the dry gel obtained in step (3) in an agate mortar to obtain precursor powder;

[0048] (5) Press the powder obtained in step (4) into a sheet material with a thickness of 8 mm and a diameter of 20 mm;

[0049] (6) Place the sheet material obtained in step (5) in a muffle furnace, heat it at a rate of 5℃ / min, first heat it to 450℃ and hold it for 2 h, then heat it to 1400℃ and hold it for 4 h, cool it to room temperature with the furnace, and then grind it in a mortar for 10 min to finally obtain a dual rare earth co-substituted M-type barium ferrite microwave absorbing material, denoted as Ba 0.8 La 0.1 Nd 0.1 Fe 12 O 19 Powder materials.

[0050] Figure 5 and Figure 6 These are Ba obtained in Example 1. 0.8 La 0.1 Nd 0.1 Fe 12 O 19 XRD diffraction patterns and SEM images of powder materials. Figure 5As shown, the XRD curve exhibits obvious diffraction peaks of M-type barium ferrite, proving that the prepared Ba... 0.8 La 0.1 Nd 0.1 Fe 12 O 19 It is an M-type barium ferrite material. For example... Figure 6 As shown, Ba 0.8 La 0.1 Nd 0.1 Fe 12 O 19 The powder material is a hexagonal sheet with a certain thickness, which conforms to the characteristics of the hexagonal lattice of M-type barium ferrite.

[0051] Example 2

[0052] A method for preparing a dual rare earth co-substituted M-type barium ferrite microwave absorbing material includes the following steps:

[0053] (1) Barium nitrate, lanthanum nitrate, neodymium nitrate, ferric nitrate and citric acid monohydrate were mixed in a molar ratio of 0.8:0.15:0.05:12:13, and deionized water was added and stirred for 40 min to dissolve and obtain a sol.

[0054] (2) Add an appropriate amount of ammonia to the sol obtained in step (1) to adjust the pH value to 8, and then place the sol in an oil bath at 130°C and continue to stir and heat for 4 hours to obtain a wet gel.

[0055] (3) The wet gel obtained in step (2) is placed in a 160℃ forced-air drying oven and dried for 6 h to form a dry gel;

[0056] (4) Grind the dry gel obtained in step (3) in an agate mortar to obtain precursor powder;

[0057] (5) Press the powder obtained in step (4) into a sheet material with a thickness of 8 mm and a diameter of 20 mm;

[0058] (6) Place the sheet material obtained in step (5) in a muffle furnace, heat it at a rate of 5℃ / min, first heat it to 450℃ and hold it for 2 h, then heat it to 1400℃ and hold it for 4 h. After cooling it to room temperature in the furnace, grind it in a mortar for 10 min to finally obtain the dual rare earth co-substituted M-type barium ferrite microwave absorbing material, denoted as Ba. 0.8 La 0.15 Nd 0.05 Fe 12 O 19 Powder materials.

[0059] Example 3

[0060] A method for preparing a dual rare earth co-substituted M-type barium ferrite microwave absorbing material includes the following steps:

[0061] (1) Barium nitrate, lanthanum nitrate, neodymium nitrate, ferric nitrate and citric acid monohydrate were mixed in a molar ratio of 0.8:0.05:0.15:12:13, and deionized water was added and stirred for 40 min to dissolve and obtain a sol.

[0062] (2) Add an appropriate amount of ammonia to the sol obtained in step (1) to adjust the pH value to 8, and then place the sol in an oil bath at 130°C and continue to stir and heat for 4 hours to obtain a wet gel.

[0063] (3) The wet gel obtained in step (2) is placed in a 160℃ forced-air drying oven and dried for 6 h to form a dry gel;

[0064] (4) Grind the dry gel obtained in step (3) in an agate mortar to obtain precursor powder;

[0065] (5) Press the powder obtained in step (4) into a sheet material with a thickness of 4 mm and a diameter of 20 mm;

[0066] (6) Place the sheet material obtained in step (5) in a muffle furnace, heat it at a rate of 5℃ / min, first heat it to 450℃ and hold it for 2 h, then heat it to 1400℃ and hold it for 4 h. After cooling it to room temperature in the furnace, grind it in a mortar for 10 min to finally obtain the dual rare earth co-substituted M-type barium ferrite microwave absorbing material, denoted as Ba. 0.8 La 0.05 Nd 0.15 Fe 12 O 19 Powder materials.

[0067] Comparative Example 1

[0068] A method for preparing barium ferrite microwave absorbing powder material by sol-gel method combined with compression molding and sintering includes the following steps:

[0069] (1) Mix barium nitrate, ferric nitrate and citric acid monohydrate in a molar ratio of 1:12:13, add deionized water and stir for 30 min to dissolve and obtain a sol;

[0070] (2) Add an appropriate amount of ammonia to the sol obtained in step (1) to adjust the pH value to 7.5, and then place the sol in an oil bath at 130°C and continue to stir and heat for 4 hours to obtain a wet gel.

[0071] (3) The wet gel obtained in step (2) is placed in a 160℃ forced-air drying oven and dried for 6 h to form a dry gel;

[0072] (4) Grind the dry gel obtained in step (3) in an agate mortar to obtain precursor powder;

[0073] (5) Press the powder obtained in step (4) into a sheet material with a thickness of 8 mm and a diameter of 20 mm;

[0074] (6) Place the sheet material obtained in step (5) in a muffle furnace, heat it at a rate of 5℃ / min, first heat it to 450℃ and hold it for 2 h, then heat it to 1400℃ and hold it for 4 h, cool it to room temperature with the furnace, and then grind it in a mortar for 10 min to finally obtain the barium ferrite microwave absorbing powder material formed by sol-gel method by pressing and sintering, denoted as BaFe 12 O 19 -1 Powder material.

[0075] Figure 1 and Figure 2 These are BaFe obtained from Comparative Example 1. 12 O 19 XRD diffraction patterns and SEM images of the powder material. (Example: ...) Figure 1 As shown, the XRD curves mainly contain BaFe. 12 O 19 The diffraction peaks show a small amount of impurity phase α-Fe₂O₃, proving that the material's main phase is M-type barium ferrite BaFe. 12 O 19 Materials. For example... Figure 2 As shown, the material is a hexagonal sheet with a certain thickness, which conforms to the characteristics of the hexagonal lattice of M-type barium ferrite.

[0076] Figure 9 This is a comparison of the XRD curves of the dual rare-earth co-substituted M-type barium ferrite microwave absorbing materials prepared in Examples 1-3. First, when x = 0.05~0.15, Examples 1-3 can all form a structure with M-type barium ferrite as the main phase, indicating that the technical solution of this invention has good applicability. Second, combined with... Figure 1 It can be seen that the BaFe obtained in Comparative Example 1 12 O 19 -1 The powder material and the dual rare earth co-substituted M-type barium ferrite microwave absorbing material obtained in Examples 1-2 both produce less α-Fe2O3, while the Ba obtained by pressing 4 mm thick discs into calcined discs in Example 3 produces less α-Fe2O3. 0.8 La 0.05 Nd 0.15 Fe 12 O 19No α-Fe₂O₃ was generated in the powder material. This indicates that the thickness of the preform after pressing affects the phase formation of the material. When the preform thickness is large, the heat transfer and gas diffusion paths inside the sample increase, and incomplete reactions may occur in local areas, resulting in a small amount of α-Fe₂O₃ impurity phase residue. Appropriately reducing the preform thickness is beneficial for uniform heat transfer and sufficient component reaction, thereby increasing the content of the main phase. Experimental results show that using a smaller thickness preform can yield lanthanum-neodymium co-substituted barium ferrite materials with higher phase purity.

[0077] Comparative Example 2

[0078] A method for preparing barium ferrite materials using a traditional sol-gel method includes the following steps:

[0079] (1) Mix barium nitrate, ferric nitrate and citric acid monohydrate in a molar ratio of 1:12:13, add deionized water and stir for 30 min to dissolve and obtain a sol;

[0080] (2) Add an appropriate amount of ammonia to the sol obtained in step (1) to adjust the pH value to 7.5, and then place the sol in an oil bath at 120°C and continue to stir and heat for 4 hours to obtain a brown wet gel.

[0081] (3) Dry the wet gel obtained in step (2) to form a dry gel;

[0082] (4) Grind the dry gel obtained in step (3) to obtain brown precursor powder;

[0083] (5) The precursor powder obtained in step (4) is first heated to 450℃ and held for 2 h, and then heated to 1400℃ and held for 4 h. After cooling to room temperature in the furnace, it is then ground in a mortar for 10 min to finally obtain the barium ferrite material, denoted as BaFe. 12 O 19 -2 Powder materials.

[0084] The dual rare earth elements prepared in Example 1 were used to replace the M-type barium ferrite absorbing material Ba. 0.8 La 0.1 Nd 0.1 Fe 12 O 19 The barium ferrite microwave absorbing powder materials BaFe prepared in Comparative Examples 1-2 12 O 19 -1 and BaFe 12 O 19 -2 Perform performance testing:

[0085] (1) The absorption performance was tested using a vector network analyzer. During the test, the absorbing material powder was mixed with solid paraffin at a mass ratio of 8:2 to prepare block paraffin samples for testing. The paraffin samples in the 2-18 GHz test range were ring-shaped with an outer diameter of 7.0 mm and an inner diameter of 3.04 mm; the paraffin samples in the 26.5-40 GHz test range were block-shaped with a length of 7.112 mm and a width of 3.556 mm.

[0086] Figure 3 and Figure 4 These are the absorbing materials BaFe obtained in Comparative Example 1. 12 O 19 -1 Absorption performance diagrams for the 2–18 GHz and 26.5–40 GHz ranges. It is evident that the material exhibits good and strong reflection loss (<-10 dB) and a wide effective absorption bandwidth near a matching thickness of 2 mm. Specifically, within the 2–18 GHz range, with a matching thickness (i.e., the sample thickness) of 1.8 mm, the effective absorption bandwidth is 3.48 GHz and the reflection loss is -14.22 dB. Within the 26.5–40 GHz range, with a matching thickness of 2.2 mm, the optimal reflection loss is -19.66 dB and the effective absorption bandwidth is 3.65 GHz. Furthermore, the natural resonance peak shifts towards lower frequencies with increasing matching thickness, thus allowing for the design of materials with different thicknesses to meet specific absorption band requirements.

[0087] Figure 7 and Figure 8 These are the absorbing materials Ba obtained in Example 1. 0.8 La 0.1 Nd 0.1 Fe 12 O 19 The absorption performance diagrams are shown for the 2–18 GHz and 26.5–40 GHz bands. It is evident that, compared to the pure barium ferrite material in Comparative Example 1, the barium ferrite with dual rare-earth lanthanum and neodymium ion substitution exhibits improved absorption performance in both bands. Specifically, this is manifested in enhanced reflection loss, reduced matching thickness, and broadened effective absorption bandwidth. Specifically, within the 2–18 GHz band, with a matching thickness of 1.7 mm, the effective absorption bandwidth is 4.64 GHz, and the reflection loss is -20.59 dB. Within the 26.5–40 GHz band, with a matching thickness of 1.9 mm, the optimal reflection loss is -21.82 dB, and the effective absorption bandwidth is 4.35 GHz.

[0088] Figure 11 In Comparative Example 2, the pure barium ferrite BaFe was produced by directly calcining the powder without pressing. 12 O 19 -2. Wave absorption properties of powder materials. Figure 11 and Figure 4 A comparison clearly shows that the barium ferrite material prepared by the traditional sol-gel method in Comparative Example 2 suffers from drawbacks such as a large matching thickness and narrow bandwidth in the 26.5–40 GHz range. Strong reflection losses are observed at the matching thickness of 3–4 mm, with a bandwidth not exceeding 2 GHz. In contrast, the pure barium ferrite BaFe obtained in Comparative Example 1 through pressing and calcination... 12 O 19 While maintaining strong reflection loss, the powder material significantly reduces the matching thickness, broadens the absorption frequency band, and significantly improves the overall absorption performance.

[0089] (2) Electromagnetic parameter testing. The test was conducted using a vector network analyzer. During the test, the microwave absorbing material powder and solid paraffin were mixed at a mass ratio of 8:2 to prepare a block-shaped paraffin sample for testing. The paraffin sample in the test range of 26.5-40 GHz was in block shape, with a length of 7.112 mm and a width of 3.556 mm.

[0090] Figure 10 Ba obtained in Example 1 0.8 La 0.1 Nd 0.1 Fe 12 O 19 Materials and BaFe obtained from Comparative Example 1 12 O 19 Comparison chart of electromagnetic parameters of material -1. From Figure 10 As can be seen from a, after substitution with two rare-earth ions, both the real and imaginary parts of the complex permittivity of the barium ferrite material are significantly improved. Figure 10 As can be seen from b, the real and imaginary parts of the complex permeability of the barium ferrite material are significantly improved after substitution with two rare earth ions. The overall improvement in the electromagnetic parameters of the material leads to enhanced electromagnetic loss, thereby improving the overall microwave absorption performance.

[0091] The above description is merely an example and illustration of the structure of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the structure of the present invention or exceed the scope defined by the present invention, and all such modifications or additions should fall within the protection scope of the present invention.

Claims

1. A method for preparing a dual rare earth co-substituted M-type barium ferrite microwave absorbing material, characterized in that, Includes the following steps: (1) Barium salt, lanthanum salt, neodymium salt, iron salt and citric acid monohydrate are mixed, and deionized water is added to dissolve and stir to obtain a transparent sol, wherein the molar ratio of the barium salt, lanthanum salt, neodymium salt, iron salt and citric acid monohydrate is 0.8:(0.05~0.15):(0.05~0.15):12:13; (2) Adjust the pH of the transparent sol to 7.5~8.5, and then heat it to obtain a viscous wet gel, wherein the heating temperature is 110~140℃ and the heating time is 2~4 h; (3) The wet gel is dried at high temperature to form a porous and fluffy bread-like dry gel, which is then ground to obtain precursor powder; (4) The precursor powder is pressed into shape, calcined at high temperature, cooled to room temperature, and then thoroughly ground to obtain the dual rare earth co-substituted M-type barium ferrite microwave absorbing material. The structural formula of the microwave absorbing material is Ba. 0.8 La 0.2-x Nd x Fe 12 O 19 x = 0.05~0.15, wherein the precursor powder is pressed into a disc with a diameter of 10~20 mm and a thickness of 3~10 mm; the high-temperature calcination is first heated to 400~500℃ and held for 2~3 h, and then heated to 1300~1400℃ and held for 4~6 h.

2. The preparation method of a dual rare earth co-substituted M-type barium ferrite microwave absorbing material according to claim 1, characterized in that: In step (1), the barium salt, lanthanum salt, neodymium salt, and iron salt are all soluble metal salts.

3. The preparation method of a dual rare earth co-substituted M-type barium ferrite microwave absorbing material according to claim 1, characterized in that: In step (2), the heating is performed using an oil bath.

4. The preparation method of a dual rare earth co-substituted M-type barium ferrite microwave absorbing material according to claim 1, characterized in that: In step (3), the drying temperature is 150~180℃ and the drying time is 4~8 h.

5. The preparation method of a dual rare earth co-substituted M-type barium ferrite microwave absorbing material according to claim 1, characterized in that: In step (4), the heating rate of the high-temperature calcination is 5~10℃ / min.

6. A method for preparing a dual rare earth co-substituted M-type barium ferrite microwave absorbing material according to any one of claims 1-5.

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