Lanthanum oxide and barium ferrite composite material and preparation method thereof

Abstract

The invention discloses a lanthanum oxide and barium ferrite composite material, the composite material is prepared by doping lanthanum oxide La2O3 with barium ferrite BaFe12O19 as a matrix, the chemical component of the composite material is Ba (1-x) LaxFe12O19, and x is more than or equal to 0.2 and less than or equal to 0.8. The range of x is any one of 0.2, 0.4, 0.6 and 0.8. The preparation method has the beneficial effects that the magnetic performance stability is improved, the electromagnetic wave absorption performance is enhanced, the impedance matching characteristic is improved, the crystallinity and microstructure of the material are optimized, no impurity phase exists, the process controllability is high, the preparation process is simple and convenient, and the cost is low.

Description

Technical Field

[0001] The present invention relates to the technical field of wave-absorbing and magnetic performance materials, and in particular to a composite material of lanthanum oxide and barium ferrite. Background Art

[0002] Ferrites are composite oxides composed of one or more transition metal elements, such as Fe, Co, and Ni. Based on their lattice structure, ferrites can be classified into spinel ferrites, magnetoplumbite ferrites, garnet ferrites, and perovskite ferrites. These ferrites can be further divided into five categories based on their magnetic properties: soft ferrites, hard ferrites, moment ferrites, spin ferrites, and piezoelectric ferrites.

[0003] Since its introduction in the early 20th century, ferrite materials have been a key focus of materials science and magnetics research. With the continuous advancement of materials science and technology, the application of ferrites has gradually expanded to various technical fields, especially in high-frequency magnetic materials, electronic equipment, communications technology, energy conversion, and environmental protection. Ferrites hold broad application prospects.

[0004] Ferrite materials, a key functional ceramic, possess irreplaceable application value in electronics, microwave communications, magnetic recording, and electromagnetic wave absorption due to their excellent magnetic and dielectric properties. However, as modern electronic technology advances toward higher frequencies, miniaturization, and integration, traditional ferrite material systems are increasingly unable to meet the demands of cutting-edge applications in terms of magnetic properties, frequency response, and temperature stability.

[0005] Therefore, it is necessary to optimize and improve the performance of existing ferrite materials, which is also one of the current research hotspots.

[0006] Barium ferrite is a type of magnetoplumbite ferrite. The magnetoplumbite system includes a variety of similar hexagonal structure compounds such as M, W, Y, Z, X and U, all of which belong to the hexagonal crystal system. Barium ferrite belongs to the M-type hexagonal structure compound, also known as M-type barium hexagonal ferrite, and its chemical formula is BaFe 12 O 19 Barium ferrite is composed of barium and iron and is typically synthesized through a solid-phase reaction at high temperatures. As a typical permanent magnet material, barium ferrite exhibits high saturation magnetization, high remanence, high coercivity, and high magnetic anisotropy. It is widely used in self-biased microwave ferrite devices, magneto-optical devices, magnetic sensors, perpendicular magnetic recording media, and wave-absorbing materials.

[0007] Research on barium ferrite began in the 1940s and garnered widespread attention in the decades that followed. With advancements in science and technology, the performance of barium ferrite has been continuously optimized, and its application areas have gradually expanded. Today, barium ferrite is widely used in a variety of industries, including magnetic materials, electronic devices, information storage, medical diagnostics, and energy.

[0008] The present invention studies barium ferrite and develops a material with better performance and a corresponding preparation method. Summary of the Invention

[0009] In order to overcome the shortcomings of the background technology, the present invention provides a composite material of lanthanum oxide and barium ferrite.

[0010] The technical solution of the present invention is: the composite material is barium ferrite BaFe 12 O 19 The composite material is made of a matrix doped with lanthanum oxide La2O3, and its chemical composition is Ba (1-x) La x Fe 12 O 19 , where 0.2≤x≤0.8.

[0011] Preferably, the range of x is any one of 0.2, 0.4, 0.6, and 0.8. When x=0.2, the chemical composition of the composite material is Ba 0.8 La 0.2 Fe 12 O 19 , its magnetic properties are the best. When x = 0.4, the chemical composition of the composite material is Ba 0.6 La 0.4 Fe 12 O 19 , its wave absorbing performance is the best.

[0012] In order to overcome the shortcomings of the background technology, the present invention provides a method for preparing a ball-milled composite material of lanthanum oxide and barium ferrite, which comprises the following steps:

[0013] 1) Barium ferrite BaFe 12 O 19 Grind into powder;

[0014] 2) Barium ferrite BaFe 12 O 19 The powder and lanthanum oxide La2O3 are uniformly mixed in proportion;

[0015] 3) drying the powder mixed in step 2 at a drying temperature for 3 hours;

[0016] 4) Place the dried powder in a ball mill, mix it with zirconium balls, and then add anhydrous ethanol to seal it;

[0017] 5) Place the ball mill containing the powder into the ball mill for spherical graphite;

[0018] 6) Dry the powder after spherical ink at the drying temperature for 1 hour;

[0019] 7) Screening out the powder;

[0020] 8) Sinter the powder into blocks.

[0021] Preferably, the drying temperature in the above steps is 60° C. to 80° C., which is convenient for drying the material quickly.

[0022] Preferably, the step 1 is to 12 O 19 Grind into powder and screen out barium ferrite BaFe with a diameter of ≤0.075mm 12 O 19 Powder, the lanthanum oxide La2O3 in step 2 is in powder form.

[0023] Preferably, step 4 is to place the dried powder in a ball mill and mix it with ball mill zirconium balls, the mass ratio of the dried powder to the ball mill zirconium balls being 1:15, and then add anhydrous ethanol at a ratio of 20 ml / 3 g and seal it.

[0024] Preferably, in step 4, the small balls of the ball-milled zirconium balls account for 20%, the medium balls of the ball-milled zirconium balls account for 50%, and the rest are large balls. The diameters of the small balls, medium balls, and large balls of the ball-milled zirconium balls are 0.5 mm, 2 mm, and 5 mm, respectively.

[0025] Preferably, the step 5 is to place the ball mill containing the powder into a ball mill for graphite, and the parameters of the ball mill are set to a speed of 300r / min to 400r / min, and the graphite time is 10h-14h.

[0026] Preferably, the ball mill parameters are set to a rotation speed of 300 r / min and a ball milling time of 13h55min.

[0027] 1. Preferably, steps 4-1 and 4-2 are added between steps 4 and 5, wherein step 4-1 is to wash the mixed powder dried in step 3 with nitric acid HNO3, anhydrous ethanol, and deionized water;

[0028] The step 4-2 is to dry the cleaned powder at a drying temperature for 20 minutes.

[0029] Preferably, the deionized water in step 4 is replaced with ultrapure water.

[0030] Preferably, the step 1 is to use a 200-mesh sieve for screening, and the step 8 is to use a 100-mesh sieve for screening powders with a diameter of ≤0.15 mm.

[0031] In order to overcome the shortcomings of the background technology, the present invention provides a sample experimental test preparation method of a ball-milled composite material of lanthanum oxide and barium ferrite, which is convenient for directly preparing a small amount of samples and testing the performance of the samples, and comprises the following steps:

[0032] 1) Barium ferrite BaFe 12 O 19 Grind into powder and sieve out the powder with a 200-mesh sieve;

[0033] 2) Barium ferrite BaFe 12 O 19 The powder and lanthanum oxide La2O3 are uniformly mixed in proportion;

[0034] 3) drying the powder mixed in step 2 at 80°C for 3 hours;

[0035] 4) washing the mixed powder dried in step 3 with nitric acid HNO3, anhydrous ethanol, and deionized water;

[0036] 5) Dry the cleaned powder at 80°C for 20 minutes;

[0037] 6) Step 4 is to place the dried powder in a ball mill and mix it with ball mill zirconium balls. The mass ratio of the dried powder to the ball mill zirconium balls is 1:15, wherein the small balls of the ball mill zirconium balls account for 20%, the medium balls of the ball mill zirconium balls account for 50%, and the rest are large balls. The diameters of the small, medium, and large balls of the ball mill zirconium balls are 0.5 mm, 2 mm, and 5 mm, respectively. Then, anhydrous ethanol is added and sealed at a ratio of 20 ml / 3 g;

[0038] 7) Place the ball mill containing the powder into the ball mill for graphite treatment. The ball mill parameters are set to a speed of 300 rpm to 400 rpm and a graphite treatment time of 10 to 14 hours.

[0039] 8) Dry the powder after spherical ink at 80℃ for 1h;

[0040] 9) screening out the powder;

[0041] 10) Add polyvinyl alcohol (PVA) to the powder and mix well. Place the mixture into a mold and press into a tablet press at a pressure of 10 MPa for 60 seconds until the powder is pressed into a sheet.

[0042] 11) The semi-finished product after pressing in step 10 is placed in a temperature of 1250° C. and kept for 3 hours;

[0043] 12) Wait for the finished product of step 11 to cool to room temperature in the furnace.

[0044] In the above step 7, the ball mill parameters are preferably set to a rotation speed of 300 r / min and a ball milling time of 13h55min.

[0045] The beneficial effects of the present invention are good magnetic properties, wave absorbing performance, low production cost, and mass production, which are specifically as follows:

[0046] ① Improve magnetic stability: by introducing La 3+ Ion substitution Ba 2+ or Fe 3+ sites, the material lattice distortion is enhanced, the magnetocrystalline anisotropy is improved, the coercivity of the material is significantly improved, and the magnetic stability and anti-interference ability of the magnetic device under high frequency conditions are improved.

[0047] ② Enhanced electromagnetic wave absorption performance: After doping with La2O3, the sample forms grain boundary pinning and grain refinement, which greatly improves the electromagnetic wave attenuation ability of the composite material.

[0048] ③Improve impedance matching characteristics: La doping 3+ The introduction of local stress and lattice defects makes the input impedance of the material closer to the free space impedance. At specific frequencies and thicknesses (such as 15-16GHz, 1.6-2.6mm), |Zin / Z0| is close to 1, which effectively suppresses the reflection of electromagnetic waves and improves absorption efficiency.

[0049] ④Optimization of material crystallinity and microstructure: XRD test shows that no second phase is generated after doping, La 3+ It successfully dissolved into the lattice structure, forming a stable magnetoplumbite phase. SEM results show that the grain size has been refined from 1.2μm to 0.6μm, which helps reduce hysteresis loss and enhance magnetic response speed.

[0050] ⑤ No impurity phase and strong process controllability: No impurity phases such as La2O3 and α-Fe2O3 were detected in the material, indicating that the solid solution doping effect is good, and the temperature, time and particle size parameters in the preparation process are reasonably controlled, which can achieve scale-up preparation from laboratory to industrial scale.

[0051] ⑥The preparation process is simple and low cost: the raw materials used are commercially available BaFe 12 O 19 and La2O3 powder, combined with low-temperature ball milling and traditional sintering technology, the overall process equipment requirements are low, and it has good promotion and batch preparation prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 BaFe 12 O 19Diagram of the crystal structure of barium ferrite.

[0053] Figure 2 BaFe 12 O 19 GSASII refined XRD diffraction pattern.

[0054] Figure 3 The present invention is in accordance with the material Ba (1-x) La x Fe 12 O 19 XRD diffraction pattern.

[0055] Figure 4 for Figure 3 XRD diffraction local enlargement diagram.

[0056] Figure 5 BaFe 12 O 19 SEM image of barium ferrite.

[0057] Figure 6 For Ba (1-x) La x Fe 12 O 19 When x=0.2 (Ba 0.2 La 0.8 Fe 12 O 19 ) of the SEM image.

[0058] Figure 7 For Ba (1-x) La x Fe 12 O 19 When x=0.4 (Ba 0.4 La 0.6 Fe 12 O 19 ) of the SEM image.

[0059] Figure 8 For Ba (1-x) La x Fe 12 O 19 When x=0.6 (Ba 0.6 La 0.4 Fe 12 O 19 ) of the SEM image.

[0060] Figure 9 For Ba (1-x) La x Fe 12 O 19 When x=0.8 (Ba0.8 La 0.2 Fe 12 O 19 ) of the SEM image.

[0061] Figure 10-13 For Ba 0.6 La 0.4 Fe 12 O 19 EDS analysis of barium ferrite.

[0062] Figure 14 For Ba 0.6 La 0.4 Fe 12 O 19 EDS distribution of barium ferrite.

[0063] Figure 15 For Ba (1-x) La x Fe 12 O 19 (x=0, 0.2, 0.4, 0.6, 0.8) Powder hysteresis loop diagram.

[0064] Figure 16 For Ba (1-x) La x Fe 12 O 19 (x=0, 0.2, 0.4, 0.6, 0.8) Variation trend of powder saturation magnetization Ms.

[0065] Figure 17 For Ba (1-x) La x Fe 12 O 19 (x=0, 0.2, 0.4, 0.6, 0.8) Variation trend of powder coercivity Hc.

[0066] Figures 18-22 Ba (1-x) La x Fe 12 O 19 RL curves in the 2-18 GHz band when x=0, 0.2, 0.4, 0.6, 0.8.

[0067] Figure 23 For Ba (1-x) La x Fe 12 O 19 RL curve for the lowest return loss value in the 2-18 GHz band.

[0068] Figures 24-28 Ba(1-x) La x Fe 12 O 19 Impedance matching diagram in the 2-18 GHz band when x=0, 0.2, 0.4, 0.6, 0.8. DETAILED DESCRIPTION

[0069] The embodiments of the present invention will be further described below with reference to the accompanying drawings:

[0070] M-type barium ferrite, chemical formula is BaFe 12 O 19 The crystal structure of barium ferrite is hexagonal ferrite, which belongs to magnetoplumbite structure. Figure 1 shown.

[0071] The crystal structure of barium ferrite is composed of alternating cubic close-packed structure and hexagonal close-packed structure, in which O 2- Along the vertical direction of the stacking layer, it is stacked in a hexagonal close-packed manner to form tetrahedrons, octahedrons and hexahedrons. 12 O 19 O2- and Ba 2+ The radii are close, so the barium ions and oxygen ions form a hexagonal close packing, Ba 2+ Fe, which is dispersed in the oxygen ion layer and has a relatively smaller radius, 3+ In O 2- The interstitial position of M-type barium ferrite. Therefore, an M-type barium ferrite molecule consists of five oxygen ion layers. A unit cell contains 2 BaFe 12 O 19 The molecule is composed of 10 layers of oxygen ions, Ba 2+ Each M-type barium ferrite unit cell contains two BaFe 12 O 19 molecules, 2 Ba 2+ , 24 Fe 3+ , 38 O 2- .

[0072] Because of La 3+ With a unique 4f electron layer structure, we use barium ferrite BaFe 12 O 19 As the matrix, we want to dope lanthanum oxide La2O3 to make La 3+ Replace Ba 2+ ions or Fe 3+ Ion sites can significantly change the magnetocrystalline anisotropy and electromagnetic parameters of the material.

[0073] Lanthanum oxide doping is mainly through La 3+ Ion replacement Ba 2+ions or Fe 3+ ion is realized. Due to La 3+ The ionic radius is smaller than Ba 2+ After doping, the lattice constant usually decreases slightly, resulting in a slight distortion of the crystal structure. This distortion affects the Fe 3 + ion coordination environment, thereby changing the strength of the superexchange interaction and the magnetocrystalline anisotropy. 3+ The high charge of Fe may induce a charge compensation mechanism, such as 3+ Fe 2+ conversion or the generation of oxygen vacancies, which further affects the magnetic properties of the material.

[0074] La 3+ Ions themselves do not have magnetic moments, and the effect of their doping on the magnetic properties of barium ferrite is mainly achieved through the following ways: Magnetic moment change: La 3+ Replace Ba 2+ After that, some Fe 3+ Converted to Fe 2+ To maintain charge balance. 2+ The magnetic moment is lower than that of Fe 3 + , thereby reducing the saturation magnetization. Lattice distortion and Fe 3+ / Fe 2+ The change in ratio affects the crystal field, thus changing the magnetocrystalline anisotropy constant and coercivity. 3+ Doping may weaken or enhance the Fe-O-Fe superexchange interaction, affecting the Curie temperature and magnetic loss of the material.

[0075] Lanthanum oxide doping can significantly improve the microwave absorption performance of barium ferrite. La3 + The introduction of doping increases grain boundary resistance and reduces dielectric loss, making it suitable for high-frequency applications. Furthermore, the reduction in grain size and increase in crystal defects caused by doping can enhance the scattering and absorption of electromagnetic waves, thereby broadening the absorption band and increasing the absorption intensity.

[0076] like Figure 1-Figure 28 As shown, this embodiment provides a composite material of lanthanum oxide and barium ferrite, wherein the composite material is barium ferrite BaFe 12 O 19 The composite material is made of a matrix doped with lanthanum oxide La2O3, and its chemical composition is Ba (1-x) La x Fe 12 O 19 , where 0.2≤x≤0.8.

[0077] Preferably, the range of x is any one of 0.2, 0.4, 0.6, and 0.8. When x=0.2, the chemical composition of the composite material is Ba 0.8 La 0.2 Fe 12 O 19 , its magnetic properties are the best. When x = 0.4, the chemical composition of the composite material is Ba 0.6 La 0.4 Fe 12 O 19 , its wave absorbing performance is the best.

[0078] As shown in the figure, XRD diffraction analysis shows that all samples have a hexagonal spatial structure group, belonging to the magnetoplumbite structure. The SEM image shows that the sample has a hexagonal flake structure. EDS analysis shows that the sample is composed of four elements: Fe, O, Ba, and La. VSM analysis shows that with the continuous increase of the doping amount x, the saturation magnetization intensity Ms tends to decrease. Compared with pure barium ferrite, the coercive force of the doped sample increases, among which Ba 0.8 La 0.2 Fe 12 O 19 The magnetic properties of La2O3 doped barium ferrite Ba (1-x) La x Fe 12 O 19 The wave absorption performance is better than that of pure barium ferrite, and the impedance matching value is improved to a certain extent. 0.6 La 0.4 Fe 12 O 19 The wave absorbing performance is the best.

[0079] In order to overcome the shortcomings of the background technology, the present invention provides a method for preparing a ball-milled composite material of lanthanum oxide and barium ferrite, which comprises the following steps:

[0080] 1) Barium ferrite BaFe 12 O 19 Grind into powder;

[0081] 2) Barium ferrite BaFe 12 O 19 The powder and lanthanum oxide La2O3 are uniformly mixed in proportion;

[0082] 3) drying the powder mixed in step 2 at a drying temperature for 3 hours;

[0083] 4) Place the dried powder in a ball mill, mix it with zirconium balls, and then add anhydrous ethanol to seal it;

[0084] 5) Place the ball mill containing the powder into the ball mill for spherical graphite;

[0085] 6) Dry the powder after spherical ink at the drying temperature for 1 hour;

[0086] 7) Screening out the powder;

[0087] 8) Sinter the powder into blocks.

[0088] The sintered blocks are the cost of the composite material.

[0089] For faster and better drying, the drying temperature in the above steps is preferably 60°C to 80°C, which is convenient for drying the material quickly. This temperature range has a fast drying speed and is available in conventional drying ovens. Of course, the drying temperature is preferably 80°C.

[0090] In order to facilitate the control of barium ferrite BaFe 12 O 19 The diameter of the powder. Preferably, the step 1 is to 12 O 19 Grind into powder and screen out barium ferrite BaFe with a diameter of ≤0.075mm 12 O 19 The lanthanum oxide La2O3 in step 2 is in powder form. The powder particle diameter is convenient for subsequent spherical graphite production and is also convenient for filtering out a small amount of large particles during production, thereby improving the efficiency of subsequent spherical graphite production.

[0091] Preferably, step 4 comprises placing the dried powder in a ball mill jar and mixing it with zirconium balls, with a mass ratio of 1:15 between the dried powder and the balls, and then placing the mixture in anhydrous ethanol at a ratio of 20 ml / 3 g, which is sealed. Zirconium balls have high hardness, with a Mohs hardness of 8.5 to 9, which is close to the hardness of diamond, and have an extremely low wear rate. They can maintain their spherical shape after long-term use, reducing pollution and replacement frequency. Conventional ceramic balls, while having acceptable hardness, have relatively poor wear resistance.

[0092] In order to better grind barium ferrite BaFe 12 O 19 Powder and lanthanum oxide La2O3. Preferably, in step 4, the small balls of the ball-milled zirconium balls account for 20%, the medium balls of the ball-milled zirconium balls account for 50%, and the rest are large balls. The diameters of the small balls, medium balls and large balls of the ball-milled zirconium balls are 0.5 mm, 2 mm and 5 mm respectively.

[0093] Preferably, step 5 is to place the ball mill containing the powder into a ball mill for inkjet printing. The ball mill parameters are set to a speed of 300 r / min to 400 r / min and an inkjet printing time of 10 hours to 14 hours. Generally, the ball mill parameters are preferably set to a speed of 300 r / min and an inkjet printing time of 13 hours and 55 minutes. Of course, the speed and inkjet printing time can be appropriately adjusted according to the amount of inkjet printed at one time.

[0094] Since factory ball mills contain impurities due to long-term use, they need to be cleaned to prevent impurities generated by frequent mixing of different materials in the laboratory. Preferably, steps 4-1 and 4-2 are added between steps 4 and 5. Step 4-1 involves cleaning the mixed powder dried in step 3 with nitric acid (HNO3), anhydrous ethanol, and deionized water. The deionized water here can be replaced with ultrapure water.

[0095] The step 4-2 is to dry the cleaned powder at a drying temperature for 20 minutes.

[0096] To facilitate screening of powder particles, preferably, a 200-mesh screen is used for screening in step 1, and a 100-mesh screen is used to screen powder with a diameter of ≤0.15 mm in step 8. The 200-mesh screen is easily available on the market and has the advantages of large domestic production, low price, and simple operation.

[0097] In order to overcome the shortcomings of the background technology, the present invention provides a sample experimental test preparation method of a ball-milled composite material of lanthanum oxide and barium ferrite, which is convenient for directly preparing a small amount of samples and testing the performance of the samples, and comprises the following steps:

[0098] 1) Barium ferrite BaFe 12 O 19 Grind into powder and sieve out the powder with a 200-mesh sieve;

[0099] 2) Barium ferrite BaFe 12 O 19 The powder and lanthanum oxide La2O3 are uniformly mixed in proportion;

[0100] 3) drying the powder mixed in step 2 at 80°C for 3 hours;

[0101] 4) washing the mixed powder dried in step 3 with nitric acid HNO3, anhydrous ethanol, and deionized water;

[0102] 5) Dry the cleaned powder at 80°C for 20 minutes;

[0103] 6) Step 4 is to place the dried powder in a ball mill and mix it with ball mill zirconium balls. The mass ratio of the dried powder to the ball mill zirconium balls is 1:15, wherein the small balls of the ball mill zirconium balls account for 20%, the medium balls of the ball mill zirconium balls account for 50%, and the rest are large balls. The diameters of the small, medium, and large balls of the ball mill zirconium balls are 0.5 mm, 2 mm, and 5 mm, respectively. Then, anhydrous ethanol is added and sealed at a ratio of 20 ml / 3 g;

[0104] 7) Place the ball mill containing the powder into the ball mill for graphite. The ball mill parameters are set to a speed of 300r / min to 400r / min and a graphite time of 10h to 14h.

[0105] 8) Dry the powder after spherical ink at 80℃ for 1h;

[0106] 9) screening out the powder;

[0107] 10) Add polyvinyl alcohol (PVA) to the powder and mix well. Place the mixture into a mold and press into a tablet press at a pressure of 10 MPa for 60 seconds until the powder is pressed into a sheet.

[0108] 11) The semi-finished product after pressing in step 10 is placed in a temperature of 1250° C. and kept for 3 hours;

[0109] 12) Wait for the finished product of step 11 to cool to room temperature in the furnace.

[0110] The finished product after cooling in step 12 can be directly used to test its performance.

[0111] Here, the ball mill parameters in step 7 can preferably be set to a rotation speed of 300 r / min and a ball milling time of 13h55min.

[0112] The following are the experimental results and analysis

[0113] 1. Ba (1-x) La x Fe 12 O 19 XRD analysis:

[0114] In order to determine the crystal structure and lattice parameters of the sample and study the microscopic properties of the material, X-ray diffraction was performed on La2O3 doped barium ferrite. Figure 2-3 As shown in the XRD diffraction patterns, all samples (x = 0, 0.2, 0.4, 0.6, 0.8) exhibit a typical magnetoplumbite hexagonal structure (space group P63 / mmc), which is completely consistent with the standard card (PDF#04-002-1906), confirming that BaFe 12 O 19 The successful synthesis of the main phase. It is worth noting that with the La3+ With the increase of doping amount (x), the diffraction peak intensity gradually decreases, indicating that La 3+ The introduction of La leads to lattice distortion and decreased crystallinity. However, no diffraction peaks of impurity phases (such as La2O3, α-Fe2O3 or BaFe2O4) were detected, indicating that La 3+ By replacing Ba 2+ Site (ionic radius: ) is completely dissolved in the lattice. In addition, the slight shift of the diffraction peak (such as the (114) crystal plane) further verifies the contraction of the lattice parameter, which is consistent with our observations on La 3+ Right 2+ This is consistent with the theoretical idea of ​​lattice strain caused by substitution.

[0115] La doping 3+ After that, the XRD peak position shifted and no second phase appeared, indicating that La 3+ Entered BaFe 12 O 19 A solid solution is formed in the main crystal structure. XRD shift analysis:

[0116] ① The difference in ionic radius causes the change in lattice constant: When La 3+ Substitute Ba in solid solution 2+ When the 3+ A smaller ionic radius reduces the lattice constant, according to Bragg's law:

[0117] 2dsinθ=nλ

[0118] When the interplanar spacing d decreases, θ must increase, so the diffraction peak shifts toward higher angles.

[0119] ② Lattice distortion and internal stress induce diffraction peak shift: La 3+ The high charge and small radius of the crystal introduce internal stress into the lattice, causing local distortion of the crystal. This also affects the average value of the lattice constant, causing subtle shifts in the XRD peaks.

[0120] 2. Ba (1-x) La x Fe 12 O 19 SEM and EDS analysis:

[0121] like Figure 5-9 The SEM images of all samples show a hexagonal flake morphology, but the grain size is significantly reduced after doping (the average grain size of the pure sample is ≈1.2μm, and it drops to ≈0.6μm when x=0.8), and the grains are refined, indicating that stress occurs inside the lattice. This phenomenon is attributed to La 3+ Grain boundary pinning effect caused by doping: La 3+Replace Ba 2+ After that, lattice distortion and local stress inhibited grain growth. However, at high doping levels (x ≥ 0.6), the grain distribution uniformity deteriorated and obvious agglomeration occurred ( Figure 8 and Figure 9 ), and La 3+ Charge imbalance caused by excess (Fe 3+ →Fe 2+ conversion) and the increase of surface energy.

[0122] In order to explore the (1-x) La x Fe 12 O 19 Elemental composition, EDS analysis of sample x = 0.6, Figure 10-14 For Ba 0.4 La 0.6 Fe 12 O 19 EDS spectrum. From the EDS graph, we can see that the sample is composed of four elements: Fe, O, Ba, and La. Fe and O elements account for a larger proportion, while Ba and La elements account for a smaller proportion. 0.4 La 0.6 Fe 12 O 19 The Fe / O ratio is consistent with the theoretical value (12:19), but it is slightly higher than the theoretical value (12:19), suggesting the existence of trace oxygen vacancies, which may be one of the key factors for the subsequent changes in magnetic properties.

[0123] Three, Ba (1-x) La x Fe 12 O 19 Electromagnetic performance analysis:

[0124] We used a vibrating sample magnetometer (VSM) to test the magnetic properties of the composite material prepared in the present invention.

[0125] Figure 15 For Ba (1-x) La x Fe 12 O 19 Hysteresis loops for powder samples (x = 0, 0.2, 0.4, 0.6, and 0.8). As can be seen from the hysteresis loops, all samples exhibit near-saturation magnetization when the external magnetic field reaches 20 kOe. As the doping level x increases, the area enclosed by the hysteresis loop decreases, resulting in a gradual decrease in the hysteresis loss of the samples. When x = 0.8, the area enclosed by the hysteresis loop is minimized, resulting in the lowest hysteresis loss. The material consumes less energy during magnetization, making it easier to magnetize and demagnetize.

[0126] Table 1 gives the(1-x) La x Fe 12 O 19 The specific magnetic parameters of the powder samples (x=0, 0.2, 0.4, 0.6, 0.8) are saturation magnetization Ms, residual magnetization Mr, residual magnetization ratio Mr / Ms and coercivity Hc. Figure 16 It can be seen that with the continuous increase of the doping amount x, the saturation magnetization Ms tends to decrease gradually. The magnetism of barium ferrite is mainly due to the magnetic Fe 3+ Contribution. (1-x) La x Fe 12 O 19 Medium non-magnetic La 3+ Right 2+ In order to maintain the electroneutrality condition, the substitution of Fe 3+ to Fe 2+ , thereby affecting the exchange interaction between iron atoms at the interface in barium ferrite, resulting in a decrease in Ms.

[0127] When x = 0, the maximum value of the saturation magnetization Ms is 62.32emu / g. When x = 0.8, the saturation magnetization Ms is 40.89emu / g. At the same time, as the doping amount x increases, the residual magnetization Mr also gradually decreases. The residual magnetization reflects the memory effect of the magnetic material. When x = 0, the sample has the strongest memory effect and the best ability to maintain the magnetization state. The ratio of the remanence ratio Mr / Ms of all samples is less than 0.50, indicating that the prepared Ba (1-x) La x Fe 12 O 19 The magnetic material has a multi-domain structure. Figure 17 From Table 1, it can be seen that the coercive force of the doped sample increases compared with the undoped sample. As the doping amount increases, the coercive force Hc first increases and then decreases. When x = 0, the minimum value of the sample coercive force Hc is 0.11kOe, and when x = 0.6, the maximum value of the sample coercive force Hc is 1.35kOe. The coercive force reflects the ability of the magnetic material to resist the rearrangement of the magnetic domain. When x = 0.6, the sample maintains the best stability in the magnetization state. Both the magnetocrystalline anisotropy field and the grain size will affect the size of the coercive force Hc. La 3+ Right 2+ Substitution of Fe 3+ to Fe 2+ , and Fe 2+ The anisotropy of Fe3+ is greater than that of Fe3+. Therefore, the coercivity of the doped sample increases compared to pure barium ferrite. The coercivity Hc decreases slightly, which may be due to the change in the sample grain size.

[0128] Table 1Ba(1-x) La x Fe 12 O 19 Magnetic parameters

[0129] x Ms(emu / g) Mr(emu / g) Mr / Ms Hc(kOe) 0 62.32 27.07 0.43 0.11 0.2 45.18 17.21 0.38 1.15 0.4 42.92 11.83 0.28 0.78 0.6 40.43 13.69 0.34 1.35 0.8 40.89 4.01 0.10 0.16

[0130] Four, Ba (1-x) La x Fe 12 O 19 Wave absorbing performance analysis:

[0131] We use a vector network analyzer to test the absorption performance of barium ferrite and study the effect of La2O3 on the absorption performance of barium ferrite. Figure 18-22 It is in the 2-18GHz band. (1-x) La x Fe 12 O 19 The RL curve of (x=0, 0.2, 0.4, 0.6, 0.8) reflects the microwave absorption performance of the sample. The frequency bandwidth of the absorbing material with a reflection loss value less than -10dB is called the effective absorbing bandwidth of the absorbing material. Figure 18 It can be seen that when x=0, the sample has no effective absorption value in the range of 2-13GHz. In the range of 13-16GHz, the sample with a thickness of 2.0mm-4.0mm has an effective absorption bandwidth, which first increases and then decreases with thickness. Figure 19 and 21 It can be seen that when x = 0.2 and 0.6, the sample has no effective absorption bandwidth within 2-18 GHz. As the thickness of the sample increases, the reflection loss peak shifts to low frequencies. It may be that the sample for testing absorption performance is not prepared well, resulting in poor absorption performance. Figure 20 It can be seen that when x=0.4, the sample has no effective absorption value in the range of 2-14GHz, and the sample with a thickness of 1.6mm-3.6mm has an effective absorption bandwidth in the range of 14-16GHz. The effective absorption bandwidth first increases and then decreases with thickness. Figure 22 It can be seen that when x=0.8, the sample has no effective absorption value in the range of 2-13 GHz, and the sample with a thickness of 1.6 mm-4.0 mm has an effective absorption bandwidth in the range of 13-16 GHz. The effective absorption bandwidth first increases and then decreases with thickness.

[0132] Figure 23 For Ba (1-x) La x Fe 12 O 19 Table 2 shows the RL curve of the lowest reflection loss value in the 2-18GHz band. (1-x) La x Fe 12 O19 The lowest reflection loss value and the lowest reflection loss extreme point corresponding to a certain matching thickness in the 2-18 GHz band are the best absorbing parameters for different samples at a certain matching thickness. When x = 0, the sample matching thickness is 3mm, and at the lowest reflection loss extreme point of 15.47 GHz, the lowest reflection loss value is -35.36 dB, and the effective absorption bandwidth is approximately 0.47 GHz. When x = 0.2, the sample matching thickness is 2.9mm, and at the lowest reflection loss extreme point of 13.49 GHz, the lowest reflection loss value is -2.54 dB, and there is no effective absorption bandwidth. When x = 0.4, the sample matching thickness is 2.6mm, and at the lowest reflection loss extreme point of 16.14 GHz, the lowest reflection loss value is -46.13 dB, and the effective absorption bandwidth is approximately 0.74 GHz. When x = 0.6, the sample matched with a thickness of 4.9 mm achieved a minimum reflection loss of -2.16 dB at the lowest reflection loss extreme point of 8.14 GHz, with no effective absorption bandwidth. When x = 0.8, the sample matched with a thickness of 2.9 mm achieved a minimum reflection loss of -40.95 dB at the lowest reflection loss extreme point of 15.28 GHz, with an effective absorption bandwidth of approximately 0.61 GHz.

[0133] The wider the effective absorption width, the better the material's absorbing performance. The larger the area enclosed by the curve and the -10dB line, the better the material's absorbing performance. When x = 0.4 and the thickness is 2.6mm, Ba (1-x) La x Fe 12 O 19 The sample has the lowest reflection loss value and the widest effective absorption bandwidth, achieving the best absorption performance. When x = 0.4 and x = 0.8, the minimum reflection loss value and effective absorption bandwidth of the obtained sample are significantly enhanced compared to undoped pure barium ferrite, indicating better absorption performance.

[0134] Table 2Ba (1-x) La x Fe 12 O 19 The lowest reflection loss value and the lowest reflection loss extreme point corresponding to a certain matching thickness in the 2-18 GHz band

[0135] x value Matching thickness / mm Minimum return loss extreme point / GHz Minimum reflection loss value / dB 0 3 15.47 -35.36 0.2 2.9 13.49 -2.54 0.4 2.6 16.14 -46.13 0.6 4.9 8.14 -2.16 0.8 2.9 15.28 -40.95

[0136] Figures 24-25 Ba in the 2-18GHz band (1-x) La x Fe 12 O 19Impedance matching diagram: In addition to magnetic loss and dielectric loss, another key factor influencing microwave absorption performance is the material's impedance matching. Optimal impedance matching is achieved when the input impedance |Zin / Z0| is equal to or close to 1, indicating that most electromagnetic waves can enter the material's interior and be absorbed, rather than being reflected at the interface between the absorber and air. As shown in the figure, when x = 0, the |Zin / Z0| value is far greater than 1 for most thicknesses, indicating poor impedance matching. When the thickness is between 1.2 mm and 2.0 mm, the |Zin / Z0| value is close to 1 at high frequencies of 15 GHz. When x = 0.2 and x = 0.6, the |Zin / Z0| value is far greater than 1 at all thicknesses, indicating poor impedance matching. When x = 0.4, the |Zin / Z0| value is around 10, far greater than 1, indicating poor impedance matching. When the thickness is between 1.2 mm and 2.0 mm, the |Zin / Z0| value is close to 1 at high frequencies of 16 GHz. When x=0.8, the value of |Zin / Z0| is much larger than 1 for most thicknesses. When the thickness is between 1.2 mm and 2.0 mm, the value of |Zin / Z0| is close to 1 at a high frequency of 15 GHz.

[0137] As the thickness of the sample increases, the value of |Zin / Z0| shifts to low frequencies. When x = 0.4 and x = 0.8, in the high frequency range, the value of |Zin / Z0| is closer to the optimal impedance matching compared to other samples. 3+ The value of |Zin / Z0| with the change of doping amount is relatively close to the optimal impedance matching, and doping La2O3 improves the absorbing performance to a certain extent.

[0138] This embodiment should not be regarded as limiting the invention, but any improvements based on the spirit of the invention should be within the scope of protection of the invention.

Claims

1. A composite material of lanthanum oxide and barium ferrite, characterized in that: The composite material is barium ferrite BaFe 12 O 19 The composite material is made of a matrix doped with lanthanum oxide La2O3, and its chemical composition is Ba (1-x) La x Fe 12 O 19 , where 0.2≤x≤0.

8.

2. The composite material of lanthanum oxide and barium ferrite according to claim 1, characterized in that: The range of x is any one of 0.2, 0.4, 0.6, and 0.

8.

3. The method for preparing a ball-milled composite material of lanthanum oxide and barium ferrite according to claim 1 or 2, characterized in that: The steps include: 1) Barium ferrite BaFe 12 O 19 Grind into powder; 2) Barium ferrite BaFe 12 O 19 The powder and lanthanum oxide La2O3 are uniformly mixed in proportion; 3) drying the powder mixed in step 2 at a drying temperature for 3 hours; 4) Place the dried powder in a ball mill, mix it with zirconium balls, and then add anhydrous ethanol to seal it; 5) Place the ball mill containing the powder into the ball mill for spherical graphite; 6) Dry the powder after spherical ink at the drying temperature for 1 hour; 7) Screening out the powder; 8) Sintering the powder into blocks; The drying temperature in the above steps is 60°C to 80°C.

4. The method for preparing a ball-milled composite material of lanthanum oxide and barium ferrite according to claim 3, wherein: The step 1 is to prepare barium ferrite BaFe 12 O 19 Grind into powder and screen out barium ferrite BaFe with a diameter of ≤0.075mm 12 O 19 powder; The lanthanum oxide La2O3 in step 2 is in powder form.

5. The method for preparing a ball-milled composite material of lanthanum oxide and barium ferrite according to claim 3, characterized in that: The step 4 is to place the dried powder in a ball mill and mix it with ball mill zirconium balls, wherein the mass ratio of the dried powder to the ball mill zirconium balls is 1:15, and then add anhydrous ethanol at a ratio of 20 ml / 3 g and seal the mixture.

6. The method for preparing a ball-milled composite material of lanthanum oxide and barium ferrite according to claim 4, characterized in that: In step 4, the small balls of the ball-milled zirconium balls account for 20%, the medium balls of the ball-milled zirconium balls account for 50%, and the rest are large balls. The diameters of the small balls, medium balls, and large balls of the ball-milled zirconium balls are 0.5 mm, 2 mm, and 5 mm, respectively.

7. The method for preparing a ball-milled composite material of lanthanum oxide and barium ferrite according to claim 3, characterized in that: The step 5 is to place the ball mill containing the powder into a ball mill for graphite, and the parameters of the ball mill are set to a speed of 300r / min to 400r / min, and a graphite time of 10h to 14h.

8. The method for preparing a ball-milled composite material of lanthanum oxide and barium ferrite according to claim 3, characterized in that: Add steps 4-1 and 4-2 between steps 4 and 5. Step 4-1 is to wash the mixed powder dried in step 3 with nitric acid HNO3, anhydrous ethanol and deionized water; The step 4-2 is to dry the cleaned powder at a drying temperature for 20 minutes.

9. The method for preparing a ball-milled composite material of lanthanum oxide and barium ferrite according to claim 3, characterized in that: In step 1, a 200-mesh sieve is used for screening, and in step 8, a 100-mesh sieve is used for screening powders with a diameter of ≤0.15 mm.

10. The method for preparing a sample of a ball-milled composite material of lanthanum oxide and barium ferrite according to claim 1 or 2, characterized in that: The steps include: 1) Barium ferrite BaFe 12 O 19 Grind into powder and sieve out the powder with a 200-mesh sieve; 2) Barium ferrite BaFe 12 O 19 The powder and lanthanum oxide La2O3 are uniformly mixed in proportion; 3) drying the powder mixed in step 2 at 80°C for 3 hours; 4) washing the mixed powder dried in step 3 with nitric acid HNO3, anhydrous ethanol, and deionized water; 5) Dry the cleaned powder at 80°C for 20 minutes; 6) Step 4 is to place the dried powder in a ball mill and mix it with ball mill zirconium balls. The mass ratio of the dried powder to the ball mill zirconium balls is 1:15, wherein the small balls of the ball mill zirconium balls account for 20%, the medium balls of the ball mill zirconium balls account for 50%, and the rest are large balls. The diameters of the small, medium, and large balls of the ball mill zirconium balls are 0.5 mm, 2 mm, and 5 mm, respectively. Then, anhydrous ethanol is added and sealed at a ratio of 20 ml / 3 g; 7) Place the ball mill containing the powder into the ball mill for graphite. The ball mill parameters are set to a speed of 300r / min to 400r / min and a graphite time of 10h to 14h. 8) Dry the powder after spherical ink at 80℃ for 1h; 9) screening out the powder; 10) Add polyvinyl alcohol (PVA) to the powder and mix well. Place the mixture into a mold and press into a tablet press at a pressure of 10 MPa for 60 seconds until the powder is pressed into a sheet. 11) The semi-finished product after pressing in step 10 is placed in a temperature of 1250° C. and kept for 3 hours; 12) Wait for the finished product of step 11 to cool to room temperature in the furnace.

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