Lanthanum-chromium co-doped strontium ferrite wave-absorbing material as well as preparation method and application thereof

Abstract

Aiming at the problem of low wave-absorbing performance of strontium ferrite prepared by a traditional method, the invention provides the preparation method of the lanthanum-chromium co-doped strontium ferrite wave-absorbing material, which comprises the following steps: step 1, preparing a solution 1 according to the amount ratio of metal elements in a target chemical formula Sr < 1-x > LaxFe < 12-y > CryO19, x being equal to y, and x being greater than 0 and less than or equal to 0.3; pouring a citric acid aqueous solution, adjusting the pH value to 7 by using ammonia water, adding polyethylene glycol, and drying to obtain a precursor; and step 2, pre-sintering the precursor, and then calcining to obtain the lanthanum-chromium co-doped strontium ferrite wave-absorbing material. The obtained strontium ferrite wave-absorbing material is applied to the aspects of wave absorption and performance, when the thickness of Sr0. 9La0. 1Fe1. 9Cr0. 1O19 is 2.48 mm, the minimum reflection loss of-61.48 dB is achieved at the frequency of 11.8 GHz, and the effective absorption bandwidth is 6.84 GHz.

Description

Technical Field

[0001] The present invention belongs to the technical field of microwave absorbing materials, and particularly relates to a lanthanum-chromium co-doped strontium ferrite microwave absorbing material, a preparation method thereof, and an application thereof. Background Art

[0002] With the rapid development of electromagnetic wave technology in civilian and military fields, such as emerging new-generation miniaturized electronics, automobiles, radars, and communications, many serious electromagnetic interference problems have emerged in daily life. Therefore, high-performance electromagnetic wave absorbing materials, as an effective method to solve these problems, have attracted much attention. An ideal and efficient electromagnetic wave absorbing material should have the characteristics of strong absorption efficiency, wide absorption bandwidth, thin matching thickness, and light density.

[0003] M-type strontium ferrite (SrFe 12 O 19 ) as a high-performance permanent magnet has properties such as large saturation magnetization intensity, high residual magnetic flux density, relatively high Curie temperature, and high coercivity. In addition, strontium ferrite has strong magnetic loss in the microwave band and is a promising microwave absorbing material.

[0004] In recent years, many researchers have improved traditional strontium ferrite by dual-ion co-doping to enhance its microwave absorption performance. For example, the research group of Zhang Shijiao studied a Zn- and Ir-doped M-type strontium ferrite composite material, which showed good microwave absorption performance at a frequency of 11.3 GHz, with a maximum reflection loss of up to -24.2 dB, and the bandwidth with a loss greater than 10 dB was 12.1 GHz (Zhang, Shijiao & Meng, Chao & Zhang, Lan & Yuan, Shaokun & Luo, Hao & Liu, Shunquan & Chang, Hong. (2020). Effect of Zn and Ir doping on Microwave Absorption of SrFe 12- 2x Zn x Ir x O 19. Journal of Magnetism and Magnetic Materials. 513. 167076. 10.1016 / j.jmmm.2020.167076.)。The research team of Jing Xiaodong from the Chinese Academy of Sciences studied the praseodymium-dysprosium co-doped M-type strontium ferrite material, and this composite material exhibited good microwave absorption performance. When the thickness was 4.17 mm, the maximum reflectivity reached -50.62 dB. (Jing, Xiaodong & Chen, Zitao & Zhao, Qianqian & Li, Zuoguang & Xiong, Xiaoqiang & Yang, Xi & Wang, Qun & Huang, Hai & Jiang, Hualiang & Zhao, Tongyun & Gong, Huayang. (2024). Praseodymium dysprosium co-doped M-type strontium ferrite: Intentionally manufacturing heterophase growth to improve microwave absorption performance. Materials Today Chemistry. 39. 102151. 10.1016 / j.mtchem.2024.102151. ). Therefore, it is necessary to develop a method for preparing strontium ferrite with better wave absorption performance. Summary of the Invention

[0005] The object of the present invention is to provide a strontium ferrite with high wave absorption performance and a preparation method thereof. When synthesizing strontium ferrite by the sol-gel method, lanthanum and chromium are co-doped, and by changing the doping content of lanthanum and chromium, Sr 1-x La x Fe 12-y Cr y O 19 powder is prepared. The results show that the effective absorption bandwidth and absorption intensity are significantly improved in the frequency range of 2 - 18 GHz. The present invention does not need to use highly toxic organic solvents, the method steps are simple, the controllability is strong, the cost is low, and the preparation period is short, which can be used for large-scale industrial production. The experimental results of the present invention all show that the lanthanum-chromium co-doped strontium ferrite material prepared by the sol-gel method exhibits more excellent electromagnetic wave absorption performance compared with the prior art.

[0006] The present invention provides a preparation method for a lanthanum-chromium co-doped strontium ferrite wave-absorbing material, comprising the following steps:

[0007] Step 1: Prepare Solution 1 according to the molar ratio of metal elements in the target compound formula Sr 1-x La x Fe 12-y Cr y O 19 Solution 1 contains Fe 3+ 、Sr 2+ 、Cr 3+ 、La 3+ ;

[0008] In the target compound formula, x is equal to y, where 0 < x ≤ 0.3;

[0009] After pouring Solution 1 into the citric acid aqueous solution, first adjust the pH to 7 with ammonia water, then add polyethylene glycol, and dry to obtain the precursor;

[0010] Step 2: Pre-calcine and then calcine the precursor to obtain the La-Cr co-doped strontium ferrite microwave absorbing material.

[0011] Preferably, in Step 1, Solution 1 is prepared using Fe(NO3)3·9H2O, Sr(NO3)2, Cr(NO3)3·9H2O, and La(NO3)3·6H2O as raw materials.

[0012] The drying specifically includes: drying in an oven at 80 °C for 4 h, and then drying in the oven at 120 °C for 5 days.

[0013] The pre-calcination specifically includes: heating rate of 3 °C / min, first heating to 200 °C and calcining for 2 h, then heating to 450 °C and calcining for 2 h, and cooling with the furnace.

[0014] The calcination specifically includes: heating to 1300 °C at a heating rate of 3 °C / min and calcining for 4 h, and cooling with the furnace.

[0015] Preferably, in Step 1, in the citric acid aqueous solution, the mass fractions of citric acid and water are 5.99 and 50 respectively.

[0016] The present invention also provides the La-Cr co-doped strontium ferrite microwave absorbing material obtained by the above preparation method.

[0017] The present invention also provides the application of the above La-Cr co-doped strontium ferrite microwave absorbing material. The chemical formula of the La-Cr co-doped strontium ferrite microwave absorbing material is Sr 0.9 La 0.1 Fe 11.9 Cr 0.1 O 19 It achieves a minimum reflection loss of -61.48 dB at a thickness of 2.48 mm and 11.8 GHz, and the effective absorption bandwidth reaches 6.84 GHz.

[0018] Advantages of the present invention

[0019] (1) The present invention prepares La-Cr co-doped M-type strontium ferrite (Sr 1-x La x Fe 12- y Cr y O 19 ) by using the sol-gel method, and changes the electromagnetic properties of strontium ferrite by changing the La-Cr co-doping content. As the co-doping content increases, the super-exchange interaction between different positions decreases, and the dielectric loss and magnetic loss first increase and then decrease, reaching the maximum at x = 0.1. At the same time, the change of the imaginary part of the dielectric constant with the doping content also improves the impedance matching of strontium ferrite to a certain extent. Therefore, changing the co-doping amount of La and Cr in strontium ferrite plays a great role in improving the entire system and microwave absorption performance of strontium ferrite.

[0020] (2) The Sr 0.9 La 0.1 Fe 11.9 Cr 0.1 O 19 prepared in the present invention has the best microwave absorption performance, with a maximum reflection loss of up to -61.5 dB, a matching thickness of 2.48 mm, and an effective bandwidth of 5.6 GHz. Compared with the prior art, the present invention can better meet the requirements of modern microwave absorption materials for being "thin, light, wide, and strong".

[0021] (3) The present invention does not require the use of highly toxic chemical reagents, the preparation method does not require complex synthesis equipment, the process is simple, the cost is low, the product purity is high, and the yield is high, and it can be used for large-scale industrial production.

[0022] (4) Compared with a variety of composite materials, the microwave absorption performance of the present invention is very excellent, and it is simple to manufacture and low in cost; compared with strontium ferrite doped with one element, the performance of the present invention is also greatly improved. Description of the drawings

[0023] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Later, some specific embodiments of the present invention will be described in detail with reference to the drawings in an exemplary but non-limiting manner. The same reference numerals in the drawings denote the same or similar components or parts. Those skilled in the art should understand that these drawings are not necessarily drawn to scale. In the drawings:

[0024] Figure 1 are the X-ray diffraction patterns of the samples obtained in Examples 1-4.

[0025] Figure 2SEM images of the samples. (a), (b), (c), and (d) are SEM images of the samples obtained in Examples 1-4, respectively.

[0026] Figure 3 Dielectric loss diagrams of the samples prepared in Examples 1-4.

[0027] Figure 4 Magnetic loss diagrams of the samples prepared in Examples 1-4.

[0028] Figure 5 Sr prepared in Example 2 0.9 La 0.1 Fe 11.9 Cr 0.1 O 19 Reflection loss diagram.

[0029] Figure 6 Reflection loss diagrams of the samples prepared in Examples 1-4 at a thickness of 2.48 mm.

[0030] Figure 7 Comparison diagram between Example 2 and some existing reports on strontium ferrite doping. Detailed implementation manners

[0031] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0032] Example 1

[0033] (1) Step 1: Weigh 9.7 g of Fe(NO3)3·9H2O and 0.42 g of Sr(NO3)2 and dissolve them together in 125 ml of water to form Solution 1. Then weigh 5.99 g of citric acid and dissolve it in 50 ml of deionized water to form Solution 2. Pour Solution 2 into Solution 1, fully mix them, add NH3·H2O until the pH = 7, add 1 g of polyethylene glycol, stir evenly, place it in an oven at 80 °C and dry for 4 h, and then place it in the oven at 120 °C and dry for 5 days.

[0034] (2) Step 2: Grind the precursor obtained in Step 1 and put it into a muffle furnace. The heating rate is 3 °C / min. First, heat it to 200 °C and pre-burn for 2 h, then heat it to 450 °C and calcine for 2 h, and cool it with the furnace to obtain a fluffy powder; grind the powder and place it in the muffle furnace. The heating rate is 3 °C / min. First, heat it to 450 °C and pre-burn for 2 h, then heat it to 1300 °C and calcine for 4 h, and naturally cool it with the furnace to obtain SrFe 12 O 19Powder. The marked product is S-1. The obtained product is uniformly mixed with paraffin wax at a mass ratio of 7:3 and pressed into a mold with an outer diameter of 7 mm and an inner diameter of 3.04 mm to prepare a composite sample for electromagnetic parameter measurement. According to the measured electromagnetic parameters, the wave absorption performance of the sample is calculated using the transmission line theory.

[0035] Example 2

[0036] (1) Step 1, Weigh 9.66 g, 0.4 g, 0.04 g, and 0.043 g of Fe(NO3)3·9H2O, Sr(NO3)2, Cr(NO3)3·9H2O, and La(NO3)3·6H2O and dissolve them together in 125 ml of deionized water to form Solution 1. Then weigh 5.99 g of citric acid and dissolve it in 50 ml of water to form Solution 2. Pour Solution 2 into Solution 1, add NH3·H2O to pH = 7 after thorough mixing, add 1 g of polyethylene glycol, stir evenly, place it in an oven at 80 °C for 4 h of drying, and then place it in the oven at 120 °C for 5 days of drying.

[0037] (2) Step 2, Grind the precursor obtained in Step 1 and put it into a muffle furnace. The heating rate is 3 °C / min. First, heat it to 200 °C for 2 h of pre-calcination, then heat it to 450 °C for 2 h of calcination, and cool it with the furnace to obtain a fluffy powder; grind the powder and place it in a muffle furnace. The heating rate is 3 °C / min. First, heat it to 450 °C for 2 h of pre-calcination, then heat it to 1300 °C for 4 h of calcination, and naturally cool it with the furnace to obtain Sr 0.9 La 0.1 Fe 11.9 Cr 0.1 O 19 Powder. The marked product is S-2. The obtained product is uniformly mixed with paraffin wax at a mass ratio of 7:3 and pressed into a mold with an outer diameter of 7 mm and an inner diameter of 3.04 mm to prepare a composite sample for electromagnetic parameter measurement. According to the measured electromagnetic parameters, the wave absorption performance of the sample is calculated using the transmission line theory.

[0038] Example 3

[0039] (1) Step 1, Weigh 9.62 g, 0.38 g, 0.08 g, and 0.087 g of Fe(NO3)3·9H2O, Sr(NO3)2, Cr(NO3)3·9H2O, and La(NO3)3·6H2O and dissolve them together in 125 ml of deionized water to form Solution 1. Then weigh 5.99 g of citric acid and dissolve it in 50 ml of water to form Solution 2. Pour Solution 2 into Solution 1, add NH3·H2O to pH = 7 after thorough mixing, add 1 g of polyethylene glycol, stir evenly, place it in an oven at 80 °C for 4 h of drying, and then place it in the oven at 120 °C for 5 days of drying.

[0040] (2) Step 2: Grind the precursor obtained in Step 1 and put it into a muffle furnace. The heating rate is 3 °C / min. First, heat it to 200 °C and pre-calcine for 2 h, then heat it to 450 °C and calcine for 2 h. After cooling with the furnace, a fluffy powder is obtained; grind the powder and place it in the muffle furnace. The heating rate is 3 °C / min. First, heat it to 450 °C and pre-calcine for 2 h, then heat it to 1300 °C and calcine for 4 h. Let it cool naturally with the furnace to obtain Sr 0.8 La 0.2 Fe 11.8 Cr 0.2 O 19 powder. Mark the product as S-3. Uniformly mix the obtained product with paraffin in a mass ratio of 7:3, and press it into a mold with an outer diameter of 7 mm and an inner diameter of 3.04 mm to prepare a composite sample for measuring electromagnetic parameters. According to the measured electromagnetic parameters, the wave absorption performance of the sample is calculated using the transmission line theory.

[0041] Example 4

[0042] (1) Step 1: Weigh 9.57 g, 0.36 g, 0.12 g, and 0.13 g of Fe(NO3)3·9H2O, Sr(NO3)2, Cr(NO3)3·9H2O, and La(NO3)3·6H2O and dissolve them together in 125 ml of deionized water to form Solution 1. Then weigh 5.99 g of citric acid and dissolve it in 50 ml of water to form Solution 2. Pour Solution 2 into Solution 1, mix well, add NH3·H2O until pH = 7, add 1 g of polyethylene glycol, stir evenly, place it in an oven at 80 °C and dry for 4 h, and then place it in the oven at 120 °C and dry for 5 days.

[0043] (2) Step 2: Grind the precursor obtained in Step 1 and put it into a muffle furnace. The heating rate is 3 °C / min. First, heat it to 200 °C and pre-calcine for 2 h, then heat it to 450 °C and calcine for 2 h. After cooling with the furnace, a fluffy powder is obtained; grind the powder and place it in the muffle furnace. The heating rate is 3 °C / min. First, heat it to 450 °C and pre-calcine for 2 h, then heat it to 1300 °C and calcine for 4 h. Let it cool naturally with the furnace to obtain Sr 0.7 La 0.3 Fe 11.7 Cr 0.3 O 19 powder. Mark the product as S-4. Uniformly mix the obtained product with paraffin in a mass ratio of 7:3, and press it into a mold with an outer diameter of 7 mm and an inner diameter of 3.04 mm to prepare a composite sample for measuring electromagnetic parameters. According to the measured electromagnetic parameters, the wave absorption performance of the sample is calculated using the transmission line theory.

[0044] The wave-absorbing material prepared by the present invention is applied to wave absorption. The molecular formula of the wave-absorbing material is Sr 1-x La x Fe12-y Cr y O 19 (where x = y = 0, 0.1, 0.2, 0.3), Sr 0.9 La 0.1 Fe 11.9 Cr 0.1 O 19 At a matching thickness of 2.48 mm, it has a minimum reflection loss of -61.48 dB at 11.8 GHz, and the effective absorption bandwidth is 6.84 GHz; SrFe 12 O 19 At a thickness of 6.42 mm, it has a minimum reflection loss of -55.84 dB at 16.76 GHz, and the effective absorption bandwidth is 4.96 GHz; Sr 0.8 La 0.2 Fe 11.8 Cr 0.2 O 19 At a thickness of 2.43 mm, it has a minimum reflection loss of -32.78 dB at 14.04 GHz, and the effective absorption bandwidth is 6.96 GHz; Sr 0.7 La 0.3 Fe 11.7 Cr 0.3 O 19 At a thickness of 9.95 mm, it has a minimum reflection loss of -30.31 dB at 2.56 GHz, and the effective absorption bandwidth is 5.04 GHz.

[0045] It can be seen from Figure 1 that Examples 1 - 4 have similar diffraction peaks, indicating that lanthanum and chromium have successfully entered the strontium ferrite lattice.

[0046] It can be seen from Figure 2 that the sample particles are hexagonal, and with the increase of the doping content, the grain size decreases.

[0047] It can be seen from Figure 3 that the dielectric loss first increases and then decreases with the increase of the doping content.

[0048] It can be seen from Figure 4 that the magnetic loss first increases and then decreases with the increase of the doping content.

[0049] It can be seen from Figure 5 that for S - 2, its microwave absorption performance is that when the matching thickness is 2.48 mm and the frequency is 11.8 GHz, the reflection loss is -61.5 dB.

[0050] It can be seen from Figure 6 that for Sr with a doping content of x = y = 0.1 0.9La 0.1 Fe 11.9 Cr 0.1 O 19 The microwave absorption performance is significantly improved.

[0051] Figure 7 For comparing Example 2 with some existing reports on the doping of strontium ferrite, the existing reports in the figure are as follows: Ca-Co doped SrFe developed by the team of Qing Yuchang from Northwestern Polytechnical University 12 O 19 (Ca 0.3 Sr 0.7 Fe 11.7 Co 0.3 O 19 ), which has a minimum reflection loss of -21.3 dB and an effective bandwidth of 4.8 GHz at a thickness of 2.0 mm, labeled as X1 here (Liu, Yuan & Li, Rong & Qing, Yuchang. (2023). Ca-Co co-doped strontium ferrite ceramic with tunable magnetic properties for enhanced microwave absorbing application. Materials Research Bulletin. 172. 112661. 10.1016 / j.materresbull.2023.112661.). The hexagonal strontium ferrite (SrFe 12 O 19 ) / graphite-carbon nitride (g-C3N4) composite developed by the research group of S. Jacob Rosarian Joy has a minimum reflection loss of -59.22 dB and an effective bandwidth of 3 GHz at a thickness of 4.0 mm, labeled as X2([4]S. Jacob Rosarian Joy, D. Rajan Babu, Study of microwave absorption properties of strontium hexaferrite (SrFe 12 O 19)and graphitic-carbon nitride (g-C3N4) composite in X-band range,Diamond andRelated Materials,Volume 151,2025,111813,ISSN 0925-9635,10.1016 / j.diamond.2024.111813.)。The Co-Zr doped SrFe 12 O 19 (SrZr 0.35 Co 0.35 Fe 11.3 O 19 ) developed by the Altaf Hussain research group has a minimum reflection loss of -33.42 dB and an effective bandwidth of 2.25 GHz at a thickness of 2.25 mm, labeled as X3 here (Altaf Hussain, Iftikhar Hussain Gul, Muhammad Zarrar Khan,Enhancement of dielectric, magnetic andmicrowave absorption properties of Co 2+ -Zr 4+ substituted SrFe 12 O 19 nanoparticles,Ceramics International,2024,ISSN 0272-8842,10.1016 / j.ceramint.2024.11.451.). The SrFe 11.6 Pr 0.4 O 19 material developed by the Jing Xiaodong research group of the Chinese Academy of Sciences has a minimum reflection loss of -50.95 dB and an effective bandwidth of 4.76 GHz at a thickness of 2 mm, labeled as X4 here (X.D. Jing,Z.G. Li, Z.T. Chen, Z.Y. Li, C.Y. Qin, H.Y. Gong, Effect of praseodymium valence change on the structure, magnetic, and microwave absorbing properties of M-type strontium ferrite: the mechanism of influence of citric acid dosage and calcination temperature, Materials Today Chemistry, Volume 30, 2023, 101537, ISSN 2468-5194, 10.1016 / j.mtchem.2023.101537.). The MWCNTs / Sr 0.5 Ba 0.5 Fe 11 Al 0.5 Cr 0.5 O 19 / PANI nanocomposite developed by the Seyyed Salman Seyyed Afghahi research group has a minimum reflection loss of -26 dB and an effective bandwidth of 2.4 GHz at a thickness of 5 mm, labeled as X5 here (Seyyed Afghahi, Seyyed Salman & Peymanfar, Reza & Javanshir, Shahrzad & Atassi, Yomen & Jafarian, Mojtaba. (2017). Synthesis, Characterization and Microwave Characteristics of Ternary Nanocomposite of MWCNTs / doped Sr-hexaferrite / PANI. Journal of Magnetism and Magnetic Materials. 423. 152–157. 10.1016 / j.jmmm.2016.09.082.). It can be seen from the figure that compared with various composite materials, the microwave absorption performance of the present invention is very excellent, and it is simple to manufacture and has low cost; compared with barium ferrite doped with two elements, the performance of the present invention has also been greatly improved.

[0052] As described above, only some specific embodiments of the present invention are provided, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. Preparation method of lanthanum-chromium co-doped strontium ferrite microwave absorption material, characterized in that, It includes the following steps: Step 1, prepare Solution 1 according to the molar ratio of metal elements in the target compound formula Sr 1-x La x Fe 12-y Cr y O 19 , where Solution 1 contains Fe 3+ , Sr 2+ , Cr 3+ , La 3+ ; In the chemical formula of the target substance, x is equal to y, and x is greater than 0 and less than or equal to 0.

3. After pouring Solution 1 into the citric acid aqueous solution, first adjust the pH to 7 with ammonia water, then add polyethylene glycol, and dry to obtain a precursor. In Step 2, pre-calcine the precursor first and then calcine it to obtain the lanthanum-chromium co-doped strontium ferrite microwave absorption material.

2. The preparation method according to claim 1, wherein: In Step 1, Solution 1 is prepared with Fe(NO3)3·9H2O, Sr(NO3)2, Cr(NO3)3·9H2O and La(NO3)3·6H2O as raw materials.

3. The preparation method according to claim 1, wherein: In Step 1, the drying specifically includes: drying in an oven at 80 °C for 4 h, and then drying in the oven at 120 °C for 5 days.

4. The preparation method according to claim 1, wherein: The pre-calcination specifically includes: The heating rate is 3 °C / min. First, heat up to 200 °C and calcine for 2 h, then heat up to 450 °C and calcine for 2 h, and cool down with the furnace.

5. The preparation method according to claim 1, wherein: The calcination specifically includes: With a heating rate of 3 °C / min, heat up to 1300 °C and calcine for 4 h, and cool down with the furnace.

6. The preparation method according to claim 1, wherein: In Step 1, in the citric acid aqueous solution, the mass fractions of citric acid and water are 5.99 and 50 respectively.

7. The lanthanum-chromium co-doped strontium ferrite microwave absorption material prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the lanthanum-chromium co-doped strontium ferrite microwave absorption material according to claim 7, characterized in that, The chemical formula of the lanthanum-chromium co-doped strontium ferrite microwave absorbing material is Sr 0.9 La 0.1 Fe 11.9 Cr 0.1 O 19 It reaches a minimum reflection loss of -61.48 dB at 11.8 GHz with a thickness of 2.48 mm, and the effective absorption bandwidth reaches 6.84 GHz.

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