Lanthanum and chromium co-doped strontium ferrite wave absorbing material and its preparation method and application

Abstract

Aiming at the problem of low strontium ferrite absorbing performance prepared by traditional methods, the present invention provides a method for preparing strontium ferrite absorbing material co-doped with lanthanum and chromium. Step 1: 1‑x La x Fe 12‑y Cr y O 19 The molar ratio of the metal elements in the solution is used to prepare solution 1, where x and y are equal, and x is greater than 0 and less than or equal to 0.3; after pouring the citric acid aqueous solution, the pH is first adjusted to 7 with ammonia water, and then polyethylene glycol is added and dried to obtain a precursor; step 2, the precursor is first pre-sintered and then calcined to obtain a lanthanum-chromium co-doped strontium ferrite wave absorbing material. The strontium ferrite wave absorbing material obtained by the present invention is used for wave absorbing. In terms of performance, Sr 0.9 La 0.1 Fe 11.9 Cr 0.1 O 19 At a thickness of 2.48 mm, it has a minimum reflection loss of ‑61.48 dB at 11.8 GHz and an effective absorption bandwidth of 6.84 GHz.

Description

Technical Field

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

[0002] With the rapid development of electromagnetic wave technology in both civilian and military applications, such as the emerging next-generation miniaturized electronics, automobiles, radar, and communications, many serious electromagnetic interference problems have emerged in daily life. Consequently, high-performance electromagnetic wave absorbing materials have attracted considerable attention as an effective solution to these problems. Ideal, efficient electromagnetic wave absorbing materials should possess strong absorption efficiency, a wide absorption bandwidth, a matching thin thickness, and a low density.

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

[0004] In recent years, many researchers have improved traditional strontium ferrites by combining dual ion doping to enhance their microwave absorption properties. For example, Zhang Shijiao's research group studied Zn- and Ir-doped M-type strontium ferrite composites. These composites exhibited excellent microwave absorption properties at a frequency of 11.3 GHz, with a maximum reflection loss of -24.2 dB and a bandwidth of 12.1 GHz where the loss was greater than 10 dB (Zhang, Shijiao & Meng, Chao & Zhang,

[0005] 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 19Jing Xiaodong's team at the Chinese Academy of Sciences studied praseodymium and dysprosium co-doped M-type strontium ferrite. The composite material exhibited excellent microwave absorption properties, with a maximum reflectivity of -50.62 dB at a thickness of 4.17 mm. (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 microwave absorption performance. Summary of the Invention

[0006] The purpose of the present invention is to provide a strontium ferrite with high wave absorption performance and a preparation method thereof. Lanthanum and chromium are co-doped when synthesizing strontium ferrite by sol-gel method, and Sr is prepared by changing the lanthanum and chromium doping contents. 1-x La x Fe 12-y Cr y O 19 Powder. 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 require the use of highly toxic organic solvents, has simple method steps, strong controllability, low cost, and a short preparation cycle, and 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 superior electromagnetic wave absorption performance than the existing technology.

[0007] The present invention provides a method for preparing a lanthanum-chromium co-doped strontium ferrite wave absorbing material, comprising the following steps:

[0008] Step 1: According to the chemical formula of the target compound Sr 1-x La x Fe 12-y Cr y O 19 The molar ratio of the metal elements in the solution 1 is prepared. Solution 1 includes Fe 3+ 、Sr 2+ Cr 3+ 、La 3+ ;

[0009] In the chemical formula of the target compound, x and y are equal, and x is greater than 0 and less than or equal to 0.3;

[0010] After pouring solution 1 into citric acid aqueous solution, the pH was adjusted to 7 with ammonia water, polyethylene glycol was added, and the mixture was dried to obtain the precursor;

[0011] Step 2: pre-sintering the precursor and then calcining it to obtain a lanthanum-chromium co-doped strontium ferrite absorbing material.

[0012] Preferably, in step 1, the solution 1 is prepared using Fe(NO3)3·9H2O, Sr(NO3)2, Cr(NO3)3·9H2O and La(NO3)3·6H2O as raw materials.

[0013] The drying specifically includes: drying in an oven at 80° C. for 4 hours, and then drying in an oven at 120° C. for 5 days.

[0014] The pre-firing specifically includes: heating at a rate of 3°C / min, first heating to 200°C for 2 hours, then heating to 450°C for 2 hours, and cooling in the furnace.

[0015] The calcination specifically includes: heating to 1300° C. at a heating rate of 3° C. / min, calcining for 4 hours, and cooling in the furnace.

[0016] Preferably, in step 1, in the citric acid aqueous solution, the mass fractions of citric acid and water are 5.99 and 50 respectively.

[0017] The present invention also provides a lanthanum-chromium co-doped strontium ferrite wave absorbing material obtained by the above preparation method.

[0018] The present invention also provides an application of the above-mentioned lanthanum-chromium co-doped strontium ferrite wave absorbing material, wherein the chemical formula of the lanthanum-chromium co-doped strontium ferrite wave absorbing material is Sr 0.9 La 0.1 Fe 11.9 Cr 0.1 O 19 The minimum reflection loss of -61.48 dB is achieved at 11.8 GHz with a thickness of 2.48 mm, and the effective absorption bandwidth reaches 6.84 GHz.

[0019] Beneficial effects of the present invention

[0020] (1) The present invention uses the sol-gel method to prepare La-Cr co-doped M-type strontium ferrite (Sr 1-x La x Fe 12- y Cr y O 19 ), the electromagnetic properties of strontium ferrite are modified by varying the lanthanum and chromium co-doping levels. As the co-doping level increases, the superexchange interaction between different positions decreases, and the dielectric loss and magnetic loss initially increase and then decrease, reaching a maximum at x = 0.1. Furthermore, the variation in the imaginary part of the dielectric constant with the doping level also improves the impedance matching of strontium ferrite to a certain extent. Therefore, varying the co-doping levels of lanthanum and chromium doped strontium ferrite significantly improves the overall system and its microwave absorption properties.

[0021] (2) Sr prepared by the present invention 0.9 La 0.1 Fe 11.9 Cr 0.1 O 19 The absorbing performance is the best, with a maximum reflection loss of up to -61.5dB, a matching thickness of 2.48mm, and an effective bandwidth of 5.6GHz. Compared with the existing technology, the present invention can better meet the requirements of modern absorbing materials for being "thin, light, wide, and strong."

[0022] (3) The present invention does not require the use of highly toxic chemical reagents, and 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.

[0023] (4) Compared with various composite materials, the wave absorbing performance of the present invention is very excellent, and the production is simple and the cost is low. Compared with strontium ferrite doped with one element, the performance of the present invention is also greatly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] 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 specific embodiments or the description of the prior art. Hereinafter, some specific embodiments of the present invention will be described in detail in an illustrative and non-limiting manner with reference to the drawings. The same reference numerals in the drawings indicate 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:

[0025] Figure 1 The X-ray diffraction patterns of the samples obtained in Examples 1-4 are shown.

[0026] Figure 2are SEM images of the samples, (a) (b) (c) (d) are SEM images of the samples obtained in Examples 1-4, respectively.

[0027] Figure 3 The dielectric loss diagram of the samples prepared in Examples 1-4.

[0028] Figure 4 Magnetic loss diagram of the samples prepared in Examples 1-4.

[0029] Figure 5 Sr prepared in 2 0.9 La 0.1 Fe 11.9 Cr 0.1 O 19 Reflection loss diagram.

[0030] Figure 6 This is a reflection loss diagram of the sample prepared in Example 1-4 when the thickness is 2.48 mm.

[0031] Figure 7 1 is a comparison chart of Example 2 and some existing reports on strontium ferrite doping. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solutions and advantages of this application more clearly understood, the present application is 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 this application and are not intended to limit this application.

[0033] Example 1

[0034] (1) Step 1: Weigh 9.7 g and 0.42 g of Fe(NO3)3·9H2O and 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, mix thoroughly, add NH3·H2O until the pH is 7, add 1 g of polyethylene glycol, stir evenly, and place in an oven to dry at 80°C for 4 h, and then place in an oven to dry at 120°C for 5 days.

[0035] (2) Step 2: Grind the precursor obtained in step 1 and place it in a muffle furnace. The heating rate is 3°C / min. First, heat it to 200°C and pre-sinter for 2h. Then heat it to 450°C and calcine for 2h. After cooling in the furnace, fluffy powder is obtained. Grind the powder and place it in a muffle furnace. The heating rate is 3°C / min. First, heat it to 450°C and pre-sinter for 2h. Then heat it to 1300°C and calcine for 4h. Then cool it naturally in the furnace to obtain SrFe 12 O 19The resulting product was uniformly mixed with paraffin wax in 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. The measured electromagnetic parameters were used to calculate the sample's absorption properties using transmission line theory.

[0036] Example 2

[0037] (1) Step 1: 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 were weighed and dissolved in 125 ml of deionized water to form solution 1. 5.99 g of citric acid was then weighed and dissolved in 50 ml of water to form solution 2. Solution 2 was poured into solution 1, mixed thoroughly, and then NH3·H2O was added until the pH was 7. 1 g of polyethylene glycol was added, stirred, and then dried in an oven at 80°C for 4 h, and then dried in an oven at 120°C for 5 days.

[0038] (2) Step 2: Grind the precursor obtained in step 1 and place it in a muffle furnace. The heating rate is 3°C / min. First, heat it to 200°C for pre-calcination for 2h, then heat it to 450°C for calcination for 2h, and then cool it in the furnace to obtain 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 pre-calcination for 2h, then heat it to 1300°C for calcination for 4h, and then cool it naturally in the furnace to obtain Sr 0.9 La 0.1 Fe 11.9 Cr 0.1 O 19 The resulting product was uniformly mixed with paraffin wax in 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. The measured electromagnetic parameters were used to calculate the sample's absorption properties using transmission line theory.

[0039] Example 3

[0040] (1) Step 1: 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 were weighed and dissolved in 125 ml of deionized water to form solution 1. 5.99 g of citric acid was then weighed and dissolved in 50 ml of water to form solution 2. Solution 2 was poured into solution 1, mixed thoroughly, and then NH3·H2O was added until the pH was 7. 1 g of polyethylene glycol was added, stirred, and then dried in an oven at 80°C for 4 h, and then dried in an oven at 120°C for 5 days.

[0041] (2) Step 2: Grind the precursor obtained in step 1 and place it in a muffle furnace. The heating rate is 3°C / min. First, heat it to 200°C for pre-calcination for 2h, then heat it to 450°C for calcination for 2h, and then cool it in the furnace to obtain 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 pre-calcination for 2h, then heat it to 1300°C for calcination for 4h, and then cool it naturally in the furnace to obtain Sr 0.8 La 0.2 Fe 11.8 Cr 0.2 O 19 The resulting product was uniformly mixed with paraffin wax in 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. Based on the measured electromagnetic parameters, the sample's absorption properties were calculated using transmission line theory.

[0042] Example 4

[0043] (1) Step 1: 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 were weighed and dissolved in 125 ml of deionized water to form solution 1. 5.99 g of citric acid was then weighed and dissolved in 50 ml of water to form solution 2. Solution 2 was poured into solution 1, mixed thoroughly, and then NH3·H2O was added until the pH was 7. 1 g of polyethylene glycol was added, stirred, and then dried in an oven at 80°C for 4 h, and then dried in an oven at 120°C for 5 days.

[0044] (2) Step 2: Grind the precursor obtained in step 1 and place it in a muffle furnace. The heating rate is 3°C / min. First, heat it to 200°C for pre-calcination for 2h, then heat it to 450°C for calcination for 2h, and then cool it in the furnace to obtain 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 pre-calcination for 2h, then heat it to 1300°C for calcination for 4h, and then cool it naturally in the furnace to obtain Sr 0.7 La 0.3 Fe 11.7 Cr 0.3 O 19 The resulting product was uniformly mixed with paraffin wax in 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. The measured electromagnetic parameters were used to calculate the sample's absorption properties using transmission line theory.

[0045] The wave absorbing material prepared by the present invention is used for wave absorbing. The molecular formula of the wave absorbing material is Sr 1-x La x Fe12-y Cr y O 19 (x=y=0, 0.1, 0.2, 0.3), Sr 0.9 La 0.1 Fe 11.9 Cr 0.1 O 19 When the matching thickness is 2.48 mm, it has a minimum reflection loss of -61.48 dB at 11.8 GHz and an effective absorption bandwidth of 6.84 GHz; 12 O 19 When the thickness is 6.42 mm, it has a minimum reflection loss of -55.84 dB at 16.76 GHz and an effective absorption bandwidth of 4.96 GHz; 0.8 La 0.2 Fe 11.8 Cr 0.2 O 19 When the thickness is 2.43 mm, it has a minimum reflection loss of -32.78 dB at 14.04 GHz and an effective absorption bandwidth of 6.96 GHz; 0.7 La 0.3 Fe 11.7 Cr 0.3 O 19 When the thickness is 9.95 mm, it has a minimum reflection loss of -30.31 dB at 2.56 GHz and an effective absorption bandwidth of 5.04 GHz.

[0046] from Figure 1 It can be seen that Examples 1-4 have similar diffraction peaks, indicating that lanthanum and chromium have successfully entered the strontium ferrite lattice.

[0047] Depend on Figure 2 It can be seen from the figure that the sample particles are hexagonal, and the grain size decreases with the increase of doping content.

[0048] Depend on Figure 3 It can be seen from the graph that the dielectric loss first increases and then decreases with the increase of doping content.

[0049] Depend on Figure 4 It can be seen from the figure that the magnetic loss first increases and then decreases with the increase of doping content.

[0050] Depend on Figure 5 It can be seen that the microwave absorption performance of S-2 is -61.5 dB when the matching thickness is 2.48 mm and the frequency is 11.8 GHz.

[0051] Depend on Figure 6 It can be seen that the Sr doping content is x=y=0.1 0.9La 0.1 Fe 11.9 Cr 0.1 O 19 The wave absorption performance is significantly improved.

[0052] Figure 7 The example 2 is used to compare with some existing reports on strontium ferrite doping. The existing reports in the figure include: Ca-Co doped SrFe 12 O 19 (Ca 0.3 Sr 0.7 Fe 11.7 Co 0.3 O 19 ), with a minimum reflection loss of -21.3 dB and an effective bandwidth of 4.8 GHz at a thickness of 2.0 mm, marked as X1 here (Liu, Yuan& Li, Rong & Qing, Yuchang. (2023). Ca-Co co-doped strontium ferrite ceramicwith tunable magnetic properties for enhanced microwave absorbingapplication. 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 material, with a minimum reflection loss of -59.22 dB and an effective bandwidth of 3 GHz at a thickness of 4.0 mm, here marked 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 and Related 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 ), with a minimum return loss of -33.42 dB and an effective bandwidth of 2.25 GHz at a thickness of 2.25 mm, denoted here as X3 (Altaf Hussain, Iftikhar Hussain Gul,

[0053] Muhammad Zarrar Khan,Enhancement of dielectric, magnetic and microwave 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.). SrFe 11.6 Pr 0.4 O 19 The material has a minimum reflection loss of -50.95 dB and an effective bandwidth of 4.76 GHz at a thickness of 2 mm, which is designated as X4 (XD Jing, ZG Li, ZT Chen,

[0054] ZY Li, CY Qin, HY Gong,Effect of praseodymium valence change on the structure, magnetic, and microwave absorbing properties of M-typestrntium ferrite: the mechanism of influence of citric acid dosage andcalcination temperature,Materials Today Chemistry,Volume 30, 2023, 101537, ISSN2468-5194, 10.1016 / j.mtchem.2023.101537.). MWCNTs / Sr developed by Seyyed Salman Seyyed Afghahi’s research group 0.5 Ba 0.5 Fe 11 Al 0.5 Cr 0.5 O 19 / PANI nanocomposite with a minimum reflection loss of -26 dB and an effective bandwidth of 2.4 GHz at a thickness of 5 mm, denoted as X5 (Seyyed Afghahi, Seyyed Salman & Peymanfar,

[0055] As can be seen from the figure, compared with various composite materials, the microwave absorption performance of the present invention is very excellent, and the preparation is simple and the cost is low. Compared with barium ferrite doped with two elements, the performance of the present invention is also greatly improved.

[0056] The above description is only part of the specific implementation methods of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any person familiar with the art within the technical scope disclosed in the present invention should be covered by the protection scope of the present invention.

Claims

1. A method for preparing a lanthanum-chromium co-doped strontium ferrite wave absorbing material, characterized in that: The following steps are involved: Step 1: According to the chemical formula of the target compound Sr 1-x La x Fe 12-y Cr y O 19 The molar ratio of the metal elements in the solution 1 is prepared. Solution 1 includes Fe 3+ 、Sr 2+ Cr 3+ 、La 3+ ; In the chemical formula of the target compound, x and y are equal, and x is greater than 0 and less than or equal to 0.3; After pouring solution 1 into citric acid aqueous solution, the pH was adjusted to 7 with ammonia water, polyethylene glycol was added, and the mixture was dried to obtain the precursor; Step 2: pre-sintering the precursor and then calcining it to obtain a lanthanum-chromium co-doped strontium ferrite absorbing material.

2. The preparation method according to claim 1, wherein: In step 1, the solution 1 is prepared using 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 hours, and then drying in an oven at 120° C. for 5 days.

4. The preparation method according to claim 1, wherein: The pre-burning specifically includes: The heating rate is 3℃ / min. First, heat to 200℃ and burn for 2h, then heat to 450℃ and burn for 2h, and cool in the furnace.

5. The preparation method according to claim 1, wherein: The calcination specifically includes: The temperature was raised to 1300°C at a heating rate of 3°C / min and calcined for 4 h, followed by cooling in the furnace.

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

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

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

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