High-entropy perovskite-type electromagnetic wave absorbing material and preparation method therefor

Abstract

The present invention belongs to the technical field of electromagnetic wave absorbing materials. A high-entropy perovskite-type electromagnetic wave absorbing material and a preparation method theref

Description

The present invention relates to the technical field of electromagnetic wave absorbing materials, in particular to a high-entropy perovskite-type electromagnetic wave absorbing material and a preparation method therefor. BACKGROUND Rapid development of communication technology has greatly contributed to the progress of science and technology and the convenience of living. Meanwhile, system hardware constantly radiates electromagnetic signals to a transmission medium space, causing the problem of electromagnetic leakage and interference to become increasingly prominent, which adversely affects normal running of electronic apparatuses and human health. In order to solve the increasingly serious problems of electromagnetic pollution and electromagnetic compatibility, the research of electromagnetic wave absorbing materials has received increasing attention. Ideal and efficient electromagnetic wave absorbing materials should feature strong absorption, a wide absorption frequency range, a thin matching thickness and light density. As a strong dielectric loss-type wave absorbing material with excellent thermal stability, the perovskite material has become a high-profile electromagnetic wave absorbing material. By doping a LaCoCh system with sodium ions, Cai Jia et al. from Guilin University of Electronic Technology found that part of Co3 was transformed into Co4', resulting in that pairs of electrons could not be formed due to different valence states of neighboring cobalt ions, and the conductivity of the material was increased. When a proportion of doped substance is 10%, a highest absorption peak occurs at 11.4 GHz with a thickness of 1.8 mm, and an effective absorption bandwidth is less than 2 GHz. After doping with sodium ions, the thickness is reduced but the effective absorption bandwidth is still narrower. At this stage, the development of perovskite wave absorbing materials mainly focuses on doping and preparation of composite magnetic loss-type materials. However, existing results can hardly satisfy the requirements for strong absorption, wide absorption frequency range, a thin matching thickness and light density of the electromagnetic wave absorbing materials. SUMMARY In view of this, the present invention provides a high-entropy perovskite-type electromagnetic wave absorbing material and a preparation method therefor, to solve the problem that an electromagnetic wave absorbing material in the prior art can hardly simultaneously satisfy the requirements for strong absorption, a wide absorption frequency range, a thin matching thickness and light density. In order to achieve the above objective, the present invention adopts the following technical solutions. The present invention provides a preparation method according to claim 1. Preferably, the cobalt salt is cobalt nitrate, cobalt sulfate or cobalt chloride; the iron salt is ferric nitrate, ferric sulfate or ferric chloride; the nickel salt is nickel nitrate, nickel sulfate or nickel chloride; the lanthanum salt is lanthanum nitrate, lanthanum sulfate or lanthanum chloride; the manganese salt is manganese nitrate, manganese sulfate or manganese chloride; and the chromium salt is chromium nitrate, chromium sulfate or chromium chloride. The polymerizing agent is citric acid; preferably the dispersant is ethylene glycol; the solvent is water. Preferably, a molar ratio of lanthanum ions, cobalt ions, chromium ions, iron ions, manganese ions, nickel ions and the polymerizing agent in the mixture is 4.8-5.2:0.8-1.2:0.8-1.2:0.8-1.2:0.8-1.2:0.8-1.2:8-12. Preferably, a mass-volume ratio of the polymerizing agent to the dispersant is 4 g-5 g:4 mL-7 mL, and a volume ratio of the dispersant to the solvent is 1-1.2:10. Preferably, an evaporation temperature is 70°C- 90°C, and evaporation time is 6 h-10 h. Preferably, a drying temperature is 70°C-100°C, and drying time is 5 h-8 h. Preferably, a calcination temperature is 1050°C-1250°C, calcination time is 3 h-5 h, and a calcination heating rate is 4°C / min-6°C / min. The present invention further provides a high-entropy perovskite-type electromagnetic wave absorbing material prepared by the preparation method for a high-entropy perovskite-type electromagnetic wave absorbing material. It can be seen from the above technical solutions that, compared with the prior art, the present invention has the following beneficial effects. (1) The high-entropy perovskite-type electromagnetic wave absorbing material has both dielectric loss and magnetic loss properties, and can be mixed with paraffin at a ratio of 4:1 with a thickness of 1.4 mm, an effective absorption frequency bandwidth can reach 2.87 GHz, and the lowest reflectivity can reach -52.042 dB. Therefore, the high-entropy perovskite-type electromagnetic wave absorbing material (La(Cro.2Mno.2Feo.2Coo.2Nio.2)03) features wide effective absorption frequency band and high absorption strength under a lower thickness. (2) The present invention takes water as a solvent, needs no highly toxic chemical reagent, is environment-friendly and pollution-free; and the preparation process is simple, has a low cost, and is suitable for large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS In order to more clearly illustrate technical solutions in the examples of the present invention or in the prior art, a brief introduction to the accompanying drawings required for the description of the examples or the prior art will be provided below. Obviously, the accompanying drawings in the following description are only some of the examples of the present invention, and those ordinary skill in the art would also be able to derive other drawings from these drawings without making creative efforts. FIG. I is an X-ray diffraction (XRD) diagram of high-entropy perovskite-type electromagnetic wave absorbing materials obtained in Examples 1-2 and Comparative examples 1-3 of the present invention; FIG. 2 is a scanning electron microscope (SEM) image of a high-entropy perovskite-type electromagnetic wave absorbing material obtained in Example 1 of the present invention; FIG. 3 is an SEM image of a high-entropy perovskite-type electromagnetic wave absorbing material obtained in Example 2 of the present invention; FIG. 4 is an SEM image of a high-entropy perovskite-type electromagnetic wave absorbing material obtained in Comparative example 1 of the present invention; FIG. 5 is an SEM image of a high-entropy perovskite-type electromagnetic wave absorbing material obtained in Comparative example 2 of the present invention; FIG. 6 is an SEM image of a high-entropy perovskite-type electromagnetic wave absorbing material obtained in Comparative example 3 of the present invention; FIG. 7 is a reflection loss diagram of high-entropy perovskite-type electromagnetic wave absorbing materials obtained in Examples 1-2 and Comparative examples 1-3 of the present invention with a thickness of 1.4 mm; FIG. 8 is an impedance matching diagram of high-entropy perovskite-type electromagnetic wave absorbing materials obtained in Examples 1-2 and Comparative examples 1-3 of the the present invention with a thickness of 1.4 mm; and FIG. 9 is a reflection loss diagram of a high-entropy perovskite-type electromagnetic wave absorbing material obtained in Example 2 of the present invention with different thicknesses. DETAILED DESCRIPTION OF THE EMBODIMENTS The present invention provides a preparation method for a high-entropy perovskite-type electromagnetic wave absorbing. The method includes: cobalt salt, iron salt, nickel salt, lanthanum salt, manganese salt, chromium salt, polymerizing agent, dispersant and a solvent are mixed to obtain a mixture; the mixture is evaporated and dried in sequence to obtain a precursor; and the precursor is calcined to obtain the high-entropy perovskite-type electromagnetic wave absorbing material. In the present invention, the cobalt salt is preferably cobalt nitrate, cobalt sulfate or cobalt chloride, and more preferably cobalt nitrate or cobalt chloride. The iron salt is preferably ferric nitrate, ferric sulfate or ferric chloride, and more preferably ferric nitrate or ferric chloride. The nickel salt is preferably nickel nitrate, nickel sulfate or nickel chloride, and more preferably nickel nitrate or nickel chloride. The lanthanum salt is preferably lanthanum nitrate, lanthanum sulfate or lanthanum chloride, and more preferably lanthanum nitrate or lanthanum chloride. The manganese salt is preferably manganese nitrate, manganese sulfate or manganese chloride, and more preferably manganese nitrate or manganese chloride. The chromium salt is preferably chromium nitrate, chromium sulfate or chromium chloride, and more preferably chromium nitrate or chromium chloride. In the present invention, the polymerizing agent is citric acid; the dispersant is preferably ethylene glycol; and the solvent is water. In the present invention, a molar ratio of lanthanum ions, cobalt ions, chromium ions, iron ions, manganese ions, nickel ions and the polymerizing agent in the mixture is preferably 4.8-5.2:0.8-1.2:0.8-1.2:0.8-1.2:0.8-1.2:0.8-1.2:8-12, and more preferably 4.9-5.1:0.9-1.1:0.9-1.1:1-1.1:0.9-1.1:0.9-1.1:9-11. In the present invention, a mass-volume ratio of the polymerizing agent to the dispersant is preferably 4 g-5 g:4 mL-7 mL, and more preferably 4.2 g-4.8 g:5 mL-6 mL. A volume ratio of the dispersant to the solvent is preferably 1-1.2:10, and more preferably 1.1-1.15:10. In the present invention, before evaporation, ammonia water is added to the mixture obtain by mixing cobalt salt, iron salt, nickel salt, lanthanum salt, manganese salt, chromium salt, polymerizing agent, dispersant and a solvent, such that the pH of the mixture is preferably 7-7.5, and more preferably 7.2-7.3. In the present invention, evaporation is performed under stirring, and an evaporation temperature is preferably 70°C-90°C, and more preferably 75°C-85°C. Evaporation time is preferably 6 h-10 h, and more preferably 8 h. A stirring speed is 5 r / min-20 r / min, and more preferably 10 r / min. In the present invention, a drying temperature is preferably 70°C-100°C, and more preferably 75°C-90°C. Drying time is preferably 5 h-8 h, and more preferably 6 h-7 h. In the present invention, calcination is performed in an air atmosphere, and a calcination temperature is preferably 1050°C-1250°C, and more preferably 1080°C-1220°C. Calcination time is preferably 3 h-5 h, and more preferably 3.5 h-4.5 h. A heating rate of calcination is preferably 4 °C / min-6 °C / min, and more preferably 4.5°C / min-5°C / min. The present invention further provides a high-entropy perovskite-type electromagnetic wave absorbing material prepared by the preparation method for a high-entropy perovskite-type electromagnetic wave absorbing material. The technical solution provided in the present disclosure is described in detail below in conjunction with examples, but they are not to be construed as limiting the scope of protection of the present invention. Example 1 A preparation method for a high-entropy perovskite-type electromagnetic wave absorbing in the example includes: (1) A precursor was prepared through a sol-gel method: 4.33 g of lanthanum nitrate hexahydrate, 0.5821 g of cobalt nitrate hexahydrate, 0.808 g of ferric nitrate nonahydrate, 0.5816 g of nickel nitrate hexahydrate, 0.3958 g of manganese chloride tetrahydrate and 0.5329 g of chromium chloride hexahydrate were weighed and dissolved in 50 mL of distilled water, then 4.2028 g of citric acid monohydrate and 5.5 mL of ethylene glycol were weighed and stirred until they were completely dissolved. A pH value of the solution was adjusted to 7 with ammonia water, and the above solution was heated at 80 °C and stirred for 8 h at a stirring speed of 10 r / min, to form sol. The sol was put into a blast drying oven for drying at 100°C for 8 h, and naturally cooled to a room temperature, and the obtained dried gel was taken out to obtain the precursor. (2) The high-entropy perovskite-type electromagnetic wave absorbing material was prepared by sintering: the precursor obtained in step (1) was placed into a muffle furnace for calcination in an air atmosphere, was heated to 1100 °C for calcination for 4 h at a heating rate of 5°C / min, and was naturally cooled to obtain a product La(Cro.2Mno.2Feo.2Coo.2Nio.2)03. Example 2 A preparation method for a high-entropy perovskite-type electromagnetic wave absorbing in the example includes: (1) A precursor was prepared through a sol-gel method: 4.33 g of lanthanum nitrate hexahydrate, 0.5821 g of cobalt nitrate hexahydrate, 0.808 g of ferric nitrate nonahydrate, 0.5816 g of nickel nitrate hexahydrate, 0.3958 g of manganese chloride tetrahydrate and 0.5329 g of chromium chloride hexahydrate were weighed and dissolved in 50 mL of distilled water, then 4.2028 g of citric acid monohydrate and 5.5 mL of ethylene glycol were weighed and stirred until they were completely dissolved. A pH value of the solution was adjusted to 7 with ammonia water, and the above solution was heated at 80 °C and stirred for 8 h at a stirring speed of 10 r / min, to form sol. The sol was put into a blast drying oven for drying at 100°C for 8 h, and naturally cooled to a room temperature, and the obtained dried gel was taken out to obtain the precursor. (2) The high-entropy perovskite-type electromagnetic wave absorbing material was prepared by sintering: the precursor obtained in step (1) was placed into a muffle furnace for calcination in an air atmosphere, was heated to 1200 °C for calcination for 4 h at a heating rate of 5°C / min, and was naturally cooled to obtain a product La(Cro.2Mno.2Feo.2Coo.2Nio.2)03. Comparative example 1 A preparation method for a high-entropy perovskite-type electromagnetic wave absorbing in the comparative example includes: (1) A precursor was prepared through a sol-gel method: 4.33 g of lanthanum nitrate hexahydrate, 0.5821 g of cobalt nitrate hexahydrate, 0.808 g of ferric nitrate nonahydrate, 0.5816 g of nickel nitrate hexahydrate, 0.3958 g of manganese chloride tetrahydrate and 0.5329 g of chromium chloride hexahydrate were weighed and dissolved in 50 mL of distilled water, then 4.2028 g of citric acid monohydrate and 5.5 mL of ethylene glycol were weighed and stirred until they were completely dissolved. A pH value of the solution was adjusted to 7 with ammonia water, and the above solution is heated at 80 °C and stirred for 8 h at a stirring speed of 10 r / min, to form sol. The sol was put into a blast drying oven for drying at 100 °C for 8 h, and naturally cooled to a room temperature, and the obtained dried gel was taken out to obtain the precursor. (2) The high-entropy perovskite-type electromagnetic wave absorbing material was prepared by sintering: the precursor obtained in step (1) was placed into a muffle furnace for calcination in an air atmosphere, was heated to 900 °C for calcination for 4 h at a heating rate of 5°C / min, and was naturally cooled to obtain a product La(Cro.2Mno.2Feo.2Coo.2Nio.2)03. Comparative example 2 A preparation method for a high-entropy perovskite-type electromagnetic wave absorbing in the comparative example includes: (1) A precursor was prepared through a sol-gel method: 4.33 g of lanthanum nitrate hexahydrate, 0.5821 g of cobalt nitrate hexahydrate, 0.808 g of ferric nitrate nonahydrate, 0.5816 g of nickel nitrate hexahydrate, 0.3958 g of manganese chloride tetrahydrate and 0.5329 g of chromium chloride hexahydrate were weighed and dissolved in 50 mL of distilled water, then 4.2028 g of citric acid monohydrate and 5.5 mL of ethylene glycol were weighed and stirred until they were completely dissolved. A pH value of the solution was adjusted to 7 with ammonia water, and the above solution was heated at 80 °C and stirred for 8 h at a stirring speed of 10 r / min, to form sol. The sol was put into a blast drying oven for drying at 100°C for 8 h, and naturally cooled to a room temperature, and the obtained dried gel was taken out to obtain the precursor. (2) The high-entropy perovskite-type electromagnetic wave absorbing material was prepared by sintering: the precursor obtained in step (1) was placed into a muffle furnace for calcination in an air atmosphere, was heated to 1000 °C for calcination for 4 h at a heating rate of 5°C / min, and was naturally cooled to obtain a product La(Cro.2Mno.2Feo.2Coo.2Nio.2)03. Comparative example 3 A preparation method for a high-entropy perovskite-type electromagnetic wave absorbing in the comparative example includes: (1) A precursor was prepared through a sol-gel method: 4.33 g of lanthanum nitrate hexahydrate, 0.5821 g of cobalt nitrate hexahydrate, 0.808 g of ferric nitrate nonahydrate, 0.5816 g of nickel nitrate hexahydrate, 0.3958 g of manganese chloride tetrahydrate and 0.5329 g of chromium chloride hexahydrate were weighed and dissolved in 50 mL of distilled water, then 4.2028 g of citric acid monohydrate and 5.5 mL of ethylene glycol were weighed and stirred until they were completely dissolved. A pH value of the solution was adjusted to 7 with ammonia water, and the above solution was heated at 80 °C and stirred for 8 h at a stirring speed of 10 r / min, to form sol. The sol was put into a blast drying oven for drying at 100°C for 8 h, and naturally cooled to a room temperature, and the obtained dried gel was taken out to obtain the precursor. (2) The high-entropy perovskite-type electromagnetic wave absorbing material was prepared by sintering: the precursor obtained in step (1) was placed into a muffle furnace for calcination in an air atmosphere, was heated to 1300 °C for calcination for 4 h at a heating rate of 5°C / min, and was naturally cooled to obtain a product La(Cro.2Mno.2Feo.2Coo.2Nio.2)03. Surface morphologies and properties of the high-entropy perovskite-type electromagnetic wave absorbing materials obtained in Examples 1-2 and Comparative examples 1-3 were tested, and test results are shown in FIGS. 1-9. It can be seen from FIG. 1 that Comparative example 1 had a second phase of a non-perovskite structure at a processing temperature of 900°C. The number of second-phase diffraction peaks of Comparative example 2 increased at a temperature of 1000°C. When the temperature rose to 1100°C, a single-phase perovskite structure was formed in Example 1. When the temperature rose to 1200°C, the material obtained in Example 2 can still maintain a desirable single-phase perovskite structure. As the temperature increased to 1300°C, the second phase was produced again in Comparative example 3. It can be seen that the high-entropy perovskite-type electromagnetic wave absorbing material obtained in the present invention had a relatively complete single-phase perovskite structure, complete crystal form and single structure. It can be seen from FIGS. 2-6 that the structure of the high-entropy perovskite-type electromagnetic wave absorbing material obtained in the present invention was regular and presents an octadecahedron structure. It can be seen from FIG. 7 that the obtained material exhibited excellent electromagnetic wave absorption performance at a sintering temperature of 1200°C, the lowest reflectivity can reach -52.04 dB, and an effective wave absorbing bandwidth can reach 3.02 GHz (11.95 GHz-14.97 GHz). The too low (900°C) or too high (1300°C) sintering temperature was not conducive to improvement in the electromagnetic wave absorption performance of the material. It is known that the high-entropy perovskite-type electromagnetic wave absorbing material obtained in the present invention had excellent electromagnetic wave absorption performance. It can be seen from FIG. 8 that the high-entropy perovskite-type electromagnetic wave absorbing material obtained in the present invention exhibits relatively excellent wave impedance matching characteristics, and the wave impedance matching characteristics in Comparative examples 1 and 3 were poor. It can be seen from FIG. 9 that the high-entropy perovskite-type electromagnetic wave absorbing material obtained in Example 1 of the present invention exhibited effective electromagnetic wave absorption performance within a thickness range of 1 mm-3mm, and the effective wave absorbing frequency bandwidth can effectively cover 6 GHz-18 GHz. The high-entropy perovskite-type electromagnetic wave absorbing material in the present 5 invention is prepared through a sol-gel method, and optimal wave absorbing performance of the high-entropy perovskite-type electromagnetic wave absorbing material can be obtained by calcining dried precursor gel at a high temperature of 1200 °C in an air atmosphere, such that working procedures of grinding and compression are omitted. The loss of the material is mainly due to dielectric loss. Compared with a traditional microwave absorbent, the high-entropy 10 perovskite-type electromagnetic wave absorbing material obtained in the present invention features a wide effective absorption frequency band and high absorption strength under low thickness; and moreover, the present invention takes water as a solvent, needs no highly toxic chemical reagent, is environment-friendly and pollution-free; and the preparation process is simple, has a low cost, and is suitable for large-scale industrial production. 15 The foregoing embodiments are merely preferred embodiments of the present invention, and it should be noted that several improvements and modifications may also be made by those of ordinary skill in the art. 29 07 24

Claims

29 07 241. A preparation method for a high-entropy perovskite-type electromagnetic wave absorbing material, wherein the high-entropy perovskite-type electromagnetic wave absorbing material is La(Cro.2Mno.2Feo.2Coo.2Nio.2)03, the preparation method comprising:5 mixing cobalt salt, iron salt, nickel salt, lanthanum salt, manganese salt, chromium salt, polymerizing agent citric acid, dispersant and a solvent, wherein the solvent is water, to obtain a mixture;evaporating and drying the mixture in sequence, to obtain a precursor; andcalcining the precursor with a calcination temperature is 1100°C-1200°C, to obtain the high-10 entropy perovskite-type electromagnetic wave absorbing material La(Cro.2Mno.2Feo.2Coo.2Nio.2)03 with an effective absorption frequency bandwidth can reach 2.87 GHz, and the lowest reflectivity can reach -52.042 dB.

2. The preparation method for a high-entropy perovskite-type electromagnetic wave 15 absorbing material according to claim 1, wherein the cobalt salt is cobalt nitrate, cobalt sulfate or cobalt chloride; the iron salt is ferric nitrate, ferric sulfate or ferric chloride; the nickel salt is nickel nitrate, nickel sulfate or nickel chloride; the lanthanum salt is lanthanum nitrate, lanthanum sulfate or lanthanum chloride; the manganese salt is manganese nitrate, manganese sulfate or manganese chloride; and the chromium salt is chromium nitrate, chromium sulfate or chromium chloride.

203. The preparation method for a high-entropy perovskite-type electromagnetic wave absorbing material according to claim 2, wherein the dispersant is ethylene glycol.

4. The preparation method for a high-entropy perovskite-type electromagnetic wave 25 absorbing material according to any one of claims 1-3, wherein a molar ratio of lanthanum ions, cobalt ions, chromium ions, iron ions, manganese ions, nickel ions and the polymerizing agent in the mixture is 4.8-5.2:0.8-1.2:0.8-1.2:0.8-1.2:0.8-1.2:0.8-1.2:8-12.

5. The preparation method for a high-entropy perovskite-type electromagnetic wave 30 absorbing material according to claim 4, wherein a mass-volume ratio of the polymerizing agent to the dispersant is 4 g-5 g:4 mL-7 mL, and a volume ratio of the dispersant to the solvent is 1-1.2:10.

6. The preparation method for a high-entropy perovskite-type electromagnetic wave absorbing material according to claim 5, wherein an evaporation temperature is 70°C- 90°C, and evaporation time is 6 h-10 h.5 7. The preparation method for a high-entropy perovskite-type electromagnetic waveabsorbing material according to claims 1, 5 or 6, wherein a drying temperature is 70°C-100°C, and drying time is 5 h-8 h.

8. The preparation method for a high-entropy perovskite-type electromagnetic wave 10 absorbing material according to claim 7, wherein calcination time is 3 h-5 h, and a calcination heating rate is 4°C / min-6°C / min.29 07 24

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