An electromagnetic wave absorbing material, its preparation method and application

Abstract

The present invention relates to a wave-absorbing material, a preparation method thereof and an application. The wave-absorbing material contains a nitride phase FeNi3N. The material preparation process of the present invention is simple and has a high wave-absorbing intensity. The magnetic synergistic effect and the effective absorption bandwidth are improved for the first time through a heterostructure, and excellent wave-absorbing performance is exhibited in the 2-18 GHz band, having broad application potential and market prospects in the fields of electromagnetic shielding and electromagnetic safety protection of communication devices.

Description

Technical Field

[0001] The present invention belongs to the technical field of wave - absorbing materials, and particularly relates to a wave - absorbing material, a preparation method thereof, and an application thereof. Background Art

[0002] With the rapid development of modern radar and microwave electronic technologies, stealth technology, as an effective means to improve the survival, penetration, and deep - strike capabilities of weapon systems, has become one of the hotspots for military powers to compete for high - tech military technologies. Radar searches for targets by emitting electromagnetic waves, and then locks the targets based on the electromagnetic waves reflected by the detected parties, and tracks, locates, and identifies them. Developing high - efficiency electromagnetic - wave - absorbing radar stealth materials is one of the effective ways to improve the survival ability of weapon systems and has become the most valuable and effective tactical penetration means in modern warfare. At the same time, in the civilian field, with the development of contemporary electronic information technology, the derived electromagnetic - wave radiation has caused thorny problems such as electromagnetic pollution, electromagnetic interference, and information leakage, which have hindered the stable development of the electronic information industry. Therefore, wave - absorbing materials that can absorb electromagnetic waves in specific frequency bands have become an important means to achieve stealth technology and anti - electromagnetic interference and have broad application prospects. At the same time, with the continuous expansion of modern application requirements and scenarios, wave - absorbing materials are given higher comprehensive requirements, that is, the thickness of the wave - absorbing body is thin, the mass is light, the absorption frequency band is wide, and the wave - absorbing efficiency is strong. Therefore, there is an urgent need to develop new wave - absorbing materials that meet the requirements of "thin, light, wide, and strong" in both military and civilian fields.

[0003] Magnetic materials can be divided into pure metal materials, magnetic oxide materials, magnetic nitride materials, etc. Magnetic materials have both dielectric loss and magnetic loss capabilities, so they have received extensive attention in the field of electromagnetic - wave absorption. However, single - component magnetic materials generally have disadvantages such as poor electromagnetic parameter matching, large density, and poor stability, and cannot meet the actual application requirements. Magnetic metal materials have strong ferromagnetism and high electrical conductivity, and have strong electromagnetic attenuation ability. However, due to their too high electrical conductivity, electromagnetic parameter impedance mismatch occurs, resulting in strong reflection of electromagnetic waves, which is not conducive to the absorption of electromagnetic waves by the materials. At the same time, metal material components have problems such as large density and poor component stability, which are not conducive to the development of light - weight and stable - performance wave - absorbing materials. Although magnetic oxides and nitrides have strong impedance - matching characteristics, due to their low magnetic loss ability and narrow effective absorption frequency band, their overall loss ability to electromagnetic waves is also weak. Summary of the Invention

[0004] Aiming at the defects of the prior art, the technical problem to be solved by the present invention is to provide a wave - absorbing material, a preparation method thereof, and an application thereof.

[0005] The present invention provides a wave - absorbing material, and the wave - absorbing material contains a nitride phase FeNi3N.

[0006] Preferably, the wave-absorbing material is pure nitride phase FeNi3N, or a heterojunction structure with coexistence of oxide phase, nitride phase and alloy phase, or coexistence of nitride phase and oxide phase or alloy phase.

[0007] The oxide phase is NiFe2O4, the nitride phase is FeNi3N, and the alloy phase is FeNi3.

[0008] The layered double metal hydroxide prepared by the coprecipitation method is heat-treated with ammonia gas to obtain a heterojunction structure with coexistence of oxide phase, nitride phase and alloy phase. Among them, the layered double metal hydroxide is nickel-iron layered double metal hydroxide (NiFe-LDH), the oxide phase is NiFe2O4, the nitride phase is FeNi3N, and the alloy phase is FeNi3. And by adjusting the temperature and time of the heat treatment, the ratio of the three phases can be adjusted, so as to adjust the wave absorption ability of electromagnetic waves.

[0009] The present invention provides a preparation method of a wave-absorbing material, including:

[0010] The NiFe-LDH nanosheets are heat-treated in an ammonia gas atmosphere to obtain a wave-absorbing material.

[0011] The preferred manner of the above preparation method is as follows:

[0012] The NiFe-LDH nanosheets are prepared according to the synthesis steps in the literature (Yufei Zhao, Xin Zhang, et al. Adv. Energy Mater. 2018, 8, 1703585), specifically as follows:

[0013] The nickel salt is dissolved in deionized water, and then the iron salt is added to obtain solution A; the formamide is dissolved in water and diluted to solution B; after solution B is heated to a certain temperature (80-100 °C), solution A is gradually added dropwise into solution B to obtain a mixed solution; a sodium hydroxide solution is prepared, and then slowly added dropwise into the above mixed solution to keep it at a certain pH value (pH = 9-11), and then the dropping is stopped, and magnetic stirring is carried out for a certain reaction time (10-60 min); after the reaction is completed, it is cooled to room temperature, then centrifuged and washed, and finally dried to obtain NiFe-LDH nanosheets.

[0014] The nickel salt is one or more of nickel nitrate hexahydrate, nickel sulfate, nickel chloride, nickel acetate; the iron salt is one or more of iron nitrate nonahydrate, iron sulfate, iron chloride, iron acetate; the ratio of the nickel salt to the iron salt is a molar ratio of 3:1-2:1.

[0015] The concentration of nickel salt in the solution A is 0.01 - 0.05 mmol / L, and the concentration of iron salt is 0.01 - 0.05 mmol / L; the volume percentage concentration of the formamide solution is 10% - 30%; the volume ratio of the solution A to the formamide solution is 1:1 - 3:1.

[0016] The coprecipitation temperature is 80 - 100 °C, and the reaction time is 10 - 60 min.

[0017] The concentration of the sodium hydroxide solution is 0.25 - 2.5 mol / L.

[0018] The process conditions for washing are: washing with distilled water 3 - 10 times.

[0019] The process parameters for drying are: freeze-drying or supercritical drying.

[0020] The heat treatment under ammonia atmosphere is specifically: the flow rate of ammonia gas introduced is 60 - 120 mL / min; the heat treatment reaction temperature is 300 - 400 °C, and the reaction time is 1 - 8 h.

[0021] Preferably, the heat treatment reaction temperature is 380 °C and the time is 2 h.

[0022] An application of the wave-absorbing material of the present invention in the fields of aircraft stealth, electromagnetic shielding, electromagnetic protection or microwave anechoic chamber.

[0023] The bimetallic oxide / nitride / alloy ternary heterojunction wave-absorbing material with magnetic synergistic effect of the present invention is synthesized by heat treatment of NiFe-LDH prepared by coprecipitation method under ammonia gas; the heterojunction material is composed of an oxide phase, a nitride phase and an alloy phase, the material has high electromagnetic wave absorption intensity, wide effective absorption bandwidth, has magnetic synergistic effect, and exhibits excellent wave-absorbing performance in the range of 2 - 18 GHz. The present invention utilizes the adjustable heat treatment temperature and reaction time under ammonia atmosphere to synthesize from pure phases (oxide phase, nitride phase, alloy phase) to two-phase heterojunctions (oxide phase / nitride phase heterojunction) and then to three-phase heterojunctions (oxide phase / nitride phase / alloy phase ternary heterojunction), adjusts the balance between the dielectric constant and magnetic permeability of the material, enables the material to meet the characteristic impedance while having good wave-absorbing efficiency, realizes the controllable adjustment of the absorption band in the wide frequency range of 2 - 18 GHz, and meets the actual application requirements of the material in different application fields. The ternary heterojunction wave-absorbing material synthesized by the present invention has broad application potential and market prospects in the fields of electromagnetic shielding of communication equipment, stealth technology in military fields, etc.

[0024] Beneficial effects

[0025] (1) The preparation method of the present invention is a simple one-step heat treatment method, and the experimental method is simple and convenient.

[0026] (2) The double-metal ternary heterojunction microwave absorption material of the present invention can achieve an absorption of -59.3 dB for electromagnetic waves at a frequency of 9.68 GHz with a relatively thin thickness of 2.02 mm.

[0027] (3) In the double-metal ternary heterojunction of the present invention, the alloy phase provides high dielectric constant and magnetic permeability. The nitride phase and the oxide phase effectively adjust the overall impedance matching of the material through their low dielectric constants. At the same time, the three-phase structure generates a magnetic synergistic effect to enhance the magnetic loss of the material, further improving the microwave absorption intensity. The prepared double-metal ternary heterojunction exhibits excellent microwave absorption performance in the range of 2 - 18 GHz. Description of the Drawings

[0028] Figure 1 are the XRD patterns and corresponding TEM images of Example 1 prepared by reacting at 300, 370, and 400 °C for two hours;

[0029] Among them, (A) are the XRD patterns of O300, N370, and A400; (B) is the TEM image of A400, (C) is the TEM image of N370, and (D) is the TEM image of O300;

[0030] Figure 2 are the three-dimensional reflection loss diagrams of O300 (A), N370 (B), and A400 (C) in Example 1.

[0031] Figure 3 is the XRD pattern of Example 2 prepared by reacting at 330 and 380 °C for two hours.

[0032] Figure 4 are the TEM image and EDX analysis of ONA380 in Example 2; among them, (a) is the TEM image of ONA380, (b), (c), (e), and (f) are the high-resolution TEM images of ONA380, and (d) is the EDX image of ONA380.

[0033] Figure 5 are the reflection loss diagrams of ON330 (a, c) and ONA380 (b, d) in Example 2. Detailed Embodiments

[0034] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0035] Table 1 Sources of Each Raw Material

[0036]

[0037] Example 1

[0038] (1) Weigh 0.4362 g of Ni(NO3)2·6H2O and dissolve it in 40 mL of distilled water. Then add 0.202 g of Fe(NO3)3·9H2O and stir magnetically until completely dissolved. This solution is Solution A.

[0039] (2) Measure 9.2 mL of formamide solution and dilute it to 40 mL with distilled water. This solution is Solution B. Pour Solution B into a three-necked flask, heat it in an oil bath to 80 °C, and then dropwise add Solution A to Solution B while stirring for 5 min.

[0040] (3) Prepare a 0.25 mol / L sodium hydroxide solution and dropwise add it to the above mixed solution. After maintaining the overall pH value at about 10, react for 10 min.

[0041] (4) Centrifuge at 4500 rpm / min for 4 min to collect NiFe-LDH, wash it 3 times with distilled water until the pH of the washed aqueous phase is neutral, and then freeze-dry for 2 days to obtain NiFe-LDH nanosheets.

[0042] (5) Place the NiFe-LDH nanosheets in a horizontal tube furnace. Under an NH3 atmosphere, heat them at a heating rate of 5 °C / min to 300, 370, and 400 °C and hold for 2 hours, then cool with the furnace, and collect the black products named O300, N370, and A400 respectively.

[0043] The O300, N370, and A400 prepared in this example are a pure oxide phase, a nitride phase, and an alloy phase respectively. The XRD results are as Figure 1 shown in A. The crystal plane diffraction peaks of O300 correspond to the cubic NiFe2O4 phase (PDF#54-0964), the crystal plane diffraction peaks of N370 correspond to the cubic FeNi3N phase (PDF#50-1434), and the crystal plane diffraction peaks of A400 correspond to the crystal planes of the cubic FeNi3 phase (PDF#38-0419). Three different pure phases were prepared at different temperatures with the same reaction time. Figure 1 B - C respectively show the TEM images of O300, N370, and A400.

[0044] In this example, 50 mg of each of the three samples was mixed with an equal weight of paraffin and pressed into an annular sample with an outer diameter of 7 mm, an inner diameter of 3.04 mm, and a thickness of about 2 mm. The microwave absorption properties were tested by a vector network analyzer (Keysight, N5234B), and the test frequency was 2 - 18 GHz. As Figure 2As is known, the reflection loss ability of O300 and A400 is poor, and there is almost no wave absorption performance in the range of 2 - 18 GHz. However, the wave absorption performance of N370 is better, and the minimum reflection loss value reaches -47.12 dB at 16.48 GHz, and the matching thickness is only 3.66 mm. The results show that the wave absorption performance of nitrides is superior to that of oxides and alloys.

[0045] Example 2

[0046] (1) Weigh 0.4362 g of Ni(NO3)2·6H2O and dissolve it in 40 mL of distilled water. Then add 0.202 g of Fe(NO3)3·9H2O and stir magnetically until completely dissolved. This solution is A.

[0047] (2) Measure 9.2 mL of formamide solution and dilute it to 40 mL with distilled water. This solution is B. Pour solution B into a three-necked flask, heat it to 80 °C in an oil bath, and then dropwise add solution A into solution B while stirring for 5 min.

[0048] (3) Prepare a 0.25 mol / L sodium hydroxide solution and dropwise add it into the above mixed solution. After maintaining the overall pH value at about 10, react for 10 min.

[0049] (4) Centrifuge at 4500 rpm / min for 4 min to collect NiFe-LDH, wash it 3 times with distilled water until the pH of the washed aqueous phase becomes neutral, and then freeze-dry for 2 days to obtain NiFe-LDH nanosheets.

[0050] (5) Place the NiFe-LDH nanosheets in a horizontal tube furnace. Under NH3 atmosphere, heat at a heating rate of 5 °C / min to 330 and 380 °C and hold for 2 hours, then cool with the furnace, and collect the black products named ON330 and ONA380 respectively.

[0051] The XRD patterns of the samples of ON330 and ONA380 prepared in this example are as Figure 3 shown. ON330 shows a mixed phase of oxide phase and nitride phase. The results of XRD refinement show that the proportions of oxide phase and nitride phase are 77.85 and 22.15 wt% respectively. ONA380 shows a three-phase mixture of oxide phase, nitride phase and alloy phase. The XRD refinement results show that the proportions of oxide phase, nitride phase and alloy phase are 33.34, 44.74 and 21.92 wt% respectively.

[0052] The TEM image of the sample of the three-phase mixture ONA380 prepared in this example is as Figure 4 shown. In ONA380, a clear phase interface can be clearly observed ( Figure 4a, b, e). The three phases combine to form NiFe2O4 / FeNi3N and FeNi3N / FeNi3 heterogeneous interfaces. Figure 4 As shown in c, and The lattice spacing can be directed to the (111) crystal plane of FeNi3N and the (311) crystal plane of NiFe2O4 respectively. Figure 4 As shown in f, and The lattice spacing can correspond to the (111) plane of FeNi3 and the (311) plane of FeNi3N. In addition, the lattice fringe contrast in the interface region is much higher than that outside the interface region, which is caused by the lattice dislocation at the interface of heterogeneous NiFe2O4 / FeNi3N and FeNi3N / FeNi3.

[0053] In this embodiment, 50 mg of paraffin wax of equal weight was mixed into two samples, and the samples were pressed into ring-shaped samples with an outer diameter of 7 mm, an inner diameter of 3.04 mm, and a thickness of about 2 mm. The wave absorption performance was tested by a vector network analyzer (Keysight, N5234B) at a test frequency of 2-18 GHz. Figure 5 As shown in the figure, ON330 has poor reflection loss capability due to the presence of too many oxide phases. ONA380 has increased interface polarization capability and magnetic coupling due to the presence of heterogeneous interface, and the minimum reflection loss value reaches -59.30dB at 9.68GHz, and the matching thickness is only 2.02mm. For ONA380, when the matching thickness is set to 2.02mm, the effective absorption bandwidth is 2.44GHz (8.68-11.12GHz).

Claims

1. An electromagnetic wave absorbing material, characterized in that, The absorbing material has a heterojunction structure with the coexistence of an oxide phase, a nitride phase, and an alloy phase. The proportions of the oxide phase, nitride phase, and alloy phase are 33.34 wt%, 44.74 wt%, and 21.92 wt% respectively. Among them, the oxide phase is NiFe2O4, the nitride phase is FeNi3N, and the alloy phase is FeNi3.

2. A preparation method of the absorbing material according to claim 1, comprising: Heat-treating NiFe-LDH nanosheets in an ammonia atmosphere to obtain the absorbing material.

3. The preparation method according to claim 2, characterized in that, The NiFe-LDH nanosheets are prepared by the following method: Dissolve nickel salt and iron salt in water to obtain solution A, then drop solution A into a formamide solution. Using the co-precipitation method, dropwise add sodium hydroxide solution, and after centrifugation, washing, and drying, obtain NiFe-LDH nanosheets.

4. The preparation method according to claim 3, characterized in that The nickel salt is one or more of nickel nitrate hexahydrate, nickel sulfate, nickel chloride, nickel acetate; the iron salt is one or more of iron nitrate nonahydrate, iron sulfate, iron chloride, iron acetate; the molar ratio of the nickel salt to the iron salt is 3:1 - 2:

1.

5. The preparation method according to claim 3, wherein The concentration of the nickel salt in solution A is 0.01 - 0.05 mmol / L, and the concentration of the iron salt is 0.01 - 0.05 mmol / L; the volume percentage concentration of the formamide solution is 10% - 30%; The volume ratio of solution A to the formamide solution is 1:1 - 3:

1.

6. The preparation method according to claim 3, wherein The co-precipitation temperature is 80 - 100 °C, and the reaction time is 10 - 60 min.

7. The preparation method according to claim 3, characterized in that, The concentration of the sodium hydroxide solution is 0.25 - 2.5 mol / L.

8. The preparation method according to claim 2, characterized in that, The heat treatment in the ammonia atmosphere is specifically as follows: The flow rate of ammonia introduced is 60 - 120 mL / min; the reaction temperature is 300 - 400 °C, and the reaction time is 1 - 8 h.

9. An application of the absorbing material according to claim 1 in the fields of aircraft stealth, electromagnetic shielding, electromagnetic protection, or microwave anechoic chamber.

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