A method for preparing a high-entropy magnetic nanopowder microwave absorber

Abstract

A method for preparing a high-entropy magnetic nanopowder microwave absorbing agent belongs to the field of microwave absorbing material preparation. The method involves mixing nickel salt, iron salt, cobalt salt, molybdenum salt, copper salt, ammonium nitrate, and fuel in a molar ratio of 1:(0.1-5):(0.1-5):(0.1-5):(0.1-5):(0-15):(1-30) to prepare an aqueous solution. The solution is heated and evaporated until it becomes a viscous gel state. Heating continues to induce a redox reaction between -3 and +5 valence N ions in the system, yielding a metal oxide composite precursor. This precursor is then ground and crushed, and a reduction reaction is carried out in a hydrogen atmosphere for a period of time to obtain the high-entropy magnetic nanopowder microwave absorbing agent. The prepared powdered microwave absorber has an average particle size of 10–100 nm, and elements such as nickel, iron, cobalt, molybdenum, and copper are uniformly dissolved and dispersed in the fine nanoparticles. The oxygen content of the powdered microwave absorber is as low as 0.17–0.52 wt%, and it has good microwave absorption performance in the range of 1–18 GHz, with an effective absorption bandwidth of ≥2 GHz.

Description

Technical Field

[0001] This invention relates to the field of microwave absorbing material preparation, and in particular to a method for preparing a high-entropy magnetic nanopowder microwave absorbing agent. Background Technology

[0002] When electromagnetic waves are incident on an absorbing material, they undergo three processes: reflection, absorption, and transmission. This process strictly follows the law of conservation of energy in physics. The vast majority of the energy incident into the material is absorbed by the absorbing agent, converted into heat or other forms of energy, and dissipated. Electromagnetic waves are formed by the coupling of electric and magnetic fields. The absorbing material interacts with either or both of the electric and magnetic fields in the incident electromagnetic wave. This interaction conforms to Maxwell's equations in physics, where a disturbance caused by the interaction of any field with the absorbing material medium will cause a change in the response of the other field, thus achieving the dissipation of the entire electromagnetic wave. Currently, reflection loss (RL) is the most effective way to quantitatively and intuitively represent the material's absorption performance. When RL = -10 dB, the energy loss of electromagnetic waves reaches 90%, and when RL = -20 dB, the energy loss reaches 99%. In practical applications, the frequency bandwidth with RL ≤ -10 dB is defined as the effective absorption bandwidth (EAB). The thinner the material, the smaller the reflection loss RL value and the wider the effective absorption bandwidth EAB, indicating that the material has better wave absorption performance.

[0003] With the application and development of microwave absorbing materials in military stealth technology, higher requirements have been placed on their performance. Developing microwave absorbing materials that are thin, light, wide, strong, and environmentally adaptable has become a current research hotspot. High-entropy alloys, with their unique multi-principal component and high-concentration composition, possess natural advantages as microwave absorbing materials. Their excellent soft magnetic properties, corrosion resistance, and oxidation resistance provide a research foundation for the development of new microwave absorbing materials. The microwave absorption performance of high-entropy alloy microwave absorbing materials can be improved through various control methods, such as adjusting the type and concentration of principal components, adding trace elements, and combining with other materials. The microwave absorption performance of high-entropy alloy microwave absorbing materials is highly controllable, and its performance can be improved through various micro-control mechanisms, such as controlling the morphology and structure, adjusting the composition of the material, changing the amount of raw materials, and adjusting the process. The multi-principal component alloying composition of high-entropy alloys has significant advantages in the application of microwave absorbing materials. The unique alloy design concept and significant high mixing entropy effect of high-entropy alloys provide a new direction for the development of new microwave absorbing materials.

[0004] To meet the demands of technological advancements for high-performance microwave absorbing materials, the preparation of fine-grained, ultrafine-grained, or even nanocrystalline high-entropy alloy microwave absorbing materials is an inevitable trend. Currently, the main methods for preparing high-entropy magnetic nanopowder microwave absorbing agents are mechanical alloying and spray drying. Mechanical alloying typically involves high-energy grinding and mixing methods, which suffer from drawbacks such as long preparation time, low efficiency, potential for uneven powder composition, powder oxidation and impurity doping leading to poor powder purity control, and significant particle agglomeration during ball milling. Spray drying is heavily reliant on spray dryers and is affected by numerous equipment parameters. However, the equipment is complex, consumes a lot of electricity, occupies a large area, requires high separation of the gas-solid mixture (generally requiring two-stage dust removal), has low thermal efficiency, and consumes a lot of energy. These factors severely impact the quality of high-entropy magnetic nanopowder microwave absorbing agents prepared by spray drying. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing high-entropy magnetic nanopowder microwave absorbing agent. The prepared high-entropy magnetic nanopowder microwave absorbing agent has the characteristics of fine particles, uniform particle size and element distribution. At the same time, the method is simple and easy to implement, highly controllable, and has a short preparation process.

[0006] The present invention adopts the following technical solution:

[0007] On one hand, the present invention provides a method for preparing a high-entropy magnetic nanopowder microwave absorbing agent, comprising:

[0008] S1. Nickel salt, iron salt, cobalt salt, molybdenum salt, copper salt, ammonium nitrate, fuel and deionized water are mixed in a set ratio and prepared into a corresponding aqueous solution. The solution is heated and stirred until it evaporates to a viscous gel state. Then, the solution is heated to carry out a combustion synthesis reaction to obtain a metal oxide composite precursor.

[0009] S2. The composite precursor prepared in step S1 is thoroughly ground and crushed, and then subjected to a reduction reaction under a hydrogen atmosphere to obtain the high-entropy magnetic nanopowder microwave absorber.

[0010] In addition to any of the possible implementations described above, another implementation is provided in which, in step S1, the metal oxide composite precursor comprises at least one of NiO and Ni2O3, at least one of FeO, Fe2O3 and Fe3O4, at least one of CoO, Co2O3 and Co3O4, and MoO2, MoO3, NiMoO4, Fe2Mo3O4, etc. 12At least one of CoMoO4 and CuMoO4, at least one of CuO and Cu2O, and any one of NiFe2O4, CoFe2O4, CuFe2O4, NiCo2O4, FeCo2O4, and CuCo2O4.

[0011] In addition to any of the possible implementations described above, another implementation is provided in which the molar ratio of nickel salt, iron salt, cobalt salt, molybdenum salt, copper salt, ammonium nitrate and fuel in step S1 is 1:(0.1-5):(0.1-5):(0.1-5):(0.1-5):(0-15):(1-30).

[0012] In addition to any of the possible implementations described above, another implementation is provided in which, in step S1, the nickel salt is any one of nickel nitrate, nickel chloride, nickel sulfate, and nickel carbonate.

[0013] In addition to any of the possible implementations described above, another implementation is provided in which, in step S1, the iron salt is any one of ferric nitrate, ferric chloride, ferric sulfate, polyferric sulfate, and polyferric chloride.

[0014] In addition to any of the possible implementations described above, another implementation is provided in which, in step S1, the cobalt salt is any one of cobalt nitrate, cobalt chloride, cobalt sulfate, and cobalt carbonate.

[0015] In addition to any of the possible implementations described above, another implementation is provided in which, in step S1, the molybdenum salt is any one of molybdenum amine, molybdenum sulfate, and molybdenum chloride.

[0016] In addition to any of the possible implementations described above, another implementation is provided in which, in step S1, the copper salt is any one of copper nitrate, copper sulfate, copper chloride, and copper carbonate.

[0017] In addition to any of the possible implementations described above, another implementation is provided in which, in step S1, the fuel is one or more of glycine, citric acid, and urea.

[0018] In addition to any of the possible implementations described above, another implementation is provided in which the conditions for the combustion synthesis reaction in step S1 are: heating temperature of 200–500 °C and heating time of 10–60 min.

[0019] In addition to any of the possible implementations described above, another implementation is provided in which, in step S2, a reduction reaction is carried out in a tube furnace under a hydrogen atmosphere, and the reaction conditions are: heating rate 2-10 °C / min, reaction temperature 300-650 °C, holding time 1-3 h, and hydrogen flow rate 500-2000 mL / min.

[0020] On the other hand, the present invention also provides a high-entropy magnetic nanopowder microwave absorbing agent, which is prepared by the above method. The high-entropy magnetic nanopowder is characterized by having good microwave absorption performance in the range of 1 to 18 GHz, an average particle size of 10 to 100 nm, uniform particle size, and uniform solid-dispersion dispersion of elements such as nickel, iron, cobalt, molybdenum, and copper in the fine nanoparticles. The effective absorption bandwidth of this high-entropy magnetic nanopowder microwave absorbing agent is ≥2 GHz, and the oxygen content of the powder is as low as 0.17 to 0.52 wt%.

[0021] The beneficial effects of this invention are as follows:

[0022] 1. The preparation method of the high-entropy magnetic nanopowder microwave absorbing agent provided by the present invention can be selected and prepared by controlling parameters such as the type and ratio of raw materials, heating rate, hydrogen reduction temperature and time, thereby controlling the performance of the synthesized high-entropy magnetic nanopowder microwave absorbing agent and realizing its application in multiple fields.

[0023] 2. The liquid combustion synthesis in the preparation method provided by the present invention can achieve uniform mixing and dispersion of the metal elements at the molecular level, and the large amount of gas released during the combustion reaction can effectively prevent the agglomeration of nanoparticles, which is conducive to the final formation of a high-entropy magnetic nanoparticle microwave absorber with uniform loading and high dispersion of each metal component particle.

[0024] 3. The composite metal powder prepared by the solution combustion synthesis + hydrogen reduction method of this invention has a low oxygen content, and the high-entropy magnetic nanopowder microwave absorber has a uniform particle size. Elements such as nickel, iron, cobalt, molybdenum, and copper are uniformly dissolved and dispersed in fine nanoparticles, laying the foundation for the preparation of high-performance high-entropy magnetic nanopowder microwave absorbers.

[0025] 4. The raw materials of this invention are cheap and readily available, the equipment is simple, the process is fast and highly controllable, and it is suitable for large-scale industrial production, with broad application prospects. Attached Figure Description

[0026] Figure 1 The diagram shown is a flowchart illustrating a method for preparing a high-entropy magnetic nanopowder microwave absorber according to an embodiment of the present invention.

[0027] Figure 2 The image shown is a scanning electron microscope image of the morphology of the high-entropy magnetic nanopowder microwave absorber prepared in Example 1. Detailed Implementation

[0028] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that the technical features or combinations of technical features described in the following embodiments should not be considered in isolation, but can be combined with each other to achieve better technical effects.

[0029] like Figure 1As shown in the figure, an embodiment of the present invention provides a method for preparing a high-entropy magnetic nanopowder microwave absorbing agent, comprising:

[0030] S1. Nickel salt, iron salt, cobalt salt, molybdenum salt, copper salt, ammonium nitrate, fuel and deionized water are mixed in a set ratio and prepared into a corresponding aqueous solution. The solution is heated and stirred until it evaporates to a viscous gel state. Then, the solution is heated to carry out a combustion synthesis reaction to obtain a metal oxide composite precursor.

[0031] S2. The composite precursor prepared in step S1 is thoroughly ground and crushed, and then subjected to a reduction reaction under a hydrogen atmosphere to obtain the high-entropy magnetic nanopowder microwave absorber.

[0032] In one specific embodiment, in step S1, the metal oxide composite precursor includes at least one of NiO and Ni2O3, at least one of FeO, Fe2O3 and Fe3O4, at least one of CoO, Co2O3 and Co3O4, and MoO2, MoO3, NiMoO4, and Fe2Mo3O4. 12 At least one of CoMoO4 and CuMoO4, at least one of CuO and Cu2O, and any one of NiFe2O4, CoFe2O4, CuFe2O4, NiCo2O4, FeCo2O4, and CuCo2O4.

[0033] In one specific embodiment, in step S1, the molar ratio of nickel salt, iron salt, cobalt salt, molybdenum salt, copper salt, ammonium nitrate and fuel is 1:(0.1-5):(0.1-5):(0.1-5):(0.1-5):(0.1-5):(0-15):(1-30).

[0034] In one specific embodiment, in step S1, the nickel salt is any one of nickel nitrate, nickel chloride, nickel sulfate, and nickel carbonate.

[0035] In one specific embodiment, in step S1, the iron salt is any one of ferric nitrate, ferric chloride, ferric sulfate, polyferric sulfate, and polyferric chloride.

[0036] In one specific embodiment, in step S1, the cobalt salt is any one of cobalt nitrate, cobalt chloride, cobalt sulfate, and cobalt carbonate.

[0037] In one specific embodiment, in step S1, the molybdenum salt is any one of molybdenum amine, molybdenum sulfate, and molybdenum chloride.

[0038] In one specific embodiment, in step S1, the copper salt is any one of copper nitrate, copper sulfate, copper chloride, and copper carbonate.

[0039] In one specific embodiment, in step S1, the fuel is one or more of glycine, citric acid, and urea.

[0040] In one specific embodiment, in step S1, the conditions for the combustion synthesis reaction are: heating temperature of 200–500°C and heating time of 10–60 min.

[0041] In one specific embodiment, in step S2, a reduction reaction is carried out in a tube furnace under a hydrogen atmosphere. The reaction conditions are: heating rate 2-10 °C / min, reaction temperature 300-650 °C, holding time 1-3 h, and hydrogen flow rate 500-2000 mL / min.

[0042] This invention discloses a high-entropy magnetic nanopowder microwave absorbing agent, prepared by the method described above. The high-entropy magnetic nanopowder is characterized by good microwave absorption performance in the range of 1–18 GHz, with an average particle size of 10–100 nm, uniform particle size, and uniform solid-dispersion dispersion of elements such as nickel, iron, cobalt, molybdenum, and copper in the fine nanoparticles. This high-entropy magnetic nanopowder microwave absorbing agent has an effective absorption bandwidth ≥2 GHz and a powder oxygen content as low as 0.17–0.52 wt%.

[0043] Example 1

[0044] Nickel nitrate, ferric nitrate, cobalt nitrate, molybdate, copper nitrate, ammonium nitrate, and glycine were weighed in a molar ratio of 1:1:1:0.15:1:0:4 and dissolved in a small amount of deionized water. The solution was stirred thoroughly with a glass rod until completely dissolved to form an aqueous solution. The mixture was heated in a temperature-controlled resistance furnace to gradually evaporate the water until the solution became a brownish-brown gel. The solution was then held at 500 °C for 25 min to induce a vigorous combustion synthesis reaction. The product after the reaction was completed was thoroughly ground to obtain a precursor powder. The prepared precursor powder was placed in a tube furnace and subjected to a reduction reaction under a hydrogen atmosphere. The temperature was increased to 500 °C at a rate of 5 °C / min, held for 1 h, and then cooled with the furnace. The hydrogen flow rate was 800 mL / min.

[0045] The prepared high-entropy magnetic nanoparticles have an average size of 32 nm, uniform particle size, and uniform solid-solution dispersion of elements such as nickel, iron, cobalt, molybdenum, and copper in the fine nanoparticles. The effective absorption bandwidth is 5–9 GHz (2.5 mm), the powder has a low oxygen content (0.27 wt%), and a specific surface area of ​​7.15 m². 2 / g.

[0046] Example 2

[0047] Nickel chloride, ferric chloride, cobalt sulfate, molybdenum chloride, copper sulfate, ammonium nitrate, and glycine were weighed in a molar ratio of 1:2:3.3:1.9:5:5:7 and dissolved in a small amount of deionized water. The solution was stirred thoroughly with a glass rod until completely dissolved to form an aqueous solution. The mixed solution was heated in a temperature-controlled resistance furnace to gradually evaporate the water until the solution became a brownish-brown gel. The solution was then held at 400 °C for 45 min to induce a vigorous combustion synthesis reaction. The product after the reaction was completed was thoroughly ground to obtain a precursor powder. The prepared precursor powder was placed in a tube furnace and subjected to a reduction reaction under a hydrogen atmosphere. The temperature was increased to 350 °C at a rate of 2 °C / min, held for 3 h, and then cooled with the furnace. The hydrogen flow rate was 1000 mL / min.

[0048] The prepared high-entropy magnetic nanoparticles have an average size of 15 nm, uniform particle size, and uniform solid-solution dispersion of elements such as nickel, iron, cobalt, molybdenum, and copper in the fine nanoparticles. The effective absorption bandwidth is 5.5–8 GHz (1.5 mm), the powder has a low oxygen content (0.27 wt%), and a specific surface area of ​​10.02 m². 2 / g.

[0049] Example 3

[0050] Nickel nitrate, ferric sulfate, cobalt chloride, molybdenum sulfate, copper carbonate, ammonium nitrate, and glycine + citric acid were weighed in a molar ratio of 1:5:4.5:3.2:2.7:15:10+5.5 and dissolved in a small amount of deionized water. The solution was stirred thoroughly with a glass rod until completely dissolved to form an aqueous solution. The mixed solution was heated in a temperature-controlled resistance furnace to gradually evaporate the water until the solution became a brownish-brown gel. The solution was then held at 450 °C for 30 min to induce a vigorous combustion synthesis reaction. The product after the reaction was completed was thoroughly ground to obtain a precursor powder. The prepared precursor powder was placed in a tube furnace and subjected to a reduction reaction under a hydrogen atmosphere. The temperature was increased to 250 °C at a rate of 9 °C / min, held for 3 h, and then cooled with the furnace. The hydrogen flow rate was 2000 mL / min.

[0051] The prepared high-entropy magnetic nanoparticles have an average size of 10 nm, uniform particle size, and uniform solid-solution dispersion of elements such as nickel, iron, cobalt, molybdenum, and copper in the fine nanoparticles. The effective absorption bandwidth is 3.5–6 GHz (2 mm), the powder has a low oxygen content (0.27 wt%), and a specific surface area of ​​12.16 m². 2 / g.

[0052] Example 4

[0053] Nickel sulfate, polyferric sulfate, cobalt chloride, molybdenum amino acid, copper chloride, ammonium nitrate, and urea were weighed in a molar ratio of 1:3.5:5:5:3.2:8:12 and dissolved in a small amount of deionized water. The solution was stirred thoroughly with a glass rod until completely dissolved to form an aqueous solution. The mixed solution was heated in a temperature-controlled resistance furnace to gradually evaporate the water until the solution became a brownish-brown gel. The solution was then held at 250 °C for 60 min to induce a vigorous combustion synthesis reaction. The product after the reaction was completed was thoroughly ground to obtain a precursor powder. The prepared precursor powder was placed in a tube furnace and subjected to a reduction reaction under a hydrogen atmosphere. The temperature was increased to 650 °C at a rate of 10 °C / min, held for 2 h, and then cooled with the furnace. The hydrogen flow rate was 500 mL / min.

[0054] The prepared high-entropy magnetic nanoparticles have an average particle size of 90 nm and uniform particle size. Elements such as nickel, iron, cobalt, molybdenum, and copper are uniformly dissolved and dispersed in the fine nanoparticles. The effective absorption bandwidth is 8.7–12.5 GHz (2.2 mm), the powder has a low oxygen content (0.27 wt%), and a specific surface area of ​​5.16 m². 2 / g.

[0055] Example 5

[0056] Nickel nitrate, polyferric chloride, cobalt nitrate, molybdenum chloride, copper nitrate, ammonium nitrate, and glycine + urea were weighed in a molar ratio of 1:0.2:0.5:1.5:0.3:12:9+5 and dissolved in a small amount of deionized water. The solution was stirred thoroughly with a glass rod until completely dissolved to form an aqueous solution. The mixed solution was heated in a temperature-controlled resistance furnace to gradually evaporate the water until the solution became a brownish-brown gel. The solution was then held at 300 °C for 50 min to induce a vigorous combustion synthesis reaction. The product after the reaction was completed was thoroughly ground to obtain a precursor powder. The prepared precursor powder was placed in a tube furnace and subjected to a reduction reaction under a hydrogen atmosphere. The temperature was increased to 550 °C at a rate of 10 °C / min and held for 3 h. The furnace was then cooled, with a hydrogen flow rate of 1200 mL / min.

[0057] The prepared high-entropy magnetic nanoparticles have an average size of 59 nm, uniform particle size, and uniform solid-solution dispersion of elements such as nickel, iron, cobalt, molybdenum, and copper in the fine nanoparticles. The effective absorption bandwidth is 6.7–10.9 GHz (2.2 mm), the powder has a low oxygen content (0.27 wt%), and a specific surface area of ​​6.19 m². 2 / g.

[0058] This invention utilizes solution combustion synthesis (SCS) to prepare a high-entropy magnetic nanopowder microwave absorber. Compared with mechanical alloying and spray drying methods, the SCS method offers several unprecedented advantages. It leverages the exothermic reaction between ammonium nitrate and metal salts (acting as oxidants in the reaction system, including nitrates, sulfates, carbonates, and chlorides) and fuels (acting as reducing agents in the reaction system), such as glycine, citric acid, and urea. The heat generated sustains the redox reaction throughout the system, and the resulting gas produces sufficiently fine and fluffy metal oxide precursors, providing a foundation for subsequent hydrogen reduction to prepare nanocomposite powders. This invention offers a simple, rapid, energy-efficient, and easily scalable method for preparing nanopowders. Furthermore, this method achieves uniform mixing of metal elements such as nickel, iron, cobalt, molybdenum, and copper at the molecular level, resulting in high purity, fine grain size, and easy control over the proportions of nickel, iron, cobalt, molybdenum, and copper, laying the foundation for the preparation of high-performance, high-entropy magnetic nanopowder microwave absorbers.

[0059] While embodiments of the present invention have been provided herein, those skilled in the art should understand that modifications can be made to the embodiments without departing from the spirit of the invention. The above embodiments are merely exemplary and should not be construed as limiting the scope of the invention.

Claims

1. A method for preparing a high-entropy magnetic nanopowder microwave absorbing agent, characterized in that, The preparation method includes: S1. Nickel salt, iron salt, cobalt salt, molybdenum salt, copper salt, ammonium nitrate, fuel and deionized water are mixed in a set ratio and prepared into a corresponding aqueous solution. The solution is heated and stirred until it evaporates to a viscous gel state. Then, the solution is heated to carry out a combustion synthesis reaction to obtain a metal oxide composite precursor. S2. The metal oxide composite precursor prepared in S1 is thoroughly ground and crushed, and a reduction reaction is carried out under a hydrogen atmosphere to obtain the high-entropy magnetic nanopowder microwave absorber. In S1, the molar ratio of nickel salt, iron salt, cobalt salt, molybdenum salt, copper salt, ammonium nitrate and fuel is 1:(0.1~5):(0.1~5):(0.1~5):(0.1~5):(0~15):(1~30); In S1, the fuel is one or more of glycine, citric acid, and urea; In S1, the conditions for the combustion synthesis reaction are: heating temperature 200-500°C, heating time 10-60 min; In S2, a reduction reaction is carried out in a tube furnace under a hydrogen atmosphere. The reaction conditions are: heating rate 2-10°C / min, reaction temperature 300-650°C, holding time 1-3h, and hydrogen flow rate 500-2000mL / min.

2. The preparation method of the high-entropy magnetic nanopowder microwave absorbing agent as described in claim 1, characterized in that, In step S1, the metal oxide composite precursor includes at least one of NiO and Ni2O3, at least one of FeO, Fe2O3 and Fe3O4, at least one of CoO, Co2O3 and Co3O4, and at least one of MoO2, MoO3, NiMoO4, and Fe2Mo3O4. 12 At least one of CoMoO4 and CuMoO4, at least one of CuO and Cu2O, and any one of NiFe2O4, CoFe2O4, CuFe2O4, NiCo2O4, FeCo2O4, and CuCo2O4.

3. The preparation method of the high-entropy magnetic nanopowder microwave absorbing agent as described in claim 1, characterized in that, In step S1, the nickel salt is any one of nickel nitrate, nickel chloride, nickel sulfate, and nickel carbonate; the iron salt is any one of ferric nitrate, ferric chloride, ferric sulfate, polyferric sulfate, and polyferric chloride; the cobalt salt is any one of cobalt nitrate, cobalt chloride, cobalt sulfate, and cobalt carbonate; the molybdenum salt is any one of molybdenum amino acid, molybdenum sulfate, and molybdenum chloride; and the copper salt is any one of copper nitrate, copper sulfate, copper chloride, and copper carbonate.

4. The preparation method of the high-entropy magnetic nanopowder microwave absorbing agent as described in claim 1, characterized in that, The prepared high-entropy magnetic nanopowder particles have an average size of 10–100 nm, an effective absorption bandwidth of ≥2 GHz, and an oxygen content as low as 0.17–0.52 wt%.

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