CN114390884A - Light iron-nickel alloy based magnetic composite wave-absorbing material and preparation method thereof - Google Patents
Light iron-nickel alloy based magnetic composite wave-absorbing material and preparation method thereof Download PDFInfo
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Abstract
The invention relates to a light iron-nickel alloy based magnetic composite wave-absorbing material and a preparation method thereof, belonging to the technical field of microwave absorbing materials. The invention takes a spherical nickel ferrite compound as a precursor, and prepares the light iron-nickel alloy based magnetic composite wave-absorbing material by a polyvinylpyrrolidone derived carbon thermal reduction method. By adjusting the compounding amount of the polyvinylpyrrolidone, the carbothermic reduction degree can be regulated and controlled, and the composition, the structure and the electromagnetic property of the product are further influenced. From a compositional standpoint, higher carbothermic reduction levels result in increased iron nickel and iron content. The iron nickel and the iron have excellent conductive magnetic conductivity, so that the filling degree is reduced, and the carbon material is beneficial to improving the impedance matching characteristic. From the structure, the multiphase interface structure and the like induce an obvious dielectric relaxation phenomenon, and are beneficial to the enhancement of dielectric loss. The effective absorption bandwidth of the composite wave-absorbing material can reach 3.48 GHz under the conditions of 50 wt% filling degree and 1.7 mm thickness. The process of the invention does not relate to highly toxic chemicals, and the required equipment has low price and low energy consumption.
Description
Technical Field
The invention belongs to the technical field of microwave absorbing materials, and particularly relates to a light iron-nickel alloy based magnetic composite wave absorbing material and a preparation method thereof.
Background
The wave-absorbing material can efficiently absorb incident microwave energy through various loss mechanisms, further weaken or completely eliminate reflected echoes, and realize electromagnetic stealth of internal targets. According to the single-layer wave absorber electromagnetic absorption model, the magnetic loss type metal-based wave absorbing material has higher complex dielectric constant and complex permeability, so that the material is more favorable for absorbing broadband microwaves under low matching thickness, and is widely used. Common magnetic loss type metal-based wave-absorbing materials comprise carbonyl iron, iron-silicon-aluminum, iron-nickel, iron-cobalt alloy and the like, but the filling degree of the materials is generally higher than 70 wt%. For example, in the oriented flaky carbonyl iron powder/epoxy resin wave-absorbing material developed by Min et al, the filling degree of the carbonyl iron powder is 75 wt% (R) ((R))Journal of Materials Science, 2017, 52). FeSiAl @ Al developed by Guo et Al2O3@SiO2The filling degree of the core-shell composite wave-absorbing material is 80 wt% ((Chemical Engineering Journal, 2020, 384). Cheng et al designed synthetic FeCo alloy absorbing materials with different Fe/Co molar ratios with a fill level of 70 wt% (Journal of Alloys and Compounds, 2017, 704). A higher filling degree means a higher amount of use, i.e. a higher cost of use. In addition, the production process of the traditional magnetic wave-absorbing material is high in cost, for example, the production process of carbonyl iron powder usually comprises a high-temperature high-pressure process and also relates to highly toxic chemicals. The common atomization powder-making equipment has higher unit price and larger energy consumption, and is difficult to obtain special characteristics including nano powder and the likeMagnetic metal powder is used. The mechanical crushing ball milling method also has the problems of large energy consumption, large noise, difficult preparation of special magnetic metal powder and the like. Therefore, how to obtain the high-efficiency magnetic loss type metal-based wave-absorbing material capable of working at a low filling degree by using a production process with low cost becomes a problem to be solved urgently.
Disclosure of Invention
In order to reduce the use cost of the magnetic loss type metal-based wave-absorbing material, the invention provides a light iron-nickel alloy-based magnetic composite wave-absorbing material and a preparation method of the light iron-nickel alloy-based magnetic composite wave-absorbing material.
A light iron-nickel alloy based magnetic composite wave-absorbing material is gray black magnetic powder, and iron, nickel, carbon and oxygen elements are uniformly distributed, wherein the mass fraction of the iron element is 20-70%, the mass fraction of the nickel element is 5-20%, powder particles are in a nearly spherical irregular polyhedral shape and have a certain adhesion phenomenon, and the particle size is between 100 and 700 nm;
the maximum effective absorption bandwidth of the light iron-nickel alloy based magnetic composite wave-absorbing material under the filling degree of 50 wt% and the thickness of 1.7 mm is 3.48 GHz; in the thickness range of 1-5 mm, the effective absorption frequency range is 3.4-18 GHz.
The preparation operation steps of the light iron-nickel alloy based magnetic composite wave-absorbing material are as follows:
(1) preparation of nickel ferrite composite
0.2737 g of nickel acetate tetrahydrate is dissolved in 30 mL of ethylene glycol to obtain a nickel salt solution; 0.5947 g of ferric chloride hexahydrate is dissolved in 30 mL of ethylene glycol to obtain a ferric salt solution;
pouring the nickel salt solution into the ferric salt solution, adding 0.5 g of ammonium acetate, and continuously stirring for 45 min to obtain a mixed solution;
transferring the mixed solution into a reaction kettle, placing the reaction kettle into an oven, reacting for 30 hours at a constant temperature of 180 ℃, and naturally cooling to room temperature; performing centrifugal separation, fully washing with deionized water and absolute ethyl alcohol, drying and grinding to obtain nickel ferrite precursor powder; heating to 350 ℃ in a muffle furnace at the heating rate of 2 ℃/min, and keeping the temperature for 1 h; continuously heating to 500 ℃ at the heating rate of 5 ℃/min, preserving the heat for 1 h, naturally cooling to room temperature, washing and drying to obtain a nickel ferrite compound; the nickel ferrite compound is magnetic orange-red powder and consists of 59-60% of iron element, 10-11% of nickel element, regular spherical shape and particle size of 100-600 nm;
(2) preparation of composite wave-absorbing material
Adding 1 g of nickel ferrite compound and 0.3-0.6 g of polyvinylpyrrolidone into 25 mL of absolute ethyl alcohol, and stirring for more than 1 h to obtain a mixed solution; drying the mixed solution at 40 ℃ in vacuum, taking out and grinding to obtain composite precursor powder; and (3) placing the composite precursor powder in a tube furnace, heating to 650 ℃ at the heating rate of 5 ℃/min in the nitrogen atmosphere, preserving the heat for 2 hours, naturally cooling, and grinding to obtain the light iron-nickel alloy based magnetic composite wave-absorbing material.
The beneficial technical effects of the invention are embodied in the following aspects:
1. the invention prepares the nickel ferrite compound by a solvent heat treatment method and an air heat treatment method, and then prepares the light iron-nickel alloy based magnetic composite wave-absorbing material by a method of compounding polyvinylpyrrolidone and then performing inert atmosphere carbothermic reduction. By adjusting the compounding amount of the polyvinylpyrrolidone, the regulation and control of the carbon thermal reduction degree of the nickel ferrite compound can be realized, and the reduction degree influences the composition and the structure of a product, thereby determining the electromagnetic property. From the composition point of view, a higher degree of reduction results in products mainly comprising iron nickel, iron and carbon, and a lower degree of reduction results in products comprising iron nickel, iron, carbon and ferroferric oxide. The iron-nickel alloy and the iron have excellent conductive magnetic permeability, so that the filling degree is reduced on the basis of ensuring higher complex dielectric constant and complex magnetic permeability, and the carbon material with controllable resistivity is beneficial to improving the impedance matching characteristic. From the structural point of view, the existence of multiphase interfaces, crystal defects and the like induces an obvious dielectric relaxation phenomenon, which is beneficial to the enhancement of dielectric loss, and the eddy current effect is effectively inhibited by the smaller particle size. Therefore, the maximum effective absorption bandwidth of the light iron-nickel alloy based magnetic composite wave-absorbing material under the filling degree of 50 wt% and the thickness of 1.7 mm is 3.48 GHz, and the effective absorption frequency range is 3.4-18 GHz within the thickness range of 1-5 mm.
2. The process of the invention does not relate to highly toxic chemicals, does not relate to the process of ultra-high temperature and high pressure, the price of the required equipment is low, the energy consumption is relatively low, and the product has a certain electromagnetic characteristic adjustment space and higher application value.
Drawings
Fig. 1 is an XRD spectrum of the prepared nickel ferrite composite.
Fig. 2 is an SEM photograph of the prepared nickel ferrite composite.
FIG. 3 is an XRD spectrum of the iron-nickel alloy based wave-absorbing material CR-0.3 prepared in example 1.
FIG. 4 is an SEM photograph of the iron-nickel alloy based wave-absorbing material CR-0.3 prepared in example 1.
FIG. 5 is an electromagnetic spectrum of the iron-nickel alloy based wave-absorbing material CR-0.3 prepared in example 1.
FIG. 6 is an XRD spectrum of the iron-nickel alloy based wave-absorbing material CR-0.5 prepared in example 2.
FIG. 7 is an SEM photograph of the iron-nickel alloy based wave-absorbing material CR-0.5 prepared in example 2.
FIG. 8 is an electromagnetic spectrum of the iron-nickel alloy based CR-0.5 absorbing material prepared in example 2.
FIG. 9 is a reflection loss curve of the Fe-Ni alloy based wave-absorbing material CR-0.5 prepared in example 2.
FIG. 10 is an XRD spectrum of the iron-nickel alloy based wave-absorbing material CR-0.6 prepared in example 3.
FIG. 11 is an SEM photograph of the iron-nickel alloy based wave-absorbing material CR-0.6 prepared in example 3.
FIG. 12 is an electromagnetic spectrum of the iron-nickel alloy based CR-0.6 absorbing material prepared in example 3.
Detailed Description
The technical scheme of the invention is further explained by combining the attached drawings.
Example 1
The preparation operation steps of the light iron-nickel alloy based magnetic composite wave-absorbing material are as follows:
(1) preparation of nickel ferrite composite
0.2737 g of nickel acetate tetrahydrate is dissolved in 30 mL of ethylene glycol to obtain a nickel salt solution; 0.5947 g of ferric chloride hexahydrate is dissolved in 30 mL of ethylene glycol to obtain a ferric salt solution;
pouring the nickel salt solution into the ferric salt solution, adding 0.5 g of ammonium acetate, and continuously stirring for 45 min to obtain a mixed solution;
transferring the mixed solution into a reaction kettle, placing the reaction kettle into an oven, reacting for 30 hours at a constant temperature of 180 ℃, and naturally cooling to room temperature; performing centrifugal separation, fully washing with deionized water and absolute ethyl alcohol, drying, and grinding to obtain nickel ferrite precursor powder; heating to 350 ℃ in a muffle furnace at the heating rate of 2 ℃/min, and keeping the temperature for 1 h; continuously heating to 500 ℃ at the heating rate of 5 ℃/min, preserving the heat for 1 h, naturally cooling to room temperature, washing and drying to obtain a nickel ferrite compound; the nickel ferrite compound is magnetic orange-red powder and consists of nickel ferrite, nickel and ferric oxide phases, wherein the mass fraction of iron element is 59%, the mass fraction of nickel element is 11%, the shape is regular sphere, and the particle size is between 100 and 600 nm;
(2) preparation of composite wave-absorbing material
Adding 1 g of nickel ferrite compound and 0.3 g of polyvinylpyrrolidone into 25 mL of absolute ethyl alcohol, and stirring for more than 1 h to obtain a mixed solution; drying in vacuum at 40 ℃, taking out and grinding to obtain composite precursor powder; and (3) placing the composite precursor powder in a tube furnace, heating to 650 ℃ at the heating rate of 5 ℃/min in the nitrogen atmosphere, preserving the heat for 2 hours, naturally cooling, and grinding to obtain the light iron-nickel alloy based magnetic composite wave-absorbing material. The composite wave-absorbing material is gray black magnetic powder, and iron, nickel, carbon and oxygen elements are uniformly distributed, wherein the mass fraction of the iron element is 23.18 percent, the mass fraction of the nickel element is 8.13 percent, powder particles are in a nearly spherical irregular polyhedral shape and show a certain adhesion phenomenon, and the particle size is 100-700 nm; the effective absorption bandwidth of the light iron-nickel alloy based magnetic composite wave-absorbing material under the filling degree of 50 wt% and the thickness of 1.7 mm is 1.68 GHz; in the thickness range of 1-5 mm, the effective absorption frequency ranges are 4.96-8.84 GHz, 11.64-12.96 GHz and 13.76-18 GHz.
Referring to fig. 1, an XRD spectrum of the composite wave-absorbing material prepared in this example 1. From fig. 1, characteristic diffraction peaks ascribed to nickel ferrite, iron trioxide and nickel can be seen. Wherein, the organic matter remained on the surface of the powder after the solvothermal reaction can be used as a carbothermic reducing agent of the main phase nickel ferrite, so that nickel and ferric oxide phases are generated after the heat treatment. According to the EDS data, the mass fraction of the iron element in the nickel ferrite compound is 59 percent, and the mass fraction of the nickel element in the nickel ferrite compound is 11 percent.
Referring to fig. 2, an SEM photograph of the composite wave absorbing material prepared in this example 1. As can be seen from FIG. 2, the prepared nickel ferrite composite particles are in a regular spherical shape, the particle size distribution is concentrated, and the particle size is between 100 and 600 nm.
Referring to fig. 3, an XRD spectrogram of the composite wave-absorbing material CR-0.3 prepared in this example 1 can see a plurality of distinct diffraction peaks from fig. 3, which are well matched with characteristic peaks of iron nickel, iron, and ferroferric oxide, and have no other peaks. Because of the difficulty of reducing iron ions and nickel ions and the distribution of the carbothermic reducing agent, different phases occur in the carbothermic product. From the EDS results, it was found that the mass fraction of iron element in CR-0.3 was 23.18%, the mass fraction of nickel element was about 8.13%, and the distribution of iron, nickel, carbon, and oxygen elements was uniform. In general, CR-0.3 is iron-nickel, iron, carbon and ferroferric oxide compound.
Referring to fig. 4, an SEM photograph of the composite wave absorbing material CR-0.3 prepared in this example 1. As can be seen from FIG. 4, after carbothermal reduction, the original regular spherical structure has been transformed into an irregular ellipsoid, and there is a more obvious adhesion growth phenomenon, and the particle size is between about 100-700 nm.
Referring to fig. 5, after the iron-nickel alloy based magnetic composite wave absorbing material CR-0.3 prepared in this example 1 is melted and mixed with 50 wt% of paraffin, an annular sample with an outer diameter of 7 mm and an inner diameter of 3.04 mm is prepared, and a complex permittivity and a complex permeability spectrum of the sample in a range of 2-18 GHz are obtained by using a standard coaxial line method. As seen in FIG. 5, the complex dielectric constant of the CR-0.3 sample smoothly changed from 8.46 at 2 GHz to 8.15 at 12.76 GHz, then rapidly increased to 9.26 at 14.08 GHz, and then rapidly decreased to 5.95 at 18 GHz. The corresponding imaginary part of the complex dielectric constant varies from 0.8 at 2 GHz to 1.6 at 18 GHz. The lower imaginary value indicates that the CR-0.3 sample is now less conductive, possibly related to the presence of the more resistive ferroferric oxide and amorphous carbon material. In addition, a relatively obvious dielectric relaxation phenomenon occurs in the range of 12-18 GHz, possibly related to the existence of a multiphase interface structure, and is beneficial to the enhancement of dielectric loss in the frequency band. The real part of the complex permeability of the CR-0.3 sample has a small variation range, from 1.17 at 2 GHz to 1.16 at 18 GHz, and the imaginary part fluctuates only around 0.1. In summary, the lower content of polyvinylpyrrolidone leads to a lower reduction degree of CR-0.3, i.e. the generation of insufficient reduced ferroferric oxide, and further leads to lower complex dielectric constant and complex permeability, so that the wave-absorbing property is poorer.
According to the electromagnetic parameters of the annular sample obtained in the embodiment 1, a single-layer uniform wave-absorbing coating model is adopted, and the reflection loss characteristic of the annular sample is obtained through simulation calculation. The effective absorption bandwidth of the light iron-nickel alloy based magnetic composite wave-absorbing material under the filling degree of 50 wt% and the thickness of 1.7 mm is 1.68 GHz; in the thickness range of 1-5 mm, the effective absorption frequency ranges are 4.96-8.84 GHz, 11.64-12.96 GHz and 13.76-18 GHz.
Example 2
The preparation operation steps of the light iron-nickel alloy based magnetic composite wave-absorbing material are as follows:
(1) preparation of nickel ferrite composite
0.2737 g of nickel acetate tetrahydrate is dissolved in 30 mL of ethylene glycol to obtain a nickel salt solution; 0.5947 g of ferric chloride hexahydrate is dissolved in 30 mL of ethylene glycol to obtain a ferric salt solution;
pouring the nickel salt solution into the ferric salt solution, adding 0.5 g of ammonium acetate, and continuously stirring for 45 min to obtain a mixed solution;
transferring the mixed solution into a reaction kettle, placing the reaction kettle into an oven, reacting for 30 hours at a constant temperature of 180 ℃, and naturally cooling to room temperature; performing centrifugal separation, fully washing with deionized water and absolute ethyl alcohol, drying, and grinding to obtain nickel ferrite precursor powder; heating to 350 ℃ in a muffle furnace at the heating rate of 2 ℃/min, and keeping the temperature for 1 h; continuously heating to 500 ℃ at the heating rate of 5 ℃/min, preserving the heat for 1 h, naturally cooling to room temperature, washing and drying to obtain a nickel ferrite compound; the nickel ferrite compound is magnetic orange-red powder and consists of nickel ferrite, nickel and ferric oxide phases, wherein the mass fraction of iron element is 59%, the mass fraction of nickel element is 11%, the shape is regular sphere, and the particle size is between 100 and 600 nm;
(2) preparation of composite wave-absorbing material
Adding 1 g of nickel ferrite compound and 0.5 g of polyvinylpyrrolidone into 25 mL of absolute ethyl alcohol, and stirring for more than 1 h to obtain a mixed solution; drying in vacuum at 40 ℃, taking out and grinding to obtain composite precursor powder; and (3) placing the composite precursor powder in a tube furnace, heating to 650 ℃ at the heating rate of 5 ℃/min in the nitrogen atmosphere, preserving the heat for 2 hours, naturally cooling, and grinding to obtain the light iron-nickel alloy based magnetic composite wave-absorbing material. The composite wave-absorbing material is gray black magnetic powder, and iron, nickel and carbon elements are uniformly distributed, wherein the mass fraction of the iron element is 66.43%, the mass fraction of the nickel element is 14.54%, powder particles are in an approximately spherical irregular polyhedral shape and have a certain adhesion phenomenon, and the particle size is between 200-700 nm; the effective absorption bandwidth of the light iron-nickel alloy based magnetic composite wave-absorbing material under the filling degree of 50 wt% and the thickness of 1.7 mm is 3.48 GHz; in the thickness range of 1-5 mm, the effective absorption frequency range is 3.4-18 GHz.
Referring to fig. 6, an XRD spectrum of the iron-nickel alloy based magnetic composite wave-absorbing material CR-0.5 prepared in this example 2 is shown. From fig. 6, six distinct diffraction peaks can be seen, corresponding to the characteristic diffraction peaks of iron and nickel, respectively. It is surmised that a higher polyvinylpyrrolidone content significantly increases the extent of carbothermic reduction, so that insufficiently reduced oxides are not present in CR-0.5. According to the EDS result, the mass fraction of the iron element in CR-0.5 is 66.43%, the mass fraction of the nickel element is 14.54%, and the iron, nickel and carbon elements are uniformly distributed. Thus, CR-0.5 is an iron-nickel, iron, carbon composite.
Referring to fig. 7, an SEM photograph of the iron-nickel alloy based magnetic composite wave absorbing material CR-0.5 prepared in this example 2 is shown. With the increase of the reduction degree, the adhesion growth phenomenon becomes more obvious, and a large number of particles are connected with each other to form micron-sized agglomerates. Wherein the particle morphology has been transformed into a nearly spherical polyhedron shape with a particle size of between 200-700 nm.
Referring to fig. 8, after the iron-nickel alloy based magnetic composite wave absorbing material CR-0.5 prepared in this example 2 is melted and mixed with 50 wt% of paraffin, an annular sample with an outer diameter of 7 mm and an inner diameter of 3.04 mm is prepared, and a complex permittivity and a complex permeability spectrum of the annular sample in a range of 2-18 GHz are obtained by using a standard coaxial line method. The real part of the complex permittivity of the sample steadily decreased from 15.88 at 2 GHz to 9.26 at 18 GHz, and the imaginary part of the complex permittivity fluctuated from 0.37 at 2 GHz to 6.26 at 18 GHz. The increase in the degree of reduction results in a significant increase in conductivity, i.e., a significant increase in the imaginary part of the complex permittivity, compared to CR-0.3. In addition, dielectric relaxation still occurs in the 7-11 GHz range, contributing to enhancement of dielectric loss in this frequency range. Owing to the improvement of the reduction degree, the content of the strong ferromagnetic phase is improved, and the complex permeability is also increased. The real part of the complex permeability of the CR-0.5 sample slowly decreases from 1.16 at 2 GHz to 0.76 at 18 GHz, and the imaginary part of the complex permeability is maintained around 0.25 in the range of 2-10 GHz and gradually decreases in the range of 10-18 GHz. Compared with a CR-0.3 sample, the real part and the imaginary part of the complex permeability of the CR-0.5 sample are both improved, which is beneficial to improving impedance matching and enhancing magnetic loss.
Referring to fig. 9, according to the electromagnetic parameters of the annular sample obtained in example 2, a single-layer uniform wave-absorbing coating model is adopted to obtain a CR-0.5 reflection loss curve graph of the magnetic composite wave-absorbing material based on iron-nickel alloy through simulation calculation. As can be seen, the CR-0.5 sample has excellent wave-absorbing property, the effective absorption frequency range of the CR-0.5 sample under 1.7 mm is 14.36-17.84 GHz, the effective absorption bandwidth can reach 3.48 GHz, and the CR-0.5 sample covers 58% of Ku wave band. In addition, the effective absorption frequency range is 3.4-18 GHz within the thickness range of 1-5 mm. In general, the increase of the addition amount of the polyvinylpyrrolidone promotes the increase of the reduction degree, and brings about the increase of the contents of conductive and magnetic conductive phases (iron and iron), thereby further promoting the complex dielectric constant and the complex magnetic conductivity and improving the reflection loss characteristic.
Example 3
The preparation operation steps of the light iron-nickel alloy based magnetic composite wave-absorbing material are as follows:
(1) preparation of nickel ferrite composite
0.2737 g of nickel acetate tetrahydrate is dissolved in 30 mL of ethylene glycol to obtain a nickel salt solution; 0.5947 g of ferric chloride hexahydrate is dissolved in 30 mL of ethylene glycol to obtain a ferric salt solution;
pouring the nickel salt solution into the ferric salt solution, adding 0.5 g of ammonium acetate, and continuously stirring for 45 min to obtain a mixed solution;
transferring the mixed solution into a reaction kettle, placing the reaction kettle into an oven, reacting for 30 hours at a constant temperature of 180 ℃, and naturally cooling to room temperature; performing centrifugal separation, fully washing with deionized water and absolute ethyl alcohol, drying, and grinding to obtain nickel ferrite precursor powder; heating to 350 ℃ in a muffle furnace at the heating rate of 2 ℃/min, and keeping the temperature for 1 h; continuously heating to 500 ℃ at the heating rate of 5 ℃/min, preserving the heat for 1 h, naturally cooling to room temperature, washing and drying to obtain a nickel ferrite compound; the nickel ferrite compound is magnetic orange-red powder and consists of nickel ferrite, nickel and ferric oxide phases, wherein the mass fraction of iron element is 59%, the mass fraction of nickel element is 11%, the shape is regular sphere, and the particle size is between 100 and 600 nm;
(2) preparation of composite wave-absorbing material
Adding 1 g of nickel ferrite compound and 0.6 g of polyvinylpyrrolidone into 25 mL of absolute ethyl alcohol, and stirring for more than 1 h to obtain a mixed solution; drying in vacuum at 40 ℃, taking out and grinding to obtain composite precursor powder; and (3) placing the composite precursor powder in a tube furnace, heating to 650 ℃ at the heating rate of 5 ℃/min in the nitrogen atmosphere, preserving the heat for 2 hours, naturally cooling, and grinding to obtain the light iron-nickel alloy based magnetic composite wave-absorbing material. The composite wave-absorbing material is gray black magnetic powder, and iron, nickel, carbon and oxygen elements are uniformly distributed, wherein the mass fraction of the iron element is 25.71 percent, the mass fraction of the nickel element is 6.18 percent, powder particles are in an approximately spherical irregular polyhedral shape and have a certain adhesion phenomenon, and the particle size is between 200 and 500 nm; the light iron-nickel alloy based magnetic composite wave-absorbing material has the effective absorption frequency ranges of 7.72-13.12 GHz, 14.28-15.72 GHz and 16.32-18 GHz within the ranges of 50 wt% filling degree and 1-5 mm thickness.
Referring to fig. 10, an XRD spectrum of the iron-nickel alloy based magnetic composite wave-absorbing material CR-0.6 prepared in this example 3. Characteristic diffraction peaks ascribed to iron nickel, iron and ferroferric oxide can be seen from the figure. Although the amount of polyvinylpyrrolidone added is further increased as compared with CR-0.5, the nonuniformity of the carbothermic reduction reaction is also increased, resulting in insufficient reduction of a partial region, i.e., formation of a ferroferric oxide phase. According to the EDS result, the mass fraction of the iron element in CR-0.6 is 25.71 percent, the mass fraction of the nickel element is 6.18 percent, and the iron element, the nickel element, the carbon element and the oxygen element are uniformly distributed. The high content of carbon element compared to CR-0.5 also directly accounts for the reduction in the degree of carbothermic reduction and indirectly reflects the inhomogeneity of the carbothermic reduction.
Referring to fig. 11, an SEM photograph of the iron-nickel alloy based magnetic composite wave absorbing material CR-0.6 prepared in this example 3. The photo shows that the phenomenon of adhesion growth is weakened, the whole particle is in a nearly spherical polyhedron shape, and the particle diameter is between 200 and 500 nm.
Referring to fig. 12, after the iron-nickel alloy based magnetic composite wave absorbing material CR-0.6 prepared in this example 3 is melted and mixed with 50 wt% of paraffin, an annular sample with an outer diameter of 7 mm and an inner diameter of 3.04 mm is prepared, and a complex permittivity and a complex permeability spectrum of the annular sample in a range of 2-18 GHz are obtained by using a standard coaxial line method. The real part of its complex permittivity smoothly changes from 7.05 at 2 GHz to 7.25 at 9.4 GHz, then decreases to 5.43 at 12.48 GHz, then increases to 6.69 at 14.4 GHz, and finally decreases to 5.8 at 18 GHz. The imaginary part of the complex dielectric constant is maintained around 0.5 at 2-8 GHz, then two relaxation peaks are present, and peaks 1.93 and 1.76 appear at 10.4 GHz and 15 GHz. The lower complex permittivity of the CR-0.6 sample compared to the CR-0.5 sample results mainly from the lower degree of reduction, i.e. the presence of the triiron tetroxide phase, and the more complex dielectric relaxation process, which is also strongly associated with the inhomogeneous carbothermal reduction process. The real part of the complex permeability slowly decreases from 1.33 at 2 GHz to 1.1 at 18 GHz, while the imaginary part of the complex permeability fluctuates around 0.2. Compared with the CR-0.5 sample, the real part of the complex permeability is slightly improved, and the imaginary part is slightly reduced, which shows that the magnetic loss is weakened. According to the electromagnetic parameters of the annular sample obtained in the embodiment 3, the reflection loss characteristic of the iron-nickel alloy based magnetic composite wave-absorbing material CR-0.6 is obtained by adopting a single-layer uniform wave-absorbing coating model and simulation calculation. The effective absorption bandwidth of the sample is 0 GHz under 1.7 mm, and the effective absorption frequency ranges are 7.72-13.12 GHz, 14.28-15.72 GHz and 16.32-18 GHz within the thickness range of 1-5 mm. In general, the complex permittivity and complex permeability are also maintained at a low level, and thus the wave-absorbing properties are not good.
It will be understood by those skilled in the art that the foregoing is merely a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included within the scope of the present invention.
Claims (2)
1. A light iron-nickel alloy based magnetic composite wave-absorbing material is characterized in that: the composite wave-absorbing material is gray black magnetic powder, and iron, nickel, carbon and oxygen elements are uniformly distributed, wherein the mass fraction of the iron element is 20-70%, the mass fraction of the nickel element is 5-20%, powder particles are in an approximately spherical irregular polyhedral shape and have a certain adhesion phenomenon, and the particle size is 100-700 nm;
the maximum effective absorption bandwidth of the light iron-nickel alloy based magnetic composite wave-absorbing material under the filling degree of 50 wt% and the thickness of 1.7 mm is 3.48 GHz; in the thickness range of 1-5 mm, the effective absorption frequency range is 3.4-18 GHz.
2. The preparation method of the light iron-nickel alloy based magnetic composite wave-absorbing material according to claim 1, which is characterized by comprising the following operation steps:
(1) preparation of nickel ferrite composite
0.2737 g of nickel acetate tetrahydrate is dissolved in 30 mL of ethylene glycol to obtain a nickel salt solution; 0.5947 g of ferric chloride hexahydrate is dissolved in 30 mL of ethylene glycol to obtain a ferric salt solution;
pouring the nickel salt solution into the ferric salt solution, adding 0.5 g of ammonium acetate, and continuously stirring for 45 min to obtain a mixed solution;
transferring the mixed solution into a reaction kettle, placing the reaction kettle into an oven, reacting for 30 hours at a constant temperature of 180 ℃, and naturally cooling to room temperature; performing centrifugal separation, fully washing with deionized water and absolute ethyl alcohol, drying and grinding to obtain nickel ferrite precursor powder; heating to 350 ℃ in a muffle furnace at the heating rate of 2 ℃/min, and keeping the temperature for 1 h; continuously heating to 500 ℃ at the heating rate of 5 ℃/min, preserving the heat for 1 h, naturally cooling to room temperature, washing and drying to obtain a nickel ferrite compound; the nickel ferrite compound is magnetic orange-red powder and consists of 59-60% of iron element, 10-11% of nickel element, regular spherical shape and particle size of 100-600 nm;
(2) preparation of composite wave-absorbing material
Adding 1 g of nickel ferrite compound and 0.3-0.6 g of polyvinylpyrrolidone into 25 mL of absolute ethyl alcohol, and stirring for more than 1 h to obtain a mixed solution; drying the mixed solution at 40 ℃ in vacuum, taking out and grinding to obtain composite precursor powder; and (3) placing the composite precursor powder in a tube furnace, heating to 650 ℃ at the heating rate of 5 ℃/min in the nitrogen atmosphere, preserving the heat for 2 hours, naturally cooling, and grinding to obtain the light iron-nickel alloy based magnetic composite wave-absorbing material.
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