CN113278399B - Hard/soft magnetic composite ferrite wave absorbing agent and preparation method thereof - Google Patents
Hard/soft magnetic composite ferrite wave absorbing agent and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a hard/soft magnetic composite ferrite wave absorber and a preparation method thereof, wherein a hard magnetic phase is zirconium-doped barium ferrite BaZrxFe12–xO19(x = 0.1-0.2), and the soft magnetic phase is ferroferric oxide Fe3O4. The preparation method forms BaZr in situ by a hydrothermal methodxFe12‑xO19/Fe2O3A compound, in which Fe is treated by heat treatment under the subsequent nitrogen atmosphere by utilizing the high-temperature reducibility of graphene2O3Reduction to Fe3O4To prepare hard/soft magnetic exchange coupling composite ferrite BaZrxFe12‑xO19/Fe3O4. By adjusting Fe3+/Ba2+Molar ratio, Ba2+/OH‒The molar ratio, the heat treatment temperature and other parameters control the content ratio of hard/soft magnetic phases in the composite, and excellent millimeter wave-centimeter wave compatible absorption performance is obtained through coordination and optimization. The hard/soft magnetic composite obtained by the invention has more hard/soft magnetic phase interfaces, not only can enhance the hard/soft magnetic exchange coupling effect to further widen the magnetic loss range, but also can enhance the interface polarization relaxation phenomenon to improve the dielectric loss, and shows more excellent comprehensive wave absorbing performance.
Description
Technical Field
The invention belongs to a wave-absorbing material and a preparation method thereof, and particularly relates to an exchange coupling hard/soft magnetic composite ferrite wave-absorbing agent with millimeter wave and centimeter wave compatible absorption characteristics and a preparation method thereof.
Background
The microwave absorbing material has great importance for attenuating electromagnetic wave pollution caused by the rapid development of information technology and defending against radar detection to realize military stealth. Recently, millimeter waves in the frequency range of 30-300 GHz have been used for radar detection due to their high resolution and all-weather characteristics, with atmospheric window frequencies of 35GHz, 94GHz, 140GHz, and 220GHz being the most studied. Meanwhile, with the rapid development of science and technology, the popularization of the 5G network is more and more extensive. The main frequency band of the 5G millimeter wave network is centered between 24GHz and 40GHz, and with the increasing of 5G electronic products, the electromagnetic radiation is more and more serious, so the research and development of the absorption material of the electromagnetic wave of the corresponding wave band are very important.
M-type barium ferrite BaFe12O19Is a multifunctional material and has been widely used for permanent magnets and high-density magnetic recording media. And is a very potential microwave absorption candidate material due to the huge magnetic loss generated by the natural resonance energy, but the effective absorption bandwidth of the barium ferrite is generally narrow due to the single magnetic resonance of the barium ferrite. Therefore, the system lacks strong magnetic loss in centimeter wave bands, and the adaptive impedance and weak attenuation cause the system to have poor absorption capacity to centimeter waves which still exist widely at present.
At the same time, some soft magnetic phases such as Ni1-xZnxFe2O4、CuFe2O4、Fe3O4And so on, there is characteristic absorption in the low frequency band of the centimeter wave due to the low magnetocrystalline anisotropy field. Therefore, the exchange coupling of soft/hard magnets is expected to achieve ideal absorption effects in both the centimeter and millimeter wave bands. Ni1-xZnxFe2O4、CuFe2O4Can be synthesized in situ with M-type barium ferrite by a sol-gel method, but because of Ni1-xZnxFe2O4、CuFe2O4The conductivity of the composite material is poor, and even if strong hard/soft magnetic exchange action is formed, the wave absorbing performance of the composite material is relatively general. And Fe3O4At present, the M-type barium ferrite/ferroferric oxide composite is generally prepared by a mechanical mixing method. Due to the physical mixing mechanism, the hard/soft magnetic phases are insufficiently mixed, and the soft/hard magnetic phases have fewer contact interfaces, which greatly weakens the hard/soft magnetic cross-linking coupling effect, thereby limiting the improvement effect of the microwave absorption performance.
Disclosure of Invention
The purpose of the invention is as follows: the invention aims to provide a hard/soft magnetic composite ferrite wave absorbing agent simultaneously having millimeter wave absorption and centimeter wave absorption performances; the second purpose of the invention is to provide a preparation method of the composite ferrite wave absorber with strong hard/soft magnetic exchange coupling effect.
The technical scheme is as follows: the invention relates to a hard/soft magnetic composite ferrite wave absorber, which comprises a hard magnetic phase for absorbing millimeter waves and a soft magnetic phase for absorbing centimeter waves; the hard magnetic phase is zirconium-doped barium ferrite, and the expression is BaZrxFe12–xO19Wherein x is 0.1 to 0.2; the soft magnetic phase is ferroferric oxide.
Further, the ferroferric oxide is spherical, the zirconium-doped barium ferrite is sheet-shaped, and the spherical ferroferric oxide is attached to the sheet-shaped zirconium-doped barium ferrite.
The hard/soft magnetic composite ferrite wave absorber adopts zirconium-doped barium ferrite as a hard magnetic phase, because of Zr4+Substitution of Fe in barium ferrite3+So that part of Fe in the system3+Conversion to Fe2+Using Fe3+And Fe2+Exchange coupling producing a product other than Fe3+The Lande factor g of the magnetic resonance sensor forms a plurality of natural resonance magnetic loss peaks, and widens the magnetic loss range. In addition, the conductivity of the ferrite is improved due to the high-valence doping effect, so that the dielectric loss of a system is obviously enhanced, and the wide effective absorption bandwidth and the thin matching thickness can be obtained at the millimeter wave band; adopting ferroferric oxide as a soft magnetic phase, Fe3O4Due to electrons in Fe2+And Fe3+The dielectric ceramic has stronger conductivity due to the jump between the two layers, and can contribute to larger dielectric loss in a microwave frequency band. Therefore, exchange coupling with the hard-magnetic phase zirconium-doped barium ferrite can achieve better absorption performance in a centimeter-wave low-frequency band. Meanwhile, the expression of the zirconium-doped barium ferrite is BaZrxFe12–xO19Wherein x is 0.1 to 0.2, which is attributed to the fact that the natural resonance peak of barium ferrite is about 35GHz, and Zr is4+Is a high valent ion if too much Zr is added4+Resulting in a too much reduction of the natural resonance peak of barium ferrite out of the high frequency range.
The invention further provides a preparation method of the hard/soft magnetic composite ferrite wave absorber, which comprises the following steps:
(1) taking nitrates of Fe, Ba and Zr as metal precursors to prepare mixed metal nitrate solution;
(2) adding NaOH solution into mixed metal nitrate solution to obtain alkaline mixed solution;
(3) adding the graphene oxide dispersion liquid into the alkaline mixed solution, fully stirring and mixing, and then placing the mixture in a reaction kettle to perform hydrothermal reaction in a sealed environment;
(4) washing and drying the precipitate after the hydrothermal reaction to obtain precursor powder, and then carrying out heat treatment on the precursor powder in a nitrogen atmosphere to obtain BaZrxFe12–xO19/Fe3O4A composite ferrite wave absorber.
In the preparation method, firstly, BaZr is formed in situ by a hydrothermal methodxFe12-xO19/Fe2O3Graphene composite, in which Fe is reduced by using high-temperature reducibility of graphene in heat treatment process under subsequent nitrogen atmosphere2O3Reduction to Fe3O4And finally forming the hard/soft magnetic composite ferrite. Fe is converted by utilizing the high-temperature reducibility of graphene oxide in the heating process2O3Reduction to Fe3O4Thereby avoiding Fe in the traditional process3O4Will be oxidized into non-magnetic alpha-Fe during high-temperature calcination2O3(ii) a And the reducibility of the graphene oxide serving as a reducing agent is moderate, so that the whole system can be ensured to be only used for Fe2O3The reduction is carried out without reducing the barium ferrite phase. The obtained composite is caused by a hard magnetic phase BaZrxFe12-xO19Can have excellent millimeter wave absorption performance. At the same time, because of the soft magnetic phase Fe3O4It may also exhibit strong absorption efficiency in the centimeter band.
Further, in the mixed metal nitrate solution of the step (1), Fe3+、Ba2+And Zr4+The molar ratio of (A) to (B) is 13-15: 1: 0.1 to 0.2. Preferably, the nitrates of Fe, Ba and Zr are iron nitrate nonahydrate, barium nitrate hydrate and zirconium nitrate pentahydrate, respectively.
Further, the alkalinity of the step (2)In the mixed solution of Ba2+With OH-In a molar ratio of 1: 120 to 150. Preferably, the pH value of the alkaline mixed solution is 13-14, so that an alkaline environment is provided for the formation of a precursor in the hydrothermal reaction.
Further, in the step (3), graphene oxide and Ba2+In a molar ratio of 1: 2-3; wherein the concentration of the graphene oxide dispersion liquid is 2-4 mg/mL.
Further, in the step (3), the temperature of the hydrothermal reaction is 260-280 ℃, and the reaction time is 36-48 h.
Further, in the step (4), the heat treatment temperature is 500-600 ℃, the heat treatment time is 3-4 h, and the heating rate of the heat treatment is 5-10 ℃/min. The purpose of the heat treatment is to form barium ferrite by adding Fe2O3Reduction to Fe3O4(ii) a Too high a heat treatment temperature may result in Fe2O3Is reduced excessively to form FeN and Fe; too low a heat treatment temperature may result in Fe2O3The reduction is insufficient, and part of Fe still exists in the system2O3。
Has the advantages that: compared with the prior art, the invention has the following remarkable advantages: the invention creatively adopts a hydrothermal method to firstly synthesize BaZr in situxFe12–xO19/Fe2O3A graphene precursor (x is 0.1-0.2), and then Fe is subjected to high-temperature reducibility of graphene in a heating process2O3Reduction to Fe3O4Forming BaZr with strong hard/soft magnetic exchange coupling actionxFe12-xO19/Fe3O4(x is 0.1 to 0.2) a composite material. By adjusting Fe3+/Ba2+Molar ratio, NO3 -/OH-The molar ratio, the heat treatment temperature and other parameters control the content ratio of hard/soft magnetic phases in the composite, and excellent millimeter wave-centimeter wave compatible absorption performance is obtained through coordination and optimization. In addition, compared with the physical mixture of the hard/soft magnetic composite, the chemically mixed hard/soft magnetic composite has more hard/soft magnetic phase interfaces, not only can enhance the exchange coupling effect of the hard/soft magnetic to further widen the magnetic loss range,and the interface polarization relaxation phenomenon can be enhanced, so that the dielectric loss is improved, and the more excellent comprehensive wave absorbing performance is shown.
Drawings
FIG. 1 is an SEM topography of a composite wave absorber prepared according to example 1;
FIG. 2 is a graph showing the relationship between the millimeter wave absorption performance of the composite wave absorber prepared in example 1 and the variation of the millimeter wave absorption performance with frequency;
FIG. 3 is a graph showing the relationship between the centimeter wave absorption performance of the composite wave absorbent prepared in example 1 and the frequency;
FIG. 4 is an SEM topography of the composite wave absorber prepared in example 2;
FIG. 5 is a graph showing the relationship between the millimeter wave absorption performance of the composite wave absorber prepared in example 2 and the variation of the frequency;
FIG. 6 is a graph showing the change of the centimeter wave absorption performance of the composite wave absorbent prepared in example 2 with frequency;
FIG. 7 is an SEM topography of the composite wave absorber prepared in example 3;
FIG. 8 is a graph showing the relationship between the millimeter wave absorption performance of the composite wave absorber prepared in example 3 and the variation of the frequency;
FIG. 9 is a graph showing the relationship between the centimeter wave absorption properties of the composite wave absorbent prepared in example 3 and the frequency;
FIG. 10 is an SEM topography of the composite wave absorber prepared in comparative example 1;
FIG. 11 is a graph showing the variation of the millimeter wave absorption performance of the composite wave absorber prepared in comparative example 1 with frequency;
FIG. 12 is a graph showing the relation between the centimeter wave absorption performance of the composite wave absorbent prepared in comparative example 1 and the frequency;
FIG. 13 is an SEM topography of the composite wave absorber prepared in comparative example 2;
FIG. 14 is a graph showing the variation of the millimeter wave absorption performance of the composite wave absorber prepared in comparative example 2 with frequency;
FIG. 15 is a graph showing the relation between the centimeter wave absorption performance of the composite wave absorbent prepared in comparative example 2 and the frequency;
FIG. 16 is an SEM topography of the composite wave absorber prepared in comparative example 3 with a heating temperature of 400 ℃;
FIG. 17 is a graph showing the relationship between the millimeter wave absorption properties of the composite wave absorber prepared in comparative example 3 at a heating temperature of 400 ℃ and the frequency;
FIG. 18 is a graph showing the change of the absorbing properties of the composite wave absorbent centimeter wave prepared in the comparative example 3 at a heating temperature of 400 ℃ with the frequency;
FIG. 19 is an SEM topography of the composite wave absorber prepared in comparative example 3 with a heating temperature of 700 ℃;
FIG. 20 is a graph showing the relationship between the millimeter wave absorption properties of the composite wave absorber prepared in comparative example 3 at a heating temperature of 700 ℃ and the frequency;
FIG. 21 is a graph showing the change of the absorbing properties of the composite wave absorber prepared at a heating temperature of 700 ℃ according to the frequency in comparative example 3;
FIG. 22 is an SEM topography of the composite wave absorber prepared in comparative example 4;
FIG. 23 is a graph showing the variation of the millimeter wave absorption performance of the composite wave absorber prepared in comparative example 4 with frequency;
FIG. 24 is a graph showing the change of the absorption properties of the composite wave absorber prepared in comparative example 4 with frequency.
Detailed Description
The technical solution of the present invention is further described in detail with reference to the accompanying drawings and examples.
Example 1
1) According to Fe3+：Ba2+：Zr4+Is 14: 1: 0.2 stoichiometric molar ratio Fe (NO)3·9H2O、Ba(NO3)2、Zr(NO3)4·5H2Placing the solution O in distilled water, and placing the solution O on a magnetic stirrer to continuously stir for 2 hours to obtain a solution A;
2) according to Ba2+：OH-1: weighing NaOH according to a molar ratio of 135 to prepare a solution, and dropwise adding the solution into the solution A to obtain an alkaline solution B;
3) preparing a graphene oxide dispersion liquid with the concentration of 3mg/mL, and oxidizing the graphene oxide/Ba into the dispersion liquid2+According to the mol ratio of 1: 2.5 adding into the solution B, and continuously stirring on a magnetic stirrerStirring for 2h to obtain a solution C;
4) transferring the solution C into a stainless steel reaction kettle, sealing, placing the stainless steel reaction kettle in a drying oven for hydrothermal reaction, setting the reaction temperature to be 270 ℃ and the reaction time to be 42 h;
5) washing the obtained precipitate with deionized water and absolute ethyl alcohol, and drying at 70 ℃ to obtain precursor powder;
6) putting the precursor powder into a tube furnace, and performing heat treatment at 500 ℃ for 3.5h in a nitrogen atmosphere at the speed of 8 ℃/min to obtain BaZrxFe12–xO19/Fe3O4Composite ferrite powder.
The wave absorbing performance of the radar absorbent with the frequency range of 26.5-40GHz prepared by the embodiment is tested by using an Agilent vector network analyzer coaxial line testing method. During testing, the wave-absorbing material powder and the solid paraffin are mixed according to the mass ratio of 6: 4 the test was carried out after homogeneous mixing at 80 ℃.
Referring to FIG. 1, it can be seen that numerous small hexagonal-shaped M-type barium ferrites are aggregated into large hexagonal-shaped sheets, i.e., cornmeal-shaped Fe3O4Clustered together. Referring to FIGS. 2 and 3, respectively, RL occurs at a thickness of 2.75mm in the centimeter band<The frequency range of-10 dB covers 8.52-10.92GHz, the effective absorption bandwidth reaches 2.4GHz, and the strongest absorption peak reaches-12.3732 dB; in the millimeter wave band, RL<The frequency range of-10 dB covers 31.05-38.85GHz, the effective absorption bandwidth reaches 7.8GHz, and the strongest absorption peak reaches-11.43 dB. The material forms partial hexagonal flaky crystals and small cluster-shaped particles at the heat treatment temperature of 500 ℃, so that the performance of the composite material at low frequency is improved, and the composite material has certain absorption effect at centimeter wave bands and millimeter wave bands.
Example 2
1) According to Fe3+：Ba2+：Zr4+Is that the ratio of 15: 1: 0.2 stoichiometric molar ratio Fe (NO)3·9H2O、Ba(NO3)2、Zr(NO3)4·5H2Placing the solution O in distilled water, and placing the solution O on a magnetic stirrer to continuously stir for 2 hours to obtain a solution A;
2) according to Ba2+：OH-1: 150 moleWeighing NaOH according to a molar ratio to prepare a solution, and dropwise adding the solution into the solution A to obtain an alkaline solution B;
3) preparing a graphene oxide dispersion liquid with the concentration of 4mg/mL, and oxidizing the graphene oxide/Ba into the dispersion liquid2+According to the mol ratio of 1: 3, adding the mixture into the solution B, and continuously stirring the mixture for 3 hours on a magnetic stirrer to obtain a solution C;
4) transferring the solution C into a stainless steel reaction kettle, sealing, placing the stainless steel reaction kettle in a drying oven for hydrothermal reaction, setting the reaction temperature at 280 ℃ and the reaction time at 48 h;
5) washing the obtained precipitate with deionized water and absolute ethyl alcohol, and drying at 80 ℃ to obtain precursor powder;
6) putting the precursor powder into a tube furnace, and carrying out heat treatment at 550 ℃ for 4h in a nitrogen atmosphere at the speed of 10 ℃/min to obtain BaZrxFe12–xO19/Fe3O4Composite ferrite powder.
The wave absorbing performance of the radar absorbent with the frequency range of 26.5-40GHz prepared by the embodiment is tested by using an Agilent vector network analyzer coaxial line testing method. During testing, the wave-absorbing material powder and the solid paraffin are mixed according to the mass ratio of 6: 4 the test was carried out after homogeneous mixing at 80 ℃.
Referring to fig. 4, it can be seen that a thick irregular barium ferrite sheet is formed in the sample, and many thin small sheets are densely arranged and stacked, so that the surface area is reduced, and simultaneously Fe is generated3O4The clusters are widely distributed in the sample. Referring to FIGS. 5 and 6, RL is measured in centimeter at a thickness of 2.3mm<The frequency range of-10 dB covers 12.44-14.72GHz, the effective absorption bandwidth reaches 2.32GHz, and the strongest absorption peak reaches-10.9858 dB; in the millimeter wave band, RL<The frequency range of-10 dB covers 32.64-40GHz, the effective absorption bandwidth reaches 7.36GHz, and the strongest absorption peak reaches-25.4153 dB. The method shows that when the heat treatment temperature is 550 ℃, more barium ferrite is formed in a sample, but the barium ferrite is not uniformly distributed, the agglomeration phenomenon is generated, the hard/soft magnetic interface is reduced, and the wave absorbing performance of the material is influenced.
Example 3
1) According to Fe3+：Ba2+：Zr4+Is 13: 1: conversion to 0.1Stoichiometric molar ratio Fe (NO)3·9H2O、Ba(NO3)2、Zr(NO3)4·5H2Placing the solution O in distilled water, and placing the solution O on a magnetic stirrer to continuously stir for 2 hours to obtain a solution A;
2) according to Ba2+：OH-1: weighing NaOH according to a molar ratio of 120 to prepare a solution, and dropwise adding the solution A to obtain an alkaline solution B;
3) preparing a graphene oxide dispersion liquid with the concentration of 4mg/mL, and oxidizing the graphene oxide/Ba into the dispersion liquid2+According to the mol ratio of 1: 2, adding the mixture into the solution B, and continuously stirring the mixture for 3 hours on a magnetic stirrer to obtain a solution C;
4) transferring the solution C into a stainless steel reaction kettle, sealing, placing the stainless steel reaction kettle in a drying oven for hydrothermal reaction, setting the reaction temperature to be 260 ℃ and the reaction time to be 36 h;
5) washing the obtained precipitate with deionized water and absolute ethyl alcohol, and drying at 60 ℃ to obtain precursor powder;
6) putting the precursor powder into a tube furnace, and carrying out heat treatment at 600 ℃ for 3h in a nitrogen atmosphere at the speed of 5 ℃/min to obtain BaZrxFe12–xO19/Fe3O4Composite ferrite powder.
The wave absorbing performance of the radar absorbent with the frequency range of 26.5-40GHz prepared by the embodiment is tested by using an Agilent vector network analyzer coaxial line testing method. During testing, the wave-absorbing material powder and the solid paraffin are mixed according to the mass ratio of 6: 4 the test was carried out after homogeneous mixing at 80 ℃.
Referring to FIG. 7, it can be seen that hexagonal M-type barium ferrite and Fe3O4The distribution is uniform, which is beneficial to the reflection of the electromagnetic wave in the material. Referring to FIGS. 8 and 9, RL exhibits a thickness of 2.7mm in the centimeter band<The frequency range of-10 dB covers 8.44-11.08GHz, the effective absorption bandwidth reaches 2.64GHz, and the strongest absorption peak reaches-13.711 dB; in the millimeter wave band, RL<The frequency range of-10 dB covers 26.5-34.77GHz, the effective absorption bandwidth reaches 8.27GHz, and the strongest absorption peak reaches-22.2451 dB. Illustrating the formation of barium ferrite and Fe in the sample at a heat treatment temperature of 600 deg.C3O4Have a large intersectionThe interface generates good hard/soft magnetic coupling effect, and improves the wave absorbing performance of the material.
Comparative example 1
The wave absorbing agent prepared by adopting a traditional mechanical mixing method comprises the following specific preparation processes:
(1) according to Fe3+：Ba2+：Zr4+Is 13: 1: 0.1 stoichiometric molar ratio Fe (NO)3·9H2O、Ba(NO3)2、Zr(NO3)4·5H2Placing the solution O in distilled water, and placing the solution O on a magnetic stirrer to continuously stir for 2 hours to obtain a solution A; according to n (Ba)2+)：n(C6H8O7) Is 1: weighing citric acid (C) at a molar ratio of 206H8O7) Preparing a solution, and adding the solution A into the solution A to obtain a solution B; dropwise adding ammonia water into the solution B, adjusting the pH to 7, and continuously stirring for 2 hours on a magnetic stirrer to obtain a neutral solution C; putting the solution C in an oven, and drying at the drying temperature of 120 ℃ for 72 h; and placing the obtained dried product in a muffle furnace, setting the temperature at 1400 ℃, and carrying out heat treatment to obtain powder A.
(2) FeCl is added3·6H2O and CH3COONa is as n (Fe)3+):n(CH3COONa) of 1:10, and dissolving in the ethylene glycol solution to obtain a solution D; and (3) placing the solution D in an oven, and drying at the drying temperature of 200 ℃ for 20 hours to prepare powder B.
(3) According to n (Ba)2+)：n(Fe3O4) A, B is weighed according to the stoichiometric molar ratio of 1:1 and dissolved in the ethanol solution to obtain a uniformly dispersed solution E; placing the solution E in an oven, and drying at 80 ℃ for 24h to obtain powder C; placing the powder C in a tube furnace, and carrying out heat treatment at 600 ℃ for 3h in a nitrogen atmosphere at the speed of 5 ℃/min to obtain BaZrxFe12–xO19/Fe3O4Composite ferrite powder.
The wave absorbing performance of the 2-18GHz frequency band radar absorbent prepared by the embodiment is tested by using an Agilent vector network analyzer coaxial line testing method. During testing, the wave-absorbing material powder and the solid paraffin are mixed according to the mass ratio of 6: 4 after mixing homogeneously at 80 ℃ were tested.
Referring to FIG. 10, it can be seen that much Fe is formed3O4The phase, hexagonal flaky barium ferrite has a lot of Fe adhered thereon3O4Particles, regions Fe outside barium ferrite3O4Agglomeration occurs and the formed composite material is not uniformly distributed. Referring to FIGS. 11 and 12, RL exhibits a thickness of 3.00mm in the centimeter band<The frequency range of-10 dB covers 10.04-12.16GHz, the effective absorption bandwidth reaches 2.12GHz, and the strongest absorption peak reaches-13.5874 dB; in the millimeter wave band, RL<The frequency range of-10 dB covers 29.54-34.36GHz, the effective absorption bandwidth reaches 4.82GHz, and the strongest absorption peak reaches-26.9793 dB. Compared with example 1, the method of example 1 increases the effective absorption intensity, and the strongest absorption peak is similar. Illustrating the use of mechanically mixed BaZrxFe12– xO19And Fe3O4The formed composite material has a certain wave absorbing effect, but the effective absorption bandwidth is narrow, and an ideal effect is not obtained.
Comparative example 2
The preparation method is the same as example 2, except that in step 3), a conventional reducing agent is used instead of the graphene oxide dispersion liquid. In this comparative example, a glucose solution having a concentration of 10mol/L was prepared, and the solution was treated with glucose/Ba2+Adding the mixture into the solution B according to the molar ratio of 10:1, and continuously stirring the mixture for 3 hours on a magnetic stirrer to obtain a solution C.
The wave absorbing performance of the radar absorbent with the frequency range of 26.5-40GHz prepared by the embodiment is tested by using an Agilent vector network analyzer coaxial line testing method. During testing, the wave-absorbing material powder and the solid paraffin are mixed according to the mass ratio of 6: 4 the test was carried out after homogeneous mixing at 80 ℃.
Referring to FIG. 13, it can be seen that much Fe was formed3O4Phase, but Fe3O4The phase is seriously agglomerated and is gathered around the barium ferrite to cover the surface of the barium ferrite. Referring to FIGS. 14 and 15, RL exhibits a thickness of 4.10mm in the centimeter band<Frequency of-10 dBThe rate range covers 6.44-7.44GHz, the effective absorption bandwidth reaches 1GHz, and the strongest absorption peak reaches-10.8376 dB; in the millimeter wave band, RL<The frequency range of-10 dB covers 26.77-32.34GHz, the effective absorption bandwidth reaches 5.57GHz, and the strongest absorption peak reaches-30.1806 dB. The traditional reducing agent, such as glucose and the like, is used, so that the reducing effect of a sample is poor, a better hard/soft magnetic phase is not formed, the interface is reduced, and the wave absorbing performance of the material is influenced. BaZr formed using glucose as reducing agentxFe12–xO19And Fe3O4The composite material has a certain wave absorbing effect, but the wave absorbing strength is low, the effective absorption bandwidth is narrow, and the effect is poor compared with that of the embodiment 1.
Comparative example 3
1) According to Fe3+：Ba2+：Zr4+Is 14: 1: 0.2 stoichiometric molar ratio Fe (NO)3·9H2O、Ba(NO3)2、Zr(NO3)4·5H2Placing the mixture in distilled water, and placing the mixture on a magnetic stirrer to stir continuously for 2 hours to obtain a solution A;
2) according to Ba2+：OH-1: weighing NaOH according to a molar ratio of 135 to prepare a solution, and dropwise adding the solution A into the solution A to obtain an alkaline solution B;
3) preparing a graphene oxide dispersion liquid with the concentration of 3mg/mL, and oxidizing the graphene oxide/Ba into the dispersion liquid2+According to the mol ratio of 1: 2.5 adding the solution B into the solution B, and continuously stirring the solution B for 2 hours on a magnetic stirrer to obtain a solution C;
4) transferring the solution C into a stainless steel reaction kettle, sealing, placing the stainless steel reaction kettle in a drying oven for hydrothermal reaction, setting the reaction temperature to be 270 ℃ and the reaction time to be 42 h;
5) washing the obtained precipitate with deionized water and absolute ethyl alcohol, and drying at 70 ℃ to obtain precursor powder;
6) putting the precursor powder into a tube furnace, and performing heat treatment at the speed of 8 ℃/min and the temperature of 400 ℃ and 700 ℃ for 3.5h respectively in the nitrogen atmosphere to obtain BaZrxFe12–xO19/Fe3O4Composite ferrite powder.
Referring to fig. 16, it is understood that hexagonal plate-like particle crystals formed at a heat treatment temperature of 400 ℃ are less and are unevenly distributed in the sample, and that small cluster-like particles are present only around hexagonal plate-like large particle crystals, resulting in extremely uneven morphology of the sample. Referring to FIGS. 17 and 18, RL is at centimeter band at a thickness of 3.35mm<The frequency range of-10 dB covers 14.08-15.92GHz, the effective absorption bandwidth reaches 1.84GHz, and the strongest absorption peak reaches-11.1225 dB. In the millimeter wave band, RL<The frequency range of-10 dB covers 29.54-34.7GHz, the effective absorption bandwidth reaches 5.16GHz, and the strongest absorption peak reaches-17.7181 dB. Referring to fig. 19, it is known that hexagonal plate-shaped large-particle crystals and small-cluster-shaped particles are tightly agglomerated together, a close packing phenomenon occurs, and a contact area with air is greatly reduced. Referring to FIGS. 20 and 21, RL is measured in centimeter at a thickness of 2.50mm<The frequency range of-10 dB covers 11.36-12.92GHz, the effective absorption bandwidth reaches 1.56GHz, and the strongest absorption peak reaches-11.3016 dB; in the millimeter wave band, RL<The frequency range of-10 dB covers 36.83-39.83GHz, the effective absorption bandwidth reaches 3GHz, and the strongest absorption peak reaches-14.5044 dB. According to the two groups of parallel experiments, when the reduction temperature of the system is too low or too high, the wave absorbing performance and the morphological characteristics of the composite wave absorbing agent are influenced, and when the temperature is too low, a very small amount of Fe is formed in the system3O4The characteristic absorption peak of barium ferrite can not be reduced more effectively, so that the wave absorbing performance in centimeter wave band is poorer; when the temperature is too high, hexagonal flaky barium ferrite and cluster-shaped Fe are generated3O4The agglomeration phenomenon is generated, the interaction interface between hard/soft magnetism is reduced, the hard/soft magnetism coupling effect is weakened, and meanwhile, the contact area of the composite wave absorbing agent and the atmosphere is greatly reduced, so that the wave absorbing bandwidth of the composite wave absorbing agent is smaller and the strength is lower.
Comparative example 4
1) According to Fe3+：Ba2+：Zr4+Is 13: 1: 0.6 stoichiometric molar ratio Fe (NO)3·9H2O、Ba(NO3)2、Zr(NO3)4·5H2O in distilled water and placing in magnetic stirringContinuously stirring the mixture for 2 hours on the device to obtain a solution A;
2) according to Ba2+：OH-1: weighing NaOH according to a molar ratio of 120 to prepare a solution, and dropwise adding the solution A into the solution A to obtain an alkaline solution B;
3) preparing a graphene oxide dispersion liquid with the concentration of 4mg/mL, and oxidizing the graphene oxide/Ba into the dispersion liquid2+According to the mol ratio of 1: 2, adding the mixture into the solution B, and continuously stirring the mixture for 3 hours on a magnetic stirrer to obtain a solution C;
4) transferring the solution C into a stainless steel reaction kettle, sealing, placing the stainless steel reaction kettle in a drying oven for hydrothermal reaction, setting the reaction temperature to be 260 ℃ and the reaction time to be 36 h;
5) washing the obtained precipitate with deionized water and absolute ethyl alcohol, and drying at 60 ℃ to obtain precursor powder;
6) putting the precursor powder into a tube furnace, and carrying out heat treatment at 600 ℃ for 3h in a nitrogen atmosphere at the speed of 5 ℃/min to obtain BaZrxFe12–xO19/Fe3O4Composite ferrite powder.
Referring to fig. 22, it is seen that in the sample where X is 0.6, large hexagonal plate-like crystals are not formed, and a large amount of cluster-like substances are formed from small particles. Referring to FIGS. 23 and 24, RL is at the centimeter band at a thickness of 3.80mm<The frequency range of-10 dB covers 9.96-11.48GHz, the effective absorption bandwidth reaches 1.52GHz, and the strongest absorption peak reaches-11.1588 dB; in the millimeter wave band, RL<The frequency range of-10 dB covers 35.78-40GHz, the effective absorption bandwidth reaches 4.22GHz, and the strongest absorption peak reaches-18.0771 dB. It is known that the sample where X is 0.6 does not form ideal barium ferrite and Fe3O4The structure has poor wave absorbing performance in centimeter wave bands, poor absorption effect in centimeter wave bands, and narrow bandwidth, and is different from the expected prepared composite wave absorbing material.
Claims (7)
1. A preparation method of a hard/soft magnetic composite ferrite wave absorber is characterized by comprising the following steps:
(1) taking nitrates of Fe, Ba and Zr as metal precursors to prepare mixed metal nitrate solution;
(2) adding NaOH solution into mixed metal nitrate solution to obtain alkaline mixed solution;
(3) adding the graphene oxide dispersion liquid into the alkaline mixed solution, fully stirring and mixing, and then placing the mixture into a reaction kettle to perform hydrothermal reaction in a sealed environment;
(4) washing and drying the precipitate after the hydrothermal reaction to obtain precursor powder, and then carrying out heat treatment on the precursor powder in a nitrogen atmosphere to obtain BaZrxFe12–xO19/Fe3O4Composite ferrite wave absorbing agent;
in the step (4), the heat treatment temperature is 500-600 ℃, the heat treatment time is 3-4 h, and the heating rate of the heat treatment is 5-10 ℃/min;
the wave absorbing agent comprises a hard magnetic phase for absorbing millimeter waves and a soft magnetic phase for absorbing centimeter waves; the hard magnetic phase is zirconium-doped barium ferrite, and the expression is BaZrxFe12–xO19Wherein x =0.1 to 0.2; the soft magnetic phase is ferroferric oxide; the ferroferric oxide is spherical, the zirconium-doped barium ferrite is flaky, and the spherical ferroferric oxide is attached to the flaky zirconium-doped barium ferrite.
2. The method for preparing a hard/soft magnetic composite ferrite wave absorber according to claim 1, wherein: in the mixed metal nitrate solution of the step (1), Fe3+、Ba2+And Zr4+The molar ratio of (A) to (B) is 13-15: 1: 0.1 to 0.2.
3. The method for preparing a hard/soft magnetic composite ferrite wave absorber according to claim 1, wherein: in the step (1), the nitrates of Fe, Ba and Zr are respectively ferric nitrate nonahydrate, barium nitrate hydrate and zirconium nitrate pentahydrate.
4. The method for preparing a hard/soft magnetic composite ferrite wave absorber according to claim 1, wherein: in the alkaline mixed solution of the step (2), Ba2+With OH‒In a molar ratio of 1: 120 to 150。
5. The method for preparing a hard/soft magnetic composite ferrite wave absorber according to claim 1, wherein: in the step (2), the pH value of the alkaline mixed solution is 13-14.
6. The method for preparing a hard/soft magnetic composite ferrite wave absorber according to claim 1, wherein: in the step (3), the graphene oxide and Ba are2+In a molar ratio of 1: 2-3; wherein the concentration of the graphene oxide dispersion liquid is 2-4 mg/mL.
7. The method for preparing a hard/soft magnetic composite ferrite wave absorber according to claim 1, wherein: in the step (3), the temperature of the hydrothermal reaction is 260-280 ℃, and the reaction time is 36-48 h.
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| CN108975898A (en) * | 2018-09-04 | 2018-12-11 | 南京航空航天大学 | A kind of efficient wave absorbing agent and preparation method thereof for millimeter wave atmospheric window |
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| CN108975898A (en) * | 2018-09-04 | 2018-12-11 | 南京航空航天大学 | A kind of efficient wave absorbing agent and preparation method thereof for millimeter wave atmospheric window |
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