Disclosure of Invention
In view of the above, the present invention provides a method for preparing a composite wave-absorbing material and a composite wave-absorbing material prepared thereby. The method of the invention is simple to operate and convenient for large-scale production; the obtained composite wave-absorbing material can overcome the defects of high density, easy agglomeration, narrow wave-absorbing frequency band and poor weather resistance of a single ferromagnetic material, and has light weight, corrosion resistance, good mechanical property and wave-absorbing property.
In order to achieve the above object, according to one aspect of the present invention, a method for preparing a composite wave-absorbing material is provided.
The method for preparing the composite wave-absorbing material comprises the following steps:
step I: synthesizing a nickel submicron sphere by a hydrothermal method;
step II: preparing a phenolic resin pyrolytic carbon coated nickel submicron sphere composite material by using the nickel submicron spheres obtained in the step I and adopting an aldehyde resin pyrolytic carbon method;
step III: and (3) coating the nickel submicron sphere composite material with the phenolic resin pyrolytic carbon obtained in the step (II), and preparing the composite wave-absorbing material of the nickel submicron sphere and the polyvinylidene fluoride coated with the phenolic resin pyrolytic carbon by adopting an ultrasonic method.
Preferably, step I comprises:
(I-1): dispersing nickel chloride hexahydrate, sodium acetate and trisodium citrate dihydrate into a mixed solution of glycerol and distilled water to form a uniform suspension, transferring the suspension into an autoclave,
(I-2): and pouring sodium hydroxide and sodium hypophosphite monohydrate dissolved in distilled water into the autoclave for reaction, thereby obtaining the nickel submicron spheres.
A hydrothermal method comprises dissolving a substance insoluble or scarcely soluble in the atmospheric conditions with an aqueous solution at high temperature and high pressure, or reacting to form a dissolved product of the substance, and precipitating a grown crystal by controlling the temperature difference of the solution in an autoclave to cause convection to form a supersaturated state. Compared with other technologies, the hydrothermal method has the advantages of high product purity, good dispersity, good crystal form, easy control and low production cost. In the invention, the uniformly dispersed nickel submicron spheres are obtained by a hydrothermal method, can be magnetically separated and washed, and is simple to operate.
Preferably, the feeding molar mass ratio of the nickel chloride hexahydrate in the step (I-1) to the sodium hypophosphite monohydrate in the step (I-2) is 1: 2-1: 3, and preferably 3: 8. Through a large amount of experimental regulation and control, the proportion range can accurately control the appearance of the sphere, and the nickel submicron sphere with uniform particle size is obtained.
Preferably, step II comprises:
(II-1): dissolving the nickel submicron spheres synthesized in the step I in a mixed solution of ethanol and distilled water through ultrasonic treatment, adding an ammonia solution with the concentration of 25 percent,
(II-2): sequentially adding resorcinol and formaldehyde into the solution obtained in the step (II-1), magnetically stirring, then placing in an oil bath for heating, completely crosslinking phenolic Resin (RF) on the nickel submicron spheres to obtain core-shell structure Ni @ RF submicron spheres, collecting the core-shell structure Ni @ RF submicron spheres through magnetic separation,
(II-3): and (3) sintering the Ni @ RF submicron spheres with the core-shell structures obtained in the step (II-2) in an inert atmosphere to obtain Ni @ C submicron spheres.
The phenolic resin carbon coating has low cost, simple experiment and excellent corrosion resistance; the magnetic separation is simple to operate, the product can be collected in a large scale, and the cost is low. And the carbon material with high dielectric is obtained by simple sintering, so that the dielectric-magnetic matching is optimized, and the wave-absorbing performance is optimized.
Preferably, the charging mass ratio of the resorcinol to the formaldehyde in (II-2) is 4: 5-6: 5, preferably 1: 1.
Preferably, the mass ratio of the resorcinol in (II-2) to the nickel submicron spheres in (II-1) is 4: 5-8: 5, preferably 6: 5. Through a series of proportion regulation and control, the phenolic resin carbon coating of the proportion obtains proper dielectric property after sintering, is beneficial to dielectric-magnetic matching, and has excellent wave-absorbing property.
Preferably, step III comprises:
(III-1): weighing the phenolic resin pyrolytic carbon coated nickel submicron sphere material obtained in the step II and PVDF according to a proportion,
(III-2): dissolving weighed PVDF in N, N-dimethylformamide, carrying out ultrasonic treatment until a transparent mixed solution is obtained, dissolving weighed phenolic resin pyrolytic carbon coated nickel submicron sphere particles in the transparent mixed solution, mechanically stirring to obtain a black suspension,
(III-3): and (3) evaporating the solvent of the black suspension obtained in the step (III-2), thereby obtaining the composite wave-absorbing material film of the phenolic resin pyrolytic carbon coated nickel submicron spheres and PVDF.
The thermal volatilization film forming in the step (III-3) is simple in operation, short in time and low in energy consumption, and can be used for mass sample forming to obtain the tough composite film.
Preferably, the mass ratio of the phenolic resin pyrolytic carbon coated nickel submicron sphere material to PVDF in the step (III-1) is 1: 9-3: 7, and more preferably 1: 4.
The invention also relates to a composite wave-absorbing material prepared by the method, which is a composite wave-absorbing material Ni @ C/PVDF with the nickel submicron spheres Ni @ C coated by the phenolic resin pyrolytic carbon and the polyvinylidene fluoride PVDF, wherein the nickel submicron spheres Ni @ C coated by the phenolic resin pyrolytic carbon is of a core-shell structure.
The nickel material can not meet the requirement of medium magnetic matching due to higher magnetism, so that the use of the nickel material in the wave-absorbing field is limited; and has the performances of unique structural characteristics, good mechanical property, high chemical stability and the like.
Compared with the prior art, the material and the method have the following advantages:
(1) according to the method, the nickel submicron spheres are synthesized by a hydrothermal method, so that the nickel submicron spheres with uniform dispersion are obtained, the sample can be magnetically separated and washed, and the operation is simple. See fig. 1.
(2) The aldehyde resin pyrolytic carbon method in the method has stable reaction, can directly wash samples by magnetic separation, has simple operation and is convenient for large-scale production.
(3) The phenolic resin pyrolytic carbon in the composite wave-absorbing material is uniformly coated on the nickel submicron spheres, so that the problem that the nickel spheres cannot be uniformly dispersed on a carbon material substrate is solved. See fig. 2.
(4) The phenolic resin pyrolytic carbon coated nickel submicron spheres Ni @ C in the composite wave-absorbing material have a core-shell structure (see figure 3), so that not only is the dielectric-magnetic matching convenient to regulate and control, but also the wave-absorbing performance is optimized; and has the performances of unique structural characteristics, good mechanical property, high chemical stability and the like.
(5) According to the composite wave-absorbing material, the nickel submicron spheres Ni @ C coated with the phenolic resin pyrolytic carbon are uniformly distributed in the PVDF matrix, so that the wave-absorbing amount of the material is greatly improved and the frequency absorbing section is widened compared with the wave-absorbing effect.
(6) The composite wave-absorbing material has excellent wave-absorbing performance, low raw material cost, simple and convenient separation means, low energy consumption and convenient large-scale production.
Examples
Preparation of Ni submicron spheres
Mixing NiCl2·6H2O (1.2g), sodium acetate (3.0g) and trisodium citrate dihydrate (0.2g) were dispersed in a mixed solution of glycerin (30mL) and distilled water (10 mL); after stirring for 1.5h, the uniform suspension was transferred to a stainless steel autoclave lined with teflon; sodium hydroxide NaOH (1.6g) and sodium hypophosphite monohydrate NaH dissolved in 20mL of distilled water2PO2·H2O (3.2g) was slowly poured into the autoclave, and after reacting at 140 ℃ for 15 hours, the solution was cooled to room temperature. Washing the obtained grey precipitate with distilled water and anhydrous ethanol for several times, collecting with magnet, and vacuum drying at 60 deg.C for 12 hr to obtain nickel submicron spheres. The SEM image of the obtained nickel submicron spheres is shown in FIG. 1, and it can be seen that the nickel submicron spheres are uniformly dispersed.
Preparation of phenolic resin pyrolytic carbon coated nickel submicron spheres
The Ni particles (100mg) synthesized above were dissolved in a mixed solution of ethanol (20mL) and distilled water (10mL) by sonication, and a concentrated ammonia solution (500. mu.L, 25 wt%) was slowly added under magnetic stirring. Then, resorcinol (0.12g) and formaldehyde (120. mu.l, 37 wt%) were successively added to the above solution, and the mixed solution was magnetically stirred at 30 ℃ for 10 hours and then left in an oil bath at 100 ℃ for 30 minutes to completely crosslink RF (phenol resin) on the Ni particles. The obtained core-shell structure Ni @ RF submicron spheres are collected by magnetic separation, washed with deionized water and ethanol for several times and dried. And heating the Ni @ RF submicron spheres to 850 ℃ at the speed of 2 ℃/min in an argon atmosphere, and sintering for 3h to obtain the Ni @ C submicron spheres. An SEM image of the resulting Ni @ C submicron spheres is shown in FIG. 2, where it can be seen that the nickel spheres are uniformly dispersed on the carbon material matrix. The TEM image of the obtained Ni @ C submicron spheres is shown in FIG. 3, and it can be seen that the obtained Ni @ C submicron spheres have a core-shell structure, and a carbon shell with the thickness of about 48nm is uniformly coated on the nickel submicron spheres.
Preparation of composite material of phenolic resin pyrolytic carbon coated nickel submicron spheres and polyvinylidene fluoride (PVDF)
The prepared phenolic resin pyrolytic carbon coated nickel submicron spheres and PVDF (polyvinylidene fluoride) are mixed according to the mass ratio of 1:4, weighing the mixture with the total mass of 0.1 g. Dissolving a certain amount of PVDF in 10mL of N, N-dimethylformamide, and carrying out ultrasonic treatment until a transparent mixed solution is obtained. And coating nickel submicron spheres on the weighed phenolic resin carbon material, dissolving the phenolic resin carbon material in the mixed solution, and ultrasonically stirring the mixed solution to obtain a black suspension. And transferring the prepared mixed solution into an evaporation dish, and placing the evaporation dish in an oven at the temperature of 70 ℃ for 4 hours to evaporate the solvent to prepare the Ni @ C/PVDF composite membrane.
And tabletting the obtained Ni @ C/PVDF composite membrane by adopting a hot pressing method, and carrying out wave absorption test by using a coaxial method. The test result is shown in FIG. 4, and the result shows that when the mass ratio of the phenolic resin pyrolytic carbon coated nickel submicron spheres to PVDF is 1:4, the maximum reflection loss at 13.61GHz under the thickness of 2mm can reach-47.58 dB, and the maximum effective absorption (the reflection loss is less than-10 dB) frequency bandwidth under the single thickness can reach 5.42 GHz.
The above-described embodiments should not be construed as limiting the scope of the invention. Those skilled in the art will appreciate that various modifications, combinations, sub-combinations, and substitutions can occur, depending on design requirements and other factors. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.