CN111500255B - Carbon nano tube/barium ferrite magnetic composite powder and preparation method thereof - Google Patents
Carbon nano tube/barium ferrite magnetic composite powder and preparation method thereof Download PDFInfo
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Abstract
The invention relates to a carbon nano tube/barium ferrite magnetic composite powder, wherein in the composite powder, a carbon nano tube forms a conductive network, and barium ferrite particles form a coating layer. In the carbon nano tube/barium ferrite magnetic composite material, the barium ferrite is used for fully coating the carbon tube, the dielectric property of the carbon nano tube is improved, and the impedance matching property of the carbon nano tube/barium ferrite magnetic composite material is effectively improved. The composite material can provide good high-wave-absorbing electromagnetic shielding performance and can meet the requirements on absorption and shielding of interference signals in the 5G communication process.
Description
Technical Field
The invention relates to the field of composite materials, in particular to a carbon nano tube/barium ferrite magnetic composite material and a preparation method thereof.
Background
In recent years, with the rapid development of radio technology and high frequency technology, electromagnetic pollution is more and more serious, and the search for a wave-absorbing material capable of resisting and weakening electromagnetic wave radiation becomes a research hotspot of material science.
Carbon nanotubes are hollow tubular materials having a large specific area, a high aspect ratio, and excellent conductivity, and can generate dielectric loss with respect to electromagnetic waves. However, the impedance matching performance between the carbon nanotube and the electromagnetic wave is poor, which easily causes reflection of the electromagnetic wave and hardly really plays a loss role on the electromagnetic wave. Therefore, the carbon nano tube is compounded with materials with better impedance matching performance, such as metal oxide, semiconductor, conductive polymer and the like, so that the impedance matching performance of the carbon nano tube can be effectively improved, and the wave absorbing performance of the carbon nano tube can be effectively improved.
The barium ferrite has relatively good impedance matching performance with electromagnetic waves, high coercive force and magnetic saturation strength, and good absorption to the electromagnetic waves. But the barium ferrite also has the defects of low conductivity, limited wave-absorbing performance and the like. The barium ferrite and the carbon nanotube are simply mixed mechanically by researchers, such as ball milling compounding, so that the impedance matching performance of the carbon nanotube can be improved, the wave absorbing performance of the carbon nanotube can be improved, the defect of larger density of the carbon nanotube can be effectively improved, and the effect of the wave absorbing material of being thin, light, wide and strong can be met (Journal of Magnetic and Magnetic Materials 2017,442, 224-. Unfortunately, in the existing barium ferrite and carbon nanotube composite material, the problems of poor dispersibility of the carbon nanotubes, damage to the ferrite structure in the mixing process and the like exist only through simple ball milling process, so that the electromagnetic wave absorption effect is limited.
Chinese patent CN 109850950A discloses a method for preparing a barium ferrite and carbon nanotube composite wave-absorbing material, which is characterized in that: (1) firstly, preparing barium ferrite; (2) adding a silane coupling agent into absolute ethyl alcohol and ammonia water, uniformly mixing to obtain a silane coupling agent solution, then mixing barium ferrite and carbon nano tubes, and adding the mixture into the silane coupling agent solution for reaction; (3) and after the reaction is finished, washing until no ammonia smell exists, and then filtering, drying and grinding to obtain the wave-absorbing material. According to the patent, the silane coupling agent is adopted to carry out connection reaction on the carbon nano tube and the barium ferrite, although the ball milling damage effect is avoided to a certain extent, the silane coupling agent is a connection site which easily causes the contact resistance of the carbon nano tube to be enhanced, the conductive advantage characteristic of the carbon nano tube is limited to be exerted, and the carbon tube is high in addition.
Disclosure of Invention
The invention aims to: aiming at the problems that the barium ferrite in the prior art has low conductivity and limited wave-absorbing performance and the ferrite structure can be damaged by directly adding and applying carbon nano tube ball milling and mixing, the carbon nano tube/barium ferrite magnetic composite powder and the preparation method thereof are provided.
In order to achieve the purpose, the invention adopts the technical scheme that:
a carbon nano tube/barium ferrite magnetic composite powder is provided, in the composite powder, a carbon nano tube forms a conductive network, and barium ferrite particles form a coating layer.
According to the magnetic composite powder material composed of the carbon nano tube and the barium ferrite, the carbon nano tube forms a conductive network, the barium ferrite particles form a coating layer, and the composite powder material composed of the carbon nano tube and the barium ferrite can maximally exert respective characteristic advantages of the two materials. The conductive network is formed by the uniform dispersion of the carbon nano tubes, so that the impedance matching of the composite material is effectively improved, and the high wave-absorbing efficiency is obtained.
Furthermore, the weight of the carbon nano tube in the carbon nano tube/barium ferrite magnetic composite powder accounts for 0.1-10%. Preferably 0.1 to 5%. The addition and application of the carbon nano tube of which the content is not more than 5 percent can better ensure the content ratio of barium ferrite, so that the wave absorbing performance is better. More preferably, the carbon nanotubes are present in a weight ratio of 0.2 to 4%. Preferably 0.3 to 3%.
Preferably, the carbon nanotubes are present in a weight ratio of 0.5 to 2%. For example, it may be 0.8%, 1%, 1.5%, 1.8%, 2%, etc.
The invention also aims to provide a preparation method for preparing the carbon nano tube/barium ferrite magnetic composite powder, which realizes the high-efficiency dispersion of the carbon nano tube in the barium ferrite magnetic composite material through better in-situ doping, forms a conductive network and obtains better composite performance.
A preparation method of carbon nano tube/barium ferrite magnetic composite powder comprises the following steps:
(1) preparing barium ferrite precursor solution;
(2) adding carbon nano tubes for dispersion, adjusting pH, and reacting to obtain wet gel;
(3) drying the obtained wet gel to obtain dry gel;
igniting the xerogel, and performing self-propagating combustion to obtain a compound containing the carbon nano tube;
(4) calcining the compound containing the carbon nano tube to obtain the carbon nano tube/barium ferrite magnetic composite powder.
The preparation method adopts a sol-gel method to prepare the barium ferrite material, and the carbon nano tubes are dispersed in the barium ferrite precursor solution, so that the effective stability of the carbon nano tubes is uniformly dispersed in wet gel. Then barium ferrite magnetic powder material containing carbon nano tubes is prepared according to a barium ferrite sol-gel method, the dispersibility of the carbon nano tubes can be effectively improved, the uniform distribution of a carbon nano tube conductive network is realized, the impedance matching performance of the composite material is effectively improved, and the composite material with high wave-absorbing performance is obtained.
In the invention, in the process of synthesizing the barium ferrite by using a sol-gel method, the carbon nano tube is added into the precursor solution, the calcining gas atmosphere is changed in the high-temperature calcining process, the carbon nano tube/barium ferrite magnetic composite material is prepared, the adding amount of the carbon nano tube in the product is less, and the obtained composite material has higher magnetic saturation strength. The carbon tube can be fully coated, so that the impedance matching performance is effectively improved, and the wave absorbing performance of the composite material is improved, and the composite material can be applied to the fields of microwave absorption, electromagnetic shielding, high-density information magnetic recording and the like. And the synthesis time is short, the synthesis process is simple, the cost can be effectively reduced, and the energy consumption is reduced.
The preparation method has the characteristics of simple and easy operation process, no need of any high-energy-consumption ball milling equipment, environmental friendliness, low production cost and easy realization of mass production. The uniform dispersion of the carbon nanotube conductive network can be realized only by a small addition proportion of the carbon nanotubes, the effect is good, and the cost is low.
As a preferred scheme of the present invention, in the step (1), the barium ferrite precursor solution is prepared by using soluble barium salt, soluble ferric salt and citric acid in water.
Further, the soluble barium salt is barium nitrate. Good solubility and high reaction conversion rate of the prepared precursor.
Further, the soluble iron salt is at least one of ferric nitrate, ferric carbonate and ferrous carbonate. Preferably ferric nitrate.
Further, the preparation of the barium ferrite precursor solution in the step (1) comprises the following steps: dissolving citric acid, barium nitrate and ferric nitrate in water to prepare a precursor solution. Preferably, the barium ferrite precursor solution is formulated at room temperature.
Further, in the barium ferrite precursor solution, Ba2+、Fe3+And citric acid in a molar ratio of 1: 10-14: 12-18. By properly controlling the mixing proportion of various raw material components in the barium ferrite precursor solution, the efficiency of forming barium ferrite by subsequent conversion of the generated barium ferrite precursor solution is higher, and the residual unreacted impurity components are less. Preferably, the molar ratio of the three components is 1: 11-13: 13-17. Preferably, the molar ratio of the three components is 1: 12: 15.
in the preferred embodiment of the present invention, in the step (2), the carbon nanotubes are added to the barium ferrite precursor solution, the pH is adjusted to 6 to 8, the solution is heated to 50 to 90 ℃, and the wet gel is formed by stirring. The wet gel is the sol referred to in the sol-gel method.
Preferably, ammonia is added dropwise to adjust the pH. The pH value is adjusted by ammonia water, the product is calcined without residue, and the purity of the obtained composite material is higher.
Preferably, the heating is carried out in a water bath to 50-90 deg.C, preferably to 60-85 deg.C, e.g., 70 deg.C, 75 deg.C, 80 deg.C, 82 deg.C, 85 deg.C.
Furthermore, the weight of the added carbon nano tube is calculated by the weight of barium ferrite corresponding to the barium ferrite precursor, and the adding proportion is 1-10%, preferably 1-5%. More preferably 1% to 3%. For example, if a barium ferrite precursor solution is prepared according to a preparation target of 100g of barium ferrite, the amount of carbon nanotubes to be added is 1 to 3 g.
Furthermore, after the carbon nano tubes are added, ultrasonic treatment is adopted to promote the uniform dispersion of the carbon nano tubes.
In a preferred embodiment of the present invention, in step (3), the obtained wet gel is dried to obtain a xerogel.
Preferably, the wet gel is dried at 100-200 ℃. Preferably, the drying time is 6-24 h. Preferably, the wet gel is dried at 140 ℃ and 180 ℃ for 10-14 h.
Further, in the step (3), the xerogel is ignited in the air to generate self-propagating combustion reaction, so as to obtain fluffy black brown powder material, namely the compound containing carbon nano tubes. The powder material is a binary composite precursor (a precursor and a carbon nanotube composite) and is a raw material for calcination treatment in the subsequent step (4).
As a preferred embodiment of the present invention, in step (4), the calcination of the carbon nanotube-containing composite is divided into two stages of calcination: a first stage calcination and a second stage calcination.
Further, the first stage calcination is calcination under an oxidizing atmosphere at a calcination temperature of 300-520 ℃. The calcination temperature is preferably 350-510 deg.C, preferably 400-500 deg.C. For example, 430 ℃, 450 ℃, 480 ℃, 490 ℃ and the like can be used.
Preferably, the first calcination time is 0.5 to 6 hours, preferably 0.5 to 4 hours, and may be, for example, 1 hour, 2 hours, 3 hours, etc.
Preferably, the oxidizing atmosphere refers to an air atmosphere.
Preferably, the oxidizing atmosphere may be another oxygen-containing gas as a sintering atmosphere.
Further, the second-stage calcination is carried out in an inert atmosphere, and the calcination temperature is 750-900 ℃. Preferably 760 ℃ and 880 ℃, preferably 780 ℃ and 840 ℃, for example 790 ℃, 800 ℃, 810 ℃, 820 ℃ and the like.
Preferably, the second stage calcination time is 10-100min, preferably 15-80min, and may be, for example, 20min, 25min, 30min, 35min, 40min, 50min, 60min, etc.
Further, the inert atmosphere refers to any one of a nitrogen atmosphere and an argon atmosphere. In the second stage of calcination, the carbon nanotubes should be kept in a better original state to avoid oxidation, so that the carbon nanotubes in the composite material can be better connected into a net by calcining in an inert atmosphere.
And further, after the second-stage calcination is finished, cooling to room temperature in an inert atmosphere to obtain the carbon nano tube/barium ferrite magnetic composite powder. And the carbon nano tube is cooled in an inert atmosphere, so that the carbon nano tube is prevented from being oxidized and lost due to the contact of residual heat in the cooling process and the oxidizing atmosphere.
Specifically, after the calcination is controlled, the carbon nanotubes are cooled in an inert atmosphere or under other protective conditions, so that the carbon nanotubes in the product are prevented from being oxidized and lost due to the fact that the carbon nanotubes are contacted with an oxidizing atmosphere due to preheating. Depending on the actual conditions, which may be cooling to a certain temperature (e.g. 200 ℃ C.) and 300 ℃ C.), the product can be exposed to a certain amount of air with little or no oxidation, the protective/inert atmosphere conditions can be relieved.
In summary, due to the adoption of the technical scheme, the invention has the beneficial effects that:
1. in the carbon nano tube/barium ferrite magnetic composite material, the barium ferrite is used for fully coating the carbon tube, the dielectric property of the carbon nano tube is improved, and the impedance matching property of the carbon nano tube/barium ferrite magnetic composite material is effectively improved. When the content of the carbon nano tube is 2 w%, the minimum reflectivity of the prepared magnetic composite material reaches-43.9 dB.
2. The carbon nano tube/barium ferrite magnetic composite material has good application prospects in the fields of microwave absorption, electromagnetic shielding and the like, for example, a complex communication environment in the 5G communication technology provides higher wave-absorbing requirements for electromagnetic shielding performance, and the composite material can provide good high wave-absorbing type electromagnetic shielding performance and can meet the shielding requirements for interference signals in the 5G communication process.
3. The preparation method of the carbon nano tube/barium ferrite magnetic composite material only needs to apply a small amount of carbon tube materials, has low cost, and can effectively improve the magnetic saturation strength of the composite material and improve the wave absorption property of the composite material.
4. The preparation process of the carbon nano tube/barium ferrite magnetic composite material is simple and easy to implement, has fewer steps, and can effectively save cost and reduce energy consumption.
Drawings
FIG. 1 is a transmission electron micrograph of pure barium ferrite.
FIG. 2 is a TEM image of the composite material when the amount of carbon nanotubes added is 2 wt%.
FIG. 3 is the hysteresis curves of pure barium ferrite obtained in different calcining atmospheres.
FIG. 4 is a hysteresis chart of the composite material at different carbon nanotube addition levels, with BF, BF/C0.5, BF/C1 and BF/C2 being carbon nanotube addition levels of 0 wt%, 0.5 wt%, 1 wt% and 2 wt%, respectively.
FIG. 5 shows the wave-absorbing properties of the material calcined under pure nitrogen.
FIG. 6 shows the wave-absorbing properties of the material obtained by calcining barium ferrite in pure air.
FIG. 7 shows the wave-absorbing properties of the material obtained by calcining barium ferrite with air and then nitrogen.
Detailed Description
The present invention will be described in detail below with reference to the accompanying drawings.
The following specific examples are given to further illustrate the technical solutions of the present invention, but it should be specifically noted that the following examples should not be construed as limiting the scope of the present invention, and those skilled in the art should make some non-essential improvements and modifications to the present invention according to the above disclosure.
[ example 1 ]
(1) 0.003mol of Ba (NO)3)2、0.036mol Fe(NO3)3·9H2Dissolving O in water, and sequentially adding 0.0512mol of citric acid C6H8O7·H20.035g (0.5 wt%) of carbon nanotubes was added to the aqueous solution of O with stirring, and NH was added dropwise thereto3·H2And O, adjusting the pH value of the solution to 7, and uniformly mixing by ultrasonic.
(2) The reaction was then stirred at 80 ℃ for 5h to form a wet gel.
(3) Drying the obtained wet gel at 160 ℃ for 12h to obtain gray black xerogel, and igniting the gray black xerogel in the air to enable the gray black xerogel to generate self-propagating combustion reaction to obtain fluffy coral-shaped black-brown powder.
(4) Calcining the obtained powder for 1h in an air atmosphere at 500 ℃, then introducing nitrogen, calcining for 0.5h at 800 ℃, and naturally cooling to room temperature to obtain the carbon nano tube/barium ferrite magnetic composite material.
[ example 2 ]
(1) 0.003mol of Ba (NO)3)2、0.036mol Fe(NO3)3·9H2Dissolving O in water, and sequentially adding 0.0512mol of citric acid C6H8O7·H2O aqueous solution, 0.07g (1 wt%) of carbon nanotubes was added with stirring, and NH was added dropwise thereto3·H2And O, adjusting the pH value of the solution to 7, and uniformly mixing by ultrasonic.
(2) The reaction was then stirred at 80 ℃ for 5h to form a wet gel.
(3) Drying the obtained wet gel at 160 ℃ for 12h to obtain gray black xerogel, and igniting the gray black xerogel in the air to enable the gray black xerogel to generate self-propagating combustion reaction to obtain fluffy coral-shaped black-brown powder.
(4) Calcining the obtained powder for 1h in an air atmosphere at 500 ℃, then introducing nitrogen, calcining for 0.5h at 800 ℃, and naturally cooling to room temperature to obtain the carbon nano tube/barium ferrite magnetic composite material.
[ example 3 ]
(1) 0.003mol of Ba (NO)3)2、0.036mol Fe(NO3)3·9H2Dissolving O in water, and sequentially adding 0.0512mol of citric acid C6H8O7·H2O aqueous solution, 0.14g (2 wt%) of carbon nanotubes was added with stirring, and NH was added dropwise thereto3·H2And O, adjusting the pH value of the solution to 7, and uniformly mixing by ultrasonic.
(2) The reaction was then stirred at 80 ℃ for 5h to form a wet gel.
(3) Drying the obtained wet gel at 160 ℃ for 12h to obtain gray black xerogel, and igniting the gray black xerogel in the air to enable the gray black xerogel to generate self-propagating combustion reaction to obtain fluffy coral-shaped black-brown powder.
(4) Calcining the obtained powder for 1h in an air atmosphere at 500 ℃, then introducing nitrogen, calcining for 0.5h at 800 ℃, and naturally cooling to room temperature to obtain the carbon nano tube/barium ferrite magnetic composite material.
[ example 4 ]
(1) 0.003mol of Ba (NO)3)2、0.036mol Fe(NO3)3·9H2Dissolving O in water, and sequentially adding 0.0512mol of citric acid C6H8O7·H2O aqueous solution, 0.21g (3 wt%) of carbon nanotubes was added with stirring, and NH was added dropwise thereto3·H2And O, adjusting the pH value of the solution to 7, and uniformly mixing by ultrasonic.
(2) The reaction was then stirred at 80 ℃ for 5h to form a wet gel.
(3) Drying the obtained wet gel at 160 ℃ for 12h to obtain gray black xerogel, and igniting the gray black xerogel in the air to enable the gray black xerogel to generate self-propagating combustion reaction to obtain fluffy coral-shaped black-brown powder.
(4) Calcining the obtained powder for 1h in an air atmosphere at 500 ℃, then introducing nitrogen, calcining for 0.5h at 800 ℃, and naturally cooling to room temperature to obtain the carbon nano tube/barium ferrite magnetic composite material.
[ COMPARATIVE EXAMPLE 1 ]
Preparation of pure barium ferrite magnetic powder
(1) 0.003mol of Ba (NO)3)2、0.036mol Fe(NO3)3·9H2Dissolving O in water, and sequentially adding 0.0512mol of citric acid C6H8O7·H2And stirring and mixing the mixture evenly in the water solution of O. NH was added dropwise thereto3·H2And O, adjusting the pH value of the solution to 7, and uniformly mixing by ultrasonic.
(2) The reaction was then stirred at 80 ℃ for 5h to form a wet gel.
(3) Drying the obtained wet gel at 160 ℃ for 12h to obtain gray black xerogel, and igniting the gray black xerogel in the air to enable the gray black xerogel to generate self-propagating combustion reaction to obtain fluffy coral-shaped black-brown powder.
(4) Calcining the obtained powder for 1h at 500 ℃ in an air atmosphere, then introducing nitrogen, calcining for 0.5h at 800 ℃, and naturally cooling to room temperature to obtain the barium ferrite magnetic composite material.
The barium ferrite magnetic composite materials prepared in comparative example 1 and example 3 were scanned using a transmission electron microscope, and the results are shown in fig. 1 to 2. FIG. 1 is a transmission electron microscope photograph of a pure barium ferrite prepared in comparative example 1. Fig. 2 is a TEM image of a composite material in which the carbon nanotube prepared in example 3 was added at 2%. It can be seen from the figure that the carbon tubes form a conductive network in the ferrite and are coated by the ferrite, which is beneficial to improving the dielectric loss of the composite material and effectively improving the impedance matching performance, thereby obtaining excellent wave-absorbing performance.
[ COMPARATIVE EXAMPLE 2 ]
Preparation of pure barium ferrite magnetic powder
According to the same synthesis reaction of step (1) to step (3) as in comparative example 1, in the calcination process in step (4), the calcination is performed in the pure nitrogen and pure air states, which are specifically as follows:
sintering in a pure nitrogen atmosphere comprises the following steps: calcining for 1h at 500 ℃ in a nitrogen atmosphere, and calcining for 0.5h at 880 ℃ in a nitrogen atmosphere to obtain the material calcined under pure nitrogen of barium ferrite.
The sintering in pure air atmosphere is as follows: sintering at 800 ℃ for 1h in air atmosphere for 1.5h to obtain the material obtained by calcining barium ferrite in pure air.
[ test 1 ]
Magnetic property test of material
The barium ferrite materials obtained in the different sintering atmospheres in comparative examples 1-2 were subjected to magnetic property tests, and the results are shown in FIG. 3, where FIG. 3 is a hysteresis chart of pure barium ferrite obtained in different sintering atmospheres. The test result shows that the barium ferrite obtained by calcining in the pure air atmosphere has sufficient oxygen sources, so that a large amount of barium ferrite can be obtained, and after high-temperature calcination, the crystal form is complete, and the barium ferrite shows larger magnetic saturation strength and coercive force. Calcination in a nitrogen atmosphere makes it difficult to efficiently form barium ferrite, resulting in almost zero magnetic saturation strength and coercive force. The barium ferrite is formed by calcining in air firstly and then calcined in nitrogen atmosphere to ensure that the crystal form of the barium ferrite is complete, and the obtained barium ferrite has similar magnetic performance to the barium ferrite calcined in air atmosphere.
The barium ferrite magnetic composite materials added with carbon nanotubes in different proportions prepared in the above examples and comparative examples were subjected to magnetic property tests, and the results are shown in fig. 4. FIG. 4 is a magnetic hysteresis curve diagram of the composite material under different carbon nanotube addition amounts, and BF, BF/C0.5, BF/C1 and BF/C2 are doped carbon nanotube/barium ferrite magnetic composite materials corresponding to carbon nanotube addition amounts of 0 wt%, 0.5 wt%, 1 wt% and 2 wt%, respectively.
It can be seen from fig. 4 that with the increase of the content of the non-magnetic carbon nanotubes, the coercive force of the composite material is gradually reduced, and the magnetic saturation strength is increased compared with that of the pure barium ferrite, which may be caused by the fact that when the barium ferrite is calcined at a high temperature, the carbon nanotubes affect the crystal morphology of the barium ferrite, resulting in an enhanced anisotropic field on the surface of the material.
FIG. 5 shows the wave-absorbing properties of the material calcined under pure nitrogen. FIG. 6 shows the wave-absorbing properties of the material obtained by calcining barium ferrite in pure air. FIG. 7 shows the wave-absorbing properties of the material obtained by calcining barium ferrite with air and then nitrogen. The maximum wave-absorbing intensity of the material calcined under the pure nitrogen of the barium ferrite is-9.6 dB, and the maximum wave-absorbing intensity of the material calcined under the pure air of the barium ferrite is-11.7 dB. The test results show that the wave absorbing performance of the material obtained by calcining in pure air and the material obtained by calcining in air and then in nitrogen is higher than that of barium ferrite obtained in pure nitrogen atmosphere, and the wave absorbing strength of the material obtained by calcining in air and then in nitrogen can reach-14.46 dB to the maximum.
[ example 5 ]
Preparation of carbon nano tube/barium ferrite magnetic composite material
Referring to the process scheme of example 4, a certain amount of barium nitrate (Ba (NO) is added first3)2) Iron nitrate (Fe (NO)3)3·9H2O), citric acid (C)6H8O7·H2O) dissolving with water, controlling Ba2+、Fe3+And citric acid in a molar ratio of 1.0:12.0: 15. adding a certain amount of carbon nano tube (5%, 10%, 20%) into barium ferrite precursor aqueous solution under stirring, performing ultrasonic treatment for 30min, and then dropwise adding ammonia water (NH)3·H2O), adjusting the pH of the solution to 7.Then, the reaction was stirred at a constant temperature of 80 ℃ for 5 hours to form a wet gel. Drying the obtained wet gel at 160 ℃ for 12h to obtain gray dry gel, and igniting the dry gel in the air to enable the dry gel to generate self-propagating combustion reaction to obtain fluffy coral-shaped black-brown powder. Calcining the black-brown powder at 500 ℃ for 1h in an air atmosphere, then introducing argon inert gas, calcining at 800 ℃ for 0.5h, keeping introducing the argon inert gas atmosphere, and naturally cooling to room temperature to obtain the carbon nano tube/barium ferrite magnetic composite material.
According to the experimental results of the above examples, the performance influence of the obtained carbon nanotube/barium ferrite magnetic composite material under different carbon nanotube addition amounts is further compared.
[ test 2 ]
Test of wave-absorbing Property
The barium ferrite materials with different sintering modes are subjected to wave-absorbing property testing, the preparation method of the wave-absorbing property testing sample is that the obtained carbon nano tube/barium ferrite magnetic composite material is mixed with polyethylene paraffin according to the weight ratio of 7:3, the mixture is pressed into a circular ring with the inner diameter of 3mm and the outer diameter of 7mm, and the wave-absorbing property of the composite material is obtained through a vector network analyzer. The results are shown in the following table.
TABLE 1 addition amount and maximum wave-absorbing property of carbon nanotubes
Through comparative analysis of different addition amounts of the carbon nanotubes, the fact that the more carbon nanotubes are added and applied is better, and the wave absorbing performance of the composite material is reduced due to the fact that the carbon nanotube content is too high.
The test results show that the carbon nanotube/barium ferrite composite material can be obtained under the condition that the carbon tube is not decomposed by calcining the carbon tube and the precursor composite under the air atmosphere of 500 ℃, and then nitrogen is introduced to raise the temperature under the condition that the carbon tube is not decomposed, so that the ferrite crystal form is complete, and the carbon nanotube/barium ferrite magnetic composite material is obtained. The wave-absorbing performance result shows that the wave-absorbing performance of the barium ferrite can be effectively improved by adding the carbon tube, wherein the maximum wave-absorbing strength can reach-43.9 dB when the addition amount of the carbon tube is 2 wt%. With the increase of the content of the carbon tube, the maximum wave-absorbing performance of the carbon tube is reduced, because the addition of excessive carbon tubes inevitably leads to the improvement of the conductivity of the carbon tube, the impedance matching performance of the carbon tube is poor, and the wave-absorbing performance of the carbon tube is reduced.
[ COMPARATIVE EXAMPLE 3 ]
Carbon nanotube addition at different times (ball milling method for adding carbon nanotubes)
For comparison, the two are compounded by adopting the current literature report and the common ball milling process. The method specifically comprises the following steps: barium ferrite powder was prepared in the same manner as in comparative example 1, and then added to a ball mill together with 0.07g of carbon nanotubes, and ball-milled for 12 hours using ethanol as a medium, followed by uniform mixing. The resulting material was dried at 80 ℃ for 4 hours to obtain a barium ferrite magnetic composite material doped with carbon nanotubes (comparative example 3).
Compared with the embodiment, the embodiment has the advantages that the carbon nanotubes are dispersed in the precursor solution, so that the dispersibility is better, and the corresponding composite material has better wave-absorbing performance. The minimum reflectivity of the magnetic composite material obtained in the comparative example 3 reaches-13.7 dB, and the effective bandwidth with the reflectivity less than-10 dB is 2.7 GHz.
[ example 6 ]
Preparation of carbon nano tube/barium ferrite magnetic composite material
A certain amount of Ba (NO)3)2、Fe(NO3)3·9H2O、C6H8O7·H2Dissolving O in water, sequentially adding into aqueous solution containing citric acid, and controlling Ba2+、Fe3+And citric acid in a molar ratio of 1.0:12.0: 15. Under the stirring state, to itAdding 2 wt.% of carbon nano tube, performing ultrasonic treatment for 30min, and then dropwise adding NH into the mixture3·H2O, adjusting the pH of the solution to 7. Then, the reaction was stirred at a constant temperature of 80 ℃ for 5 hours to form a wet gel. The wet gel is dried for 12h at 160 ℃ to obtain gray xerogel, and then the gray xerogel is ignited in the air to carry out self-propagating combustion reaction to obtain fluffy coral-shaped black-brown powder. Finally, the black-brown powder is calcined under the specific calcining conditions shown in table 2, so as to obtain the carbon nano tube/barium ferrite magnetic composite material.
Comparing different calcining modes, the method for testing the performance influence of the carbon nano tube/barium ferrite magnetic composite material is tested according to the wave-absorbing performance test method recorded in the test 2, and the calcining process control and wave-absorbing performance test results of the composite material obtained by calcining are shown in the following table.
TABLE 2 final calcination conditions and wave-absorbing Properties of the composite materials
| Numbering | First stage calcination | Second stage calcination | Wave absorbing property |
| 601 | Air atmosphere at 550 ℃ for 1h | 0.5h nitrogen atmosphere at 800 DEG C | -17.9dB |
| 602 | Air atmosphere at 500 ℃ for 1h | 0.5h nitrogen atmosphere at 800 DEG C | -43.9dB |
| 603 | Air atmosphere at 400 ℃ for 1h | 0.5h nitrogen atmosphere at 800 DEG C | -16.8dB |
| 604 | Air atmosphere at 500 ℃ for 1h | Nitrogen atmosphere at 700 ℃ for 0.5h | -23.6dB |
| 605 | Air atmosphere at 500 ℃ for 1h | 0.5h nitrogen atmosphere at 750 DEG C | -33.4dB |
| 606 | Air atmosphere at 500 ℃ for 1h | Nitrogen atmosphere at 850 ℃ for 0.5h | -32.6dB |
Through comparative analysis of the calcination process of the carbon nano tube, the calcination process is carried out in air at 500 ℃, then the calcination process is protected by nitrogen, the crystal form is controlled, the carbon nano tube is protected from being burnt and ablated, the performance improvement of the carbon nano tube/barium ferrite magnetic composite material can be better realized, and the modification effect of the carbon nano tube is exerted to the greatest extent.
Preferably, the first-stage calcination temperature is 480-520 ℃, 520 ℃ is the temperature at which the carbon nanotubes are oxidatively decomposed in an air atmosphere, the temperature is controlled not to exceed this temperature, and then the first-stage calcination is advantageously performed at a high temperature close to 500 ℃ in the test.
Preferably, the second-stage calcination temperature is 780-820 ℃, and the experimental result shows that the wave-absorbing property is better when the second-stage calcination temperature is about 800 ℃.
[ example 7 ]
Magnetic composite material preparation was carried out in the same process as in example 3 except that the pH was adjusted using sodium hydroxide solution in step 1 to prepare a barium ferrite precursor for obtaining gel. The remaining preparation process steps were as in example 3.
And (3) testing the wave-absorbing property of the obtained barium ferrite composite material, wherein the wave-absorbing property is-40.7 dB.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.
Claims (9)
1. A method for preparing carbon nanotube/barium ferrite magnetic composite powder is characterized in that in the composite powder, carbon nanotubes form a conductive network, and barium ferrite particles form a coating layer;
the composite powder is prepared by the following method:
(1) preparing barium ferrite precursor solution;
(2) adding carbon nano tubes for dispersion, adjusting pH, and reacting to obtain wet gel;
(3) drying the obtained wet gel to obtain dry gel;
igniting the xerogel, and performing self-propagating combustion to obtain a compound containing the carbon nano tube;
(4) calcining the compound containing the carbon nano tube to obtain carbon nano tube/barium ferrite magnetic composite powder;
the calcination is divided into two stages: a first stage calcination and a second stage calcination;
the first stage calcination is calcination under an oxidizing atmosphere;
the second stage of calcination is calcination under an inert atmosphere.
2. The method for preparing carbon nanotube/barium ferrite magnetic composite powder according to claim 1, wherein the weight ratio of carbon nanotubes in the carbon nanotube/barium ferrite magnetic composite powder is 0.1-10%.
3. The method for preparing carbon nanotube/barium ferrite magnetic composite powder according to claim 2, wherein the weight ratio of the carbon nanotubes is 0.1-5%.
4. The method for preparing carbon nanotube/barium ferrite magnetic composite powder according to claim 1, wherein in the step (1), the barium ferrite precursor solution is prepared by using soluble barium salt, soluble ferric salt and citric acid in water.
5. The method for preparing carbon nanotube/barium ferrite magnetic composite powder according to claim 1, wherein in the step (2), the carbon nanotube is added to the barium ferrite precursor solution, the pH is adjusted to 6-8, the solution is heated to 50-90 ℃, and the wet gel is formed by stirring.
6. The method for preparing carbon nanotube/barium ferrite magnetic composite powder according to claim 5, wherein ammonia is added dropwise to adjust pH.
7. The method for preparing carbon nanotube/barium ferrite magnetic composite powder according to claim 1, wherein the weight of the added carbon nanotube is 1-10% of the weight of the barium ferrite corresponding to the barium ferrite precursor.
8. The method for preparing the carbon nanotube/barium ferrite magnetic composite powder according to claim 1, wherein in the step (4);
the first-stage calcination is calcination in an oxidizing atmosphere, and the calcination temperature is 300-520 ℃;
the second-stage calcination is carried out in an inert atmosphere, and the calcination temperature is 750-900 ℃.
9. The method for preparing carbon nanotube/barium ferrite magnetic composite powder according to claim 8, wherein after the second stage of calcination is completed, the carbon nanotube/barium ferrite magnetic composite powder is obtained by cooling to room temperature under an inert atmosphere.
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