CN112029130B - Natural sedimentation gradient composite wave-absorbing material and preparation method thereof - Google Patents

Natural sedimentation gradient composite wave-absorbing material and preparation method thereof Download PDF

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CN112029130B
CN112029130B CN202010856008.3A CN202010856008A CN112029130B CN 112029130 B CN112029130 B CN 112029130B CN 202010856008 A CN202010856008 A CN 202010856008A CN 112029130 B CN112029130 B CN 112029130B
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absorbing material
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composite wave
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周佩珩
刘成琪
蒋文颖
陈海燕
梁廸飞
李小秋
周志鹏
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University of Electronic Science and Technology of China
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Abstract

The invention belongs to the technical field of electronic materials, and particularly relates to a naturally-settling gradient composite wave-absorbing material and a preparation method thereof. The invention realizes the effect of natural sedimentation and layering in the emulsion by utilizing the different sedimentation rates of different absorbents in the emulsion according to the Stokes formula; selecting a Waterborne Polyurethane (WPU) emulsion as a matrix, and realizing the effect of natural sedimentation film formation by utilizing the characteristics of stable shrinkage rate, moderate bulk phase viscosity and good temperature stability; the transition layer formed by natural sedimentation reduces the reflection of electromagnetic waves caused by interface jump. Compared with manual lamination, the invention effectively improves the low-frequency absorption performance, widens the absorption bandwidth, greatly reduces the complexity of the preparation of the multilayer wave-absorbing material and has certain reference significance for the design of the subsequent gradient composite wave-absorbing structure while not influencing the high-frequency absorption performance.

Description

Natural sedimentation gradient composite wave-absorbing material and preparation method thereof
Technical Field
The invention relates to the technical field of electronic materials, relates to the field of microwave composite wave-absorbing materials, and particularly relates to a naturally-settling gradient composite wave-absorbing material and a preparation method thereof.
Background
The wave-absorbing material is widely applied to solving the problem of electromagnetic interference in military use and civil use. According to different construction modes, the composite wave-absorbing material can be divided into a structural wave-absorbing material and a coating wave-absorbing material. Compared with the coating type wave-absorbing material, the structural wave-absorbing material has the characteristics of long service cycle, multiple material types and wide wave-absorbing frequency band, and is widely used.
The structural composite wave-absorbing material combines a plurality of absorbents with nonmetal-based structural materials, so that the wave-absorbing material has good wave-absorbing performance. The structural wave-absorbing material can be divided into an electric loss wave-absorbing material and a magnetic loss wave-absorbing material according to the difference of the absorption agent on the loss mechanism and the loss capacity of electromagnetic waves. The electric loss type wave absorbing material mainly absorbs electric field energy in electromagnetic waves through effects of interface polarization, electronic polarization and the like, and can be subdivided into a resistance loss type and a dielectric loss type. The magnetic loss type wave-absorbing material mainly absorbs electromagnetic waves through magnetic hysteresis loss and eddy current loss.
Compared with the uniform wave-absorbing material consisting of a single absorbent, the gradient composite wave-absorbing material has the advantages of good absorption performance, high parameter adjustability, strong material replaceability and the like, so that the gradient composite wave-absorbing material is widely researched. According to different gradients and material selection, the gradient composite wave-absorbing material can realize the effects of widening an absorption frequency band and increasing absorption points. However, most of the existing gradient wave-absorbing materials are prepared by a lamination method, namely a method of preparing one layer by one layer and then accumulating the layers in sequence. This method not only has a long time period and is complicated to operate, but also may generate a significant gradient interface, resulting in cracking at the gradient interface or interference of electromagnetic absorption due to impedance jump.
Disclosure of Invention
Aiming at the problems or the defects, the invention provides a naturally-settled gradient composite wave-absorbing material and a preparation method thereof, aiming at solving the problems that the existing multilayer wave-absorbing material has complex preparation process and is easy to generate a gradient interface.
In order to achieve the purpose, the technical scheme provided by the invention is as follows:
a gradient composite wave-absorbing material for natural sedimentation sequentially comprises the following components: the bottom iron silicon aluminum reflection layer, the iron silicon aluminum-carbon nanofiber transition layer, the middle carbon nanofiber loss layer, the iron silicon aluminum-carbon nanofiber transition layer and the top carbon black wave-transparent layer are prepared by a natural sedimentation method by taking polyurethane as a matrix.
The preparation method comprises the following steps:
step 1, mixing different fillers: calculating according to the density of the selected material and the content of each component of the composite material to be prepared, weighing, and weighing the ferrosilicon aluminum powder, the carbon nanofiber and the carbon black; then adding the material components into polyurethane emulsion (matrix) with the solid content range of 30-40% to prepare the emulsion.
Step 2, improving the surface tension of the emulsion: adding a film-forming aid with the matrix mass fraction range of 1% -3% and SDBS (sodium dodecyl benzene sulfonate) with the matrix mass fraction range of 0.5% -3% into the emulsion obtained in the step 1, wherein the matrix mass fraction is 0.1% of a defoaming agent; and then fully dispersing the obtained mixed emulsion (for example, manually stirring for 1-2min, and then mechanically stirring for 30min at the rotating speed of 500 r/min).
And 3, placing the mixed emulsion fully dispersed and uniformly mixed in the step 2 into a PVC mould for tape casting, standing at normal temperature, and taking out from the mould after the mixed emulsion naturally settles until the polyurethane-based compound is solidified, thus obtaining the required gradient composite wave-absorbing material.
The invention relates to the relationship between the descending speed of particles in emulsion and the particle density according to the Stokes formula:
Figure BDA0002646375910000021
where D is the particle diameter, ppIs the particle density, plη is the emulsion density and η is the emulsion viscosity. From the above formula, it is understood that the more dense particles fall down in the emulsion at a faster rate. Common magnetic loss type wave-absorbing materials such as alloy,The density of the ferrite is usually larger than that of the carbon-series electric loss type wave-absorbing material, so that a basis is provided for realizing a multilayer structure by natural sedimentation.
Compared with the prior art, the technical scheme of the invention has the advantages that: (1) common electric loss type wave absorbing agent carbon black and carbon nano fiber are selected, common magnetic loss type wave absorbing agent iron-silicon-aluminum alloy is selected, the density difference is ingeniously utilized, and natural sedimentation layering of the three wave absorbing agents in a polyurethane matrix is realized according to a Stokes formula in a solution; (2) the Water Polyurethane (WPU) is selected as a matrix, and the characteristic of stable shrinkage rate of the matrix is utilized, so that different absorbent components have sufficient settling time, and a stable gradient composite wave-absorbing material can be formed. The excessive viscosity of the emulsion liquid phase can cause excessive sedimentation resistance to be unfavorable for sedimentation, and the moderate bulk phase viscosity of the WPU is more favorable for the aggregation stability of the emulsion. In addition, the temperature has influence on intermolecular thermal motion, surface tension and liquid phase air pressure, so that the influence on the sedimentation of the emulsion is obvious. Compared with other materials, the WPU has high crosslinking density, high hardness after film forming and good thermal stability, and is more favorable for a natural sedimentation method which needs a long time to resist temperature change. (3) The simple natural sedimentation method is used, and the complexity of the preparation of the multi-layer wave-absorbing material is greatly reduced.
Drawings
FIG. 1 is a schematic sectional view of a naturally settled gradient composite wave-absorbing material according to an embodiment.
Fig. 2(a) is an initial state when three absorbents are added, fig. 2(b) is a state in which the three absorbents naturally settle, and fig. 2(c) is a layered state after natural settling.
FIG. 3 is a comparison graph of the wave-absorbing performance test results of the embodiment and the manual laminated wave-absorbing material.
Reference numerals: 1-a bottom layer Fe-Si-Al reflecting layer, 2-Fe-Si-Al-C nanofiber transition layer, 3-C nanofiber loss layer, 4-C nanofiber-carbon black transition layer and 5-carbon black wave-transmitting layer.
Detailed Description
The invention is further described below with reference to the accompanying drawings and the examples given. It is to be understood that the described embodiments are merely a few embodiments of the invention, and not all embodiments. All other embodiments, which can be obtained by a person skilled in the art without making creative efforts based on the embodiments of the present invention, belong to the protection scope of the present invention.
The invention aims to naturally settle and stratify Fe-Si-Al and other magnetic loss absorbents with larger density difference and carbon series electric loss absorbents in a matrix by a natural settling method, thereby obtaining a gradient composite wave-absorbing material with multiple wave-absorbing mechanisms and good wave-absorbing performance and improving the preparation complexity of a multi-layer wave-absorbing material.
As shown in figure 1, the main wave-absorbing layer of the invention is respectively a layer 1-a bottom layer Fe-Si-Al reflecting layer, a layer 3-a carbon nanofiber loss layer and a layer 5-a carbon black wave-transmitting layer. By a natural sedimentation method, a mixed transition layer, namely a layer 2-sendust-carbon nanofiber transition layer and a layer 4-carbon nanofiber-carbon black transition layer, is formed on the interface of different absorbent functional layers. The formation of the transition layers reduces the phenomenon that the electromagnetic waves cannot be transmitted due to abrupt change of components.
As shown in FIG. 2, the three absorbents floated on the surface of the emulsion in the initial state of the emulsion. With the addition of the film forming assistant, the dispersant and the defoaming agent, the three absorbents are gradually dispersed along with the change of the surface tension of the emulsion, and a naturally settled layered structure is formed after a sufficient period of time.
As shown in FIG. 3, the reflection loss of the present embodiment is less than-10 dB (absorption rate is greater than 90%) in 5-6GHz and 7.5-9GHz, and less than-20 dB (absorption rate is greater than 99%) in 6-7.5 GHz; compared with manual lamination, the wave-absorbing effect is improved at high frequency (12-18GHz), the wave-absorbing bandwidth is widened, and the advantage of natural sedimentation is displayed.
Without limitation, the bottom magnetic loss reflective layer of the present invention may be a high-density magnetic loss type material such as NiZn ferrite, and the carbon-based electrical loss wave-absorbing material may be a low-density electrical loss type wave-absorbing material such as graphene, which should be understood by those skilled in the art. The thickness of the layers of the present invention will vary depending on the mass of absorbent added, as will be appreciated by those skilled in the art.
The above description of the embodiments is only intended to facilitate the understanding of the method and core idea of the present invention; while the invention has been described with reference to specific embodiments and examples, the invention is not limited thereto.

Claims (3)

1. A gradient composite wave-absorbing material for natural sedimentation is characterized in that:
from supreme including in proper order down: the bottom iron silicon aluminum reflection layer, the iron silicon aluminum-carbon nanofiber transition layer, the middle carbon nanofiber loss layer, the carbon nanofiber-carbon black transition layer and the top carbon black wave-transparent layer are prepared by a natural sedimentation method by taking polyurethane as a matrix.
2. The preparation method of the naturally-settling gradient composite wave-absorbing material as claimed in claim 1, comprising the following steps:
step 1, mixing different fillers: calculating according to the density of the selected material and the content of each component of the composite material to be prepared, weighing, and weighing the ferrosilicon aluminum powder, the carbon nanofiber and the carbon black; then adding the material components into a polyurethane emulsion matrix with the solid content ranging from 30% to 40% to prepare emulsion;
step 2, improving the surface tension of the emulsion: adding 1-3% of film-forming additive and 0.5-3% of SDBS sodium dodecyl benzene sulfonate into the emulsion obtained in the step 1, wherein the mass fraction of the matrix is 0.1% of defoaming agent; then fully dispersing the obtained mixed emulsion;
and 3, placing the mixed emulsion fully dispersed and uniformly mixed in the step 2 into a PVC mould for tape casting, standing at normal temperature, and taking out from the mould after the mixed emulsion naturally settles until the polyurethane-based compound is solidified, thus obtaining the required gradient composite wave-absorbing material.
3. The method for preparing the naturally-settling gradient composite wave-absorbing material as claimed in claim 2, wherein the method comprises the following steps: and 2, fully dispersing the mixed emulsion in the step 2, manually stirring for 1-2min, and mechanically stirring at a rotating speed of 500r/min for 30 min.
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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN102020899A (en) * 2010-11-26 2011-04-20 中国人民解放军第三军医大学 Composite coating electromagnetic shielding paint and composite coating electromagnetic shielding material prepared therefrom
CN103725000A (en) * 2013-12-26 2014-04-16 北京工商大学 High-temperature polymer-based electromagnetic shielding functionally gradient material
CN106739321A (en) * 2016-11-30 2017-05-31 航天科工武汉磁电有限责任公司 A kind of structural wave-absorbing material and preparation method thereof
CN108192325A (en) * 2017-12-22 2018-06-22 中北大学 Low reflection height shielding electromagnetic shielding composite material and its preparation with gradient-structure

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN102020899A (en) * 2010-11-26 2011-04-20 中国人民解放军第三军医大学 Composite coating electromagnetic shielding paint and composite coating electromagnetic shielding material prepared therefrom
CN103725000A (en) * 2013-12-26 2014-04-16 北京工商大学 High-temperature polymer-based electromagnetic shielding functionally gradient material
CN106739321A (en) * 2016-11-30 2017-05-31 航天科工武汉磁电有限责任公司 A kind of structural wave-absorbing material and preparation method thereof
CN108192325A (en) * 2017-12-22 2018-06-22 中北大学 Low reflection height shielding electromagnetic shielding composite material and its preparation with gradient-structure

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
Prediction of Microwave Absorption Behavior of Grading Honeycomb Composites Based on Effective Permittivity Formulas;Peiheng Zhou等;《IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION》;20150831;第63卷(第8期);第3496-3501页 *

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