CN114621612B - Preparation method of CNT/SiCNWs composite wave-absorbing material modified by in-situ grown carbon nano tube - Google Patents

Abstract

The invention relates to a preparation method of an in-situ grown carbon nanotube modified CNT/SiCNWs composite wave-absorbing material. Co (CH) ₃ COO) ₂ ·4H ₂ O is dissolved in deionized water to prepare a cobalt acetate solution, polyvinyl butyral and SiCNWs are mixed and then added into the cobalt acetate solution to be uniformly mixed to obtain a mixed solution A; and (3) stirring the mixed solution A at the temperature of 80-100 ℃ for reaction for 24-28 hours, carrying out solid-liquid separation, and placing the solid in a nitrogen atmosphere at the temperature of 600-1000 ℃ for reaction for 2-4 hours to obtain the CNT/SiCNWs composite material modified by the in-situ grown carbon nano tube. In the invention, in-situ growth CNT/SiCNWs is obtained through PVB pyrolysis and annealing treatment under the cobalt acetate catalyst, which is favorable for constructing a uniform 3D conductive network and has better EM wave absorption.

Description

A preparation method of CNT/SiCNWs composite absorbing material modified by in-situ growth of carbon nanotubes

technical field

The invention relates to an electromagnetic wave absorbing material, in particular to a preparation method of a CNT/SiCNWs composite wave absorbing material modified by growing carbon nanotubes in situ.

Background technique

The rapid application of smart home, industrial Internet of Things, and smart city systems has led to the rapid development of wireless communication technology, causing inevitable electromagnetic (EM) wave pollution. Microwave absorbing materials can be used to solve the problem of electromagnetic pollution that seriously threatens human health. Generally, electromagnetic wave absorption requires dielectric loss and magnetic loss. Although high-density ferromagnetic materials exhibit good microwave absorption and impedance matching properties, their magnetic loss performance decreases when the temperature of the material exceeds the Curie temperature. In contrast, CNTs and SiCNWs with low density, high temperature resistance, and one-dimensional (1D) structure have attracted much attention as electromagnetic wave absorbing materials. Carbon nanotubes have excellent electrical conductivity and are usually mixed with insulating substrates such as paraffin and resin to prepare electromagnetic wave absorbing materials. In addition, carbon nanotubes form a three-dimensional (3D) conductive network in the matrix, which can enhance electromagnetic wave absorption performance. However, an excessively high filling ratio of carbon nanotubes in an insulating matrix can lead to severe impedance matching, thereby deteriorating electromagnetic wave absorption. SiCNW is a one-dimensional semiconductor material with a large specific surface area and many defects. However, the electrical conductivity of SiCNW is low, and for electromagnetic wave absorption, a large number of silicon carbide nanowires are required, and the material density and weight of the absorbing material are increased, so that it cannot meet the requirements of new absorbing materials. Due to the low electrical conductivity of SiCNW, the conduction loss of EM waves within the material is almost impossible to achieve, and effective absorption cannot be achieved only through polarization loss. Therefore, enhancing the electromagnetic wave absorption of electronic nanotubes remains challenging.

Contents of the invention

The present invention aims at the problems existing in the existing wave-absorbing materials, and provides a preparation method of CNT/SiCNWs composite wave-absorbing materials modified by in-situ growth of carbon nanotubes, that is, through polyvinyl butyral (PVB) thermal Solution, grow CNTs in situ on SiCNWs to form CNT/SiCNWs composite materials, so that CNTs and SiCNWs form a complex network structure, improve conduction and polarization loss, thereby enhancing electromagnetic wave absorption performance; and adjust the composite by controlling the ratio of CNTs and SiCNWs The conductivity of the material for the best impedance match.

A method for preparing a CNT/SiCNWs composite wave-absorbing material modified by in-situ growth of carbon nanotubes, the specific steps are as follows:

(1) Co(CH ₃ COO) ₂ ·4H ₂ O was dissolved in deionized water to prepare cobalt acetate solution, polyvinyl butyral and SiCNWs were mixed, then added to the cobalt acetate solution and mixed uniformly to obtain mixed solution A;

(2) At a temperature of 80-100°C, the mixed solution A is stirred and reacted for 24-28 hours, the solid and liquid are separated, and the solid is placed at a temperature of 600-1000°C and annealed in a nitrogen atmosphere for 2-4 hours to obtain carbon nanotubes grown in situ Modified CNT/SiCNWs composites.

The concentration of the cobalt acetate solution in the step (1) is 1-1.4wt.%.

In the step (1), the molar ratio of polyvinyl butyral to SiCNWs is 1:1-1:1.5.

The beneficial effects of the present invention are:

(1) In the present invention, under the cobalt acetate catalyst, polyvinyl butyral (PVB) is pyrolyzed, CNTs are grown in situ on SiCNWs to form a CNT/SiCNWs composite material, and the SiCNWs composite material modified by carbon nanotubes is constructed into a uniform The 3D conductive network structure significantly improves the dielectric properties and conduction loss of the composite material;

(2) The CNT/SiCNWs composite material of the present invention has excellent electromagnetic wave absorption, excellent impedance and rich attenuation properties, and can be used to prepare environmental barrier coatings used at temperatures up to 1500 ° C;

(3) The 3D conductive network possessed by the CNT/SiCNWs composite material of the present invention exhibits extremely low RCmin in the entire X-band;

(4) The method of the present invention has a simple and convenient operation process, is easy to implement, and is suitable for large-scale industrial production and application.

Description of drawings

Fig. 1 is the SEM figure of the CNT/SiCNWs composite material prepared by different annealing temperatures of embodiment 1;

Fig. 2 is the Raman spectrogram of the CNT/SiCNWs composite material prepared by different annealing temperatures in Example 1;

Fig. 3 is the TEM picture of the CNT/SiCNWs composite material that the annealing temperature of embodiment 1 is 80 ℃;

Fig. 4 is the complex dielectric constant diagram of the CNT/SiCNWs composite material prepared by different annealing temperatures in Example 1;

FIG. 5 is a diagram of the microwave absorption performance of the CNT/SiCNWs composite material prepared at different annealing temperatures in Example 1. FIG.

Detailed ways

The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

Example 1: A method for preparing a CNT/SiCNWs composite absorbing material modified by in-situ growth of carbon nanotubes, the specific steps are as follows:

(1) Co(CH ₃ COO) ₂ ·4H ₂ O was dissolved in deionized water to prepare cobalt acetate solution, polyvinyl butyral and SiCNWs were mixed, then added to the cobalt acetate solution and mixed uniformly to obtain mixed solution A; The concentration of cobalt acetate solution is 1wt.%, and the molar ratio of polyvinyl butyral to SiCNWs is 1:1;

(2) At a temperature of 80°C, the mixed solution A was stirred and reacted for 24 hours, and the solid and liquid were separated. In a nitrogen atmosphere, the solids were placed at temperatures of 600 (T1), 700 (T2), 800 (T3), and 900 (T4) and annealing at 1000°C (T5) for 2 hours to obtain in-situ grown carbon nanotube-modified CNT/SiCNWs composites;

The CNT/SiCNWs composite exhibits a small amount of one-dimensional nanophase and small carbon spheres, and the carbon nanotube-modified SiCNWs increases the nano-heterointerface, which is beneficial to the interface polarization loss; in carbon nanotubes, amorphous carbon and silicon carbide nanowires The defects increase the dipole polarization under the external alternating electromagnetic field; these combined effects make it have better electromagnetic wave absorption performance;

The SEM images of CNT/SiCNWs composites prepared at different annealing temperatures are shown in Figure 1. When the annealing temperature is 600°C (T1), there are only one-dimensional nanophases and small carbon spheres of SiCNWs; when the annealing temperature is 700°C (T2), SiCNWs A small amount of CNTs were grown in situ; when the annealing temperature was 800°C (T3), a large number of CNTs were grown in situ on SiCNWs; when the annealing temperature was increased to 900°C (T4), a large number of CNTs were grown in situ on SiCNWs CNTs, and formed a 3D conductive network; when the annealing temperature increased to 1000 °C (T5), the CNTs were significantly reduced due to the deactivation of the Co catalyst at 1000 °C;

The Raman spectra of CNT/SiCNWs composites at different temperatures are shown in Figure 2. When the annealing temperature is 600 °C, the I _D /I _G value is 0.68 (T1), and with the increase of the annealing temperature, the value (I _D /I _G ) increases first and then decreases. When the annealing temperature is 900°C, the I _D /I _G reaches the maximum value of 1.18. At this temperature, the amorphous carbon forms the most and the defect content is the most. The disordered C has dangling bonds and abundant Defects are conducive to interface scattering and polarization, and disordered C is conducive to the formation of 3D conductive network, which is conducive to conduction loss and energy dissipation, and can effectively attenuate incident EM waves; CNT/SiCNWs composite (T4 sample) has a high Defect density and low degree of graphitization;

The TEM image of the CNT/SiCNWs composite prepared at an annealing temperature of 80 °C is shown in Figure 3. CNTs and SiCNWs of different diameters are intertwined with each other. The CNTs only contain carbon and have a hollow structure with a tube wall, which is a typical CNT structure.

The complex permittivity diagrams of CNT/SiCNWs composites prepared at different annealing temperatures are shown in Figure 4, (a) and (b) respectively show the frequency dependence of CNT/SiCNWs composites in the range of 8.2-12.4GHz. Panel (a) shows an increase with increasing temperature, while first increasing and then decreasing with increasing temperature. The T1 sample has an average of 3, while the T5 sample has an average of 6.8. The enhancement of shows that the enhanced electrical energy storage is the result of increasing the crystallinity of amorphous carbon at high temperature. The average value (T1) increased from 0.2 to 2.6 (T4), as shown in panel (b). The decomposition of PVB produces amorphous carbon, which is absorbed by the Co catalyst to grow CNTs through the VSL mechanism. Amorphous carbon and CNTs provide further defects leading to dipolar polarization of the EM wave absorption mechanism. In addition, the carbon nanotube-decorated SiC nanowires form a 3D conductive network, which is beneficial for the multiple reflection and scattering of electromagnetic waves.

The complex permittivity diagrams of CNT/SiCNWs composites prepared at different annealing temperatures are shown in Fig. 5, and Fig. 5 shows the RC curves of frequencies at different annealing temperatures. When the annealing temperature is 600 °C, the T1 sample shows poor microwave absorption performance. As the annealing temperature increases, RC decreases gradually. When the temperature is 900°C, the minimum RC (RCmin) of the T4 sample is -35dB at 9.8GHz, and the EAB is 4.2GHz.

Example 2: A method for preparing a CNT/SiCNWs composite absorbing material modified by in-situ growth of carbon nanotubes, the specific steps are as follows:

(1) Co(CH ₃ COO) ₂ ·4H ₂ O was dissolved in deionized water to prepare cobalt acetate solution, polyvinyl butyral and SiCNWs were mixed, then added to the cobalt acetate solution and mixed uniformly to obtain mixed solution A; The concentration of cobalt acetate solution is 1.2wt.%, and the molar ratio of polyvinyl butyral to SiCNWs is 1:1.3;

(2) At a temperature of 90°C, the mixed solution A was stirred and reacted for 26 hours, the solid and liquid were separated, and the solid was annealed at a temperature of 800°C in a nitrogen atmosphere for 3 hours to obtain a CNT/SiCNWs composite material modified by in-situ growth of carbon nanotubes;

The CNT/SiCNWs composite exhibits a small amount of one-dimensional nanophase and small carbon spheres, and the carbon nanotube-modified SiCNWs increases the nano-heterointerface, which is beneficial to the interface polarization loss; in carbon nanotubes, amorphous carbon and silicon carbide nanowires The defects increase the dipole polarization under the external alternating electromagnetic field; these combined effects make it have more excellent electromagnetic wave absorption performance.

Example 3: A method for preparing a CNT/SiCNWs composite absorbing material modified by in-situ growth of carbon nanotubes, the specific steps are as follows:

(1) Co(CH ₃ COO) ₂ ·4H ₂ O was dissolved in deionized water to prepare cobalt acetate solution, polyvinyl butyral and SiCNWs were mixed, then added to the cobalt acetate solution and mixed uniformly to obtain mixed solution A; The concentration of cobalt acetate solution is 1.4wt.%, and the molar ratio of polyvinyl butyral to SiCNWs is 1:1.5;

(2) At a temperature of 100°C, the mixed solution A was stirred and reacted for 28 hours, the solid and liquid were separated, and the solid was annealed at a temperature of 1000°C in a nitrogen atmosphere for 4 hours to obtain a CNT/SiCNWs composite material modified by in-situ growth of carbon nanotubes;

The CNT/SiCNWs composite exhibits a small amount of one-dimensional nanophase and small carbon spheres, and the carbon nanotube-modified SiCNWs increases the nano-heterointerface, which is beneficial to the interface polarization loss; in carbon nanotubes, amorphous carbon and silicon carbide nanowires The defects increase the dipole polarization under the external alternating electromagnetic field; these combined effects make it have more excellent electromagnetic wave absorption performance.

The specific embodiments of the present invention have been described in detail above, but the present invention is not limited to the above embodiments, and various changes can be made without departing from the gist of the present invention within the scope of knowledge possessed by those of ordinary skill in the art .

Claims (2)

1. A method for preparing a CNT/SiCNWs composite wave-absorbing material modified by growing carbon nanotubes in situ, characterized in that, the specific steps are as follows: (1) Dissolve Co(CH ₃ COO) ₂ ·4H ₂ O in deionized water to prepare a cobalt acetate solution, mix polyvinyl butyral and SiCNWs, add them to the cobalt acetate solution and mix evenly to obtain a mixed solution A; Wherein the molar ratio of polyvinyl butyral to SiCNWs is 1:1-1:1.5; (2) At a temperature of 80-100°C, the mixed solution A was stirred and reacted for 24-28 hours, the solid-liquid was separated, and the solid was annealed at a temperature of 700-1000°C in a nitrogen atmosphere for 2-4 hours to obtain in-situ growth of carbon nanometers. Tube-modified CNT/SiCNWs composites. 2. The method for preparing CNT/SiCNWs composite wave-absorbing material modified by in-situ growth of carbon nanotubes according to claim 1, characterized in that: step (1) the concentration of cobalt acetate solution is 1-1.4 wt.%.

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