CN111916916B - A kind of carbon nanotube-based three-dimensional network structure composite absorbing material and preparation method thereof - Google Patents

Abstract

The invention provides a carbon nanotube-based three-dimensional network structure composite wave absorbing material and a preparation method thereof, which are characterized in that the wave absorbing material is composed of carbon nanotubes and silicon dioxide, and the silicon dioxide is coated on the outer wall of the carbon nanotubes , the preparation method includes step 1, mixing absolute ethanol and deionized water, and then adding carbon nanotubes into the obtained mixed solution; step 2, ultrasonically dispersing the mixed solution obtained in step 1; step 3, using ammonia water to disperse step 2 The pH value of the obtained mixed solution is adjusted to 8-10; Step 4, drop ethyl orthosilicate into the mixed solution obtained in Step 3, and stir with a magnetic stirrer; Step 5, use deionized water and absolute ethanol to mix the obtained mixed solution in Step 4 respectively Filtration of the solution; Step 6, put the sample obtained in Step 5 into a drying box, and then take it out and grind it into powder to obtain a carbon nanotube-based three-dimensional network structure composite wave absorbing material. Excellent absorber with the advantages of light weight, thin thickness and strong absorption properties.

Description

A kind of carbon nanotube-based three-dimensional network structure composite absorbing material and preparation method thereof

technical field

The invention relates to the technical field of preparation of structural materials, in particular to a carbon nanotube-based three-dimensional network structure composite wave absorbing material and a preparation method thereof.

Background technique

It is well known that the increasing pollution of electromagnetic waves from industrial and household electronic equipment is attracting global attention as such pollution is harmful to human health and wildlife. More importantly, the survival of the superior military forces in the war is now the key to the entire war situation. Therefore, in any case, the design and preparation of electromagnetic wave absorbing materials with high absorption efficiency, wide bandwidth, low density, and good stability in extreme environments are very critical.

In recent years, carbon materials have attracted extensive attention due to their various advantages such as structural diversification and excellent physical and chemical properties. A variety of carbon materials (carbon black, carbon nanotubes, carbon fibers, and graphene, etc.) have been used in aerospace, supercapacitors, and mechanical manufacturing. In addition, the field of electromagnetic wave absorption is also a key field for carbon materials to exert their advantages. Among them, carbon nanotubes, as a typical carbon material, have become one of the most widely studied electromagnetic wave absorbing materials due to their excellent specific surface area, low density and good conductivity absorption properties. Carbon nanotubes have many admirable inherent properties, such as high specific surface area, low density and high electrical conductivity, etc., so they can become excellent electromagnetic wave absorbers. But highly graphitized carbon nanotubes compromise impedance-matching conditions and produce more reflections of electromagnetic waves on their surfaces than absorption. Therefore, it is of great significance to study an efficient carbon nanotube composite absorbing material. To sum up the above points, it is believed that carbon nanotube-based composite materials with excellent impedance matching properties can be prepared by appropriate methods and are widely used in the field of wave absorption.

However, magnetic materials (Fe, Co, Ni and their compounds) have traditionally been used to combine with carbon nanotubes. The density of these materials is relatively high (typically 7-8 g/cm ³ ). The introduction of these high-density magnetic materials into carbon nanotubes will lead to a substantial increase in the overall density of the composite absorbing material, and may make the material susceptible to corrosion, oxidation or high temperature failure, resulting in low density of carbon nanotubes as absorbing materials. The advantages such as good stability are no longer obvious, and the designed preparation methods and raw materials are also limited. Therefore, it is urgent to develop a new preparation method of carbon nanotube-based non-magnetic wave absorbing materials to fill this gap.

SUMMARY OF THE INVENTION

The purpose of the present invention is to solve the above-mentioned deficiencies of the prior art, and to provide a three-dimensional mesh carbon nanotube prepared by introducing silicon dioxide (SiO ₂ ) to improve its impedance matching performance while maintaining the high dielectric loss of carbon nanotubes. The tube composite material has a carbon nanotube-based three-dimensional network structure composite wave absorbing material with good wave absorbing properties and a preparation method thereof.

The technical scheme adopted by the present invention to solve its technical problems is:

A carbon nanotube-based three-dimensional network structure composite wave absorbing material, characterized in that the wave absorbing material is composed of carbon nanotubes and silicon dioxide, the silicon dioxide is coated on the outer wall of the carbon nanotubes, and the silicon dioxide The thickness of the coating layer is 10 to 30 nm.

A preparation method of a carbon nanotube-based three-dimensional network structure composite wave absorbing material, characterized in that the steps of the preparation method are as follows:

Step 1. Mixing: mix absolute ethanol and deionized water to obtain a mixed solution, the mass percentage of absolute ethanol is 40~50% of that of deionized water, and the mixed solution of absolute ethanol and deionized water is put into In the container, carbon nanotubes are added into the obtained mixed solution, and the mass percentage of carbon nanotubes is 0.4-0.6% of the mixed solution;

Step 2, dispersion: ultrasonically disperse the mixed solution containing carbon nanotubes obtained in step 1 for 2~4h;

Step 3, adjust the pH value: adjust the pH value of the mixed solution obtained in step 2 to 8-10 with ammonia water;

Step 4, coating: drop ethyl orthosilicate into the mixed solution obtained in step 3, and stir with a magnetic stirrer, wherein the mass percentage of ethyl orthosilicate is 0.8~1% of the mixed solution in step 3;

Step 5. Filtration: filter the mixed solution obtained in step 4 for 3-6 times with deionized water and absolute ethanol respectively;

Step 6. Dry grinding: put the sample obtained in step 5 into a drying oven, dry it at 60°C for 12-14 hours, and then take it out and grind it into powder to obtain a carbon nanotube-based three-dimensional network structure composite wave absorbing material.

Preferably, in the step 1, the container is a glass material container.

Preferably, in the step 2, the mixed solution should be isolated from the outside air during the ultrasonic dispersion process, and sealed with a plastic film to prevent ethanol from volatilizing, resulting in a decrease in the degree of dispersion.

Preferably, in the step 3, the pH is adjusted to 9 with ammonia water, and the outside air is isolated after the mixing is completed to prevent the volatilization of the ammonia water from affecting the pH value.

Preferably, in the step 4, the ethyl orthosilicate is dropped into the mixed solution obtained in the step 3, and stirred with a magnetic stirrer for 3 hours. During the stirring process, the ethyl orthosilicate and the carbon nanotubes are fully mixed with rapid stirring. , and then stir at a slow speed to make the formed silica coating evenly coated.

Preferably, in the step 5, first filter with deionized water, and then filter with absolute ethanol, so as to wash away possible inorganic substances and organic substances respectively. Moreover, the volatilization speed of absolute ethanol is fast, and it can be dried quickly.

Preferably, in the step 6, the sample obtained in the step 5 is put into a drying oven and dried at 60° C. for 12 hours.

Preferably, the speed of the rapid stirring is 420-500 r/min, and the speed of the low-speed stirring is 80-120 r/min.

The beneficial effect of the solution of the present invention lies in the above-mentioned preparation method of the non-magnetic composite wave absorbing material based on the three-dimensional network structure of carbon nanotubes. Using carbon nanotubes as the substrate to ensure high dielectric loss of the composite material, and then mixing with a certain amount of ethyl orthosilicate to introduce SiO ₂ , that is, using the sol-gel method to generate SiO ₂ and grow the SiO ₂ coating layer. The thus obtained carbon nanotube-based three-dimensional network structure composite absorbing material not only retains the excellent properties of carbon nanotubes, but also greatly improves its impedance matching due to the presence of _SiO2 . More importantly, it ensures the corrosion resistance, oxidation resistance and high temperature stability of the material, and avoids the harsh reaction conditions required by the high temperature reaction of the previous method. The carbon nanotube-based composite wave absorbing material prepared by the above preparation method has about 120% more electromagnetic wave absorption ability than pure carbon nanotubes, and can be used as an excellent wave absorbing material with light weight, thin thickness and strong absorption characteristics. These advantages make The material can be used as a more practical wave absorbing material with the advantages of light weight, thin thickness and strong absorption properties.

Description of drawings

Figure 1 shows the XRD patterns of carbon nanotubes before and after SiO2 coating.

Figure 2 shows the scanning electron microscope pattern of the pristine carbon nanotubes not coated with SiO2, in which (a) is a low magnification image and (b) is a high magnification image.

Figure 3 shows the scanning electron microscope pattern of the carbon nanotube composite absorbing material coated with SiO2, wherein (a) is a low magnification image and (b) is a high magnification image.

Figure 4 shows the transmission pattern of the carbon nanotube composite absorbing material coated by SiO2, in which (a) is the transmission pattern and the selected area electron diffraction pattern of the carbon nanotube after coating with SiO2, (b) after coating with SiO2 High-resolution transmission images of carbon nanotubes, (c) and (d) are the element distribution and element content of the carbon nanotube composite absorber after SiO2 coating, respectively.

Figure 5 shows the impedance matching spectra of carbon nanotubes before and after SiO2 coating.

Figure 6 shows the reflection loss of carbon nanotubes at different thicknesses before and after SiO2 coating, where (a) is the reflection loss diagram of carbon nanotubes without SiO2 coating at different thicknesses, (b) is the carbon nanotubes after SiO2 coating Reflection loss plots at different tube thicknesses.

Detailed ways

Below in conjunction with accompanying drawing, the present invention is further described:

As shown in the accompanying drawings, a carbon nanotube-based three-dimensional network structure composite wave absorbing material is characterized in that the adsorption material is composed of carbon nanotubes and silicon dioxide, and the silicon dioxide is coated on the carbon nanotubes. The thickness of the outer wall, the silica coating layer is 10~30nm.

A preparation method of a carbon nanotube-based three-dimensional network structure composite wave absorbing material, characterized in that the steps of the preparation method are as follows:

Step 1. Mixing: mix absolute ethanol and deionized water to obtain a mixed solution, the mass percentage of absolute ethanol is 40~50% of that of deionized water, and the mixed solution of absolute ethanol and deionized water is put into In the container, carbon nanotubes are added into the obtained mixed solution, and the mass percentage of carbon nanotubes is 0.4-0.6% of the mixed solution;

Step 2, dispersion: ultrasonically disperse the mixed solution containing carbon nanotubes obtained in step 1 for 2~4h;

Step 3, adjust the pH value: adjust the pH value of the mixed solution obtained in step 2 to 8-10 with ammonia water;

Step 4, coating: drop ethyl orthosilicate into the mixed solution obtained in step 3, and stir with a magnetic stirrer, wherein the mass percentage of ethyl orthosilicate is 0.8~1% of the mixed solution in step 3;

Step 5. Filtration: filter the mixed solution obtained in step 4 for 3-6 times with deionized water and absolute ethanol respectively;

Step 6. Dry grinding: Put the sample obtained in step 5 into a drying oven, dry it at 60°C for 12-14 hours, and then take it out and grind it into powder to obtain a carbon nanotube-based three-dimensional network structure composite wave absorbing material.

Preferably, in the step 1, the container is a glass material container.

Preferably, in the step 2, the mixed solution should be isolated from the outside air during the ultrasonic dispersion process, and sealed with a plastic film to prevent ethanol from volatilizing, resulting in a decrease in the degree of dispersion.

Preferably, in the step 3, the pH is adjusted to 9 with ammonia water, and the outside air is isolated after the mixing is completed to prevent the volatilization of the ammonia water from affecting the pH value.

Preferably, in the step 4, the ethyl orthosilicate is dropped into the mixed solution obtained in the step 3, and stirred with a magnetic stirrer for 3 hours. During the stirring process, the ethyl orthosilicate and the carbon nanotubes are fully mixed with rapid stirring. , and then stir at a slow speed to make the formed silica coating evenly coated.

Preferably, in the step 5, first filter with deionized water, and then filter with absolute ethanol, so as to wash away possible inorganic substances and organic substances respectively. Moreover, the volatilization speed of absolute ethanol is fast, and it can be dried quickly.

Preferably, in the step 6, the sample obtained in the step 5 is put into a drying oven and dried at 60° C. for 12 hours.

Preferably, the speed of the rapid stirring is 420-500 r/min, and the speed of the low-speed stirring is 80-120 r/min.

Described ethyl orthosilicate introduces the process of carbon source:

According to the comparison and analysis of the product of this scheme and the existing technology, the performance of the product of this scheme is as follows:

Figure 1: Figure 1 shows the XRD patterns of carbon nanotubes before and after SiO2 coating, where Sample A is the XRD pattern of the original carbon nanotubes not coated with SiO2, and Sample B is the carbon nanotubes coated with SiO2 XRD patterns of composite absorbing materials;

As shown in Figure 1, comparing Sample A and Sample B, it can be seen that due to the existence of the SiO ₂ coating layer, the XRD diffraction peaks of the carbon nanotubes become weaker, which reflects the success of the SiO 2 coating from one side.

Figure 2: Figure 2 shows the scanning electron microscope pattern of the pristine carbon nanotubes not coated with SiO2, wherein (a) is a low magnification image and (b) is a high magnification image. It can be seen from the figure that the surface of the uncoated SiO2 carbon nanotubes is bare and relatively smooth;

Figure 3: Figure 3 shows the scanning electron microscope pattern of the carbon nanotube composite absorber after SiO2 coating, wherein Figure 3(a) is a low magnification image, and Figure 3(b) is a high magnification image.

From the comparison of Figure 2 and Figure 3, it can be seen that the surface of the carbon nanotubes coated with SiO2 forms aggregates, which are relatively rough, which may generate more interface losses and improve the wave absorbing performance.

Figure 4: Figure 4 shows the transmission pattern of the carbon nanotube composite absorber coated by SiO2, in which Figure 4(a) is the transmission pattern and the selected area electron diffraction pattern of the carbon nanotubes coated with SiO2. 4 (b) High-resolution transmission image of carbon nanotubes after SiO2 coating, Figure 4 (c) and Figure 4 (d) are the element distribution and element content of the carbon nanotube composite absorber after SiO2 coating, respectively , it is obvious from Figure 4 (a) that there is a layer of coating on the surface of the carbon nanotube and the coating layer is amorphous. From Figure 4 (b), it can be seen that the thickness of the coating layer is 17.98~18.23nm, It can be seen from Figure 4 (c) and Figure 4 (d) that the elements forming the composite are C, O, Si, and the content of each element is shown in Figure 4 (d). It can be determined that this method can be used in carbon nanotubes The surface is coated with a layer of SiO2.

Figure 5: Figure 5 shows the impedance matching patterns of carbon nanotubes before and after SiO2 coating, in which Sample A is the impedance matching pattern of the original carbon nanotubes not coated with SiO2, and Sample B is the carbon nanotubes coated with SiO2 Impedance matching spectra of nanotube composite absorbers,

It can be seen that the impedance matching value of Sample B is much better than that of Sample A, and the impedance matching performance is positively correlated with the wave absorbing performance, and reaching 1 is the optimal impedance matching. is the optimal value.

Figure 6: Figure 6 shows the reflection loss of carbon nanotubes at different thicknesses before and after SiO2 coating, in which Figure 6(a) is the reflection loss diagram of carbon nanotubes without SiO2 coating under different thicknesses, Figure 6(b) ) is the reflection loss diagram of carbon nanotubes with different thicknesses after SiO2 coating

It can be seen from Figure 6(a) that the reflection loss is far from -10dB (only when the reflection loss reaches -10dB can it be practically applied). Figure 6(b) shows that the carbon nanotubes coated by SiO2 are at 1.08 The reflection loss under mm thickness is as high as -54.076dB, (reaching 99.999% electromagnetic wave absorption rate). Compared with uncoated carbon nanotubes, the wave absorption performance is improved by about 120%. Therefore, it is concluded that the wave absorption performance of the product in this solution is better. it is good.

Moreover, in the prior art, there is also the prior art that silicon dioxide and carbon nanotubes are directly combined with composite materials. However, in the prior art, silicon dioxide crystals are directly mixed with carbon nanotubes, which is the same as this patent. The use of ethyl orthosilicate as the silicon source to generate SiO2 is different, and the direct use of silicon dioxide must go through steps such as rolling and high temperature, and the processing cost is relatively high. In this patent, a composite material of carbon nanotubes covered by SiO2 can be generated by using tetraethyl orthosilicate as the silicon source at normal temperature and pressure.

The loading amount and temperature of carbon nanotubes of the composite material that is directly mixed with silicon dioxide crystals and carbon nanotubes have a great influence on its performance. When the thickness is 1-5.5mm, the reflection loss is less than -7dB (under the production conditions of this patent, when the carbon nanotube loading is about 0.4~0.6 wt.%, the reflection loss exceeds -10dB at any thickness of 1-5.5mm). When the loading of carbon nanotubes reaches 5 wt.%, the reflection loss is greatly improved.

In addition, comparing the performance of the coating structure of this patent with the material of the mixed silica, the coating structure is mainly based on carbon nanotubes, which can give full play to the excellent properties of carbon nanotubes. With SiO2 microspheres as the base, the loading of carbon nanotubes is only 2~10%, and the content of SiO2 will increase the density of the composite material (the density of SiO2 is 2.2g/cm³, the density of carbon nanotubes is 1.3~2 g/cm³ ), which is not conducive to the practical application of absorbing materials.

The beneficial effect of the solution of the present invention lies in the preparation method of the above-mentioned carbon nanotube-based three-dimensional network structure composite wave absorbing material. The carbon nanotubes are used as the substrate to ensure the high dielectric loss and high electromagnetic wave absorption performance of the composite material, and then mixed with a certain amount of ethyl orthosilicate to introduce SiO ₂ , that is, the sol-gel method is used to generate SiO ₂ and make SiO ₂ . The cladding layer grows. The thus obtained carbon nanotube-based three-dimensional network structure non-magnetic composite absorbing material not only retains the excellent properties of carbon nanotubes, but also greatly improves its impedance matching due to the presence of _SiO2 . More importantly, it ensures the corrosion resistance, oxidation resistance and high temperature stability of the material, and avoids the harsh reaction conditions required by the high temperature reaction of the previous method. These advantages make the material a more practical absorber.

Claims (8)

1. A preparation method of a carbon nanotube-based three-dimensional network structure composite wave-absorbing material is characterized in that the wave-absorbing material is composed of carbon nanotubes and silicon dioxide, the silicon dioxide is coated on the outer walls of the carbon nanotubes, the thickness of the silicon dioxide coating is 10-30 nm, and the preparation method comprises the following steps:

step 1, mixing materials: mixing absolute ethyl alcohol and deionized water to obtain a mixed solution, wherein the mass percent of the absolute ethyl alcohol is 40-50% of that of the deionized water, putting the mixed solution of the absolute ethyl alcohol and the deionized water into a container, and adding carbon nano tubes into the mixed solution, wherein the mass percent of the carbon nano tubes is 0.4-0.6% of that of the mixed solution;

Step 2, dispersing: ultrasonically dispersing the mixed solution containing the carbon nano tubes obtained in the step 1 for 2-4 h;

step 3, pH value blending: adjusting the pH value of the mixed solution obtained in the step 2 to 8-10 by using ammonia water;

step 4, coating: dropping ethyl orthosilicate into the mixed solution obtained in the step 3, and stirring by using a magnetic stirrer, wherein the mass percent of the ethyl orthosilicate is 0.8-1% of the mixed solution obtained in the step 3;

and step 5, filtering: filtering the mixed solution obtained in the step 4 for 3-6 times by using deionized water and absolute ethyl alcohol respectively;

step 6, drying and grinding: and (4) putting the sample obtained in the step (5) into a drying oven, drying for 12-14 h at the temperature of 60 ℃, taking out, and grinding into powder to obtain the carbon nanotube-based three-dimensional network structure composite wave-absorbing material.

2. The method for preparing the carbon nanotube-based three-dimensional network structure composite wave-absorbing material as claimed in claim 1, wherein in the step 1, the container is a glass container.

3. The method for preparing the composite wave-absorbing material with the carbon nanotube-based three-dimensional network structure as claimed in claim 1, wherein in the step 2, the mixed solution is sealed by a plastic film while being isolated from the outside air during the ultrasonic dispersion.

4. The method for preparing the carbon nanotube-based three-dimensional network structure composite wave-absorbing material according to claim 1, wherein in the step 3, ammonia water is used for adjusting the pH value to 9, and the outside air is isolated after the mixing.

5. The method for preparing the carbon nanotube-based three-dimensional network structure composite wave-absorbing material as claimed in claim 1, wherein in the step 4, tetraethoxysilane is dropped into the mixed solution obtained in the step 3, and is stirred for 3 hours by a magnetic stirrer, wherein in the stirring process, the tetraethoxysilane and the carbon nanotube are firstly stirred rapidly, and are fully mixed, and then are stirred slowly, so that the formed silicon dioxide coating layer is coated uniformly.

6. The method for preparing the carbon nanotube-based three-dimensional network structure composite wave-absorbing material as claimed in claim 1, wherein in the step 5, the filtering is performed with deionized water and then with absolute ethyl alcohol.

7. The method for preparing the carbon nanotube-based three-dimensional network structure composite wave-absorbing material according to claim 1, wherein the sample obtained in the step 5 is placed in a drying oven and dried for 12 hours at 60 ℃ in the step 6.

8. The method for preparing a carbon nanotube-based three-dimensional network composite wave-absorbing material as claimed in claim 5, wherein the rapid stirring speed is 420-500 r/min, and the slow stirring speed is 80-120 r/min.

Images