A spiral SiC nanotube electromagnetic wave absorbing material and a preparation method thereof

Abstract

The application discloses a spiral SiC nanotube electromagnetic wave absorbing material and a preparation method thereof. The absorbing material is in the shape of DNA double helix with two nanotubes intertwined with each other. The spiral SiC nanotube is prepared by taking a spiral polypyrrole nanotube as a precursor and through a heat treatment method. The absorbing material has good stability below 1000 DEG C and excellent high-temperature resistance. The special spiral structure introduces rich interfaces to improve polarization loss. When the matching thickness is 1.4 mm, the absorbing frequency band width with a reflection loss lower than -10 dB can reach 4.2 GHz.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of electromagnetic wave absorbing material preparation, and particularly relates to a spiral SiC nanotube electromagnetic wave absorbing material and a preparation method thereof. BACKGROUND

[0002] In the field of civil use, wireless communication technology based on electromagnetic field brings great convenience to human production and life, but electromagnetic radiation also threatens the safety of human production and life at all times; in the field of military struggle, radar gradually realizes all-weather, multi-means and stereoscopic, and monitors all kinds of equipment and facilities at all times. Using electromagnetic wave absorbing material to dissipate electromagnetic wave entering the material in other forms of energy is an important means applied in the field of electromagnetic radiation protection and electromagnetic wave stealth.

[0003] It is currently a research focus to match the electromagnetic wave absorbing material with thin thickness, low filling quality, wide absorbing frequency band and strong loss capacity. It is proved that micro-nano and large length-diameter ratio are important methods to improve the performance of absorbing materials. Common one-dimensional nanomaterials such as metal nanowires and polymer nanotubes have problems such as high filling amount, thick matching thickness, poor high-temperature resistance and poor corrosion resistance. Silicon carbide (SiC) has the characteristics of high strength, good thermal shock resistance and strong chemical inertness, and combined with its own dielectric properties, it has the potential of electromagnetic wave absorbing material in multiple fields.

[0004] Early studies show that the dielectric constant of traditional one-dimensional SiC nanomaterials is low, the electromagnetic response is not obvious, and the wave absorbing performance is weak. Microstructure regulation is an effective way to improve the performance of one-dimensional nanomaterials. S. Motojima et al. prepared spiral SiC fibers with a spiral diameter of 0.5-1 μm by using SiO as the Si source and rice husk as the carbon source by CVD method (DOI: 10.1016 / 0022-0248(95)00320-7). However, the spiral SiC fibers prepared by this method have low yield and poor controllability of morphology, which makes it difficult to apply. Chen et al. prepared spiral SiC fibers with a fiber diameter of 3-5 μm by using spiral carbon fibers as a template and SiCl4 as a silicon source by high-temperature gas phase silicification (DOI: 10.1016 / S0025-5408(00)00207-5). However, the spiral SiC fibers prepared by this method have large size and it is difficult to silicify, and SiCl4 as the Si source has strong toxicity, which makes it difficult to apply. Li et al. prepared spiral SiC fibers by using spiral SiO2 fibers as a template and through surface modification and magnesium reduction (DOI: 10.1016 / j.jtice.2019.02.021). However, the spiral SiC fibers are C / SiC / Si composite fibers containing a large amount of impurities difficult to remove, have high filling amount, and have poor high-temperature resistance. One-dimensional SiC nanomaterials still need to break through technical barriers to become applicable wave absorbing agents. SUMMARY

[0005] The present application aims to provide a helical SiC nanotube electromagnetic wave absorbing material with thin matching thickness, strong loss capacity, wide absorbing frequency band and high temperature resistance.

[0006] In order to achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0007] The present application provides a helical SiC nanotube electromagnetic wave absorbing material with thin matching thickness, strong loss capacity, wide absorbing frequency band and high temperature resistance. The electromagnetic wave absorbing material is in the form of DNA double helix with two intertwined nanotubes, which can maintain good stability below 1000℃ and has excellent high temperature resistance.

[0008] When the matching thickness is 1.4 mm, the absorbing frequency band width with a reflection loss below -10 dB can reach 4.2 GHz.

[0009] A specific preparation method of a helical SiC nanotube electromagnetic wave absorbing material is as follows:

[0010] (1) Place the helical polypyrrole nanotube in a tube furnace and heat treat it in an Ar gas environment;

[0011] (2) Mix the product obtained in step (1) with Si powder and SiO2 and grind them;

[0012] (3) Place the product obtained in step (2) in a tube furnace and heat treat it in an Ar gas environment;

[0013] (4) Place the product obtained in step (3) in a tube furnace and heat treat it in an air environment;

[0014] (5) Place the product obtained in step (4) in an alkaline solution and stir it under heating conditions;

[0015] (6) Centrifuge and wash the product obtained in step (5) and dry it to obtain dry helical SiC nanotubes.

[0016] Further, in step (1), the heat treatment temperature is 400℃, the heating rate is 2℃ / min, and the heat treatment time is 4 h.

[0017] Further, in step (2), the mass ratio of the product obtained in step (1) to Si powder and SiO2 powder is 50:29:125, and the grinding time is 30 min.

[0018] Further, in step (3), the heat treatment temperature is 1400℃, the heat treatment time is 2 h, and the heating rate is 5℃ / min.

[0019] Furthermore, in step (4), the heat treatment temperature is 800 ℃, the heat treatment time is 4 h, and the heating rate is 5 ℃ / min.

[0020] Furthermore, in step (5), the alkaline solution is a 5 mol / L NaOH solution, the heating temperature is 70 ℃, and the time is 80 min.

[0021] Compared with existing technologies, the helical SiC nanotubes prepared in this invention achieve a maximum absorption intensity of -49.26 dB, meaning they can absorb 99.999% of incident electromagnetic waves. The absorption bandwidth reaches 4.2 GHz, spanning from 13.04 GHz to 17.24 GHz, almost covering the entire Ku-band. The prepared helical SiC nanotubes exhibit excellent high-temperature resistance below 1000 °C, which is of great significance for high-temperature electromagnetic wave absorbing materials. Attached Figure Description

[0022] Figure 1 This is a SEM image of a helical polypyrrole nanotube.

[0023] Figure 2 The XRD patterns are of the helical SiC nanotubes prepared in Examples 1-4.

[0024] Figure 3 SEM images of the spiral SiC nanotubes prepared in Examples 1-4: (a) Spiral SiC nanotube-1, (b) Spiral SiC nanotube-2, (c) Spiral SiC nanotube-3, (d) Spiral SiC nanotube-4.

[0025] Figure 4 The image shows the reflection loss of the spiral SiC nanotubes prepared in Example 1, with a filling amount of 50 wt% and a paraffin substrate.

[0026] Figure 5 The reflection loss diagram is for the spiral SiC nanotubes prepared in Example 2, with a filling amount of 50 wt% and a paraffin substrate.

[0027] Figure 6 The reflection loss diagram is for the spiral SiC nanotubes prepared in Example 3, with a filling amount of 50 wt% and a paraffin substrate.

[0028] Figure 7 The image shows the reflection loss of the spiral SiC nanotubes prepared in Example 4, with a filling amount of 50 wt% and a paraffin substrate.

[0029] Figure 8 Thermogravimetric analysis diagram of the helical SiC nanotubes prepared in Example 4. Detailed Implementation

[0030] The technical solution of the present invention will now be further described in conjunction with the accompanying drawings and embodiments. The following embodiments are merely exemplary and are only used to explain and illustrate the technical solution of the present invention, and should not be construed as limiting the technical solution of the present invention.

[0031] This invention employs a heat treatment method to transform helical polypyrrole nanotubes into helical SiC nanotubes, maintaining their helical morphology and resembling a DNA double helix with two nanotubes entangled together. The hollow structure of the helical nanotubes effectively reduces the filler content; the larger aspect ratio facilitates the formation of a three-dimensional conductive network, improving conductivity loss; the entangled nanotubes possess numerous interfaces, generating charge accumulation and increasing interfacial polarization loss. Furthermore, the helical SiC nanotubes prepared by this invention exhibit excellent high-temperature resistance below 1000℃.

[0032] The helical polypyrrole nanotubes involved in this invention are prepared by the following steps:

[0033] (1) Dissolve 30 mg of N-myristoyl-L-glutamic acid and 134 mg of pyrrole in 15 ml of anhydrous ethanol and sonicate for 5 min.

[0034] (2) Add the solution to 60 ml of deionized water and stir in an ice water bath for 20 min.

[0035] (3) Add 300 mg of ammonium persulfate to the solution and stir in an ice-water bath for 20 min.

[0036] (4) The product was washed with water and anhydrous ethanol and then dried under vacuum to obtain spiral polypyrrole nanotubes.

[0037] Example 1: Preparation of Helical SiC Nanotubes-1

[0038] (1) 100 mg of spiral polypyrrole nanotubes were placed in a tube furnace and heat-treated at 400 °C with a heating rate of 2 °C / min and a heat treatment time of 4 h in an Ar gas environment to obtain black powdered spiral carbon nanotubes.

[0039] (2) Mix the spiral carbon nanotubes with Si powder and SiO2 powder at a mass ratio of 50:29:125 and grind for 30 min.

[0040] (3) The ground product was placed in a tube furnace and heat-treated at 1400 °C with a heating rate of 5 °C / min and a heat treatment time of 2 h in an Ar gas environment to obtain a gray-green powder sample.

[0041] (4) The sample was placed in a tube furnace and heat-treated at 800 °C with a heating rate of 5 °C / min for 4 h in an air environment.

[0042] (5) Take 90 mg of the product and place it in a flask. Mix it with 40 ml of 1 mol / L NaOH solution and stir at 70 °C for 80 min.

[0043] (6) The product was centrifuged, washed and dried to obtain spiral SiC nanotubes-1.

[0044] Example 2: Preparation of Helical SiC Nanotubes-2

[0045] (1) 100 mg of spiral polypyrrole nanotubes were placed in a tube furnace and heat-treated at 700 °C with a heating rate of 2 °C / min and a heat treatment time of 4 h in an Ar gas environment to obtain black powdered spiral carbon nanotubes.

[0046] (2) Mix the spiral carbon nanotubes with Si powder and SiO2 powder at a mass ratio of 50:29:125 and grind for 30 min.

[0047] (3) The ground product was placed in a tube furnace and heat-treated at 1400 °C with a heating rate of 5 °C / min and a heat treatment time of 2 h in an Ar gas environment to obtain a gray-green powder sample.

[0048] (4) The sample was placed in a tube furnace and heat-treated at 800 °C with a heating rate of 5 °C / min for 4 h in an air environment.

[0049] (5) Take 90 mg of the product and place it in a flask. Mix it with 40 ml of 1 mol / L NaOH solution and stir at 70 °C for 80 min.

[0050] (6) The product was centrifuged, washed and dried to obtain spiral SiC nanotubes-2.

[0051] Example 3: Preparation of Helical SiC Nanotubes-3

[0052] (1) 100 mg of spiral polypyrrole nanotubes were placed in a tube furnace and heat-treated at 700 °C with a heating rate of 2 °C / min and a heat treatment time of 4 h in an Ar gas environment to obtain black powdered spiral carbon nanotubes.

[0053] (2) Mix the spiral carbon nanotubes with Si powder and SiO2 powder at a mass ratio of 50:29:125 and grind for 30 min.

[0054] (3) The ground product was placed in a tube furnace and heat-treated at 1600 °C with a heating rate of 5 °C / min and a heat treatment time of 2 h in an Ar gas environment to obtain a gray-green powder sample.

[0055] (4) The sample was placed in a tube furnace and heat-treated at 800 °C with a heating rate of 5 °C / min for 4 h in an air environment.

[0056] (5) Take 90 mg of the product and place it in a flask. Mix it with 40 ml of 1 mol / L NaOH solution and stir at 70 °C for 80 min.

[0057] (6) The product was centrifuged, washed and dried to obtain spiral SiC nanotubes-3.

[0058] Example 4: Preparation of Helical SiC Nanotubes-4

[0059] (1) 100 mg of spiral polypyrrole nanotubes were placed in a tube furnace and heat-treated at 400 °C with a heating rate of 2 °C / min and a heat treatment time of 4 h in an Ar gas environment to obtain black powdered spiral carbon nanotubes.

[0060] (2) Mix the spiral carbon nanotubes with Si powder and SiO2 powder at a mass ratio of 50:29:125 and grind for 30 min.

[0061] (3) The ground product was placed in a tube furnace and heat-treated at 1400 °C with a heating rate of 5 °C / min and a heat treatment time of 2 h in an Ar gas environment to obtain a gray-green powder sample.

[0062] (4) The sample was placed in a tube furnace and heat-treated at 800 °C with a heating rate of 5 °C / min for 4 h in an air environment.

[0063] (5) Take 90 mg of the product and place it in a flask. Mix it with 40 ml of 5 mol / L NaOH solution and stir at 70 °C for 80 min.

[0064] (6) The product was centrifuged, washed and dried to obtain spiral SiC nanotubes-4.

[0065] SEM images of the prepared helical polypyrrole nanotubes are shown below. Figure 1 As shown, the prepared helical polypyrrole nanotubes are double helical structures formed by two nanotubes entangled together. The XRD patterns of the helical SiC nanotubes prepared in Examples 1-4 above are shown below. Figure 2 As shown, spiral SiC nanotube-1, spiral SiC nanotube-2, and spiral SiC nanotube-3 all contain diffraction peaks of SiO2, indicating that unreacted SiO2 was not completely removed. However, spiral SiC nanotube-4 does not contain diffraction peaks of SiO2, indicating that the prepared spiral SiC nanotubes have high purity and are free of impurities.Figure 3 The image shown is a SEM image of the helical SiC nanotubes prepared in Examples 1-4. Figure 3 It can be seen that the spiral SiC nanotube-1 has a better spiral morphology, but contains unreacted SiO2; the spiral SiC nanotube-2 and spiral SiC nanotube-3 have poor spiral morphology, high degree of damage, and contain unreacted SiO2; the spiral SiC nanotube-4 has a better spiral morphology and no SiO2 residue. Figure 4 to Figure 7 The figures show the electromagnetic wave absorption performance of the helical SiC nanotubes prepared in Examples 1-4. It can be seen that the helical SiC nanotube-4 prepared under the conditions of Example 4 has the best electromagnetic wave absorption performance. When the matching thickness is 1.4 mm, the absorption bandwidth with a reflection loss of less than -10 dB can reach 4.2 GHz; when the matching thickness is 1.3 mm, the minimum reflection loss can reach -49.26 dB. Figure 8 The thermogravimetric curve of the spiral SiC nanotube-4 prepared in Example 4 shows that the mass change of the spiral SiC nanotube-4 is small in the range of room temperature to 1000 °C, indicating that it has good thermal stability.

[0066] It should be noted that the above descriptions are some embodiments of the present invention and are not intended to limit the present invention in other ways. Those skilled in the art can modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technologies. However, any modifications or equivalent substitutions made to the embodiments without departing from the content of the technical solutions of the present invention and based on the relevant technical essence of the present invention shall still fall within the protection scope of the technical solutions of the present invention.

Claims

1. A method for preparing a helical SiC nanotube electromagnetic wave absorbing material, characterized in that, Includes the following steps: (1) The spiral polypyrrole nanotubes were placed in a tube furnace and heat-treated in an Ar gas environment; (2) Mix the product obtained in step (1) with Si powder and SiO2, and grind them together; (3) Place the product obtained in step (2) in a tube furnace and heat treat it in an Ar gas environment; (4) Place the product obtained in step (3) in a tube furnace and heat treat it in an air environment; (5) Place the product obtained in step (4) in an alkaline solution and stir under heating conditions; (6) The product obtained in step (5) is centrifuged, washed and dried to obtain dried spiral SiC nanotubes; The spiral polypyrrole nanotubes are prepared through the following steps: (1) Dissolve 30 mg of N-myristoyl-L-glutamic acid and 134 mg of pyrrole in 15 ml of anhydrous ethanol and sonicate for 5 min. (2) Add the solution to 60 ml of deionized water and stir in an ice water bath for 20 min; (3) Add 300 mg of ammonium persulfate to the solution and stir in an ice-water bath for 20 min; (4) The product was washed with water and anhydrous ethanol and then dried under vacuum to obtain spiral polypyrrole nanotubes.

2. The method as described in claim 1, characterized in that, In step (1), the heat treatment temperature is 400 ℃, the heating rate is 2 ℃ / min, and the heat treatment time is 4 h.

3. The method as described in claim 1, characterized in that, In step (2), the mass ratio of the product obtained in step (1) to Si powder and SiO2 powder is 50:29:125, and the grinding is carried out for 30 min.

4. The method as described in claim 1, characterized in that, In step (3), the heat treatment temperature is 1400 ℃, the heat treatment time is 2 h, and the heating rate is 5 ℃ / min.

5. The method as described in claim 1, characterized in that, In step (4), the heat treatment temperature is 800 ℃, the heat treatment time is 4 h, and the heating rate is 5 ℃ / min.

6. The method as described in claim 1, characterized in that, In step (5), the alkaline solution is a 5 mol / L NaOH solution, the heating temperature is 70 ℃, and the time is 80 min.

7. The helical SiC nanotube electromagnetic wave absorbing material prepared by the method according to any one of claims 1-6.

8. The helical SiC nanotube electromagnetic wave absorbing material as described in claim 7, characterized in that, The electromagnetic wave absorbing material is in the form of a DNA double helix with two nanotubes intertwined.

9. The helical SiC nanotube electromagnetic wave absorbing material as described in claim 7 or 8, characterized in that, When the matching thickness is 1.4 mm, the absorption bandwidth with a reflection loss of less than -10 dB can reach 4.2 GHz.

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