CN114956830A

CN114956830A - Boron nitride coated carbon nanotube reinforced polymer conversion ceramic-based wave-absorbing material and preparation method thereof

Info

Publication number: CN114956830A
Application number: CN202210553765.2A
Authority: CN
Inventors: 李贺军; 任斌; 贾瑜军; 武霄鹏; 邓雨萌
Original assignee: Northwestern Polytechnical University
Current assignee: Northwestern Polytechnical University
Priority date: 2022-05-20
Filing date: 2022-05-20
Publication date: 2022-08-30
Anticipated expiration: 2042-05-20
Also published as: CN114956830B

Abstract

The invention relates to a boron nitride-coated carbon nanotube-reinforced polymer-converted ceramic-based wave absorbing material and a preparation method. The pretreated carbon nanotubes (CNTs) are added to boron nitride (BN) prepared from boric acid and urea. Ultrasonic dispersion treatment in the precursor solution, and then through multiple vacuum filtration-drying-heat treatment methods to obtain BN-coated CNTs nano-powder (BN-CNTs); the above-mentioned nano-powder is uniformly dispersed into liquid polycarbosilane (PCS ), BN-CNTs-reinforced polymer-converted silicon carbide (PDC-SiC) ceramic composites were prepared by low-temperature cross-linking and high-temperature pyrolysis heat treatment. The introduction of BN-CNTs improves the current situation of impedance mismatch and insufficient loss capability when PDC-SiC ceramics are used as absorbing materials, optimizes the dielectric constant of PDC-SiC, and improves its absorbing performance.

Description

Boron nitride coated carbon nanotube reinforced polymer conversion ceramic-based wave-absorbing material and preparation method thereof

Technical Field

The invention belongs to the technical field of wave-absorbing materials, and relates to a boron nitride coated carbon nanotube reinforced polymer conversion ceramic-based wave-absorbing material and a preparation method thereof.

Background

With the increasingly strong detection and tracking capability of defense systems of all countries in the world, the viability of military targets and the defense-surmounting capability of weapon systems are increasingly seriously threatened, so that the development of high-performance wave-absorbing stealth materials becomes a very important and key direction in modern defense systems. The polymer-converted silicon carbide (PDC-SiC) ceramic has excellent high-temperature creep resistance and chemical stability, the preparation process is simple, convenient and adjustable, and the ceramic becomes a wave-absorbing material with a very promising prospect due to the special dielectric and electrical properties (changed along with the change of cracking temperature). However, when the pure PDC-SiC ceramic is applied as a wave-absorbing material, the dielectric loss capability of the pure PDC-SiC ceramic is weak, the real part of the relative dielectric constant is too high, and the impedance matching with air is poor, which greatly reduces the wave-absorbing capability of the pure PDC-SiC ceramic. Therefore, how to improve the impedance matching of the PDC-SiC ceramic and improve the wave absorbing performance of the PDC-SiC ceramic is urgently needed.

Document 1 "Li Q, Yin X, Duan W, et al. electric, dielectric and microwave-absorption properties of polymer derived SiC ceramics in X band [ J ]. Journal of alloys and compounds,2013,565: 66-72" discloses the study of dielectric, electrical and microwave properties of polymer converted silicon carbide ceramics in the X band, the study was conducted at different cracking temperatures (1100-, the standard of-10 dB of reflectivity under effective loss can not be achieved, and how to improve the problem is worth thinking and solving.

Document 2 "Hong W, Dong S, Hu P, et al. in situ growth of one-dimensional nanowines on porous PDC-SiC/Si ₃ N ₄ ceramics with excellent microwave absorption properties[J]Ceramics International,2017,43(16):14301- ₃ N ₄ Nanowire modified porous PDC-SiC/Si ₃ N ₄ Method for the production of ceramics, in which Si ₃ N ₄ NWs are formed in situ in the pore channels by the gas-solid (VS) mechanism, with Si ₃ N ₄ Increasing the content of NWs, PDC-SiC/Si ₃ N ₄ The microstructure and mechanical property of the porous ceramic are changed, and the minimum reflection coefficient of the whole composite material is improved along with the increase of the content of the PDC-SiC, which is mainly benefited by the in-situ formed PDC-SiC nano particles, nano carbon and Si ₃ N ₄ The distinct interfaces between NWs enhance electron dipole polarization and interface scattering. Although the technology improves the wave-absorbing performance of the PDC-SiC to a certain extent, for the single-layer thickness of the material, the wave-absorbing frequency band is narrow, and the practical application capability is weak.

Carbon Nanotubes (CNTs) have low density, good stability, large specific surface area, and high conductivity, are high-performance wave-absorbing materials, and are often selected as a nano-filler phase to improve the dielectric loss capability of the matrix.

Document 3 "Zhang Y, Yin X, Ye F, et al. effects of multi-walled carbon nanotubes on the crystallization catalyst of PDCs-SiBCN and the third improved dielectric and EM adsorbing properties [ J ]. Journal of the European Ceramic Society,2014,34(5): 1053. sup. with 1061." discloses a method for preparing a polymer-converted derivative silicon-boron-carbon-nitride Ceramic (PDC-SiBCN) containing multi-walled carbon nanotubes as a nucleating agent to promote heterogeneous nucleation, to lower the crystallization temperature of SiC in SiBCN, and the A (SiBCN matrix) + B (SiC) + C (MWs) structure formed in MWCNTs-SiBCN is advantageous for improving the dielectric properties and the electromagnetic absorption properties of the entire composite material. However, the MWCNTs have excessively high conductivity, so that impedance matching between the whole composite material and a free space is aggravated, the effective bandwidth of the material in an X wave band is only 3GHz, and the application prospect of the material is limited. Therefore, the degree of impedance matching between CNTs and polymer conversion ceramics remains to be improved.

As a traditional two-dimensional material, hexagonal boron nitride (h-BN) has good oxidation resistance and low relative dielectric constant, is an excellent candidate material for improving polymer conversion ceramic, and the introduction of BN phase can reduce the real part of the relative dielectric constant of the composite material, thereby meeting the requirement of impedance matching and improving the wave-absorbing performance of the material. In view of this,

disclosure of Invention

Technical problem to be solved

In order to avoid the defects of the prior art, the invention provides a boron nitride coated carbon nanotube reinforced polymer conversion ceramic-based wave-absorbing material and a preparation method thereof, and solves the problems of weak PDC-SiC dielectric loss capacity and poor impedance matching property.

The invention provides a preparation method of a boron nitride coated carbon nanotube reinforced polymer conversion ceramic-based wave-absorbing material. Firstly, boric acid and urea are used as reaction raw materials to prepare a BN precursor solution, then the BN-coated CNTs nano phase (BN-CNTs) is prepared through the steps of ultrasonic dispersion, multiple vacuum filtration, drying and heat treatment, and finally the PDC-SiC ceramic composite material with uniformly distributed BN-CNTs is obtained through low-temperature crosslinking and high-temperature cracking heat treatment. The BN-CNTs reinforced PDC-SiC obtained by the invention can effectively improve the current situations of impedance mismatch and insufficient loss capacity when the current PDC-SiC ceramic is used as a wave-absorbing material.

Technical scheme

A boron nitride coated carbon nanotube reinforced polymer conversion ceramic-based wave-absorbing material is characterized in that polymer conversion silicon carbide ceramic is taken as a matrix and is compounded with BN-CNTs nano powder to form a multiphase composite material containing SiC, free carbon, BN and CNTs; wherein the mass percentage of BN-CNTs nano powder is 1% -5%; BN-CNTs are uniformly distributed in the SiC ceramic matrix.

A preparation method of the boron nitride coated carbon nanotube reinforced polymer conversion ceramic-based wave-absorbing material is characterized by comprising the following steps:

step 1: performing heat treatment on the CNTs for 2-5 h at 200-600 ℃ in Ar atmosphere, adding the heat-treated CNTs into a concentrated nitric acid solution, performing ultrasound for 0.5-2 h, and then washing the CNTs to be neutral;

step 2: mixing and dispersing boric acid and urea in deionized water, and magnetically stirring for 10-15 hours until the solution is transparent; adding the CNTs pretreated in the step 1 into a solution, performing ultrasonic dispersion treatment for 30-90 min, collecting the CNTs by using a vacuum filtration device, and drying;

and step 3: dried CNTs in flowing N ₂ In the atmosphere, raising the furnace temperature from room temperature to 800-1200 ℃ at a temperature raising rate of 3-10 ℃/min, and keeping the temperature for 3-7 h; turning off a power supply, and naturally cooling to room temperature to obtain the CNTs subjected to heat treatment;

repeating the step 2 and the step 3 for 2-6 times to obtain BN-CNTs;

and 4, step 4: carrying out ultrasonic dispersion and mixing on 0-20% by mass of BN-CNTs and liquid-phase polycarbosilane PCS for 1-4 h; in a flowing Ar atmosphere, heating the furnace temperature from room temperature to 100-300 ℃ at a heating rate of 3-10 ℃/min, and preserving the temperature for 1-3 h; turning off the power supply, and naturally cooling to room temperature to obtain a cross-linked sample;

fully grinding and screening the crosslinked sample to obtain precursor powder, and pressing the powder into a solid block;

and 5: putting the solid block into a heat treatment furnace with a resistance wire as a heating body, heating the furnace to 800-1500 ℃ from room temperature at a heating rate of 3-10 ℃/min in a flowing Ar atmosphere, and keeping the temperature for 1-4 h; and turning off the power supply, and naturally cooling to room temperature to obtain the BN-CNTs reinforced PDC-SiC ceramic.

The heating in the steps 1, 3 and 4 is carried out in a heat treatment furnace using a resistance wire as a heating body.

The concentration of the concentrated nitric acid solution is 12 mol/L.

In the step 2, the molar ratio of the boric acid to the urea is 1: 1-10.

Sieving the precursor powder in the step 4 by using a sieve of 100-400 meshes; the pressure of the tablet press is 5-20 KN.

Advantageous effects

The invention provides a boron nitride coated carbon nanotube enhanced polymer conversion ceramic-based wave-absorbing material and a preparation method thereof.A pretreated Carbon Nanotube (CNTs) is added into a Boron Nitride (BN) precursor solution prepared from boric acid and urea for ultrasonic dispersion treatment, and then BN coated CNTs nano powder (BN-CNTs) is obtained through a mode of multiple vacuum filtration, drying and heat treatment; uniformly dispersing the nano powder into liquid Polycarbosilane (PCS), and performing low-temperature crosslinking and high-temperature cracking heat treatment to prepare the BN-CNTs reinforced polymer-converted silicon carbide (PDC-SiC) ceramic composite material. The introduction of BN-CNTs improves the current situations of impedance mismatch and insufficient loss capacity when the current PDC-SiC ceramic is applied as a wave-absorbing material, optimizes the dielectric constant of the PDC-SiC and improves the wave-absorbing performance of the PDC-SiC.

Adding CNTs into a BN precursor solution prepared from boric acid and urea for ultrasonic dispersion, and drying and carrying out high-temperature heat treatment on the obtained product after suction filtration to obtain BN-CNTs powder; uniformly dispersing BN-CNTs powder into liquid-phase polycarbosilane, and preparing the BN-CNTs reinforced ceramic matrix composite through low-temperature crosslinking and high-temperature heat treatment. The material takes PDC-SiC ceramic as a matrix and is compounded with BN-CNTs nano powder to form a multiphase composite material containing SiC, free carbon and BN-CNTs. The introduction of BN-CNTs not only improves the electron transfer capability of the whole PDC-SiC ceramic structure and enhances the dielectric loss capability of the PDC-SiC, but also increases the interface layer in the composite material due to the existence of the BN phase, improves the matching impedance of the PDC-SiC and the electromagnetic wave free space, and provides the microwave absorption capability of the material. At the same cracking temperature, the minimum reflection coefficient of the BN-CNTs enhanced PDC-SiC is reduced to-49.47 dB compared with-40.32 dB of the PDC-SiC, and the maximum effective absorption bandwidth (< -10dB) is increased to 4.0GHz from 1.9 GHz. In addition, the PDC-SiC prepared by the method has the characteristics of low raw material input and equipment cost and high yield, is suitable for large-scale production, and has good application prospect.

Drawings

FIG. 1 shows scanning electron micrographs of prepared BN-CNTs (b) and primary CNTs (a), respectively. The tube diameter of the original carbon nano tube can be clearly seen to be between 40 nm and 50nm, the length reaches the micron level, and a layer of uniform coating layer is formed on the surface of the CNTs after the BN coating.

FIG. 2 shows TEM photographs of prepared BN-CNTs (a), (b) and original CNTs (c), respectively. The thickness of the coated BN phase was seen to be around 10 nm.

FIG. 3 is SEM images of PDC-SiC (a) and BN-CNTs reinforced PDC-SiC (b) ceramic materials prepared by the present invention, respectively. It can be seen that the grain size of the SiC ceramic particles is about 10 μm, and BN-CNTs are uniformly distributed on the surface of the ceramic.

FIG. 4 is a wave-absorbing performance diagram of the prepared pure PDC-SiC ceramic (a) and the BN-CNTs enhanced PDC-SiC ceramic (b) prepared by the invention. The standard of effective absorption is achieved by taking-10 dB as a material, the minimum reflectivity of the pure PDC-SiC ceramic is-40.32 dB, the effective absorption bandwidth is 1.9GHz, the minimum reflectivity of the BN-CNTs enhanced PDC-SiC ceramic is reduced to-49.47 dB, and the effective absorption bandwidth is improved to 4.0 GHz.

Detailed Description

The invention will now be further described with reference to the following examples and drawings:

example 1:

(1) firstly, putting CNTs into a heat treatment furnace with a resistance wire as a heating body, carrying out heat treatment on the CNTs for 3.5h at 400 ℃ in Ar atmosphere, then adding the CNTs subjected to heat treatment into 12mol/L concentrated nitric acid solution for carrying out ultrasonic treatment for 0.5h, and then washing the CNTs to be neutral;

(2) mixing and dispersing boric acid and urea in a molar ratio of 1: 1-10 in 200ml of deionized water, and magnetically stirring for 12 hours until the solution is transparent; adding the pretreated CNTs into the solution, performing ultrasonic dispersion treatment for 60min, collecting the CNTs by using a vacuum filtration device, and drying for later use;

(3) putting the dried CNTs into a heat treatment furnace with a resistance wire as a heating body, and placing the dried CNTs in flowing N ₂ In the atmosphere, raising the furnace temperature from room temperature to 800-1200 ℃ at a temperature raising rate of 5 ℃/min, and preserving the temperature for 5 hours; and turning off the power supply, and naturally cooling to room temperature to obtain the thermally treated CNTs.

Repeating the step 2 and the step 3 for 4 times to obtain BN-CNTs;

(4) BN-CNTs with the mass fraction of 3 percent and liquid phase Polycarbosilane (PCS) are subjected to ultrasonic dispersion mixing for 2 hours; putting the uniformly mixed sample into a heat treatment furnace with a resistance wire as a heating body, heating the furnace to 100-400 ℃ from room temperature at a heating rate of 5 ℃/min in a flowing Ar atmosphere, and keeping the temperature for 2 hours; turning off the power supply, and naturally cooling to room temperature to obtain a cross-linked sample;

fully grinding and screening the cured sample to obtain precursor powder of 100-400 meshes, and pressing the powder into a square sample with the size of 22.86mm multiplied by 10.16mm multiplied by 2.00mm by using the pressure of 5-20 KN;

(5) putting the square sample into a heat treatment furnace with a resistance wire as a heating body, heating the furnace to 800-1500 ℃ from room temperature at a heating rate of 5 ℃/min in a flowing Ar atmosphere, and keeping the temperature for 2 hours; and turning off the power supply, and naturally cooling to room temperature to obtain the BN-CNTs reinforced PDC-SiC ceramic.

Example 2

(2) mixing and dispersing boric acid and urea in a molar ratio of 1: 1-10 in 200ml of deionized water, and magnetically stirring for 12 hours until the solution is transparent; adding the pretreated CNTs into a solution, performing ultrasonic dispersion treatment for 60min, collecting the CNTs by using a vacuum filtration device, and drying for later use;

Repeating the step 2 and the step 3 for 4 times to obtain BN-CNTs;

(4) BN-CNTs with the mass fraction of 5 percent and liquid phase Polycarbosilane (PCS) are subjected to ultrasonic dispersion mixing for 2 hours; putting the uniformly mixed sample into a heat treatment furnace with a resistance wire as a heating body, heating the furnace to 100-400 ℃ from room temperature at a heating rate of 5 ℃/min in a flowing Ar atmosphere, and keeping the temperature for 2 hours; turning off the power supply, and naturally cooling to room temperature to obtain a cross-linked sample;

Example 3

Repeating the step 2 and the step 3 for 4 times to obtain BN-CNTs;

(4) carrying out ultrasonic dispersion and mixing on 10 mass percent of BN-CNTs and liquid phase Polycarbosilane (PCS) for 2 h; putting the uniformly mixed sample into a heat treatment furnace with a resistance wire as a heating body, heating the furnace to 100-400 ℃ from room temperature at a heating rate of 5 ℃/min in a flowing Ar atmosphere, and keeping the temperature for 2 hours; turning off the power supply, and naturally cooling to room temperature to obtain a cross-linked sample;

fully grinding and screening the solidified sample to obtain precursor powder of 100-400 meshes, and pressing the powder into a square sample with the size of 22.86mm multiplied by 10.16mm multiplied by 2.00mm by using the pressure of 5-20 KN;

Claims

1. a boron nitride-coated carbon nanotube-enhanced polymer-converted ceramic-based wave-absorbing material is characterized in that taking the polymer-converted silicon carbide ceramics as a matrix, compounding with BN-CNTs nano-powder, forming a kind of comprising The multiphase composite material of SiC, free carbon, BN and CNTs; the mass percentage of BN-CNTs nano-powder is 1% to 5%; BN-CNTs are uniformly distributed in the SiC ceramic matrix.

2. a preparation method of the boron nitride-coated carbon nanotube-enhanced polymer-converted ceramic-based wave absorbing material of claim 1, characterized in that the steps are as follows:

Step 1: In an Ar atmosphere, heat the CNTs at 200-600°C for 2-5 hours, then add the heat-treated CNTs to a concentrated nitric acid solution and ultrasonicate for 0.5-2 hours, and then wash the CNTs to neutrality;

Step 2: Mix and disperse boric acid and urea in deionized water, stir magnetically for 10 to 15 hours until the solution is transparent; add the pretreated CNTs in step 1 into the solution for ultrasonic dispersion for 30 to 90 minutes, use a vacuum filtration device to collect CNTs and bake them Dry;

Step 3: In a flowing N ₂ atmosphere, the oven temperature is raised from room temperature to 800-1200°C at a heating rate of 3-10°C/min for 3-7h; the power is turned off to cool down to room temperature naturally to obtain heat treatment after the CNTs;

Repeat the above steps 2 and 3 for 2 to 6 times on the heat-treated CNTs to obtain BN-CNTs;

Step 4: ultrasonically disperse and mix BN-CNTs with a mass fraction of 0% to 20% and liquid polycarbosilane PCS for 1 to 4 hours; in a flowing Ar atmosphere, increase the furnace temperature from 3 to 10 °C/min at a heating rate. The room temperature was raised to 100-300 °C, and the temperature was kept for 1-3 hours; the power was turned off and cooled to room temperature naturally to obtain the cross-linked sample;

The cross-linked sample is fully ground and sieved to obtain a precursor powder, and the powder is pressed into a solid block;

Step 5: Put the solid block into a heat treatment furnace with a resistance wire as a heating element, in a flowing Ar atmosphere, increase the furnace temperature from room temperature to 800-1500 °C at a heating rate of 3-10 °C/min, and keep the temperature. 1 ~ 4h; turn off the power and naturally cool to room temperature to obtain BN-CNTs-enhanced PDC-SiC ceramics.

3 . The method according to claim 2 , wherein the heating in the steps 1, 3 and 4 is performed in a heat treatment furnace using a resistance wire as a heating element. 4 .

4. method according to claim 2 is characterized in that: described concentrated nitric acid solution concentration is 12mol/L.

5 . The method according to claim 2 , wherein the molar ratio of boric acid and urea in step 2 is 1:1 to 10. 6 .

6 . The method according to claim 2 , wherein the precursor powder in step 4 is passed through a 100-400 mesh sieve; the tableting machine pressure is 5-20 KN. 7 .