CN114956830B - Boron nitride coated carbon nano tube reinforced polymer converted ceramic-based wave absorbing material and preparation method thereof - Google Patents
Boron nitride coated carbon nano tube reinforced polymer converted ceramic-based wave absorbing material and preparation method thereof Download PDFInfo
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Abstract
The invention relates to a boron nitride coated carbon nanotube reinforced polymer converted ceramic-based wave absorbing material and a preparation method thereof, wherein pretreated Carbon Nanotubes (CNTs) are added into 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 by a plurality of vacuum filtration, drying and heat treatment modes; uniformly dispersing the nano powder into liquid Polycarbosilane (PCS), and preparing the BN-CNTs reinforced polymer-converted silicon carbide (PDC-SiC) ceramic composite material through low-temperature crosslinking and high-temperature cracking heat treatment. The BN-CNTs are introduced to improve the current situation of impedance mismatch and insufficient loss capacity when the PDC-SiC ceramic is used as a wave absorbing material, optimize the dielectric constant of the PDC-SiC and improve the wave absorbing performance of the PDC-SiC ceramic.
Description
Technical Field
The invention belongs to the technical field of wave-absorbing materials, and relates to a boron nitride coated carbon nano tube reinforced polymer conversion ceramic-based wave-absorbing material and a preparation method thereof.
Background
With the stronger detection and tracking capability of defense systems of various countries in the world, the survivability of military targets and the outburst prevention capability of weapon systems are increasingly threatened, so that the development of high-performance wave-absorbing stealth materials has become an important and critical direction in modern national defense systems. The polymer-converted silicon carbide (PDC-SiC) ceramic has excellent high-temperature creep resistance and chemical stability, the preparation process is simple and convenient and controllable, and the ceramic becomes a promising wave-absorbing material due to the special dielectric and electrical properties (change along with the change of cracking temperature). However, when the pure PDC-SiC ceramic is applied as a wave-absorbing material, the dielectric loss capacity is weak, the real part of the relative dielectric constant is too high, and the impedance matching property with air is poor, which also greatly reduces the wave-absorbing capacity. It is highly desirable to improve the impedance matching properties of PDC-SiC ceramics and to improve their wave-absorbing properties.
The document 1"Li Q,Yin X,Duan W,et al.Electrical,dielectric and microwave-absorption properties of polymer derived SiC ceramics in X band [ J ]. Journal of alloys and compounds,2013,565:66-72 discloses research on dielectric, electric and microwave characteristics of polymer-converted silicon carbide ceramics in the X-band, the ceramics are prepared at different cracking temperatures (1100-1600 ℃), the research shows that the content of silicon carbide nanocrystals and free carbon in PDC-SiC ceramics is gradually increased along with the increase of the cracking temperature in the range of 8.2-12.4 GHz (X-band), and the generated grain boundaries generate space charge polarization and interfacial relaxation phenomena under the action of electromagnetic waves, so that the energy of the electromagnetic waves is consumed, but due to poor impedance matching property and insufficient loss capacity of the material, the average reflectivity of a cracked sample at 1400 ℃ is only-9.97 dB, the standard of the reflectivity of-10 dB under the effective loss is not reached, and the problem is worth considering and solving.
Document 2"Hong W,Dong S,Hu P,et al.In situ growth of one-dimensional nanowires on porous PDC-SiC/Si 3 N 4 ceramics with excellent microwave absorption properties[J]Ceramics International,2017,43 (16): 14301-14308 discloses an in situ grown Si 3 N 4 Nanowire-modified porous PDC-SiC/Si 3 N 4 Method for producing ceramic, wherein Si 3 N 4 NWs are formed in situ in the tunnel by a gas-solid (VS) mechanism, with Si 3 N 4 Improvement of NWs content, PDC-SiC/Si 3 N 4 Microstructure and mechanical properties of porous ceramicsCan also be changed, the minimum reflectance of the whole composite material is improved along with the increase of the PDC-SiC content, which is mainly beneficial to PDC-SiC nano particles, nano carbon and Si formed in situ 3 N 4 The different 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, the wave-absorbing frequency band of the material with single-layer thickness 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 nano-filler phases to improve dielectric loss capacity of a matrix.
The document 3"Zhang Y,Yin X,Ye F,et al.Effects of multi-walled carbon nanotubes on the crystallization behavior of PDCs-SiBCN and their improved dielectric and EM absorbing properties [ J ]. Journal of the European Ceramic Society,2014,34 (5): 1053-1061." discloses a method for preparing a polymer-converted derivatized silicon-boron-carbon-nitride ceramic (PDC-SiBCN) containing multi-walled carbon nanotubes, wherein the multi-walled carbon nanotubes, as a nucleating agent, promote heterogeneous nucleation, reduce the crystallization temperature of SiC in SiBCN, and the A (SiBCN matrix) +B (SiC) +C (MWCNTs) structure formed in MWCNTs-SiBCN is beneficial to improving the dielectric properties and electromagnetic absorption properties of the overall composite. However, the electrical conductivity of MWCNTs is too high, so that impedance matching of the whole composite material and free space is aggravated, the effective bandwidth of the material in the 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-converted ceramics has yet to be improved.
As a traditional two-dimensional material, hexagonal boron nitride (h-BN) has good oxidation resistance and low relative dielectric constant, is a candidate material for improving the excellent ceramic conversion of polymers, and can reduce the real part of the relative dielectric constant of the composite material by introducing BN phase, thereby meeting the requirement of impedance matching and improving the wave absorbing performance of the material. In view of this, it is possible,
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 nano tube reinforced polymer converted ceramic-based wave absorbing material and a preparation method thereof, and solves the problems of weaker dielectric loss capacity and poor impedance matching property of PDC-SiC.
The invention provides a preparation method of a boron nitride coated carbon nano tube reinforced polymer converted ceramic-based wave-absorbing material. Firstly, boric acid and urea are used as reaction raw materials to prepare BN precursor solution, then BN coated CNTs nano-phase (BN@CNTs) is prepared through the steps of ultrasonic dispersion, multiple vacuum suction filtration, drying and heat treatment, and finally PDC-SiC ceramic composite material with evenly distributed BN@CNTs is obtained through low-temperature crosslinking and high-temperature cracking heat treatment. The PDC-SiC with enhanced BN@CNTs obtained by the method can effectively improve the current situation that the current PDC-SiC ceramic is insufficient in impedance mismatch and loss capacity when being used as a wave absorbing material.
Technical proposal
A boron nitride coated carbon nano tube reinforced polymer conversion ceramic-based wave absorbing material is characterized in that polymer conversion silicon carbide ceramic is used as a matrix to be compounded with BN@CNTs nano powder, so that a multiphase composite material containing SiC, free carbon, BN and CNTs is formed; wherein the mass percentage of BN@CNTs nano powder is 1% -5%; bn@cnts are uniformly distributed in the SiC ceramic matrix.
The preparation method of the boron nitride coated carbon nanotube reinforced polymer conversion ceramic-based wave-absorbing material is characterized by comprising the following steps of:
step 1: performing heat treatment on CNTs for 2-5 hours at 200-600 ℃ in Ar atmosphere, adding the heat-treated CNTs into concentrated nitric acid solution, performing ultrasonic treatment for 0.5-2 hours, and washing the CNTs to be neutral;
step 2: mixing boric acid and urea, dispersing in deionized water, and magnetically stirring for 10-15 h until the solution is transparent; adding the CNTs pretreated in the step 1 into the solution, carrying out ultrasonic dispersion treatment for 30-90 min, collecting the CNTs by using a vacuum suction filtration device, and drying;
step 3: dried CNTs in flowing N 2 In the atmosphere, the furnace temperature is raised from room temperature to 800-1200 ℃ at a heating rate of 3-10 ℃/min, and the temperature is kept for 3-7 h; switch for closingNaturally cooling to room temperature after power supply is closed to obtain CNTs after heat treatment;
repeating the steps 2 and 3 for 2 to 6 times to obtain BN@CNTs;
step 4: mixing BN@CNTs with mass fraction of 0% -20% with liquid phase polycarbosilane PCS in an ultrasonic dispersion way for 1-4 h; in flowing Ar atmosphere, raising the furnace temperature from room temperature to 100-300 ℃ at a heating rate of 3-10 ℃/min, and preserving heat for 1-3 h; naturally cooling the sample to room temperature after the power supply is turned off, so as to obtain a crosslinked sample;
fully grinding and screening the crosslinked sample to obtain precursor powder, and pressing the powder into solid blocks;
step 5: placing the solid block into a heat treatment furnace taking a resistance wire as a heating body, heating the furnace from room temperature to 800-1500 ℃ at a heating rate of 3-10 ℃/min in flowing Ar atmosphere, and preserving heat for 1-4 h; and (3) closing the power supply, and naturally cooling to room temperature to obtain the PDC-SiC ceramic reinforced by BN@CNTs.
The heating in the step 1, the step 3 and the step 4 is performed in a heat treatment furnace adopting a resistance wire as a heating body.
The concentration of the concentrated nitric acid solution is 12mol/L.
And 2, the molar ratio of boric acid to urea in the step is 1:1-10.
The precursor powder in the step 4 is sieved by a 100-400 mesh sieve; the pressure of the tablet press is 5-20 KN.
Advantageous effects
According to the boron nitride coated carbon nanotube reinforced polymer converted ceramic-based wave absorbing material and the preparation method thereof, pretreated Carbon Nanotubes (CNTs) are added into 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 by a plurality of vacuum filtration-drying-heat treatment modes; uniformly dispersing the nano powder into liquid Polycarbosilane (PCS), and preparing the BN@CNTs reinforced polymer-converted silicon carbide (PDC-SiC) ceramic composite material through low-temperature crosslinking and high-temperature cracking heat treatment. The BN@CNTs are introduced to improve the current situation of impedance mismatch and insufficient loss capacity when the traditional PDC-SiC ceramic is used as a wave absorbing material, optimize the dielectric constant of the PDC-SiC and improve the wave absorbing performance of the PDC-SiC ceramic.
Adding CNTs into BN precursor solution prepared from boric acid and urea, performing ultrasonic dispersion, and performing suction filtration, and then drying and high-temperature heat treatment on the obtained product to obtain BN@CNTs powder; uniformly dispersing BN@CNTs powder into liquid phase polycarbosilane, and preparing the BN@CNTs reinforced ceramic-based composite material 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 the multiphase composite material containing SiC, free carbon and BN@CNTs. The BN@CNTs are introduced, so that the electron transfer capacity of the whole PDC-SiC ceramic structure is improved, the dielectric loss capacity of the PDC-SiC is enhanced, the existence of BN phase is increased, the interface layer in the composite material is increased, the matching impedance of the PDC-SiC and the electromagnetic wave free space is improved, and the microwave absorption capacity of the material is provided. At the same cracking temperature, the minimum reflection coefficient of PDC-SiC enhanced by BN@CNTs is reduced to-49.47 dB compared with-40.32 dB of PDC-SiC, and the maximum effective absorption bandwidth (< -10 dB) is increased from 1.9GHz to 4.0GHz. In addition, the PDC-SiC prepared by the method has the characteristics of low raw material investment, low equipment cost and high yield, is suitable for large-scale production, and has good application prospect.
Drawings
FIG. 1 is a scanning electron micrograph of prepared BN@CNTs (b) and original CNTs (a), respectively. The pipe diameter of the original carbon nano-tube can be clearly seen to be between 40 and 50nm, the length reaches the micron level, and a uniform coating layer is formed on the surface of CNTs after BN coating.
FIG. 2 is a transmission electron micrograph 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 an SEM image of PDC-SiC (a) and BN@CNTs reinforced PDC-SiC (b) ceramic materials prepared according to the invention, respectively. It can be seen that the SiC ceramic particles have a particle size of about 10 μm and that BN@CNTs are uniformly distributed on the ceramic surface.
FIG. 4 is a graph of the wave absorbing properties of the prepared pure PDC-SiC ceramic (a) and the BN@CNTs reinforced PDC-SiC ceramic (b) prepared according to the invention. The minimum reflectivity of the pure PDC-SiC ceramic is 40.32dB, the effective absorption bandwidth is 1.9GHz, the minimum reflectivity of the BN@CNTs reinforced PDC-SiC ceramic is reduced to 49.47dB, and the effective absorption bandwidth is increased to 4.0GHz.
Detailed Description
The invention will now be further described with reference to examples, figures:
example 1:
(1) Firstly placing CNTs into a heat treatment furnace taking a resistance wire as a heating body, carrying out heat treatment on the CNTs at 400 ℃ for 3.5 hours in Ar atmosphere, then adding the heat-treated CNTs into a 12mol/L concentrated nitric acid solution for ultrasonic treatment for 0.5 hour, and then washing the CNTs to be neutral;
(2) Boric acid and urea are mixed and dispersed in 200ml deionized water according to the mol ratio of 1:1-10, and magnetically stirred for 12 hours until the solution is transparent; adding the pretreated CNTs into the solution, carrying out ultrasonic dispersion treatment for 60min, collecting the CNTs by using a vacuum suction filtration device, and drying for later use;
(3) Putting the dried CNTs into a heat treatment furnace with resistance wires as heating elements, and flowing N 2 In the atmosphere, the furnace temperature is raised from room temperature to 800-1200 ℃ at a heating rate of 5 ℃/min, and the temperature is kept for 5 hours; and (5) closing the power supply, and naturally cooling to room temperature to obtain the CNTs after heat treatment.
Repeating the steps 2 and 3 for 4 times to obtain BN@CNTs;
(4) Mixing BN@CNTs with mass fraction of 3% with liquid phase Polycarbosilane (PCS) in an ultrasonic dispersion way for 2 hours; placing the uniformly mixed sample into a heat treatment furnace taking a resistance wire as a heating body, heating the furnace temperature to 100-400 ℃ from room temperature at a heating rate of 5 ℃/min in flowing Ar atmosphere, and preserving heat for 2h; naturally cooling the sample to room temperature after the power supply is turned off, so as to obtain a crosslinked sample;
fully grinding and screening the cured sample to obtain precursor powder of 100-400 meshes, and pressing the powder into square samples with the dimensions of 22.86mm multiplied by 10.16mm multiplied by 2.00mm by using the pressure of 5-20 KN;
(5) Placing the square sample into a heat treatment furnace taking a resistance wire as a heating body, heating the furnace from room temperature to 800-1500 ℃ at a heating rate of 5 ℃/min in flowing Ar atmosphere, and preserving heat for 2h; and (3) closing the power supply, and naturally cooling to room temperature to obtain the PDC-SiC ceramic reinforced by BN@CNTs.
Example 2
(1) Firstly placing CNTs into a heat treatment furnace taking a resistance wire as a heating body, carrying out heat treatment on the CNTs at 400 ℃ for 3.5 hours in Ar atmosphere, then adding the heat-treated CNTs into a 12mol/L concentrated nitric acid solution for ultrasonic treatment for 0.5 hour, and then washing the CNTs to be neutral;
(2) Boric acid and urea are mixed and dispersed in 200ml deionized water according to the mol ratio of 1:1-10, and magnetically stirred for 12 hours until the solution is transparent; adding the pretreated CNTs into the solution, carrying out ultrasonic dispersion treatment for 60min, collecting the CNTs by using a vacuum suction filtration device, and drying for later use;
(3) Putting the dried CNTs into a heat treatment furnace with resistance wires as heating elements, and flowing N 2 In the atmosphere, the furnace temperature is raised from room temperature to 800-1200 ℃ at a heating rate of 5 ℃/min, and the temperature is kept for 5 hours; and (5) closing the power supply, and naturally cooling to room temperature to obtain the CNTs after heat treatment.
Repeating the steps 2 and 3 for 4 times to obtain BN@CNTs;
(4) Mixing BN@CNTs with mass fraction of 5% with liquid phase Polycarbosilane (PCS) in an ultrasonic dispersion way for 2 hours; placing the uniformly mixed sample into a heat treatment furnace taking a resistance wire as a heating body, heating the furnace temperature to 100-400 ℃ from room temperature at a heating rate of 5 ℃/min in flowing Ar atmosphere, and preserving heat for 2h; naturally cooling the sample to room temperature after the power supply is turned off, so as to obtain a crosslinked sample;
fully grinding and screening the cured sample to obtain precursor powder of 100-400 meshes, and pressing the powder into square samples with the dimensions of 22.86mm multiplied by 10.16mm multiplied by 2.00mm by using the pressure of 5-20 KN;
(5) Placing the square sample into a heat treatment furnace taking a resistance wire as a heating body, heating the furnace from room temperature to 800-1500 ℃ at a heating rate of 5 ℃/min in flowing Ar atmosphere, and preserving heat for 2h; and (3) closing the power supply, and naturally cooling to room temperature to obtain the PDC-SiC ceramic reinforced by BN@CNTs.
Example 3
(1) Firstly placing CNTs into a heat treatment furnace taking a resistance wire as a heating body, carrying out heat treatment on the CNTs at 400 ℃ for 3.5 hours in Ar atmosphere, then adding the heat-treated CNTs into a 12mol/L concentrated nitric acid solution for ultrasonic treatment for 0.5 hour, and then washing the CNTs to be neutral;
(2) Boric acid and urea are mixed and dispersed in 200ml deionized water according to the mol ratio of 1:1-10, and magnetically stirred for 12 hours until the solution is transparent; adding the pretreated CNTs into the solution, carrying out ultrasonic dispersion treatment for 60min, collecting the CNTs by using a vacuum suction filtration device, and drying for later use;
(3) Putting the dried CNTs into a heat treatment furnace with resistance wires as heating elements, and flowing N 2 In the atmosphere, the furnace temperature is raised from room temperature to 800-1200 ℃ at a heating rate of 5 ℃/min, and the temperature is kept for 5 hours; and (5) closing the power supply, and naturally cooling to room temperature to obtain the CNTs after heat treatment.
Repeating the steps 2 and 3 for 4 times to obtain BN@CNTs;
(4) Mixing 10% of BN@CNTs and liquid phase Polycarbosilane (PCS) in an ultrasonic dispersion manner for 2 hours; placing the uniformly mixed sample into a heat treatment furnace taking a resistance wire as a heating body, heating the furnace temperature to 100-400 ℃ from room temperature at a heating rate of 5 ℃/min in flowing Ar atmosphere, and preserving heat for 2h; naturally cooling the sample to room temperature after the power supply is turned off, so as to obtain a crosslinked sample;
fully grinding and screening the cured sample to obtain precursor powder of 100-400 meshes, and pressing the powder into square samples with the dimensions of 22.86mm multiplied by 10.16mm multiplied by 2.00mm by using the pressure of 5-20 KN;
(5) Placing the square sample into a heat treatment furnace taking a resistance wire as a heating body, heating the furnace from room temperature to 800-1500 ℃ at a heating rate of 5 ℃/min in flowing Ar atmosphere, and preserving heat for 2h; and (3) closing the power supply, and naturally cooling to room temperature to obtain the PDC-SiC ceramic reinforced by BN@CNTs.
Claims (5)
1. A boron nitride coated carbon nano tube reinforced polymer conversion ceramic-based wave absorbing material is characterized in that polymer conversion silicon carbide ceramic is used as a matrix to be compounded with BN@CNTs nano powder, so that a multiphase composite material containing SiC, free carbon, BN and CNTs is formed; wherein the mass percentage of BN@CNTs nano powder is 1% -5%; BN@CNTs are uniformly distributed in the SiC ceramic matrix; the preparation method of the boron nitride coated carbon nanotube reinforced polymer conversion ceramic-based wave-absorbing material comprises the following steps:
step 1: performing heat treatment on CNTs for 2-5 hours at 200-600 ℃ in Ar atmosphere, adding the heat-treated CNTs into concentrated nitric acid solution, performing ultrasonic treatment for 0.5-2 hours, and washing the CNTs to be neutral;
step 2: mixing boric acid and urea, dispersing in deionized water, and magnetically stirring for 10-15 h until the solution is transparent; adding the CNTs pretreated in the step 1 into the solution, carrying out ultrasonic dispersion treatment for 30-90 min, collecting the CNTs by using a vacuum suction filtration device, and drying;
step 3: dried CNTs in flowing N 2 In the atmosphere, the furnace temperature is raised from room temperature to 800-1200 ℃ at a heating rate of 3-10 ℃/min, and the temperature is kept for 3-7 h; closing a power supply, and naturally cooling to room temperature to obtain CNTs after heat treatment;
repeating the steps 2 and 3 for 2 to 6 times to obtain BN@CNTs;
step 4: mixing BN@CNTs with mass fraction of 0% -20% with liquid phase polycarbosilane PCS in an ultrasonic dispersion way for 1-4 h; in flowing Ar atmosphere, raising the furnace temperature from room temperature to 100-300 ℃ at a heating rate of 3-10 ℃/min, and preserving heat for 1-3 h; naturally cooling the sample to room temperature after the power supply is turned off, so as to obtain a crosslinked sample;
fully grinding and screening the crosslinked sample to obtain precursor powder, and pressing the powder into solid blocks;
step 5: placing the solid block into a heat treatment furnace taking a resistance wire as a heating body, heating the furnace from room temperature to 800-1500 ℃ at a heating rate of 3-10 ℃/min in flowing Ar atmosphere, and preserving heat for 1-4 h; and (3) closing the power supply, and naturally cooling to room temperature to obtain the PDC-SiC ceramic reinforced by BN@CNTs.
2. The boron nitride coated carbon nanotube reinforced polymer converted ceramic based wave absorbing material of claim 1, wherein: the heating in the step 1, the step 3 and the step 4 is performed in a heat treatment furnace adopting a resistance wire as a heating body.
3. The boron nitride coated carbon nanotube reinforced polymer converted ceramic based wave absorbing material of claim 1, wherein: the concentration of the concentrated nitric acid solution is 12mol/L.
4. The boron nitride coated carbon nanotube reinforced polymer converted ceramic based wave absorbing material of claim 1, wherein: and 2, the molar ratio of boric acid to urea in the step is 1:1-10.
5. The boron nitride coated carbon nanotube reinforced polymer converted ceramic based wave absorbing material of claim 1, wherein: the precursor powder in the step 4 is sieved by a 100-400 mesh sieve; the pressure of the tablet press is 5-20 KN.
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