阅读说明：本技术 氧化石墨烯增强硅硼碳氮陶瓷复合材料及其制备方法 (Graphene oxide reinforced silicon-boron-carbon-nitrogen ceramic composite material and preparation method thereof ) 是由 李达鑫 陈庆庆 贾德昌 杨治华 蔡德龙 周玉 高巍 于 2021-01-22 设计创作，主要内容包括：本发明提供了一种氧化石墨烯增强硅硼碳氮陶瓷复合材料及其制备方法,属于陶瓷吸波材料技术领域。所述氧化石墨烯增强硅硼碳氮陶瓷复合材料包括硅硼碳氮陶瓷和分散在所述硅硼碳氮陶瓷内的氧化石墨烯,所述氧化石墨烯与所述硅硼碳氮陶瓷通过酰化反应形成的化学键连接,且所述氧化石墨烯呈平行排列的层状结构。本发明的氧化石墨烯通过酰化反应改性聚硼硅氮烷,聚硼硅氮烷相当于插层材料分布于相邻氧化石墨烯层之间,增大了相邻氧化石墨烯层之间的间距,破坏了氧化石墨烯层间的范德华力,并且氧化石墨烯键合在聚硼硅氮烷上,防止了氧化石墨烯滑移导致的分散不均匀问题,提高了氧化石墨烯在复合材料中分布的均匀性。(The invention provides a graphene oxide reinforced silicon-boron-carbon-nitrogen ceramic composite material and a preparation method thereof, belonging to the technical field of ceramic wave-absorbing materials. The graphene oxide reinforced silicon boron carbon nitrogen ceramic composite material comprises silicon boron carbon nitrogen ceramic and graphene oxide dispersed in the silicon boron carbon nitrogen ceramic, wherein the graphene oxide is connected with the silicon boron carbon nitrogen ceramic through a chemical bond formed by an acylation reaction, and the graphene oxide is in a parallel-arranged layered structure. According to the invention, the polyborosilazane is modified by the graphene oxide through an acylation reaction, the polyborosilazane is equivalent to an intercalation material and is distributed between adjacent graphene oxide layers, the distance between the adjacent graphene oxide layers is increased, the van der Waals force between the graphene oxide layers is damaged, and the graphene oxide is bonded on the polyborosilazane, so that the problem of uneven dispersion caused by the slippage of the graphene oxide is prevented, and the distribution uniformity of the graphene oxide in the composite material is improved.)

1. The graphene oxide reinforced silicon boron carbon nitrogen ceramic composite material is characterized by comprising silicon boron carbon nitrogen ceramic and graphene oxide dispersed in the silicon boron carbon nitrogen ceramic, wherein the graphene oxide is connected with the silicon boron carbon nitrogen ceramic through chemical bonds formed by acylation reaction, and the graphene oxide is in a parallel-arranged layered structure.

2. The graphene oxide reinforced silicon boron carbon nitrogen ceramic composite material as claimed in claim 1, wherein the mass ratio of the graphene oxide to the precursor of the silicon boron carbon nitrogen ceramic is 0.04-0.08: 1.

3. the graphene oxide reinforced silicon boron carbon nitrogen ceramic composite material according to claim 1, wherein the microstructure of the silicon boron carbon nitrogen ceramic consists of a silicon boron carbon nitrogen amorphous matrix phase, a free carbon phase and a silicon carbide phase.

4. A method for preparing a graphene oxide reinforced silicon boron carbon nitrogen ceramic composite material, which is used for preparing the graphene oxide reinforced silicon boron carbon nitrogen ceramic composite material as claimed in any one of claims 1 to 3, and comprises the following steps:

s1, preparing a graphene oxide dispersion liquid: adding graphene oxide into anhydrous dimethylformamide, and performing ultrasonic dispersion to obtain a graphene oxide dispersion liquid;

s2, oxidized graphene modified polysilazane: under an inert atmosphere, adding a polyborosilazane solution into the graphene oxide dispersion liquid, then adding an initiator, performing ultrasonic dispersion, then heating and refluxing, then heating to 150-;

s3, high-temperature pyrolysis: heating the graphene oxide modified polysilazane to 1300-1600 ℃ in an inert atmosphere, preserving the temperature, carrying out a pyrolysis reaction, and then naturally cooling to room temperature to obtain the graphene oxide reinforced silicon boron carbon nitrogen ceramic composite material.

5. The production method according to claim 4, wherein in step S2, the mass ratio of the graphene oxide to the polysilazane is 0.04 to 0.08: 1.

6. the method according to claim 4, wherein in step S2, the mass ratio of the initiator to the polysilazane is 0.01 to 0.04: 1.

7. the method according to claim 4, wherein the heating reflux temperature is 80 ℃ and the heating reflux time is 72 hours in step S2.

8. The method according to claim 4, wherein in step S2, the temperature is raised at a rate of 5 ℃/min and the holding time is 24 hours.

9. The method according to claim 4, wherein the temperature is increased at a rate of 5 to 10 ℃/min in step S3.

10. The method according to claim 4, wherein in step S3, the graphene oxide-modified polysilazane of step S2 is heated to 1300 ℃ and kept at the temperature for 1 to 8 hours under an inert atmosphere.

Technical Field

The invention relates to the technical field of ceramic wave-absorbing materials, in particular to a graphene oxide reinforced silicon-boron-carbon-nitrogen ceramic composite material and a preparation method thereof.

Background

With the rapid development of integrated circuit technology and wireless communication systems, electromagnetic radiation of different frequencies fills the living space of people, destroys the good ecological environment of human beings, and causes serious electromagnetic pollution. In addition, in the field of national defense and military, the research and development and competition of global electronic information countermeasure and radar detection and anti-detection are fiercely, and in the future battlefield, in order to improve the anti-radar reconnaissance capability of high-speed aircrafts such as fighters, the omnibearing stealth becomes the necessary capability of the future aircrafts. Therefore, research and development of a wave-absorbing material capable of solving electromagnetic radiation pollution and serving as a core of stealth technology have become a current research focus. In view of the severe practical service environment of such materials in the military field, the ideal electromagnetic wave absorbing material should satisfy the requirements of light weight, high temperature resistance, corrosion resistance, and high mechanical strength in addition to the requirements of impedance matching and energy loss.

Metastable silicon boron carbon nitrogen (SiBCN) ceramics have the obvious advantages of light weight, low density, high strength, good oxidation resistance, corrosion and ablation resistance, excellent high-temperature stability and the like, and can be used as a potential high-temperature structural ceramic material, but poor electromagnetic wave absorption performance is generally caused by poor dielectric properties and low conductivity of the SiBCN ceramics. By introducing conductive fillers (e.g., carbon nanotubes, carbon nanowires, carbon fibers, graphene oxide, and reduced graphene oxide) into the SiBCN ceramic, its conductivity and dielectric properties can be adjusted to some extent. However, most of the conductive filler modified ceramic composite materials reported at present are prepared by conventional methods such as blending, the conductive fillers are randomly distributed in the ceramic matrix, a high content is required to form a conductive network, and the incorporation of the conductive fillers into the ceramic matrix may cause impedance mismatch between the material and air, so that it is very necessary to introduce a proper content of the conductive fillers. In addition, the lamellar or granular structure of the conductive filler has an ultra-large specific surface area and an ultra-high specific surface energy, so that the conductive filler is easy to agglomerate or agglomerate on a ceramic matrix, the actual performance of the composite material is greatly influenced, and the attenuation effect on electromagnetic waves is weakened.

Disclosure of Invention

Aiming at the problems in the prior art, the invention provides a graphene oxide reinforced silicon boron carbon nitrogen ceramic composite material and further provides a preparation method of the graphene oxide reinforced silicon boron carbon nitrogen ceramic composite material.

In order to achieve the purpose, the invention is specifically realized by the following technical scheme:

the graphene oxide reinforced silicon boron carbon nitrogen ceramic composite material comprises silicon boron carbon nitrogen ceramic and graphene oxide dispersed in the silicon boron carbon nitrogen ceramic, wherein the graphene oxide is connected with chemical bonds formed by acylation reaction of the silicon boron carbon nitrogen ceramic, and the graphene oxide is in a parallel-arranged layered structure.

Further, the mass ratio of the graphene oxide to the precursor of the silicon-boron-carbon-nitrogen ceramic is 0.04-0.08: 1.

further, the mass ratio of the graphene oxide to the precursor of the silicon-boron-carbon-nitrogen ceramic is 0.06: 1.

furthermore, the microstructure of the silicon-boron-carbon-nitrogen ceramic consists of a silicon-boron-carbon-nitrogen amorphous matrix phase, a free carbon phase and a silicon carbide phase.

In addition, the invention provides a preparation method of the graphene oxide reinforced silicon-boron-carbon-nitrogen ceramic composite material, which comprises the following steps:

s1, preparing a graphene oxide dispersion liquid: adding graphene oxide into anhydrous dimethylformamide, and performing ultrasonic dispersion to obtain a graphene oxide dispersion liquid;

s2, oxidized graphene modified polysilazane: under an inert atmosphere, adding a polyborosilazane solution into the graphene oxide dispersion liquid, then adding an initiator, performing ultrasonic dispersion, then heating and refluxing, then heating to 150-;

s3, high-temperature pyrolysis: heating the graphene oxide modified polysilazane to 1300-1600 ℃ in an inert atmosphere, preserving the temperature, carrying out a pyrolysis reaction, and then naturally cooling to room temperature to obtain the graphene oxide reinforced silicon boron carbon nitrogen ceramic composite material.

Further, in step S2, the mass ratio of the graphene oxide to the polysilazane is 0.04 to 0.08: 1.

further, in step S2, the mass ratio of the initiator to the polysilazane is 0.01 to 0.04: 1.

further, in step S2, the initiator is one or more of dicumyl peroxide, benzoyl peroxide, di-t-butyl peroxide, methyl ethyl ketone peroxide, and cyclohexanone peroxide.

Further, in step S2, the temperature of the heating reflux is 80 ℃ and the time is 72 h.

Further, in step S2, the temperature rise rate is 5 ℃/min and the heat preservation time is 24 hours.

Further, in step S3, the temperature increase rate is 5-10 ℃/min.

Further, in step S3, the graphene oxide modified polysilazane of step S2 is heated to 1300 ℃ under an inert atmosphere and is kept warm for 1-8 h.

Compared with the prior art, the invention has the following advantages:

1. according to the invention, the polyborosilazane is modified by the graphene oxide through an acylation reaction, the polyborosilazane is equivalent to an intercalation material and is distributed between adjacent graphene oxide layers, the distance between the adjacent graphene oxide layers is increased, the van der Waals force between the graphene oxide layers is damaged, and the graphene oxide is bonded on the polyborosilazane and is tightly combined with the SiBCN amorphous matrix, so that the problem of uneven dispersion caused by the slippage of the graphene oxide is prevented, and the distribution uniformity of the graphene oxide in the composite material is improved.

2. In the graphene oxide reinforced silicon-boron-carbon-nitrogen ceramic composite material, the graphene oxide has a high dielectric constant, so that the dielectric constant of SiBCN ceramic can be improved, the impedance mismatch of the composite material can be effectively adjusted, and the wave-absorbing performance is improved. And the graphene oxide and SiBCN ceramic form tight combination through chemical bonds, so that the interface polarization effect at the combination part is enhanced, and the dielectric loss effect is improved. Meanwhile, the layered structure with the parallel distribution of the graphene oxide can reflect electromagnetic waves in multiple ways, so that the dissipation path of the electromagnetic waves is increased, the electromagnetic waves and the wave-absorbing components in the graphene oxide and SiBCN ceramics are acted for multiple times, the absorption efficiency of the electromagnetic waves is improved, and the composite material with excellent absorption performance is obtained.

3. The graphene oxide reinforced silicon-boron-carbon-nitrogen ceramic composite material disclosed by the invention is good in high temperature resistance and can be used for strong absorption of electromagnetic waves in a severe environment.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.

FIG. 1 is a flowchart of a preparation method of a graphene oxide reinforced silicon boron carbon nitrogen ceramic composite material according to an embodiment of the invention;

FIG. 2 is a TEM image of a graphene oxide reinforced silicon boron carbon nitrogen ceramic composite material according to an embodiment of the present invention;

FIG. 3 is an electromagnetic wave absorption characteristic diagram of a graphene oxide reinforced silicon-boron-carbon-nitrogen ceramic composite material prepared at different pyrolysis temperatures according to an embodiment of the invention;

fig. 4 is an electromagnetic wave absorption characteristic diagram of the graphene oxide reinforced silicon-boron-carbon-nitrogen ceramic composite material prepared from the graphene oxide dispersion liquid with different concentrations in the embodiment of the invention.

Detailed Description

It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict. In addition, the terms "comprising," "including," and "having" are intended to be non-limiting, i.e., other steps and other ingredients can be added that do not affect the results. Materials, equipment and reagents are commercially available unless otherwise specified.

For a better understanding of the invention, and not as a limitation on the scope thereof, all numbers expressing quantities, percentages, and other numerical values used in the present invention are to be understood as being modified in all instances by the term "about". Accordingly, unless expressly indicated otherwise, the numerical parameters set forth in the specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained. At the very least, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below.

The embodiment of the invention provides a graphene oxide reinforced silicon boron carbon nitrogen ceramic composite material which comprises silicon boron carbon nitrogen (SiBCN) ceramic and graphene oxide (RGO) dispersed in the silicon boron carbon nitrogen ceramic, wherein the graphene oxide is connected with the silicon boron carbon nitrogen ceramic through a chemical bond formed by acylation reaction, and the graphene oxide is in a layered structure arranged in parallel.

In this example, as shown in fig. 1, oxygen-containing functional groups such as hydroxyl (-OH), epoxy (C-O-C), carbonyl (-C ═ O), and carboxyl (-COOH) are connected to the surface of RGO, and under the action of an initiator, the oxygen-containing functional groups of RGO and the amino groups of polysilazane, which is a precursor of SiBCN ceramics, undergo an acylation reaction to obtain a novel single-source precursor, graphene oxide-modified polyborosilazane, and then the single-source precursor is pyrolyzed at a high temperature to obtain a graphene oxide-reinforced silico-boron-carbon-nitrogen ceramic composite material. Under the macroscopic view, the graphene oxide reinforced silicon-boron-carbon-nitrogen ceramic composite material is black powder.

The polyborosilazane is modified by graphene oxide through acylation reaction, the polyborosilazane is equivalent to an intercalation material distributed between adjacent graphene oxide layers, the distance between the adjacent graphene oxide layers is increased, the van der Waals force between the graphene oxide layers is destroyed, the RGO agglomeration and agglomeration problems are reduced, and the graphene oxide is bonded on the polyborosilazane, the combination with a SiBCN amorphous matrix is tight, the problem of uneven dispersion caused by the slippage of the graphene oxide is prevented, the distribution uniformity of the graphene oxide in a composite material is improved, and the graphene in the composite material is in a state parallel to each other, the transverse size is large, the graphene oxide is in full contact with SiBCN ceramics, and the reduction of the using amount of the graphene oxide is facilitated when a good conductive network is formed.

In the graphene oxide reinforced silicon-boron-carbon-nitrogen ceramic composite material, the SiBCN amorphous matrix phase is an electrical insulation matrix and has excellent wave-transmitting performance, and the RGO has a high dielectric constant and can improve the dielectric constant of the SiBCN amorphous matrix and effectively adjust the impedance mismatch of the composite material, so that electromagnetic waves incident to the composite material can permeate into the composite material from an air medium as much as possible, and are converted into heat energy, and the wave-absorbing performance of the composite material is improved. And a large number of exposed chemical bonds on the surface of the graphene oxide are easy to generate polarization relaxation/dipole relaxation under the action of an electromagnetic field, so that electromagnetic waves are attenuated through dielectric loss, and the graphene oxide and SiBCN ceramic are tightly combined through the chemical bonds, so that the interface polarization effect at the combined part is enhanced, and the high-frequency dielectric loss is improved. Meanwhile, the electromagnetic waves incident into the composite material are subjected to multiple reflection by the RGO parallel-distributed laminated structure, so that the reflection path of the electromagnetic waves entering the composite material is greatly prolonged, the dissipation path of the electromagnetic waves is increased, the electromagnetic waves and the graphene oxide and the wave-absorbing component in the SiBCN ceramic, namely free carbon and SiC, are subjected to multiple actions, the absorption efficiency of the electromagnetic waves is improved, and the composite material with excellent absorption performance is obtained.

Preferably, the microstructure of the SiBCN ceramic consists of a SiBCN amorphous matrix phase, a free carbon phase and a SiC phase. SiC and RGO cooperate, can be better the dielectric properties of regulation combined material, improve the impedance matching degree of combined material and free space, increase transmission intensity, effectively promote the absorptive capacity to the electromagnetic wave. RGO has excellent conductive performance, can form a conductive network in SiBCN ceramics, and can form a conductive path in the whole composite material by matching with the conductive network formed by free carbon in the SiBCN amorphous matrix so as to rapidly conduct an external electric field to SiC, wherein the SiC is a polarized molecule and becomes a dipole under the action of the external electric field and is regularly arranged along the direction of the electric field, so that polarization relaxation attenuates and absorbs electromagnetic waves, and the dielectric loss effect is enhanced. Therefore, the electromagnetic wave absorption capability of the composite material is greatly enhanced through the mutual matching of the SiC phase, the free carbon phase, the SiBCN amorphous matrix phase and the RGO.

The excellent conductivity of RGO reduces the impedance matching performance, the too high content of RGO in the composite material is not beneficial to the improvement of the impedance matching performance of the composite material and the free space, the composite material is easy to reflect the electromagnetic wave, so that the electromagnetic wave cannot enter the material, the attenuation effect of dielectric loss cannot be resisted by the influence of reflection, and the wave-absorbing performance is reduced; too low a content of RGO in the composite material is detrimental to the formation of conductive paths, leading to a reduced dielectric loss effect. Therefore, it is necessary to introduce an appropriate amount of RGO to improve the wave-absorbing properties. In the actual preparation process, SiBCN ceramic in the composite material is obtained by pyrolyzing polyborosilazane, which is a precursor of the SiBCN ceramic, so that the proportion of graphene oxide in the composite material is reacted by representing the proportional relation between the graphene oxide and the polyborosilazane. Through a large number of experiments, the mass ratio of the graphene oxide to the precursor of the SiBCN ceramic is preferably 0.04-0.08: 1, namely, the mass ratio of the graphene oxide to the polyborosilazane is 0.04-0.08: 1. at this content, the impedance matching and dielectric loss effects can be balanced. More preferably, the mass ratio of the graphene oxide to the precursor of the SiBCN ceramic is 0.06: 1.

another embodiment of the present invention provides a method for preparing the graphene oxide reinforced silicon-boron-carbon-nitrogen ceramic composite material, which comprises the following steps:

s1, preparing a graphene oxide dispersion liquid: adding graphene oxide into anhydrous dimethylformamide, and performing ultrasonic dispersion to obtain a graphene oxide dispersion liquid;

s2, oxidized graphene modified polysilazane: under an inert atmosphere, adding a polyborosilazane solution into the graphene oxide dispersion liquid, then adding an initiator, performing ultrasonic dispersion, then heating and refluxing, then heating to 150-;

s3, high-temperature pyrolysis: heating the graphene oxide modified polysilazane to 1300-1600 ℃ in an inert atmosphere, preserving the temperature, carrying out a pyrolysis reaction, and then naturally cooling to room temperature to obtain the graphene oxide reinforced silicon boron carbon nitrogen ceramic composite material.

In the above steps, during the heating and refluxing process of graphene oxide and polysilazane, the initiator is heated to decompose and generate free radicals, so as to initiate the copolymerization reaction of RGO and polysilazane, so that RGO is bonded with polysilazane through acylation reaction, and the polysilazane before being cross-linked and cured has relatively small molecular weight and can easily enter between adjacent RGO layers to serve as an intercalation material. And then heating to 150-250 ℃ and preserving the temperature for a period of time to promote the polymerization among the internal molecules of the polyborosilazane, so that the precursor with relatively small molecular mass originally is crosslinked and solidified to form a network structure, the infusibility is enhanced, the SiBCN ceramic is convenient to be subsequently cracked at high temperature, the collapse of the local structure caused by a large amount of volatilization during high-temperature pyrolysis is avoided, and the layered structure of the composite material is maintained. In the high-temperature pyrolysis treatment process, the microstructure of the SiBCN ceramic changes along with the increase of the pyrolysis temperature of a precursor of the SiBCN ceramic, namely polysilazane, and the introduction of RGO reduces the temperature of the polyborosilazane for crystallizing and separating out SiC nanocrystals. When the polyborosilazane is pyrolyzed at the temperature of less than 1300 ℃, the polyborosilazane is converted into a SiBCN amorphous matrix, free carbon is formed, and a microstructure that free carbon phases are dispersedly distributed on the SiBCN amorphous matrix and RGO is arranged in the SiBCN amorphous matrix in parallel is obtained, and at the moment, the wave absorbing capability of the composite material is poor. When the polyborosilazane is pyrolyzed at the temperature of 1300 ℃ or higher, the polyborosilazane is converted into a SiBCN amorphous matrix and forms free carbon, and simultaneously the SiBCN amorphous matrix can be partially crystallized to separate out silicon carbide (SiC) nanocrystalline, so that a special microstructure is obtained, wherein the free carbon phase and the SiC phase are dispersedly distributed on the SiBCN amorphous matrix, and RGO is arranged in the SiBCN amorphous matrix in parallel, and the SiC, the free carbon phase and the RGO are matched with each other at the moment, so that high dielectric loss can be caused, and the composite material can obtain excellent electromagnetic wave absorption performance.

The specific operation of step S1 is: adding graphene oxide and anhydrous dimethylformamide into a closed container, and putting the closed container into an ultrasonic machine for ultrasonic dispersion, wherein the ultrasonic power is 220-250W, and the ultrasonic time is 1-12h until single-layer graphene oxide is formed in the solution, so as to obtain a graphene oxide dispersion liquid. The single-layer graphene oxide is easier to form a uniformly distributed and parallel arranged layered structure in the SiBCN ceramic.

The concentration of the graphene oxide dispersion liquid is 2-10g/L, namely, 0.02-0.10g of graphene oxide is contained in each 10mL of anhydrous dimethylformamide.

Preferably, in step S2, the mass ratio of the graphene oxide to the polysilazane is 0.04 to 0.08: 1, more preferably 0.06: 1.

in order to better initiate the acylation reaction between RGO and polysilazane, preferably, in step S2, the mass ratio of the initiator to the polysilazane is 0.01 to 0.04: 1.

optionally, the initiator is one or more of dicumyl peroxide, benzoyl peroxide, di-tert-butyl peroxide, methyl ethyl ketone peroxide and cyclohexanone peroxide.

Too high a reflux temperature tends to cause decomposition or direct evaporation of the initiator, while low a temperature makes the effect of the initiator unstable. Preferably, in step S2, the heating reflux temperature is 80 ℃ and the time is 72 h.

Preferably, in step S2, the temperature raising rate is 5 ℃/min, and the holding time is 24h, so as to ensure sufficient crosslinking and curing to obtain the cured product.

Preferably, in step S2, the ultrasonic power of the ultrasonic dispersion is 220-.

Preferably, in step S3, the temperature increase rate is 5-10 deg.C/min. At this rate, the ceramic yield is high.

Along with the increase of the pyrolysis temperature and the prolonging of the pyrolysis time, the content of SiC is increased, the content of free carbon and SiBCN amorphous matrixes is reduced, and the microstructure and the content of the SiC phase, the free carbon phase and the SiBCN amorphous matrixes in the composite material can be optimized by controlling the pyrolysis temperature. Preferably, in step S3, the graphene oxide modified polysilazane of step S2 is heated to 1300 ℃ and incubated for 1-8h, more preferably 2h, under an inert atmosphere. Under the condition, a microstructure is formed, wherein the free carbon phase and the SiC phase are dispersed and distributed in the SiBCN amorphous matrix, and RGO is arranged in the SiBCN amorphous matrix in parallel.

In steps S2-S3, the inert atmosphere is nitrogen or argon. Since polysilazanes and the produced composite materials are highly sensitive to moisture and oxygen, all steps such as curing, pyrolysis are performed under an inert atmosphere.

The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. The following examples are examples of experimental procedures not specified under specific conditions, generally according to the conditions recommended by the manufacturer.

In the following examples, dicumyl peroxide was used as an initiator, and the concentration of the graphene oxide dispersion was 6 g/L.

Example 1

A preparation method of a graphene oxide reinforced silicon-boron-carbon-nitrogen ceramic composite material comprises the following steps:

s1, preparing a graphene oxide dispersion liquid: ultrasonically cleaning a round-bottom flask twice by using deionized water and anhydrous dimethylformamide, then adding 0.06g of graphene oxide and 10mL of anhydrous dimethylformamide into the round-bottom flask, sealing the round-bottom flask, putting the round-bottom flask into an ultrasonic machine, and ultrasonically treating the round-bottom flask for 6 hours at a power of 220w to obtain a graphene oxide dispersion liquid;

s2, oxidized graphene modified polysilazane: under an inert atmosphere, adding 1g of polyborosilazane solution into the graphene oxide dispersion liquid, then adding 0.02g of dicumyl peroxide, carrying out ultrasonic treatment for 30min at a power of 220w, then carrying out heating reflux for 72h at 80 ℃, then heating to 190 ℃ at a speed of 5 ℃/min, carrying out heat preservation for 24h, and carrying out curing crosslinking to obtain a black solid, namely graphene oxide modified polyborosilazane;

s3, high-temperature pyrolysis: and (3) respectively heating the graphene oxide modified polysilazane in the step (S2) to 1200 ℃ and 1300 ℃ at the speed of 5 ℃/min under an inert atmosphere, preserving the heat for 2h, carrying out pyrolysis reaction, and then naturally cooling to room temperature to obtain the graphene oxide reinforced silicon boron carbon nitrogen ceramic composite material.

Taking the graphene oxide reinforced silicon-boron-carbon-nitrogen ceramic composite material prepared under the conditions of 1300 ℃ and 2h of heat preservation as an example, a Transmission Electron Microscope (TEM) analysis image of the obtained graphene oxide reinforced silicon-boron-carbon-nitrogen ceramic composite material is shown in fig. 2, and in fig. 2, it can be seen that graphene oxide is uniformly dispersed in a SiBCN amorphous matrix (amorphus) and is arranged in parallel in the SiBCN amorphous matrix.

The graphene oxide reinforced silicon-boron-carbon-nitrogen ceramic composite material with the mass fraction of 20% prepared under the condition of different pyrolysis temperatures is mixed with paraffin and then pressed into a coaxial ring for electromagnetic parameter testing, the inner diameter of the coaxial ring is 3mm, the outer diameter of the coaxial ring is 7mm, the height of the coaxial ring is 2.5mm, the electromagnetic wave absorption performance of the composite material is tested, and the measurement result is shown in figure 3.

As can be seen from FIG. 3, the composite material obtained at the pyrolysis temperatures of 1300 ℃ and 1400 ℃ has excellent wave absorption performance of electromagnetic wave absorption performance, and the minimum Reflection coefficient (Reflection coefficient) is-62.71 dB. Compared with the pyrolysis temperature of 1000 ℃ and 1200 ℃, the electromagnetic wave absorption performance of the graphene oxide reinforced silicon-boron-carbon-nitrogen ceramic composite material prepared at the pyrolysis temperature of more than 1300 ℃ is excellent; the microstructure of the silicon-boron-carbon-nitrogen ceramic obtained at the pyrolysis temperature of 1000 ℃ and 1200 ℃ consists of a free carbon phase and a SiBCN amorphous matrix phase, while SiC nanocrystals are precipitated at the pyrolysis temperature of 1300 ℃, the microstructure of the silicon-boron-carbon-nitrogen ceramic obtained consists of the free carbon phase, the SiC phase and the SiBCN amorphous matrix phase, and the SiC phase enhances the electromagnetic wave absorption performance of the composite material. However, the higher pyrolysis temperature causes the content of SiC phase to be high, impedance mismatching is caused, and the electromagnetic wave absorption performance of the composite material is further weakened, so that the wave absorption performance of the electromagnetic wave absorption performance of the composite material obtained at the pyrolysis temperature of 1300 ℃ is superior to that of the composite material obtained at the pyrolysis temperature of 1400 ℃, namely, the performance of the composite material obtained by pyrolysis at 1300 ℃ for 2 hours is optimal.

Example 2

Example 2 is essentially the same as example 1, except that: in the step S1, 0g, 0.04g, 0.06g and 0.08g of graphene oxide are respectively added into 10mL of anhydrous dimethylformamide to prepare graphene oxide dispersions with the concentrations of 0g/L, 4g/L, 6g/L and 8g/L (corresponding to 4% wt GO, 6% wt GO and 8% wt GO respectively in the graph 4) so as to perform the subsequent steps S2-S3, and in the step S3, the graphene oxide modified polysilazane in the step S2 is heated to 1300 ℃ at the speed of 5 ℃/min and is kept warm for 2h in an inert atmosphere.

The electromagnetic wave absorption performance of the composite material prepared from the graphene oxide dispersion liquid with different concentrations is shown in fig. 4. As can be seen from fig. 4, the electromagnetic wave absorption performance of the composite material prepared by using the graphene oxide dispersion liquid with the mass concentration of 6% wt is optimal, and the mass ratio of the graphene oxide to the polyborosilazane is 0.06: 1.

although the present disclosure has been described above, the scope of the present disclosure is not limited thereto. Various changes and modifications may be effected therein by one of ordinary skill in the pertinent art without departing from the spirit and scope of the present disclosure, and these changes and modifications are intended to be within the scope of the present disclosure.