阅读说明：本技术 吸波型SiBCN纳米纤维及其制备方法 (Absorption type SiBCN nano-fiber 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：本发明提供了一种吸波型SiBCN纳米纤维及其制备方法,属于陶瓷吸波材料技术领域。所述吸波型SiBCN纳米纤维微观相结构由碳化硅相、自由碳相和硅硼碳氮非晶基体相组成,所述碳化硅相和所述自由碳相分散在所述硅硼碳氮非晶基体相中。本发明的SiBCN纳米纤维中的SiBCN非晶基体相为电绝缘基体,具有优异的透波性能,而SiC相和自由碳相具有良好的介电性能,可改善SiBCN纳米纤维与自由空间之间的阻抗失配,使得入射的电磁波会尽可能多地由空气介质渗透到SiBCN纳米纤维中,并转化为内部能量。而且均匀分布在电绝缘基体中的由SiC相和自由碳相组成的导电相可以进一步调节材料的介电常数,引起较高的介电损耗以增强SiBCN纳米纤维的电磁波吸收能力。(The invention provides wave-absorbing SiBCN nano-fibers and a preparation method thereof, belonging to the technical field of ceramic wave-absorbing materials. The microwave absorption type SiBCN nanofiber microstructure is composed of a silicon carbide phase, a free carbon phase and a silicon-boron-carbon-nitrogen amorphous matrix phase, wherein the silicon carbide phase and the free carbon phase are dispersed in the silicon-boron-carbon-nitrogen amorphous matrix phase. The SiBCN amorphous matrix phase in the SiBCN nano-fiber is an electric insulation matrix and has excellent wave-transmitting performance, and the SiC phase and the free carbon phase have good dielectric performance and can improve impedance mismatch between the SiBCN nano-fiber and a free space, so that incident electromagnetic waves can permeate into the SiBCN nano-fiber from an air medium as much as possible and are converted into internal energy. And the conductive phase consisting of the SiC phase and the free carbon phase which are uniformly distributed in the electric insulation matrix can further adjust the dielectric constant of the material, so that higher dielectric loss is caused to enhance the electromagnetic wave absorption capability of the SiBCN nano-fiber.)

1. The wave-absorbing SiBCN nanofiber is characterized in that a microscopic phase structure consists of a silicon carbide phase, a free carbon phase and a silicon-boron-carbon-nitrogen amorphous matrix phase, wherein the silicon carbide phase and the free carbon phase are dispersed in the silicon-boron-carbon-nitrogen amorphous matrix phase.

2. The wave-absorbing SiBCN nanofiber as claimed in claim 1, wherein the silicon carbide phase accounts for 10-50% of the mass percent, the free carbon phase accounts for 20-30% of the mass percent, and the silicon-boron-carbon-nitrogen amorphous matrix phase accounts for 20-70% of the mass percent.

3. The wave-absorbing SiBCN nanofiber as claimed in claim 2, wherein the silicon carbide phase accounts for 30% of the mass percent, the free carbon phase accounts for 20% of the mass percent, and the silicon-boron-carbon-nitrogen amorphous matrix phase accounts for 50% of the mass percent.

4. The wave absorbing SiBCN nanofiber as claimed in claim 1, wherein the diameter of the SiBCN nanofiber is 100-500 nm.

5. A method for preparing wave-absorbing SiBCN nanofibers, which is used for preparing the wave-absorbing SiBCN nanofibers according to any one of claims 1-4, the method comprises the following steps:

s1, dissolving the colloidal solid of polyborosilazane in anhydrous dichloromethane in an inert atmosphere, and standing after ultrasonic dispersion to obtain a spinning solution for electrostatic spinning;

s2, injecting the spinning solution obtained in the step S1 into electrostatic spinning equipment for electrostatic spinning to obtain a polyborosilazane spinning fiber;

s3, heating the polysilazane spinning fiber obtained in the step S2 from room temperature to 150-250 ℃ in an inert atmosphere, preserving heat, and curing and crosslinking;

and S4, heating the polysilazane spinning fiber solidified and crosslinked in the step S3 to 1600 ℃ in an inert atmosphere, preserving heat, carrying out pyrolysis reaction, and then naturally cooling to room temperature to obtain the SiBCN nanofiber.

6. The method according to claim 5, wherein in step S1, the mass concentration of the colloidal solid of polysilazane in the spinning solution is 20-60%.

7. The method of claim 5, wherein in step S2, the parameters of the electrostatic spinning are: the fiber receiving device is an aluminum plate, a needle point auxiliary electrode is additionally arranged, the receiving distance is 10-30cm, the solution advancing speed is 15-35 mu L/min, and the working voltage is 10-30 kV.

8. The method according to claim 5, wherein in step S3, the temperature is increased at a rate of 5 ℃/min, and the holding time is 24 hours.

9. The method according to claim 5, wherein in step S4, the temperature is increased at a rate of 5-10 ℃/min, and the holding time is 1-10 h.

10. The method according to claim 5, wherein the method for preparing the polysilazane colloidal solid in step S1 comprises the steps of:

s11, adding methylvinyldichlorosilane and tetrahydrofuran into a flask placed under an ice bath condition in an inert gas atmosphere, fully stirring and dissolving, then adding a tetrahydrofuran solution of borane into the flask, naturally returning the mixture solution to room temperature, and stirring and reacting overnight to generate tris (dichloromethylsilylethyl) borane;

s12, adding hexamethyldisilazane, boron trichloride and 4-methoxyphenol into a flask containing tris (dichloromethylsilylethyl) borane in sequence in an inert gas atmosphere, reacting at the temperature of 120 ℃, and then distilling under reduced pressure to remove by-products to obtain colorless transparent viscous liquid;

s13, continuously heating the liquid to the temperature of 150 ℃ and 190 ℃, continuously introducing inert gas, and keeping for 6-24h to obtain the polysilazane colloidal solid.

Technical Field

The invention relates to the technical field of ceramic wave-absorbing materials, in particular to wave-absorbing SiBCN nano-fibers and a preparation method thereof.

Background

With the rapid development of modern electronic communication, not only is the basic communication guarantee provided, but also the rapid transmission of information is gradually realized. The electromagnetic radiation and interference generated therewith make the space electromagnetic environment increasingly complex, and the electromagnetic pollution becomes a topic and a hot spot which are increasingly concerned in the actual life of people. A large amount of electromagnetic wave radiation is generated in daily household appliances, mobile phones, computers, and electronic devices, so that electromagnetic wave absorbing materials are receiving more and more attention.

The traditional wave-absorbing material mainly comprises ferrite, metal alloy, graphite and the like, has higher wave-absorbing strength, but has not wide absorption frequency band and higher density, and particularly the ferrite and metal alloy wave-absorbing material limits the further development of the material in the field due to the high density. In recent years, the reaction is carried out on silicon carbide (SiC) and silicon nitride (Si)₃N₄) The deep research of the polymer derived ceramics finds that the polymer derived ceramics have excellent high-temperature semiconductor performance and piezoresistive property, have potential application value in wave-absorbing materials and show the prospect of being used as a microwave absorbent. However, the polymer-derived ceramic has poor microwave absorption performance, and is expected to be synthesized into polymer-derived ceramic with high microwave absorption characteristics through molecular structure design of a polymer precursor, introduction of doping elements, introduction of a high dielectric dispersion phase, adjustment of a pyrolysis process and the like.

The silicon-boron-carbon-nitrogen (SiBCN) ceramic has the advantages of light weight, low thermal expansion coefficient, high hardness, high modulus, corrosion resistance, excellent high temperature resistance, oxidation resistance, creep resistance and the like, is an important ultrahigh temperature ceramic system, and is widely applied to devices and high technical fields of high temperature engines, turbines, atomic reactor walls, high temperature sensors, catalyst heat exchange systems, combustion systems, thermal protection systems, aerospace and the like. Due to the excellent performance, SiBCN ceramic is more and more emphasized in the research of preparing wave-absorbing materials used in severe environment. However, the effective absorption bandwidth of the existing SiBCN ceramic is relatively narrow, and the attenuation coefficient of electromagnetic waves is low, so that the development of the existing SiBCN ceramic in the field of microwave absorbers is greatly limited, and the electromagnetic wave absorption performance of the existing SiBCN ceramic still needs to be improved.

Disclosure of Invention

Aiming at the problem of poor electromagnetic wave absorption performance of SiBCN ceramics in the prior art, the invention provides a wave-absorbing type SiBCN nanofiber and further provides a preparation method of the wave-absorbing type SiBCN nanofiber.

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

a micro-phase structure of the wave-absorbing SiBCN nanofiber consists of a silicon carbide phase, a free carbon phase and a silicon-boron-carbon-nitrogen amorphous matrix phase, wherein the silicon carbide phase and the free carbon phase are dispersed in the silicon-boron-carbon-nitrogen amorphous matrix phase.

Further, according to the mass percentage, the silicon carbide phase accounts for 10-50%, the free carbon phase accounts for 20-30%, and the silicon boron carbon nitrogen amorphous matrix phase accounts for 20-70%.

Further, the silicon carbide phase accounts for 30%, the free carbon phase accounts for 20%, and the silicon boron carbon nitrogen amorphous matrix phase accounts for 50%.

Further, the diameter of the SiBCN nano-fiber is 100-500 nm.

In addition, the invention provides a preparation method of the wave-absorbing SiBCN nano-fiber, which comprises the following steps:

s1, dissolving the colloidal solid of polyborosilazane in anhydrous dichloromethane in an inert atmosphere, and standing after ultrasonic dispersion to obtain a spinning solution for electrostatic spinning;

s2, injecting the spinning solution obtained in the step S1 into electrostatic spinning equipment for electrostatic spinning to obtain a polyborosilazane spinning fiber;

s3, heating the polysilazane spinning fiber obtained in the step S2 from room temperature to 150-250 ℃ in an inert atmosphere, preserving heat, and curing and crosslinking;

and S4, heating the polysilazane spinning fiber solidified and crosslinked in the step S3 to 1600 ℃ in an inert atmosphere, preserving heat, carrying out pyrolysis reaction, and then naturally cooling to room temperature to obtain the SiBCN nanofiber.

Further, in step S1, the mass concentration of the colloidal solid of polysilazane in the spinning solution is 20 to 60%.

Further, in step S2, the parameters of the electrostatic spinning are: the fiber receiving device is an aluminum plate, a needle point auxiliary electrode is additionally arranged, the receiving distance is 10-30cm, the solution advancing speed is 15-35 mu L/min, and the working voltage is 10-30 kV.

Further, in step S3, the temperature rise rate is 5 ℃/min, and the heat preservation time is 24 hours.

Further, in step S4, the temperature rising rate is 5-10 ℃/min, and the heat preservation time is 1-10 h.

Further, in step S1, the method for preparing the polysilazane colloidal solid includes the following steps:

s11, adding methylvinyldichlorosilane and tetrahydrofuran into a flask placed under an ice bath condition in an inert gas atmosphere, fully stirring and dissolving, then adding a tetrahydrofuran solution of borane into the flask, naturally returning the mixture solution to room temperature, and stirring and reacting overnight to generate tris (dichloromethylsilylethyl) borane;

s12, adding hexamethyldisilazane, boron trichloride and 4-methoxyphenol into a flask containing tris (dichloromethylsilylethyl) borane in sequence in an inert gas atmosphere, reacting at the temperature of 120 ℃, and then distilling under reduced pressure to remove by-products to obtain colorless transparent viscous liquid;

s13, continuously heating the liquid to the temperature of 150 ℃ and 190 ℃, continuously introducing inert gas, and keeping for 6-24h to obtain the polysilazane colloidal solid.

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

the microstructure of the SiBCN nanofiber consists of a silicon carbide (SiC) phase, a free carbon phase and a silicon boron carbon nitrogen (SiBCN) amorphous matrix phase, wherein the SiBCN amorphous matrix phase is an electric insulation matrix and has excellent wave-transmitting performance, and the SiC phase and the free carbon phase have good dielectric performance, so that impedance mismatch between the SiBCN nanofiber and a free space can be improved, incident electromagnetic waves can penetrate into the SiBCN nanofiber from an air medium as much as possible and are converted into internal energy. And the conductive phase consisting of the SiC phase and the free carbon phase which are uniformly distributed in the electric insulation matrix can further adjust the dielectric constant of the material, so that higher dielectric loss is caused to enhance the electromagnetic wave absorption capability of the SiBCN nano-fiber.

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 flow chart of a method of preparing SiBCN nanofibers according to an embodiment of the present invention;

FIG. 2 is a transmission electron microscope (SEM) analysis of SiBCN nanofibers according to embodiments of the present invention;

FIG. 3 is an XRD analysis of SiBCN nanofibers according to an embodiment of the present invention;

FIG. 4 is a FTIR analysis chart of SiBCN nanofibers according to an embodiment of the present invention;

FIG. 5 is an electromagnetic wave absorption characteristic diagram of SiBCN nanofibers prepared at different pyrolysis temperatures according to an embodiment of the present invention;

FIG. 6 is an SEM image of SiBCN nanofibers prepared from different concentrations of spinning solutions according to embodiments of the present invention; wherein (a) represents a spinning solution having a mass concentration of 40%, (b) represents a spinning solution having a mass concentration of 45%, (c) represents a spinning solution having a mass concentration of 50%, and (d) represents a spinning solution having a mass concentration of 50%.

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 wave-absorbing SiBCN nanofiber, wherein a microscopic phase structure of the wave-absorbing SiBCN nanofiber consists of a silicon carbide (SiC) phase, a free carbon phase and a silicon boron carbon nitrogen (SiBCN) amorphous matrix phase, and the silicon carbide phase and the free carbon phase are dispersed in the SiBCN amorphous matrix phase. The free carbon refers to free carbon, and the free carbon exists in a form of graphite carbon or amorphous carbon structure in the SiBCN nanofiber structure.

The SiBCN precursor is pyrolyzed to obtain SiBCN nano-fibers, the SiBCN precursor forms a SiBCN amorphous matrix in a high-temperature ceramic process, organic matters in the SiBCN precursor are decomposed at high temperature to form free carbon, and when the pyrolysis temperature of the SiBCN precursor reaches 1600 ℃, SiC nanocrystalline is separated out from the SiBCN amorphous matrix in the high-temperature ceramic process to obtain a special microstructure in which a SiC phase and a free carbon phase are dispersed and distributed in the SiBCN amorphous matrix.

Good electromagnetic wave absorption properties are closely related to their unique microstructure, which usually consists of an amorphous matrix acting as an electromagnetic wave insulating phase and crystalline nanocrystals acting as a conducting phase. The amorphous matrix phase in the SiBCN nano-fiber is an electric insulation matrix and has excellent wave-transmitting performance. The SiC phase and the free carbon phase have good dielectric properties, and can improve impedance mismatch between SiBCN nanofibers and free space, so that incident electromagnetic waves can penetrate into the SiBCN nanofibers from an air medium as much as possible and are converted into internal energy instead of being reflected. And the conductive phase consisting of the SiC phase and the free carbon phase which are uniformly distributed in the electric insulation matrix can further adjust the dielectric constant of the material, so that higher dielectric loss is caused to enhance the electromagnetic wave absorption capability of the SiBCN nano-fiber. The free carbon has good conductivity, a conductive chain or a local conductive network is formed in the SiBCN amorphous matrix, an external electric field can be quickly conducted to SiC, the SiC is polarized molecules, and the SiC becomes a dipole under the action of the external electric field and is regularly arranged along the direction of the electric field, so that relaxation attenuation and absorption of electromagnetic waves are caused. Therefore, through the mutual matching of the SiC phase, the free carbon phase and the SiBCN amorphous matrix phase, high dielectric loss is caused, and the electromagnetic wave absorption capacity of the SiBCN nano-fiber is greatly enhanced.

Suitable microstructure and material properties are advantageous in balancing impedance matching and dielectric losses so that the electromagnetic waves enter the material as much as possible and can be totally attenuated. When the content of the free carbon phase and the SiC phase is low, the content of the SiBCN amorphous matrix phase is high, or the content of the free carbon phase and the SiC phase is high, the content of the SiBCN amorphous matrix phase is low, impedance mismatching is caused, a large amount of electromagnetic waves are reflected, the electromagnetic waves cannot enter the SiBCN nano fibers, the attenuation effect of dielectric loss cannot be overcome by the influence of reflection, and the wave absorbing performance is reduced. Therefore, preferably, the SiC phase accounts for 10-50% by mass, the free carbon phase accounts for 20-30% by mass, and the SiBCN amorphous matrix phase accounts for 20-70% by mass. When the SiC phase accounts for 10-50%, the microwave absorption capacity of the SiBCN nano-fiber can be improved; when the ratio of the SiBCN nano-fiber is more than 50%, the impedance condition between free spaces is unbalanced due to the reduction of the content of the electric insulation SiBCN amorphous matrix, so that the electromagnetic wave absorption capability of the SiBCN nano-fiber is reduced.

More preferably, the SiC phase accounts for 30% by mass, the free carbon phase accounts for 20% by mass, and the SiBCN amorphous matrix phase accounts for 50% by mass.

Optionally, the diameter of the SiBCN nano-fiber is 100-500 nm; more preferably 300 nm.

Another embodiment of the present invention provides a method for preparing the wave-absorbing SiBCN nanofibers, which is shown in fig. 1 and includes the following steps:

s1, preparing a spinning solution: dissolving the polyborosilazane colloidal solid in anhydrous dichloromethane in an inert atmosphere, and standing after ultrasonic dispersion to obtain a spinning solution for electrostatic spinning;

s2, electrostatic spinning: injecting the spinning solution obtained in the step S1 into electrostatic spinning equipment for electrostatic spinning to obtain a polysilazane spinning fiber;

s3, curing and crosslinking: under the inert atmosphere, heating the polysilazane spinning fiber obtained in the step S2 from room temperature to 150-250 ℃, and preserving heat for curing and crosslinking;

s4, pyrolysis: and under an inert atmosphere, heating the polysilazane spinning fiber cured and crosslinked in the step S3 to 1600 ℃, preserving heat, carrying out pyrolysis reaction, and then naturally cooling to room temperature to obtain the SiBCN nanofiber.

In the steps, firstly, the colloidal solid of the polysilazane is dissolved in anhydrous dichloromethane to form spinning solution with proper viscosity and applicable to electrostatic spinning, and then the spinning fiber in a nano state is obtained through electrostatic spinning. And then the spinning fiber is subjected to heat preservation at the temperature of 150-. In the process of high-temperature cracking treatment, when the pyrolysis temperature is below 1600 ℃, the polysilazane is cracked to form an SiBCN amorphous matrix phase and a free carbon phase, and at the moment, the wave-absorbing capability is almost not available, when the pyrolysis temperature is increased to 1600 ℃, the SiBCN amorphous matrix phase is gradually changed from an amorphous state to a crystalline state, a SiC phase is separated out, and simultaneously along with the change of physical properties, the SiBCN nanofiber obtains excellent electromagnetic wave absorption performance. The morphology of the prepared SiBCN nanofiber is shown in FIG. 2, and as can be seen from FIG. 2, the SiBCN nanofiber is a disordered stacked nanofiber on a microscopic scale, the surface of the fiber is smooth, and the morphology is complete.

Optionally, in step S1, the mass concentration of the polysilazane colloidal solid in the spinning solution is 20-60%. When the colloidal solid of the polysilazane is too little, the viscosity of the spinning solution is low, only liquid drops can be obtained after spinning, the surface appearance of the fiber is not smooth, but when the colloidal solid of the polysilazane is high, the viscosity of the spinning solution is too high, and the spinning process is influenced.

The method for preparing the polysilazane colloidal solid is not particularly limited, but is merely an example, which should not be construed as limiting the scope of the present invention. All reactions of the preparation method of the polysilaborazane colloidal solid are carried out in an inert atmosphere filled with argon or nitrogen by the Schlenk technique, all solutions are processed in a plastic syringe with a long needle and stored in a vacuum drier, and the preparation method specifically comprises the following steps:

s11, synthesis of tris (dichloromethylsilylethyl) borane: adding 11.7mL of methylvinyldichlorosilane and 20mL of tetrahydrofuran into a flask placed under an ice bath condition in an inert gas atmosphere, fully stirring and dissolving, then adding 15mL of borane-containing tetrahydrofuran solution into the flask, naturally returning the mixture solution to room temperature, and stirring and reacting overnight to generate tris (dichloromethylsilylethyl) borane;

s12, adding 113mL of hexamethyldisilazane, 30mL of boron trichloride and 10mg of 4-methoxyphenol into a flask containing tris (dichloromethylsilylethyl) borane in sequence in an inert gas atmosphere, reacting at the temperature of 120 ℃ for 12 hours, and then distilling under reduced pressure to remove a byproduct of trimethylchlorosilane to obtain a colorless transparent viscous liquid; in this step, boron trichloride can react with hexamethyldisilazane to form a stable six-membered boron-nitrogen ring structure, while 4-methoxyphenol promotes the polymerization of polysilaborazane by free radical action.

S13, continuously heating the liquid to 190 ℃ at 150 ℃, continuously introducing inert gas, keeping for 6-24h, further promoting the polymerization of the precursor, and finally obtaining the elastic transparent glassy solid, namely the polyborosilazane colloidal solid.

According to the preparation method, boron trichloride and tris (dichloromethylsilylethyl) borane are used as boron sources, hexamethyldisilazane is used as a nitrogen source, SiBCN ceramic precursor-polyborosilazane colloidal solid with B-C and B-N bonds is synthesized, and the SiBCN nanofiber after high-temperature pyrolysis has excellent electromagnetic wave absorption performance.

Optionally, in step S2, the parameters of the electrostatic spinning are: the fiber receiving device is an aluminum plate, a needle point auxiliary electrode is additionally arranged, the receiving distance is 10-30cm, the solution advancing speed is 15-35 mu L/min, the working voltage is 10-30kV, the environmental humidity is 20-50%, and the environmental temperature is controlled at 20-50 ℃. During electrostatic spinning, positively charged spinning solution forms jet flow under the action of a strong electric field, and the jet flow is acted by coulomb force of a negatively charged aluminum plate when falling to a fiber receiving device, so that fibers in the jet flow are straightened and aligned as far as possible, and highly aligned nano-scale fibers are obtained. The addition of the needle tip auxiliary electrode can enable an electric field during spinning to be more concentrated, and is beneficial to better arrangement of fibers, so that an oriented fiber array with excellent comprehensive performance is obtained. In the spinning voltage range of 10-30kV, the prepared SiBCN nanofiber is continuous and smooth in surface, and the diameter of the nanofiber is reduced along with the increase of the spinning voltage. When spinning voltage is less than 10kV, because the electric field force is less difficult to overcome the surface tension of spinning solution self, the draft of fibre has been hindered, make the nanofiber diameter great, along with the gradual rise of spinning voltage, electric field strength is bigger and bigger, the efflux takes place drawing and splitting more easily, form the finer nanofiber of diameter, spinning voltage further rises to more than 30kV, electric field strength is too big, lead to the efflux speed to accelerate, be unfavorable for fluidic drawing, also will lead to the fiber diameter grow, and the homogeneity worsens. The solution advancing speed can also influence the fiber diameter, the diameter of the prepared nano fiber can gradually increase along with the increase of the spinning speed, and even bead-shaped fibers are formed, and the proper solution advancing speed can ensure the uniformity of the fiber diameter distribution. The fiber prepared under the conditions is not only continuous and high in length-diameter ratio, but also smooth in surface, and contributes to improving the electromagnetic wave absorption performance.

Optionally, in step S3, the temperature raising rate is 5 ℃/min, and the heat preservation time is 24h, so as to ensure sufficient crosslinking and curing to obtain a cured product.

In order to improve the electromagnetic wave absorption performance, preferably, in step S4, the temperature rising rate is 5-10 ℃/min, and the heat preservation time is 1-10h, so as to ensure sufficient ceramization.

The proportion of the SiC phase, the free carbon phase and the SiBCN amorphous matrix phase is controlled by adjusting the heat preservation time. As the pyrolysis time is extended, the SiC content increases and the free carbon and SiBCN amorphous matrix content decreases. Preferably, in step S4, the temperature of the polysilazane spinning fiber cured and crosslinked in step S3 is raised to 1600 ℃ in an inert atmosphere and kept for 2 hours, so as to obtain a SiBCN nanofiber with a microstructure composed of a free carbon phase, a SiC phase and a SiBCN amorphous matrix phase, wherein the SiC phase accounts for 30%, the free carbon phase accounts for 20%, and the SiBCN amorphous matrix phase accounts for 50%.

In step S1, step S3, and step S4, the inert atmosphere is nitrogen or argon. Since the polyborosilazane colloidal solid raw material and the produced material are highly sensitive to moisture and oxygen, all steps such as spinning, curing, and 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.

Example 1

A preparation method of wave-absorbing SiBCN nano-fibers comprises the following steps:

s1, preparing a spinning solution: dissolving 5g of polysilaborazine colloidal solid in 5g of anhydrous dichloromethane in an inert atmosphere, magnetically stirring for 2 hours at room temperature, fully dispersing the solution by using an ultrasonic instrument, and standing for 0.5 hour to obtain a uniform and transparent spinning solution for electrostatic spinning;

s2, electrostatic spinning: injecting the spinning solution obtained in the step S1 into an electrostatic spinning device for electrostatic spinning to obtain a polysilazane spinning fiber, wherein the parameters of the electrostatic spinning are as follows: the fiber receiving device is an aluminum plate, a needle point auxiliary electrode is additionally arranged, the receiving distance is 10cm, the solution propelling speed is 25 mu L/min, the working voltage is 15kV, the environmental humidity is 30 percent, and the environmental temperature is controlled at 25 ℃; storing the polyborosilazane spinning fiber in a blast oven at 50 ℃ to prevent the fiber from absorbing moisture;

s3, curing and crosslinking: under the inert atmosphere, heating the polysilazane spinning fiber obtained in the step S2 from room temperature to 200 ℃ at the speed of 5 ℃/min, and preserving heat for 24 hours to carry out curing crosslinking;

s4, pyrolysis: and under an inert atmosphere, respectively heating the polysilazane spinning fiber cured and crosslinked in the step S3 from 200 ℃ to 1400 ℃, 1500 ℃ and 1600 ℃ at the speed of 5 ℃/min, preserving the heat for 2h, carrying out pyrolysis reaction, and then naturally cooling to room temperature to obtain the SiBCN nanofiber.

Taking the SiBCN nanofibers prepared under the pyrolysis condition of 1600 ℃ and 2 hours of heat preservation as an example, the X-ray diffraction (XRD) analysis graph and the fourier transform infrared absorption spectrometer (FTIR) analysis graph of the obtained SiBCN nanofibers are respectively shown in fig. 3-4, and it can be seen in fig. 3 that the SiBCN nanofibers contain SiC and free carbon; the SiBCN nanofibers can be seen in FIG. 4 to consist of Si-C, Si-N and B-N bonds.

The SiBCN nano-fibers with the mass fraction of 20% prepared under the conditions of different pyrolysis temperatures are 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 SiBCN nano-fibers is tested, and the measurement result is shown in figure 5.

As can be seen from FIG. 5, the dielectric properties of the obtained SiBCN nanofibers are adjustable, and the wave-absorbing properties are excellent. The minimum Reflection coefficient (Reflection coefficient) of the SiBCN nanofiber obtained at the pyrolysis temperature of 1600 ℃ is-56.9 dB, the maximum absorption bandwidth is 3.45GHz, the electromagnetic wave absorption performance is excellent, the SiBCN nanofiber obtained at the pyrolysis temperatures of 1400 ℃ and 1500 ℃ basically has no wave absorbing capacity, because the SiBCN nanofiber obtained at the pyrolysis temperatures of 1400 ℃ and 1500 ℃ consists of a free carbon phase and a SiBCN amorphous matrix phase, SiC nanocrystals are precipitated at the pyrolysis temperature of 1600 ℃, the obtained SiBCN nanofiber consists of 30% of the free carbon phase, 20% of the SiC phase and 50% of the SiBCN amorphous matrix phase, and the wave absorbing capacity of the SiBCN nanofiber is enhanced by the SiC in a specific proportion.

Example 2

Example 2 is essentially the same as example 1, except that: in step S1, spinning solutions with colloidal solid mass concentrations of polysilazane being 40%, 45%, 50% and 55% are prepared respectively to carry out the subsequent steps S2-S4, and in step S4, the solidified and crosslinked polysilazane spinning fiber obtained in step S3 is heated to 1600 ℃ from 200 ℃ at a rate of 5 ℃/min under an inert atmosphere and is kept warm for 2 hours.

The morphology of the SiBCN nanofibers obtained from the spinning solutions with different concentrations is shown in FIG. 6, and it can be seen from FIG. 6 that the fibers prepared from the spinning solution with the mass concentration of 50% have smooth surfaces and complete morphologies, and are the preferred mass concentration.

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.