阅读说明：本技术 一种柔性SiC/C纳米复合纤维及其制备方法和应用 (Flexible SiC/C nano composite fiber and preparation method and application thereof ) 是由 原晓艳 李欢欢 沙爱明 黄圣琰 郭守武 于 2021-09-16 设计创作，主要内容包括：本发明公开了一种柔性SiC/C纳米复合纤维及其制备方法和应用,以可溶性前驱体和聚合物为原材料,四氢呋喃无水乙醇为溶剂,采用静电纺丝法制备Mo-SiC/C复合纳米纤维。本发明工艺简单,制备的纤维具有良好的形貌,晶粒均匀的分布于纤维内,并表现出优异的电磁波吸收性能。(The invention discloses a flexible SiC/C nano composite fiber and a preparation method and application thereof. The invention has simple process, and the prepared fiber has good appearance, the crystal grains are uniformly distributed in the fiber, and the fiber shows excellent electromagnetic wave absorption performance.)

1. A preparation method of flexible SiC/C nano composite fibers is characterized by comprising the following steps:

s1, mixing polycarbosilane and molybdenum acetylacetonate, and dissolving in tetrahydrofuran to obtain a solution A; adding absolute ethyl alcohol into polyvinylpyrrolidone to obtain a solution B, and respectively carrying out magnetic stirring on the obtained solution A and the solution B until the solutions are in a uniform state;

s2, adding the solution A in a uniform state into the solution B in a uniform state under the action of magnetic stirring, and continuously stirring until the solution A and the solution B are fully mixed to form a stable light green spinning solution;

s3, spinning by using the spinning solution obtained in the step S2 at a constant speed to obtain precursor fibers;

s4, carrying out pre-oxidation treatment on the precursor fiber obtained in the step S3 to obtain pre-oxidized fiber;

and S5, sintering the pre-oxidized fiber obtained in the step S4 in Ar atmosphere, and annealing to obtain the flexible SiC/C nano composite fiber.

2. The method of claim 1, wherein in step S1, the polycarbosilane: molybdenum acetylacetonate: the mass-volume ratio of tetrahydrofuran is (0.5-1.0): (0-0.1): (3.55-8.88).

3. The method according to claim 1, wherein in step S1, the ratio of polyvinylpyrrolidone: the mass-volume ratio of the absolute ethyl alcohol is (0.5-1.0): (2.37-4.74).

4. The method according to claim 1, wherein in step S1, the stirring time is 30-60 min.

5. The method according to claim 1, wherein in step S2, the stirring time is 12-24 h.

6. The method of claim 1, wherein in step S3, the spinning speed is 0.1-0.4 mm/min, the voltage is 15-20 kv, the distance between the collecting drum and the spinning needle is 15-20 cm, and the rotation speed is 80-100 r/min.

7. The method according to claim 1, wherein the pre-oxidation treatment is performed at a temperature of 150 to 200 ℃ for 1 to 4 hours in step S4.

8. The method according to claim 1, wherein in step S5, the temperature rise rate of the annealing treatment is 2-5 ℃/min, the temperature is 1000-1300 ℃, and the time is 1-3 h.

9. A flexible SiC/C nanocomposite fiber prepared according to the method of claim 1.

10. Use of a flexible SiC/C nanocomposite fiber prepared according to the method of claim 1 or a flexible SiC/C nanocomposite fiber according to claim 9 for electromagnetic wave absorption.

Technical Field

The invention belongs to the technical field of preparation of electromagnetic wave absorbing materials, and particularly relates to a flexible SiC/C nano composite fiber, and a preparation method and application thereof.

Background

With the development of electromagnetic technology and electronic equipment, the negative impact of electromagnetic pollution (including natural electromagnetic and man-made pollution) on human health and the service life of electronic equipment is increasing, which makes electromagnetic wave protection one of the hot research objects. The electromagnetic shielding material can play a protective role to a certain extent, but has the defect of generating secondary pollution. The wave-absorbing material can effectively absorb or weaken electromagnetic waves entering the interior, convert electromagnetic energy into internal energy or lose energy in other forms, and fundamentally avoid the harm of the electromagnetic waves, thereby bringing about wide attention of people. However, with the diversification of the application field, the wave-absorbing material does not emphasize strong attenuation at one step, but has higher requirements on light weight, wide frequency and the like, so that the development of a novel wave-absorbing material with excellent performance is particularly important.

Among them, silicon carbide (SiC) is an ideal electromagnetic wave absorber as a wide band gap semiconductor material due to its adjustable electrical conductivity. One-dimensional (1D) SiC ceramics are of interest due to their high strength, high modulus, low density, excellent oxidation resistance, chemical stability, and good dielectric and electromagnetic properties. Especially when 1DSiC is used as the wave-absorbing material, compared with the block and the particle, an internal conductive network can be constructed so as to improve the conductivity loss of the material. There are still some application limitations, however, first, pure silicon carbide exhibits a lower dielectric constant than carbon and ferromagnetic absorbing materials, often introducing defects to increase the dielectric constant of silicon carbide to approach the appropriate impedance match for electromagnetic absorption; the existing 1D silicon carbide material can only realize single coverage of a high-frequency wave band and has limited absorption width; as high-temperature application ceramic, the preparation temperature is higher and is more than 1300 ℃. Therefore, the development of a broadband efficient 1D silicon carbide wave-absorbing material capable of being synthesized at low temperature is urgently needed. On the other hand, the introduction of magnetic elements (e.g., iron, cobalt, nickel, etc.) has proven to be an effective method to improve the electromagnetic attenuation properties of 1D silicon carbide materials. Mo is used as a transition metal and has unique excellent performance, and the application of Mo in silicon carbide material modification is not studied for a while, so that trace molybdenum source is introduced into SiC for doping modification, the generation temperature of SiC is expected to be reduced, the dielectric constant and the impedance matching capability of the SiC as an electromagnetic wave absorption material are improved, and the light flexible Mo-SiC/C nano fiber with excellent wave absorption performance is expected to be prepared.

Disclosure of Invention

The technical problem to be solved by the present invention is to provide a flexible SiC/C nanocomposite fiber, a preparation method and an application thereof, aiming at the defects in the prior art, wherein the preparation conditions are easy to implement and simple to operate, and a simple electrostatic spinning method and a high temperature pyrolysis process are mainly adopted to obtain a flexible SiC/C nanomaterial with good nanofiber morphology and excellent electromagnetic wave loss performance.

The invention adopts the following technical scheme:

a preparation method of flexible SiC/C nano composite fibers comprises the following steps:

s1, mixing polycarbosilane and molybdenum acetylacetonate, and dissolving in tetrahydrofuran to obtain a solution A; adding absolute ethyl alcohol into polyvinylpyrrolidone to obtain a solution B, and respectively carrying out magnetic stirring on the obtained solution A and the solution B until the solutions are in a uniform state;

s2, adding the solution A in a uniform state into the solution B in a uniform state under the action of magnetic stirring, and continuously stirring until the solution A and the solution B are fully mixed to form a stable light green spinning solution;

s3, spinning by using the spinning solution obtained in the step S2 at a constant speed to obtain precursor fibers;

s4, carrying out pre-oxidation treatment on the precursor fiber obtained in the step S3 to obtain pre-oxidized fiber;

and S5, sintering the pre-oxidized fiber obtained in the step S4 in Ar atmosphere, and annealing to obtain the flexible SiC/C nano composite fiber.

Specifically, in step S1, the polycarbosilane: molybdenum acetylacetonate: the mass-volume ratio of tetrahydrofuran is (0.5-1.0): (0-0.1): (3.55-8.88).

Specifically, in step S1, the polyvinylpyrrolidone: the mass-volume ratio of the absolute ethyl alcohol is (0.5-1.0): (2.37-4.74).

Specifically, in step S1, the stirring time is 30-60 min.

Specifically, in step S2, the stirring time is 12 to 24 hours.

Specifically, in the step S3, the spinning speed is 0.1-0.4 mm/min, the voltage is 15-20 kv, the distance between the collecting drum and the spinneret needle is 15-20 cm, and the rotating speed is 80-100 r/min.

Specifically, in step S4, the temperature of the pre-oxidation treatment is 150 to 200 ℃ and the time is 1 to 4 hours.

Specifically, in step S5, the temperature rise rate of the annealing treatment is 2-5 ℃/min, the temperature is 1000-1300 ℃, and the time is 1-3 h.

The invention also provides another technical scheme of the flexible SiC/C nano composite fiber.

The invention also provides the application of the flexible SiC/C nano composite fiber in electromagnetic wave absorption.

Compared with the prior art, the invention has at least the following beneficial effects:

according to the preparation method of the flexible Mo-SiC/C nano composite fiber, disclosed by the invention, the one-dimensional SiC nano fiber not only has the performances of high temperature resistance and the like of a silicon carbide material, but also can be mutually staggered to build an internal conductive network, so that electrons can be conveniently migrated in the fiber and can be conveniently transited between fibers, the conductive loss is effectively enhanced, the doping of molybdenum acetylacetonate can be obviously reduced, the SiC generation temperature is obviously reduced, the fiber has an obvious phase characteristic peak at 1100 ℃, and meanwhile, Mo is generated₂C is uniformly dispersed in the SiC/C fibers. Mo₂C not only contributes to the conductivity loss, but also increases the interface, defects and the like of the material, and is cooperated with SiC/C to obviously improve the electromagnetic wave absorption performance of the material. The nano composite fiber prepared by the method has wide application prospect in the aspect of electromagnetic wave absorption, PCS dissolved in tetrahydrofuran is taken as a silicon carbide source, PVP is added to adjust the viscosity of the spinning solution, and the required spinning solution is prepared. It is noted that the addition of molybdenum acetylacetonate has a considerable influence on the viscosity of the spinning solution, and therefore its amount must be strictly controlled to ensure the spinnability of the fibers. Preparing precursor nano-fiber by electrostatic spinning process, pre-oxidizing in air and sintering at high temperatureMo-SiC/C composite nano-fiber with different wave absorption performance.

Further, the ratio of polycarbosilane: molybdenum acetylacetonate: the mass ratio of tetrahydrofuran is (0.5-1.0): (0-0.1): (3.55-8.88), silicon carbide is used as matrix fiber, and trace amount of molybdenum acetylacetonate is introduced to modify the silicon carbide, so that PCS is not easy to dissolve in other solvents, and sufficient amount of THF is required to ensure that PCS and molybdenum acetylacetonate are fully dissolved.

Further, polyvinylpyrrolidone: the mass ratio of the absolute ethyl alcohol is (0.5-1.0): (2.37-4.74) not only ensures that PVP is completely dissolved, but also comprehensively considers the influence of the viscosity of the solution on spinning, and obtains an optimal value by adjusting the proportion of absolute ethyl alcohol.

Further, in order to fully dissolve the PCS and the PVP, the PCS and the PVP are firstly dissolved in tetrahydrofuran and ethanol respectively, and the stirring is carried out for enough time to ensure that the PCS and the PVP are uniformly dispersed, so that the full mixing of the solution in the next step is facilitated.

Furthermore, the mixed solution is mutually soluble due to the solvent, and the solute is diffused in the mixed solution to form uniform and stable spinning solution, so that sufficient time is required to be stirred, the two solutions are fully mixed, and the problems of nonuniform spinning, blockage and the like are avoided. It should also be noted that the stirring time may not be too long, since molybdenum acetylacetonate changes significantly with time.

Further, sufficient voltage is required to ensure sufficient electrostatic traction between the spinning needle and the collecting device to form nanofibers; the injection speed can not be too fast or too slow, so as to ensure that the spinning solution injected uniformly can be fully stretched into fibers under the action of static electricity; both the collection distance and the drum speed need to be in the proper range to ensure that spun fibers are collected as much as possible without changing the original morphology.

Further, in order to stabilize the fiber spun by electrostatic spinning, the fiber is placed in a blast drying oven to be pre-oxidized for 1-4 hours at the temperature of 150-200 ℃, so that tetrahydrofuran and ethanol in the fiber are fully volatilized to stabilize the fiber shape, and subsequent high-temperature heat treatment is facilitated.

Further, pre-oxidized stabilizing fiberThe fiber is sintered in an inert gas Ar atmosphere in a certain sintering system, argon is used as common inert gas, other elements cannot be doped in the sintering process of the material, the fiber can be effectively protected, air contact is blocked, the formation and purity of a phase are benefited, the temperature rising rate of the sintering system of the fiber must be within a certain range, if the temperature rising is too fast, the appearance of the fiber is difficult to maintain, and PCS cannot be timely converted into SiC. Excessive sintering temperature can result in Mo₂The C crystal grains are excessively grown and unevenly distributed, so the temperature must be appropriate.

The flexible SiC/C nano composite fiber has a nano fiber structure, so that the flexible SiC/C nano composite fiber can be used as a wave-absorbing material to construct an internal conductive network, and Mo₂The generation of C increases the internal interface and defects, thereby showing that the real part and the imaginary part of the dielectric constant are both improved, the reflection loss is enhanced, and the effective absorption width is obviously improved.

In conclusion, the method has simple process, and the prepared composite nano-fiber has complete shape, uniform diameter distribution and Mo₂The C crystal grains are uniformly distributed in the SiC/C fiber and simultaneously show excellent wave-absorbing performance

The technical solution of the present invention is further described in detail by the accompanying drawings and embodiments.

Drawings

FIG. 1 is an SEM image of Mo-SiC/C pre-oxidized nanofibers prepared by the present invention;

FIG. 2 is an SEM image of Mo-SiC/C nanofibers prepared by the invention after pyrolysis;

FIG. 3 is XRD contrast diagram of different temperature sintered Mo-SiC/C nano fiber and SiC/C nano fiber prepared by the invention, wherein 1100 and 1200 represent sintering temperature of 1100 ℃ and 1200 ℃ respectively;

FIG. 4 is a three-dimensional reflection loss diagram of Mo-SiC/C nanofibers sintered at different temperatures and SiC/C nanofibers prepared by the method as a wave-absorbing material, wherein 1100 and 1200 respectively represent sintering temperatures of 1100 ℃ and 1200 ℃;

FIG. 5 is a graph of real part (a) and imaginary part (b) of dielectric constant of Mo-SiC/C nanofibers and SiC/C nanofibers prepared by sintering at different temperatures, wherein 1100 and 1200 respectively represent sintering temperatures of 1100 ℃ and 1200 ℃;

FIG. 6 shows the effective absorption widths of Mo-SiC/C-1100 prepared by the present invention at different thicknesses;

FIG. 7 is an optical picture of a flexible Mo-SiC/C-1100 nanofiber prepared by the invention.

Detailed Description

The technical solutions of the present invention will be described clearly and completely below, and it should be apparent that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In the present invention, all the embodiments and preferred methods mentioned herein can be combined with each other to form a new technical solution, if not specifically stated.

In the present invention, all the technical features mentioned herein and preferred features may be combined with each other to form a new technical solution, if not specifically stated.

In the present invention, the percentage (%) or parts means the weight percentage or parts by weight with respect to the composition, if not otherwise specified.

In the present invention, the components referred to or the preferred components thereof may be combined with each other to form a novel embodiment, if not specifically stated.

In the present invention, unless otherwise stated, the numerical range "a-b" represents a shorthand representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, a numerical range of "6 to 22" means that all real numbers between "6 to 22" have been listed herein, and "6 to 22" is simply a shorthand representation of the combination of these values.

The "ranges" disclosed herein may have one or more lower limits and one or more upper limits, respectively, in the form of lower limits and upper limits.

As used herein, the term "and/or" refers to any and all possible combinations of one or more of the associated listed items and includes such combinations.

In the present invention, unless otherwise specified, the individual reactions or operation steps may be performed sequentially or may be performed in sequence. Preferably, the reaction processes herein are carried out sequentially.

Unless otherwise defined, technical and scientific terms used herein have the same meaning as is familiar to those skilled in the art. In addition, any methods or materials similar or equivalent to those described herein can also be used in the present invention.

The invention provides a flexible SiC/C nano composite fiber and a preparation method and application thereof, Polycarbosilane (PCS) and molybdenum acetylacetonate are dissolved in Tetrahydrofuran (THF) solution according to a proportion, polyvinylpyrrolidone (PVP) is dissolved in ethanol solvent according to a proportion, and uniform solutions are respectively prepared; mixing and stirring the two solutions for enough time to make the solutions uniform, and performing electrostatic spinning on the obtained light green solution to obtain the Mo-containing SiC/C precursor fiber with a specific composition; pyrolyzing the precursor fiber at high temperature in an inert atmosphere to obtain the expected flexible Mo-SiC/C nanofiber; mixing Mo-SiC/C nano-fibers with paraffin according to a certain proportion to prepare a dielectric sample, and testing the electromagnetic wave absorption performance of the dielectric sample; the addition of molybdenum acetylacetonate not only reduces the formation temperature of SiC, but also Mo₂The effective absorption width of the composite fiber is effectively widened by the synergistic effect of C and SiC/C. According to the invention, molybdenum acetylacetonate is taken as an additive for the first time, and the flexible SiC/C nano fiber with good electromagnetic wave absorption performance is prepared at a lower temperature through electrostatic spinning and high-temperature pyrolysis.

The invention relates to a preparation method of flexible SiC/C nano composite fibers, which comprises the following steps:

s1, putting Polycarbosilane (PCS) and molybdenum acetylacetonate into a weighing bottle, and dissolving in Tetrahydrofuran (THF) according to a certain proportion to obtain a solution A; placing polyvinylpyrrolidone (PVP) in a weighing bottle, adding anhydrous ethanol (CH)₃CH₂OH) to obtain a solution B, and stirring the obtained solution A and the solution B respectively in a magnetic stirrer for 30-60 min until the solutions are respectively uniform;

wherein, polycarbosilane: molybdenum acetylacetonate: the mass-volume ratio of tetrahydrofuran is (0.5-1.0): (0-0.1): (3.55-8.88); polyvinylpyrrolidone: the mass-volume ratio of the absolute ethyl alcohol is (0.5-1.0): (2.37-4.74).

S2, slowly adding the uniform solution A obtained in the step S1 into the uniform solution B under the magnetic stirring effect, and then stirring for 12-24 hours to fully mix the two solutions to form a stable light green spinning solution;

s3, controlling the voltage to be 15-20 kv, enabling the distance between the collecting rotary drum and the spinneret needle to be 15-20 cm, enabling the rotating speed to be 80-100 r/min, and spinning at a constant speed of 0.1-0.4 mm/min to obtain precursor fibers;

wherein, the needle head is a 23-gauge needle head with the inner diameter of 0.3 mm.

S4, collecting the precursor fiber obtained in the step S3 in an aluminum foil, and pre-oxidizing the precursor fiber in a blast drying oven at the temperature of 150-200 ℃ for 1-4 hours to obtain pre-oxidized fiber;

s5, sintering the pre-oxidized fiber obtained in the step S4 in Ar atmosphere, heating to 1000-1300 ℃ at the speed of 2-5 ℃/min, and annealing for 1-3 h to obtain the Mo-SiC/C nano composite fiber.

The Mo-SiC/C nano composite fiber prepared by the method not only has the excellent performance of silicon carbide in harsh environment resistance, but also has the morphological characteristics of high specific surface area, high length-diameter ratio and the like of the nano fiber, and the introduction of Mo element reduces the generation temperature of SiC.

Generally speaking, the sintering temperature of the silicon carbide is 1300-1500 ℃, and the XRD pattern shows that the Mo-SiC/C fiber has lower sintering temperature and the crystallinity of the silicon carbide is quite good. The pure silicon carbide fiber has lower real part and imaginary part of dielectric constant, mainly dielectric loss, narrower effective absorption width and low loss capacity, and Mo uniformly dispersed in the fiber is generated by introducing molybdenum acetylacetonate₂The C crystal grains and the SiC/C nano-fibers are mutually cooperated, so that the effective absorption width and the optimal reflection loss are obviously improved.

In conclusion, the Mo-SiC/C nano composite fiber has a simple preparation method, expected microwave absorption performance and a certain application prospect.

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. The components of the embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations. Thus, the following detailed description of the embodiments of the present invention, presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Example 1

0.5g of Polycarbosilane (PCS) is weighed and then dissolved in 7ml of Tetrahydrofuran (THF), and the solution is stirred for 30min under magnetic stirring to obtain a uniform solution A;

meanwhile, 0.5g of polyvinylpyrrolidone (PVP) is weighed and dissolved in 4ml of absolute ethyl alcohol, and the solution is stirred for 30min under magnetic stirring to obtain a uniform solution B;

slowly adding the solution A into the solution B under the action of magnetic stirring, and magnetically stirring for 12 hours until a uniform and stable spinning precursor C is formed;

then, a 23-gauge needle with the inner diameter of 0.3mm is selected, the collection drum is 15cm away from the spinneret needle at the voltage of 16kv, and spinning is carried out at a constant speed of 0.15mm/min when the rotating speed is 80 r/min;

collecting the obtained nano-fibers, pre-oxidizing the nano-fibers in a forced air drying oven at 190 ℃ for 1h, sintering the pre-oxidized nano-fibers in Ar atmosphere, heating at 5 ℃/min, and annealing at 1000 ℃ for 1h to obtain the Mo-SiC/C nano-fibers.

The spinning is uniform and continuous, the two-dimensional shape of the nanofiber is maintained, and the sintering temperature is relatively low, so that SiC crystal grains do not appear.

Example 2

Weighing 0.5g of Polycarbosilane (PCS) and 0.085g of molybdenum acetylacetonate, dissolving in 7ml of Tetrahydrofuran (THF), and stirring the solution for 30min under magnetic stirring to obtain a uniform solution A;

meanwhile, 0.5g of polyvinylpyrrolidone (PVP) is weighed and dissolved in 4ml of absolute ethyl alcohol, and the solution is stirred for 30min under magnetic stirring to obtain a uniform solution B;

slowly adding the solution A into the solution B under the action of magnetic stirring, and magnetically stirring for 12 hours until a uniform and stable spinning precursor C is formed;

selecting a No. 23 needle with the inner diameter of 0.3mm, spinning at a constant speed of 0.1mm/min when the voltage is 17kv, the distance between a collecting rotary drum and a spinning needle is 20cm and the rotating speed is 85 r/min;

collecting the obtained nano-fibers, pre-oxidizing the nano-fibers in a forced air drying oven at 200 ℃ for 2h, sintering the pre-oxidized nano-fibers in Ar atmosphere, heating at 4 ℃/min, and annealing at 1100 ℃ for 1h to obtain the Mo-SiC/C nano-fibers.

The diameter of the fiber is slightly changed due to the change of various parameters in the spinning, but the whole fiber is kept long and continuous, the crystallinity is obviously improved by improving the sintering temperature, and the real part and the imaginary part of the dielectric constant are improved.

Example 3

Weighing 0.5g of Polycarbosilane (PCS) and 1.0g of molybdenum acetylacetonate, dissolving in 7ml of Tetrahydrofuran (THF), and stirring the solution for 40min under magnetic stirring to obtain a uniform solution A;

meanwhile, 0.5g of polyvinylpyrrolidone (PVP) is weighed and dissolved in 4ml of absolute ethyl alcohol, and the solution is stirred for 40min under magnetic stirring to obtain a uniform solution B;

slowly adding the solution A into the solution B under the action of magnetic stirring, and magnetically stirring for 14 hours until a uniform and stable spinning precursor C is formed;

then, a 23-gauge needle with the inner diameter of 0.3mm is selected, the collection drum is 16cm away from the spinneret needle at the voltage of 15kv, and spinning is carried out at a constant speed of 0.4mm/min when the rotating speed is 90 r/min;

collecting the obtained nano fibers, pre-oxidizing the nano fibers in a forced air drying oven at 170 ℃ for 3h, sintering the pre-oxidized nano fibers in Ar atmosphere, heating at 3 ℃/min, and annealing at 1200 ℃ for 2h to obtain the Mo-SiC/C composite fiber.

It can be clearly seen that the crystallinity is significantly improved compared to 1100 ℃ sintering, but the solution viscosity is too high due to the increase of molybdenum acetylacetonate, and the spinning is continuously blocked so that the spinning cannot be performed. The injection speed is too high, so that the spinning solution can not be stretched into a fiber structure by voltage in time, and the spinning is not easy to carry out.

Example 4

1.0g of Polycarbosilane (PCS) and 0.085g of molybdenum acetylacetonate are weighed and dissolved in 12ml of Tetrahydrofuran (THF), and the solution is stirred for 50min under magnetic stirring to obtain a uniform solution A;

meanwhile, 1.0g of polyvinylpyrrolidone (PVP) is weighed and dissolved in 8ml of absolute ethyl alcohol, and the solution is stirred for 50min under magnetic stirring to obtain a uniform solution B;

slowly adding the solution A into the solution B under the action of magnetic stirring, and magnetically stirring for 18h until a uniform and stable spinning precursor C is formed;

then, a 23-gauge needle with the inner diameter of 0.3mm is selected, the collection drum is 17cm away from the spinneret needle at the voltage of 18kv, and spinning is carried out at a constant speed of 0.2mm/min when the rotating speed is 95 r/min;

collecting the obtained nano fibers, pre-oxidizing the nano fibers in a 160 ℃ forced air drying oven for 4 hours, sintering the pre-oxidized nano fibers in Ar atmosphere, heating at the speed of 3 ℃/min, and annealing at the temperature of 1100 ℃ for 2 hours to obtain the Mo-SiC/C composite fibers.

The PVP is too much in amount, the stirring time is too long, the viscosity is not proper, the diameter of the fiber is greatly changed, and the spinning difficulty is increased.

Example 5

1.0g of Polycarbosilane (PCS) and 0.85g of molybdenum acetylacetonate are weighed and dissolved in 12ml of Tetrahydrofuran (THF), and the solution is stirred for 55min under magnetic stirring to obtain a uniform solution A;

meanwhile, 0.5g of polyvinylpyrrolidone (PVP) is weighed and dissolved in 8ml of absolute ethyl alcohol, and the solution is stirred for 55min under magnetic stirring to obtain a uniform solution B;

slowly adding the solution A into the solution B under the action of magnetic stirring, and magnetically stirring for 24 hours until a uniform and stable spinning precursor C is formed;

then, a 23-gauge needle with the inner diameter of 0.3mm is selected, the collection drum is 19cm away from the spinneret needle at the voltage of 19kv, and spinning is carried out at a constant speed of 0.3mm/min when the rotating speed is 80 r/min;

collecting the obtained nano fibers, pre-oxidizing the nano fibers in a 180 ℃ forced air drying oven for 2h, sintering the pre-oxidized nano fibers in Ar atmosphere, heating at the speed of 2 ℃/min, and annealing at the temperature of 1300 ℃ for 3h to obtain the Mo-SiC/C composite fiber.

The spinning is uniform and continuous, the two-dimensional shape of the nanofiber is maintained, and the crystallinity is good. However, the molybdenum acetylacetonate has a great change due to the excessively long stirring time, and the spinning is difficult.

Example 6

1.0g of Polycarbosilane (PCS) and 0.085g of molybdenum acetylacetonate are weighed and dissolved in 12ml of Tetrahydrofuran (THF), and the solution is stirred for 60min under magnetic stirring to obtain a uniform solution A;

meanwhile, 1.0g of polyvinylpyrrolidone (PVP) is weighed and dissolved in 8ml of absolute ethyl alcohol, and the solution is stirred for 60min under magnetic stirring to obtain a uniform solution B;

slowly adding the solution A into the solution B under the action of magnetic stirring, and magnetically stirring for 20 hours until a uniform and stable spinning precursor C is formed;

then, a 23-gauge needle with the inner diameter of 0.3mm is selected, the collection drum is 20cm away from the spinneret needle at the voltage of 20kv, and spinning is carried out at a constant speed of 0.35mm/min when the rotating speed is 100 r/min;

collecting the obtained nano-fibers, pre-oxidizing the nano-fibers in a 150 ℃ forced air drying oven for 3h, sintering the pre-oxidized nano-fibers in Ar atmosphere, heating at the speed of 2 ℃/min, and annealing at the temperature of 1200 ℃ for 3h to obtain the Mo-SiC/C nano-fibers.

It can be seen that the fiber diameter becomes significantly coarse, the crystalline grains are well crystallized, and the dielectric constant is significantly increased.

Referring to fig. 1, the SEM image of the pre-oxidized fiber shows that the fiber maintains good morphology, has smooth surface and no protrusions when the molybdenum acetylacetonate is added for spinning, which indicates that the spinning process is feasible after the molybdenum acetylacetonate is added.

Referring to FIG. 2, SEM image of the fiber after high temperature treatment shows that the diameter of the fiber is reduced due to the high temperature sintering, and the surface is still smooth, indicating that the molybdenum acetylacetonate is uniformly dispersed in the fiber and no crystal grains are precipitated under the high temperature condition.

Referring to fig. 3, it can be seen from the XRD spectrum that pure silicon carbide fiber shows weak characteristic peak at 1200 deg.c without adding molybdenum acetylacetonate, and basically no silicon carbide is generated at 1100 deg.c, mainly based on carbon matrix. After molybdenum acetylacetonate is added, a characteristic peak obvious in SiC appears at 1100 ℃, the strength of the characteristic peak is obviously enhanced along with the rise of the heat treatment temperature, and simultaneously, the fibers added with molybdenum acetylacetonate are all accompanied by Mo₂The diffraction peak of the C phase appears, which shows that the molybdenum element is uniformly dispersed in the fiber in the form of carbide.

Referring to fig. 4, a three-dimensional reflection loss graph of the wave-absorbing material is shown, and referring to fig. 5, a relative frequency graph of a real part and an imaginary part of a dielectric constant is shown, it can be seen that as a sintering temperature is increased and molybdenum acetylacetonate is added, the corresponding real part and imaginary part are both increased, which proves that both the temperature and molybdenum acetylacetonate have a positive effect on electromagnetic wave absorption performance. The corresponding loss map shows the lowest Reflection Loss (RL)_min) The Mo-SiC/C-1100 nano-fiber is more than 5 times of the SiC/C-1100 nano-fiber at the corresponding temperature.

Referring to fig. 6 and 7, it can be seen that the effective absorption width of the nanofiber with molybdenum acetylacetonate added is significantly increased, and the full coverage of Ku and X bands and the coverage of most C bands can be realized at different thicknesses.

In summary, the flexible SiC/C nano composite fiber and the preparation method and application thereof provided by the invention have the advantages that PCS is used as a silicon carbide source, and molybdenum acetylacetonate is selectively added for modification, so that the formation temperature of silicon carbide crystal grains is remarkably reduced, and Mo uniformly distributed in the fiber is generated₂C crystal grain, which improves the real part and imaginary part of the dielectric constant and introduces multiple loss mechanisms to achieve the bestImpedance matching and electromagnetic losses. The one-dimensional flexible Mo-SiC/C nano composite fiber is directly prepared by using electrostatic spinning equipment, and the common advantages of the material and the nano structure are combined. The microwave absorbing material with good performance is prepared by a simple process.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.