Preparation Of Hollow Carbon Fibers And Investigation Into Their Microwave Absorption Performances

With the application and development of radio waves and radar systems,the problem of electromagnetic wave radiation is becoming more and more serious.It is also known as "the world's fourth-largest public hazard".It is imminent to solve such hazards.Therefore,the materials for electromagnetic waves due to loss of absorption capacity are relatively broad.Application prospects.For carbon materials,the preparation process is generally not complicated,and has the advantages of small specific gravity,high conductivity and low cost,and is widely used in aviation,machinery and chemical industries.But for a single carbon material,the wave absorption performance is poor,the wave absorption mechanism is relatively single,and it is difficult to achieve impedance matching without treatment.For the purpose of solving these problems,this thesis adopts electrospinning technology and thermal control decomposition technology to prepare hollow carbon fibers.Continue to composite magnetic nanoparticles,metal carbides,etc.with the hollow carbon fibers.And then explore the absorbing properties of the composite material,study its absorbing mechanism,and further explore the influence of the preparation parameters of the carbon-based fiber tube on the absorbing properties of the prepared composite fiber.Using polyacrylonitrile?PAN?powder and N,N-dimethylformamide?DMF?as raw materials,the PAN solution was prepared as the electrospinning precursor solution,and the precursor fiber PAN nanofiber was prepared by electrospinning technology.PAN nanofibers have typical one-dimensional characteristics of nanofibers,and are one-dimensional solid nanofibers.The precursor fiber is preoxidized at 300°C using a thermally controlled decomposition process to melt the fiber.The pre-oxidation process is more complicated,and the simple pre-oxidation in this experiment cannot maintain the one-dimensional fiber morphology.The PAN precursor fiber was calcined in a nitrogen atmosphere at 900°C,and the fiber's onedimensional morphology collapsed and appeared granular.The heat control is very critical in the preparation of carbon-based fibers.It has been experimentally verified that some inorganic hollow fibers/nanotubes can be obtained by direct annealing or by controlling the thermal decomposition of electrospun precursor fibers.Proved the concept of "limited nano-space pyrolysis" to prepare hollow carbon nanospheres,which is similar to the egg structure-with an inorganic outer shell and an organic inner shell.The precursor fiber is impregnated with Si O2 sol-gel,and then calcined,and a large-diameter carbon-based fiber tube is successfully prepared.The diameter distribution of the carbon-based fiber tube is uniform,and all are greater than 155 nm.Explore the formation mechanism of the carbon-based fiber tube,and explore its wave-absorbing performance,almost no wave-absorbing performance.Using ferrous sulfate?FeSO₄?,citric acid?C₆H₈O₇?and ferric nitrate?Fe₂?NO₃?₃·9H₂O?as raw materials,a Fe3O4 precursor solution was prepared.The carbon-based fiber tube is prepared by electrostatic spinning technology and thermal control decomposition process.The carbon fiber tube is impregnated with the precursor solution and calcined,and finally a ppy film is deposited on the surface,a conductive network is introduced,and finally the ternary composite fiber of HCF@Fe3O4@ppy is prepared.Exploring the morphological characteristics of the ternary composite fiber,it was found that the ferrite nanoparticles were attached to the inner and outer walls of the carbon-based fiber tube.And discuss its wave absorbing mechanism.The carbon fiber tube of the ternary composite fiber and the ppy film deposited on the outer layer have good conductivity and contribute a lot to the conduction loss.The presence of the interface between the ferrite nanoparticles attached to the inner and outer walls of the carbon-based fiber tube and the matrix leads to an increase in the interface relaxation loss,and this multi-polarization phenomenon also increases the absorption of electromagnetic waves.Moreover,when the fiber content of the ternary composite fiber is 20%,the sample has excellent wave absorption performance.When the matching thickness is 2mm,the peak value of the reflection loss of the sample is the lowest,reaching-26 d B.The maximum effective absorption bandwidth is 2.5GHZ?9GHZ-11.5GHZ?.Using ferrous sulfate?FeSO₄?,citric acid?C₆H₈O₇?and ferric nitrate?Fe₂?NO₃?₃·9H₂O?as raw materials,a Fe3O4 precursor solution was prepared.Using electrospinning technology and thermal control decomposition technology,and uniformly mixing two-dimensional Ti3C2?MXenes?in the electrospinning precursor solution,PAN-based precursor fibers doped with Ti3C2?MXenes?were prepared,and HCF@ Ti C@Fe3O4 fiber,and finally deposited a layer of ppy film on the surface of the fiber to prepare HCF@Ti3C2@Fe3O4@ppy quaternary composite fiber.And explore the morphological characteristics of the quaternary composite fiber,found that the ferrite nanoparticles attached to the inner and outer walls of the carbon-based fiber tube.And the two-dimensional Ti3C2 is evenly distributed in the fiber matrix,and the doping is more successful.Continuing to discuss its wave absorbing mechanism,the quaternary composite fiber carbon-based fiber tube and the ppy film deposited on the outer layer have good conductivity and contribute a lot to the conductive loss.The two-dimensional Ti3C2 doping of carbon-based fiber tubes contributes well to the dielectric loss of electromagnetic waves.At the same time,there are multiple interfaces in the composite fiber.The interface between the ferrite nanoparticles attached to the inner and outer walls of the carbon-based fiber tube and the matrix and the interface between the titanium carbide uniformly doped in the carbon-based fiber and the matrix lead to the interface With the increase of relaxation loss,this multi-polarization phenomenon also increases the absorption of electromagnetic waves.And the optimal reflection loss has reached-52 d B.