Preparation Of Lightweight Wave Absorbents Based On Carbon Fibers Via Electrospinning

Ultrafine PAN fibers, PAN/silicon oil coaxial fibers and PAN/SiO₂ coaxial fiber were successfully prepared by electrospinning, after oxidation and pyrolysis of the eletrospun fibers, Ultrafine carbon fibers, hollow carbon fibers and C/SiO₂ coaxial fibers were obtained respectively. The influence of electrospinning process parameters and solution properties on the formation of the fibers were investigated,.the wave absorbing properties of the three kind of fibers were studied for the first time.It was found that the decrease of the solid carbon fibers diameter happened at the unstable jetting stage mainly, the fiber diameter decreased as the increase of the voltage, the decrease of the flow velocity and the solution concentration. The conductivity of the soution had the most effects on the fiber diameter, the fiber diameter decreased from 1.7μm to 0.4μm when the electrospinning was carried out by adding 5%(w.t) NaCl into the PAN solution. The increase of the environment temperature can enhance the evaporation of the solvent and it can prevent the fibers from matting together. The influence of the solution concentration and the flow velocity on the amount of the beads in the fiber was investigated, the decrease of the beads occurred as the concentration and the stability of the flow velocity increased.PAN/SiO₂ coaxial fibers were prepared firstly by coaxial electrospinning using PAN as the core and SiO₂ sol as the shell, then C/SiO₂ coaxial fibers were obtained after oxidation and pyrolysis of the eletrospun fibers. The structure and cross-section morphologies of the C/SiO₂ coaxial fibers were investigated by FTIR, XRD and SEM,The results showed that SiO₂ coating with a thickness of about 20nm was successfully prepared on the carbon fibers. DTA-TG analysis also indicated an increase in oxidation resistance of the coaxial fibers.PAN/silicon oil coaxial fibers were prepared firstly by coaxial electrospinning using PAN as the shell and silicon oil as the core, and then hollow carbon fibers were obtained after oxidation and pyrolysis of the eletrospun fibers. Effects of coaxial spinneret were studied on the formation of the core-shell jets. Results showed that a coaxial jet could be obtained on the tip of the coaxial spinneret when the net length of the core nozzle than the shell nozzle, Zp was about half of the shell nozzle radius (rout). feeding rate ratio also had a great influence to the hollow structure, hollow fibers could be obtained when Vin/Vout =1. the thickness of the shell of the hollow fibers were asymmetrical, as the increase of the conductivity of the shell solution, the minimum of the shell thickness decreased. The density of the hollow carbon fibers was 0.64g/cm³, which was far less than 1.6g/cm³, the density of the solid carbon fibers.Radar absorbing properties of the three kinds of fibers were studied by voter network analyzer, the results showed that both the real part and the imaginary part of the permittivity decreased as the diameter increase of the solid carbon fibers. The conductivity value of the C/SiO₂ coaxial fibers were small, compared with uncoated carbon fibers, both the real part and the imaginary part of the C/SiO₂ coaxial fibers permittivity decreased. The permittivity value of hollow carbon fibers was over the solid carbon fibers.