【作者】 孙良奎；

【导师】 程海峰； 楚增勇；

【作者基本信息】 国防科学技术大学 ， 材料科学与工程， 2008， 硕士

【摘要】 采用静电纺丝法并通过热处理制备了超细实心碳纤维、中空碳纤维和C/SiO₂同轴复合纤维,研究了纺丝工艺条件和纺丝溶液性质对纤维形貌的影响,并首次研究了静电纺丝纤维的吸波性能。研究发现,超细实心碳纤维的直径减小主要发生在不稳定拉伸阶段,随着纺丝电压的升高、溶液流速的减小以及溶液浓度的减小,纤维的直径减小。溶液电导率对纤维的直径影响最大,向溶液中加入重量百分比5%的NaCl,得到的纤维直径由1.7μm减小到0.4μm。纺丝环境温度的升高能提高溶剂的挥发速度,加速纤维的固化,防止纤维的粘结。溶液浓度和溶液注入速度的稳定性对纤维中珠节物的数量有较大影响,随着溶液浓度的升高,纤维中珠节物明显减少,溶液注入速率稳定性的提高有利于减少纤维中的珠节物。采用同轴静电纺丝法制备了PAN/SiO₂同轴复合纤维,经过热处理得到C/SiO₂同轴复合纤维。采用SEM,FTIR,XRD表征了纤维的截面形貌和涂层结构,表明在碳纤维表面成功制备厚度约20nm的SiO₂涂层,热重分析表明纤维的抗氧化性能有所提高。以PAN为壳层,甲基硅油为芯层,采用同轴静电纺丝技术制备了PAN/硅油同轴复合纤维,经过热处理得到中空碳纤维。研究了同轴喷丝头对同轴射流形成的影响,当内针头伸出距离Zp与外针头半径的一半相当时,得到同轴射流。壳芯溶液流速比Vin/Vout对中空结构的形成有较大影响,当内外溶液流速相当时,得到的纤维呈中空结构。中空纤维壁厚不均匀,壳层溶液电导率增大,中空纤维壁厚的最小值减小。中空纤维密度较实心碳纤维有较大的降低,实心碳纤维密度约1.6g/cm³,而中空碳纤维密度为0.64g/cm³。采用网络矢量分析仪研究了三种纤维的介电常数,结果表明,随着静电纺丝实心碳纤维直径的减小,纤维/石蜡复合材料的介电常数增大;同轴复合纤维堆积电导率较小,与未涂层实心碳纤维相比,同轴复合纤维介电常数大大降低。中空碳纤维的介电常数实部比实心碳纤维高。更多还原

【Abstract】 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.更多还原