Effects Of Boron Catalyst On The Structure And Properties Of Carbon Fiber

With the development of the defence and military industry, high performance carbon fiber as one kind of the advanced materials is widely used.It has the advantages of high strength, high modulus, corrosion resistance and other excellent performance. High performance carbon fiber is based on high-quality precursor, pre-oxidized fiber. However, the skin-core structure is one of the most important factors affect the quality stability of precursor, pre-oxidized fiber. So eliminating or weakening the skin-core structure has the vital significance to the homogeneous carbon fiber.The catalyst modified method is an effective mean to alleviate the skin-core structure, then it may prepare the homogeneous carbon fiber. Because of boron as a special kind of catalyst can priority replace carbon atoms in the graphite like structure and improve the defects of carbon fiber, it also can make the disordered carbon structure transition to three-dimensional ordered graphite crystalline structures. Finally it can increase the tensile modulus and strength of CF and then make it homogeneous graphite. As things stand, Solution dipping methods are often used on precursor fiber, pre-oxidized fiber, carbon fiber modification. To some extent, it improved the mechanical properties of carbon fiber, but the results only acted on the fiber surface, the core part effect was not obvious, the radial uniformity was still also serious.The B4C nano-powders catalysts were homogeneously distributed into the inner and outer surface of the PAN spinnings solution by mechanical mixing process. Carbon fibers were prepared through the continuous pre-oxidization and carbonization. AES、FT-IR、Raman and XRD were used to investigate the change of the surface morphology and structural transformation and the mechanism of catalytic graphitization. The experiment result shows that:In the process of precursor fiber preparation, heterogeneous diffusion caused the skin-core structure, made the cortex is dense and the core is loose, eventually led to the radial structure inhomogeneity. In the process of heat treatment, this inhomogeneous two phase structure are more and more seriously and genetic to carbon fibers. In the pre-oxidation process, The DTA study found that boron carbide modified fiber pre-oxidation inhibite the pre-oxidation reaction rate, make the oxygen diffusion into the fibers more fully. The pre-oxidation fiber radial uniformity is better than the unmodified fiber.In the carbonization process, The XRD study found that the d002 diffraction peak of boron modified carbon fiber becomes more and more sharp, the peak intensity is higher and with the trend of moving to the right. In the temperature of 1600℃, the graphitization degree of the untreated carbon fiber is 23.37%, while the boron carbide doping carbon fiber’s graphitization degree is up to 52.9%. This shows the catalytic graphitization effect of boron. Furthermore, the mechanical mixing method compared with the boric acid dipping method, it has much better catalytic graphitization effect. And the boron carbide doped carbon fiber can slow down the skin-core structure. The Raman study found that boron carbide doped carbon fiber’s skin-core factor reached 0.88, While the untreated carbon fiber’s skin-core factor is 0.78, this also proved boron carbide doped carbon fiber’s skin-core is more slight.