Process Optimization And Performance Characterization For The Growth Of Carbon Nanotubes/Carbon Nanofibers On The Surface Of Carbon Fibers

This paper focused on electrochemical surface modification process in carbon fibers (CFs) reprocessing and growth of CNTs/CNFs on carbon fibers, and the major contents include:(1) The effect of electrochemical modification on the surface properties of carbon fibers and the morphology of catalyst particles. (2) the effect of catalyst type, temperature, pressure, and time during CVD on the morphology of CNTs/CNFs and the mechanical capacity of carbon fibers via changing CVD parameters. (3) The effect of CVD parameters on the mechanical capacity of growth of CNTs/CNFs on carbon fiber reinforcement composites.Through self design, modification of electrochemical treatment equipment, we developed an continuous, and effective method to obtain the uniform catalyst coating with electrochemical oxidation.we found that with the increase of the treatment intensity, carbon fibers appear different color, and specific surface area of CFs enhance 7 times than the untreated CFs when the treatment current intensity is lA(same as 250C/g), and no obvious groove is formed on the surface of CFs. Through Raman spectrum and acid base titration, it was found that R (ID/IG) and functional groups of CFs after electrochemical oxidation increases, with the increase of treatment intensity, the edge of graphite microcrystalline on the surface of carbon fibers was etched, and crystallite size decreased.the content and type of functional groups on the surface of carbon fibers increased, then the surface became uneven. But when charge loading exceeded 150C/g, the content of functional groups decreased, at the same time, excessive charge loading would damage the mechanical capacity of carbon fibers. The optimum current intensity is 100 C/g, and the optimum electrolyte is O3PNH4.Through studying the effect of catalyst particles morphology, temperature, pressure, and time during CVD on the morphology and yeild of CNTs/CNFs, It was found that uniform and orderly catalyst particles was necessary for the growth of CNTs/CNFs. The diameter of CNTs/CNFs always exceeded the catalyst particles. With the increase of treatment intensity, the diameters of CNTs/CNFs added, and the difference of diameters added. When the diameters< 7nm, carbon fibers could not grow CNTs/CNFs, and which>23nm, the diameter of CNTs/CNFs would be uncontrollable. The temperature during CVD influenced the catalyst activity. There were little CNTs/CNFs on the surface of CFs at 450℃,and excessively high temperature (exceeding 600℃) would produce amorphous carbon on the surface. Pressure and time during CVD both promoted the growth of CNTs/CNFs. Higher the pressure was, more the yeild of CNTs/CNFs would be, but excessive C atoms lead to more amorphous carbon. The efficiency of time for the growth of CNTs/CNFs was restricted. CNTs/CNFs grew rapidly above 3min during CVD process, and slowed down when the CVD time exceeded 10min. Electrochemical treatment and reduction process damaged the mechanical properties of CFs (7% and 11%), then the CVD process could repair this damage. For 500℃ and 600℃, the optimum growth times of CNTs/CNFs are 15 min and 10 min, respectively.The IFSS of CNTs/CNFs reinforcement CF composites improved 23%～90% with different CVD parameters. Through microbond test and interlaminar shear strength test, CNT-grafted carbon fiber reinforced composites possess a higher IFSS than CNF-grafted carbon fibers. With the yield of CNTs/CNFs increased, IFSS of composites climb up and then declined. For 600℃, The optimum CVD time was 10min at the pressure of 0.01 MPa, which obtained CNTs of 11.3% relative to untreated CFs.