Surface Modification of Carbon Fiber by Polymer Derived Ceramic to Strengthen the Ceramic-Based Carbon Fiber Composite

In this study, the surface of carbon fiber is sprayed with "polysilazane preceramic precursor" and pyrolyzed at different pyrolytic temperatures for coating a dense layer of amorphous SiCN ceramic film, which can be used as a surface reinforcing and protective coating. Polysilazane preceramic precursor can transform from a liquid polymer phase to silicon-based ceramic, which is called polymer derived ceramic (PDC), at high temperatures. The microstructure and chemical composition of the coatings are characterized by field emission scanning electron microscope (FESEM), energy dispersive spectrometer (EDS), and Raman scattering spectrometer. Mechanical properties, Young's modulus and tensile strength, are measured by tensile test. Electrochemical properties are investigated by electrochemical analyzer for potentiodynamic polarization, electrochemical impedance spectroscopy and chronoamperometry. Finally, the experiments are repeated with adding graphene to the polysilazane preceramic precursor to form graphene-reinforced ceramic fiber composite (GRCFC) and compared with the original data.<br/>The experimental results show that the specific strength and modulus of the ceramic-based carbon fiber composite (CCFC) are enhanced 44.26 % and 15.37 % with spraying 40 wt.% polysilazane preceramic precursor in acetone on its surface as well as pyrolyzing at 450 °C. The results of potentiodynamic polarization experiment reveal that the corrosion potential is increased from -0.0971 V to 0.5862 V, the corrosion current density is decreased from 1.72×10^-2 mA/cm² to 1.32×10^-7 mA/cm², and the corrosion rate is extremely decreased from 9.98×10^-2 mm/year to 9.54×10^-7 mm/year. Therefore, it can be shown that the PDC coating can improve the mechanical properties of carbon fiber and have good protection. The GRCFC coated with 20 wt.% polysilazane preceramic precursor mixed with 0.5 wt.% graphene in acetone with pyrolyzing at 450 °C can achieve better specific strength (enhanced 73.15 %) and specific modulus (increased 41.15 %). The results of potentiodynamic polarization experiment reveal that the corrosion potential is increased from -0.0971 V to 0.5873 V, the corrosion current density is decreased from 1.72×10^-2 mA/cm² to 3.61×10^-6 mA/cm², and the corrrosion rate is extremely decreased from 9.98×10^-2 mm/year to 2.88×10^-5 mm/year. Therefore, it can be concluded that the PDC coating incorporated with additional graphene can significantly enhance the mechanical properties and corrosion resistance of the commercial carbon fiber.