Research On The Mild Oxidation Of Mesophase Pitch-based Carbon Fiber

Mesophase pitch-based carbon fiber（MPCF） is considered to have incredible potential for development with various kinds of excellent performances like low coefficient of thermal expansion, high modulus, high thermal conductivity and so forth.It has being playing a decisive role in the fields of aerospace,automobile industry,new energy materials,cultural entertainment and civil construction,forming a new breed of material system and being applied widely in carbon fiber reinforced epoxy matrix composites（CFRP,CFRTP）and carbon fiber reinforced carbon matrix composites（C/C composites）.However,the applied carbon fiber without previous surface modifaction contains the percentage of more than 90% element carbon and shows inert surface which is not tough enough to form an effective interface.At certain temperature,CF and C/C composites will be quicken oxidized in oxidation atmosphere, and the rate of the reaction will step up as the temperature get higher,which lead to the strength of the carbon materials degraded and properties weaken.Therefore,the necessities on the research of thermal oxidation in CO₂ atmosphere and the surface microstructure of MPCF,before or after treated, is of great significance to application.Comparative study on thermal oxidation in CO₂ of CF with different structures and different carbonizing temperature by Thermo Gravimetric Analysis（TGA）, and SEM,XRD,RAMAN,etc were used to characterize and analyze the morphology and structure on the surface of CF.The results showed that the oxidation resistance of MPCF is closely related to its macrostructure and crystallite parameters.The integrated MPCF had the better oxidation resistance The samller the d002 and the bigger the Lo value of MPCF, the better the oxidation resistance.Because of the complete graphite structure,oxidation resistance of MPCF-1 was the best.Although crystal structure of MPCF-3 was more complete than MPCF-2,its cross section structure remained some cracks,showing the weak oxidation resistance.The thermal oxidation behaviour of MPCF accorded with zero order,and the activation energy of MPCF-1,MPCF-2 and MPCF-3 was 338.60KJ/mol,219.06KJ/mol and 192.82KJ/mol.Thermal oxidation in CO₂ will change the graphite degree and the morphology of MPCF,and the degree of MPCF will decrease with the treatment time.SEM revealed significant changes in the fiber surface morphology upon varied processing conditions. Some grooves and holes on fiber surface were observed.The crystalline structure of MPCF with different carbonization temperature was various.With increasing carbonization temperature,the graphite structure of MPCF tended to prefect and exhibited higher oxidation resistance.When the carbonization temperature was lower than the thermal oxidation temperature,MPCF will also occur carbonation and thermal oxidation, carbonization will affect the thermal oxidation in CO₂.