Study On Catalytic Graphitization Of PAN-based Carbon Fibers With Fe Alloy And Fe Compounds

In order to obtain carbon fibers which have high strength and high modulus,it is needed to enhance the extent of graphitization of carbon fibers.To prevent high power consumption in the graphitization process and high production cost caused by equipment damages,we should use catalyst in the process of graphitization which can make the carbon materials transform to graphite at lower heat treatment temperature(HTT).In this paper,catalytic graphitization of PAN-based carbon fibers was researched.The uniform iron alloy and its compounds coatings as catalysts in catalytic graphitization process were prepared on the surface of PAN-based carbon fibers by the electrochemical methods.(1) The catalytic graphitization effects of the coatings were investigated.The catalyst coatings include Ni-Fe alloy coating,Prussian blue and Fe-Cr₂O₃ composite coating.Ni-Fe alloy coating and Fe-Cr₂O₃ composite coating were obtained by galvanostatic method.However,Prussian blue coating was synthesized using potentiostatic deposition with the electrochemical workstation.(2) The carbon fibers with catalysts were heat treated in an electric resistance furnace.As a comparison,the bare carbon fibers after heat treatment were also studied.The related analyses of bare and catalyst-coated carbon fibers were carried out by X-ray diffraction(XRD),Raman spectrum,scanning electron microscopy (SEM) and energy dispersive spectroscopy(EDS).(3) Ni-Fe(57.91 wt%Fe) coated carbon fibers were heat treated at 1300℃for 2h,XRD detection results show that the degree of graphitization reaches 91.4%after detection of the XRD.However,the degree of graphitization of bare carbon fibers heat treated at 2800℃is only 30.1%.Moreover,the degree of graphitization of pure Fe and pure Ni coated carbon fibers heat treated at 1300℃are 86.0%and 55.5% respectively.Compared with the bare carbon fibers,PB can make the heat treatment temperature drop more than 500℃in order to reach the same extent of graphitization. PB has excellent catalytic effect when the PB-coated carbon fibers were heat treated at 1900℃,interlayer spacing(d₀₀₂) and crystallite size(Lc) reach 3.368(?) and 212(?) respectively.Contrarily,the values of d₀₀₂ and Lc are 3.414(?) and 74(?) respectively when the bare carbon fibers heat treated at 2800℃.In addition,the extent of graphitization of Fe-Cr₂O₃ coated carbon fibers is related to the Cr₂O₃ concentration in electrolyte.When the Cr₂O₃ concentration is 50g/L,Lc and d₀₀₂ of Fe-Cr₂O₃ coated carbon fibers treated at 1200℃are 288(?) and 3.357(?) which is close to the value of highly oriented graphite.In the paper,the catalytic mechanism was also discussed.