Preparation Of Macropores On The Surface Of Rayon-based Carbon Fibers And The Pore Mechanism

Macroporous rayon-based activated carbon fibers(RACF) with high strength were successfully developed.The details are as follows:(1) Macroporous activated carbon fibers with high strength were developed by employing different materials and pretreatment conditions.Firstly,rayon-based oxidized fiber and rayon-based carbon fibers were respectively pretreated by impregnation mix solution with 0.1mol/L sodium chloride(NaCl) and phosphoric acid(H₃PO₄).Then,the treated fibers were activated by water vapor at 800,900 and 1000℃respectively.We found that activation temperature impacted on the structure and properties of RACF,e.g. yield,density,surface and cross-section topography,specific surface area and fiber tensile strength.The yield,density and fiber tensile strength have obvious descend trends,whereas the numbers of macropores on fiber sufaces,specific surface area and oxygen-containing groups ratio have ascend trends with the increase of activation temperature.Compared with samples at other activation temperatures,the samples activated at 900℃have best comprehensive properties,in terms of macropore size distribution,specific surface area and strength.Moreover,the strength of activated carbon fiber developed by rayon-based carbon fiber was higher than that by rayon-based oxidized fibers.We also discussed the effects of different impregnation solutions such as NaH₂PO₄,Na₂HPO₄ and Na₃PO₄ on the resulting RACF.We found that RACF treated by NaH₂PO₄ possessed macropores with uniform distribution along the fiber axis.And compared to those RACFs treated by Na₂HPO₄ or Na₃PO₄,RACF treated by NaH₂PO₄ exhibited higher specific surface area,but a little poorer tensile strength.(2) We discussed the mechanism of macropore development on surfaces of RACF by using FTIR, XPS,TGA,XRD and SEM.We found that the introduction of impregnation solutions can introduce catalytically active points and the number of activation centers,thus enhance the structural irregularity. These activation centers can provide places for the reactions between carbon fibers and gasification agents. It can be concluded that the introduction of impregnation solutions is the key for the macropore emergence on RACF.Moreover,both the pore numbers and sizes could be controlled by the concentration of the solutions.In addition,the emergence of macropores on RACF surfaces was affected by other factors such as temperature and the structure of raw materials. (3) We proposed a model for macroporous RACF.According to RACF's surfacial and cross-sectional topography,activation process develops along the radial of the fibers,namely from the surface to the inside. RACFs produced in this study contain the microstructure of activated carbon fiber in skin and that of carbon fibers in core.