Preparation And Activation Of SiC-C Fiber

Inorganic non-metal microporous materials are expected to be used in the field of environmental protection, health and energy storage, due to their good performances such as stability, high temperature resistance and corrosion resistance. Microporous SiC ceramic fibers are especially reputed for its better heat resistance, corrosion resistance and special electromagnetic properties.Polymer-derived SiC fibers have very lower surface area although they contain plenty of micropores, because most of them are closed ones. So, pitch was added into polycarbosilane and SiC-C fiber was prepared through melt spinning, air curing and pyrolysis of the mixture. The SiC-C fiber was activated by six activation methods and the activation performances were analyzed.The spinnability, air curing condition and pyrolysis process of PCS-Pitch precursor were studied. The results indicate that uniformly mixed precursor can be obtained through dissolving method. Along with the increase of pitch content, thermal treatment temperature of the mixture should be increased so as to be suitable for melt spinning. Followed by the increase of pyrolysis temperature, the surface area of PCS-P and PCS cured fiber both appear peak values, which are 460m²/g and 540m²/g respectively. They almost declined to the value of fiber outer surface area when pyrolysis temperature exceed 800℃.The influences of CO2 and air activation on the elemental composition and surface area of SiC-C fiber were studied. The results indicate that CO₂ can remove free carbon from SiC-C fiber and the surface area around 200m²/g was obtained. The activation efficiency declined along with the increase of pyrolysis temperature. Air activation can be used in a lower temperature because of its strong oxidizing property. But the fiber surface can be easily oxidized into SiO₂. The surface area of 388m²/g can be obtained when 900℃pyrolyzed fiber activated at 600℃in air.KOH and KOH/CO₂ activation methods were also studied. It was concluded that KOH impregnate ratio is the mainly factor. When KOH impregnate ratio is high, the activation velocity of SiC( or SiC_xO_y ) is quicker than C, Si content declined remarkably; When the ratio is lower, activation velocity of the two is almost equal to each other, C content almost remains the same. KOH/CO₂ activation have the similar behavior with KOH activation, while the activation temperature and KOH impregnate ratio both have significant influences, and the surface area are lower than that obtained by KOH activation.Skin-core microstructure was obtained by KOH or KOH/CO2 activation. The skin layer is rich in C, while the inner layer is mainly composed of Si-C-O. The thickness of skin layer will increase when prolonging activation time, uplifting activation temperature or decreasing pyrolysis temperature. So, these two methods are not appropriate for the removal of C in SiC-C fiber.CO₂-KOH and ZnCl₂ activation were carried out in order to restrain the lost of Si. The results indicate that CO₂-KOH activated fibers have lower C content, while the surface area is just around 200-300m²/g. The surface area of cured fiber activated by ZnCl₂ activation is 653m²/g. but this method have no effect on 800℃pyrolyzed fiber.All the six activation methods can achieve microporous fibers, which only contain a small percent of mesopores.