THE EFFECTS OF ACTIVATION BY CARBON-DIOXIDE ON THE MECHANICAL-PROPERTIES AND STRUCTURE OF PAN-BASED ACTIVATED CARBON-FIBERS

The PAN (polyacrylonitrile)-based activated carbon fibers were developed with the end in view of increasing their efficiency in air or water-filtering applications. A continuous stabilization and a continuous, high-temperature (1300-degrees-C) carbonization process was studied. The formation of closed pores from open pores was found to take place at temperatures ranging from 800-degrees to 1000-degrees-C. The carbon fibers that developed from this temperature range were activated at 880-degrees-C in carbon dioxide. The variation in mechanical properties, microstructure, surface area, and pore-size distribution of activated carbon fibers before and after the activation process are reported in this paper. The adsorption of dye of the activated carbon fibers was also studied. The condensation reaction of the carbon basal planes during the carbonization process decreased the surface area of the carbon fiber. The diameter of most pores was 4 nm at 800-degrees-C and was less than 3.3 nm at 1100-degrees-C. After the activation process, the surface of the activated carbon fibers was etched and new small pores (diameter less than 3.9 nm) were formed in the fibers. The pores ranging from 10 to 30 nm in size in the activated carbon fibers disappeared during the activation stage. The surface area increased markedly with the activation process; it was several hundred times greater than before the process. The resultant activated carbon fibers had a greater porous structure than those that had not been activated. The activated carbon fibers also showed an excellent capacity to adsorb the basic dye.