MICROPOROSITY IN RAYON-BASED CARBONIZED AND ACTIVATED CARBON-FIBERS

Viscose rayon fibres were carbonized and activated under different conditions to obtain a variety of pore structures in the final product. These samples were characterized using the physisorption of nitrogen at 77 K. Sing's alpha(s)-method, the DR-method, and the John and Bohra method have been used to evaluate the effective micropore volume. BET-plots have been used to calculate the equivalent surface area. From the total uptake at saturation, the Gurvitsch volume has been calculated. The samples investigated show an essentially microporous character with a significant external surface as determined by the alpha(s)-method. Sample preparation under carbon dioxide appears to enhance the extraction of hydrogen from the precursor during pyrolysis. As a result, the BET-surface area is increased substantially without affecting the yield of char. Higher rates of flow of nitrogen gas during pyrolysis facilitate the evaporation of the laevoglucosan formed during decomposition of the precursor and results in a reduction in char yield. The phenomenon of nitrogen molecule trapping during adsorption-desorption has been observed with the carbonized samples.