SURFACE FRACTALITY OF WOOD CHARCOALS THROUGH SMALL-ANGLE X-RAY-SCATTERING

Geometrical properties of the pore-solid interfaces of devolatilized c harcoals from the pyrolysis of fuel woods in a bench-scale fluidized-b ed reactor were investigated through small-angle X-ray scattering. Spe cifically, surface morphological features of the interfaces were chara cterized by a single parameter indicative of the degree of surface rou ghness, that is, the surface fractal dimension, d(SF), at various rete ntion times. The surface fractal dimensions of the original wood sampl es prior to devolatilization were approximately identical for all spec ies within the range between 2.00 and 2.15, over a length scale from 5 5 to 600 Angstrom, and those for the respective charcoals from these w ood samples were influenced to different degrees by the retention time , tau, in the reactor. The d(SF)'s of the mesopores of charcoals of al l the species attained maxima at a value of tau equal to 35 s and decr eased subsequently with an increase in tau. The analysis of this unexp ected trend was facilitated by the values of the mean radii of gyratio n of the pores, estimated through the Guinier plots. The results imply that when the retention time of the charcoals in the reactor is prolo nged, the mechanism of pore enlargement and smoothening of the interfa ces can play a dominant role in altering the surface morphology and th ereby influence significantly the kinetics of chemical reactions in he terogeneous porous systems.