I. Snook et P. Mcmahon, FRACTAL PORE SURFACES IN BROWN-COAL, THEIR CHANGES ON PROCESSING AND THEIR EFFECT ON COMBUSTION, Langmuir, 9(10), 1993, pp. 2726-2729
Using small angle X-ray scattering, we show that the scattering patter
n caused by the pore surfaces of dried coal may often be interpreted a
s arising from fractally rough surfaces. In practice a wide range of v
alues of the surface fractal dimension, D(s), was found covering virtu
ally the whole allowable range. In the case of brown coal we find that
as it is dried from the bed-moist state, the scattering curve changes
from that characteristic of a mass fractal to that appropriate to a s
urface fractal. Furthermore, during upgrading of brown coal by deoxyge
nation at various processing temperatures, T, changes of the parameter
s characterizing the fractal surfaces may occur. Under some conditions
D(s) and the surface measure, N0, change very slightly with increasin
g T. However, heating in hydrogen-rich atmospheres causes dramatic inc
reases in D(s) and dramatic decreases in N0 for T above about 320-degr
ees-C. The results seem to indicate that after a very slight initial s
moothing of the pore surfaces, they become very rough and of very much
smaller extent indicating pore collapse. This correlates well with ot
her properties of the coal, and in fact we are able to relate the oxid
ation (combustion) behavior of these coals with the measured values of
N0.