R. Sakurovs, L. He, Y. Melnichenko, A. Radlinski, T. Blach, H. Lemmel, D. Mildner:
"Pore size distribution and accessible pore size distribution in bituminous coals";
Int. Journal of Coal Geology, 100 (2012), S. 51 - 64.

Kurzfassung englisch:
The porosity and pore size distribution of coals determine many of their properties, from gas release to their
behavior on carbonization, and yet most methods of determining pore size distribution can only examine a
restricted size range. Even then, only accessible pores can be investigated with these methods. Small-angle
neutron scattering (SANS) and ultra small-angle neutron scattering (USANS) are increasingly used to charac-terize the size distribution of all of the pores non-destructively. Here we have used USANS/SANS to examine
24 well-characterized bituminous and subbituminous coals: three from the eastern US, two from Poland, one
from New Zealand and the rest from the Sydney and Bowen Basins in Eastern Australia, and determined the
relationships of the scattering intensity corresponding to different pore sizes with other coal properties. The
range of pore radii examinable with these techniques is 2.5nm to 7μm. We confirm that there is a wide range
of pore sizes in coal. The pore size distribution was found to be strongly affected by both rank and type
(expressed as either hydrogen or vitrinite content) in the size range 250nm to 7μm and 5 to 10nm, but
weakly in intermediate regions. The results suggest that different mechanisms control coal porosity on differ-ent scales. Contrast-matching USANS and SANS were also used to determine the size distribution of the frac-tion of the pores in these coals that are inaccessible to deuterated methane, CD4, at ambient temperature. In
some coalsmost of the small (~10nm) poreswere found to be inaccessible to CD4on the time scale of the mea-surement (~30min-16h). This inaccessibility suggests that in these coals a considerable fraction of inherent
methane may be trapped for extended periods of time, thus reducing the effectiveness of methane release
from (or sorption by) these coals. Although the number of small pores was less in higher rank coals, the frac-tion of total pores that was inaccessiblewas not rank dependent. In the Australian coals, at the 10nm to 50nm
size scales the pores in inertinites appeared to be completely accessible to CD4, whereas the pores in the
vitrinite were about 75% inaccessible. Unlike the results for total porosity that showed no regional effects on
relationships between porosity and coal properties, clear regional differences in the relationships between
fraction of closed porosity and coal properties were found. The 10 to 50nm-sized pores of inertinites of the
US and Polish coals examined appeared less accessible to methane than those of the inertinites of Australian
coals. This difference in pore accessibility in inertinites may explain why empirical relationships between
fluidity and coking properties developed using Carboniferous coals do not apply to Australian coals.

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