『Abstract
The BET and micropore surface areas of different size fractions
of four different unweathered alkali feldspars were calculated
using gas adsorption data. BET surface area decreased with increasing
grain size. Micropore surface area accounted for 12-84% of BET
surface area. For two of the feldspars, Eifel sanidine and KB14,
micropore surface area increased with decreasing grain size; with
regard to the other two, Perth perthite and Keystone microcline,
surface area varied randomly with grain size. Micropores have
diameters≦2 nm, which is on the same scale as alkali feldspar
unit-cell dimensions. As there are no channels in the alkali feldspar
crystal structure, it was concluded that the measured micropore
surface area was due to cracks generated during the grinding involved
in sample preparation. Values for the surface roughness of the
grains were calculated assuming that micropore surface area equaled
internal surface area. Values varied between 1 and 7 for the different
grain size fractions of Perth perthite, Keystone microcline, and
Eifel sanidine. For KB14 surface roughness varied between 7 and
24. It is possible that the dissolution of feldspars proceeds
at different rates down cracks and at the outer surface of grains.
If this is the case then the present data suggest that care must
be taken when comparing surface area normalised dissolution rates
obtained from chemically similar samples which have been ground
for different periods of time with different degrees of force.』
1. Introduction and previous work
2. Sample descriptions
3. Methods
3.1. Sample preparation
3.2. Gas adsorption and surface area measurements
3.3. Determination of D
4. Results and discussion
4.1. Adsorption and desorption data
4.2. ABET, AMICRO and
SR
4.3. Location of AINT
5. Relevance to dissolution studies
6. Conclusions
acknowledgements
References