Quantitative stereological analysis of the pore-size distribution in a colloidal silica sol-gel
The pore size distribution of an unsintered colloidal gel has been determined by stereological analysis of ultramicrotomed thin sections (70 nm) of the gel. This is a novel use of the ultramicrotomy technique as the epoxy represents the porous phase of the microstructure rather than just the medium used to maintain a coherent structure during thinning. In order to obtain statistically significant pore size information a nested sampling scheme was carried out, and a total of 36 two-dimensional fields taken at 19,000 X were examined. Pore diameters were measured with a digital image analyzer which measured 15 projected diameters every 12° from the center of the feature. Stereological quantities obtained were average pore diameter (Davg), number of pores per unit area (NA), and number of pores per unit volume (NV).