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Discussion and Summary

The point of view that mercury porosimetry is the generator of a mapping from a real porous solid to an effective network of circular cylindrical tubes provides a conceptual basis for application of the Katz-Thompson mercury-porosimetry-based permeability theory. On such an effective network, d_c is always well-defined as the tube diameter that just completes a continuous pathway consisting only of tubes with diameter d > d_c. More importantly, it has also been shown that, if a real pore can be modelled by a cylinder with an elliptical cross-section, then the mercury-porosimetry-generated effective tube accurately preserves the local hydraulic conductance of this pore, thus justifying the use of eq. (1) in measuring d_c. The only element of uncertainty in the mapping is the choice of a length for the effective tube, which only affects the value of c in eq. (2) by factors of order one [8]. It should also be recalled that this is a mapping that is only useful for the calculation of fluid permeability, and not for geometric representation of the pore structure.

The nature of the mercury porosimetry effective network mapping needs to be further explored. One possible approach is via direct computer simulation of mercury porosimetry in well-defined models of porous materials, in order to better elucidate the relationship between microstructural features and their signature in an mercury porosimetry measurement. Work in this area has already begun [20].