New perspectives in mercury porosimetry

Seventy-six years ago, Washburn pioneered the concept that the structure of porous solids could be characterized by forcing a non-wetting liquid to penetrate their pores. At that time Washburn postulated that the minimum pressure P required to force a non-wetting liquid like mercury to penetrate pores of size R is given by P=K/R, where K is a constant. Nowadays that very same concept constitutes the backbone of mercury porosimetry, a technique applied routinely to the characterization of all kinds of solids. Despite its perceived fundamental and practical limitations, mercury porosimetry will continue to be regarded as a standard measure of macro- and mesopore size distributions for years to come. This is so because this time-tested technique is (1) conceptually much simpler, (2) experimentally much faster, and (3) unique in its ability to evaluate a much wider range of pore sizes, than any alternative method practised currently (e.g. gas sorption, calorimetry, thermoporometry, etc.). Clearly it would be desirable to derive as much structural information as possible from simple mercury porosimetry experiments. Surprisingly, relatively few attempts have been made in the open literature to extract much information beyond pore size distributions from mercury porosimetry data. This contribution emphasizes the need to develop concerted efforts towards expanding the interpretation of mercury porosimetry data by examining the virtues and flaws of various reported attempts to generate particle size distributions, inter- and intraparticle porosities, pore tortuosities, permeabilities, throat/pore ratios, fractal dimensions and compressibilities from mercury intrusion and/or extrusion curves.