Porosimetry

Porosimetry is a family of analytical techniques used to characterize the pore structure of porous materials by measuring how fluids or gases invade or are withdrawn from pores under controlled conditions. The data are used to determine porosity, pore-size distribution, pore volume, and related properties that influence transport, storage, and mechanical behavior of materials.

Mercury intrusion porosimetry (MIP) is a widely used method in which a sample is subjected to increasing hydrostatic pressure to force mercury into pores. Because mercury wets surfaces poorly, higher pressures are required to intrude into smaller pores. The intrusion curve is converted to a pore-throat size distribution using the Washburn equation. MIP provides total porosity and pore-volume distribution over roughly 3 nanometers to tens of micrometers, and it can reveal pore connectivity. However, the technique is destructive, involves toxic mercury, and relies on simplified pore-shape assumptions; some pore geometries can bias results, such as ink-bottle effects.

Gas adsorption porosimetry uses adsorption isotherms of nitrogen or argon (often at 77 K) to determine specific surface area (BET) and pore-size distributions (BJH or DFT methods). It is most effective for micro- and mesopores (approximately 0.3–100 nanometers) and less sensitive to macropores.

Other approaches include capillary rise and liquid intrusion methods for macropores and direct imaging techniques such as X-ray computed tomography, which can visualize pore networks in three dimensions.

Outputs include porosity, pore-size distribution, pore volume, surface area, and indicators of pore connectivity. Porosimetry is used in ceramics, soils, catalysts, rocks, membranes, cement, and energy storage materials.