April 21, 2016

Porosity analysis by mercury porosimetry

Mercury porosimetry uses the non-wetting properties of mercury to gain information on the porous characteristics of solid materials: porosity, pore volume, pore size distribution and density. During a typical porosity analysis in a mercury porosimetry analyzer, a higher pressure is needed to force intrusion of mercury in smaller pores, whereas mercury intrusion in larger pores already occurs at low pressure. In this way a wide dynamic range of pore sizes can be measured and a pore size distribution can be obtained starting from 4 nm (pressure = 400 MPa) up to approx. 800 µm (vacuum). As a consequence, mercury porosimetry is extremely suitable for materials showing broad distributions of pore sizes or mainly macropores.

Prior to the mercury porosimetry analysis, vacuum or flow degassing is used to remove moisture from the porous structure. Besides information on porosity obtained by pores located in the interior of the solid (intraparticle porosity), also information on the void space between particles (interparticle porosity) can be derived. This type of data can be used to determine different types of density: bulk density, apparent density and eventually true density if all the available porosity can be adequately accessed during the mercury porosimetry experiment.

The low and high-pressure mercury intrusion measurements are performed on the CE Instruments Pascal 140 and 440 porosity analyzer, respectively or a Micromeritics Autopore IV 9505 porosimeter. The typical result of a mercury porosimetry measurement comprises a graphical representation of the mercury intrusion curve and extrusion curve and the corresponding pore size distribution accompanied by data on pore volume, pore size, density and porosity.