Quantachrome offers instruments for determining porosity by two methods - namely, gas adsorption and mercury porosimetry.
Gas adsorption techniques permit pore radius measurements from approximately four Angstroms to five hundred Angstroms employing both classical mesopore and newer micropore methods. See Gas Sorption - Principles of Operation for further information.
Mercury porosimetry provides measurements of pore radii from several million down to eighteen Angstroms. See Mercury Porosimeter - Principle of Operation for further information.
Mercury Porosimeters - Principle of Operation
The theory of all mercury Porosimeters is based on the physical principle that a non-reactive, non-wetting liquid will not penetrate pores until sufficient pressure is applied to force its entrance. The relationship between the applied pressure and the pore size into which mercury will intrude is given by the Washburn equation:
PD= -4γ.cosΘ
where P is the applied pressure, D is the diameter, γ is the surface tension of mercury (480 dyne cm-1 and Θ is the contact angle between mercury and the pore wall, usually near 140°. As pressure increases, the instrument senses the intrusion volume of mercury by the change in capacitance between the mercury column and a metal sheath surrounding the stem of the sample cell. As the mercury column shortens, the pressure and volume data are continuously acquired and displayed by the software package.
