Pore Size Distribution

Pore Volume Distributions can be determined by either gas adsorption porosimetry (typically N₂, Ar or CO₂) or mercury intrusion porosimetry.  Gas porosimetry measures pores from 17 Angstroms to about 4000 Angstroms in diameter. Mercury porosimetry is applicable to pores from 0.006 um up to 900 um in diameter.

Gas adsorption will measure pore size by recording isotherms from low pressures to saturation pressure.  The pressure range is determined by the size range of the pores to be measured.  Isotherms of microporous materials are measured over a pressure range of approximately 0.00001 mmHg to 0.1 mmHg. Isotherms of mesoporous materials are typically measured over a pressure range of 1 mmHg to approximately 760 mmHg. Once details of the isotherm curve are accurately expressed as a series of pressure vs. quantity adsorbed data pairs, a number of different theories or models can be applied to determine the pore size distribution. Available micropore methods include: Density Functional Theory (DFT), MP-Method, Dubinin Plots (Dubinin-Radushkevich D-R, Dubinin-Astakov D-A), and Horvath-Kawazoe (H-K) calculations. Available Mesopore methods include: Barrett, Joyner and Halenda method (BJH), and Density Functional Theory (DFT).  T-Plot analysis is also available for total micropore area as well. The Particle & Surface Sciences Analytical Service Laboratory utilize the Tristar 3000 for pore size measurements.

Mercury intrusion porosimetry involves placing the sample in a penetrometer, then surrounding the sample with mercury.  Mercury is a non-wetting liquid to most materials and resists entering voids, doing so only when pressure is applied. The pressure at which mercury enters a pore is inversely proportional to the size of the opening to the void.  As mercury is forced to enter pores within the sample material, the change is measured in capacitance of capillary of the penetrometer, this capacitance is proportional to the intrusion volume. This intrusion volume is recorded with the corresponding pressure or pore size. The Particle & Surface Sciences Analytical Service Laboratory utilizes the Autopore II 9220 for our mercury porosimetry measurements.