Background information > Mercury Porosimetry Best Practice

We recommend the following procedure for mercury porosimetry to allow you to model data with PoreXpert and PoreXY.

•Service the mercury porosimeter at regular intervals.

•Check the calibration of the instrument using manufacturers reference materials or certified reference materials.

•We also recommend participation in inter-laboratory comparison exercises to check performance of your laboratory against other laboratories worldwide, by participating in inter-laboratory comparisons additional materials can become certified reference materials. This increases the range of certified reference materials for more applications.

•Use freshly distilled or research grade mercury.

•Carry out the measurements in a laboratory which is thermostatted to ± 1 degree Centigrade. A good idea for all porosimeters is to use an external temperature data logger to monitor the external temperature through out the experiment.

•Carry out a blank run with the same penetrometer / sample vessel as for the sample run, using the same pressure table with identical experimental parameters and performed at a known temperature so the density of the mercury is known.

•Set the equilibration time at each pressure to at least 1 minute this allows the mercury to reach all of the void features at each size or any shielded void features. The slower equilibrium time also reduces the thermal effects improving the accuracy and precision of your experimental data. For very tortuous systems a longer equilibrium time may be required.

If either the intrusion or extrusion curve has a discontinuity at high pressure, and looks as though it has been chopped off horizontally, you cannot use the data for PoreXpert. To cure this effect, work through the following checks in order, until the effect is cured:

•Check that you have not run out of stem volume for measuring the amount of mercury intruding the sample.

•Add one or two extra points very near the maximum pressure. This will effectively slow down the experiment at highest pressures, and reduce any heating effect in the mercury.

•If the truncation occurs at pressures which are above those necessary to fully characterise the sample, then run the experiment to a maximum pressure below the truncation, but above the point of 100%`sample intrusion.

•Get the porosimeter serviced, including a change of seals and/or pressure transducers.

•Porosity values can be measured using alternative techniques such as Pycnometry.