What Is a Porosimeter?

Liquid extrusion porosimeter from PMI

Liquid extrusion porosimeter

While exploring the topic of pore size and other characteristics of porous materials, the instruments we come across most regularly are the many and varied porometers and permeameters. Occasionally on this pore size website we have touched upon porosimeters, and for clarity I would like to return briefly to that subject today.

A porosimeter is used to measure the diameter and volume of the pores, and the distribution of pore volume, in a porous substance. The principle by which these devices work is that liquid is either forced into (intrusion) or out of (extrusion) the pores in a sample.

The mercury intrusion porosimeter may well be the one with which you are most familiar. Many porous substances will not allow a spontaneous flow of mercury into their pores, but by applying pressure the intrusion can be forced. Pore diameter can be calculated by measuring the pressure needed to make this happen, while pore volume and its distribution can be determined by the amount of mercury which intrudes. This kind of instrument will work with a wide pressure range.

Mercury is not the only liquid used in porosimeters, and indeed there are many circumstances in which users would be very wary of using this substance. Water, oil and a variety of chemical liquids can be used for intrusion porosimetry in materials which they do not wet. Again the basis of the technique is to force liquid into pores by applying whatever pressure is necessary.

Conversely, an extrusion porosimeter relies upon liquids which do wet the material. In this case the liquid is allowed to fill the pores, spontaneously, and then a pressure gradient is applied to force it out of the sample. As in intrusion porosimetry, the pressures and volumes are used to work out the pore volume and distribution. An added advantage of liquid extrusion porosimetry is that it can also be used for measuring rates of liquid flow.

Do visit the PMI website, www.pmiapp.com, if you would like to explore the diversity of porosimeters. Or if you are in the UK and would like to know more about Mercury Porosimetry For Porous Structures please visit the Meritics website.

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