Porosimetry

 ( Measurement ) 

Porosimetry is an Measurement used to determine various quantifiable aspects of a material's Porosity structure, such as pore diameter, total pore volume, surface area, and Bulk density and absolute density.

The technique involves the intrusion of a wetting liquid (often mercury) at high pressure into a material through the use of a porosimeter. The pore size can be determined based on the external pressure needed to force the liquid into a pore against the opposing force of the liquid's surface tension.

A force balance equation known as Washburn's equation for the above material having cylindrical pores is given as:

$P\_L\; -\; P\_G\; =\; -\backslash frac\{4\; \backslash sigma\; \backslash cos\; \backslash theta\}\{D\_P\}$

$P\_\{L\}$ = pressure of liquid

$P\_\{G\}$ = pressure of gas

$\backslash sigma$ = surface tension of liquid

$\backslash theta$ = contact angle of intrusion liquid

$D\_\{P\}$ = pore diameter

Since the technique is usually performed within a vacuum, the initial gas pressure is zero. The contact angle of mercury with most solids is between 135° and 142°, so an average of 140° can be taken without much error. The surface tension of mercury at 20 °C under vacuum is 480 millinewton/Metre. With the various substitutions, the equation becomes:

$D\_P\; =\; \backslash frac\{1470\; \backslash \; \backslash text\{kPa\}\; \backslash cdot\; \backslash mu\; \backslash text\{m\}\}\{P\_L\}$

As pressure increases, so does the cumulative pore volume. From the cumulative pore volume, one can find the pressure and pore diameter where 50% of the total volume has been added to give the median pore diameter.

• BET theory, measurement of specific surface
• Evapoporometry
• Porosity
• Wood's metal, also injected for pore structure impregnation and replica