Porosimetry is an

analytical technique Analytical technique is a method used to determine a chemical or physical property of a chemical substance, chemical element, or mixture. There is a wide variety of techniques used for analysis, from simple weighing to advanced techniques using high ...

used to determine various quantifiable aspects of a material's

porous Porosity or void fraction is a measure of the void (i.e. "empty") spaces in a material, and is a fraction of the volume of voids over the total volume, between 0 and 1, or as a percentage between 0% and 100%. Strictly speaking, some tests measure ...

structure, such as pore diameter, total pore volume, surface area, and

bulk Bulk can refer to: Industry * Bulk cargo * Bulk liquids * Bulk mail * Bulk material handling * Bulk pack, packaged bulk materials/products * Bulk purchasing * Baking * Bulk fermentation, the period after mixing when dough is left alone to f ...

and absolute densities. The technique involves the intrusion of a non-wetting liquid (often mercury) at high

pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and e ...

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 In physics, Washburn's equation describes capillary flow in a bundle of parallel cylindrical tubes; it is extended with some issues also to imbibition into porous materials. The equation is named after Edward Wight Washburn; also known as Lucas� ...

for the above material having cylindrical pores is given as: :

P_L - P_G = -\frac

P_

= pressure of liquid :

P_

= pressure of gas :

\sigma

= surface tension of liquid :

\theta

contact angle The contact angle is the angle, conventionally measured through the liquid, where a liquid–vapor interface meets a solid surface. It quantifies the wettability of a solid surface by a liquid via the Young equation. A given system of solid, liq ...

of intrusion liquid :

D_

= pore diameter Since the technique is usually performed within a

vacuum A vacuum is a space devoid of matter. The word is derived from the Latin adjective ''vacuus'' for "vacant" or " void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists often di ...

, the initial gas pressure is zero. The

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 mN/ m. With the various substitutions, the equation becomes: :

D_P = \frac

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.

References

Measurement Scientific techniques Porous media {{materials-sci-stub

See also

References