Hg Porosimetry Method

2 Pore Volume and Pore Size Distribution 3.2.1 Hg Porosimetry Method 

A simple model for the pore volume or the void space in a porous material is to assume it to be composed of a collection of cylindrical pores of radius r. Then a volume of a liquid that does not wet the pore wall surfaces can be forced under pressure to fill the void space. This liquid is invariably mercury because it has a high surface tension, thus the Hg penetration (or porosimetry) method is used to determine pore volumes and the pore size distribution of larger pores, i.e., those with radii larger than about 10 nm. The relationship between pore size and applied pressure. Pap, is obtained by a force balance, that is, the force due to surface tension is equated to the applied force  

The constant in this equation is slightly different from older values [2]. From this equation it can be easily seen that pressures near lO psia, which is the physical limit of most experimental systems, are required to fill pores 200 A in diameter, hence the lower limit of r = lOnm mentioned above. 

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