The adsorbent granules I am using in my adsorption studies are 300 microns in size, and is amorphous in nature. And in this regard, is it necessary to make the sample even finer by grinding it?
For the case of spherical, non-porous particles, the BET the specific surface is inversely proportional to the particle diameter multiplied by particle geometric density (Rouquerol, F, et al., 1999).
It is possible to determine absolute surface areas using highly accurate volumetric adsorption equipment as low as approximately 0.5 - 1 m2 with nitrogen as the adsorptive.
The saturation pressure of the supercooled liquid krypton is 2.63 torr, hence the number of molecules in the free space of the sample cell is significantly reduced to approximately 1/300th that of the nitrogen case. Hence, krypton adsorption at ~77K is made much more accurate, and can be applied to assess absolute surface areas down to 0.05 m2 or below.
While area is, of course, inversely proportional to particle diameter as Florian Glodeanu reminded us. This is only important if geometric surface area is of the same order of magnitude than pore surface area (i.e. in non-porous systems). In the majority of porous systems, area in pores will largely exceed geometric surface area and therefore the error you are introducing by grinding or not, is negligible. (Please note that this is not true for non-porous systems). If those aggregates are not causing diffussional limitations and as long as the area in pores is large compared to geometrical area you are safe with not grinding your sample.
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