In particular, with respect to carbons, the nonintrusive nature of SAS means that, in principle, characterization can be performed on carbons in situ during activation processes, allowing real time resolution of porosity development. Small angle scattering (SAS) techniques offer a number of advantages for the investigation of the nature and behavior of porous materials. Seifert, in Studies in Surface Science and Catalysis, 2002 1 INTRODUCTION If the predictions of the Kelvin equation are in accordance with the SAS analysis, a reconstruction of the adsorption isotherm can be obtained from the SAS data. By determining a number of scattering curves corresponding to the same sample equilibrated at various relative pressures, for both the adsorption and desorption branches of the adsorption isotherm, a correlation of the two methods could be possible. In terms of SANS, contrast matching reduces the solid/film/pore system to a binary one. In this case the adsorbed film as well as the condensed cluster of pores will cease to act as scatterers, and only the remaining empty pores will produce measurable scattering. Since the s.l.d, of H 2O and D 2O are known while the pore space s.l.d, equals to zero, contrast matching conditions are achieved if an appropriate mixture of H 2O/D 2O that has the same s.l.d, as the solid is used as the adsorbate. In the case of adsorption of a vapor by a porous material, a three phase system in terms of SAS is produced: pore/adsorbed film or capillary condensed vapor/solid. The basic principles of SAS are described in Chapter 1.2 of this book. Finally, we may note that SAS may detect both open (either conducting or not) and closed pores. Again, pore network effects referring to microporous necks controlling the entrances of larger pores is another example which can successfully be studied by SAS.
Therefore SAS method may provide critical information for these mixed class porous systems ( 22-26). For instance, coal contains all classes of pores (i.e. In addition, porous media commonly refer to a wide range of pore sizes. This means that there is an overlapping range between 1-2 nm detectable by this method. One reason being that microporous materials have sizes less than 2 nm whereas SAS is general applicable for sizes larger than 1 nm. On the other hand, SAS technique although improper for the study of microporous media, is not worthless. As a result, SAS measurements are ideal for the study of mesoporous and macroporous materials. In addition, for the study of larger inhomogeneities (up to 1 µm or even more), the area is covered by Double Crystal Diffractometers, a special kind of SANS instruments. Small angle scattering (SAS) method either with neutrons (SANS) or X-rays (SAXS) provides structural information about inhomogeneities of scattering objects, such as pores, in the size range from 1-200 nm. Kanellopoulos, in Membrane Science and Technology, 2000 2.3 Small Angle Scattering