New insights and characterization methods through sol-gel derived porous solids

Via a sol-gel process highly porous solids can be synthesized that consist of two homogeneous, isotropically distributed phases, i.e. a pore and a gel backbone phase. This route allows for an independent tuning of the specific surface area and the porosity over a wide range and thus provides model materials for a systematic investigation of complex effects. Highly porous materials are usually compliant and thus easily compressible, a property that can cause artefacts in standard characterization techniques, such as nitrogen sorption analysis. These effects can also occur, however unnoticed, in highly porous powders, granules or thin films. Sol-gel derived porous solids allow us to identify these artefacts and to exploit them for the development of new experimental techniques that are especially suited for highly porous materials in general. We review some examples where the model properties of sol-gel derived porous solids help to separate and identify effects with different origin. In particular, we highlight compression effects upon nitrogen sorption and mercury porosimetry and their evaluation in terms of the elastic properties of the material under investigation.We review methods to extract the fluid permeability of a porous solid from its relaxation behaviour after a deformation, and present examples for the separation of.different types of sites contributing to electrochemical storage or gas adsorption processes.