Permeabilities k and formation factors F of a number of monoliths made of compressed expanded graphite having different porosities were measured from gas permeation and ion diffusion experiments, respectively. The results were analyzed and discussed in the framework of a model, according to which the pores were cylinders of lengths l and diameters δ such that l = δ. Formation factors were calculated using this model and from simple assumptions concerning the packing of expanded graphite particles. For each porosity level of the monoliths, a characteristic pore size ∧ was derived from the latter hypotheses. All these results were shown to be accurate basing on three statements. First, the expected and well-known relationship k ∼ F-2 was recovered. Secondly, the calculated values were in good agreement with the experimental ones. Finally, the characteristic pore sizes ∧ were obtained from both surface area and helium pycnometry measurements, and shown to support the former calculations of ∧.

Transport in Porous Graphite: Gas Permeation and Ion Diffusion Experiments. Celzard, A., Marêché, J.F., Perrin, A.: Fuel Processing Technology, 2002, 77-78, 467-73