Tannin-based rigid foams of different bulk densities and their carbonized counterparts were investigated for the first time by X-ray microtomography. This method allowed acquisition of three-dimensional pictures of such highly porous materials. Through mathematical treatment of the images, extremely useful physical characteristics such as porosity, fraction of open cells, connectivity, tortuosity, and pore-size distribution were determined as a function of the foam's density. The obtained information was compared with independent data derived from pycnometry measurements and scanning electron microscope image analysis. The agreement was shown to be acceptable in the limit of the accuracy of the laboratory microtomograph (4 μm). Moreover, recalculating properties like permeability were shown to be quite possible based on the results of standard microtomography data.

Extended abstract of a paper presented at Microscopy and Microanalysis 2008 in Albuquerque, New Mexico, USA, August 3 – August 7, 2008

The elastic properties of cubic samples of compressed expanded graphite determined by means of ultrasonic velocity measurements are presented. These materials are highly porous and exhibit porosity-dependent anisotropic moduli. The results are analyzed according to two approaches. The first involves semi-empirical equations fitted to the experimental data, resulting in information about the shape and the connectivity of pores. It is found that pores are oblate ellipsoids, connected parallel to their direction of flatness. The second approach is based on application of the percolation theory near the rigidity threshold. The value of the critical exponent indicates that compressed expanded graphites behave like elastic networks in which central forces are predominant. Results of this study give evidence that ultrasound is a convenient and accurate method for investigation of the critical behavior of the elastic properties in highly tenuous structures.