Dielectric characterization of the water-matrix interaction in porous materials by thermal depolarization spectroscopy

We investigate the dielectric behavior of sandstone, which consists of a porous matrix with a small amount of inherent humidity, by the thermal-stimulated depolarization current technique. Nine different relaxation mechanisms are detected by the thermal sampling scheme, and are characterized. The activation energy distribution and the pre-exponential factor are obtained by analyzing the signals under the constraint of a normal distribution in the activation energy. The drying of the specimen at elevated temperature under dynamic vacuum affects some of the relaxation mechanisms. The model of Freely rotating dipoles may not account for all the drying-sensitive mechanims. It is probable that water molecules are organized in a way that provide either conductive layers over the surface of the grains or for conductive inclusions inside the bulk. Long-distance charge-transport mechanisms Lire also affected by the removal of the humidity.