ABSTRACT

We have derived a set of new relationships describing polarization parameters in porous materials with disseminated particles made of a semiconductor, such as pyrite or magnetite. We have compared various predictions of this model to a broad set of experimental data. The chargeability was found to be controlled only by the volume fraction of metallic particles in agreement with the experimental data. The relaxation time, defined from the peak frequency of the phase, was observed to be proportional to the square of the size of the metallic particles and was independent of the salinity of the pore water solution. The relationship between the peak frequency and the grain size could be used to determine the diffusion coefficient of the n- and p-charge carriers in the semiconductor. This diffusion coefficient was consistent with the mobility of the charge carriers derived from theoretical considerations or electric-conductivity measurements. The resistivity of a mixture of a porous matrix characterized by a low-chargeability and dispersed semiconductors does not depend on the content of metallic grains, as long as the grains are below a percolation threshold (< 22 vol.%). Various experiments were performed using magnetite and pyrite at different grain sizes, weight fractions, and with/without porous materials (i.e., suspended in agar gel). These data were used to test some additional aspects of the model. We found excellent agreement between the model predictions and these experimental data.

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