Transport phenomena in multiphase flows

Abstract

Electrical conductivity (ac) of AgI containing a variety of dispersions such as Al2O3, SiO2, fly ash etc. and also the AgI-AgBr system without dispersions has been measured as a function of composition, temperature and frequency. While conductivity (σ) enhancements of up to 3 orders of magnitude have been obtained, the data suggest however that the maximum enhancement obtainable by such dispersions (or in multiphase systems) is generally limited to a factor of 50 (1.7 orders of magnitude). The particle size and the concentration of the dispersoids strongly affect the magnitude of enhancement in σ. Extensive SEM studies coupled with the frequency-dependent conductivity data suggest that the enhancement is due to bulk rather than grain-boundary or surface conduction. Further, the enhancement is usually accompanied by a decrease in activation energy which suggests perhaps the fact that the dispersoids generate excess of lattice defects and thereby enhance the conductivity, which is consistent with a recent theoretical model and the latest thermoelectric power measurements.