Electrical conductivity of packed particle beds

The dependence of conductivity on particle size is derived for the case of insulating particles exhibiting surface conductivity and particle-to-particle contact resistance. Experimental results obtained on glass particle beds agree well with the physical model that emphasizes surface conductivity as a controlling factor. The proportionality of the DC resistivity to the particle size proposed in the present report was verified by the experimental data and surprisingly found to hold even for AC equivalent parallel resistance. The frequency dependence of the dielectric permittivity and of the equivalent parallel resistance was found to be well approximated by a law with exponents generally different from -1/2. For sufficiently high probing frequencies, the AC response is unencumbered by the particle-to-particle contacts and is characteristic of the bulk material