Characterization of insulating particles by dielectric spectroscopy: Case study for CaCO3 powders

This work investigates the permittivity response of crystalline calcite powders produced by pulverizing and milling from well crystallized marble. Crystal characterization of continuous solid and powder compacts was based upon XRD. The particle size of the powders has been characterized by laser granulometry. Different packing densities of the powders were investigated i.e., unpacked, tapped, pressed to form pellets by different forces. The dielectric spectroscopy demonstrates the significance of reduced particle size and material packing density. At low frequencies, particle surface state effects dominate and the applied electrical energy is stored on the surfaces. This induces surface polarization effects that are normally considered in nanodielectric technology. As the size of the particles is reduced the surface polarization effects intensify and extend their frequency range towards the higher frequencies. In the high frequency regime (i.e., f > 100 kHz) the energy supplied by the electric field is stored in the volume of the particles. The dielectric data of the powder is determined by the packing density of the particles. A potential energy model is proposed in order to help workers to envisage the implications of surface vs. volume energy absorption process of sub-micron particle compacts when subjected to AC electric fields.