Polarization and depolarization currents in kaolin

• Polarization/depolarization current was studied on green kaolin at room temperature.
• H+ and OH− ions are the main charge carriers at room temperature.
• Currents were described by power function suggesting several polarization mechanisms.
• Polarization current is represented by three exponential functions. Three polarization mechanisms were proposed.

Ceramic materials are considered dielectrics with ionic conductivity where polarization and depolarization effects play an important role. These effects take place when an external electric field is applied or removed. The measurement was performed on the kaolin samples, which contain 1.5 mass % of the physically bound water, at room temperature. Since the polarization current did not reach zero value after a long period of time, it was deduced that both the ions and electrons are the charge carriers. At room temperature, H+ and OH− ions are the main charge carriers, a role of Na+ and K+ is negligible. Power functions, which describe the time dependent currents, suggest several polarization mechanisms. The best fit of the experimental relationships between the current and time showed a sum of three exponentials, i.e. three polarization and depolarization mechanisms should be considered. We ascribed them to 1) hopping of H+ ions, 2) migration of originally trapped and then released H+ ions, and 3) migration of OH− ions.