Dielectric relaxations of confined water in porous silica ceramics

Abstract

In this study, dielectric properties of water confined in porous silica ceramics were investigated. Two porous ceramics were characterized in the frequency range \(10^{-1}~\hbox {to}~10^{7}\) Hz and temperature interval from \(-100\) to \(200^{\circ }\hbox {C}\). While the first sample was a ceramic with opened lateral pores, the second one was a ceramic with sealed lateral pores. In both ceramics, three dielectric processes were identified. The first, which appeared at lower temperatures, was attributed to the reorientation of water molecules in ice-like water cluster structures. The second is the relaxation observed over an intermediate temperature range, associated with the kinetic transition due to water molecule reorientation near a defect. At higher temperatures, the third was relaxation identified as the Maxwell–Wagner–Sillars polarization process due to the trapping of free charge carriers at the interface of the porous media. The first and second dielectric relaxations were analysed to prove the effect of the lateral surface state of the sample on water–inner surfaces of the porous media interaction. These analyses revealed a great similarity in the ice-like structure for both ceramics. However, the lateral surface state of the sample might enhance the dielectric strength of the first relaxation when lateral pores are sealed. Furthermore, it might improve the water–inner surfaces interaction when lateral pores are opened.