Dielectric relaxations of confined water in porous silica ceramics

[摘要] In this study, dielectric properties of water confined in porous silica ceramics were investigated. Two porous ceramics were characterized in the frequency range 10$^{−1}$ to 10$^7$ Hz and temperature interval from $−$100 to 200$^{\circ}$C. Whilethe first sample was a ceramic with opened lateral pores, the second one was a ceramic with sealed lateral pores. In bothceramics, three dielectric processes were identified. The first, which appeared at lower temperatures, was attributed tothe reorientation of water molecules in ice-like water cluster structures. The second is the relaxation observed over anintermediate 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 thetrapping of free charge carriers at the interface of the porous media. The first and second dielectric relaxations were analysedto prove the effect of the lateral surface state of the sample on water–inner surfaces of the porous media interaction. Theseanalyses revealed a great similarity in the ice-like structure for both ceramics. However, the lateral surface state of the samplemight enhance the dielectric strength of the first relaxation when lateral pores are sealed. Furthermore, it might improve thewater–inner surfaces interaction when lateral pores are opened.

[学科分类] 材料工程

[关键词] Confined water;porous silica;dielectric relaxation;ceramics.