Complex impedance analysis of the glass/solution interface in the glass electrode for pH measurement

The effect of hydration on the electrical properties of glass electrodes for pH measurement was investigated. During the hydration treatment, the ac and dc electrical properties of the glass matrix and the glass/solution interface in the lithium-silicate glass system were measured by complex impedance spectroscopy. IR spectra and microstructures by scanning electron microscopy (SEM) of the glass after hydration were also studied. The resistance of the glass matrix was found to decrease as the hydration proceeded with an increase of the glass/solution interface resistance, when the glass was hydrated in aqueous solutions with pH 10 and pH 4 at 80 degrees C. On the other hand, no change in the glass matrix resistance, but a rapid increase of the glass/solution interface resistance was observed when hydrated in the solution with pH 7. The observed difference in the electrical property changes upon hydration treatment in the different solutions are due to the different hydration behaviors: the thickness reduction of the glass matrix followed by the rapid dissolution of the hydrated layer at the glass/solution interface at pH 10 and pH 4, and the formation of a thick hydrated layer due to the slow dissolution at pH 7.