Impedance measurement and equivalent circuit analysis of binary alkali silicate melts

Molten oxides such as silicate melts are used in glass manufacturing processes and the chemical structure of the melts affects their physical properties and hence, the efficiency of the process in which they are used and the quality of the manufactured product. Analysis of the chemical structures using Raman or nuclear magnetic resonance spectroscopy is time consuming due to the process of preparing quenched samples and the long relaxation time of atomic nuclei. Hence, a technique for faster structural analysis is desirable. In this study, in order to accumulate basic data for in-situ estimation of the network structures of molten oxides, we systematically investigated the relationships between the alkali oxide composition and measured impedance behavior. Nyquist plots were fitted using an equivalent circuit consisting of solution resistance, charge transfer resistance, and double layer capacitance. In the present samples, the solution resistance and charge transfer resistance decreased, and double layer capacitance increased with increasing K ⁺ concentration. These results were attributed to K ⁺ behaving as a charge carrier or the double layer becoming thinner due to increasing concentration of K ⁺ ions, which increased interfacial polarization. We observed that the solution and charge transfer resistances increased, and double layer capacitance decreased, in the order of Li, Na, and K. Hence, these resistances were dependent on the ionic radius, as well as the macrostructure of the melts.