A quartz sealed Ag/AgCl reference electrode for CaCl2 based molten salts

A quartz sealed Ag/AgCl reference electrode was fabricated and studied in CaCl2 based molten salts. It performed satisfactorily in terms of reproducibility, reusability and stability in experiments that varied the temperature (700–950 °C) and service time (from hours to days). The electric resistance of the reference electrode decreased from 105 to 103 Ω when increasing the molten salt temperature from 600 to 950 °C, following well Arrhenius’ Law. The potential variation of the electrode upon changing the electrolyte composition (CaCl2, NaCl, KCl, and/or AgCl) suggested the selective conduction of Na+ ions and possibly Ca2+ ions through the thin-wall of the sealed quartz tube. Prolonged use (two to three days) of the reference electrode in the presence of both oxygen and molten chloride salt led to noticeable erosion of the quartz tube, particularly at the molten salt–quartz–gas triple phase boundary, which can be attributed to the formation of calcium and/or sodium silicates under the influence of oxygen present in the liquid and gas phases, respectively.