Development and calibration of electrochemical oxygen sensors for application to low temperature regions in liquid lead alloys cooled reactors

Widely used oxygen sensors with partially stabilized zirconia (e.g. 5 mol% YSZ) as solid electrolyte (SE) don’t work properly at temperatures below ~400°C. The reason for unreliable readings at temperature below ~400°C was believed to be a too low oxygen ionic conductivity of the SE. Therefore, 8 mol% YSZ, ScCeSZ and LSGM, featured as better conducting ceramics, were studied for their conductivity, thermo-chemical stability in lead-bismuth eutectic (LBE), mechanical strength and performance as SE in oxygen sensors. An ~5 and ~20 times higher oxygen ionic conductivity was measured for, respectively, 8 mol% YSZ and LSGM than is reported for 5 mol% YSZ (at 300-800°C). Cubic ScCeSZ transformed in rhombohedral ScCeSZ at temperatures below ~500°C, resulting in a lower conductivity than that of 5 mol% YSZ. Microstructural analyses demonstrated the thermo-chemical stability of the other ceramics in LBE at 360°C. Due to the very low strength of LSGM, 8 mol% YSZ was identified as the most promising SE. Yet, no clear difference was observed in the performance of sensors with these three ceramics as SE, which revealed to work properly at temperatures above ~380°C. Results were obtained that suggest that this lower temperature limit is determined by the electrode/SE interface impedance.