Evaluation of potentiometric oxygen sensors based on stabilized zirconia for molten 44.5% lead-55.5% bismuth alloy

A potentiometric sensor for measuring oxygen activity in molten 44.5% lead-55.5% bismuth alloy has been developed at "Institut Quimic de Sarria" laboratories. Three key points are to be considered in the design of this type of sensors for molten metals: (1) the reference system, (2) the solid state electrolyte and (3) the auxiliary electrode submerged in the molten metal. This paper evaluates the response of the sensors using two different reference systems: In/In₂O₃ and Sn/SnO as a Me/MeO reference system and a Pt/air as a gas reference system. All sensors showed a fast response time due to a change in the oxygen concentration of the environment and a good agreement between theoretical and experimental data under oxygen saturation conditions of the molten LBE. A second set of experiments evaluated the possibility of using different metallic materials as auxiliary electrodes submerged in molten 44.5% lead-55.5% bismuth alloy. The following materials were tested in the sensor design: molybdenum, P22 steel, 304 and 316L stainless steels. The sensors performance was evaluated using 90% Ar + 10% H₂, air (20% O₂) and alternating both environments. In all cases, reproducible measurements of the oxygen pressure of PbO formation were obtained.