Development of a high temperature lithium-ion sensor and reference electrode for application in nuclear reactor systems
University of New Brunswick
Chemistry control and corrosion mitigation are critical aspects for nuclear and fossil power plant operations in order to ensure efficient operation, reduce maintenance costs, and prevent equipment degradation. High temperature electrochemical sensors may be used for chemistry monitoring and corrosion measurements but can be costly to construct and typically suffer from short life spans in the aggressive, high temperature and pressure systems. A novel concept of combining the corrosion products existing on the power plant piping and the chemistry control regime in CANDU power plants is presented. A lithiated-iron-oxide, lithium ferrite (LiFe5O8), was synthesized, characterized and electrochemically tested as a solid-state high-temperature electrode up to 230°C using a platinum-based reversible hydrogen electrode for verification. Lithiated-hematite (LixFe2O3) and magnetite (Fe3O4) were confirmed as reaction products involved in the redox mechanism. Lithium-ion retention in hematite decreased with temperature as the mobility of the ion was increased; the stoichiometric coefficient x varied from 0.9 to 0.3 between 100°C to 230°C, respectively. The activity of the lithium ion in the redox process suggests potential high-temperature lithium-ion sensing capability for this electrode. An average entropy of reaction in this solid-state redox mechanism was found to be 2.92 kJ/mol/K over the 100°C to 230°C temperature range and the Gibbs Free Energy of formation of the various lithium-inserted hematites were determined as a function of temperature and lithium concentration in solution.