Li6BaLa2Ta2O12 solid State Probe for Molten Alloys

Colominas, Sergi

Nowadays, most of the energy consumption depends on carbon-based sources such as petroleum, natural gas and coal. If the current trend of CO₂ emissions continues, the increment in the global average temperature will exceed 2^oC (by 2050). Therefore, there is a need to develop new energy sources to reduce the environmental footprint. In this frame, nuclear fusion appears as a carbon-free alternative that perfectly fits in this sustainable transition. Future fusion reactors are expected to use deuterium and tritium as fuel. On the one hand, deuterium is a stable isotope that can be obtained from water. On the other hand, tritium is a radioactive isotope with a relatively short half-life (12.3 years) and must be generated in the reactor itself. For this purpose, it is suggested that lithium will react with high energy neutrons to produce this hydrogen isotope.

⁶Li + n → ⁴He + ³H + 4.8MeV

This nuclear reaction will take place in the tritium breeding modules. Molten Pb-Li alloy, in its eutectic composition, is considered the main breeding candidate. According to reaction (1), lithium will be consumed. Therefore, to maintain the eutectic composition, it is crucial to control both the concentration and the dosage of lithium. As future nuclear reactors will deal with extreme operational conditions, sensors based on solid-state electrolytes are a promising tool to monitor this lithium content.

In the present work, potentiometric sensors to measure Li concentration in molten Sn-Li alloys were constructed. These alloys will be used as a first step before Pb-Li assays. For that, Li₆BaLa₂Ta₂O₁₂(LBLTO) solid-state electrolyte was synthesized and sintered as a pellet. EIS measurements were performed to evaluate the ionic conductivity of the sintered pellets at temperatures from 30 to 300ºC. These pellets were sealed in alumina tubes using a glass binder for sensor construction. On the one hand, Sn-Li alloys with different lithium contents (from 3at%_Li up to 10at%_Li) were used in the working electrode. On the other hand, a 3at%_Li Sn-Li alloy was considered as the reference electrode. Potentiometric measurements were performed at different temperatures. Correlation curves of the recorded potentials versus the Li activity were in good agreement with the Nernst equation.