Investigations on the phase equilibria of some hydride ion conducting electrolyte systems and their application for hydrogen monitoring in sodium coolant

Electrochemical meters for measuring hydrogen levels in liquid sodium need thermodynamically stable hydride ion conducting electrolytes. In order to identify electrolytes that have high hydride ion conductivity, phase diagram of systems consisting of low melting compounds such as CaCl2–LiCl, SrBr2–LiBr, SrBr2–SrHBr and CaBr2–CaHBr were investigated by differential scanning calorimetry and their phase diagrams established. Using these information and supplementary information on effects of addition of alkaline earth hydride to these systems, potential electrolytes were tested for their use in electrochemical meters. Meters were constructed using electrolytes with (i) 22mol%SrCl2–12.2mol%CaCl2–54.5mol%LiCl–11.3mol%CaHCl, (ii) 70mol%LiCl–16mol%CaHCl–14mol%CaCl2 and (iii) 40mol%CaHBr–60mol%CaBr2 compositions. Output of meters that had Li ions in liquid phase electrolyte showed non-linearity at low hydrogen levels. Output of meters using CaBr2–40mol%CaHBr solid showed linearity in the concentration range of 50–250 ppb in sodium.