Preparation and characterization of ion-exchanged Ni-Na-β”-Al₂O₃ and Fe-Na-β”-Al₂O₃ solid electrolytes for applications in liquid metals

Accurate determinations of the thermochemical properties for the steel alloying elements (Fe, Cr, Ni, Co and Mn) dissolved as corrosion product impurities in Pb and Pb–Bi alloy (LBE) are relevant for the development of Lead-Cooled Fast Nuclear Reactors (LFRs). Ion-selective solid electrolytes are suitable for an electrochemical characterization of the dissolved impurities. Among these, ion-exchanged Ni-β”-Al₂O₃ and Fe-β”-Al₂O₃ are promising solid electrolytes for the selective detection of Ni and Fe dissolved in HLMs. In the present works we proposed a preliminary test of liquid and vapor ion-exchanges on commercial polycrystalline Na-β”-Al₂O₃ tubes at different conditions of temperature and reaction time with NiCl₂ and FeCl₂ salts, characterizing the effects on the material microstructure. The resulting Ni-Na-β”-Al₂O₃ and Fe-Na-β”-Al₂O₃ samples were only partially replaced by nickel or iron, extremely porous, damaged by molten salt corrosion, and contaminated by residual chlorides. When tested as selective sensors in molten LBE, they failed in detecting dissolved nickel or iron. Thus, ion-exchange procedure on polycrystalline Na-β”-Al₂O₃ substrates still needs to be improved by properly combining the liquid and vapor ion-exchange with optimized reaction conditions in order to increase the sodium replacement yield. Alternatively, efforts may be focused on the preparation and application of other different nickel and iron solid electrolytes.