Long-Term Behavior of the Tritides Formed by Nickel-Based Intermetallic Compounds

Some properties of the tritide phases formed by the intermetallic compounds Mg₂Ni, ZrNi, and LaNi₅ have been studied. Whereas ZrNiT₃ will retain its stoichiometry indefinitely when sufficient gaseous tritium is available, the stoichiometrics of Mg₂NiT₄ and LaNi₅T_6.9 decrease with time. Although all three intermetallic tritides can retain large quantities of the helium-3 tritium decay daughter product in the solid phase, irreversible release of helium begins after several hundred days for ZrNiT_x and Mg₂NiT_x. However, LaNi₅T_x retains all of the helium generated in the solid for at least 2400 days. NMR measurements for ZrNiT_x and Mg₂NiT_x imply that helium is retained in microscopic bubbles as previously observed in several binary metal tritides.