EFFECTS OF RADIOLYTIC TRITIUM DECAY ON THE THERMODYNAMIC BEHAVIOR OF LANI4.25AL0.75 TRITIDES

Intermetallic compounds which react with hydrogen isotopes to form reversible hydrides offer several advantages for storing and processing tritium. Advantages include safe, low pressure, high density storage, and delivery of high purity He-3-free tritium without the use of pumps. As part of a program to develop metal hydride technology for storing and processing tritium, the effects of tritium aging on the thermodynamic behavior of the tritides are under investigation. During aging of LaNi4.25Al0.75 tritides, the He-3 decay product of tritium produced in the lattice does not leave the lattice but causes changes in the thermodynamics of the gas-solid system. Among the changes noted are (1) decreased tritium desorption pressures, (2) increased slopes of desorption isotherm plateaux and (3) small quantities of irreversibly-held tritium. Absorption-desorption cycling and brief heating of samples to 350-degrees-C while loaded with deuterium partially reverses these effects. While the desorption isotherms of tritium-aged LaNi4.25Al0.75 tritides resemble the desorption isotherms of amorphous hydrogen storage materials, X-ray diffraction patterns of tritium-aged samples after desorption of tritium do not exhibit the characteristics of an amorphous material. The diffraction patterns show broadening and anisotropic effects that suggest the presence of lattice strains and orientational effects of He-3 in the LaNi4.25Al0.75 lattice. Self-interstitials, dislocations and bubbles are probably present in the aged samples.