LONG-TERM THERMAL CYCLING STUDIES ON LANI5.2

The degradation of LaNi5.2 on prolonged thermal cycling has been investigated. Static room temperature pressure-composition isotherms were measured after 10, 1500 and 10 000 cycles. The H-absorbing properties of LaNi5.2 seriously degraded after 10 000 cycles. Structural analysis of the alloy LaNi5.2 by X-ray diffraction analysis after 10 000 thermal cycles revealed the precipitation of Ni microphase, indicating possible disproportionation as the cause of degradation of the alloy. The lattice microstrains increased after 10 000 cycles. The long-range strains also exhibited anisotropic increase preferentially along the c direction of the hexagonal lattice. Thus both macro- and microstrains are observed after 10 000 cycles with a loss of H capacity. In this paper, we present the effect of temperature on the hydriding pressure, thermodynamic and structural properties of LaNi5.2.