LONG-TERM THERMAL CYCLING STUDIES ON LANI5.2

The degradation of LaNi5.2 on prolonged thermal cycling has been inves tigated. Static room temperature pressure-composition isotherms were m easured after 10, 1500 and 10 000 cycles. The H-absorbing properties o f LaNi5.2 seriously degraded after 10 000 cycles. Structural analysis of the alloy LaNi5.2 by X-ray diffraction analysis after 10 000 therma l cycles revealed the precipitation of Ni microphase, indicating possi ble disproportionation as the cause of degradation of the alloy. The l attice microstrains increased after 10 000 cycles. The long-range stra ins also exhibited anisotropic increase preferentially along the c dir ection 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, ther modynamic and structural properties of LaNi5.2.