THE EFFECT OF THERMAL ANNEALING ON THE HYDRIDING KINETICS OF URANIUM

The effects of vacuum heat pretreatments on the hydriding kinetics of uranium (pure and chromium alloyed) were studied. Two pretreatment temperature regimes were correlated with changes displayed in the two stages of the hydriding reaction. The lower pretreatment regime (below about 200 °C) has a drastic effect on the initial stage of the reaction (the "induction period". However, it does not alter the rate of the subsequent massive reaction stage. This low temperature region is associated with surface modification processes, the most prominent process being gas desorption. However, the higher pretreatment regime (above about 450 °C) affects the rate of the massive reaction stage (i.e. the velocity of the hydride reaction front) and is attributed to heat-induced changes in the microstructure of the metal (grain growth). The increased rate induced by chromium addition is attributed to the precipitation of chromium at grain boundaries. © 1990.