THE HYDRIDING KINETICS OF BETA-QUENCHED URANIUM-0.1 WT.PERCENT CHROMIUM

Different heat pretreatments were applied to pure and alloyed (0.1 wt. %Cr) uranium in order to evaluate the effects of the resulting microst ructural changes on the hydriding kinetics. Samples were studied in th e temperature range 30-300 degrees C under hydrogen pressures between 10(2) and 10(5) Pa. In the high pressure range, well above the equilib rium pressures of the hydride, a significant increase in hydride front velocity was observed for the alloyed samples quenched from the beta- phase, as compared with those gradually cooled down. This difference w as not observed for pure (unalloyed) uranium samples. No beta-phase re sidue could be identified in the quenched alloyed samples using X-ray diffraction. It is concluded that the rate change effects resulted fro m the presence of a metastable, highly strained alpha-phase supersatur ated with dissolved chromium. Higher formation equilibrium pressures w ere obtained for the latter strained phase as compared with the well a nnealed alloyed samples. Arrhenius plots of the hydride front velociti es yielded for the beta-quenched alloyed samples, an apparent activati on energy of 7.2 kcal g(-1) at. H (0.3 eV), similar to that of the wel l annealed uranium, The effect of aging of the alloyed beta-quenched s amples on the hydriding kinetics was also studied and the results were interpreted in view of the metal strain relaxation.