Uranium hydride formation study as observed by scanning surface potential imaging

Uranium is an extremely important material for commercial and military applications (i.e. nuclear power, nuclear weapons, conventional weapons, and armor systems) and, like a number of other materials, is vulnerable to corrosion by environmental gases that affect their properties, leading to component degradation, shortened lifetimes and materials failure. For uranium this is particularly true in the case of corrosion by hydrogen. A fundamental understanding of the corrosion process at the nucleation stage is of critical importance. The goal of this work is to study the role of common chemical impurities in uranium with initiation sites for the formation of destructive hydride blisters. After samples were implanted with various ions, they were first annealed under vacuum at 200°C, and then exposed to one atm of ultra-pure hydrogen at 200°C to accelerate the aging process. Scanning force microscopy surface potential imaging was used to characterize the structure and corresponding electrical properties of polycrystalline uranium surfaces that resulted from the implantation of different suspect atoms and exposure to hydrogen gas. Surface potential images revealed features related to different oxide structures, hydride spots/blisters, and other features not obvious in the corresponding topograph. In surface potential images, blisters appear as bright (higher potential) features in sharp contrast to the uranium oxide background. In a previous study possible inclusions were observed in the center of some blisters. Blister formation did not appear to correlate with implantation of any specific specie, however, distinct differences were seen between implanted and non-implanted sides of the same sample.