Engineering topics
Usov, Igor O.
Publications and source records attributed to Usov, Igor O..
Topographic and nanomechanical mapping of plutonium surfaces
Atomic force microscopy of gallium-stabilized δ-phase plutonium coupons has been used to map their topography and qualitative mechanical character, including Derjaguin-Muller-Toporov modulus, adhesion, deformation, and dissipation. Initial topographical results demonstrate that the plutonium surface is considerably rough and heterogeneous. Qualitative nanomechanical mapping revealed distinct striation patterns that are not observed in the topography images. Further investigation of the striations in the nanomechanical modes of imaging suggest that they are not measurement artifacts, or plutonium specific features. Similar investigations of stainless steel surfaces established a strong correlation between the mechanical working of the surface (i.e. cutting and grinding) and the appearance of the striations. Reimaging of the plutonium surface after moderate oxidation occurring within an inert Ar atmosphere (~1 ppm O 2 ) over the course of 13 months revealed a diminished striation pattern. It is suggested that surface stress/strain induced by the mechanical working of the metal surfaces results in the patterns of variable modulus, adhesion, deformation, and dissipation, and that these patterns are affected by the chemical changes and aging of the plutonium surface.
Effects of ion sputtering on plutonium surfaces
Scanning tunneling microscopy has been performed on an electro-polished gallium-stabilized delta-phase plutonium sample under ultra-high vacuum conditions. The images obtained were used to measure surface roughness as ion sputtering and annealing was applied to the plutonium sample. It was demonstrated that sputter/anneal cycles progressively increased the surface roughness of the plutonium. Furthermore, Auger and scanning tunneling spectroscopy measurements revealed an initially unstable and dynamically changing surface that became increasingly stable as sputter/anneal cycles were applied. The stabilized surface region contained within the sputter crater was observed to be unchanged for up to 17 months after the final sputter anneal cycle.