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.
Chemical vapor deposition of Mo tubes for fuel cladding applications
In this study, chemical vapor deposition (CVD) techniques have been evaluated for fabrication of free-standing 0.25 mm thick molybdenum tubes with the end goal of nuclear fuel cladding applications. In order to produce tubes with the wall thickness and microstructures desirable for this application, long deposition durations on the order of 50 h with slow deposition rates were employed. A standard CVD method, involving molybdenum pentachloride reduction by hydrogen, as well as a fluidized-bed CVD (FBCVD) method was applied towards these objectives. Characterization of the tubes produced in this manner revealed regions of material with fine grain microstructure and wall thickness suitable for fuel cladding applications, but lacking necessary uniformity across the length of the tubes. Finally, a path forward for the production of freestanding molybdenum tubes that possess the desired properties across their entire length has been identified and can be accomplished by future optimization of the deposition system.
Development of first ever scanning probe microscopy capabilities for plutonium
Scanning probe microscopy capabilities have been developed for plutonium and its derivative compounds. Specifically, a scanning tunneling microscope and an atomic force microscope housed in an ultra-high vacuum system and an inert atmosphere glove box, respectively, were prepared for the introduction of small non-dispersible δ-Pu coupons. Experimental details, procedures, and preliminary imaging of δ-Pu coupons are presented to demonstrate the functionality of these new capabilities. In conclusion, these first of a kind capabilities for plutonium represent a significant step forward in the ability to characterize and understand plutonium surfaces with high spatial resolution.
Spatially Resolved Thermal Transport Measurements in PyC Coated Fuel Particles
Self-regulating, low-power, compact, nuclear reactors are of immense interest to a community of sponsors who have power needs in space, underwater and in remote areas. Recent exploratory studies have provided valuable understanding into the underlying physics of self-regulation, including, how a material's self-regulation (or reactivity feedback) can be controlled by engineering its micro-scale and mesoscale properties. The approach being explored at Los Alamos National Laboratory involves a core matrix that is constructed of fuel kernels dispersed in a graphite matrix. The timing of the feedback is influenced by thermal properties of the fuel composite, which can be 'tuned' by micro-engineering. A pyrolytic carbon (PyC) layer coats the kernels to ensure that during a reactivity spike, the majority of the heat is trapped within the fuel kernel. The resulting precipitous temperature rise triggers a strong negative Doppler feedback. The ability to measure the local thermal properties of the individual materials that compose the fuel particle are crucial to fully understanding and controlling this feedback mechanism. The work covered in this presentation involves using laser-based thermal wave microscopy to measure the local thermal properties of the fuel particles. Specifically we measure the thermal conductivity and diffusivity of the fuel kernel and the PyC layer as well as the contact resistance between the kernel and the PyC layer. (authors)
Increasing the specific strength of spun carbon nanotube fibers
A spun fiber of carbon nanotubes is exposed to ion irradiation. The irradiation exposure increases the specific strength of the spun fiber.
Preparation of array of long carbon nanotubes and fibers therefrom
An array of carbon nanotubes is prepared by exposing a catalyst structure to a carbon nanotube precursor. Embodiment catalyst structures include one or more trenches, channels, or a combination of trenches and channels. A system for preparing the array includes a heated surface for heating the catalyst structure and a cooling portion that cools gas above the catalyst structure. The system heats the catalyst structure so that the interaction between the precursor and the catalyst structure results in the formation of an array of carbon nanotubes on the catalyst structure, and cools the gas near the catalyst structure and also cools any carbon nanotubes that form on the catalyst structure to prevent or at least minimize the formation of amorphous carbon. Arrays thus formed may be used for spinning fibers of carbon nanotubes.
Non-destructive elemental quantification of polymer-embedded thin films using laboratory based X-ray techniques
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Superlattice-Like Stacking Fault Array in Ion-Irradiated GaN
Controlling defects in crystalline solids is of technological importance for realizing desirable material properties. Irradiation with energetic particles is useful for designing the spatial distribution and concentration of defects in materials. Here, we performed ion irradiation into hexagonal GaN with the wurtzite structure and demonstrated the spontaneous formation of superlattice-like stacking fault arrays. It was found that the modulation period can be controlled by varying the irradiation conditions and subsequent thermal treatments.
Coated conductors
Articles are provided including a base substrate having a layer of an IBAD oriented material thereon, and, a layer of barium-containing material selected from the group consisting of barium zirconate, barium hafnate, barium titanate, barium strontium titanate, barium dysprosium zirconate, barium neodymium zirconate and barium samarium zirconate, or a cubic metal oxide material selected from the group consisting of rare earth zirconates and rare earth hafnates upon the layer of an IBAD oriented material. Such articles can further include thin films of high temperature superconductive oxides such as YBCO upon the layer of barium-containing material selected from the group consisting of barium zirconate, barium hafnate, barium titanate, barium strontium titanate, barium dysprosium zirconate, barium neodymium zirconate and barium samarium zirconate, or a cubic metal oxide material selected from the group consisting of rare earth zirconates and rare earth hafnates.
Influence of irradiation temperature on HfO2/MgO multi-layer structure
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