Master of Science

thesisElastic contact between two computer-generated isotropic rough surfaces is studied. First the surface topography parameters, including the asperity density, mean summit radius, and standard deviation of asperity heights of the equivalent rough surface, are determined using an 8-nearest neighbor summit identification scheme. Second, many cross-sections of the equivalent rough surface are traced and their individual topography parameters are determined from their corresponding spectral moments. The topography parameters are also obtained from the average spectral moments of all cross-sections. The asperity density is found to be the main difference between the summit identification scheme and the spectral moments method. The contact parameters, such as the number of contacting asperities, real area of contact, and contact load for any given separation between the equivalent rough surface and a rigid flat, are calculated by summing the contributions of all the contacting asperities using the summit identification model. These contact parameters are also obtained with the Greenwood-Williamson (GW) model using the topography parameters from each individual cross-section and from the average spectral moments of all cross-sections. Three different surfaces characterized by a different autocorrelation length, and three different sampling intervals were used to study how the method to determine topography parameters affects the resulting contact parameters. iv The contact parameters are found to vary significantly based on the method used to determine the topography parameters, and as a function of the autocorrelation length of the surface, as well as the sampling interval. The contact parameters evaluated with the summit identification model or the GW model based on topography parameters obtained from a summit identification scheme were most accurate as the actual three-dimensional (3D) rough surface is considered for the analysis instead of relying on limited data, e.g., a discrete number of cross-sections. Hence, using a summit identification model or the GW model based on topography parameters obtained from a summit identification scheme is perhaps the most reliable approach

Doctor of Philosophy

dissertationShale resources provide a tremendous opportunity for a long-term viable energy source, but the lower hydrocarbon recovery rates are hindering the economic development of shale reservoirs. One of the main reasons for the lower hydrocarbon recovery rates is the inadequate understanding of the fate of various injected fluids and the recovered hydrocarbons during various stages of exploration and production. As Darcy's law is limited in describing the multiphase fluid transport in shale, a comprehensive simulation framework is necessary, enabling the replication of the nanometer and subnanometer pores found in organic and inorganic matrices, and the simulation of the multiphase fluid flow in these nanopores, thus improving the comprehension of the pore-scale fluid transport process in shale reservoirs. A molecular dynamics simulation-based framework is developed in present research to address the above-defined challenges. The applications of various open-source molecular modeling tools are integrated to develop molecular pore structures found in the organic and inorganic matrices. An application of the general-purpose DREIDING force field is extended to simulate the kerogen. A gas-liquid (methane and water) transport is simulated in nanopores confined in the organic and inorganic matrices, and various dynamic transport properties of fluids (subjected to confinement) are determined to gain the qualitative and the quantitative understanding of the fluid flow. The present research provides a powerful molecular dynamics simulation-based framework that will enable the development of more complex models of nanoporous shale structures and address numerous challenges encountered in hydrocarbon recovery from shale reservoirs

Pressure-tailored lithium deposition and dissolution in lithium metal batteries

A porous electrode resulting from unregulated Li growth is the major cause of the low Coulombic efficiency and potential safety hazards of rechargeable Li metal batteries. Strategies aiming to achieve large granular Li deposits have been extensively explored; yet, the ideal Li deposits, which consist of large Li particles that are seamlessly packed on the electrode and can be reversibly deposited and stripped, have never been achieved. Here, by controlling the uniaxial stack pressure during battery operation, a dense Li deposition (99.49% electrode density) with an ideal columnar structure has been achieved. Using multi-scale characterization and simulation, we elucidated the critical role of stack pressure on Li nucleation, growth and dissolution processes, and developed innovative strategies to maintain the ideal Li morphology during extended cycling. The precision manipulation of Li deposition and dissolution is a critical step to enable fast charging and low temperature operation for Li metal batteries

Glassy Li Metal Anode for High-Performance Rechargeable Li Batteries

Controlling nanostructure from molecular, crystal lattice to the electrode level remains as arts in practice, where nucleation and growth of the crystals still require more fundamental understanding and precise control to shape the microstructure of metal deposits and their properties. This is vital to achieve dendrite-free Li metal anodes with high electrochemical reversibility for practical high-energy rechargeable Li batteries. Here, cryogenic-transmission electron microscopy was used to capture the dynamic growth and atomic structure of Li metal deposits at the early nucleation stage, in which a phase transition from amorphous, disordered states to a crystalline, ordered one was revealed as a function of current density and deposition time. The real-time atomic interaction over wide spatial and temporal scales was depicted by the reactive-molecular dynamics simulations. The results show that the condensation accompanied with the amorphous-to-crystalline phase transition requires sufficient exergy, mobility and time to carry out, contrary to what the classical nucleation theory predicts. These variabilities give rise to different kinetic pathways and temporal evolutions, resulting in various degrees of order and disorder nanostructure in nano-sized domains that dominate in the morphological evolution and reversibility of Li metal electrode. Compared to crystalline Li, amorphous/glassy Li outperforms in cycle life in high-energy rechargeable batteries and is the desired structure to achieve high kinetic stability for long cycle life.Comment: 29 pages, 8 figure

Enhancing the Faradaic efficiency of solid oxide electrolysis cells: progress and perspective

Abstract To reduce global warming, many countries are shifting to sustainable energy production systems. Solid oxide electrolysis cells (SOECs) are being considered due to their high hydrogen generation efficiency. However, low faradaic efficiency in scaling SOEC technology affects costs and limits large-scale adoption of hydrogen as fuel. This review covers SOECs’ critical aspects: current state-of-the-art anode, cathode, and electrolyte materials, operational and materials parameters affecting faradaic efficiency, and computational modeling techniques to resolve bottlenecks affecting SOEC faradaic efficiency

Interpreting the Presence of an Additional Oxide Layer in Analysis of Metal Oxides–Metal Interfaces in Atom Probe Tomography

International audienceAtom Probe Tomography (APT) analysis of specimens embedded with metal oxide/metal leads to nonintuitive observations of a very thin layer of oxide at the interface due to oxygen migration under the influence of electric field in metal oxides. Detailed analyses of the FeO/Fe and ZrO2/ZrO interfaces are presented, explaining observation of the interfacial oxide layer with APT. These findings are relevant to the observation made for APT analysis of devices such as resistive switching, solar cells, oxides grown on metal/alloy during oxidation and corrosion wherein metal oxide is in interface with metallic layers. Because the APT technique is based on the application of an electric field on the oxide/metal interface, oxygen ions are driven toward the metal electrode and leads to a reaction with the metal and the formation of the additional interfacial oxide layer. Atomistic simulation performed on the FeO/Fe layer subjected to electric field confirms finding of oxygen migration from the oxide layer toward the oxide/metal interface

Interpreting the Presence of an Additional Oxide Layer in Analysis of Metal Oxides–Metal Interfaces in Atom Probe Tomography

International audienceAtom Probe Tomography (APT) analysis of specimens embedded with metal oxide/metal leads to nonintuitive observations of a very thin layer of oxide at the interface due to oxygen migration under the influence of electric field in metal oxides. Detailed analyses of the FeO/Fe and ZrO2/ZrO interfaces are presented, explaining observation of the interfacial oxide layer with APT. These findings are relevant to the observation made for APT analysis of devices such as resistive switching, solar cells, oxides grown on metal/alloy during oxidation and corrosion wherein metal oxide is in interface with metallic layers. Because the APT technique is based on the application of an electric field on the oxide/metal interface, oxygen ions are driven toward the metal electrode and leads to a reaction with the metal and the formation of the additional interfacial oxide layer. Atomistic simulation performed on the FeO/Fe layer subjected to electric field confirms finding of oxygen migration from the oxide layer toward the oxide/metal interface

Interpreting the Presence of an Additional Oxide Layer in Analysis of Metal Oxides–Metal Interfaces in Atom Probe Tomography

International audienc