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- Creators: Debussy, Claude, 1862-1918
Description
Fuel cells, particularly solid oxide fuel cells (SOFC), are important for the future of greener and more efficient energy sources. Although SOFCs have been in existence for over fifty years, they have not been deployed extensively because they need to be operated at a high temperature (∼1000 °C), are expensive, and have slow response to changes in energy demands. One important need for commercialization of SOFCs is a lowering of their operating temperature, which requires an electrolyte that can operate at lower temperatures. Doped ceria is one such candidate. For this dissertation work I have studied different types of doped ceria to understand the mechanism of oxygen vacancy diffusion through the bulk. Doped ceria is important because they have high ionic conductivities thus making them attractive candidates for the electrolytes of solid oxide fuel cells. In particular, I have studied how the ionic conductivities are improved in these doped materials by studying the oxygen-vacancy formations and migrations. In this dissertation I describe the application of density functional theory (DFT) and Kinetic Lattice Monte Carlo (KLMC) simulations to calculate the vacancy diffusion and ionic conductivities in doped ceria. The dopants used are praseodymium (Pr), gadolinium (Gd), and neodymium (Nd), all belonging to the lanthanide series. The activation energies for vacancy migration between different nearest neighbor (relative to the dopant) positions were calculated using the commercial DFT code VASP (Vienna Ab-initio Simulation Package). These activation energies were then used as inputs to the KLMC code that I co-developed. The KLMC code was run for different temperatures (673 K to 1073 K) and for different dopant concentrations (0 to 40%). These simulations have resulted in the prediction of dopant concentrations for maximum ionic conductivity at a given temperature.
ContributorsAnwar, Shahriar (Author) / Adams, James B (Thesis advisor) / Crozier, Peter (Committee member) / Krause, Stephen (Committee member) / Arizona State University (Publisher)
Created2011
ContributorsDebussy, Claude, 1862-1918 (Composer)
ContributorsDebussy, Claude, 1862-1918 (Composer)
ContributorsDebussy, Claude, 1862-1918 (Composer)
ContributorsDebussy, Claude, 1862-1918 (Composer)
ContributorsDebussy, Claude, 1862-1918 (Composer)
Description
The vastly growing field of supercomputing is in dire need of a new measurement system to optimize JMRAM (Josephson junction magnetoresistive random access memory) devices. To effectively measure these devices, an ultra-low-noise, low cost cryogenic dipping probe with a dynamic voltage range is required. This dipping probe has been designed by ASU with <100 nVp-p noise, <10 nV offsets, 10 pV to 16 mV voltage range, and negligible thermoelectric drift. There is currently no other research group or company that can currently match both these low noise levels and wide voltage range. Two different dipping probes can be created with these specifications: one for high-use applications and one for low-use applications. The only difference between these probes is the outer shell; the high-use application probe has a shell made of G-10 fiberglass for a higher price, and the low-use application probe has a shell made of AISI 310 steel for a lower price. Both types of probes can be assembled in less than 8 hours for less than $2,500, requiring only soldering expertise. The low cost and short time to create these probes makes wide profit margins possible. The market for these cryogenic dipping probes is currently untapped, as most research groups and companies that use these probes build their own, which allows for rapid business growth. These potential consumers can be easily reached by marketing these probes at superconducting conferences. After several years of selling >50 probes, mass production can easily become possible by hiring several technicians, and still maintaining wide profit margins.
ContributorsHudson, Brooke Ashley (Author) / Adams, James (Thesis director) / Anwar, Shahriar (Committee member) / Materials Science and Engineering Program (Contributor) / W. P. Carey School of Business (Contributor) / Barrett, The Honors College (Contributor)
Created2016-05
Description
The goal of the paper was to examine the fatigue mechanisms of polymers and silicone based elastomers. The mechanisms of fatigue due to crazing: the alignment of polymer chains to the stress axis, and shear banding: the localized orientation of the polymer by the shear stresses from two planes, were discussed in depth in this paper. Crazing only occurs in tensile stress, is initiated on the surface of the material, and only occurs in brittle polymers. Crazing also accounts for a 40-60% decrease in density, causing localized weakening of the material and a concentration in stress. This is due to a decrease in effective cross sectional area. The mechanism behind discontinuous growth bands was also discussed to be the cause of cyclic crazing. Shear banding only occurs in ductile polymers and can result in the failure of polymers via necking. Furthermore, the high fatigue resistance of silicone elastomers was discussed in this paper. This conclusion was made because of the lack of fatigue mechanisms (crazing, discontinuous growth bands, and shears banding) in the observed elastomer's microstructure after the samples had undergone fatigue tests. This was done through an analysis of room temperature vulcanized silicone adhesives, a heat-curing silicone elastomer, and a self-curing transparent silicone rubber. Fatigue of room temperature vulcanized silicon was observed, however this was reasoned to be the failure of the adhesion of the elastomer to the steel substrate instead of the microstructure itself. Additionally, the significance of fatigue in real world applications was discussed using SouthWest Airlines Flight 812 as an example.
ContributorsWong, Christopher Stanley (Author) / Adams, James (Thesis director) / Krause, Stephen (Committee member) / Anwar, Shahriar (Committee member) / Materials Science and Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2016-05
Description
How can we change what it means to be a human? Products can be used that will allow for near-instantaneous communication with one’s friends and family wherever they are: and the newest devices do not have to be even carried around, as they can be worn instead. Wearable electronics are quickly becoming very popular, with 232.0 million wearable devices sold in 2015. This report provides an overview of current and developing wearable devices, investigates the characteristics of the average buyer for these different types of devices. Finally, marketing strategies are suggested. This work was completed in conjunction with a capstone project with Intel, where three objectives were achieved: First, a universal strain tester that could strain samples cyclically in a manner similar to the body was designed. This equipment was especially designed to be flexible in the testing conditions it could be exposed to, so samples could be tested at elevated temperatures or even underwater. Next, dogbone shaped samples for the testing of Young’s Modulus and elongation to failure were produced, and the cut quality of laser, water-jet, and die-cutting was compared in order to select the most defect-free method for reliable testing. Polydimethylsiloxane (PDMS) is a fantastic candidate material for wearable electronics, however there is some discrepancies in the literature—such as from Eleni et. al—about the impact of ultraviolet radiation on the mechanical properties. By conducting accelerated aging tests simulating up to five years exposure to the sun, it was determined that ultraviolet-induced cross-linking of the polymer chains does occur, leading to severe embrittlement (strain to failure reduced from 3.27 to 0.06 in some cases, reduction to approximately 0.21 on average). As simulated tests of possible usage conditions required strains of at least 0.50-0.70, a variety of solutions were suggested to reduce this embrittlement. This project can lead to standardization of wearables electronics testing methods for more reliable predictions about the device behavior, whether that device is a simple pedometer or something that allows the visually impaired to “see”, such as Toyota’s Blaid.
ContributorsNiebroski, Alexander Wayne (Author) / Adams, James (Thesis director) / Anwar, Shahriar (Committee member) / Materials Science and Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2016-05
Description
A novel approach, the Invariant Based Theory of Composites and the "Trace" method it proposes, has the potential to reduce aerospace composite development times and costs by over 30% thus reinvigorating the development process and encouraging composite technology growth. The "trace" method takes advantage of inherent stiffness properties of laminates, specifically carbon fiber, to make predictions of material properties used to derive design allowables. The advantages of the "trace" theory may not necessarily be specific to the aerospace industry, however many automotive manufacturers are facing environmental, social and political pressure to increase the gas mileage in their vehicles and reduce their carbon footprint. Therefore, the use of lighter materials, such as carbon fiber composites, to replace heavier metals in cars is inevitable yet as of now few auto manufacturers implement composites in their cars. The high material, testing and development costs, much like the aerospace industry, have been prohibitive to widespread use of these materials but progress is being made in overcoming those challenges. The "trace" method, while initially intended for quasi-isotropic, aerospace grade carbon-fiber laminates, still yields reasonable, and correctable, results for types of laminates as well such as with woven fabrics and thermoplastic matrices, much of which are being used in these early stages of automotive composite development. Despite the varying use of materials, the "trace" method could potentially boost automotive composites in a similar way to the aerospace industry by reducing testing time and costs and perhaps even playing a role in establishing emerging simulations of these materials.
ContributorsBrown, William Ross (Author) / Adams, James (Thesis director) / Anwar, Shahriar (Committee member) / Krause, Stephen (Committee member) / Materials Science and Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2016-05