Matching Items (338)
Description
In 2015, the United States consumed about 140.43 billion gallons of gasoline, resulting in the emission of over 1 billion metric tons of carbon dioxide, according to the U.S. Energy Information Administration. Despite continued efforts to develop more efficient engines and cleaner fuels, a major barrier to reducing energy consumption and CO2 production is the mass of the vehicle. Replacing traditional automotive materials such as iron and steel with lighter-weight materials is a big step toward improving fuel economy. Magnesium has great potential for use in the automotive industry because of its low density, about 78% less than the density of steel, and high strength-to-weight ratio. Using cast magnesium instead of steel can reduce the overall weight of a vehicle, improving performance and increasing fuel efficiency. However, magnesium’s high susceptibility to corrosion limits its feasibility as a substitute for traditional materials.
This project aimed to understand the effects of composition and phase distribution on the corrosion behavior of magnesium-aluminum (Mg-Al) alloys in an ionic liquid electrolyte. The purpose of studying corrosion in nonaqueous ILs is to determine the anodic dissolution behaviors of the alloy phases without the interference of side reactions that occur in aqueous electrolytes, such as di-oxygen or water reduction. Three commercial Mg-Al alloys were studied: AZ91D (9% Al), AM60 (6% Al), and AZ31B (3% Al). An annealed alloy containing solid-solution α-phase Mg-Al with 5 at% aluminum content (Mg5Al) was also used. The ionic liquid chosen for this project was 1:2 molar ratio choline-chloride:urea (cc-urea), a deep eutectic solvent. After potentiostatic corrosion in cc-urea, the magnesium alloys were found to form a high surface area porous morphology as corrosion duration increased. This morphology consists of aluminum-rich ridges formed by Al nanowires surrounding an aluminum-poor base area, but with an overall increase in surface Al composition, indicating selective dealloying of the Mg in cc-urea and redistribution of the Al on the surface. Further work will focus on the development of hydrophobic coatings using ionic liquids.
This project aimed to understand the effects of composition and phase distribution on the corrosion behavior of magnesium-aluminum (Mg-Al) alloys in an ionic liquid electrolyte. The purpose of studying corrosion in nonaqueous ILs is to determine the anodic dissolution behaviors of the alloy phases without the interference of side reactions that occur in aqueous electrolytes, such as di-oxygen or water reduction. Three commercial Mg-Al alloys were studied: AZ91D (9% Al), AM60 (6% Al), and AZ31B (3% Al). An annealed alloy containing solid-solution α-phase Mg-Al with 5 at% aluminum content (Mg5Al) was also used. The ionic liquid chosen for this project was 1:2 molar ratio choline-chloride:urea (cc-urea), a deep eutectic solvent. After potentiostatic corrosion in cc-urea, the magnesium alloys were found to form a high surface area porous morphology as corrosion duration increased. This morphology consists of aluminum-rich ridges formed by Al nanowires surrounding an aluminum-poor base area, but with an overall increase in surface Al composition, indicating selective dealloying of the Mg in cc-urea and redistribution of the Al on the surface. Further work will focus on the development of hydrophobic coatings using ionic liquids.
ContributorsWeiss, Anna Caroline (Author) / Sieradzki, Karl (Thesis director) / Chan, Candace (Committee member) / Materials Science and Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2016-05
Description
The concentration necessary to kill bacterial biofilms with antimicrobials is the minimum biofilm eradication concentration (MBEC). This is usually determined using an in vitro approach and will vary within different strains of bacteria. Biomedical implants produce biofilm-related infections presenting a unique challenge due to the combination of subpopulations of the bacterial community and the polysaccharide matrix presented by biofilms. The purpose of this investigation is to determine how exposure times in the order of weeks to months affect the MBEC. Using an in vitro approach, Staphylococcus aureus (UAMS-1) and methicillin-resistant Staphylococcus aureus (MRSA) biofilms were produced with a 24 hour growth time and exposed to two antimicrobials, tobramycin and vancomycin, and one combination treatment that consisted of 1:1 tobramycin: vancomycin by weight. Crystal violet screening was used in order to ensure the integrity of the biofilm matrix throughout the full time of exposure. It was determined that UAMS-1 MBECs were lowered after 56 days of exposure than after 5 days for all three treatment groups. MRSA MBECs after 5 days of exposure decreased only with in vancomycin treatment group.
ContributorsSteinhauff, Douglas Busch (Author) / Caplan, Michael (Thesis director) / Overstreet, Derek (Committee member) / Castaneda, Paulo (Committee member) / Materials Science and Engineering Program (Contributor) / Harrington Bioengineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2016-05
Description
The financial feasibility of NextPotential's X-doped photocatalyst is uncertain, the outcome depends on how much the material cost becomes reduced due to mass production techniques. If carbon taxes continue on the current trend the photocatalyst is highly likely to become financially feasible. Without carbon taxes, it is still likely the photocatalyst will achieve economical feasibility. The land area required by the photocatalyst is a feasible size. The minimal environmental downsides are that more land will be used and water will be used, but both of these are minimal compared to the benefit of eliminating carbon emissions.
ContributorsMcmullan, Kyle Jonathan (Co-author) / Lahpai, Mun (Co-author) / Donnelly, Connor (Co-author) / Puzhaev, Boris (Co-author) / Adams, James (Thesis director) / Krause, Stephen (Committee member) / Barrett, The Honors College (Contributor) / Materials Science and Engineering Program (Contributor)
Created2015-05
Description
The transition to lead-free solder in the electronics industry has benefited the environment in many ways. However, with new materials systems comes new materials issues. During the processing of copper pads, a protective surface treatment is needed to prevent the copper from oxidizing. Characterizing the copper oxidation underneath the surface treatment is challenging but necessary for product reliability and failure analysis. Currently, FIB-SEM, which is time-consuming and expensive, is what is used to understand and analyze the surface treatment-copper oxide(s)-copper system. This project's goals were to determine a characterization methodology that cuts both characterization time and cost in half for characterizing copper oxidation beneath a surface treatment and to determine which protective surface treatment is the best as defined by multiple criterion such as cost, sustainability, and reliability. Two protective surface treatments, organic solderability preservative (OSP) and chromium zincate, were investigated, and multiple characterization techniques were researched. Six techniques were tested, and three were deemed promising. Through our studies, it was determined that the best surface treatment was organic solderability preservative (OSP) and the ideal characterization methodology would be using FIB-SEM to calibrate a QCM model, along with using SERA to confirm the QCM model results. The methodology we propose would result in a 91% reduction in characterization cost and a 92% reduction in characterization time. Future work includes further calibration of the QCM model using more FIB/SEM data points and eventually creating a model for oxide layer thickness as a function of exposure time and processing temperature using QCM as the primary data source. An additional short essay on the role of SEM on the continuing miniaturization of integrated circuits is included at the end. This paper explores the intertwined histories of the scanning electron microscope and the integrated circuit, highlighting how advances in SEM influence integrated circuit advances.
ContributorsSmith, Bethany Blair (Co-author) / Marion, Branch Kelly (Co-author) / Cruz, Hernandez (Co-author) / Kimberly, McGuiness (Co-author) / Adams, James (Thesis director) / Krause, Stephen (Committee member) / Barrett, The Honors College (Contributor) / Materials Science and Engineering Program (Contributor)
Created2015-05
Description
Water scarcity is still an issue across the globe, so nonconventional desalination methods need to be developed to be able to get access to clean, safe water. One such method being studied is the pervaporation system, a membrane process that uses a vapor pressure differential to drive the system. There is a need to find the efficiency of the cold trap condenser that is used to collect the permeate so that a thermodynamic model can be fully developed to assist in the development of an industrial scale pervaporation system. An efficiency was not able to be confidently found, but it is believe to be between 95-100%.
ContributorsLuong, Kristina Jenny (Author) / Thomas, Mary Laura Lind (Thesis director) / Thomas, Elisabeth (Committee member) / Materials Science and Engineering Program (Contributor) / Chemical Engineering Program (Contributor) / School of Mathematical and Statistical Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2020-12
Description
Hyperspectral imaging is a novel technology which allows for the collection of reflectance spectra of a sample in-situ and at a distance. A rapidly developing technology, hyperspectral imaging has been of particular interest in the field of art characterization, authentication, and conservation as it avoids the pitfalls of traditional characterization techniques and allows for the rapid and wide collection of data never before possible. It is hypothesized that by combining the power of hyperspectral imaging with machine learning, a new framework for the in-situ and automated characterization and authentication of artworks can be developed. This project, using the CMYK set of inks, began the preliminary development of such a framework. It was found that hyperspectral imaging and machine learning as a combination show significant potential as an avenue for art authentication, though further progress and research is needed to match the reliability of status quo techniques.
ContributorsChowdhury, Tanzil Aziz (Author) / Newman, Nathan (Thesis director) / Tongay, Sefaattin (Committee member) / School of Politics and Global Studies (Contributor) / Materials Science and Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2020-05
Description
The story of graphene truly began in what was simply a stub in the journal Physical Review not two years after the end of World War II. In 1947, McGill University physicist P.R. Wallace authored “The Band Theory of Graphite” and attempted to develop a foundation on which the structure-property relationship of graphite could be explored; he calculates the number of free electrons and conductivity of what he describes as “a single hexagonal layer” and “suppos[es] that conduction takes place only in layers” in bulk graphite to predict wave functions, energies at specific atomic sites in the hexagonal lattice, and energy contours using a tight binding approximation for a hypothesized version of what we now call ‘armchair-style’ graphene. While Wallace was the first to explore the band structure and Brillouin Zones of single-layer graphite, the concept of two-dimensional materials was not new. In fact, for years, it was dismissed as a thermodynamic impossibility.
Everything seemed poised against any proposed physical and experimental stability of a structure like graphene. “Thermodynamically impossible”– a not uncommon shutdown to proposed novel physical or chemical concepts– was once used to describe the entire field of proposed two-dimensional crystals functioning separately from a three-dimensional base or crystalline structure. Rudolf Peierls and Lev Davoidovich Landau, both very accomplished physicists respectively known for the Manhattan Project and for developing a mathematical theory of helium superfluidity, rejected the possibility of isolated monolayer to few-layered crystal lattices. Their reasoning was that diverging thermodynamic-based crystal lattice fluctuations would render the material unstable regardless of controlled temperature. This logic is flawed, but not necessarily inaccurate– diamond, for instance, is thermodynamically metastable at room temperature and pressure in that there exists a slow (i.e. slow on the scale of millions of years) but continuous transformation to graphite. However, this logic was used to support an explanation of thermodynamic impossibility that was provided for graphene’s lack of isolation as late as 1979 by Cornell solid-state physicist Nathaniel David Mermin. These physicists’ claims had clear and consistent grounding in experimental data: as thin films become thinner, there exists a trend of a decreasing melting temperature and increasing instability that renders the films into islands at somewhere around ten to twenty atomic layers. This is driven by the thermodynamically-favorable minimization of surface energy.
Everything seemed poised against any proposed physical and experimental stability of a structure like graphene. “Thermodynamically impossible”– a not uncommon shutdown to proposed novel physical or chemical concepts– was once used to describe the entire field of proposed two-dimensional crystals functioning separately from a three-dimensional base or crystalline structure. Rudolf Peierls and Lev Davoidovich Landau, both very accomplished physicists respectively known for the Manhattan Project and for developing a mathematical theory of helium superfluidity, rejected the possibility of isolated monolayer to few-layered crystal lattices. Their reasoning was that diverging thermodynamic-based crystal lattice fluctuations would render the material unstable regardless of controlled temperature. This logic is flawed, but not necessarily inaccurate– diamond, for instance, is thermodynamically metastable at room temperature and pressure in that there exists a slow (i.e. slow on the scale of millions of years) but continuous transformation to graphite. However, this logic was used to support an explanation of thermodynamic impossibility that was provided for graphene’s lack of isolation as late as 1979 by Cornell solid-state physicist Nathaniel David Mermin. These physicists’ claims had clear and consistent grounding in experimental data: as thin films become thinner, there exists a trend of a decreasing melting temperature and increasing instability that renders the films into islands at somewhere around ten to twenty atomic layers. This is driven by the thermodynamically-favorable minimization of surface energy.
ContributorsShulman, Neal Arthur (Author) / Adams, James (Thesis director) / Islam, Rafiqul (Committee member) / Materials Science and Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2018-05
Description
Transition metal dichalcogenides (TMDs) are a family of layered crystals with the chemical formula MX2 (M = W, Nb, Mo, Ta and X = S, Se, Te). These TMDs exhibit many fascinating optical and electronic properties making them strong candidates for high-end electronics, optoelectronic application, and spintronics. The layered structure of TMDs allows the crystal to be mechanically exfoliated to a monolayer limit, where bulk-scale properties no longer apply and quantum effects arise, including an indirect-to-direct bandgap transition. Controllably tuning the electronic properties of TMDs like WSe2 is therefore a highly attractive prospect achieved by substitutionally doping the metal atoms to enable n- and p-type doping at various concentrations, which can ultimately lead to more effective electronic devices due to increased charge carriers, faster transmission times and possibly new electronic and optical properties to be probed. WSe2 is expected to exhibit the largest spin splitting size and spin-orbit coupling, which leads to exciting potential applications in spintronics over its similar TMD counterparts, which can be controlled through electrical doping. Unfortunately, the well-established doping technique of ion implantation is unable to preserve the crystal quality leading to a major roadblock for the electronics applications of tungsten diselenide. Synthesizing WSe2 via chemical vapor transport (CVT) and flux method have been previously established, but controllable p-type (niobium) doping WSe2 in low concentrations ranges (<1 at %) by CVT methods requires further experimentation and study. This work studies the chemical vapor transport synthesis of doped-TMD W1-xNbxSe2 through characterization techniques of X-ray Diffraction, Scanning Electron Microscopy, Energy Dispersive X-ray Spectroscopy, and X-ray Photoelectron Spectroscopy techniques. In this work, it is observed that excess selenium transport does not enhance the controllability of niobium doping in WSe2, and that tellurium tetrachloride (TeCl4) transport has several barriers in successfully incorporating niobium into WSe2.
ContributorsRuddick, Hayley (Author) / Tongay, Sefaattin (Thesis director) / Jiao, Yang (Committee member) / Barrett, The Honors College (Contributor) / Materials Science and Engineering Program (Contributor)
Created2024-05