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Description
ABSTRACTWith the National Aeronautics and Space Administration (NASA) Psyche Mission, humans will soon have the first opportunity to explore a new kind of planetary body: one composed mostly of metal as opposed to stony minerals or ices. Identifying the composition of asteroids from Earth-based observations has been an ongoing challenge. Although optical reflectance spectra, radar, and orbital dynamics can constrain an asteroid’s mineralogy and bulk density, in many cases there is not a clear or precise match with analogous materials such as meteorites. Additionally, the surfaces of asteroids and other small, airless planetary bodies can be heavily modified over geologic time by exposure to the space environment. To accurately interpret remote sensing observations of metal-rich asteroids, it is therefore necessary to understand how the processes active on asteroid surfaces affect metallic materials. This dissertation represents a first step toward that understanding. In collaboration with many colleagues, I have performed laboratory experiments on iron meteorites to simulate solar wind ion irradiation, surface heating, micrometeoroid bombardment, and high-velocity impacts. Characterizing the meteorite surface’s physical and chemical properties before and after each experiment can constrain the effects of each process on a metal-rich surface in space. While additional work will be needed for a complete understanding, it is nevertheless possible to make some early predictions of what (16) Psyche’s surface regolith might look like when humans observe it up close. Moreover, the results of these experiments will inform future exploration beyond asteroid Psyche as humans attempt to understand how Earth’s celestial neighborhood came to be.
ContributorsChristoph, John Morgan M. (Author) / Elkins-Tanton, Linda (Thesis advisor) / Williams, David (Committee member) / Dukes, Catherine (Committee member) / Sharp, Thomas (Committee member) / Bell III, James (Committee member) / Arizona State University (Publisher)
Created2023
Description
Electrochemical technologies emerge as a feasible solution to monitor and treat pollutants. Although electrochemical technologies have garnered widespread attention, their commercial applications are still constrained by the use of expensive electrocatalysts, and the bulky and rigid plate design of electrodes that restricts electrochemical reactor design to systems with poor electrode surface/ volume treated ratios. By making electrodes flexible, more compact designs that maximize electrode surface per volume treated might become a reality. This dissertation encompasses the successful fabrication of flexible nanocomposite electrodes for electrocatalysis and electroanalysis applications.First, nano boron-doped diamond electrodes (BDD) were prepared as an inexpensive alternative to commercial boron-doped diamond electrodes. Comparative detailed surface and electrochemical characterization was conducted. Empirical study showed that replacing commercial BDD electrodes with nano-BDD electrodes can result in a cost reduction of roughly 1000x while maintaining the same electrochemical performance.
Next, self-standing electrodes were fabricated through the electropolymerization of conducing polymer, polypyrrole. Surface characterizations, such as SEM, FTIR and XPS proved the successful fabrication of these self-standing electrodes. High mechanical stability and bending flexibility demonstrated the ability to use these electrodes in different designs, such as roll-to-roll membranes. Electrochemical nitrite reduction was employed to demonstrate the viability of using self-standing nanocomposite electrodes for electrocatalytic applications reducing hazardous nitrogen oxyanions (i.e., nitrite) towards innocuous species such as nitrogen gas. A high faradaic efficiency of 78% was achieved, with high selectivity of 91% towards nitrogen gas.
To further enhance the conductivity and charge transfer properties of self-standing polypyrrole electrodes, three different nanoparticles, including copper (Cu), gold (Au), and platinum (Pt), were incorporated in the polypyrrole matrix. Effect of nanoparticle wt% and interaction between metal nanoparticles and polypyrrole matrix was investigated for electroanalytical applications, specifically dopamine sensing. Flexible nanocomposite electrodes showed outstanding performance as electrochemical sensors with PPy-Cu 120s exhibiting a low limit of detection (LOD) of 1.19 µM and PPy-Au 120s exhibiting a high linear range of 5 µM - 300 µM.
This dissertation outlines a method of fabricating self-standing electrodes and provides a pathway of using self-standing electrodes based on polypyrrole and polypyrrole-metal nanocomposites for various applications in wastewater treatment and electroanalytical sensing.
ContributorsBansal, Rishabh (Author) / Garcia-Segura, Sergio (Thesis advisor) / Westerhoff, Paul (Committee member) / Perreault, Francois (Committee member) / Chan, Candace (Committee member) / Arizona State University (Publisher)
Created2023
Description
Perovskite solar cells are one of the rising stars in the solar cell industry. This thesis explores several approaches to enhance the properties of the perovskite layer and the solar cell devices in which they operate. They include studies of different antisolvent additives during spin coating of triple cation perovskites, the use of surfactants to improve the quality of perovskite film microstructures, the applicability of a new fabrication process, and the value of post-deposition thermal and chemical annealing processes.This thesis experimentally analyzes different antisolvents, viz., ethyl acetate, isopropyl alcohol, toluene, and chlorobenzene. It focuses on the antisolvent-assisted crystallization method to achieve homogenous nucleation of the perovskite film. Of all the antisolvents, ethyl acetate-treated films gave the best-performing device, achieving a power conversion efficiency of 15.5%.
This thesis also analyzes the effects of mixed antisolvents on the qualities of triple-cation perovskites. Different solution concentrations of chlorobenzene in ethyl acetate and isopropyl alcohol in ethyl acetate are optimized for optimal supersaturation to achieve enlarged perovskite grains. Evaluations are discussed in the context of solution polarity and boiling point of the antisolvents, where 25% chlorobenzene in ethyl acetate antisolvent mixture shows the best film properties.
Another study discusses a new fabrication process called electrical field-assisted direct ink deposition for large-scale printing of perovskite solar cells. This process involves the formation of nanodroplets under an electrical field deposited onto ITO/glass substrates. As a result, smooth Poly (3,4-ethylene dioxythiophene) polystyrene sulfonate layers are
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produced with an average effective electrical resistivity of 4.15104 0.26 -m compared to that of spin-coated films.
A successive chapter discusses the studies of the electrical field-assisted direct ink deposition of the photoactive CH3NH3PbI2 (MAPbI3) layer. Its focus is on the post-deposition chemical annealing of the MAPbI3 films in methylamine gas, termed as methylamine gas-assisted healing and growth of perovskite films. This treatment improved the smoothness, reduced porosity, increased density, and generated more uniform grain sizes. Moreover, it improved the inter-grain boundary contacts by eliminating secondary, fine-grained boundary structures. Mechanisms behind the initial liquefaction of the MAPbI3 film's subsequent re-solidification are discussed.
ContributorsGogoi, Banashree (Author) / Alford, Terry (Thesis advisor) / Petuskey, William (Thesis advisor) / Gould, Ian (Committee member) / Li, Jian (Committee member) / Arizona State University (Publisher)
Created2023
Description
Applications such as heat exchangers, surface-based cellular structures, rotating blades, and waveguides rely on thin metal walls as crucial constituent elements of the structure. The design freedom enabled by laser powder bed fusion has led to an interest in exploiting this technology to further the performance of these components, many of which retain their as-built surface morphologies on account of their design complexity. However, there is limited understanding of how and why mechanical properties vary by wall thickness for specimens that are additively manufactured and maintain an as-printed surface finish. Critically, the contributions of microstructure and morphology to the mechanical behavior of thin wall laser powder bed fusion structures have yet to be systematically identified and decoupled. This work focuses on elucidating the room temperature quasi-static tensile and high cycle fatigue properties of as-printed, thin-wall Inconel 718 fabricated using laser powder bed fusion, with the aim of addressing this critical gap in the literature. Wall thicknesses studied range from 0.3 - 2.0 mm, and the effects of Hot Isostatic Pressing are also examined, with sheet metal specimens used as a baseline for comparison. Statistical analyses are conducted to identify the significance of the dependence of properties on wall thickness and Hot Isostatic Pressing, as well as to examine correlations of these properties to section area, porosity, and surface roughness. A thorough microstructural study is complemented with a first-of-its-kind study of surface morphology to decouple their contributions and identify underlying causes for observed changes in mechanical properties. This thesis finds that mechanical properties in the quasi-static and fatigue framework do not see appreciable declines until specimen thickness is under 0.75 mm in thickness. The added Hot Isostatic Pressing heat treatment effectively closed pores, recrystallized the grain structure, and provided a more homogenous microstructure that benefits the modulus, tensile strength, elongation, and fatigue performance at higher stresses. Stress heterogeneities, primarily caused by surface defects, negatively affected the thinner specimens disproportionately. Without the use of the Hot Isostatic Pressing, the grain structure remained much more refined and benefitted the yield strength and fatigue endurance limit.
ContributorsParadise, Paul David (Author) / Bhate, Dhruv (Thesis advisor) / Chawla, Nikhilesh (Committee member) / Azeredo, Bruno (Committee member) / Jiao, Yang (Committee member) / Arizona State University (Publisher)
Created2022
Description
Intelligent engineering designs require an accurate understanding of material behavior, since any uncertainties or gaps in knowledge must be counterbalanced with heightened factors of safety, leading to overdesign. Therefore, building better structures and pushing the performance of new components requires an improved understanding of the thermomechanical response of advanced materials under service conditions. This dissertation provides fundamental investigations of several advanced materials: thermoset polymers, a common matrix material for fiber-reinforced composites and nanocomposites; aluminum alloy 7075-T6 (AA7075-T6), a high-performance aerospace material; and ceramic matrix composites (CMCs), an advanced composite for extreme-temperature applications. To understand matrix interactions with various interfaces and nanoinclusions at their fundamental scale, the properties of thermoset polymers are studied at the atomistic scale. An improved proximity-based molecular dynamics (MD) technique for modeling the crosslinking of thermoset polymers is carefully established, enabling realistic curing simulations through its ability to dynamically and probabilistically perform complex topology transformations. The proximity-based MD curing methodology is then used to explore damage initiation and the local anisotropic evolution of mechanical properties in thermoset polymers under uniaxial tension with an emphasis on changes in stiffness through a series of tensile loading, unloading, and reloading experiments. Aluminum alloys in aerospace applications often require a fatigue life of over 109 cycles, which is well over the number of cycles that can be practically tested using conventional fatigue testing equipment. In order to study these high-life regimes, a detailed ultrasonic cycle fatigue study is presented for AA7075-T6 under fully reversed tension-compression loading. The geometric sensitivity, frequency effects, size effects, surface roughness effects, and the corresponding failure mechanisms for ultrasonic fatigue across different fatigue regimes are investigated. Finally, because CMCs are utilized in extreme environments, oxidation plays an important role in their degradation. A multiphysics modeling methodology is thus developed to address the complex coupling between oxidation, mechanical stress, and oxygen diffusion in heterogeneous carbon fiber-reinforced CMC microstructures.
ContributorsSchichtel, Jacob (Author) / Chattopadhyay, Aditi (Thesis advisor) / Dai, Lenore (Committee member) / Ghoshal, Anindya (Committee member) / Huang, Huei-Ping (Committee member) / Jiao, Yang (Committee member) / Oswald, Jay (Committee member) / Arizona State University (Publisher)
Created2022
Description
Advanced fibrous composite materials exhibit outstanding thermomechanical performance under extreme environments, which make them ideal for structural components that are used in a wide range of aerospace, nuclear, and defense applications. The integrity and residual useful life of these components, however, are strongly influenced by their inherent material flaws and defects resulting from the complex fabrication processes. These defects exist across multiple length scales and govern several scale-dependent inelastic deformation mechanisms of each of the constituents as well as their composite damage anisotropy. Tailoring structural components for optimal performance requires addressing the knowledge gap regarding the microstructural material morphology that governs the structural scale damage and failure response. Therefore, there is a need for a high-fidelity multiscale modeling framework and scale-specific in-situ experimental characterization that can capture complex inelastic mechanisms, including damage initiation and propagation across multiple length scales. This dissertation presents a novel multiscale computational framework that accounts for experimental information pertinent to microstructure morphology and architectural variabilities to investigate the response of ceramic matrix composites (CMCs) with manufacturing-induced defects. First, a three-dimensional orthotropic viscoplasticity creep formulation is developed to capture the complex temperature- and time-dependent constituent load transfer mechanisms in different CMC material systems. The framework also accounts for a reformulated fracture mechanics-informed matrix damage model and the Curtin progressive fiber damage model to capture the complex scale-dependent damage and failure mechanisms through crack kinetics and porosity growth. Next, in-situ experiments using digital image correlation (DIC) are performed to capture the damage and failure mechanisms in CMCs and to validate the high-fidelity modeling results.
The dissertation also presents an exhaustive experimental investigation into the effects of temperature and manufacturing-induced defects on toughened epoxy adhesives and hybrid composite-metallic bonded joints. Nondestructive evaluation techniques are utilized to characterize the inherent defects morphology of the bulk adhesives and bonded interface. This is followed by quasi-static tensile tests conducted at extreme hot and cold temperature conditions. The damage mechanisms and failure modes are investigated using in-situ DIC and a high-resolution camera. The information from the morphology characterization studies is used to reconstruct high-fidelity geometries of the test specimens for finite element analysis.
ContributorsKhafagy, Khaled Hassan Abdo (Author) / Chattopadhyay, Aditi (Thesis advisor) / Fard, Masoud Y. (Committee member) / Milcarek, Ryan (Committee member) / Stoumbos, Tom (Committee member) / Borkowski, Luke (Committee member) / Arizona State University (Publisher)
Created2022
Description
Polyolefins have dominated global polymer production for the past 60 years, revolutionizing fields of medicine, construction, travel, packaging, and many more. However, with steadily increasing polyolefin production each year and traditionally long polyethylene (PE) and polypropylene degradation times, estimated on the order of 500 years or more, a massive challenge arises with accumulating plastic waste. While the end-of-life of polyolefins previously manufactured must be addressed, incorporation of sustainability and circularity into future commodity plastic design at the molecular level offers an opportunity to decrease their negative effects on the environment going forward. Herein, several approaches are described which aim to address the need for polymeric materials while introducing a sustainable approach to their design, either through incorporation of biosynthesized polymers or degradable units. In the first project, polymer blends of two biodegradable polymers were studied, and compared to the same blends containing a graft copolymer compatibilizer comprised of the two homopolymer counterparts. The compatibilized blends were expected to have superior mechanical performance to the uncompatibilized blend and potentially offer industrially relevant benefits. While this was not achieved, valuable insight into the polymer blend interactions were gained. The idea of compatibilizing polymer blends was further explored with blends of PE and a cellulose derivative with the aid of a custom ABA triblock compatibilizing agent. It was discovered that the compatibilizer reinforced the polymer blend by providing mechanical strength at the cost of flexibility. To approach sustainability from a different perspective, several segmented copolymer series based on telechelic PE oligomers were then synthesized and analyzed. The segmented systems exhibited similar structure to high density PE (HDPE), retained similar mechanical and thermal properties to commercial HDPE, but contained degradable units throughout the polymer backbone. Several fundamental principles were explored through the segmented and chain-extended polyolefin architecture, including the influence of reactive linkage (amide vs. ester), random vs. alternating segment structure, and PE segment molecular weight. The effects of tailoring polymer structure on thermal, mechanical, and morphological properties are described herein. The relationships established from these experiments may further guide future polymer design and contribute toward more sustainable polyolefin manufacturing.
ContributorsArrington, Anastasia Sergeevna (Author) / Long, Timothy E. (Thesis advisor) / Jin, Kailong (Committee member) / Biegasiewicz, Kyle F. (Committee member) / Matson, John B. (Committee member) / Arizona State University (Publisher)
Created2022
Description
Solid-state and non-equilibrium processings are of great interest to researchers due to their ability to control and refine bulk and/or surface microstructure of metallic alloys and push them to surpass their conventional properties limit. In this dissertation, solid-state processing i.e., Shear Assisted Processing and Extrusion (ShAPE), and non-equilibrium processes i.e., surface mechanical attrition (SMAT) and additive manufacturing (AM) techniques were used to process the magnesium and aluminum alloys respectively. A synergistic investigation of processing-induced microstructural modification and its effect on corrosion resistance was performed using various ex-situ, quasi in-situ, and in-situ electrochemical, microscopy, and spectroscopy characterization techniques. To evaluate the effect of the same processing condition on a range of microstructures, a variety of magnesium alloys such as AZ31B, Mg-3Si, ZK60, and Pure Mg were processed using a novel solid-state processing method, namely ShAPE. It induced a significant grain refinement, homogenized distribution of second phases, and low residual strain in AZ31B alloy, which contributed toward a noble breakdown potential, stable protective film, and hence better corrosion resistance compared to the parent extruded counterpart. However, with variations in composition, volume fraction, and distribution of second phases with Mg-3Si and ZK60 magnesium alloy an opposite response was inferred indicating a strong dependence of corrosion on underlying microstructure compared to a processing condition. Non-equilibrium processes, i.e. SMAT and AM were utilized to process high-strength 7xxx series aluminum alloys. Continuous high energy impacts of hard balls in room temperature (RT SMAT) and liquid nitrogen (LN2 SMAT) flow environment generated a gradient nanocrystalline surface layer with the dissolution of inherent second phase and precipitation of new phases in aluminum 7075 alloys. RT SMAT showed a reduced anodic dissolution rate and improved film resistance, which was attributed to the thicker and composite oxide layer along with new nanoscale precipitates. Lastly, reactive AM was used to process aluminum 7075 and 7050 alloys which resulted in a refined and textureless microstructure. A reduction in corrosion resistance was observed with precipitation of excessive reactive particles (Ti and B4C) in AM alloys compared to wrought counterparts.
ContributorsBeura, Vikrant Kumar (Author) / Solanki, Kiran N (Thesis advisor) / Peralta, Pedro (Committee member) / Alford, Terry (Committee member) / Ankit, Kumar (Committee member) / Joshi, Vineet V (Committee member) / Arizona State University (Publisher)
Created2022
Description
Both molecular structure of macromolecular materials and subsequent processing of these materials dictate resulting material properties. In this work novel synthetic strategies combined with detailed analytical methodology reveal fundamental structure-processing-property relationships in thermoplastic polyesters, thermoplastic polyurethanes, covalently crosslinked acetal functionalized networks, and small molecule surfactants. 4,4’ dimethyloxybisbenzoate afforded a series of novel polyester structures, and the incorporation of this monomer both increased the Tg and decreased the crystallinity in cyclohexane dimethanol based polyesters. Solubility and dynamic light scattering experiments combined with oscillatory rheology techniques provided methodology to validate polyurethane extrusion in commercial polyurethanes. Acid catalyzed hydroxyl addition to vinyl ethers provided two families of acetal functionalized poly(ethylene glycol hydrogels). Stoichiometric control of binary thiol-acrylate polymerizations afforded hydrogels with both tunable mechanical properties and predictable degradation profiles. Following this work, a photoacid generator catalyzed cationic catalysis provided acetal functionalized organogels whose mechanical properties were predicted by excess vinyl ether monomers which underwent cationic polymerization under the same reaction conditions that yielded acetal functionalization. Time resolved FT-IR spectroscopy provided new understanding in hydroxyl vinyl ether reactions, where both hydroxyl addition to a vinyl ether and vinyl ether cationic polymerization occur concurrently. This work inspired research into new reactive systems for photobase generator applications. However, current photobase generator technologies proved incompatible for carbon-Michael reactions between acetoacetate and acrylate functionalities as a result of uncontrollable acrylate free radical polymerization. The fundamental knowledge and synthetic strategies afforded by these investigations were applied to small molecule surfactant systems for fire-fighting applications. Triethylsilyl-containing zwitterionic and cationic surfactants displayed surface tensions lower than hydrocarbon surfactants, but larger than siloxane-containing surfactants. For the first time, oscillatory rheology and polarized optical light imagine rheology highlighted shear-induced micelle alignment in triethylsilyl surfactants, which provided more stable foams than zwitterionic analogues. The knowledge gained from these investigations provided fundamental structure-processing-property relationships in small molecule surfactant solutions applied as fire-fighting foams. This discovery regarding the effect of self-assembled structures in foam solutions informs the design and analysis of next generation surfactants to replace fluorocarbon surfactants in fire-fighting foam applications.
ContributorsBrown, James Robert (Author) / Long, Timothy E (Thesis advisor) / Bortner, Michael J (Committee member) / Biegasiewicz, Kyle F (Committee member) / Jin, Kailong (Committee member) / Arizona State University (Publisher)
Created2023
Description
Doping is the cornerstone of Semiconductor technology, enabling the functionalities of modern digital electronics. Two-dimensional (2D) transition metal dichalcogenides (TMDCs) have tunable direct bandgaps, strong many-body interactions, and promising applications in future quantum information sciences, optoelectronic, spintronic, and valleytronic devices. However, their wafer-scale synthesis and precisely controllable doping are challenging. Moreover, there is no fixed framework to identify the doping concentration, which impedes their process integration for future commercialization. This work utilizes the Neutron Transmutation Doping technique to control the doping uniformly and precisely in TMDCs. Rhenium and Tin dopants are introduced in Tungsten- and Indium-based Chalcogenides, respectively. Fine-tuning over 0.001% doping level is achieved. Precise analytical techniques such as Gamma spectroscopy and Secondary Ion Mass Spectrometry are used to quantify ultra-low doping levels ranging from 0.005-0.01% with minimal error. Dopants in 2D TMDCs often exhibit a broad stokes-shifted emission, with high linewidths, due to extrinsic effects such as substrate disorder and surface adsorbates. A well-defined bound exciton emission induced by Rhenium dopants in monolayer WSe2 and WS2 at liquid nitrogen temperatures is reported along with specific annealing regimes to minimize the defects induced in the Neutron Transmutation process. This work demonstrates a framework for Neutron Doping in 2D materials, which can be a scalable process for controlling doping and doping-induced effects in 2D materials.
ContributorsLakhavade, Sushant Sambhaji (Author) / Tongay, Sefaattin (Thesis advisor) / Alford, Terry (Committee member) / Yang, Sui (Committee member) / Arizona State University (Publisher)
Created2023