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- All Subjects: Materials Science
- Genre: Masters Thesis
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Description
Two dimensional (2D) Janus Transition Metal Dichalcogenides (TMDs) are a new class of atomically thin polar materials. In these materials, the top and the bottom atomic layer are made of different chalcogen atoms. To date, several theoretical studies have shown that a broken mirror symmetry induces a colossal electrical field in these materials, which leads to unusual quantum properties. Despite these new properties, the current knowledge in their synthesis is limited only through two independent studies; both works rely on high-temperature processing techniques and are specific to only one type of 2D Janus material - MoSSe. Therefore, there is an urgent need for the development of a new synthesis method to (1) Extend the library of Janus class materials. (2) Improve the quality of 2D crystals. (3) Enable the synthesis of Janus heterostructures. The central hypothesis in this work is that the processing temperature of 2D Janus synthesis can be significantly lowered down to room temperatures by using reactive hydrogen and sulfur radicals while stripping off selenium atoms from the 2D surface. To test this hypothesis, a series of controlled growth studies were performed, and several complementary characterization techniques were used to establish a process–structure-property relationship. The results show that the newly proposed approach, namely Selective Epitaxy and Atomic Replacement (SEAR), is effective in reducing the growth temperature down to ambient conditions. The proposed technique benefits in achieving highly crystalline 2D Janus layers with an excellent optical response. Further studies herein show that this technique can form highly sophisticated lateral and vertical heterostructures of 2D Janus layers. Overall results establish an entirely new growth technique for 2D Janus.layers, which pave ways for the realization of exciting quantum effects in these materials such as Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) state, Majorana fermions, and topological p-wave superconductors.
ContributorsSayyad, Mohammed Yasir (Author) / Tongay, Sefaattin (Thesis advisor) / Crozier, Peter (Committee member) / Alford, Terry (Committee member) / Arizona State University (Publisher)
Created2020
Description
Several ways exist to improve pavement performance over time. One suggestion is to tailor the asphalt pavement mix design according to certain specified specifications, set up by each state agency. Another option suggests the addition of modifiers that are known to improve pavement performance, such as crumb rubber and fibers. Nowadays, improving asphalt pavement structures to meet specific climate conditions is a must. In addition, time and cost are two crucial settings and are very important to consider; these factors sometimes play a huge role in modifying the asphalt mix design needed to be set into place, and therefore alter the desired pavement performance over the expected life span of the structure. In recent studies, some methods refer to predicting pavement performance based on the asphalt mixtures volumetric properties.
In this research, an effort was undertaken to gather and collect most recent asphalt mixtures’ design data and compare it to historical data such as those available in the Long-Term Pavement Performance (LTPP), maintained by the Federal Highway Administration (FHWA). The new asphalt mixture design data was collected from 25 states within the United States and separated according to the four suggested climatic regions. The previously designed asphalt mixture designs in the 1960’s present in the LTPP Database implemented for the test sections were compared with the recently designed pavement mixtures gathered, and pavement performance was assessed using predictive models.
Three predictive models were studied in this research. The models were related to three major asphalt pavement distresses: Rutting, Fatigue Cracking and Thermal Cracking. Once the performance of the asphalt mixtures was assessed, four ranking criteria were developed to support the assessment of the mix designs quality at hand; namely, Low, Satisfactory, Good or Excellent. The evaluation results were reasonable and deemed acceptable. Out of the 48 asphalt mixtures design evaluated, the majority were between Satisfactory and Good.
The evaluation methodology and criteria developed are helpful tools in determining the quality of asphalt mixtures produced by the different agencies. They provide a quick insight on the needed improvement/modification against the potential development of distress during the lifespan of the pavement structure.
In this research, an effort was undertaken to gather and collect most recent asphalt mixtures’ design data and compare it to historical data such as those available in the Long-Term Pavement Performance (LTPP), maintained by the Federal Highway Administration (FHWA). The new asphalt mixture design data was collected from 25 states within the United States and separated according to the four suggested climatic regions. The previously designed asphalt mixture designs in the 1960’s present in the LTPP Database implemented for the test sections were compared with the recently designed pavement mixtures gathered, and pavement performance was assessed using predictive models.
Three predictive models were studied in this research. The models were related to three major asphalt pavement distresses: Rutting, Fatigue Cracking and Thermal Cracking. Once the performance of the asphalt mixtures was assessed, four ranking criteria were developed to support the assessment of the mix designs quality at hand; namely, Low, Satisfactory, Good or Excellent. The evaluation results were reasonable and deemed acceptable. Out of the 48 asphalt mixtures design evaluated, the majority were between Satisfactory and Good.
The evaluation methodology and criteria developed are helpful tools in determining the quality of asphalt mixtures produced by the different agencies. They provide a quick insight on the needed improvement/modification against the potential development of distress during the lifespan of the pavement structure.
ContributorsKaram, Jolina Joseph (Author) / Kaloush, Kamil (Thesis advisor) / Mamlouk, Michael (Thesis advisor) / Ozer, Hasan (Committee member) / Arizona State University (Publisher)
Created2020
Description
Photocatalytic activity of titanium dioxide (titania or TiO2) offers enormous potential in solving energy and environmental problems. Immobilization of titania nanoparticles on inert substrates is an effective way of utilizing its photocatalytic activity since nanoparticles enable high mass-transport, and immobilization avoids post-treatment separation. For competitive photocatalytic performance, the morphology of the substrate can be engineered to enhance mass-transport and light accessibility. In this work, two types of fiber architectures (i.e., dispersed polymer/titania phase or D-phase, and multi-phase polymer-core/composite-shell fibers or M-phase) were explored as effective substrate solutions for anchoring titania. These fibers were fabricated using a low-cost and scalable fiber spinning technique. Polymethyl methacrylate (PMMA) was selected as the substrate material due to its ultraviolet (UV) transparency and stability against oxidative radicals. The work systematically investigates the influence of the fiber porosity on mass-transport and UV light scattering. The properties of the fabricated fiber systems were characterized by scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET), UV-vis spectrophotometry (UV-vis), and mechanical analysis. The photocatalytic performance was characterized by monitoring the decomposition of methylene blue (MB) under UV (i.e., 365 nm) light. Fabrication of photocatalytic support structures was observed to be an optimization problem where porosity improved mass transport but reduced UV accessibility. The D-phase fibers demonstrated the highest MB degradation rate (i.e., 0.116 min-1) due to high porosity (i.e., 33.2 m2/g). The M-phase fibers reported a better degradation rate compared to a D-phase fibers due to higher UV accessibility efficiency.
ContributorsKanth, Namrata (Author) / Song, Kenan (Thesis advisor) / Tongay, Sefaattin (Thesis advisor) / Kannan, Arunachala Mada (Committee member) / Arizona State University (Publisher)
Created2020
Description
Precursors of carbon fibers include rayon, pitch, and polyacrylonitrile fibers that can be heat-treated for high-strength or high-modulus carbon fibers. Among them, polyacrylonitrile has been used most frequently due to its low viscosity for easy processing and excellent performance for high-end applications. To further explore polyacrylonitrile-based fibers for better precursors, in this study, carbon nanofillers were introduced in the polymer matrix to examine their reinforcement effects and influences on carbon fiber performance. Two-dimensional graphene nanoplatelets were mainly used for the polymer reinforcement and one-dimensional carbon nanotubes were also incorporated in polyacrylonitrile as a comparison. Dry-jet wet spinning was used to fabricate the composite fibers. Hot-stage drawing and heat-treatment were used to evolve the physical microstructures and molecular morphologies of precursor and carbon fibers. As compared to traditionally used random dispersions, selective placement of nanofillers was effective in improving composite fiber properties and enhancing mechanical and functional behaviors of carbon fibers. The particular position of reinforcement fillers with polymer layers was enabled by the in-house developed spinneret used for fiber spinning. The preferential alignment of graphitic planes contributed to the enhanced mechanical and functional behaviors than those of dispersed nanoparticles in polyacrylonitrile composites. The high in-plane modulus of graphene and the induction to polyacrylonitrile molecular carbonization/graphitization were the motivation for selectively placing graphene nanoplatelets between polyacrylonitrile layers. Mechanical tests, scanning electron microscopy, thermal, and electrical properties were characterized. Applications such as volatile organic compound sensing and pressure sensing were demonstrated.
ContributorsFranklin, Rahul Joseph (Author) / Song, Kenan (Thesis advisor) / Jiao, Yang (Thesis advisor) / Liu, Yongming (Committee member) / Arizona State University (Publisher)
Created2020
Description
Miniaturization of microdevices comes at the cost of increased circuit complexity and operating current densities. At high current densities, the resulting electron wind imparts a large momentum to metal ions triggering electromigration which leads to degradation of interconnects and solder, ultimately resulting in circuit failure. Although electromigration-induced defects in electronic materials can manifest in several forms, the formation of voids is a common occurrence. This research aims at understanding the morphological evolution of voids under electromigration by formulating a diffuse interface approach that accounts for anisotropic mobility in the metallic interconnect. Based on an extensive parametric study, this study reports the conditions under which pancaking of voids or the novel void ‘swimming’ regimes are observed. Finally, inferences are drawn to formulate strategies using which the reliability of interconnects can be improved.
ContributorsVemulapalli, Sree Shivani (Author) / Ankit, Kumar (Thesis advisor) / Chawla, Nikhilesh (Committee member) / Singh, Arunima (Committee member) / Arizona State University (Publisher)
Created2020
Description
There is a high demand for customized designs of various types of cement-based materials in order to address specific purposes in the construction field. These demands stem from the need to optimize the cementitious matrix properties and reinforcement choices, especially in high reliability, durability, and performance applications that include infrastructure, energy production, commercial buildings, and may ultimately be extended to low risk/high volume applications such as residential applications. The typical tools required to guide practicing engineers should be based on optimization algorithms that require highly efficient capacity and design alternatives and optimal computational tools. The general case of flexural design of members is an important aspect of design of structural members which can be extended to a variety of applications that include various cross-sections such as rectangular, W-sections, channels, angles, and T sections. The model utilized the simplified linear constitutive response of cement-based composite in compression and tension and extends into a two-segment elastic-plastic, strain softening, hardening, tension-stiffening, and a multi-segment system. The generalized parametric model proposed uses a dimensionless system in the stress-strain materials diagram to formulate piecewise equations for an equilibrium of internal stresses and obtains strain distributions for the closed-form solution of neutral axis location. This would allow for the computation of piecewise moment-curvature response. The number of linear residual stress implemented is flexible to a user to maintain a robust response. In the present approach bilinear, trilinear, and quad-linear models are addressed and a procedure for incorporating additional segments is presented. Moreover, a closed-form solution of moment-curvature can be solved and employed in calculating load-deflection response. The model is adaptable for various types of fiber-reinforced and textile reinforced concrete (FRC, TRC, UHPC, AAC, and Reinforced Concrete). The extensions to cover continuous fiber reinforcement such as textile reinforced concrete (TRC, FRCM) strengthening and repair are addressed. The theoretical model is extended to incorporate the hybrid design (HRC) with continuous rebar with FRC to increase the ductility and ultimate moment capacity. HRC extends the performance of the fiber system to incorporate residual capacity into a serviceability-based design that reduced the reliance on the design based on the limit state. The design chart for HRC and as well as conventional RC has been generated for practicing engineering applications. Results are compared to a large array of data from experimental results conducted at the ASU structural lab facilities and other published literature.
Contributorspleesudjai, chidchanok (Author) / Mobasher, Barzin (Thesis advisor) / Neithalath, Narayanan (Committee member) / Rajan, Subramaniam (Committee member) / Arizona State University (Publisher)
Created2021
Description
Laser Powder Bed Fusion (LPBF) is an additive manufacturing (AM) technology that has emerged as the predominant technology for metal 3D printing. An alloy of particular interest to the aerospace industry is the nickel-based superalloy, Inconel 718 (IN718), which is widely used for its superior performance in elevated temperature conditions, particularly for gas-turbine engine blades and heat exchangers. With LPBF providing new ways of exploiting complex part geometry, the high-temperature properties of the AM version of the alloy must be understood. Of additional interest is how these properties change as a function of geometry and post-processing. This research focuses on the behavior of LPBF IN718 as a function of hot isostatic pressing (HIP) and specimen thickness at elevated temperatures. These results and behavior were compared to the behavior of IN718 sheet metal for properties such as True Ultimate Tensile Strength (UTS), Yield Strength, Young’s Modulus, percent elongation, and necking. The results showed dependence of strength on both thickness and HIP condition, and also exhibited a steep drop in UTS and yield strength at 1600 °F, linearly declining modulus, and excess dynamic strain ageing (DSA) behavior at certain temperatures.
ContributorsTemes, Samuel (Author) / Bhate, Dhruv (Thesis advisor) / Azeredo, Bruno (Committee member) / Das, Partha (Committee member) / Arizona State University (Publisher)
Created2021
Description
Thermal management is a critical aspect of microelectronics packaging and often centers around preventing central processing units (CPUs) and graphics processing units (GPUs) from overheating. As the need for power going into these processors increases, so too does the need for more effective thermal management strategies. One such strategy is to utilize additive manufacturing to fabricate heat sinks with bio-inspired and cellular structures and is the focus of this thesis. In this study, a process was developed for manufacturing the copper alloy CuNi2SiCr on the 100w Concept Laser Mlab laser powder bed fusion 3D printer to obtain parts that were 94% dense, while dealing with challenges of low absorptivity in copper and its high potential for oxidation. The developed process was then used to manufacture and test heat sinks with traditional pin and fin designs to establish a baseline cooling effect, as determined from tests conducted on a substrate, CPU and heat spreader assembly. Two additional heat sinks were designed, the first of these being bio-inspired and the second incorporating Triply Periodic Minimal Surface (TPMS) cellular structures, with the aim of trying to improve the cooling effect relative to commercial heat sinks. The results showed that the pure copper commercial pin-design heat sink outperformed the additive manufactured (AM) pin-design heat sink under both natural and forced convection conditions due to its approximately tenfold higher thermal conductivity, but that the gap in performance could be bridged using the bio-inspired and Schwarz-P heat sink designs developed in this work and is an encouraging indicator that further improvements could be obtained with improved alloys, heat treatments and even more innovative designs.
ContributorsYaple, Jordan Marie (Author) / Bhate, Dhruv (Thesis advisor) / Azeredo, Bruno (Committee member) / Phelan, Patrick (Committee member) / Arizona State University (Publisher)
Created2021
Description
Automation has become a staple in high volume manufacturing, where the consistency and quality of a product carries as much importance as the quantity produced. The Aerospace Industry has a vested interest in expanding the application of automation beyond simply manufacturing. In this project, the process of systems engineering has been applied to the Conceptual Design Phase of product development; specifically, the Preliminary Structural Design of a Composite wing for an Unmanned Air Vehicle (UAV). Automated structural analysis can be used to develop a composite wing structure that can be directly rendered in Computer Aided Drafting (CAD) and validated using Finite Element Analysis (FEA). This concept provides the user with the ability to quickly iterate designs and demonstrates how different the “optimal light weight” composite structure must look for UAV systems of varied weight, range, and flight maneuverability.
ContributorsBlair, Martin Caceres (Author) / Takahashi, Timothy (Thesis advisor) / Murthy, Raghavendra (Committee member) / Perez, Ruben (Committee member) / Arizona State University (Publisher)
Created2021
Description
The way a granular material is transported and handled plays a huge part in the quality of final product and the overall efficiency of the manufacturing process. Currently, there is a gap in the understanding of the basic relationship between the fundamental variables of granular materials such as moisture content, particle shape and size. This can lead to flowability issues like arching and ratholing, which can lead to unexpected downtimes in the whole manufacturing process and considerable wastage of time, energy, and resources. This study specifically focuses on the development of a model based on the surface mean diameter and the moisture content to predict the flow metric flow function coefficient (FFC) to describe the nature of flow of the material. The investigation involved three parts. The first entailed the characterization of the test materials with respect to their physical properties - density, size, and shape distributions. In the second, flowability tests were conducted with the FT4 Powder Rheometer. Shear cell tests were utilized to calculate each test specimen's flow function parameters. Finally, the physical properties were correlated with the results from the flowability tests to develop a reliable model to predict the nature of flow of the test specimens. The model displayed an average error of -6.5%. Predicted values showed great correlation with values obtained from further shear cell tests on the FT4 Rheometer. Additionally, particle shape factors and other flowability descriptors like Carr Index and Hausner Ratio were also evaluated for the sample materials. All size ranges displayed a decreasing trend in the values of Carr Index, Hausner Ratio, and FFC with increasing moisture percentages except the 5-11 micron glass beads, which showed an increasing trend in FFC. The results from this investigation could be helpful in designing equipment for powder handling and avoiding potential flowability issues.
ContributorsDeb, Anindya (Author) / Emady, Heather (Thesis advisor) / Marvi, Hamidreza (Committee member) / Jiao, Yang (Committee member) / Arizona State University (Publisher)
Created2021