Engineering Commons^™

Heterogeneous Anisotropy Index And Scaling In Multiphase Random Polycrystals, Muhammad Ridwan Murshed

Theses and Dissertations

Under consideration is the finite-size scaling of elastic properties in single and two-phase random polycrystals with individual grains belonging to any crystal class (from cubic to triclinic). These polycrystals are generated by Voronoi tessellations with varying grain sizes and volume fractions. By employing variational principles in elasticity, we introduce the notion of a 'Heterogeneous Anisotropy Index' and investigate its role in the scaling of elastic properties at finite mesoscales. The index turns out to be a function of 43 variables, 21 independent components for each phase and the volume fraction of either phase. Furthermore, the relationship between Heterogeneous Anisotropy Index …

Real-Time, Selective Detection Of Heavy Metal Ions In Water Using 2d Nanomaterials-Based Field-Effect Transistors, Guihua Zhou

Theses and Dissertations

Excessive intake of heavy metals damages the central nervous system and causes brain and blood disorders in mammals. Heavy metal contamination is commonly associated with exposure to mercury, lead, arsenic, and cadmium (arsenic is a metalloid, but classified as a heavy metal). Traditional methods to detect heavy metal ions include graphite furnace atomic absorption spectroscopy (GFAAS), inductively-coupled plasma optical emission spectroscopy (ICP-OES), and inductively-coupled plasma mass spectroscopy (ICP-MS). Recently, many new methods have been proposed to detect heavy metal ions, including atomic absorption spectrometry, fluorescent sensors, colorimetric sensors, electrochemical sensors, X-ray absorption fine structure spectroscopy, ultrasensitive dynamic light scatting assays, …

Surface Alloying Of Plain-Carbon Steels During The Casting Manufacturing Process, Michael Beining

Theses and Dissertations

At times, the surface properties of an engineered component must be improved or enhanced when compared to the bulk of the component. Thus, various methods of surface alloying, one of the most important surface engineering processes, have been studied and developed for the decades. This study is concerned with the modification of the surface of WCB plain-carbon steel to improve corrosion and wear resistance of components used in the fresh water industry. The objective is to create a corrosion and wear resistant surface on an engineered component by enriching the surfaces with nickel or nickel and chromium, while the bulk …

Effects Of Electrolyte Formulation On Graphite Anode For Wide Temperature Application, Jeremy Chang

Theses and Dissertations

In this study, we demonstrate that the low temperature power capability of a Li-ion battery can be substantially improved not by adding exotic additives into the electrolyte, but by rational design of the composition of the most commonly used solvents. Through the detailed analysis with electrochemical impedance spectroscopy, the formation of a homogenous solid electrolyte interphase (SEI) layer on the carbon anode surface is critical to ensure the performance of a Li-ion battery in a wide temperature range. Subsequent post mortem analysis after cycling of the negative electrode by XPS revealed that all the electrolyte compositions form similar compounds in …

Polymer Foam /Fly Ash Composites: Evaluation Of Mechanical, Interfacial, Thermal, Viscoelastic And Microstructural Properties, Parisa Khoshnoud

Theses and Dissertations

Fly ash, a byproduct of coal combustion process in power plants, consists of fine, powdery particles that are predominantly spherical in shape, either solid or hollow, and mostly glassy (amorphous) in nature. It is capable of being recovered and used as a low-cost reinforcing filler. Adding fly ash particles to a thermoplastic foam poses many challenges to understanding the physical, mechanical, viscoelastic, thermal, and morphological changes to the composite. The effects of fly ash particles on the foaming process; e.g. nucleating and growth steps, cell types and size, and microstructure need to be evaluated in order to develop a commercial …

High Temperature Oxidation And Metal Dusting Resistance Of Traditional Iron-Based And Novel Alumina Forming Austenitic Alloys, Wen-Chieh Lee

Theses and Dissertations

Metal dusting is a catastrophic form of corrosion and carburization, and is a disintegration of alloys into a dust of metal particles, oxides and graphite deposition products. Metal dusting and related coking phenomenon happen in industrial fields where carburizing syngas appears in the process. Metal dusting would cause damage in the form of pits and notches in pipes and other metallic equipment often causing a loss of production time or reduced component lifetimes. It is of great importance to prevent this corrosion from happening to the metal materials used by the industry.

To counter the corrosion, a new generation of …

Spacer Casting Method For Synthesis Of Magnesium Alloy Foam, Sara Karp

Theses and Dissertations

In this work, a new spacer material is developed for casting of magnesium foam. An ideal spacer material should meet the following requirements, would not react with magnesium, would withstand the melting temperature of magnesium, be easy to remove, be abundantly available and cost effective, hold its shape during infiltration, and be extrudable. The material that was found to meet these requirements was a mixture of calcium carbonate and flour that went through a heat treatment to yield a porous calcium oxide structure for infiltration. The new spacer material was extrudable and easily removed without harming the magnesium foam. Magnesium …

Analysis Of Zinc Oxide Thin Films Synthesized By Sol-Gel Via Spin Coating, Jon Carl Wolgamott

Theses and Dissertations

Abstract

Transparent conductive oxides are gaining an increasingly important role in optoelectronic devices such as solar cells. Doped zinc oxide is a candidate as a low cost and nontoxic alternative to tin doped indium oxide. Lab results have shown that both n-type and p-type zinc oxide can be created on a small scale. This can allow zinc oxide to be used as either an electrode as well as a buffer layer to increase efficiency and protect the active layer in solar cells.

Sol-gel synthesis is emerging as a low temperature, low cost, and resource efficient alternative to producing transparent conducting …

Coking Resistance Of Alumina Forming Cast Austenitic Stainless Steels, Lizeth Nayibe Ortiz Reyes

Theses and Dissertations

Coking is the process of carbon deposition from a gas phase that is encountered in many reforming, cracking and other high temperature processes. Coking in certain petrochemical processes can lead to carbon build up causing reduced process efficiency, corrosive attack and degradation of the alloy. Steam cracking of hydrocarbons is one of the most important process for manufacturing many base chemicals such as ethene, propene and other. A major influence on the energy efficiency and economics is the formation of coke on the inner wall of the reactors. With the accumulation of coke on the walls, eventually metallurgic constraints of …

Transient Nonlinear Optical Properties Of Thin Film Titanium Nitride, Sarahkatie Thomas

Theses and Dissertations

nitride (TiN) and scandium nitride (ScN), using the beam deflection characterization technique. The thin films were made at the Air Force Research Lab by controllably unbalanced magnetron sputtering. Transition metal nitrides, specifically TiN, are used widely in industry because of their unique properties, including extreme hardness and high damage threshold. The properties of thin film transition metal nitrites are dependent on the chemical structure of the thin film, which can be heavily influenced by substrate and deposition method. This durability and tunability is an asset in applications such as sensor protection and all optical computing. Two substrates, sapphire (Al_{2 …}

Analysis Of Additively Manufactured Lattice Structures Using Finite Element Methods, Christopher A. Box

Theses and Dissertations

Additive Manufacturing (AM) processes are well known for their ability to fabricate parts with complex geometries. Lattice structures leverage this ability to create parts with high strength-to-weight ratio and other desirable structural qualities. This research presents a parameterized modeling tool using common Finite Element Analysis (FEA) and scripting software with which aggregated lattice structures can be analyzed, given different geometric properties and loading conditions. A full factorial Design of Experiments is run to explore the effects of various parameters on the strength of lattice structures. Experimental compressive strength results from three FDM-produced PLA lattices are discussed and compared to predictions …

Creep Of Hi-Nicalon™ S Ceramic Fiber Tows At 900°C In Air And In Silicic Acid-Saturated Steam, Ronald K. Mitchell

Theses and Dissertations

Advanced SiC/SiC ceramic matrix composites (CMCs) are being considered for demanding aerospace applications such as aircraft engine hot-section components. In these applications the composites will be subjected to cyclic and sustained loadings at elevated temperature in aggressive combustion environments. Current aircraft engines employ Nickel-based superalloys in applications such turbine blades, where the metallic alloys must perform at or near their operating temperature limits in highly corrosive environments. The SiC/SiC composites, which offer low density, high strength and fracture toughness at elevated temperatures could potentially replace Nickel-based superalloy in aircraft engine applications. However, before the SiC/SiC composites can be safely used …

Optical Spectroscopy Of Wide Bandgap Semiconductor Heterostructures And Group-Iv Alloy Quantum Dots, Tanner A. Nakagawara

Theses and Dissertations

Efficient and robust blue InGaN multiple quantum well (MQW) light emitters have become ubiquitous; however, they still have unattained theoretical potential. It is widely accepted that “localization” of carriers due to indium fluctuations theoretically enhance their efficiency by moderating defect-associated nonradiative recombination. To help develop a complete understanding of localization effects on carrier dynamics, this thesis explores degree of localization in InGaN MQWs and its dependence on well thickness and number of wells, through temperature and power dependent photoluminescence measurements. Additionally, silicon-compatible, nontoxic, colloidally synthesizable 2-5 nm Ge_1-xSn_x alloy quantum-dots (QDs) are explored for potential visible to …

Synthesis, Characterization, And Enhanced Magnetic Properties Of Iron Carbide Nanomaterials, Brent M. Williams

Theses and Dissertations

Permanent magnets are classified as hard magnetic materials with the main purpose of generating flux for applications such as electric motors, turbines, and hard drives. High coercivity, magnetic remanence, and saturation values with high stability are some of the requirements for permanent magnets. Rare-earth magnets including neodymium and samarium based magnets are known to have superior magnetic properties due to their high magnetocrystalline anisotropy. However, due to the price of rare-earth materials development of alternate permanent magnets composed of inexpensive materials is an ongoing process. Previously cobalt carbide (Co_xC) have shown promise as a potential rare-earth free magnet …

Fabrication Of Flexible, Biofunctional Architectures From Silk Proteins, Ramendra K. Pal

Theses and Dissertations

Advances in the biomedical field require functional materials and processes that can lead to devices that are biocompatible, and biodegradable while maintaining high performance and mechanical conformability. In this context, a current shift in focus is towards natural polymers as not only the structural but also functional components of such devices. This poses material-specific functionalization and fabrication related questions in the design and fabrication of such systems. Silk protein biopolymers from the silkworm show tremendous promise in this regard due to intrinsic properties: mechanical performance, optical transparency, biocompatibility, biodegradability, processability, and the ability to entrap and stabilize biomolecules. The unique …

Engineering Icephobic Coatings: Surface Characterization Of Pt Cured Silicones, Sithara Shylaja Nair

Theses and Dissertations

Ice buildup on structures leads to problems that include reduced performance, structural damage and power outages. It is therefore important to limit the energy required for removal of ice from substrates to minimize buildup. Understanding the mechanism of ice adhesion and its dependence on variables like coating thickness, stiffness, surface free energy and morphology is critical for minimizing adhesion. Despite several developments in “icephobic” coatings, which are those that have low ice adhesion, it is important to understand adhesion on the fundamental level to make way for advanced coatings. To do so, a study has been carried out that explores …