Materials Science and Engineering Commons^™

Deformation And Adhesion Of Thin Metallic Films On Flexible Substrates, Julia Reid

All Theses

Flexible electronics are conductive circuits, components and lines integrated onto elastic substrates. These systems often consist of metallic thin films deposited onto thin sheets of glass, metals stainless steel or polymeric materials such as polyethylene or polystyrene. These systems are currently being studied for a wide variety of aeronautic and astronautical applications including: electronic skins, solar sails, and antennae structures. For applications include only moderately elevated temperatures (near 200 ¡C) and low strains (insert range), engineers have proposed incorporation metallic lines onto polymeric substrates. Like traditional microelectronic systems with films on hard substrates, the reliability is controlled by the film-substrate …

A Silicon Carbide Linear Voltage Regulator For High Temperature Applications, Javier Antonio Valle Mayorga

Graduate Theses and Dissertations

Current market demands have pushed the capabilities of silicon to the edge. High temperature and high power applications require a semiconductor device to operate reliably in very harsh environments. This situation has awakened interests in other types of semiconductors, usually with a higher bandgap than silicon's, as the next venue for the fabrication of integrated circuits (IC) and power devices. Silicon Carbide (SiC) has so far proven to be one of the best options in the power devices field.

This dissertation presents the first attempt to fabricate a SiC linear voltage regulator. This circuit would provide a power management option …

Semiconductor Nanocrystals: From Quantum Dots To Quantum Disks, Zheng Li

Graduate Theses and Dissertations

The bottom-up colloidal synthesis opened up the possibility of finely tuning and tailoring the semiconductor nanocrystals. Numerous recipes were developed for the preparation of colloidal semiconductor nanocrystals, especially the traditional quantum dots. However, due to the lack of thorough understanding to those systems, the synthesis chemistry is still on the empirical level. CdS quantum dots synthesis in non-coordinating solvent were taken as a model system to investigate its molecular mechanism and formation process, ODE was identified as the reducing agent for the preparation of CdS nanocrystals, non-injection and low-temperature synthesis methods developed. In this model system, we not only proved …

Probing And Controlling Fluid Rheology At Microscale With Magnetic Nanorods, Alexander Tokarev

All Dissertations

This Dissertation is focused on the development of new methods for characterization and control of fluid rheology using magnetic nanorods. This Dissertation consists of five chapters. In the first chapter, we review current microrheologial methods and develop a Magnetic Rotational Spectroscopy (MRS) model describing nanorod response to a rotating magnetic field. Using numerical modeling, we analyze the effects of materials parameters of nanorods and fluids on the MRS characteristic features. The model is designed for a specific experimental protocol. We introduce and examine physical parameters which can be measured experimentally. The model allows identification of MRS features enabling the calculation …

Elasto-Capillarity In Fibrous Materials, Daria Monaenkova

All Dissertations

Current advances in the manufacture of nanoporous and nanofibrous materials with high absorption capacity open up new opportunities for the development of fiber-based probes and sensors. Pore structures of these materials can be designed to provide high suction pressure and fast wicking. During wicking, due to the strong capillary action, the liquids exert stresses on the fiber network, thus the stressed state of dry and wet parts of the material differs. In this work the effect of stress reduction in fibrous materials due to the presence of wetting liquid in the pore structure is studied in details for both static …

Engineering Single-Molecule, Nanoscale, And Microscale Bio-Functional Materials Via Click Chemistry, Michael Daniele

All Dissertations

To expand the design envelope and supplement the materials library available to biomaterials scientists, the copper(I)-catalyzed azide-alkyne cycloaddition (CuCAAC) was explored as a route to design, synthesize and characterize bio-functional small-molecules, nanoparticles, and microfibers. In each engineered system, the use of click chemistry provided facile, bio-orthogonal control for materials synthesis; moreover, the results provided a methodology and more complete, fundamental understanding of the use of click chemistry as a tool for the synergy of biotechnology, polymer and materials science. Fluorophores with well-defined photophysical characteristics (ranging from UV to NIR fluorescence) were used as building blocks for small-molecule, fluorescent biosensors. Fluorophores …

Prediction Of The Wear & Evolution Of Cutting Tools In A Carbide / Ti-6al-4v Machining Tribosystem By Volumetric Tool Wear Characterization & Modeling, Mathew Kuttolamadom

All Dissertations

The objective of this research work is to create a comprehensive microstructural wear mechanism-based predictive model of tool wear in the tungsten carbide / Ti-6Al-4V machining tribosystem, and to develop a new topology characterization method for worn cutting tools in order to validate the model predictions. This is accomplished by blending first principle wear mechanism models using a weighting scheme derived from scanning electron microscopy (SEM) imaging and energy dispersive x-ray spectroscopy (EDS) analysis of tools worn under different operational conditions. In addition, the topology of worn tools is characterized through scanning by white light interferometry (WLI), and then application …

Conductivity Of Twin-Domain-Wall/Surface Junctions In Ferroelastics: Interplay Of Deformation Potential, Octahedral Rotations, Improper Ferroelectricity, And Flexoelectric Coupling, Eugene A. Eliseev, Anna N. Morozovska, Yijia Gu, Albina Borisevich, Long-Qing Chen, For Full List Of Authors, See Publisher's Website.

Materials Science and Engineering Faculty Research & Creative Works

Electronic and structural phenomena at the twin-domain-wall/surface junctions in the ferroelastic materials are analyzed. Carriers accumulation caused by the strain-induced band structure changes originated via the deformation potential mechanism, structural order parameter gradient, rotostriction, and flexoelectric coupling is explored. Approximate analytical results show that inhomogeneous elastic strains, which exist in the vicinity of the twin-domain-wall/surface junctions due to the rotostriction coupling, decrease the local band gap via the deformation potential and flexoelectric coupling mechanisms. This is the direct mechanism of the twin-wall static conductivity in ferroelastics and, by extension, in multiferroics and ferroelectrics. On the other hand, flexoelectric and rotostriction …

Dynamical Properties Of Ferroelectric Perovskites (Ba,Sr)Tio3 And Pb(Zr,Ti)O3 Systems From First Principles, Jeevaka Weerasinghe

Graduate Theses and Dissertations

A first-principles-based effective Hamiltonian scheme which incorporates coupling between ferroelectric (FE) and antiferrodistortive (AFD) motions is applied to Pb(Zr,Ti)O₃ alloys. It validates the existence of two modes of E symmetry (rather than the single E(1TO) soft mode) in the 50-75 cm^-1 range for temperatures smaller than 200 K and for compositions falling within the Rhombohedral R3c phase. Coupling between long-range-ordered FE and AFD motions is shown to be the cause of the additional mode and more insight into its nature is provided. This scheme is further used to reveal a field-induced anticrossing involving FE and AFD degrees of …

Atomistic Simulations Of Defect Nucleation And Intralayer Fracture In Molybdenum Disulphide During Nanoindentation, James A. Stewart

Graduate Theses and Dissertations

Molybdenum disulphide (MoS2) is a layered, hexagonal crystal that has a very low coefficient of friction. Due to this low coefficient of friction, MoS2 has become a well-known solid lubricant and liquid lubricant additive. As such, nanoparticles of MoS2 have been proposed as an additive to traditional liquid lubricants to provide frictional properties that are sensitive to different temperature and pressure regimes. However, to properly design these MoS2 nanoparticles to be sensitive to different temperature and pressure regimes, it is necessary to understand the mechanical response of crystalline MoS2 under mechanical loading. Specifically, the fundamental mechanism associated with the nucleation …

Measuring Ligand Exchange On The Surface Of Gold Nanoparticles: A Study Of Competitive Binding Of Ligands Utilizing Fluorescent Resonance Energy Transfer, Daniel D'Unger

All Theses

This study was conducted to track ligand exchange on the surface of metallic nanoparticles in order obtain a better understanding of binding strength of various functional groups. This study develops groundwork for further understanding ligand exchange as nanoparticles transition from engineered to natural systems. A problem exists in knowing the fate of these particles if they are released into natural systems, by accident or with intent. To gain a better understanding of what may occur we look at the binding strength of different ligands. This is done to gain knowledge of the possibility of displacement of ligands occurring in the …

Tribiology Of Engineered Surfaces In Aggressive Environments, Nathan Phillip Mitchell

All Theses

To improve the performance of sliding systems, surface modifications and coatings are often applied to opposing surfaces. This thesis focuses on characterizing two tribo-systems (DLC-DLC and steel micropatterns-flat) under their predicted application environments. The first section is focused on friction testing of micropatterned surfaces for orthopaedic device design, the second section elucidates how the sliding of diamond-like-carbon (DLC) coatings changes with temperature and humidity. The experimental design and major results of these sections are as follows.

(1) The use of micropatterning to create uniform surface morphologies has been cited as yielding improvements in the coefficient of friction during high velocity …

A Mean Curvature Model For Capillary Flows In Asymmetric Containers And Conduits, Yongkang Chen, Noël Tavan, Mark M. Weislogel

Mechanical and Materials Engineering Faculty Publications and Presentations

Capillarity-driven flows resulting from critical geometric wetting criterion are observed to yield significant shifts of the bulk fluid from one side of the container to the other during "zero gravity" experiments. For wetting fluids, such bulk shift flows consist of advancing and receding menisci sometimes separated by secondary capillary flows such as rivulet-like flows along gaps. Here we study the mean curvature of an advancing meniscus in hopes of approximating a critical boundary condition for fluid dynamics solutions. It is found that the bulk shift flows behave as if the bulk menisci are either “connected” or "disconnected." For the connected …

54th Rocky Mountain Conference On Analytical Chemistry

Rocky Mountain Conference on Magnetic Resonance

Final program, abstracts, and information about the 54th annual meeting of the Rocky Mountain Conference on Analytical Chemistry, co-endorsed by the Colorado Section of the American Chemical Society and the Society for Applied Spectroscopy. Held in Copper Mountain, Colorado, July 15-19, 2012.

Transition Of Deformation Behavior In An Ultrafine Grained Magnesium Alloy, S. K. Panigrahi, K. Kumar, N. Kumar, W. Yuan, R. S. Mishra, R. Delorme, B. Davis, R. A. Howell, K. Cho

Materials Science and Engineering Faculty Research & Creative Works

The deformation behavior of friction stirs processed magnesium alloy with average grain size ranging from 25 μm to 240 nm was studied. an evaluation of critical grain size for transition of deformation mode from twinning to slip was carried out by employing tensile and compressive tests. the role of critical grain size in transition of deformation behavior from strain hardening to softening was established. Inhomogeneous yielding was observed during tensile test of ultrafine-grained magnesium alloy below the critical grain size. © 2012 Elsevier B.V.

Rapid Oxidation Of Titanium And Its Alloys, Monica A. Cadena, Stephen Stafford

COURI Symposium Abstracts, Summer 2012

The tragedy of the Space Shuttle Columbia demonstrated the need for better understanding of materials in extreme environments. This study’s main objective was to provide more information about the behavior of materials, particularly Ti-6Al-4V, whenever conditions (such as temperature, pressure and behavior) change dramatically. The study included the microstructural analysis of Ti-6Al-4V samples that were exposed to conditions that approximate those encountered during re-entry by arc-jet experimentation. The analysis of these samples consisted of scanning electron microscopy and x-ray diffraction. The x-ray diffraction analysis showed the presence of several titanium oxides, such as Ti3-O and Ti6-O on different sections of …

Method For Producing Pressurelessly Sintered Zirconium Diboride/Silicon Carbide Composite Bodies, Shi C. Zhang, Greg Hilmas, William Fahrenholtz

Materials Science and Engineering Faculty Research & Creative Works

A method of sintering a ZrB₂-SiC composite body at ambient pressures, including blending a first predetermined amount of ZrB₂ powder with a second predetermined amount of SiC powder, wherein both powders are characterized by the presence of surface oxide impurities. Next the blended powders are mixed to yield a substantially homogeneous powder mixture and a portion of the substantially homogeneous powder mixture is formed into a green body. The body is fired to a first temperature, wherein substantially all surface oxide impurities are reduced and/or volatilized to substantially eliminate oxides from the green body, and the body …

Effect Of Disorder On Quantum Phase Transition In The Double Layered Ruthenates (Sr1−Xcax)3ru2o7effect Of Disorder On Quantum Phase Transition In The Double Layered Ruthenates (Sr1−Xcax)3ru2o7, Leonard Spinu, Zhe Qu, Jin Peng, Tijang Liu, David Forbes, Vkad Dobrosavljevic, Z Q. Mao

Physics Faculty Publications

(Sr_1−xCa_x)₃Ru₂O₇ is characterized by complex magnetic states, spanning from a long-range antiferromagnetically ordered state over an unusual heavy-mass nearly ferromagnetic (NFM) state to an itinerant metamagnetic (IMM) state. The NFM state, which occurs in the 0.4 > x > 0.08 composition range, freezes into a clusterspin glass (CSG) phase at low temperatures [Z. Qu et al., Phys. Rev. B 78, 180407(R) (2008)]. In this article, we present the scaling analyses of magnetization and the specific heat for (Sr_1−xCa_x)₃Ru₂O₇ in the 0.4 > x > 0.08 composition …

Corrosion Assessment Of Cast Aluminum Parts In Ethanol Fuel Blends, P. Wirot, J. Troset, W. Khonraeng, S. Mahabunphachai, E. Viyanit

Journal of Metals, Materials and Minerals

Nowadays, the use of ethanol fuel blends in automobiles has become more and more worldwide since the ethanol mixture would enhance the performance of the engine and fuel economy ($/mile), while reducing the hazardous exhaust released to the environment. However, the use of ethanol fuel blends may induce some material compatibility issues on some automotive parts that were not designed to be used in contact with ethanol. In other words, the humidity in the ethanol would cause corrosion problem on these parts. The goal of this study is to assess the corrosion value of two cast aluminum parts in a …

Extraction Of Tin From Hardhead By Oxidation And Fusion With Sodium Hydroxide, C Bunnakkha, C Jarupisitthorn

Journal of Metals, Materials and Minerals

In this research work, the extraction of tin from tin-iron alloy or hardhead which is the intermediate product obtained during tin smelting was investigated. The hardhead containing 32.40 wt% Sn and 45.81 wt% Fe was ground to different sizes and oxidized at 500 to 800 °C for 1 to 6 hours to form SnO2 and Fe2O3. The results indicated that an increase in oxidation temperature decreased the required oxidation time. However using too high oxidation temperature (800 °C) resulted in sintering of the oxide product.In sodium hydroxide fusion stage, effects of fusion temperature, fusion time, NaOH quantity and oxide product …