Engineering Commons^™

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 …

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 …

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 …

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 …

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 …

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 …

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 …

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 …

Tribological Behavior Of Austenitic Stainless Steel And Vanadium Carbide Coated By Trd Process, C. Lertlummeechai, P. Sricharoenchai

Journal of Metals, Materials and Minerals

In forming austenitic stainless steel sheet, galling is the major cause of tool steels failure. Coating on tool surface is an effective way to lessen galling tendency. In this paper, vanadium carbide coating by TRD process was conducted on tool steel and intentionally tempered in air to produce thicker vanadium oxide on vanadium carbide surface. Ring-on-disc wear test was conducted by sliding with austenitic stainless steel ring to investigate tribological behavior. Weight of ring was measured before and after wear tests. Chemical composition of ring surface was crosssection analyzed by EPMA. Surface of the disc was analyzed by XPS. Wear …

Preparation Of Organosilane Treated Microcrystalline (Simcc) And Simcc/Polypropylene Composites, P. Thummanukitcharoen, S. Limpanart, K. Srikulkit

Journal of Metals, Materials and Minerals

In this study, the silane treated microcrystalline cellulose (SiMCC)/polypropylene composite was prepared. In the first step, the surface modification of microcrystalline cellulose (MCC) with various concentrations of hexadecyltrimethoxysilane was carried-out in order to obtain the SiMCC having good compatibility with PP matrix. Characterizations including SEM, FT-IR, TGA and DSC were employed to analyze the structure of SiMCC. SEM revealed that MCC surface morphology was changed from rod shape into rough particles after silane treatment. In the next step, the obtained SiMCC was mixed with PP powder using twin-screw extruder. Based on TGA results, it was found that the addition of …

Low-Cycle Fatigue Of Thermally-Cycled Carbon-Epoxy Composite, Ya. B. Unigovski, A. Grinberg, E. M. Gutman, R. Shneck

Journal of Metals, Materials and Minerals

Investigation of low-cycle fatigue of composites is of vital importance for the design of structural components. In this study, the effects of thermal cycling on low-cycle fatigue behavior of carbon-epoxy laminate are investigated in a purely bending mode at strain ratios of -1 and 0.1. It is found that a very small increase in the plastic strain amplitude catastrophically shortens the fatigue life N of the composite determined as a number of cycles corresponding to 0.9 of the initial force. The preliminary thermal cycling of the composite at the temperature varied from 180°C to −195.8°C shortens N values in comparison …

Three-Body-Type Abrasive Wear Behavior Of 26% Cr Cast Iron With Molybdenum, A. Chooprajong, P. Sricharoenchai, S. Inthidech, Y. Matsubara

Journal of Metals, Materials and Minerals

Hypoeutectic 26 wt% Cr cast irons without and with Mo were prepared in order to investigate their abrasion wear resistance. The annealed specimens were hardened from 1323 K (As-H) and then tempered at three levels of temperatures between 673 and 823 K for 7.2ks, the temperature giving the maximum hardness (HTmax), lower temperature than that at HTmax (L-HTmax ) and higher temperature than that at HTmax (H-HTmax). The abrasive wear resistance was evaluated using Rubber Wheel abrasion test (three-body-type). It was found that hardness and volume fraction of retained austenite (V) in the heat-treated specimens varied with the Mo content …

The Oxidation Behaviour Of Stainless Steel Aisi 409 Coated By Decorative Nickel-Chromium Plating, T. Wongpinij, T. U-Dom, T. Suptrakun, T. Puttanasun, C. Pimpan, N. Nangnoi, P. Wongpanya

Journal of Metals, Materials and Minerals

The continuous and cyclic oxidation behaviour of ferritic stainless steel AISI 409 surfacecoated by decorative nickel-chromium plating was studied. Firstly, the plated AISI 409 steel samples were cut into rectangular pieces of 20x10x3 mm. Nickel plating was electroplated with various times, i.e., 0, 5, 10 and 15 minutes; subsequently the decorative chromium plating was performed for 5 minutes. Then, the samples were exposed to 200ºC and 300ºC. The degradation of samples was evaluated by considering weight alteration after oxidation test. The oxidation product and surface of samples were characterized by optical microscope and scanning electron microscope (SEM) with energy dispersive …

Failure Analysis Of Bearings In Air Conditioning Compressor, P. Promdirek, A. Leidig, T. Keawjarus, P. Tong-In

Journal of Metals, Materials and Minerals

Two journal bearings of a compressor were failed in service. The wear which led to crack was observed at the internal surface of both bearings. The objective of this analysis is to evaluate the reason for the wear found on the internal bearings surface. Two bearings were returned from field and others in several conditions were examined. Electron probe micro analyzer and microhardness was used for metallurgical analysis. It revealed that bearing consisted of two different layers: 1) Fe-base and 2) Al-Sn alloy. Surface worn at the internal surface which composed of Al-Sn alloy was found. The results also showed …

Corrosion Behavior Of Aisi 4140 Steel Surface Coated By Physical Vapor Deposition, C. Keawhan, P. Wongpanya, N. Witit-Anun, P. Songsiriritthigul

Journal of Metals, Materials and Minerals

The corrosion behavior of uncoated and CrN-coated onto AISI 4140 steel was studied by electrochemical technique. Firstly, the AISI 4140 steel samples were solution heat treated and oil quenched in order to achieve proper hardness. Then, they were surface-prepared with alteration of surface roughness by using SiC paper at different numbers of 180, 600, and 1200 prior to CrN coating. The samples were coated with CrN film by physical vapor deposition (PVD) technique. The corrosion behavior of the uncoated and CrN-coated samples was studied in air-saturated 3.5 wt% NaCl solution at the pH values of 2, 7 and 10 at …

A Micromechanical Flow Curve Model For Dual Phase Steels, S. Sodjit, V. Uthaisangsuk

Journal of Metals, Materials and Minerals

In the automotive industries, Dual Phase (DP) steels have become a favoured material for the car body parts due to their excellent combination of high strength and good formability. A microstructure of DP steel generally consists of a matrix of ferrite reinforced by small islands of martensite. Experimental investigations showed that effects of martensite phase fraction, morphology, and phase distribution play an important role for the mechanical and fracture behaviours of the dual phase steel. In the present work, an approach concerning FE based modelling for predicting flow curve of DP steels has been introduced using a Representative Volume Element …

Porous Niti Produced By Nitita Transient-Liquid-Assisted Method, O. Worasub, A. Bansiddhi

Journal of Metals, Materials and Minerals

This work presents a novel method for preparing porous NiTi by powder metallurgy using a vacuum sintering technique. Tantalum was used as a transient liquid phase creator, which enhanced the sinterability of NiTi powders. The effect of Ta content and powder packing on the degree of densification were investigated. The porous NiTi exhibited shape memory behavior and a large recovery strain, analyzed by differential scanning calorimetry and compressive testing, respectively, making the material promising for bone implant applications. In addition, macroporosity was created by using NaCl spaceholders. Adding 3 atomic percent of Ta and 60 volume percent NaCl space-holder resulted …

Nr/Xsbr Nanocomposites With Carbon Black And Carbon Nanotube Prepared By Latex Compounding, A. Boonmahitthisud, S. Chuayjuljit

Journal of Metals, Materials and Minerals

Two series of natural rubber/carboxylated styrene butadiene rubber (NR/XSBR) (80/20) nanocomposites containing different loadings of carbon black (CB) (3-9 phr) and carbon nanotube (CNT) (0.1-0.4 phr) have been prepared by a latex stage compounding method. Before mixing with NR/XSBR blended latex, CB and CNT were dispersed and stabilized in water by ball milling with the aid of surfactant. The obtained compounded latex was cast into sheet on a glass mold and thereafter cured in an oven at 80°C for 3 h. The tensile properties (tensile strength, modulus at 300% strain, elongation at break), dynamic mechanical properties (loss tangent, storage modulus) …

Effects Of Rare-Earth Doping On Femtosecond Laser Waveguide Writing In Zinc Polyphosphate Glass, Luke B. Fletcher, Jon J. Witcher, Neil Troy, Signo Tadeu Dos Reis, Richard K. Brow, Denise M. Krol

Materials Science and Engineering Faculty Research & Creative Works

We have investigated waveguide writing in Er-Yb doped zinc polyphosphate glass using a femtosecond laser with a repetition rate of 1 KHz. We find that fabrication of good waveguides requires a glass composition with an O/P ratio of 3.25. The dependence on laser writing parameters including laser fluence, focusing conditions, and scan speed is reported. Waveguide properties together with absorption and emission data indicate that these glasses can be used for the fabrication of compact, high gain amplifying devices.

Spin Diffusion In Bulk Gan Measured With Mnas Spin Injector, Shafat Jahangir, Fatih Dogan, Hyun Kum, Aurelien Manchon, Pallab Bhattacharya

Materials Science and Engineering Faculty Research & Creative Works

Spin injection and precession in bulk wurtzite n-GaN with different doping densities are demonstrated with a ferromagnetic MnAs contact using the three-terminal Hanle measurement technique. Theoretical analysis using minimum fitting parameters indicates that the spin accumulation is primarily in the n-GaN channel rather than at the ferromagnet (FM)/semiconductor (SC) interface states. Spin relaxation in GaN is interpreted in terms of the D'yakonov-Perel mechanism, yielding a maximum spin lifetime of 44 ps and a spin diffusion length of 175 nm at room temperature. Our results indicate that epitaxial ferromagnetic MnAs is a suitable high-temperature spin injector for GaN.

Diamond This Film Patterning Technique Using Selective Nucleation Growth, Characterization And Application, Weican Xiao

Electrical & Computer Engineering Theses & Dissertations

Diamond is the hardest bulk material with the highest thermal conductivity. It is also an excellent wide band gap material; hence, diamond is suitable for electronic, mechanical and biological applications. Unfortunately, natural diamond is prohibitively expensive for most technological applications. Polycrystalline diamond, with properties close to those of natural diamond, has been synthesized since the 1950s. Among many methods employed for diamond thin film synthesis, chemical vapor deposition (CVD) using microwave plasma (MW) is quite popular for several reasons. Well-confined plasma that does not touch the reaction chamber walls can be produced directly on the substrate. Hence, contamination in the …

Multidentate Resorcinarene Surfactants For The Phase Transfer Of Metal Nanoparticles And Nanodiamonds: Applications In Catalysis And Diamond Film Growth, Vara Prasad Sheela

Chemistry & Biochemistry Theses & Dissertations

One main objective of the present work is to functionalize cuboctahedral platinum nanoparticles with various multidentate resorcinarene surfactants and study their influence in determining their catalytic activity. We hypothesized that catalytically active and recyclable catalysts can be achieved by incomplete yet strong passivation of the nanoparticle surfaces by using multidentate resorcinarene surfactants. We have developed phase transfer protocols for functionalizing cuboctahedral platinum nanoparticles with resorcinarene thiol or amine. Fluorescence assay confirmed that both these nanoparticles contained almost comparable unpassivated metal area. The activity of such phase transferred nanoparticles was tested in the catalytic hydrogenation of allyl alcohol. The conversion of …