Engineering Science and Materials Commons^™

Development Of Advanced Polymer Nanocomposite Capacitors, Miguel Mendoza

Open Access Theses & Dissertations

The current development of modern electronics has driven the need for new series of energy storage devices with higher energy density and faster charge/discharge rate. Batteries and capacitors are two of the most widely used energy storage devices. Compared with batteries, capacitors have higher power density and significant higher charge/discharge rate. Therefore, high energy density capacitors play a significant role in modern electronic devices, power applications, space flight technologies, hybrid electric vehicles, portable defibrillators, and pulse power applications. Dielectric film capacitors represent an exceptional alternative for developing high energy density capacitors due to their high dielectric constants, outstanding breakdown voltages, …

Hafnia-Based Nanostructured Thermal Barrier Coatings For Next Generation Gas Turbine Technology, Mohammed Noor-A-Alam

Open Access Theses & Dissertations

Extensive efforts have been directed in the last several decades towards improving thermodynamic efficiency of industrial gas turbines for power generation plants. The central theme of the efforts is to increase the turbine operating temperature and, thus, allowing higher efficiency. Thermal barrier coatings (TBC) constitute an advanced technology to protect the metallic surface from high temperature exposure for long time operation. The TBCs protect the gas turbine components from high temperature and allows further increase in engine operating temperature which subsequently increases the efficiency of the gas turbine power plant. However, the current TBC materials are capable of allowing the …

Applications Of Density Functional Theory In Materials Science And Engineering, Manuel Alvarado

Open Access Theses & Dissertations

Density Functional Theory (DFT) is a powerful tool that can be used to model various systems in materials science. Our research applies DFT to two problems of interest. First, an organic/inorganic complex dye system known as a Mayan pigment is modeled to determine chemical binding sites, verifying each model with physical data such as UV/Vis spectra. Preliminary studies on palygorskite-based mayan pigments (mayacrom blue, mayacrom purple) show excellent agreement with experimental studies when using a dimer dye geometry binding with tetrahedrally-coordinated aluminum impurity sites in palygorksite. This approach is applied to a sepiolite-based organic/inorganic dye system using thioindigo attached to …

Raman And Infrared Study Of Electrospun Plla/Pcl Nanofiber Blends For Use In Tissue Engineering, Jose Luis Enriquez Carrejo

Open Access Theses & Dissertations

Recently, the biomedical engineering field has developed at a very fast pace as improved techniques and materials become available to promote its growth. Consequently, the research in polymeric biomaterials has been highly stimulated by this trend. The goal of the current research is to demonstrate the usefulness of the Raman scattering, Raman mapping, and infrared absorption spectroscopies to tissue engineering, by spectroscopically characterizing blends of PLLA and PCL polymers, which were prepared by electrospinning with and without cell addition. The proposed use of these blends is as primary biomaterials in biodegradable scaffolds used in tissue engineering. Both Raman and infrared …

Development Of A Multi-Material, Multi-Technology Fdm System For Process Improvement Experimentation, David Espalin

Open Access Theses & Dissertations

Over the last three decades, developments within the area of Additive Manufacturing (AM) have resulted in novel technologies capable of producing highly customized, complex part geometries in a fraction of the lead time required by traditional manufacturing methods (e.g., injection molding, metal casting). In particular, fused deposition modeling (FDM), a material extrusion AM process, can produce parts using production-grade thermoplastics like acrylonitrile butadiene styrene, polycarbonate, and polyetherimide. Additionally, non-commercial materials (e.g., polycaprolactone, ceramic loaded polymers, carbon nanotube loaded polymers) have been processed using FDM in part to demonstrate the potential diversity in material selection.

Recently, a myriad of personal 3D …

The Effect Of Al And B Additions On The Oxidation Behavior Of Alloys From The Nb-Cr-Si System, Nydia Judit Esparza

Open Access Theses & Dissertations

Nickel based superalloys have been developed to perform substantially in industry however as technology develops, the need and desire to increase service temperatures to improve efficiency and performance is pushing the capabilities of these alloys. These aspired requirements entail the research and development of new structural materials that surpass the abilities of nickel alloys. Research in Nb-based alloys is underway as Nb alloys have shown to be a promising alternative with similar density but higher melting temperatures than the Ni alloys. However, because Nb has poor oxidation properties extensive studies are necessary to develop an alloy that can perform as …

A Study Of Wo3 And W0.95ti0.05o3 Thin Films Using Comparative Spectroscopy, James Heyward Howard

Open Access Theses & Dissertations

Tungsten oxide (WO3) is important and well-studied in materials science, particularly for sensor applications. In this research work, we consider the innovation of adding Ti to thin films of this material. Since the characteristics of any such material are strongly dependent on the conditions and methods used in its deposition, the main objective of this project is to provide a detailed spectroscopic characterization by Raman scattering, infrared absorption, and X-ray photoelectron spectroscopy (XPS) of WO3 and of W0.95Ti0.05O3. This characterization will be based on comparison of the morphology and composition of WO3-based thin films, grown by radio frequency magnetron reactive …

Development Of Nanocomposites For Energy Storage Devices, Md Ashiqur Rahaman Khan

Open Access Theses & Dissertations

With the ever-increasing need in improving the performance and operation life of future mobile devices, developing higher power density energy storage devices has been receiving more attention. Lithium ion battery (LIB) and capacitor are two of the most widely used energy storage devices and have attracted increasing interest from both industrial and academic fields. Batteries have higher power density than capacitor but significantly longer charge/discharge rates. In order to further improve the performance of these energy storage devices, one of the approaches is to use high specific surface area nano-materials. Among all the nano-materials developed so far, one-dimensional nanowires are …

Nanoprobe I-V Characterization Of Cdte/Cds Micro And Nano-Patterned Solar Cells, Heber Prieto

Open Access Theses & Dissertations

This thesis presents a novel way to characterize micro and nano patterned cadmium telluride thin film solar cells via a nano-probe system. A historical review of CdTe-based solar cells is presented first followed by review of the technology developed to produce the patterned CdTe cells. A detailed presentation is then provided on the use of a Zyvex nanoprobing system to characterize the patterned solar cells. The I-V response of micro- and nano-patterned solar cells stimulated under different e-beam conditions is presented and analyzed. Suggestions of how to improve the technique are provided. This work documents, for the first time, the …

The Influence Of Build Parameters On The Microstructure During Electron Beam Melting Of Ti6al4v, Karina Puebla

Open Access Theses & Dissertations

With the demand of devices to replace or improve areas, such as: electronic, biomedical and aerospace industries. Improvements in these areas of engineering have been in need due to the customer’s needs for product properties requirements. The design of components must exhibit better material properties (mechanical or biocompatible) close to those of any given product. Rapid prototyping (RP) technologies that were originally designed to build prototypes may now be required to build functional end-use products. To carry out the transition, from RP to rapid manufacturing (RM), the available materials utilized in RP must provide the performance required for RM. The …

Oxidation Of Borides And Carbides With Y2o3 And Ta Additions, Salvador Manuel Rodriguez

Open Access Theses & Dissertations

The study presented here describes an investigation of an oxidation scale of a fully-sintered Y2O3-ZrB2-TiC composite exposed in air at 1173K. Upon oxidation of the boride/carbide, a ZrO2-TiO2 was expected to form similar to the ZrO2-SiO2 dual scale of an oxidized ZrB2-SiC. The 47wt% Y2O3-38wt%ZrB2-16wt%TiC composite formed a dual scale consisting primarily of an Y2O3-ZrO2-TiC inner scale with an outer scale of ZrO2-TiO2-Y2O3.

The samples oxidized with a parabolic layer growth allowing the calculation of the effective diffusion coefficient indicating that the oxidation was controlled by oxygen ingress through primarily the ZrO2-Y2O3 phase. The oxygen potential between the inner layer …

A Basic Understanding Of Rapid Mold Surface Heating Via Laser Energy, Charles Daniel Fox

Browse all Theses and Dissertations

As the research and development of surface heating methods have increased in the recent years, the consensus has been reached amongst the injection molding community that an elevated mold surface temperature near or greater than the polymer solidification temperature provides acceptable replication of the desired micro-structured parts. The laser heating experimental work and simulation development carried out includes two sample sizes similar to those used in injection molding. A 100W CO2 laser incident on three samples of different surface roughnesses has shown to have elevated temperatures via thermal cameral data and thermocouple measurements. Among five different laser spot sizes varying …

Key Factors Influencing The Structure And Electrochemical Performances Of Lifepo4 Via Sol-Gel Synthesis, Chuang Guan

Browse all Theses and Dissertations

Olivine structured LiFePO4 is a promising cathode material for the next generation of lithium ion batteries for its low cost, environmental benign, good cycling performance and safety, etc. However, its intrinsic poor electrical conductivity and diffusion capability of lithium ion greatly hinder its application in the high power recharge battery. In this research, a cost-effective sol-gel method was used to synthesize carbon coated LiFePO4 (LiFePO4/C) materials. The influences of the synthesis parameters, including the species of iron source, lithium content, chelating agents and carbon sources, PH value of the sol, and sintering conditions etc., on the structure and electrochemical properties …

Isothermal Deformation And Modeling Of Ti-6al-4v, Vamsi Krishna Vempati

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Ti-6Al-4V has attractive properties such as high strength to weight ratio, good fatigue properties and excellent corrosion resistance and these properties have made this alloy an important material for the aerospace industry. In this thesis, the deformation behavior of Ti-6Al-4V with several processing histories, was studied by conducting isothermal constant strain rate compression tests over a temperature range of 829°C to 996°C (1525°F to 1825°F) and at strain rates of 10-2 s-1, 10-1 s-1 and 100 s-1. True stress versus true strain flow curves showed a peak stress followed by flow softening. The data was analyzed to obtain constitutive equations …

Modeling The Exfoliation Rate Of Graphene Nanoplatelet Production And Application For Hydrogen Storage, Cory Knick

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Graphene is a unique and revolutionary new nanomaterial. A method for it's production had a U.S. patent application in 2002 (patent issued in 2006), it was produced via mechanical exfolia-tion in 2004, and subsequently the Nobel Prize in Physics was awarded in 2010 for it. These events have sparked a surge of graphene-related research. In order for graphene to be widely studied and incorporated into emerging technologies, a versatile method for large scale produc-tion of high-quality graphene is required. Current methods are either slow or expensive which limits the scale-up of graphene production. Very recently, the liquid phase exfoliation of …

Coupled Electromagnetic And Heat Transfer Model For Microwave Heating In Domestic Ovens, Krishnamoorthy Pitchai, Sohan Birla, Jeyamkondan Subbiah, D. D. Jones, Harshanardhan Thippareddi

Department of Food Science and Technology: Faculty Publications

Microwave ovens are used extensively for heating a variety of not-ready-to-eat food products. Non-uniform heating of foods in microwave ovens is a major concern in assuring microbiological safety of such products. The non-uniform heating of foods is attributed by complex interaction of microwaves with foods. To understand this complex interaction, a comprehensive model was developed to solve coupled electromagnetic and heat transfer equations using finite-difference time-domain based commercial software. The simulation parameters, cell size, heating time step, and number of iterations for steady state electromagnetic field were optimized. The model was validated by 30 s heating profile of a cylindrical …

Moisture Damage Characterization Of Warm-Mix Asphalt Mixtures Based On Laboratory-Field Evaluation, Yong-Rak Kim, Jun Zhang, Hoki Ban

Department of Mechanical and Materials Engineering: Faculty Publications

This study presents laboratory evaluation integrated with field performance to examine two widely used warm-mix asphalt (WMA) approaches—foaming and emulsion technology. For a more realistic evaluation of the WMA approaches, trial pavement sections of the WMA mixtures and their counterpart hot-mix asphalt (HMA) mixtures were implemented in Antelope County, Nebraska. Field-mixed loose mixtures collected at the time of paving were transported to the laboratories to conduct various experimental evaluations of the individual mixtures. Among the laboratory tests, three (two conventional and one newly attempted) were performed to characterize moisture damage potential which is the primary focus of this study. From …

Monitoring The Wall Mechanics During Stent Deployment In A Vessel, Brian Steinert, Shijia Zhao, Linxia Gu

Department of Mechanical and Materials Engineering: Faculty Publications

Clinical trials have reported different restenosis rates for various stent designs . It is speculated that stentinduced strain concentrations on the arterial wall lead to tissue injury, which initiates restenosis . This hypothesis needs further investigations including better quantifications of non-uniform strain distribution on the artery following stent implantation. A non-contact surface strain measurement method for the stented artery is presented in this work. ARAMIS stereo optical surface strain measurement system uses two optical high speed cameras to capture the motion of each reference point, and resolve three dimensional strains over the deforming surface. As a mesh stent is deployed …

Thickness-Shear And Thickness-Twist Modes In An Oblate Elliptical Ceramic Cylinder And Energy Trapping In Contoured Acoustic Wave Resonators, Huijing He, Jiashi Yang, Yi-Hua Huang

Department of Mechanical and Materials Engineering: Faculty Publications

We study shear-horizontal motions of a piezoelectric ceramic cylinder with an oblate elliptical cross section and axial poling. Exact thickness-shear and thickness-twist vibration modes are obtained. These modes show energy trapping, i.e., the vibration is mainly confined near the thick, central region and decays to almost nothing near the edges. The results are useful for the understanding and design of contoured piezoelectric resonators for strong energy trapping.

Systems And Synthetic Biology Of The Vessel Wall, Jennifer Frueh, Nataly Maimari, Ying Lui, Zoltan Kis, Vikram Mehta, Negin Pormehr, Calum Grant, Emmanuel Chalkias, Mika Falck-Hansen, Sandra Bovens, Ryan M. Pedrigi, Taka Homma, Gianfillippo Coppola, Rob Krams

Department of Mechanical and Materials Engineering: Faculty Publications

Atherosclerosis is intimately coupled to blood flow by the presence of predilection sites. The coupling is through mechanotransduction of endothelial cells and approximately 2000 gene are associated with this process. This paper describes a new platform to study and identify new signalling pathways in endothelial cells covering an atherosclerotic plaque. The identified networks are synthesized in primary cells to study their reaction to flow. This synthetic approach might lead to new insights and drug targets.