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Ice Adhesion Analysis Of Severely Aged Pdms Rubbers, Theodore R. Woll Aug 2018

Ice Adhesion Analysis Of Severely Aged Pdms Rubbers, Theodore R. Woll

Electronic Theses and Dissertations

The goal of this study was to evaluate and optimize the ice adhesion test initially developed by the University of Denver and to examine Polydimethylsiloxane (PDMS) based silicone rubbers for their ice-phobicity as a function of their physical and chemistry properties, and under severe oxidative aging. The test is based on an ice block bonded to a silicone rubber substrate and subjected to shear. In its original state, the test had severe limitations that caused the ice to be dislodged through a mixture of shear and peeling. Several steps were taken in this research to improve the test, and the ...


Defect Engineering: Novel Strengthening Mechanism For Low- Dimensional Zinc Oxide Nanostructures, Seyed Emad Rezaei Jan 2018

Defect Engineering: Novel Strengthening Mechanism For Low- Dimensional Zinc Oxide Nanostructures, Seyed Emad Rezaei

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The advent of nanomaterials has opened a new avenue for designing and fabricating materials with unique properties, e.g., superior mechanical properties. Based on a common notion, the perfect structures are assumed to exhibit better mechanical properties, such as higher yield strength and Young's modulus. Therefore, researchers have devoted an extensive amount of time to decrease defect concentration by fabricating materials with the micro/nanoscale, e.g., nanowires (NWs) and nanobelts (NBs), to enhance the mechanical characteristics of the system. However, defects are a part of the fabrication process and precise control over synthesizing procedure is needed to eliminate ...


Investigation Of Residual Stresses In Melt Infiltrated Sic/Sic Ceramic Matrix Composites Using Raman Spectroscopy, Kaitlin Noelle Kollins Jan 2017

Investigation Of Residual Stresses In Melt Infiltrated Sic/Sic Ceramic Matrix Composites Using Raman Spectroscopy, Kaitlin Noelle Kollins

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Ceramic matric composites (CMCs) are being developed for use in extreme operating conditions. Specifically, there is interest to replace superalloys with Silicon Carbide/Silicon Carbide (SiC/SiC) CMCs in the hot section of gas turbine engines because of their lower densities, high temperature performance, and oxidation resistance. Residual stresses in SiC/SiC CMCs are a direct result of the high temperature processing conditions, a mismatch in the coefficients of thermal expansion between composite constituents, and silicon crystallization expansion upon cooldown. Understanding the residual stress state and magnitudes of these stresses will enable better prediction of behavior and life performance in ...


Processing Of Ultra-Thin Film Of Un Modified C60 Fullerene Using The Langmuir-Blodgett Technique. Effect Of Structure On Stiffness And Optoelectric Properties, Hasanain Basim Altalebi Jan 2017

Processing Of Ultra-Thin Film Of Un Modified C60 Fullerene Using The Langmuir-Blodgett Technique. Effect Of Structure On Stiffness And Optoelectric Properties, Hasanain Basim Altalebi

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Monolayer films of C60 fullerene were for the first time produced successfully by using the Langmuir-Blodgett technique. The processing parameters were optimized and the structure of these films has been investigated using Scanning Tunneling Microscopy (STM) and Atomic Force Microscopy (AFM). Film stiffness was measured to be in the range of 15 MPa to 32 MPa depending on the nature of the solvent used to process the films. Optical transparency and electrical performance have been measured and correlated to the film structure. While 100% transparent, the film measured conductivity was in the range of 1013 S/m, that is orders ...


Friction Stir Welding Between Similar And Dissimilar Materials, Khaled Yousif Ali Jan 2017

Friction Stir Welding Between Similar And Dissimilar Materials, Khaled Yousif Ali

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This thesis focuses on the friction stir welding (FSW) between similar and dissimilar alloys. FSW is a solid state joining process that welds the work-pieces through a combination of heat generated by friction and mechanical stirring of the metals in the region of the joint. Being a solid state process, FSW can be used to weld alloys with significantly different melting points. This provides a significant benefit over traditional fusion welding process in a variety of applications in automotive, biomedical, aerospace, nuclear and petroleum industries. Two materials - an aluminum alloy (6061-T6, m.p. 582 - 652°C) and a steel (SAE ...


Studies Of Ionic Liquid Hybrids: Characteristics And Their Potential Application To Li-Ion Batteries And Li-Ion Capacitors, Mengxin Liu Jan 2017

Studies Of Ionic Liquid Hybrids: Characteristics And Their Potential Application To Li-Ion Batteries And Li-Ion Capacitors, Mengxin Liu

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Ionic liquids (ILs) have attracted much attention in electrochemical energy storage systems for their advantageous properties over traditional lithium salt/carbonate solvent electrolyte in terms of higher electrochemical potential windows, comparable ionic conductivity, negative vapor pressure and non-flammability. Ionic liquids can be used as the solvent-free electrolyte in electrochemical double layer capacitors (EDLCs) or can act as the important additives to the carbonate electrolyte in lithium ion batteries (LIBs). Recently, lithium ion capacitors (LICs) have emerge as a novel energy storage system to satisfy the demands for higher energy density and higher power density in portable and transportation systems. This ...


Synthesis And Characterizations Of Lithium Aluminum Titanium Phosphate (Li1+Xalxti2-X(Po4)3) Solid Electrolytes For All-Solid-State Li-Ion Batteries, Jianping Yang Jan 2017

Synthesis And Characterizations Of Lithium Aluminum Titanium Phosphate (Li1+Xalxti2-X(Po4)3) Solid Electrolytes For All-Solid-State Li-Ion Batteries, Jianping Yang

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New-generation low-emission transportation systems demand high-performance lithium ion (Li-ion) batteries with high safety insurance at broad operable temperatures. Highly conductive solid electrolyte is one of the key components for such applications. The objective of this thesis is to synthesize and characterize aluminum doped lithium titanium phosphate, i.e. Li1+xAlxTi2-x(PO4)3 (LATP), one of the solid-state electrolytes for potential applications to all solid-state lithium-ion batteries. In this research, sol-gel method and one step solid-state reaction approaches were explored and critical processes were optimized towards maximizing lithium ion conductivities at room temperature. The impacts of the processing conditions on the ...


An Experimental Investigation Of Residual Stress Development During Selective Laser Melting Of Ti-6al-4v, Nathan Charles Levkulich Jan 2017

An Experimental Investigation Of Residual Stress Development During Selective Laser Melting Of Ti-6al-4v, Nathan Charles Levkulich

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Selective laser melting (SLM) is an additive manufacturing (AM) process that gives rise to large thermal gradients and rapid cooling rates that lead to the development of undesirable residual stress and distortion. In this work, a number of different techniques (i.e., x-ray-diffraction, hole-drilling, layer-removal, and contour) were utilized to establish the effect of process parameters on residual stress development during SLM of Ti-6Al-4V. The measurements indicated that higher laser power, slower scan speed, smaller stripe width, reduced substrate overhang, and reduced build plan area each reduce the level of residual stress. In addition, the correlation between microstructure, crystallographic texture ...


Quantifying Amorphous Content Of Commercially Available Silicon Carbide Fibers, Ian Mark Wolford Jan 2016

Quantifying Amorphous Content Of Commercially Available Silicon Carbide Fibers, Ian Mark Wolford

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SiC/SiC ceramic matrix composites (CMCs) with potential applications at =2700°F (1482°C) are of significant interest to the Air Force. The high temperature performance of SiC fibers used within these composites is greatly affected by the presence of amorphous SiOC and free carbon in the fibers. Therefore quantification of this non SiC material in commercially available SiC fibers is extremely important. In this work Hi Nicalon, Hi-Nicalon Type-S, Tyranno-SA3, Cef-NITE, and Sylramic SiC fibers were studied. Changes in mass, grain size, and amorphous content were measured as a function of processing temperature and time. The amorphous material in ...


Experimental Validation Of The Calphad Approach Applied To Multi-Principle Element Alloys, Nathan J. Bryant Jan 2015

Experimental Validation Of The Calphad Approach Applied To Multi-Principle Element Alloys, Nathan J. Bryant

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High entropy alloys (HEAs) are a recent area of research in materials science. Their namesake is because their high entropy of mixing due to multiple metallic elements in a near equimolar ratio. The high entropy of mixing is supposed to suppress unwanted, brittle, ordered intermetallic phases, and form a single, randomly mixed solid solution phase. This phenomena makes HEAs a good candidate for structural applications. However, this entropy of mixing may not be enough to suppress all intermetallic phases. For this reason, the CALculation of PHAse Diagrams (CALPHAD) approach is being explored to predict phase equilibrium in HEAs. This study ...


Carbon-Based Nanostructured Materials As Electrode In Lithium-Ion Batteries And Supercapacitors, Zhuo Yao Jan 2013

Carbon-Based Nanostructured Materials As Electrode In Lithium-Ion Batteries And Supercapacitors, Zhuo Yao

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Carbon-based nancomposites attract much attention as electrode materials in electrochemical energy storage systems due to their low-cost, extraordinary high electrical and thermal conductivity, super high surface area etc. In this research, graphene nanosheets (GNS) and their nanocomposites with manganese oxides (GNS/MnOx) or silicon nanowires (GNS/SiNWs/CF) are studied for their applications in Li-ion batteries and supercapacitors. GNS powders are synthesized via a chemical oxidation of nature graphite followed by appropriate reduction process. GNS/MnOx composites are synthesized rendering MnOx nanoparticles embedded on the surfaces of GNS. SiNWs grown in carbon fibers are mechanically mixed with GNS powders. The ...


Analysis Of Laser Induced Spallation Of Electron Beam Physical Vapor Deposited (Eb-Pvd) Thermal Barrier Coatings, David Allen Beeler Jan 2013

Analysis Of Laser Induced Spallation Of Electron Beam Physical Vapor Deposited (Eb-Pvd) Thermal Barrier Coatings, David Allen Beeler

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The use of thermal barrier coatings (TBCs) has been an important factor in the efficiency improvements of jet engines due to their ability to withstand the extreme environments within the engine. With this improved resistance, TBCs have also become more difficult to remove without damaging the substrate. Mound Laser & Photonics Center, Inc. (MLPC) has developed an innovative, laser based technique to spall this coating. The intention of this work was to investigate and better understand the removal mechanism. Through experimentation and analysis (such as high speed video, Scanning Electron Microscopy and Energy Dispersive Spectroscopy, semi-logarithmic analysis, and a numerical thermal ...


A Basic Understanding Of Rapid Mold Surface Heating Via Laser Energy, Charles Daniel Fox Jan 2012

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

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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 ...


Isothermal Deformation And Modeling Of Ti-6al-4v, Vamsi Krishna Vempati Jan 2012

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 ...


Modeling The Exfoliation Rate Of Graphene Nanoplatelet Production And Application For Hydrogen Storage, Cory Knick Jan 2012

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 ...


Key Factors Influencing The Structure And Electrochemical Performances Of Lifepo4 Via Sol-Gel Synthesis, Chuang Guan Jan 2012

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

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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 ...


Graphene Based Anode Materials For Lithium-Ion Batteries, Sree Lakshmi Cheekati Jan 2011

Graphene Based Anode Materials For Lithium-Ion Batteries, Sree Lakshmi Cheekati

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Improvements of the anode performances in Li-ions batteries are in demand to satisfy applications in transportation. In comparison with graphitic carbons, transition metal oxides as well as graphene can store over twice amount of lithium per gram. Recently, graphene-based anodes for Li-ion batteries are under extensive development. In this research, lithium storage characteristics in graphene oxide (GO), GO/Manganese acetate (GO/MnAc), GO/manganese oxide (GO/MnOx) composites and Nano Graphene Platelets (NGP) were studied. The prepared GO delivered reversible capacities of 706mAh/g with an average columbic efficiency of 87%. Reversible capacities of 533 mAh/g were observed for ...


The Functionalization And Characterization Of Adherent Carbon Nanotubes With Silver Nanoparticles For Biological Applications, Adam A. Maleszewski Jan 2011

The Functionalization And Characterization Of Adherent Carbon Nanotubes With Silver Nanoparticles For Biological Applications, Adam A. Maleszewski

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The purpose of this project is to form silver nanoparticles (Ag-NP) attached to a hierarchical substrate for possible use in biological applications. The effectiveness of these Ag-NP-containing devices, including biofilters and biosensors, may be dramatically enhanced by the use of hierarchical structures such as carbon nanotubes (CNT), as they offer a high surface area surface suitable for cell-device interactions, while Ag-NP would be a suitable component in many such devices due to its plasmonic surface properties (e.g. in sensor and directed energy applications) and its anti-microbial properties (desirable for fluid filtration due to its low weight. Meaningful control over ...


Effect Of Fullerene Nano-Spheres On Evaporation Kinetics Of Fluids, Wenhu Wang Jan 2011

Effect Of Fullerene Nano-Spheres On Evaporation Kinetics Of Fluids, Wenhu Wang

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As the interest in fluid evaporation kinetics keeps increasing, it's inevitably noticed that fullerene nanospheres play an important role on it. In this study, we investigate the C60 nanospheres' effect on the evaporation kinetics and thermal transitions of different solvents (water, chlorobenzene) over the entire range of solubility. According to distinct polarity of different solvent, fullerene solution would behave differently, the trend of increasing in evaporation rate as the concentration increased was observed in aromatic solvents while the rate kept decreasing in water. The result of differential scanning calorimetry (DSC) and Raman spectroscopy provided an evidence about structuring in ...


Highly Active Porous Catalysts Fabricated By Attachment Of Palladium Nanoparticles On Hierarchical Carbon Structures, Hema Vijwani Jan 2011

Highly Active Porous Catalysts Fabricated By Attachment Of Palladium Nanoparticles On Hierarchical Carbon Structures, Hema Vijwani

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The effectiveness of metal-based catalysts can be significantly enhanced by increasing the available surface area relative to the volume through the creation of hierarchical nanostructures. The catalyst demonstrated here is palladium, which is a widely recognized heterogeneous catalyst suitable for a variety of industrial applications such as water purification, hydrogen storage, and electrochemical devices. In this study, a novel multi-scale supporting material developed in this group, has been used as support. It consists of micro-porous graphitic carbon with strongly attached carbon nanotubes. This can increase the surface area by orders of magnitude without increasing the size or weight while still ...


Surface Modification Of Carbon Structures For Biological Applications, Elizabeth Irene Maurer Jan 2010

Surface Modification Of Carbon Structures For Biological Applications, Elizabeth Irene Maurer

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Carbon substrates have a wide variety of applications, many of which are enabled by appropriate surface modifications. In particular, the use of carbon-based substrates for biological devices can be quite advantageous due to their relative inertness and biocompatibility. Moreover, graphitic carbon can take many forms ranging from flat sheets to foams, fibers, and nanotubes. In this project, larger carbon substrates such as microcellular foam and flat graphite have been modified with carbon nanotubes, and their potential use in two types of biological applications was tested. The first study involved an investigation of the growth and proliferation of osteoblast cells on ...


Fabrication And Analysis Of Compositionally Graded Functional Layers For Solid Oxide Fuel Cells, Jared Ray Mccoppin Jan 2010

Fabrication And Analysis Of Compositionally Graded Functional Layers For Solid Oxide Fuel Cells, Jared Ray Mccoppin

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Solid Oxide Fuel Cell (SOFC) structures must be optimized for high performance, increased life, and low cost. Fabrication methods are an area of research interest in bringing down the total cost of SOFCs, and can also impact cell life and performance. Graded functional layers have been shown to enhance cell performance, but current fabrication methods require multiple fabrication steps. This thesis describes a novel fabrication method capable of compositional gradation of functional layers for SOFCs. Using colloidal spray deposition technology, a controlled co-deposition strategy was utilized to fabricate SOFC's with compositionally graded cathode and anode functional layers (CGCFL/CGAFL ...


A Critical Assessment Of The High Cycle Bending Fatigue Behavior Of Boron-Modified Ti-6al-4v, Casey M. Holycross Jan 2010

A Critical Assessment Of The High Cycle Bending Fatigue Behavior Of Boron-Modified Ti-6al-4v, Casey M. Holycross

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Boron-modified Ti-6Al-4V alloys have shown increased performance in mechanical properties over unmodified alloys and are currently of interest for use in turbine engine applications. These alloys offer up to 40% increase in ultimate tensile strength, up to 30% increase in stiffness, and favorable damage characteristics while maintaining a ductility greater than 10%. These attractive properties are attributed to small additions of boron that refine the microstructure and form strong and stiff TiB whiskers. Previous research has found that these modified alloys compare favorably in fatigue. Samples machined from a powder-metallurgy forging with nominal composition Ti-6Al-4V-1B, were tested in fully-reversed bending ...


Interfacial Modification Of Microcellular Carbon: Influence Of Ceramic And Carbon Nanotube Coatings, Anil Kumar Karumuri Jan 2009

Interfacial Modification Of Microcellular Carbon: Influence Of Ceramic And Carbon Nanotube Coatings, Anil Kumar Karumuri

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Microcellular carbon is an emerging ultra lightweight and efficient thermal management material, which also has great potential as a reinforcement material for selected composites. However, these porous materials exhibit relatively low mechanical properties, and are susceptible to degradation in oxidizing environment. The scope of this research is to investigate surface modification approaches that can address these issues. Two specific objectives were: (1) to develop ceramic coatings to improve the survivability of carbon foams in high temperature applications, and (2) to develop and test modifications that can improve cellular composites involving carbon foam. It was seen that a mixed layer of ...


New Formic Acid Fuel Cell Orientations To Reduce The Cost Of Cell Components, John Calvin Holtkamp Jan 2009

New Formic Acid Fuel Cell Orientations To Reduce The Cost Of Cell Components, John Calvin Holtkamp

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Formic acid fuel cells show the potential of outperforming or replacing direct methanol fuel cells. A number of issues need to be overcome in order for fuel cells, specifically formic acid fuel cells, to be seriously considered for use in small electronic devices. One of the largest issues inhibiting the commercial success of fuel cells is the cost of the components. The catalyst and ion-conducting membrane, key components in a fuel cell, are both expensive. With the current amount of costly materials needed to construct a fuel cell, fuel cells will have limited success in becoming mainstream power sources in ...


Integrated Bipolar Plate - Gas Diffusion Layer Design For Polymer Electrolyte Membrane Fuel Cells, David N. Neff Jan 2009

Integrated Bipolar Plate - Gas Diffusion Layer Design For Polymer Electrolyte Membrane Fuel Cells, David N. Neff

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Bipolar plates compose a large portion of the weight and manufacturing costs in fuel cells. Bipolar plates are metal plates that separate each membrane-electrode assembly in a fuel cell stack. They provide structural strength, contain flow channels for fuel transport, and conduct electricity in the fuel cell. Electricity also flows through the gas diffusion layer (GDL) which lies next to the bipolar plate. Because the GDL is separate from the bipolar plate, there is a contact resistance as the electricity flows from one to the other. The scope of this thesis is to research an efficient way of manufacturing a ...


Elevated Temperature Oxidation Of Boron Modified Ti-6al-4v, Deborah May-Katherine Sweeney Jan 2008

Elevated Temperature Oxidation Of Boron Modified Ti-6al-4v, Deborah May-Katherine Sweeney

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The addition of trace amounts (~0.1 wt%) of boron to titanium alloys refines theas-cast grain size by an order of magnitude from 2000μm to 200μm. The reduced grain size has potentially beneficial effects on the processibility of titanium alloys. Reports also indicate that the room temperature corrosion resistance of the boron containing alloys may be substantially greater than conventional titanium alloys. In this study, the effects of boron addition on oxidation resistance are investigated, since conventional titanium alloys have limited corrosion resistance in air above 650°C. The mass gain per unit surface area was measured during elevated temperatures ...


Processing Nano Graphene Plates (Ngps) And Ngp Nanocomposite, Yena Li Jan 2007

Processing Nano Graphene Plates (Ngps) And Ngp Nanocomposite, Yena Li

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In recent years numerous efforts worldwide are addressing all aspects of the rapid developing field of nanocomposites. However, the most important fillers-- carbon nanotube and carbon nanofiber - are expensive. In this study, our efforts are aimed at bridging the gap in cost and properties by providing a systematic study of alternative nano materials -- nano graphene plate (NGP) and related composites. We fabricated nano graphene plates through the detailed study of raw materials, chemical treatment methods and nano particle dispersion methods. A series of thermal expansion experiments were conducted to investigate the best condition to expand acid treated graphite and expansion ...


Minute Doping Of Pulsed Laser Deposition Processed Y123 Thin Films With Tb, Ce, And Pr, Joseph William Kell Jan 2007

Minute Doping Of Pulsed Laser Deposition Processed Y123 Thin Films With Tb, Ce, And Pr, Joseph William Kell

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Three rare earth elements (Tb, Ce, and Pr) were chosen for the investigation into whether adding minute quantities (≤1 at%) of dopants could improve the film quality of YBa2C 3O7-δ(Y123) thin films. The compositions studied are (Y1-x,Rex)Ba2Cu3O7-δ (RE=Tb, Ce, Pr; x=0.1, 0.01, 0.001). Good quality thin films were produced by PLD and showed significant improvement to properties when exposed to a magnetic field. Ce and Pr (x=0.001) doped films showed modest improvement. However, the Tb doped system showed substantial ...


Comparative Characterization Of Superconducting Thin Films Fabricated By Different Techniques, Padma Prasuna S. Vemulakonda Jan 2007

Comparative Characterization Of Superconducting Thin Films Fabricated By Different Techniques, Padma Prasuna S. Vemulakonda

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The goal of this thesis is to compare the chemical and compositional profiles, grain structure and critical current densities of superconducting Yttrium Barium Copper Oxide(Y1Ba2Cu3O7-x or YBCO) layers grown by different competing techniques on a variety of substrates and buffer layers. The idea is to check if there can be variation of cationic ratios, impurities, possible diffusion of substrate/buffer layer atoms into the YBCO for different processing methods and microstructures. Pulsed Laser Deposition (PLD), Metal Organic Deposition (MOD) and Metal Organic Chemical Vapor Deposition (MOCVD) films on Ion Beam Assisted Deposited (IBAD)-textured buffer layers and, Rolling Assisted ...