UNT Theses and Dissertations - 88 Matching Results

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Amorphization and De-vitrification in Immiscible Copper-Niobium Alloy Thin Films

Description: While amorphous phases have been reported in immiscible alloy systems, there is still some controversy regarding the reason for the stabilization of these unusual amorphous phases. Direct evidence of nanoscale phase separation within the amorphous phase forming in immiscible Cu-Nb alloy thin films using 3D atom probe tomography has been presented. This evidence clearly indicates that the nanoscale phase separation is responsible for the stabilization of the amorphous phase in such immiscible sy… more
Date: May 2007
Creator: Puthucode Balakrishnan, Anantharamakrishnan
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Partner: UNT Libraries
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Surface Engineering and Characterization of Laser Deposited Metallic Biomaterials

Description: Novel net shaping technique Laser Engineered Net shaping™ (LENS) laser based manufacturing solution (Sandia Corp., Albuquerque, NM); Laser can be used to deposit orthopedic implant alloys. Ti-35Nb-7Zr-5Ta (TNZT) alloy system was deposited using LENS. The corrosion resistance being an important prerequisite was tested electrochemically and was found that the LENS deposited TNZT was better than conventionally used Ti-6Al-4V in 0.1N HCl and a simulated body solution. A detailed analysis of the cor… more
Date: May 2007
Creator: Samuel, Sonia
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Bulk and Interfacial Effects on Density in Polymer Nanocomposites

Description: The barrier properties of polymers are a significant factor in determining the shelf or device lifetime in polymer packaging. Nanocomposites developed from the dispersion of nanometer thick platelets into a host polymer matrix have shown much promise. The magnitude of the benefit on permeability has been different depending on the polymer investigated or the degree of dispersion of the platelet in the polymer. In this dissertation, the effect of density changes in the bulk and at the polymer-pl… more
Date: May 2007
Creator: Sahu, Laxmi Kumari
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Partner: UNT Libraries
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Hydrophobic, fluorinated silica xerogel for low-k applications.

Description: A new hydrophobic hybrid silica film was synthesized by introducing one silicon precursor (as modifiers) into another precursor (network former). Hybrid films have improved properties. Hydrolysis and condensation of dimethyldiethoxysilane (DMDES) (solvent (EtOH) to DMDES molar ratio R = 4, water to DMDES molar ratio r = 4, 0.01 N HCl catalyst) was analyzed using high-resolution liquid 29Si NMR. It was found that after several hours, DMDES hydrolyzed and condensed into linear and cyclic species.… more
Date: May 2004
Creator: Zhang, Zhengping
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Partner: UNT Libraries
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Charge Interaction Effects in Epoxy with Cation Exchanged Montmorillonite Clay and Carbon Nanotubes.

Description: The influence of charge heterogeneity in nanoparticles such as montmorillonite layered silicates (MLS) and hybrid systems of MLS + carbon nanotubes was investigated in cured and uncured epoxy. Epoxy nanocomposites made with cation-exchanged montmorillonite clay were found to form agglomerates near a critical concentration. Using differential scanning calorimetry it was determined that the mixing temperature of the epoxy + MLS mixture prior to the addition of the curing agent critically influenc… more
Date: May 2005
Creator: Butzloff, Peter Robert
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Partner: UNT Libraries
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Saturation and foaming of thermoplastic nanocomposites using supercritical CO2.

Description: Polystyrene (PS) nanocomposite foams were prepared using supercritical fluid (SCF) CO2 as a solvent and blowing agent. PS was first in-situ polymerized with a range of concentrations of montmorillonite layered silicate (MLS). The polymerized samples were then compression molded into 1 to 2mm thick laminates. The laminates were foamed in a batch supercritical CO2 process at various temperatures and pressures from 60°-85°C and 7.6-12MPa. The resulting foams were analyzed by scanning electron micr… more
Date: May 2005
Creator: Strauss, William C.
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Partner: UNT Libraries
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A magnetorheological study of single-walled and multi-walled carbon nanotube dispersions in mineral oil and epoxy resin.

Description: Single wall carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs) were dispersed in mineral oil and epoxy resin. The magnetorheological properties of these dispersions were studied using a parallel plate rheometer. Strain sweeps, frequency sweeps, magneto sweeps and steady shear tests were conducted in various magnetic fields. G', G", h* and ty increased with increasing magnetic field, which was partially attributed to the increasing degree of the alignment of nanotubes in a strong… more
Date: May 2005
Creator: Yang, Zhengtao
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Supercritical Silylation and Stability of Silyl Groups

Description: Methylsilsesquioxane (MSQ) and organosilicate glass (OSG) are the materials under this study because they exhibit the dielectric constant values necessary for future IC technology requirements. Obtaining a low-k dielectric value is critical for the IC industry in order to cope time delay and cross talking issues. These materials exhibit attractive dielectric value, but there are problems replacing conventional SiO2, because of their chemical, mechanical and electrical instability after plasma p… more
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Date: May 2006
Creator: Nerusu, Pawan Kumar
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Partner: UNT Libraries

Study of Conductance Quantization by Cross-Wire Junction

Description: The thesis studied quantized conductance in nanocontacts formed between two thin gold wires with one of the wires coated by alkainthiol self assembly monolayers (SAM), by using the cross-wire junction. Using the Lorenz force as the driving force, we can bring the two wires in contact in a controlled manner. We observed conductance with steps of 2e2 / h. The conductance plateaus last several seconds. The stability of the junction is attributed to the fact that the coating of SAM improves the st… more
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Date: May 2004
Creator: Zheng, Tao
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Functionalization and characterization of porous low-κ dielectrics.

Description: The incorporation of fluorine into SiO2 has been shown to reduce the dielectric constant of the existing materials by reducing the electrical polarizability. However, the incorporation of fluorine has also been shown to decrease film stability. Therefore, new efforts have been made to find different ways to further decrease the relative dielectric constant value of the existing low-k materials. One way to reduce the dielectric constant is by decreasing its density. This reduces the amount of p… more
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Date: May 2005
Creator: Orozco-Teran, Rosa Amelia
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Partner: UNT Libraries
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Modifications of epoxy resins for improved mechanical and tribological performances and their effects on curing kinetics.

Description: A commercial epoxy, diglycidyl ether of bisphenol-A, was modified by two different routes. One was the addition of silica to produce epoxy composites. Three different silane coupling agents, glycidyloxypropyl trimethoxy silane (GPS), -methacryloxypropyl trimethoxy silane (MAMS) and 3-mercaptopropyltriethoxy silane (MPS), were used as silica-surface modifiers. The effects of silica content, together with the effects of chemical surface treatment of silica, were studied. The results indicate … more
Date: May 2008
Creator: Chonkaew, Wunpen
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Polyethylene-layered double hydroxide and montmorillonite nanocomposites: Thermal, mechanical and flame retardance properties.

Description: The effect of incorporation two clays; layered double hydroxides (LDH) and montmorillonite layered silicates (MLS) in linear low density polyethylene (PE) matrix was investigated. MLS and LDH were added of 5, 15, 30 and 60 weight percent in the PE and compounded using a Brabender. Ground pellets were subsequently compression molded. Dispersion of the clays was analyzed using optical microscopy, SEM and XRD. Both the layered clays were immiscible with the PE matrix and agglomerates formed with i… more
Date: May 2008
Creator: Kosuri, Divya
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Partner: UNT Libraries
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Advanced Technology for Source Drain Resistance Reduction in Nanoscale FinFETs

Description: Dual gate MOSFET structures such as FinFETs are widely regarded as the most promising option for continued scaling of silicon based transistors after 2010. This work examines key process modules that enable reduction of both device area and fin width beyond requirements for the 16nm node. Because aggressively scaled FinFET structures suffer significantly degraded device performance due to large source/drain series resistance (RS/D), several methods to mitigate RS/D such as maximizing contact … more
Date: May 2008
Creator: Smith, Casey Eben
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Partner: UNT Libraries
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Orientation, Microstructure and Pile-Up Effects on Nanoindentation Measurements of FCC and BCC Metals

Description: This study deals with crystal orientation effect along with the effects of microstructure on the pile-ups which affect the nanoindentation measurements. Two metal classes, face centered cubic (FCC) and body centered cubic (BCC, are dealt with in the present study. The objective of this study was to find out the degree of inaccuracy induced in nanoindentation measurements by the inherent pile-ups and sink-ins. Also, it was the intention to find out how the formation of pile-ups is dependant upon… more
Date: May 2008
Creator: Srivastava, Ashish Kumar
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State accountability ratings as related to district size and diversity.

Description: All Texas school districts were examined to determine the relationship of district size and diversity to the accountability ratings of selected Texas school districts and the implications of including all data in the accountability rating system. Eight large districts and 12 small districts were matched demographically utilizing data from the 2003-2004 school year. Information from the Texas Education Agency was accessed over 2003-2004 and 2004-2005. The ratings were found to be lowered from Re… more
Date: May 2008
Creator: Starrett, Teresa M.
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Maleic anhydride grafted polypropylene coatings on steel: Adhesion and wear.

Description: Polymeric coatings are being used in a growing number of applications, contributing to protection against weather conditions and localized corrosion, reducing the friction and erosion wear on the substrate. In this study, various polypropylene (PP) coatings were applied onto steel substrates by compression molding. Chemical modification of PP has been performed to increase its adhesion to metallic surfaces by grafting of maleic anhydride (MAH) onto PP in the presence of dicumyl peroxide (DCP). … more
Date: May 2010
Creator: Mahendrakar, Sridhar
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Partner: UNT Libraries
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Bioresorbable Polymer Blend Scaffold for Tissue Engineering

Description: Tissue engineering merges the disciplines of study like cell biology, materials science, engineering and surgery to enable growth of new living tissues on scaffolding constructed from implanted polymeric materials. One of the most important aspects of tissue engineering related to material science is design of the polymer scaffolds. The polymer scaffolds needs to have some specific mechanical strength over certain period of time. In this work bioresorbable aliphatic polymers (PCL and PLLA) were… more
Date: May 2011
Creator: Manandhar, Sandeep
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Partner: UNT Libraries
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The Influence of Ohmic Metals and Oxide Deposition on the Structure and Electrical Properties of Multilayer Epitaxial Graphene on Silicon Carbide Substrates

Description: Graphene has attracted significant research attention for next generation of semiconductor devices due to its high electron mobility and compatibility with planar semiconductor processing. In this dissertation, the influences of Ohmic metals and high dielectric (high-k) constant aluminum oxide (Al2O3) deposition on the structural and electrical properties of multi-layer epitaxial graphene (MLG) grown by graphitization of silicon carbide (SiC) substrates have been investigated. Uniform MLG was s… more
Date: May 2011
Creator: Maneshian, Mohammad Hassan
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Phase Separation and Second Phase Precipitation in Beta Titanium Alloys

Description: The current understanding of the atomic scale phenomenon associated with the influence of beta phase instabilities on the evolution of microstructure in titanium alloys is limited due to their complex nature. Such beta phase instabilities include phase separation and precipitation of nano-scale omega and alpha phases in the beta matrix. The initial part of the present study focuses on omega precipitation within the beta matrix of model binary titanium molybdenum (Ti-Mo) alloys. Direct atomic sc… more
Date: May 2011
Creator: Devaraj, Arun
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Partner: UNT Libraries
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Mechanisms of Ordered Gamma Prime Precipitation in Nickel Base Superalloys

Description: Commercial superalloys like Rene88DT are used in high temperature applications like turbine disk in aircraft jet engines due to their excellent high temperature properties, including strength, ductility, improved fracture toughness, fatigue resistance, enhanced creep and oxidation resistance. Typically this alloy's microstructure has L12-ordered precipitates dispersed in disordered face-centered cubic γ matrix. A typical industrially relevant heat-treatment often leads to the formation of … more
Date: May 2011
Creator: Singh, Antariksh Rao Pratap
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Piezoresistive Polyvinylidene Fluoride/Carbon Filled Nanocomposites

Description: This thesis examines the value of using dispersed conductive fillers as a stress/strain sensing material. The effect of the intrinsic conductivity of the filler on the ability to be effective and the influence of filler concentration on the conductivity are also examined. To meet these objectives, nanocomposites of polyvinylidene fluoride (PVDF) with carbon nanofibers (CNFs) and carbon nanotubes (CNTs) were prepared by melt-blending using a twin screw extruder. Since PVDF has a potential to be … more
Date: May 2011
Creator: Vidhate, Shailesh
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Partner: UNT Libraries
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First Principle Calculations of the Structure and Electronic Properties of Pentacene Based Organic and ZnO Based Inorganic Semiconducting Materials

Description: In this thesis, I utilize first principles density functional theory (DFT) based calculations to investigate the structure and electronic properties including charge transfer behaviors and work function of two types of materials: pentacene based organic semiconductors and ZnO transparent conducting oxides, with an aim to search for high mobility n-type organic semiconductors and fine tuning work functions of ZnO through surface modifications. Based on DFT calculations of numerous structure comb… more
Date: May 2012
Creator: Li, Yun
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Effect of Retting on Surface Chemistry and Mechanical Performance Interactions in Natural Fibers for High Performance Polymer Composites

Description: Sustainability through replacement of non-renewable fibers with renewable fibers is an ecological need. Impact of transportation costs from South-east Asia on the life cycle analysis of the composite is detrimental. Kenaf is an easily grown crop in America. Farm based processing involves placing the harvested crop in rivers and ponds, where retting of the fibers from the plant (separation into fibers) can take 2 weeks or more. The objective of this thesis is to analyze industrially viable proce… more
Date: May 2013
Creator: Ramesh, Dinesh
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Interspecimen Study of Bone to Relate Macromechanical, Nanomechanical and Compositional Changes Across the Femoral Cortex of Bone

Description: Mechanics of bone is widely studied and researched, mainly for the study of fracture. This has been done mostly on a macro scale. In this work hierarchical nature of bone has been explored to investigate bone mechanics in more detail. Flexural test were done to classify the bones according to their strength and deflection. Raman spectroscopy analysis was done to map the mineralization, collagen crosslinking changes across the thickness of the bone. Nanoindentation was done to map indentation ha… more
Date: May 2013
Creator: Nar, Mangesh
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Partner: UNT Libraries
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