UNT Theses and Dissertations - 81 Matching Results

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Non-Isothermal Laser Treatment of Fe-Si-B Metallic Glass

Description: Metallic glasses possess attractive properties, such as high strength, good corrosion resistance, and superior soft magnetic performance. They also serve as precursors for synthesizing nanocrystalline materials. In addition, a new class of composites having crystalline phases embedded in amorphous matrix is evolving based on selective crystallization of metallic glasses. Therefore, crystallization of metallic glasses and its effects on properties has been a subject of interest. Previous investi… more
Date: December 2017
Creator: Joshi, Sameehan Shrikant
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Modeling of High Strain Rate Compression of Austenitic Shape Memory Alloys

Description: Shape memory alloys (SMAs) exhibit the ability to absorb large dynamic loads and, therefore, are excellent candidates for structural components where impact loading is expected. Compared to the large amount of research on the shape memory effect and/or pseudoelasticity of polycrystalline SMAs under quasi-static loading conditions, studies on dynamic loading are limited. Experimental research shows an apparent difference between the quasi-static and high strain rate deformation of SMAs. Research… more
Date: December 2017
Creator: Yu, Hao
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Effects of HALSs and Nano-ZnO Worked as UV Stabilizers of Polypropylene

Description: This work reports the outdoor weathering performance of ultraviolet (UV)-stabilized polypropylene (PP) products (using PP resins from Encore Wire). Different hindered amine light stabilizers (HALSs) and nano-ZnO were used to stabilize PP-film-based formulations that were exposed under UV light for 6 weeks simulating for in harsh outdoor weather of Dallas, Texas, USA in 2016. Characterization of the exposed PP film products was done in terms of mechanical and friction spectroscopic properties. T… more
Date: December 2017
Creator: Lu, Xinyao
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Solid Lubrication Mechanisms in Laser Deposited Nickel-titanium-carbon Metal Matrix Composites

Description: A Ni/TiC/C metal matrix composite (MMC) has been processed using the laser engineered net shaping (LENS) process from commercially available powders with a Ni-3Ti-20C (atomic %) composition. This processing route produces the in-situ formation of homogeneously distributed eutectic and primary titanium carbide and graphite precipitates throughout the Ni matrix. The composite exhibits promising tribological properties when tested in dry sliding conditions with a low steady state coefficient of fr… more
Date: December 2012
Creator: Mogonye, Jon-Erik
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Effects of Plasma, Temperature and Chemical Reactions on Porous Low Dielectric Films for Semiconductor Devices

Description: Low-dielectric (k) films are one of the performance drivers for continued scaling of integrated circuit devices. These films are needed in microelectronic device interconnects to lower power consumption and minimize cross talk between metal lines that "interconnect" transistors. Low-k materials currently in production for the 45 and 65 nm node are most often organosilicate glasses (OSG) with dielectric constants near 2.8 and nominal porosities of 8-10%. The next generation of low-k materials wi… more
Date: December 2010
Creator: Osei-Yiadom, Eric
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Growth, Structure and Tribological Properties of Atomic Layer Deposited Lubricious Oxide Nanolaminates

Description: Friction and wear mitigation is typically accomplished by introducing a shear accommodating layer (e.g., a thin film of liquid) between surfaces in sliding and/or rolling contacts. When the operating conditions are beyond the liquid realm, attention turns to solid coatings. Solid lubricants have been widely used in governmental and industrial applications for mitigation of wear and friction (tribological properties). Conventional examples of solid lubricants are MoS2, WS2, h-BN, and graphite;… more
Date: December 2010
Creator: Mensah, Benedict Anyamesem
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Microstructure Evolution in Laser Deposited Nickel-Titanium-Carbon in situ Metal Matrix Composite

Description: Ni/TiC metal matrix composites have been processed using the laser engineered net shaping (LENS) process. As nickel does not form an equilibrium carbide phase, addition of a strong carbide former in the form of titanium reinforces the nickel matrix resulting in a promising hybrid material for both surface engineering as well as high temperature structural applications. Changing the relative amounts of titanium and carbon in the nickel matrix, relatively low volume fraction of refined homogeneou… more
Date: December 2010
Creator: Gopagoni, Sundeep
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Dynamic Precipitation of Second Phase Under Deformed Condition in Mg-nd Based Alloy

Description: Magnesium alloys are the lightweight structural materials with high strength to weigh ratio that permits their application in fuel economy sensitive automobile industries. Among the several flavors of of Mg-alloys, precipitation hardenable Mg-rare earth (RE) based alloys have shown good potential due to their favorable creep resistance within a wide window of operating temperatures ranging from 150°C to 300°C. A key aspect of Mg-RE alloys is the presence of precipitate phases that leads to str… more
Date: December 2013
Creator: Dendge, Nilesh Bajirao
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Tribological Behavior of Spark Plasma Sintered Tic/graphite/nickel Composites and Cobalt Alloys

Description: Monolithic composites are needed that combine low friction and wear, high mechanical hardness, and high fracture toughness. Thin films and coatings are often unable to meet this engineering challenge as they can delaminate and fracture during operation ceasing to provide beneficial properties during service life. Two material systems were synthesized by spark plasma sintering (SPS) and were studied for their ability to meet these criteria. A dual hybrid composite was fabricated and consisted of… more
Date: December 2013
Creator: Kinkenon, Douglas
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Laser Surface Modification on Az31b Mg Alloy for Bio-wettability

Description: Laser surface modification of AZ31B Magnesium alloy changes surface composition and roughness to provide improved surface bio-wettability. Laser processing resulted in phase transformation and grain refinement due to rapid quenching effect. Furthermore, instantaneous heating and vaporization resulted in removal of material, leading the textured surface generation. A study was conducted on a continuum-wave diode-pumped ytterbium laser to create multiple tracks for determining the resulting bio-w… more
Date: December 2013
Creator: Ho, YeeHsien
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Synchrotron Radiation X-Ray Diffraction of Nickel-Titanium Shape Memory Alloy Wires During Mechanical Deformation

Description: Shape memory alloys (SMAs) are a new generation material which exhibits unique nonlinear deformations due to a phase transformation which allows it to return to its original shape after removal of stress or a change in temperature. It shows a shape memory effect (martensitic condition) and pseudoelasticity (austenitic condition) properties depends on various heat treatment conditions. The reason for these properties depends on phase transformation through temperature changes or applied stress. … more
Date: December 2015
Creator: Zhang, Baozhuo
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Improving the Long-term Performance of PVC Compositions

Description: PVC are extensively applied in many fields, such as cables, pipes, vehicles, shoes, toys and infusion bags. Generally, plasticizers are blended with PVC to improve the ability of process in industrial production; however, the toxic plasticizers will gradually migrate to the surface of products and such a leakage results in brittleness of plasticized PVC and environmental pollution. In other words, humans are frequently exposed to the potential risks. According to previous researches, cross-link… more
Date: December 2016
Creator: Yang, Yu Chia
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Defect Behaviors in Zinc Oxide and Zinc Titanates Ceramics from First Principles Computer Simulations

Description: ZnO and ZnO-TiO2 ceramics have intriguing electronic and mechanical properties and find applications in many fields. Many of these properties and applications rely on the understanding of defects and defect processes in these oxides as these defects control the electronic, catalytic and mechanical behaviors. The goal of this dissertation is to systematically study the defects and defects behaviors in Wurtzite ZnO and Ilmenite ZnTiO3 by using first principles calculations and classical simulatio… more
Date: December 2016
Creator: Sun, Wei
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Sliding Friction and Wear Behavior of High Entropy Alloys at Room and Elevated Temperatures

Description: Structure-tribological property relations have been studied for five high entropy alloys (HEAs). Microhardness, room and elevated (100°C and 300°C) temperature sliding friction coefficients and wear rates were determined for five HEAs: Co0.5 Cr Cu0.5 Fe Ni1.5 Al Ti0.4; Co Cr Fe Ni Al0.25 Ti0.75; Ti V Nb Cr Al; Al0.3CoCrFeNi; and Al0.3CuCrFeNi2. Wear surfaces were characterized with scanning electron microscopy and micro-Raman spectroscopy to determine the wear mechanisms and tribochemical phase… more
Date: December 2016
Creator: Kadhim, Dheyaa
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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The Role of Misfit Strain and Oxygen Content on Formation and Evolution of Omega Precipitate in Metastable Beta-titanium Alloys

Description: β-Ti alloys are widely used in airframe and biomedical applications due to their high ductility, high hardenability, and low elastic modulus. The phase transformations in β-Ti alloys are rather complex due to formation of metastable phases during various thermo-mechanical treatments. One such critical metastable phase, the hexagonal omega (ω) phase, can form in β-Ti alloys under quenching from the high temperature β phase and/or isothermal aging at intermediate temperature. Despite a substantia… more
Date: December 2016
Creator: Hendrickson, Mandana
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Trapping of hydrogen in Hf-based high κ dielectric thin films for advanced CMOS applications.

Description: In recent years, advanced high κ gate dielectrics are under serious consideration to replace SiO2 and SiON in semiconductor industry. Hafnium-based dielectrics such as hafnium oxides, oxynitrides and Hf-based silicates/nitrided silicates are emerging as some of the most promising alternatives to SiO2/SiON gate dielectrics in complementary metal oxide semiconductor (CMOS) devices. Extensive efforts have been taken to understand the effects of hydrogen impurities in semiconductors and its behavi… more
Date: December 2007
Creator: Ukirde, Vaishali
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Characterization of Cure Kinetics and Physical Properties of a High Performance, Glass Fiber-Reinforced Epoxy Prepreg and a Novel Fluorine-Modified, Amine-Cured Commercial Epoxy.

Description: Kinetic equation parameters for the curing reaction of a commercial glass fiber reinforced high performance epoxy prepreg composed of the tetrafunctional epoxy tetraglycidyl 4,4-diaminodiphenyl methane (TGDDM), the tetrafunctional amine curing agent 4,4'-diaminodiphenylsulfone (DDS) and an ionic initiator/accelerator, are determined by various thermal analysis techniques and the results compared. The reaction is monitored by heat generated determined by differential scanning calorimetry (DSC) a… more
Date: December 2003
Creator: Bilyeu, Bryan
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Synthesis and characterization of crystalline assembly of poly Nisopropylacry-lamide)-co-acrylic acid nanoparticles.

Description: In this study, crystalline poly(N-isopropylacrylamide-co-acrylic acid) (PNIPAm-co-AAc) nanoparticle network in organic solvents was obtained by self assembling precursor particles in acetone/epichlorohydrin mixture at room temperature followed by inter-sphere crosslinking at ~98 °C. The crystals thus formed can endure solvent exchanges or large distortions under a temporary compressing force with the reoccurrence of crystalline structures. In acetone, the crystals were stable, independent of te… more
Date: December 2004
Creator: Zhou, Bo
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries

Barrier and Long Term Creep Properties of Polymer Nanocomposites.

Description: The barrier properties and long term strength retention of polymers are of significant importance in a number of applications. Enhanced lifetime food packaging, substrates for OLED based flexible displays and long duration scientific balloons are among them. Higher material requirements in these applications drive the need for an accurate measurement system. Therefore, a new system was engineered with enhanced sensitivity and accuracy. Permeability of polymers is affected by permeant solubility… more
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Date: December 2004
Creator: Ranade, Ajit
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Low Temperature Polymeric Precursor Derived Zinc Oxide Thin Films

Description: Zinc oxide (ZnO) is a versatile environmentally benign II-VI direct wide band gap semiconductor with several technologically plausible applications such as transparent conducting oxide in flat panel and flexible displays. Hence, ZnO thin films have to be processed below the glass transition temperatures of polymeric substrates used in flexible displays. ZnO thin films were synthesized via aqueous polymeric precursor process by different metallic salt routes using ethylene glycol, glycerol, citr… more
Date: December 2006
Creator: Choppali, Uma
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Study of lead sorption on magnetite at high temperatures.

Description: Lead's uptake on magnetite has been quantitatively evaluated in the present study at a temperature of 200°C and pH of 8.5 with lead concentrations ranging from 5 ppm to175 ppm by equilibrium adsorption isotherms. The pH independent sorption behavior suggested lead sorption due to pH independent permanent charge through weak electrostatic, non-specific attraction where cations are sorbed on the cation exchange sites. The permanent negative charge could be a consequence of lead substitution which… more
Date: December 2006
Creator: Paliwal, Vaishali
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Micro and nano composites composed of a polymer matrix and a metal disperse phase.

Description: Low density polyethylene (LDPE) and Hytrel (a thermoplastic elastomer) were used as polymeric matrices in polymer + metal composites. The concentration of micrometric (Al, Ag and Ni) as well as nanometric particles (Al and Ag) was varied from 0 to 10 %. Composites were prepared by blending followed by injection molding. The resulting samples were analyzed by scanning electron microscopy (SEM) and focused ion beam (FIB) in order to determine their microstructure. Certain mechanical properties of… more
Date: December 2007
Creator: Olea Mejia, Oscar Fernando
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Supercritical CO2 foamed biodegradable polymer blends of polycaprolactone and Mater-Bi.

Description: Supercritical CO2 foam processing of biopolymers represents a green processing route to environmentally friendly media and packaging foams. Mater-Bi, a multiconstituent biopolymer of polyester, starch and vegetable oils has shown much promise for biodegradation. The polymer, however, is not foamable with CO2 so blended with another polymer which is. Polycaprolactone is a biopolymer with potential of 4000% change in volume with CO2. Thus we investigate blends of Mater-Bi (MB) and polycaprolacton… more
Date: December 2007
Creator: Ogunsona, Emmanuel Olusegun
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Long Term Property Prediction of Polyethylene Nanocomposites

Description: The amorphous fraction of semicrystalline polymers has long been thought to be a significant contributor to creep deformation. In polyethylene (PE) nanocomposites, the semicrystalline nature of the maleated PE compatibilizer leads to a limited ability to separate the role of the PE in the nanocomposite properties. This dissertation investigates blown films of linear low-density polyethylene (LLDPE) and its nanocomposites with montmorillonite-layered silicate (MLS). Addition of an amorphous ethy… more
Date: December 2008
Creator: Shaito, Ali Al-Abed
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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