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 Department: Department of Materials Science and Engineering
 Decade: 2000-2009
 Degree Level: Master's
 Collection: UNT Theses and Dissertations
Amorphization and De-vitrification in Immiscible Copper-Niobium Alloy Thin Films

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

Date: May 2007
Creator: Puthucode Balakrishnan, Anantharamakrishnan
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 systems since it substantially reduces the free energy of the undercooled liquid (or amorphous) phase, below that of the competing supersaturated crystalline phases. The devitrification of the immiscible Cu-Nb thin film of composition Cu-45% Nb has been studied in detail with the discussion on the mechanism of phase transformation. The initial phase separation in the amorphous condition seems to play a vital role in the crystallization of the thin film. Detailed analysis has been done using X-ray diffraction, transmission electron microscopy and 3D atom probe tomography.
Contributing Partner: UNT Libraries
Determination of Wear in Polymers Using Multiple Scratch Test.

Determination of Wear in Polymers Using Multiple Scratch Test.

Date: August 2004
Creator: Damarla, Gowrisankar
Description: Wear is an important phenomenon that occurs in all the polymer applications in one form or the other. However, important links between materials properties and wear remain illusive. Thus optimization of material properties requires proper understanding of polymer properties. Studies to date have typically lacked systematic approach to all polymers and wear test developed are specific to some polymer classes. In this thesis, different classes of polymers are selected and an attempt is made to use multiple scratch test to define wear and to create a universal test procedure that can be employed to most of the polymers. In each of the materials studied, the scratch penetration depth s reaches a constant value after certain number of scratches depending upon the polymer and its properties. Variations in test parameters like load and speed are also studied in detail to understand the behavior of polymers and under different conditions. Apart from polystyrene, all the other polymers studied under multiple scratch test reached asymptotes at different scratch numbers.
Contributing Partner: UNT Libraries
Development of a Novel Grease Resistant Functional Coatings for Paper-based Packaging and Assessment of Application by Flexographic Press

Development of a Novel Grease Resistant Functional Coatings for Paper-based Packaging and Assessment of Application by Flexographic Press

Access: Use of this item is restricted to the UNT Community.
Date: August 2004
Creator: Brown, Robert W.
Description: Recent commercial developments have created a need for alternative materials and methods for imparting oil/grease resistance to paper and/or paperboard used in packaging. The performance of a novel grease resistant functional coating comprised of polyvinyl alcohol (PVA), sodium tetraborate pentahydrate (borate) and acetonedicarboxylic acid (ACDA) and the application of said coating by means of flexographic press is presented herein. Application criteria is developed, testing procedures described, and performance assessment of the developed coating materials are made. SEM images along with contact angle data suggest that coating performance is probably attributable to decreased mean pore size in conjunction with a slightly increased surface contact angle facilitated by crosslinking of PVA molecules by both borate ions and ACDA.
Contributing Partner: UNT Libraries
Evaluation of hydrogen trapping in HfO2 high-κ dielectric thin films.

Evaluation of hydrogen trapping in HfO2 high-κ dielectric thin films.

Access: Use of this item is restricted to the UNT Community.
Date: August 2006
Creator: Ukirde, Vaishali
Description: Hafnium based high-κ dielectrics are considered potential candidates to replace SiO2 or SiON as the gate dielectric in complementary metal oxide semiconductor (CMOS) devices. Hydrogen is one of the most significant elements in semiconductor technology because of its pervasiveness in various deposition and optimization processes of electronic structures. Therefore, it is important to understand the properties and behavior of hydrogen in semiconductors with the final aim of controlling and using hydrogen to improve electronic performance of electronic structures. Trap transformations under annealing treatments in hydrogen ambient normally involve passivation of traps at thermal SiO2/Si interfaces by hydrogen. High-κ dielectric films are believed to exhibit significantly higher charge trapping affinity than SiO2. In this thesis, study of hydrogen trapping in alternate gate dielectric candidates such as HfO2 during annealing in hydrogen ambient is presented. Rutherford backscattering spectroscopy (RBS), elastic recoil detection analysis (ERDA) and nuclear reaction analysis (NRA) were used to characterize these thin dielectric materials. It was demonstrated that hydrogen trapping in bulk HfO2 is significantly reduced for pre-oxidized HfO2 prior to forming gas anneals. This strong dependence on oxygen pre-processing is believed to be due to oxygen vacancies/deficiencies and hydrogen-carbon impurity complexes that originate from organic precursors used in ...
Contributing Partner: UNT Libraries
Indentation induced deformation in metallic materials.

Indentation induced deformation in metallic materials.

Date: December 2005
Creator: Vadlakonda, Suman
Description: Nanoindentation has brought in many features of research over the past decade. This novel technique is capable of producing insights into the small ranges of deformation. This special point has brought a lot of focus in understanding the deformation behavior under the indenter. Nickel, iron, tungsten and copper-niobium alloy system were considered for a surface deformation study. All the samples exhibited a spectrum of residual deformation. The change in behavior with indentation and the materials responses to deformation at low and high loads is addressed in this study. A study on indenter geometry, which has a huge influence on the contact area and subsequently the hardness and modulus value, has been attempted. Deformation mechanisms that govern the plastic flow in materials at low loads of indentation and their sensitivity to the rate of strain imparted has been studied. A transition to elastic, plastic kind of a tendency to an elasto-plastic tendency was seen with an increase in the strain rate. All samples exhibited the same kind of behavior and a special focus is drawn in comparing the FCC nickel with BCC tungsten and iron where the persistence of the elastic, plastic response was addressed. However there is no absolute reason ...
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Investigation of growth kinetics of self-assembling monolayers by means of contact angle, optical ellipsometry, angle-resolved XPS and IR spectroscopy.

Investigation of growth kinetics of self-assembling monolayers by means of contact angle, optical ellipsometry, angle-resolved XPS and IR spectroscopy.

Date: August 2004
Creator: Jakubowicz, Agnieszka
Description: Absorption of octadecanethiol and p-nitrobenzenethiol onto gold surfaces from ethanol solutions has been studied by means of contact angle, optical ellipsometry, angle-resolved XPS (ARXPS), and with grazing angle total reflection FTIR. Growth of the monolayers from dilute solutions has been monitored and Langmuir isotherm adsorption curves were fitted to experimental data. A saturated film is formed within approximately 5h after immersion in solutions of concentrations ranging from 0.0005mM to 0.01mM. We found, that the final density of monolayer depends on the concentration of the solution.
Contributing Partner: UNT Libraries
A magnetorheological study of single-walled and multi-walled carbon nanotube dispersions in mineral oil and epoxy resin.

A magnetorheological study of single-walled and multi-walled carbon nanotube dispersions in mineral oil and epoxy resin.

Date: May 2005
Creator: Yang, Zhengtao
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 stronger magnetic field. The SWNT/mo dispersions exhibited more pronounced magnetic field dependence than SWNT/ep and MWNT/mo counterparts due to their much lower viscosity. The alignment of SWNTs in mineral oil increased with rising nanotube concentration up to 2.5vol% but were significantly restricted at 6.41vol% due to nanotube flocculation.
Contributing Partner: UNT Libraries
Micro and nano composites composed of a polymer matrix and a metal disperse phase.

Micro and nano composites composed of a polymer matrix and a metal disperse phase.

Date: December 2007
Creator: Olea Mejia, Oscar Fernando
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 the composites were also determined. Static and dynamic friction was measured. The scratch resistance of the specimens was determined. A study of the wear mechanisms in the samples was performed. The Al micro- and nanoparticles as well as Ni microparticles are well dispersed throughout the material while Ag micro and nanoparticles tend to form agglomerates. Generally the presence of microcomposites affects negatively the mechanical properties. For the nanoparticles, composites with a higher elastic modulus than that of the neat materials are achievable. For both micro- and nanocomposites it is feasible to lower the friction values with respective to the neat polymers. The addition of metal particles to polymers also improves the scratch resistance of the composites, particularly so for microcomposites. The inclusion of Ag ...
Contributing Partner: UNT Libraries
Modified epoxy coatings on mild steel: A study of tribology and surface energy.

Modified epoxy coatings on mild steel: A study of tribology and surface energy.

Date: August 2009
Creator: Dutta, Madhuri
Description: A commercial epoxy was modified by adding fluorinated poly (aryl ether ketone) and in turn metal micro powders (Ni, Al, Zn, and Ag) and coated on mild steel. Two curing agents were used; triethylenetetramine (curing temperatures: 30 oC and 70 oC) and hexamethylenediamine (curing temperature: 80 oC). Variation in tribological properties (dynamic friction and wear) and surface energies with varying metal powders and curing agents was evaluated. When cured at 30 oC, friction and wear decreased significantly due to phase separation reaction being favored but increased when cured at 70 oC and 80 oC due to cross linking reaction being favored. There was a significant decrease in surface energies with the addition of modifiers.
Contributing Partner: UNT Libraries
Morphological properties of poly (ethylene terephthalate) (PET) nanocomposites in relation to fracture toughness.

Morphological properties of poly (ethylene terephthalate) (PET) nanocomposites in relation to fracture toughness.

Date: August 2005
Creator: Pendse, Siddhi
Description: The effect of incorporation of montmorillonite layered silicate (MLS) on poly (ethylene terephthalate) (PET) matrix was investigated. MLS was added in varying concentration of 1 to 5 weight percent in the PET matrix. DSC and polarized optical microscopy were used to determine the crystallization effects of MLS addition. Non isothermal crystallization kinetics showed that the melting temperature and crystallization temperature decrease as the MLS percent increases. This delayed crystallization along with the irregular spherulitic shape indicates hindered crystallization in the presence of MLS platelets. The influence of this morphology was related with the fracture toughness of PET nanocomposites using essential work of fracture coupled with the infra red (IR) thermography. Both the essential as well as non essential work of fracture decreased on addition of MLS with nanocomposite showing reduced toughness.
Contributing Partner: UNT Libraries
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