Digital Commons Network^™

Synthesis And Ordering Of Nanostructures Using Laser Light, Yingfeng Guan

Doctoral Dissertations

This dissertation focuses on the formation of 1-D and 2-D nanoscale structures induced by the KrF excimer UV laser irradiation of silicon (λ=248 nm). Relatively low laser energy density (E_d<=1 J/cm²) is required to produce nanostructures. Alignment of 2-D nanoripple structures and nanoprotrusions has been realized by using Lloyd’s mirror configuration.

Laser-generated silicon microcone arrays were used as templates for the growth of nanocolumns. The formation mechanism of the microstructure is reviewed, and the origin and growth of nanocolumns are discussed. The formation mechanism of nanocolumns requires highly localized melting, which explains why they fail to form on …

A Study Of The Evolution Of Laser-Induced Periodic Surface Microstructures On Silicon And Electronic Transport In Composite Carbon Nanotube Networks, Stephen Jesse

Doctoral Dissertations

This dissertation addresses two main topics, the formation of micron-scale surface structures on single crystal silicon by irradiation with a KrF (248 nm) pulsed excimer laser source, and an investigation into electronic transport through composites of polymer (PMMA) and single-walled carbon nanotubes. It is shown that the spacing between laser-generated surface structures is determined primarily by the melt time and that the crystal orientation of the substrate can determine whether surface structures will form at all and also influence the shape of individual surface structures. During the melt/solidification cycle, the shape of liquid-vapor interface in modified by surface tension, and …

Fundamental Studies Of X-Ray And Secondary Electron Spectroscopy, Staya Prasad Mulapudi

Doctoral Dissertations

Microanalysis of submicron particles in the Scanning Electron Microscope (SEM) is only possible by using low incident electron beam energies due to smaller interaction volume and suppressed beam induced charging. Such low beam energies must use L- and M- lines rather than the familiar K-lines. The information about the fundamental parameters of X-ray emission and transport at low energies is limited, so the use of L- and M- lines is problematic. The rate of generation of X-rays from an element irradiated at some energy E depends on the product of the ionization cross-section (E) and the fluorescent yield . Unfortunately …

Nanoscale Materials Processing: Electron Beam-Induced Etching Of Silicon And Silicon Dioxide, Steven Jeffrey Randolph

Masters Theses

Both silicon and silicon dioxide can be etched with an electron beam in the presence of a xenon difluoride atmosphere in a process known as electron beam-induced etching (EBIE). In order to study the EBIE process, a Hitachi S-3500N scanning electron microscope (SEM) was modified to accept a vapor delivery system. Evidence has been presented regarding the fundamental mechanisms by which EBIE occurs, as well as the microscope variables that effect the etch process.

The effects of beam current and beam energy on the EBIE process were examined for both materials. On silicon, it was observed that the increased current …

Combinatorial Design Of Nickel-Chromium Alloys By Physical Vapor Deposition And Electron Beam Welding, Jaret James Frafjord

Masters Theses

Combinatorial methods, which include high efficiency and high throughput methods to create a large compositional range of materials, have proven to be highly effective and efficient in research and development in the chemical and pharmaceutical industries. In this thesis, similar methods for the development and optimization of metals and alloy systems are explored. Combinatorial Ni-Cr alloy samples were developed by physical vapor deposition (PVD) of a wedged film on a bulk material, and then locally melting the two by electron beam welding (EBW). A combinatorial alloy gradient was thus created along the length of the weld. The samples were rapidly …

Investigation Of Fiber Splitting In Side-By-Side Bicomponent Meltblown Nonwoven Webs Through Post Treatment, Yanbo Liu

Doctoral Dissertations

Finer fibers are increasingly desirable in the nonwoven industry in many applications due to increased specific surface area, increased surface adsorption ability, and improved filtration efficiency. Splitting bicomponent (Bico) fibers to produce finer fibrous nonwoven webs has become one of the hot topics in nonwoven industries.

Investigation of Bico fiber splitting mechanism and hence finding proper ways to achieve fiber splitting in S/S Bico MB nonwoven webs are the key issues in this research. Based on the fiber splitting mechanism, incompatible polymer pairs were chosen and appropriate post-treating methods as well as the post-treating agents were selected to facilitate fiber …

Free Radical (Co)Polymeirzation Of Methyl Methacrylate And Styrene In Room Temperature Ionic Liquids, Hongwei Zhang

Doctoral Dissertations

Conventional free radical polymerizations were carried out in a variety of room temperature ionic liquids (RTILs). Generally, methyl methacrylate (MMA) and styrene (St) were used as typical monomers to compare the polymerization behavior both in RTILs and in common volatile organic compound solvents (VOCs). In most cases, it was observed that both yields and molecular weights are enhanced in the RTIL. While we believe the “diffusion-controlled termination” mechanism makes the termination of the radical propagating chains difficult due to the highly viscous nature of RTIL, other researchers have suggested that the rapid polymerization rates are due to the high polarity …

A Study Of Charging In The Presence Of A Gaseous Environment, Xiaohu Tang

Doctoral Dissertations

Charge accumulation in insulating or semiconducting samples due to electron beam irradiation is one of the key problems in electron microscopy. One of the most promising techniques for reducing the severity of such charging is to surround the sample with a low pressure atmosphere of a gas. The charging behavior of a number of materials, surrounded by a variety of gases, has been determined to identify the important factors which control charging under these conditions. The magnitude of the surface potential was deduced from an analysis of X-ray spectra from the surface. The relationship between surface charge, gas pressure, and …

Process Property Studies Of Melt Blown Thermoplastic Polyurethane Polymers, Youn Eung Lee

Doctoral Dissertations

The primary goal of this research was to determine optimum processing conditions to produce commercially acceptable melt blown (MB) thermoplastic polyurethane (TPU) webs. The rheological/thermal properties of TPU pellets and the morphological/mechanical properties of MB TPU fibers and webs were characterized by Advanced Rheometric Expansion System (ARES), Differential Scanning Calorimetry (DSC), Fourier Transform Infrared Spectroscopy (FTIR) and etc.

The 6-inch MB line and the 20-inch wide Accurate Products MB pilot line at the Textiles and Nonwovens Development Center (TANDEC), The University of Tennessee, Knoxville, were utilized for this study. Preliminary MB studies were performed with Noveon ESTANE^® 58277 on …

Effect Of Microfissures On Corrosion Performance And Mechanical Properties Of Austenitic Stainless Steel Weld Metals, Yan Cui

Doctoral Dissertations

It is generally recognized that hot cracking or microfissuring is one of the main concerns in austenitic stainless steel welding. Microfissures formation can be attributed to the presence of liquid film along the grain boundaries near the bulk solidus temperature under a sufficient strain to rupture the liquid film. Microfissures can be controlled to a certain extent by attention to consumable composition, purity, and welding technique, but they cannot be uniquely eradiated in real weld application. The occurrence of the microfissures can be the cause of weld rejection and may induce property degradation of the weld metal. With the increase …

The Effects Of The Surface Nanocrystallization And Hardening (Snh) Process On Fatigue Resistance, Yuan Wei

Masters Theses

Nanocrystalline and coarse-grained materials have shown high resistances for the fatigue-crack initiation and growth, respectively. In this thesis, the surface- mechanical-attrition (SMA) treatment has been employed for the surface- nanocrystallization and hardening (SNH) process to produce engineered materials with coarse grains in the interior and grain-refinement progressively down to the nano-size on the surface.

The effects of the different processing parameters of the SMA treatment, including the ball size, materials, and treatment time, on the SNH process of the Ti-6Al- 4V and Ni-based Hastelloy® C-2000 Alloys were investigated from the viewpoints of the microstructure, microhardness, surface roughness, and fatigue behavior, …

Laser In-Situ Combinatorial Carbide Coating On Steel, Anshul Kumar Singh

Masters Theses

The potential for synthesizing an in-situ grown ultra-fine carbide composite coating on the surface of steel during laser surface engineering was investigated. A 2.5 KW Nd:YAG laser was employed to modify the surface of a AISI 1010 steel deposited with a precursor powder mixture of Fe, Ti, Cr and C. With the help of laser surface engineering, carbide composite coating on the surface of plain C steel was achieved. It is envisioned that such a coating will offer superior tribological properties.

Energy Dispersive Spectroscopy in supplement with X-ray Diffractometery indicated the evolution of TiC, Fe-Cr, and M_{7C3 as major …}

Measurement Of Material Creep Parameters Of Amorphous Selenium By Nanoindentation And The Relationship Between Indentation Creep And Uniaxial Creep, James Anthony Lamanna Jr.

Masters Theses

ὲ_I= BP_ⁿm

The purpose of this work was to measure the indentation creep parameters of amorphous selenium and to begin to develop a relationship between indentation creep and uniaxial creep. The data for this study was obtained by creating three different indentation creep experiments to test amorphous selenium under multiple loading conditions at multiple temperatures. The testing temperatures included 40°C, 35°C, 30°C, and 25°C. These specific temperatures were chosen to collect creep data above and below the glass transition temperature of 31°C. This indentation data was used to accomplish several objectives.

The first objective was to …

Laser-Dressing Of Alumina For Grinding Wheels, Abhijeet Ashok Khangar

Masters Theses

Higher the number of effective cutting edges on the surface of a grinding wheel, the higher is the grinding efficiency. However due to continuous grinding, efficiency is reduced as the effective cutting edges on wheel surface get worn out and blunt. Moreover, the wheel also gets loaded with metal chips during machining. Both geometric and functional characteristics of the grinding wheel have to be restored periodically. Dressing is a sharpening operation designed to generate a particular surface topography on the cutting face of the wheel. The conventional processes, like diamond dressing, do not produce consistent grinding results due to dresser …

Laser Induced Surface Modification Of Aluminium Alloys, Subhadarshi Nayak

Doctoral Dissertations

Purpose of this work is to improve surface related properties of aluminum alloys by employing a laser based technique. Two approaches were taken to achieve this goal. First approach involves a rapid solidification induced by laser without any deliberate change in chemical composition. In second approach, laser was used to deposit Fe₃0₄ on A319, producing an Fe₃0₄/Al reaction composite coating.

In-situ high-speed infrared thermographs captured during laser surface melting of A319 enabled estimation of maximum temperature, temperature gradient and cooling rate. In light of limited spatial and time resolutions of the infrared camera, …

Structure And Properties Of Cotton-Based Biodegradable/Compostable Nonwovens, Haoming Rong

Doctoral Dissertations

Cotton-based biodegradable nonwoven products have been receiving increasing attention in recent years with the growing environmental awareness throughout the world. A majority of the cotton-based nonwoven products are processed by carding with the binder fibers, and then point-bonding using a thermal calender.

In this work, different biodegradable binder fibers were used to produce cotton-based nonwovens. The structure and the properties of the resulting fabrics were studied. The effect of bonding temperature and binder fiber content on the bond morphology was investigated. The fracture and failure mechanisms of the fabrics produced with different binder fiber content and at different bonding temperature …

Thermal Aging Effects On The Microstructure, Oxidation Behavior, And Mechanical Properties Of As-Cast Ni3Al Alloys, Dongyun Lee

Doctoral Dissertations

The thermal aging effects on the microstructure, oxidation behavior at 900⁰ and 1100⁰C, and mechanical properties of IC221M (Ni₃Al based intermetallic alloy, ASTM A1002-99) were investigated. The microstructure consists of dendritic arms of the [gamma] (nickel solid solution) phase containing cube-shape [gamma]ʹ (Ni₃Al) precipitates. The interdendritic regions are mostly [gamma]ʹ (Ni₃Al) with up to 8 vol.% [gamma] + Ni₅Zr eutectic constituents. Thermal aging effects on the microstructures and how microsegregation affects the oxidation behavior were examined. Four primary changes in the microstructures were observed: (1) there is considerable homogenization of the cast microstructures with aging, (2) the volume fraction of …

Ti-8mo As An Alternative To Ti-6al-4v In Hip Replacement Implants, Brandice Annette Green

Masters Theses

In the present research, the wear and corrosion properties of a heat treated Ti-8Mo alloy are compared to that of a Ti-6Al-4V, an alloy commonly used as the material for the stem component of hip prosthesis. Ti-6Al-4V has the attractive properties of high strength to weight ratio and excellent corrosion resistance. However, the alloy has poor wear resistance and there have been biocompatibility concerns with Al and V. The heat treated Ti-8Mo is an alloy that has not yet been examined for biomaterial applications. However, the low toxicity of Mo and the possibility of improved wear resistance due to heat …