Engineering Commons^™

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 …

Microwave Pretreatment Of Corn Stover For Anaerobic Digestion, Abhishek D. Saxena

Masters Theses

Anaerobic digestion is one of the several technologies used for biomass conversion to electricity or heat. This thesis focused on microwave irradiation of corn stover as a pretreatment for anaerobic digestion, and studies its impact on methane production.

The first run comprised three sets of stover soaked overnight in water, dilute sulfuric acid and dilute acetic acid, and each treated to three different levels of microwave irradiation. The results indicated a high variability in the data of the water set, which showed that there was no clear impact of microwave pretreatment on methane production. The dilute sulfuric acid and dilute …

Ab Initio Calculation Of Electronic And Optical Properties Of Beryllium Chalcogenides (Bes, Bese, And Bete) Under The Effect Of Pressure, Aisha Ali Saif Bannan Al-Kaabi

Theses

There are several methods for materials simulation. Ab initio or first principles methods are used to solve the quantum mechanical equation which govern the behavior of a system. Ab initio calculation of the optical and electronic properties of solids is fundamental in solid state physics. APW+lo is used to examine different properties of BeS, BeSe and BeTe. Beryllium compounds show different features in structure under different pressures, and they also show a phase transition from Zinc blende to Hexagonal transitions in II-VI semiconductors. Little is known about the ground state properties of Beryllium Chalcogenides. The aim of this work is …

Effects Of Variable Contact Load On Fretting Fatigue Behavior Of Shot-Peened And Un-Peened Titanium Alloy, Chia-Hawa Lee

Theses and Dissertations

Fretting fatigue occurs between two components in contact under relative motion and reduces fatigue life when compared with plain fatigue. Shot-peening, on the other hand, is the most commonly used cold working process to improve material fatigue resistance in aeronautical industries. Nearly all work accomplished to date has assumed a constant contact load while investigating fretting fatigue. The primary goal of this study was to explore fretting fatigue behavior under constant and variable contact load configurations using both shot-peened and un-peened specimens made up of Ti-6Al-4V alloy. Contact loads were applied with four different frequencies. Applied axial loads were also …

Stabilization Of Desert Sand Using Water-Borne Polymers, Shihab Wagiealla Abdalla Mohamed

Theses

Soil stabilization is one of the various applications that have benefited from the advances in polymeric materials. In this research, three water-borne polymeric emulsions with different chemical and physical properties were tested as stabilizers for sandy soil.

This study is divided into three parts. In the first part, the performance of the three emulsions in reducing the hydraulic conductivity and improving the mechanical properties of the sand was investigated. Specimens with polymer contents of up to 2 wt. % were prepared using two preparation methods, mixing and spraying. Both types of specimens exhibited a significant improvement in the studied properties. …

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 …

Stress Corrosion Cracking And Hydrogen Embrittlement Of Martensitic Alloy Ep-823, Mohammad K. Hossain

UNLV Theses, Dissertations, Professional Papers, and Capstones

This investigation is focused on the evaluation of stress corrosion cracking (SCC), localized corrosion, and hydrogen embrittlement (HE) susceptibility of martensitic Alloy EP-823 in neutral and acidic solutions at ambient and elevated temperatures. While no failures were observed in smooth specimens in the neutral solution, failures were noticed in the 90°C acidic solution at constant-load (CL) leading to a threshold stress (O'_th) of 102 ksi. The presence of a notch reduced the O'_th value to 91 ksi in a similar environment. The ductility (%El and %RA), time-to-failure (TTF), and true failure stress (O'_r) were gradually …

Environment Assisted Cracking Of Target Structural Materials Under Different Loading Conditions, Venkataramakrishnan Selvaraj

UNLV Theses, Dissertations, Professional Papers, and Capstones

Martensitic Alloy HT-9 has been tested for its evaluation of stress corrosion cracking resistance in neutral and acidic solutions at ambient and elevated temperatures incorporating smooth and notched cylindrical specimens under constant load and slow strain rate (SSR) conditions. C-ring and U-bend specimens have also been tested for stress corrosion cracking evaluation in the acidic solution. The role of hydrogen on the cracking tendency has been evaluated by cathodic applied potential.

The results of constant load testing enabled the determination of the threshold stress for stress corrosion cracking in susceptible environments. The magnitudes of ductility parameters were reduced with increasing …

Stress Corrosion Cracking Resistance Of Martensitic Stainless Steels For Transmutation Applications, Phani P. Gudipati

UNLV Theses, Dissertations, Professional Papers, and Capstones

The susceptibility of Alloy EP-823 to stress corrosion cracking has been evaluated using smooth and notched cylindrical specimens in neutral and acidic solutions at ambient and elevated temperatures using constant load and slow strain rate testing (SSR) techniques. C-ring and U-bend specimens have also been tested in the acidic solution. The effect of hydrogen on the cracking susceptibility has been evaluated under controlled cathodic potential. While no failures were observed with smooth specimens at constant load, the notched specimens showed failure. The SSR test results indicate that the true failure stress (o'_f), time to failure and ductility parameters …

Layer-By-Layer Self -Assembly For Enzyme And Dna Encapsulation And Delivery, Amish Patel

Doctoral Dissertations

Thin wall microcapsules were formed via Layer-by-Layer Self-Assembly of alternate adsorption of oppositely charged polyelectrolyte on microcores. After the core dissolution, empty polymeric shells with 20–25 nm thick walls were obtained. These microcapsules were loaded with Myoglobin, Hemoglobin and Glucose Oxidase by opening capsule pores at low pH and closing them at higher pH. The native structure of the enzyme was not affected due to different treatments. Biocompatible nanoshells were also prepared for encasing DNA. Using the same Layer-by-Layer Self-Assembly approach nanoparticle were constructed containing DNA as one of the layers. The nanoparticles of different architecture were used to deliver …

Computational Approaches To The Design And Analysis Of Stability Of Polypeptide Multilayer Thin Films, Bin Zheng

Doctoral Dissertations

The focus of this research is the development of computational approaches to understanding the physical basis of layer-by-layer assembly (LBL), a key methodology of nanomanufacturing. The results provided detailed information on structure which cannot be obtained directly by experiments.

The model systems chosen for study are polypeptide chains. Reasons for this are that polypeptides are no less polyelectrolytes than the more usual polyions, and one can control the primary structure of a polypeptide on a residue-by-residue basis using modern synthetic methods. Moreover, as peptides constitute one of the four major classes of biological macromolecules, research in this direction is expected …

Surface Treatment Of Ferrous Alloys With Boron, Naruemon Suwattananont

Theses

Boronizing is a thermo-chemical surface hardening treatment in which boron atoms diffused into the metal substrate form the metallic boride layer, providing high hardness, corrosion resistance, and 3-10 times increasing service life. This type of surface treatment is widely used in many applications.

The purpose of this work was to investigate the structures and properties of boronized ferrous alloys. Three types of steels, AISI 1018 (plain low carbon steel), AISI 4340 (high strength alloy steel), and AISI 304 (austenitic stainless steel), were used for this study. The boronized AISI 1018 and AISI 4340 demonstrated the saw-tooth structure with average 75-76 …

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 …

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 …

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 …

Embrittlement And Localized Corrosion In Alloy Ht-9, Sudheer Sama

UNLV Theses, Dissertations, Professional Papers, and Capstones

This investigation is focused on the evaluation of stress corrosion cracking (SCC), hydrogen embrittlement (HE) and localized corrosion susceptibility of Alloy HT -9 in neutral and acidic solutions at 30, 60 and 90°C. Constant-load and slow-strain-rate (SSR) testing techniques were used to evaluate the SCC and HE behavior of this alloy by using smooth and notched tensile specimens. Hydrogen effect on the cracking behavior was evaluated by applying cathodic (negative) potential to the test specimens. Localized corrosion susceptibility was evaluated by cyclic potentiodynamic polarization technique. The results of constant load SCC testing showed a threshold stress at 80% of the …

Environment-Induced Degradations In A Target Structural Material For Transmutation Applications, Ramprashad Prabhakaran

UNLV Theses, Dissertations, Professional Papers, and Capstones

This investigation is focused on the evaluation of stress corrosion cracking (SCC) and localized corrosion behavior of Type 422 stainless steel in aqueous environments at ambient and elevated temperature. The results of constant load SCC testing using smooth specimens showed no failure in the neutral solution but a threshold stress of 97 ksi was observed in the 90°C acidic environment. SCC testing by the slow-strain-rate test method indicate that the time-to-failure, true failure stress and ductility parameters were gradually reduced with increasing temperature, showing more pronounced effect in the acidic solution. The application of a controlled cathodic potential showed further …

Fabrication, Characterization, And Modeling Of Organic Capacitors, Schottky Diodes, And Field Effect Transistors, Mo Zhu

Doctoral Dissertations

The objectives of this project are to fabricate, characterize, and model organic microelectronic devices by traditional lithography techniques and Technology Computer Aided Design (TCAD).

Organic microelectronics is becoming a promising field due to its number of advantages in low-cost fabrication for large area substrates. There have been growing studies in organic electronics and optoelectronics. In this project, several organic microelectronic devices are studied with the aid of experimentation and numerical modeling.

Organic metal-insulator-metal (MIM) and metal-insulator-semiconductor (MIS) capacitors consisting of insulating polymer poly(4-vinylphenol) (PVP) have been fabricated by spin-coating, photo lithography, and reactive ion etching techniques. Based on the fabricated …

Crystallization Kinetics Study Of The Glasses In Se–Te System, Fareed Abdul Raheem Al-Gheyath

Theses

The aim of the present work is to study the crystallization kinetics of some chalcogenide glassy alloys in the Selenium-Tellurium system. Four glassy systems have been prepared: Se₈₀Te_20-xSb_x (x= 0, 4, 6, 8, and 10); Se₇₀Te_30-xSb_x (x= 2, 6, 8, and 10); Se₈₀Te_20-xCd_x (x= 2, 4, and 10); and Se₈₀Te_20-xSn_x (x= 2, 4, and 10). The starting materials of (99.999%) purity were weighted according to their atomic percentages and sealed in evacuated silica tubes, under a pressure of about 10 …

Rehabilitation Of Concrete Structure Using Composite Materials, Ibtesam J.Saeed Al-Saifi

Theses

In the United Arab Emirates, most of the concrete structures including road, infrastructure and different types of buildings have been reported to be in need of rehabilitation. It is universally acknowledged that the environment of the countries in the Arabian Gulf is extremely severe and very aggressive to construction materials and operations. It is anticipated that the cost of rehabilitation of civil infrastructure will gradually increase over the next decade as a direct consequence of the increase in the number of structures reaching their expected service life.

Accordingly demand on rehabilitation methods will increase. In addition the severe climatic conditions …

Optimization Studies Of Thermal Bimorph Cantilevers, Electrostatic Torsion Actuators And Variable Capacitors, Wuyong Peng

Dissertations

In this dissertation, theoretical analyses and optimization studies are given for three kinds of MEMS devices: thermal bimorph cantilevers, electrostatic torsion actuators, and variable capacitors. Calculation, simulation, and experimental data are used to confirm the device behavior and demonstrate the application of the design approaches.

For thermal bimorph cantilevers, an analytical model is presented which allows theoretical analysis and quantitative optimization of the performance based on material properties and device dimensions. Bimorph cantilevers are divided into two categories for deflection optimization: either the total thickness is constant, or the cantilever has one constant and one variable layer thickness. The optimum …