Engineering Commons^™

A Positron Annihilation Study Of Rotating Beam Fatigue Damage In The Superalloy Haynes 188, D. Hoeckelman, Hollis P. Leighly

Materials Science and Engineering Faculty Research & Creative Works

No abstract provided.

Thermoplastic Composites Of Recycled High Density Polyethylene And Recycled Tire Particles, James N. Mckirahan Jr.

Masters Theses

This study identified the mechanical properties and processibility of composite materials of recycled high density polyethylene (HDPE), recycled rubber tire particles, and/or ethyl co-vinyl acetate and poly (e-caprolactone). The composites were processed using a single screw extrusion system.

Three groups of experiments were conducted, on the composites in their extruded form to investigate the mechanical properties of ultimate tensile strength, percent elongation, and hardness. The first experiment investigated the effect of recycled rubber particle concentration in the composites up to 25 percent. The second experiment investigated the effect of recycled rubber particle size on the composites of recycled HDPE and …

Influence Of Fabrication Technique On The Fiber Pushout Behavior In A Sapphire-Reinforced Nial Matrix Composite, R. Asthana, R. R. Bowman, Surendra N. Tewari

Chemical & Biomedical Engineering Faculty Publications

Directional solidification (DS) of ''powder-cloth'' (PC) processed sapphire-NiAl composites was carried out to examine the influence of fabrication technique on the fiber-matrix interfacial shear strength, measured using a fiber-pushout technique. The DS process replaced the fine, equiaxed NiAl grain structure of the PC composites with an oriented grain structure comprised of large columnar NiAl grains aligned parallel to the fiber axis, with fibers either completely engulfed within the NiAl grains or anchored at one to three grain boundaries. The load-displacement behavior during the pushout test exhibited an initial ''pseudoelastic'' response, followed by an ''inelastic'' response, and finally a ''frictional'' sliding …

Diagnostics Of Cdte Electrodeposition By Rest Potential Voltammetry, Brandon Kemp, Robert Engelken, Arif Raza, Arees Siddiqui, Omer Mustafa

Journal of the Arkansas Academy of Science

Due to the extreme sensitivity of the partial elemental currents (i.e.,iCd, iTe) and, hence, stoichiometry to deposition voltage, temperature, mass transport, and ambient light intensity during electrodeposition of semiconductor films, it is important to implement in-situ methods for monitoring the stoichiometry and related semiconductor efficacy of the growing film. We report investigation of open circuit rest potential (Eoc) voltammetry as one such method during electrodeposition of CdTe from aprotic electrolytes such as ethylene glycol. Plots of transient open circuit potential versus sweep voltage exhibit distinct transition and plateau structures corresponding to Te, CdTe, and Cd phases and correlating with the …

Iron Phosphate Glasses As A Potential Nuclear Waste Disposal Medium, Melissa G. Mesko

Masters Theses

”Phosphate glasses containing large amounts of Fe₂O₃ (up to 43wt%) were studied to determine their potential suitability as nuclear waste disposal glasses for high level radioactive wastes containing large concentrations of iron oxide, phosphate, and fluoride compounds. Glass formation and chemical durability was the prime focus of this study, while properties such as density, thermal expansion, dilatometric softening temperature, and devitrification temperature were examined as well. It was found that large amounts of simulated nuclear waste material (up to 44.4wt% Cs₂O or 37.5wt% SrO) could be incorporated into the base iron phosphate glass while retaining …

Immittance Response Of La0.6sr0.4co0.2fe0.8o3 Based Electrochemical Cells, C. C. Chen, M. M. Nasrallah, Harlan U. Anderson

Materials Science and Engineering Faculty Research & Creative Works

The ac small-signal response of La0.6Sr0.4CO02Feo.803 (LSCF) is examined via lumped parameter/complex plane analysis (LP/CPA) technique. The ac data, acquired in the frequency range lO-1≤F≤106Hz, are used to establish the role of ionic contribution in the LSCF material system using a two-terminal blocking electrode method. Spun-on yttria (8 mole percent (m/o) Y203) stabilized zirconia (8YSZ) or Ce0.85Sm0.15O2 (CSO) thin film coatings (0.3 - 1.0 µm) is used as electron blocking electrodes. The temperature dependence of the contributing elements between the terminals, obtained via LP/CPA technique and dc measurements, is evaluated. The activation energy, associated with possible oxygen transport via an …

Electrical And Thermal Transport Properties Of (La,Ca)(Cr,Co)O3, Rasit Koc, Harlan U. Anderson

Materials Science and Engineering Faculty Research & Creative Works

DC electrical conductivity and Seebeck data as functions of temperature and oxygen activity were used to explain the electrical and thermal transport properties of (La,Ca) (Cr,Co)O3. The electrical conductivity data of La (Cr,Co)O3 suggested that it depends upon Co content. At Co concentrations less than 20 mol%, Co acted as traps for the carriers and decreased the electrical conductivity of the compositions at temperatures less than 900 °C. As the Co concentration increased to above 20 mol%, electrical conductivity increased significantly due to a connecting path of available Co sites. Additional Ca substitution for La increased the electrical conductivity in …

Semiempirical Model For The Electrical Properties Of La1-Xcaxcoo3, S. R. Sehlin, Harlan U. Anderson, Don M. Sparlin

Materials Science and Engineering Faculty Research & Creative Works

A semiempirical model of the Seebeck coefficient for a small polaron hopping conductor is presented. The population of small polarons is allowed to change as a function of temperature via the mechanism of charge disproportionation. The energy required for polaron formation by the disproportionation mechanism is modeled as screened by a Coulomb interaction with nearby small polarons. The charge carrier site occupancies generated by the model are used to successfully predict the electrical conductivity and Seebeck coefficient for compositions in the La1-xCaxCoO3 system. Cobalt ion valence populations predicted by the model are used to calculate effective paramagnetic moments for LaCoO3, …

Structure And Electrical Properties Of La1-Xsrxco1-Yfeyo3. Part 1. The System La0.8sr0.2co1-Yfeyo3, L. W. Tai, M. M. Nasrallah, Harlan U. Anderson, Don M. Sparlin, S. R. Sehlin

Materials Science and Engineering Faculty Research & Creative Works

Crystal structure, thermal expansion, thermogravimetry, thermoelectricity, and electrical conductivity of compositions in the system La0.8Sr0.2Co1-yFeyO3 with 0 ≤ y ≤ 1 were studied as function of Co Fe ratio and temperature, in air. The electrical conduction mechanism is attributed to the adiabatic-hopping of p-type small polarons. At high temperatures, oxygen deficiency causes lattice expansion and a reduction in electrical conductivity. The observed temperature dependence of the Seebeck coefficient is attributed to changes in carrier concentration caused by a thermally excited charge disproportionation of Co3+ ions and by the ionic compensation of induced oxygen vacancies. The measured electrical conductivity and Seebeck …

Structure And Electrical Properties Of La1 - Xsrxco1 - Yfeyo3. Part 2. The System La1 - Xsrxco0.2fe0.8o3, L. W. Tai, M. M. Nasrallah, Harlan U. Anderson, Don M. Sparlin, S. R. Sehlin

Materials Science and Engineering Faculty Research & Creative Works

Crystal structure, thermal expansion, oxygen stoichiometry, thermoelectricity, and electrical conductivity of compositions in the system La1 - xSrxCo0.2Fe0.8O3 with 0 ≤ x ≤ 0.6 were studied as function of temperature and Sr content, in air. The solubility of Sr in the sintered perovskite-type oxide (ABO3) was limited to x ≤ 0.4. The observed p-type electrical conduction appeared to occur via a small-polaron hopping mechanism. The thermally induced oxygen loss caused a lattice expansion plus decreases in both the carrier concentration and the carrier mobility. A semi-empirical model was developed which takes into account the thermally activated disproportionation of Co3+ ions …

Method Of Forming A Plasma Sprayed Interconnection Layer On An Electrode Of An Electrochemical Cell, Charles J. Spengler, George R. Folser, Shailesh D. Vora, Lewis Kuo, Von Richards

Materials Science and Engineering Faculty Research & Creative Works

A dense, substantially gas-tight, electrically conductive interconnection layer is formed on an air electrode structure of an electrochemical cell by (A) providing an electrode surface; (B) forming on a selected portion of the electrode surface, a layer of doped LaCrO.sub.3 particles doped with an element selected from Ca, Sr, Ba, Mg, Co, Ni, Al and mixtures thereof by plasma spraying doped LaCrO.sub.3 powder, preferably compensated with chromium as Cr.sub.2 O.sub.3 and/or dopant element, preferably by plasma arc spraying; and, (C) heating the doped and compensated LaCrO.sub.3 layer to about 1100 to provide a dense, substantially gas-tight, substantially hydration-free, electrically conductive …

Anomalous-Diffusion Model Of Ionic Transport In Oxide Glasses, David L. Sidebottom, Peter F. Green, Richard K. Brow

Materials Science and Engineering Faculty Research & Creative Works

The power-law frequency dependence of both the conductivity, (), and permittivity, (), of ion-conducting materials suggests that self-similar or scale-invariant behavior influences the transport of ions at high frequencies. Using an anomalous-diffusion model, we derive relevant power-law expressions for () and () and compare these with measurements performed on LiPO3 glass. Superior fits to the measured data are obtained compared to the commonly used Kohlrausch-Williams-Watts (KWW) description of the electrical modulus, most particularly in the notorious high-frequency regime. Evaluation of our results in terms of an anomalous-diffusion model suggests the dominance of interaction-based constraints to diffusion. © 1995 The American …

Two Contributions To The Ac Conductivity Of Alkali Oxide Glasses, David L. Sidebottom, Peter F. Green, Richard K. Brow

Materials Science and Engineering Faculty Research & Creative Works

Although the frequency dependent conductivity of ion-containing glasses often displays scale invariant power law dispersion at high temperatures, the exponent increases to unity at lower temperatures. We report measurements of the conductivity of a series of alkali metaphosphate glasses including a mixed alkali composition and demonstrate that this temperature dependence results from the superposition of two power law dispersions originating from separate mechanism, and does not indicate any intrinsic change in scaling of the process which dominates at high temperatures. © 1995 The American Physical Society.

High Temperature Interfacial Phenomena In Processing Cofired Ceramics For Electronic Packaging Of Semiconductor Devices, P. D. Ownby, D. A. Weirauch Jr., J. E. Lazaroff

Materials Science and Engineering Faculty Research & Creative Works

No abstract provided.

Characterization Of Piezoceramic Crosses With Large Range Scanning Capability And Applications For Low Temperature Scanning Tunneling Microscopy, J. A. Helfrich, Shireen Adenwalla, J. B. Ketterson, G. A. Zhitomirsky

Shireen Adenwalla Papers

We have developed a large amplitude piezoceramic scanner which should have numerous applications. Scanning tunneling microscopy (STM) and other scanning probe microscopies predominantly use piezoceramics for the scanning elements. Similarly adaptive optics, high resolution lithography, and micromanipulators are other examples of research which regularly utilize piezoceramic scanners. We present a new geometry for a piezoceramic scanner which allows for both high resolution (~nanometers) and large amplitude (~400 µm) displacements. The cross-shaped geometry makes it possible to produce extremely long pieces with very high tolerances. We have shown its effectiveness by using it as the major component of a low temperature …

Nonlinear Finite Element Micromechanic Analysis Of Thermoplastic Composite Of Recycled High Density Polyethylene Reinforced With Short Glass Fibers, Qiming Lou

Masters Theses

This thesis studied the nonlinear micromechanic behavior of thermoplastic composite of recycled high density polyethylene (HDPE) reinforced with short glass fibers using finite element method. The composite material was modeled using a micromechanic unit cell to simulate the stress distribution between the plastic matrix and the fiber in the composite. Nonlinear behavior of recycled HDPE and imperfect bonding between the fiber and matrix were investigated. Load-bearing capability of the fiber was evaluated using stress partition ratio (SPR) in the composite models. The effect of fiber aspect ratio on the stress distribution of the composite was studied to optimize the material …

La Résistance Des Gants À La Coupure : Développement D'Une Méthode D'Essai, Jaime Lara, Denis Turcot, Renaud Daigle, Jérôme Boutin

Rapports de recherche scientifique

No abstract provided.

Effect Of Agricultural Fiber Reinforcement On The Mechanical Properties Of A Recycled Polyethylene Plastic Composite Material, Michael E. Courbat

Dissertations and Theses @ UNI

This study determined the effect of certain agricultural fiber reinforcements on the tensile and impact mechanical properties of a recycled polyethylene plastic composite material. The purpose of the study was to provide information on certain mechanical properties of a recycled polyethylene plastic material as part of a coordinated materials application process.

A prototype product run of the plastic composite material was done and test specimens were selected from this material. Notch impact, tensile, and flexure tests were conducted on test specimens. Test procedures complied with accepted standards from The American Society For Testing and Materials (ASTM). Tests were conducted on …

Compensation And Characterization Of Gallium Arsenide, Randy A. Roush

Electrical & Computer Engineering Theses & Dissertations

The properties of transition metals in gallium arsenide have been previously investigated extensively with respect to activation energies, but little effort has been made to correlate processing parameters with electronic characteristics. Diffusion of copper in gallium arsenide is of technological importance due to the development of GaAs:Cu bistable photoconductive devices. Several techniques are demonstrated in this work to develop and characterize compensated gallium arsenide wafers. The material is created by the thermal diffusion of copper into silicon-doped GaAs. Transition metals generally form deep and shallow acceptors in GaAs, and therefore compensation is possible by material processing such that the shallow …

Vortex Lattice Symmetry And Electronic Structure In Yba2cu3o7, Bernhard Keimer, Wan Y. Shih, Ross W. Erwin, Jeffrey W. Lynn, Fatih Dogan, Ilhan A. Aksay

Materials Science and Engineering Faculty Research & Creative Works

We report a small angle neutron scattering study of the vortex lattice in YBa₂Cu₃O₇ in magnetic fields of 0.5≤ H ≤5 T applied along and close to the c axis. Over the entire field range, the vortices form an oblique lattice with two nearly equal lattice constants and an angle of 73° between primitive vectors. Numerical calculations suggest that variations of the superconducting order parameter near the vortex core are important in stabilizing this structure. An analysis that accounts for the fourfold symmetry of the vortex core qualitatively explains both the symmetry and the orientation …

Sorption Of Chlorinated Organic Compounds By Sedimentary Rocks, Paul M. Mcginley, S. Kesaraju, Ronald D. Gruzesky

KWRRI Research Reports

The sorption of dichlorobenzene and trichlorobenzene on carbonate and shale rocks collected in Kentucky demonstrate that rock organic matter content is a good indicator of sorptive reactivity in rock systems. Although this is similar to soil systems, significant differences between sorption in rock and soil systems exist. Sorption isotherms on these rocks are nonlinear and sorption can be an order of magnitude higher than predicted using correlations from soils and their organic matter content. This sorption reaction could lead to significant concentration tailing during contaminant cleanup. Experimental elution of trichloroethylene from rock filled columns verified that cleanup times might be …

Investigation Into The Behavior Of Geometrically Nonlinear Composite Arches, John C. Bailey

Theses and Dissertations

This research modifies the existing finite element formulation of a potential energy based large deformation and moderate rotation theory. Hermitian shape functions replace the existing linear bending angle interpolations. Negligible differences between the two formulations indicate the underlying kinematics limit the accuracy, not the finite element interpolations. Using the new program, numerous nonlinear arch geometries are modeled to investigate the effects of arc length and thickness variations. Local and global snapping phenomena are captured as well as through the thickness shear driven nonlinearities.

Fatigue Behavior Of A Cross-Ply Ceramic Matrix Composite At Elevated Temperature Under Tension-Tension Loading, Craig D. Steiner

Theses and Dissertations

This study investigated the fatigue behavior and damage mechanisms of a [0-90]_4s SiC-MAS ceramic matrix composite under tension-tension loading at two elevated temperatures and two frequencies. Stress and strain hystereses, maximum and minimum strain, and modulus of elasticity were evaluated to characterize the material behavior. Microscopy and fractography were used to evaluate damage progression and mechanisms. Fatigue life was independent of frequency at both temperatures.

Total Ionizing Dose Effects In Mosfet Devices At 77 K, Kevin J. Daul

Theses and Dissertations

Total ionizing dose effects on thermal oxide and reoxidized nitrided oxide (RNO) MOSFET devices at 77 K were studied. The MOSFETs were immersed in liquid nitrogen and irradiated, using a ⁶⁰Co source, up to 1 Mrad(Si) at a dose rate of 107 rads(Si)-sec. Drain current-gate voltage characteristics were obtained and used to determine threshold voltage and transconductance. At 77 K the subthreshold slopes indicated no observed buildup of interface states in any of the transistors. Furthermore, all transistors experienced very little change in the transconductance. Typical negative shifts in threshold voltage as dose increased were observed in all of …

Model Of A Single Impurity In A Wide Bandgap Semiconductor Describing Electric Field Screening, Anthony N. Dills

Theses and Dissertations

A mathematical model of the influence on electric field screening arising from a single impurity in a wide bandgap semiconductor has been numerically investigated and compared with analytically derived solutions. The parameter set chosen to perform the comparison of analytical solution and numerical solution is based upon a bismuth silicate crystal. Both the analytical calculations and the numerical calculations are an attempt to mathematically model the internal electric field within a semiconductor. Two types of impurities were looked at: a single donor level and a single trap impurity level. In general, after an abrupt application of a voltage across the …

Photoluminescence Spectroscopy Of 4h- And 6h-Sic, William A. Davis

Theses and Dissertations

Typical undoped bulk grown SiC shows n- or p-type conductivity due to residual impurities such as nitrogen, boron, or aluminum. In order to produce high resistivity material, vanadium can be used as a compensating dopant. Since vanadium is an amphoteric dopant in SiC, it produces either a donor state, V_Si⁴⁺(3d¹) → V_Si⁵⁺(3d⁰), or an acceptor state, V_Si⁴⁺(3d¹) → V_Si³⁺(3d²). Thus, vanadium doping can compensate both n- and p-type conductivity. In this work, vanadium doped and undoped 4H- and 6H-SiC grown …

Satellite Surface Material Composition From Synthetic Spectra, Eugene L. Caudill

Theses and Dissertations

The objective of this research was to determine if measurements from a Sagnac interferometer could provide reliable estimates of satellite material composition. The Sagnac interferometer yields a spatial interferogram that can sampled by a linear detector array. The interferogram is related to the spectrum of the source through a Fourier transform. Here, spectral reflectivities of nine common satellite materials were used to simulate the spectrum on obtains from an ideal Sagnac interferometer in the beam-train of a ground-based telescope whose mission is to view satellites. The signal-to-noise ratio of the spectrum was varied to simulate the effect of range variation …

Design, Fabrication, Modeling, And Optical Characterization Of Organic Polymer Nonlinear Directional Couplers, John N. Berry

Theses and Dissertations

This research was an investigation into the suitability of a recently developed polymer, polyphenylene, as a material for integrated optical circuits (IOCs). Polymers show great promise in the area of IOCs because of material processing advantages, compatibility with most existing integrated circuit technology, and relatively strong nonlinear optical characteristics. This thesis contains an overview of: dielectric waveguides, linear and nonlinear directional coupler theory; various models useful in the design and analysis of optical waveguides; the fabrication of three different waveguide designs; the experimental apparatus and procedure used to optically characterize the waveguides; and the experimental results of the characterization. Waveguiding …

The Junction Characteristics And Current Conduction Mechanisms Of Gainp2 N+P Diodes And Solar Cells, Kitt C. Reinhardt

Theses and Dissertations

This work involves an investigation of GaInP₂ n⁺p diode and solar cell dark current mechanisms, the defect centers that affect these mechanisms, and the response of dark current and solar cell photovoltaic parameters to I MeV electron irradiation and thermal annealing. Dark current due to carrier diffusion, recombination, and tunneling were identified, and recombination current was found to dominate at the maximum power-point voltage of the GaInP2 solar cells. Carrier recombination was found to occur via defect centers at the perimeter and within the bulk of the junction. Two deep majority-hole trap centers were found at E …

A Computer Allocation Algorithm For Space Problem, Hesham Abdel Aziz Ibrahim

Archived Theses and Dissertations

No abstract provided.