Engineering Commons^™

Inclined-Field Structure, Morphology, And Pinning Of The Vortex Lattice In Microtwinned Yba2cu3o7, B. Keimer, F. Doǧan, I. A. Aksay, R. W. Erwin, J. W. Lynn, M. Sarikaya

Materials Science and Engineering Faculty Research & Creative Works

A detailed small-angle neutron scattering study of the vortex lattice in a single crystal of YBa2Cu3O7 was made for a field of 0.5 tesla inclined at angles between 0 and 80 degrees to the crystalline c axis. The vortex lattice is triangular for all angles, and for angles less than or equal to 70 degrees its orientation adjusts itself to maximize the pinning energy to densely and highly regularly spaced twin planes. These observations have important implications for the microscopic flux-pinning mechanism, and hence for the critical current achievable in YBa2Cu3O7. For large angles (about 80 degrees) the vortex lattice …

A Study Of Fatigue Failure In Superalloys Using Positron Annihilation, D. Hoeckelman, Hollis P. Leighly

Materials Science and Engineering Faculty Research & Creative Works

This study shows there are significant changes occurring in the open volume defect concentration during fatigue cycling as measured by the S parameter. These changes are dependent upon the stress ratio, R = σmin/σmax, the maximum stress, σmax, and the number of fatigue cycles. The decline in the S parameter is due to the elimination of the residual vacancies. This decline is followed by an increase due to the generation of dislocations and the formation of small microcracks. This is followed by a decline in the S parameter due to growth of the microcracks ultimately leading to failure. Copyright © …

Defect Structure Of Y1-Ycaymno3 And La1-Ycaymno3. Ii. Oxidation-Reduction Behavior, J. W. Stevenson, M. M. Nasrallah, Harlan U. Anderson, Don M. Sparlin

Materials Science and Engineering Faculty Research & Creative Works

Electrical conductivity, Seebeck coefficient, and thermogravimetric behavior of compositions in the systems Y_1-yCa_yMnO₃ and Y_1-yCa_yMnO₃ were studied as functions of temperature and ambient oxygen activity in order to determine the mechanism of electrical transport and defect structure. Compositions in Y_1-yCa_yMnO₃ exhibited very slight oxygen activity-dependent behavior as the ambient oxygen activity was reduced. A defect model which includes the thermally excited disproportionation of Mn³⁺ into Mn²⁺ and Mn⁴⁺ pairs was applied to the oxygen-activity-dependent data for La_0.80Ca_0.20MnO_{3 …}

Solid-State Science And Technology: Synthesis And Characterization Of (Ceo2)0.8(Smo1.5)0.2 Thin Films From Polymeric Precursors, C. C. Chen, Harlan U. Anderson, M. M. Nasrallah

Materials Science and Engineering Faculty Research & Creative Works

(CeO₂)_0.8(CSO) has been suggested for solid oxide fuel cell (SOFC) applications, because of its higher electrical conductivity and chemical stability, compared to other ceria-based materials. However, CSO is difficult to densify under conditions compatible with other SOFC components. A thin film synthesis technique has been developed for the fabrication of dense CSO films from precursor solutions at relatively low temperatures. Dense, smooth, and homogeneous films were obtained on Pt, single-crystal Si, and La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF) substrates by spin-coating a polymeric precursor and subsequent heat-treatment. Crystallization of the film …

Galvanic Stripping Of Fe⁺³ And Pb⁺² Ions And Dissolution Of Metallic Fe, Zn, Pb And Cd Using Di(2-Ethylhexyl)Phosphoric Acid, Luis Miguel Chia Aquije

Doctoral Dissertations

"Two systems were evaluated using the principles of the galvanic stripping process. One of them, the removal of Pb⁺² ions from di-2(ethylhexyl) phosphoric acid (D2EHPA) was performed using metallic zinc. The other, the removal of Fe⁺³ ions from D2EHPA used metallic iron as reductant and was performed simultaneously with the organic phase using a slightly acidic aqueous solution of hydrochloric acid. In addition, the dissolution of metallic zinc, iron, lead, and cadmium in D2EHPA was studied in order to better understand the anodic step in the mechanism of the galvanic stripping process.

Increased temperature was found to dramatically …

Computational And Experimental Investigation Into Fracture Of Brittle Fiber - Brittle Matrix Composite Systems, James P. Solti

Theses and Dissertations

Experimental and computational analyses provided an improved understanding of quasi-static fracture in model composite systems. Constant displacement compression tests using borosilicate glass double cleavage drilled compression test templates provided qualitative assessments of localized toughening for crack growth near cylindrical inclusions. Large crack-tip stress fields induced interfacial slip and separation prior to arrival of the main crack. Debonding and the proliferation of secondary matrix cracks characterized the role of bridging fibers along weak interfaces. Strong residual normal compressive interfacial stresses diminished the influence of crack-tip stresses; however, slip was still observed. VHS tape and computer enhanced photos record a history of …

Phase Conjugation In Optical Fiber Via Stimulated Brillouin Scattering With Feedback From A Barium Titanate Crystal, Patrick R. Emmert

Theses and Dissertations

The goal of this thesis was to obtain phase conjugation in multi-mode optical fiber via stimulated Brillouin scattering (SBS) with the aid of a barium titanate crystal which formed a phase conjugate cavity for the Stokes beam. SBS was demonstrated but the SBS threshold was unaffected by the presence of the barium titanate crystal and no evidence for the presence of phase conjugation in the optical fiber was obtained.

Cathodoluminescence Spectroscopy Of Zinc Germanium Phosphide Zngep2, Michael R. Gregg

Theses and Dissertations

Zinc Germanium Phosphide (ZnGeP₂) is a nonlinear semiconductor suitable for use as a laser tuning element over the two to six micron wavelength range. Although this crystal has been studied in the past, its luminescent properties are not yet well understood. In this present study, ZnGeP₂ has been examined using cathodoluminescence spectroscopy (CL). Specifically, the spectral dependence of the CL was obtained as a function of electron beam energy, beam current and temperature. The resulting CL was found to be polarized with a peak structure that was dependent on the polarization. This peak structure observed by CL …

Investigation Of Fatigue Behavior In Notched Cross-Ply Titanium Metal Matrix Composite At Elevated Temperature, Robert P. Baker

Theses and Dissertations

The objective of this research was to investigate the initiation and progression of damage which develops in notched (0/90)_2S SCS-6/Ti-15-3 at elevated temperature. Testing consisted of a monotonic tensile test at 427°C followed by fatigue testing performed under load control with a stress ratio of 0.1 at a frequency of 10 Hz. A crack was defined to have initiated when it had attained a length greater than or equal to 0.124 mm. Crack initiation and progression was monitored by strain and modulus observations and visual inspection via telemicroscope. The cracks were recorded with edge and face replicas. Metallographic and …

Behavior Of A Titanium Matrix Composite Under Quasi-Static Tensile And Compressive Loading, Keith L. Bearden

Theses and Dissertations

Quasi-Static tensile and compressive testing was performed on a unidirectional titanium matrix composite. The specific material was SCS-9/β 21S. The initial tensile and compressive modulus for both laminates was the same. The ninety degree laminate had a tensile and compressive modulus of 115.89 GPa. The zero degree laminate had a tensile and compressive modulus of 197.51 GPa. The ninety degree laminate exhibited a three stage stress/strain response in tension. The first stage is completely linearly elastic, however, partial debonding of the fiber from the matrix was observed. This partial debased did not effect the stress/strain response. The second stage is …

Stratified Plate Model For Composite Plate Analysis, Richard A. Coveno

Theses and Dissertations

This study continues the investigation of the stratified plate model for the analysis of composites plates. The strata theory models a composite plate as a stack of isotropic matrix and orthotropic, fiber dominated layers. Energy methods are used to derive a set of partial differential equations and boundary conditions as a function of the displacement. An assumed displacement field, of a polynomial in z and a Sine/Cosine function in x and y, generates a solution to a simply supported composite plate with cross plies. A cylindrical bending example is also solved with a polynomial in z and Sine/Cosine function in …

Effect Of Thickness And Ply Layup On The Collapse Characteristics Of Cylindrical Composite Shells With Large Cutouts, James C. Hatfield

Theses and Dissertations

This study involved a numerical and experimental investigation of the geometric instability(collapse loads/displacements) of vertically unsupported graphite/epoxy cylindrical shell panels undergoing axial compression. Symmetric quasi-isotropic and cross-ply laminates, with and without 4 X4 centralized cutouts, were investigated for three thicknesses:8,16,and 24 plies. The experimental data was compared to results from SHELL, a geometrically nonlinear finite-element computer program which incorporates a parabolic transverse shear strain distribution through the thickness. Good correlation was obtained for shells with large cutouts between the SHELL numerical data and the experimental results. This research verified that the SHELL program will provide good predictions of the collapse …

Behavior Of A Centrally Notched Cross-Ply And Unidirectional Ceramic Matrix Composite In Tension-Compression Fatigue, William A. Weidenaar

Theses and Dissertations

Centrally notched (hole), cross-ply, ((0/90)₂)_s, and unidirectional, (0)₈ laminates of Silicon Carbide fiber-reinforced Aluminosilicate glass, SiC/1723, were fatigue tested under tension-compression loading with a load ratio of -1. Damage accumulated continuously for both lay- ups, leading to eventual failure and a reduced fatigue life. Critical damage in the cross-ply consisted of longitudinal cracks in the 90° plies growing and combining with transverse cracks to effectively eliminate the 90° plies' load carrying capability and allowing the specimen to buckle. Critical damage in the unidirectional lay-up consisted of longitudinal cracks which initiated at the shear stress concentration …

The Effect Of Oxide Layers And Boron Doping On The Breakdown Of High Purity Silicon, Brian A. Hibbeln

Theses and Dissertations

For many applications such as lasers and radar drive circuits, there exists a need for solid state high voltage, high current switches. Current gaseous discharge switches fail to satisfy the ruggedness, reliability, and lifetime requirements of today's systems. A promising alternative is the Photoconductive Semiconductor Switch (PCSS). The limiting factor in the operation of these switches is the occurrence of breakdown through channels formed slightly below the surface. A theory on the formation of these channels is presented based upon band bending at the metal-semiconductor interface, a nonhomogeneous space charge due to irregular trap distributions, and thermal runaway in localized …

Processability Of Polythiophene Thin Films By Ultraviolet Photo Bleaching, Derek D. Fletcher

Theses and Dissertations

Materials possessing strong ��⁽³⁾ optical properties such as Polythiophene are sought for the production of optical switches. Polythiophene thin films produced by plasma enhanced CVD show a surface rms roughness of 10^-15 angstroms over single square micron areas which is acceptable for wave guiding in the near IR. This research investigates permanently changing the optical properties of such a thin film by exposure to UV radiation (254 nm, 35 mW/cm²), known as photo bleaching, in hope of creating a refractive index boundary for use in total internal reflection. After 60 minutes exposure the refractive index shows …

Excitation And De-Excitation Mechanisms Of Er-Doped Gaas And Algaas, David W. Elsaesser

Theses and Dissertations

Electrical and optical characterization have been performed on GaAs and Al_xGa_1-xAs samples doped with Er either by ion implantation or during Molecular Beam Epitaxial (MBE) growth. Deep Level Transient Spectroscopy (DLTS) and Temperature-Dependent Hall Effect (TDH) measurements indicated the presence of two hole traps in Er-doped GaAs, at 35 and 360 meV above the valence band maximum. The former (shallower) center was thought to be due to Er substituting for a Ga atom (Er_Ga) and giving rise to an isoelectronic impurity potential. The second center was attributed to an Er atom occupying an interstitial …

Behavior Of A Quasi-Isotropic Ply Metal Matrix Composite Under Thermo-Mechanical And Isothermal Fatigue Loading, Karl A. Hart

Theses and Dissertations

This study investigated the behavior of the SCS6/Ti-15-3 metal matrix composite with a quasi-isotropic layup when tested under static and fatigue conditions. Specimens were subjected to in-phase and out-of-phase thermo- mechanical and isothermal fatigue loading. In-phase and isothermal loading produced a fiber dominated failure while the out-of-phase loading produced a matrix dominated failure. Also, fiber domination in all three profiles was present at higher maximum applied loads and al three profiles demonstrated matrix domination at lower maximum applied loads. Thus, failure is both profile dependent and load equipment. Additional analyses, using laminated plate theory, Halpin-Tsai equations, METCAN, and the Linear …

Fatigue Behavior Of A Cross-Ply Ceramic Matrix Composite Under Tension-Tension And Tension-Compression Loading, Frank A. Opalski

Theses and Dissertations

A study was conducted which investigated the behavior of a cross-ply [0/90]_2S Nicalon/Calcium-Aluminosilicate (Nicalon/CAS) ceramic matrix composite at room temperature under tension-compression fatigue loading. Material behavior and damage was recorded by stress-strain curves, elastic modulus, hysteretic energy density, and acetate replication techniques. Tension-tension fatigue tests at a load ratio R of 0.1 (R = σ_min/σ_max) were completed which determined that 140 MPa was the maximum stress allowable in which cycle runout (1,000,000 cycles) would occur. Above this value, transverse crack density increased with respect to cycles and failure ultimately occurred. Tension-compression tests were then performed …

Open And Filled Hole Static Tensile Strength Characterization Of Metal Matrix Composite Scs-9/Β21s, Jacob T. Roush

Theses and Dissertations

SCS-9/β21s has a reduced gauge thickness, in comparison with other metal matrix composites, due to a smaller diameter fiber. This reduced gauge thickness makes it an attractive candidate for the skin of hypersonic vehicles. Tensile testing of (0/90)_2s and (O/±45/90)_s laminates was performed at room temperature, 482°C, and 650°C. Both notched and unnotched specimens were tested. Notched specimens, open and filled hole, had a width-to-diameter ratio of six. Materials 7075-T6 and Mar-m-246 were used as pins in the filled hole tensile testing. Analytical work was completed to predict material properties, elastic and plastic stress concentration factors, residual stresses, …

Electrochemical Evaluation Of The Adherence Of Zinc To Aluminum Cathodes, Jang Sop Han, Thomas J. O'Keefe

Materials Science and Engineering Faculty Research & Creative Works

Excess fluoride ions in zinc electrolyte are known to cause problems with the removal of electrowon zinc from aluminum blanks. The mechanisms responsible for this undesirable adherence were studied. Acid zinc sulfate electrolyte similar to that employed in zinc electrowinning was used. Using electrolyte containing various fluoride ion concentrations, the initial nucleation and growth morphology of zinc and the aluminum electrode surface were examined using scanning electron microscopy. Electrochemical tests were also carried out in various solutions to obtain a better understanding of the polarization behavior of the system. © 1992.

Investigation Of Strontium-Doped La(Cr, Mn)O3 For Solid Oxide Fuel Cells, Rasit Koc, Harlan U. Anderson

Materials Science and Engineering Faculty Research & Creative Works

The (La, Sr) (Cr, Mn)O₃ system was investigated in an effort to develop an interconnect and cathode materials for solid oxide fuel cells. Sintering studies were done in air at temperatures below 1500°C. Significant improvements in densification were observed with substitution of 50 mol% Mn for chromium and a density of 95% theoretical was achieved with the substitution of 70 mol% Mn for chromium in the La(Cr, Mn)O₃ system. Electrical conductivity (d.c.) measurements were made as a function of temperature and oxygen activity. At 1000°C and 1 atm oxygen, the electrical conductivity ranged from 2.2-20 S cm^{-1 …}

Structural Ceramic Incorporating Boron Carbide Whiskers For The Strengthening Thereof, P. D. Ownby, J. Liu

Materials Science and Engineering Faculty Research & Creative Works

Ceramic composites, and in particular structural ceramic composites, have enhanced strength, toughness and abrasion resistance due to the presence of up to about 40 volume percent of relatively large boron carbide whiskers. Although whiskers of various sizes were studied, those of particular interest are whiskers having an average diameter greater than about 3 micrometers, and particularly about 5 to about 8 micrometers, with an average aspect ratio of about 50. Due to the larger size, which had been predicted to be detrimental, there is less respiratory health risk when using these whiskers in the manufacturing of thse improved ceramic composites. …

Morphology, Deformation, And Defect Structures Of Ticr2 In Ti-Cr Alloys, Katherine C. Chen, Samuel M. Allen, James D. Livingston

Materials Engineering

The morphologies and defect structures of TiCr₂ in several Ti-Cr alloys have been examined by optical metallography, x-ray diffraction, and transmission electron microscopy (TEM), in order to explore the room-temperature deformability of the Laves phase TiCr₂. The morphology of the Laves phase was found to be dependent upon alloy composition and annealing temperature. Samples deformed by compression have also been studied using TEM. Comparisons of microstructures before and after deformation suggest an increase in twin, stacking faul4 and dislocation density within the Laves phase, indicating some but not extensive room-temperature deformability.

Use Of High-Energy Radiation For Degradation Of Environmental Pollutants, Robert D. Guthrie, Manjiri Patwardhan

KWRRI Research Reports

The purpose of this project was to explore the advantages and/or limitations of high-energy radiation treatment as a method for degrading organic pollutants, particularly aryl halides, in an aqueous medium. We have done analyses of ⁶⁰Co-irradiated samples and kinetic studies using pulsed electron beams. For aryl halides containing no more than two fused rings, the main products detected are those of simple halogen replacement by hydrogen, although the amount of aryl halide destroyed was always greater than the total amount of products detected. To accomplish halogen replacement by H, the reaction solvent may not be pure water but must …

The Effect Of Additives On The Nucleation And Growth Of Copper Onto Stainless Steel Cathodes, M. Sun, Thomas J. O'Keefe

Materials Science and Engineering Faculty Research & Creative Works

A potentiostatic technique has been used to study the effects of chloride ion, glue, and thiourea on the initial electrodeposition of copper. A stainless steel (AISI 304) rotating disc electrode (RDE) with an electrolyte containing 40 g/1 Cu²⁺ and 180 g/1 H₂SO₄ at 40 °C was employed. The current transients from the potential step measurements for the additive-free electrolyte could be fitted to a model that assumed progressive nucleation followed by growth of three-dimensional (3-D) centers under diffusion control. The growth mechanism and the type of nuclei were also confirmed by scanning electron microscopy (SEM) of …

An Experimental Study For The Effect Of Specimen Size On Shear Behavior Of Granular Materials, Clifton Linwood Parker Iv

Civil & Environmental Engineering Theses & Dissertations

An experimental study was undertaken to look into the effect of specimen size on the volumetric behavior of granular triaxial specimens. It was hypothesized that the specimen preparation mold creates a unique particle arrangement near the perimeter of the specimen and thus, for smaller specimen diameter relative to the particle size, it will exhibit a greater effect of the unique particle arrangement on the volumetric behavior. particles was used A single distribution of spherical glass throughout the testing. The tested specimens were 3.6, 2.8, 2.0, 1.4, 1.0, and 0.6 inches in diameter with a fixed two to one specimen height …

On The Creep Deformation Of A Cast Near Gamma Tial Alloy Ti-48al-1nb, R. W. Hayes, B. London

Materials Engineering

The steady-state creep deformation behavior of a cast two phase gamma TiAl alloy having the composition Ti---48Al---1Nb (at.%) has been studied. Tension creep tests using the stress increment technique (θθ2θ3) were conducted over the temperature range of 704–850°C at constant initial applied stress level of 103.4–241.3 MPa. The activation energy for creep over the temperature and stress regime of this study varied 317.5 kJ/mol (137.8 MPa) up to 341.0 kJ/mol (206.8 MPa) with an average value of 326.4 kJ/mol. This is well within the range of values previously measured for gamma TiAl alloys where creep controlled by volume diffusion has …

34th Rocky Mountain Conference On Applied Spectroscopy

Rocky Mountain Conference on Magnetic Resonance

Program and registration information for the 34th annual meeting of the Rocky Mountain Conference on Applied Spectroscopy, co-sponsored by the Colorado Section of the American Chemical Society and the Rocky Mountain Section of the Society for Applied Spectroscopy. Held in Denver, Colorado, August 2-6, 1992.

A Novel Technique For Deep Level Characterization Of High-Resistivity Semiconductor Materials, Sridhar Panigrahi

Electrical & Computer Engineering Theses & Dissertations

An improved photo induced current transient spectroscopy (PICTS) technique is developed for studying deep level parameters in high-resistivity semiconductor materials. A new digital data acquisition approach and improvement in the cryogenics of the system have enabled us, for the first time in our laboratory, to detect CuA level in a copper doped silicon compensated gallium arsenide (GaAs:Si:Cu) sample. The digital approach improves both the signal to noise ratio (S/N) and the efficiency of the system. Also, multiple PICTS spectra in a single thermal cycle can be obtained. In the present work, various doped and undoped gallium arsenide ( GaAs) and …

The Degradation Of Aluminium Cathodes By Fluoride Ion During Zinc Electrowinning, J. S. Han, Thomas J. O'Keefe

Materials Science and Engineering Faculty Research & Creative Works

The influence of fluoride ions on aluminum cathode surface degradation during zinc electrowinning has been studied. Electrolyte with a composition similar to that employed in plant operations has been used. A direct correlation is shown between the electrolyte fluoride content and the number of deposition cycles possible before zinc removal becomes difficult. The role of initial nucleation and starting electrode morphology is discussed in terms of the degree of adherence observed. Electrochemical tests have also been made on the electrodes at various stages of the process in an attempt to gain a better fundamental understanding of the mechanisms responsible for …