Engineering Commons^™

Understanding Corrosion Of Ni₃(Si,Nb) Alloys In Hot Sulfuric Acid, Jen-Hsien Hsu

Doctoral Dissertations

"The Sulfur-Iodine thermochemical cycle has been proposed as a method for producing large quantities of hydrogen gas from water. However, the extreme operating environments involved limit the possible materials for construction.

Through proper heat treatment and composition control, the modified patented Ni₃(Si,Nb) alloy keeps high temperature strength to greater than 750⁰C and can be deformed by cold rolling more than 50% using multiple passes and intermediate anneals. The corrosion resistance is reproducible and maintains less than 5 mpy for a broad range of boiling sulfuric acid concentrations, including 70 wt%.

In the boiling 70 wt% sulfuric acid corrosion tests, kinetic …

Ceramic Dielectrics For High Energy Density Capacity Application, Sheng Chao

Doctoral Dissertations

"The objective of this dissertation is to investigate the relationship between the processing parameters, microstructural development, defect chemistry and electrical properties of titanium oxide (TiO₂) dielectrics for high energy density capacitor applications. The effects of aliovalent dopants on the dielectric properties of TiO₂ ceramics were investigated, aiming to further improve the desired dielectric properties especially at elevated temperatures (up to 200°C). Due to the segregation of acceptor type impurities in the starting powders, space charge polarization took place in TiO₂ ceramics with relative large grain size (>̲500nm), leading to high dielectric loss and low energy storage efficiency. Increased ratio …

Borate Based Bioactive Glass Scaffolds For Hard And Soft Tissue Engineering, Steven B. Jung

Doctoral Dissertations

"The main objectives of this dissertation were to evaluate bioactive borate glass scaffolds for hard and soft tissue applications and determine the potential toxicity of the borate glasses on the adjacent and systemic tissues. Porous randomly oriented fiber scaffolds composed of bioactive borate glass were implanted in subcutaneous soft tissue sites and in calvaria defects of laboratory rats and no signs of toxicity (necrotic tissue, increase in macrophages or other immune cells) were detected in any of the adjacent tissues (hard or soft). Systemic organs (kidney and liver) of laboratory rats implanted with bioactive borate scaffolds were analyzed for possible …

Dependency Of Machinability In Gray Cast Iron On Nitride-Induced Age Strengthening, Jared Teague

Doctoral Dissertations

"Work of previous researchers has suggested that room temperature age strengthening in gray cast irons improves machinability. Verification and quantification of the machinability improvement is important to industry. Improved machinability will reduce overall manufacturing costs and reduce raw material consumption by decreasing the rate at which tools are replaced. Experimental work was performed to determine a connection between improved machinability in gray cast iron and changes in machining mechanics. An industrial tool wear study verified that age strengthening improved machinability by reducing tool wear to less than one-quarter of the unaged value. Laboratory tests on iron castings from the same …

Factors Controlling Ductility In Ultrafine Grain Aluminum Alloys Under Monotonic And Cyclic Loading, Partha Sarathi De

Doctoral Dissertations

"Ultrafine grained (UFG) Al processed by severe plastic deformation (SPD) methods are characterized by high strength and a limited uniform ductility. Friction stir processing (FSP), an offshoot of friction stir welding has emerged as a new technique to produce UFG alloys. FSP-UFG Al alloys show a distinctly different behavior with higher uniform elongation and improved high cycle fatigue life as compared to other SPD processed variants. The objective of this work was to study the microstructural basis for such mechanical behavior in FSP-UFG Al alloys.

To study the mechanical behavior of FSP Al alloys, a subsize bending fatigue and uniaxial …

Electrochemical Characterization Of Cerium-Based Conversion Coatings On Al 7075-T6, Simon Joshi

Doctoral Dissertations

"This research used electrochemical techniques to characterize the deposition and corrosion protection behavior of cerium-based conversion coatings on AI 7075-T6. Alkaline activation decreased native oxide impedance (5.9 kΩ-cm²) by ~25% promoting deposition of 250-500 mn coatings. Activation in NaOH solutions deposited coatings with large cracks and craters, whereas Na₂C0₃ activation resulted in uniform coatings, i.e., fewer cracks and almost no craters. Uniformly deposited coatings exhibited better cathodic inhibition and higher impedance (~200 kΩ-cm²) than on NaOH activated substrates (~100 kΩ-cm²). Subsurface crevices, caused by Cl⁻ and H₂O₂ in the deposition solution, were found under large cracks and craters. Thus, Na₂CO₃ …

Phosphate Post-Treatment Of Cerium-Based Conversion Coatings On Al 2024-T3, Daimon K. Heller

Doctoral Dissertations

"Phosphate post-treatment of cerium-based conversion coatings (CeCCs) on high strength aluminum alloys can significantly improve corrosion resistance. As-deposited CeCCs exhibit corrosion pits and salt tails across the specimen surface after 3 days of exposure, but post-treated CeCCs have withstood 14 days of salt spray exposure without visibly corroding. The morphology, phase, and electrochemical properties of spray deposited CeCCs were affected by post-treatment parameters such as immersion time, solution temperature, and phosphate source. The best performing coatings were post-treated in aqueous orthophosphate solutions for at least 5 min at temperatures of at least 85⁰C. These conditions converted cerium hydroxy/peroxy species in …

Characterization Of Diamond Thin Films And Related Materials, Travis K. Mckindra

Doctoral Dissertations

"Thin carbon films including sputtered deposited graphite and CO₂ laser-assisted combustion-flame deposited graphite and diamond thin films were characterized using optical and electron microscopy, X-ray diffraction and micro-Raman spectroscopy. Amorphous carbon thin films were deposited by DC magnetron sputtering using Ar/O₂ gases. The film morphology changed with the oxygen content. The deposition rate decreased as the amount of oxygen increased due to oxygen reacting with the growing film. The use of oxygen in the working gas enhanced the crystalline nature of the films. Graphite was deposited on WC substrates by a CO₂ laser-assisted O₂/C₂H₂ combustion-flame method. Two distinct microstructural areas …

Phase Equilibria In Iron Phosphate System, Liying Zhang

Doctoral Dissertations

"The main objectives of this research were to synthesize iron phosphate compounds, study phase equilibria in the iron phosphate system, focusing on the glass forming area, and investigate glass formability and properties based on the liquidus regions. Twelve iron phosphate compounds were successfully prepared and studied in terms of liquidus temperature or decomposition behavior. The liquidus surface of the Fe₃PO₇- Fe(PO₃)₃ system was re-determined and found to be significantly different from that originally presented by Wentrup in 1935. Eutectic points exist at 58.0 mole% Fe₂O₃ (1070⁰C), 42.7 mole% Fe₂O₃ (925°C), and 37.0 mole% Fe₂O₃ (907°C). The latter two eutectic points …

Fluid Flow Related Phenomena And Inclusion Motion In Continuous Casting Strands, Yufeng Wang

Doctoral Dissertations

"To improve the efficiency of the continuous casting process and the quality of its products, this dissertation mainly investigated fluid flow related phenomena and inclusion motion in continuous casting. Mathematical simulation was performed for this purpose. Both a slab caster and a billet caster were investigated. In the study of the slab caster, the application of electromagnetic brake field on the slab mold was evaluated. The results indicated that the magnetic force decelerated the high speed steel jet, stabilized the top fluctuation, and prevented the bias flow inside the mold. The other study of this slab caster involved the fluid …

Characterization Of The Corrosion Protection Mechanism Of Cerium-Based Conversion Coatings On High Strength Aluminum Alloys, William R. Pinc

Doctoral Dissertations

"The aim of the work presented in this dissertation is to investigate the corrosion protection mechanism of cerium-based conversion coatings ( CeCCs) used in the corrosion protection of high strength aluminum alloys. The corrosion resistance of CeCCs involves two general mechanisms; barrier and active. The barrier protection mechanism was influenced by processing parameters, specifically surface preparation, post-treatment, and the use of gelatin. Post-treatment and the addition of gelatin to the coating solution resulted in fewer cracks and transformation of the coating to CeP0₄, which increased the corrosion resistance by improving the barrier aspect of CeCCs. CeCCs were found to best …

Synthesis And Characterization Of Conducting Polymer Nanostructures And Their Application In Sensors, Zhe-Fei Li

Doctoral Dissertations

"A one-step synthesis technique has been used to fabricate sensors by growing polyaniline nanofibers and polyaniline/metal nanocomposites in the active area of an interdigitated electrode array. Polyaniline nanofiber sensors can be fabricated by irradiating an aqueous precursor solution containing aniline, HCl, a metal salt, and ammonium persulfate (APS) with a high pressure Hg lamp. The sensors are ready for operation after polymerization is complete, and no additional processing steps are necessary. These sensors showed faster and more intensity response to various organic vapors than conventional bulk polyaniline sensors due to their larger surface area. A chemisorption model and a diffusion …