Browsing by Subject "Metals"
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Item Application of accelerated corrosion tests to predict the service life of 2024-T3 aluminum alloy(Texas Tech University, 2001-05) Pothapragada, PraveenThe objective of this research was to quantify the effects of corrosion, based on grain direction, mass loss and pit-depths, on the static strength and fatigue life of 2024-T3 aluminum alloy. In order to achieve this objective, the test specimens were cut from flat sheets of 2024-T3 aluminum alloy and were masked with masking material to restrict corrosion to a confined area. The corrosion process was accelerated by use of an electrolytic corrosion cell After corrosion, specimens were tested in tension and fatigue. Specimens were corroded to mass loss ranges of 0-1%, 1-2%, 2-3%, and 3-4%. Tensile and fatigue tests were performed on the corroded samples and the results were interpreted. The data for corrosion pit-depths was obtained from Ultrasound analysis and Scanning Electron Microscope (SEM). The stress concentration at the pits was obtained from finite element analysis by using I-Deas® Master Series 7.Item Controlling selectivity in novel transition metal catalyzed carbon-carbon bond forming hydrogenations(2012-05) Zbieg, Jason Robert; Krische, Michael J.; Anslyn, Eric V.; Siegel, Dionicio R.; Brodbelt, Jennifer S.; Liu, Hung-WenThe focus of my graduate research in the Krische group has been the development of catalytic carbon-carbon bond forming reactions with an emphasis on controlling diastereo- and enatio-selectivity in transfer hydrogenative couplings. The broad goal of our research program has been the development and implementation of efficient green methods for carbonyl addition employing [pi]-unsaturates as surrogates to preformed organometallic reagents, thus enabling byproduct free variants of traditional carbanion chemistry. This dissertation shows the new reactions that I have developed toward this goal. These reactions includes new metal catalyzed approaches for carbonyl crotylation, aminoallylation, and vinylogous reformatsky aldol reactions.Item Geochemical effects of elevated methane and carbon dioxide in near-surface sediments above an EOR/CCUS site(2013-05) Hingst, Mary Catherine; Young, Michael H.; Romanak, Katherine DunckerCarbon capture, utilization and storage (CCUS) aims to reduce CO₂ emissions by capturing CO₂ from sources and injecting it into geologic reservoirs for enhanced hydrocarbon recovery and storage. One concern is that unintentional CO₂ and reservoir gas release to the surface may occur through seepage pathways such as fractures and/or improperly plugged wells. We hypothesize that CO₂ and CH₄ migration into the vadose zone and subsequent O₂ dilution and Eh and pH changes could create an increased potential for metal mobilization, which could potentially contaminate ground and surface waters. This potential has not been addressed elsewhere. Goals of this study are to understand how the potential for metal mobilization through soil pore water may increase due to CO₂ and CH₄ and to assess potential impact to aquifers and/or the biosphere. The study was conducted at a CCUS site in Cranfield, MS, where localized seepage of CH₄ (45%) from depth reaches the surface and oxidizes to CO₂ (34%) in the vadose zone near a plugged well. Four sediment cores (4.5-9m long) were collected in a transect extending from a background site through the area of anomalously high soil gas CO₂ and CH₄ concentrations. Sediment samples were analyzed for Eh and pH using slurries (1:1 vol. with DI water) in the field and for occluded gas concentrations, metal (Ba, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn) concentrations, moisture content, organic carbon content, and grain size in the laboratory. Data from the background reference area (no gas anomaly: occluded gas ~21% O₂, <1% CO₂, 0% CH₄) showed oxidized conditions (Eh from 464-508mV) and neutral pH (7.0-7.8) whereas samples collected near the gas anomaly (13-21% O₂, 0.1-5% CO₂, <0.1% CH₄) were more reducing (Eh 133-566mV) and more acidic (pH = 5.3-8.0). Significant correlations were found between Eh and O₂ (r = 0.95), pH and CO₂ (r = -0.88), and between these parameters and acid-leachable metals in samples from within the soil gas anomaly. Correlations quickly weaken away from the anomaly. Statistically, total metal concentrations, except for Ba, are similar in all cores. Acid-mobile metal concentrations, above 5m, increase toward the gas anomaly. The percent of water-mobile metals is very low (<2%) for all metals in all cores, indicating freely-mobile metals are not affected by elevated CO₂/CH₄. Conclusions are: 1) oxidation of CH₄ to CO₂ depletes O₂ causing reducing conditions; 2) high CO₂ and low O₂ affect Eh and pH of sediments which in turn alters mineralogy and bond strength between sediments and adsorbed ions; 3) intrusion of strongly acidic fluids (pH of acid used was 0.39) into these sediments could potentially remove weakly bonded metals or dissolve minerals. Implications from this study are that Eh needs to be considered along with pH when analyzing contamination potential, and that exposure of sediments to reducing, followed by acidic conditions, increases the potential for metal mobilization in the vadose zone. More research is needed to determine the concentration of gases (CO₂, CH₄ and O₂) that will create Eh and pH levels that could affect the mineralogy and sorption mechanism potentially leading to metal mobilization. Methods for assessing potential metal mobilization may be useful for site characterization and risk assessment.Item Humble alchemy(2014-05) White, Shalena Bethany; Williams, Jeff, M.F.A.This master's report addresses the conceptual and material investigations that were explored within my artistic research made at the University of Texas at Austin between 2011 and 2014. These works are a confluence of adornment, sculpture and installation art. These pieces incorporate ancient and contemporary metalworking techniques with raw, organic material. The notion of elegant ornamentation is expanded beyond the body into the adornment of architecture. The potential for transformation and reinvention within found elements is explored within this work. The natural resources I work with have gone through a cycle, which is interrupted when the objects are removed from the earth. I see my process in relationship to alchemical concepts of transmutation. Through manipulation, common matter evolves into precious material. The refined, meticulous craftsmanship conveys a sense of reverence and honor towards the common material. This intervention with the material is an act of preservation and veneration. This work explores my sense of intrigue about the extraordinary potential of mundane materials, and investigates conventional notions of material value.Item Investigation of high strain rate behavior of metallic specimens using electromagnetic inductive loading(2011-08) Morales, Santiago Adolfo; Ravi-Chandar, K.; Liechti, Kenneth M.Aerospace EngineeringItem Prediction of energy absorption of extruded tubes(Texas Tech University, 2000-12) Sun, JunningIn this study, the FE crush analysis was carried out using LS-DYNA. It is an advanced general purpose nonlinear FE program. LS-DYNA is suited to handle the large deformations, sophisticated material models, and complex contact interactions required to analyze crash simulations. The objective of this study was to investigate the effect of five parameters on the energy absorption of extruded tubes. The five parameters considered were: imperfection location, cross-section, impact velocity, cutout size, cutout location, and impact mass size. It was shown that the circular and hexagonal extrusions had a high energy absorption efficiency compared to triangular ones. However, the triangular extrusions had the lowest crush peak force. Additionally, cutouts introduced in the sides of the extrusions lowered the crush peak force. Increasing the kinetic energy of the impacting mass was shown to increase the crushing distance, while also increasing the peak force slightly. Finally, it was further showm that cutout and imperfection location influenced the tube folding pattern.Item Quantification of corrosion in 7075-T6 aluminum alloy(Texas Tech University, 2000-05) Obert, Brian DaleHigh strength aluminum alloys, such as 7075-T6, are widely used in aircraft structures due to their high strength-to-weight ratio, machinability. and low cost. However, due to their compositions, these alloys are susceptible to corrosion. Corrosion is a major concem involving the structural integrity of aircraft structures. Corrosion has been shown to reduce the life expectancy of these structures considerably. Aircraft, during normal operation, are subjected to natural corrosive environments due to temperature, humidity, rain, and seawater. The objective of this research was to analyze the effects of corrosion on the static strength and fatigue life of 7075-T6 aluminum alloy. Test specimens were cut form flat sheets of aluminum and covered with masking material to restrict corrosion to a confined area. The corrosion process was accelerated by use of a galvanic corrosion cell. After corrosion, specimens were tested in tension and fatigue.Item Studies toward the development of an electronically switchable ion exchange system(2004) Johnson, Ashley Michelle; Holcombe, James A.Early studies toward the development of a chemical-free means of reclaiming metals from an ion exchange system were begun by exploring the option of controlling metal-ligand interactions electrochemically. Poly-L-cysteine (PLC), a soft acid cationic metal chelator, was explored as an option for an electroactive ligand for use as an electronically switchable ion exchange system. Initial studies were conducted by immobilizing PLC onto a glassy carbon electrode creating a modified electrode. The modified electrode was characterized using electrochemical techniques, atomic spectroscopy and molecular spectroscopy. Initial studies were conducted with poly-L-cysteine immobilized onto controlled pore glass and packed in a microcolumn for low pressure liquid chromatography experiments. Flow parameters, as well as the ability of poly-L-cysteine to act as a preconcentration agent, were established. Electrochemical methods, specifically cyclic voltammetry, were used to confirm polymer attachment and to estimate that near monolayer coverage on the glassy carbon electrode surface existed. Further studies examined the kinetics of electron transfer through the use of large amplitude potential steps to demonstrate consistency with other types of modified electrodes. The pKa of the polymer was determined to be between 7.5 and 8 by using surface charge density as a function of pH. The poly-L-cysteine modified electrode, as well as an electrode modified with cysteine monomers, was evaluated for its metal binding capabilities. Using Cd2+ as a target metal, optimal binding conditions were established. Binding experiments were repeated with Co2+, Cu2+, Ni2+ and Pb2+, as well as competitive binding studies comprised of binding in the presence of all five metals. Quantitative release of bound metals was achieved by repeatedly pulsing the potential from open circuit to a number of anodic potentials. Raman microscopy was used to probe the redox states of PLC, confirm the complexation of Cd2+ to the thiol groups of PLC and to establish an average formal reduction potential for PLC of -0.3 V vs. SHE. The possibility of multiple formal potentials was explored through the use of mathematical models based on the Nernst equation. The models suggest that many formal potentials do exist although the exact nature of the distribution could not be determined. As a plausible electronically switchable ion exchange option for heavy metal oxyanions, pyrrole was electropolymerized and investigated as a ligand for toxic chromate remediation. Polypyrrole, which bears a structural similarity to poly-L- histidine, a previously studied chromate chelator, was shown to have potential to both remediate and speciate Cr(VI) from Cr3+.Item Synthesis and characterization of short-chain peptides for use in metal remediation and preconcentration(2006) Stair, Jacqueline Leslie; Holcombe, James A.Designing materials for metal remediation and preconcentration based on naturally occurring metal binding proteins has become of growing interest due to their inherent selective and strong binding, ease of synthesis and available amino acid building blocks, and environmental innocuity. One approach is through the use of immobilized synthetic biohomopolymers which can provide the selectivity based on the amino acid side chain moiety with strong binding, easy on-demand release, and reusability. An attempt to increase metal binding selectivity of these biohomopolymers was done though cross-linking at specific locations as to effectively “lock” in place the preferential binding cavity for a particular metal. The cross-linking of these materials resulted in decreased metal capacities with little to no increases in the targeted metal selectivity. This was likely due to the loss of bound metal during cross-linking and to a lack of rigidity in the overall cross-linked polymer. Short composite peptides synthesized on a commercially available resin, TentaGel were also examined as a means to increase metal selectivity. These peptides showed surprisingly high metal binding capacities, strong binding, and residue per metal binding ratios which were an order of magnitude better than results previously reported for longer chain poly-amino acids (50 – 70 residues) attached to porous glass supports. Metal binding selectivity’s were altered by changing only one amino acid and metal release under acidic conditions was surprisingly rapid for these shorter peptides. As a result of these findings, the metal binding and conformational changes between TentaGel immobilized short and long peptide chains during metal binding and release were monitored using Raman microscopy. These results indicated that metal release occurred via conformational changes in addition to proton displacement. Lastly, a method to screen multi-metal binding capabilities of combinatorial peptide libraries was developed using electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS). With the exception of metals that are bound tightly to the peptide, acid stripping of the metals in a single bead into a small volume appears as a viable quantitative analytical approach when using this method with instrumental precisions of better than ±10% for most metals when larger polymer beads (~250 µm) were employed.Item Synthesis of Calix[4]arene ligands with multiple proton-ionizable groups for complexation of multivalent metal ions(Texas Tech University, 2004-05) Fernandez, Fernando AdolfoA series of new conformationally mobile tri-ionizable calix[4]arenes has been prepared for the complexation of trivalent lanthanide ions by matching the metal ion charge (3+) with the same number of proton-ionizable groups. The A-(X)sulfonyI carboxamide group, -C(0)NHS02X, was chosen as the proton-ionizable function because its acidity may be tuned by variation of X. Three series of new di-ionizable calix[4]arene-l,3-crown-5 ethers have been prepared in the cone, 1,3-aItemate and partial cone conformations to probe the influence of conformation, acidity variations and the crown ether ring size in solvent extraction of metal ions. A dansyl fluorescent group was coupled to di-ionizable calix[4]arene-l,3- crown-5 to produce potential fluorogenic ligands.