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Niobium (Nb) has the highest superconducting transition temperature (9.2 K) of the pure metals, which makes it the most used material for the construction of superconducting radio frequency (SRF) accelerators. The performance of the accelerator is critically dependent upon the quality of Nb surface. Electropolishing (EP) in hydrofluoric acid (HF)-containing electrolytes is the currently accepted treatment process. The presence of HF is necessary for the removal of the passive oxide surface film formed in aqueous electrolytes. But HF is hazardous and must be contained without human exposure and eliminated in an environmentally appropriate manner. In the present dissertation project, HF-Free EP of Nb was performed in sulfuric acid-methanol electrolytes. Sulfuric concentrations of 0.1 M, 0.5 M, 1 M, 2 M, and 3 M were used. Cyclic voltammetry and potential hold experiments were performed in cells of both two-electrode and three-electrode setups to evaluate the electrochemical process. The influence of electrolyte concentration, temperature, and EP duration was investigated. At room temperature, both the corrosion rate and the surface quality obtained were comparable to those currently obtained with HF-based processing. With decreasing temperature, the mean current level decreased and the surface quality improved substantially. For a desired average material removal of 100 μM, nanometer scale surface roughness was obtained under multiple conditions. Mechanism of EP was also investigated by electrochemical impedance spectroscopy (EIS). The EIS diagram indicates the presence of a compact film during EP at mass transport controlled limiting current and a film-free surface during EP at ohmic controlled current. Transfer from a film-free surface to an anodic film precipitation with decreasing temperature was also observed. Microsmoothing is only achieved under mass transport control. Nb⁵⁺ ions are determined to be the mass transport limiting species. / Ph. D.

This study evaluated the potential for increasing the biological degradation of methanol and tertiary-butyl alcohol (TBA), components of a gasoline-alcohol blend, in the subsurface by stimulating the growth of the microorganisms. The primary objective of this study was to evaluate the stimulatory effect of nitrate and sulfate (alternative electron acceptors) on the biodegradation of the alcohols in the absence of molecular oxygen. This study also evaluated the effect of adding hydroxide and bicarbonate to the groundwater as buffering agents in an attempt to raise the pH of the groundwater and stabilize it against the acidic by-products of microbial metabolism. The addition of nitrate resulted in increases in the initial rates of degradation of methanol ranging from 20 to 1040 percent. After a period of time, however, an inhibitory build-up of nitrite generally occurred, essentially halting the biodegradation. The addition of nitrate resulted in a varied response on the initial degradation rates of TBA, ranging from a 60 percent decrease to a 340 percent increase. The results of the sulfate additions with methanol were varied, ranging from an 80 percent decrease to a 930 percent increase in the initial degradation rates. In some cases, an inhibitory response was evidenced after a period of time, presumably due to a build-up of sulfide. The addition of sulfate resulted in a varied response on the initial degradation rates of TBA, ranging from a 90 percent decrease to a 380 percent increase. The effect of the hydroxide and bicarbonate additions were very similar, with both compounds inhibiting the biodegradation of methanol (SO and 65 percent decreases in the initial degradation rates, respectively) while stimulating the biodegradation of TBA (140 and 180 percent increases in the initial degradation rates, respectively). / M.S.

As the world begins to focus more and more on new and more effective means of energy production, fuel cells become increasingly more popular. While different fuel cells are already found in industry today, the direct methanol fuel cell (DMFC) is becoming an increasingly more probable means for portable power production. In such applications a passive air breathing direct methanol fuel cell would be ideal. However, successful use of the passive DMFC in such applications requires that the fuel cell be capable of operating at various temperatures and relative humidities. A passive air breathing direct methanol fuel cell was developed and manufactured for this study. This work studied the effects of varying relative humidity and temperature over a probable range of operating conditions for small scale portable power applications on the performance of the fuel cell, both in relation to power production and fuel consumption. Potentiostatic, electrochemical impedance spectroscopy, and polarization tests were performed in order to characterize the performance of the fuel cell. Additionally, a one dimensional steady state isothermal mass transport model was developed to provide insight to the behavior of the fuel cell. The experimental data and model results show that increasing the fuel cell temperature and decreasing the ambient relative humidity increases the current production capabilities of the fuel cell. Further, the experimental data suggests that the major problem hindering current production in passive air breathing direct methanol fuel cells is flooding of the cathode diffusion layer. / Master of Science

Moving bed biofilm reactors (MBBRs) have been used effectively to reach low nutrient levels in northern Europe for nearly 20 years at cold temperatures. A relatively new technology to the US, the MBBR has most typically been used in a post-denitrification configuration with methanol for additional nitrate removal. Methanol has clearly been the most commonly used external carbon source for post-denitrification processes due to low cost and effectiveness. However, with the requirement for more US wastewater treatment plants to reach effluent total nitrogen levels approaching 3 mg/L, alternative electron donors could promote more rapid MBBR startup/acclimation times and increased cold weather denitrification rates. Bench-scale MBBRs evaluating four different electron donor sources, specifically methanol, ethanol, glycerol, and sulfide (added as Na2S), were operated continuously at 12 °C, and performance was monitored by weekly sampling and insitu batch substrate limiting profile testing. Ethanol and glycerol, though visually exhibited much higher biofilm carrier biomass content, performed better than methanol in terms of removal rate (0.9 and 1.0 versus 0.6 g N/m²/day.) Maximum denitrification rate measurements from profile testing suggested that ethanol and glycerol (2.2 and 1.9 g N/m²/day, respectively) exhibited rates that were four times that of methanol (0.49 g N/m²/day.) Sulfide also performed much better than any of the other three electron donors with maximum rates at 3.6 g N/m²/day and with yield (COD/NO₃-N) that was similar to or slightly less than that of methanol. Overall, the yield and carbon utilization rates were much lower than expected for all four electron donors and much lower than previously reported; indicating that there could be advantages for attached growth versus suspended growth processes in terms of carbon utilization rates. The batch limiting NO₃-N and COD profiles were also used to find effective K_s values. These kinetic parameters describe NO₃-N and COD limitations into the biofilm, which affect the overall denitrification rates. Compared to the other electron donors, the maximum rate for methanol was quite low, but the estimated K_s value was also low (0.4 mg/L N). This suggests high NO₃-N affinity and low mass transfer resistance. The other three electron donors estimated higher K_s values, indicating that these biofilms have high diffusion resistance. Biofilm process modeling is more complex than for mechanistic suspended growth, since mass transfer affects substrate to and into the biofilm. Simulating the bench-scale MBBR performance using BioWin 3.0, verified that μ_max and boundary layer thickness play key roles in determining rates of substrate utilization. Adjustments in these parameters made it possible to mimic the MBBRs, but it is difficult to determine whether the differences are due to the MBBR process or the model. / Master of Science

The use of alcohols as inexpensive octane enhancers in gasoline has contributed to an increased concern about the potential contamination of groundwater. Being highly soluble in water, alcohols may easily separate from other, more insoluble gasoline components, and rapidly enter the groundwater flow system. The alcohols are relatively tasteless and odorless, and thus, may go undetected until potentially harmful concentrations are reached. This study was designed to determine the potential for alcohol biodegradation in a groundwater system that had been previously contaminated with gasoline containing tertiary butyl alcohol (TBA). Laboratory microcosms, utilizing actual aquifer material and groundwater, were constructed to determine the rate of alcohol biodegradation in a system closely resembling the subsurface environment. The only microorganisms used were those naturally present in subsurface soil obtained aseptically. Bacterial counts and degradation kinetics were evaluated at each of three subsurface depths (10, 26, and 45 feet) and results were compared to similar studies utilizing uncontaminated aquifer material. Significant bacterial populations were found to exist at all depths studied in the contaminated subsurface system. Bacterial plate counts ranged from 10 6 to 10 7 colony forming units per gram of soil (dry weight). Methanol was found to be a readily degradable substrate. Complete degradation of up to 1000 mg/L was degraded in a matter of months. The biodegradation of methanol in the contaminated system was similar to that observed at pristine sites, indicating that a similar degradation mechanism is involved. TBA biodegradation in the contaminated system occurred and was accompanied by microbial growth. Complete TBA degradation of up to 100 mg/L occurred in less than one year. In contrast, TBA biodegradation in the uncontaminated systems occurred at a very slow rate, which appeared to be constant over time, and thus zero order. However, the zero order rate was found to vary directly with initial substrate concentration. Several mechanisms may explain TBA biodegradation, including the presence of a non-specific exocellular enzyme system. Such a system would describe observed results and suggest that a widespread potential exists for the degradation of a large number of organic compounds. / Ph. D.