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Crevice corrosion generally occurs on the crevice surface while the exterior or bold surfaces are not damaged. However, for copper and its alloys, the opposite is true; the bold surface is corroded while the crevice remains relatively corrosion-free. This unique type of corrosion is referred to as reverse crevice corrosion (RCC). In this research, commercially pure copper was chosen as the target metal to investigate RCC. Based on electrochemical measurements and surface analysis, reverse crevice corrosion was found to occur at room temperature. At elevated temperature only uniform corrosion was observed while under a deoxygenated environment, as expected, no corrosion was observed.<p> A multiple crevice assembly and a working electrode were designed especially for this research. Exposure test experiments were first performed at room temperature and 50 ºC. Several types of electrochemical tests were conducted including open circuit potential measurement, potentiodynamic measurement and electrochemical impendence spectroscopy (EIS). Atomic Force Microscopy (AFM) and Raman Spectroscopy were used to analyze the surfaces of the copper coupon.<p>The results of the exposure tests showed that RCC occurred at room temperature, but not at elevated temperature. Only uniform corrosion was observed at elevated temperature and no corrosion was occurred under a deoxygenated environment. It was found, based on the open circuit potential measurement, that the RCC process can be divided into three steps, a uniform corrosion phase, a corrosion slow-down step and a reverse crevice corrosion step. The first two steps can be combined into one phase, incubation phase. This hypothesis is supported with the results from Raman spectra and AFM. The EIS measurements revealed that the diffusion process from bulk solution to copper coupon surface is the rate controlling step for incubation phase and this diffusion process combined with the reduction of Cu (I) oxide in the crevice are the rate-controlling step corresponding to the last step.

Crevice corrosion generally occurs on the crevice surface while the exterior or bold surfaces are not damaged. However, for copper and its alloys, the opposite is true; the bold surface is corroded while the crevice remains relatively corrosion-free. This unique type of corrosion is referred to as reverse crevice corrosion (RCC). In this research, commercially pure copper was chosen as the target metal to investigate RCC. Based on electrochemical measurements and surface analysis, reverse crevice corrosion was found to occur at room temperature. At elevated temperature only uniform corrosion was observed while under a deoxygenated environment, as expected, no corrosion was observed.<p> A multiple crevice assembly and a working electrode were designed especially for this research. Exposure test experiments were first performed at room temperature and 50 ºC. Several types of electrochemical tests were conducted including open circuit potential measurement, potentiodynamic measurement and electrochemical impendence spectroscopy (EIS). Atomic Force Microscopy (AFM) and Raman Spectroscopy were used to analyze the surfaces of the copper coupon.<p>The results of the exposure tests showed that RCC occurred at room temperature, but not at elevated temperature. Only uniform corrosion was observed at elevated temperature and no corrosion was occurred under a deoxygenated environment. It was found, based on the open circuit potential measurement, that the RCC process can be divided into three steps, a uniform corrosion phase, a corrosion slow-down step and a reverse crevice corrosion step. The first two steps can be combined into one phase, incubation phase. This hypothesis is supported with the results from Raman spectra and AFM. The EIS measurements revealed that the diffusion process from bulk solution to copper coupon surface is the rate controlling step for incubation phase and this diffusion process combined with the reduction of Cu (I) oxide in the crevice are the rate-controlling step corresponding to the last step.

Three-way median polish is used to model the monthly concentrations of three kinds of ions in precipitation, namely sulphate, nitrate and hydrogen ions. In contrast to previous findings that the wet acid deposition had decreased from late 70's to early 80's, the results suggest that there is a V-shaped trend for wet acid deposition during the period of 1980 -1986 with the change point around 1983. Strong seasonality is also discovered by the analysis. Nonparametric monotone trend tests are performed on the data collected from 1980 to 1986 and on the data collected from 1983 to 1986 separately. The results are consistent with the findings from the median polish approach. A nonparametric slope estimate of the trend is obtained for each monitoring station. Based on these estimates, the slope estimate is obtained by Kriging interpolation for each integer degree grid point of longitude and latitude across the 48 conterminous states in the United States. Also, a geographical pattern in the data is suggested by hierarchical clustering and by median polishing. / Science, Faculty of / Statistics, Department of / Graduate

Cerium and zirconium oxides are materials that have unique catalytic properties and are finding many applications in industrial catalysis. Particularly, the great advances attained in the past 30 years in curbing the amount of gaseous pollutants released can be attributed to the development of catalysts employing such materials. However, oxides of sulfur are known poisons of many catalytic systems and are encountered in many commercial applications. In this investigation, polycrystalline ceria-zirconia solid solutions of various molar ratios were synthesized. High resolution x-ray photoemission spectra were obtained and examined to reveal the surface species that form on these metal oxides after exposure to sulfur dioxide under various conditions. The model catalysts are exposed to sulfur dioxide using an in-situ high-pressure reaction cell. A reliable sample platen heater was designed to allow the observation of any temperature dependency up to 673 K. The results of this study demonstrate the formation of sulfate and sulfite adsorbed sulfur species. Temperature and compositional dependencies are also displayed, with higher temperatures and ceria mole fractions displaying a larger propensity for the formation of surface sulfur species.

One of two project reports. Part B is available at http://hdl.handle.net/11375/17552 / <p> The design, construction, and initial operation of a surface analysis station were undertaken. The final UHV system is equipped for ion surface scattering, low energy electron diffraction, Auger analysis, secondary ion mass spectroscopy and residual gas analysis. </p> <p> The main goal of this project was the preliminary operation of the ion surface scattering equipment. A complete beam transport system was constructed utilizing an Einzel lens and electrostatic quadroles. </p> <p> The ion surface scattering was effected through the use of a time-of-flight (TOF) technique to obtain an energy spectrum of particles backscattered from a target surface. The TOF spectrum and subsequent energy spectrum were for 5.1 keV hydrogen ions incident on a practical silver target. </p> / Thesis / Master of Engineering (ME)

Hydrogen causes defects, for which aluminiurn alloy products are rejected. The behaviour of hydrogen in aluminium-magnesium-silicon alloy extrusion ingots, has been studied throughout the course of manufacture from freshly reduced aluminium. It is shown that hydrogen in the liquid metal is produced by temperature-dependent reaction between the metal and water vapour in the atmosphere. As the metal is received from the reduction cells, its temperature is -850 'C and its hydrogen content, >0.4 cm3/100 g, is too high for casting sound ingots. The metal is transferred first to a so-called melting furnace, where it is alloyed and stirred, thence to a holding furnace, where the composition is adjusted, the metal is degassed by gas sparging and allowed to settle before casting. The metal cools throughout these operations and as the temperature falls, the calculated value for the hydrogen content in equilibrium with the atmosphere falls in response to the reduced hydrogen solubility. The actual hydrogen content of the metal exhibited marked hysteresis in following the equilibrium value. Significant reduction of the hydrogen content occurred only when the metal was agitated. The hydrogen content never fell below the equilibrium value even during the nominal degassing operation, leading to the conclusion that gas sparging in a furnace does not positively remove hydrogen but only assists the equilibration. The hot-top DC casting process yielded a 8 m x 0.18 m diameter ingot with a virtually uniform hydrogen content. When this ingot was homogenised by heating it to 590˚C in a 7h cycle, a significant proportion of the hydrogen content was lost from the surface zone. By matching the loss to a theoretical model assuming diffusion control, it was shown that the loss of hydrogen is attenuated by trapping in micropores. The effects of simulated industrial atmospheres on the loss or absorption of hydrogen by the solid alloy were investigated in an extended series of laboratory heat-treatments. The interaction of the metal with these atmospheres was found to be determined by the nature of the oxide films formed and therefore the films were investigated by XPS and SIMS surface analysis techniques. In clean atmospheres the absorption or loss of hydrogen was determined by the balance between inward migration of protons and outward diffusion of hydrogen atoms through the oxide. Pollution of the air by chlorine or especially sulphur stimulated hydrogen absorption to a degree which seriously damaged the metal by pore growth. These effects are explained by modified compositions and structures in the surface oxide.

X-ray photoelectron spectroscopy (XPS) is the most widely used surface analysis technique for chemically probing surfaces. Its popularity stems from the large amount of information that can be gathered about the electronic states of the atoms it probes, including core shell information and valence electron information. Simple qualitative analysis (peak identification) can often be performed, but quantitative analysis is a much more complicated process. Although XPS usage has increased dramatically, so has the amount of erroneous analysis observed in the literature. In my thesis, I first present a perspective on how to improve the quality of surface and material data analysis. This chapter focuses on responsible groups, using population biology models and the Prisoner's Dilemma to describe the situation and the potential changes that must be made to counteract error propagation. I quantify errors in XPS data analysis to provide perspective on the gravity of the situation. Over 400 publications in three journals were analyzed. Additionally, another 900 journals were surveyed to determine the quantity of information in the analysis. The parameters include experimental parameters, e.g., the pass energy, peak fitting parameters, the spot size, X-ray source, and the type of spectrometer. I found that over 40% of the publications had significant errors that could potentially change the conclusions of the publication. About 35% of all papers neglected to note the type of spectrometer used, and 85% did not mention the type of software used for analysis. The latter half of this work focuses on XPS peak fitting. I present a broad overview of peak fitting, including how to determine the appropriate background and peak shapes to use, how to quantify XPS data, and how to account for other phenomena associated with photoemission. The line shape chosen for peak fitting is critical, as it is the synthetic shape that is used to model observed physical phenomena. A detailed review on typical line shapes, including the Voigt and pseudo-Voigt functions is presented, along with how to apply them in peak fitting. How and why asymmetric peak shapes are required is also discussed, including which effects cause asymmetry, and if it is inherent to the material or the method of analysis. Finally, a discussion on using constraints to properly model known effects is presented. These efforts were guided by the findings in the former half of this work. The trends presented here are not unique to XPS. Other fields and techniques have similar reproducibility problems. This work discusses possible solutions and what efforts as a community need to be taken to remedy the reproducibility crisis. Additionally, this work includes guides that have original research to improve approaches to XPS analysis, including peak fitting, constraint parameters, and the appropriate use of line shapes.

Fuel cell is a device that can directly convert chemical energy into electrical energy. For low-temperature fuel cells, catalysts are required. Fuel cells using Pt-based or other non-biological materials as catalysts are known as conventional fuel cells. Inspired from Nature, enzymes can be used as catalysts in fuel cells known as enzyme-based fuel cells. The conventional and enzymatic fuel cells share the same underlying electrochemical principles, while enzyme-based fuel cells have their intrinsic advantages and disadvantages due to enzyme properties. The objective of this thesis is to investigate the current/voltage/ power/stability capabilities of enzyme-based membrane-less H2 fuel cells in order to design the enzymatic fuel cells with improved performance. This thesis presents a facile, effective method for the construction of 3D porous carbon electrodes. The 3D porous carbon electrodes are constructed by compacting suitable carbon nanomaterials into discs. The 3D porous carbon electrodes, with large roughness, high specific surface area, and optimized pore size distribution, are able to increase the loading density of enzymes, that is, reaction sites per unit geometric electrode area. The high loading density of enzymes can result in the high current/power density of the enzyme-based membrane-less H2 fuel cells. Moreover, the large enzyme loading can bring about the improvement in fuel cell stability because current becomes limited by mass transport of dissolved gases rather than enzyme immobilization so that neither inactivation nor desorption of enzymes would influence the current output. Based on one type of 3D porous carbon electrodes, the maximum power density of enzyme-based membrane-less H2 fuel cells has increased to the mW•cm2 level by at least one order of magnitude and the half-life has also increased from several hours to one week. This thesis presents a method for the increase in power density otherwise limited by low cathodic currents due to meagre O2 in non-explosive H2-rich H2-air mixtures. The power density of enzyme-based membrane-less H2 fuel cells can be increased by re-proportioning cathode/anode geometric area ratio to balance the cathodic and anodic currents under such an unusual H2-air mixture. This thesis also demonstrates that the 3D porous carbon electrode can improve the apparent O2 tolerance of anodic catalysts – hydrogenases, which are very important for the fuel cell performance. The degrees of apparent O2 tolerance for both O2-tolerant and O2-sensitive [NiFe]-hydrogenases are greatly increased based on the 3D porous carbon electrodes, so that even an O2-sensitive [NiFe]-hydrogenase can be used as an anodic catalyst in the enzyme-based membrane-less H2 fuel cell under a non-explosive H2-rich H2-air mixture. This thesis presents a design of a test bed in which series and parallel connections of sandwich-like electrode stacks can be varied. The fuel cell test bed has demonstrated low-loss interconnects and efficient stack configuration. Operated under a non-explosive H2-air mixture containing only 4.6% O2 at 20 °C, the maximum volume power density of the fuel cell test bed exceeds 2 mW•cm3, capable of powering electronic gadgets, which is a good demonstration of electricity that originates from the buried active sites of enzymes and is transmitted by long-range electron hopping in accordance with Marcus theory.